Vehicle wheel drive system

Abstract

Vehicle Wheel Drive System The present invention relates to a vehicle wheel drive system (1) comprising: - a stator (2) intended to be fixedly mounted to a hub, - a wheel rim intended to be mounted to rotate relative to the hub, - a rotor (3) fixed to the wheel rim, the rotor (3) angularly surrounding the stator (2) with an air gap between the rotor and the stator, the wheel drive system (1) being characterized in that the rotor (3) is a squirrel-cage rotor, and in that the stator (2) has stator slots (24) in which a pin-wound winding (26-A, 26-B, 26-C) is mounted. (Figure 1)

Description

Title of the invention: Vehicle wheel drive system

[0001] The present invention relates to the fields of automobiles and electrotechnics, and more specifically concerns a vehicle wheel motorization system.

[0002] An electric or hybrid vehicle is generally equipped with an electric powertrain comprising an inverter, a high-speed internal rotor electric machine, and a gearbox. The presence of the gearbox reduces the efficiency of the powertrain compared to a powertrain using in-wheel motors, i.e., electric machines directly integrated into the vehicle's drive wheels.

[0003] Such wheel motors generally have a permanent magnet rotor, since a wound rotor would require the integration of a bulky slip ring and brush system into the wheel. Furthermore, such a slip ring and brush system is incompatible with an external rotor due to the excessively high relative speed that such an external rotor would induce between the slip rings and brushes, a speed that would lead to premature brush wear.

[0004] However, the use of permanent magnet rotors remains expensive due to the price of rare earth elements, and presents a risk of magnet demagnetization due to the temperatures reached by such a rotor during operation. Furthermore, these rotors generate a drag flux when not used for traction or propulsion of the vehicle, which affects the efficiency of the vehicle's powertrain system when traveling at high speeds. Finally, this type of permanent magnet motor has more complex fallback modes, such as a short-circuit guarantee ensuring energy decoupling from the battery, which constrains the inverter and its sizing.

[0005] There is therefore a need for an electric traction or propulsion machine that can be integrated into a vehicle wheel, which does not have the disadvantages of the prior art.

[0006] The present invention remedies at least in part the drawbacks of the prior art, by providing a wheel drive system comprising a cage rotor machine with good efficiency, small axial footprint and independence from the rare earth market.

[0007] To this end, the invention proposes a vehicle wheel motorization system comprising: - a stator designed to be mounted rigidly to a hub, - a wheel rim mounted to rotate relative to the hub, - a rotor fixed to the wheel rim, the rotor angularly surrounding the stator, with an air gap between the rotor and the stator, the wheel drive system being characterized in that the rotor is a squirrel-cage rotor, and in that the stator has stator slots in which a pin winding is mounted. The pins are, for example, U-shaped pins, or pins formed of a single conductor per phase and called "W-pin" in English.

[0008] The rotor of the motorization system according to the invention is therefore an external rotor enveloping the stator of the motorization system, the electric machine corresponding to this system being radial flux.

[0009] Thanks to the invention, the vehicle is equipped with a rare-earth-free motor system, featuring direct drive without a gearbox, and a compact axial footprint. Such a motor system is also simple to manufacture and is sufficiently robust and reliable for an electric vehicle powering the motor system with a 400V (volts) or 800V high-voltage battery. Finally, a vehicle incorporating such a wheel motor system exhibits improved efficiency compared to a vehicle whose powertrain includes a gearbox, and compared to a motor system using a conventionally wound stator. Indeed, the use of pin windings increases the power density of the stator, as the pin conductors are made of thick copper or aluminum bars, for example, with a rectangular cross-section, which allows the stator slots to be filled more effectively than a conventional copper wire.Using aluminum pin windings reduces the mass and cost of the stator.

[0010] In one embodiment of the invention, the stator has several magnetic poles per phase, with each magnetic pole extending over only two successive stator slots. The high number of poles is compatible with the maximum wheel speed in terms of frequency and allows for a reduction in the machine's radial footprint, maximizing the air gap diameter and thus achieving a high torque mass density. This embodiment, with a distributed winding, makes it possible to attenuate the harmonics of the electromagnetic force generated by the stator, and therefore improve the efficiency of the drive system. This is particularly important and beneficial with asynchronous machine technology.

[0011] Each stator slot, for example, houses only two pins. This makes it possible to reduce the axial dimension of the stator windings. The pins in the same stator slot belong to the same phase of the stator.

[0012] According to an optional and advantageous feature of the invention, the pins of each phase of the stator are electrically connected in series with each other, being formed from the same bent conductive bar. This series connection of The fact that each pin of the same phase is connected in series allows for the winding of a single phase with a single conductor, without soldering, by bending the conductor and then inserting it into the stator slots according to the method known as "continuous hairpin winding," "wave-winding," or W-pin. This involves continuous winding by winding the bent conductor around the outside of the stator. The fact that each slot has only two pins, and that each pole has only two slots, facilitates this process with a single conductor per phase. Furthermore, this method of connecting the pins of the same phase in series increases the power density per phase compared to connecting them in parallel.

[0013] As an alternative, the stator winding is made with the pins of the same phase, welded together at their ends (U-pin type winding).

[0014] Furthermore, in one embodiment of the invention, the stator comprises a non-magnetic inner portion and an outer portion made of magnetic steel, the outer magnetic steel portion being attached to the inner portion. The inner portion is, for example, made of hardened steel and provides good mechanical strength to the stator, while the outer portion, made of iron-silicon for example, can be produced by winding sheet metal. This stator structure thus makes it possible to reduce the amount of material used, facilitate the manufacture of the stator, and lower its cost.

[0015] The outer portion is optionally segmented angularly to form a plurality of angular segments. This segmentation allows the outer portion to be manufactured in pieces, which are then attached to the inner portion. Each angular segment is, for example, formed from laminated sheets. This embodiment saves material when the sheets of each angular segment are made by cutting from a large sheet.

[0016] Furthermore, the stator may include a cooling circuit housed within the internal portion of the stator, or within a cooling jacket attached to the internal portion of the stator. If the cooling circuit is housed within the internal portion of the stator, the internal portion is, for example, made of aluminum. If a cooling jacket is attached to the internal portion of the stator, the latter is, for example, made of hard, non-magnetic steel, and the cooling jacket is, for example, made of aluminum. The internal portion of the stator is then sandwiched between the cooling jacket and the external portion of the stator. This design allows for efficient cooling of the stator, the rotor also being cooled by convection of the air outside the vehicle, and by convection of the air present in the air gap during its movement.

[0017] In one embodiment of the invention, the rotor of the wheel drive system according to the invention comprises on the one hand - an annular body having two axial ends and an internal peripheral surface comprising axial notches, the axial notches opening onto each axial end of the annular body, and on the other hand - an aluminium or copper squirrel cage having bars in axial notches and rings of the same material connecting the bars at each axial end of the annular body.

[0018] The annular body is, for example, formed from laminated sheets of magnetic steel or iron-silicon, or is a single piece of magnetic steel or iron-silicon. The squirrel cage is, for example, formed by injecting aluminum into hollow portions of the annular body. The bars are then molded into the axial notches, and the rings are formed by molding at the axial ends of the annular body, the axial notches each opening onto the axial ends of the annular body. Alternatively, the cage can be made of copper and formed by welding or brazing the copper bars to the copper rings.

[0019] In a configuration where the stator has several magnetic poles per phase, each magnetic pole extending over only two successive stator slots, the stator is, for example, three-phase and has 216 stator slots forming 36 magnetic poles per phase, while the rotor has, for example, 250 axial slots. This configuration minimizes torque oscillation for a 19-inch wheel rim (48.26 centimeters in diameter). For a smaller wheel rim, for example, 17 inches (43.18 centimeters in diameter), the stator has slightly fewer poles, for example, thirty, thirty-two, or thirty-four poles, and the rotor can also have slightly fewer bars, for example, 240.

[0020] Other features and advantages of the invention will become apparent from the following description on the one hand, and from several illustrative and non-limiting examples of embodiments given with reference to the accompanying schematic drawings on the other hand, in which:

[0021] [Fig. 1] illustrates in perspective and separately, a stator and a rotor of a wheel motorization system according to the invention, in an embodiment of the invention, then in perspective, the stator installed within the rotor, the stator and rotor assembly forming an electric machine,

[0022] [Fig.2] is a cross-sectional view, in this embodiment of the invention, of the electrical machine of [Fig.1], and

[0023] [Fig.3] is a quarter enlargement of the electrical machine in cross-section of the [Fig.2], on which a winding diagram and a cooling jacket are schematically represented.

[0024] According to an embodiment of the invention, adapted to a 19-inch wheel rim, a motorization system 1 of the invention, represented [Fig.1], comprises a wound stator 2 and a squirrel-cage rotor 3, that is to say an induction rotor 3.

[0025] The drive system 1 is intended to equip a drive wheel of a vehicle, for example a front wheel of the vehicle. Each drive wheel of the vehicle can of course be equipped with a drive system 1. The stator 2 is fixed to a hub or hollow shaft of the vehicle, which receives a wheel shaft, and the rotor 3 is fixed to a 19-inch wheel rim of the vehicle, the wheel rim being fixed to the wheel shaft. The stator 2 is an internal stator, mounted within the rotor 3, which is an external rotor; this assembly is shown at the bottom of [Fig. 1]. The air gap between the stator 2 and the rotor 3 takes the form of a very thin ring of air, approximately one millimeter thick, and is therefore not visible in [Fig. 1]. The electrical machine composed of the stator 2 and the rotor 3 is a radial flux machine.

[0026] It should be noted that in this patent application, the terms "axial" (or "axial") refer, unless otherwise stated, to a direction parallel to an axis of rotation of the rotor 3 or to an axis of symmetry of the stator 2, this direction being represented by the z-axis of the orthonormal coordinate system x,y,z shown in Figures 1 and 2. Similarly, the terms "radial" refer, unless otherwise stated, to a direction orthogonal to this axis of rotation or symmetry, while the terms "angular" or "ortho-radial" refer, unless otherwise stated, to a direction orthogonal to both the axial direction and a radial direction, this orthogonal direction being in fact rotating around the axis of rotation of the rotor 3 or the axis of symmetry of the stator 2.

[0027] The stator 2 has a generally annular shape. In this embodiment of the invention, it comprises an external portion 22 made of magnetic steel, the external cylindrical periphery of which has 216 stator slots 24 opening outwards from the stator 2 and into which pins referenced 26-A, 26-B or 26-C are inserted to form a three-phase winding of the stator 2. This winding has 36 magnetic poles per phase, each pole being referenced 28-A, 28-B, or 28-C depending on the phase that supplies them.

[0028] It is understood that the pins 26-A belong to the same phase as the poles 28-A, the pins 26-B belong to the same phase as the poles 28-B and the pins 26-C belong to the same phase as the poles 28-C.

[0029] The U-shaped pins 26-A, 26-B, or 26-C of the same phase are in fact formed from a single bent conductive bar and are connected to each other at their ends to form a corrugated line, as shown in [Fig. 3] for the pins 26-B. The line is nevertheless angular due to the thickness of the conductive bar, which has a rectangular cross-section. The conductive bar is, for example, made of copper or aluminum. The corrugated conductive bar thus comprises, on the one hand, segments that are longer than the others and parallel to each other, each formed by the joining of the legs of two distinct U-shapes, and on the other hand, V-shaped junction portions between the different segments.

[0030] In a known manner, the segments of the bent conductive bar are inserted one after the other into the stator slots 24, the corrugated line of the conductive bar being wound around the stator 2 during this operation, according to the "continuous hairpin winding" method. This insertion is made over several turns of the stator 2, in this embodiment of the invention, in particular four turns, so that each magnetic pole 28-A, 28-B, or 28-C of a phase comprises four segments of the conductive bar forming the pins 26-A, 26-B, or 26-C of the same phase, as shown [Fig. 2], in particular with a magnetic pole 28-C formed of four pins 26-C.

[0031] The two segments of the same pin 26-A, 26-B or 26-C belong to two successive magnetic poles 28-A, 28-B or 28-C of the same phase. The junction portions between the segments form stator buns extending axially on either side of the stator 2.

[0032] As shown in [Fig. 1], the external portion 22 of the stator is angularly segmented, with only two angular segments 22-1 and 22-2 being shown. The angular segments are, for example, each formed of laminated sheets 0.2 to 0.35 mm (millimeters) thick, stacked one on top of the other.

[0033] Thus they can be manufactured in an inexpensive manner by cutting pieces from a strip of magnetic steel sheet, each piece of strip having teeth leaving in pairs a space intended to form a stator notch 24, the pieces of strip then being assembled for example by gluing, one on top of the other, to form an angular segment of the stator 2.

[0034] The angular segments are then joined together, for example by gluing or welding, and then attached to an internal portion 23 of the stator, annular, for example made of aluminium, in order to give sufficient rigidity to the stator 2. The internal portion 23 has in fact a higher stiffness coefficient than the external portion 22.

[0035] In this embodiment of the invention, the internal portion 23 comprises axially oriented cooling channels 232 through which a heat transfer fluid, such as glycol water, circulates. Alternatively, the internal portion 23 is made of steel. hard non-magnetic, and the stator 2 has an annular cooling jacket attached to the inner portion 23, which is then clamped between the outer portion 22 and the cooling jacket.

[0036] Returning to [Fig. 1], the rotor 3 comprises an annular body 32 with an internal diameter greater than the external diameter of the stator 2. The annular body 32 has an internal cylindrical peripheral surface on which axial notches 34 are arranged opening on either side of the body 32 onto circular axial ends of the annular body 32. The axial notches 34 are regularly distributed angularly and number 250 in this embodiment of the invention.

[0037] In this embodiment of the invention, the annular body 32 is formed of laminated sheets of magnetic steel. Alternatively, the annular body 32 is made of a single piece, or even of non-magnetic steel.

[0038] The rotor 3 also includes an aluminum squirrel cage having bars 33 (visible [Fig.2]) arranged in axial notches 34, the bars 33 being connected by rings 35 and 36 each arranged at a distinct axial end of the annular body 32. In this embodiment of the invention, this squirrel cage is molded onto the annular body 32.

[0039] The bars 33 can therefore be molded in each of the axial notches 34 while the rings 35 and 36 can be molded on the axial ends of the circular annular body 32, thus joining the bars 33 together on either side of the annular body 32, to form the squirrel cage in one molding operation.

[0040] Furthermore, the rotor 3 is cooled by air directly in contact with the rotor during the movement of the vehicle.

[0041] Figure 2 now shows how the pins of the different phases of the three-phase winding of stator 2 are arranged. The 36*3 magnetic poles 28-A, 28-B, 28-C follow one another in the order of phases A, B, and C, with the two closest magnetic poles of the same phase separated by two magnetic poles of the other two phases. Each pin of a phase has one segment in the first magnetic pole of that phase and one segment in the second magnetic pole of that phase, the one closest to the first magnetic pole.

[0042] Each magnetic pole 28-A, 28-B or 28-C extending over only two successive stator slots 24, and each stator slot 24 housing only two pins 26-A, 26-B or 26-C, each magnetic pole 28-A, 28-B or 28-C comprises only four segments of four distinct pins. In each stator slot 24, the segments of the two pins housed in that stator slot 24 are stacked radially one on top of the other, so as to fill the entire radial length of the stator slot 24. Since the pins have a rectangular cross-section, each stator slot 24 has a rectangular cross-section of width approximately equal to the width of the rectangular section of a pin, and of length approximately equal to twice the length of the rectangular section of a pin.

[0043] For example, in [Fig.2], the magnetic pole 28-C comprises: - on the one hand a first stator notch 24 comprising a segment of a first pin 26-C, housed at the bottom of this first stator notch 24, and a segment of a second pin 26-C, housed between the segment of the first pin 26-C and the opening of the first stator notch 24, and on the other hand - a second stator notch 24 comprising a segment of a third pin 26-C, housed at the bottom of this second stator notch 24, and a segment of a fourth pin 26-C, housed between the segment of the third pin 26-C and the opening of the second stator notch 24.

[0044] Figure 3 shows the winding diagram of stator 2, shown in cross-section but with junction portions between the segments of the pins composing the winding of stator 2, these junction portions forming the stator bun located at the front of Figure 3. The crosses in the segments of pins 26-A, 26-B, 26-C represent a first direction of current in the axial direction, while the dots in the segments of pins 26-A, 26-B, 26-C represent a second direction of current, opposite to the first direction of current, in the axial direction.

[0045] The four pin segments of the same pole are formed by four successive windings of the conductive bar bent around the stator 2, as shown in the diagram at the top left of [Fig.3]. As a result, each pin segment 26-A, 26-B, 26-C is electrically connected in series with the other pin segments of the same phase.

[0046] This series connection, as well as the fact of having stator slots with only two pins, makes it possible to bring a significant amount of power into the wheel motorization system according to the invention, due to the significant current that can flow in each pin segment, and the optimal filling of the stator slots with conductor.

[0047] The combination of 36 poles per phase, two stator slots per pole and two pins per stator slot, and 250 bars in the stator optimizes the efficiency of this drive system with a 19-inch wheel rim by attenuating the harmonics of the electromagnetic force produced by the stator 2 and minimizing torque oscillation. The control of this wheel drive system uses, for example, a flux-oriented vector control.

[0048] By way of example, this topology and dimensioning of the wheel drive system according to the invention makes it possible to achieve a torque of 1200 N·m (Newton-meters) and a peak power exceeding 100 kW (kilowatts). This wheel drive system proves to be robust with respect to vibrational stresses, to its location close to the brakes which generate dust, and to high temperatures.

[0049] Of course, the invention is not limited to the examples just described, and many modifications can be made to these examples without departing from the scope of the invention. For example, the wheel drive system described in this embodiment can be adapted to larger or smaller wheel rims by adjusting the number of bars in the rotor and the number of magnetic poles in the stator. Furthermore, the stator winding can have more than three phases, for example, to reduce the maximum phase current supplied by an inverter and increase reliability in the event of a failure in the vehicle's drive system.

Claims

Demands

1. Vehicle wheel drive system (1) comprising: - a stator (2) intended to be mounted rigidly to a hub, - a wheel rim mounted to rotate relative to the hub, - a rotor (3) fixed to the wheel rim, the rotor (3) angularly surrounding the stator (2), with an air gap between the rotor and the stator, the wheel drive system (1) being characterized in that the rotor (3) is a squirrel cage rotor, and in that the stator (2) has stator slots (24) in which a pin winding (26-A, 26-B, 26-C) is mounted.

2. Wheel motorization system (1) according to claim 1, wherein the stator (2) having several magnetic poles (28-A, 28-B, 28-C) per phase, each magnetic pole (28-A, 28-B, 28-C) extends over only two successive stator slots (24).

3. Wheel motorization system (1) according to claim 2, wherein each stator slot (24) houses only two pins (26-A, 26-B, 26-C).

4. Wheel motorization system (1) according to claim 3, wherein the pins (26-A, 26-B, 26-C) of each phase of the stator (2) are electrically connected in series with each other, being formed from the same bent conductive bar.

5. Wheel motorization system (1) according to any one of claims 1 to 4, wherein the stator (2) comprises an internal non-magnetic portion (23) and an external portion (22) made of magnetic steel, the external portion (22) made of magnetic steel being attached to the internal portion (23).

6. Wheel drive system (1) according to claim 5, wherein the outer portion (22) is segmented angularly so as to form a plurality of angular segments.

7. Wheel drive system (1) according to claim 6, wherein each angular segment (22-1, 22-2) is formed of laminated sheets.

8. Wheel motorization system (1) according to any one of claims 5 to 7, wherein the stator (2) has a cooling circuit housed in the internal portion (23) of the stator (2), or in a cooling jacket attached to the internal portion (23) of the stator (2).

9. Wheel motorization system (1) according to any one of claims 1 to 8, wherein the rotor (3) comprises on the one hand - an annular body (32) having two axial ends and an internal peripheral surface having axial notches (34), the axial notches (34) opening onto each axial end of the annular body (32), and on the other hand - an aluminum or copper squirrel cage having bars in the axial notches (34) and rings (35) of the same material connecting the bars to each axial end of the annular body (32).

10. Wheel drive system (1) according to claim 9, wherein the annular body (32) is formed of laminated magnetic steel sheets.

11. Wheel motorization system (1) according to any one of claims 9 or 10, taken in dependence on claim 2, wherein the stator (2) is three-phase and has 216 stator slots (24) forming 36 magnetic poles (28-A, 28-B, 28-C) per phase, while the rotor (3) has 250 axial slots (34).

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