Rotor assembly

Abstract

A rotor assembly for an electric motor includes a shaft extending along and rotatable about an axis. The rotor assembly also includes a stack of laminations coupled to the shaft, a plurality of magnets including a first magnet coupled to the stack of laminations, and a plurality of pole shoes spaced radially outward from the shaft. Each of the plurality of pole shoes is separated from the stack of laminations. The plurality of pole shoes includes a first pole shoe, and a first magnet and a second magnet are disposed between the lamination stack and the first pole shoe. The rotor assembly further includes a plurality of spacers including a first spacer disposed between the first pole shoe and the stack of laminations to reduce flux leakage of the first magnet.

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 / 957,065, 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 rotor assembly for an electric motor and to 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 apart 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, and generate magnetic flux. The stator includes a coil winding, and energization of the coil winding in the stator generates magnetic flux that interacts with the magnetic flux generated by 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 force applied to the plurality of pole shoes during rotation of the rotor assembly.

[0005] However, the magnetic flux generated by the permanent magnets is interrupted or leaked by the bridge members, such that a portion of the magnetic flux is directed towards the stack of laminations and connects the north and south poles of each permanent magnet. The leakage magnetic flux limits the amount of magnetic flux from the permanent magnets available for interaction with the magnetic flux generated by the coil winding in the stator, thus reducing the force applied to the rotor assembly and therefore also reducing the efficiency of the electric motor. The leakage of magnetic flux will occur until the bridge members reach magnetic saturation. To minimize the leakage of flux through the bridge members, the bridge members are typically designed to be as thin as possible to quickly reach magnetic saturation within the stack of laminations and thus reduce the flux leakage from the permanent magnets. However, the centrifugal force applied to the plurality of pole shoes during rotation of the rotor assembly is also applied to the bridge members. These centrifugal forces applied to the bridge members cause stress concentration on the bridge members and risk structural failure of the bridge members, especially when the bridge members are designed to be as thin as possible.

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

[0007] A rotor assembly for an electric motor is disclosed. The rotor assembly includes a shaft extending along an axis and rotatable about the axis. The rotor assembly further includes a stack of laminations coupled to the shaft, a plurality of magnets including a first magnet coupled to the stack of laminations, and a plurality of pole shoes radially outwardly spaced from the shaft. Each of the plurality of pole shoes is separated from the stack of laminations. The plurality of pole shoes includes a first pole shoe, and the first magnet is disposed between the stack of laminations and the first pole shoe. The rotor assembly further includes a plurality of spacers including a first spacer disposed between the first pole shoe and the stack of laminations to reduce flux leakage of the first magnet.

[0008] The first spacer prevents interruption or leakage of the magnetic flux of the first magnet. Thus, it is ensured that the magnetic flux of the first magnet can be used to effectively apply a force to the rotor assembly to rotate the rotor assembly. Each of the plurality of pole shoes is separated 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 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, resulting in stress concentration on any bridging member and potentially leading to structural failure of any bridging member. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] 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:

[0010] Figure 1 is a perspective view of a rotor assembly according to the present invention;

[0011] Figure 2A is a cross-sectional view of an embodiment of the rotor assembly, wherein the rotor assembly includes a stack of laminations, a plurality of pole shoes, a plurality of magnets and a plurality of spacers;

[0012] Figure 2B is Figure 2A an exploded view of;

[0013] Figure 3 is a cross-sectional view of another embodiment of the rotor assembly;

[0014] Figure 4 is a perspective view of an electric motor including the rotor assembly; and

[0015] Figure 5 is Figure 4 a perspective view of a portion of an electric drive unit of an electric motor including in dashed lines. DETAILED DESCRIPTION

[0016] Referring to the drawings, wherein like numerals represent like parts in several views, throughout Figures 1-5Shows a rotor assembly 10 for an electric motor 12. The rotor assembly 10 includes a shaft 14 that extends along an axis A1 and is rotatable about the axis A1. The rotor assembly 10 further includes a stack of laminations 16 coupled to the shaft 14, a plurality of magnets 18 including a first magnet 20 coupled to the stack of laminations 16, and a plurality of pole shoes 24 spaced radially outwardly from the shaft 14. Although not required, the plurality of magnets 18 may further include a second magnet 22 coupled to the stack of laminations 16. Each of the plurality of pole shoes 24 is separated from the stack of laminations 16. It should be appreciated that the plurality of pole shoes 24 may be referred to as a plurality of pole pieces. The plurality of pole shoes 24 includes a first pole shoe 26, and the first magnet 20 is disposed between the stack of laminations 16 and the first pole shoe 26. In embodiments having a second magnet 22, the second magnet 22 is disposed between the stack of laminations 16 and the first pole shoe 26. The rotor assembly 10 further includes a plurality of spacers 28, which includes a first spacer 30 disposed between the first pole shoe 26 and the stack of laminations 16 to reduce flux leakage of the first magnet 20.

[0017] The first spacer 30 prevents interruption or leakage of the magnetic flux of the first magnet 20. Thus, it is ensured that the magnetic flux of the first magnet 20 can be used to effectively apply a force to the rotor assembly 10 to rotate the rotor assembly 10. Each of the plurality of pole shoes 24 is separated from the stack of laminations 16. In other words, each of the plurality of pole shoes 24 is a member separated from the stack of laminations 16. Thus, a non-bridged arrangement of the pole shoes 24 and the stack of laminations 16 is formed. In other words, in the non-bridged arrangement, the pole shoes 24 and the stack of laminations 16 are not connected to each other by bridging material. Thus, the centrifugal force applied to the plurality of pole shoes 24 by the rotation of the rotor assembly 10 is not applied to any bridging member connecting the plurality of pole shoes 24 and the stack of laminations 16. Therefore, the non-bridged arrangement of the pole shoes 24 and the stack of laminations 16 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 structural failure of any bridging member.

[0018] Although the benefits of the first spacer 30 have been described with reference to the first pole shoe 26, the first magnet 20, optionally the second magnet 22, and the stack of laminations 16, it should be appreciated that these benefits may equally apply to all other spacers 28 in the plurality of spacers 28, all other pole shoes 24 in the plurality of pole shoes 24, all other magnets 18 in the plurality of magnets 18, and the stack of laminations 16. Each spacer 28 and pole shoe 24 may have the characteristics of the first spacer 30 and the first pole shoe 26 as described herein. More specifically, the plurality of spacers 28 may prevent interruption or leakage of the magnetic flux between the plurality of pole shoes 24 and the stack of laminations 16. Thus, it is ensured that the magnetic flux can be used to effectively apply a force to the rotor assembly 10 to rotate the rotor assembly 10.

[0019] The stack 16 can be made of a plurality of laminations fixed to each other, in a non-limiting example, by interlocking, welding, clamping, and / or bonding. To improve the manufacturability of the stack 16, each lamination in the stack 16 can be the same as each other lamination in the stack 16.

[0020] Each magnet of the plurality of magnets 18 (including the first magnet 20 and the second magnet 22) can be a permanent magnet. As Figures 2A to 3 shown, the first magnet 20 and the second magnet 22 can be configured to form a V shape. Each pole shoe of the plurality of pole shoes 24 (including the first pole shoe 26) 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 16 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 necessary, it should be recognized that the plurality of pole shoes 24 can be made of the same metal and / or metalloid as that constituting the stack 16.

[0021] The first spacer 30 can include a polymeric material. In a non-limiting example, the polymeric material of the first spacer 30 can be a thermoplastic, a thermoset, or an elastomer. The polymeric material of the first spacer 30 can be an engineering plastic. More specifically, the polymeric material of the first spacer 30 can be any polyolefin or polyolefin copolymer or terpolymer, 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). Although not necessary, the polymeric material of the first spacer 30 can be molded, such as overmolding, insert molding, injection molding, compression molding, and thermoforming.

[0022] The first spacer 30 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 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).

[0023] The first spacer 30 may extend at least to the first magnet 20 and may extend at least to the second magnet 22. The first spacer 30 may also be disposed between the first magnet 20 and the second magnet 22. It should be appreciated that the first spacer 30 may extend radially inwardly toward the first magnet 20 and may also extend beyond the first magnet 20, optionally encapsulating at least a portion of the first magnet 20, and then be disposed between the first magnet 20 and the second magnet 22. Similarly, it should be appreciated that the first spacer 30 may extend radially inwardly toward the second magnet 22 and may also extend beyond the second magnet 22, optionally encapsulating at least a portion of the second magnet 22, and then be disposed between the first magnet 20 and the second magnet 22.

[0024] As shown in FIG. 2 and Figure 3 as shown, the stack 16 may have a stack retainer 32, and the first pole shoe 26 may have a pole retainer 34 that is configured to mechanically cooperate with the stack retainer 32 of the stack 16 to hold the first pole shoe 26 relative to the stack 16. The mechanical cooperation of the stack retainer 32 of the stack 16 and the pole retainer 34 of the first pole shoe 26 limits the movement of the first pole shoe 26 relative to the stack 16. More specifically, the mechanical cooperation of the stack retainer 32 of the stack 16 and the pole retainer 34 of the first pole shoe 26 limits the radial movement of the first pole shoe 26 relative to the stack 16.

[0025] In addition, the mechanical cooperation between the pole retainer 34 and the lamination retainer 32 does not require direct contact between the pole retainer 34 and the lamination retainer 32. The pole retainer 34 and the lamination retainer 32 may not contact each other. In a non-limiting example, an intervening member may be provided between the pole retainer 34 and the lamination retainer 32 while still allowing the pole retainer 34 and the lamination retainer 32 to mechanically cooperate to hold the first pole shoe 26 relative to the lamination stack 16. More specifically, the first spacer 30 may be disposed between the lamination retainer 32 of the lamination stack 16 and the pole retainer 34 of the first pole shoe 26. Disposing the first spacer 30 between the lamination retainer 32 and the pole retainer 34 increases the strength of the mechanical cooperation between the pole retainer 34 and the lamination retainer 32 by reducing or eliminating any gaps or voids between the pole retainer 34 and the lamination retainer 32.

[0026] The lamination retainer 32 has a lamination retainer end 36, and the pole retainer 34 has a pole retainer end 38. The pole retainer end 38 may be disposed radially inward relative to the lamination retainer end 36. The lamination retainer end 36 may be the end of the lamination retainer 32, and the pole retainer end 38 may be the end of the pole retainer 34. Disposing the pole retainer end 38 radially inward relative to the lamination retainer end 36 limits the movement of the first pole shoe 26 relative to the lamination stack 16. More specifically, if the first pole shoe 26 is to move radially away from the lamination stack 16, the pole retainer end 38 may directly contact the lamination retainer end 36 or may contact an intervening member, such as the first spacer 30, which contacts the lamination retainer end 36. In this way, the pole retainer end 38 and the lamination retainer end 36 prevent the first pole shoe 26 from moving radially away from the lamination stack 16.

[0027] The first pole shoe 26 has a first circumferential end 42 and a second circumferential end 44 circumferentially spaced from the first circumferential end 42. The first pole shoe 26 also has an outer pole surface 40 that faces away from the axis A1 and extends between the first circumferential end 42 and the second circumferential end 44. In some embodiments, the first spacer 30 is circumferentially disposed between the first circumferential end 42 and the lamination stack 16. It should be appreciated that the first spacer 30 may alternatively be circumferentially disposed between the second circumferential end 44 and the lamination stack 16, or the first spacer 30 may be circumferentially disposed both between the first circumferential end 42 and the lamination stack 16 and between the second circumferential end 44 and the lamination stack 16. Additionally, although not required, the first spacer 30 may be integrally incorporated into a sleeve having an outer sleeve body that extends around the outer pole surface of each of the plurality of pole shoes 24, and the first spacer 30 may extend radially inward from the outer sleeve body of the sleeve.

[0028] In some embodiments, the lamination retainer 32 and the pole retainer 34 are disposed between the first magnet 20 and the second magnet 22. In embodiments where the lamination retainer 32 and the pole retainer 34 are disposed between the first magnet 20 and the second magnet 22, the mechanical cooperation for holding the first pole shoe 26 to the lamination stack 16 occurs substantially equidistantly between the first circumferential end 42 and the second circumferential end 44 of the first pole shoe 26. Thus, the mechanical cooperation for holding the first pole shoe 26 to the lamination stack 16 occurs at the substantially circumferential centroid of the first pole shoe 26, thereby preventing either the first circumferential end 42 or the second circumferential end 44 of the first pole shoe 26 from moving further away from the lamination stack 16 compared to the other of the first circumferential end 42 and the second circumferential end 44.

[0029] In other embodiments, the pole retainer 34 is disposed at the first circumferential end 42 of the first pole shoe 26. It should be appreciated that the pole retainer 34 may also be disposed at the second circumferential end 44 of the first pole shoe 26. The pole retainer 34 may further be defined as a first pole retainer 46, the lamination retainer 32 may further be defined as a first lamination retainer 48, and the lamination stack 16 may further have a second lamination retainer 50, and the first pole shoe 26 may further have a second pole retainer 52. The second pole retainer 52 of the first pole shoe 26 may be disposed at the second circumferential end 44 of the first pole shoe 26, and the second pole retainer 52 may be configured to mechanically cooperate with the second lamination retainer 50 of the lamination stack 16 to hold the first pole shoe 26 relative to the lamination stack 16.

[0030] In embodiments where the first pole retainer 46 is disposed at the first circumferential end 42 of the first pole shoe 26 and the second pole retainer 52 is disposed at the second circumferential end 44 of the first pole shoe 26, the mechanical cooperation for holding the first pole shoe 26 to the lamination stack 16 occurs both at the first circumferential end 42 and at the second circumferential end 44 of the first pole shoe 26. The two separate and circumferentially spaced mechanical cooperation positions enhance the holding of the first pole shoe 26 to the lamination stack 16. More specifically, the two separate and circumferentially spaced mechanical cooperation positions limit the amount of relative pivoting of the first pole shoe 26 relative to the lamination stack 16.

[0031] In one embodiment, one of the lamination retainer 32 and the pole retainer 34 has a generally C-shaped configuration 54 that defines a channel 56, and the other of the lamination retainer 32 and the pole retainer 34 has a generally T-shaped configuration 58 that is at least partially disposed within the channel 56. In other words, as Figure 2A and 2BAs shown, the lamination retainer 32 may have a generally C-shaped configuration 54, and the pole retainer 34 may have a generally T-shaped configuration 58, or the lamination retainer 32 may have a generally T-shaped configuration 58, and the pole retainer 34 may have a generally C-shaped configuration 54.

[0032] In another embodiment, as Figure 2A and 2B shown, the pole retainer 34 includes a pole hook 60 that defines a hook recess 62, and the lamination retainer 32 includes a lamination hook 64 that at least partially extends into the hook recess 62 defined by the pole hook 60 to hold the first pole shoe 26 to the lamination stack 16. In embodiments where the rotor assembly 10 includes a first pole retainer 46 and a second pole retainer 52, and a first lamination retainer 48 and a second lamination retainer 50, the first pole retainer 46 may include a first pole hook 66 that defines a first hook recess 68, and the first lamination retainer 48 may include a first lamination hook 70. In these embodiments, the second pole retainer 52 may include a second pole hook 72 that defines a second hook recess 74, and the second lamination retainer 50 may include a second lamination hook 76 that at least partially extends into the second hook recess 74 defined by the second pole hook 72 to hold the first pole shoe 26 to the lamination stack 16. The first pole hook 66 may have a first hook end 78, and the second pole hook 72 may have a second hook end 80, and the first hook end 78 of the first pole hook 66 and the second hook end 80 of the second pole hook 72 may extend toward each other to increase the holding strength of the first pole shoe 26 to the lamination stack 16. It should be appreciated that the first hook end 78 may be the end of the first pole hook 66, and the second hook end 80 may be the end of the second pole hook 72.

[0033] As Figure 3 shown, at least one of the lamination retainer 32 and the pole retainer 34 may have a generally mushroom-shaped configuration 82, and the other of the lamination retainer 32 and the pole retainer 34 may form a complementary retainer recess 84. In other words, as Figure 3 shown, the lamination retainer 32 may have a generally mushroom-shaped configuration 82, and the pole retainer 34 may form a retainer recess 84. Alternatively, the lamination retainer 32 may form a retainer recess 84, and the pole retainer 34 may have a generally mushroom-shaped configuration 82. The generally mushroom-shaped configuration 82 of the lamination retainer 32 or the pole retainer 34 may contact the first magnet 20 and the second magnet 22 directly or through an intervening member (such as the first spacer 30) to assist in holding the first magnet 20 and the second magnet 22. Additionally, the first spacer 30 may be disposed in the retainer recess 84 to further hold the first pole shoe 26 relative to the lamination stack 16.

[0034] It should be appreciated that the rotor assembly 10 may further include a third lamination retainer 86 and a third pole retainer 88. The third lamination retainer 86 may have any features of any lamination retainer as described herein, and the third pole retainer 88 may have any features of any pole retainer as described herein.

[0035] The lamination stack 16 extends along an axis A1 between a first lamination stack end 90 and a second lamination stack end 92. The rotor assembly 10 may further include a first end cap 94 adjacent the first lamination stack end 90 and a second end cap 96 adjacent the second lamination stack end 92. The first end cap 94 and the second end cap 96 help prevent the plurality of magnets 18 from falling out between the plurality of pole shoes 24 and the lamination stack 16. The first end cap 94 and the second end cap 96 may be integral with the first spacer 30. In other words, the first end cap 94, the second end cap 96, and the first spacer 30 may be integrally formed with each other, i.e., a single piece.

[0036] The lamination stack 16 typically defines a plurality of channels 98 between the first lamination stack end 90 and the second lamination stack end 92. The plurality of channels 98 may be configured to direct a lubricant through the rotor assembly 10 for lubrication and / or cooling of the rotor assembly 10. As shown in FIGS. 2 and Figure 3 as shown, the rotor assembly 10 may further include a plurality of rods 100 disposed in the plurality of channels 98. It should be appreciated that the plurality of rods 100 may be disposed in the plurality of channels 98 and the lamination stack 16 may still define a channel 98 configured to direct a lubricant through the rotor assembly 10 for lubrication and / or cooling of the rotor assembly 10. Alternatively, it should also be appreciated that one of the plurality of rods 100 may correspond to and be disposed in one of the plurality of channels 98. The plurality of rods 100 may be integral with the first end cap 94 and the second end cap 96. In other words, the plurality of rods 100, the first end cap 94, and the second end cap 96 may be integrally formed with each other, i.e., a single piece. The plurality of rods 100, the first end cap 94, and the second end cap 96 may be integrally formed with each other.

[0037] The first end cap 94, the second end cap 96, and / or the plurality of rods 100 may include a polymeric material. In embodiments where the first spacer 30 includes a polymeric material and the first end cap 94, the second end cap 96, and / or the plurality of rods include a polymeric material, it should be appreciated that these polymeric materials may be the same as or different from each other. In non-limiting examples, the polymeric material of the first end cap 94, the second end cap 96, and / or the plurality of rods 100 may be a thermoplastic, a thermoset, or an elastomer. The polymeric material of the first end cap 94, the second end cap 96, and / or the plurality of rods 100 may be an engineering plastic.

[0038] More specifically, the polymeric material of the first end cap 94, the second end cap 96, and / or the plurality of rods 100 can 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 oxide (PPO), polysulfone (PSU), polytetrafluoroethylene (PTFE), polyamide (including polyphthalamide), polycarbonate, polyurethane, epoxy resin, and thermoplastic elastomer (TPE). Although not required, the polymeric material of the first end cap 94, the second end cap 96, and / or the plurality of rods 100 can be molded, such as overmolding, insert molding, injection molding, compression molding, and thermoforming.

[0039] More specifically, the plurality of rods 100 can be non-magnetic, electrically conductive, and can further include carbon fibers. It should be appreciated that the first end cap 94 and / or the second end cap 96 can also be non-magnetic, can be electrically conductive, and can further include carbon fibers. At least one of the first end cap 94 and the second end cap 96 can include a second composition. The second composition of the first end cap 94 and / or the second end cap 96 can be the same as or different from the first composition of the first spacer 30. It should also be appreciated that the plurality of rods can include a second composition such that at least one of the first end cap 94, the second end cap 96, and the plurality of rods 100 can include a second composition.

[0040] The second composition of the first end cap 94, the second end cap 96, and / or the plurality of rods 100 can include any polymeric material detailed herein, as well as 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 can include carbon fibers.

[0041] As detailed herein, the first spacer 30 may be molded, such as overmolded, insert molded, injection molded, compression molded, and thermoformed. It should be appreciated that the first end cap 94, the second end cap 96, and / or the plurality of rods 100 may also be molded, such as overmolded, insert molded, injection molded, compression molded, and thermoformed. More specifically, the polymeric material of the first end cap 94, the second end cap 96, and / or the plurality of rods 100 may be molded. It should be appreciated that the first end cap 94, the second end cap 96, and the plurality of rods 100 may be molded together. The first spacer 30, the first end cap 94, the second end cap 96, and / or the plurality of rods 100 may be molded together.

[0042] The plurality of pole shoes 24 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 18 may include two magnets, three magnets, four magnets, five magnets, six magnets, seven magnets, eight magnets, nine magnets, ten magnets, eleven magnets, twelve magnets, thirteen magnets, fourteen magnets, fifteen magnets, sixteen magnets, seventeen magnets, eighteen magnets, nineteen magnets, twenty magnets, or more than twenty magnets. The plurality of magnets 18 associated with each pole shoe 24 may be a single magnet, or may be an array of multiple barrier pole magnets, including but not limited to V-shaped arrays, double V-shaped arrays, U-shaped arrays, and triangular arrays. The plurality of channels 98 and the plurality of rods 100 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 24 may define one channel, may define two channels, may define three channels, or may define more than three channels. The lamination stack 16 may also define a plurality of channels 98, 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.

[0043] The rotor assembly 10 can be configured to rotate at speeds above 20,000 revolutions per minute (RPM). In non-limiting examples, the rotor assembly 10 can 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. The lamination retainer 32 and the pole retainer 34 are capable of holding the plurality of pole pieces 24 to the lamination stack 16 at speeds of 20,000 RPM or above 20,000 RPM. Thus, the rotor assembly 10 can be considered a high-speed rotor assembly.

[0044] As Figure 4 shown, the rotor assembly 10 can be incorporated into the electric motor 12. The electric motor 12 includes a stator 102 that extends along an axis A1 and defines a stator interior 104, and the rotor assembly 10 is disposed within the stator interior 104 of the stator 102. The rotor assembly 10 can be fully disposed within the stator interior 104 of the stator 102, or the rotor assembly 10 can be only partially disposed within the stator interior 104 of the stator 102. The stator 102 can include a coil winding 106 that can be energized to generate a magnetic flux detailed herein. The plurality of spacers 28 increase the efficiency of the electric motor 12 by reducing the amount of leaking magnetic flux, and thus increase the efficiency of the force exerted by the rotating rotor assembly 10 relative to the amount of magnetic flux that needs to be generated.

[0045] In addition, a gap can be defined between the outer pole surface 40 and the stator interior 104 of the stator 102. Advantageously, this gap is minimized to minimize losses due to air friction and also to increase the torque on the rotor assembly 10. It should be appreciated that the plurality of spacers 28 can be manufactured with relatively tight tolerances, thus allowing a relatively small gap to be defined between the outer pole surface 40 and the stator interior 104 of the stator 102, and thus also minimizing losses due to air friction. This gap can be as small as 0.2 millimeters and can be proportional to the tolerance of the diameter of the rotor assembly 10 and / or proportional to the rotational speed of the rotor assembly 10. This gap can also be measured on the order of about 0.1% of the diameter of the stator 102.

[0046] As Figure 5As shown. The electric motor 12 can be incorporated into the electric drive unit 108. The electric drive unit 108 includes the electric motor 12 and a gear reduction mechanism 110 coupled to the shaft 14 of the rotor assembly 10. The gear reduction mechanism 110 can be configured to adjust the torque received from the shaft 14. The gear reduction mechanism 110 can be 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, a crossed helical gear reducer, an inclined shaft gear reducer, a parallel shaft gear reducer, a coaxial gear reducer, and combinations thereof.

[0047] The present invention has been described in an illustrative manner, and it is to be understood that the terminology used is in the nature of description rather than limitation. Many modifications and variations of the present invention are possible in light of the above teachings, and the present invention may be practiced otherwise than as specifically described.

Claims

1. A rotor assembly for an electric motor, the rotor assembly comprising: a shaft extending along an axis and rotatable about the axis; a stack of laminations coupled to the shaft; a plurality of magnets including a first magnet coupled to the stack of laminations; a plurality of pole shoes, wherein each of the plurality of pole shoes is radially outwardly spaced from the shaft and separated from the stack of laminations, wherein the plurality of pole shoes includes a first pole shoe, and wherein the first magnet is disposed between the stack of laminations and the first pole shoe; and a plurality of spacers including a first spacer disposed between the first pole shoe and the stack of laminations to reduce flux leakage of the first magnet.

2. The rotor assembly according to claim 1, wherein the first spacer comprises a polymeric material.

3. The rotor assembly according to claim 2, wherein the polymeric material is molded.

4. The rotor assembly 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 to hold the first pole shoe relative to the stack of laminations.

5. The rotor assembly according to claim 4, wherein the pole retainer and the lamination retainer do not contact each other.

6. The rotor assembly according to claim 4, wherein the first spacer is disposed between the lamination retainer and the pole retainer.

7. The rotor assembly according to claim 4, wherein the lamination retainer has a lamination retainer end and the pole retainer has a pole retainer end disposed radially inwardly relative to the lamination retainer end.

8. The rotor assembly according to claim 1, wherein the plurality of magnets further includes a second magnet disposed between the first pole shoe and the stack of laminations, and wherein the first spacer is disposed between the first magnet and the second magnet.

9. The rotor assembly according to claim 4, wherein the plurality of magnets further includes a second magnet disposed between the first pole shoe and the stack of laminations, and wherein at least one of the lamination retainer and the pole retainer is disposed between the first magnet and the second magnet.

10. The rotor assembly 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 first spacer is circumferentially disposed between the first circumferential end and the stack of laminations.

11. The rotor assembly according to claim 10, wherein the pole retainer is disposed at the first circumferential end of the first pole shoe.

12. The rotor assembly according to claim 11, 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 the second circumferential end of the first pole shoe, and wherein the second pole retainer is configured to mechanically cooperate with the second lamination retainer of the lamination stack to hold the first pole shoe relative to the lamination stack.

13. The rotor assembly according to claim 4, 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 at least partially disposed in the channel.

14. The rotor assembly according to claim 4, wherein the pole retainer includes a pole hook defining a hook recess, and wherein the lamination retainer includes a lamination hook that at least partially extends into the hook recess defined by the pole hook to hold the first pole shoe to the lamination stack.

15. The rotor assembly according to claim 14, wherein the pole retainer is further defined as a first pole retainer that includes a first pole hook defining a first hook recess, and the lamination retainer is further defined as a first lamination retainer including a first lamination hook, wherein the first pole shoe further includes a second pole retainer that includes a second pole hook defining a second hook recess, and wherein the lamination stack further includes a second lamination retainer that includes a second lamination hook that at least partially extends into the second hook recess defined by the second pole hook to hold the first pole shoe to the lamination stack.

16. The rotor assembly according to claim 15, wherein the first pole hook has a first hook end, and the second pole hook has a second hook end, and wherein the first hook end and the second hook end extend toward each other.

17. The rotor assembly according to claim 1, wherein the lamination stack extends along the axis between a first lamination stack end and a second lamination stack end, wherein the rotor assembly further includes a first end cap adjacent the first lamination stack end and a second end cap adjacent the second lamination stack end, and wherein the first end cap and the second end cap are integral with the first spacer.

18. The rotor assembly according to claim 17, wherein the lamination stack defines a plurality of channels between the first lamination stack end and the second lamination stack end, wherein the rotor assembly further includes a plurality of rods disposed in the plurality of channels, and wherein the plurality of rods are integral with the first end cap and the second end cap.

19. A motor, comprising: a stator extending along an axis and defining an interior of the stator; and the rotor assembly according to claim 1 disposed in the interior of the stator of the stator.

20. An electric drive unit, comprising: The electric motor according to claim 19, and a gear reduction mechanism, which is coupled to the shaft and configured to adjust the torque received from the shaft.

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