Patent GB-879276-A (GB)
Title: Improvements relating to steering mechanism for an aircraft ground wheel mounting
Inventor: RALPH HAROLD CYRIL ANTHONY
IPC: A47C23/16
Filed: 1959-08-04
Abstract: 879,276. Controlling vehicles. DOWTY ROTOL Ltd. July 28, 1960 (Aug. 4, 1959], No. 26590/59. Class 79(5). The ground wheel of an aircraft is steered by a power operated rack. and pinion steering mechanism, the pinion being attached to' a steerable member of the wheel mounting and the rack having a range of traverse movement ' which enables it to pass out of. meshing engagement with the pinion during free castering movement, there being spring means to cause re-engagement of the rack teeth with the pinion when the pinion turns toward meshing engagement with the rack. A nosewheel mounting, Fig. 1, comprises a fixed member 11 supported upon a hollow member 12 by bearings 13 and 14 and a thrust bearing 15, the ground wheel being carried upon a lever 18 pivoted to a crank 16 integral with the member 12, a spring type shock absorber 19 being pivoted at 21 and 22 to the lever 18 and member 12 respectively. A neck portion 23 of the member 12 carries a pinion 24 which is engaged by a rack 25 which slides between guides 26 and 27 attached to the fixed member 11. The rack may be traversed by a movable cylinder 32 which is operated by a piston 33 fixed to a rod 31 held between end members 28 and 29, fluid being supplied to the cylinder through the rod 31 which is hollow from one or other of pipes 34. and 35. The rack has teeth 42 to 45 which co-operate with a corresponding number of sockets in the pinion. The pinion sockets are formed on each side of a cylindrical web 63, Fig. 3. The end teeth 42 and 45 of the rack are formed upstandingly and downstandingly respectively (Fig. 3) and at each end the rack has a spring loaded pawl 53 or 54 directed toward the pinion. Beyond the range of the sockets 46 to 49, Fig. 4, the pinion 24 is formed with slots 59 and 61 into which the circumferential web 63 does not extend. Suppose the rack turns the pinion in a clockwise direction,. at the end of the extent of co-operation of the teeth and sockets, the pawl 53 enters the slot 59 and castering action in a clockwise direction for more than one revolution is possible, the pawl 53 being prevented from entering the sockets of the pinion by the central web. In the anti-clockwise direction, the pinion may move until the pawl enters slot 59 when, by virtue of its shape and the inclination of the pawl, the rack is constrained to move. Limit switches are provided at the ends of travel of the rack, at the point where castering begins, operation of which discontinues the supply of fluid under pressure. Under normal control for. manoeuvring the aircraft, the rack and pinion are in engagement, the castering range being arrived at by the extreme movement of the rack which discontinues the supply of pressure fluid. The steering system, Fig. 6, comprises the fluid pressure and return lines 66 and 67; a control valve 65, by-pass valve 71 and bypass control valve 75. Fluid is supplied to one side or other of the jack 32 through supply pipes 34 and 35 from the valve 65 which also connects with pressure and return lines 66 and 67. The valve 65 is/actuated by solenoids 68 and 69 and may occupy a "blind" neutral position or a position whereby one or other of lines 34 and 35 is connected to 66, the other being connected to 67. The by-pass valve 71 includes a piston closure member and is connected to a control valve 75 which normally connects the valve 71 to the pressure line 67 and maintains the piston 74 closed. The steering wheel 79 drives an input unit 78 which supplies signals to a relay 81 which also receives signals from follow up device 37 attached to the spindle of the rotary member 12 (Figs. 1 and 6). A negative supply lead is connected to the relay 81 and to valve-operating solenoids 68, 69 and 77. A positive suppiy lead 85 is connected in series with the pilot's control switch 86, the limit switches 39 and 41, which are normally closed, and the relay 81. The phase difference between the input signals received by the relay 81 energizes one or other of the solenoids 68 or 69 and operates the valve 65 and consequent operation of the jack until the follow up device cancels the signal. Solenoid 77 is energized all the time unless one of the limit switches breaks the circuit whereby the piston valve 71 is con-' nected to the return line and the jack is put at low pressure while castering. The circuit is held open by the jack in its limit position until the end of castering when the rack is reengaged by the pinion.