Power plants – Pressure fluid source and motor – Servo-motor having externally operated control valve sets...
Reexamination Certificate
2001-02-06
2002-05-21
Michalsky, Gerald A. (Department: 3753)
Power plants
Pressure fluid source and motor
Servo-motor having externally operated control valve sets...
C060S445000
Reexamination Certificate
active
06389809
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a volume control valve for a variable displacement type hydraulic rotary machine suitable for use, for example, as a variable displacement hydraulic pump or motor in a construction machine such as a hydraulic excavator.
BACKGROUND ART
Generally, a variable displacement type hydraulic rotary machine is used as a hydraulic pump serving as an oil pressure source or as a hydraulic motor for traveling or rotation, in a construction machine or the like. For example, in case of using a variable displacement type hydraulic rotary machine as a hydraulic motor for traveling, the motor volume is switched between a large volume and a small volume by means of an actuator of variable volume, whereby the hydraulic motor is rotated at a low speed with a high torque when the motor volume is large, while the motor is rotated at a high speed with a low torque when the motor volume is small.
As a volume control unit for a hydraulic motor there is known a self-pressure control type volume control unit which controls the motor volume in accordance with a load pressure acting on a hydraulic motor from the exterior (see, for example, Japanese Patent Laid Open No. SHO57-43002). In the self-pressure control type volume control unit, a load pressure of a hydraulic motor is fed as a pilot pressure to a volume control valve and the position of the volume control valve is switched selectively between a large volume position and a small volume position in accordance with the pilot pressure, thereby selectively controlling pressure oil to be fed to an actuator of variable volume.
In this conventional self-pressure control type volume control unit, the volume control valve is composed of a main change-over valve for supplying pressure oil selectively to an actuator of variable volume and a pilot valve which detects a load pressure of a hydraulic motor and which controls the main change-over valve selectively in accordance with the load pressure.
The main change-over valve is switched between a large volume position and a small volume position in accordance with a pilot pressure (load pressure) which is fed through the pilot valve, allowing a pilot pressure receiving area to be changed between the large and small volume positions to prevent the occurrence of hunching at the time of switching from one to another volume.
More particularly, when the hydraulic motor volume is switched from a small to a large volume, the load pressure tends to decrease, so there is a fear that the motor volume may be switched again from the large to the small volume as the load pressure decreases. The load pressure increases upon switching of the motor volume to the small volume, so that the motor volume is again switched from the small to the large volume. Thus, what is called hunching phenomenon occurs.
According to the foregoing conventional construction, for preventing the occurrence of such a hunching phenomenon, the pilot pressure receiving area of the main change-over valve is varied between the large volume position and the small volume position to impart, for example, such a hysteresis characteristic as shown in
FIG. 5
which will be described later to a set value of the pilot pressure (load pressure) for changing the motor volume.
In the above conventional volume control unit, since the volume control valve used in the hydraulic motor volume control unit is composed of the main change-over valve which supplies pressure oil selectively to the actuator of variable volume for the hydraulic motor and the pilot valve which selectively controls the main change-over valve in accordance with a load pressure of the hydraulic motor, it is necessary to provide the pilot valve separately from a spool of the main change-over valve, thus resulting in that the whole of the control unit becomes complicated, causing an obstacle to the attainment of size reduction.
As another conventional example, for example in Japanese Utility Model Laid Open No. SHO62-45401 (Publication No. HEI6-28345) there is disclosed a construction wherein a spool of a volume control valve constituted by a hydraulic pilot valve is formed in a stepped shape and a load pressure of a hydraulic motor is exerted as a pilot pressure on a large-diameter side of the spool, whereby the volume control valve is switched from a small volume position to a large volume position in accordance with the load pressure. In this volume control valve, a pressure oil feed/discharge port formed on a high pressure side is blocked by a land portion of the spool until the load pressure decreases in a predetermined certain range, thereby imparting a hysteresis characteristic to a set value of the pilot pressure.
However, this conventional construction is merely such that when the load pressure begins to decrease at a large motor volume, the pressure oil feed/discharge port formed on the high pressure side is blocked by a land portion of the spool to suppress the decrease of the motor volume. If the pressure oil leaks even a slight amount from the spool land portion, the motor volume switches to the small volume side and thus it is difficult to control the motor volume stably.
As a further conventional example, for example in Japanese Patent Laid Open No. HEI1-116301 there is disclosed a construction wherein, for switching the motor volume between large and small volumes using an external command pressure, a stepped portion for receiving an external command pressure is formed in a spool of a volume control valve, and on this stepped portion side an external command pressure receiving area is varied according to a slide position (drive position) of the spool.
According to this conventional construction, however, a sleeve is fitted on the stepped portion side of the spool and the external command pressure receiving area is varied according to a relative position between the stepped portion of the spool and the sleeve, thus requiring the provision of the sleeve separately from the spool. As a result, the number of components used increases and the structure of the volume control valve becomes complicated; besides, it is difficult to reduce the entire size.
DISCLOSURE OF THE INVENTION
The present invention has been accomplished in view of the problems of the conventional techniques mentioned above and it is an object of the invention to provide a volume control valve for a variable displacement type hydraulic rotary machine capable of reducing the number of components used, thereby improving the assembling work efficiency, capable of forming the whole in a compact shape and thereby attaining the reduction of size, and further capable of stabilizing and automating volume control.
For achieving the above-mentioned object and for controlling the volume of a variable displacement type hydraulic rotary machine with use an actuator of variable volume, the present invention is applied to a volume control valve for the variable displacement type hydraulic rotary machine, the volume control valve being constructed such that a load pressure of the variable displacement type hydraulic rotary machine is received as a pilot pressure to switch pressure oil to be fed to the actuator from one pressure level to another.
In one aspect of the present invention there is provided a volume control valve for a variable displacement type hydraulic rotary machine, comprising a valve housing having a spool sliding bore, with a high pressure port, a tank port, a pilot port, and a pressure oil feed/discharge port for an actuator of variable volume being formed in the spool sliding bore in axially spaced positions; a spool inserted into the spool sliding bore of the valve housing and adapted to slide axially through the spool sliding bore to selectively establish and block communication of the pressure oil feed/discharge port with the high pressure port and the tank port; a first pressure receiving portion formed in the spool to receive a pilot pressure introduced from the pilot port, thereby displacing the spool axially within the spool sliding bore; a bottomed axial bore fo
Kagiwada Hitoshi
Kobayashi Takeshi
Niidome Takashi
Hitachi Construction Machinery Co. Ltd.
Mattingly Stanger & Malur, P.C.
Michalsky Gerald A.
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