A hollow cup motor

Abstract

The application discloses a kind of hollow cup electric machines, a kind of hollow cup electric machines, including stator, outer rotor and inner rotor;The stator is located between outer rotor and inner rotor;The stator includes armature winding and coil support, armature winding is wound on coil support;The outer rotor includes permanent magnet and outer rotor core;The inner rotor includes inner rotor core, it is characterized by: the radial thickness T of the inner rotor core is expressed as polar coordinate function related to central angle θ: T=T0+T6cos (6pθ+φ6)+T i cos (ipθ+φ i );Wherein T0, T6 and T i are positive number, and 0≤T i <0.2T6<0.1T0;P is the pole pair number of permanent magnet, i is positive integer not equal to 6, φ6 and φ i represent phase, are preset constant.The radial thickness of the inner rotor core of the application improves hollow cup electric machine, can effectively adjust the harmonic content of air-gap flux density, to suppress the torque fluctuation of motor, promote the performance of motor.

Description

Technical Field

[0001] This invention belongs to the field of electric motors, and in particular relates to a hollow cup motor. Background Technology

[0002] Traditional permanent magnet synchronous motors typically consist of a single stator and a single rotor. The stator has an iron core, the armature windings are located in slots formed by the stator iron core, and the permanent magnets are located on the rotor. Due to the cogging structure of the stator iron core, the permanent magnet synchronous motor will generate periodic cogging torque, which will increase torque ripple and affect motor performance.

[0003] Using a slotless stator core can eliminate the cogging effect and improve the smoothness of motor torque. However, relative motion still exists between the stator core and the permanent magnets on the rotor, and the magnetic field in the stator core is in an alternating state, resulting in core loss and increased stator assembly temperature. To solve these problems, a coreless motor structure can be used. A coreless motor consists of one stator and two rotors, with the stator located between the two rotors. The rotor on the outer side of the stator is generally called the outer rotor, and the rotor on the inner side is generally called the inner rotor. The stator has armature windings but no stator core; the armature windings are wound on coil supports. The permanent magnets and rotor yoke are located on the outer rotor, while the inner rotor only contains the rotor yoke. When the two rotors rotate synchronously, there is no relative motion between the rotor yoke (composed of the core) and the permanent magnets, thus greatly reducing the degree of magnetic field alternation in the core and achieving the purpose of suppressing core loss.

[0004] However, the tile-shaped permanent magnets in a coreless motor will generate odd-order magnetomotive force harmonic components (first, third, fifth, and seventh orders) in the air gap. A traditional coreless motor includes a stator 1', an outer rotor 2', and an inner rotor 3'; the stator is located between the outer and inner rotors; the stator includes an armature winding 11' and a coil support 12', with the armature winding 11' wound on the coil support 12'; the outer rotor includes a permanent magnet 21' and an outer rotor core 22', while the inner rotor 3' only includes the inner rotor core. See [link to relevant documentation]. Figure 1 As shown. Because the radial thickness of the inner rotor core is uniform, the air gap permeability contains only a DC component. The air gap magnetic flux density can be obtained by multiplying the air gap magnetomotive force by the air gap magnetic flux density. Therefore, the air gap magnetic flux density of a coreless motor has odd-order harmonic components such as the first, third, fifth, and seventh orders. Among them, the amplitude of the third air gap magnetic flux density harmonic is greater than that of the fifth and seventh air gap magnetic flux density harmonics, which is the primary cause of air gap magnetic flux density waveform distortion, but it does not cause torque fluctuations in the motor. However, the fifth and seventh air gap magnetic flux density harmonics will induce fifth and seventh back electromotive force harmonics in the armature winding. The interaction between the fifth and seventh back electromotive force harmonics and the sinusoidal current will generate a sixth torque harmonic, ultimately leading to increased torque fluctuations in the motor and affecting motor performance.

[0005] In existing improved coreless motors, different permanent magnet structures are used to alleviate the above-mentioned problems. For example, Chinese Patent Publication No. CN113346650A discloses a coreless motor, including a rotor assembly and a stator assembly. The rotor assembly includes a coil and a motor shaft, and the stator assembly includes a magnet assembly. The magnet assembly is sleeved on the motor shaft, the motor shaft passes through the coil, and the motor shaft can drive the coil to rotate relative to the magnet assembly about the central axis of the motor shaft. The polarity of the magnet assembly is arranged according to a Hellbeck array combination, and the magnetic lines of force at both ends of the magnet assembly along the central axis of the motor shaft constrain the magnetic lines of force in the middle of the magnet assembly along the central axis of the motor shaft within the effective area cut by the magnetic lines of force of the coil.

[0006] The aforementioned coreless motor employs magnet components arranged in a Hale-Becker array, which enhances the magnetization effect, improves magnet utilization, and reduces fifth and seventh air gap magnetomotive force harmonics, thus helping to reduce torque ripple. However, this coreless motor has a large number of permanent magnets, and the magnetization directions of each permanent magnet are different. The processing and assembly of the permanent magnets are complex, resulting in higher motor costs and a higher susceptibility to processing errors that can degrade motor performance.

[0007] In existing improved hollow cup motors, different inner rotor structures are also used. For example, Chinese patent CN113098162A (application number 202110389758.9) discloses a hollow cup structure motor with a sunflower-shaped inner rotor, including: an outer rotor core, multiple permanent magnets, an eccentric inner rotor core, and a rotor shaft; along the radial section of the rotor shaft, the outer contour of the eccentric inner rotor core includes multiple eccentric arcs protruding towards the permanent magnets, the number of eccentric arcs is the same as the number of permanent magnets, and the eccentric arcs correspond one-to-one with the permanent magnets. The two endpoints of the eccentric arcs are on the line connecting the two sides of the corresponding permanent magnets and the center of the rotor shaft, and the center of the eccentric arc is on the line connecting the midpoint of the arc side of the corresponding permanent magnet and the center of the rotor shaft.

[0008] The radial thickness function of the inner rotor core of the aforementioned hollow-cup motor contains only a second harmonic component. The interaction between the second air gap magnetic flux density harmonic and the first permanent magnet magnetomotive force harmonic can only generate an additional third air gap magnetic flux density harmonic. Therefore, the amplitude and phase of the fifth and seventh air gap magnetic flux density harmonics cannot be adjusted, meaning that the motor's torque ripple cannot be effectively reduced. The fifth and seventh air gap magnetic flux density harmonics induce fifth and seventh back electromotive force harmonics in the armature windings. The interaction of these fifth and seventh back electromotive force harmonics with the sinusoidal current generates a sixth torque harmonic, ultimately leading to increased torque ripple and affecting motor performance. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to propose a hollow cup motor that can suppress torque fluctuations without changing the traditional permanent magnet structure, in light of the current state of the technology.

[0010] The technical solution adopted by this invention to solve the above-mentioned technical problems is as follows: a hollow cup motor, comprising a stator, an outer rotor, and an inner rotor; the stator is located between the outer rotor and the inner rotor; the stator includes an armature winding and a coil support, the armature winding being wound on the coil support; the outer rotor includes a permanent magnet and an outer rotor core; the inner rotor includes an inner rotor core, characterized in that: the radial thickness T of the inner rotor core is expressed as a polar coordinate function related to the central angle θ: T = T0 + T6cos(6pθ + φ6) + T i cos(ipθ+φ i ); where T0 and T6 are positive numbers, and 0 ≤ T i <0.2T6 <0.1T0; p is the number of pole pairs of the permanent magnet, i is a positive integer not equal to 6, φ6 and φ i The phase is a preset constant. Taking the center point of the inner rotor core in the radial cross section of the hollow cup motor as the origin and the horizontal rightward direction as the positive X-axis, the angle between the line connecting any point on the outer wall of the inner rotor core in the radial cross section of the hollow cup motor and the origin and the positive X-axis in the counterclockwise direction is the central angle θ.

[0011] This invention alters the radial thickness of the inner rotor core, causing the air gap magnetic permeability to become non-uniform in the circumferential direction, introducing harmonic components. These air gap magnetic permeability harmonics interact with the air gap magnetomotive force harmonics, changing the content of each harmonic in the original air gap magnetic flux density, thereby reducing motor torque fluctuations. Within a pair of magnetic poles, assuming the air gap magnetic permeability contains n harmonic components, its interaction with the first, third, fifth, and seventh air gap magnetomotive force harmonics can generate n±1, n±3, n±5, and n±7 air gap magnetic flux density harmonic components, respectively. Since the amplitude of the first air gap magnetomotive force harmonic is much larger than that of the third, fifth, and seventh air gap magnetomotive force harmonics, the n±1 air gap magnetic flux density harmonic has the largest amplitude, effectively adjusting the original air gap magnetic flux density harmonic content. This invention improves the radial thickness of the inner rotor core. The radial thickness function contains T6cos(6pθ+φ6), which adds a sixth harmonic component to the air gap magnetic permeability. The interaction between the sixth air gap magnetic permeability harmonic and the first permanent magnet magnetomotive force harmonic generates additional fifth and seventh air gap magnetic flux density harmonics. By adjusting the values ​​of T6 and φ6, the amplitude and phase of the sixth air gap magnetic permeability harmonic can be changed, thereby adjusting the amplitude and phase of the fifth and seventh air gap magnetic flux density harmonics. This adjusts the amplitude and phase of the fifth and seventh back electromotive force harmonics, thus reducing motor torque ripple.

[0012] A further improvement of the present invention is that T6cos(6pθ+φ6) reaches its maximum value at the junction of two adjacent permanent magnets. At this time, the fifth and seventh back electromotive force harmonics are out of phase with the sixth torque harmonic generated by the interaction of the sinusoidal current, and the two can cancel each other out, thereby further reducing the torque fluctuation of the motor.

[0013] A further improvement of this invention is that i = 4. Adding a fourth harmonic component to the radial thickness function of the inner rotor core increases the air gap permeability by a fourth harmonic component. The interaction between the fourth air gap permeability harmonic and the first permanent magnet magnetomotive force harmonic generates an additional fifth air gap magnetic flux density harmonic, thus achieving the purpose of regulating the fifth air gap magnetic flux density harmonic.

[0014] A further improvement of the invention is that i = 8. Adding an eighth harmonic component to the radial thickness function of the inner rotor core increases the air gap magnetic permeability by an eighth harmonic component. The interaction between the eighth air gap magnetic permeability harmonic and the first permanent magnet magnetomotive force harmonic generates an additional seventh air gap magnetic flux density harmonic, thereby achieving the purpose of regulating the seventh air gap magnetic flux density harmonic.

[0015] A further improvement of the present invention is that the outer rotor and the inner rotor rotate synchronously. Since the radial thickness of the inner rotor core is no longer uniform along the circumference, the outer rotor and the inner rotor should rotate synchronously to generate specific fifth and seventh air gap magnetic flux density harmonics. Simultaneously, the synchronous rotation of the outer rotor and the inner rotor allows the core and the permanent magnet to remain relatively stationary, thereby reducing core losses.

[0016] A further improvement of the present invention is that the coil support is non-magnetic. The stator of the present invention does not contain magnetic material, which can eliminate cogging torque caused by the cogging effect, thereby reducing torque fluctuations in the motor.

[0017] A further improvement of the present invention is that the armature winding is either a full-pitch winding or a short-pitch winding. The armature winding of the present invention can be a full-pitch winding to obtain a larger fundamental back electromotive force winding coefficient, thereby increasing the power density of the motor. Alternatively, the armature winding of the present invention can also be a short-pitch winding to reduce the winding coefficient of higher harmonic back electromotive force and improve the sinusoidal nature of the back electromotive force.

[0018] A further improvement of the present invention is that the armature winding surface is sinusoidal. For a coreless motor, the motor's flux linkage is the integral of the air gap magnetic flux density with respect to the winding shape, while the motor's back electromotive force (EMF) is the differential of the flux linkage with respect to time. Therefore, adjusting the shape of the armature winding helps to reduce the harmonic content of the back EMF and improve the sinusoidal nature of the back EMF waveform.

[0019] A further improvement of the present invention is that the permanent magnet has two polarities, and the polarities of the permanent magnet are alternately distributed in the circumferential direction. The alternating circumferential distribution of the permanent magnet polarities can ensure the positive and negative symmetry of the air gap magnetic field, reduce the harmonic content, and help reduce the torque fluctuation of the motor.

[0020] A further improvement of this invention is that the permanent magnet has an alternating pole structure, with only one polarity, and the permanent magnet and the outer rotor core are alternately distributed in the circumferential direction. Therefore, the amount of permanent magnet used can be significantly reduced, which helps to lower the cost of the motor and improve its cost-effectiveness.

[0021] Compared with existing technologies, the advantages of this invention are as follows: This invention improves the radial thickness of the inner rotor core. Within the range of a pair of magnetic poles, the radial thickness function of the inner rotor core contains a sixth harmonic component, meaning a sixth harmonic component is added to the air gap magnetic permeability. The interaction between the sixth air gap magnetic permeability harmonic and the first permanent magnet magnetomotive force harmonic generates additional fifth and seventh air gap magnetic flux density harmonics. By adjusting the harmonic amplitude and phase of the radial thickness function of the inner rotor core, the amplitude and phase of the sixth air gap magnetic permeability harmonic can be changed, thereby adjusting the amplitude and phase of the fifth and seventh air gap magnetic flux density harmonics, thus adjusting the amplitude and phase of the fifth and seventh back electromotive force harmonics. Ultimately, the fifth and seventh back electromotive force harmonics are out of phase with the sixth torque harmonic generated by the interaction of the sinusoidal current, and the two cancel each other out, thereby reducing motor torque fluctuations. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the cross-section of a traditional coreless motor.

[0023] Figure 2 This is a cross-sectional schematic diagram of the hollow cup motor of the present invention;

[0024] Figure 3 This is a comparison diagram of the torque waveforms of the hollow cup motor of the present invention, the conventional hollow cup motor, and the sunflower-shaped inner rotor hollow cup motor;

[0025] Figure 4 This is a cross-sectional schematic diagram of the hollow cup motor of the present invention using a sinusoidal winding;

[0026] Figure 5 This is a cross-sectional schematic diagram of the hollow cup motor of the present invention using alternating pole permanent magnets;

[0027] Figure 6 A schematic cross-sectional view of the radial thickness function of the inner rotor core of the hollow cup motor of the present invention after adding the fourth harmonic component;

[0028] Figure 7 This is a schematic cross-sectional view of the radial thickness function of the inner rotor core of the hollow cup motor of the present invention after adding the eighth harmonic component. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0030] Example 1

[0031] Depend on Figures 2-6 The image shows a preferred embodiment of the present invention. Figure 2 As shown, a hollow cup motor includes a stator 1, an outer rotor 2, and an inner rotor 3. The stator 1 is located between the outer rotor 2 and the inner rotor 3. The stator 1 includes an armature winding 11 and a coil support 12. The armature winding 11 is wound on the coil support 12 and can be a full-pitch winding or a short-pitch winding. The outer rotor 2 includes a permanent magnet 21 and an outer rotor core 22. The outer rotor core 22 is annular, and the permanent magnet 21 is located on the surface of the annular outer rotor core 22. The polarity of the permanent magnet 21 is alternately distributed in the circumferential direction. The inner rotor 3 includes only an inner rotor core. The radial thickness T of the inner rotor core is expressed as a polar coordinate function related to the central angle θ.

[0032] T = T0 + T6cos(6pθ + φ6) + T i cos(ipθ+φ i );

[0033] Where T0 and T6 are positive numbers, and 0 ≤ T i <0.2T6 <0.1T0;

[0034] p is the number of pole pairs of permanent magnet 21, i is a positive integer not equal to 6, and φ6 and φ i Represents phase, which is a preset constant;

[0035] In this embodiment, T i =0; T=T0+T6cos(6pθ+φ6); T6=0.25T0,φ6=180 ° T0 = ​​10 mm;

[0036] Taking the center point of the inner rotor core in the radial cross section of the hollow cup motor as the origin, and the horizontal rightward direction as the positive X-axis, the angle between the line connecting any point on the outer wall of the inner rotor core in the radial cross section of the hollow cup motor and the origin and the counterclockwise direction of the positive X-axis is the central angle θ.

[0037] At the junction of two adjacent permanent magnets 21, T6cos(6pθ+φ6) reaches its maximum value. The sixth harmonic component helps to adjust the amplitude and phase of the fifth and seventh air gap magnetic flux density harmonics, thereby suppressing the sixth torque harmonic component of the motor and reducing motor torque fluctuations.

[0038] like Figure 1As shown, existing traditional coreless motors have a uniform radial thickness of the inner rotor core, making it impossible to adjust the amplitude and phase of the fifth and seventh air gap magnetic flux density harmonics, resulting in significant torque fluctuations. This invention's coreless motor is compared with traditional coreless motors and sunflower-shaped inner rotor coreless motors, analyzing their torque fluctuations under the same current. Figure 3 As shown, it can be seen that the torque fluctuation of the hollow cup motor of the present invention is significantly smaller than that of the traditional hollow cup motor and the sunflower-shaped inner rotor hollow cup motor.

[0039] Example 2

[0040] Unlike Embodiment 1, the surface of the armature winding 11 of the hollow cup motor is sinusoidal in order to suppress back electromotive force harmonics. See [link to previous document]. Figure 4 As shown.

[0041] Example 3

[0042] Unlike Embodiment 1, the permanent magnets 21 of the hollow cup motor have an alternating pole structure. In this case, all permanent magnets 21 have the same polarity and are alternately distributed circumferentially and with the outer rotor core 22. This helps reduce the amount of permanent magnets 21 used and improves the motor's cost-effectiveness. See [link to previous documentation]. Figure 5 As shown. At this point, due to the asymmetry of the permanent magnets, the magnetomotive force will contain second and fourth harmonics, leading to second and fourth air gap magnetic flux density harmonics, ultimately causing third torque fluctuations. Therefore, the radial thickness T of the inner rotor core can be defined as:

[0043] T=T0+T6cos(6pθ+φ6)+T3cos(3pθ+φ3);

[0044] Where T3 = 0.1T6, T6 = 0.25T0, φ6 = 180 ° φ3=90 ° T0 = ​​10 mm;

[0045] p is the number of pole pairs of permanent magnet 21, and φ6 and φ3 represent the phase, which are preset constants;

[0046] Taking the center point of the inner rotor core in the radial cross-section of the hollow cup motor as the origin, and the horizontal rightward direction as the positive X-axis, the angle between the line connecting any point on the outer wall of the inner rotor core in the radial cross-section of the hollow cup motor and the origin, and the counterclockwise direction of the positive X-axis, is the central angle θ. At this point, the air gap magnetic permeability will have a third harmonic component. This component interacts with the first air gap magnetomotive force harmonic to generate additional second and fourth air gap magnetic flux density harmonics. The amplitude and phase of these second and fourth air gap magnetic flux density harmonics can be adjusted, reducing the third torque ripple.

[0047] Example 4

[0048] Unlike Example 1, the radial thickness function of the inner rotor core of the hollow cup motor incorporates a fourth harmonic component to adjust the fifth back electromotive force harmonic. (See [link to example]). Figure 6 As shown.

[0049] The radial thickness T of the inner rotor core is a function of:

[0050] T=T0+T6cos(6pθ+φ6)+T4cos(4pθ+φ4);

[0051] Where T4 = 0.05T6, T6 = 0.2T0, φ6 = 180 ° φ4=180 ° T0 = ​​10 mm;

[0052] p is the number of pole pairs of permanent magnet 21, and φ6 and φ4 represent the phase, which are preset constants;

[0053] Taking the center point of the inner rotor core in the radial cross section of the hollow cup motor as the origin, and the horizontal rightward direction as the positive X-axis, the angle between the line connecting any point on the outer wall of the inner rotor core in the radial cross section of the hollow cup motor and the origin and the counterclockwise direction of the positive X-axis is the central angle θ.

[0054] Example 5

[0055] Unlike Example 1, the radial thickness function of the inner rotor core of the hollow cup motor incorporates an eighth harmonic component to adjust the seventh back electromotive force harmonic. (See [link to example]). Figure 7 As shown.

[0056] The radial thickness T of the inner rotor core is a function of:

[0057] T=T0+T6cos(6pθ+φ6)+T8cos(8pθ+φ8);

[0058] Where T8 = 0.05T6, T6 = 0.2T0, φ6 = 180 ° φ8=180 ° T0 = ​​10 mm;

[0059] p is the number of pole pairs of permanent magnet 21, and φ6 and φ8 represent the phase, which are preset constants;

[0060] Taking the center point of the inner rotor core in the radial cross section of the hollow cup motor as the origin, and the horizontal rightward direction as the positive X-axis, the angle between the line connecting any point on the outer wall of the inner rotor core in the radial cross section of the hollow cup motor and the origin and the counterclockwise direction of the positive X-axis is the central angle θ.

[0061] The descriptions in the embodiments of this specification are merely illustrative of the invention and are not intended to limit the invention. The scope of protection of this invention should not be considered as limited to the specific content described in the embodiments. Any modifications, substitutions, and changes made within the spirit and principles of this invention are included within the scope of protection of this invention.

Claims

1. A hollow cup motor, comprising a stator (1), an outer rotor (2), and an inner rotor (3); the stator (1) is located between the outer rotor (2) and the inner rotor (3); the stator (1) comprises an armature winding (11) and a coil support (12), the armature winding (11) being wound on the coil support (12); the outer rotor (2) comprises a permanent magnet (21) and an outer rotor core (22); the inner rotor (3) comprises an inner rotor core, characterized in that: The radial thickness of the inner rotor core T Represented as the central angle θ Related polar coordinate functions: T = T 0+ T 6cos(6 pθ + φ 6)+ T i cos( ipθ + φ i ); in T 0、 T 6 is a positive number, and 0 ≤ T i <0.2 T 6 < 0.1 T 0; p Let be the number of pole pairs of the permanent magnet (21). i A positive integer not equal to 6. φ 6 and φ i Represents phase, which is a preset constant; T 0 represents the DC component amplitude; T 6 represents the amplitude of the 6th harmonic; T i Represents the amplitude of the i-th harmonic; Taking the center point of the inner rotor core in the radial cross-section of the hollow cup motor as the origin, and the horizontal rightward direction as the positive X-axis, the angle between the line connecting any point on the outer wall of the inner rotor core in the radial cross-section of the hollow cup motor and the origin, and the positive X-axis in the counterclockwise direction, is the central angle. θ .

2. The hollow cup motor according to claim 1, characterized in that: At the junction of two adjacent permanent magnets T 6cos(6 p θ + φ 6) Obtain the maximum value.

3. The hollow cup motor according to claim 1, characterized in that: i =4。 4. The hollow cup motor according to claim 1, characterized in that: i =8。 5. The hollow cup motor according to claim 1, characterized in that: The outer rotor (2) and the inner rotor (3) rotate synchronously.

6. The hollow cup motor according to any one of claims 1 to 5, characterized in that: The coil support (12) is non-magnetic.

7. The hollow cup motor according to any one of claims 1 to 5, characterized in that: The armature winding (11) is a full-pitch winding or a short-pitch winding.

8. The hollow cup motor according to any one of claims 1 to 5, characterized in that: The surface of the armature winding (11) is sinusoidal.

9. The hollow cup motor according to any one of claims 1 to 5, characterized in that: The permanent magnet (21) has two polarities, and the polarities of the permanent magnet (21) are alternately distributed in the circumferential direction.

10. The hollow cup motor according to claim 1, characterized in that: The permanent magnet (21) has an alternating pole structure, and the permanent magnet (21) has only one polarity. The permanent magnet (21) and the outer rotor core (22) are alternately distributed in the circumferential direction.

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