Motor rotors for reducing harmonic flux

Abstract

A permanent magnet motor is provided. The permanent magnet motor may include a plurality of laminations stacked to form a rotor. Each of the laminations may define a d axis, and first and second concave notches located on an outer circumference. The first and second concave notches may be arranged at ±180 / N electrical angles relative to the d axis. N may be a multiple of 6.

Description

Technical Field

[0001] The present application generally relates to surface groove patterns of permanent magnet electric machine rotors. Background Art

[0002] Hybrid electric vehicles and electric vehicles utilize one or more electric machines to provide propulsion for the vehicle. Various electric machine technologies are available for such applications. Permanent magnet electric machines are a typical choice for vehicle applications. Permanent magnet electric machines include a stator and a rotor. The rotor is constructed with permanent magnets. The coils in the stator are energized to generate electromagnetic flux, which interacts with the electromagnetic flux generated by the permanent magnets of the rotor. The interaction of the fluxes causes the rotor to rotate. Due to various motor design characteristics, the interacting electromagnetic fluxes generate a torque composed of harmonic components. The torque can be described as the sum of components with different frequencies. This is seen as pulsation or oscillation of the torque. Summary of the invention

[0003] According to one embodiment of the present disclosure, a permanent magnet motor is provided. The permanent magnet motor may include a plurality of laminations stacked to form a rotor. Each of the laminations may define a d axis, and first and second concave notches located on an outer circumference. The first and second concave notches may be arranged at ±180 / N electrical angles relative to the d axis. N may be a multiple of 6.

[0004] According to another embodiment of the present disclosure, a motor is provided. The motor may include a plurality of laminations stacked to form a rotor. Each of the laminations may define a d axis, and a first and a second aperture. The first and the second apertures may be arranged at ±180 / N electrical angles relative to the d axis. N may be a multiple of 6 to reduce the back electromagnetic flux of the harmonic order N-1.

[0005] According to yet another embodiment of the present disclosure, a motor is provided. The motor may include a plurality of laminations stacked to form a rotor. Each of the laminations may define a d-axis and a first concave notch located on an outer circumference. The first concave notch may include a pair of saw teeth. The first concave notch may be aligned with the d-axis and configured to reduce a back electromagnetic flux having a harmonic order of N+1. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] FIG. 1 is a diagram showing a hybrid vehicle including a typical power train and energy storage components of an electric machine.

[0007] FIG. 2A is an example of a plan view of a rotor lamination.

[0008] FIG. 2B is a cross-sectional view taken along line 2B in FIG. 2A .

[0009] 3 is a partial plan view of an exemplary rotor and stator.

[0010] 4A is a partial plan view of a prior art rotor including a peripheral groove.

[0011] Figure 4B is a partial plan view of a rotor including more than one peripheral groove.

[0012] Figure 5 is a partial plan view of a rotor including a triangular aperture disposed within the rotor.

[0013] Figure 6 is a partial plan view of a rotor including a semicircular aperture disposed within the rotor.

[0014] Figure 7 is a partial plan view of a rotor including a trapezoidal aperture disposed within the rotor.

[0015] Figure 8 is a partial plan view of a rotor including a triangular aperture and a peripheral groove disposed within the rotor.

[0016] Fig. 9 is a partial plan view of a rotor including a trapezoidal aperture and a peripheral groove disposed within the rotor.

[0017] Fig.10 is a partial plan view of a rotor including a semicircular aperture and a peripheral groove disposed within the rotor.

[0018] Fig.11 is a partial plan view of a rotor including a double semicircular circumferential groove defined by the rotor.

[0019] Fig.12 is a partial plan view of a rotor including more than one double semicircular circumferential groove defined by the rotor. DETAILED DESCRIPTION

[0020] Although exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the present invention. In fact, the words used in this specification are words used to describe rather than limit, and it should be understood that various changes can be made without departing from the spirit and scope of the present invention. In addition, the features of various implemented embodiments can be combined to form other embodiments of the present invention.

[0021] As required, detailed embodiments of the present invention are disclosed herein; however, it should be understood that the disclosed embodiments are merely examples of the present invention that may be embodied in various forms and alternative forms. The drawings are not necessarily drawn to scale; some features may be exaggerated or minimized to show details of specific components. Therefore, the specific structural and functional details disclosed herein should not be interpreted as limiting, but merely as a representative basis for teaching those skilled in the art to employ the present invention in different ways.

[0022] Permanent magnet motors are characterized by magnets mounted on or embedded in a rotor surrounded by a stator. The magnets mounted on or embedded in the rotor couple with the internal magnetic field caused by the motor's current, which is generated by the electrical input to the stator. Similar to other alternating current (AC) induction motors, electrical power is supplied through the stator windings.

[0023] The individual stator tooth sets and stator windings form a plurality of magnetic poles that produce a flux flow pattern when the stator coils are energized by a multi-phase sinusoidal voltage. For example, a three-phase motor will have a total of 8 poles and 48 slots. A set of 6 slots will be characteristic of each pole of the specific example of the 48-slot motor disclosed herein. The magnetic flux produced by the stator windings interacts with the rotor flux produced by the permanent magnets in the permanent magnet motor rotor, so that a rotor torque is produced when the stator windings are excited with a multi-phase voltage.

[0024] The permanent magnets of the rotor may be positioned or oriented in different ways to produce the desired magnetic field. Each magnetic pole may be oriented with one magnetic pole (i.e., north or south). ) The rotor core is formed by a single permanent magnet in a radially outward direction. The magnetic poles of the rotor can be formed by multiple groups of permanent magnets arranged to form magnetic poles together. One such arrangement orients the magnets in a V-shaped pattern. The inner part of the "V" is with similar poles that cooperate to form the rotor poles. Each permanent magnet can be set in a recess or cavity to hold the permanent magnet. These recesses or cavities are typically rectangular and are sized to receive the permanent magnets. The cavity can be slightly oversized at opposite ends to limit the magnetic flux leakage between the north and south poles of the individual permanent magnets. The gaps or cavities in the rotor core hinder the magnetic flux because the vacuum has a relatively low magnetic permeability compared to the rotor core material (e.g., electrical steel).

[0025] The torque generated by the stator winding and the rotor flux field forms a uniform torque component and a variable torque component. The total output torque of the motor is a combination of the two components. Due to the variable torque component, a torque pulsation phenomenon is generated, which causes the motor torque output speed oscillation when the motor is used as a motor. The torque pulsation in the electric motor is caused by the interaction between the harmonic magnetic flux generated by the permanent magnets and the current in the stator windings. The reduction of the harmonic magnetic flux generated by the permanent magnets will result in a reduction in torque pulsation as well as iron losses.

[0026] For most applications, torque ripple needs to be reduced to a controllable level, especially in the case of hybrid electric vehicle powertrain applications, where the torque ripple component occurs at a variable frequency proportional to the output shaft speed of the traction motor. High-order frequencies can usually be filtered out by the limited bandwidth in the mechanical components of the powertrain. However, lower frequencies cause mechanical oscillations that cannot be easily filtered. Such oscillations are unacceptable in hybrid electric vehicle powertrains. The presence of torque ripple from the motor at lower frequencies may cause the motor to generate undesirable vibrations and noise.

[0027] Typically, the rotor laminations may have pockets or cavities arranged around the periphery of the rotor to accommodate permanent magnets. The permanent magnets may be positioned to interact with the magnetic field generated by the stator windings. These pockets or cavities may include flux-restricted regions to minimize undesirable flux leakage between the magnets.

[0028] Referring to FIG1 , a typical plug-in hybrid electric vehicle (PHEV) is shown. The PHEV 12 may include one or more motors 14 mechanically coupled to a hybrid transmission 16. The motor 14 may be capable of operating as a motor or a generator. In addition, the hybrid transmission 16 is mechanically coupled to an engine 18. The hybrid transmission 16 is also mechanically coupled to a drive shaft 20, which is mechanically coupled to wheels 22. The motor 14 can provide propulsion and deceleration capabilities when the engine 18 is turned on or off. The motor 14 also acts as a generator and provides fuel economy benefits by recovering energy that is usually lost as heat in a friction braking system. The motor 14 can also reduce vehicle emissions by allowing the engine 18 to operate at a more efficient speed and allowing the hybrid electric vehicle 12 to operate in an electric mode in which the engine 18 is turned off under certain conditions.

[0029] The traction battery or battery pack 24 stores energy that can be used by the motor 14. The vehicle battery pack 24 generally provides a high voltage direct current (DC) output. One or more contactors 42 can isolate the traction battery 24 from the high voltage bus when open and connect the traction battery 24 to the high voltage bus when closed. The traction battery 24 is electrically coupled to one or more power electronics modules 26 via the high voltage bus. The power electronics module 26 is also electrically coupled to the motor 14 and provides the ability to transfer energy bidirectionally between the high voltage bus and the motor 14. For example, the traction battery 24 can provide a DC voltage, and the motor 14 may operate with three-phase alternating current (AC) to function. The power electronics module 26 can convert the DC voltage into a three-phase AC current to operate the motor 14. In the regenerative mode, the power electronics module 26 can convert the three-phase AC current from the motor 14 acting as a generator into a DC voltage compatible with the traction battery 24. The description herein is equally applicable to pure electric vehicles. For pure electric vehicles, the hybrid transmission 16 can be a gearbox connected to the motor 14, and the engine 18 may not exist.

[0030] The electric machine 14 may be an interior permanent magnet (IPM) electric machine including a stator 122 and a rotor 120. FIG. 2A depicts an exemplary rotor lamination 138, and FIG. 2B depicts a side view of a configuration of the stator 122 and the rotor 120 having a plurality of rotor laminations 138 and a plurality of stator laminations 136 arranged in an axially stacked relationship. The rotor laminations 138 may define a circular central opening 160 for accommodating a drive shaft having a keyway that may receive a drive key 162. The rotor laminations 138 may define a plurality of magnet openings 142 that are symmetrically disposed with respect to adjacent pairs of magnet openings 142.

[0031] A plurality of rotor sectors 124 corresponding to the rotor poles may be defined by a plurality of interpolar axes (e.g., 180, 184) emitted from the central axis of rotation 170 to the outer surface 150 of the rotor lamination 138. Each sector 124 may include a pair of magnet openings 142. The interpolar axes (e.g., 180, 184) may be positioned in the middle between adjacent magnet openings 142. It is noteworthy that FIG. 2A shows only two possible interpolar axes 180, 184 and does not show all possible interpolar axes. FIG. 2B depicts a cross-sectional view of a series of axially stacked rotor laminations 138 taken along line 2-B in FIG. 2A. The rotor laminations are stacked along the central axis 170, and the rotor 120 is configured to rotate around the central axis 170. The stator 122 surrounds the outer periphery or surface 150 of the rotor laminations 138.

[0032] 3, a partial plan view of a stator lamination 136 and a portion of a rotor lamination 138 is shown. The rotor lamination 138 and the stator lamination 136 may be constructed of an iron alloy. A small air gap 140 is located between the inner periphery of the stator lamination 136 and the outer periphery 150 of the rotor lamination 138. The stator lamination 136 may define a radially extending opening 134.

[0033] The rotor laminations 138 may define symmetrically positioned magnet openings 142 about an outer periphery 150 of each rotor lamination 138. Each magnet opening 142 may be configured to receive a magnet 144. Any number of laminations may be used in a given design, depending on design choice. The rotor laminations 138 and stator laminations 136 may be arranged in a stack along an axis of rotation 170. The axially stacked rotor laminations 138 and magnets 144 may define a plurality of magnetic poles, such as 180, 125, and 184 distributed about the axis 170.

[0034] The laminations 136 of the stator 122 may have conductors disposed in radially extending openings 134 to form windings. The stator 122 may include an iron core made of a stack of stator laminations 136 and a winding arrangement of conductors carrying an excitation current. The current flowing through the stator windings generates a stator electromagnetic flux. The stator flux may be controlled by adjusting the magnitude and frequency of the current flowing through the stator windings. Because the stator windings are contained in the openings 134 rather than being uniformly sinusoidally distributed along the inner circumference of the stator, harmonic flux may be present in the stator flux.

[0035] The rotor 120 may include an iron core made of a stack of rotor laminations 138 and a plurality of sets of permanent magnets 144 inserted into a hole or cavity 142 defined by the iron core. The permanent magnets 144 in the rotor 120 may generate a rotor electromagnetic flux. Due to the shape and size of the discrete permanent magnets, the rotor flux may include harmonic flux. The stator flux and the rotor flux may be distributed in the air gap 140. The interaction between the stator flux and the rotor flux causes the rotor 120 to rotate about the axis 170.

[0036] The magnetic poles of the rotor 120 may be geometrically defined to correspond to the sectors 124 defined by the rotor laminations 138. Each magnetic pole may be represented by a sector 124. The magnetic pole position may generally be defined by a central magnetic pole axis 125 extending radially from the axis 170 toward the outer surface 150 of the rotor 138 along the midpoint between adjacent magnet openings 142. Interpolar axes (e.g., 180, 184) may extend radially from the axis 170 toward the outer surface 150 of the rotor 138 between adjacent magnetic poles. The angular distance between two adjacent magnetic poles may define a magnetic pole pitch parameter. The arc length on the circumferential rotor surface 150 between two adjacent magnetic poles of the rotor may be referred to as the magnetic pole pitch. The magnetic pole pitch may be measured circumferentially around the outer rotor surface 150 between adjacent central polar axes 125. Each magnetic pole may have an associated surface area on the outer circumferential surface 150 of the rotor 120. Each magnetic pole may be represented by an arc length on the surface between adjacent interpolar axes 180, 184.

[0037] An electromagnetic field or signal may be formed by the sum of harmonic components having different frequencies and amplitudes. Each harmonic component may be represented as a frequency and an amplitude. A signal may include a fundamental component. The fundamental component may be the frequency component having the largest amplitude.

[0038] During operation, the fundamental component fluxes of the stator and rotor may be aligned and rotated in the same direction at the same frequency. The interaction between the fundamental components of the stator flux and the rotor flux produces torque. The harmonic fluxes of the stator and rotor may have different pole numbers, rotation speeds, and directions. Therefore, the interaction between the harmonic fluxes produces torque fluctuations (called torque ripple). The torque ripple may have harmonic components with different frequencies. The order of the torque ripple component may be defined as the ratio of the torque ripple component frequency to the rotor speed in revolutions per second.

[0039] One effect of torque ripple is that it may cause speed oscillations of the rotor. In addition, torque ripple may affect noise and vibration of the motor and components coupled to the motor. High-order torque ripple frequencies may be filtered out by the limited bandwidth of the coupled mechanical system. Lower harmonic frequencies of torque ripple may cause mechanical oscillations in the coupled system. It is desirable to reduce torque ripple to reduce vibration and noise in the system containing the motor.

[0040] Referring to Figure 4A, a partial plan view of a prior art rotor is shown. Typically, the outer circumferential surface 150 of the rotor 120 is rounded or smooth. Here, the rotor includes a concave notch or groove 152 disposed about the d-axis 125 of the rotor.

[0041] refer to Figure 4B, showing a partial plan view of a rotor according to at least one embodiment of the present disclosure. This embodiment includes three grooves instead of a single groove 152 centered on the d-axis 125. The first groove 152a is positioned at an angle of -180 / N electrical degrees, where N is an integer that is a multiple of 6, such as 6, 12, 18, etc. The second groove 152b is centered on the d-axis 125. Similar to the first groove, the third groove 152c is positioned at an angle of 180 / N electrical degrees relative to the d-axis, where N is a multiple of 6, such as 6, 12, 18, etc. The integer N can represent or be related to the electrical order of the torque ripple. The grooves and their specified positions are configured to reduce the back electromagnetic force (back electromotive force).

[0042] Back EMF is the voltage across the stator winding induced by the magnetic field created by the rotating rotor. Back EMF harmonics result in current harmonics and motor losses that may adversely affect motor efficiency. Torque ripple may also increase due to back EMF harmonics. Back EMF can be reduced to achieve reduced torque ripple and improved motor efficiency in the motor system. The rotor magnetic field along the periphery of the rotor may not be sinusoidally distributed and may contain harmonics of order N±1. Rotor magnetic field harmonics will induce back EMF harmonics of the same order. Harmful back EMF harmonics are of order N±1, where N is a multiple of 6, such as 6, 12, 18, etc. Back EMF can be improved by positioning various features at predetermined angles relative to the d-axis, such as Figure 4B shown and described below.

[0043] refer to Figure 5 , showing a partial plan view of a rotor according to another embodiment of the present disclosure. Two triangular holes or slots 154 can be positioned between the magnet cavities 142 and near the edge of the rotor 150. More specifically, the triangular holes 154 are positioned at angles of -180 / N electrical degrees and +180 / N electrical degrees relative to the d axis. The role of the triangular slots 154 is to reduce the N-1 order back EMF harmonics. For specific reference Figure 6 , the rotor 138 includes a semicircular groove 156, which is arranged with Figure 5 The semicircular groove 156 also reduces the N-1 order back electromotive force harmonics. Figure 7 , the rotor 138 includes trapezoidal slots 158 or apertures arranged in parallel with Figure 5 The same position of the triangular slot 154 in FIG. Like the triangular slot 154 and the semicircular slot 156, the trapezoidal slot reduces the N-1 order back electromotive force harmonics.

[0044] refer to Figure 8, a partial plan view of a rotor according to another embodiment of the present disclosure is shown. The rotor 138 combines the features of the single peripheral groove 152 and the triangular hole or slot 154 shown in FIG. 4A. The single peripheral groove 152 is aligned with the d-axis 125 and is configured to reduce the N+1 order back EMF harmonics. The triangular slot 154 is positioned at an angle of -180 / N electrical degrees and +180 / N electrical degrees relative to the d-axis 125. Fig. 9 A partial plan view of a rotor 138 is shown including a single peripheral groove 152 arranged about the d-axis and two trapezoidal slots 158 , each of which is positioned at an angle of −180 / N electrical degrees and +180 / N electrical degrees relative to the d-axis 125 . Fig.10 The single perimeter groove concept already mentioned above and the semicircular groove 156 are shown. The trapezoidal groove 158 and the semicircular groove 156 are each configured to reduce the N-1 order back EMF harmonics.

[0045] refer to Fig.11 , showing a partial plan view of a rotor according to another embodiment of the present disclosure. The rotor 138 may include a pair of saw teeth or grooves 152b and 152b' that intersect each other and are bisected by the d axis 125. Two grooves or saw teeth that are bisected from each other may be referred to as "double grooves" and provide the advantage of reducing the N+1 order back electromotive force harmonics. The sawtooth may be defined as having a sawtooth edge or a saw-like feature. In addition to the pair of saw teeth 152b, 152b', the triangular groove 154 described in the previous figures is also implemented. It is noteworthy that, as already described, the groove may be triangular, trapezoidal or semicircular. Like the triangular groove 154 and the semicircular groove 156, the trapezoidal groove reduces the N-1 order back electromotive force harmonics.

[0046] exist Fig.12 The concept of a double groove or sawtooth edge is described in . Here, the double groove or sawtooth is bisected by the d axis with grooves or sawtooth 152b and 152b' on each side of the d axis. Grooves 152a and 152a' are positioned at -180 / N electrical degrees and grooves 152c and 152c' are positioned at +180 / N electrical degrees. The double grooves 152b and 152b' reduce the N+1 order back EMF harmonics. Grooves 152a, 152a', 152c and 152c' reduce the N-1 order back EMF harmonics.

[0047] According to the present invention, a permanent magnet motor is provided, which has a plurality of laminations stacked to form a rotor, each of the laminations defining a d-axis, and first and second concave notches located on an outer circumference and arranged at an electrical angle of ±180 / N relative to the d-axis, where N is a multiple of 6.

[0048] According to an embodiment, the first and second concave indentations comprise a pair of saw teeth.

[0049] According to an embodiment, each of the laminations further defines a third concave notch located on the outer circumference and disposed on the d-axis.

[0050] According to an embodiment, the first, second and third concave indentations are each located between a pair of magnets.

[0051] According to an embodiment, the pair of magnets are arranged in a V-shape.

[0052] According to an embodiment, the first, second and third concave indentations are curved.

[0053] According to an embodiment, each of the first, second and third concave indentations is elliptical in shape.

[0054] According to the present invention, there is provided an electric machine having a plurality of laminations stacked to form a rotor, each of the laminations defining a d-axis, and first and second apertures arranged at ±180 / N electrical angles relative to the d-axis, where N is a multiple of 6 to reduce back electromagnetic flux having a harmonic order of N-1.

[0055] According to an embodiment, each of the laminations defines a concave notch on the circumference aligned with the d-axis, the concave notch being configured to reduce a back electromagnetic flux of harmonic order N+1.

[0056] According to an embodiment, said first and second orifices are triangular in shape.

[0057] According to an embodiment, said first and second orifices are elliptical in shape.

[0058] According to an embodiment, said first and second orifices are trapezoidal in shape.

[0059] According to an embodiment, said first and second orifices are semi-elliptical.

[0060] According to the present invention, there is provided an electric motor having a plurality of laminations stacked to form a rotor, each of the laminations defining a d-axis and a first concave notch on an outer circumference comprising a pair of serrations, wherein the first concave notch is aligned with the d-axis and is configured to reduce a back electromagnetic flux having a harmonic order of N+1.

[0061] According to an embodiment, each of the laminations further defines first and second apertures, and the first and second apertures are disposed at ±180 / N electrical angles relative to the d-axis to reduce back electromagnetic flux having a harmonic order of N-1.

[0062] According to an embodiment, said first and second orifices are triangular in shape.

[0063] According to an embodiment, said first and second orifices are elliptical in shape.

[0064] According to an embodiment, said first and second orifices are trapezoidal in shape.

[0065] According to an embodiment, each of the laminations further defines second and third concave notches located on the outer circumference, wherein each of the second and third concave notches includes a pair of serrations, and wherein the second and third concave notches are arranged at an electrical angle of ±180 / N relative to the d-axis to reduce the back electromagnetic flux with a harmonic order of N-1.

[0066] According to an embodiment, the first, second and third concave indentations are each located between a pair of magnets.

Claims

1. A permanent magnet motor, comprising: A plurality of laminations are stacked to form a rotor, each of the laminations defining a d-axis, and a first concave notch and a second concave notch located on an outer circumference and arranged at an electrical angle of ±180 / N relative to the d-axis, where N is a multiple of 6 to reduce a back electromotive force with a harmonic order of N-1. 2 . The permanent magnet motor according to claim 1 , wherein the first concave notch and the second concave notch comprise a pair of saw teeth.

3. The permanent magnet motor according to claim 1, wherein each of the laminations further defines a third concave notch located on the outer circumference and disposed on the d-axis line to reduce the back electromotive force with a harmonic order of N+1. 4 . The permanent magnet motor according to claim 3 , wherein the first concave notch, the second concave notch and the third concave notch are each located between a pair of magnets. 5 . The permanent magnet motor according to claim 4 , wherein the pair of magnets are arranged in a V shape. 6 . The permanent magnet motor according to claim 3 , wherein the first concave notch, the second concave notch and the third concave notch are curved. 7 . The permanent magnet motor according to claim 3 , wherein each of the first concave notch, the second concave notch, and the third concave notch is elliptical in shape.

8. A motor, comprising: A plurality of laminations are stacked to form a rotor, each of the laminations defining a d-axis, and a first aperture and a second aperture disposed at ±180 / N electrical angles relative to the d-axis, where N is a multiple of 6 to reduce back electromotive force having a harmonic order of N-1. 9 . The electric machine of claim 8 , wherein each of the laminations defines a concave notch on an outer circumference aligned with the d-axis, the concave notch being configured to reduce a back electromotive force having a harmonic order of N+1.

10. The electric machine of claim 8, wherein the first and second apertures are triangular in shape.

11. The electric machine of claim 8, wherein the first and second apertures are elliptical in shape.

12. The electric machine of claim 8, wherein the first aperture and the second aperture are trapezoidal in shape.

13. The electric machine of claim 8, wherein the first and second apertures are semi-elliptical.

14. A motor, comprising: A plurality of laminations stacked to form a rotor, each of the laminations defining a d-axis and a first concave notch on an outer circumference including a pair of serrations, wherein the first concave notch is aligned with the d-axis and is configured to reduce a back electromotive force having a harmonic order of N+1, Each of the laminations further defines a second concave notch and a third concave notch located on the outer circumference, wherein each of the second concave notch and the third concave notch includes a pair of serrations, and wherein the second concave notch and the third concave notch are arranged at an electrical angle of ±180 / N relative to the d-axis to reduce the back electromotive force with a harmonic order of N-1.

Images