ABS control mode, function - GF42.45-P-3000C

MODEL 163 with CODE (472a) Electronic Stability Program (ESP)

ABS pressure build-up control mode

Every ABS control starts with a normal braking process which the driver performs via the brake pedal.

The ESP control module recognizes the braking process via the stop lamp switch (S9/1) and decelerated wheel speeds.

The brake pressure is passed on via the two switchover solenoid valves (y24 and y25) and the solenoid valves (y6, y8, y10 and y12). The pressure build-up phase can thereby take place individually at each wheel during an ABS control process.

During a braking process without ABS control, pressure reduction also takes place via the solenoid valves (y6, y8, y10, y12, y24 and y25).

Fig 1: Circuit Diagram - ABS Control Mode, Function (ABS Pressure Build-Up Control Mode)

ABS pressure holding control mode

The control process shown in the example and associated valve positions relate to the FR brake.

If a wheel tends to lock during the braking process, ABS prevents a further pressure build-up . The ESP control module introduces the pressure holding phase from the slip values of the braked wheels.

The pressure holding phase is introduced by actuating (closing) the solenoid valve (y8). The solenoid valve (y9) remains closed and the pressure in the FR brake caliper remains constant as a result.

Fig 2: Circuit Diagram - ABS Control Mode, Function(ABS Pressure Holding Control Mode)

ABS pressure reduction control mode

The control process shown in the example and valve positions relate to the FR brake.

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

The pressure reduction phase is introduced by actuating (opening) the solenoid valve (y9). The solenoid valve (y8) remains actuated (closed) in this control phase.

During the pressure reduction phase brake fluid flows back into the high pressure and return pump (p2) via the accumulator (11).

From there, the brake fluid is delivered back to the master brake cylinder against the pressure prevailing in the thrust rod circuit pressure circuit.

There is a silencer (10) in each brake circuit to damp the delivery noise.

Fig 3: Circuit Diagram - ABS Control Mode, Function (ABS Reduction Control Mode)

	ESP control module, location/task/function		GF42.45-P-4500B
	Traction systems hydraulic unit, location/task/ design/function		GF42.50-P-4000C