Rotor shaft for a rotor of an electric machine

Abstract

The invention relates to a rotor shaft (1) for a rotor (2) of an electric machine (3), in particular for use in an electrically operable drive train (4) of a motor vehicle (5), the rotor shaft comprising a circumferential toothing (6) which is formed monolithically with the rotor shaft (1) and which can be brought into meshing engagement with a corresponding toothing (7) in order to transmit a torque, and a first bearing seat (8) formed on the rotor shaft (1) and a second bearing seat (9) formed on the rotor shaft (1), wherein the toothing (6) of the rotor shaft (1) is arranged axially between the first bearing seat (8) and the second bearing seat (9), wherein a first rolling bearing (10) having an inner ring (11), connected to the rotor shaft (1) for conjoint rotation therewith, is arranged on the first bearing seat (8), and wherein a raceway (12) for rolling elements (14) guided in a cage (13), on which raceway the rolling elements (14) roll, is formed on the second bearing seat (9).

Description

[0001] Rotor shaft for a rotor of an electric machine

[0002] The present invention relates to a rotor shaft for a rotor of an electric machine, in particular for use in an electrically operated drive train of a motor vehicle, comprising a monolithic circumferential toothing formed with the rotor shaft, which can be brought into gear engagement with a corresponding toothing for the transmission of a torque, and a first bearing seat formed on the rotor shaft and a second bearing seat formed on the rotor shaft.

[0003] A rotor shaft is, as is well known, part of the rotor of an electric machine, as described, for example, in DE 10 2021 208 941 A1. The rotor shaft of a rotor, which is usually housed in a stator, is rotatably supported in corresponding bearing mounts of a housing, for which two or more bearing points are provided. Suitable rolling bearings, often needle or ball bearings, are used for this purpose. The rotor rotates when the electric machine is in operation, thus generating a torque that is transmitted to downstream mechanical components.

[0004] For this purpose, the rotor shaft is equipped with a separate pinion featuring external teeth that mesh with a secondary gear. The separate pinion is connected to the rotor shaft via a splined connection. The rolling bearings supporting the rotor shaft in the housing are conventional bearings comprising an inner ring, an outer ring, and rolling elements guided in a cage between them. The inner ring is pressed onto the rotor shaft, while the outer ring is mounted in a suitable receptacle on the housing. This two-part design necessitates complex machining of the interfaces on both the rotor shaft and the required additional pinion / gear, as well as increased assembly effort for the components. Furthermore, a correspondingly large tolerance range exists with regard to the gearing, since both the splined connection and the toothing of the pinion to the secondary gear exhibit a certain tolerance.Increased manufacturing and assembly effort is also required with regard to the bearing of the rotor shaft, on the one hand for the formation of the shaft-side bearing seats for the inner ring, and on the other hand with regard to the rings of the rolling bearing itself, so that a corresponding total tolerance also results with regard to the bearing.

[0005] The invention is based on the problem of specifying an improved rotor shaft.

[0006] This problem is solved by a rotor shaft for a rotor of an electric machine, in particular for use in an electrically operated drive train of a motor vehicle, comprising a monolithic circumferential toothing formed with the rotor shaft, which can be brought into gear engagement with a corresponding toothing to transmit a torque, and a first bearing seat formed on the rotor shaft and a second bearing seat formed on the rotor shaft, a first rolling bearing with an inner ring mounted on the rotor shaft is arranged on the first bearing seat and a raceway for rolling elements guided in a cage is formed on the second bearing seat, on which the rolling elements roll.

[0007] This rotor shaft offers the technical advantage of high structural integrity, as the gearing for torque transmission is formed directly and monolithically with the shaft. This avoids potential weak points that could arise from assembly or joining processes. The rotor shaft according to the invention is also simplified in its design, since only a single shaft component is used, on which the relevant interfaces—namely, the gearing required for the output and the corresponding bearing arrangements—are directly integrated. This eliminates the need for an additional, separate pinion, as the gear section with the external teeth is an integral part of the rotor shaft.Likewise, at least a significantly simplified rolling bearing can be used, which does without a separate inner ring, since the rolling elements roll directly on the corresponding raceway, which in turn is integrally machined onto the rotor shaft.

[0008] From an economic perspective, the rotor shaft according to the invention can also simplify production and improve the design reliability of the electric machine, especially in demanding applications such as in a motor vehicle drive train.

[0009] In summary, an assembly-optimized rotor shaft can be provided with a bearing concept consisting of a preferably recessed raceway located directly on the shaft and a conventional first rolling bearing. The raceway located directly on the rotor shaft is situated at the second bearing seat and is designed so that the rotor shaft, including the other rotor components, can be assembled or inserted from an axial direction. This is achieved, firstly, by the advantageously recessed or lowered direct raceway and, secondly, by the design of the bearing with a needle roller cage, the cage of which is advantageously spread open during assembly. The axial position of the needle roller cage is advantageously ensured by a U-profile.

[0010] To ensure assembly of the rotor shaft including all rotor components from one direction, the size of the optional support bearing (first rolling bearing), which is designed as a conventional rolling bearing, is advantageously matched to the gear teeth.

[0011] In summary, this concept allows the gearing to be mounted directly on the shaft and eliminates the need for the inner bearing ring at the second bearing seat, thus eliminating assembly steps and achieving higher accuracy with regard to the gearing.

[0012] rotor

[0013] A rotor is the rotating part of an electric machine. The rotor comprises, in particular, a rotor shaft and one or more rotor bodies, formed from stacks of rotor laminations and fixed to the rotor shaft. The rotor shaft can be hollow, which reduces weight and allows lubricant or coolant to be supplied to the rotor body.

[0014] For the purposes of this patent application, a rotor shaft is a component of a rotor in an electric machine, serving to transmit mechanical rotational energy and absorb mechanical loads. The rotor shaft is thus a component that can be rigidly connected to other functional elements of the rotor, such as magnets or windings, and / or be an integral part of these elements. It also serves as a mounting point for the rotor bearings, thereby contributing to the precise positioning of the rotor within the stator and ensuring a uniform air gap. The rotor shaft preferably comprises a cylindrical base with various components adapted to it, such as bearing seats, raceways for rolling elements, and / or a toothed section for torque transmission.According to the invention, the gear teeth are monolithically integrated with the shaft, resulting in increased load-bearing capacity and service life, as well as reduced assembly effort. Furthermore, bearing seats can be formed on the shaft, which allow for the installation of rolling bearings and thus support the bearing and guidance of the rotor.

[0015] The rotor shaft is preferably made of steel or high-strength aluminum to meet the required mechanical properties such as strength, hardness, and durability. For special applications where weight savings are critical, such as in aerospace or high-speed applications, composite materials or specially treated metals can also be used, offering high strength at a reduced weight.

[0016] In this context, it can also be advantageous for the rotor shaft to be designed as a hollow shaft. Besides the resulting weight reduction, this also allows a cooling fluid to be supplied to the rotor shaft, which can contribute to optimized cooling of the rotor, particularly in high-performance automotive applications.

[0017] For the purposes of this patent application, a gear is an extensive sequence of teeth arranged on the rotor shaft and serving to transmit torque and mechanical power by engaging with a corresponding gear on another component, such as a transmission shaft. A key function of the gear is to enable efficient, slip-free transmission of torque between the rotor shaft and other machine elements. In particular, the gear also enables reversible transmission, meaning that the electric machine can operate effectively in both forward and reverse directions.

[0018] The teeth can have different profiles, such as involute, cycloidal, or other specialized shapes, tailored to the specific requirements of the application. In terms of materials, gears can advantageously be made of hardened steel or special alloys that exhibit high wear resistance to ensure the durability and reliability of the transmission components.

[0019] To allow for easy assembly, the toothing can preferably also be designed as a plug-in toothing.

[0020] For the purposes of this patent application, a bearing seat is an element or area of ​​a rotor shaft that serves to receive and position a bearing. The bearing seat is preferably an integral part of the rotor shaft and is designed for the precise and stable support of the shaft or rotor within the electric machine. The function of the bearing seat essentially consists of positioning a bearing securely and accurately, thereby ensuring the correct alignment of the rotor shaft.

[0021] The bearing seat design incorporates a defined geometric shape tailored to the specific type of bearing. This can include a cylindrical, conical, or otherwise shaped surface, depending on the bearing used. The bearing seat is advantageously designed with high dimensional accuracy to ensure an optimal fit for the bearing.

[0022] It is generally conceivable that a plain or a rolling bearing sits on the bearing seat. Bearing seats designed for rolling bearings, such as ball or roller bearings, are preferred. It is also possible for the rolling elements of a rolling bearing to roll directly on the bearing seat. In this case, the bearing seat also forms the raceway for the rolling elements of the rolling bearing. Bearing seats can also include additional features such as grooves or contact surfaces for retaining rings, which enable precise axial positioning of the bearing. In highly loaded applications, bearing seats can also be provided with additional reinforcements or special coatings to reduce wear and increase durability.

[0023] career

[0024] For the purposes of this patent application, a raceway is a surface on a bearing seat on which rolling elements, such as balls or rollers, roll. This raceway is an integral part of the rotor shaft and serves to guide the rolling elements and enable efficient load transmission.

[0025] The raceway advantageously includes a hardened or coated surface to increase the durability and performance of the raceway and / or bearing. The geometric design of the raceway can be tailored to the shape of the rolling elements. For example, the raceway can be cylindrical for cylindrical rollers or spherical for balls to ensure optimal contact area and load distribution. The raceway can therefore be flat or profiled. A profiled raceway can, for example, guide the rolling elements along the raceway. A flat raceway, on the other hand, can allow for a certain degree of axial movement of the rolling elements along the raceway.

[0026] In this context, the raceway can also be treated with special polishing processes or superfinishing techniques to achieve an extremely smooth surface. Furthermore, it is conceivable to provide the raceway with additional coatings such as ceramics or special metal alloys to increase its hardness and corrosion resistance. The raceway can also be heat-treated and / or cryogenically treated to optimize its performance and durability under extreme operating conditions.

[0027] rolling bearings

[0028] A rolling bearing can be single-row or multi-row.

[0029] A rolling bearing preferably has an inner ring. The inner ring can be made of a metallic and / or ceramic material. It is generally possible to form the inner ring in one piece or in multiple pieces, particularly in two pieces. A rolling bearing further preferably has an outer ring. The outer ring can be made of a metallic and / or ceramic material. It is generally possible to form the outer ring in one piece or in multiple pieces, particularly in two pieces.

[0030] The rolling elements of a rolling bearing are in the shape of a ball or a roller. They roll on the raceways of the rolling bearing and their function is to transmit the force acting on it, for example, in a radial rolling bearing, from the outer ring to the inner ring and vice versa. Roller-shaped rolling elements can be selected, for example, from the group of symmetrical self-aligning rollers, asymmetrical self-aligning rollers, cylindrical rollers, needle rollers, and / or tapered rollers.

[0031] The rolling elements are guided within the cage and spaced apart from each other. The cage can be made of one piece or multiple pieces.

[0032] Within the rolling bearing, the rolling elements can roll, particularly on the inner ring raceway of the inner ring. For this purpose, the surface of the inner ring raceway can advantageously be designed to be wear-resistant, for example, through a suitable surface treatment process and / or by applying an additional layer of material. The inner ring raceway can be flat or profiled. A profiled inner ring raceway can, for example, guide the rolling elements on the inner ring raceway. A flat inner ring raceway, on the other hand, can allow, for example, a certain degree of axial displacement of the rolling elements on the inner ring raceway.

[0033] The rolling elements can roll within the rolling bearing, particularly on the outer ring raceway. For this purpose, the surface of the outer ring raceway can advantageously be designed to be correspondingly wear-resistant, for example, by means of a suitable surface treatment process and / or by applying a suitable additional material layer.

[0034] The outer ring raceway can be flat or profiled. A profiled outer ring raceway can, for example, guide the rolling elements on the outer ring raceway. A flat outer ring raceway, on the other hand, can, for example, allow a certain degree of axial displacement of the rolling elements on the outer ring raceway.

[0035] A rolling bearing may have a seal to prevent lubricant from escaping the bearing or dirt or moisture from entering it. For this purpose, the seals used may be provided with one or more sealing lips that bear against a component of the rolling bearing. These are designed to seal the bearing for as long as possible, ideally over its entire service life, while also ensuring that the friction caused by the seal is not excessive. It is particularly preferred that the seal is made of an elastic, and preferably rubber-elastic, material. The elastic material may preferably consist entirely or partially of an elastomer, with the elastomers preferably being selected from the group of vulcanizates of natural rubber and silicone rubber.According to a further preferred embodiment of the invention, it can be provided that a rolling bearing is configured for rotational speeds greater than 10,000 rpm.

[0036] Advantageous embodiments of the invention

[0037] According to an advantageous embodiment of the invention, a first circumferential groove and / or a second circumferential groove can be provided adjacent to the raceway, into which the cage engages and is thereby fixed in its axial position relative to the raceway, either with or without play. The use of circumferential grooves adjacent to the raceway, into which the cage for the rolling elements engages, offers technical advantages with regard to the precision and flexibility of the bearing arrangement. These grooves enable a precisely defined axial positioning of the cage, thereby minimizing the risk of axial play. This results in improved smooth running and higher load-bearing capacity of the shaft. The option of choosing between bearing arrangements with and without play also allows for a customized adaptation to the specific requirements of the application.

[0038] In a further development of the invention, the cage can have a U-shaped cross-section with two lateral cage legs that axially engage the raceway machined on the rotor shaft. This axial engagement allows for simple axial fixing of the mounting position of the rolling element assembly. The raceway is machined with a slight radial elevation on the shaft component, meaning that corresponding circumferential grooves or recesses are formed on both sides of the raceway into which the cage legs engage. One or more radial projections can be formed on one or both cage legs, serving for radial cage guidance on the rotor shaft. As an alternative to a U-shaped cage, it is also conceivable that flanges are formed on the rotor shaft adjacent to the raceway, on which the cage is axially guided. Axial fixing of the mounting position of the rolling element assembly is also possible in this way.According to a further preferred embodiment of the invention, the first rolling bearing can also be designed as a ball bearing. Using a ball bearing at the first bearing seat offers the advantage of particularly low friction and high load-bearing capacity. Ball bearings are known for their ability to efficiently carry both radial and axial loads, which increases the flexibility and range of applications of the rotor shaft in various configurations of electrical machines. Economic advantages result from the standardization of ball bearings, leading to cost savings in procurement and maintenance.

[0039] Furthermore, according to another advantageous embodiment of the invention, the rolling elements that run on the raceway of the second bearing seat can be designed as needles or rollers. The use of rollers as rolling elements on the raceway of the second bearing seat offers advantages, particularly with regard to load-bearing capacity. Compared to bearing balls, rollers can withstand higher radial loads, which improves the reliability and durability of the rotor shaft in demanding applications such as in an automotive powertrain. In addition, roller bearings often have a longer service life, leading to a reduction in maintenance requirements and associated costs.

[0040] According to a further particularly preferred embodiment of the invention, the gear teeth may have a pitch circle diameter that is larger than or equal to all other diameters of the rotor shaft. Designing the gear teeth with a pitch circle diameter that is larger than or equal to the other diameters of the rotor shaft offers the advantage of improved power transmission capability. A larger diameter of the gear teeth allows for the transmission of greater forces and distributes the loads more effectively across the gear teeth, resulting in reduced wear and an increased service life. This is particularly important for drive systems in vehicles where high power and torque are required. Furthermore, the invention may also be further developed such that the raceway has a diameter that is smaller than that of the axially adjacent sections of the rotor shaft.This allows for a rotor shaft configuration where the raceway is "encased" in the rotor shaft. This can contribute to a radially compact design of the rotor shaft and also simplify the axial insertion of the rotor shaft or rotor into a stator.

[0041] This stepped design thus enables, in particular, the axial insertion of the rotor, which incorporates this rotor shaft, into the stator. This is combined with the previously described simplified design of the rotor shaft and the elimination of the separate pinion and the inner bearing ring at the second bearing seat. The design of the recessed raceway, formed directly on the shaft component, and the corresponding diameter dimensioning therefore allow the rotor components to be assembled from a single direction, as well as the rotor itself.

[0042] In a further preferred embodiment of the invention, the first bearing seat can also be located at a first distal end of the rotor shaft. Positioning the first bearing seat at the first distal end of the rotor shaft enables optimal force transmission. This arrangement also contributes to improved mechanical stability and a reduction in bending stresses, which technically results in less wear at the bearing points.

[0043] It can also be advantageous to further develop the invention such that the rotor shaft includes a third bearing seat, preferably located at a second distal end of the rotor shaft. Adding a third bearing seat at the second distal end of the rotor shaft increases the stability of the overall shaft bearing arrangement. This leads to improved precision in rotor positioning within the electric motor. The more precise alignment of the rotor also contributes to reducing imbalances and vibrations, which in turn minimizes noise and wear. The additional support at both ends of the rotor shaft thus significantly reduces the risk of bearing damage and resulting failures.

[0044] According to a further preferred embodiment of the invention, a second rolling bearing with an inner ring mounted on the rotor shaft can be arranged at the third bearing seat. The rigid connection of the inner ring of the rolling bearing to the rotor shaft ensures a direct and efficient transmission of torque. Furthermore, the direct connection of the inner ring to the rotor shaft increases the overall mechanical stability of the shaft, which can be particularly important in applications requiring high speeds or high torques.

[0045] The invention can also advantageously be implemented such that the cage of the rolling elements running on the rotor shaft is designed to be expandable. As described, ultimately only rolling element rings are used, comprising a plurality of individual rolling elements, in particular needles, which are held in a cage. Each cage or rolling element ring is slightly expandable so that it can be easily placed onto the raceway during assembly. In the assembly position, the cage constricts again accordingly, so that the best possible enclosure of the rolling element raceway is ensured. The cage can have a locking mechanism, i.e., a corresponding locking geometry is present that allows the cage to be opened locally and thus expanded, and then closed again in the assembly position.

[0046] Furthermore, it can also be advantageous for the raceway to be designed so that it lies radially within the root diameter and the lamination seat of the rotor shaft. Positioning the raceway within the root diameter and the lamination seat minimizes the overall dimensions of the rotor shaft. This results in a more compact motor design, which is particularly beneficial in space-constrained applications such as electric vehicles and other mobile applications. This configuration also allows for better shaft centering and balance, which can contribute to a reduction in vibration and noise during operation. This design also permits axial run-out of the tool used to produce the gear teeth, such as a broaching tool, as it can easily traverse the raceway during its axial movement without coming into contact with it.

[0047] Furthermore, it may be preferable for the diameter of the rolling elements running on the raceway to be such that the outer diameter of the rolling elements is larger than the tip diameter of the gear teeth. The larger outer diameter of the rolling elements relative to the tip diameter of the gear teeth, and the associated more robust design, makes the entire bearing structure more resistant to overload and mechanical shock. The larger outer diameter of the rolling elements also generally means that each individual element wears less quickly, as the load is distributed more effectively.

[0048] In a further development of the invention, it can also be provided that the diameter of the raceway is smaller than the diameter of the root circle of the gear teeth. This design allows axial run-out of the tool used to produce the gear teeth, for example a broaching tool, since it can easily run over the raceway during its axial movement without coming into contact with it.

[0049] Furthermore, the raceway diameter may be smaller than the diameter of a receiving section machined directly onto the rotor shaft for a rotor lamination stack. An elongated, cylindrical receiving section for a rotor lamination stack, which is shrunk onto this receiving section, can be axially connected to the raceway. Since the outer diameter of this receiving section is slightly larger than the outer diameter of the second rolling element raceway, the tool used to integrally form the cylindrical receiving section on the shaft component can, in turn, extend axially.

[0050] In a further preferred embodiment of the invention, the first rolling bearing can have an outer ring whose diameter is smaller than the root diameter of the gear teeth. A smaller outer ring can lead to a reduction in material consumption and thus costs. Furthermore, the lower weight of the bearing can contribute to a reduction in the overall weight of the machine, which is particularly advantageous in mobile and transportable applications. This configuration also allows the gear teeth of the rotor shaft to be machined with the first rolling bearing already mounted, since a suitable tool can be guided axially over the first rolling bearing without colliding with it.

[0051] According to a further preferred embodiment of the invention, the rotor shaft has a first contact shoulder, wherein both the outer diameter of the contact shoulder and the outer diameter of the first rolling bearing lie radially within the root circle diameter. This allows axial positioning of the rolling bearing to be achieved, with the contact shoulder being designed such that a suitable tool can axially pass over both the contact shoulder and the rolling bearing for the purpose of producing the gear teeth.

[0052] Furthermore, it is also preferred that the rotor shaft's splines be arranged axially between the first and second bearing seats. The axial positioning of the splines between the first and second bearing seats promotes a uniform force distribution and stabilizes the shaft during operation under load. This central position can also help reduce bending stresses on the shaft that could arise from off-center forces if the splines were located closer to one of the shaft's ends. This results in a more even load distribution and increased overall system stability. The symmetrical arrangement of the splines between the bearing seats can also help minimize vibrations and noise that can be caused by imbalances or asymmetrical loads.

[0053] The rolling elements that run on the raceway of the second bearing seat are preferably needles or rollers, i.e., needle or roller assemblies are used as rolling element rings. The needles or rollers can be of the same or different lengths and / or diameters, depending on the available installation space. In addition to the rotor shaft itself, the invention further relates to a rotor for an electric machine, comprising a rotor shaft of the type described above and a rotor lamination stack arranged thereon.

[0054] Finally, the invention relates to an electric machine comprising a stator and a rotor of the type described above, which is inserted into the stator.

[0055] The invention will now be explained in more detail with reference to figures, without limiting the general concept of the invention.

[0056] It shows:

[0057] Figure 1 shows a schematic representation of a motor vehicle with an electric drivetrain.

[0058] Figure 2 shows an electric machine in an axial section view.

[0059] Figure 3 shows a first embodiment of a rotor shaft in an axial sectional view,

[0060] Figure 4 shows a first embodiment of a rotor shaft in a perspective view,

[0061] Figure 5 shows a second embodiment of a rotor shaft in an axial sectional view,

[0062] Figure 6 shows a third embodiment of a rotor shaft in an axial sectional view,

[0063] Figure 7 shows a third embodiment of a rotor shaft in a perspective view, Figure 8 shows a fourth embodiment of a rotor shaft in an axial sectional view,

[0064] Figure 9 shows a fifth embodiment of a rotor shaft in an axial sectional view.

[0065] Figure 3 shows a rotor shaft 1 for a rotor 2 of an electric machine 3, as illustrated by way of example in Figure 2. This electric machine 3 is intended in particular for use in an electrically operated drive train 4 of a motor vehicle 5, as sketched in Figure 1.

[0066] As can be clearly seen from Figure 3, the rotor shaft 1 comprises a monolithic, circumferential toothing 6, which can be engaged with a corresponding toothing to transmit torque. Furthermore, the rotor shaft 1 has a first bearing seat 8 and a second bearing seat 9 formed on the rotor shaft 1. The toothing 6 of the rotor shaft 1 is arranged axially between the first bearing seat 8 and the second bearing seat 9.

[0067] At the first bearing seat 8 a first rolling bearing 10 with an inner ring 11 which is non-rotatably connected to the rotor shaft 1 is formed and at the second bearing seat 9 a raceway 12 for rolling elements 14 which are guided in a cage 13 and on which the rolling elements 14 roll.

[0068] Figure 3 also shows that a first circumferential groove 15 and a second circumferential groove 16 adjoin the raceway 12, into which the cage 13 engages and is thereby fixed in its axial position relative to the raceway 12 with or without play.

[0069] The first rolling bearing 10 is designed as a ball bearing, while the rolling elements 14 rolling on the raceway 12 of the second bearing seat 9 are designed as rollers. The first bearing seat 8 is formed at a first distal end 21 of the rotor shaft 1. Figure 3 shows an embodiment of the rotor shaft 1 in which the toothing 6 has a pitch circle diameter 17 that is larger than or equal to all other diameters of the rotor shaft 1, which facilitates or enables axial insertion of the rotor shaft into a corresponding connecting structure such as a stator. The raceway 12 also has a diameter 18 that is smaller than that of the axially adjacent sections 19, 20 of the rotor shaft 1. This causes the raceway 12 to be "cut" into the rotor shaft 1.

[0070] In the embodiment of the invention shown in Figure 3, the raceway 12 is designed such that it lies radially within the base circle diameter 26 and the lamination stack seat 27 of the rotor shaft 1. The cage 13 is designed to be expandable and can thus be slid axially onto the rotor shaft 1.

[0071] In the first embodiment, the diameter 28 of the rolling elements 14 rolling on the raceway 12 is designed such that the circumscribed diameter 29 of the rolling elements 14 is larger than the tip diameter 17 of the toothing 6.

[0072] Furthermore, the first rolling bearing 10 has an outer ring 30 whose diameter 31 is smaller than the root circle diameter 26 of the gearing 6. The rotor shaft 1 also has a first contact shoulder 32, wherein both the outer diameter 33 of the contact shoulder 32 and the outer diameter 34 of the first rolling bearing 10 lie radially within the root circle diameter 26.

[0073] All these geometric configurations result in the rotor shaft 1 being able to be inserted axially into a stator of an electric machine in a simple and easy-to-assemble manner, which will be explained in more detail below.

[0074] Due to the lower-lying raceway 12 and the use of a needle roller cage with an expandable cage 13, the gear teeth 6 can be mounted directly on the rotor shaft 1, as described above. The raceway 12 is designed to lie below the root circle diameter 26 and the lamination stack seat 27, thus ensuring clearance for the machining tools used on the gear teeth 6. Simultaneously, the diameter 28 of the rolling elements 14 at the second bearing seat 9 is designed such that the circumscribed circle diameter 29 of the rolling elements 14 is larger than the tip circle diameter 17 of the gear teeth 6.

[0075] The axial position of the needle roller assembly, formed by the cage 13 and the rolling elements 14 inserted therein, is ensured by the needle roller assembly engaging laterally as a U-profile over the second bearing seat 9. Alternatively, the cage 13 can also be guided by lateral flanges of the rotor shaft 1 in a conventional design, although this is not shown in Figure 3. For assembly, the cage 13 is spread open sufficiently to be placed onto the raceway 12. The cage 13 can be designed with or without a locking mechanism. Separate outer rings can be pressed into the housing for the needle roller bearing that encompasses the needle roller assembly.

[0076] At the first bearing seat 8, the first rolling bearing 10 is designed with regard to assembly in such a way that the fully assembled rotor 2 including rotor shaft 1 can be inserted into the stator 35 from one direction.

[0077] Depending on the bearing dimensions and installation space requirements, three possible mounting configurations are conceivable: in the first case, the first rolling bearing 10, designed as a support bearing, is already mounted on the rotor shaft 1; in the second case, the first rolling bearing is located separately in a bearing cap, as shown in Figures 3-8; and in the third case, the optional support bearing to the left of the toothing 6 is not present, and the rotor shaft 1 is only supported on one side relative to the toothing 6, as shown in Figure 9.

[0078] In case 1, shown for example in Figure 3, the bearing arrangement is designed such that the outer ring 30 of the rolling bearing 10 is smaller than the root circle diameter 26 of the gear teeth 6. This allows the fully assembled rotor 2, including rotor shaft 1 and bearings, to be inserted into the stator 35 from one side. Simultaneously, the lower contact shoulder 32 and the lower press fit for the rolling bearing 10 provide sufficient clearance for the gear cutting tools.

[0079] In the second case, shown exemplified in Figures 6 and 7, the rolling bearing 10 is pressed into a bearing cap before rotor assembly. To ensure that the rotor can be mounted into the stator 35 from one direction, both the contact shoulder 32 and the bearing seat 8 for the rolling bearing 10 are located below the root diameter 26. When the rotor assembly is inserted, the rotor shaft 1 is pressed onto the inner ring 11 of the rolling bearing. In this case as well, clearance is provided for the machining tools of the gear teeth 6.

[0080] In the third case, shown in Figure 9, the rolling bearing to the left of the toothing 6 is not present; that is, the bearing arrangement is one-sided and consists of two bearing points located to the right of the toothing. Nevertheless, the rotor assembly can be axially inserted into the stator 35 from one side due to the design of the second bearing seat 9 with its recessed raceway 12. For this purpose, all diameters or geometries on the rotor shaft 1 adjacent to the toothing 6 are smaller than the root diameter 26.

[0081] In summary, this design eliminates the need for a separate pinion and the interfaces required for it, and significantly simplifies the overall assembly of the rotor assembly.

[0082] Figure 4 shows the first embodiment of a rotor shaft 1 known from Figure 3 in a perspective view.

[0083] In the second embodiment of a rotor shaft 1, shown in Figure 5, the rotor shaft 1 includes a third bearing seat 22, which is formed at a second distal end 23 of the rotor shaft 1. A second rolling bearing 24 with an inner ring 25 that is non-rotatably connected to the rotor shaft 1 is arranged at the third bearing seat 22. Figure 8 shows the rotor shaft 1 known from Figures 6-7 with a total of three bearing points.

[0084] The invention is not limited to the embodiments illustrated in the figures. The foregoing description is therefore not to be considered limiting, but rather explanatory. The following claims are to be understood as meaning that a named feature is present in at least one embodiment of the invention. This does not preclude the presence of further features. Where the claims and the foregoing description define 'first' and 'second' features, this designation serves to distinguish between two similar features without establishing any hierarchy.

[0085] List of reference signs

[0086] 1 rotor shaft

[0087] 2 Rotor

[0088] 3 electric machine

[0089] 4 Powertrain

[0090] 5 Motor vehicle

[0091] 6 gear teeth

[0092] 8 bearing seat

[0093] 9 bearing seat

[0094] 10 rolling bearings

[0095] 11 Inner ring

[0096] 12 Career

[0097] 13 Cage

[0098] 14 rolling elements

[0099] 15 Nut

[0100] 16 Nut

[0101] 17 Head circle diameter

[0102] 18 diameter

[0103] Section 19

[0104] Section 20

[0105] 21 End

[0106] 22 bearing seat

[0107] 23 End

[0108] 24 rolling bearings

[0109] 25 inner ring

[0110] 26 foot circle diameter

[0111] 27 sheet metal package seat

[0112] 28 diameter

[0113] 29 Circumscribed circle diameter

[0114] 30 outer ring

[0115] 31 Diameter of mounting shoulder Outer diameter Outer diameter of stator

Claims

Claims 1. Rotor shaft (1 ) for a rotor (2) of an electric machine (3), in particular for use in an electrically operated drive train (4) of a motor vehicle (5), comprising a monolithic circumferential toothing (6) formed with the rotor shaft (1 ), which can be brought into gear engagement with a corresponding toothing for the transmission of a torque, and a first bearing seat (8) formed on the rotor shaft (1 ) and a second bearing seat (9) formed on the rotor shaft (1 ), characterized in that a first rolling bearing (10) with an inner ring (11) attached to the rotor shaft (1 ) is arranged on the first bearing seat (8) and a raceway (12) for rolling elements (14) guided in a cage (13) is formed on the second bearing seat (9), on which the rolling elements (14) roll.

2. Rotor shaft according to claim 1, characterized in that a first circumferential groove (15) and / or a second circumferential groove (16) adjoins the raceway (12) into which the cage (13) engages and is thereby fixed in its axial position relative to the raceway (12) with or without play.

3. Rotor shaft (1 ) according to one of the preceding claims, characterized in that the toothing (6) has a pitch circle diameter (17) which is larger than or greater than equal to all other diameters of the rotor shaft (1 ).

4. Rotor shaft (1 ) according to one of the preceding claims, characterized in that the raceway (12) has a diameter (18) which is smaller than the axially adjacent sections (19, 20) of the rotor shaft (1 ).

5. Rotor shaft (1 ) according to one of the preceding claims, characterized in that the first bearing seat (8) is formed at a first distal end (21 ) of the rotor shaft (1 ).

6. Rotor shaft (1 ) according to one of the preceding claims, characterized in that the cage (13) of the rolling elements (14) rolling on the rotor shaft (1 ) is designed to be expandable.

7. Rotor shaft (1 ) according to one of the preceding claims, characterized in that the raceway (12) is designed such that it lies radially within the root circle diameter (26) and the lamination stack seat (27) of the rotor shaft (1 ).

8. Rotor shaft (1 ) according to one of the preceding claims, characterized in that the diameter (28) of the rolling elements (14) rolling on the raceway (12) is designed such that the circumscribed diameter (29) of the rolling elements (14) is larger than the pitch circle diameter (17) of the toothing (6).

9. Rotor shaft (1 ) according to one of the preceding claims, characterized in that the first rolling bearing (10) has an outer ring (30) whose diameter (31 ) is smaller than the root circle diameter (26) of the toothing (6).

10. Rotor shaft (1) according to one of the preceding claims, characterized in that the rotor shaft (1 ) has a first contact shoulder (32), wherein both the outer diameter (33) of the contact shoulder (32) and the The outer diameter (34) of the first rolling bearing (10) lies radially within the base circle diameter (26).

11. Rotor shaft (1) according to one of the preceding claims, characterized in that the toothing (6) of the rotor shaft (1) is arranged axially between the first bearing seat (8) and the second bearing seat (9).

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