Patent Publication Number: US-2015075623-A1

Title: Valve device, storage system for liquefied gas fuel, vehicle, and storage method for liquefied gas fuel

Description:
TECHNICAL FIELD 
     The present invention relates to a valve device which prevents liquefied gas fuel such as dimethyl ether (hereafter, referred to as DME) from leaking out when the liquefied gas fuel is used, a storage system for liquefied gas fuel including the valve device, a vehicle equipped with the storage system, and a storage method for liquefied gas fuel. 
     BACKGROUND ART 
     Recently, using liquefied gas fuel such as dimethyl ether (DME) as alternative fuel to diesel fuel used in a diesel engine is drawing attention. In a case of filling a vehicle from a filling station, since DME fuel has properties similar to LP gas and is liquefied at about 5 atm at normal temperature, there is employed a pressurized filling method in which the DME is pressurized in the filling station. 
     However, in a vehicle such as a truck which needs to carry a large amount of fuel, the filling speed is slow and the filling time is long when a differential pressure between the pressure in a fuel tank and the filling pressure of a filling facility is small in the filling by the pressurized filling method. Particularly, in high-temperature conditions such as summer, the pressure in the fuel tank is high and the filling speed becomes even slower in some cases. 
     In view of this, there is proposed a filling method called pressure balanced filling method in which a vapor phase portion of the fuel tank of the vehicle and a vapor phase portion of a storage tank of a filling station are connected to each other through piping to balance the internal pressure of the fuel tank and the internal pressure of the storage tank (see Patent Document 1 for example). 
     This pressure balanced filling method is described with reference to  FIG. 10 . A storage system  3 X configured to supply DME to an engine  2  of a vehicle  1 X includes a main tank (fuel tank)  4 , a sub tank (fuel tank)  5 , and a coupling (filling device)  6 . The coupling  6  is provided with a liquid phase filling port  6   a  and a vapor phase filling port  6   b.    
     A liquid phase line  7  extends from the liquid phase filling port  6   a  to branch in the middle, and includes a filling pipe  21  connected to a first liquid phase valve (liquid phase on-off valve)  20   a  of the main tank  4  and a second liquid phase valve  20   b  of the sub tank  5 , a supply pipe  23  extending from a first pump  22  and connected to the engine  2 , a return pipe  24  for returning excess fuel from the engine  2  to the main tank  4 , and a replenishment pipe  26  extending from a second pump  25  and connected to the main tank  4 . The filling pipe  21  and the replenishment pipe  26  are provided with check valves  27   a  and  27   b,  respectively. 
     A vapor phase line  8  extends from the vapor phase filling port  6   b  to branch in the middle and is connected to a first vapor phase valve  10 Xa of the main tank  4  and a second vapor phase valve  10 Xb of the sub tank  5 . 
     In the filling, a nozzle  33  including a liquid phase filling port  33   a  and a vapor phase filling port  33   b  which are connected to a meter  32  connected to a storage tank  31  of a filling station  30  is connected to the coupling  6  and the filling is performed with the first vapor phase valve  10 Xa, the second vapor phase valve  10 Xb, the first liquid phase valve  20   a,  and the second liquid phase valve  20   b  being opened. 
     At this time, since the liquid and vapor phases are together in the coupling  6 , vapor phase portions Ga and Gb of the main tank  4  and the sub tank  5  communicate with a vapor phase portion Gs of the storage tank  31  with the filling of the DME. This balances the pressures of the vapor phase portions Ga, Gb, and Gs, and the filling speed of the DME can be increased. 
     In the case of supplying the DME to the engine  2 , the DME is supplied to the engine  2  from the first pump  22  through the supply pipe  23 , and the excess fuel is returned from the engine  2  through the return pipe  24 . At this time, a third liquid phase valve  20   c  and a fourth liquid phase valve  20   d  which are provided respectively in the supply pipe  23  and the return pipe  24  are opened. 
     When the DME in the main tank  4  is consumed and the main tank  4  is to be replenished with the DME from the sub tank  5 , a fifth liquid phase valve  20   e  of the sub tank  5  and the first liquid phase valve  20   a  of the main tank  4  are opened, and the main tank  4  is replenished with the DME from the second pump  25  through the replenishment pipe  26 . 
     At this time, the first vapor phase valve  10 Xa and the second vapor phase valve  10 Xb are opened, and the vapor phase portion Ga of the main tank  4  and the vapor phase portion Gb of the sub tank  5  are thus made to communicate with each other with the replenishment of the DME. This balances the pressures of the vapor phase portions Ga and Gb, and the replenishment speed of the DME can be increased. 
     Meanwhile, a pipe for liquefied gas fuel such LP gas and DME needs to be provided with a device which prevents a large amount of fuel from leaking out due to fuel pipe breakage caused by accidents and the like. An on-off valve of a fuel tank thus includes an excess flow valve which blocks a flow passage when fuel or gas flows through at a specified flow rate or more. 
     Here, an example of the on-off valve including this excess flow valve is described with reference to  FIG. 11 . The first vapor phase valve  10 Xa includes a flow passage  12  in a housing  11 X. A first opening portion  13  of the flow passage  12  is a communication port with the main tank  4 , and a second opening portion  14  of the flow passage  12  is a communication port with the vapor phase line  8 . Moreover, the first vapor phase valve  10 Xa includes a main valve  15 X configured to open or block the flow passage  12  and an excess flow valve  17  configured to block the first opening portion  13 . A space between the main valve  15 X and the housing  11 X is sealed by O-rings Or. In addition, the excess flow valve  17  and a fixed shaft (isolation member)  19  are joined to each other. 
     The excess flow valve  17  has the following structure according to a relationship between a spring  18  disposed in the flow passage  12  and passing resistance of the vapor phase DME flowing through the flow passage  12 . The pressure applied to the excess flow valve  17  reaches or exceeds the set pressure of the spring  18  and the excess flow valve  17  blocks the flow passage  12  when the vapor phase DME flows at the specified flow rate or more. When the excess flow valve  17  closes upward in the drawing and blocks the first opening portion  13 , the fixed shaft  19  also moves upward. 
     Moreover, the excess flow valve  17  has the following structure. In a case of reopening the excess flow valve  17 , a handle  16  is operated to close the main valve  15 X and the main valve  15 X is moved downward. This causes the fixed shaft  19  to move downward and the excess flow valve  17  is opened. 
     However, in the pressure balanced storage system  3 X described above, when the nozzle  33  is connected to the coupling  6  in the vehicle and the filling is started, the internal pressures of the main tank  4  and the sub tank  5  are higher than the internal pressure of the storage tank  31  in some cases. In this case, the vapor phase DME in vapor phase line  8  instantly flows from the storage system  3 X to the storage tank  31 . 
     This flow of the vapor phase DME to the storage tank  31  at the start of the filling is greater than the specified flow rate and the excess flow valve  17  is closed. Accordingly, the pressures cannot be balanced and the filling speed decreases. 
     The flow rate at this time and the specified flow rate for preventing leakage due to piping accidents differ too greatly. When the specified flow rate is set to a flow rate required for travelling, the specified flow rate is smaller than the flow rate in the filling. Accordingly, the excess flow valve  17  is activated in the filling and blocks the flow passage  12 . Hence, the pressures cannot be balanced and the filling flow rate decreases. Meanwhile, when the specified flow rate is set to the flow rate in the filling, the specified flow rate is greater than the flow rate in piping accidents and the like. Accordingly, pipe leakage due to accidents in travelling cannot be prevented. 
     Providing pipes and excess flow valves for each purpose is conceivable. However, in this case, the device becomes complicated and the cost increases. 
     PRIOR ART DOCUMENT 
     Patent Document 
     Patent Document 1: Japanese patent application Kokai publication No. 2007-262903 
     SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
     The present invention has been made in view of the problems described above, and an object thereof is to provide a valve device capable of forcedly opening an excess flow valve which prevents a fluid from flowing out at a specified flow rate or more, a storage system for liquefied gas fuel including the valve device, a vehicle equipped with the storage system, and a filling method for liquefied gas fuel. 
     Means for Solving the Problem 
     A valve device of the present invention for solving the problems described above includes: a flow passage through which fluid in vapor phase flows; a main valve which blocks or opens the flow passage; and an excess flow valve which block the flow passage when the fluid in vapor phase flows from one side to opposite of the flow passage at a predetermined flow rate or more, the valve device configured to include: a pressure chamber into which the fluid in liquid phase flows; and an isolation member which maintains the excess flow valve in an open state by using pressure of the fluid in liquid phase flowing into the pressure chamber. 
     In this configuration, the pressure of the fluid in liquid phase is made to act on the isolation member by causing the fluid in liquid phase to flow into the pressure chamber when the flow passage through which the fluid in vapor phase flows is desired not to be closed. The excess flow valve can be thereby forcedly set to the open state and be prevented from blocking the flow passage. 
     The excess flow valve described herein is a device which can prevent the fluid in vapor phase from flowing from the one side to the opposite side of the flow passage at the specified flow rate or more and which allows the fluid in vapor phase to flow from the opposite side to the one side. The excess flow valve can thus prevent a large amount of fluid in vapor phase from leaking out due to piping damage and the like in a system in which the valve device is provided. 
     Moreover, the valve device described above may further include: a pressure release passage which releases the pressure in the pressure chamber from the pressure chamber to the flow passage; and a pressure release valve which blocks or opens the pressure release passage. In this case, it is possible to release the pressure in the pressure chamber to the flow passage after the excess flow valve is forcedly maintained in the open state, and the excess flow valve can thereby operate normally to block the flow passage. This can easily solve the problem of the excess flow valve not operating which occurs when the pressure remains in the pressure chamber. 
     In addition, a storage system for liquefied gas fuel of the present invention for solving the problems described above is a storage system for liquefied gas fuel including the valve device described above and is configured to include: at least one fuel tank which stores liquefied gas fuel; a vapor phase line which allows the liquefied gas fuel in vapor phase to flow between the fuel tank and a filling source via the flow passage of the valve device; a liquid phase line which delivers the liquefied gas fuel in liquid phase from the filling source to the fuel tank; and a branching pressure line which guides the liquefied gas fuel in liquid phase from the liquid phase line to the pressure chamber of the valve device when the fuel tank is being filled with the liquefied gas fuel in liquid phase from the filling source. 
     In this configuration, it is possible to guide the liquefied gas fuel in liquid phase from the branching pressure line to the pressure chamber in the valve device and forcedly open the excess flow valve when the fuel tank is being filled with the liquefied gas fuel from the filling source by using the so-called pressure balanced filling method. 
     Due to this, the flow passage is not blocked by the excess flow valve even if the internal pressure of the fuel tank is greater than the pressure of the filling source in the start of the filling or during the filling and a large amount of liquefied gas fuel in vapor phase flows from the fuel tank to the filling source. Accordingly, it is possible to prevent reduction of the filling speed and fill the fuel tank with the liquefied gas fuel in a short time. 
     Furthermore, the aforementioned storage system for liquefied gas fuel preferably includes a control device which opens the pressure release valve after the fuel tank is filled with the liquefied gas fuel in liquid phase from the filling source, until a predetermined determination condition is satisfied. 
     In addition, a vehicle for solving the problems described above is configured to be equipped with the storage system for liquefied gas fuel described above. This configuration can prevent a large amount of fuel from leaking out by the action of the excess flow valve and also prevent the excess flow valve from operating during the filling work of the fuel to improve the filling speed. 
     Moreover, a storage method for liquefied gas fuel for solving the problems described above is a storage method for liquefied gas fuel using the valve device described above, characterized in that the method comprises, while at least one fuel tank which stores liquefied gas fuel is filled with the liquefied gas fuel in liquid phase from a filling source and an internal pressure of the filling source and an internal pressure of the fuel tank are balanced by causing the liquefied gas fuel in vapor phase to flow between the fuel tank and the filling source via the flow passage of the valve device, causing the liquefied gas fuel of the liquid phase to flow into the pressure chamber of the valve device to maintain the excess flow valve in the open state with the isolation member by using pressure of the liquefied gas fuel in liquid phase flowing into the pressure chamber. 
     In this method, the liquefied gas fuel of the liquid phase is made to flow into the pressure chamber of the valve device to maintain the excess flow valve of the valve device in the open state, and the excess flow valve is thus not closed when the pressures of vapor phase portions of the liquefied gas fuel are balanced. Accordingly, the filling time of the liquefied gas fuel can be reduced in a simple method. 
     In addition, in the aforementioned storage method for liquefied gas fuel, it is preferable that the pressure release valve is opened to reduce the pressure in the pressure chamber after the fuel tank is filled with the liquefied gas fuel from the filling source, until the a predetermined determination condition is satisfied. 
     Effects of the Invention 
     In the present invention, the excess flow valve can prevent the fluid from leaking out at the specified flow rate or more, and the excess flow valve can be forcedly opened. Particularly, in the storage system for liquefied gas fuel, it is possible to suppress reduction of the filling speed and reduce the time required for filling of the liquefied gas fuel by forcedly opening the excess flow valve during the filling. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view showing a storage system for liquefied gas fuel in a first embodiment of the present invention. 
         FIG. 2  is an enlarged cross-sectional view showing a valve device in  FIG. 1  and shows a state where an excess flow valve is forcedly opened. 
         FIG. 3  is an enlarged cross-sectional view showing the valve device in  FIG. 1  and shows a state where pressure in a pressure chamber is released. 
         FIG. 4  is a flowchart showing a method of controlling a solenoid valve in a case of releasing the pressure in the pressure chamber of the valve device shown in  FIG. 3 . 
         FIG. 5  is an enlarged cross-sectional view showing the valve device in  FIG. 1  and shows a state where the excess flow valve is closed. 
         FIG. 6  is an enlarged cross-sectional view showing the valve device in  FIG. 1  and shows a state where a main valve is closed. 
         FIG. 7  shows a state where tanks are filled with liquefied gas fuel from an external storage tank of the storage system for liquefied gas fuel in the first embodiment of the present invention. 
         FIG. 8  shows a state where one fuel tank is replenished with the liquefied gas fuel from another fuel tank in the storage system for liquefied gas fuel in the first embodiment of the present invention. 
         FIG. 9  is a schematic view showing a storage system for liquefied gas fuel in a second embodiment of the present invention. 
         FIG. 10  is a schematic view showing a conventional storage system for liquefied gas fuel. 
         FIG. 11  is an enlarged cross-sectional view showing a valve device in  FIG. 10 . 
     
    
    
     MODES FOR CARRYING OUT THE INVENTION 
     A valve device of an embodiment of the present invention, a storage system for liquefied gas fuel including the valve device, a vehicle equipped with the storage system, and a method of controlling the storage system are described below with reference to the drawings. In the embodiment, description is given of a vehicle using dimethyl ether (hereafter, referred to as DME) as the liquefied gas fuel. However, the present invention can be applied to a case of using, for example, liquefied petroleum gas (LPG), liquefied natural gas (LNG), liquefied butane gas (LBG), liquefied hydrogen fuel, or the like. 
     First, a vehicle equipped with a storage system for liquefied gas fuel in a first embodiment of the present invention is described with reference to  FIG. 1 . As shown in  FIG. 1 , this storage system  3  includes a first vapor phase valve (valve device)  10   a  and a second vapor phase valve (valve device)  10   b  instead of the first vapor phase valve  10 Xa and the second vapor phase valve  10 Xb of the conventional storage system  3 X in  FIG. 10 . Moreover, the storage system  3  includes a first branching pressure line  28   a  configured to guide liquid phase DME from a filling pipe  21  to the first vapor phase valve  10   a  and a second branching pressure line  28   b  configured to guide the Liquid phase DME from the filling pipe  21  to the second vapor phase valve  10   b.    
     As shown in  FIG. 2 , the first vapor phase valve  10   a  (since the second vapor phase valve  10   b  has the same configuration, description thereof omitted) includes a pressure chamber  40 , a pressure opening portion  41 , a pressure release passage  42 , and a solenoid valve (pressure release valve)  43 , in addition to the configuration of the conventional first vapor phase valve  10 Xa in  FIG. 11 . 
     The first vapor phase valve  10   a  in the first embodiment of the present invention is provided in a storage system  3  including: a liquid phase line  7  which delivers the liquid phase DME; and a vapor phase line  8  through which vapor phase portions Ga, Gb, and Gs respectively of tanks  4  and  5  and a storage tank  31  communicate with each other, the storage system  3  being a so-called pressure balanced type in which the pressures of the vapor phase portions Ga, Gb, and Gs are balanced in the filling of the DME. The first vapor phase valve  10   a  has the following configuration. 
     The first vapor phase valve  10   a  includes a flow passage  12  through which the vapor phase portion Ga of the main tank  4  and the vapor phase line  8  communicates with each other and through which vapor phase DME flows and a main valve  15  which blocks or opens the flow passage  12 , as well as an excess flow valve  17  which blocks the flow passage  12  when the vapor phase DME flows from a first opening portion  13  to a second opening portion  14  of the flow passage  12  at a specified flow rate or more. In addition to this configuration, the first vapor phase valve  10   a  includes the pressure chamber  40  which communicates with the first branching pressure line  28   a  branching from the liquid phase line  7  and into which the liquid phase DME flows and a fixed shaft (isolation member)  19  which maintains the excess flow valve  17  in an open state by using the pressure of the liquid phase DME flowing into the pressure chamber  40 . 
     The pressure chamber  40  is provided in the main valve  15 , on the axis of the fixed shaft (isolation member)  19  connected to the excess flow valve  17 . The fixed shaft  19  operates in an up-down direction in the drawing, and one end of the fixed shaft  19  is joined to the excess flow valve  17  while the other end is disposed in pressure chamber  40  in such a way that the pressure in the pressure chamber  40  acts on the other end. 
     Due to this configuration, when the liquid phase DME flows through the filling pipe  21  in filling with the liquid phase DME from the storage tank  31  or replenishment with the liquid phase DME from the sub tank  5 , the liquid phase DME flows into the pressure chamber  40  from the first branching pressure line  28   a.  The pressure of the liquid phase DME in the pressure chamber  40  thus acts on the fixed shaft  19  and force in a downward direction in the drawing can be applied to the fixed shaft  19 . 
     Since the fixed shaft  19  is pushed by the pressure, the excess flow valve  17  is not activated and the open state can be maintained even when the vapor phase DME flows at the specified flow rate or more at which the excess flow valve  17  is to be closed. 
     The pressure release passage  42  is a flow passage through which the pressure chamber  40  and the flow passage  12  communicate with each other, specifically, is a flow passage through which the pressure chamber  40  and the vapor phase line  8  communicate with each other via a gap between O-rings Or between the main valve  15  and a housing  11 . Moreover, the solenoid valve  43  is provided in the middle of the pressure release passage  42 . The solenoid valve  43  is formed of a plunger  44  and an electromagnet  45 . The solenoid valve  43  is normally closed and is opened to open the pressure release passage  42  by an ECU (control device)  9  when the power is ON. 
     Due to this configuration, when pressure is built up in the pressure chamber  40 , it is possible to release the pressure in the pressure chamber  40  by opening the solenoid valve  43  and shift the state of the excess flow valve  17  from the open state to the activated state. 
     Next, operations of the first vapor phase valve  10   a  are described with reference to  FIGS. 2 to 6 . Here, the outlined arrows in the drawing show the flow of vapor phase DME, the solid arrows show an operation of the fixed shaft  19 , and the dotted arrow shows the flow of liquid phase DME. 
     As shown in  FIG. 2 , in the case where the main tank  4  is filled with the DME from the storage tank  31  or is replenished with the DME from the sub tank  5 , the liquid phase DME flows into the pressure chamber  40  from the liquid phase line  7  through the first branching pressure line  28   a.  Since the pressure of the liquid phase DME flowing into the pressure chamber  40  acts on the fixed shaft  19 , the excess flow valve  17  can be maintained in the open state. 
     Due to this, the excess flow valve  17  is not closed in the filling or replenishment of the DME. Accordingly, it is possible to increase the filling or replenishment speed and reduce the filling or replenishment time. 
     As shown in  FIG. 3 , after the main tank  4  is filled with the DME from the storage tank  31  or is replenished with the DME from the sub tank  5 , the solenoid valve  43  is activated to open the pressure release passage  42  and cause the pressure chamber  40  and the vapor phase line  8  to communicate with each other. The pressure in the pressure chamber  40  can be thus released to the vapor phase line  8 . 
     At this time, the pressure in the pressure chamber  40  is greater than the pressure in vapor phase line  8 . Accordingly, when the pressure chamber  40  and the vapor phase line  8  communicate with each other, the liquid phase DME turns into the vapor phase DME due to this pressure difference, and the pressure is released from the pressure chamber  40  to the vapor phase line  8 . This can suppress a case where the excess flow valve  17  does not operate while the vehicle is travelling which occurs when the pressure remains in the pressure chamber  40 . 
     An example of the control of the solenoid valve  43  is described with reference to the flowchart shown in  FIG. 4 . Step S 1  is performed in which an engine key is set to ON (hereafter, referred to as key ON) at the start of an engine  2 . Next, step S 2  is performed in which the ECU  9  determines whether the tank  4  has been filled or replenished with the DME. When the ECU  9  determines in step S 2  that the tank has been filled or replenished with the DME, step S 3  is performed in which the ECU  9  causes an electric current to flow to the solenoid valve  43  and opens the solenoid valve  43 . When step S 3  is performed, the solenoid valve  43  is opened and the pressure in the pressure chamber  40  is released to the vapor phase line  8 . 
     Next, step S 4  is performed in which the ECU  9  determines whether to maintain the open state of the solenoid valve  43 . In step S 4 , the ECU  9  determines whether to maintain the open state of the solenoid valve  43  by determining whether a predetermined determination condition is satisfied. The predetermined determination condition is satisfied when the pressure in the pressure chamber  40  falls to such a level that the excess flow valve  17  can block the flow passage  12  if the vapor phase DME flows through the flow passage  12  at the specific flow rate or more. 
     For example, there is used a method in which elapse of a predetermined power-on time is used as the condition and the ECU  9  determines to close the solenoid valve  43  after the elapse of the predetermined power-on time. To be more specific, there is used a method in which, after three to five seconds elapses from the key ON, the ECU  9  determines that the pressure in the pressure chamber  40  is sufficiently released and the solenoid valve  43  is to be closed. Alternatively, there is used a method in which the ECU  9  determines to close the solenoid valve  43  when the pressure in the pipe of the liquid phase line  7  becomes equal to the pressure in the main tank  4 . 
     When the ECU  9  determines in step S 4  not to maintain the open state of the solenoid valve  43 , i.e. to close the solenoid valve  43 , the step S 5  is performed next in which the ECU  9  cuts the supply of electric current to the solenoid valve  43  to close the solenoid valve  43 , and this control method is terminated. 
     In this control method, since the pressure built up in the pressure chamber  40  can be released in the key ON, the excess flow valve  17  can be made to operate while the vehicle is travelling. Hence, if a large amount of vapor phase DME flows, it is possible to block the flow passage  12  and prevent leakage of the DME. 
     In this control method of the solenoid valve  43 , it is only necessary to reduce the pressure in the pressure chamber  40  and allow the excess flow valve  17  to operate. For example, the control method may be such that step S 2  is omitted and the solenoid valve  43  is turned on simultaneously with the key ON. Moreover, in step S 4 , it is only necessary to determine whether the pressure in the pressure chamber  40  is sufficiently reduced, specifically, is reduced to such a pressure that the excess flow valve  17  can operate, and step S 4  is not limited to the methods described above. 
     In addition, although the key ON is used as a trigger for activating the solenoid valve  43 , the solenoid valve  43  may be configured to be activated when the pressure in the pressure chamber  40  is high. In this case, the pressure in the pressure chamber  40  can be released while the vehicle is travelling, for example, after the main tank  4  is replenished with the DME from the sub tank  5  while the vehicle is travelling. 
     When the pressure is released from the pressure chamber  40 , as shown in  FIG. 5 , the operation of the excess flow valve  17  is made possible. In cases other than the case where the main tank  4  is filled with the DME from the storage tank  31  or is replenished with the DME from the sub tank  5 , there is no flow of the liquid phase DME in liquid phase line  7 . Accordingly, no liquid phase DME flows into the pressure chamber  40  through the first branching pressure line  28   a,  and the pressure in the pressure chamber  40  thus does not increase. Hence, if the vapor phase DME flows at the specified flow rate or more, the excess flow valve  17  is closed and blocks the flow passage  12 . This can prevent a case where a large amount of DME leaks out due to piping damage or the like. 
     As shown in  FIG. 6 , when the excess flow valve  17  is closed and the storage system  3  needs a repair or when maintenance of the vehicle  1  is to be performed, a handle  16  is turned to cause the main valve  15  to operate and thereby block the flow passage  12 . At this time, the fixed shaft  19  is pushed by the main valve  15  and sets the excess flow valve  17  to the open state. Even when the excess flow valve  17  is set to the open state, the vapor phase DME does not flow because the main valve  15  blocks the flow passage  12 . 
     Due to this, it is possible to return the excess flow valve  17  to its normal position and also prevent a case where the vapor phase DME flows in the maintenance of the vehicle and the like. 
     Note that the present invention can be used for a valve device including a conventional excess flow valve. For example, the present invention can be applied to an on-off valve in which the excess flow valve  17  is internally disposed. Moreover, the embodiment is described by giving an example in which the first vapor phase valve  10   a  is configured such that the main valve  15  is closed by manually rotating the handle  16 . However, the main valve  15  may be configured to be opened and closed by, for example, a solenoid valve. 
     In addition, in the embodiment, first to fifth liquid phase valves  20   a  to  20   e  each have a structure which includes no excess flow valve  17  of the conventional first vapor phase valve  10 Xa shown in  FIG. 11 . However, the present invention is not limited to this and the first to fifth liquid phase valves  20   a  to  20   e  may be any valve devices which are openable and closable. 
     Next, operations of the storage system  3  including the aforementioned first vapor phase valve  10   a  are described with reference to  FIGS. 7 and 8 . Here, the outlined arrows show the flow of the vapor phase DME and the solid arrows show the flow of the liquid phase DME. 
     In a case where the main tank  4  is to be filled with the DME from the storage tank  31 , a nozzle  33  is first connected to a coupling  6  as shown in  FIG. 7 . The coupling  6  is configured such that a flow passage is opened when the nozzle  33  is connected and the flow passage is blocked when the nozzle  33  is not connected. Moreover, the coupling  6  is configured such that the liquid phase line  7  and the vapor phase line  8  are simultaneously connected to a filling station  30  when the nozzle  33  is connected. 
     Each of the valves  10   a,    10   b,  and  20   a  to  20   e  is normally opened except for the case where the excess flow valve  17  is closed and the storage system  3  needs to be repaired and the case where the maintenance of the vehicle is to be performed. When the coupling  6  and the nozzle  33  are connected to each other, the vapor phase portions Ga, Gb, and Gs communicate with each other through the first vapor phase valve  10   a  of the main tank  4  and the second vapor phase valve  10   b  of the sub tank  5 . Moreover, liquid phase portions Fa, Fb, and Fs communicate with each other through the first liquid phase valve  20   a  of the main tank  4  and the second liquid phase valve  20   b  of the sub tank  5 . 
     When the liquid phase DME is pressurized by a not-illustrated pump and the filling of the main tank  4  and the sub tank  5  from the filling station  30  is started, the main tank  4  and the sub tank  5  are filled with the liquid phase DME supplied through the liquid phase line  7 . At this time, the pressures of the vapor phase portions Ga, Gb, and Gs are balanced by the vapor phase line  8 . 
     At this time, the filling pressure is applied to the pressure chamber  40  of the first vapor phase valve  10   a  from the first branching pressure line  28   a  and to the pressure chamber  40  of the second vapor phase valve  10   b  from the second branching pressure line  28   b.  Then, as described in  FIG. 2 , the excess flow valve  17  of the first vapor phase valve  10   a  and the excess flow valve  17  of the second vapor phase valve  10   b  are fixed to the open state. 
     Fixing the excess flow valves  17  to the open state while the tanks  4  and  5  are filled with the DME from the filling station  30  can prevent the case where the excess flow valves  17  are closed during the filling of the DME, thereby causing reduction of the filling flow rate and reduction of the filling speed of the DME, which is the problem in the conventional technique, and reduce the filling time of the DME. 
     When the key is set to ON to start the vehicle after the filling of the DME from the filling station  30  is completed, the solenoid valves  43  are activated as described in  FIG. 3  to release the pressure built up in the pressure chambers  40  of the first vapor phase valve  10   a  and the second vapor phase valve  10   b  during the filling of the DME, and the excess flow valves  17  are set to an operable state. 
     As shown in  FIG. 8 , the DME is supplied from the main tank  4  to the engine  2  by a first pump  22  while the vehicle is travelling. At this time, excess fuel is returned from the engine  2  to the main tank  4 . 
     When the DME in the main tank  4  is consumed, a second pump  25  replenishes the main tank  4  with the DME from the sub tank  5 . At this time, since the first vapor phase valve  10   a  and the second vapor phase valve  10   b  are opened, the internal pressures of the main tank  4  and the sub tank  5  are balanced, i.e. the pressures of the vapor phase portions Ga and Gb are balanced. 
     At this time, as described above, the filling pressure is applied to the pressure chamber  40  of the first vapor phase valve  10   a  from the first branching pressure line  28   a,  and the excess flow valve  17  of the first vapor phase valve  10   a  is maintained in the open state. Meanwhile, in the second vapor phase valve  10   b,  the vapor phase DME flows from the vapor phase line  8  to the sub tank  5 , i.e. from the second opening portion  14  to the first opening portion  13 . Accordingly, the excess flow valve  17  is not closed. 
     Due to this, also in the case where the main tank  4  is replenished with the DME from the sub tank  5 , the main tank  4  can be replenished with the DME from the sub tank  5  without reduction of the replenishment speed. Moreover, in the case where the main tank  4  is replenished with the DME from the sub tank  5 , it is preferable to open the solenoid valve  43  of the first vapor phase valve  10   a  after the replenishment to release the pressure in the pressure chamber  40  of the first vapor phase valve  10   a.    
     According to the operation described above, in the filling with the DME from the storage tank  31  or the replenishment with the DME from the sub tank  5 , the excess flow valve  17  of the tank (in the case of filling, the main tank  4  and the sub tank  5 , in the case of replenishment, the main tank  4 ) which is filled or replenished with the DME receives the filling pressure and is forcedly opened. Accordingly, even when the internal pressure of the tank becomes greater than the pressure of the supply side during the filling, the flow passage  12  is not blocked by the excess flow valve  17 . Hence, it is possible to avoid reduction of the filling speed or the replenishment speed and reduce the filling time or the replenishment time. 
     Moreover, since the operations and effects described above can be obtained in a simple configuration by a simple method, problems occurring in the case where the DME is used as fuel of a vehicle can be solved at a low cost. 
     In addition, since the solenoid valve  43  is configured to be turned on with the key ON after the filling or replenishment of the DME is completed and to be turned off after the pressure in the pressure chamber  40  is released, the excess flow valve  17  can be operate normally after the filling or replenishment of the DME is completed. Hence, it is possible to prevent a case where a large amount of DME leaks out due to piping breakage. 
     Next, a storage system for liquefied gas fuel in a second embodiment of the present invention is described with reference to  FIG. 9 . This storage system  50  has a configuration including only the main tank  4  of the storage system  3  in the first embodiment, and includes a fuel tank  51 , a coupling  52 , a liquid phase line  53 , and a vapor phase line  54 . Moreover, the storage system  50  includes, in the fuel tank  51 , liquid phase valves  55   a  to  55   c  and a third vapor phase valve  10   c  having the same configuration as the first vapor phase valve  10   a  described above. Furthermore, the storage system  50  includes a third branching pressure line  56  which branches from the liquid phase line  53  to extend to the third vapor phase valve  10   c.  The storage system  50  operates in the same way as the aforementioned storage system  3 , except that replenishment cannot be performed while the vehicle is travelling. 
     The vehicle  1  equipped with the storage system  3  or  50  for liquefied gas fuel in the first or second embodiment of the present invention can prevent a large amount of DME from leaking out by the action of the excess flow valve  17  and also prevent the excess flow valve  17  from operating during the filling work of the DME to improve the filling speed. The storage system  3  or  50  is particularly preferably applied to a case of filling a large-capacity fuel tank provided in a large truck capable of travelling for a long distance. 
     INDUSTRIAL APPLICABILITY 
     In the valve device of the present invention, the excess flow valve can prevent fluid from leaking out at a specified flow rate or more, and the excess flow valve can be forcedly opened when the action thereof is not required. Particularly, in the storage system for liquefied gas fuel, it is possible to suppress reduction of the filling speed and reduce the time required for filling of the liquefied gas fuel by forcedly opening the excess flow valve during the filling. The present invention can be thus utilized in a vehicle equipped with an engine using liquefied gas fuel such as DME. 
     EXPLANATION OF REFERENCE NUMERALS 
     
         
           1  Vehicle 
           2  Engine (internal combustion engine) 
           3  Storage system 
           4  Main tank (fuel tank) 
           5  Sub tank (fuel tank or filling source) 
           6  Coupling (filling port) 
           7  Liquid phase line 
           8  Vapor phase line 
           9  ECU (control device) 
           10   a  First vapor phase valve (valve device) 
           10   b  Second vapor phase valve (valve device) 
           11  Housing 
           12  Flow passage 
           13  First opening portion 
           14  Second opening portion 
           15  Main valve 
           16  Handle 
           17  Excess flow valve 
           18  Spring (biasing member) 
           19  Fixed shaft (isolation member) 
           20   a  to  20   e  First liquid phase valve to fifth liquid phase valve 
           21  Filling pipe 
           22  First pump 
           23  Supply pipe 
           24  Return pipe 
           25  Second pump 
           26  Replenishment pipe 
           27   a,    27   b  Check valve 
           28   a  First branching pressure line 
           28   b  Second branching pressure line 
           30  Filling station 
           31  Storage tank (filling source) 
           32  Meter 
           33  Nozzle 
           40  Pressure chamber 
           41  Pressure opening portion 
           42  Pressure release passage 
           43  Solenoid valve (pressure release valve)