Rotor shaft for an electric motor

Abstract

A rotor shaft (8) for an electric motor (2) of a motor vehicle (1), the rotor shaft being intended to rotate about an axis of rotation (X1), characterized in that it comprises a first hollow part (13) and a second hollow part (14), the second part extending in the continuation of the first part along the axis of rotation, the second part being welded to the first part.

Description

[0001] DESCRIPTION

[0002] TITLE: Rotor shaft for an electric motor

[0003] Technical field of the invention

[0004] The invention relates to a rotor shaft for an electric motor. The invention also relates to an electric motor comprising such a rotor shaft. The invention further relates to a motor vehicle comprising such an electric motor.

[0005] State of the prior art

[0006] More and more motor vehicles are now equipped with an electric motor designed to drive the vehicle's drive wheels. Electric motors are usually combined with a speed reducer to drive the vehicle's drive wheels at a suitable rotational speed. A rotor shaft of the electric motor is guided in rotation by rolling bearings integrated into the electric motor, and mechanically connected to the speed reducer via a drive pinion. The drive pinion generally induces axial forces on the rotor shaft.

[0007] It nevertheless appears desirable to propose speed reducers arranged relative to the electric motor so as to induce radial forces on the rotor shaft. These radial forces tend to cause the rotor shaft to bend between the two rolling bearings. This bending can be all the more significant as the distance separating the two rolling bearings is significant. A bending of the rotor shaft modifies an air gap of the electric motor and therefore disrupts the operation of the electric motor. Furthermore, known electric motors require a large quantity of materials and are generally very heavy.

[0008] Presentation of the invention

[0009] The aim of the invention is to provide an electric motor which overcomes the above drawbacks and improves the electric motors known from the prior art.

[0010] More specifically, a first object of the invention is an electric motor which is relatively light and whose rotor shaft can withstand significant radial forces without bending excessively.

[0011] Summary of the invention

[0012] The invention relates to a rotor shaft for an electric motor of a motor vehicle, the rotor shaft being intended to rotate about an axis of rotation, the rotor shaft comprising a first hollow part and a second hollow part, the second part extending in the extension of the first part along the axis of rotation, the second part being welded to the first part.

[0013] The first portion may comprise a first surface and a second surface, the first surface extending perpendicular to the axis of rotation, the second surface extending parallel to the axis of rotation, and the second portion may comprise a third surface and a fourth surface, the third surface extending perpendicular to the axis of rotation, the fourth surface extending parallel to the axis of rotation, the first surface bearing against the third surface, the second surface cooperating with the fourth surface to center the second portion relative to the first portion. The first portion may be obtained by forging. The second portion may be obtained by forging.

[0014] The first portion may include a fifth surface extending perpendicular to the axis of rotation, and the second portion may include a sixth surface extending perpendicular to the axis of rotation, the fifth surface extending opposite the sixth surface at a distance from the sixth surface, a weld bead extending between the fifth surface and the sixth surface.

[0015] The first portion may include an outer diameter substantially equal to an outer diameter of the second portion at a junction between the first portion and the second portion. The first portion may include a recess opposite a recess of the second portion, an outer diameter of the recess of the first portion being substantially equal to an outer diameter of a recess of the second portion at a junction between the first portion and the second portion.

[0016] The rotor shaft may have an outside diameter greater than or equal to 50mm.

[0017] The invention also relates to an electric motor comprising a rotor shaft as defined above, a first bearing and a second bearing guiding the rotor shaft in rotation, the first bearing being mounted on the first part of the rotor shaft and the second bearing being mounted on the second part of the rotor shaft.

[0018] The rotor shaft may further comprise a drive pinion capable of inducing radial forces on the rotor shaft. The invention also relates to a motor vehicle comprising an electric motor as defined above.

[0019] The invention also relates to a method of manufacturing a rotor shaft as defined above, the manufacturing method comprising:

[0020] - the manufacture of a first hollow part of the rotor shaft by forging,

[0021] - the manufacture of a second hollow part of the rotor shaft by forging, then

[0022] - the assembly of the first part to the second part according to a flat support, then

[0023] - welding the first part to the second part, then,

[0024] - machining an outside diameter of the rotor shaft without contact with a heat-affected zone by welding the first part to the second part.

[0025] Presentation of figures

[0026] These objects, characteristics and advantages of the present invention will be explained in detail in the following description of a particular embodiment made without limitation in relation to the attached figures among which:

[0027] Figure 1 is a schematic view of a motor vehicle equipped with an electric motor according to one embodiment of the invention.

[0028] Figure 2 is a partial sectional view of a rotor shaft of the electric motor of Figure 1.

[0029] Figure 3 is a sectional view of an interface between a first portion and a second portion of the rotor shaft of Figure 2. Detailed Description

[0030] Figure 1 schematically illustrates a motor vehicle 1 according to one embodiment of the invention. The vehicle 1 may in particular be a private vehicle, a utility vehicle, a truck or even a bus. In particular, the vehicle 1 is a so-called "electric" vehicle. It comprises an electric motor 2 intended to drive the drive wheels of the vehicle.

[0031] The electric motor 2 comprises a rotor 3 and a stator 4. The stator 4 comprises a stack of laminations 5A and a set of electrical coils 5B arranged on either side of the stack of laminations 5A. The stator 4 is secured to a casing 6 of the electric motor 2. The rotor 3 is a wound rotor. The rotor 3 also comprises a stack of laminations 7A and a set of electrical coils 7B arranged on either side of the stack of laminations 7A. The coils 5B and 7B are intended to produce a magnetic field when an electric current flows through them. The rotor 3 is separated from the stator 4 by a radial air gap e. The coils 7B of the rotor cooperate with the coils 5B of the stator to rotate the rotor 3 relative to the stator around an axis of rotation X1.

[0032] The rotor 3 comprises a rotor shaft 8 extending parallel to the axis of rotation X1. The rotor shaft 8 supports the coils 7. The rotor shaft 8 is guided in rotation by two bearings 9A and 9B, in particular two rolling bearings. The bearings may in particular be mounted to bear against the casing 6 of the electric motor. The stacks of sheets 7A and the coils 7B extend between the two bearings 9A and 9B. The rotor shaft 8 may comprise a first end inside the casing 6 and a second end projecting outside the casing 6. The rotor shaft 8 therefore comprises a portion 10 which extends outside the casing 6. This portion 10 supports a drive pinion 11. The drive pinion 11 is intended to cooperate with a speed reducer 12. The drive pinion 11 is thus mounted cantilevered on the rotor shaft 8, that is to say it is not positioned between the two bearings 9A and 9B.The two bearings 9A and 9B can be relatively far from each other due to the presence of the reducer 12 which requires the installation of functions inherent to a reducer, in particular a secondary shaft, a differential, or a parking brake.

[0033] The drive pinion 11 may comprise helical teeth intended to cooperate with gear means of the reducer 12. Generally, the drive pinion 11 is intended to receive forces F1 oriented radially, that is to say perpendicular to the axis of rotation X1. These forces tend to cause the rotor shaft 8 to bend. However, as we will see in more detail later, the rotor shaft 8 comprises increased rigidity compared to the rotors known from the state of the art, which makes it possible to attenuate or even cancel this deformation.

[0034] Indeed, the rotor shaft has an increased outer diameter, this outer diameter can reach at least 50 mm, or even at least 55 mm, which represents an increase of at least 10%, or even at least 20%, compared to the rotor shafts of the electric motors of motor vehicles known from the state of the art and of the same power as the electric motor 2. This increase in diameter gives the rotor shaft 8 increased rigidity and therefore allows it to better withstand the radial forces generated by the reducer 12, as well as the torsional forces linked to the transmission of a rotational torque. The power transmitted by the electric motor 2 can thus be increased by approximately 25%.

[0035] The rotor shaft 8 is formed by assembling a first part 13 and a second part 14 fixed to each other. The first part 13 extends in the extension of the second part along the axis of rotation X1. One end of the first part 13 is therefore in contact with one end of the second part 14. The two-part design 13, 14 of the rotor shaft 8 makes it possible to provide a central recess in the rotor shaft. The rotor shaft 8 thus remains relatively light despite its increased outer diameter.

[0036] Each of the two parts 13 and 14 of the rotor shaft 8 is hollow, that is to say that each of the two parts 13 and 14 respectively comprises a recess 15 and 16 extending parallel to the axis of rotation X1. In other words, the first part 13 and the second part 14 each have a tubular shape. The recesses 15 and 16 may extend over the entire length of the first part 13 and respectively of the second part 14. Alternatively, the recesses 15 and 16 may extend over only a portion of the first part 13 and / or and respectively of the second part 14, for example over at least half of the first part 13 along the axis of rotation X1 and / or respectively over at least half of the second part 14 along the axis of rotation X1. The recesses 15 and 16 extend at least as far as the junction J of the first part 13 to the second part 14. The recess 15 therefore communicates with the recess 16.The combination of recesses 15 and 16 forms the central recess of the rotor shaft 8.

[0037] The first bearing 9A is mounted on the first part 13 of the rotor shaft 8 and the second bearing 9B is mounted on the second part 14 of the rotor shaft 8. The junction J between the two parts 13 and 14 is therefore established between the two bearings 9A and 9B. This junction extends generally in a plane perpendicular to the axis of rotation X1. As we will see, this junction J is particularly rigid and is capable of supporting the radial forces and the torsional forces induced by the reducer 12 via the drive pinion 11. As a note, according to the illustrated embodiment, it is the first part 13 of the rotor shaft which supports the drive pinion 12. Alternatively, the configuration presented could be reversed, that is to say that it is the second part 14 of the rotor shaft which could support the drive pinion 12.

[0038] The first part and the second part may be made of the same metal, for example C48 steel. Advantageously, the first part 13 and the second part 14 are obtained by forging. Such a method is particularly economical. In particular, such a method makes it possible to avoid producing the recesses 15, 16 by a machining operation. In particular, the walls of the recesses 15, 16 may be left raw at the end of the forging operation. The manufacture of each of the parts 13, 14 therefore consumes a smaller quantity of material.

[0039] The first part 13 and the second part 14 are secured to each other by welding. The first part and the second part can be secured by local melting of the materials constituting the first part 13 and the second part 14. Alternatively, the first part 13 can be welded to the second part 14 with a filler metal. In all cases, the welding process and the geometry of the two parts 13 and 14 are adapted so that a zone heat-affected by the welding process does not extend to the outer diameter D3 of the first part or to the outer diameter D4 of the second part. Thus, the hardness of the first part and the second part is not increased at their respective outer diameter. Each of these two parts can thus be machined following the welding process without any particular difficulty.

[0040] In relation to Figure 2, the recess 15 may have an outside diameter D1 substantially equal to an outside diameter D2 of the recess 16, at least at the junction J. The recesses 15 and 16 may comprise variable dimensions along the axis of rotation X1. The recess 15 and / or the recess 16 may be non-opening at their respective end opposite the junction J. Preferably, the central recess may form an open cavity at least at one end of the rotor shaft 8, so as to be able to evacuate a gas which is released during welding.

[0041] The first part 13 may have an outside diameter D3 substantially equal to an outside diameter D4 of the second part 14, at least at the junction J. The connection between the two parts 13 and 14 does not require any local increase in the diameter of the rotor shaft 8. The rotor shaft 8 made up of the two parts 13 and 14 can thus be assembled simply within the electric motor 2, like a rotor shaft in a single part. The first part 13 may optionally have portions further away from the junction J along the axis of rotation X1 whose outside diameter is less than or equal to the outside diameter D3. Similarly, the second part 14 may optionally have portions further away from the junction J along the axis of rotation X1 whose outside diameter is less than or equal to the outside diameter D4.

[0042] The first part 13 and the second part 14 are assembled to each other by a flat support, perpendicular to the axis of rotation X1 and by a short centering, before the welding connection of these two parts. Such an assembly makes it possible to obtain good coaxiality between the two parts 13 and 14.

[0043] The interface between the two parts 13 and 14 is now described in more detail with reference to FIG. 3. The first part 13 comprises a first surface 21 extending perpendicular to the axis of rotation X1. The first part 13 also comprises a second surface 22 extending parallel to the axis of rotation. The second surface 22 is in particular a cylindrical surface whose axis of revolution coincides with the axis of rotation X1. Similarly, the second part 14 comprises a third surface 23 extending perpendicular to the axis of rotation X1, and a fourth surface 24 extending parallel to the axis of rotation. The fourth surface 24 is a cylindrical surface whose axis of revolution coincides with the axis of rotation X1.

[0044] The first surface 21 bears against the third surface 23. More precisely, at least three points of the first surface 21 are in contact with three points of the third surface 23. The position of the second part relative to the first part is therefore defined by the surfaces 21 and 23 bearing against each other. The second surface 22 cooperates with the fourth surface 24 to center the second part relative to the first part. The second surface 22 and the fourth surface 24 are therefore two centering surfaces. The second surface 22 may have slight play relative to the fourth surface 24. For example, an H7 / G6 adjustment may be provided between the second surface 22 and the fourth surface 24.

[0045] Note that the second surface 22 is arranged on a centering nose 31 projecting from the first part towards the second part. This centering nose 31 takes place in a counterbore 32 provided in the second part. The length of the nose 31 along the axis of rotation X1 is smaller than the depth of the counterbore 32 so that the end of the nose 31 is not in contact with the bottom of the counterbore 32. In addition, between the third surface 23 and the fourth surface 24, the second part 14 comprises a chamfer 33 intended to avoid any interference with a fillet formed between the first surface 21 and the second surface 22. The first surface 21 does not extend to the outer periphery of the first part 13. Similarly, the third surface 23 does not extend to the outer periphery of the second part 14.On the contrary, the first surface 21 and the third surface 23 extend radially only up to approximately half the thickness of the first part and respectively of the second part.

[0046] The first part 13 and the second part 14 further comprise a fifth surface 25 and a sixth surface 26 respectively. The fifth surface 25 and the sixth surface 26 extend perpendicular to the axis of rotation X1. The fifth surface 25 extends opposite the sixth surface 26 at a distance from the sixth surface. An annular groove 34 is thus formed between the fifth surface 25 and the sixth surface 26. The surfaces 21, 23, 25 and 26 each have the shape of a disc. The surfaces 25 and 26 are positioned radially further outward than the surfaces 21 and 23.

[0047] A weld bead 35 may extend in the annular groove 34, between the fifth surface 25 and the sixth surface 26. The weld bead 35 is thus set back relative to the outer diameters D3 and D4 of the first part 13 and the second part 14. The weld bead 35 is thus located outside an area that can be machined after the first part has been welded to the second part. The weld bead 35 may extend over the entire circumference of the rotor shaft 8. The radial dimensions of the fifth surface 25 and the sixth surface 26 are sufficiently large so that the outer diameters D3 and D4 of the first part and the second part are outside an area thermally affected by the welding process.

[0048] As a note, in the event that the first part is welded to the second part with a filler metal, it is advantageous to provide chamfers 36, 37 at the external edge of the surfaces 21 and 23. These chamfers make it possible to improve the cohesion produced by the weld bead 35.

[0049] To manufacture the rotor shaft 8, the following procedure can be used. First, the first part 13 and the second part 14 of the rotor shaft are manufactured by forging. Then, the surfaces 21, 22, 23, 24, 25, 26 can be optionally machined, in particular ground, so as to obtain reduced geometric tolerances. Then, the first part 13 is assembled to the second part 14 by pressing the surfaces 21 and 23 against each other. Then, the first part is secured to the second part by welding. Advantageously, the first part 13 and the second part 14 can be welded "from the outside", that is to say with a tool arranged outside the first part 13 and the second part 14, and not with a tool passing through one or other of the recesses 15, 16. The first part 13 can for example be welded to the second part 14 by means of a laser welding process.The heat-affected zone of the welding process and / or the weld bead 35 do not extend to the outer diameter of the first part or the second part. Finally, the outer diameter of the rotor shaft can be machined without contact with a heat-affected zone or with the weld bead resulting from the welding of the first part to the second part.

[0050] The rotor shaft 8 thus manufactured can then be assembled to an electric motor 2 and mechanically connected to the reduction gear 12. Contrary to a popular belief that a rotor shaft made of a single piece is more rigid than a rotor shaft made of two pieces welded to each other, the invention proposes a rotor shaft made of two pieces which is both particularly rigid and light. The rotor shaft 8 is thus sufficiently rigid to withstand the radial forces and the torsional forces applied to it. The electric motor 2 can thus operate correctly and nevertheless remain light.

Claims

CLAIMS 1. Rotor shaft (8) for an electric motor (2) of a motor vehicle (1), the rotor shaft being intended to rotate around an axis of rotation (X1), characterized in that it comprises a first hollow part (13) and a second hollow part (14), the second part extending in the extension of the first part along the axis of rotation, the second part being welded to the first part.

2. Rotor shaft (8) according to the preceding claim, characterized in that the first part (13) comprises a first surface (21) and a second surface (22), the first surface extending perpendicular to the axis of rotation (X1), the second surface extending parallel to the axis of rotation, and in that the second part comprises a third surface (23) and a fourth surface (24), the third surface extending perpendicular to the axis of rotation, the fourth surface extending parallel to the axis of rotation, the first surface (21) bearing against the third surface (23), the second surface (22) cooperating with the fourth surface (24) to center the second part relative to the first part.

3. Rotor shaft (8) according to one of the preceding claims, characterized in that the first part (13) is obtained by forging, and / or in that the second part (14) is obtained by forging.

4. Rotor shaft (8) according to one of the preceding claims, characterized in that the first part (13) comprises a fifth surface (25) extending perpendicular to the axis of rotation (X1), and in that the second part (14) comprises a sixth surface (26) extending perpendicular to the axis of rotation, the fifth surface (25) extending opposite the sixth surface (26) at a distance from the sixth surface, a weld bead (35) extending between the fifth surface and the sixth surface.

5. Rotor shaft (8) according to one of the preceding claims, characterized in that the first part (13) comprises an outer diameter (D3) substantially equal to an outer diameter (D4) of the second part (14) at a junction (J) between the first part and the second part, and / or in that the first part comprises a recess (15) opposite a recess (16) of the second part, an outer diameter (D1) of the recess (15) of the first part being substantially equal to an outer diameter (D2) of a recess (16) of the second part at a junction (J) between the first part and the second part.

6. Rotor shaft (8) according to one of the preceding claims, characterized in that it comprises an external diameter (D3, D4) greater than or equal to 50 mm.

7. Electric motor (2) for a motor vehicle (1), characterized in that it comprises a rotor shaft (8) according to one of the preceding claims, a first bearing (9A) and a second bearing (9B) guiding the rotor shaft (8) in rotation, the first bearing (9A) being mounted on the first part (13) of the rotor shaft and the second bearing (9B) being mounted on the second part (14) of the rotor shaft.

8. Electric motor (2) according to the preceding claim, characterized in that the rotor shaft (8) further comprises a drive pinion (11) capable of inducing radial forces (F1) on the rotor shaft 9. Motor vehicle (1), characterized in that it comprises an electric motor (2) according to one of claims 7 or 8.

10. Method for manufacturing a rotor shaft (8) according to one of claims 1 to 6, characterized in that it comprises: - the manufacture of a first hollow part (13) of the rotor shaft by forging, - the manufacture of a second hollow part (14) of the rotor shaft by forging, then - the assembly of the first part to the second part according to a flat support, then - welding the first part to the second part, then, - machining an outside diameter (D3, D4) of the rotor shaft without contact with a zone heat affected by the welding of the first part to the second part.

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