A component for a stator segment

Abstract

A component for a segment of a laminated stator core (Fig.1, 10) of an electrical machine comprises a planar body (Fig.3A, 24) comprising an elongate head portion 30 having first and second ends (Fig.

Description

This invention relates to a component for a segment of a laminated stator core of an electrical machine. The invention also relates to a segment of a laminated stator core comprising a plurality of components in accordance with the present invention, to a stator core comprising a plurality of assembled segments in accordance with the present invention and to a stator comprising the stator core in accordance with the present invention. It is known to form a laminated stator core from a plurality of assembled stator core segments, each of which comprises a plurality of identical planar components which are aligned and secured together to form a laminated stator core segment. The components typically comprise an arcuate, part-circular head and a radially inwardly extending shank portion. In the laminated stator core segment, electrical windings are formed around the aligned shank portions, as is known in the art. The laminated stator core segments are assembled to form the stator core. Typically, one end of the arcuate head portion of each of the laminated components is provided with a projection and the opposite end of the arcuate head portion is provided with a complementarily shaped recess. The projection of each of the laminated components of each stator core segment is seated in the recess in a corresponding component of an adjacent, identical stator core segment. The engagement of the projections and recesses interlocks adjacent stator core segments and helps to ensure that they are correctly positioned within a stator housing and with respect to a rotor. In order to produce an efficient, quiet motor with low torque ripple and cogging, the stator should preferably have the following features: 1. A low-reluctance magnetic path of sufficient flux carrying capacity between adjacent stator core segment components. 2. Accurate positioning of the stator core segment components within the housing. 3. Physical stability of the stator core segment components within the housing. 4 A large window area for maximum copper fill. 5. A low thermal resistance path between the stator core segment components and the housing. In several of the known arrangements, the inter-engaged projections and recesses on the laminated stator core components result in a significant air gap. Not only does this require a higher magnetising force to establish a given flux density than compared with a true metal-to-metal contact, but in addition the magnetic flux tends to concentrate more in the metal-to-metal contact areas and slightly less in the regions of the air gaps, leading to premature saturation in the areas of direct contact. In addition, if the projections and recesses are not formed precisely, additional airgaps may be introduced between abutting components in addition to the air gaps between the projections and recesses, resulting in a line contact between adjacent laminations. This can in turn result in misalignment of adjacent stator core segments, which can adversely affect the performance of the stator. In accordance with a first aspect of the present invention, a component for a segment of a laminated stator core of an electrical machine, comprises: a planar body comprising an elongate head portion having first and second ends and a shank portion extending from the head portion in a radial direction from a location between the first and second ends; a projection coplanar with the head portion and extending from one end of the head portion; and a recess in the opposite end of the head portion for receipt of the projection of the head portion of an identical, laterally located component; the projection comprising first and second straight lateral side walls inclined towards each other and a rounded apex joined to, and interconnecting, the lateral side walls of the projection; and the recess comprising first and second straight lateral side walls inclined to each other at the same angle as the first and second lateral side walls of the projection and an apex joined to, and interconnecting, the lateral side walls of the recess. By use of the projection and recess as referred to above, a V-shaped interlock between abutting components is achieved, which results in accurate alignment of adjacent stator core segments and minimises or reduces air gaps between adjacent stator core segments. Preferably, the lateral side walls of each projection and of each recess are configured to produce a surface-to-surface contact between the first lateral side walls of the projection and the recess of an identical, laterally located component and between the second lateral side walls of the projection and the recess of an identical, laterally located component By forming a surface-to-surface contact between the lateral side walls of each projection and its associated recess, air gaps between adjacent components are minimised or reduced and magnetic flux transmission between adjacent components is thereby improved. Preferably, the first side walls of the projection and of the recess are inclined at the same angle to the radial direction and the second side walls of the projection and the recess are inclined at the same angle to the radial direction. Preferably, the first and second side walls of the projection are of the same length and the first and second side walls of the projection are of the same length. Preferably, the projection and the recess are symmetrical about an axis extending perpendicular to a radial direction. In one embodiment, the first and second side walls of the projection extend from a location from or near the inner and outer edges of the head portion. Preferably, the distance between the outer ends of the first and second side walls of the projection is at least 50% of the width of the head portion. In one embodiment, the first and second side walls of the recess extend from a location from or near the inner and outer edges of the head portion. Preferably, the distance between the outer ends of the first and second side walls of the recess is at least 50% of the width of the head portion. In one embodiment, the projection and recess are configured to leave a gap between the apex of the projection and the apex of the recess when the projection is received in the recess with the first and second side walls of the projection in abutment with the first and second side walls respectively of the recess. The head portion of the component may be arcuate. In accordance with a second aspect of the present invention, a stator core segment comprises a plurality of components in accordance with the first aspect of the invention, aligned and secured together. In accordance with a third aspect of the present invention, stator core comprises a plurality of stator core segments in accordance with the second aspect of the invention, wherein the projections of the components of each stator core segment are received in the corresponding recesses of an adjacent stator core segment. In accordance with a fourth aspect of the present invention, a stator comprises a stator core in accordance with the third aspect of the invention. The present invention further includes an electrical apparatus, for example an electrical motor, comprising a stator in accordance with the fourth aspect of the invention. By way of example only, specific embodiments of the present invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a perspective view of an embodiment of motor stator core in accordance with the present invention; Figure 2 is a perspective view of the motor stator core of Figure 1, showing one segment of the stator core removed; Figure 3 is a front view of two adjacent, inter-engaged laminated components forming part of the segments of the stator core of Figure 1; Figure 4 is an illustration of the inter-engaged portions of the two laminated components of Figure 3, to a larger scale; Figure 5 is a perspective view of one end of a head of one of the laminated components shown in Figure 3; and Figure 6 is a perspective view of the other end of a head of one of the laminated components shown in Figure 3. Figures 1 and 2 illustrate an embodiment of motor stator core 10 in accordance with the present invention. As an overview, the stator core 10 comprises an outer ring portion 12 from the inner face of which a plurality of identical shank portions 14 extend radially inwardly. In this embodiment, there are nine identical shank portions 14, which are equally angularly spaced around the periphery of the outer ring portion 12, but the number of shank portions will be dependent on the characteristics of the motor of which the stator is intended to form part. The innermost end of the shank portions 14 are arcuate and are separated by a gap 16 from a rotor 18, which does not form part of the invention. As best seen in Figure 2, the stator core 10 is formed from a plurality of identical stator core segments 20 which are assembled to form the stator core. This facilitates the winding of coils around the shank portion 12 of each stator core segment 20, which can then be assembled to form the finished stator. Each stator core segment 20 is formed from a steel having the desired magnetic properties. As shown in the figures, rather than being formed from one solid piece of steel, each stator core segment 20 is formed from a plurality of identical stator laminations 24. The laminations 24 are stamped from steel sheet which in this embodiment is 0.35mm thick and the edges of each lamination 24 extend perpendicularly to the planar faces of each lamination. The laminations have an electrically insulting coating (not visible in the drawings) and as will be explained later a plurality of laminations 24 are bonded together to form a stator core segment 20, in order to reduce the generation of eddy currents. In this particular embodiment, each stator comprises forty-eight identical laminations 24, but the number of laminations can be selected to suit the particular circumstances. With particular reference to Figures 3 to 5, each stator lamination 24 is planar and comprises a curved, part-annular head or yoke portion 30 having a first end 32 and a second end 34, and a straight shank portion 36 extending radially inwardly from the inner edge of the head or yoke portion 30 from a position midway between the two ends 32, 34 of the head or yoke 30. The first end 32 of the head or yoke portion 30 of each lamination is provided with a projection 40 and the opposite end 34 the head or yoke portion 30 of each lamination is provided with a complementarily shaped recess 42. As will be explained, the projection 40 of each head or yoke portion 30 of each lamination 24 of a stator core segment 20 is received in the corresponding recess 42 of the head or yoke portion 30 of a lamination 24 of an adjacent segment 20 to form the motor stator core 10 as shown in Figure 1. The outermost edge of each lamination 24 is also provided with a V-shaped recess 46 to assist in the rotational alignment of the complete stator assembly with respect to the motor housing by means of assembly tooling pins projecting into the V-shaped recesses 46. Each shank portion 36 comprises straight parallel side walls 48,50 extending from the inner face of the head or yoke portion 30 and the radially inner end of each shank portion 36 terminates in a slightly enlarged head 52 having a part-circular radially inner face 54 arranged coaxially with the part-annular head or yoke portion 30. In use, the radially inner face 54 is spaced from the outer surface of a rotor 18 by a gap 16 as described previously with reference to Figure 1. The projection 40 of the head or yoke portion 30 of each stator lamination 24 is generally triangular when viewed in a direction perpendicularly to the plane of the lamination 24 and comprises two straight side walls 60, 62 which are the same length and which are each inclined at an angle a of 40° to the nominal radial direction shown by axis R - R, and which merge into a rounded apex 66 located at the centre of the head or yoke portion 30 in the radial direction. The projection 40 is therefore symmetrical about an axis passing perpendicularly to the axis R - R. The ends of the side walls 60,62 remote from the rounded apex 66 merge with the radially outermost and innermost walls 68, 70 of the head or yoke portion 30 by means of respective shoulder side wall portions 72, 74. The distance x between the radially outermost end of the straight side wall 60 and the radially innermost end of the straight side wall 62 occupies approximately 85% of the maximum available width y of the head or yoke portion 30 in the radial direction, i.e. approximately 85% of the maximum width of the portion of the head or yoke from which the projection 40 extends, and in this particular embodiment is 3.47 mm in length. The distance x can vary according to the circumstances, but it should preferably be at least 50% of the maximum available width y of the head or yoke portion 30, i.e. at least 50% of the maximum width of the portion of the head or yoke from which the projection 40 extends. The recess 42 at the opposite end of each head or yoke portion 30 of each stator lamination 24 is also generally triangular and is shaped to receive the projection 40 of an adjacent stator lamination 24 as a close fit. The recess 42 therefore comprises two straight side walls 80, 82 which are of the same length and which are each inclined to the nominal radial direction at the same angle a as the side walls 60, 62 of the projection 40 and which merge into a rounded apex 84. The ends of the straight side walls 80, 82 of the recess 42 remote from the apex 84 merge with the radially outermost and innermost edge walls 68, 70 of the head or yoke portion 30 by means of rounded connecting walls 86, 88. The recess 42 is therefore symmetrical about an axis passing perpendicularly to the axis R - R. In the same way as for the projection 40, the distance x between the radially outermost end of the straight side walls 80 and the radially innermost end of the straight side wall 82 occupies approximately 85% of the maximum available width y of the head or yoke portion 30 in the radial direction, i.e. approximately 85% of the maximum width of the portion of the head or yoke into which the recess 42 extends. The distance x can vary according to the circumstances, but it should preferably be at least 50% of the maximum available width y of the head or yoke portion 30, i.e. at least 50% of the maximum width of the portion of the head or yoke into which the recess 42 extends. The side walls 60, 62 of each projection 40 are in close abutment with the respective side walls 80, 82 of the associated recess 42 of the head or yoke portion 30 of the adjacent lamination 24, providing a close metal-to-metal contact, which in this particular embodiment results in a nominal contact area A (the shaded area on Figure 6) of 0.46 mm2 between each pair of abutting side walls 60, 80; 62, 82, i.e. a total nominal contact area of (2 x 0.46 mm2) = 0.92 mm2 for each interlocking projection 40 and associated recess 42, which represents 92% of the available nominal cross-section area. However, it will be apparent from Figure 4 in particular that a small gap 90 (in this embodiment having a maximum depth z of 0.03mm) is present between the tip of the apex 66 of the projection 40 and the base of the concave apex 84 of the associated recess 42. This is achieved by designing the radius of the apex 84 of the recess 42 to be smaller than the corresponding radius of the apex 66 of the convex projection 40 to prevent the condition that, when allowing for tolerances of real parts, contact only occurs at the apexes 66, 84 of the projection and recess and not on the straight sides 60, 80; 62, 82. It will also be observed that the head or yoke portion 30 of each shank portion is provided with two elongate slots 92, 94 extending generally in the circumferential direction and that each shank portion 36 is provided with a radially extending slot 96 towards its radially inner end. The slots 92, 94, 96 are pressed out of the lamination 24 but the material pressed out to form the slots is only partially sheared, leaving the pressed out material attached to the lamination 24, thereby forming it into a projection proud of the rear surface and correspondingly recessed below the opposing surface of the lamination, thereby forming an interlock feature between adjacent laminations 24. There is one so-called ‘blank lamination’ formed at one end of the stator core segment 20 that has the material pressed out to form the slots 92, 94, 96 being fully stamped out to leave a slot without leaving a projection, and this lamination then provides a flat end to the stack without a ‘bump’ left by the preceding lamination. In use, a stator core segment 20 is formed by aligning a plurality (in this embodiment, forty-eight) identical stator laminations 24 and bonding the laminations together in a conventional manner, for example using a known dielectric adhesive or by the stamped mechanical interlock features 92, 94, 96 in the lamination 24. Alignment of the laminations 24 is facilitated by the interlocking action of features 92, 94, 96 in each stator lamination 24. This forms stator core segments 20 comprising a head or yoke portion 30’ formed from the aligned head or yoke portions 30 of the laminations 24 and the radially inwardly extending shank portion 14 formed from the aligned shank portions 36 of the laminations 24, which forms a winding core 14. Ina conventional manner, insulated conducting wire, for example insulated copper wire (not shown in the drawings), would be wound around the winding core 36’ to form the stator windings. When sufficient stator core segments 20 have been formed (in this embodiment, nine) they are assembled to form the stator core 10 as shown in Figure 1. As described previously, the projections 40 of the laminations 24 of each stator core segment 20 are received in the corresponding recesses 42 of the laminations 24 of an immediately adjacent stator core segment 20, as shown in the figures. The projections 40 and recesses 42 align the stator core segments 20 correctly with respect to each other and with respect to a housing bore 100 (see Figure 3) within which the stator core 10 is located. In addition, the projections 40 and recesses 42 securely and accurately lock the stator core segments 20 together, and as a consequence they do not rely on the housing bore 100 to align them, or to keep them aligned, with respect to one another. By providing the laminations 24 (and the stator core segments 20 formed from the laminations 24) with the projections 40 and corresponding recesses 42 as described, a relatively large surface-to-surface contact between the projections 40 and recesses 42 is achieved, which contributes to the magnetic circuit efficiency of the assembled stator 10. Of course, and as is well known, by constructing the stator segments from a plurality of laminations electrically insulated from each other, the generation of eddy currents is reduced and cooling of the stator is improved. Forming the stator core segments 20 from a plurality of assembled laminations also allows the laminations to be stamped from metal sheet, and it has been found that the shape of the interlocking projections 40 and recesses 42 as described allows for slightly more robust stamping tooling of the recesses 42 as compared with known recess shapes. The invention is not restricted to the details of the foregoing embodiment.

Claims

1. A component for a segment of a laminated stator core of an electrical machine, comprising:a planar body comprising an elongate head portion having first and second ends and a shank portion extending from the head portion in a radial direction from a location between the first and second ends;a projection coplanar with the head portion and extending from one end of the head portion; anda recess in the opposite end of the head portion for receipt of the projection of the head portion of an identical, laterally located component;the projection comprising first and second straight lateral side walls inclined towards each other and a rounded apex joined to, and interconnecting, the lateral side walls of the projection; andthe recess comprising first and second straight lateral side walls inclined to each other at the same angle as the first and second lateral side walls of the projection and an apex joined to, and interconnecting, the lateral side walls of the recess.

2. A component as claimed in claim 1, wherein the lateral side walls of each projectionand of each recess are configured to produce a surface-to-surface contact between the first lateral side walls of the projection and the recess of an identical, laterally located component and between the second lateral side walls of the projection and the recess of an identical, laterally located component.

3. A component as claimed in claim 1 or claim 2, wherein the first side walls of the projection and of the recess are inclined at the same angle to the radial direction and the second side walls of the projection and the recess are inclined at the same angle to the radial direction.

4. A component as claimed in claim 3, wherein the first and second side walls of the projection are of the same length and the first and second side walls of the projection are of the same length.

5. A component as claimed in any of the preceding claims wherein the projection and the recess are symmetrical about an axis extending perpendicular to a radial direction.

6. A component as claimed in any of the preceding claims, wherein the first and second side walls of the projection extend from a location from or near the inner and outer edges of the head portion.

7. A component as claimed in claim 6, wherein the distance between the outer ends of the first and second side walls of the projection is at least 50% of the width of the head portion.

8. A component as claimed in any of the preceding claims, wherein the first and second side walls of the recess extend from a location from or near the inner and outer edges of the head portion.

9. A component as claimed in any of the preceding claims, wherein the distance between the outer ends of the first and second side walls of the recess is at least 50% of the width of the head portion.

10. A component as claimed in any of the preceding claims, wherein the projection and recess are configured to leave a gap between the apex of the projection and the apex of the recess when the projection is received in the recess with the first and second side walls of the projection in abutment with the first and second side walls respectively of the recess.

11. A component as claimed in any of the preceding claims, wherein the head portion is arcuate.

12. A stator core segment comprising a plurality of components as claimed in any of the preceding claims, aligned and secured together.

13. A stator core comprising a plurality of stator core segments as claimed in claim 12, wherein the projections of the components of each stator core segment are received in the corresponding recesses of an adjacent stator core segment.

14. A stator comprising a stator core as claimed in claim 13.

15. An electrical apparatus comprising a stator as claimed in claim 14.

16. A motor comprising a stator as claimed in claim 14.

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