Rotor having longitudinal recesses in outer surface between V-slot poles

An electric motor includes a stator having a stator surface and a rotor rotatable relative to the stator. The rotor includes a plurality of poles, each of which is defined by a pair of magnets positioned in a V-shaped arrangement having a vertex positioned radially inward. The magnets present a mechanical pole angle of the corresponding pole. The rotor also includes a rotor surface that is opposite the stator surface. The rotor surface includes a plurality of circumferentially-spaced pole segments, each of which spans a respective mechanical pole angle. The rotor also includes a plurality of longitudinally extending recesses, each of which is positioned between adjacent pole segments.

BACKGROUND

The embodiments described herein relate generally to electric motors, and more particularly, to electric motors including a v-slot rotor.

Permanent magnet rotors utilizing a V-slot design are known. The V-slots facilitate increasing a volume of magnets within a rotor pole. These designs are useful but typically result in increases in magnetic flux leakage through the interpolar area between the magnets of adjacent poles. A V-slot design also provides increased reluctance. While useful, there is a need for a rotor which provides a more constant power over a wide speed range for a given motor size and configuration, which may be dictated by physical constraints placed on the motor.

SUMMARY

In one aspect, an electric motor is provided. The electric motor includes a stator having a stator surface and a rotor rotatable relative to the stator. The rotor includes a plurality of poles, each of which is defined by a pair of magnets positioned in a V-shaped arrangement having a vertex positioned radially inward. Each of the poles includes a mechanical pole angle defined by the pair of magnets. The rotor also includes a rotor surface opposite the stator surface. The rotor surface includes a plurality of circumferentially-spaced pole segments, each of which spans a respective mechanical pole angle. Moreover, the rotor includes a plurality of longitudinally extending recesses defined in the rotor surface. Each of the recesses is positioned between adjacent pole segments.

In another aspect, an electric motor is provided. The electric motor includes a stator having a stator surface and a rotor rotatable relative to the stator about an axis of the rotor. The rotor includes a plurality of rotor poles, each of which is defined by a pair of magnets positioned at a mechanical pole angle relative to one another in a V-shaped arrangement. The rotor also includes a rotor surface opposite the stator surface, with the rotor and stator surfaces defining an air gap therebetween. The rotor surface has a rotor surface contour including circumferentially-alternating first and second segments, with each of the first segments spanning the mechanical pole angle of each respective rotor pole. A first air gap distance is defined between the stator surface and each of the first segments of the rotor surface contour, and a second air gap distance is defined between the stator surface and each of the second segments of the rotor surface contour. The second air gap distance is greater than the first air gap distance.

The drawing figures do not limit the present invention to the specific embodiments disclosed and described herein. While the drawings do not necessarily provide exact dimensions or tolerances for the illustrated components or structures, the drawings are to scale with respect to the relationships between the components of the structures illustrated in the drawings.

DETAILED DESCRIPTION

The following detailed description of embodiments of the disclosure references the accompanying drawings. The embodiments are intended to describe aspects of the disclosure in sufficient detail to enable those skilled in the art to practice the disclosure. Other embodiments can be utilized, and changes can be made without departing from the scope of the claims. The following detailed description is, therefore, not to be taken in a limiting sense. The scope of the present disclosure is defined only by the appended claims, along with the full scope of equivalents to which such claims are entitled.

In the following specification and the claims, reference will be made to several terms, which shall be defined to have the following meanings. The singular forms “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise. “Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not.

As used herein, the terms “axial” and “axially” refer to directions and orientations extending substantially parallel to a longitudinal axis of the electric motor. The terms “radial” and “radially” refer to directions and orientations extending substantially perpendicular to the longitudinal axis of the electric motor. In addition, as used herein, the terms “circumferential” and “circumferentially” refer to directions and orientations extending arcuately about the longitudinal axis of the electric motor. Moreover, directional references, such as, “top,” “bottom,” “front,” “back,” “side,” and similar terms are used herein solely for convenience and should be understood only in relation to each other. For example, a component might in practice be oriented such that faces referred to herein as “top” and “bottom” are in practice sideways, angled, inverted, etc. relative to the chosen frame of reference.

In the exemplary embodiment, the electric motor10is illustrated as a brushless permanent magnet, inner rotor motor. As will be described, an inner rotor motor has magnets positioned radially-inward relative to windings, which act as the stator. However, according to some aspect of the present invention, the rotor may alternately be an outer rotor motor or dual rotor motor.

As shown inFIGS. 1-3, the illustrated electric motor10generally includes a stator assembly12, a rotor assembly14supported for rotation relative to the stator assembly12, a controller housing16enclosing control electronics (not shown) for controlling operation of the electric motor10, a housing18including a base portion20and an endshield22, a first bearing assembly32, and a second bearing assembly34. The base portion20of the housing18is generally cylindrical in shape and includes a closed end36proximate the first bearing assembly32and an open end38opposite the closed end36for receiving at least a portion of the stator assembly12and the rotor assembly14. The endshield22cooperates with the base portion20to substantially define a motor chamber in which the stator assembly12and the rotor assembly14are at least substantially housed. The controller housing16is coupled to the endshield22and encloses the control electronics and other various power and controller components of electric motor10therein. While the illustrated embodiment is one configuration of the electric motor10, it is noted that electric motors of various configurations are contemplated, including, for example, electric motors having vented or otherwise open motor housings or shells, etc.

In the exemplary embodiment, the closed end36of the base portion20includes a first bearing support (not shown) sized and shaped to receive and secure the first bearing assembly32therein. For example, and without limitation, the first bearing support may include a recessed portion defined in the closed end36. Alternatively, the first bearing support may be any structure or component configured to receive and secure the first bearing assembly32and that enables the electric motor10to function as described herein.

The endshield22includes a second bearing support40defined therein and positioned substantially in a center of the endshield22such that it is aligned axially with the first bearing support and concentric with the rotation axis “A.” The second bearing support40is sized and shaped to receive and secure the second bearing assembly34therein. For example, and without limitation, as shown inFIG. 1, the second bearing support40is a recessed portion or bearing cup defined in the endshield22. Alternatively, the second bearing support40is any structure or component, such as an aperture, configured to receive and secure the second bearing assembly34and that enables the electric motor10to function as described herein.

The first bearing assembly32and the second bearing assembly34are configured to rotatably support the rotor assembly14. In particular, the rotor assembly14preferably includes a rotor shaft42fixedly supporting a rotor core44with the rotor shaft42extending axially through each of the bearing assemblies32and34. In the exemplary embodiment, each of bearing assemblies32and34is a ball bearing assembly including a plurality of steel balls (not shown) positioned between outer races46aand46band inner races48aand48b, respectively. The outer races46aand46bof the first and second bearing assemblies32and34are fixedly coupled to the first and second bearing supports, respectively. The inner races48aand48bare fixedly coupled to the rotor shaft42and are configured to rotate relative to the outer races46aand46bvia the interposed steel balls. In alternative embodiments, the first and second bearing assemblies can be any type of bearing and/or bearing assembly that enables the electric motor10to function as described herein, such as, without limitation, sleeve bearings, plain bearings, fluid bearings, and/or active magnetic bearings.

As best shown inFIG. 3, in the exemplary embodiment, the stator assembly12is a three-phase stator assembly having twelve slots. In accordance with certain aspects of the present invention, the stator assembly12can alternatively be configured as a single phase or different multi-phase motor and can have an alternative number of slots. In the exemplary embodiment, the stator assembly12is a segmented stator that includes a plurality of stator segment assemblies28combined to form the segmented stator assembly12. Each of the stator segment assemblies28includes a toothed core26, axially-opposite insulators30, and a winding24. The windings24are configured to be electrically energized to generate an electromagnetic field. The windings24are fabricated from wire (e.g., aluminum or copper) coiled or otherwise wound around the teether of the toothed core26. The insulators30surround the toothed core26and are positioned between the toothed core26and the windings24to facilitate electrical isolation of the winding24from the respective core26. While the segmented stator assembly12is illustrated for purposes of disclosure, it is contemplated that the electric motor10may include a stator assembly of various other configurations (e.g., an endless (non-segmented) toroidal core having alternative or no core insulation, etc.) and having different shapes.

In the exemplary embodiment, the toothed core26includes a solid core. A solid core can be a complete, one-piece component, or can include multiple non-laminated sections coupled together to form a complete solid core. The toothed cores26may be formed, for example, and without limitation, from a soft magnetic composite material, a soft magnetic alloy material, and/or a powdered ferrite material. It is noted that the use of soft magnetic composite materials and soft magnetic alloys in a solid core26facilitate 3-dimensional flux paths and facilitate reducing high frequency losses (e.g., losses at frequencies above sixty (60) Hz) when compared with laminated stator yokes. The use of soft magnetic composite materials and soft magnetic alloys also facilitates increasing the structural rigidity of the toothed cores26, which facilitates improving performance and minimizing noise.

Alternatively, the toothed cores26may be formed from a stack of laminations, or the cores may be integrally formed into an annular shape and fabricated from a plurality of laminations in the form of plates stacked one on top of the other. For example, and without limitation, in such a laminated structure, the laminations are stacked or placed in face-to-face contact such that the stack extends axially along the rotation axis “A” a predetermined length. The plurality of laminations may be interlocked (i.e., coupled to each other) or loose laminations. The laminations are fabricated from a magnetically permeable material, such as, for example, a steel or a steel alloy. Additionally, in some embodiments, a laminated stator core may be skewed by angularly offsetting laminations. For example, the skewed design may involve angularly offsetting each lamination a given angle relative to the axially adjacent lamination.

Each exemplary insulator30is fabricated from a thermoplastic synthetic resin suitable for use in the electric motor10. For example, and without limitation, each insulator30may be fabricated by injection molding the resin into the shape of the insulator30. However, it is contemplated that the insulators30may be fabricated from any non-conductive material that enables the insulators30to function as described herein. Furthermore, the insulators30may be fabricated by methods other than molding. For example, they may be fabricated by coating the core or by machining. Each insulator30is positioned on a respective toothed core26and located between a corresponding winding24and the respective core26. Each insulator30may be formed from two identical components coupled together to form a substantially tubular shape that extends radially when positioned on cores26. In addition, each insulator30is coupled to the corresponding core26such that the insulator30covers the entirety of the radial surfaces of the respective core. That is, each preferred insulator30covers substantially the entire core26except for a radially inner end surface of the core.

In the exemplary embodiment, as described above, the rotor assembly14includes the rotor core44coupled to the rotor shaft42. The rotor core44is substantially cylindrical in shape having an outside nominal diameter D1smaller than an inside diameter D2of an inner surface60of the stator assembly12. The difference between D1and D2defines a first air gap, or basic air gap, of the electric motor10. In the exemplary embodiment, the rotor core44is a permanent-magnet rotor and includes a plurality of substantially rectangular permanent magnets50. Alternatively, the rotor core44is any type of rotor that enables the electric motor10to function as described herein. In the exemplary embodiment, the rotor shaft42is fixedly coupled to the rotor core44and positioned concentrically relative thereto so as to extend along the rotation axis “A.” The rotor shaft42a first end52that extends forward from the rotor core44and a shorter second end54that extends rearward from the rotor core44.

While the magnets50are describe above as being substantially rectangular, it is noted that alternative magnet shapes are within the ambit of certain aspects of the present invention, as long as the angular relationships of each pole are maintained in accordance with the principles of the present inventions, as described below.

The rotor core44and the magnets50are configured to rotate with the rotor shaft42. In the exemplary embodiment, the rotor core44may be fabricated from a plurality of laminations56(seeFIG. 4) stacked or placed in face-to-face contact such that the rotor core44extends axially along the rotation axis “A” a predetermined length. The plurality of laminations56may be interlocked (i.e., coupled to each other) or loose laminations. Alternatively, in some embodiments, the rotor core44may be a solid core, formed without laminations.

In the exemplary embodiment, the rotor core44includes a plurality of V-shaped magnet slots58extending through the rotor core44, substantially parallel to the rotation axis “A.” The V-shaped magnet slots58are circumferentially positioned at substantially regular intervals about the rotation axis “A.” Each of the V-shaped magnet slots58is configured to receive two of the magnets50therein to secure the pair of magnets50in a V-shaped arrangement. As will be described, each V-shaped arrangement or V-shaped magnet slot58defines a magnetic pole of the rotor assembly14, meaning the illustrated electric motor10is a ten (10) pole motor. The illustrated embodiment includes ten (10) V-shaped magnet slots58, thus defining ten (10) pole sectors62. It is noted that the rotor core44may include more or fewer pole segments, depending on the electric motor design requirements. It is also noted that the magnets50are shown schematically for purposes of illustration but are generally sized to fit tightly within the V-shaped magnet slots58to facilitate a secure, non-moving fit with the rotor core44. Additionally, or alternatively, the magnets50may be secured in the V-shaped magnet slots58with adhesive, fasteners, etc.

FIG. 4is an enlarged cross-sectional view of the rotor core44, particularly illustrating one of the laminations56. As described above, in the exemplary embodiment, the lamination56defines ten (10) pole sectors62. End portions64of each of the V-shaped magnet slots58are positioned radially outward from the rotation axis “A” of the rotor assembly14, which is shown as the center of the lamination56. A vertex66of each of the V-shaped magnet slots58is thus positioned radially inward. A plurality of radial pole pitch lines100extend through the center of the lamination56(i.e., rotation axis “A”), with each radial pole pitch line100being centered angularly between an adjacent pair of the V-shaped magnet slots58such that the adjacent pair of the V-shaped magnet slots58are disposed symmetrically about the respective radial pole pitch line100. Each radial pole pitch line100defines the boundary between two adjacent pole sectors62, wherein adjacent radial pole pitch lines100define a pole sector62. Each pole segment includes a central pole axis102that passes through the center of the lamination56and bisects the respective pole sector62(i.e., is angularly centered between adjacent radial pole pitch lines100). InFIG. 4, only the vertical-most central pole axis102is shown for clarity.

As used herein, a pole pitch angle is defined as the angle between identical points on two adjacent pole sectors62. For example, and without limitation, a pole pitch angle104of the lamination56is illustrated inFIG. 4as the angle between adjacent radial pole pitch lines100, where the central pole axis102is positioned between the adjacent radial pole pitch lines100at an angle equal to one-half of the pole pitch angle104. The pole pitch angle is determined by dividing three hundred and sixty degrees (360°) (one full turn of the rotor) by the number of pole sectors62of the rotor core44. For example, in the exemplary embodiment, the ten (10) pole rotor core has a pole pitch angle104equal to thirty-six degrees (36°), i.e. three hundred and sixty degrees (360°) divided by ten (10) poles.

FIG. 5is an enlarged view of a portion of the lamination56shown inFIG. 4, illustrating the configuration of a V-shaped magnet slot58with respect to a respective pole sector62. In the exemplary embodiment, radial lines106extend through the center of the lamination56(i.e., rotation axis “A”), with each radial line106passing through a radially-outward, inwardly-facing corner of a respective magnet50(inwardly facing refers to the inner portion of the V-shaped magnet slot58). The two respective lines106of a V-shaped magnet slot58define a mechanical pole angle108of a pole110of the rotor assembly14. As used herein, the pole110is a magnetic pole of the rotor defined as the active or effective magnet pole area of the V-shaped magnet arrangement. In the exemplary embodiment, the effective magnet pole area is equal to an arc or segment112(also referred to as a pole segment) of the rotor core surface spanning the mechanical pole angle108. As shown inFIG. 4, the central pole axis102bisects the mechanical pole angle108and the V-shaped magnet slot58. That is, the vertex of the V-shaped magnet slot58lies on the central pole axis102, and the V-shaped magnet slot is disposed such that it is symmetric with the central pole axis102.

Referring toFIGS. 4 and 5, in the exemplary embodiment, the rotor core44, or the laminations56that make up a stacked rotor core44, includes an outer surface contour120. The outer surface contour120includes a plurality of circumferentially-alternating first and second segments112and114, respectively. The outer surface contour120defines a plurality of axially extending recesses116(shown inFIG. 1) of the rotor core44. More particularly, each second segment114of the outer surface contour120defines one of the recesses116. The first segments112are arcuate in shape (preferably extending along a common arc that defines the rotor nominal outside diameter D1), and each first segment112spans the corresponding mechanical pole angle108. The first segments112are substantially centered on the rotation axis “A” of the rotor assembly14to define the nominal outside diameter D1. As such, the first segments112provide a substantially uniform air gap width W1between the inner surface60of the stator assembly12and the first segments112. The second segments114span the distance between adjacent first segments112. The second segments114are substantially the same in shape and form, being generally arcuately concave with respect to the inner surface60of the stator assembly12. As such, the second segments114provide a substantially non-uniform air gap between the inner surface60of the stator assembly12and the second segments114. Most preferably, the second segments114are each at least substantially centered on a respective radial pole pitch line100and are symmetric thereabout.

The non-uniform air gap varies from the air gap width W1, corresponding to the intersection of one of the second segments114with one of the first segments112of the first pole110, to a maximum air gap width of W2(at a midpoint of the second segment114) and back to the air gap width W1, corresponding to the intersection of the second segment114with an adjacent first segment112of an adjacent second pole110. The non-uniform air gap width W2facilitates increasing the saliency of the rotor assembly14by reducing flux leakage from the rotor assembly14to the stator assembly12and increasing reluctance at the space between the poles110. In one suitable embodiment, the maximum distance the second segments114extend radially inward a distance of at least two-hundredths of an inch (0.02″) relative to the first segments112, as indicated by W3.

In the exemplary embodiment, the mechanical pole angle108is in the range between about forty-seven percent (47%) and about fifty-three percent (53%) of the pole pitch angle104. In the illustrated embodiment, the rotor core44is a ten (10) pole rotor. As such, the mechanical pole angle108is in the range between about seventeen degrees (17°) and about nineteen degrees (19°) for the ten pole rotor. This facilitates increasing the flux density within the span of the mechanical pole angle108, which has the effect of increasing the back electromotive force (or “back emf”) of the electric motor10for the same magnet volume. This back emf increase for the same magnet volume facilitates generating more effective power from the electric motor10. The non-uniform air gap width W2facilitates focusing the flux density through the first segment112areas of the rotor core44defined by the mechanical pole angle108, which increases the operating efficiency and reducing current load of the electric motor10.

The angles discussed above are geometric and are expressed as mechanical degrees. For the design of electric motors, electrical degrees are also employed so that results can be generalized. It is noted that each pole pitch angle (or pole sector62) of the electric motor10is equal to one-hundred and eighty electrical degrees (180° electrical), as the magnetic poles are one-hundred and eighty electrical degrees (180° electrical) apart. An electrical degree is a unit of measurement of time as applied to alternating current—one complete cycle equals three-hundred and sixty electrical degrees (360° electrical). For example, one cycle in a rotating electric motor is accomplished when the rotating field moves from one pole to the next pole of the same polarity. There are three-hundred and sixty electrical degrees (360° electrical) in this time period. Therefore, in a two (2) pole (one (1) pole pair) electric motor there are three-hundred and sixty electrical degrees (360° electrical) in one revolution, and the electrical and mechanical degrees are equal. In a machine with more than two (2) poles, the number of electrical degrees per revolution is obtained by multiplying the number of pole pairs by three hundred and sixty degrees (360°). Thus, in the exemplary embodiment, the electric motor10includes ten (10) poles, or five (5) pole pairs and the number of electrical degrees is equal to one thousand and eight hundred (1800° electrical), i.e., five (5) pole pairs times three-hundred and sixty electrical degrees (360° electrical). As such, each mechanical degree of rotation of the electric motor10is equal to five (5) electrical degrees, i.e., one thousand and eight hundred (1800° electrical) divided by three hundred and sixty degrees (360°).

As described above, the effective magnet pole area is equal to the arc or span of the segment112. In the exemplary embodiment, the effective magnet pole area is in a range between and including about eighty-five electrical degrees (85° electrical) and about ninety-five electrical degrees (95° electrical), where the pole sector62spans one hundred and eighty electrical degrees (180° electrical). As such, the mechanical pole angle108may be determined by the following equation:
(360÷No. of rotor poles)×(effective magnet pole area÷180)
Where “No. of rotor poles” equals the number of poles110(or pole sectors62) of the rotor core44and the “effective magnet pole area” is in the range of 85° electrical to 95° electrical. In the illustrated embodiment, the rotor core44is a ten (10) pole rotor. As such, the mechanical pole angle108is in the range between and including about seventeen degrees (17°) and about nineteen degrees (19°). In other words, the most preferred mechanical pole angle108for the illustrated electric motor10is about one-half (½) of three hundred and sixty (360) divided by ten (10) poles.

FIG. 6is a schematic view of an alternative lamination200constructed in accordance with another embodiment of the present invention. In this second embodiment, the lamination200defines twenty-eight (28) pole sectors202, each of which includes a V-shaped magnet slot204, substantially parallel to the rotation axis “A.” The V-shaped magnet slots204are circumferentially positioned at substantially regular intervals about the rotation axis “A.” Each of the V-shaped magnet slots204is configured to receive two permanent magnets therein, such as magnets50(not shown inFIG. 6). End portions206of each of the V-shaped magnet slots204are positioned radially outward from the rotation axis “A.” A vertex208of each of the V-shaped magnet slots204is thus positioned radially inward. A plurality of radial pole pitch lines210extend through the center of the lamination200(i.e., rotation axis “A”), with each radial pole pitch line100being centered angularly between an adjacent pair of the V-shaped magnet slots204such that the adjacent pair of the V-shaped magnet slots204are disposed symmetrically about the respective radial pole pitch line210. Each radial pole pitch line100defines the boundary between two adjacent pole sectors202, wherein adjacent radial pole pitch lines210define a pole sector202. Each pole segment includes a central pole axis212(only one (1) shown inFIG. 6for clarity) that passes through the center of the lamination200and bisects the respective pole sector202(i.e., is angularly centered between adjacent radial pole pitch lines210).

FIG. 7is an enlarged view of a portion of the lamination200shown inFIG. 6, illustrating the configuration of the V-shaped magnet slot204with respect to a respective pole sector202. A pole pitch angle214is as the angle between adjacent radial pole pitch lines210, where the central pole axis212is positioned between the adjacent radial pole pitch lines210at an angle equal to one-half of the pole pitch angle214.

In this second embodiment, the radial lines216extend through the center of the lamination200, with each radial line216passing through a radially-outward, inwardly-facing corner of a respective magnet50. The two respective lines216of a V-shaped magnet slot204define a mechanical pole angle218of a pole220. The central pole axis212bisects the mechanical pole angle218and the V-shaped magnet slot204. That is, the vertex208of the V-shaped magnet slot204lies on the central pole axis212, and the V-shaped magnet slot is disposed such that it is symmetric with the central pole axis212.

The lamination200includes an outer surface contour222, which includes a plurality of circumferentially-alternating first and second segments224and226, respectively. The outer surface contour222defines a plurality of axially extending recesses, such as the recesses116(shown inFIG. 1), of the rotor core44. More particularly, each second segment226of the outer surface contour222defines one of the recesses116. The first segments224are arcuate in shape (preferably extending along a common arc that defines the rotor nominal outside diameter D1), and each first segment224spans the corresponding mechanical pole angle218. The first segments224are substantially centered on the rotation axis “A” of the rotor assembly14to define the nominal outside diameter D1. As such, the first segments224provide a substantially uniform air gap width W4between the inner surface60of the stator assembly12and the first segments224. The second segments226span the distance between adjacent first segments224. The second segments226are substantially the same in shape and form. More specifically, each second segment226is generally V-shaped segment with respect to the inner surface60of the stator assembly12. Each second segment226most preferably has a vertex228that is centered on a respective radial pole pitch line210.

Each of the magnets50present a generally flat, radially outer magnet end230opposite the vertex228. Each of the V-shaped second segments226include a first section232that is parallel to a magnet end230of a first pole sector202, and a second section234that is parallel to a magnet end230of an adjacent pole sector202. The first and second sections232and234are spaced a distance236from the respective magnet ends230. In one preferable embodiment, the distance236is at least twenty-five thousandths of an inch (0.025″), although other suitable distances are within the ambit of certain aspects of the present invention.

The non-uniform air gap varies from the air gap width W4, corresponding to the intersection of one of the second segments226with one of the first segments224of the first pole220, to a maximum air gap width of W5(at a midpoint of the second segment226) and back to the air gap width W4, corresponding to the intersection of the second segment226with an adjacent first segment224of an adjacent second pole220. The non-uniform air gap width W4facilitates increasing the saliency of the rotor assembly14by reducing flux leakage from the rotor assembly14to the stator assembly12and increasing reluctance at the space between the poles220. In one suitable embodiment, the second segments226extend radially inward a distance of at least two-hundredths of an inch (0.02″) relative to the first segments224.

An effective magnet pole area of each pole220is equal to the arc or span of the first segment224. In this second embodiment, the effective magnet pole area is in a range between and including about eighty-five electrical degrees (85° electrical) and about ninety-five electrical degrees (95° electrical), where the pole sector202spans one hundred and eighty electrical degrees (180° electrical). As such, the mechanical pole angle218may be determined by the following equation:
(360÷No. of rotor poles)×(effective magnet pole area÷180)
Where “No. of rotor poles” equals the number of poles220(or pole sectors202) of the rotor core and the “effective magnet pole area” is in the range of 85° electrical to 95° electrical. In the illustrated embodiment, the rotor core is a twenty-eight (28) pole rotor. As such, the mechanical pole angle218is in the range between and including about six point one (6.1°) and about six point eight degrees (6.8°). In other words, the most preferred mechanical pole angle218for this second embodiment of the electric motor10is about one-half (½) of three hundred and sixty (360) divided by twenty-eight (28) poles.

Described herein are embodiments of an electric motor with an improved V-slot rotor having poles with a magnet angle producing more back emf per turn at lower flux density. The electric motor also includes rotor surface enhancements that facilitate increasing flux density at the rotor poles. One advantage of the disclosed electric motor includes improving torque/amp linearity by almost 20+% at peak current levels over typical known V-slot motors. The disclosed V-slot rotor has an effective magnetic pole angle between eighty-five degrees electrical (85° electrical) to ninety-five degrees electrical (95° electrical), which is advantageous in that it facilitates increasing the volt/turn back emf. Another advantage is that the disclosure provides an electric motor with increased motor efficiency and reduced current load.