EP1058278B1 - Wound magnetic circuit - Google Patents

Description

The present invention relates to a wound magnetic circuit and a method of manufacturing such a circuit.

Magnetic wound circuits are used in many fields including current sensors and transformers. In applications such as current sensors, accuracy is closely related to the magnetic properties of the materials used and the accuracy of manufacture. Accurate accuracy often defeats the need to reduce manufacturing costs and reduce the size of components.

The document JP-A-11121241 shows two insulating flanges to isolate two coils on a toric magnetic core.

A method of manufacturing a winding on a ring-shaped magnetic circuit is described in the European Patent EP 668 596 . The process described in this patent, which attempts to meet the criteria mentioned above, comprises the steps of winding a conductive wire coated with a thermo-adherent around a cylindrical mandrel to form a coil, to open a circuit magnetic by removing the lips of the air gap, put the coil on the magnetic circuit and then close the magnetic circuit.

There are several disadvantages to this conventional process. First, it is very difficult to remove the coil from the cylindrical mandrel and then thread it onto the core. Second, the opening and closing of the magnetic circuit, like any plastic deformation, deteriorates the magnetic properties of the circuit.

In view of these disadvantages, the object of the present invention is to provide a wound magnetic circuit having a precise electrical and magnetic behavior and which can be manufactured industrially economically.

Objects of the invention are realized by the method of manufacturing a wound magnetic circuit according to claim 1, and the wound magnetic circuit of claim 4.

In the present invention, a method of manufacturing a wound magnetic circuit having an electrical coil and a magnetic core comprises the steps of making the coil by winding a conductive wire on a mandrel having a slightly conical outer surface, and threading the coil on an open spiral-shaped magnetic core, which coil is first formed before establishing the specified magnetic properties of the magnetic material of the coil. After threading the coil on the magnetic core, the ends of the core are deformed in a direction substantially orthogonal to the plane of the magnetic circuit to bring them closer together. Advantageously, this method deforms the magnetic material to a minimum so as not to degrade these magnetic properties.

The coil can be threaded onto the magnetic core during removal of the mandrel, which reduces the time and cost of manufacturing the wound magnetic circuit. For this purpose, it is advantageous that an end of the magnetic core is inserted into a cavity at one end of the mandrel to facilitate the threading of the coil on the magnetic core.

The wound magnetic circuit may further comprise a flange and a connector, the flange and the connector being each arranged at a respective end of the coil, the coil being mounted on the magnetic core formed of a magnetic ring-shaped wire. The flange facilitates the threading of the coil on the core by its shape and dimensions, on the one hand, and by the reduction of the coefficient of friction, on the other hand. For this purpose, the flange can advantageously have a chamfered inner surface to facilitate its monitoring of the curvature of the core. The flange also prevents damage to the insulation of the electrical wire by friction on the torus.

The mandrel of the device for manufacturing a wound magnetic circuit, around which the coil is formed, may have an outer surface of slightly conical shape. This facilitates the removal of the spool from the mandrel.

The angle α of the cone may be very small and have, for example, a tan α value between 0.001 and 0.01. The difference in diameter of the coil between the ends is thus negligible.

The mandrel may further comprise a cavity at its end to allow the insertion of the end of the magnetic core into the cavity, and thus facilitate the assembly of these components.

• la Fig. 1 est une vue en perspective d'un mandrin et d'une bobine formée sur le mandrin et prête à être insérée sur un noyau magnétique, selon l'invention;
• la Fig. 2 est une coupe longitudinale de l'ensemble montré à la Fig. 1;
• la Fig. 3 est une vue d'un fil magnétique continu utilisé pour former le noyau magnétique;
• la Fig. 4 est une vue d'un noyau magnétique découpé du fil magnétique continu; et
• les Figures 5 à 7 sont des vues en perspective montrant divers étapes dans la fabrication de la bobine.

Other objects and advantageous aspects of the invention will emerge from the following description and claims, and the accompanying drawings, in which:

• the Fig. 1 is a perspective view of a mandrel and a coil formed on the mandrel and ready to be inserted on a magnetic core, according to the invention;
• the Fig. 2 is a longitudinal section of the set shown in the Fig. 1 ;
• the Fig. 3 is a view of a continuous magnetic wire used to form the magnetic core;
• the Fig. 4 is a view of a cut-off magnetic core of the continuous magnetic wire; and
• the Figures 5 to 7 are perspective views showing various steps in the manufacture of the coil.

A wound magnetic circuit 1 comprises a coil 2 and a magnetic core 3. The coil 2 comprises a flange 4 at an anterior end 19, a connector 5 at the other end (10), and a conductive wire 6 wound around a central cavity 7 and extending between the connector 5 and the flange 4. The conductive wire 6 may be, for example, a conventional copper wire provided with an insulating layer and adherent to form the coil. The wire can also be only insulating, the application of a follower being done during the formation of the coil.

The connector 5 has terminals 8 for connecting the wound magnetic circuit to an electronics or other device. The terminals 8 are housed in a housing 9 of the connector which also serves as a support for an end 10 of the coil and the end of the conductive wires of the coil which are electrically connected to the terminals 8. The connection of the conductive wires to a device Outside is therefore facilitated by the integration of the connector 5 to the coil during the manufacture of the coil, and at the same time allows to protect and ensure a good connection between the conductors of the coil and an external electronics.

The flange 4, at the other end of the coil 2, serves as a support for the insertion end of the coil and provides an inner guide surface 11 for protecting the wire at the threading end of the coil against abrasion during the threading on the core 3 which can lead to short circuits between turns. In addition, the guidance of the end of the coil by the flange 4 during the deformation of the coil during its threading on the ring core, is significantly improved. Indeed, the flange 4 allows to define well the shape and the dimensions of the guide surface 11 and reduce the coefficient of friction between the coil and the magnetic core 3. In particular, the flange comprises a chamfer 18 to follow the curvature of the magnetic core 3.

After the threading of the connector 8 and the flange 4 on a mandrel 12, as shown in FIG. Fig. 5 one end of the conductive wire is connected to a terminal 8a of the connector and the coil 2 is then wound on the mandrel 12 as shown in FIG. Fig. 6 . At the end of the winding, the other end of the conductor wire is connected to one of the terminals 8b. The connection between the wire and the terminals 8a, 8b can be made by wound connection or by other conventional means. The coil may have one or more additional windings connected to one or more additional terminals, such as 8c.

The mandrel 12 extends along an axis of rotation A to one end 13. The mandrel has a conical outer surface 14 to facilitate the removal of the spool from the mandrel and its threading on the magnetic core 3. L angle α of the cone can be very small, for example tan a can have a value between 0.001 and 0.01, so that the influence of the cone on the variation of diameter of the coil is negligible while keeping the advantage of facilitating removing the spool from the mandrel. It should be noted that this advantage is even more important that the son are coated with an adherent product for maintaining the shape of the coil.

The mandrel has a positioning portion 17 for positioning and locking the relative rotation of the connector 5 on the mandrel. The mandrel further comprises a recess 15 at its end for the insertion of an end 16 of the magnetic core 3 during the step of threading the coil 2 on the core, as shown in FIGS. figures 1 , 2 and 7 . After the formation of the spool on the mandrel 12, the spool 2 can thus be easily and directly threaded onto the magnetic core 3, as shown in FIG. Fig. 7 by the action of a pusher 20 engaging the connecting end 5 (see Fig. 1 ). The pusher is in the form of a fork that is straddling the connector behind flanges 21 of the connector after the winding operation. The pusher moves in the direction (P) parallel to the axis (A) of the mandrel, so as to position the coil 2 accurately on the magnetic core 3. In the case of the use of a wire provided a heat-adhesive layer, the coil can be heated, or kept hot, to allow its deformation during the threading on the core 3.

The ring core 3 is made of a conventional magnetically permeable material, such as iron-nickel, and it may be of any suitable shape (wire, flat, sheet, or assembly of such elements). Typically, to have good magnetic properties, the material used is annealed after its deformation in the form of open torus, because the large plastic deformations degrade the magnetic properties. It is no longer possible to anneal the torus once the coil is mounted on it.

In the present invention, the plastic deformations of the magnetic material are minimized to decrease the influence of deformations on the magnetic properties. For this purpose, the magnetic material has, for example, the shape of a wire 3 'shaped helical turn, as shown in FIG. Fig. 3 , and then cut along the dotted lines e1 and e2. Several individual turns are thus formed, as shown in FIG. Fig. 4 , the turns being ready for assembly of the coil, as described above, the only plastic deformation of the individual turns being carried out after mounting the coil to bring the ends 16, 16 'of the magnetic core 3. The ends 16, 16 'are deformed by rotation in a substantially orthogonal direction (O) to the plane of the magnetic circuit and form an air gap of a specified length depending on the application.

During the formation of the helical turn, the pitch (P) can be adjusted to correspond to the required spacing, in the orthogonal direction (O) at the plane of the circuit, between the ends 16, 16 'so as to allow the insertion of the coil on the core. The thickness (E) of the longitudinal cut of the turn to form the individual turns can be adjusted so that, after the deformation in rotation of the ends 16, 16 'of the magnetic circuit in the substantially orthogonal direction (O) to plane of the circuit, the ends are separated by the specified gap length. In this case, the thickness (E) of the blank is substantially equal to the length of the gap.

The magnetic material can therefore be annealed after the formation of the turn, or after cutting individual turns, so that the only deformation that undergoes the magnetic core after being annealed, is due to the approximation of the ends 16, 16 'of the magnetic circuit.

Claims (6)

1. Method for fabricating a wound magnetic circuit (1) having an electric coil (2) and a magnetic core (3) comprising the steps of forming the coil (2) by winding a conductor wire (6) on a mandrel (12) having a slightly conical outer surface (14), before or during the winding operation of arranging a flange (4) offering an internal guiding surface (11) on the mandrel (12) to form an anterior end (19) of the coil (2), this end being intended to be inserted firstly on the magnetic core (3), of inserting the coil (2) on a magnetic core (3) of open spiral shape having ends (16, 16'), this spiral first being formed before establishing specified magnetic properties of the magnetic material of the spiral, and of deforming the ends (16, 16') of the magnetic core in a direction essentially orthogonal (0) to the plane of the wound magnetic circuit to draw them towards each other.
2. The method according to claim 1, characterized in that the coil (2) is inserted onto the magnetic core (3) when the mandrel (12) is being removed.
3. The method according to claim 2, characterized in that one end (16) of the magnetic core (3) is inserted in a cavity (15) at one end (13) of the mandrel (12) to facilitate insertion of the coil (2) on the magnetic core (3).
4. A wound magnetic circuit (1) comprising an electric coil (2) and a magnetic core (3), the coil (2) comprising a conductive wire (6), a flange (4) offering an internal guiding surface (11) and a connector (5), the flange (4) and the connector (5) each being arranged at a respective end of the coil (2), the coil, the flange and the connector being mounted on the magnetic core (3) formed of a toroidal-shaped magnetic wire.
5. A wound magnetic circuit according to the preceding claim, characterized in that the inner cavity (7) of the coil (2) is of slightly conical shape.
6. A wound magnetic circuit according to one of claims 5 or 6 characterized in that it is manufactured using one of the methods according to one of claims 1 to 4.

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