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

MODEL 163 as of 1.9.02 with CODE (472) Electronic Stability Program (ESP)

MODEL 170 with ENGINE 111,112 with CODE (472) Electronic Stability Program (ESP)

MODEL 202 with ENGINE 111, 605, 611 with CODE (472) Electronic Stability Program (ESP)

MODEL 203 with CODE (472) Electronic Stability Program (ESP)

MODEL 208 with ENGINE 111 with CODE (472) Electronic Stability Program (ESP)

MODEL 209 with CODE (472) Electronic Stability Program (ESP)

Shown using model 209 as an example

Brake application in normal operation

ABS control mode - build up pressure

Each ABS control phase begins with normal application of the brakes when the driver presses the brake pedal.

The ESP control unit detects that the brakes have been applied by means of the reduced wheel speeds.

The brake pressure is built up via the two change-over solenoid valves (y18 and y19) and the solenoid valves (y6, y8, y10 and y12). This pressure build-up phase can occur separately at each wheel during the ABS control mode.

Fig 1: Circuit Diagram - ABS Closed-Loop Operation Function (ABS Control Mode - Build Up Pressure)

With normal brake application, pressure is built up via the same solenoid valves.

Shown using model 209 as an example

ABS control mode - hold pressure

The control procedure and value positions illustrated in the example refer to the FR brake.

If one wheel begins to lock during the braking procedure, the ABS prevents additional pressure build up. The ESP control unit initiates the pressure holding phase using the slip values of the braked wheels.

The pressure holding phase is initiated by controlling the solenoid valve (y8). In this control phase, the solenoid valves (y8 and y9) remain closed. The pressure in the FR brake caliper therefore remains constant.

Fig 2: Circuit Diagram - ABS Closed-Loop Operation Function (ABS Control Mode - Hold Pressure)

Shown using model 209 as an example

ABS control mode - reduce pressure

The control procedure and value positions illustrated in the example refer to the FR brake.

The ESP control unit initiates the pressure reducing phase using the slip values of the braked wheels.

The pressure reducing phase is initiated by opening the solenoid valve (y9). Solenoid valve (y8) remains closed during this control phase.

During the pressure reduction phase brake fluid flows back into the front axle pump (p1) via the accumulator (11).

Fig 3: Circuit Diagram - ABS Closed-Loop Operation Function (ABS Pressure Control Mode - Reduce Pressure)

From there the brake fluid is delivered back into the master brake cylinder against the pressure prevailing in the front axle circuit.

Each brake circuit has a muffler (12) to dampen the pumping sound.

ESP control unit, location/task/function	Model 163 Applicable as of 9/02	GF42.45-P-4500M
	Model 170, 202, 208 Model 203 up to 7/01	GF42.45-P-4500C
	Model 203 from 8/01 Model 209	GF42.45-P-4500T
Traction systems hydraulic unit, location/task/ design/function		GF42.50-P-4000D