TECHNICAL FIELD

[0001] The present disclosure relates generally to electric rotary motors, and more particularly to an assembly for an axial airgap electric rotary motor.

BACKGROUND ART

[0002] An electric motor converts electrical energy into mechanical rotational power. Most electric motors operate through the interaction between a stator magnetic field and a rotor magnetic field to generate force within the motor. Rotating motors ordinarily include a stationary component known as a stator and a rotating component known as a rotor. Adjacent faces of the rotor and stator are separated by a small airgap traversed by magnetic flux linking the rotor and stator. Such motors are conventionally classifiable as being either radial or axial airgap types. A radial airgap type is one in which the rotor and stator are separated radially by an air gap and the traversing magnetic flux is directed predominantly perpendicular to the axis of rotation of the rotor. Thus, a radial flux motor has flux running radially in and out from the center of the shaft. Radial airgap types are commonly used and have been studied extensively. In contrast, in an axial airgap motor, the rotor and stator are separated axially by an air gap and the traversing magnetic flux flow includes flow parallel to the rotational axis. Thus, an axial flux motor has flux running axially parallel to the axis of rotation.

[0003] U.S. Patent Publication No. 2010/0295389, entitled “Axial Flux Switched Reluctance Motor and Methods of Manufacture,” discloses an axial flux motor that utilizes one or more rotor discs spaced along a rotor shaft and stator elements distributed circumferentially about the rotor discs and forming pairs of radially extending stator poles for axially straddling the rotor discs. U.S. Patent No. 7,378,763, entitled “Linear Motor,” discloses a stator core divided into two parts with each of the parts being made of a soft magnetic powder and a mover comprising a section of soft magnetic material and a permanent magnet. A soft magnetic material exhibits high permeability and low magnetic coercivity and may be efficiently magnetized and demagnetized. A permanent magnet has a high magnetic coercivity and strongly retains its magnetization and resists being demagnetized. U.S. Patent No. 7,884,508, entitled “Linear Motor,” also discloses a stator core divided into two parts formed of a soft magnetic powder and a mover that has at least one section also formed of a soft magnetic material. BRIEF SUMMARY

[0004] With parenthetical reference to corresponding parts, portions or surfaces of the disclosed embodiment, merely for the purposes of illustration and not by way of limitation, the present disclosure provides an electric motor assembly (15) comprising: a stator (20); a rotor (30) configured to rotate about a central axis (16) relative to the stator (20); the stator (20) comprising a stator body section (23a, 23b, 23c) and a first stator pole section (22a) extending radially from the stator body section (23a, 23b, 23c); the rotor (30) comprising a rotor shaft portion (31) orientated about the central axis (16), a first rotor pole section (32a,

132) extending radially from the rotor shaft portion (31) relative to the central axis (16), and a second rotor pole section (32b) extending radially from the rotor shaft portion (31) relative to the central axis (16) and spaced axially from the first rotor pole section (32a) relative to the central axis (16); the first stator pole section (22a) disposed axially between the first rotor pole section (32a, 132) and second rotor pole section (32b) relative to the central axis (16) and radially overlapping (27) both the first rotor pole section (32a, 132) and the second rotor pole section (32b) relative to the central axis (16); a first axial air gap (52a) between the first rotor pole section (32a, 132) and the first stator pole section (22a); a second axial air gap (52b) between the second rotor pole section (32b, 132) and the first stator pole section (22a); the stator comprising windings (26a, 26b) operatively configured to be selectively energized to provide a flux path across the first axial air gap (52a) and the second axial air gap (52b); and the first rotor pole section (32a, 132) comprising a plurality of radially extending solid unitary pole pieces (33, 133) spaced circumferentially about the central axis (16).

[0005] The plurality of radially extending solid unitary pole pieces (33, 133) may be each formed of a metal powder material. The plurality of radially extending solid unitary pole pieces (33, 133) may be each formed of a soft magnetic composite material. The second rotor pole section (32b) may comprise a plurality of radially extending solid pole pieces (33,

133) spaced circumferentially about the central axis (16). The plurality of radially extending solid pole pieces (33, 133) of the second rotor pole section (32b) may be each formed of a soft magnetic composite material.

[0006] The stator (20) may comprise a second stator pole section (22b) extending radially from the stator body section (23a, 23b, 23c) relative to the central axis (16) and spaced axially from the first stator pole section (22a) relative to the central axis (16); the second rotor pole section (22b) may be disposed axially between the first stator pole section (32a) and second stator pole section (32b) and may radially overlap (27) both the first stator pole section (32a) and the second stator pole section (32b); a third axial air gap (52c) may be between the second rotor pole section (32b) and the second stator pole section (22b); and the windings (26b) may be operatively configured to be selectively energized to provide a flux path across the third axial air gap. Each of the plurality of radially extending solid pole pieces (33) of the first rotor pole section (32a) may comprise discrete pole pieces having an inner end (34) and an outer end (35).

[0007] The first stator pole section (22a) may comprise a plurality of magnets (24) and flux concentrators (25) spaced circumferentially about the central axis (16). The windings may comprise a first conductive coil (26a) orientated about the central axis (16) and disposed axially between the first rotor pole section (32a) and the second rotor pole section (32b) and disposed radially between the first stator pole section (22a) and the rotor shaft (31). The windings may comprise a first conductive coil (26a) orientated about the central axis (16) and disposed axially between the first rotor pole section (32a) and the second rotor pole section (32b) and disposed radially between the first stator pole section (22a) and the rotor shaft (31), and a second conductive coil (26b) orientated about the central axis (16) and disposed radially between the second stator pole section (22b) and the rotor shaft (31).

[0008] The rotor (30) may comprise a first rotor toroid section (42a, 142) extending radially from the rotor shaft portion (31) relative to the central axis (16); the first rotor toroid section (42a, 142) may be disposed axially between the first rotor pole section (32a) and the second rotor pole section (32b) relative to the central axis (16); and the first rotor toroid section (42a, 142) may radially overlap (43) both the first rotor pole section (32a) and the second rotor pole section (32b) relative to the central axis (16). The windings may comprise a first conductive coil (26a) orientated about the central axis (16) and disposed axially between the first rotor pole section (32a) and the second rotor pole section (32b); the first conductive coil (26a) may be disposed radially between the first stator pole section (22a) and the first rotor toroid section (42a); and a first inner radial clearance (53a) may be between the first conductive coil (26a) and the first rotor toroid section (42a). The electric motor may comprise a first outer radial clearance (54a) between the first rotor pole section (32a) and the stator body section (23a, 23b, 23c). The first rotor toroid section (42a, 142) may be formed of a soft magnetic composite material.

[0009] The plurality of radially extending solid pole pieces (133) spaced circumferentially about the central axis (16) and the first rotor toroid section (142) may be formed as a unitary piece, having a monolithic and isotropic structure, and being of a uniform composition. The plurality of radially extending solid pole pieces and the first rotor toroid section may be formed of a soft magnetic composite material.

[0010] The plurality of radially extending solid pole pieces (133) spaced circumferentially about the central axis (16) may be formed as a unitary piece, having a monolithic and isotropic structure, and being of a uniform composition of soft magnetic composite material.

[0011] The motor may comprise a third rotor pole section (32c), a fourth rotor pole section (32d), a second stator pole section (22b), and a third stator pole section (22c); and the first rotor pole section (32a), the first stator pole section (22a), the second rotor pole section (32b), the second stator pole section (22b), the third rotor pole section (32c), the third stator pole section (22c), and the fourth rotor pole section (32d) may be stacked in the axial direction.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 is an isometric partial cutaway view of a first embodiment of the improved electric motor assembly.

[0013] FIG. 2 is an exploded isometric view of the motor assembly shown in FIG. 1.

[0014] FIG. 3 is a longitudinal cross-sectional view of the motor assembly shown in FIG.

1

[0015] FIG. 4 is a transverse cross-sectional view of the motor assembly shown in FIG. 1.

[0016] FIG. 5 is an isometric view of the rotor assembly shown in FIG. 1

[0017] FIG. 6 is an isometric view of a rotor pole section and inner toroid shown in FIG.

5.

[0018] FIG. 7 is a top plan view of the rotor pole section and toroid shown in FIG. 6.

[0019] FIG. 8 is a side view of the rotor pole section and toroid shown in FIG. 6.

[0020] FIG. 9 is a top plan view of the rotor pole section shown in FIG. 6.

[0021] FIG. 10 is an exploded isometric view of the rotor pole section shown in FIG. 9.

[0022] FIG. 11 is a transverse cross-sectional view of the rotor pole section shown in

FIG. 9, taken generally on line A- A of FIG. 9.

[0023] FIG. 12 is an enlarged cross-sectional view of the rotor pole section shown in FIG. 11, taken generally within the indicated circle B of FIG. 11.

[0024] FIG. 13 is an isometric view of a second embodiment of a rotor pole section and inner toroid shown in FIG. 6.

[0025] FIG. 14 is a top plan view of the rotor pole section and toroid shown in FIG. 13. [0026] FIG. 15 is a side view of the rotor pole section and toroid shown in FIG. 13.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] At the outset, it should be clearly understood that like reference numerals are intended to identify the same structural elements, portions or surfaces consistently throughout the several drawing figures, as such elements, portions or surfaces may be further described or explained by the entire written specification, of which this detailed description is an integral part. Unless otherwise indicated, the drawings are intended to be read (e.g., cross- hatching, arrangement of parts, proportion, degree, etc.) together with the specification, and are to be considered a portion of the entire written description of this invention. As used in the following description, the terms "horizontal", "vertical", "left", "right", "up" and "down", as well as adjectival and adverbial derivatives thereof (e.g., "horizontally", "rightwardly", "upwardly", etc.), simply refer to the orientation of the illustrated structure as the particular drawing figure faces the reader. Similarly, the terms "inwardly" and "outwardly" generally refer to the orientation of a surface relative to its axis of elongation, or axis of rotation, as appropriate.

[0028] An improved electric motor assembly is provided, an embodiment of which is generally indicated at 15. As shown in FIG. 1, motor 15 generally includes motor housing 17 containing stator 20 and rotor 30 configured to rotate about axis 16 relative to stator 20 and motor housing 17. As shown in FIGS. 1-3, housing 17 is a generally hollow cylindrical member comprising right end 17a having an opening from which rotor 30 projects, outer cylindrical casing 17b, and left end bell 17c having a portion projecting into the interior of rotor shaft 31 of rotor 30. Stator 20 is fixedly supported in housing 17 between shaft end 17a and end bell 17c of housing 17 such that stator 20 does not rotate relative to motor housing 17. Rotor 30 is rotationally supported in housing 17 by annular bearing 60, positioned radially between the outer cylindrical surface of shaft end clamp 46 of rotor 30 and the inner cylindrical surface of housing end 17a of housing 17, and annular rolling bearings 61, positioned radially between the inner cylindrical surface of shaft 31 of rotor 30 and the outer cylindrical surface of end bell 17c of housing 17. Rotor 30 is thereby rotationally supported in housing 17 between shaft end 17a and end bell 17c of housing 17 such that rotor 30 is operationally rotatable about axis 16 relative to motor housing 17 and stator 20.

[0029] Stator 20 is a generally cylindrical member elongated about axis 16 and having an inner space in which rotor 30 rotates about axis 16 relative to stator 20. Stator 20 is primarily formed from three sections 21a, 21b and 21c that are stacked in the axial direction interior to housing cylinder 17b of housing 17 and sandwiched between shaft end 17a and end bell 17c of housing 17. These individual stator pole sections 21a, 21b and 21c are glued, bolted, clamped or otherwise fastened together in housing 17 to form stator 20.

[0030] As shown, stator section 21a generally comprises outer cylindrical yoke or body portion 23a, stator pole section 22a projecting radially inward from outer body portion 23a, and inner coil 26a. Coil 26a comprises a plurality of conductive windings that may be selectively energized via leads 70a as desired to magnetically interact with rotor 30 to exert a torque on and rotational movement of rotor 30 relative to stator 20.

[0031] In this embodiment, pole section 22a generally comprises a plurality of circumferentially spaced alternating permanent magnets 24 and flux concentrators 25 that extend radially in from and are supported by outer cylindrical body portion 21a. Each of magnets 24 extends axially along longitudinal axis 16 of yoke portion 21a and is positioned radially about axis 16 on the inner circumference of body portion 21a to thereby form magnetic poles. Magnets 24 are permanently affixed around the inner circumference of body portion 21a. Each of concentrators 25 also extends axially along longitudinal axis 16 of yoke portion 21a and is positioned radially about axis 16 on the inner circumference of body portion 21a. Concentrators 25 are permanently affixed around the inner circumference of body portion 21a between magnets 24. Thus, stator pole section 22a includes a plurality of flux concentrators 25 between a plurality of magnetic poles 24, with each of flux concentrators 25 and magnetic poles 24 extending axially along longitudinal axis 16 and positioned radially about axis 16 such that each flux concentrator 25 alternates with each magnetic pole 24 on the inner circumference of cylindrical outer body portion 21a about axis 16.

[0032] As shown, stator section 21b generally comprises outer cylindrical yoke or body portion 23b, stator pole section 22b projecting radially inward from outer body portion 23b, and inner coil 26b. Coil 26b comprises a plurality of conductive windings that may be selectively energized via leads 70b as desired to magnetically interact with rotor 30 to cause torque and rotational movement of rotor 30 relative to stator 20.

[0033] In this embodiment, pole section 22b generally comprises a plurality of circumferentially spaced alternating permanent magnets 24 and flux concentrators 25 that extend radially in from and are supported by outer cylindrical body portion 21b. Each of magnets 24 extends axially along longitudinal axis 16 of yoke portion 21b and is positioned radially about axis 16 on the inner circumference of body portion 21b to thereby form magnetic poles. Magnets 24 are permanently affixed around the inner circumference of body portion 21b. Each of concentrators 25 also extends axially along longitudinal axis 16 of yoke portion 21b and is positioned radially about axis 16 on the inner circumference of body portion 21b. Concentrators 25 are permanently affixed around the inner circumference of body portion 21b between magnets 24. Thus, stator pole section 22b includes a plurality of flux concentrators 25 between a plurality of magnetic poles 24, with each of flux concentrators 25 and magnetic poles 24 extending axially along longitudinal axis 16 and positioned radially about axis 16 such that each flux concentrator 25 alternates with each magnetic pole 24 on the inner circumference of cylindrical outer body portion 21b about axis 16.

[0034] As shown, stator section 21c generally comprises outer cylindrical yoke or body portion 23c, stator pole section 22c projecting radially inward from outer body portion 23c, and inner coil 26c. Coil 26c comprises a plurality of conductive windings that may be selectively energized via leads 70c as desired to magnetically interact with rotor 30 to cause torque and rotational movement of rotor 30 relative to stator 20.

[0035] In this embodiment, stator pole section 22c generally comprises a plurality of circumferentially spaced alternating permanent magnets 24 and flux concentrators 25 that extend radially in from and are supported by outer cylindrical body portion 21c. Each of magnets 24 extends axially along longitudinal axis 16 of yoke portion 21c and is positioned radially about axis 16 on the inner circumference of body portion 21c to thereby form magnetic poles. Magnets 24 are permanently affixed around the inner circumference of body portion 21c. Each of concentrators 25 also extends axially along longitudinal axis 16 of yoke portion 21c and is positioned radially about axis 16 on the inner circumference of body portion 21c. Concentrators 25 are permanently affixed around the inner circumference of body portion 21c between magnets 24. In this embodiment, concentrators 25 are of a uniform composition and are formed from metal powder such as a soft magnetic composite (SMC) material. Thus, stator pole section 22c includes a plurality of flux concentrators 25 between a plurality of magnetic poles 24, with each of flux concentrators 25 and magnetic poles 24 extending axially along longitudinal axis 16 and positioned radially about axis 16 such that each flux concentrator 25 alternates with each magnetic pole 24 on the inner circumference of cylindrical outer body portion 21c about axis 16.

[0036] Coils 26a, 26b and 26c comprise electromagnetic windings that include at least one turn. Coils 26a, 26b and 26c are each wound with copper, aluminum wires, ribbons, or any other material suitable for the intended purpose and understood by one of ordinary skill in the art. While coils 26a, 26b and 26c are shown with a relatively square cross-section, other embodiments may include an annular coil having a circular or oblong cross-section. [0037] Rotor 30 is a generally cylindrical member elongated about axis 16 and generally includes shaft 31 having at the left end annular retaining shoulder 45 and having at the right end annular end clamp 46. In this embodiment, four rotor disks or pole sections 32a, 32b, 32c and 32d and three toroid sections 42a, 42b and 42c are stacked in the axial direction on shaft 31 and sandwiched between shaft retaining shoulder 45 and shaft clamp 46. Moving left to right with reference to FIGS. 1-3, rotor pole section 32d is stacked against the right annular face of retaining shoulder 45, toroid 42c is stacked against the right annular face of rotor pole section 32d, rotor pole section 32c is stacked against the right annular face of toroid 42c, toroid 42b is stacked against the right annular face of rotor pole section 32c, rotor pole section 32b is stacked against the right annular face of toroid 42b, toroid 42a is stacked against the right annular face of rotor pole section 32b, rotor pole section 32a is stacked against the right annular face of toroid 42a, and end clamp 46 is stacked against the right annular face of rotor pole section 32a and bolted to rotor shaft 31 to clamp the rotor assembly together. These individual rotor pole sections 32a, 32b, 32c and 32d and rotor toroid sections 42a, 42b and 42c are glued, bolted, clamped or otherwise fastened together and on shaft between retaining shoulder 45 and end clamp 46 to form rotor 30.

[0038] As shown in FIGS. 4-12, each of stator pole sections 32a, 32b, 32c and 32d are annular disk-shaped members formed of a plurality of radially extending solid pole pieces 33 spaced circumferentially about central axis 16 and radially retained in solid support plate 39. In this embodiment, pole pieces 33 are solid unitary pieces with high permeability, low coercivity, high electric resistivity, structural strength and low eddy current loss. In this embodiment, pole pieces 33 have a monolithic and isotropic structure, are of a uniform composition, and are formed from a metal powder such as a soft magnetic composite material. Soft magnetic composite materials exhibit high permeability and low magnetic coercivity and typically comprise iron powder particles that are each coated and bonded with electrically insulating material to form a solid bulk material. The iron powder particles typically have high purity and compressibility and the particle coating provides high electrical resistivity, insulating each individual particle, which restricts eddy current creation. The coated powder is pressed into a die to form a solid material, which is then heat-treated using low temperatures to cure the bond. Thus, by way of example and without limitation, pole pieces 33 may be manufactured using a powdered metal compaction process in which powdered magnetic material is compacted in a custom die to form a solid unitary piece. Other types of materials and powders may be used as alternatives to form solid unitary pole piece 33, depending on the application. Examples include, without limitation, low carbon steels, silicon steels, cobalt-iron based alloys, phosphorous-iron based alloys, nickel-iron based alloys, additive manufactured (AM) powder iron or iron alloys, pure iron power particles encapsulated with inorganic insulation, and other ferromagnetic powder particles coated with an electrical insulating film.

[0039] As shown, each of radially extending solid pole pieces 33 spaced circumferentially about central axis 16 are further radially supported by retaining ring 38 in support plate 39. As shown in FIGS. 4, 5 and 10-12, in this embodiment each of the solid pole pieces 33 comprise discrete linear pole pieces having inner end 34 and outer end 35. Inner ends 34 of pole pieces 33 are spaced about axis 16 at the same radial distance from axis 16 and outer ends 35 of pole pieces 33 are spaced about axis 16 at the same radial distance from axis 16. Outer ends 35 of each discrete pole piece 33 include inwardly extending radial notches 36. Notches 36 are configured to receive retaining ring 38, which is secured in notches 36 by the transfer molding material of support plate 39. In this embodiment, as an example and without limitation, retaining ring 38 may be fiberglass or titanium. In this embodiment, support plate 39 is formed of an injected transfer molding material, examples of which may include, without limitation, thermoset plastic and epoxy resin.

[0040] As shown in FIGS. 4-12 and 16-18, in this embodiment each of rotor toroid sections 42a, 42b, and 42c are annular square solid unitary toroidal members orientated about axis 16. In this embodiment, rotor toroid sections 42a, 42b, and 42c are solid unitary pieces with high permeability, low coercivity, and high resistivity. In this embodiment, rotor toroid sections 42a, 42b, and 42c have a monolithic and isotropic structure, are of a uniform composition and are formed from a metal powder such as a soft magnetic composite material. For example, and without limitation, rotor toroid sections 42a, 42b, and 42c may be manufactured using a powdered metal compaction process in which powdered magnetic material is compacted in a custom die. Other types of materials and powders may be used as alternatives, depending on the application. Examples include, without limitation, low carbon steels, silicon steels, cobalt-iron based alloys, phosphorous-iron based alloys, nickel-iron based alloys, additive manufactured powder iron or iron alloys, pure iron power particles encapsulated with inorganic insulation, and other ferromagnetic powder particles coated with an electrical insulating film.

[0041] As shown, inner ends 34 of pole pieces 33 radially overlap their adjacent toroid sections such that inner ends 34 of pole pieces 33 are spaced a radial distance from axis 16 that is greater than the inner radius of toroid sections 42a, 42b and 42c and less than the outer radius of toroid sections 42a, 42b and 42c, respectively. Outer ends 35 of pole pieces 33 radially overlap their adjacent stator pole sections such that outer ends 35 of pole pieces 33 are spaced a radial distance from axis 16 that is greater than the inner radius of stator pole sections 22a, 22b and 22c, respectively.

[0042] As shown in FIGS. 1-3, the four rotor pole sections 32a, 32b, 32c and 32d and the three stator pole sections 22a, 22b and 22c are alternately stacked in the axial direction and in part radially overlap each other, with axial air gaps 52a, 52b and 52c therebetween. Moving right to left with reference to FIGS. 1-3 and regarding radial overlap 27 between stator 20 and rotor 30, the left annular face of rotor pole section 32a faces the right annular face of stator pole section 22a across axial air gap 52a in their radial overlap 27, the right annular face of rotor pole section 32b faces the left annular face of stator pole section 22a across axial air gap 52b in their radial overlap 27, the left annular face of rotor pole section 32b faces the right annular face of stator pole section 22b across axial air gap 52c in their radial overlap 27, the right annular face of rotor pole section 32c faces the left annular face of stator pole section 22b across axial air gap 52d in their radial overlap 27, the left annular face of rotor pole section 32c faces the right annular face of stator pole section 22c across axial air gap 52e in their radial overlap 27, and the right annular face of rotor pole section 32d faces the right annular face of stator pole section 22c across axial air gap 52f in their radial overlap 27. As shown, outer ends 35 of pole pieces 33 radially overlap their adjacent stator pole sections such that outer ends 35 of pole pieces 33 are spaced a radial distance from axis 16 that is greater than the inner radius of stator pole sections 22a, 22b and 22c, respectively.

[0043] Moving right to left with reference to FIGS. 1-3 and regarding radial overlap 28 between stator 20 and rotor 30, the left annular face of rotor pole section 32a faces the right annular face of coil 26a across axial air gap 52a in their radial overlap 28, the right annular face of rotor pole section 32b faces the left annular face of coil 26a across axial air gap 52b in their radial overlap 28, the left annular face of rotor pole section 32b faces the right annular face of coil 26b across axial air gap 52c in their radial overlap 28, the right annular face of rotor pole section 32c faces the left annular face of coil 26b across axial air gap 52d in their radial overlap 28, the left annular face of rotor pole section 32c faces the right annular face of coil 26c across axial air gap 52e in their radial overlap 28, and the right annular face of rotor pole section 32d faces the right annular face of coil 26c across axial air gap 52f in their radial overlap 28. Regarding radial overlap 27 and 28 between housing 17 and rotor 30, the left annular face of rotor pole section 32d faces the right annular face of housing bell end 17c across axial air gap or clearance 56b in their radial overlap 27 and 28, and the right annular face of rotor pole section 32a faces the right annular face of housing end 17a across axial air gap or clearance 56a in their radial overlap 27 and 28.

[0044] Moving right to left with reference to FIGS. 1-3 and regarding the radial air gaps or clearances between stator 20 and rotor 30 where they axially overlap, the outer cylindrical surface of rotor pole section 32a faces the inner cylindrical surface of housing 17b across radial air gap 54a in their axial overlap, the outer cylindrical surface of rotor pole section 32b faces the inner cylindrical surface of stator body 21a across radial air gap 54b in their axial overlap, the outer cylindrical surface of rotor pole section 32c faces the inner cylindrical surface of stator body 21b across radial air gap 54c in their axial overlap, and the outer cylindrical surface of rotor pole section 32d faces the inner cylindrical surface of stator body 21c across radial air gap 54d in their axial overlap. Similarly, the outer cylindrical surface of rotor toroid section 42a faces the inner cylindrical surface of coil 26a across radial air gap 53a in their axial overlap, the outer cylindrical surface of rotor toroid section 42b faces the inner cylindrical surface of coil 26b across radial air gap 53b in their axial overlap, and the outer cylindrical surface of rotor toroid section 42c faces the inner cylindrical surface of coil 26c across radial air gap 53c in their axial overlap.

[0045] Accordingly, stator 20 comprises stator pole section 22a extending radially from stator body section 23a. Rotor 30 comprises rotor shaft 31 orientated about the central axis 16 with rotor pole section 32a extending radially from rotor shaft 31 relative to the central axis 16 and rotor pole section 32b extending radially from rotor shaft 31 and spaced axially from rotor pole section 32a relative to the central axis 16. Stator pole section 22a is disposed axially between rotor pole section 32a and rotor pole section 32b relative to central axis 16 and radially overlapping 27 both rotor pole section 32a and rotor pole section 32b relative to the central axis 16 with axial air gap 52a between rotor pole section 32a and stator pole section 22a and axial air gap 52b between rotor pole section 32b and stator pole section 22a. Windings coils 26a are operatively configured to be selectively energized to generally provide a flux path that extends from stator pole section 22a across axial air gap 52a into rotor pole section 32a, radially through pole pieces 33 of rotor pole sections 32a from outer ends 35 of pole pieces 33 of rotor pole section 32a to inner ends 34 of pole pieces 33 of rotor pole section 32a, axially through rotor toroid 42a, radially through pole pieces 33 of rotor pole sections 32b from inner ends 34 of pole pieces 33 of rotor pole section 32b to outer ends 35 of pole pieces 33 of rotor pole section 32b, and across axial air gap 52b into stator pole section 22a. [0046] Windings coils 26b are operatively configured to be selectively energized to generally provide a flux path that extends from stator pole section 22b across axial air gap 52c into rotor pole section 32b, radially through pole pieces 33 of rotor pole sections 32b from outer ends 35 of pole pieces 33 of rotor pole section 32b to inner ends 34 of pole pieces 33 of rotor pole section 32b, axially through rotor toroid 42b, radially through pole pieces 33 of rotor pole sections 32c from inner ends 34 of pole pieces 33 of rotor pole section 32c to outer ends 35 of pole pieces 33 of rotor pole section 32c, and across axial air gap 52d into stator pole section 22b.

[0047] Windings coils 26c are operatively configured to be selectively energized to generally provide a flux path that extends from stator pole section 22c across axial air gap 52e into rotor pole section 32c, radially through pole pieces 33 of rotor pole sections 32c from outer ends 35 of pole pieces 33 of rotor pole section 32c to inner ends 34 of pole pieces 33 of rotor pole section 32c, axially through rotor toroid 42c, radially through pole pieces 33 of rotor pole sections 32d from inner ends 34 of pole pieces 33 of rotor pole section 32d to outer ends 35 of pole pieces 33 of rotor pole section 32d, and across axial air gap 52f into stator pole section 22c.

[0048] Accordingly, a series of annular coils 26a, 26b and 26c and stator pole sections 22a, 22b and 22c may be stacked axially to form a multiphase motor. In the embodiment shown in FIGS. 1-3, three-phase motor 15 includes three stator assembly sections 21a, 21b and 21c enclosed in housing 17. Stator assembly sections 21a, 21b and 21c are aligned axially in housing 17 and are sandwiched between end portion 17a and end portion 17c of housing 17. Stator section 21a is for the first of the three phases, stator section 21b is for the second of the three phases, and stator section 21c is for the third of the three phases.

[0049] Motor 15 includes rotary encoder 65 for determining the angular position of rotor 30 via encoder magnet assembly 66 mounted on shaft 31. With the feedback information provided by encoder 65, the position of rotor 30 is known and the motor controller can generate the magnetic field so that electric motor 15 rotates at the desired speed and torque. Drive electronics, based on encoder 65 angular position feedback received by the motor controller, generate and commutate the stator fields to vary the speed and direction of motor 15. Accordingly, motor 15 will selectively apply a torque on rotor 30 in one direction about axis 16 at varying speeds and will apply a torque on rotor 30 in the opposite direction about axis 16 at varying speeds. Other position sensors may be used as alternatives. A position sensor may be any electrical device for measuring the position, or a derivative of position, or distance from an object, examples of which include an encoder, a resolver, a linear variable differential transformer, a variable resistor, a variable capacitor, a laser rangefinder, an ultrasonic range detector, an infrared range detector, or other similar devices.

[0050] FIGS. 13-15 show a second embodiment 132 of the rotor pole sections and toroids stacked on shaft 31. In this embodiment, the rotor pole sections and toroids are formed as one unitary piece 132. In this embodiment, combined rotor pole and toroid section 132 is a solid unitary piece with high permeability, low coercivity, and high resistivity. In this embodiment, sections 132 have a monolithic and isotropic structure, are of a uniform composition and are formed from a metal powder such as a soft magnetic composite material. For example, and without limitation, sections 132 may be manufactured using a powdered metal compaction process in which powdered magnetic material is compacted in a custom die. Other types of materials and powders may be used as alternatives, depending on the application. Examples include, without limitation, low carbon steels, silicon steels, cobalt- iron based alloys, phosphorous-iron based alloys, nickel-iron based alloys, additive manufactured powder iron or iron alloys, pure iron power particles encapsulated with inorganic insulation, and other ferromagnetic powder particles coated with an electrical insulating film.

[0051] As shown, rotor pole section 132 does not include a support plate or a retaining ring. Instead, rotor pole section 132 comprises a plurality of radially extending solid pole pieces 133 spaced circumferentially about central axis 16 and radially extending like spokes from solid inner support ring 137, which includes integrated toroid 142, to individual outer ends 135. In this embodiment, each of solid pole pieces 133 are formed from a metal powder such as a soft magnetic composite material, inner support ring 137 is formed from a metal powder such as a soft magnetic composite material, and toroid 142 is formed from a metal powder such as a soft magnetic composite material, to thereby form a unitary monolithic integrated structure. Such structure may be a monolithic element constructed by an additive manufacturing process. As shown, the inner ends 134 of pole pieces 133 are integral to solid inner support ring portion 137, which radially overlaps adjacent toroid portion 142, with the inner radius of inner support ring portion 137 being the same as the inner radius of axially adjacent toroid portion 142 and the outer radius of inner support ring portion 137 being the same as the outer radius of axially adjacent toroid portion 142. Outer ends 135 of pole pieces 133 radially overlap their adjacent stator pole sections such that outer ends 135 of pole pieces 133 are spaced a radial distance from axis 16 that is greater than the inner radius of stator pole sections 22a, 22b and 22c, respectively. [0052] The improved electric motor assembly 15 provides a number of advantages over the prior art. Such advantages include high magnetic permeability, high resistivity, reduced eddy current losses, low core loss, increased structural integrity due to the solid construction of the pole pieces when compared to slit lamination-formed poles, for example, improved machinability, more precise dimensional control in production, easier manufacturing, less lead time, and lower cost.

[0053] The present invention contemplates that many changes and modifications may be made. The diameter size of the components are scalable, depending on the performance desired from the final motor. The length of the assembled motor, the axial thickness of the pole sections, and the number of pole sections are scalable, again depending on the performance desired and the practical manufacturing limits of the components. Therefore, while the presently preferred form of the motor assembly has been shown and described, those persons skilled in this art will readily appreciate the various additional changes and modification may be made without departing from the spirit of the invention, as defined and differentiated by the following claims.