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.

Description

TECHNICAL FIELDThis invention relates generally to a closed loop hydraulic system including a charging system providing variable charge pressure, and more particularly, to a closed loop hydraulic system providing variable charge pressure relief through an electrohydraulic proportional relief valve and control means therefor responsive to at least a pressure condition in the closed circuit for providing charge flow sufficient to meet charge requirements without parasitic power losses.BACKGROUND ARTParasitic power losses are a concern with closed loop hydraulic systems, including, but not limited to, hydrostatic vehicle proportion drives and differential steering systems. It has been found that a major contributor to such parasitic losses in these systems is the wasted hydraulic power of the charge flow being throttled across a charge relief valve. Charge systems typically provide power proportional to engine power at a constant pressure for system oil makeup and control actuation. Un...

AI Technical Summary

Benefits of technology

According to one aspect of the present invention, a closed loop hydraulic system having variable charge pressure 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 and are operative to reduce the charging system pressure, without incurring parasitic power losses. 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.

Problems solved by technology

Parasitic power losses are a concern with closed loop hydraulic systems, including, but not limited to, hydrostatic vehicle proportion drives and differential steering systems.

It has been found that a major contributor to such parasitic losses in these systems is the wasted hydraulic power of the charge flow being throttled across a charge relief valve.

However, it has previously been problematic to reduce charge flow in a closed loop system without incurring corresponding parasitic power losses.

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