PROSPECTS  FOR  ELECTRIC VEHICLES
A STUDY OF LOW-POLLUTION POTENTIAL VEHICLES - ELECTRIC
Department of Health, Education and Welfare / National Center for Air Pollution Control
                                       HJUttkJnc.

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             PROSPECTS FOR ELECTRIC VEHICLES

A STUDY OF LOW-POLLUTION-POTENTIAL VEHICLES - ELECTRIC
                           by

                       J. H. B. George
                       L. J. Stratton
                       R. G. Acton
                          for


    DEPARTMENT OF HEALTH, EDUCATION AND WELFARE

     NATIONAL CENTER FOR AIR POLLUTION CONTROL
                   Contract No. PH 86-67-108
                        May 15, 1968
                         C-69260
                      Arthur D. Little, Inc.
                        15 Acorn Park
                    Cambridge, Massachusetts

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                     TABLE OF CONTENTS





                                                       Page




 List of Tables                                             v




 List of Figures                                            vii




 Acknowledgement                                          ix







 I.  SUMMARY                                           1




        A.  PURPOSE AND SCOPE                           1




        B.  FINDINGS                                    1




        C.  RECOMMENDATIONS                            4




 II.  APPROACH                                           7




III.  CRITERIA FOR ELECTRIC VEHICLES                     11




        A.  DEVELOPMENT OF VEHICLE SPECIFICATIONS       11




        B.  POWER AND ENERGY CALCULATIONS             14




        C.  ELECTRIC TRANSMISSION PARAMETERS           19




IV.  ELECTRIC TRANSMISSION SYSTEM                       26




        A.  MOTORS                                    26




        B.  CONTROLS                                  33




        C.  SPEED REDUCERS                             38




        D.  COOLING REQUIREMENTS                       39




 V.  ELECTROCHEMICAL POWER SOURCES                    40





        A.  CONVENTIONAL BATTERIES                     40





        B.  BATTERIES UNDER DEVELOPMENT               43
                             in




                                                       Arthur ZD.lUttlc.llnr.

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                TABLE OF CONTENTS (Continued)
                                                       Page
 V.   ELECTROCHEMICAL POWER SOURCES (Continued)
         C.   FUEL CELLS
         D.   ELECTROCHEMICAL HYBRIDS
 VI.  MECHANICAL-ELECTRICAL HYBRIDS
         A.   TECHNICAL PROSPECTS
         B.   COST FACTORS
         C.   REFUELING
         D.   SUMMATION AND RECOMMENDATIONS
53

56

58
VII.  PROSPECTS AND REQUIREMENTS FOR ELECTRIC VEHICLES    67
67

72

77

78
APPENDIX A   NOTES ON ELECTRIC VEHICLE DEVELOPMENT
             IN THE UNITED STATES

APPENDIX B   NOTES ON FOREIGN ACTIVITY
83
89
                             IV
                                                       3rthur 3l.lUttk.Ilnr.

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                            LIST OF TABLES


Table No.                                                             Page

     1        Electric Vehicle Specifications                              12


     2        Public Health Service Cycle                                 20


     3        City Bus Cycle                                            20


     4        Electric Transmission Parameters                            25


     5        Hybrid Vehicle Specifications                               65
     6        Generalized Technical Parameters For Electro-
              chemical Power Sources                                   68
    B-1       Specifications of Some British Experimental
              Electric Vehicles                                          92
                                                                       Arthur ZD.3Uttle.3lnr.

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                          LIST OF FIGURES


Figure No.                                                          Page

    1        Standardized Acceleration Curves                         13

    2        Acceleration Versus Velocity For Selected Vehicles         16

    3        Power Requirements For The Family Car At
             Maximum Acceleration                                  18

    4        Power-Speed Characteristic Curves For Electric
             Motor                                                  21

    5        Motor Selection For Family Car                          23

    6        Allowable Rotor Speeds                                 27

    7        Weights of DC Motors                                   30

    8        Weight Versus Power of AC Motors                       32

    9        Weight of Control Unit                                  36

   10        Various Electrical Systems for Electrical-Mechanical
             Hybrids                                                59

   11        Power/Weight Ratios For  Internal Combustion
             Engines                                                61

   12        Approximate  Cost Levels  For Internal Combustion
             Engines                                                62

   13        Weight of Generator, Rectifier,  Speed Increaser
             and Voltage Regulator                                   64
                                  VII

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                    LIST OF FIGURES (Continued)


Figure No.                                                          Page

  B-1        British Electrically Driven Milk Truck                     90


  B-2        The Scamp:  A Developmental Vehicle                    90
  B—3       Prototype Electric Car Built in Italy By Subsidiaries
             of Rowan Controller Corporation                         95
                                 VIII

                                                                   3rthur ZD.HittleJnr.

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                             ACKNOWLEDGEMENT
       The assistance of the following organizations in providing material for this study is
gratefully acknowledged:
       Allis-Chalmers Manufacturing Company
       Allmanna Svenska Elektriska Aktiebolaget (ASEA)
       Argonne National Laboratory
       Atomics International, a division of North American Rockwell Corporation
       Brown Boveri and Company Ltd.
       Robert Bosch GmbH
       Chloride Electrical Storage Co. Ltd.
       Compagnie Fran9aise Thomson-Houston
       Eagle-Picher Company
       Electric Fuel Propulsion, Incorporated
       ESB Incorporated
       Esso Research and Engineering Company
       Ford Motor Company
       General Electric Company
       General Motors Corporation
       Gould-National Batteries, Incorporated
       Gulf General Atomic
       Gulton Industries, Incorporated
       Lead Development Association
       Leesona  Corporation
       McDonnell-Douglas  Corporation
       Montecatini-Edison  S.p.a.
       Rowan Controller Company
       Scottish  Aviation Ltd.
       Shell Research Ltd.
       Siemens  Schuckertwerke A.G.
       Societe Le Carbone  Lorraine
       Standard Oil  Company (Ohio)
       Texas Instruments Incorporated
       TRW, Incorporated
       UCLA (Professor G. A. Hoffman)
       Union Carbide Corporation
       United Kingdom Electricity Council
       U. S. Army Engineer R&D Laboratories
       W&E Vehicles
       Westinghouse Electric Corporation
       Yardney Electric Corporation
                                      IX

                                                                       Arthur 2D.llittlc.3lnr.

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                                   I. SUMMARY
 A.  PURPOSE AND SCOPE

       This report presents the results of a study conducted  by Arthur D.  Little, Inc. for
the National Center  for Air Pollution Control concerning electrically powered vehicles of
low pollution potential. A parallel study  concerning unconventional thermal, mechanical,
and  nuclear  power  sources  for  vehicles  has recently  been  completed by  the Battelle
Memorial Institute - Columbus Laboratories.*

       The  major purpose of the present study is to  assess the  state of the  art in the
technologies on  which the future development of electric highway vehicles depends. The
assessment is made on the basis that there will be no major change in the patterns of urban
transportation and focuses upon the technical requirements of the vehicle. As a framework
for the study, technical and, to a  lesser extent, cost criteria were established for six classes
of electric  vehicles, most  of which correspond  closely  in performance  to  existing
conventionally  powered types. On  the basis of  these criteria the prospects  for vehicle
application of various electric motor  and control systems and a wide range  of electrical
power sources including  batteries,  fuel  cells, and  engine-generator-battery hybrids  are
compared. The study identifies the most  promising  systems  for further development and
estimates the magnitude of the shortfall in their present  characteristics. Recommendations
are made for the expansion of future effort in these areas, taking into account the expected
contributions from existing programs in the public and private sectors of the economy.
B.  FINDINGS

       (1) The technical state of the art in motors and controls is generally more advanced
than that of power sources in relation to the needs of electric highway vehicles.


       (2) Minimum energy and power densities for electrochemical power sources capable
of giving acceptable performance in the six classes of vehicles are listed below. The figures
are based  on reasonable  estimates of  the weight assignable to  the  power  source and
propulsion system and of the weight of suitable electric motors and controls.

                            Family    Commuter    Utility    Delivery    City    City
                              Car         Car        Car      Van      Taxi     Bus
 Conventional construction
    Energy density (w-hr/lb)   135
    Power density (w/lb)        94
 Lightweight construction
    Energy density (w-hr/lb)     87
    Power density (w/lb)        60
41
46


28
31
26
40

18
28
50
55

33
36
96
45

64
30
81
36

55
25
  * Battelle Memorial Institute, "Study of Unconventional Thermal, Mechanical, and Nuclear Low-Pollution-
   Potential Power Sources for Urban Vehicles," by J. A. Hoess, etal.. Summary Report to U.S. Dept. of
   Health, Education and Welfare, March 15, 1968.
                                                                                   ZD.ILttttcJnr.

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        (3)  In a hybrid power source the important technical parameter for the battery is
 the power density; energy density is of only secondary importance. The power densities
 required for batteries in vehicles of conventional construction having 40% of the peak power
 supplied by a gas piston engine and 60% by a battery are as follows:
                          Family    Commuter    Utility    Delivery    City    City
                           Car          Car         Car        Van      Taxi    Bus

     Power density (w/lb)   92           38          34        43        35      25
For the family car, the power density requirement is virtually equal to that for a purely
battery powered vehicle; for the other vehicles the requirement is not much lower.

       (4) The technical requirements for the family  car power source can be met only by
high  temperature alkali-metal batteries; these  systems,  as yet in the early  stages of
development, are also the most promising for the commuter car, the delivery van, and the
city taxi.  If lightweight construction is used metal-air batteries are potentially capable of
meeting the requirements for all vehicles except the family car. Alkali-metal batteries with
organic  electrolytes seem likely to have insufficient power density for use in vehicles, and
combining them with high-power-density batteries is clearly too costly a solution.

       (5) Although  of  limited energy  density the lead-acid battery  seems likely to be
capable of meeting the requirements of the utility car of lightweight construction.

       (6) The  fuel cell's prospects as an electric  vehicle  power source seem unfavorable,
mainly because  of its extra complexity  and cost  and its lower power density. Its much
simpler mode of refueling, however, would be a major advantage.

       (7) The  most practical  present  choice  of motor  for an  electrical vehicle  is a
high-speed dc  machine with mechanical commutator,  operating at speeds of up to 19,000
rpm for the smaller vehicles, air cooled, and with integral speed reducers. Such motors are
already being developed for aerospace and military applications.

       Control of high-speed  dc motors is  best achieved  by a chopper circuit containing
silicon controlled rectifiers (SCR's). These  circuits are at  present rather  heavy for the
amount of power they control. However,  they  can  be developed for operation at high
voltage (500 volts in the case of the bus and family car) so as to be relatively lightweight.

       (8) Because ac motors can be  run at higher maximum speeds, they have a higher
output per pound than dc motors  and hence permit weight reduction; these will doubtless
be adopted when the technologies  for inversion  and control are further  advanced. The
development of solid-rotor ac motors instead of the squirrel-cage induction type will lead to
greater weight  reduction and simplify the problems of inversion and control.
                                                                            Arthur 21.1Uttlr,llttr.

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       The controller for the ac motor would be a variable-frequency, variable-voltage SCR
inverter circuit. Experimental circuits developed to date are, however, extremely heavy and
require capacitor banks across the battery when an induction motor is used.

       (9) Regenerative braking would reduce the power source requirements somewhat
for vehicles that make frequent stops. However, for the majority of vehicles, the amounts of
energy recovered do not appear likely to justify the added cost and complexity.

       (10) The recharging of electric vehicles is best achieved at slow rates. Rapid recharge
would call for large investment in  facilities and would  introduce  a number  of severe
technical  difficulties. Occasional long  trips could  be  accomplished by replacement of
batteries at service stations.

       (11) The  first  costs of electric vehicles  will inevitably be  higher than  those of
equivalent  internal-combustion-powered  vehicles.  Part  of this may be offset  by  lower
maintenance requirements and longer life, but much of the difference would have to be
regarded as a social cost for the elimination of  air  pollution.  If an  additional  SI,000 is
acceptable in the retail cost of the family car, the cost target for the battery is in the vicinity
of 95 cents per pound. Allowable  costs in the  commercial vehicles  would  be somewhat
higher.  High-temperature alkali metal batteries have  some prospects of meeting these cost
requirements.  Metal-air  batteries are likely  to be somewhat costlier but might still be
acceptable for commercial vehicles.

       (12) The  duplication  in  functional  capabilities tends to give  hybrid vehicles a
fundamentally higher cost structure than pure electrics.  The higher  cost may, however, be
acceptable in commercial vehicles, and existing technology would permit low cost lead-acid
batteries to meet  the power density requirements of  a hybrid city bus, making this vehicle
an attractive possibility.

       (13) Present federal spending on  research and development on electrochemical
power sources, and  exclusive of the major fuel cell hardware programs for space vehicles, is
estimated  to be in the vicinity of $10 million annually. However, only a small proportion of
this  is  directly relevant to the needs of electric vehicle development for  civilian use.
Expenditure by private industry on power source development relating to electric vehicles is
estimated at $5-7 million annually.

       (14) The  time  scale for the  development of electric vehicles will be  determined
mainly by progress in battery technology and by the magnitude of the effort which sustains
it. Assuming  that the  latter is adequate,  high-temperature alkali metal batteries appear
likely to require a period of the order of ten years before  they can be considered as practical
and economic power sources for use in vehicles.  Certain metal-air systems, having promise
for application in commercial vehicles,  might  be made available in a somewhat shorter
period.  At  least comparable periods of time would be needed to develop sufficiently low
cost manufacturing processes for the motors and controls.
                                                                            Arthur ZD.Itttlc.llnr.

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 C.  RECOMMENDATIONS
       (1) The  power source requirement  for  electric  vehicles calls for a major and
sustained  effort  in the development of batteries with high energy density and high power
density.  The requirements for the most significant classes of vehicles can be fully met only
by batteries having alkali-metal  anodes and molten salt (or possibly ceramic) electrolytes,
which  necessitate high temperature  operation.  If  such  batteries are  to be brought  to
maturity within  a ten-year period a coordinated program under federal sponsorship should
be set up to do the following:

      (a)   Explore comprehensively the electrochemistry of the limited number
           of elements having the reactivity and potential low cost  availability to
           function as anode or cathode materials in high-temperature alkali metal
           batteries.  The  physical chemistry of molten salt and ceramic systems
           appropriate for use as electrolytes should also be investigated.

      (b)   Examine the materials selection problems associated with such bat-
           teries, giving particular regard to choice of current collectors, separa-
           tors, sealants, and structural materials generally.

      (c)   Investigate suitable low-cost engineering solutions for the problems of
           thermal insulation, temperature control, and safety, which are  com-
           mon to all members of this class of batteries.

      (d)   Develop, in collaboration with industry, the one or two most practical
           battery systems arising from these research programs.

     (2)  Support should be given to  the further development  of rechargeable  metal-air
batteries.  For those of relatively conventional design the principal problems rest with the
basic electrochemistry. Other types, which employ engineering solutions to the fundamental
electrochemical difficulties, should be supported in the development stage.

     (3) The  development of high rate lead-acid batteries should be supported in view of
their prospects in hybrid-powered commercial vehicles.

     (4) The problems of adapting the technologies of high speed air-cooled dc commutator
electric motors and of sophisticated  dc chopper controllers for low cost  mass production
should be investigated. Studies should be  initiated as to the techniques -  such as extensive
automation and use of microelectronic, modules — by which cost reductions might best be
achieved.

     (5) Possible techniques for  the  low cost manufacture of solid-rotor synchronous ac
motors and of squirrel-cage ac induction motors with inverters  should be  investigated. The
technology of these  machines (known also as brushless dc motors) would  also benefit
directly from the advances in dc chopper controllers and high-speed dc motors.
                                                                             3rthxtr ZD.ILittlc.Knr.

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     (6)  Some general encouragement should be given to developing the use of lightweight
materials, particularly  plastics, reinforced and otherwise, and the lighter metals,  for use in
present day conventional automobiles. Advances in this area will help to hasten the advent
of electrically powered vehicles by lessening the severity of the requirements on  the power
source. Similar considerations hold for tires designed to minimize rolling resistance.

     (7)  The  potential merit  of electric vehicles,  relative to other  approaches toward
alleviation  of the air pollution problem, should be periodically re-evaluated  in the light of
the  progress  and  pattern of  development  taking  place  in the  various contributing
technologies.
                                                                              Arthur ZD.lUttlc.Knr.

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                                   II.  APPROACH
       The pollution of the atmosphere by the exhaust products of the internal combustion
engine,  particularly in the cities, is  a  subject of increasingly serious concern. Viewed as a
purely  technical problem, abatement  can  be  approached  in  several ways.  The  most
straightforward is to modify  the engine and exhaust system with devices which will either
suppress pollutants or convert them into less noxious products.  A great  deal of effort is
presently being expended in this approach, and it may well prove to be the most satisfactory
for the immediate  future. However,  the  tendency of an internal combustion engine to
pollute  increases  with its age,  and  the  effectiveness of conversion devices, usually involving
catalytic combustion, decreases  with  time;  thus the suppression of  pollution  may be
adequate in  a new vehicle but quite  unsatisfactory by the time it  is two or three years old.

       Another approach is to replace the internal combustion engine with a type of prime
mover that  has  no  significant pollution problem. In principle there are a  large  number of
possibilities, including electric power sources, external combustion systems, inertial energy
systems and a variety of exotic energy conversion devices. In practice, however, the practical
options are quite limited.

       A  third  approach is to alter the transportation system  through major  changes in
conventional public facilities or through such concepts as the rental of small, self-driven.
taxi-like vehicles for journeys within  the urban centers.

       The  subject matter of this  study is concerned with the second general approach and
specifically with the prospects for self-propelled electric vehicles.

        It is necessary to make numerous assumptions as the basis for a  study of this type,
many of them  rather arbitrary,  and  many  of them having a  significant bearing on the
findings  of the  study.  We  are  well  aware  of this  and consider our work as a  first
approximation which may suggest directions for further more refined and specific analysis.

       The  study is based upon a consideration of the requirements for six  types of electric
vehicles: a family car, a commuter car.  a utility car, a delivery van, a city taxi and a city bus.
With the exception of the utility  car these represent the great majority of vehicles that now
provide transportation  in  the  urban  environment. The model for the family car is the
familiar  full-sized,  six-passenger  automobile, which  represents almost  SO'/r  of the  total
vehicle  population  of this country.  The commuter car is modeled on  the much  smaller,
four-seater,  European-type compact  car, whose  population has  been steadily increasing in
recent years, primarily for commuter travel. The delivery  van is somewhat  less well defined
but can be regarded as a typical panel  truck with a carrying capacity of about one ton. The
city  bus is  the  characteristic full-sized  vehicle  with a  carrying capacity of about 80
passengers including standees.  The other two vehicles contain an element of invention. The
city  taxi is outwardly  similar to the family car but has been arbitrarily assigned lower
performance capabilities in view of  its working pattern in the dense traffic of city  streets.
The utility car is a  small vehicle intended purely for local  trips, such as might be taken by a
                                                                                    ai.ltittlc.llnr.

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housewife on shopping errands or possibly for short-range commuting. While each of these
vehicles is  a candidate for electric propulsion in  its own right, it is clear that the greatest
interest attaches  to  the family  car  in  view of its  preponderance  in  the total  vehicle
population.

       The first step in the selection of weight and performance parameters for the various
vehicles involved  an  examination of  the published data for virtually all vehicle  models
manufactured over the last ten years in the United  States and Western Europe.  From these
vehicle  specifications,  reasonably appropriate values  were established  for  weight  and
performance in each of the classes. The calculation of power requirements  necessitated some
assumptions about frontal cross-sectional area, degree of streamlining,  and tire friction. The
values chosen for the  drag  coefficient  were  liberally  low, reflecting  the best present
aerodynamic design practice,  while  the  estimates for  tire friction were conservative, since
there is some element of compromise with safety in the design of low-friction-loss tires.

       The parameters for acceleration are believed to represent reasonable values for new
vehicles.  It  would  not  be fair, however,  to insist that the electric vehicle should have an
acceleration  equal  to that of a typical  new,  carefully tuned vehicle  with a conventional
engine. The performance of an electric  vehicle should remain fairly constant with time,
while that of most conventional vehicles is at least fractionally lower  than  when new after
three or four  years on the road. Accordingly, adverse weighting of the vehicles that formed
the basis  for the  assumed  parameters was at  least partially offset  by  considering only
vehicles whose power capabilities were on the lower side of normal. Thus, the acceleration
for the family car is typical of that for a six-cylinder vehicle, even though more than 80% of
the vehicles in this category now have eight-cylinder engines.

       Probably of even greater influence on the findings of the study than the assumptions
about performance are those  about driving cycles and  their relationship to vehicle range.
The energy  consumed  by a vehicle  per  mile  of driving is very heavily influenced  by  the
number of stops made, by the rate of acceleration, and by the velocity. The selection of any
particular driving  pattern thus  has  a  major effect  on  the  range  obtainable from a given
quantity  of stored energy. Fortunately, the arbitrariness of the assumption is partially offset
by the fact that vehicles are generally driven at relatively high speed when not in stop-and-go
traffic; the  energy consumption per mile is  therefore very much more constant than it
would be if people were in the habit of driving at modest speed on the open road.

       The  technical requirements for the six classes of vehicles have been established  by
the following procedure. The maximum power requirements corresponding to the maximum
acceleration performance assumed  for the vehicles were first calculated; this provided a basis
for setting  the power  rating  of each vehicle. The requirements for stored energy were
calculated from the energy expenditure  for each vehicle when following a standard urban
driving cycle. (Since the driving pattern for the city bus involves an unusual number of stops
per mile, a  separate driving cycle was developed  and  used  for this vehicle.) Assumptions
about total  range  varied  with the type of vehicle;  in  general, the criterion was to take a
relatively low value but one that would be justifiable in  the application for  which the vehicle
was intended. For example, the  family car has a range of 200 miles, the commuter car 100
miles, and the utility car only 50 miles.
                                                                                     ZD.1tittlc.3lnr.

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       To bring into focus the technical requirements for electric vehicles, our approach has
been to remove conceptually from the conventionally powered vehicles those components
(engine, transmission,  radiator,  muffler, etc.)  which are inseparably  associated  with the
functioning of the internal combustion engine and to replace them with an electrical power
source, motors, and a control system  of equal total weight. This procedure considers electric
vehicles as modifications and neglects the possibilities of weight  optimization which would
result from special design. Our basis has been some prior   work by Hoffman,* who analyzed
the weights of the components of a great many vehicle models and found a recurring pattern
in the weight distribution. Among passenger cars whose size and  power varied over a  wide
range, for example, the weight of the  replaceable components was never far from 35% of the
curb weight of the vehicle. Hoffman  also considered the  proportion of vehicle weight which
could be assigned to the power source and propulsion unit if lightweight materials such as
plastic body panels and magnesium  frames were used. He concluded  that this would  raise
the allowable proportion to  50%.  Our analysis has  been conducted on the bases of  both
conventional and lightweight construction, using proportions close to Hoffman's for the cars
and estimated values for the delivery van and city bus.

       A  major element in our further analysis is the assumption of representative weights
for the  motors and  controls used in these various vehicles so that a total weight  could  be
allocated to the power source. The pattern of the study  is  thus to relate the  prospects for
the electric vehicle largely to the requirements of its power source. The justification for this
assumption is that the  technology in the electrical and electronic areas is relatively further
advanced  toward  the  vehicle objective than  is that  of electrochemical  power sources.
Projections in these areas can thus be made with relatively  greater confidence. The derived
results of the above calculations  are then expressed as requirements for  energy density
(watt-hours per pound) and power density (watts per pound) for the power source.

       Power source volume is  also of some significance,  but to a first approximation it
would seem secondary  to considerations of weight. The great majority of the possible power
sources  which  are candidates for vehicle application  have densities which  are  broadly
comparable with each other and with the power systems they would replace. Moreover, the
electrochemical  power  sources would seem to have greater flexibility  for utilizing internal
space within the vehicle.

       The question of mechanical-electrical hybrid power sources has also been considered
as part  of this  study,  although practical  power systems  of this type  would inevitably
produce some degree of air pollution. No attempt has been made to  consider the relative
merits  of various hybrid approaches on  the  basis  of their  relative  contribution to air
pollution; they  have  been  regarded solely  as  alternative electrical  power  sources.  The
approach  was  to assign the  available power source weight to the engine-generator-battery
combination and from  the estimated weights for the first  two components determine the
power densities required from the battery.

       Much of this report is concerned  with a review of the present and projected state  of
the art in the technologies of electric motors and  control systems and electrochemical power
sources.  Using  the  technical requirements  of the  electric  vehicles   as a  yardstick  for
assessment of present achievement and future progress, we have developed some conclusions
and recommendations concerning the preferred direction  for further effort.
* G. A. Hoffman, Transportation Research, Vol. 1, No. 3, 1967.

                                          9
                                                                                   2l.llittle.3lnr.

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       The  question  of costs is of comparable importance  but is even more difficult  to
bring into focus, since it frequently relates to manufacturing processes which in many cases
are barely  in  the  conceptual stage.  Such conclusions about  costs as can be drawn are,
however, integrated into our assessment of the needs for further research and development
programs.

       The  conclusions  to be drawn from  our study, while cautiously optimistic for the
prospects of electric vehicles, are not to be interpreted as indicating the likelihood of their
imminent appearance.  A vast amount  of further technical  effort  is called  for  if the
large-scale use  of  electric vehicles is to become a reality, even twenty years from now.
Nevertheless it  seems  that it can be done, and  the effort should  be made if the  social cost  of
air pollution is sufficiently  great and other approaches to the problem are less attractive.
Such  decisions, however, are in the political realm; this report is to be  considered primarily
as a contribution to the technical evaluation of the problem.
                                         10

                                                                             9rthur ZD.lUttle.llnr.

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                     III.  CRITERIA FOR ELECTRIC VEHICLES
A. DEVELOPMENT OF VEHICLE SPECIFICATIONS

       In this section technical criteria  are  established  for  the  six classes of electrical
vehicles.  As a basis for  this,  the  electric vehicles  have  been considered as comparable
alternatives  to  existing vehicles powered by internal  combustion engines.  Though new
requirements for vehicles do appear from time to time, one year's car generally behaves very
much like another's, and motorists have  become accustomed to certain kinds of response
from the vehicles they drive. This is not to say that all of today's vehicles show identical
performance but, rather,  that there are minimum standards of acceleration and comfort to
which any  new vehicle must conform if it is  to achieve commercial success.  Furthermore,
any vehicle  which  cannot  perform like  most of those with which it mingles presents a
serious hazard on crowded roads.

       In addition to performance, the vehicle controls must be similar in "feel" to those of
conventional vehicles. This, however,  is largely a matter of proper design of the electrical
controls and does not necessarily involve weight and power consumption.

       The choice  of vehicles and of  vehicle parameters for this study (Table 1) were made
 after discussions with representatives of the National Center for Air Pollution Control and
 Battelle  Memorial Institute. Most  of  these vehicles represent types of conventional  motor
 vehicles  now used in and around our cities. For completeness, we have included in the study
 a  "utility"  vehicle, whose performance  is not  comparable with  that  of today's highway
 vehicles  but which  may find acceptance in specialized uses and locations. Its specifications
 correspond  closely to those of many of the electric vehicles developed  in  the  United
 Kingdom.

       The  reported performances of a number of selected types of internal combustion
powered  vehicles in each of the six classes were examined and norms were established for
their maximum acceleration; these figures are tabulated on lines 1 and 2.  Using the  actual
acceleration curves as a guide we then drew standardized acceleration curves and normalized
them to  the acceleration  specifications. These curves, shown  in Figure  1, were  used  as the
basis for all further calculations of maximum power and energy requirements.

       The maximum performance of a vehicle can  be  concisely stated as the relationship
between  velocity and time while it is driven from  rest at full power. It is not necessary to
consider  grade climbing separately, because at any given speed there is a simple relationship
between  maximum level-road acceleration) and  grade climbing ability.

       The weights assigned to the vehicles listed in Table 1  were based on data for current
vehicles of similar capacity  and performance.  The  weights assignable to propulsion, energy
storage, controls, etc.  in line 7a were obtained by use of the general procedure of Hoffman*
-  i.e., by  totaling the weights for all those  components of the  conventionally  powered
 op cit.

                                        11
                                                                                   ZD.lUttlc.3Jnr.

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                                           TABLE 1
                             ELECTRIC VEHICLE SPECIFICATIONS
Assumptions
  1. Acceleration to
  2.             in
  3. Range
  4. Seats or payload
  5. Loaded weight*
  6. Curb weight
  7. Weight assignable to propulsion,
      energy storage, controls
      a.  conventional construction
      b. lightweight construction
  8. Frontal area
  9. Drag coefficient
 10. Elec. transmission efficiency


(mph)
(sec)
(mi)
(Ib)
(Ib)
(Ib)
I
(Ib)


(ft2)

(%)
Family
Car
60
15
200
6
4,000
3,500

1,250
1,750
25
0.35
82
Commuter
Car
60
30
100
4
2,500
2,100

750
1,050
18
0.25
77
Utility
Car
30
10
50
2
1,700
1,400

500
700
18
0.25
72
Delivery
Van
40
20
60
2,500
7,000
4,500

1,400
2,000
42
0.85
79
City
Taxi
40
15
150
6
4,000
3,500

1,250
1,750
25
0.35
76
City
Bus
30
15
120
10,000
30,000
20,000

5,000
7,000
80
0.85
85
70
94
85
100
100
122
22
30
29
80
20
26
12
16
17
65
8
11
49
66
62
56
45
57
36
48
47
77
75
99
135
180
159
55
300
353
Derived Parameters
11.  Max. power delivered by motors
                                (kw)
                                
-------
   70
   60
   50
£  40
e

4-*
o  30
   20
    10
            Circles Represent
            Normalization
            Points
                      10
15       20

 Time (sec)
25
30
                                  100

                                   90

                                   80

                                   70

                                   60 T
                                       I
                                   50  £
                                                                     _o
                                                                     v
                   30

                   20

                   10
35
          FIGURE 1    STANDARDIZED ACCELERATION CURVES
                                 13

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vehicles which  would not be required in the same form in an electric vehicle. The assignable
weight for vehicles with conventional construction  is shown on line 7a and for lightweight
construction on line 7b.

       The values chosen for the range of the electric vehicle, line 3, are on the low side of
average for internal combustion powered vehicles in the case of the family car, city taxi and
city bus. For the commuter car, utility car, and delivery van, we chose values which might
represent reasonable daily ranges for vehicles which are not likely to be used continuously
for long periods.


B.  POWER AND ENERGY CALCULATIONS

       Two sets of calculations are needed to define the power and energy requirements of
a vehicle.  First, we must know the maximum power and the velocity at which this maximum
occurs. Second, we  must calculate the total energy consumed when  the vehicle  operated
under various driving conditions.


     1.  Power  Requirements

       The power expended  by the vehicle can be represented by the following expression:

                   instantaneous power = velocity [mass x acceleration
                                      + aerodynamic drag + rolling resistance]

The maximum  power requirement is determined by expressing all the quantities on the right
hand side in terms of velocity as a variable. The expression is then differentiated and  the
resulting function put equal to zero.

       a.  Acceleration

       The first step was to express the maximum  linear acceleration in terms of velocity.
This was done  by synthesizing simple analytical expressions which fitted the graphical data
reasonably  well  within  the  normalization  limits  of the performance  curves. These
expressions,* which are shown graphically in Figure  2, are as follows:

Family Car:    a = 20   0.500 v + 5.3 x l(T3v2 - 2.2 x  l(Tsv3  - 8(1 + lO'V) "'
 * The symbols and units used in the analytical expressions are as follows:


     a       acceleration (ft sec"2)                      M      weight of vehicle (Ib)
     A       frontal area (ft2)                          S      distance travelled (ft)
     CQ     drag coefficient (dimensionless)               t      time (sec)

     g       gravitational constant (32.2 ft sec"2)          v      velocity (ft sec"2)
                                          14

                                                                              Arthur ZH.1Uttlr.3lnr.

-------
Commuter Car:          a = 7.0 - 0.028v - 1.3 x 10'3 v2 + 0.9 x 10's v3

Utility Car and          a = 6.6 - 0.046v - 1.3 x 10'V + 0.7 x 10-sv3
Delivery Van:

City Taxi:               a = 9.0 - 0.053v - 3.0 x 10"3v2 + 3.0 x 10'5v3

City Bus:               a = 5.2 + 0.006v - 5.3 x 10'3v2 + 7.0 x 10'5v3
       From these expressions, the power expended on linear acceleration during periods of
maximum acceleration  can be expressed as a  function of v, namely
                                   Mav
                                    g
If the power required for rotational acceleration is assumed to be 10% of that for linear, the
total power used for acceleration is

                                 1.1 Mav
       b. Aerodynamic Drag

       Estimates given in the literature for power consumption caused by aerodynamic drag
vary considerably.  For example, using a 2000-lb vehicle traveling at 60 mph, Hoffman*
finds 9.7 hp and the Morse panel** finds 17 hp. Basically, the reason for these discrepancies
is varying judgments as to  the practicability of employing good  aerodynamic body styling.
We take  an optimistic view and believe that the arguments of Tenniswood et alJ are sound.
These authors reason that the incentive to reduce air resistance in gasoline-propelled vehicles
is comparatively  weak, because  no initial cost saving is achieved; in electric vehicles, how-
ever, particularly those designed  for high speed, it can  affect  first  cost by reducing  the
battery capacity required for a given range. We believe that, compared with the problems of
developing satisfactory power sources, improving the aerodynamic characteristics of vehicle
bodies would  be  relatively  easy. We have therefore employed optimistic values  for the drag
coefficients, CQ, in  the following expression:


                       Drag force =  1.19 x 10~3 CDAv2  pounds

The values assumed  for frontal area, A (Table  1, line  8)  reflect a moderate  degree of
streamlining.

  *op cit.
**77>e Automobile and Air Pollution: A Program for Progress, Report of the Panel on Electrically Powered
  Vehicles (R.S. Morse, Chairman), U.S. Dept. of Commerce, October 1967.
  TD.M. Tenniswood and H.A. Graetzel, Ford Motor Co. (SAE paper no. 670177), 1967.

                                            15

                                                                              3rthur ai.1Littlc.Ilnr.

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   9.0
   8.0
   7.0
   6.0
8  5.0
.c
Q.
C
o



1  4.0


S
u
   3.0
   2.0
   1.0
                                           Utility Car and

                                           Delivery Van
               10
                                                              Family Car
                                                            Commuter Car

                                                           	I	
                                                     13.0







                                                     12.0






                                                     11.0






                                                     10.0






                                                      9.0






                                                      8.0  r^

                                                          I

                                                          %
                                                                              7.0
                                                                                   o
                                                                                   '
                                                      6.0  "5
                                                          u
                                                          u
                                                                              5.0
                                                                              4.0
                                                                              3.0
                                                                              2.0
                                                     1.0
20
30        40


Velocity (mph)
50
60
70
   FIGURE  2    ACCELERATION VERSUS VELOCITY FOR SELECTED VEHICLES
                                    16

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        c. Rolling Resistance
       When a vehicle  moves  at uniform velocity over a smooth road,  that portion of
resistance which is not due to aerodynamic drag results principally from the work done in
distorting the tires, together with a small addition from wheel bearing and gearbox friction.
Some authorities,  such  as the  Morse panel, treat rolling resistance as a  constant force
dependent upon tire characteristics and vehicle weight, but this does not agree with the data
presented by Tenniswood  et al., Hoffman, and StiehJer et al.* Combining the available data,
we have derived an empirical equation relating rolling resistance to vehicle weight and speed.
If the latest developments in  low-loss tires are employed, the resistance would be less than
the values calculated from the  equation,  but we have taken a  cautious approach for the
following reasons:   1) much of the reduction  in rolling resistance of improved tires is lost if
correct inflation pressures  are not maintained; 2) a soft ride may be demanded by buyers of
electric automobiles, and on rough roads this would require that energy be absorbed either
in the tires or by the suspension  system;  3) federal safety requirements for tires cannot at
present be met by tires with very low  rolling resistance.

       Our empirical expression for the  rolling resistance, which also includes the losses in
the gearbox and bearings, is:
           Rolling resistance =-|1 (1 + 1.4 x l(T3v+ 1.2 x l(Tsv2) pounds.
       d. Calculations of Maximum Power
       The final expression for instantaneous power under conditions of maximum accel-
eration is thus:


_v_  I J.I Ma  + i 19x 10-3 CDAv2 +-M-  (1 + 1.4 x  10"3v+ 1.2 x l(T5v2)  horsepower
J J \J  I    jj                           Jv/                                 J

 where a is related to v by the expressions given above in subsection a and the factor 550 con-
 verts ft  Ib sec" '  to horsepower. This expression is plotted in Figure 3 for the family car. In
 this case the total power requirement does not pass through a maximum value in the velocity
 range of 0-60 mph, and the conditions for maximum power are those for maximum accelera-
 tion  at 60 mph. A number of the other vehicles show maxima at velocities in the 20-40 mph
 range. Values for the maximum power, which is that delivered at the output of the gearbox,
 are shown in line 11 of Table 1.
   R. D. Stiehler, M. N. Steel, G. G. Richey, J. Mandel, and R. H. Hobbs. J. Res. Nat. Bur. Std.,
   Vol. 64 0,1960.
                                         17

                                                                                   ZD.IUttlr.Knr.

-------
                      Linear Plus
                      Rotational
                      Acceleration
                                         Rolling Resistance
                                         Plus Aerodynamic
                                         Drag
         10
20       30
    Velocity (mph)
40
50
60
FIGURE 3    POWER REQUIREMENTS FOR THE FAMILY CAR
             AT MAXIMUM ACCELERATION
                        18

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     2. Energy Requirements

      The energy requirements for each vehicle, corresponding to the values for the range,
listed on line  3, are heavily  dependent upon the driving cycle or pattern of use involved.
Thus, for a given quantity of energy stored,  the  range of an  electric vehicle operating
nonstop at constant velocity  might be several times  that when operating in city traffic with
frequent stops.

       The selection of an appropriate driving cycle is somewhat arbitrary. After consulta-
tion with representatives of the National Center for Air Pollution Control, we have adopted,
for all vehicles except the city bus, the "Public Health Service Cycle" derived from a driving
cycle (LA4) based on studies in the city of Los Angeles. This cycle is set out in Table 2.
For  the city bus, another cycle  was devised  which reproduces the statistical observation
that its average velocity is 12 mph and that it makes ten stops per mile; this cycle is shown
in Table 3.


       On the basis of these  driving cycles and the assumed parameters for the vehicles, we
calculated the  delivered energy requirements for the  various ranges. These are shown on line
14 of Table 3. The requirements  for stored  energy, line 15, were derived by dividing the
delivered requirement by the electric transmission efficiency.
C. ELECTRIC TRANSMISSION PARAMETERS

       The weights allotted to the motors, control systems, cabling, etc. for the six classes
of electric vehicles have been estimated on the basis that high-speed dc motors with silicon
controlled rectifier chopper control  circuits would  be the most appropriate system. The
factors affecting this choice are considered later, in Section IV. This subsection contains
details of the specifications for  the  various components of the electrical transmission for
each class of vehicle.

       One  of the  fundamental characteristics  of electric  motors and electromagnetic
machines in general is their ability to deliver a constant torque over their entire speed range.
By proper control, a motor can be made to deliver its rated torque or fraction thereof at any
speed from zero up to the physical limit  of its rotating member. By overloading the motor,
one can  produce  150% to 200% torque for short periods of time; the amount of overload
torque obtainable and the length of time the motor can deliver it without damage depend
on the details of the design of  its motor particularly as it affects thermal capacity. Since
horsepower is the product of torque and  speed, the maximum horsepower from a given size
motor is obtained  by operating it at its highest speed. The rated maximum speed is dictated
by the  mechanical stress limit  of the rotor.  These fundamental motor relationships are
summarized in Figure 4.
                                          19

                                                                             3rthur ZD.lUttlc.3nr.

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                                       TABLE 2
                            PUBLIC HEALTH SERVICE CYCLE
Velocity Mode
(mph)
0
0-19
19
19-44
44-52
52
52-37
37
37-31
31-0
Mode Time
(sec)
30
8
15
12
7
9
12
16
5
13
Cumulative
(sac)
30
38
53
65
72
81
93
109
114
127
                                                                      Acceleration Rate
                                                                          (mph/sec)
                                                                           + 2.38


                                                                           + 2.08

                                                                           + 1.14


                                                                          - 1.25


                                                                          - 1.20

                                                                          -2.38
                                       TABLE 3
                                   CITY BUS CYCLE
Velocity Mode
(mph)
0-15.7
15.7
15.7-19.0
19.0-0
Time
(sec)
6.60
13.30
1.35
7.95
Distance
(ft)
76
306
35
111
                                                                      Acceleration Rate
                                                                         (mph/sec)
                                                                          + 2.4


                                                                          + 2.4

                                                                          -2.4
                        29.2
528
Average speed = 12.2 mph
                                           20
                                                                                      2l.1Uttlr.ilnr.

-------
                                                        Maximum Power Attained
                                                          at Maximum Speed
O

I
                                       Speed
         FIGURE 4   POWER-SPEED CHARACTERISTIC CURVES FOR ELECTRIC MOTOR
                                  21

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     The selection of one or more motors for a given vehicle application involves matching
motor characteristic curves of the type shown in Figure 4 to the power demand profile for
the vehicle, such' as that  for the family car in Figure 3. This matching is shown in Figure 5
where the  dashed  line represents the characteristics of the smallest dc motor which could
meet the power requirements entirely within its rated power capabilities.  Since maximum
power demand will  in practice be relatively  infrequent and of short duration, one could
safely select a motor wriich would have these capabilities on 100% overload. The power-
speed  relationship for the chosen motor is shown  by the solid sloping line. It can be seen
that the maximum power output of which this motor is capable and which is attained at its
maximum motor speed will be  significantly greater than the maximum power demand of the
vehicle. The vehicle cannot, however, use a smaller  motor because of its need for substantial
power at lower speeds and cannot utilize the full capability of a larger motor because of the
limited output of the power source. A smaller motor could be used if  a gear changing
mechanism or torque converter were inserted into the  power train, but such devices  are
undesirable because they  introduce extra  weight, cost, and power inefficiency.


     The selection  of motors is also influenced by certain  general engineering consider-
ations.  For example,  we have chosen to use a motor for each wheel in the family car,
delivery van, city taxi, and city bus (the latter being a six-wheel vehicle); this has been done
to obtain  certain  benefits resulting from  separate control of the power applied to  the
individual wheels.* Normally,  the use of several small motors rather than one large motor
would incur a weight penalty: for motors of a given  speed, the power output per unit weight
increases with increasing size,  since  magnetic and  thermal  designs become more efficient.
This characteristic can be offset, however, by designing  the  smaller motors to operate at
higher maximum speeds.

      Estimates  of the weights of these high-speed  dc  motors  have been  based on  dc
machines now used  in aerospace and torpedo propulsion applications. It  is assumed that
these motors would  be cooled by forced air from a separate blower system. The weights of
the controllers have also been estimated from existing devices, some of which are being used
in lift trucks and other electric  motor control applications.

     To size the controllers and vehicle cabling, we have had to make assumptions about the
maximum voltage for the electrical system in each  of the vehicles. The values selected were
500  volts for the family car and city bus, 250 volts for the commuter car, delivery  van, and
city  taxi, and  125 volts  for the utility  car. Allowance has also been made for the weight
associated  with the  electric cabling,  component mounting, cooling system,  and  a  speed
reducer for each motor-wheel system.

     Estimates based on the present state of the art have also been made for the efficiency
of the individual motors  and controllers. Speed-reducer efficiencies were already considered
in the calculation of energy requirements.
* A compromise of two wheels per motor was made for the commuter car and the utility car.
                                       22

                                                                          Arthur ai.llittkKnr.

-------
Power-Speed Line for
Motor Capable of
Powering Vehicle
without Overload
   94
a
x:
o
a.
                                                  Power-Speed Line for
                                                  Motor Selected
                      Power Demand of
                      Vehicle at Maximum
                      Acceleration
                                                  Power Demand of
                                                  Vehicle at Constant
                                                  Velocity
                                          60
                              Vehicle Velocity (mph)
            FIGURE  5    MOTOR SELECTION FOR FAMILY CAR
                                   23

-------
       The results of these analyses are presented in Table 4 and the total weight of the
electric transmission  system is entered in line 16 of Table 1. It can be seen that this weight
amounts to some 5-6% of the curb weight of all vehicles except the family car (for which it
is about 10%)  and the city  bus (about 3%). The effects of matching the motor to the profile
of vehicle power demand can be seen by comparing the estimates for the maximum possible
output of the  motors in the family car (56 hp) with the maximum actually used (23.5 hp).
Each motor thus has a potential output of 1.0 hp per Ib but a useful output of only 0.41  hp
per Ib.

       From the values for electric transmission  weight  presented in Table 4 and included
in Table I, line 16,  it is possible to estimate allowable  weights for the power source  by
subtraction  from the weights given on lines 7a and 7b of Table 1.  The results are shown  on
line  17.  Combining  these  with the  calculated power and energy demand of the vehicle
enables us  to calculate the  required energy densities and power densities for power sources
capable of  meeting the vehicle specifications. These values are entered on lines 18 and 19 of
Table  I and form the background to the review of the state of the art in  electrochemical
power sources  in Section V.

       The approach taken  in this study  focuses attention  on the  energy  and power
capabilities  of the power source per unit weight  rather than per unit volume.  The justifi-
cation for  this  is  that the average  densities  of  electric motors,  controllers, and electro-
chemical power  sources are, with the possible exception of ambient-temperature fuel cells,
fairly similar to those of the components they  would replace in an internal-combustion-
powered vehicle.  Moreover, since the electrical system is interconnected by cabling rather
than mechanical links, it has greater flexibility for location within  the vehicle. Thus it seems
reasonable  for a first consideration  to  assume that w-hr/lb and w/lb can be used  as yard-
sticks of the technical merit of a power source for vehicle applications.

       The analysis of power and energy requirements carried out here has been concerned
only with the  demands of  the vehicle for mechanical energy.  Present-day automobiles use
significant  amounts of energy  for a variety of other purposes. Most prominent are the
demands for heating  and air conditioning, the former amounting to a maximum of perhaps
five  thermal kilowatts and  the  latter to two electrical kilowatts in the average family car.
The  additional  demand for lights and various ancillary power equipment can amount to a
sizable fraction of a  kilowatt. In our analysis we  have neglected  these demands, since  an
auxiliary gasoline-fed  burner is probably  the most appropriate  type  of heating device, and
air conditioning is not yet regarded in  most of the United States as a necessity.
                                         24

                                                                            3rthur

-------
      ro
Maximum power delivered to wheel
speed reducers                (hp)
                             (kw)
Number of motors
Maximum power delivered to wheel
speed reducers by each motor   (hp)
Maximum motor speed         (rpm)
Fraction of maximum motor speed
at which motor delivers its
maximum power*  to the wheel
speed reducers
Maximum power output of which each
motor is capable at its maximum
speed
Weight of motors
Motor efficiency
System voltage
Weight of controller
Controller efficiency
Weight of speed reducers
Weight of cables, mounting, etc.  (Ib)
Weight of cooling system
Overall efficiency (excluding speed
reducers)
Overall weight of electrical system
(including speed reducers)

'Assuming 100% overload capability.
               TABLE 4


ELECTRIC TRANSMISSION PARAMETERS

Family Car      Commuter Car      Utility Car    Delivery Van
                                                                                                                             City Taxi
                                                                                                                            City Bus
                                                                  0.42
                                                                   56
                     0.48
                       31
0.56
14.5
0.48
34.5
(hp)
(Ib)
(%)

(Ib)
(%)
(Ib)
(Ib)
(Ib)
ed
(%)
n
(Ib)

4 x 57 = 228
88
500
50
93
15
45
10
82
348

2 x 33 = 66
85
250
30
91
6
12
4
77
118

2 x 18 = 36-
80
125
28
90
3
12
3
72
82

4 x 36= 144
85
250
66
93
12
30
7
79
259

4x32 = 128
83
250
48
92
8
20
6
76
210

6 x 70 = 420
90
500
90
95
30
60
15
85
615
ta
n

-------
                      IV.  ELECTRIC TRANSMISSION SYSTEM


     This section discusses the state of the art of electric transmission systems as it applies
to the criteria for the vehicle classes arrived at in Section III.

     The function  of the electric transmission system is to  drive and control the speed of
the wheels of the vehicle, using the  power of the battery, fuel cell, or hybrid power source.
The system consists of one or more motors geared  through  speed reducers to the wheels of
the vehicle, a control unit for each motor, and electric cables that join the control units to
the power source.  Since  the control units,  motors, and  speed reducers  have certain
unavoidable  losses, the resulting heat must be dissipated by  a cooling system, the weight of
which must be assigned to the electric transmission system.

     In  a battery-powered vehicle,  it is extremely  important  to have high efficiency
throughout the electric transmission system, since battery power is limited. Replacement of
the automatic  transmission  with a fixed-ratio speed reducer  increases the overall efficiency;
however, some weight  penalty is imposed upon the motors, since they are called upon to
deliver high  torques at extremely low speeds. This  weight penalty is not  too  severe if
high-speed motors and  large  speed  reduction  ratios  are used, as  discussed  in subsequent
sections.
A.  MOTORS

     The maximum rated  speed  of a  motor depends upon the rotor construction, which
varies with  the  type of motor. The most  important  limitation is the  rotor peripheral
velocity; this is determined by the  speed and the rotor diameter, as shown in Figure 6 for
four types  of rotor construction.  Obviously, the smaller the diameter,  the  higher  the
allowable rotor speed.

          For the low-horsepower  requirements of small vehicles, motors of relatively small
diameter can be  used, and thus very high rotor speeds are possible. This helps to counteract
the intrinsically greater efficiency of large motors: by operating the low-horsepower motors
at higher speeds than the  high-horsepower motors, one can largely avoid the penalty in
pounds  per  horsepower imposed  upon smaller machines. Further significance of  the
information  contained in Figure 6  will be discussed when the relative advantages of ac and
dc motors are discussed later in this section.

     Since high  speed is a  requirement  for obtaining a high horsepower  per  pound, it is
desirable to  have a small diameter and hence a long  rotor. At  the present state of the art,
therefore, only  conventionally shaped, cylindrical-rotor  dc  and ac  motors  capable  of
high-speed operation can be considered for vehicle propulsion.

     The two unconventional dc  motors  described  below are discussed for  the sake of
completeness but must be excluded from vehicle use consideration at this time.
                                         26

                                                                                  ZD.Hittle.Knr.

-------


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Inductor Rotor
Squirrel Cage
Rotor
dc Motor Rotor
Salient Pole
          4    6  8  10
           Rotor Diameter (in.
20
40   60
FIGURE 6    ALLOWABLE ROTOR SPEEDS
               27

-------
     Pancake-shaped motors, of which the most common is the printed-circuit dc motor, are
large in diameter and short in length; consequently they have high rotor stresses at high
speeds and are not acceptable for electric vehicles. Widely used in low-inertia, fast-response
drives, such motors have axial working air gaps instead of the annular gaps of conventional
motors. This produces a different physical configuration, but the torque per ampere is about
the same.

     So-called homopolar  dc motors  are  unacceptable because,  as  explained  later,  the
characteristics of control systems do not permit use of any motor which requires extremely
high currents  and correspondingly low  voltages.  This is unfortunate, since their voltage
requirement nicely matches the low voltage  available from batteries. Homopolar motors also
employ liquid metal brushes, which do not permit the maximum speed that is theoretically
possible for the type of rotor construction  used. The  only appreciable application of these
machines has been in homopolar generators; these supply extremely heavy  currents at a few
tens of volts and are desirable because of the smooth dc power they  generate.

     1.  Direct-Current Traction Motors

     Direct-current  motors have been used for a number of years in  electric locomotives and
have established a good performance record. These motors have carbon brushes and copper
bar commutators and are of series field construction.  In this form of construction  the
armature current establishes the field flux;  proper  control of  the armature voltage provides
high torque at  low speed and decreasing torque at higher speeds.  Thus, an approximately
constant horsepower characteristic can be achieved over most of the speed range.

     Since  dc traction motors are built in relatively large sizes  with  high horsepower ratings,
they are not usable in their present form for  electric vehicle propulsion. However,  the
general  design technology of traction motors  for  electric locomotives is  adaptable to  the
production of reliable dc motors for electric vehicles. Present traction motors have relatively
large rotors and do  not operate at the  high speeds required  for electric vehicles, but  the
peripheral velocities of the rotor and commutator establish design guidelines for scaling. It is
customary  to have  a  maximum  rated speed which corresponds to commutator peripheral
velocities of 12,000 ft/min, with overspeed during wheel slippage of 20,000 ft/min. This
corresponds to  rotor peripheral velocities  of approximately  15,000 ft/min and 25,000
ft/min, respectively.

     Direct-current  traction motors have  also been applied to  fork lift trucks, delivery vans,
and golf carts. In these applications cost  did not justify  developing the lightest and highest
speed motor. Instead, the selection was  based on  available electric equipment. Therefore,
these applications do not represent attempts to  extend  the state of the art.

     The applications where effort has been made  to obtain the maximum horsepower per
pound  are in electric torpedo propulsion  and aircraft dc generators and motors; even these
do not represent the ultimate, however, because their speed is restricted by the nature of the
systems in which  they  are  used.  If motors for vehicles were designed like these special
motors and  run at speeds approaching their maximum rated values, they could deliver about
one horsepower per pound, at least in the  larger sizes.
                                          28

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     The effect of speed is illustrated in Figure 7. For a given increase in horsepower per
pound, it can be seen that the speed of a small motor must be increased more than that of a
large motor. Fortunately, for the range of vehicle horsepower considered in this study, the
necessary  speeds  (12-19,000 rpm; see  Table  4) are within  the capabilities of  today's
bearings. The accompanying stresses are within the rated design values, and reasonable brush
wear is maintained.

     It must be emphasized that the values plotted in Figure 7 are based on the motors'
maximum horsepower rating - i.e., the horsepower they can deliver at their maximum rated
speed and torque.  Normally, aircraft dc generators are not rated in this manner, so  published
specifications must be carefully interpreted.

     Because of the high performance which  can be obtained from dc motors and the ease
with which they can  be controlled, they are currently being used in small electric vehicles
and  in  larger experimental vehicles.  In  general, they provide a very acceptable  interim
solution  to the electric transmission system. To obtain higher horsepower per pound and
eliminate the brush wear problem of the dc commutator motor, however, an ac motor must
be used.
     2.  Alternating-Current Induction Motors

     In   an  induction  motor,  the  rotor  is a  squirrel-cage arrangement  of conductors
imbedded in steel.  This robust construction permits a high rotor speed (see Figure 6).  In
addition,  the active length of the rotor can be longer  than that normally  used  for a dc
commutator motor.  These  features enable  an ac induction  motor  to  have  a  higher
horsepower per pound.

     Since the induction motor requires alternating current and the battery provides direct
current,  one of the functions of the control unit is to act as an inverter,  controlling the
speed of the motor by  varying the frequency of the ac power. The control unit must also
provide the proper  voltage-to-frequency ratio to enable the motor to deliver its rated torque
over the entire speed range.  The resulting torque vs speed curve differs greatly from that
normally associated with an induction motor; however, it is completely consistent with the
principle  that any  electromagnetic  machine is  capable of constant torque over its entire
speed range.

     Induction  motors  for vehicle propulsion are similar in construction to high-perform-
ance aircraft motors of the low-slip variety. Such motors have  low-resistance rotors that
minimize losses.  Normally, low-slip designs would be  unsuitable  because  of their high
starting currents; with a current-limiting control, however, starting current is not a problem,
and the motor design can be optimized for maximum efficiency.
                                          29

                                                                             arthur 2J.lLittIc.Knr.

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0.1
                    10
20
Output (hp)
50
100
                         FIGURE 7    WEIGHTS OF DC MOTORS
                                      30

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     Recent experimental electric vehicles and  rapid transit systems have used induction
motors. By taking maximum advantage of their desirable characteristics, manufacturers have
been able to build induction motors that provide approximately two horsepower per pound.
(This is based on the horsepower at maximum rated speed; induction motors generally lack
the overload capability of dc motors, so the figure is an estimate based on 200% overload
capability for five  minutes.)  Figure 8 includes  data on  two recently publicized induction
motors.

     Since the above applications have used induction motors of high horsepower, speeds
exceeding the 13-19,000  rpm range have not been necessary. It is doubtful that a high
horsepower-to-weight ratio could be maintained for lower-rated motors by increasing their
speed,  because  bearing  problems would be encountered. However, the use of induction
motors  eliminates  brush wear at the expense of some increase in control unit weight and
cost; this advantage will be further discussed later.
     3.  Synchronous Motors

     The synchronous motor  is another possible contender  for powering  future electric
vehicles. In  this type  of motor, ac power is  supplied to the  stator to produce a rotating
magnetic field, and the  rotor revolves synchronously with the field.  The most common
design  has a "wound  field" — i.e., excitation current is supplied to  the rotor through slip
rings and creates strong north and south poles in passing through the rotor windings. While
such a motor must have brushes to make connection with the slip rings, the brush wear is far
less than with the commutator of a dc motor.

     Nevertheless, a truly brushless motor is desirable because brushes are a possible source
of trouble. The simplest form  of brushless synchronous motor uses  permanent magnets in
the rotor and,  therefore, needs no  brushes, but its  power output is too low for vehicular
applications. A promising recent development is the solid-rotor brushless machine; much
work has been done on this design for aerospace generators, and various experimental units
have been built.  These have characteristically been heavier  than  comparable  motors of
wound-field  construction, but  they have the  offsetting ability to be run  at  higher speeds.
This advantage  cannot be fully utilized in small motors for the lighter vehicles, because their
bearings cannot withstand the speeds permitted by the rotor. (Sophisticated,  high-perform-
ance bearings are too expensive for the uses considered here.)  The speed capability of the
solid rotor might, however, prove  advantageous for applications in  vehicles such as buses
that require  larger, more powerful motors.

     The principal advantage of synchronous motors over induction motors is that the
former  require a lighter, less  complex control  unit. Synchronous  motors receive rotor
excitation power directly from the battery; their control  units supply  power to the  stator
only. Induction motors, on the other hand, obtain excitation power from the control unit
via  the  stator circuit.  As a result, their control units must  be more powerful and thus
heavier. Furthermore,  to prevent excessive heating of the battery, they must provide storage
for the  excitation power that  cycles back and forth from the motor. This storage usually
takes the form of a capacitor bank across  the battery terminals, which involves a further
weight increase.

                                          31

                                                                                   ZD.ltttlr.Knr.

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  1000

   800

   600


   400
   200
•&
1
   100
    80
    60
    40
    20
    10











^
.s



/









'>*'

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     Because of this advantage of the synchronous motor over  the induction motor,  it
would be desirable to use synchronous motors. Until the brushless variety is fully developed,
the slip-ring, wound-field synchronous motor is perhaps the most  desirable solution for
powering an electric vehicle, if the higher control cost of  the  ac motor approach can be
justified.

     The synchronous  motors  which might be  used could be  patterned  after aircraft
generators.  As with aircraft dc generators, the technology is highly developed and is directly
applicable to air-cooled and  special oil-cooled  machinery.  The  weights of a few standard
aircraft generators  with slip-ring-fed rotors are shown in Figure 8 when rated as motors. Also
shown is the weight of a solid-rotor machine developed for a high-speed application.

     The cost of  high-speed air-cooled  or oil-cooled  motors with  integral  gear reducers
cannot be closely estimated from available data; the requirements for aerospace applications
differ greatly from  those for  mass-produced electric vehicle drive motors, even though
speeds, ratings, and technologies are similar. As a rough estimate, the manufacturing cost in
large  quantities of  motor and gear  reducer might ultimately  be  about  $4 per vehicle
horsepower  for a dc commutator motor. For an ac induction  motor, it might be as low as $2
per vehicle  horsepower. The cost  of solid-rotor synchronous motors would range between
these limits, approaching the upper figure for those of higher  speed.
B.  CONTROLS

     Historically  the speed  of  dc traction  motors  has been  controlled by  inserting a
resistance in series with the motor so as to regulate the current from the dc power source. In
addition to switching resistance into  and out of the circuit, switching of the field circuit
between series and  parallel connection is  also customary. This manner of speed control
causes jerky  performance  and is  inefficient from  the standpoint of conserving battery
power.

     Because  a battery supplies an essentially fixed dc voltage, and because the speed of a dc
machine varies with  the input voltage, a control must be used  that will effectively vary the
voltage  with  negligible  losses. The advent of  solid-state devices  has made  such control
possible. Instead  of  reducing voltage  by inserting resistance into the  circuit, these devices
achieve  the  same effect by  rapidly  interrupting the  current. The longer the  interval of
disconnection, the lower the  average voltage that the motor receives. The motor current is
not interrupted during the  time that the battery is disconnected; rather, the motor circuit is
closed on itself.

     The switching  elements  which are  used to disconnect the motor winding from  the
power source are silicon power transistors or silicon controlled  rectifiers (SCR's). The
difference between  them  is that SCR's can be  turned off only by  reversing their
anode-to-cathode voltage for  a short time; silicon power transistors can be shut off simply
by interrupting their control  current.  Both devices are  turned on by applying a low-power
pulse to their control terminals. In the case of the power transistor,  the low-power pulse
                                           33

                                                                             Srtbur ZD.lttttlc.Dnr.

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must persist for the duration of power conduction. Power transistors were initially used, but
SCR's are now preferred  because  of their hjgher power handling capability, even though
they require special turnoff circuits. Both devices have essentially unlimited life.
     1.  Chopper for Direct-Current Motor

     Frequently the control for a dc motor is termed a chopper, since it connects the
battery  to the motor intermittently.  As explained above, the rapid interruption is timed to
achieve  the desired average voltage. A number of different schemes are possible: some use a
fixed on-time  with  variable off-time,  while  others use  a variable on-time and  a fixed
off-time; still others  use a combination of these two. In general, it is desirable to operate at
the highest possible chopping frequency so as  to minimize the fluctuation of current; some
compromise must be made, however,  to reduce switching losses.
    The chopper is not only much more efficient than the switch resistor type, but it also
permits very exacting control of current. This, in turn, permits continuous, stepless torque
control. Probably more important, the current can be limited to protect the motor and the
solid-state controls themselves; with proper current limiting, high reliability can be expected
from the chopper and motor. For example, if maximum torque is required from the motor,
the current limit can  be set at, say, twice rated motor current. This will enable the motor to
deliver approximately twice its rated torque. Both the motor and control should be designed
to withstand this current for perhaps 5 minutes; in this way, both the motor and the control
are protected even if the motor is stalled.

    The 5-minute rating of the motor is an arbitrary figure.  It could be designed to be 1 or
2 minutes or even  10 minutes. The particular design  will depend upon  the overall  system
efficiency, weight,  driving pattern, etc. However, the solid-state component in the chopper
must be capable of carrying the overload current continuously, since its overload capability
is extremely limited. Most of the other components in  the chopper, except those that have a
thermal storage capacity, must also be able to carry the overload current on  a continuous
basis.

    In principle, the  efficiency of the controller can be extremely high, since  the process is
basically lossless. However,  when the SCR is carrying current, it exhibits a  1-volt drop,
which  when multiplied by the current gives the  forward conduction loss. In addition, there
are switching losses, blocking losses, and losses associated with the free-wheeling diode that
closes the motor on itself during the times that the SCR blocks the current from the battery
to  the motor.  Other losses are associated with the  turnoff capacitor  and its associated
charging circuitry.

    The efficiency of the chopper is  greatly affected  by the voltage of the system, because
conduction loss due to the 1-volt drop is relatively less at higher voltages. Considering this
loss alone in the case of a 12-volt system, the efficiency cannot exceed  92%. When the other
losses are included,  a  rather  low overall  efficiency  would result. Therefore,  it is essential to
use a high system voltage.
                                         34

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     High voltage is important not only for increasing efficiency, but also for reducing the
weight of the chopper. The physical size of the solid-state components is dependent upon
the current and is unaffected by the voltage. This independence of voltage does not hold for
the capacitive and inductive components in the chopper, however; their size and weight are
in general related to the power handled and also to the precise design of the chopper.

     As a rule, it is best to use as high a voltage as possible to reduce the magnitude of the
current. To keep the rated current below 100 amperes and hence the overload current below
200  amperes, it is  necessary  to use voltages of the order  of 150-500V for the range of
vehicles studied. For these voltages the weights which should be achievable are shown in
Figure 9.  These weights  assume fan cooling of the  choppers, which is possible because of
their high efficiencies (90% or more). Heavy contactors and circuit breakers should not be
necessary, because of the  current-limiting capability of the chopper.

     Considering the small size of the chopper,  it might  be  feasible to attach it  directly to
the motor housing. In this way,  dissipation of heat from  the solid-state power handling
components could be increased, and heavy-current carrying terminals could be avoided. This
concept is  analogous to  the incorporation of silicon diodes within the housing of present
automobile alternators.

     Although the basic  principle of the chopper is well understood, the device has only
recently been applied to experimental fork lift trucks, delivery vans, and other vehicles. The
technology is available, but it will require a great deal of development to bring the chopper
from a promising concept to readily available equipment for electric vehicles.

     The  present manufacturing  cost of a chopper control is about S20 per vehicle
horsepower.  However,  considering  the actual material   costs  and  the   fact  that  the
manufacturing processes lend themselves to automation, an order-of-magnitude reduction to
$2 per horsepower would appear to be reasonable.

     All the logic functions associated with the  timing and control of the chopper could be
done  with  microelectronic integrated circuit modules. These  are incredibly small and can
perform many control functions at an extremely reasonable cost. Therefore, it would seem
that a great deal of ingenuity and development should be directed toward applying chopper
technology to a mass-produced, reliable, low-cost product.

     To accomplish regenerative braking, all that is necessary  is a slight rearrangement of
the basic power handling component and a small amount of additional logic. Regenerative
braking is only beginning to make an appearance in chopper circuits, and much innovation is
needed; e.g.,  through appropriate current sensing and making the circuit changeovers at
current zero, it would  be possible to do away with all the large contactors or dc current
interrupters which are frequently incorporated in choppers.

     Highly efficient regenerative braking can permit the return  of power to  the battery.
The amount returned depends upon the driving power of the vehicle as well as circuit design
and efficiency. For vehicles such as buses that make frequent starts and stops, it has been

                                          35
                                                                            3rthur ZD.lUttle.llnr.

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1000



 800





 600







 400
 200
•E  10°

5


   80





   60
  40
  20
  10
     - X*        X|
     X         X
    h-  X
      X
    x

                                        X
                                      -x-
                                         X

                                            J	I
    10
                   20
   40      60    80  100


Motor Output (hp)
200
                FIGURE 9   WEIGHT OF CONTROL UNIT
                                36

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reported that the saving in  power can be as much as 30%. For  vehicles  that use a more
normal driving pattern, however, the energy saving is not large enough to justify the cost of
adding this feature.

       Regenerative braking does  not  make conventional brakes unnecessary, for it is of
little  use at low  speed;  most  of the power is  returned  during the initial period of
deceleration.
     2.  Inverter for Induction Motor

       When an induction motor is used as a propulsion means, an inverter is used as the
control  for varying its torque and speed. An inverter takes dc power from the battery and
changes it  to ac  power of the appropriate  voltage and frequency; thus, it combines the
voltage-adjusting function of the chopper with an ability to vary the frequency as well.

       Inverters  using SCR's for driving induction motors over wide speed  ranges are
relatively new. They are just coming onto the market for industrial variable-speed drives and
have been used with a few experimental electric vehicles.

       As  with  the chopper, power  SCR's are used  in an  inverter  to connect the three
motor windings to the battery on a time-varying basis. In essence, at least three choppers are
required, one for each of the three phases of the motor, because each  phase must be
cyclically  energized  and each  carries the  same  peak  current.  In  practice, it  is  often
convenient  to use essentially six  choppers,  each  capable of delivering half the required
voltage. As  with the chopper, the peak current is the limiting factor in  design.

       In  addition  to all  the  components associated  with a  chopper,  a large  bank of
capacitors must be placed  across the dc input. This results from the fact that reactive power
must  be handled  by the inverter.  A further component which must be added is a special
speed-sensing tachometer. A signal from this tachometer is used to determine the frequency
of the inverter.

       The size and weight of an inverter are typically about  three times those of a chopper
of equivalent power and voltage, excluding the capacitor bank across the dc input. The
estimated weights are graphically shown in Figure 9 as a function of voltage and power. A
manufacturing  cost  of $5 per vehicle  horsepower should  eventually be  possible,  again
excluding the capacitor bank and tachometer.

       The fact that the inverter has  a more complex logic  requirement than the chopper
should not  increase the ultimate cost; specialized integrated circuits would be developed for
vehicle inverters to accommodate all the complex functions.  As in the case of the chopper,
current  limiting is essential  and must be applied with instantaneous control to protect both
the inverter and the motor, as well as to provide torque control.

       If  regenerative braking is  considered justified by the application,  it can  be
incorporated  within the  inverter at a slight increase in cost by  using the motor as an
induction  generator. This  does not  require that  the solid-state components  be shifted
around, as  in the  case of the chopper circuit, but only that additional  logic be incorporated.

                                        37

                                                                           3rthur ZD.lttttlr.Knr.

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To protect both motor and inverter, the controlling of the SCR's must be timed so as to
limit the rate at which power is returned to the battery.
    3. Static Commutator for Synchronous Motor

       As with the induction  motor, the speed  and torque of a synchronous motor are
controlled by varying both the voltage and the frequency of the power supplied. However,
the control for a synchronous motor differs somewhat from an inverter; it is called a static
commutator for purposes of distinction as well as to indicate its functional relation to the
copper bar commutator of a conventional dc motor. The commutator and brush assembly
of a dc motor in effect chop  the  dc input into variable-frequency power for the  motor
windings; when this is accomplished by a separate static commutator, the roles of stator and
rotor can be interchanged. This permits a large reduction in the current that  the slip rings
must carry, because the current in  the rotor of a dc motor is much larger than that in the
stator.

       The power circuit of the  static commutator is identical to that of the inverter,
except that it needs no capacitor  bank across the dc supply. However, the control  of the
SCR's  is somewhat  different:  the position-sensing  tachometer attached  to  the  motor
determines which windings should  be energized at any given moment. The tachometer can
take a number of forms; experimental arrangements have been employed using photoelectric
detectors,  Hall detectors,  and reluctance detectors.  The information from  the position
sensor is used to control the main power SCR's.

       The size of  the static commutator is  about  the same as that of the  inverter. The
weights given in Figure 9 and the cost of $5 per vehicle horsepower also apply for the basic
static commutator; to these figures must be added the small weight of the tachometer and
its associated cost.
C.  SPEED REDUCERS

       To  couple a high-speed motor to the wheel, a speed reducer with a relatively large
reduction ratio is needed. For railroad traction, a gearbox with a low reduction ratio is used;
these are very rugged but heavy units. At the other extreme, very lightweight gearboxes have
been developed  for torpedo propulsion systems, but these are designed for short life and
thus are not suitable for vehicular use. It would seem that a compromise between these two
technologies would lead to a gearbox with the desired reliability and light weight.

       The large experimental electric vehicles  built  to date have used planetary gearboxes
that are  directly connected to the motor and employ oil cooling.  This  is a  lightweight
arrangement particularly suited to motors of relatively high horsepower.
                                         38

                                                                                ZD.UtttleJnr.

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       Another solution is the "motorized wheel," in which the motor and gear reduction
unit are incorporated  in the hub of the wheel. This compact arrangement is now used in
some earth-moving equipment and might be well suited to large vehicles like buses.

       On  small experimental electric cars, double timing belts have  been used to achieve
relatively  high speed-reduction ratios.  Belt  drives  are  an extremely  lightweight  and
inexpensive means for  coupling the motor to the wheels.

       In view of the  mature technology of speed reduction devices, adapting one or more
of these approaches should not be difficult. The principal task is to make a detailed analysis
that will indicate which offers the lowest cost and best arrangement.  For the small utility
car,  which  would  use air-cooled motors of rather low  power, the  multiple timing  belt
approach seems  desirable; for the bus, the oil-cooled gearbox  or possibly the motorized
wheel might be preferable.


D. COOLING  REQUIREMENTS
       The heat losses which occur in the motor, the speed reduction unit, and the control
unit  must be removed by a cooling system. Air cooling, which is  the simplest  method,
requires a constant-speed blower  and  duct arrangement.  The more elaborate  oil-cooling
system requires  an oil pump, heat exchanger, and other components. In both cases, the heat
to be rejected would be used to warm the passenger compartment during the winter and
discharged to the surroundings  in warmer weather. The motor may have to operate for
sustained periods at  extremely low speed, so it cannot be used to drive the cooling system;
the system must be separately driven.
                                      39

                                                                        3rthur ZD.lUttlrJnr.

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                     V.  ELECTROCHEMICAL POWER SOURCES
       This section contains a review of the present state of the art of those electrochemical
power sources, batteries and fuel cells,which have prospects of application as the prime
power source in electric vehicles, together with some prognosis of their future development.
Consideration  is also given to the possibility of hybrid electrochemical systems consisting of
battery-battery and fuel cell-battery combinations. (The possible application of batteries in
mechanical-electrical systems is covered in Section VI.) The review of electrochemical power
sources is organized into  four subsections covering conventional batteries,  batteries under
development, fuel cells, and electrochemical hybrid combinations.
A.  CONVENTIONAL BATTERIES
     1.  Lead-Acid

       The lead-acid  battery is the oldest of the secondary battery systems and has been in
existence  for over 100 years. It is also the most important system economically, accounting
for about 80% of the more than S500  million annual sales of secondary batteries in the
United States.  While  the  largest proportion of these sales is for the specific application of
starting, lighting, and ignition (SLI) in vehicles powered by internal combustion engines, a
substantial volume  is used as the power source for non-highway electric vehicles, such as
fork lift trucks, golf carts, and mine locomotives.

       SLI  batteries are designed for float service with occasional high power discharge and
are not suitable for traction service,  which involves repeated deep discharge cycling.  Bat-
teries for  traction applications have thicker plates and are generally of more rugged  con-
struction.  Their delivered energy density is  now in the range of  10-14 w-hr/lb. While  high
power drains cause a decrease in delivered energy, power densities of as much as 35  w/lb can
be sustained for short periods.

       The major virtues  of the lead-acid system are its high degree of reliability (a typical
lifetime of four to six years in traction service under a continuous daily cycle of full charge
and discharge) at low cost (OEM  prices approximate S0.25/lb for SLI and $0.50-0.60/lb for
traction type batteries). While these virtues make lead-acid today's most important  practical
battery system  for electric traction,* its low energy density eliminates it from consideration
as the primary  energy source for almost all of the six classes of vehicles under consideration
in this study. The sole possible exception is the utility car with lightweight construction, the
specifications for which are close  to the upper limit  of the lead-acid battery's  technical
capabilities.

       The  question  arises  as to the potential  for improvement  in  the lead-acid system.
Incremental advances in energy density are certainly possible, and in fact there has already
been a substantial improvement (of the order of 30%)  in these  parameters over the last
15-20 years and this  is expected to continue. For example, a  major U.S.  manufacturer is
  The extensive history of lead-acid battery use in highway vehicles, particularly in the United
  Kingdom, is reviewed in Appendices A and B.
                                         40

                                                                            3rtb«r

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about  to introduce a new industrial battery with an energy density of 16 w-hr/lb at a ten
hour discharge rate. These advances have primarily resulted from the utilization of lighter,
stronger materials for cases, improvement in the design of the plates, new grid alloys, more
porous and durable separators, etc. Somewhat more radical changes are being worked on by
a group in England (U.K. Electricity Council Research Centre), which is investigating im-
provements in capacity that  might result from pumping electrolyte  through  the  battery
plates, although the extra  complexity may make  the scheme unattractive. Some publicity
has been given in the United States to the use of traces of cobalt salts in the electrolyte to
improve energy density (Electric Fuel Propulsion,  Inc., see also Appendix A). The presence
of cobalt in closely controlled proportions can lessen grid corrosion, thereby permitting the
use of thinner plates and yielding a higher energy density; it does, however, increase the rate
of shedding of active material from the plates, thus shortening battery life.

        With regard to power density, the maxima achieved in today's conventional lead-acid
batteries are only  moderately  below the demands  of the vehicle types as listed in Table  1.
Operation  at  high power density does lower the  energy storage capacity of the battery,
however, and  rapid charge and discharge raises the internal temperature of the battery and
tends to shorten  its life. An interesting recent  development is that  of a high rate lead-acid
battery for pulse discharge and having "pile type"  construction. This battery, being devel-
oped  by Gould-National Batteries,  Inc. for the U.S. Navy Electronics Laboratory,  has a
power density of around 60-70 w/lb and might possibly find application in hybrid electrical
vehicle systems (see Sections IV-D and VI).

        Thus the limitations on its energy density would seem to preclude the large scale use
of lead-acid batteries as a prime energy source for highway vehicles. Much wider use of these
batteries, based on their low cost, rechargeability,  and availability is, however, foreseen for
such applications as transportation within industrial plants, hospitals, airports,  resorts, and
off-highway shopping centers  and  communities. Anticipated advances and cost  improve-
ments  in motors and control systems will also  benefit  electric vehicles used for these pur-
poses.

     2. Nickel-Cadmium

       The salient technical features of the nickel-cadmium battery are its excellent service
life, an energy density of 12-14 w-hr/lb, which is closely comparable to that of the lead-acid
battery; and a power density  which in certain constructions can be as high as 300 w/lb.
There  are two major types  of nickel-cadmium batteries: those  with pocket plates, which
have cycle  lives in excess of 3000 or so, and those with sintered plates, whose cycle lives are
less than half  as great but which have very high power densities.  Because of its low energy
density it is,  like the  lead-acid  system, outside the scope of our primary  power source
specifications  for  electric vehicles,  except perhaps for the  small utility vehicle. Its high
power  density however makes it  an attractive prospect on technical  grounds for  various
types of hybrid power source, as will be discussed in  Sections V-D,  VI and VII.  This is
especially true of the  'bipolar' nickel-cadmium battery developed by Gulton Industries, Inc.
for high discharge rate  applications. This battery has very thin sintered plates attached to
thin  metal  sheets which act as  the  connectors between adjacent cells. The thin  electrode
design  permits the achievement of power densities of around 300 w/lb.
                                         41

                                                                            Arthur ZD.lUttle.lfnr.

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       The nickel-cadmium battery has not been used in  traction  applications, except to a
limited extent in lift trucks in Continental Europe and in a demonstration automobile in
Sweden (Appendix  B). The major drawback is its cost, which on a per pound basis is about
five times that of the lead-acid traction battery. Since a significant part of these costs derives
from  the  costs of nickel and cadmium, they are unlikely  to fall sufficiently to change the
nickel-cadmium  battery's competitive  position. A further argument can be raised against
cadmium  on the grounds of availability:  supplies of the  element  are not great enough to
support a major application in electric vehicles, and since it is a by-product of lead and zinc,
its production cannot be economically expanded for its own sake. Thus the nickel-cadmium
battery in any form seems unlikely to play a major role in electric vehicle development.
     3.  Nickel-Iron

       The nickel-iron  system has an energy density  slightly lower than those of  nickel-
 cadmium and lead-acid and a  lifetime which can be measured  in decades. It is also a very
rugged battery, capable of withstanding much physical and electrical abuse. Its power den-
sity, however, is  not as great as that  of the nickel-cadmium system,  and because of the
smaller  volume of production  and the processing costs involved, its price structure is not
significantly lower. The major reasons why the nickel-iron battery  has  not  found  greater
general  application are  its poor charge retention and low electrical efficiency in charging,
both of which characteristics lead to excessive gassing and a high maintenance requirement.
Although it has  found  some  acceptance in European lift  trucks and  in  U.S. mine loco-
motives, the low  energy density of the system gives it  little relevance as  a potential power
source for electric highway vehicles.

     4.  Silver Batteries

       There are two secondary batteries  which use silver oxide cathodes: the silver-zinc
system  and the  silver-cadmium  system. The former  battery has a  high energy density
amounting in certain configurations to about 60 w-hr/lb, and  an excellent power density of
as much as 200 w/Ib. properties which on technical grounds would appear to make it a
significant  contender for many  electric vehicle  applications. It has,  in fact,  been  used
recently  in certain experimental  electric vehicles, most notably the CM  "Electrovair" and
the Yardney Electric converted Renault Dauphine (see Appendix A). However, the cycle life
at full discharge seldom  exceeds 40-50 cycles, and the high cost and relative scarcity of silver
rule it out  for large scale use.  The 500-lb battery in  the Electrovair II was reported  to cost
some SI 5.000. or S30/lb; and about 30% of the packaged weight is accounted for by silver,
which now has a  raw material cost of about S35/lb. Yardney Electric has suggested that the
silver might be leased, but the poor cycle life is a difficult  problem and lack of availability
unsurmountable.  Its  use therefore seems likely to be restricted  to demonstration vehicles
and test bed evaluations.
                                         42

                                                                          Arthur

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       The properties of silver-cadmium batteries are in many ways intermediate between
those of nickel-cadmium and silver-zinc batteries. Their energy density of about 25 w-hr/lb
and  their  high  power density, comparable to that of silver-zinc  batteries, make  them
marginal candidates from a technical standpoint for certain of the vehicle applications  listed
in Table 1. However, as  with silver-zinc, high cost and insufficient availability of materials
eliminate them from serious consideration for large scale use.
B. BATTERIES UNDER DEVELOPMENT

       The technical parameters  of the  conventional batteries described in  the  previous
subsection clearly fall short, particularly in energy density, of the requirements specified in
Table  1.  Since conventional batteries use  materials with  relatively high equivalent weights,
an obvious route  to improvement lies in the  use  of reactions which have higher energy
release and employ  active  materials of low equivalent weight. The source of energy in all
batteries  is the oxidation-reduction reaction which  takes place between the active materials
of the positive (cathode) or oxidizing plate and the negative (anode) or reducing plate. The
energy released,  corresponding to the weights of these active materials alone, can be calcu-
lated  and sets an upper limit for the energy density of a given battery system. In practice,
when  the  weights  of case,  grids, separators,  electrolyte, and supporting structures  are
considered, the practically  attainable energy density is only some 10-20% of this theoretical
maximum. Nonetheless, it  is evident that  the higher the  energy  release in the  cell reaction,
the higher the energy density of the resulting battery.

       Prime  candidates for use as anode materials in high energy density batteries are the
alkali metals, in particular lithium and sodium. Their very reactivity, however, imposes some
severe restriction on their mode of utilization. They cannot be used with conventional aque-
ous electrolytes, because of the  rapid direct chemical reaction; their use  is possible only in
combination with  nonreactive electrolytes, in particular molten salts  and organic liquids.
The  former introduce the  complication of a high operating temperature  and, in many in-
stances, severe problems in materials selection,  while the latter tend to  be hampered by low
electrolytic conductivity, poor shelf life,  and cathode polarization problems, which limit
their power density.

       The other  major approach  to improvement in energy density  is the use of atmos-
pheric oxygen as the cathodic oxidizing agent.  The weight of the cathode in the battery is
then  limited  to that of a catalytically active oxygen  electrode, the  oxidant (air) being
available  in limitless amount with no weight penalty.

       Power densities are a reflection  of the kinetics of the various electrochemical reac-
tions taking place in the battery. They can  be improved by attention to certain physical
factors, particularly  the surface  area of the electrode,  and are increased at elevated tempera-
tures. For  this latter reason, the  molten  salt systems are particularly favored for applications
involving high power density.

       This subsection reviews  the status of the  work  presently under way  on improved
battery systems for use in electric vehicles.

                                       43

                                                                           ,3rthur ZD.lUttlf.3lnr.

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     1.  High-Temperature Alkali Metal Batteries

       a. Lithium-Chlorine

       The  battery with the highest potential energy density of those now under investiga-
tion is based on lithium and chlorine as reactants and is being developed by  the General
Motors Corporation. Its theoretical energy density is approximately  1000 w-hr/lb, and it has
an open  circuit potential of 3.5 volts. In its work to  date, GM has demonstrated the cell's
capability for generating very  high current densities - on the order of several thousand
amperes  per square foot.

       The  principal liabilities of  the lithium-chlorine battery are the difficulties associated
with storing chlorine gas under pressure and at temperatures of around  650°C, and the
tendency of the  cell to self-discharge. The first  problem  is being  tackled by using highly
adsorbent charcoal to reduce the pressure of the stored chlorine. This approach seems quite
successful, although  a  great deal more needs to be learned about the cycling capability of
charcoal  in this application.

       While its  electrochemical  characteristics are very encouraging, the  lithium-chlorine
battery  presents  many  novel and  extremely challenging problems in materials engineering,
and extensive development will clearly be needed before the system can be made practical.
The question of hazards arising from the storage of chlorine gas under pressure and at high
temperatures seems, at this stage at least, likely to limit the chances of such a battery's being
adopted  as a power source for vehicles.

       It is  not possible to  make  any accurate estimates of the effective energy and power
densities, still less the costs, to be expected for the lithium-chlorine battery. Much depends
on the complexity of the safety engineering and packaging  that would be necessary. It seems
likely,  however,  that the  system  will easily possess the technical  capabilities  required to
satisfy the most exacting of the electric vehicle's specifications.

       With regard to costs, a theoretical minimum quantity of about 25 pounds of lithium
would be required for a battery capable of meeting the requirements of the  family car. At
today's  price for lithium, $7/lb, this corresponds to  SI75. The actual quantity of lithium
needed might be  half as much  again as the 25 pounds, but with anticipated lower produc-
tion costs of the  metal in quantity the  resulting materials cost for lithium  might not be
much more than  $100.  While this  is a significant item, it would not appear to rule out the
system from further consideration.

       Maintenance of  the  operating temperature is  a problem with all high-temperature
battery systems.  In a well-insulated system, the  self-discharge rate is usually sufficient to
maintain temperature.  However, good  insulation tends  to be an embarrassment  when the
battery is working at high power levels, either on charge or on discharge, since the excessive
amount of heat generated  causes  an undesirable rise in  the internal temperature. On the
other hand, if the battery is to be shut down for long periods, it seems essential that some
kind of built-in combustion heater  be included in the system.
                                        44

                                                                            9rthur

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        b.  Sodium-Sulfur
       Another approach to the use of alkali metals in high-temperature batteries is being
taken by the Ford Motor Company. Ford's cell uses sodium and sulfur as the reactants, and
the electrolyte  is a special ceramic material permeable  only to sodium ions. The properties
of the ceramic are critical for the effective functioning of this battery. While the sodium-
sulfur battery does not have the theoretical energy density of the lithium-chlorine system
(300-600 w-hr/lb, depending on  the extent of the reaction, versus more than 1000 w-hr/lb),
it does have two major  practical advantages. First is the lower temperature  of operation,
approximately  300°C. At  this temperature,  sulfur is a  liquid, and  containment of the
cathode materials thus presents far  fewer engineering problems than in the lithium-chlorine
system. The second  advantage is that the battery reactants, sodium  and sulfur, are both
extremely abundant  and very inexpensive; there are thus no immediate and fundamental
reasons why the battery might  not eventually develop into  a low-cost power source for
large-scale use.

       Since Ford's  work  is proprietary,  relatively little  specific information is available.
Present efforts  are apparently confined to experiments with single cells, the goals being to
determine the factors affecting electrical efficiency and cycle life and to find solutions for
the various  engineering  and  materials selection  problems which  are  encountered.  Since
multi-cell work is bound to raise a whole new series of problems concerned  with design and
with maintenance of the electrical  balance of cells in the battery, it is not possible to make
an accurate  prediction of the time scale for the development of this battery into a practical
power source for vehicles.
       c. Capacitive Storage

       A third approach  to high-temperature battery development has been taken by the
Standard Oil Company (Ohio). SOHIO's work was originally based on the use of carbon
electrodes with very high  surface  areas to provide capacitive energy storage. All electrolyte-
electrode interfaces have double layer capacitances; however, these are in general quite small
and do not store significant quantities of energy. In the case of porous carbon electrodes,
the internal surface can reach huge  values, and the amounts of energy that can be stored
capacitively become comparable with those stored in a battery of equivalent weight. Elec-
trolytic condensers with capacities of the order of farads can be set up by immersing porous
carbon electrodes in an aqueous electrolyte such as sulfuric acid. A very substantial enhance-
ment in capacity  and hence in the capability  for energy storage, can, however, be obtained
by using a  molten salt electrolyte. A  further bonus comes from the much higher breakdown
voltages of these  electrolytes, which  permit the cells to be operated at levels of 3 volts or
more, compared  with a maximum of 1.8 volts or so in aqueous systems. Since the energy
storage is proportional to the square of the voltage, this means a substantially greater energy
density.
                                      45

                                                                                  2D.lttttlp.Knr.

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       In practice, the SOHIO device, which contains a molten potassium chloride-lithium
chloride  eutectic as the electrolyte, does not  behave as a pure capacitor.  It was  found
preferable  to  substitute  aluminum  for carbon  at  the negative electrode (to reduce self-
discharge, due to lithium solubility), and the lithium  enters  the aluminum interstitially. At
the positive electrode it seems likely that the chloride ion is at least partly discharged but is
adsorbed very strongly on the carbon and so never appears as a gas. The system may thus be
partly a capacitor and partly a special  type of lithium-chlorine battery in which the  active
materials remain within the current collectors. The fall-off in voltage as the cell is discharged
is intermediate between those typical of batteries and capacitors.

       At  its present stage of development  the SOHIO device appears to  be capable of
attaining an energy density of 50 w-hr/lb and a  power density of 150 w/lb in its packaged
condition.  Experimental  batteries  with 30-kwh storage capacity are now being designed.
Thermal insulation is provided by a vacuum container which will maintain operating temper-
ature for 40 hours without auxiliary heat. The self-discharge  rate is low, taking approxi-
mately 20 days from full charge. While the SOHIO battery seems likely to have inherently
lower energy densities than those of other types of high-temperature systems, with improve-
ments in the technology of the carbon  cathodes, its energy density might eventually be
raised to about 100 w-hr/lb. Estimates of cost are necessarily very tentative  because of the
novelty of some  of the fabrication processes, but it appears that in  large-scale production
they might approach a level of $1.50/lb. Preliminary indications are that the lifetime will be
about three years. With a pilot manufacturing plant going into operation SOHIO's battery
seems to be most advanced of the high-temperature systems now under development.
       d. Lithium Cells With Tellurium, Selenium, and Other Non-Metals

       Other  types  of  high-temperature  cells involving lithium  anodes and  molten
nonmetallic elements  as  the  cathodes  are  under investigation  at  the  Argonne  National
Laboratory. The electrolyte is a relatively low melting ternary eutectic mixture of lithium
fluoride, chloride, and iodide made into a solid paste by the carefully controlled addition of
micron  sized particles of lithium aluminate. The majority of the work  has been  focused
upon the lithium-tellurium and  lithium-selenium couples, the cell reaction  resulting in the
formation of lithium  telluride or selenide, which remains dissolved in the molten  cathode.
Operating temperatures are necessarily  above those of the  melting points of the cathode
elements  and  are  in the 470-500° C range for  lithium-tellurium  and 350-400° C for
lithium-selenium.

       The great virtue of these systems is the extremely high degree of reversibility of the
electrode  reactions  and  their capacity  for  sustaining current densities of approximately
10,000 amperes per square foot. Polarization of the cells is very low and entirely accounted
for by internal resistance. The major constructional material is Armco iron and corrosion is
apparently no great problem. Projections based upon the behavior of single cells having an
electrode area of 10 square centimeters indicate that  the packaged energy densities would be
90 w-hr/lb for Li/Te and 120 w-hr/lb for Li/Se. Power densities are very high: 200-500  w/lb
for Li/Te and 300-600 w/lb for Li/Se.
                                         46

                                                                           3rtbur 3t.ltittlc.Dnr.

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       Probably the greatest handicap to the development of these cells for vehicle applica-
tions is the cost and relative scarcity of the cathodic elements. Because of this some prelimi-
nary experiments were carried out in recent months with a lithium-phosphorus cell, but the
necessity of working above the melting point of red phosphorus requires operating tempera-
tures above 600°C, and the observed voltage of the cell is only about 1  volt versus 1.75 volts
for Li/Te and 2.4 volts for Li/Se.  This  initial  work  with phosphorus has therefore been
unpromising. The most recent work has been with the lithium-sulphur system and has been
very encouraging as far as it has  gone. This system appears to have great promise as a
vehicular power source.

       Sodium cells are not of interest because of the higher melting points  of the sodium
salt electrolytes and the greater tendency  of sodium to dissolve in the electrolyte.
     2.  Alkali Metal Batteries With Organic Electrolytes

       The use  of nonreactive organic liquids as electrolytic solvents in alkali metal bat-
teries permits ambient-temperature operation and thus avoids many of the difficulties asso-
ciated  with molten salt and  ceramic  electrolytes. It has its full share of disadvantages,
however, since for a variety of reasons, organic liquids are inferior electrolytic solvents.

       A great deal of work has been done over the last five years, much of it supported by
NASA,  on the  selection  of cathodes and organic electrolyte  combinations for use with
lithium  anodes in primary batteries. The major  problems have been the identification of
non-aqueous electrolytic solvents compatible with lithium and having sufficiently high con-
ductivity, and of cathode materials capable of sustaining even very small current densities
without extremely high polarization. Some progress  has been  made, although the  best of
these systems can  support current densities only 5-10% as great as those possible in conven-
tional aqueous batteries.

       The development of rechargeable systems is at an even earlier stage. In work carried
out  some  three or  four  years ago, the  Lockheed  Aircraft Company demonstrated the
rechargeability of a lithium-silver chloride battery having a lithium  perchlorate-propylene
carbonate electrolyte. The best of these cells showed  some 40 or 50 cycles of operation at
almost 80% discharge before the  capacity fell off significantly.  This system was not devel-
oped further, because the high  equivalent weight of the cathode gave it no substantial
advantage in energy density over many  aqueous systems. Other attempts  at recharging
organic electrolyte batteries have encountered severe problems with lithium plating and with
the recycling or solubility in the electrolyte  of the cathode materials (generally halides or
sulfides of transition metals).

       More recently, Gulton Industries, Inc. has  engaged in the development  of a recharge-
able lithium-nickel fluoride battery having a potassium hexafluorophosphate-propylene car-
bonate electrolyte. Claims have been made that  this battery system has the potential to
                                         47

                                                                           Arthur ZD.1Uttle.llnr.

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attain a packaged energy density of 150 w-hr/lb and a power density of 20-30 w/lb; how-
ever, the  published technical information* shows that achievements to date fall short of
these goals. On repeated cycling a nominally 0.025 amp-hr cell discharged for 8 hours at 20
ma (the current density at the electrodes being 0.1 ma/cm2) showed a voltage decrease of
from 3.0  to 1.4, the value at the midpoint being 1.75 volts. If these conditions are typical,
then a 13-amp-hr  cell which apparently weighs 0.55 pound would deliver  27 w-hr/lb, or
approximately  40  w-hr/lb  if the cell were discharged completely. High discharge currents
have been reported, but only for pulse conditions of perhaps a few milliseconds. The falloff
in voltage at a steady discharge current density of  only 0.1  ma/cm2  indicates  that  high
power  densities are unlikely to be attained under sustained conditions. A five-hour discharge
rate may well be the practical limit for this  type of battery.

       Gulton  has had more success than other groups in recharging lithium non-aqueous
batteries,  but even so  they have found it necessary to use low current densities and very thin
coatings of active  material  on the  current collector to achieve significant  cycle life. The
latter requirement, of course, tends  to decrease  the energy density of the cell.

       As a class, rechargeable alkali metal batteries with organic electrolytes seem a  long
way from practicality for  vehicle use. Their difficulties derive from fundamental  electro-
chemical  problems which even in comparison  with  the engineering problems faced by the
high-temperature batteries, could take a long time to resolve. Gulton Industries, however, is
optimistic about their prospects and has entered into a vehicle development program  with
American Motors Corporation (see  Appendix A) to  use its battery with a high-rate nickel-
cadmium  battery in the hybrid power source described in Section V-D. The  long-term cost
estimates  for the lithium battery have been  estimated to be in the range of  $4 - 5/lb.

       The Electrochimica  Corporation  has  also advocated the  use of organic electrolyte
lithium batteries in electric vehicles. Its work  has  been concentrated on a lithium-copper
fluoride system, and claims are made that this system has particularly high current densities
for this class of battery. Lacking specific information, we cannot make a detailed assessment
of the  system.  It is not claimed to  be rechargeable,  however, and therefore is not yet at a
stage for consideration in vehicles.
     3.  Metal-Air Batteries

       The employment of air cathodes represents another general approach to the develop-
ment of batteries with higher energy density. In most programs in this area, aqueous electro-
lytes have been used in combination with relatively conventional metal anode materials. The
concept is not new; low-rate zinc-air primary  batteries have been available for more than
half a century. The novelty in  the recent work is in the use of air cathodes capable of
supporting very much  higher current densities than  those  of the  conventional  cells, an
advance derived from fuel cell technology.
* H. N. Seiger, S. Charlip, A. E. Lyall, and R. C. Shair, Organic Electrolyte Batteries, paper
  presented at 21st Annual Power Sources Conference, Atlantic City, N. J., May 16-18, 1967.
                                          48

                                                                             Arthur ZD.TUttlr.llnr.

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       The electric vehicle application requires rechargeable batteries, which present addi-
tional problems to air-cell technology.Problems arise with the rechargeability of the  anode
and with the oxidation resistance of the air cathode, which has to withstand oxygen  evolu-
tion  or be supported by an auxiliary third electrode for recharging. The work on zinc-air
cells is hampered  by the classic difficulties of recharging the zinc electrode, of  which
dendrite growth is the most significant. The following paragraphs review the present  activi-
ties in metal-air battery development.
       a.  Zinc-Air (General Atomic)

       One of the most prominent  of the programs  on zinc-air batteries is that being
conducted at General  Atomic, now a division of the Gulf Oil Corporation. The work  is
supported in part by the Edison Electric Institute, and the British company, Joseph Lucas
Ltd.,  has  become a partner in the program.  The basic approach  taken  is to avoid the
dendrite growth problem by pumping the electrolyte over the surface of the electrode. The
technique is very effective but results in considerable engineering complexity. On discharge,
the reaction product,  zinc oxide, is swept out of the cell and stored separately, being fed
back in again on charge. The cathode is of sintered nickel with a palladium catalyst, and  air is
forced through it with a compressor. The system appears to have a near-term energy density
capability of 50-60 w-hr/lb and a power density capability of 30-35 w/lb. These figures are
net after subtracting the parasitic power load  for pumps, compressors, and other auxiliary
equipment. This latter drain is estimated at a fairly constant 15% of gross power output in
the size range of greatest interest, 20-80 kw.

       The largest modules built to date have  been sized at 1 5 kwh, 4-5  kw at 36 volts, and
they will be used to determine the  performance of the system on extended cycling. A full
charge can be completed in about  two hours. If the system is not abused electrically,  it
would appear to have a cycle life comparable to that of the lead-acid battery. Carbon
dioxide contamination  of the electrolyte is a  problem but may be dealt with by changing
the electrolyte occasionally, perhaps  with the same frequency as oil is now changed in a
gasoline engine.

       Realistic estimates place the cost of the General Atomic battery in the  range from
about $1.50/lb for one designed with good energy storage but only limited power capability
to about $3.30/lb for one with the highest power density of which the system is capable. At
present, the major objective of General Atomic's project is the electric lift truck application.
       b. Zinc-Air (Leesona)

       The Leesona Corporation is also very active in metal-air battery development. While
 much  of its  effort is in the  primary  zinc-air field,  it is  also investigating electrically
 rechargeable secondary  battery  systems.  It  has developed a  mechanically  rechargeable
 zinc-air battery, which is now being delivered to the Army and Marine Corps. The latter
 battery,  which is designed as a power source for military communication systems, is far too
 costly to consider as a vehicular power source. Even if anode costs were simply those of the
 materials, with a credit for the discharged anode, mechanically rechargeable systems would
 still appear to be several times too expensive for consideration in vehicles.

                                        49

                                                                                  ZD.lUttleJnr.

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       The work on secondary  zinc-air  batteries  at  Leesona is based on configurations
which are similar to those of the company's primary metal-air batteries. Much of its effort is
directed  at improving separators, both organic and inorganic; Leesona is  a licensee of the
inorganic separator developed by the  Astropower  Laboratory of McDonnell-Douglas, Inc.
(see below).  Leesona is  also investigating the effect of close control of  charging current
density and pulse charging in attempts to solve the problem of dendrite growth.

       The Leesona primary zinc-air battery delivers as much as 116 w-hr/lb in radio service
and can  sustain steady discharge at  a power density of  18 w/lb.  Such favorable parameters
are unlikely to carry over to electrically rechargeable secondary systems, where good cycle
life is possible only when the battery is not completely discharged.

       The future costs of  Leesona's electrically rechargeable  zinc-air  battery, manu-
factured  in quantity, can only be guessed, because  so much depends on the quantities and
costs  of catalysts required  for the  cathode and the degree of complexity in the battery
structure; a figure of $1.50-S2.00/lb might be reasonable.  It is generally  agreed that the
technical problems associated with such  cells  are  far from being solved and their intro-
duction lies in the indefinite future.
       c. Sodium-Air

       An interesting variant on metal-air batteries — one which permits the use of an alkali
metal anode -  is the sodium-air battery being developed by the Atomics International
Division  of North American Rockwell Corporation. Each cell of this battery is essentially
two cells: one is a sodium-sodium amalgam cell with a molten salt electrolyte, and  the other
is  formed by the  sodium amalgam with an air  cathode in  an aqueous sodium hydroxide
electrolyte.  The  system is made feasible by the development of a very low-melting eutectic
sodium  salt mixture as the electrolyte  for the sodium-sodium amalgam cell, in which the
sodium  ion is the sole current-carrying species. Because of the low melting point the
temperature of operation is not much  above  100°C, which is quite compatible  with the
operation of the  sodium amalgam-air cell.

       The sodium-air battery is still at an early stage of development. Experience with it is
limited  to prototype models  which generate  about 25 watts and which have completed
about 50 operating cycles. The air cathode, which has not been optimized, is a  modified
form of  an American Cyanamid electrode containing about 10 milligrams of platinum per
square inch. The relatively low temperature of operation permits the use of plastics, partic-
ularly polypropylene, as materials of construction. The  molten salt electrolyte is contained
in  a porous alumina disc in some designs and is  unconstrained in others.

       Projections based on extrapolations from early results indicate that energy densities
for a 20-kw battery would be in the range of 100-150 w-hr/lb and power densities  would be
25-35 w/lb, with  ultimate capabilities significantly higher than these figures.  The  power
densities are, however, based on current densities that may necessitate uneconomically large
quantities of platinum in the air cathodes.
                                         50

                                                                                  21.lUttle.3nr.

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       In addition to the platinum,  mercury is also a major material cost. Overall manu-
facturing  costs for the  battery on a large  scale are estimated at  being  in the $1.50  to
S2.00/lb range, which is similar to those projected for many of the high-temperature bat-
teries. The cost related to the engineering complexity of the sodium-air cell is offset by the
use of economical plastic materials in its construction.

       From the operational standpoint the  sodium-air concept has a number of attractive
features for possible application as a vehicle power source. It has a much lower temperature
of operation than the  other alkali  metal-molten  salt systems, and its power density is likely
to be higher than those of the organic electrolyte batteries. Moreover.it retains the molten
anode feature and thus avoids the difficulties of dendrite formation on recharge. A further
consequence of the molten and thus structureless anode is that mechanical rechargeability is
more likely to be  economically feasible than with other types of metal-air battery.

       On the negative side, the cell appears  to be rather complex,and operating experience
with it  is limited. The long-term  stability of the low-melting eutectic mixture  may  be a
questionable feature, but  the self  discharge rate at the sodium amalgam-sodium hydroxide
interface is apparently  low.

       Atomics International has  recently formulated a design in which the two cells of the
battery  are  constructed  as separate entities  and the  sodium amalgam is pumped between
them. While this  would  require somewhat greater quantities of mercury,  cell construction
would  be simplified,  reliability would be  enhanced,  and it  is predicted that overall costs
would be reduced.
       d. Other Metal-Air Batteries

        In addition to the work reviewed above,there is a great deal of other activity in the
field of rechargeable metal-air batteries. On the basis of the little information that has been
published, none of it appears to be at a more advanced stage than  the programs already
described.  Union Carbide and ESB, Inc.  are working on electrically rechargeable zinc-air
systems generally similar  to  that of Leesona. Yardney Electric Corporation, in a program
partly  sponsored by the Ford Motor Company, is developing its"Rotoxel"zinc-air cell  in
which  dendrite formation at the zinc anode is prevented by rotating the zinc anode against a
doctor blade; this cell uses silver catalysts at its air cathode. The Astropower Laboratory  of
McDonnell-Douglas Corporation is also investigating rechargeable zinc-air cells, making use
of its novel inorganic separator developed originally for heat sterilizable silver-zinc batteries;
this  separator is  reported to achieve a  significant reduction of dendrite  growth on  zinc
during recharge.

       Globe-Union, Inc., in a program sponsored by the U.S. Army Electronics Command,
is investigating a lithium-moist air battery in nonaqueous solvents. While this might  rep-
resent  the ultimate in theoretical energy  density for metal-air cells, the practical difficulties
appear to be overwhelming.
                                         51

                                                                                   21.ltittlc.Ilnr.

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       General Telephone and Electronics has a program on the iron-air battery. In view of
the maturity of the technology of rechargeable iron electrodes,  this might be a promising
approach.

       Zaromb  Research  Corporation is investigating aluminum-air cells,  but in spite of
their attractive theoretical energy  densities, they are relatively unpromising. Less than half
the theoretical voltage is  obtained, leaving the rest  to appear as heat. As the aluminum
electrode cannot be  recharged electrically,  the system can be  considered  potentially re-
chargeable only on a mechanical basis.  The General Electric Company has developed a
mechanically rechargeable magnesium-air  battery conceptually similar to the Leesona zinc-
air system but has not advanced it  as a possible vehicle power source. General Electric is also
investigating  rechargeable cadmium-air systems, as is  Union Carbide. These latter systems,
however, are  not being considered  as potential power sources for vehicles.
     4.  Nickel-Zinc

       While  the  high level of  present interest in this system is not directly  related to
electric  vehicle development,  the nickel-zinc battery has, potentially at least, performance
parameters which merit consideration for vehicle applications. The substitution of zinc for
cadmium  should  give  it approximately double  the  energy  density of the nickel-cadmium
system (i.e., about  30 w-hr/lb), and the power density should be comparably high. There is
no problem of material availability with zinc; the costs of the battery should be appreciably
less than  those of  nickel-cadmium batteries, although as a nickel-alkaline system it is still
likely to be expensive compared with lead-acid.

       The major difficulty with the nickel-zinc system is the classic problem of obtaining
an adequate cycle  life from  any  rechargeable  battery  containing  a zinc anode. General
Telephone and Electronics, which is one of the companies investigating nickel-zinc cells, has
reported cycle lives of 100-200 but at only 50%  discharge, which nullifies its advantage over
nickel-cadmium  in  energy density. General Electric has reported improved cycle life by
incorporating  calcium hydroxide in the electrolyte to  limit the concentration of soluble
zincate, but this  too lowers  the  energy  density. Also active  in the field  are Texas Instru-
ments, Eagle Richer, Yardney Electric, and others.

       Even if perfected, the  nickel-zinc battery would still  seem to be  too costly as the
prime power source  for  an  electric vehicle, but it might have  some promise  in hybrid
mechanical-electrical systems (see Section VI). Until a reasonable lifetime has been demon-
strated,  however, its prospects as a vehicle power source remain speculative.
                                         52

                                                                            Arthur ZD.lUttkllttr.

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C.  FUEL CELLS

        Fuel cells are essentially steady-state primary batteries and are of interest for electric
vehicle applications mainly  because vehicles so powered  would have  no requirement for
electrical recharging. They would thus be no more restricted in range than are convention-
ally powered vehicles. Because of this, energy density is not a meaningful parameter for fuel
cells; an evaluation  of their  applicability to  vehicles turns upon their power density, relia-
bility, and potential  cost.

        Fuel cells, which exist in a wide variety of types, can be differentiated by the nature
of  the fuel used  - hydrogen; water-soluble substances such  as hydrazine, methanol and
ammonia; hydrocarbons  —  and by their temperature of  operation: ambient,  moderately
elevated (80-150°C), or  high (500-1 OOCfC).   Since hydrogen  reacts so easily in a fuel cell
but is an inconvenient fuel  to handle, several  types  of fuel cells convert  other fuels into
hydrogen as the first step. These are called indirect fuel cells. The types of greatest interest
for vehicle application are ambient-temperature hydrogen systems, both direct and  indirect,
and soluble fuel  systems. On a conceptual basis the  U.S. Army has also considered a
high-temperature fuel cell-battery hybrid system involving a high-temperature hydrocarbon
fuel cell.
     1. Ambient-Temperature Hydrogen Systems

        Ambient-temperature  hydrogen fuel cells  have reached a relatively  high degree of
reliability, and several thousand hours of trouble-free operation are now commonplace. The
major  limitations of these systems for application in electric vehicles are their relatively low
power density and their high  estimated production costs. As a general rule,  restrictions on
current densities imposed by  problems of heat dissipation and electrode  polarization limit
power densities to levels of around 30 w/lb or so.  More serious is the cost restriction, which
has  two major causes:  1) precious  metal catalysts are necessary to generate acceptable
current densities and 2) the problems controlling materials transfer across the boundaries of
fuel cells make the engineering problems of the latter more complex than those of batteries.
       The present state of the art in ambient-temperature hydrogen-air fuel cells is such
that cells can be operated with no precious metal catalyst at all, but the current densities
would be too low for vehicle applications. A loading of about 5 milligrams of platinum per
square centimeter of electrode  presently appears necessary  to give a power density of 25
w/lb to a hydrogen-air fuel cell  and this may be improved to 50 w/lb in ten years.* Present
costs of such cells are no reliable index of future  costs, since they are all essentially hand-
made. The most optimistic estimates  for  future  volume production  are in the range of
* The Automobile and Air Pollution:  A Program for Progress, Report to the Panel on Electrically
  Powered Vehicles (R. S. Morse, Chairman), U. S. Department of Commerce, October 1967.
                                         53

                                                                             3rrbur

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$100-5150 per kw. To this must be added  the  cost of the fuel supply system. Cylinder
hydrogen is probably  impractical due to its  bulk and weight; liquid hydrogen is a distinct
possibility  but will certainly add significant  costs for cryogenic storage. Indirect  fuel cells
would require equipment to reform  hydrocarbons or methanol or to crack ammonia. None
of these  possibilities appears likely to involve the addition of less than S50/kw to the first
cost; and thus, S150-$200/kw seems  to be a limiting cost range for such systems.

       Operational costs are likely to be quite moderate if hydrocarbons or methanol are
used as fuel, since the conversion efficiency of the fuel cell is much higher than that of the
internal combustion engine. The extent to which  there would be a  road tax  on fuel-cell-
powered vehicles  is a major  unknown  factor here. In addition,  fuel cells with alkaline
electrolytes would need occasional changes of electrolyte because of gradual contamination
with atmospheric carbon dioxide.
     2.  Soluble Fuel Systems

       Soluble fuel types will in general involve even higher first costs than will hydrogen
fuel  cells.  Those using ammonia or methanol call for much higher loadings of platinum
catalysts per unit area, and their power density is not as great. Relatively low costs would be
associated with a hydrazine-fed  fuel cell, but this material is presently too costly (hydrazine
hydrate costs  approximately Sl.OO/lb) and there  seems little prospect for a great enough
cost  reduction to make it a practical fuel.
     3.  Direct Hydrocarbon Fuel Cells

       Research activity continues with direct hydrocarbon fuel cells,  using aqueous elec-
trolytes,  particularly phosphoric acid, at temperatures of about  150°C.  While the reactivity
of the hydrocarbons is higher than was earlier thought possible, the quantities of precious
metal catalyst required are still, and are likely to remain, orders of magnitude higher than
those which could be contemplated in an electric vehicle.
     4.  Platinum Availability

       The use of platinum in fuel cells is potentially restricted not only by cost but also by
availability. On the basis of today's technology, a full sized car powered by a fuel cell might
have a platinum requirement in the range of 1 to 10 pounds. This should be compared with
an annual world production  of  this element of about  60,000 pounds and an estimated
reserve of 10  million pounds. Clearly, the world's present apparent resources of platinum are
not sufficient to support the widespread use of fuel cells in vehicles. Considerable research
effort is being expended in a search for alternative and noncritical catalyst materials, but the
results to date are not particularly promising.
                                        54

                                                                            3rthur 2l.1Uttle.llnr.

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       High-temperature fuel cells capable of utilizing hydrocarbons directly do not use
precious metal catalysts and hold promise of a lower ultimate cost structure than those for
other types of  fuel cells. They are, unfortunately, excessively  heavy, and the problems of
reliability and control are exacerbated by the elevated temperatures.
     5.  Overload Capability

       A consideration of the fuel cell's prospects solely in terms of cost per kilowatt may
lead to an excessively pessimistic outlook, since some  allowance should  be  made  for its
overload capabilities.  Power rating is a term calling for close definition; if the demand  for
maximum power is infrequent, a much lower rating is possible for the fuel cell than would
be  possible with a  battery power source. For example, Union Carbide's hydrogen-oxygen
fuel cell for the GM Electrovan* had a rating of 32 kw  but a maximum output of 160 kw.
The exact degree and duration of overload possible with a given fuel cell system will vary
with its individual  peculiarities,  but it seems reasonable to take a factor of three as being
representative. In such a case the family car of Table  1  might be adequately powered by a
30-kw  cell rather than one of 90 kw. Even so, at an estimated S200/kw,  the fuel cell would
be prohibitively costly.
     6.  Present Applications

       While much effort is being expended in the United States and elsewhere on fuel cell
development, relatively little is focused on highway vehicle applications, most probably for
the reasons of cost. Major engineering programs at General Electric. Pratt & Whitney Divi-
sion of United Aircraft,  Allis Chalmers, Union Carbide, Texas Instruments, and Monsanto
have  been  concerned more with  the  fuel cell's  application  as a power source  for space
satellites, both manned and unmanned, as a means of generating electricity from natural gas
in the home (a program at Pratt & Whitney in which the Institute of Gas Technology also
participates), as  a  power source for the military  in  the field, and as a power source  for
industrial vehicles, particularly fork  lift trucks. Overseas,  ASEA  in Sweden has  built fuel
cells for submarine propulsion. (This and other European activities are  reviewed in Appen-
dix B.)

       Direct application of the fuel cell to highway vehicle propulsion has  been confined
to two experimental vehicles:  the GM Electrovan, powered by a Union Carbide hydrogen-
oxygen cell, and an M-37 truck modified by the U.S. Army Engineers R&D Laboratory to
use a Monsanto hydrazine-air  cell.  Some  notes  on these two  vehicles are contained in
Appendix A. In  Europe the French Government is sponsoring an electric car program based
upon a 25-kw hydrogen-oxygen fuel cell system (see Appendix B).
 See Appendix A.
                                        55

                                                                           3rthur 3l.HittIc.3nr.

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 D.   ELECTROCHEMICAL HYBRIDS
        Many of the electrochemical power sources reviewed in this section have had certain
 favorable properties for the electric vehicle application, but some of their other properties
 might be unacceptable. The most common situation, exemplified by  fuel cells and alkali
 metal-organic  electrolyte  batteries, is  good energy density  allied with  inadequate  power
 density. One solution  to this difficulty is to use a combination or hybrid power source in
 which each component provides properties which complement those of the other. Thus, a
 low-energy-density, high-power-density battery such as nickel-cadmium can be combined
 with a high-energy, low-power battery or fuel cell.

        There are a number of fairly apparent drawbacks to electrochemical hybrid systems.
 First, they are  more complex than a single power source and thus require significantly more
 complicated control equipment. Second, the energy efficiency of the  hybrid tends to be low
 because of the losses involved in the internal redistribution of charge among the components
 of the power source. A further difficulty is that, future high-temperature systems aside, the
 most suitable battery for the hybrid systems is nickel-cadmium which has the limitations of
 high cost and materials availability problems, previously noted. As mentioned elsewhere in
 Sections VI and VII, the development  of high-power-density "pile-type" lead-acid batteries
 would improve the prospects of hybrid  power sources.

        In spite of these difficulties, electrochemical hybrid systems offer enough advantages
 to have been the subject of a number of detailed  paper studies and the power source for at
 least one experimental vehicle. There are two subcategories   fuel cell-battery hybrids and
 battery-battery hybrids.
     1. Fuel Cell-Battery Hybrids

        Fuel  cell-battery hybrids offer possibilities for improving the prospects of the fuel
cell as a vehicle power source on two counts. The battery can be chosen to give the overall
system an  adequate power density and, since its specific costs are likely to be lower than
those of the  fuel cell, the overall cost per kilowatt will be lessened. The system retains the
fuel  cell's advantages of rapid refueling and a range limited only by the size of the fuel tank.

        Union Carbide Corporation, which built the hydrogen-oxygen fuel cell  for the CM
Electrovan,*  has carried out a conceptual study of coupling a fuel cell with nickel-cadmium
batteries for  the  same application.  It concluded that  the same performance could  be
obtained by reducing the fuel cell stack weight from 1345 to 690 pounds and incorporating
427  pounds of nickel-cadmium batteries. Further weight savings would be effected in other
* See Appendix A.
                                       56

                                                                                 ZD.1Uttle.Knr.

-------
parts of the system. The study was not intended to find the optimum makeup of the system
but was merely a first approach based on the present state of the art. The battery would be
capable of putting out 128 kw of power for short periods; based on a rule of thumb of $3/lb
for nickel-cadmium battery costs, it would give peak power capability for about $10 per kw,
considerably less than could ever be expected from a fuel cell.

       Union  Carbide  has also  constructed  for demonstration purposes a small electric
motorcycle powered by a hybrid combination of hydrazine-air fuel cell.and nickel-cadmium
batteries. The power rating of the fuel cell in the system was 0.8 kw.

       Another approach to fuel cell-battery hybrid  power sources is being studied at  the
U.S. Army Engineers R&D Laboratories at  Fort Belvoir. This  concept would combine  a
high-temperature hydrocarbon-air  fuel cell of the type  being developed at Texas Instru-
ments, Inc., with a high-temperature alkali-metal battery (for which the SOHIO system  is a
likely candidate). The advantages  include the ability to use conventional fuels directly,  a
high power density due  to  the properties of the  battery, and the possibility of using  waste
heat from the fuel cell to maintain the temperature of the system, thus eliminating the need
for a separate heater.

       The high-temperature fuel cell-battery hybrid has certain logistic attractions for  the
military because  it is designed  to  operate on  standard  hydrocarbon fuels, but it seems  a
rather remote  possibility for general  application. If the technical problems of their develop-
ment  can  be solved adequately, high temperature batteries are likely to be the sole power
source in a vehicle. The fuel cell would add increased range capabilities but at a higher first
cost and much greater complexity.
     2.  Battery-Battery Hybrids

       The most prominent example of the battery-battery hybrid is a system proposed by
Gulton Industries, Inc., presumably to be the power source for the experimental vehicle be-
ing developed in Gulton's joint program with American Motors Corporation. It will consist
of a high-energy-density lithium-nickel fluoride battery (see  Section V-B-2) in combination
with  a high-power-density "bipolar" nickel-cadmium battery.  The latter has a  pile-type
construction and has been developed by Gulton specifically for applications involving high
discharge rates.  The hybrid system is expected to combine the best features of both bat-
teries.

       The General Electric Company has used a hybrid  battery system in its small experi-
mental electric vehicle (see Appendix A). The major energy source is a lead-acid battery; to
enhance the vehicle's acceleration, a small nickel-cadmium battery having about 5% of the
capacity  of the  lead-acid  battery is connected  in  parallel with it. The  system apparently
operates  successfully, and the vehicle  has significantly better  performance than it would
have with lead-acid batteries alone.
                                       57

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                     VI.  MECHANICAL-ELECTRICAL HYBRIDS
       The power source for an electric vehicle can, of course, be an electrical generator
activated by some kind of combustion engine. This is the basic system used in diesel-electric
locomotives and, to a limited extent, in large diesel-powered off-highway vehicles for heavy
construction work. Combustion engines are inevitably a source of some pollution, but it is
reasonable  to expect that the pollution could be minimized if they were specially designed
to operate at a  constant power output,  as would be possible  in a hybrid system.  The
fluctuating  power demand  would  be met by  a battery connected  in  parallel  with the
generator. The system might take any one of the  four forms shown in Figure 10.

       Hybrid  systems can, in principle,  have  any desired ratio  of  engine-generator to
battery power. In practice,  however, it  would seem desirable  to have the engine-generator
capable of supplying the average power level used by the vehicle plus sufficient reserve to
ensure that the battery never  became fully  discharged in normal driving situations. This
would make the  hybrid vehicle  independent  of  battery  charging  facilities  and would
eliminate from consideration engines which are uneconomically small,* since the  power/cost
ratio of engines decreases significantly as the size  falls to a few kilowatts.

       An  engine much larger than the average power rating is undesirable, however, since if
it were being run at constant  power, much  energy would be  wasted  in overcharging the
battery. Shutting off the engine when the battery is fully charged is not a solution to this
difficulty, because the vehicle could not then respond rapidly to a demand for  power greater
than could  be supplied  by the battery alone.

       The driving cycle used in the calculations of vehicle performance parameters (Table
2) indicates that the average power demand in the moving vehicle is about 24% of the peak
demand. This may be somewhat on the  low side for vehicle performance as a whole, since
the cycle is concerned  with  city driving  conditions.  We have therefore arbitrarily chosen to
consider the prospects  for mechanical-electrical hybrids on the  basis of the engine's having a
continuous power output equal to 40% of the peak power demand. This would provide a
good  reserve for unusually prolonged operation at high power demand  and also permit the
use of power-consuming auxiliaries such as air conditioning.

       Of  the four possible systems shown in Figure  10 we consider the ac generator-dc
motor combination (d)  the most immediately  promising. The ac generator is attractive
because it has  no brush maintenance and replacement problems, and because it can run at
high speeds and is thus very compact. Moreover, the  technology of mass producing such
* The few hybrid vehicles in commercial production for use on the highway utilize a relatively small engine-
  jenerator system manufactured by G&M Power Plant Co. Ltd., of Ipswich, England.  Designed for attach-
  ment to electric milk trucks and similar vehicles, the engine-generator serves merely to extend the range of
  what are essentially battery-powered vehicles.
                                          58

                                                                             3rthur

-------
(a)

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D-C
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D-C
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A-C
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(c)

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                              FIGURE 10   VARIOUS ELECTRICAL SYSTEMS FOR
                                          ELECTRICAL-MECHANICAL HYBRIDS

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generators is  well  advanced  because of  the  general  introduction  of the alternator  in
conventionally powered vehicles  some  five or six years ago.  A  dc motor  is preferred,
however,  for traction; as explained in Section IV, the principal reason is the high cost and
weight of the inverter system needed by an  ac motor for speed control.

       To evaluate the technical  requirements  of the  hybrid system, we follow the same
general procedure as  that used for the purely electrochemical power source. From the
weight available for the power sources (line 17 of Table 1), we subtract the weight of an  ac
generator, rectifier, speed increaser, and  voltage regulator rated at 40% of the final peak
power requirement for each vehicle. The remaining weight can then be distributed between
the prime mover and  the battery. Our approach  has been to estimate weights for the former
based upon existing technology and then calculate  the power density which is required from
the battery. Provided it is sufficient to meet the demand for maximum power, the energy
density of the battery is of secondary  importance, since the source of energy is the fuel fed
to the prime mover.

        Five different  classes of engines could conceivably be employed in a  mechanical-
electrical  hybrid system. Three of these - the gas piston engine,  the diesel piston engine,
and  the  gas  turbine  engine  - involve  internal combustion;  the others  - the  Rankine
cycle (steam)  engine and the Stirling engine — involve external combustion. The latter two
can be operated at lower overall pollution levels than the former, since external  combustion
can be carried out in  a comparative excess of air (although oxide of nitrogen production is
enhanced); nevertheless, the data available  on steam engines and Stirling engines in the size
range of interest (reviewed  in the recent report* by the Battelle Memorial Institute)  are  so
meager that a separate analysis of their prospects in hybrids is not justified. Since their
power/weight  ratio appears to fall within  the  same range as the  diesel piston engine, the
calculations for this engine can be used  as a  first approximation for them.

       Representative data  for  the technical performance of gas piston engines and diesel
piston engines in the size range of interest  (6-60 kw) are plentiful, and  some data exist for
the gas turbine at  the upper end  of  this  range.  Figure  11  shows some estimates of the
weight-to-power ratio  for  these types of  engines, and Figure 12  shows estimates of the
corresponding factory  costs per kilowatt.  These data are for engines with anticipated life
times of 2500 operating hours, manufactured in quantities greater than a hundred thousand
units  annually and designed  for constant  power service  at their rated load  in a hybrid
vehicle. Their parameters therefore correspond  more closely  to the  engine technology  of
long-haul  truck service and  industrial applications, where average operation is close to the
rated  power level, rather than to  that of conventional  automobile engines, whose average
operation  calls for only 20-25%  of the maximum rated power. For gasoline and  diesel
engines, which are very mature products,  the power rating  is the main influence on the
power/weight ratio, and production volume  is the main determinant of costs.

        The  technology of gas turbines  is well advanced,  but  the translation of this
technology into economic solutions  to  the problem of automotive propulsion is in its
infancy.  Few  units exist in the size range of interest, and the estimated values in Figures 1 1
and 12, particularly of cost, must be regarded as very approximate.

 * Battelle Memorial Institute, "Study of Unconventional Thermal, Mechanical, and Nuclear Low-Pollution-
  Potential Power Sources for Urban Vehicles," by J. A. Hoess, eta/.. Summary Report to U. S. Dept. of
  Health, Education and Welfare, March 15, 1968.

                                         60
                                                                                    3l.lLittlf.Hnr.

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  100
I
•5 10
                                10
                             Rating (kw)
100
 FIGURE 11   POWER/WEIGHT RATIOS FOR INTERNAL COMBUSTION ENGINES
                            61

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   70
   60
   50
I  40
o
Q
   30
CO
   20
   10
                                   Diesel
                                   Piston
                                   Gasoline
                                   Piston
                                10

                        Continuous Rating (kw)
Gas
 urbine
                                              \
    \
             SI
             100
          FIGURE 12    APPROXIMATE COST LEVELS FOR
                        INTERNAL COMBUSTION ENGINES
                            62

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       The  weight  estimates  for  the ac generator  are  taken from  Figure  13.  These
correspond to machines  running at speeds of 12,000  rpm in the higher end of the power
range and as high as 16,000 rpm in the lower end. They are representative of the technology
used in equipment which is already in existence, particularly for aircraft applications, and
which  might  be manufactured at low unit cost if sufficient demand  developed. (Figure 13
also  makes allowance for the relatively small extra weight associated with the rectifier and
the speed which the system requires.)

       Using the data from Figures 11 and 13, the weights of generator and engine rated at
40% of the peak  power requirement have been  calculated for each of the  six classes of
vehicle and for each of the three engine types. The permissible weight for  the battery and
thus its required power  density are  derived from these  calculations and are presented in
Table 5. The first two lines of the table are, respectively, lines 12 and 17 of Table 1.

       The results of the calculations, which at first sight are somewhat surprising, indicate
that  the  power  density  requirements for  the  batteries in hybrid vehicles are only slightly
lower than for those in  vehicles powered solely by batteries.  These requirements are not
particularly sensitive to the arbitrary choice of a  40/60 prime-mover-to-battery ratio. Thus,
among vehicles  with  gasoline engines and with conventional  construction the  family car
shows essentially no change,  while in  the most favorable case, the city bus, the reduction is
above 30%,  from  36  w/lb to 25 w/lb. In the case of the diesel engine, the power density
requirement for many hybrid vehicles is actually greater than when  the battery  is the sole
power source; this results from the  relatively high weight which  must be assigned to the
diesel engine.

       Although the engines which would be used in the  hybrid are smaller than  those used
in corresponding conventionally powered vehicles, the  weight differences are not great. The
larger maximum  power capability of conventional  vehicles does not call for substantially
greater weight, because the engine is not built to run steadily at the higher power level.  Also,
the power density of internal combustion  engines  decreases  as the size falls,  so a  small
decrease  in  average  power  level does not return a  proportional decrease in weight.  The
decrease in battery power density requirement for the  hybrid involving a gas turbine engine
is somewhat  greater than for the two piston engines, but unfortunately the technology of
small gas  turbines is not  well established, and their cost, which might be in the range of
$40-$ 100 per kilowatt in  the  size range of interest, is likely to be discouragingly high.

       The major differences between the battery requirements in the pure electric and the
hybrid is that, in the latter,  1) energy density is of small  importance and 2)  the maximum
power density is reduced  by about one-fifth.  The power density requirements  for the family
car,  however,  still restrict the  choice of batteries primarily to the high-temperature alkali
metal type (among  which the  SOHIO system's high power  density capability might be
particularly attractive); the sole exception to this statement is the nickel-cadmium battery,
which has excellent power characteristics but low energy density.

       For vehicles other than the family car, the power density requirements of the hybrid
could be satisfied  by metal-air battery systems; for various technical reasons, however (such
as corrosion at the air cathode), this class of battery does not appear to be suitable for the
                                           63

                                                                                    3l.ltittlf.3lnr.

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4 6 8 10 20 40 60 80 100 20
             Generator Rating (kw)

FIGURE 13   WEIGHT OF GENERATOR, RECTIFIER,
            SPEED INCREASER AND VOLTAGE
            REGULATOR
                 64

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                                          TABLE 5
                             HYBRID VEHICLE SPECIFICATIONS3
Maximum output of hybrid
   power source
(kw)
Weight assignable to hybrid
   power source                 (Ib)
     Conventional construction
     Lightweight construction

Weight assigned to generator,
   rectifier, speed increaser, and
   voltage regulator             (Ib)

Weight assigned to engine        (Ib)
   Gas piston
   Diesel piston
   Gas turbine

Weight available for battery      (Ib)
   Conventional construction
   Gas piston
   Diesel piston
   Gas turbine

Weight available for battery      (Ib)
   Lightweight construction
   Gas piston
   Diesel piston
   Gas turbine

Power density of battery         (w/lb)
   Conventional construction
   Gas piston
   Diesel piston
   Gas turbine

Power density of battery         (w/lb)
   Lightweight construction
   Gas piston
   Diesel piston
   Gas turbine
                                       Family
                                        Car
85
          902
         1,402
           70
          279
          715
           89
          553
          117
          743
         1,053
          617
         1,243
           92
          440
           69
            48
            83
            41
                   Commuter
                      Car
29
          632
          932
           30
          150
          395
           44b
          452
          207
          558b
          752
          507
          858
           38
           82
           30
           23
           34
           20
Utility
Car
17
418
618
20
105
295
32b
293
103
366b
493
303
566
34
97
27
20
33
18
Delivery
Van
62
1,141
1,741
55
233
600
72
853
486
1,014
1,453
1,086
1,614
43
76
36
25
34
23
City
Taxi
47
1,040
1,540
44
196
512
63
800
484
933
1,300
984
1,433
35
58
30
22
28
20
City
Bus
159
4,385
6,385
115
416
1,010
135
3,854
3,260
4,135
5,854
5,260
6,135
25
29
23
16
18
15
a) 40% of power supplied by prime mover, 60% supplied by battery
b) Power rating for commuter and utility car application considered to approach lower limits of feasible ap-
   plication of gas turbine.
                                               65
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"float  charge" service  characteristic of  the  hybrid application. More important is the
possibility  that  the  lead-acid  battery  might  qualify  for the  non-family-car  hybrid
applications. The power requirements are  somewhat high for it, except for the city bus, but
its power density might be increased with further development of pile-type construction.

       From  a  cost standpoint, the  prospects for  the  hybrid  vehicle are  generally
unfavorable. In the smaller vehicles  there would be virtually no saving in the  cost of the
prime  mover to  offset  the extra cost  of the generator, electric motors, control system,
battery, cabling,  etc.  of the hybrid. The  nickel-cadmium battery, whose present technical
capabilities make the  hybrid vehicle an immediately feasible proposition, is too expensive at
$3/lb and  could not be manufactured in the required quantities because of  insufficient
supplies of cadmium. Although  they obviously face a prolonged period of development,
high-temperature alkali metal batteries could eventually prove feasible for hybrids; however,
their energy density would make them  even more attractive as the sole power  source of a
purely electric vehicle, which is inherently a less complex and thus less costly solution.

       There appears to be one possible exception to these negative conclusions. In the case
of the  city bus, the largest of the vehicle types considered, existing lead-acid batteries have a
power  density  adequate for the hybrid.  In the diesel-powered version, the cost  of the
battery might  be about  S3000-S4000, an acceptable figure in comparison with average  total
costs of about  $30,000 for conventional  full-sized city buses. The  slight reduction in the size
of the  engine would produce a small saving to offset the cost of motors and controls in this
size range, but the economic attractiveness, if any, would probably  come from  lower fuel
and maintenance costs,  which are always  important in commercial/industrial applications.
Enthusiasm  for the hybrid city  bus is,  however,  tempered by these  facts:  1) it  is still
basically an internal-combustion-powered vehicle and will contribute to air pollution, and 2)
the number of buses  is  relatively small, so the elimination of their pollutants would make
only a small contribution to solving the overall problem.
                                           66

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        VII.  PROSPECTS AND REQUIREMENTS FOR ELECTRIC VEHICLES
       This section reviews the prospects for the six classes of electric vehicles, mainly in
terms of the ability of the projected state of the art in electrochemical power sources to
meet their technical requirements within an acceptable level of cost. The future technology
of motors and controls can be projected with somewhat greater confidence, although cost
estimates are based on large extrapolations and  are, at best, very  approximate. Some con-
sideration is also given to the problems relating to the refueling of electric vehicles.

       The  findings of this study indicate the technical areas where most effort is necessary
if the development of electric vehicles is to be accelerated. From these findings, and taking
into account the anticipated progress of existing research and development programs in both
the public and  private sectors of the economy, a number of recommendations are made
concerning the emphasis and direction of future effort.
A.  TECHNICAL PROSPECTS

       The general technical capabilities of the various electrochemical power sources con-
sidered in Section V are summarized in Table 6 on the basis of values that might be attained
when the systems now under development  reach maturity. While these generalized figures
may not  accurately apply to some individual systems, they will suffice for a first analysis of
vehicle requirements.
     1.  Family Car

                                    Conventional                   Lightweight
                              Battery or     Gas Piston       Battery or     Gas Piston
Requirements:                  Fuel Cell       Hybrid         Fuel Cell      Hybrid

  Energy Density (w-hr/lb)        135            -              87

  Power Density (w/lb)             94           92              60            48
       The technical requirements for the power source of the family car are the most
demanding of those for all six types of vehicles considered. This is somewhat discouraging,
since vehicles in this general category  comprise approximately 80%  of all vehicles on U.S.
highways and are thus responsible for a correspondingly large proportion of the air pollution
caused by vehicles. It is apparent from the requirements shown in Table 1 that only  the high
temperature alkali  metal  batteries have  any prospects  of simultaneously satisfying the
energy density and power density needs of this vehicle, regardless of the kind of construc-
tion. While a  number of the  metal-air batteries might, with further development, meet the
requirements for energy density in the family car with lightweight construction, they cannot
meet the power density requirement. The same is true for fuel cells, and particularly so for
organic electrolyte batteries.
                                       67

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                                        TABLE 6
                     GENERALIZED TECHNICAL PARAMETERS FOR
                          ELECTROCHEMICAL POWER SOURCES
             System
High temperature alkali metal batteries
   (rechargeable)
Maximum Energy
    Density
    (w-hr/lb)

     > 100
Maximum Power
    Density
    (w/lb)

    > 100
Metal-air batteries
   (rechargeable)
    50-80
    30-40
Alkali metal batteries with organic
  electrolytes (rechargeable)
    75-100
     15-20
Lead-acid

  Special construction
    15-20
    20-30

       60
Nickel-cadmium

  Special construction
     15-20
    75-100

       300
Fuel cells
                                  30-40
                                           68
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       As shown in Section VI, the power density requirements for a mechanical-electrical
hybrid in a family car are not much lower than for the purely electrochemical power source.
They can,  of course, be satisfied by  high-temperature batteries and also by the nickel-
cadmium battery, but the costs of the former are uncertain  and those of the  latter are
known to be too high. Pile-type lead-acid batteries, if their further development is success-
ful, might also be marginally capable of meeting the hybrid power source requirements for
the family car.

       Among electrochemical  hybrid systems the power density  of air-breathing fuel cells
is likely to  be too low to allow the hybrid to provide a sufficiently  high power density, even
in  combination with high-power-density batteries. The high energy density of the lithium-
organic electrolyte battery in hybrid combination with a high rate nickel-cadmium  battery
could satisfy the technical  requirement;  this is  unlikely  to be a suitable power  source,
however, because of  the particularly formidable technical  problems associated with the
development of rechargeable lithium-organic electrolyte batteries and the unavoidably high
cost structure that this system would entail.

       Thus, with  the  marginal exceptions noted above, it can  be concluded that  high-
temperature alkali metal batteries are the only electrochemical power sources which appear
technically  suitable for use in the family car.
     2.  Commuter Car

                                    Conventional                   Lightweight
                              Battery or    Gas Piston       Battery or     Gas Piston
Requirements:                  Fuel Cell       Hybrid         Fuel Cell       Hybrid

  Energy Density (w-hr/lb)         41            -              28

  Power Density (w/lb)            46            38              31            23
       Power source  requirements for  the  commuter car are less stringent than  for the
family car. Besides being  a  lighter vehicle and having lower acceleration capability, it has
only one-half the  range; as  a consequence,  the energy density requirement is about one-
third, and the power density requirement is  about one-half, those of the family car. High-
temperature  alkali metal  batteries should be able to meet these requirements with ease.
Metal-air batteries  would have adequate  energy density capability, but the maximum power
density required in the commuter car with conventional construction is somewhat above the
upper  range  of the expected capability of devices  using air cathodes. With  lightweight
construction, the power source  requirements should fall easily into the range of capabilities
of metal-air batteries and also of fuel cells.

       Among hybrid power sources, a  high-power-density battery in combination with a
fuel  cell, lithium-organic electrolyte  battery or an engine-generator would all qualify. The
power requirements are,  however, too  high for  existing lead-acid batteries,  and nickel-
cadmium batteries  are unacceptable on the grounds of cost and material availability.
                                          69

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       The commuter car thus appears also to require high-temperature alkali metal bat-
teries,  but rechargeable metal-air batteries would appear to have prospects of providing an
adequate alternative.
     3.  Utility Car

                                    Conventional                   Lightweight
                               Battery or     Gas Piston       Battery or     Gas Piston
Requirements:                  Fuel Cell       Hybrid          Fuel Cell      Hybrid
  Energy Density (w-hr/lb)         26             -               18

  Power Density (w/lb)            40            34               28            20
       The requirements for the utility car are the most modest of the series. Considering
first the requirements for lightweight construction, the power source needs can be met by
lead-acid batteries of the type representative  of the best of today's technology and com-
fortably within what normal evolution should provide within a few years. With conventional
construction the utility car has a rather high power density requirement, close to the upper
range  likely to be achieved by metal-air batteries. High-temperature alkali metal batteries, of
course, easily satisfy all requirements of the utility car.

       While a number of hybrid power source  systems, both mechanical-electrical and
electrochemical, are technically feasible power sources for the utility car, their complexity
makes them inappropriate for such  a small vehicle.

       Thus, improved lead-acid batteries would seem to be technically adequate for this
vehicle application; the higher performance  metal-air batteries and high-temperature alkali
metal  batteries  offer potential alternatives whose merit might be determined on the basis of
cost.
     4.  Delivery Van

                                    Conventional                   Lightweight
                              Battery or    Gas Piston       Battery or     Gas Piston
Requirements:                  Fuel Cell       Hybrid         Fuel Cell      Hybrid

  Energy Density (w-hr/lb)         50            -              33

  Power Density (w/lb)            55            43              36            25
                                         70

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       The  requirements for the delivery van with conventional construction show the need
for a relatively high power density of 55  w/lb. This is likely to be above the developed
capabilities  of the metal-air battery systems and of fuel cells.  As in the case of the family
car, it would appear that the delivery van will require high-temperature alkali metal batteries
as its power source. In a hybrid with a gas piston engine, the power density requirement for
the battery  falls to 43 w-hr/lb, but this is still attainable only  by the  high-temperature and
nickel-cadmium batteries.

       With lightweight construction, however, the power source requirements for the van
fall into a range  likely to  be  attained by  metal-air batteries,  and in the gas piston hybrid
vehicle the battery requirements might be accommodated by  the lead-acid system.

       While high-temperature alkali metal batteries  seem in  general to  be the indicated
power source  for  the delivery  van, it is evident that a much  wider range  of  possibilities
would be opened up through the use of lightweight  construction.
     5.  City Taxi

                                    Conventional                   Lightweight
                               Battery or     Gas Piston       Battery or    Gas Piston
Requirements:                  Fuel Cell       Hybrid          Fuel Cell       Hybrid

   Energy Density (w-hr/lb)         96             -               64

   Power Density (w/lb)            45            35               30            22
       For the city taxi the energy density requirement is high, since it is equivalent to that
of the family car but scaled down in proportion to its somewhat shorter range. The lower
acceleration performance  demanded of the city taxi, however, reduces the power density
requirement to less than one-half of that for the family car. With conventional construction,
this reduced power density still seems to  be  above the expected capability range  for the
rechargeable metal-air batteries, and  high-temperature  alkali metal  battery systems again
appear necessary. In  a hybrid vehicle with a gas piston engine, the nickel-cadmium battery
would be satisfactory, and improved lead-acid  batteries  might also meet the power density
requirements.

       With lightweight construction, metal-air batteries should be capable of meeting the
power source requirements for the city taxi, although the energy density specification might
be close to the upper limit in some systems. Lightweight construction would also appear to
qualify the lead-acid  system for inclusion  as  the battery in the  gasoline-powered  hybrid
system.
                                       71

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     6.  City Bus

                                    Conventional                   Lightweight
                               Battery or     Gas Piston       Battery or     Gas Piston
Requirements:                  Fuel Cell       Hybrid          Fuel Cell       Hybrid

  Energy Density (w-hr/lb)         81             -               55             -
  Power Density (w/lb)            36            25               25             15
       The city bus with conventional construction has a high energy density requirement,
a consequence of the frequent stops in its driving cycle and the value assumed for the range
(which may be rather high for city driving service). The  power density  requirement of 36
w/lb is comparatively moderate. High-temperature alkali metal batteries are capable of
meeting both energy density and power density requirements, and the latter is also within
the range of metal-air batteries. A relaxation of the range specifications would thus allow
the latter  system  to be an  acceptable power  source for the city  bus. With lightweight
construction, the power source requirements should be well within the range of capabilities
of metal-air batteries.

       Hybrid systems offer some attractive possibilities for the city bus. For both conven-
tional and  lightweight construction and for  the three types of prime movers, power density
requirements calculated  for  the  battery are within the  range  of lead-acid systems.  The
hybrid bus system thus appears to be feasible using components from existing technology
which are likely to have an acceptable cost.
B.  COST FACTORS
     1.  Considerations of First Cost

       Cost estimates for the classes of electric vehicles under consideration in this study
involve even greater uncertainties than in the evaluation of the technical factors.  It is clear
that no vehicle, electric or otherwise, has any prospect of becoming competitive until it is
manufactured  and marketed on a scale generally comparable with that of today's conven-
tional vehicles; for passenger cars, the minimum level may be of the order of 100,000 units
annually. Even then,  it seems very likely that the electric vehicle will have a significantly
higher first cost.  As a broad  approximation,  fuel costs may be  about the  same for both
electric  and internal-combustion-powered vehicles when  allowance is made for the heavy
fuel tax on refined petroleum products.

       A higher first  cost may be acceptable for commercial vehicles, where the well recog-
nized lower maintenance and longer life  of electric vehicles will be a partial offset. But for
commercial and  especially for private vehicles it will be necessary to regard the increased
expenditure as a social  cost  attributable to  the necessity of eliminating  sources  of  air
pollution. In  these circumstances the desirability of electric vehicles must, of course,  be
evaluated in comparison with other potential solutions to this problem.
                                         72

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     2.  Family Car

       Some broad perspectives on the costs of electric vehicles can be obtained by follow-
ing the  same general  approach as for  the technical  factors, namely by taking an existing
vehicle  and considering which components should be replaced  in  the conversion from  a
conventional to an electric power source. If we take the family car as an example and assign
to it a  factory price of $1400, some $500 might be eliminated  by  removal of the engine,
transmission, gearbox, and other ancillaries directly related to the  use of an internal combus-
tion power plant. Replacement of these by electric motors, SCR controllers, speed reducers,
cabling, etc., according to the specifications shown in  Table 4 would, on the most optimistic
assumptions, add approximately $650 back to the cost. (This is  based upon cost estimates
per vehicle horsepower of $4 for a dc commutator motor, $2 for the controller system and
$1 for cabling and miscellaneous; see Section IV.)

       Thus even before we consider the cost of the power source,  the factory price of the
electric  vehicle would  already be some 10% higher than  that of a conventionally  powered
car.  The cost which  can  be  tolerated for  the power source is thus a rather subjective
quantity, as there are clearly  no savings to demonstrate.  In our opinion, an electric  family
car might be justifiable if its retail price were not more than approximately $1000 over that
of a corresponding conventionally powered vehicle. Since average distribution costs should
be unchanged, this would  translate into a permissible  increase of $1000 in the factory price.

       Such a differential might be regarded as a premium for longer life and lower main-
tenance, but for  private cars, some  further incentive —  probably in the form of selective
taxation - would almost certainly be necessary. While $1000 is a  relatively large sum  today,
the period  under consideration is in the 1980's at the earliest, due to the time required for
technical development and cost  reduction. By then, personal  affluence should  have in-
creased  to an extent that such additional expenditure might be much  less significant.

       If the allowable weight for the battery in an adequately powered family  car with
conventional construction  is 900 pounds (Table  1) the allowable factory cost for the battery
must be in the  region of $0.95/lb. With lightweight construction  the allowable cost per unit
weight of a battery just meeting specifications would  be lower than this, for two reasons: 1)
it  would be heavier (~1400  pounds), and 2) the use of  lightweight nonferrous metals for
structural members and plastic materials for body panels is likely to increase the manufac-
turing costs, leaving  less  money to be spent on the battery. In this situation,  to meet  the
cost criteria we have set, a  figure of $0.50/lb is probably all that could be tolerated.

       These estimates are somewhat clouded by the question of  battery replacement, since
it  is unlikely that the life  of  the battery will be as great  as that  of  the rest of the vehicle.
Costs amortized over a five-year period are probably low enough to be written off against
operating costs, but it must be recognized that a five-year lifetime introduces a significant
new technical requirement for the battery.
                                         73

                                                                           3rthur ZD.lUttlc.lfnr.

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     3.  Commuter Car

       For the commuter car the assumed factory price might be $800, with $200 assigned
to engine,  transmission,  etc.  Using  the  same basis  for  the costs of electric motors and
controllers as for the family car, we find that the electrical components are comparably but
slightly  more expensive than the ones they replace ($210 vs $200).  Thus, the cost of the
power source can be  equated with the extra retail price which we  have  assumed can be
borne by the electric vehicle. If this is set  at $500,  the cost of the power source in the
commuter  car  with conventional  construction must  be about  $0.75/lb. Such  a battery
would have less than one-third the energy density and less than one-half the power density
of the family car's power  source. The performance of a battery capable of meeting the
family car's requirements  of 135 w-hr/lb  and 94  w/lb would support a cost  of about
$1.90/lb in the commuter car; at $0.95/lb the first cost of the vehicle would be close to that
of a conventionally powered vehicle.
     4.  Utility Car

       Since no well-established model exists for a utility car constructed  from conven-
tional materials, the permissible cost of the necessary battery can only be estimated by
judicious guesswork. Figures of $0.40-0.50/lb and a total cost  of under $200 appear to be
appropriate.

     5.  Commercial Vehicles

       Somewhat  less stringent cost requirements may hold in the commercial vehicle
category, since - for the van and bus, at least  - production volumes are lower and  unit
costs relatively higher than is the case for passenger cars. Moreover, since the percentage of
operating time is very much higher for commercial than for private vehicles and since the
longer life and expected lower maintenance costs are better recognized, a higher cost struc-
ture for the battery can be tolerated. Inspection  of the data for assignable weight indicates
that $1.00-1.50/lb might be a reasonable estimate of the allowable cost for a power source
which met the minimum technical requirements for the van, taxi, and bus with conventional
construction.
     6.  Future Cost Structure of Power Sources

       The above cost estimates for the vehicle power source, crude as they are, form some
basis for an assessment of the prospects of the various power sources. As a point of compar-
ison, it may be noted that today's lowest cost battery system, lead-acid, has an OEM price
of approximately $0.25/lb in the  high-volume application of automobile starter  batteries.
This is based upon relatively low-cost raw materials, the most expensive of which is lead at
$0.13-0.16/lb, and a very  mature manufacturing technology. For the lower production vol-
ume and longer-lived industrial lead-acid battery, OEM prices are in the range of $0.50-0.60/lb.
Standard types of nickel-cadmium batteries, which are manufactured on a much smaller
scale than lead-acid and use high cost materials (the raw materials costs being approximately
                                          74

                                                                          3rthur 3l.3Uttlr.3nr.

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$0.80/lb for nickel and $3/lb for cadmium), have a representative cost of about $3/lb in the
0.1  to 1.0 kw-hr size range.

        Estimates of the  potential cost structure of the new types of batteries now under
development are  very speculative. Among the high-temperature alkali metal batteries we
believe  that the capacitive storage device of SOHIO and the sodium-sulfur battery of Ford
have prospects of achieving a cost level of  approximately $1.50/lb  in volume produc-
tion; this seems to be a sufficiently encouraging basis for anticipating an ultimate price in
the $ 1.00/lb range.

        Metallic lithium, presently at $7/lb and with prospects of its price falling 50% as its
production volume increases,  might seem an  expensive element for inclusion in a vehicle
battery. However, its low equivalent weight  results in a low requirement per battery,  and
with a  lithium content of only 5-10%, the cost of this  element should not be prohibitive.
The CM  lithium-chlorine battery seems likely to have a somewhat higher potential cost
structure, less on account of the lithium than on  the materials engineering problems asso-
ciated with the handling  of  chlorine and the temperature (over 100°C higher than the other
systems). The  lithium-selenium  and lithium-tellurium systems under investigation at the
Argonne National Laboratory offer no prospect of developing into low-cost batteries be-
cause of the cost and the present scarcity of the cathode materials, selenium and tellurium.
The recent work there on a high-temperature lithium-sulfur  battery does, however, hold
promise of yielding a low-cost battery.

        Most of the rechargeable metal-air batteries now under development use acceptably
low-cost materials (zinc, sodium, iron)  as anodes. While air is free, a significant material cost
is  involved  in  the catalysts needed for effective  and long-lived air cathodes and for the
structural material of the cathode itself if it is to be used for oxygen evolution on recharge.

        Electrically rechargeable metal-air batteries fall into two broad classes: those which
involve  some engineering  artifice and those which have a relatively conventional construc-
tion. Among the  former are the zinc-air batteries of General Atomic and Yardney Electric
and the sodium-air battery of Atomics International. Both the zinc-air batteries are of some
mechanical complexity, and the sodium-air battery may entail an appreciable materials cost
for mercury. While there can be no firm estimates at this  stage,  the initial costs of these
"engineering artifice"  metal-air batteries in quantity production might be in  the region of
$3/lb with good  prospects of falling to the  $1.50-$2.00/lb region as experience with the
systems grows.

        Conventionally rechargeable zinc-air batteries, such  as those being investigated by
Leesona, ESB,  Union Carbide, and McDonnell-Douglas,  may cost close to $1.50/lb, since
they would  be  of simpler construction. However, the fundamental  technical problems asso-
ciated with  the recharging of the zinc  electrode are so great that such batteries may never
attain a cycle life acceptable  for vehicle applications.
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       The characteristics  of mechanically rechargeable metal-air batteries developed by
Leesona  in  the zinc-air system, and considered conceptually by Atomics International for
sodium-air, are not sufficiently established for conclusions to be drawn about their applic-
ability to vehicles. When their technology matures, first costs are likely to be comparable
with those  of other metal-air batteries; but  operating costs will depend largely  on the
economics of reconstituting  spent  anodes, probably at  centralized service stations, and at
present these appear to be unfavorable. This type of battery would  be attractive, however, if
it could be recharged electrically in regular service and mechanically recharged only during
an occasional long trip.

       The very  approximate cost criteria which we have set for electric vehicles would
appear to eliminate the  prospects  of the fuel cell, either  as the sole power source  or in a
hybrid combination with batteries. A fuel cell is inherently a more complex and thus more
costly  device than a battery,  because it has to accommodate the orderly passage of materials
across  its boundaries  in addition  to heat and electricity. Moreover, there  is as  yet no
indication  that fuel cells whose performance  is adequate for vehicular application will not
require precious metal catalysts. Because of these limitations, ambient-temperature fuel cells
seem unlikely  to attain an  ultimate cost structure of less  than  S2 to S3/lb.  Although
high-temperature fuel cells will probably have lower costs, their power densities appear to be
too  low.  Any equipment  required for  pre-treatment of the fuel, such as reforming or
thermal cracking, will add further to the first costs.

       Some general comments on the  costs of hybrid systems have already been made in
Section VI. If the hybrid  is to be considered as a substitute for  the  conventional  vehicle
power plant,  it  is apparent  that the cost of the engine, generator and battery  must be
compared with that of the battery or fuel cell of the purely electric vehicle. If we use the
family car as an example and apply the cost criteria for the gasoline piston engine shown in
Figure 12, the engine-generator costs for a 40-60, prime mover-battery  hybrid  would be
about  $500 (allowing about  S2/kw for the ac generator  rectifier and speed increaser). With
$650 assigned to motors  and controllers, offset by only $500  for  the replaced  engine
transmission, gearbox, etc., the net extra cost is $650 plus that of the battery. If the total
cost is to be  kept within  $1000 of the cost  of a conventionally powered family  car, it is
apparent that the cost of the  necessary 51-kilowatt  battery,  weighing not  more than 550
pounds,  must  be $350 or less. Only the high-temperature alkali  metal batteries and  the
nickel-cadmium system have  prospects of this technical capability, and in this situation the
latter is,  of course, too expensive by a factor  of at least  five. The cost  criteria for the alkali
metal  battery  used  in a hybrid system  are  somewhat  more demanding than when this
battery is used in a purely electric vehicle, so that when such batteries  become available
there would seem to be no incentive for using them in hybrids.

       As  previously noted,  the best prospects for the hybrid vehicle appear to lie with the
commercial vehicles, and particularly the  city  bus. The calculations of  Section VI indicated
that a  5000-pound battery with a power density of 29 w/lb (or less if lightweight construc-
tion is used) would be adequate in a diesel-powered hybrid. It  should be possible for a
specially  designed lead-acid battery to meet these criteria, using existing technology, for a
cost of about $3000. Such a  hybrid-powered bus would undoubtedly have higher first costs
than a  conventional bus, but the percentage increase should be substantially less than for the
smaller vehicles.
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       To summarize, it seems apparent that electric vehicles are likely to have higher first
costs than conventional vehicles, even in high-volume production and with maturation of
the contributing technologies. Some of this cost differential may be acceptable on the basis
of lower operating costs due to  a  reduced maintenance  requirement and longer life, but
most must be attributed to the social benefits of decreased air pollution. On the assumption
that an additional $1000 might be  placed on the retail price of the family car and perhaps
an additional S500 for the commuter car, high-temperature alkali metal batteries appear to
offer the best chances of meeting the cost criteria. Metal-air batteries will probably have a
somewhat higher cost structure and be acceptable only in commercial vehicles.  Fuel cells are
likely to be too expensive, and mechanical-electrical hybrid systems appear promising only
in the case of the city bus.
C.  REFUELING

       It is  apparent  that  the large-scale introduction  of electric vehicles would have a
major  impact on  a  number of important  sectors of the national economy.  This study,
however,  is concerned with the technology of the vehicle itself; the effects of the large
increase  in the  use  of power on the electrical generating industry,*  the changes in the
demand for materials, the impact on the petroleum industry, and the effect on the myriad
of ancillary suppliers to the vehicle manufacturers are outside its scope. Consideration is
given to the question of vehicle  refueling, however, since it  has direct bearing on the
selection of the vehicle power source.

       Present-day conventional  vehicles are  refueled by the simple expedient of filling
their tanks with gasoline or diesel oil as appropriate. The whole operation can be carried out
in five to ten minutes. There would be no change in  procedure for a mechanical-electrical
hybrid, and an equivalent procedure is possible for a fuel-cell-powered system, although the
nature of the fuel might set some special restrictions. A vehicle powered entirely by bat-
teries,  however,  clearly needs a totally different method of refueling. This problem has been
considered in terms of  the three general options of rapid recharge,  slow recharge, and
mechanical replacement.

       Rapid recharge would involve the acceptance of a full charge by the battery within a
period often minutes or  so,  comparable to the time it  takes to refuel a conventional vehicle.
A moment's  consideration  suggests that this mode of recharge is rather impractical. To
recharge the battery in the family car in ten minutes would require a power source with a dc
output  of approximately one megawatt (allowing for inefficiencies). While we have not
determined the probable capital costs of a dc rectifying system with this power capability, it
is likely to be excessively high, even when manufactured on a large scale. Moreover, such a
requirement for power would be likely to invoke a demand charge from the supplying utility.
The  implications for the vehicle itself are even more severe. Factors such as safety, insula-
tion, and  the cost of batteries are likely to hold the voltage of its electrical system to a max-
imum of 500 volts. At this voltage,  the wiring in the vehicle would need to carry  a current of
about 2000 amperes during recharge, which would require heavy and costly quantities of cop-
per cabling. A further consideration is the large and probably damaging amount  of heat gen-
erated in the  battery due to the inefficiencies of the charging processes.

'Complete conversion to electric vehicles today would create  an additional load  averaging about 40% of
  present electrical power consumption.

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       From the standpoint of battery technology, rapid recharging would be feasible only
for systems having the highest power density. The ratio of maximum energy density to
maximum power density, having the units of time, is a good index of a reasonable minimum
recharging period for a battery. For this to  be as low as ten minutes, the ratio must be less
than 1:6; only the nickel-cadmium battery and possibly the SOHIO system seem likely to
meet this criterion.

       Slow recharge of a battery is considered to mean a charging period of from four to
perhaps eight hours.  The obvious time for this is at home overnight, or possibly at metered
outlets when the vehicle is parked during the day. The rectifying equipment could be either
on the vehicle or at  the outlet. The  advantages to  this approach  are the converse of the
disadvantages of rapid recharge: slow recharging involves a very much lower investment cost
in recharging equipment, the weight and cost of cables  on  the vehicle is less, the electrical
efficiency is higher so that energy is conserved, there is less damage to  the battery due to
heating, and its lifetime is consequently lengthened. Home recharging also  has  the great
advantage of making the motorist independent of visits to a service station, at least for
refueling,  and  it would  have  the  desirable  effect of spreading  the load on  the  electrical
generating system largely onto the off-peak hours.

       The  obvious  disadvantage  of  slow recharge is  that the  vehicle is unusable tor a
substantial  part of the time. This probably would not be a serious difficulty, since the great
majority of trips are undertaken for  relatively short distances and on  a fairly fixed daily
schedule. Longer trips might depend on exchanging depleted batteries for fully charged ones
at service stations, which  raises  questions  of  ownership and of battery standardization.
Battery  leasing with a metered use charge,  might well  be the procedure adopted. Maint-
enance work on  batteries,  such  as occasional electrolyte replacement in alkaline systems,
might be carried out during their residence time in the service stations.

       For batteries with air cathodes an alternative to replacing the batteries on  extended
trips is  the replacement of the anode alone. However, this procedure is certainly more
complex and probably more costly.

       It thus appears that the formidable technical difficulties associated with rapid re-
charging make slow recharging the necessary method of  refueling, with mechanical substitu-
tion of batteries being used to  extend the range on occasional long trips. This arrangement is
less than ideal, but it appears to have enough advantages to make it acceptable.
D.  SUMMATION AND RECOMMENDATIONS

       The general  conclusion  to  be drawn  from  this analysis of the requirements for
electric vehicles is that the necessary technology  appears attainable, and that the cost of
electric vehicles, while higher than that of conventional vehicles, might still be acceptable.  A
very substantial technical effort  is called for if the required  technologies are to be brought
to maturity. One of the objectives of this study is to identify areas in which more  effort
might profitably be made.
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       For  the  electric  vehicle to achieve performance broadly comparable to that of
today's internal  combustion powered cars, a low-cost, high-temperature alkali metal battery
must be developed. The major virtues of this class of battery are their high energy density,
which  is a consequence of the high reactivity of the alkali metals, and  their high  power
density, due to the rapid rate at which the electrochemical  reactions take place  at the
elevated temperatures. Since the alkali metals are well above  their melting point in these
batteries,  many  technical problems of anode  recharging are avoided. Of the alkali metals,
only lithium and  sodium are  serious candidates: lithium  because  it is  the  lightest,  and
sodium because it is the cheapest. Calcium, although having a high  melting point (840°C),
might provide an alternative anode  material for high-temperature batteries; no work has been
done in this area, however. Among cathode materials the most promising elements are sulfur
and chlorine. It  is  also possible that phosphorus might be acceptable but its electrochemical
properties are almost completely unexplored.
       Bringing the technology of high-temperature alkali metal  batteries to maturity will
obviously be no easy task, since very formidable problems in materials selection and safety
are evidently involved. Much engineering inventiveness will be required in the development
of auxiliary heaters and insulation in the systems for temperature control, these complex-
ities being appropriate only for batteries of the size capable of powering vehicles. The public
acceptance of high  temperature alkali-metal batteries is also a major question; the presence
of a 900-pound battery containing alkali metals and elements such as chlorine or sulfur at a
temperature possibly as high as 600°C is obviously not a particularly desirable feature for
the family car. Effective, low cost insulating materials are clearly essential, and  the design
must make the battery  as crash-proof as possible. Groups presently developing batteries in
this class are optimistic that this can be done.

       Given  the  requirement that the  performance  of a conventional vehicle must be
matched,  metal-air  batteries appear  to be too  power-limited for application in  the  family
car.  They are likely to  be somewhat more costly on both a weight and performance basis
than the  high-temperature systems, although neither  technology is advanced  enough to
generate  firm cost  estimates.  Metal-air batteries do, however, appear to have  reasonable
prospects for the commercial vehicles, particularly if advances are made in the utilization of
lighter structural materials. The metal-air batteries in general have a major advantage in that
they operate at temperatures close to ambient. For these reasons, further development of
the metal-air systems seems fully justified. Moreover, there are prospects that the pattern of
transportation, particularly in  the  cities, may change sufficiently  in the  future in the direc-
tion of smaller and less powerful vehicles so that the  metal-air  battery would provide a
completely adequate power source.

       Alkali metal  batteries using organic  electrolytes share  the large  advantage of oper-
ation at ambient temperatures and have high energy density, but their power density is low.
The  major problems limiting their future  potential as a vehicle power source are the ques-
tions of whether they can ever be recharged at practical current densities and whether they
can  achieve an  adequate cycle life. As in  the metal-air  batteries,  it is conceivable that
mechanical  artifices might  be  introduced  into  these  systems to  overcome the electro-
chemical problems, but as yet such approaches have not been investigated. In view of its
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relatively less attractive prospects this class of battery  does not appear to merit a major
effort  to adapt  it for use as a vehicle power source. However, it will  undoubtedly see
further development in view of its potential applications in other areas.

       Prospects for the fuel cell as a vehicular power source are rated as unfavorable partly
because of its power density limitation but mainly  because of its inherently greater com-
plexity and cost relative  to batteries. There thus seems to be no justification for a fuel cell
development  program  oriented exclusively toward civilian  highway vehicles, although fuel
cells might well find vehicle applications in the  military or specialized industrial fields.

       Our consideration of the technology of electric motors and controllers shows that
vehicular requirements are certainly attainable and, in  fact, can  be largely met  today. The
major  development effort for the future relates to the lowering of costs to a level acceptable
for the vehicle application. The  opening  up of such a large market  for these components
would  be a strong incentive  for manufacturers  to  make  such cost reductions, but it is
evident that specifically  oriented research programs will be needed to devise  production
techniques that will yield the extremely low unit costs demanded.

       Any formulation  of recommendations  for additional research and development pro-
grams  in the technologies relating to electric vehicles must take into account existing and
planned programs in these areas by other  agencies, both public and private. A considerable
budget is already allocated by the government for support  of research and development on
electrochemical  power sources  and the electrical technologies relating  to motors and con-
trols. The two agencies most involved are the Department of Defense and NASA.

       Within the Defense Department the greatest expenditures are  by the  Army. Pro-
grams  carried out and sponsored by the Engineering Research and Development Laboratory
at Fort Belvoir,  Virginia, have been concerned with novel electrical  propulsion systems for
military vehicles,  with emphasis on gas  turbine generators and fuel  cells as the  power
sources. Support has been given to work on fuel cells using  hydrocarbons (either directly in
high-temperature systems or via a reforming or thermal  cracking  step), fuel cells  using
hydrazine, and various development programs concerning  electric motor and  control sys-
tems, both ac and dc, which might be employed. The Army Tank Automotive Command at
Warren, Michigan is also working on electrical systems development,  complementing  the
work at Fort  Belvoir.  At the Electronics  Command  at Fort Monmouth, N.J.,  support has
been given to work on fuel cells and on metal-air and lithium-organic electrolyte batteries.
The latter is concerned  mainly  with primary batteries and is thus of little relevance  to
vehicles.

       Work supported  by the Navy has  included programs on lithium-organic electrolyte
primary batteries and  on the  identification of more effective and lower cost catalysts for
ambient-temperature fuel cells. The Navy is also concerned with the technology  of advanced
high speed electric motors, primarily for torpedo application.

       The  Air Force has supported  most of the  earlier work on rechargeable lithium-
organic electrolyte batteries; it has also supported work on metal-oxygen batteries (which
are closely related to the metal-air systems), and on fuel cells and rechargeable batteries for
satellite applications.  Much of the initial development of static inverter technology was
carried out under Air Force sponsorship.
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       NASA's work in electrochemistry and electrochemical engineering includes the spon-
sorship of major fuel cell programs and related support for manned spacecraft power sources
and  the  development of improved sealed, rechargeable  batteries, particularly high rate
nickel-cadmium  and silver systems for satellite application. NASA has also supported a good
deal of work on lithium-organic  electrolyte primary  batteries, some on metal-oxygen sys-
tems, and has also been active in  static inverter technology.

       Total expenditures by all  government agencies for research and development in the
field of electrochemical power sources  have been estimated at approximately $10 million
annually, exclusive of the large fuel cell hardware projects relating to the Apollo manned
spacecraft program. Expenditures  of a further $5 million or so can probably be attributed to
developments in the motors and controls field that have some bearing  on the technology of
electric vehicles. This latter  figure includes estimates for that portion  of the electric trans-
mission  systems developed for high-speed  rail transportation which are applicable to self-
propelled electric vehicles. The size of these amounts  naturally varies with the definition of
the relevance of the program and fluctuations in contract appropriations from year to year.

       It is also important to recognize that most of the federally sponsored programs have
been focused on such different objectives that they have only a very limited contribution to
make to  the development of commercially viable electric vehicles. Thus,  while  NASA fuel
cell programs have demonstrated  that efficient and reliable fuel cells with electrical outputs
of several kilowatts are feasible, the details of the technology are not  translatable into the
needs of a mass-produced, low-cost power source. Similarly, the work on vehicle systems
being carried out by the Army naturally focuses on military field situations which involve
specific requirements very different from those of the civil environment. When the specific
content of the programs are taken into account, it can be seen that only a small proportion
of the federal expenditures are applicable to the problems of civilian electric vehicle devel-
opment.

       An  account of private research effort in power  source development has been given in
the body of this report. An  overall  figure can only be  a crude estimate, but it would appear
that expenditures  by U.S. private industry  on novel power source development relating to
electric vehicles  total S5-7 million annually. A substantial fraction of  this is represented by
the programs of the two major automobile  manufacturers, and  a proportion  of  the re-
mainder is invested in anticipation of later support from federal agencies.

       The magnitude of the technical problems involved in the  development of batteries
capable of meeting  vehicle  power  source requirements and the increasing urgency of air
pollution abatement in the  cities both  point  to  the  need  for an acceleration of technical
effort if electric vehicles are to  be an effective solution. If the assumptions about  vehicle
performance made in  this study  are correct,  the  major  effort should clearly be directed
toward  extension  of the  scale of  work on high-temperature  alkali  metal batteries. The
existing work in this area  at GM, Ford, SOHIO,  and Argonne National Laboratory is valid
and  valuable, but considering  the  magnitude of the  technical problems and the massive
implications of  the development, a more comprehensive and coordinated program appears
to be needed.
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       Such a program might involve basic electrochemical studies of all elements that have
prospects of satisfying both technical and cost criteria for the vehicle battery; these should
include lithium, sodium, and possibly calcium,  magnesium, and  aluminum  as anodes and
sulfur, chlorine, and possibly phosphorus as cathodes. The prospects of air cathodes in high
temperature systems should also be evaluated, and for completeness some attention should
be given to the potentialities as cathodes of the halides and sulfides of the transition metals.
An important part  of the  program would be the characterization  of the molten salt and
ceramic systems which would be the electrolytes of these batteries. Other work should focus
on  the  materials selection  and engineering problems of the battery. Noncorrodable con-
ductive materials for current collectors and suitable inorganic materials for separators and
supporting  structures,  sealants, and insulating materials are all needed.  Materials selection
and engineering design optimization are usually specific to a particular  battery system,  so
that the initial work should be  concentrated as far as possible on developments having the
greatest general  application. The  technology of  low-cost thermal control systems, heaters,
and insulation is another important area.

       The other major technical area deserving additional support  is that of rechargeable
metal-air batteries.  While  their  projected performance  is  not  adequate  for  the most
demanding  of the  vehicle applications, it may well be acceptable for the types of vehicles
which  may evolve  from new patterns of transportation within the city.  The technical
problems of  directly rechargeable  metal-air batteries  will  respond, if at  all, to increased
emphasis on  the basic electrochemistry of the systems. The engineering solutions such as
those being worked on  at  General Atomic and Atomics  International can, however,  be
supported at  the development stage, since their difficulties are of a less fundamental nature.
Further work on the problem of developing  low-cost catalysts  for air cathodes is desirable
and such work would also contribute to fuel cell technology.

       In the area of motors  and controls the development of low-cost manufacturing
techniques  for components and systems should be encouraged; the technology is already in
existence, but the chief emphasis has been on specialized, low-volume  applications where
cost is not important. While the prospect of large commercial markets will certainly stim-
ulate  private research  expenditures in  this field, some judicious seeding of development
funds could bring the technologies more sharply into focus for electric vehicle applications.

       In summary the technology  of electric vehicles appears to  be attainable, quite
possibly at  an acceptable cost. But this is  unlikely to come about in less than ten to fifteen
years and then  only if substantial efforts are made at the present stage in the planning and
execution of  programs - particularly  in the field of power source development — which are
specifically oriented toward the performance and cost  parameters demanded by the vehicle
application. The technical risks of this endeavor are too great for the investment to be borne
by private capital alone, particularly since the major objective is a technology desirable for
its social good rather than for its profit potential.
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                                   APPENDIX A
     NOTES ON ELECTRIC VEHICLE DEVELOPMENT IN THE UNITED STATES
       While electric  automobiles  represented a  significant proportion of all highway
vehicles in the early 1900's, they had been almost completely displaced by the 1920's, due
to improvements in the internal combustion engine. Apart from some occasional attempts
to market small specialized electric cars, the only continuing commercial  activity in recent
years, relating to highway vehicles, has been the manufacture of electric delivery trucks by
the Battronic Truck Corp., a company jointly owned by the Boyertown Auto Body Works,
ESB,  Inc.,  and  Smith's  Delivery  Vehicles  Limited, a  major  British  manufacturer.
Gould-National  Batteries, Inc., manufactured a line of electric trucks in the mid-I950's, but
discontinued the activity due to lack of demand.  Cushman  Motors, Inc., manufactured a
dozen  small, three-wheel vehicles  powered by  lead-acid batteries for  the Post Office
Department  in  1959, and four larger vehicles  were purchased in 1962 from a division of
ESB. Inc. At about the same time,  National Union  Electric Corporation converted some
50-60 Renault Dauphines to electric drive, the product being called the "Henney Kilowatt."
Electric utility  companies  bought many  of them,  and several have been  the  subject of
further conversions described below. While not highway vehicles, electric  golf carts are, of
course, a flourishing product, and personnel carriers for use at airports,  resorts, and  large
industrial plants are becoming commonplace.

       Over the last few years there has been considerable activity in experimental electric
vehicle development, mainly in  anticipation of their much wider  use in  the future.  This
Appendix contains notes on some of these activities.
A. AMERICAN MOTORS CORPORATION - GULTON INDUSTRIES
       AMC and Gulton  have  announced a joint program to develop a small electric car
making  use of  a hybrid  combination of Gulton's  lithium-nickel fluoride batteries and
high-power-density bipolar nickel-cadmium batteries (a concept described  in Section V).
The vehicle will seat three persons and weigh about 1100 pounds. The power sources will be
two  75-pound lithium  batteries for energy storage  and two 25-pound  nickel-cadmium
batteries to provide adequate  power.  With regenerative braking,  a  150-mile range is
projected. The limiting  feature to this development would appear to  be the state of the art
in lithium batteries,  which  have as  yet  not demonstrated  a convincing  degree  of
rechargeability in practical battery configurations nor an adequate shelf life.
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B. ELECTRIC FUEL PROPULSION, INC.

       This  small   company  is  manufacturing  electric cars by  conversion  of  the
 conventionally  powered Renault-10.  The power source  is eight  12-volt,  205 amp-hour
 (5-hour rate) lead-acid batteries weighing approximately 1600 pounds. The batteries contain
 a cobalt additive which is claimed to reduce grid corrosion and thus give relatively longer life
 at high charging rates. The car is heavy-4040 pounds curb weight compared with  1735
 pounds for the original Renault-10-but the performance specifications are quite impressive:
 0-40 mph in 12  seconds, a maximum speed of 60 mph and a range of 70-120 miles under
 city driving conditions.  The car  has a regenerative braking system. A substantial number
 (now approaching fifty) of these  cars have been purchased or are on order by  electric
 utilities and other companies interested in the electric propulsion  field. Their evaluation
 should provide some valuable data  on  the operating costs of highway  vehicles powered  by
 lead-acid batteries.
 C. ESB--BATTRONIC

        As mentioned above, ESB, Inc., participates in the electric highway vehicle field via
 its part-ownership of Battronic Truck Corp. The principal product of the latter company is a
 delivery truck having a loaded gross weight of 9500 pounds. The load and battery weight
 combined  are 5000  pounds and can be mutually adjusted to  suit the route requirements
 within  load limits of 2000 to 3000 pounds. The batteries used are 84-volt lead-acid systems
 with capacities of either 425 or 340 amp-hours. The range of the vehicles is about 40 miles
 with a top speed of 25 mph.

        ESB also operates a converted Renault Dauphine of the Henney Kilowatt type. This
 vehicle is powered by twelve 6-volt golf cart batteries rated at 140 amp-hours (5-hour rate),
 which give it a maximum speed of 40 mph, a range of 25 to 35 miles, and an acceleration of
 from 0 to 29 mph in  3 seconds.
 D. FORD MOTOR COMPANY

        Published reports of Ford's activities with experimental vehicles are confined to its
 work with the "Comuta," a  small vehicle built by English  Ford, one  of which has been
 shipped to  Ford's Dearborn headquarters.  Comments  on  the  Comuta are  included in
 Appendix B.
 E.  GENERAL ELECTRIC
        In October 1967, General Electric announced that it had built an experimental car
 having  a maximum speed of 55 mph on level ground and a range of 40-50  miles under
 normal stop-and-go driving. The vehicle, which had a magnesium frame and a fiberglass-poly-
 ester body, weighed 2300 pounds and could carry two adults and two children.  A novel
 feature was the use  of lead-acid batteries as the main energy source with nickel-cadmium

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batteries in  parallel to  provide power for acceleration and  hill climbing. The combined
weight of batteries in the hybrid power source was about 40% of the vehicle's curb weight.
F. GENERAL MOTORS

       General Motors Corporation has constructed two full-size electric vehicles primarily
for use as test beds-the Electrovair II, a converted Corvair powered by silver-zinc batteries,
and the Electrovan, a converted GMC Handivan powered by a hydrogen-oxygen fuel cell.
Both  vehicles have substantially the same motor and  control system, a novel, lightweight,
high-speed (13,000 rpm) ac squirrel cage induction motor. This motor, which weighs  130
pounds  and is  capable  of delivering a maximum of  1.3  horsepower per pound, receives
power from a  thyristor  inverter. The present weight of the controls, however, tends to
eliminate the weight advantage of the  motor system used; the electrical system has a total
weight of 550  pounds. The voltage of the  system, 530 volts,  is the highest used in  any
electrochemically powered vehicle.

       Both vehicles were designed to have substantially the same performance as their
conventionally  powered  counterparts. In the case of the Electrovair II, this  meant  an
acceleration  of  0 to 60 mph in  16 seconds and a top speed of 80 mph. The Electrovair's
silver-zinc batteries, provided by Yardney Electric, weigh about 650 pounds and give a range
of 40-80 miles under normal driving conditions. The hydrogen-oxygen fuel  cell in  the
Electrovan was  manufactured by Union Carbide and operates on cryogenically stored fuel
and oxidant. It  has a continuous power rating of 32 kw. A favorable characteristic of fuel
cells is their capability of responding to temporary overload; the fuel cell in the Electrovan
has an overload capability of up to 160 kw.  Both vehicles are much heavier than their con-
ventionally powered counterparts: 3400 pounds versus 2600 pounds for the Electrovair and
7100  pounds versus 3250 pounds for the Electrovan.
G. GOULD-NATIONAL BATTERIES, INC.

       In cooperation with North Star Electric, a Minnesota electric utility, Gould-National
has recently modified two Henney Kilowatt Renault Dauphines with improved battery and
control systems. The original twelve 6-volt, 180 amp-hour golf cart batteries were replaced
with eighteen  12-volt, 80 amp-hour automotive starter batteries of newly improved design,
having a polypropylene case, internal connectors, glass mat separators, and improved plate
construction. These batteries give 20 watt-hours per pound at the 20-hour rate. Using a GE
solid-state control system, the modified  Henney  Kilowatts  have  a range of 65  miles
compared with 35-40 miles for the original models under comparable conditions.
H. ROWAN CONTROLLERS, INC.

       The activities of this Westminster, Maryland, based company in the electric vehicle
field are covered in the section on Italian activity in Appendix B.
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I.  U. S. ARMY ENGINEER RESEARCH AND DEVELOPMENT LABORATORIES

       As part of the U. S. Army's continuing development programs on various approaches
to electrical propulsion in vehicles (see Section VII), USAERDL has converted  an  M-37
truck to fuel  cell power. The power source  was a  hydrazine-air  fuel cell developed by
Monsanto and constructed  in 5-kw modules.  Four modules were  used  in  the initial
conversion to give a 20-kw rating, but the design allows for later use of an 8-module, 40-kw
fuel cell.
       The curb weight of the converted truck was 6000 pounds, of which 700 pounds was
taken up by a conventional dc series motor, 525 pounds by the 20-kw fuel cell system, and
300 pounds by the controller. All of these weights are believed subject to further reduction.
The 20-kw power source permitted a maximum speed of 47 mph and steady climbing up a
20% grade.  When the  40-kw system is installed,  accelerative performance  will  be fully
comparable with trucks having the standard 94-hp gasoline engine.
J.  WEST PENN POWER COMPANY

       West Penn  Power (a unit of Allegheny Power System  Inc.) is an electric utility
headquartered  at  Greensburg,  Pa.  It  has constructed  a small,  open electric car for
demonstration  purposes. The chassis and suspension were taken  from a Volkswagen sedan,
and an aluminum body was built onto it.The power source is an assembly of six 12-volt, 205
amp-hour lead-acid batteries, and the motor is a conventional 7.1-hp dc traction motor of
the type used  in the Henney Kilowatt. The  control system designed by West  Penn uses
thyristors. The overall curb  weight is 2160  pounds. With this system a maximum speed of
50 mph has been attained, and under favorable driving conditions the range is as much as 50
miles.
K. WESTINGHOUSE

       In 1967  Westinghouse  announced the availability of the  "Markette," an electric
passenger vehicle for highway  use, capable of carrying two  passengers. The vehicle  was
derived from the golf carts and personnel carriers which Westinghouse has manufactured
since its acquisition in 1964 of Electric Marketeer of Redlands, California. It was intended
as an  auxiliary  vehicle  for special  uses  where  its quietness,  economy, and  smooth
performance would offset its limited  speed and  acceleration.  With a curb weight of 1730
pounds, the Markette carried 792 pounds of lead-acid batteries (twelve 6-volt, 217 amp-
hour),  and  its two 4.5-hp dc series motors provided a top speed of 25 mph in 12 seconds
from a standing start. The range at one stop per  mile was about 50 miles. The vehicle  was
designed  from existing state of the art  components and was priced at "under $2000."
Optimal solid-state controls to give it greater operating economy would cost about another
$500.
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       The Markette has recently been temporarily withdrawn from production because it
does not comply with all of the new federal safety requirements. This points up a significant
difficulty  for developers of electric vehicles, since changes in specifications can be very
costly for vehicles made in small quantities.
L YARDNEY ELECTRIC

       The Yardney Electric Company is operating a Henney Kilowatt in which silver-zinc
batteries have been substituted for lead-acid. The higher energy density and power density
of the silver  batteries give much improved performance. In the original conversion four
batteries were used,  each having  fourteen 85 amp-hour cells. Their total weight was 240
pounds  in contrast to the 700 pounds of lead-acid batteries which they replaced. Maximum
speed was 55 mph, acceleration  0-30 mph  in 5  seconds, and a steady-speed range of 80
miles. Yardney is now planning to reconvert the vehicle for use with batteries of the same
type  but improved  design (the original were intended for service in military aircraft), with
which it hopes to improve performance still further.
M. ACTIVITIES OF INDIVIDUALS

       Besides  these  activities of industry and government  there are also  instances of
conversion  of  conventionally  powered vehicles to electric drive by individuals. Among
these are the conversion of an  MG roadster by Mr. William Roden of San Diego, California,
and of a Karmann Ghia by Dr. Hugo Myers of Los Angeles. Mr. John Hoke of Washington,
D. C. has constructed  his own electric car based  on a conventional small car chassis. AM
three of these vehicles are in regular use.
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                                   APPENDIX B
                          NOTES ON FOREIGN ACTIVITY
       While interest in electric vehicles is less widespread in Europe and Japan than in the
United States, many countries, particularly the United Kingdom, are quite active in vehicle
design,  control development,  and investigation  of new  types  of electrochemical  power
sources. The motivation of this interest is generally  concern about air pollution,  although
the use of small electric vehicles to relieve traffic congestion and parking problems in the
cities is equally important.  In Europe, petroleum-based fuels are  taxed more heavily than in
the United States, and, as a result, there is proportionately greater incentive to use electric
vehicles. In the materials handling field, for example, well over half of European lift trucks
are electric. Electric propulsion is thus at a higher level of acceptance than in the United
States.

       The following are some notes on the more prominent of the foreign activities.
A. UNITED KINGDOM

       Activity in electric highway vehicle development in the United Kingdom takes place
at two levels. The  first involves the manufacture of electric trucks for specialized purposes,
primarily  milk delivery, and  is a well-established commercial undertaking.  The second
concerns the development  of a small car, generally a two  seater for use as a commuter
vehicle in urban areas. In addition, some research is being done on novel types of electro-
chemical power sources.

       The use of electric trucks on  United Kingdom highways has increased substantially
over the last 15 years;  by  the  end of 1967 there were approximately 45,000 in service.
About 85% of them are for domestic milk delivery. The most prominent manufacturers are
Austin Crompton Parkinson (ACPEV), Smith's Delivery Vehicles, Stanley Engineering, and
W & E Vehicles. A typical truck having  a carrying capacity of about 3000 pounds is shown
in Figure B-l. Power  sources for these vehicles are typically 72-volt, 300 amp-hr lead-acid
batteries, which give a range of 20-30 miles with 200 stops and a maximum speed of about
15  mph. Their robustness,  ease of maintenance, and low-operating costs make them very
popular with dairies and  others engaged in door-to-door delivery.

       Hybrid electric trucks have recently appeared  in  the United Kingdom. Some new
models being offered by Austin Crompton Parkinson achieve extended range through use of
a  small propane-fed engine generator.

       Electric car development, which is still at the prototype stage, has focused on small
vehicles, usually two seaters, to be powered by lead-acid batteries and to be priced at around
$800. A photograph of the  "Scamp", a typical vehicle of this type, is shown  in Figure B-2.
These vehicles generally have a maximum speed of about 40 mph and a range of 30-40 miles

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                                              Courtesy of W&E Vehicles
FIGURE B-1   BRITISH ELECTRICALLY DRIVEN MILK TRUCK
                                    Courtesy of Scottish Aviation, Ltd.
      FIGURE B-2   THE SCAMP: A DEVELOPMENTAL VEHICLE
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under non-stop driving conditions. Table B-l  lists specifications for some of them. The two
Electricity Council Minis and the Peel Trident are conversions from conventionally powered
cars, but the Scamp (of which a dozen were built) and the Ford Comuta were designed as
electrics. All are two-seaters except the Trident, which is essentially a single-seater.

       Besides the cars listed in Table B-l, design, mock-up, and prototype construction is
being undertaken by Tube Investments, Hamblinetta (Flamenco), Carter Engineering (Carter
Coaster), and Telearchics Ltd.  (Winn City Car).  These cars  are being designed to have
lightweight plastic bodies.

       Most research on power sources has concentrated on fuel  cells. Shell Oil Company
carries out its research in England and has successfully demonstrated a 5-kw fuel cell system
operating on reformed  methanol with air as the oxidant. Chloride Electrical Storage,  the
largest British battery manufacturer, has shown a 2-kw hydrogen-oxygen cell fed by cylinder
gas; it is used to power an in-plant tractor truck. Energy Conversion  Ltd. is also active in
fuel cell research.

       In the battery field there is considerable interest in improved lead-acid batteries with
thinner plates and  higher energy  and power density. This work is  being carried out by
battery companies such as Chloride and  Oldham and at the laboratories of the Electricity
Council.  In the metal-air battery field, Joseph  Lucas Ltd. and Crompton-Parkinson (Division
of Hawker Siddeley)  have cooperative programs with General Atomic and  Leesona, respec-
tively. British Motors has recently announced  its interest  in  developing a vehicle to be
powered by a zinc-air battery of the Leesona type in its subsidiary ACPEV, jointly owned
with Crompton-Parkinson. No comment  was, however, made on the prospective economic
feasibility of such a vehicle.

       Work on  solid-state control systems is  going on at Lansing Bagnall, Ltd. and at
ACPEV.  The initial  application for this  development is, of course, in  the electric truck-
materials  handling  area.  Programs aimed  at improving the characteristics of motors  are
being carried out at Bristol University and the  laboratories of the Electricity  Council at
Capenhurst.
B. FRANCE

       The  major French activity in electric vehicles is a government-coordinated program
directed toward the development of a fuel-cell-powered car by 1971. Present  plans call for
the power source to be a hydrogen-oxygen fuel cell with a  rated power of 25 kw.

       Various  aspects of this development  program are being  conducted by specialized
contractors.  The  government-controlled automobile company, Renault, will  build the
vehicle, and companies such as CSF and C. F. Thomson-Houston are developing motors and
control systems.
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               Electricity Council
               AEI Mini-1
               Electricity Council
               Telearchics  Mini-2
                                                                          TABLE B-1
                                           SPECIFICATIONS Of SOME BRITISH EXPERIMENTAL ELECTRIC VEHICLES
                                       Curb
                                      Weight
                                       (Ib)
          Motor hp
          (Continuous
           Rating)
2,499     12hp
2,378     2 at 3 hp
 Controls
Thyristor
Carbon pile
Batteries

96 v, 66 amp-hr
(1-hr rate)
829 Ib
64 v, 110 amp-hr
(1-hr rate)
Acceleration

0-30 in 12
seconds

0-20 in 5
seconds
Maximum Speed
(mph)
41


40

Range
(miles)
30 non-stop at
37 mph

28 non-stop at
40 mph
                                                                               823 Ib
               Peel Engineering
                Trident
  600     24 volt
           5hp
Carbon pile     24 v, 153 amp-hr   0-30 in 7
                                 seconds
35
               Scottish Aviation
                Scamp
1,000     2at2.7hp      Carbon pile
               48 v, 105 amp-hr   0-30 in 10.5
               (5-hr rate)         seconds
               400 Ib
35
30 non-stop
               Ford Comuta
1,200     2 24 volt       Thyristor       48 v, 85 amp-hr    0-30 in 14
           5 hp                         (1-hrrate)         seconds
                                                    > 30
               40 at 25 mph
£

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       A  major  fuel cell  program  is under way at the Institut Franchise du Petrole
supported by development  work on carbon-based electrodes at Societ^ le Carbone Lorraine
and on sintered-metal-based electrodes at Ugine-Carbone. Other types of fuel cells are also
under investigation: there are programs on a Bacon-type fuel cell at ONIA (Office National
Industrial  d'Azote)  and on  hydrazine fuel cells at Alsthom. This  latter  company has
recently announced a joint vehicle development program with the automobile manufacturer,
Peugeot. Metal-air batteries are under investigation at CIPEL.

       An interesting example of electric vehicle  application in  France is the use of a
battery-powered bus  between the airport and the city of Marseilles. This is a full-size vehicle
weighing 36,000 pounds and capable of carrying 26  people seated plus 54 standing. It is
powered  by  a 96-volt, 750  amp-hour lead-acid  battery  that provides a range of  50
kilometers.
C.  GERMANY

       A small but significant number of electric delivery trucks were in use on German
highways prior to 1950; the system of license fees was then changed so that the  fees were
based largely on weight, and this virtually eliminated the vehicles. In recent years there has
been a revival of interest, although on a much smaller scale than in the United States and the
United Kingdom. However, self-propelled rail cars powered  by lead-acid  batteries are in
substantial use on the German national railroads. They were introduced after World War II,
and about 300 are now in service.

       Most of the  work in Germany on novel power sources has been focused upon fuel
cells.  Both Siemens-Schuckertwerke and Varta  have  large groups working  on hydrogen-
oxygen fuel  cell development, and Bosch has sponsored work on methanol fuel cells at the
Battelle Institute  in  Frankfurt.  The group  at  Varta has  an interesting  concept for
regenerative  braking. The energy from the generator is  used to electrolyze water, providing
hydrogen and oxygen which are stored and used subsequently in the fuel cell.
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D.  ITALY

       Italian participation in electric car development is confined to the design and con-
struction of  small experimental vehicles  with  relatively conventional  motor and control
systems, powered by lead-acid batteries.One of the more prominent of these vehicles, shown
in Figure  B-3, was built by Ghia S.p.A. and De Tomaso Automobili, subsidiaries of the
Rowan Controller Company of Westminster, Maryland. This four/five seat vehicle has a curb
weight of 1,300 pounds and is powered by lead-acid golf cart type batteries. The maximum
speed is 40 mph and the range 50-100  miles, depending on driving conditions. A relatively
inexpensive solid-state controller is used which operates by switching the field current of the
two 8-kw dc compound motors  specially  designed for this application by the General
Electric Company. The controller circuit is also utilized for regenerative braking.

       A very small  electric vehicle called the "Urbanina" of unconventional design and for
use in congested downtown locations has also  been exhibited. This car  weighs only 800
pounds. The  passenger compartment holds two people  and  is in  the  form of a rotating
turret. A range of 50  miles and top speed of  38 mph  have  been reported. Other Italian
electric cars involve conversions of conventional  Fiat 500's.
E. SWEDEN

       Urban concentration in Sweden is much less than in other developed countries, and
the comparatively large  distances between  populated centers make electric vehicles less
immediately  attractive; nevertheless,  interest  in  their development  is strong.  The  most
notable Swedish  activity is in fuel cell development: ASEA has constructed the world's
largest fuel cell system, which uses cracked ammonia and has a power rating of 240 kw. The
immediate  application was as a  power source for submarines, but smaller modules of the
system have been used to power experimental  lift trucks, and electric highway vehicles are
also under consideration.

       In a recent demonstration co-sponsored  by  the local Stockholm electrical utility,
ASEA exhibited an electrically powered SAAB. This vehicle contained a 120-volt nickel-
cadmium  battery  weighing 1,000 pounds.  It had a range of 25 miles,  falling to about 15
miles in city traffic. The top speed was 43 mph.
F. BELGIUM

       The  most significant work on electric vehicles in Belgium  is being carried out by
Ateliers de Constructions Electriques Charleroi (ACEC), which has developed a  full sized
diesel-electric bus. This vehicle has twin electric motors built into its back wheels. While
built largely for experimental purposes, the bus spends most of its time in local service in
the town of Charleroi. In the present model no auxiliary traction battery is used; electricity
is supplied by the diesel-powered generators as needed.
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01
                                                                               Courtesy of Rowan Controller Corporation.
                                           FIGURE B-3   PROTOTYPE ELECTRIC CAR BUILT IN ITALY



                                          BY SUBSIDIARIES OF ROWAN CONTROLLER CORPORATION

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G. JAPAN

       Japanese development of electric vehicles has been focused mainly on the conversion
of small, conventionally powered cars to electric propulsion. The work has been prompted
by the country's increasing concern about air pollution caused by heavy traffic in the cities.
Three of these  program are collaborative efforts involving a number of manufacturers and
are organized by three utility  companies: Tokyo Electric, Kansai  Electric,  and Chubu
Electric. The Kansai Electric and Tokyo Electric groups used standard lead-acid batteries in
conversions  of  800 cc and  360 cc vehicles, respectively, while Chubu Electric Battery
Company  developed a special 80-volt, 400 amp-hour lead-acid battery for its conversion of a
1, 500-cc vehicle. All  these vehicles are reported to have maximum speeds of the order of 40
mph and  a  range  of about 50  miles at  steady  driving.  All have thyristor controls and
regenerative  braking.

       An interesting recent development is the announcement by Tokyo Shibaura Electric
Company  (Toshiba) of a small car powered by a high-speed brushless dc motor.  Rated at 27
hp at 20,000 rpm, the motor gave the vehicle a maximum speed of 62 mph.

       In  addition to the above activity, the city of Osaka is reported to be contemplating
purchase of a fleet of small electric buses for downtown use.
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