Pneumatic rear axle brake circuit, function

W42.25-0115-06

1.1 2/2 solenoid valve

1.2 3/2-way valve

1.3 Relay valve

2.1 Inlet/outlet valve 1

2.2 Inlet/outlet valve 2

2.3 2-way valve

12.07 Brake wear sensor

12.08 Rpm sensor

13.05 Brake value sensor

16.07 Proportioning relay valve

18.07 Trailer control valve

22.01 Combination brake cylinder

31.08 Drive axle axle modulator

33.06 Redundancy valve

V1 Supply, circuit 1

V2 Supply, circuit 2

a Supply pressure (V1 and V2)

c Brake pressure

b Redundancy circuit (pneumatic control pressure)

When the system is not controlling and not braking, the 3/2-way valve (1.2) in the redundancy valve (33.06) is switched to open. If during an electropneumatic braking operation a pressure of approx. 0.3 to 0.5 bar is applied via the inlet/outlet valves 1 (2.1) and the inlet/outlet valves 2 (2.2) in the drive axle axle modulator (31.08), the 3/2-way valve (1.2) switches and the pneumatic control pressure in the redundancy circuit is removed.

If the control unit detects the conditions for ABS control from the available wheel speeds, the inlet/outlet valves 1 (2.1) and 2 (2.2) vent the appropriate combination brake cylinder (22.01); the redundancy function must not be activated. In this case, after the 3/2-way valve (1.2) switches over, the 2/2 solenoid valve (1.1) is energized and the pressure between the master control unit of the 3/2-way valve (1.2) and the valve seat of the 2/2 solenoid valve (1.1) is maintained. This switches the 3/2-way valve (1.2) to the closed position and the redundancy circuit remains deactivated.

When the 2/2 solenoid valve (1.1) is de-energized again, the pressure in the control line drops.

If electropneumatic brake pressure regulation fails, the 3/2-way valve (1.2) in the redundancy valve (33.06) is switched to open. The pneumatic control pressure modulated by the brake value sensor (13.05) actuates the relay valve (1.3). Brake pressure can now pass via the 2-way valves (2.3) to the combination brake cylinders (22.01).

In the case of redundancy at the rear axle, the pneumatic control pressure modulated by connection 21 of the brake value sensor (13.05) is relayed by the redundancy valve (33.06) back to an additional control surface in the brake value sensor (13.05) and the brake pressure at the front axle is boosted.

The brake pressure effective at the rear axle in the case of redundancy is limited. It roughly corresponds to an ALB setting of "semi-laden" in order to prevent overbraking at the rear axle when the vehicle is empty and to ensure adequate braking when the vehicle is fully laden.

In the event of failure of electropneumatic brake pressure regulation at the rear axle, there is no ABS control at either the front or the rear axle.