Traction system hydraulic unit, component description - GF42.50-P-4001MCC

MODEL 451.3/4

Fig 1: Locating ESP Control And Hydraulic Units

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Location

The hydraulic unit is located on the vehicle underfloor.

Fig 2: Identifying ESP Control Unit Components

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Function diagram

Fig 3: Traction System Hydraulic Unit Function Diagram

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

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.