DE102021133281A1 - Electromagnetic valve, in particular for switching a fuel injector - Google Patents

Abstract

The present invention relates to an electromagnetic valve, in particular for switching a fuel injector, such as a fuel injector for gaseous fuel, preferably hydrogen, and includes an armature which is movably guided in an armature guide in the axial direction of the valve and is designed to seal a throttle point in a closed position , a coil which is designed to lift the armature from the closed position by means of magnetic force, and a magnetic core which at least partially encloses the coil. The invention is characterized in that when the armature is in a maximum raised position from the closed position, an axial residual air gap remains between the magnet core and the armature so that magnetic field lines caused by the coil are not guided without interruption via a metallic, magnetizable connection of the magnet core and armature.

Description

The present invention relates to an electromagnetic valve, in particular an electromagnetic valve for switching a fuel injector, such as a fuel injector for injecting gaseous fuel, in particular hydrogen. Typically, the fuel is injected into the combustion chamber of an internal combustion engine, in which it is used to move a piston through combustion and the resulting expansion. However, the present invention is not limited to valves for fuel injectors, but extends to all technical areas in which electromagnetic valves are used.

Nevertheless, electromagnetic switching valves are known, in particular from the injection of fuel into the combustion chamber of an engine, in which a connection between two volumes filled with fluid is released or closed with a linearly movable valve member (armature) inside an injector.

The closing delay during which a valve remains in its open position, although the coil that lifts the armature (by means of magnetic force) out of its closed position is already de-energized is particularly troublesome when controlling such valves.

The dynamics of the solenoid valve are particularly influenced by eddy currents in the solid, ferromagnetic components (e.g. magnetic core and armature), which impede the build-up and breakdown of the magnetic field generated by the coil and thus the magnetic force, and thus delay it. In order to achieve an improved, in particular a dynamic, more quickly responding switching behavior of the actuator, it is desirable to minimize eddy currents and thus the opening and/or closing delay.

This is achieved with the present invention, which comprises an electromagnetic valve and a fuel injector which includes this electromagnetic valve and which overcomes or at least alleviates the aforementioned problems. The present invention focuses on reducing the closing delay time and shows the advantages that can be achieved with the invention on the basis of this, although the invention is also advantageous for the opening delay.

The invention is implemented by a device according to claim 1, advantageous developments of the invention being defined in the dependent claims.

According to the invention, an electromagnetic valve is therefore provided, in particular for switching a fuel injector, such as a fuel injector for gaseous fuel, preferably hydrogen, which has an armature which is movably guided in an armature guide in the axial direction of the valve and is designed to, in a closed position, Seal throttle point, a coil which is designed to lift the armature from the closed position by means of magnetic force, and comprises a magnetic core which encloses the coil at least partially. The electromagnetic valve is characterized in that when the armature is in a maximum lifted position from the closed position, an axial residual air gap remains between the magnet core and the armature in order to avoid uninterrupted, i.e. non-continuous, magnetic field lines caused by the coil via a metallic, magnetizable connection of the magnet core and to guide anchor. In this case, the closed lines of the magnetic field lines are not continuously guided via a metallic, magnetizable connection. Preferably, each of the closed lines must perform at least one media jump through a non-magnetizable or only weakly magnetizable material.

The closing delay time is significantly influenced by the design of the valve and by an axial residual air gap. It is clear to a person skilled in the art that the air gap is the distance between a magnetic core face or a magnetic core and an armature face or the armature. The axial residual air gap is now a remaining air gap that occurs when the armature is in a position that is maximally lifted from the closed position, in which the armature is maximally deflected by magnetic force in the direction of the magnet core. In contrast to the prior art, the armature does not lie flat on the magnetic core, but rather an axial residual air gap remains, which the magnetic field lines have to bridge even when the armature is in a maximum attracted state.

This means that the air gap is made up of the armature stroke and the remaining axial air gap. The axial residual air gap is the difference between the air gap and the armature stroke. The air gap or the residual air gap is filled with air or fuel and/or non-magnetizable or only weakly magnetizable materials. Ferromagnetic, strongly magnetizable media are not assigned to the air gap.

A higher axial residual air gap leads to a reduction in the magnetic force that can act in the upper stop. In addition, the inductance of the electromagnet is reduced due to a higher axial residual air gap, which means that the influence of eddy currents, which cause build-up and dissipation of the magnetic field and the magnetic force derived from it is reduced. Both effects, ie the reduction of the magnetic force and the reduction of the eddy currents, lead to an earlier closing of the armature and thus in particular to a reduction in the closing delay.

The axial residual air gap can be implemented using various implementations. It is important that the axial residual air gap between the armature and the magnetic core is filled with a non-magnetic or only (very) weakly magnetizable medium (e.g. air, fuel, non-ferromagnetic materials), so that the air gap does not disappear when the armature is attracted. This causes the magnetic force to rise sharply and prevents the armature from dropping after activation (very long closing delay) or even completely prevents it (due to remanence effects due to the non-linear, hysteresis-prone B-H characteristics of ferromagnetic materials).

The axial residual air gap can, for example, be implemented using a metallic stop, e.g. a metallic elevation on the armature. The stop should be located as far as possible outside the core area of the magnetic field or at least be designed with a very small stop surface in order to avoid or minimize a "magnetic short circuit", i.e. a direct metallic contact between the armature and the magnetic core, what - how previously described - would lead to a long delay in closing.

A further possibility is the coating of the armature end face or the stop face of the magnet core with a non-magnetizable layer.

Furthermore, according to the invention, it can be provided that the axial residual air gap between the magnet core and the armature is generated by a disk or a stack of disks, which has at least two disks stacked one on top of the other in the axial direction, preferably with the stack of disks being arranged between the respective end faces of the magnet core and the armature and /or is only weakly or non-magnetizable.

It is clear to a person skilled in the art that the pane or panes can also be applied in one layer or in layers, with the term pane or panes only being referred to below for the sake of simplicity.

A disk or the stack of disks is provided as a spacer between the armature and the magnetic core, which prevents movement of the armature beyond the axial residual air gap defined by the disk or the stack of disks. The design as a stack of disks is advantageous because adding the disks allows a variable spacing of the axial residual air gap to be generated. In a maximum tightened position of the armature, the disk stack is clamped between the magnet core and the armature, so that there is no longer direct contact between the magnet core and the armature, which are each made of a ferromagnetic material.

According to an optional development of the invention, it can be provided that the at least two discs of the disc stack consist of two different materials, with a first of the at least two discs preferably being a plastic disc, in particular a polyamide film, and a second of the at least two discs is a metallic, non-magnetisable sheet metal disc.

The use of a (non-metallic) plastic film, in particular a polymide film, has the advantage that it is less rigid than a sheet metal disc, which dampens the impact of the armature on the upper stop when opening and thus reduces the bouncing that typically occurs. In addition, there is no continuous metallic contact between the armature and magnetic core in the upper rest position, so that in contrast to a variant in which the disk stack is made up of metal disks throughout, there is no flow of electrons between the armature and magnetic core. This also leads to a reduction in eddy currents, which are nothing more than the movement of (negative) charges, i.e. electrons.

According to an advantageous development of the present invention, it can be provided that a first of the at least two panes of the stack of panes is a plastic film or plastic pane, in particular a polyamide film, which is sandwiched between two sheet metal panes. In this case, of course, there must be at least three discs.

This is particularly advantageous in order to reduce the mechanical stress on the plastic pane due to the continuous impact of the armature or the magnet core. In connection with a slotted design of the armature or the magnetic core, this is all the more advantageous, since the punching effect that would otherwise occur puts a lot of strain on the plastic disk and will damage it after a relatively short time.

Advantageously, according to the invention, it can be provided that when the armature is in a tightened state, the magnetic core touches a sheet-metal disk of the stack of disks and/or the Anchor touches a sheet metal disc of the disc stack.

Accordingly, it is therefore advantageous if the outer layer of the stack facing the armature or the magnetic core is a sheet metal layer, since this is best able to withstand the forces that occur due to its material properties.

According to an optional development of the present invention, it can be provided that the thickness of the disks of the stack of disks is in the range of 10-100 μm, preferably in the range of 10-50 μm. It can also be provided that the plastic disk, in particular the polyamide disk, has a thickness in the range of 10-50 μm, whereas the at least one metal disk used in the stack has a thickness in the range of 10-100 μm. Accordingly, it is therefore possible for the discs, which are made of different materials, to also have different thicknesses.

According to an advantageous variation of the present invention, it can be provided that the armature has an axially extending slot in order to interrupt a circumferential eddy current, preferably wherein the slot has the shape of a cylinder sector in a cylindrically shaped part of the armature.

Eddy currents, which negatively affect the dynamics of the solenoid valve, flow primarily in solid (i.e. non-laminated) electrically conductive materials (e.g. iron and iron alloys). In order to prevent or at least reduce the influence of eddy currents, the armature and/or magnetic core can each be provided with one or more slots (or similar interruptions in the solid armature body or the solid magnetic core body). The slits can be axially continuous or leave a residual web and assume any desired shape in axial cross section, for example rectangular, wedge-shaped, etc. The slits prevent the formation of very large, circular and circumferential eddy currents and thereby improve the closing distortion. An axially continuous slit (without a remainder) is generally more effective than a slit with a remainder.

Accordingly, it can therefore advantageously be provided that the slot in the armature starts from the end face of the armature facing the magnetic core and preferably extends over the entire axial length of the armature. In this case, it can also be provided that the slot in the armature extends in the axial direction only as far as a first reduction in cross section.

It can also be provided according to the invention that the magnet core has a slot running in the axial direction in order to interrupt an eddy current acting in the circumferential direction, the slot preferably having the shape of a cylindrical sector.

It is also possible that the slot in the magnet core starts from the end face of the magnet core facing the armature and preferably extends over the entire axial length of the magnet core. As already explained above, however, it is sufficient to improve the closing delay if the slot does not extend over the entire axial length. It is sufficient if the slot is only formed in a region in which eddy currents occur to a greater extent.

According to the invention, it can also be provided that the valve comprises a spring element which is designed to urge the armature into the closed position. The spring member serves to urge the armature toward its closed position to move the armature from the energized to the closed position (when the coil is in a de-energized state).

According to the invention, it can also be provided that the disk stack has the shape of a circular ring, in the middle of which there is a recess for the passage of a spring element. The spring element then acts directly on the armature, for example, and is supported by the magnetic core with its end opposite thereto.

The shape of a continuous circular disk is also possible, in which case the spring element then acts directly on the stack of disks.

According to a further advantageous modification, it can be provided that the armature guide surrounds the armature on the peripheral side and is made of a non-ferromagnetic material. This contributes to the fact that the magnetic field lines formed by the electromagnet can actually only be closed via the air gap.

Furthermore, according to the present invention, it can be provided that a lower stop of the armature, in which the throttle point that can be closed by the armature is arranged, is made of a non-ferromagnetic material. This contributes to the fact that the magnetic field lines formed by the electromagnet can actually only be closed via the air gap.

The invention also relates to a fuel injector, in particular a fuel injector for a gaseous fuel, preferably hydrogen, comprising an electromagnetic valve for switching th of the injector according to one of the variants discussed above.

The invention also includes an electromagnetic valve, in particular for switching a fuel injector, which has an armature which is movably guided in an armature guide in the axial direction of the valve and is designed to seal off a throttle point in a closed position, a coil which is designed to to lift the armature from the closed position by means of magnetic force, and having a magnetic core which at least partially encloses the coil, the armature and/or magnetic core having/have a slot running in the axial direction in order to interrupt an eddy current acting in the circumferential direction, preferably wherein the slot has the shape of a sector of a cylinder.

• 1: eine teilweise Schnittdarstellung eines erfindungsgemäßen Ventils nach einer ersten Ausführungsform in Schließstellung,
• 2: eine Darstellung des prinzipiellen Schaltverhaltens eines Elektromagnetventils,
• 3: eine Darstellung zum Erläutern des Zusammenhangs von Magnetkraft und Luftspalt,
• 4: eine teilweise Schnittdarstellung eines erfindungsgemäßen Ventils nach der ersten Ausführungsform in Offenstellung,
• 5: eine teilweise Schnittdarstellung eines erfindungsgemäßen Ventils nach einer zweiten Ausführungsform in Schließstellung,
• 6: eine teilweise Schnittdarstellung eines erfindungsgemäßen Ventils nach der zweiten Ausführungsform in Offenstellung,
• 7: eine teilweise Schnittdarstellung eines erfindungsgemäßen Ventils nach einer dritten Ausführungsform in Schließstellung,
• 8: eine teilweise Schnittdarstellung eines erfindungsgemäßen Ventils nach einer vierten Ausführungsform in Schließstellung,
• 9: eine teilweise Schnittdarstellung eines erfindungsgemäßen Ventils nach der vierten Ausführungsform in Offenstellung,
• 10: eine teilweise Schnittdarstellung eines erfindungsgemäßen Ventils nach einer fünften Ausführungsform in Schließstellung, und
• 11a-c: perspektivische Darstellungen eines Ankers, mit und ohne einen axial verlaufenden Schlitz zum Unterbrechen von Wirbelströmen.

Further features, details and advantages of the invention can be seen from the following description of the figures. show:

• 1 : a partial sectional view of a valve according to the invention according to a first embodiment in the closed position,
• 2 : a representation of the basic switching behavior of a solenoid valve,
• 3 : a representation to explain the relationship between magnetic force and air gap,
• 4 : a partial sectional view of a valve according to the invention according to the first embodiment in the open position,
• 5 : a partial sectional view of a valve according to the invention according to a second embodiment in the closed position,
• 6 : a partial sectional view of a valve according to the invention according to the second embodiment in the open position,
• 7 : a partial sectional view of a valve according to the invention according to a third embodiment in the closed position,
• 8th : a partial sectional view of a valve according to the invention according to a fourth embodiment in the closed position,
• 9 : a partial sectional view of a valve according to the invention according to the fourth embodiment in the open position,
• 10 : a partial sectional representation of a valve according to the invention according to a fifth embodiment in the closed position, and
• 11a-c 1: Perspective representations of an armature, with and without an axial slot for interrupting eddy currents.

1 1 shows the basic structure of an electromagnetic valve 1 according to the invention. Only a partial sectional view is shown along the longitudinal axis in the axial direction of the valve 1, with the remaining sectional view resulting from a reflection on the axis of symmetry 26, which is not shown for reasons of clarity.

The electromagnetic valve 1 comprises a housing 18, a magnetic core 6, which is designed in one or more parts and (at least partially) can be located inside and/or outside of the housing 18. The valve 1 also comprises a coil 5 which is (at least partially) surrounded by the magnetic core 6 and which is optionally surrounded and fixed by a coil casing 19, an armature 2 which is guided in an armature guide 3 and which, when the valve 1 is closed, is guided by a prestressed Spring element 16 is pressed against a first stop 17 (lower stop), so that a throttle point 4 is sealed. Optionally, at least one shim 23 for setting the pretensioning force of the spring element 16 and at least one shim 22 for setting the armature stroke 24 can be provided. The armature stroke is the maximum possible axial movement of the armature 2 from its closed position to the second stop 20 (=upper stop), the second stop 20 preferably being able to correspond to the end face 14 of the magnet core.

The distance between the magnet core face 14 and the armature face 13 in the closed position of the valve 1 is referred to as the air gap. It is made up of the armature stroke 24 and the axial residual air gap 7. The axial residual air gap 7 is the difference between the air gap and the armature stroke 24. The air gap can be filled with air or fuel and/or non-magnetizable or only weakly magnetizable materials. Ferromagnetic, strongly magnetizable media are not assigned to the air gap.

The function of the in 1 illustrated valve 1 based on 2 explained, which shows the basic switching behavior (opening phase and closing phase) of the electromagnetic valve 1. At time t ₀ the valve 1 is in the starting position, so that the armature 2 seals the throttle point 4 . If an electrical control signal is now activated at time t ₀ , a magnetic field 8 is formed around the coil 5 due to the current flowing in the coil 5, which is guided and amplified by the ferromagnetic magnetic core 6 and the ferromagnetic armature 2 (see magnetic field line 8 in 1 ).

As a result, a magnetic force is formed between the armature 2 and the magnet core 6, which tends to reduce the air gap and to move the armature 2 in the direction of the magnetic core 6. At time t ₁ the magnetic force has overcome the prestressing force of the spring 16 (plus other forces that may be applied, such as frictional forces) and the armature 2 begins to move in the direction of the magnetic core 6 (see Fig 2 ). The magnetic force usually increases as the air gap decreases (see Fig 3 ), whereby deviations from a monotonous course are also possible due to special designs for influencing the magnetic force-stroke characteristic (characteristic influence).

If the armature 2 reaches the upper stop 20 at time t ₂ , it is abruptly decelerated and usually reaches a static rest position after a bouncing phase, so that the throttle point 4 is fully open (see also 4 ). The spring force changes during the tightening process depending on the spring rate and the further deformation of the spring. From a certain point in time, the intensity of the electrical control signal can be reduced in order to keep the armature 2 in the open position, which results in a reduction in the magnetic force (point in time t ₃ ).

This is followed by a closing process in which the control signal is terminated at time t ₄ . As a result, the magnetic force decreases and the armature 2 initially remains in its upper rest position until the magnetic force has dropped to a value below the restoring spring force (plus any counteracting frictional forces) (time t ₅ ). The armature 2 is then pressed back into the lower stop 17 by the spring 16 and hits the throttle point 4 (time t ₆ ), which it possibly closes again after a bouncing phase (time t ₇ ). The magnetic force will continue to decrease over time until it is (almost) completely dissipated and the original state is restored.

The period of time between the start of the control signal (time t ₀ ) and the start of the armature movement toward the upper stop 20 (time t ₁ ) is referred to as the opening delay (OD=opening delay). The period of time between the end of the control signal (time t ₄ ) and the impact of the armature 2 on the lower stop 17 (time t ₆ ) is referred to as the closing delay (English: CD=closing delay). Both the phase of the closing delay and the opening delay are in 2 highlighted by a double arrow in the timeline.

The dynamics of the solenoid valve 1 is influenced in particular by eddy currents in the solid, ferromagnetic components (magnetic core 6 and armature 2), which impede the build-up and breakdown of the magnetic field and thus the magnetic force and thus delay it. In order to achieve dynamic switching behavior of the actuator, it is advantageous to minimize eddy currents in order to improve the opening and closing delay.

The magnetic force is significantly influenced by the design and the axial residual air gap. A larger axial residual air gap reduces the magnetic force in the upper stop 20. In addition, a larger axial residual air gap usually reduces the inductance of the electromagnet, so that the influence of eddy currents, which impede the build-up and decay of the magnetic field and thus the magnetic force, and delay, is reduced. Both effects lead to an earlier closing of the armature and thus to a reduction in the closing delay.

1 shows an exemplary implementation for an axial residual air gap, which can be realized using various design options. It is important that the axial residual air gap between the armature 2 and the magnetic core 6 is filled with a non-magnetic or only very weakly magnetizable medium (e.g. air, fuel such as diesel, gasoline, natural gas, hydrogen or similar, non-ferromagnetic materials ), so that when the armature 2 is attracted there is no vanishing air gap, as a result of which the magnetic force increases significantly. 3 shows the connection with a reduction in the air gap and the associated increase in the magnetic force. The very strong magnetic force prevents the armature 2 from dropping after activation (and leads to a very long closing delay) or even completely prevents it from dropping (due to remanence effects due to the non-linear, hysteresis-prone BH characteristics of ferromagnetic materials).

In 1 the axial residual air gap is implemented via a metallic stop, which is designed as an armature elevation 21. The armature elevation 21, which is located outside the core area of the magnetic field 18, prevents / minimizes a "magnetic short circuit", i.e. a direct metallic contact between the armature 2 and the magnetic core 6, which - as described above - leads to a long delay in closing would lead.

4 shows that 1 associated image, in which the electromagnetic valve 1 is in its open position. The armature 2 is attracted to the maximum and contacts the upper stop 20 with its armature elevation 21. The magnetic field lines 8, each of which always forms a closed circle, can therefore not spread continuously via direct contact between the armature 2 and the magnet core 6. It is always necessary that each magnetic field line has the axial residual air spalt 7 overcomes, which brings with it the aforementioned advantages.

5 shows a further embodiment of an electromagnetic valve 1 according to the invention, in which the armature elevation 21 of the armature 2 is arranged in the core area of the magnetic field. Compared to the first embodiment in 1 and 4 the anchor elevation 21 is arranged further radially outwards.

One recognizes in 6 , which shows the attracted state of the armature 2, that the magnetic field line 8 (shown as an example) can use a direct metallic contact between the components at its radially inner transition from the armature 2 to the magnet core 6, whereas the radially outer transition from the magnet core 6 to the armature 2 can continue to take place only via the axial residual air gap 7. In the 6 illustrated magnetic field lines 8 have an orientation that corresponds to the clockwise direction.

7 shows a further embodiment of the electromagnetic valve 1 according to the invention. In contrast to the previous embodiment, the armature end face 13 is provided with a non-magnetizable (or only weakly magnetizable) coating 27 whose thickness defines the axial residual air gap 7 . If the armature 2 and the magnetic core 6 are moved towards one another, the coating 27 ensures that the distance between these components cannot fall below a minimum.

It is clear to the person skilled in the art that, in order to achieve the advantages of the present invention, it is also possible to arrange the coating 27 on the end face on the magnet core 6 and/or the coil casing 19 opposite the armature end face 13 . A plastic layer, for example a polyamide layer, is particularly suitable as the coating.

8th shows a further embodiment of the electromagnetic valve 1 according to the invention, in which a disk 9 is arranged between the armature 2 and the magnet core 6 instead of a coating. The advantage of providing a disk 9 lies in the simplified manufacturability of the electromagnetic valve 1, since no coating, which is expensive to apply, but only the insertion of a disk between the armature 2 and the magnetic core 6 is required.

Any non-magnetizable (or only weakly magnetizable) material can be used as the material for the disk 9, for example a plastic disk, in particular a polymide disk, or a metallic, non-magnetizable sheet metal. It is advantageous if the thickness of the disk is in the range from 20 to 500 μm.

In particular, the use of (non-metallic) polymide discs or foils has the advantage that they are less rigid than metal sheet metal, which dampens the impact of the armature 2 on the upper stop when opening and thus reduces bouncing. In addition, there is no direct metallic contact between the armature 2 and the magnetic core 6 in the upper resting position, so that, in contrast to the variant with metal disks, there is no flow of electrons between the armature and the magnetic core.

9 shows an electron flow 29, which can take place via the metal disc 28, as an example of a conversion of the disc 9 with a (non-magnetizable) metallic material in the form of a metal disc 28. The use of a material that prevents the conduction of electrons reduces eddy currents, which are nothing more than the movement of (negative) charges, i.e. electrons. Therefore, the use of plastic or polymide as a disk or part of a disk stack or coating between the armature 2 and the magnet core 6 is particularly appropriate.

10 shows a disc stack 10 arranged between the armature 2 and the magnet core 6, in which several discs 11, 12 are stacked one on top of the other in the axial direction, so that when the armature 2 is attracted, the distance from the magnet armature 6 is defined by the thickness of the discs 11, 12 stacked on top of each other . Advantageously, it can be provided that the at least two discs 11, 12 are firmly connected to one another, so that the individual discs 11, 12 of the disc stack 10 not only rest loosely on one another, but are fastened to one another, for example glued or the like. Furthermore, the stack of discs 10 can also be attached to an end face 13 of the armature 2 or an end face 14 of the magnet core 6 .

It is particularly advantageous if, as in 10 shown, the disk stack 10 has a sheet metal disk 11 on its flat sides facing the magnet core end face 14 and the armature end face 13, and a plastic disk 12, in particular a polyamide disk, is provided between the sheet metal disks 11.

The mechanical stress during clamping between the armature 2 and the magnetic core 6 is better tolerated by a sheet metal disc, in particular if the armature 2 or the magnetic core 6 has a slot 15 running in the axial direction, which extends towards a respective end face 13, 14.

For example, such a slot 15 in the 11a-c shown, where in 11a an armature 2 is shown without a slot 15 in order to show the eddy currents that form. These are shown with a circle that closes in the circumferential direction of the armature 2 and characterizes the basic characteristics of the eddy currents occurring in the armature 2 .

Eddy currents, which negatively affect the dynamics of the solenoid valve 1, flow primarily in solid (ie non-laminated) electrically conductive materials (eg iron and iron alloys). In order to prevent or at least reduce the influence of eddy currents, the armature 2 and/or magnetic core 6 can each be provided with one or more slots (or similar interruptions in the solid body) (see Fig 11b & 11c ). The at least one slot 15 prevents the formation of very large, circular eddy currents and thereby improves the closing delay.

In order to interrupt such an eddy current, a slot 15 can be provided which prevents the eddy current circuit from closing. Such a slot is, for example, in 11b shown, which here has the exemplary shape of a cylinder sector. Other configurations of the slot 15 can be subject to any shape in their axial cross section, ie, for example, rectangular, wedge-shaped or the like. It is also not necessary for the slot to be smaller than or equal to half the diameter of the width of the armature 2.

In 11b For example, the slot 15 is present only in the upper part of the armature 2, which is characterized by an enlarged cross-section towards the lower part of the armature 2. However, it is also possible for the slit to also run into the lower part, as long as the sealing of the throttle point 4 is ensured.

The at least one slot 15 can be axially continuous (in the upper part of the armature 2) or leave a residual web 30, cf. 11c . An axially continuous slit (without a residual web 30) is usually more effective than a slit with a residual web 30.

It can be seen that the slot 15 means that the armature face 13 no longer has the cross section of a circle. This is particularly disadvantageous when a disc made of plastic, in particular polymide, is provided between the armature 2 and the magnet core 6 . The permanent impact of the armature end face on this disc produces a punching effect which leads to damage to the disc. Thus, the use of plastic discs, in particular polyamide discs in combination with a slotted armature 2 and/or magnet core 6, has the disadvantage that the at least one slot 15 present in the armature 2 and/or magnet core 6 acts on the plastic disc like the stamp of a punching machine and destroy them. It is therefore advantageous if the disk of a stack of disks 10 that comes into direct contact with an end face is a sheet metal disk, since this offers the advantage of significantly increased robustness and can better withstand the punching effect.

Alternatively or additionally, it can be provided that the slot 15 provided in the armature 2 and/or the magnetic core 6 is filled with a non-magnetizable material, so that at least the end face of the armature 2 or the magnetic body 6 is flat and the punching effect is not occurs.

Reference List

1

solenoid valve

2

anchor

3

anchor guide

4

throttle point

5

Kitchen sink

6

magnetic core

7

axial residual air gap

8th

magnetic field lines

9

disc

10

disc stack

11

first disc; especially plastic film

12

second disc; especially non-magnetizable sheet metal disc

13

anchor face

14

magnetic core face

15

slot

16

spring element

17

lower anchor stop

18

Housing

19

coil coating

20

upper stop

21

anchor elevation

22

Armature Stroke Dial

23

Spring-loaded dial

24

hub

25

sealing surface

26

axis of symmetry

27

coating

28

sheet metal disc

29

electron flow

30

remaining web

X

axial direction

Claims (15)

Electromagnetic valve (1), in particular for switching a fuel injector, comprising: an armature (2) which is movably guided in an armature guide (3) in the axial direction (X) of the valve (1) and is designed to have a throttle point ( 4), a coil (5) which is designed to lift the armature (2) from the closed position by means of magnetic force, and a magnetic core (6) which at least partially encloses the coil (5), characterized in that in a When the armature (2) is in the maximum lifted position from the closed position, an axial residual air gap (7) remains between the magnetic core (6) and the armature (2) in order to avoid uninterrupted magnetic field lines (8) caused by the coil (5) via a metallic, magnetizable Lead connection of magnetic core (6) and armature (2). valve (1) after claim 1 , wherein the axial residual air gap (7) between the magnetic core (6) and the armature (2) is generated via a disk (9) or a stack of disks (10) which has at least two disks (11, 12) stacked one on top of the other in the axial direction (X). , preferably wherein the disk stack (10) is arranged between the respective end faces (13, 14) of the magnetic core (6) and the armature (2) and/or is non-magnetizable. valve (1) after claim 2 , wherein the at least two discs (11, 12) of the disc stack (10) consist of two different materials, wherein preferably a first disc (11) of the at least two discs (11, 12) is a plastic film, in particular a polyamide film, and a second disk (12) of the at least two disks (11, 12) is a metallic, non-magnetizable sheet metal disk. Valve (1) according to any one of the preceding claims 2 or 3 , wherein a first disc (11) of the at least two discs (11, 12) of the disc stack (10) is a plastic film, in particular a polyamide film, which is sandwiched between two metal discs (12). Valve (1) according to any one of the preceding claims 3 or 4 , wherein when the armature (2) is attracted, the magnetic core (6) touches a sheet metal disc (12) of the stack of discs (10) and/or the armature (2) touches a sheet metal disc (12) of the stack of discs (10). Valve (1) according to any one of the preceding claims 2 - 4 , wherein the thickness of the discs (11, 12) of the disc stack (10) is in the range of 10-100 microns, preferably in the range of 10-50 microns. Valve (1) according to any one of the preceding claims, wherein the armature (2) has a slot (15) extending in the axial direction (X) to interrupt a circumferential eddy current, preferably wherein the slot (15) has the shape of a sector of a cylinder . valve (1) after claim 7 , wherein the slot (15) in the armature (2) starts from the end face (13) of the armature (2) facing the magnetic core (6) and preferably extends over the entire axial length of the armature (2). Valve (1) according to any one of the preceding claims, wherein the magnetic core (6) has a slot (15) running in the axial direction (X) in order to interrupt a circumferential eddy current, preferably wherein the slot (15) has the shape of a sector of a cylinder . valve (1) after claim 9 , wherein the slot (15) in the magnet core (6) starts from the end face (14) of the magnet core (6) facing the armature (2) and preferably extends over the entire axial length of the magnet core (6). Valve (1) according to any one of the preceding claims, further comprising a spring element (16) which is designed to urge the armature (2) into the closed position. Valve (1) according to any one of the preceding claims 2 - 11 , wherein the disk stack (10) has a circular ring shape, in the middle of which a recess for the passage of a spring element (16) is provided. Valve (1) according to one of the preceding claims, in which the armature guide (3) surrounds the armature (2) on the peripheral side and is made of a non-ferromagnetic material. Valve (1) according to one of the preceding claims, wherein a lower stop (17) of the armature (2), in which the throttle point (4) which can be closed by the armature (2) is arranged, is made of a non-ferromagnetic material. Fuel injector, in particular fuel injector for a gaseous fuel, preferably hydrogen, comprising an electromagnetic valve (1) for switching the injector according to one of the preceding claims.

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