Electronic accelerator, location/design/function

CAN

CAN

Vehicle speed

signal

ASR control module

Electronic accelerator control module

HFM engine control module

Accelerator pedal

Actuator motor

Throttle valve

Set value

potentiometer

Actual value

potentiometer

Actuator

Throttle control

Pushbutton switch

Tempomat

Operation

Valid only for engines fitted with HFM.

The electronic accelerator (EA) operates in combination with the acceleration slip regulation (ASR) and is designed to improve the starting-off and accelerating performance as well as driving stability.

The idle speed control, cruise control and electronic throttle control functions 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 altered by the accelerator pedal operating through the throttle control. The signal voltage of the set value potentiometer is relayed to the EA control module. The throttle valve position is tapped as a voltage at the actual value potentiometer and is supplied to the EA control module as an input signal. The actuator motor of the throttle valve is operated via an output stage in the EA control module.

The input signals of the set value and actual value potentiometers are compared in the EA control module. If the two signals differ, the throttle valve position is adjusted in line with the set value.

The ignition timing is briefly retarded in order to be able to achieve an immediate reduction in engine torque.

In contrast to the cruise control module, the electronic accelerator (EA) control module is able to alter the position of the throttle valve irrespective of the position of the accelerator pedal.

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Emergency running mode

If a fault develops at the EA, the system is switched off. When the accelerator is depressed, the throttle valve is now operated only mechanically, in which case the throttle valve is able to open only approx. 2/3.

If faults exist at the safety contacts, the engine speed is limited to about 1200 rpm via the safety fuel shutoff. When 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 car.

ASR control

If the set value (accelerator pedal) is higher than the torque which can be transmitted to the road, the wheels spin (slip). The slip is detected by the ASR control module and transmitted via the CAN databus to the EA control module. The position of the throttle valve is reduced. In other words, so long as slip exists, the ASR control module determines the maximum possible position of the throttle valve.

If a fault exists and the variation between set value (accelerator pedal position) and actual value (throttle valve position) is excessive, the safety fuel shutoff is activated.

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EBR control

The engine braking regulation (EBR) is activated in 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 driver eases off the accelerator 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.

Cruise control function

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

If, for example, the brake light switch is faulty and the vehicle is decelerated > 1.5 m/s2,

the deceleration is detected in the processor and the actuator switches at the maximum possible speed to the driver input. If the driver requests a higher speed via the accelerator pedal, the cruise control system is deactivated.

If the ASR control module detects drive slip during the cruise control mode, priority is given to reducing engine power output. If the ASR control mode is active for longer than 0.5 ms, the cruise control is switched off.

If the difference in speed between the front and rear wheels is excessive, the Tempomat is switched off after 0.5 s.

Maximum difference in speed:

up to 149 km/h 3km/h

as of 150 km/h 5 km/h

When the cruise control mode is active, the slaved safety contact is bridged by a switching transistor.