EP2406805B1 - Electromagnetic actuator with permanent magnet - Google Patents

Description

The present invention relates to a permanent magnet electromagnetic actuator conventionally comprising a magnetic armature, a movable pallet, a spring mechanism and electrical means comprising at least one conductor whose current makes it possible to vary the flux in the magnetic circuit in order to modify the balance between the magnetic force and that of the spring. The document WO 03/017308A discloses an electromagnetic actuator according to the preamble of claim 1.

The object of the invention is to provide an actuator with very high sensitivity, that is to say operating with a minimum value of ampere-turns generating however at least one gap a flow variation sufficient to counterbalance the mechanical force and cause the movement of a pallet.

The idea underlying the invention is to work on a flow bypass scheme, the change of the flux at the gap or air gaps being obtained indirectly because of a configuration of the magnetic circuit in which occurs an imbalance of the magnetic reluctances seen by the magnet. In this case, the conductor or conductors capable of generating flow by passage of the current which runs through (s) cooperates (s) with a frame which is closed, and therefore has no gap but at least a reluctance of balanced. On the other hand, the flow produced has an effect aimed at unbalancing said reluctances seen by the magnet, which rebalances the system and makes it possible to break - at the level of the gaps concerned by the flow variations - the equilibrium with the mechanical restoring forces.

For this purpose, the actuator of the invention, more precisely comprising a permanent magnet, a ferromagnetic armature, a pallet creating at least one gap with the armature and movable between at least one open position and one closed position, mechanical means for returning the pallet in the open position and at least one electrical conductor capable of generating a magnetic flux in the armature, is essential in that the armature forms a closed magnetic loop in which the conductor or conductors are capable of generating a magnetic flux, the magnet being disposed in the moving vane and generating flux in two parallel magnetic circuits, one of which comprises a portion of the armature and the other formed in the pallet, has a cap saturable zone by the magnet or an air zone.

The principle of the structure of the invention consists in generating a strong variation of flux on the polar surface or surfaces of the pallet with a minimum of ampere-turns, thanks to the modification of the balance of the reluctances obtained in the set of said circuit.

According to one possible configuration, the pallet comprises two air gaps.

More precisely, the pallet may be U-shaped whose legs are connected by the magnet. In this configuration, one of the two magnetic circuits in parallel is constituted by the magnet, two portions of the legs and the base of the U. The saturable plug area is then preferably located in said base of the U.

The second circuit in parallel is then constituted, besides the magnet, by the remaining portions of the jambs, the gaps, and the section of the armature connecting the polar surfaces forming the air gaps with the pallet.

Alternatively the pallet may be U-shaped whose legs are placed on either side of the central branch comprising the magnet, their free ends forming two air gaps with a portion of the closed loop of the frame.

According to the invention, the closed magnetic loop may either comprise a coil wound around a portion of the closed loop of the armature separate from the parallel magnetic circuits, or surround at least two power supply conductors of an electrical circuit.

The closed loop of the frame can obviously take various forms, for example rectangular, circular shape, etc.

According to one possibility, a conductor is wound around a portion of the frame. It is then created, in case of passage of a current in the coil, a magnetic flux in the armature, and consequently in the section of the latter which is part of the second magnetic circuit supplied with flux by the magnet in parallel with the base of the U.

The variation of the resulting reluctance in this portion of the second circuit causes an imbalance in the two branches of reluctances seen by the magnet, which it compensates by varying the flow in the first circuit in parallel, thereby breaking the balance with the mechanical forces of recall.

According to one variant, at least two conductive wires pass through the central window of the armature.

• La figure 1 représente schématiquement une première forme possible d'actionneur pour l'invention, avec une bobine entourant une portion de l'armature ; et
• La figure 2 montre le schéma électromagnétique équivalent à la structure de la figure 1.

The invention will now be described in more detail, with reference to examples illustrated by the appended figures, for which:

• The figure 1 schematically represents a first possible form of actuator for the invention, with a coil surrounding a portion of the armature; and
• The figure 2 shows the electromagnetic pattern equivalent to the structure of the figure 1 .

With reference to the figure 1 , the armature (1) forms a loop surmounted by the two lateral jambs (3, 4) of the U constituting the pallet (2). A permanent magnet (5) joins these two legs (3, 4). The buckle of the frame (1) is provided with a coil (6) surrounding one of its branches. The base of the pallet (2) has a cap area (7) saturable by the magnet (5).

Magnetic operation is explained in figure 2 . Without electrical fault, the magnet globally sees two branches of magnetic reluctance in parallel.

It first saturates the reluctance Rshunt_pal so that the following inequality is true: $$\mathit{Rshunt\_pal}\left(\mathit{phi}\mathit{1}\right)+\mathit{Rpal\_haut}\mathit{1}\left(\mathit{phi}\mathit{1}\right)+\mathit{Rpal\_haut}\mathit{2}\left(\mathit{phi}\mathit{1}\right)>\mathit{Rent}\mathit{1}+\mathit{Rent}\mathit{2}+\mathit{Rpal\_bas}\mathit{1}\left(\mathit{phi}\mathit{2}\right)+\mathit{Rpal\_bas}\mathit{2}\left(\mathit{phi}\mathit{2}\right)+\mathrm{R}\mathit{1}\left(\mathit{phi}\mathit{2}\right)$$

avec phi1+phi2 = flux généré par l'aimant (aux fuites magnétiques près).It then generates in each branch a magnetic flux such as: $$\mathit{Rshunt\_pal}\left(\mathit{phi}\mathit{1}\right)*\mathit{phi}\mathit{1}+\mathit{Rpal\_haut}\mathit{1}\left(\mathit{phi}\mathit{1}\right)*\mathit{phi}\mathit{1}+\mathit{Rpal\_haut}\mathit{2}\left(\mathit{phi}\mathit{1}\right)*\mathit{phi}\mathit{1}=\mathit{Rent}\mathit{1}*\mathit{phi}\mathit{2}+\mathit{Rent}\mathit{2}*\mathit{phi}\mathit{2}+\mathit{Rpal\_bas}\mathit{1}\left(\mathit{phi}\mathit{2}\right)*\mathit{phi}\mathit{2}+\mathit{Rpal\_bas}\mathit{2}\left(\mathit{phi}\mathit{2}\right)*\mathit{phi}\mathit{2}+\mathrm{R}\mathit{1}\left(\mathit{phi}\mathit{2}\right)*\mathit{phi}\mathit{2}$$

with phi1 + phi2 = flux generated by the magnet (near magnetic leakage).

Material reluctances like Rpal, R1 and R2 are nonlinear and saturable

The Rmat_gauche and Rmat_droit reluctances can represent a gap and / or a saturable magnetic material.

The Rent1 and Rent2 reluctances represent the equivalent gap between the pallet and the armature.

When an electrical fault appears, the coil generates a magnetic flux in the branch Rbas, R1 and R2. This has the effect of increasing the value of R1 and R2. This is valid regardless of the direction of the current but the value of ampere-turns required depends on the direction of the current.

The flux of the coil therefore tends to increase R1 (phi) * phi and increase R2 (phi) * phi. Seen from the magnet, the previous balance is modified. The magnet then generates more magnetic flux in the circuit containing the base of the U (Rshunt_pal (phi1) * phi1 + RpaI_haut1 (phi1) * phi1 + Rpal_haut2 (phi1) * phi1) than in the other circuit in parallel. Phi1 increases and Phi2 decreases, resulting in a variation of flux and therefore of magnetic force, with an immediate consequence on the equilibrium with the mechanical forces of the actuator, which is broken: the actuator changes state.

This solution is very advantageous insofar as, with little magnetic flux generated by the coil, it is possible to create a large flow variation on the pallet.

As already mentioned with reference to the values of the Rmat_gauche and Rmat_droit reluctances, the magnet may be fixed to the pallet but may also not be, without changing the intrinsic equilibrium of the magnetic circuit.

Many other configurations than the one represented in figure 1 are possible, the example as illustrated can not be considered exhaustive of the invention. Thus, the respective shapes of the armature and its inner window may vary, as long as the constraint of the closed magnetic circuit is respected. Similarly, the pallet is not necessarily right U, since the magnet is arranged according to the features previously highlighted.

Claims (6)

1. An electromagnetic actuator with flux bypass, comprising a permanent magnet (5), a ferromagnetic armature (1), a vane (2) which defines at least one air gap with the armature (1) and which can move between an open position and a closed position, mechanical return means for returning the vane (2) to the open position, and at least one electric conductor capable of generating a magnetic flux in the armature (1), characterized in that the armature (1) forms a closed magnetic loop in which the conductor(s) are capable of generating a magnetic flux, the magnet being positioned in the mobile vane (2) and generating fluxes in two magnetic circuits in parallel, one of which comprises a portion of the armature (1), while the other is formed in the vane (2) and comprises a plug area (7) that can be saturated by the magnet (5) or an air zone.
2. The electromagnetic actuator according to the preceding claims, characterized in that the vane (2) comprises two air gaps.
3. The electromagnetic actuator according to the preceding claim, characterized in that the vane (2) is in the shape of a U, the legs of which (3, 4) are connected by the magnet (5).
4. The electromagnetic actuator according to the preceding claim, characterized in that the plug area (7) able to be saturated is positioned in the base of the U.
5. The electromagnetic actuator according to any one of the preceding claims, characterized in that a conductor (6) is wound around a portion of the armature (1).
6. The electromagnetic actuator according to any one of claims 1 to 3, characterized in that at least two conductive wires pass through the central window of the armature (1).

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