NL2002208C2

NL2002208C2 - Solenoid valve with an inductive proximity sensor.

Info

Publication number: NL2002208C2
Application number: NL2002208A
Authority: NL
Inventors: Jan Zee; Jorik Melis Elbert Waerdt
Original assignee: Asco Controls Bv
Priority date: 2008-11-14
Filing date: 2008-11-14
Publication date: 2010-05-17

Description

P29640NL00/RR

Short title: Solenoid valve with an inductive proximity sensor.

The invention relates to a solenoid valve for the regulation of a medium flow, in particular a so-called balanced 3-way valve. "Balanced" in this context means that the force which is necessary for opening and closing the valve is independent of the medium pressure. The medium pressure can be present on an arbitrary one of the inlet or outlet 5 ports of the valve, without this medium pressure having an influence on the force which is necessary for opening and closing of the valve. Balance is obtained by equally large pressure surfaces of an axially moveable valve element of the valve, the so-called core. The surfaces are each facing the axial moving direction, are oppositely directed and are provided upstream of a closing area of the valve.

10 From the state of the art numerous variants are known of solenoid valves. See for example US-2,971,090 and US-3,077,207. Each of the herein disclosed solenoid valves comprises a housing with three inlet and outlet ports respectively en between them a core which is moveable in the axial direction in an axial bore of the housing. The core and/or the housing are provided with sealing elements like O-rings. Furthermore, seats are provided 15 against which the sealing elements depending on the position of the core can come to lie sealing against. The core moves up and down when a coil is energized and de-energized in order to release or shut of pressurized medium through the valve. Once the coil is energized a so-called plugnut or static core is magnetized and pulls the moving core to a new position. This could be a limited position at the end of the stroke or, in case of a proportional valve, 20 any position between opened and closed. A spring or other suitable element may be provided for pushing the core back in its original pre-defined position once the coil is deenergized. At the moment when the solenoid valve is in process it is unknown if the valve is actually functioning as it is supposed to be. It remains unknown whether the valve is open or closed and what the performance of the valve is.

25 Applicant sells for some years a balanced 3-way solenoid valve of the direct acting type under the ASCO series 327. This type of solenoid valve for example is used to steer large butterfly valves and ball valves which are used in the process industry and petrochemical industry. These valves need to be absolutely reliable in order to be able to guarantee the end product of the process it helps steering. Because of the varying 30 environmental conditions and process conditions like temperature and medium used, the valves need to cope with high demands and for example be resistant against a large scope of conditions in order to be able to provide reliable sealings under a certain required pressure. It is also known to provide solenoid valves with an on/off detection. See for -2- example US-5,691,813, where a position sensor for monitoring the position of a valve element of a solenoid valve is described. The position sensor here comprises reflector means associated with the valve element and arranged to reflect energy, for example visible light, from a suitable source. When the valve element is in a first position the reflected 5 energy is incident upon a detector. Movement of the valve away from this first position results in less or even no reflected light being incident upon the detector. Thus it is possible to provide an indication whether the valve element is in its closed position rather than in its fully open position.

The disadvantage of this type of position sensor is that its functioning leaves to be 10 desired. For example, it needs a reflecting surface on the valve element, and is rather expensive and difficult to build in. Furthermore, it has large dimensions and the reflector means and light source are sensitive to moisture and pollution, and thus also for the medium used.

The present invention aims to at least partly overcome the abovementioned 15 disadvantages, or to provide a usable alternative. In particular the invention aims to provide a solenoid valve with an improved position sensor for its valve element.

This aim is achieved by a solenoid valve according to claim 1. With this the valve comprises a housing having an axial bore which is in flow connection with at least one inlet and outlet port. A valve element is moveable to and fro in the axial direction of the bore. An 20 electrical coil for generating a magnetic field is provided for moving the valve element between a first (closed) end position and a second (open) end position. An inductive proximity sensor is provided as position sensor for accurately detecting at least one of the end positions of the valve element and thus provide a reliable indication of whether the valve is open or closed in a particular direction or for a specific set of inlet and outlet ports. The 25 inductive proximity sensor provides the solenoid valve with a number of advantages. First of all the inductive proximity sensor is able to fulfil its function in every medium. It operates contactless, and is insensitive for moisture and pollution. Also it operates well and reliable under various conditions, like high pressures of over 50 bar and/or temperatures between -50 and +120 degrees Celsius. It operates frictionless, is relative simple to build in, has a 30 high resolution, and a relative large measurement range. Further it is suitable to detect all kinds of metal objects, and the sensor itself does not have a moving mass.

In a particular embodiment the inductive proximity sensor is provided at the side of the valve where the electrical coil is positioned. This has the advantage that the other side of the valve, that is to say the side where the moving valve element and inlet and outlet ports 35 are present, remains free for the placement of optional parts, like for example a manual operator. Furthermore, the positioning of the sensor at this side of the valve, which mostly shall also be the upper side of the valve, has the advantage that it does not interrupt the -3- flow between the inlet and outlet ports. Also in this specific position the wiring of the sensor lies at the same side of the valve and can even be combined with the wiring of the electrical coil.

In a further embodiment a static core is provided next to the moving area of the valve 5 element which static core extends at least partly inside the electrical coil. The static core is magnetisable by the electrical coil. The inductive proximity sensor may then be positioned adjoining to the static core. The static core may form an explosion proof housing for the sensor by at least partly integrating the inductive proximity sensor inside the static core. This is possible as long as the inductive proximity sensor remains positioned outside the 10 magnetic field of the electrical coil, in particular above the coil.

In an even further embodiment a non-metal protector cap is positioned between the electrical coil and the inductive proximity sensor. Preferably, a sealing is provided between the non-metal protector cap and the opening in the static core. The non-metal protector cap has the advantage that it makes the valve pressure resistant towards the side of the 15 inductive proximity sensor. Further it protects the sensor and at the same time it may form an adjustment for the sensor.

Further preferred embodiments are stated in the dependant claims.

The invention shall be further clarified below with reference to the accompanying 20 drawings in which:

Fig. 1 shows a sectional view of an embodiment of a solenoid valve according to the invention having an inductive proximity sensor;

Fig. 2 shows a partial view of fig. 1 at the location of the connection between the sensor and the static core; and 25 Fig. 3 schematically shows the functioning of the inductive proximity sensor.

In figure 1 the entire solenoid valve has been indicated with the reference numeral 1. The valve 1 is of the balanced 3-way type and comprises a housing 2 with an inlet port 3 and two outlet ports 4, 5. The ports 3,4,5 connect to an axial bore 7 which is also provided 30 in the housing 2. A valve element 8 is moveable up and down in the axial direction y of the bore 7. The valve element 8 comprises a head part 8’ which is provided with sealing rings 9, 10 which can come to lie sealing against respective seats 9’, 10’ of the housing 2 depending on the position of the valve element 8. Above the valve element 8 a static core or so-called plugnut 12 is provided. This static core 12 is magnetisable by means of an electrical coil 13. 35 A thus generated magnetic field is able to move the valve element 8 between a first end position (starting position), in which its sealing ring 9 lies sealing against its seat 9’ (figure 1) and a second end position in which its sealing ring 10 lies sealing against its seat 10’. In this -4- way either a flow connection between the inlet port 3 and outlet port 10 or a flow connection between the inlet port 3 and outlet port 9 can be obtained. Springs 15 are provided which serve the purpose of pushing the valve element 8 back towards its original starting position (first end position).

5 The valve 1 further comprises a position sensor which according to the invention is formed by an inductive proximity sensor 17. The sensor 17 is attached on top of the valve 1 partly inside and partly above the static core 12. The sensor 17 cooperates with a detection surface 18 which is provided on a staff shaped detection organ 19 (see also fig. 2). The detection organ 19 is connected with the valve element 8 in such a way that it moves up and 10 down along with it and runs freely moveable through an axial opening in the static core 12. A core 30 of the sensor 17 emits an electromagnetic field EF and looks for changes in the field brought about by the movement of the valve element 8 (see fig. 3). The resulting magnetic field is then obtained by a sensing coil 31 and is representative for a distance “a” between the front side of the sensor 17 and the facing side of the detection surface 18. This distance 15 “a” in turn can be reduced to an actual axial position of the valve element 8 inside the bore 7, in particular whether the valve is in its first or second end position.

Advantageously the inductive proximity sensor 17 is connected to indication means IM for sending out a feedback signal when the sensor 17 detects the situation that one of the end positions for the valve element 8 is reached. For example these indication means 20 may be a control unit which is designed for further analysing the detected signal and/or to send out a steering signal to a process the solenoid valve is steering. In its simplest form the indication means are formed by a light indicator like a LED which for example is mounted on the outside of the valve housing. Thus it is immediately visible to an operator, controller or user what state the valve is in (open or closed).

25 The inductive proximity sensor 17 may be designed to only detect the detection surface 18 when it comes close enough to the front side of the sensor 17, that is to say when it reaches its upper end position, and only then sent out a feedback signal. It may also be designed to detect various intermediate positions of the valve element when it moves from its one end position towards its other end position, preferably in an analogous way.

30 As can be seen in fig. 2 the inductive proximity sensor 17 is screwed partly into a threaded opening 20 in the static core 12. Before connecting the sensor 17 with the static core 12, a plastic protector cap 21 is positioned inside the opening 20. With this a sealing ring 22 is provided between the outer wall of the cap 21 and the inner wall of the opening 20 in the static core 12 in order to provide for a proper sealing there between. In its mounted 35 position the inductive proximity sensor 17 presses against the cap 21. Advantageously this does not damage the front surface of the sensor 17, no matter how firmly the sensor 17 is screwed into the threaded opening 20. In fact it even protects the sensor 17 against any -5- possible influence of medium flowing through the valve 1. By choosing a suitable thickness for the cap 21, a proper positioning of the sensor 17 can be obtained relative to the desired end position of the detection surface 18 (and thus also of the valve element itself) it needs to detect. Finally the assembly of the sensor 17 being screwed against the cap 21 presses the 5 sealing ring 22 firmly against the walls of the opening 20 and thus makes the valve 1 pressure resistant.

Besides the embodiments shown numerous variants are possible. For example instead of the shown 3-way valve the invention may also be used for other types of solenoid valves, for example with different numbers of ports, or with a rotational valve instead of a 10 translational valve. The various parts of the valve, like the housing, the valve element, etc. may have other dimensions and/or other shapes and/or constructional details. The protector cap may also be dispensed with, and the inductive proximity sensor may be connected in different ways and/or in different positions with the static core or valve housing. The inductive proximity sensor preferably has a measurement range of at least 1.5 mm, and 15 preferably has a precision of at least 0.01 mm. Other ranges and precisions are also possible.

Thus owing to the invention a solenoid valve is obtained which is able to give a reliable feedback of the axial position of the valve element to an operator or the like. This feedback can give an external signal to a control unit or deliver a perceptible signal to a user 20 of the fact whether or not the valve is open or closed. This makes it possible to more closely watch the functioning of the valve and thus use the valve in more critical circumstances. As soon as malfunction occurs, appropriate measures can immediately be taken.

Claims

An electromagnetic valve comprising: - a housing with an axial bore in flow communication with at least one inlet port and an outlet port; - a valve element that is movable to and fro in the axial direction of the bore; 5. an electric coil for generating a magnetic field for moving the valve element between a first end position in which it abuts sealingly against a seat to uncouple the inlet and outlet port from one another, and a second end position in which it is spaced apart from the seat is arranged to create a flow port for connecting the inlet and outlet port to each other; and - a position sensor for detecting positions of the valve element in the axial direction of the bore, characterized in that the position sensor is an inductive proximity sensor.

Electromagnetic valve according to claim 1, wherein the inductive proximity sensor is provided on the side of the valve where the electric coil is positioned and opposite the side where the valve element and the inlet and outlet ports are present.

3. Electromagnetic valve according to claim 2, wherein a static core magnetizable by the electric coil is provided between the valve element and the inductive proximity sensor.

4. Electromagnetic valve according to claim 3, wherein a detection member extends movably through an axial opening in the static core, which detection member is connected to the valve element in such a way that it moves along with the valve element, and which detection member comprises a detection surface on the side of the inductive proximity sensor.

5. Electromagnetic valve as claimed in any of the claims 3-4, wherein the inductive proximity sensor extends at least partially in a corresponding opening in the static core.

Electromagnetic valve according to one of the preceding claims, wherein a non-metal protective cap is provided between the electric coil and the inductive proximity sensor.

The electromagnetic valve of claim 6, wherein a seal is provided between the non-metallic protective cap and the opening in the static core.

8. Electromagnetic valve according to claims 5 and 6 or 7, wherein the non-metal protection cap is placed in the opening in the static core, and wherein the inductive proximity sensor is placed against the non-metal protection cap.

9. Electromagnetic valve according to any one of the preceding claims, wherein means are provided for transmitting a feedback signal when the inductive proximity sensor detects the reaching of one of the end positions of the valve element.

An electromagnetic valve according to any one of the preceding claims, wherein the inductive proximity sensor has a measuring range of at least 1.5 mm.

The electromagnetic valve of any one of the preceding claims, wherein the inductive proximity sensor has an accuracy of at least 0.01 mm.

12. Electromagnetic valve according to one of the preceding claims, wherein the valve is a balanced 3-way electromagnetic valve.