The present invention relates to a brushless motor, and more particularly, to a brushless motor capable of cogging torque and torque ripples of the motor by means of design structures such as a shape of an opposing surface of a pole shoe, a shape of an outer circumferential surface of a rotor, and shapes and arrangement of permanent magnets.
A brushless direct current (BLDC) motor may have relatively high efficiency and prevent friction and abrasion that are problems of a direct current motor in the related art. Therefore, recently, the BLDC motor has been applied, as a motor for rotating a cooling fan, to a hybrid vehicle.
The BLDC motor refers to a motor in which an electronic commutation mechanism is installed instead of a brush and a commutator eliminated from the DC motor. Further, among the BLDC motors, an inner-rotor-type BLDC motor has a rotor having permanent magnets at a center thereof and configured to rotate, and a stator around which a drive coil is wound is fixed. That is, the stator around which the drive coil is wound is fixed to an outer side of the rotor, and the rotor having the permanent magnets provided therein is configured to rotate.
However, in the brushless motor, a magnitude of magnetic resistance (a degree to which a flow of magnetic flux is hindered) varies depending on a rotation position when the rotor rotates. A pulsation of motor torque occurs because of a difference in magnetic resistance. In the permanent magnet-type motor, the pulsation of torque, which occurs when the rotor rotates before electricity is applied to the coil of the motor, is referred to as cogging torque. Because of the pulsation of torque, the motor has an excitation source against vibration and noise, which eventually causes noise of the motor that may affect a cooling fan that is a system configured to operate by using the motor.
Accordingly, there is a need to improve noise and vibration characteristics of the motor by reducing torque ripples that are fluctuation widths of cogging torque of the brushless motor.
Korean Patent No. 1603667 (registered on Mar. 9, 2016)
The present invention has been made in an effort to solve the above-mentioned problem, and an object of the present invention is to provide a brushless motor capable of cogging torque and torque ripples of the motor by means of design structures such as a shape of an opposing surface of a pole shoe, a shape of an outer circumferential surface of a rotor, and shapes and arrangement of permanent magnets.
The present invention provides a brushless motor including: a stator in which a plurality of teeth is provided inside a stator core and spaced apart from one another, and pole shoes respectively formed at tips of the teeth; and a rotor rotatably disposed inside the stator and having a plurality of permanent magnets, in which an opposing surface of the pole shoe, which faces the rotor, is formed in a curved shape having one or more constant curvatures, and in which the rotor is formed in an anisotropic circular shape in which a distance between an outer circumferential surface of the rotor and a rotation center of the rotor varies depending on a position of the outer circumferential surface of the rotor.
The rotor may be configured such that a distance from the rotation center of the rotor to the outer circumferential surface of the rotor along a q-axis of the rotor is smaller than a distance from the rotation center of the rotor to the outer circumferential surface of the rotor along a d-axis of the rotor, and an outer circumferential surface of the rotor adjacent to the d-axis of the rotor has an arc shape.
A portion where the outer circumferential surface of the rotor adjacent to the d-axis of the rotor has the arc shape may be defined as a d-axis rotor portion, and a radius of curvature of the d-axis rotor portion may be smaller than a distance from the rotation center of the rotor to the d-axis rotor portion.
In the brushless motor according to the first embodiment of the present invention, the opposing surface of the pole shoe may be formed in an arc shape formed concavely inward.
A center of curvature of the opposing surface of the pole shoe may be positioned on the same line as a width direction centerline of each of the teeth. A radius of curvature of the opposing surface of the pole shoe may be larger than a radius of curvature of the d-axis rotor portion.
A radius of curvature of the opposing surface of the pole shoe may be larger than a distance from the rotation center of the rotor to the outer circumferential surface of the rotor.
In the brushless motor according to the second embodiment of the present invention, one side and the other side of the opposing surface of the pole shoe may each be formed in an arc shape based on a width direction center of the pole shoe.
One side of the opposing surface of the pole shoe may be defined as a first arc portion based on the width direction center of the pole shoe, the other side of the opposing surface of the pole shoe may be defined as a second arc portion based on the width direction center of the pole shoe, and a radius of curvature of the first arc portion and a radius of curvature of the second arc portion may be equal to each other.
A line, which connects a circumferential center of the first arc portion and a center of curvature of the first arc portion, and a line, which connects a circumferential center of the second arc portion and a center of curvature of the second arc portion, may be parallel to each other.
A line, which connects a circumferential center of the first arc portion and a center of curvature of the first arc portion, and a line, which connects a circumferential center of the second arc portion and a center of curvature of the second arc portion, may define a predetermined angle therebetween so as to meet at an upper side of the opposing surface of the pole shoe.
A line, which connects a circumferential center of the first arc portion and a center of curvature of the first arc portion, and a line, which connects a circumferential center of the second arc portion and a center of curvature of the second arc portion, may define a predetermined angle therebetween so as to meet at a lower side of the opposing surface of the pole shoe.
The first arc portion and the second arc portion may be symmetric with respect to a width direction centerline of each of the teeth.
A radius of curvature of the first arc portion and a radius of curvature of the second arc portion may each be larger than a radius of curvature of the d-axis rotor portion.
In the brushless motor according to the example of the present invention, the plurality of permanent magnets may each include a pair of unit permanent magnets, and the pair of unit permanent magnets may each be a straight permanent magnet.
The pair of unit permanent magnets may be disposed in a V shape toward the rotation center of the rotor, and an angle between the pair of unit permanent magnets may be 130° or more and 140° or less.
The plurality of permanent magnets may each be a straight permanent magnet.
In the brushless motor according to the present invention, the outer circumferential surface of the rotor may have convex surfaces and concave surfaces formed alternately in a circumferential direction, the plurality of permanent magnets may each be disposed inside the convex surface, and the two adjacent permanent magnets may be symmetric with respect to the concave surface positioned between the two adjacent permanent magnets.
An end of a flux barrier of the rotor may be formed in parallel with the outer circumferential surface of the rotor, such that a rotor bridge has a constant thickness.
In the brushless motor according to the present invention, twelve teeth may be provided inside the stator core, and eight permanent magnets may be provided in the rotor.
According to the present invention, the size of the air gap may vary depending on the position according to the rotation of the rotor, thereby greatly reducing the magnetic resistance according to the change in position of the air gap. Therefore, it is possible to innovatively reduce the cogging torque of the motor and implement a counter electromotive force waveform having a maximum sinusoidal shape by reducing a distortion rate against a spatial high harmonic wave of a counter electromotive force. Therefore, it is possible to reduce the torque ripple, reduce noise caused by the spatial high harmonic wave generated in the motor, and properly maintain a motor control algorithm that follows the counter electromotive force waveform.
In addition, the temporal change in magnetic flux may be maintained at a minimum level to reduce the temporal change in magnetic flux interlinking the permanent magnets. Therefore, it is possible to reduce a loss of eddy current of the permanent magnet, improve the energy efficiency of the motor, reduce energy consumption, and improve the performance of the motor.
Hereinafter, the present invention will be described with reference to the accompanying drawings.
The rotor 200 may be rotatably disposed inside the stator 100 and have a plurality of permanent magnets 300. The permanent magnets 300 may be individually seated in slits 250 formed in the rotor 200 and radially disposed inside an outer circumferential surface of the rotor 200.
In contrast, in the present invention, as illustrated in
First, the rotor 200 of the present invention will be specifically described. With reference back to
More specifically, the outer circumferential surface RS of the rotor according to the present invention has convex surfaces convexly formed, and concave surfaces concavely formed, and the convex surfaces and the concave surfaces are alternately formed in the circumferential direction. In this case, as illustrated, in the present invention, the plurality of permanent magnets 300 may be respectively provided inside the convex surfaces of the outer circumferential surface of the rotor. Therefore, the convex surface of the outer circumferential surface RS of the rotor corresponds to a d-axis of the rotor, and the concave surface of the outer circumferential surface RS of the rotor corresponds to a q-axis of the rotor. The number of convex surfaces of the outer circumferential surface RS of the rotor may be equal to the number of permanent magnets 300.
The d-axis of the rotor is an axis along which the magnetic flux is concentrated. The d-axis corresponds to a line that connects a magnetic pole portion and the rotation center O of the rotor, i.e., a line that connects centers of the permanent magnets 300. The q-axis of the rotor is an axis orthogonal to the d-axis at an electrical angle and corresponds to a line that connects the rotation center O of the rotor and a center between the adjacent permanent magnets 300 spaced apart from each other. That is, in the rotor 200 of the present invention, a distance from the rotation center O of the rotor to the outer circumferential surface RS of the rotor along the q-axis may be shorter than a distance from the rotation center O of the rotor to the outer circumferential surface RS of the rotor along the d-axis.
Because the outer circumferential surface RS of the rotor is formed in an anisotropic circular shape as described above, a size of an air gap between the rotor 200 and the stator 100 periodically changes when the rotor 200 rotates, such that a change in magnetic resistance according to a change in position of the air gap may be reduced. The anisotropic circular shape of the outer circumferential surface RS of the rotor may be coupled to the shape of the opposing surface RS of the rotor of the present invention to be described below, thereby maximizing the effect of reducing a magnetic resistance change rate.
However, even when the outer circumferential surface RS of the rotor of the present invention is formed in an anisotropic circular shape, a shape of a flux barrier may be appropriately implemented to maintain a constant thickness of a rotor bridge. More specifically,
Next, the pole shoe 130 according to the present invention will be described. As described above, the opposing surface PS of the pole shoe 130 of the present invention may be formed in a curved shape. The curved shape will be described with reference to the specific embodiment.
First, a pole shoe according to a first embodiment of the present invention will be described with reference to
The pole shoe of the present example may be formed in an arc shape formed concavely inward in the opposing surface of the pole shoe over the entire opposing surface of the pole shoe. Therefore, the pole shoe may have a curved surface having a constant curvature from one end to the other end of the opposing surface of the pole shoe.
In this case, as illustrated in
Further, in the present example, a radius R_p of curvature of the opposing surface CL of the pole shoe may be larger than a radius R_d of a d-axis rotor portion and larger than a distance D from the rotation center O of the rotor to the outer circumferential surface RS of the rotor. That is, as illustrated in
In this case, all the rotation center O of the rotor, a center 200d-o of curvature of the d-axis rotor portion, and the center 130-o of curvature of the opposing surface of the pole shoe may be disposed on a straight line and coincident with the width direction centerline CL of each of the teeth.
Next, a pole shoe according to a second embodiment of the present invention will be described with reference to
The width direction center PC of the pole shoe may mean a center of the opposing surface PS of the pole shoe. The width direction center PC may be coincident with the width direction centerline CL of each of the teeth 120, and the width direction centerline CL of the teeth 120 may pass through the rotation center O of the rotor. Hereinafter, based on the width direction center PC of the pole shoe, one side (a left side based on the drawings) of the opposing surface PS of the pole shoe will be referred to as a first arc portion A, and the other side (a right side based on the drawings) of the opposing surface PS of the pole shoe will be referred to as a second arc portion B.
In the present invention, the opposing surface PS of the pole shoe may have the first arc portion A and the second arc portion B respectively formed at one side and the other side based on the center PC. Therefore, the air gap between the opposing surface PS of the pole shoe and the outer circumferential surface RS of the rotor may vary depending on the positions. More specifically, the first arc portion A is formed from one end of the opposing surface of the pole shoe to the width direction center PC of the pole shoe in the rotation direction of the rotor, such that the air gap between the first arc portion A and the outer circumferential surface RS of the rotor may vary depending on the positions. The second arc portion B is formed from the width direction center PC of the pole shoe to the other end of the opposing surface of the pole shoe, such that the air gap between the second arc portion B and the outer circumferential surface of the rotor may vary depending on the positions. According to the present invention described above, the air gap may vary twice depending on the positions on the single pole shoe 130.
This is to reduce cogging torque. In the present invention described above, the shape design of the pole shoe may intentionally increase the change in air gap between the opposing surface PS of the pole shoe and the outer circumferential surface RS of the rotor, thereby minimizing a magnetic resistance change rate in the air gap between the two adjacent pole shoes.
(Here, Tcogging means cogging torque, Φg means interlinkage magnetic flux, R means magnetic resistance, and θ means a rotation angle.)
Equation 1 is an equation for calculating cogging torque in the motor. As shown in Equation 1, the cogging torque is proportional to the square of the amount of interlinkage magnetic flux Φg passing through the air gap and proportional to the magnetic resistance change rate (dR/dθ) according to the change in position of the air gap. Therefore, eventually, it is possible to minimize the magnetic resistance change rate in the air gap to reduce the cogging torque. According to the present invention, the air gap varies depending on the position on the opposing surface PS of the pole shoe, such that the magnetic resistance R and the magnetic resistance change rate (dR/dθ) may be reduced, and thus the cogging torque and the torque ripple, which is a range of fluctuation of the cogging torque, may be reduced.
Hereinafter, more specified embodiments of the pole shoe 130 of the present example will be described. As described above, the opposing surface PS of the pole shoe 130 of the present example may include the first arc portion A and the second arc portion B. In this case, a first connection line AL, which is a line that connects a circumferential center A-c of the first arc portion A and a center A-o of a circle made by extending the first arc portion A, and a second connection line BL, which is a line that connects a circumferential center B-c of the second arc portion B and a center B-o of a circle made by extending the second arc portion B, may be parallel to each other or define a predetermined angle therebetween.
With reference back to
In this case, in the example illustrated in
Further, in the above-mentioned examples, as illustrated in
Further, in the present invention, a radius R_A of the first arc portion A, which corresponds to one side of the opposing surface RS of the pole shoe, and a radius R_B of the second arc portion B, which corresponds to the other side of the opposing surface RS of the pole shoe, may each be larger than the radius R_d of the d-axis rotor portion 200d. With reference back to
As illustrated in
Further, as illustrated in
As described above, in the present invention, the stator, more specifically, the opposing surface of the pole shoe and the outer circumferential surface of the rotor are designed to have the above-mentioned shapes and structures, such that the size of the air gap may vary depending on the position according to the rotation of the rotor, thereby greatly reducing the magnetic resistance according to the change in position of the air gap. Therefore, it is possible to innovatively reduce the cogging torque of the motor and implement a counter electromotive force waveform having a maximum sinusoidal shape by reducing a distortion rate against a spatial high harmonic wave of a counter electromotive force. Therefore, it is possible to reduce the torque ripple, reduce noise caused by the spatial high harmonic wave generated in the motor, and properly maintain a motor control algorithm that follows the counter electromotive force waveform.
In addition, the temporal change in magnetic flux may be maintained at a minimum level to reduce the temporal change in magnetic flux interlinking the permanent magnets. Therefore, it is possible to reduce a loss of eddy current of the permanent magnet, improve the energy efficiency of the motor, reduce energy consumption, and improve the performance of the motor.
Hereinafter, the permanent magnet 300 of the present invention will be described.
The permanent magnets 300 according to the example of the present invention may each include a pair of unit permanent magnets 301 and 302. In this case, the pair of unit permanent magnets 301 and 302 may each be a straight permanent magnet. As illustrated in
In this case, as illustrated in
Alternatively, according to another example of the present invention, the permanent magnets 300 may each be configured as a straight permanent magnet.
Meanwhile, as described above, the convex surfaces and the concave surfaces of the outer circumferential surface RS of the rotor according to the present invention may be alternately formed in the circumferential direction, and the permanent magnets 300 may each be provided inside the convex surface. In this case, the present invention may provide a structure in which the two adjacent permanent magnets, among the permanent magnets, are symmetric with respect to the concave surface positioned between the two permanent magnet. More specifically, with reference to
Further, in the motor of the present invention in the more specific embodiment of the present invention, twelve teeth 120 are provided inside the stator core 110, a total of twelve slots 150 are formed in the stator 100, eight permanent magnets 300 are provided on the rotor 200, and a total of eight poles are formed in the rotor 200, such that an inner-rotor-type motor having the eight poles and the twelve slots may be implemented.
As described above, according to the present invention, the above-mentioned specific structures and shapes of the pole shoes, the rotor, and the permanent magnets may be combined with one another, thereby innovatively reducing the cogging torque and the torque ripples generated in the motor.
While the embodiments of the present invention have been described with reference to the accompanying drawings, those skilled in the art will understand that the present invention may be carried out in any other specific form without changing the technical spirit or an essential feature thereof. Therefore, it should be understood that the above-described embodiments are illustrative in all aspects and do not limit the present invention.
Number | Date | Country | Kind |
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10-2021-0054205 | Apr 2021 | KR | national |
Filing Document | Filing Date | Country | Kind |
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PCT/KR2022/003792 | 3/18/2022 | WO |