Abstract:
A fuel cell module has a fuel cell that supplies a drive power to a vehicle, a case that covers the fuel cell, and a current breaker that is attached to the case. The current breaker is manually operable from outside the case, and is capable of interrupting an output of the fuel cell to outside the case. The current breaker interrupts current at the time of a manual operation, thereby securing safety from high voltage of the fuel cell module during a vehicle maintenance operation and the like.

Description:
INCORPORATION BY REFERENCE 
     This is a division of application number 10/160,174 filed 4 Jun. 2002, which claims priority to Japanese Application No. 2001-175673 filed 11 Jun. 2001, the contents of which are incorporated herein by reference in their entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a fuel cell module and a fuel cell motor vehicle equipped with the fuel cell module. More particularly, the invention relates to a technology for ensuring safety at the time of maintenance of the vehicle or the like by shutting off the output of electric current from the fuel cell module. 
     2. Description of the Related Art 
     In recent years, motor vehicles employing fuel cells as a drive energy source have drawn attention, and have been produced as prototypes as an approach to solving environmental issues. An example of such motor vehicles is a fuel cell motor vehicle in which a fuel cell is installed at a site near a center of the vehicle, such as a space below a seat, taking into consideration the weight balance of the vehicle, the installation space, etc. Lately, installation of a fuel cell in a forward portion of a vehicle is considered. The development of fuel cell motor vehicles is now at a stage where near-future widespread commercialization is aimed and expected. 
     A fuel cell capable of driving a vehicle produces relatively high voltage. Therefore, during maintenance of the vehicle or the like, output of voltage from the fuel cell module, if any, is undesired in terms of safety. Furthermore, since cooling water is circulated between the fuel cell module and a radiator, and is delivered into the interior of the fuel cell, an intermediate electric potential between the potential of the positive electrode and the potential of the negative electrode of the fuel cell may occur in the cooling water. That is, due to the cooling water, the intermediate electric potential is extracted out of the fuel cell module. That is, the fuel cell has a characteristic that high voltage can occur between the cooling water and the positive electrode, and between the cooling water and the negative electrode. This characteristic of the fuel cells is not considered in the conventional safety measures against electricity leakage and the like. There is another problem of an insufficient safety measure against electricity leakage and the like in the case of breakage of a fuel cell module caused at the time of a collision of the vehicle with an object. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the invention to provide a fuel cell module and a fuel cell motor vehicle capable of ensuring safety from high voltage output of a fuel cell at the time of a maintenance operation and the like. 
     The invention provides a fuel cell module including a fuel cell that supplies a drive electric power to a vehicle, a case that covers the fuel cell, and a current breaker that is attached to the case, and that is manually operable from outside the case, and that is capable of interrupting an output of the fuel cell to outside the case. 
     In this fuel cell module, the fuel cell is covered by the case. The case may entirely enclose the fuel cell, or may partially shield the fuel cell from an outside environment, at a portion of the solid angle that faces the fuel cell. The output terminals of the fuel cell are connected to a motor, a circuit and the like that are disposed in a space outside the case, via the current breaker. The output terminals of the fuel cell and the current breaker are interconnected without wiring extending in the space outside the case. Therefore, when the current breaker is put into a disconnected state, a portion to which output voltage of the fuel cell is applied does not exist in an external space that is shielded from the fuel cell by the case, so that leakage of current from the fuel cell to the space outside the case is prevented in a good manner. 
     According to a further aspect of the invention, there is provided a fuel cell motor vehicle equipped with the above-described fuel cell module. In this fuel cell motor vehicle, the fuel cell module is installed in a forward portion of the vehicle, and the current breaker is disposed in a side surface of the fuel cell module which faces in a transverse direction of the vehicle. In a preferred fuel cell motor vehicle, the current breaker may be disposed at a position in the side surface which is toward a rear of the vehicle. 
     If a vehicle collides with an object during a run of the vehicle, it is often the case that the vehicle collides with an object present forward of the vehicle. In such a collision, a forward portion of the vehicle receives a great impact in a longitudinal direction with respect to the vehicle, so that front and rear surfaces of the fuel cell module strike adjacent portions of the vehicle, and can therefore receive great pressures. 
     In the fuel cell motor vehicle, the current breaker is disposed at a position in the side surface which is toward a rear of the vehicle. At this position, there is a relatively small possibility of the current breaker striking adjacent portions of the vehicle. Should the current breaker strike an adjacent portion of the vehicle, only a relatively weak impact will occur, so that the danger of breakage of the current breaker is small. Therefore, even after a collision, the function of the current breaker is retained, so that safety against high voltage can be secured at the time of repair or the like. In particular, if the current breaker is disposed in a side surface of the fuel cell module which is toward the rear of the vehicle, breakage of the current breaker can be avoided in the case of a collision where a forward portion of the vehicle is crushed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above mentioned embodiment and other embodiments, objects, features, advantages, technical and industrial significance of this invention will be better understood by reading the following detailed description of the preferred embodiments of the invention, when considered in connection with the accompanying drawings, in which: 
         FIG. 1  is a schematic top plan view of a forward portion of a fuel cell motor vehicle equipped with an exemplary fuel cell module in accordance with an embodiment of the invention; 
         FIG. 2  is a schematic longitudinal sectional view of a service plug in accordance with the embodiment of the invention; and 
         FIG. 3  is a simplified circuit diagram of a fuel cell module illustrating a function of the service plug in accordance with the embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In the following description and the accompanying drawings, the present invention will be described in more detail in terms of preferred embodiments. 
       FIG. 1  is a schematic top plan view of a forward portion of a fuel cell motor vehicle equipped with a fuel cell module in accordance with an embodiment of the invention. In  FIG. 1 , a fuel cell module  20  is disposed in an engine room formed in a forward portion of the vehicle. The fuel cell module  20  has a fuel cell stack  24  that is contained in a fuel cell stack case  22  (hereinafter, simply referred to as “case  22 ”). Although the case  22  tightly encloses the fuel cell stack  24  in reality, an upper surface of the case  22  is removed in  FIG. 1  to show the structure of the fuel cell stack  24  and the like provided in the case  22  for the sake of illustration. 
     The fuel cell stack  24  is formed by a first stack  26  and a second stack  28  disposed in parallel. Each of the first stack  26  and the second stack  28  is formed by stacking platy unit cells  25 . The stacks  26 ,  28  have equal numbers of unit cells, and are designed to produce equal voltages. The stacking direction of both the first stack  26  and the second stack  28  is a left-right direction with respect to the vehicle. The stacks  26 ,  28  are clamped in the stacking direction by metallic end plates  30 ,  32  disposed on the right and left side ends of the stacks. The end plates  30 ,  32  have a relatively great thickness (of, e.g., about 15 mm). The polarity of the unit cells disposed in the stack  26  is opposite to the polarity of the unit cells of the stack  28 . For example, the positive pole of the stack  26  is on the left side, and the negative pole thereof is on the right side in  FIG. 1 . In the stack  28 , the positive pole is on the right side and the negative pole thereof is on the left side. End portions of the stack  26  and the stack  28  on the end plate  32  side are electrically interconnected, so that the two stacks  26 ,  28  form a body of unit cells connected in series which produces a desired high voltage. 
     End portions of the stack  26  and the stack  28  on the end plate  30  side are provided with end electrodes  34 ,  36  of the in-series connected unit cell body formed by the stacks  26 ,  28 . For example, according to the aforementioned direction of arraying the unit cells, the electrode  34  stacked on the stack  26  is the positive pole, and the electrode  36  stacked on the stack  28  is the negative pole. The electrodes  34 ,  36  are bent in the stacking direction at a border between the stack  26  and the stack  28  (that is, a middle portion of the fuel cell stack  24  with respect to a longitudinal direction of the vehicle), and therefore have a letter-L shape. The portion of each electrode  34 ,  36  bent in the stacking direction extends through a hole formed in a central portion of the end plate  30  with respect to the vehicle longitudinal direction, and protrudes from the end plate  30  toward a side of the vehicle. The protruded portions of the electrodes  34 ,  36  are used as terminals  38 . 
     The end plates  30 ,  32  are fixed to the case  22 . The stacks  26 ,  28  undergo dimensional changes in the stacking direction due to thermal expansion and contraction and the like. Therefore, coned disc spring stacks (not shown) are disposed between the end plate  30  and the electrode  34  and between the end plate  30  and the electrode  36  so that the unit cells of the stacks  26 ,  28  are constantly pressed against each other by a suitable force. 
     The end plate  30  is provided with a relay  40 , an electric circuit and a distributor (not shown). The relay  40  is electrically connected to the positive-pole terminal  38  and the negative-pole terminal  38  via a bus bar (hereinafter, referred to as “flexible bus bar”)  42 . The flexible bus bar  42  is bolted to the relay  40  and the terminals  38 . 
     A service plug  50  is attached to a side surface toward a side to the vehicle (the end plate  30 —side surface) of the case  22 , at a position toward the rear of the vehicle. The service plug  50  is made up of a fixed part  52  fixed to the case  22 , and a plug part  54  that is provided outside the case  22  and is removable from the fixed part  52 . A terminal support  60  is provided on the end plate  30 , at a position near the service plug  50 . The terminal support  60  serves as a junction to electrically connect the relay  40  and the fixed part  52  of the service plug  50 . That is, a harness  62  connected to the fixed part  52  and a bus bar  64  connected to the relay  40  are electrically interconnected at the terminal support  60 . Thus, the relay  40  and the fixed part  52  of the service plug  50  are electrically connected separately for the positive pole and the negative pole. 
     A power output cable  66  is led from the fixed part  52  of service plug  50  to the outside of the case  22 . The power output cable  66  and the harness  62  connected to the fixed part  52  are electrically connected by the plug part  54 . 
     In the above-described construction, electric power generated by the fuel cell module  20  is output via the relay  40 , the service plug  50  and the power output cable  66 . The output can be interrupted by the relay  40  and the service plug  50 . The relay  40  electrically disconnects the connecting terminals to the flexible bus bar  42  and the connecting terminals to the bus bar  64  with respect to the positive pole and the negative pole in accordance with a control signal from an external device. For example, during a normal state, such as a run of the vehicle or the like, the relay  40  is held in an on-state to allow output from the fuel cell module  20 . In accordance with the control signal output, for example, in a case where a collision sensor (not shown) detects a collision of the vehicle, the relay  40  is switched to an off-state to interrupt output from the fuel cell module  20 . 
     The service plug  50  allows output from the fuel cell module  20  during a state where the plug part  54  is coupled to the fixed part  52 . However, when the plug part  54  is pulled off of the fixed part  52 , the power output cable  66  and the harness  62  are electrically disconnected. This disconnection is accomplished inside the case  22 , and there exists no site or portion to which an output voltage of the fuel cell stack  24  is applied. Thus, the service plug  50  serves as a current breaker that can be manually operated from outside the case  22 . For example, at the time of maintenance, safety from high voltage of the fuel cell module  20  can be ensured if a serviceperson changes the service plug  50  into the disconnected state. 
     A piping is provided between the fuel cell module  20  and a radiator (not shown) for circulation of cooling water. Cooling water, after being cooled by the radiator, flows into the fuel cell stack  24  via an inlet  70 , and passes through gap spaces formed in the fuel cell stack  24 , thereby receiving heat produced by combustion of hydrogen. Then, cooling water flows out via an outlet  72 , and is returned to the radiator. Since the cooling water contacts the electrodes of the unit cells while flowing in the fuel cell stack  24 , the cooling water is affected by the electric potentials of the electrodes, and therefore has electric potential that is between the positive potential (+V) of the electrode  34  and the negative pole (−V) of the electrode  36 . For example, if the inlet  70  and the outlet  72  are formed in the end plate  32 , the cooling water basically has an electric potential present near the end plate  32  (an approximately zero potential). 
     The service plug  50  will be further described below.  FIG. 2  is a schematic longitudinal sectional view of the service plug  50 . The fixed part  52  attached to the case  22  has four male terminals  80  that are arranged, for example, in a longitudinal line. These male terminals  80  form two pairs of terminals corresponding to the positive and negative poles. For example, male terminals  80   a ,  80   b  correspond to the positive poles. The male terminal  80   a  is connected to the harness  62 , and the male terminal  80   b  is connected to the power output cable  66 . The female terminals  80   c ,  80   d  correspond to the negative pole. The male terminal  80   c  and the male terminal  80   d  are connected to the harness  62  and the power output cable  66 , respectively. The plug part  54  has female terminals  82  that electrically connect the two pairs of male terminals  80  separately. When the plug part  54  is fitted to the fixed part  52 , the male terminals  80   a ,  80   b  are electrically connected by the female terminal  82   a , and the male terminals  80   c ,  80   d  are electrically connected by the female terminal  82   b . When the plug part  54  is pulled off from the fixed part  52  as shown in  FIG. 2 , the male terminals  80   a ,  80   b  are electrically disconnected, and the male terminals  80   c ,  80   d  are electrically disconnected. 
       FIG. 3  is a simplified circuit diagram of the fuel cell module  20  for illustrating functions of the service plug  50 . This circuit diagram shows the stacks of unit cells and the service plug  50 , but does not show other circuit elements such as the relay  40  and the like. Removing the service plug  50  from the plug part  54  simultaneously breaks the electrical connection between the positive pole of the fuel cell stack  24  and the outside of the case  22  and the electrical connection between the negative pole of the fuel cell stack  24  and the outside of the case  22 . An intermediate electric potential given to the cooling water is extracted from the fuel cell module  20  to the outside of the case  22  (as indicated by a terminal  84  in  FIG. 3 ). 
     If the service plug is designed to disconnect only one of the pole lines, for example, only the positive pole-side line, no current flows through a circuit connecting the positive side and the negative side of the power output cable  66 . In that case, however, current can flow between the negative pole and the cooling water indicated by the terminal  84 . That is, if a circuit is formed between the negative pole side of the power output cable  66  and the cooling water, there is a possibility of leakage current. Such an undesired event is prevented in the fuel cell module  20  in this embodiment because the service plug  50  disconnects the two poles. 
     To remove the service plug  50 , a serviceperson raises a handle  92  provided in an upper portion of the plug part  54  as indicated by an arrow  90  in  FIG. 2 . The plug part  54  has a built-in mechanism that moves the female terminal  82  horizontally (in a direction indicated by an arrow  94 ) in association with the rising action of the handle  92 . Since the service plug  50  is attached to a side surface of the fuel cell module  20  as described above, a serviceperson conventionally must perform actions of inserting a service person&#39;s hand to sides of the plug part  54  and then pulling the plug part  54  horizontally. However, since various devices are disposed in the engine room, it is not easy to secure a space for inserting a hand. Furthermore, the action of pulling the plug part  54  horizontally with a hand inserted from above does not easily produce a sufficient force on the plug part  54 . To eliminate these difficulties and facilitate the breakage of current, the handle  92  is provided in an upper portion of the plug part  54 , and a construction is provided such that raising the handle  92  will remove the plug part  54  from the fixed part  52 . It should be noted herein that if the serviceperson pulls the handle  92 , the female terminal  82   a  and the female terminal  82   b  are simultaneously pulled off. That is, the positive pole-side connection and the negative pole-side connection are simultaneously broken by a single action, thereby avoiding an event that one of the pole connections is left unbroken due to an operation error made by a serviceperson. 
     Although in the above-described construction, the case  22  covers the entire fuel cell stack  24 , it is also possible to provide a case that partially covers the fuel cell stack  24 . For example, the case  22  may be a case that mainly covers a portion that would be exposed to view when the engine hood is opened, that is, a case that covers an upper surface of the fuel cell stack  24  or an upper surface and side surfaces thereof, and has an opening in the bottom. 
     It is also possible to adopt a construction in which the service plug  50  is connected and disconnected in association with the opening and closing of the case  22 . Examples of the construction are a construction in which the case  22  can be opened only after the service plug  50  is put into a disconnected state, a construction in which the service plug  50  enters a disconnected state in association with an action of opening the case  22 , etc. The above-described construction achieves an improvement in the safety from high voltage generated by the fuel cell stack  24 , for example, in the case where a serviceperson opens the case  22  for maintenance of the fuel cell module  20 , or the like. 
     According to the fuel cell module of the invention, output to the outside of the fuel cell can be prevented by the current breaker that is manually operable from outside. Therefore, safety in a maintenance operation and the like can be secured. Furthermore, the simultaneous disconnection of both the positive pole and the negative pole prevents leakage current between the potential of the positive pole and the intermediate potential given to the cooling water and leakage current between the intermediate potential and the potential of the negative pole, so that safety during a service operation and the like is ensured. Still further, since the manually operable current breaker is disposed on a side surface of the case which faces in the transverse direction of the vehicle (in particular, at a rearward site on such a side surface), the possibility of breakage of the current breaker at the time of a collision is reduced, and the function of the current breaker is secured. Therefore, safety during a maintenance operation and the like after a collision is attained. 
     While the invention has been described with reference to preferred embodiments thereof, it is to be understood that the invention is not limited to the preferred embodiments or constructions. To the contrary, the invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the preferred embodiments are shown in various combinations and configurations, which are exemplary, other combinations and configurations, including more, less or only a single element, are also within the spirit and scope of the invention.