Variable flow hydraulic system

A variable flow hydraulic system for supplying pressurized fluid in a machine, the machine having a power source for driving the hydraulic system and a work circuit having at least one fluid actuator for performing work in response to an applied hydraulic fluid flow, the hydraulic system comprising:

• a reservoir for storing hydraulic fluid for use in the work circuit;
• a fixed displacement pump having an inlet port and an outlet port, the fixed displacement pump configured to be driven by the power source for providing a fixed flow of pressurized hydraulic fluid;
• a variable displacement pump having an inlet port, an outlet port, a de-stroking actuator, and a compensator for controlling the de-stroking actuator, the variable displacement pump configured to be driven by the power source to provide a variable flow of pressurized hydraulic fluid to be applied to the work circuit;
• a flow sensitive unloading valve having an inlet valve port, a first outlet valve port, and a second outlet valve port, the unloading valve configured to discretely switch fluid flow entering the inlet valve port between the first and the second outlet valve ports based on a fluid signal applied to the unloading valve;
• and
• a conduit system for distributing fluid flow between the reservoir, the fixed and the variable displacement pumps, the flow sensitive unloading valve, and the work circuit, wherein the outlet port of the fixed displacement pump is fluidly coupled to the inlet valve port, the first outlet valve port bypasses the work circuit, the second outlet valve port is fluidly coupled to the work circuit, and the outlet port of the variable displacement pump is also fluidly coupled to the work circuit;
• wherein the conduit system has a restriction for generating the fluid signal applied to the unloading valve in response to the fluid flow applied to the work circuit to discretely switch the fixed fluid flow from the fixed displacement pump between being applied to the work circuit and bypassing the work circuit.

A method of applying a variable flow of pressurized hydraulic fluid to a work circuit in a machine, the work circuit having at least one fluid actuator for performing work in response to the applied fluid flow, the method comprising:

• pumping a fixed fluid flow using a fixed displacement pump;
• pumping a variable fluid flow using a variable displacement pump;
• applying the variable fluid flow pumped by the variable displacement pump to the work circuit;
• generating a flow signal based upon the fluid flow being applied to the work circuit, the flow signal representative of first and second flow states;
• and
• bypassing the fixed fluid flow pumped by the fixed displacement pump around the work circuit when the flow signal is in the first state and directing the fixed fluid flow to the work circuit when the flow signal is in the second state.