Stator for an axial-flux electric machine, cooled by a dielectric liquid

Abstract

The invention relates to an axial-flux electric machine (1) comprising: - a stator (2), - a rotor (3) secured to a rotary shaft (34), and - a casing (22) housing the stator (2), the casing (22) comprising a main wall (20) through which the rotary shaft (34) passes, and two concentric side walls (21, 23), first ends of which are secured to the main wall (20), the stator comprising: - a plurality of teeth (24) secured to the main wall (20) and projecting axially towards the rotor (3), - winding supports (25) arranged on the teeth (24) and housing stator windings (28), the electric machine (1) comprising a membrane (27) secured to second ends of the side walls (21, 23), the membrane (27) and the casing (22) forming a sealed chamber for cooling the stator windings (28).

Description

[0001] DESCRIPTION

[0002] Title of the invention: Stator of an axial flux electric machine cooled by a dielectric liquid

[0003] The present invention relates to the fields of electrical engineering and mechanics, and more specifically concerns an axial flux electric machine.

[0004] Currently, electric or hybrid electric vehicles use electric traction or propulsion motors, which are generally radial flux electric machines, that is, the stator windings of such a machine generate a magnetic field in a radial direction relative to an axial direction corresponding to the axis of rotation of the machine.

[0005] In order to reduce the size of the electric traction or propulsion motor of such a vehicle, it is envisaged to use, instead of a radial flux electric machine, an axial flux electric machine. This latter type of machine is in fact generally more compact at least in one axial direction corresponding to the axis of rotation of the machine, which gives it a discoid appearance.

[0006] The power density provided by an axial flux electric machine intended for automobile traction or propulsion means that the active parts of the machine are subject to high currents, which cause their temperature to rise. These active parts generally include stator windings, which must be efficiently cooled so that the temperature rise due to the currents passing through them does not damage them.

[0007] Efficient cooling of the stator windings can be achieved with a cooling jacket in which a coolant circulates, however such a jacket has a bulk around a machine casing which may not be compatible with certain electric or hybrid powertrain architectures. Another solution is to spray the stator windings with a dielectric heat transfer fluid such as oil, the machine then being coupled to a cooling circuit in which the dielectric heat transfer fluid is cooled. This solution nevertheless has the disadvantage of degrading the performance of the machine due to the presence of heat transfer fluid in the air gap, which generates friction with a rotor of the axial flux electric machine.The present invention aims to remedy at least in part the aforementioned drawbacks by providing an axial flux electric machine and an electric or hybrid vehicle comprising such a machine, which make it possible to effectively cool the stator windings of the electric machine without degrading its performance and without requiring a cooling jacket.

[0008] To this end, the invention proposes an axial flux electric machine, comprising:

[0009] - a stator,

[0010] - a rotor attached to a rotating shaft and

[0011] - a casing housing the stator, the casing comprising a main wall crossed by the rotating shaft and two concentric side walls, the first ends of which are integral with the main wall, the stator comprising:

[0012] - a plurality of teeth secured to the main wall and projecting axially towards the rotor,

[0013] - winding supports arranged on the teeth, and

[0014] - stator windings housed in the winding supports, the electrical machine being characterized in that it comprises a membrane secured to second ends of the side walls, the membrane and the casing forming a sealed chamber for cooling the stator windings.

[0015] It should be noted that in this patent application, the term "axial" (or "axial") refers, unless otherwise stated, to a direction parallel to the axis of rotation of the rotor of the electric machine. Similarly, the term "radial" refers, unless otherwise stated, to a direction orthogonal to the axis of rotation of the rotor of the electric machine, and secant to this axis of rotation, while the terms

[0016] "angular / ment" or "ortho-radial / e" refer, unless otherwise stated, to a direction orthogonal to the axial direction and to a radial direction, this orthogonal direction being in fact rotating around the axis of rotation of the rotor.

[0017] The electrical machine according to the invention comprises at least one stator and at least one rotor, for example it comprises two stators on either side of the rotor in an axial direction. In the latter case the two stators are preferably made in a similar manner, that is to say that the electrical machine according to the invention then comprises in particular two sealed chambers. Of course the sealed chamber(s) each comprise at least one heat transfer fluid inlet and one heat transfer fluid outlet. The casing housing the stator is for example a portion of a casing of the electrical machine, or a casing dedicated to the stator, the casing of the machine including for example this casing dedicated to the stator.For example, the main wall is a wall of the machine casing, arranged orthogonally to an axis of rotation of the rotor, or a magnetic steel plate attached to this wall of the machine casing and serving as a stator yoke, when the side walls are secured to this plate. The teeth being secured, possibly by means of a plate, to the main wall, the latter is generally flat on the side of the teeth, but can of course include grooves or ribs for fixing the teeth or the plate. The main wall includes, for example, on the other side of the teeth, cooling channels using a different heat transfer fluid than that used in the sealed chamber.

[0018] The side walls of the casing are, for example, cylindrical or formed from several concentric cylindrical walls, for example to allow a rotor hub to be partially housed in the electric machine, in particular when the side walls are also central side walls of a casing of the electric machine.

[0019] Thanks to the invention, during operation of the electrical machine, the heat transfer fluid present in the sealed chamber cannot escape from it other than through an oil outlet connected to a cooling circuit for the heat transfer fluid. The heat transfer fluid therefore does not penetrate into the air gap and does not hinder the rotation of the rotor. In addition, the membrane being thin, for example of the order of half a millimeter, it allows a reduced air gap to be maintained between the stator and the rotor, and therefore does not degrade the magnetic performance of the electrical machine. The membrane is sufficiently flexible so that its positioning is tolerant of the various clearances existing between the side walls of the electrical machine on which it is fixed. The membrane is preferably made of a composite synthetic material, for example a polymer reinforced with glass or carbon fibers.The membrane is for example overmolded on the second ends of the side walls.

[0020] The membrane takes the form, for example, of a flat crown whose circular ends are attached to counterbores formed at the second ends of the side walls. The membrane is, for example, glued or overmolded onto these counterbores.

[0021] The membrane must withstand axial forces due in particular to the pressure of the heat transfer fluid in the sealed chamber, and to the depressions created by the rotation of the rotor. This resistance is obtained in particular by its attachment to the fixed elements of the electrical machine, which helps to prevent tearing or deformation of the membrane. Such tearing or deformation could generate leaks of heat transfer fluid and / or possibly generate friction with the rotor, thus degrading the membrane and the performance of the electrical machine.

[0022] In one embodiment of the invention, the membrane is secured to at least one of the axial end surfaces of the teeth. For example, the membrane is bonded to each axial end surface of the teeth on the air gap side. This makes it possible both to prevent the membrane from deforming in an area located radially at the stator teeth, and to choose a more flexible membrane than if it were only fixed to the second ends of the side walls.

[0023] The axial flux electric machine according to the invention preferably comprises means for securing the membrane to at least one of the winding supports arranged on one of the teeth. These securing means are complementary to the securing of the membrane to the side walls of the casing, and possibly to the securing of the membrane to at least one of the stator teeth. These securing means make it possible to prevent deformation of the membrane around the teeth and therefore to choose a more flexible membrane than if it were only fixed to the second ends of the side walls. These securing means are, for example, glue or attachment means made of the same material as the membrane or fixed to it.

[0024] The winding support comprising a wall for holding one of the stator windings, arranged in contact with the membrane, the securing means comprising for example at least one fixing pin capable of holding the membrane and the holding wall against each other, and an orifice for the passage of the fixing pin in the holding wall. This holding wall is a first holding wall orthogonal to the axis of rotation of the rotor and surrounding the tooth onto which the winding support is threaded. The winding support comprises a second holding wall on the other side of the winding relative to the first holding wall. The fixing pin is for example glued to the membrane or made in one piece with the membrane.The use of a fixing pin rather than gluing the membrane to the retaining wall makes it possible to avoid requiring equal axial clearances on the one hand between the axial end surface of the tooth and the membrane, and on the other hand between the retaining wall and the membrane. The retaining wall forming a frame around an axial end surface of the tooth, the securing means preferably comprise at least one fixing pin on each side of the frame. The membrane is for example fixed by four fixing pins on the periphery of each tooth, each pin being caught in a retaining wall of a winding support. Maintaining a minimum distance between the rotor and the membrane is all the more ensured when the number of pins is large and the pins are distributed homogeneously around each tooth. Each pin is for example centered angularly and radially on one side of the frame formed by the retaining wall.

[0025] The fixing pin comprises, for example, a foot, a head and a body connecting the foot and the head, the head being capable of elastically deforming in the passage hole so as to interpose the retaining wall between the foot and the head. The use of a pin whose head passes elastically into the passage hole of the retaining wall allows easy disassembly of the membrane for replacement during maintenance or repair of the electrical machine.

[0026] The foot is preferably fixed on a face of the membrane located opposite the retaining wall. The foot is for example fixed on this face or in the thickness of the membrane without piercing it, in order to maintain the sealing of the sealed chamber. Alternatively, the foot is fixed on the other side of the membrane, the body passing through the membrane. In this variant, an additional sealing device, such as a flat annular seal, is possibly arranged between the foot and the membrane, in particular if the latter is not elastomer. Similarly, in a variant where the pin takes the form of a screw, such a sealing device is possibly added between the screw head and the membrane, if the screw head is fixed on the other side of the membrane relative to the retaining wall.

[0027] Preferably, however, the foot is fixed to the face of the membrane by gluing or by gripping in a weave of the membrane. Similarly, in a variant where the pin takes the form of a screw, the screw head is preferably fixed to the face of the membrane by gluing or by gripping in a weave of the membrane. By "grip" is meant a wedging, that is to say that the foot or the screw head are intermingled in the fibers of the membrane. If the membrane does not comprise fibers, it comprises, for example, a non-through housing into which the foot or the screw head can be inserted by elasticity. The invention also relates to an electric or hybrid vehicle comprising an electric machine according to the invention.

[0028] Other characteristics and advantages of the invention will become apparent from the following description on the one hand, and from several examples of embodiment given for informational and non-limiting purposes with reference to the attached schematic drawings on the other hand, in which:

[0029] [fig 1] is a half-sectional view of a stator and a rotor mounted on a rotating shaft, of an electrical machine according to the invention, in one embodiment of the invention,

[0030] [fig 2] is a front view of the stator and rotating shaft of figure 1, in which a sealing membrane of the electric machine has been made transparent, and

[0031] [fig 3] is a sectional view of a fixing pin in a portion of the waterproofing membrane mentioned in relation to figure 2, in the corresponding embodiment.

[0032] According to one embodiment of the invention, an axial flux electrical machine 1 according to the invention, shown in Figure 1, comprises at least one stator 2 and one rotor 3 secured to a rotating shaft 34 mounted to move about an axis of rotation X. Only one half of the stator 2 and one half of the rotor 3 seen in section are shown, their other halves being symmetrical with respect to the axis of rotation X.

[0033] The electrical machine 1 also comprises a casing, not shown, housing together the stator 2, the rotor 3 and another stator, not shown, arranged axially on the other side of the rotor 3 relative to the stator 2. This other stator is arranged symmetrically to the stator 2 relative to the rotor 3 and is of a structure similar to the stator 2. However, as a variant, the electrical machine 1 comprises a single stator.

[0034] In this embodiment of the invention, the stator 2 comprises a dedicated casing 22 comprising a main wall 20 arranged orthogonally to the axis of rotation X and fixed to a wall of the casing of the electrical machine. This main wall 20 is a magnetic steel plate, in the form of a flat crown, on which are glued or fixed by interlocking, teeth 24 of the stator (also called stator teeth) also made of magnetic steel. The main wall 20 is perforated in its center for the passage of the rotating shaft 34. Alternatively, the teeth are integral with the main wall 20. In this embodiment of the invention, the teeth 24 each have a trapezoidal shape and are distributed angularly and regularly around the axis of rotation X, as visible in Figure 2. The teeth 24 therefore have the shape of right prisms whose height is parallel to the axial direction.On each of the teeth 24 is threaded a winding support 25 made of insulating synthetic material (for example polymer). The winding support 25 comprises a trapezoidal hollow body, of a shape complementary to the tooth 24 on which the hollow body is threaded, and comprises two holding walls 252, 254 of a stator winding 28, orthogonal to the axis of rotation X and each connected to a separate axial end of the hollow body. A stator winding 28 is therefore arranged around each hollow body threaded onto a stator tooth 24. Each stator winding is for example formed of a copper wire winding. The ends of the stator windings 28 are each electrically connected to phase conductors, not shown, inside or outside the casing 22.

[0035] The casing 22 also comprises two concentric side walls 21, 23 each secured to the main wall 20 by a first of their ends. In this embodiment of the invention, the side walls 21, 23 are cylindrical, but may alternatively be of different shape. The side walls 21, 23 are for example welded or made of the same material as the main wall 20. They are for example made of steel or aluminum. The side wall 23 is proximal to the rotating shaft 34 and the side wall 21 is distal to the rotating shaft 21. The main wall 20 and the side walls 21, 23 are dimensioned to house the teeth 24, the stator windings 28 and the winding supports 25 without these elements which they house extending axially beyond the second ends of the side walls 21, 23.

[0036] A membrane 27 made of a polymer reinforced with glass or carbon fibers, for example made of polyamide called PA6 GF35 or PA12 GF35, is fixed to the second ends of the side walls 21, 23 by being overmolded to counterbores arranged on these second ends of the side walls 21, 23. The membrane 27, the main wall 20 and the side walls 21, 23 form a sealed chamber in which the active parts of the stator 2 can be bathed in a heat-transferring dielectric cooling liquid such as oil, the oil arriving in this sealed chamber via a heat-transferring liquid inlet 222 and leaving the sealed chamber via a heat-transferring liquid outlet 224, the inlet 222 and the outlet 224 being orifices arranged in the main wall 20. This inlet 222 and this outlet 224 are connected to a non-conductive cooling circuit. shown. The oil entering or exiting through these ports is represented by arrows through these ports in Figure 1.

[0037] It should be noted that other holes are possibly provided in the main wall 20 for the passage of the electrical connections of the stator windings or the phase conductors outside the casing 22, a sealing device being provided at these holes to prevent leaks of the cooling liquid contained in the sealed chamber. For example, overmolding of all the electrical connections is provided behind these holes for the passage of the electrical connections or the phase conductors, the overmolding also overmolding the periphery of these holes on the main wall 20. The electrical connections or the phase conductors can of course, as a variant, pass through one of the side walls 21, 23 of the casing 22.

[0038] The rotor 3 takes the form of a disc with a hole in its center to allow the passage of the rotating shaft 34. It comprises a fixing hub (not shown) for the rotating shaft 34. The rotor 3 comprises a body 32 made of composite material, for example reinforced with glass or carbon fibers, this body 32 comprising a circular portion connected to the fixing hub, and branches extending radially from this circular portion to a circular flange 36 of the rotor 3.

[0039] The rotor 3 comprises magnetic poles 30 of trapezoidal shape, each housed between the branches of the body 32. These magnetic poles 30 have a surface of dimension at least equal to that of an axial end surface 240 of a tooth 24 so as to receive the major part of the magnetic field created by a stator winding 28. Of course, if the teeth have a shape other than a trapezoidal shape, the magnetic poles 30 preferably have a shape identical to this different shape. The magnetic poles 30 are for example formed of small permanent magnets bonded together by a resin possibly loaded with magnetic powder, or are themselves bonded magnets. The hoop 36 allows the magnetic poles 30 to be held in their housings between the branches of the body 32 despite the centrifugal force exerted by the rotation of the rotor 3 during operation of the electrical machine 1.

[0040] In order to prevent the membrane 27 from deforming, for example due to the pressure of the cooling liquid in the sealed chamber, or vibrations of the electrical machine 1 in operation, the membrane 27 is glued to the axial end surface 240 of each tooth 24, this axial end surface 240 being arranged in contact with the membrane 27. In addition, in this embodiment of the invention, fixing pins 4 are fixed on the one hand to the membrane 27 and on the other hand to the holding walls 252 of each winding support 25, these holding walls 252 being proximal to the membrane 27 relative to the holding walls 254. As can be seen in FIG. 2, the membrane 27 is fixed to each holding wall 252 by four fixing pins 4, one fixing pin 4 being arranged on each side of the trapezoidal frame formed by the holding wall 252 that is to say on each side of the tooth 24 surrounded by this holding wall 252.In addition, each fixing pin 4 is centered on the side of the trapezoidal frame on which it is fixed, both radially and angularly. Of course, other positions and other quantities of fixing pins are conceivable. Figure 3 shows an example of a fixing pin 4 used in this embodiment of the invention. The fixing pin 4 comprises a foot 40, a body 42 and a head 44 of overall conical shape, the body 42 connecting the base of the conical shape of the head 44 to the foot 40 which takes for example the form of a disc, of larger diameter than that of the body 42, cylindrical. The fixing pin 4 is for example made of polyamide.

[0041] As seen in Figure 3, each fixing pin 4 is fixed to the membrane 27 without piercing it, in order to preserve the sealing of the sealed chamber. The foot 40 of each fixing pin 4 is for example glued or stuck in the fibers of the membrane 27.

[0042] As visible in Figure 1, each holding wall 252 has passage orifices for the fixing pins 4. Each passage orifice is formed in a counterbore of the holding wall 252 arranged on the side of the stator winding 28. Thus when a fixing pin 4 is fixed by its foot 40 to the membrane 27 on the side of the holding wall 252 opposite the passage orifice, the head 44 of the pin is inserted by elasticity into the passage orifice and the counterbore retains the base of the head 44 of the pin 4. The pin 4 thus holds the membrane 27 against the holding wall 252 and prevents it from deforming.

[0043] Of course, the invention is not limited to the examples which have just been described and numerous adjustments can be made to these examples without departing from the scope of the invention. In particular, the characteristics of the different variant embodiments of the invention envisaged in this application can be combined to achieve the invention, insofar as these variants are not incompatible with each other.

Claims

CLAIMS 1- Axial flux electric machine (1), comprising: - a stator (2), - a rotor (3) secured to a rotating shaft (34) and - a casing (22) housing the stator (2), the casing (22) comprising a main wall (20) crossed by the rotating shaft (34) and two concentric side walls (21, 23) of which first ends are integral with the main wall (20), the stator comprising: - a plurality of teeth (24) secured to the main wall (20) and projecting axially in the direction of the rotor (3), - winding supports (25) arranged on the teeth (24), and - stator windings (28) housed in the winding supports (25), the electrical machine (1) being characterized in that it comprises a membrane (27) secured to second ends of the side walls (21, 23), the membrane (27) and the casing (22) forming a sealed chamber for cooling the stator windings (28). 2- Electrical machine (1) with axial flux according to claim 1, in which the membrane (27) takes the form of a flat crown whose circular ends are attached to counterbores formed at the second ends of the side walls (21, 23). 3- Axial flux electrical machine (1) according to claim 1 or 2, in which the membrane (27) is secured to at least one of the axial end surfaces (240) of the teeth (24). 4- Electrical machine (1) with axial flux according to any one of claims 1 to 3, comprising means for securing the membrane (27) to at least one of the winding supports (25) threaded onto one of the teeth (24). 5- Axial flux electrical machine (1) according to claim 4, in which the winding support (25) comprises a holding wall (252) for one of the stator windings (28), arranged in contact with the membrane (27), the securing means comprise at least one fixing pin (4) capable of holding the membrane (27) and the holding wall (252) against each other, and an orifice for the passage of the fixing pin (4) in the holding wall (252). 6- Axial flux electric machine (1) according to claim 5, in which the retaining wall (252) forms a frame around an axial end surface (240) of the tooth (24), the securing means comprising at least one fixing pin (4) on each side of the frame. 7- Axial flux electric machine (1) according to claim 5 or 6, in which the fixing pin (4) comprises a foot (40), a head (44) and a body (42) connecting the foot (40) and the head (44), the head (44) being capable of deforming by elasticity in the passage orifice so as to interpose the retaining wall (252) between the foot (40) and the head (44). 8- Electrical machine (1) with axial flux according to claim 7, in which the foot (40) is fixed on a face of the membrane (27) located opposite the retaining wall. (252). 9- Axial flux electric machine (1) according to claim 8, in which the foot (40) is fixed to the face of the membrane (27) by gluing or by being taken into a weaving of the membrane (27). 10- Electric or hybrid vehicle comprising an electric machine (1) according to any one of claims 1 to 9.

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