Method of manufacturing a rotor assembly

Abstract

A method of manufacturing a rotor assembly for an electric motor is disclosed. The rotor assembly includes a stack of laminations extending along an axis, a plurality of magnets including a first magnet and a second magnet each coupled to the stack of laminations, and a plurality of pole shoes including a first pole shoe spaced apart from and separated from the stack of laminations. The rotor assembly also includes a plurality of spacers including a first spacer spaced from the stack of laminations. The method includes the step of disposing a first magnet and a second magnet between a stack of laminations and a first pole shoe. The method further includes the step of disposing a first spacer between the stack of laminations and the first pole shoe to reduce flux leakage between the stack of laminations and the first pole shoe.

Description

Cross - Reference to Related Applications

[0001] This application claims the benefit of priority and all advantages of U.S. Non - Provisional Patent Application No. 17 / 957,110, filed on September 30, 2022, the entire content of which is incorporated herein by reference. Technical Field

[0002] The present invention generally relates to a method of manufacturing a rotor assembly for an electric motor and to a method of manufacturing an electric motor including the rotor assembly. Background Art

[0003] An electric motor includes a rotor assembly and a stator disposed around the rotor assembly. The rotor assembly typically includes a shaft, a stack of laminations disposed around the shaft, and a plurality of pole shoes radially spaced from the stack of laminations. Typically, permanent magnets are embedded in the rotor assembly, usually between the stack of laminations and the plurality of pole shoes. The stator typically includes a coil winding, and energizing the coil winding in the stator generates a magnetic flux that interacts with the permanent magnets to apply a force that causes the rotor assembly to rotate.

[0004] Typically, the stack of laminations and the plurality of pole shoes are physically connected to each other by a plurality of bridge members, thus forming what is commonly referred to as a bridged rotor assembly. Each bridge member is integral with both the stack of laminations and one of the plurality of pole shoes and is typically made of the same material as the stack of laminations and the plurality of pole shoes. The bridge member prevents the plurality of pole shoes from moving away from the stack of laminations due to the centrifugal forces applied to the plurality of pole shoes during rotation of the rotor assembly.

[0005] However, the magnetic flux generated by the coil winding of the stator is interrupted or leaked by the bridge members, such that a portion of the magnetic flux is directed towards the stack of laminations and away from the plurality of magnets. Consequently, any magnetic flux leaked through the bridge members cannot interact with the permanent magnets, thus reducing the force applied to the rotor assembly and also reducing the efficiency of the electric motor. To minimize the leakage of the flux through the bridge members, the bridge members are typically designed to be relatively thin. However, the centrifugal forces applied to the plurality of pole shoes by the rotation of the rotor assembly are also applied to the bridge members. These centrifugal forces applied to the bridge members result in stress concentration on the bridge members and a risk of structural failure of the bridge members, especially when the bridge members are designed to be relatively thin.

[0006] Thus, there is still a need to provide an improved method of manufacturing a rotor assembly for an electric motor. Summary of the Invention

[0007] A method of manufacturing a rotor assembly for an electric motor is disclosed. The rotor assembly includes a stack of laminations extending along an axis, a plurality of magnets including a first magnet and a second magnet each coupled to the stack of laminations, and a plurality of pole shoes including a first pole shoe spaced from and separate from the stack of laminations. The rotor assembly further includes a plurality of spacers including a first spacer spaced from the stack of laminations.

[0008] The method includes the steps of: disposing the first magnet and the second magnet between the stack of laminations and the first pole shoe. The method further includes the step of: disposing the first spacer between the stack of laminations and the first pole shoe to reduce flux leakage between the stack of laminations and the first pole shoe.

[0009] The first spacer prevents interruption or leakage of magnetic flux between the first pole shoe and the stack of laminations. Thus, it is ensured that the magnetic flux is directed towards the first magnet and the second magnet to interact with the first magnet and the second magnet and effectively apply a force to the rotor assembly to cause the rotor assembly to rotate.

[0010] Each of the plurality of pole shoes is separate from the stack of laminations, thus forming a non-bridged arrangement of the pole shoes and the stack of laminations. Thus, the centrifugal force applied to the plurality of pole shoes by the rotation of the rotor assembly is not also applied to any bridging member connecting the plurality of pole shoes and the stack of laminations. Therefore, the non-bridged arrangement of the pole shoes and the stack of laminations eliminates the concern of the centrifugal force applying a force on any bridging member, causing stress concentration on any bridging member and potentially causing structural failure of any bridging member. In addition, the method provides an inexpensive, reproducible, timely and simple manufacturing process for producing a rotor assembly including the qualities mentioned above. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Other advantages of the present invention will be readily appreciated as the present invention will become better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings, in which: Figure 1 is a flow chart depicting a method of manufacturing a rotor assembly according to the present invention; Figure 2 is a perspective view of the rotor assembly; Figure 3 is Figure 2 a cross-sectional view of the rotor assembly of Figure 4 is Figure 2 another cross-sectional view of the rotor assembly of Figure 5 is a perspective view of the first end cap, the second end cap and a plurality of rods extending therebetween; Figure 6is a perspective view of another embodiment of the rotor assembly; Figure 7A is Figure 6 a cross-sectional view of an embodiment of the rotor assembly shown in Figure 7B is Figure 7A an exploded view of Figure 8 is Figure 6 a cross-sectional view of another embodiment of the rotor assembly shown in Figure 9 is a perspective view of an electric motor including the rotor assembly; and Figure 10 is including Figure 9 a perspective view of a part of an electric drive unit of an electric motor in which is shown in dashed lines. DETAILED DESCRIPTION

[0012] Referring to the drawings, in which like numerals indicate like parts in several views, Figure 1 a method of manufacturing a rotor assembly 20 for an electric motor 22 is shown in

[0013] The rotor assembly 20 includes a stack of laminations 24 extending along an axis A1, a plurality of magnets 26 including a first magnet 28 and a second magnet 30 each coupled to the stack of laminations 24, and a plurality of pole shoes 32 including a first pole shoe 34 spaced apart from and separated from the stack of laminations 24. The rotor assembly 20 further includes a plurality of spacers 36 including a first spacer 38 spaced apart from the stack of laminations 24. Although not required, the first magnet 28 and the second magnet 30 may be disposed between the stack of laminations 24 and the first pole shoe 34. Additionally, the rotor assembly 20 may further include a shaft 40 extending along the axis A1 and rotatable about the axis A1. The stack of laminations 24 may be coupled to the shaft 40, and each of the plurality of pole shoes 32 (including the first pole shoe 34) may be spaced radially outwardly from the shaft 40.

[0014] The first spacer 38 prevents interruption or leakage of magnetic flux between the first pole shoe 34 and the lamination stack 24. Thus, it ensures that the magnetic flux is directed towards the first magnet 28 and the second magnet 30 to interact with the first magnet 28 and the second magnet 30 and effectively apply a force to the rotor assembly 20 to rotate the rotor assembly 20.

[0015] Each of the plurality of pole shoes 32 is separated from the lamination stack 24, thus forming a non-bridged arrangement of the pole shoes 32 and the lamination stack 24. In other words, each of the plurality of pole shoes 32 can be a member separated from the lamination stack 24, and the plurality of pole shoes 32 and the lamination stack 24 are not connected to each other by bridging material. Thus, the centrifugal force applied to the plurality of pole shoes 32 by the rotation of the rotor assembly 20 is not applied to any bridging member connecting the plurality of pole shoes 32 and the lamination stack 24. Therefore, the non-bridged arrangement of the plurality of pole shoes 32 and the lamination stack 24 eliminates the concern of the centrifugal force applying a force on any bridging member, resulting in stress concentration on any bridging member and potentially causing a structural failure of any bridging member. In addition, the method 200 provides an inexpensive, reproducible, timely, and simple manufacturing process for producing a rotor assembly 20 having the qualities mentioned above.

[0016] Although the benefits of the first spacer 38 have been described with reference to the first pole shoe 34, the first magnet 28, the second magnet 30, and the lamination stack 24, it should be understood that these benefits can equally apply to all other spacers 36 among the plurality of spacers 36, all other pole shoes 32 among the plurality of pole shoes 32, all other magnets 26 among the plurality of magnets 26, and the lamination stack 24. Each spacer 36 and pole shoe 32 can have the characteristics of the first spacer 38 and the first pole shoe 34 as described herein. More specifically, the plurality of spacers 36 can prevent interruption or leakage of magnetic flux between the plurality of pole shoes 32 and the lamination stack 24. Thus, it ensures that the magnetic flux is directed towards the plurality of magnets 26 to interact with the plurality of magnets 26 and effectively apply a force to the rotor assembly 20 to rotate the rotor assembly 20.

[0017] Although not necessary, the step 204 of disposing the first spacer 38 between the lamination stack 24 and the first pole shoe 34 includes disposing the first spacer 38 such that the first spacer 38 extends at least to the first magnet 28. In addition, the step 204 of disposing the first spacer 38 between the lamination stack 24 and the first pole shoe 34 can include disposing the first spacer 38 such that the first spacer 38 is disposed between the first magnet 28 and the second magnet 30. The step 204 of disposing the first spacer 38 between the lamination stack 24 and the first pole shoe 34 can result in the first spacer 38 extending radially inwards towards the first magnet 28 and further extending beyond the first magnet 28, optionally encapsulating at least a portion of the first magnet 28, and then being disposed between the first magnet 28 and the second magnet 30.

[0018] The stack 24 can be made of a plurality of laminations fixed to each other, in non-limiting examples, by interlocking, welding, clamping, and / or bonding. To improve the manufacturability of the stack 24, each lamination in the stack 24 can be the same as each other lamination in the stack 24.

[0019] Each magnet in the plurality of magnets 26 (including the first magnet 28 and the second magnet 30) can be a permanent magnet. As Figure 4 and Figures 7A to 8 shown, the first magnet 28 and the second magnet 30 can be configured to form a V shape. Each pole shoe 32 in the plurality of pole shoes 32 (including the first pole shoe 34) can be made of metal and / or metalloid, including but not limited to iron, cobalt, nickel, silicon, manganese, aluminum, steel (including electrical steel), and combinations thereof. The stack 24 can be made of metal and / or metalloid, including but not limited to iron, cobalt, nickel, silicon, manganese, aluminum, steel (including electrical steel), and combinations thereof. Although not required, it should be recognized that the plurality of pole shoes 32 can be made of the same metal and / or metalloid as that constituting the stack 24.

[0020] Although not required, the step 202 of disposing the first magnet 28 and the second magnet 30 between the stack 24 and the first pole shoe 34 can be before the step 204 of disposing the first spacer 38 between the stack 24 and the first pole shoe 34. It should be recognized that the step 204 of disposing the first spacer 38 between the stack 24 and the first pole shoe 34 can be immediately after the step 202 of disposing the first magnet 28 and the second magnet 30 between the stack 24 and the first pole shoe 34, or there can be one or more intervening steps therebetween.

[0021] The method 200 can further include the step of disposing the shaft 40 within the stack 24 such that the shaft 40 extends along the axis A1. Although not required, the step of disposing the shaft 40 within the stack 24 can be performed after the step 204 of disposing the first spacer 38 between the stack 24 and the first pole shoe 34. It should be recognized that the step of disposing the shaft 40 within the stack 24 can be immediately after the step 204 of disposing the first spacer 38 between the stack 24 and the first pole shoe 34, or there can be one or more intervening steps therebetween.

[0022] The first spacer 38 may comprise a polymeric material. In a non-limiting example, the polymeric material of the first spacer 38 may be a thermoplastic, a thermoset, or an elastomer. The polymeric material of the first spacer 38 may be an engineering plastic. More specifically, the polymeric material of the first spacer 38 may be any polyalkene or polyolefin, including its copolymers and terpolymers, such as polyethylene (including high-density polyethylene (HDPE) and low-density polyethylene (LDPE)), polypropylene (PP), polybutene, and polybutylene terephthalate (PBTR), acrylic resins, such as acrylonitrile butadiene styrene (ABS) or polymethyl methacrylate (PMMA), polyoxymethylene (POM) or any acetal copolymer or acetal terpolymer, polyketone, polyether ketone, and / or polyarylether ketone, such as polyetheretherketone (PEEK) and polyetherketoneketone (PEKK), polyetherimide (PEI), polyimide, polyvinyl chloride (PVC), polyphenylene sulfide (PPS), polyphenylene ether (PPO), polysulfone (PSU), polytetrafluoroethylene (PTFE), polyamide (including polyphthalamide), polycarbonate, polyurethane, epoxy resin, and thermoplastic elastomer (TPE).

[0023] The first spacer 38 may further comprise a first composition that includes any polymeric material detailed herein and optional fillers and / or additives, such as plasticizers, carbon (including carbon fiber), ceramic materials, and / or minerals (including calcium carbonate, silica, clay, and kaolin), fibers (including glass fiber, carbon fiber, aramid fiber, basalt fiber, and paper fiber), stabilizers (including oxidation stabilizers, ultraviolet (UV) stabilizers, heat stabilizers, light absorbers, reinforcing agents, acid scavengers, metal deactivators), and flame retardants (including aluminum hydroxide, phosphorus compounds, and bromine compounds).

[0024] Although not required, the polymeric material of the first spacer 38 may be molded, such as overmolding, insert molding, injection molding, compression molding, and thermoforming. The step 204 of disposing the first spacer 38 between the stack 24 and the first pole shoe 34 may include molding the first spacer 38 such that the first spacer 38 is disposed between the stack 24 and the first pole shoe 34. It should be appreciated that molding the first spacer 38 such that the first spacer 38 is disposed between the stack 24 and the first pole shoe 34 may include any one of in-situ forming, overmolding, insert molding, injection molding, compression molding, and thermoforming.

[0025] Each of the plurality of pole shoes 32, including the first pole shoe 34, has an outer pole surface 42 facing away from the axis A1. The first pole shoe 34 has a first circumferential end 44 and a second circumferential end 46 circumferentially spaced from the first circumferential end 44. The outer pole surface 42 of the first pole shoe 34 extends between the first circumferential end 44 and the second circumferential end 46. The step 204 of disposing the first spacer 38 between the stack 24 and the first pole shoe 34 may include circumferentially disposing the first spacer 38 between the first circumferential end 44 and the stack 24.

[0026] As Figures 2 to 4 shown, the rotor assembly 20 may further include a sleeve 48 that includes an outer sleeve body 50 and a plurality of spacers 36. In other words, the plurality of spacers 36 may be incorporated into the sleeve 48 together with the outer sleeve body 50. The outer sleeve body 50 of the sleeve 48 is disposed around the outer pole surface 42 of each of the plurality of pole shoes 32 to hold each of the plurality of pole shoes 32 relative to the stack 24. The plurality of spacers 36 extend radially inward from the outer sleeve body 50 toward the shaft 40. The first spacer 38 may extend radially inward from the outer sleeve body 50 toward the shaft 40. The plurality of spacers 36 includes the first spacer 38. Additionally, although not required, the plurality of spacers 36 may include a second spacer 52 that extends radially inward from the outer sleeve body 50 toward the shaft 40. The first spacer 38 and the second spacer 52 are disposed between the first pole shoe 34 and the stack 24 to reduce flux leakage between the first pole shoe 34 and the stack 24.

[0027] The outer sleeve body 50 holds the first pole shoe 34 relative to the stack 24 so as to prevent the first pole shoe 34 from moving away from the stack 24 when a centrifugal force is applied to the first pole shoe 34 by the rotation of the rotor assembly 20. Further, the outer sleeve body 50, the first spacer 38, and the optional second spacer 52 prevent magnetic flux interruption or leakage between the first pole shoe 34 and the stack 24. Thus, ensuring that the magnetic flux is directed toward the first magnet 28 and the second magnet 30 to interact with the first magnet 28 and the second magnet 30 and effectively apply a force to the rotor assembly 20 to rotate the rotor assembly 20.

[0028] Although the benefits of the outer sleeve body 50, the first spacer 38, and the optional second spacer 52 have been described with reference to the first pole shoe 34, the first magnet 28, the second magnet 30, and the lamination stack 24, it should be appreciated that these benefits may equally apply to all other spacers 36 among the plurality of spacers 36, all other pole shoes 32 among the plurality of pole shoes 32, all other magnets 26 among the plurality of magnets 26, and the lamination stack 24. Each spacer 36 and pole shoe 32 may have the characteristics of the first spacer 38, the second spacer 52, and the first pole shoe 34 as described herein. More specifically, the outer sleeve body 50 may hold each of the plurality of pole shoes 32 relative to the lamination stack 24, thereby preventing the plurality of pole shoes 32 from moving away from the lamination stack 24 when a centrifugal force is applied to each pole shoe 32 by the rotation of the rotor assembly 20. In addition, the outer sleeve body 50 and the plurality of spacers 36 prevent an interruption or leakage of the magnetic flux between the plurality of pole shoes 32 and the lamination stack 24. Thus, ensuring that the magnetic flux is directed towards the plurality of magnets 26 to interact with the plurality of magnets 26 and effectively apply a force to the rotor assembly 20 to rotate the rotor assembly 20.

[0029] The step 204 of disposing the first spacer 38 between the lamination stack 24 and the first pole shoe 34 may further include coupling the sleeve 48 to the lamination stack 24. Coupling the sleeve 48 to the lamination stack 24 may include disposing the outer sleeve body 50 around the outer pole surface 42 of each of the plurality of pole shoes 32 to hold each of the plurality of pole shoes 32 relative to the lamination stack 24. In addition, the method 200 may further include the step of disposing the second spacer 52 between the lamination stack 24 and the first pole shoe 34.

[0030] Although not required, the second spacer 52 may at least extend to the second magnet 30. The second spacer 52 may also be disposed between the first magnet 28 and the second magnet 30. It should be appreciated that the second spacer 52 may extend radially inward from the outer sleeve body 50 towards the second magnet 30 and may also extend beyond the second magnet 30, optionally encapsulating at least a portion of the second magnet 30, and then disposed between the first magnet 28 and the second magnet 30. It should also be appreciated that both the first spacer 38 and the second spacer 52 may be disposed between the first magnet 28 and the second magnet 30 and may be fixed to each other, formed integrally, or otherwise coupled between the first magnet 28 and the second magnet 30.

[0031] Although not required, sleeve 48 may include a polymeric material. It should be appreciated that sleeve 48 may include the same polymeric material as first spacer 38. In non-limiting examples, the polymeric material of sleeve 48 may be a thermoplastic, a thermoset, or an elastomer. The polymeric material of sleeve 48 may be an engineering plastic. More specifically, the polymeric material of sleeve 48 may be, but is not limited to, any polyalkene or polyolefin, including its copolymers and terpolymers, such as polyethylene (including high density polyethylene (HDPE) and low density polyethylene (LDPE)), polypropylene (PP), polybutene, and polybutylene terephthalate (PBTR), acrylic resins, such as acrylonitrile butadiene styrene (ABS) or polymethyl methacrylate (PMMA), polyoxymethylene (POM) or any acetal copolymer or acetal terpolymer, polyketone, polyether ketone, and / or polyarylether ketone, such as polyetheretherketone (PEEK) and polyetherketoneketone (PEKK), polyetherimide (PEI), polyimide, polyvinyl chloride (PVC), polyphenylene sulfide (PPS), polyphenylene oxide (PPO), polysulfone (PSU), polytetrafluoroethylene (PTFE), polyamide (including polyphthalamide), polycarbonate, polyurethane, epoxy resin, and thermoplastic elastomer (TPE).

[0032] Sleeve 48 may also include a first composition that includes any of the polymeric materials detailed herein and optional fillers and / or additives, such as plasticizers, carbon (including carbon fiber), ceramic materials, and / or minerals (including calcium carbonate, silica, clay, and kaolin), fibers (including glass fiber, carbon fiber, aramid fiber, basalt fiber, and paper fiber), stabilizers (including oxidation stabilizers, ultraviolet (UV) stabilizers, heat stabilizers, light absorbers, reinforcing agents, acid scavengers, metal deactivators), and flame retardants (including aluminum hydroxide, phosphorus compounds, and bromine compounds).

[0033] Although not required, the polymeric material of sleeve 48 may be molded, such as overmolding, insert molding, injection molding, compression molding, and thermoforming. Step 204 of disposing first spacer 38 between stack 24 and first pole shoe 34 may include molding sleeve 48 such that first spacer 38 is disposed between stack 24 and first pole shoe 34. Additionally, the step of disposing a second spacer between stack 24 and first pole shoe 34 may include molding sleeve 48 such that second spacer 52 is disposed between stack 24 and first pole shoe 34. It should be appreciated that molding sleeve 48 such that either or both of first spacer 38 and second spacer 52 are disposed between stack 24 and first pole shoe 34 may include any of in-situ forming, overmolding, insert molding, injection molding, compression molding, and thermoforming.

[0034] The outer sleeve body 50 of the sleeve 48 and the plurality of spacers 36 of the sleeve 48 can be integral. In other words, the outer sleeve body 50 of the sleeve 48 and the plurality of spacers 36 of the sleeve 48 can be formed as one piece with each other (i.e., a single piece). The outer sleeve body 50 of the sleeve 48 and the plurality of spacers 36 of the sleeve 48 can be integrally formed together as a unit, or can be formed separately first and then joined to become a unit. The method 200 can include the steps of: forming the outer sleeve body 50 and the plurality of spacers 36 such that the outer sleeve body 50 and the plurality of spacers 36 are integral with each other. The step of forming the outer sleeve body 50 and the plurality of spacers 36 such that the outer sleeve body 50 and the plurality of spacers 36 are integral with each other can be carried out simultaneously (i.e., at the same time) with the step 204 of disposing the first spacer 38 between the lamination stack 24 and the first pole shoe 34.

[0035] In addition, as Figure 4 shown, the first pole shoe 34 can define a first recess 54, and the first spacer 38 can be at least partially disposed in the first recess 54. In an embodiment including the sleeve 48, the first spacer 38 being at least partially disposed in the first recess 54 further couples the sleeve 48 and the first pole shoe 34. The first spacer 38 can have a hook-like configuration and can extend radially away from the shaft 40 to be disposed in the first recess 54 of the first pole shoe 34. The first recess 54 can be disposed adjacent to the first magnet 28. The method 200 can further include the step of: disposing the first spacer 38 at least partially in the first recess 54. The step of disposing the first spacer 38 at least partially in the first recess 54 can be carried out simultaneously (i.e., at the same time) with the step 204 of disposing the first spacer 38 between the lamination stack 24 and the first pole shoe 34.

[0036] Also as Figure 4 shown, the first pole shoe 34 can define a second recess 56, and the second spacer 52 can be at least partially disposed in the second recess 56. In an embodiment including the sleeve 48, the second spacer 52 being at least partially disposed in the second recess 56 further couples the sleeve 48 and the first pole shoe 34. The second spacer 52 can have a hook-like configuration and can extend radially away from the shaft 40 to be disposed in the second recess 56 of the first pole shoe 34. The second recess 56 can be disposed adjacent to the second magnet 30. The method 200 can further include the step of disposing the second spacer 52 at least partially in the second recess 56. The step of disposing the second spacer 52 at least partially in the second recess 56 can be carried out simultaneously (i.e., at the same time) with the step 204 of disposing the first spacer 38 between the lamination stack 24 and the first pole shoe 34.

[0037] The outer sleeve body 50 has an outer sleeve surface 58 facing away from the axis A1. The outer sleeve surface 58 is in contact with air during the rotation of the rotor assembly 20. The outer sleeve surface 58 can be smooth to reduce air friction. Alternatively, the outer sleeve body 50 can include aerodynamic features 60 recessed in the outer sleeve surface 58 to reduce air friction. The aerodynamic features 60 can include, but are not limited to, grooves, a series of grooves, pits, or a series of pits. The method 200 can include forming the sleeve 48 such that the outer sleeve surface 58 of the sleeve 48 includes aerodynamic features 60 recessed in the outer sleeve surface 58.

[0038] The stack 24 extends along the axis A1 between a first stack end 62 and a second stack end 64. The rotor assembly 20 can further include a first end cap 66 adjacent to the first stack end 62 and a second end cap 68 adjacent to the second stack end 64. The first end cap 66 and the second end cap 68 help prevent the plurality of magnets 26 from falling off between the plurality of pole shoes 32 and the stack 24.

[0039] The first end cap 66 and the second end cap 68 include a polymer material. In embodiments including the first spacer 38 and the optional sleeve 48 (including a polymer material), the first end cap 66 (including a polymer material), and the second end cap 68 (including a polymer material), it should be recognized that these polymer materials can be the same as or different from each other. In a non-limiting example, the polymer materials of the first end cap 66 and the second end cap 68 can be thermoplastics, thermosets, or elastomers. The polymer materials of the first end cap 66 and the second end cap 68 can be engineering plastics.

[0040] More specifically, the polymer materials of the first end cap 66 and the second end cap 68 can be, but are not limited to, any polyalkene or polyolefin, including their copolymers and terpolymers, such as polyethylene (including high-density polyethylene (HDPE) and low-density polyethylene (LDPE)), polypropylene (PP), polybutene, and polybutylene terephthalate (PBTR), acrylic resins, such as acrylonitrile butadiene styrene (ABS) or polymethyl methacrylate (PMMA), polyoxymethylene (POM) or any acetal copolymer or acetal terpolymer, polyketone, polyether ketone, and / or polyarylether ketone, such as polyetheretherketone (PEEK) and polyetherketoneketone (PEKK), polyetherimide (PEI), polyimide, polyvinyl chloride (PVC), polyphenylene sulfide (PPS), polyphenylene ether (PPO), polysulfone (PSU), polytetrafluoroethylene (PTFE), polyamide (including polyphthalamide), polycarbonate, polyurethane, epoxy resin, and thermoplastic elastomer (TPE).

[0041] Although not required, the polymeric materials of the first end cap 66 and the second end cap 68 may be molded, such as overmolding, insert molding, injection molding, compression molding, and thermoforming. Method 200 may further include the step of molding the first end cap 66 and the second end cap 68. It should be recognized that molding the first end cap 66 and the second end cap 68 may include any one of in-situ molding, overmolding, insert molding, injection molding, compression molding, and thermoforming.

[0042] The step of molding the first end cap 66 and the second end cap 68 may be carried out simultaneously (i.e., at the same time) with the step of molding the first spacer 38, such that the first end cap 66 and the second end cap 68 are integral with the first spacer 38. As Figure 6 shown, the first end cap 66 and the second end cap 68 may be integral with the first spacer 38. In other words, the first end cap 66, the second end cap 68, and the first spacer 38 may be integrally formed with each other, i.e., a single piece. In this embodiment, the first end cap 66 and the second end cap 68 may have a first composition (i.e., the same composition as the first spacer 38). It should also be recognized that the step of molding the first end cap 66 and the second end cap 68 may be carried out simultaneously (i.e., at the same time) with step 204 of disposing the first spacer 38 between the stack 24 and the first pole shoe 34.

[0043] Alternatively, the step of molding the first end cap 66 and the second end cap 68 may be separate from (i.e., at different times) the step of molding the first spacer 38. It should be recognized that the step of molding the first end cap 66 and the second end cap 68 may be after the step of molding the first spacer 38, or the step of molding the first end cap 66 and the second end cap 68 may be before the step of molding the first spacer 38. As Figure 3 shown, the first end cap 66 and the second end cap 68 may be separate components from the first spacer 38. The first end cap 66 and the second end cap 68 may have a second composition different from the first composition of the first spacer 38. It should also be recognized that the step of molding the first end cap 66 and the second end cap 68 may be separate from (i.e., at different times) step 204 of disposing the first spacer 38 between the stack 24 and the first pole shoe 34.

[0044] The second composition of the first end cap 66 and the second end cap 68 may include any polymer material detailed herein and optional fillers and / or additives such as plasticizers, carbon (including carbon fibers), ceramic materials, and / or minerals (including calcium carbonate, silica, clay, and kaolin), fibers (including glass fibers, carbon fibers, aramid fibers, basalt fibers, and paper fibers), stabilizers (including oxidation stabilizers, ultraviolet (UV) stabilizers, heat stabilizers, light absorbers, reinforcing agents, acid scavengers, metal deactivators), and flame retardants (including aluminum hydroxide, phosphorus compounds, and bromine compounds). In one embodiment, the second composition includes a thermoplastic and a filler encapsulated by the thermoplastic. In this embodiment, the filler may include carbon fibers.

[0045] The stack 24 may define a plurality of channels 70 between the first stack end 62 and the second stack end 64. As Figure 3 , Figure 4 and Figures 7A to 8 shown, the rotor assembly 20 may further include a plurality of rods 72 disposed in the plurality of channels 70. It should be appreciated that one rod 72 of the plurality of rods 72 may correspond to and be disposed in one of the plurality of channels 70. Although not required, as Figure 5 shown, the plurality of rods 72 may be integral with the first end cap 66 and the second end cap 68. In other words, the plurality of rods 72, the first end cap 66, and the second end cap 68 may be integrally formed with each other (i.e., a single piece). The plurality of rods 72, the first end cap 66, and the second end cap 68 may be integrally formed with each other. The step of molding the first end cap 66 and the second end cap 68 may include molding the plurality of rods 72 such that the plurality of rods 72 are integral with the first end cap 66 and the second end cap 68.

[0046] The plurality of rods 72 may include a polymer material. In embodiments where the first spacer 38 and the optional sleeve 48 include a polymer material and the first end cap 66, the second end cap 68, and / or the plurality of rods 72 include a polymer material, it should be appreciated that these polymer materials may be the same as each other. In a non-limiting example, the polymer material of the plurality of rods 72 may be a thermoplastic, a thermoset, or an elastomer. The polymer material of the plurality of rods 72 may be an engineering plastic.

[0047] More specifically, the polymeric material of the plurality of rods 72 can be, but is not limited to, any polyalkene or polyolefin, including its copolymers and terpolymers, such as polyethylene (including high-density polyethylene (HDPE) and low-density polyethylene (LDPE)), polypropylene (PP), polybutene, and polybutylene terephthalate (PBTR), acrylic resins, such as acrylonitrile butadiene styrene (ABS) or polymethyl methacrylate (PMMA), polyoxymethylene (POM) or any acetal copolymer or acetal terpolymer, polyketone, polyether ketone, and / or polyarylether ketone, such as polyetheretherketone (PEEK) and polyetherketoneketone (PEKK), polyetherimide (PEI), polyimide, polyvinyl chloride (PVC), polyphenylene sulfide (PPS), polyphenylene ether (PPO), polysulfone (PSU), polytetrafluoroethylene (PTFE), polyamide (including polyphthalamide), polycarbonate, polyurethane, epoxy resin, and thermoplastic elastomer (TPE).

[0048] Although not required, the polymeric material of the plurality of rods 72 can be molded, such as overmolding, insert molding, injection molding, compression molding, and thermoforming. Method 200 can further include the step of molding the plurality of rods 72. The step of molding the plurality of rods 72 can be carried out simultaneously (i.e., at the same time) with the step of molding the first end cap 66 and the second end cap 68. In other words, the first end cap 66, the second end cap 68, and the plurality of rods 72 can be molded together. Additionally, although not required, the first spacer 38 (optionally incorporated into the sleeve 48), the first end cap 66, the second end cap 68, and the plurality of rods 72 can all be molded together. Alternatively, the first end cap 66, the second end cap 68, and the plurality of rods 72 can be molded together after molding the first spacer 38 (optionally incorporated into the sleeve 48). It should be appreciated that molding the plurality of rods 72 can include any one of in-situ forming, overmolding, insert molding, injection molding, compression molding, and thermoforming.

[0049] In addition, the plurality of rods 72 can be non-magnetic, electrically conductive, and can further include carbon fibers. It should be appreciated that the first end cap 66 and / or the second end cap 68 can also be non-magnetic, electrically conductive, and can further include carbon fibers. It should also be appreciated that the plurality of rods can include a second composition. In other words, the first end cap 66, the second end cap 68, and the plurality of rods 72 can all include the second composition.

[0050] Method 200 may further include the steps of: disposing a plurality of rods 72 within a plurality of channels 70 such that the plurality of rods 72 are integral with the first end cap 66 and the second end cap 68. In some embodiments, the step of disposing the plurality of rods 72 within the plurality of channels 70 such that the plurality of rods 72 are integral with the first end cap 66 and the second end cap 68 includes molding the plurality of rods 72, the first end cap 66, and the second end cap 68. Although not required, the step of disposing the plurality of rods 72 within the plurality of channels 70 such that the plurality of rods 72 are integral with the first end cap 66 and the second end cap 68 may be performed after the step of disposing the shaft 40 within the stack 24. It should be appreciated that the step of disposing the plurality of rods 72 within the plurality of channels 70 such that the plurality of rods 72 are integral with the first end cap 66 and the second end cap 68 may be immediately after the step of disposing the shaft 40 within the stack 24, or there may be one or more intervening steps therebetween.

[0051] The first end cap 66 has a first end cap outer surface 74 facing away from the axis, and the second end cap 68 has a second end cap outer surface 76 facing away from the axis A1. Although not required, as Figure 2 and 3 shown, the outer sleeve surface 58, the first end cap outer surface 74, and the second end cap outer surface 76 may be flush with each other. In other words, the outer sleeve surface 58, the first end cap outer surface 74, and the second end cap outer surface 76 may each extend the same radial distance away from the axis A1 and may form a single continuous surface. Additionally, the single continuous surface formed by the outer sleeve surface 58, the first end cap outer surface 74, and the second end cap outer surface 76 may not deviate from the same radial distance away from the axis A1 as the first end cap 66, the outer sleeve body 50, and the second end cap 68 extend along the axis A1. The single continuous surface aids in the manufacturability and aerodynamic performance of the rotor assembly 20. Method 200 may include molding the first end cap 66, the second end cap 68, and the sleeve 48 such that the outer sleeve surface 58, the first end cap outer surface 74, and the second end cap outer surface 76 are flush with each other.

[0052] Now turning to Figures 7A to 8, the stack 24 may have a stack retainer 78, and the first pole shoe 34 may have a pole retainer configured to mechanically cooperate with the stack retainer 78 of the stack 24 to hold the first pole shoe 34 relative to the stack 24. The mechanical cooperation between the stack retainer 78 of the stack 24 and the pole retainer 80 of the first pole shoe 34 limits the movement of the first pole shoe 34 relative to the stack 24. More specifically, the mechanical cooperation between the stack retainer 78 of the stack 24 and the pole retainer 80 of the first pole shoe 34 limits the radial movement of the first pole shoe 34 relative to the stack 24. The method 200 may further include the step of engaging the stack retainer 78 and the pole retainer 80 to hold the first pole shoe 34 relative to the stack 24. The step of engaging the stack retainer 78 and the pole retainer 80 to hold the first pole shoe 34 relative to the stack 24 may be before step 204 of setting the first spacer 38 between the stack 24 and the first pole shoe 34.

[0053] The mechanical cooperation between the pole retainer 80 and the stack retainer 78 does not require direct contact between the pole retainer 80 and the stack retainer 78. The pole retainer 80 and the stack retainer 78 may not contact each other. In a non-limiting example, an intervening member may be provided between the pole retainer 80 and the stack retainer 78 while still allowing the pole retainer 80 and the stack retainer 78 to mechanically cooperate to hold the first pole shoe 34 relative to the stack 24. More specifically, the first spacer 38 may be provided between the stack retainer 78 of the stack 24 and the pole retainer 80 of the first pole shoe 34. Setting the first spacer 38 between the stack retainer 78 and the pole retainer 80 increases the strength of the mechanical cooperation between the pole retainer 80 and the stack retainer 78 by reducing or eliminating any gaps or voids between the pole retainer 80 and the stack retainer 78.

[0054] The method 200 may further include the step of setting the first spacer 38 between the stack retainer 78 and the pole retainer 80. It should be appreciated that the step of setting the first spacer 38 between the stack retainer 78 and the pole retainer 80 may be performed simultaneously (i.e., at the same time) with step 204 of setting the first spacer 38 between the stack 24 and the first pole shoe 34 and / or the step of molding the first spacer 38.

[0055] The lamination retainer 78 has a lamination retainer end 82, and the pole retainer 80 has a pole retainer end 84. The pole retainer end 84 can be disposed radially inwardly relative to the lamination retainer end 82. The lamination retainer end 82 can be the end of the lamination retainer 78, and the pole retainer end 84 can be the end of the pole retainer 80. Disposing the pole retainer end 84 radially inwardly relative to the lamination retainer end 82 limits the movement of the first pole shoe 34 relative to the lamination stack 24. More specifically, if the first pole shoe 34 moves radially away from the lamination stack 24, the pole retainer end 84 can directly contact the lamination retainer end 82, or can contact an intervening member, such as the first spacer 38, which contacts the lamination retainer end 82. Thus, the pole retainer end 84 and the lamination retainer end 82 prevent the first pole shoe 34 from moving radially away from the lamination stack 24.

[0056] In some embodiments, the lamination retainer 78 and the pole retainer 80 are disposed between the first magnet 28 and the second magnet 30. In embodiments where the lamination retainer 78 and the pole retainer 80 are disposed between the first magnet 28 and the second magnet 30, the mechanical cooperation for holding the first pole shoe 34 to the lamination stack 24 occurs substantially equidistantly between the first circumferential end 44 of the first pole shoe 34 and the second circumferential end 46 of the first pole shoe 34. Thus, the mechanical cooperation for holding the first pole shoe 34 to the lamination stack 24 occurs at the approximate circumferential centroid of the first pole shoe 34, thereby preventing either the first circumferential end 44 of the first pole shoe 34 or the second circumferential end 46 of the first pole shoe 34 from moving further away from the lamination stack 24 than the other of the first circumferential end 44 and the second circumferential end 46.

[0057] In other embodiments, the pole retainer 80 is disposed at the first circumferential end 44 of the first pole shoe 34. It should be appreciated that the pole retainer 80 can also be disposed at the second circumferential end 46 of the first pole shoe 34. The pole retainer 80 can further be defined as a first pole retainer 86, the lamination retainer 78 can further be defined as a first lamination retainer 88, and the lamination stack 24 can further have a second lamination retainer 90, and the first pole shoe 34 can further have a second pole retainer 92. The second pole retainer 92 of the first pole shoe 34 can be disposed at the second circumferential end 46 of the first pole shoe 34, and the second pole retainer 92 can be configured to mechanically cooperate with the second lamination retainer 90 of the lamination stack 24 to hold the first pole shoe 34 relative to the lamination stack 24.

[0058] Method 200 may further include the steps of: engaging a second lamination holder 90 and a second pole holder 92 to hold the first pole shoe 34 relative to the lamination stack 24. In an embodiment where the first pole holder 86 is disposed at the first circumferential end 44 of the first pole shoe 34 and the second pole holder 92 is disposed at the second circumferential end 46 of the first pole shoe 34, the mechanical cooperation for holding the first pole shoe 34 to the lamination stack 24 occurs both at the first circumferential end 44 of the first pole shoe 34 and at the second circumferential end 46 of the first pole shoe 34. The two separate and circumferentially spaced mechanical cooperation positions enhance the holding of the first pole shoe 34 to the lamination stack 24. More specifically, the two separate and circumferentially spaced mechanical cooperation positions limit the amount of relative pivoting of the first pole shoe 34 relative to the lamination stack 24.

[0059] In one embodiment, one of the lamination holder 78 and the pole holder 80 has a generally C-shaped configuration 94 defining a channel 96, and the other of the lamination holder 78 and the pole holder 80 has a generally T-shaped configuration 98 at least partially disposed within the channel 96. In other words, as Figure 7A and 7B shown, the lamination holder 78 may have a generally C-shaped configuration 94 and the pole holder 80 may have a generally T-shaped configuration 98, or the lamination holder 78 may have a generally T-shaped configuration 98 and the pole holder 80 may have a generally C-shaped configuration 94. Method 200 may further include the step of: at least partially disposing the generally T-shaped configuration 98 within the channel 96 defined by the generally C-shaped configuration 94.

[0060] In another embodiment, as Figure 7A and 7B shown, the pole holder 80 includes a pole hook 100 defining a hook recess 102, and the lamination holder 78 includes a lamination hook 104 that at least partially extends into the hook recess 102 defined by the pole hook 100 to hold the first pole shoe 34 to the lamination stack 24. Method 200 may further include the step of: at least partially disposing the lamination hook 104 into the hook recess 102 defined by the pole hook 100 to hold the first pole shoe 34 to the lamination stack 24.

[0061] In embodiments where the rotor assembly 20 includes a first pole retainer 86 and a second pole retainer 92, as well as a first lamination retainer 88 and a second lamination retainer 90, the first pole retainer 86 may include a first pole hook 106 that defines a first hook recess 108, and the first lamination retainer 88 may include a first lamination hook 110. In these embodiments, the second pole retainer 92 may include a second pole hook 112 that defines a second hook recess 114, and the second lamination retainer 90 may include a second lamination hook 116 that at least partially extends into the second hook recess 114 defined by the second pole hook 112 to hold the first pole shoe 34 to the lamination stack 24. The first pole hook 106 may have a first hook end 118, and the second pole hook 112 may have a second hook end 120, and the first hook end 118 of the first pole hook 106 and the second hook end 120 of the second pole hook 112 may extend toward each other to increase the holding strength of the first pole shoe 34 to the lamination stack 24. It should be appreciated that the first hook end 118 may be the end of the first pole hook 106, and the second hook end 120 may be the end of the second pole hook 112. Method 200 may further include the step of at least partially disposing the second lamination hook 116 into the second hook recess 114 defined by the second pole hook 112 to hold the first pole shoe 34 to the lamination stack 24.

[0062] As Figure 8 shown, at least one of the lamination retainer 78 and the pole retainer 80 may have a generally mushroom-shaped configuration 122, and the other of the lamination retainer 78 and the pole retainer 80 may form a complementary retainer recess 124. In other words, as Figure 8 shown, the lamination retainer 78 may have a generally mushroom-shaped configuration 122, and the pole retainer 80 may form a retainer recess 124. Alternatively, the lamination retainer 78 may form a retainer recess 124, and the pole retainer 80 may have a generally mushroom-shaped configuration 122. The generally mushroom-shaped configuration 122 of the lamination retainer 78 or the pole retainer 80 may contact the first magnet 28 and the second magnet 30 directly or through an intervening member (such as the first spacer 38) to assist in holding the first magnet 28 and the second magnet 30. Additionally, the first spacer 38 may be disposed in the retainer recess 124 to further hold the first pole shoe 34 relative to the lamination stack 24. Method 200 may further include contacting the generally mushroom-shaped configuration 122 of either the lamination retainer 78 or the pole retainer 80 with the first magnet 28 and the second magnet 30 to assist in holding the first magnet 28 and the second magnet 30.

[0063] It should be appreciated that the rotor assembly 20 may further include a third lamination retainer 126 and a third pole retainer 128. The third lamination retainer 126 may have any of the features of any lamination retainer described herein, and the third pole retainer 128 may have any of the features of any pole retainer described herein. The method 200 may further include the step of engaging the third lamination retainer 126 and the third pole retainer 128 to hold the first pole shoe 34 relative to the lamination stack 24.

[0064] The plurality of pole shoes 32 may include two pole shoes, three pole shoes, four pole shoes, five pole shoes, six pole shoes, seven pole shoes, eight pole shoes, nine pole shoes, ten pole shoes, or more than ten pole shoes. The plurality of magnets may include four magnets, six magnets, eight magnets, ten magnets, twelve magnets, fourteen magnets, sixteen magnets, eighteen magnets, twenty magnets, or more than twenty magnets. The plurality of channels 70 and the plurality of rods 72 may include two channels and two rods, three channels and three rods, four channels and four rods, five channels and five rods, six channels and six rods, seven channels and seven rods, eight channels and eight rods, nine channels and nine rods, ten channels and ten rods, eleven channels and eleven rods, twelve channels and twelve rods, thirteen channels and thirteen rods, fourteen channels and fourteen rods, fifteen channels and fifteen rods, sixteen channels and sixteen rods, seventeen channels and seventeen rods, eighteen channels and eighteen rods, nineteen channels and nineteen rods, twenty channels and twenty rods, or more than twenty channels and more than twenty rods. Each pole shoe 32 may define one channel, may define two channels, may define three channels, or may define more than three channels. The lamination stack 24 may further define a plurality of channels 70 and may define one channel, two channels, three channels, four channels, five channels, six channels, seven channels, eight channels, nine channels, ten channels, or more than ten channels.

[0065] The rotor assembly 20 may be configured to rotate at a speed of more than 20,000 revolutions per minute (RPM). In non-limiting examples, the rotor assembly 20 may be configured to rotate between about 20,000 RPM and about 50,000 RPM, between about 20,000 RPM and about 40,000 RPM, between about 20,000 RPM and about 30,000 RPM, and between about 20,000 RPM and about 25,000 RPM. In some embodiments, the sleeve 48 is capable of holding the plurality of pole shoes 32 to the lamination stack 24 at a speed of 20,000 RPM or more than 20,000 RPM. In other embodiments, the lamination retainer 78 and the pole retainer 80 are capable of holding the plurality of pole shoes 32 to the lamination stack 24 at a speed of 20,000 RPM or more than 20,000 RPM. Thus, the rotor assembly 20 may be considered a high-speed rotor assembly.

[0066] AsFigure 9 As shown, the rotor assembly 20 can be incorporated into the electric motor 22. The electric motor 22 includes a stator 130 that extends along an axis A1 and defines a stator interior 132, and the rotor assembly 20 can be disposed within the stator interior 132 of the stator 130. The rotor assembly 20 can be completely disposed within the stator interior 132 of the stator 130, or the rotor assembly 20 can be only partially disposed within the stator interior 132 of the stator 130. A method of manufacturing an electric motor includes the steps of manufacturing the rotor assembly 20 and disposing the rotor assembly 20 within the stator interior 132 of the stator 130.

[0067] The stator 130 can include a coil winding 134 that can be energized to generate a magnetic flux detailed herein. The plurality of spacers 36 improve the efficiency of the electric motor 22 by reducing the amount of leaking magnetic flux, and thus improve the efficiency of the force applied to rotate the rotor assembly 20 relative to the amount of magnetic flux that needs to be generated.

[0068] In addition, a gap can be defined between the outer sleeve surface 58 of the sleeve 48 or the outer pole surface 42 of the first pole shoe 34 and the stator interior 132 of the stator 130. Advantageously, this gap is minimized to minimize losses due to air friction. It should be appreciated that the sleeve 48 can be manufactured with relatively tight tolerances, thus allowing a relatively small gap to be defined between the outer sleeve surface 58 of the sleeve 48 and the stator interior 132 of the stator 130 or between the outer pole surface 42 of the first pole shoe 34 and the stator interior 132 of the stator 130, and thus also minimizing losses due to air friction. The gap can be between XX millimeters and XX millimeters.

[0069] As Figure 10 As shown, the electric motor 22 is incorporated into an electric drive unit 136. The electric drive unit 136 includes the electric motor 22 and a gear reduction mechanism 138 coupled to the shaft 40 of the rotor assembly 20. The gear reduction mechanism 138 can be configured to adjust the torque received from the shaft 40. The gear reduction mechanism 138 can be, but is not limited to, a planetary gear set, a reduction gearbox (such as a two-stage reduction gearbox), a worm gear reducer, a helical gear reducer, a spur gear reducer, a hypoid gear reducer, a bevel gear reducer, a gear train reducer, a cycloidal gear reducer, a magnetic gear reducer, an orthogonal gear reducer, an inclined shaft gear reducer, a parallel shaft gear reducer, a coaxial gear reducer, and combinations thereof. A method of manufacturing the electric drive unit 136 includes the steps of manufacturing the electric motor 22 and coupling the electric motor 22 to the gear reduction mechanism 138. More specifically, the step of coupling the electric motor 22 to the gear reduction mechanism 138 can include coupling the shaft 40 of the rotor assembly 20 to the gear reduction mechanism 138.

[0070] The present invention has been described in an illustrative manner, and it is to be understood that the terminology used is descriptive in nature and not restrictive. Many modifications and variations of the present invention are possible in light of the above teachings, and the invention may be practiced otherwise than as specifically described.

Claims

1. A method of manufacturing a rotor assembly for an electric motor, the rotor assembly including a stack of laminations extending along an axis, a plurality of magnets including a first magnet and a second magnet each coupled to the stack of laminations, a plurality of pole shoes including a first pole shoe spaced from and separated from the stack of laminations, and a plurality of spacers including a first spacer spaced from the stack of laminations, the method comprising the steps of: Disposing the first magnet and the second magnet between the stack of laminations and the first pole shoe; And Disposing the first spacer between the stack of laminations and the first pole shoe to reduce flux leakage between the stack of laminations and the first pole shoe.

2. The method according to claim 1, wherein the step of disposing the first spacer between the stack of laminations and the first pole shoe includes disposing the first spacer such that the first spacer extends at least to the first magnet.

3. The method according to claim 1, wherein the step of disposing the first spacer between the stack of laminations and the first pole shoe includes disposing the first spacer such that the first spacer is disposed between the first magnet and the second magnet.

4. The method according to claim 1, further comprising the following steps: Disposing a shaft within the stack of laminations such that the shaft extends along the axis.

5. The method according to claim 1, wherein the first spacer includes a polymeric material, and wherein the step of disposing the first spacer between the stack of laminations and the first pole shoe includes molding the first spacer such that the first spacer is disposed between the stack of laminations and the first pole shoe.

6. The method according to claim 1, wherein the step of disposing the first magnet and the second magnet between the stack of laminations and the first pole shoe is before the step of disposing the first spacer between the stack of laminations and the first pole shoe.

7. The method according to claim 1, wherein the first pole shoe has a first circumferential end and a second circumferential end circumferentially spaced from the first circumferential end, and has an outer pole surface facing away from the axis and extending between the first circumferential end and the second circumferential end, and wherein the step of disposing the first spacer between the stack of laminations and the first pole shoe includes disposing the first spacer circumferentially between the first circumferential end of the first pole shoe and the stack of laminations.

8. The method according to claim 1, wherein the stack of laminations extends along the axis between a first stack end and a second stack end, wherein the rotor assembly further includes a first end cap adjacent the first stack end and a second end cap adjacent the second stack end, and wherein the first end cap and the second end cap include a polymeric material, and the method further includes the step of molding the first end cap and the second end cap.

9. The method according to claim 8, wherein the first spacer comprises a polymeric material, and wherein the step of disposing the first spacer between the stack of laminations and the first pole shoe comprises molding the first spacer such that the first spacer is disposed between the stack of laminations and the first pole shoe, and wherein the step of molding the first end cap and the second end cap is performed simultaneously with the step of molding the first spacer such that the first end cap and the second end cap are integral with the first spacer.

10. The method according to claim 8, wherein the first spacer comprises a polymeric material, and wherein the step of disposing the first spacer between the stack of laminations and the first pole shoe comprises molding the first spacer such that the first spacer is disposed between the stack of laminations and the first pole shoe, and wherein the step of molding the first end cap and the second end cap is separate from the step of molding the first spacer.

11. The method according to claim 10, wherein the first spacer has a first composition, and wherein at least one of the first end cap and the second end cap has a second composition different from the first composition of the first spacer.

12. The method according to claim 8, wherein the stack of laminations defines a plurality of channels between the first stack of laminations end and the second stack of laminations end, and further comprises the steps of: Dispose a plurality of rods in the plurality of channels such that the plurality of rods are integral with the first end cap and the second end cap.

13. The method according to claim 1, wherein each of the plurality of pole shoes has an outer pole surface facing away from the axis, and wherein the step of disposing the first spacer between the stack of laminations and the first pole shoe further comprises coupling a sleeve to the stack of laminations, the sleeve including an outer sleeve body and the first spacer extending radially inward from the outer sleeve body toward the axis, and wherein coupling the sleeve to the stack of laminations comprises disposing the outer sleeve body around the outer pole surface of each of the plurality of pole shoes to hold each of the pole shoes relative to the stack of laminations.

14. The method according to claim 1, wherein the stack of laminations has a lamination retainer, and the first pole shoe has a pole retainer configured to mechanically cooperate with the lamination retainer, and the method further comprises the steps of: Engage the lamination retainer and the pole retainer to hold the first pole shoe relative to the stack of laminations.

15. The method according to claim 14, further comprising the following steps: Dispose the first spacer between the lamination retainer and the pole retainer.

16. The method according to claim 14, wherein one of the lamination retainer and the pole retainer has a generally C-shaped configuration defining a channel, and the other of the lamination retainer and the pole retainer has a generally T-shaped configuration, and the method further comprises the steps of: Dispose the substantially T-shaped configuration at least partially in a channel defined by the substantially C-shaped configuration.

17. The method according to claim 14, wherein the pole retainer includes a pole hook defining a hook recess, and the lamination retainer includes a lamination hook, and the method further comprises the steps of: Dispose the lamination hook at least partially into a hook recess defined by the pole hook to hold the first pole shoe to the stack of laminations.

18. The method according to claim 14, wherein the pole retainer is further defined as a first pole retainer, wherein the lamination retainer is further defined as a first lamination retainer, wherein the lamination stack further has a second lamination retainer, wherein the first pole shoe further has a second pole retainer disposed at a second circumferential end of the first pole shoe and configured to mechanically cooperate with the second lamination retainer, and the method further comprises the steps of: Engage the second lamination retainer and the second pole retainer to hold the first pole shoe relative to the stack of laminations.

19. A method of manufacturing an electric motor, the electric motor including a stator defining an interior of the stator, the method comprising the steps of: Manufacturing a rotor assembly according to claim 1; and Disposing the rotor assembly in the interior of the stator of the stator.

20. A method of manufacturing an electric drive unit, the electric drive unit including a gear reduction mechanism, the method comprising the steps of: Manufacturing an electric motor according to claim 19; And Coupling the electric motor to the gear reduction mechanism.

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