Functional Operation

The electronic and mechanical components perform all control processes. The electronic components get the required voltage through used circuit 15 in the fuse box. The following components generate input signals for the electronic accelerator system control unit:

^ Accelerator pedal position sensor,
^ Electronic accelerator throttle actuator,
^ ABS/ASR control unit,
^ Starter lock-out/backup lamp switch,
^ Cruise control switch,
^ Electronic speedometer,
^ Stop lamp switch.

The electronic accelerator control unit monitors and processes the input signals. It activates the following components with output signals:


^ Electronic accelerator throttle actuator,
^ ABS/ASR control unit,
^ Fuel pump relay (on engines 116 and 117).
Engine systems control unit (on engines
103, 104 and 119).
^ CIS-E control unit (only on engines 103 and 104).


In vehicles with engines 103 or 104 the accelerator pedal position sensor also sends the signal for idle position through the electronic accelerator control unit to the CIS-E control unit to operate deceleration fuel shutoff.

Whenever the ignition is on, the electronic accelerator system operates. The accelerator pedal position sensor signals the position of the accelerator pedal (actual position) to the control unit.


The control unit calculates an output signal to control the accelerator actuator according to the accelerator pedal position sensor signal. The actuator thus moves to a position corresponding to that of of the accelerator pedal position sensor. The linkage rod connects the actuator output lever with the throttle valve. The actual accelerator pedal position corresponds to the opening angle of the throttle valve, by means of which the engine transmits a specific torque to the drive wheels. If the rear wheels spin, the accelerator pedal position selected by the driver (accelerator pedal position) is greater than the torque that can be transmitted to the road. The ABS/ASR control unit recognizes this spin and sends an output signal (throttle valve nominal position) to the electronic accelerator pedal control unit. The control unit signals the actuator to close the throttle valve compared to the position the driver calls for with the accelerator pedal. As long as the accelerator pedal position is too advanced for the torque that can be transmitted to the road, the drive torque is reduced until the spin at a drive wheel falls below a specified threshold. The electronic accelerator system can set the throttle valve anywhere between idle and wide open throttle. Or if a wheel starts to spin, the ASR system can close the throttle valve towards idle.


If the drive wheels spin, the telescoping rod lets the ASR system close the throttle valve against the nominal position set by the accelerator pedal. The telescoping rod (backup linkage) is a limp-home design to allow driveability at reduced engine power if the electronic system fails (the accelerator pedal becomes harder to move after a short freeplay). Besides the above, the electronic accelerator control unit also includes the cruise control system.

FEATURES:
^ Control of the throttle valve always occurs through the electronic system.
^ The electronic accelerator control unit includes the cruise control system.
^ Driving is still possible with reduced engine power if the electronic system fails.

The monitoring (safety) circuits of the electronic accelerator system constantly check the signals from the accelerator actuator, accelerator pedal position sensor, the ABS/ASR control unit, and the output drivers. Should a fault be detected, the system switches off and the ASR warning lamp lights.



IGNITION SWITCH (POSITION 2)
Whenever the ignition is turned on (ignition switch, position 2), the electronic accelerator system turns on. The electronic accelerator control unit, the accelerator pedal position sensor and the throttle actuator get voltage. Also, the fuel pump relay and the engine systems control unit activate through the safety switch of the actuator (voltage at circuit 15). It supplies voltage to the fuel pumps for approx. 1 second. In addition, the ignition switch supplies the cruise control switch with voltage.

When the driver pushes the accelerator pedal, the connecting linkage (Bowden cable) conveys the pedal position to the accelerator pedal position sensor.

The accelerator pedal position sensor's potentiometer sends the electronic accelerator control unit a voltage signal corresponding to the pedal position of the accelerator pedal.


The actuator potentiometer also sends a voltage signal (the throttle valve actual position signal). The system control unit compares both signals (actuator/throttle actual position and accelerator pedal position). If they differ, the control unit adapts the actuator position to the accelerator position (accelerator pedal position). The control unit activates the DC actuator motor through the output driver. Moreover, there is an information exchange between the ABS/ASR control unit and the electronic accelerator control unit whenever the ignition is on. The electronic accelerator control unit determines whether the maximum usable throttle valve opening is less than the one selected by the driver. If the driver chooses too great a throttle opening for the available traction, the ABS/ASR control unit selects the largest throttle opening compatible with traction.


The monitoring elements of the system check the signals from the accelerator pedal position and throttle valve actual position sensor, the actuator and the ABS/ASR control unit. The monitoring elements also check the output drivers.


DRIVING OPERATION
During driving, the electronic and mechanical components control the adjustment of the throttle valve The desired vehicle speed thus depends on the position of the accelerator pedal. Torque control starts (depending on the driving speed) as soon as the wheel speed difference exceeds the thresholds set in the drive torque control system (of the ASR system).

ASR drive torque control occurs by closing, holding or opening the throttle valve. if the wheel speed difference falls below the threshold, then the throttle valve opening corresponds to the accelerator position initiated by the driver.


DRIVING WITH CRUISE CONTROL
When the ignition is turned on the cruise control is ready for use. To put it in operation, the vehicle speed must be above approx. 40 km/h (25 mph). Once the vehicle is driving at the desired speed, a short tap of the cruise control switch toward ACCEL/SET or DECEL/SET sets the speed, until the driver sets a new speed or the system is disengaged. For example, to set the vehicle speed to traffic flow, hold the switch either toward ACCEL/SET or DECEL/SET until the desired speed is reached. For small changes of speed, short taps of the switch either toward ACCEL/SET or toward DECEL/SET will raise or lower the speed by approx. 1 km/h.

The vehicle speed memory can accept a higher speed as long as the throttle valve does not stand at wide open throttle, and it can accept a lower speed as long as the throttle is not in idle position or deceleration. The acceleration of the vehicle (under ACCEL/SET) is limited to 0.7 meter per second square. When the switch is released, the new vehicle set speed is retained.

If the switch is tapped OFF or if the brake pedal is applied, the cruise control switches off, and the vehicle speed control returns to the throttle position setting the driver determines with the accelerator pedal. When cruise control is switched off, the actuator motor closes the throttle valve toward idle.


The cruise control system remains operational after it is switched off, until the ignition is turned off, over a vehicle speed of 40 km/h (25 mph). if the switch is tapped toward RESUME after applying the brake pedal or moving the switch to OFF, the vehicle accelerates independently with an acceleration limited to 1 meter per second square to the last speed determined by the SET function. The last vehicle set speed is erased when the ignition is turned off. If the set speed is exceeded by the driver using the accelerator pedal, for example while passing, the vehicle automatically returns to the previous set speed as soon as he releases the pedal.

If the engine does not have enough power to continue at the set speed when climbing a hill, the vehicle falls below the set speed. It returns to the set speed as soon as the road is not so steep, unless the speed has fallen below 40 km/h (25 mph) or the brakes have been applied.

If engine braking is not sufficient when driving downhill, the set speed will be exceeded, and the driver will have to use the brakes if necessary. If the brakes are not used, the cruise control will resume the vehicle set speed as soon as the road levels off.


CAUTION: Never move the gear selector lever to position N when driving with cruise control or the engine can race.


The last vehicle speed stored in the cruise control unit is erased whenever the ignition is turned off. When the ignition is turned on, the vehicle speed memory is assigned the value 0 km/h - mph. In this way it is assured that there will be no unknown vehicle speed stored when beginning driving, for example after a change of driver. The vehicle speed is continuously monitored by the electronic accelerator control unit. Every change of vehicle speed is detected and analyzed by the computer.

If a change of vehicle speed is selected with the cruise control switch, the computer in the control unit matches the prescribed values of 0.7 meter per second square to the switch position ACCEL/SET, or 1 meter per second square to switch position RESUME. When the cruise control is turned off, the safety switch in the electronic accelerator control unit monitors the return of the actuator to the actual accelerator pedal position.

If for any reason the vehicle slows by more than 1.5 meter per second square (for example if the brake lamp switch fails during braking), the slowdown is detected by the computer, and the actuator closes the throttle valve with the fastest actuator speed possible.