COUPLING FOR TURNING SHAFTS THAT ALLOWS AXIAL DISCHARGE BY MEANS OF ROLLING ENERGIES
Patent Information
- Application Number
- AT2022743512T
- Authority / Receiving Office
- AT · AT
- Patent Type
- Patents
- Current Assignee / Owner
- Priority Date
- 2021-08-10
- Filing Date
- 2022-07-20
- Publication Date
- 2026-04-15
- Estimated Expiration
- 2042-07-20
Abstract
Description
DESCRIPTION TITLE OF THE INVENTION: COUPLING OF ROTARY SHAFTS ALLOWING AXIAL DISPLACEMENT BY MEANS OF ROLLING ELEMENTS TECHNICAL FIELD OF THE INVENTION
[0001] The present invention relates generally to the mechanical transmission of torque.
[0002] It relates more particularly to a device for coupling two shafts, comprising: - rolling elements adapted to be engaged in grooves provided in the shafts, and - a holding base adapted to hold the rolling elements engaged in the grooves in relative position.
[0003] It also concerns a powertrain comprising: - an electric machine which includes an output shaft, - a speed reducer (such as a multi-speed gearbox, a single-speed mechanical reducer, etc.) comprising a primary shaft, and - a shaft coupling device as mentioned above, allowing the torque to be transmitted between the output shaft and the primary shaft.
[0004] The invention finds a particularly advantageous application in a hybrid powertrain, in particular for a motor vehicle. It is even more particularly advantageous when the powertrain comprises an axial flux electric machine, but also applies in a powertrain with a radial flux electric machine. STATE OF THE ART
[0005] An electric or hybrid motor vehicle has a powertrain that includes an electric machine coupled to a speed reducer, the latter being able to be a simple pinion mechanism, a variator, a gearbox, etc.
[0006] The electric machine then has a rotor which is mounted on an output shaft, which is connected to the input of the reducer, and more precisely to its primary shaft.
[0007] For example, the electrical machine may be of the axial flux type and have a rotor flanked by two stators. The stators are then slightly spaced from the rotor to avoid any friction. Thus, on each side of the rotor there is a space called an air gap.
[0008] The performance of the electrical machine depends on the value of these air gaps, their consistency around the axis of rotation of the rotor, and the symmetry of these air gaps on either side of the rotor.
[0009] The slightest geometry error has consequences on the performance of the motor and its lifespan. For example, since the electric machine is of the axial flux type, it is understood that a difference in values between the two air gaps causes the rotor to be attracted by the nearest stator. This force can be significant. It can also be cyclical and lead to fatigue of the materials making up the electric machine. The rotor support bearings are also subjected to greater stress and need to be sized according to these stresses. Such sizing results in excess weight and significant costs.
[0010] These problems are inherent in the very concept of an axial flux electric machine. They can be caused or increased by external stresses from the gearbox. In fact, the pinions used in the gearbox generally have helical teeth that exert axial thrusts that can cause movements in the electric machine, and therefore variations in the size of the air gaps.
[0011] This is why the coupling between the output shaft of the electric machine and the primary shaft of the reducer is generally achieved by means of splines allowing these two shafts to slide relative to each other.
[0012] The disadvantage of such a mechanical connection is that any misalignment between the output of the electric machine and the input of the reducer is likely to prevent the splines from sliding freely within each other, which can cause displacement of components in the electric machine. Even if this displacement is limited to a few tenths of a millimeter, it can cause a significant loss of power (particularly in the case of an axial flux machine) and a significant drop in the service life of the electric machine and its bearings (in all cases). PRESENTATION OF THE INVENTION
[0013] To overcome this problem, the present invention proposes not to size the various components of the powertrain according to these constraints, but rather to introduce a mechanical device between the output of the electric machine and the input of the reducer which does not transmit the axial forces due to a misalignment between the output of the electric machine and the input of the reducer.
[0014] More particularly, the invention proposes a coupling device as defined in the introduction, in which the holding base comprises a junction part from which several parallel arms extend, each carrying at least two retaining means adapted to hold two rolling elements in relative position.
[0015] Thus, thanks to the invention, the coupling device forms, for example, a sort of “ball slide” and the holding base forms a sort of “cage”.
[0016] The shape of this support base is special and is therefore space-saving, which makes it possible to significantly increase the depth of the grooves made in the shafts to be coupled and the number of rolling elements in the same space. Therefore, the coupling device is able to transmit very high torques.
[0017] Furthermore, any misalignment or axial displacement between the primary shaft and the output shaft can be taken up by the rolling elements, which will prevent any transmission of axial force between these two shafts.
[0018] As a result, these defects will have no effect on the internal geometry of the electrical machine, and in particular on the geometric characteristics of the air gaps. Thus, the performance of the electrical machine and the service life of the bearings can be preserved.
[0019] Other advantageous and non-limiting characteristics of the device according to the invention, taken individually or in all technically possible combinations, are the following: - said joining part has a peripheral edge from which said arms extend; - which arms all extend on the same side of the joining part; - the support base comprises a number of arms which is at least equal to three, which is preferably at least equal to six, and which is even more preferably equal to eight; - a number of rolling elements is provided for each arm which is between three and five, and which is preferably equal to four; - the means for retaining each rolling element comprises two fingers which are placed on either side of the rolling element and which extend projecting from one of the faces of the arm.
[0020] The invention also relates to a powertrain as defined in the introduction, in which: - one of the output shaft and primary shaft has a hollow end and the other of the output shaft and primary shaft has a first end which is engaged inside said hollow end, - the coupling device is as mentioned above and comprises rolling elements engaged in grooves made hollow on said first end and in said hollow end, said grooves extending longitudinally along axes parallel to an axis of rotation of the output shaft.
[0021] Other advantageous and non-limiting characteristics of the powertrain according to the invention, taken individually or in all technically possible combinations, are the following: - the grooves have, over at least part of their lengths accommodating the rolling elements, uniform arc-shaped sections with opening angles greater than 160°, preferably between 165° and 175°; - the hollow end is carried by the output shaft, which output shaft is formed of at least two parts, one of which forms a ring inside which the grooves are made, said grooves extending over the entire length of the ring; - the first end is carried by the primary shaft, and the grooves are made on a sleeve which is fixed to another part of the primary shaft, said sleeve having a small diameter portion fixed to said other part of the primary shaft and a large diameter portion over the entire length of which the grooves extend; - each of the grooves made hollow on said first end has in its bottom a groove for receiving one of the arms of the coupling device; - the electric machine is axial flux.
[0022] Of course, the various features, variants and embodiments of the invention may be combined with each other in various combinations to the extent that they are not incompatible or mutually exclusive. DETAILED DESCRIPTION OF THE INVENTION
[0023] The description which follows with reference to the appended drawings, given as non-limiting examples, will make it clear what the invention consists of and how it can be implemented.
[0024] On the attached drawings:
[0025] [Fig. 1] is a schematic sectional view of a part of a powertrain according to the invention;
[0026] [Fig. 2] is a schematic sectional view of the output shaft of the electric machine of the powertrain of Figure 1 and the means for transmitting the torque of the output shaft;
[0027] [Fig. 3] is a front view of a ball slide of the power unit of Fig. 1;
[0028] [Fig. 4] is a schematic sectional view along section planes A-0 and OB of Figure 3;
[0029] [Fig. 5] is a schematic sectional view along the section plane CC of Figure 3;
[0030] [Fig. 6] is a schematic sectional view along the section plane DD of Figure 2. Device - Electric machine
[0031] In Figure 1, a part of a powertrain 10 is shown.
[0032] Such a powertrain 10 is preferably designed to be installed in a motor vehicle (car, truck, etc.), although alternatively, it could be installed in other types of installations.
[0033] This powertrain 10 is preferably hybrid in the sense that it comprises at least two engines, one electric and the other thermal. Alternatively, it could comprise only one electric engine.
[0034] Here it comprises an electric machine 100, an internal combustion engine (not shown) and a speed reducer 200.
[0035] The electric machine 100 could be of the radial flux type. However, preferably, it is of the axial flux type.
[0036] The electrical machine 100 used here comprises a hollow casing 120 in two parts bolted to each other, which delimit a housing inside which are located here a rotor 130 and two stators 140 arranged on either side of the rotor 130.
[0037] The stators 140 are fixedly mounted in the casing 120. They each have the shape of a disc pierced in its center and centered on the axis A1 of the rotor 130 (hereinafter called the axis of rotation A1). Each of these stators carries windings of electrical wires which, when supplied with electric current, allow a magnetic flux to be generated which passes through the rotor 130 in a direction substantially parallel to the axis of rotation A1. This is the reason why this type of electrical machine is referred to as an axial flux machine.
[0038] The rotor 130 also has the shape of a disc pierced in its center. It has a thickness such that an air gap is provided between each of its two circular faces and the stator 140 which faces it.
[0039] In practice, it comprises a central hub 131 (figure 2) and a peripheral hoop 132 (figure 1) which hold between them magnets (monobloc or formed from a plurality of unit magnets) regularly distributed around the axis of rotation A1.
[0040] As shown in Figure 2, the central hub 131 is bolted to an output shaft 110 which extends axially along the axis of rotation A1.
[0041] Thanks to this architecture, when the stators 140 are supplied with electric current, they force the output shaft 110 to pivot around this axis of rotation A1.
[0042] Thus the electric machine is able to generate a motor torque (when it is in motor mode). Conversely, when its output shaft 110 is rotated, it can behave as an alternator capable of generating an electric current (we speak of generator mode).
[0043] The output shaft 110 could be made from a single piece.
[0044] However, preferably, it comprises at least two parts bolted to each other, including a main part 115 (on the left in Figure 2) and a ring 116 (on the right). These two parts have, on their outer faces, flanges for their fixing by bolts 118.
[0045] As also shown in Figure 2, the rotor 130 is mounted on the main part 115 of the output shaft 110 and is secured thereto via the bolts 118.
[0046] Ball bearings 150 are provided around each of two parts 115, 116 to guide the pivoting of the output shaft 110 around the axis of rotation A1.
[0047] Here, the ring 116 is hollow. More precisely, it has the overall shape of a tube. It thus forms a hollow end 111 for the output shaft 110.
[0048] At this stage of the description, it may be noted that the casing 120 illustrated in FIG. 1 delimits a hermetic chamber in a part of which circulates a fluid for cooling the static parts of the electrical machine 100 and for lubricating the moving parts of the speed reducer 200.
[0049] The casing 120 then has a conduit which allows a pressurized fluid inlet to communicate with the interior of the output shaft 110, which has a central through-hole for this purpose. The casing 120 also has two passages for electrical conductors for supplying the stators. - Reducer
[0050] The speed reducer 200 is shown in Figure 1.
[0051] This is a gearbox, but alternatively it could be a single-ratio gear reducer, a belt reducer, a variator, etc.
[0052] This reducer 200 comprises a primary shaft 210 through which the torque generated by the electric machine (in motor mode) and by the internal combustion engine arrives, and a secondary shaft 220 which generally rotates at a different speed than that of the primary shaft 210 and through which the torque is transmitted to the wheels of the vehicle. As will appear below, the primary shaft 210 is not a single piece but comprises two independent parts which can pivot relative to each other.
[0053] These two primary 210 and secondary 220 shafts are mounted in a sealed casing 230 (composed of two parts fixed together), so as to extend along parallel axes and to be able to pivot freely around these axes in the casing 230.
[0054] The primary shaft 210 is more particularly designed to extend longitudinally along the axis of rotation A1 and pivot around this axis.
[0055] For this, the primary shaft 210 is supported at its two ends by a ball bearing 240 engaged in the casing 230, while the secondary shaft 220 carries at its two ends an inclined roller bearing 241 engaged in the casing 230.
[0056] The primary shaft has a first end 211 (on the left in FIG. 1) by which one of its parts is coupled to the output shaft 110 of the electric machine 100, and a second end (not visible) by which another of its parts is coupled to the internal combustion engine.
[0057] The gearbox has several gears for the combustion engine internal and at least one report for the electric machine 100 (it preferably has several, here two).
[0058] The primary shaft 210 is then formed of three parts, including a sleeve 210C (on the left), a hollow part 210A (in the center) and a solid part 210B (on the right) which is partly engaged inside the hollow part 210A. These parts are mounted coaxially in the extension of each other. The sleeve 210C is fixed (here by a tight fit) in the hollow part 210A, while the solid part 210B can freely pivot relative to the other two parts thanks to a roller bearing 214.
[0059] The hollow portion 210A and the sleeve 210C of the primary shaft 210 are permanently coupled with the output shaft 110 of the electric machine 100.
[0060] The hollow part 210A carries two fixed teeth 215, 216 (figure 2) forming two toothed wheels which mesh with idler gears carried by the secondary shaft 220 (figure 1). A dog clutch device mounted on the secondary shaft 220 makes it possible to select one or the other of these two toothed wheels or to disconnect the electrical machine 100 from the secondary shaft 220.
[0061] The solid part 210B of the primary shaft 210 is coupled to the crankshaft of the internal combustion engine. It is preferably coupled thereto permanently, without using a clutch. It carries two idler gears 217, 218 which mesh with toothed wheels carried by the secondary shaft 220. A dog clutch device 217A mounted on the primary shaft 210 makes it possible to select one or the other of these idler gears. The solid part 210B of the primary shaft 210 also carries a fixed gear 219 which cooperates with a gear of a third shaft, not shown, which makes it possible in particular to offer other speed ratios and to connect the gearbox to an alternator-starter.
[0062] The secondary shaft 220 also carries fixed teeth 223 by which it can transmit its torque to a differential (not shown) of the motor vehicle.
[0063] As shown in Figure 2, the 210C sleeve has a tubular shape, with a central conduit allowing the passage of cooling and lubricating fluid.
[0064] It has, at one end (right in the drawings), a portion of smaller section than the rest of the sleeve, by which it is forcibly engaged inside the hollow part 210A of the primary shaft 210. - Coupling
[0065] In summary, as shown in Figure 2, the output shaft 110 of the electric machine 100 comprises a main part 115 and a ring 116 fixed together, while the primary shaft 210 of the gearbox comprises a sleeve 210C and a hollow part 210A fixed together and rotatably mounted on a solid part 210B of this primary shaft 210.
[0066] Ideally, the axis of the output shaft 110 of the electric machine 100 and the axis of the primary shaft 210 of the gearbox are merged (this is also the reason why these two axes are here called under the same name “axis of rotation A1”).
[0067] Unfortunately, due to manufacturing and assembly defects or due to forces exerted on the various components of the powertrain 10, it happens that these axes are not exactly aligned, and that they shift and / or tilt relative to each other.
[0068] A coupling device 300 is then provided between the output shaft 110 and the primary shaft 210 which is special in that it makes it possible to transmit very high torques and to compensate for these defects, i.e. to prevent axial movements and forces from being transmitted by the gearbox to the output shaft 110 of the electrical machine 100.
[0069] This coupling device 300 comprises rolling elements 310 engaged in grooves 112, 212 made hollow on the first end 211 of the primary shaft 210 and inside the hollow end 111 of the output shaft 110. These grooves 112, 212 extend longitudinally along axes parallel to the axis of rotation A1 and therefore form tracks for the rolling elements 310.
[0070] More precisely, as shown in Figure 6, the ring 116 of the output shaft 110 of the electrical machine 100 has grooves 112 which extend hollow in its internal face, along longitudinal axes parallel to each other, and which are regularly distributed all around the axis of rotation A1.
[0071] Preferably, between three and ten separate grooves 112 are provided. Here, exactly eight are provided.
[0072] These grooves 112 are all identical. They extend over the entire length of the ring 116 and are profiled in the sense that their cross sections (in planes orthogonal to the axis of rotation A1) have the same geometry from one end of the ring 116 to the other.
[0073] Each cross-section of one of the grooves 112 here has the shape of an arc of a circle. The angular sector of this arc of a circle has an opening angle of between 165° and 175°, preferably of the order of 170°.
[0074] Thanks to their uniform geometry from one end of the ring 116 to the other, these grooves 112 form tracks for the rolling elements which can be used over the entire length of the ring. Therefore, it is possible to provide a ring of reduced length, which increases the compactness of the powertrain 10.
[0075] As shown in Figure 2, the first end 211 of the primary shaft 210 of the gearbox (the one coupled to the output shaft 110) is formed by the sleeve 210C.
[0076] Thus, it is the sleeve 210C which has on its external face the grooves 212 in which the rolling elements 310 are engaged.
[0077] This 210C sleeve has a tubular shape with a large diameter 211C main part and a smaller diameter 212C end part.
[0078] The grooves 212 extend hollowly in the external face of the main part 211C of the sleeve 210C, in parallel with each other, and are regularly distributed all around the axis of rotation A1.
[0079] As many grooves are provided on the input shaft 210 as in the output shaft 110.
[0080] Here again, these grooves 212 are all identical and profiled, with a cross-section in the shape of an arc of a circle having an opening angle ideally between 165° and 175°.
[0081] The diameter of the end portion 212C is adjusted so as to be able to forcefully engage the sleeve 210C in the hollow portion 210A of the primary shaft 210.
[0082] The diameter of the main part 211C is larger and is provided such that the geometric cylinder which is centered on the axis of rotation A1 and which passes through the bottom of the grooves 212 has a diameter greater than or equal to that of the end part 212C. Thus, these grooves 212 open outside this end part 212C. Also, these grooves 212 can be produced over the entire length of the main part 211C with a simple tool (typically a single milling cutter of suitable shape) and have a uniform profile over the entire length thereof. In this way, these grooves 212 form tracks for the rolling elements which can be used from one end of the main part 211C to the other. Consequently, it is possible to provide a sleeve 210C of reduced length, which increases the compactness of the powertrain 10. Backstage
[0083] As shown in Figures 2 to 5, the coupling device 300 of the output shaft 110 with the primary shaft 210 comprises, in addition to the rolling elements 310 already mentioned, a holding base 320 of particular shape, which ensures the relative locking in position of the rolling elements 310 in the grooves 112, 212 of the shafts.
[0084] As a preliminary point, it can be specified that the rolling elements 310 will preferably be spherical balls.
[0085] The holding base 320 comprises a junction portion 330 from which several rectilinear and parallel arms 340 extend, each of which carries means 350 for retaining at least two rolling elements 310.
[0086] Here, as clearly shown in Figures 3 to 5, the joining part 330 has the shape of a flat ring. It delimits a central opening for the passage of the lubricating and cooling fluid.
[0087] This junction part 330 is intended to be placed against the free end of the sleeve 21 OC of the primary shaft 210. It then extends along a plane orthogonal to the axis of rotation A1.
[0088] The arms 340 then extend from the peripheral edge of the flat ring, on the same side of it (here right side).
[0089] They extend parallel to the axis of rotation A1.
[0090] It could be provided that this arm is housed at the junction between the two output shafts 110 and primary 210 (by interposing itself between the sleeve 210C and the ring 216).
[0091] However, here, the arms are designed to fit into grooves provided at the bottom of the grooves 112, 212 of one of these two shafts.
[0092] As shown very clearly in Figure 6, they are here provided to be housed in grooves 212A preferably provided at the bottom of the grooves 212 of the sleeve 210C of the primary shaft 210.
[0093] These grooves 212A are profiled and have dimensions equal, apart from the mounting clearance, to the dimensions of the arms 340 of the holding base 320.
[0094] The arms 340 and the grooves 212A here have rectangular cross-sections.
[0095] As clearly shown in Figures 3 to 5, each arm 340 preferably comprises four means 350 for retaining rolling elements 310.
[0096] Here, the rolling elements being balls, the retaining means 350 of each rolling element 310 comprises two fingers 351 placed on either side of the rolling element 310. These two fingers 351 extend projecting from one of the faces of the arm (here projecting from the external face).
[0097] As shown in Figure 3, each finger 351 extends over a width (in an orthoradial direction relative to the axis of rotation A1) identical to the width of the arm 340 which carries it, so as not to extend beyond the latter.
[0098] Furthermore, each finger 351 extends over a height relative to the arm (in a radial direction relative to the axis of rotation A1) which is greater than the radius of the rolling elements 310, but less than the diameter thereof. Thus, each rolling element 310 can be clipped between the two fingers 351 which enclose it, which then facilitates the handling of the coupling device 300.
[0099] The holding base 320 is preferably made of a single piece. In this case, it is made of plastic. The plastic material thus used may typically be the same as that used to manufacture standard ball bearing cages.
[0100] The number of arms 340 and retaining means 350 on each arm 340 depends on the number of rolling elements used. The number of pairs of fingers 351 is at least greater than two and here equal to four per arm 340, the number of arms here being equal to eight.
[0101] Once the rolling elements 310 are installed in the grooves 112 of the shaft of output 110 and in the corresponding grooves 212 of the primary shaft 210 and held by the holding base 320, they allow the torque to be transmitted well from one shaft to the other.
[0102] Preferably, the rolling elements 310 are mounted with radial clearance in the grooves, this clearance being less than 0.1 mm.
[0103] The rolling elements 310 also make it possible to transmit no axial force from one shaft to the other (along the axis of rotation A1), even if the two shafts are slightly offset. Indeed, the grooves form tracks in which the rolling elements 310 can roll freely even when the two shafts are offset by 0.1 mm or inclined by 0.1 degrees.
[0104] Thus, the coupling device 300 forms a sort of ball slide.
[0105] As shown in Figure 2, this ball slide is preferably mounted in the output shaft 110 so as to be free to slide in the latter, with a clearance of a few millimeters.
[0106] Its stroke is however limited, on one side, by the main part 115 of the output shaft 110, and on the other, by the hollow part 210A of the primary shaft 210.
[0107] As mentioned above, a lubricating fluid is provided to circulate within the main portion 115 of the output shaft 110.
[0108] As shown in Figure 3, this fluid flows into the ball slide, keeping it lubricated and cool.
[0109] Sealing means are then provided to prevent the fluid which comes from inside the output shaft 110 and then oils and cools the ball slide from escaping other than through the inside of the hollow part 210A of the primary shaft 210.
[0110] These sealing means firstly comprise a first set of seals 401, 403 provided on the hollow part 210A of the primary shaft 210 and at the end of the ring 116 of the output shaft 110, which makes it possible to guarantee the seal between the primary shaft 210 and the output shaft 110, to the right of the ball slide. This first set comprises in particular a sealing ring 401 which is placed at the free end of the ring 116 of the output shaft 110.
[0111] These sealing means also comprise a second seal 402 located between the main part 115 and the ring 116 of the output shaft 110, and which provides sealing to the left of the ball slide. Process
[0112] The assembly of the coupling device is then carried out as follows.
[0113] During a first step, the coupling device 300 is assembled. The rolling elements 310 are then each blocked between the two fingers 351 which enclose it.
[0114] This device is then engaged inside the ring 116. It is held in position there by the aforementioned sealing ring 401.
[0115] Later, the gearbox can be assembled to the engine, by engaging the sleeve 210C inside the coupling device 300. Variants
[0116] The present invention is in no way limited to the embodiment described and shown, but those skilled in the art will be able to provide any variation in accordance with the invention.
[0117] For example, the hollow end could belong to the primary shaft while the end of the output shaft would be engaged inside this hollow end, the coupling device being interposed radially between these two ends.
[0118] As further examples, the rolling elements could have different shapes, for example roller shapes of very short lengths.
Claims
DEMANDS
1. Coupling device (300) for two shafts (110, 210), comprising: - rolling elements (310) adapted to be engaged in grooves (112, 212) provided in the shafts (110, 210), and - a support base (320) adapted to maintain in relative position the rolling elements (310) engaged in the grooves (112, 212), characterized in that the support base (320) comprises a junction part (330) from which extend several parallel arms (340) which each carry at least two retaining means (350) adapted to maintain in relative position two rolling elements (310).
2. Coupling device (300) according to the preceding claim, wherein said junction part (330) has a peripheral edge from which said arms (340) extend, which arms (340) all extend on the same side of the junction part (330).
3. Coupling device (300) according to any one of the preceding claims, wherein the support base (320) has a number of arms (340) which is at least three, which is preferably at least six, and which is even more preferably eight.
4. Coupling device (300) according to any one of the preceding claims, wherein there is a number of rolling elements (310) for each arm (340) which is between three and five, and which is preferably equal to four.
5. Coupling device (300) according to any one of the preceding claims, wherein the retaining means (350) of each rolling element (310) comprises two fingers (351) which are positioned on either side of the rolling element (310) and which extend in projection from one of the faces of the arm (340).
6. Powertrain (10) comprising: - an electrical machine (100) which includes an output shaft (110), and - a speed reducer (200) comprising a primary shaft (210), one of the output shafts (110) and primary shaft (210) having a hollow end (111) and the other of the output shaft (110) and primary shaft (210) having a first end (211) which is engaged inside said hollow end (111), characterized in that it further comprises a coupling device (300) according to one of the preceding claims, the rolling elements (310) of which are engaged in grooves (112, 212) formed in hollow on said first end (211) and in said hollow end (111), said grooves (112, 212) extending longitudinally along axes parallel to an axis of rotation (A1) of the output shaft.
7. Powertrain (10) according to the preceding claim, wherein the grooves (112, 212) have, over at least part of their lengths accommodating the rolling elements (310), uniform arc-shaped sections with opening angles greater than 160°, preferably between 165° and 175°.
8. Powertrain (10) according to any one of claims 6 and 7, wherein the hollow end (111) is carried by the output shaft (110), which output shaft (110) is formed of at least two parts (115, 116), one of which forms a ring (116) in which grooves (112) are formed, said grooves (112) extending over the entire length of the ring (116).
9. Powertrain (10) according to any one of claims 6 to 8, wherein the first end (211) is carried by the primary shaft (210), and wherein the grooves (212) are made on a sleeve (210C) which is fixed on another part (210A) of the primary shaft (210), said sleeve (210C) having a small diameter portion fixed to said other part (210C) of the primary shaft (210) and a large diameter portion over the entire length of which the grooves (212) extend.
10. Powertrain (10) according to any one of claims 6 to 9, wherein each of the grooves (212) formed in relief on said first end (211) has in its bottom a groove (212A) for receiving one of the arms (340) of the coupling device (300).
11. Powertrain (10) according to any one of claims 6 to 10, wherein the electric machine (100) is axial flux.