Fluid handling – With indicator – register – recorder – alarm or inspection means – Position or extent of motion indicator
Reexamination Certificate
2000-06-14
2001-04-24
Chambers, A. Michael (Department: 3753)
Fluid handling
With indicator, register, recorder, alarm or inspection means
Position or extent of motion indicator
C137S884000, C137S625640, C137S625650
Reexamination Certificate
active
06220284
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a pilot operated directional control valve having a position detecting function, improved by permitting the detection of operating positions of a valve member such as a spool, through the use of a magnet.
BACKGROUND ART
The directional control valve capable of monitoring the changeover operation of a spool utilizing a magnet is well known as disclosed in, for example, Japanese Examined Utility Model Publication No. 7-31021(Japanese Unexamined Utility Model Publication No. 2-88079). This directional control valve is provided on both ends of a spool with respective pistons for receiving pilot fluid pressure, and is adapted to change over the spool by the fluid pressure acting on the pistons. This directional control valve has a magnet mounted on one piston, and has a detection coil for detecting the change in magnetic flux, installed at a position opposite to the magnet mounted on a casing, whereby the directional control valve detects the moving speed of the piston, or the spool from the magnitude of the induced voltage generated in the detection coil by the change in magnetic flux when the magnet moves together with the piston, and judges whether the moving speed is normal or not.
However, since the above-described conventional directional control valve is constituted so that the magnet is installed at a position which is exposed to the pressure chamber adjacent to an end face of the piston, the magnet will directly contact a pilot 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. This would bring about drawbacks of reducing the detecting accuracy due to the decrease in magnetic force, or incurring poor sliding conditions.
Furthermore, the above-described valve is constituted so as to make the detection coil generate an induced voltage in response to the change in magnetic flux with the movement of the magnet, and to detect the moving speed of the spool from the magnitude of the induced voltage to judge whether the moving speed is normal or not, but can not detect operating positions of the spool.
DISCLOSURE OF INVENTION
The main technical problem of the present invention is to provide a pilot operated directional control valve having a position detecting function, capable of detecting operating positions of a valve member via the piston for driving the valve member.
The other technical problem of the present invention is to prevent the magnet from contacting the pilot fluid and being affected by the pilot fluid, and thus to maintain a stable detecting accuracy and operating characteristics.
In order to solve the above-described problems, in accordance with the directional control valve of the present invention, a magnet for position detecting is mounted on the piston provided on one end of a valve member, and a magnetic sensor for detecting the magnetism from the magnet is installed at a portion opposite to the magnet, in the casing. The position where the magnet is installed on the piston is a portion, on one end side of the piston, adjacent to a breathing chamber defined by the piston and an end face of the valve member. This breathing chamber is hermetically shut off from the pilot pressure chamber disposed on the opposite side of the breathing chamber, in the piston, by the piston packing on the outer periphery of the piston so as to prevent the pilot fluid from flowing into the breathing chamber.
In the directional control valve having the above-described features, the piston is driven by the pilot fluid supplied into the pilot pressure chambers, and the valve member is changed over via the piston. A magnetic flux density from the magnet moving together with the piston is detected by the magnetic sensor, and operating positions of the piston, or those of the valve member are detected by the change in magnetic flux density with the movement of the magnet.
Herein, since the magnet is installed at a position adjacent to the breathing chamber of the piston, the magnet is prevented from directly contacting the pilot fluid. Therefore, even if the pilot fluid contains water, chemical mist, particles of magnetic material such as metallic particles, or the like, there is no risk of the magnet rusting, corroding, or adsorbing particulates. This prevents the decreasing in magnetic force, and the occurring of a malfunction due to adsorbed particulates, permitting the maintaining of a stable performance.
In accordance with a specific embodiment of the present invention, the magnet is provided on the outer periphery of the piston, and the magnetic sensor is provided at a portion in the casing, adjacent to the outer periphery of the piston.
In accordance with another specific embodiment of the present invention, a housing is formed in the surface opposite to the valve member, in the piston, the magnet is installed in the housing so as to be situated adjacent to the pressure receiving surface of the piston, and the magnetic sensor is provided at a position opposite to the pressure receiving surface, in the casing.
In accordance with still another specific embodiment of the present invention, there is provided a double-pilot type directional control valve having two pistons and two pilot valves, wherein two pilot valves are concentratedly provided on one end side of a casing, and wherein, on the other side of the casing, a magnet and a magnetic sensor are provided on one piston and on the casing, respectively.
In the present invention, the piston having at least a magnet may be coupled to the valve member.
In the present invention, it is preferable that the magnetic sensor is installed so as to be able to detect the magnetism from the magnet over the whole stroke of the piston, and that it is therefore constituted so as to detect all operating positions of the piston from the change in magnetic flux density with the displacement of the magnet.
Thereby, not only the stroke end positions of the piston, or the valve member, but also positions on the way of the stroke can be known. It is therefore possible to easily discriminate, by a discrimination circuit, whether the valve member has normally operated or not, from the relations between the position and the operating time of the valve member from the initiation to the termination of a stroke thereof. This permits taking precautionary measures before a failure happens, and preventing a long downtime of working system due to a failure or an accident.
REFERENCES:
patent: 3598360 (1971-08-01), Merriner et al.
patent: 4409580 (1983-10-01), Ishigaki
patent: 5244002 (1993-09-01), Frederick
patent: 5326070 (1994-07-01), Baron
patent: 5623967 (1997-04-01), Hayashi
patent: 5687698 (1997-11-01), Mastro et al.
patent: 5829481 (1998-11-01), Tajima et al.
patent: 1 279 509 (1972-06-01), None
Hayashi Bunya
Ishikawa Makoto
Chambers A. Michael
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
SMC Corporation
LandOfFree
Pilot operated directional control valve having position... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Pilot operated directional control valve having position..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Pilot operated directional control valve having position... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2548576