Wheel brake cylinder, location/task/design

B42.10-0431-01

B42.10-0432-01

Arrangement:

Located on the rear axle, beside the wheels, vehicle's inner side.

1 Combination cylinder of the wheel brake

B42.10-0384-12

Purpose:

To produce braking force on rear axle wheels, on vehicles with pneumatic drum or disc brake.

Structure:

1 Piston

2 Sealing ring

3 Spring

4 Cylinder

5 Relief nut

6 Cap

7 Relief bolt

8 Valve spring

9 Piston

10 Sealing ring

11 Braking pressure connection (13.02)

12 Relay valve pressure connection (16.01)

13 Piston

14 Diaphragm

15 Return spring

16 Fork rod

A Pressure chamber

B Gateway orifice

C Pressure chamber

D Passage hole

E Spring chamber

F Valve seat

G Spring chamber

H Breather orifice

b Brake pressure

c Control pressure

Operation:

I Drive position
The chamber (A) is depressurized and communicating with the atmosphere through the connection (11) and through the service brake exhaust valve.
The chamber (C) is pressurized through the parking brake valve and through the connection (12), keeping the piston (1) in its position against the spring force (3).

II Service braking
The compressed air coming from service brake pedal valve (13.02) reaches the chamber (A) through the connection (11) and actuates on the diaphragm (14), producing a force that is transmitted to the piston (13) and to the rod (16), displacing them.
Through the brake lever (clearance adjuster), the force transmission is processed, proportionally to the application pressure of the wheel brake. The actuation force available at rod depends on the pressure in the chamber (A) and the useful surface of the diaphragm (14), which varies according to the cylinder's stroke. When the application of the pressure on the chamber (A) ceases, the spring (15) action on the piston (13) and on the diaphragm (14), return them to their original position. Through the hole (H), the air is fed into or pushed out of the chamber (G) during the operation of the cylinder, avoiding the formation of vacuum or counter pressure.

III Auxiliary and parking braking
Relieving the pressure in chamber (C), through the parking brake valve (14.12) and the connection (12), the piston (1) displaces itself due to the action of spring (3), actuating on the diaphragm (14), the piston (13) and the rod (16), producing braking force proportional to the pressure relief processed in chamber (C). In the case of total relief, the spring action (3) is the maximum, characterizing the parking brake operation. In order to release the brake, the chamber (C) is pressurized by the parking brake valve (14.12) and the connection (12), until the specified relief pressure is reached.

During the piston movement (1) it is necessary to ensure a communication between the chamber (E) and the atmosphere, in such a way that the formation of vacuum or counter pressure is avoided.
In the cylinders of this series, this problem is solved through a valve integrated in the piston (1) and that works the following way:
a) Application of the parking brake:
By relieving the pressure existing in the chamber (C), the piston (1) moves by the spring (3) action, and it is necessary to let the air get in the chamber (E), in order to avoid the formation of vacuum. The necessary air comes from the chamber (A) and goes through the hole (B), acts on the piston (9) and, as it does not have sufficient pressure to overcome the spring force (8), penetrates through the opened valve seat (F) and of the chamber (e) hole (D). This air is clean, coming from the pipe that connects the combination brake cylinder to the service brake valve.
b) Releasing of the parking brake:
Equally, if the chamber (C) is pressurized, the piston (1) will travel against the spring action (3) and the air present in the chamber (E) will go to the atmosphere by the route opposite to the one described above.
c) Application of the service brake:
In the most common operation position, the chamber (C) is pressurized, and the piston (9) touches the stopper and presses the seal (10). This way, the compressed air that penetrates inside the chamber (A) in a service brake operation does not have access to the gateway orifice (B), what only occurs if the chamber (C) pressure is relieved, opening the seal (10). In this case, the air flows through the orifice (B) and actuates on the piston (9), overcoming the resistance of the spring (8) and closing the valve seat (F), with no more access to hole (D) and, consequently, to chamber (E).

IV Mechanical relief device
In the case of insufficient pressure in the parking brake circuit, the cylinder can be mechanically released. To do so, turn the relief nut (5) with a wrench and, consequently, the relief bolt (7), counterclockwise. Due to the existing thread in the cover central bore (6), the relief bolt (7) touches the piston (1) pulling it against the spring force (3) and relieving the brakes.