a five-speed starting clutch automatic transmission vehicle
TRANSCRIPT
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400 Commonwealth Drive, Warrendale, PA 15096-0001 U.S.A. Tel: (724) 776-4841 Fax: (724) 776-5760 Web: www.sae.or
SAE TECHNICAL
PAPER SERIES 2003-01-0248
A Five-Speed Starting Clutch Automatic
Transmission Vehicle
Chi-Kuan Kao, Anthony L. Smith and Patrick B. UsoroGeneral Motors Corp
Reprinted From: Transmission & Driveline Systems Symposium 2003(SP-1760)
2003 SAE World CongressDetroit, Michigan
March 3-6, 2003
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ABSTRACT
A wet multi-plate clutch, designated as the starting
clutch, is used to replace the torque converter in the
automatic transmission in order to improve vehicle fuel
economy. The transmission ratio spread must be
increased to compensate for the torque multiplication of
the torque converter and avoid penalizing the 0-60 mph
acceleration performance. The main challenge of thisconcept is the control of the starting clutch to ensure
acceptable vehicle drivability. This paper describes the
system of a five-speed starting clutch automatic
transmission vehicle and shows vehicle test results.
Vehicle test data show that (i) the fuel economy benefit of
the starting clutch is significant, and (ii) a starting clutch
transmission can be designed to equal or better the 0-60
mph acceleration performance of a torque converter
transmission by proper selection of the gear ratios.
INTRODUCTION
A torque converter is a hydro-mechanical device thatconnects the engine with the transmission in an
automatic transmission. The function of the torque
converter is to provide fast and smooth vehicle launch
through its torque multiplication and driveline torsional
damping capabilities. One major drawback of the torque
converter is its relatively lower efficiency over the operating
cycle. The torque converter efficiency can be improved by
controlling the torque converter slip with a torque converter
clutch (TCC) [1]. Further efficiency improvement can be
achieved by replacing the torque converter with a wet
clutch [2], designated as the starting clutch. The
torsional damper spring is retained for its primary function
of filtering engine-firing pulses when the clutch is locked.
A viscous converter clutch (VCC) [3] is also used in some
passenger cars to lockup torque converter clutch early
with viscous damping to improve fuel economy without
sacrificing drivability. A viscous converter clutch is a
torque converter clutch with a viscous damper located
between the torque converter clutch and turbine to improve
drivability by damping engine torque fluctuation when early
lockup the torque converter clutch [3]. Its drawback is that
it adds additional cost and it maintains a small slip even
when the torque converter clutch is locked.
The concept of using a starting clutch in automatic
transmissions is not new [2]. Borg-Warner used a starting
clutch for a 3-speed automatic transmission in 1949 [4]. In
the 1980s they put the starting clutch at the output of a
continuously variable transmission (CVT) as a start-up
and protective device [5]. The Borg-Warner starting clutch
with CVT design was successfully used in Suzukis
production vehicles with 1000cc and 1300cc engines [6]
Honda introduced a mass production starting clutch CVT
called Multi-Matic transmission for 1500cc engines [7].
Although there is currently no production discrete-step
transmission with a starting clutch, prospects for such a
transmission are not far fetched if wide-ratio-spread five
(or more-) speed automatic transmission can be designed
and torque-converter type of vibration-free drivability can be
achieved with intelligent starting clutch slip control as
explained below.
To improve vehicle fuel economy without sacrificing
vehicle acceleration performance and drivability when
replacing the torque converter with a starting clutch, the
following two issues must be addressed. First, the overalgear ratio spread must be increased to provide a deep
underdrive to emulate the torque multiplication of a torque
converter during launch and an overdrive to maintain fue
economy in highway driving. Since the overall gear ratio
has to be increased, to maintain small ratio steps for shif
quality, it is necessary to add an extra speed ratio to the
transmission; consequently, a 5-speed automatic
transmission is typically required. Second, the starting
clutch slip needs to be effectively controlled to achieve
smooth vehicle launch, good engine torsional isolation,
and fuel economy improvement. Thus, a well-synthesized
starting clutch control system is essential to the success
of the system.
In this paper, a GM passenger car equipped with a V6
3300 engine and a wide-ratio spread (6:1) experimental 5-
speed automatic transmission was used to evaluate
vehicle drivability and fuel economy improvement. Genera
issues such as cost, integration challenges, and
customer acceptance were outside the scope of this
work.
2003-01-0248
A Five-Speed Starting Clutch AutomaticTransmission Vehicle
Chi-Kuan Kao, Anthony L. Smith and Patrick B. UsoroGeneral Motors Corp
Copyright 2003 SAE International
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STARTING CLUTCH CONTROL ALGORITHM
The schematic of a starting clutch vehicle is shown in Fig.
1. The torque generated by the engine is transmitted
through the wet multi-plate starting clutch, the damper
spring, the transmission gearset, and the axle to the
vehicle. A damper spring is placed after the starting clutch
to provide filtering of engine torque disturbances such as
engine firing pulses when the starting clutch is locked.
This damper spring is similar to that of a production torqueconverter clutch.
Figure 1. Schematic of a Starting Clutch Vehicle
The starting clutch controller regulates the hydraulic
pressure on the starting clutch to allow smooth torque
transmission from the engine to the vehicle, and control
the slip between the engine and transmission for torsional
vibration isolation and improved fuel economy. The overall
transmission control block diagram is shown in Fig. 2.
Figure 2. Transmission Control Block Diagram for the
Starting Clutch Vehicle
The gearshift control algorithm can be found in [8, 9]. As
shown in Fig. 2, the starting clutch control system usesthe engine torque (Te), engine speed (
e ), starting clutch
speed (transmission input speed (t
)), throttle position
( ), and brake information to control the starting clutch
pressure (Psc). This information can also be used to
control engine spark timing and throttle. In this paper,
spark control and electronic throttle control were not used
to control the starting clutch.
VEHICLE IMPLEMENTATION AND RESULTS
The starting clutch control algorithm was implemented in
a GM passenger car with a V6 3.3L PFI engine and a five
speed wide-ratio spread (6:1) experimental transmission.
A starting clutch with a damper spring was used to
replace the torque converter. The stick diagram of the
automatic transmission is shown in Fig.3.
The starting clutch and the damper spring fit in the torqueconverter compartment. A 32-bit microprocessor is used
to control the transmission with a 5 msec loop time. The
control software was written in MODULA-GM and
extensive instrumentation was employed in the vehicle to
measure engine, starting clutch, and transmission
speeds, axle torque, pressures internal to the
transmission, brake signal, gas pedal and throttle
positions so that the transmission control system could
be debugged, tested and verified. A linear solenoid valve
was used to control the starting clutch pressure.
Figure 3. Stick Diagram of the Experimental Five-Speed
Starting Clutch Automatic Transmission
Two different baseline transmissions were available fo
installation in the same vehicle for comparison. One was
the 3T40 three-speed production transmission with torque
converter clutch (TCC), and the other was a five-speed
5.5:1 ratio spread experimental transmission equipped
with a viscous converter clutch (VCC) [3] to enable early
clutch apply. Ratio comparisons for the vehicles equipped
with the three transmissions are listed in Table 1.
VEHICLE TEST RESULTS
The fuel economy, wide-open-throttle (WOT) acceleration
performance, and part-throttle launch drivability of the
starting clutch vehicle in comparison with torque converter
vehicles are discussed in this section.
INPUT
OUTPUT
F1
CB5
CBRC345
C123
CREV
CB24
ST. CL.
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Table 1. Ratio Comparisons for the Starting Clutch and
Torque Converter Vehicles
3-Speed
with TCC
5-Speed with
VCC
5-Speed with
Starting Clutch
Gear
Ratio
N/V Gear
Ratio
N/V Gear
Ratio
N/V
1 2.84 95 2.667 162 2.909 177
2 1.6 53 1.556 95 1.636 100
3 1 33 1 61 1 61
4 - - 0.667 41 0.667 41
5 - - 0.485 30 0.485 30
Chain
Ratio
0.84 1.53 1.53
Fuel economy
The fuel economy tests were performed at the GM
Powertrain Warren West Emissions Laboratory using thesame vehicle, engine, driver, dynamometer, and
preparation procedures during a one-week test period to
ensure consistent and reliable results. Three
transmissions were installed in the same vehicle, one at a
time, for the tests. These include (i) a three-speed 3T40
(THM 125C) production transmission, (ii) a five-speed
experimental transmission with viscous converter clutch
using very aggressive fuel economy shift schedule, with
very early viscous converter clutch engagement starting in
second gear at 9 mph for zero throttle, and (iii) the starting
clutch automatic transmission. The fuel economy
improvements of the starting clutch equipped vehicle over
the other two baseline vehicles are listed in Table 2.
The table lists fuel consumption during the EPA II hot city
and highway cycles, and the 55/45 combined cycles. This
data shows that the starting clutch transmission provides
fuel economy improvements of 11.4% over the three-
speed 3T40 production transmission and 7.2% over the 5-
speed experimental transmission with viscous converter
clutch for the combined 55/45 EPA cycles. These results
are consistent with simulation predictions and
expectations.
Launch Performance
Figure 4 shows a comparison of the vehicle acceleration
versus time traces during a wide-open-throttle (WOT)
launch for the starting clutch vehicle and a production
3T40 torque converter vehicle. This data shows that the
peak vehicle acceleration for the torque converter vehicle
reaches 0.56 g because of the torque multiplication from
the torque converter and starts to decrease when the
torque converter approaches the coupling mode where
there is no torque multiplication. The peak vehicle
acceleration for the starting clutch vehicle reaches 0.54 g;
this high acceleration is maintained because of the high
N/V (engine speed in rpm over vehicle speed in mph) ratio
in first gear (Table 1).
The 0-60 mph time comparison of these vehicles and the
5-speed VCC experimental vehicle is presented in Table
3. This data shows that the starting clutch 0-60 mph
performance is better than the production 3T40
transmission vehicle because of the increased ratio
spread (Table 1) and slightly worse than the 5-speed VCC
experimental transmission vehicle because of the highfirst gear N/V along with the torque converter. Clearly, a
starting clutch transmission can be designed to equal or
exceed the 0-60 mph performance of a torque converter
transmission by proper selection of gear ratios.
Table 2. Vehicle Fuel Economy Comparison
Vehicle (Avg.)
MPG
(Avg.)
% Impr.
(Avg.)
% Impr.
3-Speed
with TCC
Trans.
Hot City MPG
Hwy MPG
Comb. 55/45
20.24
33.18
24.55
Base
Line
5-Speed
with VCC
Trans.
HotCity MPG
Hwy MPG
Comb. 55/45
21.12
34.21
25.51
4.3%
3.1%
3.9%
Base
Line
5-Speed
Starting
Clutch
Trans.
HotCity MPG
Hwy MPG
Comb. 55/45
23.00
35.58
27.35
13.6%
7.2%
11.4%
8.9%
4.0%
7.2%
.
Figure 4. Comparison of Wide Open Throttle Vehicle
Launches
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Table 3. Vehicle 0 - 60 mph Performance Comparison
Transmission (Avg.)
Seconds
3-Speed (3T40) Production Trans. 10.54
5-Speed with VCC 8.88
5-Speed Starting Clutch Trans. 9.27
Figure 5 compares the 30% throttle vehicle launch for the
starting clutch and the production 3T40 vehicles. The
starting clutch vehicle has a very smooth launch, but with
a lower peak acceleration than the production vehicle.
The higher peak acceleration for the production vehicle is
due to the effects of the torque converter. Notice that while
the acceleration of the torque converter equipped vehicle
decays from the peak value, that of the starting clutch
equipped vehicle sustains a steady value.
This set of tests shows very good starting clutch vehicle
launch drivability achieved with the control strategy
developed in this project.
Figure 5. Comparison of 30% Throttle Vehicle Launches
SUMMARY
A starting clutch control algorithm was developed toachieve vehicle drivability that is comparable with that of a
torque converter equipped vehicle. The starting clutch
control system uses engine speed, starting clutch speed
(transmission input speed), throttle position, and brake
information to control the starting clutch pressure. The
control system was developed and implemented in a GM
passenger car. The vehicle had a 3300 V6 PFI engine and
a five-speed electronically controlled wide-ratio spread
(6:1) experimental transmission. Fuel economy tests were
performed at the GM Powertrain Warren West Emissions
Laboratory using the same vehicle with three different
transmissions: (1) 3T40 production 3-speed automatic
transmission, (2) experimental 5-speed automatic
transmission with a viscous converter clutch, and (3
experimental 5-speed automatic transmission with a
starting clutch. The fuel economy, acceleration
performance, and drivability of the starting clutch vehicle
were compared with that of the two torque converte
vehicles.
Vehicle tests showed that for the combined FTP cyclesthe starting clutch transmission provided a fuel economy
improvement of 11.4% over the production 3T40 3-speed
transmission and 7.2% over the experimental 5-speed
transmission with viscous converter clutch. The viscous
converter clutch apply schedule was very aggressive; GM
proprietary best fuel economy shift schedule was adopted
and the converter clutch apply started in second gear at 9
mph vehicle speed for zero throttle. Vehicle test data
showed that the 0-60 mph time for the starting clutch
vehicle is shorter than the production 3T40 3-speed
transmission vehicle because of the wide ratio spread (6:1
compared to 2.84:1) and slightly longer than the
experimental 5-speed automatic with a torque converterbecause the torque multiplication of the torque converte
was not completely compensated for.
CONCLUSION
Starting clutch control algorithms were developed and
successfully implemented in an experimental five-speed
automatic transmission vehicle equipped with a starting
clutch to replace the torque converter. Vehicle tests
showed that a starting clutch transmission could provide
significant vehicle fuel economy improvement over a
torque converter transmission without penalizing
acceleration performance when a wide-ratio-spread five
speed automatic transmission is used. General issues
such as cost, integration challenges, and custome
acceptance were not examined.
REFERENCES
1. Hiramatsu, T., Akagi, T., and Yoneda, H.,Contro
Technology of Minimal Slip-Type Torque Converte
Clutch, SAE-850460, 1985.
2. Gott, P.G., Changing Gears: The Development of the
Automotive Transmission, Society of Automotive
Engineers, Inc., 1991.3. Tung, S.C. and Linden, J.L., Modeling Torque
Converter Clutch Viscous Damper Performance,
SAE-850459, 1985.
4. Smirl, R., Transmission, U.S. Patent 2,700,312
January 25, 1949.
5. Schneider, K.F., Hydro-electronic Tension Bel
Continuously Variable Transmission for Passenge
Cars, SAE-894079.
6. Hirano, S., Miller, A.L., and Schneider, K.F., SCVT
A State of the Art Electronically Controlled
Continuously Variable Transmission, SAE-910410.
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