Hydraulic system having an adjustable hydrostatic machine

Abstract

A hydraulic system with an adjustable hydrostatic machine is provided that includes an adjustment mechanism. The adjustment mechanism interacts with an actuating device which has at least one actuating piston delimiting an actuating pressure space. The system has a regulating valve with which, for the displacement of the actuating piston and therefore for the actuation of the adjustment device, the supply and removal of pressure medium into and from the actuating pressure chamber can be controlled, wherein the regulating valve has a valve piston which is subjected to a force of a feedback spring, which force is dependent on the position of the adjustment mechanism. The valve piston is additionally subjected to a counterforce acting counter to the force of the feedback spring, and an actuating component is provided, with which the valve piston can be subjected to a control force acting in the same direction as the counterforce or to a control force acting counter to the counterforce.

Description

[0001]This nonprovisional application is a continuation of International Application No. PCT / EP2008 / 006851, which was filed on Aug. 20, 2008, and which claims priority to German Patent Application No. 10 2007 039 173.2, which was filed in Germany on Aug. 20, 2007, and which are both herein incorporated by reference.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The invention relates to a hydraulic system having an adjustable hydrostatic machine, an adjusting device which cooperates with the hydrostatic machine, and a regulating valve, wherein the adjusting device comprises at least a first adjusting piston which is influenced on an adjusting piston surface by an adjusting pressure, and wherein the regulating valve comprises a regulating element which is influenced in the direction of a first end position of the valve by a force dependent upon the position of the first adjusting piston, and which is influenced at a second end by an adjusting force for the purpose of ...

AI Technical Summary

Benefits of technology

[0011]By virtue of the provision of a counter-force which acts upon the regulating element and against the force which is dependent upon the position of the adjusting piston, a balance of forces can be achieved on the regulating valve in a rest position of the first adjusting piston even in the event of disappearing control signals when no control force is generated onto the regulating element. Since the control force generated by the actuating means is directed in the same direction as the counter-force or in the opposite direction thereto, it is possible, starting from the rest position of the adjusting device determined by the counter-force in the event of a disappearing signal, for the adjusting device to be deflected in two opposite directions by the actuating means. The hydrostatic system in accordance with the invention thus has the advantage that not only can a hydraulic pump be adjusted between e.g. a zero delivery volume and its maximum delivery volume but also that hydrostatic machines which can be pivoted in opposite directions, such as e.g. pumps provided for two delivery devices or else a pump / motor unit, as used in braking energy recovery devices, can be controlled in a convenient manner.

[0021]The regulating valve can be designed as a 3 / 3-port directional control valve. The use of a 3 / 3-port directional control valve renders it possible to provide in addition a neutral position of the regulating valve between the two end positions. This neutral position is determined by a defined regulating valve position. In this neutral position of the regulating valve, the adjusting pressure chamber delimited by the adjusting piston surface of the first adjusting piston can be connected in a restricted manner to a tank volume and is connected in a restricted manner to the adjusting pressure source.

Problems solved by technology

Although the proposed hydrostatic system permits convenient integration into a pump unit by reason of the arrangement of the feedback spring on the one hand and the proportional magnet on the other hand, it is, however, disadvantageous that a central position of the adjusting piston is not possible in the event of a disappearing control signal and a hydrostatic machine which can be adjusted in two opposite directions can only be moved to its neutral position by the generation of a control force by the proportional magnet.

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