ABS closed-loop operation function - GF42.45-P-3000TX

MODEL 211, 219.3 up to 31.5.06 except CODE (494) USA version except CODE (498) Japan version 

MODEL 211, 219.3 up to 30.6.06 with CODE (494) USA version with CODE (498) Japan version 

Fig 1: ABS Control Mode Diagram - Pressure Buildup

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

ABS control mode - pressure buildup 

Antilock brake system (ABS) closed-loop operation 

ABS control mode - pressure buildup 

Each ABS control phase begins with normal application of the brakes when the driver presses the brake pedal. The SBC control unit (A7/3n1) calculates the brake pressure and starts with the control.

The ESP control unit (N47-5) detects the brake application from the SBC control unit via signals (SBC pedal value sensor, wheel speeds, brake pressure)

The left front separation valve and right front separation valve are closed. They only remain closed during the control and are otherwise opened (de-energized).

The left front outlet control valve, right front outlet control valve, left rear outlet control valve and right rear outlet valve are likewise closed. The left front inlet control valve, right front inlet control valve, left rear inlet control valve and right rear inlet control valve are open. The front axle and rear axle balance valves remain open.

The pressure from the pressure reservoir (3) can now be built up at the brake calipers of the front axle via the left front dividing piston (7) and right front dividing piston (8). The pressure is increased directly at the rear axle.

Fig 2: ABS Closed-Loop Operation Pressure Holding Diagram

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

ABS closed-loop operation pressure holding, shown on the right front wheel brake (FR) 

ABS closed-loop operation pressure holding 

The control process shown in the example and the valve positions refer to the right front wheel brake (FR).

If a wheel shows a tendency to lock during the brake application, the ABS prevents a further buildup of pressure. The ESP control unit introduces the pressure holding phase from the slip values of the braked wheels.

The pressure holding phase is introduced by actuating the right front inlet control valve and front axle balance valve. In this control phase the right front inlet control valve, front axle balance valve and right front outlet control valve remain closed, as a result the pressure in the brake caliper of the right front wheel brake (FR) remains constant.

Fig 3: ABS Closed-Loop Operation Pressure Reduction Diagram

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

ABS closed-loop operation pressure reduction, shown on right front wheel brake (RF) 

ABS closed-loop operation, depressurization 

The control process shown in the example and the valve positions refer to the right front wheel brake (FR).

The ESP control unit introduces the pressure reduction phase from the slip values of the braked wheels.

The pressure reduction phase is introduced by actuating (opening) the right front outlet control valve. The right front inlet control valve remains actuated (closed) in this control phase.

Brake fluid flows back into the reservoir via the return line during the pressure reduction phase.