GB1502425A - Stroke control apparatus for a variable stroke hydraulic pump - Google Patents

Abstract

1502425 Fluid pressure servomotor systems LUCAS INDUSTRIES Ltd 7 May 1975 [2 April 1974] 14462/74 Heading G3P A variable stroke hydraulic main pump P includes means to automatically return the pump to substantially zero stroke in the event of pressure failure of boost pump B. The main pump P is of reversible swash-plate type driven by motor E and connected via lines 62, 63 with hydraulic motor M. The angle of the swash-plate 104, Fig. 1 (not shown) is controlled by a rod 12 via a moving- seat piston and cylinder servomotor arrangement (105, 106). Rod 12 can be moved in either direction by an external manual lever (44), Fig. 3 (not shown) which acts through a spring loaded linkage (45) on a pin (46) engaging in groove 15, between flanges 13, 14 attached to the rod. Disposed opposite the latter is a device 50 having a plunger 55 which is normally urged leftwards to the position shown by the boost pump output pressure communicated via line 61 to act on a stepped portion of the plunger against the bias of a spring (57), Fig. 4 (not shown). Should the boost pump pressure fail, the spring (57) urges plunger 55 rightwards causing interacting pivoted levers 31, 37 to move towards each other so that abutments 34, 40 thereon engage flanges 13, 14 to override all other controls and move the swashplate to the zero stroke position. The control mechanism also includes a device 16 having a slidable sleeve 17 with a shoulder 18 subject in chamber 25 to the higher of the main pump pressures in lines 62, 63 communicated thereto via selector valve V and lines 65, 66. During normal operation an increase in pressure causes sleeve 17 and rod 19 to move leftwards against the bias of spring 24, thus pivoting levers 31, 37 to reduce the pump stroke and thus the pressure. Should the pressure rise excessively, then valve 26 unseats to communicate pressure from chamber 25 to a piston and cylinder actuator 28 causing the latter to displace rod 19 leftwards relative to sleeve 17 so as to move the swash-plate to the zero stroke position. The periphery of bush 23 of device 16 is part-spherical to enable the bush to tilt slightly under load from rod 19 to thus reduce stiction.