ESP Hydraulic Unit

Location
The left of engine compartment

Task
The traction systems hydraulic unit (A7/3) carries out the control functions of the brake moment control circuit.

Design

Design (Part 2 Of 2):

Function
Solenoid Valves (Hold) (Release) (A7/3y6-y13)
For the control, one 2/2-way valve is used for each wheel for pressure build-up, pressure holding and pressure holding/pressure reduction Function in ABS control mode.

Inlet Solenoid Valves (A7/3y22 and y23)
The inlet solenoid valves (Y22 and Y23) which are resistant to high pressure are located in the suction lines to the high pressure and return pumps (pi and p2). Their Task is to allow the pilot pressure of 3-5 bar through to the high pressure and return pumps (p1 and p2) during ASR and ESP control. They are also used to control the circuit pressure. They are closed during ASR and ESP control-pressure holding.

Switchover Solenoid Valves (A7/3y18 and y19)
The switchover solenoid valves for front or rear axle circuits (A7/3y18 and y19) shut off the line system between the wheel brakes and master brake cylinder during ASR and ESP control-pressure build-up and pressure holding. They are open during ASR and ESP control-pressure reduction.
At the same time they are designed as pressure limiting valves and open at approx. 170 bar. The brake fluid flowing away via the switchover solenoid valves is led back to the master brake cylinder.

High pressure and return pump (A7/3m1)
The high pressure and return pumps (p1 and p2) integrated in the hydraulic unit (A7/3) are used for ASR and ESP pressure supply and return during ASS, ASR or ESP controls. There is a silencer (10) in each brake circuit to damp the delivery noise.
The low pressure accumulators (11) take up the brake fluid flowing back in the ABS/ASR/ESP pressure reduction phase and deliver it to the high pressure and return pumps.
The low pressure accumulators (11) take up the brake fluid flowing back in the ABS/ASR/ESP pressure reduction phase and deliver it to the high pressure and return pumps

ESP Brake Pressure Sensor (B34)
The ESP brake pressure sensor is attached to the inlet of the line for the front axle circuit.