Motor with Noise-Reducing Rotor Notch

Abstract

A rotor assembly for an electric machine, such as for an electrified powertrain, includes: a rotor having an inner diameter surface and an outer diameter surface; and a rotor shaft connected to and surrounded by the rotor. The rotor has equally spaced rotor poles, each having an orthogonal axis (“q-axis”) and a pair of direct axes (“d-axes”). At each of the poles of the rotor, the rotor defines at least three arcuate notches, including a central notch bisected by the q-axis and a pair of additional arcuate notches symmetrically flanking the central notch. The rotor may include embedded permanent magnets that may be arranged in a double-V configuration. Each additional notch may be positioned within the sweep of the top-layer opening angle of the magnet. The central notch and / or the pair of additional notches may define a tangentially continuous chamfer that smoothly transitions the notch into the outer diameter surface.

Description

BACKGROUND OF THE INVENTION

[0001] Electric traction motors, generators, and motor - generator units are collectively referred to in the art as rotating electrical machines. In a typical radial - flux machine, a cylindrical stator circumscribes a cylindrical rotor, where the stator and rotor are spaced a short distance from each other by a radial air gap. Equally - spaced stator teeth project radially inwardly toward the outer diameter surface of the rotor, where adjacent stator teeth are separated from each other by respective stator slots. Each stator slot is filled with wire or solid segments to thereby form a set of stator windings. In a polyphase embodiment of the electrical machine, an AC input voltage is applied to the stator windings via corresponding phase leads. Thereafter, the energized stator produces a rotating stator magnetic field.

[0002] In an interior permanent magnet (“IPM”) machine, individual laminations forming the core structure of the rotor are embedded with purposefully - arranged permanent magnets, e.g., a double - V configuration of magnets constructed of neodymium iron boron (“NdFeB”), samarium cobalt (“SmCo”), ferrite, or other magnetic materials having magnetic properties well - suited for the application. Unlike the electromagnets produced by the sequential energization of the stator windings, the embedded rotor magnets collectively establish a time - varying rotor magnetic field. The stator and rotor magnetic fields interact to generate and sustain the motive force within the aforementioned stator - rotor air gap, where the generated gap force ultimately imparts rotation to the rotor and the attached rotor shaft. Permanent magnet synchronous reluctance motors (“PM - SRMs”) can also be used in applications requiring relatively high - speed operation, power density, and efficiency.

[0003] Rotating electrical machines are a major source of radiated noise in many applications, including in electrified powertrains, where one or more motors are employed as torque sources, e.g., as high - voltage propulsion motors. Such machine noise tends to be most prevalent at the dominant winding and torque - ripple orders, e.g., at the third harmonic of the pole - pass order for an exemplary three - phase motor. Typical electric and hybrid - electric vehicle powertrains tend to attempt to minimize the effects of undesired noise, vibration, and harshness (“NVH”) by skewing the rotor or stator. However, such skewing techniques can have the undesired effect of reducing the overall machine performance and operating efficiency. Similar results can be produced by imposing more stringent NVH constraints in the overall electromagnetic design of the machine. Thus, there is a need for a more efficient method to reduce harmonic noise within an electrified powertrain employing a rotating electrical machine. SUMMARY OF THE INVENTION

[0004] The present disclosure relates to an improved rotor design for reducing noise, vibration, and harshness ("NVH") effects in an electrified powertrain employing a rotating electric machine. In an exemplary motor vehicle application, for example, the electrified powertrain may be used to propel a vehicle along a road surface. As noted above, the main components of a rotating electric machine include a cylindrical stator and a rotor. In a typical radial flux configuration, the stator may surround or circumscribe the rotor such that a radial stator-rotor air gap is defined between the outer diameter surface of the rotor and the inner diameter surface of the stator. Possible embodiments of the rotor include a set of permanent magnets embedded in corresponding cavities of the rotor, for example, as a double-V configuration for each rotor pole. The stator includes stator windings disposed in stator slots, where such stator slots open into the radial stator-rotor air gap.

[0005] To provide the various benefits disclosed herein and specifically to reduce targeted NVH orders, the outer diameter surface of the rotor is modified to define arcuate notches that are symmetric for each rotor pole. The rotor notches may extend along the entire axial length of the rotor or, in different embodiments, the notches may be isolated to specific laminations. At least three rotor notches may be used at each magnetic pole of the rotor, where, in other embodiments, additional pairs of rotor notches may be added. An electric machine according to an exemplary embodiment has 8 rotor poles and 72 stator slots, where there are 18 stator teeth per rotor pole. Other embodiments of the electric machine may be envisioned within the scope of the present disclosure that will similarly benefit from reduced NVH effects when equipped with the disclosed rotor notches as set forth herein.

[0006] As will be understood by one of ordinary skill in the art, each of the rotor poles of an electric machine has an orthogonal axis ("q-axis") and a direct axis ("d-axis"), where the d-axis forms a rotating reference frame with the q-axis. At each of the rotor poles, magnetic flux is generated by the stator windings along the d-axis. At the same time, motor torque is generated along the q-axis between the rotor poles. For each rotor pole, the rotor notches contemplated herein include a notch aligned with and bisected by the q-axis ("q-axis notch"). The q-axis notch is symmetrically flanked by additional pairs of rotor notches ("d-axis notches") that are positioned at a calibrated angular distance from the d-axis of the pole. Thus, a single q-axis notch forms a central notch at the corresponding rotor pole, where at least one d-axis notch is positioned on each side of the q-axis / central notch.

[0007] In certain embodiments, one or more additional pairs of notches may flank the central notch, for example, when two additional pairs of notches are used, the rotor may have a total of 5 notches per rotor pole. Collectively, including the disclosed rotor notches at each of the magnetic poles of the rotor significantly reduces noise without affecting motor torque and efficiency.

[0008] The specific size, shape, and / or position of the rotor notch can be adjusted for a given application to maximize noise reduction at a target order and to evenly distribute the vibration energy throughout the motor. The notch can be arcuate, e.g., circular, elliptical, or polygonal. Optionally, a tangentially continuous chamfer or another suitable transition profile can be used with the notch to smoothly transition or bend the notch into the outer diameter surface of the rotor. Such chamfers can help avoid rotor stress concentrations and noise, especially at higher machine speeds.

[0009] In an exemplary embodiment, a rotor assembly for a motor includes a cylindrical rotor and a rotor shaft. The rotor having an inner diameter surface and an outer diameter surface includes a plurality of equally spaced rotor poles, each having an orthogonal axis (“q-axis”). The rotor shaft is connected to the inner diameter surface and is surrounded by the rotor. When the stator of the motor is energized, such rotor shaft together with the rotor rotates about a rotational axis. At each of the equally spaced rotor poles, the rotor defines at least three arcuate notches, including a central notch bisected by the q-axis of the pole and a pair of additional arcuate notches symmetrically flanking the central notch.

[0010] In some embodiments, the rotor includes multiple sets of permanent magnets embedded within the rotor adjacent to the outer diameter surface. Such magnets form equally spaced rotor poles.

[0011] At each of the equally spaced rotor poles, when the rotor is viewed along the rotational axis, the permanent magnets can optionally be arranged in a double-V configuration. As understood in the art, such a magnet configuration defines a respective top-layer magnet opening angle on either opposite side of the rotor pole. Each of the pair of additional notches can be positioned within the sweep or angular range of one of the respective top-layer opening angles.

[0012] The motor has a stator having N stator slots. A pair of additional notches can be located at approximately 360 / N degrees away from the nearest d-axis to thereby reduce the Nth torque ripple order harmonic, e.g., in the range of 345 - 375 degrees. In some embodiments, the stator can have 72 slots, i.e., N = 72. In other embodiments, other numbers of stator slots can be used. In certain applications, 360 / N can provide an optimized response.

[0013] A pair of additional notches symmetrically flanking the central notch at each rotor pole can have the same size and shape. In some configurations, the central notch can have the same size and shape as the pair of additional notches, or the central notch can have a different size and / or shape.

[0014] In certain configurations, the central notch and the pair of additional notches can define a tangentially continuous chamfer that smoothly transitions the notch into the outer diameter surface.

[0015] The present disclosure also discloses a rotating electrical machine. An embodiment of the machine includes a rotor that is circumscribed by a stator and has an inner diameter surface and an outer diameter surface. The rotor includes equidistantly spaced rotor poles, each having a corresponding q-axis. A rotor shaft is connected to the inner diameter surface of the rotor, is surrounded by the rotor, and is configured to rotate about a rotational axis together with the rotor when the stator is energized. As noted above, at each of the equidistantly spaced rotor poles, the rotor defines at least three arcuate notches, including a central notch bisected by the q-axis and a pair of additional arcuate notches symmetrically flanking the central notch.

[0016] An electrified powertrain is also disclosed. The powertrain can include a traction power inverter module (“TPIM”) that is connected to a battery pack and is configured to convert a direct current (“DC”) voltage from the battery pack to an alternating current (“AC”) voltage. The powertrain also includes a rotating electrical machine, as described above, that is energized by the AC voltage from the TPIM. A transmission is coupled to the rotor shaft and is powered by the machine.

[0017] The present disclosure also presents the following technical features.

[0018] 1. A rotor assembly for an electric machine, comprising:

[0019] a rotor having an inner diameter surface and an outer diameter surface, wherein the rotor includes a plurality of equidistantly spaced rotor poles, each having an orthogonal axis (“q-axis”) and a pair of direct axes (“d-axes”); and

[0020] a rotor shaft connected to the inner diameter surface, surrounded by the rotor, and configured to rotate about a rotational axis together with the rotor when the stator of the machine is energized;

[0021] wherein, at each of the equidistantly spaced rotor poles, the rotor defines at least three arcuate notches, including a central notch bisected by the q-axis and a pair of additional arcuate notches symmetrically flanking the central notch, and wherein each of the additional arcuate notches is located at a calibrated angular distance away from a respective one of the d-axes.

[0022] 2. The rotor assembly according to technical solution 1, wherein the cylindrical rotor includes multiple sets of permanent magnets embedded in the rotor adjacent to the outer diameter surface to thereby form the equidistantly spaced rotor poles.

[0023] 3. The rotor assembly according to Technical Solution 2, wherein at each of the equidistantly spaced rotor magnetic poles, when observing the rotor along the rotation axis, the permanent magnets are arranged in a double-V configuration, thereby defining a corresponding top-layer magnet opening angle on either side of the rotor pole, and each of the pair of additional notches is positioned within the sweep of one of the corresponding top-layer opening angles.

[0024] 4. The rotor assembly according to Technical Solution 3, wherein the electric machine has a stator having N stator slots, and the pair of additional notches are located at approximately 360 / N degrees away from the nearest d-axis, thereby reducing the Nth torque ripple order harmonic.

[0025] 5. The rotor assembly according to Technical Solution 4, wherein N = 72.

[0026] 6. The rotor assembly according to Technical Solution 1, wherein the pair of additional notches symmetrically flanking the central notch have the same size and shape.

[0027] 7. The rotor assembly according to Technical Solution 6, wherein the central notch has the same size and shape as the pair of additional notches.

[0028] 8. The rotor assembly according to Technical Solution 7, wherein the central notch and the pair of additional notches define a tangential continuous chamfer that smoothly transitions the notches into the outer diameter surface.

[0029] 9. A rotating electric machine, comprising:

[0030] A stator;

[0031] A rotor, circumscribed by the stator and having an inner diameter surface and an outer diameter surface, wherein the rotor includes a plurality of equidistantly spaced rotor magnetic poles, each having an orthogonal axis ("q-axis") and a pair of direct axes ("d-axes"); and

[0032] A rotor shaft, connected to the inner diameter surface, surrounded by the rotor, and configured to rotate about a rotation axis together with the rotor when the stator is energized;

[0033] Wherein at each of the equidistantly spaced rotor magnetic poles, the rotor defines at least three arcuate notches, including a central notch bisected by the q-axis and a pair of additional arcuate notches symmetrically flanking the central notch, and wherein each of the additional arcuate notches is located at a calibrated angular distance away from a corresponding one of the d-axes.

[0034] 10. The rotating electrical machine according to aspect 9, wherein the rotor includes a plurality of sets of permanent magnets embedded in the rotor adjacent to the outer diameter surface, thereby forming the equally spaced rotor magnetic poles.

[0035] 11. The rotating electrical machine according to aspect 10, wherein at each of the equally spaced rotor magnetic poles, when the rotor is viewed along the axis of rotation, the permanent magnets are arranged in a double-V configuration, thereby defining a respective top-layer magnet opening angle on either side of the rotor pole, and each of the pair of additional notches is positioned within the sweep of one of the respective top-layer opening angles.

[0036] 12. The rotating electrical machine according to aspect 11, wherein the stator defines N stator slots, and the pair of additional notches are located at 360 / N degrees away from the nearest d-axis, thereby reducing the Nth torque ripple order harmonic.

[0037] 13. The rotating electrical machine according to aspect 12, wherein N = 72.

[0038] 14. The rotating electrical machine according to aspect 9, wherein the pair of additional notches flanking the central notch symmetrically have the same size and shape.

[0039] 15. The rotating electrical machine according to aspect 14, wherein the central notch has the same size and shape as the pair of additional notches.

[0040] 16. The rotating electrical machine according to aspect 15, wherein the central notch and the pair of additional notches define a tangentially continuous chamfer that smoothly transitions the notches into the outer diameter surface.

[0041] 17. An electrified powertrain, comprising:

[0042] A battery pack;

[0043] A traction power inverter module (“TPIM”) connected to the battery pack and configured to convert a direct current (“DC”) voltage from the battery pack into an alternating current (“AC”) voltage;

[0044] A rotating electrical machine energized by the AC voltage from the TPIM and comprising:

[0045] A stator;

[0046] A rotor circumscribed by the stator and having an inner diameter surface and an outer diameter surface, wherein the rotor includes a plurality of equally spaced rotor magnetic poles, each having a quadrature axis (“q-axis”) and a pair of direct axes (“d-axes”); and

[0047] A rotor shaft, connected to the rotor, surrounded by the rotor, and configured to rotate about the axis of rotation together with the rotor when the motor is energized; and

[0048] A transmission, coupled to the rotor shaft and powered by the motor;

[0049] wherein, at each of the equidistantly spaced rotor magnetic poles, the rotor defines at least three arcuate notches, including a central notch bisected by the q-axis and a pair of additional arcuate notches symmetrically flanking the central notch, and wherein each of the additional arcuate notches is located at a calibrated angular distance from a respective one of the d-axes.

[0050] 18. The electrified powertrain according to aspect 17, wherein:

[0051] The rotor includes multiple sets of permanent magnets embedded within the rotor adjacent to the outer diameter surface of the rotor to thereby form the equidistantly spaced rotor magnetic poles; and

[0052] At each of the equidistantly spaced rotor magnetic poles, when the rotor is viewed along the axis of rotation, the permanent magnets are arranged in a double-V configuration to thereby define a respective top-layer magnet opening angle on either side of the rotor pole, and each of the pair of additional notches is positioned within the sweep of one of the respective top-layer opening angles.

[0053] 19. The electrified powertrain according to aspect 18, wherein the stator defines N stator slots, and the pair of additional notches are located at 360 / N degrees from the nearest d-axis to thereby reduce the Nth torque ripple order harmonic.

[0054] 20. The electrified powertrain according to aspect 19, wherein the at least three arcuate notches have the same size and shape as the pair of additional notches and define a tangentially continuous chamfer that smoothly transitions the notches into the outer diameter surface of the rotor.

[0055] The foregoing summary is not intended to represent every possible embodiment or every aspect of the present disclosure. Rather, the foregoing summary is intended to illustrate some novel aspects and features disclosed herein. When taken in conjunction with the accompanying drawings and the appended claims, the foregoing features and advantages of the present disclosure, as well as other features and advantages, will become readily apparent from the following detailed description of representative embodiments and modes for carrying out the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1is a schematic illustration of an electrified powertrain having a rotating electric machine, the rotor of which is configured with noise-reducing peripheral notches as set forth herein.

[0057] Figure 2 is for use with Figure 1 the rotor shown in, a schematic illustration of an exemplary notch configuration.

[0058] Figure 3 is Figure 2 a schematic illustration of an exemplary pole of the rotor shown in, depicting embedded permanent magnets arranged in a V-shaped configuration.

[0059] Figure 4 and Figure 5 are schematic illustrations of alternative rotor notches that may be used as part of a representative electrified powertrain of Figure 1 .

[0060] The present disclosure is subject to modification and alternative forms, and representative embodiments are shown by way of example in the drawings and are described in detail below. The inventive aspects of the present disclosure are not limited to the disclosed embodiments. On the contrary, the present disclosure is intended to cover modifications, equivalents, combinations, and alternatives falling within the scope of the present disclosure as defined by the appended claims. DETAILED DESCRIPTION

[0061] Referring to the drawings, in which like reference numerals refer to the same or similar components throughout the several views, an electrified powertrain 10 is schematically illustrated in Figure 1 , for example, on an exemplary motor vehicle 11. The powertrain 10 includes a rotating electric machine 12 having a rotor assembly 14A and a stator 16. When the stator 16 is energized, the rotor assembly 14A supplies motor torque (arrow T M ) to a transmission (“T”) 20, such as a stepped gear automatic transmission. Although omitted for simplicity of illustration, the electrified powertrain 10 may also include an internal combustion engine configured to produce engine torque. When so equipped, the engine torque produced, alone or in combination with the motor torque (arrow T M ) from the electric machine 12, is selectively provided to the transmission 20.

[0062] To reduce targeted noise, vibration, and harshness (“NVH”) orders in the electric machine 12, the peripheral outer diameter surface 30 of the rotor 14 of the rotor assembly 14A is modified to define depressions or notches 40 that are symmetric about a given rotor pole (see Figure 2 ). As will be understood by those of ordinary skill in the art, as noted above, the electric machine 10 has a direct axis (“d-axis”)) and a quadrature axis (“q-axis”). As set forth below, the disclosed notches are arranged according toFigures 2 - 5 arranged in the manner shown in or relative to such an axis.

[0063] When Figure 1 the vehicle 11 is implemented as a hybrid electric vehicle, the electric motor 12 and / or the engine may provide power to the transmission 20. Optionally, the vehicle 11 may be a battery electric vehicle, in which case, power may be provided to the transmission 20 only by the motor torque (arrow T M ) from the electric motor 12. The disclosed improvements relate to the construction of the electric motor 12 and may be implemented without limitation in HEV and EV embodiments of the vehicle 11 and in non-vehicle applications (e.g., power plants, cranes, mobile platforms, and robots, etc.).

[0064] The rotor assembly 14A of the electric motor 12 is positioned adjacent to the stator 16 and is separated therefrom by an air gap G, where such an air gap G forms a magnetic flux barrier. The stator 16 and the rotor 14 of the rotor assembly 14A may be constructed of a stack of thin laminations (e.g., electrical steel or other ferromagnetic materials), where each layer is typically about 0.2 mm - 0.5 mm thick, as would be understood by one of ordinary skill in the art. According to a non-limiting exemplary embodiment, the rotor assembly 14A is concentrically arranged within the stator 16 such that the stator 16 circumscribes the rotor assembly 14A. In such an embodiment, the air gap G is a radial air gap, and the electric motor 12 is implemented as a radial flux type machine. However, other embodiments may be implemented where the relative positions of the rotor assembly 14A and the stator 16 are reversed. For the sake of consistency in the description, the embodiments Figure 1 will be described below where the rotor assembly 14A resides radially within the stator 16 without limiting the construction to such a configuration.

[0065] Figure 1 The rotor 14 schematically shown in may optionally include a set of embedded permanent magnets, collectively referred to herein as rotor magnets 55 (see Figure 3 ). In such an embodiment, the electric motor 12 is an interior permanent magnet (“IPM”) machine, or optionally a synchronous reluctance machine. For example, the rotor magnets 55 may be constructed of ferrite, neodymium iron boron, samarium cobalt, alnico, etc. or other materials suitable for the application. In such an embodiment, the rotor magnets 55 are embedded within individual steel laminations of the rotor 14 and may have one or more layers in different embodiments. Thus, the shown configuration of the rotor magnets 55 is an example of one possible way to implement an IPM machine.

[0066] Continuing to refer to Figure 1 the exemplary vehicle 11, the electrified powertrain 10 may include an alternating current (“AC”) voltage bus 13. A high voltage battery pack (“B HV”)24 (e.g., lithium-ion, lithium-sulfur, nickel metal hydride, or other high-energy voltage supply) selectively energizes the AC voltage bus 13 via the traction power inverter module (“TPIM”) 28. The AC voltage bus 13 conducts the AC bus voltage (“VAC”) to the motor 12 or conducts the AC bus voltage (“VAC”) from the motor 12. When operating in the drive or motive mode, the motor torque (arrow T M ) is imparted to the rotor shaft 14R of the rotor assembly 14A, wherein the rotor shaft 14R is journaled, splined, or otherwise connected to the inner diameter surface 34 of the rotor 14. Then, the motor torque (arrow T M ) is directed to the coupled load, e.g., the transmission 20 and / or one or more road wheels 22.

[0067] The electrified powertrain 10 may also include a direct current to direct current (“DC-DC”) converter 26 configured to decrease or increase a relatively high DC bus voltage (“VDC”) as needed. The DC-DC converter 26 is connected between the battery pack 24 and the TPIM 28 via the positive (+) and negative (-) rails of the corresponding DC voltage bus 15. In some configurations, an auxiliary battery pack (“B AUX ) 124 may be connected to the DC-DC converter 26, wherein the auxiliary battery pack 124 may be implemented as a lead-acid battery or a battery constructed of another suitable application chemical and is configured to store or supply a 12 - 15 V auxiliary voltage (“V AUX ) to one or more connected auxiliary devices (not shown).

[0068] Reference Figure 2 and Figure 3 , Figure 1 The stator 16 of Figure 3 has radially projecting stator teeth 16T ( Figure 3 ) extending inwardly from a cylindrical stator housing or core 16C. That is, the stator teeth 16T extend from the stator core 16C of Figure 1 , which has an annular outer diameter surface 33 that faces inwardly toward the outer diameter surface 30 of the rotor 14. The inner diameter surface 31 of the stator 16 is the radially innermost surface of the stator teeth 16T. Adjacent stator teeth 16T are separated from each other by corresponding stator slots 37, as will be understood by those of ordinary skill in the art. The stator slots 37 are substantially filled with electrical conductors, typically copper wire or copper bars / “hairpins”. Such conductors together form the stator winding 32. When the stator winding 32 is sequentially energized by the polyphase output voltage from the Figure 1 TPIM 28, a rotating stator magnetic field is generated. The stator magnetic poles formed by the generated rotating stator field interact with the rotor poles provided by the various groups of rotor magnets 55 to cause Figure 1and 3 the rotor shaft 14R rotates, as well as a load (e.g., the road wheel 22) coupled thereto.

[0069] The number, type, position, and / or relative orientation of the rotor magnets 55 ultimately affect the magnitude and distribution of the magnetic flux in the ferromagnetic material of the electric machine 12. As shown, when the rotor 14 is viewed along its axis of rotation, the rotor magnets 55 may be arranged in an overall V-shaped configuration. In such a V-shaped configuration, the ends of the rotor magnets 55 are adjacent to the outer diameter surface 30 of the rotor 14, and the ends of the rotor magnets 55 are spaced closer together than the opposite ends of the rotor magnets 55 that are located closer to the rotor shaft 14R (see Figure 3 ). Moreover, when viewed axially as in Figure 3 , the rotor magnets 55 may be symmetrically distributed with respect to the q-axis, where a larger first pair of rotor magnets 55 (e.g., rectangular bar magnets arranged in a double-V pattern as shown) are positioned adjacent to the q-axis for a given rotor pole. The first pair of rotor magnets 55 is flanked by a smaller second pair of rotor magnets 55, which are likewise arranged in the typical double-V configuration depicted in Figure 3 .

[0070] As shown in the close-up view in Figure 2 , in order to provide the benefits of reducing various NVH disclosed herein, the peripheral outer diameter surface 30 of the rotor 14 is modified to define evenly spaced notch features 40. The notches 40 are arranged symmetrically in each magnetic pole of the rotor 14 and may have the same or different sizes and / or shapes. Thus, the sizes and shapes shown are examples of the present teachings and are non-limiting.

[0071] With respect to the outer diameter surface 30, each rotor notch 40 has a notch width r 1 and a notch depth r 2 , where, for optimal NVH reduction, r 1 > r 2 . However, other embodiments may be contemplated, where r 1 ≤r 2 , which may be sufficient in certain applications. The width r 1 of each notch 40 provides a smooth tangential continuous transition to the outer diameter surface 30 of the rotor 14 to reduce stress concentration in the rotor 14. In other embodiments, non-tangential / non-smooth curves or other transition profiles may be used as a compromise between NVH benefits and stress / manufacturing simplicity.

[0072] Figure 3 Illustrates a single magnetic pole of the rotor 14 of the rotor assembly 14A. The rotor 14 may define an air cavity 39 adjacent to the rotor shaft 14R, e.g., to reduce weight, where one such air cavity 39 extends fromFigure 3 is visible in the perspective view. As will be understood by those of ordinary skill in the art, Figure 3 the illustration in [reference] shows an 8-pole embodiment of the rotor 14, where the remaining 7 poles are the same as the Figure 3 exemplary pole of [reference] and are thus omitted for simplicity and clarity of illustration. However, the disclosed rotor notches 40 can be used in a wide range of machine configurations, including different combinations of rotor poles (e.g., 4, 6, 8, 10, etc.) and stator slots (e.g., 24, 36, 48, 72, etc.). Thus, Figure 3 the 8-pole embodiment of [reference] is non-limiting and illustrative of only one possible configuration.

[0073] For each rotor pole, the rotor notch 40 contemplated herein includes a central q-axis notch N 2 and at least a pair of additional d-axis notches N 2 symmetrically flanking the q-axis notch N 1 and N 3 . As used herein, the term "symmetrically flanking" means that the d-axis notches N 1 and N 3 are equidistant from the q-axis notch N 2 . In other embodiments, one or more additional pairs of notches 40 can be used at each rotor pole, where the notches N 4 and N 5 represent such additional pairs.

[0074] In terms of the relative positions of the central q-axis notch N 2 and the flanking d-axis notches N 1 and N 3 , the q-axis bisects the q-axis notch N 2 , as shown. As will be understood, a line drawn from the center of the rotor shaft 14R through the radially outermost corner (point P) of the top permanent magnet 55 defines a top magnet opening angle θ on either side of the rotor pole. The rotor notches N 1 and N 3 are positioned within the sweep or angular range of the respective opening angle θ to ensure maximum interaction with the magnetic flux. If used, the additional rotor notches N 4 and N 5 can be positioned outside the sweep of the top magnet opening angle θ. For a motor 12 having N slots in its stator 16, the flanking d-axis notches 40 (i.e., Figure 4 and Figure 5 the N 1 and N 3 ) can be located 360 / N degrees away from the d-axis to significantly reduce the Nth torque ripple order harmonic. For example, a 72-slot embodiment of the motor 12 can be away fromFigure 3 Each d-axis shown therein is positioned at an angular distance of 360 / 72 = 5 degrees from its adjacent d-axis notch N 1 and N 3 .

[0075] Relative to the surface profile geometry of the rotor notch 40, the size and shape of the notch 40 can be adapted to a given application in order to maximize noise reduction and to evenly distribute the vibration energy in the Figure 1 motor 12. Collectively, including the notch 40 at each rotor pole of the motor 12 significantly reduces machine noise without affecting motor torque and efficiency. In various embodiments, the notch 40 can be a circular, elliptical or polygonal bow-shaped feature. As Figure 2 shown, a tangentially continuous chamfer 19 or another suitable transition profile or contour can be used with the notch 40 to provide a smooth transition to the adjacent "notch-free" region of the outer diameter surface 30. Such a chamfer 19 will help avoid rotor stress concentration and noise, especially at higher rotational speeds of the rotor assembly 14A.

[0076] Figure 4 and Figure 5 illustrate two possible embodiments of the rotor notch 40 (i.e., the central q-axis notch N 2 and the d-axis notches N 2 symmetrically flanking the q-axis notch N 1 and N 3 ). In the Figure 4 configuration, the q-axis notch N 1 and N 3 has different sizes and shapes relative to the flanking notches N 2 . For example, the q-axis notch N 2 can be a circular notch lacking the Figure 2 chamfer 19, while the flanking notches N 1 and N 3 have the chamfered appearance of the notch 40 shown in Figure 2 . Such a configuration can be used to reduce NVH effects relative to a rotor assembly lacking the disclosed notch 40.

[0077] Optionally, the notches N 1 、N 2 and N 3 can have the same size and shape, for example, as Figure 5 shown. When the notches N 1 、N 2 and N 3 are equally sized and similarly shaped, especially when the notch 40 has a chamfer, as shown, Figure 1the motor 12 can enjoy optimal noise reduction. However, those of ordinary skill in the art will understand that, relative to Figure 4 the q-axis notch N in 2 the circular shape, when forming the individual laminations of the rotor 14, the chamfer profile of the notch 40 will require more complex processing. Thus, the selection of shape, size, and position is a performance-manufacturing trade-off.

[0078] Similarly, the formation of the rotor assembly 14 from a stack of laminations having the same perimeter shape will facilitate manufacturing, where the result of such a configuration is an elongated notch 40 extending along the longitudinal axis of rotation of the rotor assembly 14A. Optionally, two sets of rotor laminations can be formed, where one set has Figure 4 or Figure 5 the perimeter shape shown in

[0079] and the other set is circular and thus lacks the notch 40. In such embodiments, the laminations having the notch 40 can be positioned at the desired axial location of the rotor 14. Such an approach can achieve certain NVH effects as well as a more targeted reduction of its harmonic orders. Figure 1 As will be understood by those of ordinary skill in the art, in view of the foregoing disclosure, the advantage that incorporating the disclosed rotor notch 40 into the Figure 2 rotor 14 can provide is to reduce tonal noise at the target winding and slot orders. The formation of the notch 40 effectively enlarges the

[0080] air gap G of Figure 2 , however, this reduces the torque capacity of the motor 12. Thus, the size and number of such rotor notches 40 should be minimized to, for example, three rotor notches 40 per rotor pole in order to ensure a minimal degradation of torque performance. This teaching can be applied to appropriately configured rotor assemblies 14 to reduce specific harmonic orders, including those of IPM machines and synchronous reluctance machines. During the stamping of the rotor laminations, once the desired surface geometry is applied to the rotor assembly 14, no additional processing is required.

[0080] Although some best modes and other embodiments have been described in detail, there are various alternative designs and embodiments for practicing the teachings defined in the appended claims. Those skilled in the art will understand that modifications can be made to the disclosed embodiments without departing from the scope of the present disclosure. Additionally, this concept expressly includes combinations and sub-combinations of the described elements and features. The detailed description and the drawings are supportive and descriptive of the teachings, where the scope of the teachings is defined only by the claims.

Claims

1. A rotor assembly for an electric machine, comprising: a rotor having an inner diameter surface and an outer diameter surface, wherein the rotor includes a plurality of equally spaced rotor poles, each having an orthogonal axis ("q-axis") and a pair of direct axes ("d-axes"); and a rotor shaft connected to the inner diameter surface, surrounded by the rotor, and configured to rotate about a rotational axis together with the rotor when the stator of the electric machine is energized; wherein, at each of the equally spaced rotor poles, at least three arcuate notches are defined on the outer diameter surface of the rotor, including a central notch bisected by the q-axis and a pair of additional arcuate notches symmetrically flanking the central notch, and wherein each of the additional arcuate notches is located at a calibrated angular distance away from a respective one of the d-axes; wherein the cylindrical rotor includes multiple sets of permanent magnets embedded within the rotor adjacent to the outer diameter surface to thereby form the equally spaced rotor poles; wherein, at each of the equally spaced rotor poles, when the rotor is viewed along the rotational axis, the permanent magnets are arranged in a double-V configuration to thereby define a respective top-layer magnet opening angle on either side of the rotor pole, and each of the pair of additional arcuate notches is positioned within the sweep of one of the respective top-layer opening angles; wherein the tips of the double-V configuration of the permanent magnets face the outer diameter surface of the rotor; each permanent magnet is located between a respective q-axis and a respective d-axis such that the double-V configuration has a vertex relative to the respective q-axis; wherein the pair of additional arcuate notches symmetrically flanking the central notch have the same size and shape; wherein the central notch has the same size and shape as the pair of additional arcuate notches.

2. The rotor assembly according to claim 1, wherein, the electric machine has a stator having N stator slots, and the pair of additional arcuate notches are located at approximately 360 / N degrees away from the nearest d-axis to thereby reduce the Nth torque ripple order harmonic.

3. The rotor assembly according to claim 2, wherein, N＝72。 4. The rotor assembly according to claim 1, wherein, the central notch and the pair of additional arcuate notches define a tangentially continuous chamfer that smoothly transitions the central notch and the pair of additional arcuate notches into the outer diameter surface.

5. A rotating electric machine, comprising: a stator; a rotor circumscribed by the stator and having an inner diameter surface and an outer diameter surface, wherein the rotor includes a plurality of equally spaced rotor poles, each having an orthogonal axis ("q-axis") and a pair of direct axes ("d-axes"); and a rotor shaft connected to the inner diameter surface, surrounded by the rotor, and configured to rotate about a rotational axis together with the rotor when the stator is energized; Wherein, at each of the equidistantly spaced rotor poles, at least three arcuate notches are defined on the outer diameter surface of the rotor, including a central notch bisected by the q-axis and a pair of additional arcuate notches symmetrically flanking the central notch, and wherein each of the additional arcuate notches is located at a calibrated angular distance away from a respective one of the d-axes; Wherein, the rotor includes multiple sets of permanent magnets embedded within the rotor adjacent to the outer diameter surface, thereby forming the equidistantly spaced rotor poles; Wherein, at each of the equidistantly spaced rotor poles, when observing the rotor along the rotational axis, the permanent magnets are arranged in a double-V configuration, thereby defining a respective top-layer magnet opening angle on either side of the rotor pole, and each of the pair of additional arcuate notches is positioned within the sweep of one of the respective top-layer opening angles; Wherein, the tips of the double-V configuration of the permanent magnets face the outer diameter surface of the rotor; Each permanent magnet is located between a respective q-axis and a respective d-axis such that the double-V configuration has a vertex with respect to the respective q-axis; Wherein, the pair of additional arcuate notches symmetrically flanking the central notch have the same size and shape; Wherein, the central notch has the same size and shape as the pair of additional arcuate notches.

6. The rotating electrical machine according to claim 5, Wherein, the stator defines N stator slots, and the pair of additional arcuate notches are located at 360 / N degrees away from the nearest d-axis, thereby reducing the Nth torque ripple order harmonic.

7. The rotating electrical machine according to claim 6, Wherein, N＝72。 8. The rotating electrical machine according to claim 5, Wherein, the central notch and the pair of additional arcuate notches define a tangentially continuous chamfer that smoothly transitions the central notch and the pair of additional arcuate notches into the outer diameter surface.

9. An electrified powertrain, comprising: a battery pack; a traction power inverter module ("TPIM") connected to the battery pack and configured to convert a direct current ("DC") voltage from the battery pack into an alternating current ("AC") voltage; a rotating electrical machine energized by the AC voltage from the TPIM and including: a stator; a rotor circumscribed by the stator and having an inner diameter surface and an outer diameter surface, wherein the rotor includes a plurality of equidistantly spaced rotor poles, each having an orthogonal axis ("q-axis") and a pair of straight axes ("d-axes"); and a rotor shaft connected to the rotor and circumscribed by the rotor and configured to rotate about a rotational axis together with the rotor when the machine is energized; and a transmission coupled to the rotor shaft and powered by the machine; Wherein, at each of the equidistantly spaced rotor poles, at least three arcuate notches are defined on the outer diameter surface of the rotor, including a central notch bisected by the q-axis and a pair of additional arcuate notches symmetrically flanking the central notch, and wherein each of the additional arcuate notches is located at a calibrated angular distance away from the respective one of the d-axes; Wherein, the rotor includes multiple sets of permanent magnets embedded within the rotor adjacent to the outer diameter surface of the rotor to thereby form the equidistantly spaced rotor poles; and At each of the equidistantly spaced rotor poles, when the rotor is viewed along the rotational axis, the permanent magnets are arranged in a double-V configuration to thereby define a respective top-layer magnet opening angle on either side of the rotor pole, and each of the pair of additional arcuate notches is positioned within the sweep of one of the respective top-layer opening angles; Wherein, the tips of the double-V configuration of the permanent magnets face the outer diameter surface of the rotor; Each permanent magnet is located between a respective q-axis and a respective d-axis such that the double-V configuration has a vertex relative to the respective q-axis; Wherein, the pair of additional arcuate notches symmetrically flanking the central notch have the same size and shape; Wherein, the central notch has the same size and shape as the pair of additional arcuate notches.

10. The electrified powertrain according to claim 9, Wherein, the stator defines N stator slots, and the pair of additional arcuate notches are located at 360 / N degrees away from the nearest d-axis to thereby reduce the Nth torque ripple order harmonic.

11. The electrified powertrain according to claim 10, Wherein, the at least three arcuate notches have the same size and shape as the pair of additional arcuate notches and define a tangentially continuous chamfer that smoothly transitions the at least three arcuate notches into the outer diameter surface of the rotor.

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