Closed loop hydraulic system with variable charge pressure

Abstract

A closed loop hydraulic system having a variable charge pressure capability without parasitic power losses is disclosed. The present system includes a variable displacement hydraulic pump driven by a power source, a tilt control means for controlling a tilt angle of the variable displacement hydraulic pump, and a hydraulic motor having a pair of inlet/outlet ports connected in a closed circuit to a pair of inlet/outlet ports of the variable displacement hydraulic pump by way of a pair of main conduits. The system has a charging system including a charge pump driven by a power source, the charge pump including an inlet connected to a supply of oil, and an outlet port connected to the closed circuit for supplying pressurized oil to the variable displacement hydraulic pump. The charge system further includes an electrohydraulic proportional relief valve including means for varying an operating pressure setting thereof, which electrohydraulic proportional relief valve is connected to the charging system for controlling the pressure level of the pressurized oil supplied to the variable displacement hydraulic pump. The means for varying the operating pressure setting of the proportional relief valve are controlled by control means responsive to at least a pressure condition in the closed circuit. According to another aspect of the invention, the charging system is also connected to a hydraulic circuit of the tilt control means for supplying pressurized oil thereto.

Dependencies are inferred from the claim text.