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

MODEL 164

Shown on model designation 164.1

Fig 1: Identifying Traction System Hydraulic Unit

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

The traction system hydraulic unit is located in the left front of the engine compartment. It carries out the closed-loop operation of the braking torque control circuit and controls intervention by the brake system for:

Electronic Stability Program (ESP)
Antilock brake system (ABS)
Acceleration Slip Regulation (ASR)
Engine braking regulation control (MSR)
Electronic brake force distribution (EBV)
ESP®-trailer stabilization (164.8 only)
Distronic (DTR) (164.8 only)

Fig 2: Identifying Traction System Hydraulic 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.

Function

The switching components of the ABS, ASR and ESP are combined in the traction system hydraulic unit .

For control per wheel one 2/2 directional control valve each are used for the function of pressure buildup/holding and pressure holding/depressurization.

High pressure and return pump

The self-priming high pressure and return pumps integrated in the traction system hydraulic circuit are used for pressure buildup, depressurization during ASR-/ESP controls and for return delivery during ABS controls. A damper is fitted to each brake circuit to damp the delivery noise.

The low-pressure reservoir takes up brake fluid in the ABS/ ASR/or ESP pressure reduction phase and passes it on to the high pressure/return flow pump.

Switchover solenoid valves

During ABS, ASR and ESP controls, the switchover solenoid valves shut off the self-priming pumps for the pressure circuit (DK1) (FL and RR) and the self-priming pumps for the pressure circuit (DK2) (FR und RL) between the wheel brakes and the master brake cylinder. They are designed simultaneously as pressure limiting valves and open at approx. 150 bar.

The brake fluid flowing away via the switchover solenoid valve is lead back to the master brake cylinder.

Solenoid valves, pressure holding/depressurization

For control per wheel, one directional control valve each is used for the pressure buildup/holding functions and pressure holding/depressurization functions in ABS/ASR und ESP closed-loop operation:

Left front solenoid valve (pressure hold)
Left front solenoid valve (pressure release)
Right front solenoid valve (pressure hold)
Right front solenoid valve (pressure release)
Left rear solenoid valve (pressure hold)
Left rear solenoid valve (pressure release)
Right rear solenoid valve (pressure hold)
Right rear solenoid valve (pressure release)

Intake solenoid valves

The inlet solenoid valves are opened during the ASR/ESP pressure buildup phases when the calculated pressures in the respective brake caliper are 60 bar and one of the

Left front solenoid valve (pressure hold),
Right front solenoid valve (pressure hold),
Left rear axle solenoid valve (pressure hold) or
Right rear solenoid valve (pressure hold)

is actuated.

If the calculated pressure are > 60 bar, the

Pressure circuit 1 inlet solenoid valve and
Pressure circuit 2 inlet solenoid valve

also remain open during the ASR-/ESP holding phases.