Traction systems hydraulic unit, function - GF42.50-P-4000-04A

Models 129, 140, model 210 with engine 119

Fig 1: Identifying Traction Systems Hydraulic Unit (Models 129, 140, Model 210)

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

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

Solenoid valves (hold) (release) (A7/3y6-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 function.

Precharge solenoid valves (A7/3y16 and y17)

The precharge solenoid valves (y16 or y17) are located in the charging lines to the high pressure and return pumps (p1 and p2). Their task is to allow the pilot pressure of 3-15 bar through to the high pressure and return pumps (p1 and p2) during ASR and ESP control.

Switchover solenoid valves (A7/3y18 and y19)

The switchover solenoid valves for front or rear axle circuits (A7/3y18 or y19) shut off the line system between the wheel brakes and master brake cylinder during ESP control. At the same time they are designed as a pressure limiting valve and open at approx. 170 bar.

The brake fluid flowing away via the switchover solenoid valves is damped by the pressurizing piston unit (14) and returned to the master brake cylinder via the charging piston.

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 or ESP pressure supply and return during ABS, 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.