Patent Publication Number: US-2022231570-A1

Title: Motor

Description:
TECHNICAL FIELD 
     The present invention relates to a motor. 
     BACKGROUND ART 
     Motors are apparatuses configured to convert electrical energy to mechanical energy to obtain rotational forces and are widely used for vehicles, home appliances, industrial machines, and the like. 
     Particularly, an electronic power steering (EPS) system in which the motor is used secures turning stability and provides a rapid restoring force by driving the motor according to traveling conditions using an electronic control unit (ECU). Accordingly, a driver of a vehicle can drive safely. 
     A motor includes a shaft and a stator. The shaft may have a hollow shape. Magnets may be attached to an outer circumferential surface of the shaft. In this case, the hollow shaft has a problem of difficulty in aligning positions of the magnets. This is because it is difficult to form guides for aligning the magnets due to a process of machining the hollow shaft. When there are no guides, which guide the magnets, on the shaft, and when the magnets are overmolded, a problem of misalignment of the magnet may occur. In addition, when the magnets are surrounded by a can or adhesive member, there is a risk of movement of the magnet. 
     Meanwhile, an adhesive is used to fix the magnets to the shaft. When the adhesive is used, there is a problem in that a long time is required for curing. In addition, when the magnets are overmolded, a problem of misalignment of the magnet may occur, and there is a problem in that it is difficult to check the misalignment. In addition, in the case of overmolding, since a thickness is large, there is a difficulty in securing a gap with respect to the stator. 
     Technical Problem 
     The present invention is directed to providing a motor allowing a magnet disposed on an outer circumferential surface of a hollow shaft to be aligned and fixed. 
     In addition, the present invention is directed to providing a motor in which a gap between a magnet and a stator is reduced, of which a process is simplified, and in which a position of the magnet is checked. 
     Technical Solution 
     One aspect of the present invention provides a motor including a stator, a shaft having a hollow and disposed inside the stator, and a magnet disposed on an outer circumferential surface of the shaft, wherein the shaft includes a plurality of protrusions in contact with the magnet, and the plurality of protrusions include first faces protruding from the outer circumferential surface of the shaft and second faces concavely disposed in an inner circumferential surface of the shaft. 
     Another aspect of the present invention provides a motor including a stator, a shaft having a hollow and disposed inside the stator, and a magnet disposed on an outer circumferential surface of the shaft, wherein the shaft includes a plurality of second holes passing through an inner side to an outer side of the shaft and a plurality of protrusions which are disposed in the plurality of second holes and of which at least parts protrude from the outer circumferential surface of the shaft and are in contact with the magnet. 
     The plurality of protrusions may be disposed to be spaced apart from each other in a circumferential direction of the shaft, and a separation distance between the plurality of protrusions in the circumferential direction may be greater than or equal to a width of the magnet. 
     The plurality of protrusions may be disposed to be spaced apart from each other in an axial direction of the shaft, and a separation distance between the protrusions in the axial direction may be smaller than or equal to a length of the magnet. 
     One protrusion of the plurality of protrusions may be disposed in an axial direction of the shaft, and a length of the one protrusion in the axial direction may be greater than ½ times a length of the magnet. 
     Each of the first face and the second face may include at least one flat surface. 
     The first face may include a curved surface in contact with the magnet. 
     A height from the outer circumferential surface of the shaft to an outer end of the protrusion may be smaller than a height of the magnet in a radial direction of the shaft. 
     The shaft may include a first hole which passes from in inner side to an outer side of the shaft, and the protrusion may extend from an edge of the first hole. 
     The motor may include a cover disposed outside the magnet, and the cover may include a groove in which the protrusion is disposed. 
     Threads may be disposed at a side surface of the protrusion and the second hole. 
     A knurling structure may be disposed on the protrusion. 
     Still another aspect of the present invention provides a motor including a stator, a shaft disposed inside the stator, a magnet coupled to the shaft, and a cover disposed outside the magnet, wherein the cover includes a first part and a second part extending from one side of the first part, an inner surface of the magnet is in contact with an outer surface of the shaft, an outer surface of the magnet is in contact with an inner surface of the first part, a part of an inner surface of the second part is in contact with the outer surface of the shaft, and the remaining part of the inner surface of the second part is disposed to be spaced apart from the outer surface of the shaft so that a space is disposed between the outer surface of the shaft and the inner surface of the second part. 
     The cover may include a third part extending from the other side of the first part, a part of an inner surface of the third part may be in contact with the outer surface of the shaft, and the remaining part of the inner surface of the third part may be disposed to be spaced apart from the outer surface of the shaft so that a space is disposed between the outer surface of the shaft and a surface of the other end of the magnet. 
     The cover may include a plurality of first regions disposed to be spaced apart from each other in a circumferential direction around a center of the shaft, and a distance from the outer surface of the shaft to the first region in a radial direction may be smaller than a shortest distance from the outer surface of the shaft to the outer surface of the magnet in the radial direction. 
     The magnet may include a first unit magnet and a second unit magnet, the first region may be disposed between the first unit magnet and the second unit magnet, and the first region may be disposed in an axial direction. 
     The cover may include a second region constituting a multilayer in a radial direction from a center of the shaft. 
     The cover may include a first layer and a second layer stacked on the first layer in the second region, and one side edge of the second layer may be disposed to be inclined with respect to one side edge of the first layer. 
     The cover may include a third region having a different thickness in the radial direction from a center of the shaft. 
     An outer surface of the cover may include a stop region. 
     The cover may be a member in which epoxy is impregnated in fiber. 
     The shaft may include a protrusion in contact with the magnet, and the protrusion may be disposed to be spaced apart from the cover. 
     Advantageous Effects 
     According to the embodiment, a useful effect of easily aligning a magnet disposed on an outer circumferential surface of a hollow shaft is provided. 
     According to the embodiment, a useful effect of preventing movement of the magnet when the magnet is surrounded in an overmolding manner or by a can is provided. 
     According to the embodiment, since a size of each protrusion can be formed to be small, the number of the protrusions can be increased, and thus there is an advantage of more precisely guiding a position of the magnet. 
     According to the embodiment, there is an advantage of easily forming the protrusion through an embossing or punching process. 
     According to the embodiment, there is an advantage of preventing the magnet from escaping in a process using a knurling structure formed on a side surface of the protrusion. 
     According to the embodiment, there is an advantage of improving the performance of a motor by minimizing a thickness of a cover to significantly reduce a gap between the magnet and the stator. 
     According to the embodiment, since the position of the magnet can be checked from the outside of the cover, there is an advantage of easily identifying a defect of the magnet. 
     According to the embodiment, since an adhesive is not used when the magnet is fixed to the shaft, there is an advantage of reducing a process time. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a view illustrating a motor according to an embodiment. 
         FIG. 2  is a perspective view illustrating a shaft. 
         FIG. 3  is a side cross-sectional view illustrating protrusions of the shaft. 
         FIG. 4  is a side cross-sectional view illustrating a modified example of the protrusion of the shaft. 
         FIG. 5  is a side cross-sectional view illustrating another modified example of the protrusion of the shaft. 
         FIGS. 6 and 7  are side cross-sectional views illustrating still other modified examples of the protrusion of the shaft. 
         FIG. 8  is a perspective view illustrating the shaft on which magnets are disposed on an outer circumferential surface thereof. 
         FIG. 9  is a view illustrating a separation distance between the protrusions. 
         FIG. 10  is a view illustrating a size of the magnet. 
         FIG. 11  is a front view illustrating the shaft in order for comparing a height of the protrusion and a height of the magnet. 
         FIG. 12  is a view illustrating the shaft on which a cover is disposed in an overmolding manner. 
         FIG. 13  is a side cross-sectional view illustrating the shaft illustrated in  FIG. 12 . 
         FIG. 14  is a view illustrating protrusions disposed at upper sides of the magnets. 
         FIG. 15  is a view illustrating protrusions disposed at lower sides of the magnets. 
         FIG. 16  is a view illustrating protrusions disposed at upper sides and lower sides of the magnets. 
         FIG. 17  is a view illustrating the shaft including protrusions and second holes. 
         FIG. 18  is a perspective view illustrating the shaft including protrusions which are a modified example thereof. 
         FIG. 19  is a side cross-sectional view illustrating the shaft on which a cover is disposed in an overmolding manner. 
         FIG. 20  is a view illustrating the shaft on which the cover is disposed. 
         FIG. 21  is a view illustrating a state in which the cover is surrounding the magnets disposed on the outer circumferential surface of the shaft. 
         FIG. 22  is a side cross-sectional view illustrating the shaft, the magnet, and the cover. 
         FIG. 23  is a plan cross-sectional view illustrating the shaft, the magnet, and the cover. 
         FIG. 24  is a plan cross-sectional view illustrating the shaft and the magnet which show a second region and a third region of the cover. 
         FIG. 25  is a view illustrating one side edge of the cover in the second region. 
         FIG. 26  is a perspective view illustrating the shaft including the protrusions. 
         FIG. 27  is a plan cross-sectional view illustrating the shaft including the protrusion and the magnet. 
     
    
    
     MODES OF THE INVENTION 
     Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
     However, the technical spirit of the present invention is not limited to some embodiments which will be described and may be realized using various other embodiments, and at least one component of the embodiments may be selectively coupled, substituted, and used to realize the technical spirit within the range of the technical spirit. 
     In addition, unless clearly and specifically defined otherwise by context, all terms (including technical and scientific terms) used herein can be interpreted as having customary meanings to those skilled in the art, and meanings of generally used terms, such as those defined in commonly used dictionaries, will be interpreted by considering contextual meanings of the related technology. 
     In addition, the terms used in the embodiments of the present invention are considered in a descriptive sense and not for limiting the present invention. 
     In the present specification, unless clearly indicated otherwise by the context, singular forms include the plural forms thereof, and in a case in which “at least one (or one or more) among A, B, and C” is described, this may include at least one combination among all possible combinations thereof. 
     In addition, in descriptions of components of the present invention, terms such as “first,” “second,” “A,” “B,” “(a),” and “(b)” can be used. 
     The terms are only to distinguish one element from another element, and an essence, order, and the like of the element are not limited by the terms. 
     In addition, it should be understood that, when an element is referred to as being “connected or coupled” to another element, such a description may include both of a case in which the element is directly connected or coupled to another element and a case in which the element is connected or coupled to another element with still another element disposed therebetween. 
     In addition, in a case in which any one element is described as being formed or disposed “on or under” another element, such a description includes both a case in which the two elements are formed or disposed in direct contact with each other and a case in which one or more other elements are interposed between the two elements. In addition, when one element is described as being disposed “on or under” another element, such a description may include a case in which the one element is disposed at an upper side or a lower side with respect to another element. 
       FIG. 1  is a view illustrating a motor according to the embodiment. 
     Referring to  FIG. 1 , the motor according to the embodiment may include a shaft  100 , a magnet  200 , a stator  300 , a cover  400 , a housing  500 , and a busbar  600 . Hereinafter, the term “inside” denotes a direction toward the shaft  100  in a radial direction of the motor, and the term “outside” denotes a direction opposite to “inside.” 
     The shaft  100  may be a hollow member of which one side is open. Both ends of the shaft  100  may be rotatably supported by bearings in a axial direction. Portions, of which outer diameters are different, of the shaft  100  may be divided and disposed in the axial direction. 
     The magnet  200  is disposed on an outer circumferential surface of the shaft  100 . The magnet  200  is rotated in conjunction with rotation of the shaft  100 . The magnet  200  may be provided as a plurality of magnets. 
     The stator  300  is disposed outside the shaft  100  and the magnet  200 . The stator  300  may include a stator core  310 , insulators  320  installed on the stator core  310 , and coils  330  wound around the insulators  320 . The coil  330  generates a magnetic field. The stator core  310  may be one member or a combination of a plurality of divided cores. In addition, the stator core  310  may be formed in a form in which a plurality of thin steel plates are stacked, but the present invention is not necessarily limited thereto. For example, the stator core  310  may also be formed as one single part. 
     The cover  400  fixes the magnet  200  to the shaft  100 . The cover  400  surrounds some regions of the magnet  200  and some regions of the shaft  100 . The cover  400  may be a molded member formed in an overmolding manner or a can member or adhesive member surrounding the magnet  200 . 
     The housing  500  may be disposed outside the stator  300 . The housing  500  may be a cylindrical member of which an upper portion is open. The housing  500  accommodates the shaft  100 , the magnet  200 , the stator  300 , and the cover  400  thereinside. In addition, the housing  500  may accommodate the bearing which supports the shaft  100 . 
     The busbar  600  is disposed on the stator  300 . The busbar  600  connects the coils  330  wound around the cores of the stator  300 . 
       FIG. 2  is a perspective view illustrating the shaft  100 , and  FIG. 3  is a side cross-sectional view illustrating protrusions  110  of the shaft  100 . 
     The shaft  100  is a hollow member and may be formed through a pressing process. 
     Referring to  FIGS. 2 and 3 , the shaft  100  includes the plurality of protrusions  110  in contact with the magnets  200 . The plurality of protrusions  110  are disposed on the outer circumferential surface of the shaft  100 . The plurality of protrusions  110  may be disposed to be spaced apart from each other in a circumferential direction O of the shaft  100 . In addition, the plurality of protrusions  110  may be disposed to be spaced apart from each other in an axial direction X of the shaft  100 . The protrusions  110  serve to arrange and fix the magnets  200  disposed on the outer circumferential surface of the shaft  100 . 
     The plurality of protrusions  110  include first faces  111  and second faces  112 . The first faces  111  may protrude from the outer circumferential surface of the shaft  100 . The second faces  112  may be concavely disposed in an inner circumferential surface of the shaft  100 . 
     The first faces  111  may include first-1 faces  111   a  and first-2 faces  111   b . The first-1 faces  111   a  are portions protruding from the outer circumferential surface of the shaft  100 . The first-2 faces  111   b  connect the outer circumferential surface of the shaft  100  and the first-1 faces  111   a . The first-1 face  111   a  may include a flat surface, and the first-2 face  111   b  may include a curved surface in contact with the magnet  200 . The curved surface of the first-2 face  111   b  is in line contact with a side surface of the magnet  200  to guide the magnet  200  to be smoothly inserted between the protrusions  110 . In addition, a knurling structure may be applied to the first-2 face  111   b  to increase a fixing force between the shaft and the magnet. 
     The second faces  112  may include second-1 faces  112   a  and second-2 faces  112   b . The second-1 faces  112   a  are portions concavely formed in the inner circumferential surface of the shaft  100 . The second-2 face  112   b  connects the inner circumferential surface of the shaft  100  and the second-1 face  112   a . The second-1 face  112   a  may include a flat surface, and the second-2 face  112   b  may include a curved surface. 
     The first face  111  and the second face  112  may be formed through an embossing process performed on an inner side of the hollow shaft  100 . A distance t 2  between the first face  111  and the second face  112  may be the same as a thickness t 1  of the shaft  100  around the protrusion  110 . 
       FIG. 4  is a side cross-sectional view illustrating a modified example of the protrusion  110  of the shaft  100 . 
     Referring to  FIG. 4 , in the modified example of the protrusion  110 , a first-2 face  111   b  may be disposed to be inclined in a direction toward a first-1 face  111   a . In addition, a second-2 face  112   b  may be disposed to be inclined in a direction toward a second-1 face  112   a . A side cross-sectional shape of the protrusion  110  may be a substantially trapezoidal shape. In addition, a knurling structure may be applied to the first-2 face  111   b  to increase the fixing force between the shaft and the magnet. 
       FIG. 5  is a side cross-sectional view illustrating another modified example of the protrusion  110  of the shaft  100 . 
     Referring to  FIG. 5 , the plurality of protrusions  110  may be disposed in the circumferential direction of the shaft  100 , but one protrusion  110  may be disposed in the axial direction of the shaft  100 . In one protrusion  110 , a first-1 face  111   a  and a second-1 face  112   a  may be longitudinally disposed in the axial direction. In addition, a knurling structure may be applied to the first-2 face  111   b  to increase the fixing force between the shaft and the magnet. The first face  111  and the second face  112  may be formed through a beading process performed on the inner side of the hollow shaft  100 . 
       FIGS. 6 and 7  are side cross-sectional views illustrating still other modified examples of the protrusion  110  of the shaft  100 . 
     Referring to  FIGS. 6 and 7 , the shaft  100  may include a first hole  113  passing through the inner side to an outer side of the shaft  100 . The first hole  113  may be formed in a quadrangular shape. The protrusion  110  may extend from an edge of the first hole  113 . A side surface of the protrusion  110  may include a flat surface  114  in contact with the magnet  200 . The protrusion  110  may be provided as a plurality of protrusions disposed in the circumferential direction of the shaft  100 . In addition, the protrusion  110  may be provided as a plurality of protrusions disposed in the axial direction of the shaft  100 . In addition, a knurling structure may be applied to the flat surface  114 , which is in contact with the magnet  200 , of the side surface of the protrusion to increase the fixing force between the shaft  100  and the magnet  200 . 
     For example, as illustrated in  FIG. 6 , a first face  111  of the protrusion  110  may be disposed to be inclined downward. In addition, a second face  112  of the protrusion  110  may also be disposed to be inclined downward. 
     Alternatively, as illustrated in  FIG. 7 , a first face  111  of the protrusion  110  may be disposed to be inclined upward. In addition, a second face  112  of the protrusion  110  may also be disposed to be inclined upward. 
     Although the protrusions  110  having various shapes are illustrated, the present invention is not limited thereto, and the protrusion  110  may be changed to a protrusion  110  having one of various shapes formed through an embossing process performed on the inner side of the shaft  100 . 
     By using the protrusion  110 , the magnet  200  disposed on the shaft  100  may be guided and fixed. Since the magnet  200  is directly guided and fixed to the shaft  100 , there is an advantage of omitting a rotor core. 
     In addition, the protrusion  110  may be implemented to have a small size, and the number of the protrusions  110  may be relatively greatly increased when compared to a general guide structure. Accordingly, there is an advantage of more precisely guiding a position of the magnet  200 . 
     In addition, there is an advantage of easily forming the protrusion  110  through the embossing process. 
       FIG. 8  is a perspective view illustrating the shaft  100  on which the magnets  200  are disposed on the outer circumferential surface thereof. 
     Referring to  FIG. 8 , the plurality of magnets  200  are disposed on the outer circumferential surface of the shaft  100 . The magnet  200  is disposed between the protrusions  110  in the circumferential direction of the shaft  100 . The side surface of the protrusion  110  is in contact with the side surface of the magnet  200 . 
       FIG. 9  is a view illustrating a separation distance between the protrusions  110 , and  FIG. 10  is a view illustrating a size of the magnet  200 . 
     Referring to  FIGS. 9 and 10 , a separation distance W 1  between the protrusions  110  in the circumferential direction may be greater than or equal to a width W 2  of the magnet  200 . This is to allow the magnet  200  to be positioned between the protrusions  110  in the circumferential direction of the shaft  100 . 
     In addition, referring to  FIGS. 9 and 10 , a separation distance L 1  between the protrusions  110  in the axial direction may be smaller than or equal to a length L 2  of the magnet  200 . This is to guide the magnet  200  using at least two protrusions  110  disposed at the same column in the axial direction. 
     Meanwhile, as illustrated in  FIG. 5 , when one protrusion  110  is disposed in the axial direction of the shaft  100 , a length L 3  of the corresponding protrusion  110  may be greater than ½ times the length L 2  of the magnet  200 . This is a minimum length of the protrusion  110  so that the magnet  200  is guided and fixed by the protrusions  110  without being misaligned. 
       FIG. 11  is a front view illustrating the shaft  100  in order for comparing a height of the protrusion  110  and a height of the magnet  200 . 
     Referring to  FIG. 11 , a height H 1  from the outer circumferential surface of the shaft  100  to an outer end of the protrusion  110  may be smaller than a height H 2  of the magnet  200  in a radial direction of the shaft  100 . A center of a width of the protrusion  110  in the circumferential direction of the shaft  100  may be a reference point of the height H 1  of the protrusion  110 . In addition, a center of a width of the magnet  200  in the circumferential direction of the shaft  100  may be a reference point of the height H 2  of the magnet  200 . This is in consideration of a position of the cover  400  which covers the magnet  200 . Although the protrusion  110  is illustrated in  FIG. 11 , even in the case of each of protrusions  120  having different shapes, a height from the outer circumferential surface of the shaft  100  to an outer end of the protrusion  120  may be smaller than the height H 2  of the magnet  200 . 
       FIG. 12  is a view illustrating the shaft  100  on which the cover  400  is disposed in the overmolding manner, and  FIG. 13  is a side cross-sectional view illustrating the shaft  100  illustrated in  FIG. 12 . 
     Referring to  FIGS. 12 and 13 , the cover  400  may be a molded member formed in the overmolding manner. The cover  400  includes grooves  410  in which the protrusions  110  are disposed. Since the protrusions  110  are disposed in the grooves  410 , a coupling force between the cover  400  and the shaft  100  increases, and a coupling force between the cover  400  and the magnet  200  increases. 
       FIG. 14  is a view illustrating protrusions  110  disposed at upper sides and lateral sides of the magnets  200 . 
     Referring to  FIG. 14 , the protrusions  110  include first-1 protrusions  110 A disposed at the lateral sides of the magnets  200  and first-2 protrusions  110 B disposed at the upper sides of the magnets  200 . Since the first-2 protrusion  110 B is disposed at the upper side of the magnet  200  to be in contact with an upper end of the magnet  200 , the magnet  200  may be prevented from escaping upward from a regular position. 
       FIG. 15  is a view illustrating protrusions  110  disposed at lower sides and the lateral sides of the magnets  200 . 
     Referring to  FIG. 15 , the protrusions  110  may include first-1 protrusions  110 A disposed at the lateral sides of the magnets  200  and first-3 protrusions  110 C disposed at the lower sides of the magnets  200 . Since the first-3 protrusion  110 C is disposed at the lower side of the magnet  200  to be in contact with the magnet  200 , the magnet  200  may be prevented from escaping downward from the regular position. 
       FIG. 16  is a view illustrating protrusions  110  disposed at the upper sides and the lower sides of the magnets  200 . 
     Referring to  FIG. 16 , the protrusions  110  may include first-1 protrusions  110 A disposed at the lateral sides of the magnets  200 , first-2 protrusions  110 B disposed at the upper sides of the magnets  200 , and first-3 protrusions  110 C disposed at the lower sides of the magnets  200 . Since the first-2 protrusion  110 B is in contact with the upper end of the magnet  200 , the magnet  200  is prevented from escaping upward from the regular position, and since the first-3 protrusion  110 C is in contact with the lower end of the magnet  200 , the magnet  200  is prevented from escaping downward from the regular position. 
     Although the protrusion  110  has been illustrated as described above, a protrusion  120 , which has a form different from the form described above, illustrated in each of  FIGS. 17 to 19  may also include at least one of the first-1 protrusion disposed at the lateral side of the magnet  200 , the first-2 protrusion disposed at the upper side of the magnet  200 , and the first-3 protrusion  110 C disposed at the lower side of the magnet  200 . 
       FIG. 17  is a view illustrating the shaft  100  including the protrusions  120  and second holes  130 . 
     Referring to  FIG. 17 , the shaft  100  may include the second holes  130  passing through the inner side to the outer side of the shaft  100 . The plurality of second holes  130  may be disposed in the circumferential direction of the shaft  100 . In addition, the plurality of second holes  130  may be disposed in the axial direction of the shaft  100 . The plurality of second holes  130  may be formed through a punching process. 
     The protrusions  120  may be disposed in the plurality of second holes  130 . The protrusion  120  is disposed so that at least a part of the protrusion  120  protrudes from the outer circumferential surface of the shaft  100  in a state in which the protrusion  120  is inserted into the second hole  130 . The protrusion  120  may be formed of a plastic resin. The protrusion  120  is in contact with the magnet  200 . A thread capable of increasing a coupling force between the protrusion  120  and the shaft  100  may be formed in an area of a side surface, with which the shaft  100  is in contact, of the protrusion  120 . A knurling structure for increasing the fixing force between the magnet  200  and the shaft  100  may be applied to the portion, which is not in contact with the shaft  100 , of the side surface of the protrusion  120 . 
       FIG. 18  is a perspective view illustrating the shaft  100  including protrusions  120  which are a modified example thereof. 
     Referring to  FIG. 18 , although a plurality of second holes  130  may be disposed in the circumferential direction, one second hole  130  having a long hole shape may be disposed in the axial direction of the shaft  100 . In addition, although the plurality of protrusions  120  may also be disposed in the circumferential direction to correspond thereto, one protrusion  120  may be disposed in the axial direction of the shaft  100 . A knurling structure for increasing the fixing force between the magnet  200  and the shaft  100  may be applied to a portion, which is not in contact with the shaft  100 , of the side surface of the protrusion  120 . 
     Referring to  FIG. 17 , a separation distance W 3  between the protrusions  120  in the circumferential direction may be greater than or equal to the width W 2  of the magnet  200 . This is to allow the magnet  200  to be positioned between the protrusions  120  in the circumferential direction of the shaft  100 . 
     In addition, a separation distance L 4  between the protrusions  120  in the axial direction may be smaller than or equal to the length L 2  of the magnet  200 . This is to allow at least two protrusions  120 , which are disposed at the same column in the axial direction, to guide the magnet  200 . 
     Referring to  FIG. 18 , when one protrusion  120  is disposed in the axial direction, a length L 5  of the protrusion  110  may be greater than ½ times the length L 2  of the magnet  200 . This is a minimum length of the protrusion  120  so that the magnet  200  may be guided and fixed by the protrusions  120  without being misaligned. 
       FIG. 19  is a side cross-sectional view illustrating the shaft  100  on which the cover  400  is disposed in an overmolding manner. 
     Referring to  FIG. 19 , the cover  400  includes grooves  420  in which the protrusions  120  are disposed. Since the protrusion  120  is disposed in the groove  420 , a coupling force between the cover  400  and the shaft  100  increases, and a coupling force between the cover  400  and the magnet  200  increases at the same time. 
       FIG. 20  is a view illustrating the shaft on which the cover  400  is disposed, and  FIG. 21  is a view illustrating a state in which the cover  400  is surrounding the magnets  200  disposed on the outer circumferential surface of the shaft  100 . 
     Referring to  FIGS. 20 and 21 , the cover  400  may be an adhesive member which surrounds the magnet  200  to fix the magnet  200  to the shaft  100 . For example, the cover  400  may be a member in which a matrix is impregnated in reinforced fiber. 
     The cover  400  is a member in a semi-cured state and serves as an adhesive sheet which fixes the magnet  200  to the shaft  100 . The reinforced fiber may be mainly carbon fiber, glass fiber, aramid fiber, or the like, and the matrix may be an epoxy resin, a polyester resin, or a thermoplastic resin. The carbon fiber has features of high tensile strength and high tensile modulus as mechanical properties and high heat resistance and high fire resistance as thermal properties. The glass fiber has features of high tensile strength and high tensile modulus as mechanical properties and a low coefficient of linear expansion as a thermal property. Both of the carbon fiber and the glass fiber have a high electrical insulation property. 
     In a state in which a part of the cover  400  is in contact with the shaft  100  and the magnet  200 , when the shaft  100  rotates, the cover  400  may be wound around the shaft  100  in the form of naturally surrounding the magnet  200 , and thus there is an advantage of a simple and rapid process. 
     The cover  400  may be divided into a first part  410 , a second part  420 , and a third part  430  in the axial direction. The second part  420  extends from one side of the first part  410 . The third part  430  extends from the other side of the first part  410 . 
     The first part  410  is a part which covers the magnet  200 , and the second part  420  and the third part  430  are parts in contact with the shaft  100 . 
       FIG. 22  is a side cross-sectional view illustrating the shaft  100 , the magnet  200 , and cover  400 . 
     Referring to  FIG. 22 , an inner surface of the magnet  200  is in contact with an outer surface of the shaft  100 . In addition, an outer surface of the magnet  200  is in contact with an inner surface  401  of the first part  410 . A part of an inner surface  402  of the second part  420  is in contact with the outer surface of the shaft  100 , and the remaining part of the inner surface  402  of the second part  420  is disposed to be spaced apart from the outer surface of the shaft  100 . A space S 1  is formed between the outer surface of the shaft  100 , a surface of one end  203  of the magnet  200 , and the inner surface  402  of the second part  420 . 
     In addition, a part of an inner surface  403  of the third part  430  is in contact with the outer surface of the shaft  100 , and the remaining part of the inner surface  403  of the third part  430  is disposed to be spaced apart from the outer surface of the shaft  100 . A space S 2  is formed between the outer surface of the shaft  100 , a surface of the other end  204  of the magnet  200 , and the inner surface  403  of the third part  430 . 
       FIG. 23  is a plan cross-sectional view illustrating the shaft  100 , the magnet  200 , and the cover  400 . 
     Referring to  FIG. 23 , the cover  400  may include a plurality of first regions A 1 . The plurality of first regions A 1  may be disposed to be spaced apart from each other in the circumferential direction around a center of the shaft. In the first region A 1 , a distance R 1  from the outer surface of the shaft  100  to the first region A 1  in the radial distance is smaller than a shortest distance R 2  from the outer surface of the shaft  100  to the outer surface of the magnet  200  in the radial direction. A side end of the outer surface of the magnet  200  in the circumferential direction may be a reference point of the shortest distance R 2  from the outer surface of the shaft  100  to the outer surface of the magnet  200  when a bread shape of the outer surface of the magnet  200  is considered. 
     The first region A 1  is disposed between a first unit magnet  200 A and a second unit magnet  200 B in the circumferential direction. In addition, the first region A 1  is longitudinally disposed in the axial direction. 
     Since the first region A 1  is visually distinguished from the other regions of the cover  400 , a layout of the magnet  200  may be checked visually or checked through an image in a state in which the cover  400  surrounds the magnet  200 . Accordingly, an operator may easily check whether there is a problem in the layout of the magnet  200 . 
       FIG. 24  is a plan cross-sectional view illustrating the shaft  100  and the magnet  200  which show a second region A 2  and a third region A 3  of the cover. 
     Referring to  FIG. 24 , the cover  400  may be wound around the shaft  100  to constitute a multilayer. Hereinafter, a region in which the cover  400  constitutes the multilayer in the radial direction is referred to as the second region A 2 , and a region having a thickness t 2  different from a thickness t 1  of one region in the radial direction from the center of the shaft is referred to as a third region A 3 . 
     The cover  400  may include a first layer  400 A and a second layer  400 B stacked on the first layer  400 A in the second region A 2 . In the drawing, although the first layer  400 A and the second layer  400 B are illustrated, the present invention is not limited thereto, and more layers, such as a third layer, a four layer, and the like, may be formed. Accordingly, the second region A 2  may be a region in which three or more layers are formed. 
     In  FIG. 24 , although it is illustrated that a position of the second region A 2  and a position of the third region A 3  are the same, the present invention is not limited thereto, and the position of the second region A 2  and the position of the third region A 3  may be also be different. 
     An outer surface of the cover  400  may include a stepped region A 4 . 
       FIG. 25  is a view illustrating one side edges E 1  and E 2  of the cover  400  in the second region A 2 . 
     Referring to  FIG. 25 , in the second region A 2 , one side edge E 2  of any one layer may be disposed to be inclined with respect to one side edge E 1  of another layer. In addition, in the second region A 2 , the other edge E 4  of any one layer may be disposed to be inclined with respect to the other side edge E 3  of another layer. This may be a feature which is naturally formed in a process in which an end of the cover  400  is finished and attached after the cover  400  is wound around the shaft  100 . 
       FIG. 26  is a perspective view illustrating the shaft including the protrusions, and  FIG. 27  is a plan cross-sectional view illustrating the shaft  100  including the protrusion and the magnet  200 . 
     Referring to  FIGS. 26 and 27 , the shaft  100  includes the plurality of protrusions  110  in contact with the magnet  200 . The plurality of protrusions  110  are disposed on the outer circumferential surface of the shaft  100 . The plurality of protrusions  110  may be disposed to be spaced apart from each other in the circumferential direction of the shaft  100 . In addition, the plurality of protrusions  110  may be disposed to be spaced apart from each other in the axial direction X of the shaft  100 . The protrusions  110  serve to arrange and fix the magnet  200  disposed on the outer circumferential surface of the shaft  100 . The protrusion may be formed through an embossing process performed on the inner side of the hollow shaft  100 . 
     The protrusions  110  serve to fix the magnet  200  to prevent the magnet from being misaligned while the cover  400  surrounds the magnet  200 . The protrusion  110  may be disposed to be spaced apart from the cover  400 . 
     As described above, the motor according to one exemplary embodiment of the present invention has been specifically described with reference to the accompanying drawings. The above description is only an example describing a technological scope of the present invention. Various changes, modifications, and replacements may be made by those skilled in the art without departing from the spirit and scope of the present invention. Therefore, the embodiments disclosed above and in the accompanying drawings should be considered in a descriptive sense only and not to limit the technological scope. The technological scope of the present invention is not limited by the embodiments and the accompanying drawings. The scope of the present invention should be interpreted by the appended claims and encompass all equivalents falling within the scope of the appended claims.