Pressure regulator

Claim 1

A hydraulic pressure regulator for an adjustable hydraulic machine comprising, in combination, a cylinder, a differential piston axially movable in said cylinder and defining in the latter a pair of pressure chambers to opposite sides of said differential piston; a control element for the hydraulic machine; means connecting said control element with said differential piston for controlling the position of said control element depending on the position of said piston in said cylinder; means for constantly applying hydraulic fluid at a control pressure to one of said pressure chambers; a control passage connected to the other pressure chamber; a pilot piston valve having a neutral position for controlling, when moved from said neutral position, the supply of hydraulic fluid to said control passage and the discharge of hydraulic fluid from said control passage, in dependence on the direction of movement of said pilot piston valve from said neutral position so as to feed hydraulic fluid into said other pressure chamber or to discharge hydraulic fluid therefrom; passage means for directing fluid at said control pressure against said pilot piston valve for urging the latter in one direction; resilient control force means for urging said pilot piston valve in the other direction; a pressure regulating valve in said control passage; a compensating piston; means for causing any pressure difference across said pressure regulating valve to act on said compensating piston to move the latter in one direction or the other from a neutral position; and mechanical follow-up means in engagement with said pilot piston valve and said compensating piston for moving said pilot piston valve in response to movement of said compensating piston so as to assist the force of the hydraulic fluid or of said control force means acting on said pilot piston valve to return the latter to said neutral position, so as to avoid over-travel of said differential piston.