Fluid handling – With indicator – register – recorder – alarm or inspection means – Position or extent of motion indicator
Reexamination Certificate
2000-06-09
2001-07-24
Chambers, A. Michael (Department: 3753)
Fluid handling
With indicator, register, recorder, alarm or inspection means
Position or extent of motion indicator
C137S625650, C137S884000, C137S625640
Reexamination Certificate
active
06263915
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a directional control valve having a position detecting function, capable of detecting operating positions of a valve member such as a spool.
2. Discussion of Background
The directional control valve capable of detecting the operating position of a spool is well known as disclosed in, for example, Japanese Unexamined Utility Model Publication No. 2-66784. This known directional control valve is provided with a magnet on the outer periphery of a spool and provided with a magnet sensor on a casing. This directional control valve is arranged so that, when the spool moves to one changeover position, the magnet approaches the magnetic sensor, and the magnetic sensor is turned on, and that, when the spool moves to the other changeover position, the magnet moves away from the magnetic sensor, and the magnetic sensor is turned off. Thus, this directional control valve detects that the spool has been changed over by the on/off of the magnetic sensor.
However, since the above-described conventional directional control valve installs the magnet at a position situated in the fluid passage on the outer periphery of the spool, the magnet directly contacts the hydraulic fluid. Therefore, when the fluid contains water, chemical mist, particulates of magnetic material such as metallic powder, or the like, there has often arisen the problem that the contact of the magnet with these substances makes the magnet rust, corrode, or adsorb the particulates, thereby bringing about drawbacks of reducing the detection accuracy due to the decrease in magnetic force, or incurring poor sliding conditions.
Furthermore, although the above-described known directional control valve can detect the position of the spool situated at a stroke end by detecting the magnet, this directional control valve can not detect any position of the spool on the way of a stroke. Therefore, even if the spool makes an irregular movement deficient in smoothness due to some abnormality, it can not detect this abnormality. This has made it difficult to take suitable precautions against a failure or an accident before they happen, and has thus raised a problem in the maintenance and management.
In addition, a magnetic sensor for detecting a magnet is generally constituted so as to be turned on when the magnetic flux density is above a fixed value, and to be turned off when it is below another fixed value. Therefore, during the driving stroke of the spool, if the magnetic flux density becomes higher than the fixed value due to the approach of a magnet, the magnetic sensor is turned on even before the spool arrives at a stroke end, and conversely, during the return stroke of the spool, if the magnetic flux density becomes lower than the other fixed value due to the moving-away of the magnet, the magnetic sensor is turned off even before the spool arrives at the return-stroke end. Therefore, even if the magnetic sensor stops on the spot for some reason at the instant when the magnetic sensor are turned on or turned off, the magnetic sensor only outputs an on/off signal notifying that the spool has been completely changed over. It is thus impossible for conventional magnetic sensors to detect an abnormality.
SUMMARY OF THE INVENTION
The technical problem of the present invention is to provide a directional control valve having a position detecting function, capable of detecting the operating positions of the valve member over the whole stroke thereof, without using a magnet and a magnetic sensor as in the conventional art.
In order to solve the above-described problems, the directional control valve of the present invention comprises a plurality of ports; a valve hole to which each of these ports is opened; a casing having the ports and the valve hole; a valve member slidably received in the valve hole and changing over flow passages; driving means for driving said valve member; a detection coil disposed on the casing and generating an alternating magnetic field; a detection head which is disposed so as to be displaced in synchronization with the valve member and which changes the impedance of the detection coil by approaching or moving away from the detection coil in the alternating magnetic field; and a signal processing circuit applying an alternating voltage to the detection coil and detecting operating positions of the valve member from the change in impedance of the detection coil.
In the directional control valve of the present invention having the above-described features, when the detection head moving in synchronization with the valve member approaches or moves away from the detection coil, the impedance of the detection coil changes in response to the distance from the detection head, so that the operating position can be detected from this change in impedance. It is therefore possible to discriminate whether the valve member has normally operated or not, from the relations between the operating position and the operating time, and thus to take suitable precautions against a failure or an accident before they happen.
Since there is no need to dispose a magnet in the flow passage of a hydraulic fluid on the outer periphery as in the conventional art, even if the hydraulic fluid is at a high temperature or contains water, chemical mist, magnetic particles such as metallic powders, or the like, it is unnecessary to take countermeasures against rusting or corroding, the adsorption of magnetic particles, the reduction in magnetic force, the change in temperature, etc. This permits the achievement of a simple, long-life, and high-reliability directional control valve.
In accordance with a specific embodiment of the present invention, there are provided a piston which changes over the valve member by operating under the action of a pilot fluid pressure and which is disposed on at least one end side of the valve member, the detection head disposed on one piston, and the detection coil disposed on the casing portion.
In accordance with another preferable embodiment of the present invention, the above-described detection coil is a high-frequency coil for generating a high-frequency magnetic field, and the above-described detection head is formed of metal. Alternatively, the above-described detection coil is a low-frequency coil for generating a low-frequency magnetic field, and the above-described detection head is formed of magnetic body and is adapted to be taken in and out of the hollow portion of the coil by the movement of the piston.
REFERENCES:
patent: 4953590 (1990-09-01), Kakinuma et al.
patent: 5101856 (1992-04-01), Kakinuma et al.
patent: 5623967 (1997-04-01), Hayashi
patent: 5785087 (1998-07-01), Takahashi et al.
patent: 5826616 (1998-10-01), Golden
patent: 2-66784 (1990-05-01), None
patent: 2-66785 (1990-05-01), None
patent: 2-88079 (1990-07-01), None
Hayashi Bunya
Ishikawa Makoto
Chambers A. Michael
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
SMC Corporation
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