DE102011089488A1 - Rotor for an electric machine with magnets fixed by thermoplastic material and corresponding production method - Google Patents

Abstract

A rotor for an electric machine and a method for producing such a rotor will be described. The rotor (15) has a rotor body (9) with a plurality of recesses (5) and a plurality of magnets (7) received in the recesses (5) of the rotor body (9). The magnets (7) are at least partially surrounded by a thermoplastic material and fixed by this in the recesses (5). Compared to conventional thermosetting adhesives thermoplastic materials allow a simpler, positive locking of the magnets (7) in the rotor body (9). In the thermoplastic material (13) may be embedded magnetic or magnetizable particles, so that with the thermoplastic material (13) filled gap (11) between the magnets (7) and the walls of the recesses (5) to the entire, of the rotor generated magnetic field can contribute.

Description

Field of the invention

The present invention relates to a rotor for an electric machine and a method for manufacturing such a rotor.

State of the art

Electric machines are often used, for example in the form of synchronous machines as motors or generators in electric or hybrid drives for motor vehicles. In this case, the electric machine has a stationary stator and a rotor, which can be rotated about an axis of rotation relative to this stator.

The rotor has a generally substantially cylindrical rotor body. The rotor body is usually made of a magnetizable material, e.g. made of a metal such as iron or an iron-containing alloy. Frequently, the rotor body is composed of a plurality of circular plates which form fins of the rotor body.

In the vicinity of the lateral surface of the rotor body a plurality of recesses are provided. In these recesses permanent magnets can be inserted during assembly of the rotor, which generate the necessary for the operation of the rotor in the electric machine magnetic field. Alternatively, bodies of nonmagnetic but magnetizable material may be introduced into the recesses and subsequently magnetized. Subsequently, the term "magnet" is used as a generic term for both permanent magnetic material and for subsequently magnetizable material.

To be able to introduce the magnets or the magnetizable body in the recesses in the rotor body, they are generally designed to be slightly smaller than the recesses, so that there is a small clearance each between a magnet and walls of the recess. During operation of the electric machine, high forces can act on the rotor and the magnets received therein. In order to prevent the magnets from shifting undesirably within the recesses, the magnets must be fixed in relation to the rotor body.

Conventionally, the magnets are fixed, for example by means of thermosetting adhesives within the recesses. DE 10 2009 054584 A1 describes such a rotor for an electric machine.

However, it has been observed that the bonding of the magnets with the aid of thermosetting adhesives can be disadvantageous with regard to the processing outlay and with regard to the processing time.

Disclosure of the invention

The invention proposed herein makes possible in its embodiments a simplified manufacture of a rotor for an electric machine with simultaneous reliable fixing of the magnets in the rotor body.

It is proposed according to embodiments of the invention, at least partially surround the magnets received in the recesses of the rotor body with a thermoplastic material to fix them in this way in the recesses.

When manufacturing the rotor, the magnets arranged in the recesses of the rotor body can be fixed in the recesses by injecting a thermoplastic material.

An insight or idea on which these embodiments of the invention are based can be seen in that it has been observed that in the conventional gluing of magnets into the rotor body considerable processing effort must be operated. The thermoset material used for bonding generally needs to be maintained at an elevated temperature during a curing phase. This hardening phase can take between ten and 60 minutes. The need to heat the rotor body during this curing phase and wait for the adhesive to cure has been found to make it difficult for large scale production.

It has therefore been recognized that fixing the magnets within the recesses can be made better with the aid of thermoplastic materials. Thermoplastic materials are typically plastics that can be deformed in a certain temperature range at elevated temperatures, for example, more than 220 ° C. This process is reversible, that is, it can be repeated as often as desired by cooling and reheating to the molten state, unless thermal deterioration of the material occurs, for example, as a result of overheating.

The thermoplastic material can be liquefied during the manufacturing process by heating to suitable temperatures and introduced into the recesses of the rotor body, for example by injection molding to There to surround the magnets and fix them in this way in the recesses. Upon cooling of the thermoplastic material hardens this. Although the thermoplastic material usually due to poor adhesion capabilities with the material of the magnet does not allow permanent cohesive bonding of the magnets in the recesses of the rotor body, there is a positive fixing of the magnets within the recesses.

Thermoplastic materials are generally composed of little or no branched, ie linear carbon chains which are interconnected only by weak physical bonds. Due to these weak bonds thermoplastic materials can be reversibly brought into a flowable state by heating. In this flowable state thermoplastic materials can be advantageously processed in the so-called injection molding process. Even in a thermoplastic state, in which the material is not yet heated so much that it is flowable, but already soft and no longer dimensionally stable, the thermoplastic material can be processed forming. Before heating or after cooling, the thermoplastic material is solid. However, the thermoplastic material does not have to be stiff in this state, but may have some elasticity or flexibility.

Typical thermoplastic materials are e.g. Acrylonitrile butadine styrene (ABS), polyamides (PA), polyphthalamides (PPA), polyphenylene sulfide (PPS), polylactate (PLA), polymethyl methacrylate (PMMA), polycarbonate (PC), polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polystyrene (PS), polyetheretherketone (PEEK) and polyvinyl chloride (PVC). Polyamides, polyphthalamides, polyphenylene sulfide and polyetheretherketone are particularly suitable in terms of temperature requirements of 140 ° C to 200 ° C due to their temperature resistance, the temperature resistance and cost of the specified materials increase in the order given.

The thermoplastic material may also be formed as a thermoplastic elastomer.

Thermoplastic elastomers (TPE) are typically plastics that behave at room temperature comparable to the classic elastomers, but can be plastically deformed under heat and thus have a thermoplastic behavior. In conventional elastomers, space network molecules are usually cross-linked chemically and the crosslinks can not be dissolved without decomposing the material. In thermoplastic elastomers elastic polymer chains are typically incorporated into thermoplastic material. Therefore, such materials can be processed by purely physical processes through a combination of high shear forces, heat input and subsequent cooling. The thermoplastic elastomers may have rubber-elastic properties, although no chemical crosslinking is carried out by time-consuming and temperature-intensive vulcanization. A renewed heating can again lead to a melting and thus the possibility of plastic deformation of the material. Thermoplastic elastomers can thus be processed by injection molding. From the group of thermoplastic elastomers, e.g. thermoplastic polyester elastomers (TPC) due to the temperature resistance up to 160 ° C especially.

The thermoplastic material may contain magnetic or magnetizable particles.

The thermoplastic material used to fix the magnets can thus contribute to the magnetic field generated by the rotor due to the magnetic particles contained therein.

The thermoplastic material may have a proportion of magnetic or magnetizable particles in the range of 10-90 vol% (volume percent), preferably in the range of 20% -70 vol%. The higher the proportion of magnetic or magnetizable particles, the stronger the magnetic field generated by the thermoplastic material can be. On the other hand, a high proportion of particles can lead to reduced flowability during the injection of the thermoplastic material during manufacture of the rotor.

The magnetic or magnetizable particles can in principle consist of any ferromagnetic or magnetizable materials. For example, the particles may be provided as a fine metal powder, for example as iron, ferrite and / or NdFeB powder. The particles may be homogeneously distributed within the thermoplastic material.

According to one embodiment of the invention, each of the magnets used for the rotor made entirely of a permanent magnetic material and fills an associated recess in the rotor body or in one or more of the fins of the rotor body except for an adjacent gap. This necessary for an introduction of the magnet into the recess gap is filled to fix the magnet with the thermoplastic material. The thermoplastic material thus adjoins the magnet and can partially or completely surround it and thus fix it in a form-fitting manner in the recess after curing of the thermoplastic material.

Since the thermoplastic material itself is generally not magnetic, similar to previously used thermoset adhesives, the gap filled with the thermoplastic material initially acts as an air gap, thus reducing the magnetic field caused by the rotor. However, if the thermoplastic material is mixed with magnetic or magnetisable particles, the mixture of thermoplastic material and magnetic particles provided in the gap can also contribute to the overall magnetic field of the rotor.

In this embodiment, the gap, i. a clearance between the magnet and the wall of the recess, be dimensioned larger than conventional rotors, without this would be accompanied by excessive deterioration of the magnetic properties of the rotor. This makes it easier to assemble the rotor with regard to introducing the magnets into the rotor body.

In an alternative embodiment of the invention, thermoplastic material mixed with permanent magnetic particles can completely fill a recess in the rotor body.

According to this embodiment can be dispensed with bulky, expensive permanent magnets in the rotor body. Instead, the magnets received in the recesses are formed by permanent magnetic particles contained in the thermoplastic material.

The recesses in the rotor body can be filled in such an embodiment simply by injection molding with the thermoplastic material. Although the thermoplastic material added with permanent magnetic particles will generally produce a lower magnetic field than a single solid permanent magnet, such a rotor electrical machine design may be of particular interest in applications where lower power requirements exist because of its simplified manufacturing capability.

It should be understood that possible features and advantages of embodiments of the invention will be described herein in part with reference to a rotor for an electric machine and partially with respect to a method of manufacturing such a rotor. One skilled in the art will recognize that the various features may be suitably combined or interchanged with each other and, in particular, may also be transferred from the rotor to the manufacturing process and vice versa in order to arrive at further embodiments and possibly synergy effects.

Brief description of the drawings

Hereinafter, embodiments of the present invention will be described with reference to the drawings, wherein neither the drawings nor the description are to be construed as limiting the invention.

1 shows a perspective view of a rotor according to the invention during assembly;

2 shows a partial plan view of a rotor according to the invention.

The drawings are only schematic and not to scale.

Embodiments of the invention

1 shows a rotor body 9 a rotor 15 for an electric machine. The rotor body 9 consists of several disc packs 1 together, in turn, of a plurality of stacked lamellae 3 be formed in the form of thin stamped metal sheets.

In each of the slats 3 are provided in the area near the outer periphery substantially rectangular cutouts. The stacked lamellae 3 form by the aligned arranged punched holes recesses 5 inside the rotor body 9 ,

In the recesses 5 be cuboid permanent magnets recorded. Alternatively, cuboidal bodies of magnetizable material in the recesses 5 be introduced and subsequently magnetized. The cuboid magnets 7 have a geometry that is substantially equal to the geometry of the recesses 5 is, where the magnets 7 are slightly smaller than the recesses 5 to bring in the magnets 7 in the recesses 5 due to a sufficient lateral clearance jamming or tilting of the magnets 7 in the recesses 5 to avoid.

As in the simplified partial view from above 2 can be seen, forms due to the compared to the recesses 5 smaller dimensions of the magnets 7 adjacent to the magnets 7 A gap 11 , In this gap 11 becomes a thermoplastic material during manufacture of the rotor 13 injected and filled this gap in this way. The thermoplastic material 13 is heated to an elevated temperature in order to to bring it into a liquid or at least plastically deformable state. Too rapid cooling of the thermoplastic material 13 when injecting into the recesses 5 The rotor body can also be avoided 9 to be preheated. By subsequent cooling, the thermoplastic material solidifies 13 and thereby fixes the adjacent magnet 7 positively in the recess 5 ,

To the thermoplastic material 13 also give magnetic properties and thus prevent the gap 11 magnetically acts as an air gap, the thermoplastic material 13 magnetic or magnetizable particles are mixed, for example in the form of an iron powder. The size of the particles and their volume fraction in the thermoplastic material can be adapted to the magnetic properties to be achieved and / or rheological. For example, particle sizes of 5 .mu.m to 50 .mu.m and volume fractions in the range of 20% to 70% can be used. Instead of iron, other ferromagnetic or magnetizable materials can be used for the particles.

In an alternative embodiment (not shown in the drawing) is dispensed with the use of one-piece permanent magnets or one-piece body made of magnetizable material. Instead, the entire recess 5 filled with a thermoplastic material, which can serve as a magnet itself after curing due to the embedded therein magnetic or magnetizable particles. Although the magnetic field strength that can be generated by such a thermoplastic material will generally be lower than is the case with one-piece permanent magnet bodies, the reduced manufacturing outlay can be the formation of injectable magnets that are injection-molded into the recesses 5 be justified.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102009054584 A1 [0006]

Claims (10)

Rotor ( 15 ) for an electric machine, comprising: a rotor body ( 9 ) with a plurality of recesses ( 5 ); a plurality of magnets ( 7 ) in the recesses ( 5 ) of the rotor body ( 9 ) are included; characterized in that the magnets ( 7 ) at least partially of a thermoplastic material ( 13 ) are surrounded and by this in the recesses ( 5 ) are fixed. Rotor according to claim 1, wherein the thermoplastic material ( 13 ) is a thermoplastic elastomer. Rotor according to one of claims 1 or 2, wherein the thermoplastic material ( 13 ) contains magnetic or magnetizable particles. Rotor according to claim 3, wherein the thermoplastic material ( 13 ) contains between 10 and 90% by volume of magnetic or magnetisable particles. Rotor according to one of claims 1 to 4, wherein each of the magnets ( 7 ) completely made of permanent magnetic material and an associated recess ( 5 ) except for an adjacent gap ( 11 ) and where the gap ( 11 ) with the thermoplastic material ( 13 ) is filled out. Rotor according to one of claims 3 or 4, wherein thermoplastic material mixed with permanent magnetic particles ( 13 ) a recess ( 5 ) in the rotor body ( 9 ) completely. Method for producing a rotor ( 15 ) according to one of claims 1 to 6, comprising: providing a rotor body ( 9 ) with a plurality of recesses ( 5 ); Arranging and fixing a plurality of magnets ( 7 ) in the recesses ( 5 ) of the rotor body ( 9 ); characterized in that the magnets ( 7 ) by injecting a thermoplastic material ( 13 ) in the recesses ( 5 ) of the rotor body ( 9 ) are fixed. The method of claim 7, wherein each of the magnets ( 7 ) completely made of permanent magnetic material and an associated recess ( 5 ) except for an adjacent gap ( 11 ) and where the gap ( 11 ) by injecting the thermoplastic material ( 13 ) in the gap ( 11 ) is completed. Method according to claim 7, wherein a recess ( 5 ) in the rotor body completely with magnetic particles mixed with thermoplastic material ( 13 ). Electric machine (10) comprising: a stator, a rotor rotatable about a rotation axis relative to the stator ( 15 ) characterized in that the rotor ( 15 ) as a rotor ( 15 ) is formed according to one of claims 1 to 6.

Images