EP0026695B1 - Electromagnet with mobile equipment having a permanent magnet, particularly for a contactor - Google Patents

Abstract

A moving system constituted by a permanent magnet and pole-pieces is accurately guided in axial translational motion within the coil unit of an electromagnet and enclosed within a coil form member, the axis of magnetization being perpendicular to the axis of the coil unit. Air-gap zones are located at both ends of the coil unit and a stationary yoke surrounds the two ends of the coil. Flat portions of the yoke which are parallel to the axis of magnetization each penetrate respectively into one air-gap zone so as to ensure that, at least in one stable position of the moving system, a flat portion of the yoke is in contact with one of the pole-pieces while the other flat portion is in contact with the other pole-piece. Better magnetic coupling between the coil, the air-gaps and the permanent magnet as well as higher operating efficiency are achieved.

Description

The present invention relates to an electromagnet with movable equipment with permanent magnet, in particular for contactor.

The known electromagnets of this center comprise a movable assembly consisting of a permanent magnet and two pole pieces conducting the flux fixed respectively to each pole face of said magnet perpendicular to the magnetization axis of the magnet. These pole pieces have arms projecting from the pole faces, and at least one of the pole pieces has arms whose ends are bent at right angles defining, with at least one arm of the other pole piece, two airgap zones cooperating with a cylinder head mounted on a coil which cooperates magnetically with the magnet. These airgap zones are arranged on either side of the supply axis, said magnetization axis of the magnet being perpendicular to that of the coil, the fisxed yoke surrounding the two ends of the coil and planar parts of the cylinder head parallel to the magnetization axis each penetrating respectively into an air gap area so that, for at least one stable position of the moving element, a planar part of the cylinder head is in contact with one of the pole pieces while the other flat part is in contact with the other pole piece.

In the foregoing, the cylinder head has been arbitrarily considered as carrying a fixed reference with respect to which the armature is movable. It goes without saying, however, that the movements of the cylinder head and of the armature seen in relation to other references may be different.

We know the advantages of introducing permanent magnets in the magnetic circuits of electromagnets: better efficiency, greater stroke, greater forces at the end of the stroke, possibility of bistable operation:

Some of these electromagnets are in rotary movement, others in translational movement. These are better suited for controlling contactors.

Known electromagnets of this kind have a certain number of drawbacks which limit their efficiency. Mainly, due to their arrangement, part of the flux of the coil closes in the air or by parasitic magnetic parts and is not used to counter the flux of the permanent magnet. Likewise, part of the flow of the permanent magnet closes in the air and is not used to cooperate with the flow of the coil.

Finally, in the case of a monostable operation, only part of the flow of the coil passes through the air gaps.

On the other hand, from a mechanical point of view, the guidance of the moving assembly is uncertain, which leads to incomplete or wedge air gap closings. It is also difficult, even at the cost of tight tolerances, to ensure the simultaneous closing of the air gaps.

Thus, in the electromagnet described in document FR-A-2,358.006, the parallelism and the nominal spacing of the plane parts of the cylinder head are dependent on the following tolerances: cambering angles in the cylinder heads, length of the core , crushing and perpendicularity of the crimps of the core on the cylinder heads, thickness of the cylinder heads. However, a correction of the bearing surfaces of the flat parts of the cylinder heads cannot be carried out when the coil is in place.

In addition, it is often asked in contactors that the coil can easily be changed. This operation is impossible in the electromagnet conforming to the aforementioned document.

The present invention aims to produce an electromagnet which, by eliminating the aforementioned drawbacks, provides improved magnetic coupling between the coil, the air gaps and the permanent magnet, and a higher efficiency.

This result is obtained, in accordance with the invention, by the fact that the moving assembly is located inside the coil and that guide means are provided to allow its translational movement along the axis of the coil so to form a plunger core. In addition, the core of the coil has a substantially rectangular section occupied by the magnet and the pole pieces; the airgap zones are arranged at the two ends of the coil, and the fixed cylinder head is parallel to the axis of the coil and situated outside the coil so as to magnetically join together the flat parts of the cylinder head .

Thanks to these characteristics, the entire flux of the coil is used to counter the flux of the permanent magnet. Conversely, the entire flux of the permanent magnet cooperates with the flux of the coil. In addition, the location of the plunger core makes it possible to ensure precise guidance in a simple manner.

According to a first embodiment of the invention, designed to obtain two stable positions in the absence of excitation of the coil, each pole piece forms two arms extending respectively on either side of the axis d magnetization. At least one pole piece has ends of its arms bent at right angles and the ends of one pole piece are cambered beyond the arms of the other pole piece relative to the magnetization axis.

The first pole piece envelops the second and its cambered ends are outside the cylinder head, while the ends of the second are inside the cylinder head. The first pole piece, in one position, touches a flat part of the cylinder head, while the other pole piece touches the other flat part of the cylinder head. In the other position, the roles of the flat parts of the cylinder head are reversed with respect to the pole pieces, and there are thus two stable positions.

According to a second embodiment of the invention, designed to obtain a single stable position in the absence of excitation of the coil, a first pole piece forms a single arm extending on a first side of the axis d magnetization, while the other pole piece has, on the first side of the magnetization axis, an arm the end of which is arched at right angles beyond said single arm of the first pole piece with respect to the magnetization axis, and, on the second side of the magnetization axis, two magnetically joined arms, the ends of which are respectively bent at right angles one beyond the other with respect to the axis of magnetization.

In a first position, which is only stable, the magnetic circuit is closed by the single arm of the first pole piece and by the other pole piece. In the other position, the first pole piece remains off and this position is not stable.

According to an advantageous embodiment of the invention, the cylinder head comprises two U-shaped half-cylinder heads, which fit together in an adjustable manner so as to be able to adjust the spacing between the flat parts of the half-cylinder heads.

While retaining great simplicity of manufacture, it is thus possible to ensure that the magnetic circuit on the two pole pieces is simultaneously closed.

The movable assembly is preferably provided with a guide rod arranged along the axis of the coil, and sliding in bearings fixed on stirrups which are fixed respectively on each half-cylinder head.

Thanks to guidance: precise, the risks of incomplete or corner closing of the magnetic circuit are practically eliminated.

In a particular embodiment of the invention, the moving assembly comprises two magnets with parallel axes, between which the guide rod passes, and the magnets are immobilized by plates arranged perpendicular to the guide rod and comprising tongues crimped in holes or slots in the pole pieces.

According to an alternative embodiment of the invention, a compression coil spring is disposed on the guide rod, between; on the one hand, the body of the movable assembly and, on the other hand, a washer applied by said spring against a shoulder of the guide rod, a fixed stop cooperating with said washer being provided to define the point of the stroke of the moving part where the spring begins its return action.

In this embodiment, one of the pole pieces can have its arms arched opposite the axis of the coil, said. coil then comprising a winding produced on a frame formed by two separable half-frames before winding.

Alternatively, one of the pole pieces can have its arms arched, one towards the axis of the coil and the other in the opposite direction, the coil then comprising a monobloc frame.

According to an alternative embodiment of. the invention, the breech is in a U to at least partially wrap the ends of the coil, the pole piece furthest from the breech having its arms arched towards the breech to at least partially wrap the branches of the U of the cylinder head, and the other pole piece being straight.

Other features and advantages of the invention will emerge from the detailed description which follows.

• ― la: figure 1 est une vue en coupe verticale suivant I―I de la figure 2 de l'électro-aimant suivant l'invention, dans un mode de réalisation en fonctionnement bistable;
• ― la figure 2 est une vue en coupe suivant: II―II de la figure 1;
• ― la figure 3 est une vue analogue à la figure 1, mais dans une mode de réalisation en fonctionnement monostable;
• - les figures 4 et 5 sont des vues. analogues à la figure 1, dans une variante de disposition des pièces polaires, avec l'adjonction d'un ressort de rappel; et
• ― la figure 6 est une vue analogue dans une variante de réalisation faisant intervenir une culasse en U.

In the appended drawings, given by way of nonlimiting examples:

• - The: Figure 1 is a vertical sectional view along I ― I of Figure 2 of the electromagnet according to the invention, in one embodiment in bistable operation;
• - Figure 2 is a sectional view along: II ― II of Figure 1;
• - Figure 3 is a view similar to Figure 1, but in one embodiment in monostable operation;
• - Figures 4 and 5 are views. analogous to FIG. 1, in a variant arrangement of the pole pieces, with the addition of a return spring; and
• - Figure 6 is a similar view in an alternative embodiment involving a U-shaped cylinder head.

Referring to Figures 1 and 2, the electromagnet comprises a coil 1 with its coil 2 wound along the axis 3 of the coil. A fixed yoke 4 surrounds the coil going from one end of the core of the coil to the other end of this core. In practice, this cylinder head comprises two half-cylinder heads: 4a, 4b in the shape of a U, fitting one into the other along the axis 3 of the coil. and held together by screws 5. Elongated holes 5a made in one of the half-cookers allow this interlocking to be adjusted.

Inside the core of the coil is a plunger core capable of moving in translation along the axis 3 of the coil. This plunger core is constituted by a movable assembly which comprises, on the one hand, a permanent magnet 6 arranged so that its magnetization axis 7 is perpendicular to the axis 3 of the coil and on the other hand two pole pieces flux conductors 8 and 9, fixed respectively to each pole face, N, S of the magnet 6, perpendicular to its magnetization axis 7. Each pole piece 8, 9 has two arms 10a, 10b and respectively 11a, 11b projecting of the polar faces N, S of the magnet 6.

In the example described, the magnet 6 consists of two magnets 6a, 6b with axes 7a, 7b for purely constructive reasons. In what follows, all of these two magnets will generally be designated by the reference 6 for convenience.

The arms of the pole pieces are bent at right angles to the axis 3 of the coil, by determining parallel ends 12a, 12b and respectively 13a, 13b. More precisely, the ends 12a, 12b of the pole piece 8 are located respectively beyond the ends 13a, 13b of the pole piece 9 with respect to the magnetization axis 7.

In this way two air gap zones are defined, located respectively between the parallel ends 12a ― 13a on the one hand, and 12b-13b on the other hand. These airgap zones are arranged at the two ends of the coil 1, on either side of the magnetization axis 7.

On the other hand, flat parts 14a ― 14b of the yokes 4a, 4b, parallel to the magnetization axis 7, each penetrate respectively into an air gap area. The poinary pieces 8, 9 are fixed to the magnet 6 by plates 15 perpendicular to the axis 3 of the coil, and having tongues 16 crimped in slots of the pole pieces.

A guide rod 17 is made integral with the movable assembly and is guided along the axis 3 of the coil by bearings 18 fixed on stirrups 19, themselves fixed on each half-yoke 4a ― 4b by screws.

The guide rod 17 passes between the magnets 6a, 6b (FIG. 2) and passes right through the mobile assembly while being fixed to the latter by nuts 20 (FIG. 1).

The core of the coil 1 has a substantially rectangular section (Figure 2), almost filled with magnets and pole pieces.

The operation of this electromagnet is as follows

When the movable assembly (shown in the intermediate position in FIG. 1) occupies its extreme low position, the flow leaving the permanent magnet 6 via the pole face N passes through the pole piece 8, the arm 10a, the arched end 12a and the flat part 14a of the cylinder head 4a. From there, through the U-shaped arms of the half-cylinder heads, 4a, 4b, it passes to the flat part 14b of the cylinder head 4b, to the cambered end 13b, to the pole piece 9 and to the pole face S of the magnet 6.

The closed air gaps 12a-14a and 13b-14b give forces in the same direction which keep the moving element in its extreme low position.

If the coil is excited in a direction creating a flow opposite to the previous one, the previous forces are canceled and attractive forces appear between the air gaps 13a-14a and 12b-14b, bringing the moving assembly into its extreme high position.

We therefore have a bistable operation, but without using a restoring force and with better efficiency.

Of course, to avoid shunting the air gap 12a-14a, it is necessary to provide in the cylinder head 4a an opening 21a sufficient around the arm 10a. Likewise for the arm 10b with the opening 21b. These openings also facilitate the assembly of the half-cylinder heads on the coil fitted with its plunger core.

Furthermore, it is necessary to obtain simultaneous and complete closure of the air gaps for each extreme position, so as not to see a considerable reduction in the performance of the electromagnet.

As all the airgap surfaces are parallel to each other and the translational movement of the mobile assembly is well guided, the closings at the corner of the airgaps are avoided.

When assembling the mobile assembly, it is easy to obtain identical distances between the arched ends 12a-13a and 12b-13b respectively.

To obtain complete closure of the air gaps, it then suffices to adjust the distance between the flat parts 14a and 14b of the cylinder heads, by adjusting, for example, the interlocking of the half-cylinder heads. This can be done simply by blocking the screws 5 only when the electromagnet is energized.

We will now describe, with reference to FIG. 3, an alternative embodiment of the invention intended to provide monostable operation.

In this figure, the elements identical or analogous to those of the embodiment described above bear the same reference number increased by 100. Unless otherwise stated, only the new or different elements will be described.

The pole piece 109 here has only one arm 111a, arched at 113a. On the other hand, parallel to the arm 11 Ob of the pole piece 8, another arm 110c has been added magnetically joined to the arm 110b and having an end 112c bent at a right angle so as to be in the plane which the end previously occupied. 13b of the arm 11b in the embodiment of FIG. 1. It follows from this arrangement that, in the high position of the moving assembly, there is nothing changed - compared to the previous case On the contrary, in the position low, the magnetic circuit cannot be closed by the pole piece 109, which does not have a lower arm to cooperate with the flat part 114b, so that the flat parts 114a and 114b of the half-yokes 104a and 104b are magnetically directly joined by the pole piece 108 and its arms and arched ends, without passing through the permanent magnet 106. Under the effect of the reaction of a controlled mechanical load, or under the effect of a return spring, the mobile team will therefore return to its ha position after the excitation of the coil has been cut off. The operation of the electromagnet has therefore become monostable.

We will now describe, with reference to FIG. 4, another embodiment of the invention. In this embodiment, the elements identical or similar to those of the preceding embodiments have been given the same reference number ence with the number 2 as the number of the contests. The description that follows will focus on the differences.

The pole piece 209 is rectilinear and has no arched ends, the surface of the air gaps being given directly by the edge (or cross section) of the arms 211 a and 211 b. The decrease in the airgap area gives a greater slope to the force curve as a function of the stroke, which may be acceptable or desirable in. certain cases.

On the other hand, the ends. curved 212a and 212b of the pole piece 208 are curved outward with respect to the axis 203 of the coil. It follows that the forces are generated further from the axis 203, but the corresponding torque can be collected by the guide rod 217. On the other hand these outward curvatures require for the assembly to realize the framework of the coil 201 into two separable parts before winding.

The air gap 12a-14a of FIG. 1 is now replaced by an air gap 212a-214a, the flat part 214a of the half-yoke 204a being at the same level as the flat part 14a of FIG. 1.

The notion of air gap zone therefore remains valid if these zones are defined with reference to the magnetization axis 7 or 207.

This arrangement limits the leakage flow between the pole pieces 208 and 209 and it facilitates the installation of a return spring.

A coil spring 222 is disposed on one end of the guide rod 217. This spring is compressed between the plate 215a and a washer 223, itself abutting on an elastic ring 224 inserted in a groove of the rods guide 217. Another elastic ring 225 can replace the nut 20 of FIG. 1. On the other hand, the bearing 218a can be screwed more or less deeply on the stirrup 219a and locked by a nut 226. A shoulder 227 of the bearing 218a serves as a fixed stop for the washer 223, in. the movement of the latter towards. the corresponding end of the race. It can therefore be seen that the moment of travel can be adjusted when the spring 222 exerts its restoring force on the moving assembly.

With these differences, the operation is substantially the same as for the embodiment of FIG. 1.

The last embodiment described can be performed: in a monostable version (Figure 5). In this version, the pole piece 309 has only one arm. 311a, and la. pole piece 308 has a third arm 310c magnetically joined to the arm 310b. These provisions are similar to those shown in Figure 3 and provide monostable operation according to the operating explanations given in connection with this figure.

The curvature 312a of the pole piece 308 is still directed towards the outside, but the curvature 312b is directed towards the inside as well as the arm 310c. This arrangement facilitates mounting and allows the use of a one-piece coil frame.

We will now describe, with reference to FIG. 6, a simplified variant embodiment of the invention. In this variant, the cylinder head 404- comprises a single U-shaped part which at least partially envelops the ends of the coil 401, the ends of the branches of the U constituting flat parts 4.14a, 4-14b.

The moving equipment is analogous to. that shown in Figure 3, with this difference quie, if the pole piece 408 has arms 410a, 410b, arched at 412a, 412b so as to wrap the branches 414a; 414b of the U of the cylinder head, the pole piece 409 is rectilinear as in the case of FIG. 4 and only works by the song of the arms 411 a, 411 b.

The clearance between the moving part and the reel is expected to be very small, so that it is the framework of the reel which serves as a guide for this crew.

Elastic blades. 430 of non-magnetic material are attached to the cylinder head to play a role. reminder.

In. this embodiment, the electromagnet is bistable. We could make it monostable by the modifications exposed above.

Thanks to the progress made by the invention in the field of magnetic coupling, it has been possible to obtain a remarkable improvement in efficiency. Thus, with an iron section of 25 mm 2 and a magnet thickness of 2 mm, a displacement of 4 mm can be obtained with forces at the end of the stroke. the order of 10 Newton; using only a power on the order of one watt.

We find the advantages of magnetic circuits with a magnetless plunger. permanent, in particular as regards the magnetic coupling between the coil and the air gaps, as well as for guiding the moving element.

Of course, the invention is not limited to the examples described but covers everything. technological variant within the reach of ordinary skill in the art.

Claims (10)

1. An electromagnet especially for a contactor and comprising a moving system movable by translation and constituted by at least one permanent magnet (6, 106, 206, 306, 406) and two flux-conducting pole-pieces (8, 9; 108, 109; 208, 209; 308, 309; 408, 409) secured respectively to each pole face of said magnet at right angles to the axis of magnetization (7, 107, 207, 307, 407) of the magnet, said pole-pieces being provided with arms (10a, 10b, 11a, 11b; 110a, 110b, 110c; 111a; 210a, 210b, 211a, 211b; 310a, 310b, 310c, 311a; 410a, 410b, 411a, 411b) which project from the pole faces, at least one of the pole-pieces being provided with arms whose ends (12a, 12b, 13a, 13b; 112a, 112b, 112c, 113a; 212a, 212b; 312a, 312b, 310c; 412a, 412b) are bent at right angles so as to define two air-gap zones with at least one arm of the other pole-piece, said air-gap zones being adapted to cooperate with a yoke (4,104, 204, 304, 404) mounted on a coil unit (1, 101, 201, 301, 401) which cooperates magnetically with the magnet, said. air-gap zones being located on each side of the magnetization axis, said axis of magnetization being perpendicular to that (3, 103, 203, 303, 403) of the coil unit the stationary yoke surrounding the two ends of the coil unit, while flat portions (14a, 14b; 114a, 114b; 214a, 214b; 314a, 314b; 414a, 414b) of the yoke, which are parallel to the axis of magnetization, each penetrate respectively into one air-gap zone so that, in at least one stable position of the moving system, one flat portion of the yoke is in contact with one of the pole-pieces whilst the.other flat portion is in contact with the other pole-piece, characterized in that said moving system is placed within the interior of the coil unit (1,101, 201, 301, 401), guiding means being provided so as to permit translational displacement of said system along the axis (3, 103, 203, 303, 403) of the coil unit in such a manner as to constitute a sliding armature, in that the space inside the coil unit has a substantially rectangular cross-section occupied by the magnet (6, 106, 206, 306, 406) and the pole-pieces (8, 9, 108, 109, 208, 209, 308, 309, 408, 409), in that the air-gap zones are located at the two ends of the coil unit, and in that the stationary yoke (4, 104, 204, 304, 404) is parallel to the axis of the coil unit such as to magnetically connect together the flat portions (14a, 14b; 114a, 114b; 214a, 214b; 314a, 314b; 414a, 414b).

2. An electromagnet according to claim 1 and having two stable positions when the coil is not energized, characterized in that each pole-piece (8, 9; 208, 209; 408, 409) forms two arms (10a, 10b; 210a, 210b, 410a, 410b and respectively 11a, 11b; 211a, 211b; 411a, 411 b) extending respectively on each side of the axis of magnetization (7, 207, 407), in that the arms (10a, 10b; 210a, 210b; 410a, 410b) of at least one pole piece (8; 208; 408) has end portions (12a, 12b; 212a, 212b; 412a, 412b) which are bent at right angles and in that said end portions are bent beyond the arms of the other pole-piece (9, 209, 409) with respect to the axis of magnetization.

3. An electromagnet according to claim 1 and having a single stable position when the coil is not energized, characterized in that a first pole-piece (109; 309) forms a single arm (111 a; 311 a) extending on a first side of the axis of magnetization (107, 307) whilst the other pole-piece (108; 308) is provided on the first side of the axis of magnetization with an arm (110a, 310a) whose end portion (112a; 312a) is bent at right angle beyond said single arm (111a, 311a) of the first pole-piece (109; 309) with respect to the axis of magnetization and is provided on the second side of the axis of magnetization with two magnetically coupled arms (110b, 110c; 310b, 310c) whose end portions (112b, 112c; 312b, 312c) are respectively bent at right angles and one (112b; 312b) beyond the other (112c, 310c) with respect to the axis of magnetization.

4. An electromagnet according to claim 2 or claim 3, characterized in that the yoke (4; 104; 204; 304) comprises two U-shaped half-yokes (4a, 4b; 104a, 104b; 204a, 204b; 304a, 304b) which can be adjustably interengaged so as to permit adjustment of the spacing between the flat portions (14a, 14b; 114a, 114b; 214a, 214b; 314a, 314b) of said half-yokes.

5. An electromagnet according to claim 4, characterized in that the moving system is provided with a guide rod (17; 117; 217; 317) placed along the axis of the coil unit and slidably mounted in bearings (18; 118; 218; 318) secured on stirrups (19, 119, 219, 319) which are secured respectively on each half-yoke.

6. An electromagnet according to claim 5, characterized in that the moving system comprises two magnets (6a, 6b) having parallel axes between which the guide rod (17) passes and in that the magnets (6a, 6b) are locked in position by means of plates (15) located at right angles to the guide rod (17) and provided with tongues (16) force-fitted in holes or slots of the pole-pieces (8, 9).

7. An electromagnet according to claim 5 or claim 6, characterized in that a helical compression spring (222) is placed on the guide rod (217) between on the one hand the body of the moving system and on the other hand a washer (223) applied by said spring (222) against an annular shoulder (224) of the guide rod (217), a stationary stop (227) cooperating with said washer (223) and being adapted to define the point of the travel of the moving system at which the spring begins its restoring action.

8. An electromagnet according to claim 7, characterized in that the arms (210a, 210b) of one (208) of the pole-pieces are bent away from the axis (203) of the coil unit, said unit comprising a winding formed on a frame consisting of two half-frames which are separable prior to winding.

9. An electromagnet according to claim 7, characterized in that one arm (31Ob) of one (308) of the pole-pieces is bent towards the axis (303) of the coil unit (301) whilst the other arm (310a) is bent in the contrary direction, said coil unit (301) comprising a one-piece frame.

10. An electromagnet according to claim 2 or claim 3, characterized in that the yoke (404) has the shape of a U so as to embrace the ends of the coil unit (401) at least to a partial extent, the arms (410a, 410b) of the pole-piece (408) which is located at the greatest distance from the yoke being bent towards yoke (404) in order to embrace the branches (414a, 414b) of the U of the yoke at least to a partial extent whilst the other pole-piece (409) is rectilinear.

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