Multiple function hydraulic system with a variable displacement pump and a hydrostatic pump-motor

Abstract

A hydraulic system includes a first pump and a plurality of valves that control fluid flow from the first pump to several actuators. Variable source orifices in the control valves are connected in parallel between the first pump and a node, and variable bypass orifices in the control valves are connected in series between the node and a tank. Pressure at the node controls displacement of the first pump. Each control valve also has a metering orifice for varying fluid flow between the node and one of the actuators. A hydrostatic pump-motor, coupled between two ports of a given actuator, is driven in a motoring mode by fluid exiting one of those ports. In a pumping mode, the hydrostatic pump-motor forces lower pressure fluid exhausting from one port into the other port of the given actuator.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application claims benefit of U.S. provisional patent application no. 61 / 452,885 filed on Mar. 15, 2011.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT[0002]Not ApplicableBACKGROUND OF THE INVENTION[0003]1. Field of the Invention[0004]The present invention relates to hydraulic systems having a plurality of pumps and a plurality of independently controllable hydraulic actuators; and more particularly to controlling the plurality of pumps and allocating the resultant fluid flow to the plurality of hydraulic actuators.[0005]2. Description of the Related Art[0006]Hydraulic systems have at least one hydraulic pump that supplies pressurized fluid which is feed through control valves to drive several different hydraulic actuators. A hydraulic actuator is a device, such as a cylinder-piston arrangement or a hydraulic motor that converts the flow of hydraulic fluid into mechanical motion.[0007]Because loads of different magnit...

AI Technical Summary

Benefits of technology

The present hydraulic system has a flow summation node that controls the displacement of a first pump. Each control valve has a metering orifice that regulates fluid flow between the summation node and the associated hydraulic actuator. The control valves also have a variable flow source orifice and a variable bypass orifice that change in size as the metering orifice enlarges or shrinks. The technical effect of this design is that it allows for precise control of hydraulic actuators, even at low speeds, through the use of valves that adjust fluid flow based on the size of the metering orifice.

Problems solved by technology

Without some further compensation mechanism, this deprives the boom actuator of the necessary fluid required to operate as commanded.

Some of these mechanisms use pressure compensators and a load sensing pump, while other ones use pilot pressure signals from the operator controls to create throttling losses for the low pressure functions.

All these throttling losses generate heat and add inefficiency to the hydraulic system in order to enable the multifunction operation commanded by a machine operator.

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