Patent GB-765060-A (GB)
Title: An improved hand brake for motor vehicles, more particularly heavy motor vehicles and omnibuses
IPC: B60T13/04
Filed: 1954-12-24
Abstract: 765,060. Vehicle hand brake mechanism. MASCHINENFABRIK AUGSBURG-NURNBERG AKT.-GES. Dec. 24, 1954 [Jan. 20, 1954], No. 37334/54. Class 103 (1). In a vehicle hand-brake mechanism a separate device for pre-stressing the brake shoes is provided characterized in that it is constructed as part of the brake rod linkage and is moved in one direction by one or more springs and in the other direction by air pressure in such a manner that one single rocking of the hand-brake lever, besides the pre-stressing, can produce the full braking action. In the embodiment illustrated, the hand-brake linkage consists of a hand lever 2 pivoted at 1 to the vehicle frame and provided with a ratchet and pawl mechanism 3, 6 for locking purposes. Pivoted to an arm 7 of the hand lever 2 is a multi-piston cylinder 9; the piston rod 10 thereof being articulated through a guide 11 to a rod 12 secured through a pin and slot connection 12a with the brake shoe operating mechanism 13, 15, 16, 17. A compressed air reservoir 60 supplies air in the rest position I of the hand lever 2 via pipe 56, control valve 55 and pipe 57 to the inlet 58 of the cylinder 9. The compressed air acts on piston 19 and displaces it inwardly, thereby compressing spring 28, and the hollow shaft 24 of the piston 19 forces sleeve 50 along to bring groove 49 into working region of balls 48 housed in hub 46 to allow the balls to come out of locking engagement with the grooves 52 in the piston rod 10. At the same time, compressed air passes through the throttling apparatus 35, 36, 37 and radial holes 31 in wall of shaft 24 to the annular potshaped piston 20. The delay causes the piston 20 to become operative only after displacement of the groove 49 to completely release the wheel brake mechanism. When the hand lever is moved to position II, the flow of compressed air from reservoir 60 is interrupted and the cylinder 9 is connected to exhaust via pipe 57 and outlet 59. As pressure drops in the cylinder 9 the springs 44 move the piston 20 into the compressed air space in the cylinder and this movement causes the brake linkage to be tensioned such that the brake shoes are lightly applied and all brake clearances are compensated. During this movement, the piston rod 10 is moved between the balls 48 which are retracted into groove 49 of the sleeve 50 (as shown in the top half of Fig. 2). When the brake shoes abut the brake drum, the piston rod 10 remains with a groove 52 corresponding to this position in the region of the balls 48. At this moment, the escaping compressed air also enables the release of the weaker spring 28 and the latter moves the piston 19 along until it abuts with its projecting shaft against the cover 33 of the cylinder 9. The shaft 24 takes the sleeve 50 along and moves its groove out of region of the balls 48 to lock the piston rod (as shown in the bottom half of Fig. 2). Further movement of the hand lever 2 to position III enables the operator to transmit any desired braking power without having to overcome any lost-motion in the rod linkage and between the parts to be braked.