Miniature direct current motor

Abstract

The invention provides a miniature direct current motor. The miniature direct current motor comprises a stator shell and a rotor core, the stator shell is provided with an inner cavity of a polygonal structure, a circle of continuous or discontinuous permanent magnets are arranged on the cavity wall of the inner cavity, and the permanent magnets form a plurality of pairs of magnetic poles which are alternately distributed in the circumferential direction of the inner cavity. The rotor core is arranged in the inner cavity and rotationally connected with the stator shell, the rotor core is provided with a plurality of winding parts, each winding part is wound with a coil, the end part, facing the permanent magnet, of each winding part forms an arc surface, and the arc surfaces are concyclic and concentric with the rotor core; an air gap is formed between each arc surface and the permanent magnet, and the size, corresponding to each magnetic pole, of each air gap is gradually increased from the middle area of the magnetic pole to the boundary areas on the two sides of the magnetic pole. According to the micro direct current motor provided by the invention, the cogging torque of the motor can be improved, the low-voltage starting capability and the low-speed operation stability of the motor are improved, and the noise and vibration of the motor can be reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of micro motors, and in particular relates to a micro DC motor. Background Art

[0002] At present, with the rapid development of electronic equipment, the application of micro DC motors is becoming more and more extensive, and the market's requirements for motor performance are also constantly increasing. The micro DC motor is mainly composed of a stator permanent magnet and a rotor core wrapped with a DC coil. When the DC coil continuously passes alternating current, a corresponding alternating magnetic field is formed on each pole of the rotor core. The alternating magnetic field forms a magnetic coupling with the magnetic poles of the stator permanent magnet to drive the rotor core to rotate.

[0003] For micro DC motors, cogging torque is a key factor affecting their performance. Cogging torque is generated by the interaction between the teeth of the stator permanent magnets and the rotor core. This is mainly because when the magnetic poles of the stator permanent magnets and the teeth of the rotor core are in different positions, the magnetic permeability of the main magnetic circuit will change. Even when the motor winding coil is de-energized, the rotor core will still tend to stay at several fixed angles in the rotating circumference due to the influence of the cogging torque, which manifests as poor low-voltage starting capability of the motor. When the motor is powered on and rotated, the cogging torque will manifest as additional pulsating torque, causing noise, vibration and speed fluctuations. Especially when the motor is running at low speed, the cogging torque has a greater impact on the operating stability, which seriously restricts the operating performance of the micro DC motor. The industry is in urgent need of finding a solution. Summary of the invention

[0004] The embodiment of the present invention provides a micro DC motor, which aims to improve the motor cogging torque, reduce the motor operation noise and vibration, and improve the motor low-voltage starting capability and low-speed operation stability.

[0005] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is as follows: a miniature DC motor is provided, comprising a stator housing and a rotor core; the stator housing has an inner cavity with a polygonal structure, a circle of continuous or discontinuous permanent magnets is arranged on the cavity wall of the inner cavity, and the permanent magnets form multiple pairs of magnetic poles alternately distributed along the circumference of the inner cavity; the rotor core is arranged in the inner cavity and is rotatably connected to the stator housing, the rotor core has multiple winding parts, each winding part is wound with a coil, and the ends of each winding part facing the permanent magnet form arc surfaces, and each arc surface is cocircular and concentric with the rotor core; wherein each arc surface forms an air gap with the permanent magnet, and the size of the air gap corresponding to each magnetic pole gradually increases from the middle area of ​​the magnetic pole to the boundary areas on both sides.

[0006] In one possible implementation, the inner cavity is square, the permanent magnet is a continuous structure embedded in the inner cavity, and the permanent magnet is divided into four poles based on the line connecting the midpoints of two sets of opposite sides of the inner cavity, and the thickness of each pole in the radial direction of the rotor core gradually decreases from the middle area to the boundary areas on both sides.

[0007] In some embodiments, the surface of the magnetic pole facing the rotor core is an inner pole arc surface, the radius of the inner pole arc surface is greater than the radius of the rotor core, and the center of the inner pole arc surface is located on the diagonal line of the inner cavity.

[0008] Exemplarily, the corner area of ​​the inner cavity has a transition fillet, the radius of the transition fillet is less than or equal to half the length of the inner cavity side, and the surface of the magnetic pole facing away from the rotor core is in contact with the transition fillet.

[0009] In a possible implementation, the permanent magnet is a discontinuous structure formed by four magnetized steels distributed at intervals on the cavity wall of the inner cavity, the four magnetized steels are opposite to each other, and the magnetization directions of adjacent magnetized steels are opposite.

[0010] In some embodiments, the inner cavity is octagonal, and four magnetized steels are respectively mounted and fixed on four side cavity walls of the inner cavity.

[0011] Exemplarily, the inner cavity includes four first cavity walls that are opposite to each other in pairs, and four second cavity walls that are opposite to each other in pairs, and each second cavity wall is located between two adjacent first cavity walls; the magnetized steel matches the size of the second cavity wall, and each magnetized steel is respectively mounted on each second cavity wall.

[0012] For example, the size ratio of the first cavity wall to the second cavity wall in the circumferential direction of the rotor core is 1:1 to 5:1.

[0013] In a possible implementation, the permanent magnet has two pairs of magnetic poles, and the rotor core has seven winding parts.

[0014] In some embodiments, a rotor shaft is provided at the center of the rotor core, and both ends of the rotor shaft are rotatably engaged with the stator housing via bearings.

[0015] The beneficial effect of the micro DC motor provided by the present invention is that: compared with the prior art, in the micro DC motor of the present invention, the permanent magnet is fixed on the inner cavity wall of the stator shell as a continuous integral structure or a discontinuous split structure, and can form multiple pairs of magnetic poles alternately distributed along the circumference of the inner cavity. After the coils wound on each winding part of the rotor core are passed through an alternating current, the magnetic flux lines can be gathered on the arc surfaces of their respective ends to form alternating polarities, and the polarities on each arc surface interact with the magnetic poles close thereto to drive the rotor core to rotate; since the air gap between the arc surface and the permanent magnet corresponds to the size of each magnetic pole area, it gradually increases from the middle area to the boundary areas on both sides of the magnetic pole, thereby forming an uneven air gap, which can not only improve the cogging torque of the motor, enhance the low-voltage starting capability and low-speed operation stability of the motor, but also improve the magnetic flux density waveform in the air gap, reduce the harmonic content and the pulsating torque during motor operation, thereby reducing the noise and vibration of the motor and improving the motor performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A schematic diagram of the axial cross-sectional structure of a micro DC motor provided in an embodiment of the present invention;

[0017] Figure 2 For along Figure 1 Schematic diagram of the cross-sectional structure of the middle II line;

[0018] Figure 3 A schematic diagram of the structure of a permanent magnet used in an embodiment of the present invention;

[0019] Figure 4 This is a schematic diagram of a radial cross-sectional structure of a micro DC motor provided in another embodiment of the present invention.

[0020] In the figure: 10, stator housing; 100, inner cavity; 101, transition fillet; 102, first cavity wall; 103, second cavity wall; 11, permanent magnet; 111, inner pole arc surface; 112, magnetized steel; 20, rotor core; 200, arc surface; 21, coil; 30, air gap; 40, rotor shaft; 50, bearing. DETAILED DESCRIPTION

[0021] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0022] It should be noted that when an element is referred to as being "disposed on" another element, it may be directly on another element or indirectly on another element. It should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", "front", "back", "top", "bottom", "inside", "outside", etc. is based on the orientation or positional relationship shown in the accompanying drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention. The terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meanings of "multiple" and "several" are two or more, unless otherwise clearly and specifically defined.

[0023] Please also read Figures 1 to 4 , the micro DC motor provided by the present invention is now described. The micro DC motor comprises a stator housing 10 and a rotor core 20; the stator housing 10 has an inner cavity 100 of a polygonal structure, a circle of continuous or discontinuous permanent magnets 11 is arranged on the wall of the inner cavity 100, and the permanent magnets 11 form multiple pairs of magnetic poles distributed alternately along the circumference of the inner cavity 100; the rotor core 20 is arranged in the inner cavity 100 and is rotatably connected to the stator housing 10, the rotor core 20 has multiple winding parts, each winding part is wound with a coil 21, and the ends of each winding part facing the permanent magnet 11 form arc surfaces 200, and each arc surface 200 is cocircular and concentric with the rotor core 20; wherein each arc surface 200 forms an air gap 30 with the permanent magnet 11, and the size of the air gap 30 corresponding to each magnetic pole gradually increases from the middle area of ​​the magnetic pole to the boundary areas on both sides.

[0024] It should be noted that, in this embodiment, the permanent magnet 11 can be a continuous annular integral structure embedded in the wall of the inner cavity 100 of the stator housing 10, forming multiple pairs of magnetic poles alternating in NS in the circumferential direction, and forming an uneven air gap with circumferential size variation through the surface shape design of each magnetic pole facing the rotor core 20, or it can be a discontinuous structure composed of multiple magnetic steels or magnetic tiles with different magnetization directions. Since each magnetic steel or magnetic tile is spaced from each other, an uneven air gap with circumferential size variation can also be formed. The coil 21 wound on each winding part on the rotor core 20 can be a three-phase DC winding method, and the number of winding parts can be six to form a symmetrical winding structure, or seven winding parts can be used for winding to form an asymmetrical winding structure.

[0025] It should be understood that the larger the air gap 30 is, the smaller the electromagnetic coupling force between the arc surface 200 and the magnetic pole is. In this embodiment, the size of the air gap 30 corresponding to the middle area of ​​each magnetic pole is smaller, and the size of the air gap 30 corresponding to the two side boundary areas of each magnetic pole is larger. The use of uneven air gap 30 can improve the magnetic flux waveform of the no-load air gap 30 and reduce the cogging torque.

[0026] Compared with the prior art, the micro DC motor provided in this embodiment has a permanent magnet 11 fixed on the wall of the inner cavity 100 of the stator housing 10 as a continuous integral structure or a discontinuous split structure, which can form a plurality of pairs of magnetic poles alternately distributed along the circumference of the inner cavity 100. After the coils 21 wound on each winding part of the rotor core 20 are passed through an alternating current, the magnetic flux lines can be gathered on the arc surfaces 200 at their respective ends to form alternating polarities. The polarities on each arc surface 200 interact with the magnetic poles close thereto to drive the rotor core 20 to rotate. Since the size of the air gap 30 between the arc surface 200 and the permanent magnet 11 corresponding to each magnetic pole area gradually increases from the middle area to the boundary areas on both sides of the magnetic pole, an uneven air gap 30 is formed, which can not only improve the cogging torque of the motor, enhance the low-voltage starting capability and low-speed operation stability of the motor, but also improve the magnetic flux density waveform in the air gap 30, reduce the harmonic content and the pulsating torque during motor operation, thereby reducing the noise and vibration of the motor and improving the motor performance.

[0027] In some embodiments, see Figures 1 to 3 The inner cavity 100 is square, the permanent magnet 11 is a continuous structure embedded in the inner cavity 100, and the permanent magnet 11 is divided into four poles based on the line connecting the midpoints of two sets of opposite sides of the inner cavity 100, and the thickness of each pole in the radial direction of the rotor core 20 gradually decreases from the middle area to the boundary areas on both sides.

[0028] It can also be considered here that the micro DC motor provided in this embodiment is a square motor. The permanent magnet 11 as a continuous integral structure can be a structure whose outer periphery matches the shape of the inner cavity 100, and the inner wall is a nearly circular structure. The permanent magnet 11 is evenly divided into four NS staggered poles, and each pole covers a range of 90°. Based on this structure, it can not only meet the uneven design requirements of a small air gap 30 in the middle area of ​​each pole and a large air gap 30 in the boundary areas on both sides, but also form a thicker size in the middle area of ​​the pole relative to the boundary areas on both sides, thereby increasing the magnetic force in the middle area of ​​the pole. The unevenly distributed magnetic force and the uneven air gap can be matched to produce a larger magnetic coupling effect between the middle area of ​​the pole and each arc surface 200 passed in sequence, thereby further improving the cogging torque, improving the low-voltage starting capability and low-speed operation stability of the motor, and improving the running noise and vibration of the motor.

[0029] In this embodiment, see Figure 3The surface of the magnetic pole facing the rotor core 20 is an inner pole arc surface 111 , the radius of the inner pole arc surface 111 is greater than the radius of the rotor core 20 , and the center of the inner pole arc surface 111 is located on the diagonal line of the inner cavity 100 .

[0030] The inner side surface of each magnetic pole, that is, the surface facing the rotor core 20, is formed into an inner pole arc surface 111, so that four inner pole arc surfaces 111 with angles different by 90° together constitute a continuous inner circumferential surface of the permanent magnet 11. Since the radius of the inner pole arc surface 111 is greater than the radius of the rotor core 20, and the center of the inner pole arc surface 111 is located on the diagonal line of the inner cavity 100, it is equivalent to the eccentric design of each inner pole arc surface 111 compared to the center of the rotor core 20, and the thickness change of each magnetic pole is connected with the change of the air gap 30. The nearly regular sine curve can utilize the eccentric magnetic field to reduce harmonics, so that the magnetic force of each arc surface 200 entering the magnetic pole range increases uniformly, and the magnetic force of each arc surface 200 leaving the magnetic pole range decreases uniformly, thereby reducing or even eliminating the cogging torque in the edge areas on both sides of the magnetic pole, that is, the cogging torque only exists in the middle area of ​​the magnetic pole (the magnetic force in this area is the largest and the air gap 30 is the smallest), thereby achieving the purpose of reducing the cogging torque, thereby reducing the running noise and vibration of the motor, and improving the low-voltage starting capability and low-speed operation stability of the motor.

[0031] Specifically, Figure 2 and Figure 3 As shown, the corner area of ​​the inner cavity 100 has a transition fillet 101, the radius of which is less than or equal to half the length of the inner cavity 100, and the surface of the magnetic pole away from the rotor core 20 is in contact with the transition fillet 101. By designing the transition fillet 101 in contact with the outer surface of the magnetic pole, each magnetic pole is actually formed into a structure close to a crescent shape. At the same time, in order to ensure the thickness of the middle area of ​​each magnetic pole, the size of the transition fillet 101 is designed to be no more than half the length of the inner cavity 100, so that the overall output torque of the motor can be guaranteed to be unaffected to the greatest extent while reducing the cogging torque.

[0032] As a specific implementation method, Figure 3 As shown, the side length dimension A of the permanent magnet 11 is A=B, the outer circle dimension, i.e., the dimension E≤A / 2 of the transition fillet 101, the center G of the inner pole arc surface 111 is located on a circle with a radius C and a center O of the rotor core 20, and is located on the extension line of the line HO connecting the center point H of the inner pole arc surface 111 and the center O of the rotor core 20.

[0033] It should be noted that the permanent magnet 11 as a continuous whole can be processed by powder die-casting, which not only has low processing costs, but also has high stability of the overall structure itself, is convenient for assembly with the stator housing 10, and is conducive to improving assembly positioning accuracy, thereby ensuring the position accuracy of each magnetic pole and thus the operation stability of the motor.

[0034] As a modified implementation of the permanent magnet 11, please refer to Figure 4 The permanent magnet 11 is a non-continuous structure formed by four magnetized steels 112 that are spaced apart and distributed on the cavity wall of the inner cavity 100. The four magnetized steels 112 are opposite to each other, and the magnetization directions of adjacent magnetized steels 112 are opposite. The four magnetized steels 112 of the non-continuous structure are mounted and fixed separately, and the intervals between the magnetized steels 112 can be used to naturally form an uneven air gap, thereby reducing the cogging torque. The magnetic field of each magnetized steel 112 forms a non-concentric distribution with the rotor core 20, thereby reducing harmonics and optimizing the running noise of the motor. At the same time, the magnetized steel 112 can directly use conventional rectangular magnets, which helps to reduce the overall cost and save expensive magnetic materials.

[0035] In this embodiment, if Figure 4 As shown, the inner cavity 100 is an octagon, and four magnetized steels 112 are respectively mounted and fixed on four side cavity walls of the inner cavity 100. The four cavity walls that are opposite to each other in the octagonal structure can be directly used as the mounting surface of each magnetized steel 112, thereby forming an uneven air gap between the arc surface 200 and the magnetic pole, with a simple structure and low cost, and reliable and labor-saving assembly.

[0036] Specifically, the inner cavity 100 includes four first cavity walls 102 that are opposite to each other, and four second cavity walls 103 that are opposite to each other, and each second cavity wall 103 is located between two adjacent first cavity walls 102; the magnetized steel 112 matches the size of the second cavity wall 103, and each magnetized steel 112 is respectively mounted on each second cavity wall 103. The two side edges of the magnetized steel 112 correspond to two corners of the octagonal structure, thereby forming an installation mode in which the magnetized steel 112 is embedded in the trapezoidal groove formed by two adjacent first cavity walls 102, which can not only ensure the installation reliability of the magnetized steel 112, but also ensure the installation position accuracy of the magnetized steel 112.

[0037] It should be noted that, in this embodiment, the size ratio of the first cavity wall 102 and the second cavity wall 103 in the circumferential direction of the rotor core 20 is 1:1 to 5:1. Since the size of the second cavity wall 103 matches the size of the magnetized steel 112, and the larger the size of the magnetized steel 112, the higher the overall torque output capacity of the motor, and the corresponding cogging torque will also increase, the size of the second cavity wall 103 can be reduced as much as possible to improve the cogging torque while meeting the output torque requirements of the motor, thereby improving the electromagnetic noise during the operation of the motor and enhancing the low-voltage starting capability.

[0038] For some possible implementations, see Figure 2 and Figure 4 , the permanent magnet 11 has two pairs of magnetic poles, and the rotor core 20 has seven winding parts. That is to say, the motor structure in this embodiment is actually a seven-slot four-pole structure, and the seven winding parts can form an asymmetric winding structure on the rotor core 20, so that the side magnetic pressure can always be formed on the rotor core 20 during the operation of the motor. The side magnetic pressure can always press the rotor core 20 on the rotational matching part between it and the stator housing 10, avoiding radial runout of the rotor core 20, thereby improving the operating stability of the rotor core 20 and further reducing the operating noise and vibration.

[0039] It is important to understand that, see Figure 1 In this embodiment, a rotor shaft 40 is provided at the center of the rotor core 20, and both ends of the rotor shaft 40 are rotatably matched with the stator housing 10 through bearings 50. The use of bearings 50 at both ends to achieve rotatable matching with the stator housing 10 can improve the connection stability of the rotor core 20 while ensuring that the rotor core 20 rotates flexibly and conveniently. At the same time, the asymmetric winding structure formed by the seven winding parts can always have side pressure on the rotor shaft 40 and press against the inner ring surface of the bearing 50, thereby avoiding radial runout of the rotor shaft 40, improving the rotation stability of the rotor core 20, and reducing noise and vibration.

[0040] It should be explained that the micro DC motor provided in this embodiment is used as a three-phase DC motor. Therefore, based on the idea of ​​an asymmetric winding structure, the rotor core 20 can also be designed to have a non-integer multiple of three winding parts, such as eight, ten, eleven winding parts, etc., as long as the number of coils 21 of one phase is different from the number of coils 21 of the other two phases.

[0041] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A micro DC motor, characterized in that: include: The stator shell has an inner cavity with a polygonal structure, a circle of continuous or discontinuous permanent magnets is arranged on the cavity wall of the inner cavity, and the permanent magnets form a plurality of pairs of magnetic poles that are alternately distributed along the circumference of the inner cavity; A rotor core is disposed in the inner cavity and is rotatably connected to the stator housing, wherein the rotor core has a plurality of winding parts, each of which is wound with a coil, and each of which has an end portion facing the permanent magnet and forms an arc surface, and each of the arc surfaces is cocircular and concentric with the rotor core; Wherein, an air gap is formed between each of the arc surfaces and the permanent magnet, and the size of the air gap corresponding to each of the magnetic poles gradually increases from the middle area of ​​the magnetic pole to the boundary areas on both sides.

2. The micro DC motor according to claim 1, characterized in that: The inner cavity is square, the permanent magnet is a continuous structure embedded in the inner cavity, and the permanent magnet is divided into four magnetic poles based on the line connecting the midpoints of two groups of opposite sides of the inner cavity, and the thickness dimension of each magnetic pole in the radial direction of the rotor core gradually decreases from the middle area to the boundary areas on both sides.

3. The micro DC motor according to claim 2, characterized in that: The surface of the magnetic pole facing the rotor core is an inner pole arc surface, the radius of the inner pole arc surface is greater than the radius of the rotor core, and the center of the inner pole arc surface is located on the diagonal line of the inner cavity.

4. The micro DC motor according to claim 3, characterized in that: The corner area of ​​the inner cavity has a transition fillet, the radius of the transition fillet is less than or equal to half the length of the inner cavity side, and the surface of the magnetic pole away from the rotor core is in contact with the transition fillet.

5. The micro DC motor according to claim 1, characterized in that: The permanent magnet is a discontinuous structure formed by four magnetized steels distributed at intervals on the cavity wall of the inner cavity. The four magnetized steels are opposite to each other, and the magnetization directions of adjacent magnetized steels are opposite.

6. The micro DC motor according to claim 5, characterized in that: The inner cavity is octagonal, and the four magnetized steels are respectively mounted and fixed on four side cavity walls of the inner cavity.

7. The micro DC motor according to claim 6, characterized in that: The inner cavity includes four first cavity walls that are opposite to each other in pairs, and four second cavity walls that are opposite to each other in pairs, and each of the second cavity walls is located between two adjacent first cavity walls; the magnetized steel matches the size of the second cavity wall, and each of the magnetized steel is respectively mounted on each of the second cavity walls.

8. The micro DC motor according to claim 7, characterized in that: A size ratio of the first cavity wall to the second cavity wall in the circumferential direction of the rotor core is 1:1 to 5:

1.

9. The micro DC motor according to claim 1, characterized in that: The permanent magnet has two pairs of magnetic poles, and the rotor core has seven winding parts.

10. The micro DC motor according to any one of claims 1 to 9, characterized in that: A rotor shaft is passed through the center of the rotor core, and both ends of the rotor shaft are rotatably matched with the stator housing through bearings.

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