Electric machine and household appliance

Abstract

Embodiments of the present application provide an electric machine, wherein the electric machine comprises a stator (1) fixedly arranged around an electric machine axis and comprising a stator core (11) and a stator winding (12) arranged on the stator core (11), and a rotor (2) arranged rotatable around the electric machine axis and comprising a permanent magnet (21), wherein the electric machine has a cogging torque in a first waveform and a permanent magnet torque in a second waveform, a phase of the first waveform and a phase of the second waveform match each other, so that a crest and a trough of the first waveform are opposite to a trough and a crest of the second waveform respectively, so that the cogging torque and the permanent magnet torque can offset each other. Furthermore, the present application also provides a corresponding household appliance. According to certain embodiments of the present application, the fluctuation of the output torque of the electric machine can be reduced, and the noise during the operation of the electric machine can be reduced.

Description

Technical Field

[0001] This application relates to an electric motor and a household appliance. Background Technology

[0002] Currently, electric motors are widely used in various fields. Especially in household appliances like fans, single-phase brushless DC motors are commonly used. Single-phase brushless DC motors have advantages such as easy installation, small size, high efficiency, and low price. However, single-phase brushless DC motors suffer from large torque fluctuations, which leads to significant noise during operation. Therefore, the use of single-phase brushless DC motors is limited in environments with strict noise requirements.

[0003] Torque ripple in single-phase brushless DC motors can be caused by cogging torque and permanent magnet torque. Fluctuations in permanent magnet torque are the primary reason for the large torque ripple in single-phase brushless DC motors. However, this portion of the torque ripple caused by permanent magnet torque originates from the operating principle of single-phase brushless DC motors and is essentially impossible to eliminate. Furthermore, to address the starting dead point problem, existing single-phase brushless DC motors typically increase the difference between the positive and negative peaks of the cogging torque waveform. This exacerbates the torque ripple in single-phase brushless DC motors.

[0004] It is known that torque ripple can be improved by reducing cogging torque. For example, sinusoidal magnetization can be used to smooth out changes in cogging torque, reducing its rate of change and amplitude. However, this method only improves vibration performance at low fan speeds. Torque ripple is a major source of vibration and noise when the fan is running at high speeds. Existing technologies have not been very effective in addressing this issue. Summary of the Invention

[0005] The purpose of embodiments of this application is to provide an improved motor and a household appliance for reducing noise.

[0006] According to a first aspect of this application, embodiments of this application provide an electric motor comprising: a stator fixedly arranged about a motor axis and including a stator core and stator windings arranged on the stator core; and a rotor arranged to rotate about a motor axis and including permanent magnets, wherein the motor has a cogging torque of a first waveform and a permanent magnet torque of a second waveform, the phases of the first waveform and the second waveform being matched such that the peaks and troughs of the first waveform are opposite to the troughs and peaks of the second waveform, respectively, thereby canceling out the cogging torque and the permanent magnet torque.

[0007] This reduces the fluctuation of the motor's output torque and lowers the noise during motor operation. In particular, the motor can maintain small torque fluctuations and low noise throughout its entire operating range.

[0008] In this article, directional terms such as "radial," "axial," and "circumferential" are relative to the motor axis.

[0009] According to an optional embodiment of this application, the motor is a single-phase brushless DC motor. By matching the phases of the first and second waveforms, the cogging torque and permanent magnet torque can be canceled out, thereby reducing the fluctuation of the output torque. This method does not require reducing the peak-to-valley amplitude of the cogging torque and does not affect the starting of the single-phase brushless DC motor. Furthermore, the motor can exhibit small torque fluctuations and low noise throughout its operating range.

[0010] According to an optional embodiment of this application, both the first waveform and the second waveform can be trapezoidal waves. This helps to achieve a better cancellation effect, thereby more effectively reducing the fluctuation of the motor's output torque.

[0011] According to an optional embodiment of this application, both the first waveform and the second waveform can be square waves. This also helps to achieve a better cancellation effect, thereby more effectively reducing the fluctuation of the motor's output torque.

[0012] According to an optional embodiment of this application, the first waveform may include a plateau segment, a rising segment, and a falling segment in each of its cycles, wherein the plateau segment of the first waveform accounts for more than 80%. This helps to achieve a more stable output torque.

[0013] Optionally, the second waveform includes a plateau segment, a rising segment, and a falling segment in each of its cycles, with the plateau segment accounting for more than 80% of the second waveform. This helps to achieve a more stable output torque.

[0014] According to an optional embodiment of this application, the first waveform is an inverted trapezoidal wave with the plateau section at the trough. Alternatively or additionally, the second waveform is a positive trapezoidal wave with the plateau section at the crest. This achieves a better cancellation effect, and the output torque correspondingly has a smooth plateau section.

[0015] According to an optional embodiment of this application, the torque variation in the plateau section of the first waveform may be less than 20% of the torque variation over the entire cycle of the first waveform. Alternatively or additionally, the torque variation in the plateau section of the second waveform may be less than 20% of the torque variation over the entire cycle of the second waveform. This also helps to improve the cancellation effect.

[0016] According to an optional embodiment of this application, the stator core may include a stator yoke, stator teeth extending radially from the stator yoke, and stator tooth shoes located at the ends of the stator teeth away from the stator yoke. The stator tooth shoes may include a first tooth shoe portion extending from the stator teeth in a first circumferential direction in the same direction as the rotor's rotation, and a second tooth shoe portion extending in a second circumferential direction opposite to the first circumferential direction. The first angle spanned by the first tooth shoe portion in the circumferential direction may be greater than the second angle spanned by the second tooth shoe portion in the circumferential direction, such that the peak of the first waveform aligns with the trough of the second waveform. Thus, the phase of the cogging torque can be adjusted through a specific structure of the stator core to achieve mutual cancellation between the cogging torque and the permanent magnet torque.

[0017] Optionally, the first angle is 2% to 6% larger than the second angle. This helps to achieve the desired peak phase of the cogging torque, so that the peak of the cogging torque can be more accurately aligned with the trough of the permanent magnet torque.

[0018] According to an optional embodiment of this application, a tooth groove can be formed between adjacent stator teeth in the circumferential direction. A dividing line centrally located between adjacent stator teeth in the circumferential direction divides the tooth groove into a first tooth groove portion closer to the first tooth shoe portion and a second tooth groove portion closer to the second tooth shoe portion. The angle spanned by the first tooth groove portion in the circumferential direction is less than 60%, particularly less than 50%, of the angle spanned by the second tooth groove portion in the circumferential direction. This helps to more accurately align the peaks of the cogging torque with the troughs of the permanent magnet torque.

[0019] According to an optional embodiment of this application, the stator core may include a stator yoke, stator teeth extending radially from the stator yoke, and stator tooth shoes located at the ends of the stator teeth away from the stator yoke. The stator tooth shoes have an inner arc side facing the motor axis. The center of the inner arc side may be offset relative to the motor axis by a first offset distance in a first offset direction, the first offset direction being a direction away from the stator tooth shoes from the motor axis. This helps to achieve the desired waveform of the permanent magnet torque, thereby obtaining a better cancellation effect.

[0020] By adjusting the size of the first eccentricity distance, a better cancellation effect can be obtained.

[0021] According to an optional embodiment of this application, the first eccentricity distance is 20% to 40% of the stator radius, or more than 30% of the stator radius.

[0022] According to an optional embodiment of this application, the first eccentricity distance is between 3 mm and 7 mm, particularly 5.0 mm.

[0023] According to an optional embodiment of this application, the stator core may include a stator yoke, stator teeth extending radially from the stator yoke, and stator tooth shoes located at the ends of the stator teeth away from the stator yoke. The stator tooth shoes have an outer arc side facing away from the motor axis. The center of the outer arc side may be offset by a second eccentric distance relative to the motor axis along a second offset direction, the second offset direction being a direction offset by 90° relative to the direction from the motor axis toward the stator tooth shoes along the rotor's rotational direction. This allows adjustment of the waveform shape and peak value of the cogging torque, making the cogging torque more suitable for canceling out the permanent magnet torque.

[0024] Of particular advantage is that by adjusting the size of the second eccentricity, the cogging torque can be made to have a desired waveform close to a square wave or trapezoidal wave. This helps to achieve a better cancellation effect.

[0025] According to an optional embodiment of this application, the second eccentricity distance is 1% to 2.5% of the stator radius.

[0026] According to an alternative embodiment of this application, the second eccentricity distance is between 0.25 mm and 0.4 mm, particularly 0.37 mm.

[0027] According to an alternative embodiment of this application, the rotor may surround the stator radially outside the stator, such that an air gap is formed between the outer arc side of the stator tooth shoe and the rotor. The aforementioned offset of the center of the outer arc side can change the shape of the air gap.

[0028] According to an optional embodiment of this application, the stator core may include a stator yoke, stator teeth extending radially from the stator yoke, and stator tooth shoes located at the ends of the stator teeth remote from the stator yoke. The radial thickness of the stator yoke is, for example, less than 25% of the radial thickness of the stator core, particularly 20% to 25% of the radial thickness of the stator core.

[0029] In existing electric motors, the stator yoke dimensions are typically configured to consider factors such as motor size, heat dissipation, reduction of magnetic reluctance and eddy current losses, or enhancement of mechanical strength. In this application, the stator yoke dimensions are designed in conjunction with torque cancellation to reduce the influence of permanent magnet performance on torque, thereby ensuring effective torque cancellation. This broadens the applicability of the torque cancellation effect according to the exemplary embodiments of this application.

[0030] Optionally, the radial thickness of the stator yoke is 1.55 mm or more.

[0031] According to an optional embodiment of this application, the permanent magnets of the rotor are radially magnetized, resulting in a trapezoidal, square, or saddle-shaped magnetic waveform on the rotor's surface. This facilitates the achievement of a square or trapezoidal permanent magnet torque. The permanent magnet torque can be better matched with the cogging torque to achieve a superior cancellation effect. Simultaneously, the waveform of the permanent magnet torque can be adjusted. The permanent magnet torque can be better matched with the cogging torque to achieve a superior cancellation effect.

[0032] Alternatively or additionally, when the motor is operating, the current flowing through the stator windings has a trapezoidal, square, or saddle-shaped waveform. The surface magnetic waveform of the rotor can be matched in particular with the waveform of the current flowing through the stator windings.

[0033] According to a second aspect of this application, embodiments of this application provide a household appliance, wherein the household appliance is equipped with a motor according to exemplary embodiments of this application. The household appliance optionally includes a fan, the fan including the motor and an impeller, the motor being arranged to drive the impeller to rotate. The fan and the household appliance can have low vibration noise. In particular, even when the fan is rotating at high speed, it can still have low vibration noise. This improves the user experience.

[0034] The household appliances mentioned include, for example, ovens, microwave ovens, refrigerators, air conditioners, or washing machines. Attached Figure Description

[0035] The principles, features, and advantages of this application will be better understood below with reference to the accompanying drawings. The drawings include:

[0036] Figure 1 A cross-sectional view of an electric motor according to an exemplary embodiment of this application is schematically shown;

[0037] Figure 2 The cogging torque curve and permanent magnet torque curve of an electric motor according to an exemplary embodiment of this application are schematically shown.

[0038] Figure 3 The cogging torque, permanent magnet torque, and output torque of an electric motor according to an exemplary embodiment of this application are schematically illustrated.

[0039] Figure 4 The cogging torque, permanent magnet torque, and output torque of an electric motor according to an exemplary embodiment of this application are schematically illustrated.

[0040] Figure 5 schematically shown Figure 3 and Figure 4 Comparison results of output torque in the illustrated embodiments;

[0041] Figure 6 schematically shown Figure 3 The permanent magnet torque of the motor in the illustrated embodiment;

[0042] Figure 7 The stator core of an electric motor according to an exemplary embodiment of this application is schematically shown; and

[0043] Figure 8 The rotor of an electric motor according to an exemplary embodiment of this application is schematically shown.

[0044] List of reference numerals

[0045] 1. Stator

[0046] 11 Stator Core

[0047] 111 Stator yoke part

[0048] 112 stator teeth

[0049] 113 Stator toothed shoe

[0050] 1131 First toothed boot section

[0051] 1132 Second toothed boot section

[0052] 1133 Inner arc side

[0053] 1134 Outer arc side

[0054] 114 tooth groove

[0055] 1141 First tooth groove

[0056] 1142 Second tooth groove

[0057] 12 stator windings

[0058] 2 rotors

[0059] 21 permanent magnet

[0060] 22 Rotor yoke ring

[0061] 91. Cogging torque curve

[0062] 92 Permanent Magnet Torque Curve

[0063] 93 Output Torque Curve Detailed Implementation

[0064] To make the technical problems to be solved, the technical solutions, and the beneficial technical effects of this application clearer, the application will be further described in detail below with reference to the accompanying drawings and several exemplary embodiments. It should be understood that the specific embodiments described herein are only for explaining this application and are not intended to limit the scope of protection of this application.

[0065] To better understand this application, exemplary embodiments of this application will be described below with reference to the accompanying drawings.

[0066] Figure 1 A cross-sectional view of an electric motor according to an exemplary embodiment of this application is shown schematically. Figure 2 The cogging torque curve 91 and permanent magnet torque curve 92 of an electric motor according to an exemplary embodiment of this application are schematically shown.

[0067] like Figure 1 As shown, the motor includes a stator 1 and a rotor 2. The stator 1 is fixedly arranged about the motor axis L. The stator 1 includes a stator core 11 and stator windings 12 arranged on the stator core 11. The rotor 2 is arranged to rotate about the motor axis L. The rotor 2 includes a permanent magnet 21.

[0068] The motor has a cogging torque exhibiting a first waveform and a permanent magnet torque exhibiting a second waveform. Figure 2 The diagram schematically illustrates a cogging torque curve 91 with a first waveform and a permanent magnet torque curve 92 with a second waveform. It can be seen that the phases of the first waveform and the second waveform are matched, such that the peaks and troughs of the first waveform are opposite to the troughs and peaks of the second waveform, respectively, thus the cogging torque and the permanent magnet torque can cancel each other out. Figure 2 The output torque curve 93 is also schematically shown. Since the cogging torque and the permanent magnet torque cancel each other out, the output torque curve 93 of the motor does not have obvious fluctuations.

[0069] This reduces the fluctuation of the motor's output torque and lowers the noise during motor operation. In particular, the motor can maintain small torque fluctuations and low noise throughout its entire operating range.

[0070] The motor is in particular a single-phase brushless DC motor.

[0071] Typically, both cogging torque and permanent magnet torque cause torque ripple in single-phase brushless DC motors. To address the starting dead point issue, existing single-phase brushless DC motors increase the difference between the positive and negative peaks of the cogging torque waveform. Furthermore, since a single-phase brushless DC motor has only one winding, each current commutation inevitably causes the permanent magnet torque to become zero. This results in periodic torque ripples in the output torque, which increase with the load. This is the primary reason for the large torque ripple in single-phase brushless DC motors. This torque ripple caused by the permanent magnet torque originates from the operating principle of single-phase brushless DC motors and is essentially impossible to eliminate.

[0072] However, according to this application, by matching the phases of the first and second waveforms, the cogging torque and permanent magnet torque can be mutually canceled, thereby reducing the fluctuation of the output torque. This method only adjusts the phase of the peak and valley values, without adjusting the magnitude of the peak and valley values, and does not affect the starting of the single-phase brushless DC motor. Furthermore, the motor can exhibit small torque fluctuations and low noise throughout its entire operating range.

[0073] exist Figure 1 In the illustrated embodiment, the motor is an external rotor motor, wherein the rotor 2 is arranged radially outside the stator. The rotor 2 may also include, for example, a rotor yoke 22. The rotor yoke 22 may surround the permanent magnet 21 radially outside.

[0074] According to an exemplary embodiment of this application, the motor can be used in household appliances. For example, the motor can be used in a fan of a household appliance. The fan may include the motor and an impeller, the motor being arranged to drive the impeller to rotate. The fan can be used to assist in functions such as cooling, drying, and / or ventilation. The fan and the household appliance can have low vibration noise. In particular, even when the fan is rotating at high speed, it can still have low vibration noise. This improves the user experience.

[0075] Figure 3 The cogging torque Tc, permanent magnet torque Tm, and output torque To of an electric motor according to an exemplary embodiment of this application are schematically illustrated.

[0076] Figure 3 The upper part shows the cogging torque Tc of the motor. Figure 3 The middle section shows the permanent magnet torque Tm of the motor. In this embodiment, both the first waveform of the cogging torque Tc and the second waveform of the permanent magnet torque Tm are trapezoidal waves. The peak-to-valley amplitude of the cogging torque Tc is approximately 9 mN·m. The peak-to-valley amplitude of the permanent magnet torque Tm is approximately 12 mN·m.

[0077] It can be seen that the phases of the first waveform and the second waveform are matched, so that the peaks and troughs of the first waveform are opposite to the troughs and peaks of the second waveform, respectively.

[0078] Figure 3 The lower part shows the motor's output torque To. Because the cogging torque Tc and the permanent magnet torque Tm cancel each other out, the motor's output torque To has relatively small fluctuations. For example, the peak-to-valley amplitude of the output torque To is approximately 5 mN·m. Therefore, the peak-to-valley amplitude of the output torque To can be smaller than that of the cogging torque Tc and the permanent magnet torque Tm. Furthermore, within each cycle, the output torque To remains around 10 mN·m for most of the time, with relatively short periods of fluctuation.

[0079] Figure 4The cogging torque Tc, permanent magnet torque Tm, and output torque To of an electric motor according to an exemplary embodiment of this application are schematically illustrated.

[0080] Figure 4 The upper part shows the cogging torque Tc of the motor. Figure 4 The middle section shows the permanent magnet torque Tm of the motor. In this embodiment, the first waveform of the cogging torque Tc and the second waveform of the permanent magnet torque Tm are sine waves (or approximately sine waves). The peak-to-valley amplitude of the cogging torque Tc is approximately 12 mN·m. The peak-to-valley amplitude of the permanent magnet torque Tm is approximately 16 mN·m.

[0081] It can be seen that the phases of the first waveform and the second waveform are matched, so that the peaks and troughs of the first waveform are opposite to the troughs and peaks of the second waveform, respectively.

[0082] Figure 4 The lower part of the figure shows the motor's output torque To. Because the cogging torque Tc and the permanent magnet torque Tm cancel each other out, the motor's output torque To has relatively small fluctuations. For example, the peak-to-valley amplitude of the output torque To is approximately 8 mN·m. Therefore, the peak-to-valley amplitude of the output torque To can be smaller than the peak-to-valley amplitudes of the cogging torque Tc and the permanent magnet torque Tm.

[0083] When the first and second waveforms are sine waves, by making the first and second waveforms complementary, the fluctuation of the motor's output torque To can also be reduced.

[0084] Figure 5 schematically shown Figure 3 and Figure 4 The comparison results of the output torque in the illustrated embodiments. Figure 5 The upper part schematically shows Figure 3 and Figure 4 The output torque in the illustrated embodiment varies with time. Figure 5 The lower part schematically shows Figure 3 and Figure 4 The torque fluctuation of the motor in the illustrated embodiment varies with the output torque. Figure 5 In the middle, the light-colored curve corresponds to Figure 3 In the illustrated embodiment, the dark curve corresponds to Figure 4 The example shown.

[0085] Compared to cases where both the first and second waveforms are sine waves, cases where both are trapezoidal waves can more effectively reduce fluctuations in the motor's output torque. The peak and valley amplitudes of the motor's output torque can be reduced to a greater extent. The motor's output torque can remain essentially constant for most of the cycle.

[0086] When both the first and second waveforms are trapezoidal waves, the torque fluctuation rate of the motor's output torque is relatively small.

[0087] The motor according to exemplary embodiments of this application is particularly applicable to fans, especially fans in household appliances. For example, the motor can be used in oven fans. As an example, the operating range of an oven fan motor is approximately between 3 mN·m and 12 mN·m. Exemplary embodiments of this application can reduce torque ripple throughout the entire operating range of the motor.

[0088] In an exemplary embodiment according to this application, both the first waveform and the second waveform can be square waves. This waveform configuration can achieve a better cancellation effect and also helps to effectively reduce the fluctuation of the motor's output torque.

[0089] The following is combined Figure 3 and Figure 6 Further explanation of exemplary embodiments according to this application. Figure 6 schematically shown Figure 3 The permanent magnet torque Tm of the motor in the illustrated embodiment.

[0090] In this embodiment, the second waveform of the permanent magnet torque Tm is a positive trapezoidal wave with the plateau segment at its peak. The first waveform is an inverted trapezoidal wave with the plateau segment at its trough. The plateau segment at the peak of the second waveform can be opposite to the plateau segment at the trough of the first waveform. This achieves a better cancellation effect, and the output torque can correspondingly have a smooth plateau segment.

[0091] like Figure 6 As shown, the second waveform includes a plateau segment, a rising segment, and a falling segment in each of its cycles. The plateau segment of the second waveform accounts for more than 80%. Correspondingly, the falling segment and the rising segment can together account for less than 20%. This helps to achieve a more stable output torque. For example, the plateau segment can correspond to a 150° rotation angle, and the rising segment and the falling segment can together correspond to a 30° rotation angle.

[0092] The torque variation in the plateau section of the second waveform is particularly low, below 20% of the torque variation over the entire cycle of the second waveform. For example, the torque variation over the entire cycle of the second waveform is approximately 12 mN·m, while the torque variation in the plateau section is approximately 1.7 mN·m. Within the plateau section of the second waveform, the permanent magnet torque Tm remains approximately constant. This also contributes to improved cancellation effectiveness.

[0093] Similarly, see, for example Figure 3 The first waveform can include plateau segments, rising segments, and falling segments in each of its cycles. The plateau segment accounts for more than 80% of the first waveform.

[0094] The torque variation in the plateau section of the first waveform can be less than 20% of the torque variation in the entire cycle of the first waveform.

[0095] A particularly advantageous aspect is that the plateau section of the first waveform is opposite to the plateau section of the second waveform. Consequently, the motor's output torque can also have a longer, smoother plateau section.

[0096] Figure 7 A cross-section of the stator core 11 of an electric motor according to an exemplary embodiment of this application is schematically shown. This stator core 11 can be used, for example, in... Figure 1 The motor shown.

[0097] like Figure 7 As shown, the stator core 11 includes a stator yoke 111, stator teeth 112 extending radially from the stator yoke 111, and stator tooth shoes 113 located at the ends of the stator teeth 112 away from the stator yoke 111. The stator tooth shoes 113 include a first tooth shoe portion 1131 extending from the stator teeth 112 in a first circumferential direction in the same direction as the rotation direction Dr of the rotor 2, and a second tooth shoe portion 1132 extending in a second circumferential direction opposite to the first circumferential direction. The first tooth shoe portion 1131 spans a first angle α1 in the circumferential direction greater than the second angle α2 spanned by the second tooth shoe portion 1132 in the circumferential direction, such that the peak of the first waveform and the trough of the second waveform are opposite. Therefore, the phase of the cogging torque Tc can be adjusted through the specific structure of the stator core 11 to achieve mutual cancellation between the cogging torque Tc and the permanent magnet torque Tm.

[0098] Optionally, the first angle α1 is 2% to 6% larger than the second angle α2. This helps to achieve the desired peak phase of the cogging torque Tc, so that the peak of the cogging torque Tc can be more accurately aligned with the trough of the permanent magnet torque Tm.

[0099] A tooth groove 114 is formed between adjacent stator tooth shoes 113 in the circumferential direction. A dividing line centrally located between adjacent stator teeth 112 in the circumferential direction divides the tooth groove 114 into a first tooth groove portion 1141 closer to the first tooth shoe portion 1131 and a second tooth groove portion 1142 closer to the second tooth shoe portion 1132. It should be understood that this dividing line is a virtual straight line extending in the radial direction. The angle spanned by the first tooth groove portion 1141 in the circumferential direction is, for example, less than 60%, and particularly less than 50%, of the angle spanned by the second tooth groove portion 1142 in the circumferential direction. This helps to more accurately align the peak of the cogging torque Tc with the trough of the permanent magnet torque Tm.

[0100] For example, the first toothed portion 1141 spans a distance of 0.5 mm in the circumferential direction, and the second toothed portion 1142 spans a distance of 1.0 mm in the circumferential direction.

[0101] According to an exemplary embodiment of this application, the stator gear shoe 113 may have an inner arc side 1133 facing the motor axis L. The center O1 of the inner arc side 1133 may be offset by a first eccentric distance relative to the motor axis L along a first offset direction, the first offset direction being a direction away from the stator gear shoe 113 from the motor axis L. This helps to prevent torque drop in the plateau section of the permanent magnet torque. The permanent magnet torque can have a more stable plateau section. See, for example, [example missing]. Figure 6 In the middle of the plateau section of the permanent magnet torque, only minor fluctuations exist. This helps to achieve the desired waveform of the permanent magnet torque, thereby obtaining a better cancellation effect.

[0102] Optionally, the first eccentricity is 20% to 40% of the stator radius. For example, the first eccentricity is more than 30% of the stator radius.

[0103] Alternatively or additionally, the first eccentricity distance is between 3 mm and 7 mm, particularly 5.0 mm.

[0104] According to an exemplary embodiment of this application, the stator gear shoe 113 may have an outer arc side 1134 facing away from the motor axis L. The center O2 of the outer arc side 1134 may be offset by a second eccentric distance relative to the motor axis L along a second offset direction. The second offset direction is a direction offset by 90° relative to the direction from the motor axis L toward the stator gear shoe 113 along the rotation direction Dr of the rotor 2. This allows adjustment of the waveform and peak value of the cogging torque, making the cogging torque more suitable for canceling out the permanent magnet torque.

[0105] Optionally, the second eccentricity is 1% to 2.5% of the stator radius. Alternatively or additionally, the second eccentricity is between 0.25 mm and 0.4 mm, particularly 0.37 mm. This helps to achieve a better offsetting effect.

[0106] The rotor 2 can surround the stator 1 radially outside the stator 1, such that an air gap is formed between the outer arc side 1134 of the stator tooth shoe 113 and the rotor 2. The aforementioned offset of the center of the outer arc side 1134 can change the shape of the air gap.

[0107] According to an exemplary embodiment of this application, the radial thickness T1 of the stator yoke 111 is less than 25% of the radial thickness T2 of the stator core 11. In conventional motors, the dimensional configuration of the stator yoke 111 typically takes into account factors such as motor size, heat dissipation, reduction of magnetic reluctance and eddy current losses, or enhancement of mechanical strength. In this application, the dimensional design of the stator yoke 111 is combined with torque cancellation, with the aim of reducing the influence of the performance of the permanent magnet 21 on the amplitude, so as to ensure the effectiveness of torque cancellation.

[0108] Optionally, the radial thickness T1 of the stator yoke 111 is 20% to 25% of the radial thickness T2 of the stator core 11.

[0109] Optionally, the radial thickness T1 of the stator yoke 111 is 1.55 mm or more.

[0110] This allows the magnetic field of the stator yoke 111 to be in a relatively saturated state. This helps to reduce the influence of the permanent magnet performance on the air gap magnetic field, making the air gap magnetic field more stable and the torque output more stable.

[0111] Figure 8 The rotor 2 of an electric motor according to an exemplary embodiment of this application is schematically shown. This rotor 2 can be used, for example, in... Figure 1 The motor shown.

[0112] The rotor 2 may include a permanent magnet 21 and a rotor yoke 22. The rotor yoke 22 may surround the permanent magnet 21 radially outward. The permanent magnet 21 may be made of, for example, a rubber magnetic strip.

[0113] The permanent magnet 21 of rotor 2 can be radially magnetized, so that the surface magnetic waveform of rotor 2 is a square wave, trapezoidal wave, or saddle wave, such as... Figure 8 As shown on the right side. This helps to achieve a permanent magnet torque that is square or trapezoidal in shape. Simultaneously, the waveform of the permanent magnet torque can be adjusted. The permanent magnet torque can be better matched with the cogging torque to achieve a better cancellation effect. In particular, when the surface magnetic waveform of rotor 2 is a saddle wave, the motor achieves good performance, balancing high efficiency and low noise.

[0114] When the motor is operating, the current flowing through the stator winding 12 can have a square wave, trapezoidal wave, or saddle wave waveform. This also helps to achieve a permanent magnet torque that is square or trapezoidal. The surface magnetic waveform of the rotor 2 can be matched with the waveform of the current flowing through the stator winding 12.

[0115] Although specific embodiments have been described above, these embodiments are not intended to limit the scope of this application, even when only a single embodiment is described with respect to a particular feature. The feature examples provided in this application are intended to be illustrative and not limiting, unless otherwise stated. In practice, multiple features may be combined with each other as needed and where technically feasible. In particular, features from different embodiments may also be combined with each other. Various substitutions, modifications, and alterations are conceived without departing from the spirit and scope of this application.

Claims

1. An electric machine, wherein, The motor includes: A stator (1), which is fixedly arranged around the motor axis, and includes a stator core (11) and stator windings (12) arranged on the stator core (11); and The rotor (2) is arranged to rotate about the motor axis and includes a permanent magnet (21). The motor has a cogging torque in the form of a first waveform and a permanent magnet torque in the form of a second waveform. The phases of the first waveform and the second waveform are matched, so that the peaks and troughs of the first waveform are opposite to the troughs and peaks of the second waveform, respectively, thereby the cogging torque and the permanent magnet torque can cancel each other out.

2. The motor according to claim 1, wherein, Both the first and second waveforms are trapezoidal waves; and / or Both the first and second waveforms are square waves.

3. The motor according to claim 1 or 2, wherein, The first waveform includes plateau, rising, and falling segments in each period, with the plateau segment accounting for more than 80% of the first waveform; and / or The second waveform includes a plateau segment, a rising segment, and a falling segment in each of its cycles, with the plateau segment accounting for more than 80% of the second waveform.

4. The motor according to claim 3, wherein, The first waveform is an inverted trapezoidal wave located at the trough of the plateau segment; and / or The second waveform is a positive trapezoidal wave at the crest of the plateau section; and / or The torque variation in the plateau section of the first waveform is less than 20% of the torque variation over the entire cycle of the first waveform; and / or The torque variation in the plateau section of the second waveform is less than 20% of the torque variation over the entire cycle of the second waveform.

5. The motor according to any one of claims 1-4, wherein, The stator core (11) includes a stator yoke (111), stator teeth (112) extending radially from the stator yoke (111), and stator tooth shoes (113) located at the ends of the stator teeth (112) away from the stator yoke (111). The stator tooth shoes (113) include a first tooth shoe portion (1131) extending from the stator teeth (112) in a first circumferential direction in the same direction as the rotation direction of the rotor (2) and a second tooth shoe portion (1132) extending in a second circumferential direction opposite to the first circumferential direction. The first tooth shoe portion (1131) spans a first angle in the circumferential direction greater than the second angle spanned by the second tooth shoe portion (1132) in the circumferential direction, such that the crest of the first waveform is opposite to the trough of the second waveform.

6. The motor according to claim 5, wherein, The first angle is 2% to 6% larger than the second angle; and / or A tooth groove (114) is formed between adjacent stator tooth shoes (113) in the circumferential direction. The dividing line located in the middle between adjacent stator teeth (112) in the circumferential direction divides the tooth groove (114) into a first tooth groove portion (1141) closer to the first tooth shoe portion (1131) and a second tooth groove portion (1142) closer to the second tooth shoe portion (1132). The angle spanned by the first tooth groove portion (1141) in the circumferential direction is less than 60%, and in particular less than 50%, of the angle spanned by the second tooth groove portion (1142) in the circumferential direction.

7. The motor according to any one of claims 1-6, wherein, The stator core (11) includes a stator yoke (111), stator teeth (112) extending radially from the stator yoke (111), and a stator tooth shoe (113) located at the end of the stator teeth (112) away from the stator yoke (111). The stator tooth shoe (113) has an inner arc side (1133) facing the motor axis. The center of the inner arc side (1133) is offset by a first eccentric distance relative to the motor axis in a first offset direction, which is the direction away from the stator tooth shoe (113) from the motor axis.

8. The motor according to claim 7, wherein, The first eccentricity is 20% to 40% of the stator radius, or more than 30% of the stator radius; and / or The first eccentricity is between 3 mm and 7 mm, and in particular 5.0 mm.

9. The motor according to any one of claims 1-8, wherein, The stator core (11) includes a stator yoke (111), stator teeth (112) extending radially from the stator yoke (111), and a stator tooth shoe (113) located at the end of the stator teeth (112) away from the stator yoke (111). The stator tooth shoe (113) has an outer arc side (1134) facing away from the motor axis. The center of the outer arc side (1134) is offset by a second eccentric distance relative to the motor axis in a second offset direction. The second offset direction is a direction that is offset by 90° relative to the direction from the motor axis toward the stator tooth shoe (113) in the rotation direction of the rotor (2).

10. The motor according to claim 9, wherein, The second eccentricity is 1% to 2.5% of the stator radius; and / or The second eccentricity is between 0.25 mm and 0.4 mm, and in particular 0.37 mm.

11. The motor according to claim 9 or 10, wherein, The rotor (2) surrounds the stator (1) radially outside the stator (1), such that an air gap is formed between the outer arc side (1134) of the stator tooth shoe (113) and the rotor (2).

12. The motor according to any one of claims 1-11, wherein, The stator core (11) includes a stator yoke (111), stator teeth (112) extending radially from the stator yoke (111), and stator tooth shoes (113) located at the ends of the stator teeth (112) away from the stator yoke (111), wherein, The radial thickness of the stator yoke (111) is less than 25% of the radial thickness of the stator core (11), particularly 20% to 25% of the radial thickness of the stator core (11); and / or The radial thickness of the stator yoke (111) is greater than 1.55 mm.

13. The motor according to any one of claims 1-12, wherein, The permanent magnet (21) of the rotor (2) is radially magnetized, so that the surface magnetic waveform of the rotor (2) is a trapezoidal wave, a square wave, or a saddle wave; and / or When the motor is working, the current flowing through the stator winding (12) has a trapezoidal waveform, a square wave waveform, or a saddle wave waveform.

14. The motor according to any one of claims 1-13, wherein, The motor is a single-phase brushless DC motor.

15. A household appliance, wherein, The household appliance is provided with a motor according to any one of claims 1-14, wherein the household appliance optionally includes a fan, the fan including the motor and an impeller, the motor being arranged to drive the impeller to rotate.

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