Electronic accelerator position / design / function

CAN

CAN

Vehicle speed signal

ASR control module

Electronic accelerator control module

LH-SFI engine control module

Accelerator pedal

Throttle valve actuator motor

Set value potentiometer

Actual value

potentiometer

Throttle control

Cruise control switch

DI/KSS control module

Actuator

Throttle valve actuator motor

Set value

potentiometer

Actual value

potentiometer

Actuator 2

Only engine 120

Function

Valid only for engines with LH-SFI.

The electronic accelerator (EA) operates in combination with acceleration slip regulation (ASR) and is designed to improve starting-off and acceleration performance as well as driving stability. The functions of idle speed control, cruise control and electronic throttle control are integrated in the electronic accelerator (EA) control module.

The EA control module is supplied with voltage at ignition ON.

The position of the set value potentiometer is changed with the accelerator pedal through the throttle control. The signal voltage of the set value potentiometer is passed on to the EA control module. The throttle valve position is tapped as a voltage at the actual value potentiometer and is supplied as an input signal to the EA control module. The actuator motor for the throttle valve is operated through an output stage in the EA control module. The input signals supplied by the set value and actual value potentiometers are compared in the EA control module. If the two signals differ, the position of the throttle valve is corrected in line with the specified value.

The ignition timing is retarded for a short period in order to be able to achieve an immediate reduction in torque. In contrast to the cruise control module, the electronic accelerator (EA) control module is able to control the throttle valve so as to open and close it irrespective of the position of the accelerator pedal.

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Emergency running system

In the event of a fault in the EA, the system is switched off. When the accelerator is depressed, the throttle valve is now operated only mechanically, with the throttle valve being able to open only about 2/3 of total travel.

In the event of faults at the safety contacts, engine speed is limited to about 1200 rpm through the safety fuel shutoff. If the accelerator pedal is not depressed, the idle speed safety contact is closed and the slaved safety contact is open.

In both cases it is possible to continue driving the vehicle.

ASR control

If the set value (accelerator pedal) is higher than the input torque which can be transmitted to the road, the wheels will spin (slip). This slip is detected by the ASR control module and transmitted through the CAN databus to the EA control module. The position of the throttle valve is reduced, in other words so long as slip is present, the ASR control module determines the maximum possible throttle valve position. This signal is passed simultaneously to the DI control module and the ignition timing is retarded for a short time in order to achieve an immediate reduction in torque.

If a fault results in a major difference between set value (accelerator pedal position) and actual value (throttle valve position), the safety fuel shutoff is activated.

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EBR control

The engine braking regulation (EBR) is active subject to the following conditions:

1. vehicle speed from 20 up to 120 km/h

2. no ASR control active

3. opening angle of throttle valve < 22.5°

If slip occurs at the driven wheels when the accelerator is eased back or during a downshift, this is detected by the ASR control module and the throttle valve is opened for a short time until no further slip occurs.

Throttle control

The throttle control linkage is linked by the input lever and the internal spring capsule by means of a loose connection to the throttle valve.

On engine 120 the EA actuator for the left bank of cylinders (positioned on right of engine) has "no" connection to the throttle control linkage.

In this case, the position of the throttle valve is altered only by means of the electrical/electronic actuation.

Cruise control function

The cruise control function can only be activated at the vehicle speed of more than 40 km/h by pressing the cruise control switch (S40). The cruise control switches off if the brake pedal or clutch pedal is depressed.

If, for example, the stop lamp is faulty and the vehicle is decelerated > 1.5 m/s2, the deceleration is detected by the processor and the actuator moves at the maximum possible speed to the driver input. If the driver requests a higher speed through the accelerator pedal, the cruise control system is not operational. If the ASR control module detects acceleration slip when the cruise control mode is activated, priority is given to reducing engine output. If the ASR control mode is in operation for more than 0.5 ms, the cruise control is switched off.

If the difference in speed between front wheels and rear wheels is too great, the cruise control is switched off after 0.5 s.

Maximum difference in speed:

up to 149 km/h 3km/h

from 150 km/h 5 km/h

If the cruise control mode is active, the slaved safety contact is bridged with a switching transistor.