Braking Moment Control Circuit

NOTE: For model name/model number cross reference refer to Model Designation Table. Application and ID






The corresponding functions in the ABS hydraulic unit (A7/3) are controlled by the electrical /electronic components.
On model 202 up to 07/96 the ABS control module (N47-7) is supplied with voltage via the overvoltage protection relay (K1).
On model 202 as of 08/96 and models 170 and 208 the voltage is supplied via the relay module (K40 or K40/4).

The ABS control module (N47-7) receives Input signals from the following components:

^ 3 rpm sensors
^ Stop lamp switch

The input signals are processed into output signals in the ABS control module for the following components:

^ Solenoid valves
^ Return pump (via relay)
^ ABS MIL (actuation - direct, serial or via CAN data bus)

Based on the Input. signals, the ABS control module (N47-7) decides which of the four operating modes

^ Normal mode
^ ABS control mode, pressure build-up
^ ABS control mode, hold pressure
^ ABS control mode, pressure reduction

are to be initiated.

Normal Mode
In this case there are no differences in speed (which necessitate a control mode). All the solenoid valves in the ABS hydraulic unit (A7-3) are de-energized. The system is ready for braking. This operating mode is also set when there is a fault in the ABS.

ABS Control Mode
The ABS control module (N47-7) recognizes from the wheel speed signals that the conditions for ABS control exist. The corresponding solenoid valves are actuated by the ABS circuits in the ABS control module (N47-7).
The left or right front axle solenoid valves in the ABS hydraulic unit (A7/3) are actuated separately.
The solenoid valves for the rear axle act together on both rear wheels for the ABS control process. if an ABS control process is effective, a rapid change In pressure between pressure build-up, hold pressure and pressure reduction takes place at the wheel brakes.
This ABS control process can be felt via a pulsating brake pedal.