Method for assembling an electric machine and a laminated stator core and a stator lamination adapted to that method

Abstract

The present invention relates to a method for non-rotatably mounting a laminated stator core (11) of an electrical machine in a housing (1) of that machine. According to the invention, at least some of the stator laminations (10) of the laminated stator core (11) are each provided with one or more radially outward protruding parts (104) that together form one or more axial rows of protruding parts (104) in the stator core (11). Upon mounting the stator core (11) in the housing (1), such rows of protruding parts (104) are each inserted into a respective axial groove (2) in the housing (1) that is sized to provide an interference-fit therebetween.

Description

[0001] METHOD FOR ASSEMBLING AN ELECTRIC MACHINE AND A LAMINATED

[0002] STATOR CORE AND A STATOR LAMINATION ADAPTED TO THAT METHOD

[0003] The present invention relates to a method for mounting a stator of an electric machine inside a housing thereof, as well as to a design of a laminated stator core of such stator, in particular of an individual lamination thereof, that is specifically adapted to such assembly method.

[0004] Such an electric machine is well known in the art, for example in its application as a traction motor with generator functionality in (battery) electric passenger cars and other motor vehicles. Besides the stator that is non-rotatably mounted in its housing, the electric machine further includes a rotor that is rotatably mounted radially inside the stator on a rotor shaft of the electric machine.

[0005] In particular in the said battery electric vehicle application of the electric machine, optimizing its operating efficiency by minimizing losses is essential for optimizing driving range in relation to battery capacity and weight. In order to minimize the electrical losses in the stator core, these are typically laminated, i.e. constructed from a number of mutually stacked individual laminations. By laminating the stator core parasitic, so-called Eddy currents, induced during operation of the electric machine, are suppressed. Especially so when the individual laminations are mutually electrically insulated as is customary practice. Moreover, in order to minimize the magnetic hysteresis losses in the stator core, these are typically made from so-called (silicon) electrical steel. For the same reason, it is known to stress-relief anneal the stator laminations, i.e. to reduce or remove internal stresses in stator core. Namely, these internal stresses are known to be detrimental to the said magnetic hysteresis losses, but to inevitably result from, at least, the blanking of the stator laminations from sheet material, but possibly also from interlocking (e.g. riveting; clinching) or welding these, as is typically done for facilitating the subsequent handling and / or processing of the stator core after stacking. The intensity of such annealing heat treatment in terms of the temperature and duration can be optimized according to need, as for instance described in US-10199910 B2 and JP-5228379 B.

[0006] The stator laminations are generally ring-shaped with multiple, radially inwardly extending recesses provided in its inner circumference, each recess defined between two adjacent stator teeth or poles that thus project radially inward from an at least largely solid, radially outer ring-shaped segment of the stator laminations. In the stack of stator laminations that is the laminated stator core, the said recesses form axially extending slots, wherein electrical conductors, such as bars or wires of copper, are wound to form the stator of the electric machine. During operation of the electric machine, these stator windings are energized by an alternating current, so as to generate a rotating magnetic field for exerting a torque on the rotor shaft via the rotor.

[0007] Underlying the present invention is the observation by applicant that in certain applications thereof, the electric machine experiences higher magnetic hysteresis losses then what might be expected against the above, known technical background. In particular, this observation is linked to the mounting of the stator in its housing by way of an interference-fit in radial direction, such as in particular a shrink-fit that is a well-known, convenient, and often preferred assembly method. However, such radial interference-fit causes stress in the said outer ring-segment of the stator laminations that are detrimental to the magnetic performance of the stator.

[0008] The present invention therefore aims to provide a method for non-rotatably mounting a stator of an electrical machine in a housing, which assembly method should not only be convenient and but also to a large extend stress-free.

[0009] According to the invention, at least some of the stator laminations of the laminated stator core of the stator are each provided with one or more radially outward protruding parts, hereinafter denoted as ear parts, that together form one or more axial rows of ear parts in the laminated stator core. Upon mounting the stator in the housing, each such row of ear parts is inserted into a respectively corresponding axial groove in the housing that is sized, in particular slightly undersized relative to the row of ear parts in cross-section, to provide an interference-fit with the respective row of ear parts. By this assembly method, the stator laminations and in particular the outer ringsegments thereof are favorably not, at least not substantially and / or additionally, stressed. In particular in this respect, such interference-fit between the row or rows of ear parts and the housing grooves is preferably realized by pressing the stator into the housing, i.e. by means of a (mechanically realized) press-fit rather than a (thermally realized) shrink-fit.

[0010] Preferably, the ear parts of the stator lamination are arranged rotationally symmetrically on its circumference. For example, when the stator lamination is provided with two ear parts these are provided opposite from one another, providing the stator lamination with a 180erotational symmetry. Generally speaking, such rotational symmetry amounts to M divided by N times 360e, with N representing the number of ear parts of the stator lamination and with M being an integer between 1 and N-1 .

[0011] Preferably the stator laminations of the laminated stator core are interconnected before the core is mounted in the housing. Hereby, the integrity of the stator in terms of the desired mutual radial alignment and tangential orientation of its laminations will be reliably maintained during the said mounting. In this respect, the mutual gluing of adjacent stator laminations is preferred over the physical interlocking or welding thereof, to minimize and favorably distribute stress.

[0012] Further according to the invention, at least one of the one or more ear parts of the respective stator laminations may be provided with a hole. Before mounting the stator in the housing, a guide rod is first inserted through such holes in the respective axial row of ear parts in the laminated stator core. Upon mounting the stator in the housing, the mutual alignment thereof and / or of the individual laminations of the stator is favorably promoted, such that a distortion of the stator during press fitting is favorably minimized by the guide rod. After such mounting, the guide rod is removed from the stator. Thus, in this latter, second embodiment of the invention, the stator laminations of the stator core need not be interconnected to reliably maintain their mutual alignment and orientation during press fitting. Hereby, an earlier process step of interlocking or gluing the laminations, can be favorably omitted.

[0013] Preferably in this second embodiment of the invention, the guide rod is connected to and extends from a support base whereupon the stator is placed before mounting it in its housing. More preferably, before mounting the stator in the housing, the guide rod extends beyond the laminated stator core and through a guide hole in an end cap of the housing, located opposite an open end of the housing via which the stator is mounted. Hereby, the said mutual alignment of stator and housing is favorably promoted even better. In particular to this end, the said ear part holes, the guide rod and the guide hole are correspondingly dimensioned, i.e. are shaped and sized at least substantially without clearance there between.

[0014] More preferably also in this second embodiment of the invention, the said mutual alignment of stator and housing is yet further promoted by providing the stator laminations with at least two ear parts that are each provided with a hole, such that a set of two guide rods can be applied. In this case, preferably a more substantial clearance in radial direction of the stator laminations is provided between one of the two ear part holes and the corresponding guide rod, so as not to over-determine the positioning of the stator by the guide rods.

[0015] As an alternative to the above-discussed guide rod, in a third optional embodiment of the invention, a centering mandrel can be applied for promoting the said mutual alignment of stator and housing yet further. This centering mandrel is provided on the radial inside of the laminated stator core before mounting it in its housing. In particular in this case, the outer circumference of the centering mandrel is correspondingly dimensioned, i.e. is shaped and sized to narrowly fit the inner circumference of the stator core, preferably substantially without any clearance there between. Preferably, the centering mandrel is connected to and extends from the said support base. Preferably also, the centering mandrel is provided with an extension that extends beyond the stator core and through a central, bearing hole in the said end cap of the housing, likewise substantially without clearance there between. Such bearing hole is provided in the housing to support the rotor shaft of the rotor of the electric machine. More preferably, the centering mandrel is applied in combination with the afore-mentioned guide rod, so as to not only center the stator core in radial direction, but to also position it in tangential direction.

[0016] Yet further according to the invention and specifically in case the respective stator laminations are provided with at least two ear parts provided with the hole, the laminated stator core may be conveniently held together between a bolt head and a bolt nut of each of two bolts that each extend through the holes of a respective axial row of ear parts thereof. Hereby, such laminated stator core can be conveniently handled as a whole also before the above-discussed centering mandrel, guide rod or set of two guide rods is applied, i.e. is inserted in the stator core (and without requiring the clinching, welding, gluing or otherwise interconnecting the laminations thereof).

[0017] Before mounting the laminated stator core in the housing, such holding bolts are removed. Preferably, however, these holding bolts are only removed after the abovediscussed centering mandrel, guide rod or set of two guide rods is applied, i.e. is inserted in the stator core. Therefore, in a fourth embodiment of the invention, the stator laminations are each provided with exactly three or exactly four ear parts provided with the hole, thus forming three, respectively four axial rows of ear parts in the stator core. Two such rows being associated with the two holding bolts, the third row with the guide rod applied in combination with the centering mandrel, or the third and the fourth row with the set of guide rods.

[0018] In particular according to the present invention, the ear parts in a particular axial row of ear parts are preferably not contiguous, meaning that not every stator lamination in the laminated stator core is provided with an ear part in that particular axial row of ear parts. For example, the stator laminations may be alternatingly provided with the ear part, or two or more stator laminations without an ear part may be provided between each pair of adjacent stator laminations with the ear part. This provides a free space in the axial direction of the stator core to accommodate a bending of the ear parts when these are pressed into a respective housing groove, thus favorably limiting stresses associated with the press-fit. In this case, the stator laminations can still be manufactured, i.e. blanked as identical parts, by rotating each lamination relative to its neighboring lamination when these are stacked to form the stator core. For example, if each stator lamination is manufactured with N ear parts that are mutually equally spaced along its circumference with a 360 / N degree angle between them, these can be stacked while rotating each subsequently stacked lamination over (360 / N) / R degrees relative to the previously stacked lamination with R being an integer larger than 1 . Hereby, every Rthlamination in the lamination stack is provided with the ear part in each of the N*R axial rows of ear parts of that stack in total (that are to be inserted in N*R axial housing grooves).

[0019] Alternatively according to the present invention and likewise to reduce the stresses associated with the press-fit between the stator and the housing, an ear part may be composed of a central section that is connected -along its entire tangential width- to the outer ring-segment of the respective stator lamination and of at least one side section or tab, that is located to a tangential side of the central section and that is not connected to said outer ring-segment. With this particular design of the ear part, the deformation and stressing thereof by the press-fit of the stator in the housing will be favorably oriented in tangential, i.e. circumferential direction and, moreover, concentrated in the said side section thereof, i.e. away from the ring-segment of the respective stator lamination. The ear part can be provided with two such tabs, one on either tangential side of its central section connected to the said outer ring-segment.

[0020] Preferably, in the stack of stator laminations that is the laminated stator core, the ear part / parts of not every lamination is / are provided with such tab or tabs. This provides a free space in the axial direction of the stator core to accommodate a bending of the tabs under influence of the press-fit with the housing, thus reducing the stressing thereof. This latter aspect can also be implemented by providing the tabs on opposite tangential sides of the central section of the ear parts between subsequent, i.e. directly adjacent laminations in the stator core. Or by providing the tabs on different radial positions of the central section of the ear parts between subsequent laminations in the stator core.

[0021] If the housing is made of aluminum, as is common in its motor vehicle application, it can potentially be damaged by the press fitting of the laminated stator core with comparatively harder steel laminations. In this respect, the formation of (loose) debris would be especially undesirable. To reliably avoid such damage and / or debris, a respective housing groove can according to the invention be favorably lined with a steel strip, at least in part and at least when mounting the stator. Such groove liner can consist of one or more flat strips, each covering (part of) a side or a bottom surface of the respective housing groove. Or such groove liner can be U-shaped to cover both side surfaces and the bottom surface of the respective housing groove. Moreover, such groove liner can be provided permanently and can then even be fixed to the respective housing groove, for example by gluing the steel strip to the inside surface thereof. Or such groove liner can be provided only temporarily (i.e. before mounting / press fitting the stator inside the housing), to be removed from the housing (i.e. pulled out from between the housing and the stator) after mounting the stator. In this case, the press-fit is ultimately established directly between the stator and the housing, and the groove liner / steel strips can be reused.

[0022] In the following, the present invention is explained further and in more detail with reference to the drawings, whereof: figure 1 schematically illustrates a typical example of the internal parts of an electric machine of known design, including a laminated stator core; figure 2 schematically illustrates the mounting of the known laminated stator core in a housing of the electric machine in accordance with the know art; figure 3 provides a plan view of a laminated stator core that is composed of a number of mutually stacked stator laminations designed in accordance with the present invention, both before and after mounting such stator core in its housing; figure 4 illustrates a first embodiment of an assembly method of mounting the laminated stator core inside the housing according to the invention; figure 5 illustrates an optional aspect of the assembly method according to the invention; figure 6 illustrates an aspect of a blanking process for manufacturing the stator laminations designed in accordance with the invention; figure 7 illustrates a second embodiment of an assembly method of mounting the laminated stator core inside the housing according to the invention; figure 8 provides a plan view of the stator lamination in an alternative design suitable for the assembly method according to the invention; figure 9 provides an isometric view of a number of mutually stacked stator laminations according to figure 8; figure 10 schematically illustrates another alternative stator lamination design suitable for the assembly method according to the invention; and figure 11 schematically illustrates the use of a housing groove liner in the assembly method according to the invention.

[0023] Figure 1 depicts the internal parts of an electric machine, in particular a permanent magnet-type synchronous machine. These internal parts concern a stator lamination 10, a rotor lamination 20, a stator core 11 that is a stack of the stator laminations 10, a rotor core 21 that is a stack of rotor laminations 20, a stator 12 that consists of the laminated stator core 11 with windings 13 of an electrical conductor attached thereto, and a rotor 22 that consists of the rotor core 21 with permanent magnets 23 attached thereto and of a rotor shaft 24.

[0024] These internal parts of the electric machine are mounted in a housing 1 of electric machine, whereby the laminated stator core 11 is often fixed to the housing 1 by providing an interference-fit there between, as is schematically illustrated in figure 2. In the art, such interference-fit is commonly realized by shrink fitting the stator core 11 with a cylindrical outer contour of diameter Dso inside the housing 1 having a circular inner contour of diameter Dhi that is somewhat smaller than the outer stator diameter Dso, whereto the housing 1 is heated to expand its inner contour to beyond the outer contour of the stator.

[0025] According to the present invention this known assembly method comes with the disadvantage that the stator laminations 10 are compressively stressed in radial inward direction by the shrink-fit between the laminated stator core 11 and the housing 1. Namely, such compressive stress is known to be detrimental to the magnetic performance of the stator 12 in operation of the electric machine. The present invention provides for an alternative, new method for mounting the stator core 11 in its housing 1 that, in combination with a dedicated novel design of the stator laminations 10, to a substantial extent avoids a detrimental stressing thereof. This new assembly method and stator lamination design are illustrated in figure 3.

[0026] In figure 3, on the left side, the stator lamination 10 according to the present invention is shown. As is common in the art, the stator lamination 10 is generally ringshaped with a solid radially outer ring-segment 101 and with multiple, radially inwardly extending stator recesses 102 provided in its inner circumference for accommodating the stator windings 13 (see figure 1). Each stator recess 102 is defined by and between two adjacent stator teeth 103 that extend radially inward from the radially outer ring-segment 101 .

[0027] The illustrated embodiment of the stator lamination 10 according to the invention is provided with four radially outward projecting parts 104, denoted as ear parts 104. These ear parts 104 form four rows of mutually overlapping ear parts 104 in the axial direction of the stack of stator laminations that is the laminated stator core 11. Additionally, as shown on the right side of figure 3, the housing 1 is provided with four axial grooves 2 on its inside, which axial grooves 2 are each positioned and sized to provide an interference press-fit in tangential direction with a respective one of the said four rows of ear parts 104 of the stator core 11. By this assembly method, the outer ring-segments 101 of the stator laminations 10 remain favorably stress-free when mounting the stator core 11 in its housing 1 . As is shown in figure 3 and as is preferred for equally distributing the load during operation of the electric machine, the four ear parts 104 are arranged at equal, i.e. 90eintervals along the outer contour of the stator lamination 10.

[0028] With the stator lamination design and assembly method according to the present invention, it is preferable to leave a gap 3 between the laminated stator core 11 and the housing 1 by providing the stator laminations 10 with an outer diameter that is smaller than the inner diameter of the housing 1 . This gap 3 not only favorably relaxes a manufacturing tolerance and / or surface quality requirement for the inner diameter of the housing 1 but can also be used to channel a cooling medium along the outside of the stator core 11 for actively cooling it when the electric machine is in operation.

[0029] As illustrated on the left side of figure 3, the ear parts 104 can be designed with a central section 105 that is connected -along its entire tangential dimension / width- to the outer ring-segment 101 of the respective stator lamination 10 and with two side sections 106, denoted as tabs 106 -one to each tangential side of the central section 105- that are not connected to said outer ring-segment 101 . This specific design of the stator laminations 10 is considered preferable as facilitating a bending deformation of the ear parts 104 thereof that accompanies the said press-fit. To further enhance this latter aspect of the invention, it is preferable that the ear parts 104 of at least every other lamination 10 in the stack of stator laminations that is the laminated stator core 11 is not provided with the tabs 106 to provide a free space for accommodating such bending deformation. To the same effect, the ear parts 104 can alternatively each be provided with only one tab 106 provided on a respective tangential side of the central section 105 thereof that alternates between successive laminations 10 in the stator core 11 (not illustrated). Or by providing the tabs 106 on different radial positions of the central section 105 of the ear parts 104 between such successive laminations 10 (see figure 8).

[0030] As also illustrated in figure 3, the ear parts 104 can be provided with a hole 107. In the stack of stator laminations that is the laminated stator core 11 , the holes 107 of the rows of mutually overlapping ear parts 104 define axially oriented channels 108 that can be advantageously made use of in accordance with the present invention as follows.

[0031] Firstly, as illustrated in figure 4 in a cross-section I along the line A-B (indicated in figure 3) thereof, the laminated stator core 11 can be placed over guide rods 31 that extend vertically upwards from a support base 32, which guide rods 31 extend through a respective one of such axial channels 108 and serve to favorably mutually align the stator laminations 10 and to prevent the movement thereof, respectively of the stator core 11 as whole, when the housing 1 and the stator core 11 are press-fitted. Preferably a more substantial clearance in radial direction of the stator laminations 10 is provided between the hole 107a of one of the ear parts 104a thereof, forming a respective one 108a of the two axial channels 108 wherein the guide rods 31 are inserted, so as not to over-determine the positioning of the stator 12 by the guide rods

[0032] 31.

[0033] Furthermore, the housing 1 is preferably also placed over the guide rods 31 that thereto extend beyond the laminated stator core 11 , as illustrated in figure 4, while the housing 1 is provided with corresponding guide holes 4 in an end cap 5 thereof. Thus, the guide rods 31 additionally serve to (pre-)align the housing 1 relative to the stator core 11 before and during the actual press-fitting thereof that is illustrated in crosssection II of figure 4. Upon completion of the press-fit illustrated in cross-section III of figure 4, the guide rods 31 are removed from the assembly 6 of the stator core 11 and the housing 1 , typically by lifting such assembly 6 up and away from the support base

[0034] 32, as illustrated in cross-section IV of figure 4.

[0035] It is noted that the end cap 5 of the housing 1 is typically further provided with a centrally located bearing hole 7 that serves to accommodate (a bearing of) the rotor shaft 24 (see figure 8). Moreover, the length of the housing 1 typically exceeds the length (height) of the laminated stator core 11 , such that in the said assembly 6 thereof free spaces 8 are available between the housing 1 and the stator core 11 to either axial side thereof. These free spaces 8 serve to accommodate the said stator windings 13 (see figure 7). In order to avoid that the stator 12 rests on its stator windings 13 during the said press-fitting, the support base 32 includes a ring-shaped element 321 that engages (only) the outer ring-segment 101 of the lowermost stator lamination 10 of the stator core 11 . Furthermore, in figure 4 the support base 32 is shown to include a, likewise ring-shaped, stopper 322 that defines the ultimate position of the housing 1 relative to the stator core 11 during the said press-fitting.

[0036] Secondly, as illustrated in figure 5, before mounting the laminated stator core 11 in its housing 1 it can be held together between a bolt head 42 and a bolt nut 43 of two holding bolts 41 , which holding bolts 41 are thereto inserted through two of the said axial channels 108 defined by the holes 107 of the rows of mutually overlapping ear parts 104. Hereby, the stator core 11 is conveniently held together as a whole in subsequent handling and / or processing steps, such as being placed over the said guide rods 31 as part of the above-discussed assembly method.

[0037] When combining the above first and second uses thereof, at least four ear parts 104 per stator lamination 10 are required for simultaneously accommodating the said two guide rods 31 and the said two holding bolts 41. However, from a manufacturing cost perspective, three ear parts 104 per stator lamination 10 are preferred. In particular in blanking the stator laminations 10 from a sheet metal strip 51 , efficient use of such starting material 51 is made when two parallel, but mutually staggered tracks T1 , T2 of such stator laminations 10 with three ear parts 104 are blanked from a single strip 51 , as is illustrated in figure 6. Namely, in this case the sheet metal strip 51 has less than double the width that would be needed for a single track T1 of such stator laminations 10 because these can be partially nested between the said two tracks T1 +T2.

[0038] To accommodate such preferred the stator lamination design with three ear parts 104, one of the above-discussed two guide rods 31 can be replaced with a centering mandrel 35 placed on the support base 32, as illustrated in figure 7. The centering mandrel 35 has an outer diameter Dmo that corresponds to the inner diameter Dsi of the laminated stator core 11 (see figure 2) and thus blocks the radial movement of that core 11 , while the one remaining guide rod 31 blocks tangential movement thereof.

[0039] The centering mandrel 35 is preferably segmented (not illustrated), such that it can be expanded in radial direction after being placed inside the laminated stator core 11 , to firmly contact the stator teeth 103 (see figure 3) thereof. Preferably also, the centering mandrel 35 is provided with an extension 36 that extends beyond the stator core 11. In this case, the housing 1 is placed not only over the said one remaining guide rod 31 via the said guide hole 4 in its end cap 5, but also over the said mandrel extension 36 via the said bearing hole 7 therein. Thus, the mandrel extension 36 and the guide rod 31 additionally serve to (pre-)align the housing 1 relative to the stator core 11 before and during the actual press-fitting thereof.

[0040] A specific embodiment of the stator lamination 10 according to the invention is illustrated in figures 8 and 9, with figure 8 providing a plan view of such stator lamination 10 and with figure 9 providing an isometric view of a section of a stack of such stator laminations 10. In this specific embodiment, each ear part 104 of the stator lamination 10 is provided with two tabs 106, i.e. one on either (tangential) side thereof. Moreover, the tabs 106a, 106b, 106c of each respective ear part 104a, 104b, 104c are located at a radial position that is different between the ear parts 104 of the stator lamination 10. Preferably, such difference in radial positions of the tabs 106 between the ear parts 104 corresponds to a size of the tabs 106 in radial direction or is slightly larger than that. In this case, when the laminated stator core 11 is assembled by stacking such stator laminations 10, each subsequently stacked lamination 10 is rotated over the angle between its ear parts 104 relative to the lamination 10 that is preceding it in the stack (e.g. -in case of three, equally spaced ear parts 104- over 120e, 240eand 360e=0eand so on). Then the tabs 106 are allowed to bend in axial direction in the stack of stator laminations that is the laminated stator core 11 , because between each pair of two radially overlapping, adjacent tabs 106c1 , 106c2 there is a free space defined in axial direction by the two, relatively rotated intermediate stator laminations 10 having tabs 106a, 106b at different radial positions. With this particular design of the ear part 104, i.e. by such (radially) staggered placement of the tabs 106, the deformation and / or stressing thereof due to the press-fit of the stator core 11 in the housing 1 is optimally accommodated.

[0041] Another specific embodiment of the stator lamination 10 according to the invention is illustrated in figure 10. In this latter specific embodiment, the radially outer contour 109 of the stator lamination 10 between the ear parts 104 thereof is provided undulating. Hereby, a side surface area of the stator laminations 10 -and thus of the laminated stator core 11 as a whole- is increased relative to the known contour thereof shown in figure 8 that is provided with circular arc segments between the ear parts 104. By this feature -i.e. by any deviation from a circular arc segment- the heat transfer away from the stator core 11 when the electric machine is in operation is favorably enhanced. This latter embodiment of the stator lamination 10 is particularly effective in combination with the said channeling of cooling medium through the gap 3 between the stator core 11 and the housing 1. Furthermore, a different undulation pattern can be applied to each section 109a, 109b, 109c of the outer lamination contour 109 between the pairs of adjacent ear parts 104 of the stator lamination 10. For example and as illustrated in figure 9, an offset in tangential direction can be applied between such undulation patterns of the said outer contour sections 109a, 109b, 109c. In this case, by the said relative rotation of the subsequent stator laminations 10 when the stator core 11 is assembled, the peaks 110 and valleys 111 of the undulation patterns do not (at least not completely, or not fully) overlap in axial direction. Hereby, the cooling medium that is channeled through the above-mentioned gap 3 (that is embodied by the said valleys 111 overall) becomes (more) turbulent and will thus more effectively transfer heat away from the stator core 11 . This latter effect will become more pronounced, the closer the corrugation peaks 110 extend to the housing 1 .

[0042] In figure 10 a further, independent aspect of the invention is illustrated, i.e. unrelated to the shown undulating shape of the radially outer contour 109 of the stator lamination 10. Namely, parts 91 of the inside of the housing 1 that are located between housing parts 92 provided with the axial grooves 2 are recessed relative to these latter housing parts 92. By this feature, the said gap 3 between the laminated stator core 11 and the housing 1 can be favorably implemented in the electric machine without having to also (i.e. in order to additionally cover the gap 3) increase the radial extent of the ear parts 104 of the stator laminations 10 and / or without having to also increase an outer diameter of the housing 1 .

[0043] In figure 11 yet a further, independent aspect of the invention is illustrated. Namely, according to the invention a respective axial groove 2 in the housing 1 is provided with a groove liner 112. The groove liner 112 is provided in the press-fit contact with the stator core 11 , which contact -at least in the shown embodiment - occurs via the tabs 106 on either side of the ear part 104 of the stator lamination 10. In figure 11 , the groove liner 112 is in the form of two strips 112 that are provided on either tangential side of the groove 2 and that extend along the axial length of the groove 2. The groove liner 112 according to the invention has a material hardness comparable to (or exceeding) that of the stator lamination 10 core 11 , e.g. by being made from (stainless) steel. The groove liner 112 protects the housing 1 from being damaged by press fitting the stator core 11 .

[0044] The present invention, in addition to the entirety of the preceding description and all details of the accompanying figures, also concerns and includes all the features of the appended set of claims. Bracketed references in the claims do not limit the scope thereof but are merely provided as non-binding examples of the respective features. The claimed features can be applied separately in a given product or a given process as the case may be, but it is also possible to apply any combination of two or more of such features therein.

[0045] The invention(s) represented in the present disclosure is (are) not limited to the embodiments and / or the examples that are explicitly mentioned herein, but also encompasses amendments, modifications, and practical applications thereof, in particular those that lie within reach of the person skilled in the relevant art.

Claims

CLAIMS1 . A method for assembling an electric machine, wherein a stator core (11) made of stacked stator laminations (10) and a housing (1) are connected to each other in a rotationally fixed manner by means of an interference-fit, characterized in that at least a part of the stator laminations (10) is provided with a number of ear parts (104) protruding radially outwardly relative to an outer ring segment (101 ) of the respective stator lamination (10), that the housing (1) is provided with an at least equal number of grooves (2), and in that the said interference-fit is realized between the ear parts (104) of the stator laminations (10) and the grooves (2) of the housing (1).

2. The assembly method according to claim 1 , characterized in that the said interference-fit is realized as a press-fit by pressing the ear parts (104) of the stator laminations (10) into the grooves (2) of the housing (1 ).

3. The assembly method according to claim 1 or 2, characterized in that the ear parts (104) of at least some of the pairs of subsequent stator laminations (10) in the stator core (11) do not overlap in axial direction.

4. The assembly method according to a preceding claim, characterized in that the ear parts (104) of the stator laminations (10) each comprise a central section (105) and at least one side section (106) in circumferential direction, whereof the central section (105), in circumferential direction, is completely connected to the outer ring segment (101) of the respective stator lamination (10) and whereof the side section (106) is connected to the central section (105), but not to such outer ring segment (101).

5. The assembly method according to claim 4, characterized in that the side sections (106) of two otherwise axially overlapping ear parts (104) of two subsequent stator laminations (10) in the stator core (11 ), do themselves not overlap, either by these two ear parts (104) each being provided with only one such side section (106) on mutually opposite sides in the circumferential direction thereof, and / or by the side sections (106) of these two ear parts (104) being provided at mutually different radial positions on the central section (105) thereof.

6. The assembly method according to a preceding claim, characterized in that, prior to the realization of the said interference-fit, a liner (112) is provided in or applied to thehousing grooves (2), which groove liner (112) is at least present in the contact between the stator core (11 ) and the housing (1 ) and groove liner (112) is made from a harder material than the housing (1) is.

7. The assembly method according claim 6, characterized in that, following the realization of the said interference-fit, the groove liner (112) is removed from the housing grooves (2).

8. The assembly method according to a preceding claim, characterized in that the outer contour of the stator laminations (10) between the ear parts (104) thereof is located away form an inner contour of the housing (1 ), such that a gap (3) is realized there between.

9. The assembly method according to claim 8, characterized in that the outer contour of the stator laminations (10) between the ear parts (104) thereof deviates from a circular arc shape.

10. The assembly method according to a preceding claim, characterized in that, prior to the realization of the said interference-fit, the stator laminations (10) or the stator core (11 ) are mutually interconnected.

11. The assembly method according to a preceding claim, characterized in that one or more of the ear parts (104) of the stator laminations (10) is or are provided with a hole (107) that coincides between stator laminations (10) of the stator core (11 ), and thus forms a respective channel (8) in the axial direction of the stator core (11 ), and in that, during the realization of the said interference-fit, a guide rod (31) is placed in each such axial channel (8), each guide rod (31) preferably extending through a respective guide hole (4) provided in an end cap (5) of the housing (1).

12. The assembly method according to a preceding claim, characterized in that, during the realization of the said interference-fit, a mandrel (35) is placed radially inside the stator core (11), which mandrel (35) preferably extends through a hole (7) provided in an end cap (5) of the housing (1) for accommodating (a bearing of) a rotor shaft (24) of a rotor core (21) of the electric machine.

13. An electric machine with a housing (1) provided with a number of grooves (2) andwith a stator core (11) made of stacked stator laminations (10), whereof at least a part is provided with an at most equal number of ear parts (104) protruding radially outwardly relative to an outer ring segment (101) of a respective stator lamination (10), characterized in that an interference-fit is realized between the grooves (2) of the housing (1 ) and the ear parts (104) of the stator laminations (10).

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