Wound rotor for electrical machine

Abstract

Wound rotor for an electric machine. One aspect of the invention relates to a wound rotor for an electric machine, comprising: a cylindrical rotor body (15) for mounting around a rotor shaft, said rotor body having teeth (16) and open slots (17) extending axially around the outer periphery of said rotor body; electrical windings extending axially, each around a tooth of the rotor body; insulating shims (14) extending axially, each within a slot of the rotor body, between two consecutive windings; a layer of gluing varnish distributed at least over the rotor windings; and varnish receptacles (141, 142) housed on at least one outer surface (14c) of the rotor to receive excess varnish. Figure to be published with the abbreviation: Figure 6

Description

Title of the invention: Wound rotor for electric machine TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to a wound rotor for an electric machine comprising varnish receptacles ensuring a reduction of skinning effects on the varnishes used to bond the rotor windings. The invention also relates to an electric machine comprising such a rotor and a method for manufacturing such a rotor.

[0002] The invention finds applications in the field of rotating electrical machines such as alternators, electric motors and reversible machines. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] In the automotive field, it is well known that electric machines are used in numerous functions, such as vehicle propulsion, vehicle starters, etc. These electric machines are equipped with a stator comprising permanent magnets or wound poles (electromagnets) surrounding a rotating rotor. The rotor rotates around a central axis. Various types of rotors exist, including the wound rotor, which has conductors forming the rotor windings. Such an electric machine is designed to operate in a "motor" mode, in which the stator is electrically powered and creates a rotating magnetic field and then a torque relative to the inductor poles, driving the rotor to rotate, for example, to start an internal combustion engine.Combined with specific electronic functions, this electric machine can also operate in a "recharge" mode in which the rotating rotor induces a voltage in the stator which transforms it into an electric current to recharge the battery.

[0004] An example of a wound rotor 10 is shown in perspective in [Fig. 1] and in a top view in [Fig. 2]. This wound rotor 10 has a cylindrical body 15, formed by a stack of thin laminations in the shape of a ring, called a lamination pack. The rotor body 15 is mounted around a rotor shaft 11 extending along a central axis XX. The outer surface of the rotor body 15 has an arrangement of teeth 16 and slots 17 alternating with each other. The teeth 16 and the slots 17 extend axially around the outer periphery of the rotor body 15, along the central axis XX. The slots 17 are cavities, open to the outside of the rotor body 15, which receive phase windings connected together. The windings are generally obtained from a continuous electrically conductive wire, usually a copper wire. Each winding forms an electrical coil 13 around a tooth 16 of the rotor body.A wound rotor 10 therefore has the same number of windings 13, teeth 16 and notches 17. Shims. Insulating spacers 14 are housed in each of the slots 17 of the rotor body 15. In other words, an insulating spacer 14, simply called a spacer, is installed in each slot 17, between two teeth 16 and two consecutive windings 13. Each spacer 14 extends axially over the entire height of the windings 13. Two locking discs 12 are mounted on either side of the winding assembly, facing each other to hold the rotor elements in place.

[0005] A bonding varnish is generally applied along the windings 13 to ensure the windings are held together both axially and radially. This bonding varnish, more simply called varnish, is applied to the rotor by a dipping / rolling operation of the rotor in a varnish bath. More precisely, the rotor 10 is immersed in a varnish bath, in which it is rotated to impregnate the windings with varnish, thereby bonding the electrical wires forming the windings together and securing the windings 13 to the rotor body, while also creating electrical insulation around said windings. After the dipping / rolling operation, a polymerization operation cures the varnish onto the rotor. During this polymerization operation, the varnish tends to migrate onto the outer surface of the rotor 10, which is still rotating.This migration of varnish onto the outer surface of the rotor, and in particular onto the outer surface of the teeth 16 and the outer surface of the discs 12, creates an excess thickness on these outer surfaces, resulting in skinning effects on the rotor, notably a failure to maintain the correct air gap between the outer circumference of the rotor and the inner circumference of the stator. These skinning effects can lead to a risk of the electrical machine seizing up during operation and, consequently, to the machine being scrapped or requiring rework, which in all cases generates additional manufacturing costs.

[0006] There is therefore a real need for a wound rotor with minimized skin effects. Summary of the invention

[0007] To address the aforementioned problems of excessive varnish thickness on the rotor's outer surfaces, the applicant proposes a wound rotor equipped with varnish receptacles to collect excess varnish and thus prevent skinning on the rotor's outer surfaces. The applicant also proposes an electrical machine incorporating such a rotor, as well as a method for manufacturing this rotor.

[0008] The "outer surface" or "outer face" of a rotor element refers to the surfaces / faces of the element furthest radially from the central axis XX or the surfaces / faces furthest axially from the rotor core, i.e., from the most central sheet of the stack of sheets forming the rotor body. In contrast, the "inner surfaces" or "inner faces" of a rotor element are the surfaces / faces of the elements closest radially to the central axis XX or the surfaces / faces closest axially to the core of the rotor.

[0009] According to a first aspect, the invention relates to a wound rotor for an electric machine, comprising: • a cylindrical rotor body intended to be mounted around a rotor shaft with axis of rotation XX, said rotor body having axially extending teeth and notches, • electrical windings extending axially, each around a tooth of the rotor body, • insulating shims extending axially, each within a notch in the rotor body, between two consecutive windings, • a layer of gluing varnish spread at least on the rotor windings, and • varnish receptacles located on at least one external surface of the rotor to receive excess varnish.

[0010] This rotor has the advantage of being equipped with receptacles designed to collect excess varnish, thus preventing the build-up caused by excess varnish on the rotor's exterior surfaces. These varnish receptacles also have the advantage of retaining the winding wires within the rotor's internal structure.

[0011] In addition to the characteristics mentioned in the preceding paragraph, the wound rotor according to one aspect of the invention may have one or more additional characteristics from among the following, considered individually or according to all technically possible combinations: • The varnish receptacles are located on an outer face of the insulating shims. Since the insulating shims have no impact on rotor performance, the presence of receptacles in the insulating shims does not alter its performance in any way. • Each insulating wedge has, on its outer face, an extra thickness in which the varnish receptacles are formed. As with the varnish receptacles, the presence of this extra thickness has no effect on the rotor's performance. • nail polish receptacles have at least one through or non-through orifice. • the orifices have a circular or oblong cross-section. • the receptacles have at least one groove ensuring drainage of excess varnish. • the receptacles have at least one chamfer extending axially on the outer face of the wedge, along the excess thickness. • the grooving comprises a set of grooves opening onto at least one chamfer, the set of grooves ensuring the flow of excess varnish and the chamfer ensuring the retention of said excess varnish. • the grooves of the set of grooves are parallel to each other and oriented in an oblique direction relative to an axis of the rotor shaft. • the grooves of the set of grooves are parallel to each other and oriented in a direction perpendicular to an axis of the rotor shaft.

[0012] A second aspect of the invention relates to an electrical machine comprising a rotor and a stator, the rotor being in conformity with the rotor according to the first aspect of the invention.

[0013] A third aspect of the invention relates to a method for manufacturing a wound rotor according to the first aspect of the invention, comprising the following operations: • fabrication of varnish receptacles on an external surface of a rotor body or an external face of at least one insulating shim, • winding an electrically conductive wire around the teeth of the rotor body to create windings, • mounting of insulating shims in each notch of the rotor body, between two windings, • Installation of locking discs at each axial end of the windings, • dipping and rolling the rotor in a varnish bath, and • polymerization of the varnish-impregnated rotor. BRIEF DESCRIPTION OF THE FIGURES

[0014] Other advantages and features of the invention will become apparent from the following description, illustrated by the figures in which:

[0015] The [Fig. 1], already described, represents a perspective view of a wound rotor according to the prior art;

[0016] Figure 2, already described, represents a schematic top view of a wound rotor according to the state of the art;

[0017] Fig. 3 represents a schematic top view of a notch between two windings of a rotor wound according to the prior art;

[0018] Figure 4 shows a schematic top view of an insulating wedge housed in a rotor body notch according to the invention;

[0019] Figure 5 represents a schematic front view of an insulating wedge according to a first embodiment of the invention;

[0020] Figure [Fig. 6] represents a schematic perspective view of an insulating wedge according to a second embodiment of the invention;

[0021] Figure 7 represents a schematic front view of an insulating wedge according to the second embodiment of the invention;

[0022] Figure 8 represents a schematic front view of an insulating wedge according to a third embodiment of the invention;

[0023] Figure 9 represents a schematic front view of an insulating wedge according to a fourth embodiment of the invention;

[0024] Figure 10 represents a schematic front view of an insulating wedge according to a fifth embodiment of the invention;

[0025] Fig. 11 represents a perspective view of an insulating wedge according to a sixth embodiment of the invention;

[0026] Figure 12 shows a cross-sectional profile view of an insulating wedge according to the sixth embodiment of the invention; and

[0027] Figure 13 represents, in the form of a functional diagram, the manufacturing process of the wound rotor according to the invention. DETAILED DESCRIPTION

[0028] Examples of embodiments of a wound rotor equipped with one or more varnish receptacles are described in detail below, with reference to the accompanying drawings. These examples illustrate the features and advantages of the invention. It should be noted, however, that the invention is not limited to these examples.

[0029] In the figures, identical elements are identified by identical reference numerals. For the sake of readability, the size scales between represented elements are not respected.

[0030] An example of a notch 17 of a rotor body 15 is shown in [Fig. 3]. As explained in connection with Figures 1 and 2, the rotor body 15 is formed by a stack of thin sheets in the shape of a ring. The outer surface of the rotor body 15 is provided with teeth 16 and notches 17 arranged alternately with each other. The slots 17 are cavities, open to the outside of the rotor body 15, and each receiving an insulating layer 18, for example insulating paper, as well as two windings 13. One winding 13 surrounds a tooth 16. A slot 17 is therefore traversed by the windings 13 surrounding the two teeth 16 adjacent to said slot 17. In the example of [Fig.3], the slot 17 is housed between the teeth 16a and 16b and receives a portion of the winding 13a surrounding the tooth 16a and a portion of the winding 13b surrounding the tooth 16b.

[0031] As shown in [Fig. 4], an insulating wedge 14 is installed in each slot 17, between the two windings 13a and 13b that pass through said slot 17. The insulating wedge 14, more simply called a wedge, has a shape adapted to the shape of the slot 17 and is mounted by axial sliding (parallel to the central axis XX) inside the slot 17. The shape of the wedge 14 is complementary to the space separating the two windings 13a, 13b inside the slot 17. To this end, the wedge 14 has two inner faces 14a, 14b in contact with the two windings 13a, 13b respectively, and an outer face 14c opening outside the rotor body 15 and extending between the adjacent teeth 16a, 16b. The wedge 14 is made of an electrically insulating material, such as plastic.The wedge 14 thus allows not only the windings 13 to be locked tangentially and radially inside the notch 17 but also the two windings 13a and 13b passing through the same notch 17 to be electrically isolated.

[0032] According to the invention, the wound rotor 10 is provided with one or more receptacles adapted to receive excess varnish during the operations of dipping / rolling the rotor in the varnish bath and polymerizing the varnish-impregnated rotor. These receptacles, or varnish receptacles, are grooves or orifices, through or non-through, formed on an external surface of the rotor and whose role is to collect the excess varnish flowing onto the external surfaces of the rotor when the rotor is rotating during the dipping and / or polymerization operations.

[0033] In certain embodiments of the invention, the varnish receptacles are located on the outer faces 14c of the shims 14, that is, the face of the shims extending between the outer faces of the two teeth 16 adjacent to said shim. Preferably, but not necessarily, at least one varnish receptacle is formed on the outer face of each shim 14 of the rotor. This varnish receptacle may be in the form of an orifice or a groove. Various embodiments of the receptacles will be described, in which it will be considered that each shim has several receptacles; however, those skilled in the art will understand that the shims may have only one receptacle and that only some of the shims of a rotor may be equipped with one or more of these receptacles.

[0034] In some embodiments, and as shown in Figures 4 and 5, the wedge 14 has, on its outer face 14c, an additional thickness 140 extending over all or part of the height h of the wedge. The height h of the wedge 14 is the dimension of said wedge measured axially along the axis XX; the height h of the wedge 14 is approximately equal to the height of the windings 13a, 13b extending on either side of the wedge 14.

[0035] The extra thickness 140 can extend over the entire height of the wedge, between the two rotor locking discs, or only over a part of this height. This additional thickness has a width 1, less than or equal to the width of the outer face 14c of the shim 14, and a thickness e (relative to the original outer face 14c of the shim) adapted to the depth chosen for the receptacles. The thickness e of the additional thickness 140 can at most be equal to the radial distance between the outer face 14c of the shim 14 and the outer face 16c of the teeth 16 adjacent to said shim.

[0036] The shim 140 and the spacer 14 are monolithic, meaning they form a single piece. To achieve this, the shim 140 is formed with the spacer 14 during the manufacturing process of said spacer. If the spacer is made of plastic, the shim can be formed by plastic injection molding in a mold having the shape of the spacer with its shim.

[0037] In an embodiment shown in [Fig.5], the wedge 14 has an overthickness 140 extending over the entire height h of the wedge 14. This overthickness 140 has a rounded shape, that is to say, it has a cross-section in the shape of an arc of a circle. In this embodiment, the receptacles are formed by two chamfers 141a, 141b extending axially (parallel to the central axis XX) on either side of the overthickness 140. The chamfers 141a, 141b each have a beveled surface 141d opening onto a flat surface 141c, the beveled surface 141d connecting the overthickness 140 and the flat surface 141c and allowing the varnish to flow from said overthickness 140 to said flat surface 141c.Thus, the excess varnish that flows onto the over-thickness 140 migrates, under the effect of the rotation of the rotor, to the chamfers 141a, 141b where it is retained on the flat surfaces 141c of said chamfers, without generating a skin effect on the outer surface of the rotor.

[0038] In another embodiment, shown in Figures 6 and 7, the wedge 14 has an overstud 140 extending over the entire height h of the wedge 14 or over only a part of the height h. The overstud 140 may have a rounded shape (i.e. a section in the shape of an arc of a circle as in [Fig.7] or [Fig.5]) or a trapezoidal shape (as in [Fig.6]) with an outer flat face 140a and two oblique lateral faces 140b extending each on either side of the outer flat face 140a to the respective chamfers 141b, 141a. Whatever the shape of the overthickness 140 (rounded or trapezoidal), the latter has several grooves or striations 142a, 142b, 142c, forming a groove 142, leading to one or two chamfer(s) 141 as described in the embodiment of [Fig.5].Thus, the excess varnish flows through the grooves of the slot 142 to the chamfer 141 where it is retained on the flat surface 141c of said chamfer, without creating a skin effect on the outer surface of the rotor. In the embodiment shown in Figures 6 and 7, the grooves of the slot 142 are parallel to each other and oriented in an oblique direction relative to the other. to the central axis XX, this oblique direction favors the flow of varnish towards one of the chamfers 141 when the rotor is rotating; the shim 14 may then have only one chamfer 141, the varnish flowing along the grooves of the slot 142 towards the chamfer 141 (see example in [Fig. 6]). Of course, in the embodiment shown in Figures 6 and 7, the shims 14 may also have two chamfers 141a, 141b, extending on either side of the grooves of the slot 142 (variant not shown in the figures).

[0039] In another embodiment, shown in [Fig. 8], the wedge 14 has an additional thickness 140 extending over the entire height h of the wedge 14 or over only a portion of the height h. This additional thickness 140 is identical to that described previously in connection with Figures 6 and 7 and may be rounded or trapezoidal in shape. Regardless of the shape of the additional thickness 140, it comprises a first and a second set of grooves or striations, respectively 142a, 142b, 142c and 143a, 143b, 143c, which form a double intersecting groove 142, 143. This double cross groove 142, 143 includes a first groove 142 formed of a set of grooves 142a, 142b, 142c parallel to each other and oriented along a first oblique direction with respect to the central axis XX, this first groove 142 being identical to that described in connection with [Fig.7].The double cross groove 142, 143 also includes a second groove 143, formed of a set of grooves 143a, 143b, 143c parallel to each other and oriented along a second oblique direction different from the first oblique direction. The second groove 143 forms, with the first groove 142, a mesh, also called double intersecting groove 142, 143. The grooves of the first groove 142 open onto a first chamfer 141a (such as that described in the embodiment of [Fig.5]) extending axially along a first side of the mesh 142, 143. The grooves of the second groove 143 open onto a second chamfer 141b, identical to the first chamfer 141a but extending axially along a second side of the mesh 142, 143, symmetrical to the first side with respect to the mesh 142, 143.In this embodiment, the excess varnish flows both through the first groove 142 to the first chamfer 141a and through the second groove 143 to the second chamfer 141b, the varnish being retained in the first and second chamfers without causing a skin effect on the outer surface of the rotor.

[0040] In another embodiment, shown in [Fig. 9], the wedge 14 has an additional thickness 140 extending over the entire height h of the wedge 14 or over only a portion of the height h. This additional thickness 140 is identical to that described previously in connection with Figures 6 and 7 and may be rounded or trapezoidal in shape. Whatever its shape, the additional thickness 140 has several grooves or striations 142a, 142b, 142c, forming a groove 142, opening onto two chamfers. 141a and 141b, such as that described in the embodiment of [Fig. 5]. The two chamfers 141a, 141b are identical and extend axially on either side of the over-thickness 140. In the embodiment of [Fig. 9], the grooves of the slotting 142 are parallel to each other and oriented in a direction substantially perpendicular to the central axis XX. Each groove of the slotting 142 therefore connects the first chamfer 141a with the second chamfer 141b, which allows the varnish to flow towards one of the chamfers when the rotor is rotating. Thus, the excess varnish flows through the slotting 142 to the chamfers 141a, 141b where it is retained on the flat surfaces of said chamfers, without creating a skin effect on the outer surface of the rotor.

[0041] In other embodiments, such as those shown in Figures 10, 11, and 12, the wedge 14 has several holes 144, 145 distributed on the outer face 14c of said wedge. These holes 144, 145 may be aligned along a longitudinal axis parallel to the central axis XX or, conversely, scattered regularly or irregularly on the outer face to the right, left, and / or center. They may be formed directly in the outer face 14c of the wedge 14 or on an additional thickness 140 as described previously in connection with Figures 6 and 7. They may be made in the wedge 14 by drilling through said wedge or formed as part of the wedge during its manufacture. The orifices may have a circular cross-section (like the orifices 144 in [Fig. 10]) or an oblong cross-section (like the orifices 145 in Figures 11 and 12), with straight walls (perpendicular to the central axis XX) or slanted walls (forming a non-right angle with respect to the central axis XX). In an alternative design shown in [Fig. 10], the orifices 144 are blind orifices, i.e., non-through orifices, whose role is to retain excess varnish as it flows onto the outer face 14c of the wedge during rotor rotation. According to another alternative shown in figures 11 and 12, the orifices 145 are through orifices, the opening of which is connected to an internal channel 146. The internal channel 146 can be a groove formed inside the structure of the wedge 14 and into which the orifices 145 open.Thus, the excess varnish flows through the orifices 145 to the internal channel 146 where it is retained without causing a skin effect on the outer surface of the rotor.

[0042] Those skilled in the art will understand that all the variants and alternatives described above in connection with Figures 10 to 12 can be combined with one another. For example, circular cross-section holes can be through-holes opening into an internal channel; similarly, oblong cross-section holes can be blind and / or made directly on the outer surface 14c of the wedge (without any additional thickness); all the features described in connection with Figures 10 to 12 can thus be combined, the combinations not being limited to the representations of figures 10, 11 and 12.

[0043] In all the embodiments described above, the varnish receptacles, whatever their shape, number and positioning, are housed in the wedge 14, which has the advantage that the very structure of the rotor is not modified and that, consequently, the performance of the rotor is not impacted by the presence of the receptacles.

[0044] However, according to an alternative not shown in the figures, the receptacles can be grooves or non-through holes formed on the outer surface of the rotor body 15, between the rotation shaft 11 and the windings 13. These receptacles can be made by stamping the outermost sheets of the stack of sheets forming the rotor body 15. In this alternative, the performance of the rotor must be re-evaluated according to the shape, number and positioning of the varnish receptacles.

[0045] Regardless of the embodiment chosen, the wound rotor according to the invention can be produced by following the steps of process 200 shown in [Fig. 13]. The first step 210 consists of forming varnish receptacles on the outer surface of the rotor body or on the outer face of at least one shim 14. When the varnish receptacles are housed in the shim 14, and the shim 14 is made of plastic, said receptacles can be formed during the manufacture of the shim by plastic injection molding. The following step 220 consists of winding an electrically conductive wire around the teeth 16 of a rotor body 15 to create windings 13. These windings 13 are connected to each other using any of the usual techniques.Once the windings 13 are formed, insulating shims 14 are mounted (step 230) in each notch 17 of the rotor body, between two adjacent windings, to bond the windings of each winding together and to insulate the two windings 13a, 13b passing through the same notch 13. The process 200 continues with step 240 of installing a locking disc 12 at each of the axial ends of the windings 13; these discs hold the windings in place. Step 250 of dipping and rolling the rotor 10 in a varnish bath is then carried out to bond the windings of each winding together and ensure electrical insulation of each winding. Finally, step 260 of polymerizing the varnish-impregnated rotor is carried out to solidify the varnish.

[0046] During the dipping / rolling 240 and polymerization 250 operations, the rotor 10 is rotated to ensure the most even distribution of the varnish possible over the entire rotor. It is during these operations 240 and 250 that the invention comes into play, the varnish receptacles allowing the flow of excess varnish to be directed. varnish and / or to retain this excess varnish in order to avoid skinning effects on the outer surface of the rotor.

[0047] Although described through a number of examples, variants and embodiments, the wound rotor according to the invention includes various variants, modifications and improvements which will be obvious to a person skilled in the art, it being understood that these variants, modifications and improvements are part of the scope of the invention.

Claims

Demands

1. Wound rotor (10) for an electric machine, comprising: - a cylindrical rotor body (15) intended to be mounted around a rotor shaft with axis of rotation XX, said rotor body having axially extending teeth (16) and notches (17), - electrical windings (13) extending axially each around a tooth of the rotor body, - insulating shims (14) extending axially each in a notch of the rotor body, between two consecutive windings, - a layer of gluing varnish distributed at least on the windings of the rotor, and - varnish receptacles (141, 142) housed on at least one external surface (14c) of the rotor to receive excess varnish.

2. Rotor according to claim 1, characterized in that the varnish receptacles are located on an outer face (14c) of the insulating wedges.

3. Rotor according to claim 1, characterized in that each insulating wedge has, on its outer face, an overthickness (140) in which the varnish receptacles are formed.

4. Rotor according to any one of claims 1 to 3, characterized in that the varnish receptacles have at least one through or non-through orifice.

5. Rotor according to claim 4, characterized in that the orifices have a circular or oblong cross-section.

6. Rotor according to any one of claims 1 to 3, characterized in that the receptacles have at least one groove (142) ensuring a flow of excess varnish.

7. Rotor according to claims 3 and 6, characterized in that the receptacles have at least one chamfer (141) extending axially on the outer face of the wedge, along the overthickness.

8. Rotor according to claims 6 and 7, characterized in that the grooving comprises a set of grooves (142a, 142b, 142c) opening onto at least one chamfer (141), the set of grooves ensuring a flow of excess varnish and the chamfer ensuring the retention of said excess varnish.

9. Rotor according to claim 8, characterized in that the grooves of the set of grooves are parallel to each other and oriented in an oblique direction with respect to an axis of the rotor shaft.

10. Rotor according to claim 8, characterized in that the grooves of the set of grooves are parallel to each other and oriented in a direction perpendicular to an axis of the rotor shaft.

11. An electrical machine comprising a rotor and a stator, characterized in that the rotor conforms to any one of the preceding claims.

12. A method for manufacturing a wound rotor according to any one of claims 1 to 10, comprising the following operations: - making varnish receptacles on an outer surface of a rotor body (15) or an outer face (14c) of at least one insulating shim (14), - winding an electrically conductive wire around the teeth (16) of the rotor body to create windings (13a,13b), - mounting insulating shims in each notch (17) of the rotor body, between two windings (13a and 13b), - installing locking discs (12) at each axial end of the windings, - dipping and rolling the rotor in a varnish bath, and - polymerizing the varnish-impregnated rotor.

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