Patent Application
20230396106
The invention relates to a rotor for an electric motor having a rotor body with a cylindrical rotor core and with a number of surface magnets and a sleeve-like protective cover which is positioned on the outer circumference of the rotor body. The invention further relates to a method and a device for producing such a rotor and an electric motor having such a rotor.
In a modern motor vehicle, electric motors are used in many different ways as drives for different adjusting elements. Electric motors are used, for example, as window lifter drives, sliding roof drives or seat adjuster drives, as steering drives (EPS, Electrical Power Steering) as cooling fan drives or as gear actuators. Such electric motors have to have a relatively high torque density or power density and to be operationally reliable even at high temperatures.
An electric motor, as an energy converter of electrical energy into mechanical energy, contains a stator which forms the stationary motor part and a rotor which forms the moving motor part. In the case of an internal rotor motor, the stator is generally provided with a stator yoke on which stator teeth are arranged radially to the center, i.e. protruding inwardly in a star-shaped manner, the free ends thereof facing the rotor forming the so-called pole shoe.
In particular, a brushless electric motor as an electrical (three phase) machine generally has a stator which is provided with a field winding or stator winding and which is arranged coaxially to a rotor with one or more permanent magnets.
The rotor generally has a rotor body with a cylindrical punched-packed (rotor) laminated core as the central rotor core. The rotor core is joined to a motor shaft of the electric motor, for example fixedly to the shaft. The rotor core has, for example, receivers into which the permanent magnets are pressed. Alternatively, for example, it is also conceivable that the permanent magnets are fastened or held as surface magnets on an outer circumference of a lateral surface of the rotor core. To this end, it is conceivable, for example, that the surface magnets are joined to the lateral surface by a material connection, in particular by means of an adhesive or epoxy. Holding devices for fastening and/or holding the surface magnets on the lateral surface without a material connection are also conceivable.
The surface magnets in this case conventionally have a bread loaf-shaped cross-sectional shape. In other words, the permanent magnets of the rotor are designed as surface-mounted bread loaf-shaped magnets. A bread loaf-shaped cross-sectional shape, in particular, is to be understood to mean here and hereinafter the shape of a box-shaped bread loaf with a rectangular shape in which one of the longitudinal sides is configured to be curved outwardly in a convex manner. Due to the curvatures of the surface magnets, the outer circumference of the rotor body does not have a circular shape.
During the operation of the electric motor, large centrifugal forces act on the surface magnets of the rotor as a result of the high rotational speeds, whereby the risk increases of the surface magnets being undesirably released from the lateral surface. In order to prevent that a surface magnet is released from the lateral surface and blocks the electric motor in a gap region between the rotor and the stator, generally a sleeve-like protective cover (protective tube) is positioned on the rotor body as an anti-slip device.
Typically, an edge of the protective cover for fastening to the rotor body is bent radially inwardly (crimped) over the circumference, so that the rotor body is axially encompassed by the protective cover on the end face. The shaping or crimping takes place here, for example, by means of roller burnishing or by pressing.
During the roller burnishing or rolling, the material of the protective cover is deformed over the circumference. Since the protective cover to be deformed is not held all around by the rotor core due to the curvatures of the surface magnets, it results in the material of the protective cover being partially constricted during the roller burnishing, whereby it can lead to a formation of cracks and a reduction in the mechanical stability of the protective cover associated therewith.
During the pressing, a round tool is pressed from above on the end face against the protective cover or the rotor body. Relatively large forces are required, so that the resulting mechanical (compressive) stresses lead to bulking, i.e. compression, curving or cambering, of the protective cover, whereby the material of the protective cover migrates radially into the air gap between the rotor and the stator.
A protective cover for a rotor, which has a flange collar which is crimped for fastening to the rotor body on the end face, is disclosed in published, non-prosecuted German patent application DE 10 2019 205 993 A1. The flange collar has a plurality of recesses running tangentially and axially, the stresses occurring during the crimping being reduced thereby.
The object of the invention is to specify a particularly suitable rotor for an electric motor and a corresponding electric motor. The object of the invention is also to specify a particularly suitable method and a particularly suitable device for producing such a rotor. In particular, a cost-effective assembly of the rotor with less effort and in which the required assembly forces are reduced is intended to be made possible.
Regarding the rotor, the object is achieved by the features of the independent rotor claim and regarding the method by the features of the independent method claim and regarding the device by the features of the independent device claim and regarding the electric motor by the features of the independent electric motor claim according to the invention. Advantageous embodiments and developments form the subject matter of the dependent claims.
The rotor according to the invention is suitable and configured for an electric motor, in particular for an internal rotor configured as a surface permanent magnet (SPM) motor of a motor vehicle. In other words, the rotor according to the invention is configured, in particular, as an SPM rotor.
The rotor has a rotor body which can be joined or is joined to a motor shaft, fixedly to the shaft. The rotor body has a cylindrical rotor core which is configured, for example, as a punch-packed laminated core (laminated rotor core) with a number of rotor laminations stacked in an axial direction. A number of permanently magnetic surface magnets are arranged so as to be distributed as rotor magnets or pole magnets on the outer circumference of a lateral surface of the rotor core. The surface magnets have a bread loaf-shaped cross-sectional shape with a convex curvature oriented toward the outer circumference. The rotor core has, in particular, an equal-sided polygonal or multi-cornered bottom surface so that the lateral surface has in a tangential or azimuthal direction, i.e. along the outer circumference, a number of bearing surfaces with the same surface area for the surface magnets.
For protecting the surface magnets against slipping, a sleeve-like protective cover is positioned on the outer circumference of the rotor body. According to the invention, the protective cover has a flange collar at least on an end face, the flange collar being shaped into the radially indented regions or flanks between the curvatures of tangentially adjacent surface magnets in a positive and/or non-positive manner. As a result, a particularly suitable rotor is produced.
According to the invention, therefore, the space between the surface magnets is used for fastening the protective cover to the rotor body. Since in these regions the spacing between the rotor body and a surrounding stator is greater than in the region of the curvatures (or the crests thereof), a bulky (compressed, curved, cambered) material of the protective cover, due to the shaping, does not negatively affect the air gap or the electric motor.
In contrast to the prior art, the crimped edge or flange collar on the end face of the protective cover is thus not shaped over the entire circumference but only at the points arranged between the curvatures. According to the invention, therefore, the non-circular external circumferential shape of the rotor body is used for fastening the protective cover.
The conjunction “and/or” is to be understood to mean here and hereinafter such that the features linked by this conjunction can be configured together and as alternatives to one another.
A “positive fit”, a “positive connection” or a “form-locking connection” between at least two parts connected together is understood here and hereinafter, in particular, to mean that the parts connected together are held together at least in one direction by a direct interlocking of the contours of the parts themselves or by an indirect interlocking via an additional connecting part. The “blocking” of a mutual movement in this direction is thus dictated by the shape.
A “non-positive fit”, a “non-positive connection” or a “force-locking connection” between at least two parts connected together is understood here and hereinafter to mean, in particular, that the parts connected together are prevented from sliding off one another due to a frictional force acting therebetween. If a “connecting force” producing this frictional force is absent (i.e. the force which pushes the parts together, for example a screw force or the weight force itself) the non-positive connection cannot be maintained and thus can be released.
“Axial” or an “axial direction” is understood to mean here and hereinafter, in particular, a direction parallel (coaxial) to the axis of rotation of the electric motor, i.e. perpendicular to the end faces of the rotor. Accordingly “radial” or a “radial direction”, is understood to mean here and hereinafter, in particular, a direction oriented perpendicularly (transversely) to the axis of rotation of the electric motor along a radius of the rotor or the electric motor. “Tangential” or a “tangential direction” is understood to mean here and hereinafter, in particular, a direction along the circumference of the rotor (circumferential direction, azimuthal direction), i.e. a direction perpendicular to the axial direction and to the radial direction.
In an advantageous embodiment, the rotor body has a holding device positioned on the rotor core on the end face for fastening and/or holding the surface magnets on the lateral surface of the rotor core without a material connection. The curvatures of the surface magnets radially protrude over the outer circumference of the holding device. In other words, the curvatures of the surface magnets form the radially outermost points of the rotor body. Since the holding device is slightly smaller and also that no magnet is located in the axial direction in the regions between the curvatures, during the shaping process the material of the protective cover can also be forced downwardly, i.e. axially away from the shaped end face, into the free region, which leads to a reduced bulk of material in the radial direction. As a result, the protective cover nestles against the rotor body in a particularly compact manner in terms of installation space so that in the installed state an air gap which is as uniform as possible is produced between the rotor and the stator.
A “material fit” or a “material connection” between at least two parts connected together is understood to mean here and hereinafter, in particular, that the parts which are connected together are held together on their contact surfaces by a material association or cross linking (for example due to atomic or molecular bonding forces), optionally by the action of an additive. Accordingly, “without a material connection” means, in particular, that when the surface magnets are fastened no material connection is present between the surface magnets and the lateral surface. The surface magnets are thus fastened by means of the holding device to the rotor core merely in a positive and/or non-positive manner.
The holding device has, for example, two one-piece, i.e. integral or monolithic, holding rings (insulation disks) which are arranged on the opposing end faces of the rotor core. The holding rings, which are designed for example as injection-molded parts, have in each case a circular ring-shaped annular body with radially external holding contours projecting axially in the direction of the rotor core.
The holding rings are produced, in particular, from a glass fiber-reinforced plastics material, for example from a polyamide (PA), in particular PA 6.6 GF30, or from a polyphenylene sulfide (PPS), in particular PPS GF30, or a polyoxymethylene (POM), in particular POM GF30. The abbreviation GF30 stands in this case for a glass fiber content of 30%.
The holding contours are configured such that they engage radially and tangentially positively between the surface magnets. As a result, the surface magnets are held on the lateral surface in the radial and tangential direction without a material connection. For the axial fixing of the surface magnets, for example, it is provided that the surface magnets are gripped axially between the two holding rings. To this end, the surface magnets are radially covered at least in some portions by the annular body. In particular, therefore, an axial positive connection is implemented between the holding rings.
Thus, the geometry required for holding and/or fastening the surface magnets is only provided on the holding device, whereby the rotor core can have a particularly simple geometric shape. In particular, the rotor core has no additional receivers or contours or projections on the lateral surface, whereby the rotor laminations and thus the rotor core can be produced particularly simply and cost-effectively. Moreover, due to the arrangement of the permanent magnets on the lateral surface, the magnetic field lines of the permanent magnets inside the rotor core are not disturbed.
The method according to the invention is provided and is suitable and configured for producing an above-described rotor. The embodiments in connection with the rotor also expediently apply to the method and vice versa.
If the method steps are described hereinafter, this results in advantageous embodiments for the device, in particular by this device being configured to carry out one or more of these method steps.
According to the method, a rotor body and a protective cover are provided. The sleeve-like protective cover, for example, is designed to be substantially pot-shaped, for example. This means that the protective cover has a (cover) base as a bearing surface on the end face for the rotor body. The base or the bearing surface has, for example, a central recess as a through-opening for a motor shaft. A region of the protective cover on the end face opposing the bearing surface is designed as a flange collar of the protective cover and, after the rotor body has been inserted into the protective cover, is shaped, press-fitted or crimped into the radially indented regions between the curvatures of the tangentially adjacent surface magnets in a positive and/or non-positive manner. This means that the assembly forces for joining the protective cover to the rotor body are incorporated in a targeted manner in the intermediate regions between the curvatures. As a result, in particular in the region of the holding device, the required assembly forces are reduced and there is substantially no radially protruding deformation of the protective cover into the air gap region, whereby the system reliability is improved in the case of an electric motor. The method can be substantially used in all SPM rotors with bread loaf-shaped magnets, irrespective of the number of poles.
In contrast to the prior art, the shaping or crimping of the protective cover does not take place by roller burnishing or pressing, but substantially by press-fitting in the intermediate regions of the protective cover. In other words, the material of the protective cover is constricted in a targeted manner or locally in the intermediate regions and thus nestles against the non-circular external contour of the rotor body.
In a suitable development, the protective cover has a chamfer which is widened radially on the end face as an insertion aid for the rotor body. In other words, on the end face the protective cover has an oversized portion protruding into the air gap so that the rotor body can be inserted in the manner of a funnel. As a result, the insertion of the rotor body into the protective cover is simplified. The rotor body is introduced via the chamfer into the protective cover, wherein the chamfer is then bent inwardly or straightened radially by means of a first punch before the shaping of the flange collar. This means that the first punch radially inwardly bends the oversized portion of the protective cover protruding into the air gap. The bent chamfer forms, for example, the flange collar for the subsequent shaping or crimping step.
In an expedient embodiment, the flange collar after the shaping thereof is pressed by means of a second punch against the rotor body on the outer circumference thereof. This takes account of the fact that the material of the protective cover is pushed away by the shaping or by the crimping in the region of the curvatures. In other words, before the shaping process the curvatures substantially bear against the inner circumference of the protective cover, wherein due to the shaping the protective cover lifts away from the curvatures. This means that due to the deformation of the protective cover a clear (radial) spacing can be formed between the curvatures and the protective cover. The protective cover is thus deformed radially into the air gap in the region of the curvatures. This deformation in the region of the curvatures is remedied by the subsequent second punching process and the protective cover in the region of the curvatures is thus pushed or pressed again against the surface magnets. As a result, it is ensured that the protective cover does not bulk inadmissibly into the air gap.
The advantages and embodiments set forth regarding the rotor and/or the method are expediently also able to be transferred to the device described below and vice versa. The device according to the invention is provided and is suitable and designed for producing an above-described rotor. The device has a crown tool which is provided and designed to shape a flange collar of the protective cover into the radially indented regions between the curvatures of tangentially adjacent surface magnets of the rotor body in a positive and/or non-positive manner. The device also has, for example, a first and second punch. As a result, a particularly suitable device can be produced.
The crown tool of the device does not deform the protective cover tangentially over the circumference but merely at intervals or locally at the free spaces exposed by the curvatures between the rotor body and the protective cover.
In an expedient embodiment, the crown tool has a cylindrical tool body with a crown ring on the end face facing the rotor. The crown ring is configured to shape or deform the flange collar. A central projection which engages in a through-opening of the rotor body during the shaping process is also provided on the tool body. The through-opening of the rotor body serves for receiving a rotor shaft or motor shaft in the installed state. The bolt-shaped or cylindrical projection, for example, engages in a positive manner in the central through-opening so that the rotor body is positioned, stabilized and centered during the shaping process. The crown ring and the projection are formed integrally, i.e. in one piece or monolithically, on the tool body. The projection is designed, for example, as a pin or journal of the tool body. For the shaping, the crown tool is lowered from above in the manner of a punch on the end face onto the rotor body which is provided with the protective cover, wherein the projection engages in the through-opening and wherein the crown ring deforms, press-fits or crimps the flange collar in some regions.
In a conceivable embodiment, the crown ring has a number of axially protruding crown-shaped or castellation-shaped projections which are arranged so as to be tangentially distributed over the tool body circumference. Preferably, each castellation-shaped projection has a radially inwardly oriented shaping lug which shapes the flange collar during the shaping process. As a result, a particularly suitable tool and thus a particularly suitable device is produced for producing the rotor.
In a preferred application, the above-described rotor is part of an electric motor. The electric motor according to the invention is, for example, suitable and designed for a power steering system of a motor vehicle. The advantages and embodiments set forth regarding the rotor and/or the method and/or the device are also able to be transferred expediently to the electric motor and vice versa.
The electric motor has a stator and a motor shaft which is rotatably mounted relative thereto and on which the rotor is mounted fixedly to the shaft. The electric motor is configured, for example, as a brushless electric motor in the manner of an internal rotor.
In an application for a power steering system, the electric motor is arranged in the region of a driver's cab, wherein a particularly smooth motor operation is ensured by the rotor according to the invention since the surface magnets and the protective cover are held without vibrating on the rotor core. As a result, a generation of noise of the electric motor is reduced in an advantageous and simple manner, which is advantageously transferred to the user comfort of the motor vehicle.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a rotor for an electric motor, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
Parts and sizes which correspond to one another are always provided in all of the figures with the same reference signs.
Referring now to the figures of the drawings in detail and first, particularly to
The rotor 2 in this embodiment is configured as an SPM rotor with ten permanent magnetic surface magnets 16 for generating a magnetic excitation field. The surface magnets 16, which are provided with reference signs merely by way of example, are arranged in a tangential or azimuthal direction T on the rotor core 6 so as to be distributed on the outer circumference of the lateral surface 12. The surface magnets 16 are configured as bread loaf-shaped magnets and have in each case an approximately bread loaf-shaped cross-sectional shape in the axial direction A, wherein the surface magnets 16 are arranged so as to be positioned on a respectively assigned bearing surface 14 of the lateral surface 12. In the assembled state of the rotor 2, the surface magnets 16 are held and/or fastened by means of a holding device 18 on the lateral surface 12 of the rotor core 6 without a material connection.
The holding device 18 has two holding rings or insulation disks 20. As is relatively clearly visible with reference to
On a lower face facing the rotor core 6, the annular bodies 24 have in each case ten holding contours 30 on the outer circumference and ten fastening projections 32 on the inner circumference. The holding contours 30 and the fastening projections 32 are integrally formed so as to protrude axially from the lower face of the annular body 24. The holding contours 30 are arranged so as to be distributed uniformly along the outer circumference of the annular body 24. The fastening projections 32 are arranged so as to be distributed along the inner circumference, wherein the fastening projections 32, in particular, are integrally formed, i.e. in one piece or monolithically, in the region of one respective radially internal tooth end of the tooth projections 28.
As can be identified, for example, in the view of
For reducing the moment of inertia of the rotor 2, the rotor core 6 is provided with ten recesses 34 penetrating the lamination core. The recesses 34 are arranged so as to be distributed uniformly around the central through-opening 10 in the tangential direction T. The recesses 34 are provided with reference signs merely by way of example in the figures.
As is visible in particular in
The holding contours 30, which are arranged radially externally in the radial direction R, have an approximately trapezoidal cross-sectional shape in the axial direction. The bottom sides of the cross-sectional shape are oriented in the tangential direction T. The radially internal bottom side has a shorter dimension in comparison with the radially external bottom side. The leg sides running between the bottom sides run obliquely to the tangential direction T and obliquely to the radial direction R.
As is visible in particular in
As is visible relatively clearly in the plan view of
For protecting the surface magnets 16 against slipping, a sleeve-like protective cover 36 is positioned on the outer circumference of the rotor body 4. The protective cover 36 is preferably produced from a steel, in particular a stainless steel. In other words, the protective cover 36 is, in particular, a stainless steel cover.
A method for producing the rotor 2, in particular for fastening the protective cover 36 to the rotor body 4, by means of a device not shown in more detail is explained in more detail hereinafter by way of
In a first method step, the rotor body 4 is inserted into the protective cover 36. The protective cover 36 on the end face facing the rotor body 4, for example, has a chamfer 38 (
As is visible in particular in
After the insertion of the rotor core 4 into the protective cover 36, the chamfer 38 is bent or straightened radially inwardly by means of a (first) punch 43 shown in
In the next method step, a flange collar 44 (crimped edge) is shaped on the end face of the protective cover 36. The flange collar 44 is an axial portion of the protective cover 36 on the end face which, for example, encompasses therewith the straightened chamfer 38. The flange collar 44, which has not been shaped, protrudes at least partially axially over the inserted rotor body 4. In the views of
After the rotor body 4 has been inserted into the protective cover 36, the flange collar 44 is shaped, press-fitted or crimped into the radially indented regions 42 between the curvatures 40 in a positive and/or non-positive manner. This means that the assembly forces for joining the protective cover 36 to the rotor body 4 are introduced into the intermediate regions in a targeted manner. In other words, the free spaces or free surfaces formed between the flanks of the curvatures 40 are used as points of attack for a shaping tool. This means that the surface of the protective cover 36 in the regions 42 is radially inwardly deformed or crimped radially inwardly as local press-fitted surfaces.
For shaping the flange collar 44, the device has a crown tool 46 as a shaping punch. The crown tool 46 of the device, shown separately in
The bolt-shaped or cylindrical projection is inserted, for example, as a pin or journal into the recess 52. Alternatively, the projection can also be integrally formed in one piece on the tool body 48. The diameter of the projection is slightly smaller than the internal diameter of the through-opening 10.
The crown ring 50 has ten crown projections or castellation-shaped projections 54 which are arranged so as to be distributed over the circumference. The castellation-shaped projections 54 have in each case a radially inwardly oriented shaping lug 56. The shaping lug 56 has an axially inclined ramp as a shaping contour for the flange collar 44.
For the shaping, the crown tool 46 is lowered in the manner of a punch in the direction of the end face 22a from above the rotor body 4 provided with the protective cover 36. The projection engages in the through-opening 10 so that the rotor body 4 and the crown tool 46 are centered and oriented so as to be axially aligned with one another. When the crown tool 46 is lowered, the flange collar 44 is shaped, press-fitted or crimped by means of the shaping lugs 56 into the regions 42.
The upper edge of the flange collar 44 is crimped radially inwardly into the regions 42 by the crown tool 46, so that the holding ring 20—and thus the rotor body 4—in the regions 42 is axially encompassed at least in some portions by the flange collar 44.
For reducing the spacings 58, in a third method step the flange collar 44 is thus axially and radially pressed against the rotor body 4 or the holding ring 20 by means of a (second) punch 59 shown in
By the (second) punch 43 the material of the protective cover 36 in the region of the flange collar 44 is pressed from outside onto the rotor body 4 so that the spacings 58 are substantially shaped to zero. In other words, the protective cover 36 or the flange collar 44 nestles against the curvatures 40 on the outer circumferential side. The protective cover 36 thus encompasses in the region of the flange collar 44 the outer contour of the rotor body 4 in a radially and tangentially positive manner.
According to the method, therefore, the space between the surface magnets 16 is used for the targeted introduction of the assembly forces. Since the holding ring 20 is radially slightly smaller than the outer circumference of the rotor body 4, and at this point no surface magnet 16 is located in the axial direction, the material of the protective cover 36 is forced both radially and axially into the free regions 42 during the shaping by the crown tool 46, which leads to a smaller bulk of the material in the radial direction. In particular, the material is forced axially downwardly, i.e. in the direction of the end face 22b, into the free region, whereby a radial bulk of the material is reduced. The bulky material in these regions 42 does not negatively affect the electric motor or the air gap, since the spacing toward the stator in these regions 42 is substantially greater than in the region of the curvatures 40. According to the method, a targeted radial bulking of the protective cover 36 is brought about or taken into consideration merely in the regions 42 at which the radial spacing to the stator is greater.
The claimed invention is not limited to the above-described embodiments. Rather, other variants of the invention can be derived therefrom by a person skilled in the art within the context of the disclosed claims, without departing from the subject of the claimed invention. In particular, all of the individual features described in connection with the various exemplary embodiments can be combined together in different ways within the scope of the disclosed claims, without departing from the subject of the claimed invention.
Thus the crown tool 46, for example, is also inventive per se and thus represents an invention in its own right.
The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2021 205 178.2 | May 2021 | DE | national |
| 10 2021 209 396.5 | Aug 2021 | DE | national |
This application is a continuation, under 35 U.S.C. § 120, of copending International Patent Application PCT/EP2022/063528, filed May 19, 2022, which designated the United States; this application also claims the priority, under 35 U.S.C. § 119, of German Patent Applications DE 10 2021 205 178.2, filed May 20, 2021, DE 10 2021 209 396.5, filed Aug. 26, 2021; the prior applications are herewith incorporated by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2022/063528 | May 2022 | US |
| Child | 18452837 | US |
