Bridgeless and webless rotor assembly using polymer composites

Abstract

The present invention relates to bridgeless and webless type rotor assemblies using polymer composites. A rotor assembly for a permanent magnet motor includes a first assembly including a first plurality of laminations and a second assembly including a second plurality of laminations. The first assembly is located radially inward of the second assembly. The first assembly and the second assembly define a first opening therebetween. A first permanent magnet and a second permanent magnet are located in the first opening. A polymer material surrounds the first permanent magnet and the second permanent magnet in the first opening. An outer layer surrounds the rotor assembly.

Description

TECHNICAL FIELD

[0001] The information provided in this section is for the purpose of generally presenting the context of the disclosure. The work of the inventors currently named in this section relates to developments that were made over time that were not necessarily a part of a particular prior to the filing date of this disclosure, and which might not necessarily be regarded as prior art by those skilled in the art. Their work was developed while studying and working except that described in this section as being by, for, and / or with others.

[0002] The present disclosure relates to electric machines, and more particularly to electric machines including a bridgeless and webless rotor assembly. BACKGROUND

[0003] Electric vehicles, such as battery electric vehicles (BEVs), fuel cell vehicles, and hybrid vehicles, include one or more electric machines. During operation, the electric machines operate as motors to propel the vehicle. The battery system can be recharged using utility power, by another vehicle, during regenerative braking, and / or by an internal combustion engine (for hybrid vehicle applications). During operation, power generated during braking of the vehicle can be used to recharge the vehicle's battery system. Instead of using mechanical brakes, the electric machines operate as generators to brake the vehicle and generate electrical power used to recharge the battery system.

[0004] The electric machines include a rotor assembly having permanent magnets. During operation as a motor to generate torque or as a generator to generate electrical power, the rotor assembly rotates within a stator. Web and bridge structures are typically used for structural support in the magnetic flux path. As can be appreciated, the rotor assembly needs to be robust as it is stressed during operation by mechanical, electrical, and magnetic forces. SUMMARY

[0005] A rotor assembly for a permanent magnet motor includes a first assembly including a first plurality of laminations and a second assembly including a second plurality of laminations. The first assembly is radially inward of the second assembly. The first assembly and the second assembly define a first opening therebetween. A first permanent magnet and a second permanent magnet are located in the first opening. A polymer material surrounds the first permanent magnet and the second permanent magnet in the first opening. An outer layer surrounds the rotor assembly.

[0006] In other features, the third assembly includes a third plurality of laminations, wherein the second assembly and the third assembly define a second opening therebetween. A third permanent magnet and a fourth permanent magnet are located in the second opening. A polymer material surrounds the third permanent magnet and the fourth permanent magnet located in the second opening.

[0007] In other features, the rotor assembly does not include a web, and wherein the rotor assembly does not include a bridge. The outer layer is made of carbon fiber. The first opening is "V" shaped and extends into the outer layer. The polymeric material includes a resin. The resin is selected from the group consisting of: epoxy, polyurethane, polyester, bismaleimide, acrylic, cyanate ester, polyimide, phenolic, benzoxazine, and vinyl ester. The resin further includes a discontinuous filler material. The discontinuous filler material includes one or more materials selected from the group consisting of: silica, alumina, mineral, boron nitride, aluminum nitride, silicon nitride, basalt, and glass fiber.

[0008] In other features, the first assembly includes: a first sub-assembly including a first plurality of laminations of the first plurality of laminations; and a second sub-assembly including a second plurality of laminations of the first plurality of laminations. The first sub-assembly and the second sub-assembly define a side-facing surface that includes a circumferential segment and other segments, and wherein the circumferential segment defines a larger gap than the other segments. The side-facing surface of the first sub-assembly and the second sub-assembly define a stair-step pattern.

[0009] In other features, the first sub-assembly and the second sub-assembly include a side-facing surface that includes a circumferential segment and a diagonal segment, and wherein the circumferential segment defines a larger gap than the diagonal segment. The first sub-assembly and the second sub-assembly include a side-facing surface that includes a circumferential segment, a diagonal segment, and a preserved segment, and wherein the circumferential segment defines a larger gap than the diagonal segment. At least one of the first sub-assembly and the second sub-assembly defines a female opening, and the other of the first sub-assembly and the second sub-assembly defines a male protrusion that is received within the female opening.

[0010] In other features, the male protrusion is "T" shaped and includes a first arm and a second arm. First and second gaps are defined between the first and second arms and the female opening. The polymeric material is located in the first and second gaps.

[0011] A rotor assembly for a permanent magnet motor includes a first assembly including a first plurality of laminations. A second assembly includes a second plurality of laminations, wherein the first assembly and the second assembly define a first opening therebetween. A third assembly includes a third plurality of laminations. The second assembly and the third assembly define a flux barrier therebetween. A first permanent magnet and a second permanent magnet are located in the first opening. A polymeric material surrounds the first permanent magnet and the second permanent magnet in the first opening. A carbon fiber outer layer surrounds the rotor assembly. The rotor assembly does not include a web, and wherein the rotor assembly does not include a bridge.

[0012] In other features, the flux barrier includes a polymeric material mixed with magnetic particles.

[0013] In other features, the fourth assembly includes a fourth plurality of laminations and a third permanent magnet and a fourth permanent magnet located in the second opening. A polymer material surrounds the third permanent magnet and the fourth permanent magnet located in the second opening. The third assembly and the fourth assembly define the second opening therebetween.

[0014] In other features, the first opening, the flux barrier, and the second opening are "V" shaped and extend to an outer layer of carbon fiber.

[0015] In other features, the polymer material includes an epoxy resin and the discontinuous filler material includes one or more materials selected from the group consisting of: silicon dioxide, aluminum oxide, minerals, boron nitride, aluminum nitride, silicon nitride, basalt, and glass fibers.

[0016] 1. A rotor assembly for a permanent magnet motor, the rotor assembly comprising:

[0017] a first assembly including a first plurality of laminations;

[0018] a second assembly including a second plurality of laminations,

[0019] wherein the first assembly is radially inward of the second assembly, and wherein the first assembly and the second assembly define a first opening therebetween;

[0020] a first permanent magnet and a second permanent magnet located in the first opening;

[0021] a polymer material surrounding the first permanent magnet and the second permanent magnet in the first opening; and

[0022] an outer layer surrounding the rotor assembly.

[0023] 2. The rotor assembly of Aspect 1, further comprising:

[0024] a third assembly including a third plurality of laminations, wherein the second assembly and the third assembly define a second opening therebetween; and

[0025] a third permanent magnet and a fourth permanent magnet located in the second opening,

[0026] wherein the polymer material surrounds the third permanent magnet and the fourth permanent magnet located in the second opening.

[0027] 3. The rotor assembly of Aspect 1, wherein the rotor assembly does not include a web, and wherein the rotor assembly does not include a bridge, and wherein the outer layer is made of carbon fiber.

[0028] 4. The rotor assembly of aspect 1, wherein the first opening is "V" shaped and extends to the outer layer.

[0029] 5. The rotor assembly of aspect 1, wherein the polymeric material comprises a resin.

[0030] 6. The rotor assembly of aspect 5, wherein the resin is selected from the group consisting of: epoxy, polyurethane, polyester, bismaleimide, acrylic, cyanate ester, polyimide, phenolic, benzoxazine, and vinyl ester.

[0031] 7. The rotor assembly of aspect 5, wherein the resin further comprises a discontinuous filler material.

[0032] 8. The rotor assembly of aspect 7, wherein the discontinuous filler material comprises one or more materials selected from the group consisting of: silica, alumina, mineral, boron nitride, aluminum nitride, silicon nitride, basalt, and glass fiber.

[0033] 9. The rotor assembly of aspect 2, wherein the first assembly comprises: a first sub-assembly comprising a first plurality of laminations of the first plurality of laminations; and a second sub-assembly comprising a second plurality of laminations of the first plurality of laminations.

[0034] 10. The rotor assembly of aspect 9, wherein the first sub-assembly and the second sub-assembly define a side-facing surface comprising circumferential segments and other segments, and wherein the circumferential segments define a greater gap than the other segments.

[0035] 11. The rotor assembly of aspect 10, wherein the side-facing surfaces of the first sub-assembly and the second sub-assembly define a stepped pattern.

[0036] 12. The rotor assembly of aspect 10, wherein the first sub-assembly and the second sub-assembly comprise a side-facing surface comprising circumferential segments and diagonal segments, and wherein the circumferential segments define a greater gap than the diagonal segments.

[0037] 13. The rotor assembly of aspect 9, wherein the first sub-assembly and the second sub-assembly comprise a side-facing surface comprising circumferential segments, diagonal segments, and preserved segments, and wherein the circumferential segments define a greater gap than the diagonal segments.

[0038] 14. The rotor assembly of Scheme 9, wherein at least one of the first subassembly and the second subassembly defines a female opening and the other of the first subassembly and the second subassembly defines a male protrusion that is received within the female opening.

[0039] 15. The rotor assembly of Scheme 14, wherein the male protrusion is “T” shaped and includes a first arm and a second arm, and the rotor assembly further includes a first gap and a second gap defined between the first arm and the second arm and the female opening, and wherein the polymeric material is located in the first gap and the second gap.

[0040] 16. A rotor assembly for a permanent magnet motor, the rotor assembly comprising:

[0041] a first assembly including a first plurality of laminations;

[0042] a second assembly including a second plurality of laminations, wherein the first assembly and the second assembly define a first opening therebetween;

[0043] a third assembly including a third plurality of laminations, wherein the second assembly and the third assembly define a flux barrier therebetween;

[0044] a first permanent magnet and a second permanent magnet located in the first opening;

[0045] a polymeric material surrounding the first permanent magnet and the second permanent magnet in the first opening; and

[0046] a carbon fiber outer layer surrounding the rotor assembly,

[0047] wherein the rotor assembly does not include a web, and wherein the rotor assembly does not include a bridge.

[0048] 17. The rotor assembly of Scheme 16, wherein the flux barrier includes a polymeric material mixed with magnetic particles.

[0049] 18. The rotor assembly of Scheme 17, further comprising:

[0050] a fourth assembly including a fourth plurality of laminations; and

[0051] a third permanent magnet and a fourth permanent magnet located in the second opening,

[0052] wherein the polymeric material surrounds the third permanent magnet and the fourth permanent magnet located in the second opening, and wherein the third assembly and the fourth assembly define a second opening therebetween.

[0053] 19. The rotor assembly of Aspect 17, wherein the first opening, the flux barrier, and the second opening are "V" shaped and extend to the outer layer of carbon fiber.

[0054] 20. The rotor assembly of Aspect 16, wherein the polymeric material comprises an epoxy resin and the discontinuous filler material comprises one or more materials selected from the group consisting of: silica, alumina, mineral, boron nitride, aluminum nitride, silicon nitride, basalt, and glass fiber.

[0055] Further areas of applicability of the present disclosure will become apparent from the detailed description, claims and drawings. The detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. BRIEF DESCRIPTION OF DRAWINGS

[0056] The present disclosure will become more fully understood from the detailed description, the claims and the accompanying drawings, wherein:

[0057] Figure 1A is a side view of an example of a pole portion of a rotor assembly;

[0058] Figure 1B and Figure 1C is an example of a method for manufacturing a rotor assembly of Figure 1A ;

[0059] Figure 2A is a side view of an example of a rotor assembly according to the present disclosure;

[0060] Figure 2B is a side view of an example of a portion of a rotor assembly according to the present disclosure;

[0061] Figure 2C is an example of a method for manufacturing a rotor assembly of Figure 2A ;

[0062] Figures 3-6 is a cross-sectional view of an example layout of a stack of adjacent layers of a rotor assembly according to the present disclosure;

[0063] Figure 7 and Figure 8 are charts illustrating base torque and top speed power for different configurations of a rotor assembly;

[0064] Figures 9-12 is a side view of an additional example of a pole portion of a rotor assembly according to the present disclosure;

[0065] Figure 13 is a side view of an example of a pole portion of a rotor assembly according to the present disclosure; and

[0066] Figure 14 is according to the present disclosure Figure 13 a cross-sectional view of an example layout of a stack of adjacent layers of a rotor assembly.

[0067] In the drawings, reference numerals can be repeated among the figures for like and / or identical elements. DETAILED DESCRIPTION

[0068] A rotor assembly according to the present disclosure is characterized by the lack of webs or bridge structures that are typically used for structural support of the flux path. These webs / bridge structures are replaced by non-magnetic material, such as polymer, which results in higher performance of the electric machine.

[0069] In some examples, the rotor assembly includes a radially inner assembly having a first plurality of laminations, an intermediate assembly including a second plurality of laminations, and a radially outer assembly including a third plurality of laminations. Permanent magnets and a polymer material are located between the radially inner assembly, the intermediate assembly, and the radially outer assembly to hold the rotor assembly together. An outer ring made of carbon fiber or another material is disposed around an outer circumference of the rotor assembly to increase the strength of the rotor assembly.

[0070] In some examples, the polymer material is pressurized during processing to pre-stress the outer ring (and core / magnets). Permanent magnets are disposed between the radially inner assembly and the intermediate assembly and between the intermediate assembly and the radially outer assembly. The permanent magnets are in direct contact with the radially inner assembly, the intermediate assembly, and the radially outer assembly.

[0071] In some examples, an air gap between the rotor and the stator varies along the circumferential outer surface. The radially outer surface of the radially inner assembly is closer to the stator than the outer surfaces of the intermediate assembly and the radially outer assembly.

[0072] In other examples, the polymer is adhesively (chemically or mechanically) bonded to the surface of the laminations (e.g., electrical steel (e-steel) laminations) such that it is able to transfer a tensile force of at least 5 MPa while under tension.

[0073] In some examples, the radially inner assembly is divided into first and second sub-assemblies that are joined by a material such as polymer. The polymer layer thickness can vary to account for variations in the magnet and electrical steel surface location (within manufacturing tolerances).

[0074] In some examples, the interface between the first and second sub-assemblies has a staircase arrangement that allows close spacing of the radial faces of the sub-assemblies and greater spacing between the circumferential faces. In other features, the first and second sub-assemblies are interlocked together.

[0075] Reference is now made to Figure 1AFIG. 1 shows a portion of an example of a rotor assembly 10 without webs. The rotor assembly 10 includes a plurality of laminations 11 that define a first V-shaped opening 12 (a single first V-shaped opening is shown for one of the magnetic poles). In some examples, a protrusion 23 extends into the first V-shaped opening 12 to position permanent magnets 20 and 22. A bridge 13 is positioned across radially outer portions 14 and 16 of the first V-shaped opening 12. The permanent magnets 20 and 22 are located in the first V-shaped opening 12. There is no web located in a central portion 18 between the permanent magnets 20 and 22.

[0076] The plurality of laminations 11 also define a second V-shaped opening 32 (a single second V-shaped opening is shown for one of the magnetic poles). A bridge 33 is positioned across radially outer portions 34 and 36 of the second V-shaped opening 32. There is no web located in a central portion 36 between the permanent magnets 40 and 42. The permanent magnets 40 and 42 are located in the second V-shaped opening 32. There is no web located in a central portion 38 of the second V-shaped opening 32. The plurality of laminations 11 can include notches 46 and 48 on sides thereof.

[0077] A carbon fiber outer layer 50 has an interference fit onto the plurality of laminations 11 to strengthen the rotor assembly 10. The carbon fiber outer layer 50 creates tensile stress in the carbon fiber outer layer 50 and compressive stress in the laminations / polymer. This ensures that the deflection of the rotor assembly is low enough to avoid hitting the stator. The compressive stress in the laminations typically requires a web, magnet, or polymer to support the load.

[0078] In some examples, the permanent magnets typically have a 0.1 mm clearance with the openings in the laminations to allow for insertion. The addition of the carbon fiber outer layer 50 increases the effective air gap between the rotor and the stator. The removal of the webs is important to maintain performance. As will be described below, the removal of the bridges further improves performance.

[0079] Referring now to Figure 1B and Figure 1C , a method for manufacturing a rotor assembly is shown. In Figure 1B , the method 80 involves creating a carbon fiber sleeve and then press fitting a rotor into the carbon fiber sleeve. At 62, the method includes wrapping carbon fiber filaments around a mandrel in the shape of an outer surface of a rotor assembly. At 64, resin is applied to the carbon fiber filaments and then cured. At 66, the carbon fiber sleeve is removed from the mandrel. At 68, the carbon fiber sleeve is cut to a predetermined length. At 70, the rotor is press fitted into the carbon fiber sleeve.

[0080] Figure 1B Advantages of the method in include ease of mass production of long sleeves, relatively straightforward creation of interference stresses, and press fitting is a line friendly process. Figure 1BChallenges faced by the method in include high interference levels, which can be a challenge to press on without damaging the carbon fiber sleeve.

[0081] In Figure 1C the carbon fiber sleeve is wound directly onto the rotor assembly. At 82, the rotor assembly is installed on a filament winding machine. At 84, carbon fiber filaments are wound onto the rotor assembly using high tension. At 86, resin is applied to the carbon fiber filaments and cured. At 88, the rotor is removed from the filament winding machine. At 90, optionally, the outer diameter of the rotor assembly is machined.

[0082] Figure 1C Advantages of the method in include elimination of machining of the inner diameter of the carbon fiber. There is also the possibility of higher interfacial stress. Figure 1C Challenges faced by the method of include the requirement for special winding equipment with high fiber tension. The time required to individually wind each rotor is relatively long (so this is most useful for low production volumes).

[0083] Reference is now made to Figure 2A and Figure 2B , which show an example of a rotor assembly 100. In Figure 2A the rotor assembly 100 is shown as including a plurality of magnetic poles 104 and an outer sleeve 106, such as a carbon fiber sleeve. In Figure 2B an example of a rotor portion 108 of the rotor assembly 100 is shown. In this example, the rotor portion 108 corresponds to a single magnetic pole, and the rotor assembly 100 includes 8 magnetic poles, although additional or fewer magnetic poles can also be used.

[0084] The rotor assembly 100 can include N sets of magnets arranged between (N+1) assemblies, each assembly including a plurality of laminations, where N is greater than or equal to 1. In the examples below, the rotor assembly 100 includes N=2 sets of permanent magnets and N+1=3 assemblies, each assembly including a plurality of laminations. As can be appreciated, N can equal 1, 2, 3, etc.

[0085] In Figure 2A the example, the rotor assembly 100 includes the following: a radially inner assembly 110 including a first plurality of laminations, an intermediate assembly 124 including a second plurality of laminations, and a radially outer assembly 143 including a third plurality of laminations. In some examples, the radially inner assembly 110 is star-shaped and common to all magnetic poles. The intermediate assembly 124 has a "V" shaped cross-section, and the radially outer assembly 143 has a generally triangular cross-section and has a radially outer arcuate surface. The radially outer arcuate surface, as well as a radially outer end of the intermediate assembly 124, is located radially inward of a radially outer edge of the radially inner assembly 110.

[0086] A first V-shaped opening 112 is defined between the radially inner assembly 110 and the intermediate assembly 124. A second "V"-shaped opening 132 is defined between the intermediate assembly 124 and the radially outer assembly 143. Permanent magnets 120 and 122 are located in the first V-shaped opening 112, and permanent magnets 140 and 142 are arranged in the second "V"-shaped opening 132. Protrusions 145 can be arranged on the surfaces of the radially inner assembly 110, the intermediate assembly 124, and the radially outer assembly 143 to help position the permanent magnets 120, 122, 140, and 142. The first plurality of laminations of the radially inner assembly 110 can include notches 144 and 145 on the sides thereof.

[0087] The polymer material 147 fills open spaces in the first V-shaped opening 112, the second V-shaped opening 132, and fills open spaces radially outward of the radially outer arcuate surfaces of the radially outer assembly 143. More specifically, the polymer material 147 fills the radially outer portions 114 and 116 of the first "V"-shaped opening 112, the central portion 118 between the permanent magnets 120 and 122, and / or fills other open areas. The polymer material 147 fills the radially outer portions 134 and 136 of the second "V"-shaped opening 132, the central portion 138 between the permanent magnets 140 and 142, and / or fills other open areas.

[0088] The carbon fiber outer layer 106 has an interference fit to the outer surface of the rotor assembly 100. As can be appreciated, the webs and bridges are omitted and replaced with the polymer material 147. In some examples, the polymer material 147 comprises a cohesive polymer composite. In some examples, the polymer material 147 comprises a resin, such as a polymeric resin or a thermoset resin. In some examples, the resin is selected from the group consisting of epoxy, polyurethane, polyester, bismaleimide, acrylic, cyanate ester, polyimide, phenolic, benzoxazine, and vinyl ester. In some examples, an epoxy resin is used with a discontinuous filler material, such as silica, alumina, mineral, boron nitride, aluminum nitride, silicon nitride, basalt, and glass fibers. In some examples, the polymer material 147 has high strength (> 50 MPa or > 100 MPa), high modulus (> 10 GPa), high temperature resistance (Tg > 150 0 C), and strong adhesion to electrical steel (> 15 MPa).

[0089] In some examples, the laminations are made from electrical steel for the prototype using stamping or machining, although other materials or processes could be used. Eliminating the web and bridges means that the laminations are no longer a single piece. In some examples, there are 1 + 2*P lamination assemblies per rotor assembly, where P is the number of poles. These multiple pieces can be stamped from a sheet of material in their respective positions or more tightly nested together to allow better utilization of the material.

[0090] Referring now to Figure 2C , an example manufacturing process is shown. The method 160 includes stamping out lamination shapes at 162. At 164, multiple lamination pieces are bonded together into a subassembly with a predetermined thickness using an adhesive. In some examples, mechanical interlocking is used to join the lamination pieces together instead of or in addition to the adhesive. For example, the predetermined thickness can be in the range of 10-100 layers.

[0091] At 166, the magnets and lamination subassembly are inserted into a mold. Optionally, a carbon fiber outer layer can be inserted into the mold. At 168, the mold is filled with resin to adhere the pieces together. At 170, the resin is cured and then the rotor assembly is removed from the mold.

[0092] When a carbon fiber outer layer is added after molding, it can be assembled by press fitting or overwrapping. When the carbon fiber outer layer is placed in the mold, pre-stressing is done by applying pressure on the polymer material 147 to store elastic energy in the carbon fiber outer layer. The polymer material 147 pushes on the carbon fiber outer layer to pre-stress the carbon fiber outer layer. This stress is largely retained after curing. However, some stress will be lost due to the curing shrinkage of the polymer material 147.

[0093] Referring now to Figures 3-6 , various examples of adjacent layers of a rotor assembly (along A-A in Figure 2B ) are shown. In the first stack 150 in Figure 3 , the layers are as follows: carbon fiber layer 106, lamination of radial outer assembly 143, polymer layer 152, permanent magnet 140, polymer layer 154, lamination of intermediate assembly 124, polymer layer 156, permanent magnet 120, polymer layer 158, and lamination of radial inner assembly 110.

[0094] In the second stack 200 in Figure 4 , the layers are as follows: carbon fiber layer 106, polymer layer 204, lamination of radial outer assembly 143, permanent magnet 140, lamination of intermediate assembly 124, permanent magnet 120, and lamination of radial inner assembly 110.

[0095] InFigure 5 In the third stack 250, the layers are as follows: carbon fiber layer 106, laminations of the radially outer assembly 143, permanent magnet 140, laminations of the intermediate assembly 124, permanent magnet 120, polymer layer 254, and laminations of the radially inner assembly 110.

[0096] In the fourth stack 300, the layers are as follows: carbon fiber layer 106, laminations of the radially outer assembly 143, permanent magnet 140, polymer layer 304, laminations of the intermediate assembly 124, permanent magnet 120, polymer layer 306, and laminations of the radially inner assembly 110. Figure 6

[0097] Tolerance stack-up of the lamination sub-assemblies and magnets can cause variations in the position of the components of the rotor assembly. In some examples, the carbon fiber layer 106 contacts a uniform cylindrical surface to increase the strength of the carbon fiber outer layer. Polymer material can be used to position components and occupy gaps in the stack to create a uniform cylindrical surface. If the polymer material is injected into the flux barrier region (near the magnets), everything will be pushed to the outside of the mold (see, for example, Figure 3 , Figure 5 and Figure 6 ). Figure 3 , Figure 5 and Figure 6 are slight variations of each other that can occur depending on the injection parameters.

[0098] If the polymer material 147 is injected on the outer diameter surface, everything will be pushed towards the center of the rotor ( Figure 4 ), resulting in a variable air gap. Figure 4 The variable air gap in

[0099] Referring now to Figure 7 and Figure 8 , the base torque and power output at the highest speed are shown for different configurations of the rotor assembly. Option 1 corresponds to a rotor stack with webs and bridges. Option 2 corresponds to a rotor stack with webs, bridges, and a carbon fiber outer layer. Option 3 corresponds to a rotor stack with a carbon fiber outer layer without webs but with thinner bridges. Option 4 corresponds to a rotor stack with a carbon fiber outer layer without webs or bridges ( Figure 3 ). Option 5 corresponds to a rotor stack with a carbon fiber outer layer without webs, bridges, and clearance. Option 6 corresponds to a rotor stack with a carbon fiber outer layer without webs, bridges, and clearance, with a variable air gap ( Figure 4 ). Option 7 corresponds to a rotor stack with a carbon fiber outer layer without webs and bridges, but with tolerance stack-up behind the large permanent magnets ( Figure 5 ). As can be seen, there is a significant improvement in the base torque and the highest speed power when the webs and bridges are removed.​

[0100] Referring now to Figures 9-11 , a right half pole portion of the additional rotor assembly is shown. In Figure 9 , the radially inner assembly of rotor assembly 500 is further divided into a first sub-assembly 518 including a fourth plurality of laminations and a second sub-assembly 520 including a fifth plurality of laminations. A gap 530 is defined between the first sub-assembly 518 and the second sub-assembly 520. In some examples, the gap 530 is stepped and has a circumferentially extending portion 538 and a radially extending portion 534. In some examples, the circumferentially extending portion 538 is wider than the radially extending portion 534 to allow for additional movement in the radial direction.

[0101] An alternative approach to handling the challenges caused by tolerance stack-up is to split the radially inner assembly into a first sub-assembly 518 and a second sub-assembly 520. The stepped shape in Figure 9 can be used to maintain a high permeability flux path between the first sub-assembly 518 and the second sub-assembly 520. In this design, the radial surfaces are in close proximity, while the circumferential surfaces can move in and out to handle tolerance variations in the magnet region.

[0102] In some examples, a magnetic polymer material is disposed between the first sub-assembly 518 and the second sub-assembly 520 to preserve some of the magnetic flux permeability. In some examples, a soft magnet composite material or other alternative material can be used to make the second sub-assembly 520 in this configuration.

[0103] Referring now to Figure 10 , the radially inner assembly of rotor assembly 550 is further divided into a first sub-assembly 518 including a fourth plurality of laminations and a second sub-assembly 520 including a fifth plurality of laminations. A gap 544 is defined between the first sub-assembly 518 and the second sub-assembly 520. In some examples, the gap 544 includes a circumferentially extending portion 558 and an obliquely extending portion 562. In some examples, the gap defined by the circumferentially extending portion 558 is wider than the gap defined by the obliquely extending portion 562 to allow for additional movement in the radial direction.

[0104] Referring now to Figure 11 , the radially inner assembly of rotor assembly 600 is further divided into a first sub-assembly 518 including a fourth plurality of laminations and a second sub-assembly 520 including a fifth plurality of laminations. A gap 610 is defined between the first sub-assembly 518 and the second sub-assembly 520. In some examples, the gap 610 includes a circumferentially extending portion 614, a radially extending portion 616, and a preserved portion 618. In some examples, the preserved portion 618 forms an angle relative to the obliquely extending portion 616. In some examples, the angle is between 70 0 and 110 0Other angles can be used, however. In some examples, the gap defined by the circumferentially extending portion 614 is wider than the gap defined by the obliquely extending portion 616 and the retention portion 618 to allow additional movement in the radial direction.

[0105] Referring now to Figure 12 The rotor assembly includes a radially inner assembly that is split into a first sub-assembly 710 and a second sub-assembly 714. The first and second sub-assemblies include interlocking mating features 718. For example, the second sub-assembly 714 includes a male portion 738 (e.g., a “T” shaped portion including arms 740 and 742) that is received by a female portion 744 (e.g., a complementary “T” shaped opening 744 in the first sub-assembly 710), although other mating shapes can be used. In some examples, circumferential gaps 746 and 748 are disposed between the arms 740 and 742 and corresponding surfaces of the “T” shaped opening 744, respectively. In some examples, the circumferential gaps 746 and 748 are filled with a polymer material.

[0106] The rotor includes multiple lamination assemblies (e.g., 143, 124, and 710) that are movable to accommodate tolerances and to eliminate air gaps. The radially movable lamination assemblies (e.g., 712) are designed to occupy the clearance between the magnetic poles to maintain magnetic flux continuity. The interlocking features transfer centrifugal loads to / from the outer assembly to the inner assembly. In some examples, the circumferential gaps 746 and 748 are filled with a polymer material to carry some of the load of the lamination assemblies rather than relying solely on the carbon fiber outer layer.

[0107] Advantages include the use of separate lamination assemblies that enable better utilization of raw materials because the parts can be more tightly nested together. The separate lamination assemblies also enable the use of grain-oriented steel.

[0108] Referring now to Figure 13 Another example of a rotor assembly 800 according to the present disclosure is shown. Another alternative approach to address variable tolerances involves absorbing the gap in the empty flux barrier layer (not including magnets). In some examples, the polymer material in the flux barrier layer includes magnetic particles to ensure magnetic flux path continuity for the permanent magnets in the other slots.

[0109] The rotor assembly 800 includes a radially inner assembly 810 including a first plurality of laminations, a second assembly 814 including a second plurality of laminations, a third assembly 820 including a third plurality of laminations, and a radially outer assembly 830 including a fourth plurality of laminations.

[0110] In some examples, the second assembly 814 and the third assembly 820 have a "V" shaped cross-section. The radially outer assembly 830 has a generally planar cross-section and has an arcuate radially outer surface.

[0111] A first V-shaped opening 816 is defined between the radially inner assembly 810 and the second assembly 814. A second "V" shaped opening 822 is defined between the second assembly 814 and the third assembly 820. A third "V" shaped opening 845 is defined between the third assembly 820 and the radially outer assembly 830. Permanent magnets 842 and 844 are located in the first V-shaped opening 112 and permanent magnets 846 and 848 are arranged in the third "V" shaped opening 845. A polymer material is arranged in the open space in the first V-shaped opening 816, the third V-shaped opening 845. The carbon fiber outer layer 831 has an interference fit to the outer surface of the rotor assembly 800.

[0112] Referring now to Figure 14 , a stack 870 corresponding to the rotor assembly 800 is shown. The stack 870 includes the carbon fiber outer layer 831, the radially outer assembly 830, the permanent magnet 846, the third assembly 820, the polymer layer 822, the second assembly 814, the permanent magnet 842, and the radially inner assembly 810.

[0113] The foregoing description is merely illustrative in nature and is not intended to limit the disclosure, its application or uses in any way. The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be limited to such examples. It should be understood that one or more steps within a method, or examples, can be performed by vertically or horizontally spaced apart components, or components that are not directly connected to each other, without changing the principles of the disclosure. Further, while the above examples have been described with respect to particular embodiments, it will be apparent that those skilled in the art, on accommodation of this disclosure, can effect equivalent embodiments without using the particular detailed language. In other words, described embodiments are not mutually exclusive, and permutations of one or more embodiments with each other remain within the scope of the disclosure.

[0114] Spatial and functional relationships between elements (for example, between modules, circuit elements, semiconductor layers, etc.) are described using various terms, including "connected," "engaged," "coupled," "adjacent," "near," "on," "above," "below," and "positioned." Unless specifically described as "direct," relationships between components, as described by the foregoing terms, can be indirect as opposed to direct. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical A OR B OR C using the non- exclusive logical OR ("OR"), and it should be interpreted that "at least one of A, B, and C" and "at least one of A or B or C" each depend on the entire scope of the term before the term "one of" to provide a complete disjunctive scope. That is, a set including at least one of A, B, and C would include: A alone, AB, AC, BC, or ABC, when the term "one of" is read in the disjunctive.

[0115] In the drawings, the direction of arrows, as indicated by the arrows, generally demonstrates the flow of information (such as data or instructions) illustrated, such as from one element to another. For example, when elements A and B exchange various information, but the information transmitted from element A to element B is relevant to the illustration, an arrow can be directed from element A to element B. This one-way arrow does not imply that no other information is transmitted from element B to element A. Further, for information sent from element A to element B, element B can send a request for the information or receive an acknowledgement to element A.

Claims

1. A rotor assembly for a permanent magnet motor, the rotor assembly comprising: a first assembly comprising a first plurality of laminations; a second assembly comprising a second plurality of laminations, a third assembly comprising a third plurality of laminations, wherein the second assembly and the third assembly define a second opening therebetween; wherein the first assembly is radially inward of the second assembly, and wherein the first assembly and the second assembly define a first opening therebetween; a first permanent magnet and a second permanent magnet located in the first opening; a third permanent magnet and a fourth permanent magnet located in the second opening, a polymeric material surrounding the first permanent magnet and the second permanent magnet in the first opening and the third permanent magnet and the fourth permanent magnet located in the second opening; and an outer layer surrounding the rotor assembly; wherein the first assembly comprises a first sub-assembly comprising a first plurality of laminations of the first plurality of laminations and a second sub-assembly comprising a second plurality of laminations of the first plurality of laminations; wherein the first sub-assembly and the second sub-assembly define a side-facing surface comprising circumferential segments and other segments, and wherein the circumferential segments define a greater gap than the other segments; wherein the side-facing surface of the first sub-assembly and the second sub-assembly define a stepped pattern.

2. The rotor assembly of claim 1, wherein, the rotor assembly does not include webs, and wherein the rotor assembly does not include bridges, and wherein the outer layer is made of carbon fiber.

3. The rotor assembly of claim 1, wherein, the first opening is "V” shaped and extends to the outer layer.

4. The rotor assembly of claim 1, wherein, the polymeric material comprises a resin.

5. The rotor assembly of claim 4, wherein, the resin comprises at least one of: an epoxy, a polyurethane, a polyester, a bismaleimide, an acrylic, a cyanate ester, a polyimide, a phenolic, a benzoxazine, and a vinyl ester.

6. The rotor assembly of claim 4, wherein, the resin further comprises a discontinuous filler material.

7. The rotor assembly of claim 6, wherein, the discontinuous filler material comprises at least one of: silica, alumina, a mineral, boron nitride, aluminum nitride, silicon nitride, basalt, and glass fiber.

8. The rotor assembly of claim 1, wherein, the first sub-assembly and the second sub-assembly comprise a side-facing surface comprising circumferential segments and diagonal segments, and wherein the circumferential segments define a greater gap than the diagonal segments.

9. The rotor assembly of claim 1, wherein, the first sub-assembly and the second sub-assembly comprise a side-facing surface comprising circumferential segments, diagonal segments, and a preserved segment, and wherein the circumferential segments define a greater gap than the diagonal segments.

10. The rotor assembly of claim 1, wherein, at least one of the first sub-assembly and the second sub-assembly defines a female opening and the other of the first sub-assembly and the second sub-assembly defines a male protrusion that is received within the female opening.

11. The rotor assembly of claim 10, wherein, the male protrusion is "T” shaped and comprises a first arm and a second arm, and the rotor assembly further comprises a first gap and a second gap defined between the first arm and the second arm and the female opening, and wherein the polymeric material is located in the first gap and the second gap.

12. A rotor assembly for a permanent magnet motor, the rotor assembly comprising: a first assembly comprising a first plurality of laminations; a second assembly comprising a second plurality of laminations, wherein the first assembly and the second assembly define a first opening therebetween; a third assembly comprising a third plurality of laminations, wherein the second assembly and the third assembly define a magnetic flux barrier therebetween; a fourth assembly comprising a fourth plurality of laminations, wherein the third assembly and the fourth assembly define a second opening therebetween; a first permanent magnet and a second permanent magnet located in the first opening; a third permanent magnet and a fourth permanent magnet located in the second opening, a polymer material surrounding the first permanent magnet and the second permanent magnet in the first opening and the third permanent magnet and the fourth permanent magnet located in the second opening; and a carbon fiber outer layer surrounding the rotor assembly, wherein the rotor assembly does not include webs, and wherein the rotor assembly does not include bridges; wherein the first assembly comprises a first sub-assembly comprising a first plurality of laminations of the first plurality of laminations and a second sub-assembly comprising a second plurality of laminations of the first plurality of laminations; wherein the first sub-assembly and the second sub-assembly define a side-facing surface comprising circumferential segments and other segments, and wherein the circumferential segments define a greater gap than the other segments; wherein the side-facing surface of the first sub-assembly and the second sub-assembly define a stepped pattern.

13. The rotor assembly of claim 12, wherein, the magnetic flux barrier comprises a polymer material mixed with magnetic particles.

14. The rotor assembly of claim 13, wherein, the first opening, the magnetic flux barrier, and the second opening are "V” shaped and extend to the carbon fiber outer layer.

15. The rotor assembly of claim 12, wherein, the polymer material comprises an epoxy resin, and the discontinuous filler material comprises at least one of the following: silicon dioxide, aluminum oxide, a mineral, boron nitride, aluminum nitride, silicon nitride, basalt, and glass fiber.

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