Patent GB-981497-A (GB)
Title: Spring devices
Inventor: KENMIR CHARLES VIVIAN
IPC: B64C13/42
Filed: 1962-10-09
Abstract: 981,497. Spring units. BOULTON PAUL AIRCRAFT Ltd. Aug. 26, 1963 [Oct. 9, 1962], No. 38227/62. Heading F2S. A spring device 21 comprises a cam member 33, a cam follower 41 carried by the rod 40 of the piston 38 of a piston-and-cylinder unit 37, 38 and normally urged into engagement with the cam surface of the cam member by fluid pressure to which the piston 38 is subjected, and control means 43 for controlling the fluid pressure, the spring characteristics of the device being dependent upon the controlled fluid pressure and upon the contour of the cam surface. Fig. 1 shows a flying control system of an aircraft which includes four hydraulic actuators 11 each incorporating a spring device 21 having an output member 13 pivotally connected at 14 to one end of a lever 15 pivoted, intermediate its ends at 23, to an input member 22 of the spring device 21 and at its other end to a rod 17 axially-slidable in a bearing 18, all four of the rods 17 being connected to a common output member 20. Each rod 13 has a piston 29 which divides a working cylinder 30 in a casing 24 into hydraulic chambers 27, 28. A torque motor 25, carried by the casing 24, receives controlling electrical input signals through a line 12 and is connected to a rotary valve 26 movement of which adjusts the supply and exhaust of fluid pressure to and from the chambers 27, 28 the rotary valve unit 26 being supplied with pressure fluid through a supply connection 31 and having a drain connection, not shown. A pick-off in electrical connection with the input 12 of the torque motor 25 and associated with the input 12 of the member 13 interrupts the input signal 12 when the required displacement of the rod 13 has occurred. The input member 22 of the spring device 21 has a recess 32 which slidingly accommodates the cam 33 movement of which is limited by the end faces 34, 35 of the recess 32, the corresponding end of the member 22 being supported by rollers 22a, Fig. 4, in a main housing 11. If failure occurs of one actuator 11 the spring device 21 allows the remaining actuators to function normally for while the three correct-operating actuators continue to cause angular displacements of the levers 15 about the pivotal connections 23, since the failed actuator is static, the corresponding lever 15 pivots about the pivot 14 linear displacement of the member 22 being allowed by the spring device 21 the system continuing in its operation unhampered apart from the loss of power. After the clearance space between the cam slider 33 and the recess 32 has been taken up the slider 33 and the member 22 move together so that the cam roller 41 rolls up one of the cam surfaces 36 to displace the piston 38 within the cylinder 37 against the controlled hydraulic pressure maintained constant by means of an electrohydraulic servo valve 43, and against a return spring 39. Since the effect of the latter is negligible, the pressure supplied through the duct 42 is constant, and the cam surface 36 is straight the effective rate of the spring device is zero. If the hydraulic pressure in the spring device falls below the required value a piston 48 in a cylinder 47, connected by a duct 46 with the pressure chamber 37, is urged upwardly by a spring 52 whereupon a switch 57 is closed to give a warning of failure, the electro-hydraulic servo-valve being automatically operated to place the cylinder 37 in communication with a drain in order to free the spring device. The clearance at either end of the slider 33 in the slot 32 can be omitted where discrepancy between the several actuators can be tolerated. The cam surfaces can be slightly concave or converse to give respectively positive or negative spring rate characteristics. The linear type of cam can be replaced by a rotary cam. The electro-hydraulic servo-valve 43 can be connected so that the pressure is a function, e.g. of an aircraft Mach number.