Field of the technology

The disclosure relates generally to rotating electric machines. More particularly, the disclosure relates to a rotor of a permanent magnet machine. Furthermore, the disclosure relates to a permanent magnet machine.

Background

Rotating electric machines, such as motors and generators, generally comprise a stator and a rotor which are arranged so that a magnetic flux is developed between these two. In a typical permanent magnet“PM” machine, the rotor is provided with permanent magnets whereas the stator is provided with stator windings, e.g. a three-phase winding. The permanent magnets of the rotor and electrical currents in the stator windings cause a magnetic flux to flow across the airgap between the rotor and the stator. Torque is produced by the magnetic flux and an active component of the electrical currents of the stator windings.

A rotor of a permanent magnet machine comprises typically a ferromagnetic core structure, a shaft, and permanent magnet elements arranged to produce magnetic fluxes to form magnetic poles of the rotor. When designing a rotor of a permanent magnet machine there are various aspects to be taken into account. The electro- magnetic characteristics of the rotor should be such that it can provide desired performance with sufficiently low losses, the mechanical characteristics of the rotor should be such that the mechanical structures of the rotor can withstand the ensued mechanical stresses, and the thermal characteristics of the rotor should be such that the heat caused by the losses can be removed from the rotor. Furthermore, the high price of permanent magnet materials causes a need to minimize the amount of permanent magnet material used in the rotor.

A rotor of a permanent magnet machine may have buried permanent magnet elements which are placed in cavities of a ferromagnetic core structure so that the ferromagnetic core structure surrounds the permanent magnet elements. An advantage of a rotor having buried permanent magnet elements is that the permanent magnet elements are reliably supported by the ferromagnetic core structure. A challenge related to a rotor having buried permanent magnet elements is that the ferromagnetic core structure surrounding the permanent magnet elements provides ferromagnetic paths for leakage fluxes and thus a part of the magnetic flux generated by the permanent magnets is wasted. As an alternative, a rotor of a permanent magnet machine may have surface mounted permanent magnet elements which are placed on the outer surface of a ferromagnetic core structure. Permanent magnet elements are often attached to the outer surface of a ferromagnetic core structure using epoxy or cyanoacrylate adhesive. This approach has its challenges especially in cases where there are many permanent magnet elements adjacent to each other, i.e. segmented permanent magnets, and/or where surfaces of the ferromagnetic core structure on which the permanent magnet elements are attached are formed by a stack of ferromagnetic steel sheets so that the surfaces are perpendicular to the ferromagnetic steel sheets.

Summary

The following presents a simplified summary in order to provide a basic understanding of some embodiments of the invention. The summary is not an extensive overview of the invention. It is neither intended to identify key or critical elements of the invention nor to delineate the scope of the invention. The following summary merely presents some concepts of the invention in a simplified form as a prelude to a more detailed description of exemplifying embodiments of the invention.

In this document, the word“geometric” when used as a prefix means a geometric concept that is not necessarily a part of any physical object. The geometric concept can be for example a geometric point, a straight or curved geometric line, a geometric plane, a non-planar geometric surface, a geometric space, or any other geometric entity that is zero, one, two, or three dimensional.

In accordance with the invention, there is provided a new rotor for a permanent magnet machine. A rotor according to the invention comprises: a rotor core structure, and - permanent magnet elements placed on support surfaces of the rotor core structure, the support surfaces belonging to the outer surface of the rotor core structure.

The rotor core structure comprises protrusions between adjacent ones of the support surfaces so that the permanent magnet elements are between the protrusions and mechanically supported by the protrusions in a circumferential direction, i.e. in a direction of movement when the rotor is rotating. The protrusions have grooves on surfaces facing towards the permanent magnet elements, and the permanent magnet elements have grooves on surfaces substantially perpendicular to the support surfaces. The rotor comprises locking elements located partially in the grooves of the protrusions and partially in the grooves of the permanent magnet elements so that the locking elements are arranged to lock the permanent magnet elements to the rotor core structure. The above-mentioned locking elements and the respective grooves in the permanent magnet elements and in the protrusions of the rotor core structure enable the permanent magnet elements to be surface mounted permanent magnet elements that are shape-locked to the rotor core structure.

In a rotor according to an exemplifying and non-limiting embodiment, the grooves of the permanent magnet elements are perpendicular to the grooves of the protrusions, and the locking elements comprise elongated bars which are partially located in the grooves of the permanent magnet elements and whose ends are in the grooves of the protrusions.

In accordance with the invention, there is provided also a new permanent magnet machine. A permanent magnet machine according to the invention comprises:

- a stator comprising stator windings, e.g. a three-phase winding, and - a rotor according to the invention, the rotor being rotatably supported with respect to the stator.

Exemplifying and non-limiting embodiments of the invention are described in accompanied dependent claims. Various exemplifying and non-limiting embodiments of the invention both as to constructions and to methods of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific exemplifying embodiments when read in conjunction with the accompanying drawings.

The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in dependent claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of“a” or “an”, i.e. a singular form, throughout this document does not exclude a plurality.

Brief description of the figures

Exemplifying and non-limiting embodiments of the invention and their advantages are explained in greater detail below in the sense of examples and with reference to the accompanying drawings, in which: figures 1 a, 1 b, 1 c, 1 d, and 1 e illustrate details of a rotor according to an exemplifying and non-limiting embodiment, figure 2 illustrates a rotor according to an exemplifying and non-limiting embodiment, and figure 3 illustrates a permanent magnet machine according to an exemplifying and non-limiting embodiment.

Description of exemplifying and non-limiting embodiments

The specific examples provided in the description given below should not be construed as limiting the scope and/or the applicability of the appended claims. Furthermore, it is to be understood that lists and groups of examples provided in the description given below are not exhaustive unless otherwise explicitly stated.

Figures 1 a, 1 b, 1 c, and 1 d illustrate details of a rotor according to an exemplifying and non-limiting embodiment. The rotor comprises a rotor core structure 101 . In this exemplifying case, the rotor core structure 101 comprises laminated elements composed of ferromagnetic steel sheets that are electrically insulated from each other and stacked on each other in the axial direction of the rotor. The axial direction is parallel with the z-axis of a coordinate system 199 shown in figures 1 a, 1 b, 1 c, and 1 d. As shown in figures 1 a and 1 c, the rotor core structure 101 comprises also non-laminated elements made of e.g. solid steel or aluminum. The rotor comprises permanent magnet elements placed on support surfaces of the rotor core structure 101 , where the support surfaces belong to the outer surface of the rotor core structure 101 . In figure 1 a, one of the support surfaces is denoted with a reference 1 14. As shown in figure 1 a, the support surfaces are partially formed by the stacked ferromagnetic steel sheets so that the support surfaces are perpendicular to the ferromagnetic steel sheets. In figure 1 a, two of the permanent magnet elements are denoted with references 102 and 103. For the sake of illustration, permanent magnet elements to be placed on the support surface 1 14 are not shown in figure 1 a. In the exemplifying rotor illustrated in figures 1 a-1 d, the permanent magnet elements have substantially a cuboid shape and the support surfaces of the rotor core structure 101 are planar. It is however also possible to use permanent magnet elements having curved shapes.

The rotor core structure 101 comprises protrusions between adjacent ones of the support surfaces so that the permanent magnet elements are between the protrusions and mechanically supported by the protrusions in the circumferential direction, i.e. in a direction of movement when the rotor is rotating. The protrusions shown in figure 1 a are denoted with references 104, 105, and 106. The protrusions have grooves on surfaces facing towards the permanent magnet elements. In figure 1 a, a groove of the protrusion 104 is denoted with a reference 107. The permanent magnet elements have grooves on surfaces substantially perpendicular to the support surfaces of the rotor core structure 101 . In figure 1 b, a groove of the permanent magnet element 102 is denoted with a reference 108. The rotor comprises locking elements located partially in the grooves of the protrusions and partially in the grooves of the permanent magnet elements so that the locking elements are arranged to lock the permanent magnet elements to the rotor core structure 101 . One of the locking elements is denoted with a reference 109 in figure 1 a. Figure 1 c illustrates how a locking element 129 is connected to a groove 127 of the protrusion 105. For the sake of illustration, the permanent magnet elements are not shown in figure 1 c. The above-mentioned locking elements and the respective grooves in the permanent magnet elements and in the protrusions of the rotor core structure 101 enable the permanent magnet elements to be surface mounted permanent magnet elements that are shape-locked to the rotor core structure 101 . Advantageously, the rotor comprises thermal paste between the permanent magnet elements and the support surfaces of the rotor core structure 101 . In figure 1 a, the thermal paste is denoted with a reference 1 17.

In the exemplifying rotor illustrated in figures 1 a-1 d, the grooves of the permanent magnet elements are perpendicular to the grooves of the protrusions. The locking elements comprise elongated bars which are partially located in the grooves of the permanent magnet elements and whose ends are in the grooves of the protrusions. The elongated bar of the locking element 109 is denoted with a reference 1 10 in figure 1 a, and the elongated bar of the locking element 129 is denoted with a reference 130 in figure 1 c.

In the exemplifying rotor illustrated in figures 1 a-1 d, the rotor core structure 101 comprises end-plates that have cavities containing parts of outermost ones of the locking elements that are partially in the grooves of the permanent magnet elements adjacent to the end-plates. In figures 1 a and 1 c, one of the end-plates is denoted with a reference 1 1 1 . The other end-plate is not shown. One of the cavities of the end-plate 1 1 1 is denoted with a reference 1 12 in figure 1 a, and another one of the cavities of the end-plate 1 1 1 is denoted with a reference 132 in figure 1 c. The locking elements shown in figures 1 a and 1 c are examples of the above-mentioned outermost locking elements. The locking element 109 shown in figure 1 a comprises locking pins that are substantially perpendicular to the elongated bar 1 10. One of the locking pins of the locking element 109 is denoted with a reference 1 13. The locking element 129 shown in figure 1 c comprises locking pins that are substantially perpendicular to the elongated bar 130. One of the locking pins of the locking element 129 is denoted with a reference 133. As illustrated by the section view shown in figure 1 c, the locking pins protrude into the cavities of the end-plate 1 1 1 . Thus, the outermost locking elements that are partially in the grooves of the permanent magnet elements adjacent to the end-plates are supported not only by the protrusions of the rotor core structure 101 but also by the end-plates. In this exemplifying case, the above-mentioned cavities of the end-plates are through- holes of the end-plates.

In the exemplifying rotor illustrated in figures 1 a-1 d, the permanent magnet elements are arranged to form arrays of permanent magnet elements between adjacent protrusions of the rotor core structure 101 . Thus, the exemplifying rotor illustrated in figures 1 a-1d comprises segmented permanent magnets. It is however also possible that there is a single piece of permanent magnet material between adjacent protrusions of the rotor core structure 101 . In figure 1 a, the array of permanent magnet elements that is between the protrusions 105 and 106 of the rotor core structure 101 is denoted with a reference 1 15. For the sake of illustration, the array of permanent magnet elements 1 15 and the respective locking elements are shown separately in figure 1 d. As illustrated in figure 1 d, the permanent magnet elements comprise grooves so that the grooves of adjacent permanent magnet elements constitute tubular channels containing those of the locking elements that are located between the permanent magnet elements. In figure 1 d, one of the locking elements between adjacent permanent magnet elements is denoted with a reference 1 18. These locking elements are elongated bars that are advantageously dimensioned to extend into the grooves of the protrusions of the rotor core structure to implement shape-locking between the permanent magnet elements and the rotor core structure.

The exemplifying rotor illustrated in figures 1 a-1 d comprises intermediate elements between permanent magnet elements that are successive in the direction parallel with the protrusions of the rotor core structure 101 , i.e. in the z-direction of the coordinate system 199. In figures 1 a and 1 d, one of the intermediate elements is denoted with a reference 1 16. As illustrated in figure 1 d, the intermediate elements comprise grooves constituting, together with the grooves of the permanent magnet elements adjacent to the intermediate elements, tubular channels containing those of the locking elements that are located between the intermediate elements and the permanent magnet elements. In figure 1 d, one of these locking elements is denoted with a reference 1 19. These locking elements are advantageously dimensioned to extend into the grooves of the protrusions of the rotor core structure. Figure 1 e shows the arrangement shown in figure 1 d so that some of the permanent magnet elements are not presented in order to illustrate the locking elements more clearly. The locking elements such as the locking element 109 shown in figures 1 a, 1 d, and 1 e can be made of for example nylon or metal e.g. steel. The locking elements such as the locking elements 1 18 and 1 19 shown in figures 1 d and 1 e can be made of for example fiberglass, nylon, or metal e.g. steel. The intermediate elements can be made of e.g. nylon or metal such as e.g. steel or aluminum. The intermediate elements shown in figures 1 a and 1 d can be used for adjusting the z-directional length of the array of permanent magnet elements to be suitable for the rotor core structure in cases where the permanent magnet elements have fixed dimensions and it would not be cost effective to adjust the dimensions of the permanent magnet elements. In a rotor according to an exemplifying and non-limiting embodiment, corresponding intermediate elements are used for adjusting the x-directional width of the array of permanent magnet elements. A rotor according to an exemplifying and non-limiting embodiment comprises intermediate elements of the kind mentioned above, and the intermediate elements comprise radial cooling ducts. In exemplifying cases where the intermediate elements are made of flexible material such as e.g. nylon, the intermediate elements can be used as wedges which are mounted after mounting the permanent magnet elements and the locking elements, and which tighten the array of the permanent magnet elements. In the exemplifying case shown in figures 1d and 1 e, the lower portions of the intermediate elements have a tapering, wedge-type shape.

Figure 2 shows an end-view of a rotor 200 according to an exemplifying and non- limiting embodiment. The axial direction of the rotor is parallel with the z-axis of a coordinate system 299. In this exemplifying case, the rotor core structure comprises segments 201 , 202, 203, 204, and 205 that are successive to each other in the circumferential direction.

Figure 3 shows a section view of a permanent magnet machine according to an exemplifying and non-limiting embodiment. The section plane is parallel with the yz- plane of a coordinate system 399. The permanent magnet machine comprises a rotor 300 according to an exemplifying and non-limiting embodiment of the invention and a stator 340. The rotor 300 is rotatably supported with respect to the stator 340. Arrangements for rotatably supporting the rotor 300 with respect to the stator 340 are not shown in figure 3. The stator 340 comprises stator windings 341 for generating a rotating magnetic field in response to being supplied with alternating currents. The stator windings 341 can be for example a three-phase winding. The rotor 300 can be for example such as illustrated in figures 1 a-1d and/or in figure 2.

The exemplifying permanent magnet machine illustrated in figure 3 is an inner rotor radial flux permanent magnet machine. It is to be noted that a rotor according to an embodiment of the invention can be, as well, a rotor of an outer rotor radial flux permanent magnet machine or a rotor of an axial flux permanent magnet machine. Correspondingly, a permanent magnet machine according to an embodiment of the invention can be, as well, an outer rotor radial flux permanent magnet machine or an axial flux permanent magnet machine.

The specific examples provided in the description given above should not be construed as limiting the scope and/or the applicability of the appended claims. Lists and groups of examples provided in the description given above are not exhaustive unless otherwise explicitly stated.