Induction rotor assembly with thin foil

Abstract

The present disclosure provides an induction rotor assembly. The induction rotor assembly includes a stack of stacks, a plurality of foils, a plurality of conductor bars, a first end ring, and a second end ring. The stack includes a body having a peripheral surface with a plurality of grooves extending from a first end to a second end. Each of the plurality of foils is disposed in one of the plurality of grooves. Each foil is disposed between each conductor bar and each groove. Each of the plurality of conductor bars includes a first conductor end and a second conductor end. A first end ring mates with a surface of each of the first conductor ends. A second end ring mates with a surface of each second conductor end, and a plurality of conductor bars extend between the first end ring and the second end ring.

Description

Technical Field

[0001] The present disclosure relates to induction rotor assemblies, and more particularly to systems and methods for manufacturing cast induction rotor assemblies having conductive bars with thin foils. Background Art

[0002] An induction motor typically consists of a stator and a rotor. The stator is usually stationary, while the rotor rotates and consists of a series of conductive bars arranged in a circular pattern around the rotor body. When current is applied to the stator, it creates a magnetic field that interacts with the rotor and the conductive bars. This interaction causes the rotor to rotate, generating mechanical energy.

[0003] Many current traction motors, particularly those in electric vehicles, use bar windings to increase the stator's fill factor. However, bar windings can induce a high skin effect, or the tendency of the alternating current to distribute within each bar, resulting in a current density that is highest near the bar surface and decreases exponentially with depth within each bar. This high skin effect results in undesirable electrical resistance, significantly increasing losses and limiting the motor's power density, speed, and torque capabilities.

[0004] While current induction rotor assemblies achieve their intended purpose, a need exists for a system and method of manufacturing an induction rotor having conductor bars with improved electrical conductivity within the conductors. Summary of the Invention

[0005] According to several aspects of the present disclosure, an induction rotor assembly is provided. The induction rotor assembly includes a stack, a plurality of foils, a plurality of conductor bars, a first end ring, and a second end ring. The stack includes a body having a first end and an opposite second end arranged along a longitudinal axis. The body has an outer peripheral surface extending from the first end to the second end along the longitudinal axis, and the outer peripheral surface has a plurality of grooves extending from the first end to the second end. Each of the plurality of foils is disposed in one of the grooves. Each of the plurality of conductor bars is disposed in each of the grooves, and each of the plurality of foils is disposed between each of the plurality of conductor bars and each of the grooves. Each of the plurality of conductor bars includes a first conductor end and a second conductor end, the first conductor end extending axially beyond the first end of the stack and the second conductor end extending axially beyond the second end of the stack. A first end ring engages with a surface of each first conductor end to interlock each of the plurality of conductor bars to the first end ring. A second end ring engages with a surface of each second conductor end to interlock each of the plurality of conductor bars to the second end ring, with the plurality of conductor bars extending between the first end ring and the second end ring.

[0006] According to another aspect of the present disclosure, an induction rotor assembly has a body comprising a plurality of laminated steel plates.

[0007] According to another aspect of the present disclosure, an inductive rotor assembly has a plurality of foils, the plurality of foils being pure copper or a copper-graphene composite material.

[0008] According to another aspect of the present disclosure, an inductive rotor assembly has a plurality of foils having a graphene volume of less than or equal to 20%.

[0009] According to another aspect of the present disclosure, an inductive rotor assembly has a plurality of foils including an adhesive on one side of each foil.

[0010] According to another aspect of the present disclosure, an inductive rotor assembly has a plurality of foils, each foil of the plurality of foils having a thickness between 20 microns and 30 microns.

[0011] According to another aspect of the present disclosure, an inductive rotor assembly has a plurality of foils, each foil of the plurality of foils protruding from a groove.

[0012] According to another aspect of the present disclosure, an inductive rotor assembly has a plurality of foils, each foil of the plurality of foils including a coating at least partially having a roughened surface.

[0013] According to another aspect of the present disclosure, an inductive rotor assembly has a plurality of foil layers disposed between each groove and each conductor bar.

[0014] According to another aspect of the present disclosure, an inductive rotor assembly has a plurality of conductor bars formed of at least one of copper or aluminum.

[0015] According to another aspect of the present disclosure, an induction rotor assembly includes first and second end rings each cast on a first conductor end and a second conductor end of each of a plurality of conductor bars, respectively.

[0016] According to another aspect of the present disclosure, an induction rotor assembly has first and second end rings formed of aluminum.

[0017] According to several aspects of the present disclosure, a vehicle electric motor is provided. The vehicle electric motor includes a stator and an induction rotor assembly. The induction rotor assembly is configured to rotate due to a rotating magnetic field generated by the stator. The induction rotor assembly includes a laminated stack, a plurality of foils, a plurality of conductor bars, a first end ring, and a second end ring. The laminated stack includes a body having a first end and an opposite second end arranged along a longitudinal axis. The body has an outer peripheral surface extending from the first end to the second end along the longitudinal axis, and the outer peripheral surface has a plurality of grooves extending from the first end to the second end. Each of the plurality of foils is disposed in one of the grooves. Each of the plurality of conductor bars is disposed in one of the grooves, and each of the plurality of foils is disposed between each of the plurality of conductor bars and each of the grooves. Each of the plurality of conductor bars includes a first conductor end and a second conductor end, the first conductor end extending axially beyond the first end of the laminated stack and the second conductor end extending axially beyond the second end of the laminated stack. The first end ring mates with a surface of each first conductor end to interlock each of the plurality of conductor bars to the first end ring. The second end ring cooperates with a surface of each second conductor end to interlock each of the plurality of conductor bars to the second end ring, and the plurality of conductor bars extend between the first end ring and the second end ring.

[0018] According to another aspect of the present disclosure, a vehicle motor includes a plurality of pure copper foils or foils of a copper-graphene composite material.

[0019] According to another aspect of the present disclosure, a vehicle motor includes a plurality of foils, and a thickness of each of the plurality of foils is between 20 microns and 30 microns.

[0020] According to another aspect of the present disclosure, a vehicle motor includes a plurality of conductor bars formed of at least one of copper or aluminum.

[0021] According to several aspects of the present disclosure, a method is provided. The method includes laminating a plurality of steel sheets to form a stack having a first end and an opposite second end axially spaced apart along a longitudinal axis. A plurality of grooves are provided on an outer peripheral surface of the stack and extend from the first end to the second end. The method includes placing a plurality of foils in the plurality of grooves. The method includes forming a conductor bar in each groove such that each of the plurality of foils is disposed between each conductor bar and the stack. The first conductor end extends axially beyond the first end of the stack. The method also includes casting a first end ring around each first conductor end of each conductor bar, and casting a second end ring around each second conductor end of each conductor bar to at least partially surround and electrically connect the first conductor end and the second conductor end of each of the plurality of conductor bars.

[0022] According to another aspect of the present disclosure, the method includes a plurality of foils including pure copper or a copper-graphene composite material.

[0023] According to another aspect of the present disclosure, the method includes placing a preformed foil when placing the plurality of foils in the plurality of recesses.

[0024] According to another aspect of the present disclosure, the method includes placing the foils in place when placing the plurality of foils in the plurality of grooves.

[0025] Further areas of applicability will become apparent from the description provided herein.It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

[0027] Figure 1 is a perspective view illustrating a vehicle having an electric machine with an induction rotor assembly according to the present disclosure.

[0028] Figure 2 According to the present disclosure Figure 1 A schematic exploded view of an induction rotor assembly is shown, wherein the induction rotor assembly includes a plurality of conductor bars.

[0029] Figure 3 According to the present disclosure Figure 2 A perspective view of a stack of layers of an induction rotor is shown with copper graphene foils positioned in grooves of the stack.

[0030] Figure 4 According to the present disclosure Figure 2 and Figure 3 A perspective view of a lamination stack of an induction rotor is shown having an annular feature extending circumferentially around the lamination stack.

[0031] Figure 5 It is shown that according to the present disclosure Figure 3 Flowchart of a method for manufacturing an induction rotor assembly with graphene copper foil is shown. DETAILED DESCRIPTION

[0032] The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses.

[0033] refer to Figure 1, a vehicle 10 is shown having a vehicle motor 12 or inverter according to the principles of the present disclosure. The vehicle motor 12 provides power to the vehicle 10 and receives power from at least one battery (not shown). The vehicle motor 12 is shown with an exemplary vehicle 10, and the vehicle 10 is an electric vehicle or a hybrid vehicle having wheels 14 driven by the vehicle motor 12. The vehicle motor 12 includes an induction motor. Although the vehicle 10 is shown as a passenger road vehicle, it should be understood that the vehicle motor 12 can be used with various other types of vehicles. For example, the vehicle motor 12 can be used in a marine vehicle (such as a ship) or an aerial vehicle (such as a drone or a passenger aircraft). In addition, the vehicle motor 12 can be used as a stationary power source separate and independent from the vehicle.

[0034] Figure 1 A cross-sectional view of vehicle motor 12 is depicted, showing stator 16 and inductive rotor assembly 18. Stator 16 is a stationary part of the rotating system within vehicle motor 12 and is typically constructed of steel. Electric power is supplied to stator 16 and converted into a rotating magnetic field. Inductive rotor assembly 18 rotates due to the rotating magnetic field and provides torque to vehicle 10 as motive power.

[0035] Figure 2 A schematic exploded perspective view of the inductive rotor assembly 18 is shown. The inductive rotor assembly 18 includes a lamination stack 20, a plurality of foils 22, a plurality of conductor bars 24, a first end ring 26, and a second end ring 28.

[0036] The stack 20 includes a body 30 having a first end 32 and an opposite second end 34 to define a longitudinal axis A. The body 30 is constructed from a plurality of laminated steel sheets stacked axially. The body 30 may be steel or a steel alloy. The body 30 has an outer peripheral surface 36 extending coaxially with the longitudinal axis A from the first end 32 to the second end 34.

[0037] like Figure 2 As shown, the outer peripheral surface 36 has a plurality of longitudinal walls 38 that define a plurality of open longitudinal grooves 40 formed therethrough from the first end 32 to the second end 34. The longitudinal grooves 40 may extend along the length L of the stack 20. L Slightly inclined relative to the longitudinal axis A. Alternatively, the longitudinal groove 40 may be parallel to the longitudinal axis A.

[0038] Figure 3A plurality of foils 22 are shown arranged in a plurality of grooves 40 of the lamination stack 20. The plurality of foils 22 are constructed from a copper-graphene composite material and may include, for example, up to 20% graphene by volume. The copper-graphene composite material provides improved mechanical and electrical performance within the induction rotor assembly 18. Furthermore, the use of foils 22 comprising copper or a copper-graphene composite material improves current flow because copper has a 64% higher electrical conductivity than aluminum, which increases the efficiency of utilizing the skin effect at higher frequencies. Furthermore, the use of copper-graphene foils 22 adjacent to the grooves 40 can eliminate welding and internal laminar shorting that can occur during casting of the induction rotor assembly 18 due to molten aluminum between laminations in the induction rotor assembly 18 without the copper-graphene foils 22 in the grooves 40.

[0039] Each of the plurality of foils 22 is formed or folded into each groove 40 so that the foil 22 contacts and conforms to the surface geometry of each groove 40. In some cases, an adhesive may be provided on at least one side of the foil 22 (e.g., on one side of the surface of the adjacent stack 20 and the groove 40). In one example, the thickness of each of the plurality of foils 22 may be between 20 microns (μm) and 30 microns (μm), and the length (e.g., the axial length of the groove 40) may be 60 mm. In addition, at least one side of each foil 22 (e.g., the side configured to contact the liquid aluminum and / or the conductor bar 24) may include a rough or jagged surface, which facilitates improved bonding between the foil 22 and the conductor bar 24. The rough or jagged surface may remove surface oxides from the melt to better fill the mold. In some cases, a coating on the foil 22 may be used to form the rough or jagged surface, wherein the coating creates the rough surface. The roughness of the rough or jagged surface may be determined at least in part based on the surface tension of the aluminum melt. In an example, the coating on the foil 22 includes a copper-silver (Cu-Ag) or copper-nickel (Cu-Ni) based coating, and the coating can be applied using a cold spray or physical vapor deposition (PVD) method. When the coating includes copper-silver (Cu-Ag), the weight percentage (wt.%) of the copper-silver (Cu-Ag) can be between 25 and 35. In addition, at least some of the longitudinal walls 38 can include a surface roughness that is replicated on the foil 22 prior to the casting process.

[0040] like Figure 3As shown, and in some cases, multiple foils 22 can protrude from the groove 40 in one or two directions (e.g., parallel to the longitudinal axis A). When multiple foils 22 protrude from the groove 40, the foils 22 can facilitate better bonding to other components during subsequent casting. In one example, the protruding foils 22 can extend from the groove 40 in a direction proximal to the ingate. The protruding foils 22 can extend from the groove aligned with the longitudinal axis A and can be bent (e.g., 90°) at the edge 42 of the groove so that the protrusions 44 contact the body 30 and are perpendicular to the groove 40 and the longitudinal axis A. In some cases, the protrusions 44 can be welded to the protrusions 44 of other foils 22 disposed in other grooves 40. During high-pressure die casting of the induction rotor assembly 18, the bent protrusions 44 (near the ingate side) can prevent the foils 22 from shifting during the casting process.

[0041] refer to Figure 4 , an annular feature 46 is shown secured to the outer peripheral surface 36 of the lamination stack 20. The annular fixture 46 extends around at least a portion of the outer peripheral surface 36 and can be cylindrical and / or annular in form. The annular feature 46 is configured to retain the foil 22 in the groove 40 after placement of the foil 22 and during casting of the conductor bar 24. The annular fixture 46 can be removed after casting the conductor bar 24. The annular fixture 46 can include a material (e.g., steel) having a melting temperature higher than the melting temperature of the material (e.g., aluminum) of the conductor bar 24.

[0042] like Figure 2 As shown, each of the plurality of conductor bars 24 is disposed in each of the longitudinal grooves 40. Each of the plurality of foils 22 is disposed between each of the plurality of conductor bars 24 and each of the plurality of grooves 40. For convenience, Figure 2 One conductor bar 24 is shown removed to illustrate a longitudinal groove 40 defined by the longitudinal wall 38. The conductor bar 24 carries the induced current in the rotor assembly 18, which interacts with the magnetic field generated by the stator 16 and generates torque. Each of the plurality of conductor bars 24 has a first conductor end 41. The first conductor end 41 extends axially beyond the first end 32 of the lamination stack 20. Each of the plurality of conductor bars 24 also has a second conductor end 42. The second conductor end 42 extends axially beyond the second end 34 of the lamination stack 20. Each conductor bar 24 has a conductor length L extending parallel to the longitudinal axis A. C The conductor bar 24 may be made of aluminum or copper.

[0043] like Figure 2As shown, a first end ring 26 is adjacent to and secured to each of the first conductor ends 41 of each of the plurality of conductor bars 24 at a first end 32 of the stack 20. A second end ring 28 is adjacent to and secured to each of the second conductor ends 42 of each of the plurality of conductor bars 24 at a second end 34 of the stack 20. The first end ring 26 at least partially surrounds the first end 32 and electrically couples the first end 32 to the conductor bars 24. The second end ring 28 at least partially surrounds the second end 34 and electrically couples the second end 34 to the conductor bars 24. The first end ring 26 and the second end ring 28 are preferably cast from aluminum or a cast aluminum alloy. However, it should be understood that the first end ring 26 and the second end ring 28 may be cast from other conductive materials.

[0044] Now refer to Figure 5 , a flow chart illustrating a method 100 for manufacturing an inductive rotor assembly 18 having a graphene-copper foil according to the present disclosure is shown.

[0045] The method begins at block 102. Block 102 depicts laminating a plurality of steel sheets to define a laminated stack 20. The laminated stack 20 includes a first end 32 and a second end 34. The second end 34 is axially spaced from the first end 32 along a longitudinal axis A. The steel sheets are laminated together such that the grooves of each sheet mate to define a groove 40 extending along the longitudinal axis A. The grooves 40 are angularly spaced about and equidistant from the longitudinal axis A. The method then moves to block 104.

[0046] Block 104 depicts placing the plurality of foils 22 in the plurality of grooves 40. A variety of methods can be used to form the plurality of foils 22 and place them in the grooves 40. In examples, the foils 22 can be formed using 3D additive manufacturing, metal printing, spray coating, and can include other highly conductive materials. Additionally, the foils 22 can include a highly conductive layer surface finish using the previously listed formation methods to better bond to the conductor bars 24.

[0047] In one example, the foil 22 can be preformed and bent, folded, or otherwise formed to conform to the geometry of each groove 40. The preformed foil 22 is then placed into the groove 40. In this example, placing the foil 22 includes using an automated process (e.g., a robotic arm) to place the foil 22 and / or shape the foil 22. In some cases, placing multiple foils 22 can include placing multiple foils 22 into each groove 40. In addition, before placing the multiple foils 22 in each groove 40, the foil 22 and / or the stack 20 can be preheated (e.g., preheated to 150-350° C.) to facilitate metallurgical bonding between the foil 22 and the conductor bar 24. Placing the multiple foils 22 can include forming an intermetallic phase at the interface between each foil 22 and the conductor bar 24. The intermetallic phase can be disposed over the entire surface of the foil 22 or dispersed over the surface of the foil 22.

[0048] In another example, placing the foil 22 includes placing and shaping the foil 22 in place. Placing and shaping the foil 22 in place may include placing the foil 22 in each groove 40 and then shaping each foil 22 to conform to the geometry of each individual groove 40. For example, the foil 22 may be folded into each groove 40 and then pushed using a fine needle to conform to the contours of the groove 40. The foil 22 may have a thickness between 20 micrometers (μm) and 30 micrometers (μm).

[0049] In some cases, placing the foil 22 may include placing an annular feature 46 around the circumference of the lamination stack 20 prior to casting the conductor bar 24. The annular feature 46 serves to hold the foil 22 in place as the casting material (e.g., aluminum) flows through the groove 40. The annular feature 46 is typically removed by minor machining after the conductor bar 24 is cast.

[0050] In addition, placing the foil 22 in each groove 40 can include bending a protrusion 44 of the foil 22. In this case, bending the protrusion 44 includes bending the protrusion 44 over the edge of the groove 40 so that the bent protrusion 44 substantially contacts and aligns with the axial surface 48 of the stack 20. The bent protrusion 44 can be bent using an automated process (e.g., a robotic arm). In addition, the bent protrusion 44 can be welded to an adjacent bent protrusion 44 of an adjacent foil 22. The method 100 then moves to block 106.

[0051] Block 106 depicts forming a conductor bar 24 in each of the plurality of grooves 40. Each conductor bar 24 is formed on the foil 22 in each groove 40, and the foil 22 is disposed between each conductor bar 24 and the stack 20. The conductor bar 24 is formed to include a length greater than the stack length L. L Long conductor length L C, such that the first conductor end 41 and the second conductor end 42 extend outwardly beyond the first end 32 and the second end 34, respectively, of the stack 20. In some cases, the conductor bar 24 is pre-formed and placed into each groove 40. In other cases, the conductor bar 24 is cast into position in each groove 40. The conductor bars 24 are formed and / or positioned such that the first conductor end 41 and the second conductor end 42, respectively, of each of the plurality of conductor bars 24 extend axially outwardly beyond the first end 32 and the second end 34, respectively, of the stack 20. The method 100 then moves to block 108.

[0052] Block 108 depicts casting the first end ring 26 around the first conductor end 41 and the second end ring 28 around the second conductor end 42. Casting the first end ring 26 and the second end ring 28 can include placing the stack 20 having the plurality of conductor bars 24 positioned therein, the plurality of conductor bars 24 being placed into a shape. The shape defines the first end ring 26 and / or the second end ring 28 and can be any suitable shape and size for casting the first end ring 26 and / or the second end ring 28. The first end ring 26 is cast around the first conductor end 41 on each conductor bar 24. The first end ring 26 is cast to at least partially surround the first conductor end 41 of each of the plurality of conductor bars 24 and electrically connect it to the first end ring 26. Additionally, the second end ring 28 is cast around the second conductor end 42 on each of the plurality of conductor bars 24. The second end ring 28 is cast to at least partially surround the second conductor end 42 of each of the plurality of conductor bars 24 and electrically connect it to the second end ring 28.

[0053] Casting the first and second end rings 26, 28 includes injecting molten material into the shape of and around the first and second conductor ends 41, 42 of each conductor bar 24. The first and second end rings 26, 28 are preferably cast from aluminum or an aluminum alloy. It should be understood that the first and second end rings 26, 28 may be cast from some other conductive material. Casting the first and second end rings 26, 28 includes flowing the molten material into and around the first and second conductor ends 41, 42 of each conductor bar 24 as it solidifies. Casting processes that may be used to cast the first and second end rings 26, 28 include high-pressure die casting, low-pressure die casting, sand casting, or squeeze casting.

[0054] Casting the first and second end rings 26, 28 may also include compressing the molten material as it solidifies. Compressing the molten material as it solidifies during the casting process reduces porosity on the finished in situ cast product and improves mechanical properties of the finished product.

[0055] Additionally, casting the first end ring 26 and the second end ring 28 may further include vibrating each conductor rod 24 at an ultrasonic frequency for a predetermined period of time during the solidification of the molten material of the cast first end ring 26 and / or second end ring 28. Preferably, the ultrasonic frequency is 20 kHz or higher. The conductor rod 24 may be vibrated for a period of less than 20 seconds. Vibrating the conductor rod 24 during the solidification of the molten material during the casting process may break up aluminum oxide disposed on the outer surface of the first conductor end 41 and / or the second conductor end 42 of the conductor rod 24. Vibrating the conductor rod 24 also improves wettability between the molten material and the conductor rod 24. The method 100 then ends.

[0056] The present disclosure provides numerous advantages and benefits over prior art induction rotor assemblies. For example, the use of copper and / or copper graphene foil 22 between the lamination stack 20 and the conductor bar 24 improves current flow near the outer surface of the conductor bar 24 because copper has a 64% higher electrical conductivity than aluminum, which increases the skin effect at higher frequencies. Additionally, the use of copper graphene composite foil 22 with adjacent grooves 40 eliminates welding and internal laminar shorting that occurs during the casting of the induction rotor assembly 18 from the aluminum molten material, which occurs between the lamination layers of the lamination stack 20 without the foil 22. Furthermore, the induction rotor assembly 18 has higher rotor resistance and higher starting torque during startup, and lower resistance during normal operation, resulting in higher machine efficiency due to lower rotor losses. Thus, the induction rotor assembly 18 disclosed herein increases rotor resistance during startup due to the skin effect (e.g., higher rotor current frequency) and reduces resistance during normal operation (e.g., very low rotor current frequency) due to the higher electrical conductivity of the copper graphene foil 22, which improves the overall efficiency of the induction rotor assembly 18 and the vehicle electric machine 12.

[0057] This description is merely illustrative in nature and is in no way intended to limit the present disclosure, its application, or use. The broad teachings of the present disclosure can be implemented in many forms. Therefore, although this disclosure includes specific examples, the true scope of the disclosure should not be so limited, as other modifications will become apparent upon study of the drawings, the specification, and the appended claims.

Claims

1. An induction rotor assembly, comprising: a stack of layers, the stack comprising a body having a first end and an opposite second end disposed along a longitudinal axis, wherein the body has an outer peripheral surface extending from the first end to the second end along the longitudinal axis, wherein the outer peripheral surface has a plurality of grooves extending from the first end to the second end; a plurality of foils, wherein each of the plurality of foils is disposed in one of the recesses; a plurality of conductor bars, wherein each of the plurality of conductor bars is disposed in each of the grooves, wherein each of the plurality of foils is disposed between each of the plurality of conductor bars and each of the grooves, and wherein each of the plurality of conductor bars includes a first conductor end and a second conductor end, the first conductor end extending axially beyond the first end of the stack and the second conductor end extending axially beyond the second end of the stack; a first end ring that cooperates with a surface of each first conductor end to interlock each of the plurality of conductor bars to the first end ring; and A second end ring cooperates with a surface of each second conductor end to interlock each of the plurality of conductor bars to the second end ring, and wherein the plurality of conductor bars extend between the first end ring and the second end ring.

2. The induction rotor assembly according to claim 1, wherein: The body comprises a plurality of laminated steel sheets.

3. The induction rotor assembly according to claim 1, wherein: The plurality of foils are made of pure copper or a copper-graphene composite material.

4. The induction rotor assembly according to claim 3, wherein: The graphene volume of the plurality of foils is less than or equal to 20%.

5. The induction rotor assembly according to claim 1, wherein: The plurality of foils includes an adhesive on one side of each foil.

6. The induction rotor assembly according to claim 1, wherein: Each foil of the plurality of foils has a thickness between 20 microns and 30 microns.

7. The induction rotor assembly according to claim 1, wherein: Each foil of the plurality of foils protrudes from the groove.

8. The induction rotor assembly according to claim 1, wherein: Each foil of the plurality of foils includes a coating at least partially having a rough surface.

9. The induction rotor assembly according to claim 1, wherein: A plurality of foil layers are disposed between each groove and each conductor bar.

10. The induction rotor assembly of claim 1, wherein: The plurality of conductor bars are formed of at least one of copper or aluminum.

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