FR2825535A1 - Method of fabrication of a rotor for an electric machine, uses wrapping of winding in a fixing material which is melted by an external induction coil, and preheats core to reduce temperature gradient over winding during melting - Google Patents

Abstract

The rotor (10) is made on a core (14) carrying an electrical winding (16) formed from conductors (18) which are coated with electrically insulating material and wrapped in a layer of fixing material. The fixing material is heated by an external induction coil (40) and allowed to cool. The core is pre-heated before this to reduce temperature gradients in the winding.

Description

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"Method of manufacturing a rotor"
The invention provides a method of manufacturing a rotor for a rotary electrical machine.

 In known manner, rotary electrical machines comprise a rotor and a stator on each of which an electrical winding can be produced.

 The rotary electric machine can be an alternator which makes it possible to transform a rotational movement of the rotor into an electric current. The electric machine can also be a motor which makes it possible to transform an electric current which crosses a winding of the rotor into a rotational movement of the rotor. The machine can be reversible and therefore transform mechanical energy into electrical energy and vice versa.

 Each electrical winding consists of a winding of at least one electrically conductive element which is coated with a layer of electrically insulating material. In cross section, a winding therefore consists of a horizontal and vertical juxtaposition of sections of the electrically conductive element which are linked together by a varnish.

 The winding of the rotor of a rotary electrical machine is generally carried out in a coil body, made of electrically insulating plastic, consisting of an annular element of which an axial half-section in the shape of a U.

 The coil body guides the electrically conductive element during its winding. However, it is common for the transverse wings of the coil body to deviate slightly from each other, thus causing poor winding. The electrically conductive element can be caught in the transverse wings raised by petals. During transport before the impregnation of varnish, it may also occur a partial radial collapse of certain sections of the electrically conductive element of the winding which spreads the sides of the body

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de bobine et provoque son élargissement. Ainsi lorsque l'on vient intercaler le bobinage réalisé entre les deux roues polaires, l'élargissement est compacté ce qui risque de détruire la couche isolante électrique, notamment celle des brins axiaux du conducteur, et ainsi créer des contacts entre eux qui provoquent une perte de résistance. De plus, l'élargissement radial peut empêcher le contact entre le noyau sur lequel sont montés le bobinage et les deux roues polaires, ce qui crée un entrefer parasite du noyau par rapport aux roues polaires, et par conséquent une perte de puissance et de rendement de la machine électrique tournante.

of coil and causes its widening. So when one comes to interpose the winding produced between the two pole wheels, the enlargement is compacted which risks destroying the electrical insulating layer, in particular that of the axial strands of the conductor, and thus creating contacts between them which cause a loss of resistance. In addition, the radial widening can prevent contact between the core on which the winding is mounted and the two pole wheels, which creates a parasitic air gap of the core with respect to the pole wheels, and therefore a loss of power and efficiency. of the rotating electric machine.

Varnish is then deposited on the winding and is hardened, thus freezing the winding faults.

The hardening of the varnish can be obtained by heating the winding in an oven. This step is therefore very long.

In addition, the coil body, generally made of plastic, forms a heat shield between the winding, the core, and the pole wheels, which hinders the transfer and dissipation of the heat produced by the passage of current in the conductive element. electric, during the operation of the rotating electrical machine, and decreases the efficiency of the rotating electrical machine.

In order to limit these problems, in accordance with French patent application No. 00. 06853 of May 29, 2000, another solution consists in using an electrically conductive element which is coated with at least one layer of electrically insulating material and which is coated with a bonding layer which comprises a bonding material which makes it possible to bond adjacent sections of the coated electrical conductor element to one another.

The bonding material also makes it possible to link the winding and the core.

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 It is thus possible to remove the coil body so as to promote the transfer and dissipation of the heat produced in the winding during the operation of the rotor.

 To do this, during the winding step, the coated and coated electrical conductor element can be guided transversely by two transverse flanges which determine the width of the winding. The two transverse flanges allow the maintenance of the coated and coated electrical conductor element.

 Then, the method of manufacturing such a winding comprises a step of changing the state of the connecting material which consists in causing it to soften or melt so that it at least partially fills the interstices existing between the adjacent sections of the conductive element then which again causes it to solidify and links together the adjacent sections of the conductive element.

 The state change step can then include a step of heating the bonding material. This can be carried out in an oven. However, it is advantageous to cause softening or melting of the bonding material by heating the conductive element by the Joule effect. To do this, it is necessary to circulate a current of sufficient intensity in the conductive element so as to cause it to heat up.

 However, the rotor core consists of a solid piece which is preferably made of steel and which tends to absorb the heat produced by the Joule effect in the winding.

 The transfer and dispersion of the heat from the winding to the rotor core causes a temperature gradient in the winding.

 Indeed, part of the heat produced by the inner turns of the winding, that is to say those located at the

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 contact or near the nucleus, is absorbed by the nucleus which limits the increase in their temperatures.

 Therefore, at the end of the heating step, the temperature reached by the connecting material which coats the inner turns of the conductive element is lower than that reached by the connecting material of the other turns. The difference between these two temperatures can reach several tens of degrees Celsius.

 Since the temperature of the conductive element must remain below a maximum temperature, so as not to damage the layer of electrical insulating material, the temperature reached by the bonding material which coats the inner turns of the conductive element is generally lower than the softening or melting temperature of the bonding material.

 Consequently, the bonding material cannot bond the adjacent sections of the inner turns of the conductive element to one another.

 This is detrimental to the performance of the rotating electric machine.

 When the machine is in operation, the lower turns of the winding can vibrate, causing noise.

Decoupling the winding from the core can also cause noise. In addition, the vibrations of the interior turns on each other promote wear of the layer of insulating material, which increases the risk of short circuits.

 In order to remedy these drawbacks, the invention provides a method of manufacturing a rotor which comprises a core on which is produced at least one electrical coil comprising at least one electrically conductive element which is wound so as to form the coil , which is coated with at least one layer of electrical insulating material, and which is coated

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 of a bonding layer which comprises a bonding material which makes it possible to bond together adjacent sections of the coated conductive element, of the type which comprises a step of winding the coated conductive element so as to form the electrical winding , and of the type whose winding step is followed by a step of changing the state of the bonding material, in particular the Joule heating of a conductive element, which causes the bonding material to soften or melt so that it at least partially fills the interstices existing between the adjacent sections of the conductive element then which again causes it to solidify in order to link together the adjacent sections of the conductive element, characterized in that the step of changing d he state is preceded by a step of preheating the core, so as to limit the temperature gradients in the winding.

 According to other characteristics of the invention: - the preheating of the core is carried out by induction; - An induction coil is arranged near the external annular lateral face of the rotor winding; - an induction coil is located near an external transverse face of the core; - We use the winding to form an induction coil.

 - the preheating of the core is obtained by infrared radiation; the preheating of the core is obtained by heating the conductive elements of the winding by the Joule effect at a temperature below the hardening temperature of the bonding material; - The bonding material of the outer bonding layer is a polymer of the thermosetting type;

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 - The bonding material of the outer bonding layer is a polymer of the thermoplastic type.

 Other characteristics and advantages of the invention will appear on reading the detailed description which follows for the understanding of which reference will be made to the appended drawings in which: - Figure 1 shows in axial section schematically and partially a rotor of rotating electric machine; - Figure 2 shows on a large scale the detail D2 of Figure 1, before the step of changing the state of the bonding material; - Figure 3 is a view similar to that shown in Figure 2, after the step of changing the state of the bonding material according to the prior art; - Figure 4 shows in axial section schematically and partially, a rotary electrical machine rotor which comprises an electrical insulating material interposed between the winding and the core; FIG. 5 schematically represents the evolution of the temperature of the winding and of the core of a rotor of the type shown in the previous figure during the step of changing the state of the bonding material according to the state of the technical; - Figure 6 shows in axial section schematically and partially, a rotor of a rotating electrical machine which comprises an electrical and thermal insulating material interposed between the winding and the core; FIG. 7 schematically represents the evolution of the temperature of the winding and of the core of a rotor of the type shown in the previous figure during the step of changing the state of the bonding material according to the state of the technical;

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 - Figure 8 schematically shows the evolution of the temperature of the winding and the core of a rotor of the type shown in Figure 4 during the step of changing the state of the bonding material according to the invention; - Figure 9 is a view similar to that shown in Figure 2 after the step of changing the state of the bonding material according to the method of the invention; - Figures 10 to 13 are schematic views which illustrate exemplary embodiments of devices which allow to perform the step of preheating the rotor core according to the invention.

 There is shown in Figure 1, schematically, a rotor 10 of a rotating electrical machine which is integral with an output shaft 12.

 The rotor is mainly composed of a core 14 on which an electrical winding 16 is produced.

 The electric winding 16 is for example constituted by the winding in turns of an electrically conductive element, such as a copper wire, which is coated with at least one layer of electrically insulating material.

 Figure 2 shows on a large scale, in a cross section, a portion of the winding of the conductive element 18 coated with a layer 20 of electrical insulating material.

 The conductive element 18 is here a copper wire.

 The coated conductive element 18 is also coated with a bonding layer 22 of bonding material which enables adjacent sections of the conductive element 18 to be bonded together.

 In known manner, in accordance with FIG. 3, an electrical insulating sheet is interposed between the electrical winding 16 and the core 14. It makes it possible to reduce or eliminate the risks of short circuits between the winding 16 and the core 14.

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 Advantageously, the electrical insulating sheet 24 also makes it possible to hold the coil 16 on the core 14. To do this, it can be coated or impregnated with a bonding material similar or not to the bonding material of the bonding layer. 22.

 In order to optimize their specific functions, the bonding material of the bonding layer 22 and the bonding material which coats or impregnates the electrical insulating sheet 24 are chemically and thermally compatible.

 The material of the electrical insulating sheet 24 can also be a thermal conductor. This makes it possible, during the operation of the rotary electrical machine, to promote the evacuation, towards the core 14, of the heat produced by the circulation of the electric current in the conductive element 18. The insulating sheet 24 can also extend over the transverse walls of the winding 16 so as to eliminate the risks of short circuits between the winding 16 and the pole wheels, not shown, of the rotary electric machine.

 During the manufacture of the rotor 10, the connection of the adjacent sections of the conductive element 18 is advantageously obtained by a step of changing the state of the material of the connection layer 22.

 The state change step causes the bonding material to soften or melt so that it at least partially fills the interstices existing between the adjacent sections of the conductive element 18, then again causes it to solidify and binds them together. adjacent sections of the conductive element 18.

 The step of change of state corresponds to a modification of the structure of the bonding material, that is to say a movement of some of the atoms constituting it with respect to each other.

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 The step of changing the state of the material includes a step of heating the bonding layer 22 to a hardening temperature which is greater than or equal to the melting temperature of the bonding material, so as to melt or soften it to that it flows or flows so as to preferably almost entirely fill the interstices existing between the adjacent sections of the conductive element 18.

 The heating step and followed by a cooling step during which the bonding material hardens or solidifies again.

 The hardening or solidification temperature of the bonding material is the temperature above which the structure of the material is modified so that the material allows the bonding of the elements with which it is at least partially in contact.

 The bonding material is advantageously a polymer.

 Thus, when the polymer is of the thermosetting type, the curing temperature will be referred to in the following description and in the claims as its crosslinking temperature.

 Thus, when the polymer is of the thermoplastic type, the melting temperature will be referred to in the following description and in the claims as its melting temperature.

 When the bonding material is a polymer, the heating step allows its polymerization and the cooling step allows its solidification which ensures the rigid connection of the adjacent sections of the coated conductive element 18.

 The insulating sheet 24 can also be coated with a bonding material such as a polymer. Thus the steps of heating to a temperature greater than or equal to the hardening temperature of the bonding material and

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 cooling make it possible to link it to the core 14 of the rotor 10 and to the adjacent sections of the coated conductive element 18 so as to strengthen the connection of the winding 16 and of the core 14.

 The heating step consists of heating the electrically conductive element 18 coated and coated by the Joule effect so as to bring the temperature of the bonding material to a temperature greater than or equal to its hardening temperature.

 However, the insulating sheet 24 allows the transfer of the heat produced by the Joule effect from the winding to the core 14.

This heat transfer causes a temperature gradient inside the winding 16. The internal turns of the winding of the winding 16 which are located near the core 14 are at a temperature below the temperature of the other turns of the winding of the winding 16.

 Figure 5 illustrates this phenomenon. It offers three curves 30, 32 and 34 which represent the changes in the temperature of the core 14, the temperature of the inner turns of the winding and the temperature of the outer turns of the winding respectively during Joule heating of the winding. 16.

 Here the heating lasts 30 seconds. This duration makes it possible to bring the outer turns to a temperature of 240 C. The hardening temperature of the bonding material being of the order of 200 C, the temperature of the conductive element 18 is sufficient to allow the polymerization and the bonding of the exterior turns.

 Since a large amount of heat is transferred from the inner turns to the core 14, the temperature of these turns does not increase enough to allow the polymerization of the bonding material, thus preventing the bond between the adjacent sections of the turns

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 interior of the conductive element 18. In fact, the temperature of the order of 130 C does not allow the change of state of the bonding material.

 FIG. 3 partially represents an interior zone of the winding 16 of the rotor 14, the bonding layer 22 of the interior turns has not changed state, while the bonding layer of the turns located towards the outside has polymerized so as to link them together.

 To overcome these drawbacks, it is possible that the electrical insulating sheet 24 is also thermal insulating. A rotor of this type is shown in Figure 6.

 The sheet 24 strongly limits the heat transfer between the internal turns of the winding 16 and the core 14 so as to strongly limit or eliminate the temperature gradient in the winding.

 This effect is represented in FIG. 7 in which the curves 32 and 34, which represent the changes in the temperature of the inner turns of the winding and the temperature of the outer turns of the winding respectively during heating by the Joule effect of the winding 16, are confused.

 However, during the operation of the rotary electric machine, such an insulating sheet 24 greatly limits the evacuation of the heat produced by the winding 16, which significantly reduces the performance of the electric machine.

 In addition, the sheet 24 is thick, which increases the size of the rotor 10.

 In order to eliminate these drawbacks, the invention proposes that the step of changing state is preceded by a step of preheating the core 14, so as to limit the

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 temperature gradients in the winding 16 so that the temperature is substantially homogeneous.

 The limitation of the temperature gradients in the winding 16 results from the decrease in the difference between the temperature of the conductive element 18 of the winding 16 and that of the core 14, which reduces the heat transfers between these two elements.

 The rotor 10 then comprises an electrical insulating sheet 24, the material of which is also a thermal conductor, so as to minimize the size of the rotor 10 and to promote the evacuation of the heat produced during its operation in order to optimize the performance of the electric machine. rotating.

 FIG. 8 which is similar to FIGS. 5 and 7 illustrates the evolution of the temperatures in the core 14 and in the winding 16. The temperatures of the different turns of the winding 16 are then substantially identical.

 According to the invention, the core 14 is preheated to a temperature which is here of the order of 100 C. The preheating temperature must be greater than 800C and lower than the polymerization temperature of the material of the bonding layer 22.

 During this step, the temperature of the winding 16 changes in a similar fashion to that of the core 14.

 Then, in known manner, the conductive element 18 is heated by Joule effect to a temperature higher than the hardening temperature of the layer of the bonding material, here of the order of 240 C.

 The preheating step of the core 14 can be carried out in different ways.

 For example, the preheating of the core 14 can be carried out by induction.

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 The core 14 is then made of magnetic steel so that it heats up when it is subjected to an alternating magnetic field.

 In accordance with FIG. 10, an induction coil 40 is arranged near the external annular lateral face 42 of the winding 16 of the rotor 10.

 The induction coil 40 may consist of a tubular winding 44 of a conductive wire 46. Here the winding comprises four turns.

 The inside diameter of the winding 44 is substantially greater than the outside diameter of the winding 16. Thus, during the preheating step, the rotor 10 is arranged in the center of the induction coil 40 which is supplied by an alternating current of so as to create a magnetic field and cause preheating of the core 14.

 The coil 40 can also consist of a spiral winding 48. It is then located near an external transverse face 50 of the core 14.

 In accordance with FIG. 11, so as to optimize the preheating of the core 14, a coil 40 is arranged near each external transverse face 50 of the core 14.

 According to another variant, the winding 16 is used to constitute the induction coil 14.

In this case the conductive element 18 is supplied by a first current during the preheating step, then by a second current during the state change step.
The first current which is an alternating current has an intensity which is less than 50A so as to control the heating of the conducting element 18 by Joule effect
The second current which is a direct current has an intensity which is higher than that of the first current and

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 which is greater than 30A so as to allow the change of state of the bonding material fairly quickly.

 Advantageously, during the preheating phase, the temperature of the external convex cylindrical wall of the core 14 is lower than the hardening temperature of the bonding material.

 The preheating of the core 14 can also be obtained by infrared heating. In this case emitters 52 of infrared radiation, represented in FIG. 12, are arranged near the external transverse faces 50 of the core 14.

 FIG. 13 represents a preheating device 54 such as an electrical heating resistor which makes it possible to preheat the core 14 by thermal conduction.

 The preheating device 54 can be arranged in the orifice intended to receive the output shaft 12.

 It is also possible that the preheating of the core 14 is obtained by heating the conductive element 18 of the winding 16 by the Joule effect at a temperature below the hardening temperature of the bonding material.

 In this case, during the preheating step, the conductive element 18 is supplied with a current whose intensity allows it to be heated to a temperature below the hardening temperature. This allows the preheating of the core 14 by thermal transfer.

 Then, during the step of change of state, the conductive element 18 is supplied by another current whose intensity allows the heating of the conductive element 18 to a temperature higher than the hardening temperature of the bonding material. .

 Such a method makes it possible to control the evolution of the temperature of the winding 16 so as to ensure a connection

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 optimum of the adjacent sections of the conductive element 18, while using a very thin insulating sheet 24 which in particular makes it possible to minimize the size of the rotor 10 and to optimize the thermal transfer from the winding 18 to the core 14 during operation of the rotating electric machine.

Claims (9)

1. Method for manufacturing a rotor (10) which comprises a core (14) on which is produced at least one electric coil (16) comprising at least one electrically conductive element (18) which is wound so as to form the coil (16), which is coated with at least one layer (20) of electrical insulating material, and which is coated with a bonding layer (22) which comprises a bonding material which makes it possible to bond adjacent sections of the conductive element (18) coated, of the type which comprises a step of winding the conductive element (18) coated so as to form the electric winding (16), and of the type whose step of winding is followed a step of changing the state of the bonding material, in particular the Joule heating of a conductive element (18), which causes the bonding material to soften or melt so that it at least partially fills the interstices existing between adjacent sections of the element ent conductor (18) then which again causes it to solidify to link together the adjacent sections of the conductive element (18), characterized in that the step of change of state is preceded by a step of preheating the core (14), so as to limit the temperature gradients in the winding (16).  2. Manufacturing method according to the preceding claim, characterized in that the preheating of the core (14) is carried out by induction.  3. Manufacturing method according to the preceding claim, characterized in that an induction coil (40) is arranged near the external annular side face (42) of the winding (16) of the rotor (10).  4. Manufacturing method according to one of claims 2 or 3, characterized in that an induction coil (40) is located <Desc / Clms Page number 17>  near an outer transverse face (50) of the core (14).  5. Manufacturing process according to one of claims 2 to 4, characterized in that the winding (16) is used to form an induction coil.  6. Manufacturing method according to any one of the preceding claims, characterized in that the preheating of the core (14) is obtained by infrared radiation.  7. Manufacturing method according to any one of the preceding claims, characterized in that the preheating of the core (14) is obtained by heating the conductive element (18) of the winding (16) by Joule effect at a lower temperature. at the hardening temperature of the bonding material.  8. Manufacturing method according to any one of the preceding claims, characterized in that the bonding material of the external bonding layer (22) is a polymer of the thermosetting type.  9. The manufacturing method according to any one of claims 1 to 7, characterized in that the bonding material of the outer bonding layer (22) is a polymer of the thermoplastic type.