Patent Description:
Motors are devices obtaining rotational forces by converting electrical energy into mechanical energy and are widely used in vehicles, household appliances, industrial equipment, and the like.

In particular, an electronic power steering (EPS) system in which the motor is used drives the motor in an electronic control unit according to a driving condition to ensure turning stability and provide a rapid restoring force. Thus, a driver of a vehicle may drive safely.

The motor includes a stator and a rotor. The stator may include teeth forming a plurality of slots, and the rotor may include a plurality of magnets disposed to face the teeth. Adjacent teeth among the teeth are disposed to be spaced apart from each other to form a slot open (SO).

In this case, owing to a difference in permeability between the stator made of a metal material and air of the SO which is an empty space while the rotor rotates, a cogging torque may occur. Since the cogging torque causes noise and vibration, reduction in cogging torque is the most important factor for improving quality of the motor.

However, since performance and quality of the motor may be varied according to a shape of a groove formed in the tooth, the motor is required to be capable of maintaining the performance while reducing the cogging torque through a design of the groove.

<CIT>, <CIT> and <CIT> disclose electric motors having rotor teeth shaped with protrusions and grooves to address the cogging torque issue.

Embodiments are directed to providing a motor capable of reducing a cogging torque.

Further, embodiments are directed to providing a motor capable of improving a quality thereof by reducing a cogging torque through a design with respect to a width and a depth of a groove formed in each tooth on the basis of a slot open.

The problems to be solved by the present invention are not limited to those described above, and other problems not mentioned above should be clearly understood by those skilled in the art from the following description.

In the present description and drawings, any examples and technical descriptions of apparatuses, products and/or methods which are not covered by the claims should be taken as background art or examples useful for understanding the invention.

Embodiments can provide an advantageous effect of significantly reducing a cogging torque by forming a groove in a tooth of a stator to increase a main cogging order.

In accordance with the embodiments, when a groove is disposed in a tooth of a stator in a six-pole nine-slot motor, in a state in which a main cogging order is "ninth order," an advantageous effect of preventing a significant increase in cogging torque can be provided.

Further, in accordance with the embodiments, a quality of a motor can be improved by reducing a cogging torque through a design with respect to a width and a depth of a groove formed in each tooth on the basis of a slot open. For example, the motor can reduce the cogging torque by defining the width and the depth of the groove in a relationship with the slot open.

Further, the motor can reduce the cogging torque by defining a depth of the groove in a relationship with a length of a protrusion.

Various beneficial advantages and effects of embodiments are not limited by the detailed description and should be easily understood through detailed descriptions of the embodiments.

When a description is made as "at least one (or more) of A and B, and C," it may include one or more of all combinations which can be combined with A, B, and C.

Further, in describing components of embodiments of the present invention, the terms first, second, A, B, (a), (b), and the like can be used.

These terms are intended to distinguish one component from other components, but the nature and the order or sequence of the components is not limited by those terms.

Further, when a component is described as being "connected," "coupled," or "linked" to another component, it may include not only the component is directly connected, coupled, or connected to another component, but also the component may be "connected," "coupled," or "linked" to another component through still another component therebetween.

Further, when a component is described as being formed or disposed "on (above) or under (below)" of another component, the term "on (above) or under (below)" includes not only when two components are in direct contact with each other, but also when one or more of still another component is formed or disposed between the two components. Also, when described as being "on (above) or under (below)," the term "on (above) or under (below)" may mean not only an upward direction but also a downward direction based on one component.

Hereinafter, embodiments be described in detail with reference to the drawings, the same reference numerals are given to the same or corresponding components regardless of a number of the drawing, and duplicate descriptions thereof will be omitted herein.

<FIG> is a diagram illustrating a motor according to a first embodiment, <FIG> is a diagram illustrating a first angle and a second angle, and <FIG> is a diagram illustrating the first angle.

Referring to <FIG>, a motor <NUM> according to the first embodiment may include a shaft <NUM>, a rotor <NUM>, and a stator <NUM>.

The shaft <NUM> may be coupled to the rotor <NUM>. When an electromagnetic interaction occurs in the rotor <NUM> and the stator <NUM> through a supply of a current, the rotor <NUM> rotates and thus the shaft <NUM> is rotated by being interlocked with the rotation of the rotor <NUM>. The shaft <NUM> may be connected to a steering shaft of a vehicle to transmit power to the steering shaft. The shaft <NUM> may be supported on a bearing.

The rotor <NUM> rotates due to an electrical interaction with the stator <NUM>. The rotor <NUM> is disposed in the stator <NUM>. The rotor <NUM> may include a rotor core <NUM> and a magnet <NUM> coupled to the rotor core <NUM>. The rotor <NUM> may be implemented as a type in which the magnet <NUM> is coupled to an outer circumferential surface of the rotor core <NUM>. In such a type of the rotor <NUM>, in order to prevent separation of the magnet <NUM> and increase a coupling force, a separate can member <NUM> may be coupled to the rotor core <NUM>. Alternatively, the rotor <NUM> may be integrally formed with the magnet <NUM> and the rotor core <NUM> through dual injection of the magnet <NUM> and the rotor core <NUM>.

The rotor <NUM> may be implemented in a type in which a magnet is coupled to an interior of the rotor core. Such a type of the rotor <NUM> may be provided with a pocket into which the magnet <NUM> is inserted in the rotor core <NUM>.

Meanwhile, the rotor <NUM> may be configured such that the magnet <NUM> is disposed in the rotor core <NUM>, which is a single cylindrical product, in one stage. Here, the one stage refers to a structure in which the magnet <NUM> may be disposed such that a skew is not present on an outer circumferential surface of the rotor <NUM>. Therefore, a height of the rotor core <NUM> may be formed to be equal to that of the magnet <NUM> based on a longitudinal cross section of the rotor core <NUM> and a longitudinal cross section of the magnet <NUM>. That is, the magnet <NUM> may be implemented to cover an entirety of the rotor core based on a height direction (axial direction). Here, the axial direction may be a length direction of the shaft <NUM>.

The stator <NUM> may be disposed on an outer side of the rotor <NUM>. The stator <NUM> causes an electrical interaction with the rotor <NUM> to induce a rotation of the rotor <NUM>.

A sensing magnet <NUM> is a device coupled to the shaft <NUM> so as to be interlocked with the rotor <NUM> to detect a position of the rotor <NUM>. Such a sensing magnet may include a magnet and a sensing plate. The magnet may be coaxially coupled to the sensing plate. The sensing magnet <NUM> may include a main magnet disposed adjacent to a hole forming an inner circumferential surface in a circumferential direction and a sub-magnet formed at an edge of the main magnet. The main magnet may be arranged equal to a drive magnet inserted into the rotor of the motor. The sub-magnet is more subdivided than the main magnet and comprised of many poles. Thus, a rotation angle may be further divided and measured, and driving of the motor may be made smoother.

The sensing plate may be formed of a metal material in the form of a disc. The sensing magnet may be coupled to an upper surface of the sensing plate. Further, the sensing plate may be coupled to the shaft <NUM>. A hole through which the shaft <NUM> passes is formed in the sensing plate.

A sensor for detecting a magnetic force of the sensing magnet may be disposed on a printed circuit board (PCB) <NUM>. In this case, the sensor may be a Hall integrated circuit (IC). The sensor detects variations in a north pole and a south pole of the main magnet or the sub-magnet to generate a sensing signal. The PCB <NUM> may be coupled to a lower surface of a cover of a housing and installed above the sensing magnet such that the sensor faces the sensing magnet.

The motor <NUM> according to the first embodiment may reduce a cogging torque and a torque ripple by reducing a width of the magnet <NUM> to increase a frequency of the cogging torque waveform per unit period. A detailed description thereof is as follows. In describing the embodiment, the width of the magnet <NUM> may be defined as a length of an arc formed by an inner circumferential surface of the magnet <NUM> in contact with the rotor core <NUM>.

Referring to <FIG> and <FIG>, a plurality of magnets <NUM> are attached to the outer circumferential surface of the rotor core <NUM>. Further, the stator <NUM> may include a plurality of teeth <NUM>. The magnet <NUM> may be disposed to face the tooth <NUM>.

For example, the motor <NUM> may be a six-pole nine-slot motor including six magnets <NUM> and nine teeth <NUM>. The number of the teeth <NUM> corresponds to the number of the slots. Further, a north pole and a south pole of the magnet <NUM> may be alternately disposed in a circumferential direction of the rotor core <NUM>.

An inner circumferential surface <NUM> of the magnet <NUM> is in contact with the outer circumferential surface of the rotor core <NUM>. The width of the magnet <NUM> of the motor <NUM> according to the first embodiment may be described through a first angle R11 and a second angle R12.

First, the first angle R11 represents an angle obtained by dividing <NUM> degrees, which are angles formed by the outer circumferential surface of the rotor core <NUM>, by the number of the magnets <NUM>. For example, when the number of the magnets <NUM> is six, the first angle R11 is <NUM> degrees. An arc length of the rotor core <NUM> corresponding to the first angle R11 becomes a reference for setting the width of the magnet <NUM>. In this case, an actual width of the magnet <NUM> may be formed on the outer circumferential surface of the rotor core <NUM> to be increased or decreased in consideration of a width of a protrusion for guiding the magnet <NUM>.

Next, the second angle R12 means an angle between a first extension line L11 and a second extension line L12. Here, the first extension line L11 means an imaginary line extending from an end point of any one side of the inner circumferential surface <NUM> to a central point C of the rotor core <NUM> on a transverse cross section of the magnet <NUM>. Here, the transverse cross section of the magnet <NUM> means a cross section of the magnet <NUM> cut in a direction perpendicular to the axial direction of the motor.

The arc length of the rotor core <NUM> corresponding to the second angle R12, which is an angle between the first extension line L11 and the second extension line L12, becomes another reference for setting the width of the magnet <NUM>.

The first angle R11 becomes a conventional reference angle for setting the width of the magnet <NUM>, and the second angle R12 becomes a reference angle for setting the width of the magnet <NUM> to have a width that is smaller than that of the magnet <NUM> based on the first angle R11.

<FIG> shows graphs illustrating comparison of values of a torque and a torque ripple which correspond to a reduction ratio of a width of a magnet.

Referring to <FIG>, in the case of the six-pole nine-slot motor, it can be seen that a torque ripple which is lower than a reference line B representing a target torque ripple was measured at a point at which a ratio of the second angle R12 to the first angle R11 ranges from <NUM> to <NUM>.

Further, it can be seen that a torque was measured to be higher than a reference line A representing a target reference torque at a point at which the ratio of the second angle R12 to the first angle R11 ranges from <NUM> to <NUM> so that the measured torque satisfied a required torque.

<FIG> is a diagram illustrating an optimum shape of an outer circumferential surface of the magnet for reducing a torque ripple.

Referring to <FIG>, a point on an outer circumferential surface of the magnet <NUM>, which is farthest from the center C of the rotor core <NUM> to the outer circumferential surface of the magnet <NUM>, is referred to as P10 of <FIG>. An imaginary reference line connecting the center C of the rotor core <NUM> to P10 of <FIG> is referred to as Z of <FIG>.

Generally, the outer circumferential surface of the magnet <NUM> is designed to be disposed along S11 of <FIG>. S11 of <FIG> is a line representing a circumference having a radius F11 from a first origin point P11 away from the center C to P10 of <FIG> on the reference line Z of <FIG>.

Meanwhile, the outer circumferential surface of the magnet <NUM> of the rotor according to the embodiment is designed to be disposed along S12 of <FIG>. S12 of <FIG> is a line representing a circumference having a first radius F12 from a second origin point P12 away from the center C to P10 of <FIG> on the reference line Z of <FIG>. Here, the second origin point P12 is disposed on an outer side of the first origin point P11 in a radial direction of the rotor core <NUM>.

The shape of the outer circumferential surface of the magnet <NUM> is for reducing a torque ripple in a high speed condition.

<FIG> and <FIG> are graphs showing torque ripples occurring in a high speed rotation condition.

Referring to <FIG> and <FIG>, in the case of a motor including a magnet of which an outer circumferential surface is formed along S11 of <FIG>, as shown in Region A of <FIG> and Region A of <FIG>, it can be confirmed that noise was significantly increased in an <NUM> band. <NUM> represents a state in which the motor rotates at <NUM> revolution per minute (RPM), and it can be seen that the torque ripple was significantly increased in a high speed rotation.

Referring to <FIG>, in order to reduce the torque ripple in the rotor according to the embodiment, the shape of the outer circumferential surface of the magnet <NUM> is changed so as to have a curvature radius that is smaller than that of a general magnet such as S12 of <FIG>.

In particular, when a second radius F13 is <NUM>, the magnet <NUM> may be designed such that the first radius F12 ranges from <NUM> to <NUM>. Here, the first radius F12 is a curvature radius of the outer circumferential surface of the magnet <NUM> and is a distance from the second origin point P12 to P of <FIG>. The second radius F13 corresponds to a curvature radius of the inner circumferential surface of the magnet <NUM>.

For example, when a distance from the center C of the rotor core <NUM> to P10 of <FIG> is <NUM>, the first radius F12 may be <NUM>, and the second radius F13 may be <NUM>. Therefore, a distance from the center C of the rotor core <NUM> to the second origin point P12 corresponds to <NUM>.

In the above conditions, measured results of a cogging torque and a torque ripple of the six-pole nine-slot motor are as follows.

<FIG> is a table comparing a cogging torque and a torque ripple of Comparative Example with those of Example.

Referring to <FIG>, MW of <FIG> represents a ratio of the second angle R12 to the first angle R11, and MOF of <FIG> means a distance from the center C of the rotor core <NUM> to the second origin point P12.

In the case of Comparative Example, conditions are such that the ratio of the second angle R12 to the first angle R11 is <NUM>, and the distance from the center C of the rotor core <NUM> to the second origin point P12 is <NUM>.

In the case of Example, conditions are such that the ratio of the second angle R12 to the first angle R11 is <NUM>, and the distance from the center C of the rotor core <NUM> to the second origin point P12 is <NUM>.

In the above conditions, measured results of the cogging torques, the torque ripples, and the torque of Comparative Example and Example are as follows.

First, it is shown that there was no significant difference between a maximum torque of Comparative Example and that of Example. However, it is shown that the cogging torque and the torque ripple were significantly reduced. In particular, it is shown that a high speed torque ripple was significantly reduced from <NUM> (Comparative Example) to <NUM> (Example). This is exhibited as being much lower than a target reduction value of the torque ripple.

<FIG> is a graph showing a torque ripple of the motor according to the first embodiment in a high speed rotation condition.

Referring to <FIG>, unlike Region A of <FIG>, noise was significantly reduced in the <NUM> band and thus the torque ripple was reduced.

<FIG> is a diagram illustrating a groove of a tooth.

Referring to <FIG> and <FIG>, the stator <NUM> may include a stator core 300a and a coil <NUM>.

The stator core 300a may be formed by stacking a plurality of plates in the form of a thin steel sheet. Alternatively, the stator core 300a may be formed by coupling or connecting a plurality of divided cores.

An annular yoke <NUM> may be provided in the stator core 300a, and a tooth <NUM> protruding from the yoke <NUM> toward a center of the stator core 300a may be provided. The coil <NUM> is wound around the tooth <NUM>. A plurality of teeth <NUM> may be disposed along an inner circumferential surface of the annular yoke <NUM> at regular intervals. Although nine teeth <NUM> in total are shown in <FIG>, the present invention is not limited thereto and may be variously modified according to the number of poles of the magnet <NUM>.

The magnet <NUM> may be attached to the outer circumferential surface of the rotor core <NUM>. A distal end of the tooth <NUM> is disposed to face the magnet <NUM>.

Referring to <FIG>, the tooth <NUM> may include a body <NUM> and a shoe <NUM>. The coil <NUM> of <FIG> is wound around the body <NUM>. The shoe <NUM> is disposed on a distal end of the body <NUM>. A distal end surface of the shoe <NUM> is disposed to face the magnet <NUM>. A winding space P of the coil <NUM> of <FIG> is formed between adjacent teeth <NUM>. The shoes of adjacent teeth <NUM> are disposed to be spaced apart from each other to form a slot open (SO). The SO is an inlet of the winding space P and a nozzle for winding the coil is inserted into the SO. Here, the body <NUM> of the tooth <NUM> may be referred to as a first body.

An inner circumferential surface of the shoe <NUM> may include a groove <NUM>. The groove <NUM> may be formed to be concave on the inner circumferential surface of the shoe <NUM>. A shape of the groove <NUM> is shown as a square shape, but the present invention is not limited thereto. Further, the groove <NUM> may be disposed in an axial direction of the stator core 300a. In other words, the groove <NUM> may be disposed to be long from an upper end to a lower end of the stator core 300a in a height direction of the stator core 300a.

Two grooves <NUM> may be disposed. Referring to <FIG>, the two grooves <NUM> may be symmetrically disposed based on a reference line L passing through a center of a width of the body <NUM> of the tooth <NUM> and the center C of the stator core 300a. The groove <NUM> serves to correspond to the SO causing a variation in magnetic flux density, thereby increasing a frequency of a waveform of a cogging torque per unit period to serve to significantly reduce the cogging torque.

<FIG> is a table showing a main cogging order increased by the motor according to the first embodiment.

Referring to <FIG>, in the case of the six-pole nine-slot motor, a main cogging order corresponds to eighteen which is the least common multiple of six that is the number of the magnets <NUM> and nine that is the number of slots. Here, the main cogging order means the number of vibrations of the cogging torque waveform per unit rotation (one revolution) of the motor. Here, the number of vibrations represents the number of repetitions of a cogging torque waveform forming a peak. Further, the number of the slots corresponds to the number of the teeth <NUM>.

In the case of the six-pole nine-slot motor with the two grooves <NUM>, since the number of the slots may be regarded as increasing from nine to twenty-seven due to the two grooves <NUM>, the main cogging order is increased three times from <NUM> to <NUM>. As described above, since the increase of the main cogging order three times due to the two grooves <NUM> means that the number of vibrations of the cogging torque waveform is increased three times, the cogging torque may be significantly reduced.

<FIG> is a diagram illustrating a width of the groove, and <FIG> shows graphs illustrating a variation in cogging torque waveform according to the width of the groove.

Referring to <FIG> and <FIG>, a width W11 of the groove <NUM> is set to be within <NUM>% to <NUM>% of a width W12 of the SO. Here, the width W11 of the groove <NUM> means a distance from one side end of an inlet of the groove <NUM> to the other side end thereof based on a circumferential direction of the stator core <NUM>. Here, the width W12 of the SO means a distance from one side end of an inlet of the SO to the other side end thereof based on the circumferential direction of the stator core <NUM>.

As shown in <FIG>, when the width W11 of the groove <NUM> deviates from <NUM>% to <NUM>% of the width W12 of the SO, there occurs a problem that a component of the stator, i.e., the main cogging order that is equal to the number of poles of the magnet <NUM>, is included in the cogging torque waveform.

However, as shown in <FIG>, when the width W11 of the groove <NUM> is within <NUM>% to <NUM>% of the width W12 of the SO, it can be confirmed that only the cogging torque waveform corresponding to a main cogging order of "<NUM>" was detected.

When the groove <NUM> is included in the shoe <NUM>, in a state in which the rotor <NUM> with no skew is included and a main cogging order is "<NUM>," there is a problem that a magnitude and dispersion of the cogging torque are expanded.

<FIG> is a diagram illustrating a shoe having an inner circumferential surface formed of a curved surface.

Referring to <FIG>, the motor <NUM> according to the first embodiment is formed such that the curvature center of the inner circumferential surface of the shoe <NUM> coincides with the center C of the stator core <NUM> of <FIG>. In particular, a center of an imaginary circle O connecting the inner circumferential surfaces of the plurality of shoes <NUM> coincides with the center C of the stator core <NUM> of <FIG>.

<FIG> is a table comparing a cogging torque of a motor in which an inner circumferential surface of the shoe is formed of a flat surface with a cogging torque of a motor of which a curvature center of an inner circumferential surface of a shoe <NUM> coincides with a center of the stator core <NUM>.

An column A of <FIG> represents a case in which the inner circumferential surface of the shoe is a flat surface in a motor including six poles and nine slots and a rotor with no skew. Further, an column B of <FIG> represents a case in which the a curvature center of the inner circumferential surface of the shoe coincides with the center C of the stator core <NUM> in the motor including six poles and nine slots and a rotor with no skew.

Referring to the column A of <FIG>, there was an effect of significantly reducing the cogging torque at an 18th main cogging order, but a problem occurred in that the cogging torque is significantly increased more than a reference value at a 9th main cogging order.

Referring to the column B of <FIG>, it can be confirmed that there was an effect of reducing the cogging torque more than the reference value at the 18th main cogging order and even at the 9th main cogging order.

<FIG> is a table comparing a deviation and an output of the cogging torque of the motor in which the inner circumferential surface of the shoe is a flat surface with those of the cogging torque of the motor of which the curvature center of the inner circumferential surface of the shoe <NUM> coincides with the center C of the stator core <NUM>.

An column A of <FIG> represents a case in which the inner circumferential surface of the shoe is a flat surface in a motor including six poles and nine slots and a rotor with no skew. Further, an column B of <FIG> represents a case in which the curvature center of the inner circumferential surface of the shoe coincides with the center C of the stator core <NUM> in the motor including six poles and nine slots and a rotor with no skew.

Referring to the column A of <FIG>, as a result of three sample tests, it can be seen that a deviation between a maximum value (<NUM> N/m) and a minimum value (<NUM> N/m) of the cogging torque was very large at the 9th main cogging order.

Meanwhile, referring to the column B of <FIG>, as the result of the three sample tests, it can be seen that a deviation between a maximum value (<NUM> N/m) and a minimum value (<NUM> N/m) of the cogging torque was not relatively large at the 9th main cogging order.

Further, in the column B of <FIG>, it can be confirmed that an output was increased more than that of the column A of <FIG> by as much as about <NUM>%.

<FIG> is a graph showing a cogging torque improvement state corresponding to a main cogging order in the motor according to the first embodiment.

A red bar in <FIG> indicates a cogging torque when the inner circumferential surface of the shoe is a flat surface in the motor including six poles and nine slots, and a rotor with no skew. A blue bar in <FIG> indicates a cogging torque when the curvature center of the inner circumferential surface of the shoe coincides with the center C of the stator core <NUM> in the motor including six poles and nine slots, and the rotor with no skew.

Referring to <FIG>, the cogging torque indicated by the red bar and the coating torque indicated by the blue bar were not significantly different from each other at a 6th main cogging order and the 18th main cogging order. On the other hand, it can be confirmed that, at the 9th main cogging order, the coating torque indicated by the blue bar was significantly reduced as compared with the cogging torque indicated by the red bar so that reduction performance of the cogging torque was significantly improved.

<FIG> is a diagram illustrating a motor according to a second embodiment that is part of the invention, and <FIG> is a cross-sectional view illustrating the motor according to the second embodiment. Here, <FIG> is a cross-sectional view taken along line A-A of <FIG>. In <FIG>, a y-direction means the axial direction, and an x-direction means the radial direction. Further, the axial direction is perpendicular to the radial direction.

Referring to <FIG> and <FIG>, a motor 1a according to the second embodiment may include a housing <NUM>, a cover <NUM>, a stator <NUM> disposed on an inner side of the housing <NUM>, a rotor <NUM> disposed on an inner side of the stator <NUM>, a shaft <NUM> coupled to the rotor <NUM>, and the sensing part <NUM>. Here, the inner side means a direction disposed toward the center C based on the radial direction, and an outer side means a direction opposite to the inner side.

The housing <NUM> and the cover <NUM> may form an outer shape of the motor 1a. Here, the housing <NUM> may be formed in a cylindrical shape having an opening formed on an upper portion of the housing <NUM>.

The cover <NUM> may be disposed to cover the open upper portion of the housing <NUM>.

Therefore, the housing <NUM> is coupled to the cover <NUM> so that an accommodation space may be formed in the inner side of the housing <NUM>. Further, as shown in <FIG>, the stator <NUM>, the rotor <NUM>, the shaft <NUM>, and the sensing part <NUM> may be disposed in the accommodation space.

The housing <NUM> may be formed in a cylindrical shape. A pocket for accommodating a bearing <NUM> for supporting a lower portion of the shaft <NUM> may be provided in a lower portion of the housing <NUM>. Further, a pocket for accommodating a bearing <NUM> for supporting an upper portion of the shaft <NUM> may be provided even in the cover <NUM> disposed in the upper portion of the housing <NUM>.

The stator <NUM> may be supported on an inner circumferential surface of the housing <NUM>. Further, the stator <NUM> is disposed on an outer side of the rotor <NUM>. That is, the rotor <NUM> may be disposed on the inner side of the stator <NUM>.

<FIG> is a cross-sectional view illustrating the stator of the motor according to the second embodiment, and <FIG> is an enlarged view illustrating Region A1 of <FIG>.

Referring to <FIG>, the stator <NUM> may include a stator core <NUM>, a coil <NUM> wound around the stator core <NUM>, and an insulator <NUM> disposed between the stator core <NUM> and the coil <NUM>.

The coil <NUM> forming a rotating magnetic field may be wound around the stator core <NUM>. Here, the stator core <NUM> may be formed of one core or by coupling a plurality of divided cores.

Further, the stator core <NUM> may be formed by stacking a plurality of plates in the form of a thin steel sheet, but the present invention is not necessarily limited thereto. For example, the stator core <NUM> may be formed of a single product.

The stator core <NUM> may include a yoke <NUM> and a plurality of teeth <NUM>.

The yoke <NUM> may be formed in a cylindrical shape. Thus, the yoke <NUM> may include a ring-shaped cross section.

The tooth <NUM> may be disposed to protrude from the yoke <NUM> in the radial direction (x direction) based on a center C. Further, the plurality of teeth <NUM> may be disposed to be spaced apart from each other on an inner circumferential surface of the yoke <NUM> in a circumferential direction. Thus, a slot which is a space in which the coil <NUM> may be wound may be formed between the teeth <NUM>. In this case, the teeth <NUM> may be provided as twelve teeth, but the present invention is not necessarily limited thereto.

The tooth <NUM> may be disposed to face a magnet <NUM> of the rotor <NUM>. In this case, an inner surface 1314a of the tooth <NUM> is disposed to be spaced a predetermined distance from an outer circumferential surface of the magnet <NUM> based on the radial direction. Here, the inner surface 1314a may be formed with a predetermined curvature <NUM>/R20 based on the center C of the motor 1a. Accordingly, a length of the inner surface 1314a may be obtained by a formula for calculating a length of an arc.

The coil <NUM> is wound around each of the teeth <NUM>.

Referring to <FIG>, the tooth <NUM> may include a body part <NUM> around which the coil <NUM> is wound, a protrusion <NUM> disposed on an end portion of the body part <NUM>, and a groove <NUM> formed to be concave on the inner surface 1314a of the protrusion <NUM>. In this case, the protrusion <NUM> may include a first region 1314c in which a first surface 1314b is formed and a second region 1314d protruding inward from the first region 1314c based on the radial direction. Here, the body part <NUM> may be referred to as a body, and the protrusion <NUM> may be referred to as a shoe.

The body part <NUM> may be disposed to protrude from the yoke <NUM> in the radial direction (x direction) based on the center C. Further, the body parts <NUM> may be disposed to be spaced apart from each other on the inner circumferential surface of the yoke <NUM> in the circumferential direction.

Further, the coil <NUM> may be wound around the body part <NUM>.

The protrusion <NUM> may extend to protrude inward from the end portion of the body part <NUM>.

Referring to <FIG> and <FIG>, the protrusions <NUM> are disposed to be spaced apart from each other so that an opening may be formed at an inner side of the slot. Here, the opening means the SO. For example, the SO may indicate between one end of the protrusion <NUM> of one tooth <NUM> among the plurality of teeth <NUM> and the other end of the protrusion <NUM> of another tooth <NUM> adjacent to the one tooth <NUM>.

Thus, the SO means a space between an end point P20 of one protrusion <NUM> and an end point P20 of another protrusion <NUM> disposed adjacent to the one protrusion <NUM>. The SO may be disposed to have a predetermined distance W21. The distance W21 of the SO may be referred to as a distance between the protrusions <NUM> or referred to as a width of the SO.

As shown in <FIG>, the protrusion <NUM> may include the first region 1314c in which the first surface 1314b is formed and the second region 1314d based on the radial direction. Further, the groove <NUM> may be formed in the second region 1314d including the inner surface 1314a and a second surface 1314e. Here, the inner surface 1314a of the protrusion <NUM> may be formed with the predetermined curvature <NUM>/R20 based on the center C of the motor 1a.

Further, a side surface of the protrusion <NUM> may include the first surface 1314b extending from the body part <NUM> and the second surface 1314e extending from the first surface 1314b.

The first surface 1314b of the first region 1314c may be formed to have a first inclination θ1 with respect to the side surface 1313a of the body part <NUM>. Further, the second surface 1314e of the second region 1314d may be formed to have a second inclination θ2 with respect to the first surface 1314b.

As shown in <FIG>, the first inclination θ1 may be an obtuse angle of an outer side between the side surface 1313a and the first surface 1314b of the body part <NUM>. Further, the second inclination θ2 may be an obtuse angle of an inner side between the first surface 1314b and the second surface 1314e.

In this case, the first inclination θ1 may be different from the second inclination θ2, but the present invention is not necessarily limited thereto. For example, in consideration of performance and a cogging torque of the motor 1a due to the teeth <NUM>, the first inclination θ1 and the second inclination θ2 may be the same inclination.

The first region 1314c is a region connected to the end portion of the body part <NUM> and may include the first surfaces 1314b formed at both sides based on the circumferential direction. As shown in <FIG>, the first region 1314c is disposed between the body part <NUM> and the second region 1314d.

Referring to <FIG> and <FIG>, the first inclination θ1 between the body part <NUM> and the protrusion <NUM> may range from <NUM>° to <NUM>°. As shown in <FIG>, the first inclination θ1 between the side surface 1313a of the body part <NUM> and the first surface 1314b of the protrusion <NUM> may range from <NUM>° to <NUM>°.

<FIG> is a graph showing a variation in cogging torque according to an angle between the body part and the protrusion of a stator core disposed in the motor according to the second embodiment.

Referring to <FIG>, it can be seen that the cogging torque is significantly reduced within a range from <NUM>° to <NUM>° of the first inclination θ1 between the side surface 1313a of the body part <NUM> and the first surface 1314b of the protrusion <NUM>.

<FIG> shows graphs illustrating a variation in cogging torque waveform according to a first inclination between the body part and the protrusion of the stator core disposed in the motor according to the second embodiment.

As the first inclination θ1 between the side surface 1313a of the body part <NUM> and the first surface 1314b of the protrusion <NUM> is decreased from <NUM>° to <NUM>°, it can be confirmed that an amplitude of the cogging torque waveform was gradually decreased.

The second region 1314d is a portion of the protrusion <NUM> extending inward from the first region 1314c. As shown in <FIG>, the second region 1314d may include the inner surface 1314a on which the groove <NUM> is formed and the second surface 1314e.

In this case, the second region 1314d may be formed to have a predetermined length L20.

The length L20 may be a length of the second surface 1314e. Specifically, the length L20 may be provided as a length from an inner edge of the first surface 1314b to an edge of one side of the inner surface 1314a.

Further, the length L20 of the second surface 1314e may be <NUM>/<NUM> of the distance W21 of the SO based on the radial direction. In this case, the length L20 may be referred to as a depth of the protrusion <NUM>.

The groove <NUM> may be formed to be concave outward on the inner surface 1314a based on the radial direction.

As shown in <FIG> and <FIG>, two cross sections of the grooves <NUM> in a direction perpendicular to the axial direction of the shaft <NUM> have been shown as two examples having a rectangular shape, but the present invention is not necessarily limited thereto. For example, in consideration of the cogging torque, the groove <NUM> may be formed as one groove <NUM> or two or more grooves <NUM>. Alternatively, the groove <NUM> may be formed in a semi-circular shape having a predetermined radius or formed in a parabolic shape.

Referring to <FIG>, the groove <NUM> may be formed in a quadrangular shape having a predetermined width W22 based on the circumferential direction and a predetermined depth D based on the radial direction.

The two grooves <NUM> may be symmetrically disposed based on a reference line CL passing through a center of the width of the protrusion <NUM> and a center of the body part <NUM> based on the circumferential direction.

Further, a first distance L21 between the grooves <NUM> formed on the inner surface 1314a based on the circumferential direction may be equal to a second distance L22 from one end of the protrusion <NUM> to the groove <NUM>. In this case, the first distance L21 and the second distance L22 may be distances on the inner surface 1314a in the circumferential direction.

Owing to the width W22 of the groove <NUM>, the cogging torque of the motor 1a may be decreased.

The width W22 of the groove <NUM> may be <NUM> to <NUM> times a distance between one end of one protrusion <NUM> among the plurality of teeth <NUM> and one end of another protrusion <NUM> among the plurality of teeth <NUM> adjacent to the one protrusion <NUM>. For example, the width W22 of the groove <NUM> may be <NUM> to <NUM> times the distance W21 of the SO formed between the protrusions <NUM>. That is, this may be represented as distance W21:width W22=<NUM>:<NUM> to <NUM>.

<FIG> is a table showing variations in cogging torque and torque when the width of the groove is <NUM> to <NUM> times the width of the SO in the motor according to the second embodiment, <FIG> is a graph showing the cogging torque when the width of the groove is <NUM> to <NUM> times the width of the SO in the motor according to the second embodiment, <FIG> is a graph showing a cogging torque waveform of a motor of Comparative Example, and <FIG> is a graph showing a cogging torque waveform of the motor according to the second embodiment when the width of the groove is <NUM> times the width of the SO. Here, the motor provided as Comparative Example is a case in which the width of the SO is equal to that of the groove, and the widths of the SO and the groove may be provided as <NUM>. Further, a depth of the groove is <NUM>. In this case, a value of <NUM> mN in <FIG> represents the cogging torque of the motor of Comparative Example.

The width W22 of the groove <NUM> may be formed within a range of <NUM> to <NUM> times the distance W21 of the SO. That is, this may be represented as distance W21:width W22=<NUM>:<NUM> to <NUM>.

Referring to <FIG> and <FIG>, the cogging torque of the motor 1a according to the second embodiment may be maximally reduced by <NUM>% (W22=<NUM>) as compared with the motor of the Comparative Example. For example, it can be confirmed that the cogging torque of the motor 1a was reduced until the width W22 of the groove <NUM> of the motor 1a reached <NUM> and was increased again. In this case, it can be confirmed that a variance in torque of the motor 1a according to the second embodiment is not significant as compared with a result value of <NUM> which is a torque of the motor of Comparative Example.

<FIG> is a graph showing pulsation of a cogging torque (repetitive torque waveform) of the motor of Comparative Example, and <FIG> is a graph showing pulsation of a cogging torque (repetitive torque waveform) of the motor according to the second embodiment. Referring to <FIG> and <FIG>, it can be confirmed that an amplitude between a maximum value and a minimum value of the cogging torque of the motor 1a were smaller than an amplitude between a maximum value and a minimum value of the cogging torque of the motor of Comparative Example.

<FIG> is a table showing variations in cogging torque and torque when the width of the groove is <NUM> to <NUM> times the width of the SO in the motor according to the second embodiment, <FIG> is a graph showing variations in the cogging torque when the width of the groove is <NUM> to <NUM> times the width of the SO in the motor according to the second embodiment, and <FIG> is a graph showing a cogging torque waveform of the motor according to the second embodiment when the width of the groove is <NUM> times the width of the SO.

Referring to <FIG> and <FIG>, the cogging torque of the motor 1a according to the second embodiment may be reduced by <NUM>% (W2=<NUM>) at most as compared with the motor of Comparative Example. For example, it can be confirmed that the cogging torque of the motor 1a was reduced until the width W22 of the groove <NUM> of the motor 1a reached <NUM> and was increased again. In this case, it can be confirmed that a variance in torque of the motor 1a according to the second embodiment is not significant as compared with a result value of <NUM> which is a torque of the motor of Comparative Example.

<FIG> is a graph showing the pulsation of the cogging torque (repetitive torque waveform) of the motor according to the second embodiment. Referring to <FIG> and <FIG>, it can be confirmed that an amplitude between the maximum value and the minimum value of the cogging torque of the motor 1a were smaller than the amplitude between the maximum value and the minimum value of the cogging torque of the motor of Comparative Example.

Thus, when the width W22 of the groove <NUM> is <NUM> to <NUM> times a distance between one end of one protrusion <NUM> among the plurality of teeth <NUM> and one end of another protrusion <NUM> among the plurality of teeth <NUM> adjacent to the one protrusion <NUM>, the cogging torque is effectively reduced so that quality of the motor 1a may be improved.

In particular, when the width W22 of the groove <NUM> is <NUM>, the cogging torque of the motor 1a is maximally decelerated. That is, when the width W22 of the groove <NUM> is <NUM> times the distance W21 of the SO, the cogging torque of the motor 1a is maximally decelerated.

Owing to the depth D of the groove <NUM>, the cogging torque of the motor 1a may be decreased.

The depth D of the groove <NUM> may be <NUM> to <NUM> times the length L20 of the second surface 1314e based on the radial direction. For example, the depth D of the groove <NUM> may be formed within a range of <NUM> to <NUM> times the length L20 from an edge of one side of the first surface 1314b of the protrusion <NUM> to the inner surface 1314a. That is, this may be represented as length L20:depth D=<NUM>:<NUM> to1.

Further, since the length L20 of the second surface 1314e may be provided as <NUM>/<NUM> of the distance W21 of the SO based on the radial direction, the depth D of the groove <NUM> may be formed in a range of <NUM> to <NUM> times the distance W21 of the SO formed between the protrusions <NUM> based on the radial direction.

<FIG> is a table showing variations in cogging torque and torque when the depth of the groove is <NUM> to <NUM> times the length of the second surface in the radial direction in the motor according to the second embodiment, <FIG> is a graph showing the cogging torque when the depth of the groove is <NUM> to <NUM> times the length of the second surface in the radial direction in the motor according to the second embodiment, and <FIG> is a graph showing a cogging torque waveform when the depth of the groove is <NUM> times the length of the second surface in the radial direction in the motor according to the second embodiment. Here, the motor provided as Comparative Example is a case in which the depth of the protrusion is equal to that of the groove, and the length of the second surface and the dept of the groove may be provided as <NUM>. In this case, a value of <NUM> mN in <FIG> represents the cogging torque of the motor of Comparative Example.

The depth D of the groove <NUM> may be formed within a range of <NUM> to <NUM> times the distance L20 of the second surface 1314e. That is, this may be represented as length L20:depth D=<NUM>:<NUM> to <NUM>.

Further, when the length L20 of the second surface 1314e is <NUM>/<NUM> of the distance W21 of the SO, the depth D of the groove <NUM> may be formed within a range of <NUM> to <NUM> times the distance W21 of the SO.

Referring to <FIG>, the cogging torque of the motor 1a according to the second embodiment may be maximally reduced by <NUM>% (D=<NUM>) as compared with the motor of Comparative Example. For example, it can be confirmed that the cogging torque of the motor 1a was reduced until the depth D of the groove <NUM> of the motor 1a reached <NUM> and was increased again. In this case, it can be confirmed that a variance in torque of the motor 1a according to the second embodiment is not significant as compared with a result value of <NUM> which is a torque of the motor of Comparative Example.

<FIG> is a graph showing the pulsation of the cogging torque (repetitive torque waveform) of the motor according to the second embodiment. Referring to <FIG> and <FIG>, it can be confirmed that an amplitude between a maximum value and a minimum value of the cogging torque of the motor 1a were smaller than the amplitude between a maximum value and a minimum value of the cogging torque of the motor of Comparative Example.

<FIG> is a table showing variations in cogging torque and torque when the depth of the groove is <NUM> to <NUM> times the length of the second surface in the radial direction in the motor according to the second embodiment, <FIG> is a graph showing the cogging torque when the depth of the groove is <NUM> to <NUM> times the length of the second surface in the radial direction in the motor according to the second embodiment, and <FIG> is a graph showing a cogging torque waveform when the depth of the groove is <NUM> times the length of the second surface in the radial direction in the motor according to the second embodiment.

Referring to <FIG> and <FIG>, the cogging torque of the motor 1a according to the second embodiment may be maximally reduced by <NUM>% (D=<NUM>) as compared with the motor of Comparative Example. For example, it can be confirmed that the cogging torque of the motor 1a was reduced until the depth D of the groove <NUM> of the motor 1a reached <NUM> and was increased again. In this case, it can be confirmed that a variance in torque of the motor 1a according to the second embodiment is not significant as compared with a result value of <NUM> which is a torque of the motor of Comparative Example.

<FIG> is a table showing variations in cogging torque and torque when the depth of the groove is <NUM> and the width of the groove is <NUM> to <NUM> times the width of the SO in the motor according to the second embodiment, <FIG> is a graph showing the cogging torque when the depth of the groove is <NUM> and the width of the groove is <NUM> to <NUM> times the width of the SO in the motor according to the second embodiment, and <FIG> is a graph showing the cogging torque waveform when the depth of the groove is <NUM> and the width of the groove is <NUM> times the width of the SO in the motor according to the second embodiment.

As shown in <FIG> and <FIG>, when the depth D of the groove <NUM> is <NUM>, the cogging torque is reduced as much as possible. Accordingly, as shown in <FIG>, a variance in cogging torque of the motor 1a according to the width W22 of the groove <NUM> can be confirmed based on when the depth D of the groove <NUM> is <NUM>. That is, the depth D of the groove <NUM> of the motor 1a is fixed and thus variations and critical values in cogging torque and torque due to the width W22 of the groove <NUM> can be confirmed. In this case, the distance W21 of the SO may be <NUM>, and the length L20 of the second surface 1314e which is the depth of the protrusion <NUM> may be <NUM>.

Referring to <FIG>, the cogging torque of the motor 1a according to the second embodiment may be maximally reduced by <NUM>% (W2=<NUM>) as compared with the motor of Comparative Example. For example, it can be confirmed that the cogging torque of the motor 1a was reduced until the width W22 of the groove <NUM> of the motor 1a reached <NUM> and was increased again. In this case, it can be confirmed that a variance in torque of the motor 1a according to the second embodiment is not significant as compared with a result value of <NUM> which is a torque of the motor of Comparative Example.

<FIG> is a table showing variations in cogging torque and torque when the width of the groove is <NUM> and the depth of the groove is <NUM> to <NUM> times the length of the second surface in the radial direction in the motor according to the second embodiment, <FIG> is a graph showing the cogging torque when the width of the groove is <NUM> and the depth of the groove is <NUM> to <NUM> times the length of the second surface in the radial direction in the motor according to the second embodiment, and <FIG> is a graph showing a cogging torque waveform when the width of the groove is <NUM> and the depth of the groove is <NUM> times the length of the second surface in the radial direction in the motor according to the second embodiment.

As shown in <FIG> and <FIG>, when the width W22 of the groove <NUM> is <NUM>, the cogging torque is reduced as much as possible. Accordingly, as shown in <FIG>, a variance in cogging torque of the motor 1a according to the depth D of the groove <NUM> can be confirmed based on when the width W22 of the groove <NUM> is <NUM>. That is, the width W22 of the groove <NUM> of the motor 1a is fixed and thus variations and critical values in cogging torque and torque due to the depth D of the groove <NUM> can be confirmed. In this case, the distance W21 of the SO may be <NUM>, and the length L20 of the second surface 1314e which is the depth of the protrusion <NUM> may be <NUM>.

Therefore, it can be confirmed that a variance in cogging torque of the motor 1a is larger due to the width W22 rather than the depth D of the groove <NUM>. Accordingly, the motor 1a may preferentially reduce the cogging torque by adjusting a size of the width W22 rather than the depth D of the groove <NUM>.

Further, in the motor 1a, when the width W22 of the groove <NUM> is <NUM> and the depth D thereof is <NUM>, the cogging torque is reduced as much as possible by <NUM>%. That is, in the motor 1a, when the width W22 of the groove <NUM> is <NUM> times the distance W21 of the SO and the depth D of the groove <NUM> is <NUM> times the depth of the protrusion <NUM>, the cogging torque is reduced as much as possible.

Here, the length L20 of the second surface 1314e may be provided as a length from an inner edge of the first surface 1314b to an edge of one side of the inner surface 1314a. Further, since the length L20 may be <NUM>/<NUM> of the distance W21 of the SO, when the depth D of the groove <NUM> is <NUM> times the distance W21 of the SO, the cogging torque is decreased as much as possible.

Meanwhile, the width W22 of the groove <NUM> may be <NUM> to <NUM> times the distance W21 of the SO formed between the protrusions <NUM>, and the depth D of the groove <NUM> may be <NUM> to <NUM> times the length L20 of the second surface.

When the depth D of the groove <NUM> is <NUM> and the width W22 of the groove <NUM> ranges from <NUM> to <NUM>, the cogging torque of the motor 1a is significantly decreased.

A ratio of the width W22 of the groove <NUM> to the depth D thereof may range from <NUM> to <NUM>. Accordingly, when the width W22 of the groove <NUM> is <NUM> to <NUM> times the depth D of the groove <NUM>, the cogging torque of the motor 1a is optimally reduced. That is, this may be represented as depth D:width W22 of the groove <NUM>=<NUM>:<NUM> to <NUM>.

The insulator <NUM> isolates the stator core <NUM> from the coil <NUM>. Thus, the insulator <NUM> may be disposed between the stator core <NUM> and the coil <NUM>.

Accordingly, the coil <NUM> may be wound around the tooth <NUM> of the stator core <NUM> in which the insulator <NUM> is disposed.

The rotor <NUM> is disposed on an inner side of the stator <NUM>. Further, the rotor <NUM> may include a hole, into which the shaft <NUM> is inserted, at a central portion of the rotor <NUM>. Thus, the shaft <NUM> may be coupled to the groove of the rotor <NUM>.

Referring to <FIG>, the rotor <NUM> may include a rotor core <NUM> and the magnet <NUM> disposed on an outer circumferential surface of the rotor core <NUM>.

The rotor <NUM> may be classified into the following types according to a coupling method between the rotor core <NUM> and the magnet <NUM>.

As shown in <FIG>, the rotor <NUM> may be implemented in a type in which the magnet <NUM> is coupled to the outer circumferential surface of the rotor core <NUM>. In such a type of the rotor <NUM>, in order to prevent separation of the magnet <NUM> and increase a coupling force, a separate can member (not shown) may be coupled to the rotor core <NUM>. Alternatively, the rotor <NUM> may be integrally formed with the magnet <NUM> and the rotor core <NUM> through dual injection of the magnet <NUM> and the rotor core <NUM>.

Also alternatively, the rotor <NUM> may be implemented in a type in which the magnet <NUM> is coupled to an interior of the rotor core <NUM>. Such a type of the rotor <NUM> may be provided with a pocket into which the magnet <NUM> is inserted into the rotor core <NUM>.

The rotor core <NUM> may be formed by stacking a plurality of plates in the form of a thin steel sheet. Alternatively, the rotor core <NUM> may be manufactured in a single core form comprised of a single cylinder.

Also alternatively, the rotor core <NUM> may be made in the form in which a plurality of pucks (unit cores) forming a skew angle are stacked.

Further alternatively, the rotor core <NUM> may include a hole formed to allow the shaft <NUM> to be inserted thereinto.

The magnet <NUM> may be provided as eight magnets <NUM>, but the present invention is not necessarily limited thereto.

The shaft <NUM> may be coupled to the rotor <NUM>. When an electromagnetic interaction occurs in the rotor <NUM> and the stator <NUM> through a supply of a current, the rotor <NUM> rotates and thus the shaft <NUM> is rotated by being interlocked with the rotation of the rotor <NUM>. In this case, the shaft <NUM> may be supported on the bearing <NUM>.

The shaft <NUM> may be connected to a steering shaft of a vehicle. Thus, the steering shaft may receive power due to a rotation of the shaft <NUM>.

The sensing part <NUM> may detect a magnetic force of the sensing magnet installed to be capable of being rotationally interlocked with the rotor <NUM> to determine a current position of the rotor <NUM>, thereby detecting a rotated position of the shaft <NUM>.

The sensing part <NUM> may include a sensing magnet assembly <NUM> and a PCB <NUM>.

The sensing magnet assembly <NUM> is coupled to the shaft <NUM> to be interlocked with the rotor <NUM> to detect a position of the rotor <NUM>. In this case, the sensing magnet assembly <NUM> may include a sensing magnet and a sensing plate. The sensing magnet may be coaxially coupled to the sensing plate.

The sensing magnet may include a main magnet disposed adjacent to a hole forming an inner circumferential surface in a circumferential direction and a sub-magnet formed at an edge of the main magnet. The main magnet may be arranged equal to a drive magnet inserted into rotor <NUM> of the motor. The sub-magnet is more segmented than the main magnet and comprised of many poles. Thus, a rotation angle may be further divided and measured, and driving of the motor may be made smoother.

The sensing plate may be formed of a metal material in the form of a disc. The sensing magnet may be coupled to an upper surface of the sensing plate. Further, the sensing plate may be coupled to the shaft <NUM>. Here, a hole through which the shaft <NUM> passes is formed in the sensing plate.

A sensor for detecting a magnetic force of the sensing magnet may be disposed on the PCB <NUM>. In this case, the sensor may be provided as a Hall IC. Further, the sensor may generate a sensing signal by detecting a variation in a north pole and a south pole of the sensing magnet.

Claim 1:
A motor comprising:
a shaft (<NUM>);
a rotor (<NUM>) to which the shaft (<NUM>) is coupled;
a stator (<NUM>) disposed on an outer side of the rotor (<NUM>),
wherein the stator (<NUM>) includes a stator core (<NUM>) having a plurality of teeth (<NUM>), and a coil (<NUM>) wound around each of the teeth,
wherein each of the teeth (<NUM>) includes a body part (<NUM>) around which the coil (<NUM>) is wound, a protrusion (<NUM>) disposed on an end portion of the body part (<NUM>), and two grooves (<NUM>) formed on an inner surface (1314a) of the protrusion (<NUM>),
wherein, in a circumferential direction of the stator core (<NUM>), respective ends of the protrusions (<NUM>) of adjacent teeth (<NUM>) of the stator core have a distance (W21) therebetween, and each groove (<NUM>) has a width (W22) in a range of <NUM> to <NUM> times the distance (W21),
wherein the protrusion (<NUM>) has a side surface including a first surface (1314b) extending from the body part (<NUM>) and a second surface (1314e) extending from the first surface (1314b),
wherein the first surface (1314b) has a first inclination (θ1) with respect to a side surface (1313a) of the body part (<NUM>), and the second surface (1314e) has a second inclination (θ2) with respect to the first surface (1314b),
wherein the first inclination (θ1) is an obtuse angle of an outer side between the side surface (1313a) and the first surface (1314b) of the body part (<NUM>), and the second inclination (θ2) is an obtuse angle of an inner side between the first surface (1314b) and the second surface (1314e), and
wherein the grooves (<NUM>) are symmetrically disposed based on a reference line (CL) passing through a center of a width of the protrusion (<NUM>) in a circumferential direction and a center of the body part (<NUM>),
characterized in that a first distance (L21) between the grooves is equal to a second distance (L22) from one end of the protrusion (<NUM>) to the groove (<NUM>),
wherein a depth (D) of each groove (<NUM>) is <NUM> to <NUM> times the distance (W21),
wherein the length (L20) of the second surface (1314e) in a radial direction from an inner edge of the first surface (1314b) to an edge of the inner surface (1314a) is <NUM>/<NUM> of the distance (W21),
wherein the first inclination (θ1) is in a range of <NUM>° to <NUM>°.