Arrangement/Purpose/Design/Function of ETS Hydraulic Unit

MODEL 163 with CODE (212a) Electronic traction system (ETS)




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A7/3 ASR/ETS/ESP Hydraulic Unit





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All switching components of the ABS and ETS systems are combined in the ETS hydraulic unit (A7/3).

A 2/2-way valve for build-up/hold pressure or hold/release pressure functions is used on each wheel for control. The self priming high pressure/return pumps (p1, p2) integrated in the hydraulic unit (A7/3) are used to supply pressure to the ETS and return the brake fluid for ABS control. The inlet pipes of the self priming high pressure/return pumps (p1, p2) contain the inlet solenoid valves (y26, y27).
The inlet solenoid valves (y26, y27) are opened only once a pressure of 60 bar has been reached in the respective brake calipers during the ETS pressure build-up phase. They are opened for the time it takes to actuate solenoid valves (y6, y8, y10 or y12).

When pressures of > 60 bar are reached in one of the respective brake calipers during ETS control, the inlet solenoid valves (y26, y27) remain open.

During ETS control, the switchover solenoid valves (y24, y25) lock the front and rear axle circuits 1 (VL and HR) and 2 (VR and HL) to the brake master cylinder. They are also designed to function as a pressure relief valve and open at approx. 150 bar. A muffler (10) is fitted for each brake circuit to reduce delivery noise.

During the ABS pressure reduction phase the fluid flows back to the high-pressure/return pump via the low-pressure accumulator (11).