Patent Publication Number: US-2020280080-A1

Title: Fuel cell system

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese patent application No. 2019-037111, filed on Mar. 1, 2019, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND 
     The present disclosure relates to a fuel cell system, and relates to a fuel cell system that supplies fuel gas from a plurality of fuel gas tanks to a plurality of fuel cells. 
     In recent years, a fuel cell system, which uses, as a power source, a fuel cell that generates electric power by a fuel gas and an oxidant gas being reacted with each other in an automobile or the like, has been widely used. In such a fuel cell system, a plurality of fuel gas tanks and a plurality of fuel cell stacks are coupled to each other through pipes in order to increase the amount of electric power generation in the system. Further, in such a fuel cell system, when a plurality of fuel gas tanks and a plurality of fuel cell stacks are coupled to each other through pipes, the pressures of the fuel gas tanks provided in parallel to each other are made uniform by coupling pipes for sending gas from the fuel gas tanks provided in parallel to each other. Japanese Unexamined Patent Application Publication No. 2018-14177 discloses an example of such a fuel cell system. 
     The fuel cell system disclosed in Japanese Unexamined Patent Application Publication No. 2018-14177 includes a communication path that connects fuel supply paths of adjacent fuel cell units to each other, and an opening and closing mechanism that opens and closes the communication path. Further, a path opening and closing control unit of a fuel cell system  1  is configured to control the operation of the opening and closing mechanism so that the pressure difference between the fuel tanks of the adjacent fuel cell units is reduced. Thus, it is possible to prevent the fuel gas from being excessively charged in some fuel tanks by making the respective pressures of the fuel tanks of the fuel cell units equal to each other. 
     SUMMARY 
     However, the fuel cell system disclosed in Japanese Unexamined Patent Application Publication No. 2018-14177 has a problem that when the pressure of the fuel gas tank becomes lower than the opening pressure of a pressure reducing valve, and when the consumption of the fuel gas of one fuel cell stack is higher than that of the other fuel cell stack, the possibility of occurrence of a sealing failure due to the mixing of foreign matter is increased by the fuel gas flowing backward to the pressure reducing valve provided to correspond to the one fuel cell stack of which the pressure has been reduced. 
     The present disclosure has been made to solve the above-described problem, and an object thereof is to improve the reliability of a pressure reducing valve provided in a fuel cell system. 
     A first exemplary aspect is a fuel cell system, including: first and second fuel gas tank units each configured to store a fuel gas; first and second fuel cell stacks each configured to generate electric power by the fuel gas being supplied thereto; a main stop valve provided inside each of the first and second fuel gas tank units and configured to control whether to send the fuel gas; first and second injectors each configured to adjust an amount and a timing of supply of the fuel gas to the respective first and second fuel cell stacks, the first and second injectors being provided to correspond to the first and second fuel cell stacks, respectively; a fuel supply pipe configured to constitute a flow path of the fuel gas between the main stop valves in the first and second fuel gas tank units and the first and second injectors; a pressure reducing valve provided in the fuel supply pipe and configured to adjust a pressure of the fuel gas; a high-pressure communication pipe provided so as to communicate a first flow path with a second flow path, the first and the second flow paths being the fuel supply pipes serving as flow paths for the fuel gases sent from the first and the second fuel gas tank units among the fuel supply pipes upstream of the pressure reducing valve, respectively; and a low-pressure communication pipe provided so as to communicate a third flow path with a fourth flow path, the third and the fourth flow paths being the fuel supply pipes serving as flow paths for the fuel gases supplied to the first and the second fuel cell stacks among the fuel supply pipes downstream of the pressure reducing valve, respectively. 
     With the fuel cell system according to the present disclosure, by using the low-pressure communication path provided downstream of the pressure reducing valve, it is possible to allow gas, which is generated by the backflow of the fuel gas caused by the pressure difference between the first and the second fuel cell stacks, to flow from a high-pressure fuel cell stack side to a low-pressure fuel cell stack side without using the pressure reducing valve. 
     According to the present disclosure, it is possible to improve the reliability of a pressure reducing valve provided in a fuel cell system. 
     The above and other objects, features and advantages of the present disclosure will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a configuration diagram of a fuel cell system according to a first embodiment; 
         FIG. 2  is a configuration diagram of the fuel cell system according to a comparative example; 
         FIG. 3  is a configuration diagram of the fuel cell system according to a second embodiment; 
         FIG. 4  is a diagram for explaining a problem with an operation of injectors in the fuel cell system according to the second embodiment; and 
         FIG. 5  is a diagram for explaining a method for controlling the injectors in the fuel cell system according to the second embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
     First,  FIG. 1  shows a configuration diagram of a fuel cell system  1  according to a first embodiment. As shown in  FIG. 1 , the fuel cell system  1  according to the first embodiment includes a filling port  10 , manifolds  11   a  to  11   g,  pressure sensors  12   a  and  12   b,  fuel gas tank units  13   a  to  13   e,  a pressure reducing valve  14 , a first injector (e.g., an injector  15   a ), a second injector (e.g., an injector  15   b ), a first fuel cell stack (e.g., a fuel cell stack  16   a ), and a second fuel cell stack (e.g., a fuel cell stack  16   b ). 
     The filling port  10  is a connecting port for filling the fuel tank in the fuel cell system  1  with a fuel gas from an external fuel gas tank. The manifolds  11   a  to  11   g  are pipe connecting components for joining and branching pipes in the fuel cell system  1 . The pressure sensor  12   a  detects the pressure of a fuel gas supplied from the filling port  10  to each of the fuel gas tank units  13   a  to  13   e.  Further, the pressure sensor  12   b  detects the pressure of a fuel gas sent from each of the fuel gas tank units  13   a  to  13   e.  The fuel gas tank units  13   a  to  13   e  each store a fuel gas, and each send the stored fuel gas in accordance with an instruction from the outside. Note that in the example shown in  FIG. 1 , the fuel gas tank units  13   a  and  13   b  are coupled to each other in parallel and constitute a first fuel gas tank unit, and the fuel gas tank units  13   c  to  13   e  are coupled to each other in parallel and constitute a second fuel gas tank unit. 
     It should be noted that the fuel gas tank units  13   a  to  13   e  each include a fuel gas tank  20 , a check valve  21 , and a main stop valve  22 . The fuel gas tank  20  is a tank that stores a fuel gas. The check valve  21  allows a fuel gas supplied from the filling port  10  to the fuel gas tank  20  to flow from the filling port  10  toward the fuel gas tank  20 , and prevents a backflow of the fuel gas from the fuel gas tank  20  to the filling port  10 . The main stop valve  22  performs switching to determine whether or not the fuel gas is sent from the fuel gas tank  20  to the fuel cell stacks  16   a  and  16   b.    
     The pressure reducing valve  14  reduces the pressure of the fuel gases sent from the fuel gas tank units  13   a  to  13   e  and sends them toward the fuel cell stacks  16   a  and  16   b.  In the example shown in  FIG. 1 , the pressure reducing valve  14  includes a first pressure reducing valve  14   a  and a second pressure reducing valve  14   b.  However, the number of pressure reducing valves that constitutes the pressure reducing valve  14  is determined by the relation between the allowable flow rate per one pressure reducing valve and the amount of gas that flows through the pipe in which the pressure reducing valve  14  is provided. That is, the number of pressure reducing valves included in the pressure reducing valve  14  can be one. 
     The injectors  15   a  and  15   b  are provided to correspond to the fuel cell stacks  16   a  and  16   b,  respectively, and each of these injectors adjusts the amount and timing of supply of the fuel gas to a respective one of the fuel cell stacks  16   a  and  16   b.  Each of the fuel cell stacks  16   a  and  16   b  generates electric power by the fuel gas being supplied thereto. 
     The pipes that connect components constituting the fuel cell system  1  to one another are described below with reference to  FIG. 1 . As shown in  FIG. 1 , the fuel gas filled via the filling port  10  is distributed to two branched pipes by the manifold  11   a.  One of the branched pipes is connected to the first fuel gas tank unit constituted of the fuel gas tank units  13   a  and  13   b,  and the other is connected to the second fuel gas tank unit constituted of fuel gas tank units  13   c  to  13   e.  Further, in the fuel gas tank units  13   a  and  13   b,  the pipes at the respective input sides are connected to each other by the manifold  11   b,  and the fuel gas is supplied to each of the fuel gas tank units through the manifold  11   b.  In the fuel gas tank units  13   c  to  13   e,  the pipes at the respective input sides are connected to one another by the manifold  11   c,  and the fuel gas is supplied to each of the fuel gas tank units through the manifold  11   c.    
     In the fuel gas tank units  13   a  and  13   b,  the pipes at the respective output sides are connected to each other by the manifold  11   d,  and the fuel gas is sent to each of the fuel gas tank units through the manifold  11   d.  Then, the fuel gases, which are sent through the pipes connected to the main stop valves  22  of the fuel gas tank units  13   a  and  13   b,  are joined by the manifold  11   d,  and are provided to the manifold  11   f  through one pipe. In the fuel gas tank units  13   c  to  13   e,  the pipes at the respective output sides are connected to one another by the manifold  11   e,  and the fuel gas is sent to each of the fuel gas tank units through the manifold  11   e.  Further, the fuel gases sent through the pipes connected to the main stop valves  22  of the fuel gas tank units  13   c  to  13   e  are joined by the manifold  11   e,  and are provided to the manifold  11   f  through one pipe. The manifold  11   f  joins the fuel gases sent from the fuel gas tank units  13   a  to  13   e  and sends them to the pressure reducing valve  14 . 
     It should be noted that in the fuel cell system  1  according to the first embodiment, fuel supply pipes constituting flow paths for a fuel gas are provided between the main stop valves  22  of the fuel gas tank units  13   a  to  13   e  and the injectors  15   a  and  15   b.  Further, among the fuel supply pipes upstream of the pressure reducing valve  14 , the fuel supply pipe serving as a flow path for the fuel gases sent from the fuel gas tank units  13   a  and  13   b  is defined as a first flow path L 1 . Further, among the fuel supply pipes upstream of the pressure reducing valve  14 , the fuel supply pipe serving as a flow path for the fuel gases delivered from the fuel gas tank units  13   c  to  13   e  is defined as a second flow path L 2 . Furthermore, the first flow path L 1  is connected to the second flow path L 2  by the manifold  11   f  so that the fuel gases sent through the first and the second flow paths L 1  and L 2  are sent to one pipe (e.g., a high-pressure communication pipe L 3 ). That is, the high-pressure communication pipe L 3  is provided so as to communicate the first flow path L 1  with the second flow path L 2 . 
     Further, among the fuel supply pipes downstream of the pressure reducing valve  14 , the fuel supply pipe serving as a flow path for the fuel gases supplied to the fuel cell stack  16   a  is defined as a third flow path L 5 . Further, among the fuel supply pipes downstream of the pressure reducing valve  14 , the fuel supply pipe serving as a flow path for the fuel gases supplied to the fuel cell stack  16   b  is defined as a fourth flow path L 6 . Furthermore, in the example shown in  FIG. 1 , the fuel gas sent from the pressure reducing valve  14  is sent to the manifold  11   g  through a low-pressure communication pipe L 4 , and is branched into the third and the fourth flow paths L 5  and L 6  by the manifold  11   g.  That is, in the example shown in  FIG. 1 , the third and the fourth flow paths L 5  and L 6  are provided so as to communicate with each other through the low-pressure communication pipe L 4 . 
     In other words, in the fuel cell system  1  according to the first embodiment, an outlet of the first flow path L 1  and an outlet of the second flow path L 2  are connected to each other. Further, one end of the high-pressure communication pipe L 3  is connected to the part of the first flow path L 1  to which the second flow path L 2  is connected. Further, an inlet of the third flow path L 5  and an inlet of the fourth flow path L 6  are connected to each other. Further, one end of the low-pressure communication pipe L 4  is connected to the part of the third flow path L 4  to which the fourth flow path L 5  is connected. Furthermore, in the fuel cell system  1  according to the first embodiment, the pressure reducing valve  14  is provided so as to be sandwiched between the other end of the high-pressure communication pipe L 3  and the other end of the low-pressure communication pipe L 4 . 
     The above-described fuel cell system  1  according to the first embodiment improves the reliability of the pressure reducing valve  14  by preventing a backflow to the pressure reducing valve  14 . Therefore, an effect of preventing the backflow to the pressure reducing valve  14  in the fuel cell system  1  according to the first embodiment is described with reference to a fuel cell system  100  according to a comparative example shown in  FIG. 2 . 
       FIG. 2  is a configuration diagram of the fuel cell system  100  according to the comparative example. As shown in  FIG. 2 , in the fuel cell system  100  according to the comparative example, the fuel gases sent from the fuel gas tank units  13   a  and  13   b  are sent to the first pressure reducing valve  14   a  through a first flow path L 111 . Further, the fuel gases sent from the fuel gas tank units  13   c  to  13   e  are sent to the second pressure reducing valve  14   b  through a second flow path L 112 . Further, the fuel gas of which the pressure is reduced by the first pressure reducing valve  14   a  is sent to the injector  15   a  through a third flow path L 115 . The fuel gas of which the pressure is reduced by the second pressure reducing valve  14   b  is sent to the injector  15   b  through a fourth flow path L 116 . Further, in the fuel cell system  100  according to the comparative example shown in  FIG. 2 , the first flow path L 111  is connected to the second flow path L 112  by a high-pressure communication pipe L 113 . On the other hand, in the fuel cell system  100  according to the comparative example, the third flow path L 115  and the fourth flow path L 116  are not connected and are independent from each other. 
     Further, in this fuel cell system  100  according to the comparative example, when the internal pressure of one of the fuel cell stacks  16   a  and  16   b  becomes lower than that of the other in a state where the fuel gases stored in the fuel gas tank units  13   a  to  13   e  are reduced and the pressures of the fuel gases sent from the fuel gas tank units  13   a  to  13   e  are reduced, a backflow (a flow in the direction from the fuel cell stack toward the fuel gas tank unit) of the fuel gas to the pressure reducing valve occurs. In the example shown in  FIG. 2 , the internal pressure of the fuel cell stack  16   b  is lower than that of the fuel cell stack  16   a.  Further, in the example shown in  FIG. 2 , a path, through which the fuel gas flows from the injector  15   a  provided to correspond to the fuel cell stack  16   a  toward the injector  15   b  provided to correspond to the fuel cell stack  16   b  through the high-pressure communication pipe L 13 , is generated. Further, when this flow of the fuel gas is generated, a backflow to the first pressure reducing valve  14   a  occurs. It should be noted that such a backflow to the first pressure reducing valve  14   a  may cause a failure due to foreign matter mixing in the seal of the pressure reducing valve  14 . 
     On the other hand, unlike in the fuel cell system  100  according to the comparative example, in the fuel cell system  1  according to the first embodiment shown in  FIG. 1 , a backflow to the pressure reducing valve  14  does not occur. As shown in  FIG. 1 , in the fuel cell system  1  according to the first embodiment, the flow of fuel gas is generated, when the internal pressure of the fuel cell stack  16   b  becomes lower than that of the fuel cell stack  16 a, in an area in which the low-pressure communication pipe L 4 , the third flow path L 5 , and the fourth flow path L 6  downstream of the pressure reducing valve  14  are closed. That is, in the fuel cell system  1  according to the first embodiment, a backflow of fuel gas to the pressure reducing valve  14  does not occur. 
     As described above, in the fuel cell system  1  according to the first embodiment, the high-pressure communication pipe L 3  that communicates the pipes supplying the fuel gas to the injectors to each other is provided downstream of the pressure reducing valve  14 . By doing so, in the fuel cell system  1  according to the first embodiment, even when the pressure of the fuel gas sent from the fuel gas tank unit is reduced and an internal pressure difference between different fuel cell stacks develops, it is possible to prevent a backflow of the fuel gas to the pressure reducing valve  14 . Accordingly, the lifetime of the pressure reducing valve  14  and the reliability thereof can be improved. 
     Second Embodiment 
     In a second embodiment, a fuel cell system  2  that is a modified example of the fuel cell system  1  according to the first embodiment will be described. Note that in the description of the second embodiment, the components described in the first embodiment are denoted by the same reference symbols as those in the first embodiment, and the description thereof will be omitted. 
       FIG. 3  shows a configuration diagram of the fuel cell system according to the second embodiment. As shown in  FIG. 3 , the fuel cell system  2  according to the second embodiment is different from the first embodiment in regard to the pipe connection relation of the fuel supply pipes. Specifically, in the fuel cell system  2  according to the second embodiment, the fuel gases sent from the fuel gas tank units  13   a  and  13   b  are sent to the first pressure reducing valve  14   a  through a first flow path L 11 . Further, the fuel gases sent from the fuel gas tank units  13   c  to  13   e  are sent to the second pressure reducing valve  14   b  through a second flow path L 12 . Further, the fuel gas of which the pressure is reduced by the first pressure reducing valve  14   a  is sent to the injector  15   a  through a third flow path L 15 . The fuel gas of which the pressure is reduced by the second pressure reducing valve  14   b  is sent to the injector  15   b  through a fourth flow path L 16 . Further, in the fuel cell system  2  according to the second embodiment shown in  FIG. 3 , the first flow path L 11  is connected to the second flow path L 12  by a high-pressure communication pipe L 13 . Further, in the fuel cell system  2  according to the second embodiment, the third flow path L 15  and the fourth flow path L 16  are connected to each other by a low-pressure communication pipe L 14 . 
     Note that as shown in  FIG. 2 , the first flow path L 11  is connected to the high-pressure communication pipe L 13  by a manifold  11   h.  The second flow path L 12  is connected to the high-pressure communication pipe L 13  by a manifold  11   i.  The third flow path L 15  is connected to the low-pressure communication pipe L 14  by a manifold  11   j.  The fourth flow path L 16  is connected to the low-pressure communication pipe L 14  by a manifold  11   k.    
     That is, in the fuel cell system  2  according to the second embodiment, the first pressure reducing valve  14   a  is provided at the end of the outlet side of the first flow path L 11 , and the second pressure reducing valve  14   b  is provided at the end of the outlet side of the second flow path L 12 . Further, the first flow path L 11  and the second flow path L 12  are connected to each other by the high-pressure communication pipe L 13 . Further, the third flow path L 15  is provided so as to connect the first pressure reducing valve  14   a  to the first injector  15   a,  and the fourth flow path L 16  is provided so as to connect the second pressure reducing valve  14   b  to the second injector  15   b.  Furthermore, the low-pressure communication pipe L 14  is provided so as to connect the third flow path L 15  to the fourth flow path L 16 . 
     As described above, in the fuel cell system  2  according to the second embodiment, the pipes downstream of the first and the second pressure reducing valves  14   a  and  14   b  are connected to each other by the low-pressure communication pipe L 14 . By doing so, like in the fuel cell system  1  according to the first embodiment, in the fuel cell system  2  according to the second embodiment, backflows of fuel gases to the first and the second pressure reducing valves  14   a  and  14   b  can be prevented. 
     Further, one of the features of the fuel cell system  2  according to the second embodiment is a method for operating the injectors  15   a  and  15   b.  Therefore, a problem that may occur due to the method for operating the injectors in the fuel cell system  2  will be described. 
       FIG. 4  shows a diagram for explaining a problem with an operation of the injectors in the fuel cell system according to the second embodiment. As shown in  FIG. 4 , when the injectors  15   a  and  15   b  are operated at timings different from each other in the fuel cell system  2  according to the second embodiment, both of the first and the second pressure reducing valves  14   a  and  14   b  are operated in response to operating one of the injectors. Accordingly, when the injectors  15   a  and  15   b  are operated at timings different from each other as in the example shown in  FIG. 4 , the number of operations of the first and the second pressure reducing valves  14   a  and  14   b  becomes more than the number of operations of the injectors, thereby causing a problem that the respective lifetimes of the components to be set become different from each other. 
     Therefore, in the fuel cell system  2  according to the second embodiment, when one of the injectors  15   a  and  15   b  is operated, the other injector is also simultaneously operated.  FIG. 5  shows a diagram for explaining a method for controlling the injectors in the fuel cell system according to the second embodiment. As shown in  FIG. 5 , in the fuel cell system  2  according to the second embodiment, it is possible to prevent the number of operations of the pressure reducing valves from increasing by simultaneously operating the injectors  15   a  and  15   b.    
     As described above, in the fuel cell system  2  according to the second embodiment, it is possible to prevent the number of operations of the first and the second pressure reducing valves  14   a  and  14   b  from increasing by simultaneously operating the injectors  15   a  and  15   b  when they are operated. Accordingly, in the fuel cell system  2  according to the second embodiment, it is possible to set the durability of the components or the lifetimes thereof to be uniform. 
     From the disclosure thus described, it will be obvious that the embodiments of the disclosure may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure, and all such modifications as would be obvious to one skilled in the art are intended for inclusion within the scope of the following claims.