Importance

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Abstract

A variable flow hydraulic system including a fixed displacement pump and a variable displacement pump for supplying pressurized hydraulic fluid in a machine is disclosed herein. Along with the dual pumps, the system includes a reservoir, a flow sensitive unloading valve, and a conduit system for distributing fluid flow between the system components. The reservoir stores fluid for use in a work circuit with an actuator for performing work in response to applied fluid flow. The fixed and variable displacement pumps are driven by a power source (e.g., an engine) to provide a fixed and a variable fluid flow, respectively. The variable flow is applied to the work circuit. As for the fixed flow, the unloading valve switches the fixed flow to either bypass or be applied to the work circuit in response to a flow signal, which depends upon the fluid flow being applied to the work circuit. The flow signal can be a differential pressure signal generated as the flow applied to the work circuit passes through a restriction in the conduit which supplies fluid flow to the work circuit. As the fixed flow is switched to and bypassed from the work circuit, the inherent flow compensation characteristics of the variable displacement pump provide for smooth, accurate, responsive and efficient machine operation.

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First Claim