Fluid system

Claim 1

A fluid system comprising a unidirectional fluid pump having a displacement control means such that the fluid displacement of said fluid pump is adapted to be varied between a minimum and a maximum fluid flow displacement position, said pump having a high pressure fluid outlet and a low pressure fluid inlet; a main fluid cylinder having a main piSton reciprocably mounted therein and movable in response to fluid pressure acting on the opposite sides of said piston, said main fluid cylinder piston having connecting rods extending from the opposite sides thereof externally of said main fluid cylinder, said rods being so sized that the opposite pressure responsive areas of said main cylinder piston on which fluid pressure acts to move said piston in opposite directions are equal; a first directional flow control means having a first pair of ports, one of which is in fluid communication with said pump inlet port while the other valve port is in communication with said pump outlet port, said first directional flow control means having a second pair of valve ports which respectively communicate with the opposite sides of said main piston within said main fluid cylinder, said first directional flow control means being selectively movable to one position for forming a closed loop circuit between said fluid pump and said main fluid cylinder to connect the pump outlet port pump to one side of said main piston and direct fluid pressure thereagainst, while connecting the other side of said main piston to said pump inlet port to exhaust fluid pressure from said main fluid cylinder associated with the other side of said main piston, whereby, said main piston may be selectively reciprocated within said main fluid cylinder in response to fluid flows selectively communicated by said first directional control means to the opposite sides of said main piston from said fluid pump, said first directional control means being movable to another position wherein communication between said main fluid cylinder and said fluid pump is closed and said pump inlet port and said pump outlet port are fluidly connected in a closed loop fashion, said main piston being movable in one direction when fluid pressure is directed against one side of said main piston and at a rate of movement which is a function of the amount of displacement of said fluid pump, said main cylinder piston being movable in an opposite direction when fluid pressure is directed against the other side of said main piston and a rate of movement which is a function of the amount of displacement of said fluid pump; a second fluid cylinder having a second piston reciprocably movable therein in response to pressure fluid acting thereon, said second piston having a connecting rod extending from one end thereof, said extending end of said connecting rod being operatively coupled to said pump displacement control means, said pump displacement control means being moved between said fluid flow displacement positions as said second piston is reciprocated within said second fluid cylinder; a second source of fluid pressure; means for selectively communicating said second source of fluid pressure to the opposite sides of said second piston, said last mentioned means comprising: first and second fluid feed control means for respectively controlling the rate of fluid flow from said second source to the opposite sides of said second piston to act against said second piston and move the same in opposite directions at a rate which is a function of the rate of fluid flow through said first and second fluid feed control means; second directional flow control means for selectively controlling the flow of fluid from said second source of fluid pressure to said first and second fluid feed control means whereby the rate of change in the displacement of said fluid pump between said minimum and maximum flow displacement positions is selectively controlled and thus the rate of movement of said main piston in opposite directions is selectively controlled.