Variable displacement pump control assembly

Claim 1

Compensating means for a variable displacement pump of the type comprising a housing having pump means, high and low fluid pressure zones, and a fluid pressure actuated member having restricted communication with said high pressure zone and operatively engaged with said pump means to vary the displacement thereof; said compensating means comprising a valve member movable in said housing between positions opening and closing a bleed passage from said fluid pressure actuated member to said low pressure zone; spring means in said housing biasing said valve member to a position closing said bleed passage; said valve member having first opposed areas including an area on one side exposed to fluid pressure in said high pressure zone and an area on the other side exposed to fluid pressure in said high pressure zone via orifice means; said valve member having second opposed areas respectively exposed to fluid pressure in said high pressure zone and to a fluid pressure sensing passage in said housing which is communicated with the downstream side of a variable area orifice in the pressure feed path between said high pressure zone and a fluid motor actuated by fluid flowing from said high-pressure zone through said variable area orifice; said spring means retaining said valve member in said bleed passage closing position when the differential in fluid pressures acting on said second opposed areas is less than predetermined value; pressure and horsepower compensating pilot valves in said housing each operative, upon increase of fluid pressure in said high pressure zone to predetermined value, to open communication between said other side of said valve member and said low pressure zone for movement of said valve member by the then predominant fluid pressure acting on said one side of said valve member to open said bleed passage to bleed fluid pressure acting on said fluid pressure actuated member to said low pressure zone with consequent movement of said fluid pressure actuated member in pump displacement decreasing direction; each pilot valve including a spring biased pilot valve member with said horsepower compensating pilot valve having a spring follower engaged with a cam surface on said fluid pressure actuated member operative to increase the spring bias on the pilot valve member of said horsepower compensating pilot valve as said fluid pressure actuated member moves in a displacement decreasing direction; the aforesaid pressure differential, when exceeding such predetermined value, effecting movement of said valve member against said spring means to open said bleed passage to bleed said fluid pressure actuated member to said low pressure zone while said pilot valves are closed whereby said fluid pressure actuated member moves in a displacement decreasing direction.