Patent GB-812984-A (GB)
Title: Improvements in or relating to aircraft steering mechanism
IPC: B64C25/50
Filed: 1956-06-20
Abstract: 812,984. Vehicle power steering. CLEVELAND PNEUMATIC TOOL CO. June 20,1956 [Sept. 16, 1955], No. 19067/56. Class 79(5)  In an aircraft steering mechanism comprising an upper member 10, Fig. 1, connected to the airframe (not shown) and a relatively rotatable lower member 11 carrying the steerable wheels 12, a steering collar 13 is rotatably mounted on the member 10 and is connected to the member 11 by torque arms 18, a cylinder 19 being pivoted on an axis 23 to the member 10 and a co-operating piston rod 24 being pivoted on an axis 27 to the collar 13, the piston and cylinder being connectable to a fluid pressure source (not shown) by a rotary valve 29 controlled by a rod 38 mounted on the member 10, whereby opening the valve causes axial movement of the piston and cylinder and hence relative rotation of the members 10, 11 to deflect the wheels 12 and the valve is closed by the relative rotation between the members 10, 11. As further shown in Fig. 1 the cylinder 19 and the valve 29 carry arms 21, 22 pivoted on the axis 23 to the member 10, the valve 29 being connected by pipes 31, 32 to the pressure source and a return reservoir, respectively. A valve operating arm 33 is connected by pin and slot connection 41, 42 to an arm 39 on the pilot-controlled rod 38. In operation, pilot-rotation of the rod 38 causes the valve 29 to connect one or other end of the cylinder 19 to the pressure source, whereby the piston rod 24 is axially moved relatively to the. cylinder, hence the member 11 is rotated relatively to the part 10 to effect power steering of wheels 12. Duringthe axial movement of the piston rod 24 the cylinder and valve pivot about the axis 23 to return the arm 33 to its original or neutral position relative to the valve thus cutting off the pressure supply to the cylinder to give a "follow-up" action. In theh neutral position of the valve the rod 38 is disposed in lin with and mid-way between the axis 23 and the pin 41. In a modification, Figs. 8, 9, 10 and 17, the undercarriage comprises relatively rotatable and telescapic members 11a, 12a, the member 12a carrying the steerable wheels 13a and being connected by links 16a to the steering ring 14a relatively rotatable on the member 11a, and the ring 14a being rotated by piston and cylinder units 17a, 18a. Mounted on the member 11a is a control mechanism C connected by pines 23a, 24a to the units 17a, 18a by a pipe 21a to the source of pressure and by a pipe 22a to a return reservoic, the units 17a, 18a being cross connected by pipes 80a. The control mechanism C comprises an accumulator A, damping orifices O and the control valve V. The accumulator A comprises a spring loaded piston 84a, Fig. 9 carrying a poppet valve 88a and disposed in a cylinder 81a arranged between the exhaust port 93a of the valve V and the exhaust pipe 22a. The damping orifices O each comprise a spring loaded valve member 66a, Fig. 10, disposed in a bore 63a and having orifices 74a, 77a only the orifice 74a being operative when the member 66a is seated at 68a. The member 66 a  is disposed between a motor port 68a of the valve V and the associated motor pipe 23a or 24a. The damping orifices O serve to prevent wheel shimmy. The valve V comprises a disc 31a disposed in a space 30a and keyed to a shaft 32a, the disc co-operating with the ports 93a, 61a and an inlet port 55a connected to the supply pipe 21a. Secured to the shaft 32a is an arm 101a, Fig. 17, carrying at its ends pulley 104a 106a, the arm being acted on by spring loaded plungers 107a serving to urge the arm into a neutral position. The pulleys carry a cable 118a which wraps around the ring 14a and is secured to a pulley 117a which is adapted to be rotated by the aircraft pilot. In operation rotation of the pulley 117a causes tension in one or other run of the cable 118 a  whereby the arm 101a is turned to rotate the valve disc 31a, hence pressurizing the units 17a, 18a, which causes steering rotation of the ring 14a. Such rotation of the ring 14a causes the tension in the run of the cable 118a to be relieved by taking up the slack, hence returning the arm 101a to its neutral position to shut off the power steering.