Means and method for varying margin pressure as a function of pump displacement in a pump with load sensing control

A pump system comprising:

• a variable fluid displacement pump having a pump pressure line fluidly connected to a fluid pressure load;
• a servo connected to said pump for varying the fluid displacement of the pump, said servo including an elongated servo piston slidably mounted in a servo housing;
• a load sensing control operatively connected by said pump pressure line to said pump, said load sensing control being operatively connected to said pressure load by a load sensing signal line, and said load sensing control also being operatively connected to said servo for varying the fluid displacement of said pump;
• a variable orifice associated with the servo and located downstream from said pump and said load sensing control, said variable orifice being fluidly connected by a servo pressure conduit to the load sensing control such that the difference in the fluid pressure in said pump pressure line and the pressure sensed by said load sensing control varies proportionally in relation to the magnitude of the fluid displacement of said pump;
• the variable orifice being defined by a gap formed between the servo housing and the elongated servo piston, the gap resulting from the elongated servo piston having a transverse cross sectional area that varies along the length thereof.

A method of varying a fluid pressure differential across a load sensing control valve in a variable fluid displacement pump having a movable swashplate, the steps of the method comprising,

• connecting said pump by a fluid pressure line to a fluid pressure load,
• connecting said load sensing control valve to said fluid pressure line,
• connecting said load sensing control valve to said fluid pressure load with a load sensing signal line, the fluid pressure differential being defined as a pressure difference between the fluid pressure line and the load sensing signal line at the load sensing control valve,
• providing a servo means downstream of the load sensing control valve and coupled to the swashplate so as to move said swashplate and thereby vary the displacement of the pump,
• connecting said load sensing control valve to the servo means with a servo control pressure line and providing a hydraulic servo control pressure signal from said load sensing control valve to said servo means based upon the fluid pressure differential across the load sensing control valve,
• imposing a drain line including a variable orifice connected to the servo control pressure line between said load sensing control valve and said servo means to automatically modulate the hydraulic servo control pressure signal reaching said servo means,
• controlling the size of said variable orifice by mechanical feedback from said swashplate.