Hydraulic Control Assembly - Antilock Brakes: Locations

GF42.50-P-4001MCC Traction System Hydraulic Unit, Component Description







1 Hydraulic unit
N47-5 ESP control unit

Location
The hydraulic unit is located on the vehicle underfloor.







1 Hydraulic unit
2 Inlet of tandem master brake cylinder
3 Outlet to respective brake caliper or wheel brake cylinder
N47-5 ESP control unit

Function diagram







5a Front wheel brake, right
5b Front wheel brake, left
6a Rear wheel brake, right
6b Rear wheel brake, left

7 Check valve
9 Check valve of return pump
10 Damper
11 Low-pressure reservoir
12 Self-priming pump (front axle)
13 Self-priming pump (rear axle)

b1 Front axle brake pressure sensor
b3 Left front pressure sensor
b4 Right front pressure sensor
b5 Left rear pressure sensor
b6 Right rear pressure sensor
m1 High pressure and return pump
y6 Left front solenoid valve (pressure hold)
y7 Left front solenoid valve (release)
y8 Right front solenoid valve (pressure hold)
y9 Right front solenoid valve (pressure release)
y10 Left rear axle solenoid valve (pressure hold)
y11 Left rear axle solenoid valve (pressure release)
y12 Right rear solenoid valve (pressure hold)
y13 Right rear solenoid valve (pressure release)
y18 Front axle switchover solenoid valve
y19 Rear axle switchover solenoid valve
y22 Front axle inlet solenoid valve
y23 Rear axle inlet solenoid valve
A Traction system hydraulic unit
B Master brake cylinder
HZ1 Pump pressure circuit 1 (front axle)
HZ2 Pump pressure circuit 2 (rear axle)

Functional principle
The switching components for ABS, ASR, ESP and EBV are combined in the hydraulic unit.
For control purposes, one 2/2 way valve is used on each wheel for the pressure buildup, pressure hold and pressure release functions.

The high-pressure and return pumps in the hydraulic unit are required for pressure buildup and pressure release during ASR and ESP interventions and for return delivery during ABS intervention. A damper is fitted to each brake circuit to damp the delivery noise. The low pressure reservoir takes up the brake fluid during the ABS/ASR or ESP depressurization phase and delivers it to the high pressure/return flow pump.

During ABS, ASR and ESP interventions, the switchover solenoid valves shut off the self-priming pump pressure circuit 1 (front axle) and self-priming pump pressure circuit 2 (rear axle) between the wheel brakes and the master brake cylinder.

The brake fluid passing through the switchover solenoid valves is directed back to the master brake cylinder.

Pressure limiting
Switchover valves without pressure limiting valves are used on the ESP version installed. Protection against excess pressure is provided by reducing the maximum permissible current in the coils of the switchover valves (USV) to 1.24 A.