Motor

Abstract

In order to suppress harmonics associated with grooves of salient poles and demagnetization of magnets in the case of a step skew structure, a motor 1 according to the present disclosure comprises: a stator 20 that accommodates a rotor 30; and the rotor 30 that includes a first rotor portion 31A and a second rotor portion 31B having the same number of magnetic poles. The rotor 30 has a skew structure in which the positions of the magnetic poles of the first rotor portion 31A and the second rotor portion 31B are different in the circumferential direction by a prescribed mechanical angle ΦM. The stator 20 comprises: a plurality of salient poles 211; slots 212 between the salient poles 211; and at least one groove G provided for each of the inner surfaces 211A of the salient poles 211 on the inner side in the radial direction. The groove G is disposed at a position where the mechanical angle between two adjacent slots 212 is equally divided in the circumferential direction. The grooves G formed in all the salient poles 211 have the same width in the circumferential direction. The prescribed mechanical angle ΦM is substantially the smallest angle among angles for canceling harmonics generated by harmonics generated during the rotation of the rotor 30 and caused by the number of slots 212 being converted due to the effect of the groove G.

Description

motor

[0001] This disclosure relates to a motor equipped with a rotor having a skewed structure.

[0002] Patent Document 1 discloses a permanent magnet type rotating electric machine comprising a rotor having magnetic poles of a plurality of permanent magnets arranged at predetermined intervals in the circumferential direction, and a stator having a plurality of salient poles facing the permanent magnets and arranged at predetermined intervals in the circumferential direction, wherein auxiliary grooves are provided on the surfaces of the salient poles facing the permanent magnets, the circumferential width of the auxiliary grooves is the same as or approximately the same as the width of the openings of the winding slots, the circumferential spacing of the auxiliary grooves is approximately equal in the circumferential direction, preferably equal, in conjunction with the openings of the winding slots, and if the circumferential spacing of the openings of the winding slots is W, the circumferential width of the openings of the winding slots and the circumferential width of the auxiliary grooves is c, then 0.040 < c / W < 0.125, and relative skew is applied between the rotor and the stator, with the skew angle in the range of electrical angles from 65 to 78 degrees.

[0003] Furthermore, Patent Document 1 states that, according to the above configuration, magnetic saturation caused by leakage flux generated between each salient pole of the stator can be mitigated, torque pulsation under load can be reduced, and permeance pulsation due to the winding slots and auxiliary grooves can be reduced, thus making it possible to reduce cogging torque as well.

[0004] Furthermore, Patent Document 1 employs a continuous skew structure in which the magnetic poles gradually change in the circumferential direction as the axial direction is advanced.

[0005] Japanese Patent Publication No. 2008-199894

[0006] Incidentally, skew structures include stepped skew, which shifts the magnet arrangement in the circumferential direction over a predetermined section in the axial direction of the rotor.

[0007] Furthermore, if auxiliary grooves (also simply called "grooves") are provided, harmonics will be generated as a result. In the case of stepped skew, if an angle is selected from the skew angles of 65 to 78 degrees disclosed in Patent Document 1 that can reduce these harmonics, there is a risk of demagnetization of the magnet at the skew end.

[0008] This disclosure has been made in view of these circumstances, and one of its objectives is to suppress demagnetization of the magnet while suppressing harmonics associated with forming grooves at the salient poles when the skew structure is stepped skew.

[0009] The motor of the present disclosure is a motor having a rotor having a skew structure, the motor comprising: a stator that rotatably houses the rotor radially inward; the rotor including a first rotor portion and a second rotor portion having the same number of magnetic poles, each having a magnet, and the same number of magnetic poles formed evenly in the circumferential direction, the rotor having a skew structure such that the positions of the magnetic poles of the first rotor portion and the second rotor portion are circumferentially different by a predetermined mechanical angle, the stator comprising: a plurality of salient poles evenly spaced apart in the circumferential direction; a plurality of slots provided between the salient poles and evenly spaced apart in the circumferential direction; stator coils disposed within the slots; and at least one groove provided for each salient pole and formed on the radially inward inner surface of the salient pole facing the rotor, the groove being positioned to evenly divide in the circumferential direction the mechanical angle between the circumferential center of one of the slots and the rotation axis of the motor and the circumferential center of the other slot adjacent to the first slot and the rotation axis. The grooves formed on all of the salient poles have equal width in the circumferential direction, and the predetermined mechanical angle is substantially the smallest angle that cancels out harmonics generated when harmonics caused by the number of slots generated during rotor rotation are transformed by the influence of the grooves.

[0010] According to this disclosure, when the skew structure is stepped skew, it is possible to suppress demagnetization of the magnet while suppressing harmonics associated with forming grooves on the salient poles.

[0011] This is a schematic cross-sectional view showing an example of the cross-sectional structure of the motor of the first embodiment according to this disclosure. This is a cross-sectional view (cross-sectional view in a plane perpendicular to the axial direction) of the motor of the first embodiment according to this disclosure. This is a diagram for explaining the skew structure of the first embodiment according to this disclosure. This is a graph showing the relationship between the number of grooves formed for each salient pole and the reference skew electrical angle of the first embodiment according to this disclosure. This is a diagram showing the case when the number of grooves formed for each salient pole of the first embodiment according to this disclosure is 1. This is a diagram showing the case when the number of grooves formed for each salient pole of the first embodiment according to this disclosure is 2. This is a diagram for explaining the skew structure of the motor of the embodiment according to the first embodiment according to this disclosure. This is a diagram for explaining the skew structure of the motor of comparative example 3 of the first embodiment according to this disclosure. This is a graph showing the excitation force of the motor of the embodiment according to the first embodiment according to this disclosure and the motor of the comparative example. This is a diagram for explaining the groove depth, etc., of the first embodiment according to this disclosure. This is a diagram for explaining the shape of the grooves formed for each salient pole of the second embodiment according to this disclosure.

[0012] Hereinafter, embodiments for implementing this disclosure (hereinafter referred to as "Embodiments") will be described in detail with reference to the attached drawings. Throughout the description of the embodiments, the same elements are denoted by the same numbers or reference numerals.

[0013] Furthermore, the dimensional ratios in the drawings differ from the actual dimensional ratios and are merely for illustrative purposes to make the explanation easier to understand; there is no guarantee that identical parts are depicted with the same dimensions across different drawings.

[0014] Furthermore, for the sake of readability, in drawings, only some of the parts with the same attribute that exist in multiple locations may be assigned reference numerals.

[0015] <<First Embodiment>> The motor 1 of the first embodiment according to this disclosure will be described with reference to Figures 1 to 9. Although the use of the motor 1 (also called a rotating electric machine) is not particularly limited, the motor 1 can be suitably used, for example, for vehicle drive systems used in hybrid vehicles and electric vehicles.

[0016] Figure 1 is a schematic cross-sectional view showing an example of the cross-sectional structure of the motor 1 of the first embodiment according to this disclosure.

[0017] In the following explanation, the direction in which the rotation axis 12 (center of rotation) of the motor 1 extends is defined as the axial direction. In the axial direction, the side of the stator core 21 that moves away from the axial center C0 is defined as the axial outer side, and the side of the stator core 21 that moves toward the axial center C0 is defined as the axial inner side.

[0018] Furthermore, when viewed in a plane perpendicular to the axial direction, the side away from the rotation axis 12 is defined as the radially outward side, and the side toward the rotation axis 12 is defined as the radially inward side.

[0019] Furthermore, the direction along the rotation axis 12 is defined as the circumferential direction.

[0020] Figure 2 is a cross-sectional view (a cross-sectional view taken from a plane perpendicular to the axial direction) of the motor 1 of the first embodiment according to the present disclosure, and in Figure 2, the groove G (see Figures 5 and 6) is not shown.

[0021] The motor 1 of the first embodiment is an inner rotor type, and as shown in Figure 1, the motor 1 comprises a motor case 10, a stator 20 fixed to the motor case 10, and a rotor 30 housed in the stator 20.

[0022] Specifically, the stator 20 is fixed to the motor case 10 by bolts BT, and the stator 20 rotatably houses the rotor 30 radially inward (rotatably surrounding the radially outward side of the rotor 30).

[0023] [Stator 20] The stator 20 comprises a stator core 21 formed by stacking multiple annular electromagnetic steel plates in the axial direction, and a stator coil 22 provided wound around the stator core 21.

[0024] Furthermore, the stator core 21 is not limited to a laminated core made of stacked electromagnetic steel sheets, but may also be a compacted core made by compressing and solidifying magnetic powder.

[0025] (Stator Core 21) As shown in Figure 2, the stator core 21 comprises a plurality of salient poles 211 (also called teeth) evenly spaced apart in the circumferential direction, and a plurality of slots 212 which are the spaces between the salient poles 211. In other words, each of the plurality of slots 212 is provided between the salient poles 211 and is evenly spaced apart in the circumferential direction.

[0026] Furthermore, as will be explained later, the stator core 21 is provided with at least one groove G (see Figures 5 and 6) formed on the radially inward inner surface 211A of the salient pole 211 facing the rotor 30, for each salient pole 211.

[0027] (Stator coil 22) The stator coil 22 is provided in a wound manner around the salient pole 211 (see Figure 2), and as shown in Figure 1, it comprises a slot insertion portion 221 located within the slot 212 and coil end portions 222 provided on the axially outer sides of both end faces of the stator core 21.

[0028] Therefore, the stator 20 comprises salient poles 211 of a plurality of stator cores 21 that are spaced apart and evenly arranged in the circumferential direction, slots 212 of the plurality of stator cores 21 that are spaces between the salient poles 211, a stator coil 22 having a slot insertion portion 221 disposed within the slots 212, and grooves G formed on the inner surface 211A of the radially inward salient pole 211 that is provided for each salient pole 211 and faces the rotor 30.

[0029] Furthermore, the grooves G formed in all salient poles 211 are positioned to have equal width in the circumferential direction and to evenly divide the mechanical angle θ (see Figure 2) between two adjacent slots 212 in the circumferential direction, in order to reduce the 48th harmonic of rotation (harmonics caused by the number of slots 212).

[0030] More specifically, the mechanical angle θ between two adjacent slots 212 (see Figure 2) is the mechanical angle between the line passing through the circumferential center of one slot 212 and the rotation axis 12 of the motor 1 and the line passing through the circumferential center of the other slot 212 adjacent to the first slot 212 and the rotation axis 12 of the motor 1. The grooves G formed in all salient poles 211 are positioned to equally divide the circumferential mechanical angle θ between their adjacent lines in the circumferential direction.

[0031] [Rotor 30] As shown in Figure 1, the rotor 30 comprises a rotor core 31 formed by stacking multiple annular electromagnetic steel plates in the axial direction, a rotor shaft 32 fixed to the rotor core 31, multiple magnets 33 provided for each magnetic pole (region between the q axes in Figure 2), and a pair of end plates 34 provided on both end faces of the rotor core 31. The end plates 34 may be omitted.

[0032] (Rotor core 31) The rotor core 31 is a cylindrical member having an axial hole 310 in the center, and as shown in Figure 1, it comprises a first rotor portion 31A and a second rotor portion 31B.

[0033] As mentioned above, the first embodiment shows that the rotor core 31 is a laminated core made of laminated electromagnetic steel sheets, but the rotor core 31 may also be a compacted core made by compressing and solidifying magnetic powder.

[0034] Therefore, the rotor 30 includes the first rotor portion 31A and the second rotor portion 31B provided by the rotor core 31. Details of the first rotor portion 31A and the second rotor portion 31B will be described later.

[0035] Furthermore, as shown in Figure 2, the rotor core 31 has a magnet hole 311 that penetrates in the axial direction, and a magnet 33 (described later) is inserted and fixed into the magnet hole 311.

[0036] As will be described later, the rotor shaft 32 is fixed in the shaft hole 310 by shrink fitting or press fitting, and the rotor core 31 rotates together with the rotor shaft 32.

[0037] (Rotor shaft 32) As shown in FIG. 1, the rotor shaft 32 is a cylindrical member having a hollow portion inside through which a coolant flows, is rotatably supported by the motor case 10 via a bearing 14a and a bearing 14b, and serves as the rotating shaft 12 of the motor 1. Note that the rotor shaft 32 is not necessarily limited to a cylindrical member, and may be a columnar member having no hollow portion.

[0038] (Magnet 33) The motor 1 according to the first embodiment is an embedded permanent magnet synchronous motor, and a magnet 33 is embedded inside a rotor core 31.

[0039] The magnet 33 is in the form of a sintered magnet and is formed of neodymium or the like. However, the magnet 33 is not necessarily limited to a sintered magnet, and may be a magnet formed of a bonded magnet material.

[0040] In the first embodiment, as an example, as shown in FIG. 2, the plurality of magnets 33 are arranged in a rotationally symmetric manner for each magnetic pole (region between q-axes) when viewed in the axial direction.

[0041] Note that the plurality of magnets 33 are arranged in a manner where S poles and N poles alternately appear in the circumferential direction, and in the first embodiment, the number of magnetic poles (regions between q-axes) is eight, but the number of magnetic poles is arbitrary.

[0042] Furthermore, in the first embodiment, the plurality of magnets 33 have a linear shape (rectangular cross-section) when viewed in the axial direction, but are not necessarily limited to such a shape.

[0043] That is, some or all of the plurality of magnets 33 may have an arcuate shape when viewed in the axial direction.

[0044] Note that in the first embodiment, as described later, the magnet 33 is provided for each core block forming the first rotor portion 31A and the second rotor portion 31B.

[0045] In the first embodiment, the rotor 30 has a skew structure in which the positions of the magnetic poles (regions between q-axes) of the first rotor portion 31A and the second rotor portion 31B are shifted in the circumferential direction by a mechanical angle Y determined from the skew electrical angle Φ (i.e., positioned at different locations in the circumferential direction), which will be described in detail below.

[0046] First, the same core block is used for the first rotor section 31A and the second rotor section 31B.

[0047] Therefore, as shown in Figure 2, both the first rotor section 31A and the second rotor section 31B are equipped with multiple magnets 33 (three magnets 33 in this example) for each magnetic pole (region between the q axes), and have the same number of magnetic poles (eight magnetic poles in this example) formed evenly in the circumferential direction.

[0048] Figure 3 is a diagram illustrating the skew structure of the first embodiment according to the present disclosure, and shows the relationship of the misalignment between the first rotor portion 31A and the second rotor portion 31B.

[0049] In Figure 3, the lines showing the lamination of the electrical steel sheets are omitted, and only the core block units forming the first rotor section 31A and the second rotor section 31B are depicted.

[0050] Furthermore, Figure 3 shows a side view of the rotor core 31 (a side view taken from the front along the longitudinal direction of the rotation axis 12), and mainly illustrates one of the q-axis boundaries of the multiple magnetic poles (regions between q-axis) in the circumferential direction.

[0051] As shown in Figure 3, in the first embodiment, the rotor 30 comprises a pair of first rotor sections 31A provided at both ends in the axial direction (up and down direction of the paper), and two second rotor sections 31B provided between the first rotor sections 31A.

[0052] In the first embodiment, the rotor 30 (more specifically, the rotor core 31) has a V-shaped skew structure in which the q-axis positions of the first rotor portion 31A and the second rotor portion 31B are circumferentially different by a mechanical angle Y determined by the skew electrical angle Φ.

[0053] The electrical angle is the angle expressed with one cycle of inverter switching when current flows through the stator coil 22 being 360 degrees. The relationship between the electrical angle and the mechanical angle, which is the angle when the rotor 30 rotates mechanically, is given by: Electrical angle (deg) = (Number of magnetic poles P / 2) × Mechanical angle (deg). Therefore, the mechanical angle Y determined from the skew electrical angle Φ is given by: Mechanical angle Y = (2 / Number of magnetic poles P) × Skew electrical angle Φ.

[0054] Specifically, as shown in Figure 3, when the mechanical angle determined by the skew electrical angle Φ is Y, and the initial position of the rotor 30 is denoted as 0 (deg) for explanatory purposes, the q-axis of the first rotor section 31A is at a position of -Y / 2 (deg) in the circumferential direction in terms of mechanical angle, and the q-axis of the second rotor section 31B is at a position of Y / 2 (deg) in the circumferential direction in terms of mechanical angle.

[0055] Here, since the q-axis is the boundary between magnetic poles, in the first embodiment, the rotor 30 has a V-shaped skew structure in which the positions of the magnetic poles of the first rotor portion 31A and the second rotor portion 31B (the region between the q-axis in Figure 2) are circumferentially different by a mechanical angle Y determined by the skew electrical angle Φ.

[0056] In the first embodiment, in order to reduce the excitation force, a groove G (see Figures 5 and 6) is formed on the inner surface 211A (see Figure 2) of the radially inward salient pole 211 facing the rotor 30 for each salient pole 211. This will be explained in detail below.

[0057] First, based on the demagnetization requirements of the magnet 33, the upper limit value Φmax of the skew electrical angle Φ is determined.

[0058] For example, when the skew electrical angle Φ is large, the overlap in the circumferential direction of the magnets 33 of the first rotor section 31A and the second rotor section 31B, which are adjacent in the axial direction, decreases. In other words, one end of the magnet 33 of the first rotor section 31A in the circumferential direction (for example, the end on the north pole side in the magnetization direction) and the other end of the magnet 33 of the second rotor section 31B, which is adjacent in the axial direction (direction of the rotation axis 12), in the circumferential direction (for example, the end on the south pole side in the magnetization direction) come closer together.

[0059] As the overlap of the magnets 33 of the first rotor section 31A and the second rotor section 31B in the circumferential direction decreases, the leakage flux flowing axially between one circumferential end of the magnet 33 of the first rotor section 31A and the other circumferential end of the magnet 33 of the second rotor section 31B increases. This leakage flux acts as a magnetic field component in the opposite direction to the other magnet 33 (for example, the leakage flux of the magnet 33 of the first rotor section 31A acts as a magnetic field component in the opposite direction to the magnet 33 of the second rotor section 31B), causing the magnetization of the magnet 33 to decrease and demagnetization to occur.

[0060] Therefore, when the skew electrical angle Φ is increased from a state where the rotor 30 does not have a skew structure and the skew electrical angle Φ is 0 degrees, we consider how to keep the demagnetization rate of the magnet 33 to a predetermined level, compared to the case where the rotor 30 does not have a skew structure.

[0061] For example, let's consider the case where the demagnetization rate of magnet 33 is limited to 5%, and the electrical angle that needs to be limited for this purpose will be defined as the upper limit of the skew electrical angle Φ, Φmax.

[0062] The upper limit of the skew electrical angle Φ, Φmax, is the upper limit of the skew electrical angle Φ required to suppress the demagnetization rate of the magnet 33 to a predetermined level. It can be set as needed and is not limited to suppressing the demagnetization rate of the magnet 33 to 5%.

[0063] Furthermore, the upper limit of the skew electrical angle Φ, Φmax, is such that if a skew electrical angle Φ greater than that is provided for the rotor 30 compared to a case without a skew structure, the demagnetization rate of the magnet 33 exceeds 5%. In other words, if the skew electrical angle Φ of the skew structure is less than or equal to the upper limit Φmax, it becomes a skew structure that can suppress the demagnetization rate of the magnet 33 to less than 5%.

[0064] Next, based on the mechanical angle θ (deg) between the circumferential centers of adjacent slots 212 of the stator core 21 shown in Figure 2, the number of magnetic poles (regions between the q axes in Figure 2) P (eight in this example), and the number of grooves G formed for each salient pole 211 of the stator core 21 N, the reference skew electrical angle X, which is the skew electrical angle corresponding to the number of grooves G N, is determined according to the following formula (1).

[0065] X = θ × (P / 2) / {2 × (N+1)} .....(1) Since θ is the circumferential mechanical angle between adjacent slots 212, if the number of slots 212 is S, then θ (deg) = 360 (deg) / S can be calculated, and the number of grooves G N is a natural number (i.e., an integer greater than or equal to 1).

[0066] Furthermore, the reference skew mechanical angle Z (degrees), which is the skew mechanical angle corresponding to the number of grooves G N expressed as the reference skew electrical angle X (degrees), is given by the following formula (A): Z = θ / {2 × (N + 1)} ・・・・・・・・・・・(A)

[0067] The reference electrical skew angle X (deg) and the reference mechanical skew angle Z (deg) are angles that cancel out the harmonics (96th rotational order) generated in conjunction with the groove G.

[0068] This makes it possible to cancel out harmonics generated by the groove G (harmonics caused by the combined magnetic flux of the rotor magnetic flux and stator magnetic flux at the tip of the salient pole 211 generated when the rotor 30 rotates).

[0069] Furthermore, the 96th harmonic of rotation is a harmonic that is generated when the 48th harmonic of rotation, which is caused by the number of slots 212 generated when the rotor rotates 30 times, is transformed by the influence of groove G.

[0070] To explain in more detail the angle required to cancel out the harmonics (96th rotational order) generated in conjunction with the groove G, equations (1) and (A) are formulas for determining the angle required to shift the period of the harmonics (96th rotational order) generated in adjacent rotor sections (first rotor section 31A, second rotor section 31B) by half a period.

[0071] Therefore, in a skewed structure that satisfies equations (1) and (A), harmonics (96th rotational order) generated in adjacent rotor sections overlap and cancel each other out.

[0072] This effect can also be obtained at angles that are odd multiples of the reference skew electrical angle X (deg) and the reference skew mechanical angle Z (deg).

[0073] This is because doubling the reference electrical skew angle X (deg) and the reference mechanical skew angle Z (deg) results in a one-period shift (a shift of half a period x 2), causing the phases of the harmonics (rotational 96th order) to coincide and the wave to become larger. However, a shift of half a period x 3 results in a 1.5-period shift, causing the harmonics (rotational 96th order) to again have opposite phases and cancel each other out.

[0074] However, in skew structures where the reference skew electrical angle X (deg) and the reference skew mechanical angle Z (deg) given by equations (1) and (A) are odd multiples of 3 or more, the skew angle becomes large, which may cause demagnetization of the magnet 33.

[0075] In other words, the reference skew electrical angle X (deg) and reference skew mechanical angle Z (deg) given by equations (1) and (A) are fundamental equations that yield the smallest angle necessary to cancel out the harmonics (96th rotational order) generated by the groove G.

[0076] Figure 4 is a graph showing the relationship between the number of grooves G formed for each salient pole 211 in the first embodiment of the present disclosure and the reference skew electrical angle X, with the upper limit value Φmax of the skew electrical angle Φ also shown by a dotted line.

[0077] Furthermore, the upper limit of the skew electrical angle Φ, Φmax, is the upper limit when the demagnetization rate of the magnet 33 is limited to a predetermined demagnetization rate (5% in this example), as explained earlier.

[0078] As shown in Figure 4, increasing the number of grooves G N from 1 to 2, ... reduces the reference skew electrical angle X (deg) obtained by Equation 1.

[0079] In other words, the reference skew electrical angle X (deg), which is the skew electrical angle required for the skew structure to cancel out the harmonics (96th rotational order) generated by the groove G, becomes smaller.

[0080] Furthermore, in Figure 4, since the upper limit of the skew electrical angle Φ, Φmax, explained earlier, is greater than the reference skew electrical angle X (deg) obtained by setting N=1, the number of grooves G N can be selected from natural numbers of 1 or greater.

[0081] If the upper limit of the skew electrical angle Φ, Φmax, is 5.5 degrees, then the reference skew electrical angle X (degrees) when the number of grooves G, N = 1, will be greater than the upper limit of the skew electrical angle Φ, Φmax. Therefore, in order to suppress the demagnetization rate of the magnet 33 to less than 5%, the number of grooves G, N, must be selected from a natural number of 2 or more.

[0082] In other words, the reference skew electrical angle X (deg), which is the skew electrical angle required for a skew structure to cancel out the harmonics (96th rotational harmonics) generated in conjunction with the grooves G, can be reduced by increasing the number of grooves G, thereby achieving both the cancellation of harmonics and the suppression of the demagnetization rate of the magnet 33 to a predetermined demagnetization rate.

[0083] Figure 5 shows the case where the number N of grooves G formed for each salient pole 211 in the first embodiment of the present disclosure is 1.

[0084] As shown in Figure 5, when N is 1, a groove G is formed on the radially inward inner surface 211A of each salient pole 211, facing the rotor 30, such that the circumferential center of the groove G is located at a position where the space between adjacent slots 212 is divided equally in the circumferential direction by the same mechanical angle θ1. The groove G opens radially inward.

[0085] Figure 6 shows the case where the number of grooves G formed for each salient pole 211 in the first embodiment of the present disclosure is 2.

[0086] As shown in Figure 6, when N is 2, a groove G is formed on the radially inward inner surface 211A of the salient pole 211 facing the rotor 30, such that the circumferential center of the groove G is located at a position where the space between adjacent slots 212 is divided into three equal parts (equal divisions) in the circumferential direction by the same mechanical angle θ2, and the groove G opens radially inward for each salient pole 211.

[0087] Then, based on a reference skew electrical angle X (deg) corresponding to the number N of grooves G selected, the range of the skew electrical angle Φ shown in the following formula (2) is determined, and the skew electrical angle Φ (deg) of the magnetic poles of the first rotor section 31A and the second rotor section 31B (the region between the q axes in Figure 2) is manufactured as a skew structure that satisfies that range.

[0088] 0.75 × X ≤ Φ ≤ 1.25 × X ・・・・・・・(2) In Equation 2, the lower limit is 0.75 times the reference skew electrical angle X (deg), and the upper limit is 1.25 times the reference skew electrical angle X (deg), which takes manufacturing tolerances into account.

[0089] Therefore, the skew electrical angle Φ (deg) that satisfies equation (2) is substantially the smallest angle among those that cancel out harmonics generated when the rotor 30 rotates and are converted by the influence of the groove G, that is, it is an angle equal to the reference skew electrical angle X within a predetermined tolerance range, and is an angle that can suppress demagnetization while taking manufacturing tolerances into account and making it easy to cancel out harmonics.

[0090] Furthermore, using the reference skew mechanical angle Z as a reference, the skew electrical angle Φ in equation (2) is expressed in terms of mechanical angle: skew mechanical angle Φ Ｍ (deg), that is, the skew mechanical angle Φ, which is the angle that cancels out the harmonics (96th rotational order) generated in conjunction with the groove G. Ｍ The range is given by the following equation (B), and the skew mechanical angle Φ of the magnetic poles of the first rotor section 31A and the second rotor section 31B (the region between the q axes in Figure 2) Ｍ (deg) is manufactured as a skew structure that satisfies that range. 0.75 × Z ≤ Φ Ｍ ≤ 1.25 × Z ・・・・・・(B) Note that the skew mechanical angle Φ that satisfies equation (B) is ΦＭ (deg) to the predetermined mechanical angle Φ Ｍ It is also said that.

[0091] And, similar to the skew electrical angle Φ (deg), the skew mechanical angle Φ that satisfies equation (B) is also given. Ｍ (deg) is the substantially smallest angle among those that cancel out harmonics generated when the rotor 30 rotates and the harmonics generated by the groove G are transformed. In other words, it is an angle that is equal to the reference skew mechanical angle Z within a predetermined tolerance range, and is an angle that can suppress demagnetization while taking manufacturing tolerances into account and making it easy to cancel out harmonics.

[0092] As explained earlier, in order to suppress the demagnetization rate of the magnet 33 to the desired level while allowing an error within the range of Equation 2, the skew electrical angle Φ (deg) of the magnetic poles of the first rotor section 31A and the second rotor section 31B (the region between the q axes in Figure 2) is set to satisfy the following Equation (3).

[0093] Φ < Φmax ・・・・・・・・・・・・・・・(3) Note that Φmax is the upper limit of the skew electrical angle Φ.

[0094] More specifically, the number of grooves G should be such that the skew electrical angle Φ (deg) satisfies equation (3). Note that, as previously shown, equation (3) may also be satisfied when the number of grooves G is 1.

[0095] As described above, in the motor 1 equipped with a rotor 30 having a skew structure according to the first embodiment, if the circumferential mechanical angle between adjacent slots 212 is θ (deg), the number of magnetic poles (region between the q axes in Figure 2) is P, the upper limit of the skew electrical angle Φ is Φmax, the number of grooves G formed for each salient pole 211 is N, and the skew electrical angle is Φ, then it is preferable that the number of grooves G N and the skew electrical angle Φ satisfy the following equations (1) to (3), as explained earlier.

[0096] X = θ × (P / 2) / {2 × (N+1)} ・・・・・・(1) 1.0 × X ≤ Φ ≤ 1.2 × X ・・・・・・・(2) Φ < Φmax ・・・・・・・・・・・・・・・(3) Note that X is the reference skew electrical angle.

[0097] By the way, in order to avoid obstructing the flow of magnetic flux from the salient pole 211 to the rotor 30, it is preferable to have a small number of grooves G N.

[0098] Therefore, in the example shown in Figure 4, the number of grooves G N will satisfy equation 3 above if it is a natural number of 1 or more, but it is preferable to select the smallest natural number among them.

[0099] In other words, for each salient pole 211, it is preferable that the number N of grooves G formed on the radially inward inner surface 211A of the salient pole 211 facing the rotor 30 be the smallest natural number that satisfies equations (1) to (3) above. In the example of Figure 4, it is preferable that the number N of grooves G be 1.

[0100] Furthermore, by ensuring that the number N of grooves G is the smallest natural number that satisfies equations (1) to (3) above, the flow of magnetic flux from the salient pole 211 to the rotor 30 is not obstructed.

[0101] Next, we will describe an example demonstrating the reduction effect of the excitation force [N] of the motor 1 as described above, and a comparative example for comparison.

[0102] First, in the motor 1 of the embodiment, the number of slots 212 S in the stator core 21 is 48, and the circumferential mechanical angle θ between adjacent slots 212 is 7.5 [= 360 (deg) / 48] (deg). This point is also the same for the motors of Comparative Examples 1, 2, and 3 described later.

[0103] Furthermore, in the motor 1 of the embodiment, the number of magnetic poles (regions between the q axes in Figure 2) P is 8, and with the number of grooves G N being 1, the reference skew electrical angle X obtained according to Equation 1 is 7.5 [= {7.5 (deg) × (8 / 2)} / {2 × (1 + 1)}] (deg).

[0104] Furthermore, the motors in Comparative Examples 1, 2, and 3, described later, also have eight magnetic poles.

[0105] Furthermore, since the reference skew electrical angle of 7.5 degrees satisfies the upper limit of the skew electrical angle Φ, this reference skew electrical angle of 7.5 degrees was adopted as the skew electrical angle Φ for motor 1 in the embodiment. Consequently, the demagnetization rate of the magnet 33 in motor 1 in the embodiment is less than 5%.

[0106] Figure 7 is a diagram illustrating the skew structure of the motor 1 in an embodiment of the first embodiment according to the present disclosure, and corresponds to Figure 3.

[0107] In Figure 7, the skew structure is shown using the skew mechanical angle Y, which is determined from the skew electrical angle Φ. When converted to the skew electrical angle Φ, it becomes 7.5 [= 1.875 (deg) × 4] (deg), as explained above.

[0108] As shown in Figure 7, the motor 1 of the embodiment has a rotor 30 (rotor core 31) comprising a pair of first rotor sections 31A provided at both ends in the axial direction (up and down direction on the plane of the paper), and two second rotor sections 31B provided between the first rotor sections 31A.

[0109] When the initial position of the rotor 30 is denoted as 0 degrees for explanatory purposes, the q-axis of the first rotor section 31A is at a position of -0.9375 degrees in the circumferential direction in terms of mechanical angle, and the q-axis of the second rotor section 31B is at a position of 0.9375 degrees in the circumferential direction in terms of mechanical angle.

[0110] In other words, the motor 1 of the embodiment has a V-shaped skew structure in which the rotor 30 (more specifically, the rotor core 31) has a circumferential difference in the positions of the magnetic poles (region between the q-axis in Figure 2) of the first rotor portion 31A and the second rotor portion 31B by a mechanical skew angle of 1.875 degrees, or an electrical skew angle of 7.5 degrees.

[0111] As shown in Figure 7, the skew structure is designed to cancel out the 96th rotational excitation force.

[0112] On the other hand, the motor of Comparative Example 1 does not have grooves G and a skew structure, and the motor of Comparative Example 2 has grooves G similar to the motor 1 of Example 1, but does not have a skew structure.

[0113] Figure 8 is a diagram illustrating the skew structure of the motor of Comparative Example 3 of the first embodiment of the present disclosure, and the skew structure is shown in terms of the skew mechanical angle.

[0114] As shown in Figure 8, the motor of Comparative Example 3 does not have groove G, but has a V-shaped skew structure composed of three stages, and the skew mechanical angle is the same as that of motor 1 of the embodiment.

[0115] Furthermore, as shown in Figure 8, the motor of Comparative Example 3 also has a skew structure that cancels out the 96th rotational excitation force.

[0116] Figure 9 is a graph showing the excitation force of motor 1 of the first embodiment of the present disclosure and a motor of a comparative example. In Figure 9, torque [Nm] is plotted on the horizontal axis and excitation force [N] is plotted on the vertical axis.

[0117] Furthermore, the graph on the left side of Figure 9 shows the excitation force of order (48th rotational order in this example) caused by the number S of slots 212 (48 in this example), while the graph on the right side of Figure 9 shows the excitation force of twice the number S of slots 212 (96th rotational order) that occurs as a consequence of the decrease in the excitation force of order (48th rotational order in this example) caused by the number S of slots 212 (48 in this example).

[0118] Comparing Comparative Example 1 and Comparative Example 2, Comparative Example 2, by having groove G, is able to reduce the 48th rotational excitation force, but as a consequence, the 96th rotational excitation force increases.

[0119] However, in the embodiment, both the 48th and 96th rotational excitation forces are reduced, and the excitation force is reduced even when compared to Comparative Example 3, which has a V-shaped skew structure. Note that since Comparative Example 3 does not have groove G, the excitation force effect at the 48th rotational excitation force is not as effective as in Comparative Example 2.

[0120] Thus, if the motor 1 of the first embodiment has a number N of grooves G that satisfy equations 1 to 3 shown above, and has a skew structure, it is possible to significantly reduce the excitation forces of the 48th and 96th rotational orders, thereby realizing a motor 1 with good NV performance (noise and vibration performance), and also satisfies the conditions for keeping the demagnetization rate of the magnet 33 low, so that the demagnetization of the magnet 33 can be kept low.

[0121] On the other hand, as briefly explained earlier, groove G may become a factor that obstructs the flow of magnetic flux from salient pole 211 to rotor 30, and next, we will explain the suitable depth of groove G, etc.

[0122] Figure 10 is a diagram for explaining the depth of the groove G in the first embodiment of the present disclosure, and corresponds to Figure 5.

[0123] As shown in Figure 10, the stator 20 (more specifically, the stator core 21) is provided for each slot 212 and has an opening 212A that opens radially inward.

[0124] Furthermore, when the radial width of the opening 212A is denoted as d1 and the radial depth of the groove G is denoted as d3, if the radial depth d3 of the groove G is greater than or equal to d1, the effect of the groove G as a groove that reduces the excitation force (slot number-derived excitation force (in this example, the 48th rotational harmonic)) can be reliably obtained. Therefore, it is preferable that the radial depth d3 of the groove G satisfies the following equation (4): d1 ≤ d3 ・・・・・・・・・・(4)

[0125] Furthermore, when the distance from the stator coil 22 adjacent to the opening 212A to the opening 212A is d2, if the radial depth d3 of the groove G is d1 + d2 or less, the obstruction of the magnetic flux flow from the salient pole 211 to the rotor 30 can be significantly reduced. Therefore, it is more preferable that the radial depth d3 of the groove G satisfies the following equation (5): d1 ≤ d3 ≤ d1 + d2 ... (5)

[0126] By setting the radial depth d3 of the groove G in this way, it is possible to reduce the excitation force while significantly reducing the obstruction of the magnetic flux flow from the salient pole 211 to the rotor 30.

[0127] Furthermore, the circumferential width of the grooves G formed in all salient poles 211 is equal to the circumferential width of the opening 212A provided in the slot 212.

[0128] Thus, when the circumferential width of the groove G is equal to the circumferential width of the opening 212A, it is not possible to provide more grooves G than the number obtained by dividing the circumferential width of the inner surface 211A of the salient pole 211 by the circumferential width of the opening 212A.

[0129] Therefore, if the circumferential width of the groove G is equal to the circumferential width of the opening 212A, the number of grooves G provided for each salient pole 211 is set to be less than or equal to the integer part of the value obtained by dividing the circumferential width of the inner surface 211A of the salient pole 211 by the circumferential width of the opening 212A. For example, the number of grooves G provided for each salient pole 211 is 2 or less.

[0130] <<Second Embodiment>> Next, the motor 1 of the second embodiment according to this disclosure will be described with reference to Figure 11.

[0131] The motor 1 of the second embodiment has the same basic configuration as the motor 1 of the first embodiment. Below, we will mainly describe the differences from the first embodiment, and may omit explanations of the similarities.

[0132] Specifically, in the second embodiment, the motor 1 has a different shape from the first embodiment in the groove G formed on the radially inward inner surface 211A facing the rotor 30 (more specifically, the rotor core 31) of the salient pole 211, and opening radially inward.

[0133] Figure 11 is a diagram illustrating the shape of the groove G formed for each salient pole 211 in the second embodiment of the present disclosure.

[0134] As shown in Figure 11, in the second embodiment, the groove G has a stepped shape in which the width in the circumferential direction is narrower on the radially outer side W2 than on the radially inner side W1.

[0135] The influence of the gap (also called the air gap) between the rotor 30 and the stator 20 on the magnetic flux is predominantly determined by the circumferential width of the groove G on the side closer to the rotor 30. A wider radial inner width W1 of the groove G suppresses harmonics, while a narrower radial outer width W2 ensures a wider magnetic path MC between the groove G and the slot 212.

[0136] Therefore, with this structure, a wide magnetic path MC is secured between the groove G and the slot 212, maintaining good magnetic flux flow to the rotor 30, thereby suppressing torque reduction while also suppressing harmonics.

[0137] In the second embodiment, the groove G is shown to have a stepped shape. However, as described above, the shape is not limited to a stepped shape as long as a wide magnetic path MC can be secured. Basically, any shape in which the width of the groove G narrows as it moves radially outward is acceptable.

[0138] Therefore, for example, the groove G may be triangular in shape, with its circumferential width gradually narrowing towards the radially outward direction.

[0139] Although the above has been explained based on specific embodiments, this disclosure is not limited to the embodiments described above.

[0140] In the above embodiment, as shown in Figure 7, the rotor 30 has a V-shaped skew structure composed of two stages, a first rotor section 31A and a second rotor section 31B. However, the rotor section may be increased to have a V-shaped skew structure composed of three or more stages, as shown in Figure 8.

[0141] Alternatively, the rotor 30 may have a W-shaped skew structure, which consists of two V-shaped skew structures, a first rotor section 31A and a second rotor section 31B, arranged in the axial direction.

[0142] Furthermore, the rotor 30 may have a skew structure that changes in a step-like manner in the axial direction.

[0143] Thus, the scope of this disclosure also includes modifications and improvements to the embodiments, which will be apparent to those skilled in the art from the claims.

[0144] Furthermore, the following additional information is disclosed regarding the above embodiment. [Addendum 1] A motor having a rotor having a skew structure, the motor comprising: a stator that rotatably houses the rotor radially inward; the rotor including a first rotor section and a second rotor section having the same number of magnetic poles, each having a magnet; the rotor having a skew structure such that the positions of the magnetic poles of the first rotor section and the second rotor section differ by a predetermined mechanical angle in the circumferential direction; the stator comprising: a plurality of salient poles evenly spaced apart in the circumferential direction; a plurality of slots provided between the salient poles and evenly spaced apart in the circumferential direction; stator coils disposed within the slots; and at least one groove provided for each salient pole and formed on the radially inward inner surface of the salient pole facing the rotor, the groove being positioned to evenly divide the mechanical angle between the circumferential center of one of the slots and the rotation axis of the motor and the circumferential center of the other slot adjacent to the first slot and the rotation axis, in the circumferential direction. A motor in which the grooves formed on all of the salient poles have equal width in the circumferential direction, and the predetermined mechanical angle is substantially the smallest angle that cancels out harmonics generated when harmonics caused by the number of slots generated during rotor rotation are transformed by the influence of the grooves. [Note 2] A motor in which, if the reference skew mechanical angle is a skew mechanical angle corresponding to the number of grooves, Z is the mechanical angle between the line passing through the circumferential center of one of the slots and the axis of rotation and the line passing through the circumferential center of the other slot adjacent to the first slot and the axis of rotation, and the number of grooves is N (where N is an integer of 1 or more), then the predetermined mechanical angle is an angle equal to the reference skew mechanical angle Z that satisfies the following formula (A) within a predetermined tolerance range. Z = θ / {2 × (N + 1)} ・・・・・・・・・・・・ (A) [Note 3] The predetermined mechanical angle is Φ Ｍ Therefore, the predetermined mechanical angle ΦＭ The motor according to Supplementary Note 2, which satisfies the following formula (B): 0.75×Z ≦ Φ Ｍ ≦ 1.25×Z ····· (B) [Supplementary Note 4] The motor according to any one of Supplementary Notes 1 to 3, wherein the stator includes an opening provided for each of the slots and opening radially inward, where d1 is a radial width of the opening, d3 is a radial depth of the groove, and the radial depth d3 of the groove satisfies the following formula (4): d1 ≦ d3 ······· (4) [Supplementary Note 5] The motor according to any one of Supplementary Notes 1 to 4, wherein the grooves formed in all the salient poles have a shape whose width decreases toward a radially outer side. [Supplementary Note 6] The motor according to any one of Supplementary Notes 1 to 5, wherein the stator includes an opening provided for each of the slots and opening radially inward, a circumferential width of the groove formed in all the salient poles is equal to a circumferential width of the opening provided for the slot, and the number of the grooves provided for each salient pole is less than or equal to an integer part of a value obtained by dividing a circumferential width of the inner surface of the salient pole by the circumferential width of the opening.

[0145] Furthermore, the following additional information is disclosed regarding the above embodiment. [Addendum 1] A motor having a rotor having a skew structure, the motor comprising: a stator that rotatably houses the rotor radially inward; the rotor including a first rotor section and a second rotor section having the same number of magnetic poles, each having a magnet; the rotor having a skew structure in which the positions of the magnetic poles of the first rotor section and the second rotor section are shifted in the circumferential direction by a mechanical angle determined by the skew electrical angle; the stator comprising: a plurality of salient poles evenly spaced apart in the circumferential direction; a plurality of slots which are spaces between the salient poles; stator coils disposed within the slots; and grooves provided for each salient pole and formed on the radially inward inner surface facing the rotor. A motor in which the number of grooves N and the skew electrical angle Φ satisfy the following equations (1) to (3), where θ is the circumferential mechanical angle between adjacent slots, P is the number of magnetic poles, Φmax is the upper limit of the skew electrical angle, N is the number of grooves formed for each salient pole (where N is an integer of 1 or more), and Φ is the skew electrical angle. X = θ × (P / 2) / {2 × (N + 1)} ・・・・・・・(1) 1.0 × X ≤ Φ ≤ 1.2 × X ・・・・・・・(2) Φ < Φmax ・・・・・・・・・・・・・・・・(3) [Note 2] The motor in which the number of grooves N is the smallest natural number that satisfies equations (1) to (3), as described in Note 1. [Note 3] The motor according to Note 1 or Note 2, wherein the upper limit Φmax is the value of the electrical angle of the skew structure such that the demagnetization rate of the magnet is 5% compared to the case in which the rotor is not provided with a skew structure. [Note 4] The motor according to any one of Notes 1 to 3, wherein the stator is provided for each of the slots and has an opening that opens radially inward, and the radial width of the opening is d1, the distance from the stator coil adjacent to the opening to the opening is d2, and the radial depth of the groove is d3, such that the radial depth d3 of the groove satisfies the following formula (4): d1 ≤ d3 ≤ d1 + d2 ..... (4)

[0146] 1...Motor, 20...Stator, 211...Salliative pole, 211A...Inner surface, 212...Slot, 212A...Opening, 22...Stator coil, 30...Rotor, 31A...First rotor section, 31B...Second rotor section, 33...Magnet, d1...Width, d2...Distance, d3...Depth, G...Groove, N...Number of grooves, P...Number of magnetic poles, Y...Mechanical angle determined from skew electrical angle, θ...Mechanical angle, Φ...Skew electrical angle, Φmax...Upper limit

Claims

1. A motor having a rotor having a skew structure, the motor comprising: a stator that rotatably houses the rotor radially inward; the rotor including a first rotor section and a second rotor section having the same number of magnetic poles, each having a magnet; the rotor having a skew structure such that the positions of the magnetic poles of the first rotor section and the second rotor section differ by a predetermined mechanical angle in the circumferential direction; the stator comprising: a plurality of salient poles evenly spaced apart in the circumferential direction; a plurality of slots provided between the salient poles and evenly spaced apart in the circumferential direction; stator coils disposed within the slots; and at least one groove provided for each salient pole, formed on the radially inward inner surface of the salient pole facing the rotor, the grooves being positioned to evenly divide the mechanical angle between the circumferential center of one slot and the rotation axis of the motor and the circumferential center of the other slot adjacent to the first slot and the rotation axis, the grooves formed on all the salient poles having equal width in the circumferential direction, The predetermined mechanical angle is the substantially smallest angle among those that cancel out harmonics generated when harmonics caused by the number of slots during rotor rotation are transformed by the influence of the grooves.

2. The motor according to claim 1, wherein Z is a reference skew mechanical angle which corresponds to the number of grooves, θ is the mechanical angle between the line passing through the circumferential center of one slot and the axis of rotation and the line passing through the circumferential center of the other slot adjacent to the first slot and the axis of rotation, and N is the number of grooves (where N is an integer of 1 or more), and the predetermined mechanical angle is an angle equal to the reference skew mechanical angle Z that satisfies the following formula (A) within a predetermined tolerance range.

3. The predetermined machine angle is Φ Ｍ Therefore, the predetermined mechanical angle Φ Ｍ However, the motor according to claim 2 satisfies the following formula (B): 0.75 × Z ≤ Φ Ｍ ≦ 1.25×Z・・・(B) 4. The stator is provided for each of the slots and has an opening that opens radially inward, and the motor according to any one of claims 1 to 3, wherein the radial width of the opening is d1 and the radial depth of the groove is d3, and the radial depth of the groove satisfies the following formula (4): d1 ≤ d3 ・・・・・・(4) 5. The motor according to any one of claims 1 to 3, wherein the grooves formed in all of the salient poles have a shape that narrows in width toward the radially outward direction.

6. The motor according to any one of claims 1 to 3, wherein the stator is provided for each of the slots and has an opening that opens radially inward, the circumferential width of the grooves formed in all of the salient poles is equal to the circumferential width of the opening provided for the slot, and the number of grooves provided for each salient pole is less than or equal to the integer part of the value obtained by dividing the circumferential width of the inner surface of the salient pole by the circumferential width of the opening.

Images