Patent GB-1197204-A (GB)
Title: Braking Systems
Inventor: THOMAS GORDON FREDERICK FRANK
IPC: B60T17/16
Filed: 1967-07-18
Abstract: 1,197,204. Brake locking systems. WESTINGHOUSE BRAKE & SIGNAL CO. Ltd. 10 July 1968 [18 July, 1967], No. 32926/67. Heading F2F. A fluid-operated braking system incorporating fluid-released locking means and supplied by fluid at three pressures for " emergency " or " parking " brake application, " service " brake application, and " lock release " respectively, has further means whereby, in the absence of the third of these pressures, and upon " service " application, the secondmentioned pressure is applied to the locking means to render it inoperative at least until a subsequent " brake release" of the braking element is effected by release of the secondmentioned fluid pressure. As shown in Fig. 1, the locking means 2 is normally rendered inoperative by application of the " third fluid pressure " at 26 to a first annular chamber 14. This pressure forces an annular piston 12 downwards, the piston in turn forcing rollers 16 out of wedging engagement between the tapered surface 17 of a fixed annulus 18 and the brake-operating member 3 against the bias of a spring 20. If the " third fluid pressure " fails, and an " emergency/parking " application of the brake is made by admission of a " first fluid pressure " to the emergency/parking chamber 4 above diaphragm 24, the locking means becomes effective. To release the locking means in the above circumstances a knob 35 is pushed in until a detent 38 on rod 36 engages a spring 39. This brings element 32 of a control valve 31 into contact with a valve seat 31. The element 32 is however hemi-spherical, has holes 33, and is backed by a rubber disc 34. A " service " application of the brake is now made by admission of a " second fluid pressure " at 23 to chamber 22. Fluid flows along a conduit 29 to the chamber of valve 31, passes through holes 33 and past disc 34, acting as a one-way valve, and reaches a second annular chamber 15 by way of a passage 27. In consequence a furtherannular piston 10 is forced downwards, in turn forcing downwards piston 12 and rollers 16. When the " service " application is being released, the fluid in chamber 15 and passage 27 is trapped by the one-way valve 31, so that the locking means remains ineffective while the brake operating member 3 travels upwards. When member 3 has reached a " brakes released " position a cam member 42 on it causes a further rod 40 to push back element 32 and rod 36 until a detent 37 engages spring 39. The locking means 2 is thus again rendered effective When the operating knob 35 is in the outer (normal) position, the " second fluid pressure " is made available in chamber 15 every time a " service " application is made by reason of conduit 29, the now-open valve 31 and passage 27, but the pressure is relieved on " brakes release " : the locking means 2 is rendered inoperative by the " third fluid pressure " at 26. In Fig. 2 the control valve 31 and rod 40 are replaced by an apertured piston 46, incorporating a one-way ball valve 48, and a spring-loaded exhaust valve 52 whose exhaust passage is constitututed by the clearance around its stem 53. In this case the locking release procedure is initiated by pulling knob 35 out instead of pushing it in, whereby rod 55 is withdrawn from piston 46 to render valve 48 operative. The complete system of Fig. 4 provides a reservoir 65 supplying the " second fluid pressure " to the service chamber of the complete actuator 1 through service control valve 60 and service line 64; reservoir 66 supplies the " first fluid pressure " to the emergency/parking chamber through control valve 61 and line 68 ; and the " third fluid pressure " is supplied to the locking means by reservoir 66 through control valve 61 and line 67. A variable load valve 63 may be provided, but to enable maximum service pressure to be available to release the locking means a by-pass valve 69 may also be provided. Preferably the fluid is compressed air.