EPA-AA-TEB-80-14
Emissions and Fuel Economy of a Cadillac Prototype
with Modulated Displacement Engine.
by
Edward Anthony Barth
April 1980
Test and Evaluation Branch
Emission Control Technology Division
Office of Mobile Source Air Pollution Control
Environmental Protection Agency
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Background
The Environmental Protection Agency receives information about many
systems which appear to offer potential for emission reduction or fuel
economy improvement compared to conventional engines and vehicles.
EPA's Emission Control Technology Division is interested in evaluating
all such systems, because of the obvious benefits to the Nation from the
identification of systems that can reduce emissions, improve fuel economy
or both. EPA invites developers of such systems to provide complete
technical data on the system's principle of operation, together with
available test data on the system. In those cases for which review by
EPA technical staff suggests that the data available shows promise,
confirmatory tests are run at the EPA Motor Vehicle Emission Laboratory
at Ann Arbor, Michigan. The results of all such test projects are set
forth in a series of Test and Evaluation Reports, of which this report
is one.
The deactivation of one or more engine cylinders is a method that has
been proposed as offering potential for vehicle fuel economy improvements.
At low power output, the throttle is nearly closed. This introduces a
throttling loss which is the energy the engine must expend to draw the
fuel/air mixture through the carburetor throttle opening. By operating
an engine on a reduced number of cylinders and operating these cylinders
at higher power levels, the throttling losses are appreciably reduced.
The operating cylinders are therefore run at a high brake-mean-effective
pressure (BMEP) and therefore potentially more efficiently.
A cylinder deactivation system is being considered for use in several
1981 Cadillac models. Other cylinder deactivation systems are currently
under development in the United States. Because EPA had not recently
tested a cylinder deactivation system designed for current vehicles, EPA
contacted the Cadillac Motor Division of GM and requested the loan of a
vehicle with a cylinder deactivation system installed. Cadillac made
available a system installed in a prototype vehicle.
EPA is also testing other cylinder deactivation systems. A similar
system was tested in a demonstration vehicle provided by Eaton. The
results of these tests are reported in TEB report #80-16 "Emissions and
Fuel Economy of the Eaton Valve Selector." An aftermarket retrofit
system was tested in several 1979 V-8 vehicles. The results of these
tests are reported in a TEB report #80-18, "Emissions and Fuel Economy
of the Automotive Cylinder Deactivation System (ACDS)." Six years ago,
EPA also tested a vehicle with 4 cylinders deactivated. The results of
that test are given in TAEB report #75-11, "Evaluation of the MSU 4
Cylinder Conversion Technique for V-8 Engines".
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The conclusions drawn from the EPA evaluation tests are necessarily of
limited applicability. A complete evaluation of the effectiveness of an
emission control system in achieving performance improvements on the
many different types of vehicles that are in actual use requires a much
larger sample of test vehicles than is economically feasible in the
evaluation test projects conducted by EPA. The conclusions from the EPA
evaluation test can be considered to be quantitatively valid only for
the specific test cars used; however, it is reasonable to extrapolate
the results from the EPA test to other types of vehicles in a directional
manner, i.e. to suggest that similar results are likely to be achieved
on other types of vehicles.
Description
The test vehicle had an Eaton Valve Selector system installed. This is
a valve deactivstion system being developed by the Eaton Corporation for
installation by the vehicle manufacturer. The concept is to improve
vehicle fuel economy by selectively shutting off engine cylinders during
periods of light engine loads. The cylinders are deactivated by a mechanical
system that unloads the intake and exhaust valve rocker arm fulcrum
points. A more detailed description of the Eaton Valve Selector is
given in the appendix.
In this application, the valve selector is integrated into the total
vehicle/engine package. Engine rpm, water temperature, throttle angle,
manifold vacuum and transmission gearing are monitored by a set of
sensors. This information is fed into an electronic control unit.
Based on this information and programmed instructions, the number of
operating cylinders is determined and appropriate signals are sent to
the valve selector.
Test Vehicle Description
The test vehicle was a 1979 Cadillac Coupe. De Ville that had a 6.0 liter
Cadillac engine installed to replace the stock 7.0 liter engine.
Cadillac had installed the Eaton Valve Selector system on this engine.
This installation included the electromechanical valve selector, electronic
control unit, engine sensors and a modified camshaft. The engine sensors
interfacing with the electronic control unit included rpm, water temperature,
throttle angle, manifold vacuum and transmission gear. The vehicle had
a single point, throttle body, digital, electronic fuel injection
system. A closed loop emission control system was used. Additional
vehicle details are given in the appendix.
Test Procedures
Exhaust emission tests were conducted according to the 1977 Federal Test
Procedure (FTP) described in the Federal Register of June 28, 1977 and
the EPA Highway Fuel Economy Test (HFET) described in the Federal Register
of September 10, 1976. The vehicle was not tested for evaporative
emissions.
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The selection of cylinder deactivation modes was accomplished by the
vehicle operator sequencing the control logic after starting the vehicle.
It required 15 to 20 seconds to perform this task. Since the control
logic always resets to the 8 cylinder mode when turned off, it was
necessary to reset the control logic for bag 1 (cold start) and bag 3
(hot start) of FTP for the 4 cylinder and automatic modes. Therefore,
30 seconds of idle time was added to bag 1 and bag 3 of the FTP. For
comparability 30 seconds of idle was added to all FTP's including the
eight cylinder mode.
Additional tests were conducted as an evaluation tool. These consisted
of steady state emission tests and acceleration tests.
Discussion of Results
The objective of this test program was to further evaluate the potential
fuel economy benefits of cylinder deactivation and to determine the
effects on vehicle emissions. These test results are summarized in the
tables and figures in the following paragraphs. Additional tabulations
of the data are given in the appendix.
1. Federal Test Procedure
The results are given in Table 1 below. The operation of this
vehicle on 4 cylinders instead of 8 cylinders caused HC and CO
emissions to increase, NOx to decrease, and fuel economy to increase.
Operation of this vehicle in the automatic mode caused little
change in either HC emissions or fuel economy and caused reductions
in CO and NOx emissions.
Table 1
Cadillac Modulated Displacement Prototype Vehicle
FTP Mass Emissions
(grams per mile)
Test Number HC CO O>2 NOx MPG
8 cylinder (baseline)
80-1997 .33 2.86 744 1.36 11.8
80-2001 .34 3.46 745 1.55 11.8
4 Cylinder
80-2003 .85 38.71 602 1.55 13.3
80-2007 1.31 72.27 605 1.16 12.3
80-2334 .92 38.60 586 1.20 13.7
Automatic Selection
80-2009 .32 2.05 718 1.31 12.3
80-2271 .29 2.75 763 1.32 11.5
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2.
In the 8 cylinder mode the vehicle's NOx emissions did exceed the 1981
emission standards of 0.41 gm/mi HC, 3.4 gm/mi CO and 1.0 gm/mi
NOx. Fuel economy was 11.8 mpg. Vehicle-driveability was good.
In the 4 cylinder mode there were significant changes in emissions
and fuel economy compared with operation on 8 cylinders. HC emissions
increased by a factor of 3 tc 1.03 gm/mi, CO increased by a factor
of 15.8 to 49.86 gm/mi (There was considerable variability in CO
emissions results.), and NOx decreased 10%. Fuel economy increased
11%. HC, CO and NOx emissions all exceeded the 1981 emission
standards. Vehicle driveability was poor. There was stretchiness
(a lack of response to accelerator pedal movement), insufficient
power to follow most acceleration rates, engine lag (delay in
response to pedal movement), and many more transmission shifts than
normal.
In the automatic mode HC emissions were not significantly changed
from operation with 8 cylinders. CO decreased 24% and NOx decreased
10%. Fuel economy was not significantly changed. NOx emissions
again exceeded the 1981 emission standards. Vehicle driveability
was good.
Highway Fuel Economy Test
Overall, the vehicle had the least emissions in the automatic
cylinder deactivation mode. Fuel Economy was best in the 4 cylinder
mode. These results are given in Table II below.
Table II
Cadillac Modulated Displacement Prototype Vehicle
HFET Emissions
Test Number
8 Cylinder (baseline)
80-1998
80-2002
HC
.06
.06
CO
.33
.29
466
463
NOx
1.89
2.30
MPG
19.0
19.1
4 Cylinder
80-2004
80-2008
80-2335
.19
.21
.23
15.41
17.83
21.56
371
380
383
2.01
1.94
1.35
22.4
21.7
21.2
Automatic
80-2010
80-2014
80-2264
80-2272
.04
.04
.04
.04
.18
.07
.09
.08
451
448
449
458
.98
1.05
.95
1.01
19.6
19.8
19.7
19.4
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In the eight cylinder mode, the vehicle's average emissions were
0.06 gm/mi HC, 0.32 gm/mi CO, and 2.10 gin/mi NOx. Fuel economy was
19.0 gm/mi. Drivesbility was good.
In the 4 cylinder mode there were again significant changes in
emissions and fuel economy from operation on 8 cylinders. HC
emissions tripled to 0.21 gm/mi, CO emissions increased by a
factor of 57 to 18.27 gm/mi, and NOx emissions decreased 15%. Fuel
economy increased 14%. The same driveability problems encountered
in the 4 cylinder, FTP tests were observed. Namely, there was
stretchiness, lack of power for acceleration, engine lag and more
transmission shifts than normal.
In the automatic mode, HC emissions were reduced 33%, CO emissions
were reduced 67%, and NOx emissions decreased 52% when compared to
8 cylinder operation. Fuel economy increased by approximately 3%.
3. Steady State Tests
Overall, the operation of the vehicle on a reduced number of cylinders
caused mixed effects on emissions. HC and CO emissions were quite
low in all modes for most speeds and relatively unaffected by the
number of cylinders in operation. NOx emissions tended to remain
unchanged as the number of operating cylinders increased. However,
when operating on 8 cylinders, NOx emissions increased markedly at
45 mph and, when operating on 4 cylinders, NOx emissions increased
markedly at 55 mph.
Compared to the 8 cylinder mode, fuel economy showed a 6 to 33%
improvement when the vehicle was operated with 4 cylinders. Similarly
when compared to the 8 cylinder mode, fuel economy showed a 0 to
18% improvement when the vehicle was operated in the automatic
mode. The 4 cylinder and automatic modes showed similar emission
and fuel economy results at 35 and 45 mph but differed at 55 mph.
This was expected because in the automatic mode, the vehicle would
probably select 4 cylinders for the light engine loads imposed at
35 and 45 mph, but switch to either 6 or 8 cylinders for the moderate
engine loads imposed at 55 mph.
The results are tabulated in Table IV in the Appendix. The fuel
economy results are plotted in Figure 1 on the following page.
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15
TETROV STHTE: F-UETL.
i UL.R-C: MQI>UI_F»TE:C> r> i
i N
Automatic Mode
El 4 Cylinder Mode
A 8 Cylinder Mode (.Baseline)
15
2S
VEH
Figure 1
4. Discussion of results
When this test vehicle was operated with a reduced number of
cylinders, FTP fuel economy increased up to 11%. HFET fuel economy
increased between 3 and 14%. However, the benefits in the automatic
mode, the most probable mode the vehicles would have when marketed,
was minimal. This trend is in agreement with information supplied
by Cadillac personnel. They had said the fuel economy benefits for
the FTP and HFET cycles would be no more than 5%.
The greatest fuel economy benefits for the modulated displacement
test vehicle occurred during steady state tests. Fuel economy
increases ranged from 0 to 33% during these steady state tests. To
achieve these benefits in actual vehicle driving would require a
very steady vehicle speed. Therefore, the larger fuel economy
benefits of the system would probably only occur when the vehicle
was operated on level roads with a cruise control.
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5. Acceleration Tests
At the conclusion of the emission tests, acceleration tests were
performed on the vehicle using a chassis dynamometer. To minimize
tire slippage, the chassis dynamometer's front and rear rolls were
coupled together for this test. The results are summarized below
in Table V. Complete results are given in the appendix.
Table III
Cadillac Modulated Displacement Prototype Vehicle
Average Acceleration Times
seconds
Speeds
0-25
0-35
0-45
0-55
8 Cylinder
4.3
6.6
9.4
13.2
6 Cylinder
6.3
9.4
13.3
18.4
4 Cylinder
11.4
17.0
23.6
34.0
Note: These acceleration tests were not necessarily conducted at
wide open throttle. During the course of testing, it became evident
that under some operating conditions, the vehicle would accelerate
best at part throttle. These acceleration tests were conducted for
best acceleration.
Conclusions
The vehicle did not meet the 1981 NOx standards cf 1.0 gram/mile when
tested in the 8 cylinder mode. FTP emissions were .34 gm/mi HC, 3.16
gm/mi CO and 1.46 gm/mi NOx. Fuel economy for the FTP was 11.8 mpg and
for the HFET it was 19.0 mpg.
In the 4 cylinder mode, the Modulated Displacement vehicle showed a
sharp increase in emissions over 8 cylinder emission levels. HC in-
creased by a factor of 3, CO increased by a factor of 15.8, and NOx
decreased 10%. Fuel economy increased 11% for the FTP and 14% for the
HFET. The vehicle did not meet the 1981 emission standards for HC, CO
or NOx.
In the automatic mode, the Modulated Displacement vehicle, except for a
CO reduction, showed little change in emissions from 8 cylinder emission
levels. HC was unchanged, CO decreased 24%, and NOx decreased 10%. FTP
fuel economy was essentially unchanged. HFET fuel economy increased by
approximately 3%.
The vehicle was unable to follow the FTP and HFET driving schedules in
the 4 cylinder mode. Vehicle driveability was acceptable in the 8
cylinder and automatic modes for both the FTP and HFET.
The largest fuel economy benefits for the modulated displacement vehicle
will probably only be achieved when the vehicle is operated at constant
speeds by the vehicle's cruise control unit.
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Test Vehicle Description
Chassis model year/make - 1979 Cadillac Coupe DeVille
Vehicle I.D. 6D47T99140709
Emission Control System - Prototype Cadillac with modulated
displacement engine
Engine
type Otto Spark, OHV, V-8
special features .... Eaton valve selectors installed on 4 cylinders
bore x stroke 96.0 x 103.0 mm/3.78 x 4.06 in.
displacement 6.0 liter/368 CID
compression ratio ... 8.2:1
maximum power @ rpm . . 145 horsepower/108kW
fuel metering Rochester, single point, throttle body, digital, electronic
fuel injection
fuel requirement .... Unleaded, tested with Indolene HO
Drive Train
transmission type ... 3 speed automatic
final drive ratio. . . . 2.41
Chassis
type 2 door sedan
tire size P215-75R15
curb weight 4350
inertia weight ...... 4500
passenger capacity ... 6
Emission Control System
basic type air injection
dual bed catalyst
closed loop
EGR
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10
Eaton Valve Selector Description
Principle of Operation
"The conventional spark-ignition engine has its power output controlled
by a throttle. At low power output, the throttle is nearly closed in
order to limit the amount of fuel-air mixture drawn into the cylinder.
However, this small throttle opening introduces a "throttling loss",
which is the energy the engine must expend to draw fuel-air through the
throttle opening. Because of this, an engine runs most efficiently when
unthrottled.
"The unthrottled state can be approached by operating only the number of
cylinders needed to give the required power, and operating them at high
power-per-cylinder levels. In doing so, the throttle is at a wider
opening and there are fewer cylinders drawing air through that opening.
This reduces the vacuum in the intake manifold, thereby reducing the
throttling loss per cylinder. Also, there are fewer cylinders experiencing
throttling loss. This strategy is accomplished through use of the Eaton
Valve Selector. At low power levels, valve selectors deactivate the
valves on one or more of the cylinders; for full power output, they
restore valve operation.
"In each of the deactivated cylinders, the piston continues to reciprocate,
but the intake and exhaust valves are closed. Since the gases in the
cylinders are merely compressed and expanded by the piston, no energy is
consumed as pumping losses, although normal frictional losses are still
present. Furthermore, by closing both valves the cylinders are not
cooled by the flow of air and, consequently, there is no hesitation in
firing once the valves are reactivated."*
Eaton Valve Selector Hardware
To deactivate the cylinders Eaton has developed a mechanical system to
unload the intake and exhaust valve rocker arm fulcrum points. The
system is shown in Figures 2 and 3 and described below.
"On the conventional overhead valve pushrod configuration, the selector
is mounted on the intake and exhaust valve rocker arm studs, above the
rocker arm fulcrums. In the enabled mode, as shown in Figure 2, the
selector body is restrained from moving upward by contact between
projections on the body and the blocking plate above it. The fulcrum is
held down by the body and the valves operate normally.
"When the selector is energized (to deactivate the valves) as shown in
Figure 3, the blocking plate is rotated by the solenoid to align windows
in the blocking plate with the projections on the body. As the rocker
arm is lifted by the pushrod, the fulcrum rides up the stud and lifts
the body, since the body is no longer restrained by the blocking plate.
The rocker arm pivots about the tip of the valve and the valve remains
closed.
* Eaton Corporation product literature, "Eaton Valve Selector - A Unique
System for Conserving Energy in Automotive Engines"
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11
BLOCKING PLATE
BODY PROJECTIONS
BODY
FULCRUM
Figure 2
Valve Enabled
Figure 3
Valve Deactivated
Eaton Valve Selector Mechanical Details
"The body is spring loaded downward, but is internally constrained to a
maximum downward position. This internal spring provides correct valve
gear action and ensures normal hydraulic lifter function when the valve
gear is in the deactivated mode.
"The solenoid force is less than that required to overcome blocking
plate/body friction when the valve is lifted. This prevents deactivation
of the valve while it is lifted, which would cause the valve to seat
abruptly.
"The valve selector has also been adopted to rocker shaft engines and
overhead cam/finger follower engines."*
"The four standard cylinders without the valve selector have zero valve
lash due to the action of the hydraulic lifters. The four cylinders
with the deactlvators must have a few thousandths of an inch (tenth of a
millimeter) hydraulic lifter clearance to permit the mechanism to function.
To compensate for these differences, the camshaft profile is modified
for the four cylinders with deactivators. This gives the valve selector
cylinders a camshaft lift profile that is equivalent to the standard
camshaft lift."
* Eaton Corporation product literature, "Eaton Valve Selector - A Unique
System for Conserving Energy in Automotive Engines"
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12
Table IV
Cadillac Modulated Displacement Prototype 1981 Vehicle
Steady State Emissions
(grains per mile)*
Test Number
8 Cylinder
80-1999
80-1999
80-2247
80-2000
80-2270
80-2000
80-2270
80-2000
80-2270
4 Cylinder
80-2005
80-2249
80-2006
80-2249
80-2006
80-2248
80-2006
80-2248
Automatic
80-2011
80-2011
80-2012
80-2012
80-2012
Vehicle Speed
(Baseline)
0 mph*
25 mph
25 mph
35 mph
35 mph
45 mph
45 mph
55 mph
55 mph
0 mph*
25 mph
35 mph
35 mph
45 mph
45 mph
55 mph
55 mph
0 mph*
25 mph
35 mph .
45 mph
55 mph
HC
2.23
.79
.06
.09
.06
.05
.05
.05
.06
.79
.05
.07
.05
.04
.04
.03
.03
.93
.07
.08
.04
.02
CO
6.70
.01
.04
.00
.00
.00
.00
.00
.00
2.87
.03
.00
.00
.00
.00
.02
.00
.00
.00
.02
.00
.00
CO,
5834
373
372
356
354
371
368
451
455
4218
280
300
290
352
345
367
372
6972
374
301
348
459
NOx
1.40
.41
.30
.78
.61
1.56
1.41
.45
.44
3.82
.78
.59
.55
.64
.29
2.07
1.30
2.85
.33
.57
.60
.61
MPG
.67
23.8
23.8
24.9
25.0
23.9
24.1
19.6
19.5
.48
31.7
29.5
30.5
25.2
25.7
24.1
23.8
.77
23.7
29.5
25.5
19.3
* 0 mph (idle) mass emissions are given in grams per hour and fuel
economy is given in gallons per hour.
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13
Table V
Acceleration Tests on Prototype Modulated Displacement Cadillac
seconds
Speeds 8 Cylinder 6 Cylinder 4 Cylinder
run 1 run 2 run 1 run 2 run 1 run 2
0-5 mph
0-10 mph
0-15 mph
0-20 mph
0-25 mph
0-30 mph
0-35 mph
0-40 mph
0-45 mph
0-50 mph
0-55 mph
.8
1.5
2.3
3.2
4.3
5.4
6.6
7.9
9.4
11.4
13.2
.8
1.5
2.3
3.2
4.3
5.4
6.6
7.9
9.3
11.3
13.3
1.3
2.2
3.4
4.8
6.3
7.9
9.5
11.4
13.3
15.6
18.6
1.1
2.1
3.2
4.5
6.2
7.7
9.3
11.1
13.0
15.2
18.2
1.9
3.6
5.9
8.4
11.1
14.0
16.7
19.7
23.3
27.7
33.6
2.0
3.8
6.1
8.7
11.6
14.5
17.3
20.3
23.9
28.3
34.4
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