Abstract:
A fuel cell system mounted on a vehicle, includes: a fuel cell configured to cause electrochemical reaction between an anode gas and a cathode gas to proceed; and a fuel cell casing that is configured to place the fuel cell therein, wherein the fuel cell casing has a bottom face that is formed in an approximately rectangular shape, the fuel cell casing is positioned such that longitudinal sides of the approximately rectangular shape are parallel to a left-right direction of the vehicle, and the bottom face has a rib that is extended only in a front-back direction of the vehicle is provided on the bottom face.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to Japanese Patent Application No. 2014-232043 filed on Nov. 14, 2014, the entire contents of which are incorporated by reference herein. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    The present invention relates to a fuel cell system. 
         [0004]    2. Related Art 
         [0005]    It is known heretofore to use a fuel cell as a power source of a vehicle. The fuel cell includes a fuel cell stack. The fuel cell stack is made up by stacking a plurality of fuel-cell unit cells and then fixing the stack with holts or the like from their both sides. However, when a shock is applied to the fuel cell as an example, force with which the fuel-cell unit cells are fixed may temporarily lower below an internal pressure of the fuel cell stack. As a result, liquids such as a refrigerant liquid flowing a refrigerant flow path and a generated water accumulating in a reactant gas flow path may leak out of the fuel cell stack. 
         [0006]    Normally, the fuel cell stack is mounted on a vehicle as it is housed in a fuel cell casing. The fuel cell casing is sealed for purposes of heat reservation in its inside as well as for prevention of intrusions of foreign matters from its outside. Therefore, a liquid which has leaked out of the fuel cell stack may reside in the fuel cell easing and flow over an unexpected range, causing short-circuits or current leakage. 
         [0007]    In order to solve these and other problems, there is a technique, as a related art, of forming a plurality of grooves which extend longitudinally and laterally, respectively, i.e. extend in a grid-like shape, on an upper surface of a bottom face of the fuel cell, casing (e.g.,. JP 2006-221855 A). As a result of this, liquid can be accumulated in those grooves. 
       SUMMARY 
       [0008]    However, with the technique of JP 2008-221855 A, protruded portions corresponding to recessed portions in the upper surface as the grooves are formed in a lower surface of the bottom face of the fuel cell casing so as to obtain a generally constant plate thickness of the bottom face of the fuel cell casing. Since these protruded portions extend longitudinally and laterally, respectively, the vehicle, when running in flooded places, may suffer a problem that the protruded portions orthogonal to a vehicle&#39;s progressional direction is affected by pressure of water that has intruded into the vehicle, as it would he the case conventionally. Also, it has conventionally been desired that the fuel cell casing be improved in rigidity. 
       Solution to Problem 
       [0009]    The present invention, having been accomplished to solve at least part of the above-described problems, can be implemented in the following aspects. 
         [0010]    (1) In one aspect of the invention, there is provided a fuel cell system mounted on a vehicle. The fuel ceil system includes: a fuel cell configured to cause electrochemical reaction between an anode gas and a cathode gas to proceed; and a fuel cell casing that is configured to place the fuel cell therein, wherein the fuel cell casing has a bottom face that is formed in an approximately rectangular shape, the fuel cell easing is positioned such that longitudinal sides of the approximately rectangular shape are parallel to a left-right direction of the vehicle, and the bottom face has a rib that is extended only in a front-back direction of the vehicle is provided on the bottom face. According to this aspect, by virtue of the rib provided along the front-back direction of the vehicle, when the vehicle rims on an immersed path, a possibility that the fuel cell easing may be affected by pressure of water that has intruded into the vehicle can be suppressed. Also, the fuel cell easing is so positioned that longer sides of its generally rectangular shape are directed along the left-right direction of the vehicle. Therefore, by virtue of the rib extending along the shorter sides, rigidity of the fuel cell casing in the up-and-down direction can be improved, as compared with cases where the rib extends along the longer sides or where the ribs are provided in a grid-like shape. 
         [0011]    (2) In the fuel cell system of the above-described aspect, the fuel cell casing may comprise a plurality of members including a member having the bottom face, the member having: a first hole that is used to fix the member to another member of the fuel cell casing; and a second hole that is a hole other than the first hole and is used to position the member relative to the another member of the fuel cell casing. In a case where the hole to be used for the fixation and the hole to be used for the positioning are of the same hole, there is a possibility that using the hole, which has been used for the positioning, for the fixation with use of the fixing jig may be forgotten. However, according to this aspect, such a possibility can he prevented. 
         [0012]    (3) In the fuel cell system of the above-described aspect, the member having the bottom face and the another member of the fuel cell casing may be fixed to each other by a bolt with a plain washer or a holt with a conical spring washer. According to this aspect, an extent to which at least one of the member having the bottom face and the another member of the fuel cell casing is scraped off during the tightening of the holt can be reduced. 
         [0013]    The present invention may be implemented in various forms. For example, the invention can be implemented in such forms as fuel cell system manufacturing methods, computer programs for implementing such manufacturing methods, recording mediums with those computer programs recorded thereon, and the like. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0014]      FIG. 1  is an appearance view of a fuel cell system to be used in one embodiment of the present invention; 
           [0015]      FIG. 2  is an exploded perspective view showing a fuel cell casing; 
           [0016]      FIG. 3  is a view showing a lower cover; 
           [0017]      FIG. 4  is schematic views for explaining absorption of external force by ribs; 
           [0018]      FIG. 5  is an explanatory view of a method for assembling together the lower cover and a stack casing; 
           [0019]      FIG. 8  is an explanatory view of a positioning method; 
           [0020]      FIG. 7A  is a schematic view showing a fixing jig for fixing the lower cover and the stack casing; 
           [0021]      FIG. 7B  is a schematic view showing a fixing jig for fixing the lower cover and the stack casing; 
           [0022]      FIG. 8A  is an explanatory view for explaining an advantage of using a bolt with a conical spring washer; 
           [0023]      FIG. 8B  is an explanatory view for explaining an advantage of using the bolt with a conical spring washer; and 
           [0024]      FIG. 9  is a schematic view showing an example in which holes to be used for fixation and holes to be used for positioning are of the same. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
     A. Embodiment: 
       [0025]      FIG. 1  is an appearance view of a fuel cell system  10  to be used in one embodiment of the invention. The fuel cell system  10  includes a fuel cell system casing  140  and a frame  200 . The fuel cell, system  10  is mounted on a vehicle. In this embodiment, the fuel cell system  10  is provided under a vehicle interior in which a driver is to be accommodated. Referring to  FIG. 1 , an X-axis positive direction represents a forward direction of the vehicle, a Y-axis positive direction represents an upward direction of the vehicle, and a Z-axis positive direction represents a rightward direction of the vehicle. The XYZ-axes are similarly applicable also to the drawings subsequent to  FIG. 1 . 
         [0026]    The fuel cell system casing  140  includes a fuel cell casing  100  and an auxiliary machinery casing  130 . Individual members in the fuel cell system casing  140  are sealed from one another by gaskets so as to prevent foreign matters such as water and dust from intruding inside. 
         [0027]    The fuel cell produces electrochemical reaction between hydrogen gas as an anode gas and oxygen gas as a cathode gas. The fuel cell casing  100  has a fuel cell housed therein. The fuel cell is made up by stacking fuel-cell unit cells. The fuel-cell unit ceils are stacked in a left-right direction of the vehicle (Z-axis direction). 
         [0028]    The auxiliary machinery casing  130  houses therein a plurality of auxiliary machines (not. shown) to be used for the fuel cell. In this case, the plurality of auxiliary machines are exemplified by a hydrogen pump, an injector, an exhaust/drain valve, valves, sensors or the like. In addition to the auxiliary machines, piping for cooling water, wiring lines for supplying electric power to the individual auxiliary machines, and the like are also provided in the auxiliary machinery casing  130 . 
         [0029]    Surfaces of the auxiliary machinery casing  130  are covered with NV (Noise Vibration) covers  141 ,  142  to suppress outward conduction of vibrations and noise generated from the auxiliary machines (see  FIG. 1 ). In this embodiment, the NV covers  141 ,  142  each have an outer layer formed from hard resin and an inner layer formed from urethane foam. 
         [0030]    In this embodiment, a plurality of auxiliary machines are fixed to a plate-shaped manifold  120 . Also, a side face of the auxiliary machinery casing  130  on a left side (Z-axis negative direction side) of the vehicle is covered with the manifold  120 . The manifold  120  defines flow paths for hydrogen gas, oxygen gas and cooling water that cools the fuel cell. Also, the manifold  120  has a function of securing insulation from high-voltage components in the fuel cell casing  100  as well as a function of compressing fuel-cell unit cells to one another. 
         [0031]    The frame  200  is provided at an underside of the fuel cell system casing  140 . The frame  200  serves to fix the fuel cell system casing  140 , which is effectuated by inserting bolts  112 A,  112 B into bosses  111 A,  111 B, respectively, formed in the fuel cell casing  100  of the fuel cell system casing  140 . For reduction of vibrations, a rubber vibration insulator is provided between the fuel cell system casing  140  and the frame  200 . Then, the frame  200  is tightened to an unshown vehicle body. 
         [0032]      FIG. 2  is an exploded perspective view showing the fuel cell casing  100 . The fuel cell casing  100  is made up of a plurality of members. The fuel cell casing  100  includes a plate-shaped manifold  120  for covering a side face of the fuel cell, on the right side (Z-axis positive direction side) of the vehicle (see  FIG. 1 ), a stack casing  105  for covering side faces of the fuel cell other than the vehicle right-side (Z-axis positive direction-side) side face of the fuel cell as well as its top face, and a lower cover  115  for covering a bottom face of the fuel cell. The lower cover  115  is a member including a bottom face of the fuel cell casing  100 . A gasket  107  is provided between the stack casing  105  and the lower cover  115 . The gasket  107  makes it possible to prevent foreign matters such as water and dust from intruding to inside of the fuel cell casing  100 . 
         [0033]      FIG. 3  is a view showing the lower cover  115 . As can be seen from  FIG. 3 , the lower cover  115  is provided with ribs  116  extending only along a front-back direction of the vehicle (X-axis direction). That is, the ribs  116  extending only along the front-back direction of the vehicle are provided on the bottom face of the fuel cell casing  100 . In other words, surfaces between one rib  116  and another rib  116  extend along the front-back direction of the vehicle. With such an arrangement, when the vehicle runs on an immersed path, pressure that the vehicle receives from water being in contact with the bottom face of the fuel cell casing  100  can be reduced, as compared with cases where the ribs  116  extend along the left-right direction of the vehicle (Z-axis direction). 
         [0034]    Also, for example, when the vehicle runs on a bad road or when the bottom face of the vehicle body rubs against the road surface, the bottom face of the fuel cell casing  100  receives a force directed from lower toward upper side and another force directed from front toward rear side. However, by the provision of the ribs  118  extending only along the front-back direction of the vehicle, the fuel cell casing  100  can be prevented from being deformed. 
         [0035]    The lower cover  115  is formed into a generally rectangular shape. In other words, the bottom face of the fuel cell casing  100  is formed into a generally rectangular shape. It is noted here that the term ‘generally rectangular shape’ refers to a shape having one set of shorter sides and one set of longer sides, where its corners may be round or part of the sides may be curved. 
         [0036]    The fuel cell casing  100  is so positioned that, the longer sides of its generally rectangular shape are directed along the left-right direction of the vehicle (Z-axis direction). That is, the ribs  116  are provided along the shorter sides of the fuel cell casing  100 . With such an arrangement, rigidity of the fuel cell casing  100  in the up-and-down direction (Y-axis direction) can be improved, as compared, with cases where the ribs  116  are provided along the longer sides of the fuel cell casing  100 . As a result of this, the lower cover  115  can be thinned. Thus, the fuel cell system  10  can be housed in a place under the vehicle interior, which is a place having a relatively small space in the up-and-down direction (Y-axis direction). 
         [0037]    Also, the extending direction of the ribs  116  is set so as to cross the stacking direction of the fuel-cell unit cells (Z-axis direction). Thus, external force in the stacking direction toward the fuel-cell unit cells can be absorbed. 
         [0038]      FIG. 4  is schematic views for explaining absorption of external force by the ribs  116 . The topmost drawing shows a state in which no external force is applied in a horizontal direction to the ribs  118 . The middle drawing shows a state in which a tensile-direction external force is applied in the horizontal direction to the ribs  116 . In this case, the tensile-direction external force can be absorbed by the ribs  116  being elongated in the horizontal direction. The bottom drawing shows a state in which a compressional-direction external force is applied in the horizontal direction to the ribs  116 . In this case, the compressional-direction external force can be absorbed by the ribs  116  being compressed in the horizontal direction. 
         [0039]    Also, since the ribs  116  are formed so as to be protruded downward, recessed portions are formed on the top surface of the lower cover  115 . Therefore, water in the fuel cell casing  100  can be stored therein. 
         [0040]      FIG. 5  is an explanatory view of a method for assembling together the lower cover  115  and the stack casing  105 . The lower cover  115  includes first holes  117 A for use of fixation with the stack casing  105 , which is another member of the fuel cell casing  100 , and second holes  118 A which are other than the first holes  117 A and which are used for positioning relative to the stack casing  105 . The stack casing  105  includes third holes  117 B corresponding to the first holes  117 A, and fourth holes  118 B corresponding to the second holes  118 A. In this figure, holes of the lower cover  115  with no signs added thereto are the first holes  117 A, and holes of the stack casing  105  with no signs added thereto are the third holes  117 B. In addition, a groove  106  for providing the gasket  107  is formed in the stack casing  105 , and the gasket  107  (not shown in  FIG. 5 ) is preparatorily inserted into the groove  106  of the stack casing  105  before positioning. 
         [0041]    As to the assembling method, first, positioning of the lower cover  115  and the stack casing  105  is performed by using the second holes  118 A and the fourth holes  118 B. In this embodiment, a pin  300  is used, for the positioning. 
         [0042]      FIG. 6  is an explanatory view of a positioning method. First, the pin  300  is inserted into a fourth hole  118 B of the stack casing  105 . Next, with the pin  300  fixed to the stack casing  105 , the pin  300  is inserted into a second hole  118 A of the lower cover  115 . 
         [0043]    Without performing the positioning using the second hole  118 A, after the lower cover  115  is temporarily placed on the stack casing  105 , a position of the lower cover  115  relative to the stack casing  105  needs to be adjusted so as to accomplish an alignment between the positions of the first holes  117 A of the lower cover  115  and the positions of the third holes  117 B of the stack casing  105 . During the process of this adjustment, there is a possibility that the gasket  107  may be rubbed or twisted or departed from the groove. The result of this may be such that the gasket  107  is not compressed as designed, with a degraded scalability of a gap between the stack casing  105  and the lower cover  115 . 
         [0044]    However, by performing the positioning using the second hole  118 A, the possibility that the gasket  107  is rubbed or twisted or departed from the groove can be suppressed. As a result of this, such a possibility can be suppressed that the gasket  107  is not compressed as designed to lead to a degraded sealability of the gap between the stack casing  105  and the lower cover  115 . 
         [0045]    After the positioning, the first holes  117 A of the lower cover  115  and the third boles  117 B of the stack casing  105  are fixed (see  FIG. 5 ). In this embodiment, bolts are used as the fixing jig. In this process, the pins  300  are inserted into the second hole  118 A of the lower cover  115  and the fourth hole  118 B of the stack casing  105 . Therefore, unreasonable tightening due to a misalignment between the position of the first hole  117 A and the lower cover  115  and the position of the third hole  117 B of the stack casing  105  can be prevented. Thus, the working time can be shortened. 
         [0046]    After the fixation, the pins  300  are removed from the second hole  118 A of the lower cover  115  and the fourth hole  118 B of the stack casing  105 , by which the assembling is ended. 
         [0047]    In a case where the first hole  117 A to be used for the fixation and the second hole  118 A to be used, for the positioning relative to the stack casing  105  are of the same hole, there is a possibility that using the hole, which is used for the positioning, for the fixation with use of the fixing jig may be forgotten. However, setting the first hole  117 A and second hole  118 A as different holes makes it possible to prevent such an occurrence. 
         [0048]      FIG. 7A  and  FIG. 7B  are schematic views showing a fixing jig for fixing the lower cover  115  and the stack casing  105 . In this embodiment, a bolt  400  with a conical spring washer  410  attached thereto is used as the fixing jig.  FIG. 7A  is a view as the bolt  400  with the conical spring washer  410  attached is viewed from the conical spring washer  410  side.  FIG. 7B  is a view as the bolt  400  with the conical spring washer  410  attached is viewed sideways. Advantages of using the bolt  400  with the conical spring washer  410  attached will be described below. 
         [0049]      FIG. 8A  and  FIG. 8B  are explanatory views for explaining an advantage of using the bolt  400  with the conical spring washer  410  attached.  FIG. 8A  shows a case where the lower cover  115  and the stack casing  105  are fixed, by using only the bolt  400  without using the conical spring washer  410 .  FIG. 8B  shows a case where the lower cover  115  and the stack casing  105  are fixed by using the bolt  400  with the conical spring washer  410  attached. 
         [0050]    The gasket  107  is used normally as it is compressed. Therefore, the gasket  107 , if not preparatorily compressed, is protruded out of the groove  106  of the stack casing  105  (see  FIG. 8A ). When the gasket  107  is protruded out of the groove  106 , the lower cover  115  is inclined as shown in  FIG. 8A . As a result, the body of the lower cover  115  and paint applied to the lower cover  115  are scraped off by the flange of the bolt  400 , force for tightening the bolt  400  is absorbed by fractional force. Also, scraped part of the lower cover  115  may corrode. For these reasons, there arises a need for equipment to compress the gasket  107  in the process of fixing the stack casing  105  and the lower cover  115 . 
         [0051]    On the other hand, in cases where the lower cover  115  and the stack casing  105  are fixed, and have been fixed, by using the bolt  400  with the conical spring washer  410  attached, the above-described problem can be suppressed. That is, with use of the conical spring washer  410 , the lower cover  115 , even though inclined in the process of fixation, comes into contact with the conical spring washer  410  and not with the flange of the bolt  400 . As a result, since the conical spring washer  410  is a member independent of the bolt  400 , an extent to which the lower cover  115  is scraped off during the tightening of the bolt  400  can be reduced. This effect can he produced not only when the bolt with the conical spring washer attached is used but also when a bolt with a plain washer attached is used. 
         [0052]    In this embodiment, the stack casing  105  is formed from aluminum and the lower cover  115  is formed from iron. Therefore, as shown in  FIG. 8B , the stack casing  105  and the lower cover  115  differ in coefficient of thermal expansion from each other. As a result, on condition that the stack casing  105  and the lower cover  115  have been fixed for a long period, the holt  400  comes to be loosened as a consequence of its expansion and contraction due to heat. 
         [0053]    On the other hand, in cases where the lower cover  115  and the stack casing  105  are fixed, and have been fixed, by using the bolt  400  with the conical spring washer  410  attached, the above-described problem can be suppressed. That is, in the case where the stack casing  105  and the lower cover  115  have been fixed for a long time, even though the bolt  400  has come to be loosened as a consequence of its expansion and contraction due to heat, the conical spring washer  410  exerts force in the up-and-down direction, so that force for fixing the lower cover  115  and the stack casing  105  can be retained. 
       B. Modification: 
     B1. Modification 1: 
       [0054]    In the above embodiment, the pins  300  are used for positioning. However, the invention is not limited to this. Methods other than that in which pins are used to do positioning are exemplified by a method in which a jig for fixing the lower cover or the stack casing is provided with protruded portions and the protruded portions are inserted into holes of the lower cover and the stack casing to achieve the positioning. 
       B2. Modification 2: 
       [0055]    In the above embodiment, holes to be used, for fixation and holes to be used for positioning are different ones. However, the invention is not limited to this. 
         [0056]      FIG. 9  is a schematic view showing an example in which holes to be used for fixation and holes to be used for positioning are of the same. That is, a threaded pin  310 , which is retained to a hole of either the lower cover or the stack casing, is inserted into another hole of the other of the lower cover and the stack casing, by which a hole to be used for fixation can be used also as a hole to be used for positioning. 
         [0057]    The present invention is not limited to the above-described embodiment and modifications and may be fulfilled in various configurations unless those configurations depart from the gist of the invention. For example, technical features in the embodiment and modifications corresponding to technical features in the individual aspects described in the section of Summary may be replaced or combined with one another, as required, in order to solve part or entirety of the above-described problems or to achieve part or entirety of the above-described advantageous effects. Moreover, those technical features may he deleted, as required, unless herein otherwise described as indispensable.