Assembly for electric motor with improved stator and protective housing

Abstract

The invention relates to an assembly for an electric motor (10) comprising a stator (12) and a protective housing (14) substantially cylindrical in revolution about a common axis (X), assembled by inserting the stator (12) into the protective housing (14). The stator (12) and protective housing (14) are configured such that there are a plurality of local expansion gaps between the stator (12) and the protective housing (14). The expansion gaps are dimensioned to allow local elastic deformation of the protective housing (14) at the expansion gap, said elastic deformation compensating for a stress related to a predetermined thermal contraction of the protective housing (14). Figure for the abstract: Figure 2

Description

Title of the invention: Assembly for an electric motor with improved stator and protective casing

[0001] The invention relates to the field of electric motors and in particular brushless direct current electric motors intended in particular for vehicle equipment.

[0002] Many electric motors are used in automotive vehicle equipment, particularly for wiping devices.

[0003] In order to protect electric motors from their environment, it is known to protect the electric motor by placing a protective casing around the stator of the electric motor. This protective casing also ensures heat transfer by conduction in order to allow dissipation of the thermal energy produced by the motor to the outside.

[0004] The stator of the electric motor is generally force-mounted in the protective casing. However, such force-mounted mounting can lead to the formation of metal shavings which can cause electrical problems. Another solution is to use pins to fix the casing to the stator, which poses problems of logistical management of these parts or to glue them together, which has the disadvantage of reducing the thermal conductivity between the components of the motor, and consequently hindering the dissipation of the heat generated by the motor during its operation.

[0005] It is therefore preferable to mount the stator in the protective casing by shrinking, that is to say by first heating the casing to expand it, then slipping it onto the stator. Cooling the casing then causes it to shrink and therefore become fixed to the stator from which it can no longer be removed.

[0006] However, it is important that the hooping does not have an influence on the air gap between stator and rotor, that is to say that the latter is not reduced by any possible deformation of the stator due to the forces that the latter undergoes due to the retraction of the casing during its cooling.

[0007] Furthermore, regardless of how the stator and the protection board are assembled, during its operation, the motor may see its temperature drop to -40°C. However, this creates a retraction of the casing generating forces which can potentially deform the stator and thus reduce the air gap between the stator and the rotor.

[0008] This phenomenon occurs particularly when the casing is made of a material having a higher coefficient of thermal expansion than the stator. Indeed, in this case, the material of the casing will shrink more than that of the rotor and may deform plastically and therefore induce significant forces on the stator. We speak in particular of differential expansion.

[0009] The invention therefore aims to prevent the reduction of the air gap between stator and rotor in the event of deformation by thermal expansion of the casing.

[0010] To this end, the invention relates to an assembly for an electric motor comprising a stator and a protective casing of generally symmetrical shapes around a common axis, assembled by inserting the stator into the protective casing, characterized in that the stator and protective casing are configured so that there are a plurality of local expansion gaps between the stator and the protective casing, the expansion gaps being dimensioned so as to allow local elastic deformation of the protective casing at the expansion gap, said elastic deformation making it possible to compensate for a force linked to a predetermined thermal contraction of the protective casing.

[0011] Due to the fact that there are a plurality of local expansion gaps between the stator and the protective casing, dimensioned so as to allow local elastic deformation of the protective casing at the expansion gap making it possible to compensate for a force linked to a predetermined thermal contraction of the protective casing, the card material is prevented from deforming plastically and inducing significant forces on the stator. Thus, there is no risk of the air gap of the motor being affected.

[0012] In other words, the expansion gap creates a "reserve" of space between the stator and the casing, the dimensions of which are related to the relative differential expansion of the two materials from which the stator and the casing are made. The dimensions of the expansion gap are, among other things, calculated based on the expansion coefficients of the casing and stator materials, their dimensions, and the predetermined thermal contraction force.

[0013] The invention may have one or more of the following aspects taken alone or in combination.

[0014] According to a first embodiment of the invention, the protective casing comprises for example a plurality of radial projections and contact zones, the expansion spaces being formed by the spaces between the radial projections and the stator.

[0015] Preferably, each radial projection is for example arranged between two contact zones. This makes it possible to distribute the expansion spacings around the periphery of the protective casing.

[0016] According to a particular embodiment of the invention, the radial projections are for example in the general shape of a lobe. Such a shape is easy to produce and allows significant elastic deformation.

[0017] According to another particular embodiment of the invention, the radial projections are for example in the general shape of a notch. Such a shape is easy to produce and allows significant elastic deformation.

[0018] Advantageously, the radial projections are for example uniformly distributed around the circumference of the protective casing.

[0019] According to a second embodiment of the invention, the protective casing comprises, for example, a plurality of through slots, the through slots forming the expansion spaces.

[0020] Advantageously, the predetermined thermal expansion of the protective casing corresponds for example to a thermal contraction force of the stator taking place during a drop in temperature of the electric motor assembly below -10°C, preferably below -20°C, and more preferably below -40°C.

[0021] In order to avoid assembly using pins or gluing, the protective casing is for example assembled to the stator by force fitting or by shrink fitting and the predetermined thermal expansion of the protective casing corresponds to a thermal contraction force of the protective casing taking place during assembly by shrink fitting.

[0022] Preferably, the stator is for example made of an alloy essentially comprising steel and the protective casing is made of an alloy essentially comprising magnesium or aluminum. Since aluminum and magnesium have coefficients of expansion much higher than that of steel, it is thus ensured that it is indeed the protective casing which will deform to compensate for the forces linked to thermal shrinkage of the electric motor assembly. Brief description of the figures

[0023] The invention will be better understood on reading the following description given solely by way of example and with reference to the appended drawings in which:

[0024] [Fig-1] [Fig. 1] is an exploded perspective view of an assembly for an electric motor according to a first embodiment of the invention;

[0025] [Fig.2] [Fig.2] is an axial sectional view of the electric motor assembly of [Fig.l];

[0026] [Fig.3] [Fig.3] is a view similar to [Fig.2] and of a protective casing according to a third particular embodiment of the invention;

[0027] [Fig.4] [Fig.4] is a view similar to [Fig.2] and of a protective casing according to a third particular embodiment of the invention. Detailed description

[0028] In all figures, elements having identical functions bear the same reference numbers.

[0029] The following embodiments are examples. Although the description refers to a or more embodiments, this does not necessarily mean that each reference relates to the same embodiment, or that the features apply only to a single embodiment. Single features of different embodiments may also be combined or interchanged to provide other embodiments.

[0030] [Fig.l] shows an exploded perspective view of an assembly 10 of an electric motor according to a first embodiment of the invention. The electric motor in question is, for example, a brushless motor.

[0031] The electric motor assembly 10 comprises a rotor 11, a stator 12 and a protective casing 14.

[0032] The stator 12 is preferably made of an alloy essentially comprising steel and the protective casing 14 is preferably made of an alloy essentially comprising aluminum or essentially comprising magnesium.

[0033] As can be seen in [Fig. 2], in which the stator 12 is inserted into the protective casing 14, the stator 12 has a generally symmetrical shape around a longitudinal axis XX of symmetry which is normal to the plane of FIGS. 2 to 4 and 6. The longitudinal axis XX here passes through the center of the cross-section of the stator 12.

[0034] Conventionally, the stator 12 comprises an assembly of sheets 16 comprising a plurality of teeth 18. The teeth 18 define between them a plurality of notches 20. The notches 20 are intended to receive electromagnetic windings 21 (for reasons of clarity, a single wire per notch is shown schematically).

[0035] Also conventionally, the teeth 18 have a T shape and are oriented towards the inside of the stator 12, that is to say towards its axis of symmetry, here the longitudinal axis XX. In the example of [Fig. 2], the stator 12 comprises nine teeth 18 distributed regularly around the internal periphery of the stator 12. This number can naturally vary. Thus, the stator 12 comprises nine notches 20.

[0036] The protective casing 14 also has a generally symmetrical shape around a longitudinal axis XX, which is its axis of symmetry and is here normal to the plane of the figures. In the position shown in [Fig.2], which is the insertion position in which the stator 12 is inserted into the protective casing, the longitudinal axes of the stator 12 and of the protective casing 14 are merged in the longitudinal axis XX.

[0037] In the first embodiment of the invention as shown in [Fig. 2], the protective casing 14 comprises a plurality of radial projections 22 and areas of direct contact 24 with the stator 12. The contact areas 24 are more precisely in direct contact with the external surface of the stator 12 as can be seen in the figures.

[0038] The radial projections 22 are oriented towards the outside of the protective casing 14, that is to say opposite its axis of symmetry, here the longitudinal axis XX.

[0039] The radial projections 22 are, in the embodiment shown in the figures, distributed according to an axial symmetry around the longitudinal axis of the protective casing 14.

[0040] In the first embodiment as shown in [Fig. 1], the cross-section of the radial projections 22 has an internal contour having a continuously varying curvature along the contour. In other words, the cross-section of the locking projections 22 does not have a break in continuity along its contour, or does not form an angle along its contour.

[0041] In the example shown in [Fig.l], the locking projections 22 have a lobe-shaped cross-section. Such a shape does not have any discontinuity. Thus, in this particular example, the cross-section of the stator 12 has a “flower” shape, of which each radial projection 22 is a “petal”.

[0042] Preferably, each locking projection 22 is arranged opposite a notch 20. In other words, the stator 12 comprises as many locking projections 22 as notches 20. The stator 12 therefore here comprises nine locking projections 22 uniformly distributed around the longitudinal axis XX of the stator 12.

[0043] The stator 12 and protective casing 14 are configured such that there are a plurality of local expansion gaps 24 between the stator 12 and the protective casing 14.

[0044] The expansion spaces 26 are here formed by the spaces between the radial projections 22 and the stator 12. Thus, there are as many expansion spaces 26 as there are radial projections 22.

[0045] Each radial projection 22 being arranged between two contact zones 24, the expansion spaces 16 are each delimited by a radial projection 22 and the two contact zones 24 which are located on either side of the radial projection 22.

[0046] As a result and taking into account the lobe shape of the radial projections 22, the expansion spaces 26 are delimited by a lobed surface.

[0047] The expansion gaps 26 are dimensioned so as to allow local elastic deformation of the protective casing 14 at the expansion gap 26. The elastic deformation is determined so as to compensate for a force linked to a predetermined thermal contraction of the protective casing 14.

[0048] The dimensions of the local expansion spaces 26 will be chosen as a function of the material of the protective casing 14, the material of the stator 12, in particular their respective thermal expansion coefficients, their dimensions and the predetermined thermal contraction of the protective casing 14 which can be calculated as a function of the conditions of this thermal contraction.

[0049] In particular, in a first variant, the predetermined thermal expansion of the protective casing 14 corresponds to a thermal contraction force of the stator 12 taking place during a temperature drop of the electric motor assembly 10 below -10°C, preferably below -20°C, and more preferably below -40°C

[0050] Preferably, the radial contact projections 22 are uniformly distributed over the circumference of the protective casing 14, in order to best distribute the forces linked to the thermal contraction of the protective casing 14. However, this is only a non-limiting example.

[0051] In another variant, the protective casing 14 being assembled to the stator 12 by shrink fitting, the predetermined thermal expansion of the protective casing 14 corresponds to a thermal contraction force of the protective casing 12 taking place during assembly by shrink fitting.

[0052] In [Fig.l], there are nine radial projections 22, but this is of course only a non-limiting example, the radial projections 22 being able to be more or less numerous.

[0053] In the second embodiment of the invention illustrated in [Fig. 3], the radial projections 22 are generally crenellated. Thus, the contact zones 24 are substantially wider than in the first embodiment. Furthermore, the expansion spaces 26 are delimited by a crenellated surface.

[0054] In [Fig. 3], there are twelve radial projections 22, but this is of course only a non-limiting example, the radial projections 22 being able to be more or less numerous.

[0055] According to a third embodiment illustrated in [Fig. 4], the protective casing 14 comprises a plurality of through slots. In this embodiment, the through slots form the expansion spaces 26. Through slots 26 are understood to mean discontinuities in the casing 14 passing through the entire thickness of the casing 14 and extending along the axis XX of the casing 14.

[0056] In [Fig. 4], there are six through slots 26, but this is of course only a non-limiting example, the through slots 26 being able to be more or less numerous. The protective casing 14 is thus divided into six sections 28 whose cross-section at the axis XX is in the shape of an arc of a circle.

[0057] The through slots 26 allow, by allowing a deformation of these sections 28 so as to close them, to absorb the thermal expansion forces of the protective casing 14.

[0058] Preferably, the through slots 26 are uniformly distributed around the protective casing in order to best distribute the forces linked to the thermal contraction of the protective casing 14. However, this is only a non-limiting example.

[0059] The invention is not limited to the embodiments presented and other embodiments embodiment will be clear to those skilled in the art. In particular, it is possible to provide different shapes for the stator and the protective casing than those shown in the figures. It may also be provided that the protective casing of the first embodiment has cooling fins similar to those of the second embodiment and arranged in the same way. List of references

[0060] 10: Electric motor assembly 11: Rotor 12: Stator 14: Protective casing 16: Sheet metal assembly 18: Stator teeth 20: Stator notches 21: Electromagnetic winding 22: Radial projections of the protective casing 24: Contact areas of the protective casing 26: Expansion gaps 28: Crankcase sections

Claims

Claims

1. An assembly for an electric motor (10) comprising a stator (12) and a protective casing (14) of generally symmetrical shapes around a common axis (XX), assembled by inserting the stator (12) into the protective casing (14), characterized in that the stator (12) and protective casing (14) are configured so that there are a plurality of local expansion gaps (16) between the stator (12) and the protective casing (14), the expansion gaps (16) being dimensioned so as to allow local elastic deformation of the protective casing (14) at the expansion gap (16), said elastic deformation making it possible to compensate for a force linked to a predetermined thermal contraction of the protective casing (14).

2. An electric motor assembly (10) according to claim 1, wherein the protective casing (14) comprises a plurality of radial projections (22) and contact areas (24), the expansion gaps (16) being formed by the gaps between the radial projections (22) and the stator (12).

3. An electric motor assembly (10) according to claim 2, wherein each radial projection (22) is disposed between two contact areas (24).

4. An electric motor assembly (10) according to claim 2 or 3, wherein the radial projections (22) are generally lobe-shaped.

5. An electric motor assembly (10) according to claim 2 or 3, wherein the radial projections (22) are generally slot-shaped.

6. An electric motor assembly (10) according to any one of claims 2 to 5, wherein the radial projections (22) are uniformly distributed around the circumference of the protective casing (14).

7. An electric motor assembly (10) according to claim 1, wherein the protective housing (14) comprises a plurality of through slots, the through slots forming the expansion gaps (16).

8. An electric motor assembly (10) according to any preceding claim, wherein the predetermined thermal expansion of the protective casing (14) corresponds to a thermal contraction force of the stator (12) occurring during a temperature drop of the electric motor assembly (10) below -10°C, preferably less than -20°C, and more preferably less than -40°C.

9. An electric motor assembly (10) according to any preceding claim, wherein, the protective casing (14) being assembled to the stator (12) by shrink fitting, the predetermined thermal expansion of the protective casing (14) corresponds to a thermal contraction force of the protective casing (12) taking place during the shrink fitting assembly.

10. An electric motor assembly (10) according to any preceding claim, wherein the stator (12) is made of an alloy essentially comprising steel and the protective casing (14) is made of an alloy essentially comprising magnesium or aluminum.

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