ROTOR ARRANGEMENT

Abstract

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

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Non-Provisional Patent Application No. 17 / 957,065, filed September 30, 2022, the contents of which are hereby incorporated by reference in their entirety. BACKGROUND OF THE INVENTION 1. Field of the Invention

[0002] The invention relates generally to a rotor assembly for an electric motor and to an electric motor comprising the rotor assembly. 2. Description of related technology

[0003] Electric motors include a rotor assembly and a stator disposed around the rotor assembly. Rotor assemblies typically include a shaft, a lamination stack disposed around the shaft, and a plurality of pole pieces radially spaced from the lamination stack. Permanent magnets are typically embedded in the rotor assembly, usually between the lamination stack and the plurality of pole pieces, and generate magnetic flux. Stators include coil windings, and energization of the coil windings in the stator generates magnetic flux, which interacts with the magnetic flux generated by the permanent magnets to exert a force that causes the rotor assembly to rotate.

[0004] Typically, the lamination stack and the multiple pole pieces are physically connected to each other via multiple bridges, forming what is known as a bridge rotor assembly. Each bridge is unitary with both the lamination stack and one of the multiple pole pieces and is typically constructed of the same material as the lamination stack and the multiple pole pieces. The bridge prevents the multiple pole pieces from moving away from the lamination stack due to centrifugal forces exerted on the pole pieces during rotation of the rotor assembly.

[0005] However, the magnetic flux generated by the permanent magnets is disturbed or strayed by the bridge, so that some of the magnetic flux is directed to the lamination stack, connecting the north and south poles of each permanent magnet. Stray magnetic flux limits the amount of magnetic flux from the permanent magnets available to interact with the magnetic flux generated by the stator coil windings, thereby reducing the force exerted on the rotor assembly and thus reducing the efficiency of the electric motor. Magnetic flux straying occurs until the bridge reaches magnetic saturation. To minimize stray flux through the bridge, the bridge is typically constructed as thin as possible so that magnetic saturation in the lamination stack is quickly reached, thus reducing the stray flux from the permanent magnets.However, the centrifugal forces exerted on the multiple pole pieces by rotation of the rotor assembly are also exerted on the bridge. These centrifugal forces exerted on the bridge lead to stress concentration on the bridge and a risk of structural failure of the bridge, especially if the bridge is designed to be as thin as possible.

[0006] Thus, there remains a need to provide an improved rotor assembly for an electric motor. SUMMARY OF THE INVENTION AND ADVANTAGES

[0007] A rotor assembly for an electric motor is disclosed. The rotor assembly includes a shaft extending along and rotatable about an axis. The rotor assembly also includes a lamination stack coupled to the shaft, a plurality of magnets including a first magnet coupled to the lamination stack, and a plurality of pole pieces spaced radially outward from the shaft. Each pole piece of the plurality of pole pieces is separate from the lamination stack. The plurality of pole pieces includes a first pole piece, and the first magnet is disposed between the lamination stack and the first pole piece. The rotor assembly further includes a plurality of spacers including a first spacer disposed between the first pole piece and the lamination stack for reducing leakage flux of the first magnet.

[0008] The first spacer prevents disturbance or straying of the magnetic flux of the first magnet. This ensures that the magnetic flux of the first magnet is available to efficiently exert a force on the rotor assembly to rotate the rotor assembly. Each pole piece of the plurality of pole pieces is separate from the lamination stack, forming a bridgeless arrangement of the pole pieces and the lamination stack. As a result, the centrifugal forces exerted on the plurality of pole pieces by rotation of the rotor assembly are not also exerted on a bridge connecting the plurality of pole pieces and the lamination stack. Thus, the bridgeless arrangement of the pole pieces and the lamination stack eliminates concerns about centrifugal forces exerting a force on any bridge, resulting in stress concentration on any bridge and potentially leading to structural failure of any bridge. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Further advantages of the present invention will become readily apparent as the invention becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings, in which: Fig. 1 is a perspective view of the rotor assembly according to the invention; Fig. 2A is a cross-sectional view of an embodiment of the rotor assembly, the rotor assembly including a lamination stack, a plurality of pole pieces, a plurality of magnets, and a plurality of spacers; Fig. 2B an exploded view of Fig. 2A; Fig. 3 a cross-sectional view of another embodiment of the rotor assembly; Fig. 4 is a perspective view of an electric motor including the rotor assembly; and Fig. 5 is a perspective view, partly in phantom, of an electric drive unit comprising the electric motor of Fig. 4 includes. DETAILED DESCRIPTION OF THE INVENTION

[0010] With reference to the figures, in which like numerals indicate like parts throughout the several views, in Fig. 1-5, a rotor assembly 10 for an electric motor 12 is shown. The rotor assembly 10 includes a shaft 14 extending along and rotatable about an axis A1. The rotor assembly 10 also includes a lamination stack 16 coupled to the shaft 14, a plurality of magnets 18 including a first magnet 20 coupled to the lamination stack 16, and a plurality of pole pieces 24 spaced radially outward from the shaft 14. Although not required, the plurality of magnets 18 may also include a second magnet 22 coupled to the lamination stack 16. Each pole piece of the plurality of pole pieces 24 is separate from the lamination stack 16. It should be understood that the plurality of pole pieces 24 may be referred to as a plurality of pole pieces. The plurality of pole pieces 24 include a first pole piece 26, and the first magnet 20 is disposed between the laminated core 16 and the first pole piece 26.In the embodiments with the second magnet 22, the second magnet 22 is disposed between the lamination stack 16 and the first pole piece 26. The rotor assembly 10 further includes a plurality of spacers 28, including a first spacer 30 disposed between the first pole piece 26 and the lamination stack 16 to reduce stray flux of the first magnet 20.

[0011] The first spacer 30 prevents disturbance or straying of the magnetic flux of the first magnet 20. This ensures that the magnetic flux of the first magnet 20 is available to efficiently exert a force on the rotor assembly 10 to rotate the rotor assembly 10. Each pole piece of the plurality of pole pieces 24 is separate from the lamination stack 16. In other words, each pole piece 24 of the plurality of pole pieces 24 is a separate component from the lamination stack 16. This forms a bridgeless arrangement of the pole pieces 24 and the lamination stack 16. In other words, in the bridgeless arrangement, the pole pieces 24 and the lamination stack 16 are not connected to one another by a bridge material. As a result, the centrifugal forces exerted on the plurality of pole pieces 24 by rotation of the rotor assembly 10 are not also exerted on a bridge connecting the plurality of pole pieces 24 and the lamination stack 16.Thus, the bridgeless arrangement of the pole pieces 24 and the lamination stack 16 eliminates concerns that centrifugal forces will exert a force on any bridge, resulting in stress concentration on any bridge and potentially leading to structural failure of any bridge.

[0012] Although the advantages of the first spacer 30 have been described with reference to the first pole piece 26, the first magnet 20, optionally the second magnet 22, and the lamination stack 16, it should be understood that these advantages apply equally to all other spacers 28 of the plurality of spacers 28, all other pole pieces 24 of the plurality of pole pieces 24, all other magnets 18 of the plurality of magnets 18, and the lamination stack 16. Each spacer 28 and each pole piece 24 may have the same properties as the first spacer 30 and the first pole piece 26 described herein. More specifically, the plurality of spacers 28 may prevent interference or straying of the magnetic flux between the plurality of pole pieces 24 and the lamination stack 16. This ensures that the magnetic flux is available to efficiently apply a force to the rotor assembly 10 to rotate the rotor assembly 10.

[0013] The laminated core 16 may be formed from multiple laminations, which are secured together by interlacing, welding, clamping, and / or bonding, in non-limiting examples. To improve the manufacturability of the laminated core 16, each lamination of the laminated core 16 may correspond to any other lamination in the laminated core 16.

[0014] Each of the plurality of magnets 18, including the first magnet 20 and the second magnet 22, may be a permanent magnet. The first magnet 20 and the second magnet 22 may be configured to form a V-shape, as shown in Fig. 2A-3. Each pole piece of the plurality of pole pieces 24, including the first pole piece 26, may be composed of metals and / or metalloids, including, but not limited to, iron, cobalt, nickel, silicon, manganese, aluminum, steel, including electrical steel, and combinations thereof. The lamination stack 16 may be composed of metals and / or metalloids, including, but not limited to, iron, cobalt, nickel, silicon, manganese, aluminum, steel, including electrical steel, and combinations thereof. Although not required, it should be understood that the plurality of pole pieces 24 may be composed of the same metals and / or metalloids from which the lamination stack 16 is composed.

[0015] The first spacer 30 may comprise a polymeric material. In non-limiting examples, the polymeric material of the first spacer 30 may be a thermoplastic, a thermoset, or an elastomer. The polymeric material of the first spacer 30 may be an engineering plastic. More specifically, the polymeric material of the first spacer 30 may be a polyalkene or polyolefin, including copolymers and terpolymers thereof, such as polyethylene, including high-density polyethylene (HDPE) and low-density polyethylene (LDPE), polypropylene (PP), polybutylene and polybutylene terephthalate (PBTR), acrylates, such as acrylonitrile butadiene styrene (ABS) or polymethyl methacrylate (PMMA), polyoxymethylene (POM), or any acetal copolymers or acetal terpolymers, polyketones, polyether ketones, and / or polyarylether ketones, such asPolyetheretherketone (PEEK) and polyetherketoneketone (PEKK), polyetherimide (PEI), polyimides, polyvinyl chloride (PVC), polyphenylene sulfide (PPS), polyphenylene oxide (PPO), polysulfone (PSU), polytetrafluoroethylene (PTFE), polyamides, including polyphthalamide, polycarbonates, urethanes, epoxies, and thermoplastic elastomers (TPE). Although not required, the polymer material of the first spacer 30 can be molded, such as overmolded, overmolded, injection molded, compression molded, and thermoformed.

[0016] The first spacer 30 may also comprise a first composition comprising any of the polymeric materials specified herein, as well as 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 fibers, carbon fibers, aramid fibers, basalt fibers, and paper fibers, stabilizers, including oxidation stabilizers, ultraviolet (UV) stabilizers, heat stabilizers, light absorbers, strengtheners, acid scavengers, metal deactivators, and flame retardants, including, for example, aluminum hydroxide, phosphorus compounds, and brominated compounds.

[0017] The first spacer 30 may extend at least to the first magnet 20 and may extend to at least the second magnet 22. The first spacer 30 may also be disposed between the first magnet 20 and the second magnet 22. It is understood that the first spacer 30 may extend radially inward toward the first magnet 20 and may also extend past the first magnet 20, optionally enclosing at least a portion of the first magnet 20, and then be disposed between the first magnet 20 and the second magnet 22. Likewise, it is understood that the first spacer 30 may extend radially inward toward the second magnet 22 and may also extend past the second magnet 22, optionally enclosing at least a portion of the second magnet 22, and then be disposed between the first magnet 20 and the second magnet 22.

[0018] As in Fig. 2 and Fig. 3, the laminated core 16 may include a laminated core retainer 32, and the first pole piece 26 may include a pole retainer 34 configured to mechanically cooperate with the laminated core retainer 32 of the laminated core 16 to retain the first pole piece 26 relative to the laminated core 16. The mechanical cooperation of the laminated core retainer 32 of the laminated core 16 and the pole retainer 34 of the first pole piece 26 limits movement of the first pole piece 26 relative to the laminated core 16. More specifically, the mechanical cooperation of the laminated core retainer 32 of the laminated core 16 and the pole retainer 34 of the first pole piece 26 limits radial movement of the first pole piece 26 relative to the laminated core 16.

[0019] Furthermore, the mechanical interaction between the pole holding device 34 and the lamination holding device 32 need not require direct contact between the pole holding device 34 and the lamination holding device 32. The pole holding device 34 and the lamination holding device 32 may not be in contact with each other. In one non-limiting example, there may be an intermediate component disposed between the pole holding device 34 and the lamination holding device 32 that still allows the pole holding device 34 to mechanically interact with the lamination holding device 32 to hold the first pole piece 26 relative to the lamination stack 16. More specifically, the first spacer 30 may be disposed between the lamination holding device 32 of the lamination stack 16 and the pole holding device 34 of the first pole piece 26.By disposing the first spacer 30 between the lamination fixture 32 and the pole fixture 34, the strength of the mechanical interaction between the pole fixture 34 and the lamination fixture 32 is increased by reducing or eliminating any gaps or voids between the pole fixture 34 and the lamination fixture 32.

[0020] The lamination fixture 32 has a lamination end 36, and the pole fixture 34 has a pole fixture end 38. The pole fixture end 38 may be disposed radially inwardly of the lamination end 36. The lamination end 36 may be the end point of the lamination fixture 32, and the pole fixture end 38 may be the end point of the pole fixture 34. By disposing the pole fixture end 38 radially inwardly of the lamination end 36, the movement of the first pole piece 26 with respect to the lamination stack 16 is limited. More specifically, when the first pole piece 26 is moved radially away from the lamination stack 16, the pole fixture end 38 may either directly contact the lamination end 36 or may contact an intermediate component, such as a lamination sleeve. B. touch the first spacer 30 which touches the sheet metal holding device end 36.As a result, the pole holder end 38 and the lamination holder end 36 prevent the first pole piece 26 from moving radially away from the lamination stack 16.

[0021] The first pole piece 26 has a first circumferential end 42 and a second circumferential end 44 circumferentially spaced from the first circumferential end 42. The first pole piece 26 also has a pole outer surface 40 facing away from the axis A1 and extending between the first and second circumferential ends 42, 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 understood 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 between both the first circumferential end 42 and the lamination stack 16 and the second circumferential end 44 and the lamination stack 16.Furthermore, although not required, the first spacer 30 may be integrated into a sleeve having an outer sleeve body extending around the pole outer surfaces of all of the plurality of pole pieces 24, and the first spacer 30 may extend radially inward from the outer sleeve body of the sleeve.

[0022] In some embodiments, the lamination holder 32 and the pole holder 34 are disposed between the first magnet 20 and the second magnet 22. In embodiments where the lamination holder 32 and the pole holder 34 are disposed between the first magnet 20 and the second magnet 22, the mechanical interaction that holds the first pole piece 26 to the lamination stack 16 occurs approximately equidistant between the first circumferential end 42 of the first pole piece 26 and the second circumferential end 44 of the first pole piece 26.Thus, the mechanical interaction that holds the first pole piece 26 to the lamination stack 16 occurs at the approximate circumferential center of gravity of the first pole piece 26, thereby preventing either the first circumferential end 42 of the first pole piece 26 or the second circumferential end 44 of the first pole piece 26 from moving farther than the other circumferential end—the first or second 42, 44—from the lamination stack 16.

[0023] In further embodiments, the pole holding device 34 is disposed at the first circumferential end 42 of the first pole piece 26. It should be understood that the pole holding device 34 may also be disposed at the second circumferential end 44 of the first pole piece 26. The pole holding device 34 may also be defined as a first pole holding device 46, the lamination holding device 32 may also be defined as a first lamination holding device 48, and the lamination stack 16 may further include a second lamination holding device 50, and the first pole piece 26 may further include a second pole holding device 52. The second pole holding device 52 of the first pole piece 26 may be disposed at the second circumferential end 44 of the first pole piece 26, and the second pole holding device 52 may be configured to mechanically cooperate with the second lamination holding device 50 of the lamination stack 16 to hold the first pole piece 26 relative to the lamination stack 16.

[0024] In the embodiments where the first pole retaining device 46 is disposed at the first circumferential end 42 of the first pole piece 26 and the second pole retaining device 52 is disposed at the second circumferential end 44 of the first pole piece 26, the mechanical engagement that holds the first pole piece 26 to the lamination stack 16 occurs at both the first circumferential end 42 of the first pole piece 26 and the second circumferential end 44 of the first pole piece 26. Two separate and circumferentially spaced locations of mechanical engagement enhance the retention of the first pole piece 26 to the lamination stack 16. More specifically, two separate and circumferentially spaced locations of mechanical engagement limit the relative pivoting amount of the first pole piece 26 with respect to the lamination stack 16.

[0025] In one embodiment, the blank holder 32 or the pole holder 34 has a generally C-shaped configuration 54 defining a channel 56, and the other of the blank holder 32 or the pole holder 34 has a generally T-shaped configuration 58 partially disposed within the channel 56. In other words, the blank holder 32 may be configured as shown in Fig. 2A and Fig. 2B may have the generally C-shaped configuration 54 and the pole holding device 34 may have the generally T-shaped configuration 58, or the sheet holding device 32 may have the generally T-shaped configuration 58 and the pole holding device 34 may have the generally C-shaped configuration 54.

[0026] In a further embodiment as shown in Fig. 2A and Fig. 2B, the pole retainer 34 includes a pole hook 60 defining a hook recess 62, and the lamination retainer 32 includes a lamination hook 64 extending at least partially into the hook recess 62 defined by the pole hook 60 to retain the first pole piece 26 to the lamination stack 16. In embodiments where the rotor assembly 10 includes first and second pole retainers 46, 52 and first and second lamination retainers 48, 50, the first pole retainer 46 may include a first pole hook 66 defining 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 defining a second hook recess 74, and the second lamination retainer 50 may include a second lamination hook 76 extending at least partially into the second hook recess 74 defined by the second pole hook 72 to retain the first pole piece 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 strength of the retention of the first pole piece 26 to the lamination stack 16. It is understood that the first hook end 78 may be the end point of the first pole hook 66 and the second hook end 80 may be the end point of the second pole hook 72.

[0027] As in Fig. 3, the sheet metal holding device 32 and / or the pole holding device 34 may have a generally mushroom-shaped configuration 82, and the other of the sheet metal holding device 32 and the pole holding device 34 may form a complementary support device recess 84. In other words, the sheet metal holding device 32 may be configured as shown in Fig. 3 may have the generally mushroom-shaped configuration 82, and the pole retainer 34 may form the retainer recess 84. Alternatively, the lamination retainer 32 may form the retainer recess 84, and the pole retainer 34 may have the generally mushroom-shaped configuration 82. The generally mushroom-shaped configuration 82 of either the lamination retainer 32 or the pole retainer 34 may contact the first magnet 20 and the second magnet 22, either directly or through an intermediate component, such as the first spacer 30, to assist in retaining the first and second magnets 20, 22. Further, the first spacer 30 may be disposed in the retainer recess 84 to further retain the first pole piece 26 relative to the lamination stack 16.

[0028] It should be understood that the rotor assembly 10 may further include a third lamination fixture 86 and a third pole fixture 88. The third lamination fixture 86 may have any of the features of any of the lamination fixtures described herein, and the third pole fixture 88 may have any of the features of any of the pole fixtures described herein.

[0029] The lamination stack 16 extends along the 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 being expelled from between the plurality of pole pieces 24 and the lamination stack 16. The first end cap 94 and the second end cap 96 may be unitary 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 integral with each other, i.e., one-piece.

[0030] 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 conduct lubricant through the rotor assembly 10 for lubricating and / or cooling the rotor assembly 10. The rotor assembly 10 may include a plurality of bars 100 disposed in the plurality of channels 98, as shown in Fig. 2 and Fig. 3. It is understood that the plurality of rods 100 may be disposed within the plurality of channels 98, and the lamination stack 16 may further define channels 98 configured to conduct lubricant through the rotor assembly 10 for lubricating and / or cooling the rotor assembly 10. Alternatively, it is also understood that a rod of the plurality of rods 100 may correspond to and be disposed within a channel of the plurality of channels 98. The plurality of rods 100 may be unitary 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 integral with each other, i.e., one-piece. The plurality of rods 100, the first end cap 94, and the second end cap 96 may be integrally formed with each other.

[0031] The first end cap 94, the second end cap 96, and / or the plurality of rods 100 may comprise a polymeric material. In embodiments where the first spacer 30 comprises a polymeric material and the first end cap 94, the second end cap 96, and / or the plurality of rods comprise a polymeric material, it should be understood that these polymeric materials may be the same or different from one another. 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.

[0032] 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 a polyalkene or polyolefin, including copolymers and terpolymers thereof, such as polyethylene, including high density polyethylene (HDPE) and low density polyethylene (LDPE), polypropylene (PP), polybutylene and polybutylene terephthalate (PBTR), acrylates, such as acrylonitrile butadiene styrene (ABS) or polymethyl methacrylate (PMMA), polyoxymethylene (POM) or any acetal copolymers or acetal terpolymers, polyketones, polyether ketones and / or polyarylether ketones, such as polyvinyl alcohol (PVAR), polyvinyl chloride (PVLC), polyvinylpyrrolidone (PVLC), polyvinyl alcohol (PVLC), polyvinylpyrrolidone ... and / or vinylpyrrolidone. E.g. polyetheretherketone (PEEK) and polyetherketoneketone (PEKK), polyetherimide (PEI), polyimides, polyvinyl chloride (PVC), polyphenylene sulfide (PPS), polyphenylene oxide (PPO), polysulphone (PSU), polytetrafluoroethylene (PTFE), polyamides, including polyphthalamide, polycarbonates, urethanes, epoxies and thermoplastic elastomers (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 may be formed, such as overmolded, overmolded, injection molded, compression molded, and thermoformed.

[0033] More specifically, the plurality of rods 100 may be non-magnetic, may be electrically conductive, and may further comprise carbon fiber. It is understood that the first end cap 94 and / or the second end cap 96 may also be non-magnetic, may be electrically conductive, and may further comprise carbon fiber. The first end cap 94 and / or the second end cap 96 may comprise a second composition. The second composition of the first end cap 94 and / or the second end cap 96 may be the same as or different from the first composition of the first spacer 30. It is also understood that the plurality of rods may comprise the second composition, such that the first end cap 94 and / or the second end cap 96 and / or the plurality of rods 100 may comprise the second composition.

[0034] The second composition of the first end cap 94, the second end cap 96, and / or the plurality of rods 100 may comprise any of the polymeric materials specified herein, as well as 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 fibers, carbon fibers, aramid fibers, basalt fibers, and paper fibers, stabilizers, including oxidation stabilizers, ultraviolet (UV) stabilizers, heat stabilizers, light absorbers, strengtheners, acid scavengers, metal deactivators, and flame retardants, including aluminum hydroxide, phosphorus compounds, and brominated compounds. In one embodiment, the second composition comprises a thermoplastic and a filler encapsulated by the thermoplastic. In this embodiment, the filler may comprise carbon fiber.

[0035] As described herein, the first spacer 30 may be formed, such as overmolded, overmolded, injection molded, compression molded, and thermoformed. It should be understood that the first end cap 94, the second end cap 96, and / or the plurality of rods 100 may also be formed, such as overmolded, overmolded, 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 understood that the first end cap 94, the second end cap 96, and / or 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.

[0036] The plurality of pole pieces 24 may include two pole pieces, three pole pieces, four pole pieces, five pole pieces, six pole pieces, seven pole pieces, eight pole pieces, nine pole pieces, ten pole pieces, or more than ten pole pieces. 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. In association with each pole piece 24, the plurality of magnets 18 may be a single magnet or may be arrays having multiple blocking pole magnets, including, but not limited to, V-shaped arrays, double V-shaped arrays, U-shaped arrays, and delta-shaped 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 piece 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 the multiple 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.

[0037] The rotor assembly 10 may be configured to rotate at a speed greater than 20,000 revolutions per minute (RPM). In non-limiting examples, the rotor assembly 10 may be configured to rotate at about 20,000 RPM to about 50,000 RPM, about 20,000 RPM to about 40,000 RPM, about 20,000 RPM to about 30,000 RPM, and about 20,000 RPM to about 25,000 RPM. The lamination retainer 32 and the pole retainer 34 may retain the plurality of pole pieces 24 to the lamination stack 16 at speeds of 20,000 RPM and above. Thus, the rotor assembly 10 may be considered a high-speed rotor assembly.

[0038] The rotor assembly 10 can be incorporated into an electric motor 12 as shown in Fig. 4. The electric motor 12 includes a stator 102 that extends along the 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 may be disposed entirely within the stator interior 104 of the stator 102, or the rotor assembly 10 may be disposed only partially within the stator interior 104 of the stator 102. The stator 102 may include coil windings 106 that can be energized to generate the magnetic flux described herein. The plurality of spacers 28 increases the efficiency of the electric motor 12 by reducing the amount of stray magnetic flux, thereby increasing the efficiency of the force exerted to rotate the rotor assembly 10 with respect to the required amount of magnetic flux to be generated.

[0039] Furthermore, a gap may be defined between the pole outer surface 40 and the stator interior 104 of the stator 102. It is advantageous to reduce this gap as much as possible to minimize losses due to air friction and also to increase the torque at the rotor assembly 10. It will be appreciated that the plurality of spacers 28 can be manufactured to relatively high tolerances, thereby allowing a relatively small gap to be defined between the pole outer surface 40 and the stator interior 104 of the stator 102, thus also minimizing losses due to air friction. The gap may even be as small as 0.2 millimeters and may scale with the tolerances of the diameter of the rotor assembly 10 and / or scale with the speed of the rotor assembly 10. The gap may also scale on the order of approximately 0.1% of the diameter of the stator 102.

[0040] The electric motor 12 can be integrated into an electric drive unit 108 as shown in Fig. 5. 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 may be configured to modulate torque received from the shaft 14. The gear reduction mechanism 110 may be a planetary gear set, a reduction gear, such as a two-stage reduction gear, a worm gear reduction gear, a helical gear reduction gear, a spur gear reduction gear, a hypoid gear reduction gear, a bevel gear reduction gear, a pinion gear reduction gear, a cycloidal gear reduction gear, a magnetic reduction gear, an orthogonal reduction gear, a bent-axis reduction gear, a parallel-shaft reduction gear, a coaxial reduction gear, and combinations thereof.

[0041] The invention has been described in an illustrative manner; and it is to be understood that the terminology used is intended to be 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 invention may be practiced otherwise than as specifically described. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] US 17 / 957,065

[0001]

Claims

[1] A rotor assembly for an electric motor, the rotor assembly comprising: a shaft extending along an axis and rotatable about it; a laminated core coupled to the shaft; a plurality of magnets including a first magnet coupled to the laminated core; a plurality of pole pieces, each pole piece of the plurality of pole pieces being spaced radially outwardly from the shaft and separate from the lamination stack, the plurality of pole pieces including a first pole piece and the first magnet being disposed between the lamination stack and the first pole piece; and a plurality of spacers comprising a first spacer disposed between the first pole piece and the lamination stack for reducing leakage flux of the first magnet. [2] The rotor assembly of claim 1, wherein the first spacer comprises a polymer material. [3] A rotor assembly according to claim 2, wherein the polymer material is molded. [4] The rotor assembly of claim 1, wherein the lamination stack includes a lamination retainer and the first pole piece includes a pole retainer configured to mechanically cooperate with the lamination retainer to retain the first pole piece relative to the lamination stack. [5] The rotor assembly of claim 4, wherein the pole holding device and the lamination holding device are not in contact with each other. [6] The rotor assembly of claim 4, wherein the first spacer is disposed between the lamination holding device and the pole holding device. [7] The rotor assembly of claim 4, wherein the lamination fixture has a lamination fixture end and the pole fixture has a pole fixture end disposed radially inwardly of the lamination fixture end. [8] The rotor assembly of claim 1, wherein the plurality of magnets further comprises a second magnet disposed between the first pole piece and the lamination stack, and wherein the first spacer is disposed between the first magnet and the second magnet. [9] The rotor assembly of claim 4, wherein the plurality of magnets further comprises a second magnet disposed between the first pole piece and the lamination stack, and wherein the lamination holding device and / or the pole holding device are disposed between the first magnet and the second magnet. [10] The rotor assembly of claim 1, wherein the first pole piece has a first circumferential end and a second circumferential end circumferentially spaced from the first circumferential end, and has a pole outer surface facing away from the axis and extending between the first and second circumferential ends, and wherein the first spacer is circumferentially disposed between the first circumferential end and the lamination stack. [11] The rotor assembly of claim 10, wherein the pole holding device is disposed at the first circumferential end of the first pole piece. [12] The rotor assembly of claim 11, wherein the pole holding device is further defined as a first pole holding device, wherein the lamination holding device is further defined as a first lamination holding device, wherein the lamination stack further comprises a second lamination holding device, wherein the first pole piece further comprises a second pole holding device disposed at the second circumferential end of the first pole piece, and wherein the second pole holding device is configured to mechanically cooperate with the second lamination holding device of the lamination stack to hold the first pole piece relative to the lamination stack. [13] The rotor assembly of claim 4, wherein one of the lamination fixture and the pole fixture has a generally C-shaped configuration defining a channel, and the other of the lamination fixture and the pole fixture has a generally T-shaped configuration partially disposed within the channel. [14] The rotor assembly of claim 4, wherein the pole holding device comprises a pole hook defining a hook recess, and wherein the lamination holding device comprises a lamination hook extending at least partially into the hook recess defined by the pole hook for holding the first pole piece to the lamination stack. [15] The rotor assembly of claim 14, wherein the pole holding device is further defined as a first pole holding device comprising a first pole hook defining a first hook recess, and the lamination holding device is further defined as a first lamination holding device comprising a first lamination hook, wherein the first pole piece further comprises a second pole holding device comprising a second pole hook defining a second hook recess, and wherein the lamination stack further comprises a second lamination holding device comprising a second lamination hook extending at least partially into the second hook recess defined by the second pole hook for holding the first pole piece to the lamination stack. [16] The rotor assembly of 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 of claim 1, wherein the lamination stack extends along the axis between a first lamination stack end and a second lamination stack end, the rotor assembly further comprising 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 unitary with the first spacer. [18] The rotor assembly of claim 17, wherein the lamination stack defines a plurality of channels between the first lamination stack end and the second lamination stack end, the rotor assembly further comprising a plurality of bars disposed in the plurality of channels, and wherein the plurality of bars are unitary with the first end cap and the second end cap. [19] Electric motor comprising: a stator extending along an axis and defining a stator interior; and the rotor assembly of claim 1, which is arranged in the stator interior of the stator. [20] Electric drive unit comprising: the electric motor according to claim 19, and a gear reduction mechanism coupled to the shaft and configured to modulate torque received from the shaft.

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