Patent Application
20230223814
The disclosure is directed to a stator arrangement of an electric machine and to an electric machine for driving a motor vehicle.
During operation of an electric machine, it is necessary to support a reaction torque of the rotating rotor, which reaction torque acts on the stator. To this end, the lamination stack carrying the stator winding is usually secured directly to a housing of the machine by an interference fit or press fit. The invention is directed to an electric machine in which the lamination stack is secured to a separate stator carrier and in which the stator and stator carrier are inserted in a machine housing and secured therein. An arrangement of this kind is shown and described in DE 10 2015 221 777 A1, for example. The connection between the stator carrier comprising multiple parts and the housing is formed as a screw connection, and the threaded bolts are acted upon by tensile forces as well as by transverse forces absorbing the above-mentioned reaction torque. Accordingly, this arrangement necessitates special dimensioning of the threaded bolts. Further, the axially one-sided support of the reaction torque may lead to a twisting of the stator core. In the subject matter of DE 10 2015 221 777 A1, this is to be prevented by axially extending stabilizing rods.
In an electric machine formed as vehicle drive, the requirements respecting the fastening of the stator are particularly demanding because reliable torque support must also be ensured under alternating thermal stress loads within the entire operating temperature range from approximately −40° C. to +140° C. Because of the use of different materials with different thermal expansion behaviors and the resulting lengths and diameter changes in the elements of the stator arrangement, it may prove difficult in terms of construction to achieve an optimal layout of the joining areas. Further, as is also generally stated in DE 10 2015 221 777 A1, a fluid cooling jacket and seal arrangements formed in addition to the joining connection can be provided between the stator carrier and the housing. In this case, changes in temperature—also due to trapped air volumes—can lead to changes in pressure, component stresses induced thereby, and possibly also leaks. The prior known solution can be disadvantageous in further respects, also with respect to a noise, vibration and harshness behavior (abbreviated NVH), i.e., the phenomenon of unwanted occurrence of reciprocal component/aggregate vibrations and associated bothersome noises.
One aspect of the invention is to improve a stator arrangement of an electric machine of the type mentioned in the introduction and to overcome the disadvantages described above.
Advantageous configurations and further developments of aspects the invention will be apparent from the following description and the figures.
Accordingly, a stator arrangement of an electric machine is proposed that comprises a substantially cylindrical stator carrier with a radially inner joining surface and with a radially outer joining surface, a lamination stack being arranged at the inner joining surface, and the stator carrier with the outer joining surface being received by an inner joining surface of a housing of the electric machine.
First, it is suggested according to one aspect of the invention that the connection between the stator carrier and the housing be carried out by an interference fit. However, it has turned out in this regard that undesirably high mechanical stresses can occur locally when providing a conventional, that is, a circumferentially closed, interference fit due to inevitable manufacturing tolerances and assembly tolerances of the parts. This is also the case in particular when at least one of the joining partners is not formed rotationally symmetrical around the common center axis and joining axis. In case of an unfavorable tolerance stack-up, mismatches may be produced with respect to the mutual orientation of adjoining component parts, which either requires re-machining of the joint or renders the already produced assemblies unusable.
The inventors had the insight that a symmetrical distribution of mechanical stresses does not occur in a conventional interference fit of stator carrier and housing with respect to the center axis in circumferential direction. On the contrary, mechanical stress peaks occur due to design-dependent deviations in symmetry of the joined component parts in different radial directions.
It is further provided according to one aspect of the invention that one of the joining surfaces of the stator carrier and housing, which cooperate with one another is formed interrupted in circumferential direction.
Because of the interference fit of the connection partners which is interrupted in circumferential direction as a result, an excessive tension and a deformation of the joining partners possibly resulting from this can be prevented at critical positions. Such a position may be a fastening area of the stator carrier in the form of a segmented annular collar or of individual screw lugs for screwing to the machine housing.
As a result, the rest of the associated disadvantageous effects such as mismatches or misorientations with respect to neighboring component parts or leakage problems are also minimized or entirely eliminated. After-machining of the unit comprising the joining partners or of an element cooperating with the latter may be dispensed with. At the same time, as a result of interrupting the joining surface, a pressure equalization channel can be provided for an air volume located between a joining surface and a seal arrangement. Accordingly, no additional mechanical stresses occur during changes in temperature due to changes in volume.
Screw bolts or other axial fasteners used for axially securing the stator between the stator carrier and the machine housing do not experience transverse forces at least substantially and can accordingly be optimized chiefly with respect to their tensile loading. The interference fit provided between the stator carrier and the housing successfully supports reaction torque which may occur, that is, at least substantially without the assistance of the axial connection elements. In this way, the reaction torque can be distributed axially along the extension of the stator and the lamination stack can be prevented from twisting.
As a result of the suggested interference fit, the stator carrier with the lamination stack secured thereto is more firmly coupled to the machine housing so that a mutual vibration of these parts is at least sharply curtailed and suppressed and the NVH behavior is accordingly also noticeably improved.
On the whole, the above-mentioned solution to the stated problem allows an operationally reliable securing and torque support of the stator without the disadvantageous effects mentioned in the introduction. The solution further allows wider tolerances for joining the connection partners.
According to an advantageous aspect, the stator carrier can have two outer joining surfaces which are spaced apart from one another axially and which are formed with a larger outer diameter compared to a circumferential area of the stator carrier located axially between these two joining surfaces, at least one of these joining surfaces of the stator carrier being interrupted in circumferential direction. Accordingly, both joining surfaces can also be formed interrupted. An axial split or forming axially divided joining surfaces contributes to a further reduction of stresses. The two axially spaced joining surfaces can be provided, respectively, at different axial end areas of the stator carrier and can therefore be substantially as far apart from one another as possible.
Further advantageously, a fluid cooling jacket can be formed in the stator arrangement axially at the circumferential region between the joining surfaces of the stator carrier and housing. Further, seal arrangements are formed between the stator carrier and the housing for producing a fluid-tight connection of the parts, these seal arrangements being closed in circumferential direction and located adjacent to one of the joining surfaces of the stator carrier in each instance. Because at least one or both of the joining surfaces are formed interrupted, sealing elements utilized at the seal arrangement, for example, O-rings, are loaded and deformed approximately uniformly in circumferential direction.
Insofar as a plurality of stress-critical positions or directions occur in the opposing joining area in circumferential direction, it may be advantageous to form one of the mutually cooperating joining surfaces of the stator carrier and housing to be repeatedly interrupted in circumferential direction corresponding to these positions or directions, as a result of which at least two joining surface segments occur. Such joining surface segments can be realized, for example, as local diameter changes in the casting blank of the stator carrier.
For the purpose of a spatial homogenization of mechanical stresses that occur, it may be useful that the joining surface segments of two joining surfaces of the stator carrier which are axially spaced apart are arranged offset to one another in circumferential direction and/or that they are formed with a different circumferential extension.
In a stator arrangement, particularly for a vehicle drive, the housing can advantageously comprise a ferrous casting material and the stator carrier can be produced from an aluminum casting material.
The connection of the inner joining surface of the stator carrier to the lamination stack can also be carried out with an interference fit in the stator arrangement proposed herein. Accordingly, the stator carrier is connected to the radially adjoining elements by both its radially inner joining surface and its radially outer joining surface by an interference fit.
According to a further aspect of the invention, an electric machine for driving a motor vehicle comprises a stator arrangement as described above and a rotor which is rotatably supported relative to the latter.
The invention will be described in the following referring to an exemplary embodiment form shown in the drawings.
The drawings show:
The stator 14 comprises a substantially cylindrical stator carrier 18 made from an aluminum casting material, two collar-shaped, radially outwardly directed fastening areas 22 being formed thereon at a front end portion 20. The fastening areas 22, which are formed as fastening lugs in the present instance, have through-openings 22a for producing a screw connection 24 to the housing 12. As will be apparent from
Still referring to
The stator carrier 18 is configured to be substantially not rotationally symmetrical by the fastening areas 22, which are formed opposite one another at the center axis A. Accordingly and also owing to the manufacturing tolerances and assembly tolerances, high mechanical stresses can occur locally in an unwanted manner particularly in the mutual connection area of the stator carrier 18 and housing 12. By way of a remedy, it is provided to form at least one of the mutually cooperating joining surfaces 710, 720; 50 of the stator carrier 18 and housing 12 to be interrupted in circumferential direction. An excessive stressing and deformation possibly resulting therefrom at critical positions are prevented by the resulting interference fit of connection partners which is interrupted in circumferential direction.
As will be seen from
The interference fit existing between the inner joining surface 60 of the stator carrier 18 and the lamination stack 26 is comparatively noncritical with respect to mechanical stresses due to the spaced spatial position relative to the two fastening areas 22. Therefore, the inner joining surface 60 is formed circumferentially closed, and an outer joining surface 80 of the lamination stack 26 cooperating with the inner joining surface 60 can optionally have corresponding cutouts for absorbing mechanical stresses which may possibly occur. Accordingly, the stator carrier 18 is connected by its radially inner joining surface 60 and its radially outer joining surface 70 by an interference fit to the radially adjoining elements 12, 26 so as to be fixed with respect to rotation relative to it.
Thus, while there have shown and described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2020 207 236.1 | Jun 2020 | DE | national |
This is a U.S. national stage of Application No. PCT/EP2021/065317 filed Jun. 8, 2021. Priority is claimed on German Application No. DE 10 2020 207 236.1 filed Jun. 10, 2020 the content of which is incorporated herein by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/065317 | 6/8/2021 | WO |
