Patent GB-950974-A (GB)
Title: Improvements relating to fluid motors
IPC: F15B15/08
Filed: 1961-09-21
Abstract: 950,974. Fluid-pressure apparatus. WESTINGHOUSE AIR BRAKE CO. Sept. 21, 1961 [Sept. 21, 1960], No. 33783/61. Heading F1P. [Also in Division F2] A fluid-operated motor comprises a cylinder 6, Fig. 3, in which is axially slidable a power piston 20 and a differential piston 24 arranged on one side of the power piston, the differential piston, when in abutment with the power piston, presenting an effective area greater than the effective area of the power piston alone and being movable between a first position in which when abutted by the power piston the latter is in one of its extreme positions and a second position in which when abutted by the power piston the latter is in a position intermediate its two extreme positions. The motor may comprise two cylinders 6, 7, the rod 21 of the piston 20 of cylinder 6 operating the forward and reverse mechanism of a transmission and the rod 21 of the piston 20 of cylinder 7 operating a gear change mechanism of the transmission. Each cylinder has a sleeve 16 which is located centrally therein by a screw 18 and guides the power piston 20 and the smaller ends 27, 29 of differential pistons 24, 25, the larger ends 26, 28 being guided in the cylinders 6, 7. Each differential piston is provided with an axially-adjustable sleeve 30, 32 and a lock-nut 31, 33 by which the overall length of each differential piston can be adjusted. Normally a control valve supplies fluid pressure to the chambers 9, 15 at each end of each motor so that the large diameter ends 26, 27 of the differential pistons abut the sleeves 16 and the small diameter ends abut the power pistons which are thus held in a neutral position. If chamber 9 of cylinder 6 is connected by the control valve to atmosphere, the pressure in chamber 15 moves the differential piston 25 and power piston to the left to a position determined by abutment of the sleeve 30 with stops 117. When the pressure is reconnected to the chamber 9, the pistons 20, 25 are returned to their initial positions. Movement of the power piston 20 to the right occurs when chamber 15 is connected to atmosphere unless the sleeve 32 is adjusted so that it abuts a stop 11b while the large diameter end 28 of piston 25 abuts the sleeve 16. Selection of chamber 9 or 15 of cylinder 7 to atmosphere moves its power piston to the right or left in a similar manner. In an alternative embodiment, the differential pistons have a fixed length. The control valve for selectively connecting one chamber at a time to atmosphere comprises a cylindrical casing having a bore 45, Figs. 4 and 6, into which open ports 94, 95, 96 97 connected to the four chambers 9, 15 of the cylinders 6, 7. A further pair of ports. 101 may be provided for connection to the chambers of a third motor. The bore 45 is supplied with fluid pressure through an inlet port 4 and normally all four ports 94, 95, 96, 97 are uncovered so that fluid pressure is supplied to all four chambers 9, 15 of the cylinders 6, 7 A spool 47 is disposed in the bore 45 and is connected to a handle 79 by which it can be moved angularly and axially from a neutral position to a position wherein a valve disc 74 is located over a selected port and the chamber 9 or 15 connected to that port is connected to atmosphere to effect operation of the relevant piston 20. The spool 47 is urged to a central position by a spring device 58 and can be releasably retained in its neutral angular position or operative positions by a spring-pressed ball 107. The handle 79 is of cruciform cross-section, the arms of the cruciform engaging slots 88 in the casing to locate the spool in its correct axial position before it is rotated to bring the valve disc 74 over a selected port.