GB572936A - Improvements in or relating to hydraulic rams - Google Patents

Abstract

572,936. Fluid pressure servomotor control systems. COLLEY, R. H. Sept. 16, 1943, No. 15227. [Class 135] Fluid-pressure apparatus comprising a reciprocatable piston adapted to be set to and maintained in either of its end positions or an intermediate position by the continuing supply of fluid to it is described as applied to the control of a change-speed gear for the supercharger of an aircraft engine, the valves which determine the path of flow of the fluid being operated by solenoids automatically controlled by aneroid devices responsive to the altitude of the aircraft. As shown, a differential piston 13, 14, connected to a lever 11 operating the change-speed gear, is arranged in a cylinder 10 having ports 22, 23 at the ends, a central drain port 19 which is uncovered by the piston as it approaches either end of its stroke, and further ports 20, 21 both open or partly so when the piston is in its intermediate position. The flow of fluid from the supply line 28 is controlled by a pair of spring-pressed two-position valves 24, 25 operated by solenoids 40, 41 which are connected to a battery 46 and put into and out of operation by switches 42, 43 automatically actuated by expansible capsules 44, 45. Fig. 1 shows the piston 13 in its intermediate position in which it is maintained when both valves 24, 25 are raised, the flow of fluid from supply 28 to drain 33 being as shown by the arrows ; any movement of the piston away from the midposition will close one of the ports 20, 21 and thus cause a pressure build-up on one side which acts to return the piston to midposition. When both valves 24, 25 are lowered, the piston moves to the left-hand position shown in Fig. 2, while movement to the righthand position, Fig. 3, is effected by raising valve 24 only ; in both cases any movement away from the end positions closes the port 19 causing a pressure build-up with the piston to the appropriate end. The capsules 44, 45 and switches 42, 43 are so arranged that at ground level the switch 42 is closed and the switch 43 open, both solenoids being energized to maintain the valves 24, 25 in the raised position and thus keep the piston 13 in the mid-position shown in Fig. I to set the supercharger at its lowest speed ; as the aircraft rises the switch 42 opens and both solenoids are de-energized to move the parts into the position shown in Fig. 2 in which the supercharger is set to medium speed. Finally, on further increase in altitude, the switch 43 closes to energize the solenoid 40 and so raise the valve 24 to move the piston to its third position, Fig. 3, and so give the highest speed drive to the supercharger. Modified arrangements of the switches 42, 43 are described as is also a construction in which a manually -operable switch is provided to enable the pilot to over-ride the automatic control and set the supercharger to high, medium or low speed as desired..