ABS/DSC control unit

Design

The control unit basically consists of following components:

• Two microcontrollers
  
• Interface modules for adaptation to speed sensor input signals, analog/digital input signals, diagnosis bus and CAN bus signals
  
• Driver modules for speed sensor outputs, relays and indicator lamps
  
• Power output stages to activate solenoid valves and the return pump in the hydraulic unit
  
• Power supply modules for the active speed sensors and steering wheel sensor
  
• Memory module (diagnosis defect code memory)
  

Note

The ABS/DSC control unit is ready for operation as of ignition lock position 2. The power is applied via the DME main relay. The power supply is retained for approx. 5 - 20 seconds after switching off the ignition (DME holding circuit).

Safety Concept

The main safety feature in the ABS/DSC control unit is the parallel signal conditioning and processing in the two microcontrollers.

Since both microcontrollers work through the same program, the output variables must be identical when the input variables are identical. If this is not the case, a fault is detected and the entire ABS/DSC system is shut down. This internal fault monitoring facility is constantly in progress.

In addition, after exceeding a driving speed of 6 km/h at the beginning of every trip, the solenoid valves and return pump are temporarily activated and the feedback to the output stages is monitored. The entire system is also shut down if a fault occurs.

The speed sensors and speed sensor lines are monitored both when stationary as well as when driving by different methods such as voltage level monitoring of the speed sensor lines, comparison of wheel speeds with a reference speed, static slip monitoring etc.

The solenoid valve lines are monitored dependent on the drive status for a break and short to positive or ground.

The switch-on status and run-on of the return pump motor are also monitored electrically. If no voltage is applied at the pump motor for a certain time after activation or if the voltage is not below a specified minimum value within a certain period of time on completion of activation, a fault is detected and the entire system is shut down.

Note

After a safety shut-down, the normal service brake system as well as the engine control are still available without restrictions.