HOW IT WORKS

1. Starting Position

The control arm 25 of the ASA is fixed to the anchor bracket in a position where the toe of the rack 19 is touching the top of the notch in the control disk 24. The depth of the notch determines the pre-set running clearance that will be maintained between brake lining and brake drum.

2. Rotation through the clearance angle A

The ASA rotates through the angle A until the toe of the rack 19 touches the bottom of the notch in the control disk 24. The Brake shoes are expanded but, when excess clearance exists because the drums and linings are worn, the linings do not touch the brake drum.

3. Rotation through the excess clearance angle B

As the ASA continues to rotate, the rack 19 is prevented from moving down any further by the bottom of the notch in the control disk 24, which is anchored by the fixed control arm. The rotation of the ASA forces the pinnion 6 of the one way clutch over the teeth of the rack. The pinnion rotates freely as the one way clutch assembly slips in this direction of rotation. During this movement the camshaft expands the brake shoes until the linings touch the brake drum.

4. Rotation into the elasticity angle C

When the brake linings are being pressed with increasing force into the the brake drum, the torque on the camshaft and the worm wheel increases rapidly. This torque, transmitted through the worm wheel 21 forces the worm screw 9 back onto the coil spring 14, which compresses, so that the cone clutch between the worm screw 9 and the cone clutch housing 4 is disengaged.

5. Rotation through elasticity angle C

As the ASA continues to rotate, the rack is still prevented from moving with the rotation by the control disk, which is anchored. The movement of the pinnion over the rack now causes the whole one way clutch assembly to turn and it is free to do so because the cone clutch 4 & 9 is disengaged.

6. Rotation back through elasticity angle C

The return springs 17 & 18 hold the toe of the rack down against the bottom of the notch in the control disk 24. The rack turns the one way clutch assembly freely because the cone clutch 4 & 9 is disengaged.

7. Rotation back into the clearance angle A

As the pressure of brake linings on drum drops, so does the torque on the camshaft, worm wheel 21 and worm screw 9, allowing the coil spring 14 to re-extend and push the worm screw back into the cone clutch housing 4, thus re-engaging the torque sensitive clutch.

8. Rotation back through the clearance angle A.

As the ASA rotates back, the toe of the rack 19 is lifted from contact with the bottom of the notch in the control disk 24 to contact with the top of the notch.

9. Eliminating the slack with rotation back through the excess clearance angle B

As the ASA finishes the rotation back to its starting position, the rack 19 is prevented from moving with it by the toe of the rack, which is pressing against the top of the notch in the anchored control disk 24. As the ASA rotates, the teeth in the stationary rack rotate the pinnion 6 in the one-way clutch assembly and, because both clutches are now engaged, the worm screw 9 is turned with it. The worm screw turns the worm wheel 21 and the worm wheel turns the camshaft. Such rotation of the camshaft reduces the excess clearance between brake lining and brake drum - QED.