SBC control unit, function - GF42.46-P-4500-03T

Functional representation 

Fig 1: Functional Representation Of SBC Control Unit

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Function 

The functions of the SBC control unit are divided as follows:

• Signal conditioning
• Function logic component
• Safety circuit

  The SBC control unit monitors and controls the following additional functions: 

  • Selftest
  • Precharging the hydraulic system
  • Dry braking of the brake disks
  • SBC Hold

  Signal conditioning 

  The following input signals are processed by the function logic component for calculations or as information:

  • For brake pedal speed
    • SBC pedal value sensor signal
    • Front axle pre-pressure sensor signal
  • For actuation of the high-pressure charging pump
    • Memory sensor signal
  • To compute the vehicle speed and ABS control cycles
  • Wheel speed sensor signals

Function logic section 

The conditioned input signals are processed in the logic section and converted into output signals:

• RPM sensor signals:

  The 4 wheel speed signals are passed on via the CAN SBC and discrete lines to the ESP, SPS [PML] and BAS control unit.

• Signals to the ESP, SPS [PML] and BAS control unit: The wheel pressure signals of all 4 wheels, the stop lamp switch signal (S9/1), the front axle pre-pressure signal, the storage pressure and pedal travel are passed on for further processing to the ESP, SPS [PML] and BAS control unit via the CAN SBC.
• pressure regulators (consisting of one input and output control valve):

The pressures calculated by the ESP control unit are adjusted at the brake calipers of the individual wheels.

• Basic brake function: 

  In the event of failure of the ESP, SPS [PML] and BAS control unit or of a missing or faulty communication between the ESP control unit and SBC control unit (A7/3n1) a basic brake function for the brake booster as well as a fixed installed brake force distribution is made available.

• Brake servo assistance in the pre-run and run-on phase: 

  The SBC control unit takes care of the necessary brake servo assistance during the pre-run and the run-on phase.

  Safety circuit 

  The task of the safety circuit is to detect faulty signals of the sensors, faults in the control unit and in the electrical and hydraulic line system. The following actions are performed:

  • Monitoring of the high-pressure charging pump during actuation.
  • Permanent monitoring of valves.
  • Permanent monitoring of pressure sensors.
  • Permanent monitoring of supply voltage (if the operating voltage is below 10 V or a voltage of 16 V is exceeded, then the system is switched off).
  • Storage of faults.
  • Displays of warning messages in the multifunction display in the instrument cluster.