Brake Application At Rear Axle Function - Mercedes Benz Actros

Requirements

• Vehicle moves.
• System pressure (V1, V2) in circuit 1 and circuit 2. 
• The electric brake control is operational.
• No faults are indicated in the driver information system (FIS) display in the Instrument (INS).

V1 System pressure (circuit 1)

V2 System pressure (circuit 2)

a System pressure

b Brake pressure

c Redundant brake pressure

d Control pressure

12.08 Rpm sensor

13.07 Brake value sensor

22.01 Combination brake cylinder

31.08 Drive-axle axle modulator

33.08 Front axle redundancy valve

33.10 Rear axle redundancy valve

A11 Electronic brake system (EBS) control unit

FB Parking brake

Function sequence

1. The brake pedal is depressed.
2. The sensors in the brake value sensor (13.07) register the pedal travel electrically for the brake system (BS) control unit (A11).
3. The brake system (BS) control unit (A11) uses the pedal travel to compute the specified deceleration of the vehicle.
4. Vehicles without code (ZX2) EPB II Via connection 21 the pneumatic component of the brake value sensor (13.07) directs a redundant brake pressure (c) corresponding to the pedal travel to the closed rear axle redundancy valve (33.10).
5. The brake control (BS) control unit (A11) uses the calculated specified deceleration to actuate the electronics of the drive axle-axle modulator (31.08 or 31.13).
6. The electronics of the drive-axle axle modulator (31.08 or 31.13) convert the control command from the brake control (BS) control unit (A11) into electrical control signals for the internal valves and causes them to apply the brake pressure (b).
7. Supply pressure (a) is directed from connections 11 and 12 as brake pressure (b) though connections 21 and 22 of the drive-axle axle modulator (31.08 or 31.13) into the combination brake cylinders (22.01) of the rear wheel brakes; the wheels are braked.
8. During the entire brake application, the electronics of the drive-axle axle modulator (31.08 or 31.13) record the values from the internal pressure sensors and the signals from the rpm sensors (12.08) on the rear wheels and transmits these to the brake control (BS) control unit (A11).
9. To calculate the actual deceleration and the wheel slip, the brake control (BS) control unit (A11) evaluates the signals and values of the drive-axle axle modulator (31.08 and 31.13). If the actual deceleration deviates from the specified deceleration, the brake control (BS) control unit (A11) causes the drive-axle axle modulator (31.08 or 31.13) to reduce or increase the brake pressure (b).
10. The driver releases the brake pedal and the brake application is complete. The applied brake pressure (b) and the applied redundant brake pressure (c) are released again through ventilation connection 3.

In the case of ABS control, the internal valves of the drive-axle axle modulator (31.08 or 31.13) perform the "pressure buildup", "pressure hold" and "pressure release" functions in the same way as the ABS solenoid valves on the front axle.

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