Electronic Accelerator

Electronic Accelerator System Schematic:

PURPOSE
The electronic accelerator control unit (N4/1) controls the cruise control, idle speed functions and electronic engine control (electronic accelerator pedal) for ABS/ASR III to insure smooth and consistent operation regardless of engine temperature and load.

LOCATION AND I.D.
The electronic accelerator control unit is located in the module box (F23) and is color coded light orange.

OPERATION
When the ignition switch is in the ON position, the idle speed control function is in operation. The position of the throttle valve for idle speed and ABS/ASR III is determined by the control unit via the nominal value (accelerator pedal input) potentiometer in the electronic accelerator actuator (M16/1). The actual value potentiometer in the electronic accelerator actuator signals the position of the throttle valve. The electronic accelerator control unit compares the signals and specifies the position of the throttle valve via the output signal. This signal is used by the electronic accelerator actuator to adjust the throttle valve.

Before starting the engine, the throttle valve position is determined by the engine temperature. Once the engine is running, the idle speed and ABS/ASR III are controlled by the electronic accelerator control unit which provides a constant idle RPM and limits the maximum torque output to the drive wheels. For torque output regulation (ABS/ASR III), the control unit uses the input signal from the ABS/ASR control unit.

The electronic accelerator control unit uses the following information to determine the throttle position:

Input Signals
^ Base module (N16/1)
^ ABS/ASR control unit (N30/1)
^ LH control unit (N3/1)
^ Idle speed contact switch (S29/3)
^ Electronic accelerator actuator (M16/1 with throttle valve)
^ Stop lamp switch (S9/1)
^ Starter lockout/backup lamp switch, selector lever position recognition (S16/3)
^ Cruise control switch (S40)
^ A/C compressor engagement signal
^ Data exchange via controller area network (CAN)
^ Wheel speed sensors (L6/1 - L6/4)
^ Diode matrix (V2)

Output signals
^ Electronic accelerator actuator (M16/1 with throttle valve)
^ ABS/ASR control unit (N30/1)
^ LH control unit (N3/1)
^ EZL/AKR ignition control unit (N1/3)
^ Impulse readout (malfunction memory) via 38-pole diagnostic socket (X11/4)
^ Data exchange via controller area network (CAN)

Idle speed control function
The idle speed control function uses the following information to determine the correct idle speed:
^ Engine speed (TN-signal)
^ Coolant temperature
^ Vehicle speed signal
^ Selector lever position
^ A/C compressor engagement signal

Idle Speed/Temperature Chart:

During idle, the control unit keeps the engine speed at a constant RPM depending on engine coolant temperature.

Warm-up RPM Chart:

Warm-up Control Function
The warm-up control is effective at all engine temperatures. After each start-up (accelerator pedal in idle position) the engine increases the idle speed for approx 20 seconds. Between 20 °C (68 °F) and 30 °C (86 °F) the engine speed is 800 - 900 RPM.

Diode Matrix Location (V2):

DIODE MATRIX SIGNAL
When additional consumers are turned on (e.g. A/C, heated seats, rear window defogger), an engagement signal is transmitted to the diode matrix (V2) for RPM increase. This signal is passed on to the electronic accelerator control unit to increase the idle speed.

A/C engagement Control Function
When the A/C compressor is turned on, the throttle valve opening is increased before the A/C compressor engages. This keeps the engine idle speed at a nearly constant RPM.