Patent GB-1122837-A (GB)
Title: Improvements in brake systems for vehicles
IPC: B60T8/74
Filed: 1966-11-22
Abstract: 1,122,837. Fluid-pressure brakes. ROBERT BOSCH G.m.b.H. 22 Nov., 1966 [23 Nov., 1965], No. 52202/66. Headings F2E and F2F. In an anti-skid braking system for a vehicle, using compressed air as the pressure medium in the brake cylinder 9, the brake cylinder comprises a trailing piston 20 coupled to the brake piston 17, the trailing piston 20 being provided with clamping elements 39 which are adapted to be actuated by the pressure medium for retaining the piston in position in the cylinder when wheel locking occurs and in which a working chamber 34 situated adjacent to the clamping elements 39 communicates with a pressure chamber through a valve 46 controlled by a control device for automatically preventing the braking power from rising in the brake cylinder if the wheels lock. In operation, when the brakes are applied, compressed air is supplied from a compressor 1, a conduit 2 to a pressure regulator 3 to which an air reservoir 5 is connected and thence via conduit 6 through a control valve 7 to the line 8 leading to the brake cylinder 9. Compressed air enters the brake cylinder 9 through the connection 12 and acts on the brake piston 17 to displace the latter with its piston-rod 18 and the trailing piston 20 in the braking direction so that the wheel brakes 11 are applied and the vehicle retarded. The slide valve 46 remains closed during this operation. Should wheel locking occur, a switch element 54 is actuated to close the electrical circuit and current flows through a coil 52 and an armature 50 is moved into the coil, thus causing the slide valve 46 to be actuated through the rod 47 and allow the two control bores 47 and 48 to be brought into alignment. Part of the compressed air acting on the brake piston 17 now flows into the counter pressure chamber 42 between the brake piston 17 and the trailing piston 20. From the counter pressure chamber 42, the compressed air passes through a bore 43 into a chamber 34 behind the annular diaphragm 36 to force the latter radially outwardly together with the clamping segments 39 which are forced against the internal wall 15 of the brake cylinder 9. The trailing piston 20 is consequently held in position in the cylinder 9 and the pressure is able to build up quickly in the relatively small counter pressure chamber 42 to counteract further movement of the brake piston 17 and prevent further movement in the braking direction to release the locked brake when the brake piston 17 is pushed back slightly. A small part of the pressure then flows through a throttle 35, but the clamping segments 39 are still held firmly against the cylinder wall 15 so that the trailing piston cannot move. When the brakes are released, the locked wheel of the vehicle is freed again and the current to the coil 52 is interrupted by the switch element 54 and current ceases to flow in the coil 52, thus moving the armature 50 outwardly due to the effort of a spring 51 which moves the slide valve 46 back to its initial position and close the apertures 47, 48. The compressed air present in the counter pressure chamber 42 and the chamber 34 flows through the throttle 35 to the chamber 33 and via a bore 40 to the chamber 41 and to outside atmosphere. Should the brake pressure again lock the wheel the process described will be repeated. The clamping segments 39 and the diaphragm 36 may be replaced by a magnetic powder clutch adapted to hold the trailing piston in the brake cylinder when the electromagnet 50, 52 is energized. A further embodiment is disclosed in the Specification (Fig. 3, not shown) in which the trailing piston may be constructed in a shallower form as a complete disc having a peripheral groove which receives a sealing ring 57 which is also adapted to act as a clamping ring.