SINGLE SHEET HOLDER AND SHARP KNILLING

Abstract

An electric machine includes a rotor that is press-fitted to a knurled section of a shaft. The rotor encloses a laminated core consisting of several individual laminations. Each lamination encloses a disk that defines a central bore. Slots are defined in the disk. Each slot is configured to receive a magnet that at least partially defines a magnetic pole of the electric machine. The central bore has a circumference that includes a number of recesses. Each recess engages the disk. A stator is arranged radially outside the rotor.

Description

CROSS-REFERENCE TO RELATED REGISTRATIONS

[0001] This application claims an earlier filing date than the provisional application serial no. 63 / 694,505, filed on 13 September 2024, the entire contents of which are incorporated herein by reference. BACKGROUND OF THE INVENTION

[0002] In fields dealing with rotor construction, such as for AC generators, motors, and similar electrical machines, a rotor shaft is typically pressed into a set of individual laminations (called a laminated core) to create a complete rotor. Such an electrical machine is a traction motor, commonly used in drive systems.

[0003] Rotors have been built this way for many years and are commercially acceptable. However, the pressing process can also introduce compression, warping, dents, and gaps into the rotor's lamination stack. Warping, dents, and gaps caused by compression can negatively affect the overall rotor function and are therefore undesirable.

[0004] It is desirable to provide assembly improvements that can minimize the undesirable effects of pressing operations and improve engine performance. BRIEF DESCRIPTION OF THE INVENTION

[0005] A single sheet for an electric machine rotor is disclosed. The single sheet has a disk that defines a central bore. Slots are defined in the disk. Each slot is configured to receive a magnet that at least partially defines a magnetic pole of the electric machine. The central bore encloses a circumference that has a number of recesses. Each recess of the number of recesses penetrates the disk.

[0006] A rotor for an electric machine is also disclosed. The rotor includes a laminated core containing several individual laminations. Each individual lamination encloses a disk defining a central bore. Slots are defined in the disk. Each slot is configured to receive a magnet that at least partially defines a magnetic pole of the electric machine. The central bore has a circumference that includes a number of recesses. Each recess of the number of recesses penetrates the disk.

[0007] An electric machine is also disclosed, comprising a rotor press-fitted to a knurled section of a shaft. The rotor includes a laminated core comprising several individual laminations. Each individual lamination encloses a disk defining a central bore. Slots are defined in the disk. Each slot is configured to receive a magnet that at least partially defines a magnetic pole of the electric machine. The central bore has a circumference that includes a number of recesses. Each recess extends into the disk. A stator is arranged radially outside the rotor. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The following descriptions should not be considered restrictive in any way. With reference to the accompanying drawings, identical elements are numbered the same: Fig. Figure 1 shows a schematic cross-section of an electric machine that includes a rotor lamination stack; Fig. Figure 2 shows a partial view of a single rotor lamination on the shaft of the rotor lamination stack of the Fig. 1 from. Fig. 3 forms a single recess feature of the rotor single sheet of the Fig. 2 off, and Fig. 4 shows a cross-sectional view of the shaft of the Fig. 1-3 before installing the rotor lamination package. DETAILED DESCRIPTION OF THE INVENTION

[0009] Fig. Figure 1 illustrates a highly schematic traction motor 100, which includes a stator 110 arranged around a rotor 120. The rotor 120 is constructed from a set of several individual laminations 122, each lamination 122 enclosing several slots. A partial view of an exemplary lamination 122 is shown in Fig. 2 illustrated.

[0010] With reference to the Fig. 1 and Fig. 2. The individual laminations 122 are mounted on a shaft 130. Each individual lamination 122 encloses several slots 210 that accommodate magnets 212 (e.g., permanent magnets). The magnets 212 define the rotor poles of the traction motor 100.

[0011] During motor operation, interactions between an electromagnetic field generated by the stator 110 and the electromagnetic field of the magnets 212 cause the rotor 120 to rotate. Since the rotor 120 is mechanically supported and attached to the shaft 130, its rotation drives the rotation of the shaft 130, and this rotation is transmitted to any systems connected to the shaft 130. Operations of the traction motor 100 can be controlled using any control configuration according to existing concepts.

[0012] The combined set of individual laminations 122 is referred to as a lamination stack 124. To hold the lamination stack 124 on the shaft 130, the lamination stack 124 has a central bore 220 that is pressed onto the shaft 130. A section of the shaft 130 that holds the lamination stack 124 is knurled. Knurling consists of small protrusions or knobs that extend outward from an outer diameter of the shaft 130. An exemplary knurling pattern is shown in Fig. Figure 4 illustrates this with multiple knurling 132 extending along a surface of the shaft 130 in a region of the shaft 130 where the laminated core 124 is press-fitted in place. The knurling 132 is staggered such that multiple knurling 132 are present at a given axial position on the shaft 130 relative to a shaft axis A. This axial staggering of the knurling 132 ensures that all individual laminations 122 installed in the knurled section of the shaft are in contact with multiple knurling 132 to maintain the press fit. In some examples, a knurled section 131 of the shaft 130 is at least as long as the laminated core 124.

[0013] In alternative examples, the knurling 132 can include other geometries (e.g., diamond- or trapezoidal geometries). In some examples, all knurling 132 are identical. In other examples, the knurling 132 can be formed using a combination of several geometries and sizes.

[0014] The individual laminations 122 are stacked either by welding, interlocking, or gluing to form the lamination stack 124. During the assembly of the traction motor 100, the lamination stack 124 is press-fitted onto the shaft 130. If the circumference of the central bore 220 is circular and the press fit and force are too high, the lamination stack 124 may be damaged. Similarly, if a knurling 132 of the wrong size is used, the resulting lamination stack 124 may be loose in the finished assembly. To increase manufacturing efficiency, standardized knurling tools can be used in some examples to create the knurling. If this is the case, the possibility of incorrect press fit and force increases.

[0015] To reduce the possibility of an interference fit and an excessive force requirement, and to increase the range of standardized knurling tools that can be used for a given sheet metal stack 124, each individual sheet 122 includes several excluded features 230. The excluded features are sections of the circumference of the central bore 220 that extend radially outward into the individual sheet 122 and away from the center of the central bore 220.

[0016] In one example, the excluded features are elliptical (i.e., they form an arc that is a segment of an ellipse). The use of elliptical recesses for the excluded features minimizes the stress concentration on the inner circumference of the lamination stack 124, while providing sufficient interference fit to statically hold the lamination stack 124 to the shaft 130. In alternative examples, the excluded features may include other geometries (e.g., diamond- or trapezoidal geometries). In some examples, all excluded features are identical in shape and dimensions. In other examples, the excluded features may be formed using a combination of several geometries and sizes.

[0017] With further reference to the Fig. 1-2 and on Fig. 4, illustrated Fig. 3 a close view of a subsection 201 of the Fig.2. Subsection 201 includes a single recess 230 and illustrates a depth 231 from a radially outermost section of the knurling 132 to the recess 230 and a depth 233 from the shaft 130 to the recess 230. Each recess 230 is defined with a depth 233 of sufficient length such that the depth 231 is greater than zero when manufacturing tolerances are taken into account. Although illustrated in the examples as an arc-shaped indentation in the circumference of the central bore 220, it is understood that the recesses 230 can be achieved using alternative shapes. For example, in some alternatives, the edges of each recess can be defined by a straight edge aligned with a radius of the shaft 130, and the recess encloses an identical arc shape to the circumference of the central bore 220 at the position of the recess 230.

[0018] The inclusion of the recesses 230 allows the press fit between the central bore 220 of the lamination stack 124 and individual knurling 132 of the shaft 130 to be the same as in a configuration without recesses 230, while simultaneously minimizing the pressing force required to press the lamination stack 124 into place. This, in turn, allows the use of a standard knurling tool to form the knurling 132 on the shaft without increasing the risk of an unsuitable press fit and force.

[0019] The recesses 230 function by allowing the lamination stack 124 to skip or not contact a percentage of the knurling 132 at any given axial position on the shaft 130. In some examples, the recesses 230 are dimensioned to skip a number of knurling 132 in the range of 55%–65% of the knurling 132 at a given axial position. In other examples, the recesses 230 are dimensioned to skip approximately 58% of the knurling 132 at a given axial position.

[0020] In some examples, the number of holes 230 on each individual sheet 122 is an integer that is a multiple of the number of poles of the individual sheet 122. For example, if the individual sheet 122 defines a four-pole machine, the number of holes 230 on each individual sheet 122 could be four, eight, twelve, sixteen, twenty, or any other multiple of four. In some specific implementations, the number of poles is equal to the number of holes 230.

[0021] In some examples, each individual sheet 122 in the sheet stack 124 encloses the same number and size of recesses 230. In these examples, the recesses 230 of each individual sheet 122 are aligned with the recesses 230 of each other individual sheet in the sheet stack 124 such that, when the sheet stack 124 is assembled, the recesses 230 of the entire sheet stack 124 are located at the same radial positions.

[0022] In one specific implementation, a four-pole electric machine is constructed using a laminated core 124 having eight recesses 230 on the central bore 220. The shaft 130 has a total of 224 knurling 132 at each axial position. Each recess 230 skips 14 knurling 132 on the shaft 130, resulting in a total of 12 knurling 132 skipped at each axial position of the shaft 130.

[0023] The term "approximately" is intended to include the degree of error associated with measurements of the specified quantity based on equipment available at the time of filing the application. For example, "approximately" may include a range of ± 8% of a given value.

[0024] The terminology used herein is intended to describe only particular embodiments and is not intended to limit the invention. As used herein, singular forms "a", "an", and "the" are to include all plural forms, unless the context clearly indicates otherwise. Furthermore, it is understood that the terms "comprises" and / or "comprehensive," when used in this patent specification, indicate the presence of the aforementioned features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0025] Although the invention has been described with reference to a preferred embodiment or embodiments, the person skilled in the art understands that various modifications can be made and equivalents used for its elements without departing from the scope of protection of the invention. Furthermore, many modifications can be made to adapt the teachings of the invention to a particular situation or material without deviating from its essential scope. The invention is therefore not intended to be limited by the particular embodiment considered to be the best way of carrying out this invention, but rather includes all embodiments that fall within the scope of protection of the claims.

Claims

[1] Single sheet for an electric machine rotor, the single sheet comprising: a disc that defines a central bore; Slots defined in the disk, each slot configured to receive a magnet that at least partially defines a magnetic pole of the electric machine; and wherein the central bore has a circumference that includes a number of recesses, each recess penetrating the disk by a number of recesses. [2] Single sheet according to claim 1, wherein the number of recesses is an integer which is a multiple of the number of magnetic poles of the electric machine. [3] Single sheet according to claim 2, wherein the number of recesses is equal to the number of magnetic poles of the electric machine. [4] Single sheet according to claim 1, wherein one of the recesses is elliptical. [5] Rotor for an electric machine, the rotor comprising: a sheet metal package that includes a large number of individual sheets; and wherein each individual sheet includes a disk defining a central bore, slots defined in the disk, each slot being configured to accommodate a magnet forming at least a part of a magnetic pole of the electric machine, and wherein the central bore has a circumference including a number of recesses, each recess penetrating the disk by a number of recesses. [6] Rotor according to claim 5, wherein each individual sheet includes the same number of recesses as each other individual sheet of the plurality of individual sheets. [7] Rotor according to claim 6, wherein the recesses of each individual sheet are radially aligned with the recesses of each other individual sheet in the sheet stack. [8] Rotor according to claim 5, wherein the number of recesses in each individual sheet is an integer which is a multiple of the number of magnetic poles of the electric machine. [9] Rotor according to claim 8, wherein the number of recesses in each individual sheet is equal to the number of magnetic poles of the electric machine. [10] Electric machine comprising the following: a rotor that is press-fitted onto a knurled section of a shaft, the rotor enclosing a laminated core comprising a plurality of individual laminations, each individual lamination enclosing a disk defining a central bore, slots defined in the disk, each slot configured to receive a magnet defining at least a part of a magnetic pole of the electric machine, and the central bore having a circumference enclosing a plurality of recesses, each recess penetrating the disk; and a stator that is positioned radially outside a rotor. [11] Electric machine according to claim 10, wherein the knurled section of the shaft includes shaped knurling that projects from an outer surface of the shaft, and wherein each recess skips a number of knurling at an axial position of the knurling. [12] Electric machine according to claim 11, wherein a number of knurling points that is skipped by each recess lies in a range of 55%-65% of a total number of knurling points at the axial position of the recess. [13] Electric machine according to claim 11, wherein the number of knurling points skipped by each recess is about 58% of the total number of knurling points at the axial position of the recess. [14] Electric machine according to claim 11, wherein the shaped knurling is evenly distributed around the shaft in the knurled section such that the number of knurling at each axial position in the rendered section is the same. [15] Electric machine according to claim 11, wherein the knurled section of the shaft is at least as long as the total length of the plurality of individual laminations. [16] Electric machine according to claim 10, wherein each recess of the number of recesses is elliptical. [17] Electric machine according to claim 10, wherein each individual sheet includes the same number of recesses as each other individual sheet of the plurality of individual sheets. [18] Electric machine according to claim 17, wherein the recesses of each lamination stack are radially aligned with the recesses of each other individual lamination in the lamination stack. [19] Electric machine according to claim 10, wherein the number of recesses in each individual sheet is an integer which is a multiple of the number of magnetic poles of the electric machine. [20] Electric machine according to claim 19, wherein the number of recesses in each individual sheet is equal to the number of magnetic poles of the electric machine.

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