Stator core or a rotor core for an electrical machine with reduced eddy current losses and high magnetic conductivity and mechanical strength

A stator core or a rotor core for an electrical machine, the core including a plurality of teeth separated by slots in a circumferential direction of the core, and a plurality of lamination stacks arranged one after another in an axial direction of the core, and separated from each other in the axial direction by cooling ducts. Each lamination stack includes at its each end in the axial direction at least one slit tooth section providing a discontinuity in the electrical conductivity of the lamination material and thereby reducing eddy current losses at the respective slit tooth section, and between the slit tooth sections at least one regular tooth section.

TECHNICAL FIELD

The present invention relates to a stator core or a rotor core for an electrical machine.

BACKGROUND

Referring toFIGS. 1, 2 and 3, a conventional stator core10(or a rotor core10) for an electrical machine comprises a plurality of stator teeth20separated by stator slots30in a circumferential direction100of the stator core10, and a stator yoke170. Each stator tooth20consists of a plurality of corresponding lamination teeth80,140of thin laminations70,130, the lamination teeth80,140of each lamination70,130being separated by lamination slots90in the circumferential direction100. The stator yoke170consists of a plurality of corresponding regular lamination yokes180of the laminations70,130. A plurality of lamination stacks40is arranged one after another in an axial direction50of the stator core10, each lamination stack40comprising a plurality of laminations70,130stacked one after another in the axial direction50such that each pair of neighboring laminations70,130is in contact with each other. The lamination stacks40are separated from each other in the axial direction50by cooling ducts60.

It is conventionally known to form lamination stacks40of solely regular laminations70(embodiment ofFIG. 1), each regular lamination70comprising a plurality of regular lamination teeth80separated by lamination slots90in the circumferential direction100to form respective regular stator tooth sections110and stator slot sections120in the axial direction50. In the context of this disclosure a “regular lamination tooth” shall be considered to refer to a lamination tooth with no slit160providing a discontinuity in the electrical conductivity of the lamination material.

It is furthermore conventionally known, e.g. from JP2011097737, to form lamination stacks40of solely slit laminations130(lamination stack embodiment not shown), each slit lamination130comprising a plurality of slit lamination teeth140separated by lamination slots90in the circumferential direction100to form respective slit stator tooth sections150(seeFIG. 4) and stator slot sections120in the axial direction50, each slit lamination tooth140comprising a slit160providing a discontinuity in the electrical conductivity of the lamination material.

It is furthermore conventionally known, e.g. from JP5058097, to provide lamination stacks40with end plates next to cooling ducts60, the end plates comprising slits160that provide discontinuity in the electrical conductivity of the end plate material. The slits160have a function to reduce eddy current losses; in the case of JP2011097737 caused by axial magnetic flux at the ends of the stator core10, and in the case of JP5058097 caused by shift of magnetic flux from inner interval pieces to the stator core10.

While the slits160reduce eddy current losses, at the same time they reduce the magnetic conductivity in the desired flux direction, and mechanical strength of the stator core10. There therefore remains a desire to reduce eddy current losses while at the same time reducing the magnetic conductivity and mechanical strength of the stator core10as little as possible.

SUMMARY

One object of the invention is to provide an improved stator core for an electrical machine. Particularly the object is to provide a stator core with reduced eddy current losses and high magnetic conductivity and mechanical strength.

This object is achieved by the device according to appended claim1.

The invention is based on the realization that eddy current losses have significance at a plurality of laminations closest to axial ends of lamination stacks, and that all the significant eddy current losses can be removed by providing each axial end of the lamination stacks with slit stator tooth sections extending over the plurality of laminations. At the same time a maximal magnetic conductivity and mechanical strength of the stator core is maintained where the eddy current losses have no significance by providing regular stator tooth sections between the slit stator tooth sections. The eddy current losses have most significance at stator teeth close to the tops of the same, but may also have significance at any other parts of the stator teeth and at the stator yoke.

According to a first aspect of the invention, there is provided a stator core or a rotor core for an electrical machine. The core comprises a plurality of teeth separated by slots in a circumferential direction of the core, and a plurality of lamination stacks arranged one after another in an axial direction of the core. The lamination stacks are separated from each other in the axial direction by cooling ducts. Each lamination stack comprises a plurality of laminations arranged one after another in the axial direction such that each pair of neighboring laminations is in contact with each other. Each lamination stack comprises among the plurality of laminations a plurality of regular laminations, each regular lamination comprising a plurality of regular lamination teeth separated by lamination slots in the circumferential direction to form respective regular tooth sections and slot sections when at least two regular laminations are arranged next to each other. Each lamination stack further comprises among the plurality of laminations a plurality of slit laminations, each slit lamination comprising a plurality of slit lamination teeth separated by lamination slots in the circumferential direction to form respective slit tooth sections and slot sections when at least two slit laminations are arranged next to each other. Each slit lamination tooth comprises at least one slit providing a discontinuity in the electrical conductivity of the lamination material, the at least one slit being configured to reduce eddy current losses at the respective slit lamination. Each lamination stack comprises at its each end in the axial direction at least one slit tooth section, and between the slit tooth sections at least one regular tooth section.

According to one embodiment of the invention, each slit tooth section comprises at least five slit lamination teeth, such as at least ten slit lamination teeth or at least twenty slit lamination teeth.

According to one embodiment of the invention, both the regular laminations and the slit laminations have the same thickness.

According to one embodiment of the invention, all of the plurality of slit laminations are identical with each other.

According to one embodiment of the invention, all of the plurality of regular laminations are identical with each other.

According to one embodiment of the invention, all of the plurality of regular laminations are, apart from the slits, identical with all of the plurality of slit laminations.

According to one embodiment of the invention, each regular lamination comprises solely regular lamination teeth.

According to one embodiment of the invention, each slit lamination comprises solely slit lamination teeth.

According to one embodiment of the invention, all of the plurality of regular lamination teeth are identical with each other.

According to one embodiment of the invention, all of the plurality of slit lamination teeth are identical with each other.

According to one embodiment of the invention, all of the plurality of regular lamination teeth are, apart from the slits, identical with all of the plurality of slit lamination teeth.

According to one embodiment of the invention, the at least one slit does not reach in the radial direction extreme contours of the respective slit lamination.

According to one embodiment of the invention, the at least one slit does not reach any contour of the respective slit lamination.

According to one embodiment of the invention, at least some of the slit laminations further comprise slit lamination yokes provided with a plurality of slits, wherein the slit lamination yokes form slit lamination yoke sections when at least two slit lamination yokes are arranged next to each other, and wherein the core comprises at least one slit lamination yoke section.

According to one embodiment of the invention, each of the two lamination stacks farthest out in the axial direction comprises a slit lamination yoke section at its end facing away from the core in the axial direction.

DETAILED DESCRIPTION

Referring toFIG. 4, a stator core10(or a rotor core10) according to one embodiment of the invention comprises a plurality of lamination stacks40arranged one after another in an axial direction50of the stator core10. The lamination stacks40are separated from each other in the axial direction50by cooling ducts60. Each lamination stack40comprises a plurality of laminations70,130arranged one after another in the axial direction50such that each pair of neighboring laminations70,130is in contact with each other. The laminations70,130may comprise electrical steel as a lamination material, and they may in addition comprise an appropriate coating on the surface of the lamination material.

Each lamination stack40comprises a plurality of regular laminations70e.g. such as that shown inFIG. 2. Each regular lamination70comprises a plurality of regular lamination teeth80separated by lamination slots90in the circumferential direction100. When at least two regular laminations70are arranged next to each other, i.e. stacked one after another in the axial direction50, they form respective regular stator tooth sections110and stator slot sections120.

Each lamination stack40further comprises a plurality of slit laminations130e.g. such as those shown inFIGS. 3, 5 and 6, each slit lamination130comprising a plurality of slit lamination teeth140separated by lamination slots90in the circumferential direction100. When at least two slit laminations130are arranged next to each other, i.e. stacked one after another in the axial direction50, they form respective slit stator tooth sections150and stator slot sections120. Each slit lamination tooth140comprises a slit160providing a discontinuity in the electrical conductivity of the lamination material, the slit160being configured to reduce eddy current losses at the respective slit lamination130.

Each lamination stack40comprises at its each end in the axial direction50a slit stator tooth section150, and between the slit stator tooth sections150a regular stator tooth section110. The slit stator tooth sections150may comprise e.g. five, ten or twenty slit lamination teeth140. At least some of the slit laminations130may furthermore comprise slit lamination yokes190provided with a plurality of slits160. When at least two slit lamination yokes190are arranged next to each other, i.e. stacked one after another in the axial direction50, they form respective slit lamination yoke sections200. In particular, each of the two lamination stacks40farthest out in the axial direction50may comprise a slit lamination yoke section200at its end facing away from the stator core10in the axial direction50. The axial end regions of the stator core10are particularly exposed to axial magnetic flux due to the winding ends outside of the stator core10, and therefore at these regions the corresponding eddy current losses may have significance even at the stator yoke170.

Both the regular laminations70and the slit laminations130may have the same thickness. All the slit laminations130may be identical with each other, and all the regular laminations70may also be identical with each other. All the regular laminations70may also, apart from the slits160, be identical with all the slit laminations130. Each regular lamination70may comprise solely regular lamination teeth80, and each slit lamination130may comprise solely slit lamination teeth140. All the regular lamination teeth80may be identical with each other, and all the slit lamination teeth140may also be identical with each other. All the regular lamination teeth80may also, apart from the slits160, be identical with all slit lamination teeth140.

Referring toFIG. 5, instead of one slit160, each slit lamination tooth140may comprise a plurality of slits160. The number of slits160can be two, three, four, or more. The slits160may be positioned such that they do not reach in the radial direction extreme contours of the slit lamination teeth140. Referring toFIG. 6, the slits160may furthermore be positioned such that they do not reach any contour of the slit lamination teeth140. According toFIGS. 3, 5 and 6the slits160are provided close to or at the tops of the slit lamination teeth140i.e. close to in the radial direction innermost extreme contours of the slit lamination teeth140where the eddy current losses probably have most significance, but the slits160can also be provided at any other parts of the slit lamination teeth140. Furthermore, as shown inFIG. 6, the slits160may even be provided to form slit lamination yokes190. It is to be understood that each of the different slit lamination teeth140shown inFIGS. 5 and 6may be used alone or in combination with any of the remaining slit lamination teeth140, and also in combination with both regular lamination yokes180and slit lamination yokes190.

The slits160may be formed by removing lamination material from the slit lamination teeth140. The slits160may have a width of e.g. 0.5 to 2 mm, and they may form narrow openings in the slit lamination teeth140. The slits160may also be formed by locally changing the electrical conductivity of the lamination material without removing lamination material from the slit lamination teeth140. This can be achieved e.g. by mechanically forming the slit lamination teeth140.

The invention is not limited to the embodiments shown above, but the person skilled in the art may modify them in a plurality of ways within the scope of the invention as defined by the claims. Particularly, it is to be understood that the invention can be applied not only to stators of electrical machines but also to rotors of the same.