Electric machine with variable cross-sectional area constant perimeter trapezoidal teeth

A radial flux electric machine includes a rotor configured to rotate about an axis of rotation and a stator fixedly positioned proximate the rotor. At least one of the rotor or the stator may include a plurality of teeth annularly arranged about the axis of rotation. Each tooth of the plurality of teeth may extend in a radial direction such that a plurality of cross-sectional areas of each tooth in a plurality of planes perpendicular to the radial direction may vary. And perimeters of the plurality of cross-sections may be substantially the same across the plurality of perpendicular planes.

TECHNICAL FIELD

The present disclosure relates to a radial flux electric machine.

BACKGROUND

The current disclosure relates to electrical machines, and in particular to radial flux electrical machines. Electric machine (or electrical machine) is a general term for machines that rely on electromagnetic forces for its operation. The two main parts of an electric machine can be described in mechanical or electrical terms. In mechanical terms, the rotor is the rotating part, and the stator is the stationary part of an electrical machine. In electrical terms, the armature is the power-producing component and the field is the magnetic field producing component of an electrical machine. The armature can be on the rotor or the stator, and the magnetic field can be provided by either electromagnets or permanent magnets mounted on either the rotor or the stator. Electric machines are electromechanical energy converters and include, among others, electric motors, and electric generators. An electric motor converts electricity to mechanical power while an electric generator converts mechanical power to electricity. The moving part of the electric machine can be rotating (rotating electric machines) or linear (linear electric machines). Electric machines operate on the principle that electrical current generates electromagnetic flux and vice versa. In some electric machine, a rotor comprising permanent magnets is configured for rotating in an electromagnetic field generated by a plurality of electromagnets through which electricity is passed.

Electrical machines can be categorized as axial flux electric machines and radial flux electric machines. The fundamental difference between these types of machines lie in the orientation of the magnetic field in these machines. In radial flux electric machines, the working magnetic flux crosses the air gap between the stator and the rotor in the radial plane, while in axial flux electric machines, the magnetic flux crosses the air gap parallel to the axis of rotation. A large number of solutions are known aimed at reducing the stray fields of permanent magnets and windings of an electric machine, as well as increasing the concentration of the magnetic flux density in the stator and rotor cores, and strive to ensure the same values of the magnetic flux density in all parts of the core. There are also a large number of solutions aimed at providing a high fill factor for permanent magnet electric machines. Some of these solutions use complex tooth shapes to improve electric machine performance. While some of these solutions effectively uses the volume of the tooth, they do not sufficiently reduce the leakage fluxes of the electric machine. In addition, in some cases, the complex tooth shapes makes it difficult to provide a high winding fill factor for electric machines. The radial flux electric machines of the current disclosure alleviates some or all of the above-mentioned issues. A decrease in leakage fluxes and an increase in the fill factor in embodiments of electric machines of the current disclosure may allow for increased power and efficiency of electrical machines. However, the scope of the current disclosure is defined by the claims and not by the ability to solve any problem.

SUMMARY

Several embodiments of an electric machine and methods of fabricating and using an electric machine are disclosed. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only. As such, the scope of the disclosure is not limited solely to the disclosed embodiments. Instead, it is intended to cover such alternatives, modifications and equivalents within the spirit and scope of the disclosed embodiments. Persons skilled in the art would understand how various changes, substitutions and alterations can be made to the disclosed embodiments without departing from the spirit and scope of the disclosure.

In one embodiment, an electric machine having a plurality of trapezoidal teeth is disclosed. The electric machine may include a plurality of electromagnetic coils. Each coil may include a non-uniform trapezoidal cavity therethrough and may be configured to contain therein one tooth of the plurality of teeth. Each tooth may be formed of multiple pieces that, when assembled together form a trapezoidal tooth.

In some embodiments, the trapezoidal shape of the multipiece tooth, in which the cross-sectional area increases in the radial direction towards the rotor, and the winding coils are shifted as close as possible to the air gap, may significantly reduce the leakage fields of the electric machine. Pre-forming a tooth with a constant cross-sectional perimeter in the radial direction leads to an increase in the fill factor of the electric machine and improves the performance, efficiency torque and power of the electric machine.

In one embodiment, a radial flux electric machine is disclosed. The electric machine may include a rotor configured to rotate about an axis of rotation and a stator. At least one of the rotor or the stator may include a plurality of teeth annularly arranged about the axis of rotation. The electric machine may also include a plurality of electromagnetic coils. Each coil of the plurality of electromagnetic coils may have a non-uniform trapezoidal cavity therethrough. Each cavity may be configured to contain therein one tooth of the plurality of teeth. Each tooth of the plurality of teeth may be formed of multiple pieces that, when assembled together correspond to a shape of the non-uniform trapezoidal cavity.

Various embodiments of the electric machine may alternatively or additionally include one or more of the following aspects: when the multiple pieces of each tooth are assembled together, an external perimeter of each tooth corresponds to an internal perimeter of the cavity of a corresponding coil; each tooth includes a core tooth-portion and at least one wedge-shaped portion; each tooth includes a core tooth-portion and at least two wedge-shaped portions disposed on opposite sides of the core portion; in a plane perpendicular to the axis of rotation, the core tooth-portion has a substantially rectangular cross-sectional shape and the at least one wedge-shaped portion has a substantially triangular cross-sectional shape; in a plane perpendicular to a radial direction, the core tooth-portion and the at least one wedge-shaped portion has a substantially rectangular cross-sectional shape; the core tooth-portion and the at least one wedge-shaped portion of each tooth are coupled together using an adhesive material; the core tooth-portion of each tooth is integrally formed with an annular ring that extends around the axis of rotation; when the multiple pieces of each tooth are assembled together, each tooth defines external surfaces having two sets of opposing faces, the opposing faces of each set of the two sets being non-parallel to each other; the opposing faces of adjacent teeth are parallel to each other; each face of the two sets of opposing faces is inclined in a radial direction; the opposing faces of one set of opposing faces converge towards each other in a radially outward direction and the opposing faces of the other set of opposing faces diverge from each other in the radially outward direction; a cross-section of each tooth in a plane perpendicular to the axis of rotation has a trapezoidal shape, and a cross-section of each tooth in a plane perpendicular to a radial direction has a rectangular shape; a perimeter of the cross-sections perpendicular to a radial direction is substantially a constant in the radial direction; an area of the cross-sections perpendicular to the radial direction varies in the radial direction; the stator includes the plurality of teeth, and the area of the cross-section perpendicular to the radial direction increases in the radial direction towards the rotor; a cross-section of each tooth in an axial plane has an isosceles trapezoidal shape; at least one piece of the multiple pieces of each tooth is formed of a soft magnetic composite (SMC); the stator includes the plurality of teeth, and wherein a first piece of the multiple pieces of each tooth is integral with and extends radially from an annular stator ring that extends around the axis of rotation, and a second piece of the multiple pieces of each tooth is non-integrally formed with the first piece; the electric machine is one of an electric motor or an electric generator.

In another embodiment, a radial flux electric machine is disclosed. The electric machine may include a rotor configured to rotate about an axis of rotation and a stator fixedly positioned proximate the rotor. At least one of the rotor or the stator may include a plurality of teeth annularly arranged about the axis of rotation. Each tooth of the plurality of teeth may extend in a radial direction such that a plurality of cross-sectional areas of each tooth in a plurality of planes perpendicular to the radial direction may vary. And perimeters of the plurality of cross-sections may be substantially the same across the plurality of perpendicular planes.

Various embodiments of the electric machine may alternatively or additionally include one or more of the following aspects: a shape of each tooth in at least one of an axial plane or a radial plane of the electric machine is a trapezoid; the shape of each tooth in at least one of an axial plane or a radial plane of the electric machine is an isosceles trapezoid; the plurality of teeth are annularly arranged on the stator; the rotor is disposed radially outwards of the stator, a width of each tooth in a radial plane increases in the radial direction towards the rotor, and a length of each tooth in an axial plane decreases in the radial direction towards the rotor; each tooth extends in the radial direction such that a cross-sectional area of each tooth in a plane perpendicular to the radial direction increases in the radial direction toward the rotor; the rotor is disposed radially inwards of the stator, and a cross-sectional area of each tooth of the plurality of teeth in a plane perpendicular to the radial direction increases in the radial direction toward the rotor; the plurality of teeth are annularly arranged on the rotor; the electric machine further includes a plurality of electromagnetic coils, and wherein each coil of the plurality of electromagnetic coils extends around a separate tooth of the plurality of teeth; each coil includes copper wire having one of a square, rectangular, or circular cross-sectional shape; the wire is multi-strand and each coil is wound in the form of a spiral in the radial direction along a tooth; each coil includes copper foil wound around a tooth such that a flat side of the foil extends over an entire length of the tooth in the radial direction; each coil includes a rib of copper foil wound in the form of a spiral in the radial direction along a tooth; each tooth includes a soft magnetic composite (SMC) material; each tooth includes multiple pieces coupled together; the multiple pieces include a core portion integrally formed with an annular ring that extends around the axis of rotation and one or more wedge portions coupled to the core portion; the one or more wedge portions include at least two wedge portions disposed on opposite sides of the core portion; the electric machine is an electric motor or an electric generator; one of the stator or the rotor includes an outer part and an inner part and wherein the stator and rotor are separated by a double air gap; the outer part and the inner part connected together by a connecting portion made of a magnetically conductive material.

In another embodiment, a radial flux electric machine is disclosed. The electric machine may include a rotor configured to rotate about an axis of rotation, a plurality of electromagnetic coils, and a stator. The stator may include an annular stator ring extending about the axis of rotation and a plurality of multi-part teeth circumferentially arranged on the stator ring. Each multi-part tooth of the plurality of multi-part teeth may include a core tooth-portion integrally formed with the stator ring and at least one additional tooth-portion separate from the stator ring. Each coil of the plurality of electromagnetic coils may be mounted on a different multi-part tooth of the plurality of multi-part teeth such that each coil surrounds a corresponding core tooth-portion of the multi-part tooth with a gap between the coil and the core tooth-portion. The at least one additional tooth-portion may be disposed in the gap.

Various embodiments of the electric machine may alternatively or additionally include one or more of the following aspects: the core tooth-portion each multi-part teeth is formed of a soft magnetic composite (SMC); the annular stator ring is formed of a soft magnetic composite (SMC); the annular stator ring includes two mirror-symmetric halves coupled together along a plane of symmetry perpendicular to the axis of rotation; the two mirror-symmetric halves are attached together along the plane of symmetry using an adhesive material; the annular stator ring includes multiple axially stacked annular rings, at wherein at least two of the stacked annular rings are made of a soft magnetic composite (SMC); the core tooth-portion of each multi-part tooth extends outward in a radial direction from the annular stator ring; a cross-sectional of each of the core tooth-portion and the at least one additional tooth-portion along a plane perpendicular to the radial direction has a substantially rectangular shape; a cross-section of the core tooth-portion along a plane perpendicular to the axis of rotation has a substantially rectangular shape; a cross-section of the at least one additional tooth-portion along the plane perpendicular to the axis of rotation has a substantially triangular shape; a cross-sectional of each tooth of the plurality of multi-part teeth along the plane perpendicular to the axis of rotation has a substantially trapezoidal shape; the at least one additional tooth-portion includes a pair of additional tooth-portions arranged symmetrically on opposite sides of the core tooth-portion; the core tooth-portion and the at least one additional tooth-portion of each tooth of the plurality of multi-part teeth are coupled together using an adhesive material; a difference between coefficients of thermal expansion of materials of the core tooth-portion, the at least one additional tooth-portion, and the adhesive material is less than about 20%; the at least one additional tooth-portion of each multi-part tooth is wedged between an internal surface of a coil of the plurality of electromagnetic coils and an external surface of the core tooth-portion; a coil of the plurality of electromagnetic coils surrounds the core tooth-portion of each tooth such that at least two gaps are formed between an inner surface of the coil and opposite sides of the core tooth-portion, and wherein the at least one additional tooth-portion includes at least two additional tooth-portions disposed in a different gap of the at least two gaps; a cross-section of each multi-part tooth of the plurality of multi-part teeth in a plane perpendicular to a radial direction has a rectangular shape; a perimeter of the cross-section is substantially a constant in the radial direction; an area of the cross-section varies in the radial direction; the electric machine is an electric motor or an electric generator.

In another embodiment, a radial flux electric machine is disclosed. The electric machine may include a rotor configured to rotate about an axis of rotation, a plurality of electromagnetic coils, and a stator. The stator may have an annular stator ring and a plurality of core tooth-portions extending in a radial direction. The annular stator ring and the plurality of core tooth-portions may be integrally formed of a Soft Magnetic Composite (SMC). The SMC may include one or more isotropic ferromagnetic materials, a magnetic saturation induction of greater than or equal to about 1.6 Tesla, and an electrical resistivity greater than 10 micro-ohm/m.

Various embodiments of the electric machine may alternatively or additionally include one or more of the following aspects: the stator includes a plurality of multi-part teeth symmetrically arranged on the annular stator ring, wherein each tooth of the plurality of multi-part teeth includes one of the plurality of core tooth-portions and at least one additional tooth-portion non-integrally formed with the one of the plurality of core tooth portions; a pair of additional tooth-portions are arranged on opposite sides of an associated core tooth-portion; a cross-section of the core tooth-portion of each tooth along a plane perpendicular to the axis of rotation has a substantially rectangular shape, and a cross-section of each additional tooth portion of the at least one additional tooth-portions along the plane perpendicular to the axis of rotation has a substantially triangular shape; a cross-section of each of the core tooth-portions and the at least one additional tooth-portions along a plane perpendicular to the radial direction has a substantially rectangular shape; a cross-section of each tooth of the plurality of multi-part teeth in a plane perpendicular to the axis of rotation has a trapezoidal shape; a cross-section of each tooth of the plurality of multi-part teeth in a plane perpendicular to the radial direction has a substantially rectangular shape, and a perimeter of the cross-section is substantially a constant in the radial direction, and an area of the cross-section varies in the radial direction; the rotor is disposed radially outwards of the stator to form an air gap between the rotor and the stator, and the area of the cross-section increases in the radial direction toward the air gap; each tooth of the plurality of multi-part teeth defines external surfaces having two sets of opposing faces, the opposing faces of each set of the two sets being non-parallel to each other, and adjacent side faces of adjacent teeth being parallel to each other; each face of the two sets of opposing faces is inclined in a radial direction; the opposing faces of one set of opposing faces converge towards each other in a radially outward direction and the opposing faces of the other set of opposing faces diverge from each other in the radially outward direction; the at least one additional tooth-portions is formed of the SMC; at least one additional tooth-portion is formed of an isotropic material other than SMC; the annular stator ring includes two mirror-symmetric bodies coupled together along a plane of symmetry perpendicular to the axis of rotation; the two mirror-symmetric bodies are attached together along the plane of symmetry using an adhesive material, wherein a difference between coefficients of thermal expansion of the SMC and the adhesive material is less than about 20%; the magnetic saturation induction of the SMC is greater than or equal to about 2.4 Tesla; the magnetic saturation induction of the SMC is greater than or equal to about 2.5 Tesla; the resistivity of the SMC is greater than about 100 micro-ohm/m; the electric machine is an electric motor; the electric machine is an electric generator.

In another embodiment, a radial flux electric machine is disclosed. The electric machine may include an inner stator and an outer rotor configured to rotate about the stator. The outer rotor may include a rotor base and a plurality of annularly arranged permanent magnets axially extending from the rotor base parallel to an axis of rotation of the rotor. A cylindrical core may extend from the rotor base encircling the plurality of permanent magnets. The core may be formed of a Soft Magnetic Composite (SMC). A sleeve may encircle the rotor. The sleeve may support the cylindrical core and the cylindrical core may support the plurality of permanent magnets. The cylindrical core may be positioned radially between the sleeve and the plurality of permanent magnets.

Various embodiments of the electric machine may alternatively or additionally include one or more of the following aspects: at least one of the sleeve or the rotor base is made of non-magnetic material; the non-magnetic material is a composite material including at least one of carbon fiber, glass fiber, or aramid fiber; the non-magnetic material includes at least one of stainless steel or aluminum; the sleeve is made of a magnetic material; the magnetic material includes a soft magnetic material including laminated electrical steel sheets; the magnetic material is a solid body made of steel; the sleeve includes stiffening ribs disposed on recesses formed on an external surface of the cylindrical core; the cylindrical core extends from a first end coupled to the rotor base to a second end, wherein the sleeve includes a balancing ring located at the second end of the cylindrical core, and wherein the balancing ring is configured to provide dynamic balancing of the rotor; the sleeve extends over the balancing ring; the balancing ring is formed of a non-magnetic material; the plurality of permanent magnets are arranged on the rotor base in a substantially circular pattern around the axis of rotation; the plurality of permanent magnets are arranged on the rotor base such that the magnetic axis of each permanent magnet of the plurality of permanent magnets intersect at the axis of rotation; the rotor base is formed of aluminum or steel; the rotor base includes air vents configured to direct airflow along the axis of rotation when the rotor base rotates; the rotor base is integral with the sleeve and the balancing ring; the plurality of permanent magnets are attached to the cylindrical core using an adhesive, and wherein a difference between coefficients of thermal expansion of materials of the plurality of permanent magnets, the cylindrical core, and the adhesive is less than about 20%; the sleeve is integral with the rotor base to form a single piece; the cylindrical core and the sleeve both have a non-uniform radial thickness about the axis of rotation, and wherein thicker regions of the sleeve are located adjacent to a center of each permanent magnet; and the electric machine is one of electric motor or an electric generator.

In some embodiments, a method of assembling a coil on an irregular-shaped multi-part tooth of an electric machine is disclosed. The method may include inserting at least one wedge-portion of the multi-part tooth into an opening of the coil such that a broader end of the at least one wedge-portion extends out of the opening in the coil. The method may also include mounting the coil with the inserted at least one wedge-portion on a core tooth-portion of the multi-part tooth such that the broader end of the at least one wedge-portion remains extended out of the opening in the coil, exerting a force on the broader end of the at least one wedge-portion to tighten the coil on the multi-part tooth.

Various embodiments of the disclosed method may alternatively or additionally include one or more of the following aspects: exerting a force on the broader end of the at least one wedge-portion includes pushing the broader end of the at least one wedge-portion into the opening in the coil; the opening in the coil extends from a first end to a second end, wherein inserting the at least one wedge-portion includes inserting the at least one wedge-portion into the opening such that the broader end extends out of the second end of the opening, and exerting the force includes pushing the broader end towards the first end of the opening; the opening in the coil extends from a first end to a second end, wherein a width of the opening at the first end differs from the width of the opening at the second end, and wherein a length of the opening at the first end differs from a height of the opening at the second end; a shape of the opening at the first end and the second end is rectangular; a perimeter of the opening at the first end is substantially the same as the perimeter of the opening at the second end; an area of the opening at the first end varies from the area of the opening at the second end; an area of the opening increases from the first end to the second end; inserting the at least one wedge-portion into the opening of the coil includes inserting at least two wedge-portions into the opening; mounting the coil includes mounting the coil on the core tooth-portion such that the core tooth-portion is disposed between the at least two wedge-portions; using an adhesive material to attach the at least two wedge-portions and the core tooth-portion of the multi-part tooth together; the multi-part tooth is a part of a stator of the electric machine; the core tooth-portion of the multi-part tooth is one of a plurality of core tooth-portions symmetrically arranged on an annular stator ring that extends around a central axis, and wherein the core tooth-portion extends outward in a radial direction from the annular stator ring; the plurality of core tooth-portions are integrally formed with the annular stator ring; in a plane perpendicular to the central axis, the core tooth-portion has a substantially rectangular cross-sectional shape and the at least one wedge-portion has a substantially triangular cross-sectional shape; in a plane perpendicular to the radial direction, the core tooth-portion and the at least one wedge-portion have a substantially rectangular cross-sectional shape; the coil includes a winding of a copper wire around the opening, the wire having one of a square, rectangular, or circular cross-sectional shape; the coil includes a winding of a copper stranded wire in a spiral around the opening; the electric machine is an electric motor; and the electric machine is an electric generator.

In some embodiments, a method of fabricating a coil for mounting on a tooth of a stator or a rotor of an electric machine is disclosed. The method may include winding a wire about a mandrel to form a coil having a first shape corresponding to the shape of the mandrel, removing the coil having the first shape from the mandrel, and applying a mechanical force on the coil to change the shape of the coil from the first shape to a second shape. The second shape may correspond to the shape of the tooth. The method may also include mounting the coil of the second shape on the tooth.

Various embodiments of the disclosed method may alternatively or additionally include one or more of the following aspects: the wire is formed of a plurality of strands of an electrical conductor; the wire is formed by twisting together an electrical conductor or made in the form of a Litz wire; the wire has a circular cross-sectional shape; the wire has one of a square or a rectangular cross-sectional shape; the first shape is a cylindrical shape or any shape with a substantially constant perimeter; the second shape is a trapezoidal shape; winding the wire about the mandrel includes winding the wire about the mandrel in a spiral pattern to form coil having an internal cavity extending from a first end to a second end; applying a mechanical force on the coil includes selectively increasing a size of the cavity at one of the first end or the second end; applying a mechanical force on the coil includes changing a shape of the internal cavity; changing the shape of the internal cavity includes changing a cross-sectional shape of the internal cavity along a plane perpendicular to a central axis of the internal cavity from a circular shape to a rectangular shape; a width and a length of the rectangular shape both vary from the first end to the second end; a perimeter of the rectangular shape is substantially a constant from the first end to the second end and an area of the rectangular shape varies from the first end to the second end; the area of the rectangular shape increases from the first end to the second end; changing the shape of the internal cavity includes changing a 3-dimensional shape of the inner cavity from a cylindrical shape to a trapezoidal shape; applying a mechanical force on the coil includes inserting a second mandrel into the internal cavity of the coil to change a shape of the first end of the internal cavity compared to a shape of the second end of the internal cavity; applying a mechanical force on the coil includes applying a first mechanical force to increase a dimension of the internal cavity at one of the first end or the second end and a second mechanical force to decrease a dimension of the internal cavity at the other of the first end or the second end; the first mechanical force acts towards a central axis of the internal cavity and the second mechanical force acts away from the central axis; applying a mechanical force on the coil includes stretching the wire of the coil that defines at least one of the first end or the second end of the internal cavity; the wire is made of copper.

In one embodiment, an electric machine is disclosed. The electric machine may include a rotor configured to rotate about an axis of rotation, a stator having a plurality of teeth annularly arranged on a stator core about the axis of rotation, a plurality of electromagnetic coils, and a base plate. Each coil of the plurality of electromagnetic coils may be mounted on a separate tooth of the plurality of teeth, and the base plate may be located adjacent to the plurality of electromagnetic coils and the stator core. The base plate may be in thermal contact with the plurality of electromagnetic coils and the stator core such that as the plurality of electromagnetic coils and the stator core heat during operation, the base plate is configured to serve as a common heat sink for the plurality of electromagnetic coils and the stator core.

Various embodiments of the disclosed electric machine may alternatively or additionally include one or more of the following aspects: each coil of the plurality of electromagnetic coils is in contact with the base plate directly or through a thermally-conductive material disposed therebetween; the stator core is in contact with the base plate directly or through a thermally-conductive material disposed therebetween; further include a motor housing thermally connected to the base plate to enable heat generated by the plurality of electromagnetic coils and stator core to be dissipated through the base plate and the motor housing; the base plate includes a first side and a second side opposite the first side, wherein the plurality of electromagnetic coils and the stator core are in thermal contact with the first side of the base plate and the motor housing is in thermal contact with the second side of the base plate; the second side of the base plate includes cooling fins that extend therefrom; the cooling fins include a plurality of pins; the base plate includes a cylindrical hub portion extending around the axis of rotation; the stator core includes an annular stator ring that extends around the cylindrical hub portion of the base plate; an inner annular surface of the annular stator ring is in contact with an outer annular surface of the cylindrical hub portion of the base plate directly or through a thermally-conductive material disposed therebetween; the stator core includes an annular stator ring that extends around the axis of rotation and each tooth of the plurality of teeth includes a core tooth-portion integral with the annular stator ring; each tooth of the plurality of teeth further includes one or more additional tooth-portions non-integrally formed with the core tooth-portion; a pair of additional tooth-portions includes tooth-portions arranged on opposite sides of the core tooth-portion; when all the tooth parts are assembled together, each tooth defines external surfaces having two sets of opposing faces, the opposing faces of each set of the two sets being non-parallel to each other, and wherein each face of the two sets of opposing faces is inclined in a radial direction; opposing faces of adjacent teeth are substantially parallel to each other; a cross-section of each tooth in a plane perpendicular to the radial direction has a rectangular shape, and wherein a perimeter of the cross-section is substantially a constant in the radial direction and an area of the cross-section varies in the radial direction; the base plate is formed of aluminum; the base plate includes air vents configured to direct air to the plurality of electromagnetic coils when the rotor rotates; the electric machine is an electric motor; the electric machine is an electric generator.

In yet another embodiment, an electric machine is disclosed. The electric machine may include a rotor configured to rotate about an axis of rotation, a stator having a stator core and a plurality of teeth annularly arranged on the stator core about the axis of rotation, a plurality of electromagnetic coils, and a base plate. Each coil of the plurality of electromagnetic coils may be mounted on a separate tooth of the plurality of teeth. The base plate may be located adjacent to the plurality of electromagnetic coils and the stator core. The base plate may have a first side and an opposing second side. The first side may be in thermal contact with the plurality of electromagnetic coils and the stator core. A liquid-coolant channel may be defined on the second side of the base plate such that as the coils and the stator core heats during operation, the base plate is configured to transfer the heat to a liquid coolant in the liquid-coolant channel to dissipate heat from the plurality of electromagnetic coils and the stator core.

Various embodiments of the disclosed electric machine may alternatively or additionally include one or more of the following aspects: each coil of the plurality of electromagnetic coils is in contact with the base plate directly or through a thermally-conductive material disposed therebetween; the stator core is in contact with the base plate directly or through a thermally-conductive material disposed therebetween; further include a motor housing thermally connected to the base plate to enable heat generated by the plurality of electromagnetic coils and stator core to be dissipated through the base plate and the motor housing; the base plate includes a first side and a second side opposite the first side, wherein the plurality of electromagnetic coils and the stator core are in thermal contact with the first side of the base plate and the motor housing is in thermal contact with the second side of the base plate; a wall of the liquid-coolant channel is a portion of the second side of the base plate directly opposite a portion of the first side of the base plate that is in thermal contact with the plurality of electromagnetic coils; the liquid-coolant channel extends around the axis of rotation and an annular region on the second side of the base plate serves as a wall of the liquid-coolant channel; the annular region on the second side of the base plate includes a plurality of fins that extend into the liquid-coolant channel; the plurality of fins is arranged about the axis of rotation; further include a coolant inlet configured to direct the coolant into the liquid-coolant channel and a coolant outlet configured to direct the coolant out of the liquid-coolant channel; the base plate includes a cylindrical hub portion extending around the axis of rotation and the stator core includes an annular stator ring that extends around the cylindrical hub portion of the base plate, and the liquid-coolant channel passes through the cylindrical hub portion along the axis of rotation; an inner annular surface of the annular stator ring is in contact with an outer annular surface of the cylindrical hub portion of the base plate directly or through a thermally-conductive material disposed therebetween; each tooth of the plurality of teeth includes a core tooth-portion integrally formed with the annular stator ring and at least one additional tooth-portion non-integrally formed with the core tooth-portion; the annular stator ring and the core tooth-portion are formed of a Soft Magnetic Composite (SMC); when the core tooth-portion and at least one additional tooth-portion are assembled together, each tooth defines external surfaces having two sets of opposing faces, the opposing faces of each set of the two sets being non-parallel to each other, and wherein each face of the two sets of opposing faces is inclined in a radial direction; opposing faces of adjacent teeth are parallel to each other; a cross-section of each tooth in a plane perpendicular to the radial direction has a trapezoidal shape, and wherein a perimeter of the cross-section is substantially a constant in the radial direction and an area of the cross-section varies in the radial direction; the base plate is formed of aluminum; the electric machine is an electric motor; the electric machine is an electric generator.

DETAILED DESCRIPTION

It should be noted that all relative terms such as “about,” “substantially,” “approximately,” etc. are used to indicate a possible variation of up to 15% (unless noted otherwise or another variation is specified). For example, the cross-sectional area of a first region described in this disclosure as being substantially equal to, or substantially the same as, the cross-sectional area of a second region covers a variation in cross-sectional area of up to 15% in its ambit. Similarly, a dimension substantially equal “t” units (width, length, etc.) covers a variation of up to 15%. Additionally, a dimension described as being between a range (e.g., X-Y, X to Y, etc.) includes the two boundaries. That is, a dimension between X-Y can be any dimension between X−15% to X+15%. Unless indicated otherwise, all terms relating to the shape of an object or area refers to approximate shapes. For example, a cross-sectional shape described as being square (rectangular, trapezoidal, etc.) does not necessarily refer to an exact square (unless it is described as being such). Instead, slight variations in the described shape (e.g., resulting from manufacturing processes, tolerances, etc.) are also covered. For example, the corners of cross-sectional area described as being square may have rounded (or chamfered) corners, variations in corner angle of up to 15%, variations in parallelism between the opposite sides of 15%, etc.

Unless defined otherwise, all terms of art, notations and other scientific terms or terminology used herein have the same meaning as is commonly understood by one of ordinary skill in the art to which this disclosure belongs. Some of the components, structures, and/or processes described or referenced herein are well understood and commonly employed using conventional methodology by those skilled in the art. Therefore, these components, structures, and processes will not be described in detail. All patents, applications, published applications and other publications referred to herein are incorporated by reference in their entirety. If a definition or description set forth in this disclosure is contrary to, or otherwise inconsistent with, a definition and/or description in these references, the definition and/or description set forth in this disclosure prevails over those in the references that are incorporated by reference. None of the references described or referenced herein is admitted as prior art to the current disclosure.

Various embodiments of the current disclosure include a radial flux electric machine. As used herein, an electric machine (or electrical machine) is a device that operates based on electromagnetic forces. In general, any type of electromechanical energy converter that operates on, or generates, electricity is an electric machine. Although not required, in some embodiments, the electric machine may be an electric motor or an electric generator. During operation, an electric machine generates magnetic flux. In a radial flux electric machine, at least some portions of the generated magnetic flux extends perpendicular to the axis of rotation of the machine. Electric machines include a stator and a rotor separated by an air gap. In a radial flux electric machine, the working (or main) magnetic flux may extend between the rotor and the stator through the air gap in the radial plane.FIG. 1illustrates an exemplary radial flux electric machine10of the current disclosure. Internal details of electric machine10will be described with reference toFIGS. 2 and 3. Electric machine10illustrated inFIG. 1may be an air-cooled system with a housing50. External ribs52may be positioned on the surface of the housing50between an end shield54and a stator base plate56. As illustrated inFIG. 1, the base plate56may include a plurality of pins58extending therefrom. The ribs52and pins58may assist in transferring the heat generated by the electric machine10during operation to the surrounding air. In the discussion below, electric machine10in the form of an electric motor will be described. However, the description is equally applicable to other types of electric machines, such as, for example, an electric generator. When electric machine10operates, its shaft20rotates.

Electric machines of the current disclosure may include a rotor configured to rotate about an axis of rotation and a stator. As used herein, a stator is any stationary or fixed part, component, or assembly (of components) of the electric machine, and the rotor is a part, component, or assembly that is configured to move with respect to the stator. In some embodiments, the rotor may be configured to rotate about an axis of rotation relative to the stator. The rotor is coupled to a shaft (rotor shaft) that rotates with the rotor. The axis about which the rotor (and the shaft) rotates is referred to as the “axis of rotation.”FIG. 2illustrates a cross-sectional view of electric machine10(ofFIG. 1) along an axial plane of the machine10, andFIG. 3illustrates a cross-sectional view of machine10along a radial plane of machine10. Axial plane refers to an imaginary plane that that the axis of rotation of the machine lies in (or is a part of). In other words, every point of the axis of rotation of the machine lines in the axial plane. InFIG. 2, the axis of rotation1000of machine10lies in the axial plane, and the axial plane bisects the machine10into two symmetric halves. Radial plane refers to a plane that extends perpendicular to the axis of rotation. The axis of rotation1000extends perpendicular (e.g., into and out of the paper) to the radial plane.

In the discussion below, reference will be made toFIGS. 2 and 3. Electric machine10includes a rotor200and a stator100. The rotor200is configured to rotate about the axis of rotation1000with respect to the stator100. The stator100includes a stator core110comprising a plurality of teeth120, and the rotor200includes a rotor core210comprising a plurality of permanent magnets220. Electromagnetic coils300are mounted on the teeth120of the stator100. The rotor200is connected to the shaft20that is configured to rotate about the axis of rotation1000. When electric power is provided to the coils300, a magnetic field is generated. Based on the generated magnetic field, magnetic flux flows between the rotor200and the stator100, thereby providing a rotary force to the rotor. Electric machine10may be used as a power source in any application. For example, in an electric vehicle, the electric machine10may drive the wheels of the electric vehicle.

In electric machines of the current disclosure, at least one of the rotor and/or the stator may include a plurality of teeth annularly arranged about the axis of rotation. As used herein, teeth refers to projections that protrude from a body. The teeth may include a series of substantially similar projections that protrude from the body. For example, in embodiments where the rotor includes teeth, a series of substantially similar projections that protrude from a body or a core of the rotor comprise the teeth. And in embodiments where the stator includes teeth, a series of substantially similar projections that protrude from a body or core of the stator comprise the teeth. In a radial flux electric machine, the teeth protrude in the radial plane. In other words, the teeth line in the radial plane and protrude (inward or outward) in the radial direction. Each projection forms a tooth. Typically, the projections (or teeth) are configured or shaped to direct a substantial portion of the magnetic flux between the stator and the rotor. With reference toFIGS. 2 and 3, in electric machine10, the stator100includes a plurality of teeth120arranged annularly and symmetrically about the axis of rotation1000on a core110of the stator100. As will be explained in more detail later, each tooth120includes multiple pieces or parts that are arranged together to form a composite or a multi-part tooth120. The outline of three teeth120are shown using dashed lines inFIG. 3. As will be described in more detail later, each tooth120may have a trapezoidal cross-sectional shape in both the axial plane (seeFIG. 2) and the radial plane (seeFIG. 3).

As can be seen inFIG. 3, the rotor200is separated from the stator100by an air gap250. In some embodiments, as described previously, depending on the configuration of the rotor200and the stator100, multiple air gaps may separate the rotor200and the stator100. In the exemplary embodiment illustrated inFIGS. 2 and 3, the stator100includes nine teeth120and the rotor200includes ten permanent magnets220(identified using dashed lines inFIG. 3). However, this is only exemplary. In general, any number of teeth120and permanent magnets220may be provided. As best seen inFIG. 3, each permanent magnet220may include multiple permanent magnet segments222coupled together in the form of an arc about the axis of rotation1000. Any number of segments222may be included in each permanent magnet220. In some embodiments, all permanent magnets220may include the same number of segments222. In some embodiments, the multiple segments222may be attached together (e.g., by an adhesive material) to form a permanent magnet220. Any type of permanent magnet may be used. In some embodiments, the permanent magnets220may include one or more of ferrites, alnico, samarium cobalt, or a neodymium alloy. In some embodiments, each permanent magnet220may be coated with an electrically non-conductive material. In some embodiments, adjacent permanent magnets220may be separated from each other by spacers224. The spacers224may be made of an electrically non-conductive material and may be attached to the adjacent permanent magnets220by an adhesive material (e.g., glue). In some embodiments, the spacers224may be eliminated and adjacent permanent magnets220may be separated from each other by a space or a gap.

The electric machines of the current disclosure may include a plurality of electromagnetic coils. An electromagnetic coil (or an electric coil) may include one or more turns of an electrical conductor that generates a magnetic field when an electric current is passed through the conductor (e.g., in electric motors), or generates a voltage across the conductor when a magnetic field passes over the coil. In some embodiments, the turns of electrical conductor may be configured or shaped like a coil, loop, twist, curl, or a spiral. In some embodiments, an electromagnetic coil may be an electrical conductor that contains a series of conductive wires configured to be wrapped around a ferromagnetic core. In general, electromagnetic coils of the current disclosure may be associated with the stator or the rotor of the electric machine. That is, in some embodiments, the plurality of coils may be coupled to (e.g., mounted, installed, wound on, etc.) the rotor and in other embodiments, the plurality of coils may be coupled to the stator. In the exemplary embodiment of electric machine10illustrated inFIGS. 2 and 3, a plurality of electromagnetic coils300are coupled to the stator100. It should also be noted that the configuration of the electric machine10illustrated inFIGS. 2 and 3is only exemplary.

In the electric machine10ofFIGS. 2 and 3, a single rotor200is positioned radially outwards a single stator100. However, this configuration is only exemplary, and electric machines of the current disclosure may have other configurations.FIGS. 8A-8Eare schematic illustrations of exemplary configurations of electric machines of the current disclosure showing the layout of the stator100relative to the rotor200. In each case, the rotor200is connected to a shaft20that rotates about the axis of rotation1000, and includes a plurality of permanent magnet segments220arranged annularly about the axis of rotation1000. And the stator includes a plurality of teeth120arranged annularly about the axis of rotation1000. Each tooth120comprises multiple parts and has a trapezoidal cross-sectional shape in both the axial and radial planes (as inFIGS. 2, 3). And coils300are mounted on one or more of the teeth120.

FIG. 8Aschematically illustrates the electric machine10ofFIGS. 2 and 3where the rotor200is positioned outside the stator100. In such an embodiment, a width of each tooth120in the radial plane increases in the radial direction (seeFIG. 3) towards the air gap250(and the rotor200), and a length of each tooth120in an axial plane decreases in the radial direction towards the air gap250(seeFIG. 2). That is, with reference toFIGS. 2 and 3,1>2and w1<w2. In electric machine10A ofFIG. 8B, the rotor200is positioned radially inwards of the stator100. That is, in contrast with electric machine10ofFIG. 8A, the rotor200of machine10A is positioned closer to the axis of rotation1000than its stator100.FIG. 8Cillustrates a cross-sectional view of electric machine10A (ofFIG. 8B) in the radial plane. In electric machine10A ofFIGS. 8B and 8C, the width of the stator tooth120in the radial plane (seeFIG. 8C) decreases in a radially inward direction towards the rotor200and the air gap250, and its length in the axial plane (view illustrated inFIG. 8B) increases in the radially inward direction towards the rotor200.

Electric machine10B ofFIG. 8Dincludes two stators100A,100B positioned on opposite sides of the rotor200. Both the inner and the outer stator100A,100B include a plurality or multi-part teeth120annularly arranged about the axis of rotation1000. In electric machine10B, the width of each tooth120(in the radial plane) of the inner stator100A increases in the radially outward direction toward the rotor200(and air gap250), and the width of each tooth120of the outer stator100B decreases in the radially inward direction toward the rotor200(and air gap250). Conversely, as shown inFIG. 8D, the length of each tooth120(in the axial plane) of the inner stator100A decreases in the radially outward direction toward the rotor200, and the length of the teeth120(in the axial plane) of the outer stator100B increases in the radially inward direction toward the rotor200. In other words, if the width of a tooth120decreases in one direction its length increases in that same direction, and vice versa.

Electric machine10C ofFIG. 8Eincludes two rotors200A,200B positioned on opposite sides of the stator100. In such a configuration, the width of the stator tooth120(in the radial plane) increases in a radially outward direction towards the outer rotor200B and decreases in a radially inward direction towards the inner rotor200A. Conversely, as evident fromFIG. 8E, the length of the stator tooth120(in the axial plane) decreases in a radial outward direction toward the outer rotor200B and increases in a radially inward direction toward the inner rotor200A. The cross-sectional area of each tooth120may increase in the radially outward direction. In electric machines10-10C (ofFIGS. 8A-8E), a coil300is mounted on each tooth120such that it is positioned close to the air gap250between the stator and the rotor.

FIG. 9illustrates an exemplary electric machine10F which includes an inner stator100A and an outer stator100B positioned on radially opposite sides of the rotor200. Each of the inner and outer stators100A,100B are separated from the rotor200by an air gap250(not visible inFIG. 9). That is, electric machine10F is a double air gap electric machine. A coil300is mounted on the inner stator100A. Unlike the double stator electric machine10B ofFIG. 8D, in electric machine10F ofFIG. 9, a coil300is not mounted on the outer stator100B. Instead, a coil300is only mounted on the teeth120of the inner stator100A.

FIG. 10illustrates an exemplary double stator electrical machine10G which differs from an electrical machine10F (ofFIG. 9) in that the inner and outer stators100A,100B are connected by a magnetically conducting bridge140. Bridge140may be made of any suitable material, such as, for example, laminated steel, SMC, etc. SMC may provide isotropic magnetic properties (i.e., the ability to conduct magnetic flux the same in all directions) to the bridge140. It should be noted that the configurations of electric machines discussed above are only exemplary. Many other variations are possible. Each of these variations of electric machines include multi-part teeth120having a trapezoidal cross-sectional shape in the radial and axial planes with coils300mounted on one or more teeth120, as will be discussed in more detail later.

FIGS. 11-22are schematic illustrations of some exemplary variations of radial flux electric machines of the current disclosure having multi-part teeth120with a trapezoidal cross-sectional shape in the radial and axial planes. In these figures, a cross-sectional representation of the electric machine in the axial plane is shown on the left side and a cross-sectional representation of the electric machine in the radial plane is shown on the right side. For the sake of brevity, only aspects of each electric machine that are different from other described embodiments will be described below. In the electric machine ofFIG. 11, the rotor200is mounted radially outside the stator100. A plurality of multi-part teeth120are assembled and arranged in the form of a ring on the stator100. Coils300extend around each tooth120. In the rotor200, the permanent magnets220are annularly arranged in slots formed a drum230of the rotor200to form an air gap250between the stator100and the rotor200.

In the electric machine ofFIG. 12, the rotor200is installed radially between an inner and an outer stator100A,100B. The inner stator100A is made in the form of a ring and contains trapezoidal teeth120. As will be explained later (with reference toFIGS. 23A-23K), in the electric machines ofFIGS. 11 and 12, each tooth120is formed of a core tooth-portion122formed integrally with an annular part130of the stator core110and one or more additional wedge-shaped tooth-portions124A-124F assembled together to form a trapezoidal tooth120. The rotor200is configured to rotate between the inner and outer stators100A,100B with air gaps250formed between each of the inner and outer stators100A,100B and the rotor200. Electric machines with two air gaps (e.g.,FIGS. 12, 13, etc.) are referred to as double air gap electric machines.

In the electric machine ofFIG. 13, as in the embodiment ofFIG. 12, the rotor200is installed between the inner and outer stators100A,100B, and the inner stator100A is made in the form of a ring and includes a plurality of multi-part teeth120. The inner and outer stators100A,100B are connected by a magnetically conductive bridge140. The electric machine ofFIG. 14is similar to the electric machine ofFIG. 11, except that its teeth120are formed separate parts that are assembled on the stator100(see, e.g.,FIGS. 23L-23N, 24A-24D). That is, in the embodiment ofFIG. 14, as will be described with reference toFIGS. 23L-23N, each tooth120may be formed of multiple parts that are separate from the stator core110.

FIG. 15illustrates an electric machine where the rotor200is installed between inner and outer stators100A,100B, and the teeth120are separate from the stator100(as explained with reference toFIG. 14). The electric machine ofFIG. 16is similar to the electric machine ofFIG. 15except that a bridge140connects the inner and outer stators100A,100B. In the electric machine ofFIG. 17, the rotor200is installed between inner and outer stators100A,100B that are connected together by a bridge140. The inner stator100A includes multi-part trapezoidal teeth120similar to that in the electric machine ofFIG. 12, and the outer stator100A is made of separate arc-shaped segments arranged in a ring. The electric machine ofFIG. 18is similar to the electric machine ofFIG. 17except that its teeth120on the inner stator100A are similar to that in the electric machine ofFIG. 14.

In electric machine ofFIG. 19, the rotor200is mounted inside the stator100, and the stator teeth120are assembled on the outer stator100made in the form of a ring. In the electric machine ofFIG. 20, the rotor200is installed between the inner and outer stators100A,100B that are connected together by a bridge140. The outer stator100B, made in the form of a ring and includes teeth120with coils300mounted thereon. In the electric machine ofFIG. 21, the rotor200is installed between the inner and outer stators100A,100B. Both the inner and outer stators100A,100B are made in the form of rings and includes trapezoidal teeth120with coils300mounted thereon. The electric machine ofFIG. 22is similar to the electric machine ofFIG. 21except that the inner and outer stators100A,100B are connected by a bridge140.

The above described embodiments of electric machines are only exemplary. There may be many variations to the above-described embodiments. Since a person skilled in the art would be able to recognize these variations based on the above disclosure, these variations are not discussed further herein. Furthermore, although the teeth120are described as being part of the stator100in the above described embodiments of electric machines, this is not a limitation. That is, in some embodiments, the teeth120may alternatively or additionally be part of the rotor200. For the sake of brevity, in the discussion below, exemplary aspects of the current disclosure will be discussed with reference to the configuration of electric machine10illustrated inFIGS. 2 and 3. It should be emphasized that this discussion applies equally to other configurations of electric machines (such as, for example, the configurations discussed above).

FIGS. 4A-4Cillustrate different views of the stator100separated from other components of electric machine10ofFIGS. 2 and 3.FIGS. 4A and 4Billustrate perspective views of the stator100, andFIG. 4Cillustrates a cross-sectional view of the stator100in the axial plane. Each coil300is mounted, or installed, on a tooth120. In some embodiments, a coil may be installed on a tooth such that the inner surface of the coil300fits snugly against the outer surface of the tooth120. In some such embodiments, the external shape (or profile) of the coil300may be substantially the same as the external shape of the tooth120that it is mounted on.FIG. 5illustrates an electrical connection diagram of an exemplary 3-phase winding140of electrical machine10. As best seen inFIGS. 4A-4B, each tooth120of stator100is separated from an adjacent tooth120by a slot160that accommodates the coils300mounted on the adjacent teeth120. As illustrated inFIG. 5, the coils300mounted on the teeth120of the electric machine10collectively form a 3-phase winding310. It should be noted that, although the stator100is described as including teeth120, in some embodiments, the rotor200may alternatively or additionally include teeth120.

FIGS. 6A-6D and 7A-7Eillustrate different aspects of an electromagnetic coil300that may be mounted on a tooth120. In the embodiments illustrated inFIGS. 6A-6D, the coil300is made, or formed of, a foil312of an electrically conductive material, and in the embodiments illustrated inFIGS. 7A-7E, the coil300is made of an electrically conductive wire314. As would be recognized by a person skilled in the art, a foil is a strip of electrical conductor having a thickness and a width. The width of the foil will typically be larger than its thickness. That is, a foil is a thin strip of an electrically conductive material. In general, any type of an electrical conducting material may be used to form the coil300. In some embodiments, copper may be used. In some embodiments, the foil312may be coated with an electrically insulating material.

In the exemplary embodiments of coil300illustrated inFIGS. 6A and 6B, the coil300comprises multiple turns of foil312surrounding a central cavity320that extends from a first end322to a second end324of the coil300. As illustrated inFIG. 6B, the coil300is mounted on a tooth120such that the tooth120extends through the cavity320. In some embodiments, as shown inFIGS. 6A and 6B, the width of the foil312(i.e., the width along the flat side of the foil) may extend the entire width of a tooth120in the radial direction of the tooth (i.e., along the radial axis2000). In some embodiments, as illustrated inFIGS. 6C and 6D, a rib of foil312(i.e., a strip of foil312having a width smaller than the width of the tooth120) may be wound, e.g., in the form of a spiral, in the radial direction along the tooth120to form a coil300(see, e.g.,FIGS. 6C, 6D).

In some embodiments, as illustrated inFIGS. 7A-7E, the coil300may be made using one or more strands of an electrically conductive (e.g., copper) wire314. In some embodiments, the wire314may be coated with an electrically insulating material. In some embodiments, as shown inFIGS. 7A-7C, the wire314may be wound in the form of a spiral to define the central cavity320of coil300. The spirally wound wire314may extend from the first end322to the second end324of the coil300. The wire314may have any cross-sectional shape. In some embodiments, as illustrated inFIG. 7D, the wire314may have a circular cross-sectional shape. In some embodiments, as illustrated inFIG. 7E, the wire314may have a square or rectangular cross-sectional shape. It should be noted that these illustrated cross-sectional shapes are only exemplary. In general, the wire314may have any cross-sectional shape. In some embodiments, to reduce eddy current losses, multiple wires314may be twisted together in the form of a Litz wire. As would be recognized by a person skilled in the art, a Litz wire consists of multiple wire strands, individually insulated, and twisted or woven together, arranged in one of several patterns. These patterns may serve to equalize the proportion of the overall length over which each strand is at the outside of the conductor. The use of stranded wires or Litz wire may be beneficial to reduce eddy current losses and increase the efficiency of the electrical machine. An exemplary method of forming the coil300using the foil312or the wire314will be described later with reference toFIGS. 45-47.

In various embodiments, each coil of the disclosed electric machine may have a non-uniform trapezoidal cavity therethrough. Non-uniform trapezoidal cavity refers to a cavity that has a non-uniform cross-sectional shape along a length portion thereof. In non-uniform cavity, a parameter related to a cross-sectional dimension of the cavity varies over at least a portion of the length of the cavity. Any parameter related to the dimension (e.g., width, height, length, area, perimeter, or another measure related to a dimension) may vary over (i.e., not be a constant over) a portion of the length of the cavity. In some embodiments, in a non-uniform cavity, an area (or another measure related to dimension) of the cavity may not be uniform along a portion of the cavity length. In some embodiments, the area (or another dimensional measure) of the cavity may not be uniform over the entire length (i.e., from one end of the cavity to the other end) of the cavity. In some embodiments, in a non-uniform cavity, one parameter (e.g., perimeter) may be uniform while another parameter (e.g., area) may be non-uniform over a portion of the cavity or the entire cavity.

As explained previously (with reference toFIGS. 6A-7E), whether made of foil312or wire314, the coil300may include a cavity320that extends from its first end322to second end324. In various embodiments, cavity320may be a non-uniform trapezoidal cavity. That is, a cross-sectional dimension related parameter of the cavity may vary at least over a portion of the length between the first and second ends322,324. With reference toFIG. 6B, coil300is mounted on a tooth120such that the interior surfaces of its cavity320mates closely with, or is snug against, the exterior surfaces of the tooth120. As a consequence of such mounting, the internal shape of the cavity320of coil300may be substantially the same as (or similar to) the external shape of the tooth120. With reference toFIGS. 2 and 3, the cross-sectional shape of each tooth120in the radial and axial plane may be trapezoidal. In other words, the tooth120may be trapezoidal shaped. The width and length of each tooth120varies in the radial direction. That is, as illustrated inFIG. 2, the lengthof tooth120varies from1to2in the radially outward direction of tooth120(along radial axis2000), and as illustrated inFIG. 3, the width w of tooth120varies from w1to w2in the radially outward direction of tooth120. As will be explained later (with reference to26A-26D), the perimeter of the cross-section of the tooth120in a plane perpendicular to the radial direction may be substantially a constant in its radial direction while the area of the cross-section varies in the radial direction. In some embodiments, each tooth120may have a trapezoidal cross-sectional shape that is non-uniform in the radial direction. The cavity320of coil300may also have a similar trapezoidal cross-sectional shape that is non-uniform in the radial direction.

In various embodiments, each cavity of the coil may be configured to contain therein one tooth of the plurality of teeth. In general, the tooth may be contained or disposed in the coil cavity in any manner. That is, in some embodiments, each tooth may be snugly received in a coil cavity, while in other embodiments, the tooth may be loosely received in cavity. In some embodiments, portions of the external surface of the tooth may contact portions of the internal surface of the cavity that contains the tooth. In some embodiments, an interfacial material may be disposed between the mating surfaces of the cavity and the coil. With reference toFIG. 6B, in some embodiments, a tooth120is snugly contained in cavity320of coil300such that at least some portions of the outer surface of the tooth contact portions of the inner surface of the cavity320. However, this is not required, and tooth120may be contained in cavity320in any manner. That is, in some embodiments, the outer surface of tooth120in the cavity320may not make physical contact with the inner surface of the cavity320. In some embodiments, the outer surface of the tooth120and the inner surface of the cavity320may be separated by another material.

In various embodiments, each tooth may be formed of multiple pieces that, when assembled together correspond to a shape of the non-uniform trapezoidal cavity of the coil. As used herein, a piece refers to a portion or a part of the whole. A piece may have any size and shape. The tooth may be formed of any number of pieces or parts and these multiple parts may have any shape and may be assembled together in any manner. For example, in some embodiments, the multiple parts may be glued or secured together in another manner. In some embodiments, the multiple parts may be merely loosely or tightly placed together. In the embodiment of electric machine10ofFIGS. 2 and 3, the non-uniform trapezoidal cavity320of the coil300is configured to contain the multiple parts that form a multi-piece tooth120. The size and shape of the cavity320is configured to receive the multi-part tooth120therein. In some embodiments, the size of cavity320of coil300may be substantially the same as the size of tooth120. In some embodiments, the cavity320may be sized slightly smaller than the tooth120such that, when the multi-part tooth120is assembled (as will be described later with reference toFIGS. 45-47), the coil300expands to snugly receive the tooth120in cavity320.

FIGS. 23A-23Killustrate different exemplary embodiments of teeth120of electric machine10arranged on the core110of its stator100. In these embodiments, each tooth120includes multiple pieces or parts arranged together to form the complete multi-part tooth120.FIGS. 23A-23Dillustrate one exemplary embodiment of multi-part teeth120,FIGS. 23D-23Hillustrate other exemplary embodiments of teeth120, andFIGS. 23I-23Killustrate further exemplary embodiments of multi-part teeth120. In should be noted that these illustrated embodiments are only exemplary and electric machines of the current disclosure may include other types of multi-part teeth in the stator and/or the rotor.

FIG. 23Aillustrates a perspective view andFIG. 23Billustrates an enlarged portion ofFIG. 23Ashowing the structure of a single tooth120.FIGS. 23C and 23Dillustrate cross-sectional views ofFIG. 23Ain the radial and axial planes, respectively. Stator core110includes a ring-shaped or annular part130. Each multi-part tooth120of the stator100extends in a radially outward direction from the annular part130. When stator100and rotor200are assembled to form an electric machine10, each tooth120extends radially outwards towards the air gap250(seeFIGS. 2 and 3). As explained previously, tooth120has a multi-part construction. In the exemplary embodiment of tooth120illustrated inFIGS. 23A-23D, each tooth120has a core tooth-portion122and two additional tooth-portions124A,124B assembled together to form the tooth120.

Core tooth-portion122is integral with the annular part130of stator core110, and each additional tooth-portion124A,124B is installed on an opposite side face of the core tooth-portion122. The terms “integral with” and “integrally formed,” are used to indicate that two parts are connected to form a single part that practically cannot be dismantled without destroying the integrity of the part. In some cases, the two integrally formed parts may be formed as a single part. In some embodiments, one or more of the additional tooth-portions may be shaped like a wedge. As used herein, a wedge-shaped portion is part with a narrower end and a broader end. With reference toFIG. 23B, each additional tooth-portion124A,124B is a wedge-shaped component that extends from a narrower first end126to a broader second end128. Although the first and second additional tooth-portions124A,124B are illustrated as identical components in this embodiment, this is not a requirement.

FIGS. 23E-23Hillustrate exemplary embodiments of tooth120having a core tooth-portion122and one additional tooth-portion124C or124D that are assembled to form the tooth120. In these embodiments, the core tooth-portion122is integral with the annular part130of core110, and the additional tooth-portion124C,124D is wedge-shaped. The additional tooth-portion124C or124D is installed on one side face of the core tooth-portion122to form the tooth120. While the core-tooth portion122(of the tooth120) ofFIGS. 23E(and23A) extends radially outward from the annular part130along the radial axis2000, the core tooth-portion122of the tooth ofFIG. 23Gextends radially outwards from its annular part130inclined at an angle γ with the radial axis2000. The core tooth-portion122may be inclined at any angle γ. In some embodiments, the angle of inclination γ will be similar to that described with reference toFIGS. 28A and 28B. It should be noted that, in some embodiments (e.g., the embodiment ofFIG. 23E), the angle of inclination γ may be zero. That is, the core tooth-portion122may extend radially outward along the radial axis2000and a single additional tooth-portion may be installed on one side face of the core tooth-portion122to form the tooth120. In the embodiment ofFIGS. 23I-23K, each tooth120has a core tooth-portion122and four additional tooth-portions112a,124A,112e, and112fthat are assembled to form the tooth120. Core tooth-portion122is integral with the annular part130of core110, a first pair of additional tooth-portions124A and124B are positioned on opposite side faces of the core tooth-portion122, and a second pair of additional tooth portions112eand112fare arranged on top and bottom faces of the core tooth-portion12a. It should be noted that the embodiments of tooth120discussed above are only exemplary, and the electric machines of the current disclosure may include other configurations (e.g., having a different number and other shapes of additional tooth-portions) of tooth120. It should also be noted that the illustrated shapes of the different parts (i.e., core tooth-portion and the additional tooth portion(s)) of tooth120are also exemplary. In general, the constituent parts of a tooth120may have any suitable shape such that, when they are assembled, the external shape of the tooth120corresponds to the shape of the non-uniform trapezoidal cavity320of the coil300.

In the embodiments of multi-part teeth described above with reference toFIGS. 23A-23K, one part (i.e., core tooth-portion122) of each tooth120is formed integral with the annular part130of the stator core110and at least one additional tooth-portion is formed separate from (i.e., not integrated with) the core110. However, such a configuration is not required. In some embodiments, all parts of the tooth may be separate from the stator core110. These separate parts may be assembled to form the tooth120.FIGS. 23L and 23Millustrate exemplary embodiments of a tooth120formed as separate components assembled on a hub132(seeFIG. 23N) to form the stator100. In the embodiment ofFIG. 23L, at its base134the core tooth-portion122includes a rib136configured to be inserted into a correspondingly shaped groove in the hub132when assembling the stator100. In the embodiment ofFIG. 23M, the base134of the core tooth-portion122includes a groove138that fits on a correspondingly shaped rib on the hub132when assembling the stator100(seeFIG. 24B). When all teeth120are assembled on the hub132, the bases134of the teeth120may collectively form the annular part130of the stator100(seeFIG. 24D).

FIGS. 24A-24Dillustrate the installation of an exemplary tooth120(of the type illustrated inFIG. 23M) on the hub132to form the stator100. As illustrated inFIG. 24A, the coil300is first mounted on the multi-part tooth120. An exemplary method of mounting a coil300on a tooth120is described later. As illustrated inFIG. 24B, the tooth120with the coil300mounted thereon is installed on the hub132by inserting the groove138on the base134of the core tooth-portion122into the correspondingly shaped rib on the hub132. Additional teeth120are then mounted on the hub132as illustrated inFIGS. 24C and 24Dto complete the assembly of the stator100.

In some embodiments, the multiple parts of the tooth120(core tooth-portion122and additional tooth portions124A-124F) and the coil300may be coupled together using an adhesive material (e.g., a high temperature glue). In some embodiments, the adhesive material may be filled with a filler material (e.g., to impart desirable properties to the adhesive). Any type of adhesive material may be used. In some embodiments, the coefficient of thermal expansion (CTE) of the adhesive material may be such that, when the tooth120heats up during operation of the electric machine, the thermo-mechanical stresses (induced due to CTE mismatch) induced in the tooth120and the coil300are within acceptable limits (i.e., the stresses are below a value that may cause failure). In some embodiments, the CTE of the adhesive material may be within about 20% of the CTEs of the tooth components (e.g., steel laminations, SMC, etc.). In some embodiments, the CTE of the adhesive material may be within about 20% of the CTEs of the tooth components and the coil300.

In some embodiments, as illustrated inFIGS. 25A and 25B, a cage142(or circumferentially wrapped bandage) may be installed on the stator100. The cage142(or bandage) may assist in keeping the parts of the tooth120(and/or coil300) from protruding into the air gap250between the stator100and the rotor200(seeFIG. 3) during operation. In some embodiments, windows may be provided on the surface of the cage142the faces the rotor200. In some embodiments, the cage142may also be attached to the teeth120using an adhesive material. In embodiments of tooth120where the core tooth-portion122is integral with the annular part130of the stator core110(see, e.g.,FIGS. 23A-23K), the coil300and the additional tooth-portions124A-124F are installed on the core tooth-portion122integrated with the core110, as is described later. After all teeth120and the coils300are installed, in some embodiments, the cage142may be installed on the stator100. The cage142may be made of a non-magnetic material with low electrical conductivity or of a soft magnetic material with a relative magnetic permeability of greater than or equal to about 10 with low electrical conductivity. Making the cage142from a soft magnetic material results in suppression of high harmonics of the pulsating magnetic field, which leads to a decrease in vibration and noise.

Because of the configurations of the core tooth-portion122and the additional tooth-portion(s), each tooth120may have a trapezoidal cross-sectional shape in both the radial plane (see, e.g.,FIGS. 3, 23C) and the axial plane (see, e.g.,FIGS. 2, 23D). In some embodiments, as illustrated inFIG. 23B, the opposite side faces C and D of each tooth120are not parallel to each other, and the opposite top and bottom faces A and B of a tooth120are also not be parallel to each other (see, e.g.,FIG. 23D). The opposite side faces C, D of adjacent teeth120may however be parallel to each other such that the slot160formed between the adjacent teeth120has a constant width in the radial direction (see, e.g.,FIG. 23C). That is, side face C of one tooth120may be parallel to side face D of the adjacent tooth120.

In an embodiment where the rotor200is positioned outwards of the stator100(seeFIGS. 2 and 3), the opposite side faces C and D of each tooth120may diverge from each other in the radially outward direction (see, e.g.,FIG. 23C), and the top and bottom faces A and B may converge towards each other in the radially outward direction (see, e.g.,FIG. 23D). In an embodiment of an electric machine with an outer rotor200and an inner stator100(FIGS. 2, 3) the width of each tooth120in the radial plane (FIG. 3) may increase in the radial direction (e.g., increases from w1to w2inFIG. 3) towards the rotor200, and a length of each tooth120in an axial plane (FIG. 2) may decrease in the radial direction towards the rotor200(e.g., decreases from1to2inFIG. 2). The coil300may be mounted on each multi-part tooth120of the stator100with its inner surface snug against the outer surface of the tooth120(i.e., faces A, B, C, and D ofFIGS. 23C and 23D) such that the outer surface of the coil300has substantially the same shape as the underlying surface of the tooth120. In some embodiments, the coil300may be mounted on tooth120such that its radially outward end is positioned close to the air gap250and the poles (of the permanent magnets) of rotor200(see, e.g.,FIG. 3). It should be noted that although the discussion above makes specific reference to features (faces A, B, C, D, etc.) identified in the tooth120ofFIGS. 23A-23D, the discussion above is equally applicable to all embodiments of tooth120(in stator and/or rotor).

An electric machine10of the current disclosure may include a stator100and a rotor200that is configured to rotate with respect to the stator100about an axis of rotation1000. At least one of the stator100or the rotor200may include a plurality of teeth120that are annularly arranged about the axis of rotation1000. An electromagnetic coil300may be mounted on each tooth120. Each coil300may have a non-uniform trapezoidal cavity320, and each tooth120may be formed of multiple pieces. When the multiple pieces are assembled, the external shape of the tooth120may correspond to the shape of the coil cavity320that receives the tooth120. In some embodiments, as will be described later with reference toFIGS. 26A-26D, the external perimeter of each tooth120may correspond to an internal perimeter of the cavity320. In some embodiments, after a coil300is mounted on a multi-part tooth120, the external perimeter of the tooth120may correspond to the internal perimeter of the cavity320at each point in the radial direction of the tooth120.

In some embodiments, the multiple pieces of each tooth120may include a core tooth-portion122and at least one additional tooth-portion124A-124F (see, e.g.,FIGS. 23A-23M). In some embodiments, each tooth120may include a core tooth-portion122and two additional tooth-portions124A,124B disposed on opposite sides of the core tooth-portion122(see, e.g.,FIGS. 23A, 23K-23M). In some embodiments, the additional tooth-portions1124A,124B may be wedge-shaped. That is, these tooth-portions may extend from a narrower first end126to a broader second end128.

In some embodiments, each tooth120may only include a core tooth-portion122and a single additional tooth portion124C positioned on one side surface of the core tooth-portion122(see, e.g.,FIG. 23H). In some embodiments, each tooth120amay include a core tooth-portion122and a pair of wedge-shaped additional tooth-portions124A,124B disposed on opposite sides of the core tooth-portion122and another pair of additional tooth-portions112e,112fdisposed on the top and bottom surfaces of the core tooth-portion122(see, e.g.,FIG. 23K). Each additional tooth-portion of a pair may be substantially identical. In some embodiments, after a tooth120is assembled, in a plane perpendicular to the axis of rotation100, the entire multi-part tooth120may have a trapezoidal cross-sectional shape, the core tooth-portion122(or tooth120) may have a substantially rectangular cross-sectional shape and each additional tooth-portion124A,124B,124C may have a substantially triangular cross-sectional shape (see, e.g.,FIG. 23C, 23H). And in a plane perpendicular to a radial direction, the multi-part tooth, the core tooth-portion122, and the additional tooth-portions124A,124B,124C may each have a substantially rectangular cross-sectional shape (see, e.g.,FIGS. 23A, 23F).

Regardless of how many parts a multi-part tooth120is made of, and the specific shape of these parts, after a tooth120is assembled, a cross-section of each tooth120in the radial plane (see, e.g.,FIGS. 3, 23C, 23H) and the axial plane (see, e.g.,FIGS. 2, 23D) may have a trapezoidal shape (and in some embodiments, an isosceles trapezoidal shape). In some embodiments, as will be explained later with reference toFIGS. 26A-26D, the perimeter of the cross-section of a tooth120in a plane perpendicular to the radial direction of the tooth120is substantially a constant in the radial direction, and the area of the cross-section varies in the radial direction. In an embodiment of the electric machine with an inner stator100and an outer rotor200(see,FIGS. 2, 3), or an external stator100and internal rotor200(see,FIGS. 8B, 8C) the cross-sectional area increases in the radial direction towards the rotor200. In some embodiments, the cross-sectional area of a tooth120in a plane perpendicular to the axis of rotation1000may decrease in the axial direction from the center to the sides of the tooth120(see, e.g.,FIGS. 27A-27D).

When the multiple pieces of each tooth120are assembled, each tooth120may define external surfaces having two sets of opposing faces. For example, in the embodiment of tooth120illustrated inFIG. 23B, opposing side surfaces C and D form one set of opposing faces and the opposing top and bottom surfaces A and B form another set of opposing faces. The opposing faces C, D (and A, B) of each set are non-parallel to each other. Each face of the two sets is inclined in the radial direction of the tooth120(seeFIGS. 23C, 23D). In some embodiments (e.g., in an embodiment with an outer rotor200and an inner stator100), the opposing faces (A, B) of one set may converge towards each other in a radially outward direction (see, e.g.,FIG. 23D) towards the air gap250(seeFIG. 2), and the opposing faces (C, D) of the other set may diverge from each other in the radially outward direction towards air gap250(seeFIGS. 3, 23C). In some embodiments (e.g., in an embodiment with an inner rotor200and an outer stator100), the top and bottom opposing faces may diverge from each other towards the air gap250(seeFIG. 6B) and the opposing side faces may converge towards each other towards air gap250(seeFIG. 6C).

The different parts of tooth120(i.e., core tooth-portion and additional tooth-portions) may be made of any suitable material (e.g., steel laminations, Soft Magnetic Composite (SMC), etc.). In some embodiments, both the core tooth-portion122and the additional tooth-portions124A-124F of each tooth120may be made of the same material (e.g., SMC). In some embodiments, core tooth-portion122may be made of a first material and the additional tooth-portions124A-124F may be made of a second material. For example, in some embodiments, the core tooth-portion122may be made of an SMC and the additional tooth portions124A-124F may be made from another isotropic material, for example another SMC). This is due to the passage through core tooth-portion122and the additional tooth portions124A-124F magnetic flux, which changes in 3 directions and not in a plane. In embodiments where the core tooth-portion122is formed integrally with the annular part130of the stator core110(see, e.g.,FIGS. 23A, 23G), both the core tooth-portion122and the annular part130may be made of the same material (e.g., SMC).

In various embodiments of the current disclosure, each tooth of the plurality of teeth of the electric machine extends in a radial direction such that a plurality of cross-sectional areas of each tooth in a plurality of planes perpendicular to the radial direction vary, and perimeters of the plurality of cross-sections are substantially the same across the plurality of perpendicular planes. Any direction that extends perpendicular (or substantially perpendicular) to the axis of rotation of the electric machine is a radial direction of electrical machine. For example, in the embodiment illustrated inFIGS. 1 and 2, any direction that generally extends perpendicular to the axis or rotation1000is a radial direction. In some embodiments, the radial direction may extend along, or be coincident with, a radial axis of the tooth of the electric machine. As explained previously, in some embodiments, each tooth120(of the stator100and/or the rotor200) has a trapezoidal cross-sectional shape in both the radial plane (seeFIG. 3) and the axial plane (seeFIG. 2), and the width of tooth120in the radial plane (seeFIG. 3) increases in a radially outward direction (i.e., towards the rotor200), while the length of the tooth120in the axial plane (seeFIG. 2) decreases in that same direction.

FIGS. 26A-26Dare cross-sectional images of a tooth120along different planes.FIG. 26Aillustrates the cross-sectional image of a single tooth120in the axial plane (compare withFIG. 2). The tooth120is shown hatched inFIG. 26A. As evident fromFIG. 26A, the cross-sectional shape of tooth120in the axial plane is trapezoidal (i.e., a quadrilateral with one pair of opposing parallel sides and another pair of opposing non-parallel sides). In some embodiments, as will be explained with reference toFIGS. 31A and 31B, the cross-sectional shape of tooth120in the axial and/or the radial planes is an isosceles trapezoid (i.e., a trapezoid where the length of the opposite sides are equal). As also evident fromFIG. 26A, the length of tooth120decreases with increasing distance in the radial direction, that in this embodiment, is coincident with the radial axis2000.FIGS. 26B-26Dillustrate cross-sections of tooth120at different planes (A-A, B-B, and C-C) perpendicular to the radial direction.FIG. 26Bis the cross-sectional view of teeth120along plane A-A,FIG. 26Cis the cross-sectional view of teeth120along plane B-B, andFIG. 26Dis the cross-sectional view of teeth120along plane C-C. As can be seen fromFIGS. 26B-26D, in planes perpendicular to the radial direction of the tooth120, the tooth120has a rectangular cross-sectional shape.

In should be noted that, although, perfect rectangles with square corners (i.e., 90° corners) are illustrated inFIGS. 26B-26D, this is only exemplary. As previously explained, in some embodiments, these cross-sectional shapes may not be perfect rectangles. As would be recognized by a person skilled in the art, in some embodiments, the opposite sides of the rectangles may not be perfectly parallel, the adjacent sides may not be perfectly perpendicular, and the corners may be rounded and/or chamfered. As illustrated inFIGS. 26B-26D, in embodiments of electric machines with an inner stator100and outer rotor200(seeFIGS. 2-3), the rectangular shape gets shorter and wider as the distance in the radial direction increases. That is, as the distance in the radial direction increases from the axis of rotation1000, the length of the tooth120decreases (i.e., a1>b1>c1and a3>b3>c3), and the width of the tooth120increases (i.e., a2<b2<c2and a4<b4<c4). Although not required, in some embodiments, the opposite sides of the cross-sectional shape may be equal. That is, (a1=a3)>(b1=b3)>(c1=c3), and (a2=a4)<(b2=b4)<(c2=c4). In other words, tooth120gets progressively shorter and wider in the radially outward direction from the axis of rotation1000. The cross-sectional area of tooth120(i.e., the cross-sectional area in the plane perpendicular to the radial direction) also varies in the radially outward direction. In an embodiment where the rotor200is outside the stator100(e.g.,FIGS. 2, 3), the cross-sectional area may increase in the radially outward direction (i.e., SA<SB<SC). In other embodiments of electric machines, the area may vary in a different manner along the radial direction. For example, in electric machines with an inner rotor and outer stator (seeFIG. 8B-8C), the cross-sectional area may increase in the radially inward direction.

With reference toFIGS. 26A-26D, the perimeter of each tooth120in the radial direction may be substantially a constant, while the cross-sectional area of each tooth120in the radial direction may vary. That is, the perimeter of the cross-sections of tooth120along planes A-A, B-B, and C-C (seeFIGS. 26B-26D) may be substantially the same, while its cross-sectional area in these planes may not be a constant (or may vary). That is, (a1+a2+a3+a4)≈(b1+b2+b3+b4)≈(c1+c2+c3+c4), and SA≠SB≠SC. Irrespective of the configuration of the electric machine, in all embodiments, the perimeter of each tooth (in a cross-section perpendicular to the radial direction) may remain substantially a constant along the radial direction while its cross-sectional area may vary in this direction.

FIGS. 27A-27Dare cross-sectional views of a tooth120along different planes. LikeFIG. 24A,FIG. 27Aillustrates the cross-sectional image of a tooth120in the axial plane.FIGS. 27B-27Dillustrate cross-sections of tooth120at different planes (D-D, E-E, and F-F) perpendicular to the axis of rotation1000(or parallel to the radial direction) along the axial direction of tooth120(i.e., along the axis of rotation1000).FIG. 27Bis the cross-sectional view of tooth120along plane D-D,FIG. 27Cis the cross-sectional view of tooth120along plane E-E, andFIG. 27Dis the cross-sectional view of tooth120along plane F-F. As illustrated in these figures, in the axial direction from the middle to the end of the tooth120, the cross-sectional area of the tooth120decreases. That is, SD>SE>SF. In other words, the cross-sectional area of the tooth120in a plane perpendicular to radial direction (and the radial axis2000in some embodiments) varies in the radial direction (seeFIGS. 26B-26D), and the cross-sectional area of the tooth in a plane perpendicular to the axis of rotation1000(or parallel to the radial direction) varies in the axial direction (seeFIGS. 27B-27D). In an embodiment of electric machine100where the rotor200is outside the stator100(FIGS. 2, 3), the cross-sectional area of each tooth120increases in the radial direction (seeFIGS. 26B-26D) and decreases in the axial direction (seeFIGS. 27B-27D).

FIGS. 28A and 28Billustrate geometrical details of an exemplary tooth120(of electric machine10ofFIG. 2, 3).FIG. 28Ais a cross-sectional view of the tooth120in the radial plane andFIG. 28Bis a perspective view of the tooth120(looking down on the tooth). As explained previously, in embodiments of an electric machine with an inner stator100and outer rotor200, each tooth120becomes wider in the radial plane as it extends radially outward (seeFIG. 3). As shown inFIG. 28A, the opposite side surfaces C, D of tooth120forms an angle γ with the radial direction (and the radial axis2000in some embodiments) of the tooth120. The value of angle γ may be determined by the number of teeth120in electric machine100. In general, angle 2γ (which is the angle between the opposite side surfaces C, D of tooth120) equals about 360 degrees divided by the number of teeth120. That is, 2γ≈360°/n, where n is the number of teeth. For example, for an electric machine10with nine teeth120(seeFIG. 3), the angle 2γ≈360/9=40°. Thus, each side surface C, D of tooth120is inclined by about 20° from the radial axis2000. With reference toFIG. 28B, the front and back surfaces of tooth120makes an angle β in the axial plane of the tooth120. Angle β is also determined by the number of teeth of the electric machine (100). A tooth120having a substantially constant perimeter in the radial direction leads to the correlations (seeFIG. 28B): h1=d1; d1=r*Sin(γ); h1=r*Tan(β); r*Sin(γ)=r*Tan(β); Sin(γ)=Tan(β); β=Arctan(Sin(γ)), or β=1/Tan(Sin(γ)).

FIGS. 29A and 29Billustrate the cross-sectional view of an exemplary tooth120in the radial plane. Tooth120ofFIG. 29Bincludes a pole piece or a shoe112, while tooth120ofFIG. 29Adoes not. As shown in these figures, the width of tooth120increases in the radial direction (along radial axis2000) (i.e., towards air gap250, seeFIGS. 2, 3). As explained with reference toFIGS. 26A-26D, the geometrical dimensions of the tooth120are such that the cross-sectional area of the tooth120increases in the radial direction. In both an embodiment of the tooth120with a shoe112(FIG. 29B) and without (FIG. 29A), the increase in cross-sectional area (SA<SB<SC) along the radial direction may be smooth. In some embodiments, the increase in cross-sectional area may be monotonic. In some embodiments, the rate of variation (increase or decrease) of the cross-sectional area may be a constant. A smooth variation (increase or decrease) in cross-sectional area towards the air gap250enables the use of the radially outermost end114(or tip) of the tooth120and the shoe112(if a shoe is used) as a magnetic conductor (or a magnetic field concentrator) even when a large current is flowing through the coil300mounted on the tooth120.

FIG. 30is a schematic illustration of a tooth120and a portion of the rotor200of the electric machine10ofFIGS. 2 and 3. As can be seen inFIG. 30, the air gap250that exists between the stator100and the rotor200is formed between the radially outermost end114of the tooth120and the rotor200(the permanent magnets of the rotor). As illustrated inFIG. 30, in some embodiments, the coil300may be mounted on the tooth120such the radially outermost end316of the coil300is positioned as close as possible to the air gap250. The radial distance y between the radially outermost end316of the coil300and the radially outermost end114of the tooth120may depend on the application and fabrication methods used. In some embodiments, the distance y may be less than or equal to about 20% of the air gap250. In some embodiments, the distance y may be between 0-20% of the air gap250. In some embodiments, the radially outermost end316of the coil300may be substantially coincident with the radially outermost end114of the tooth120(i.e., y≈0). In other words, the radially outermost end316of the coil300may not protrude beyond the radially outer-most end114of the tooth120.

As also illustrated inFIG. 30, in some embodiments, the radially outermost end114of the tooth120may be rounded or curved such that the radially outermost ends114of all the teeth120have a substantially circular profile. The cross-sectional shape of the tooth120in the axial plane and the radial plane may be an isosceles trapezoid or non-isosceles trapezoid.FIGS. 31A and 31Bare schematic illustrations (in the radial plane or the axial plane) of a tooth120having an isosceles trapezoidal shape and a tooth120A having a non-isosceles trapezoidal shape. It should be noted that the teeth of an electric machine of the current disclosure may have an isosceles or a non-isosceles trapezoidal shape in the radial plane (seeFIG. 3) and/or the axial plane (seeFIG. 2). The trapezoidal geometry of tooth120, as well as a smooth increase in the cross-sectional area of the tooth in the radial direction and the location of the coil on the tooth close to the gap may assist in reducing leakage fluxes of the electrical machines and thereby assist in increasing its efficiency and power output.

As explained above, in some embodiments, the electric machines of the current disclosure may include a stator100and a rotor200configured to rotate with respect to the stator100about an axis of rotation1000(see, e.g.,FIGS. 2, 3, 8A-22). At least one of the stator100or the rotor200may include a plurality of teeth120that are annularly arranged about the axis of rotation1000. The plurality of teeth120may be annularly arranged on the stator100or on the rotor200. Each tooth120may extend in a radial direction such that the cross-sectional areas (e.g., SA, SB, SC) of each tooth120in a plurality of planes (e.g., A-A, B-B, C-C) perpendicular to the radial direction varies (see, e.g.,FIGS. 26A-26D). The perimeters of the plurality of cross-sections may be substantially a constant across the plurality of perpendicular planes. That is, the cross-sectional area of each tooth in a plane perpendicular to the radial direction may vary along the radial direction while the perimeter of the cross-sections remains substantially a constant in this direction (see, e.g.,FIGS. 26A-26D).

In some embodiments, the cross-sectional area of each tooth120in a plane perpendicular to the axis of rotation1000varies along the axial direction (see, e.g.,FIGS. 27A-27D). As explained previously, based on the configuration of the rotor200and the stator100, the cross-sectional area may increase or decrease towards the rotor200when a plurality of teeth are located on the stator. The cross-sectional shape of each tooth120in both the radial plane and the axial plane may be trapezoidal (see, e.g.,FIGS. 2, 3, 6A-22). In some embodiments, the cross-sectional shape of each tooth120in the radial and/or axial plane is a non-isosceles trapezoid (see, e.g.,FIG. 31A). While in some embodiments, the cross-sectional shape of each tooth120in the radial and/or axial plane is an isosceles trapezoid (see, e.g.,FIG. 31B). In embodiments where the rotor200is disposed radially outwards of the stator100(see, e.g.,FIGS. 2, 3), a width of each tooth in a radial plane (seeFIG. 3) increases in the radial direction towards the rotor200, and a length of each tooth in an axial plane (seeFIG. 2) decreases in the radial direction towards the rotor200.

As explained previously, the electric machine may also include a plurality of electromagnetic coils300. The method of forming a coil300is described later with reference toFIGS. 48-52. Each coil300may be mounted on, and extend around, a separate tooth120of the electric machine (see, e.g.,FIGS. 8A-22). The method of mounting a coil300on a multi-part tooth120is described later with reference toFIGS. 45-47. Each coil300may include an electrical conductor (e.g., copper wire) in the form of a wire314having any cross-sectional shape or a flat foil312. In some embodiments, the wire314may have one of a square, rectangular, or circular cross-sectional shape (see, e.g.,FIGS. 7D, 7E). Any type of wire314may be used to form the coil300. The wire may include a single strand or multiple strands (e.g., twisted together). In some embodiments, the wire may be a multi-strand wire (see, e.g.,FIGS. 7A, 7B). In some embodiments, each coil300may be wound in the form of a spiral in the radial direction along a tooth120(see, e.g.,FIG. 7B). In some embodiments, in place of a wire, a foil312(e.g., a copper foil) may be used to form the coil300(see, e.g.,FIGS. 6A-6D). The foil312may be wound around a tooth120such that a width of the foil extends over the entire length of the tooth120in the radial direction (see, e.g.,FIG. 6A). Alternatively, in some embodiments, a thinner foil (e.g., a foil having a width less than the length of the tooth120in the radial direction) may be wound (e.g., on a rib) in the form of a spiral in the radial direction along the tooth120(see, e.g.,FIGS. 6C, 6D).

As explained previously, teeth120may include multiple parts (core tooth-portion122and one or more additional tooth-portions124A-124F) coupled together (see, e.g.,FIGS. 23A-23M). As also explained previously, these multiple parts may be made of the same material or of different materials (SMC, etc.). In some embodiments, the core tooth-portion122may be integrally formed with an annular ring130of the stator core110that extends around the axis of rotation1000. In some embodiments, one or more of the additional tooth-portions (e.g.,124A,124B,124E,124F) may be wedge-shaped and disposed on opposite sides of the core tooth-portion122. Each tooth120extends in the radial direction such that the cross-sectional area of the tooth120in a plane perpendicular to the radial direction may vary in the radial direction toward the rotor. In embodiments where the rotor200is positioned radially outwards of the stator100, the cross-sectional area of the tooth120increases in the radial direction towards the rotor200.

In various embodiments of electric machines of the current disclosure, the stator may include an annular stator ring extending about the axis ofROTATION. As used herein, an annular stator ring is a ring-shaped structure associated with the stator. The ring-shaped structure may be disposed about the axis of rotation of the electric machine. With reference toFIGS. 23A-23K, for example, stator100of electric machine10includes an annular part130that extends around the axis of rotation1000. Various embodiments of the electric machines of the current disclosure may also include a plurality of multi-part teeth circumferentially arranged on the stator ring. In other words, the plurality of teeth may each include multiple parts and they may be positioned on or near the circumference of the annular stator ring. As best seen inFIGS. 23A and 23C, in embodiments of the current disclosure, a plurality of multi-part teeth120are circumferentially arranged on the annular part130of stator100.

In various embodiments, each multi-part tooth of the plurality of multi-part teeth may include a core tooth-portion integrally formed with the stator ring and at least one additional tooth-portion separate from the stator ring. That is, the core tooth-portion may be connected to the stator ring such that they form a single component and the at least one additional tooth-portion forms one or more additional components. In some embodiments, core tooth-portion and the stator ring may be formed as a single part and the additional tooth-portion(s) may be formed as separate parts. In some embodiments, the core tooth-portion and the stator ring may be formed as separate parts but may be attached together (e.g., fused or otherwise irremovably attached) to form a single part that may not be easily disassembled without destroying the integrity of the part, while the additional tooth-portion(s) may be attached together in a way that they may be easily separated from the stator ring.

As explained previously with reference toFIGS. 23A-23M, each tooth120of electric machine10may include multiple parts (e.g., core tooth-portion122and additional tooth-portions124A-124F) arranged together. In the exemplary embodiments of the tooth120discussed with reference toFIGS. 23A-23K, the core-tooth portion122of each tooth120is integrally formed with the annular part130(of the stator core110) that extends around the axis of rotation1000, and one or more additional tooth-portions124-124K positioned on the side surfaces and/or the top and bottom surfaces of the core tooth-portion120to form the tooth120.

FIG. 32Aillustrates an exemplary embodiment of the annular part130of the stator core110with a plurality of core tooth-portions122arranged annularly on the annular part130. Each core tooth-portion122extends radially outwards from the annular part130and includes a part of a multi-part tooth112(seeFIG. 23A). In the embodiment of annular part130illustrated inFIG. 32A, each core tooth-portion122extends radially outwards from the annular part130along the radial axis2000. However, as explained with reference toFIG. 23G, this is not a requirement. That is, in some embodiments, the core tooth-portion122may extend radially outwards from the annular part130but may be inclined with respect to the radial axis2000.

The stator core110that forms the annular part130may be formed as a single part (i.e., not multiple parts that are joined together) as illustrated inFIG. 32A. In some embodiments (e.g., when the stator core110is made of SMC or another brittle material), fabricating a stator core110as a single part may be difficult and/or expensive. During fabrication of the stator core110and the operation of the electric machine, the parts of the core110may experience significant stresses (e.g., compression during fabrication, alternating pulsating loads, and thermo-mechanical forces, etc. during operation, etc.). These large stresses may limit the size of the stator core110that may be fabricated as a single part. For example, in some embodiments, the ratio of the thickness (e.g., thickness of the core-tooth portion122) to the axial length (i.e., the height along the axis of rotation1000) of the stator core110that may be reliably fabricated as a single part may be less than or equal to about 1:6. Larger sized stator cores110may be fabricated as multiple parts in some embodiments.

As illustrated inFIGS. 32B-32E, a stator core110may be made of multiple parts and then attached together.FIGS. 32B and 32Cillustrate an exemplary stator core110made of two mirror-symmetric halves110A,110B that are attached together along the plane of symmetry to form the stator core110. As illustrated in these figures, each half of the core110A,110B includes a half122A,122B of the core tooth-portion122. The two halves110A,110B may be attached together using any type of adhesive material. In some embodiments, a permanent adhesive (e.g., an adhesive that cannot be removed easily without destroying the integrity of the part) may be used to attach the two halves110A,110B of the core110together. The CTE of the adhesive material used to attach the two halves110A,110B of the core110may within about 20% of the CTE of the material that forms the core110to reduce CTE mismatch induced thermo-mechanical stresses. In general, the stator core110may be formed by any number of parts that are joined together.FIGS. 32D and 32Eillustrate an exemplary stator core110made of three parts110A,110B,110C that are joined together (e.g., using the adhesive material discussed above).

To increase the strength of the stator100, one or more parts of the stator core110may be made of laminated electric steel sheets assembled together. In some embodiments, multiple laminated steel sheets (e.g., silica-steel sheets) between, e.g., about 0.014″ to 0.018″ (29 to 26 gauge) thick and coated with a very thin layer of insulation (e.g., about 0.001″ thick insulation layer) may be attached together to form a laminated steel part of the stator. In some such embodiments, a multi-part tooth120of the type described with reference toFIG. 23Kmay be used. The annular part130and the core tooth-portion122can be made of laminated steel or an isotropic material (SMC), and the additional portions124A-124F may be made of isotropic material such as SMC. Due to the three-dimensionality of the magnetic fields, using a pair of additional tooth-portions124A,124B on the opposite side surfaces of the core tooth-portion122and another pair of additional tooth-portions124E,124F on the opposite top and bottom surfaces of the core tooth-portion122may provide suitable magnetic performance.

FIGS. 33A-33Cillustrate an exemplary stator core110made of multiple materials. With reference to these figures, the stator core110includes upper and lower annular parts130A,130C attached to a central annular part130B to form the annular part130of core111. As shown inFIG. 33C, the upper and lower annular parts130A,130C may be identical components. In general, annular parts1300A,130B, and130C may be made of any material (e.g., SMC, laminated steel, etc.) The upper and lower annular parts130A,130C may be made by attaching rings made of laminated steel together. The central annular part130B may be made of SMC. In some embodiments, as best seen inFIG. 33B, core tooth-portion122may extend radially outwards from the central annular part130B, and the upper and lower additional tooth-portions124E and124F may be attached to the upper and lower annular parts130A,130C and the top and bottom surfaces of the core-tooth portion122The additional toothed portions124A,124B,124E, and124F may be made of an isotropic material (SMC), and the upper and lower annular portions130A,130C, the central annular portion130B, and the core tooth portion122may be made of laminated steel or isotropic material (SMC).

In various embodiments of the current disclosure, each coil of the plurality of electromagnetic coils is mounted on a different multi-part tooth of the plurality of multi-part teeth such that each coil surrounds a corresponding core tooth-portion of the multi-part tooth with a gap between the coil and the core tooth-portion, and the at least one additional tooth-portion is disposed in the gap. Each multi-part tooth may be associated with a separate electromagnetic coil. The coil may extend around the core-tooth portion of that multi-part tooth such one or more spaces or gaps are formed between the coil and the core tooth-portion. And the additional tooth-portions are positioned in these spaces or gaps. In some embodiments, as illustrated (for example) inFIGS. 4A, 23F, 23H, 23J, 23K, the core tooth-portion124of each multi-part tooth120is mounted on a coil300such that the coil300extends around the core tooth-portion124with one or more gaps formed between the outer surfaces of the core tooth-portion124and the inner surface of the coil300. In the embodiment ofFIG. 4andFIG. 23A, where the multi-part tooth120is formed of a core tooth-portion122and a pair of additional tooth-portions124A,124B positioned on opposite side surfaces of the core tooth-portion122, two gaps are formed between the opposite side surfaces of the core tooth-portion124and the inner surface of the coil300when the coil300is mounted on the core tooth-portion122. One of the additional tooth-portions124A,124B is positioned in one gap and the other additional tooth-portion124B is positioned in the other gap. In the embodiment ofFIG. 23Fwhere the multi-part tooth120is formed of a core tooth-portion122and a single additional tooth-portion124C, this additional tooth-portion124C is positioned in the gap formed between the side surface of the core tooth-portion122and the coil300. And, in the embodiment ofFIG. 23K, four gaps are formed between the external surfaces of the core tooth-portion122and the inner surface of the coil300, and each addition tooth-portion124A,124B,124E,124F is positioned in a separate gap.

In some embodiments, electric machines (electric motor or generator) of the current disclosure may include a stator100and a rotor200configured to rotate with respect to the stator100about an axis of rotation1000(see, e.g.,FIGS. 2, 3, 8A-22). At least one of the stator100or the rotor200may include a plurality of multi-part teeth120that are arranged about the axis of rotation1000. The stator100may include an annular stator ring or part130extending about the axis of rotation1000(see, e.g.,23A,23G,23K, etc.). In some embodiments, the plurality of multi-part teeth120may be circumferentially arranged on the stator ring130. Each multi-part tooth120may include a core tooth-portion122integrally formed with the stator ring130and at least one additional tooth-portion (e.g., additional tooth-portions124A,124B,124E,124F) formed separate from the stator ring130. The electric machine may also include a plurality of electromagnetic coils300. And each coil300may be mounted on a separate tooth120such that the coil300surrounds the core tooth-portion122of the multi-part tooth120with gap(s) formed between the coil300and the core tooth-portion122(see, e.g.,23E-23F,23I-23K,24A, etc.), and the additional tooth-portion may be disposed in the gap(s).

In some embodiments, the annular part (or ring)130may be formed of SMC. In some embodiments, the annular part130may be formed of laminated steel. In some embodiments, one portion of the annular part130may be formed of one material (e.g., laminated steel) while another portion is made of another material. In some embodiments, the annular part130may be formed as a single part (see, e.g.,FIG. 32A). In other embodiments, the annular part130may be made of multiple parts (see, e.g.,FIGS. 32B-32E). In some embodiments, the annular part130of the stator100may include two mirror-symmetric halves coupled together along a plane of symmetry perpendicular to the axis of rotation1000(see, e.g.,32B-32C). The annular part130may include two or more substantially identical parts attached together (see, e.g.,FIG. 32B-32E). Any type of adhesive material may be used to attach the parts of the stator ring114together. The CTE of the adhesive material may be within about 20% of the CTE of the attached components.

The annular stator ring130may include multiple (two, three, four, etc.) axially stacked annular parts (see, e.g.,FIGS. 32B-33C). In some embodiments, each of the stacked annular parts may be made of the same material (e.g., SMC, laminated steel), while in other embodiments, the stacked annular parts may be made of different materials. For example, with reference to the annular part130ofFIG. 33B, the top and bottom annular parts130A,130C may be made of one of laminated steel or SMC, and the central annular part130B may be made of the other of laminated steel or SMC.

The core tooth-portion122of each multi-part tooth120may extend outward in a radial direction from the annular stator ring114(see, e.g.,FIGS. 23C, 23G). In some embodiments, the core tooth-portion122extends radially outward from the annular stator ring130along the radial axis2000of the stator ring130(see, e.g.,FIG. 23C). In some embodiments, the core tooth-portion122extends radially outward from the annular stator ring130inclined from the radial axis2000(see, e.g.,FIG. 23G).

A cross-section of each of the core tooth-portion122and the at least one additional tooth-portion124A-124F along a plane perpendicular to the radial direction has a substantially rectangular shape (see, e.g.,FIG. 23A, 23F, 23K). In some embodiments, a cross-section of the core tooth-portion112aalong a plane perpendicular to the axis of rotation has a substantially rectangular shape and a cross-section of the at least one additional tooth-portion along the plane perpendicular to the axis of rotation has a substantially triangular shape (see, e.g.,FIGS. 23C, 23H). In some embodiments, a cross-section of each multi-part tooth120in the radial plane has a trapezoidal shape (see, e.g.,FIGS. 3, 23C, 23H). In some embodiments, the cross-sectional shape of each multi-part tooth112in the axial plane is also trapezoidal (see, e.g.,FIGS. 2, 23D). In some embodiments, the cross-sectional shape of the tooth120in the radial and/or the axial plate is an isosceles trapezoid (see, e.g.,FIGS. 31A, 31B). In some embodiments, the perimeter of the cross-sectional area of each multi-part tooth120in a plane perpendicular to the radial direction of the tooth is substantially a constant in the radial direction while the area of the cross-sectional are varies in the radial direction (see, e.g.,FIGS. 26A-26D). Each tooth120may include a pair of additional tooth-portions124A,124B,124E,124F arranged symmetrically on opposite sides of the core tooth-portion124(see, e.g.,FIGS. 23C, 23K). In some embodiments, each tooth120includes a first pair of additional tooth-portions124A,124B arranged symmetrically on a first pair of opposite sides (e.g., opposite side surfaces) of the core tooth-portion122and a second pair of additional tooth-portions124E,124F arranged symmetrically on a second pair of opposite sides (e.g., top and bottom surfaces) of the core tooth-portion122(see, e.g.,FIG. 23K).

The core tooth-portion122and the additional tooth-portions of each multi-part tooth120may be coupled together using an adhesive material. In some embodiments, the multiple parts of the mule-part tooth120and the coil300may be attached together by the adhesive material. Any suitable type of adhesive material (e.g., glue) may be used. In some embodiments, the adhesive material may include a filler material to modify the properties of the adhesive material. In some embodiments, the CTE of the adhesive material may be within about 20% of the CTE of the materials of the tooth120. In some embodiments, the CTE of the adhesive material may be within about 20% of the CTE of the materials of the tooth120and the coil300.

At least one additional tooth-portion of each multi-part tooth120may be wedged between an internal surface of the coil300and an external surface of the core tooth-portion122(see, e.g.,FIGS. 23F, 23K, 24A). In some embodiments, the coil300surrounds the core tooth-portion122of each tooth120such that at least two gaps are formed between an inner surface of the coil300and opposite sides of the core tooth-portion122, and each additional tooth-portion is disposed in a different gap (see, e.g.,FIGS. 23K, 24A). In some embodiments, each tooth120includes a single wedge-shaped additional tooth-portion disposed in a gap between the coil300and the core tooth-portion122(see, e.g.,FIG. 23F).

Various embodiments of the electric machines of the current disclosure may include a stator having an annular stator ring and a plurality of core tooth-portions extending in a radial direction. As used herein, an annular stator ring is a ring-shaped component of the stator. Further, teeth are a series of projections that protrude from the annular stator ring. Each projection form a tooth. Core tooth-portion is a portion of the tooth that is attached to the stator core. As explained previously, with reference toFIGS. 23A-23K and 32A-32E, in some embodiments, stator100of electric machine10includes a stator core110with an annular part130that extends around the axis of rotation1000. As can also be seen in these figures, a core tooth-portion124extends in a radial direction from the annular part130of the stator core110. The core tooth-portion124forms a part of the multi-part teeth120of the stator100.

In various embodiments, the annular stator ring and the plurality of core tooth-portions are integrally formed of a Soft Magnetic Composite (SMC). As used herein, the term “integrally formed” indicates that the stator ring and the core tooth-portion are connected to form a single part that practically cannot be dismantled without destroying the integrity of the part. In some cases, the stator ring and the core tooth-portion are formed as a single part. In some embodiments, the core tooth-portion and the stator ring may be formed as separate parts but may be attached together (e.g., fused or otherwise irremovably attached) to form a single part that may not be easily disassembled without destroying the integrity of the part. Soft magnetic composites (SMC) may include ferromagnetic powder particles, which in some embodiments, are coated with a layer of electrical insulating film. In some embodiments, the SMCs may include ferromagnetic powder particles surrounded by an electrical insulating film. The components made of SMC may be manufactured by conventional powder metal compaction techniques. In some case, an integrally formed SMC stator core may offer several advantages over traditional laminated steel cores. For example, these stator cores may exhibit one or more of three-dimensional (3D) isotropic ferromagnetic behavior, very low eddy current losses, relatively low total core loss at medium and high frequencies, improved thermal characteristics, and a reduced weight. Any now-known or later-developed SMC may be used in embodiments of the current disclosure. In some embodiments, a commercially available SMC (e.g., Sintex® SMC, Somaloy 130i, Somaloy 500, Somaloy 700 IP, Somaloy 700 3P, Somaloy 700 5P, or another suitable SMC) may be used.

As explained previously with reference toFIGS. 23A-23M, each tooth120of electric machine10includes multiple parts (e.g., core tooth-portion122and additional tooth-portions124A-124F) arranged together. In the exemplary embodiments of the tooth120discussed with reference toFIGS. 23A-23K(andFIGS. 32A-32E), the core-tooth portion122of each tooth120that extends radially outward from the annular part130of the stator core110is integrally formed with the annular part130. One or more additional tooth-portions124-124K are positioned on the side surfaces and/or the top and bottom surfaces of the core tooth-portion122to form the multi-part tooth120. In the embodiment of tooth120illustrated inFIG. 23A(andFIGS. 21A-32E), each core tooth-portion124extends in a radial direction outwards from the annular part130along the radial axis2000of a tooth120. However, as explained with reference toFIG. 23G, this is not a requirement. That is, in some embodiments, the core tooth-portion122may extend radially outwards from the annular part130inclined with respect to the radial axis2000.

The integrally formed core tooth-portion122(of a tooth120) and the annular part130may be made of the same material. In some embodiments, the integrally formed annular part130and core tooth-portion122may be formed of an SMC. The additional tooth-portions124A-124F that are assembled with the core tooth-portion122to form a complete tooth120may be formed of SMC or another isotropic material ( ). In some embodiments, both the core tooth-portion122and the additional tooth-portions124A-124F may be formed of SMC. In some embodiments, the core tooth-portion122(and annular part130) may be made of SMC It is also contemplated that, in some embodiments, the core tooth-portion122(and annular part130) may be made of steel laminations while some or all of the additional tooth-portions124A-124F are formed of SMC.

In some embodiments, as described with reference toFIGS. 33A-33C, the stator core110may include upper and lower annular parts130A,130C attached to a central annular part130B to form the annular part130of core110. In some such embodiments, as best seen inFIG. 33B, the core tooth-portion122may be integrally formed with the central annular part130B and extend outward in a radial direction from the central annular part130B. In general, annular parts130A,130B, and130C may be made of any material (e.g., SMC, laminated steel, etc.). In some embodiments, the central annular part130B and the core tooth-portion122may be formed of SMC and the upper and lower annular parts130A,130C may with laminated steel.

As explained previously, any suitable SMC may be used to fashion the integrally formed annular stator ring130and the plurality of core tooth-portions122. In various embodiments of the current disclosure, the SMC may include one or more isotropic ferromagnetic materials, a magnetic saturation induction of at least 1.6 Tesla, and an electrical resistivity over 10 micro-ohm/m. A ferromagnetic material is a substance that conducts a magnetic field well. Examples of ferromagnetic materials include iron, cobalt, nickel, gadolinium, chromium dioxide (CrO2), and others. In some embodiments of the current disclosure, the ferromagnetic material may be an iron-based material. An isotropic material has one or more properties that are the same value in different directions. Any property of the material may be the same in different directions. In some embodiments, one or more magnetic properties of the isotropic ferromagnetic material may be the same in different directions. In some embodiments, the magnetic saturation induction and/or the electrical resistivity of the material may be the same in all directions. Magnetic saturation induction is an indicator or how much magnetism can be induced in a material or a component made of the material. Because of magnetic saturation, there is a point of diminishing returns beyond which applying an increased magnetic field will give rise to minimal additional magnetic induction. Magnetic saturation induction characterizes the saturation of the soft magnetic material to a state in which the induction does not increase with a further increase in the magnetic field strength. Electrical resistivity is a fundamental property of a material that indicates how strongly the material resists electric current. It is the inverse of electrical conductivity that quantifies how well a material conducts electricity. A low value of electrical resistivity indicates that a material readily allows electric current to pass through.

In some embodiments, the SMC material used to fashion the integrally formed annular stator ring130and the plurality of core tooth-portions122may be an isotropic ferromagnetic material having a magnetic saturation induction greater than or equal to (≥) about 1.6 Tesla and an electrical resistivity greater than about 10 micro-ohm/m. In some embodiments, the SMC may have a magnetic saturation induction ≥about 2.4 Tesla. In some embodiments, the magnetic saturation induction of the SMC may be ≥about 2.5 Tesla. In some embodiments, the magnetic saturation induction of the SMC may be between about 2.4-2.6 Tesla. The electrical resistivity of the SMC may be ≥about 10 micro-ohm/m (μΩ/m). In some embodiments, the electrical resistivity of the SMC may be ≥about 100 μΩ/m (≥about 150 μΩ/m, ≥about 300 μΩ/m, ≥about 400 μΩ/m, or ≥about 500 μΩ/m). In some embodiments, the electrical resistivity of the SMC may be within about 10-600 μΩ/m. The isotropy of the properties of the SMC may assist in generating a three-dimensional magnetic field in the volume of the tooth120. A magnetic saturation induction ≥about 1.6 Tesla of the SMC may help to maintain the properties of a magnetic conductor or a magnetic field concentrator and, accordingly, reduce leakage fluxes and increase torque values and the power of the electric machine10. Electrical resistivity of the SMC ≥about 100 μΩ/m may assist in reducing eddy current losses at a wide range of speeds and frequencies of operation of the electric machine10. Thus, fashioning the integrally formed annular stator ring130and the plurality of core tooth-portions122of an SMC may result in an increase in the efficiency of electric machine by increasing the magnetic flux density and reducing the magnetic losses.

In some embodiments, a radial flux electric machine of the current disclosure may be an electric motor or an electric generator. The electric machine may include a rotor200configured to rotate about an axis of rotation1000, a plurality of electromagnetic coils200, and a stator100(see, e.g.,FIGS. 8A-22). In some embodiments, the stator100may have an annular stator ring130and a plurality of core tooth-portions122extending from the stator ring130in a radial direction (see, e.g.,23A-23K). The annular stator ring130and the plurality of core tooth-portions122may be integrally formed of a Soft Magnetic Composite (SMC). In some embodiments, the SMC may include one or more isotropic ferromagnetic materials and have magnetic saturation induction ≥about 1.6 Tesla and an electrical resistivity ≥about 10 μΩ/m. The stator100may include a plurality of multi-part teeth120symmetrically arranged on the annular stator ring130, and each tooth120may include one of the plurality of core tooth-portions122and at least one additional tooth-portion124A,124B,124E,124F that are non-integrally formed with the core tooth portion122(see, e.g.,23A,23B,23I-23K). One pair of additional tooth portions124A,124B may be positioned on opposite side surfaces of the core tooth-portion122to form a tooth120(see, e.g.,FIGS. 23A-23C). One pair of additional tooth portions124A,124B may be positioned on opposite side surfaces of the core tooth-portion122and another pair of additional tooth-portions124E,124F may be positioned on oppositely positioned top and bottom surfaces of the core tooth-portion122(see, e.g.,FIGS. 23I-23K). In some embodiments, only a single wedge shaped portion may be used as the additional-tooth portion.

In some embodiments, a cross-section of the core tooth-portion122of each tooth120along a plane perpendicular to the axis of rotation1000of the electric machine may have a substantially rectangular shape and the cross-section of each additional tooth portion may have a substantially triangular shape (see, e.g.,FIGS. 23, 23H, 23I). In some embodiments, a cross-section of each of the core tooth-portions122and at least one pair of additional tooth-portions124A-124F along a plane perpendicular to the radial direction may have a substantially rectangular shape. A cross-section of each multi-part tooth120in a radial plane, or in a plane perpendicular to the axis of rotation1000, may have a trapezoidal shape. The cross-sectional area of each tooth120in a plane perpendicular to the radial direction of the tooth120may vary in the radial direction while the perimeter of the cross-sectional area remains substantially a constant in the radial direction (see, e.g.,FIGS. 26A-26D). In embodiments where the rotor200is disposed radially outwards of the stator100to form an air gap250between the rotor200and the stator100(see, e.g.,FIGS. 2, 3), the cross-sectional area may increase in the radial direction toward the air gap250. The cross-sectional area of a tooth120in a plane perpendicular to the axis of rotation1000may decrease in the axial direction from the center of the tooth120towards its sides (see, e.g.,FIGS. 27A-27D).

In some embodiments, each multi-part tooth120defines external surfaces having two sets of opposing faces (e.g., faces A, B and faces C, D ofFIG. 23B). The opposing faces of each set of the two sets may be non-parallel to each other. That is, faces A and B may be non-parallel to each other and faces C, D may be non-parallel to each other. In some embodiments, each face of the two sets of opposing faces may be inclined in a radial direction. The opposing faces of one set of opposing faces may converge towards each other in a radially outward direction (e.g., faces A, B ofFIG. 23D) and the opposing faces of the other set of opposing faces diverge from each other in the radially outward direction (e.g., faces C, D ofFIG. 23C). Adjacent side faces of adjacent teeth may be parallel to each other. That is, side face C of one tooth120may be parallel to side face D of the adjacent tooth120(see, e.g.,FIGS. 23A-23C).

In some embodiments, the annular stator ring130of the electric machine may include two mirror-symmetric bodies130A,130B coupled together along a plane of symmetry perpendicular to the axis of rotation1000(see, e.g.,FIGS. 32B, 32C). The annular stator ring130may include multiple substantially annular components attached together. The two mirror-symmetric bodies130A,130B may be attached together along the plane of symmetry using an adhesive material. In some embodiments, the difference between the coefficients of thermal expansion of materials of the two mirror-symmetric bodies (or the SMC) and the adhesive material may be less than about 20%.

Any now-known or later-developed SMC may be used to fashion the integrally formed annular stator ring130and the plurality of core tooth-portions122. In some embodiments, a commercially available SMC (e.g., Sintex® SMC, Somaloy 130i, Somaloy 500, Somaloy 700 IP, Somaloy 700 3P, Somaloy 700 5P, or another suitable SMC) may be used. The magnetic saturation induction of the SMC may be ≥about 2.4 Tesla or ≥about 2.5 Tesla. In some embodiments, the resistivity of the SMC may be ≥about 100 μΩ/m or ≥about 150 μΩ/m.

Various embodiments of the electric machines of the current disclosure may include an inner stator and an outer rotor configured to rotate about the inner stator. As explained previously, electric machines of the current disclosure may have different configurations (see, e.g.,FIGS. 8A-22). In some embodiments, the electric machine may include an inner stator100and an outer rotor200(see, e.g.,FIGS. 2, 3) that rotates with respect to the stator100around the axis of rotation1000. The electric machines of the current disclosure may include a rotor base. The rotor base may be part of the rotor. The rotor base refers to any component of the rotor that allows for the coupling of the permanent magnets of the rotor to the shaft (e.g., shaft20) of the electric machine. The electric machine may also include a plurality of annularly arranged permanent magnets axially extending from the rotor base parallel to an axis of rotation of the rotor. A permanent magnet may be a magnet that retains its magnetic properties in the absence of an inducing magnetic field or current. Permanent magnet may be object made from a material that is magnetized and creates its own persistent magnetic field. The material from which permanent magnets are made is called magnetically hard. It differs from a soft magnetic material by an increased hysteresis loop. In general, any type of a permanent magnet known in the art (now known or later developed) may be used to form the permanent magnets. In some embodiments, the permanent magnets may be made of a rare earth (RE) material, such as, for example, neodymium-iron-boron (NdFeB), samarium-cobalt (SmCo), etc. Given the high cost and relative scarcity of RE materials, in some embodiments, the permanent magnets may be non-RE magnets (e.g., ferrite magnets). It is also contemplated that, in some embodiments, the permanent magnets may be hybrid magnets, where a combination of RE magnets and ferrite magnets are used.

In some embodiments, the electric machine may also include a cylindrical core extending from the rotor base. In some embodiments, the core may be configured to conduct magnetic fluxes. The core may also provide structure for fixing the permanent magnets of the rotor. In some embodiments, the core may extend from the rotor base such that it encircles the plurality of permanent magnets. Although not a requirement, in some embodiments, the core may be formed of a SMC. A SMC cylindrical core may exhibit one or more of three-dimensional (3D) isotropic ferromagnetic behavior. It may also exhibit very low eddy current losses and relatively low total core loss at medium and high frequencies. Additionally, a SMC core may also exhibit improved thermal characteristics and a reduced weight. Thus, there may be distinct advantages for using a SMC core in some disclosed electric machines.

The electric machine may also include a sleeve that encircles the rotor. The sleeve may be a structure that protects the rotor and/or increases the strength of the rotor. In some embodiments, the sleeve may be a bandage. The sleeve may be in the form of a ring, belt, or another annular structure that extends around some or all rotor components. In some embodiments, the sleeve may protect the rotor components against the influence of centrifugal (or centripetal) forces when the rotor rotates. In some embodiments, the sleeve may support the cylindrical core and the cylindrical core may support the plurality of permanent magnets. For example, the sleeve may provide structural support for the core and the core may provide structural support for the plurality of permanent magnets. In some embodiments, the cylindrical core may be positioned radially between the sleeve and the plurality of magnets.

FIG. 34Ais an illustration of an exemplary rotor200coupled to the shaft20of the electric machine10(see alsoFIGS. 2-3). As explained previously with reference toFIGS. 1-3, during operation of the electric machine10, the rotor200is positioned radially outwards of the stator100, and it rotates with respect to the stator100about the axis of rotation1000. The rotor200may include a rotor base904. As illustrated inFIG. 34A, in some embodiments, rotor base904may have a disk-like structure. However, a disk-like structure is not a requirement, and the rotor base904may have any suitable shape and configuration. The rotor base904may be fastened (or coupled) to the shaft20such that they rotate as one. That is, when the electric machine10operates, both the rotor base904and the shaft20rotates.

As explained previously (e.g., with reference toFIGS. 1-3), one or more permanent magnets may be suspended from the rotor base904(e.g., see permanent magnets220ofFIG. 2).FIG. 34Bis a cross-sectional view andFIGS. 36 and 37sectional views of the rotor200ofFIG. 34A. As can be seen in these figures, the permanent magnets220may be arranged to form an annular ring around the axis of rotation1000. Rotor200may also include a rotor core910and a sleeve908that both extend around the axis of rotation1000. The core910may extend around the permanent magnets220, and the sleeve908may extend around the core910. Thus, the plurality of permanent magnets220, the core910, and the sleeve908may form three concentric annular rings around the axis of rotation1000. The core910may be a cylindrical component with the permanent magnets200mounted on its inner cylindrical wall. The sleeve908may be a cylindrical component with the core abutting its inner cylindrical wall. In some embodiments, the core910may be mounted on the inner cylindrical wall of the sleeve908. As best seen inFIGS. 34B and 36, the core910may be sandwiched between the plurality of permanent magnets220and the sleeve908.

Rotor200may also include one or more balancing rings. The term “balancing ring” refers to a structure that assists in the balancing of the rotor. In some embodiments, the balancing rings allow for the dynamic balancing of the rotor by redistributing the weight of the rotor. For example, in some embodiments, the balancing ring may support weights (e.g., screws) that can be manipulated (e.g., screwed in or out) to redistribute the weight of the rotor. In some embodiments, a balancing ring922may be provided at one end (e.g., top end) of sleeve908(seeFIG. 36). Alternatively, or additionally, in some embodiments, a balancing ring926may be provided at the bottom end of sleeve908(seeFIG. 37). In some embodiments, only one of balancing rings922,926may be provided while in other embodiments, both balancing rings922,926may be provided. Providing both balancing rings922,926may enable two-plane balancing or rotor200. It should be noted that the structure and location of balancing rings922,926illustrated in these figures in only exemplary. In general, one or more balancing rings may be provided at any location of the rotor200.

With specific reference toFIG. 34B, in some embodiments, a plurality of permanent magnets220may be annularly arranged on rotor base904such that they extend axially from the rotor base904parallel to the axis of rotation1000of the rotor200. The permanent magnets220may be radially magnetized and segmented to reduce eddy current losses. The term “magnetic axis” indicates an axis of permanent magnet magnetization of the permanent magnets. The domains are oriented with respect to this axis when the magnets are magnetized. As a result, two opposite poles (e.g., north and south poles) of a permanent magnet220are formed along this magnetic axis. In a permanent magnet, the magnetic axis extends between its north and south poles. In some embodiments, when the permanent magnets220are arranged in a cylindrical pattern as shown inFIGS. 36 and 37(andFIG. 3), the magnetic axis of the individual permanent magnet220may extend in a radial direction. In some embodiments, the magnetic axes of the plurality of permanent magnets220may intersect each other at (or near) the axis of rotation1000.

FIGS. 38A and 38Billustrates the core910and the permanent magnets220of the rotor200. In some embodiments, permanent magnets220with radial magnetization and alternating polarity are fixed or mounted on the inner surface of the cylindrical core910, for example, using an adhesive (e.g., see alsoFIG. 3). The permanent magnets220may be positioned such that the north pole of one permanent magnet220faces radially inwards (i.e., towards the axis of rotation1000) while the south pole of its adjacent magnets220faces radially inwards. In some embodiments, as explained previously (with reference toFIGS. 2-3), each permanent magnet220may be made of multiple permanent magnet segments222attached together. That is, the permanent magnets220may be segmented about the axis of rotation1000. In some embodiments, as best seen inFIGS. 38A and 38B, the permanent magnets220may also be segmented along the axis of rotation (i.e., lengthwise along the axis of rotation1000). The plurality of the permanent magnets220may be annularly arranged about the axis of rotation1000such that adjacent permanent magnets220are spaced apart from each other by a spacer224(or a gap).FIG. 38Cillustrates an exemplary spacer224. The spacer224may be a solid or a hollow component that separates the adjacent permanent magnet segments220. In some embodiments, the spacer224may be made of a non-conductive material. Although not a requirement, in some embodiments, the spacer224may extend the entire length of the core910. Segmenting the permanent magnets220may assist in the reduction of eddy current losses. As explained previously, the permanent magnets220may be rare earth (RE) magnets (e.g., NdFeB, SmCo, etc.), ferrite magnets, or other known types of magnets.

Outer rotor200may also include a cylindrical core910. The cylindrical core910may extend from rotor base904to encircle the plurality of permanent magnets220. In some embodiments, cylindrical core910may be formed of a SMC. The cylindrical core910may support one side (e.g., radially outer side) of the plurality of permanent magnets220. In some embodiments, the permanent magnets220may be mounted on the cylindrical core910(e.g., on the radially inner side of the cylindrical core910). The permanent magnets220may be attached to the core910using, for example, an adhesive material. For example, an adhesive layer may bond the radially outer side of the permanent magnets220with the radially inner side of the core910.

Sleeve908may encircle the cylindrical core910. In some embodiments, as illustrated inFIGS. 36 and 37, the sleeve908may extend around the radially outer side of the cylindrical core910. The sleeve908may physically contact and support the cylindrical core910. In some embodiments, an adhesive material may attach the radially inner side of the sleeve908to the radially outer surface of the core910. The sleeve908may support the plurality of permanent magnets220(via the core910). Since the sleeve908supports the radially outer surface of the core910, it may protect the core910from cracking due to centrifugal forces during rotation of rotor200. The core910may be positioned radially between sleeve908and plurality of permanent magnets220. In some embodiments, the sleeve908may be attached to the rotor base904using an adhesive material. In some embodiments, the sleeve908may be integrated with, or made integral with, the rotor base904(e.g., the sleeve908and the rotor base904may be formed as a single part of the same material).

In some embodiments, the sleeve908and/or the rotor base904may be made of aluminum or a non-magnetic composite material like carbon fiber, glass fiber, and/or an aramid fiber like Kevlar. A non-magnetic composite material is a multicomponent material, non-conductive for magnetic flux and made of two or more components with significantly different physical and/or chemical properties. In general, the sleeve908and the rotor base904may be made of a magnetic material or a non-magnetic material. The non-magnetic material (of the sleeve908and/or the rotor base904) may be a composite material. In some embodiments, the composite non-magnetic material may include at least one of carbon fiber, glass fiber, aramid fiber, Kevlar, or another suitable fiber. For example, fibers (carbon, glass, aramid, Kevlar, etc.) may be weaved together to form the sleeve908. In some such embodiments, the sleeve908may be in the form of a bandage. The bandage may be flexible, semi-flexible, or rigid. In some embodiments, the fibers may be embedded in a matrix of another material (e.g., an epoxy, etc.) to form the composite non-magnetic material. In some embodiments, the non-magnetic material (of the sleeve908and/or the rotor base904) may include (or be) at least one of stainless steel or aluminum. In some embodiments, the sleeve908and/or the rotor base904may be made of a magnetic material. The magnetic material may include a soft magnetic material, such as, for example, laminated electrical steel sheets. In some embodiments, the magnetic material may be steel. In some embodiments, the sleeve908and the rotor base904may be a single integrated part made of, for example, steel.

In some embodiments, the sleeve908may be assembled as a package with the core910and the permanent magnets220. In some embodiments, sleeve908may include a stiffening rib disposed on a recess formed on an external surface of the cylindrical core910. The term “stiffening ribs” indicates elements or features configured to increase the strength of the rotor structure. In some embodiments, sleeve908may extend over the balancing ring926and the free end of the plurality of permanent magnets220. In some embodiments, the sleeve908may extend over the balancing ring922. In some embodiments, the cylindrical core910may extend from a first end coupled to rotor base904to a second end. See, for example,FIGS. 34A-34B. In some embodiments, the balancing rings922,926may extend around a free end of the cylindrical core910.

FIG. 35illustrates an exemplary shaft20that is configured to rotate about the axis of rotation1000ofFIGS. 2, 3).FIGS. 36-37illustrate partial views of exemplary outer rotor200. Outer rotor200includes first balancing ring922and second balancing ring926. The first balancing ring922may be disposed at a first end of cylindrical core910coupled to rotor base904. The second balancing ring926may be disposed at a second end of cylindrical core910opposite rotor base904. In some embodiments, the second balancing ring926may provide dynamic balancing of the rotor200, and the first balancing ring922may provide a static balancing. First and second balancing rings922,926may be configured to be attached to sleeve908and/or the cylindrical core910. One or both of the balancing rings922,926may include holes924.

Cylindrical core910together with the permanent magnets220may be attached to rotor base904, which couples rotor200to shaft20. In some embodiments, the sleeve908may be folded around the end of cylindrical core910and permanent magnets220, clamping them on both end sides of outer rotor200(see, e.g.,FIG. 36). In some embodiments, the sleeve908may be made of a non-conductive material, or a material with a low electrical conductivity, or a non-magnetic non-conductive composite material. In some embodiments, cavities or holes may be drilled in these weights during precise static and dynamic balancing. In some embodiments, the required weight changes may be made in two planes (e.g., using the two balancing rings922and926). Weights may be installed into balancing ring holes924. In some embodiments, second balancing ring926may be located at the first end of cylindrical core910(the end that is coupled to rotor base904). In some embodiments, the first and/or second balancing rings922,926may be formed of a non-magnetic composite material. In some embodiments, the first and/or second balancing rings922,926may be formed of a non-magnetic material. In some embodiments, the first and/or second balancing rings922,926may include one or more screws for balancing the outer rotor200.

In some embodiments, plurality of permanent magnets220may be arranged on rotor base904in a substantially circular pattern around the axis of rotation1000(see, e.g.,FIGS. 3, 36-38B). Adjacent magnets220are separated by a spacer224, made of non-magnetic material or any soft magnetic material like a SMC. In some embodiments, plurality of permanent magnets220are arranged on rotor base904such that a magnetic axis of each permanent magnet of plurality of permanent magnets220extend towards the axis of rotation (e.g., axis of rotation1000). In some embodiments, the plurality of permanent magnets220are arranged on rotor base904such that a magnetic axis of each permanent magnet of plurality of permanent magnets220intersect at (or proximate to) the axis of rotation.

In some embodiments, rotor base904may be formed of aluminum or steel. In some embodiments, the rotor base904may be integral with sleeve908and one or more balancing ring (e.g.,922,926). The plurality of permanent magnets220may be attached to cylindrical core910using an adhesive. In some embodiments, a difference between coefficients of thermal expansion (CTE) of materials of plurality of permanent magnets220, cylindrical core910, and the adhesive may be less than about 20% to reduce CTE mismatch induced thermo-mechanical stresses during thermal excursions. The cylindrical core910may be attached to rotor base904using an adhesive. The electric machine may be an electric motor or an electric generator. In some embodiments, cylindrical sleeve910may be made in the form of a package assembled from laminated sheets of electrical steel.

FIG. 38Dillustrates a view of exemplary cylindrical rotor core910. As explained previously, in rotor200, spacers224separate adjacent permanent magnets220in the plurality of permanent magnets200mounted on the inside surface of the cylindrical core910(seeFIG. 38A-38C). As an alternative to (or in addition to) spacers224, in some embodiments, the cylindrical core910may include integrated spacers928. These spacers928may protrude inward in a radial direction from the inside cylindrical surface of the core910. The integrated spacers928may define slots929therebetween to house the permanent magnets220therein. When the permanent magnets220are mounted on these slots929, the spacers928separate adjacent permanent magnets220in the plurality of permanent magnets200mounted on the inside surface of the cylindrical core910.FIGS. 42A-42Billustrate cross-sectional views of exemplary outer rotor200in the radial plane. As illustrated in these figures, when the permanent magnets220are disposed in the slots929(seeFIG. 38D) between the spacers928on the inside surface of the rotor core910, the spacers928separate adjacent permanent magnets220from each other in the circumferential direction. The spacers928may have any thickness in the radial direction. In some embodiments, the thickness of the spacers928may not exceed the thickness of the permanent magnets220(in the radial direction) so that the spaces928do not protrude into the air gap250between the outer rotor200and the inner stator100(seeFIG. 3). In some embodiments, to limit the pulsating moment, the thickness of each spacer928may be such that it is less than or equal to about half the thickness of a permanent magnet220.

FIG. 39illustrates a cross section view of the rotor200. Sleeve908may be installed in rotor200by any method. In some embodiments, to install the sleeve908, stops930may be provided on the two ends (e.g., top and bottom ends) of the rotor200(e.g., on either side of sleeve908). In embodiments where sleeve908is in the form of a bandage, the sleeve908may be installed on the rotor200by winding (or wrapping) the sleeve material around the outer surface of rotor core910(seeFIG. 40). The winding may be performed such that each protrusion and each depression on a surface of core910(or the outer surface of the rotor) are filled in one operation. This winding may serve to increase the strength and rigidity of rotor200during operation and to reduce vibration and noise. The winding (as shown inFIG. 40) may be done with a composite tape, with a composite thread (not shown), or a combination of both. Although the use of stops930to form the sleeve908is described, this is only exemplary. The winding may also be accomplished without the stops930.

In some embodiments, the rotor base904the sleeve908may be an integrated component. In such cases, the rotor base904and the sleeve908may be formed together as one integrated part, for example, of a composite material. In some embodiments, an adhesive material may be used to secure the permanent magnets220and/or the spacers224on cylindrical core910, the rotor base904, the sleeve908, and the balancing rings922,926. The adhesive material may be selected such that its coefficient of thermal expansion (CTE) is close (e.g., about 20%) to the CTEs of the materials to be bonded in order to reduce stress during heating of the bonded elements.

As best seen inFIG. 40, rotor base904may include one or more ventilation holes932. Ventilation holes932may be configured to direct air flow along the axis of rotation1000(i.e., parallel to the axis of rotation1000). In some embodiments, this air is directed into the rotor (towards the stator positioned within the rotor) when the rotor200rotates (see, e.g.,FIG. 2). In some embodiments, the ventilation holes932may be configured to operate as fan blades when rotor200rotates to cool one or more components of an electric machine. In some embodiments, blades, vanes, or other air-moving features may be provided around (or proximate) the ventilation holes932to direct air along the axis of rotation1000(or into holes932and towards the stator during rotor rotation).

FIG. 41illustrates a view of exemplary outer rotor200. In some embodiments, to increase the permissible maximum rotational speed of the rotor200, one or more slots934may be provided on the outer surface (e.g., radially outer surface) of the cylindrical core910. As can be understood fromFIG. 41, each slot934may be positioned opposite the middle of each of permanent magnet220(one permanent magnet220is shown using dashed lines inFIG. 41). In some embodiments, the inner mating surface of the sleeve908includes corresponding ribs936that are received in the slots934when the core910is mounted within the sleeve908. In embodiments where the sleeve908is a bandage that is wrapped around the core910(as described with reference toFIG. 40), the slots934may be configured to receive the material of sleeve908and form stiffening ribs936. That is, the portion of the sleeve908that is received in the slots934when the sleeve908is mounted or wrapped around the core910forms stiffening ribs936. The stiffening ribs936increase the strength of the rotor core910without increasing its size (e.g., thickness). The middle of each permanent magnet220corresponds to the location of the lowest magnetic flux density. Therefore, positioning the slots934opposite the middle of the permanent magnets220assists in reducing leakage flux and increasing the strength of the core910without increasing its size. In some embodiments, the rotor200may be made without a sleeve908.

FIG. 43illustrates a view of exemplary outer rotor200having a rotor base904, a cylindrical core910, a plurality of permanent magnets220, and a sleeve908. As illustrated inFIG. 43, the cylindrical core910may have a non-uniform thickness (in the radial plane) about the axis of rotation1000. In the illustrated embodiment, the outer surface of the cylindrical core910forms an undulating surface (with its radius varying, or increasing and decreasing, about the axis of rotation1000) and the outer surface of the core910is a cylindrical surface. The non-uniform thickness of the core910occurs as a result of the different types of inner and outer surfaces. In the illustrated embodiment, the outer surface of the sleeve908is cylindrical and its inner surface (that mates with undulating outer surface of the core910) is a corresponding undulating surface. Thus, the sleeve908also has a non-uniform thickness (i.e., a varying thickness about the axis of rotation1000) as a result of the difference between its inner and outer surfaces.

As can be seen inFIG. 43, a thicker region X (or a location of higher thickness) of cylindrical core910corresponds to the thinner region (or the location of lower thickness) of the sleeve908, and thinner region Y of the core910corresponds to a thicker region of the sleeve908. As can be seen inFIG. 43, the thicker region X of core910is positioned between adjacent permanent magnets220and the thinner region Y of the core910is positioned adjacent to the middle of each permanent magnet220. Also, the thicker region of the sleeve908is positioned adjacent to the middle of each permanent magnet220and its thinner region is positioned between two permanent magnets220. The middle of a permanent magnet220corresponds to the location of the lowest magnetic flux density. Positioning the thicker regions of the sleeve908adjacent to (or proximate) the middle of each permanent magnet220increases the strength of the rotor200without increasing its size. It should be noted that the undulating outer surface of the core910and the inner surface of the sleeve908in exemplary embodiment of rotor200discussed with reference toFIG. 43is only exemplary. In general, a non-uniform thickness of the core910and/or sleeve908may be provided in any manner. In some embodiments, the thickness of the core910and/or sleeve908may vary, for example, in a step-wise manner in the circumferential direction (i.e., about the axis of rotation1000).

FIG. 44illustrates an exemplary core910of a rotor200. In the illustrated embodiment, permanent magnets220are disposed (or embedded) in the core910. In some embodiments, the permanent magnets220may be disposed in a star pattern in the core910. The core910may include slots in a corresponding star pattern to receive the permanent magnets220. It should be noted that the star pattern is only exemplary, and in general, the permanent magnets220may be disposed in any pattern (e.g., circular, etc.) in the core910. In some embodiments, the core910may include circumferentially spaced-apart slots to receive permanent magnet segments.

With reference toFIGS. 4A-4CandFIGS. 6A-7C, for efficient operation of the electric machine, it is preferable that the inner surface of the electromagnetic coil300that is mounted on a multi-part tooth120contacts, or is snug against, the outer surface (surface A, B, C, D ofFIG. 23B) of the tooth120. Because of the trapezoidal shape (or the varying cross-sectional area of the tooth120in the radial direction) of the tooth120, it is difficult to mount a pre-fabricated coil300on the tooth120such that the mating surfaces of the cavity320of the coil300(see, e.g.,FIGS. 6A-7C) and the external surface of the tooth120contact along the entire radial direction of the tooth. While it may be possible to wind a wire (or a foil) directly onto the tooth120(or on a pre-assembled core110with teeth112) to form a coil300, such a process would increase manufacturing cost. Winding a wire on the tooth120would also decrease the filling density of the slot160between the teeth120(see, e.g.,FIGS. 4A-4B) and result in a low fill factor of the electric machine. Forming the tooth120of multiple parts (as discussed above) enables a prefabricated coil300to be installed, or mounted, on the tooth120while maintaining a high fill factor value. The parts of the multi-part tooth120are assembled inside the coil300to form the trapezoidal shape of the tooth120inside the cavity320(or the opening) of the coil300.

FIGS. 45A-45Fillustrate an exemplary method of mounting (or installing) a coil300on an exemplary multi-part tooth120.FIGS. 46A-46Care simplified schematic illustrations depicting different stages during mounting a coil300on tooth120. In the discussion below, reference will also be made toFIGS. 46A-46C. In the discussion below, the method of installing the coil300on the embodiment of tooth120described with reference toFIG. 24Awill be described. Coils300can also be installed in other embodiments of teeth120in a similar manner. In the illustrated embodiment, the multi-part tooth120that includes a discrete core tooth-portion122(i.e., a core tooth-portion122which is not integrated with the annular part130of core110as in the embodiment ofFIG. 23A) with a groove138on its base134, and two additional tooth-portions124A and124B. A pre-fabricated (pre-formed, pre-wound, etc.) coil300may be installed on the multi-part tooth120formed of these multiple tooth portions122,124A,124B. Although not a requirement, in the illustrated embodiment, the two additional tooth-portions124A,124B are identical.

The tooth120is made of multiple parts such that the previously formed coil300can be mounted on the tooth120such that the multiple parts of the tooth120fits within the cavity320of the coil300. With reference toFIG. 45A, the pre-formed coil300includes an electrical conductor (wire, foil, etc.) that extends around a central cavity320(or opening) of the coil300. The cavity320extends from a first end322to a second end324of the coil300. In some embodiments, each additional tooth-portion124A,124B may be identical in structure and may be wedge-shaped. Each additional tooth-portion124A,124B may extend from a broader end128to a narrower end126. After assembly, the first end322of coil300will be positioned proximate the stator core110and its second end324will be positioned proximate the air gap250(seeFIG. 2).

In some embodiments, the method for installing the coil300on the multi-part tooth120incudes inserting at least one additional tooth-portion124A,124B of the multi-part tooth120into the cavity320of the coil300such that a broader second end128of the inserted additional tooth-portion(s)124A,124B extends out of the cavity320. For example, as best seen inFIG. 46A, the two additional tooth-portions124A,124B are inserted into the cavity320of the coil300such that the broader second ends128of the two additional tooth-portions124A,124B extents (or protrudes) from the cavity320through its second end324. In embodiments where the tooth120includes only a single additional tooth-portion (e.g., tooth portions124C,124D ofFIGS. 23E and 23H), this single tooth portion will be inserted into the cavity320of the coil300such that its broader end protrudes out from one end of the cavity320. In embodiments where the tooth120includes multiple additional tooth-portions (seeFIGS. 23A, 23I-23K), one or more of these multiple additional tooth-portions will be inserted into the cavity320.

In some embodiments, as illustrated inFIG. 45A-46C, both the additional tooth-portions124A,124B are inserted into the cavity320. The two additional tooth-portions124A,124B may be pressed against the opposite side walls of the cavity320(i.e., against the inner walls of the coil300) such that a gap is formed in the cavity320between the two additional tooth-portions124A,124B. That is, as can be seen inFIGS. 45D and 46A, the two additional tooth-portions124A and124B are placed in the cavity320such that a side surface of each additional tooth-portion124A,124B contacts (or is pressed against) an opposite surface on the inside of the cavity320to form a gap between the two additional tooth-portions124A,124B.

As best seen inFIGS. 45D and 46A, the additional tooth-portions124A,124B are inserted into the cavity320such that the broader second end128of the inserted tooth portion124A,124B extends out (or protrudes from) of the cavity320at its second end324. As best seen inFIG. 46B, the coil300(with the inserted additional tooth-portions124A,124B is then mounted on the core tooth-portion122of the multi-part tooth120such that the broader second end128of the inserted additional tooth-portion124A,124B remains extended out of the cavity320of the coil300. As illustrated inFIG. 46C, a force F is applied on the protruding second ends128of the additional tooth-portion124A,124B to push the additional tooth-portions further into the cavity320(i.e., towards the first end322of the cavity320). As the additional tooth-portion124A,124B enters further into the cavity320, they press against the sides of the core tooth-portion122and the inner walls of the cavity320to tighten the coil on the multi-part tooth120(see, e.g.,FIG. 45E, 46C). In some embodiments, as illustrated inFIG. 45F, an adhesive material (or a glue) may then be applied to couple the multiple parts of the multi-part tooth120together and to the inner walls of the coil cavity320.

It should be noted that the embodiment discussed above is only exemplary. There may be many variations to the described method based on the configuration of coil and the tooth.FIGS. 23E-23FandFIG. 23Halso depict an exemplary method of installing a coil300on some other configurations of multi-part tooth120. As explained previously, additional tooth-portion124C (ofFIG. 23E) or124D (ofFIG. 23H) may first be inserted into cavity320of coil300such that the broader end of the additional tooth-portion124C or124D extends out of opening320. The coil300with the additional tooth-portion124C or124D may then be positioned over the core tooth-portion122such that broader end of the additional tooth-portion124C or124D remains extended out of the cavity320. A force may then be applied to the broader end of the additional tooth-portion124C or124D to push it further into the cavity320thereby snugly fitting the coil300around the multi-part tooth120. Application of the force may drive the broader end of the additional tooth-portion124C or124D further into coil300towards the annular part130of core110to tighten the coil300on the multi-part tooth120(see, e.g.,FIG. 23F). In some embodiments, adhesive material may then be applied to couple the multiple parts of the multi-part tooth120together.

FIGS. 23I-23Jillustrate another exemplary method of installing a coil300on a multi-part tooth120. As in the embodiment described with reference toFIG. 45A-46C, a pair of additional tooth-portions124A and124B may first be positioned in the cavity320of coil300(seeFIG. 23J). In this configuration, the broader end of the two additional tooth-portions124A and124B may protrude or extend out of the cavity320(see,FIG. 23J). The core tooth-portion122with the additional tooth-portions124E,124F positioned on its opposite sides (e.g., top and bottom sides, seeFIG. 23J) may then be inserted into the cavity320of the coil300through the space between the two additional tooth-portions124A,124B. When the core tooth-portion122is inserted into the cavity320, the broader ends of one or both of the additional tooth-portions124A,124B may remain protruded out of the cavity320. A force may then be applied to push at least a portion of the protruding broader end(s) into the cavity320. As the additional tooth-portion(s)124A,124B enters further into the cavity320, they press against the sides of the core tooth-portion122, the additional tooth-portions124E,124F, and the inner walls of the cavity320to tighten the coil300on the multi-part tooth120(see, e.g.,FIG. 23K). In some embodiments, an adhesive material may then be applied to couple the parts together with the coil. Any type of adhesive material may be used to couple the parts of the multi-part tooth120together. In some embodiments, the adhesive material may have a coefficient of thermal expansion close to the coefficient of thermal expansions of the tooth and/or the coil materials to reduce the CTE mismatch induced thermo-mechanical stresses when the parts heat up during operation. In some embodiments, the CTE mismatch between the adhesive material and the different parts of the multi-part tooth120may be below about 20%.

The described methods of mounting the coil300on a multi-part tooth120is applicable to embodiments of tooth120where the core tooth-portion122is separate from the core110(e.g., the embodiments ofFIGS. 23L and 23M) and to embodiments of tooth120where the core tooth-portion122is integrated with the core110(e.g., the embodiments ofFIGS. 23A-23K). In general, the method of assembling a coil on an irregular-shaped multi-part tooth of an electric machine may include inserting at least one additional tooth portion (e.g., a wedge-shaped tooth portion or a wedge-portion) of the multi-part tooth into an opening of the coil such that a broader end of the at least one wedge-portion extends out of the cavity (or opening) in the coil. As used herein, the term “irregular-shaped” refers that the cross-section that varies along the length. In some embodiments, irregular-shaped volume may best be described by a geometric figure other than regular or simple figures (circle, cylinder, cube, parallelepiped, etc.). The term “wedge-portion” indicates a part having a broader end and a narrower end. In some embodiments, the wedge-portion may be in the form of a wedge. The term “cavity” or “opening” refers to an inner hollow part of the coil. The coil with the inserted at least one wedge-portion is positioned on a core tooth portion of the multi-part tooth such that the broader end of the at least one wedge-portion remains extended out of the cavity in the coil. The method may also include exerting a force on the broader end of the at least one wedge-portion to tighten the coil on the multi-part tooth.

In some embodiments, exerting a force on the broader end of the at least one wedge-portion may include pushing the broader end of the at least one wedge-portion into the cavity of the coil (i.e., the coil opening). In some embodiments, the opening in the coil may extend from a first end to a second end. And inserting the at least one wedge-portion may include inserting the at least one wedge-portion into the opening such that the broader end extends out of the second end of the opening. In some embodiments, exerting the force may include pushing the broader end towards the first end of the opening. The opening or the cavity in the coil may extend from a first end to a second end. In some embodiments, a width of the opening at the first end may differ from the width of the opening at the second end, and a length of the opening at the first end may differ from a height of the opening at the second end. In some embodiments, a shape of the opening at the first end and the shape of the opening at the second end may be rectangular (see, e.g.,FIG. 7B). Since the electromagnetic coil fits snugly on the surface of a tooth, in some embodiments, the shape of the coil cavity or opening may correspond to (or may be substantially similar to) the shape of the tooth. Therefore, a perimeter of the opening at the first end of the coil cavity may be substantially the same as the perimeter of the opening at the second end of the coil cavity (see, e.g., discussion of the shape of tooth120with reference toFIGS. 26A-26B). In some embodiments, an area of the coil opening at the first end may vary from the area of the opening at the second end. In some embodiments, the area of the coil opening may increase from the first end to the second end. In some embodiments, inserting at least one wedge-portion into the coil opening may include inserting at least two wedge-portions into the opening.

Mounting the coil on a tooth may include mounting the coil on the core tooth portion such that the core tooth portion is disposed between the at least two wedge-portions. In some embodiments, an adhesive material may be used to attach the at least two wedge portions and the core tooth-portion of the multi-part tooth together. The multi-part tooth may be a part of a stator of the electric machine. In some embodiments, the core tooth portion of the multi-part tooth may be one of a plurality of core tooth portions symmetrically arranged on an annular stator ring that extends around a central axis of the electric machine. The core tooth portion may extend outward in a radial direction from the annular stator ring. In some embodiments, the plurality of core tooth-portions are integrally formed with the annular stator ring. In some embodiments, in a plane perpendicular to the central axis, the core tooth portion may have a substantially rectangular cross-sectional shape and the at least one wedge-portion may have a substantially triangular cross-sectional shape (see, e.g.,FIG. 23B, 23F, 23K). In some embodiments, in a plane perpendicular to the radial direction, the core tooth portion and the at least one wedge-portion may have a substantially rectangular cross-sectional shape. In some embodiments, the coil may include a winding of a copper wire around the coil opening or cavity (see, e.g.,7A-7C). The wire may have one of a square, rectangular, or circular cross-sectional shape (see, e.g.,7D,7E). In some embodiments, the coil may include a winding of a copper stranded wire in a spiral configuration around the opening. In some embodiments, the electric machine may be an electric motor. In some embodiments, the method wherein the electric machine may be an electric generator.

An exemplary method of assembling a coil on an irregular-shaped multi-part tooth of an electric machine may include a step of inserting at least one wedge-portion of the multi-part tooth into an opening of the coil such that a broader end of the at least one wedge-portion extends out of the opening in the coil. The method may include a step of mounting the coil with the inserted at least one wedge-portion on a core tooth portion of the multi-part tooth such that the broader end of the at least one wedge-portion remains extended out of the opening in the coil. The method may include a step of exerting a force on the broader end of the at least one wedge-portion to tighten the coil on the multi-part tooth.

FIG. 47illustrates a flow chart of an exemplary method of installing a coil on a multi-part tooth. With additional reference toFIGS. 45A-46C, the method may include a step of inserting at least one wedge-portion (e.g., additional tooth-portion124A,124B) of a multi-part tooth120into an opening (e.g., cavity320) of a coil300such that a broader end (second end128) of the at least one wedge-portion extends out of the opening in the coil (step810). The method may also include a step of mounting the coil300with the inserted at least one wedge-portion124A,124B on a core tooth portion122of multi-part tooth120such that the broader end of the at least one wedge-portion remains extended out of the opening in the coil (step820). The method may further include exerting a force (e.g., Force F ofFIG. 46C) on the at least one wedge-portion124A,124B to push its broader end128into the opening in the coil. In method of assembling outer rotor assembly, the opening in the coil may extend from a first end to a second end, wherein inserting the at least one wedge-portion includes inserting the at least one wedge-portion into the opening such that the broader end extends out of the second end of the opening and the step of exerting the force includes pushing the broader end towards the first end of the opening (step830).

Exemplary methods of forming coils300for electric machines of the current disclosure are described below. In some embodiments, the coils may be irregular shaped coils. As used herein, the term irregular shaped coil indicates that the cross-section of the coil varies along its length. As explained previously with reference toFIGS. 6A-7C, coils300of the current disclosure may include a cavity320that extends from a first end322to a second end324. In some embodiments, a dimension related to the cross-section of the cavity320of an irregular shaped coil varies along at least a portion of the distance (e.g., length) between the first and second ends322,324. In some embodiments, the cross-sectional area varies from the first to the second end322,324. Various embodiments of forming irregularly shaped coils of the current disclosure may include forming a coil, winding a wire around a mandrel to form the coil in the shape of the mandrel, removing the coil from the mandrel, and exerting a mechanical force on the coil to change the shape of the coil to correspond to the shape of a tooth. The tooth may be part of the stator or the rotor or the electric machine. In some embodiments, the coil may then be mounted on the tooth.

As used herein, the term “mandrel” refers to a device (shaft, spindle, or workpiece) upon which the wire or foil that forms the coil is supported or wound to form a coil of the first shape. In some embodiments, the mandrel may be a shaft or a rod (e.g., a cylindrical shaft). Any type of mechanical force (compressive force, tensile force, pulling, pushing, etc.) may be applied to the coil to change its shape. In some embodiments, the mechanical force may result in deformation of the coil. As explained previously with reference toFIGS. 6A-7E, the coils300of the current disclosure may be made of wires or foils. In some embodiments where the coil is made of a wire, the wire may include a single-strand wire or a multi-strand wire. The term “strand” refers to a current or electrical conductor isolated from other current conductors of the wire. The term current or “electrical conductor” refers to a material or an object that allows for the flow of charge or current in one or more directions. In some embodiments, the wires that form a coil may be twisted together. That is, the strands of the wires may be twisted together. In some cases, twisting the strands together may assist in reducing eddy current losses.

FIGS. 48A-48Dillustrate the steps of fabricating a coil300in an exemplary embodiment. As shown inFIG. 48A, coil300may be made from a wire314. Wire314may be single-strand wire or a multi-strand wire314. Coil300may be wound in a form of a spiral in the radial direction. In some embodiments, coil300may be wound around a cylindrical mandrel to form spiral shaped winding. As such, a first shape of coil300after winding on a cylindrical mandrel may correspond to the shape of the mandrel. The cylindrical cavity of the coil300that results after winding on the cylindrical mandrel may have a constant perimeter and a constant cross-sectional area along the length of the cavity. It should be noted that the cylindrical mandrel and the resulting cylindrical shape are only exemplary. In general, the mandrel may have any shape (i.e., a rod of any cross-sectional shape), and the coil that results from winding on that mandrel may have a corresponding cross-sectional shape. For example, if the mandrel used to wind the wire has a rectangular cross-sectional shape, the cavity of the coil that results from that winding operation will also have a substantially similar rectangular cross-sectional shape.

As shown inFIG. 48B, coil300may be placed on a fabrication station952using one or more separation mandrels956. The separation mandrels956may support the coil during application of mechanical force to change the shape of the coil cavity from the first to the second shape. In some embodiments, a mount954may affix a portion of coil300to the station952so that coil300may not move during fabrication. As shown inFIG. 48C, a wedge mandrel958may be driven between the separation mandrels956to change the shape of coil300. The wedge mandrel958may be pushed into the cavity of the coil through the gap between the two separation mandrels956(seeFIGS. 48B and 48C) to push diametrically opposite ends of the internal cavity walls outward. Force may be applied to wedge mandrel958, for example, in a downward direction960as shown inFIG. 48Cto push the wedge mandrel958into the space between the separation mandrels956. As the wedge mandrel958moves downward into the coil cavity, the separation mandrels956may be driven outwards (shown using arrows inFIG. 48C) by the wedge faces of wedge mandrel958. As the separation mandrels956moves outward, the internal walls of the coil cavity may also be pushed outward. As a result of this force in the radially outward direction on diametrically opposite ends of the coil cavity, as shown inFIG. 48D, a second shape of coil300may be formed. The second shape may correspond to a shape of a tooth120. That is, after application of the force (as shown inFIGS. 48B-49D), similar to the external shape of a tooth120(explained with reference toFIGS. 48A-49D), the cavity320of the coil300that snugly fits on the surface of the tooth120may have a substantially constant perimeter along its length from the first end322to the second end324while its cross-sectional area along the length varies. The second shape may be rectangular or trapezoidal. In some embodiments, the cavity320may have a trapezoidal 3-dimensional shape with a rectangular cross-sectional area in planes perpendicular to an axis that extends between the first and second ends322,324of the coil300(see, e.g.,FIGS. 6C, 7A, 48B-48D). In some embodiments, at least one end of the internal cavity of coil300may expand (or plastically deform) as a result of the force applied by wedge mandrel958. An exemplary embodiment of a coil300with its cavity320in the second shape is shown inFIGS. 6A-6D and 7A-7B. As explained previously, although a wire314is used to form the coil300in the method described above, a coil300may also be similarly formed using a foil312.

FIGS. 49A-49Dillustrate another exemplary method of fabricating a coil. As shown inFIG. 49A, coil300may be placed on fabrication station952using one or more guide separation mandrels962. Mount954may affix a portion of coil300so that coil300may not move during fabrication. As shown inFIG. 49B, separation mandrel962may include lower portion964and upper portion966. Lower portion964may be driven inside of a coil to shape the coil and upper portion966may be configured to restrict movement of separation mandrel962such as to keep separation mandrel962against mount954. As shown inFIG. 49C, wedge mandrel958may be driven between guide separation mandrels962to change a shape of coil300. Force may be applied to mandrel958opposite fabrication station952(e.g., in direction958downward as shown), and separation mandrels962may be driven by the wedge faces of wedge mandrel958. As shown inFIG. 49D, a second shape of coil300may be formed. The second shape may correspond to a shape of a tooth120. The second shape may be similar to that described above. In some embodiments, at least one end of the internal cavity of coil300may expand as a result of the force applied by wedge mandrel958. The resulting second shape of coil300may be similar to that shown relative to coil300shown inFIGS. 6A-6D and 7A-7B.

As explained previously (with reference toFIGS. 45A-46C), a coil300is mounted on a tooth120of a rotor or a stator such that the cavity320of the coil300fits snugly on the tooth120. In some embodiments, after a coil300is formed as described above (e.g., with reference toFIG. 48A-48D or 49A-49D), the shape of its cavity320may not sufficiently correspond to the shape of the tooth120. In some such embodiments, after the coil300is formed as described above, a force may be applied to the external surfaces of the coil300and/or the internal walls of its cavity320to finish (or fine-tune) the shape the cavity320to the shape of the tooth120.FIGS. 50A-50Dillustrate views of an exemplary method of fabricating a coil. As shown inFIGS. 50A-50B, a coil300(after changing the shape of its cavity to the second shape as described with reference to48A-48D and49A-49D) may be placed on protrusion576with its cavity around the protrusion. Forming blocks572,574may contact and apply a mechanical force (e.g., a compressive force) on the external surfaces of the coil300to change a shape of coil300once coil300is positioned on protrusion576. As shown inFIGS. 50C-50D, forming blocks572,574may be driven inwards (e.g., with force578) towards protrusion576to change the shape of the coil cavity to final desired shape. The resulting shape of coil300may be trapezoidal and correspond to the shape of the multi-part tooth120(described with reference to48A-49D). In some embodiments, only one pair of oppositely positioned blocks574(or572) may apply a compressive force on the coil300mounted on the protrusion576. In some embodiments, a first pair of oppositely positioned blocks574may apply a compressive force on the coil300while a second pair of oppositely positioned blocks572may merely rest on the coil surface, for example, to prevent it from bulging in the direction of blocks572as a result of the force application.

In some embodiments, a wedge piece may be used to finish the shape of the coil cavity to the final desired shape.FIGS. 51A-51Billustrate view of a method of fabricating a coil. As shown inFIGS. 51A-51B, a wedge mandrel582and base584may be used to finish the shape of the cavity320of the coil300. In some embodiments, the wedge mandrel582may be moved (e.g., up and down inFIG. 51A) in the cavity320of the coil300to finish (or fine-tune) the inner walls of the cavity320to the final desired shape. In some embodiments, as illustrated inFIG. 51B, wedge mandrel582may be pressed to one side of coil300against base584to finish the shape of one side of the coil cavity to the final desired shape. In some embodiments, coil300may be flipped and the process repeated to form or finish the other side. Mandrel582may be wedge shaped so as to form a trapezoidal inside of coil300. In some embodiments, a mechanical force may be used to decrease the size of the internal cavity at the other end (e.g., a clamp) while mandrel582is pressed against base584. In such embodiments, mandrel582may be acting in a direction away from a central axis of coil300(e.g., axis2000shown inFIG. 6D), and the mechanical force to decrease the size of the internal cavity at the other end may be acting in a direction towards the central axis of coil300.

FIG. 52illustrates a method910of fabricating a coil for mounting on a tooth120of a stator or a rotor of an electric machine. Steps of method910may include a step920of winding a wire (or a foil) about a mandrel to form a coil having a first shape corresponding to the shape of the mandrel. For example, in some embodiments, a wire314(or foil312) may be wound around a circular rod or a shaft to form (or deform) a cylindrical winding of the wire314with a cylindrical cavity therethrough. Steps of method910may include a step930of removing the coil having the first shape from the mandrel. For example, in an embodiment where a wire is wound on a circular shaft to form a circular coil, the coil may be removed from the shaft. In step920, the material of the wire may be plastically deformed such that the coil retains its circular shape when it is removed from the mandrel in step930. Steps of the method may include step930of applying a mechanical force on the coil to change the shape of the coil from the first shape to a shape that corresponds to the tooth. For example, if the tooth has a rectangular shape, in this step, a mechanical force is applied to the circular coil of wire so that the shape of its cylindrical cavity changes to a cavity having a rectangular cross-sectional shape. Steps of the method may include step940of mounting the coil of the second shape on the tooth.

In some embodiments, coil the wire may be formed of a number of strands of an electrical conductor. The wire may have any number (e.g., 2-3000) of strands. In some embodiments, wire314may be formed by twisting together an electrical conductor or made in the form of a Litz wire. A Litz wire is made of many wire strands which may be individually insulated and twisted or woven together. In some cases, a Litz wire may assist in distributing a current equally among the multiple wire strands and thereby reducing its resistance.

Wire314may have a circular cross-sectional shape or a rectangular cross-sectional shape. As previously explained, the coils300of the current disclosure may be made using a wire314or a foil312. It should be noted that although the above described coil fabricating method810is described using a wire314, this is only exemplary. The method910can also be performed using a foil312. For the sake of brevity, the method of fabricating a coil300will be described with reference to a wire314. The coil300can also be formed using a foil312in a similar manner.

With reference to step920, the wire314may be wound on a mandrel to form a coil having any shape (i.e., any first shape). In some embodiments, the first shape of coil may be a cylindrical shape or a trapezoidal shape. That is, the coil formed as a result of winding the wire314on the mandrel may have a cylindrical (or trapezoidal) cavity320that extends along its length. In some embodiments, the step of winding wire314about mandrel (i.e., step920) includes forming a coil having an internal cavity320extending from a first end322to a second end324. In some embodiments, the step of applying mechanical force (i.e., step940) on the coil includes selectively increasing a size of the internal cavity320at one of the first end322or the second end324. In some embodiments, the step of applying the mechanical force (i.e., step940) on the coil may include changing a shape of the internal cavity320. For example, the cross-sectional shape of the internal cavity320may be changed from one shape (e.g., circular cross-sectional shape) to a different shaped (e.g., rectangular cross-sectional shape). In some embodiments, changing the shape of the internal cavity may include changing a cross-sectional shape of the internal cavity along a plane perpendicular to a central axis of the internal cavity from a circular shape (see, e.g.,FIG. 49A) to a trapezoidal shape (see, e.g.,FIGS. 50C-50D).

In some embodiments, a width and a height of the trapezoidal shape both may vary from the first end to the second end (see, e.g.,FIGS. 7B, 48A-48D). In some embodiments, a perimeter of the trapezoidal shape may be substantially a constant from the first end to the second end and an area of the trapezoidal shape varies from the first end to the second end. In some embodiments, the area of the trapezoidal shape increases from the first end to the second end. In some embodiments, the step of applying a mechanical force930on the coil may include inserting a second mandrel into the internal cavity of the coil to change a shape of the first end of the internal cavity compared to a shape of the second end of the internal cavity. The term “second mandrel” indicates a solid material configured to change the shape of the coil from cylindrical to trapezoidal.

The step of applying a mechanical force930on the coil may include applying a first mechanical force (e.g., mechanical force in direction960) to increase a dimension of the internal cavity at one of the first end or the second end and a second mechanical force to decrease a dimension of the internal cavity at the other of the first end or the second end. In some embodiments, the first mechanical force may act towards a central axis of the internal cavity and the second mechanical force acts away from the central axis. In some embodiments, the step of applying a mechanical force930on the coil includes stretching the wire of the coil that defines at least one of the first end or the second end of the internal cavity. In some embodiments, the wire may be made of copper.

Various embodiments of the current disclosure include an electric machine. As used herein, an electric machine (or electrical machine) may be device that operates based on electromagnetic forces. In general, any type of electromechanical energy converter that operates on, or generates, electricity may be an electric machine. Although not required, in some embodiments, the electric machine may be an electric motor or an electric generator. During operation, an electric machine generates magnetic flux. In a radial flux electric machine, at least some portions of the generated magnetic flux may extend perpendicular to the axis of rotation of the machine. Electric machines may include a stator and a rotor separated by an air gap. In a radial flux electric machine, the working (or main) magnetic flux may extend between the rotor and the stator through the air gap in the radial plane.

FIGS. 53, 54, and 55depict different views of an exemplary electric machine10. Exemplary electric machine10may include a stator100, a rotor200, a base plate56, a plurality of teeth120, and electromagnetic coils300. Electric machine10may be an air-cooled system with a housing50. External ribs52may be positioned on the surface of the housing50between an end shield54and a stator base plate56. As illustrated inFIG. 53, the stator base plate56may include a plurality of pins58extending therefrom. The external ribs52and the pins58may assist in transferring the heat generated by the electric machine10during operation to the surrounding air. In the discussion below, electric machine10in the form of an electric motor will be described. However, the description is equally applicable to other types of electric machines, such as, for example, an electric generator. When electric machine10operates, its shaft20may rotate. The components of electric machine10will be described in greater detail below.

Electric machines of the current disclosure may include a rotor configured to rotate about an axis of rotation and a stator having a plurality of teeth annularly arranged on a stator core about the axis of rotation. In general, a stator may be any stationary component (or assembly of components) of an electric machine and a rotor may be any electric machine component (or assembly of components) that is configured to move with respect to the stator. In some embodiments, the stator may be fixedly positioned with respect to the rotor. In some embodiments, the rotor may be configured to rotate about an axis of rotation with respect to the stator. The rotor may be coupled to a shaft (rotor shaft) that rotates with the rotor. The axis about which the rotor (and the shaft) rotates may be referred to as the “axis of rotation.” As used herein, a plurality of teeth may refer to projections that protrude from a body. The teeth may include a series of substantially similar projections that protrude from the body. For example, in embodiments where the stator includes teeth, a series of substantially similar projections that protrude from a body or core of the stator may include the teeth. Additionally, or alternatively, in embodiments where the rotor includes teeth, a series of substantially similar projections that protrude from a body or core of the rotor may include the teeth. In a radial flux electric machine, the teeth may protrude in the radial plane. In other words, the teeth in the radial plane may protrude (inward or outward) in the radial direction. Each projection may form a tooth. Typically, the projections (or teeth) may be configured or shaped to direct a substantial portion of the magnetic flux between the stator and the rotor.

A stator core may refer to a main body of the stator which may be made of a single or multiple parts and may support and protect the rotating magnetic field. The stator core may be made of soft magnetic material for conducting the magnetic flux of an electric machine. A plurality of teeth annularly arranged on the stator core about an axis of rotation may refer to the teeth protruding from the core in a radial plane about the axis of the rotor shaft of the rotating electric machine. In some embodiments, a stator core may include an annular stator ring that extends around the axis of rotation and each tooth of the plurality of teeth may include a core tooth-portion integral with the annular stator ring. An annular stator ring may refer to a ring-shaped structure. The ring-shaped structure may be disposed around the axis of rotation of the electric machine. A core tooth-portion may refer to the part protruding from the annular stator ring of the stator ring in the radial plane. The term “integral” may be used herein to indicate that two parts are connected to form a single part that practically cannot be dismantled without destroying the integrity of the part. In some cases, the two integrally formed parts may be formed as a single part. Additionally, or alternatively, each tooth of the plurality of teeth may include one or more additional tooth-portions non-integrally formed with the core tooth-portion. The one or more additional tooth-portions being non-integrally formed with the core tooth-portion may refer to the one or more additional tooth-portions being attached together in a way that they may be easily separated from the annular stator ring. In some embodiments, the additional tooth-portions may be wedge-shaped. In some embodiments, a pair of additional tooth-portions may include tooth-portions arranged on opposite sides of the core tooth-portion. As another example, a pair of additional tooth-portions may also include tooth-portions arranged on the top and bottom surfaces of the core tooth-portion.

In certain embodiments, when all the tooth parts are assembled together, each tooth may define external surfaces having two sets of opposing faces, the opposing faces of each set of the two sets being non-parallel to each other, and wherein each face of the two sets of opposing faces may be inclined in a radial direction. That is, for example, for a tooth having faces A-D, a pair of faces A and B may be non-parallel to each other and another pair of faces C and D may be non-parallel to each other. Additionally, or alternatively, the opposing faces of adjacent teeth may be substantially parallel to each other. That is, for example, face C of one tooth may be parallel to face D of an adjacent tooth. The opposite side faces may be parallel to each other such that a slot formed between the adjacent teeth has a constant width in the radial direction. In some embodiments, a cross-section of each tooth in a plane perpendicular to the radial direction may have a rectangular shape, and a perimeter of the cross-section may be substantially a constant in the radial direction and an area of the cross-section may vary in the radial direction.

FIG. 53illustrates a cross-sectional view of electric machine10along an axial plane of the electric machine10. InFIG. 53, the axis of rotation1000of electric machine10lies in the axial plane, and the axial plane bisects the electric machine10into two symmetric halves. The radial plane extends perpendicular to the axis of rotation, and the axis of rotation1000extends perpendicular (e.g., into and out of the paper) to the radial plane. Electric machine10may include a stator100and a rotor200. The rotor200may be configured to rotate about the axis of rotation1000with respect to the stator100. The stator100may include a stator core110including a plurality of teeth120, and the rotor200may include a rotor core210which is installed a plurality of permanent magnets220. Electromagnetic coils300may be annularly mounted on the teeth120of the stator100. The rotor200may be connected to the shaft20that may be configured to rotate about the axis of rotation1000. When electric power is provided to the electromagnetic coils300, a magnetic field may be generated. Based on the generated magnetic field, magnetic flux may flow between the rotor200and the stator100, thereby providing a rotary force to the rotor200. Electric machine10may be used as a power source in any appropriate application. For example, in an automobile, the electric machine10may drive the wheels of the automobile.

The stator100of electric machine10may include a plurality of teeth120arranged annularly and symmetrically about the axis of rotation1000on a stator core110of the stator100. Each tooth120may include multiple pieces or parts that may be arranged together to form a composite or a multi-part tooth120. Each tooth120may have a rectangular or trapezoidal cross-sectional shape in both the axial plane and the radial plane. The width and length of each tooth120may vary in the radial direction. That is, as illustrated inFIG. 53, the length l of tooth120may vary from l1to l2in the radially outward direction of tooth120(along radial axis2000) and the width of tooth120may vary in the radially outward direction of tooth120(not shown). In some embodiments, such as the electric machine10depicted inFIG. 54, a tooth may include a core tooth-portion122and a pair of additional tooth-portions124A and124B positioned on opposite side surfaces of the core tooth-portion122.

The electric machines of the current disclosure may include a plurality of electromagnetic coils. An electromagnetic coil (or an electric coil) may include one or more turns (or a winding) of an electrical conductor that may generate a magnetic field when an electric current is passed through the conductor (e.g., in electric motors), or that may generate a voltage across the conductor when a magnetic field passes over the coil. In some embodiments, the turns of an electrical conductor may be configured or shaped like a coil. In some embodiments, an electromagnetic coil may be an electrical conductor that contains a series of conductive wires that may be configured to be wrapped around a ferromagnetic core. In general, electromagnetic coils of the current disclosure may be associated with the stator or the rotor of the electric machine. That is, in some embodiments, the plurality of coils may be coupled to (e.g., mounted, installed, wound on) the rotor and in other embodiments, the plurality of coils may be coupled to the stator. In some embodiments, each coil of the plurality of electromagnetic coils may be mounted on a separate tooth of the plurality of teeth. In these embodiments, each tooth of the plurality of teeth protruding from the stator core may include an electromagnetic coil including one or more turns of an electrical conductor.

FIG. 54depicts a perspective view of the stator100of the exemplary electric machine10ofFIG. 53andFIG. 55depict a cross-sectional view of the stator100in the axial plane. Each electromagnetic coil300may be mounted, or installed, on a tooth120. In some embodiments, an electromagnetic coil300may be installed on a tooth120such that the inner surface of the electromagnetic coil300fits snugly against an outer surface of the tooth120. In some such embodiments, an external shape (or profile) of the electromagnetic coil300may be substantially the same as the external shape of the tooth120that it is mounted on. Each tooth120of the stator100may be separated from an adjacent tooth120by a slot160that may accommodate the electromagnetic coils300mounted on the adjacent teeth120. In embodiments where the tooth includes the core tooth-portion122and the additional tooth-portions124A and124B, the core tooth-portion122of each multi-part tooth120may be mounted on an electromagnetic coil300such that the electromagnetic coil300extends around the core tooth-portion122with one or more gaps forming between the outer surfaces of the core tooth-portion122and the inner surface of the electromagnetic coil300. In such embodiments, two gaps may be formed between the opposite side surfaces of the core tooth-portion122and the inner surface of the electromagnetic coil300, and one of the additional tooth-portions124A or124B may be positioned in one gap and the other additional tooth-portion124B or124A may be positioned in the other gap. It should also be noted that, although the stator100is described as including teeth120, in some embodiments, the rotor200may alternatively or additionally include teeth120.

Electric machines of the current disclosure may include a base plate located adjacent the plurality of electromagnetic coils and the stator core. A base plate may refer to a piece or combination of parts attached to the stator such that it may assemble the stator core and electromagnetic coils on it. The base plate may be made of heat-conducting materials to conduct and remove heat from its sources. For example, the base plate may be formed of aluminum. The base plate may be in thermal contact with the plurality of electromagnetic coils and the stator core such that as the plurality of electromagnetic coils and the stator core heat during operation, the base plate may be configured to serve as a common heat sink for the plurality of electromagnetic coils and the stator core. Thermal contact (or thermal connection) refers to the proximity between the base plate and the plurality of electromagnetic coils such that good heat exchange occurs between them. In some embodiments, when two bodies are in thermal contact, or is thermally connected, heat exchange between the two bodies occur by conduction heat transfer mechanism. That is, the two bodies may be in physical contact. Although the two bodies may be in direct physical contact when they are thermally connected (or are in thermal contact), they do not have to be. For example, the two bodies in thermal contact may be in physical contact with each other via a thermal interfacial material (e.g., thermally conductive grease, etc.) disposed between the two bodies. If a thermal interface material is thus disposed, conductive heat transfer occurs between the two bodies (in thermal contact) through the thermal interface material between them. A common heat sink may refer to a passive heat exchanger which may transfer the heat generated by the plurality of electromagnetic coils and the stator core to a fluid medium, for example, air or a liquid coolant, where it may dissipate away from the electric machine, allowing regulation of the electric machine's temperature.

In some embodiments, each coil of the plurality of electromagnetic coils and/or the stator core may be in contact with the base plate directly or through a thermally-conductive material disposed therebetween. A thermally-conductive material may refer to a material which improves the exchange and transfer of heat energy between systems. The above described thermal interface material may be a thermally-conductive material. The thickness of the thermally-conductive material and its thermal conductivity may impact the exchange and transfer of heat energy. As such, in some embodiments, the thermally-conductive material disposed between the plurality of electromagnetic coils and the stator core and the base plate may be a thin layer of the thermally-conductive material to reduce its thermal resistance. The thickness of the thermally-conductive material depends on the application. In applications were the thermal conductivity of the thermally-conductive material is high, the thickness of the thermally-conductive material may be higher.

In some embodiments, the electric machine may further include a motor housing thermally connected to the base plate to enable heat generated by the plurality of electromagnetic coils and stator core to be dissipated through the base plate and the motor housing. A motor housing may refer to a casing which may be configured to accommodate the stator and rotor of the electric machine inside. A motor housing may be made of heat-conducting material and contain ribs to increase the heat transfer surface. In some embodiments, the base plate may include a first side and a second side opposite the first side, wherein the plurality of electromagnetic coils and the stator core may be in thermal contact with the first side of the base plate and the motor housing may be in thermal contact with the second side of the base plate. A side may refer to a surface of the base plate which may be upright, the top, the bottom, the front, or the back of the base plate. In certain embodiments, the second side of the base plate may include cooling fins that extend therefrom. Cooling fins may refer to surfaces extending from an object which increase the rate of heat transfer to or from the environment by increasing convection. Cooling fins increase the surface area of an object, which may result in an economical and satisfactory solution to heat transfer problems. Cooling fins may be made of a heat-conducting material to increase the heat transfer surface. The cooling fins may have any shape and configuration. In some embodiments, the cooling fins may include plate-like structures that protrude from the base plate. In some embodiments, the cooling fins may include a plurality of pins. Pins may have any cross-sectional shape (e.g., circular, square, rectangular, etc.) and may enhance heat transfer from the surface by increasing the area from which heat can be removed. In some embodiments, the pins may represent an efficient cooling solution as they may have a large surface area in relation to other heat-sink methods. In addition, the spacing between the pins may allow air to flow through these spaces and create turbulence at the surface. The turbulence may assist in breaking up any boundary layers that may exist at the surface of the fins (and increase the convective heat transfer coefficient of the surface). Pin heat sinks may consist of a base and an array of embedded pins, whose dimensions (e.g., length, thickness, density, material) may be customized to fit various applications depending on heat loads involved, available space, and airflow.

In some embodiments, the base plate may include a cylindrical hub portion extending around the axis of rotation. As used herein, a cylindrical hub portion may refer to a portion of the base plate having a cylindrical configuration which serves to fix the stator core. The cylindrical hub portion may be made of heat-conducting material for conducting and removing heat from its sources. Additionally, the stator core may include an annular stator ring that extends around the cylindrical hub portion of the base plate. As used herein, an annular stator ring may be a ring-shaped structure. The ring-shaped structure may be disposed around the axis of rotation of the electric machine. The annular stator ring extending around the cylindrical hub portion may refer to the annular stator ring completely or partially covering the cylindrical hub portion in such a way which surrounds the sides of the cylindrical hub portion. In some embodiments, an inner annular surface of the annular stator ring may be in contact with an outer annular surface of the cylindrical hub portion of the base place directly or through a thermally-conductive material disposed therebetween. In some embodiments, the base plate may include air vents configured to direct air to the plurality of electromagnetic coils when the rotor rotates. Air vents may refer to pathways, openings, cavities, or outlets that allow entry of air therethrough. In some embodiments, the air vents may be associated with vanes that operate similar to fan blades to blow air through the air vents. The air vents (and vanes if any) may be designed and configured to direct air flow to cool the electrical machine.

InFIGS. 54, 55, and 56, electromagnetic coils300are shown to fit tightly between the base plate56and teeth120of the stator100. The electromagnetic coils300may be in direct contact with a first side602of the base plate56and teeth120or may be in thermal contact with the first side602of the base plate56and teeth120via a thermally conductive filler material. The stator core110may fit snugly against a cylindrical hub portion132of the stator100. The hub portion132may be connected to the stator base plate56. The base plate56and its cylindrical hub portion132may be made in the form of one single piece or two separate parts and made of a heat-conducting material, for example, aluminum. A second side604of the stator base plate56may be equipped with cooling fins made in the form of pins58, which may significantly increase the cooling surface of the second side604of the stator base plate56. The electromagnetic coils300may also fit tightly or contact the teeth120of the stator core110on which they are mounted with the help of a thermally conductive filler. During operation of the electric machine, as schematically illustrated inFIG. 53, portion of the heat generated in the electromagnetic coils300(e.g., due to electric current passing through the coils) may conduct through the teeth120and the cylindrical hub portion132to the base plate56.

As also illustrated inFIG. 53, a portion of the heat generated in the coils300may conduct directly to the base plate56that is in thermal contact therewith. In embodiments where the coils300are thermal contact with the base plate56due to direct physical contact (between the coils300and the base plate56), heat from the coils300may conduct directly into the base plate56. In embodiments, where a thermally-conductive material (or thermally conductive filler) is provided between the coils300and the base plate56, the heat from the coils300may conduct into the base plate56through the thermally-conductive material. Thus, thermal contact between the coils300and the base plate56provides an additional and shorter pathway for the heat to conduct out of the coils300. Since the coils300are in thermal contact with the base plate56, heat may readily pass from the coils300to the base plate56through this path. That is, as opposed to the heat passing from the coils300into the base plate56via the tooth120and the cylindrical hub portion132, thermal contact between the coils300and the base plate56provides a more direct heat conduction pathway to the base plate56. Air flow across the pins58on the second side604of the base plate56may then remove the heat from the base plate56.

Thus, it may be appreciated from the discussion above that the heat generated by the electromagnetic coils300and the stator core110with teeth120may be conducted through the stator base plate56and its cylindrical hub portion132and released into the environment. In addition, as illustrated inFIG. 53, a portion of the heat from the stator base plate56may pass through the housing50connected to it and may also be released into the environment through its outer ribbing52. The housing50may be made of a thermally conductive material. The stator base plate56may act as an air-cooled radiator for the electrical machine10. In addition,FIG. 53depicts exemplary heat conduction paths600from the coil300to the base plate56.

The inner surface of the housing50and/or the outer surface of the rotor200may also have internal ribbing or fins (not shown). These fins for an electric machine10, much like ventilation holes, may be intended to stir the air when the rotor200rotates. This may allow heat to be removed from heating sources in the form of magnets and a rotor core and be transferred to the housing50and further into the environment.

In the discussion above, electric machine10is described as being an air-cooled machine. However, this is only exemplary. In some embodiments, electric machine10may be liquid cooled. Electric machines of the current disclosure may include a liquid-coolant channel configured to direct a cooling liquid therethrough. The cooling liquid (or coolant) may remove the heat generated by the coils300from the electric machine. In some embodiments, the liquid-coolant channel may be defined on the second side of the base plate such that as the coils and the stator core heats during operation, the base plate is configured to transfer the heat to a liquid coolant in the liquid-coolant channel to dissipate heat from the plurality of electromagnetic coils and the stator core. In some embodiments, the liquid-coolant channel may be defined through the base plate. A liquid-coolant channel refers to a cavity or a passageway that is configured to allow the flow of a liquid therethrough. The liquid may be configured to remove the heat from the walls of the channel. Any liquid that is configured to flow through the liquid-coolant channel may serve as the coolant. When the temperature of the liquid flowing through the channel is lower than the parts to be cooled, the liquid removes the heat from the parts and thereby cools the parts. Any known liquid coolant (e.g., water, oil, glycol mixtures, dielectric fluid, etc.) may be directed through the liquid-coolant channel.

In some embodiments, a wall of the liquid-coolant channel may be a portion of the second side of the base plate directly opposite a portion of the first side of the base plate that is in thermal contact with the plurality of electromagnetic coils. The liquid-coolant channel may extend around the axis of rotation such that an annular region on the second side of the base plate may serve as a wall of the liquid-coolant channel. Additionally, or alternatively, the annular region on the second side of the base plate may include a plurality of fins that extend into the liquid-coolant channel. The plurality of fins may be arranged about the axis of rotation. The fins may increase the surface area from which heat can be removed by the liquid coolant flowing in the liquid-coolant channel. In some embodiments, the fins may be in the form of pins. As explained previously, the pins may be columnar projections (of any cross-sectional shape) that project into the liquid-coolant channel from the second side of the base plate. In some embodiments, the liquid-coolant channel may have a coolant inlet and a coolant outlet. The coolant inlet may be configured to direct the coolant into the liquid-coolant channel and the coolant outlet may be configured to direct the coolant out of the liquid-coolant channel. Any aperture that is configured to direct the coolant therethrough (e.g., into or out of the channel) may serve as the coolant inlet and the coolant outlet.

In some embodiments, the coolant intel and the coolant outlet may have fluid fittings (couplings, etc.) or may be otherwise configured to direct the coolant into and out of the channel in a hermetic manner. In some embodiments, the coolant inlet and/or coolant outlet may be fluidly connected to a radiator or a heat exchanger. The heat exchanger may be configured to remove heat from the coolant. In some embodiments, the coolant inlet, heat exchanger, and the coolant outlet may form a closed loop such that heated coolant from the coolant outlet is cooled in the heat exchanger and directed back into the electric machine through the coolant inlet. Any type of heat exchanger may be used. In some embodiments, the coolant outlet may be fluidly connected to a common heat exchanger (or radiator) of the system that the electric machine is a part of. For example, in embodiments where the electric machine is part of an electric vehicle (e.g., used to power the wheels of the electric vehicle), the coolant outlet may be connected to common radiator of the electric vehicle. In some such embodiments, the liquid coolant used to cool the electric machine may be a coolant that is used to cool other components of the electric vehicle (or other system that the electric machine is a part of). It should be noted that although a liquid coolant is described above, in general, and fluid coolant (liquid or gas) may be used to cool the electric machine. In embodiments where a gas coolant is used to cool the electric machine, the coolant gas may be directed through the coolant channels in the base plate.

FIGS. 57-60illustrate different views of exemplary liquid cooled electric machines700of the current disclosure.FIG. 57depicts an exemplary liquid-coolant channel702defined on the second side604of the stator base plate56. Liquid-coolant channel702may be a cavity defined between the second side604of the stator base plate56and a casing cover712of the housing50. Channel702may extend around the axis of rotation1000of the electric machine700to form an annular passage that extends around the electric machine (see, e.g.,FIG. 60). In some embodiments, as best seen inFIGS. 57 and 60, the channel702may be positioned directly below (or adjacent to) the coils300that are mounted on the multi-part teeth120. The radial position (or the radial distance from the axis of rotation1000) of the channel702may be substantially the same as that of the coils300. As illustrated inFIG. 57, a radial dimension (e.g., radial width r1) of the channel702may also be substantially the same as (or correspond to) the radial dimension (e.g., radial width r2) of the coils300. That is, the annular channel702may trace a path that has substantially the same radial size as the coils300around the axis of rotation1000(see, e.g.,FIG. 60). Although a single channel702is illustrated and described, this is only exemplary. In some embodiments, multiple coolant channels (e.g., multiple radially spaced apart channels) may be provided. It should also be noted that although the channel702ofFIG. 57is defined between the second side604of the base plate56and the casing cover712, this is only exemplary. Many variations are possible. In some embodiments, the channel702may extend through the base plate56.

As shown inFIG. 57, gaskets706may be provided between the base plate56and the casing cover712to seal the channel702and prevent leaks. As shown inFIG. 57, fins716may extend from second side604of the base plate56into the channel702to increase the heat transfer surface of the base plate56. The fins716may extend around the axis of rotation1000to form radially spaced apart annular plates that project into the channel702from the base plate56. As explained previously, the illustrated pattern of fins716is merely exemplary. Many other patterns are possible. In some embodiments, the fins716may be configured as pins. That is, multiple columnar projections may protrude into the channel702from the base plate56. Although not visible inFIG. 57, base plate56(and/or casing cover712) may also include a coolant inlet that is configured to direct a coolant into the channel702and a coolant outlet that is configured to direct the coolant out of the channel702. In some embodiments, multiple coolant inlets and/or outlets may be provided.

In some embodiments, liquid coolant channels may also extend through other components of electric machine700.FIGS. 58-60illustrate exemplary liquid-coolant channels704through the cylindrical hub portion132of the stator100. In some embodiments, channels for the passage of liquid may also extend through stator core110and/or the housing50. The heat generated by the electromagnetic coils300and the stator core110(and/or other components) may pass (e.g., by conduction) through the stator base plate56and its cylindrical hub portion132into liquid-coolant channels702and704. The liquid flowing through the channel702,704may then transfer the heat to a radiator (not shown) for cooling. The cooled liquid from the radiator may be directed back to the channels702and/or704. In some embodiments, the liquid may flow through the channels702and/704under pressure. In some embodiments of an electric machine with an internal rotor200, coolant channels for removing heat may be located in the middle part of the housing50and its bearing parts.

Directly cooling the coils300of the electric machine by keeping the coils300in thermal contact with the rotor base provide an additional easier path to cool the coils300. That is, rather than relying on the heat form the coils300to be transferred to the external environment via the tooth120, hub portion132, and the base plate56, keeping the coils300in thermal contact with the base plate56enables easier and more effective cooling of the coils300. Improving the cooling of electric machines results in improvements in efficiency and power of the electric machines.

The above-described embodiments of electric machine and related methods are only exemplary. Many variations are possible. Some possible variations are described in U.S. Pat. Nos. 9,502,951 and 10,056,813, which are incorporated by reference in their entirety herein. The methods described above need not be performed in the order discussed or indicated. Further, several steps may be omitted, combined, and/or some steps added. Furthermore, although some aspects of the electric machine are described with reference to an electric machine of a particular configuration, the described aspects may be used in an electric machine having any configuration. Other embodiments of the electric machine and related methods will be apparent to those skilled in the art from consideration of the disclosure herein.