Technical notes/JSAE Review 15 (1994) 341-365 345

Technical Notes

Development of an electronic throttle control system

Toshikazu Ibaraki a, Hiroshi Miyata h, Toshio Uchida c, Mitsuru Takada d, Naoto Kushi c " Engine Engineering Dit~ision 3, Toyota Motor Corporation, 1200, Misvuku, Susono, Sizuoka, 410-11 .lapan

h Electronics Engineering Dit,ision 1, T~vota Motor Corporation, I, Toyota-cho, Toyota, Aichi, 471 Japan Vehicle El aluation and Engineering DiL'ision 1, Toyota Motor Corporation, 1200, Misyuku, Susono, Sizuoka, 410 11 Japan

d Engine Engineering Dil,ision 1, Toyota Motor Corporation, 1, Toyota-cho, Toyota, Aichi, 471 Japan Planning Dit,ision, Toyota Motor Corporation, 1, Tovota-cho, Toyota, Aichi, 47l Japan

Received 29 March 1993

1. Introduction

For the purpose of improving stability and drivability of vehicles, Electronic Throttle Control Systems [ETCS] have been introduced by some manufacturers. In 1993, Toyota also developed an ETCS, which has the advantages and capabilities of acceleration control for every road surface condition and driving situation.

The design points of the developed ETCS are described, and the advantages of the throttle system and how it is controlled to get the maximum benefits of acceleration control capability are explained in this paper.

2. Overview of ETCS

Intake Sub throttle valve ste 7'e se '=

Main-throttle Main throttle valve position sensor

Fig. 1. Serial double valve electronic throttle body.

2.1. Securing safe O, through the throttle mechanism

The first prerequisite in applying ETCS to commercial vehicles is to ensure complete safety during operation [1]. In order to meet this requirement, a serial double valve throttle body is employed, as shown in Fig. 1.

The throttle body has a sub-throttle valve, driven by an electric motor, upstream of the main throttle valve, which is mechanically connected to the acceleration pedal by a linear linkage. A return spring is provided on the opening side of the throttle valve. The stepping motor has little detention torque when the power is off, and by constantly operating this motor the sub-throttle valve is controlled to have the optimal opening.

The features of this throttle body are as follows: (1) If the drive system of the sub-throttle valve is not working, the engine output can be reduced by the driver lifting the foot off the accelerator pedal, which causes the main throttle valve to close. This is a fail-safe function.

(2) If the drive system of the sub-throttle valve malfunc- tions, a return spring causes the throttle valve to open fully. This will permit the vehicle to be driven to a safe place using the main throttle valve.

These features ensure that the developed system ensures sufficient safety.

2.2. System description

Figure 2 shows the control system configuration. The throttle control ECU interfaces with the ECU of the engine and automatic transmission, and with that of ABS [Anti- lock Brake System] to receive vehicle operation status data, such as wheel speed and opening degree of the main throttle. With the given data, the optimum control method to meet the driving conditions is selected to calculate the target opening degree of the sub throttle valve which drives the motor that positions the throttle at the calculated position.

0389-4304/94/$07.00 <~'~ 1994 Society of Automotive Engineers of Japan, Inc. and Elsevier Science B.V. All rights reserved SSI)I 0 3 8 9 - 4 3 0 4 ( 0 4 ) 0 0 0 3 9 5 JSAE9435766

346 Technical note,s /'.ISAE Ret:iew IS (1994) 341-305

Intake Sub throttle I~ ~1' l~ position . . . ~ . ' I~hStep motor

M~ittrottle F[~ ' ~ '~k ' "H ' " ' " (~

J I Accelerator pedal

automatic ~ j transmission ECU ~ I.~..-- ~

motor re ay Slip control indicator light

Wheel speed sensor

Wheel speed sensor

......... Mechanical hnkage

I ........... E iectric signat

Wheel speed sensor

F I

1 Crank sensor Speed sensor

' : II Wheel speed sensor

Electronic ] l

Throttle /~ ABS ECU Control System J~ ]

ECU I [ i"'Slip control I

i I qcuto~switch[ j ~ '

Slip control cut o f f - - ] & warning t indicator light . . . . . . . j

Fig. 2. ~.'.mrol s~stcm diagr wa

3. Effect o f e lectronic throttle control system

The system described above has the following newly added controls: (1) high /x road surface non linear control, (2) low Ix road surface non linear control, (3) driven wheel slip reduction control ( Ix = friction coefficient)

(1) and (2) can only be achieved by constantly operat- ing the electronic throttle control as engine output control is made in accordance with the amount of acceleration pedal depression. (2) and (3) are together called "Slip Control".

3.1. Control description of high and low tx road surface non linear control

For conventional engines, the opening degree of a throttle is directly proportional to the amount of accelera- tion pedal depression; this determines engine output char- acteristics. The objective of the developed system is to achieve optimum torque characteristics for better control of drive power by changing the opening degree of the throttle to meet all road surface and driving conditions.

From Fig. 3 which shows an example of the control, it can be seen that engine torque is controlled in the area where the amount of pedal depression is only small for high IX road surface, and the torque is controlled in all ranges for low IX road. In consideration of these two characteristics, the system has enabled achieving the opti- mum engine torque characteristics for the road surface condition without complicated maneuvering by automatic change of the throttle opening based on the road surface friction coefficient data estimated from vehicle informa- tion.

3.2. Description of drit,en wheel slip control

For the purpose of driven wheel slip control, traction control systems have been commercially adopted on vehi- cles by various automakers. This system feeds back the amount of slip of driven wheels to obtain a target slip rate, and it reduces the slip rate without relation to the amount of pedal depression. For this reason, it has the advantage that safe and stable driving is feasible regardless of who drives the vehicle, but it does not control the drive power by the amount of the pedal depression. On the contrary, the developed system is a new slip reduction control system aiming at giving a certain range of drive power control through the amount of pedal depression with re- spect to safety on low # road surfaces.

Motion equation (1) for the drive system during acceler- ation is given by the following:

l ~ b = f # . W . R , (1)

Linear mechanical accelerator linkage

. . . . . High F road surface non linear control

. . . . . Low F road surface non linear control 400

E. 300 . . " " - ' . ' " . . . . Z - . , .

m 200 ." , * ' +

• ,=,,,=, .9- ° 100 • .

"~ 0 '- revolution 2400 rpm LU -100 , I l i

0 25 5O 75 100 Amount of accelerator pedal depression (%)

Fig. 3. Example of torque control in non linear control.

Technical notes /JSAE Reciew 15 (19q4) 341-365 347

1 = inertial moment of drive system, & = angular velocity of driven wheel,

T = torque of driven wheel. At - friction coefficient, W = weight on driven wheel, R - effective radius of a tire.

Here, /x- W is the reaction force on the road surface and it contributes to the acceleration of the vehicle [2].

The conventional traction control system uses feed back of thc torque of a driven wheel as obtained by Eq. (1), so th~,t the slip rate will be able to converge on the target valuc. If the current slip rate is exceeded by the target rate. the right side of Eq. (1) is used as a negative value to lower the slip rate by reducing the acceleration of the driven wheels. At this instant, even if the pedal is de- pressed, the driven wheels reduce their speed, and the drive power does not correspond to the amount of pedal depression. For this reason, the developed slip reduction control prevents speed reduction of the driven wheels under control by controlling the torque of the driven wheel, so that the latter 's angular velocity converges to the target value, using the target angular velocity as a positive wdue. Furthermore. as the target angular velocity of the driven wheel is regarded as variable to the amount of pedal depression, correspondence between the amount of pedal depression and drive power is maintained.

For this reason, the developed system will provide drive power which corresponds to the amount of pedal depres- sion even when the wheels are slipping, and at the same time. the drive power can be minutely and simply adjusted.

Amount of Open 1/4

pedal depression close ~ , , ) r

Yaw velocity 20 (deg/sec) 0

Steering 180 angle (deg) 0

80

Speed 60 (km/h)

40

20 control o,,¢,, =uu~.t,,.,,, w, ,m.,,

Testing conditions With Slip Control

3.5m 3.5m Without Slip Control

(.---_sT_~ r,og 1 ~3Orn k~cgeTga~ingt-1 0 rn [ ~ . . . . T- "

Initial veloc i ty : 40Krn /h

Fig. 4. Effect of Slip Control during lane changing on low p_ road surface.

minimal, resulting in stable maneuverability. As described above, the developed ETCS has contributed to better con- trollability of a vehicle undergoing high torque on a slip- pery road, and added to the assurance of safety when maneuvering the vehicle.

3.3. Non-linear control and effect of slip control of dricen wheel 4. Conclusions

Figure 4 indicates the motions of a vehicle changing driving lanes while accelerating with the pedal depressed to a constant depth, on a low profile road surface. Without the slip control system, lane changing causes a larger slip rate to reduce horizontal drag with a large yaw velocity. This indicates that the vehicle is in an unstable condition and co-called " rear dr i f t" occurs.

t towever, with the slip control system, lane changing causes wheel slip, but its continuation is prevented by the slip reduction control and the low p. surface non linear control enables the tires to resume complete gripping of the road surface. This contributes to a low change the yaw velocity . and the operation of the steering wheel is kept

The developed ETCS provides excellent control of drive power and high maneuvering stability on slippery roads, However, ETCS is still undergoing development, and is expected to become a highly functional and value adding system through further research and development.

References

[1] Asayama, Y. ct al., Current Stands and Future Prospects on Drive by Wire Technology (in Japanese with English summary) Journal of JSAE Vol. 44. No.8, pp.112-122 (1990).

[2] lkeda, S. et al., Trend of Traction Control Systems, (in Japanese) Journal of JSAE Vol. 42, No.3, p. 336-341 (1988).