LDTP 78-08
Technical Report
Investigation of the Requested Alternate
Dynamometer Power Absorption for the
Ford LTD
by
Glenn D. Thompson
April, 1978
Standards Development and Support Branch
Emission Control Technology Division
Office of Mobile Source Air Pollution Control
Office of Air and Waste Management
U.S. Environmental Protection Agency
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Abstract
Concern about the EPA fuel economy measurements has focused greater
attention on the dynamometer and the dynamometer adjustment. Specifi-
cally, the alternate procedures for determining the dynamometer power
absorption to simulate the vehicle road experience affords an oppor-
tunity for both greater precision and possible abuse. Because of the
possibility for abuse, it was decided to occasionally check the appro-
priateness of the alternate dynamometer power absorptions requested by
vehicle manufacturers.
The question of the representativeness of the requested dynamometer
power absorption for the Ford LTD was first raised during the summer of
1977. This report collects and summarizes the pertinant available data
which have been generated by the EPA Emission Control Technology Division,
the EPA Certification Division, and by Ford Motor Company.
It is concluded that a dynamometer power absorption of 12.3 horsepower
simulates the typical road experience of the Ford LTD. The dynamometer
power absorption requested by Ford, 9.5 horsepower, is inappropriate
for this vehicle. Some of this discrepancy occurred because of the
increased inflation pressures used by Ford during their road tests of
this vehicle. These tire pressures are considered unrepresentative of
anticipated consumer use of the vehicle because they exceed the typical
inflation pressures used in dealer preparation of the vehicle for con-
sumers. Even with the increased road tire inflation pressures, the
recent road data indicate a dynamometer power absorption of 10.8
horsepower is required to simulate the road experience of this vehicle.
The data also indicate that the rear axle load of at least one of the
certification vehicles was unrepresentatively low compared to the axle
loads of the production LTD vehicles. This axle load significantly
affects the tire energy dissipation during the dynamometer test, and
consequently the total energy required from the vehicle during the EPA
tests.
The unrepresentative nature of the EPA tests of the LTD resulted in
reduced NOx emissions measurements for the vehicle and in significantly
increased vehicle fuel economy. The predicted increase in NOx emissions,
if the vehicle were tested with appropriate dynamometer adjustment, is
estimated to be 0.07 gm/mi. The increased dynamometer power absorption
would be expected to decrease the urban fuel economy measurements of the
vehicle by 0.26 mi/gallon. The predicted decrease in the highway fuel
economy would be 0.6 mi/gallon, or about 3 percent.
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I. Purpose
The question of the representativeness of the test vehicle and the
requested dynamometer power absorption for the Ford LTD was first raised
during the summer of 1977. This report collects and summarizes the per-
tinent available data which have been generated by the EPA Emission
Control Technology Division, the EPA Certification Division, and by Ford
Motor Company.
II. Background
During the summer of 1977, ECTD personnel became aware of several
requests for alternate dynamometer power absorption which appeared to be
anomalously low. One of these was the 9.5 horsepower requested by Ford
Motor Company for the Ford LTD. This vehicle was certified in both the
4500 and 5000 pound inertia weight classes. The requested alternate
dynamometer power absorption was 3.2 horsepower below the 12.7 horsepower
specification for a 4500 pound inertia weight vehicle and 3.9 horsepower
below the 13.4 horsepower specified for a 5000 pound vehicle in the
current Federal Register table. This large difference seemed particularly
questionable since there is no obvious reason, such as exceptional
aerodynamics, to expect this large discrepancy for a conventional front
engine, rear axle drive vehicle.
The concern over the appropriateness of this requested dynamometer
adjustment resulted in an ECTD test program which was conducted in
August 1977. The report of this program concluded that the alternate
dynamometer power adjustments requested for this vehicle did not appro-
priately reflect the road experience of the vehicle as reported by Ford.
In addition, this report questioned the representativeness of the certi-
fication vehicle with respect to the production vehicle. The report of
August 1977, which is attached as Appendix A, has been the basis for
the additional investigations which have been conducted.
III. Discussion
Since the original EPA report, two additional investigations have
been conducted. Ford Motor Company conducted road and dynamometer tests
on one production LTD to support their original request. In October 1977,
when the 1978 model year vehicles became available in the rental car
fleet, EPA rented a Ford LTD and performed road coastdowns on this vehicle
at the Transportation Research Center of Ohio (TRC) test track. The
vehicle was then brought to EPA for the dynamometer coastdown tests.
This report considers all of the available data first based on the
original coastdown time submitted by Ford for the prototype certification
vehicle, secondly based on the road coastdown obtained by Ford from the
production vehicle, and finally based on the coastdown time obtained by
EPA from the rental vehicle.
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A. Analysis of the Dynamometer Data Based on the Ford Road Data
from the Prototype Vehicle
The original prototype vehicle used by Ford to collect the road
data submitted to EPA in support of the request for an alternate dynamo-
meter adjustment was a Ford LOT equipped with Uniroyal HR78X15 tires. The
corrected road coastdown time reported for this vehicle was 18.58
seconds. The dynamometer power absorption reported for this coastdown
time was 9.5 horsepower.
When the subsequent vehicles were tested at EPA and Ford, vehicle-
dynamometer coastdown times were obtained for diverse dynamometer power
absorptions. The data from the EPA measurements of the production
vehicles are given in Appendix B. Plots of the vehicle-dynamometer
coastdown times are presented for the EPA and Ford measurements in
Appendices B and C respectively. The dynamometer adjustment corres-
ponding to the original road coast down time of 18.58 seconds can be
obtained from these plots. The average values of the dynamometer power
absorptions from each series of measurements are summarized in Table 1.
Table 1
DYNAMOMETER POWER ABSORPTION CORRESPONDING
TO THE ORIGINAL PROTOTYPE COASTDOWN
TIME OF 18.58 SECONDS
Ford Original Request 9.5 hp
EPA Original Confirmatory Test (August 1977) 12.3 hp
Ford Production Vehicle Tests (November 1977, average
of two .dynamometers) 9.8 hp
EPA Production Vehicle Tests (average of four
dynamometers) 9.4 hp
Table 1 indicates that for all tests, except those performed on the
certification vehicle, 9.5 horsepower is a reasonable dynamometer
power absorption corresponding to a coastdown time of 18.58 seconds.
The test on the certification vehicle, however, required 12.3 horsepower
to match the coastdown time of 18.58 seconds.
It is extremely unlikely that test variability could account for
all of the apparent discrepancy of almost three horsepower. Therefore,
the vehicle data were reviewed in an attempt to identify any vehicle
differences.
The certification vehicle was significantly different from the
other vehicles in the test series. The prototype and all production
vehicles had an average rear axle load of 2104 pounds. The certification
vehicle, however, had a rear axle load of only 1910 pounds. In addition,
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the certification vehicle was equipped with Michelin steel belted tires
while all of the other vehicles were equipped with Uniroyal steel belted
radial tires. In the case of the certification vehicle, the reduced
rear axle loads would decrease the tire power dissipation by about 10
percent or approximately 0.7 horsepower. A recent EPA report indicated
Michelin radial tires had a rolling resistance of about 15 percent lower
than the rolling resistance of Uniroyal tires, at least for the tires
investigated. If this difference was valid for the 1978 Ford vehicles,
then the tire rolling resistance on the certification vehicle would
have been 15 percent, or about 1.1 horsepower less than for the production
vehicle.
The vehicle-dynamometer coastdown time is a measure of the power
dissipation for the total vehicle and dynamometer system. If the vehicle
tire energy dissipation is decreased, but the vehicle-dynamometer coast-
down remains unchanged, then the dynamometer power absorption must be
increased to compensate for the reduction in tire losses. In the case
of the certification vehicle, it is estimated that approximately 1.8
horsepower or about two thirds of the discrepancy between the results of
this vehicle and the remaining vehicles can be attributed to actual
differences between the vehicles. The remaining 0.9 horsepower was
probably induced by random variations in the vehicle and dynamometer
system. This variability is much more consistant with the variability of
about one horsepower observed during the EPA tests of the production
vehicle and the variability of 1.4 horsepower observed by Ford during
their production vehicle tests.
B. Analysis of the Dynamometer Data Based on the Ford Road
Coastdowns of Production Vehicles
In November 1977, Ford Motor company conducted a series of coastdown
tests on a production Ford LTD. The purpose of this investigation was
to corroborate the original data used in support of the request for an
alternate dynamometer adjustment. The corrected road coast time obtained
from this vehicle was 17.47 seconds. Table 2 presents the dynamometer
adjustments obtained for this coastdown time from each of the data
sources given in the Appendices.
Table 2
DYNAMOMETER POWER ABSORPTION CORRESPONDING
TO THE FORD PRODUCTION VEHICLE COASTDOWN
TIME OF 17.42 SECONDS
EPA Original Tests (August 1977) 13.3 hp
Ford Production Vehicle Tests (November 1977) 11.0 hp
EPA Production Vehicle Tests (December 1977) 10.6 hp
Again, all of the results are in reasonable agreement at about 10.8
horsepower except those obtained from the Ford certification vehicle.
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As before these differences are primarily attributed to the differences
between this test vehicle and the production vehicles.
C. EPA Road Coastdown Tests
The major purpose of the road tests conducted by EPA on the rented
production Ford LTD was to verify the road coastdown data submitted by
Ford.
The road test portion of the program was conducted by TRC personnel.
The vehicle was first driven for about 250 miles for drive train component
brake-in. The vehicle system was then allowed to equilibrate to ambient
temperatures over night. Prior to the vehicle warm-up for the coastdown
tests the vehicle tires were adjusted to the recommended cold inflation
pressures. The vehicle was then warmed up for approximately one half
hour at 50 mph. Twenty coastdowns were subsequently conducted, ten in each
direction of the TRC track. Ten of the coastdowns, five in each direction,
were started at approximately 60 mph. The remainder were started at
approximately 40 mph. It was necessary to divide the coastdowns into
these two speed ranges because of the relatively short, 1 km, section of
constant grade track available on the TRC skid pad.
The data analysis was conducted in the manner described in the data
analysis section of the EPA Recommended Practice for Road Load Deter-
mination except that a Av/At approximation was used for the vehicle
deceleration during the coastdown.
A two term model of the acceleration versus velocity was chosen,
that is: „
A = aQ + a2v (1)
where:
A = the calculated deceleration of the vehicle
v = the vehicle velocity
a_ and a~ are coefficients to be fitted by the
regression analysis.
Additional terms were added to equation 1 to account for the direc
tional dependent effects caused by track grade and wind. The grade
effect was assumed to be independent of velocity while the wind effect
was assumed to be linearity dependent on the vehicle velocity.
The a_ terms of the regression will contain a constant term intro-
duced by the ambient wind. This correction to still air conditions was
made using the measured value for the ambient wind. In addition, since
the a_ terms represents the aerodynamic drag, an air density correction
was applied to this term to correct to the standard ambient conditions
given in the EPA recommended practice. The corrected coefficients
which were obtained are:
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a* = 0.3526 mi/hr-sec
a* = 0.0001225 hr/mi-sec
(2)
The coefficients of equation 2 were used to calculate the total road
force on the vehicle from the vehicle mass and the estimates of the rota-
tional inertias of the rotating components of the vehicle. The 55 to 45
mph dynamometer coastdown time interval necessary to reproduce this
force was then calculated by correcting for the difference between the
total effective vehicle mass during the road coastdowns and the dynamo-
meter simulated mass plus the rotational inertia of the drive train
components. The final, dynamometer "target" coastdown time obtained
from the EPA track measurements was:
AT = 16.08 seconds (3)
The dynamometer adjustment results, based on this coastdown time
are given in Table 3.
Table 3
DYNAMOMETER POWER ABSORPTION CORRESPONDING
TO THE EPA PRODUCTION VEHICLE COASTDOWN
TIME OF 16.1 SECONDS
Ford Production Vehicle Tests 12.7 hp
EPA Production Vehicle Tests 12.3 hp
The certification vehicle tests are not represented in Table 3
because no data were obtained for coast down times shorter than about
17.5 seconds.
IV. Analysis
This section analyzes the presented data to judge the most appropriate
coastdown time and dynamometer adjustment for the Ford LTD. The effects
of this dynamometer power absorption on exhaust emissions and fuel eco-
nomy versus the power absorption used during the EPA tests are then in-
vestigated.
A. The Appropriate Dynamometer Power Absorption
The analysis of the data presented in Tables 1 through 3 require
decisions on two basic questions:
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1. What are the axle loads and tire combinations of the repre-
sented production vehicles?
2. Which coastdown time best represents the road experience of
the vehicle?
In response to the first question, the original prototype vehicle
and all production vehicles considered in this program were equipped
with Uniroyal tires and had rear axle loads of approximately 2100 pounds.
Only the certification vehicle, which was not equipped with a spare tire
or jack, had a rear axle load less than 2000 pounds. Hopefully, Ford
Motor Company intends to provide spare tires with the production vehicles,
therefore the heavier configuration must be judged as most appropriate
to represent the production vehicles.
Addressing the appropriate road coastdown times, the choices are
the original prototype coast down time of- 18.58 seconds, the Ford pro-
duction vehicle coast down time of 17.42 seconds, and the EPA production
vehicle coastdown time of 16.10 seconds. Since the question really
pertains to the production vehicle coastdown time, the coast down time
of the production vehicles should receive primary attention. There is
further reason to disregard the original prototype coastdown time be-
cause Ford had the the greatest possible incentive to reproduce this
value during their subsequent confirmatory tests, but obtained times more
than one second slower. It is subsequently considered that the important
evaluation is between the Ford and EPA coastdown times on the production
vehicles.
The test data were reviewed to attempt to locate the reason for the
discrepancy between the EPA and Ford results. An obvious difference
observed between the Ford and EPA test conditions was the tire inflation
pressures.
The Ford road tests were conducted at tire inflation pressures of
30 and 32 psi, front to rear respectively, while the EPA tests were con-
ducted with inflation pressures of 26 and 28 psi. This difference in
tire pressure would theoretically be expected to cause a change of about
0.8 horsepower in the vehicle road power and a reduction of about 0.8
seconds in the road coastdown time.
TRC personnel had been instructed to conduct the road tests at the
normal tire inflation pressures recommended by the manufacturer; there-
fore the basis for the test pressure difference was investigated. TRC
personnel reported that the vehicle was prepared by the local Ford
dealer who had inflated the tires to approximate 26-28 psi. In addi-
tion, the consumer safety information contained in the vehicle glove
box was based on the tire inflation pressure of 26-28 psi.
The vehicle owner's manual did not specifically recommend any tire
inflation pressures but referred the reader to the'decal on the jamb of
the passenger door. This decal recommended tire inflation pressures of
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26-28 psi for the best vehicle ride and 30-32 for maximum fuel economy.
Since either inflation pressure might be considered as recommended
by the manufacturer, a brief telephone survey of local Ford dealers was
conducted to ascertain which inflation pressure might be considered nor-
mal for the vehicle, at least as originally delivered to the customer.
All dealers responded that the vehicles were normally prepared for the
consumer with tire inflation pressures of 26-28 psi or lower. It was
therefore concluded that tire inflation pressures of 30-32 psi are not
typical for this vehicle even at the time of dealer preparation. Con-
sequently, the high tire inflation pressures cannot be considered typi-
cal for the normal use of this vehicle.
In addition, the EPA recommended practice for road load determina-
tion currently chooses standard ambient conditions of 68°F. The Ford
procedure for road load determination chooses 74°F as the standard condi-
tions. This difference in standard conditions would increase the vehicle
road load approimately 2 percent and therefore decrease the corrected
coastdown time by about 0.3 seconds.
The average U.S. annual temperature is about 60°F, even lower than
the EPA standard temperature (1). Consequently, test results corrected
to 68°F are certainly more representative of typical owner use than
results corrected to 7A°F.
These txjo effects, temperature and tire pressure, nearly explain
the observed differences between the two test results. The remaining
differences must be attributed to test and vehicle variability. Since
the EPA test conditions were much closer to typical consumer vehicle use,
the EPA results are judged to be more representative of the in-use
experience of the vehicle. Consequently, the dynamometer adjustment of
12.3 horsepower is considered representative of typical vehicle experi-
ence.
B. The Emission and Fuel Economy Effects of the Dynamometer
Adjustment
In December 1977, the Certification Division conducted exhaust
emissions and fuel economy measurements as a function of dynamometer
power absorption. The vehicle used was a Ford LTD. The data from the
Certification Division tests are given in Appendix D. Regression
analyses of these data conclude that the vehicle fuel economy significantly
decreases with increasing dynamometer power absorption, the NOx emissions
increase with increasing dynamometer power absorption, and the HC and
CO emissions tend to decrease with increasing power absorption. The
regressions statistics indicate there is little confidence that the
(1) U.S. Bureau of the Census, Statistical Abstract of the United
States: 1975 (96th edition) Washington, D.C. 1975.
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slopes of the HC and CO regression lines are different from zero. There-
fore, the statistically significant effects are the increase in NOx
emissions and the degradation of the vehicle fuel economy with increasing
dynamometer power absorption. The fuel economy and NOx missions data,
together with the regression lines are plotted in Figures 1 and 2.
The plots of the data demonstrate the strong dependence of the
vehicle fuel economy on the dynamometer power absorption. The statis-
tical confidence in the effects of the dynamometer power absorption on
the vehicle fuel economy was, as expected, very high. The confidence
in the prediction of the effects on NOx emissions was, however, somewhat
weaker. The statistical uncertainty in the effects on NOx emissions was
primarily caused by the, possibly outlier, datum from the test at the
lowest dynamometer power absorption.
The regression lines can be used to predict the effect on NOx emis-
sions and fuel economy if the vehicle had been tested at the higher,
more representative, dynamometer power absorptions. The deficiency in
the dynamometer adjustment for the vehicle during the applicable emis-
sions tests was, therefore, 9.5 horsepower versus 12.3 for vehicles
without air conditioning and 10.5 versus 13.5 horsepower for air condi-
tioned vehicles. The predicted increase in NOx emissions would be
approximately 0.07 gm/mi for both of the two cases.
Including the predicted NOx increase of 0.07 gm/mi most of the
certification vehicles tested to represent the LTD engine families would
still have met the NOx standard. There was, however, one which would
have exceeded the 2.0 gm/mi standard but would have been certified
because of round-off tolerances (2). It should be noted that this analy-
sis strongly depends on the slope of the NOx versus dynamometer power
absorption regression, shown in Figure 2. If, for example, the datum at
the lowest dynamometer power absorption were judged to be an outlier and
deleted, the slope of the regression would increase and failure of these
vehicles with high NOx emissions would probably be predicted. Considering
this sensitivity of the regression and the normal test variability, the
success or failure of this particular vehicle, if tested at a represen-
tative dynamometer power absorption, cannot be accurately predicted.
The same discrepancy in the dynamometer power absorption would
result in a predicted decrease in fuel economy of about 0.26 mi/gallon
for the urban cycle. The highway fuel economy would be expected
to decrease approximately 0.6 mi/gallon, or about 3 percent
for vehicles both with and without air conditioning. Based on current
sales predictions, such a decrease in the fuel economy of this vehicle
would be expected to lower the Ford Corporate Average Fuel Economy for
1978 (3).
(2) C. Larson, discussion, February 1977.
(3) J.D. Murrell, discussion, February 1977.
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Vehicle Fuel Economy
versus
Dynamometer Power Absorption
TEST VEHICLE: Ford LTD 8A1-351W-F-64
INERTIA WEIGHT CATEGORY: 5000 pounds
I
C
o
u
K
0)
3
O
•H
25
24
23
22
21
20
19
18
17
16
15
Highway Fuel Economy
Regression Line.
Urban Fuel Economy
Regression Line
10 11 12 13 14 15
16
Figure 1
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Nitrogen Oxide Emissions
versus
Dynamometer Power Absorption
TEST VEHICLE: Ford LTD 8A1-351W-F-64
INERTIA WEIGHT CATEGORY: 5000 pounds
to
c
o
•H
CO
CO
•H
0)
o
^
4-J
•H
2.1"
2.0"
1.7-
•H
X
c 1.6
c
a>
1.5.
1.4,
"Regression Line
10
11 12 13 14 15 16
Dynamometer Power Absorption (horsepower)
Figure 2
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V. Conclusions
It is concluded that the EPA tests of the Ford LTD were unrepre-
sentative because:
1. The road data submitted by Ford is unrepresentative of antici-
pated consumer use of the vehicle because of the tire pressures
used during the dealer preparation of the vehicle for consumer
use.
2. At least one of the certification test vehicles submitted to
EPA had a rear axle load unrepresentative of production LTDs
tested. This unrepresentativeness of the vehicle had an
additional effect of reducing the power required from the
engine during certification tests.
It is further concluded that the unrepresentative nature of these
tests resulted in reduction of the NOx emissions measurements for these
vehicles. Most of the vehicles tested to represent the LTD would still
be expected to meet the exhaust emission standards if these vehicles
were tested at the higher, more representative dynamometer power absorp-
tion. One test vehicle was, however, sufficiently close to the 2.0 gm/mi
NOx standard that the success or failure of this particular vehicle
cannot be accurately predicted.
The unrepresentative nature of the EPA fuel economy tests resulted
in a significant increase in the vehicle fuel economy for the Ford LTD.
This increase could affect the 1978 Ford Corporate Average Fuel Economy.
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APPENDIX A
EPA Report of August 1977
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Abstract
Concern about the EPA fuel economy measurements has focused greater
attention on the dynamometer and the dynamometer adjustment. Specifi-
cally the alternate procedures for determining the dynamometer adjust-
ment to simulate the vehicle road experience affords an opportunity for
both greater precision and possible abuse. Because of the possibility
for abuse it was decided to occasionally check the coast down times of
the certification test vehicle on the dynamometer, with the dynamometer
adjusted to the requested power setting, versus the road coast down
times reported for the vehicle by the manufacturer. While this proce-
dure assumes the validity of the submitted road coast down data, it does
provide an easy and convenient check that the dynamometer experience of
the test vehicle is similar to the reported road experience. It insures
that vehicle components such as tires and drive train lubricants are
effectively the same on the EPA test vehicle as on the vehicle which was
road tested by the manufacturer.
The Ford LDT was selected for such a "quick check" since the alter-
nate dynamometer adjustment requested by the manufacturer, 9.5 horse-
power, was considered unusually low. This vehicle is being certified in
both the 4500 and 5000 pound inertia weight classes. The requested
alternate power adjustment is 3.9 horsepower below the 13.4 horsepower
specified for a 5000 pound vehicle in the current Federal Register table
and 3.2 horsepower below the 12.7 horsepower specification for a 4500
pound inertia weight vehicle. This large difference seemed particularly
questionable since there is no obvious reason, such as exceptional aero-
dynamics, to expect this large discrepancy for a conventional front
engine, rear axle drive vehicle.
The investigation concludes that when the certification vehicle is
operated on the dynamometer, the requested dynamometer adjustment of 9.5
horsepower at 50 mph, does not result in an accurate dynamometer sim-
ulation of the reported road experience of the vehicle tested by Ford.
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Background:
Concern about the EPA fuel economy measurements has focused greater
attention on the dynamometer and the dynamometer adjustment. Specifi-
cally the alternate procedures for determining the dynamometer adjust-
ment to simulate the vehicle road experience affords an opportunity for
both greater precision and possible abuse. Because of the possibility
for abuse it was decided to occasionally check the coast down times of
the certification test vehicle on the dynamometer, with the dynamometer
adjusted to the requested power setting, versus the road coast down
times reported for the vehicle by the manufacturer. While this proce-
dure assumes the validity of the submitted road coast down data, it does
provide an easy and convenient check that the dynamometer experience of
the test vehicle is similar to the reported road experience. It insures
that vehicle components such as tires and drive train lubricants are
effectively the same on the EPA test vehicle as on the vehicle which was
road tested by the manufacturer.
Discussion:
The Ford LTD was selected for such a "quick check" since the alter-
nate dynamometer adjustment requested by the manufacturer, 9.5 horse-
power, was considered unusually low. This vehicle is being certified in
both the 4500 and 5000 pound inertia weight classes. The requested
alternate power adjustment is 3.9 horsepower below the 13.4 horsepower
specified for a 5000 pound vehicle in the current Federal Register table
and 3.2 horsepower below the 12.7 horsepower specification for a 4500
pound inertia weight vehicle. This large difference seemed particularly
questionable since there is no obvious reason, such as exceptional
aerodynamics, to expect this large a discrepancy for a conventional
front engine, rear axle drive vehicle.
EPA tested two 1975 Ford LTD's in the recent road load project.
The results of these measurements, 11.6 horsepower for one vehicle and
12.6 horsepower for the other vehicle, are in better agreement with the
current Federal Register table than with the Ford requests (1). The
mean of the two EPA results, 12.2 horsepower would be the best EPA
estimate of the appropriate dynamometer adjustment for this vehicle
based on the road load project measurements. The frontal area based
equation which is proposed for the 1979 model year also yields dyna-
mometer adjustments which are nearer the current table than are the Ford
requested dynamometer adjustments. Using frontal area data submitted by
Ford for the 1975 vehicles, the proposed equation predicts a dynamometer
adjustment of 12.4 horsepower for these vehicles (2).
Because of the apparent discrepancies between the EPA measurements
and predictions, and the requested dynamometer adjustment, a certifica-
tion vehicle, vehicle number 8A1-351W-F-64, was selected for this quick
check. Ford personnel were invited to observe these tests. The tests
were conducted on dynamometer number 4, the same dynamometer which was
used for the recent certification running change tests on this vehicle.
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For these tests the vehicle was prepared in the same manner it
would be treated for certifications testing. The fuel tank was filled
to approximately 40% capacity as indicated by the vehicle fuel gauge.
The vehicle was then placed on the dynamometer and the restraining cable
explicitly checked by the dynamometer operator to insure the cable
tension was typical of normal EPA dynamometer testing. At this time the
tire inflation pressures were also checked and adjusted to 45 psi. The
dynamometer inertia weight simulation was however adjusted for 5000
pounds since this was the inertia weight simulation used by Ford to
develop the requested dynamometer adjustment.
The EPA vehicle and dynamometer warmup procedure requires the
vehicle be driven for 30 minutes at approximately 50 mph. The Ford
personnel present requested that the Ford warm-up procedure be used in
these tests. This procedure calls for the vehicle to be repeatedly
accelerated to 70 mph, then allowed to coast, with the transmission
engaged, down to 40 mph. Previous EPA tests have not shown a signifi-
cant difference between the dynamometer power absorber settings which
result from either of these warm-up methods. Therefore, the Ford re-
quest was granted, and the gradual acceleration-deceleration warm-up
pattern was repeated for 30 minutes.
Coast downs, from 55 mph to 45 mph were then performed for five
nominal horsepower settings. The total dynamometer absorbed power, the
indicated dynamometer absorbed power and the coast down times are given
in Table 1.
Table 1
Dynamometer No. 4, IW = 5000 pounds, 8/19/77
Total Dynamometer Indicated Dynamometer Coast Down
Power at 50 mph Power at 50 mph Time Interval
(horsepower) (horsepower) (sec)
9.2 6.5 22.9
9.3 6.6 22.7
10.2 7.4 20.8
10.2 7.4 21.0
10.2 7.4 21.4
11.4 , 8.6 19.9
11.3 8.5 20.0
12.2 9.4 19.1
12.2 9.4 18.5
13.0 10.2 17.6
13.0 10.2 17.7
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The coast down times are plotted versus the total dynamometer power
at 50 mph in Figure 1. An equation of the form:
Hp = a + bt + ct2 (1)
was fitted to the total dynamometer power and coast down time data by
the method of least squares. The resulting coefficients of the line
were:
a = 38.1 hp
b = -1.92 hp/sec „
c = 0.0289 hp/sec
This line is also plotted in Figure 1.
Ford reported the target dynamometer coast down time to be 18.58
seconds. This target dynamometer coast down time was calculated by
correcting the road coast down times to the time appropriate for a
standard set of ambient conditions. In addition corrections were made
to adjust for the difference in the inertia weight of the vehicle as
road tested, and the dynamometer simulated inertia weight category of
5000 pounds. A vertical line corresponding to 18.58 seconds is shown on
Figure 1. This line intersects the curve at 12.3 horsepower which is
2.8 horsepower higher than the dynamometer adjustment requested by Ford.
This difference between the EPA and Ford results is considered signi-
ficant.
Immediately following the coastdown tests the vehicle was weighed,
including the test driver, on the EPA scales. The total vehicle weight,
and each axle load were:
front axle load 2520 pounds
rear axle load 1910 pounds
total vehicle weight 4420 pounds
Throughout the tests the observing Ford personnel were insistent
that the test vehicle should be ballasted so that the rear axle load was
equivalent to the rear axle load of the vehicle Ford dynamometer tested.
The rear axle load and total weight reported for the Ford vehicle were:
rear axle load 2156 pounds
total vehicle weight 4834 pounds
The vehicle road tested by Ford was approximately 400 pounds heavier
than the EPA certification vehicle. The rear axle load on the Ford road
vehicle was also greater than the rear axle load on the certification
vehicle. In addition, the ratio of the load on the rear axle to the
total vehicle weight was greater on the Ford road vehicle than it was on
the vehicle supplied for certification.
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I
ex
o
01
S
o
0)
S
O
O
CO
CO
4-1
O
H
-5-
Dynamometer No. 4
IW = 5000 pounds
8/18/77
14
13
12 •
11 • •
10 "
17
18
19
20
21
22
23
Coast Down Time (sec)
Figure 1
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-6-
Mr. D.W. Berens of Ford stated that the vehicles Ford had road
tested had been carefully prepared to reflect the aerodynamic and weight
characteristics of the standard or base vehicles presented in the Ford
Part I application. Mr. Berens also stated that the vehicle road
tested by Ford was equipped with the same displacement engine as the
certification vehicle, however the transmissions and rear axles might be
different.
Mr. Clayton LaPointe of Ford was adamant that it was inappropriate
to perform dynamometer tests on the Ford certification vehicle without
ballasting the vehicle. Mr. LaPointe felt it was unrealistic to expect
the dynamometer simulation of the unballasted vehicle to reflect the
road experience of the Ford coastdown vehicle. Mr. LaPointe estimated
the difference in tire power dissipation between the ballasted and
unballasted configuration could be approximately one horsepower at 50
mph.
The results of these tests certainly support Mr. LaPointe's con-
tention that the dynamometer experience of the unballasted vehicle is an
unrealistic representation of the road experience of the vehicle road
tested by Ford. However, if the road vehicle is representative of the
intended 1978 product, was a non-representative vehicle supplied by Ford
for exhaust emission certification and fuel economy testing?
To insure the accuracy of EPA exhaust emission and fuel economy
tests the dynamometer experience of the vehicle during these measure-
ments must accurately simulate the road experience of the intended
production vehicle. If it is necessary to adjust the rear axle load to
correctly simulate the road experience, this should also be done during
the certification testing.
Conclusions:
1) When the certification vehicle is operated on the dynamometer,
the requested dynamometer adjustment of 9.5 horsepower at 50 mph, does
not result in an accurate dynamometer simulation of the reported road
experience of the vehicle tested by Ford.
2) The vehicle road tested by Ford was significantly different
from the vehicle provided for certification testing.
Recommendations:
1) It is recommended that the vehicle discrepancy be resolved.
That is, which vehicle best represents the vehicle Ford intends to sell?
The road experience of the intended sales vehicle should be determined,
then the dynamometer adjustment necessary to simulate the road experi-
ence of the intended sales vehicle should be used for certification and
fuel economy testing. The weight and weight distribution of the certi-
fication vehicle should be adjusted, if necessary, to simulate the
intended sales vehicle.
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-7-
2) The requested dynamometer adjustments for other Ford vehicles
should be checked.
3) The "representativeness" of all Ford certification and fuel
economy vehicles should be investigated.
References
1. G.D. Thompson, EPA Technical Support Report for Regulatory Action,
"Light-Duty Vehicle Road Load Determination", December 1976.
2. G.D. Thompson, EPA Technical Support Report for Regulatory Action,
"Prediction of Dynamometer Power Absorption to Simulate Light-Duty
Vehicle Road Load", April 1977.
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APPENDIX B
EPA Dynamometer Data
from the
Ford LTD Rental Vehicle
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FORD LTD (TRC RENTAL VEHICLE)
IWC = 5000 Pounds
Nominal
Actual
Power (Hp)
13.5
12.5
11.5
10.5
9.5
8.5
7.5
Dyno
15.12
15.96
16.61
17.67
18.63
19.96
21.23
Mean Co
//I Dyno
15.34
16.18
16.74
17.80
18.71
20.22
21.49
as
(
#2
(sec)
Dyno #3 Dyno
14.41
15.54
16.25
16.74
18.05
19.57
20.58
15.12
16.06
16.88
17.86
18.64
20.19
21.30
Average Coastdown
Time for all Dynos
(seconds)
15.00
15.94
16.62
17.52
18.51
19.98
21.15
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Dynamometer Power Absorption
versus
Average Coastdown Time
Ford LTD (Rental Vehicle)
IWC 5000 Pounds
12-
13-
Dynamometer
Power
Absorption !ۥ
(horsepower)
Each point is the average of the
results obtained from four EPA
light-duty vehicle certification
dynamometers.
16
4-
17 18
Coastdown Time (sec)
19
20
21
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APPENDIX C
Ford Motor Company Data
Tests of November 1977
-------
Test Vehicle Characteristics Supplied
by Ford for the Production LTD
Vehicle:
Vehicle No.:
1978 Ford LTD - 4 Door Sedan
313-T-025
Road Test Data:
Total weight:
Rear axle load:
Front tire pressure:
Rear tire pressure:
Corrected road coastdown time:
4770 pounds
2089 pounds
30 psi
32 psi
17.42 seconds
Dynamometer Test Data:
Total weight:
Rear axle load:
Rear tire pressure
Inertia weight category
Dynamometer power absorption
corresponding to a coastdown
time of 17.42 seconds
Test Cell 2
4760 Ibs.
2090 Ibs.
45 psi
5000 Ibs.
10.36
Test Cell 6
4792 Ibs.
2090 Ibs.
45 psi
5000 Ibs.
11.75
-------
Coastdown Time
versus
Dyamometer Power Absorption
Ford LTD - November 1977
13 4-
12 4.
Dynamometer
Power
Absorption
(horsepower)
11
10
Ford Motor Company Data
Ford Emission Test Cell//2
IWC: 5000 Ibs.
-*-
15
16 17 18
Coastdown Time (sec)
19
-------
Coastdown Time
versus
Dynamometer Power Absorption
Ford LTD - November 1977
15'
14"
Ford Motor Company Data
Ford Emission Test Cell Number 6
IWC: 5000 Ibs.
13'
Dynamometer
Power Ab-
sorption
(Horsepower)
12'
11'
10'
15
16
17
18
19
Coastdown Time (sec)
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APPENDIX D
Effects of Dynamometer Power Absorption
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TABLE D-l
Vehicle Emissions and Urban Fuel Economy
versus
, Dynamometer Power Absorption
Dynamometer
Power Absorption
(HP)
6.3
9.5
9.5
12.7
15.9
Hydrocarbons
(gm/mi)
0.75
0.82
0.90
0.73
0.81
Carbon
Monoxide
(gm/mi)
10.5
12.0
13.7
11.0
11.1
Nitrogen Carbon
Oxides Dioxide
(gm/mi) (gm/mi)
1.85 552
1.65 552
1.50 566
1.83 579
2.00 583
Urban
Fuel Economy
(mi/gal)
15.5
15.5
15.0
14.9
14.7
TEST VEHICLE: Ford LTD 8A1-351W-F-64
INERTIA WEIGHT CATEGORY: 5000 pounds
-------
Table D-2
Highway Fuel Economy
versus
Dynamometer Power Absorption
Dynamometer Highway Fuel
Power Absorption Economy
(Hp) (mi/gal)
6.3 24.8
6.3 25.0
9.5 23.7
9.5 23.0
9.5 23.2
12.7 21.1
12.7 21.4
12.7 21.1
15.9 19.7
15.9 19.3
TEST VEHICLE: Ford LTD 8A1-351W-F-64
INERTIA WEIGHT CATEGORY: 5000 pounds
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