GB812589A - Improvements in or relating to steering mechanism - Google Patents

Abstract

812,589. Vehicle power steering. CLEVELAND PNEUMATIC TOOL CO. Dec. 17, 1956 [March 15, 1956], No. 38388/56. Class 79(5) Ground steering mechanism for an aircraft landing gear having a pair of members 10, 13 capable of relative rotation, to one of which the steerable portion 11 of the landing gear is attached, comprises a cam 37 fixed to the member 13 and provided with a plurality of spaced ramp surfaces inclined in a manner whereby pressure applied successively to them causes rotation of the mmber 13, a plurality of motors 16 mounted on the other member 10 and each including a movable element carrying a cam follower 54 adapted to exert the pressure on the ramp surfaces, and control means operated by rotation of the member 13 to actuate the motors successively as each ramp surface moves into the path of the corresponding follower. In the example the member 13 comprises a collar which is connected by torque arms 14 to a telescoping member 11 carrying the aircraft wheels 12. The cam 37 is provided with six lobes 42 and each cam follower 54 is mounted on a shaft 53 supported by projections 52 provided on a piston 33 in a cylinder 34. The shafts 53 carry bearings 56 co-operating with guide slots 51. The control means comprises a distributor Valve assembly 80 having a rotor 64 which in the example is rotated in the same direction as the cam 37 and at six times the speed, the rotor 64 and cam 37 being drivingly connected through gearing, part of which is shown at 81, 39. Fig. 7a shows the connections between the cylinders 24a, b, c, distributor valve 80 and pump P with a control valve V for clockwise rotation of the cam 37. The pump P is connected through a pressure line 66, valve chamber 65 and valve port 72a to the cylinder 34a. The cylinder 34b is in a change-over condition and is cut off by a land 74 on the valve rotor 64. Cylinder 34c is connected through a port 72c, valve chamber 70 and pressure line 67 to a reservoir 81. Counter clockwise rotation of the cam 37 is effected by reversing the valve V so that the pressure line 66 is connected to the reservoir 81 and the pressure line 67 to the pump P. A pressure sensitive relief valve R maintains a back pressure in the line connecting the valve V to the reservoir 81, thereby producing a back pressure in the cylinder 34 connected to the reservoir so that free play is automatically taken up. The valve V is so arranged that when steering is not required the pressure lines 66, 67 are connected together. The pressure lines 66, 67 preferably include flow restricting orifices 82, 83 which serve to dampen shimmying of the wheels 12. The operative surfaces of the cam 37 are so designed as. to produce a constant torque steering mechanism. The number of cam lobes 42, cylinders 34 and the height of the cam lobes may be varied from that shown, and the cylinders may be circumerentially spaced so as to engage spaced lobes rather than surfaces on adjacent lobes. The mechanism may provide full 360 degrees steering.