ESP Hydraulic Unit

Location
The left front wheelhouse

Task
The traction systems hydraulic unit (A7/3) carries out the control of the driving dynamics system at the wheel brakes.

Design















Function
The switching components of the ABS, ASR and ESP driving dynamics control systems are combined in the traction systems hydraulic unit (A7/3).

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 actuated in cycles for pressure build-up/pressure reduction during ASR/ESP controls and for return flow during ABS controls.

Low Pressure Accumulator (11)
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 and p2).

Solenoid Valves (Hold) (Release (A7/3-y6 - 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 (A7/3y18 and y19)
During ASR and ESP controls the switchover solenoid valves (y18 and y19) shut off whichever the RA and FA high-pressure circuits is active at the time from the master brake cylinder. At the same time they are designed as pressure limiting valves and open at pressure values greater than 150 bar. The brake fluid flowing away via the switchover solenoid valves is led back to the master brake cylinder.

Inlet Solenoid Valves (A7/3y22 and y23)
The inlet solenoid valves (y22, y23) are opened during the ASR/ESP pressure build-up phases.

Measures For Reducing Noise
In all control phases the self-priming high pressure and return pumps (p1 and p2) are actuated in cycles demand-dependent and to reduce noise. Various silencing components (13, 14) are fitted to further reduce noise. There is a silencer (12) in each brake circuit (FA, RA) to damp the delivery noise.