EP0146421A1 - Electromagnet with yokes and an armature having a permanent magnet with pole pieces at its pole faces protecting beyond the magnet axis, this axis being perpendicular to the direcion of movement - Google Patents

Abstract

The electromagnet comprises yokes (31, 32a) movable relative to an armature (21a) and a coil (25) surrounding a part of the magnetic circuit, this armature (21a) comprising a magnet (22a) provided with two parts poles (23a, 24a) projecting on either side of this magnet, at least one (24a) of said pole pieces having ends bent at right angles to define air gaps generating opposing forces in a direction perpendicular to the axis of the the permanent magnet (22a). A second frame (21b) identical to the first (21a) is arranged parallel and facing the first. Two yokes (31; 32a, 32b) join the airgap zones of the two armatures located opposite one another so that the magnetic circuit consists of a succession of armature and yoke forming a rectangle. Two coils (25, 28) are arranged on the opposite sides of the above-mentioned rectangle. Use in particular for producing electromagnets of low inertia, of small size and with low leakage flux.

Description

The present invention relates to an electromagnet comprising yokes and a frame comprising a permanent magnet provided, on its polar faces, with pole pieces projecting from the axis of the magnet, the relative movement of the armature relative to the yokes having a direction perpendicular to the axis of the permanent magnet of the armature.

According to French patent 2,358,006, an electromagnet whose structure meets the above definition is known, at least one of the pole pieces of the frame having cambered ends.

French Patent 2,466,844 to the Applicant describes an electromagnet modified with respect to that described in French Patent 2,358,006 in the sense that the armature is placed in the coil.

French patents 2,520,152 and European patent 0 086 121 of the Applicant describe electromagnets perfected compared to that described in French patent 2 466 844 to allow the electromagnet to operate in a monostable manner, possibly by permuting the mobile and fixed parts.

On the other hand, according to the German patent 2,407,184 and the French patent 2,486,303, there is known an electromagnet having two coils located one next to the other and the four ends of which are connected in pairs by two armatures. H-shaped. However, unlike the electromagnets used previously, these armatures are not movable in a translational movement, but in a rotational movement.

The electromagnet described in French Patent 2,388,386 also includes two coils located one next to the other, the four ends of which are connected in pairs by two armatures. These frames are movable in translation along the axis of the magnet.

In addition, we know according to interna demand PCT patent WO 82/03 944 an electromagnet modified compared to that described in French patent 2 358 006 in the sense that the fixed and movable parts thereof are reversed and that a second assembly consisting of a magnet and pole pieces is added symmetrically, which after the aforementioned inversion also becomes fixed.

The electromagnet described in French patent 2,520,152 has the drawback of generating flow losses through the leakage flow between the armature and the cylinder head. These flux losses can be demonstrated by means of a spectrum obtained by CAD, when the electromagnet is excited and is at the start of movement.

Furthermore, the yokes of this electromagnet being bent, their ends must be strictly parallel and precisely positioned to obtain the simultaneous closing of the air gaps, which requires costly manufacturing precautions.

On the other hand, in certain cases, the mass of the armature can give the electromagnet insufficient resistance to shocks and due to the inertia, a long operating time, especially when the electromagnet is used. to control the opening of a short-circuit current limiting circuit breaker.

Also in the case of replacing an existing conventional electromagnet, with a low height in the direction of its movement, the current _structures' often lead to implementation difficulties.

In addition, the coils of these electromagnets are not easily removable to allow maintenance or change of nominal voltage of the electromagnet.

The object of the present invention is to remedy the drawbacks of known electromagnets.

The electromagnet targeted by the invention comprises yokes, a frame, movable relative to each other and a coil surrounding part of the magnetic circuit, said armature comprising a permanent magnet provided on its two polar faces with two pole pieces projecting on either side of the axis of this permanent magnet, at least one of said pole pieces having cambered ends to define with the other pole piece two airgap zones into which the ends of the yokes penetrate so that each airgap zone has two airgaps generating opposing forces in a direction perpendicular to the axis of the permanent magnet.

According to the invention, this electromagnet is characterized in that a second frame of the same shape as the first is arranged in parallel and facing the first, in that two cylinder heads join the airgap zones of the two frames located in look at each other so that the magnetic circuit consists of a succession of armature and yoke.

This arrangement allows direct and short connections between the air gap zones facing each other which considerably limit the magnetic flux of leakage.

According to one embodiment of the invention, the succession of armature and cylinder head forms at least one rectangle and two coils are arranged on opposite sides of said rectangle.

According to an advantageous version of the invention, the coils are arranged around the frames.

Thus the electromagnet has in the direction of movement, a space equal to that of an electromagnet having only one coil.

According to another embodiment, two magnetic circuits in the shape of a rectangle are joined to have a common branch around which a coil is arranged. According to a feature of this embodiment, the electromagnet has an axial symmetry in the direction of movement. According to another characteristic of the preceding embodiments, the reinforcements are curved so that the rectangular path of the flow becomes a circular path.

According to a particular embodiment of the invention, a permanent magnet is interposed between the ends of at least one of the cylinder heads so as to obtain a monostable operation.

The addition of this magnet therefore makes it possible to obtain in a simple manner a monostable operation for the electromagnet.

Other features and advantages of the invention will appear in the description below.

• - la figure 1 est une vue en coupe longitudinale d'une première version d'un électro-aimant conforme à l'invention,
• - la figure 2 est une vue en coupe longitudinale d'une seconde version d'un électro-aimant conforme à l'invention,
• - la figure 3 est une vue en coupe longitudinale d'une troisième version d'un électro-aimant conforme à l'invention,
• - la figure 4 est une vue en coupe d'une quatrième version ; et
• - la figure 5 celle d'une cinquième version.

In the appended drawings given by way of nonlimiting examples,

• FIG. 1 is a view in longitudinal section of a first version of an electromagnet according to the invention,
• FIG. 2 is a view in longitudinal section of a second version of an electromagnet according to the invention,
• FIG. 3 is a view in longitudinal section of a third version of an electromagnet according to the invention,
• - Figure 4 is a sectional view of a fourth version; and
• - Figure 5 that of a fifth version.

In the embodiment of FIG. 1, the bistable operating electromagnet comprises fixed yokes 11,12, a mobile assembly comprising an armature 1a, of section substantially in the shape of an H, mobile relative to the yokes 11, 12 and a coil 5 surrounding part of the magnetic circuit.

The frame 1a comprises a permanent magnet 2a, provided on its two polar faces with two pole pieces 3a, 4a, which project on either side of the axis of the magnet 2a.

One 4a of the pole pieces has its ends arched relative to the axis of the magnet 2a, to define with the other pole piece 3a, two airgap zones into which penetrates Trent the ends 13a, 14a of the yokes 11, 12. Thus each area of air gap comprises two air gaps generating antagonists _the forces F, F _{2a 'in} a direction perpendicular to the axis of the permanent magnet 2a.

The bending at right angles to the ends of the pole piece 4a makes it possible to have parallel forces for the two airgap zones.

It can be seen in FIG. 1 that the mobile assembly also includes a second frame 1b made up of homologous elements 2b, 3b, 4b. This frame 1b has the same shape as the first 1a and is arranged parallel and facing the first. In addition, the ends 13a, 13b; 14a, 14b of the two yokes 11, 12 join the airgap zones of the two frames 1a, 1b located opposite one another.

Thus, the magnetic circuit of the electromagnet consists of a succession of armature and yoke forming a rectangle.

Furthermore, a second coil 8 is arranged parallel to the first coil 5.

In the embodiment shown in Figure 1, the coils 5, 8 are arranged respectively around the yokes 11, 12 which form two opposite sides of the above rectangle defined by the magnetic circuit.

Furthermore, these coils 5, 8 each comprise a plastic carcass 6, 9 which can be molded around the yokes 11, 12 which act as a core for the corresponding coil 5, 8.

On the side faces 6a, 6b; 9a, 9b of the plastic casings 6, 9 are plated with plates 15a, 15b of metal or non-magnetic alloy such as brass, which serve to space the curved ends at right angles to the pole pieces 4a, 4b of the carcasses of the coils and guiding the movement of the magnetic plates 1a, 1b in the direction of the arrows F _1a , F _2a ; F _1b , F _2b is- i.e. perpendicular to the axis of the coils 5 and 8.

• lorsque les bobines 5 et 8 sont excitées dans le sens H₁, des forces F_1a, F1b sont engendrées sur les armatures 1a et 1b qui déplacent celles-ci vers l'une des positions stables (vers le bas de la figure 1).

The operation of the bistable electromagnet which has just been described is as follows:

• when the coils 5 and 8 are excited in the direction H ₁ , forces F _1a , F1b are generated on the armatures 1a and 1b which move them towards one of the stable positions (towards the bottom of FIG. 1).

Conversely, when the coils 5 and 8 are excited in the direction H ₂ opposite to the direction H ₁ , reverse forces F _{2a '} F _2b are generated on the armatures 1a and 1b which move them towards the other stable position (towards the top of figure 1).

The flow path in the magnetic circuit of the electromagnet is represented by arrows in solid line when the coils 5 and 8 are excited in the direction H ₁ and vice versa by arrows in dotted line when the coils are excited in the direction H ₂ .

It can be seen that direct and short links exist between the airgap zones facing each other. Thanks to these, a very reduced leakage flow is obtained.

The path of the magnetic flux which follows the outline of a rectangle or a square is close to the ideal path generated in a torus. This path is traveled in one direction or the other depending on the direction of the excitation H ₁ or H ₂ .

The magnetic potentials in the coils and permanent magnets have a regular distribution along the path of the flux.

We also note that the air gaps are located very close to the coils 5 and 8.

On the other hand, the structure of the element, of the electromagnet allows precise positioning by means of the plates 15a, 15b of the yokes 11, 12 which constitute planar cores for the coils 5, 8. These plates 15a, 15b can serve as a means for fixing the electromagnet.

In a modified version, the width of the polar pieces res 3a, 3b at the air gaps could be greater than that shown so as to increase the surface area of these air gaps.

For the same purpose, the ends of the pole pieces 3a, 3b could be arched like the ends of the pole pieces 4a, 4b.

In addition, the structure of the electromagnet allows easy disassembly of the coils 5, 8 and facilitates the coupling of the coils 5, 8 in parallel or in series in order to reduce the current consumption.

Furthermore, by swapping the polarities of a magnet such as the magnet 2b, movements in the opposite direction are obtained on the armatures.

In addition, in this case by performing a mechanical coupling between the plates 1a, 1b, the resistance of the electromagnet to impact is improved.

It would also have been possible to put coils around the reinforcements 1a and 1b, possibly in addition to the coils 5 and 8 around the cylinder heads 11 and 12.

In the embodiment of FIG. 2, where the previous homologous reference marks are increased by 20, the electromagnet comprises, as in the case of FIG. 1, two fixed armatures 21a, 21b of section substantially in H arranged parallel and opposite l one of the other.

Similarly, two movable yokes 31 and 32a, 32b join the airgap zones located opposite one another so that the magnetic circuit is constituted by a succession of armature and yoke forming a rectangle.

In addition, as in the case of Figure 1, two coils 25, 28 are arranged on opposite sides of the above rectangle.

Furthermore, each frame 21a, 21b consists of two pole pieces 23a, 24a; 23b, 24b projecting on either side of a permanent magnet 22a, 22b.

The pole piece 24a, 24b has two curved ends at right angles which define with the other pole piece 23a, 23b two airgap zones into which the opposite ends 33a, 33b 34a, 34b of the yokes 31 penetrate; 32a, 32b.

The electromagnet shown in Figure 2 differs mainly from that of Figure 1 in that the coils 25 and 28 are placed around the assembly of each armature 21a, 21b, cam for patent FR 2 466 844 .

Furthermore, by way of example, one of the magnetic yokes is composed of two elements 32a, 32b between which a permanent magnet 36 of small thickness is interposed.

The end 34b of the element 32b is arched in the manner of a bayonet so that it can be located in the extension of the element 32a which is entirely planar. This end 34b as well as the opposite end 34a of the planar element 32a penetrate into the lower airgap zones of the frames 21a and 21b.

The operation of the electromagnet shown in FIG. 2 is similar to that of the embodiment according to FIG. 1.

However, the permanent magnet 36 reinforces the magnetic flux passing in the direction of the arrows shown in solid lines and which causes the displacement of the yokes in the direction F ₁ and counteracts the magnetic flux passing in the opposite direction (arrows in dotted lines which tend move the cylinder heads in direction F ₂ ).

However, this flow can nevertheless flow due to the leakage reluctances between the elements 32a and 32b and the small thickness of the permanent magnet 36 compared to that of the magnets 22a and 22b.

Thus the electromagnet shown in FIG. 2 has a monostable operation, the rest position corresponding to the displacement of the yokes in the direction F ₁ and the working position corresponding to the displacement in the direction ^F ₂ .

Of course, a permanent magnet identical to the magnet 36 could be symmetrically interposed in the yoke 31 broken down into two elements like the yoke 32a, 32b.

Furthermore, it can be seen in FIG. 2 that the opposite planar faces 26a, 26b; 29a, 29b of the plastic carcasses of the coils 25 and 28 are set back with respect to the opposite ends of the pole pieces 23a and 23b and that guide means constituted by a plate 37 join the two yokes 31 and 32a, 32b.

This guide plate 37 can be connected to an external device (not shown) to which the overall movement of the cylinder heads can be transmitted, the armatures 21a, 21b and the coils 25, 28 being in this case fixed.

The plate 37 may for example be made of brass, sliding in slots 38a, 38b formed between the adjacent edges of the carcasses 26, 29 made of plastic of the coils 25 and 28.

This plate 37 can be crimped into a hole in the armature 31, or have a notch enclosing the assembly formed by the armature elements 32a, 32b and the permanent magnet 36.

The plate 37 can be replaced by two columns extending on either side of the coils 25 and 28.

Thus, in the embodiment shown in Figure 2, the yokes 31, 32a, 32b which are movable have a low inertia with respect to the two frames 21a, 21b which are fixed, which is advantageous for the speed of operation of the electro -magnet.

This inertia could be further reduced, by reducing the length of the cylinder head 31 and by arching the ends of the pole pieces 23a, 23b towards each other, which at the same time would increase the airgap surfaces.

The carcasses 26 and 29 of the coils 25 and 28 could then be easily overmolded on the frames 21a, 21b, under conditions allowing precise positioning of the airgap surfaces.

The overall height in the direction of movement of the electromagnet shown in Figure 2 is small since the coils 25 and 28 are placed opposite one another parallel to this movement.

Furthermore, the guide means allow a slight false parallelism of the cylinder heads. A complete closure of the air gaps is thus obtained even in the case where the positioning of the pole pieces is not rigorous.

In FIG. 3, the marks of which are identical to those of FIG. 2 after adding 20, the armature 41a has been rotated by 90 ° along its axis and the cut has been made at the level of the pole piece 43a. The frame 41b is unchanged, but its coil has been removed. On the other hand, a symmetrical frame 41c of 41b has been added with respect to 41a. The coil of 41c is also deleted. The means for guiding the two cylinder heads 51 and 52 have not been shown. The circulation of the flow is represented as above according to the field H ₁ - H ₂ of the coil 45.

Instead of having a flow circulation along a rectangle, two opposite sides of which are provided with coils, we see that we now have two rectangles having a common side, on which a single coil is arranged. This symmetrical arrangement has advantages of compactness.

We can also consider that the sections represented at 41b and 41c come from a single curved frame in an arc of a circle concentric with the frame 41a with a magnet 42 made of magnetic rubber.

FIG. 4 represents such an arrangement, after adding 20 to the preceding homologous references.

The armature 61b is curved over 360 ⁰ so as to form a pot-shaped electromagnet. To perfect the symé trie of revolution, the central frame 61a also has a cylindrical shape and is constituted by a solid cylindrical pole piece 64a provided at its two ends with openings playing the role of the ends arched at right angles.

The pole piece 64a is surrounded by an annular magnet 62a radially magnetized, itself surrounded by a hollow cylindrical pole piece 63a. Of course, the thicknesses of the pole pieces can decrease as one moves away from the axis of the pot.

The yokes 71 and 72 are joined together and guided by elements 77 transmitting the movement of the electromagnet. They have an annular shape.

Instead of having a cylindrical arrangement along the axis of displacement F ₁ - F _21, it is also possible to transform the arrangement of FIG. 2 to have a cylindrical arrangement along an axis perpendicular to the displacement F1-F2, as in FIG. 5, after adding 20 to the previous homologous benchmarks.

It can be seen that the coils 85 and 88 are curved in concentric arcs of a circle at the center of the electromagnet, the permanent magnets 82a and 82b having a radial magnetization whose axis of symmetry or main axis is always perpendicular to the displacement F ₁ - F ₂ . The ends of the pole pieces 84a and 84b are no longer bent at right angles but the curve of these pieces, as well as that of the pieces 83a, 83b; 91 and 92 also makes it possible to have parallel forces for the different airgap zones. This arrangement requires more expensive tools than for the previous cases, but it makes it possible to have a circular flow path, therefore having a shorter length than for a rectangular or square path. In addition, the permanent magnets are even closer to the air gaps.

In the same way, we can also transform the arrangement of Figure 4 so that, on each side of the axis of the coil, the flow path in the plane of the figure is circular, with a common central part. There is thus a horizontal eight-shaped path, which due to the symmetry along the axis of the coil, gives a volume in the form of a torus whose interior is occupied by the coil. We thus arrive at a structure minimizing the paths of the flux in iron and of the current in copper.

Of course, the invention is not limited to the examples which have just been described and numerous modifications can be made to them without departing from the scope of the invention.

Thus, the yoke 32a, 32b of FIG. 2 could have wings bent at 90 °, the magnet 36 being in this case disposed between these wings, so that the positioning of the air gaps does not depend on the thickness of the magnet 36 and the bending of the element 32b.

The air gaps described in the above examples are of the constant surface and distance between variable surfaces type. Without departing from the scope of the invention, it would be possible to obtain an air gap with variable surface with a constant distance between surfaces, for example in the case of the embodiment according to FIG. 1 by leveling the end 13a of the cylinder head 11 a slightly below the level of the guide plate 15a and by bringing the corresponding ends of the pole pieces 3a and 4a. Such air gaps are however less effective than those described taking into account friction and the risks of incomplete closure.

The structures described below can also receive the improvements contained in the invention patent entitled "Electromagnet with bistable operation, with permanent magnet", filed the same day by the Applicant.

Claims (10)

1. Electromagnet comprising yokes (11, 12; 31, 32a; 51, 52; 71, 72; 91, 92), an armature (1a, 21a, 41a, 61a, 81a) movable with respect to the 'other, and a coil (5, 25, 45, 65, 85) surrounding a part of the magnetic circuit, said armature (1a, 21a, 41a, 61a, 81a) comprising a permanent magnet (2a, 22a, 42a, 62a, 82a) provided on its two polar faces with two pole pieces (3a, 4a; 23a, 24a; 43a, 44a; 63a, 64a; 83a, 84a) projecting on either side of the axis of this permanent magnet, at minus one (4a, 24a, 44a, 64a, 84a) of said pole pieces having arched ends to define with the other pole piece (3a, 23a, 43a, 63a, 83a) two airgap zones into which ends penetrate cylinder heads (11, 12; 31, 32a; 51, 52; 71, 72; 91, 92) so that each air gap zone has two air gaps generating opposing forces in a direction perpendicular to the main axis of the permanent magnet (2a, 22a, 42a, 62a, 82a), characterized e n that at least one second frame (1b, 21b, 41b, 61b, 81b) of the same shape as the first (1a, 11a, 61a, 81a) is arranged parallel and opposite the first, in that two cylinder heads (11, 12; 31, 32a, 32b; 51, 52; 71, 72; 91, 92) join the airgap zones of the two armatures located opposite one another so that the magnetic circuit consists of a succession of armature and yoke. 2. Electromagnet according to claim 7a 1, characterized in that the succession of armature and yoke forms at least one rectangle and in that two coils (5, 8; 25, 28) are arranged on the opposite sides of said rectangle . 3. Electromagnet according to claim 2, characterized in that the coils (25, 28) are arranged around the armatures (21a, 21b). 4. Electromagnet according to claim 3, character se in that a permanent magnet (36) is interposed between the ends (34a, 34b) of at least one of the yokes so as to obtain a monostable operation. 5. Electromagnet according to one of claims 3 or 4, characterized in that the yokes (31, 32a, 32b) are joined by a guide means (37) free relative to the frames (21a, 21b) and to coils (25, 28), this guide means being connected to an external device. to which the movement of the above-mentioned cylinder heads is transmitted. 6. Electromagnet according to one of claims 3 to 5, characterized in that the carcasses (26, 29) of the coils (25, 28) are made of plastic overmolded respectively on frames (21a, 21b). 7. electromagnet according to claim 1, characterized in that it comprises two armatures (41b, 41c; 61b, 61c) arranged symmetrically on either side of the axis of a central armature (41a, 61a ) and have equally symmetrical magnetic polarities, so that the magnetic circuit consists of two rectangles having a common branch at (41a, 61a). 8. Electromagnet according to claim 7, characterized in that only the central armature (41a, 61a) is equipped with a coil (45, 65). 9. Electromagnet according to claim 1, characterized in that the second frame (61b) is curved in an arc of a circle concentric with the central frame (61a), in that the magnetic axis of this second frame is directed towards the central frame (61a) and in that only this first frame (61a) is provided with a coil (65) so as to constitute a pot-shaped electromagnet. 10. Electromagnet according to claim 3, characterized in that the coils (85, 88) with their permanent magnets (82a, 82b) and their pole pieces (83a, 84a, 83b, 84b) as well as the cylinder heads (91 , 92) are curved in concentric arcs of a circle in the center of the electromagnet, so that the flow path has a circular shape.

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