Rotor for a synchronous motor

A rotor for a synchronous motor includes teeth arranged at regular intervals, project from a rotor core in the radial direction, and taper in a cross-section in the direction of the rotor core. The rotor also includes tangentially magnetized magnets that are arranged in gaps between the teeth and are trapezoidal in cross-section. The teeth are connected via a flexible joint to the rotor core, and the teeth are deflected in the tangential direction such that in every other gap between two teeth, first magnets rest against outer stops at the ends of the teeth facing away from the rotor core.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to Application No. 16181819.0, filed in the European Patent Office on Jul. 29, 2016, which is expressly incorporated herein in its entirety by reference thereto.

FIELD OF THE INVENTION

The present invention relates to a rotor for a synchronous motor, e.g., having magnets that are tangentially magnetized and arranged in gaps between teeth of the rotor. This placement is meant to concentrate the flux because each tooth is thereby magnetized by its two adjacent magnets.

BACKGROUND INFORMATION

In the case of a rotor of a synchronous motor, it is described in European Published Patent Application No. 2 696 469 to place tangentially magnetized magnets having a trapezoidal cross-section between teeth of the rotor that taper in the direction of the center of the rotor. The interspaces or gaps situated between the teeth and widening toward the center of the rotor are substantially filled by the magnets having a trapezoidal cross-section.

Due to the tangential magnetization of the magnets, the teeth act as magnetic poles vis-à-vis the stator. Via the two teeth surrounding a magnet, the flux of the magnets is virtually completely direction to the air gap between the stator and rotor. In contrast, in an also common radial magnetization of the magnets, only a portion of the flux is directed to the air gap while another portion is merely directed by a magnetic yoke within the rotor to the adjacent magnet.

One problem in the production of such a system and similar systems by which the magnetic flux from the rotor to the stator is able to be maximized relates to the production-related tolerances of the shape of the magnets. While these tolerances do not cause any problems in the case of radially magnetized magnets that are bonded to the rotor, these tolerances may lead to problems with tangentially magnetized magnets that are inserted between teeth of the rotor. The gaps between the teeth must also be able to accommodate magnets at the upper end of the tolerance range, meaning that gaps between the magnets and the teeth may occur with the magnets that happen to have smaller shapes. Such gaps may have the result that the magnets do not sit in the rotor with the required stability and may detach during the operation. The symmetry of the rotor may also be lost, thereby creating considerable additional cogging forces, which, for example, interfere with the precise positioning with the aid of such a motor.

SUMMARY

Example embodiments of the present invention provide a rotor for a synchronous motor as well as a method for its production, which allow for a symmetrical and stable placement of the magnets in the rotor despite production-related tolerances in the shape of the magnets.

According to an example embodiment of the present invention, a rotor for a synchronous motor includes teeth that are disposed at regular intervals, project from a rotor core in the radial direction, and taper in cross-section in the direction of the rotor core. In addition, the rotor has tangentially magnetized magnets that are trapezoidal in cross-section and are situated in gaps between these teeth. An important feature of the rotor is that the teeth are connected to the rotor core via a flexible joint and that the teeth are deflected in the tangential direction such that in every other gap between two teeth, first magnets are resting against outer stops at the ends of the teeth facing away from the rotor core.

If the first magnets are inserted first during the production of this rotor, then the prevailing reluctance forces drive these magnets as far away as possible from the rotor core towards the ends of the teeth, where they finally come to rest against the outer stops provided there. Even magnets whose dimensions are at the upper margin of the specification do reach this position because the teeth are able to be deflected in the tangential direction due to the flexible joints, thereby creating sufficient room even for the larger magnets. When the remaining magnets are inserted in the following step, less room is available for these magnets, and the teeth can also no longer be pressed tangentially toward the side. The remaining magnets are thus pressed outwardly only up to a position in which their slanted sidewalls enter into a positive engagement with the tapering sidewalls of the teeth.

As a result, a rotor is obtained in which, despite a certain variance in the dimensions of the magnets, each magnet is stably retained in its respective position in the tangential direction by its adjacent teeth. Furthermore, the field lines of each magnet are not required to overcome an air gap toward the side teeth.

It may be provided that remaining second magnets are retained closer to the rotor core than the first magnets by a positive engagement with lateral surfaces of the teeth.

It may further be provided that the magnets are divided into two parts. For example, each magnet may be divided into an outer magnet piece, having a trapezoidal cross-section, and an inner magnet piece, e.g., having a trapezoidal or rectangular cross-section.

The inner magnet pieces may rest against inner stops premolded on the rotor core between the teeth, so that all inner magnet pieces are located at a same distance from the rotor core.

A first gap may be located between the outer magnet piece and the inner magnet piece of each first magnet, and either (a) a second gap, smaller than the first gap, may be located between the outer magnet piece and the inner magnet piece of remaining second magnets or (b) no gap may be located between the outer magnetic piece and the inner magnetic piece of the remaining second magnets.

The rotor may be arranged as a secondary part of a rotary or linear synchronous motor, e.g., a segment of a rotary rotor having an infinite radius.

The rotor may be produced by inserting all outer magnet pieces of the first magnets into every other gap between the teeth, and tangentially deflecting the teeth adjacent to the first magnets so that the inserted outer magnet pieces rest against the outer stops.

The method of producing the rotor may further include inserting inner magnet pieces, and pushing the inner magnet pieces toward the rotor core by magnetic repulsion of a respective outer magnet piece so that the inner magnet pieces rest against inner stops provided on the rotor core.

The method may also include inserting outer magnet pieces of remaining second magnets into empty gaps between the teeth, the outer magnet pieces of the remaining second magnets moving away from the rotor core so that the remaining second magnets are retained a positive engagement with lateral surfaces of the teeth.

DETAILED DESCRIPTION

FIGS. 1 and 2illustrate a segment of a rotor1according to an example embodiment, of the present invention.FIG. 1is an exploded view of rotor1, from which the method for its production can be understood.FIG. 2is a cross-sectional view through rotor1, in which the rotor axis is situated perpendicular to the drawing plane.

Disposed on a rotor core1.1facing the center of rotor1are outwardly projecting teeth1.2, which are connected via a weakened spot acting as flexible joint1.3to rotor core1.1in each case. A flexible joint1.3having the thinnest possible configuration also provides the advantage that minimal magnetic flux reaches the rotor core where it would not be able to contribute to the torque of the motor.

Furthermore, teeth1.2have at their outwardly directed ends, i.e., the ends facing away from rotor core1.1, outer stops1.4for first magnets2a. In addition, outwardly projecting inner stops1.5are provided on rotor core1.1, which are arranged as projections on rotor core1.1in the gaps between teeth1.2.

Rotor1may be arranged in the form of a laminated core. The shape of an individual sheet is evident fromFIG. 2. Magnets2a,2bhave a symmetrical trapezoidal shape in cross-section, or in other words, they taper outwardly in their cross-sections, i.e., are broader toward rotor core1.1than on the side facing away from rotor core1.1.

The shape of magnets2a,2bgenerally corresponds to the shape of the gaps between teeth1.2because the teeth widen in the direction of rotor core1.1. The side surfaces of teeth1.2and magnets2a,2bthat are in contact with one another are inclined at the same angle relative to the radial direction.

Magnets2a,2bmay be divided, e.g., into a respective outer magnet piece2.1and an inner magnet piece2.2. The two magnet pieces2.1,2.2are subdivided such that at least outer magnet piece2.1has a symmetrical trapezoidal form in cross-section. This may also apply to inner magnet piece2.2, which, however, may also have other shapes, such as a cuboidal shape, which is rectangular in cross-section.

As illustrated inFIG. 2, first magnets2a, which fill every other gap between teeth1.2, are located at a slightly greater distance from rotor core1.1, and are resting against outer stops1.4of teeth1.2. In contrast, remaining magnets2bare located slightly lower or closer to rotor core1.1. They do not reach outer stops1.4. A positive fit between the lateral boundaries of teeth1.2and remaining magnets2bprevents magnets2bfrom moving farther toward the outside.

The divided arrangement of magnets2a,2bprovides the result that, as described above, outer magnet pieces2.1are alternately positioned farther away or closer to rotor core1.1. Because of the magnetic repulsion between the inner and outer magnet pieces2.1,2.2, which are magnetized in pairs having the same orientation in each case, inner magnet pieces2.2are pressed completely toward the inside until they come to rest against inner stop1.5of rotor core1.1. This results in a gap2.3between the two magnet pieces2.1,2.2that has a different width in the radial direction. It is greater in the case of first magnets2athan for remaining magnets2b, where it may also vanish in the extreme case so that magnet pieces2.1,2.2are in direct contact with each other. This is the case if the dimensions of involved magnets2a,2bor magnet pieces2.1,2.2are at the upper end of the specification.

The creation of this system of magnets2a,2band/or of their magnet pieces2.1,2.2becomes clear when considering the method for producing rotor1. This method is explained with reference toFIG. 1.

In a first step S1, outer magnet pieces2.1of first magnets2aare slipped into every other gap between teeth1.2in rotor1. They are pressed up to outer stops1.4by reluctance forces. Since teeth1.2are tangentially or laterally deflectable due to flexible joints1.3, the gaps are able to also accommodate first magnets2athat are at the Upper end of the specification or production variances with regard to their dimensions.

In another, e.g., second, step S2, all inner magnet pieces2.2are then slipped into rotor1, these magnets remaining in the inner position through a direct repulsion or through reluctance forces.

In another, e.g., third, step S3, outer magnet pieces2.1of remaining magnets2bare slipped into the gaps that still remain free. Because of teeth1.2that were already tangentially deflected by outer magnet pieces2.1of first magnets2a, they are unable to fully reach outer stops1.4and thus are located slightly closer to rotor core1.1and are radially repelled by inner magnet pieces2.2. In the process, inner magnet pieces2.2are pushed towards rotor core1.1or against inner stops1.5.

The second and third steps S2and S3may also be switched in a variation of the method.

The arrangement of teeth1.2and magnets2a,2bthus has the result that magnets2a,2balways assume a particularly defined position regardless of a certain production variance of their dimensions. At most, minor fluctuations remain in the radial position of remaining magnets2b(or of their outer magnet piece2.1), so that a highly symmetrical rotor results as a whole, whose magnets assume defined and thus stable positions. Rotor1has an even number of magnets2a,2b.

The fluctuations in the dimension of magnets2a,2bare compensated by adapting the radial position of the neighboring magnets and are unable to add up across multiple magnets, which could lead to a considerable asymmetry and loosely sitting magnets. In other words, tolerances in the dimensions of the magnets are compensated for in an uncomplicated manner.

This compensating effect is able to be achieved even if magnets2a,2bare not split into two parts as illustrated. However, magnets2a,2bmay also be divided into three or more pieces or be made up of a single, trapezoidal magnet piece.

For motors that are to rotate particularly quickly, inner magnet pieces2.2and/or remaining magnets2bmay also be omitted. For reasons of stability, the omitted elements may be replaced by correspondingly shaped placeholders made of a non-magnetic material. Even then, averaging the different sizes of the magnets due to the tangentially deflectable teeth1.2is achieved.

Outer stops1.4need not necessarily be premolded on teeth1.2. Other forms of stops may be provided as well, such as a ring encircling rotor1or a sleeve, each preventing first magnets2afrom sliding out of rotor1.

It should be appreciated that the principles described herein is not limited to rotary motors. The secondary part of a linear motor may be constructed as described herein, a linear motor corresponding to the borderline case of a rotor segment having an infinite radius of curvature. Thus, a rotor is not restricted to rotary motors.