Abstract:
A liquid level detector may include a rotator fixed to an arm, a magnet fixed to the rotator, and a supporter rotatably supporting the rotator. The supporter may include a body, and an outer circumference wall disposed along a rotation direction of the arm on an outer circumference side of the magnet. The rotator may include a cover covering an end part of the outer circumference wall, and an opposing wall opposing at least one of an inner circumference surface and an outer circumference surface of the outer circumference wall. A first clearance between the supporter and the magnet may communicate with an outer space via a second clearance between the outer circumference wall and the cover and a third clearance between the outer circumference wall and the opposing wall. The first clearance may be larger than at least one of the second clearance and the third clearance.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2015-020085 filed on Feb. 4, 2015, the contents of which are hereby incorporated by reference into the present application. 
     TECHNICAL FIELD 
     An art disclosed herein relates to a liquid level detector configured to detect a level of liquid (for example, a device configured to detect an amount of fuel stored in a fuel tank of an automobile or the like). 
     BACKGROUND 
     Japanese Patent Application Publication No. 2006-208211 discloses a liquid level detector that includes a float, an arm that revolves as the float moves, a body that has a revolving shaft of the arm, and a holder that houses a cylindrical-shape magnet. The holder covers the revolving shaft. A recessed portion is provided in the holder on an inner circumference side of the magnet, for allowing the revolving shaft to be fitted thereinto. The revolving shaft is fitted into the recessed portion to thereby allow the recessed portion to function as a bearing. A magnetism detecting element is disposed at the revolving shaft, for detecting changes in magnetic flux of the magnet that moves as the revolving arm revolves. 
     In this liquid level detector, a step portion of the body and/or a projecting portion of the holder complicate a route from an outside of the liquid level detector to the revolving shaft. Metal powders or the like in the fuel are thereby prevented from reaching the revolving shaft. 
     SUMMARY 
     In the above-described liquid level detector, there is a possibility that, even if the route from an outside of the liquid level detector to the revolving shaft is complicated, fine foreign substances may reach the revolving shaft. When fine foreign substances accumulate around the revolving shaft, a clearance between the revolving shaft and the holder is clogged with the foreign substances, resulting in that the arm can no longer revolve. 
     The present disclosure provides an art to suppress that foreign substances in a liquid interferes with a revolution of the arm. 
     The application discloses a liquid level detector. The liquid level detector may comprise: a float; an arm attached to the float and configured to convert a vertical motion of the float into a rotary motion of the arm; a rotator configured of a resin and fixed to the arm at a center of the rotary motion; a magnet fixed to the rotator; a supporter rotatably supporting the rotator; and a magnetic sensor covered by the supporter and configured to output a signal corresponding to a rotation of the magnet opposing the magnetic sensor via the supporter. The supporter may comprise: a body housing the magnetic sensor; and an outer circumference wall projecting from the body toward the rotator and disposed along a rotation direction of the arm on an outer circumference side of the magnet. The rotator may comprises: a cover covering an end part of the outer circumference wall, the end part located opposite to the body; and an opposing wall opposing at least one of an inner circumference surface and an outer circumference surface of the outer circumference wall and configured to slide relative to the outer circumference wall corresponding to the rotation of the arm. A clearance between the supporter and the magnet may communicate with an outer space of the liquid level detector via a clearance between the outer circumference wall and the cover and a clearance between the outer circumference wall and the opposing wall The clearance between the supporter and the magnet may be larger than at least one of the clearance between the outer circumference wall and the cover and the clearance between the outer circumference wall and the opposing wall. 
     In the above-described configuration, the clearance between the supporter and the magnet is larger than at least one of the clearance between the outer circumference wall and the cover and the clearance between the outer circumference wall and the opposing wall. Large foreign substances mixed with the fuel may not pass through the clearance between the outer circumference wall and the cover or the clearance between the outer circumference wall and the opposing wall, and hence may not reach the clearance between the supporter and the magnet. According to this configuration, relatively large foreign substances may be prevented from reaching the clearance between the supporter and the magnet. Moreover, in the above-described configuration, the rotator rotates while the outer circumference wall and the opposing wall slide. In other words, the opposing wall functions as a bearing of the rotator. The opposing wall and the outer circumference wall are opposed to each other on an outer circumference side of the magnet. According to this configuration, the opposing wall, which functions as the bearing, may be disposed at a position distant from the rotation center of the rotator, without making the magnet large. Consequently, with a vertical motion of the float, a relatively large moment may be generated at the opposing wall. Similarly, a relatively large moment may also be generated at the outer circumference wall. Accordingly, even if foreign substances are caught in the clearance between the outer circumference wall and the opposing wall or the clearance between the outer circumference wall and the cover, the moment generated by the vertical motion of the float can cause the rotator to rotate. It is possible to suppress foreign substances in the liquid interfering with a revolution of the arm. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a configuration of a fuel supply system; 
         FIG. 2  shows a longitudinal cross-section of a magnetic sensor unit; 
         FIG. 3  shows an enlarged view of a region III of  FIG. 2 ; and 
         FIG. 4  shows an enlarged view of a region at the same position as that of the region III of  FIG. 2  in the magnetic sensor unit in a variation. 
     
    
    
     DETAILED DESCRIPTION 
     Some features of embodiments described herein will be listed. Notably, technical features described herein are each independent technical element, and exhibit technical usefulness thereof solely or in combinations. 
     (Feature 1) 
     In a liquid level detector, an outer circumference surface of the opposing wall may oppose the inner circumference surface of the outer circumference wall. The clearance between the outer circumference wall and the cover may be smaller than the clearance between the outer circumference wall and the opposing wall. In this configuration, the clearance between the outer circumference wall and the cover may be located on the outer circumference side of the clearance between the outer circumference wall and the opposing wall. According to this configuration, it is possible to suppress foreign substances entering the clearance between the outer circumference wall and the opposing wall. 
     (Feature 2) 
     In the liquid level detector, an outer circumference surface of the opposing wall may oppose the inner circumference surface of the outer circumference wall. The magnet may be disposed along an inner circumference surface of the opposing wall. A part of the clearance between the outer circumference wall and the opposing wall may be larger than another part of the clearance between the outer circumference wall and the opposing wall. If the foreign substances that have entered the clearance between the opposing wall and the outer circumference wall are substances adsorbed by the magnet, such as iron powders, the substances are adsorbed by the magnet, which is held in the outer circumference wall, in the clearance between the opposing wall and the outer circumference wall. Consequently, a part of the clearance between the opposing wall and the outer circumference wall can be increased to thereby store the foreign substances adsorbed by the magnet. It is thereby possible to suppress the foreign substances, which are adsorbed by the magnet, interfering with the rotation of the arm. 
     (Feature 3) 
     In the liquid level detector, a storing space may be disposed on a route from the outer space of the liquid level detector to the clearance between the supporter and the magnet, via the clearance between the outer circumference wall and the cover and the clearance between the outer circumference wall and the opposing wall. The storing space may open toward an inflow direction of the liquid flowing through the route. According to this configuration, the foreign substances that enter the route can be stored in the storing space. It is thereby possible to suppress the foreign substances accumulating in each clearance. 
     Representative, non-limiting examples of the present invention will now be described in further detail with reference to the attached drawings. This detailed description is merely intended to teach a person of skill in the art further details for practicing preferred aspects of the present teachings and is not intended to limit the scope of the invention. Furthermore, each of the additional features and teachings disclosed below may be utilized separately or in conjunction with other features and teachings to provide improved liquid level detectors, as well as methods for using and manufacturing the same. 
     Moreover, combinations of features and steps disclosed in the following detailed description may not be necessary to practice the invention in the broadest sense, and are instead taught merely to particularly describe representative examples of the invention. Furthermore, various features of the above-described and below-described representative examples, as well as the various independent and dependent claims, may be combined in ways that are not specifically and explicitly enumerated in order to provide additional useful embodiments of the present teachings. 
     All features disclosed in the description and/or the claims are intended to be disclosed separately and independently from each other for the purpose of original written disclosure, as well as for the purpose of restricting the claimed subject matter, independent of the compositions of the features in the embodiments and/or the claims. In addition, all value ranges or indications of groups of entities are intended to disclose every possible intermediate value or intermediate entity for the purpose of original written disclosure, as well as for the purpose of restricting the claimed subject matter. 
     As shown in  FIG. 1 , a fuel supply system  1  is a system configured to supply, to an internal combustion engine not illustrated, fuel in a fuel tank  4  mounted in an automobile. In the present embodiment, the fuel is gasoline, or a mixed fuel containing gasoline and alcohol (e.g., ethanol). The fuel supply system  1  includes a fuel meter  60  and a fuel pump module  10 . The fuel meter  60  is used for a display device of the automobile, not illustrated. The fuel pump module  10  is disposed in the fuel tank  4 . The fuel meter  60  and the fuel pump module  10  are electrically connected by a plurality of lines  52 ,  54 , and  56 . 
     The fuel pump module  10  includes a fuel pump unit  12  and a fuel amount detector  20 . The fuel pump unit  12  is housed in the fuel tank  4 . The fuel pump unit  12  is attached to a set plate  6  configured to close an opening in the fuel tank  4 . The fuel pump unit  12  sucks in the fuel in the fuel tank  4 , pressurizes the fuel thus sucked in, and discharges the fuel. The fuel discharged from the fuel pump unit  12  is supplied to the engine through a discharge port  14 . 
     The fuel amount detector  20  includes a float  22 , an arm  24  to which the float  22  is fixed, and a magnetic sensor unit  30  configured to detect a rotation angle of the arm  24 . The float  22  floats on the surface of the fuel in the fuel tank  4  and moves up and down depending on the liquid level of the fuel. The float  22  is rotatably attached to a leading end of the arm  24 . A base end of the arm  24  is supported to be rotatable with respect to the magnetic sensor unit  30 . For this reason, when the float  22  moves up and down depending on the liquid level of the fuel in the fuel tank  4 , the arm  24  thereby swingably rotates with respect to the fuel pump unit  12 . 
     The arm  24  includes a float attachment part  24   a , a base part  24   b , and a fulcrum part  24   c . The float attachment part  24   a  is configured of a metal that has a resistance to fuel, such as stainless steel, for example. The float attachment part  24   a  is configured of a columnar rod-like member bent at an intermediate position. The float  22  is attached to a leading end of the float attachment part  24   a . The base part  24   b  is fixed to a base end of the float attachment part  24   a.    
     The base part  24   b  and the fulcrum part  24   c  are configured of a resin having a resistance to fuel (e.g., a polyphenylene sulfide resin (hereinafter referred to as “PPS”)). The base part  24   b  has a flat-plate shape. The fulcrum part  24   c  is fixed to the base part  24   b  at an intermediate position. The fulcrum part  24   c  is rotatably supported by the magnetic sensor unit  30 . 
     As shown in  FIGS. 1 and 2 , the fulcrum part  24   c  includes a cover  24   d , an opposing wall  24   e , and an engagement wall  24   f . Notably,  FIG. 2  shows a cross-sectional view of the magnetic sensor unit  30  and the fulcrum part  24   c , and is a cross-sectional view that represents a cross-section in vertical directions (the vertical directions of  FIG. 1 ), passing through a rotational axis X of  FIG. 1 . Moreover, the horizontal directions of  FIG. 2  correspond to the vertical directions of  FIG. 1 . The cover  24   d  has a disk shape. The rotational axis X of the arm  24  coincides with a rotational axis of the cover  24   d . The opposing wall  24   e  projects on a surface of the cover  24   d  on the magnetic sensor unit  30 &#39;s side. The opposing wall  24   e  has a cylindrical shape. The central axis of the opposing wall  24   e  coincides with the rotational axis X. On an outer circumference side of the opposing wall  24   e , the engagement wall  24   f  is disposed with a spacing from an outer circumference surface of the opposing wall  24   e . The engagement wall  24   f  extends forming a circle along an outer circumference edge of the cover  24   d . An engagement flange  24   g  of the engagement wall  24   f  on the magnetic sensor unit  30 &#39;s side extends toward the rotational axis X. The engagement flange  24   g  is disposed along the entire circumference of the engagement wall  24   f . Notably, in a variation, the engagement flange  24   g  may not be disposed along the entire circumference of the engagement wall  24   f . For example, one engagement flange  24   g  may be disposed only at a portion of the engagement wall  24   f  in a circumference direction, or a plurality of the engagement flanges  24   g  may be disposed discretely at the engagement wall  24   f  in the circumference direction. 
     A magnet  26  is fitted into the inner circumference of the opposing wall  24   e . The magnet  26  is fitted into an inner circumference surface of the opposing wall  24   e . The magnet  26  is a permanent magnet. The magnet  26  has a disk shape. The center of the magnet  26  is located on the rotational axis X. The magnet  26  has an N pole in one semicircular part and an S pole in the other semicircular part. The magnet  26  rotates as the arm  24  swingably rotates. Consequently, an orientation of a magnetic field generated by the magnet  26  changes as the arm  24  swingably rotates. 
     The magnetic sensor unit  30  revolvably supports the arm  24 . As shown in  FIG. 2 , the magnetic sensor unit  30  includes a body  32 , an outer circumference wall  34 , a cover portion  46 , a magnetic sensor  40 , and lead wires  45  and  47 . 
     The body  32  is configured of a material having a low permeability to alcohol (PPS in the present embodiment). At the body  32 , the outer circumference wall  34  that receives a part of the fulcrum part  24   c  of the arm  24  is disposed, the part housing the magnet  26 . The outer circumference wall  34  has a cylindrical shape that has the central axis that coincides with the rotational axis X. The outer circumference wall  34  has an inner circumference flange  34   a  that extends toward an inner circumference side and an outer circumference flange  34   b  that extends toward an outer circumference side, at an end opposite to the body  32 . Each of the inner circumference flange  34   a  and the outer circumference flange  34   b  has an annular shape that encircles the rotational axis X. 
     The opposing wall  24   e  is disposed on an inner circumference side of the outer circumference wall  34 . An inner circumference surface of the outer circumference wall  34  and an outer circumference surface of the opposing wall  24   e  are opposed to each other with a clearance. As shown in  FIG. 3 , if the central axis of the outer circumference wall  34  and the center of the cover  24   d  are disposed on the rotational axis X, an inner circumference surface of the inner circumference flange  34   a  of the outer circumference wall  34  and the outer circumference surface of the opposing wall  24   e  are opposed to each other with a clearance CL 3  that encircles the rotational axis X. In a part where no inner circumference flange  34   a  is disposed, in other words, in a part on the body  32 &#39;s side with respect to the inner circumference flange  34   a , the inner circumference surface of the outer circumference wall  34  and the outer circumference surface of the opposing wall  24   e  are opposed to each other along the entire circumference of the rotational axis X, with a clearance CL 2  that encircles the rotational axis X. The clearance CL 2  is larger than the clearance CL 3 . 
     As shown in  FIG. 2 , the outer circumference flange  34   b  engages with the fulcrum part  24   c . The arm  24  is thereby supported so as not to fall off from the magnetic sensor unit  30 . In particular, an end of the outer circumference wall  34  opposite to the body  32  is wholly covered by the cover  24   d  coupled to an end of the opposing wall  24   e  opposite to the body  32 . The cover  24   d  spreads toward the outer circumference side with respect to the outer circumference wall  34 . The outer circumference edge of the cover  24   d  is located on the outer circumference side of the outer circumference flange  34   b . The engagement wall  24   f  that extends from the outer circumference edge of the cover  24   d  toward the body  32  encircles the rotational axis X while being opposed to the outer circumference flange  34   b . The engagement flange  24   g  disposed at an end of the engagement wall  24   f  on the body  32 &#39;s side is located on the body  32 ′ side of the outer circumference flange  34   b.    
     As shown in  FIG. 3 , the fulcrum part  24   c  and the outer circumference wall  34  are disposed with clearances CIA to CL 7  in between. The clearance CIA is the one between an end of the outer circumference wall  34  opposite to the body  32  and a surface of the cover  24   d  on the body  32 &#39;s side. The clearance CL 5  is the one between an outer circumference edge of the outer circumference flange  34   b  and an inner circumference surface of the engagement wall  24   f . The clearance CL 6  is the one between a surface of the outer circumference flange  34   b  on the body  32 ′ side and a surface of the engagement flange  24   g  opposite to the body  32 . The clearance CL 7  is the one between an inner circumference surface of the engagement flange  24   g  and an outer circumference surface of the outer circumference wall  34 . 
     Notably, a surface of the engagement flange  24   g  on the body  32 &#39;s side is disposed with a clearance CL 8  between itself and the body  32 . 
     The body  32  houses the magnetic sensor  40 . The magnetic sensor  40  is housed in the body  32 , while being covered by the cover portion  46 . The cover portion  46  is configured of a material having a low permeability to gasoline (an epoxy resin in the present embodiment). The cover portion  46  is housed in the body  32  by being disposed in a molding die of the body  32 , namely, by so-called insert molding, when the body  32  is to be molded. 
     The magnetic sensor  40  detects a rotary motion of the arm  24 , and based on that detected result, outputs to the fuel meter  60  a signal that represents an analog amount corresponding to a liquid level of fuel stored in the fuel tank  4  (see  FIG. 1 ). The signal that represents an analog amount is, for example, an analog voltage signal, a signal through PWM (an abbreviation of Pulse Width Modulation), a signal transmitted with use of digital communication such as CAN (an abbreviation of Controller Area Network) or LAN (an abbreviation of Local Area Network), and the like. The magnetic sensor  40  is a magnetic-type sensor that detects a rotation angle of the arm  24 , and a known sensor that utilizes a Hall IC, for example, can be used therefor. Specifically, the magnetic sensor  40  includes a detecting circuit  42 , and an input/output circuit  44  connected to the detecting circuit  42 . The detecting circuit  42  has a Hall element that detects an orientation of a magnetic field of the magnet  26 . The input/output circuit  44  has a capacitor. The entire surface of the magnetic sensor  40  is covered by the cover portion  46 . The detecting circuit  42  is disposed on an end part side of the cover portion  46 . In particular, the detecting circuit  42  is disposed at an end part opposite to an end on a side where the lead wire  47  described below penetrates the cover portion  46 . The input/output circuit  44  is disposed approximately at the center of the cover portion  46 . 
     The three lead wires  45  extend from the input/output circuit  44  on a side of the input/output circuit  44 , opposite to the detecting circuit  42 . Upper end parts of the three lead wires  45  are connected to lower end parts of the three lead wires  47 , respectively. Upper end parts of the three lead wires  47  are connected to terminals  48  of the power source line  52 , the output line  54 , and the ground line  56 , respectively. The power source line  52 , the output line  54 , and the ground line  56  penetrate the set plate  6  to thereby be connected to the fuel meter  60 . The lead wires  45  and  47  and the terminals  48  are configured of a conductor having a high conductivity (copper in the present embodiment). 
     The magnetic sensor  40  is covered by the cover portion  46  by being disposed in a molding die of the cover portion  46 , namely, by the so-called insert molding, when the cover portion  46  is to be molded. The lead wires  45  are covered by the cover portion  46 . Moreover, end parts of the lead wires  47  on the lead wires  45 &#39;s side are covered by the cover portion  46 . The lead wires  47  extend from connecting positions of the lead wires  47  and  45 , respectively, in a direction separating away from the magnetic sensor  40 , penetrate the cover portion  46  and the body  32 , and are exposed to an outside of the body  32 . 
     The fuel meter  60  has a CPU  64  and a display  62 . The CPU  64  supplies electric power to the fuel liquid level detector  20 , particularly to the magnetic sensor  40 , via the power source line  52 . The signal output from the magnetic sensor  40  is input to the CPU  64  via the output line  54 . The CPU  64  uses the signal input from the magnetic sensor  40 , determines an amount of fuel stored in the fuel tank  4 , and displays on the display  62  the fuel amount thus determined. The CPU  64  and the display  62  can be configured as in the ones in the conventionally-known fuel meter, respectively. Notably, the ground line  56  is grounded in the CPU  64 . 
     (Liquid Amount Detecting Method) 
     Next, a liquid amount detecting method will be described. The CPU  64  supplies electric power to the magnetic sensor  40  while the automobile is driven (i.e., while the engine is running). The magnetic sensor  40  outputs a signal corresponding to an orientation of a magnetic field of the magnet  26 . When the liquid level of the fuel in the fuel tank  4  changes, the float  22  moves in vertical directions, and the arm  24  rotates as the float  22  moves in the vertical directions. The magnet  26  rotates on its own axis as the arm  24  rotates. Consequently, the orientation of the magnetic field of the magnet  26  changes depending on the rotation of the arm  24 , in other words, the liquid level of the fuel in the fuel tank  4 . Accordingly, the signal output from the magnetic sensor  40  is correlated with the liquid level of the fuel in the fuel tank  4 . 
     When the signal output from the magnetic sensor  40  is input to the CPU  64 , the CPU  64  determines an amount of fuel stored in the fuel tank  4 , and displays on the display  62  the fuel amount thus determined. In particular, the CPU  64  uses a database or a function that is stored in the CPU  64  and shows a relation between a signal output from the magnetic sensor  40  and a fuel amount, to thereby determine the fuel amount. The database or the function is predetermined by execution of an experiment or a simulation, and stored in the CPU  64 . 
     (Relations Among the Clearances CL 1  to CL 8 ) 
     The clearance CL 1  between the body  32  and the magnet  26  is surrounded by the outer circumference wall  34 . The clearance CL 1  communicates with an outer space of the fuel liquid level detector  20  via the clearances CL 2  to CL 8 . 
     In the state where the fulcrum part  24   c  is located at a reference position in a direction vertical to the rotational axis X (i.e., as shown in  FIG. 2 , a position where the central axis of the magnet  26  supported by the fulcrum part  24   c  coincides with the central axis of the outer circumference wall  34 ), a width of the clearance CL 3  (hereinafter referred to as a “width W 1 ”) is provided to extend so as to form a circle along a rotation direction of the arm  24 . At this time, each of the clearances CL 5  and CL 7  (hereinafter referred to as a “width W 1 +α”) is larger than the clearance CL 3 . 
     The opposing wall  24   e  and the inner circumference flange  34   a  slide to thereby cause the arm  24  to rotate relative to the body  32 . In other words, the opposing wall  24   e  functions as a bearing of the arm  24 . According to this configuration, the bearing of the arm  24  can be disposed at an outer circumference of the magnet  26 . Consequently, without making the magnet  26  large, a diameter of the bearing can be increased. 
     If the arm  24  rotates, the size of the clearance CL 3  becomes 0 at a sliding section of the opposing wall  24   e  and the inner circumference flange  34   a , whereas the width of the clearance CL 3  becomes twice as large as the width W 1  (hereinafter referred to as “W 1 ×2”) at a section opposite to that sliding section with the rotational axis X interposed therebetween. On the other hand, the width of each of the clearances CL 5  and CL 7  becomes a width W 1 +α+W 1  on an outer circumference side of the position where the width of the clearance CL 3  is a width 0, and becomes a width a on an outer circumference side of the position where the width of the clearance CL 3  is the width W 1 ×2. 
     In the state where the fulcrum part  24   c  is located at a reference position in a rotational axis X&#39;s direction (i.e., a position where the clearances CL 4  and CL 6  are identical), the width of each of the clearances CL 4  and CL 6  (hereinafter referred to as a width “W 2 ”) is smaller than the width of the clearance CL 1  (hereinafter referred to as a width “W 3 ”), and smaller than the width of the clearance CL 8  (hereinafter referred to as a width “W 4 ”). Moreover, if the fulcrum part  24   c  is located at the reference position in the rotational axis X&#39;s direction, the width W 3  of the clearance CL 1  is smaller than the width W 4  of the clearance CL 8 . In this configuration, the fulcrum part  24   c  moves relative to the magnetic sensor unit  30  in the rotational axis X&#39;s direction, by a width twice as large as the width W 2  of the clearances CL 4  and CL 6 . 
     In the situation where the fulcrum part  24   c  is located both at the reference position in the direction vertical to the rotational axis X, and at the reference position in the rotational axis X&#39;s direction, the width W 2  of each of the clearances CL 4  and CL 6  is smaller than the width W 1  of the clearance CL 3 . 
     In the configuration in the present embodiment, as shown by an arrow of  FIG. 3 , the fuel passes through the clearances CL 8 , CL 7 , CL 6 , CL 5 , CL 4 , CL 3 , and CL 2  in this order, and reaches the clearance CL 1 . If foreign substances are mixed with the fuel, the foreign substances pass through the clearance CL 8 . A storing groove  34   c  that opens toward the clearance CL 8  is disposed in the outer circumference wall  34 . The storing groove  34   c  is disposed to extend so as to form a circle along the rotation direction of the arm  24 . The foreign substances that have passed through the clearance CL 8  flow into the storing groove  34   c  along a flow of the fuel. A portion of the foreign substances mixed with the fuel is thereby stored in the storing groove  34   c . Consequently, it is possible to suppress the foreign substances entering the clearances CL 1  to CL 7 , which are located downstream of the clearance CL 8 . 
     Moreover, it is possible to suppress the foreign substances that are not stored in the storing groove  34   c  and flow downstream from the clearance CL 7  entering downstream of the clearance CL 4 , by means of the clearances CL 6  and CL 4  that have a relatively small width. Consequently, the foreign substances can be prevented from entering the clearances CL 1  to CL 3 . 
     Furthermore, when the arm  24  rotates, a larger moment is generated in the clearances CL 6  and CL 4  than in the clearances CL 1  to CL 3 . Accordingly, hindrance to the arm  24 &#39;s rotation due to foreign substances being caught in the arm  24 &#39;s clearances can be prevented more effectively in the case where the foreign substances are caught in the clearances CL 6  and CL 4  than in the case where the foreign substances are caught in the clearances CL 1  to CL 3 . 
     Out of the foreign substances that have reached downstream of the clearance CL 3 , the ones adsorbed by the magnet, such as iron powders, are adsorbed by the magnet  26  onto the outer circumference surface of the opposing wall  24   e . The clearance CL 2 , which has a width larger than that of the clearance CL 3 , is disposed downstream of the clearance CL 3 . The foreign substances adsorbed by the magnet  26  are stored in the clearance CL 2 . It is thereby possible to suppress the foreign substances adsorbed by the magnet  26  from being caught in the clearances CL 2  and CL 3 . 
     (Variation 1) 
     In the above-described embodiment, the opposing wall  24   e  and the inner circumference flange  34   a  slide to thereby cause the arm  24  to rotate relative to the body  32 . However, the engagement wall  24   f  and the outer circumference flange  34   b  may slide to thereby cause the arm  24  to rotate relative to the body  32 . In this case, the width of the clearance CL 5  may be smaller than that of each of the clearances CL 3  and CL 7 . In the present variation, the engagement wall  24   f  is an example of the “opposing wall”. In the present variation, the inner circumference surface of the outer circumference wall  34  may not be opposed to the opposing wall  24   e.    
     (Variation 2) 
     In the above-described embodiment, in the case where the fulcrum part  24   c  is located at the reference position in the direction vertical to the rotational axis X, the width of the clearance CL 3  is larger than that of each of the clearances CL 5  and CL 7 . However, the width of the clearance CL 3  may be identical to at least one of the widths of the clearances CL 5  and CL 7 . If the width of the clearance CL 3  is identical to the width of the clearance CL 5 , the opposing wall  24   e  and the inner circumference flange  34   a  may slide and the engagement wall  24   f  and the outer circumference flange  34   b  may slide, to thereby cause the arm  24  to rotate relative to the body  32 . If the width of the clearance CL 3  is identical to the clearance CL 7 , the opposing wall  24   e  and the inner circumference flange  34   a  may slide and the engagement wall  24   f  (particularly the engagement flange  24   g ) and the outer circumference wall  34  may slide, to thereby cause the arm  24  to rotate relative to the body  32 . 
     (Variation 3) 
     In the above-described embodiment, in the case where the fulcrum part  24   c  is located both at the reference position in the direction vertical to the rotational axis X and at the reference position in the rotational axis X&#39;s direction, the width of each of the clearances CL 1  to CL 8  is entirely uniform. However, the width of each of the clearances CL 1  to CL 8  may not be entirely uniform. For example, the width of the clearance CL 2  may be identical to the width of the clearance CL 3 , partially in the rotation direction of the arm  24 . 
     (Variation 4) 
     In the above-described embodiment, the engagement wall  24   f  extends so as to form a circle along the outer circumference edge of the cover  24   d . However, the engagement wall  24   f  may not extend as aforementioned along the outer circumference edge of the cover  24   d , and may be disposed discretely at the outer circumference edge of the cover  24   d.    
     (Variation 5) 
     In the above-described embodiment, the storing groove  34   c  is formed at an end of the outer circumference wall  34  on the body  32 &#39;s side. However, the position of the storing groove  34   c  is not limited thereto. For example, the storing groove  34   c  may be formed in the outer circumference flange  34   b . In this case, the storing groove  34   c  may open toward the clearance CL 7 . 
     (Variation 6) 
     In each of the above-described embodiments, the magnet  26  is exposed from the fulcrum part  24   c . However, the magnet  26  may be housed in the fulcrum part  24   c . In the present variation, a clearance between the body  32  and a surface of the fulcrum part  24   c  on the body  32 &#39;s side that covers a surface of the magnet  26  on the body  32 &#39;s side is an example of the “clearance between the supporter and the magnet”. 
     (Variation 7) 
     The “liquid level detector” in the present disclosure may be a device that detects an amount of liquid in a container, for example, an amount of water stored in a water storage tank, and the like, other than the fuel amount detector  20  that detects the amount of fuel in the fuel tank  4 . 
     (Variation 8) 
     In the above-described embodiment, the magnetic sensor  40  outputs to the fuel meter  60  a signal related to an analog amount corresponding to a liquid level of the fuel stored in the fuel tank  4 . The CPU  64  in the fuel meter  60  then uses the signal that has been output from the magnetic sensor  40  and represents the analog amount, to determine a fuel amount. However, the magnetic sensor  40  may convert the analog amount corresponding to the liquid level of the fuel stored in the fuel tank  4  into a fuel amount, and output to the CPU  64  a signal corresponding to the fuel amount. The magnetic sensor  40  may convert the analog amount into the fuel amount, with a technique similar to that of the CPU  64  in the above-described embodiment. The CPU  64  may determine the fuel amount from the signal corresponding to the fuel amount, which has been input from the magnetic sensor  40 , and display on the display  62  the fuel amount thus determined. 
     (Variation 9) 
     In the above-described embodiment, the opposing wall  24   e  of the arm  24  has a cylindrical shape that has a uniform thickness along the rotational axis X&#39;s direction. However, the cylindrical shape may not have a uniform thickness along the direction of the rotational axis X of the opposing wall  24   e . For example, as shown in  FIG. 4 , at the opposing wall  24   e , two cylindrical portions  124  and  125  that have widths different from each other may be disposed adjacently in the rotational axis X&#39;s direction. The cylindrical portion  124  may be disposed on the cover  24   d &#39;s side, in other words, on an upstream side, of the cylindrical portion  125 . An inner diameter of the cylindrical portion  124  may be equal to an inner diameter of the cylindrical portion  125 , and an outer diameter of the cylindrical portion  124  may be larger than an outer diameter of the cylindrical portion  125 . In this case, the outer circumference wall  34  may not have the inner circumference flange  34   a . In other words, the outer circumference wall  34  may have an inner circumference surface that is spaced from the rotational axis X by a constant distance on its entire surface. The clearance CL 2 ′ between the inner circumference surface of the outer circumference wall  34  and an outer circumference surface of the cylindrical portion  125  may be larger than a clearance CL 3 ′ between the inner circumference surface of the outer circumference wall  34  and an outer circumference surface of the cylindrical portion  124 .