Abstract:
A battery system having a cooling liquid that undergoes heat exchange with a battery assembly is reduced in size. The battery system in which a battery assembly is contained in a battery box is characterized by including the cooling liquid that is contained in the battery box and that undergoes heat exchange with the battery assembly, and a circulation passageway and a circulation pump that introduce a cooling gas lighter in specific gravity than the cooling liquid into the cooling liquid. The cooling gas floating up in the cooling liquid stirs the cooling liquid. This stirring action increases the flow rate of the cooling liquid, and therefore makes it possible to obtain high cooling capability even in a construction that employs a small-size circulation pump.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to an electric power supply system in which an electric power supply device is contained in a container box, and more particularly to adjustment of the temperature of the electric power supply device. 
         [0003]    2. Description of the Related Art 
         [0004]    Vehicle-driving electric power supplies (e.g., secondary batteries, or fuel cells) mounted in hybrid electric motor vehicles, electric motor vehicles, fuel cell motor vehicles, etc. need to be cooled since a battery element thereof produces a gas if a proper temperature is exceeded. 
         [0005]    As a cooling technology of this kind, a construction shown in FIG. 5 is disclosed in Japanese Patent Application Publication No. 2003-346924 (JP-A-2003-346924). In this drawing, a battery assembly 101 is contained in a box 102. This box 102 is filled with a cooling liquid. The box 102 is provided with a circulation passageway 103 that causes a cooling liquid to flow into the box 102 and that causes the cooling liquid to flow out from the box 102. 
         [0006]    The circulation passageway 103 is provided with a circulation pump 104 for forcing the cooling liquid to circulate, and with a radiator 105 for cooling the cooling liquid that flows out from the box 102. 
         [0007]    According to the foregoing construction, the cooling water whose temperature has risen due to the cooling of the battery assembly 101 can be cooled by the radiator 105, and can be sent into the box 102 again. Therefore, the battery assembly 101 can be efficiently cooled. 
         [0008]    By increasing the flow rate of the cooling liquid that flows through the box 102, the cooling rate of the battery assembly 101 can be raised. Related technologies are also disclosed in Japanese Patent Application Publication No. 11-238530 (JP-A-11-238530), Japanese Patent No. 2746751, and the Japanese Patent Application Publication No. 2006-127921 (JP-A-2006-127921). 
         [0009]    However, in order to increase the flow rate of the cooling liquid, it is necessary to heighten the pressure of the circulation pump 104, which involves the possibility of a size increase of the pump 104. 
         [0010]    In particular, in battery assemblies for vehicles, since it is necessary to juxtapose a plurality of batteries in a limited space, the intervals between adjacent batteries need to be set small. However, reduced intervals between adjacent batteries cause a decline in the flow rate of the cooling liquid that flows along battery surfaces due to pressure loss, thus giving rise to a possibility of the cooling of the battery assembly 101 becoming insufficient. Therefore, in order to heighten the cooling capability, the pressure of circulation pump 104 needs to be heightened by increasing the size thereof. 
       SUMMARY OF THE INVENTION 
       [0011]    Accordingly, it is an object of the invention to reduce the size of an electric power supply system that has a heat-exchange fluid that undergoes heat exchange with an electric power supply device. 
         [0012]    A first aspect of the invention is an electric power supply system in which an electric power supply device is contained in a container box, the system being characterized by including: a first heat-exchange fluid that is contained in the container box and that undergoes heat exchange with the electric power supply device; and an introduction device that introduces a second heat-exchange fluid lighter in specific gravity than the first heat-exchange fluid into the first heat-exchange fluid. 
         [0013]    In this aspect, the first heat-exchange fluid may be a liquid, and the second heat-exchange fluid may be a liquid or a gas. 
         [0014]    Besides, the introduction device may include a circulation passageway that returns the second heat-exchange fluid separated from the first heat-exchange fluid by a specific gravity difference into the first heat-exchange fluid. 
         [0015]    Besides, the circulation passageway may be provided with a circulation pump that forces the second heat-exchange fluid to circulate. 
         [0016]    Besides, the electric power supply system may further include a cooling device that cools the second heat-exchange fluid that is introduced into the first heat-exchange fluid via the circulation passageway. 
         [0017]    Besides, the electric power supply system may further include a heating device that heats the second heat-exchange fluid that is introduced into the first heat-exchange fluid via the circulation passageway. 
         [0018]    As a material of the second heat-exchange fluid, air, nitrogen an AT fluid or a silicon oil may be used. 
         [0019]    According to the first aspect of the invention, the first heat-exchange fluid can be caused to flow by causing the second heat-exchange fluid to move in the first heat-exchange fluid due to a specific gravity difference. Therefore, even in the case where the flow rate of the second heat-exchange fluid when it is introduced into the first heat-exchange fluid is set relatively low, decline in the cooling capability can be curved. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is a perspective view of a battery assembly; 
           [0021]      FIG. 2  is a sectional view of a battery system; 
           [0022]      FIG. 3  is a plan view of the battery system; 
           [0023]      FIG. 4  is a sectional view of a battery system in accordance with a second embodiment; and 
           [0024]      FIG. 5  is a schematic diagram of a related-art battery system. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0025]    Embodiments of the invention will be described hereinafter with reference to the drawings. A first embodiment of the invention will be described below.  FIG. 1  is a perspective view of a battery assembly  1  as an electric power supply device.  FIG. 2  is a sectional view of a cylindrical battery of a battery system taken along a direction orthogonal to a lengthwise direction thereof.  FIG. 3  is a sectional view of the cylindrical battery of the battery system taken along the lengthwise direction thereof. 
         [0026]    Firstly, an overall construction of the battery system of the first embodiment will be described. In the battery system  4  of the first embodiment, a cooling liquid (first heat-exchange fluid)  51  is contained within a battery box  3  that contains the battery assembly  1 . The battery system  4  also has a circulation passageway  21  for introducing a cooling gas (second heat-exchange fluid)  52  that is lighter in specific gravity than the cooling liquid  51  into the cooling liquid  51 , and for returning the cooling gas  52  separated from the cooling liquid  51  due to the difference in specific gravity into the cooling liquid  51  after cooling the cooling gas  52  via a cooler  22 . 
         [0027]    By causing the cooling gas  52  to float up within the cooling liquid  51 , the cooling liquid  51  can be stirred. This stirring action increases the flow rate of the cooling liquid  51  flowing along the surfaces of the cylindrical batteries  11 , and therefore can raise the cooling rate of the battery assembly  1 . 
         [0028]    Besides, since the cooling gas  52  naturally floats up in the cooling liquid  51  due to the specific gravity difference therebetween, the pressure of a circulation pump (circulation device)  23  for sending the cooling gas  52  into the cooling liquid  51  can be set low. Therefore, the circulation pump  23  can be reduced in size. 
         [0029]    Next, with reference to  FIG. 1 , the construction of the battery assembly  1  will be described in detail. The battery assembly  1  is constructed of a plurality of cylindrical batteries  11  extending between a pair of battery folders  12   a ,  12   b  that are disposed facing each other. Each cylindrical battery  11  is constructed of a lithium-ion battery. Two opposite ends of each cylindrical battery  11  are provided with positive and negative threaded shaft portions  13 ,  14 , respectively, each of which has on its outer peripheral surface a thread-grooved portion  13   a ,  14   a.    
         [0030]    In each of the battery folders  12   a ,  12   b , a plurality of insertion hole portions  121   a ,  121   b  (the insertion hole portions  121   b  are not shown) for inserting the positive and negative threaded shaft portions  13 ,  14  of the cylindrical batteries  11  are formed. In a mounted state, the positive and negative threaded shaft portions  13 ,  14  are protruded outward from the battery folder  12  through insertion hole portions  11   a ,  11   b.    
         [0031]    Adjacent cylindrical batteries  11  are disposed in opposite directions along the direction of an arrow Y (i.e., the orientations of the positive electrode and the negative electrode are set so as to oppose each other in the direction Y). Adjacent cylindrical batteries  11  are serially connected by bus bars  15 . 
         [0032]    The bus bars  15  are inserted on to the positive and negative threaded shaft portions  13 ,  14  of the cylindrical batteries  11 . Fastening nuts  16  are placed over the bus bars  15  and are fastened to the positive and negative threaded shaft portions  13 ,  14 , so that the cylindrical batteries  11  are fixed to the battery folders  12 . 
         [0033]    Next, with reference to  FIGS. 2 and 3 , the construction of the battery system  4  (the electric power supply system) will be described in detail. 
         [0034]    The battery folders  12   a ,  12   b  of the battery assembly  1  are fixed to a bottom surface of the battery box  3 , and the cylindrical batteries  11  are disposed in a direction parallel to the bottom surface of the battery box  3  (i.e., in a direction in an XY plane). 
         [0035]    The battery box  3  contains the cooling liquid  51 , in which the battery assembly  1  is submerged. Examples of the material of the cooling liquid  51  include a fluorine-based inert liquid that is high in heat conductivity and excellent in insulation characteristic. 
         [0036]    Within the battery box  3 , a space portion  3   a  is formed between a ceiling portion of the battery box  3  and the cooling liquid  51 . The circulation passageway  21 , linked to the space portion  3   a  in communication, has an extension pipe portion  21 ′ that extends between the battery assembly  1  and the bottom surface of the battery box  3 . 
         [0037]    The extension pipe portion  21 ′ is provided in a region immediately under central portions of the cylindrical batteries  11  in the lengthwise direction, and extends in the direction of the X-axis (the direction orthogonal to the lengthwise direction of the cylindrical battery  11  and parallel to the bottom surface of the battery box  3 ). 
         [0038]    Besides, the extension pipe portion  21 ′ has a plurality of coolant discharge opening portions  21 ′ a  that are aligned in the direction of the passageway. The pitch of the coolant discharge opening portions  21 ′ a  is set substantially equal to the pitch of the cylindrical batteries  11  in the direction of an arrow X (the direction of the passageway). 
         [0039]    The circulation passageway  21  is provided with the circulation pump  23  for forcing the cooling gas  52  into the extension pipe portion  21 ′, and the cooler (cooling device)  22  for cooling the cooling gas  52  that flows thereinto from the space portion  3   a.    
         [0040]    Examples of the material of the cooling gas  52  include air and nitrogen. Incidentally, the circulation passageway  21  and the circulation pump  23  constitute an introduction device described in the appended claims. 
         [0041]    Next, the cooling operation of the battery system  4  performed to cool the battery assembly  1  will be described. 
         [0042]    When the temperature of the battery assembly  1  heated due to the charging or discharging of electricity exceeds a threshold value (e.g., 60° C.), the circulation pump  23  and the cooler  22  are driven. The battery assembly  1  is provided with a temperature detection sensor. The circulation pump  23  and the cooler  22  are driven on the basis of the temperature information from the temperature detection sensor. 
         [0043]    Due to the cooling of the heated battery assembly  1 , the temperature of the cooling liquid  51  (in particular, of regions around cylindrical batteries  11 , and an upper-side region of the cooling liquid  51 ) is higher than before the circulation pump  23  is started to drive. In other words, after the circulation pump  23  is started to drive, heat transfers efficiently from the heated battery assembly  1  to the cooling liquid  51 . 
         [0044]    The cooling gas  52  sent out into the extension pipe portion  21 ′ due to the pressure action of the circulation pump  23  is discharged from the coolant discharge opening portions  21 ′ a  into the cooling liquid  51 , in the form of bubbles. 
         [0045]    Bubbles of the cooling gas  52  float up in the cooling liquid  51  due to the specific gravity difference, and reach the space portion  3   a.    
         [0046]    As the cooling gas  52  floats up in the cooling liquid  51 , heat transfers from the cooling liquid  51  to the cooling gas  52 , so that the cooling liquid  51  is cooled. Therefore, the cooling rate of the battery assembly  1  can be raised. 
         [0047]    Besides, the cooling gas  52  floating up in the cooling liquid  51  stirs the cooling liquid  51 . Therefore, the flow rate of the cooling liquid  51  flowing along the surfaces of the cylindrical batteries  11  increases, so that the cooling rate of the battery assembly  1  will be raised. 
         [0048]    Besides, since the cooling gas  52  floats up in the cooling liquid  51  due to the specific gravity difference, there is no need to heighten the pressure of the circulation pump  23  in order to cause the cooling gas  52  to float up. Therefore, the circulation pump  23  can be reduced in size. 
         [0049]    The cooling gas  52  released into the space portion  3   a  flows into the circulation passageway  21 , and is cooled by the cooling action of the cooler  22 , and then is introduced into the cooling liquid  51  again by the circulation pump  23 . 
         [0050]    Thus, in the first embodiment, an end of the circulation passageway  21  is linked to the space portion  3   a  of the battery box  3  in communication, and the other end of the circulation passageway  21  extends in a region below the battery assembly  1  within the battery box  3 , and the circulation passageway  21  can be made as a closed system. Therefore, it becomes possible to stop the entrance of an undesired substance from outside the circulation passageway  21 , and to prevent the impairment of the insulation property of the cooling liquid  51  and the cooling gas  52 . 
         [0051]    Modifications of the first embodiment will be described below. Instead of the cooling gas  52 , a cooling liquid lighter in specific gravity than the cooling liquid  51  (e.g., AT fluid or silicon oil) can be used. 
         [0052]    Furthermore, it is also permissible to employ a construction in which cool air is led into the cooling liquid  51  from a radiator that cools the battery box  3  from outside. This allows the cooler  22  to be omitted, and therefore allows a cost reduction. 
         [0053]    Furthermore, although the extension pipe portion  21 ′ is formed by one pipe, a plurality of pipes may be employed. Due to the provision of a plurality of extension pipe portions  21 ′, the cooling gas  52  can be uniformly discharged into the cooling liquid  51 . Therefore, the cooling rate of the battery assembly  1  can be further improved. 
         [0054]    Furthermore, although in the foregoing embodiment, the coolant discharge opening portions  21 ′ a  formed in the extension pipe portion  21 ′ are equally pitched, the pitch of the coolant discharge opening portions  21 ′ a  may be set in accordance with the temperature distribution in the battery assembly  1 . For example, in the case where there is a high-temperature region in the battery assembly  1  in which the temperature is higher than in other regions, the coolant discharge opening portions  21 ′ a  may be formed so that the cooling gas  52  is discharged concentratedly to the high-temperature region. 
         [0055]    Furthermore, since the cooling liquid  51  having higher temperature moves to an upper side, it is also permissible to employ a construction in which the extension pipe portion  21 ′ is disposed at a position higher than in the first embodiment, so that an upper-side portion of the cooling liquid  51  is concentratedly cooled. 
         [0056]    A second embodiment of the invention will be described. 
         [0057]    An overall construction of a battery system of the second embodiment will be described. In the battery system  5  of the second embodiment, a heat-exchange liquid (first heat-exchange fluid)  53  is contained within a battery box  3  that contains a battery assembly  1 . The battery system  5  also has a circulation passageway  21  for introducing a heat-exchange gas (second heat-exchange fluid)  54  that is lighter in specific gravity than the heat-exchange liquid  53  into the heat-exchange liquid  53 , and for returning the heat-exchange gas  54  separated from the heat-exchange liquid  53  due to the difference in specific gravity into the heat-exchange liquid  53  after cooling or heating the heat-exchange gas  54  via a cooler  22 . 
         [0058]    By causing the heated heat-exchange gas  54  to float up in the heat-exchange liquid  53 , the heat-exchange liquid  53  can be stirred. This stirring action increases the flow rate of the heat-exchange liquid  53  flowing along the surfaces of the cylindrical batteries  11 , therefore can quickly raise the temperature of the battery assembly  1  to a proper temperature if the battery assembly  1  has low temperature (e.g., −10° C.). 
         [0059]    Besides, since the heat-exchange gas  54  naturally rises in the heat-exchange liquid  53  due to the specific gravity difference therebetween, the pressure of the circulation pump  23  for sending the heat-exchange gas  54  into the heat-exchange liquid  53  can be set low. Therefore, the circulation pump  23  can be reduced in size. 
         [0060]    In the case where the cooled heat-exchange gas  54  is introduced into the heat-exchange liquid  53 , substantially the same effect as in the first embodiment can be achieved. In addition, as the heat-exchange liquid  53 , the same material as used for the cooling liquid  51  in the first embodiment can be used. 
         [0061]    Besides, as the heat-exchange gas  54 , the same material as used for the cooling gas  52  in the first embodiment may be used, and may be a liquid, for example, an AT fluid, a silicon oil, etc., that is lighter in specific gravity than a fluorine-based inert liquid. 
         [0062]    Next, with reference to  FIG. 4 , the construction of the battery system  5  of the second embodiment will be described in detail.  FIG. 4  is a sectional view of the battery system  5  of the second embodiment. The same component elements as those in the first embodiment will be suffixed with the same reference characters, and the detailed description thereof will be omitted. 
         [0063]    The circulation passageway  21  linked to a space portion  3   a  in communication is provided with the cooler (cooling device)  22 , a heater (heating device)  24  and the circulation pump  23 . The cooler  22  cools the heat-exchange gas  54  that flows in from the space portion  3   a . The heater  24  heats the heat-exchange gas  54  that flows in from the space portion  3   a.    
         [0064]    The battery assembly  1  is provided with a temperature detection sensor (not shown). The cooler  22 , the heater  24  and the circulation pump  23  are driven on the basis of the temperature information from the temperature detection sensor. Incidentally, the cooler  22 , the heater  24  and the circulation pump  23  are driven by a control circuit (not shown). 
         [0065]    Next, the cooling operation of the battery system  5  performed to cool the battery assembly  1  will be described. If the control circuit determines that the temperature of the battery assembly  1  is lower than the proper temperature (e.g., −10° C. to 60° C.) on the basis of the temperature information from the temperature detection sensor, the control circuit drives the heater  24  and the circulation pump  23 . 
         [0066]    The heat-exchange gas  54  sent out into the extension pipe portion  21 ′ due to the pressure action of the circulation pump  23  is discharged from the heat-exchange discharge opening portions  21 ′ b  into the heat-exchange liquid  53  in the form of bubbles. 
         [0067]    Bubbles of the heat-exchange gas  54  float up in the heat-exchange liquid  53  due to the specific gravity difference, and reach the space portion  3   a.    
         [0068]    As the heat-exchange gas  54  floats up in the heat-exchange liquid  53 , heat transfers from the heat-exchange gas  54  to the heat-exchange liquid  53 , so that the heat-exchange liquid  53  is heated. Therefore, the temperature of the battery assembly  1  can be quickly raised to a proper temperature. 
         [0069]    Besides, the heat-exchange gas  54  floating up in the heat-exchange liquid  53  stirs the heat-exchange liquid  53 . Therefore, the flow rate of the heat-exchange liquid  53  flowing along the surfaces of the cylindrical batteries  11  increases, so that the cooling rate of the battery assembly  1  will be raised. 
         [0070]    Besides, since the heat-exchange gas  54  floats up in the heat-exchange liquid  53  due to the specific gravity difference, there is no need to heighten the pressure of the circulation pump  23  in order to cause the heat-exchange gas  54  to float up. Therefore, the circulation pump  23  can be reduced in size. 
         [0071]    The heat-exchange gas  54  released into the space portion  3   a  flows into the circulation passageway  21 , and is heated by the heating action of the heater  24 , and then is introduced into the heat-exchange liquid  53  by the circulation pump  23  again. 
         [0072]    Thus, in the second embodiment, an end of the circulation passageway  21  is linked to the space portion  3   a  of the battery box  3  in communication, and the other end of the circulation passageway  21  extends in a region below the battery assembly  1  within the battery box  3 , and the circulation passageway  21  can be made as a closed system. Therefore, it becomes possible to stop the entrance of an undesired substance from outside the circulation passageway  21  into the heat-exchange liquid  53  and the heat-exchange gas  54 , and to prevent the impairment of the insulation property of the heat-exchange liquid  53  and the heat-exchange gas  54 . 
         [0073]    If the temperature of the battery assembly  1  is beyond the proper temperature, the cooler  22  and the circulation pump  23  are driven to quickly cool the battery assembly  1  as in the first embodiment. 
         [0074]    Although in the second embodiment, the heat-exchange gas  54  cooled by the heat-exchange liquid  53  is heated by the heater  24 , it is also permissible to employ a construction in which, for example, a portion of the exhaust gas from the vehicle or a portion of hot air jetted from the airconditioner provided in the cabin is introduced into the heat-exchange liquid  53 . This allows the heater  24  to be omitted, and therefore allows a cost reduction of the battery system  5 . 
         [0075]    Although in the foregoing first and second embodiments, the cylindrical batteries  11  are lithium-ion batteries, it is also permissible to use other types of secondary batteries (electric power supply device), capacitors (electric power supply device), and a fuel cell (electric power supply device). 
         [0076]    These electric power supply devices can be used as an electric power supply for driving a motor in, for example, in the electric motor vehicles (EV), hybrid electric motor vehicles (HEV), and fuel cell vehicles (FCV). 
         [0077]    While the invention has been described with reference to the example embodiment thereof, it is to be understood that the invention is not limited to the example embodiment and construction. To the contrary, the invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the example embodiment 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 sprit and scope of the invention.