GB1344449A - Hydrostatic servo-steering mechanism for the steering of automotive vehicles and like machines - Google Patents

Abstract

1344449 Power steering VYZKUMNY USTAV STAVEBNICH A ZEMNICH STROJU 24 April 1972 [22 April 1971] 18953/72 Heading B7H A hydrostatic servo-steering mechanism for a vehicle, e.g. an earthmover, includes a power circuit 1 (shown in heavy lines) including a pump 3, a distributer valve 7 and a servomotor 10; a steering circuit 2 including an input pump 18 actuated by the steering wheel 20 and an output motor 30 connected to the steerable wheels 15, 151 and means for varying the steering ratio of the steering circuit 2. The steering ratio may be varied either continuously or in steps. In a first embodiment (Fig. 1) the input or control pump 18 is connected by steering lines 21, 22 and branch lines 24, 25 to the distributer valve 7 to control the flow of pressure fluid from the pump 3 to the servomotor 10. The steering lines 21, 22 are also connected by lines 28, 29 to the opposite ends of piston and cylinder output motor 30 which acts as a follow-up or feed-back cylinder. The motor 30 has a differential piston 31 which divides the cylinder 30 into three chambers 32, 33, 34. The central chamber 33 is connected by line 35 and selector valve 23 either to steering line 21 or 22. With the valve 23 in the position shown the chamber 33 is connected to steering line 22 and this arrangement provides a high steering ratio (i.e. a large number of turns of the steering wheel from lock to lock) which is suitable when the earth mover is being driven on the highway or in the event of a pump failure when the cylinder 30 acts as a telemotor. With the valve 23 in its second position the chamber 33 is connected to the steering line 21 to provide a low steering ratio suitable for use when the earthmover is in operation. The valve 23 may be shifted manually or may be automatically shifted from its second position to its first position should the pressure in either of the steering lines 21 or 22 rise above a predetermined value (e.g. in the event of a pump failure). In a second embodiment (Fig. 4) the steering circuit is provided with two feed-back cylinders 40, 40<SP>1</SP> which are connected to the steering lines 21, 22 by a selector valve 23<SP>111</SP> and again the two positions of the valve 23<SP>111</SP> provide a high (as shown) or low steering ratio. In a third embodiment (not shown) the feedback cylinder is a conventional double acting piston and cylinder and the steering ratio is varied by adjusting the effective length of the steering arm 14<SP>1</SP> by moving the connection with the piston-rod along the arm. The connection may be moved by a screw or by a pneumatic or hydraulic motor. In a fourth embodiment (not shown) the steering ratio is varied by varying the displacement of input pump 18. The pump may be a duplex pump having two constant displacement sections arranged in parallel and a selector valve is used to connect either one or both sections into the steering circuit. Alternatively the pump may be a variable displacement pump.