FIELD OF THE INVENTION

The present invention relates to rotating electric machines, and more particularly to a core structure of a rotating electric machine. BACKGROUND OF THE INVENTION

The invention relates to a core for an electric machine with a stator and a rotor having an air gap between the stator and the rotor, the core being formed of a plurality of plates fastened together in an axial direction, which plates in turn form radially extending teeth and slots between them for a winding on a first side of the core facing towards the air gap and a core back on a second side of the core opposite to the first side and restricted to the bottoms of the slots, a plural number of venting conduits leading from the teeth to the second side formed through the core. The electric machine in question is typically an electric motor, although a generator might also be concerned.

Cooling of rotating electric machines is an important dimensioning factor in motor drives. The cooling affects directly the loadability of the motor, and certain maximum temperatures should not be exceeded so that the insulations of the electrical machine, for example, are not deteriorated. A commonly applied cooling solution in core structures of machines of this type is a stator consisting of two or more parts, with air ducts being formed between the stator parts to lead air therein from the stator air gap. Problems relating to this conventional solution arise from its complex structure and problems of manufacture. To make a stator core of two or more parts sufficiently strong to be pressed against a frame is problematic. In addition, in an electric motor in which the rotor produces all or some of the pressure needed in the cooling circuit, dynamic pressure is lost into the air ducts when an air gap is crossed.

US Patent 31 16429 discloses a prior art solution in which a plural number of air ducts are formed at regular intervals along the stator core length. The stator in question is thus a stator core having a plurality of parts. The ducts in question are formed by means of straight duct supports installed radially between the stator core stacks to allow air to flow in conduits formed by the duct supports and the stator stack sides facing them. Since air coming from the radial rotor ducts is in a strong circumferential motion, the straight duct supports force the air to turn from this almost circumferential motion to a radial motion on a very short distance equal to the length of the air gap. This turn causes a strong single resistance and thereby loss of dynamic pressure and, in addition, an unevenly distributed flow field in the stator.

US Patent 6498408 discloses a stator air duct solution in which the duct supports have a wavelike or a zigzag shape to increase turbulence in the air ducts. Also the cross-sectional profile of the duct supports has been strongly shaped to achieve the same result. Despite these measures almost all the problems of the prior art air duct solution are present also here and the increased turbulence does not necessarily enhance the cooling flow.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a novel core structure for an electric machine in which the above problems are solved. This is achieved by a core structure of the invention which is characterized by what is stated in the independent claim.

The invention is based on the idea of shaping the actual core plates so that they provide the core with venting conduits conveying cooling air. Hence the core does not need to be divided into parts. The venting conduits are formed through the core in a radial direction using different kinds of core plates, a suitable combination of which allows a desired structure containing venting conduits to be achieved. Moreover, this allows the core to be made stronger and easier to manufacture because prior art ducts and complicated supports for the core can be disposed of. Further still, a core, such as a stator or a rotor produced with this technique can be wired in a normal manner.

In the solution according to the invention venting ducts made by shaping the core plates are easy to design in an advantageous manner with regard to the flow of air. The only restriction to the design is caused by the tooth width of the core and by the minimum tooth neck required by die cutting.

Some preferred embodiments of the invention are disclosed in the dependent claims and in the disclosure of the invention below.

LIST OF FIGURES

In the following the invention will be disclosed in greater detail by means of one preferred embodiment and with reference to the accompanying drawings, in which

Figure 1 is a cross-sectional view in an axial direction of an electric machine, showing only the portion above the symmetry plane formed by the shaft of the electric machine; Figure 2 shows a part of a core plate of a first shape suitable for a stator core;

Figure 3 shows a part of a core plate of a second shape suitable for a stator core;

Figure 4 shows a part of a core plate of a third shape suitable for a stator core;

Figure 5 is a perspective view of a part of a stator formed of core plates according to Figures 1 to 3;

Figure 6 is a perspective view of the rear side of the part shown in Figure 5;

Figure 7 is a part of a core plate of a second shape suitable for a rotor core;

Figure 8 is a part of a core plate of a third shape suitable for a rotor core;

Figure 9 is a part of a core plate of a fourth shape suitable for a rotor core;

Figure 10 is a perspective view of a part of a rotor core formed of core plates according to Figures 7 to 10; and

Figure 1 1 shows a cross section of a part of a stator and a rotor having venting conduits.

DETAILED DISCLOSURE OF THE INVENTION

Figures 2 to 6 illustrate a core of the invention in connection with an embodiment in which the core is a stator core for a rotating electric machine. Reference is made to Figure 1 which shows an axial cross-section of an electric machine that the invention relates to. The electric machine in question is typically an electric motor, although a generator might also be concerned. The electric machine is provided with a stator 2 attached to its frame 1 from the ends of the stator core and having in its core channel a coaxial rotor 3 rotatably mounted in bearings 4 arranged to the frame 1 . This forms an annular air gap 5 between the stator 2 and the rotor 3 for leading cooling air to the stator 2 for cooling it. As the stator core is attached from its ends to the stator frame, a space 100 for cooling air is left between the core and the frame.

Reference is also made to Figures 2 to 6 in which a core 2 of an embodiment is formed of a plural number of stator plates 6, 7 and 8 fastened together in an axial direction, the plates forming radially extending teeth 9 and slots 10 between them for a stator winding 1 1 on the inner circumference side or a first side of the stator core 2 and a stator back 12 on the outer circumference side or a second side of the stator core 2 in an area between the outer circumference and a circumference defined by the bottoms of the slots 10, a plural number of venting conduits 13 leading from the teeth 9 on the inner circumference or the first side of the stator core 2 to the outer circumference or the second side of the stator core 2 formed at the same time through the stator core 2. In an embodiment relating to a stator of the rotating electric machine, the plates or laminations from which the core is stacked, are referred to as stator plates.

An aspect of the embodiment of the invention is that the core 2 is formed of core plates 6, 7 and 8 dissimilar in shape, and the venting conduits 13 are formed using these plates. In this example the stator plates 6, 7 and 8 have three different shapes.

The stator plate 6 of a first shape has a through-hole 14 in the area of the stator back 12, the hole being substantially in line with a stator tooth 9.

The stator plate 7 of a second shape has a hole 15 coinciding with the hole 14 in the stator plate 6 of the first shape and a conduit 16 extending to this hole 15 from a tooth 9 on the inner circumference of the stator 2 or the first side of the core through the entire thickness of the stator plate 7.

The stator plate 8 of a third shape has a hole 17 coinciding with the holes 14 and 15 of the stator plates 6 and 7 of the first and the second shape, respectively, and a conduit 8 extending from this hole 17 to the outer circumference of the stator core 2 or the second side of the core through the entire thickness of the stator plate 8.

In a complete stator core 2 the stator plates 7 and 8 of the second and the third shape are arranged side by side to provide assemblies BC of a predetermined thickness, the assemblies B and C of the stator plates 7 and 8 together forming venting conduits 13 of a predetermined size, as mentioned above, leading from the inner circumference of the stator core 2, i.e. from the air gap, to the outer circumference of the stator core, and assemblies A formed of the stator plates 6 of the first shape are arranged alternately with assemblies BC formed of the stator plates 7 and 8 of the second and the third shape, respectively, so that assemblies BC formed of the stator plates 7, 8 of the second and third shape and located at a distance from one another are interconnected by their venting ducts 13 through the holes 14 in the stator plates 6 of the first shape. At the same time, all the holes 14, 15 and 17 of the stator plates 6, 7 and 8 form axial conduits 19 through the stator back 12.

The stator plates 7 and 8 may be piled to form stacks of specific predetermined thicknesses, i.e. assemblies B and C, and the cutting needed for the venting conduits 13 may be made either directly to a sub-assembly B and C or to single stator plates 7 and 8, depending of course on the thickness of an individual stator plate 7 and 8, for example.

Stacks made of the stator plates 6, i.e. assemblies A, that alternate with assemblies BC made of assemblies B and C, are typically substantially thicker than assembly BC. The thickness of assembly A, i.e. the distance between the venting conduits 13, is determined by the desired venting power and the strength requirements of the stator 2.

In the embodiment of Figures 5 and 6 and as described above, the core formed of the plates 6, 7, 8 builds axial venting conduits through the holes 14, 15, 17. Cooling air flows through the venting conduits 13 and axial venting conduits 19 of the stator core when the rotating rotor sets the air in the air gap between the stator and the rotor into movement.

In another embodiment of the invention the core comprises plates of the second and third shape for producing venting ducts from the tooth of the core to the back of the core, i.e. from the first side of the core to the second side of the core. In the embodiment, the core comprises further plates of a fourth shape which are formed as solid plates. The fourth shape is similar to the first shape with the exception that there are no holes 14 in the fourth shape as in the first shape. In an embodiment where plates of the fourth shape are used in the core together with assemblies BC, axial conduits are not formed in the back of the core structure. For the venting to be effective, axial grooves are formed to the frame structure surrounding the core so that the air from the venting conduits can exit the core structure. As the core structure in the embodiment is a stator, the stator formed of first assemblies BC and the plates of the fourth shape provide a mechanically strong structure. The mechanical strength, cooling properties and magnetic properties of the stator can be changed by varying the number and thus the thickness of the solid plates between the first assemblies BC in the core structure.

According to another embodiment, the first assembly BC comprises one or more plates of the first shape 6. In this embodiment the core thus comprises plates of four shapes. With the first assembly having the plate of the first shape, the venting conduits from the first side of the core to the second side of the core are formed of the plate 7 having an opening towards the first side of the core, the plate of the first shape 6 having a hole 14 and the plate 8 having an opening towards the second side of the core. With reference to Figures 2, 3 and 4, the flow channel is formed of the conduit 16, hole 14 and conduit 18. The first assembly may be formed of different combinations of the plates of the first, second and third shapes as long as a conduit is formed between the first side of the core and the second side of the core. The conduit may also be branched if so desired by combining the shapes in a suitable manner.

Figures 7, 8 and 9 show core plates that are suitable for forming a rotor for a rotating electric machine. Figure 7 shows a plate 27 of a second shape having a hole 35 and a conduit 36 extending to the hole 35 from the tooth 29 through the entire thickness of the plate 27. The core plate of Figure 7 corresponds to the core plate of Figure 3 intended for a stator core.

Figure 8 shows a plate 28 of a third shape. The plate 28 comprises a hole 37 and a conduit 38 extending from the hole 37 to the second side of the core through the entire thickness of the plate 28. The hole 37 is substantially in the same position with the hole 35 in the plate of the second shape. The core plate of Figure 8 corresponds to the core plate of Figure 4. The core plate of Figure 8 is intended for a rotor core.

Figure 9 shows a plate 40 of a fourth shape. The fourth shape is a solid plate that does not have any holes or conduits for ventilation purposes. The shown plate 40 of the fourth shape can be modified into a plate of the first shape by producing holes in the plate to a position in which they correspond to the holes 35 and 37 of the plates of the second and the third shapes. The first shape is shown in Figure 2 for a stator core.

In the invention first assemblies BC comprising plates of the second shape and the third shape are provided in the core. The core shapes of Figures 7, 8 and 9 are intended for producing a rotor core having the venting conduits 33. As shown in Figure 10, the rotor core is stacked from the core plates similarly as in connection with the stator core. In Figure 10, the first assemblies BC are shown in a structure having plates 40 of the fourth shape . As a plate of the fourth shape is a solid structure, axial conduits are not formed. When replacing the plates 40 of the fourth shape with the plates of the first shape, which has a hole coinciding with the holes of the plates of the second and third shapes, axial conduits are formed in the back of the core and these conduits are used for cooling the core structure with the flowing air.

When the plates of the second, third and fourth types 27, 28, 40 intended for forming a rotor are stacked to form a core, axial conduits need to be formed between the shaft of the rotor and the rotor core. The axial conduits which form a passage for the cooling air of the rotating rotor can be formed by providing the surface of the shaft with axial grooves or ribbings to allow air to pass between the surface of the shaft and the second side of the core.

The shapes presented in Figures 7, 8 and 9 and the plate of the first shape not presented in the drawings are applied similarly as the shapes presented in Figures 2, 3 and 4 and the plate of the fourth shape not presented in the drawings. Some of the shapes are intended for forming a stator core while other shapes are intended for forming a rotor core.

In order to provide an optimal control of the air flow coming from the air gap 5 into the venting conduits 13, 33, the mouths of the conduits in the plates 7 of the second shape (i.e. the mouths of the air conduits 13), which are connected to the air gap 5, are shaped to face the flow from the air gap 5. Also in these core plates 7, 27, the cross-sections of the conduits 16, 36 (i.e. the venting conduits 13, 33) increase towards the hole 15, 35.

In order to reduce discharge resistance to the air flow leaving the venting conduits 13, 33 , the cross-section of the conduits 18, 38 of the core plates of the third shape 8 increases towards the outer surface of the core back 12.

With regard to the manufacture of the core plates 6, 7, 8, 27, 28 and 40 the conduits and the holes in them may be made by die cutting, laser cutting, water cutting or possibly partly by drilling (the axial conduits 19).

When the stator 2 or rotor 3 of the embodiment is being implemented, a stator back of a relatively great thickness is required but then again in rapidly rotating machines thickness tends to be considerably greater than usual. All cuts, conduits, holes or slots in the stator plates 6, 7, 8, 27, 28 and 40 must be large enough to avoid blocking during resin if ication.

It is also possible to increase the cooling area by cutting the conduits at slightly different points of the teeth 9, 29, whereby the stator plates form a ribbing on the surface of the conduit.

Figures 7 to 10 show an embodiment of the invention in which the core formed of core plates or laminations is a rotor core. Similarly as with the embodiment relating to a stator core, the rotor core is formed of plates having different shapes that are stacked to form a laminated rotor structure having venting conduits leading from the teeth of the rotor core, i.e. from a first side of the rotor to the core back, i.e. to a second side of the core. With the above definitions, the first side of the rotor core is the side facing the air gap between the stator and the rotor, and the second side of the rotor core is the rotor back facing the shaft of the rotor.

Figure 1 1 shows a cross section of a segment of stator and rotor cores formed according to the invention. Specifically, Figure 1 1 shows the venting conduits 16, 18 of the stator core and venting conduits 36, 38 of the rotor core.

In the drawings the core plates are presented as segments forming a part of core layer. Multiple of such segments form one layer of a stacked core structure. The core plates may also be complete layers having the form of a cross-section of the core.

The above specification is only meant to illustrate the basic idea of the invention. A person skilled in the art may therefore modify its details within the scope of the accompanying claims.