System Introduction
NOTE: For model name/model number cross reference refer to Model Designation Table. Application and ID
General Information
The Acceleration Slip Regulation (ASR) IV known from model 202 was modified and is designated as version 5 (ASR V).
ASR V can be switched off with the "ASR OFF" switch. For this reason, the ASR warning lamp control was changed as follows:
- While driving, the warning lamp blinks as soon as ASR V is operating (i.e. when wheel slip due to acceleration is detected).
- When actuating the "ASR OFF" switch, the warning lamp in the instrument cluster lights continuously.
- If wheel slip is detected, the warning lamp (Ale2l) will blink to inform the driver, however, engine torque control is not activated.
Below is a listing of modifications as compared to ASR IV:
- Elimination of ASR charging pump (M15).
- Modified ASR hydraulic unit (A7/3) with self-primeing high-pressure/return pump.
- Elimination of special ASR venting.
- Standard brake fluid reservoir.
- Acceleration Slip Regulation/Speed-Sensitive Power Steering (ASR/SPS) control module (N471) with integrated speed-sensitive power steering (SPS) control circuit (model 140 only).
- "ASR OFF" switch.
- Blinking ASR warning lamp.
- Left and right rear axle VSS sensor on wheel carrier.
- Only one brake pad wear sensor on the rear axle.
- Engine Braking Regulation (EBR) is integrated into ASR. EBR reduces drive wheel slip due to engine braking effects (engine torque) when decelerating and provides directional stability.
Electronic Traction System (ETS) and ASR are exclusive systems, they are not interchangeable.
Block Diagram - ASR V
Component Locations - ASR V
ASR/SPS Control Module (N47/1)
The ASR/SPS control module (N47/1) is installed in the module box on models 129 and 140 (A) and in the front passenger footwell on model 202 (B). Data is exchanged with the EA/CC/ISC control module (N4/1), the engine control module (N3/4) or LH-SFI control module(s) and the DI control module via the CAN data bus.
On model 140 only, the control module also incorporates the electronics and control circuit for speed-sensitive power steering (SPS).
Exchange, replacement control modules must be coded using the HHT. Follow instructions on HHT display.
The control module has three functions:
- Signal processing.
- Logic section.
- Safety circuit.
NOTE:
- On models 129 and 140, the control module connector incorporates two plastic spreader pins. When the control module is properly inserted into the module box, the spreader pins insulate special shorting contact on the harness connector.
- If the shorting contacts touch their adjacent pins (e.g.: the control module is not properly inserted into the module box, or the spreader pins are damaged) the ABS or ASR MIL will come on. However, no DTC will be stored for this situation.
Voltage Supply
Models 129, 140
Voltage for the ASR/SPS control module ((N47/1) is supplied via the base module (N16/1) in the module box. The circuit is protected by fuse F1 (10A) in the base module.
Model 202
Voltage for the ASR/SPS control module (N47/1) is supplied via the overvoltage protection relay (K1). The circuit is protected by a 15A fuse.
ASR OFF Switch (S76/5)
When the ASR OFF switch (S76/5) is activated, the engine torque control circuit is switched off and the brake torque control circuit remains active (becoming similar in function to ETS). Engine braking regulation (EBR) also remains active, but is switched to a less sensitive mode.
The ASR warning lamp (Ale2l) illuminates continuously, after the switch is activated. If wheel slip is detected, the warning lamp will blink to inform the driver, however, engine torque control remains inactive.
Vehicle Speed Signal (VSS) Sensors
The ASR/SPS control module receives speed signals from four single-edged VSS sensors.
Left and right front axle VSS sensors (L-6/1 and L6/2)
The front axle VSS sensors (L6/1 and L6/2) are mounted on the front axle steering knuckle.
Left And Right Rear Axle VSS Sensors (L6/3 and L6/4)
The rear axle VSS sensors (L6/;3 and L6/4) are mounted on the rear axle wheel carrier (previously mounted on the rear axle center piece). The speeds of the rear wheels are checked separately via rotors on the rear axle.
Brake Torque Control Circuit
The ASR/ETS hydraulic unit (A7/3) and the functions of the engine torque control circuit (via N4/1) are controlled by the ASR/SPS control module (N47/1).
The ASR/SPS control module (N47/1) receives input signals from the following components:
- VSS sensors (L6/1, L-6/2, L-6/3, L-6/4),
- Parking brake switch (S12),
- Stop lamp switch (S9/1),
- EA/CC/ISC control module (N4/1, throttle valve dependent value) via CAN data bus,
- ASR OFF switch (S76/5).
The input signals are processed into output signals in the ASR/SPS control module (N47/1) for the following components:
- Solenoid valves (A7/3y6 - y12) (via relay A7/3k1),
- High-pressure/return pump (A7/3m1) (via relay A7/3k2),
- EA/CC/ISC control module (N4/1, throttle valve control value) via CAN data bus,
- Engine control module (N3/4) or LH-SFI control module (N3/1 or N3/2 and N3/3) (throttle valve control value) via CAN data bus,
- ASR warning lamp (A1e21),
- ABS MIL (A1e17),
- ASR MIL (A1e22).
Based on the input signals, the ASR/SPS control module (N47/1) decides which of the following five operating modes must be selected:
- Normal mode,
- ABS control mode,
- ASR control mode,
- ASR OFF mode,
- EBR control mode (see "Engine torque control circuit").
Normal Mode
No VSS differences which require a control mode exist.
All solenoid valves in the ASR/ETS hydraulic unit (A7/3) are in the basic position, i.e. de-energized. The system is constantly monitoring all inputs.
This is also the default mode. The system returns to this mode if a fault is present in ASR or ABS.
ABS Control Mode
If the available VSS's indicate that one or more wheels are about to lock due to braking, the ASR/SPS module (N47/1) activates the ABS control mode. The appropriate solenoid valves are actuated by the ABS output circuits in the ASR/SPS control module.
The left or right front axle solenoid valves in the ASR/ETS hydraulic unit (A7/3) are actuated separately.
The left an right axle solenoid valves are actuated jointly for the ABS control mode.
ASR Control Mode
If the available VSS's indicate that one or both drive wheels are spinning due to acceleration the ASR/SPS control module (N47/1) activates the ASR control mode.
As soon as a drive wheel begins to spin, the ASR/SPS control module actuates the high-pressure/return pump (A7/3m1), the switch over/solenoid valve (A7/45), the inlet solenoid valve (A7/y15) and solenoid valves for the rear axle. The left and right rear axle solenoid valves are actuated separately. The rear wheels are braked to reduce slip.
If necessary, a throttle reduction signal is sent to the EA/CC/ISC control module (N4/1, see "Engine torque control circuit, ASR control mode").
ASR control mode is immediately interrupted if the stop lamp switch (S9/1) is actuated by depressing the brake pedal.
ASR Off Mode (ASR OFF)
If the ASR OFF switch (S76/5) is activated, the engine torque control circuit is switched off (a throttle reduction signal is not sent to the EA/CC/ISC control module [N4/1]). Only the brake torque control circuit is active, and a controlled brake application occurs in the starting-off to 25 mph (40 km/h) range.
The controlled brake application is retained up to a maximum of 50 mph (80 km./h), but the brake torque is progressively reduced (similar in function to ETS).
Engine Torque Control Circuit
ASR Control Mode
If the engine torque is too high (ie. wheel spin), the throttle valve opening is reduced by the EA/CC/ISC actuator (M16/1) and the ignition point is retarded to optimize traction.
There are three control ranges within ASR control mode.
- Control range when one drive wheel spins and vehicle speed less than or equal to 25 mph (40 km/h).
The slip threshold of the engine torque control is higher than that of the brake torque control. Therefore, the brake torque control is activated first. Priority is given to maximum traction. If the drive wheel continues to spin, the engine torque control is also activated.
- Control range when both drive wheels spin or vehicle speed is greater than 25 mph (40 km/h).
The slip threshold of the brake torque control is higher than that of the engine torque control. Initially, the throttle valve position is reduced. If the wheels continue to spin, the brake torque control is also activated. Priority is given to maximum directional stability.
- Control range when cornering at vehicle speeds between approximately 13 - 75 mph (20 - 120 km/h).
Depending on lateral acceleration, the engine torque control comes into operation sooner than for the previous control mode. This increases the directional stability during cornering.
Engine Braking Regulation (EBR) Control mode
If the ASR/SPS control module (N47/1) detects slip at the drive wheels when the vehicle decelerates, a throttle valve increase signal is sent to the EA/CC/ISC control module (N4/1) via the CAN data bus. Thereby, engine torque is slightly increased so that the drive wheels do not spin (engine braking regulation = EBR). As a result, the lateral control of the vehicle is stabilized. This takes place without the driver being informed (ASR warning lamp does not illuminate).
The maximum throttle valve opening is 17°.