Pilot operated directional control valve having position detecting function

Abstract: The present invention provides a pilot operated directional control valve having a position detecting function which is capable of detecting operating positions of a valve member via the piston for driving the valve member. To achieve this, a magnet 21 is installed on the portion of a piston 12a which is abutted against one end of a spool 6 and which is adjacent to a breathing chamber 9 sealed off from a pilot pressure chamber 13a. A magnetic sensor 21 for detecting the magnetism from the magnet 21 is mounted in the casing 4 on the portion opposite to the magnet 21.

Description: The present invention relates to a pilot operated directional control valve having a position detecting function in which the detection of operating positions of a valve member such as a spool through the use of a magnet is improved. A directional control valve capable of monitoring the changeover operation of a spool by utilising a magnet is well known and is 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 mounted on a casing at a position opposite to the magnet, 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 magnet is installed at a position in the above-described conventional directional control valve 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 has the drawbacks of reducing the detecting accuracy due to the decrease in magnetic force, or causing poor sliding conditions. Furthermore, the above-described valve is arranged so that the detection coil generates an induced voltage in response to the change in magnetic flux with the movement of the magnet, and to detect the speed of the spool from the magnitude of the induced voltage to judge whether the speed is normal or not, but can not detect operating positions of the spool. EPA 0844425 describes a valve spool detection apparatus in which a shiftable valve spool has a plurality of distinct targets carried thereon. The targets are preferably axially spaced and located at one end of the valve spool. A detector mounted in the valve detects each target as each target enters a detection field of the detector. The detector generates a distinct output indicative of one target positioned within the detection field of the detector. A control determines, in response to the output from the detector, the exact valve spool position. In accordance with 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 magnet is installed 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 piston by piston packing on the outer periphery of the piston which prevents the pilot fluid from flowing into the breathing chamber. In the directional control valve having the above-described construction, the piston is driven by the pilot fluid supplied into the pilot pressure chamber, and the valve member is changed over via the piston. The magnetic flux density of 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. 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 a decrease in magnetic force and malfunctioning due to adsorbed particulates, so permitting the maintaining of a stable performance. In accordance with a specific embodiment, 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, a recess, hereinafter termed a "housing", is formed in the surface of the piston opposite to the valve member, 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 in the casing at a position opposite to the pressure receiving surface. In accordance with still another specific embodiment, there is provided a double-pilot type directional control valve having two pistons and two pilot valves, wherein the two pilot valves are provided on one side of the casing, and wherein, on the other side of the casing, the magnet and the magnetic sensor are provided on one piston and on the casing, respectively. The piston having at least one magnet may be coupled to the valve member. 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 therefore arranged 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 along the stroke can be detected. It is therefore possible to easily discriminate, by a discrimination circuit, whether the valve member is operating normally or not, from the relationship between the position and the operating time of the valve member from the initiation to the termination of a stroke thereof. This allows precautionary measures to be taken before a failure happens, and prevents a long downtime of a working system due to a failure or an accident. The invention will now be further described by way of example with reference to the accompanying drawings in which: Fig. 1 is a longitudinal sectional view of a first embodiment of the directional control valve in accordance with the present invention. Fig. 2 is an enlarged view showing the main section of Fig. 1. Fig. 3 is a partially sectional fragmentary schematic illustration showing a second embodiment of the directional control valve in accordance with the present invention. Fig. 4 is an enlarged view showing the main section of Fig. 3. Fig. 5 is an enlarged sectional view showing the main section of Fig. 4. Fig. 1 shows the first embodiment of the directional control valve in accordance with the present invention. The directional control valve here exemplified is a single-pilot type directional control valve wherein a main valve 1 is changed over by one pilot valve 2. The main valve 1 has a construction as a 5-port valve, and includes a casing 4 constructed of non-magnetic material. The casing 4 comprises a first member 4a of cuboid shape, a second member 4b which is connected to one end of the first member 4a and which also serves as an adapter for mounting the pilot valve 2, and a third member 4c which is connected to the other end of the first member 4a and which functions as an end cover. A supply port P and two discharge ports E1 and E2 are provided on either of the upper and lower surfaces of the first member 4a, and two output ports A and B are provided on the other surface. Inside the first member 4a, there is provided a valve hole 5 to which these ports are each opened being arranged in the axial direction. In the valve hole 5, there is slidably received a spool 6 which is a valve member for changing over flow passages and which is constructed of non-magnetic material. On the outer periphery of the spool 6, there are provided a plurality of sealing members 7 for mutually defining flow passages connecting the above-mentioned ports, and on the outer peripheries of both end portions of the spool 6, there are provided respective end sealing members 8 for shutting off the breathing chambers 9 facing the ends of the spool 6, from the passages of the hydraulic fluid in the valve hole 5. Reference numeral 10 in Fig. 1 denotes a guide ring for stabilizing the sliding of the spool 6. On the other hand, in the second member 4b and the third member 4c, the piston chamber 11a and 11b are formed, respectively, at positions facing both ends of the spool 6. A first piston chamber 11a formed in the second member 4b has a large diameter, and a first piston 12a of large diameter is slidably received in the piston chamber 11a, while a second piston chamber 11b formed in the third member 4c has a smaller diameter than the first piston chamber 11a, and a second piston 12b of small diameter is slidably received in the piston chamber 11b. Each of these pistons 12a and 12b is adapted to move in synchronization with the spool 6 by being abutted against the end face of the spool 6 as representatively shown by the second piston 12b, or by being unitarily coupled to the spool 6 as representatively shown by the first piston 12a. In the example shown in Fig. 2, in order to connect the piston to the spool 6, a hook 14a provided for the piston 12a is engaged with a locking groove 14b on the outer periphery of the spool 6, but the method for coupling the piston 12a to the spool 6 is not particularly limited. First and second pressure chambers 13a and 13b are formed on the back sides of the pistons 12a and 12b, that is, on the opposite sides of the piston surfaces abutting against the spool 6, respectively. Between the pistons 12a and 12b, and the spool 16, there are formed the breathing chambers 9 and 9 which are opened to the outside, respectively. The pressure chambers 13a and 13b are hermetically shut off from the breathing chambers 9 and 9 by piston packing 15 and 15 mounted on the outer peripheries of the piston 12a and 12b, respectively. The first pressure chamber 13a situated adjacent to the first piston 12a of large diameter communicates with the supply port P through the pilot fluid passages 16a and 16b via a manual operating mechanism 17 and the above-mentioned pilot valve 2, while the second pressure chamber 13b situated adjacent to the second piston 12b of small diameter always communicates with the supply port P through the pilot fluid passage 16c. When the pilot valve 2 is in the "off" state, that is, when the first pressure chamber 13a is not supplied with a pilot fluid, the second piston 12b is pushed by the pilot fluid pressure supplied to the second pressure chamber 13b, so that the spool 6 is situated at the first changeover position moved to the left side, as shown in Fig. 1. Once the pilot valve 2 is turned "on", that is, the first pressure chamber 13a is supplied with the pilot fluid, the spool 6 is pushed by the first piston 12a, so that the spool 6 moves to the right side and occupies the second changeover position. This is because the acting force of fluid pressure acting on the first piston 12a is larger than that acting on the second piston 12b due to the difference in the pressure receiving area between the two piston 12a and 12b. The above-mentioned manual operating mechanism 17 is adapted to directly connect the pilot fluid passages 16a and 16b by depressing an operating element 17a, and to thereby make the first pressure chamber 13a communicate with the supply port P. This operating state is the same as that in which the pilot valve 2 is "on". Here, the above-mentioned pilot valve 2 is an electromagnetically operated solenoid valve for opening/closing pilot fluid passages by energizing a solenoid. Since its constitution and operation are the same as the known one, a specific explanation thereof is omitted. The above-described directional control valve is provided with a position detecting mechanism 20 for detecting the operating positions of the spool 6. As shown in Fig. 2, the position detecting mechanism 20 comprises a magnet 21 mounted on any one of the pistons (in Fig. 2, the first piston 12a is exemplified), and a magnetic sensor 22 which is installed at a position adjacent to the casing 4 and which detects the magnetism from the magnet 21. The position detecting mechanism 20 is adapted to detect, by means of the magnetic sensor 22, the change in magnetic flux density when the magnet 21 moves together with the piston 12a, and detects operating positions of the piston 12a, or the spool 6, from the changes in magnetic flux density. The magnet 21 is produced by mixing metallic powder having magnetic property into soft elastic base material such as synthetic resin or synthetic rubber and forming the obtained mixture into annular body having a notch at a part of circumference thereof. The magnet 21 is installed at a position on the outer periphery of the piston 12a, adjacent to the breathing chamber 9 and more interior than the piston packing 15. More specifically, the magnet 21 is installed at the above-mentioned position by fitting the annular magnet 21 into a mounting groove 23 formed on the outer periphery of the piston 12a in a state where the diameter thereof is elastically expanded. In this case, it is preferable to make the thickness of the magnet 21 slightly less than the depth of the mounting groove so that the outer peripheral surface of the magnet 21 becomes lower than that of the piston 12a in order to prevent the outer peripheral surface of the magnet 21 from rubbing against the inner peripheral surface of the piston chamber 11b. This permits not only the prevention of the increase in sliding resistance of the piston 12a due to the rubbing of the magnet 21 against the inner peripheral surface of the piston chamber, but also the prevention of suffering an adverse effect on the sliding of the piston 12a even if the magnet 21 adsorbs some magnetic particulates in the atmosphere. Thus, by disposing the magnet 21 at a position adjacent to the breathing chamber 9, on the outer periphery of the piston 12a, the magnet 21 can be prevented from directly contacting the pilot fluid. As a consequence, even if the pilot fluid contains water, chemical mist, magnetic particles such as metallic powder, or the like, there is no risk of the magnet rusting, corroding, or adsorbing magnetic particulates due to the contact of the magnet 21 with these substances. This prevents the reduction in position detecting accuracy due to the decrease in magnetic force, or the occurrence of a malfunction of the piston 12a due to adsorbed particulates. On the other hand, the magnetic sensor 22 is installed at a position adjacent to the magnet 21, in the housing 25 formed in the second member 4b of the casing 4, so as to be able to detect the magnetism from the magnet 21 over the whole stroke of the spool 6. More specifically, the magnetic sensor 22 is disposed at a position such that, when the spools 6 is situated at any one of the stroke ends, the magnetic sensor 22 is the closest to the magnet 21 and detects the highest magnetic flux density, and that, when the spool 6 is situated at the other stroke end, the magnetic sensor 22 is away from the magnet 21 and detects the lowest magnetic flux density. The magnetic sensor 22 is constituted so as to be connected to a discriminating circuit (not shown) through a lead wire 26, and to output a detection signal corresponding to a magnetic flux density to this discriminating circuit. In the discriminating circuit, data necessary for position detection such as the interrelations of the operating position with the magnetic flux density, operating time, and fluid pressure when the piston 12a (consequently the spool 6) normally operates, have been inputted in advance. Once a detection signal from the magnetic sensor 22 is inputted, the discriminating circuit measures the positions at both stroke ends of the piston 12a and each position during a stroke based on the above-mentioned data, and can discriminate whether the changeover operation of the piston 12a and consequently that of the spool 6 has been normal or not, from the relations between the operating time and the position of the piston 12a from the initiation to the termination of a stroke thereof. Thereby, it is possible to detect a sign of failure and to take precautionary measures against a failure in advance, and thereby to avoid an situation such that the operation of device stops for a long time due to the occurrence of a failure or an accident. Herein, the operating positions, operating times, etc. for the piston 12a which have been detected, can be displayed on a display device in the form of numeral values or graphs. In the above-described embodiment, a single magnetic sensor 22 is provided, but two magnetic sensors may be provided on both stroke ends of the piston 12a so as to be each situated at positions opposite to the magnet 21. In this case, operating positions of the spool 6 can be known from the change in magnetic flux density which has been detected through the two magnetic sensors, by setting the positional relations between the two magnetic sensors and the magnet as follows. When the piston 12a is situated at one stroke end, one magnetic sensor detects the highest magnetic flux density while the other magnetic sensor detects the lowest magnetic flux density. On the other hand, when the piston 12a is situated at the other stroke end, the situation becomes reverse of the former case. In the above-described embodiment, although the magnet 21 is mounted on the outer periphery of the piston 12a, it may be mounted on any other portion of the piston. In Fig. 3, a second embodiment of the present invention which is differs in the method for mounting a magnet from the first embodiment, is representatively shown by a double-pilot type directional control valve having two pilot valves. The directional control valve of the second embodiment has two pilot valves 2a and 2b, and two manual operating mechanisms 17a and 17b. The pilot valves 2a and 2b are concentratedly mounted on the one end side (adjacent to the first piston 12a) of the casing 4. The two valves 12a and 12b have the same size, and are each abutted against the end faces of the spool 6 without being unitarily coupled to the spool 6. Also, a first pressure chamber 13a communicates with the supply port P through the pilot fluid passages 30a and 30b via the first pilot valve 2a and the first manual operating mechanism 17a, and a second pressure chamber 13b communicates with the supply port P through the pilot fluid passages 30a and 30c via the second pilot valve 2b and the second manual operating mechanism 17b. The above-described directional control valve is constituted so as to alternately supply the first pressure chamber 13a and the second pressure chamber 13b with a pilot fluid by means of the two pilot valves 2a and 2b, and thereby to drive the two pistons 12a and 12b to change over the spool 6. In this directional control valve, a position detecting mechanism 20 is provided on the side of the second piston 12b opposite to the side where the two pilot valves 2a and 2b are disposed. More specifically, as shown in Figs. 4 and 5, in the second piston 12b, there is formed a housing 31 which extends in the axial direction from the surface abutted against the spool 6 to the pressure receiving surface, and a magnet 21 is installed on the inner bottom portion of the housing 31 so as to be situated adjacent to the pressure receiving surface. On the other hand, in the third member 4c of the casing 4, a mounting groove 32 is formed at the back of the wall surface opposite to the pressure receiving surface of the second piston 12b, from the lower surface side toward the upper surface side of the second member 4b, and a magnetic sensor 22 is inserted into the mounting groove 32, and then fastened with a screw 33. The above-mentioned magnetic sensor is adapted to detect the change in magnetic flux density when the magnet 21 approaches or moves away from the magnetic sensor 22 with the movement of the second piston 12b. Since constitutions and operations, or preferred modifications of the second embodiment other than the foregoing are substantially the same as those of the first embodiment, description thereof is omitted. The position detecting mechanism 20 in each of the above-described embodiments does not necessarily require using the above-described method in which all operating positions of the spool 6 are detected from the change in magnetic flux density with the movement of the piston, but the position detecting mechanism 20 may use a method in which only both stroke ends of the spool 6 are detected by turning on/off the magnetic sensor at both stroke ends of the spool 6. In the above-described first embodiment, as a single-pilot type directional control valve, a directional control valve having large and small pistons 12a and 12b was shown. Of course, however, the directional control valve may be of the spring-return type which has a return spring in place of the second piston of 12b of small diameter, and which always energizes the spool 6 in the return direction by the energizing force of the return spring. Alternatively, the constitution of the position detecting mechanism 20 in the first embodiment may be applied to the double-pilot type directional control valve having two pilot valves. In this case, the two pilot valves may be concentratedly disposed on one side of the casing, as in the second embodiment, or may be disposed one for each of both sides. Also, the position detecting mechanism 20 may be disposed on the first piston side, or may be disposed on the second piston side. As has been described hereinbefore in detail, in accordance with the present invention, by installing the magnet for position detecting on the piston, operating positions of the valve member can be detected via the piston. At this time, in addition, by installing the magnet at a position adjacent to the breathing chamber in the piston, it is possible to prevent the magnet from contacting the pilot fluid. Therefore, even if the pilot fluid contains water, chemical mist, magnetic particles such as metallic powder, or the like, there is no risk of the magnet rusting, corroding, or adsorbing magnetic particulates due to the contact of the magnet 21 with these substances. This prevents the reduction in position detecting accuracy due to the decrease in magnetic force, or the occurrence of a malfunction of the piston 12a due to adsorbed particulates, which permits the maintaining of a stable performance.

Claims: A pilot operated directional control valve having a position detecting function, comprising a casing (4) having a plurality of ports (P, E1, E2, A, B) and a valve hole (5) into which each of the ports is opened, a valve member (6) for changing over flow passages between the ports, the valve member being slidably received in the valve hole, a piston chamber (11a, 11b) formed at at least one end of the valve member, a piston (12a, 12b) slidably received in the piston chamber, the piston (12a, 12b) being operative by the action of pilot fluid pressure to change over the valve member, a chamber (9) defined by the casing, the piston and the valve member, an end sealing member (8) for shutting off the chamber from hydraulic fluid passages in the valve hole (5), the end sealing member (8) being mounted on the outer periphery of an end portion of the valve member (6), a magnet (21) which moves together with the piston, at least one magnetic sensor (22) for detecting the magnetism from said magnet, the at least one magnetic sensor (22) being mounted at a position on the casing (4) adjacent to the magnet (21), and at least one pilot valve (2) for supplying a pilot pressure chamber (13a, 13b) adjacent to one end of the piston with pilot fluid, characterised in that the chamber is a breathing chamber (9) opened to the exterior; in that the valve includes piston packing (15) for shutting off the pilot pressure chamber (13a, 13b) from the breathing chamber (9), the piston packing (15) being mounted on the outer periphery of the piston (12a, 12b), and in that the magnet (21) is installed at a position on the piston (12a, 12b) adjacent to the breathing chamber (9) and inward of the piston packing (15). A directional control valve as claimed in Claim 1, wherein the magnet (21) is provided on the outer periphery of the piston (12a) and wherein the magnetic sensor (22) is provided at a portion of the casing (4) adjacent to the outer periphery of the piston chamber (11). A directional control valve as claimed in Claim 1, further comprising a recess (31) formed in the surface of the piston (12b) adjacent to the valve member (6), the recess extending towards a pressure receiving surface of the piston, wherein the magnet (21) is installed in the recess (31) so as to be situated adjacent to the pressure receiving surface, and wherein the magnetic sensor (22) is disposed in the casing at a position opposite to the pressure receiving surface, A directional control valve as claimed in Claim 3, wherein the directional control valve is a double-pilot type directional control valve having two pistons (12a, 12b) and two pilot valves (2a, 2b), wherein the two pilot valves are disposed on one side of the casing (4), and wherein the magnet (21) and the magnetic sensor (22) are disposed on the side opposite to the side where the pilot valves (2a, 2b) are installed. A directional control valve as claimed in any preceding Claim wherein the piston (12a, 12b) and the valve member (6) are unitarily coupled. A directional control valve as claimed in any preceding Claim wherein the magnetic sensor (22) is disposed so as to be able to detect the magnetism from the magnet (21) over the whole stroke of the piston (12a), and wherein the magnetic sensor (22) is arranged to detect all operating positions of the piston from the change in magnetic flux density with the displacement of the magnet (21).

Inventors: HAYASHI BUNYA, ISHIKAWA MAKOTO, HAYASHI, BUNYA, ISHIKAWA, MAKOTO, Hayashi, Bunya, SMC Corp. Tsukuba Technical Center, Ishikawa, Makoto, SMC Corp. Tsukuba Tech. Center
Applicants: SMC CORP, SMC CORPORATION
Application year: 2000
Main classification: F15B13
IPC codes: F15B13, F16K31, F15B15, F16K37