Field of the disclosure

The disclosure relates to a linear electric machine that can be, for example but not necessarily, a magnetically levitated linear electric machine.

Background

This section illustrates background information without admission of any technique described herein representative of the state of the art.

A linear electric machine comprises a stator and a mover which is linearly movable with respect to the stator in the longitudinal direction of the linear electric machine. The mover and the stator are provided with magnetically operating means for converting electric energy into linear movement of the mover when the linear electric machine operates as a linear motor, and for converting linear movement of the mover into electric energy when the linear electric machine operates as a linear generator. The magnetically operating means may comprise for example windings for generating a magnetic field moving with respect to the windings when alternating currents are supplied to the windings. Furthermore, the magnetically operating means may comprise equipment for generating force in response to the moving magnetic field generated with the multiphase windings. The above-mentioned equipment may comprise for example permanent magnets, electromagnets, electrically conductive structures, and/or mechanical structures providing a spatial reluctance variation. The windings can be located in the stator and the equipment for generating force in response to a moving magnetic field can be located in the mover. It is also possible that the windings are located in the mover and the equipment for generating the force in response to the moving magnetic field is located in the stator. A linear electric machine may comprise for example a rail or two or more parallel rails which serve as a stator along which a mover that comprises windings is moveable. In this exemplifying case, the windings of the mover and the one or more rails are able interact so that desired magnetic forces are generated between the mover and the one or more rails. For another example, a linear electric machine may comprise a tubular stator so that at least a part of the mover that is magnetically interacting with the tubular stator is inside the tubular stator.

In conjunction with many linear electric machines, such as e.g. many magnetically levitated linear electric machines, the windings are used not only for generating a thrust force in the longitudinal direction of a linear electric machine but also for generating levitation forces in transverse directions of the linear electric machine. An inconvenience related to many linear electric machines is that an ability of a magnetic circuit of a linear electric machine to generate levitation forces in transverse directions is strongly dependent on a transverse direction so that the ability to generate a levitation force in a first transverse direction may differ strongly from the ability to generate a levitation force in a second transverse direction that is perpendicular to the first transverse direction.

Summary

The following presents a simplified summary in order to provide a basic understanding of some aspects of various invention embodiments. 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 linear electric machine that comprises: a first element comprising a first ferromagnetic core-structure, and - a second element comprising a second ferromagnetic core-structure and windings for conducting electric currents, the first and second elements being linearly movable with respect to the each other in the longitudinal direction of the linear electric machine.

The windings comprise first winding portions for producing a first magnetic flux through a first airgap between the first and second ferromagnetic core-structures and second winding portions separate from the first winding portions and for producing a second magnetic flux through a second airgap between the first and second ferromagnetic core-structures. The first and second airgaps are angled, i.e. not parallel, with respect to each other when seen along the longitudinal direction of the linear electric machine.

The above-mentioned airgaps that are angled with respect to each other facilitate a control of transverse magnetic forces acting between the first and second elements because the airgaps that are angled with respect to each other make different transverse directions more equal when considering the ability of the magnetic circuit of the linear electric machine to generate magnetic forces in the different transverse directions. The angle between the airgaps when seen along the longitudinal direction of the linear electric machine can be for example from 10 degrees to 1 10 degrees, or from 25 degrees to 90 degrees, or from 45 degrees to 75 degrees.

Exemplifying and non-limiting embodiments are described in accompanied dependent claims.

Various exemplifying and non-limiting embodiments 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 and non limiting 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 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 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 and 1 b illustrate a linear electric machine according to an exemplifying and non-limiting embodiment, figures 2a and 2b illustrate a linear electric machine according to another exemplifying and non-limiting embodiment, and figures 3a, 3b, and 3c illustrate linear electric machines according to exemplifying and non-limiting embodiments.

Description of the exemplifying 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. Lists and groups of examples provided in the description given below are not exhaustive unless otherwise explicitly stated.

Figure 1 a shows a cross-section of a linear electric machine according to an exemplifying and non-limiting embodiment. The geometric section plane is parallel with the xy-plane of a coordinate system 199. Figure 1 b shows a view of a section taken along a geometric line A-A shown in figure 1 a. The geometric section plane related to figure 1 b is parallel with the yz-plane of the coordinate system 199. The linear electric machine comprises a first element 101 that comprises a first ferromagnetic core-structure 103. The linear electric machine comprises a second element 102 that comprises a second ferromagnetic core-structure 104 and first windings for conducting electric currents. The first and second elements 101 and 102 are linearly movable with respect to the each other in the longitudinal direction of the linear electric machine. The longitudinal direction is parallel with the z-axis of the coordinate system 199. In this exemplifying linear electric machine, the second ferromagnetic core-structure 104 comprises two portions so that the first ferromagnetic core-structure 103 is between the two portions of the second ferromagnetic core-structure 104 so that there are first and second airgaps 107 and 108 between the first ferromagnetic core-structure 103 and the second ferromagnetic core-structure 104. The first ferromagnetic core-structure 103 may comprise for example electrically insulated steel sheets stacked on each other in the x-direction of the coordinate system 199. Correspondingly, the second ferromagnetic core-structure 104 may comprise electrically insulated steel sheets stacked on each other in the x-direction of the coordinate system 199. It is also possible that the first and/or the second ferromagnetic core-structure comprise/comprises ferrite or suitable soft magnetic composite such as e.g. Somaloy®.

The windings of the second element 102 comprise first winding portions 105 for producing a first magnetic flux through the first airgap 107 and second winding portions 106 for producing a second magnetic flux through the second airgap 108. The exemplifying linear electric machine illustrated in figures 1 a and 1 b is a switched reluctance“SR” machine where the first ferromagnetic core-structure 103 is toothed for directing reluctance forces to the first element 101 in response to supplying electric currents to the windings of the second element 102.

The first and second ferromagnetic core-structures 103 and 104 are mechanically arranged so that the first airgap 107 narrows and the second airgap 108 widens when the first element 101 moves with respect to the second element in a first transverse direction perpendicular to the longitudinal direction. The first transverse direction is the positive y-direction of the coordinate system 199. Correspondingly, the first airgap 107 widens and the second airgap 108 narrows in response to a movement of the first element 101 with respect to the second element 102 in a direction opposite to the first transverse direction. The first and second airgaps 107 and 108 are angled with respect to each other so that both the first and second airgaps 107 and 108 get narrower in response to a movement of the first element 101 with respect to the second element 102 in a second transverse direction that is perpendicular to the longitudinal direction and perpendicular to the first transverse direction. The second transverse direction is the positive x-direction of the coordinate system 199. In the exemplifying linear electric machine illustrated in figures 1 a and 1 b, the first element 101 comprises a third ferromagnetic core-structure 109 and the second element 102 comprises a fourth ferromagnetic core-structure 1 10 and winding portions 1 15 and 1 16 for carrying electric currents. The first and third ferromagnetic core-structures 103 and 109 are symmetrical to each other with respect to a geometric symmetry plane 120 that is parallel with the yz-plane of the coordinate system 199, and the second and fourth ferromagnetic core-structures 104 and 1 10 are symmetrical to each other with respect to the geometric symmetry plane 120.

The exemplifying linear electric machine illustrated in figures 1 a and 1 b can be, for example but not necessarily, a magnetically levitated linear electric machine. A magnetic force acting between the first and second elements 101 and 102 in the ±y- directions of the coordinate system 199 is adjustable by controlling a difference between electric currents of the winding portions 105 and 106 and a difference between electric currents of the winding portions 1 15 and 1 16. A magnetic force acting between the first and second elements 101 and 102 in the ±x-directions of the coordinate system 199 is adjustable by controlling a difference between the arithmetic average of the electric currents of the winding portions 105 and 106 and the arithmetic average of the electric currents of the winding portions 1 15 and 1 16. Tilting of the first element 101 with respect to the second element 102 around a geometric line parallel with the z-axis of the coordinate system 199 is adjustable by controlling a difference between the arithmetic average of the electric currents of the winding portions 105 and 1 16 and the arithmetic average of the electric currents of the winding portions 106 and 1 15. Correspondingly, tilting of the first element 101 with respect to the second element 102 around a geometric line parallel with the x- axis of the coordinate system 199 is adjustable by controlling a difference between electric currents of different parts of the windings which are successively in the z- direction of the coordinate system 199 so that the upper winding portions such as the winding portions 105 and 1 15 are unbalanced with respect to the lower winding portions such as the winding portions 106 and 1 16. Tilting of the first element 101 with respect to the second element 102 around a geometric line parallel with the y- axis of the coordinate system 199 is adjustable by controlling a difference between electric currents of different parts of the windings which are successive in the z- direction of the coordinate system 199 so that the left-hand side winding portions such as the winding portions 105 and 106 are unbalanced with respect to the right- hand side winding portions such as the winding portions 1 15 and 1 16.

In an exemplifying case where the linear electric machine illustrated in figures 1 a and 1 b is a magnetically levitated linear electric machine, the linear electric machine may comprise safety bearings for preventing the first and second ferromagnetic core structures 103 and 104 from hitting each other during a failure of magnetic levitation. The safety bearings are not shown in figures 1 a and 1 b.

A linear electric machine according to an exemplifying and non-limiting embodiment is single-sided so that the linear electric machine comprises ferromagnetic core structures such as the ferromagnetic core structures 103 and 104 shown in figure 1 a but no ferromagnetic core structures such as the ferromagnetic core structures 109 and 1 10 shown in figure 1 a. In this exemplifying case, a transverse magnetic force that is adjustable by controlling the arithmetic average of electric currents of separate winding portions can be used for compensating for e.g. the gravity force.

Figure 2a shows a cross-section of a linear electric machine according to an exemplifying and non-limiting embodiment. The geometric section plane is parallel with the xy-plane of a coordinate system 299. Figure 2b shows a view of a section taken along a geometric line A-A shown in figure 2a. The geometric section plane related to figure 2b is parallel with the yz-plane of the coordinate system 299. The exemplifying linear electric machine illustrated in figures 2a and 2b can be, for example but not necessarily, a magnetically levitated linear electric machine. The linear electric machine comprises a first element 201 that comprises a first ferromagnetic core-structure 203. The linear electric machine comprises a second element 202 that comprises a second ferromagnetic core-structure 204 and windings for conducting electric currents. The first and second elements 201 and 202 are linearly movable with respect to the each other in the longitudinal direction of the linear electric machine. The longitudinal direction is parallel with the z-axis of the coordinate system 299. In this exemplifying linear electric machine, the first ferromagnetic core-structure 203 comprises two portions so that the second ferromagnetic core-structure 204 is between the two portions of the first ferromagnetic core-structure 203 so that there are first and second airgaps 207 and 208 between the first ferromagnetic core-structure 203 and the second ferromagnetic core-structure 204. The first and second airgaps 207 and 208 are angled with respect to each other when seen along the longitudinal direction of the linear electric machine, i.e. along the z-axis of the coordinate system 299. The first ferromagnetic core-structure 203 may comprise for example electrically insulated steel sheets stacked on each other in the x-direction of the coordinate system 299. Correspondingly, the second ferromagnetic core-structure 204 may comprise electrically insulated steel sheets stacked on each other in the x-direction of the coordinate system 299. It is also possible that the first and/or the second ferromagnetic core-structure comprise/comprises ferrite or suitable soft magnetic composite such as e.g. Somaloy®.

The windings of the second element 202 comprise first winding portions 205 for producing a first magnetic flux through the first airgap 207 and second winding portions 206 for producing a second magnetic flux through the second airgap 208. The exemplifying linear electric machine illustrated in figures 2a and 2b is a flux switching permanent magnet “FSPM” machine where the second element 202 comprises permanent magnets successively in the longitudinal direction so that slots constituted by the second ferromagnetic core-structure 204 and containing the windings are between the permanent magnets. In figure 2b, one of the permanent magnets is denoted with a reference 212. Longitudinally adjacent ones of the permanent magnets have magnetization directions opposite to each other. In figure 2b, the magnetization directions of the permanent magnets are depicted with arrow heads. The second ferromagnetic core-structure 204 comprises advantageously flux-barriers for limiting stray fluxes of the permanent magnets. In figure 2b, one of the flux-barriers is denoted with a reference 221 . The flux-barriers can be e.g. apertures of the second ferromagnetic core-structure 204.

In the exemplifying linear electric machine illustrated in figures 2a and 2b, the first element 201 comprises a third ferromagnetic core-structure 209 and the second element 202 comprises a fourth ferromagnetic core-structure 210 and winding portions 215 and 216. The first and third ferromagnetic core-structures 203 and 209 are symmetrical to each other with respect to a geometric symmetry plane 220 that is parallel with the yz-plane of the coordinate system 299, and the second and fourth ferromagnetic core-structures 204 and 210 are symmetrical to each other with respect to the geometric symmetry plane 220.

Figure 3a shows a cross-section of a linear electric machine according to an exemplifying and non-limiting embodiment. The geometric section plane is parallel with the xy-plane of a coordinate system 399, and the longitudinal direction of the linear electric machine is parallel with the z-axis of the coordinate system 399. The exemplifying linear electric machine illustrated in figure 3a can be, for example but not necessarily, a magnetically levitated linear electric machine. The linear electric machine comprises a first element 301 that comprises a first ferromagnetic core structure 303. The linear electric machine comprises a second element 302 that comprises a second ferromagnetic core-structure 304 and first windings for conducting electric currents to magnetize the first and second ferromagnetic core structures 303 and 304. The first and second elements 301 and 302 are linearly movable with respect to the each other in the longitudinal direction of the linear electric machine. Furthermore, the first element 301 comprises a third ferromagnetic core-structure 309, and the second element 302 comprises a fourth ferromagnetic core-structure 310 and second windings for conducting electric currents to magnetize the third and fourth ferromagnetic core-structures 309 and 310. The first element 301 further comprises a fifth ferromagnetic core-structure 319, and the second element 302 comprises a sixth ferromagnetic core-structure 320 and third windings 325 and 326 for conducting electric currents to magnetize the fifth and sixth ferromagnetic core-structures 319 and 320.

As shown in figure 3a, the airgaps between the first and second ferromagnetic core structures 303 and 304 are angled with respect to each other when seen along the longitudinal direction of the linear electric machine, i.e. along the z-axis of the coordinate system 399. The first and third ferromagnetic core-structures 303 and 309 are symmetrical to each other with respect to a geometric symmetry plane parallel with the yz-plane of the coordinate system 399. Correspondingly, the second and fourth ferromagnetic core-structures 304 and 310 are symmetrical to each other with respect to the geometric symmetry plane. Thus, a portion 350 of the linear electric machine can produce magnetic forces both in the positive and negative x-directions of the coordinate system 399.

The third and fourth ferromagnetic core structures 309 and 310 are a first distance D1 away from the first and second ferromagnetic core structures 303 and 304 in a transverse direction perpendicular to the longitudinal direction of the linear electric machine. In figure 3a, the transverse direction is parallel with the x-axis of the coordinate system 399. The fifth and sixth ferromagnetic core structures 319 and 320 are a second distance D2 away from the third and fourth ferromagnetic core structures 309 and 310 in the transverse direction, wherein the fifth and sixth ferromagnetic core structures 319 and 320 are nearer to the third and fourth ferromagnetic core structures 309 and 310 than to the first and second ferromagnetic core structures 303 and 304. The distance D2 is longer than the distance D1 . As shown in figure 3a, a first airgap between the fifth and sixth ferromagnetic core-structures 319 and 320 and a second airgap between the fifth and sixth ferromagnetic core-structures 319 and 320 are parallel with the above- mentioned transverse direction when seen along the longitudinal direction of the linear electric machine.

The above-described linear electric machine where the distance D2 is greater than the distance D1 is advantageous in cases where the linear electric machine needs to be so wide in the above-mentioned transverse direction, i.e. the x-direction of the coordinate system 399, that thermal expansion causes a significant change in the width of the linear electric machine. In the linear electric machine illustrated in figure 3a, the width of the portion 350 is so small that thermal expansion in the x-direction of the coordinate system 399 does not disturb the operation of the portion 350. The thermal expansion may change the positions of the fifth and sixth ferromagnetic core-structures 319 and 320 relative to each other in the x-direction of the coordinate system 399, but this is not a problem since the airgaps between the fifth and sixth ferromagnetic core-structures 319 and 320 are parallel with the x-axis of the coordinate system 399 when seen along the longitudinal direction of the linear electric machine, i.e. x-directional thermal expansion does not change these airgaps. Figure 3b shows a cross-section of a linear electric machine according to an exemplifying and non-limiting embodiment. The linear electric machine illustrated in figure 3b is otherwise like the linear electric machine illustrated in figure 3a, but the oblique airgaps are arranged in a different way. Figure 3c shows a cross-section of a linear electric machine according to an exemplifying and non-limiting embodiment. The linear electric machine illustrated in figure 3c is otherwise like the linear electric machine illustrated in figure 3b, but the frame structures of the first and second elements 301 and 302 are different from those of the linear electric machine illustrated in figure 3b. Beneficial constructions of the frame structures depend on factors such as for example: material properties, mechanical stresses, and usage of the linear electric machine.

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