A lamellar pack for electric motors for automotive applications

Abstract

A lamellar pack (1) for an electric motor for automotive applications comprises stacked annular lamination layers (2), each comprises lamination segments (7), defining annular sectors. The side edges (71) of adjacent lamination segments (7) are spaced from each other by a gap (21). In preferred embodiments, the gaps (21) of different lamination layers (2) define a stepped pattern with a plurality of steps (8', 8"), each step (8', 8") defined by a first gap (21a', 21a") of a first lamination layer (2a', 2a"), and a second gap (21b', 21b") of a second lamination layer (2b', 2b"), closest to the first gap (21a', 21a"), that is spaced from the first gap (21a', 21a") in the circumferential direction. The steps (8', 8") can arranged in a helical fashion to reduce electromagnetic effects of the discontinuities within the layers (7).

Description

[0001] Title: “A lamellar pack for electric motors for automotive applications”

[0002] DESCRIPTION

[0003] Field of the invention

[0004] The present invention relates to the field of electric motors for automotive applications. In particular, the present invention relates to a lamellar pack for such a motor.

[0005] Background of the invention

[0006] Electric motors are well-known to comprise a stator, with a central cavity, and a rotor arranged in the stator cavity and connected to a rotation shaft. The stator and the rotor are usually made of ferromagnetic materials, to guide a magnetic field generated by currents in stator and / or rotor windings.

[0007] In order to reduce power losses, the stator and / or the rotor can be formed as a lamellar pack comprising lamination layers stacked on each other.

[0008] It is known that each lamination layer can be formed of plural lamination segments, each corresponding to an annular sector of the layer. The lamination segments are arranged side by side, with contact along their side edges. In some examples, the side edges of adjacent segments are shaped to interlock with each other.

[0009] Lamellar packs are also known, where the lamination segments of consecutive layers are staggered with a zig-zag pattern, meaning that, starting from the side edge of a lamination segment of one layer, and moving to successive layers, the closest side edge is found in an alternate manner on the left and then on the right. An example of such arrangement is shown in figure 3. Figure 4 shows another known arrangement, where the zig-zag is not formed by individual lamination segments, but by bricks of stacked lamination segments.

[0010] This arrangement reduces concentration of electromagnetic field, which occurs because of the side edges of the segments forming discontinuities in the material of the layer, and which is particularly felt if the lamination segments of all the layers are exactly aligned in the axial direction.

[0011] Prior art drawback

[0012] It is known that mechanical stress upon a magnet reduces its magnetic performance. The applicant perceived that each lamination segment is subject to mechanical stress along its side edges when it is positioned in contact with the adjacent segments.

[0013] This stress is also related to the segments not having all exactly the same shape. In fact, the segments are usually cut from a lamination sheet by a punch and a complementary matrix with sharp edges. With successive cutting cycles, the sharp edges progressively wear, causing the segments to slightly change their shape, and in particular to become progressively wider. Thus, greater compression and mechanical stress is required to place the side edges of adjacent segments in contact without overlapping.

[0014] Summary of the invention An object of the present invention is to provide a lamellar pack with a higher magnetic performance.

[0015] This and other objects are achieved by a lamellar pack and an electric motor including the lamellar pack, according to any one of the appended claims.

[0016] According to the invention, adjacent lamination segments of a layer have their side edges spaced by a gap.

[0017] Despite the gap being possibly small, this prevents contact between adjacent segments, regardless of their size increase. Therefore, no mechanical stress is applied on the side edges of the segments, and tests of the applicant show that the magnetic performance can be approximately 50% higher.

[0018] The spacing of the segments increases the need to avoid their axial alignment.

[0019] Thus, in preferred embodiments, gaps of different layers define a stepped pattern, more preferably a helical pattern, with the maximum angular distribution of the discontinuities defined by the side edges of the lamination segments, affecting the magnetic field.

[0020] Brief description of the drawings

[0021] The present invention will now be described in more detail hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown.

[0022] FIG. 1 is a top view of a lamellar pack according to one embodiment of the invention, FIG. 2 is a perspective view of the lamellar pack of figure 1 ,

[0023] FIG.s 3 and 4 are schematic side views of stepped patterns formed by lamination segments of the lamellar pack, according to the prior art,

[0024] FIG.s 5 to 7 are schematic side views of stepped patterns formed by lamination segments of the lamellar pack according to some embodiments of the invention.

[0025] Detailed description

[0026] A lamellar pack 1 includes a plurality of lamination layers 2 made of a ferromagnetic material, which are stacked in an axial direction X-X, that is the direction of a central axis. The lamination layers 2 are glued to each other.

[0027] In particular, the lamination layers 2 are stacked between a first end surface 31 and a second end surface 32. The first and second end surfaces 31, 32 may be identical to each other, but they are nevertheless distinguished herewith for the purpose of defining a preferred observation direction of the lamellar pack 1, from the first end surface 31 toward the second end surface 32.

[0028] In a known manner, the lamellar pack 1 has an outer side surface 41 connecting the end surfaces 31, 32. In preferred embodiments, the outer surface 41 has a cylindrical main portion, centered on the central axis. Moreover, the lamellar pack 1 preferably has a central through channel 5 extending up to the end surfaces 31, 32. Thus, the lamination layers 2 preferably have an annular shape. An inner surface 42 of the lamellar pack 1 faces the channel 5.

[0029] In case of a stator, the channel 5 may be designed to house a rotor. In case of a rotor, the channel 5 may be designed to house a shaft. In preferred embodiments, the inner surface 42 has a cylindrical main portion centered on the central axis.

[0030] Still in a known manner, the lamellar pack 1 may have has a number of through slots 6 extending up to the end surfaces 31, 32. The through slots 6 may be designed to house conductive windings and / or permanent magnets (not shown). The through slots 6 are spaced to each other in a circumferential direction around the central axis. The through slots 6 may be open to the outer surface 41, or to the inner surface 42, or may be fully encircled by material of the lamellar pack 1.

[0031] Each lamination layer 2 comprises a plurality of lamination segments 7. Each lamination segment 7 has two side edges 71 spaced to each other in a circumferential direction around the central axis. Moreover, each lamination segment 7 has an outer edge 72, at the outer surface 31 of the lamellar pack 1, and preferably an inner edge 73, at the inner surface 32 of the lamellar pack 1.

[0032] Therefore, each lamination segment 7 defines an annular sector with a respective angular width in the circumferential direction, measured around the central axis between the side edges 71. Within each layer 2, a layer number of lamination segments 7 are arranged side by side, adjacent to each other along their side edges 71.

[0033] In the preferred embodiments, all the lamination segments 7 of the same layer 2 have the same angular width, and are shifted from each other by a constant circumferential angle that is a submultiple of 360°. More preferably, all the lamination segments 7 have the same angular width also between different layers 2.

[0034] In detail, the angular width is substantially a submultiple of 360°, in particular slightly smaller than a submultiple of 360°, for reasons that are apparent from the description below, such as smaller than a submultiple of 360° by less than 5% of said submultiple, preferably less than 1° smaller than a submultiple of 360°.

[0035] In one aspect of the invention, side edges 71 of adjacent lamination segments 7 within the same layer 2 are spaced from each other by a gap 21. The gap 21 has a gap width in the circumferential direction, which is greater than zero all along the side edges 71 of the lamination segments 7, from their inner edges 73 to their outer edges 72.

[0036] In particular, this applies to all the segments 7 of the relevant layers 2. Moreover, it preferably applies to a plurality of layers 2, preferably all the layers 2. Thus, for each one of a plurality of layers 2, preferably all the layers 2, all the lamination segments 7 of the layer 2 are not in contact with each other.

[0037] It is to be noted that the gap width can be significantly smaller than the width of the lamination segments 7. In general, the gap width is preferably smaller than 5% of the segment width. For example, a lamination segment 7 can be tens of cm wide, while the gap 21 van be less than 1 mm wide, preferably tens of micrometers wide. In fact, while the lack of contact achieves the effect of avoiding mechanical stress of the segments 7, and therefore increasing the magnetic performance, the gap width is preferably set as small as possible to avoid magnetic field concentration.

[0038] In various embodiments, the side edges 71, as well as the gaps 21, can be straight and extend in a radial direction, or can be straight and extend transverse to the radial direction, or they can be curved and / or include corners. Preferably, the side edges 71 and the gaps 21 do not extend straight in the radial direction. In this manner the concentration of magnetic field caused by a single gap 21 is not concentrated in a small circumferential position, but is distributed.

[0039] Preferably, the lamination segments 7, and in particular their side edges 71 and the gaps 21 therebetween, are not aligned in the axial direction X-X for all the layers 2. Instead, the lamination segments 7 of different layers 2 define a stepped pattern with a plurality of steps 8’, 8”. Each step 8’, 8” is substantially a stagger between gaps 21 of different layers 2, by a stagger angle that should be identified as follows.

[0040] Each step 8’, 8” is formed by gaps 21 of two layers 2, namely a first layer 2a’, 2a” and a second layer 2b’, 2b”. The first and second layers 2a’, 2a”, 2b’, 2b” must be consecutive, meaning that there is no further layer 2 between them.

[0041] When different steps 8’, 8” are considered, each step 8’, 8” involves a respective first layer 2a’, 2a”, which may be different from the first layer 2a’, 2a” of another step 8’, 8”, and the same is true for the second layers 2b’, 2b”. In particular, a layer 2 that is a second layer 2b’ for a first step 8’, may be at the same time a first layer 2a” for a second step 8”, as shown in figure 5. For the purpose of uniform definition of the stagger angles, when the two layers 2a’, 2a”, 2b’, 2b” of a step 8’, 8” are considered, the closer to the first end surface 31 will be taken as the first layer 2a’, 2a”, and the closer to the second end surface 32 will be taken as the second layer 2b’, 2b”.

[0042] In more detail, a step 8’, 8” involves a first gap 21a’, 21a” of a first lamination layer 2a’, 2a” and a second gap 21b’, 21b” of a second lamination layer 2b’, 2b”. Thus, the first gap 21a’, 21a” is formed between side edges 71 of two first lamination segments 7a’, 7a” of the first layer 2a’, 2a”, and the second gap 21b’, 21b” is formed between side edges 71 of two second lamination segments 7b’, 7b” of the first layer 2a’, 2a”.

[0043] Among all the gaps 21 of the second lamination layer 2b’, 2b”, the second gap 21b’, 21b” of a particular step 8’, 8” is the one closest to the first gap 21a’, 21a” of the step 8’, 8”. In particular, one of the second segments 7b’, 7b” delimiting the second gap 21b’, 21b” partially overlaps one of the first segments 7a’, 7a” delimiting the first gap 21a’, 21a”.

[0044] A step 8’, 8” is defined if the first and second gaps 21a’, 21a”, 21b’, 21b” of the step 8’, 8” are spaced in the circumferential direction by a stagger angle. Instead, in case a first gap 21a’” is axially aligned to a second gap 21b’”, this does not define a step 8’, 8”, and this will be named an alignment pattern 9.

[0045] If a step 8’, 8” is defined, its stagger angle will be taken as the circumferential offset angle measured from the first gap 21a’, 21a” to the second gap 21a’, 21a”. It is to be noted that, as the second gap 21a’, 21a” is the gap 21 of the second layer 7 closest to the first gap 21, assuming that all the lamination segments 7 have the same angular width, an absolute value of the stagger angle cannot be greater than half the angular width.

[0046] When plural steps 8’, 8” are considered, the stagger angle should be measured for all the steps 8’, 8” in the same angular orientation, that is either always clockwise, or always anticlockwise. Thus, with a selected measuring orientation, if the second gap 21b’, 21b” follows the first gap 21a’, 21a” in the measuring orientation, the stagger angle will be positive. Instead, if it precedes the first gap 21a’, 21a”, the stagger angle will be negative.

[0047] Preferably, when a step 8’, 8”, with a stagger angle having a certain sign, is defined by a first gap 21a’, 21a” and a second gap 21b’, 21b” of a first and a second layer 2a’, 2a”, 2b’, 2b”, then every couple of gaps 21 of the first and second layers 2a’, 2a”, 2b’, 2b” closest to each other define a step 8’, 8” with a stagger angle with the same sign. This for example applies when all the lamination segments 7 have the same angular width.

[0048] In a preferred embodiment, a sequence of at least two steps 8’, 8” should be present, which are consecutive in the axial direction X-X, where the stagger angles of all these steps 8’, 8” have the same sign. By an appropriate selection of the angular orientation of measurement, these steps 8’, 8” will have all a positive sign.

[0049] Two steps 8’, 8” cannot be considered axially consecutive if there is a step 8’, 8” in any layer 2 between them. Instead, two steps 8’, 8” can still be considered axially consecutive in case they are connected through one or more intermediate layers 2 by one or more alignment patterns 9.

[0050] In more detail, a first step 8’ and a second step 8” are axially consecutive if any of the two following conditions is satisfied. The first condition is that the second gap 21b’ of the first step 8’ is the same as the first gap 21a” of the second step 8”, as shown in figures 5 and 6. The second condition is that the second gap 21b’ of the first step 8’ and the first gap 21a” of the second step 8” form together an alignment pattern 9 or are joined by an uninterrupted sequence of alignment patterns 9, as shown in figure 7.

[0051] While a sequence of two steps 8’, 8” with positive stagger angles may already reduce the concentration of the discontinuities for the electromagnetic field, the longer is the sequence of steps 8’, 8” with the same sign, the better is the effect. Possibly, all the stagger angles of all the steps 8’, 8” of the lamellar pack 1 are positive according to the same angular orientation of measure. In this case, the gaps 21 defining the steps 8’, 8” of the sequence are arranged in a helical arrangement.

[0052] In the preferred embodiment, at least one step 8’, 8” is defined for every couple of consecutive lamination layers 2, possibly one step 8’, 8” for every couple of gaps 21 closest to each other of every couple of lamination layers 2, as shown in figure 5.

[0053] In fact, despite some alignment patterns 9 may be permitted, the lower is the number of alignment patterns 9 interleaved in the sequence of steps 8’, 8”, the better is the effect. Alignment patterns 9 may be provided in particular embodiments related to special manufacturing processes. In particular, in one embodiment the lamination segments 7 are assembled in bricks, each consisting of an axial substack of identical lamination segments 7 which are exactly aligned in the axial direction X-X. The bricks can be arranged side by side to form an annular substack, and the annular substacks can be arranged one upon each other with a stagger angle to provide the sequence of steps 8’, 8” of the invention, as shown in figure 7.

[0054] It is further to be noted that, where a high number of layers 2 is provided, and a quite long sequence of steps 8’, 8” with positive stagger angles is found, it is not particularly detrimental if this is followed by another quite long sequence of steps 8’, 8” with negative stagger angles, as shown in figure 6.

Claims

CLAIMS1. A lamellar pack (1) for an electric motor for automotive applications, comprising a plurality of annular lamination layers (2), made of a ferromagnetic material and stacked and glued on each other in an axial direction (X-X) between a first and a second end surface (31, 32), wherein:- each lamination layer (2) comprises a plurality of lamination segments (7), each lamination segment (7) having two side edges (71) and defining an annular sector with a respective angular width in a circumferential direction, lamination segments (7) of the same lamination layer (2) being adjacent to each other along their side edges (71), wherein:- side edges (71) of adjacent lamination segments (7) are spaced from each other by a gap (21),- lamination segments (7) of different lamination layers (2) define a stepped pattern with a plurality of steps (8’, 8”), each step (8’, 8”) comprising a first gap (21a’, 21a”) of a first lamination layer (2a’, 2a”) of the step (8’, 8”) and a second gap (21b’, 21b”) of a second lamination layer (2b’, 2b”) of the step (8’, 8”), the first and second lamination layers (2a’, 2a”, 2b’, 2b”) of the step (8’, 8”) being consecutive to each other, the second gap (21b’, 21b”) being the gap (21) of the second lamination layer (2b’, 2b”) of the step (8’, 8”) that is closest to the first gap (21a’, 21a”), the first and second gaps (21a’, 21a”, 21b’, 21b”) of each step (8) being spaced in the circumferential direction by a stagger angle,- in a sequence of at least two steps (8’, 8”), which are consecutive in the axial direction(X-X), stagger angles of the steps (8’, 8”), measured in a common circumferential orientation for said at least two steps (8’, 8”), are all positive,- the gaps (21) of different lamination layers (2) define at least one alignment pattern (9), each alignment pattern (9) defined by a first gap (21a’”) of a first lamination layer (2) of the alignment pattern (9) being axially aligned to a second gap (21b’”) of a second lamination layer (2) of the alignment pattern (9), the first and second lamination layers (2) of the alignment pattern (9) being consecutive to each other,- at least one alignment pattern (9) is arranged in the axial direction (X-X) between the steps (8’, 8”) of said sequence of at least two steps (8’, 8”).

2. The lamellar pack (1) of claim 1, wherein, for each one of a plurality of layers (2), preferably all the layers (2), all the lamination segments (7) of the layer (2) are not in contact with each other.

3. The lamellar pack (1) of claim 1 or 2, wherein:- the lamination segments (7) are assembled in bricks, each consisting of an axial substack of identical lamination segments (7) which are exactly aligned in the axial direction (X-X),- the bricks are arranged side by side to form an annular substack, and- the annular substacks are arranged one upon each other with a stagger angle to provide said sequence of steps (8’, 8”).

4. An electric motor for automotive applications, including a stator and a rotor, wherein the stator and / or the rotor comprises a lamellar pack (1) according to any claim 1-3.

Images