901,836. Steering vehicles. DOWTY ROTOL Ltd. Sept. 12, 1960 [Sept. 17, 1959], No. 31790/59. Class 79(5). The wheels of an aircraft nosewheel are steered through a pair of jacks 62 and 63. The jacks are operated in series for steering and may be put into a parallel state of operation for castering. The wheels 105, Fig. 2, are carried by a shaft 104 attached to a shaft 106 pivotable within a strut 89 retractable about trunnions 107. A cylinder 62 is pivoted to a pair of arms 88 attached to the strut 89 and its piston 90 is pivoted to a pair of arms 92 attached to a sleeve 93 rotatably mounted on the strut 89. A second cylinder 63 is pivoted to a pair of arms 99 attached to a sleeve 100 rotatably mounted on the strut, and its piston is pivoted to a pair of arms 94 attached to the sleeve 93. As shown in Fig. 1, the cylinder 63 and its piston are shown in the reversed positions. At the position wherein both pistons are extended, the wheels are in the mid-position. Contraction of cylinder 62 will rotate sleeve 93 in a clockwise direction, and because of the connection of sleeves 100 and 93 through cylinder 63, the sleeve 100 will move in an anticlockwise direction imparting a steering movement to the wheels through links 103. Contraction of cylinder 63 will move the sleeve 100 in a clockwise direction because of the substantially solid connection through cylinder 63 between the strut 89 and sleeve 93, imparting an opposite steering movement. The steering movements are imparted under the control of a valve comprising a steering selector spool 13, Fig. 1, connected by a linkage, not shown, to the pilot's manual steering control, and an isolating valve comprising a two-position change-over valve 30, a pair of by-pass valves 68 and 71, a pair of stop valves 78 and 79 and two pairs of one-way restrictors 64, 67, 65 and 70. The valve body comprises the communicating passages and the valve spools the lands and annuli and axial and radial bores shown. Valve spool 30 is urged to the left hand position by spring 51 and valve spool 13 is biased to the neutral position by spring 26. Passage 28 communicates with a pressure fluid supply and 27 with a reservoir when the steering system is put into operation, moving valve spool 30 against its spring pressure to the right, causing stop valves 78 and 79 to open. If, now, the spool 13 is moved to the left by the steering selector, the connection 62a of cylinder 62 is connected to the fluid supply, causing it to retract, the connection 62b being connected, via flow restrictor 65 to reservoir, and connection 63b of cylinder 63 is connected via flow restrictor 64 to the pressure fluid, locking the cylinder open, connection 63a also being connected to reservoir. Movement of selector 13 to the right will supply pressure fluid to connections 63a and 62b and will connect 63b and 62a to reservoir. A follow-up control, not shown, is provided to return spool 13 to the neutral position when the steering angle is reached. By-pass valves 71 and 68 are provided in cross connections 69 and 66 and have parts 73 and 72 of greater diameter forming double acting hydraulic pistons. When the chamber 74 is subjected to the same pressure as ducts 53 and 58, the valves will be closed. When the steering selector valve opens duct 28 to pressure and valve 30 moves to the position of Fig. 1A, chamber 74 is open to pressure, but when the forces on the smaller ends of -the pistons 72 and 73 exceed those on the larger ends, the by-pass valves open. The wheels may be put in a position for damped castering by applying pressure to duct 57 by operating a valve, not shown, whereby, through annulus 43, bores 50, 46, 49, annulus 41, ducts 56 and 55 the valves 71 and 68 are operated. There is no pressure at 28 or in chamber 74 and spool 13 is in the central position. Stop valves 78 and 79 close ducts 59 and 54 and the connections 62a and 62b are connected to one another through 56,.69 and 53 and the connections 63a and 63b are connected with each other through ducts 55, 66 and 58. The one-way flow restrictors 65 and 70 damp the fluid flow. When the strut is about to be retracted, pressure is applied to duct 61, the steering selector being rendered inoperative at the same time, and the steering selector spool 13 is centred. The pressure is applied through annulus 42, and duct 85 to chamber 82 to unseat valves 83 and 84 and also through ducts 60 and 77 to chamber 74 causing the by-pass valves to shut off 69 and 66. At the same time a low pressure is applied to 57 and to 56 and 55 through 43. 50, 46, 49 and 41 and duct 53 is connected to reservoir through 47, 45, 48, 40, 54, past shut-off valve 79, 86 and 32. Duct 56 is also connected to reservoir through 44, 59, 78. 86 and 32 and thus the cylinders 62 and 63 are both extended and the wheels centred.