LDTP - 78 - 06
Technical Report
Investigation of the Requested Alternate
Dynamometer Power Absorption for the
Ford Mercury Marquis
by
Glenn D. Thompson
March, 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 Mercury Marquis was first raised during the
summer of 1977. This report collects and summarizes the pertinent
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 adjustment of 11.4 horsepower is
representative of typical, recommended vehicle use. The dynamometer
adjustment requested by Ford, 8.8 horsepower is certainly inappropri-
ately low. Some of the discrepancy between the original requested power
absorption and the EPA results occurred because of the increased tire
pressures used by Ford during their road tests. These tire pressures
are considered unrepresentative of anticipated consumer use of the
vehicle because they are significantly higher than the tire pressures
used by Ford dealers in preparation of the vehicles for consumer use.
Even with the increased tire inflation pressures the recent tests indi-
cate a dynamometer adjustment of 10.8 horsepower is necessary to sim-
ulate the road experience of the vehicle.
The EPA exhaust emission certification and fuel economy measurements of
the Ford Mercury Marquis were unrepresentative because of the inappro-
priately low dynamometer adjustments used during these tests. The
unrepresentative nature of these tests resulted in reduced NOx emission
measurements for the vehicle and resulted in significantly increased
vehicle fuel economy. If the vehicle were tested at the representative
dynamometer power absorption, it is predicted that the NOx emissions
would increase approximately 0.05 gm/mi. The predicted decrease in the
urban fuel economy would be about 0.25 mi/gal, while the highway fuel
economy would be expected to decrease about 1.5 mi/gal. The composite
urban-highway fuel economy would be expected to decrease approximately
0.6 mi/gallon, or about 3 percent.
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Purpose
The question of the representativeness of the test vehicle and the
requested dynamometer power absorption for the Mercury Marquis 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.
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 the most outstanding of these was the 8.8 horsepower reques-
ted by Ford Motor Company for the Mercury Marquis. This request was 34%
below the 13.4 horsepower specified by the Federal Register, for testing a
vehicle of the inertia weight category of the Marquis. The concern over
the appropriateness of this requested dynamometer adjustment resulted in
an ECTD test program which was conducted in July 1977. The report of
this program concluded that the alternate dynamometer power adjustments
requested for this vehicle did not appropriately reflect the road exper-
ience of the vehicle as reported by Ford. In addition, this report
questioned the representativeness of the certification vehicle with
respect to the production vehicle. The report of July 1977, which is
attached as Appendix A, has been the basis for the additional investiga-
tions which have been conducted.
Discussion
This report first considers all of the available data, assuming the road
data submitted by Ford is correct. The second section of the report
challenges the road data, and the final section documents the effects
the indicated descrepancies in dynamometer adjustment would probably have
on the fuel economy and exhaust emissions of this vehicle.
A. Analysis of the Dynamometer Data assuming Validity of the Ford Road
Data
In response to the questions raised by the first EPA report, Ford Motor
Company conducted a series of road and dynamometer tests on three
production Mercury Marquis. The results of these tests are given in
Table 1 of Appendix B and are summarized in Table 1.
Table 1
Ford Production Marquis Tests
November 1977
Average Corrected Road Average Dynamometer Power
Coastdown Times Absorption
(sec) (horsepower)
16.72 10.67
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For comparison the data presented by Ford in their request for an alter-
nate dynamometer power absorption is given in Table 2.
Table 2
Data Presented by Ford in Support of the
Requested Alternate Dynamometer Power Absorption
Corrected Road Dynamometer Power
Coastdown Time Absorption
(sec) (horsepower)
16.98 8.8
In the request for the alternate dynamometer adjustment Ford reported a
corrected road coastdown time 0.26 seconds or 1.5%, longer than the
production vehicle coastdown time. This would indicate the production
vehicles had slightly greater actual road load than the prototype vehicle.
However, this degree of consistency of the Ford road data indicates the
original road data is probably representative of the vehicle road exper-
ience for the test conditions used. In contrast, the difference between
the requested dynamometer adjustment of 8.8 horsepower and the November
1977 test results of 10.7, was 1.9 horsepower, or 21 percent of the
requested dynamometer adjustment. The early EPA results of 10.5 horse-
power tend to corroborate the November results from Ford.
In October 1977, the 1978 model year vehicles became available in the
rental car fleet. EPA subsequently rented a Ford Mercury Marquis, 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. The resulting test data are pre-
sented in Table 2 of Appendix B, and average values are plotted in
Figure 1. Matching the original Ford road coastdowns time of 16.98
seconds with this vehicle required an average of 10.6 horsepower.
Matching the road coastdown time obtained by Ford from the production
vehicle, 16.7 seconds, required an average dynamometer power absorption
of 10.9 horsepower. All of the test results, based on Ford road coast-
down times, are summarized in Table 3.
All of the data show reasonable agreement, except the alterante dynamo-
meter power absorption requested by Ford for the certification vehicle.
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Table 3
Summary of Dynamometer Power Absorption Determination
for the Mercury Marquis
Average Dynamometer Power
Test Series (horsepower)
Ford Certification Request 8.8
EPA Tests on the Certification
Vehicle, July 1977 using the Ford 10.5
corrected road coastdown time of 16.98 seconds.
Ford Tests on Production 10 7
Vehicles, November 1977
EPA Tests on a 1978 Rental
Vehicle, January 1978 using the 10.6
Ford corrected road coastdown time of
16.98 seconds
EPA Tests on a 1978 Rental Vehicle
January 1978, using the Ford production 10.9
corrected road coastdown time of 16.7 seconds
Throughout this extended investigation, Ford indicated the differences
between the original request and the subsequent tests were a result of
the variations among dynamometers. Reasonable estimates of the dyna-
mometer variability can be obtained from the multiple dynamometer tests
which were conducted. The Ford confirmation tests of November 1977
consisted of six dynamometer coastdown tests on two different dynamo-
meters. The two Ford dynamometers differed on the average by about one
horsepower. Even including variations in the road test times, the
twelve determined dynamometer adjustments were between 9.72 horsepower
and 11.86 horsepower. In the case of the EPA production vehicle coast-
downs, tests were conducted on all four of the EPA certification dyna-
mometers which were available. At the original Ford road coastdown time
of 16.98 seconds, the test results ranged only from 10.2 to 10.9 horse-
power. Thus, there is no evidence dynamometer-to-dynamometer variations
could cause the extremely low value for the dynamometer adjustment
originally requested by Ford.
B. Comparison of the Submitted Ford Road Data
with EPA Track Results
The major purpose of the road tests conducted by EPA on the rented
production Mercury Marquis was to verify the road coastdown data sub-
mitted 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 com-
ponent brake-in. The vehicle system was then allowed to equilibrate to
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Average Vehicle Dynamometer Coastdown Time
versus
Dynamometer Power Absorption
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Each point is the average
of the results obtained
from four EPA light-duty
vehicle certification
dynamometers.
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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 + a2v2 (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 directional
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 an term of the regression will contain a constant term introduced 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~ term 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:
a* = 0.284 mi/hr-sec
(2)
a* = 0.000132 hr/mi-sec
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
rotational 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 differences between
the total effective vehicle mass during the road coastdowns and the
dynamometer 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 = 16.31 seconds (3)
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This coastdown time gave an average dynamometer adjustment of 11.4
horsepower based on the EPA dynamometer tests of December 1977, plotted
in Figure 1. This value is significantly greater than the average
dynamometer power absorbtion of 10.6 horsepower obtained from these data
using the coastdown time of 16.98 seconds reported by Ford for the
prototype vehicle. It is also greater than the dynamometer power absor-
ption of 10.9 horsepower which was obtained from the EPA dynamometer
data based on the coastdown time of 16.72 seconds reported by Ford for
their production vehicle tests.
The test data were reveiwed to attempt to locate the reason for this
discrepancy. 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 conducted
with inflation pressures of 26 and 28 psi. This difference in tire
pressure would theoretically be expected to cause a change of about 0.5
horsepower in the vehicle road power. Since the differences between the
Ford and EPA results from production vehicles were approximately this
amount, these differences were attributed to the difference in the tire
inflation pressure during the road tests.
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 approximately 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 owners manual did not specifically recommend any tire infla-
tion pressures but referred the reader to the decal on the jamb of the
passenger door. This decal recommended tire inflation pressures of 26-
28 psi for best vehicle ride and 30-32 psi 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
normal for the vehicle, at least as originally delivered to the customer.
All dealers responded that the vehicles were normaly 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 typical
for the normal use of this vehicle.
The dynamometer adjustment of 11.4 horsepower is therefore more repre-
sentative of typical, recommended vehicle use than the power absorption
values obtained from data collected at the evaluated tire pressures.
The dynamometer adjustment requested by Ford, 8.8 horsepower is certainly
inappropriately low.
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C. 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 absorp-
tion. The vehicle used was a Ford LTD which was tested at the appropri-
ate weight category to represent the Mercury Marquis. This vehicle was
used because it is a full sized Ford vehicle, as is the Marquis, and it
was available at the EPA laboratory. The data from the Certification
Division tests are given in Appendix C. 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 regression
statistics indicate there is little confidence that the slopes of the HC
and CO regression lines are different from zero. Therefore 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 emissions data, together with the regression
lines are plotted in Figures 2 and 3.
The plots of the data demonstrate the strong dependence of the vehicle
fuel economy on the dynamometer power absorption. The statistical
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 dyna-
mometer power absorption.
The regression lines can be used to predict the effect on NOx emissions
and fuel economy if vehicles had been tested at the higher, more repre-
sentative, dynamometer power absorptions. When predicting this effect
it should be noted that Mercury Marquis were not selected as EPA exhaust
emissions certification vehicles. Because of the extreme low road load
requested for these vehicles the test vehicles selected to represent the
Mercury engine family categories were Ford LTDs. If the more representative
power absorption of 11.4 horsepower had been requested for the Marquis,
these vehicles would presumably have been selected. The alternate
dynamometer adjustment requested for the LTD was 9.5 horsepower. The
discrepancy in the dynamometer adjustment for the vehicle during the
applicable emissions tests was therefore 9.5 horsepower versus 11.4 for
vehicles without air conditioning and 10.5 versus 12.5 horsepower for
air conditioned vehicles. The predicted increase in NOx emissions would
be approximately 0.05 gm/mi for both of the two cases.
Including the predicted NOx increase of 0.05 gm/mi most of the certification
vehicles tested to represent the Mercury Marquis would still have met
the NOx standard. There was, however, one which would have equaled the
2.0 gm/mi standard but would have been certified because of round-off
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Vehicle Fuel Economy
versus
Dynamometer Power Absorption
TEST VEHICLE: Ford LTD 8A1-351W-F-64
INERTIA WEIGHT CATEGORY: 5000 pounds
n)
60
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24
23 f
22
21
20 .
19 -
18 '
17 .
16
15
Highway Fuel Economy
Regression Line
Urban Fuel Economy
Regression Line
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6 7 8 9 10 11 12 13 14 15 16
Dynamometer Power Absorption (horsepower)
Figure 2
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Nitrogen Oxide Emissions
versus
Dynamometer Power Absorption
TEST VEHICLE: Ford LTD 8A1-351W-F-64
INERTIA WEIGHT CATEGORY: 5000 pounds
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tolerances. It should be noted that this analysis strongly depends on
the slope of the NOx versus dynamometer power absorption regression,
shown in Figure 3. 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 representative dynamometer
power absorption cannot be accurately predicted.
The Mercury Marquis was tested as a fuel economy vehicle. Therefore, in
this case the horsepower discrepancy between the dynamometer power
absorption during the test and a representative value was 8.8 versus
11.4 horsepower for vehicles without air conditioning and 9.7 versus
12.5 horsepower for vehicle equipped with air conditioners. The pre-
dicted decrease in fuel economy would be 0.24 and 0.26 mi/gallon respectively
for the urban cycle. The predicted highway fuel economy decrease would
be 1.5 and 1.6 mi/gallon respectively. The composite urban-highway fuel
economy would be expected to decrease approximately 0.6 mi/gallon, or
about 3 percent for vehicle 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.
Conclusions
It is concluded that the EPA tests of the Ford Mercury Marquis were
unrepresentative because:
1. The dynamometer adjustment requested by Ford was inappropriate
for the road data submitted by Ford;
2. The road data submitted by Ford is unrepresentative of anticipated
consumer use of the vehicle because the tire pressures used during
these road tests were significantly higher than the tire pressures
used during the dealer preparation of the vehicle for consumer use.
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 Mercury Marquis would still
be expected to meet the exhaust emission standards if these vehicles were
tested at the higher, more representative dynamometer power absorption.
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 Mercury Marquis.
This increase could effect the 1978 Ford Corporate Average Fuel Economy.
C. Larson, discussion, February 1977.
2
J.D. Murrell, discussion, February 1977.
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APPENDIX A
EPA Report of July 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 time of
the test vehicle on the dynamometer, when the dynamometer is adjusted to
the requested power setting, versus the road coast down times reported
for the vehicle by the manufacturer. While this procedure 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.
The Ford Mercury Marquis was selected for such a "quick check"
since the alternate dynamometer adjustment requested by the manufac-
turer, 8.8 horsepower, was considered unusually low. This requested
alternate power adjustment is 4.6 horsepower below the 13.4 horsepower
specified by the current Federal Register table and 4.2 horsepower below
the results of EPA measurements on a 1975 Mercury Marquis. This report
concludes that the requested dynamometer power adjustement of 8.8 horse-
power, when used in conjunction with the certification test vehicle,
does not accurately reflect the road experience of the Mercury Marquis,
as reported by Ford.
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Background:
Concern about the EPA fuel economy measurements has focused g'reater
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 Mercury Marquis was selected for such a "quick check"
since the alternate dynamometer adjustment requested by the manufac-
turer, 8.8 horsepower, was considered unusually low. This requested
alternate power adjustment is 4.6 horsepower below the 13.4 horsepower
specified for this 5000 pound vehicle in the current Federal Register
table. This larga^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 measurements on a 1975 Mercury Marquis estimated the appropriate
dynamometer adjustment to be 13.0 horsepower. In response to requests
for reference frontal area information, Ford submitted the same area data,
26 square feet, for both the 1975 and the 1978 model. It is therefore
concluded that no significant reduction in the size of the Mercury Marquis
has occurred between 1975 and 1978. Using the submitted frontal area data,
the proposed road load equation for 1979 model year predicts a dynamo-
meter adjustment of 13.0 horsepower for this vehicle.
It was originally intended to coast the Mercury Marquis from 55 to
45 mph immediately following the highway fuel economy test. In this
manner -the highway schedule would be used as the vehicle warm-up, and
the actual test horsepower adjustment would be confirmed versus the road
measurements. Unfortunately this could not be arranged because of
scheduling problems. At the time the test could be scheduled, the
vehicle was placed on the dynamometer and warmed up for approximately 30
minutes. Coast downs, from 55 mph to 45 mph were then performed for
four horsepower settings. The total dynamometer absorbed power; the
indicated dynamometer absorbed power and the coast down times are given
in Table 1.
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Table 1
Dynamometer No. 1, 7/9/77
Total Dynamometer Indicated Dynamometer Coast Down
Power at 50 mph . Power at 50 mpn" Time Interval
(horsepower) (horsepower) (sec)
8,8 6.2 19.2
8.8 6.1 19.4
9.8 7.0 18.5
9.8 7.0 18.5
10.8 8.0 17.5
10.8 8.0 17.6
11.8 9.0 16.7
11.8 9.0 16.8
The coast down times are plotted against total dynamometer power at
50 mph in Figure 1. A "reasonable" fit line is also drawn in Figure 1.
Ford reported a road coast down Lime of 15.8 seconds for the road test.
After correction to standard ambient conditions and adjustment to the
dynamometer simulated inertia weight Ford calculated the target dynamo-
meter coast down time to be 16.98 seconds. The dynamometer power
adjustment corresponding to this dynamometer coast down time was re-
ported to be 8.8 forsepower. A verticle line corresponding to 17
seconds is shown on Figure 1. This line intersects the curve at 11.5
horsepox^er.
The Ford representative was asked by Certification Division person-
nel for his explanation of this 2.7 horsepower difference. The response
attributed the difference to variations in the vehicle warm-up procedure
on the dynamometer. The EPA procedure recommends 30 minutes warm-up at
50 mph while the Ford procedure calls for 30 minutes warm-up with the
speeds slowly varying between 70 mph and 40 mph. While it seemed very
unlikely this minor variation in warm-up procedure would cause a 2.7
horsepower difference, it was decided to re-run the dynamometer coast
downs on the vehicle utilizing the Ford method of preconditioning.
The results of these coast downs are given in Table 2 and are
plotted in Figure 2. In this instance the dynamometer adjustment
corresponding to a 17 second coast down is 9.9 horsepower.
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DYNAMOMETER NO. 1
7/9/77
VEHICLE FUEL TANK NEARLY EMPTY
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11.5
15
16 17 18
COAST DOM TIME (SEC)
19
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FIGURE 1
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DYNAMOMETER NO. 6
7/16/77
VEHICLE FUEL TANK FULL
15
16 17 18
COAST DOWN TIME (SEC)
FIGURE 2
19
20
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Table 2
Dynamometer No. 6, 7/16/77
Total Dynamometer Indicated Dynamometer Coast Down
Power at 50 mph Power at 50 mph Time Interval
(horsepower) (horsepower) (sec)
7.8 5.4 19.0
7.8 5.4 19.0
8.8 6.4 17.9
8.8 6.4 18.1
9.8 7.3 17.2
9.8 7.3 17.1
10.8 8.3 16.2
10.8 8.3 16.1
11.8 9.3 15.2
11.8 9.3 15.3
10.0 7.5 16.8
10.0 7.5 16.8
Since this power adjustment is significantly different from the
previous results of 11.5 horsepower, efforts were made to resolve this
1.7 horsepower discrepancy. Three parameters were identified which had
changed between the two measurements; the warm-up procedure, the test
dynamometer and the quantity of fuel in the vehicle tank. It was con-
sidered improbable that either the warm-up procedure or the difference
in the quanity of fuel in the vehicle tank could have this large an
effect. Therefore it was decided to investigate the possible effect
caused by the change in the test dynamometer. The first step was to
verify the previous results on the first dynamometer. However in this
case the fuel tank was filled to capacity and the Ford warm-up procedure
was used. These data are presented in Table 3 and plotted in Figure 3.
Table 3
Dynamometer No. 1, 7/16/77
Total Dynamometer Indicated Dynamometer Coast Down
Power at 50 mph Power at 50 mph Time Interval
(horsepower) (horsepower) (sec)
11.5 8.7 16.6
11.5 8.7 16.6
10.8 8.0 17.2
10.8 8.0 17.4
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DYNAMOMETER NO. 1
7/16/77
VEHICLE FUEL TANK FULL
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15
16 17 18
COAST DOWN TIME (SEC)
FIGURE 3
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The dynamometer adjustment obtained was 11.1 horsepower. While
similar to the previous results, there is a difference of 0.4 horse-
power. The most recent tests were conducted with a full tank of fuel,
while the first coast downs were conducted with a nearly empty fuel
tank. Checking the fuel records showed approximately 20 gallons, or
about 100 pounds of fuel, were added to the vehicle between tests. Tire
power consumption is very nearly proportional to the vertical load on
the tires, therefore this increase in load would increase tire losses
and therefore reduce the dynamometer power adjustment necessary to
achieve the same coast down time interval. The rear axle load on the
vehicle was measured to be 2040 pounds with a full tank of fuel.
Consequently the tire losses would be expected to be 5.3 percent greater
with the full tank of fuel than with an empty fuel tank. The submitted
Ford data gives a computed total corrected road power of 18.23 horse-
power. Therefore, if the dynamometer adjustment necessary to reproduce
the same coast down time was 11.5 total dynamometer horsepower, 6.7
horsepower was being dissipated in the vehicle tires. After the vehicle
fuel tank was filled, the tire power dissipation would be about 5.3
percent greater, or 0.34 additional horsepower. Therefore to maintain
the same total horsepower, the expected dynamometer adjustment would be
11.16 horsepower.
The dynamometer adjustments, after correction for differences in
the rear axle loads, are in very good agreement. The difference, 0.06
horsepower may be attributed to the differences in the vehicle warm-up
procedure or may simply be the limits of the test precision. In either
case it is not considered significant. This indicates the different
preconditioning methods did not produce the 2.7 horsepower difference as
suggested by Ford.
The difference between tests two and three, 1.2 horspoewer is
considered significant. This difference was attributed to the differ-
ences between the dynamometers. It was hypothesized that one of the two
dynamometers might yield an anomalous result, while all other EPA
dynamometers might be in good agreement. To test this hypothesis the
measurements were repeated on certification dynamometer No. 3. This
dynamometer gave an intermediate value of 10.5 horsepower for the same
coast down time. The data from these measurements are presented in
Table 4 and are plotted in Figure 4.
Table 4
Dynamometer No. 3, 7/18/77
Total Dynamometer Indicated Dynamometer Coast Down
Power at 50 mph Power at 50 mph Time Interval
(horsepower) (horsepower) (sec)
11.1 8.5 16.4
11.1 8.5 16.3
10.3 7.8 17.3
10.3 7.8 17.2
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—9—
DYNAMOMETER NO. 3
7/16/77
VEHICLE FUEL TANK FULL
12 -
w
:s
o
FU
W
en
Pi
O
o
P4
11
10.5
10,,
o
W
PQ
H
W
s
H
O
H
9,.
8.
-4-
15
16 17 18
COAST DOM TIME INTERVAL (SEC)
FIGURE 4
19
20
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-10-
The results of the test series are summarized in Figure 5 where all
measurements, conducted under similar vehicle conditions are plotted.
These measurements were conducted with the same test personnel, the same
instrumentation, the vehicle fuel tank was filled prior to each test and
the vehicle warm-up was the same in each instance. The dynamometer is
the only parameter known to vary between the tests. The range of the
observed variations, 1.2 horsepower, is within the range of dynamometer
variations reported in the recent EPA Technical Support Report "Compari-
son of Dynamometer Foxier Absorption Characteristics and Vehicle Road
Load Measurements." It is, however, unknown if this variation is the
extreme of the variations which might be observed since only dynamo-
meters No. 1, No. 3 and No. 6 were used.
The mean of the three EPA measurements conducted under similar
conditions is 10.5 horsepower. These measurements were conducted with
a full tank of fuel; however, EPA certification and fuel economy mea-
surements are conducted with the fuel tank 40 percent filled. Using the
weight method previously described, correcting to the situation of a 40
percent full fuel tank, the estimated mean dynamometer power is 10.7
horsepower. The difference between this result and the Ford result of
8.8 horsepower is definitely significant. If a dynamometer adjustment
of 8.8 horsepower is used for the certification vehicle, this will not
represent the road experience of the vehicle tested by Ford. It is also
very unlikely that a dynamometer adjustment of 8.8 horsepower would
represent the road experience of the certification vehicle.
It may be informative to speculate how Ford may have obtained a
dynamometer adjustment of 8.8 horsepower for their test vehicles. The
problem, in addition to the dynamometer to dynamometer variations is the
question of vehicle selection. The Ford test vehicle had reported axle
loads, when dynamometer tested, of 2722 and 2281 pounds front to rear
respectively. The axle loads measured at EPA for the Certification
vehicle were 2760 and 2040 respectively, with a full fuel tank. There
is the possibility of a difference in driver weights, and in the possi-
bility for scale inaccuracies, however the front/rear weight distribu-
tions are 54.4/45.6 for the Ford vehicle, but 57.5/42.5 for the certi-
fication vehicle.
It appears that about 250 pounds of ballast were added to the trunk
of.the Ford test vehicle in addition to a full fuel tank. The rear axle
load on the vehicle tested by Ford was about 300 pounds greater than
would be anticipated for the rear axle load of the certification vehicle
with a 40 percent full fuel tank. This would cause abnormally high tire
power dissipation and result in a reduction of the necessary dynamometer
power adjustment to match the road coast down time. In support of this
speculation, the data submitted by Ford includes an operator note that
one test sequence was aborted because of tire failure. Using the pre-
vious method for estimating the changes in the tire power dissipation
with changes in axle load, a 300 pound increase in the axle load would
decrease the dynamometer adjustment by about one horsepower. If such a
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-11-
COMPOSITE DYNAMOMETER MEASUREMENTS
7/16/77
VEHICLE FUEL TANK FULL
DYNAMOMETER NO. 1
DYNAMOMETER NO. 3
DYNAMOMETER NO. 6
15
16
17
18
19
20
FIGURE 5
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-12-
vehicle was coast down tested on a dynamometer which gave low power
absorption results, such as EPA dynamometer No. 6, a dynamometer adjust-
ment of about 8.8 horsepower could be expected.
The original EPA recommended practice for road load determination
did recommend ballasting the vehicle to match the dynamometer simulated
inertia weight. The current, revised version, does not recommend bal-
lasting, and requires the front/rear axle weight distribution of the
test vehicles to agree within +_ 2% to the certification vehicle. It is
assumed that Ford is well aware of the effects which result from changes
in rear axle loads since the Ford coast down procedure calls for the
dynamometer tests to be conducted with vehicle engine operating from an
auxiliary fuel tank.
Conclusions:
1) A dynamometer adjustment of 8.8 horsepower, as requested by
Ford, does not result in an accurate dynamometer simulation of the road
experience of the vehicle tested by Ford when the certification vehicle
is operated on the dynamometer.
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.
2) The requested alternate dynamometer adjustments of other Ford
vehicles should be examined more thoroughly. These vehicles should be
tested if any anomolies seem apparent.
3) The apparent 1.2 horsepower difference between dynamometers
needs to be resolved. Some of this variation may be attributed to the
differences in dynamometer calibration while some may be caused by para-
meters not currently considered in this dynamometer calibration process.
Dynamometer to dynamometer calibration differences are currently be-
lieved to have a range of about 0.6 horsepower. Examples of parameters
which are not currently considered are the vehicle restraint, the dif-
ferences in dynamometer rear roll bearings and changes in roll bearing
• friction when under vehicle supporting loads. In any case, it should be
noted that the range of the dynamometer adjustment specified in"the
current Federal Register is only 6.2 horsepower. If there are dynamo-
meter to dynamometer differences of 1.2 horsepower in the simulation of
-------
-13-
the vehicle road load, this is almost 20% of the range of this para-
meter. The simulation of the vehicle road load is possibly the most
important parameter, with respect to composite fuel economy, in the EPA
simulation of the vehicle road experience. Clearly such a large random
effect in this parameter is undesirable.
-------
APPENDIX B
-------
Table B-l
Ford Submitted Data for Confirmation of
Alternate Dynamometer Power Absorption Request
November, 1977
VEHICLE: 1978 Mercury 4-Door Sedans -
INERTIA WEIGHT CLASS: 5000 pounds
ROAD TIRE PRESSURE: Front-30 psi; Rear-32 psi
DYNO TIRE PRESSURE: Rear-45 psi
Vehicle
Number
313-T-823
313-T-823
313-T-825
313-T-825
313-T-826
313-T-826
313-T-823
313-T-823
313-T-825
313-T-825
313-T-826
313-T-826
Corrected
Coastdown
Time
(sec)
16.79
17.09
16.98
(70-20)
17.04
16.43
(70-20)
16.00
(70-20)
16.79
17.09
16.98
(70-20)
17.04
16.43
(70-20)
16.00
(70-20)
Dynamometer
Cell
Number
2
2
2
2
2
2
6
6
6
6
6
6
Total
Dynamometer
Power
(horsepower)
9.88
9.85
9.72
10.06
10.24
10.95
11.10
11.09
11.04
11.05
11.22
11.86
AVERAGE
16.72
10.67
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Table B-2
EPA Dynamometer Coastdown Data
Mercury Marquis (TRC Rental Vehicle)
Nominal
Actual
Power (Hp)
12.95
11.95
10.90
9.85
7.75
6.75
Dyno
15.25
15.93
16.93
17.76
20.17
21.58
Mean Coastdown Time
(sec)
//I Dyno #2 Dyno #3
15.42
16.28
16.98
17.98
20.37
21.73
14.66
15.61
16.22
17.31
19.49
20.96
Dyno #4
—
15.87
16.61
17.70
19.81
21.14
Average Coastdowi
Time for All Dym
(seconds)
15.11
15.92
16.69
17.69
19.96
21.35
-------
APPENDIX C
Effects of Dynamometer Power Absorption
-------
Table C-l
Vehicle Emissions and Urban Fuel Economy
versus
Dynamometer Power Absorption
Dynamometer
Power Absorption
(HP)
Carbon Nitrogen Carbon
Hydrocarbons Monoxide Oxides Dioxide
(gm/mi) (gm/mi) (gm/mi) (gm/mi)
Urban
Fuel Economy
(mi/gal)
6.3
9.5
9.5
12.7
12.7
15.9
0.75
0.82
0.90
0.73
0.75
0.81
10.5
12.0
13.7
11.0
11.0
11.1
1.85
1.65
1.50
1.83
1.65
2.00
552
552
566
579
577
583
15.5
15.5
15.0
14.8
14.9
14.7
TEST VEHICLE: Ford LTD 8A1-351W-F-64
INERTIA WEIGHT CATEGORY: 5000 pounds
-------
Table C-2
Highway Fuel Economy
versus
Dynamometer Power Absorption
Dynamometer Highway Fuel
Power Absorpton 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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