FIELD

In a wider perspective, the invention relates to how to find a better and easier way to attach to each other a central element and one or more surrounding elements each having an aperture such as central aperture for the central element. From an exemplary view only, the central element can be a shaft or tube or rod, preferably long enough to accommodate/support several or even a long stack of those consecutive surrounding elements. The invention relates also to one or more surrounding elements, as such.

From a more specific perspective, in a preferred embodiment regarding electric machines such as electric motors and generators, the invention relates to how to find a better and easier way to attach to each other a rotor shaft (central element) and one or both end plates (a surrounding element) of the rotor or one or more rotor discs (a surrounding element), each end plate and rotor disc having an aperture for the central element.

In the art of electric motors, the rotor discs are called core elements because they belong to rotor core. In this context, electric machine refers especially to electric motors and to electric generators. Supported to rotor shaft, the core elements of the rotor are approximately circular, plate-like core elements made of magnetically conductive material, the material such as electric steel having high value of relative permeability. In the middle of each core element, there is an aperture so a central hole for the shaft of the rotor.

Stack of core elements (surrounding elements, so rotor discs) are as- sembled on the rotor shaft (central element), and end plates (also surrounding elements) are assembled to both ends the stack of core elements. One aspect relating to electric motors and the rotors of those motors is the way how is it is secured that, the end plates (surrounding elements) and the core elements (surrounding elements) between the end plates remain firmly together in the stack on consecutive core elements. This is an important aspect because the rotational speed of the rotor and included rotor core can be several thousand rpm (revolutions per minute).

BACKGROUND Regarding electric motors, especially non-induction type electric motors such as reluctance motors or PM (permanent magnet) motors, it has been a common practice to use axially oriented stud bolts as binding means for holding the core elements and end plates together on the shaft of the rotor. Those stud bolts are extending through stack of core elements and also though the end plates that are assembled to both ends the stack of core elements. Those stud bolts are equipped with associated tightening means such as nuts.

Regarding fixing/attaching end plates to rotor shaft, another prior art technology has been a heat shrink - technology that also can be called shrink fit - technology. When using heat shrink technology to fix end plates of the rotor to the shaft of the rotor, what is needed is a particular heating facility and the particular challenge is the need of precise tolerances in manufacturing of the shaft and the end plates. In rotors of a PM (permanent magnet) motor, in the end plate the aperture/hole for the rotor shaft is dimensioned with positive (loose) tolerance to the shaft, whereas in rotors of reluctance motor, in the end plate the aper- ture/hole for the rotor shaft is dimensioned with negative tolerance to the shaft.

The tolerances must be carefully dimensioned, and the reason behind is that end plate acts radially like an extremely short spring with high spring constant to produce the compressive force towards the shaft of the rotor. The important role of precise dimensions relating to tolerances can be understood better when realizing that 100 Celsius degrees heating of an end plate with 50 mm shaft hole expands the central aperture/hole only 60 micrometers, so the tolerances must correspond to this range in order to provide loose fit when the end plate is heated up. Also, one must take into account the expansion caused by centrifugal forces of the rotor when in final use, to make sure there is still sufficient fit at higher speeds. Regarding heat shrink technology, it can be said that it is not a cost effective to use heat shrink technology requiring high tolerance for the manufacturing the items (end plate, shaft) that are supposed to be fixed together with that technology. Regarding used of stud bolts, they are not an optimal solution in regard to costs and the needed manual work. The location of the binding means can also create problems for the electro-magnetic operation of the rotor.

Therefore, there is a need for an improvement.

BRIEF DESCRIPTION

The present invention seeks to provide an improvement. According to an aspect of the present invention, there is provided a surrounding element as specified in claim 1.

According to another aspect of the present invention, there is provided a rotor for an electric machine, as specified in claim 14.

According to a further aspect of the present invention, there is provided an electric machine, as specified in claim 15.

The basic idea behind the improvement is to modify, near the aperture/hole, the stiffness of the surrounding element. Regarding electric machines such as electric motors, the basic idea is the modify the stiffness of the end plate and/or stiffness of the rotor disc (core element), near the central aperture/hole.

The improvement provides advantages. It is possible to use cost effective methods of low-tolerance manufacturing, compared to earlier high-tolerance machining. Also, in assembly process, simple method like press fit - method can be used, without a need for heat shrink facility.

The preferred embodiments are discussed in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be described in greater detail by means of preferred embodiments with reference to the attached drawings, in which: Figure 1 illustrates an end plate of a rotor, with curved projections and cuts, Figure 2 illustrates an end plate of the rotor, said end plate being supported to shaft of the rotor.

Figure 3 illustrates a rotor comprising a rotor shaft with several rotor discs (core elements) between the end plates of the rotor.

Figure 4 illustrates a rotor disc (core element) of a rotor, with some dimension markings,

Figure 5 illustrates an end plate of the rotor, but with straight linear projections and cuts.

Figure 6 illustrates another variation of the cuts and projections/protrusions. DESCRIPTION OF EMBODIMENTS

Referring to figures, in the wider perspective, the invention relates to how to find a better and easier way to attach to each other a central element SH and one or more surrounding elements 101-104 and/or PL1, PL2.

In an embodiment, the surrounding elements 101-104 are core elements of a rotor 800 of an electric machine. In other words the surrounding elements 101-104 are rotor discs. Electric machine can be an electric motor or an electric generator. Additionally or alternatively, the surrounding elements can be end plates PL1, P2 of the rotor 800.

Rotor 800 comprises several consecutive core elements (rotor discs) 101-104. In practice, the number of consecutive core elements (so rotor discs) can be clearly higher than in this shown embodiment where there are only four core elements 101-104. For example there may be several hundred consecu- tive/parallel core elements.

Core elements 101-104 are typically laminated together for forming the stack of consecutive core elements. Core elements 101-104 are insulated from each other, so they are not in galvanic contact with each other. Stack of core elements 101-104 with end plates PL1 PL can be called a rotor core. Rotor core is supported on the shaft SH of the rotor. At the end of the stack of core elements, there are end plates PLl, PL2. Originally, the root of this invention comes from a desire to modify the end plates, such as PLl, in such way that it/they can be fixed to shaft SH in an easier way.

The core elements 101-104 and the end plates PLl, PL2 are those surrounding elements, they are supported on the central element which is shaft SH in an embodiment.

Regarding achieving suitable compression between the fingerlike projections F1-F20 and central element SH such as shaft SH, in an embodiment the diameter of the shaft SH or other central element is such that it correspond to diameter of the central aperture API plus 2 x (doubled) width of the cut, like cut CI between the finger-like projections, like F20, Fl.

Regarding the shape of the central aperture API and the related central element SH such as shaft SH, instead of round circular shape, the shape can be square-shaped, for example.

Regarding the shape of the outer circumference (rim) RI of the surrounding element like end plates PLl, PL2 and rotor discs 101-104, instead of strictly round circular shape, the shape may be discontinuous having cutaway areas.

Let us now discuss about core element 101, which is the first element at the first end El of the rotor. The other core elements 102-104 can have same structures as core element 101. The core element 101 may be a round plate which is made of material having first magnetic conductance. In an embodiment, the core element 101 may have a constant thickness. For example, the material of the core element 101 may be electrical steel having high value of relative permeability.

Also the end plates are PLl, PL2 can be a round plate of constant thickness.

When discussing about the surrounding elements PLl, 101-104, PL2„ in the following a reference is made mainly to end plate PLl, shown in figure 1, but the later discussed features are relevant also with the other surrounding ele- ments, meaning the other end plate PL2 and the core elements 101-104 which can also be called rotor discs 101-104.

Surrounding element like PL1, has an aperture API such as central aperture for accommodating the central element SH.

The inventions relates especially to surrounding element, either alone or assembled on a central element like shaft SH or tube.

Regarding rotors, the invention relates to a device 800 (such as rotor) comprising a tube, shaft SH or other central element SH and one or more surrounding elements like PL1, 101-104, PL2 Each surrounding element, like PL1, comprises a wall Wl and an aperture API in the wall Wl. The aperture API in the wall of the surrounding element is arranged to accommodate the central element SH.

As can been seen in figures 1-2, next to the aperture API of the wall Wl and ending to the edge of the aperture API, the wall Wl comprises several fingerlike projections Fl - F20. Projections are between related cuts CI - C20 forming the finger-like projections F1-F20 therebetween.

Each projection extend in the wall Wl to a direction that at least partly deviates from the radial direction RD of the surrounding element PL1, so as to cause the projections to create spring-effect towards the aperture API (filled with element SH) and central element SH therein, preferably in the direction between the outer circumference of the surrounding element and the aperture of the surrounding element.

When analyzing the surrounding element PL1, PL, 101-104, we can state that the surrounding element is such that next to the aperture API of the wall and ending to the circumference APRI of the aperture API, the wall Wl of the surrounding element comprises several fingerlike projections F1-F20, F51, F70 (in fig 5) between related cuts C1-C20 forming the projections F1-F20; F51, F70 therebetween. Each projection F1-F20; F51, F70 extend in the wall Wl to a direction that at least partly deviates from the radial direction RD of the surrounding element PL1, 101-104, so as to cause the projections F1-F20; F51, F70 to create spring-effect. In an embodiment, in a pursuit to create even better spring action, at least 50 % of the length the projection, like of projection Fl, deviates from the radial direction RD of the surrounding element PL1. In the embodiment of figs 1- 2, most part so almost whole of the length of the projection, like Fl, deviates from the radial direction RD of the surrounding element PL1.

In figures 1-2, at the inner end (closer to aperture API) of the projections, so at the tip of the projections, the projections may be directed to direction that is the same direction as the radius (having radial direction RD) in that same point.

However, regarding embodiment of fig 5, the whole length of projections, now marked with F51, F70, deviates from the radial direction RD of the surrounding element, now PL51 in fig. 5. According to figure 5, projections F51, F70 have straight linear form, the inclination angle of those linear projections i.e protrusions F51, F70 may be 10-80 degrees, compared the radial direction RD (RD shown in fig. 4). In an exemplary embodiment of figure 5, the above mentioned inclination angle is about 45 degrees. In an embodiment, the above mentioned inclination angle is between 35-55 degrees.

Referring to figures 1-3 and 5 and to exemplary dimensions, in an embodiment, the thickness of the surrounding elements such as end plates PL1, PL2 is between 5-10 mm and are made of steel. In an embodiment, the thickness of other kind of surrounding element like rotor disc 101 i.e. core element 101 of figures 3-4 is around 500 micrometres.

In broader perspective regarding the relative dimensioning of the cuts C1-C20 and the related finger-like projections F1-F20 i.e protrusions F1-F20, it can be stated that the tangential extent of the finger (finger = projection i.e. protrusion, like F1-F20) end (tip) facing the central aperture API circumference (rim) APRI, is between 60 % and 10 %, preferably between 50 % and 20 %, compared to the tangential extent of the finger's geometry projection (geometrical concept, not physical item) on the central aperture API circumference APRI. Here, "finger end" is the tip of the projection/protrusion. Tangential extent of the finger-like projection/protrusion F1-F20 can be regarded to be the width of the finger-like projection/protrusion. In other words, we compare the width of the finger-like protrusion F1-F20 to the geometry projection of the same protrusion. As can be understood, the geometry pro- jection (of the fingerlike projection/protrusion) on the aperture API circumference (rim) APRI is not be confused with fingerlike projections F1-F20 itself.

Referring to figures 1-2 and 4, in an embodiment, when considered in the radial direction RD, the extent-length EL of the projection, like Fl, is at least 10 % of the extent length ELW of the wall Wl. In this context, extent length ELW of the wall Wl is the distance from the circumference (rim) APRI of the aperture API within the wall Wl to the outer circumference RI of the wall Wl. One possible exemplary diameter of surround elements PL1, PL2, 101-104 is about 30 cm, then the radial length i.e. extent length ELW the wall Wl is about 10 cm.

However, in an embodiment, the extent length of the finger-like pro- jections F1-F20 i.e protrusions F1-F20 can be a lot less than the above mentioned 10 % of the radial extent length ELW of the wall Wl. Therefore, regarding real physical dimensions, in an embodiment, regarded in radial direction, the extent length of the finger-like projections F1-F20 i.e protrusions F1-F20 might be as short as 1 micrometres, with about similar length of the cuts C1-C20.

In an embodiment, the extent length of the projections F1-F20 and/or cuts C1-C20 is between 1 micrometre and 5 cm. Preferably the above mentioned length is between 1 micrometre and 100 micrometres, flexibility is achieved, without weakening the structure.

Referring to suitable maximum extent-length of the projection, like Fl, in an embodiment, when considered in the radial direction RD, the extent- length EL of the projection is 50 % or less of the extent length ELW of the wall Wl. Here, the extent length ELW of the wall is the distance from the circumference (rim) APRI of the aperture API within the wall to the outer circumference rim) RI of the wall Wl. The outer ends i.e roots i.e starting points of the finger-like projections F1-F20 between each two concecutive bottoms of the cuts C1-C20 form a circle on the wall Wl of the surrounding element PL1 such as of the disc PL1.

Referring to figures 1-2, in an embodiment, the projections F1-F20 have curved form. This relates to the fact that the cuts C1-C20 have curved form, so the side edges of the projections F1-F20 become curved. The projections, such as projection Fl, have side edges SE1A, SE1B facing the previous projection F20 and next projection F2. Therefore, projections F1-F20 have curved form at both edges.

In an different embodiment, according to figure 5, projections F51, F70 have straight linear form. Also here, projections, like F50, have first and second side edges SE51A, SE51B. First side edge SE51A of the projection F51 faces the side of the previous projection F70. Second side edge SE51B of the projection F51 faces the side of the next projection, and wherein the projections have straight linear form at both side edges. Central aperture is marked with AP51.

The cuts, such as cuts C1-C20 in figures 1-2, are made with laser cutting.

Figure 6 illustrates another variation of the cuts and projections. The cuts CC1-CC3 and finger-like projections/protrusions FF2, FF3 have a "wormlike" shape having the edge direction thereof alternating from left to right (or right to left), compared to the radial/radius direction RD. Therefore, also in this embodiment the direction of the finger-like projections/protrusions FF2, FF3 and relates cuts CC1-CC3, deviates from the radial/radius direction RD.

With reference to figures 1-2, the projections F1-F20 form a symmetrical circle of projections, said circle surrounding said aperture API and said central element SH. The same can be seen also from fig. 5 with straight projections F51, F70.

Referring to primary embodiment, the central element SH is the shaft of the rotor 800, and one or more of the surrounding elements is the end plate PL1, PL2 of the rotor or the rotor core disc 101-104 of the rotor 800. In addition to above mentioned surrounding element like disc or plate, the invention also relates to a rotor for an electric machine. Additionally, the invention also relates to an electric machine, comprising a rotor 800. Electric machine can be, for example, a reluctance motor or a permanent magnet motor (PM motor).

As discussed, in addition to end plate PL1, PL2, also a rotor disc 101- 104 so a core element of a rotor are surrounding elements. Therefore, referring now to figure 4, the core element 101 of the rotor 800 comprises the above discussed structures, such as projections (marked only Fl and F20) between related cuts (marked only CI and C20), and central aperture API for the shaft. For the rotor disc use, the rotor disc has voids V1-V4 to facilitate inserting of permanent magnet rods.

The end plates PL1, PL2 and the core elements (rotor discs) 101-104 can be assembled on the shaft SH by press-fit technology, no need for heat shrink - technology.

Yet another variation of the theme is an embodiment, where the central element SH is the liquid transfer tube of a heat exchanger, and then the surrounding element is the heat exchange flange supported to said tube. In that scenario, the central element SH in figure 2 would be the transfer tube and surrounding element, like PL1, would be heat exchange flanges but separated from other flanges. In this embodiment the finger-like projections/protrusions in heat transfer flange would press themselves against the surface of the tube. In heat exchanger use the invention provides benefits because the diameter/thickness of the tube may vary.

The above discussed embodiments are only examples. Although the specification may refer to "an" embodiment in several locations, this does not necessarily mean that each such reference is to the same embodiment(s), or that the feature only applies to a single embodiment. Single features of different embodiments may also be combined to provide other embodiments. Furthermore, words "comprising" and "including" should be understood as not limiting the described embodiments to consist of only those features that have been mentioned and such embodiments may contain also features/structures that have not been specifically mentioned.

It should be noted that while the Figures illustrate various embodiments, they are simplified diagrams that only show some structures and/or func- tional entities. It is apparent to a person skilled in the art that the described device and relates items or larger entities may also comprise other functions and structures than those described in Figures and text. It will be obvious to a person skilled in the art that, as technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the example embodiments described above but may vary within the scope of the claims.