Patent GB-1140104-A (GB)
Title: Brake systems
Inventor: GIBBONS PETER FREDERICK
IPC: B60T13/26
Filed: 1966-06-29
Abstract: 1,140,104. Fluid pressure brakes; valves. WESTINGHOUSE BRAKE & SIGNAL CO. Ltd. 13 June, 1967 [29 June, 1966], No. 29084/66. Headings F2F and F2V. The invention provides a brake system including a " spring-applied " brake actuator 4, Fig. 1, an " air-applied " actuator 1 and a common control valve 13 connected to air reservoir 11. Control valve 13, in a first manner of operation, delivers a first variable output on line 17, comprising an air pressure dependent upon the degree of operation, which controls the " air-applied " actuator 1 and is also applied to input 35 of a valve unit 5. A second output 20 of the control valve 13 is connected via limiting valve 21 to a second input 36 of valve unit 5, comprising in a second manner of operation of control valve 13 either a first air pressure corresponding to the " spring-applied " actuator 4 exerting no braking effort, or a second air pressure corresponding to this actuator exerting maximum braking effort: valve unit 15 includes a further input 31 connected to air reservoir 11 and an output 32 connected to the " spring-applied " actuator 4 and is so constructed that whilst the first air pressure is delivered to it from the second output 20 of control valve 13 the air pressure delivered by it to " spring-applied " actuator 4 is inversely related to the air pressure delivered from the first output of control valve 13 to " air-applied " actuator 1. Whilst the second air pressure is delivered from the second output 20 of control valve 13 to valve unit 15, the delivery of air pressure from output 32 to " spring-applied " actuator 4 is such that this actuator exerts maximum braking effort, irrespective of the air pressure delivered from the first output of control valve 13. In the embodiment shown, brake actuator 1 comprises a " service " chamber 2, in addition to " emergency " chamber 3 connected to control valve 13, and actuator 4 comprises an " air-applied " " service " chamber 5 in addition to " spring applied " actuator 6, the additional chambers 2, 5 being connected to an air pressure line 10 by pedal valve 7 for normal " service " operation of the brakes. The common control valve 13 is operable in the " first manner " referred to by movement of handle 23 from left to right in the gate, to deliver a variable air pressure at output 16 giving a graduated brake control: further movement at right angles to this direction then controls operation of " on-off " valve 20 constituting the " second manner " of operation referred to. Valve unit 15.-Port 32, Fig. 2, communicating with the " spring-applied " actuator is alternatively connected to port 31, communicating with the air-pressure supply, or to exhaust port 34 by means of a self-tapping valve system comprising a movable member 38, 41, biased by spring 40 and co-operating with a fixed valve seat 39 and a movable seat 42 carried by movable piston member 43. Member 43 is biased by spring 44 and contains passageways such that normally ports 32, 34 are in communication, valve 38, 39 then being shut. Air pressure, when applied from the control valve to port 36, which communicates by passageway 45 with the upper side of piston 46, forces this piston down and extension shaft 47 then drives member 43 downwards also, whereby valve 41, 42 shuts and valve 38, 39 is opened. In this state of the system, a variable air pressure from the first output of the control valve, applied to post 35 tends to lift piston 46, acting on its underside, and so re-close valve 38, 39 and re-open valve 41, 42. The initial action of air pressure at port 35 is enhanced, since it also acts on a larger annular piston 51, pressure on which is communicated to piston 46 via spring 55, floating collar 56 and boss 57: the travel of piston 57 is however limited by means of adjustable stop 54. In a modification, piston (51, Fig. 3, not shown) houses a smaller free piston (58) and pressures on this and on piston (46) which in this embodiment is also free, are communicated to a collar (60) fixed on shaft 47, by means of springs (59, 60). In a modification, the pressure at which valve 38/39, Fig. 4, will lap off depends upon springs 61, 57, 44 and is determined by the setting of screwed stop 63, which is inserted in a second screwed stop 63 limiting the movement of piston 51. A second self-lapping valve 64 is provided, having a double piston member 67, 68 forming therebetween a chamber 69 having an exhaust port 70. Extension 71 of piston 68 is provided with conduit 78 and forms a valve seat 72 cooperating with valve closure member 73, which is biased by spring 74. Closure member 73 forms a second valve with fixed seat 75 and chamber 77 is connected to chamber 37 by means of conduit 76. Port 80 communicates with the " spring-applied " brake actuator; when air pressure is fed from the second output of the common control valve to chamber 79 piston 67 is forced down, opening valve 73, 75 whereby air pressure from port 31 is communicated to port 80, via valve 38, 39, chamber 37, conduit 76 and chamber 77. When the pressure necessary to retain the " spring-applied " actuator fully off is reached, the pressure on piston 68 co-operates with spring 74 to close valve 73, 75, valve 72, 73 being kept closed by the pressure in chamber 79. The " spring- applied " actuator is exhausted by the relative reduction in pressure on piston 67 causing valve 72, 73 to be opened whereby port 80 is connected to exhaust port 70 via conduit 78. In a modification of this arrangement the pressure at which valve (38, 39, Fig. 5, not shown) will lap off depends on the setting of an adjusting screw (81) which controls via a collar (82) the degree of compression of spring (61); the degree of compression of spring (59) is limited by a circlip (84) which may be fitted to any one of a number of grooves (86) in the spring retaining body (87). Alternatively, a threaded screw collar may be used.