GF42.50-P-4000-04D Traction System Hydraulic Unit, Function

GF42.50-P-4000-04D Traction system hydraulic unit, function





The switching components of the ABS, ASR and ESP driving dynamics control systems are combined in the traction system hydraulic unit (A7/3).

High-pressure and return pump (A7/3m1)
The front axle pump (p1) and rear axle pump (p2) integrated in the traction system hydraulic unit (A7/3) are actuated pulsed for pressure buildup/reduction during ASR/ESP controls and for return delivery during ABS controls.

Solenoid valves for pressure holding/pressure reduction (A7/3y6 up to y13)
For pressure control one 2/2 directional control valve is used for the functions of pressure buildup/hold and pressure hold for each wheel in ABS/ASR and ESP closed-loop operation.

Low-pressure reservoir (11)
The low pressure accumulator (11) takes up brake fluid during the ABS/ASR or ESP pressure reduction phase and delivers it to the front axle pump (p1) and rear axle pump (p2).

Switchover solenoid valves (A7/3y18 and y19)
The switchover solenoid valves (y18 and y19) shut off during ASR and ESP controls the respective rear axle and front axle active high pressure circuits against the master brake cylinder. They are also designed as pressure relief valves and open at pressures > 150 bar. The brake fluid passing through the switchover solenoid valves is directed back to the master brake cylinder.

Inlet solenoid valves (A7/3y22 and y23)
The inlet solenoid valves (y22 and y23) are opened during the ASR/ESP pressure buildup phases.

Brake pressure sensors (B34, B34/1, B34/2)
The ESP Mk20 (model 203 up to 7/01) has 2 brake pressure sensors. ESP brake pressure sensor 1 (B34/1) records the brake pressure in the front axle circuit, ESP pressure sensor 2 (B34/2) records the pressure in the rear axle circuit.

ESP Electronic Stability Program Mk25 (model 203 as of 8/01, model 209) has only one brake pressure sensor (B34) which monitors the front axle circuit.

The brake pressure signals of the brake pressure are conveyed to the control unit for calculating the controls.

Noise reduction measures
In all control phases the front axle pump (p1) and the rear axle pump (p2) are actuated pulsed depending on the requirement and to minimize noise.

Various damping components (13, 14) are installed to further reduce noise levels. Each brake circuit has a damper (12) to muffle the pumping sound.