Self-regulated hydraulic control system

In a "high-low" hydraulic circuit for rapidly advancing the piston of a hydraulic motor means from a rest position during a first portion of a working stroke until an increased resistance to movement of the piston is encountered and subsequently driving the piston at a lower speed against the increased resistance to complete said working stroke, said system including a first relatively low-displacement, high-pressure pump having an intake and an outlet, a second relatively high-displacement, low-pressure pump having an intake and an outlet, and hydraulic circuit means for connecting said first and second pump means to said fluid motor means to drive said piston through said working stroke and to subsequently rapidly return said piston to said rest position;

• the improvement wherein said hydraulic motor means includes a cylinder having a piston operatively mounted therein for reciprocatory movement and having a rod projecting from a rod end of the cylinder, means on said cylinder and piston defining first, second and third working faces on said piston respectively exposed to first, second and third hydraulically separate chambers within said cylinder, said first and second faces being of equal area and facing opposite ends of said cylinder and said third face facing in the same direction as said first face and having an area greater than that of said first face, first, second and third ports in said cylinder communicating respectively with said first, second and third chambers;
• and said hydraulic circuit means comprises a multi-position reversing valve controlled first circuit means for connecting the intake and outlet of said first pump to said first and second ports of said motor means in a closed-loop circuit to selectively enable said first pump to drive said piston in a working stroke from said rest position or a return stroke to said rest position in accordance with the position of said reversing valve, second circuit means including a pilot actuated, two-position valve operable in a first position to connect said third port to the outlet of said first pump and operable in a second position to connect said third port to the outlet of said second pump, said two-position valve including opposed first and second pressure actuated pilots operable to position said two-position valve in its first position when the pressure in said first pilot exceeds the pressure in said second pilot and to position said two-position valve in said second position when the pressure in said second pilot exceeds the pressure in said first pilot, first conduit means in said second circuit means connecting said second pilot to said first port, second conduit means in said second circuit means connecting said first pilot to the intake side of one of said pumps, a dual-stage, pilot-actuated sequence valve in said second conduit means operable to maintain a normally closed position blocking flow from said first pilot until the pressure in said first pilot rises above a selected first pressure at which said sequence valve opens and to remain open until the pressure in said first pilot drops below a second pressure substantially less than said first pressure, and a one-way check valve connected in said second conduit means in parallel with said sequence valve accommodating flow toward said first pilot.