Patent Publication Number: US-2021175760-A1

Title: Sensing device

Description:
TECHNICAL FIELD 
     The present invention relates to a sensing device. 
     BACKGROUND ART 
     In an electronic power steering (EPS) system, an electronic control unit drives a motor according to driving conditions to secure turning stability and provide quick reinforcing force so that a driver can stably travel. 
     An EPS system includes a sensor assembly configured to measure a torque, a steering angle, and the like of a steering shaft to provide a proper torque. The sensor assembly may include a torque sensor configured to measure a torque applied to the steering shaft and an index sensor configured to measure an angular acceleration of the steering shaft. In addition, the steering shaft may include an input shaft connected to a handle, an output shaft connected to a power transmission structure at a side of a wheel, and a torsion bar which connects the input shaft and the output shaft. 
     The torque sensor measures a torsion degree of the torsion bar to measure a torque applied to the steering shaft. In addition, the index sensor detects rotation of the output shaft to measure an angular acceleration of the steering shaft. In the sensor assembly, the torque sensor and the index sensor may be disposed to be integrally formed. 
     The torque sensor may include a housing, a rotor, a stator including a stator tooth, and a collector and measure the torque. 
     In this case, the torque sensor may have a magnetic type structure in which the collector is provided to be disposed outside the stator tooth. 
     However, when an external magnetic field is generated, since the collector serves as a passage of the magnetic field in the structure, there is a problem in that the collector affects a magnetic flux value of a Hall integrated circuit (IC). Accordingly, a problem occurs in that an output value of the torque sensor is changed and thus the torsion degree of the torsion bar cannot be measured accurately. 
     Particularly, since many electric devices are used in a vehicle, a torque sensor is frequently affected by an external magnetic field, and thus there is a need for a torque sensor which is not affected by an external magnetic field. 
     Technical Problem 
     The present invention is directed to providing a sensing device capable of avoiding magnetic interference of an external magnetic field generated from the outside when a torque is measured. 
     Specifically, the present invention is directed to providing a sensing device in which a collector is disposed between stator teeth to prevent the collector from serving as a passage of external magnetic fields. 
     In addition, the present invention is directed to providing a sensing device in which a magnet is rotatably disposed between stator teeth to charge the stator teeth. 
     In addition, the present invention is directed to providing a sensing device in which a stator is not separated from a housing. 
     In addition, the present invention is directed to providing a sensing device in which coaxial driving of a stator is secured. 
     Objectives to be solved by embodiments are not limited to the above-described objectives, and other objectives which are not described above will be clearly understood by those skilled in the art from the following specification. 
     Technical Solution 
     One aspect of the present invention provides a sensing device including a stator including a stator tooth and a rotor including a magnet, wherein the stator tooth includes a first stator tooth and a second stator tooth disposed inside the first stator tooth, the first stator tooth includes a plurality of first teeth, the second stator tooth includes a plurality of second teeth, the first tooth overlaps the second tooth in a radial direction from a center of the stator, the stator includes a stator holder and a stator body which is coupled to the stator holder and on which the first stator tooth and the second stator tooth are disposed, a the stator body includes a protrusion, and the protrusion is in contact with a lower end of the first stator tooth or a lower end of the second stator tooth. 
     Another aspect of the present invention provides a sensing device including a stator including a stator tooth and a rotor including a magnet, wherein the stator tooth includes a first stator tooth having a first radius and a second stator tooth having a second radius, the first stator tooth includes a plurality of first teeth, the second stator tooth includes a plurality of second teeth, the first tooth overlaps the second tooth in a radial direction from a center of the stator, the stator includes a stator holder and a stator body which is coupled to the stator holder and on which the first stator tooth and the second stator tooth are disposed, the stator body includes a protrusion, and the protrusion is in contact with a lower end of the first stator tooth or a lower end of the second stator tooth. 
     Still another aspect of the present invention provides a sensing device including a stator and a rotor of which at least a portion is disposed in the stator, wherein the stator includes a stator holder, a stator body coupled to the stator holder, a first stator tooth disposed on the stator body, and a second stator tooth having a radius which is greater than a radius of the first stator tooth, the first stator tooth includes a first body and a plurality of first teeth connected to the first body and spaced apart from each other, the second stator tooth includes a second body and a plurality of second teeth connected to the second body and spaced apart from each other, the plurality of first teeth and the plurality of second teeth overlap in a radial direction, the stator body includes a protrusion, and the protrusion is in contact with a lower end of the first body or a lower end of the second body. 
     The stator body may include an inner part, an outer part, and a partition plate connecting the inner part and the outer part, wherein the protrusion may include a first protrusion and a second protrusion, the first protrusion may protrude from a lower end of the inner part and may be in contact with a lower end of the first stator tooth, and the second protrusion may protrude from a lower end of the outer part and may be in contact with the lower end of the first stator tooth. 
     The stator body may include the inner part, the outer part, and the partition plate connecting the inner part and the outer part, and the partition plate may include a first hole through which a first tooth of the first stator tooth passes and a second hole through which a second tooth of the second stator tooth passes. 
     A width of a lower end of the first tooth may be greater than a width of an upper end of the first tooth. 
     A width of the first hole may be smaller than the width of the lower end of the first tooth and greater than the width of the upper end, and a width of the second hole may be smaller than a width of a lower end of the second tooth and greater than a width of an upper end of the second tooth. 
     The sensing device may include a housing and a sub-gear disposed in the housing, the stator may include a main gear engaged with the sub-gear, and the main gear may be disposed on an outer circumferential surface of the stator body. 
     Yet another aspect of the present invention provides a sensing device including a stator including a stator tooth and a stator holder, a rotor including a magnet, and a housing disposed outside the stator holder, wherein the stator tooth includes a first stator tooth and a second stator tooth disposed inside the first stator tooth, the first stator tooth includes a plurality of first teeth, the second stator tooth includes a plurality of second teeth, and the first tooth overlaps the second tooth in a radial direction from a center of the stator, and the sensing device further includes a first member, wherein the first member is disposed between the housing and the stator holder. 
     Yet another aspect of the present invention provides a sensing device including a stator including a stator tooth and a stator holder, a rotor including a magnet, and a housing disposed outside the stator holder, wherein the stator tooth includes a first stator tooth having a first radius and a second stator tooth having a second radius, wherein the first stator tooth includes a plurality of first teeth, the second stator tooth includes a plurality of second teeth, and the first tooth overlaps the second tooth in a radial direction from a center of the stator, and the sensing device further includes a first member, wherein the first member is disposed between the housing and the stator holder. 
     Yet another aspect of the present invention provides a sensing device including a stator and a rotor of which at least a portion is disposed in the stator, wherein the stator includes a stator holder, a stator body coupled to the stator holder, a first stator tooth disposed on the stator body, and a second stator tooth having a radius which is greater than a radius of the first stator tooth, the first stator tooth includes a first body and a plurality of first teeth connected to the first body and spaced apart from each other, the second stator tooth includes a second body and a plurality of second teeth connected to the second body and spaced apart from each other, and the plurality of first teeth and the plurality of second teeth overlap in a radial direction, and the sensing device further includes a housing disposed outside the stator holder and a first member, wherein the first member is disposed between the housing and the stator holder. 
     The sensing device may further include a second member coupled to the stator holder, wherein the second member may be disposed under the housing to overlap the housing in an axial direction. 
     The second member may be disposed under the first member, and an upper surface of the second member may be in contact with the first member. 
     The housing may include a hole through which the stator holder passes, and the first member may be disposed inside the hole. 
     The first member may include a body having a ring shape and a flange part extending from the body in the radial direction, wherein an outer circumferential surface of the body is in contact with an inner wall of the hole, and an upper surface of the flange part may be in contact with a lower surface of the housing. 
     Yet another aspect of the present invention provides a sensing device including a stator including a stator tooth and a stator holder, a rotor including a magnet, and a housing disposed outside the stator holder, wherein the stator tooth includes a first stator tooth and a second stator tooth disposed inside the first stator tooth, the first stator tooth includes a plurality of first teeth, the second stator tooth includes a plurality of second teeth, and the first tooth overlaps the second tooth in a radial direction from a center of the stator, and the sensing device further includes a second member coupled to the stator holder, wherein the second member is disposed under the housing to overlap the housing in an axial direction 
     Yet another aspect of the present invention provides a sensing device including a stator including a stator tooth and a stator holder, a rotor including a magnet, and a housing disposed outside the stator holder, wherein the stator tooth includes a first stator tooth having a first radius and a second stator tooth having a second radius, the first stator tooth includes a plurality of first teeth, the second stator tooth includes a plurality of second teeth, and the first tooth overlaps the second tooth in a radial direction from a center of the stator, and the sensing device further includes a second member coupled to the stator holder, wherein the second member is disposed under the housing to overlap the housing in an axial direction. 
     Yet another aspect of the present invention provides a sensing device including a stator and a rotor of which at least a portion is disposed in the stator, wherein the stator includes a stator holder, a stator body coupled to the stator holder, a first stator tooth disposed on the stator body, and a second stator tooth having a radius which is greater than a radius of the first stator tooth, the first stator tooth includes a first body and a plurality of first teeth connected to the first body and spaced apart from each other, the second stator tooth includes a second body and a plurality of second teeth connected the second body and spaced apart from each other, and the plurality of first teeth and the plurality of second teeth overlap in a radial direction, and the sensing device further includes a second member coupled to the stator holder, wherein the second member is disposed under the housing to overlap the housing in an axial direction. 
     The stator holder may include a groove, wherein the groove may be disposed along an outer circumferential surface of the stator holder, and the second member may be a member having a ring shape and disposed in the groove. 
     Advantageous Effects 
     In a sensing device according to embodiments having the above-described structure, since a pair of collectors are disposed between a pair of stator teeth and sensors are disposed between the collectors, when a torque is measured, magnetic interference of an external magnetic field generated from the outside can be prevented or minimized. 
     Since a first tooth of a first stator tooth and a second tooth of a second stator tooth are disposed to overlap in a radial direction and a magnet is rotated between the first tooth and the second tooth, the first tooth and the second tooth can be charged in different poles. 
     There is an advantage of increasing a magnitude of a collected flux. 
     There is an advantage of easily coupling the stator tooth to a stator body. 
     There is an advantage of easily coupling the collector to a housing. 
     There is an advantage of preventing a stator from being separated from the housing. 
     There is an advantage of preventing the housing from being worn due to friction between the stator holder and a hole of the housing so that coaxial rotation of the stator is secured. 
     Various and useful advantages and effects of the embodiments are not limited to the above-described contents and will be more easily understood from descriptions of the specific embodiments. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view illustrating a sensing device according to an embodiment. 
         FIG. 2  is an exploded perspective view illustrating the sensing device illustrated in  FIG. 1 . 
         FIG. 3  is a cross-sectional perspective view illustrating the sensing device taken along line A-A of  FIG. 1 . 
         FIG. 4  is a perspective view illustrating a stator of the sensing device according to the embodiment. 
         FIG. 5  is an exploded perspective view illustrating the stator of the sensing device according to the embodiment. 
         FIG. 6  is a cross-sectional view illustrating the stator of the sensing device according to the embodiment. 
         FIG. 7  is a perspective view illustrating a stator body of the stator. 
         FIG. 8  is a plan view illustrating the stator body of the stator. 
         FIG. 9  is a cross-sectional view illustrating the stator body of the stator. 
         FIG. 10  is a view illustrating coupling of a first stator tooth and a second stator tooth and the stator body. 
         FIG. 11  is a view illustrating a state in which a first tooth is inserted into a first hole. 
         FIG. 12  is a view illustrating a protrusion of the stator body for fixing first and second bodies. 
         FIG. 13  is a view illustrating a fusing process of the protrusion of the stator body. 
         FIG. 14  is a side view illustrating the first stator tooth. 
         FIG. 15  is a side view illustrating the second stator tooth. 
         FIG. 16  is a plan view illustrating the first stator tooth, the second stator tooth, and a magnet. 
         FIG. 17  is a view illustrating a first pole and a second pole of the magnet. 
         FIG. 18  is a view illustrating a second angle. 
         FIG. 19  is a view illustrating a third angle. 
         FIG. 20  is a graph showing a flux with respect to a first angle, the second angle, and the third angle. 
         FIG. 21  is an exploded perspective view illustrating a rotor. 
         FIG. 22  is a view illustrating the magnet. 
         FIG. 23  is a plan view illustrating the magnet. 
         FIG. 24  is a perspective view illustrating an arrangement of the magnet with respect to the first stator tooth and the second stator tooth. 
         FIG. 25  is a view illustrating collectors. 
         FIG. 26  is a view illustrating the collectors disposed between the first stator tooth and the second stator tooth. 
         FIG. 27  is a view illustrating positions of sensors and positions of the collectors. 
         FIG. 28  is a view illustrating a circuit substrate. 
         FIG. 29  is a perspective view illustrating a housing when viewed from above. 
         FIG. 30  is a perspective view illustrating the housing when viewed from below. 
         FIG. 31  is a view illustrating the housing in which the collectors and the sensors are disposed. 
         FIG. 32  is a cross-sectional view illustrating a connector housing and a pin of the housing. 
         FIG. 33  is a view illustrating a first member and a second member. 
         FIG. 34  is a view illustrating the first member and the second member installed in a stator holder. 
         FIG. 35  is a view illustrating a first gear and a second gear which are engaged with a main gear. 
         FIG. 36  is a view illustrating a directionality of an external magnetic field with respect to the stator tooth. 
         FIG. 37  is a view illustrating a state in which the sensor avoids an external magnetic field having a z-axis directionality. 
         FIG. 38  is a view illustrating a state in which the first and second stator teeth avoid an external magnetic field having a y′-axis directionality. 
         FIG. 39  is a graph showing a comparison of an amount of change in angle corresponding to an external magnetic field in a z-axis direction between a comparative example and an example. 
         FIG. 40  is a graph showing a comparison of an amount of change in angle corresponding to the external magnetic field in a y′-axis direction between the comparative example and the example. 
     
    
    
     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, 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 to limit 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 combinations which can be combined with A, B, and C. 
     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 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. 
     Hereinafter, example embodiments of the invention will be described in detail with reference to the accompanying drawings. Components that are the same or correspond to each other will be denoted by the same reference numerals regardless of the figure numbers, and redundant descriptions will be omitted. 
       FIG. 1  is a perspective view illustrating a sensing device according to an embodiment,  FIG. 2  is an exploded perspective view illustrating the sensing device illustrated in  FIG. 1 , and  FIG. 3  is a cross-sectional perspective view illustrating the sensing device taken along line A-A of  FIG. 1 . In  FIGS. 1 and 2 , a z-direction denotes an axial direction, and a y-direction denotes a radial direction. In addition, the axial direction is perpendicular to the radial direction. 
     Referring to  FIGS. 1 to 3 , a sensing device  1  according to the embodiment may include a stator  100 , a rotor  200  of which one portion is disposed in the stator  100 , a first collector  300  disposed in the stator  100 , a second collector  400  disposed to be spaced apart from the first collector  300  in the radial direction in the stator  100 , sensors  500  disposed between the first collector  300  and the second collector  400 , a circuit substrate  600  electrically connected to the sensors  500 , a housing  700  coupled to the circuit substrate  600 , a first member  800 , and a second member  900 . 
     In this case, the stator  100  may be connected to an output shaft (not shown), and the rotor  200  of which at least one portion is rotatably disposed in the stator  100  may be connected to an input shaft (not shown) but is not necessarily limited thereto. 
     In this case, the rotor  200  may be rotatably disposed with respect to the stator  100 . In addition, the second collector  400  may be disposed inside the first collector  300  in the radial direction. In this case, the term “inside” may denote a direction of being disposed toward a center C in the radial direction, and the term “outside” may denote a direction opposite to “inside”. 
       FIG. 4  is a perspective view illustrating the stator of the sensing device according to the embodiment,  FIG. 5  is an exploded perspective view illustrating the stator of the sensing device according to the embodiment, and  FIG. 6  is a cross-sectional view illustrating the stator of the sensing device according to the embodiment. 
     The stator  100  may be connected to the output shaft (not shown) of a steering shaft. 
     Referring to  FIGS. 4 to 6 , the stator  100  may include a stator holder  110 , a stator body  120 , a first stator tooth  130 , and a second stator tooth  140 . 
     The stator holder  110  may be connected to an output shaft of an electric steering system. Accordingly, the stator holder  110  may rotate in conjunction with rotation of the output shaft. The stator holder  110  may be formed in a cylindrical shape. In addition, the stator holder  110  may be formed of a metal material but is not necessarily limited thereto, and the stator holder  110  may also be formed of another material in consideration of a predetermined strength or more to be fixedly fitted to the output shaft. 
     The stator holder  110  may include a groove  111 . The groove  111  is concavely formed in an outer circumferential surface of the stator holder  110 . The groove  111  is disposed along the outer circumferential surface of the stator holder  110 . The second member  900  (see  FIG. 2 ) is inserted into the groove  111 . 
     The stator holder  110  may be coupled to the stator body  120 . 
     The stator body  120  may be disposed on an end portion of one side of the stator holder  110 . The stator body  120  may be coupled to the stator holder  110  through an insert-injection method using a synthetic resin like a resin. A main gear  121  may be formed in an outer circumferential surface of the stator body  120 . The main gear  121  transmits a torque of the stator  100  to a first gear  1100  and a second gear  1200 . 
     The first stator tooth  130  and the second stator tooth  140  may be disposed to be spaced apart from each other in the radial direction. In addition, the first stator tooth  130  and the second stator tooth  140  may be fixed to the stator body  120 . The first stator tooth  130  includes a first body  131  and first tooth  132 . The second stator tooth  140  includes a second body  141  and second tooth  142 . 
       FIG. 7  is a perspective view illustrating the stator body of the stator,  FIG. 8  is a plan view illustrating the stator body of the stator, and  FIG. 9  is a cross-sectional view illustrating the stator body of the stator. 
     Referring to  FIGS. 7 to 9 , the stator body  120  includes an inner part  121 , an outer part  122 , and a partition plate  123 . Each of the inner part  121  and the outer part  122  has a cylindrical shape. The outer part  122  is disposed to be spaced outward from the inner part  121  in the radial direction. The partition plate  123  connects the inner part  121  and the outer part  122 . The inner part  121 , the outer part  122 , and the partition plate  123  may be integrally formed. The stator holder  110  may be coupled to an inner side of the inner part  121 . A space S may be formed between the outer part  122  and the inner part  121 . The partition plate  123  may be formed in a plate shape. The partition plate  123  may be disposed between the inner part  121  and the outer part  122 . 
     As illustrated in  FIG. 9 , the space S may be divided into a first space S 1  and a second space S 2  by the partition plate  123 . A magnet  230  may be disposed in the first space S 1 , and the sensors  500  may be disposed in the second space S 2 . The partition plate  123  may be disposed under a reference line L 1 , and the reference line L 1  is a virtual horizontal line passing through a center of the outer part  122  in the axial direction. 
     Meanwhile, the partition plate  123  may include first holes  124  and second holes  125 . The first holes  124  and the second holes  125  are for arranging the first stator tooth  130  and the second stator tooth  140 . 
     Referring to  FIG. 6 , the first body  131  and the second body  141  may be disposed in the first space S 1 . The first tooth  132  and the second tooth  142  may be disposed in the second space S 2 . 
     The plurality of first holes  124  may be formed to be spaced apart from each other in a circumferential direction. In addition, the first tooth  132  is disposed in the second space S 2  by passing through the first holes  124 . In this case, the number of the first holes  124  is the same as the number of first teeth  132 . The first hole  124  may be disposed close to an inner circumferential surface of the outer part  122 . As illustrated in  FIG. 8 , the first hole  124  may be formed in the partition plate  123  to be in contact with the inner circumferential surface of the outer part  122 . 
     The plurality of second holes  125  may be formed to be spaced apart from each other in the circumferential direction. In this case, the second hole  125  may be disposed to be spaced outward from the first hole  124  in the radial direction. In addition, the second tooth  142  is disposed in the second space S 2  by passing through the second holes  125 . In this case, the number of the second holes  125  is the same as the number of second teeth  142  of the second stator tooth  140 . The second hole  125  may be disposed close to an outer circumferential surface of the inner part  121 . As illustrated in  FIG. 8 , the second hole  125  may be formed in the partition plate  123  to be in contact with the outer circumferential surface of the inner part  121 . 
     The first stator tooth  130  and the second stator tooth  140  may be disposed between the outer circumferential surface of the inner part  121  and the inner circumferential surface of the outer part  122  of the stator body  120 . In this case, each of the first stator tooth  130  and the second stator tooth  140  may be formed of a metal material to be charged by rotation of the magnet  230 . 
     In addition, the first stator tooth  130  may be fixed to the inner circumferential surface of the outer part  122  by an adhesive member (not shown) such as a glue, and the second stator tooth  140  may be fixed to the outer circumferential surface of the inner part  121  by an adhesive member (not shown) such as a glue but are not necessarily limited thereto. For example, the first stator tooth  130  and the second stator tooth  140  may be fixed to the stator body  120  by coupling members (not shown), through caulking methods, or the like. 
       FIG. 10  is a view illustrating coupling of the first stator tooth and the second stator tooth and the stator body. 
     Referring to  FIGS. 9 and 10 , a boss  129  is disposed to extend downward from the partition plate  123 . A sidewall of the boss  129  and the outer part  122  are spaced apart from each other to form a first slot U 1 . The first tooth  132  is inserted into the first slot U 1  and passes through the first hole  124  to be positioned in the second space S 2 . In addition, another sidewall of the boss  129  and the inner part  121  are spaced apart from each other to form a second slot U 2 . The second tooth  142  is inserted into the second slot U 2  and passes through the second hole  125  to be positioned in the second space S 2 . 
     In a process in which the first stator tooth  130  is coupled to the stator body  120 , the first slot U 1  guides the first tooth  132  to the first hole  124  so that the first stator tooth  130  is easily coupled to the stator body  120 . 
     In a process in which the second stator tooth  140  is coupled to the stator body  120 , the second slot U 2  guides the first tooth  132  to the second hole  125  so that the second stator tooth  130  is easily coupled to the stator body  120 . 
       FIG. 11  is a view illustrating a state in which the first tooth is inserted into the first hole. 
     Referring to  FIG. 11 , in the first tooth  132 , a width W 2  of a lower surface in the circumferential direction is greater than a width W 1  of an upper surface in the circumferential direction. In this case, the lower surface is a surface adjacent to the first body  131 , and the upper surface is a surface opposite to the lower surface. When viewed from the front, the first tooth  132  may have a trapezoidal shape. Such a shape of the first tooth  132  is for inducing a difference in magnetic flux density to guide a magnetic flux to flow toward the first body  131  and also for increasing a coupling force between the first stator tooth  130  and the stator body  120 . 
     In addition, a width W 3  of the first hole  214  may be greater than the width W 1  of the upper surface of the first tooth  132  in the circumferential direction and smaller than the width W 2  of the lower surface of the first tooth  132  in the circumferential direction. This is for fitting the first tooth  132  into the first hole  214 . While the first tooth  132  is inserted into the first hole  124  toward the second space S 2 , a side surface of the first tooth  132  is inserted into the first hole  124  along an inner wall of the first hole  124 . In this process, the side surface of the first tooth  132  is press-fitted to the inner wall of the first hole  124  so that a coupling force is increased. 
     Meanwhile, an upper surface of the first body  131  may be in contact with a lower surface of the partition plate  123 . 
     Although not illustrated in the drawing, the second tooth  142  and the second hole  125  may also be coupled through a method which is the same as the above-described method that the first tooth  132  is coupled to the first hole  124 . 
       FIG. 12  is a view illustrating a protrusion of the stator body for fixing the first and second bodies, and  FIG. 13  is a view illustrating a fusing process of the protrusion of the stator body. 
     In  FIG. 13 , a symbol “I” denotes an inward direction toward a center of the stator, and in  FIG. 13 , a symbol “O” denotes an outward direction opposite to the inward direction. 
     Referring to  FIGS. 12 and 13 , the stator body  120  includes a first protrusion  126  and a second protrusion  127 . The first protrusion  126  is disposed to protrude from a lower end of the inner part  121  in the axial direction. The first protrusion  126  is disposed along the inner part  121  having an annular shape. The second protrusion  127  is disposed to protrude from a lower end of the outer part  122  in the axial direction. The second protrusion  127  is disposed along the outer part  122  having an annular shape. 
     The first protrusion  126  has an outer circumferential surface  126   a  and an inner circumferential surface  126   b . The inner circumferential surface  126   b  is continuous with an inner wall of the outer part  122 . The outer circumferential surface  126   a  may be inclined with respect to the inner circumferential surface  126   b . The outer circumferential surface  126   a  may be disposed obliquely in a direction from the lower end of the outer part  122  toward a lower end of the inner circumferential surface  126   b . When fusion is in progress in the axial direction like in a direction F of  FIG. 13 , the first protrusion  126  is deformed to cover a lower end of the first body  131 . The first protrusion  126  prevents the first stator tooth  130  from being separated from the stator body  120  in the axial direction. 
     The second protrusion  127  has an outer circumferential surface  127   a  and an inner circumferential surface  127   b . The inner circumferential surface  127   b  is continuous with an inner wall of the inner part  121 . The outer circumferential surface  127   a  may be inclined with respect to the inner circumferential surface  127   b . The outer circumferential surface  127   a  may be disposed obliquely in a direction from the lower end of the inner part  121  toward a lower end of the inner circumferential surface  127   b . When fusion is in progress in the axial direction like in the direction F of  FIG. 13 , the second protrusion  127  is deformed to cover a lower end of the second body  141 . The second protrusion  127  prevents the second stator tooth  140  from being separated from the stator body  120  in the axial direction. 
       FIG. 14  is a side view illustrating the first stator tooth, and  FIG. 15  is a side view illustrating the second stator tooth. 
     Referring to  FIGS. 5 and 14 , the first stator tooth  130  may include the first body  131  having a ring shape and a plurality of first teeth  132  spaced apart from each other and protruding from the first body  131  in the axial direction. For example, the first teeth  132  may be disposed to be spaced apart from each other in the circumferential direction and may extend upward from an upper side of the first body  131 . The first body  131  and the plurality of first teeth  132  may be integrally formed. In this case, the first body  131  may be referred to as a first tooth body. 
     The first tooth  132  may be formed in a shape of which a lower side is wide and an upper side is narrow. For example, when the first tooth  132  is viewed in the radial direction, a width of the lower side is greater than a width of the upper side. As illustrated in  FIG. 10 , the first tooth  132  may be formed in a trapezoidal shape. 
     In addition, since the first tooth  132  passes through the first hole  124 , the upper surface of the first body  131  may be in contact with the lower surface of the partition plate  123 . 
     Referring to  FIGS. 5 and 15 , the second stator tooth  140  may include the second body  141  having a ring shape and a plurality of second teeth  142  spaced apart from each other and protruding from the second body  141  in the axial direction. For example, the second teeth  142  may be disposed to be spaced apart from each other in the circumferential direction and may extend upward from an upper side of the second body  141 . The second body  141  and the plurality of second teeth  142  may be integrally formed. In this case, the second body  141  may be referred to as a second tooth body. 
     The second tooth  142  may be formed in a shape of which a lower side is wide and an upper side is narrow. For example, when the second tooth  142  is viewed in the radial direction, in the second tooth  142 , a width of the lower side is greater than a width of the upper side. As illustrated in  FIG. 11 , the second tooth  142  may be formed in a trapezoidal shape. 
     In addition, since the second tooth  142  passes through the second hole  125 , an upper surface of the second body  141  may be in contact with the lower surface of the partition plate  123 . 
     Referring to  FIG. 14 , a height H 1  of the first body  131  is smaller than a height H 2  of the first tooth  132  on the basis of an upper surface  131   a  of the first body  131 . In addition, referring to  FIG. 15 , a height H 3  of the second body  141  is smaller than a height H 4  of the second tooth  142  on the basis of an upper surface  141   a  of the second body  141 . In addition, the height H 1  of the first body  131  may be the same as the height H 3  of the second body  141 , and the height H 2  of the first tooth  132  may be the same as the height H 4  of the second tooth  142 . However, the present invention is not limited thereto, and the height H 2  of the first tooth  132  may also be different from the height H 4  of the second tooth  142 . 
       FIG. 16  is a plan view illustrating the first stator tooth, the second stator tooth, and the magnet. 
     Referring to  FIG. 16 , the first stator tooth  130  is disposed outside the second stator tooth  140 . In this case, based on the center C, the first stator tooth  130  may be formed to have a first radius R 1 , and the second stator tooth  140  may be formed to have a second radius R 2 . The first radius R 1  is greater than the second radius R 2 . 
     When viewed in the radial direction (y-direction), the first tooth  132  and the second tooth  142  may be disposed to overlap in the radial direction. Such an arrangement of the first tooth  132  and the second tooth  142  has an effect of reducing magnetic flux leakage. 
       FIG. 17  is a view illustrating a first pole and a second pole of the magnet. 
     Referring to  FIG. 17 , the magnet includes first poles  230 A and second poles  230 B. The first pole  230 A and the second pole  230 B may be alternately disposed in a circumferential direction of the magnet. 
     The first poles  230 A and the second poles  230 B may respectively include N-pole areas NA and S-pole areas SA. Each of the first pole  230 A and the second pole  230 B may have a multilayer structure in which the N-pole area NA and the S-pole area SA are positioned at inner and outer sides thereof. In the first pole  230 A, the N-pole area NA may be disposed at a relatively outer side, and the S-pole area SA may be disposed inside the N-pole area NA. In the second pole  230 B, the N-pole area NA may be disposed at a relatively inner side, and the S-pole area SA may be disposed outside the N-pole area NA. 
     The N-pole area NA of the first pole  230 A and the S-pole area SA of the second pole  230 B are disposed adjacent to each other. The S-pole area SA of the first pole  230 A and the N-pole area NA of the second pole  230 B are disposed adjacent to each other. 
     When the magnet  230  rotates so that the first tooth  132  approaches the S-pole area SA and is charged with an S-pole, since the second tooth  142  approaches the N-pole area NA, the second tooth  142  is charged with an N-pole. Alternatively, when the magnet  230  rotates so that the first tooth  132  approaches the N-pole area NA and is charged with an N-pole, since the second tooth  142  approaches the S-pole area SA, the second tooth  142  is charged with an S-pole. Accordingly, the sensors  500  may measure an angle using a magnetic field applied through the first collector  300  and the second collector  400 . 
     In the sensing device according to the embodiment, the first tooth  132  and the second tooth  142  overlap in the radial direction. Two ends of the second tooth  142  may overlap the first tooth  132 . For example, positions and sizes of the first tooth  132  and the second tooth  142  may be designed so that a first angle Θ 1 , a second angle Θ 2 , and a third angle Θ 3  are the same. 
     The first angle Θ 1  denotes an angle formed by two ends of the first pole  230 A based on the stator center C. For example, in a case in which there are eight first poles  230 A and eight second poles  230 B, the first angle Θ 1  may be 22.5°. 
       FIG. 18  is a view illustrating the second angle Θ 2 . 
       FIG. 19  is a view illustrating the third angle Θ 3 . 
     Referring to  FIGS. 17 and 18 , the second angle Θ 2  denotes an angel formed by two ends P 1  of the first tooth  132  based on the stator center C. A reference point G used when the two ends P 1  of the first tooth  132  are defined in the axial direction will be described below. The reference point G corresponds to a point, which corresponds to a middle point of a height H 1  of a body  231  of the magnet  230 , of the first tooth  132  when the first tooth  132  is disposed to face the body  231  of the magnet  230 . The height H 1  of the body  231  of the magnet  230  denotes a height between an upper surface  231   a  and a lower surface  231   b  of the magnet  230  in the axial direction. An angle Θ 4  between the first tooth  132  and another first tooth  132  at the reference point G may be the same as the second angle Θ 2 . 
     Referring to  FIGS. 17 and 19 , the third angle Θ 3  denotes an angle formed by two ends P 2  of the second tooth  142  based on the stator center C. A reference point G used when the two ends P 2  of the second tooth  142  are defined in the axial direction will be described below. The reference point G corresponds to a point, which corresponds to the middle point of the height H 1  of the body  231  of the magnet  230 , of the second tooth  142  when the second tooth  142  is disposed to face the body  231  of the magnet  230 . An angle Θ 5  between the second tooth  142  and another second tooth  142  at the reference point G may be the same as the third angle Θ 3 . 
       FIG. 20  is a graph showing a flux with respect to the first angle Θ 1 , the second angle Θ 2 , and the third angle Θ 3 . 
     Referring to  FIG. 20 , it may be seen that in a state in which the second angle Θ 2  and the third angle Θ 3  are set to be the same, as the second angle Θ 2  and the third angle Θ 3  become closer to the first angle Θ 1 , a flux magnitude increases, and as the second angle Θ 2  and the third angle Θ 3  become farther away from the first angle Θ 1 , the flux magnitude decreases. It may be seen that, in a case in which sizes and positions of the first tooth  132  and the second tooth  142  are arranged so that the second angle Θ 2  and the third angle Θ 3  are the same as the first angle Θ 1 , the flux magnitude of the first and second stator tooth  130  and  140  is the largest. 
       FIG. 21  is an exploded perspective view illustrating the rotor. 
     Referring to  FIGS. 2 and 21 , the rotor  200  may include a rotor holder  210 , a rotor body  220 , and the magnet  230 . The rotor holder  210 , the rotor body  220 , and the magnet  230  may be integrally formed. 
     The rotor holder  210  may be connected to the input shaft of the electric steering system. Accordingly, the rotor holder  210  may be rotated in conjunction with rotation of the input shaft. The rotor holder  210  may be formed in a cylindrical shape. In addition, an end portion of the rotor holder  210  may be coupled to the rotor body  220 . The rotor holder  210  may be formed of a metal material but is not necessarily limited thereto, and the rotor holder  210  may also be formed of another material in consideration of a predetermined strength or more to be fixedly fitted to the input shaft. 
     The rotor  200  may include a protrusion  211  of the rotor holder  210 . The protrusion  211  may be disposed to extend from an outer circumferential surface of the rotor holder  210  in the radial direction. 
     The rotor body  220  is disposed at one side of the outer circumferential surface of the rotor holder  210 . The rotor body  220  may be an annular member. A groove  221  may be disposed in an inner circumferential surface of the rotor body  220 . The groove  221  is a groove into which the protrusion of the rotor holder  210  is inserted. 
     The magnet  230  is coupled to the rotor body  220 . When the rotor holder  210  rotates, the magnet  230  is rotated in conjunction with the rotation of the rotor holder  210 . 
       FIG. 22  is a view illustrating the magnet  230 , and  FIG. 23  is a plan view illustrating the magnet  230 . 
     Referring to  FIGS. 22 and 23 , the magnet  230  may include the body  231  having a ring shape and a protrusion  232  protruding from an upper surface of the body  231 . The protrusion  232  may be provided as a plurality of protrusions  232 . The protrusion  232  may include a first part  232   a  and a second part  232   b . The first part  232   a  protrudes upward from the upper surface of the body  231 . The second part  232   b  may be disposed to protrude from the first part  232   a  in a radial direction of the magnet  230 . The second part  232   b  may protrude inward further than an inner circumferential surface of the body  231 . The protrusion  232  is for improving a coupling force to the rotor body  220 . The first part  232   a  prevents slip between the rotor body  220  and the magnet  230  in a rotation direction, and the second part  232   b  prevents separation of the rotor body  220  and the magnet  230  in the axial direction. 
       FIG. 24  is a perspective view illustrating an arrangement of the magnet  230  with respect to the first stator tooth and the second stator tooth. 
     Referring to  FIG. 24 , the magnet  230  is disposed between the first tooth  132  and the second tooth  142 . The body  231  of the magnet  230  is disposed to face the first tooth  132  and the second tooth  142 . The protrusions  232  of the magnet  230  are disposed above the first tooth  132  and the second tooth  142 . 
       FIG. 25  is a view illustrating the collectors,  FIG. 26  is a view illustrating the collectors disposed between the first stator tooth and the second stator tooth, and  FIG. 27  is a view illustrating positions of the sensors and positions of the collectors. 
     Referring to  FIGS. 2 and 25 to 27 , the collectors may include the first collector  300  and the second collector  400 . The first collector  300  and the second collector  400  collect a flux of the stator  100 . In this case, the first collector  300  and the second collector  400  may be formed of a metal material and disposed to be spaced apart from each other in the radial direction. 
     The first collector  300  may include first collector bodies  310  and a first extension  320 . The first extension  320  extends from the first collector bodies  310 . The first collector bodies  310  may include a first-1 collector body  310 A and a first-2 collector body  310 B. The first-1 collector body  310 A is disposed at one side of the first extension  320 . The first-2 collector body  310 B is disposed at the other side of the first extension  320 . Each of the first-1 collector body  310 A and the first-2 collector body  310 B may include a flat surface. The first extension  320  may include a curved surface having a predetermined curvature. 
     The second collector  400  may have second collector bodies  410  and a second extension  420 . The second extension  420  extends from the second collector bodies  410 . The second collector bodies  410  may include a second-1 collector body  410 A and a second-2 collector body  410 B. The second-1 collector body  410 A is disposed at one side of the second extension  420 . And the second-2 collector body  410 B is disposed at the other side of the second extension  420 . Each of the second-1 collector body  410 A and the second-2 collector body  410 B may include a flat surface. The second extension  420  may include a curved surface having a predetermined curvature. 
     The first-1 collector body  310 A and the second-1 collector body  410 A are disposed to overlap in the radial direction. The first-2 collector body  310 B and the second-2 collector body  410 B are disposed to overlap in the radial direction. The first extension  320  and the second extension  420  do not overlap in the radial direction. 
     The sensor  500  detects a change in magnetic field occurring between the stator  100  and the rotor  200 . The sensor  500  may be a Hall integrated circuit (IC). The sensor  500  detects an amount of magnetization of the stator  100  which occurs due to an electric interaction between the magnet  230  of the rotor  200  and the stator  100 . The sensing device  1  measures a torque on the basis of the detected amount of magnetization. 
     The sensors  500  may include a first sensor  500 A and a second sensor  500 B. The first sensor  500 A and the second sensor  500 B may be disposed at opposite sides around the center C of the stator. 
     The first sensor  500 A is disposed between the first-1 collector body  310 A and the second-1 collector body  410 A. The first-1 collector body  310 A may be disposed outside the first sensor  500 A. The second-1 collector body  410 A may be disposed inside the first sensor  500 A. 
     The second sensor  500 B is disposed between the first-2 collector body  310 B and the second-2 collector body  410 B. The first-2 collector body  310 B may be disposed outside the second sensor  500 B. The second-2 collector body  410 B may be disposed inside the second sensor  500 B. 
     The first extension  320  may include a plurality of first brackets  321 . The first brackets  321  may be disposed to extend inward from an upper surface of the first extension  320 . The second extension  420  may include a plurality of second brackets  421 . The second brackets  421  may be disposed to extend inward from an upper surface of the second extension  420 . Each of the first bracket  321  and the second bracket  421  may include a hole. The first bracket  321  and the second bracket  421  are to be coupled to the housing. 
       FIG. 28  is a view illustrating the circuit substrate. 
     Referring to  FIG. 28 , the first sensor  500 A and the second sensor  500 B are disposed on the circuit substrate. The first sensor  500 A and the second sensor  500 B are disposed in a state in which the first sensor  500 A and the second sensor  500 B stand upward on the circuit substrate  600 . The first sensor  500 A and the second sensor  500 B are disposed to face each other. 
       FIG. 29  is a perspective view illustrating the housing when viewed from above, and  FIG. 30  is a perspective view illustrating the housing when viewed from below. Referring to  FIGS. 2, 29, and 30 , the housing may include a housing body  710 , a first protruding part  720 , a second protruding part  730 , third protruding parts  721 , and fourth protruding parts  731 . 
     The housing body  710  has a plate shape which includes an upper surface and a lower surface and of which upper and lower portions are open. A hole  713  is disposed at a central portion thereof. The stator holder  110  is positioned inside the hole  713 . 
     The first protruding part  720  is disposed along a circumference of the hole  713 . The first protruding part  720  protrudes from the upper surface of the housing body  710 . 
     The second protruding part  730  is disposed along the circumference of the hole  713 . The second protruding part  730  protrudes from the upper surface of the housing body  710 . 
     The first protruding part  720  and the second protruding part  730  may be disposed on the same circumference. In addition, the first protruding part  720  and the second protruding part  730  may be disposed to be spaced apart from each other in the circumferential direction. Holes  740  may be disposed between the first protruding part  720  and the second protruding part  730  in the circumferential direction. Two holes  740  may be disposed. The holes  740  are holes through which the sensors pass. 
     The circuit substrate  600  is installed on a lower surface  712  of the housing body  710 . A first cover  701  may be coupled to a lower side of the housing body  710  to cover the circuit substrate  600 . 
     The first protruding part  720  may include the third protruding parts  721 . The third protruding parts  721  protrude upward from an upper surface of the first protruding part  720 . The plurality of third protruding parts  721  may be provided. 
     The second protruding part  730  may include the fourth protruding parts  731 . The fourth protruding parts  731  protrude upward from an upper surface of the second protruding part  730 . The plurality of fourth protruding parts  731  may be provided. 
     The third protruding parts  721  are to be coupled to the first brackets  321 . The fourth protruding parts  731  are to be coupled to the second brackets  421 . 
     Holes  750  in which the first gear  1100  and the second gear  1200  are disposed may be disposed in the housing body  710 . 
       FIG. 31  is a view illustrating the housing in which the collectors and the sensors are disposed. 
     Referring to  FIG. 31 , the first collector  300  and the second collector  400  are coupled to the housing  700 . 
     The first extension  320  is disposed outside the first protruding part  720 . The first bracket  321  is coupled to the third protruding part  721 . The third protruding part  721  is press-inserted into the hole formed in the first bracket  321 . After the press-insertion, the third protruding part  721  may be fused. 
     The second extension  420  is disposed inside the second protruding part  730 . The second bracket  421  is coupled to the fourth protruding part  731 . The fourth protruding part  731  is press-inserted into the hole formed in the second bracket  421 . After the press-insertion, the fourth protruding part  731  is fused. 
     The first sensor  500 A is disposed between the first-1 collector body  310 A and the second-1 collector body  410 A. 
     The second sensor  500 B is disposed between the first-2 collector body  310 B and the second-2 collector body  410 B. 
     The first gear  1100  and the second gear  1200  may be rotatably disposed on an upper surface  711  of the housing body  710 . The first gear  1100  or the second gear  1200  is engaged with the main gear  121  of the stator body  120 . A second cover  702  may be disposed at an upper side, at which the first gear  1100  and the second gear  1200  are disposed, of the housing body  710 . The second cover  702  is coupled to the housing body  710 . 
       FIG. 32  is a cross-sectional view illustrating a connector housing and a pin of the housing. 
     Referring to  FIG. 32 , the housing  700  includes a connector housing  760  and a pin  770 . The pin  770  electrically connects the circuit substrate  600  and an external cable. One side of the pin  770  is connected to the circuit substrate  600  disposed at a lower side of the housing  700 . The other side of the pin  770  is exposed inside the connector housing  760 . An entrance of the connector housing  760  may be perpendicular to the axial direction. The pin  770  may have a shape bent in a “1” shape. 
       FIG. 33  is a view illustrating the first member and the second member, and  FIG. 34  is a view illustrating the first member and the second member installed in the stator holder. 
     Referring to  FIGS. 33 and 34 , the first member  800  is for preventing a sidewall of the hole  713  of the housing body  710  from being worn and for preventing coaxial misalignment of the sensing device. As described above, the first tooth  132  and the second tooth  142  are disposed to overlap in the radial direction. In addition, the sensors  500  are disposed between the first tooth  132  and the second tooth  142  in the radial direction. Accordingly, in a case in which shaking occurs in the radial direction, since distances between the first tooth  132 , the sensors  500 , and the second tooth  142  are changed, the sensing device may be damaged critically, or a performance problem of the sensing device may occur. 
     The first member  800  may be a member having a ring shape. The first member  800  may include a body  810  and a flange part  820 . The body  810  is a cylindrical member. The body  810  may be disposed along an inner wall of the hole  713  of the housing body  710 . The body  810  is disposed between the outer circumferential surface of the stator holder  110  and the inner wall of the hole  713  of the housing body  710 . The flange part  820  has a shape extending from a lower end of the body  810  in the radial direction. The flange part  820  is disposed to be contactable with the lower surface of the housing body  710 . In addition, the flange part  820  may be disposed to cover one portion of the first cover  701 . In addition, the first member  800  may be formed of a metal material. 
     A lower surface of the flange part  820  may be in contact with an upper surface of the second member  900 . 
     The first member  800  physically separates the hole  713  of the housing body  710  from the stator holder  110  when the stator holder  110  rotates, and thus the first member  800  serves to prevent the inner wall of the hole  713  of the housing body  710  from being worn when the stator holder  110  rotates. As a result, the first member  800  secures coaxial rotation of the stator holder  110 . 
     The housing  700  is hooked on the main gear  121  of the stator body  120  and thus is not separated upward from the stator  100  in the axial direction. However, the housing  700  may be separated downward from the stator  100 . The second member  900  serves to prevent the housing  700  from being separated downward from the stator  100 . The second member  900  may have a c-ring shape. The second member  900  may be formed of a metal material. The second member  900  may be formed of an elastically deformable material. 
     The second member  900  is coupled to the groove  111  of the stator holder  110 . The groove  111  is concavely formed along the outer circumferential surface of the stator holder  110 . The second member  900  is positioned under the lower surface of the housing body  710  in a state in which the second member  900  is coupled to the stator holder  110 . In addition, the second member  900  may be disposed under the first member  800  to support the lower surface of the flange part  820  of the first member  800 . 
       FIG. 35  is a view illustrating the first gear  1100  and the second gear  1200  which are engaged with the main gear  121 . 
     Referring to  FIGS. 2 and 35 , the first gear  1100  and the second gear  1200  which are engaged with the main gear  121  are disposed as sub-gears. The main gear  121 , the first gear  1100 , the second gear  1200 , and third sensors  610  are for measuring an angle of the steering shaft. 
     The main gear  121  is engaged and rotated with the first gear  1100  and the second gear  1200 . The main gear  121  is disposed on the outer circumferential surface of the stator body  120 . The first gear  1100  and the second gear  1200  are rotatably disposed on the housing body  710 . Gear ratios between the main gear  121 , the first gear  1100 , and the second gear  1200  are predetermined. For example, in a case in which a total angle of the main gear  121  is 1620°, the first gear  1100  may be designed to rotate 15.6 times and the second gear  1200  may be designed to rotate 14.625 times when the main gear  121  rotates 4.5 times. In this case, the total angle is an angle calculated by accumulating rotation of the main gear  121  when all the gears return to a state before rotating. 
     Magnets may be disposed on the first gear  1100  and the second gear  1200 . The magnets are disposed to face the third sensors  610 . The third sensors  610  are mounted on the circuit substrate. 
       FIG. 36  is a view illustrating a directionality of an external magnetic field with respect to the stator tooth,  FIG. 37  is a view illustrating a state in which the sensor avoids an external magnetic field having a z-axis directionality, and  FIG. 38  is a view illustrating a state in which the first and second stator teeth avoid an external magnetic field having a y′-axis directionality. 
     Referring to  FIG. 36 , an external magnetic field greatly affects the sensing device in the z-axis direction which is the axial direction and the y′-axis direction perpendicular to the z-axis direction. In this case, the y′-axis direction denotes a direction toward the sensor  500 , which is the radial direction perpendicular to the axial direction. 
     Referring to  FIG. 37 , the sensor  500  of the sensing device according to the embodiment is disposed in a state in which the sensor  500  stands in the z-axis direction. Accordingly, an area of the sensor  500  when viewed in the z-axis is much smaller than an area of the sensor  500  when viewed in the y′-axis direction. Accordingly, the sensing device according to the embodiment has an advantage in that an effect of the external magnetic field on the sensor  500  is small in the z-axis direction. 
     Referring to  FIG. 38 , when the state in which the sensor  500  stands in the z-axis direction is considered, a circumferential magnetic field in the y′-axis direction may greatly affect the sensor  500 . However, since the circumferential magnetic field in the y′-axis direction is induced along the first stator tooth  130  and the second stator tooth  140 , the circumferential magnetic field flows without affecting the sensor  500 . Accordingly, the sensing device according to the embodiment has an advantage in that an effect of the external magnetic field on the sensor  500  is also small even in the y′-axis direction. 
       FIG. 39  is a graph showing a comparison of an amount of change in angle with respect to an external magnetic field in the z-axis direction between a comparative example and an example. 
     Referring to  FIG. 39 , in the case of the comparative example, a sensing device has a structure in which a stator tooth is vertically disposed and a sensor is horizontally disposed, and it may be seen that, as an external magnetic field in a z-axis direction increases, an amount of change in angle increases linearly, and thus the measured angle is greatly changed according to the external magnetic field. 
     Conversely, in the case of the example, it may be seen that, even when an external magnetic field in a z-axis direction increases, a change in angle barely occurs, and thus the angle is barely affected by the external magnetic field. 
       FIG. 40  is a graph showing a comparison of an amount of change in angle with respect to the external magnetic field in the y′-axis direction between the comparative example and the example. 
     Referring to  FIG. 40 , in the case of the comparative example, the sensing device has the structure in which the stator tooth is vertically disposed and the sensor is horizontally disposed, and it may be seen that, as an external magnetic field in the y′-axis direction increases, an amount of change in angle increases linearly, and thus the measured angle is greatly changed according to the external magnetic field. 
     Conversely, in the case of the example, it may be seen that, even when an external magnetic field in the y′-axis direction increases, a change in angle barely occurs, and thus the angle is barely affected by the external magnetic field. 
     REFERENCE NUMERALS 
       
     
       
         
           
               
               
             
               
                   
               
             
            
               
                 100: STATOR 
                 110: STATOR HOLDER 
               
               
                 120: STATOR BODY 
                 130: FIRST STATOR TOOTH 
               
               
                 140: SECOND STATOR TOOTH 
                 200: ROTOR 
               
               
                 210: ROTOR HOLDER 
                 220: ROTOR BODY 
               
               
                 230: MAGNET 
                 300: FIRST COLLECTOR 
               
               
                 400: SECOND COLLECTOR