Axial flux electric machine with thermal guide between each coil and each associated tooth

Abstract

The invention relates to an axial flux electric machine comprising a casing enclosing at least one rotor and at least one stator, each stator comprising a stator body (6), teeth (7) regularly distributed circumferentially on the stator body (6) and coils (8) wound around the teeth (7). In addition, each stator comprises thermal guides (9), each of the thermal guides (9) being positioned between a coil (8) and the tooth (7) on which the coil (8) is wound, each thermal guide (9) being in contact with the coil (8) and with the casing so as to conduct the heat from the coils (8) to the casing only by thermal conduction in each thermal guide (9).

Description

[0001] AXIAL FLUX ELECTRIC MACHINE WITH THERMAL GUIDE BETWEEN EACH COIL AND EACH ASSOCIATED TOOTH

[0002] Technical field

[0003] The invention relates to the field of axial flux electrical machines.

[0004] This type of axial flux electric machine can find applications in particular in electric or hybrid vehicles, such as cars, buses, trucks, construction machinery.

[0005] Prior art

[0006] In recent decades, the development of electrical machines has focused mainly on radial flux electrical machines.

[0007] Radial flux electrical machines typically comprise a coaxial rotor and stator, one surrounding the other. Thus, the magnetic flux can pass radially from the rotor to the stator and vice versa, via a radial air gap which is defined as the radial clearance between the rotor and the stator.

[0008] In contrast, axial flux machines are characterized by at least one rotor and at least one stator that are arranged successively one behind the other in the axial direction (of the rotor's axis of rotation), so that the magnetic flux path between the rotor and the stator is axial. In other words, the rotor and the stator face each other and are separated by an axially thick air gap (or axial clearance between the rotor and the stator).

[0009] The rotor of permanent magnet axial flux electric machines generally comprises permanent magnets bonded to the rotor yoke or inserted into a rotor body, in which case the permanent magnets are separated by radial arms from the rotor body. The stator generally comprises a ferromagnetic stator body with or without teeth. The electrical winding in the stator slots can be distributed or concentric, meaning that each winding surrounds a tooth.

[0010] In the context of the development of high power and torque density machines for electric or hybrid traction, particularly for electric or hybrid vehicle applications, the topology of axial flux machines is positioned among those with the highest potential, in particular due to the high axial size constraint. Axial flux electric machines are also of interest for stationary applications as well as for wind turbine applications.

[0011] Generally, axial flux electric machines allow higher power and torque densities than radial flux electric machines.

[0012] This gain is generally achievable by increasing the number of pole pairs in the rotor, which increases the rotation frequency as well as the rotor losses (i.e. losses in the magnets). In addition, the use of a tooth winding allows for a reduction in the coil heads, but increases the harmonic content in the air gap, causing an increase in losses in the stator iron and in the magnets.

[0013] As a result, axial flux machines tend to heat up more and controlling heating and cooling is therefore an important issue for this type of machine.

[0014] Patent application US2013 / 0285487 seeks to cool the stator coils. To do this, the coils include cooling channels in the coils for circulating a fluid in these channels, within the coils themselves. However, this architecture is complicated to implement and requires a cooling fluid that circulates in the channels.

[0015] Patent application US2015 / 0364956 also seeks to cool the coils, but unlike the previously cited application, this patent application seeks to create an air gap in contact with the coils to promote cooling. However, the cooling is only based on thermal convection by an air gap, which is not very efficient.

[0016] The technical problem of the invention consists in improving the cooling of the coils, by a simple and inexpensive solution, preferably requiring no circulation of fluid in the stator, and more particularly no forced circulation.

[0017] Summary of the invention

[0018] To solve the technical problem, the invention relates to an axial flux electric machine comprising a casing enclosing at least one rotor and at least one stator, each stator comprising a stator body, teeth regularly distributed circumferentially on the stator body and coils wound around the teeth. In addition, each stator comprises thermal guides, each of the thermal guides being positioned between a coil and the tooth on which the coil is wound, each thermal guide being in contact with the coil and with the casing so as to conduct heat from the coils to the casing solely by thermal conduction in each thermal guide.

[0019] Advantageously, the thermal guide material has a thermal conductivity strictly greater than the thermal conductivity of the stator body material.

[0020] Preferably, the material of the thermal guide is metallic, preferably comprising aluminum, copper, and / or an alloy of aluminum and / or copper.

[0021] According to one configuration of the invention, each thermal guide comprises a first plate surrounding the tooth, over substantially the entire surface of the tooth facing the coils. According to a variant of the invention, each thermal guide comprises a second plate, the second plate covering the tooth so as to form a cap facing said rotor, or the second plate covering an axial end surface of the coils facing the rotor to hold the coils in position.

[0022] Advantageously, each thermal guide is split in the radial direction, over the entire radial length of the thermal guide or over substantially the entire radial length of the thermal guide.

[0023] Advantageously, the different thermal guides are independent of each other or several thermal guides are connected to each other. Preferably, all the thermal guides are connected to each other so as to form a single part, and even more preferably, the thermal guides are connected to each other by substantially radial junctions extending over the surface of the stator body between the teeth.

[0024] Preferably, the electrical machine comprises a first electrically insulating layer, preferably non-thermally insulating, between each thermal guide and the associated coil, the first electrically insulating layer preferably being a first sheet or a first varnish.

[0025] Preferably, each first electrically insulating layer is a first varnish covering both the thermal guide and the associated coil so as to connect them together.

[0026] Advantageously, the electric machine comprises a second thermal insulating layer, and preferably electrically insulating, between each thermal guide and the associated tooth, the second thermal insulating layer preferably being a second sheet or a second varnish.

[0027] According to one embodiment of the invention, each first electrically insulating layer and / or each second thermal and electrically insulating layer may be made of anodized aluminum.

[0028] According to one configuration of the invention, each thermal guide and the associated coil may be embedded in a coating material.

[0029] Preferably, each thermal guide comprises a fixing means for fixing it to the casing and / or the stator body.

[0030] Preferably, the fixing means comprises at least one strip capable of being fixed to the casing or folded, at the periphery of the stator body, under the stator body. According to a variant of the invention, the axial flux electric machine comprises two rotors and a stator, or two stators and a rotor. List of figures

[0031] Other characteristics and advantages of the electrical machine according to the invention will appear on reading the following description of non-limiting examples of embodiments, with reference to the figures appended and described below.

[0032] Figure 1 represents a first variant of an axial flux electric machine according to the invention.

[0033] Figure 2 represents a second variant of an axial flux electric machine according to the invention.

[0034] Figure 3 shows a stator in longitudinal sectional view of an axial flux electric machine according to the invention.

[0035] Figure 4 illustrates a first variant of a stator thermal guide of an axial flux electric machine according to the invention.

[0036] Figure 5 illustrates a second variant of a stator thermal guide of an axial flux electric machine according to the invention.

[0037] Figure 6 illustrates a third variant of a stator thermal guide of an axial flux electric machine according to the invention.

[0038] Figure 7 illustrates a fourth variant of a stator thermal guide of an axial flux electric machine according to the invention.

[0039] Figure 8 illustrates a fifth variant of a stator thermal guide of an axial flux electric machine according to the invention.

[0040] Figure 9 illustrates another type of thermal guide of an axial flux electric machine according to the invention.

[0041] Figure 10 illustrates a sectional view of another variant of an axial flux electric machine stator according to the invention. Description of the embodiments

[0042] The invention relates to an axial flux electric machine comprising a casing enclosing at least one rotor and at least one stator.

[0043] The casing may comprise two flanges directly connected to each other, or two flanges and an outer cylinder (also called a "liner"), or any other similar design, with one flange positioned at each axial end of the outer cylinder. Thus, the casing forms an outer envelope of the electric machine. This outer envelope serves as protection for the stator(s) and rotor(s) located inside this outer envelope. The outer envelope also serves to position and fix the active parts of the electric machine. In addition, this outer envelope may serve to cool the electric machine, by convection with the ambient outside air or by the circulation of a heat transfer fluid in and / or around the outer envelope (in and / or around the cylinder and / or the flanges). The casing is then considered as a cold source.

[0044] Each stator comprises a stator body, teeth regularly distributed circumferentially on the stator body, and coils wound around the teeth. The teeth are fixed to the stator body, and the teeth extend axially from the stator body.

[0045] The rotor may, for example, comprise a rotor disc made of metallic material and permanent magnets. Thus, when an electric current passes through the stator coils of the electrical machine, an electromagnetic torque is produced and rotates the rotor of the machine, thanks to the interaction between the stator field produced by the winding and the rotor field produced by the permanent magnets. Conversely, when the rotor is rotated by any rotation means (a rotation shaft, for example), the permanent magnets generate a magnetic field that induces a magnetomotive force (EMF) in the stator coils. This makes it possible to transform the mechanical rotational energy of the rotor into electrical energy in the stator.Therefore, the electric machine can be used as an electric motor that transforms electricity into mechanical energy by rotating the rotor, or as an electric generator that transforms rotating mechanical energy into electrical energy.

[0046] According to the invention, the axial flux machine can thus comprise at least one rotor and at least one stator which are arranged successively one behind the other in the axial direction (of the axis of rotation of the at least one rotor), so that the path of the magnetic flux between each successive rotor and stator (i.e. which follow one another directly) is axial. In other words, each successive rotor and stator face each other and are separated by an air gap of axial thickness (or axial clearance between the rotor and the stator). According to the invention, each stator comprises thermal guides, each of the thermal guides being positioned between a coil and the tooth on which the coil is wound. In other words, each thermal guide is associated with a coil, itself associated with the tooth on which it is mounted (the thermal guide is interposed between the coil and the tooth). The thermal guides are capable of capturing the heat from the coils to evacuate it.Therefore, they have good thermal conduction.

[0047] Each heat guide is in contact with the coil and with the housing so as to conduct heat from the coils to the housing solely by thermal conduction in each heat guide. In other words, each heat guide has at least a first portion positioned between the coil and the tooth to capture heat from the coil and at least a second portion, such as an extension, which allows the recovered heat to be transmitted from the coil to the housing.

[0048] The contact of the thermal guide with the coil and with the casing may be direct or indirect. By indirect contact, it is meant that the contact takes place by at least one layer or at least one intermediate part (a first electrically insulating layer for example) and in fact in the absence of an air gap or other convective exchange. In other words, the guide may be in direct contact with an intermediate part or an intermediate layer, itself in direct contact with the casing or with the coil. Of course, the invention may comprise several intermediate parts and / or several intermediate layers so that the thermal guide is in indirect contact with the casing and / or the coil, the different intermediate parts or layers being in direct contact with each other and one of them being in direct contact with the casing or the coil and another in direct contact with the thermal guide.Thus, the heat exchange from the coils to the casing via the thermal guide is almost exclusively by thermal conduction. The casing is cooled by natural convection with the surrounding air or by the circulation of a heat transfer fluid in circuits arranged in the casing.

[0049] Preferably, the contact between the thermal guide and the housing may be direct so as to facilitate cooling and avoid additional thermal resistance. Alternatively, the thermal guide may be attached directly (without any intermediate part) to the housing by a fastening means, such as a screw, a rivet, a weld or a flange. For example, the thermal guide may comprise an extension attached to the first part positioned between the coil and the tooth, the extension for example allowing direct contact with the housing.

[0050] The use of thermal guides according to the invention makes it possible to do away with means of cooling by circulation of a fluid in the stator, generally requiring a pump (or other means) to put the fluid into circulation and sealing means.

[0051] Thus, cooling thanks to the invention is simple and effective.

[0052] The material of the thermal guides may advantageously have a thermal conductivity strictly greater than the thermal conductivity of the stator body, for example at least 10% greater than the thermal conductivity of the stator body material. Thus, heat can be efficiently evacuated from the coils to the housing by conduction.

[0053] More preferably, the material of the thermal guide may be metallic, preferably comprising aluminum or copper or an aluminum or copper alloy. These materials have good thermal conductivities for dissipating heat by conduction.

[0054] Advantageously, each thermal guide may comprise a first plate (or "thin sheet", i.e. for example a plate whose thickness is less than one fifth of the smaller of the other two dimensions) surrounding the tooth, over substantially the entire surface of the tooth opposite the coils. This first plate thus forms a first part. This first plate is positioned over the entire interface surface between the tooth and the coil, or substantially over this entire interface surface. This solution makes it possible to increase the exchange surface and therefore to recover a maximum of heat. By "substantially over this entire interface surface", it is meant that the surface of the first plate may be slightly smaller than the interface surface between the tooth and the coil, so as to allow a slot in the plate, i.e. a clearance, at least over a part of this surface to limit the looping of the induced currents.

[0055] According to a variant of the invention, each thermal guide may comprise a second plate (or “thin sheet”).

[0056] According to a first configuration of this variant, the second plate can cover the tooth, at the axial end of the tooth, so as to form a cap. Thus, each thermal guide covers the entire surface of the tooth or substantially the entire surface of the tooth. In addition to recovering a maximum of heat, this solution can facilitate assembly and slightly increase the rigidity of the thermal guide. Therefore, it is possible to first mount the coils on the thermal guide, then mount the thermal guide-coil assembly on the tooth, thus making assembly easier. In addition, this solution also makes it possible to collect part of the heat released by the permanent magnets so as to conduct it towards the housing and thus evacuate it. In this case, the solution makes it possible to cool both the coils and the magnets.By "substantially the entire surface of the tooth" is meant that the surface of the thermal guide may be slightly smaller than the surface of the tooth, so as to allow a slot in the plate, i.e. a clearance, at least over a portion of this surface to limit the looping back of induced currents. In other words, the cap may be slotted over at least a portion to limit the induced currents.

[0057] According to a second configuration of this variant (which may or may not be combined with the first configuration), the second plate may cover the axial end surface of the coils which is opposite the axial end surface of the coils in contact with the stator body. As a result, the second plate may serve to hold the coils axially in position between the stator body and the second plate. In addition, this second plate makes it possible to increase the exchange surface between the thermal guide and the coil and thus improve the cooling of the electrical machine. Furthermore, unlike the first configuration of this variant, the second plate may not protrude axially from the teeth in the direction of the rotor so as not to increase the axial air gap and thus not to deteriorate the performance of the machine. Indeed, the thickness of the second plate may be located over the axial length of the teeth, close to the axial end of the teeth.Furthermore, this configuration can be advantageous for assembly. Indeed, the second plate can be used as an axial stop for mounting the coils before mounting the thermal guide-coil assembly in the stator. This solution also allows some of the heat released by the permanent magnets to be collected so as to conduct it towards the housing and thus evacuate it. In this case, the solution allows both the coils and the magnets to be cooled.

[0058] According to a configuration of the invention, each first plate and / or second plate of each thermal guide may for example have a thickness of between 0.5 and 5 mm, preferably between 1 and 2 mm. As a result, the thermal guide fits into a very limited space, which makes it possible to limit the filling around the tooth with the thermal guide circulating the stator current and thus not to deteriorate the performance of the machine.

[0059] According to an advantageous embodiment of the invention, each thermal guide can be split in the radial direction, over the entire radial length of the thermal guide or over substantially the entire radial length of the thermal guide. This radial slot makes it possible to limit the looping of currents induced in the thermal guide, in particular when the thermal guide is made of magnetic metallic material.

[0060] The slot of the thermal guide passes axially through the thermal guide. “Substantially over the entire radial length” means that the slot may not be the entire length so that the thermal guide is not in two independent parts but is connected by a bead (or a junction) of material so that it is in a single part, to facilitate assembly, in particular the assembly of the coils before carrying out the assembly of the thermal guide-coil assembly on the associated tooth.

[0061] When the thermal guide slot is along the entire radial length, the thermal guide is then in two independent parts.

[0062] According to one configuration of the invention, the different thermal guides can be independent of each other. As a result, the coils can be mounted on each thermal guide and then each thermal guide-coil assembly on the tooth associated with this assembly. Mounting on the stator body can thus be facilitated.

[0063] Alternatively, several thermal guides can be connected together. For example, assemblies of 3 or 4 thermal guides can be made in one piece. Preferably, all the thermal guides can be connected together so as to form a single piece. In other words, the machine can comprise a thermal guide means in one piece, this guide means comprising thermal guides, each thermal guide being positioned between each coil and the tooth with which it is associated. For example, this thermal guide means can be made by a shell stamped to take the shape located around the stator body and the teeth, covering or not the surface of the teeth facing the rotor (forming or not a cap on each tooth). This solution allows mounting of all the thermal guides and all the coils in a single operation on the stator body and therefore reducing the assembly time.

[0064] Preferably, the thermal guides may be connected to each other by substantially radial junctions extending over the surface of the stator body between the teeth. In other words, the radial junctions are on the surface of the stator body located between the teeth. They also allow for increased heat recovery since these radial junctions are in contact with the coils on the radial surface of the coils.

[0065] Advantageously, these radial junctions can extend over the entire radial length of the teeth, to increase the exchange surface. They are therefore on the surface of the notches which separate the teeth, the notches allowing the winding to be placed around the teeth.

[0066] Preferably, the electrical machine may comprise a first electrically insulating layer, and optionally a non-thermally insulating layer, between each thermal guide and the associated coil. Thus, short circuits which could be generated by friction between the coil and the thermal guide can be avoided, in particular when the thermal guide has good electrical conduction properties, in particular if it is metallic and more particularly if it comprises copper or a copper alloy.

[0067] When the first electrically insulating layer is also thermally non-insulating, heat conduction is facilitated from the coils to the thermal guide.

[0068] When using a first electrically insulating layer (and preferably not thermally insulating), the contact between the coil and the thermal guide is indirect, the first electrically insulating layer then forming an interface piece between the two.

[0069] “A first electrically insulating layer” means a layer which has an electrical conductivity strictly lower than that of the coil and strictly lower than that of the thermal guide, for example at least 10% lower than these values.

[0070] By "a first electrically insulating and non-thermally insulating layer" is meant that the first electrically insulating layer has a thermal conductivity maximizing the heat exchange from the coils to the thermal guide.

[0071] According to one configuration, the first electrically insulating layer may be a first sheet (i.e., a thin plate, for example, 0.1 to 0.2 mm thick) or a first varnish. The first sheet may, for example, be mounted on the thermal guide and then the coils may be mounted on (around) the first sheet.

[0072] The first sheet can be made of plastic, for example.

[0073] When using a varnish, the varnish can then cover the surface of the thermal guide which is opposite the coils so as to avoid direct contact between the thermal guide and the coils.

[0074] According to an advantageous embodiment of the invention, each first electrically insulating layer may be a first varnish covering both the thermal guide and the associated coil so as to connect them together. Thus, the first varnish forms a mechanical cohesion between the coil and the thermal guide.

[0075] Advantageously, the electric machine may comprise a second thermally insulating, and preferably electrically insulating, layer between each thermal guide and the associated tooth. By adding this second layer, the thermal guide can better evacuate heat towards the casing by limiting the conduction of heat towards the tooth.

[0076] A "second thermal insulating layer" means a second layer which has a thermal conductivity strictly lower than that of the tooth and strictly lower than that of the thermal guide, for example at least 10% lower than these values. A "second thermal insulating and electrically insulating layer" means that the second thermal insulating layer also has an electrical conductivity which prevents short circuits.

[0077] According to one configuration, the second thermal insulating layer may be a second sheet (i.e. a thin plate, the thickness of which is for example less than one fifth of the other dimensions of the plate and for example the thickness of which is less than 1 mm) or a second varnish. The second sheet may for example be mounted on the tooth and then the thermal guide may be mounted on the second sheet.

[0078] When using a second varnish instead of a second sheet (or in addition to the second sheet), the second varnish can then cover the surface of the thermal guide which is opposite the tooth so as to avoid direct contact between the thermal guide and the tooth.

[0079] According to one configuration of the invention, each first electrically insulating layer and / or each second thermal and electrically insulating layer may be made of anodized aluminum. Indeed, anodized aluminum has very good electrical insulating properties, which reduces the risk of short circuits.

[0080] Advantageously, each thermal guide and the associated coil can be embedded in a coating material. The coating material further facilitates heat recovery. In addition, when the coil-thermal guide assembly is made before it is mounted on the tooth, this assembly can be embedded in a coating material in a simple mold and this mold can be reused for the other coil-thermal guide assemblies for the other teeth.

[0081] The varnish differs from the coating material by its thickness. For example, Nomex® varnish with a thickness of about 0.13 mm can be used. The varnish layer is thin, for example strictly less than 1 mm, while the coating material is much thicker (relative to the varnish). Indeed, the thickness of the coating material is generally greater than 2 mm to allow its application. In addition, the application technique is very different. Indeed, the varnish is generally applied by covering a surface with the varnish material (in liquid or viscous form, the layer hardens), for example using a brush, while the coating material is placed in a mold (or in a structure acting as a mold) and the coating material fills all the available space in the mold.

[0082] The coating material may in particular be a resin, such as an epoxy resin which has good thermal conduction properties. Advantageously, each thermal guide may comprise a fixing means for its fixing to the casing and / or to the stator body. Thus, the thermal guide may be directly fixed to the casing (thus it is also in direct contact with the casing, which facilitates heat dissipation) or be fixed to the stator body, being in direct or indirect contact with the casing.

[0083] According to a variant of the invention, the fixing means may comprise at least one blade capable of being fixed to the casing by screwing, welding, clamping or riveting for example. Alternatively, the blade may be folded, at the periphery of the stator body, under the stator body. By being folded over the periphery of the stator body, it may be in direct contact with the casing, while facilitating assembly. Indeed, the stator can be mounted with the thermal guides and then this assembly can be mounted in the casing without having to fix each thermal guide to the casing. In this way, the blade can therefore be held during the clamping of the stator body to the casing. The folded surface can be defined according to the heat transfer requirements, and may preferably cover almost the entire surface of the stator body to increase the exchange surface with the casing.

[0084] According to advantageous variants of the invention, the axial flux electric machine may axially comprise a succession of rotors and stators. The multiplication of rotors and / or stators makes it possible to increase performance (torque and power in particular), and this in a restricted space requirement.

[0085] Preferably, the axial flux electric machine may comprise two rotors and one stator, two stators and one rotor, or a stack of alternating stators and rotors. The stators as described are particularly suitable for stators at the axial ends of the electric machine, for example for an electric machine with two stators and a central rotor, particularly when the thermal guides are attached to the end plates of the housing. When the thermal guides can be attached to the outer cylinder of the housing, the stator can be used anywhere, including in a machine with two rotors and a central stator.

[0086] More particularly, the invention may relate to an axial flux electric machine with permanent magnets passing through the rotor. The stator according to the invention is suitable for this type of machine and makes it possible to reduce the axial size of the machine.

[0087] A machine with two rotors and one stator can thus successively axially comprise a first rotor, a central stator (i.e. between the two rotors) and a second rotor. A machine with two stators and one rotor can thus successively axially comprise a first stator, a central rotor (i.e. between the two stators) and a second stator. The invention further allows a method of assembling an axial flux electric machine as described in any one of the aforementioned variants or combinations of variants, in which the coils are wound around the thermal guides, then each coil-thermal guide assembly is mounted on a tooth, the coil-thermal guide assemblies corresponding to the coils wound around the thermal guides.

[0088] Figure 1 illustrates, in a schematic and non-limiting manner, a first variant of an axial flux machine according to the invention.

[0089] The axial flux machine comprises a casing 2. The casing 2 comprises an outer cylinder 5 and two flanges 3, one flange 3 at each axial (or longitudinal) end of the outer cylinder 5, so that the flanges 3 and the outer cylinder 5 form an outer casing. The machine could alternatively not comprise an outer cylinder and comprise two flanges connected together to form an outer casing. Inside the casing 2, the electrical machine here comprises a rotor 1 and two stators 100. The stators 100 are located on either side of the rotor 1, along the axis of rotation A of the rotor. In other words, along the axis A of rotation of the rotor, there is a stator 100, then the rotor 1 and then another stator 100. The rotor 1 is a rotor with permanent magnets 4, passing completely through the rotor (but the magnets could not be passing through according to a variant).Thus, the permanent magnets 4 face the two stators 100, which makes it possible to reduce the axial size of the electric machine.

[0090] Figure 2 illustrates, in a schematic and non-limiting manner, a second variant of an axial flux machine according to the invention.

[0091] The axial flux machine comprises a casing 2. The casing 2 comprises an outer cylinder 5 and two flanges 3, one flange 3 at each axial (or longitudinal) end of the outer cylinder 5, so that the flanges 3 and the outer cylinder 5 form an outer casing. The machine could alternatively not comprise an outer cylinder and comprise two flanges connected together to form an outer casing. Inside the casing 2, the electrical machine here comprises a stator 100 and two rotors 1 . The rotors 1 are located on either side of the stator 100, along the axis of rotation A of the rotor. In other words, along the axis of rotation A of the rotor, there is a rotor 1 , then the stator 100 and then another rotor 1 . The rotors 1 are permanent magnet rotors 4, completely glued to a rotor yoke but other types of permanent magnet mounting are of course possible.

[0092] Figures 1 and 2 illustrate two variants of axial flux electric machine according to the invention but the invention is not limited to this type of electric machine. In particular, the invention could be an electric machine with a single rotor and a single stator or an electric machine with other numbers of rotors and / or stators.

[0093] In Figures 1 and 2, the stator body and the teeth can be formed from a single piece (monobloc) or the teeth can be attached to the stator body. Other solutions can of course be considered.

[0094] Figure 3 illustrates, in a schematic and non-limiting manner, a longitudinal sectional view of a stator and a casing of an axial flux electric machine according to the invention.

[0095] A longitudinal section means a section in a plane which includes the longitudinal axis (represented by the dot-dash line).

[0096] The electric machine comprises a casing with two flanges 3 (only one is shown) and an outer cylinder 5. The flange 3 is positioned at a longitudinal end of the outer cylinder 5 to form, with the latter, an outer casing. Alternatively, the casing could not comprise an outer cylinder.

[0097] Inside the casing there are (at least) one stator and (at least) one rotor (not shown).

[0098] The stator comprises a stator body 6 and teeth 7 which extend axially (the axis being represented by the dot-and-dash line) from the stator body 6. The teeth 7 serve as a support for the winding of the coils 8 which are wound around the teeth 7.

[0099] In addition, the electric machine comprises thermal guides 9 positioned between the teeth 7 and the associated coils 8 (each coil 8 being mounted on a tooth 7, and therefore associated with a tooth 7) over substantially the entire surface located between the coils 8 and the teeth 7 so as to recover the heat from the coils.

[0100] Each thermal guide 9 is also in contact with the casing (not visible in the figure).

[0101] Figure 4 illustrates, in a schematic and non-limiting manner, a first variant of an axial flux electric machine stator according to the invention.

[0102] The stator comprises a stator body 6, here of substantially annular shape, delimited by an internal cylindrical surface, an external cylindrical surface and two flat end surfaces.

[0103] On one of the two flat end surfaces of the stator body 6, there are teeth 7 which extend axially, from this flat end surface towards the rotor (not shown to facilitate visualization). The teeth 7 here have a substantially trapezoidal section but other shapes could of course be envisaged.

[0104] A thermal guide 9 is positioned around each of the teeth 7 to capture the heat from the coils 8 which surround each thermal guide 9 (and therefore each tooth 7). The thermal guides 9 therefore have properties for capturing the heat and conducting it by conduction to the casing (not shown to facilitate understanding).

[0105] In the central tooth of the figure, the coil which surrounds the thermal guide 9 is not shown so as to allow the thermal guide 9 to be viewed.

[0106] Each thermal guide 9 comprises a first plate which substantially surrounds the tooth 7 and a strip 11 intended to be fixed (or at least in contact) with the casing.

[0107] The thermal guide 9 is split so as to prevent the magnetic flux from looping back into the thermal guide. In other words, the thermal guide 9 comprises a slot 10. As shown, the slot 10 extends over the entire axial length of the thermal guide 9. The slot 10 also extends radially, over the entire radial length of the strip 11. The slot leaves a non-zero clearance between the two parts of the thermal guide 9 on either side of the slot 10. Alternatively, this slot could be filled with a non-magnetic material, such as a polymer. The thermal guide 9 could have a longitudinal part made of non-magnetic material. In other words, each thermal guide comprises a means for preventing the magnetic flux from looping back into the thermal guide.

[0108] Figure 5 illustrates, in a schematic and non-limiting manner, a second variant of an axial flux electric machine stator according to the invention.

[0109] The stator comprises a stator body 6, here of substantially annular shape, delimited by an internal cylindrical surface, an external cylindrical surface and two flat end surfaces.

[0110] On one of the two flat end surfaces of the stator body 6, there are teeth 7 which extend axially, from this flat end surface towards the rotor (not shown to facilitate visualization). The teeth 7 here have a substantially trapezoidal section but other shapes could of course be envisaged.

[0111] A thermal guide 9 is positioned around each of the teeth 7 to capture the heat from the coils 8 which surround each thermal guide 9 (and therefore each tooth 7). The thermal guides therefore have properties for capturing the heat and conducting it by conduction to the casing (not shown to facilitate understanding).

[0112] In the central tooth of the figure, the coil which surrounds the thermal guide 9 is not shown so as to allow the thermal guide 9 to be viewed.

[0113] Each thermal guide 9 comprises a first plate 17 which substantially surrounds the tooth 7 and a strip 11 intended to be fixed (or at least in contact) with the casing.

[0114] Furthermore, the thermal guide comprises a second plate 13 so as to cover the tooth: the second plate 13 covers the surface of the tooth 7 opposite the rotor.

[0115] The thermal guide 9 is slotted so as to prevent the magnetic flux from looping back into the thermal guide. In other words, the thermal guide 9 comprises a slot 10. As shown, the slot 10 extends over the entire radial length of the second plate 13. The slot leaves a non-zero clearance between the two parts of the second plate 13 on either side of the slot 10. Alternatively, this slot could be filled with a non-magnetic material, such as a polymer. In other words, each thermal guide comprises a means for preventing the magnetic flux from looping back into the thermal guide.

[0116] Figure 6 illustrates, in a schematic and non-limiting manner, a third variant of an axial flux electric machine stator according to the invention.

[0117] The stator comprises a stator body 6, here of substantially annular shape, delimited by an internal cylindrical surface, an external cylindrical surface and two flat end surfaces.

[0118] On one of the two flat end surfaces of the stator body 6, there are teeth 7 which extend axially, from this flat end surface towards the rotor (not shown to facilitate visualization). The teeth 7 here have a substantially trapezoidal section but other shapes could of course be envisaged.

[0119] A thermal guide 9 is positioned around each of the teeth 7 to capture the heat from the coils 8 which surround each thermal guide 9 (and therefore each tooth 7). The thermal guides therefore have properties for capturing the heat and conducting it by conduction to the casing (not shown to facilitate understanding).

[0120] In the central tooth of the figure, the coil which surrounds the thermal guide 9 is not shown so as to allow the thermal guide 9 to be viewed.

[0121] Each thermal guide 9 comprises a first plate which substantially surrounds the tooth 7 and a strip 11 intended to be fixed (or at least in contact) with the casing.

[0122] In order to avoid magnetic feedback, the thermal guide 9 does not cover the inner lower surface 12 of the tooth 7. In other words, the first plate of the thermal guide covers the upper surface and the two lateral surfaces of the tooth 7, without covering the lower surface (or at least without covering the entirety of this surface). Alternatively, the thermal guide could comprise at least one portion of non-magnetic material on the inner surface of the tooth. In other words, each thermal guide comprises a means for avoiding feedback of the magnetic flux in the thermal guide.

[0123] Figure 7 illustrates, in a schematic and non-limiting manner, a fourth variant of an axial flux electric machine stator according to the invention.

[0124] The stator comprises a stator body 6, here of substantially annular shape, delimited by an internal cylindrical surface, an external cylindrical surface and two flat end surfaces. On one of the two flat end surfaces of the stator body 6, there are teeth 7 which extend axially, from this flat end surface towards the rotor (not shown to facilitate visualization). The teeth 7 here have a substantially trapezoidal section but other shapes could of course be envisaged.

[0125] A thermal guide 9 is positioned around each of the teeth 7 to capture the heat from the coils 8 which surround each thermal guide 9 (and therefore each tooth 7). The thermal guides 9 therefore have properties for capturing the heat and conducting it by conduction to the casing (not shown to facilitate understanding).

[0126] In the central tooth of the figure, the coil which surrounds the thermal guide 9 is not shown so as to allow the thermal guide 9 to be viewed.

[0127] Each thermal guide 9 comprises a first plate 17 which substantially surrounds the tooth 7 and a strip 11 intended to be fixed (or at least in contact) with the casing. Furthermore, the thermal guide 9 comprises a second plate 13 so as to cover the tooth: the second plate 13 covers substantially the entire surface of the tooth 7 opposite the rotor.

[0128] The thermal guide 9 is split so as to prevent the magnetic flux from looping back into the thermal guide. In other words, the thermal guide 9 comprises a slot 10 which extends over the entire radial length of the second plate 13. In addition, this slot cuts the thermal guide 9 in two: the thermal guide here comprises two independent parts separated by the slot 10. The slot 10 leaves a non-zero clearance between the two parts of the second plate 13 on either side of the slot 10. Alternatively, this slot could be filled with a non-magnetic material, such as a polymer. In this case, the thermal guide would then be in a single part. In other words, each thermal guide comprises a means for preventing the magnetic flux from looping back into the thermal guide.

[0129] Figure 8 illustrates, in a schematic and non-limiting manner, a fifth variant of an axial flux electric machine stator according to the invention.

[0130] The stator comprises a stator body 6, here of substantially annular shape, delimited by an internal cylindrical surface, an external cylindrical surface and two flat end surfaces.

[0131] On one of the two flat end surfaces of the stator body 6, there are teeth 7 which extend axially, from this flat end surface towards the rotor (not shown to facilitate visualization). The teeth 7 here have a substantially trapezoidal section but other shapes could of course be envisaged.

[0132] A thermal guide 9 is positioned around each of the teeth 7 to capture the heat from the coils 8 which surround each thermal guide 9 (and therefore each tooth 7). The thermal guides 9 therefore have properties for capturing the heat and conducting it by conduction to the casing (not shown to facilitate understanding).

[0133] In the central tooth of the figure, the coil which surrounds the thermal guide 9 is not shown so as to allow the thermal guide 9 to be viewed.

[0134] Each thermal guide 9 comprises a first plate 17 which substantially surrounds the tooth 7 and a strip 11 intended to be fixed (or at least in contact) with the casing.

[0135] Furthermore, the thermal guide 9 comprises a second plate 13 so as to cover the tooth and thus form a cap: the second plate here covers the entire surface of the tooth opposite the rotor.

[0136] The thermal guide 9 comprises a slot 10 which extends at least over the entire radial length of the lamella 11. To avoid the re-looping of the magnetic flux, a portion of the thermal guide may be made of non-magnetic material or, for example, the lower surface of the teeth may not be covered (or not completely covered) by the thermal guide. In other words, each thermal guide comprises a means for avoiding the re-looping of the magnetic flux in the thermal guide.

[0137] In Figures 4 to 8, the heat guide comprises a lamella 11 extending radially in the direction opposite the stator body. Alternatively, this lamella 11 could be folded over the stator body.

[0138] In Figures 4 to 8, the thermal guides are independent of each other, but they could alternatively be connected to each other by radial (and / or circumferential) junctions covering the surface of the stator body located between the teeth. These radial junctions could connect several thermal guides to each other or connect all the thermal guides so as to form a single part. In this case, the electrical machine comprises a thermal guide means which comprises the different thermal guides and the radial junctions for connecting these thermal guides to each other.

[0139] In Figures 5, 7 and 8, the second plate covers the surface of the teeth to form a cap around the tooth. Alternatively or additionally, the second plate could cover the axial end surface of the coils facing the rotor to increase the exchange surface between the coils and the thermal guide and to facilitate maintaining the coils in axial position (in other words, the second plate can then serve as an axial stop for the coils).

[0140] Figure 9 illustrates, in a schematic and non-limiting manner, a partial sectional view of an example of a thermal guide with a blade folded onto the stator body, of an axial flux electric machine stator according to the invention. This is a sectional view in a longitudinal plane (the axis in phantom lines represents the longitudinal axis).

[0141] The stator comprises a stator body 6 from which teeth 7 extend in the longitudinal direction (along the longitudinal axis).

[0142] A thermal guide 9 is positioned around these teeth 7, between the teeth 7 and the coil 8 which is surrounded around the teeth (and surrounded by the thermal guide 9).

[0143] In order to ensure that the thermal guide 9 is held in position, the latter comprises a strip 16 folded over the stator body 6 (folded over the end surface of the stator body, opposite that from which the teeth 7 extend).

[0144] In the figure, the thermal guide 9 comprises a first plate which substantially (or entirely) covers the surface between the teeth 7 and the coils 8 but the thermal guide could comprise a second plate to completely or at least partially cover the end surface of the teeth facing the stator. In other words, this folded lamella version could adapt to the variants of figures 4 to 8 without departing from the scope of the invention. The lamella 16 is in contact with the casing (not shown) so as to facilitate the conduction of heat.

[0145] Figure 10 illustrates, in a schematic and non-limiting manner, a sectional view of another example of an axial flux electric machine stator according to the invention.

[0146] This is a section in a plane orthogonal to the radial direction passing through the axis of a tooth 7.

[0147] The stator comprises a stator body 6 and teeth 7 extending longitudinally from an end surface of the stator body 6. The phantom axis represents the longitudinal axis of the axial flux electric machine.

[0148] Around teeth 7, there are successively, from the inside to the outside:

[0149] • A second thermal insulating layer 14;

[0150] • The thermal guide 9 (according to one of the variants of figures 4 to 8 and / or figure 9 for example);

[0151] • A first electrically insulating layer 15;

[0152] • The 8 reels.

[0153] Preferably, the second thermal insulating layer 14 may also be electrically insulating and / or the first electrically insulating layer 15 may be thermally conductive. The first and second layers, respectively electrically insulating 15 and thermally insulating 14, may cover the entire surface of the layer located just below it and with which it is in contact.

[0154] Of course, when the thermal guide comprises a second plate which covers the surface of the tooth facing the rotor, the second thermal insulating layer 14 can also cover this surface of the tooth 7 facing the rotor, being positioned between this surface of the tooth 7 and the second plate.

[0155] In the various figures, the different elements are represented by a space between them only to facilitate visualization but of course, these elements are in contact with each other.

Claims

Claims 1. An axial flux electrical machine comprising a casing (2) enclosing at least one rotor (1) and at least one stator (100), each stator (100) comprising a stator body (6), teeth (7) regularly distributed circumferentially on the stator body (6) and coils (8) wound around the teeth (7), characterized in that each stator comprises thermal guides (9), each of the thermal guides (9) being positioned between a coil (8) and the tooth (7) on which the coil (8) is wound, each thermal guide (9) being in contact with the coil (8) and with the casing (2) so as to conduct heat from the coils (8) to the casing (2) solely by thermal conduction in each thermal guide (9).

2. Electrical machine according to claim 1, in which the material of the thermal guide (9) has a thermal conductivity strictly greater than the thermal conductivity of the material of the stator body (6).

3. Electrical machine according to claim 2, wherein the material of the thermal guide (9) is metallic, preferably comprising aluminum, copper, and / or an alloy of aluminum and / or copper.

4. Electrical machine according to one of the preceding claims, in which each thermal guide (9) comprises a first plate (17) surrounding the tooth (7), over substantially the entire surface of the tooth (7) opposite the coils (8).

5. Electrical machine according to one of the preceding claims, in which each thermal guide (9) comprises a second plate (13), the second plate covering the tooth (7) so as to form a cap facing said rotor, or the second plate covering an axial end surface of the coils facing the rotor to hold the coils in position.

6. Electrical machine according to one of the preceding claims, in which each thermal guide (9) is split in the radial direction, over the entire radial length of the thermal guide (9) or over substantially the entire radial length of the thermal guide (9).

7. Electrical machine according to one of the preceding claims, in which the different thermal guides (9) are independent of each other or in which several thermal guides (9) are connected to each other and preferably all the thermal guides are connected to each other so as to form a single part, and more preferably, the thermal guides are connected to each other by substantially radial junctions extending on the surface of the stator body (6) between the teeth (7).

8. Electrical machine according to one of the preceding claims, in which the electrical machine comprises a first electrically insulating layer (15), preferably non-thermally insulating, between each thermal guide (9) and the coil (8) associated, the first electrically insulating layer being (15) preferably a first sheet or a first varnish.

9. Electrical machine according to claim 8, in which each first electrically insulating layer (15) is a first varnish covering both the thermal guide (9) and the associated coil (8) so as to connect them together.

10. Electrical machine according to one of claims 8 or 9, in which each first electrical insulating layer (15) is made of anodized aluminum.

11. Electrical machine according to one of the preceding claims, in which the electrical machine comprises a second thermal insulating layer (14), and preferably electrically insulating, between each thermal guide (9) and the associated tooth (7), the second thermal insulating layer (14) preferably being a second sheet or a second varnish.

12. Electrical machine according to one of claims 11, in which each second thermal and electrical insulating layer (14) is made of anodized aluminum.

13. Electrical machine according to one of the preceding claims, in which each thermal guide (9) and the associated coil (8) can be embedded in a coating material.

14. Electrical machine according to one of the preceding claims, in which each thermal guide (9) comprises a fixing means for fixing it to the casing (2) and / or to the stator body (6).

15. Electrical machine according to claim 14, wherein the fixing means comprises at least one strip (11, 16) capable of being fixed to the casing (2) or folded, at the periphery of the stator body (6), under the stator body (6).

16. Axial flux electric machine according to one of the preceding claims, comprising two rotors (1) and one stator (100), or two stators (100) and one rotor (1).

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