Patent Application
20240275226
This application claims priority to European Patent Application No. 23155820.6 filed on Feb. 9, 2023, the contents of which are hereby incorporated by reference in its entirety.
The invention relates to a permanent magnet rotor.
The invention furthermore relates to a method for manufacturing a permanent magnet rotor.
A known prior art permanent magnet rotor is disclosed in US2010133927A1. The rotor is an external rotor comprising an annular side wall, an end cover directly connected to said annular side wall and a cavity formed between said side wall and said end cover. A plurality of openings are formed in the side wall and a plurality of magnetic tiles are received in the openings. A magnetic yoke shell is also disposed against said side wall, wherein said side wall and said end cover are integrally formed by injection molding.
The permanent magnet rotor according to the invention as defined in claim 1 has the advantage of providing an improved fixing of the magnets to the rotor, or at least provides an alternative to known fixing arrangements or methods.
This object is achieved according to a first aspect of the invention with a permanent magnet rotor for a motor, the rotor comprising a generally cylindrical outer section and a bearing section arranged radially inwards of the generally cylindrical outer section for rotatably supporting the rotor, wherein the generally cylindrical outer section and the bearing section are connected by a generally radially extending cover wall, wherein the generally cylindrical outer section, the bearing section and the generally radially extending cover wall define at least partly a space for receiving a stator, the generally cylindrical outer section comprising: an annular ring made out of a magnetic material, a plurality of annularly disposed magnets arranged radially inwards of said annular ring and an inner wall arranged radially inwards of said magnets and having a substantially cylindrical inner surface, wherein each magnet has a first and a second end in the circumferential direction and is provided with a radially inwards facing surface having a central section and first and second tapered end sections in the circumferential direction, wherein the thickness of the inner wall is substantially constant in the central section and increases in the first and second end sections towards the first and second ends of the magnet respectively, wherein the inner wall is formed by overmolding the plurality of magnets with a polymer material.
The magnets are thus fixed to the annular ring via the overmolding of the polymer material.
The substantially cylindrical inner surface of the inner wall may contain grooves or recesses formed during molding due to the tooling pins holding the magnets against the annular ring.
The terms “circumferential” and “radial” are used in relation to a rotation axis of the rotor.
The annular ring can be made for example out of steel forming a magnetic yoke.
Due to the shape of the magnets with tapered end sections, the magnets can be fixed to the annular ring without the use of adhesive, as the overmolding polymer material can flow over the magnets to cover the entire inner surface of the generally cylindrical outer section. The tapered sections of the magnets facilitate the flow of the overmolding polymer material to the center section of the magnets, thus reducing the necessary thickness of the polymer material covering the magnets and in turn reducing the weight of the rotor.
The overmolding polymer can in one embodiment completely enclose the magnets and the annular ring in order to protect these parts from contact with unwanted elements.
The central section of the magnet extends over at least 40% of the magnet in the circumferential direction. The first and/or second tapered end section extends over at least 10% of the magnet in the circumferential direction. This ratio of tapered end section to non-tapered central section has been found to provide, when overmolded with the polymer material, a sufficient fixing of the magnet to the annular ring whilst enabling the covering of the entire magnet surface with a thin layer of polymer in order to reduce weight and minimizing the gap between the magnets and the stator.
The bearing section has a central opening for receiving a rotationally fixed shaft. The bearing section can be supported on the fixed shaft by two axially spaced rolling element bearings.
In one embodiment the bearing section comprises a bearing sleeve made out of metal for receiving an outer bearing race for one of the rolling element bearings. The bearing sleeve can have a profiled radial outer surface. The bearing section can additionally or alternatively comprise an outer bearing race of one of the rolling-element bearings.
Advantageously, the annular ring, the magnets and at least one of the bearing sleeve or the outer bearing race are overmolded in one step by a polymer, whereby the generally radially extending cover wall is formed out of the polymer in the same step. By overmolding the magnets and the bearing parts in one step to form the rotor, additional assembly steps e.g. fixing the magnets to the annular ring with adhesive and attaching bearing parts can be eliminated.
In the same molding step a plurality of metallic threaded inserts for attaching a fan can be provided in the radially extending cover wall such that the threaded inserts are fixed in the cover wall by overmolding.
Alternatively the annular ring made out of a magnetic material, preferably steel, can be provided with threaded attachment points for attaching a fan.
In another aspect a cooling fan motor is provided comprising a stator having a stack of steel laminations and a plurality of winding coils arranged in circumferentially spaced slots in the steel laminations and a permanent magnet rotor according to any of the above embodiments of the invention.
A cooling fan is attached to the radially extending cover wall via the threaded inserts molded into the radially extending cover wall.
In a further aspect of the invention, a method for manufacturing a permanent magnet rotor is provided, the permanent magnet rotor comprising a generally cylindrical outer section and a bearing section arranged radially inwards of the generally cylindrical outer section, whereby the generally cylindrical outer section and the bearing section are connected by a generally radially extending cover wall, the generally cylindrical outer section, the bearing section and the generally radially extending cover wall defining at least partly a space for receiving a stator, the method comprising the steps of:
In one embodiment, before the overmolding step d), a plurality of metallic threaded inserts for attaching a fan are positioned in the molding tooling such that they are fixed in the radially extending cover wall formed in the overmolding step d). Preferably at least three of such threaded inserts are positioned in the molding tooling.
In another embodiment, before the overmolding step d) an outer bearing race is positioned in the molding tooling such that it is overmolded by the polymer material in the overmolding step d).
By incorporating the metallic threaded inserts and/or the bearing outer race in the overmolding step d) the assembly steps of the rotor with fan are reduced. For example, press-fitting of bearing parts can be avoided.
The generally radially extending cover wall can be advantageously formed without metallic reinforcement. This is achieved by increasing the thickness of the cover wall and/or providing the cover wall with reinforcing ribs. In one embodiment the reinforcing ribs extend radially from the central opening in the cover wall to each of the plurality of metallic threaded inserts.
The features of the magnets described with respect to the rotor according to the invention can apply equally to the magnets used in the above method.
Embodiments will now be described by way of example only with reference to the accompanying drawings, in which:
A shaft 9 is fixedly attached to control unit housing 7 or is integrally formed therewith. The permanent magnet rotor 2 is arranged to rotate around the shaft 9. For this purpose two rolling bearings 10, 11 are arranged at opposite axial ends of the rotor 7.
The permanent magnet rotor 2 comprises a generally cylindrical outer section 12 and a bearing section 13 arranged radially inwards of the generally cylindrical outer section for rotatably supporting the rotor 2. The generally cylindrical outer section 12 and the bearing section 13 are connected by a generally radially extending cover wall 14, which is arranged on a second side of the stator 3 in the axial direction 8 opposite to the control unit 4. The generally cylindrical outer section 12, the bearing section 13 and the generally radially extending cover wall 14 define at least partly a space 15 for receiving the stator 3, such that the stator 3 is arranged radially between the generally cylindrical outer section 12 and the bearing section 13. The bearing section 13 has a central opening 31 for receiving the shaft 9, such that the rotor 2 is supported in the shaft via the two rolling bearings 10, 11.
The generally cylindrical outer section 12 of the rotor 2 comprises an annular ring 16 made out of a magnetic material, e.g. steel, and a plurality of annularly disposed magnets 17 arranged radially inwards of said annular ring 16, preferably contacting the annular ring 16. An inner wall 18 of the cylindrical outer section 12 is arranged radially inwards of said magnets 17.
As can be seen in
Referring to
The thickness of the inner wall 18 is substantially constant in the area of the central section 22 of the magnets 17 and increases in the area of the first and second tapered end sections 23 of the magnets 17 towards the first and second ends of the magnets 17 respectively.
The inner wall 18 may contain grooves or recesses 28 formed during molding due to the tooling pins holding the magnets 17 against the annular ring 16.
The shape of the magnets 17 with tapered end sections 23 enable the magnets 17 to be fixed to the annular ring 16 without the use of adhesive, as the overmolding polymer material can flow over the magnets 17 to cover the entire inner surface of the generally cylindrical outer section. The tapered sections 23 of the magnets facilitate the flow of the overmolding polymer material to the center section of the magnets, thus reducing the necessary thickness of the polymer material covering the magnets and in turn reducing the weight of the rotor 2.
As shown in
The generally radially extending cover wall 14 is advantageously formed out of the polymer material without metallic reinforcement. This is achieved by increasing the thickness of the cover wall 14 and/or providing the cover wall with reinforcing ribs 30. In the embodiment shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 23155820.6 | Feb 2023 | EP | regional |
