Traction systems hydraulic unit, function - GF42.50-P-4000-04C

Model 163 

The ABS, ASR and ESP switching components are combined in the traction systems hydraulic unit(A7/3)  . For the control, one 2/2-way valve is used for each wheel for the pressure build-up/pressure holding and pressure holding/pressure reduction functions.

High pressure and return pump (A7/3m1) 

The self-priming high pressure and return pumps (p1, p2) integrated in the traction systems hydraulic unit (A7/3) are used for pressure buildup/pressure reduction during ASR/ESP controls and for return flow during ABS controls. There is a silencer (10)  in each brake circuit (DK, SK) to damp the delivery noise.

The low pressure accumulator (11)  takes up the brake fluid in the ABS, ASR or ESP pressure reduction phase and delivers it to the high pressure and return pumps (p1/p2)

Solenoid valves (hold) (release) (A7/3y6-y13) 

For the control, one 2/2-way valve is used for each wheel for the pressure build-up/pressure holding and pressure holding/pressure reduction functions in ABS, ASR and ESP control mode.

Switchover solenoid valves (A7/3y24 and y25) 

During ABS, ASR and ESP controls the switchover solenoid valves (y24 and y25) shut off the pressure circuits SK  (FL and RR) and DK  (FR and RL) between the wheel brakes and the master brake cylinder. At the same time they are designed as pressure limiting valves and open at approx. 150 bar.

The brake fluid flowing away via the switchover solenoid valves is led back to the master brake cylinder.

Inlet solenoid valves (A7/3y26 and y27) 

The inlet solenoid valves (y26, y27) are opened during the ASR/ESP pressure build-up phases when the calculated pressures in the respective brake caliper are μ 60 bar and one of the solenoid valves (y6, y8, y10 or y12) is actuated.

If the calculated pressures are > 60 bar, the inlet solenoid valves (y26, y27) also remain open during the ASR/ESP holding phases.