SOLENOID VALVE

Abstract

In order to reduce the friction of a dry-running solenoid valve (1) with a valve housing (2), in which an electric coil (3) and a magnet armature (5) are arranged, and with a valve element (8) which can be actuated by the magnet armature (5) in an axial actuating direction for opening and closing the solenoid valve (1), in which the coil (3) generates a magnetic flux which, when the solenoid valve (1) is actuated, flows via a magnetically conductive valve housing outer wall (2c) of the valve housing (2) to the magnet armature (5), it is provided according to the invention that a magnetically conductive flux element (12) be provided in the valve housing (2) and introduce at least 80%, preferably at least 90%, and particularly preferably 100%, of the magnetic flux flowing over the valve housing outer wall (2c) into an armature end face (5B), facing the coil (3), of the magnet armature (5).

Claims

1. Dry-running solenoid valve (1) for injecting a gaseous fuel into a combustion chamber or a prechamber of an internal combustion engine, with a valve housing (2), in which an electric coil (3) and a magnet armature (5) are arranged, and with a valve element (8) that can be actuated by the magnet armature (5) in an axial actuation direction for opening and closing the solenoid valve (1), wherein the coil (3) generates a magnetic flux, when the solenoid valve (1) is actuated, which flux flows via a magnetically conductive valve housing outer wall (2c) of the valve housing (2) to the magnet armature (5), characterized in that a magnetically conductive flux element (12) is provided in the valve housing (2), which flux element introduces at least 80%, preferably at least 90%, and particularly preferably 100%, of the magnetic flux flowing over the valve housing outer wall (2c) into an armature end face (5B), facing the coil (3), of the magnet armature (5).

2. Solenoid valve (1) according to claim 1, characterized in that the flux element (12) is arranged, transversely to the actuation direction, in a region adjoining the valve housing outer wall (2c) of the valve housing (2) and is arranged, in the actuation direction, between the coil (3) and the magnet armature (5).

3. Solenoid valve (1) according to claim 1 or 2, characterized in that the flux element (12) is designed as a preferably closed flux ring.

4. Solenoid valve (1) according to one of claims 1 through 3, characterized in that the flux element (12) has a higher magnetic conductivity than the valve housing outer wall (2c).

5. Solenoid valve (1) according to one of claims 1 through 4, characterized in that the flux element (12) has a cross-section in the form of a trapezoid, and preferably a rectangular trapezoid.

6. Solenoid valve (1) according to one of claims 1 through 5, characterized in that the coil (3) is arranged on a coil carrier (4), wherein an end section (4a), axially facing the magnet armature (5), of the coil carrier (4) is designed as an end stop for the magnet armature (5) in order to limit the axial movement of the magnet armature (5) in the actuating position in order to limit a valve lift of the valve element (8).

7. Solenoid valve (1) according to claim 6, characterized in that the coil carrier (4) is formed from a plastic, and the coil (3) is completely integrated into the coil carrier (4).

8. Solenoid valve (1) according to one of claims 1 through 7, characterized in that the valve housing (2) forms a cylinder in the region of the magnet armature (5), and the magnet armature (5) forms a piston which is axially movable in the cylinder, wherein a compression space (KR) is formed between a first armature end face (5A), facing away from the coil (3), of the magnet armature (5) and an opposite valve housing wall (2d) in the actuation direction, wherein at least one throttle opening (13) is arranged in the magnet armature (5) and connects the first armature end face (5A) to an opposite, second armature end face (5B).

9. Solenoid valve (1) according to claim 8, characterized in that a sealing element (14) for sealing the compression space (KR) is arranged on the peripheral surface (5U) of the magnet armature (5).

10. Solenoid valve (1) according to one of claims 1 through 9, characterized in that the valve opening (9) is provided in an axial end (E1) of the valve housing (2), and that at least one feed opening (10) for a preferably gaseous medium is provided in the valve housing (2), which feed opening is connected to the valve opening (9) within the valve housing (2).

11. Solenoid valve (1) according to one of claims 1 through 10, characterized in that the magnet armature (5) has an armature shaft (6), and the valve element (8) has a valve shaft (7) which is separate from the armature shaft (6), wherein the magnet armature (5) actuates the valve shaft (7) via the armature shaft (6) when the solenoid valve (1) is actuated.

12. Solenoid valve (1) according to claim 11, characterized in that a buffer element (15) made of plastic is arranged between the armature shaft (6) and the valve shaft (7).

13. Solenoid valve (1) according to claim 12, characterized in that the buffer element (15) is formed from a tribologically-optimized plastic, and preferably from a plastic that contains polytetrafluoroethylene.

14. Solenoid valve (1) according to one of claims 1 through 13, characterized in that a spring element (11) is arranged in the valve housing (2) and exerts a restoring force on the valve element (8) in order to hold the valve element (8) in the closed position when the solenoid valve (1) is in the non-actuated state.

15. Internal combustion engine having a cylinder head and at least one combustion chamber, wherein, on the cylinder head, at least one solenoid valve (1) according to one of claims 1 through 14 is arranged in order to supply a preferably gaseous fuel to the combustion chamber or a prechamber upstream of the combustion chamber.

Description

[0021] The present invention is described in greater detail below with reference to FIG. 1, which shows an advantageous embodiment of the invention by way of example, schematically and in a non-limiting manner. The drawing shows:

[0022] FIG. 1 a sectional view of a solenoid valve in an advantageous embodiment.

[0023] FIG. 1 shows an advantageous embodiment of the solenoid valve 1 according to the invention. The shown solenoid valve 1 is designed as a dry-running valve and is provided for injecting a gaseous fuel into the combustion chamber or a prechamber, upstream of the combustion chamber, of an internal combustion engine (not shown). The solenoid valve 1 has a valve housing 2 which here is designed to be substantially cylindrical and has a valve axis A. To the left of the valve axis A, the solenoid valve 1 is shown in the closed state, and, to the right of the valve axis A, in the open state. At a first axial end E1 of the valve housing 2, a fastening section B is provided - in this case, in the form of a thread with which the solenoid valve 1 can be fastened to a cylinder head (not shown) of an internal combustion engine. Of course, other types of fastening would also be possible.

[0024] An electric coil 3 is provided in the valve housing 2 and runs annularly around the central valve axis A. The coil 3 can be supplied with energy in the form of an electrical voltage or an electrical current via suitable electrical terminals (not shown) in order to generate an (electro)magnetic field in a known manner. Depending upon the structural design of the solenoid valve 1, the terminals can be provided, for example, radially on the outside of the valve housing 2 or on a second axial end E2, opposite the first axial end E1, of the valve housing 2. However, the coil 3 does not have to be designed in one piece; instead, several coil segments which are electrically connected could also be arranged to be distributed around the valve axis A. The coil 3 is preferably arranged on a coil carrier 4, which in this case is designed in the shape of a ring substantially the same as the coil 3 and is arranged in an annular opening provided for this purpose in the valve housing 2. The coil carrier 4 is preferably magnetically non-conductive. Essentially, this means that its magnetic conductivity is negligibly small compared to the other parts forming the magnetic circuit M. The coil 3 and the coil carrier 4 preferably form a common component. In this case, the coil 3 is completely integrated into the coil carrier 4, i.e., surrounded on all sides by the coil carrier 4; only the electrical terminals of the coil 3, which are not shown, suitably extend out of the coil carrier 4. The coil carrier 4 can be formed, for example, from a suitable plastic, from which the coil 3 is, for example, encapsulated by casting.

[0025] Furthermore, a magnet armature 5 is arranged in the valve housing 2, which magnet armature is movable in an axial actuation direction in the direction of the valve axis A. The magnet armature 5 interacts magnetically with the coil 3 to actuate the valve and has for this purpose an armature end face 5A facing the coil 3. In the example shown, the magnet armature 5 is designed to be substantially cylindrical, having an axial first armature end face 5A, facing away from the coil 3, and an opposite, second armature end face 5B facing the coil 3, as well as having an armature peripheral surface 5U. On the magnet armature 5, e.g., on the second armature end face 5B in the example shown, a central cylindrical armature shaft 6 is arranged which is axially guided within a cylindrical opening of the valve housing 2, and which is movable in synchrony with the magnet armature 5 in the axial direction. The armature shaft 6 can be integrally formed with the magnet armature 5 or can be connected to the magnet armature 5 in another suitable manner.

[0026] Furthermore, a valve opening 9 is arranged in the valve housing 2 of the solenoid valve 1 - in this case, in the first axial end E1 of the valve housing 2. The valve opening 9 can be opened and closed by means of a valve element 8 which can be actuated by the magnet armature 5. The valve element 8 is connected in this case to a substantially cylindrical valve shaft 7 which extends along the valve axis A in the interior of the valve housing 2. The armature shaft 6 and the valve shaft 7 can be rigidly connected to one another - for example, designed in one piece. However, these are preferably designed as separate components so that the movement of the armature shaft 6 can be decoupled from the movement of the valve shaft 7, as will be explained in more detail below. In the shown solenoid valve 1, a spring element 11 is also arranged within the valve housing 2, which exerts a restoring force on the valve shaft 7 and the valve element 8 connected thereto so that the valve element 8, when the solenoid valve 1 is in an unactuated state, returns to the closed position (in FIG. 1, on the left of the valve axis A) in order to close the valve opening 8.

[0027] To actuate the solenoid valve 1, an electrical current or an electrical voltage is applied to the coil 3, wherein a magnetic flux is generated by the coil 3. By means of the magnetic flux, an electromagnetic attractive force is exerted on the magnet armature 5, by means of which the magnet armature 5 is moved in the direction of actuation against the spring force of the spring element 11 in the direction of the coil 3. The armature shaft 6 connected to the magnet armature 5 presses on the valve shaft 7, as a result of which the valve element 8 is moved from the closed position in which the valve opening 9 is closed (to the left of the valve axis A) into the open position in which the valve opening 9 is released (to the right of the valve axis A), as indicated by the downward arrow along the valve axis A in FIG. 1. The available path between the closed position and the open position is also referred to as the valve lift.

[0028] As soon as the energy supply of the coil 3 is interrupted or reaches a sufficiently low level at which the restoring force of the spring element 11 (possibly supported by a compressive force in the combustion chamber acting on the underside of the valve element 8) exceeds the magnetic attraction force of the coil 3, the valve element 8 is displaced from the open position back into the closed position, as indicated by the upward arrow along the valve axis A in FIG. 1. Of course, stepless control or regulation of the valve lift would also be possible with appropriate control of the coil 3, so that valve positions can also be realized between the closed position and the open position. For example, it would be conceivable for the valve lift to be controlled or regulated steplessly, depending upon the applied coil voltage or the coil current. As a result, for example, the flow of the preferably gaseous fuel could be steplessly adjusted to a certain given combustion process.

[0029] In the shown example, the valve element 8 has a substantially conical valve disk 8a which, in the closed position, rests sealingly against a valve seat of the valve housing 2, as shown on the left of the valve axis A. In the open position, the valve element 8 is lifted off the valve seat in the actuation direction and releases a certain cross-section of the valve opening 9, as shown on the right of the valve axis A. As a result, a preferably pre-compressed medium such as a gaseous fuel can flow from a feed opening 10, arranged in this case in the side of the valve housing 2, through the interior of the valve housing 2 to the valve opening 9, as indicated by the arrows in FIG. 1. Of course, several feed openings 10 can also be provided. The medium can be supplied to the feed opening 10, for example, from a reservoir (not shown). The medium, e.g., the fuel, can be supplied through the valve opening 9 to, for example, a combustion chamber or a prechamber of an internal combustion engine (not shown).

[0030] In the example shown, the valve element 8 closes the valve seat from the outside, but the reverse variant would, of course, also be possible in which the valve element 8 is arranged entirely in the valve housing 2 and closes the valve seat from the inside - as for example in the case of a known needle valve or an injector for liquid fuel. The valve seat also does not have to be arranged directly on the valve housing 2, but could, for example, be formed by a separate valve seat element, which is arranged on the valve housing 2. In this way, different materials for the valve housing 2 and the valve seat element can advantageously be used. Since the valve seat is a region subjected to relatively high mechanical stress due to the closing movement of the valve element 8, a valve seat ring made of a suitable low-wear material such as a hardened steel, for example, can be used as the valve seat element. In this case, a more cost-effective material can preferably be used for the rest of the valve seat housing 2.

[0031] The spring element 11, which biases the valve element 8 in the closed state in the direction of the valve seat, is designed in this case in the form of a helical spring which annularly surrounds the valve shaft 7. The helical spring is arranged in a space provided for this purpose in the valve housing 2, through which the gaseous fuel also flows. A shoulder on which a disk is arranged is formed on the valve shaft 7. The helical spring is arranged in the axial direction between the disk and a shoulder in the valve housing and exerts a spring force on the valve shaft 7 in the axial direction - in this case, upwards. Of course, other suitable spring elements 11 could also be used, such as disk springs, etc., and it would also be conceivable for the spring element 11 to have a nonlinear spring characteristic in order to influence the opening characteristic of the solenoid valve, such as, for example, a progressive or degressive spring characteristic. Of course, the shown embodiment is to be understood only as an example, and other embodiments of the solenoid valve 1 would also be possible.

[0032] The valve shaft 7 and the valve element 8 are produced from a material which is suited to the temperatures, forces, and pressures to be expected that occur during operation of the solenoid valve 1. If, for example, a metallic material is selected, it should also be sufficiently corrosion-resistant with respect to the medium, e.g., a gaseous fuel, for which the solenoid valve 1 is intended.

[0033] If the electric coil 3 is supplied with energy, a magnetic flux is generated which forms a magnetic circuit M. The magnetic circuit M is closed by the valve housing 2 and the magnet armature 5, as is indicated in FIG. 1. As a result, a magnetic force acts on the magnet armature 5, through which the magnet armature 5 is axially attracted in the direction of the coil 3, as a result of which the valve element 8 opens (or vice versa closed). In this case, the magnetic flux of the magnetic circuit M runs radially within the coil 3 in a substantially axial direction through a first valve housing section 2a, axially below the coil 3 via a second valve housing section 2b extending radially outwards and adjoining the first valve housing section 2a. The magnetic flux runs from the second valve housing section 6b via an adjoining, radially outer, third valve housing section 6c, which also forms the valve housing outer wall of the valve housing 2. The magnetic circuit M is finally closed via the movable magnet armature 5 which, in the example shown, is arranged in the axial direction above the coil 3. The coil 3, including the coil carrier 4, is thereby seated in this case in an annular recess which is formed in the radial direction between the first and third valve housing sections 6a, 6c.

[0034] The valve housing 2, at least in the region around the coil 3 in which the magnetic circuit M forms, is made of a magnetically conductive material, such as a ferromagnetic metal, for example. However, the entire valve housing 2 is preferably made of the same ferromagnetic material, which facilitates the production of the valve housing 2. In an analogous manner, the magnet armature 5 is also made of a magnetically conductive material, at least in the region of the magnetic circuit 5, in order to close the magnetic circuit 5. However, the entire magnet armature 5 is preferably produced from the same material, which simplifies production.

[0035] Preferably the armature shaft 6 is not magnetically conductive at least in the region of the magnetic circuit 5, in order to produce no disruptive lateral magnetic forces on the armature shaft 6, which could have a negative effect on the actuating force of the valve element 8 - for example, due to increased friction. The solenoid valve 1 is designed as a so-called dry-running valve, which means that no separate lubricant is provided for lubricating the movable parts of the solenoid valve 1. In particular, if relatively dry gases are used as a fuel, it is important with such dry-running valves that the friction between armature shaft 6 and the section of valve housing 2 in which the armature shaft 6 is guided (here, first housing section 6a) be minimized as much as possible. To achieve this, it is therefore advantageous if no lateral forces, or as few lateral forces as possible, act on the magnet armature 5 and on the armature shaft 6, in order to reduce the friction in the guide of the armature shaft 6.

[0036] According to the invention, at least one magnetically conductive flux element 12 is therefore arranged in the valve housing 2, in order to guide at least 80%, preferably at least 90%, and particularly preferably 100%, of the magnetic flux of the magnetic circuit M flowing over the magnetically conductive valve housing outer wall - in this case, the third housing section 2c - into the second armature end face 5B, facing the coil 3, of the magnet armature 5 (or vice versa, depending upon the direction of the magnetic flux). In the example shown, the flux element 12 is arranged in a radial direction, i.e., transversely to the actuation direction, in a region adjoining the valve housing outer wall 2c of the valve housing 2. The flux element 12 extends in the valve housing 2 from the valve housing outer wall 2c inwards in the radial direction. In the actuation direction, the flux element 12 is arranged between the coil 3 and the magnet armature 5.

[0037] By using the flux element 12, a larger proportion of the magnetic flux can flow in the axial direction into the magnet armature 5, or the proportion of the magnetic flux flowing from the valve housing outer wall 2c in the radial direction into the magnet armature 5 is reduced. As a result, lateral forces acting on the magnet armature 5 can be reduced, whereby frictional forces between the armature shaft 6 and the valve housing 2 can be reduced. As a result of this reduction in the friction losses, the actuating speed of the valve element 8 can subsequently be increased, so that very dynamic opening and closing processes can be realized. It is particularly advantageous if the flux element 12 has a higher magnetic conductivity than the valve housing outer wall 2c. As a result, the magnetic resistance of the preferred magnetic circuit can be reduced, and consequently the proportion of the magnetic flux flowing into the armature end face 5B via the flux element 12 can be increased.

[0038] This can also be used, for example, in an advantageous manner to reduce the radial extent of the solenoid valve 1 - in this case, for example, the diameter of the valve housing 2 - with an essentially constant actuating force of the valve element 8, since the magnet armature 5 can be designed to be smaller in the radial direction. Alternatively, the actuating force of the valve element 8 could also be increased, given the same size of the solenoid valve 1. At the same time, the efficiency of force generation is also increased, so that a smaller dimensioned coil 3 can optionally be used. Preferably, the flux element 12, as in the example shown, is designed as a preferably closed flux ring, which is arranged in the radial direction between an end section 4a of the coil carrier 4 and the valve housing outer wall 2c. In the axial direction, the flux ring 12 is arranged between the coil 3 and the magnet armature 5. The flux element 12 is preferably made of a material having a high magnetic conductivity, e.g., of the same material as the magnet armature 5 and/or the valve housing 2 or the magnetically conductive section of the valve housing 2.

[0039] According to another advantageous embodiment of the solenoid valve 1, the coil 3 is arranged on a coil carrier 4, wherein an end section 4a, axially facing the magnet armature 5, of the coil carrier 4 is formed as an end stop for the magnet armature 5. As a result, the axial movement of the magnet armature 5 in the actuating position can be limited, in order to thereby limit the valve lift of the valve element 8. In the example shown, the flux element 12 is arranged in the radial direction between the end section 4a of the coil carrier 4 and the valve housing outer wall 2c. The flux element 12 is arranged to be substantially flush with a step on the inner side of the valve housing outer wall 2c, and is arranged flush with an axial end face, facing the magnet armature 5, of the first housing section 2a.

[0040] The end section 4a of the coil carrier 4 projects beyond the end face by a certain length I, as shown in FIG. 1. Due to the structural design of the coil carrier 4, including the end section 4a, this length I can be predetermined so that the valve lift can be easily limited, without separate components being required. The entire coil carrier 4, or at least the end section 4a, could, for example, be made of a suitable material with certain suspension and/or damping properties. As a result, the noise and the mechanical load on the magnet armature 5 and the end section 4a when the magnet armature 5 meets the end section 4a can be reduced. This is advantageous for reducing the noise emission and increasing the service life.

[0041] When the valve element 8 returns to the closed position from the open position after actuation of the solenoid valve 1, the valve element 8 generally strikes the valve seat due to the restoring force of the spring element 11. On the one hand, this can lead to undesired noise generation and, on the other, to increased mechanical stress on both the valve element 8 and the valve seat, which can lead to increased wear on the valve element 8 and/or the valve seat. This can be the case in particular with spring elements 11 with large restoring forces, which are advantageous for high closing speeds. In order to prevent this, a pneumatic damping in the solenoid valve 1 is provided, according to another advantageous embodiment of the solenoid valve 1.

[0042] For this purpose, the valve housing 2 forms a cylinder in the region of the magnet armature 5, and the magnet armature 5 forms a piston which is axially movable in the cylinder. A compression space KR is formed between the first armature end face 5A, facing away from the coil 3, of the magnet armature 5 and an opposite valve housing wall 2d of the valve housing 2 in the actuation direction. In addition, at least one throttle opening 13, which connects the first armature end face 5A to an opposite, second armature end face 5B, is arranged in the magnet armature 5.

[0043] A suitable sealing element for sealing the compression space KR is also preferably arranged on the peripheral surface 5U of the magnet armature 5 -for example, in the form of a known piston sealing ring or O-ring. Preferably, in the valve housing 2, as shown in FIG. 1, a relief opening, and in particular a relief bore, is provided which connects the space below the magnet armature 5 to the space in which the spring element 11 is arranged. As a result, a pressure relief of the space below the magnet armature 5 is realized in order to prevent the movement of the magnet armature 5 being damped even when the solenoid valve 1 is opened. For a good pressure relief effect, the relief bore is preferably arranged such that it is flush with the throttle opening 13.

[0044] This results in a simple and effective damping of the magnet armature 5 during the closing of the solenoid valve 1, wherein the damping characteristic can be influenced by the structural design of the solenoid valve 1 - in particular, by the size of the first armature end surface 5A - by the volume of the compression space KR, the effectiveness of sealing of the magnet armature 5 in the cylinder, and the number, the profile, and cross-section of the throttle opening(s) 13. The pneumatic damping allows the speed at which the valve element 8 strikes the valve seat to be reduced to preferably at most 0.5 m/s, so that the noise and the wear can be reduced.

[0045] Preferably, the damping characteristic is selected such that a substantially undamped movement takes place at the beginning of the closing movement, and that the damping occurs only shortly before the closed position. This allows the solenoid valve 1 to be closed quickly and still achieve the smoothest possible contact with the valve seat. Rapid opening and closing of the solenoid valve 1 is advantageous for achieving a very accurate quantity control of the preferably gaseous medium, and for carrying out several sequential opening and closing operations in a short time.

[0046] Up to now, the armature shaft 6 and the valve shaft 7 were often rigidly connected to each other - for example, integrally formed or welded. In particular, with relatively large solenoid valves 1, as are used for example in large motors, the moving components of the solenoid valve 1 - in particular, the magnet armature 5, the armature shaft 6, the valve shaft 7, and the valve element 8 - have comparatively large masses, which cause non-negligible inertial forces when the solenoid valve 1 is actuated. In particular, due to the mass of the magnet armature 5 and the armature shaft 6, an inertial force which acts on the valve element 8 via the valve shaft 7 can therefore occur when closing the solenoid valve 1. In the example shown, when the valve element 8 strikes the valve seat in the closed position, this inertial force causes an additional tensile force to be exerted upwards, which can have a negative effect on the noise generation and on the wear of the valve element and/or the valve seat.

[0047] According to another advantageous embodiment of the solenoid valve 1, the armature shaft 6 and the valve shaft 7 are therefore designed to be separate from each other, wherein a buffer element 15 made of plastic is advantageously arranged between the armature shaft 6 and the valve shaft 7. Given the separate execution, the movement of the magnet armature 5, including armature shaft 6, can be decoupled from the movement of the valve element 8, including valve shaft 7, in the closing movement. As a result, the load on the valve element 8 and the valve seat can be reduced, because, when solenoid valve 1 is being closed, only the inertial force of the masses of the valve element 8 and of the valve shaft 7 still act on the valve element 8 and the valve seat. Given the arrangement of the buffer element 15, a direct, and in particular metallic, contact between the armature shaft 6 and the valve shaft 7 is prevented, so that the noise generation and also the wear on the contact surface can be reduced as a result.

[0048] The buffer element 15 is preferably made of a tribologically-optimized plastic, such as, for example, a plastic filled with polytetrafluoroethylene (PTFE), so that the lowest possible friction between the peripheral surface of the buffer element 15 and the valve housing 2 occurs. Particularly with dry-running valves without additional lubricant, this is advantageous, because this further improves the efficiency of the solenoid valve 1, and/or the actuating force can be increased. If the end section 4a of the coil carrier 4, as shown, is used as an end stop for the magnet armature 5, the buffer element 15 can also, advantageously, be designed to compensate for any temperature-dependent changes in the valve lift. For this purpose, a suitable material is used for the buffer element 15, and the buffer element 15 is dimensioned in such a way that the (maximum) valve lift, when the magnet armature 5 rests against the end stop of the coil carrier 4, is as constant as possible in relation to the temperature. It is sufficient in this case if the compensation is realized at least within a temperature range to be expected for the use of the solenoid valve 1.

[0049] Finally, it should be mentioned that the shown solenoid valve 1 is, naturally, to be understood only as an example, and is shown in simplified form in order to illustrate the basic structure and the mode of operation. The specific structural design, such as, for example, the dimensioning, material selection, design of the valve element 8, etc., is naturally the responsibility of the person skilled in the art and depends upon the field of application of the solenoid valve 1.