Parking brake adjustment function

D42.10-0055-12

Low brake pressure

1 Adjusting screw

2 Spring

3 Ball bearing

4 Spring

5 Adjusting nut

6 Piston (primary piston)

7 Secondary piston

A Position A of thread flank

B Position B of thread flank

C Contact area

D42.10-0054-12

High brake pressure

1 Adjusting screw

2 Spring

3 Ball bearing

4 Spring

5 Adjusting nut

6 Piston (primary piston)

7 Secondary piston

8 Friction plates

A Position A of thread flank

B Position B of thread flank

C Contact area

Function

The parking brake is adjusted during the first phase of service brake operation, i.e. when the hydraulic pressure in the brake system is still low. As from a certain pressure the adjusting nut is no longer able to turn. The adjustment takes place when the clearance due to brake lining and brake disc wear has become greater than the basic clearance.

I Low brake pressure

When the service brake is operated, the piston (6) is pressed towards the brake pad. The adjusting nut (5) follows this movement and the adjusting screw (1) remains pressed in the opposite direction due to the force of the spring (2). The

adjusting screw cannot turn due to the shape of the bolt head. The thread flank of the adjusting nut is moved from position A to position B.

When the piston (6) moves along further the thread of the adjusting nut (5) is pressed against the thread of the adjusting screw (1) and the pistons released from the contact area C. The spring (4) is compressed slightly, but the spring (2) is so stiff that the adjusting screw stays pressed in.

As the adjusting nut (5) abuts the ball bearing (3) and is released from the contact area C, it can turn in the thread of the adjusting screw and move outwards. This increases the effective length of the adjusting screw which compensates for the longer stroke of the spring brake cylinder.

II High brake pressure



The brake is only adjusted automatically at low brake pressure.

When the hydraulic pressure in the brake system exceeds a certain level, the secondary piston (7) is pressed towards the brake pad proportionate to the piston (6).

The secondary piston (7) presses on the adjusting nut (5) via the friction washers (8) and the locking ring which is then pressed against the contact area C of the piston (6).

The friction at the contact area is higher as a result and prevents the adjusting nut (5) turning any further.

Due to the brake pressure on the secondary piston (7) the adjusting screw is drawn outwards at the same time over the thread of the adjusting nut; therefore no adjustment can take place.