SYNCHRONE RELUCTANT ELECTRIC MACHINE

Abstract

Synchronous reluctance electromachine (10) comprising the following: a stator (12) with a plurality of electrical windings; a rotor (20) which is arranged in a cylindrically shaped cavity formed in the stator (12) and contains several electrical steel sheets (22) which are mounted on a shaft (26), wherein the wave (26) defines a longitudinal axis, wherein each of the electrical steel sheets (22) has a plurality of poles and wherein each of the poles has a plurality of slots (31) arranged near an outer edge region (24), and wherein the slots (31) of the electrical steel sheets (22) are aligned longitudinally; and a plurality of packages (36, 136, 236) composed of anisotropic material, arranged in the slots (31); wherein the plurality of packages (36, 136, 236) composed of anisotropic material are arranged in a first subset (31a, 31b) of the slots (31); and a second subset (31c, 31d) of the slots (31) remains empty.

Description

TECHNICAL FIELD

[0001] This disclosure relates to synchronous reluctance electric machines and, more particularly, to a rotor assembly for such electric machines. BACKGROUND

[0002] A reluctance electric machine generally includes a rotor rotatably mounted within a stator. The stator generally includes a plurality of windings and alternating-polarity magnetic poles. The rotor is made of steel or another ferrous material, preferably including one or a plurality of inherent poles. The rotor is made of a ferromagnetic material, such as soft iron. Torque is generated by the phenomenon of magnetic resistance. The stator is controlled by a control unit to generate a rotating magnetic field that induces a magnetic field in the rotor. The interaction of these two magnetic fields generates torque on the rotor.

[0003] A synchronous reluctance electric machine may have an equal number of stator and rotor poles. The projections on the rotor may be arranged to introduce internal flux barriers, i.e., holes that direct the magnetic flux along a d-axis. Generally, the axis in the direction of greatest magnetic resistance is called a direct axis or d-axis, while the axis 90 degrees in front of the direct axis is called a quadrature axis or q-axis, which has the least magnetic resistance. Pole numbers are known to be 4 and 6. When the spaces or notches between the rotor poles are opposite the stator poles, the magnetic circuit of the electric machine has low magnetic resistance; however, when the rotor poles are aligned with the stator poles, the magnetic circuit has high magnetic resistance.Once one pair of stator poles is energized, the next pair of rotor poles is moved to align with the energized stator poles to minimize the resistance path through the machine. Rotational motion is enabled by sequentially energizing the stator poles to cause the rotor to transition to the next energized pole. The synchronous reluctance electric machine is designed to operate using an alternating current at a controlled frequency supplied to the stator windings. The rotor has a plurality of inherent poles to create a variable resistance in the electric machine's magnetic circuit, which is dependent on the rotor's angular position. These inherent poles can be created by milling the axial slots along the length of the rotor.

[0004] EP 2 991 207 A1 discloses a dynamoelectric machine with a reluctance and permanent magnet rotor, wherein the rotor is composed of at least three axially adjacent sections arranged one behind the other to form at least two different rotor sub-package types. One of the rotor sub-package types is a reluctance pack that has flux barriers or anisotropic soft magnetic material.

[0005] JP H09-219944 A discloses a rotor with an embedded structure comprising an iron rotor core and laminated elements embedded in the rotor core. The laminated elements comprise a highly hardened material and a low-permeability material that includes a permanent magnet.

[0006] The document JP 2003 - 274 590 A discloses a rotor of a permanent magnet synchronous motor in which disc-shaped permanent magnets are inserted, the magnetic force of which is directed by anisotropic sheets.

[0007] US 4 459 502 A discloses a rotor in which grain-oriented steel is used to form the sheets of magnetic material.

[0008] The document JP 2001 - 251 796 A discloses a permanent magnet rotor in which magnetic pole surfaces on one side of two supports are connected to magnetic pole surfaces on both sides of a magnetic substance in order to avoid demagnetization and to increase the magnetic force of the magnet.

[0009] The document WO 2013 / 103 118 A1 discloses a permanent magnet synchronous motor that uses plastic-bonded anisotropic permanent magnets. SUMMARY

[0010] A synchronous reluctance electric machine is described and includes a stator having a plurality of electrical windings, and a rotor disposed within a cylindrically shaped cavity formed within the stator. The rotor includes a plurality of electrical laminations mounted on a shaft, the shaft defining a longitudinal axis.

[0011] Each of the electrical laminations includes a plurality of poles, and each of the poles includes a plurality of slots arranged near an outer edge region. The slots of the electrical laminations are aligned longitudinally. A plurality of stacks composed of anisotropic material are arranged in the slots.

[0012] The above features and advantages and other features and advantages of the present teachings will be readily apparent from the following detailed description of some of the best modes and other modes for carrying out the present teachings as defined in the appended claims, taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In the following, one or more embodiments are described by way of example with reference to the accompanying drawings, in which: Fig. 1 shows a schematic representation of a cross-sectional view of a synchronous reluctance electric machine having an annular stator forming a cylindrically shaped cavity into which a coaxial rotor is inserted according to the disclosure; Fig. Figure 2 shows a schematic representation of a cross-sectional view of a single pole section of a single sheet of the invention described with reference to Fig. 1 described synchronous reluctance electric machine having a pole arrangement including a plurality of slots arranged near an outer peripheral region thereof, in which anisotropic packages are inserted into the slots according to the disclosure; Fig. 3 shows a schematic representation of a perspective view of a first embodiment of the anisotropic package including a lamination stack consisting of a plurality of anisotropic laminations with spaced-apart non-magnetic spacers according to the disclosure; Fig. 4 shows a schematic representation of a perspective view of a second embodiment of the anisotropic package, which according to the disclosure has a stack of sheets composed of a plurality of anisotropic sheets, each having a plurality of cavities acting as flow barriers; and Fig. 5 shows a schematic representation of a perspective view of a third embodiment of the anisotropic package, which according to the disclosure includes a stack of sheets composed of a plurality of anisotropic sheets. DETAILED DESCRIPTION

[0014] The following text refers to the drawings, which serve only to illustrate certain exemplary embodiments and are not intended to limit the scope of the invention in any way. Fig. 1 shows a schematic representation of a cross-sectional view of a synchronous reluctance electric machine 10 having an annular stator 12 forming a cylindrically shaped cavity into which a coaxial rotor 20 is inserted, with an air gap 14 formed between the stator 12 and the rotor 20. The rotor 20 includes a rotatable shaft 26 having ends extending through openings formed in end caps of the stator 12, with suitable mounting and bearing devices disposed therein. The shaft 26 defines a longitudinal axis with radial lines orthogonal to the longitudinal axis. The stator 12 includes a plurality of electrical windings (not shown) arranged circumferentially. The electrical windings are connected to a suitable device, e.g.an inverter, which can be controlled by a control unit to generate rotating electric fields that induce magnetic fields adjacent to the rotor 20 to generate mechanical torque in the rotor 20. The electric machine 10 can be used as a torque motor and / or an electric power generator. The overall operation of a synchronous reluctance electric machine 10 is known to those skilled in the art and is therefore not described in detail here.

[0015] The rotor 20 consists of a plurality of disc-shaped laminations 22 made of isotropic steel or another ferromagnetic material, such as compressed iron powder. The plurality of laminations are stacked and pressed together or otherwise firmly assembled on the shaft 26 for rotation therewith. The rotor 20 includes a plurality of pole sections 25 arranged circumferentially around the rotor shaft 26, preferably at predetermined identical intervals. A pole section 25 of an individual lamination 22 is shown with reference to Fig. 1 and is schematically illustrated in additional detail with reference to Fig. 2. Embodiments of the rotor 20 may have two pole sections 25, four pole sections 25, six pole sections 25, eight pole sections 25, or any other suitable number of pole sections 25.

[0016] The rotor 20 is preferably manufactured such that the magnetic permeability is lower in the direction of a d-axis 28, i.e., exhibits increased magnetic resistance, and is higher in the direction of a q-axis 29, i.e., exhibits reduced magnetic resistance. The principle of operation of reluctance machines is based on the presence of a variable magnetic resistance in the air gap 14, a low magnetic resistance in the direction of the q-axis 29, and a high magnetic resistance in the direction of the d-axis 28.

[0017] The pole portion 25 of the single lamination 22 of the rotor 20 includes a pole assembly 30 having a plurality of slots 31 arranged, as shown, in layers 31a, 31b, 31c, and 31d located near an outer peripheral region thereof, wherein the layers 31a, 31b, 31c, and 31d are fixed relative to the outer peripheral region 24. Four layers are shown, but any number of layers may be used. When the plurality of laminations 22 are assembled onto the shaft 26, the slots 31 are aligned and arranged parallel to the longitudinal axis defined by the shaft 26.

[0018] Each of the pole arrangements 30 defines the d-axis 28 and the q-axis 29, wherein the d-axis 28 is aligned with the center of the magnetic pole and the q-axis 29 is orthogonal to the d-axis 28 and aligned with a center of two magnetic poles of the rotor. The d-axis 28 indicates an orientation with the lowest inductance, while the q-axis 29 indicates an orientation with the highest inductance. Therefore, there is a d-axis 28 and a q-axis 29 associated with the respective pole arrangements 30.

[0019] A utilization ratio is defined as follows: ξ,=Lq / Ld wherein: ξ, corresponds to the utilization ratio, L d the inductance along the d-axis 28, and L q the inductance along the q-axis 29.

[0020] As is known to those skilled in the art, the performance of a synchronous reluctance electric machine improves with an increased utilization ratio.

[0021] Anisotropic packets 36 are inserted into the slots 31. A surface portion 38 of one of the anisotropic packets 36 is identified and indicates the portion of the anisotropic packet 36 visible at both ends of the rotor 20. All slots associated with the respective layer 31a, 31b, 31c, and 31d may be hollow 34, or all slots associated with one or more of the layers 31a, 31b, 31c, and 31d may contain an anisotropic packet 36. As shown, the slots 31 of layers 31a and 31b remain hollow 34, while the slots 31 of layers 31c and 31d contain anisotropic packets 36.

[0022] Fig. Figure 3 shows a schematic representation of a first embodiment of the anisotropic stack 36, which includes a lamination stack 42 consisting of a plurality of anisotropic laminations 44 with interposed, non-magnetic spacers 46. The surface portion 38 of the anisotropic stack 36, as well as a lamination rolling direction 40, are indicated, in which the anisotropic laminations 44 are axially layered. An anisotropic material is a material that has unequal physical properties along different axes. The anisotropic laminations 44 described herein preferably have magnetic properties related to core loss and induction permeability, which change depending on the rolling direction of the material as it is processed.In particular, the anisotropic sheets 44 described herein exhibit reduced core loss and increased induction permeability in the rolling direction compared to orthogonal directions of the material. The plurality of anisotropic sheets 44, in one embodiment, may be made from a grain-oriented steel material. In one embodiment, the grain-oriented steel material includes a magnetic iron-silicon alloy processed by cold rolling, which serves to achieve the preferred magnetic properties associated with core loss and induction permeability. Alternatively, the plurality of anisotropic sheets 44 may be made from an amorphous metal alloy formed using a rapid solidification process.

[0023] The sheet rolling direction 40 for the plurality of anisotropic sheets 44 is indicated, as are the preferred dominant d-axis 28 and q-axis 29 of the rotor 20 when the anisotropic stack 36 is inserted into the rotor 20. The non-magnetic spacers 46 can be made by oxide deposition on surfaces of the anisotropic sheets 44, or from aluminum or aluminum oxide, or include both, depending on the required thickness. The thicknesses of the anisotropic stacks 36 and the non-magnetic spacers 46 are preferably determined using engine simulation under simulated engine load conditions and taking into account the magnetic properties, permeability, temperature, torque development, and other factors. A depth 50 of the anisotropic stack 36, which indicates the length the anisotropic stack 36 protrudes into the slot 31 of the rotor 20, is also shown.Preferably, the axis of the low-reluctance anisotropic stack 36 is aligned, as shown, with the Q-axis 29 of the rotor 20, which corresponds to the cold rolling direction 40 for the plurality of anisotropic sheets 44. The depth 50 of the anisotropic stack 36 may be limited to reduce eddy current loss and facilitate insertion.

[0024] Fig. 4 shows a schematic representation of a second embodiment of the anisotropic stack 136, which includes a lamination stack 142 consisting of a plurality of anisotropic laminations 144, each having a plurality of cavities 146 that act as flux barriers, in which the anisotropic laminations 144 are radially layered. The cavities 146 can be manufactured using a suitable technology, e.g., by stamping or laser cutting. Each of the anisotropic laminations 144 has a flat surface into which the cavities 146 are machined. The flat surfaces of the stacked anisotropic laminations 144 have shapes that are arranged analogously to a cross-sectional shape of at least a portion of the associated slot 31 of the rotor 20 into which the anisotropic stack 136 is installed. A surface portion 138 of one of the anisotropic packets 136 is identified and indicates the portion of the anisotropic packet 136 that is visible at both ends of the rotor 20.

[0025] Each of the plurality of anisotropic sheets 144 is preferably fabricated from a grain-oriented steel material. In one embodiment, the grain-oriented steel material comprises a magnetic iron-silicon alloy processed by cold rolling, which serves to achieve the preferred magnetic properties associated with core loss and permeability in the rolling direction. Alternatively, the plurality of anisotropic sheets 144 may be fabricated from an amorphous metal alloy formed using a rapid solidification process.

[0026] The sheet rolling direction 40 for the plurality of anisotropic sheets 144 is indicated, as is the preferred predominant d-axis 28 and q-axis 29 of the rotor 20 when the anisotropic stack 136 is inserted into the rotor 20. A depth 50 of the anisotropic stack 136, which indicates the length the anisotropic stack 136 extends into the slot 31 of the rotor 20, is also shown. Preferably, the q-axis 29 of the rotor 20, as shown, is aligned with the low-reluctance axis of the anisotropic stack 136, which corresponds to the cold rolling direction 40 for the plurality of anisotropic sheets 144.Accordingly, this embodiment of the anisotropic stack 136 includes a lamination stack 142 consisting of a plurality of anisotropic laminations 144, each having a plurality of cavities 146 that act as flux barriers, with a q-axis 29 of the rotor aligned with the low magnetic reluctance axis corresponding to the cold rolling direction for the material. No spacer is required between the individual anisotropic laminations 144. However, the end portion of the lamination stack 142 does not present any barriers to the d-axis flow path. This leakage path runs in the direction of low material permeability, perpendicular to the rolling direction, so that leakage is relatively low.

[0027] Fig.5 shows a schematic representation of a third embodiment of the anisotropic stack 236, which includes a lamination stack 242 composed of a plurality of anisotropic laminations 244. A surface portion 238 of the anisotropic stack 236 is identified and indicates the portion of the anisotropic stack 236 visible at both ends of the rotor 20. Each of the anisotropic laminations 244 has a planar surface with a shape arranged analogously to a cross-sectional shape of at least a portion of the associated slot 31 of the rotor 20 into which the anisotropic stack 236 is installed. Each of the plurality of anisotropic laminations 244 is preferably made of a grain-oriented steel material.In one embodiment, the grain-oriented steel material comprises a magnetic iron-silicon alloy processed by cold rolling, which serves to achieve the preferred magnetic properties associated with permeability in the rolling direction. Alternatively, the plurality of anisotropic sheets 244 may be made from an amorphous metal alloy formed using a rapid solidification process.

[0028] The sheet rolling direction 40 for the plurality of anisotropic sheets 244 is indicated, as is the preferred predominant d-axis 28 and q-axis 29 of the rotor 20 when the anisotropic stack 236 is inserted into the rotor 20. A depth 50 of the anisotropic stack 236, which indicates the length the anisotropic stack 236 extends into the slot 31 of the rotor 20, is also shown. Preferably, the q-axis 29 of the rotor 20, as shown, is aligned with the low reluctance axis of the anisotropic stack 236, which corresponds to the cold rolling direction 40 for the plurality of anisotropic sheets 244.

[0029] This disclosure improves the rotor utilization of a synchronous resistance rotor. Alternatively, motor performance in terms of motor torque per ampere and efficiency can be improved. Furthermore, improved utilization of an embodiment of a synchronous reluctance electric machine can be achieved using grain-oriented electrical laminations that are axially inserted into the rotor slots. The grain-oriented electrical laminations are placed axially into the rotor slots of the radial laminations, resulting in a hybrid structure with axial and radial laminations. A high utilization ratio (L q >>L d) can increase torque development and improve motor efficiency. Increased utilization also improves the high-speed performance of the electric machine. The increase in rotor utilization is achieved by increasing the q-axis inductance through the axial introduction of a grain-oriented lamination, while leaving the d-axis inductance unaffected. The use of radial and axial laminations enables higher pole counts and thus higher speed operation, increased torque per ampere, and increased peak motor torque to achieve similar performance.

[0030] As used in this specification and the claims, the terms "e.g.," "for example," "for instance," "such as," and "like," and the verbs "comprise," "include," "have," and their other verb forms, when used in connection with a listing of one or more components or other elements, are each to be interpreted as open-ended, meaning that the listing is not to be construed as excluding other additional components or elements. Other terms are to be interpreted in their broadest reasonable meaning, unless used in a context that requires a different interpretation.

[0031] It should be understood that although the use of words such as preferred, preferably, preferable or more preferred is used in the above description, the described feature may be desirable, it may nevertheless not be necessary and embodiments lacking it may be considered within the scope of the disclosure, which scope is defined by the following claims.

[0032] When reading the claims, it is intended that when words such as "a", "an", "at least one" or "at least a part" are used, it is not intended to limit the claim to only one element unless expressly stated to the contrary.

[0033] The detailed description and the drawings or figures support and describe the present teachings, but the scope of the present teachings is defined solely by the claims. While some of the best modes and other modes contemplated for carrying out the present teachings have been described in detail, various alternative designs and embodiments for practicing the present teachings are contemplated in the appended claims.

Claims

[1] Synchronous reluctance electric machine (10) comprising: a stator (12) having a plurality of electrical windings; a rotor (20) arranged in a cylindrically shaped cavity formed in the stator (12) and containing a plurality of electrical sheets (22) mounted on a shaft (26), wherein the shaft (26) defines a longitudinal axis, wherein each of the electrical sheets (22) has a plurality of poles and wherein each of the poles has a plurality of plug-in locations (31) arranged near an outer edge region (24), and wherein the slots (31) of the electrical sheets (22) are aligned in the longitudinal direction; and a plurality of packages (36, 136, 236) composed of anisotropic material arranged in the slots (31); wherein the plurality of packages (36, 136, 236) composed of anisotropic material are arranged in a first subset (31a, 31b) of the slots (31); and a second subset (31c, 31d) of the slots (31) remains empty. [2] The synchronous reluctance electric machine (10) of claim 1, wherein the stacks (36, 136, 236) include a radially stacked plurality of laminations (144) made of a grain-oriented steel material. [3] The synchronous reluctance electric machine (10) of claim 1, wherein the stacks (36, 136, 236) include an axially stacked plurality of laminations (44) made of a grain-oriented steel material. [4] The synchronous reluctance electric machine (10) of claim 1, wherein the stacks (36, 136, 236) include a plurality of laminations (44, 144) made of a grain-oriented steel material, and wherein the grain-oriented steel material comprises an iron-silicon magnetic alloy. [5] A synchronous reluctance electric machine (10) according to claim 1, wherein each of the electrical sheets (22) comprises a disc-shaped electrical sheet. [6] Rotor (20) for a synchronous reluctance electric machine (10), the rotor (20) comprising: a plurality of electrical sheets (22) mounted on a shaft (26), wherein the shaft (26) defines a longitudinal axis; wherein each of the electrical sheets (22) includes a plurality of poles; wherein each of the poles includes a plurality of slots (31) arranged near an outer edge region (24), wherein the slots (31) of the electrical sheets (22) are aligned in the longitudinal direction; and a plurality of packages (36, 136, 236) composed of anisotropic material arranged in the slots (31); wherein the plurality of packages (36, 136, 236) composed of anisotropic material are arranged in a first subset (31a, 31b) of the slots (31); and a second subset (31c, 31d) of the slots (31) remains empty.

Images