Patent Publication Number: US-2022214236-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 a 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 the 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 the torque applied to the steering shaft. In addition, the index sensor detects rotation of the output shaft to measure the angular acceleration of the steering shaft. In the sensor assembly, the torque sensor and the index sensor may be disposed together to be integrally formed. 
     The torque sensor may include a stator, which has a housing, a rotor, and 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 disposed outside the stator tooth. 
     However, when an external magnetic field is generated, since the collector in the structure may serve as a path of the external magnetic field, there is a problem of affecting a flux value of a Hall integrated circuit (IC). Accordingly, since an output value of the torque sensor is changed, there is a problem in that the torsion degree of the torsion bar may not be accurately measured. 
     Particularly, as more electric devices are used in a vehicle, since the number of cases increases in which a torque sensor is affected by an external magnetic field, a torque sensor, which is not affected by an external magnetic field, is required. 
     In addition, when the collector has an annular shape and the housing moves, the housing in which the collector is disposed and the stator teeth are eccentrically moved, a length of the collector and a length of the stator tooth are changed in a redial direction, and thus there is a problem of increasing sensitivity to a magnetic flux to be measured. 
     Technical Problem 
     The present invention is directed to providing a sensing device which is not affected by a magnetic field interference due to an external magnetic field generated by an external device when a torque is measured. 
     Particularly, the present invention is directed to providing a sensing device which decreases sensitivity to a magnetic flux to be measured according to movement of a housing. 
     Objectives that should be solved according to 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 sensing device further comprises a sensor and a collector which are disposed between the first stator tooth and the second stator tooth in the radial direction, the first stator tooth includes a first region corresponding to the collector in a circumferential direction, the second stator tooth includes a second region corresponding to the collector in the circumferential direction, and each of a central angle of the first region and a central angle of the second region is 180° or less. 
     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 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 sensing device further comprises a sensor and a collector which are disposed in a space between the first stator tooth and the second stator tooth in the radial direction, the collector includes a first collector and a second collector, and when a virtual line passing through the center of the stator in the radial direction is defined as a first reference line, and a virtual line perpendicular to the first reference line in the radial direction is defined as a second reference line, the first collector and the second collector are symmetrically disposed with respect to the first reference line at only one side of the second reference line. 
     Still 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 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 sensing device further comprises a sensor and a collector which are disposed in a space between the first stator tooth and the second stator tooth in the radial direction, the sensor includes a first sensor and a second sensor, the collector includes a first body disposed opposite to the first sensor, a second body extending from the first body and disposed opposite to the second sensor, and extension parts extending from the first body and the second body, and an angle formed by both ends of the collector based on a curvature center of the extension part is 180° or less. 
     The sensor may include a first sensor and a second sensor, and the collector may include a first body disposed opposite to the first sensor, a second body extending from the first body and disposed opposite to the second sensor, and extension parts extending from the first body and the second body. 
     The sensor may include a first sensor and a second sensor, the first collector may include a first body disposed opposite to the first sensor and a first extension part extending from the first body, and the second collector may include a second body disposed opposite to the second sensor and a second extension part extending from the second body. 
     The first body and the second body may be connected to be bent. 
     The sensing device may further include a housing configured to accommodate a circuit board, wherein the housing may include a first hole through which the first sensor passes and a second hole through which the second sensor passes, and the first hole and the second hole may be connected to be bent. 
     The sensing device may further include a housing configured to accommodate a circuit board, wherein the collector may include bent parts disposed at both ends to be bent outward, and the housing may include grooves in which the bent parts are disposed. 
     The housing may include a protrusion having an annular shape protruding in an axial direction, and the grooves may be concavely disposed in an inner circumferential surface of the protrusion. 
     The sensor may be disposed between the collector and the first stator tooth in the radial direction. 
     Advantageous Effects 
     A sensing device according to an embodiment having a structure described above has an advantage of decreasing sensitivity to a magnetic flux to be measured even when a collector moves. 
     In addition, since the collector is disposed between a pair of stator teeth and a sensor is disposed between collectors, a magnetic field interference due to an external magnetic field generated by an external device when a torque is measured can be prevented or minimized. 
     In addition, since a first tooth of a first stator tooth and a second tooth of a second stator tooth, which are disposed to be spaced apart from each other in a radial direction, are disposed to overlap, and a magnet is rotated between the first tooth and the second tooth, the first tooth and the second tooth may be charged to different poles. 
     In addition, there is an advantage of increasing a magnitude of a flux being collected. 
     In addition, a magnetic field interference due to an external magnetic field introduced from an inner side of a stator holder can be prevented or minimized. 
     In addition, a magnetic field interference due to an external magnetic field introduced from a side surface of the sensing device can be prevented or minimized. 
     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 of 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. 
         FIGS. 9 and 10  are cross-sectional views illustrating the stator body of the stator. 
         FIG. 11  is a side view illustrating a first stator tooth. 
         FIG. 12  is a side view illustrating a second stator tooth. 
         FIG. 13  is a plan view illustrating the first stator tooth, the second stator tooth, and a magnet. 
         FIG. 14  is a view illustrating a first pole and a second pole of the magnet. 
         FIG. 15  is a view illustrating a second angle (Θ 2 ). 
         FIG. 16  is a view illustrating a third angle (Θ 3 ). 
         FIG. 17  is a graph showing a flux versus a first angle (Θ 1 ), the second angle (Θ 2 ), and the third angle (Θ 3 ). 
         FIG. 18  is an exploded perspective view illustrating a rotor. 
         FIG. 19  is a view illustrating the magnet. 
         FIG. 20  is a plan view illustrating the magnet. 
         FIG. 21  is a perspective view illustrating an arrangement of the magnet with respect to the first stator tooth and the second stator tooth. 
         FIG. 22  is a perspective view illustrating the first stator tooth. 
         FIG. 23  is a perspective view illustrating the second stator tooth. 
         FIG. 24  is a plan view illustrating the first stator tooth. 
         FIG. 25  is a plan view illustrating the first stator tooth and the second stator tooth. 
         FIG. 26  is a view illustrating the first tooth, the second tooth, and a third tooth which are concentrically disposed. 
         FIG. 27  is a plan view which illustrates a flow of an external magnetic field introduced from an inner side of a stator holder and illustrates the first stator tooth and the second stator tooth. 
         FIG. 28  is a cross-sectional view which illustrates a flow of the external magnetic field guided to the third tooth and illustrates the first stator tooth. 
         FIG. 29  shows side cross-sectional views illustrating the first stator tooth, the second stator tooth, a sensor, and a collector. 
         FIG. 30  is a view illustrating the collector. 
         FIG. 31  is a view illustrating the collector disposed between the first stator tooth and the second stator tooth, wherein a first region of the first stator tooth and a second region of the second stator tooth are illustrated. 
         FIG. 32  is a view illustrating the collector disposed between the first stator tooth and the second stator tooth, wherein a position of the collector with respect to a first reference line and a second reference line is illustrated. 
         FIG. 33  is a view illustrating a shape of the collector with respect to a curvature center of an extension part of the collector of  FIG. 32 . 
         FIG. 34  is a view illustrating a housing in which the collector and the sensor are disposed. 
         FIG. 35  is a view illustrating a groove in a protrusion disposed in the housing illustrated in  FIG. 34 . 
         FIG. 36  is a bottom view illustrating the housing illustrated in  FIG. 34 . 
         FIG. 37  is a view illustrating a relative position of the collector with respect to the first stator tooth and the second stator tooth when the collector moves to any one side. 
         FIG. 38  is a view illustrating a relative position of the collector with respect to the first stator tooth and the second stator tooth when the collector moves to the other side. 
         FIG. 39  is a comparison graph of sensitivity to a magnetic flux measured by the sensing device according to Example and a sensing device according to Comparative example. 
         FIG. 40  is a view illustrating a first gear and a second gear which are engaged with a main gear. 
         FIG. 41  is a view illustrating a direction of an external magnetic field with respect to the stator tooth. 
         FIG. 42  is a view illustrating an avoidance state of the sensor from an external magnetic field having a z-axis direction. 
         FIG. 43  is a view illustrating an avoidance state of the first and second stator teeth from an external magnetic field having a y′-axis direction. 
         FIG. 44  is a comparison graph of an amount of a change in angle according to an external magnetic field in a z-axis direction between Comparative example and Example. 
         FIG. 45  is a comparison graph of an amount of a change in angle according to an external magnetic field in a y′-axis direction between Comparative example and 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 possible combinations of 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 of the sensing device taken along line A-A of  FIG. 1 . In  FIGS. 1 and 2 , a z direction means an axial direction, and a y direction means a radial direction. In addition, the axial direction and the radial direction are perpendicular to each other. 
     Referring to  FIGS. 1 to 3 , a sensing device  1  according to the embodiment may include a stator  100 , a rotor  200  of which a part is disposed inside the stator  100 , a sensor  500 , a circuit board  600  electrically connected to the sensor  500 , a housing  700  to which the circuit board  600  is coupled, 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 the part is disposed inside the stator  100  may be connected to an input shaft (not shown), but the present invention is not necessarily limited thereto. 
     In this case, the rotor  200  may be rotatably disposed with respect to the stator  100 . Hereinafter, “inside” means a direction toward a center C in the radial direction, and “outside” means 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 an 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 apparatus. Accordingly, the stator holder  110  may be rotated 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 be formed of another material by considering a predetermined strength or more so that the output shaft is fixedly inserted thereinto. 
     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 . A fixing 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 one end portion of the stator holder  110 . The stator body  120  may be coupled to the stator holder  110  in an insertion-injection molding manner using a synthetic resin such as a resin. A main gear  121  may be formed on an outer circumferential surface of the stator body  120 . The main gear  121  transmits a rotational force of the stator body  120  to a first gear  1100  (see  FIG. 40 ) and a second gear  1200  (see  FIG. 40 ). 
     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 , first teeth  132 , and third teeth  133 . The second stator tooth  140  includes a second body  141  and second teeth  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  FIGS. 9 and 10  are cross-sectional views illustrating the stator body of the stator. 
     Referring to  FIGS. 7 to 10 , the stator body  120  includes an inner part  121 , an outer part  122 , and a partition plate  123 . The inner part  121  and the outer part  122  have cylindrical shapes. 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 an integrated part. 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 . 
     The space S may be divided into a first space S 1  and a second space S 2  by the partition plate  123 . The sensor  500  may be disposed in the first space S 1 , and a magnet  230  may be disposed in the second space S 2 . The partition plate  123  may be disposed at a lower level than a virtual horizontal line L 1 . In this case, the virtual horizontal line L 1  passes through a center of the outer part  122  in the axial direction. 
     Meanwhile, the partition plate  123  may include a first hole  124  and a second hole  125 . The first hole  124  and the second hole  125  are for arranging the first stator tooth  130  and the second stator tooth  140 . 
     The first body  131  and the second body  141  may be disposed in the first space S 1 , and the first tooth  132  and the second tooth  142  may be disposed in the second space S 2 . 
     The first hole  124  may be formed as a plurality of first holes  124  spaced apart from each other in a circumferential direction. In addition, the first tooth  132  is disposed in the second space S 2  to pass through the first hole  124 . In this case, the number of the first holes  124  is the same as the number of the 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 second hole  125  may be formed as a plurality of second holes  125  spaced apart from each other in a circumferential direction. In this case, the second hole  125  may be disposed to be space inward from the first hole  124  in the radial direction. In addition, the second tooth  142  is disposed in the second space S 2  to pass through the second hole  125 . In this case, the number of the second holes  125  is the same as the number of the 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 . 
     A plurality of third holes  127  may be formed to be spaced apart from each other in the circumferential direction. The third hole  127  may be disposed between the second hole  125  and the second hole  125  in the circumferential direction. The third tooth  133  is disposed in the second space S 2  to pass through the third hole  127 . In this case, the number of the third holes  127  may be the same as the number of the third teeth  133  of the first stator tooth  130 . The third hole  127  may be disposed close to the outer circumferential surface of the inner part  121 . The third hole  127  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, the first stator tooth  130  and the second stator tooth  140  may be formed of metal materials to be electrically 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 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 glue, but the present invention is 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 a coupling member (not shown) or in a caulking manner. 
     A boss  126  is disposed to extend downward from the partition plate  123 . A side wall of the boss  126  is spaced apart from the outer part  122  to constitute a first slot U 1 . The first tooth  132  is inserted into the first slot U 1 , passes through the first hole  124 , and is positioned in the second space S 2 . In addition, a side wall of the boss  126  is spaced apart from the inner part  121  to constitute a second slot U 2 . The second tooth  142  and the third tooth  133  are inserted into the second slot U 2 , pass through the second hole  125  and the third hole  127 , respectively, and are 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  to facilitate the coupling therebetween. 
     In a process in which the second stator tooth  130  is coupled to the stator body  120 , the second slot U 2  guides the second tooth  142  and the third tooth  133  to the second hole  125  and the third hole  127 , respectively, to facilitate the coupling therebetween. 
       FIG. 11  is a side view illustrating the first stator tooth, and  FIG. 12  is a side view illustrating the second stator tooth. 
     Referring to  FIGS. 5 and 11 , the first stator tooth  130  may include the first body  131  and the plurality of first teeth  132  protruding from the first body  131  in the axial direction to be spaced apart from each other. 
     Referring to  FIGS. 5 and 12 , the second stator tooth  140  may include the second body  141  and the plurality of second teeth  142  protruding from the second body  141  in the axial direction to be spaced apart from each other. 
     A height H 1  of the first body  131  is smaller than a height H 2  of the first tooth  132  based on an upper surface  131   a  of the first body  131 . In addition, a height H 3  of the second body  141  is smaller than a height H 4  of the second tooth  142  based on an upper surface  141   a  of the second body  141 . However, the present invention is not limited thereto, and the height H 2  of the first tooth  132  and the height H 4  of the second tooth  142  may also be different. 
       FIG. 13  is a plan view illustrating the first stator tooth, the second stator tooth, and the magnet. 
     Referring to  FIG. 13 , the first stator tooth  130  is disposed outside the second stator tooth  140 . The first tooth  132  and the second tooth  142  may be disposed to overlap in the radial direction when viewed in the radial direction (y direction). Such an arrangement of the first tooth  132  and the second tooth  142  has an effect of reducing a leakage of a magnetic flux. 
       FIG. 14  is a view illustrating a first pole and a second pole of the magnet. 
     Referring to  FIG. 14 , 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 each include an N-pole region N and an S-pole region S. Each of the first pole  230 A and the second pole  230 B may have a multi-layer structure in which the N-pole region N and the S-pole region S are divided to be positioned at inner and outer sides. 
     In the first pole  230 A, the N-pole region N may be disposed at a relatively outer side, and the S-pole region S may be disposed at a side further inward than the N-pole region N. In the second pole  230 B, the N-pole region N may be disposed at a relatively inner side, and the S-pole region S may be disposed at a side further outward than the N-pole region N. 
     The N-pole region N of the first pole  230 A is disposed adjacent to the S-pole region S of the second pole  230 B. The S-pole region S of the first pole  230 A is disposed adjacent to the N-pole region N of the second pole  230 B. 
     When the magnet  230  rotates so that the first tooth  132  becomes closer to the S-pole region S and is charged to an S-pole, since the second tooth  142  becomes closer to the N-pole region N, the second tooth  142  is charged to an N-pole. In addition, when the magnet  230  rotates so that the first tooth  132  becomes closer to the N-pole region N and is charged to an N-pole, since the second tooth  142  becomes closer to the S-pole region S, the second tooth  142  is charged to an S-pole. Accordingly, the sensor  500  may measure an angle using a magnetic field applied through the first stator tooth  130 , the second stator tooth  140 , and a collector  300  (see  FIG. 29 ). 
     In the sensing device according to the embodiment, the first tooth  132  and the second tooth  142  overlap in the radial direction. Both ends of the second tooth  142  may overlap the first tooth  132 . For example, when a position and a size of the first tooth  132  and a position and a size the second tooth  142  are designed, a first angle Θ 1 , a second angle Θ 2 , and a third angle Θ 3  may be the same. 
     The first angle Θ 1  denotes an angle formed by both ends of the first pole  230 A based on the stator center C. For example, when the number of the first poles  230 A is 8, and the number of the second poles  230 B is 8, the first angle Θ 1  may be 22.5°. 
       FIG. 15  is a view illustrating the second angle Θ 2 , and  FIG. 16  is a view illustrating the third angle Θ 3 . 
     Referring to  FIG. 15 , the second angle Θ 2  denotes an angle formed by both ends P 1  of the first tooth  132  based on the stator center C. A reference point G 1  for defining the both ends P 1  of the first tooth  132  in the axial direction will be described below. When the first tooth  132  is disposed to face the body  231  of the magnet  230 , the reference point G 1  corresponds to a point of the first tooth  132  corresponding to a midpoint of the height H 1  of the body  231  of the magnet  230 . The height H 1  of the body  231  of the magnet  230  means 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 the first tooth  132  at the reference point G 1  may be the same as the second angle Θ 2 . 
     Referring to  FIG. 16 , the third angle Θ 3  denotes an angle formed by both ends P 2  of the second tooth  142  based on the stator center C. A reference point G 2  for defining the both ends P 2  of the second tooth  142  in the axial direction will be described below. When the second tooth  142  is disposed to face the body  231  of the magnet  230 , the reference point G 2  corresponds to a point of the second tooth  142  corresponding to a midpoint of the height H 1  of the body  231  of the magnet  230 . An angle Θ 5  between the second tooth  142  and the second tooth  142  at the reference point G 2  may be the same as the third angle Θ 3 . 
       FIG. 17  is a graph showing a flux versus the first angle Θ 1 , the second angle Θ 2 , and the third angle Θ 3 . 
     Referring to  FIG. 17 , 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, a magnitude of a flux increases as the second angle Θ 2  and the third angle Θ 3  become similar to the first angle Θ, and the magnitude of the flux decreases as the second angle Θ 2  and the third angle Θ 3  become different from the first angle Θ 1 . When the size and the position of the first tooth  132  and the size and the position of 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 , it may be seen that the magnitude of the flux of the first and second stator teeth  130  and  140  is highest. 
       FIG. 18  is an exploded perspective view illustrating the rotor. 
     Referring to  FIGS. 2 and 18 , 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 an integrated part. 
     The rotor holder  210  may be connected to an input shaft of the electric steering apparatus. 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 be formed of another material by considering a predetermined strength or more so that the input shaft is fixedly inserted thereinto. 
     The rotor holder  210  may include a protrusion  211 . 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 . The magnet  230  is rotated in conjunction with the rotor holder  210  when the rotor holder  210  rotates. 
       FIG. 19  is a view illustrating the magnet, and  FIG. 20  is a plan view illustrating the magnet. 
     Referring to  FIGS. 19 and 20 , the magnet  230  may include the ring-shaped body  231  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  220 . The protrusion  232  is for increasing a coupling force with the rotor body  220 . The first part  232   a  prevents a 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  from the magnet  230  in the axial direction. 
       FIG. 21  is a perspective view illustrating an arrangement of the magnet with respect to the first stator tooth and the second stator tooth. 
     Referring to  FIG. 21 , the magnet  230  is disposed between the first tooth  132  and the second tooth  142 . In addition, the magnet  230  is disposed between the third tooth  133  and the first tooth  132 . 
     The body  231  of the magnet  230  is disposed to face the first tooth  132 , the second tooth  142 , and the third tooth  133 . The protrusion  232  of the magnet  230  is disposed at a higher level than the first tooth  132 , the second tooth  142 , and the third tooth  133 . 
       FIG. 22  is a perspective view illustrating the first stator tooth. 
     Referring to  FIG. 22 , the first stator tooth  130  may include the first body  131 , the first teeth  132 , the third teeth  133 , and an extension part  134 . The first body  131  may be a ring-shaped member. 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. The extension part  134  protrudes inward from the first body  131 . The third tooth  132  is connected to the extension part  134 . 
     Each of the first tooth  132  and the third tooth  133  may be formed in a shape of which a lower side is wide and an upper side is narrow. For example, when viewed in the radial direction, in each of the first tooth  132  and the third tooth  133 , a width of the lower side may be smaller than a width of the upper side. Each of the first tooth  132  and the third tooth  133  may be formed in a trapezoidal shape. In addition, since the first tooth  132  passes through the first hole  124 , and the third tooth  133  passes through the third hole  127 , the upper surface of the first body  131  and an upper surface of the extension part  134  may be in contact with a lower surface of the partition plate  123 . 
       FIG. 23  is a perspective view illustrating the second stator tooth. 
     Referring to  FIG. 23 , the second stator tooth  140  may include the second body  141  and the second teeth  142 . 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 tooth  142 . The second body  141  and the plurality of second teeth  142  may be integrally formed. 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 viewed in the radial direction, a width of the lower side may be greater than a width of the upper side of the second tooth  142 . The second tooth  142  may have a trapezoidal shape. 
     The second body  141  may include a protruding part  141   a . The protruding part  141   a  may be an annular member bent to protrude outward further than the second tooth  142 . The protruding part  141   a  reduces an air gap between the sensor  500  and the second body  141  to increase an amount of a flux applied to the sensor  500 . 
       FIG. 24  is a plan view illustrating the first stator tooth. 
     Referring to  FIG. 24 , a shortest distance R 1  from the center C of the first stator tooth  130  to the first tooth  132  is greater than a shortest distance R 2  from the center C of the first stator tooth  130  to the third tooth  133 . The third tooth  133  is disposed closer to the center C of the first stator tooth  130  than the first tooth  132 . This is to guide an external magnetic field introduced from an inner side of the stator holder  110  to the third tooth  133 . 
       FIG. 25  is a plan view illustrating the first stator tooth and the second stator tooth. 
     Referring to  FIG. 25 , a diameter D 3  formed by the plurality of third teeth  133  is smaller than a diameter D 1  formed by the plurality of first teeth  132 , and a diameter D 2  formed by the plurality of second teeth  142  is smaller than the diameter D 1  formed by the plurality of first teeth  132 . Based on the magnet  230 , the first tooth  132  is disposed outside the magnet  230 , and the second tooth  142  and the third tooth  133  are disposed inside the magnet  230 . 
       FIG. 26  is a view illustrating the first tooth, the second tooth, and the third tooth which are concentrically disposed. 
     Referring to  FIG. 26 , the first tooth  132 , the second tooth  142 , and the third tooth  133  may be concentrically disposed. The second tooth  142  and the third tooth  133  may be disposed on a virtual first circumference O 1 , and the first tooth  132  may be disposed on a virtual second circumference O 2  different from the virtual first circumference O 1 . The second tooth  142  and the third tooth  133  may be alternately disposed in a circumferential direction of the stator  100 . The first circumference O 1  is disposed inside the second circumference O 2 . This is to disperse the external magnetic field introduced from the inner side of the stator holder  110  in all directions through the second teeth  142  and the third teeth  133 . 
     Meanwhile, a width t 3  of a lower end of the third tooth  133  in the circumferential direction may be smaller than a width t 1  of a lower end of the first tooth  132  in the circumferential direction. In addition, the width t 3  of the lower end of the third tooth  133  in the circumferential direction may be smaller than a width t 2  of a lower end of the second tooth  142  in the circumferential direction. 
       FIG. 27  is a plan view which illustrates a flow of the external magnetic field introduced from the inner side of the stator holder and illustrates the first stator tooth and the second stator tooth, and  FIG. 28  is a cross-sectional view which illustrates a flow of an external magnetic field guided to the third tooth and illustrates the first stator tooth. 
     Referring to  FIG. 27 , external magnetic fields W 1  and W 2  introduced along the stator holder  110  flow toward the first stator tooth  130  and the second stator tooth  140  in a radial direction of the stator  200 . The external magnetic fields W 1  and W 2  are guided to be dispersed to the second teeth  142  and the third teeth  133 . 
     Referring to  FIG. 28 , the external magnetic field W 1  flowing into the third tooth  133  is guided to the extension part  134 . In this case, an external magnetic field M 1  flowing into the third tooth  133  may be offset by an external magnetic field M 2  introduced from the magnet  230  to the first tooth  132  and guided to the extension part  134 . As described above, since the external magnetic field introduced along stator holder  110  is guided to the first stator tooth  130  and is offset, there is an advantage of considerably reducing an influence of the external magnetic field on the sensor  500 . 
     In &lt;Table 1&gt; below, a torque of Comparative example and a torque of Example are compared. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Torque of Comparative 
                 Torque of 
               
               
                   
                 Example (Nm) 
                 Example (Nm) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 External Magnetic Field 
                 0.41 Nm 
                 0.05 Nm 
               
               
                 in Radial Direction 
               
               
                 1000 A/m 
               
               
                   
               
            
           
         
       
     
     In Comparative example, a sensing device does not include a structure like the third tooth  133 . In Example, the sensing device includes the third tooth  133 . When there is no external magnetic field in the radial direction, a torque of 0 Nm is normal. When an external magnetic field of 1000 A/m is applied to Comparative example and Example in the radial direction, a torque of 0.41 Nm is measured in Comparative example so that it may be seen that Comparative example is greatly affected by the external magnetic field. However, in the case of Example, the measured torque is 0.05 Nm, and thus it may be seen that Example is hardly affected by the external magnetic field. 
       FIG. 29  shows side cross-sectional views illustrating the first stator tooth, the second stator tooth, the sensor, and the collector. 
     Referring to  FIG. 29 , only one collector  300  is disposed between the first stator tooth  130  and the second stator tooth  140 . In addition, in order to increase a flux applied to the sensor  500 , the protruding part  141   a  is disposed on the second stator tooth  140 . 
     When the collector  300  is disposed inside the sensor  500  to be spaced apart from the first stator tooth  130 , there is an advantage in that the sensing device  1  is less affected by an external magnetic field introduced from an external device in the radial direction. In addition, since the protruding part  141   a  is bent outward in the radial direction, the air gap between the protruding part  141   a  and the stator holder  110  increases, and thus there is an advantage of reducing an influence of the external magnetic field introduced through the stator holder  110 . 
     Since one collector  300  is disposed between the sensor  500  and the second body  142 , a structure of the sensing device can be simplified, a size of the sensing device can be decreased, a manufacturing process and a manufacturing cost can be reduced, and performance of the sensing device can also be secured when compared to a case in which two collectors are disposed therein. 
       FIG. 30  is a view illustrating the collector. 
     Referring to  FIG. 30 , the collector  300  collects a flux of the stator  100 . In this case, the collector  300  may be formed of a metal material. The collector  300  may be a semicircular member. The collector  300  may include a first body  310 , a second body  320 , and extension parts  330 . The first body  310  and the second body  320  are disposed to face the sensor  500 . The second body  320  may extend from the first body  310 . The extension parts  330  may extend from the first body  310  and the second body  320 . Each of the first body  310  and the second body  320  may include a flat surface having a flat shape. The extension part  330  may include a curved surface. The extension parts  330  may include bent parts  340 . The bent part  340  may be disposed to be bent outward from an end of the extension part  330 . The bent part  340  is for coupling the housing  700  and the collector  300 . 
       FIG. 31  is a view illustrating the collector disposed between the first stator tooth and the second stator tooth, wherein a first region of the first stator tooth and a second region of the second stator tooth are illustrated. 
     Referring to  FIGS. 30 and 31 , the first stator tooth  130  may include a first region R 1 . The second stator tooth  140  may include a second region R 2 . The first region R 1  is a region in which the first stator tooth  130  corresponds to the collector  300  in the circumferential direction of the stator  100 . The second region R 2  is a region in which the second stator tooth  140  corresponds to the collector  300  in the circumferential direction of the stator. The first region R 1  is disposed so that a central angle thereof is 180° or less about the center C of the stator  100  in the circumferential direction. The second region R 2  is disposed so that a central angle is 180° or less about the center C of the stator  100  in the circumferential direction. 
     The sensor  500  detects a change in magnetic field generated between the stator  100  and the rotor  200 . The sensor  500  may be a Hall integrated circuit (IC). The sensor  500  detects a magnetization amount of the stator  100  generated due to an electrical 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 magnetization amount. 
     The sensor  500  may include a first sensor  510  and a second sensor  520 . The first sensor  510  may include a first-1 sensor  511  and a first-2 sensor  512 . The second sensor  520  may include a second-1 sensor  521  and a second-2 sensor  522 . The first sensor  510  is disposed opposite to the first body  310 . The second sensor  520  is disposed opposite to the second body  320 . 
       FIG. 32  is a view illustrating the collector disposed between the first stator tooth and the second stator tooth, wherein a position of the collector with respect to a first reference line and a second reference line is illustrated. 
     Referring to  FIGS. 30 and 32 , the collector  300  may include a first collector  300 A and a second collector  300 B. The first collector  300 A includes the first body  310 . The second collector  300 B includes the second body  320 . The first collector  300 A and the second collector  300 B may be symmetrically disposed with respect to a second reference line S 2 . In addition, each of the first collector  300 A and the second collector  300 B may be disposed at only one side of a first reference line S 1 , and each of a part of the first collector  300 A and a part of the second collector  300 B may be disposed not to extend to the other side of the first reference line S 1 . In this case, the first reference line S 1  means a virtual line passing through the center C of the stator in the radial direction, and the second reference line S 2  means a virtual line which passes through the center C of the stator in the radial direction and is perpendicular to the first reference line S 1 . 
       FIG. 33  is a view illustrating a shape of the collector with respect to a curvature center of the extension part of the collector. 
     Referring to  FIG. 33 , the extension part  330  of the collector  300  may include the curved surface. The collector  300  may be formed so that an angle R 3  formed by both ends of the extension part  330  about the curvature center of the extension part  330  is 180° or less. 
       FIG. 34  is a view illustrating the housing in which the collector and the sensor are disposed,  FIG. 35  is a view illustrating a groove in a protrusion disposed in the housing illustrated in  FIG. 34 , and  FIG. 36  is a bottom view illustrating the housing illustrated in  FIG. 34 . 
     Referring to  FIGS. 34 to 36 , the housing  700  may include a housing body  710  and a protrusion  720 . The housing body  710  has a plate shape including an upper surface  711  and a lower surface  712  and has a form of which an upper portion and a lower portion are open. A hole  713  is disposed in a center of the housing body  710 . The stator holder  110  is positioned inside the hole  713 . The circuit board  600  may be installed on the lower surface  712  of the housing body  710 . The sensor  500  is installed on the circuit board  600 . The sensor  500  may pass through the housing  700  and may be disposed on the upper surface  711  of the housing  700 . A cover may be coupled to a lower side of the housing body  710  and may cover the circuit board  600 . 
     The protrusion  720  may protrude from the upper surface  711  of the housing  700  in the axial direction. The protrusion  720  is disposed along a circumference of the hole  713 . The protrusion  720  may be an annular member. An inner circumferential surface of the protrusion  720  may be in contact with an outer circumferential surface of the collector  300 . 
     Referring to  FIG. 35 , the protrusion  720  may include a groove  721 . The groove  721  may be concavely formed in the inner circumferential surface of the protrusion. Two grooves  721  may be disposed. The bent parts  340  of the collector  300  are coupled to the grooves  721 . 
     Referring to  FIG. 36 , the housing  700  may include a first hole  731  through which the first sensor  510  passes and a second hole  732  through which the second sensor  520  passes. The first hole  731  and the second hole  732  are formed to pass through the upper surface  711  and the lower surface  712  of the body of the housing  700 . In addition, the first hole  731  and the second hole  732  may be connected to be bent. 
       FIG. 37  is a view illustrating a relative position of the collector with respect to the first stator tooth and the second stator tooth when the collector moves to any one side, and  FIG. 38  is a view illustrating a relative position of the collector with respect to the first stator tooth and the second stator tooth when the collector moves to the other side. 
     Referring to  FIG. 37 , for example, when the housing  700  moves leftward with respect to the center C of the stator  100  in the drawing, the collector  300  also moves leftward in conjunction with the housing  700 . When the collector  300  moves so that a position of any one point of the collector  300  moves from a point P 1  (see  FIG. 37 ) to a point P 2  (see  FIG. 37 ), the entire collector  300  becomes closer to the first stator tooth  130  but becomes farther away from the second stator tooth  140  at the same time. Accordingly, an amount of a change in sensitivity to a magnetic flux measured by the sensor  500  is not large. 
     Conversely, referring to  FIG. 38 , when the housing  700  moves rightward with respect to the center C of the stator  100  in the drawing, a position of any one point of the collector  300  moves from the point P 1  (see  FIG. 38 ) to a point P 3  (see  FIG. 38 ) so that the entire collector  300  becomes farther away from the first stator tooth  130  but becomes closer to the second stator tooth  140 . Accordingly, an amount of a change in sensitivity to a magnetic flux measured by the sensor  500  is not large. 
     In this case, the sensitivity to the measured magnetic flux means a degree of a change in measured magnetic flux corresponding to a relative rotation angle between the stator  100  and the rotor  200 . 
     As described above, the reason why the amount of a change in sensitivity to the measured magnetic flux is not large even when the collector  300  moves is that the collector  300  is disposed at only any one side with respect to the reference line passing through the center C of the stator  100  as illustrated in  FIGS. 31 to 33 . 
     When an entire shape of the collector  300  is an arc shape or annular shape disposed over both regions divided by the reference line passing through the center C of the stator  100 , and when the collector  300  moves leftward in the drawing as in  FIG. 37 , one region of the collector  300  disposed at any one side with respect to the reference line passing through the center C of the stator  100  becomes closer to the first stator tooth  130 , and the other region of the collector  300  disposed at the other side with respect to the reference line passing through the center C of the stator  100  becomes closer to the second stator tooth  140  at the same time. 
     Thus, since a gap between the collector  300  and the first stator tooth  130  is reduced, and a gap between the collector  300  and the second stator tooth  140  is reduced at the same time, there is a problem in that sensitivity to a magnetic flux to be measured is greatly increased. However, in the sensing device according to the embodiment, since the collector  300  is disposed at any one side with respect to the reference line passing through the center C of the stator  100 , there is an advantage of fundamentally eliminating such a problem. 
       FIG. 39  is a comparison graph of sensitivity to a magnetic flux measured by the sensing device according to Example and a sensing device according to Comparative example. 
     Referring to  FIGS. 31 and 39 , Example 1, Example 2, Example 3, and Example 4 show sensitivity to a magnetic flux measured by the first-1 sensor  511 , the first-2 sensor  512 , the second-1 sensor  521 , and the second-2 sensor  522  according to movement of the housing  700 . Comparative example 1, Comparative example 2, Comparative example 3, and Comparative example 4 show sensitivity to a magnetic flux measured by four sensors of a sensing device including a collector having an annular shape. 
     In the case of Comparative examples 1 to 4, as movement of the housing  700  is enlarged, sensitivity to a magnetic flux to be measured is greatly increased. However, it may be seen that sensitivity to a magnetic flux to be measured in Examples 1 to 4 is not considerably increased even when movement of the housing  700  is enlarged. In the case of Examples 1 to 4, it may be seen that the sensitivity to the measured magnetic flux is decreased by about 70% to 80% when compared to Comparative examples 1 to 4. 
       FIG. 40  is a view illustrating the first gear and the second gear which are engaged with the main gear. 
     Referring to  FIGS. 2 and 40 , the sensing device  1  includes the first gear  1100  and the second gear  1200  as sub-gears engaged with the main gear  121 . 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 , the first gear  1100 , and the second gear  1200  are engaged with each other and rotate. 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 determined in advance. For example, when a total angle of the main gear  121  is 1620°, the first gear  1100  and the second gear  1200  may be respectively designed to rotate 15.6 times and 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 states 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 board. 
       FIG. 41  is a view illustrating a direction of an external magnetic field with respect to the stator tooth,  FIG. 42  is a view illustrating an avoidance state of the sensor from an external magnetic field having a z-axis, and  FIG. 43  is a view illustrating an avoidance state of the first and second stator teeth from an external magnetic field having a y′-axis. 
     Referring to  FIG. 41 , an external magnetic field greatly affects the sensing device in a z-axis direction which is the axial direction and in a y′-axis direction perpendicular to the z-axis direction. In this case, the y′-axis direction means a direction toward the sensor  500  in the radial direction perpendicular to the axial direction. 
     Referring to  FIG. 42 , the sensing device  500  according to the embodiment is disposed in a state in which the sensor  500  is erected in the z-axis direction. Accordingly, an area of the sensor  500  when viewed in the z-axis direction is considerably 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 influence of the external magnetic field on the sensor  500  is inevitably small in the z-axis direction. 
     Referring to  FIG. 43 , an external magnetic field in the y′-axis direction may greatly affect the sensor  500  due to the state in which the sensor  500  is erected in the z-axis direction. However, since the external magnetic field in the y′-axis direction is induced along the first stator tooth  130  and the second stator tooth  140 , the external magnetic field flows without affecting the sensor  500 . Accordingly, the sensing device according to the embodiment has an advantage in that an influence of the external magnetic field on the sensor  500  is small even in the y′-axis direction. 
       FIG. 44  is a comparison graph of an amount of a change in angle according to an external magnetic field in the z-axis direction between Comparative example and Example. 
     Referring to  FIG. 44 , in the case of Comparative example in which the sensing device has a structure including a stator tooth disposed vertically and a sensor disposed to lie down, it may be seen that an amount of a change in angle increases linearly as the external magnetic field increases in the z-axis direction so that a measured angle is greatly changed according to the external magnetic field. 
     However, in the case of Example, it may be seen that, even when the external magnetic field in the z-axis direction increases, an angle is hardly changed, and thus the sensing device is not affected by the external magnetic field. 
       FIG. 45  is a comparison graph of an amount of a change in angle according to an external magnetic field in the y′-axis direction between Comparative example and Example. 
     Referring to  FIG. 45 , in the case of Comparative example in which the sensing device has the structure including the stator tooth disposed vertically and the sensor disposed to lie down, it may be seen that an amount of a change in angle increases linearly as the external magnetic field in the y′-axis direction increases so that a measure angle is greatly changed according to the external magnetic field. 
     However, in the case of Example, it may be seen that, even when the external magnetic field in the y′-axis direction increases, an angle is hardly changed, and thus the sensing device is not 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 : COLLECTOR 
               500 : SENSOR 
               600 : CIRCUIT BOARD 
               700 : HOUSING