ESP control mode, function - GF42.45-P-3700C

MODEL 163 with CODE (472a) electronic stability program (ESP)

Brake intervention to stabilize the vehicle is introduced by the ESP control module.

At the start of ESP control the switchover solenoid valves (y24 and y25) are switched to the "shut-off position" (closed) and the high pressure and return pump (m1) is actuated. The BAS solenoid valve (A7/7y1) in the brake booster for (A7/7) is actuated (opened). This leads atmospheric pressure to the back of the diaphragms in the brake booster, generating pressure of approx. 5 bar which is applied as pilot pressure at the suction sides of the high pressure and return pumps (p1, p2)

Generally there is no ESP control at speeds < 10 km/h.

ESP pressure build-up control mode

The control process shown in the example and the valve positions relate to the RR brake and actuated BAS solenoid valve (A7/7y1)

The self-priming high pressure and return pump (p1) draws in brake fluid under pilot pressure via the inlet solenoid valve (y26), opened during the pressure build-up phase, and produces high pressure at the wheel brake cylinder 6a.

The pressure limiting valve integrated in the switchover solenoid valve (y24) serves to limit high pressure (approx. 150 bar).

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

ABS pressure holding control mode

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

ESP pressure holding control mode starts if no more brake is required to prevent drive slip.

The inlet solenoid valve (y26) and solenoid valve (y12) are closed. As a result the high pressure and return pump (p1) cannot increase the pressure in the brake caliper any more.

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

ESP pressure reduction control mode

The control process shown in the example and the valve positions relate to the RR brake ESP pressure reduction control mode starts if the brake pressure required to prevent drive slip is too high.

The pressure reduction phase is initiated by opening the solenoid valve (y13). The solenoid valve (y12) remains closed.

The self-priming high pressure and return pump (p1) is also actuated and the switchover solenoid valve (y24) closed in this control phase.

The brake fluid flows back to the brake fluid reservoir via the self-priming high pressure and return pump (p1), pressure limiting valve integrated in the switchover solenoid valve (y24) and the master brake cylinder.

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

At the end of the pressure reduction phase the system pressure (approx. 150 bar) between the self-priming high pressure and return pump (p1), switchover solenoid valve (y24) and solenoid valve (y12) is initially led to both brake calipers of the circuit after the high pressure and return pump (m1) is switched off.

This prevents the system pressure in the tandem master brake cylinder being released suddenly and the noise build-up associated with this.

	ESP control module, location/task/function		GF42.45-P-4500B
	Traction systems hydraulic unit, location/task/ design/function		GF42.50-P-4000C
	BAS solenoid valve, location/task/function		GF42.31-P-4002A