GB738380A - Improvements in and relating to pneumatic gear motors, and rotary actuators incorporating such motors - Google Patents

Abstract

738,380. Gear motors. WESTERN MANUFACTURING (READING), Ltd. May 7, 1953 [May 19, 1952], No. 12575/52. Class 110 (2). [Also in Group XXIX] A pneumatic, reversible gear motor 1, 2, which may be used as an actuator for aircraft controls, has alternative inlet chambers 6, 7 and exhaust ports 8, 9 and valve means for restricting the supply of working gas (air) to a predetermined pressure range. Trip means are used to shut off the air supply when a shaft 39 being driven by the motor has turned through a predetermined number of revolutions, and brake means bring the motor to a standstill. The plant may include a centrifugal governor, Fig. 2, or a pneumatic governor, Fig. 11, and solenoid-actuated valves, Fig. 10. In one arrangement, Fig. 1, with gears 1, 2 rotating clockwise and anti-clockwise respectively, air enters a chamber 6 and mostly is exhausted to atmosphere through ports 8, 9. The remainder of the air is exhausted through a port 5 and the pressure here is controlled by a piston valve 23 having grooves 24, 25 spaced longitudinally to equal the distance between ducts 18, 19. The gear motor is supplied with an excess of air to allow a quantity to flow through exhaust ducts 12, 15, 18, groove 25 to an exhaust 20. The back pressure is regulated by a governor 27, acting on the valve 23. If the motor runs too fast, the valve 23 is dis. placed to move a groove and the exhaust port partly or wholly out of alignment and thus increase the back pressure. The governor shaft 26 is driven through gearing 31, 32. The pinion 31, through gears, also drives the output shaft 39. This carries trip cams 40, 41, one of which, when the shaft 39 has rotated through the requisite number of revolutions, closes an air supply valve by contacting a bell-crank lever 45 and causing axial movement to a valve such as 57 controlling the air supply from a pipe 65. In Fig. 1 when the cam 40 strikes the bell-crank 45, relieving the pressure on a push rod 52 and a tappet 54, a spring 67 closes the valve 57 stopping the air supply to inlet chamber 7. At the same time a bell crank 46 is released and the opposite valve 58 is opened ready for a supply of compressed air. During running conditions compressed air is supplied to a brake cylinder 81, moves a piston 82 to the right, Fig. 2, until it contacts a seal 83, preventing further loss of air from the cylinder, this motion also separating a friction ring 75 from a rotatable disc 74 and permitting rotation of the gears 1, 2. The air is supplied to the brake cylinder through ducts 84, 86, 88, 95, a ball valve 94 closing the connections to the other side of the motor. When the air supply ceases, the piston 82 moves backwards and the brake discs 74, 75 come into contact stopping the motor. The supply of compressed air from a pipe 108 is under control of electromagnetic solenoids 111, 112 and springs 109, 110 which act on valves 104, 105. The original supply of compressed air is controlled by a valve 119 having flats 123 on its mushroom head. As an alternative to the centrifugal governor 27 the pneumatic governor, Fig. 11, may be used. This comprises a member 129 with a piston 130, a venturi throat 132 and a spindle 143, springs 135, 137 pressing the member 129 to the left. When the motor speed becomes excessive, the rate of flow of compressed air through the throat attains a critical speed and air is extracted from a balance chamber 139, lowering the pressure therein and causing the annular member 129, overcoming the resistance of springs 135, 137 to move to the right and restrict the size of the passage through the venturi. This reduces the quantity of compressed air passing through a duct 146 to the gear motor. Either governor, centrifugal or pneumatic, may be dispensed with. Electric limit switches may replace the limit valves described above and a different type of gearing used.