MODEL   219.3

A7/3 SBC hydraulic unit A7/3n1 SBC control unit The SBC hydraulic unit is located in the engine compartment behind the right headlamp.
		P42.46-2105-81

Task The SBC hydraulic unit carries out the brake application which the driver specifies via the brake pedal. The SBC hydraulic unit carries out the control of systems influencing vehicle dynamics, Electronic Stability Program (ESP), antilock brake system (ABS), acceleration slip regulation (ASR) and Brake Assist (BAS) at the wheel brakes.

It regulates the brake pressure separately at each individual wheel. In the event of a system failure a hydraulic basic brake function continues to be available.

Design 3 Pressure reservoir A7/3 SBC hydraulic unit A7/3n1 SBC control unit A7/3m1 High-pressure charging pump The pressure reservoir (3), high-pressure charging pump and the SBC control unit are attached to the SBC hydraulic unit.
		P42.46-2106-11

P42.46-2084-09

R Return flow pipe S Suction pipe Sensors and actuators outside the hydraulic unit 1 Operating unit 2 Pedal value simulator 7 Left front dividing piston 8 Right front dividing piston VL Front wheel brake, left VR Front wheel brake, right HL Rear wheel brake, left HR Rear wheel brake, right B37/1 SBC pedal value sensor S9/1 Stop lamp switch

Design of hydraulic unit 3 Pressure reservoir A7/3 SBC hydraulic unit A7/3b1 Front axle pre-pressure sensor A7/3b2 Reservoir pressure sensor A7/3b3 Left front pressure sensor A7/3b4 Right front pressure sensor A7/3b5 Left rear pressure sensor A7/3b6 Right rear pressure sensor A7/3m1 High-pressure charging pump

A7/3y1 Left front separation valve A7/3y2 Right front separation valve A7/3y3 Front axle balance valve A7/3y4 Rear axle balance valve A7/3y6 Left front inlet control valve A7/3y7 Left front outlet control valve A7/3y8 Right front inlet control valve A7/3y9 Right front outlet control valve A7/3y10 Left rear inlet control valve A7/3y11 Left rear outlet control valve A7/3y12 Right rear inlet control valve A7/3y13 Right rear outlet control valve

Function The SBC control unit receives the driver's braking requirement from the signals from the SBC pedal value sensor, Front axle pre-pressure sensor and stop lamp switch. The SBC control unit calculates from this the optimum brake pressure for each wheel and actuates the corresponding actuators in the SBC hydraulic unit. In the event of the failure of the complete system a hydraulic base brake function without any electronic control

The specified pressure requirements calculated by the ESP control unit (N47-5) for carrying out the functions of ESP, ASR and ABS are conveyed to the SBC control unit via the SBC CAN (system's own CAN connection). Thereupon the SBC control unit actuates the actuators of the SBC hydraulic unit which carry out the controls of ESP, ASR and ABS.

Functions of individual actuators and sensors The switching components of the vehicle dynamic control systems SBC, ABS,ASR and ESP are combined in the SBC hydraulic unit . High-pressure charging pump The self-priming high-pressure charging pump integrated in SBC hydraulic unit charges the pressure reservoir (3) with 160 bar. Pressure reservoir (3) The pressure reservoir supplies the pressure required for braking and control. The SBC control unit regulates the reservoir pressure between 140 and 160 bar by actuating the high-pressure charging pump. Left and right front dividing pistons (7 and 8) The closed loop is separated from the hydraulic circuit (emergency operation) by the dividing piston. Therefore the dividing pistons transmit the pressure in the control circuit into the front axle hydraulic circuit during an SBC brake application. As the front axle hydraulic circuit is a sealed unit as a result of the left and right separation valves being closed

the pressure is built up in the front axle brake circuit by the force of the dividing pistons. The exact and rapid pressure control (the control pressure is between 0 and 150 bar) is achieved by means of 4 pressure modulators, in each case consisting of an inlet and outlet control valve. Left front inlet control valve, right front inlet control valve, rear left inlet control valve and right rear inlet control valve For pressure control, one inlet control valve each is used for each wheel for the functions pressure buildup and pressure holding during brake applications and in SBC/ABS/ASR and ESP-closed-loop operation. The inlet control valves are simultaneously designed as pressure limiting valves and open at pressure values > 190 bar. Left front outlet control valve, right front outlet control valve, left rear outlet control valve and right rear outlet control valve For pressure control one control valve is used for each wheel for the functions pressure holding and depressurization during brake applications and in SBC/ABS/ASR and ESP closed-loop operation.

Left front separation valve and right front separation valves The left front separation valve and right front separation valve are de-energized open and after the brake pedal is pressed shut off the closed loop relative to the operating unit. If the electrohydraulic brake fails, the opened valves form a hydraulic connection to the brake pedal. The pedal value simulator (2) is located in the operating unit (1) outside the hydraulic unit. After the separation valves have shut off the control circuit to the operating unit (1), the pedal value simulator (2) which acts mechanically/hydraulically (2), generates the braking feel to which the driver is accustomed regardless of the hydraulic on the wheel side by compressing a non linear spring pack hydraulically by means of a bypass. Front axle balance valves and rear axle balance valves The balance valves are open during normal brake application when the vehicle is moving straight ahead. They form a pressure compensation

between the left and right wheel. If the driver applies the brake while cornering, the valves are closed to allow the brake to be applied individually at each wheel. Front axle pre-pressure sensor This sensor records the pressure produced at the brake pedal by the driver. Reservoir pressure sensor Records the pressure prevailing in the pressure reservoir (3). The reservoir specified pressure is between 140 and 160 bar. Left front pressure sensor, right front pressure sensor, left rear pressure sensor and right rear pressure sensor Through the pressure sensors the SBC control unit records the respective brake pressure at the individual brake calipers. The SBC control unit conveys these pressures to the ESP control unit in a permanent data exchange.