Patent GB-1225516-A (GB)
IPC: B62D5/097
Filed: 1968-04-17
Abstract: 1,225,516. Power-assisted steering mechanism. TRW Inc. 17 April 1968 [15 Dec. 1967], No. 18210/68. Heading B7H. [Also in Division G3] A controller 20 in a hydrostatic steering system comprises a spool valve 39 axially shiftable through mechanical means upon rotating an input shaft 28, an admittance valve 30 arranged between a fluid pressure pump 11 and an inlet passage 101 leading to the spool valve 39, and a pilot valve 103 which is cam-operated upon shifting of the spool valve 39 in either direction from a neutral position to vent fluid from the downstream side of the admittance valve 30 so that differential pressure opens the admittance valve to supply pressure fluid to the spool valve 39 for controlled application to a steering ram 13. The controller 20 has a housing 36 including an inlet port P connected to the pump 11, an outlet port R connected to a reservoir 12, and a pair of control ports C 1 , C 2  connected to the ram 13. The spool valve 39 is disposed in a bore 38 in the housing and is connected to the input shaft 28 by a ball 84 seated in the shaft and engaging a helical groove 83 in the valve so that rotation of the shaft relative to the valve causes axial displacement of the valve. Such relative rotation is limited by a pin 86 projecting from the input shaft 28 into a slot 88 in the valve 39, and resisted by a resilient coupling 89 secured by a bolt 93 to the shaft and engaging teeth 70 in the valve. Inlet grooves P<SP>1</SP>, P<SP>11</SP> in the wall of the bore 38 are interconnected by a passage 76 and supplied through the inlet passage 101, control grooves C<SP>1</SP> 1 , C<SP>1</SP> 2  are in respective communication with the control ports C 1 , C 2 , and an outlet groove R<SP>1</SP> is connected by a passage 77 to a groove R<SP>11</SP> from which fluid flow to the outlet port R is blocked by the pilot valve 103 when the spool valve 39 occupies its neutral position. A control pump 51 for metering fluid directed to the steering ram 13 comprises a fixed internally-toothed gear 52, an orbital gear 53 driven by the input shaft 28 through the resilient coupling 89, spool valve 39 and a wobble shaft 64, and a rotary commutator valve 54. The admittance valve 30 comprises a poppet member 96 having one end 98 biased into engagement with a seat 100 in the inlet port P by a spring 99. A chamber 97b at the other end of the poppet member 96 is pressurized from from the inlet port through a restricted orifice102 and communicates with the pilot valve 103 through a passage 107. The pilot valve 103 includes a valve member 106 which is biased by a spring 113 into a position wherein communication of the passage 107 and groove R<SP>11</SP> with a passage 108 leading to the outlet port R is blocked and has an arcuate end 116 in engagement with a cam surface 117 on the spool valve 39. When the spool valve 39 occupies its neutral position and the input shaft 28 is rotated, the control pump 51 is hydraulically locked so that rotation of the valve is prevented and the resilient coupling 89 twists to permit the shaft to turn in relation to the valve. Upon consequent axial displacement of the valve 39 the cam surface 71 actuates the pilot valve 103 to connect the passage 107 and groove R<SP>11</SP> to the outlet port R. Release of pressure in the chamber 97b results in opening of the admittance valve 30 so that further displacement of the valve 39 is effective to direct fluid from the pump 11 through the control pump 51 to the steering ram 13.