Abstract:
A fuel-level measuring apparatus measures the level of fuel in a vehicle fuel tank. The apparatus can ensure a sufficient capacity of the fuel tank and sense the fuel level even when the fuel tank has a thin or complicated shape. A fuel-level measuring apparatus that senses the level of fuel in a vehicle fuel tank disposed below a floor panel of a vehicle includes a tank band that secures the fuel tank to a body of the vehicle, and a strain gauge attached to the tank band. The fuel level can be obtained from strain in the tank band detected by the strain gauge.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2014-060025, filed Mar. 24, 2014, entitled “FUEL-LEVEL SENSING APPARATUS.” The contents of this application are incorporated herein by reference in their entirety. 
     BACKGROUND 
     1. Field 
     The present application relates to a fuel-level measuring apparatus that measures the fuel level in a fuel tank installed in a vehicle. 
     2. Description of the Related Art 
     In a vehicle that uses gasoline or light oil as fuel, it is necessary to indicate the fuel level in a fuel tank so that the driver can know when the tank needs to be refilled and how far the car can drive. 
     A known fuel-level measuring apparatus that measures the fuel level in a fuel tank is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2013-50410. The apparatus disclosed therein includes a float provided in a fuel tank, the float moving up and down with the surface level of the fuel, and, by making a float arm of the float slide over a resistor plate and converting the surface level into an electric potential difference, the apparatus measures the height of the surface and indicates the fuel level calculated from the height of the surface to a driver. 
     However, the technique disclosed in Japanese Unexamined Patent Application Publication No. 2013-50410 has the following problems: because the fuel-level measuring apparatus, such as the float, is disposed in the fuel tank, the capacity of the fuel tank decreases by an amount corresponding to the volume of the fuel-level measuring apparatus; because the fuel-level measuring apparatus needs to be disposed in the fuel tank, the shape of the fuel tank is restricted and cannot be thin or complicated; and, because the surface level of the fuel in the tank changes significantly depending on the orientation and driving conditions of the vehicle, it is impossible to measure the accurate fuel level. 
     SUMMARY 
     The present application provides a fuel-level measuring apparatus that can ensure a sufficient capacity of a fuel tank, can accurately measure the fuel level in the fuel tank regardless of the orientation and driving conditions of a vehicle, and can measure the fuel level even when the fuel tank has a thin or complicated shape. 
     According to a first aspect of the embodiment, a fuel-level measuring apparatus that measures the level of fuel in a vehicle fuel tank disposed below a floor panel of a vehicle includes: a tank band that secures the fuel tank to a body of the vehicle; and a strain gauge attached to the tank band. The fuel level is obtained from strain in the tank band detected by the strain gauge. 
     According to a second aspect of the embodiment, the tank band is attached along a bottom surface of the fuel tank, an elastic member is disposed between the bottom surface of the fuel tank and a top surface (a first surface) of the tank band, and the strain gauge is attached to a surface of the tank band, at a position immediately below the fuel tank and where the elastic member is not disposed. 
     According to a third aspect of the embodiment, the tank band has a substantially hat shape in section taken in the longitudinal direction thereof and includes edge portions at both ends in the width direction and a projecting portion projecting toward the fuel tank further than the edge portions. The strain gauge is attached to one of the edge portions in the width direction of the tank band. 
     According to a fourth aspect of the embodiment, the tank band has a substantially hat shape in section taken in the longitudinal direction thereof and includes edge portions at both ends in the width direction and a projecting portion projecting toward the fuel tank further than the edge portions. The strain gauge is attached to a middle portion of the projecting portion in the longitudinal direction. 
     According to the first aspect of the embodiment, the fuel tank is disposed below the floor panel, and the tank band for securing the fuel tank to the body receives the total weight of the fuel tank and the fuel in the tank. The strain gauge attached to the tank band detects the strain in the tank band caused by the total weight, and the fuel level in the vehicle fuel tank can be obtained from the detected signal. In this configuration, because the fuel-level measuring apparatus does not need to be disposed in the fuel tank, the fuel tank may have a sufficient capacity. Furthermore, because the design flexibility of the fuel tank increases, the fuel level can be obtained even in fuel tanks incapable of accommodating the fuel-level measuring apparatus, such as those having a thin or complicated shape. Furthermore, because the fuel level is obtained not from the surface level, which is likely to be influenced by the orientation and driving conditions of the vehicle, but from the strain caused by the weight, which is less likely to be influenced by the orientation and driving conditions of the vehicle, the fuel level can be obtained regardless of the orientation and driving conditions of the vehicle. 
     According to the second aspect of the embodiment, the tank band is attached along the bottom surface of the fuel tank, an elastic member is disposed between the bottom surface of the fuel tank and the top surface of the tank band, and the strain gauge is attached to the side edge surface (a second surface) of the tank band, at a position immediately below the fuel tank and where the elastic member is not disposed. Because the elastic member disposed between the fuel tank and the tank band serves as a cushioning member, the elastic member can reliably receive the load applied to the tank band and appropriately support the fuel tank. In particular, because the fuel tank does not move away from the tank band and is kept supported by the tank band even when a large load is applied thereto, such as when the vehicle drives over a bump, the strain in the tank band caused by the load applied by the fuel tank can be constantly measured with the strain gauge attached thereto, and the fuel level can be obtained. 
     According to the third aspect of the embodiment, the tank band has a substantially hat shape in section taken in the longitudinal direction thereof and includes edge portions at both ends in the width direction and a projecting portion projecting toward the fuel tank further than the edge portions. The strain gauge is attached to one of the edge portions in the width direction of the tank band. Thus, the elastic member and the strain gauge can be efficiently disposed on the tank band. Furthermore, because the strain gauge is disposed on the surface of the tank band adjacent to the fuel tank, there is less possibility of an object, such as a stone on a road, hitting the strain gauge while the vehicle is driving, and hence, it is possible to protect the strain gauge. 
     According to the fourth aspect of the embodiment, the tank band has a substantially hat shape in section taken in the longitudinal direction thereof and includes edge portions at both ends in the width direction and a projecting portion provided therebetween and projecting toward the fuel tank further than the edge portions. The strain gauge is attached to a middle portion of the projecting portion in the longitudinal direction. Because this portion is more sensitive to a change in load due to an increase or decrease in fuel level in the fuel tank than the other portions, an obvious change in load occurs in this part. Hence, the strain gauge attached to this part can detect an obvious change in strain in the tank band due to an increase or decrease in fuel level, compared with a strain gauge attached to another part, making it possible to obtain the fuel level. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a sectional view of a configuration in which a fuel tank provided with a fuel level measuring apparatus according to one embodiment of the present application is disposed below a floor panel, as viewed from the center of the vehicle&#39;s width; and  FIG. 1B  is a plan view of a tank band. 
         FIG. 2  is a sectional view taken along line II-II in  FIG. 1A . 
         FIG. 3  is an enlarged view of portion III indicated in  FIG. 2 . 
         FIG. 4  is an enlarged sectional view of the vicinity of a strain gauge attached to a middle portion, in the longitudinal direction, of a projecting portion of the tank band shown in  FIG. 1 . 
         FIG. 5  is a graph showing the relationship between the fuel level and the stress. 
         FIG. 6  is a sectional view of another type of fuel tank provided with a fuel level measuring apparatus according to the embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment of the present application will be described with reference to the attached drawings. Embodiment 
     First, the configuration of the present application will be described with reference to  FIGS. 1 to 3 . In these drawings, “Fr” denotes the front side, “Rr” denotes the rear side, “Le” denotes the left side, and “Ri” denotes the right side of a vehicle  10 .  FIG. 1A  is a sectional view of a configuration in which a fuel tank  20  of the present application is disposed below a floor panel  11   a,  as viewed from the center of the vehicle&#39;s width, and  FIG. 1B  is a plan view of a tank band  30  that is used to secure the fuel tank  20  to a body  11 . The fuel tank  20  is disposed below the floor panel  11   a  of the body  11  of the vehicle  10 , such as a passenger car, a bus, or a truck. Cushioning members  12  formed of rubber, flexible resin, or the like are disposed between the floor panel  11   a  and the fuel tank  20 . The body  11  includes cross members  13  extending below the floor panel  11   a.  The fuel tank  20  is supported by two tank bands  30 , whose ends are fixed to the cross members  13  of the body of the vehicle  10 . Each of the tank bands  30  is formed in an elongated shape having its longitudinal direction and certain width in its width direction perpendicular to the longitudinal direction. 
     The fuel tank  20  is formed as a single component of synthetic resin. Alternatively, the fuel tank  20  may be formed by joining an upper tank portion, which is formed of a steel plate or synthetic resin, and a lower tank portion, which is also formed of a steel plate or synthetic resin, at flanges provided along the outer circumference thereof, by using adhesive or a bolt and nut. 
     The fuel tank  20  has, in a bottom surface  20   a  thereof, two (right and left) tank-band fitting grooves  21  to which the two (right and left) tank bands  30 , extending in the front-rear direction of the vehicle  10 , are fitted. Furthermore, a fuel supply pipe  22  through which fuel is supplied from a fuel supply port (not shown) of the vehicle  10  to the fuel tank  20 ; an air-bleeding pipe  23 ; and a fuel supply pipe  24  through which the fuel is supplied from the fuel tank  20  to an engine (not shown) by means of a fuel pump (not shown) are provided in the top surface of the fuel tank  20 . 
     The right and left tank bands  30  are formed of bent steel plates, and each tank band  30  has a projecting portion  31  that is provided at a middle portion, in the longitudinal direction, of the top surface (the surface facing the fuel tank  20 ) so as to extend over the entire length, as viewed in section taken in the longitudinal direction of the tank bands  30 . The tank band also has edge portions  32  formed on both sides of the projecting portion  31 . In other words, the tank bands  30  have a substantially hat shape in sectional view. 
     Each projecting portion  31  includes, in the longitudinal direction of the tank band  30 , a horizontal portion  31   a  extending in the front-rear direction of the vehicle  10 ; a front attaching portion  31   c  formed on the front side of the horizontal portion  31   a;  a front slope portion  31   b  formed between the horizontal portion  31   a  and the front attaching portion  31   c;  a rear attaching portion  31   e  formed on the rear side of the horizontal portion  31   a ; and a rear slope portion  31   d  formed between the horizontal portion  31   a  and the rear attaching portion  31   e.    
     An elastic member  33  formed of rubber, flexible resin, or the like is bonded, with adhesive, to a portion of the projecting portion  31 , the portion including the entire horizontal portion  31   a  and the top surfaces, near the horizontal portion  31   a,  of the front slope portion  31   b  and rear slope portion  31   d.    
     The fuel tank  20  is disposed at a predetermined position below the floor panel  11   a,  and the top surfaces of the elastic members  33  on the right and left tank bands  30  are fitted to the right and left tank-band fitting grooves  21 . The right and left tank bands  30  each have one front attachment hole in the front attaching portion  31   c  and one rear attachment hole in the rear attaching portion  31   e . Support bolts  34  are inserted into the attachment holes, and screw portions of the support bolts  34  are made to pass through holes provided in the cross members  13  of the body  11  of the vehicle  10 . Then, the support bolts  34  are fastened with tank-attaching nuts  35 . In this way, the fuel tank  20  disposed below the floor panel  11   a  is fixed to the body  11  and supported by the right and left tank bands  30 . 
     The fuel tank  20  may be entirely or partially (i.e., only at the bottom surface  20   a ) covered with a metal or resin cover, with a rubber or flexible resin layer therebetween, for protection from stones etc. In such a case, grooves to which the right and left tank bands are fitted are provided in the bottom surface of the cover, so that they serve the same function as the tank-band fitting grooves  21  in the fuel tank  20 . 
     A strain gauge  41  is attached to the side edge  32  of the projecting portion  31  of one of the right and left tank bands  30 , at the middle (center) position in the longitudinal direction. Although one strain gauge  41  is enough, more than one strain gauge  41  may be provided in case of fault or damage. Furthermore, the strain gauge  41  may be attached to the back surface of the edge  32 . 
     The strain gauge  41  is bonded to the edge  32  of the tank band  30  with adhesive such that the longitudinal directions of the strain gauge  41  and tank band  30  are parallel to each other. The top surface of the strain gauge  41  may be covered with a protection member formed of rubber, resin, or the like. 
     A gauge lead wire extending from the strain gauge  41  is connected to a strain-level measuring device  42  that detects the strain in the tank bands  30  and is formed of a power supply circuit, a bridge circuit, and an amplifier. The strain-level measuring device  42  is installed somewhere in the vehicle  10 , but not on the fuel tank  20 . 
     The strain-level measuring device  42  is connected to a processing device  43  that calculates the weight of the fuel  45  from the strain in the tank bands  30  and, moreover, calculates the level of the fuel  45  from the weight of the fuel  45 . The processing device  43  is installed somewhere in the vehicle  10 , but not on the fuel tank  20 . 
     The processing device  43  is disposed in an instrument panel provided at a driver&#39;s seat to indicate the results obtained by the processing device  43  and is connected to a fuel gauge  44  that indicates, using a needle or a bar graph, the level of the fuel  45  in the form of ratio to the capacity of the fuel tank  20  (i.e., from a full state to an empty state). 
     As described above, the fuel-level measuring apparatus  40  of the present application includes the tank bands  30 , the strain gauge  41 , the strain-level measuring device  42 , the processing device  43 , and the fuel gauge  44 . 
     Next, a method of how the fuel-level measuring apparatus  40  calculates the level of the fuel  45  in the fuel tank  20  from the strain in the tank bands  30  detected by the strain gauge  41  will be described. 
     Many metals experience expansion or contraction, which is minimal mechanical change, when a force is applied thereto (such expansion and contraction are generally called “strain”). The strain changes the electrical resistance of the metal. The strain gauge  41  and the strain-level measuring device  42  to which the strain gauge  41  is connected are sensors that detect, as an electric signal, the “strain” caused by a force applied to the metal. The strain and the electrical resistance are proportional to each other by a constant called “resistance change rate”, and the resistance change rate is determined by a passive component. Hence, the force (i.e., load) causing the strain can be obtained by multiplying the detected strain by the resistance change rate of the passive component of the strain gauge  41 . The present application provides a fuel-level detecting apparatus that obtains the level of the fuel  45  in the fuel tank  20  by detecting, with the strain gauge  41 , the strain in the tank bands  30  that support the fuel tank  20 . 
     Fuel is supplied from the fuel supply port (not shown) in the vehicle  10  to the fuel tank  20  through the fuel supply pipe  22 . The fuel supplied to the fuel tank  20  is supplied to the engine (not shown) through the fuel supply pipe  24  by the fuel pump (not shown). 
     When the level of the fuel  45  in the fuel tank  20  is increased by supplying fuel, the total weight of the fuel tank  20  (i.e., the sum of the weight of the fuel tank  20  and the weight of the fuel  45 ) increases. On the other hand, when the level of the fuel  45  is decreased by the engine consuming the fuel during driving, the total weight of the fuel tank  20  decreases. In short, the total weight of the fuel tank  20  increases or decreases in proportion to an increase or decrease in level of the fuel  45 . 
     Because the fuel tank  20  supported by the tank bands  30  at the bottom surface  20   a  thereof is disposed below the floor panel  11   a  of the vehicle  10  and is fixed to the body  11 , the tank bands  30  are subjected to the total weight of the fuel tank  20 . Hence, the strain due to the load (i.e., the total weight of the fuel tank  20 ) occurs in the tank bands  30 . A material of the tank bands  30  may be selected from any types including resins, metals and the like as known in the art, which have proper strain characteristics to allow the strain gauge  41  mechanically connected to the bands to convert the strain of the tank bands to electric signals, in responding to the total weight of the fuel tank  20 . 
     When the load applied to the tank bands  30  increases as the level of the fuel  45  in the fuel tank  20  increases, the surfaces of the tank bands  30  adjacent to the fuel tank  20  expand at the projecting portions  31  and the periphery thereof and contract at the front slope portions  31   b  and rear slope portions  31   c  of the projecting portions  31 . 
     For verification, three strain gauges were attached to the tank band  30  supporting the fuel tank  20 , as shown in the plan view in  FIG. 1B , and the values detected by the strain gauges while the fuel was supplied were recorded and compared. The stresses (MPa) corresponding to the level of the fuel  45  (L) detected by a first strain gauge ( 41   a ) (see  FIG. 4 ) attached to a middle portion of the projecting portion  31  in the longitudinal direction, a second strain gauge ( 41   b ) attached to an edge of the front slope portion  31   b  of the tank band  30 , and a third strain gauge ( 41   c ) attached to an edge of the rear slope portion  31   d  of the tank band  30  are plotted on the graph in  FIG. 5 . As shown in  FIG. 5 , in each strain gauge, the detected stress increases (or decreases in the case of minus) linearly as the fuel level increases. Thus, there is a linear relationship between the fuel level and the stress. Meanwhile, the stress detected by the first strain gauge was about three to five times those detected by the second and third strain gauges for the same level of the fuel  45 . This shows that the first strain gauge ( 41   a ) can detect the stress applied to the tank band due to an increase in the level of the fuel  45  in a greater magnitude than the other strain gauges. Accordingly, it may be considered that the strain gauge ( 41   a ) attached to the middle portion of the projecting portion  31  of the tank band  30  in the longitudinal direction can most precisely detect the level of the fuel  45 . 
     Hence, the strain gauge  41  attached to the edge  32  of the tank band  30  and the strain gauge  41   a  attached to the middle portion of the projecting portion  31  of the tank band  30  in the longitudinal direction detect the strain (expansion) in the tank band  30  when the load applied to the tank band  30  increases as the level of the fuel  45  increases and detect a decrease in strain due to the expanded tank band  30  returning to the original state when the load applied to the tank band  30  decreases as the level of the fuel  45  decreases. 
     The strain gauge  41  detects the strain occurring in the tank band  30  as an electric signal and transmits the electric signal. 
     The strain-level measuring device  42  calculates the strain in the tank bands  30  from the electric signal received from the strain gauge  41  and sends data about the strain level to the processing device  43 . 
     The processing device  43  calculates the level of the fuel  45  from the strain data received from the strain-level measuring device  42 , using a predetermined arithmetic expression, a map, or the like. 
     When the fuel tank  20  is filled with the fuel  45  to the limit of its capacity, the total weight of the fuel tank  20  is equal to the sum of the weight of the fuel tank  20  and the weight of the fuel  45  that fills the fuel tank  20  to the limit of its capacity, and at this time, the load applied to the tank bands  30  is maximum. The level of the fuel  45  calculated by the processing device  43  from the electric signal generated by the strain occurring at this time is regarded as the limit of the capacity of the fuel tank  20 , and at this time, the needle of the fuel gauge  44  points to “F”, indicating a full tank. 
     Furthermore, when the level of the fuel  45  in the fuel tank  20  is zero, the total weight of the fuel tank  20  is equal to the weight of the fuel tank  20 , and at this time, the load applied to the tank bands  30  is minimum. The level of the fuel  45  calculated by the processing device  43  from the electric signal generated by the strain occurring at this time is regarded as zero, and at this time, the needle of the fuel gauge  44  points to “E”, indicating “empty tank”. 
     The fuel gauge  44  indicates the level of the fuel  45 , which is provided by the processing device  43 , in the form of ratio to the capacity of the fuel tank  20  (i.e., full, ¾ full, ½ full, ¼ full, and empty), using a scale and needle, a bar graph, or the like. 
     The present application is suitable for various types of vehicle including cars, such as passenger cars, freight cars, and buses, and diesel electric locomotives that use gasoline or light oil as fuel and have a fuel tank disposed and fixed below the floor panel of the vehicle. 
       FIG. 6  is a schematic view of another type of fuel tank provided with a fuel level measuring device according to the embodiment of the present invention as shown above. This fuel tank  200  has an elastic or flexible (expandable and retractable) body the inside of which is filled with a fuel. The tank body  200  is configured to expand to charge the fuel inside and shrink to discharge the fuel therefrom, responding to the change of the remaining amount (level) of fuel. The fuel tank body  200  secures the tank body to a vehicle body (not shown). As shown in  FIG. 6 , a tank band  300  may be provided to support and hold the body of the tank  200  in a manner similar to  FIG. 1 . A strain gauge  410  may typically be attached to the tank band  300  at a middle position thereof in the longitudinal direction. However, the position of the gauge  410  is not limited and may be selected from any other places as shown in  FIGS. 1-4 . Any aspects and features discussed for the tank band and the gauge in the present application may be applied to this type of fuel tank. 
     As shown above, the fuel level measuring apparatus according to embodiments of the present invention can be mounted to the outside of the tank body by utilizing a tank band or any such supporting structure designed to hold the tank body, without a necessity of a float or other level detecting devices provided typically inside the tank body. Accordingly, this feature of the invention allows even any types of fuel tanks to easily measure the fuel level, with the tank band and the strain gauge according to the present invention, even in a case where they have no space or a limited space inside the tank for detecting the level of fuel.