Patent Description:
As a motor of a vehicle evolves to have a specification such as a higher torque and a higher speed, a robust design has been required for a rotor structure applied to the motor.

A rotor used in a general motor has a structure in that a stacked rotor core, which is formed by stacking a plurality of disc-shaped rotor core members, is provided and a magnet is attached to an outer side surface of the rotor core.

The motor using such a permanent magnet exhibits a cogging torque. The cogging torque refers to a non-uniform torque of a stator inevitably occurring in a motor using the permanent magnet and means a torque in a radial direction intended to move to a position where magnetic energy of the motor is at a minimum, that is, to an equilibrium state.

The cogging torque is caused by a sudden change in magnetic flux near a boundary between an N pole and an S pole of the magnet. It is important to reduce the cogging torque because the cogging torque causes noise and vibration and deteriorates performance of the motor. Particularly, it is more important to reduce the cogging torque in a motor used in an actuator for precise position control.

However, when a skew angle is applied in a state where each puck is attached to a rotor to which a plurality of magnets are attached, or three-stage magnets are simultaneously magnetized, neighboring pucks exert influences on each other during the magnetization, and the cogging torque and a back electromotive force harmonic wave are deteriorated due to influences from vertically opposite polarities even after the magnetization.

In addition, a plurality of magnets are installed in the rotor. According to an installation type of the magnets, the rotor is classified into an inner permanent magnet (IPM) rotor in which the magnets are inserted into and coupled to the inside of a rotor core and a surface permanent magnet (SPM) rotor in which the magnets are attached to a surface of the rotor core.

In the case of an IPM motor, a coupling hole is provided in the rotor core, and the magnet is inserted into the coupling hole. An adhesive is used to fix the magnet to the coupling hole. When the adhesive is applied to the coupling hole, a process of injecting and curing the adhesive between the magnet and the coupling hole is complicated and a process time increases. In addition, there is a problem that the process time increases because an additional process is required to confirm whether the adhesive is cured.

<CIT> discloses a brushless motor whose rotor is designed with a view of enabling easy positioning of magnets while forming a flux barrier and a motor using the rotor for an electric motor. <CIT> discloses a motor with a rotor with a plurality of rotor core members and a plurality of magnets mounted on the outer rotor surface in a skewed manner.

An embodiment is directed to providing a motor having magnets attached to a rotor core and spaced apart from each other.

In addition, an embodiment not part of the claimed invention is directed to providing a motor in which the magnet is fixed to a coupling hole of the rotor core without an adhesive.

The problems to be solved by the present invention are not limited to the above-mentioned problems and those skilled in the art may apparently understand other problems not mentioned herein based on the following descriptions.

The invention is a motor as defined in the independent claim <NUM>. Further embodiments of the invention are defined in dependent claims <NUM>-<NUM>.

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.

According to an embodiment, magnets are spaced apart from each other so that the cogging torque and back electromotive force harmonic wave can be improved.

According to other embodiments not part of the claimed invention the magnets are fixed to a rotor core without an adhesive so that a manufacturing process can be simplified and a manufacturing time can be reduced.

The coupling between the magnet and the rotor core can be improved.

A bearing is supported through a second holder so that the structure can be simplified.

The various and useful advantages and effects of the present invention are not limited to the above descriptions and may be more easily understood in the course of describing specific embodiments of the present invention.

The present invention is illustrated in the example of <FIG> and the related description. While the other embodiments discussed below are not all specifically claimed, the related description is useful as background information and to provide a better understanding of the invention and its context. The terms including ordinal numbers such as first and second may be used to describe various elements, but the elements are not limited by the terms. The terms are used only for the purpose of distinguishing one element from another element. The term "and/or" includes any one of a plurality of relevant listed items or a combination thereof.

The terms used herein are merely for the purpose of illustrating a particular embodiment and are not intended to limit the embodiments of the present invention.

In the description of an embodiment, when an element is described as being formed "on or under" another element, the expression "on or under" includes at least one of that two elements come into direct contact with each other or that the other element is disposed between the two elements. In addition, the expression "on or under" may include not only the upward direction but also the downward direction with respect to one element.

Hereinafter, the embodiments will be described in detail with reference to the accompanying drawings. The same reference numerals in different drawings may indicate the same or corresponding elements, and a duplicate description thereof will be omitted.

Referring to <FIG>, a motor <NUM> according to an embodiment of the present invention may include a rotating shaft <NUM>, a rotor <NUM>, a stator <NUM>, and a housing <NUM>.

The rotating shaft <NUM> may be coupled to the rotor <NUM>. When an electromagnetic interaction occurs between the rotor <NUM> and the stator <NUM> through a current supply, the rotor <NUM> rotates and the rotating shaft <NUM> rotates in conjunction with the rotor <NUM>. The rotating shaft <NUM> may be supported by a bearing.

The rotor <NUM> is disposed inside the stator <NUM>. The rotor <NUM> may include a rotor core and a magnet coupled to the rotor core. The rotor <NUM> may be classified into the following forms according to the coupling type between the rotor core and the magnet.

The rotor <NUM> may be implemented as a type in which the magnet is coupled to an outer circumferential surface of the rotor core. According to the rotor <NUM> of the above type, an additional can member may be coupled to the rotor core to prevent separation of the magnet and increase a coupling force. Alternatively, the magnet and the rotor may be integrally formed by double injection molding.

The rotor <NUM> may be implemented as a type in which the magnet is coupled to an inside of the rotor core. For the rotor <NUM> of the above type, a pocket into which the magnet is inserted may be provided in the rotor core.

Meanwhile, the rotor core may be classified into two types.

First, the rotor core may be formed by stacking a plurality of plates in the form of a thin steel plate. Here, the rotor core may be formed as a single piece that does not form a skew angle or may be formed of a plurality of unit cores (pucks), which form a skew angle, to be coupled to each other.

Second, the rotor core may be formed as a single cylinder. Here, the rotor core may be formed as a single piece that does not form a skew angle or may be formed of a plurality of unit cores (pucks), which form a skew angle, to be coupled to each other.

Meanwhile, each of the unit cores may include a magnet outside or inside the unit core.

The stator <NUM> causes an electrical interaction with the rotor <NUM> to induce rotation of the rotor <NUM>. A coil may be wound on the stator <NUM> to cause the interaction with the rotor <NUM>. The specific configuration of the stator <NUM> to wind the coil is as follows.

The stator <NUM> may include a stator <NUM> core including a plurality of teeth. The stator <NUM> core may be provided with an annular yoke and teeth which protrude from an inner circumferential surface of the yoke toward a center of the stator <NUM> core, may be provided. The teeth may be provided at regular gaps along a circumference of the yoke. Meanwhile, the stator <NUM> core may be formed by stacking a plurality of plates in the form of a thin steel plate. In addition, the stator <NUM> core may be formed by coupling or connecting a plurality of split cores to each other.

The housing <NUM> is formed in a cylindrical shape so that a stator <NUM> assembly may be coupled to an inner wall thereof. An upper portion of the housing <NUM> may be implemented to be open, and a lower portion of the housing <NUM> may be implemented to be closed. A bearing mounting space configured to accommodate a bearing for supporting a lower portion of the rotating shaft <NUM> may be provided at the lower portion of the housing <NUM>. A cover may be coupled to the upper portion of the opened housing <NUM>.

<FIG> is a view showing a first embodiment of the rotor which is an element of the present invention.

Referring to <FIG>, the rotor <NUM> as an element of the present invention may include a rotor core <NUM> surrounding the rotating shaft <NUM> and a plurality of magnets <NUM> coupled to the rotor core <NUM>, the magnets <NUM> may be disposed to be spaced apart from the magnets <NUM> adjacent in the axial direction of the rotating shaft <NUM> by a predetermined gap, and the sum of the spaced gaps of the magnets <NUM> may be set to have a ratio of <NUM> to <NUM> times an axial length of the stator <NUM>.

According to the present invention, the magnets <NUM> disposed in the rotor core <NUM> are spaced apart from each other in the direction of the rotating shaft <NUM> to reduce the cogging torque.

When the rotor core <NUM> is integrally formed, the magnets <NUM> provided in a curved shape may be disposed on an outer surface of the rotor core <NUM> to have a layered structure. In this case, the magnets <NUM> may be disposed to be spaced apart from the magnets <NUM> adjacent in the axial direction of the rotating shaft <NUM> by a predetermined gap. Here, the sum of the gaps of the magnets <NUM> formed of a multi-layered structure may be disposed to have a ratio of <NUM> to <NUM> times the axial length of the stator <NUM>.

Here, the gaps formed between the magnets <NUM> having the layered structure and the adjacent magnets <NUM> having the layered structure may be equal to each other.

In addition, when the rotor core <NUM> is provided with a plurality of rotor cores, a height of each rotor core <NUM> is set to be higher than a height of the magnet <NUM> so that the magnets <NUM> adjacent to each other in the axial direction of the rotating shaft <NUM> may be disposed to be spaced apart from each other by a predetermined gap even when the rotor cores <NUM> are tightly coupled to each other.

<FIG> is a view showing a second embodiment of the rotor <NUM> which is an element of the present invention.

Referring to <FIG>, the rotor core <NUM> may be provided with a plurality of rotor cores and disposed to be spaced apart from the rotor cores <NUM> adjacent in the axial direction of the rotating shaft <NUM> by a predetermined gap. In this case, the gap of the rotor core <NUM> may be adjusted by press-fitting equipment.

The rotor core <NUM> and the magnet <NUM> may have the same height. When the rotor cores <NUM> are disposed to be spaced apart from each other, the sum of the gaps between the rotor cores <NUM> may be the same as the sum of the gaps of the magnets <NUM>.

In addition, the sum of the gaps between the rotor cores <NUM> is calculated as the sum of a first gap and a second gap formed by the rotor cores <NUM>, in which the first gap and the second gap may be formed at the same gap.

The sum of the gaps between the rotor cores <NUM>, in other words, the sum of the first gap and the second gap may be disposed to have a ratio of <NUM> to <NUM> times the axial length of the stator <NUM>.

<FIG> is a view showing a third embodiment of the rotor <NUM> which is an element of the present invention. <FIG> is a view showing a shape of a spacer <NUM> which is an element of <FIG>.

Referring to <FIG>, a spacer <NUM> may be provided between the rotor cores <NUM> to define the gap between the rotor cores;
When the rotor cores <NUM> are disposed, the spacer <NUM> may allow adjacent rotor cores <NUM> to be spaced by a predetermined gap. The spacer <NUM> may be disposed between the rotor cores <NUM> to allow the rotor cores <NUM> to be disposed at regular gaps. The spacer <NUM> may be smaller than an outer diameter of the rotor core <NUM> so that an interference of the spacer <NUM> to the magnet <NUM> may be minimized.

In one embodiment, the spacer <NUM> may be provided in a circular ring shape and the rotating shaft <NUM> may be inserted into the spacer <NUM>. The circular spacer <NUM> having a constant thickness may stably support the gap formed by the spacer <NUM> when the rotor <NUM> rotates. The circular ring-shaped spacer <NUM> is shown in <FIG>, but the shape of the spacer <NUM> is not limited and may be modified into various shapes.

In addition, the spacer <NUM> disposed between the rotor cores <NUM> allows the gap between the rotor cores <NUM> to be maintained constantly, and the gap between the rotor cores <NUM> may be an axial length of the spacer <NUM>. Here, the sum of axial lengths of a plurality of spacers <NUM> may be disposed to have a ratio of <NUM> to <NUM> times an axial length of the stator <NUM>.

<FIG> is an enlarged view of an internal structure of the motor <NUM> according to an embodiment of the present invention.

Referring to <FIG>, the stator <NUM> is disposed adjacent to the outside of the rotor <NUM>.

In the structure where the plurality of rotor cores <NUM> are coupled, the magnet <NUM> attached to the rotor core <NUM> protrudes from an upper surface and a lower surface of the stator <NUM> in the axial direction of the rotating shaft <NUM>. In other words, when viewed from a side surface of the stator <NUM>, the magnet <NUM> is disposed to protrude upward and downward from the stator <NUM>.

Here, the sum of a height h2 at which the magnet <NUM> protrudes from the upper surface of the stator <NUM> and a height h1 at which the magnet <NUM> protrudes from the lower surface of the stator <NUM> is equal to the sum of the gaps (D1+D2) between the magnets <NUM>. In other words, the sum of the height h of the stator <NUM> is equal to the sum of the heights of the magnets <NUM> having a multi-layered structure.

In addition, the height h2 at which the magnet <NUM> protrudes from the upper surface of the stator <NUM> may be equal to the height h1 at which the magnet <NUM> protrudes from the lower surface of the stator <NUM>.

The arrangement of the magnets <NUM> is intended to arrange the magnets <NUM> at a center of the stator <NUM> so that an influence of the gap of the magnet <NUM> on the stator <NUM> is minimized.

<FIG> is a view showing a change amount of a cogging torque according to the gap ratio of the magnet of the present invention.

Referring to <FIG>, a graph shows changes in the cogging torque and the back electromotive force harmonic wave according to the change in the gap of the magnets <NUM>.

Table <NUM> shows quantitative values of the graph of <FIG>.

It can be confirmed that the cogging torque decreases within a predetermined range as the ratio of the gaps formed by the magnets <NUM> increase.

It can be confirmed that the cogging torque decreases gently when the gap ratio increases from <NUM>% to <NUM>%.

Thereafter, it can be confirmed that the cogging torque decreases sharply in the range of <NUM>% to <NUM>%, and the cogging torque increases again as the gap ratio increases from the vicinity of <NUM>%.

Accordingly, it can be confirmed that the gap ratio according to the present invention is in the range of <NUM>% to <NUM>% to reduce the cogging torque, and it is more effective to reduce the cogging torque when the gap ratio is in the range of <NUM>% to <NUM>%.

<FIG> are views showing embodiments which are not part of the claimed invention.

Referring to <FIG>, the motor 1a according to an embodiment may include a rotating shaft <NUM>, a rotor <NUM>, and a stator <NUM>.

The rotating shaft <NUM> may be coupled to the rotor <NUM>. When an electromagnetic interaction occurs between the rotor <NUM> and the stator <NUM> by supplying a current, the rotor <NUM> rotates and the rotating shaft <NUM> rotates in conjunction with the rotor <NUM>. The rotating shaft <NUM> may be connected to a steering shaft of the vehicle to transmit power to the steering shaft.

The rotor <NUM> rotates through the electrical interaction with the stator <NUM>. The rotor <NUM> may be disposed inside the stator <NUM>.

A coil may be wound on the stator <NUM> to cause the electrical interaction with the rotor <NUM>. The specific configuration of the stator <NUM> for winding the coil is as follows. The stator <NUM> may include a stator core including a plurality of teeth. The stator core may be provided with an annular yoke portion, and the teeth may be provided around which the coil is wound from an inner circumferential surface of the yoke toward a center of the stator core. The teeth may be provided at regular gaps along an outer circumferential surface of the yoke portion. Meanwhile, the stator core may be formed by stacking a plurality of plates in the form of a thin steel plate. In addition, the stator core may be configured to have a plurality of split cores coupled or connected to each other.

The motor may include a bus bar <NUM>. The bus bar <NUM> may be disposed on the stator <NUM>. The bus bar <NUM> may include a terminal inside an annular mold member.

A housing <NUM> of the motor may accommodate the rotor <NUM> and the stator <NUM> therein. The housing <NUM> may include a body <NUM> and a bracket <NUM>. The body <NUM> has a cylindrical shape. The body <NUM> may be formed of a metal material such as aluminum. In addition, the body <NUM> is open at the top thereof. The bracket <NUM> covers the open top of the body <NUM>. The stator <NUM> may be disposed inside the body <NUM>, and the rotor <NUM> may be disposed inside the stator <NUM>. A bearing <NUM> may be disposed at a center of the bracket <NUM>. The bearing <NUM> may be double injection-molded and integrated with the bracket <NUM>.

A sensing magnet <NUM> is a device configured to be coupled to the rotating shaft <NUM> to interlock with the rotor <NUM> so as to detect a position of the rotor <NUM>.

A sensor configured to sense a magnetic force of the sensing magnet <NUM> may be disposed on a printed circuit board <NUM>. Here, the sensor may be a Hall integrated circuit (IC). The sensor generates a sensing signal by sensing changes in N and S poles of the sensing magnet <NUM>.

<FIG> is a view showing coupling holes and magnets of the rotor.

Referring to <FIG>, the rotor <NUM> may include a rotor core <NUM> and a magnet <NUM>. The rotor core <NUM> may be implemented by stacking a plurality of plates in the form of a circular thin steel plate. A hole 2210a to which the rotating shaft <NUM> is coupled may be disposed at a center of the rotor core <NUM>. The rotor core <NUM> may include a plurality of coupling holes <NUM>. The coupling hole <NUM> is formed through the rotor core <NUM> in the height direction of the rotor core <NUM>. The height direction of the rotor core <NUM> in the motor is a direction parallel to the axial direction of the rotating shaft <NUM>. The magnet <NUM> is inserted into the coupling hole <NUM>. The number of the coupling holes <NUM> is equal to the number of the magnets <NUM>. The coupling holes <NUM> are disposed at regular gaps in a circumferential direction of the rotor core <NUM>. A plane shape of the coupling hole <NUM> may be rectangular.

Gap portions G may be disposed on both sides of the coupling hole <NUM>. The gap portion G signifies a portion separated apart from the magnet <NUM>. The gap portion G is configured to prevent magnetic flux from leaking to an adjacent magnet <NUM>. Meanwhile, a bridge portion <NUM> is disposed between adjacent coupling holes <NUM>. The bridge portion <NUM> is disposed between the gap portions G of the adjacent coupling holes <NUM>.

<FIG> is a view showing the rotor. <FIG> and <FIG> are exploded perspective views of the rotor shown in <FIG>.

Referring to <FIG>, the rotor <NUM> may be formed by stacking a plurality of rotor cores <NUM>. For example, the rotor <NUM> may be formed by stacking three rotor cores 2210A, 2210B, and 2210C. Around a second rotor core 2210B disposed at a center of the rotor cores, a first rotor core 2210A may be disposed on the top of the second rotor core, and a third rotor core 2210C may be disposed on the bottom of the second rotor core. Each of the first, second and third rotor cores 2210A, 2210B and 2210C may be stacked to form a skew angle. In addition, the magnet (<NUM> of <FIG>) is disposed inside each of the first, second and third rotor cores 2210A, 2210B, and 2210C.

Meanwhile, the rotor <NUM> may include a first holder <NUM> and a second holder <NUM>. The first holder <NUM> and the second holder <NUM> serve to fix the magnet <NUM> to the coupling hole <NUM> without an adhesive.

The first holder <NUM> may be disposed between the first rotor core 2210A and the second rotor core 2210B or between the second rotor core 2210B and the third rotor core 2210C. For example, the first holder <NUM> may be disposed between the second rotor core 2210B disposed at the center and the first rotor core 2210A disposed on the top of the second rotor core 2210B. In addition, the first holder <NUM> may be disposed between the second rotor core 2210B disposed at the center and the third rotor core 2210C disposed on the bottom of the second rotor core 2210B. The second rotor core 2210B disposed at the center may be interposed between the two first holders <NUM>.

The second holder <NUM> may be disposed on the top of the first rotor core 2210A disposed on the uppermost side. Alternatively, the second holder <NUM> may be disposed on the bottom of the third rotor core 2210C disposed on the lowermost side. Two second holders <NUM> may be disposed with the rotor core <NUM> therebetween.

<FIG> is a perspective view showing the first holder viewed from above. <FIG> is a perspective view showing the second holder viewed from below. <FIG> is a plan view of the first holder.

The first holder <NUM> may include a base plate <NUM>, first protrusions <NUM>, and second protrusions <NUM>.

The base plate <NUM> may be formed in a disc shape. A through-hole 2231a is formed at a center of the base plate <NUM>. The rotating shaft <NUM> passes through the through-hole 2231a.

The first protrusions <NUM> may protrude from an upper surface of the base plate <NUM>. The second protrusions <NUM> may protrude from a lower surface of the base plate <NUM>. The first protrusions <NUM> and the second protrusions <NUM> are disposed at regular gaps with respect to the circumferential direction of the first holder <NUM>. Positions of the first protrusions <NUM> and positions of the second protrusions <NUM> correspond to positions of the gap portion (G in <FIG>) of the coupling hole <NUM> of the rotor core <NUM>.

Referring to <FIG>, <FIG> and <FIG>, the first protrusion <NUM> may be forcibly fitted into the coupling hole <NUM> of the first rotor core 2210A disposed on the upper side. Specifically, the plurality of first protrusions <NUM> may be forcibly fitted into the gap portions (G in <FIG>) of the coupling holes <NUM> toward the low surface of the first rotor core 2210A disposed on the upper side, respectively. Alternatively, the plurality of second protrusions <NUM> may be forcibly fitted into the gap portions (G in <FIG>) of the coupling holes <NUM> toward the upper surface of the second rotor core 2210B disposed at the center, respectively.

Alternatively, the second protrusion <NUM> may be forcibly fitted into the coupling hole <NUM> of the third rotor core 2210C disposed on the lower side. Specifically, the plurality of second projections <NUM> may be forcibly fitted into the gap portions (G in <FIG>) of the coupling holes <NUM> toward the upper surface of the third rotor core 2210C disposed on the lower side, respectively. Alternatively, the plurality of first protrusions <NUM> may be forcibly fitted into the gap portions (G in <FIG>) of the coupling holes <NUM> toward the lower surface of the second rotor core 2210B disposed at the center, respectively.

The first protrusions <NUM> may be shifted from the second protrusions <NUM> with respect to the circumferential direction of the first holder <NUM>. This is because the first rotor core 2210A and the second rotor core 2210B or the second rotor core 2210B and the third rotor core 2210C are disposed to be shifted from each other to form a skew angle.

Two first protrusions <NUM> may be disposed in one coupling hole <NUM>. The number of the first protrusions <NUM> disposed in the first holder <NUM> may be double the number of the magnets <NUM>. In addition, two second protrusions <NUM> may be disposed in one coupling hole <NUM>. The number of the second protrusions <NUM> disposed in the first holder <NUM> may be double the number of the magnets <NUM>.

<FIG> is a view showing the first protrusion inserted into the coupling hole of the rotor core.

Referring to <FIG>, the first protrusion <NUM> is forcibly fitted into the gap portion G. The first protrusion <NUM> disposed between the coupling hole <NUM> and the magnet <NUM> presses the magnet <NUM> so that the magnet <NUM> is fixed to the coupling hole <NUM>. The second protrusion <NUM> is also forcibly fitted into the gap portion G in the same manner as the first protrusion <NUM> so that the magnet <NUM> is fixed to the coupling hole <NUM>.

<FIG> is a view showing a shape of the first protrusion.

Referring to <FIG> and <FIG>, a sectional shape of the first protrusion <NUM> corresponds to a planar shape of the spacing space between the coupling hole <NUM> and the magnet <NUM>. For example, the sectional shape of the first protrusion <NUM> may include a first region <NUM> and a second region <NUM>.

A sectional shape of the first region <NUM> may have a triangular shape as a whole. A first surface <NUM> of the first region <NUM> comes into contact with a side surface of the coupling hole <NUM> of the rotor core <NUM>. A second surface <NUM> of the first region <NUM> comes into contact with an outer surface of the coupling hole <NUM>. A third surface <NUM> of the first region <NUM> comes into contact with a side surface of the magnet <NUM>.

The second region <NUM> may correspond to a shape recessed around a corner defining a boundary between a side surface and an inner surface of the coupling hole <NUM>. For example, a sectional shape of the second region <NUM> may be rectangular. The second region <NUM> may be connected to an inner end of the first region <NUM>.

With reference to the bridge portion <NUM>, a first protrusion 2232a, which is coupled to the coupling hole 2211A disposed on one side, and a first protrusion 2232b, which is coupled to the coupling hole 2211B disposed on the other side, may be symmetrically disposed. A distance W2 between the first protrusion 2232a and the first protrusion 2232b facing each other may be greater than a width W1 of the bridge portion <NUM>.

Although not shown in the drawings, a function, shape, and size of the second protrusion <NUM> may be the same as those of the above first protrusion <NUM>.

<FIG> is a perspective view showing the second holder viewed from above. <FIG> is a perspective view showing the second holder viewed from below. <FIG> is a plan view of the second holder.

Referring to <FIG>, the second holder <NUM> may include a second base plate <NUM>, third protrusions <NUM>, and a support portion <NUM>.

The second base plate <NUM> may be formed in a disc shape. A second through-hole 2241a is formed at a center of the second base plate <NUM>. The rotating shaft <NUM> passes through the second through-hole 2241a.

The third protrusions <NUM> may protrude from a lower surface of the second base plate <NUM>. Here, the lower surface of the second base plate <NUM> refers to a surface that faces the upper surface or the lower surface of the rotor core <NUM> when the second holder <NUM> is mounted on the rotor core <NUM>. The third protrusions <NUM> are disposed at regular gaps with respect to a circumferential direction of the second holder <NUM>. Positions of the third protrusions <NUM> correspond to the positions of the gap portions (G in <FIG>) of the coupling holes <NUM> of the rotor core <NUM>.

The shape and size of the third protrusion <NUM> may be the same as the shape and size of the first protrusion <NUM> or the shape and size of the second protrusion <NUM>. In addition, positions of the third protrusions <NUM> correspond to the positions of the first protrusions <NUM> and the second protrusions <NUM>. For example, Referring to <FIG>, the second holder <NUM> is coupled to the upper surface of the first rotor core 2210A, and the first holder <NUM> is coupled to the lower surface of the first rotor core 2210A, with respect to the first rotor core 2210A. Here, because the first protrusion <NUM> and the third protrusion <NUM> are coupled to the same coupling hole <NUM>, the position of the third protrusion <NUM> of the second holder <NUM> corresponds to the position of the first protrusion <NUM> of the first holder <NUM>. Alternatively, with respect to the third rotor core 2210C, the second holder <NUM> is coupled to the lower surface of the third rotor core 2210C, and the first holder <NUM> is coupled to the upper surface of the third rotor core 2210C. Here, because the second protrusion <NUM> and the third protrusion <NUM> are coupled to the same coupling hole <NUM>, the position of the second protrusion <NUM> of the second holder <NUM> corresponds to the position of the second protrusion <NUM> of the first holder <NUM>.

The support portion <NUM> may protrude from the upper surface of the second base plate <NUM>. The support portion <NUM> may include a third through-hole 2243a disposed at a center thereof. The third through-hole 2243a communicates with the second through-hole 2241a. An inner diameter of the third through-hole 2243a may be the same as an outer diameter of the rotating shaft <NUM>. The support portion <NUM> may support the bearing <NUM> (in <FIG>).

Referring to <FIG>, the second holder <NUM> may include a concave portion <NUM>. The concave portion <NUM> may be formed to be concave on the upper surface of the second holder <NUM>. The concave portion <NUM> may be disposed at regular gaps along the circumferential direction of the second holder <NUM>. The concave portion <NUM> may be a weight reducing shape generated during injection molding. Accordingly, a weight of the second holder <NUM> may be minimized.

The above descriptions are merely illustrative of the technical idea of the present invention.

Claim 1:
A motor comprising:
a housing (<NUM>);
a rotating shaft (<NUM>) extending along an axial direction;
a stator (<NUM>) disposed in the housing and having an axial length (h) in the axial direction between a first end surface and a second end surface; and
a rotor (<NUM>) coupled to the rotating shaft (<NUM>) and disposed inside the stator,
wherein the rotor (<NUM>) includes a rotor core (<NUM>) surrounding the rotating shaft (<NUM>) and a plurality of magnets (<NUM>) coupled to the rotor core on an outer surface thereof in a skewed manner,
wherein the rotor core comprises a plurality of rotor core members (<NUM>),
charcterized in that the rotor core members (<NUM>) are spaced apart from each other in the axial direction, with predetermined gaps between adjacent rotor core members in the axial direction,
wherein the gaps between the rotor core members (<NUM>) consist of a first gap and a second gap between rotor core members, and wherein the first gap is equal to the second gap
wherein the magnets (<NUM>) are spaced apart from each other in the axial direction, wherein gaps (D1) between adjacent magnets in the axial direction are equal to each other,
wherein the sum of the gaps between the magnets (<NUM>) ranges from <NUM> to <NUM> times the axial length of the stator (<NUM>),
wherein a first one of the magnets (<NUM>) protrudes in the axial direction with respect to the first end surface of the stator (<NUM>) by a first axial length (h1), while a second one of the magnets (<NUM>) protrudes in the axial direction with respect to the second end surface of the stator (<NUM>) by a second axial length (h2), and
wherein the sum of the first and second axial lengths (h1, h2) is equal to the sum of the gaps between the magnets (<NUM>).