Abstract:
Provided is a liquid surface detection device providing for compactness and enabling a reduction in displacement of a rotating shaft of a magnet. In the liquid surface detection device, which is provided with a holder rotating in response to displacement of a float, said displacement accompanying a change in a liquid surface, which is provided with a magnet affixed to the holder and rotating along with the holder, and which is provided with a magnetic detection element detecting a magnetic force change accompanying the rotating motion of the magnet, said liquid surface detection device is provided with: a body section that provides on the holder, first and second rotating sections sandwiching the magnet therebetween in the rotary axis direction of the magnet, said body section being provided with a first rotary support section that places the magnetic detection element opposite the magnet in the rotary axis direction of the magnet, and that rotatably supports the first rotation section of the holder; and a cover that is affixed to the body section, and is provided with a second rotary support section that rotatably supports the second rotating section of the holder.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a liquid surface detection device that detects a surface of liquid such as fuel in a fuel tank. 
       BACKGROUND ART 
       [0002]    A conventional liquid surface detection device is, for example, disclosed in PTL 1. In this liquid surface detection device, as a magnet rotates with a shaft along with vertical motions of a float that follows fluctuations of the liquid surface, output voltage of a magnetic resistance element, more specifically a magnetic detection element, which is attached to a body opposite the magnet, changes. A position of the float, in other words, a liquid surface of the fuel, is detected by the output voltage of the magnetic resistance element. The liquid surface detection device can be made smaller by reducing a projected area viewed from the rotary axis direction of the magnet by placing the magnetic detection element on the rotary axis of the magnet or in the rotary axis direction of the magnet. 
       CITATION LIST 
     Patent Literature 
       [0003]    [PTL 1] JP-A-2003-172653 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0004]    However, in the liquid surface detection device, an approximate bottom-formed holding hole that rotatably holds the shaft is formed on the body, and the shaft rotatably fits into the holding hole. As the portion that rotatably holds the shaft is a single bearing structure including the shaft and the holding hole, the rotary axis of the shaft is displaced by the impact of irregular fluctuations of the liquid surface. Moreover, the rotary axis of the magnet fixed to the shaft is also displaced. Therefore, the output voltage of the magnetic detection element is more likely to be affected by said displacement. 
         [0005]    Therefore, the invention is made in view of the problems described above and an object of the invention is to provide a liquid surface detection device providing for compactness and enabling a reduction in displacement of the rotary axis of the magnet. 
       Solution to Problem 
       [0006]    A liquid surface detection device according to the invention including: a holder rotating in response to displacement of a float, the displacement accompanying a change in a liquid surface; a magnet affixed to the holder and rotating along with the holder; and a magnetic detection element detecting a magnetic force change accompanying the rotating motion of the magnet, in which a body section that provides on the holder a first rotating section and a second rotating section sandwiching the magnet therebetween in the rotary axis direction of the magnet, the body section being provided with a first rotary support section that places the magnetic detection element opposite the magnet in the rotary axis direction of the magnet and that rotatably supports the first rotation section of the holder, and a cover that is fixed to the body section and is provided with a second rotary support section that rotatably supports the second rotating section of the holder are provided. 
         [0007]    Furthermore, the first rotary support section has a sliding surface of which cross-section is formed in a circular shape and vertical to the rotary axis direction of the magnet, and the first rotating section includes a slide receiving surface that rotatably holds an outer circumference of the sliding surface. 
         [0008]    Further, the second rotating section has a sliding surface of which cross-section is formed in a circular shape and vertical to the rotary axis direction of the magnet, and the second rotary support section includes a slide receiving surface that rotatably holds an outer circumference of the sliding surface. 
       Advantageous Effects of Invention 
       [0009]    With the above-mentioned configuration, the invention can attain the object of providing a liquid surface detection device providing for compactness and enabling a reduction in displacement of the rotary axis of a magnet. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0010]    [ FIG. 1 ]  FIG. 1  is a top view of a liquid surface detection device of one embodiment of the invention. 
           [0011]    [ FIG. 2 ]  FIG. 2  is a sectional view taken along line A-A of  FIG. 1 . 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0012]    Hereinafter, one embodiment of the invention will be described with reference to the accompanying drawings. 
         [0013]    A liquid surface detection device F of the invention is installed in a fuel tank, not illustrated, which stores liquid fuel such as gasoline. 
         [0014]    The liquid surface detection device F mainly includes a body section  1 , a holder  2 , a magnet  2   a,  magnetic detection element  3 , and a cover  4 . 
         [0015]    The body section  1  has first resin bodies  11  and a second resin body  12 . 
         [0016]    The first resin bodies  11  are made of resin material such as polyacetal (hereinafter, “POM”), and has a plurality of terminals  1   a  that are built therein by primary molding. On a part that is exposed from the first resin bodies  11  of the terminals  1   a,  a magnetic detection element  3  and an electronic part (condenser or register for noise absorption)  5  are mounted. 
         [0017]    After mounting the magnetic detection element  3  and the electronic part  5  on the terminals  1   a,  the first resin bodies  1  are insert-molded by the second resin body  12  that is made of the same resin material as the first resin bodies  11 , so as to form the body section  1 . Along with the terminals  1   a,  the magnetic detection element  3 , and the electronic part  5 , the first resin bodies  11  are sealed by the second resin body  12  in an air tight manner. 
         [0018]    The body section  1  includes a first rotary support section  1   b  that rotatably supports the holder  2 . The first rotary support section  1   b  is integrally formed with the second resin body  12 . The first rotary support section  1   b  has a cylindrical shape and protrudes to the side of the holder  2  that includes the magnet  2   a.  The first rotary support section  1   b  having a cylindrical shape has a sliding surface of which cross-section is formed in a circular shape and vertical to the rotary axis direction of the magnet  2   a.  On the rotary axis of the first rotary support section  1   b  in the body section  1 , a magnetic detection surface  3   a  of the magnetic detection element  3  is provided opposite the magnet  2   a.    
         [0019]    Moreover, on the back side of the body section  1  (opposite the side on which the holder  2  is provided), positioning bosses  1   c  are provided for determining positions to be attached to a fuel pump, an attachment stay, and the like. On the sides of the body section  1 , hooks  1   d  are provided to be attached to the fuel pump, the attachment stay, and the like. The positioning bosses  1   c  and the hooks  1   d  are integrally formed with the second resin body  12 . 
         [0020]    In order to produce the body section  1 , a plurality of mutually connected terminals  1   a  are insert-molded with the first resin bodies  11  by primary molding. After the insert molding, the terminals  1   a  are cut by press, and the magnetic detection element  3  and the electronic part  5  are welded to the cut terminals  1   a  by resistance welding or soldered thereto. Furthermore, the first resin bodies  11  are secondarily formed by the second resin body  12 . The body section  1  is produced by this production method. 
         [0021]    The holder  2  is made of resin material such as POM, and the magnet  2   a  is fixed by insert molding. 
         [0022]    The magnet  2   a  is made of, for example, neodymium-ferrite material, having a cylindrical shape with the rotary axis of the magnet  2   a  as the center. In this embodiment, two poles are magnetized. 
         [0023]    The holder  2  includes a flange section  2   b,  an arm attachment section  2   b   1 , a first rotating section  2   b   2 , and a second rotating section  2   b   3 . 
         [0024]    The flange section  2   b  has a disk shape, and is so formed that spreads radially outwards with the rotary axis of the holder  2  as the center in a direction vertical to the rotary axis direction of the holder  2 . 
         [0025]    On the upper side of the flange section  2   b  (upper side in  FIG. 2 ), an arm attachment section  2   b   1  is provided. The arm attachment section  2   b   1  is for attachment of a float arm  6  that transmits to the holder  2  motions of a float, not illustrated, which floats accompanying a change in a liquid surface. 
         [0026]    On the lower side of the flange section  2   b,  a retaining section  2   b   4  that retains the magnet  2   a  and a first rotating section  2   b   2  are provided. 
         [0027]    The retaining section  2   b   4  has a hollow cylindrical shape, with its lower side being narrower than the outer shape of the magnet  2   a,  including a first hole  2   b   5  that is exposed by the magnet  2   a.    
         [0028]    The first rotating section  2   b   2  is provided below the retaining section  2   b   4 . The first rotating section  2   b   2  has a hollow cylindrical shape, and a hole of the first rotating section  2   b   2  communicates with the first hole  2   b   5  of the retaining section  2   b   4 . The first rotating section  2   b   2  rotatably supports the holder  2 , as a part of the inner circumferential surface of the hollow cylindrically shaped hole  2   b   5  is a slide receiving surface that slides over the sliding surface of the outer circumference of the cylindrical shape of the first rotary support section  1   b  of the body section  1 . 
         [0029]    On the upper side of the flange section  2   b,  in addition to the arm attachment section  2   b   1 , a second rotating section  2   b   3  is provided. 
         [0030]    The second rotating section  2   b   3  has a hollow cylindrical shape, including a second hole  2   b   6  that is exposed by the magnet  2   a.  The second rotating section  2   b   3  is located above the first rotating section  2   b   2 , sandwiching the magnet  2   a  therebetween, in the rotary axis direction of the magnet  2   a.  The center axis of the hollow cylindrically shaped first rotating section  2   b   2  and that of the second rotating section  2   b   3  are arranged coaxially. The rotary axis of the magnet  2   a  is also arranged coaxially with them. The second rotating section  2   b   3  has a circular cross-sectional shape vertical to the rotary axis direction of the magnet  2   a,  with the outer circumference being a sliding surface. 
         [0031]    The holder  2  is placed in a manner such that by engaging the first rotating section  2   b   2  with the first rotary support section  1   b  of the body section  1 , the magnet  2   a  of the holder  2  is placed opposite the magnetic detection surface  3   a  of the magnetic detection element  3 , so that a magnetic pole change of the magnet  2   a  accompanying the rotating motions of the holder  2  can be detected by the magnetic detection element  3 . By configuring the body section  1  and the holder  2  with the same resin material, sliding of the holder  2  is improved. 
         [0032]    The magnetic detection element  3  is made of, for example, Hall IC, and electrically fixed to the terminals  1   a  by laser welding or resistance welding. To and from the magnetic detection element  3 , power is supplied and a detected signal is transmitted through a lead wire  7  that is connected to the terminals  1   a  electrically. 
         [0033]    The cover  4  is made of resin material such as POM. The cover  4  is fixed to the body section  1 , preventing fall of the holder  2 . The cover  4  includes a second rotary support section  4   a,  a base section  4   b,  a top plate section  4   c,  a first wall section  4   d,  and a second wall section  4   e.    
         [0034]    As shown in  FIG. 2 , the cover  4  has a shape of a ladle turned upside down, which is defined by the base section  4   b,  the top plate section  4   c,  the first wall section  4   d,  and the second wall section  4   e.    
         [0035]    The second rotary support section  4   a  is provided on the top plate section  4   c,  protruding downward as shown in  FIG. 2 . The second rotary support section  4   a  has a hollow cylindrical shape, and its inner circumferential surface is a slide receiving surface that slides over the outer circumferential sliding surface of the second rotating section  2   b   3 . The second rotary support section  4   a  rotatably supports the second rotating section  2   b   3 . 
         [0036]    The base section  4   b  has a flat-plate shape, and is fixed to the body section  1  for fixing the cover  4  to the body section  1 . The base section  4   b  is fixed to the body section  1  by appropriate means such as laser welding. 
         [0037]    The top plate section  4   c  has a flat-plate disk shape. As shown in  FIG. 1 , viewed from the top, the liquid surface detection device F has a cut-out portion at the top and at the bottom. At the middle of the top plate section  4   c,  the second rotary support section  4   a  is provided. 
         [0038]    The first wall section  4   d  and the second wall section  4   e  are separated. When the liquid surface detection device F is viewed from above, the first wall section  4   d  and the second wall section  4   e  have a circular arc shape. From a portion where the first wall section  4   d  and the second wall section  4   e  are separated, the float arm  6  is exposed, and the first wall section  4   d  and the second wall section  4   e  function as a stopper to regulate the rotating range of the float arm  6 . At the lower end of the first wall section  4   d  (portion in contact with the body section  1 ), fixed pieces  4   d   1  are provided. Like the base section  4   b,  the fixed pieces  4   d   1  are also fixed to the body section  1  by appropriate means such as laser welding. 
         [0039]    As described above, by providing the body section  1  that provides on the holder  2  the first rotating section  2   b   2  and the second rotating section  2   b   3  sandwiching the magnet  2   a  therebetween in the rotary axis direction of the magnet  2   a , the body section being provided with the first rotary support section  1   b  that places the magnetic detection element  3  opposite the magnet  2   a  in the rotary axis direction of the magnet  2   a  and that rotatably supports the first rotation section  2   b   2  of the holder  2 , and the cover  4  that is fixed to the body section  1  and is provided with the second rotary support section  4   a  that rotatably supports the second rotating section  2   b   3  of the holder  2 , the liquid surface detection device F providing for compactness and enabling a reduction in displacement of the rotary axis of a magnet can be provided. 
         [0040]    Furthermore, the first rotary support section  1   b  provided on the body section  1  has a circular sliding surface as a cross-sectional shape vertical to the rotary axis direction of the magnet  2   a,  and the first rotating section  2   b   2  includes a slide receiving surface that rotatably supports the outer circumference of the sliding surface, so that displacement of the rotary axis of the magnet  2   a  can be reduced. Especially, by providing the first hole  2   b   5  that is exposed by the magnet  2   a,  the first rotating section  2   b   2  allows the first rotary support section  1   b  to be inserted into the first hole  2   b   5  and the first rotary support section  1   b  to comes close to the magnet  2   a.  In the limited space between the magnet  2   a  and the magnetic detection element  3 , the magnetic detection element  3  is covered and protected by the second resin body  12 , enabling rotatable support reducing displacement of the rotary axis of the magnet  2   a.    
         [0041]    Furthermore, the second rotating section  2   b   3  of the holder  2  has a sliding surface of which cross-section is formed in a circular shape and vertical to the rotary axis direction of the magnet  2   a,  and the second rotary support section  4   a  of the cover  4  includes a slide receiving surface that rotatably holds the outer circumference of the sliding surface, so that a wide distance can be set between the sliding surface of the second rotating section  2   b   3  and the slide receiving surface of the second rotary support section  4   a  in the rotary axis direction of the sliding portion, enabling rotatable support reducing displacement of the rotary axis of the magnet  2   a.    
         [0042]    Furthermore, by a simple configuration of the holder  2  and the cover  4  sequentially layered and arranged on the body section  1  that includes the magnetic detection element  3 , the liquid surface detection device F can be obtained. Therefore, the production process can be simplified, resulting in production cost reduction. 
         [0043]    Furthermore, the terminals  1   a  are mounted with the magnetic detection element  3  and the electronic part  5 , so that a circuit board, which is required conventionally, is not necessary. Therefore, the configuration can be simplified, resulting in further production cost reduction. 
         [0044]    The above-mentioned explanations are illustrative of the invention. Needless to say, various changes and modifications can be made without departing from the gist of the invention. In the embodiment, the first rotary support section  1   b  of the body section  1  may include a circular sliding surface as a cross-sectional shape vertical to the rotary axis direction of the magnet  2   a,  and the first rotating section  2   b   2  may include a slide receiving surface that rotatably supports the outer circumference of the sliding surface. Alternately, the second rotary support section  4   a  may include a circular sliding surface as a cross-sectional shape vertical to the rotary axis direction of the magnet  2   a,  and the second rotating section  2   b   3  may include a slide receiving surface that rotatably holds the outer circumference of the sliding surface. 
       INDUSTRIAL APPLICABILITY 
       [0045]    The invention can be applied to a liquid surface detection device that detects a surface of liquid in a fuel tank. 
       REFERENCE SIGNS LIST 
       [0046]    F liquid surface detection device 
         [0047]      1  body section 
         [0048]      1   b  first rotary support section 
         [0049]      2  holder 
         [0050]      2   a  magnet 
         [0051]      2   b   2  first rotating section 
         [0052]      2   b   3  second rotating section 
         [0053]      3  magnetic detection element 
         [0054]      4  cover 
         [0055]      4   a  second rotary support section