Low-noise position-sensorless electric motor for small household appliances

Abstract

The present invention relates to the technical field of electric motors, and particularly relates to a low-noise position-sensorless electric motor for small household appliances. The electric motor comprises a stator assembly and a rotor assembly arranged inside a stator, wherein the electric motor is an 8-pole 12-slot electric motor; the stator assembly comprises a stator core, with the outer diameter of the stator core being 70-150 mm, and the ratio of the inner diameter to the outer diameter of the stator core being 0.5-0.7; the rotor assembly comprises a rotor core and rotor permanent magnets; the surface of a d-axis of the rotor core comprises at least one eccentric arc segment; and the rotor permanent magnets are embedded in the rotor core. By means of the above technical solution, the present invention has the advantages of reducing noise, lowering costs by eliminating the need for a position sensor, and improving the reliability of the electric motor.

Description

Low-noise position sensorless motor for small household appliances TECHNICAL FIELD

[0001] The present application relates to a motor, in particular to a low-noise position sensorless motor for small household appliances. BACKGROUND

[0002] In the field of small household appliances, such as a blender, a coffee machine, etc., the driving motor thereof needs to have a wide speed range operation capability, that is, the motor has a maximum torque output at a low speed of about 500 rpm (revolutions per minute), and the motor can also operate at a speed of about 20000 rpm and has a constant power output.

[0003] However, a conventional three-phase six-step method for generating a square wave current to drive a direct current permanent magnet brushless motor is difficult to meet this requirement, so a permanent magnet synchronous motor driven by a sinusoidal wave current generated by space vector control is needed, which can operate according to the maximum torque at low speed and can also operate at high speed by using a field weakening method. Since such small household appliances are usually applied in situations in contact with people, low noise is one of the important indicators of their performance evaluation, and in particular, high-frequency screeching cannot be generated during operation to avoid adverse effects on user experience and physical and mental health.

[0004] In addition, in order to realize stable operation at low speed and large torque, a position sensor is usually used to collect the rotor position signal in real time to drive the normal operation of the motor in conventional small household appliances. The commonly used position sensors include Hall devices and rotary encoders, which not only increase the cost of the motor, but also are easy to damage and fail, thereby reducing the reliability of the motor.

[0005] Therefore, the position sensorless control method, especially high-frequency injection, has become an urgent development direction for such motor driving methods. SUMMARY

[0006] In order to solve the problems in the related art, the present application provides a low-noise position sensorless motor for small household appliances, which solves the problems of large noise of the motor and easy damage and failure of the position sensor installed on the motor, thereby increasing the cost and reducing the reliability of the motor.

[0007] The technical scheme is as follows:

[0008] A low-noise, sensorless motor for small household appliances includes a stator assembly and a rotor assembly disposed within the stator assembly; characterized in that the motor is an eight-pole, twelve-slot motor; the stator assembly includes a stator core with an outer diameter of 70mm-150mm and an inner diameter-to-outer diameter ratio of 0.5-0.7; the rotor assembly includes a rotor core and a rotor permanent magnet; the d-axis surface of the rotor core includes at least one eccentric arc; the rotor permanent magnet is embedded within the rotor core.

[0009] Through the above technical solution, by coordinating the eight-stage twelve-slot configuration in the motor, the harmonic number of radial electromagnetic force waves in the air gap of the motor can be significantly reduced, thereby greatly reducing motor noise, especially high-frequency howling. By controlling the ratio of the inner diameter to the outer diameter of the stator core between 0.5 and 0.7, that is, controlling the stator split ratio between 0.5 and 0.7, the optimal electromagnetic output performance of the motor can be guaranteed during use.

[0010] By ensuring that the d-axis surface of the rotor core includes at least one eccentric arc, it is possible to guarantee that the motor's back electromotive force is sinusoidal and its total harmonic content is less than 5%, and to reduce the cogging torque, thereby reducing the motor's torque fluctuation and thus reducing the motor's vibration and noise.

[0011] Preferably, eight rotor permanent magnets are evenly arranged along the circumference of the rotor core; twelve teeth are evenly arranged along the circumference of the stator core.

[0012] Preferably, the d-axis surface of the rotor core includes eight eccentric arcs, the central axis of the eight eccentric arcs is equidistant from the center of the rotor assembly, the eight eccentric arcs are arranged sequentially along the circumference of the rotor core, and there is a connecting segment between adjacent eccentric arcs; the rotor permanent magnets and the eccentric arcs are arranged in a one-to-one correspondence.

[0013] Through the above technical solution, the motor is a sensorless motor, and the saliency ratio of the motor is greater than or equal to 1.2.

[0014] By embedding the rotor permanent magnets within the rotor core and ensuring the motor's saliency ratio is greater than or equal to 1.2 (i.e., the ratio of q-axis inductance to d-axis inductance is greater than or equal to 1.2), the motor can be controlled using a high-frequency injection sensorless control method. This eliminates the need for a position sensor within the motor, thereby reducing investment costs and improving reliability.

[0015] Preferably, coil windings are respectively wound around the outer periphery of the twelve teeth.

[0016] Preferably, each of the eight rotor permanent magnets includes two magnets, and the two magnets of each rotor permanent magnet are symmetrically distributed along the central axis of the corresponding eccentric arc, and the included angle between the two magnets of each rotor permanent magnet is greater than 90°.

[0017] By using the above technical solution, and by arranging two magnets on each of the eight rotor permanent magnets in a V-shape, the saliency ratio of the motor can reach 1.33. This allows the motor to meet the saliency ratio requirements of the high-frequency injection algorithm, thereby eliminating the need to install position sensors inside the motor and enabling control of the motor through the high-frequency injection algorithm. This reduces the production cost of the motor and improves its reliability.

[0018] Preferably, each of the eight rotor permanent magnets comprises a single magnet, and the width direction of the single magnet of each rotor permanent magnet is symmetrically distributed along the central axis of the corresponding eccentric arc.

[0019] By using the above technical solution, and by setting single magnets in the eight rotor permanent magnet bodies in a straight line arrangement, the saliency ratio of the motor can reach 1.29. Therefore, the motor can meet the requirements of the high-frequency injection algorithm for the motor saliency ratio, thereby realizing the control of the motor by the high-frequency injection algorithm without installing position sensors in the motor, thus reducing the production cost of the motor and improving the reliability of the motor.

[0020] Preferably, the surface of the rotor core is fitted with a non-conductive and non-magnetic sheath.

[0021] By using a non-conductive and non-magnetic material to make the sheath and securing it to the outer surface of the rotor core, centrifugal force can be prevented from damaging the rotor during high-speed rotation. The non-conductive sheath also reduces eddy current losses, decreases rotor heating, and improves motor performance, thereby enhancing motor reliability and extending its lifespan. Furthermore, when the motor operates at 20,000 rpm, its losses are reduced by approximately 130W compared to a motor with a conductive sheath, further contributing to extended lifespan, improved reliability and stability, and reduced operating costs.

[0022] In summary, the beneficial effects of a low-noise sensorless motor for small household appliances are as follows: by using an eight-stage, twelve-slot configuration in the motor, the harmonic order of the radial electromagnetic force wave in the air gap of the motor can be significantly reduced, thereby greatly reducing motor noise, especially high-frequency howling; by controlling the ratio of the inner diameter to the outer diameter of the stator core between 0.5 and 0.7, i.e., controlling the stator split ratio between 0.5 and 0.7, the optimal electromagnetic output performance of the motor can be guaranteed during use.

[0023] By ensuring that the d-axis surface of the rotor core includes at least one eccentric arc, it is possible to guarantee that the motor's back electromotive force is sinusoidal and its total harmonic content is less than 5%, and to reduce the cogging torque, thereby reducing the motor's torque fluctuation and thus reducing the motor's vibration and noise.

[0024] By embedding the rotor permanent magnets into the rotor core and ensuring that the motor saliency ratio is greater than or equal to 1.2 (i.e., the ratio of q-axis inductance to d-axis inductance is greater than or equal to 1.2), the motor can be controlled using a high-frequency injection sensorless control method. This eliminates the need to control the motor by installing a position sensor inside the motor, thereby reducing the cost of motor investment and improving the reliability of the motor.

[0025] By using a non-conductive and non-magnetic material to make the sheath and securing it to the outer surface of the rotor core, centrifugal force can be prevented from damaging the rotor during high-speed rotation. The non-conductive sheath also reduces eddy current losses, decreases rotor heating, and improves motor performance, thereby enhancing motor reliability and extending its lifespan. Furthermore, when the motor operates at 20,000 rpm, its losses are reduced by approximately 130W compared to a motor with a conductive sheath, further contributing to extended lifespan, improved reliability and stability, and reduced operating costs.

[0026] It should be understood that the above general description and the following detailed description are merely exemplary and do not limit the invention. Attached Figure Description

[0027] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0028] Figure 1 is a schematic diagram of the structure of the present invention;

[0029] Figure 2 is a schematic diagram of the exploded structure of the present invention;

[0030] Figure 3 is a top view of the stator core in this invention;

[0031] Figure 4 is a schematic diagram of the installation of the permanent magnet in Embodiment 1 of the present invention;

[0032] Figure 5 is a schematic diagram of the installation of the permanent magnet in Embodiment 2 of the present invention;

[0033] Figure 6 is a top view of the rotor core in this invention;

[0034] Figure 7 is a comparison table of radial stress for different pole slot numbers of the motor in this invention;

[0035] Figure 8 is a comparison table of back electromotive force between the eccentric arc rotor and the full circular rotor in this invention;

[0036] Figure 9 is a comparison table of harmonic orders between the eccentric arc rotor and the full circular rotor in this invention;

[0037] Figure 10 is a comparison table of cogging torque between the eccentric arc rotor and the full circular rotor in this invention;

[0038] In the diagram, 1. Rotor core; 2. Rotor permanent magnet; 3. Stator core; 4. Coil winding; 5. Sheath; 6. Rotor shaft; 7. Stator front end plate; 8. Stator rear end plate; 9. Motor front bearing; 10. Motor rear bearing; 11. Motor front end cover; 12. Motor rear end cover; 13. Motor housing. Detailed Implementation

[0039] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of apparatuses and methods consistent with some aspects of the invention as detailed in the appended claims.

[0040] Example 1: As shown in Figures 1-4 and 6-10, a low-noise sensorless motor for small household appliances is provided. The motor's drive current is a sinusoidal current, and it includes a stator assembly and a rotor assembly disposed within the stator assembly.

[0041] The motor is an eight-pole, twelve-slot motor. Eight rotor permanent magnets 2 are arranged sequentially along the circumference of the rotor core 1, and twelve teeth are evenly arranged along the circumference of the stator core 3. The radial force wave harmonic order of the eight-pole, twelve-slot electromagnetic structure is a multiple of 4, far less than the multiple of 2 of the ten-pole, twelve-slot, or fourteen-pole, twelve-slot electromagnetic structures. Therefore, the eight-pole, twelve-slot electromagnetic structure can significantly reduce the harmonic order of the motor's radial force wave, thereby reducing motor noise, especially high-frequency howling.

[0042] The stator assembly includes a stator core 3, with coil windings 4 wound around the outer periphery of twelve teeth respectively. The ratio of the inner diameter to the outer diameter of the stator core 3 is 0.5-0.7, that is, the stator split ratio is controlled between 0.5 and 0.7, which can ensure that the motor is in optimal electromagnetic output performance during use. If the stator split ratio is greater than 0.7, the stator winding slot space is too small, the stator winding wire diameter is too thin and the internal resistance is too large, which will cause the motor to have excessive copper loss and low efficiency. If the stator split ratio is less than 0.5, the rotor outer diameter is too small, the motor torque is too small and the output is insufficient. The outer diameter of the stator core 3 is 70mm-150mm, and the rated input power is 100W-3500W. A stator front end plate 7 and a stator rear end plate 8 are respectively provided at both ends of the axis of the stator core 3.

[0043] The rotor assembly includes a rotor core 1 and a rotor permanent magnet 2. The rotor permanent magnet 2 is embedded in the rotor core 1. The motor is a sensorless motor, and the saliency ratio of the motor is greater than or equal to 1.2. By embedding the rotor permanent magnet 2 in the rotor core 1 and ensuring that the motor saliency ratio is greater than or equal to 1.2 (i.e., the ratio of q-axis inductance to d-axis inductance is greater than or equal to 1.2), the motor can be controlled using a high-frequency injection sensorless control method. This eliminates the need to control the motor by installing a position sensor inside the motor, thereby reducing the motor's investment cost and improving its reliability.

[0044] The d-axis surface of the rotor core 1 includes at least one eccentric arc, which ensures that the motor back electromotive force is sinusoidal and its total harmonic content is less than 5%, and reduces the cogging torque, thereby reducing the motor torque fluctuation and thus reducing the motor vibration noise.

[0045] In this embodiment, as shown in Figure 6, the d-axis surface of the rotor core 1 includes eight eccentric arcs, that is, the rotor d-axis is composed of eight eccentric arcs with an eccentricity of L1 and a radius of R1; the central axis of the eight eccentric arcs is at the same distance from the center of the rotor assembly, and the eight eccentric arcs are arranged sequentially along the circumference of the rotor core 1, with connecting segments between adjacent eccentric arcs; the rotor permanent magnet 2 and the eccentric arcs are arranged in a one-to-one correspondence.

[0046] Each of the eight rotor permanent magnets 2 includes two magnets. The two magnets of each rotor permanent magnet 2 are symmetrically distributed along the central axis of the corresponding eccentric arc, and the included angle between the two magnets of each rotor permanent magnet 2 is greater than 90°. By having each of the eight rotor permanent magnets 2 include two magnets, and the two magnets are arranged in a V-shape, the saliency ratio of the motor can reach 1.33. Therefore, the motor can meet the saliency ratio requirements of the high-frequency injection algorithm, thereby realizing the control of the motor by the high-frequency injection algorithm without installing a position sensor inside the motor, thus reducing the production cost of the motor and improving the reliability of the motor.

[0047] The outer surface of the rotor core 1 is fitted with a non-conductive and non-magnetic sheath 5. The material of the non-conductive and non-magnetic sheath 5 is such as carbon fiber or glass fiber. After the sheath 5 is made of a non-conductive and non-magnetic material and is fastened to the outer surface of the rotor core 1, the non-conductive nature of the sheath 5 can prevent centrifugal force from damaging the rotor when the rotor rotates at high speed. The non-conductivity of the sheath 5 can reduce the eddy current loss of the sheath 5, reduce rotor heating, improve motor performance, thereby improving the reliability of the motor and extending its service life. In addition, when the motor runs at 20,000 rpm, the motor loss is reduced by about 130W compared to the motor using a conductive sheath 5, which helps to extend the service life of the motor, thereby improving the reliability and stability of the motor and reducing the operating cost of the motor.

[0048] A rotor shaft 6 is provided along the central axis of the rotor core 1. The device also includes a motor housing 13, a front motor cover 11 and a rear motor cover 12 which are adapted to be provided at both ends of the motor housing 13. The front motor cover 11 and the rear motor cover 12 are respectively provided with a front motor bearing 9 and a rear motor bearing 10 arranged in the direction of rotation. The front motor bearing 9 and the rear motor bearing 10 are respectively sleeved on the rotor shaft 6. The stator is adapted to be provided in the motor housing 13 between the front motor bearing 9 and the rear motor bearing 10.

[0049] Example 2: As shown in Figures 1-3 and 5-10, a low-noise sensorless motor for small household appliances is provided. The motor's drive current is a sinusoidal current, and it includes a stator assembly and a rotor assembly disposed within the stator assembly.

[0050] The motor is an eight-pole, twelve-slot motor. Eight rotor permanent magnets 2 are arranged sequentially along the circumference of the rotor core 1, and twelve teeth are evenly arranged along the circumference of the stator core 3. The radial force wave harmonic order of the eight-pole, twelve-slot electromagnetic structure is a multiple of 4, far less than the multiple of 2 of the ten-pole, twelve-slot, or fourteen-pole, twelve-slot electromagnetic structures. Therefore, the eight-pole, twelve-slot electromagnetic structure can significantly reduce the harmonic order of the motor's radial force wave, thereby reducing motor noise, especially high-frequency howling.

[0051] The stator assembly includes a stator core 3 and coil windings 4 wound on the stator core 3. The ratio of the inner diameter to the outer diameter of the stator core 3 is 0.5-0.7, that is, the stator ratio is controlled between 0.5 and 0.7, which ensures that the motor is in optimal electromagnetic output performance during use. If the stator ratio is greater than 0.7, the stator winding slot space is too small, the stator winding wire diameter is too thin and the internal resistance is too large, which will cause the motor to have excessive copper loss and low efficiency. If the stator ratio is less than 0.5, the rotor outer diameter is too small, the motor torque is too small and the output is insufficient. The outer diameter of the stator core 3 is 70mm-150mm, and the rated input power is 100W-3500W. The stator front end plate 7 and the stator rear end plate 8 are respectively provided at both ends of the axis of the stator core 3.

[0052] The rotor assembly includes a rotor core 1 and a rotor permanent magnet 2. The rotor permanent magnet 2 is embedded in the rotor core 1, and the saliency ratio of the motor is greater than or equal to 1.2. By embedding the rotor permanent magnet 2 in the rotor core 1, the motor is a sensorless motor, and the motor saliency ratio is greater than or equal to 1.2, that is, the ratio of q-axis inductance to d-axis inductance is greater than or equal to 1.2. This allows the motor to be controlled using a high-frequency injection sensorless control method, thus eliminating the need to control the motor by setting a position sensor in the motor. This reduces the cost of motor investment and improves the reliability of the motor.

[0053] The d-axis surface of the rotor core 1 includes at least one eccentric arc, which ensures that the motor back electromotive force is sinusoidal and its total harmonic content is less than 5%, and reduces the cogging torque, thereby reducing the motor torque fluctuation and thus reducing the motor vibration noise.

[0054] In this embodiment, as shown in Figure 6, the d-axis surface of the rotor core 1 includes eight eccentric arcs, that is, the rotor d-axis is composed of eight eccentric arcs with an eccentricity of L1 and a radius of R1; the central axis of the eight eccentric arcs is at the same distance from the center of the rotor assembly, and the eight eccentric arcs are arranged sequentially along the circumference of the rotor core 1, with connecting segments between adjacent eccentric arcs; the rotor permanent magnet 2 and the eccentric arcs are arranged in a one-to-one correspondence.

[0055] Each of the eight rotor permanent magnets 2 comprises a single magnet, and the width direction of each single magnet in the rotor permanent magnet 2 is symmetrically distributed along the central axis of the corresponding eccentric arc. By having each of the eight rotor permanent magnets comprise a single magnet, and each single magnet is arranged in a straight line, the saliency ratio of the motor can reach 1.29. Therefore, the motor can meet the saliency ratio requirements of the high-frequency injection algorithm, thereby eliminating the need to install a position sensor inside the motor and enabling control of the motor through the high-frequency injection algorithm. This reduces the production cost of the motor and improves its reliability.

[0056] The outer surface of the rotor core 1 is fitted with a non-conductive and non-magnetic sheath 5. The material of the non-conductive and non-magnetic sheath 5 is such as carbon fiber or glass fiber. After the sheath 5 is made of a non-conductive and non-magnetic material and is fastened to the outer surface of the rotor core 1, the non-conductive nature of the sheath 5 can prevent centrifugal force from damaging the rotor when the rotor rotates at high speed. The non-conductivity of the sheath 5 can reduce the eddy current loss of the sheath 5, reduce rotor heating, improve motor performance, thereby improving the reliability of the motor and extending its service life. In addition, when the motor runs at 20,000 rpm, the motor loss is reduced by about 130W compared to the motor using a conductive sheath 5, which helps to extend the service life of the motor, thereby improving the reliability and stability of the motor and reducing the operating cost of the motor.

[0057] A rotor shaft 6 is provided along the central axis of the rotor core 1. The device also includes a motor housing 13, a front motor cover 11 and a rear motor cover 12 which are adapted to be provided at both ends of the motor housing 13. The front motor cover 11 and the rear motor cover 12 are respectively provided with a front motor bearing 9 and a rear motor bearing 10 arranged in the direction of rotation. The front motor bearing 9 and the rear motor bearing 10 are respectively sleeved on the rotor shaft 6. The stator is adapted to be provided in the motor housing 13 between the front motor bearing 9 and the rear motor bearing 10.

[0058] Operating principle: After assembling the stator and rotor into a motor, the permanent magnets in the rotor are embedded, and the saliency ratio of the motor is greater than or equal to 1.2, which allows the motor to be controlled by a high-frequency injection sensorless control method, thereby reducing costs and improving reliability. In addition, the motor's eight poles and twelve slots and the non-circular design of the rotor's outer surface can greatly reduce the motor's noise.

[0059] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention herein. This application is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not invented by the invention. The specification and examples are to be considered exemplary only, and the true scope and spirit of the invention are indicated by the appended claims.

[0060] It should be understood that the present invention is not limited to the structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A low-noise, sensorless motor for small household appliances, comprising a stator assembly and a rotor assembly disposed within the stator assembly; characterized in that, The motor is an eight-pole twelve-slot motor; the stator assembly includes a stator core with an outer diameter of 70mm-150mm and an inner diameter-to-outer diameter ratio of 0.5-0.7; the rotor assembly includes a rotor core and a rotor permanent magnet; the d-axis surface of the rotor core includes at least one eccentric arc; the rotor permanent magnet is embedded in the rotor core.

2. The low-noise sensorless motor for small household appliances according to claim 1, characterized in that, Eight rotor permanent magnets are evenly arranged along the circumference of the rotor core; twelve teeth are evenly arranged along the circumference of the stator core.

3. A low-noise, sensorless motor for small household appliances according to claim 2, characterized in that, The d-axis surface of the rotor core includes eight eccentric arcs. The central axis of each of the eight eccentric arcs is equidistant from the center of the rotor assembly. The eight eccentric arcs are arranged sequentially along the circumference of the rotor core, with connecting segments between adjacent eccentric arcs. The rotor permanent magnets and the eccentric arcs are arranged in a one-to-one correspondence.

4. A low-noise, sensorless motor for small household appliances according to claim 1, characterized in that, The motor is a sensorless motor, and the saliency ratio of the motor is greater than or equal to 1.

2.

5. A low-noise, sensorless motor for small household appliances according to claim 3, characterized in that, Each of the eight rotor permanent magnets includes two magnets. The two magnets of each rotor permanent magnet are symmetrically distributed along the central axis of the corresponding eccentric arc, and the included angle between the two magnets of each rotor permanent magnet is greater than 90°.

6. A low-noise, sensorless motor for small household appliances according to claim 3, characterized in that, Each of the eight rotor permanent magnets comprises a single magnet, and the width direction of the single magnet of each rotor permanent magnet is symmetrically distributed along the central axis of the corresponding eccentric arc.

7. A low-noise, sensorless motor for small household appliances according to claim 2, characterized in that, Coil windings are respectively wound around the outer periphery of the twelve teeth.

8. A low-noise, sensorless motor for small household appliances according to claim 1, characterized in that, The surface of the rotor core is fitted with a non-conductive and non-magnetic sheath.

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