GB1217287A - Hydraulic control system for a vehicle steering system. - Google Patents

Abstract

1,217,287. Vehicle power steering. TYRONE HYDRAULICS Inc. 27 Aug., 1969 [13 May, 1969], No. 42688/69. Heading B7H. An hydraulic control system for the steering system of a vehicle comprises two engine-driven pumps 49, 59 delivering liquid through a control valve 63 to the steering system of the vehicle, the rate of delivery of the liquid from the pumps being in proportion to the speed of the engine and the control valve 63 being influenced by the fluid pressure from the first pump 49 such that below a certain engine speed the liquid flow from both pumps is delivered to the steering system and above a certain engine speed the liquid flow from only the first pump is delivered to the steering system. For this purpose, a restriction 65 is placed in the line from the first pump 49 and a connection 85, 87 is made before and after the restriction with each end of the control valve 63. The spool 67 of the control valve is urged by a spring 83 into a position which permits the liquid flow from both pumps to be delivered to the control valve 37 of the steering system. At low engine speeds the pressure differential before and after the restriction 65 does not affect the valve 63 but at high speeds the effect of the pressure differential is such as to cause the spool 67 to move against the spring 83 and to permit the flow from the first pump 49 only to be delivered to the control valve 37 of the steering system, the liquid flow from the second pump 59 being returned to the reservoir 44. The steering system may include steering rams 25, 27 coupled to the wheels of the vehicle and influenced by control valve 37 operated by a steering wheel 39 as shown in Fig. 1 or alternatively the rams may operate the rear traction unit of an articulated vehicle to steer the vehicle, Fig. 4 (not shown).