Variable displacement pump control assembly

Pressure compensating means for a variable displacement pump of the type including a housing having intake, delivery, and drain ports, pump means in said housing operative to deliver fluid under pressure from said intake port to said delivery port, and a piston reciprocable in a first bore in said housing exposed to fluid under pressure in said delivery port via first orifice means in said housing and being engaged with said pump means to vary the displacement of said pump means according to the magnitude of the pressure in said delivery port;

• said housing having a second bore intersected by passages communicating with said delivery port, with said first bore, and with said drain port;
• said pressure compensating means comprising a valve member reciprocable in said second bore between first and second positions closing and opening communication between said first bore and said drain port, said valve member having one end portion exposed to fluid pressure in said delivery port and an opposite end portion exposed to fluid pressure in said delivery port via second orifice means in said housing;
• spring means in said housing biasing said valve member to said first position;
• and a pilot valve in said housing opened responsive to increase in fluid pressure in said delivery port to predetermined magnitude to bleed fluid pressure acting on said opposite end portion to said drain port whereby predominant fluid pressure in said delivery port acting on said one end portion is effective to move said valve member to said second position to provide a bleed passage to said drain port from said first bore thus to decrease the fluid pressure in said first bore for movement of said piston in a direction to decrease the capacity of said pump means until the fluid pressure in said delivery port and acting on said pilot valve is less than such predetermined magnitude to permit closing of said pilot valve with consequent equalization of fluid pressure acting on said end portions of said valve member and movement of the latter to said first position;
• said valve member having opposed areas respectively exposed to fluid pressure in said delivery port and to fluid pressure in a sensing passage which intersects said second bore and which is communicated with the downstream side of a variable area orifice in the pressure feed path from said delivery port to a fluid motor actuated by flow of fluid through said variable area orifice from said delivery port to said fluid motor;
• a predetermined fluid pressure differential acting on said opposed areas being effective to move said valve member to said second position against said spring means to bleed said first bore to said drain port thus to decrease the fluid pressure in said first bore for movement of said piston in a direction to decrease the capacity of said pump means.

Pressure compensating means for a variable displacement pump of the type which includes a pressure chamber to which fluid pressure from the high pressure zone of said pump is conducted by way of a restricted passage to act on a pump displacement varying means in said chamber;

• said pressure compensating means comprising a pilot operated valve assembly having a pilot valve member which opens and closes communication between the high and low pressure zones of said pump responsive to the fluid pressure in said high pressure zone being greater than or less than predetermined magnitude, and a main valve member in said pump having first opposed areas respectively exposed to said high pressure zone and to said high pressure zone via orifice means in said main valve member, said main valve member being moved upon opening of said pilot valve to provide a bleed passage from said chamber to said low pressure zone when said pilot valve is open and to close said bleed passage when said pilot valve is closed, said bleed passage when open decreasing the fluid pressure in said chamber for movement of said pump displacement varying means for decreased displacement of said pump;
• spring means in said pump biasing said main valve member to bleed passage closing position when said pilot valve is closed, said main valve member moving against said spring bias means to open said bleed passage when said pilot valve is open;
• said main valve member having second opposed areas respectively exposed to said high pressure zone and to a fluid pressure sensing passage in said pump which is communicated with the downstream side of a variable area orifice in the pressure feed path from said high pressure zone to a fluid motor actuated by fluid under pressure flowing through said variable area orifice from said high pressure zone;
• said main valve member being moved to bleed passage opening position while said pilot valve is closed when the differential between fluid pressure in said high pressure zone and fluid pressure in said sensing passage exceeds the bias force of said spring means.