Axial Flux Stator Core

Abstract

An axial flux stator core (50) and its manufacture are proposed. The axial flux stator core (50) has a spirally layered structure (24), the axial flux stator core (50) having a first longitudinal side (16) and a second longitudinal side (18), and the axial flux stator core (50) comprises a metal strip (14) wound to form the spirally layered structure (24). The first side (16) of the metal strip (14) has a plurality of slots (20) having a slot width that varies along the metal strip (14), the first side (16) forming a plurality of stator teeth (26), the slots (20) defining tooth separations between each pair of adjacent stator teeth (26), and the second side (18) forming an annular stator yoke (28) connecting the stator teeth (26).

Description

[Technical Field]

[0001] The proposed technology relates generally to the field of axial flux motors and generators, and in particular to axial flux stators. [Background technology]

[0002] An axial flux motor or axial gap motor is an electric motor with an architecture in which the magnetic flux between the rotor and stator is aligned parallel to the axis of rotation.

[0003] One type of axial-flux stator has an annular stator yoke with stator teeth extending axially relative to the stator yoke. The stator yoke and stator teeth together form a stator core. A coil of electrically insulated conductor, such as wire or flat copper strip, is wound around each stator tooth to create a magnetic field parallel to the axis of rotation. It is known to fabricate such axial-flux stator cores from a metal strip by forming multiple slots in one side of the metal strip and winding the metal strip to form a helically layered structure. The side without the slots forms the annular stator yoke, and the side with the slots forms the stator teeth. The slots define tooth separation between the stator teeth. The slots have a fixed shape, meaning that the tooth separation is radius-independent. The innermost and outermost layers of the helically layered structure have the same tooth separation as the rest of the layers. By extension, this means that the stator teeth have a radial profile with sharp corners at the innermost and outermost layers.

[0004] Axial-flux motors are typically shorter and wider than equivalent radial-flux motors. In some applications, for example, when mounted coaxially to a vehicle drive shaft or drive axle, having a narrower width is advantageous. The stator diameter generally sets the width of an axial-flux motor. Furthermore, in axial-flux stators with cores having a helically layered structure, the coils of the stator teeth project radially outward from the stator yoke and stator teeth, thus contributing to the stator diameter. Summary of the Invention [Problem to be solved by the invention]

[0005] It is an object of the proposed technology to provide greater flexibility when forming coils on stator teeth in axial flux stators.It is a further object of the proposed technology to reduce the width of axial flux stators having a helically layered structure. [Means for solving the problem]

[0006] In a first aspect of the proposed technology, a method is proposed for manufacturing an axial-flux stator core from a metal strip or elongated metal sheet having a first longitudinal side and a second longitudinal side. The method includes forming a plurality of slots in the first side of the metal strip, each having a slot width that varies or changes along the metal strip or first side. The method further includes winding or rolling the metal strip to form a helically layered or laminated structure, the first side forming a plurality of stator teeth, the slots defining a tooth separation or tooth gap between each pair of adjacent stator teeth, and the metal strip forming an annular stator yoke connecting the stator teeth.

[0007] In a second aspect of the proposed technology, a system for manufacturing an axial-flux stator core from a metal strip or elongated metal sheet having a first longitudinal side and a second longitudinal side is proposed. The system includes a punching tool configured to form a plurality of slots in the first side of the metal strip, each slot having a slot width that varies or changes along the metal strip or first side. The system further includes a rolling tool or winding roller configured to wind or roll the metal strip to form a helically layered or laminated structure, the first side forming a plurality of stator teeth, the slots defining a tooth separation or tooth gap between each pair of adjacent stator teeth, and the metal strip forming an annular stator yoke connecting the stator teeth.

[0008] In a third aspect of the proposed technology, an axial-flux stator core having a spirally layered or laminated structure is proposed, comprising a metal strip or elongated metal sheet having a first longitudinal side and a second longitudinal side, wound to form the spirally layered structure. The first side of the metal strip has a plurality of slots, each having a slot width that varies or changes along the metal strip or first side. The first side forms a plurality of stator teeth, the slots defining a tooth separation or tooth gap between each pair of adjacent stator teeth, and the metal strip forms an annular stator yoke connecting the stator teeth.

[0009] In a fourth aspect of the proposed technology, a method for manufacturing an axial flux stator is proposed. The method may include any of the steps or features of the first aspect of the proposed technology. In addition, the method further includes forming or winding a coil of electrically insulated conductor on each of the stator teeth.

[0010] A fifth aspect of the proposed technology provides an axial flux stator including an axial flux stator core according to the third aspect of the proposed technology. The axial flux stator further includes a plurality of coils individually positioned on or wound around the stator teeth. In other words, the axial flux stator further includes a plurality of coils, each of which is individually positioned on or wound around one of the stator teeth. In other words, the axial flux stator further includes a plurality of coils, each of which is individually positioned on or wound around one of the stator teeth. It is understood that each coil is positioned on or wound around the stator tooth to which it is attached. It is understood that the coils are electromagnetic coils. It is further understood that each coil may include an electrically insulated conductor.

[0011] For example, the axial flux stator core or axial flux stator may be for an electric motor or a generator. In a sixth aspect of the proposed technology, an axial flux motor or a generator is proposed, which includes the axial flux stator core according to the third aspect of the proposed technology or the axial flux stator according to the fifth aspect of the proposed technology.

[0012] It is understood that the slot width is aligned with the metal strip or parallel to the first side of the metal strip. Varying slot widths along the metal strip mean that the tooth separation varies radially for a helically layered structure. This allows for greater flexibility when forming coils on the stator teeth and allows for optimization of the radial profile of the stator teeth. For example, the radial profile can be adapted for different types or sizes and shapes of insulated conductors forming the coils wound on the stator teeth.

[0013] The metal strip may be silicon steel or electrolytic steel, and it is understood that the formation of the multiple slots and the winding of the metal strip are synchronized so that the slots overlap in a spirally layered configuration to form stator teeth on a first side of the metal strip.

[0014] It is understood that an axial flux stator core defines axial, radial, and tangential directions relative to the axis of rotation during use, for example, in an electric motor or generator. Similarly, a spirally layered structure defines axial, radial, and tangential directions relative to the axis of rotation during winding of the metal strip. The axis of rotation during use and winding may be the same, meaning that the stated directions coincide. For example, the axial direction is the same both during use and winding.

[0015] A longitudinal side is understood herein as extending longitudinally relative to the strip. It is specified that the slot has a slot width that varies or changes along the metal strip. It is understood that the first longitudinal side and the second longitudinal side may be parallel. It is specified that the slot width varies along the metal strip. In other words, consecutive slots may have different slot widths. It is understood that each tooth extends radially, tangentially, and axially relative to the helically layered structure. It is further understood that each slot extends tangentially and axially. It is further understood that the tooth separation is aligned tangentially to the helically layered structure.

[0016] Each slot may define a first slot edge and a second slot edge in the metal strip, the first slot edge and the second slot edge being spaced apart and connected to or extending from the first side of the metal strip. It is understood that the separation of the first slot edge and the second slot edge defines the slot width. Each slot may further define a third slot edge, the third slot edge being spaced apart from the first side of the metal strip and interconnecting the first slot edge and the second slot edge. The first slot edge and the second slot edge may be straight or linear. The first slot edge and the second slot edge may be parallel, meaning that each slot has a constant slot width from the third slot edge toward the first side of the metal strip. The first slot edge and the second slot edge may be transverse to or perpendicular to the first side of the metal strip. It is understood that the third slot edge may be straight or linear and may be perpendicular to the first and second slot edges, or may be aligned with or parallel to the first edge of the metal strip. In other words, the slot width of each slot may be constant or invariant across the metal strip or perpendicular to the first side of the metal strip. In other words, each slot outlines a rectangle that opens at the first side of the metal strip. The constant slot width allows for the slot to be formed by two or more notches using the same cooperating punch and die. The constant slot width also allows for pre-wound coils to be pressed into the stator teeth. By extension, the constant slot width allows for the use of flat conductors in the coil, with either the wide or narrow side of the conductor facing the stator teeth.

[0017] It is understood that in an axial flux stator, each coil may correspond to the stator tooth on which it is formed or positioned. In a fourth aspect of the proposed technology, it is specified above that the method includes forming a coil of electrically insulated conductor on each of the stator teeth. It is understood that this includes forming a plurality of coils separately from the stator core and mounting one of the plurality of coils on each of the stator teeth, or pressing one of the plurality of coils onto each of the stator teeth. In a fifth aspect of the proposed technology, it is specified above that the coils are individually positioned on the stator teeth. In other words, each stator tooth comprises one of the plurality of coils. It is further specified that each coil may comprise an electrically insulated conductor. Each coil may be a prefabricated coil, meaning that the coil is formed or wound separately from the stator core.

[0018] For example, the conductor of each coil may be a flat conductor strip having a first wide side and a first narrow side. The first wide side may be positioned to face a stator tooth on which the coil is wound or mounted. This means that the first wide side constitutes the inner side of the conductor or coil. In other words, the coil may be a multi-layer flat conductor coil that extends radially. Alternatively, the first narrow side may be positioned to face a stator tooth on which the coil is wound or mounted. This means that the first narrow side constitutes the inner side of the conductor or coil. In other words, the coil may be a single-layer multi-layer flat conductor coil that extends axially. It is understood that the conductor may have a second wide side facing in the opposite direction to the first wide side, and that the first narrow side may interconnect the first and second wide sides. It is further understood that the conductor may have a second narrow side facing in the opposite direction relative to the first narrow side, and that the second narrow side may interconnect the first and second wide sides. In these two examples, it is understood that the coil is positioned such that the first wide side is juxtaposed to or in contact with the second wide side within the coil.

[0019] The spirally layered structure may have multiple spirally or radially arranged layers. It is understood that the layers contact each other to form a radially sandwiched structure. It is further understood that the spirally layered structure surrounds a radially outermost layer and a radially innermost layer. The slots in one layer or each layer of the spirally layered structure may have the same slot width.

[0020] The spirally arranged structure may have a radially inner half and a radially outer half that together form the spirally arranged structure. It is understood that the inner half and the outer half are joined at a center between the innermost layer and the outermost layer. It is further understood that the innermost layer forms a portion of the inner half and the outermost layer forms a portion of the outer half. It is further understood that the innermost layer and the outermost layer are each comprised of multiple layers. The slot width of the slots in the radially outermost layer may be greater than the slot width of the slots in the other layers in the outer half. The slot width of the slots in the radially innermost layer may be greater than the slot width of the slots in the other layers in the inner half.

[0021] The slot width of the slot in the outermost layer may be greater than the slot width of the adjacent second outermost layer. Similarly, the slot width of the slot in the second outermost layer may be greater than the slot width of the adjacent third outermost layer. Similarly, the slot width of the slot in the third outermost layer may be greater than the slot width of the adjacent fourth outermost layer. The slot width of the innermost layer may be equal to or greater than the slot width of the adjacent second innermost layer. The slot width may be the same in or among a majority of the spirally arranged layers, or even more than 60, 70, or 80% of the layers.

[0022] As discussed above, adjacent stator teeth define a tooth separation or tooth gap between the stator teeth. The tooth separation may vary with radius or between layers. The tooth separation of the outermost layer may be greater than the tooth separation of the adjacent inner layer. The tooth separation of the innermost layer may be greater than the tooth separation of the adjacent outer layer. In other words, each stator tooth may have a tooth width. It is understood that the tooth width is tangential to the helically layered structure. The tooth width may vary with radius or between layers. The tooth width of the outermost layer may be smaller than the tooth width of the adjacent inner layer. The tooth width of the innermost layer may be smaller than the tooth width of the adjacent outer layer. The features described herein contribute to a radial profile or cross section of the stator tooth having rounded corners. The rounded corners allow the coil to be tightly wound on the tooth and reduce radial protrusion of the coil relative to the tooth.

[0023] The plurality of slots may comprise a first subset of slots and a second subset of slots. The slots of the first subset may have equal slot widths, and the slots of the second subset may have equal slot widths. One or more slot widths of the second subset may be greater than one or more slot widths of the first subset. The proposed system may further comprise a controller or control unit connected to the punching tool and the rolling tool. It is understood that the controller is arranged to control the function of the punching tool and the rolling tool. The controller may be configured to synchronize the punching tool and the rolling tool such that the slots overlap in a helically layered structure to form stator teeth on the first side of the metal strip. The controller may be configured to operate the punching tool and the rolling tool to vary the slot width along the metal strip or along the first side. The controller may be configured to operate the punching tool and the rolling tool to form the first subset of slots and the second subset of slots.

[0024] In the proposed method, winding the metal strip may include positioning a first subset of slots in a first layer of the spirally layered structure and positioning a second subset of slots in a second layer of the spirally layered structure. In the proposed system, the controller may be configured to operate the punching tool and the rolling tool to position the first subset of slots in the first layer of the spirally layered structure and position the second subset of slots in the second layer of the spirally layered structure. In the proposed axial flux stator core, the first subset of slots may be positioned in the first layer of the spirally layered structure and the second subset of slots may be positioned in the second layer of the spirally layered structure.

[0025] The second layer may be positioned radially outside the first layer. For example, the second layer may be the outermost layer, and the first layer may be positioned between the innermost and outermost layers. Alternatively, the second layer may be the innermost layer, and the first layer may be positioned between the innermost and outermost layers. The first and second layers may be juxtaposed.

[0026] In the proposed method and axial-flux stator core, the multiple slots may be formed by a cooperating punch and die that notches a first side of the metal strip. The punching tool of the proposed system may include a cooperating punch and die configured to notch the first side of the metal strip and form the multiple slots. It is understood that a single notch forms a slot having a fixed dimension or fixed slot width. In other words, the notch has a notch width along the metal strip or parallel to the first side of the metal strip.

[0027] Each slot of the first subset may be formed by a single notch. The controller may be configured to operate the punching tool and the rolling tool to form each slot of the first subset by a single notch. Each slot of the second subset may be formed by shifting the metal strip relative to the first notch, punch, and die, and making a second notch that overlaps the first notch. The controller may be configured to operate the punching tool and the rolling tool to form each slot of the second subset by shifting the metal strip relative to the first notch, punch, and die, and making a second notch that overlaps the first notch.

[0028] In other words, each slot in the first subset may be formed by making a notch a first number of times, and each slot in the second subset may be formed by making a notch a second number of times greater than the first number. The controller may be configured to operate the punching tool and the rolling tool to form each slot in the first subset by making a notch a first number of times and to form each slot in the second subset by making a notch a second number of times greater than the first number. The notches forming the slots may overlap. It will be understood that this requires a number of notches that is two or more. For example, each slot in the first subset may be formed by a single notch and each slot in the second subset may be formed by two overlapping notches, or each slot in the first subset may be formed by two overlapping notches and each slot in the second subset may be formed by three overlapping notches.

[0029] More generally, the plurality of slots may comprise a subset of slots, each of the slots of the subset being formed by two or more overlapping notches. The controller may be configured to operate the punching tool and the rolling tool to form the subset of slots, each of the slots of the subset being formed by two or more overlapping notches. It is specified above that the plurality of slots may be formed by cooperating punches and dies that cut into the first side of the metal strip. It is understood that the overlapping notches that form the slots have different positions along the metal strip or parallel to the first side of the metal strip. In other words, when forming one slot of the subset of slots, the metal strip may be shifted relative to the punch and die between the notches, or the controller may be configured to operate the punching tool and the rolling tool to shift the metal strip relative to the punch and die between the notches.

[0030] It is understood that each notch has a notch width along the metal strip or parallel to the first side of the metal strip. Therefore, overlapping notches form slots having a slot width greater than the notch width of a single notch. It is understood that a subset includes at least two slots. The number of notches forming the slots of a subset may vary along the metal strip or between slots of the subset of slots. Additionally or alternatively, the overlap of notches forming one slot of a subset may vary along the metal strip or between slots, or the relative position between notches forming one slot of a subset may vary along the metal strip or between slots. In other words, the above-mentioned shift between notches may vary along the metal strip or between slots of the subset of slots.

[0031] For example, a first slot of the subset may be formed by a first number of overlapping notches. A second slot of the subset may be formed by a second number of overlapping notches. It is understood that the first number and the second number are greater than one. The first number and the second number may be the same, and the relative positions between the second number of notches may be different from the relative positions between the first number of notches. Additionally or alternatively, the second number may be different from the first number. It is understood that the plurality of slots may further comprise a further subset of slots, each of the slots of the further subset being formed by a single notch or two or more overlapping notches. It is further understood that the controller may be configured to operate the punching tool and the rolling tool to form a further subset of slots, each of the slots of the further subset being formed by a single notch or two or more overlapping notches.

[0032] The proposed method may further include forming one or more weld seams joining adjacent layers of the spirally layered structure. The proposed system may further include a weld configured to form one or more weld seams joining adjacent layers of the spirally layered structure. The proposed axial flux stator core may include one or more weld seams joining adjacent layers of the spirally layered structure. The weld seams may prevent the spirally layered structure from unraveling. The weld seams may extend radially relative to the spirally layered structure. Each weld seam may extend across all layers of the spirally layered structure. The weld seams may be located on a second side or on a stator yoke.

[0033] It is specified that the metal strip forms an annular stator yoke connecting the stator teeth. Further, a second side of the metal strip may form the annular stator yoke. This means that the second side does not form a plurality of additional stator teeth.

[0034] Alternatively, the method according to the first aspect of the proposed technology may further include forming a plurality of additional slots in the second side of the metal strip, each of the second slots having a slot width that varies or changes along the metal strip or the second side. In the second aspect of the proposed technology, the punching tool may further be configured to form a plurality of additional slots in the second side of the metal strip, each of the additional slots having a slot width that varies or changes along the metal strip or the second side. In the third aspect of the proposed technology, the second side of the metal strip may have a plurality of additional slots, each of the additional slots having a slot width that varies or changes along the metal strip or the second side. In the fourth aspect of the proposed technology, the method may further include forming or winding a coil of electrically insulated conductor on each of the additional stator teeth. In the fifth aspect of the proposed technology, the axial flux stator may further include a plurality of coils that may be individually positioned on or wound around the additional stator teeth. In other words, each coil may be individually positioned on or wound around one of the stator teeth or an additional stator tooth. In the spirally layered structure, the second side may form a plurality of additional stator teeth, with additional slots defining tooth separations or gaps between each pair of adjacent additional stator teeth, and an annular stator yoke connecting the additional stator teeth. The annular stator yoke may be positioned between the stator teeth and the additional stator teeth. The additional slots may have the same characteristics as the slots or be provided in the same manner as the slots. Similarly, the additional stator teeth may have the same characteristics as the stator teeth or be provided in the same manner as the stator teeth.

[0035] A more complete understanding of the above and other features and advantages of the proposed technology will become apparent from the following detailed description of preferred embodiments of the proposed technology, taken in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0036] [Figure 1] 1 is a schematic diagram of a system for manufacturing an axial flux stator core. [Figure 2] FIG. 2 is a perspective view of an axial flux stator core being manufactured using the system of FIG. 1. [Figure 3] Figure 3a is a planar projection showing the final geometric shape of the axial flux stator core of Figure 2. Figure 3b is a planar projection showing the final geometric shape of the axial flux stator core of Figure 2. Figure 3c is a planar projection showing the final geometric shape of the axial flux stator core of Figure 2. [Figure 4] Figure 4a is a planar projection showing the location of a coil on one of the stator teeth of the axial flux stator core of Figure 2. Figure 4b is a planar projection showing an alternative coil location on one of the stator teeth of the axial flux stator core of Figure 2. [Figure 5] FIG. 10 is a perspective view of an axial flux stator core having additional stator teeth. DETAILED DESCRIPTION OF THE INVENTION

[0037] A system 10 for manufacturing an axial flux stator core 50 is shown schematically in FIG. 1. The system 10 includes a punching tool 12 into which a metal strip 14 of silicon steel is fed. The metal strip 14 has a first longitudinal side 16 and a second longitudinal side 18. The punching tool 12 includes a cooperating punch 32 and die 34 that cut into the first side 16 of the metal strip 14 to form a plurality of slots 20 in the first side 16.

[0038] The system 10 also includes a rolling tool 22 having a roller 58 operatively connected to the electric motor 54 by a belt 56. The rolling tool 22 winds the metal strip 14 around the roller 58 after it passes through the punching tool 12, thereby forming a spirally layered structure 24 having a plurality of spirally arranged sandwiched layers 36 in contact with one another.

[0039] The system 10 includes a controller 30 connected to and synchronizing the punching tool 12 and the rolling tool 22 to overlap the slots 20 in the spirally layered structure 24. Thus, the first side 16 of the metal strip 14 forms a plurality of stator teeth 26, and the slots 20 define tooth separations between adjacent pairs of the stator teeth 26. The second side 18 of the metal strip 14 forms an annular stator yoke 26 connecting the stator teeth 26.

[0040] The controller 30 operates the punching tool 12 and the rolling tool 22 to form several subsets of slots 20. An initial subset is formed in which the slots 20 are positioned in the innermost layer 38 of the spirally layered structure 24. Each of the slots 20 in the initial subset is formed by the controller 30 operating the punching tool 12 and the rolling tool 22 to form the slot by punching a first notch, shifting the metal strip 14 relative to the punch 32 and die 34, and punching a second notch that overlaps the first notch. In this way, a wider slot width is achieved than with a single notch. The shift of the metal strip 14 is gradually reduced, which means that the slot width varies along the metal strip 14 in the innermost layer 38. A second subset is formed in which the slots 20 are positioned between the innermost layer 38 and the third, outermost layer 40. The controller 30 operates the punching tool 12 and the rolling tool 22 to form each of the slots 20 by a single notch with the punching tool 12, meaning that the slots 20 in the second subset have the same slot width, but the slot width is narrower than that of the initial subset. A third subset is formed in which the slots 20 are positioned in the third outermost layer 40. Each of the slots 20 in the third subset is formed by the controller 30 operating the punching tool 12 and the rolling tool 22 to form the slot 20 by punching a first notch, shifting the metal strip 14 relative to the punch 32 and die 34, and punching a second notch that overlaps the first notch. In this way, a wider slot width is achieved than in the second subset. The shifting of the metal strip is the same for all of the slots 20 in the third subset, meaning that the slots 20 have the same slot width. A fourth subset is formed in which slots 20 are positioned in the second outermost layer 42 .The fourth subset of slots 20 are formed in the same manner as the third subset of slots 20, except that the greater shift in the metal strip 14 between the first and second notches results in a greater slot width. A final subset is formed with slots 20 positioned on the outermost layer 44. The final subset of slots 20 are formed in the same manner as the fourth subset of slots 20, except that the greater shift in the metal strip 14 between the first and second notches results in an even greater slot width. The slot width of the slots 20 is indicated in FIG. 2 by double arrows 52.

[0041] It should be noted that the numbering of the layers and subsets corresponds to radial position in the spirally layered structure 24, and that different numbering not related to radial position may be used. For example, the fourth outermost layer may be considered the first layer, the slots 20 of the fourth outermost layer may be considered the first subset, the third outermost layer 40 may be considered the second layer, and the slots 20 of the third outermost layer 40 may be considered the second subset. This means that the slots 20 of the first subset have equal slot widths formed by a single notch, and the slots of the second subset have equal slot widths formed by two notches, with the slot widths of the second subset being larger than one or more slot widths of the first subset.

[0042] Each slot 20 defines a first slot edge 62, a second slot edge 64, and a third slot edge 66 on the metal strip 14. The first slot edge 62 and the second slot edge 64 are spaced apart and connected to the first side 16 of the metal strip 14, thus defining the slot width 52. The third slot edge 66 is spaced apart from the first side 16 and interconnects the first slot edge 62 and the second slot edge 64. The first slot edge 62 and the second slot edge 64 are straight and parallel. The first slot edge 62 and the second slot edge 64 are similarly perpendicular to the first side 16 of the metal strip 14. The third slot edge 66 is parallel to the first edge 16 of the metal strip 14. Thus, each slot 20 outlines a rectangle having a slot width 52 that is constant across the strip 14 .

[0043] The resulting spirally layered structure 24 has an outermost layer 44 with a slot width greater than that of the adjacent inner layer 42. The slot width of the innermost layer 38 is equal to or greater than that of the adjacent outer layer. This means that the tooth separation varies with radius. Each of the stator teeth 26 has a tooth width aligned tangentially to the spirally layered structure 24, and the tooth width varies with radius. The tooth width of the outermost layer 44 is smaller than that of the adjacent inner layer 42, and the tooth width of the innermost layer 38 is smaller than that of the adjacent outer layer. The radial profile of the stator teeth 26 has rounded corners, as can be seen in FIG. 3a. This allows the coil 46 to be tightly wound and not protrude too much radially relative to the stator teeth 26, as shown in FIG. 4.

[0044] In alternative embodiments, the number of notches may be different, and the overlap between notches may be different. For example, the notch width of the punching tool 12 may be half that of the example above. Each slot 20 in the initial subset is formed by three overlapping notches with an equal shift between the notches. Each slot 20 in the second subset is also formed by three overlapping notches, but with a shorter shift than the initial subset. Each slot 20 in the third subset is formed by three overlapping notches with a shift similar to that of the initial subset. Each slot 20 in the fourth subset is formed by three overlapping notches with a longer shift between the notches than the initial subset. Each slot 20 in the final subset is formed by four overlapping notches with an equal shift between the notches.

[0045] See further FIG. 3c , system 10 further includes welds (not shown) that form four radially extending weld seams 48 in stator yoke 28 that join adjacent layers of spirally layered structure 24 and prevent unraveling when spirally layered structure 24 is removed from the rolling tool.

[0046] The spirally arranged structure 24 has a radially inner half 58 and a radially outer half 60 that join at a center (dashed line) between the innermost layer 38 and the outermost layer 44, as shown in Figure 3a. The slot widths 52 of the slots 20 in the radially outermost layer 44 are greater than the slot widths 52 of the slots 20 in the other layers in the outer half 60, which can be seen in Figure 2. Similarly, the slot widths 52 of the slots 20 in the radially innermost layer 38 are greater than the slot widths 52 of the slots 20 in the other layers in the inner half 58.

[0047] The system 10 is shown above to implement a method in which an axial flux stator core 50 is manufactured from a metal strip 14 having a first longitudinal side 16 and a second longitudinal side 18. In summary, slots are formed in the first side 16 of the metal strip, with the slot width varying along the metal strip 14. The metal strip 14 is rolled to form a spirally layered structure 24 having a first side forming a plurality of stator teeth 26 and a second side forming an annular stator yoke 28 connecting the stator teeth 26.

[0048] The resulting axial flux stator core 50 has a spirally layered structure 24 formed by rolled metal strip 14 having a first longitudinal side 16 and a second longitudinal side 18. The overall geometry of stator core 50 is shown in Figures 3a-3c. First side 16 of metal strip 14 has a plurality of slots 20 with widths that vary along metal strip 14. First side 16 forms a plurality of stator teeth 26, and second side 18 forms an annular stator yoke 28 connecting stator teeth 26.

[0049] To produce an axial-flux stator (not shown), a coil 46 of electrically insulated conductor 76 is wound around each of the stator teeth 26, as shown in FIG. 4a. The axial-flux stator (not shown) can be installed in an axial-flux motor or generator (not shown). Each conductor 76 is a coated flat copper strip having a first wide side 68 and an opposing second wide side 70. These are interconnected by first narrow sides (not shown) and second narrow sides (not shown) that face in opposite directions (perpendicular to the plane of the sheet) from the first wide side 68 and second wide side 70 and are perpendicular thereto. The first wide side 68 is the inner side that faces the stator teeth 26. Thus, the coil 46 constitutes a radially extending multilayer flat conductor coil. An alternative embodiment is shown in FIG. 4b, in which each conductor 76 is a coated flat copper strip but is wound in a different manner. The coils 46 are prefabricated separately from the axial-flux stator core 50, and are mounted by pressing the coils 46 onto the stator teeth 26. In each coil 46, a first narrow side 72 of the flat copper strip is positioned facing toward the stator tooth 26, and a second narrow side 74 is positioned facing away from the stator tooth 26. The first wide side 68 and an opposing second wide side (not shown) face in opposite directions (perpendicular to the plane of the sheet) and are connected by the first narrow side 72 and the second narrow side 74. This means that the first narrow side 72 constitutes the inner surface of the conductor 76. Thus, the coils 46 are single-layer flat conductor coils that extend in the axial direction.

[0050] An alternative embodiment of a spirally layered structure 24 for an axial-flux stator core 50 is shown in FIG. 5 . The structure 24 has the features shown in FIG. 2 . Additionally, the structure 24 further has a plurality of additional teeth 56 formed by additional slots 54 in the second side 18 of the metal strip 14. The spirally layered structure 24 is manufactured by a system 10 similar to the system described in connection with FIG. 1 . The system 10 includes an additional punching tool (not shown) having an additional cooperating punch (not shown) and die (not shown) that cuts into the second side 18 of the metal strip 14 and forms a plurality of additional slots 54 in the second side 18. The slots in the first side 16 and the additional slots 54 in the second side 18 are arranged in pairs. A controller 30 of the system is connected to and controls the additional punching tool (not shown) so that, in each pair, the additional slot 54 is positioned directly opposite the slot 20 and has the same slot width 52 as the slot 20. The controller 30 operates an additional punching tool (not shown) in the same manner as the punching tool 12. For example, the varying slot width 52 is achieved by the rolling tool 22 punching two overlapping notches while varying the shift of the metal strip 14 between the notches. As the rolling tool 22 forms the spirally layered structure 24, the additional slots 54 overlap in the same manner as the slots 20, forming additional teeth 56 on the second side 18. [Explanation of symbols]

[0051] 10 Systems 12 Punching tools 14 Metal Strips 16 First side of metal strip 18 Second side of metal strip 20 slots 22 Rolling Tools 24 Spiral layered structure 26 stator teeth 28 Stator yoke 30 Controllers 32 Punch 34 Die 36 layers 38 innermost layer 40 Third outermost layer 42 Second outermost layer 44 outermost layer 46 Coil 48 Weld Seam 50 Axial Flux Stator Core 52 slot width 54 More Slots 56 More Teeth 58 The radially inner half of the spirally layered structure 60 The radially outer half of the spirally layered structure 62 first slot edge 64 second slot edge 66 Third slot edge 68 First Wide Side 70 Second Wide Side 72 First narrow side 74 Second narrow side 76 Conductor

Claims

1. A method for manufacturing an axial flux stator core (50) from a metal strip (14) having a first longitudinal side (16) and a second longitudinal side (18), comprising: forming a plurality of slots (20) in the first side (16) of the metal strip (14), each slot (20) having a slot width (52), the slot width (52) varying along the metal strip (14); winding the metal strip (14) to form a helically layered structure (24), the first side (16) forming a plurality of stator teeth (26), the slots (20) defining tooth separations between each pair of adjacent stator teeth (26), and the metal strip (14) forming an annular stator yoke (28) connecting the stator teeth (26); A method comprising:

2. 2. The method of claim 1, wherein each slot (20) defines a first slot edge (62) and a second slot edge (64) on the metal strip (14), the first slot edge (62) and the second slot edge (64) being spaced apart and connected to the first side (16) of the metal strip (14), and the first slot edge (62) and the second slot edge (64) being straight.

3. 3. The method of claim 1, wherein the spirally layered structure (24) has a plurality of spirally arranged layers (36) surrounding a radially outermost layer (44) and a radially innermost layer (38), and wherein the slot width (52) of the slot (20) in the outermost layer (44) is greater than the slot width (52) of an adjacent second outermost layer (42).

4. 4. The method of claim 3, wherein the slot width (52) of the slot (20) in the second outermost layer (42) is greater than the slot width (52) in the adjacent third outermost layer (40).

5. 5. The method of claim 1, wherein the plurality of slots comprises a subset of slots, each of the slots of the subset being formed by two or more overlapping notches.

6. 5. The method of claim 1, wherein the plurality of slots comprises a first subset of slots and a second subset of slots, the slots of the first subset having equal slot widths, the slots of the second subset having equal slot widths, and the slot widths of the second subset being greater than the slot widths of the first subset.

7. 7. The method of claim 6, wherein the plurality of slots (20) are formed by cooperating punches (32) and dies (34) that cut into the first side (16) of the metal strip (14), each slot (20) of the first subset being formed by a single notch, and each slot (20) of the second subset being formed by a first notch, shifting the metal strip (14) relative to the punch (32) and die (34), and a second notch that overlaps the first notch.

8. 1. An axial flux stator core (50) having a spirally layered structure (24), the axial flux stator core (50) comprising a metal strip (14) having a first longitudinal side (16) and a second longitudinal side (18) and wound to form the spirally layered structure (24), the first side (16) of the metal strip (14) having a plurality of slots (20), each slot (20) having a slot width (52), the slot width (52) varying along the metal strip (14), the first side (16) forming a plurality of stator teeth (26), the slots (20) defining tooth separations between each pair of adjacent stator teeth (26), and the second side (18) forming an annular stator yoke (28) connecting the stator teeth (26).

9. 9. The axial flux stator core of claim 8, wherein each slot defines a first slot edge and a second slot edge on the metal strip, the first slot edge and the second slot edge being spaced apart and connected to the first side of the metal strip, and the first slot edge and the second slot edge being straight.

10. 9. The axial flux stator core of claim 8, wherein the spirally layered structure has a plurality of spirally arranged layers, wherein a slot width of a slot in an outermost layer is greater than a slot width of an adjacent second outermost layer, wherein a slot width of a slot in the second outermost layer is greater than a slot width of an adjacent third outermost layer, and wherein the slot width is the same within and among a majority of the spirally arranged layers.

11. 11. The axial flux stator core of claim 8, wherein the plurality of slots comprises a first subset of slots and a second subset of slots, the slots of the first subset having equal slot widths and the slots of the second subset having equal slot widths, the slots of the first subset being positioned within a first layer of the spirally layered structure and the slots of the second subset being positioned within a second layer of the spirally layered structure, the slot width of the second subset being greater than the slot width of the first subset, and the second layer being positioned radially outside the first layer.

12. 1. A system (10) for manufacturing an axial flux stator core (50) from a metal strip (14) having a first longitudinal side (16) and a second longitudinal side (18), comprising: a punching tool (12) configured to form a plurality of slots (20) in the first side (16) of the metal strip (14), each slot (20) having a slot width (52), the slot width (52) varying along the metal strip (14); a rolling tool (22) configured to wind the metal strip (14) to form a helically layered structure (24), the first side (16) forming a plurality of stator teeth (26), the slots (20) defining tooth separations between each pair of adjacent stator teeth (26), and the second side (18) forming an annular stator yoke (28) connecting the stator teeth (26); A system (10) comprising:

13. 8. A method for manufacturing an axial flux stator, comprising the method of any one of claims 1 to 7, the method comprising: The method further includes forming a coil (46) of electrically insulated conductor on each of the stator teeth (26).

14. 12. An axial flux stator comprising the axial flux stator core (50) of any one of claims 8 to 11, further comprising a plurality of coils (46) individually positioned on the stator teeth (26).

15. 15. An axial flux motor or generator comprising the axial flux stator of claim 14.

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