Patent GB-1423057-A (GB)
Title: Self-adjusting device
IPC: F15B15/24
Filed: 1973-04-17
Abstract: 1423057 Slack adjusters ALFRED TEVES GmbH 17 April 1973 [19 April 1972 13 Feb 1973] 18505/73 Heading F2E A self-adjusting device, e.g. for a drum or disc brake, has an adjusting nut 4 rotatable on the thread of an adjusting spindle 3 and, for limiting the return stroke or movement of an actuating piston 1 of the device, a driving bush 10 arranged to be axially shiftable and rotatable about its longitudinal axis on the nut 4, the driving bush limiting said return movement by abutting against a friction surface 14 presented by the actuating piston with a friction surface 13 of the bush, the adjusting nut having a pin 12 engaging with a slot 11 in the driving bush extending at an angle to the longitudinal axis of the bush to allow the rotation with axial shift of the latter. A torsion spring 15 is provided to cause the driving bush to follow when the friction surfaces presented by the piston and the bush move away from one another due to an actuating piston stroke, the friction surfaces, the nut, the bush and the spindle being so dimensioned that, when the friction surface 14 presented by the actuating piston abuts against the friction surface 13 of the driving bush, the latter will turn less easily than the adjusting nut on the spindle thread, whereas during movement by the piston in the actuating direction the driving bush will turn more easily than the nut on the spindle. The driving bush has its friction surface tapered, such that it increases in a cross-section in the opposite direction to the actuating direction of movement of the piston and is arranged after a return stroke of the piston to abut against the part of the piston presenting the friction surface thereof. As shown, the head 5 of the nut 4 has an annular groove 6 in which is disposed a clamp ring 7 radially outwardly biased to establish a connection between the piston 1 and the nut 4, the ring, when the piston moves to the left, being completely disposed within the groove by action thereagainst of the the bevelled edge 9 of a groove 8 in the piston. The spindle 3, connected for example to a brake caliper, has a threaded fit with the nut 4 providing backlash corresponding to the clearance or free play required by the brake. In operation, when the ring 7 is pressed into the groove 6 the bush 10 is moved by the spring 15 in the operating direction of the piston and the bush 10 is rotated through a small angle under the influence of the forward power stroke, the nut 4 remaining stationary after moving leftward to the extent of its backlash. With a decrease in pressure, the ring 7 expands to push the piston back to its original position whereby the surfaces 13, 14 abut to secure the bush against further rotational movement in either direction; the nut 4 is caused to be turned under the influence of the return stroke of the piston on the bush whereby the desired adjustment is obtained. The ring 7 may constitute the only return spring for the piston and for the brake itself. In modifications, a wheel brake cylinder (20), Fig. 2 (not shown), contains two axially movable pistons (1), (1<SP>1</SP>), the piston 1 having a bore (2) into which the spindle 3 and nut 4 project, the head (5) of the nut (4) having a groove (6) in which is received a clamp ring (7) which acts as a slipping clutch for the nut in the bore 2 and does not act as a return spring, (b) the spindle 33, Fig. 3, is secured to a second piston 31<SP>1</SP> and the nut 34 carries a torsion spring 51 abutting a surface 52 thereof and the bush 40, the spring being provided with a bent leg located in a deepened part of the groove 60 and in contact with the spindle 33 to provide a slipping clutch; alternatively, the latter is provided by a spring clip separate from the spring 51. The nut 34 may have a frusto-conical friction surface 66 which abuts against a correspondingly shaped edge 67 of the piston 30.