Patent GB-1447202-A (GB)
Title: Vehicle wheel spring brake actuators
IPC: B60T17/08
Filed: 1975-01-17
Abstract: 1447202 Spring brake actuators SVENSKA AB BROMSREGULATOR 17 Jan 1975 [30 Jan 1974] 2074/75 Heading F2F A vehicle wheel spring brake actuator with fluid pressure release comprises a piston 3 movable forwardly in a cylinder 1 under the action of a spring 4 for brake application, an axially movable push rod 7 for transmitting force from the actuator to the brake, and a transmission mechanism 8-17 which when engaged transmits motion from the piston 3 to the push rod 7 in the brake applying forward direction, the transmission mechanism 8-17 being disengageable in order to allow the push rod 7 to return rearwardly whilst the piston 3 remains in its forward position in the absence of fluid under pressure in a chamber 5; the transmission mechanism comprises a nut 8 in non-self-locking engagement with screw-threads on the push rod 7, the nut 8 being normally prevented from rotating by an arrangement comprising a one-way clutch 10 and a dog clutch 14, the dog clutch 14 being spring-loaded by a spring 15 into engagement but being disengageable by manually rotating an exterior control member 19 whereby the nut 8 is allowed to rotate and so permit the push rod 7 to move rearwards. In the embodiment of Fig. 1 the cylinder 1 of the spring brake actuator is attached to a service brake actuator cylinder 2. The central part of the piston 3 constitutes a hollow piston rod 6 guided in a tubular guide 1A. In the absence of a fluid pressure in the chamber 5 to overcome spring 4, the force from spring 4 will be transmitted to nut 8 and rod 7 via a flange 6A on the piston rod 6 and an anti-friction bearing 9. In this embodiment the one-way clutch 10 which may be a free-wheel mechanism or a locking spring is arranged between nut 8 and a clutch ring 11 which is mounted for rotation relative to the nut 8. The clutch ring 11 is provided with teeth for co-operation with teeth on a clutch member 13 to constitute the dog clutch 14. The clutch member 13 is axially movable but rotationally immovable, being provided with a projection in engagement with a groove in push rod 7; the clutch member 13 is provided with an oblique or helical control groove 13A into which extends a control pin 18 which also extends into a circumferential groove in the piston rod 6 and having a length at least equal to the length of groove 13A. A sleeve 19A of member 19 has a longitudinal slot for the pin 18. Thus if, after a brake application by the spring 4, no fluid pressure is available in chamber 5, manual release can be effected by rotating member 19. This causes clutch member 13 to move to the right to release dog clutch 14, and the nut 8 is now free to rotate on rod 7 with the result that piston 3 will move leftwardly under the influence of spring 4, and that under the influence of a return spring in the brake rigging (e.g. spring 22) the push rod 7 will move rightwardly until halted by a stop plate 24. When the control member 19 is released the dog clutch 14 is re-engaged under the influence of spring 15. In the modified arrangement of Fig. 2 (not shown) the clutch ring (11) and the clutch member (13<SP>1</SP>) are placed to the left of a modified nut (8<SP>1</SP>), and the dog clutch (14) is held engaged by a spring (15<SP>1</SP>) between the piston rod (6<SP>1</SP>) and the clutch member (13<SP>1</SP>). A helical or oblique control slot (13A<SP>1</SP>) is arranged in the piston rod (6<SP>1</SP>) and the control pin (18<SP>1</SP>) extends into a control tube (25) co-acting with the clutch member (13<SP>1</SP>) and moving the latter towards the left when the control member (19) is turned.