Magnetic modulation gear

Abstract

A magnetic modulation gear 1 includes: a magnetic modulation body 50 having a plurality of magnetic pole pieces 54a arranged in a circumferential direction; an inner magnetic pole body 41a having a plurality of inner magnets 41b arranged in the circumferential direction and disposed on an inner diameter side of the magnetic modulation body 50; and an outer magnetic pole body 12 having a plurality of outer magnets 12a arranged in the circumferential direction and disposed on an outer diameter side of the magnetic modulation body 50. The magnetic modulation gear 1 has a harmonic countermeasure structure for suppressing magnetic flux harmonics of the inner magnetic pole body 41a.

Description

Magnetic modulation gear

[0001] This invention relates to a magnetic modulation gear.

[0002] Conventionally, magnetic modulation gears are known that arrange multiple magnetic pole pieces between two magnets positioned on the inner and outer circumferences, thereby modulating the magnetic flux distribution between the inner and outer magnets (see, for example, Patent Document 1).

[0003] Japanese Patent Publication No. 2017-17984

[0004] Conventional magnetic modulation gears have not taken into consideration cogging torque caused by manufacturing errors. The object of the present invention is to suitably suppress cogging torque caused by manufacturing errors in magnetic modulation gears.

[0005] The present invention relates to a magnetic modulation gear comprising: a magnetic modulator having a plurality of magnetic pole pieces arranged in the circumferential direction; an inner magnetic pole body disposed on the inner diameter side of the magnetic modulator and having a plurality of inner magnets arranged in the circumferential direction; and an outer magnetic pole body disposed on the outer diameter side of the magnetic modulator and having a plurality of outer magnets arranged in the circumferential direction, wherein the gear has a harmonic suppression structure that suppresses the magnetic flux harmonics of the inner magnetic pole body.

[0006] According to the present invention, cogging torque caused by manufacturing errors can be effectively suppressed in a magnetically modulated gear.

[0007] This is a cross-sectional view of a magnetic modulation gear according to an embodiment. This is a cross-sectional view taken along line III-III in Figure 1. This figure shows the relationship between the integral variable in the torque derivation formula and the angles of the inner magnet, outer magnet, and pole piece. This is a graph showing the FFT analysis results of the magnetic flux density waveform obtained from the analysis. This is a graph showing the FFT analysis results of the torque waveform analyzed under two conditions: with and without eccentricity of the input shaft. This is a graph showing the FFT analysis results of the measured torque waveform. This figure shows an example of a harmonic suppression structure in which the corner on the outer diameter side of the inner magnet is formed into an R shape. This figure shows an example of a harmonic suppression structure in which a continuous skew structure is adopted for the inner magnet. This figure shows an example of a harmonic suppression structure in which a stepped skew structure is adopted for the inner magnet. This is a graph to explain the effect of the harmonic suppression structure example, showing the amplitude of the 199.3rd order component when the torque waveform obtained from the analysis is subjected to FFT analysis, and the reduction rate of the normalized peak torque.

[0008] Embodiments of the present invention will be described in detail below with reference to the drawings.

[0009] [Configuration of Magnetic Modulation Gear] Figure 1 is a cross-sectional view of the magnetic modulation gear 1 according to this embodiment, and Figure 2 is a cross-sectional view taken along line III-III in Figure 1. In the following description, the direction along the central axis Ax of the magnetic modulation gear 1 is referred to as the "axial direction," the direction perpendicular to the central axis Ax is referred to as the "radial direction," and the rotational direction around the central axis Ax is referred to as the "circumferential direction." Furthermore, within the axial direction, the side connected to the external driven member (left side in Figure 1) is referred to as the "output side," and the opposite side (right side in Figure 1) is referred to as the "input side."

[0010] As shown in Figures 1 and 2, the magnetic modulation gear 1 according to this embodiment comprises a casing (frame) 10, an input-side cover 20 and an output-side cover 30 that cover both sides of the casing 10 in the axial direction, and an input shaft 40 and a magnetic modulator 50 whose main parts are housed inside these covers.

[0011] The casing 10 is formed in a substantially cylindrical shape with a central axis Ax, and has a stator yoke 11 and an outer magnetic pole body 12 on its inner circumference. The stator yoke 11 is formed in a cylindrical shape and fitted inside the casing 10. The outer magnetic pole body 12 is composed of a plurality of outer magnets 12a. The plurality of outer magnets 12a are permanent magnets such as neodymium magnets, and have a greater number of pole pairs than the inner magnets 41b of the input shaft 40 described later. Multiple magnets with different polarities are attached to the inner surface of the stator yoke 11 so as to be arranged alternately (including multiple alternating groups) in the circumferential direction. However, the outer magnetic pole body 12 may be in the shape of a single ring, or it may be made of divided outer magnets 12a arranged in the circumferential direction. Also, on the inner circumference of the casing 10, on the input side of the stator yoke 11, a bearing 61 (for example, a ball bearing) is arranged to rotatably support the magnetic modulator 50. The support of the bearing 61 is not limited to the casing 10, but may also be supported by, for example, a cover 20.

[0012] The input-side cover 20 is positioned on the input side of the casing 10 and covers the inner opening of the casing 10 from the input side. The outer circumference of the input-side cover 20 is fitted with the casing 10 using a spigot joint. A bearing 62 (for example, a ball bearing) that rotatably supports the input shaft 40 is positioned on the inner circumference of the input-side cover 20.

[0013] The output-side cover 30 is positioned on the output side of the casing 10 and covers the inner opening of the casing 10 from the output side. The outer circumference of the output-side cover 30 is fitted with the casing 10 using a spigot joint. A bearing 63 (for example, a ball bearing) that rotatably supports the magnetic modulator 50 is positioned on the inner circumference of the output-side cover 30.

[0014] The input shaft 40 is a shaft that rotates around a central axis Ax and comprises a disc portion 41 and a motor connecting portion 42. This input shaft 40 is rotatably supported by a bearing 62 positioned between it and the input-side cover 20 and a bearing 64 positioned between it and the magnetic modulator 50. The motor connecting portion 42 extends from the disc portion 41 toward the axial input side. The tip of the motor connecting portion 42 protrudes outward from the input-side cover 20, and this protruding portion is connected to a motor (not shown). Note that the motor connecting portion 42 may be a hollow type that does not protrude from the cover 20, or it may be connected to something other than a motor.

[0015] The disc portion 41 has an inner magnetic pole body 41a on its outer circumference, which is positioned on the inner diameter side of the outer magnetic pole body 12. The inner magnetic pole body 41a is composed of a plurality of inner magnets 41b. The plurality of inner magnets 41b are permanent magnets such as neodymium magnets, and are attached to the outer surface of the disc portion 41 so that multiple magnets with different polarities are arranged alternately (including multiple alternating groups) in the circumferential direction. However, the inner magnetic pole body 41a may be a single ring shape, or it may be a collection of divided inner magnets 41b arranged in the circumferential direction.

[0016] The magnetic modulator 50 has an output shaft portion 51, a cylindrical portion 52, and a bearing support ring 55. Of these, the output shaft portion 51 and the bearing support ring 55 are examples of support portions according to the present invention and are parts for rotatably supporting the intermediate magnetic pole body 54 (magnetic pole piece 54a), which will be described later.

[0017] The output shaft portion 51 is a metal shaft that rotates around the central axis Ax and is positioned on the output side of the intermediate magnetic pole body 54, which will be described later. Approximately half of the output side of the output shaft portion 51 protrudes outward from the output side cover 30, and this protruding portion is connected to the driven member (not shown). Note that the output shaft portion 51 may be a hollow type that does not protrude outward, or the shaft that is the input side in Figure 1 may be used as the output shaft (this also works for driving for speed increase purposes). Approximately the axial center of the output shaft portion 51 is rotatably supported by a bearing 63 positioned between it and the output side cover 30. In addition, a bearing 64 (for example, a ball bearing) that rotatably supports the input shaft 40 is positioned at the input side end of the output shaft portion 51. The output side end of the cylindrical portion 52 is connected to the outer circumference of the output shaft portion 51 at the axial position between the bearing 63 and the bearing 64.

[0018] The bearing support ring 55 is made of metal (for example, stainless steel) and is positioned on the input side of the intermediate magnetic pole body 54, which will be described later. The bearing support ring 55 is fixed to the outer circumference of the input end of the cylindrical portion 52, and the inner ring of the bearing 61, which is positioned between the bearing support ring 55 and the casing 10, is fitted onto its outer surface.

[0019] The cylindrical portion 52 is formed in a substantially cylindrical shape with a central axis Ax and has an intermediate pole body 54 positioned in the axial direction corresponding to the outer pole body 12 and the inner pole body 41a. The intermediate pole body 54 has a plurality of pole pieces 54a. The plurality of pole pieces 54a are arranged at predetermined intervals in the circumferential direction and are formed as an annular shape overall. The plurality of pole pieces 54a (intermediate pole body 54) are arranged concentrically on the inner diameter side of the outer pole body 12 and on the outer diameter side of the inner pole body 41a, with predetermined gaps between them. Each pole piece 54a is constructed by stacking thin electromagnetic steel sheets (laminated steel sheets) in the axial direction.

[0020] Adjacent magnetic pole pieces 54a in the circumferential direction are connected by connecting portions 54b between them. The connecting portions 54b are made of resin and constitute a part of the resin portion 56, which will be described later. The outer circumferential surface of the connecting portion 54b is recessed inward from the outer circumferential surface of the magnetic pole piece 54a. However, the inner and outer circumferential surfaces of the connecting portion 54b may be flush with the corresponding surface of the magnetic pole piece 54a, or the inner circumferential surface may be recessed outward. Furthermore, the connecting portion 54b may be integrally formed with the magnetic pole piece 54a using electromagnetic steel sheet. In this case, the radial position and width of the connecting portion 54b are not particularly limited, but they may be configured to obtain suitable torque performance, for example, as described in International Publication No. 2023 / 026804.

[0021] Of the cylindrical portion 52, the portion excluding the magnetic pole pieces 54a is a resin portion 56 made of resin (for example, super engineering plastic). In other words, of the magnetic modulator 50, the portion excluding the output shaft portion 51, the bearing support ring 55, and the intermediate magnetic pole body 54 (multiple magnetic pole pieces 54a) is the resin portion 56. Resin is also filled between the multiple magnetic pole pieces 54a, and this portion constitutes the aforementioned connecting portion 54b. The output-side end of the resin portion 56 protrudes inward and is connected to the output shaft portion 51. On the inner circumference of this end, multiple protrusions 57 are arranged circumferentially, projecting toward the inner diameter. These multiple protrusions 57 are molded to correspond to multiple recesses 51a on the outer circumferential surface of the output shaft portion 51, and the engagement of these protrusions 57 and recesses 51a firmly fixes the output shaft portion 51 and the cylindrical portion 52 (resin portion 56), suppressing mutual movement in the radial and axial directions. The input-side end of the resin part 56 supports a bearing support ring 55 on its outer circumference.

[0022] [Operation of the Magnetic Modulation Gear] As shown in Figures 1 and 2, in the magnetic modulation gear 1, when the input shaft 40 rotates around the central axis Ax by a drive source M such as a motor, the spatial magnetic flux waveform formed by the inner magnetic pole body 41a (inner magnet 41b) of the input shaft 40 is modulated to the same frequency as the outer magnetic pole body 12 (outer magnet 12a) by the intermediate magnetic pole body 54 (magnetic pole piece 54a). Then, rotational torque is transmitted to the magnetic modulator 50 using the magnetic force between the intermediate magnetic pole body 54 and the outer magnetic pole body 12. In this way, the rotational motion input to the input shaft 40 is reduced and output to the driven member E connected to the output shaft portion 51 of the magnetic modulator 50. Alternatively, the intermediate magnetic pole body 54 may be fixed and the outer magnetic pole body 12 may be mounted on a rotatable low-speed rotor, and the output may be taken from the low-speed rotor. The drive source M may be a motor, or it may be another device that converts natural energy such as an engine into mechanical energy. Furthermore, regardless of the drive source M, there may be something that inputs rotation in some form. The driven member E may be attached to the output side, or it may also have a gear attached.

[0023] Here, the reduction ratio R of the magnetic modulation gear 1 is expressed by the following equation (7) when the output shaft is the intermediate magnetic pole body 54, and by the following equation (8) when the output shaft is the outer magnetic pole body 12. R = Np / Ni ... (7) R = No / Ni ... (8) where Np is the number of magnetic poles of the intermediate magnetic pole body 54 (number of magnetic pole pieces 54a: number of magnetic pole pieces), No is the number of pole pairs of the outer magnet 12a (number of outer pole pairs), and Ni is the number of pole pairs of the inner magnetic pole body 41a (number of inner pole pairs). In addition, the following relationship holds between the number of magnetic pole pieces Np, the number of outer pole pairs No, and the number of inner pole pairs Ni. Np = Ni ± No ... (9)

[0024] [Theoretical Derivation of Cogging Torque] In exploring countermeasures against cogging caused by manufacturing errors (including assembly errors, etc.), the inventors theoretically derived the torque generated by the magnetically modulated gear and determined the relevant term for cogging torque, which is not the main torque.

[0025] The generated torque of the magnetic gear can be derived using the virtual displacement method. The virtual displacement method is a technique for obtaining the transmission torque by angularly differentiating the magnetic energy stored in the gap. The magnetomotive force and permeance required for this calculation are defined by the following equations (1) to (3). Inner magnet magnetomotive force: Outer magnet magnetomotive force: Pole piece permeance:

[0026] The variables in equations (1) to (3) are as follows. Integration variables δ and θ i , θ o , θ p The relationship with is shown in Fig. 3. j, k, l: Natural numbers θ i , θ o , θ p : Angles of the inner magnet, outer magnet, and pole piece F j , F k , P l : N i , N o , N p amplitudes of, n I , n O , n P : nth component (n pulsations per rotation) A J , A K , A L : n I , n O , n P amplitudes of, P o : Average permeance

[0027] Here, in equations (1) to (3), the first terms on the right sides of equations (1) and (2), and the first and second terms on the right side of equation (3) correspond to the normal fundamental wave components and harmonic components. On the other hand, in equations (1) to (3), the second terms on the right sides of equations (1) and (2), and the third term on the right side of equation (3) correspond to terms for manufacturing errors. In the present invention, by setting the terms corresponding to this manufacturing error, the terms of the cogging torque caused by the manufacturing error are clarified.

[0028] Substituting the above equations (1) to (3) into the derived formula for transmission torque by the virtual displacement method and proceeding with the calculation results in a huge amount of polynomials. Therefore, the calculation is performed by narrowing down the target to the 199.3 - order component observed in the actual machine and taking into account the following three points. - Since the integral of one period of a trigonometric function is zero, torque does not occur when the coefficient of δ is not zero. Therefore, only focus on the terms where the coefficient of δ becomes zero. - The manufacturing error components of n I , n O , n P take the lower - order terms of eccentricity and deformation (assuming 1 - 4 orders). - j, k, and l take odd components without half - wave symmetry (assuming 3, 5, 7, 9,...).

[0029] As a result, the following equation (4) is obtained as the applicable term.

[0030] Here, as shown in the first item of the above - mentioned three points, the torque generation condition is that the coefficient of the integral variable δ becomes zero. As a result, the unknown parameters of the above coefficient are obtained as follows. However, N i = 3, N p = 26.

[0031] The numerical values of the obtained parameters n I , j, and l correspond to the eccentricity of the inner magnetic pole 41a, the 9th - order harmonic component of the inner magnetic pole 41a, and the fundamental wave component of the permeance of the intermediate magnetic pole 54. That is, cogging torque occurs when these phenomena occur. In other words, by reducing any one of these three phenomena, the above - mentioned torque generation condition is broken, and the cogging torque can be suppressed. Note that the order of the cogging torque in this case is obtained by substituting numerical values into the second term on the right - hand side of the above equation (4), and as shown in the following equation (6), 199.3 orders are obtained.

[0032] [Verification by Analysis and Measurement] Next, the results of the theoretical derivation described above were verified by analysis. Specifically, the torque generation conditions described above were confirmed by analysis. The permeance fundamental wave component of the intermediate magnetic pole body 54 (magnetic pole piece) is present without needing analysis. As shown in Figure 4, the presence of a 9th-order component of the magnetic flux harmonics of the inner magnetic pole body 41a was confirmed. When the calculation was performed with the inner magnetic pole body 41a (input shaft 40) eccentric, an increase in the 199.3-order cogging torque was confirmed, as shown in Figure 5.

[0033] Next, the results of the theoretical derivation described above were verified by measurements on the actual machine. When the measured torque waveform was analyzed using FFT, it was confirmed that 199.3-order cogging was occurring, as shown in Figure 6. Therefore, the validity of the theoretical derivation results described above was confirmed by verification using both analysis and actual measurement.

[0034] [Harmonic Suppression Structure] According to the theoretical derivation of cogging torque described above, cogging torque can be effectively suppressed by reducing any of the following: "eccentricity of the inner magnetic pole body 41a," "9th harmonic component of the inner magnetic pole body 41a," or "permeance fundamental wave component of the intermediate magnetic pole body 54." Of these, reducing the eccentricity of the inner magnetic pole body 41a requires ensuring the concentricity of the three cylindrical structures, which is difficult to manage. Therefore, the magnetic modulation gear 1 of this embodiment is provided with a harmonic suppression structure that suppresses the harmonic component of the inner magnetic pole body 41a. Alternatively, adjustments may be made to ensure the concentricity of the three cylindrical structures.

[0035] Specifically, as a harmonic suppression structure, the magnetic modulation gear 1 has rounded corners on the outer diameter side of each inner magnet 41b when viewed from the axial direction, as shown in Figure 7. More specifically, each inner magnet 41b should be formed in a shape where the radial thickness decreases from the center to the ends in the circumferential direction. For example, as shown by the dashed line in Figure 7, each inner magnet 41b may be formed in a semicircular (U-shaped) form where the outer diameter side surface is directly connected to the inner diameter side surface when viewed from the axial direction.

[0036] Alternatively, as a harmonic suppression structure, a skew structure may be provided in which each inner magnet 41b is twisted in the circumferential direction. Specifically, the skew structure of each inner magnet 41b may be a continuous skew structure in which the circumferential position differs continuously according to the axial position, as shown in Figure 8, or a stepped skew structure in which the circumferential position differs in steps according to the axial position, as shown in Figure 9. Stepped skew is preferable to continuous skew in terms of structural simplicity. The number of steps in the stepped skew is not particularly limited. The skew structure only needs to be such that the outer magnet 12a and pole piece 54a and the inner magnet 41b have relatively different circumferential positions according to the axial position. In other words, the inner magnet 41b may not be skewed, while the outer magnet 12a and pole piece 54a are skewed. Both stepped skew and continuous skew may be included.

[0037] Figure 10 is a graph illustrating the effect of the harmonic suppression structure example described above. It shows the amplitude of the 199.3rd order component and the reduction rate of the normalized peak torque when the torque waveform obtained from the analysis is subjected to FFT analysis. Among those with an R-shaped outer diameter corner (outer diameter R-shape), "a" to "e" have different sizes of R (radius of curvature), with the rightmost part of the figure having a larger radius of curvature. The following can be said from Figure 10: - When the input shaft (inner magnetic pole body 41a) is eccentric from a state where it is not concentric, the torque harmonic component increases significantly. - With an outer diameter R-shape, the harmonic component decreases as the radius of curvature increases, but the peak torque decreases. - The stepped skew provides a suppression effect on torque harmonics while keeping the reduction rate of peak torque small.

[0038] [Technical Effects of This Embodiment] According to this embodiment, a harmonic suppression structure is provided that suppresses the magnetic flux harmonics of the inner magnetic pole body 41a. This reduces the harmonic components of the inner magnetic pole body 41a, and consequently, effectively suppresses cogging torque caused by manufacturing errors, which were not considered in the conventional method. Specifically, the inventors theoretically derived the torque generated by the magnetic modulation gear and identified the corresponding term of cogging torque caused by manufacturing errors. Based on this, they demonstrated that cogging torque can be effectively suppressed by reducing the harmonic components of the inner magnetic pole body 41a. Furthermore, they confirmed that this theoretical approach shows good agreement with analysis and actual measurements.

[0039] [Other] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above. Further details shown in the above embodiments can be modified as appropriate without departing from the spirit of the invention.

[0040] As described above, the present invention is useful for effectively suppressing cogging torque caused by manufacturing errors in magnetic modulation gears.

[0041] 1 Magnetic modulation gear 12 Outer magnetic pole body 12a Outer magnet 40 Input shaft 41a Inner magnetic pole body 41b Inner magnet 50 Magnetic modulator 51 Output shaft section 54 Intermediate magnetic pole body 54a Magnetic pole piece

Claims

1. A magnetic modulation gear comprising: a magnetic modulator having a plurality of pole pieces arranged in the circumferential direction; an inner pole body disposed on the inner diameter side of the magnetic modulator and having a plurality of inner magnets arranged in the circumferential direction; and an outer pole body disposed on the outer diameter side of the magnetic modulator and having a plurality of outer magnets arranged in the circumferential direction, wherein the gear has a harmonic suppression structure that suppresses the magnetic flux harmonics of the inner pole body.

2. The magnetic modulation gear according to claim 1, wherein the harmonic suppression structure has a skew structure in which the outer magnet, the pole piece and the inner magnet have relative circumferential positions that differ depending on the axial position.

3. The magnetic modulation gear according to claim 2, wherein each of the plurality of inner magnets has a skew structure in which the circumferential position differs depending on the axial position.

4. The magnetic modulation gear according to claim 3, wherein each of the plurality of inner magnets includes a stepped skew structure in which the circumferential position differs in stages according to the axial position.

5. The magnetic modulation gear according to claim 3, wherein each of the plurality of inner magnets includes a continuous skew structure in which the circumferential position is continuously different depending on the axial position.

6. The magnetic modulation gear according to claim 1, wherein, as the harmonic suppression structure, each of the plurality of inner magnets is formed in a shape in which the radial thickness decreases from the center in the circumferential direction toward the end.

Images