EP0936636A2 - Electromagnet - Google Patents

Abstract

The actuator has an opening magnet (22) and a closing magnet (23) with coils (4,12) within cores (5,11). The produced magnetic field (20,21) operates upon an armature plate (10). The core elements have diffusion directions (1-3,17-19) with different magnetic materials (6-8,13-15). The materials which are nearer to the coil in the diffusion direction have a smaller saturation flux density, which is achieved with a smaller field strength than the materials further from the coils.

Description

The invention relates to an electromagnet according to the preamble of claim 1.

In order to generate the strongest possible electromagnetic fields, electromagnets with a coil and a ferromagnetic core are generally used. The core is located in and / or surrounds the coil. If a current is passed through the coil, a magnetic field with the field strength H builds up around the coil in accordance with the law on flooding. Under the force of the magnetic field, the magnetic dipoles present in the core material orient themselves in the field direction and thus increase the magnetic flux density or induction in comparison to an air coil from B ₀ to B. The resulting flux density is therefore dependent on the field strength H. The functional relationship is due to the nonlinear magnetization curve B = µ (H) * H described. Self-induction acts in the coil, so that the current and the field strength H dependent on it increase with a delay. Furthermore, the build-up of the magnetic field is delayed by eddy currents that arise in the core material, which hinder the diffusion of the magnetic field into the core and lead to losses.

To achieve a short response time with an electromagnet, the electromagnetic field should build up quickly and can also be dismantled and despite the small dimensions of the Electromagnets have a large final force. This is particularly so important for very dynamic systems, e.g. at Actuators for actuating gas exchange valves of internal combustion engines. Electromagnetic actuators gas exchange valves usually have two solenoids, an opening magnet and a closing magnet with one coil and one core, between their pole faces an armature arranged coaxially to a valve axis is. The armature acts on a valve stem via an armature tappet of the gas exchange valve. For actuators based on the principle a preloaded spring mechanism acts on the mass oscillator on the anchor. Usually two preloaded spring mechanisms are used Compression springs, namely an upper and a lower Valve spring. The upper valve spring loads in the opening direction and the lower valve spring in the closing direction of the gas exchange valve. If the magnet is not excited, the armature is replaced by the Valve springs in an equilibrium position between the magnets held.

If the actuator is activated at start, either the Closing magnet or the opening magnet temporarily overexcited or the anchor with a start-up routine with its resonance frequency stimulated to be attracted to out of balance become. In the closed position of the gas exchange valve the armature on the pole face of the energized closing magnet and is held by this. The closing magnet clamps the in Valve spring acting in the opening direction further forward. To do that To open the gas exchange valve, the closing magnet is switched off and the opening magnet is switched on. The in the opening direction Acting valve spring accelerates the armature over the Equilibrium position, so that this from the opening magnet is attracted. The anchor hits the pole face of the Opening magnet and is held by this. To do that To close the gas exchange valve again, the opening magnet switched off and the closing magnet switched on. In the Valve spring acting in the closing direction accelerates the armature beyond the equilibrium position to the closing magnet. Of the Anchor is attracted by the closing magnet, strikes the Pole surface of the closing magnet and is held by this.

The flight time of the anchor between the opening magnet and the Closing magnet is very short and is usually not enough that the Core of the catching magnet completely from the magnetic field of the Coil is interspersed after a voltage is applied to it has been. To ensure that the core is completely free of the magnetic field penetrates or the magnet has sufficient attraction has reached as soon as the anchor comes into its area of effect, the catching magnet must be activated before the anchor detaches from the holding magnet. This leads to unnecessary energy expenditure. Furthermore, with the mostly relatively sluggishly appealing Magnet does not react to abrupt disturbances become.

It is known to make iron cores from thin insulated from each other Build up sheets with their contact surfaces across the electrical Field lines lie, i.e. perpendicular to the winding of the Coil (see H. Linse, electrical engineering for mechanical engineers, 8th, revised edition, Teubner 1987, p. 66 ff). Step through it only small tensions in the individual sheets and thus small Eddy currents.

It is also known from DE 37 29 418 A1 to have a coil core in Longitudinal side by side from different materials to manufacture. The coil core consists of a composite body, that of at least two mechanically clamped materials exists, at least one of which is ferromagnetic and in Longitudinal axis anisotropic, soft magnetic Possesses properties. The composite body becomes a soft magnetic Body associated with a lower coercive force than the ferromagnetic part of the composite body and is sufficiently magnetostatically coupled to it. The mechanical stresses in the composite body result in Longitudinal direction of the coil core is a magnetic preferred direction. If an external magnetic field acts on the coil core, it changes the direction of magnetization in the composite body more or less erratic when a certain field strength is exceeded or is fallen below, which can generate pulses.

Due to the additional soft magnetic body you can in one Hysteresis cycle two pulses are generated. Can also also short coil cores can be used.

The object of the invention is an electromagnet to develop the greatest attraction in the shortest possible time or holding force generated to thereby in particular an actuator for actuating a gas exchange valve To be able to control valve movement better. The task is solved according to the invention by the features of claim 1, while advantageous refinements and developments of Invention can be found in the dependent claims.

H: Feldstärke

µ: Permeabilität µ = µ0 · µR

µ₀: magnetische Feldkonstante, Permeabilität des Vakuums

µ_r: materialabhängige Permeabilitätszahl

The following applies to the magnetic flux density B: W = µ · H

H: field strength

µ: permeability µ = µ 0 · ΜR

µ ₀ : magnetic field constant, permeability of the vacuum

µ _r : material-dependent permeability number

In the case of ferromagnetic materials, the permeability number µ _r (H) depends on the field strength H, and in fact it drops at a specific field strength H _S. The magnetic flux density B characterized rises in a first region with the field strength H almost linearly and aims at a field strength H _S, in a second non-linear region, a saturation flux density B _s to. The invention is based on the knowledge that at a field strength H _S , in which one is in the area of the saturation flux density B _S , less eddy currents occur in the core material and the diffusion rate v _{D of} the magnetic field into the core material is many times greater than in one Field strength H at which you are still in the linear range of B. The following applies to the diffusion rate v _D : V D ≈ t σµ

Velocity values higher by a factor of 200 to 300 are achieved (see Feinwerktechnik & Messtechnik 90 (1982) 5, B. Aldefeld: Felddiffusion in Elektromagneten, p. 222 ff.). Furthermore, the permeability μ in the case of core materials with a lower saturation flux density B _S is smaller overall and thus the diffusion rate is greater.

In the coil core according to the invention, the material closer to the coil in the diffusion direction has a smaller saturation flux density B _S , which is achieved at a smaller field strength H _S than the material which is further away from the coil. If the electromagnet is activated or a voltage is applied to the coil, a voltage arises through self-induction in the coil, which delays the current increase I and thus the increase in the magnetic field strength H. However, the coil core according to the invention already achieves the saturation flux density B _{S of} the materials closer to the coil in the diffusion direction in the rise phase of the magnetic field strength H, ie with a small magnetic field strength H _S , so that a low permeability μ and a high diffusion speed v _D. If the area in the coil core is referred to as the diffusion front, in which the flux density has dropped to a defined small value, then the materials in the diffusion direction are preferably matched to the course of the magnetic field strength in such a way that a small permeability μ and a high diffusion speed v _D occurs. The more materials are used, the better they can be matched to the course of the magnetic field strength, ideally with an infinite number of materials, for example through stepless material transitions in special alloys.

With a high diffusion speed of the magnetic field increases an outwardly acting surface A of the electromagnet quickly to and thus the attraction F.

The following applies to the attraction: F = B 2nd 2µ 0 · A

It can also be seen from the equation that the materials with a low saturation flux density B _S produce a lower final force F _E. On average, however, a sufficient final force F _E can be achieved overall by the choice of materials with higher saturation flux densities B _S.

In one embodiment of the invention it is proposed that to use electromagnets according to the invention in an actuator, with the one as described above, a gas exchange valve Internal combustion engine is actuated via an anchor. By the the electromagnet can be activated more quickly become, for example, only after the anchor of a opposite, previously holding magnets which saves energy. Furthermore, the shorter Response time of the electromagnet the valve movement more precisely can be regulated, in particular, may occur Faults are reacted to more quickly.

kennlinienbeeinflußten Elektromagneten" (KLB-Magnet) einzusetzen. Der Spulenkern des KLB-Magneten weist vorzugsweise im Bereich der Spule in Richtung des entsprechend geformten Ankers eine Stufe auf, wodurch der Anker früher in das Magnetfeld des fangenden KLB-Magneten eintritt. Die Flugzeit des Ankers bis in das Magnetfeld des fangenden Magneten ist kürzer als bei einem zum Anker hin flachen Spulenkern bzw. flachen Polfläche. Damit der KLB-Magnet nach der kurzen Flugzeit schon ein möglichst starkes Magnetfeld aufgebaut hat und seine besondere Wirkung entfalten kann, muß dieser bei herkömmlichen Elektromagneten besonders früh aktiviert werden, d.h. bevor sich der Anker vom haltenden Elektromagneten löst, wodurch unnötige Energie verbraucht wird und die Gefahr entsteht, daß sich der Anker bei zusätzlich hinzutretenden Einflüssen leichter von der Polfläche des haltenden Magneten löst. Daher ist es besonders vorteilhaft einen KLB-Magneten entsprechend dem erfindungsgemäßen Elektromagneten mit einem schnellen Kraftaufbau auszuführen. Energie wird eingespart und die Gefahr vermindert, daß sich der Anker ungewollt zu früh löst. Möglich ist auch weitere, dem Fachmann bekannte Konstruktionen zur Erhöhung der Kraft oder Beschleunigung des Kraftaufbaus mit dem erfindungsgemäßen Elektromagneten zu kombinieren, wie beispielsweise mit einem aus gegeneinander isolierten Blechen aufgebauten Spulenkern, wie oben beschrieben.So that a catching electromagnet, for example the opening magnet, acts as early as possible on the armature with as large a force as possible after it has detached itself from a previously holding electromagnet, the closing magnet, it is known as a so-called

characteristic-influenced electromagnet "(KLB magnet). The coil core of the KLB magnet preferably has a step in the area of the coil in the direction of the correspondingly shaped armature, as a result of which the armature enters the magnetic field of the catching KLB magnet earlier. The flight time of the armature The magnetic field of the capturing magnet is shorter than that of a flat coil core or flat pole face, so that the KLB magnet has built up as strong a magnetic field as possible after the short flight time and can exert its special effect with conventional electromagnets activated particularly early, ie before the armature detaches from the holding electromagnet, which consumes unnecessary energy and there is a risk that the armature will separate more easily from the pole face of the holding magnet if there are additional influences. Magnets according to the invention Execute electromagnets with a quick power build-up. Energy is saved and the risk of the anchor unintentionally loosening too early is reduced. It is also possible to combine further constructions known to the person skilled in the art to increase the force or acceleration of the force build-up with the electromagnet according to the invention, such as, for example, with a coil core constructed from mutually insulated sheets, as described above.

The electromagnet according to the invention can be used in addition to Actuators for gas exchange valves, preferably in all areas of application be used where possible faster strength building is required.

Further details of the invention and the resulting ones Advantages are the following description of exemplary embodiments refer to. In the description and in the Numerous features are presented in connection with claims and described. Those skilled in the art will find the features useful also consider individually and other useful ones Combine combinations.

Fig. 1

einen Ausschnitt eines Aktuators mit zwei Elektromagneten,

Fig. 2

einen Stromverlauf über der Zeit,

Fig. 3

einen Verlauf einer Magnetfeldstärke über der Zeit,

Fig. 4

einen Verlauf einer Permeabilitätszahl über der Feldstärke bei einem ferromagnetischen Stoff,

Fig. 5

drei Verläufe von Flußdichten von drei verschiedenen Materialien und

Fig. 6

eine Variante nach Fig. 5.

Show it:

Fig. 1

a section of an actuator with two electromagnets,

Fig. 2

a current curve over time,

Fig. 3

a course of a magnetic field strength over time,

Fig. 4

a profile of a permeability number over the field strength in the case of a ferromagnetic substance,

Fig. 5

three courses of flux densities from three different materials and

Fig. 6

a variant of FIG. 5th

Fig. 1 shows a section of an actuator 9, the one Opening magnet 22 and a closing magnet 23. The Electromagnets 22, 23 each have a coil 4, 12 that is surrounded by a coil core 5, 11. Will be on one of the coils 4, 12 a voltage is applied, the current I rises through the Self-induction delayed on (Fig. 2). Around the coil 4, 12 creates a magnetic field 20, 21, the field strength H corresponding the current intensity I rises with a delay (FIG. 3). The Magnetic field 20, 21 spreads from the coil 4, 12 in the coil core 5, 11, i.e. be in the coil core 5, 11 existing magnetic dipoles aligned in the field direction what is also referred to as diffusion.

The coil cores 5, 11 have different ferromagnetic materials 6, 7, 8, 13, 14, 15 in the diffusion direction 1, 2, 3, 17, 18, 19. Ferromagnetic materials have a permeability number µ _r that depends on the field strength H, and this rises first to a maximum value and then falls again (FIG. 4). Out of context B = µ r µ O H results from the fact that the flux density B of a certain field strength H _S, in which the relative permeability μ _r falls, at a saturation flux density B approaches _S (Fig. 5 and 6).

5 and 6, the flux density B is plotted against the field strength H for two different material combinations, in FIG. 5 for the closing magnet 23 and in FIG. 6 for the opening magnet 22. The further the material 6, 7, 8, 13, 14, 15 in the diffusion direction 1, 2, 3, 17, 18, 19 from the coil 5, 12, the greater its saturation flux density B _S6 , B _S7 , B _S8 , B _S13 , B _S14 , B _S15 , which is achieved in the diffusion direction 1, 2, 3, 17, 18, 19 at a higher field strength H _S6 , H _S7 , H _S8 , H _S13 , H _S14 , H _S15 . In the case of the closing magnet 23 in FIG. 5, the materials 6, 7, 8 in the diffusion direction 1, 2, 3 each have a greater increase in the flux density B in the case of small field strengths H, while the materials 13, 14, 15 of the opening magnet 22 have in the diffusion direction 17, 18, 19 with small field strengths H a smaller increase in the flux density B, a combination between the materials 13, 14, 15 of the opening magnet 22 and that of the closing magnet 23 being possible. A combination of materials in the direction of diffusion 1, 2, 3, 17, 18, 19 could be, for example, mild steel, structural steel and Armco iron.

The diffusion has a velocity v _D , which depends on the permeability µ and thus on the permeability number µ _r , namely: V D ≈ t σµ

The diffusion rate v _D is very large with a small permeability number and thus in the saturation range of a material. If the field strength H increases according to FIG. 3, the field strength H _S6 or H _S13 of materials 6 or 13 is reached early, still in the rise phase of H, and then that of materials 7, 8 or 14, 15. Already in In the rise phase of H, particularly high diffusion velocities V _{D are} achieved and thus a particularly rapid build-up of force.

In the opening direction 24, for example, with an exhaust valve a great deal of force is applied to the valve to open an exhaust gas pressure. The opening magnet 22 is for this preferably as a so-called characteristic-influenced magnet (KLB magnet), i.e. the opening magnet 22 has a stepped pole face 25 or is corresponding in the direction 16 of the molded anchor 10 executed stepped. This will be preferred achieved in that the coil 12 of core material 13 surrounded offset in the direction 16 of the armature 10 is. The opening magnet 22 thus acts with its magnetic field 21 earlier on from the closing magnet 23 in the opening direction 24 moving anchor 10. The flight time of anchor 10 from Closing magnet 23 into the effective range of the opening magnet 22 is therefore particularly short. The magnetic field 21 must can be built up quickly, so that a construction according to the invention of the coil core 11 with different materials 13, 14, 15 is particularly advantageous.

Claims (3)

Electromagnet with a coil and a coil core, which consists of at least two ferromagnetic materials, characterized in that in the direction of diffusion (1, 2, 3, 17, 18, 19) of the magnetic field (20, 21) of the coil (4, 12) Coil core (5, 11) has different materials (6, 7, 8, 13, 14, 15), the ones lying closer to the coil (4, 12) in the diffusion direction (1, 2, 3, 17, 18, 19) Materials (6, 13) have a lower saturation flux density B _S that can be achieved with a smaller field strength H _S than the materials (7, 8, 14, 15) that are further away from the coil (4, 12). Electromagnet according to claim 1, characterized by the Use with an actuator (9) with which a gas exchange valve an internal combustion engine is actuated via an armature (10). Electromagnet according to claim 1 or 2, characterized in that the coil core (11) in the direction (16) of the shaped anchor (10) is stepped. (KLB magnet)

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