Patent GB-1361494-A (GB)
Title: Hydraulic servomotor controllers
IPC: B62D5/097
Filed: 1971-06-21
Abstract: 1361494 Power steering TRW Inc 21 June 1971 29009/71 Heading B7H [Also in Divisions F1 and G3] A servomotor control 18, for use in a power steering system having a main pump 16 and a double-acting hydraulic servomotor 17, comprises flow and return ports 28, 30, a valve 40 and a steering shaft 26 for moving the valve relative to a valve chamber, the valve being connected to a fluid displacement pump 42 and movable in opposite directions from a neutral position at which fluid pressure at the servomotor is balanced to either one of a pair of operating positions at which the fluid pressure at the servomotor is balanced to either one of a pair of operating positions at which the fluid pressure at the servomotor is unbalanced, the valve 40 being hydraulically biased towards neutral position with a force corresponding in magnitude to the differential existing at the flow and return ports 28 and 31 or servomotor ports 29 and 31 in the control 18. The servomotor has an hydraulic cylinder provided with a piston 20 fitted with a piston-rod 23 for actuating the vehicle steering linkage under the control of control 18 through the steering shaft 26. Port 28 supplies fluid under pressure, while port 30 returns fluid to the pump 16, while the ports 29, 31 are connected to opposite ends of the cylinder 19. The pump 42 comprises gears 43, 44, the gear 43 being internally toothed and mounted stationarily within housing 24 and the gear 44 being externally toothed, Fig. 4. The number of teeth 46 of the gear 43 exceeds by one the number of teeth 47 of gear 44, such that gear 44 not only rotates but orbits relative to gear 43, thus forming expanding and contracting fluid pockets supplied with fluid through a valve 41. Grooves M, P, M<SP>1</SP>, C, R, C<SP>1</SP>, M<SP>2</SP>, R<SP>1</SP> and R<SP>2</SP> are formed in the bore wall 62 surrounding valve 40. A ball 92, Fig. 1, engages a helical groove 94 in the inner wall of valve 40, such that rotation of the valve 40 also causes axial shifting. The valve is connected to gear 44 by a wobble shaft 96 spaced from the head 102 of an extension of shaft 26 by a spring 103 to maintain the shaft 96 in position. A spring 104 produces a centering force for the valve 40. Fig. 1 shows the neutral position of the valve 40 in which the fluid pressure at the servomotor is balanced, the control 18 being blocked since grooves P, P<SP>1</SP> and P<SP>2</SP> are blocked by the valve 40, thus shutting off the supply from pump 16. Clockwise rotation of shaft 26 causes leftward axial shift of valve 40, thereby admitting fluid pressure to the righthand side of piston 20 causing rod 23 to move leftwards while shaft 96 rotates with gear 44. Should the pump 16 be inoperative due to malfunction this rotation of the gear 44 produces a flow of fluid under pressure directed to the right hand side of piston 20. Since the pressure in chamber 78 within valve 40 exceeds that in a chamber 83 the valve 40 is unbalanced toward neutral position, the unbalanced force acting on end walls 84, 86 of the valve 40 varying in accordance with the reaction forces to which the steered wheels are subjected. Thus the torque required to rotate shaft 26 improves the drivers "feel". Similarly, when the operating shaft 26 is rotated counterclockwise the valve 40 is shifted rightwardly, Fig. 3 (not shown), there is an unbalancing force tending to urge the valve 40 leftwardly, this force being supplemented by the force of spring 104. In a modification, Figs. 8-10 (not shown), a valve (41a) is rotated at the orbital speed of the gear (44a) by mounting the valve (41a) on a stationary pin (122). A finger (123) projects from the shaft (96a) into the valve (41a) thereby rotating the valve 41a about the pin 122. In another modification, Figs. 11 and 12 (not shown), the hydraulic reaction force is set to a predetermined limit by a spring (170) pressing a valve (163) against an abutment pin 174.