Patent GB-1330154-A (GB)
Title: Fluid-pressure actuators
IPC: F16D65/28
Filed: 1971-11-10
Abstract: 1330154 Brake actuators WESTINGHOUSE BRAKE & SIGNAL CO Ltd 10 Nov 1971 [9 Dec 1970] 58438/70 Headings F2E and F2F A fluid-pressure actuator comprises a hollow body 1 within which is a pressure-responsive member 10 to which is operatively connected an output member 64 movable in opposite directions, one side of the pressure-responsive member forming one wall 15 of a first chamber 6 having communicating therewith a first port 4 through which a first fluid pressure can be applied to the chamber to act on said one side of the pressure-responsive member to move that member in one direction and thereby correspondingly move the output member in one of the opposite directions of movement and the other side of the pressure-responsive member forming one wall 10 of a second chamber 7 having communicating therewith a second port 5 through which a second fluid pressure can be applied to the second chamber to act on said other side of the pressure-responsive member to move that member in the opposite direction and thereby correspondingly move the output member in the other of its opposite directions of movement; an adjustment means 49 operative upon the stroke of the output member 64 exceeding a predetermined amount to telescope the output member relative to the pressure responsive member 10, the adjustment means including inhibiting means by which the adjustment means is rendered inoperative so as to telescope the two members for so long as the second fluid pressure is present whilst the first fluid pressure is absent. As shown, an annular piston 10 is slideable in a bore 9 of the body 1 which is provided with trunnions 2 by which the actuator is pivotally mounted, and a piston 18 also slideable in the bore 9 is prevented from rotating by a spigot 22 projecting into an axial slot in the piston. A nut 24 is threadedly engaged with a tubular element 25 which carries a projection 28 extending in an axial slot 29 of the piston 18 so that the element is prevented from rotation with respect to the piston; the nut has a clutch face 29 which is urged into engagement with a clutch face 39 on the body by a spring 35 acting through a thrust bearing 31 and a bearer 33 formed with a slot 36 which receives a pin 37 to prevent rotational but not axial movement of the bearer. A tubular member 40 has a shoulder 42a engaged by the end 44 of the piston 10 which, with the element 25 is clamped between that shoulder and a second shoulder 42 on the member 40. The adjustment means is constituted by helical threads 50 on the member 40 and a spring-loaded pawl 51. The member 40 carries a projection 55 engageable with any one of a series of slots 56 in the bearer 33 and is in screw-threaded engagement with a rod-like output member 64 provided with a cross-head 66 for connection to the brakes of a railway vehicle and which member is fully extended when no fluid pressure is applied to the ports 4 or 5; in this condition the face 15 of the piston 10 engages the face 14 of the wall 12 of the body, the projection 55 is engaged in a slot 56 of the bearer 33 and the clutch faces 38, 39 are engaged under the action of the spring 35. Application of fluid pressure to the chamber 8 urges the piston 18 to overcome the force of the spring 35 to cause the nut 24 to spin to the right and move axially until the bearer 33 engages a shoulder 69 on the body. Fluid pressure applied to port 4 acts on the face 15 of the piston 10 to move the piston, element 40 and rod 64 to the right whereby the brakes of a rail vehicle are applied. Release of fluid pressure from the chamber 6 permits the piston, element 40 and member 64 to be returned to the left by the return springs of the vehicle brakes, this return being assisted by fluid pressure in the chamber 7 and which is effective on the face 16 of the piston; the clutch faces 38, 39 are maintained disengaged by the presence of fluid pressure in chamber 8. When it is desired to maintain the brakes applied without the retention of fluid pressure in chamber 6, fluid pressure is released from chambers 7, 8. If the wear of the brakes has reached a degree in excess of a pre-determined amount, the movement of the element 40 and member 64 will be such that the pawl 51 rides over the tooth 50 with which it is engaged to fall into engagement with the next successive tooth whereby during return movement to the left and upon release of the brakes the element 40 will rotate to cause the element to be screwed along the member 64.