Brake application at front axle, function

W42.25-1169-79

Shown on 4-channel system

12.07 Brake wear sensor

12.08 Rpm sensor

13.08 Central Brake Unit (CBU)

20.02 Single-circuit diaphragm brake cylinder

30.03 Pressure limiting valve with vent

- Only in model 374.65, 375.4, 944.03/23, 950.62

31.13 Drive-axle axle modulator

33.21 3/2-way valve for auxiliary braking effect

- Only in model 374.65, 375.4, 944.03/23, 950.62

45.01 ABS solenoid valve

- For 4-channel system only

NV System pressure (ancillary consumers)

V2 System pressure (circuit 2)

a System pressure

b Brake pressure

c Redundant brake pressure

d Control pressure

A110a1 Telligent brake system (BS) control unit

AV Outlet valve

B Brake value sensor

D Pressure sensor

EV Intake valve

PV Proportioning valve

RD Redundancy valve

RV Relay valve

SV Control valve

W Position sensor

WV Shuttle valve

When the brake pedal is operated, the position sensors (W) register the pedal travel and report it to the brake system (BS) control unit (A110a1).

So that the electropneumatic brake circuit is not overlaid by redundant brake pressure (c), the redundancy valve (RD) is closed electrically by the brake system (BS) control unit (A110a1).

The proportioning valve (PV) is actuated by the brake system (BS) control unit (A110a1) and forwards the available system pressure (a) to the relay valve (RV) as the control pressure (d) according to the target deceleration calculated by the brake system (BS) control unit (A110a1).

-----------------------------------------------------------------------------------------

According to the control pressure (d) from the proportioning valve (PV), the relay valve (RV) now sends the available system pressure (a) as brake pressure (b) to connections 21 and 22.

The pressure sensor (D) reports the brake pressure (b) set by the relay valve (RV) to the brake control (BS) control unit (A110a1).

The brake pressure (b) set at connections 21 and 22 then flows over the shuttle valve (WV) in the 3/2-directional control valve for secondary braking (33.21) (only for model 374.65, 375.40, 944.03/23, 950.62) and over the ABS solenoid valves (45.01) (only for 4-channel system) to the front axle's single-circuit diaphragm brake cylinder (20.02).

-----------------------------------------------------------------------------------------

 Model 374.65, 375.4, 944.03/23, 950.62:

The pressure limiting valve with vent (30.03) and the 3/2-way valve for auxiliary braking effect (33.21) in these vehicles serve to satisfy the legal requirement for auxiliary braking effect in the event of failure of the pneumatic front axle brake circuit. Depending on the location of the defect, the left front wheel is braked with a pressure of 2.5 bar. The pressure is supplied from the reservoir pressure (NV) circuit.

The rpm sensors (12.08) evaluate any wheel rpm change and provide the brake system (BS) control unit (A110a1) with feedback on the actual deceleration attained and the wheel slip. If the actual deceleration attained deviates from the target deceleration, the brake control (BS) control unit (A110a1) corrects accordingly.

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