ROTOR FOR AN ELECTRIC MACHINE WITH STRIP-SHAPED RETAINING ELEMENTS

Description

[0001] The invention relates to a rotor for an electric machine, in particular for an electric motor or an electric generator, comprising a rotor shaft, a base body which is non-rotatably connected to the rotor shaft and surrounds the rotor shaft, and a plurality of permanent magnets which are connected to the base body on the outside in a ring-shaped arrangement.

[0002] The permanent magnets of such a rotor must be connected to the base body in such a way that they are secured against being lost during operation of an electric machine containing the rotor. This is usually achieved by a metal or plastic casing surrounding the permanent magnets and the base body, or by inserting the permanent magnets into designated pockets in the base body. However, such casings for the permanent magnets mean that the magnetically relevant distance between the rotor's permanent magnets and the electrical coils of the stator surrounding the rotor must be relatively large, since this distance is determined not only by the gap required for contactless rotation of the rotor within the stator, but also by the radial thickness of the casing.However, a relatively large magnetically relevant distance leads to a relatively poor efficiency of the electric machine.

[0003] To minimize the resulting disadvantages, attempts are usually made to design the casing with the smallest possible radial thickness. However, this is only possible to a limited extent, for example, with a plastic casing manufactured by injection molding, which typically requires wall thicknesses of at least 0.5 millimeters. Furthermore, extremely thin-walled casings, which are manufactured as separate components and placed over the permanent magnets already attached to the base body during rotor assembly, are highly susceptible to damage, negatively impacting the assembly process.

[0004] An electric machine with a metal casing, which can be designed either as a solid hollow cylinder or with a cage structure, is known from DE 38 44 074 C2.

[0005] DE 43 31 803 A1 further discloses an electric motor in which, to facilitate the assembly of the rotor, the permanent magnets are held on a carrier by means of retaining clips, wherein the retaining clips have web-shaped sections that project into external recesses of the permanent magnets. In addition, in the electric motor according to DE 43 31 803 A1, the permanent magnets are also attached to a base body of the rotor by means of a covering that surrounds them and the retaining clips.

[0006] WO 2012 / 049236 A2 discloses a rotor for an electric motor in which permanent magnets are fixed by a sheet metal cage consisting of two half-shells.

[0007] DE 10 2014 223 330 A1 describes a rotor for an electric motor in which holding elements are provided for permanent magnets. These elements extend from the two end faces of a rotor body and only partially along the longitudinal extent of the associated permanent magnets, which runs along the rotor's axis of rotation. The two holding elements, each originating from different axial ends of the rotor and associated with a single permanent magnet, are connected to each other at their ends.

[0008] The invention is based on the objective of making the magnetically relevant distance between the permanent magnets of the rotor and the stator of the electric machine as small as possible in the most advantageous way possible, in order to achieve the highest possible efficiency of the electric machine.

[0009] This problem is solved by means of an electric machine according to claim 6, which comprises a rotor according to claim 1. Advantageous embodiments of such a rotor and such an electric machine according to the invention are the subject of further claims and / or will become apparent from the following description of the invention.

[0010] According to the invention, a rotor for an electric machine, in particular for an electric motor (e.g., for a drive motor of a pump in a motor vehicle) or an electric generator, is provided, comprising a rotor shaft, a base body non-rotatably connected to and surrounding the rotor shaft, and a plurality of permanent magnets connected externally to the base body in an annular arrangement. A plurality of rib-shaped retaining elements are provided, each of which externally covers at least one of the permanent magnets, in particular by direct contact. It may be provided that the retaining elements extend (at least partially) only over a section of the rotor shaft or over the entire longitudinal extent of the associated permanent magnet(s).According to the invention, it is further provided that the retaining elements cover the respective permanent magnet(s) either on their outer surface exclusively in a section located centrally with respect to the circumferential direction of the rotor (which preferably also includes the exact center) or exclusively on a side surface of each permanent magnet.

[0011] The retaining elements should therefore not cover at least the edges of the permanent magnets where the respective outer surfaces transition into one of the associated side surfaces and which preferably run parallel along the rotor's axis of rotation. This makes it possible to create the smallest possible magnetically effective distance between the permanent magnets of a rotor according to the invention and the stator of an electric machine according to the invention, which is preferably arranged coaxially with it. If the permanent magnets are exclusively surrounded or covered on the outside by the retaining elements, as is preferably provided, the (smallest) distance between the permanent magnets and the stator can even be reduced to the radial height of the gap required for contactless rotation of the rotor relative to the stator, taking into account form and positional tolerances.

[0012] For the permanent magnets to be covered by at least some of the retaining elements exclusively on one side surface of each permanent magnet, a shape for the side surfaces is required in which they do not run exactly radially with respect to the rotor's axis of rotation, at least in sections. This can be achieved, for example, by having the side surfaces, or at least sections thereof, run in a plane that is not aligned exactly radially with respect to the rotor's axis of rotation. Similarly, a stepped profile of the side surfaces or undercuts (with respect to the radial direction) can be provided in the side surfaces.According to the invention, the outer surface of the permanent magnets is understood to be the surface that radially defines the respective permanent magnets and thereby defines the cross-sectional area of ​​these permanent magnets to the greatest extent and in particular to at least 80% or 90% with respect to the circumferential direction.

[0013] An embodiment of the rotor according to the invention, in which the retaining elements cover the respective permanent magnets at least also on their outer surface in a section central to the circumferential direction of the rotor, can be particularly advantageous if the permanent magnets have rectangular cross-sectional areas. Such permanent magnets, which are also known as block magnets, are frequently used in electrical machines because they are inexpensive to manufacture.However, a disadvantage of such permanent magnets lies in the fact that they define an outer circumference of the rotor, which in cross-section corresponds approximately to a polygon. This, in combination with a stator that limits a substantially cylindrical inner volume, as is preferably provided in an electric machine according to the invention, leads to a non-uniform distance between the permanent magnets and the stator around the circumference of the rotor, and, with respect to the circumferential direction of the rotor, the greatest or at least relatively large distance in the center of the individual permanent magnets. According to the invention, these sections of the outer surfaces of the permanent magnets can therefore be advantageously used to create at least a radially effective connection between the permanent magnets and the base body by means of overlapping contact with the holding elements.The overlapping or contacting of these sections by the retaining elements is not detrimental with regard to achieving the smallest possible magnetically effective distance, because the smallest distance for permanent magnets with rectangular cross-sectional areas is already located in the area of ​​the edges that represent the transition between the outer surfaces and the side surfaces of the permanent magnets. The retaining elements therefore do not prevent this smallest distance from being minimized to the level required for contactless operation.

[0014] In order to achieve the best possible connection between the permanent magnets and the base body, it is preferably possible to provide that even with permanent magnets having rectangular cross-sectional areas, retaining elements are provided which cover the respective permanent magnets exclusively on one side surface.

[0015] If the permanent magnets have annular segment-shaped cross-sectional areas, it is advantageous to use only those retaining elements that cover the respective permanent magnets exclusively on one side surface. The smallest distance between the permanent magnets and the stator can then preferably be located over the entire outer surface of the permanent magnets.

[0016] According to a first embodiment of the invention, the retaining elements, or at least some of them, extend from the two end faces or longitudinal axial ends of the base body only partially along the longitudinal extent of the associated permanent magnet(s) running along the rotational axis of the rotor, and terminate freely at the corresponding other axial end. For this purpose, the retaining elements should be dimensioned to be relatively stable or rigid in order to achieve a sufficiently secure connection between the permanent magnets and the base body of the rotor.

[0017] On the other hand, in a second embodiment of the rotor according to the invention, it is provided that the retaining elements, or at least some of them, extend over the entire longitudinal extent of the associated permanent magnet(s) and that they are connected to one or both end faces of the permanent magnet(s) directly or indirectly in such a way that they mutually support an outward radial load on these retaining elements. This also makes it possible to achieve a sufficiently secure connection between the permanent magnets and the rotor body using relatively weak or flexible retaining elements.

[0018] According to the invention, all or at least some of the retaining elements are connected to a connecting ring at both of their longitudinal ends. This connection can be detachable or permanent, in which case it can also be integral.

[0019] Specifically, according to the invention, these retaining elements are permanently connected at one of their longitudinal ends to a first connecting ring. This makes it possible to mount all retaining elements simultaneously in an arrangement secured by the connecting ring, or to slide them onto the already pre-assembled combination of base body and permanent magnets. Subsequently, the other longitudinal ends of the retaining elements are secured by a detachable connection to a second connecting ring or by a connection to each other.

[0020] Preferably, the retaining elements and / or the connecting ring(s), if present, are made of one or more plastics (preferably PPS). This makes them cost-effective to manufacture, particularly by injection molding. Furthermore, these components can therefore have relatively low masses.

[0021] The invention is explained in more detail below with reference to embodiments illustrated in the drawings. The drawings show, in some cases in simplified form: Fig. 1: a rotor for an electric machine according to the prior art in a perspective view; Fig. 2: a cross-section through a section of the rotor according to the Fig. 1 Fig. 3: a cross-section through a section of a rotor according to the invention in a first embodiment; Fig. 4: an electric machine according to the invention with a rotor according to the Fig. 3 in a partial cross-section; Fig. 5: the rotor of the electric machine according to the Fig. 4in a perspective view; Fig. 6: a rotor according to an embodiment not covered by the claims, in a side view; Fig. 7: a rotor according to a second embodiment in a perspective view; Fig. 8: the rotor according to the Fig. 7 in a rear view; and Fig. 9: a rotor according to a third embodiment in a rear view.

[0022] The Fig. 1 and 2Figure 1 shows a rotor 1 for an electric machine according to the prior art. This rotor 1 comprises a rotor shaft 2, a base body 3 non-rotatably connected to and surrounding the rotor shaft 2, and a plurality of permanent magnets 4, which are designed as block magnets and therefore have rectangular cross-sectional areas. The permanent magnets 4 are connected to the base body 3 externally in a ring-shaped arrangement. A tubular casing 5, which can be made of metal or plastic, for example, also serves to connect the permanent magnets 4 to the base body 3. Fig. 1 only partially depicted.

[0023] In such a rotor 1 according to the prior art, a relatively large magnetically effective distance results between the permanent magnets 4 of the rotor 1 and a stator 6 of an electric machine comprising these two components, since in the design of the smallest distance between the permanent magnets 4 and the stator 6, on the one hand a gap width between the covering 5 and the stator 6, which must be dimensioned so large that it avoids contact between the rotor 1 and the stator 6 taking into account the permissible form and position tolerances, and on the other hand the radial thickness of the covering 6 must be taken into account.

[0024] A rotor 1, as it appears in various configurations in the Figs. 3 to 9As shown, this disadvantage is avoided by not providing any covering or overlap of the permanent magnets in the area of ​​those edges where the outer surfaces 7 of the rectangular cross-sectional permanent magnets 4 transition into their respective side surfaces 8 and which have the smallest distance to the stator 6. Accordingly, the distance between the permanent magnets 4 and the stator 6 can be reduced to such an extent that, in the area of ​​these edges, the distance between the permanent magnets 4 and the stator 6 corresponds to the gap width that must be provided for in the design to prevent contact between the rotor 1 and the stator 6, taking into account permissible form and positional tolerances. Figs. 2 and 3 The comparison illustrates this result.

[0025] In the Figs. 3 to 9In the illustrated embodiments of rotors 1, each of which is to be combined with a stator 6 that defines a cylindrical inner volume, the goal of the smallest possible distance between the permanent magnets 4 and the stator 6 is achieved by providing web-shaped retaining elements 9, each of which partially covers and contacts at least one of the permanent magnets 4 on its outer surface, wherein the retaining elements 9 cover the respective permanent magnet(s) 4 either on their outer surface 7 exclusively in a section located centrally and, in particular, exactly in the middle with respect to the circumferential direction of the rotor 1, or exclusively on a side surface 8 of each permanent magnet 4.

[0026] In the design of a rotor according to the Figs. 3 to 6Each permanent magnet 4 is provided with two retaining elements 9, one of which extends from a first end face and the other from a second end face of the associated permanent magnet 4 or base body 3 over a section of the longitudinal extent of the associated permanent magnet 4 and covers the outer surface 7 of the respective permanent magnet 4. All of the retaining elements 9 extending from the first end faces of the permanent magnets 4 or from the first end face of the base body 3 are connected to a first connecting ring 10 and are formed integrally with it, with this connecting ring 10 resting loosely against the corresponding end faces of the permanent magnets 4 and the base body 3.Similarly, all of the retaining elements 9, which extend from the second end faces of the permanent magnets 4 and the base body 3, are connected to a second connecting ring 10.

[0027] The in the Figs. 3 to 5 The illustrated embodiment of a rotor 1 according to the invention differs from that according to the Fig. 6The retaining elements 9 are designed to be relatively short, extending only over a portion of the longitudinal extent of the respective permanent magnet 4 that is significantly less than half of this longitudinal extent. The ends of the retaining elements 9 that cover the respective permanent magnets 4 are therefore free. To achieve a sufficiently secure connection between the permanent magnets 4 and the base body 3 using such retaining elements 9, these retaining elements 9 should be dimensioned to be sufficiently stable and rigid. For this purpose, a design of the retaining elements 9 and the connecting rings 10, preferably formed integrally with them, made of metal is recommended.

[0028] In the case of rotor 1 according to the Fig. 6In contrast, it is provided that the individual retaining elements 9 each extend over half the longitudinal extent of the associated permanent magnet 4, so that the two retaining elements 9 assigned to each permanent magnet 4 abut or contact each other at the longitudinal axial center of this permanent magnet 4. Furthermore, a connection between these two retaining elements 9 per permanent magnet 4 is provided by means of a combination of a recess in one of these retaining elements 9 and a projection 11 of the other retaining element 9 engaging in this recess.

[0029] In the Figs. 7 to 9In the illustrated embodiments of the rotors 1 according to the invention, in addition to retaining elements 9 that cover the respective permanent magnets 4 exclusively in a section of their outer surfaces 7 located centrally with respect to the circumferential direction of the rotor 1, retaining elements 9 are also provided that cover two adjacent permanent magnets 4 at their respective adjoining side surfaces 8. This allows for a larger number of retaining elements 9, thereby enabling a sufficiently secure connection of the permanent magnets 4 to the base body 3 even with relatively small retaining elements 9.The overlap of the side surfaces 8 of the permanent magnets 4, which in these embodiments are also designed as block magnets with rectangular cross-sectional areas, is achieved by arranging these side surfaces such that they are inclined relative to the exact radial orientation such that the distance between adjacent side surfaces 8 of neighboring permanent magnets 3 increases with increasing radial distance from the axis of rotation 12 of the rotor 1. This is particularly evident from the . Figs. 8 and 9 evident.

[0030] Specifically, in the case of rotors 1, according to the Figs. 7 to 9It is provided that all of the retaining elements 9 extend from the first end faces of the permanent magnets 4 and the base body 3 over the entire longitudinal extent of the permanent magnets 4, the retaining elements 9 being formed integrally with a connecting ring 10 that loosely rests against these first end faces. In order to achieve the highest possible load-bearing capacity of the retaining elements 9 against radial expansion, it is further provided that at least those retaining elements 9 which cover the respective permanent magnets 4 exclusively in a section of their outer surfaces located centrally with respect to the circumferential direction of the rotor 1, are directly connected in the area of ​​the second end faces of the permanent magnets 4 and the base body 3 (see figure). Fig. 9 ) or indirectly (cf. Figs. 7 and 8 are connected to each other.

[0031] In the case of rotor 1 according to the Figs. 7 and 8Radially oriented connecting hooks 13, arranged at the respective longitudinal ends, serve this purpose. A further connecting ring 10 is guided within these hooks. In this specific embodiment, the connecting ring 10 is designed as a conventional O-ring made of an elastomer. In the assembled state, this connecting ring 10 is elastically prestressed or expanded to ensure sufficient pressure when pressing the retaining elements 9, which comprise the connecting hooks 13, against the respective permanent magnets 4. It is also possible, either exclusively or, more preferably, additionally, for the other retaining elements 9, which cover the respective permanent magnets 4 on one side surface 8, to be provided with corresponding connecting hooks 13 in which the elastic connecting ring 10 is guided.

[0032] Alternatively or in addition to the use of a connecting ring 10 in the form of an O-ring, a connecting ring 10 made of another material, in particular of a (different) plastic or of metal, for example also in the form of a wire that is guided once or several times through the connecting hooks 13 and connected to each other at its ends, can also be used.

[0033] In the case of rotor 1 according to the Fig. 9In contrast, it is provided that the retaining elements 9 each have a circumferentially extending connecting web 14 at their respective longitudinal axial ends, the two circumferentially located ends of which are hook-shaped and thus serve as connecting hooks 13. These connecting hooks 13 are designed and configured to interlock with the adjacent connecting hook 13 of a neighboring connecting web 14 in order to provide mutual support, under a radially expanding load, at least for those retaining elements 9 which cover the respective permanent magnets 4 exclusively in a section of their outer surfaces 7 located centrally with respect to the circumferential direction of the rotor 1.In order to provide appropriate support for those retaining elements 9 that cover the respective permanent magnets 4 on a side surface 8, it can be provided, for example, that the connecting webs 14 are also connected to these retaining elements 9 or are formed in one piece.

[0034] In order to ensure that rotors 1 also comply with the Figs. 7 to 9 an axial positional locking of the retaining elements 9 or of the one-piece formed units consisting of connecting ring 10, retaining elements 9, connecting web 14 (in the case of the rotor 1 according to the Fig. 9 ) and connecting hooks 13 on or relative to the permanent magnets 4 and the base body 3 supporting them, the connecting hooks 13 extend radially inwards to such an extent that they are in partial overlap with the front face of the base body 3 there, so that they serve as stops effective in the longitudinal axial direction. Reference symbol list

[0035] 1 Rotor 2 Rotor shaft 3 Base body 4 Permanent magnet 5 Tubular casing 6 Stator 7 Outer surface of a permanent magnet 8 Side surface of a permanent magnet 9 Retaining element 10 Connecting ring 11 Projection 12 Rotation axis of the rotor 13 Connecting hook 14 Connecting bridge

Claims

1. Rotor (1) for an electric machine, comprising a rotor shaft (2), a main body (3) which is connected to the rotor shaft (2) for conjoint rotation and surrounds the rotor shaft (2), and a plurality of permanent magnets (4) which are connected to the outside of the main body (3) in a ring-shaped arrangement, wherein a plurality of strip-shaped holding elements (9) are provided, each of which contacts at least one of the permanent magnets (4) in portions on the outside, wherein the holding elements (9) cover the respectively assigned permanent magnet or magnets (4) either on their outer surface (7) exclusively in a portion located centrally with respect to the circumferential direction of the rotor (1) or exclusively on a side surface (8) of each permanent magnet (4), wherein the outer surface (7) of the permanent magnets (4) is the surface which delimits the respective permanent magnets (4) radially on the outside and thereby delimits the cross-sectional area of these permanent magnets (4) in relation to the circumferential direction to the greatest extent and in particular to at least 80% or 90%, characterized in that • the holding elements (9) extend at least partially from the two end faces of the main body (3) and in each case only in portions over the longitudinal extension of the associated permanent magnet or magnets (4) that runs along the rotational axis (12) of the rotor (1), and end freely at the corresponding other axial end and / or • the holding elements (9) extend at least partially completely along the longitudinal extension of the associated permanent magnet or magnets (4) and are connected to one another directly or indirectly at the two end-face ends of the permanent magnets (4) in such a way that an outwardly directed radial load on these holding elements (9) is mutually supported by the holding elements (9), for which purpose these holding elements (9) are non-detachably connected to a first connecting ring (10) with one of their longitudinal-axial ends and are detachably connected to a second connecting ring (10) or connected to one another with the other of their longitudinal-axial ends.

2. Rotor (1) according to claim 1, characterized in that the permanent magnets (4) are covered on the outside exclusively by the holding elements (9).

3. Rotor (1) according to claim 1 or 2, characterized in that the permanent magnets (4) have rectangular or circular-ring-segment shaped cross-sectional areas.

4. Rotor (1) according to any one of the preceding claims, characterized in that the holding elements (9) are at least partially made of plastic and / or the connecting ring or rings (10) are made of plastic.

5. Electric machine comprising a rotor (1) according to any one of the preceding claims and comprising a stator (6) surrounding the rotor (1).

6. Electric machine according to claim 5, characterized in that the stator (6) defines a cylindrical internal volume.