Motor unit consisting of stator and housing for improving the roundness of the inner surface of the stator

Abstract

The present invention relates to an electric motor unit comprising a stator with an outer lateral surface and a through-opening with a cylindrical inner lateral surface, and a housing with a receiving area, wherein the stator is arranged in a force-fit manner in the receiving area of ​​the housing, in particular by means of a transverse press fit, and wherein in the unconnected state the shape of the receiving area of ​​the housing differs from the shape of the outer lateral surface of the stator and / or wherein in the unconnected state the inner lateral surface of the stator is non-cylindrical.

Description

State of the art

[0001] The present invention relates to a motor unit for an electric motor consisting of a stator and a housing, and to a method for manufacturing the motor unit.

[0002] The motor performance (power, power-to-weight ratio, etc.) of electric motors depends heavily on how small the nominal air gap between the rotor and stator can be. A significant obstacle to achieving smaller air gaps is manufacturing-related deviations from an electromagnetically ideal outer shape of the rotor or inner shape of the stator. On the stator side, the ideal inner shape is often perfectly cylindrical (excluding slots). A typical geometric deviation arises from the force-fit installation of an almost round stator (with comparatively high rotational symmetry) into a non-rotationally symmetrical housing; put simply, the stator is pressed into the housing in an irregular shape during installation. When the stator is bonded in place, the temperature of the three components—housing, stator, and adhesive—is similar during the actual joining process, typically room temperature. Only after joining is the temperature raised significantly (typically...(to over 150°C) to thermally activate and cure the adhesive. The different coefficients of thermal expansion of the materials also lead to deformations and mechanical stresses, which are frozen in place as the adhesive cures (apart from purely mechanical elasticity). Different heat capacities within the overall assembly (due to material or geometry) result in different curing times or durations for the adhesive, which in turn can lead to asymmetries or out-of-roundness. This out-of-roundness can be accepted in motor design by deliberately increasing the diameter difference between the rotor outer diameter and the stator inner diameter (i.e., the air gap), which can result in significant performance disadvantages.Furthermore, an undesirable variation in the air gap width across the circumference can lead to uncontrollable fluctuations in electromagnetic forces, which can negatively affect the noise, vibration, and harshness (NVH) behavior. Disclosure of the invention

[0003] The electric motor unit according to the invention, particularly for an electric bicycle, comprising the features of claim 1 for an electric motor comprising the features of claim 9, and the method for manufacturing the electric motor unit comprising the features of claim 4, has the advantage that the roundness of the stator can be improved after assembly. This allows the air gap in the electric motor between the rotor and stator to be reduced, thereby improving the motor performance and the NVH (noise, vibration, and harshness) behavior. According to the invention, this is achieved by an electric motor unit comprising a stator with an outer cylindrical surface and a through-bore with a cylindrical inner cylindrical surface, as well as a housing with a receiving area. The cylindrical shape of the inner cylindrical surface refers in particular to the condition after the stator has been mounted in the receiving area of ​​the housing.The stator is arranged in the receiving area of ​​the housing by means of a force-fit and / or material-fit connection, in particular by means of a transverse press fit and / or by bonding. In the unconnected state, the shape of the receiving area of ​​the housing deviates from the shape of the outer surface of the stator and / or the inner surface of the stator is non-cylindrical in the unconnected state. Thus, by means of suitable geometric allowances, undesirable deformation of the inner surface of the stator can be avoided and it can be ensured that the inner surface of the stator corresponds to the target geometry, i.e., is cylindrical, after assembly. This allows a rotor to be inserted into the through-hole of the stator with low tolerances and ensures a small air gap between the stator and the rotor, which does not deviate from the target geometry depending on the angle.This can bring advantages in terms of engine performance and NVH behavior, among other things.

[0004] The dependent claims describe preferred embodiments of the invention.

[0005] Preferably, in its unassembled state, the receiving area of ​​the housing exhibits a deviation from a perfect cylindrical shape, with the outer surface of the stator being cylindrical. This allows the forces acting in the frictional and / or material-fit connection between the stator and the receiving area of ​​the housing to be specifically adjusted to ensure a cylindrical inner surface of the stator after assembly.

[0006] Preferably, the form deviation of the receiving area corresponds essentially to the inverse deformation of the inner surface of the stator when the receiving area of ​​the housing has no form deviation. This compensates for the deformation caused by the joining process and minimizes the difference between the target and actual geometry of the inner surface of the stator. By determining the deformation of the stator without form deviation and adjusting the form deviation of the receiving area accordingly, a suitable form deviation can be easily approximated to ensure a nearly cylindrical inner surface after assembly. The form deviation of the receiving area can be optimized in several iterative steps. The inverse deformation is preferably adapted to the diameter ratio between the inner surface and the receiving area.

[0007] The shape of the housing's receiving area preferably widens or narrows in the longitudinal direction. This ensures that, after assembly, the inner surface is cylindrical in the longitudinal direction and that different thermal expansions of the housing along the longitudinal axis are compensated for.

[0008] Furthermore, the invention relates to a method for manufacturing an electric motor unit. The method comprises the step of manufacturing a housing with a receiving area. The housing can, for example, be manufactured in a metal die-casting process, and the receiving area can then be machined. In a further step, a stator with an outer surface and a through-opening with an inner surface is manufactured. The shape of the receiving area of ​​the housing differs from the shape of the outer surface of the stator, and / or the inner surface is non-cylindrical. The stator is preferably manufactured from cut and stacked electrical steel sheets. After the housing and the stator have been manufactured, the stator is inserted into the receiving area of ​​the housing to form a force-fit and / or material-fit connection between the housing and the stator.In particular, the stator is inserted into the receiving area of ​​the housing by means of a transverse press fit. For this purpose, the housing is preferably heated (typically to over 200 °C) to enlarge the inner diameter of the receiving area sufficiently to allow the cold, i.e., unheated and uncooled, stator to be easily inserted. As the housing cools down, it contracts, and the stator is positively locked into the receiving area. The housing preferably has a non-cylindrical external geometry. In particular, the external geometry is highly asymmetrical. This asymmetry can lead to uneven thermal expansion and different stress states at various locations within the housing when heated.Without the adaptation of the receiving area, the inner surface, and / or the outer surface according to the invention, the inner surface of the stator may become non-circular and deviate from a cylindrical shape. The fit between the receiving area of ​​the housing and the outer surface of the stator is preferably an interference fit.

[0009] Preferably, the receiving area of ​​the housing is formed non-cylindrically by means of non-circular turning, a turn-based relief machining process, or form honing. This can enable precise manufacturing of the receiving area.

[0010] The non-cylindrical shape of the inner stator surface is preferably achieved by thermally and / or mechanically pre-stressing the stator at the outer surface and simultaneously machining the inner surface. This allows the inner surface to be machined cost-effectively using conventional methods, with the desired non-roundness resulting after releasing the pre-stress. The pre-stress can be applied, for example, using a deformation tool or a honing jig.

[0011] Preferably, the forces exerted by thermal and / or mechanical preloading correspond to the forces exerted by the frictional connection between the stator and the receiving area of ​​the housing. This ensures that, after the stator is mounted in the housing, its inner surface is as cylindrical as possible.

[0012] Furthermore, a non-cylindrical shape for the housing's receiving area is preferably achieved by thermally and / or mechanically pre-tensioning the housing against an outer geometry and simultaneously machining the receiving area. The housing is usually already machined, allowing the thermal and / or mechanical pre-tensioning to be easily and cost-effectively integrated into the manufacturing process to improve the dimensional accuracy of the stator's inner surface.

[0013] Preferably, the method further comprises the steps of inserting a measuring stator into the receiving area of ​​the housing to form a force-fit connection between the housing and the measuring stator. Subsequently, the deformation of an inner surface of the measuring stator is determined between its original cylindrical state and its installed state. The receiving area of ​​the housing is then manufactured such that the form deviation of the receiving area corresponds to the inverse deformation of the inner surface of the measuring stator. Preferably, the form deviation is scaled to match the diameter ratio between the receiving area and the inner surface. These steps can be performed once to determine the form deviation or more frequently to improve the geometric quality of the final result or to adapt to changing production conditions.These steps allow for a simple determination of the form deviation, enabling reliable adjustment of the measuring area to ensure the most cylindrical possible inner surface of the stator after assembly. After determining the deformation of the measuring stator, the stator can be removed from the housing so that the housing's form deviation can be adjusted, or a new housing with the adjusted form deviation can be manufactured. In its original state, the measuring stator preferably has a cylindrical inner and outer surface.

[0014] Furthermore, the invention relates to an electric motor, particularly for an electric bicycle, comprising a previously described electric motor unit and a rotor, wherein the rotor is arranged within the through-hole of the stator. The stator's preferably cylindrical inner surface can allow for the installation of a larger rotor in order to reduce the air gap, thereby improving the electric motor's performance. A circumferentially constant air gap can also contribute to improved NVH (noise, vibration, and harshness) behavior.

[0015] Preferably, the air gap between the rotor and the stator is less than or equal to 0.3 mm. In particular, the air gap between the rotor and the stator is less than or equal to 0.2 mm, and most preferably less than or equal to 0.1 mm. This enables high motor power from the electric motor. Brief description of the drawings

[0016] A preferred embodiment of the invention is described in detail below with reference to the accompanying drawings. The drawing shows: Fig. 1 a schematic top view of a housing of an electric motor unit according to the preferred embodiment of the invention, Fig. 2 a schematic view of a stator after it has been inserted into a receiving area of ​​the housing to form the electric motor unit according to the preferred embodiment, Fig. 3 a schematic view of an electric motor with a rotor which is incorporated into the electric motor unit according to the preferred embodiment of the invention, Fig. 4 a schematic sectional view of the housing for the electric motor unit according to the preferred embodiment of the invention, Fig. 5 a schematic view of a step for manufacturing the stator for the electric motor unit according to the preferred embodiment of the invention and Fig. 6 another schematic view of the electric motor unit according to the preferred embodiment of the invention. Embodiments of the invention

[0017] The following refers to the Fig. 1 to 6 an electric motor unit 1 for an electric motor 100 and a method for manufacturing the electric motor unit 1.

[0018] Preferably, all identical components, elements and / or units in all figures are provided with the same reference numerals.

[0019] Fig. Figure 1 shows a section perpendicular to a longitudinal axis LL of a housing 20 of the electric motor unit 1. The housing 20 has a receiving area 21 which is designed to receive a stator 10 by means of a frictional connection.

[0020] The housing 20 has a rectangular outer geometry 22. The receiving area 21 is appropriately adapted to the outer geometry 22 of the housing 20 in order to, for example, avoid material accumulations.

[0021] Fig. Figure 2 shows a section perpendicular to the longitudinal axis LL through the stator 10 and the housing 20, with the stator 10 positioned in the receiving area 21 of the housing 20. The housing 20 was heated to increase the inner diameter of the receiving area sufficiently to allow easy insertion of the cold stator 10. Due to the asymmetry of the housing 20, it expands radially differently, and the shape of the receiving area 21 was chosen to resemble an outer surface 11 of the stator 10 when heated and expanded.

[0022] The stator 10 is approximately hollow cylindrical and has a through-opening 12 with a cylindrical inner surface 13. Furthermore, the stator 10 has an outer surface 11 on its outside.

[0023] Fig. Figure 3 shows a section perpendicular to the longitudinal axis LL through the electric motor 100 with a rotor 2, which is arranged in the through-opening 12 of the electric motor unit 1. The rotor 2 is cylindrical, so that a constant air gap d results between the cylindrical inner surface 13 of the stator 10 and the rotor. The air gap d is preferably less than or equal to 0.3 mm, more preferably less than or equal to 0.2 mm, and most preferably less than or equal to 0.1 mm.

[0024] The case 20 has evolved into Fig. 3 compared to the case 20 in Fig. 2 cooled down, causing it to contract and forcefully fix the stator 10. The receiving area 21 lies flush against the outer surface 11 of the stator 10.

[0025] The outer surface 11 and the receiving area 21 are in Fig. 3 approximately cylindrical. The housing 20 preferably exerts a radial force on the stator 10 that is as uniform as possible around its circumference in order to prevent deformation of the cylindrical inner surface 13 of the stator 10. If the inner surface 13 deforms, a cylindrical shape, or a cylindrical contour, can be ensured in the assembled state by making the inner surface 13 non-cylindrical in the unconnected state.

[0026] Fig. Figure 4 shows a longitudinal section of the housing 20 along the longitudinal axis LL. The housing 20 has a cup shape, with a base 23 on one underside and a flanged area 24 on the top. The base 23 and the flanged area 24 are connected by the receiving area 21. The receiving area 21 is hollow cylindrical, widening towards the base. This allows for compensation of differing thermal expansions of the housing 20 in the flanged area 24 and the base 23, so that the receiving area 21 forms a straight opening when heated.

[0027] Fig. Figure 5 shows a step in the production of the stator 10. The stator 10 is mechanically pre-tensioned at its outer surface 11, while the inner surface 13 of the through-hole 12 is machined to a cylindrical shape. The forces exerted by the mechanical pre-tensioning preferably correspond to the forces acting in the assembled state due to the frictional connection between the receiving area 21 and the stator 10. After the pre-tensioning is released, the inner surface 13 is preferably non-cylindrical and only acquires its cylindrical shape through the frictional connection in the receiving area 21 of the housing. Similarly, the receiving area of ​​the housing can also be machined by mechanical pre-tensioning.

[0028] As an alternative to preloading the stator 10, the through-hole 12 of the stator 10 can also be produced by means of non-circular turning, turn-based freeform machining or form honing.

[0029] Fig.Figure 6 shows a longitudinal section through the housing 20 and a measuring stator 14 perpendicular to the longitudinal axis LL. In its original state, the measuring stator 14 preferably has a cylindrical inner surface 13 and a cylindrical outer surface 11. When the measuring stator 14 is force-fitted into the receiving area 21 of the housing 20, it is deformed, causing the inner surface 13 to become non-cylindrical. The difference between the circular dashed line and the line of the inner surface 13 indicates the deformation v.

[0030] To improve the cylindricity of the inner surface 13 of the electric motor unit 1, a shape deviation f from the original shape is provided for the receiving area 21 of the housing 20, which essentially corresponds to the inverse deformation v of the inner surface 13 of the measuring stator 14. For example, if the inner surface 13 of the measuring stator 14 deforms radially inward by 1 mm, a shape deviation of 1 mm outward is provided radially at the corresponding position of the receiving area 21. The measuring stator 14 can also correspond to the stator 10.

Claims

[1] Electric motor unit comprising: - a stator (10) with an outer lateral surface (11) and a through-hole (12) with a cylindrical inner lateral surface (13), and - a housing (20) with a recording area (21), - wherein the stator (10) is arranged in a force-fit and / or material-fit manner in the receiving area (21) of the housing (20) and - wherein in the unconnected state the shape of the receiving area (21) of the housing (20) differs from the shape of the outer surface (11) of the stator (10) and / or wherein in the unconnected state the inner surface (13) of the stator (10) is non-cylindrical. [2] Electric motor unit according to claim 1, wherein in the unconnected state the receiving area (21) of the housing (20) has a shape deviation from a perfect cylindrical shape and wherein the outer surface of the stator is cylindrical. [3] Electric motor unit according to claim 2, wherein the shape deviation (f) of the receiving area (21) essentially corresponds to the inverse deformation (v) of the inner lateral surface (11) of the stator (10) in a receiving area (21) of the housing (20) without shape deviation (f). [4] Electric motor unit according to one of the preceding claims, wherein the shape of the receiving area (21) of the housing (20) widens or narrows in the longitudinal direction (LL). [5] Method for manufacturing an electric motor unit (1) comprising the steps: - Manufacturing a housing (20) with a receiving area (21), - Manufacturing a stator (10) with an outer surface (11) and a through-hole (12) with an inner surface (13), wherein the shape of the receiving area (21) of the housing (20) differs from the shape of the outer surface (11) of the stator (10) and / or wherein the inner surface (13) is non-cylindrical, - Inserting the stator (10) into the receiving area (21) of the housing (20), in particular by means of a transverse press fit, in order to form a force-fit and / or material-fit connection between the housing (20) and the stator (10). [6] Method according to claim 5, wherein the receiving area (21) of the housing (20) is formed non-cylindrically by means of non-circular turning, a rotary-based free machining or form honing. [7] Method according to one of claims 5 or 6, wherein the non-cylindrical shape of the inner surface (13) of the stator (10) is produced by thermally and / or mechanically pre-tensioning the stator (10) on the outer surface (11) and simultaneously rounding the inner surface (13). [8] Method according to claim 7, wherein the forces through thermal and / or mechanical preloading correspond to the forces through the frictional connection. [9] Method according to any one of claims 5 to 8, wherein a non-cylindrical shape of the receiving area (21) of the housing (20) is produced by thermally and / or mechanically pre-tensioning the housing (20) on an outer geometry (22) and simultaneously rounding the receiving area (21). [10] Method according to any one of claims 5 to 9, further comprising the step: - Inserting a measuring stator (14) into the receiving area (21) of the housing (20) to form a force-fit and / or material-fit connection between the housing (20) and the measuring stator (14), - Determining the deformation (v) of an inner surface (13) of the measuring stator (14) between the original state and the installed state, - wherein the receiving area (21) of the housing (20) is manufactured such that the shape deviation (f) of the deformation of the receiving area (21) from a perfect cylindrical shape corresponds to the inverse deformation of the measuring stator (14). [11] Electric motor, in particular for an electric bicycle, comprising an electric motor unit (1) according to one of claims 1 to 3 and a rotor (2), wherein the rotor (2) is arranged within the through-opening (12) of the stator (10). [12] Electric motor according to claim 10, wherein an air gap (d) between the rotor and the stator is less than or equal to 0.3 mm, in particular less than or equal to 0.2 mm.

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