Abstract:
A fuel tank system includes: a fuel tank; a canister; a vent pipe; a valve member that is provided at the vent pipe and is sectioned into a tank-side main chamber, a canister-side main chamber and a back pressure chamber; a pipe configured to open an interior of the canister to the atmosphere; a negative pressure pump that is provided at the pipe, and applies negative pressure through the canister and the vent pipe to a fuel tank interior; a judging means for judging absence/presence of perforation of the fuel tank from behavior of air pressure at a time when negative pressure is generated at the negative pressure pump; and a negative pressure application path that communicates the pipe with the back pressure chamber, and that is configured to apply negative pressure from the negative pressure pump to the back pressure chamber without the negative pressure going through the canister.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 USC 119 from Japanese Patent Application No. 2014-237077 filed Nov. 21, 2014, the disclosure of which is incorporated by reference herein. 
     BACKGROUND 
     Technical Field 
     The technique of the present disclosure relates to a fuel tank system and a method for sensing perforation. 
     Related Art 
     A fuel tank system, in which a valve member (a diaphragm valve) is provided at a vent pipe that communicates a fuel tank with a canister, is known (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 2013-144942). In this fuel tank system, at usual times, the valve member is closed and the fuel tank is sealed. On the other hand, at the time of carrying out sensing as to whether or not perforation has arisen at the fuel tank (hereinafter simply called “perforation sensing”), by applying negative pressure to a back pressure chamber of the valve member and opening the valve member, negative pressure of a pump for diagnosis is introduced into the fuel tank. Concretely, negative pressure from the pump for diagnosis is applied to the back pressure chamber by providing a canister-side bypass path that communicates the vent pipe, that is at the canister side, and the back pressure chamber of the valve member. 
     In such a fuel tank system, some time is required from the application of negative pressure by the pump for diagnosis until the valve member opens, and this time affects the time required for perforation sensing. 
     SUMMARY 
     An object of an embodiment of the present invention is to provide, in a structure in which a valve member is provided at a vent pipe that communicates a fuel tank with a canister, a fuel tank system and a perforation sensing method that can shorten the time needed for perforation sensing. 
     A fuel tank system relating to a first aspect of the present invention includes: a fuel tank that can accommodate fuel at an interior thereof; a canister that, by an adsorbent, adsorbs and desorbs evaporated fuel that is generated within the fuel tank; a vent pipe that communicates the fuel tank with the canister, and that is configured to send the evaporated fuel within the fuel tank to the canister; a valve member that is provided at the vent pipe and is sectioned into a tank-side main chamber, that communicates with the vent pipe that is at a fuel tank side, a canister-side main chamber that communicates with the vent pipe that is at a canister side, and a back pressure chamber that is disposed at a side of a valve member main body which is opposite a side at which the tank-side main chamber and the canister-side main chamber are disposed; a pipe configured to open an interior of the canister to the atmosphere; a negative pressure pump that is provided at the pipe for opening to the atmosphere, and applies negative pressure through the canister and the vent pipe to the fuel tank interior; a judging means for judging absence/presence of perforation of the fuel tank from behavior of air pressure at a time when negative pressure is generated at the negative pressure pump; and a negative pressure application path that communicates the pipe with the back pressure chamber, and that is configured to apply negative pressure from the negative pressure pump to the back pressure chamber without the negative pressure going through the canister. 
     In this fuel tank system, the fuel tank and the canister are communicated by the vent pipe, and the valve member is provided at the vent pipe. The fuel tank can be sealed due to the valve member being closed. 
     When negative pressure is generated at the negative pressure pump, negative pressure is introduced, through the canister and the vent pipe, into the canister-side main chamber of the valve member. Further, negative pressure is also introduced, through the negative pressure application path, into the back pressure chamber of the valve member. 
     On the other hand, tank internal pressure is introduced into the tank-side main chamber of the valve member. Therefore, the internal pressure at the main chamber (the tank-side main chamber and the canister-side main chamber) side becomes high with respect to the internal pressure of the back pressure chamber, and the valve member main body moves, and the valve member opens. When the valve member opens, the negative pressure of the negative pressure pump can be introduced, through the vent pipe, into the fuel tank. 
     The judging means judges the absence/presence of perforation of the fuel tank, from the air pressure behavior at the time when negative pressure is generated at the negative pressure pump as described above. 
     In this fuel tank system, negative pressure from the negative pressure pump is introduced into the back pressure chamber from the negative pressure application path, that communicates the pipe for opening to the atmosphere and the back pressure chamber, and without going through the canister. As compared with a structure in which negative pressure is introduced via the canister, the speed of the decrease in the internal pressure of the back pressure chamber becomes faster by an amount corresponding to lack of air passage resistance (pressure loss) that is due to the adsorbent of the canister. Accordingly, the time from the generating of negative pressure at the negative pressure pump to the opening of the valve member is shortened, and as a result, the time required for perforation sensing can be shortened. 
     A method for sensing perforation relating to a second aspect of the present invention includes, with respect to a fuel tank system having: a fuel tank that can accommodate fuel at an interior thereof; a canister that, by an adsorbent, adsorbs and desorbs evaporated fuel that is generated within the fuel tank; a vent pipe that communicates the fuel tank with the canister, and that is configured to send the evaporated fuel within the fuel tank to the canister; a valve member that is provided at the vent pipe and is sectioned into a tank-side main chamber, that communicates with the vent pipe that is at a fuel tank side, a canister-side main chamber, that communicates with the vent pipe that is at a canister side, and a back pressure chamber, that is disposed at a side of a valve member main body which is opposite a side at which the tank-side main chamber and the canister-side main chamber are disposed; a pipe configured to open an interior of the canister to the atmosphere; a negative pressure pump that is provided at the pipe for opening to the atmosphere, and applies negative pressure through the canister and the vent pipe to the fuel tank interior; and a negative pressure application path that communicates the pipe with the back pressure chamber, and that is configured to apply negative pressure from the negative pressure pump to the back pressure chamber without the negative pressure going through the canister, the method comprising: applying negative pressure through the negative pressure application path to the back pressure chamber by causing negative pressure to be generated at the negative pressure pump; and detecting behavior of air pressure at a time when the negative pressure is generated, and judging absence of presence of perforation of the fuel tank. 
     In this perforation sensing method, negative pressure is applied to the back pressure chamber due to negative pressure being generated at the negative pressure pump. Thereupon, the valve member that is provided at the vent pipe is opened, and the negative pressure from the negative pressure pump can be applied, through the canister and the vent pipe, to the fuel tank. Then, the behavior of the air pressure at the time of generating negative pressure is detected, and the absence/presence of perforation of the fuel tank is judged. 
     In this perforation sensing method as well, negative pressure from the negative pressure pump is introduced into the back pressure chamber from the negative pressure application path, that communicates the pipe for opening to the atmosphere and the back pressure chamber, and without going through the canister. As compared with a structure in which negative pressure is introduced via the canister, the speed of the decrease in the internal pressure of the back pressure chamber becomes faster by an amount corresponding to lack of air passage resistance (pressure loss) that is due to the adsorbent of the canister. Accordingly, the time from the generating of negative pressure at the negative pressure pump to the opening of the valve member is shortened, and as a result, the time required for perforation sensing can be shortened. 
     Because an embodiment of the present invention is as described above, the time required for perforation sensing can be shortened in a structure in which a valve member is provided at a vent pipe that communicates a fuel tank and a canister. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein: 
         FIG. 1  is a schematic structural view showing the overall structure of a fuel tank system of a first embodiment; 
         FIG. 2A  is a cross-sectional view showing, partially and in an enlarged manner, the fuel tank system of the first embodiment in a state in which a diaphragm valve is closed; 
         FIG. 2B  is a cross-sectional view showing, partially and in an enlarged manner, a state in which the diaphragm valve is open; and 
         FIG. 3  is a graph showing, in the fuel tank system of the first embodiment, changes over time in pressure measured by a pressure sensor for diagnosis, after a pump for diagnosis has been operated. 
     
    
    
     DETAILED DESCRIPTION 
     A fuel tank system  12  of a first embodiment relating to the technique of the present disclosure is shown in  FIG. 1 . 
     The fuel tank system  12  has a fuel tank  14  that can accommodate fuel at the interior thereof. The lower portion of an inlet pipe  15  is connected to the upper portion of the fuel tank  14 . The opening portion at the upper end of the inlet pipe  15  is a refueling port  16 . A refueling gun is inserted into the refueling port  16 , and the fuel tank  14  can be refueled. The refueling port  16  of the inlet pipe  15  is usually closed by a fuel cap  18 , and, at times of refueling, the fuel cap  18  is removed by a refueling operator or the like. 
     A fuel lid  20  is provided at a panel of the vehicle body, further toward the outer side than the fuel cap  18 . When information that a lid release switch  22 , that is provided in the vehicle cabin or the like, has been operated is sent to a control device  32 , the fuel lid  20  is opened by the control device  32  under predetermined conditions. The control device  32  is an example of the judging means relating to the technique of the present disclosure. 
     A fuel pump  24  is provided within the fuel tank  14 . The fuel pump  24  and an engine  26  are connected by a fuel supply pipe  28 . Due to the fuel pump  24  being driven, fuel within the fuel tank  14  can be sent through the fuel supply pipe  28  to the engine  26 . 
     A tank internal pressure sensor  30  is provided at the fuel tank  14 . Information of the tank internal pressure within the fuel tank  14 , which information is sensed by the tank internal pressure sensor  30 , is sent to the control device  32 . 
     A canister  34  is provided at the exterior of the fuel tank  14 . An adsorbent such as activated carbon or the like is accommodated within the canister  34 . The vapor layer within the fuel tank  14  and the canister  34  are connected by a vent pipe  36 , and vapor within the fuel tank  14  can be made to flow into the canister  34 . The evaporated fuel within the vapor that flows-in is adsorbed by the adsorbent of the canister  34 , and vapor other than that (the atmospheric air component) is discharged into the atmosphere from a pipe  40  for opening to the atmosphere. 
     A purge pipe  38  that communicates with the engine  26  is connected to the canister  34 . Negative pressure that is generated at the time when the engine  26  operates is applied to the canister  34 , and the evaporated fuel that has been adsorbed by the adsorbent within the canister  34  can be desorbed. The evaporated fuel (vapor) that was desorbed is sent to the engine  26  and burned. At this time, atmospheric air is introduced into the canister  34  through the pipe  40  for opening to the atmosphere. 
     A pump  42  for diagnosis is provided at the pipe  40  for opening to the atmosphere. The driving of the pump  42  for diagnosis is controlled by the control device  32 . The pump  42  for diagnosis is used at the time of diagnosing trouble or the like with the fuel tank system  12 , by applying a predetermined pressure from the canister  34  through the vent pipe  36  to the fuel tank. The pump  42  for diagnosis is an example of the negative pressure pump relating to the technique of the present disclosure. 
     A full-tank restricting valve  44  is provided at the end portion at the fuel tank side of the vent pipe  36  so as to be positioned at the upper portion of the fuel tank  14  interior. 
     A diaphragm valve  46  is provided at an intermediate portion (the portion between the fuel tank  14  and the canister  34 ) of the vent pipe  36 . The diaphragm valve  46  is an example of the valve member relating to the technique of the present disclosure. Hereinafter, as needed, the portion of the vent pipe  36  that is further toward the fuel tank  14  side than this diaphragm valve  46  is called a tank-side vent pipe  36 T, and the portion of the vent pipe  36  that is further toward the canister  34  side than the diaphragm valve  46  is called a canister-side vent pipe  36 C. 
     As shown in detail in  FIG. 2A , the diaphragm valve  46  has a valve housing  48  that is shaped as a cylindrical tube and is connected to the tank-side vent pipe  36 T. One end side of the canister-side vent pipe  36 C is housed at the interior of the valve housing  48 . The one end side of the canister-side vent pipe  36 C is bent so as to become coaxial with the valve housing  48 , and this end portion is made to be a valve seat  50 . 
     The opening portion of the valve seat  50  can be closed by a valve member main body  54 . The valve member main body  54  is mounted to a diaphragm  56 . The interior of the valve housing  48  is sectioned above and below by the diaphragm  56 . Of the interior of the valve housing  48 , the space that is further toward the upper side than the diaphragm  56  in  FIG. 2A  is made to be a back pressure chamber  58 . On the other hand, the space that is further toward the lower side than the diaphragm  56  in  FIG. 2A  is made to be a main chamber  52 . Moreover, of the main chamber  52 , the portion that corresponds to the one end side of the canister-side vent pipe is made to be a canister-side main chamber  52 C, and the other portion is made to be a tank-side main chamber  52 T. 
     A compression coil spring  60  is housed in the back pressure chamber  58 . The compression coil spring  60  applies elastic force in the direction heading toward the valve seat  50  (the arrow S 1  direction) to the valve member main body  54 . Moreover, the diaphragm  56  as well applies elastic force in the arrow S 1  direction to the valve member main body  54 . Due thereto, the valve member main body  54  is urged in the direction of closing the opening portion of the valve seat  50 . The valve member main body  54  fits tightly to the valve seat  50  in a case in which, for example, the internal pressures of the canister side main chamber  52 C, the tank-side main chamber  52 T and the back pressure chamber  58  are all around the same. Due thereto, the opening portion of the valve seat  50  is closed, and movement (flowing-through) of vapor between the tank-side main chamber  52 T and the canister-side main chamber  52 C is inhibited. Namely, the diaphragm valve  46  enters into a closed state, and movement of vapor in the vent pipe  36  is inhibited. 
     In contrast, when, for example, the internal pressures of the back pressure chamber  58  and the canister-side main chamber  52 C are negative pressures that are a predetermined value or more greater than the internal pressure of the tank-side main chamber  52  (i.e., the back pressure chamber  58  and the canister-side main chamber  52 C are in states in which the internal pressures thereof are low), the valve member main body  54  moves toward the back pressure chamber  58  side against the elastic forces of the compression coil spring  60  and the diaphragm  56 , and opens the opening portion of the valve seat  50 . Due thereto, movement (flowing-through) of vapor between the tank-side main chamber  52 T and the canister-side main chamber  52 C becomes possible. Namely, the diaphragm valve  46  enters into an open state, and movement of vapor in the vent pipe  36  becomes possible. 
     A negative pressure application path  62  is provided at the pipe  40  for opening to the atmosphere so as to branch-off from the portion thereof between the pump  42  for diagnosis and the canister  34 . Further, the negative pressure application path  62  communicates with the back pressure chamber  58 . Negative pressure from the pump  42  for diagnosis can be applied through this negative pressure application path  62  to the back pressure chamber  58 . 
     A pressure sensor  64  for diagnosis is provided at the pipe  40  for opening to the atmosphere at the portion thereof between the pump  42  for diagnosis and the canister  34 . The pressure sensor  64  for diagnosis detects pressure P of this portion, and sends that information to the control device  32 . On the basis of the change in the pressure P after the pump  42  for diagnosis is operated, the control device  32  judges whether or not there is perforation of the fuel tank  14 . 
     Operation of the fuel tank system  12  of the present embodiment is described next. 
     In the fuel tank system  12  of the present embodiment, perforation sensing of the fuel tank  14  can be carried out as described hereinafter. 
     When the control device  32  operates the pump  42  for diagnosis, negative pressure is introduced through the negative pressure application path  62  into the back pressure chamber  58 . Further, negative pressure is introduced into the canister-side main chamber  52 C as well, through the canister  34  and the canister-side vent pipe  36 C. Namely, negative pressure from the pump  42  for diagnosis is introduced into both the back pressure chamber  58  and the canister-side main chamber  52 C. 
     At this time, tank internal pressure is introduced through the tank-side vent pipe  36 T into the tank-side main chamber  52 T. Therefore, of the pressure that is applied to the diaphragm  56  and the valve member main body  54 , the pressure from the main chamber side becomes higher by an amount corresponding to the tank internal pressure that is introduced into the tank-side main chamber  52 T. When the pressure from the main chamber side becomes higher, as shown in  FIG. 2B , the diaphragm  56  and the valve member main body  54  move, and the diaphragm valve  46  opens. Due thereto, negative pressure from the pump  42  for diagnosis can be introduced through the vent pipe  36  into the fuel tank  14 . 
     Here, in a case in which there is no perforation of the fuel tank  14 , the pressure P that is measured by the pressure sensor  64  for diagnosis decreases over time and reaches (falls to) a predetermined pressure, as shown by solid line L 2  of  FIG. 3 . In contrast, in a case in which there is perforation of the fuel tank  14 , the pressure P that is measured by the pressure sensor  64  for diagnosis is as solid line L 1  of  FIG. 3 . Namely, even if negative pressure is applied to the fuel tank  14 , vapor is introduced into the fuel tank  14  from the hole that has opened-up, and the pressure P does not reach (fall to) the predetermined pressure. 
     Accordingly, if the relationship between time and the pressure that is measured by the pressure sensor  64  for diagnosis is a relationship such as the solid line L 2  of  FIG. 3 , it can be judged that there is no perforation of the fuel tank  14 . On the other hand, if the relationship between time and the pressure that is measured by the pressure sensor  64  for diagnosis is a relationship such as the solid line L 1  of  FIG. 3 , it can be judged that there is perforation of the fuel tank  14 . 
     As described above, basically, perforation sensing is carried out by operating the pump  42  for diagnosis and opening the diaphragm valve  46  and applying negative pressure to the fuel tank  14 . 
     However, in a case in which the tank internal pressure is very low (e.g., is 2 KPa or more lower than atmospheric pressure), the diaphragm valve  46  does not open due to the relationship with the performance of the pump  42  for diagnosis. Namely, when the pump  42  for diagnosis is operated, negative pressure from the pump  42  for diagnosis is introduced into both the back pressure chamber  58  and the canister-side main chamber  52 C. However, because the tank internal pressure that is a very low pressure is being introduced into the tank-side main chamber, the internal pressure of the main chamber  52  does not become high, to the extent that the diaphragm valve  46  opens, with respect to the internal pressure of the back pressure chamber  58 , and the diaphragm valve  46  does not open. 
     In this case, the relationship between time and the pressure measured by the pressure sensor  64  for diagnosis becomes a relationship such as solid line L 3  of  FIG. 3 . Namely, because the diaphragm valve  46  is not opened, the volume of the space into which the negative pressure of the pump  42  for diagnosis is introduced becomes small (concretely, becomes small by an amount corresponding to the volume of the vapor layer at the tank-side vent pipe  36  and the fuel tank  14 ). Therefore, the pressure that is measured by the pressure sensor  64  for diagnosis falls rapidly over time, and reaches (falls to) the predetermined pressure earlier than the solid line L 2  (refer to the solid line L 3  of  FIG. 3 ). 
     By the way, even if there was perforation of the fuel tank  14 , atmospheric pressure would be introduced into the fuel tank  14  from that hole, and therefore, the tank negative pressure would become lower, by 2 KPa or more, than atmospheric pressure. Accordingly, if the relationship between time and the pressure measured by the sensor  64  for pressure diagnosis is a relationship such as the solid line L 3  of  FIG. 3 , it can be judged that there is no perforation of the fuel tank  14 . 
     A fuel tank system of a comparative example is considered next. In a fuel tank system of a comparative example, the negative pressure application path  62  is not provided, and instead, a canister-side bypass path that communicates the canister-side vent pipe  36 C and the back pressure chamber  58  is provided. In the fuel tank system of the comparative example as well, when the pump  42  for diagnosis is operated, negative pressure is introduced into the canister-side main chamber  52 C via the canister  34  and the canister-side vent pipe  36 C. Further, negative pressure is introduced also into the back pressure chamber  58  via the canister  34 , the canister-side vent pipe  36 C and the canister-side bypass path. Due thereto, the diaphragm valve  46  opens and negative pressure can be applied to the fuel tank  14 , except for cases in which the tank internal pressure is very low. 
     At this time, in the fuel tank system of the comparative example, at the time when negative pressure is introduced into the back pressure chamber  58 , the negative pressure is introduced via the canister  34 , and therefore, is subjected to air passage resistance due to the adsorbent that is within the canister  34 . 
     In contrast, in the fuel tank system  12  of the present embodiment, because the negative pressure application path  62  is provided, negative pressure can be introduced into the back pressure chamber  58  without going through the canister  34 . Namely, negative pressure can be introduced without being subjected to air passage resistance (pressure loss) due to the adsorbent of the canister  34 . As a result, as compared with the fuel tank system of the comparative example, the timing at which the diaphragm valve  46  opens can be made to be earlier, and negative pressure can be applied to the fuel tank  14  at an earlier stage. Accordingly, in the fuel tank system  12  of the present embodiment, the time required for perforation sensing can be shortened. 
     In the above-described embodiment, as the diaphragm valve  46 , an example is given in which the diameter of the tank-side vent pipe  36 T is enlarged and the valve housing  48  is structured, and, on the other hand, the canister-side vent pipe  36 C is accommodated in the valve housing  48 , and the end portion of the canister-side vent pipe  36 C is made to be the valve seat  50 . However, the diaphragm valve  46  is not limited to this, and the structures of the canister-side vent pipe  36 C and the tank-side vent pipe  36 T may be the opposite. 
     Further, in the above-described embodiment, an example is given in which changes in air pressure are measured and perforation is sensed by the pressure sensor  64  for diagnosis that is provided at the portion between the pump  42  for diagnosis and the canister  34 . However, the pressure sensor that is used in perforation sensing is not limited to this, and perforation sensing can be carried out by using the tank internal pressure sensor  30 . Note that, in this case, if it can be confirmed by the tank internal pressure sensor  30  that that the interior of the fuel tank  14  is a negative pressure that is less than or equal to a predetermined value, it can be judged, without operating the pump  42  for diagnosis, that there is no perforation. 
     In the above-description, the diaphragm valve  46  is given as an example of the valve member relating to the technique of the present disclosure, but the valve member is not limited to the diaphragm valve  46 . For example, there may be a structure in which the diaphragm  56  is eliminated, and the diameter of the valve member main body  54  is increased such that the outer periphery of the valve member main body  54  contacts the inner periphery of the valve housing  48 . In this structure, the valve member main body  54  alone sections the main chamber  52  and the back pressure chamber  58 , and moves to the position of closing the vent pipe  36  by contacting the valve seat  50 , and moves to the position of opening the vent pipe  36  by moving apart from the valve seat  50 . 
     All publications, patent applications, and technical standards mentioned in the present specification are incorporated by reference into the present specification to the same extent as if such individual publication, patent application, or technical standard was specifically and individually indicated to be incorporated by reference.