Trailer control in the event of an electrical fault in the brake system, function

W42.25-1232-79

12.07 Brake wear sensor

12.08 Rpm sensor

13.08 Central Brake Unit (CBU)

18.07 Trailer control valve

20.02 Single-circuit diaphragm brake cylinder

22.01 Combination brake cylinder

24.04 Pressure ratio valve

31.13 Drive-axle axle modulator

35.02 Coupling head for supply

35.03 Coupling head for brake

A110a1 Electronic brake system (EBS) control unit

CAN 6 Brakes CAN

V1 System pressure (circuit 1)

V2 System pressure (circuit 2)

V3 System pressure (circuit 3)

a System pressure

b Brake pressure

c Redundant brake pressure

d Control pressure

AS Breakaway coupling

AV Outlet valve

B Brake value sensor

D Pressure sensor

EV Inlet valve

FB Parking brake

PV Proportioning valve

RD Redundancy valve

RE Control electronics

RV Relay valve

W Position sensor

General information

If there is a failure of the electronics, the trailer or semitrailer is braked via the purely pneumatic redundancy circuit.

An error message is output on the driver information system (FIS) display in the Instrument (INS) (P2).

Function

The actuation of the brake pedal causes the pneumatic component of the brake value sensor (B) to send a system pressure (a) proportional to the pedal travel via connection 23 to the trailer control valve (18.07) as a redundant brake pressure (c).

The relay valve (RV) in the trailer control valve (18.07) then actuates the pending reservoir pressure (a) as brake pressure (b) to match the redundant brake pressure on the coupling head for the brake (35.03).

When the brake pedal is released, the applied brake pressure (b) and the redundant brake pressure (c) are released via the vent, connection 3.