Rotor shaft for an electric motor

Description

1 / 11 ROTOR SHAFT FOR AN ELECTRIC MOTOR Technical Field of the Invention

[001] 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. Previous Technique

[002] Increasingly, motor vehicles are equipped with an electric motor designed to drive the vehicle's drive wheels. Electric motors are generally associated with a speed reducer to drive the vehicle's drive wheels at an adapted rotational speed. The electric motor's rotor shaft is guided in rotation by bearings integrated into the electric motor and mechanically connected to the speed reducer by means of a drive pinion. The drive pinion generally induces axial forces on the rotor shaft.

[003] However, it seems desirable to provide speed reducers arranged in relation to the electric motor so as to induce radial forces on the rotor shaft. These radial forces tend to bend the rotor shaft between the two bearings. This bending can be even more significant when the distance separating the two bearings is large. A bending of the rotor shaft modifies an air gap of the electric motor and therefore disturbs the operation of the electric motor.

[004] In addition, known electric motors require a large amount of material and are generally very heavy. Presentation of the Invention

[005] The objective of the invention is to provide an electric motor that solves the above disadvantages and improves upon known state-of-the-art electric motors. Petition 870250089849, dated 02 / 10 / 2025, page 7 / 24 2 / 11

[006] More precisely, a first objective of the invention is an electric motor that is both relatively lightweight and whose rotor shaft can withstand significant radial forces without bending excessively. Summary of the Invention

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

[008] The first part may comprise a first surface and a second surface, the first surface extending perpendicularly to the axis of rotation, the second surface extending parallel to the axis of rotation, and the second part may comprise a third surface and a fourth surface, the third surface extending perpendicularly to the axis of rotation, the fourth surface extending parallel to the axis of rotation, the first surface resting against the third surface, the second surface cooperating with the fourth surface to center the second part in relation to the first part.

[009] The first part can be obtained by forging. The second part can be obtained by forging.

[010] The first part may comprise a fifth surface extending perpendicularly to the axis of rotation, and the second part may comprise a sixth surface extending perpendicularly 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.

[011] The first part may comprise an outside diameter substantially equal to the outside diameter of the second part at a junction between Petition 870250089849, dated 02 / 10 / 2025, page 8 / 24 3 / 11 the first part and the second part. The first part may comprise a recess opposite a recess of the second part, an outside diameter of the recess of the first part being substantially equal to an outside diameter of a recess of the second part at a junction between the first part and the second part.

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

[013] 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.

[014] The rotor shaft may additionally comprise a drive pinion capable of inducing radial forces on the rotor shaft.

[015] The invention also relates to a motor vehicle comprising an electric motor as defined above.

[016] The invention also relates to a method for manufacturing a rotor shaft as defined above, the manufacturing method comprising: - to manufacture a first hollow section of the rotor shaft by forging, - to manufacture a second hollow part of the rotor shaft by forging, then - Assemble the first part to the second part using a flat support surface, then - Weld the first part to the second part, then - Machining an outer diameter of the rotor shaft without contact with a heat-affected zone from welding the first part to the second part. Presentation of the Figures

[017] These objectives, characteristics and advantages of the present invention will be presented in detail in the following description of a specific embodiment, Petition 870250089849, dated 02 / 10 / 2025, page 9 / 24 4 / 11 presented by way of non-limiting example in connection with the attached figures, among which:

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

[019] Figure 2 is a partial cross-sectional view of a rotor shaft of the electric motor in Figure 1.

[020] Figure 3 is a cross-sectional view of an interface between a first part and a second part of the rotor shaft of Figure 2. Detailed Description

[021] Figure 1 schematically illustrates a motorized vehicle (1) according to an embodiment of the invention. The motorized vehicle (1) may be, in particular, a passenger vehicle, a utility vehicle, a truck or even a bus. In particular, the motorized vehicle (1) is an “electric” vehicle. It comprises an electric motor (2) intended to drive the drive wheels of the motorized vehicle (1).

[022] 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 electric coils (5B) arranged on both sides of the stack of laminations (5A). The stator (4) is fixed to a housing (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 electric coils (7B) arranged on both sides of the stack of laminations (7A). The coils (5B) and (7B) are designed to produce a magnetic field when powered by electric current. The rotor (3) is separated from the stator (4) by a radial air gap (e). The rotor coils (7B) cooperate with the stator coils (5B) to rotate the rotor (3) relative to the stator (4) around an axis of rotation (X1).

[023] The rotor (3) comprises a rotor shaft (8) extending parallel to the axis of rotation (X1). The rotor shaft (8) supports the coils (7B). The rotor shaft (8) is guided in rotation by two bearings (9A) and (9B), in particular two Petition 870250089849, dated 02 / 10 / 2025, p. 10 / 24 5 / 11 rolling bearings. The bearings (9A, 9B) can, in particular, be mounted against the housing (6) of the electric motor (2). The lamination stacks (7A) and coils (7B) extend between the two bearings (9A) and (9B). The rotor shaft (8) may comprise a first end inside the housing (6) and a second end projecting out of the housing (6). The rotor shaft (8) therefore comprises a portion (10) that extends out of the housing (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 therefore mounted in cantilever on the rotor shaft (8), i.e., it is not positioned between the two bearings (9A) and (9B).The two bearings (9A) and (9B) may be relatively far apart from each other due to the presence of the speed reducer (12), which requires the implementation of functions inherent to a reducer, such as a secondary shaft, a differential or a parking brake.

[024] The drive pinion (11) may comprise helical teeth intended to cooperate with the gear means of the speed reducer (12). In general, the drive pinion (11) is intended to receive radially oriented forces (F1), i.e., perpendicular to the axis of rotation (X1). These forces tend to bend the rotor shaft (8). However, as we shall see in more detail later, the rotor shaft (8) has greater rigidity compared to known rotors of the prior art, which allows this deformation to be attenuated or even eliminated.

[025] In fact, the rotor shaft (8) has an increased outer diameter, which 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 with the rotor shafts of electric motors for motor vehicles (1) known from the prior art and with the same electric motor power (2). This increase in diameter gives the rotor shaft (8) greater rigidity and therefore allows it to support Petition 870250089849, dated 02 / 10 / 2025, page 11 / 24 6 / 11 better the radial forces generated by the speed reducer (12), as well as the torsional forces related to the transmission of a rotational torque. The power transmitted by the electric motor (2) can thus be increased by about 25%

[026] 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 into the continuation of the second part (14) 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 (13, 14) design of the rotor shaft (8) allows the creation of a central recess in the rotor shaft (8). The rotor shaft (8) therefore remains relatively light despite its increased outer diameter.

[027] Each of the two parts (13) and (14) of the rotor shaft (8) is hollow, that is, each of the two parts (13, 14) comprises, respectively, a recess (15) and (16) that extend 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 only over a part of the first part (13) and / or, 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 to the junction (J) of the first part (13) with 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).

[028] 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, 14) is therefore located between the two bearings (9A, 9B). This junction (J) generally extends in a perpendicular plane. Petition 870250089849, dated 02 / 10 / 2025, page 12 / 24 7 / 11 to the axis of rotation (X1). As we shall see, this joint (J) is particularly rigid and capable of supporting the radial and torsional forces induced by the speed reducer (12) through the drive pinion (11). Note that, according to the illustrated embodiment, it is the first part (13) of the rotor shaft (8) that supports the drive pinion (11). Alternatively, the configuration presented could be reversed, i.e., it is the second part (14) of the rotor shaft (8) that could support the drive pinion (11).

[029] The first part (13) and the second part (14) can be made of the same metal, for example, C48 steel. Advantageously, the first part (13) and the second part (14) are obtained by forging. This process is particularly economical. In particular, this process makes it possible to avoid producing the recesses (15, 16) by a machining operation. In particular, the walls of the recesses (15, 16) can be left as forged at the end of the forging operation. The manufacture of each of the parts (13, 14) therefore consumes a smaller amount of material.

[030] The first part (13) and the second part (14) are joined together by welding. The joining of the first part (13) and the second part (14) can be achieved by local fusion of the materials that constitute 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, 14) are adapted so that a heat-affected zone of the welding process does not extend to the outer diameter (D3) of the first part (13) or to the outer diameter (D4) of the second part (14). Thus, the hardness of the first part (13) and the second part (14) does not increase at their respective outer diameters. Each of these two parts (13, 14) can therefore be machined after the welding process without any particular difficulty.

[031] With reference to Figure 2, the recess (15) may have an outer diameter (D1) substantially equal to the outer diameter (D2) of the recess (16), at least in Petition 870250089849, dated 02 / 10 / 2025, p. 13 / 24 8 / 11 junction level (J). The recesses (15, 16) may have variable dimensions along the axis of rotation (X1). The recess (15) and / or the recess (16) may be closed at their respective ends opposite the junction (J). Preferably, the central recess may form an open cavity at at least one end of the rotor shaft (8) in order to allow the evacuation of gas released during welding.

[032] The first part (13) may have an outer diameter (D3) substantially equal to the outer diameter (D4) of the second part (14), at least at the junction (J). The fastening between the two parts (13, 14) does not require any local increase in the diameter of the rotor shaft (8). The rotor shaft (8), consisting of the two parts (13, 14), may therefore be easily mounted inside the electric motor (2) as a one-piece rotor shaft. The first part (13) may optionally comprise portions further from the junction (J) along the axis of rotation (X1), whose outer diameter is less than or equal to the outer diameter (D3). Similarly, the second part (14) may optionally comprise portions further from the junction (J) along the axis of rotation (X1), whose outer diameter is less than or equal to the outer diameter (D4).

[033] The first part (13) and the second part (14) are joined together by a flat support surface, perpendicular to the axis of rotation (X1), and by a short centering, before the welding connection of these two parts. This assembly allows for good coaxiality between the two parts (13, 14).

[034] The interface between the two parts (13, 14) is now described in more detail with reference to Figure 3. The first part (13) comprises a first surface (21) extending perpendicularly to the axis of rotation (X1). The first part (13) also comprises a second surface (22) extending parallel to the axis of rotation (X1). 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) that Petition 870250089849, dated 02 / 10 / 2025, p. 14 / 24 9 / 11 extends perpendicularly to the axis of rotation (X1) and a fourth surface (24) extends parallel to the axis of rotation (X1). The fourth surface (24) is a cylindrical surface whose axis of revolution coincides with the axis of rotation (X1).

[035] The first surface (21) rests on 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 (14) in relation to the first part (13) is therefore defined by the support of the surfaces (21, 23) against each other. The second surface (22) cooperates with the fourth surface (24) to center the second part (14) in relation to the first part (13). The second surface (22) and the fourth surface (24) are therefore two centering surfaces. The second surface (22) may have a slight clearance in relation to the fourth surface (24). For example, an H7 / G6 fitting may be provided between the second surface (22) and the fourth surface (24).

[036] As an observation, the second surface (22) is disposed on a centering tip (31) that projects from the first part (13) towards the second part (14). This centering tip (31) is housed in a recess (32) provided in the second part (14). The length of the tip (31) along the axis of rotation (X1) is less than the depth of the recess (32), so that the tip end (31) does not come into contact with the lower part of the recess (32). Furthermore, 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).

[037] 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 other hand, the first surface (21) and the third surface (23) extend radially only approximately to Petition 870250089849, dated 02 / 10 / 2025, p. 15 / 24 10 / 11 half the thickness of the first part (13) and, respectively, of the second part (14).

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

[039] A weld bead (35) can extend into the annular groove (34), between the fifth surface (25) and the sixth surface (26). The weld bead (35) is therefore recessed relative to the external diameters (D3, D4) of the first part (13) and the second part (14). The weld bead (35) is therefore located outside a zone susceptible to machining after welding the first part (13) to the second part (14). The weld bead (35) can extend around 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 external diameters (D3, D4) of the first part (13) and the second part (14) are outside a heat-affected zone of the welding process.

[040] As an observation, in the case where the first part (13) is welded to the second part (14) with a filler metal, it is advantageous to provide bevels (36, 37) on the outer edge of the surfaces (21, 23). These bevels allow to improve the cohesion produced by the weld bead (35).

[041] 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 (8) are manufactured by forging. Then, the surfaces (21, 22, 23, 24, 25, 26) Petition 870250089849, dated 02 / 10 / 2025, page 16 / 24 11 / 11 can optionally be machined, in particular ground, in order to obtain reduced geometric tolerances. Then, the first part (13) is mounted on the second part (14) placing the surfaces (21,23) in support contact with each other. Then, the first part (13) is fixed to the second part (14) by welding. Advantageously, the first part (13) and the second part (14) can be welded “from the outside”, i.e., with a tool disposed externally to the first part (13) and the second part (14), and not with a tool that passes through one or the 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) does not extend to the outer diameter of the first part (13) or the second part (14).Finally, the outer diameter of the rotor shaft (8) can be machined without contact with a heat-affected zone or with the weld bead (35) resulting from welding the first part (13) to the second part (14).

[042] The rotor shaft (8) thus manufactured can then be mounted on an electric motor (2) and mechanically connected to the speed reducer (12). Contrary to the preconceived notion that a rotor shaft made of a single piece is more rigid than a rotor shaft made of two welded pieces, the invention proposes a rotor shaft made of two pieces that is particularly rigid and lightweight. The rotor shaft (8) is therefore sufficiently rigid to withstand the radial and torsional forces applied to it. The electric motor (2) can therefore operate correctly while remaining lightweight. Petition 870250089849, dated 02 / 10 / 2025, page 17 / 24

Claims

1 / 3 CLAIMS 1. Rotor shaft (8) for an electric motor (2) of a motorized vehicle (1), the rotor shaft being intended to rotate around a rotation axis (X1), CHARACTERIZED in that it comprises a first hollow part (13) and a second hollow part (14), the second part extending in continuation of the first part along the rotation axis, 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 perpendicularly 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 perpendicularly to the axis of rotation, the fourth surface extending parallel to the axis of rotation, the first surface (21) resting against the third surface (23), the second surface (22) cooperating with the fourth surface (24) to center the second part in relation 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 perpendicularly to the axis of rotation (X1), and in that the second part (14) comprises a sixth surface (26) extending perpendicularly 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. Petition 870250089849, dated 02 / 10 / 2025, page 18 / 24 2 / 3 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 to 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 outer diameter (D3, D4) greater than or equal to 50 mm.

7. Electric motor (2) for a motorized 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) additionally comprises a drive pinion (11) capable of inducing radial forces (F1) on the rotor shaft.

9. Motorized 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: - manufacturing a first hollow part (13) of the rotor shaft by forging, - manufacturing a second hollow part (14) of the rotor shaft by forging, then - assembling the first part to the second part with a flat bearing surface, then - welding the first part to the second part, then - machining an outer diameter (D3, D4) of the rotor shaft without contact with a heat-affected zone from the welding of the first part to the second part.

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