Patent GB-735588-A (GB)
Title: Improvements in or relating to mechanism for steering wheels on aircraft
Inventor: HAYMAN RICHARD LOWELL
IPC: B64C25/50
Filed: 1952-12-18
Abstract: 735,588. Fluid -pressure servomotors; hydraulic machines and accumulators. HAYMAN, R. L., and DRISKEL, D. W., [trading as HASKEL ENGINEERING ASSOCIATES]. Dec. 18, 1952, No. 32092/52. Classes 69 (2) and 135. Mechanism for steering an aircraft wheel by a hydraulic servomotor comprises an accumulator which is normally connected to both ends of the cylinder of the servomotor, and a control valve which, when moved from its normal position to cause operation of the servomotor, disconnects one end of the cylinder from the accumulator and causes the latter to be recharged. In one embodiment the servopiston 43, Fig. 14, is connected by a link 41, Fig. 7, and lever 40 to a shaft 24 which carries a lever 26 linked to the steerable wheel. The control valve 59 is centred by a spring (not shown in the diagrammatic view of Fig. 14) and is connected by a lever (not shown) to a link 84 connected to follow-up mechanism comprising a lever 85 which pivots about a fixed pin 87 and has a bush 89 in which a boss of a yoke 90 is pivoted. Slots 90A, 90B in the yoke receive pins 98, 86E which are fixed respectively to an arm 99 secured to the shaft 24 and to a lever 86D having a boss which may be locked to an input shaft 30 to be angularly movable therewith by a device consisting of balls 94 which are urged radially outwardly by upward movement of a plunger 86A in response to increased compression of a spring 115 by a piston 101 which is subject on its lower face to the pressure of the hydraulic supply. Thus, the steering is effected under the control of the shaft 30, which is connected to the rudder control of the aircraft, only when fluid pressure is admitted, under the control of a pilot's switch, to the servo-mechanism.'' The control valve has a circumferentially grooved central land 61 coacting with a pressure supply port 60 and end lands which, in the normal position of the valve partially obturate ports 63, 64, which are interconnected'by a passage 66 and communicate by a passage 69 with the accumulator 68. The two ends of the servo-cylinder 44 are connected to ports 54, 55 of the valve by passages 50, 52 and 51, 53 incorporating check valves 48, 49 which open to permit flow from the control valve to the cylinder 44 and have drillings (not shown) to allow a restricted flow in the reverse direction to prevent " shimmying ". Thus, upon displacement of the control valve, pressure fluid is directed to one end of the cylinder 44 whilst fluid displaced from the other end escapes through the drilling in one of the check valves to the passage 66 whence it passes to the accumulator, which it enters at a point just below a valve seat 121, Fig. 11, and depresses a spring-loaded piston 118 until the latter, in the fully charged position, causes an abutment 127 to engage a nut on the stem of a valve 120 and open the valve to allow the escaping fluid to pass to exhaust 122. Ball check valves 200, 201, shown diagrammatically in Fig. 14 as external to the control valve housing, but actually incorporated in the housing, interconnect the passages 52, 53 with the passage 66 and serve to prevent the formation of a depression behind the piston when the apparatus is functioning merely as an anti- " shimmying " device. In a modification the input to the servo-mechanism is by way of a cable 215, Fig. 27, and pulley 216 to which is connected by a link 218, a lever 220 pivoted at 221 and linked to a point 223 which is connected to an actuating lever 225 for the control valve 59 and also has a follow-up connection by way of a link 230, lever 232 and links 235, 236 with the servo-piston 43. The latter actuates the steerable wheel through a lever 238 mounted on a shaft 239 which carries a lever 240A connected to a link 241. When no fluid pressure is applied to the inlet 212 of the mechanism, a spring-pressed valve member 211 interconnects the two ends of the servocylinder by ports 210A, 210C and an axial passage 210B in the valve member 211 and also connects them with the accumulator 68 by way of a passage 66, these connections being broken when the valve member 211 is depressed by supply pressure. The control valve 59 has a pair of lands coacting with ports 63, 64 which in the normal position of the valve are partially opened to the accumulator. A chek valve 246 in the exhaust 245 is loaded tb open at a comparatively high pressure to enable the accumulator to be charged each time the steering control is operated. A lightly loaded check valve 244 opening in the opposite direction is also fitted in the exhaust. Check valves 48, 49 as in the first example are also provided. In a further modification a moving cylinder 303, Fig. 29, operates the steerable wheel through a connection 310, the piston 302 being anchored by a link 301. The follow-up action is effected by movement of the housing of the control valve 59 with the cylinder 303, and a lever 316, pivoted to the moving cylinder and connected to an input member 319, operates the valve. The hydraulic system is similar to that of the first example.