Pilot operated directional control valve having position detecting function

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 is improved through the use of light.

A directional control valve capable of detecting the changeover position of a spool by utilising a magnet is well known and is disclosed in, for example, Japanese Unexamined Utility Model Publication No. 2-66784 (Japanese Utility Model Application No. 63-144027 on microfilm). In this directional control valve the changeover position of the spool is detected by mounting a magnet on the spool, mounting a magnetic sensor on a casing, and detecting the magnet moving together with the spool by means of the magnetic sensor.

However, this known directional control valve described in the above-mentioned known document employs a method wherein a magnet is used as an object to be detected, and wherein the magnetism from this magnet is detected by a magnetic sensor, and therefore, the conventional directional control valve is susceptible to an external magnetic field. For example, with a welder in which a large current flows or where a large-sized motor is used, the magnetic sensor can malfunction due to the external magnetic field generated by electrical current. This makes it difficult to maintain a given detecting accuracy, and has created a reliability problem.

The above-mentioned document does propose detecting the changeover position of a spool using an optical sensor. With this method positions of the spool can be detected without being affected by an external magnetic field but the document does not show any specific construction for embodying this proposal.

An object of the present invention is to provide a simply constructed pilot operated directional control valve having a position detecting function which is improved by permitting the detection of operating positions of a valve member such as a spool using an optical sensor.

A further object of the present invention is to increase the ease of maintenance by disposing the optical sensor at a predetermined position on a casing of the directional control valve.

In accordance with the present invention there is provided a pilot operated directional control valve having a position detecting function, comprising 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 for changing over flow passages, a piston chamber formed on at least one end side of the valve member, a piston which is slidably received in the piston chamber and which operates by the action of pilot fluid pressure to change over the valve member, a pilot valve for supplying the piston with a pilot fluid, a through hole formed at a portion of the casing and an optical sensor disposed so as to be able to project and receive light through the through hole for detecting operating positions of the piston by the reflected light.

In the directional control valve having the above-described features, when the piston is supplied with a pilot fluid by the pilot valve, the pilot fluid pressure causes the piston to change over the valve member. At this time, through the through hole of the casing, the projection of light to the piston and the reception of the reflected light is performed by the optical sensor, and thereby operating positions of the piston, or of the valve member, are detected in response to the change in quantity of received light.

Thus, in accordance with the present invention, it is possible to detect positions of a valve member using an optical sensor and thus without being affected by external magnetic field. In addition, since the directional control valve is constituted so that movement of the valve member is not directly detected but rather indirectly by detecting the piston, the structure of a detecting mechanism becomes simpler. If the directional control valve were constituted to directly detect a valve member, the through hole would have to be formed at a place at which the valve member inside the valve hole can be seen therethrough so that light could be projected and received relative to the valve member. However, since such a place corresponds to a portion of the casing directly facing a hydraulic fluid passage, it would be necessary to form the through hole and install the optical sensor in such a way as not to cause leakage of fluid. This would make the structure complicated and machining difficult. However by providing the through hole at a portion of the casing where light can be projected and received relative to the piston through the through hole, it is possible to install the detecting mechanism at a place independent passages for hydraulic fluid. This eliminates the necessity for structure to prevent hydraulic fluid leakage.

In accordance with a specific embodiment, the directional control valve comprises breathing chambers which are opened to the outside and which are each disposed between the valve member and the piston, an object to be detected which protrudes parallel with the axis of the valve member and which is situated on the end face of the piston adjacent to a breathing chamber, and a recess in which the object to be detected fits and which is disposed in a wall surface of the breathing chamber, in the casing. The through hole is formed at a position facing the recess, whereby the object to be detected is detectable in the recess.

Thereby, even if the body of the piston can not be directly detected because the installation site for the optical sensor cannot be around the piston chamber, the piston can reliably be detected via the object to be detected. In addition, even if the optical sensor is made to directly face the object to be detected by making the through hole opened to the recess, there is no need to worry about a hydraulic fluid or a pilot fluid leaking through this through hole, since the recess is formed within the breathing chamber.

In accordance with a preferred embodiment, the object to be detected has an annular shape of the same diameter as that of the piston, and the recess has an annular shape of the same diameter as that of the piston chamber.

In accordance with another specific embodiment, the through hole is formed at a position opposite to an end face of the piston, on the central axis of the piston and the optical sensor is disposed so as to project and receive light relative to the end face of the piston. Operating positions of the piston are detected based on the change in quantity of the received light caused by the change in the distance due to the displacement of the piston.

This embodiment can be suitably employed in a double-pilot operated directional control valve having two pistons and the two pilot valves, in the case where the two pilot valves are provided on one side of the casing. By installing the optical sensor on the other side of the casing where no pilot valve is provided, the installation of the optical sensor becomes simpler and also the maintenance thereof becomes much easier.

The invention will now be further described by way of example with reference to the accompanying drawings in which: <ul id="ul0001" list-style="none"><li>Fig. 1 is a longitudinal sectional view of a first embodiment of the directional control valve in accordance with the present invention.</li><li>Fig. 2 is an enlarged view showing a main section of Fig. 1.</li><li>Fig. 3 is a longitudinal sectional view showing the main section of a second embodiment of the directional control valve in accordance with the present invention.</li><li>Fig. 4 is a longitudinal sectional view showing a main section of a third embodiment of the directional control valve in accordance with the present invention.</li><li>Fig. 5 is an enlarged view showing the main section of Fig. 4.</li></ul>

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 operated 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. 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.

On the outer periphery of the spool 6, there are provided a plurality of sealing members 7 for mutually defining flow passages connecting the ports, and on the outer periphery of each 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 end 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 chambers 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 first 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 second piston chamber 11b. These pistons 12a and 12b are unitarily coupled to the spool 6 as represented by the first piston 12a, or abutted against the end faces of the spool 6 as represented by the second piston 12b, respectively, and thereby the pistons 12a and 12b move in synchronization with the spool 6.

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 6, 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 pistons 12a and 12b, respectively.

The first pressure chamber 13a situated adjacently 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 adjacently 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 the 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 shifted 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 the fluid pressure acting on the first piston 12a is larger than that acting on the second piston 12b due to the difference in pressure receiving area between the two pistons 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 thereby to make the first pressure chamber 13a communicate with the supply port P. This operating state is the same as that in the case where 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 the solenoid. Since the constitution and operation of the pilot valve 2 are the same as the known one, specific explanation thereof is omitted.

The above-described directional control valve is provided with a position detecting mechanism 20 for detecting operating positions of the spool 6 via any one of the pistons (exemplified in drawings is the first piston 12a). As shown in Fig. 2, the position detecting mechanism 20 comprises the object to be detected 21 formed on the end face adjacent to the breathing chamber 9, of the first piston 12a, the recess 22 in which the object to be detected 21 is fit and which is formed in the wall surface of the breathing chamber 9 in the first portion 4a of the casing 4, the through hole 23 and the optical sensor housing 24 formed so as to be opened to a portion of the side wall of the recess 22, and the optical sensor 25 disposed in the housing 24. The optical sensor 25 has the function of projecting light into the recess 22 through the through hole 23, and also has the function of receiving the reflected light from the object to be detected 21. Here, the through hole 23 may be fit over with a transparent material such as glass or synthetic resin.

The object to be detected 21 has annular shape with the same diameter as that of the first piston 12a, and is formed so as to protrude from an end face of the piston parallel and coaxially with the axis of the spool 6. On the other hand, the recess 22 is formed into annular shape with the same diameter as that of the piston chamber 11a. If the piston 12a is moved to the first changeover position shown in Figs. 1 and 2, the object to be detected 21 occupies a undetectable position that is deviated from the through hole 23, and if the piston 12a is moved to the second changeover position opposite to the first changeover position, the object to be detected 21 occupies the detectable position which covers the through hole 23. When the object to be detected 21 is located at a undetectable position, since the reflected light from the object to be detected 21 is not received by the optical sensor 25, the optical sensor 25 is in the "off" state, and no detection signal is outputted. On the other hand, when the object to be detected 21 is located at the detectable position, since the reflected light from the object to be detected 21 is received by the optical sensor 25, the optical sensor 25 turns "on", and a detection signal is outputted. Thus, by detecting the presence/absence of the object to be detected 21 using the optical sensor 25, it is possible to detect operating positions of the spool 6 via the piston 12a. Here, the object to be detected 21 may additionally have a light reflecting plate.

In a second embodiment shown in Fig. 3 through holes 23a and 23b, and optical sensors 25a and 25b are installed at the two spots on the inlet side and the bottom side of the recess 22. In the case where the object to be detected 21 is moved from the first changeover position to the second changeover position as shown in drawings, the first optical sensor 25a situated on the inlet side detects the startup of the piston 12a by turning on upon detecting the reflected light, and the second optical sensor 25b situated on the bottom side detects the arrival at the stroke end, of the piston 12a when turning on upon detecting the reflected light. Conversely, in the case where the object to be detected 21 is returned from the second changeover position to the first changeover position, the second optical sensor 25b situated on the bottom side detects the startup of the piston 12a by turning off, and the first optical sensor 25a situated on the inlet side detects the arrival at the return stroke end, of the piston 12a when turning off.

Thus, in accordance with the above-described directional control valve, use of the optical sensors 25, 25a , and 25b permits the detection of positions of the spool 6 without being effected by external magnetic field. In addition, the present embodiment is constituted so as not to directly detect the movement of the spool by the optical sensor 25, 25a, and 25b, but to indirectly detect positions of the spool by detecting the piston, so that a position detecting mechanism 20 can be built into a place independent of flow passages of the hydraulic fluid. This simplifies the installation structure of the position detecting mechanism.

Furthermore, since the present embodiment is constituted so as to detect the movement of the piston 12a via the object to be detected 21 formed on the piston 12a, it is possible to reliably detect the piston 12a via the object to be detected 21, even if the body portion of the piston 12a can not be directly detected because an installation site for the optical sensors 25, 25a, and 25b can not be secured around the piston chamber 11a. In addition, even if the optical sensor 25, 25a, and 25b are made to directly face the object to be detected 21 by making the through hole 23, 23a, and 23b opened to the recess 22, there is no need to worry about the hydraulic fluid or the pilot fluid leaking through the through hole 23, since the recess 22 is formed within the breathing chamber 9.

Moreover, the optical sensors 25, 25a and 25b may be connected to a discriminating circuit (not shown), with the discriminating circuit discriminates whether the changeover operation of the piston 12a (and consequently spool 6) is normal or not, based on detection signals from the optical sensors 25, 25a and 25b. In this case, in the discriminating circuit, the relations between the operating time and the operating position when the spool 6 normally operates, and the range of the operating time to be judged as an abnormal operation, etc. have been inputted in advance. The discriminating circuit is constituted so as to discriminate whether the changeover operation of the spool 6 is normal or not, by comparing the signals from the optical sensors 25, 25a, and 25b with the above-mentioned input data. Thereby, it is possible to predict a sign of failure beforehand and to take precautionary measures against it, thereby avoiding an situation such that the operation of device stops for a long time due to the occurrence of a failure or an accident.

In the above-described first embodiment, as a single-pilot type directional control valve, there was shown a directional control valve having two pistons 12a and 12b, large and small. However, it goes without saying that the directional control valve may be of the spring-return type which has a return spring in place of the second piston 12b of small diameter, and which always energizes the spool 6 in the return direction by the energizing force of the return spring.

Also, the above-described directional control valve may be a double-pilot type valve having two pistons and two pilot valves.

Fig. 4 shows a third embodiment of the present invention. The directional control valve of the third 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, and a position detecting mechanism 30 is provided on the side adjacent to the second piston 12b opposite to the side on which the two valves 2a and 2b are provided.

Although the above-mentioned two valves 12a and 12b have the same size, and are each abutted against an end face of the spool 6 without being unitarily coupled to the spool 6, they may be unitarily coupled to the spool 6. The 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 the second pressure chamber 13b communicates with the supply port P through the pilot fluid passage 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 drive the two pistons 12a and 12b to change over the spool 6 by alternately supplying the first pressure chamber 13a and the second pressure chamber 13b with the pilot fluid by means of the two pilot valves 2a and 2b.

The position detecting mechanism 30 has a through hole 31 formed on the third member 4c of the casing 4, and a optical sensor 32 mounted on the third member 4c so as to be able to project and receive light, through the through hole 31, relative to the object to be detected 35 on an end face of the second piston 12b. The through hole 31 is formed by fitting a transparent member such as glass or synthetic resin over the hole formed at a position opposite to the end face of the piston 12b, on the central axis of the piston 12b. The optical sensor 32 is removably installed with a retaining ring in the housing 33 formed in the third member 4c. Here, the object to be detected may additionally have a light reflecting plate as required.

In this position detecting mechanism 30, when the piston 12b is moved between the first changeover position and the second changeover position, the quantity of the reflected light received by the optical sensor 32 changes in response to the change in distance between the piston 12b and the optical sensor 32, so that operating positions of the piston 12b, or the spool 6 can be detected over the whole stroke, from the change in quantity of the received light.

The constitution of the above-described third embodiment has an advantage as follows. In the double-pilot type directional control valve having two pistons 12a and 12b and two pilot valves 2a and 2b as shown in drawings, wherein the two pilot valves 2a and 2b are concentratedly disposed on one end of the casing 4, by disposing the position detecting mechanism 30 on the other side on which the pilot valves 2a and 2b of the casing 4 are not installed, not only the installation of the position detecting mechanism 30 becomes simpler, but also the repair or exchange of the optical sensor 32 or the through hole 31 at their failure becomes easier, and in some cases the third member 4c may be exchanged as a whole. This permits a speed-up in working.

Of course, however, the construction of the position detecting mechanism in the third embodiment can also be applied to the single-solenoid type directional control valve shown in the first embodiment.

As have been described hereinbefore in detail, in accordance with the present invention, there is provided a simply constructed pilot operated directional control valve having a position detecting function, capable of detecting, through the use of light sensors, operating positions of a valve member such as a spool.

Also, by disposing the position detecting mechanism including the optical sensor on the side opposite to the side on which the pilot valves of the casing are provided, not only the installation of the position detecting mechanism becomes simpler, but also the repair or exchange of the optical sensor at is failure becomes easier, which results in an improvement in ease of maintenance.