GB2620400A

GB2620400A - Stator core assembly

Info

Publication number: GB2620400A
Application number: GB2209870.1A
Authority: GB
Inventors: Boubaker Nadhem; Wilkinson Michael
Original assignee: Safran Electrical and Power SAS
Current assignee: Safran Electrical and Power SAS
Priority date: 2022-07-05
Filing date: 2022-07-05
Publication date: 2024-01-10
Also published as: GB202209870D0

Abstract

A stator core assembly for an electric machine comprising an annular back iron 110 having a longitudinal axis 101 and comprising radially oriented openings 111, 112 and teeth 120 where at least one tooth of the teeth comprises at least one mounting projection 121, 122. The back iron and teeth are configured such that the mounting projection can be inserted in a radial direction with respect to the longitudinal axis into the openings to mount the tooth to the back iron. The back iron and the tooth may be configured so that the projection can be slidably received by the opening to prevent relative movement therebetween along the longitudinal axis. The teeth may comprise at least two projections and the openings may comprise at least two openings to receive those projections, where the two projections are disposed at different axial positions along the tooth with respect to the longitudinal axis. The openings may be a blind hole or a through hole. The opening may comprise a rectangular hole and the projection may have a rectangular cross section configured to be received by the rectangular hole. The back iron may comprise FeSi and the teeth may comprise FeCo. The back iron and the teeth may be made up from separate laminations.

Description

STATOR CORE ASSEMBLY

Technical Field

The invention relates to a stator core for an electric machine for use in an aircraft. In particular, the invention relates to a stator core assembly and related methods of manufacture.

Background of the Invention

Electric machines can be used for electrical power generation or to provide motive power in aircraft. An electric machine is typically formed of an assembly of magnetic circuit components, comprising a rotor and a stator. As is well known, rotation of the rotor relative to the stator causes interaction of the magnetic field generated by the rotor with windings provided on the stator, generating an induced electromotive force (EMF) and/or electrical current. In a permanent magnet generator, the rotor's magnetic field is produced by permanent magnets, which induces an AC voltage in the stator windings as the stator windings pass through the moving magnetic field of the permanent magnet. In a motor, a rotating AC current supplied to the windings of a stator can induce torque in a rotor.

Methods of manufacturing stator cores for electric machines can be hindered by the proximity of adjacent teeth during the winding operation, and magnetic properties of stator cores made by known methods can be improved upon.

There exists a need for an improved stator core and related method of manufacture.

Summary of the Invention

According to an aspect, there is provided a stator core assembly comprising any or all of the following features: an annular back iron having a longitudinal axis and comprising a plurality of radially oriented openings; and a plurality of teeth, at least one tooth of the plurality of teeth comprising at least one mounting projection; wherein the annular back iron and the at least one tooth are configured such that the at least one mounting projection can be inserted in a radial direction with respect to the longitudinal axis into at least one of the plurality of radially oriented openings, to mount the at least one tooth to the annular back iron.

By arranging at least one tooth to be radially insertable into the annular back iron, in contrast to arrangements in which the teeth and back iron are formed from an integral component, the stator assembly can be manufactured with improved material yield, cost effectiveness and precision tolerances. For example, this arrangement facilitates more efficient needle winding of the individual stator teeth prior to assembly. There is also provided a greater degree of freedom in terms of the relative dimensions of the components. Furthermore, different materials may be selected for the teeth and the back iron, allowing the material properties to be tailored for each component.

The annular back iron and the at least one tooth may be configured such the at least one mounting projection can be slidably received, in a radial direction, by the at least one radially oriented opening to prevent relative movement therebetween along the longitudinal axis. At least one tooth of the plurality of stator teeth may comprise at least two mounting projections. The plurality of radially oriented openings may comprise at least two radially oriented openings. This provides a more robust stator assembly in which the teeth can be accurately positioned with respect to the back iron.

At least one of the plurality of radially oriented openings may be a blind hole or a through hole. The at least one radially oriented opening may comprise a rectangular hole. The mounting projection may have a rectangular cross section configured to be received by the rectangular hole. This provides an arrangement for mounting the teeth to the back iron using components that are simpler to manufacture.

The annular back iron may comprise FeSi or FeCo. At least one of the plurality of teeth may comprise FeCo. By forming the teeth from FeCo, the magnetic performance of the stator is improved. By forming the annular back iron from FeSi, the mechanical performance of the stator is improved.

A first tooth of the plurality of stator teeth may have a first stator winding wound therearound. A second tooth of the plurality of stator teeth may have a second stator winding wound therearound. The second stator tooth may be adjacent the first tooth. This has the advantage of providing a double winding arrangement.

The at least two mounting projections may be disposed at different axial positions along the at least one tooth with respect to the longitudinal axis. This has the advantage of providing a more robust assembly.

The annular back iron may comprise a plurality of core laminations. The at least one tooth of the plurality of stator teeth may comprise a plurality of tooth laminations. The plurality of tooth laminations may be separate from the plurality of core laminations. Given that laminations are typically formed from a rolled metal sheet, the microstructural anisotropy can cause imbalances in the magnetic properties of the stator teeth. By arranging at least one tooth to be insertable into the annular back iron according to the invention, the anisotropy of each tooth can be preferentially aligned with the radial direction of the annular back iron when inserted therein. In particular, this arrangement allows the rolling direction of each tooth lamination to be aligned with the radial direction when assembled with the back iron. Furthermore, using separate laminations allows the thickness of a given tooth lamination to be different to the thickness of a given core lamination.

At least one of the plurality of core laminations may have a radial thickness being constant around the entire circumference thereof. This has the advantage of simplifying manufacturing.

The axial length of the teeth may be arranged to be shorter than that of the annular back iron. In this way, at least one axial end of the annular back iron may overhang at least one of the plurality of teeth in the axial direction. This has the advantage of providing space to locate an end cap onto the stator.

According to another aspect, there is provided a tooth for the stator core assembly as described hereinabove. The tooth may comprise at least one mounting projection. The at least one mounting projection may be suitable for insertion into the annular back iron described hereinabove.

According to another aspect, there is provided an annular back iron for the stator core assembly described hereinabove. The annular back iron may comprise a plurality of radially oriented openings for receiving mounting projections of the plurality of teeth described hereinabove.

According to another aspect, there is provided a method of assembly of a stator core for an electric machine, comprising any or all of the following the steps: providing an annular back iron comprising a plurality of radially oriented openings; providing at least one tooth comprising at least one mounting projection; and mounting the at least one tooth to the annular back iron by inserting the at least one mounting projection into at least one of the plurality of radially oriented openings.

Before the mounting step, the method may comprise the step of winding a stator winding onto the at least one tooth. Providing the at least one tooth may comprise providing at least one first tooth lamination and at least two second tooth laminations. The at least one first tooth lamination may be longer than the at least two second tooth laminations. The method may comprise bonding the at least one first tooth lamination between the at least two second tooth laminations such that the at least one first tooth lamination provides the at least one mounting projection.

The plurality of radially oriented openings may be through holes. The step of providing the annular back iron may comprise providing at least one plain annular lamination between at least two crenellated laminations. The step may further comprise bonding the plain annular and crenellated laminations together such that crenellations in the crenellated laminations form the plurality of radially oriented openings.

According to another aspect, there is provided an electric machine comprising the stator core assembly described hereinabove.

Brief Description of the Drawings

Further features and advantages of the present invention will become apparent from the following description of embodiments thereof, presented by way of example only, and by reference to the drawings, in which: Figure 1 is a perspective view showing a stator according to an embodiment; Figure 2A is a perspective view of a stator tooth according to an embodiment; Figure 2B is a cross section of the stator tooth according to an embodiment; Figure 2C is another cross section of the stator tooth according to an embodiment; Figure 3 is an exploded view illustrating the assembly of a stator according to an embodiment; Figure 4 is a perspective view of part of an assembled stator according to an embodiment; Figure 5 is a perspective view of a stator according to another embodiment; Figure 6 is a perspective view of an annular back iron of the stator according to an embodiment; Figure 7A is an exploded view of stator core laminations according to an embodiment; Figure 7B is an exploded view of core portions of the stator according to an embodiment; Figure 8 is a schematic diagram of an aircraft according to an embodiment.

Detailed Description

A conventional magnetic core for a stator, including the back iron and teeth for receiving windings, is commonly formed from stacking together annular laminations. The sheets from which such annular laminations are manufactured must have an area larger than the circular footprint of the stator, which depends upon the outer diameter of the stator. This leads to a large proportion of the lamination material being wasted. Furthermore, conventional stators with a large outer diameter require complex progression tooling of wide strips of lamination material; this increases the manufacturing lead time and cost. Furthermore, it is difficult to access the interior of the continuous ring of a conventional stator for the purposes of manually or automatically winding the conductor thereon, further increasing manufacturing lead time.

A magnetic core for an electric machine is disclosed in the context of an aircraft engine assembly. An electric machine typically includes a stator having a plurality of magnetic teeth from a back iron, and a rotor configured to rotate about a longitudinal axis of the stator. In this arrangement, the stator is an assembly formed of an annular back iron with a plurality of teeth connected thereto. The stator teeth are configured to receive conductors, for example in the form of copper windings. The rotor of such an electric machine includes a plurality of magnetisable elements such as permanent magnets. As such, the electric machine formed from the stator and the rotor can act as a generator when the rotor rotates within the stator thereby inducing an electric current in the windings of the stator, and can also act as an electric motor when an electric current provided in the windings induces rotation of the rotor.

An arrangement for connecting the teeth to the annular back iron is provided. The teeth can be mounted to the annular back iron via a mechanical connection interface. The interface can include a projection and an opening, together forming at least one cooperating or mating pair. One or more projections on a stator tooth can cooperate with a corresponding number of radially oriented openings in the annular back iron. The openings can be blind holes or recesses formed in the inner wall of the annual back iron, or they can be through-holes formed through the thickness of the wall of the annular back iron. The interface is configured for insertion of a stator tooth into the annular back iron in a radial direction with respect to the longitudinal axis of the stator. The longitudinal axis will be understood to be the axis about which the stator is arranged such that a rotor rotates about the longitudinal axis when the device is in operation. It may be termed a rotational axis of the electric machine.

Figure 1 illustrates a stator core 100 according to embodiments of the invention. The stator core 100 is a stator core assembly which comprises an annular back iron 110 and a plurality of stator teeth 120. The stator core 100 has a longitudinal axis 101. The annular back iron 110 has an annular form and, when assembled with suitable stator teeth, provides a stator core for an electric machine. In the arrangement shown, the annular back iron 110 has an annular form in which the wall thickness may be substantially constant around the longitudinal axis 101. However, the skilled person will appreciate that the annular back iron 110 may also comprise local protrusions or lugs to facilitate interfacing with or mounting to the housing. The annular back iron 110 can comprise a plurality of core laminations. Each core lamination comprises an annulus of back iron material, from which portions may be removed to create the illustrated openings. The annular back iron 110 can thus comprise a plurality of core laminations stacked in the direction of longitudinal axis 101 and bonded together to form a laminated stator core. It will be understood that the bonding of the core laminations may a chemical bonding (such as glue), a mechanical connection provided by interlocking components, a welded joint, or any other suitable bonding technique.

The stator core 100 also comprises a plurality of stator teeth 120. At least one tooth 120 can be formed of a plurality of tooth laminations. When assembled with the annular back iron 110, a tooth 120 can thus comprise a plurality of tooth laminations stacked along a direction of the longitudinal axis 101 and bonded together to form a laminated tooth.

Further, the plurality of stator teeth 120 are arranged to extend from the annular back iron 110 in a radial direction toward the longitudinal axis 101. The tooth laminations are separate from the core laminations. That is to say, the tooth laminations are not arranged integrally with the core laminations. The stator 100 may be arranged such that, for at least one tooth 120, none of the tooth laminations of the tooth 120 are integral or integrally formed with any of the core laminations. For example, a tooth lamination and a core lamination can be cut as separate pieces from the same or different metal sheets, and the tooth and core laminations can be joined via alternative means, such as those described below.

As will be described in more detail, at least one stator tooth 120 is connected to the annular back iron 110 at a connection interface 140. The stator core 100 may comprise any number of stator teeth 120. In the arrangement shown, the stator core 100 has 60 stator teeth 120. The number of stator teeth 120 in the stator core 100 may be equal to the number of connection interfaces 140. The stator teeth 120 are evenly distributed in a circular array, concentric with the circumference of the annular back iron 110. The stator teeth 120 are arranged around the longitudinal axis 101 such that a plurality of slots 130 are defined in between the teeth. A slot 130 is defined between each adjacent pair of stator teeth 120.

In this way, the stator teeth 120 are configured to receive stator windings (not shown).

The stator core 100 may comprise windings around every tooth 120 in a double winding arrangement. As such, the stator core 100 may comprise a first tooth with a first winding wound therearound, and a second tooth, adjacent to the first tooth, having a second winding wound therearound. A full set of wound stator teeth may be provided to the core in this manner. In an alternative arrangement, the stator core 100 may comprise windings around alternative teeth 120 in a single winding arrangement.

Figures 2A-2C and 3 show further detail of the shape of a stator tooth 120 and its assembly into the annular back iron 110. The stator tooth 120 may have a body portion 127 which may have a quadrilateral cross section. In the arrangement shown, the body portion 127 has a rectangular cross-section, but it will be understood that the body portion may have a differently shaped cross section, such as a trapezoidal cross section. The stator tooth may comprise at least one mounting projection 121. The mounting projection 121 can form part of the connection interface 140. The mounting projection 121 may extend from the stator tooth 120 from a first surface of the body portion 127. The mounting projection 121 may be cuboidal or rectangular in cross-section. In the arrangement shown, a first mounting projection 121 and a second mounting projection 122 extend from the first surface of the body portion 127. As shown in Figure 2A, the mounting projections 121, 122 can thus form a crenellated or notched surface on the body portion 127.

The body portion 127 may comprise at least one tooth tip 123. The at least one tooth tip 123 may be in the form of a shelf extending from an edge of the body portion 127. In the arrangement shown, the body portion 127 comprises two tooth tips 123. The tooth tips 123 are configured such that when the stator tooth 120 is connected to the annular back iron 110, the tooth tips 123 extend in a circumferential direction from opposite edges of a second surface of the body portion 127, being opposite the first surface of the body portion. In this way, the stator tooth 120 can have a T-shaped cross-section along the longitudinal axis to secure stator windings in the slots 130.

With reference to Figures 26 and 2C, the stator tooth 120 may comprise a first tooth lamination 125 and a second tooth lamination 126. The tooth laminations 125, 126 may be configured to be stacked together to form the stator tooth 120 shown in Figure 2A. As such, the tooth laminations 125, 126 may have a T-shaped cross section. The first tooth lamination 125 may be longer than the second tooth lamination 126. In the arrangement shown, the body portion of the first tooth lamination 125 is longer than that of the second tooth lamination 126. The stator tooth 120 may comprise: one or more first tooth laminations 125, each first tooth lamination being arranged to form parts of both the body portion 127 and a mounting projection 121 or 122 of the stator tooth; and one or more second tooth laminations 126 arranged to form parts of the body portion 127.

By virtue of the first and second tooth laminations 125, 126, the stator tooth 120 may be formed in five sections: a first section comprising at least one second tooth lamination 126, a second section comprising at least one first tooth lamination 125, a third section comprising at least one second tooth lamination 126, a fourth section comprising at least one first tooth lamination 125, and a fifth section comprising at least one second tooth lamination 126. As such, the longer first tooth laminations 125 can define the first and second mounting projections 121, 122 of the stator tooth 120. It will be understood that additional mounting projections may be formed in the stator tooth 120 by adding additional sections comprising at least one first tooth lamination 125 and at least one second tooth lamination 126 in an alternating manner.

With reference to Figure 3, the annular back iron 110 comprises a plurality of radially oriented openings 111, that is to say the openings 111 extend at least partly through the radial thickness of the annular back iron 110. The openings 111 are distributed around the longitudinal axis 101 of the stator core 100. The openings 111 can form the corresponding part of the connection interfaces 140, together with the mounting projections 121. In the illustrated arrangement, a first opening 111 is configured to receive a first mounting projection 121 on the stator tooth 120 to thereby form a mating pair in the connection interface 140. The stator core assembly 100 can thus comprise a plurality of connection interfaces 140 distributed around the longitudinal axis 101.

In the arrangement shown, each connection interface 140 includes two mating pairs: the first mounting projection 121 corresponding to the first opening 111, and a second mounting projection 122 corresponding to the second opening 112. In a stator core assembly 100 having more than one mating pair per connection interface, it will be understood that mating pairs are disposed at different axial positions to one another along the longitudinal axis 101 of the stator 100. In the illustrated arrangement, the openings 111, 112 are formed through the full thickness t/ of the annular back iron 110. It will be appreciated that the connection interfaces 140 may include any number of mating pairs.

By virtue of the arrangement described above, at least one mounting projection 121 can be slidably received by at least one corresponding opening 111 in a radial direction with respect to the longitudinal axis 101 of the stator 100. In this way, the stator tooth 120 can be restricted from moving in the direction of the longitudinal axis 101. Furthermore, the stator tooth can be restricted from moving in the circumferential direction with respect to the longitudinal axis 101.

Figure 4 illustrates a section of a stator core assembly 100 having an annular back iron 110 and a plurality of stator teeth 120. The space between adjacent pairs of stator teeth is configured to define a slot 130 for receiving stator windings. The longitudinal edges of stator teeth 120 on either side of a slot 130 may be separated by a gap 131. The gap may be configured to allow the passage of a needle of a needle winding machine along the slot 130 in the direction of the longitudinal axis 101 of the stator 100. In the arrangement shown, a gap 131 is formed between the tooth tips of a pair of adjacent stator teeth 120.

The stator 100 may comprise a shoulder 113. The shoulder 113 may be a portion of the annular back iron 110 extending further along the longitudinal axis 101 than the stator teeth 120. Therefore, the axial extent of the annular back iron 110 may be greater than the axial extent of at least one stator tooth 120. The axial length of the shoulder 113 may be adjusted by selecting the number and/or thickness of core laminations and tooth laminations accordingly. This arrangement is made possible by the use of separate core laminations and tooth laminations. In prior stator arrangements, the stator core and the plurality of teeth may be provided in a single integral lamination which would not permit the provision of a shoulder 113 without requiring additional steps after assembly of the laminations, such as machining. In contrast, the arrangement described herein can provide a shoulder 113, for example, by providing thicker and/or a greater number of stator core laminations as compared to the tooth laminations. The shoulder 113 is advantageous in that it provides an interface on which an end cap of the stator 100 can be located, without requiring additional fixing means. The shoulder 113 may extend around substantially the entire circumference of the annular back iron 110.

With reference to Figures 1 to 4, a method of assembling a stator 100 is provided. The annular back iron 110 may be formed of a plurality of stator core laminations. The core laminations may each be formed from a metal sheet. The metal sheet may be or may comprise FeSi, FeCo or any other suitable electrical steel. At least one core lamination may be formed from the sheet by cutting or stamping, but other suitable processes may be adopted. The plurality of core laminations may then be stacked together and bonded together to form the annular back iron 110. The openings 111, 112 of the connection interface 140 may be formed by machining of the annular back iron 110.

Instead of stacking together annular core laminations, the annular back iron 110 may be formed by an alternative method comprising coiling a single continuous metal strip. The metal may be FeSi or FeCo. In other words, the method may involve providing a single continuous strip of core material and arranging the strip in a helical manner about a longitudinal axis 101 of the stator 100 in order to form the plurality of core laminations made from a single strip of material. The resulting annular back iron 110 may be described as slinky shaped. After coiling, the annular back iron 110 may be machined as mentioned earlier in order to form the openings 111, 112 of the connection interfaces 140.

The method of assembling the stator 100 further comprises providing a plurality of stator teeth 120. A stator tooth 120 can be formed by stacking together stator tooth laminations.

The different tooth laminations required may be formed by stamping or cutting a metal sheet, preferably comprising FeCo. The sheet may be a rolled metal sheet. Preferably, the tooth laminations are cut or stamped from the metal sheet such that the radial direction of the stator tooth 120 (with respect to the orientation of the tooth when assembled with the stator core) is parallel to the rolling direction. This has the advantage of improving and rendering the magnetic properties of the resulting stator teeth 120 more uniform and consistent.

Sections of at least one first tooth lamination 125 and at least one second tooth lamination 126 may be stacked together in succession to form the required number of mounting projections 121, 122, as described in relation to Figures 2A-2C. The method may further comprise winding a stator tooth 120 with stator windings, for example copper wire. Such a winding step may be performed by an automated needle winding machine. Preferably the winding step is performed before insertion of the stator tooth 120 into the annular back iron 110. The method further comprises mounting at least one tooth 120 into the annular back iron 110 by inserting at least mounting projection 121 into at least one of the corresponding openings 111.

Figure 5 illustrates an alternative stator core assembly 200 according to embodiments of the invention. The stator 200 comprises a plurality of stator teeth 120 and an annular back iron 210 having a longitudinal axis 201. The stator teeth 120 may have any or all of the features of that described in relation to the stator core assembly 100 above. The annular back iron 210 is substantially similar to the annular back iron 110 described above, except for the arrangement of the openings of the connection interface 240.

Figure 6 illustrates an alternative annular back iron 210. In this arrangement, the openings 211 are in the form of blind holes from the inner radial surface of the annular back iron 210. In other words, the openings 211 can be provided as recesses in the inner wall of the annular back iron 210 which do not extend through the full thickness thereof. Aside from having blind holes instead of through holes, the annular back iron 210 may otherwise be similar to the annular back iron 110 with respect to the number and positions of the openings, the arrangement of the mating pairs and connection interfaces, and the way in which at least one stator tooth 120 can be inserted into the stator core. In particular, the annular back iron 210 may comprise a first opening 211 and a second opening 212, each configured to form a mating pair with two corresponding mounting projections. It will be appreciated that the height of the tooth laminations of the stator teeth, in particular the height of the first tooth laminations 125, can be adjusted as required according to the depth of the openings 211, so that the outer radial surface of the stator tooth 120 with respect to the longitudinal axis 201 can be contiguous with the inner surface of the annular back iron 210.

The annular back iron 210 may be formed from a similar method as mentioned in relation to the annular back iron 110 described above. Namely, the annular back iron 210 may be formed from a plurality of stator core laminations stacked together, bonded and subsequently machined in order to form the openings 211. Differently to the method described in relation to annular back iron 110, the method to manufacture the annular back iron 210 may involve a different machining step which removes material from the inner wall of the annular back iron 210 without cutting through the full thickness of the annular back iron 210. This is in contrast to the method of manufacturing the annular back iron 110, which may involve cutting apertures through the full thickness of the annular back iron 110. Alternatively, the stator 210 may be formed by coiling a continuous metal strip and subsequently machining the openings 211 as required, in the manner described above in relation to back iron 110.

Figures 7A and 7B illustrate an alternative manufacturing method for the annular back iron 210. Instead of stamping or laser cutting plain annular core laminations from a sheet of rolled material as described in relation to the annular back iron 110 above, the annular back iron 210 can instead be formed from two different types of lamination. The first type of lamination is a plain stator lamination 214 comprising an annulus of core lamination material, which may be FeSi as discussed above. These may be substantially the same as the core laminations used to provide the annular back iron 110. The second type of lamination is a crenellated stator lamination 216. The crenellated stator lamination 216 comprises a plurality of crenellations 216a distributed around the circumference of the crenellated stator lamination 216. The crenellations 216a face radially inwards to the longitudinal axis 201. The number of crenellations 216a can be adjusted to match the number of connection interfaces 240 required.

To form the annular back iron 210, the plain stator laminations 214 may be stacked and bonded together to form a plain core portion 215, each comprising a plurality of plain stator laminations 214. The method of manufacturing the annular back iron 210 further comprises stacking together and bonding a plurality of crenellated stator laminations 216 to form a crenellated core portion 217. The annular back iron 210 may be formed by stacking together at least one crenellated core portion 217 between at least two plain core portions 215 and bonding them together. In the arrangement shown, since each connection interface 240 comprises two openings 211, 212, the annular back iron 210 is formed by stacking together three plain core portions 215 and two crenellated core portions 217 in an alternating manner.

With reference to Figure 6, it will be understood that moving along the longitudinal axis 201, the annular back iron 210 comprises: a first section made from a plain core portion 215, a second section made from a crenellated core portion 217, a third section made from a plain core portion 215, a fourth section made from a crenellated core portion 217, and a fifth portion made from a plain core portion 215. It will be appreciated that in order to provide more than two openings per connection interface 240, this sequence may be repeated to provide additional crenellated core portions 217 provided between additional plain core portions 215.

An alternative method of manufacturing the annular back iron 210 may be performed by coiling a continuous metal strip in the slinky-shaped arrangement described above. The metal strip may comprise crenellations along its length, the crenellations being positioned such that, when the strip is coiled up, the crenelated and/or non-crenellated sections align with one another form the annular back iron 210 with blind holes.

The methods of manufacturing the annular back iron 210 may be adopted to form the annular back iron 110 shown in Figure 3, which comprises blind holes instead of through holes. After forming the annular back iron 210 as described in relation to Figure 7, machining or grinding may be performed on the outer circumferential surface of the annular back iron 210 in order to remove sufficient material to convert the blind holes into through holes, thereby arriving at the annular back iron 110 as shown in Figure 3.

Figure 8 is a schematic diagram illustrating an aircraft 1. The aircraft comprises a driving or driven element 2 and an electric machine 10 connected to the driven element 2 by a drive shaft 3. The electric machine comprises the stator core assembly 100 having the back iron 110 and the plurality of stator teeth 120. A rotor 11 is connected to the drive shaft 3 and configured to rotate within the stator 100. It will be understood that the stator in Figure 8 may be the stator 200 according to an alternative embodiment.

Various modifications, whether by way of addition, deletion and/or substitution, may be made to all of the above described embodiments to provide further embodiments, any and/or all of which are intended to be encompassed by the appended claims.

Claims

Claims 1. A stator core assembly for an electric machine comprising: an annular back iron haying a longitudinal axis and comprising a plurality of radially oriented openings; and a plurality of teeth, at least one tooth of the plurality of teeth comprising at least one mounting projection; wherein the annular back iron and the at least one tooth are configured such that the at least one mounting projection can be inserted in a radial direction with respect to the longitudinal axis into at least one of the plurality of radially oriented openings, to mount the at least one tooth to the annular back iron.
The stator core assembly according to claim 1, wherein the annular back iron and the at least one tooth are configured such the at least one mounting projection can be slidably received by the at least one radially oriented opening to prevent relative movement therebetween along the longitudinal axis.
The stator core assembly according to claim 1 or claim 2, wherein at least one tooth of the plurality of stator teeth comprises at least two mounting projections and the plurality of radially oriented openings comprises at least two radially oriented openings.
The stator core assembly according to claim 3, wherein the at least two mounting projections are disposed at different axial positions along the at least one tooth with respect to the longitudinal axis.
The stator core assembly according to any preceding claim, wherein at least one of the plurality of radially oriented openings is a blind hole or a through hole.
The stator core assembly according to any preceding claim, wherein the at least one radially oriented opening comprises a rectangular hole and the mounting projection has a rectangular cross section configured to be received by the rectangular hole.
The stator core assembly according to any preceding claim, wherein the annular back iron comprises FeSi and at least one of the plurality of teeth comprises FeCo. 2. 3. 4. 5. 6. 7.
8. The stator core assembly according to any preceding claim, wherein a first tooth of the plurality of stator teeth has a first stator winding wound therearound, and a second tooth of the plurality of stator teeth, adjacent the first tooth, has a second stator winding wound therearound.
9. The stator core assembly according to any preceding claim, wherein the annular back iron comprises a plurality of core laminations and the at least one tooth of the plurality of stator teeth comprises a plurality of tooth laminations, the plurality of tooth laminations being separate from the plurality of core laminations.
10. The stator core assembly according to claim 9, wherein at least one of the plurality of core laminations has a radial thickness being constant around the entire circumference thereof.
11. The stator core assembly according to claim 9 or claim 10, wherein at least one axial end of the annular back iron overhangs at least one of the plurality of teeth in the axial direction.
12. A tooth for the stator core assembly of any of claims 1 to 11, comprising at least one mounting projection, suitable for insertion into the annular back iron of any of claims 1 to 11.
13. An annular back iron for the stator core assembly of any of claims 1 to 11, comprising a plurality of radially oriented openings for receiving mounting projections of the plurality of teeth of any of claims 1 to 11.
14. A method of assembly of a stator core for an electric machine, comprising the steps of: providing an annular back iron comprising a plurality of radially oriented openings; providing at least one tooth comprising at least one mounting projection; and mounting the at least one tooth to the annular back iron by inserting the at least one mounting projection into at least one of the plurality of radially oriented openings.
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18.A method of assembly according to claim 14, wherein, before the mounting step, the method comprises the step of winding a stator winding onto the at least one tooth.A method of assembly according to claim 14 or claim 15, wherein providing the at least one tooth comprises providing at least one first tooth lamination and at least two second tooth laminations, the at least one first tooth lamination being longer than the at least two second tooth laminations, and bonding the at least one first tooth lamination between the at least two second tooth laminations such that the at least one first tooth lamination provides the at least one mounting projection.A method of assembly according to any of claims 14 to 16, wherein the plurality of radially oriented openings are through holes, and the step of providing the annular back iron comprises providing at least one plain annular lamination between at least two crenellated laminations, and bonding the plain annular and crenellated laminations together such that crenellations in the crenellated laminations form the plurality of radially oriented openings.An electric machine comprising the stator core assembly according to any of claims 1 to 11.