WO2019156600A1

WO2019156600A1 - Stator for an electric machine and method of assembly thereof

Info

Publication number: WO2019156600A1
Application number: PCT/RU2019/050013
Authority: WO
Inventors: Aleksandr Mettalinovich Tishin; Aleksandr Nikolaevich DOROSHENKO
Original assignee: Aleksandr Mettalinovich Tishin
Priority date: 2018-02-06
Filing date: 2019-02-06
Publication date: 2019-08-15
Also published as: RU2682895C1

Abstract

The invention relates to electrical engineering, in particular, to a stator for an electric machine. The stator comprises multiple stator teeth (1) comprising windings (5) arranged thereon, multiple stator back segments (9) arranged between stator teeth (1), wherein each of the stator teeth (1) comprises at least one slot (4) arranged on the end side (2) thereof, and wedges (7, 12) inserted into the slots (4), thus providing a form closure of the teeth (1) with stator back segments (9), wherein the teeth slots are formed by a groove open from the side of both end and lateral sides of the stator teeth (1). Further disclosed is a method of the stator assembly. Teeth (1) and stator back segments (9 )are made of anisotropic electrical steel. The invention provides improved specific properties of electric machines, increased material utilization rate, as well as decreased production costs and stator weight.

Description

STATOR FOR AN ELECTRIC MACHINE AND METHOD OF ASSEMBLY THEREOF

FIELD OF THE INVENTION

[0001] The present invention relates to electrical engineering, more specifically, to electric machines. Yet more specifically, the present invention relates to a stator for an electric machine with a number of slots per pole and phase less than 1 and a stator structure with semi-closed slots.

BACKGROUND OF THE INVENTION

[0002] Electric machines (EM) have found industrial application in transport, power engineering, communications, spacecraft and other areas. The primary components of an EM include a stator (a stationary member of the electric machine) and a rotor rotating about the stator. The stator consists of a stator back (also referred to as a stator yoke) and teeth coupled with the stator back and having the windings placed thereon.

[0003] EM manufacturers aim to improve specific properties of the machines such as a net power per EM unit weight and a specific torque per EM unit weight. Usually, these are achieved by increasing efficiency of the EM at acceptable EM heating levels. The main methods of improving the efficiency include decreasing heat losses in a stator core (i.e., in the "stator iron") and decreasing ohmic losses in the stator windings.

[0004] Known EM structures utilize a stator back comprising a ring member with stator teeth protruding therefrom, the teeth usually formed integral with the ring of the stator back with the teeth axes extending radially with respect to the EM. In this case, due to the fact that the magnetic flux during the EM operation in the stator teeth area passes in a radial direction, whereas in the stator back area the flux passes in a tangential direction (i.e., along the circumference of the stator back), isotropic electrical steel grades are used for manufacturing EM stators in order to provide substantially uniform magnetic properties of the stator back along its entire length (i.e., in a circumferential direction) to provide uniformity of the magnetic flux passing therethrough during the EM operation. Further, when the stator back is made of an integral ring-shaped member, the material waste ratio is extremely high, with material utilization rate being of only about 20%.

[0005] In other known prior art solutions, the stator teeth are manufactured separately from the stator back and the teeth are then coupled with the stator back. Such solutions simplify the process of manufacturing the stator teeth and further decrease labor intensity of winding the stator windings thereon. Further, such solutions allow using anisotropic steel for manufacturing the stator teeth. However, the stator back in the above solutions is still made integral and has a conventional ring shape, and thus should be made of isotropic steel. Moreover, the process of assembling a stator with the use of individual winding teeth is a complex technical task requiring precision manufacturing of the cores for such teeth and using a non-shrinking compound for stator potting to provide an operational stability of the stator.

[0006] US 4912353 discloses a two-piece motor stator having a stator core and a plurality of teeth, wherein the stator core has slots made in the inner surface thereof for receiving tip portions of said teeth, wherein a plurality of grooves are further made in said inner surface of said stator core, said grooves being arranged to be transverse to the magnetic flux in order to decrease mechanical stress during operation of the electric machine. Said grooves made in the stator back core increase magnetic reluctance of the stator core.

[0007] US 6880229 discloses an electrical machine comprising a plurality of separately formed teeth that can be axially inserted into a stator ring after forming the windings thereon, the teeth including a male dovetail structure. The stator back is made integral and has a ring shape comprising multiple slots for receiving the teeth.

[0008] In the above prior art solutions, the stator with separately formed teeth is assembled by mechanically affixing the teeth to the integral stator back body. A disadvantage of such solutions is that individual teeth must be precisely linked with each other, and the process of affixing the individual teeth requires an integrally formed ring-shaped stator back which decreases weight/dimensions ratio of the stator due to a high material waste caused by manufacturing an integral stator ring; further, only isotropic steel grades can be used for manufacturing the prior art stator rings.

[0009] RU 147 322 discloses a stator for an electric machine, the stator comprising a set of coils each formed by windings affixed via an insulator to the core formed by a package of identical T-shaped plates with a base comprising a slot and a protrusion on the opposite sides thereof, wherein the T-shaped portions of the plates formed into the package are stacked one over another, and plate base protrusions of one package are received by the slots of another package during the assembly, and wherein at least two plates in each package are arranged with respect to each other in such a manner that the protrusions and slots in the bases of said plates are located on opposite sides. Therefore, each stator tooth according to RU 147 322 is formed integrally with a section of a stator back. This prior art structure provides an increase in material utilization rate during manufacture of stator elements; however, due to an essentially transverse direction of magnetic flux passing through the tooth and the stator back, respectively, during the EM operation, only isotropic steels can be used as the teeth and stator back material in said prior art solution. Besides, in this solution, gaps may occur at a junction of the protrusions and the slots of the bases of the T-shaped plates, resulting from the wear of a blanking tool used for manufacturing said plates, which gasp will lead to an increase in the reluctance to the magnetic flux closure through the plates during EM operation.

[0010] Therefore, there is a need for an electric machine with improved power- and torque-related specific properties, featuring an improved efficiency (efficiency ratio, power coefficient) and low production costs due to decreasing material consumption and providing a more lightweight device.

SUMMARY OF THE INVENTION

[0011] It is an object of the present invention to provide a stator for an electric machine with improved operational properties while retaining substantially equal electric machine weight, or decreasing the weight of the electric machine stator while retaining operational properties of the electric machine, that enables to further decrease material consumption during manufacture, and to simplify the process of assembly of the electric machine stator.

[0012] The object is achieved by a stator for an electric machine, the stator comprising multiple stator teeth comprising windings arranged thereon, multiple individual stator back segments of a stator back, the segments being arranged between the stator teeth, wherein each of the stator teeth comprises at least one slot arranged on the end side thereof facing the stator back when the stator is assembled, i.e. in a radially outward direction, with wedges inserted into the slots, thus providing a form closure of the teeth with the stator back segments, wherein the teeth slots are formed by a groove open from the side of both end and lateral sides of the stator teeth.

[0013] This arrangement, when the slot is arranged from both the end side, i.e., from the teeth side facing the radially outward direction, and from the side of the stator teeth lateral sides, allows inserting the wedge into the stator teeth during a stator assembly step both from the end sides and from the lateral sides of the teeth.

[0014] In one embodiment, the teeth slots are formed by laser cutting or electroerosion cutting.

[0015] In an advantageous embodiment of the stator of the present invention, all the stator back segments are made of anisotropic electrical steel, wherein the direction of best magnetic properties of the steel coincides with the direction of the magnetic flux path in the stator back segments. In this case, said direction of best magnetic properties of anisotropic steel is arranged along the extension of the segments, i.e., in the circumferential direction of the stator back, and therefore, in a direction transverse to the longitudinal axis of the stator teeth.

[0016] The solution of the present invention allows manufacturing both the stator teeth and the stator back from anisotropic electrical steel, wherein the direction of best magnetic properties of anisotropic steel in the teeth coincides with the tooth axis, while it coincides in the stator back with the circumferential direction or the longitudinal direction of each stator back segment, respectively.

[0017] The use of a wedge inserted into a longitudinal slot of a tooth further compensates for gaps invariably formed and growing during the manufacture and assembly of stators due to a punch tool wear, particularly achieved by pressing the tooth members against the stator back segments, thus eliminating the risk of a significant increase in magnetic reluctance of the stator teeth to a magnetic flux closure through the tooth shaft and the stator back.

[0018] Windings on stator teeth are formed preferably using a winding wire with a rectangular cross-section. [0019] When manufacturing each stator tooth as an individual member onto which sections of the windings are wound, the windings can be arranged with turns touching as opposed to scramble winding in case of conventional mesh windings, thus approximately doubling the winding factor while minimizing an average turn length for the stator teeth and thus decreasing winding losses which is a value of a second power of the winding factor for the slot formed around a tooth neck, and linearly dependent on an average turn length of the windings section.

[0020] In one embodiment, stator teeth sections facing the stator back when the stator is assembled have a dovetail shape widening towards the teeth end side. This arrangement, when the stator teeth sections facing the stator back have a dovetail shape widening towards the teeth end side, simplifies a form closure of the teeth with the stator back segments during and after the stator assembly, i.e., after inserting the wedges into the teeth slots. Further, the above tooth shape combined with complementary shape of the back segment edges provides a simple and secure attachment of the stator elements with respect to each other, preventing the elements from falling out of the mount if the stator is assembled with a mount prior to inserting the wedges into the slots.

[0021] In one embodiment, the wedges have a plate shape having a substantially rectangular cross-section and are inserted into the slot from the teeth end side.

[0022] In one embodiment, the wedges have a bar or pin shape made of a soft magnetic material or a non-soft magnetic material and are inserted into the tooth slots from the teeth lateral side.

[0023] In one embodiment, the tooth wedges are made of a high thermal conductivity material. This arrangement, when the wedges are made of a high thermal conductivity material, allows reducing thermal stress occurring in the stator teeth base area of an electric machine. [0024] The object of the invention is further achieved by a method of assembly of an electric machine stator, the method comprising the steps of:

providing multiple individual stator teeth comprising windings arranged thereon,

providing multiple individual stator back segments of a stator back, forming at least one slot on the end side of each of the teeth, the end side facing a radially outward direction when the stator is assembled,

wherein the teeth slots are formed by a groove open from the side of both end and lateral sides of the stator teeth,

arranging the stator teeth between the stator back segments in alternating manner, and

inserting wedges into the slots of at least some of the stator teeth, thus providing a form closure of the teeth with the stator back segments; connecting the teeth windings in accordance with a winding arrangement pattern for the electric machine.

[0025] The stator according to the present invention can be assembled using a mount or without using thereof.

[0026] In one embodiment, all stator back segments are made of anisotropic electrical steel, wherein the direction of best magnetic properties of the steel coincides with the longitudinal direction of the segments.

[0027] In one embodiment, the teeth sections facing the stator back have a dovetail shape widening towards the teeth end side. [0028] In one embodiment, the windings on the stator teeth are formed preferably using winding wire with a rectangular cross-section. [0029] In one embodiment, the tooth wedges are formed in a plate shape having a substantially rectangular cross-section and are inserted into the tooth slots from the teeth end side.

[0030] In one embodiment, the tooth wedges are formed in a bar shape and are inserted into the tooth slots from the teeth lateral side.

[0031] In one embodiment, the tooth wedges are made of a high thermal conductivity material.

[0032] As used herein, the term "individual stator back segments" refers to the stator back segments formed as individual or separate elements independently from the stator teeth to be arranged between the stator teeth in an alternating manner, wherein the stator back, in this case, is formed of said stator back segments and stator tooth bases arranged therebetween. Accordingly, the number of the stator back segments is equal to the number of the stator teeth in the electric machine.

[0033] The technical effect provided by the present invention consists in an improvement of specific properties of the electric machine, a decrease in production costs and stator weight, the invention further providing a simplified method of assembly of an electric machine stator, providing a more optimal use of anisotropic (including transformer) steel grades with significantly reduced losses caused by a magnetic reversal (by 15% to 20% compared to the prior art solutions), and significantly simplifying the process of winding the wire with a high density and uniformity of the windings in order to lower Joule losses.

[0034] Therefore, the present technical solution provides forming individual stator teeth such that to provide a simple and most effective process of applying windings thereon, and further provides forming a stator back from individual relatively short segments, wherein each segment can be made of anisotropic electrical steel, thus improving magnetic properties of the stator back and therefore increasing operational efficiency of the electric machine with a significant increase in a material utilization rate.

[0035] In contrast to the prior art solutions, the stator structure and the method of stator assembly of the present invention provide forming a stator back from individual arc-shaped segments arranged between stator teeth. The arrangement, when the stator back is formed from individual segments (with each segment being relatively short), allows using anisotropic steel for manufacturing all the segments, thus potentially achieving best magnetic properties of the stator back in a direction coinciding with the longitudinal direction or extension, i.e., with the direction of the largest dimension, of the stator back segments, thus attaining magnetic properties of the stator back along its entire circumference exceeding the magnetic properties of all prior art stators with stator backs made of isotropic electrical steel. Said direction of best magnetic properties usually coincides with the rolling direction of anisotropic steel. Furthermore, the arrangement, when the stator back is made up of individual segments, lets achieve material utilization rate significantly exceeding (up to several times) the material utilization rate achieved during manufacturing of an integral ring stator, with the latter material utilization rate usually not exceeding 20%.

[0036] Therefore, according to the present invention, both stator teeth and stator back segments can be all made of anisotropic electrical steel. In the present invention, the direction of the largest dimension is the direction of the stator back segments coinciding with the circumferential direction of the stator back (with the stator in an assembled state), with flux closure during electric machine operation also occurring along said direction. The direction of the largest dimension of the stator back segments further generally coincides with the direction of the tangent line passing through the center of the arc-shaped stator back segment. In this case, anisotropic steel (in contrast to special-purpose (precision) isotropic electrical steel) displays analogous or similar magnetic properties; however anisotropic steel is 50-60 times cheaper than special-purpose precision isotropic steel. Therefore, the stator for an electric machine allows to create an electric machine with operational properties achievable in the prior art only by using expensive special-purpose isotropic steel grades (such as 49K2FA) as a stator back material.

[0037] The arrangement, when the stator back magnetic circuit is made of anisotropic steel having best magnetic properties in a circumferential direction of the stator back, provides manufacturing a stator back of smaller thickness compared to the stator back made of expensive isotropic steel, or provides a more efficient EM using identical EM dimensions. Therefore, tooth slots can be increased by 10 to 20%, thus allowing to accommodate a greater number of winding turns, and therefore, to increase specific properties of the electric motor. The windings can be made using winding wire with a rectangular cross-section, thus achieving maximum winding factor. In particular, according to calculations, with e.g. 14 stator poles in the stator of the present invention, tooth neck thickness can be decreased by about 25%, while stator back width can also be decreased. Therefore, a larger number of winding wire turns can be arranged on each tooth while achieving the same winding factor. Thus, the required torque for the electric machine can be achieved at lower currents.

[0038] Further, the present structure of a stator for an electric machine does not require especially precise tooth core manufacturing, thus potentially minimizing gaps between adjacent stator core elements and providing necessary stator strength and mechanical stability in operation.

[0039] The present technical solution can be used in a regular or inverted electric machine structure, i.e., wherein the stator is arranged inside or outside the rotor. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The present invention is further described with reference to the accompanying drawings, wherein :

[0041] FIG. 1 shows a schematic cross-section of an electric machine section with a stator of the present invention;

[0042] FIG. 2 shows an enlarged view of the interface area between the stator back segment and the stator tooth side facing the stator back with a slot for a wedge arranged on the end side;

[0043] FIG. 3 shows a side view of a stator tooth of the present invention with a tooth slot according to the first embodiment;

[0044] FIG. 4 shows a side view of a stator tooth of the present invention with a tooth slot according to the second embodiment;

[0045] FIG. 5 shows a schematic view of a stator of the present invention, wherein the teeth (without windings) and stator back segments are assembled on a mount;

[0046] FIG. 6 shows a schematic perspective view of a stator tooth of the present invention formed by a package of plates;

[0047] FIG. 7 shows an alternative embodiment of the interface area between the tooth and the stator back segments.

DETAILED DESCRIPTION OF THE INVENTION

[0048] FIG. 1 shows a schematic view of an electric machine comprising multiple stator teeth 1 and a stator back closing magnetic flux between the stator teeth 1. Each tooth 1 comprises windings 5 preferably made of wire with a rectangular cross-section to increase the winding factor. The arrangement, when the wire windings on the teeth are done using a winding wire with a rectangular cross-section approximately, allows to double the winding factor compared to that of the mesh windings, whereas the average turn length of the windings 5 is minimal. The winding factor increase and the decrease in length of each turn lowers ohmic losses in the stator and thus increases EM efficiency. At this step, windings 5 can be provided for each individual tooth separately, or the windings 5 can be done using a common wire for a group of teeth 1 of one electric machine phase.

[0049] Each tooth 1 has a symmetry plane A-A hereinafter referred to as the longitudinal axis A-A of the tooth 1 extending in a stator radial direction. Each tooth 1 comprises a slot 4 arranged on the tooth end face or end side 2 of the tooth facing the stator back when the stator is assembled, i.e. in a radially outward direction, the slot extending in a tooth radial direction, preferably along the symmetry plane A-A thereof, at a depth of approximately 40% to 75% of the tooth height. The radially outward direction means a direction (indicated in FIG. 1 by arrow 23) along the axis A-A of the tooth 1 from the tooth pole side 15 to the tooth end side 2. The slot 4 substantially extends over the entire height of the core 6 of the tooth 1, and the slot is open in the direction of the tooth end side or surface 2 as well as in the directions of tooth lateral sides or surfaces 14, the plane of which is substantially parallel to the plane of the electric machine stator. The slot width H is selected based on the thickness Q of the tooth core 6 and on the external diameter of the stator; for stators having a diameter of several decimeters, the slot width H can range from 0.1 to 1.5 mm. The slot 4 can be widened on the end side 2 of the tooth 1 (as shown in FIG. 2) in order to facilitate insertion of the wedge 7 into the slot. The height of stator tooth 1 is defined as the distance between the inner surface of stator back segments 9 and the tooth pole side 15 facing the electric machine rotor 3, with said distance measured along the axis A-A of the tooth 1. The height of the core 6 of the tooth 1 (similarly to the height of the stator back core) is defined as the width of the tooth core 6 plate package or stack and the width of the stator back segments 9 closing the magnetic flux between teeth 1, with said height measured in a direction transverse to the electric machine stator plane. Calculations carried out by the claimant show that slot 4 depth measured along the axis A-A of the tooth 1 does not substantially affect torque produced by the motor.

[0050] As seen in FIG. 3 and FIG. 4, at least one recess 13 can further be formed along the slot 4, said recess thus widening the slot 4, the recess 13 used for insertion of a bar- or pin-shaped wedge 12 made of a soft magnetic material or a non-soft magnetic material from lateral sides of the tooth 1. The recess 13 preferably comprises a cylindrical hole formed along the slot across the entire height of the tooth core 6 and extending between the opposite lateral sides 14 of the tooth 1. However, the cross- section of the recess 13 may not be circular; the cross-sectional shape of the wedge 12 should complement the cross-section of the recess 13. In addition to the recess 13, a recess 20 can be further formed along the length of the slot in the bottom portion thereof, the recess 20 used for compensating for elastic stress acting on the tooth when the tooth is wedged during the stator assembly.

[0051] The stator of the present invention is assembled using the following method. Stator teeth 1 comprising windings 5 and slots 2 are positioned in a circumferential direction within a ring mount 16 alternating with the stator back segments 9 in such a manner that each tooth 1 is surrounded by two adjacent stator back segments 9, as shown in FIG. 5, and each stator back segment 9 is in turn surrounded by two adjacent teeth 1. The stator back can be assembled using a mount or without using thereof.

[0052] Teeth 1 form a dovetail 8 shape on the side facing the stator back when the stator is assembled, the dovetail 8 widening towards the end side 2 of the tooth 1 and thus forming a recess 18 of the dovetail 8, the recess 18 being formed by the recess inner surfaces 21, whereas both ends of the stator back segments are tapered thus forming a tapered protrusion 17 forming a pointed shape, the protrusion 17 being formed by the protrusion outer surfaces 22 and being complementary to the recess 18 of the teeth in the interface area with the stator back segments 9. During a mount-assisted assembly, the protrusions 17 of back segments 9 enter the recesses 18 of stator teeth thus providing a form closure therebetween preventing each tooth 1 and each stator back segment 9 from falling out of the mount (see FIG. 5). The teeth and the stator back segments can be preliminarily fixed relative to each other without the mount, for example, by means of a magnetic holder.

[0053] It should be noted that the dovetail 8 shape of the stator teeth 1 at their interface with the stator back segments 9 and the tapered protrusion 17 shape of the stator back segments 9 coupled therewith are merely exemplary embodiments of the form closure between the stator elements during the stator assembly. Naturally, the form closure can also be achieved by providing a mirrored interface area between teeth 1 and the stator back segments 9, e.g., as shown in FIG. 7, wherein stator teeth 1 are provided with double-sided protrusions 19 on the side facing the stator back, the protrusions 19 entering or received during the stator assembly by complementary slots formed on the ends of the stator back segments 9 .

[0054] As shown in the enlarged view of the interface area between the stator back segments 9 and the stator teeth 1 in FIG. 2, a manufacturing gap L of about 0.1 mm is provided between the stator back segments and the teeth during assembly. The gap L provides unobstructed assembly of the stator back segments 9 and the stator teeth 1 in a mount or in another holder.

[0055] After positioning all the teeth 1 and the stator back segments 9 in the mount according to FIG. 5, the stator structure is secured together by inserting wedges 7 into the tooth slots 4 along the A-A axis of the teeth shown in FIG. 1. Due to elastic deformation of the tooth portions located on both sides of the slot 4 (i.e., due to a movement of the dovetail 8 halves in a tangential direction of the stator as a result of the gaps 4 widening due to the wedging caused by inserting the wedges 7), the manufacturing gaps L are decreased or eliminated, with the surfaces 21 of the recess 18 and the surfaces 22 of the protrusion 17 abutting against each other, thus the stator is secured in a rigid structure essentially without any interface gaps between the surfaces 21, 22 of the teeth 1 and the stator back segments, wherein the form closure between the stator teeth 1 and the of the stator back segments 9 is provided. The above arrangement further minimizes or even eliminates the gaps in interface areas between the stator core elements and provides necessary stator strength and mechanical stability in its operation, as well as minimizes the magnetic reluctance of the stator core to the magnetic flux closure through the tooth shaft and the stator back during the operation of the electric machine.

[0056] The wedges 7, 12 are preferably made of a high thermal conductivity material, thus reducing thermal stress occurring in the stator teeth base area of an electric machine.

[0057] The wedges 7 can be inserted into the slot 4 from the end side 2 of the teeth or from the lateral side 14 of the stator teeth. In the former case, wedges 7 can be formed by a metal or polymer plate with a substantially rectangular cross-section having a pointed lower end to facilitate insertion thereof into the slot 4 along the A-A axis of the tooth. Thickness of the plate is selected to be slightly larger than slot 4 width H to provide secure form closure of the recesses 18 of the end part of each tooth 1 with the adjacent protrusions 17 of the stator back segments 9 caused by wedging of the end side 2 of the tooth 1. The wedge 7 length, i.e., its dimension in the direction of the tooth core 6 height, can be equal to the slot length in the longitudinal direction or can be smaller than the slot length, while the mount 16, in case of its use for assembling the stator, can also extend along only a portion of the stator core height. [0058] In the configuration with the wedges inserted from the tooth lateral side 14, the wedges can be formed by a wedge 12 formed of a metal or polymer shaft or rod of a substantially circular cross-section with a diameter slightly larger than the diameter D of the recess 13. During the stator assembly, the wedges 12 can be inserted from one or both lateral sides 14 of the tooth 1. In a particular embodiment for stators having a diameter of about several decimeters, the diameter of the wedge 12 rod can range from 1.5 mm to 5 mm. As the cores 6 of both the teeth 1 and the stator back segments 9 are preferably formed by a package or a stack of flat plates, a form closure for each stator tooth 1 with respect to the adjacent stator back segments can be achieved simply by inserting the wedge 12 rod from both lateral sides 14 of the tooth only partially into a portion of the recess 13 length, i.e., only for a part of the tooth core 6 height.

[0059] The wedges 7 are preferably made of a composite material with thermal conductivity 2.5 times higher than thermal conductivity of copper. A composite material that expands upon mount can theoretically be used as a wedge. In this case, the composite material is forced into tooth slots under pressure during stator assembly and the material is then set, thus causing it to expand and provide a form closure between the stator back segments and the stator teeth.

[0060] After inserting the wedges 7 into the tooth 1 slots 4, the mount can be removed. In subsequent steps, windings of individual teeth 1 or groups of teeth 1 can be connected in accordance with the electrical circuit of the electric machine, and the stator structure can be potted using a conventional method.

[0061] Both all the stator back segments 9 and all the teeth 1 are preferably made of anisotropic electrical steel with improved magnetic properties along the rolling direction. The magnetic flux direction 10 in the stator back segments 9 and the magnetic flux direction 11 in the tooth cores 6 coincide with the direction of best magnetic properties of the anisotropic electrical alloy used to form the stator back segments 9 and the teeth 1. Therefore, the thickness W of the stator back segments and the thickness Q of the tooth cores 6 can be decreased while retaining identical operational properties of the electric machine. Therefore, EM weight is reduced and the copper winding factor of the stator is increased, thus improving specific properties of the EM and improving its efficiency. Furthermore, anisotropic steel is much cheaper compared to a special-purpose isotropic steel with identical magnetic parameters, which reduces EM production costs. An electric machine of the same size can have significantly improved specific properties as discussed hereinabove.

[0062] The tooth cores 6 and the stator back segments 9 are preferably made using a conventional method by piling individual flat plates cut from sheets of electrical steel (see FIG. 5) to reduce eddy currents in the stator cores. Further, the present invention provides a significant increase in material utilization rate compared to prior art stators by forming the stator back from individual segments.

[0063] Therefore, the present technical solution both retains all the advantages achieved in the prior art solutions wherein stator teeth 1 are formed separately, and further reduces the electric machine weight and production costs by using anisotropic steel and increasing a material utilization rate when forming the stator back due to a significant decrease in material waste resulted in the process of cutting steel sheets to form the stator back; the solution further improves operational properties (in particular, efficiency) of the electric machine of the same dimensions or decreases the size of the electric machine while maintaining its efficiency coefficient. Further, synchronous EM based on permanent magnets and formed with a stator of the present invention exhibit lower loss values and improved weight/size properties compared to similar prior art solutions. The disclosed stator structure provides record efficiency values for an electric machine (efficiency of up to 98%, depending on the power) and high specific output performance (up to 8-10 kW/kg, depending on RPM) without using expensive materials, in particular high silicon steel grades (10JNEX900).

[0064] In operation, the stator of the present invention can provide a reduction in active element mass (of permanent magnets, electrical steel and copper) of up to 1.5 times and more, thus further decreasing losses and providing a cumulative effect. For instance, the use of the novel stator structure in an electric machine design (27 kW, 6000 RPM) allows for a reduction in axial length from 100 mm to 60 mm without using expensive steel grades while retaining efficiency. Tests and calculations made by the authors have resulted in a positive conclusion regarding prospective mass production of stators of the present invention for synchronous electric machines based on permanent magnets.

[0065] Calculations made in the course of development of the present invention have indicated that, compared to prior art electric machines with a solid magnetic core and non-removable teeth, the stator of the present invention provides a potential reduction in the stator core height of over 1.5 times while retaining identical nominal torque values.

List of reference numerals

1. Tooth

2. Tooth end side/surface

3. Rotor

4. Tooth slot

5. Windings

6. Tooth core

7. Wedge

8. Tooth dovetail

9. Stator back segment

10. Magnetic flux direction in stator back segments 11. Magnetic flux direction in tooth cores

12. Wedge

13. Recess

14. Lateral side/surface

15. Polar side

16. Mount

17. Protrusion

18. Recess

19. Protrusion

20. Recess

21. Recess surface

22. Protrusion surface

23. Radially outward direction

W - Stator back segment thickness Q - Tooth core thickness

L - Manufacturing gap

A-A - Tooth axis

Claims

1. A stator for an electric machine, the stator comprising :

multiple stator teeth comprising windings arranged thereon, and multiple individual stator back segments of a stator back, the segments being arranged between the stator teeth, wherein

each of the stator teeth comprises at least one slot arranged on the end side thereof facing a radially outward direction when the stator is assembled, with wedges inserted into the slots, thus providing a form closure of the teeth with the stator back segments,

wherein the teeth slots are formed by a groove open from the side of both end and lateral sides of the stator teeth.

2. The stator according to claim 1, wherein all stator back segments are made of anisotropic electrical steel, wherein the direction of best magnetic properties of the steel coincides with the direction of magnetic flux paths in the stator back segments.

3. The stator according to claim 1, wherein the windings on the stator teeth are formed using a winding wire with a rectangular cross- section.

4. The stator according to claim 1, wherein stator teeth sections facing the stator back when the stator is assembled have a dovetail shape widening towards the teeth end side.

5. The stator according to any of claims 1-4, wherein the wedges have a plate shape having a substantially rectangular cross-section and are inserted into the slot from the teeth end side.

6. The stator according to any of claims 1-4, wherein the wedges are formed in a bar shape and are inserted into the tooth slots from the teeth lateral side.

7. The stator according to any of claims 1-6, wherein the tooth wedges are made of a high thermal conductivity material.

8. A method of assembly of an electric machine stator, the method comprising the steps of:

providing multiple stator teeth comprising windings arranged thereon, providing multiple individual stator back segments of a stator back, forming at least one slot on the end side of each of the teeth, the end side facing a radially outward direction when the stator is assembled,

arranging the stator teeth between the stator back segments, and inserting wedges into the slots of the stator teeth, thus providing a form closure of the teeth with the stator back segments;

connecting the teeth windings in accordance with a winding arrangement pattern for the electric machine.

9. The method according to claim 8, wherein all stator back segments are made of anisotropic electrical steel, wherein the direction of best magnetic properties of the steel coincides with the direction of magnetic flux paths in the stator back segments.

10. The method according to claim 8, wherein teeth sections facing the stator back have a dovetail shape widening towards the teeth end side.

11. The method according to claim 8, wherein the windings on the stator teeth are formed using a winding wire with a rectangular cross- section.

12. The method according to any of claims 8-11, wherein the tooth wedges are formed in a plate shape having a substantially rectangular cross-section and are inserted into the tooth slots from the teeth end side.

13. The method according to any of claims 8-11, wherein the wedges are formed in a bar shape and are inserted into tooth slots from the teeth lateral side.

14. The method according to any of claims 8-13, wherein the wedges are made of a high thermal conductivity material.