Patent Publication Number: US-2023163409-A1

Title: Fire extinguishing system for battery of vehicle

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims priority to Korean Patent Application No. 10-2021-0161827, filed Nov. 23, 2021, the entire contents of which is incorporated herein for all purposes by this reference. 
     BACKGROUND OF THE PRESENT DISCLOSURE 
     Field of the Present Disclosure 
     The present disclosure relates to a fire extinguishing system for a battery of a vehicle, and more particularly, to a fire extinguishing system for a battery of a vehicle, the fire extinguishing system being able to rapidly and accurately detect a fire generated in a battery pack and to effectively suppress the fire immediately after detecting. 
     Description of Related Art 
     Recently, as the interest in energy efficiency and problems with environment contamination and exhaustion of fossil fuels is increased, eco-friendly vehicles that can substantially replace the vehicle with an internal combustion engine have been developed. 
     As eco-friendly vehicles, a Battery Electric Vehicle (BEV) using a battery as a power source, a Fuel Cell Electric Vehicle (FCEV) using a fuel battery as a main power source, a Hybrid Electric Vehicle (HEV) using both an engine and a motor as a power source for driving a vehicle, etc. may be exemplified. 
     Such eco-friendly vehicles (xEVs) all have something in common in that they are all driven by driving a motor using power accumulated in a battery. Such an electric vehicle is mounted with a high-voltage pack that supplies power to a motor and the high-voltage battery pack supplies power to the electric parts in the vehicle such as the motor while being repeatedly charged and discharged while the vehicle is driven. 
     The battery pack of electric vehicles generally includes a battery case, a battery module disposed in the battery case, and a Battery Management System (BMS) that collects information such as the voltage, current, and temperature of cells forming the battery module and is configured to control operation of the cells. Furthermore, the battery pack includes a configuration that prevents a fire by cutting a fuse or disconnecting a relay connected to an inverter when a short circuit is generated or an overcurrent flows in the battery pack. 
     A fire may occur in the battery pack in an electric vehicle due to various reasons such a collision and malfunction of parts while the electric vehicle is driven. If a fire of the battery pack is not suppressed well, the fire may cause total destruction of the vehicle, which may result in a large loss of objects and lives. Recently, as electric vehicles are increasingly used, the danger of a fire in a battery or surrounding high-voltage electrical wires due to external shock or an internal short circuit has increased. 
     A fire of a battery may rapidly spread due to structures and sub stances inside and outside the battery and public transportation vehicles such as a bus carry many passengers, so it is necessary to rapidly cope with a fire for the safety of passengers, and when the first response fails, it may result in a catastrophe. 
     Nevertheless, a method of preparing and using a fire extinguisher at the best is used at present as a method that can cope with a fire of a vehicle. Even in the instant case, when a driver does not use a fire extinguisher at a proper time, early extinguishing fails and the fire may spread throughout a vehicle. Furthermore, a fire occurs at a battery, it is difficult to completely extinguish the fire by only using a small fire extinguisher or spraying an extinguishing agent due to the substances in the battery. 
     Furthermore, because a driver is in a vehicle while driving, it is difficult to recognize a fire before a lot of smoke is generated even if a fire occurs at a battery. Furthermore, because buses have a large and long body unlike passenger cars, it is more difficult to recognize whether a fire has occurred. 
     Furthermore, in accordance with the types of vehicles including a large-size bus, there is an external protective structure such as case covering the battery cells of a battery mounted on the roof, etc. Accordingly, even if a driver recognizes a fire at a proper time, it is difficult to spray an extinguishing agent into the battery case, and even if a driver sprays an extinguishing agent, the extinguishing agent does not reach well the battery cells in the battery case, so effective extinguishing is impossible. 
     Generally, because a large-size bus, etc. are provided with a plurality of battery packs and each of the battery packs is provided with an expensive fire sensor to determine battery packs with a fire, there is a problem that the manufacturing cost considerably increases. Furthermore, even if an expensive gas sensor (gas concentration measurement sensor) that detects gas concentration is provided as a fire sensor at each battery pack, there is a possibility of mis-detecting. 
     The information included in this Background of the present disclosure is only for enhancement of understanding of the general background of the present disclosure and may not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art. 
     BRIEF SUMMARY 
     Various aspects of the present disclosure are directed to providing a fire extinguishing system for a battery of a vehicle, the fire extinguishing system being able to rapidly and accurately detect a fire generated in a battery of a vehicle and to effectively suppress the fire immediately after detecting. 
     The objectives of the present disclosure are not limited to those described above and other objectives not stated herein would be apparently understood by those who have ordinary skills in the art that the present disclosure belongs to (hereafter, ‘those skilled in the art’) from the following description. 
     To achieve the objectives, an exemplary embodiment of the present disclosure provides a fire extinguishing system that includes: a gas discharger provided at a battery pack and configured to discharge gas in the battery pack; a gas channel configured so that the gas produced from the battery pack and discharged through the gas discharger flows through the gas channel when a fire occurs; an extinguishing agent tank in which an extinguishing agent is kept; a heat exchange channel provided in the extinguishing agent tank, connected to the gas channel so that the gas supplied through the gas channel flows through the heat exchange channel, and facilitating heat exchange between the gas flowing through the heat exchange channel and the extinguishing agent kept in the extinguishing agent tank; and a nozzle provided at the battery pack, connected to the extinguishing agent tank through an extinguishing agent supply channel, and supplying the extinguishing agent, which is supplied from the extinguishing agent tank, into the battery pack, in which the extinguishing agent kept in the extinguishing agent tank is supplied through the extinguishing agent supply channel by internal pressure of the extinguishing agent tank increased during the heat exchange. 
     Therefore, according to the fire extinguishing system for a battery of a vehicle of the present disclosure, it is possible to rapidly and accurately detect a fire that occurs at a battery in a vehicle and can effectively suppress the fire immediately after detecting. 
     According to an exemplary embodiment of the present disclosure, it is possible to supply an extinguishing agent in an extinguishing agent tank to a battery pack without a separate pressurizing unit such as a pump or a compressor by use of flammable gas, which is discharged from a battery pack when a fire occurs, as a thermal medium. Accordingly, it is possible to reduce the installation cost of the system and to suppress a fire even in a situation in which power cannot be supplied to drive a pump or a compressor. 
     Furthermore, it is possible to suppress a following fire using carbon dioxide, which was converted by the catalyst converter from carbon monoxide in flammable gas produced from a battery pack, as an extinguishing agent in re-ignition after a primary fire. 
     Furthermore, when one assistant fire sensor simply and inexpensively configured is provided for each battery pack and one main fire sensor (gas concentration measurement sensor) which is configured to measure a gas concentration is provided in the gas channel to which the battery packs are connected in the present disclosure, it is possible to detect a battery fire and recognize all battery packs with a fire using only the one expensive main fire sensor for the plurality of battery packs. 
     Because an inexpensive assistant fire sensor is used to recognize a battery pack with a fire and only one expensive main fire sensor is used to finally determine a battery pack with a fire, mis-detecting of a fire may be prevented and the manufacturing cost may be considerably reduced as compared with when an expensive gas concentration measurement sensor is provided for each battery pack, as in the related art. 
     Furthermore, because the fire extinguishing system of the present disclosure performs the function of a pressure balancing element, it is possible to balance the pressure inside and outside the battery pack without installing several pressure balancing elements on the battery pack. 
     The methods and apparatuses of the present disclosure have other features and advantages which will be apparent from or are set forth in more detail in the accompanying drawings, which are incorporated herein, and the following Detailed Description, which together serve to explain certain principles of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a view showing an example when a well-known pressure balancing element is provided on a battery case; 
         FIG.  2    is a perspective view of the well-known pressure balancing element known in the art; 
         FIG.  3    is a view showing the entire configuration of a fire extinguishing system according to an exemplary embodiment of the present disclosure; 
         FIG.  4    is a block diagram showing detecting elements, a control element, and operating elements of the fire extinguishing system according to an exemplary embodiment of the present disclosure; 
         FIG.  5    is a cross-sectional view showing a pressure balancing element provided at a battery case of a battery pack in an exemplary embodiment of the present disclosure; 
         FIG.  6    and  FIG.  7    are cross-sectional views showing the configuration of a ventilation valve of the fire extinguishing system according to an exemplary embodiment of the present disclosure; 
         FIG.  8    and  FIG.  9    are views showing an operation state of an assistant fire sensor disposed at the ventilation valve in an exemplary embodiment of the present disclosure; 
         FIG.  10    is a view showing an example of the configuration of a catalyst converter which may be used in the fire extinguishing system according to an exemplary embodiment of the present disclosure; 
         FIG.  11    is a flowchart showing the general operation process of the fire extinguishing system according to an exemplary embodiment of the present disclosure; 
         FIG.  12    is a flowchart illustrating an operation process in a primary battery fire of the fire extinguishing system according to an exemplary embodiment of the present disclosure; 
         FIG.  13    is view showing a gas flow path in a primary battery fire in the fire extinguishing system according to an exemplary embodiment of the present disclosure; 
         FIG.  14    is a flowchart illustrating an operation process in a secondary battery fire (re-ignition) of the fire extinguishing system according to an exemplary embodiment of the present disclosure; and 
         FIG.  15    is view showing a gas flow path in a secondary battery fire in the fire extinguishing system according to an exemplary embodiment of the present disclosure. 
     
    
    
     It may be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various features illustrative of the basic principles of the present disclosure. The specific design features of the present disclosure as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particularly intended application and use environment. 
     In the figures, reference numbers refer to the same or equivalent parts of the present disclosure throughout the several figures of the drawing. 
     DETAILED DESCRIPTION 
     Reference will now be made in detail to various embodiments of the present disclosure(s), examples of which are illustrated in the accompanying drawings and described below. While the present disclosure(s) will be described in conjunction with exemplary embodiments of the present disclosure, it will be understood that the present description is not intended to limit the present disclosure(s) to those exemplary embodiments of the present disclosure. On the other hand, the present disclosure(s) is/are intended to cover not only the exemplary embodiments of the present disclosure, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the present disclosure as defined by the appended claims. 
     Description of specific structures and functions included in embodiments of the present disclosure are only an example for describing the exemplary embodiments according to the concept of the present disclosure and the exemplary embodiments according to the concept of the present disclosure may be implemented in various ways. The present disclosure is not limited to the exemplary embodiments described herein and should be construed as including all changes, equivalents, and replacements that are included in the spirit and the range of the present disclosure. 
     It will be understood that, although the terms first and/or second, etc. may be used herein to describe various elements, but these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. For instance, a first element discussed below could be termed a second element without departing from the teachings of the present disclosure. Similarly, the second element could also be termed the first element. 
     It is to be understood that when one element is referred to as being “connected to” or “coupled to” another element, it may be directly connected to or directly coupled to another element or be connected to or coupled to another element, including the other element intervening therebetween. On the other hand, it is to be understood that when one element is referred to as being “directly connected to” or “directly coupled to” another element, it may be connected to or coupled to another element without the other element intervening therebetween. Furthermore, the terms used herein to describe a relationship between elements, that is, “between”, “directly between”, “adjacent” or “directly adjacent” should be interpreted in the same manner as those described above. 
     Like reference numerals indicate the same components throughout the specification. The terms used herein are provided to describe embodiments without limiting the present disclosure. In the specification, a singular form includes a plural form unless specifically stated in the sentences. The terms “comprise” and/or “comprising” used herein do not exclude that another component, step, operation, and/or element exist or are added in the stated component, step, operation, and/or element. 
     Embodiments of the present disclosure will be described hereafter in detail with reference to the accompanying drawings. 
     The present disclosure was designed to provide a fire extinguishing system for a battery of a vehicle, the fire extinguishing system being able to rapidly and accurately detect a fire generated in a battery pack and to effectively suppress the fire immediately after detecting. 
     If it is possible to detect early a fire of a battery pack in a vehicle, it is possible to enable a driver and passengers to rapidly and safely escape out of the vehicle by giving a warning within a short time period when a fire occurs. 
     To the present end, the fire extinguishing system according to an exemplary embodiment of the present disclosure is configured to be able to early detect a fire generated at a battery pack, and give a warning and automatically suppress the fire immediately after detecting. 
     As for a common fire generation mechanism of the battery in electric vehicles, an overvoltage is generated in a battery or external shock is applied to the battery, the membrane may be decomposed and an electrolyte may be pyrolyzed when the membrane is damaged. 
     In the instant case, high-temperature flammable gas is produced from battery cells and it is possible to know that the main component of the flammable gas is carbon monoxide (CO) from battery fire tests. The point in time when flammable gas is emitted is the point in time when early extinguishing is possible. 
     Thereafter, when gas expands in the battery and the gas and electrolyte leak out of the battery cells, thermal runway is generated, which may result in explosion of the battery. It is almost impossible to suppress the fire from the present point in time. Accordingly, it is required to rapidly detect emission of flammable gas and suppress a fire in an early stage by spraying an extinguishing agent to the battery pack with a fire at the point in time of emission of the flammable gas. 
     According to an exemplary embodiment of the present disclosure, a fire is detected using gas which is emitted from a battery cell in an early stage, that is, a flammable gas emission stage in which a fire of the battery cell may be suppressed. That is, a fire is recognized and determined in an early stage by detecting gas which is emitted by pyrolysis of an electrolyte in a battery cell, etc. 
     In the instant case, a pressure balancing element which is provided at a battery pack is used to detect gas. The battery packs that are mounted in vehicles are necessarily provided with such a pressure balancing element. 
     A common automotive battery pack includes a battery case and a battery module disposed in the battery case, and the battery module includes a plurality of unit batteries, that is, battery cells. The battery cells forming the battery module of a battery pack are sealed in the battery case. 
     According to an exemplary embodiment of the present disclosure, the internal temperature of the battery case repeats increasing and decreasing, depending on the charging/discharging states of the battery cells. There should be a passage through which gas can flow inside and outside when the internal temperature repeats increasing and decreasing. 
     The pressures inside and outside the battery case can keep balanced only when a gas passage is in the battery case, so it is possible to prevent the battery pack from expanding or contracting. For the present purpose, the battery case of a battery pack is provided with a pressure balancing element that provides a passage for gas to flow between the inside and the outside. 
       FIG.  1    is a view showing an example when a well-known pressure balancing element is provided on a battery case. As shown in the figure, a pressure balancing element  4  through which gas flows in and out of a battery case at normal times is provided at a battery case  2  of a battery pack  1 . The pressure balancing element  4  has a passage for gas to flow in and out of the battery case  2 . 
     A battery module is accommodated in the battery case  2  shown in  FIG.  1   , and battery cells of the battery module are sealed by the battery case. In the present battery pack, the internal temperature of the battery case  2  repeats increasing and decreasing, in accordance with the charging/discharging states of the battery cells. 
     To prevent the battery case  2  from expanding or contracting, as shown in the figure, a plurality of pressure balancing elements  4  is provided at the battery case so that gas flows in and out of the battery case through the gas passages of the balancing elements at normal times (when a fire does not occur). Accordingly, it is possible to prevent expansion and contraction of the battery case  2  and pressure can keep balanced inside and outside the battery case. 
       FIG.  1    is a perspective view showing a well-known pressure balancing element as a reference view for helping understand the present disclosure. As shown in the figure, the well-known pressure balancing element  4  includes a plate  5  which is configured to be fixed in close contact with the external surface of a battery case (indicated by ‘2’ in  FIG.  1   ), and a vent portion integrally disposed at the center portion of the plate  5 . 
     In the well-known pressure balancing element  4 , a plurality of vents  7  through which gas can pass is formed at the vent portion  6  positioned at the center portion as a plurality of passages for gas to flow in and out of the battery case. 
     Accordingly, pressures inside and outside the battery case may be balanced while gas passes through the vents  7  of the vent portion  6  with the plate  5  fixed to the external surface of the battery case. 
     In the well-known pressure balancing element  4 , the vents (gas passages  7 ) are formed in a small size at the vent portion  6  to prevent external moisture from flowing into the battery case. 
     One vent  7  is not enough for pressure adjustment (pressure balancing), so a plurality of small vents is formed at the pressure balancing element  4 , and a plurality of pressure balancing elements is provided at each battery pack. 
     In the present disclosure, new types of pressure balancing element and ventilation valve that perform not only the pressure adjustment (pressure balancing) function in a battery pack at normal times, but a function of discharging gas, which is produced from battery cells, only to a passage (a gas passage to be described below) in which a main fire sensor is positioned rather than to the outside in a fire are used. 
       FIG.  3    is a view showing the entire configuration of a fire extinguishing system according to an exemplary embodiment of the present disclosure. A fire extinguishing system that automatically detects a fire of a battery pack  1  in an early stage and suppresses the fire immediately after detecting is exemplarily shown in  FIG.  3   .  FIG.  4    is a block diagram showing detecting elements, a control element, and operating elements of the fire extinguishing system according to an exemplary embodiment of the present disclosure. 
     As for the detailed configuration, the fire extinguishing system according to an exemplary embodiment of the present disclosure includes a gas discharger provided at a battery pack and configured to be able to discharge gas in the battery case  2 . 
     The gas discharger in an exemplary embodiment of the present disclosure may be a pressure balancing element  110  which is provided at the battery case  2  and provides a passage for gas to flow in and out of the battery case. 
       FIG.  5    is a cross-sectional view showing a pressure balancing element provided at a battery case of a battery pack in an exemplary embodiment of the present disclosure. As shown in the figure, the pressure balancing element  110  includes: a vent portion  111  disposed on the battery case  1  of the battery pack  1  and including a vent  112  through which air can pass and which is formed between the inside and outside of the battery case; a connector  113  coupled to the vent portion so that the internal space thereof communicates with the vent  112  of the vent portion  111 ; and a venting channel  116  provided in a structure extending a predetermined length from the connector  113  and including an internal passage that communicates with the internal space of the connector  113 , the vent  112 , and the internal space of the vent portion  111 . 
     As described above, the vents of the vent portion that are formed as gas passages in the well-known pressure balancing element have very small size and channel cross-sectional area to prevent inflow of moisture. However, in the pressure balancing element  110  of the present disclosure, the vent  112  of the vent portion  111  has relatively large size and channel cross-section, and the connector  113  and the venting channel  116  that extend predetermined length from the vent  112  are provided. Accordingly, there is almost no possibility that moisture flows into the battery case  2  through the venting channel  116  including a predetermined length as long as sealing is maintained well only at the joints of the components. 
     In an exemplary embodiment of the present disclosure, a ventilation-waterproof film member  117  that passes gas but blocks external moisture may be provided at the vent  112  of the vent portion  111 . The ventilation-waterproof film member  117 , as shown in  FIG.  5   , is provided in a structure that blocks the vent  112  of the vent portion  111 . 
     In an exemplary embodiment of the present disclosure, as the ventilation-waterproof film member  117 , a fluorine resin film that can block moisture and pass gas, in detail, a film member made of expanded polytetrafluoroethylene (ePTFE) known as the brand name, Gore-Tex®, may be used. 
     In the instant case, a ventilation-waterproof film member  117  that can discharge moisture in the battery case  2  and can prevent moisture outside the battery case from flowing inside through the vent  112  of the vent portion  111  may be used. 
     The vent portion  111  may be formed in a plate shape protruding outwardly from the surface of the battery case  2  and the vent  112  including a predetermined diameter or size may be formed at the protruding end portion of the vent portion  111 . In an exemplary embodiment of the present disclosure, the vent portion  111  may be formed toward the outside on the surface of the battery case  2  in a pipe shape having a circular cross-section, that is, a circular pipe shape. 
     The connector  113  has a configuration in which a large-diameter portion  113  a being relatively large in diameter is formed to an end portion and a small-diameter portion  113   c  being relatively small in diameter is formed at another rend portion, and a tapered portion  113   b  of which the diameter gradually decrease is formed between the large-diameter portion  113  a and the small-diameter portion  113  a. 
     The large-diameter portion  113   a  may be thread-fastened to the external surface of the vent portion  111 , and to the present end, threads may be formed on the internal surface of the large-diameter portion  113   a  and the external surface of the vent portion  111 . The small-diameter portion  113   c  is coupled to the venting channel  116 , and the internal surface of the small-diameter portion  113   c  fitted on the external surface of the venting channel  116  or the external surface of the small-diameter portion  113   c  may be fitted on the internal surface of the venting channel  116 . 
     The surfaces of the small-diameter portion  113   c  and the venting channel  116  may be coupled and fixed by thermal bonding. As the venting channel  116 , a pipe-shaped member such as a hose or a tube may be used and a member made of a material which may be thermally bonded to the connector  113  may be used. 
     A sealing protrusion  114  may protrude inwardly from the internal surface of the connector  113 , and the connector  113  and the vent portion  111  are thread-fastened so that the sealing protrusion  114  presses the ventilation-waterproof film member  117  to the vent portion  111  with the sealing member  115  inserted therein. The sealing member  115  is provided for airtightness (sealing) between the connector  113 , the vent portion  111 , and the ventilation-waterproof film member  117 , and may be an O-ring made of an elastic material such as rubber. 
     The ventilation-waterproof film member  117  is provided to be accommodated on the external surface of a protruding end portion of the vent portion  111 , and is pressed to the vent portion  111  by the sealing member  115  when the large-diameter portion  113   a  of the connector  113  is thread-fastened to the external surface of the vent portion  111 . The edge portion of the ventilation-waterproof film member  117  is pressed by the sealing protrusion  114  and the sealing member  115 , so that the ventilation-waterproof film member  117  may be fixed to the external surface of the protruding end portion of the vent portion  111 . 
     In an exemplary embodiment of the present disclosure, the sealing protrusion  114  may be formed to have an L-shaped cross-section having an open side on the internal surface of the large-diameter portion  113   a  of the connector  113 . Accordingly, when the large-diameter portion  113  a of the connector  113  is thread-fastened to the vent portion  111  with the circular sealing member  115  inserted in the sealing protrusion  114  having an L-shaped cross-section, the sealing member  115  can press the ventilation-waterproof film member  117  through the opening of the sealing protrusion  114 . 
     The size of the vent  112  which is a gas passage through which gas passes may be relatively freely designed in the present disclosure, and the vent  112  may be made greater than the vent  112  of the well-known pressure balancing element  110 , so there is an advantage that it is possible to decrease the number of pressure balancing element to 1 for each battery pack. 
     Meanwhile, as shown in  FIG.  3   , the fire extinguishing system according to an exemplary embodiment of the present disclosure may further include a ventilation valve  120  provided at the outlet of the venting channel (indicated by ‘ 116 ’ in  FIG.  5   ) of the pressure balancing element  110  provided at the battery pack  1 , and a gas channel  130  extending from the ventilation valve  120 . 
     The fire extinguishing system according to an exemplary embodiment of the present disclosure may further include: a main fire sensor  140  provided in the gas channel  130 ; a catalyst converter  154  provided in the gas channel  130  and converting and discharging flammable gas discharged through the gas channel from the battery pack  1 ; an extinguishing agent tank  170  keeping an extinguishing agent for suppressing a fire at the battery pack  1 ; a controller  160  outputting a control signal to supply the extinguishing agent to a battery pack  1  with fire when the main fire sensor  140  detecting a fire; and valves controlled to open or close in response to the control signal output from the controller  160  so that the extinguishing agent kept in the extinguishing agent tank  170  may be supplied to the battery pack. 
     The controller  160  may be a Battery Management System (BMS). A check valve  129  that prevents gas, which has passed through the ventilation valve, from flowing backward to the main fire sensor  140  and the catalyst converter  154  may be provided between the ventilation valve  120  and the main fire sensor  140  in the gas channel  130 . 
       FIG.  6    and  FIG.  7    are cross-sectional views showing the configuration of a ventilation valve of the fire extinguishing system according to an exemplary embodiment of the present disclosure.  FIG.  6    shows the state at normal times and  FIG.  7    shows the state when a fire occurs. 
     As shown in the figures, the ventilation valve  120  may include: a ventilation port  122  connected to the venting channel  116  of the pressure balancing element  110 ; an atmosphere port  123  connected to the atmosphere side; a valve housing  121  including a connection port  124  to which the gas channel  130  is connected; a valve body  125  provided in the internal space of the valve housing  121  and being moved to close the atmosphere port  123  by gas discharged from the battery pack  1  when a fire occurs; and a spring  126  provided to support the valve body  125  in the internal space of the valve housing  121 . 
     The internal space of the valve housing  121  communicates with the internal space of the venting channel  116 . Accordingly, the internal space of the valve housing  121  communicates with the internal space of the venting channel  116  and the internal space of the connector  113  of the pressure balancing element  110 , and also communicates with the internal space of the vent portion  111  and the internal space of the battery case  2  with the ventilation-waterproof film member  117  therebetween. 
     The atmosphere port  123  of the ventilation valve  120  may be formed at the upper end portion of the valve housing  121  and an inlet-output channel (indicated by ‘ 128 ’ in  FIG.  3   ) through which air flows inside and outside between the atmosphere port  123  and the atmosphere may be connected to the atmosphere port  123 . 
     The connection port  124  of the ventilation port  120  may be formed on the side of the valve housing  121 . The valve body  125  of the ventilation valve  120  is positioned to open the atmosphere port  123  at normal times and to always open the connection port  124 . 
     The spring  126  is provided under the valve body  125  and maintains the position of the valve body  125  so that the valve body  125  keeps open the atmosphere port  123  and the connection port  124  at the position. The spring  126  maintains the position of the valve body  125  so that the valve body  25  keeps the connection port  124  open not only when a fire occurs but at normal times. 
     As may be seen from  FIG.  6    and  FIG.  7   , the valve body  125  has the shape of the plate  5  and is transversely provided in the internal space of the valve housing  12 , and the spring  126  under the valve body  125  is disposed between the valve housing  121  and the valve body  125  to support the valve body  125  thereon. 
     As described above, the connection port  124  is a port which is always open regardless of whether a fire occurs, whether gas is discharged from the battery pack  1 , and the position of the valve body  125 . Referring to  FIG.  6   , it may be seen that the valve body  125  supported by the spring  126  is positioned higher than the connection port  124  at normal times. Accordingly, the connection port  124  is a port which is open always rather than being closed by the valve body  125 . 
     On the other hand, the atmosphere port  123  is a port which is opened or closed by the valve body  125 , that is, the valve body  125  opens the atmosphere port  123  at normal times, but the atmosphere port  123  is closed by the valve body  125  when a fire occurs. 
     When a fire occurs, gas produced from the battery pack  1  passes through the pressure balancing element  110  and then flows into the valve housing  121  of the ventilation valve  120  through the ventilation port  122 . The gas flowing inside pushes up the valve body  125  and the valve body  125  is moved toward the atmosphere port  123  against the force of the spring  126 , closing the atmosphere port  123 . The connection port  124  keeps open regardless of the position of the valve body  125  even a fire occurs. 
     Accordingly, when the atmosphere port  123  is open, the internal spaces of the atmosphere port  123  and the valve housing  121 , the internal spaces of the venting channel  116  and the connector  113  of the pressure balancing element  110 , and the internal space of the vent portion  111  formed with the ventilation-waterproof film member  117  therebetween are used as gas passages for pressure balancing inside and outside the battery case  2 . 
     At normal times, as shown in  FIG.  6   , gas flows in and out of the battery pack  1  through the pressure balancing element  110  and the ventilation valve  120  with the atmosphere port  123  open, and pressure is balanced inside and outside the battery pack  1 . 
     In a fire, as shown in  FIG.  7   , because the atmosphere port  123  is closed by the valve body  125 , gas produced from the battery pack  1  is not discharged to the atmosphere. The gas produced from the battery pack  1  may be discharged only through the connection port  124  which is always open, and the gas discharged through the connection port  124  flows to the main fire sensor  140  through the gas channel  130 . 
     Accordingly, the gas is detected by the main gas sensor  140  and the controller  160  can determine that a fire has occurred based on a signal from the main fire sensor  140 . The gas is the gas produced from the battery pack  1  in the early stage of a fire, in detail, flammable gas produced from the battery cells  3  accommodated in the battery case  2 . The main component of the flammable gas is carbon monoxide (CO). 
     The ventilation valve  120  may be provided with an assistant fire sensor  150  in an exemplary embodiment of the present disclosure. The assistant fire sensor  150  is provided to detect a fire that occurs in the battery pack  1  independently from the main fire sensor  140 . 
     The assistant fire sensor  150 , as shown in  FIG.  6    and  FIG.  7   , may include: a first magnet resistor  151  provided on the valve body  125 ; a second magnet resistor  152  provided and fixed at a position close to the atmosphere port  123  on the internal surface of the valve housing  121  so that the first magnet resistor  151  may be attached when the valve body  125  moves to the position for closing the atmosphere port  123 ; and a wire  153  connecting the first magnet resistor  151  and the controller  160  to each other so that elasticity may be transmitted. 
     The controller  160 , though not shown, may have a current applier that applies a current to the wire  153  connected between the first magnet resistor  151  and the controller  160 , and a current detector that detects a current value which is applied to the wire  153 . Accordingly, a current including a predetermined value may be applied through the wire  153  from the current applier of the controller  160 , and simultaneously, the value of a current flowing through the wire  153  may be detected by the current detector. 
     Referring to  FIG.  6    and  FIG.  7   , it may be seen that the first magnet resistor  151  is attached to a side of the valve body  125  and the second magnet resistor  152  is attached to the internal surface of the valve housing  121  at a side facing the first magnet resistor  151 . In the present structure, a shock-absorbing member  127  may be provided on another side of the valve housing  125  or at another side on the internal surface of the valve housing  121 . 
     The shock-absorbing member  127  may be made of a material having elasticity and shock-absorbing ability such as rubber. As shown in  FIG.  7   , when a fire occurs and the valve body  125  is moved up by the force of gas in the figure and closes the atmosphere port  123 , the shock-absorbing member  127  prevents direct contact between the valve body  125  and the valve housing  121  and absorbs shock between the valve body  125  and the valve housing  121 . 
       FIG.  8    and  FIG.  9    are views showing an operation state of the assistant fire sensor provided at the ventilation valve  120  in an exemplary embodiment of the present disclosure, in which  FIG.  8    shows the state at normal times (when a fire does not occur) and  FIG.  9    shows the state when a fire occurs. 
     At normal times, as shown in  FIG.  8   , when a current is applied through the wire  153  from the controller  160 , electricity is transmitted to only the wire  153  and the second magnet resistor  152  of the valve housing  121 . However, when a fire occurs, the first magnet resistor  151  is attached to the second magnet resistor  152  by magnetism, as shown in  FIG.  9   , when the valve body  125  is moved by gas produced from the battery pack  1  and closes the atmosphere port  123 . 
     When the first magnet resistor  151  and the second magnet resistor  152  are brought in contact with and attached to each other, a resistance value in the elasticity path is increased by the combination of the first magnet resistor  151  and the second magnet resistor  152 , so that the value (i.e., intensity) of the current flowing through the wire  153  changes. 
     That is, the value (a reference current value) A 1  of a current that flows through a path formed by only the wire  153  and the first magnet resistor  151  with the first magnet resistor  151  and the second magnet resistor  152  separated would be relatively high. Furthermore, when the first magnet resistor  151  and the second magnet resistor  152  come in contact with each other, the entire resistance value increases and the value (the actual current value) A 2  of a current that flows through the wire  153 , first magnet resistor  151 , and the second magnet resistor  152  would be lower than that when the two magnet resistors are separate from each other. 
     Accordingly, the controller  160  is set to read out the value of a current flowing through the wire  153  (a signal value from the assistant fire sensor), and to determine that a fire has occurred when the value of a current is a predetermined value or less than the predetermined value. The controller  160  can determine that a fire has occurred when the detected value of a current decreases to a set value or less. 
     Alternately, the controller  160  may be set to determine that a fire has occurred when a variation of a current value is a predetermined amount or more. As described above, the controller  160  can read out the value of a current flowing through the wire  153  of the assistant fire sensor  150  and primarily determine whether a fire has occurred at the battery pack  1  based on the variation of the current value. 
     Although only one battery pack  1  is shown in  FIG.  3   , a fire extinguishing system may be configured for a plurality of battery packs mounted in a vehicle. That is, the pressure balancing element  110 , the ventilation valve  120 , and the inlet-outlet channel  128  may be provided for each of battery packs  1 . 
     In the instant case, the gas channels connected to the connection ports  124  of the ventilation valves  120  are combined as a single gas channel  130  and the combined single gas channel  130  is connected to the inlet of the catalyst converter  154 . The single gas channel connected to the inlet of the catalyst converter  154  is a first channel  131  to be described below. 
     The check valve  129  is provided in each of the gas channels connected to the connection ports  124  of the ventilation valves  120  and the main fire sensor  140  is provided in the combined signal gas channel  130 . 
     An extinguishing agent supply channel  171  is connected between the extinguishing agent tank  170  and a nozzle  172  provided at each of the battery pack  1 . A second valve  182  to be described below is provided in the extinguishing agent supply channel  171  connected between the extinguishing agent tank  170  and the nozzle  172  of each of the battery packs  1 . 
     The nozzles  172  of the battery packs  1  are connected to a buffer tank  155  to be described below through an assistant supply channel  137 , and a fourth valve  184  to be described below may be provided in the assistant supply channel  137 . 
     In the fire extinguishing system configured for a plurality of battery packs  1  in the present way, an assistant fire sensor  150  which is a primary fire sensor provided in the ventilation valve  120  is also provided at each of the battery packs  1  together with the pressure balancing element  110  and the ventilation valve  120 . 
     As a result, the controller  160  can determine battery packs with a fire based on signals from the assistant fire sensors  150  provided for the battery packs  1 , respectively. That is, when a current value which is a signal value from the assistant fire sensor  140  is a predetermined value or less than the predetermined value or a variation of the current value is a predetermined amount or less at a battery pack of all of the battery packs  1 , the battery pack may be determined as a battery pack with a fire. 
     The main fire sensor  140  may be a sensor which is provided in the first channel  131  of the gas channel  130  and detects gas produced from battery cells  3  when a fire occurs, and for example, may be a carbon monoxide sensor that detects concentration of carbon monoxide (CO). 
     The main fire sensor  140  is connected to the controller  160  and inputs a signal which is generated when a fire is detected to the controller. Accordingly, the controller  160  can recognize that a fire has occurred in a battery pack  1  based on a signal from the main fire sensor  140 . 
     For example, when the concentration of carbon monoxide in gas detected by the main fire sensor  140  is a set concentration or more, the controller  160  can determine that a fire has occurred in a battery pack  1 . 
     Accordingly, as described above, the controller  160  can recognize a battery pack at which a fire has actually occurred of all of the battery packs mounted in a vehicle based on a signal from the assistant fire sensor  150 , and can finally determine that a fire has occurred at the battery pack  1  mounted in the vehicle based on a signal from the main fire sensor  140 . 
     The gas channel  130  is connected to the ventilation valve  120  and the gas channel  130  includes the first channel  131  connected to the inlet of the catalyst converter  154  from the connection port  124  of the ventilation valve  120 , and the second channel  132  connected to a heat exchange channel  133  provided in the extinguishing agent tank  170  from the outlet of the catalyst converter  154 . 
     That is, the gas channel  130  is connected to the heat exchange channel  133  provided in the extinguishing agent tank  170 . The second channel  132  is connected to an end portion of the heat exchange channel  133  and a third channel  134  is connected to another end portion of the heat exchange channel  133 . 
     The check valve  129  and the main fire sensor  140  are provided in the first channel  131 . Accordingly, when a fire occurs, high-temperature flammable gas which is discharged from the battery pack  1  passes through the pressure balancing element  110  and the ventilation valve  120  and then sequentially passes through the check valve  129  and the main fire sensor  140  while flowing through the first channel  131 . 
     Thereafter, the high-temperature flammable gas that has passed through the main fire sensor  140  passes through the catalyst converter  154  and the high-temperature gas that has passed through the catalyst converter  154  flows to the heat exchange channel  133  through the second channel  132 . 
     The heat exchange channel  133  is a gas channel through which the high-temperature gas, which has passed through the first channel  131  and the second channel  132 , flows, and is provided so that the extinguishing agent kept in a liquid state in the extinguishing agent tank  170  and the high-temperature gas passing through the heat exchange channel  133  can exchange heat with each other. 
     The high-temperature gas passing through the heat exchange channel  133  is gas that has sequentially passed through the first channel  131 , the catalyst converter  154 , and the second channel  132 , that is, gas including high-temperature carbon dioxide converted from carbon monoxide of the gas while passing through the catalyst converter  154  after being produced and discharged from the battery pack  1  when a fire occurs. The gas that has passed through the heat exchange channel  133  flows to the third channel  134 . 
     Carbon dioxide which is an extinguishing agent is kept in a liquid state in the extinguishing agent tank  170  at normal times and the extinguishing agent supply channel  171  is connected to the outlet of the extinguishing agent tank  170 . 
     The extinguishing agent supply channel  171  is connected to the nozzle  172  provided at the battery pack  1  and the nozzle  172  is provided to be able to spray an extinguishing agent into the battery case  2 . A second valve  182  which is controlled to open or close by the controller  160  is provided in the extinguishing agent supply channel  171 . 
     As a result, when high-temperature gas passes through the heat exchange channel  133  provided in the extinguishing agent tank  170 , heat exchange is made between the high-temperature gas and the liquid-state carbon dioxide, so that the pressure in the extinguishing agent tank  170  increases. 
     When the second valve  182  is opened in the instant state, the carbon dioxide at high pressure in the extinguishing agent tank  170  may be discharged to the extinguishing agent supply channel  171  and then sprayed into the battery pack  1  through the nozzle  172  by high vapor pressure even without a pressurizing unit such as a pump or a compressor. 
     The third channel  134  is connected to the inlet of the buffer tank  155  and an end portion of the fourth channel  135  is connected to an outlet of the buffer tank  155 . Another end portion of the fourth channel  135  is connected to the gas channel, that is, the first channel  131  at the front end portion (upstream side) of the catalyst converter  154 . 
     An assistant supply channel  137  is connected to the nozzle  172  provided at the battery pack  1  between the nozzle  172  and another outlet of the buffer tank  155 . A connection channel  136  connecting the second channel  132  and the third channel  134  is separately provided between the channels. 
     A first valve  181  which is controlled to open or close by the controller  160  is provided in the second channel  132 . The connection channel  136  diverges from the second channel  132  between the catalyst converter  154  and the first valve  182 , and the first valve  181  is positioned between the heat exchange channel  133  and the point at which the connection channel  136  diverges from the second channel  132 . 
     A third valve  183  which is controlled to open or close by the controller  160  is provided in the connection channel  136 , a fourth valve  184  which is controlled to open or close by the controller  160  is provided in the assistant supply channel  137 , and a fifth valve  185  which is controlled to open or close by the controller  160  is provided in the fourth channel  135 . 
     Referring to  FIG.  4   , the main fire sensor  140  and the assistant fire sensor  150  are shown as detecting elements, the first valve  181 , the second valve  182 , the third valve  183 , the fourth valve  184 , and the fifth valve  185  are shown as operating elements, and the controller  160  that is configured to control opening and closing of the valves  181  to  185  is shown. 
     The valves  181  to  184  are electronic valves that are individually opened or closed in responses to control signals output from the controller  160 , are provided to open or close corresponding channels, respectively, and a solenoid valve may be used as an example of the valves. 
     When determining that a fire has occurred at the battery pack through the assistant fire sensor  150  and the main fire sensor  140 , the controller  160  is configured to control opening and closing of the valves so that gas produced from the battery pack  1  can pass sequentially through the catalyst converter  154  and the heat exchange channel  133  and so that the extinguishing agent in the extinguishing agent tank  170  may be supplied to the battery pack  1  with a fire. 
     The fire extinguishing system according to an exemplary embodiment of the present disclosure may further include a warning device  200  that operates to give a warning of a fire in response to a control signal output from the controller  160  when the controller  160  determines that a fire has occurred based on signals from the main fire sensor  140  and the assistant fire sensor  150 . 
     The warning device  200  may be a sound output device which is provided to output an alarm that gives warning of a fire in a vehicle or a display in a vehicle that moves up or display a warning message that gives warning of a fire. The sound output device may include a speaker mounted in a vehicle and the display may be the display of a cluster. 
     The configuration of the fire extinguishing system according to an exemplary embodiment of the present disclosure was described above in detail. As described above, the catalyst converter  154  that converts carbon monoxide, which is contained in high-temperature flammable gas which is produced and discharged from a battery pack when a fire occurs, into carbon dioxide is used in the present disclosure. 
     In the fire extinguishing system according to an exemplary embodiment of the present disclosure, the catalyst converter  154  is connected to the first channel  131  of the gas channel  130 . Accordingly, in the early stage of a battery fire, high-temperature flammable gas that was generated from a battery cell  3  of the battery pack  1  and has passed through the pressure balancing element  110  and the ventilation valve  120  is not discharged out of the vehicle and flows to the catalyst converter  154  through the first channel  131 . As a result, carbon monoxide in the high-pressure flammable gas is converted into carbon dioxide while the flammable gas passes through the catalyst converter  154 . 
     The catalyst converter  154  may be a catalyst converter in which a carrier including an oxidation catalyst of precious metal such as platinum, rhodium, palladium is accommodated in a case or may be a catalyst converter which is used in the exhaust gas purifier of common vehicles or has a similar configuration. 
     Gas which is produced when a fire occurs at a lithium ion battery includes a large amount of carbon monoxide (CO), some quantity of hydrogen fluoride (HF), a small amount of sulfur dioxide (SO 2 ), and a very small amount of hydrocarbon (HCl). of these components, the main component of flammable gas is carbon monoxide which is a flammable gas, and not only carbon monoxide, but sulfur dioxide is a flammable gas. 
     According to the catalyst converter that utilizes an oxidation catalyst, flammable gas may be completely converted into inflammable gas. For example, carbon monoxide may be converted into carbon dioxide which is inflammable gas by an oxidation reaction. 
       2CO+O 2 →2CO 2  
 
       2SO 2 +O 2 →2SO 3  
 
       FIG.  10    is a view showing an example of the configuration of a catalyst converter which may be used in the fire extinguishing system according to an exemplary embodiment of the present disclosure. As shown in the figure, the catalyst converter  154  has a configuration in which a carrier  154   b  including an oxidation catalyst of precious metal is accommodated in a case  154   a.    
     The case  154   a  of the catalyst converter  154  has a body  154   c  including a shape of cylinder including a constant diameter, and an inlet  154   d  and an outlet  154   e  formed in cone shapes and integrally coupled to both end portions of the body  154   c , respectively. 
     When a fire occurs and gas is discharged at an excessively high speed from the battery pack  1 , catalyst oxidation reactivity in the catalyst converter  154  may be insufficient, so it is required to adjust the gas speed in the catalyst converter  154  by appropriately setting the cross-sectional sizes of the body  154   c  and the inlet  154   d . It is possible to find out an optical cross-section combination by repeatedly testing the catalyst reactivity that depends on the channel cross-sectional areas of the passages of the body  154   c  and the inlet  154   d.    
     Meanwhile, according to an exemplary embodiment of the present disclosure, the extinguishing agent in the extinguishing agent tank  170  may be naturally supplied to the battery pack  1  without a pump or a compressor by use of the heat of the gas that has passed through the catalyst converter  154 , and to the present end, a heat exchanger that can transmit the heat of the high-temperature gas that has passed through the catalyst converter  154  to the extinguishing agent tank  170  is provided. 
     In the present disclosure, the heat exchanger enables heat exchange between the extinguishing agent kept in a liquid state in the extinguishing agent tank  170  and the high-temperature gas that has passed through the catalyst converter  154 . 
     In an exemplary embodiment of the present disclosure, the heat exchanger may be configured by installing the heat exchange channel  133 , through which gas can flow, in the extinguishing agent tank  170  and connecting the heat exchange channel  133  in the extinguishing agent tank  170  to the second channel  132  so that high-temperature gas that has passed through the catalyst converter  154  can flow through the heat exchange channel  133 . 
     Accordingly, while the high-temperature gas that has passed through the catalyst converter  154  flows through the heat exchange channel  133 , the heat of the high-temperature gas may be supplied to the inside of the extinguishing agent tank  170  by heat exchange in the heat exchange channel  133 . When the heat of the high-temperature gas is transmitted to the carbon dioxide kept as an extinguishing agent in the extinguishing agent tank  170 , high pressure is generated in the extinguishing agent tank  170 . 
     Accordingly, carbon dioxide which is an extinguishing agent may be naturally discharged out of the extinguishing agent tank  170  by the high pressure in the extinguishing agent tank  170  even without a pump or a compressor, and the extinguishing agent discharged from the extinguishing agent tank  170  may be supplied to the nozzle  172  of the battery pack  1  with a fire through the extinguishing agent supply channel  171 . 
     Carbon dioxide is in a gaseous state at room temperature, but is liquefied when pressure is applied, so carbon dioxide may be kept in a liquid state in the extinguishing agent tank  170  which is a high-pressure gas container. When the second valve  182  is opened to discharge carbon dioxide, carbon dioxide can flow in a liquid state (or gas state) through the extinguishing agent supply channel  171 , but may be vaporized and sprayed from the nozzle  172 . 
     Carbon dioxide has a large advantage that it is not contaminated after being used, and pressure of liquid-state carbon dioxide is very high, so liquid-state carbon dioxide may be discharged by the pressure thereof even without help of a pressurizing unit. 
     According to an exemplary embodiment of the present disclosure, when a primary battery fire occurs, the gas that has passed through the catalyst converter  154  flows to the heat exchange channel  133 , increasing the temperature in the extinguishing agent tank  170 . Accordingly, the vapor pressure in the extinguishing agent tank  170  is increased, so that the extinguishing agent in the extinguishing agent tank  170  may be supplied to the nozzle  172  of the battery pack  1 . 
     The extinguishing agent supplied from the extinguishing agent tank  170  to the nozzle  172  through the extinguishing agent supply channel  171  is sprayed into the battery case  2  of the battery pack  1 , primarily suppressing the fire a battery cell  3 . 
     In the early stage of a battery fire, the gas (including carbon dioxide) that has passed through the catalyst converter  154 , as described above, is used only to increase the temperature and pressure in the extinguishing agent tank  170  by flowing through the heat exchange channel  133  and is not used as an extinguishing agent for suppressing the battery fire. 
     Furthermore, in an early stage of a battery fire, in a primary battery fire before re-ignition, the gas that has passed through the heat exchange channel  133  in the extinguishing agent tank  170  undergoes a recirculation process in which the gas flows to the buffer tank  155  through the third channel  135  and then to the first channel  131 . 
     The gas may flow backward into the battery pack  1  due to a rapid pressure change in the recirculation process of the gas, so there is a demand for an auxiliary storage space for suppressing a rapid pressure change. 
     Accordingly, the buffer tank  155  is provided and used at the auxiliary storage process in the present disclosure. In the early stage of a battery fire, in a primary battery fire before re-ignition, the gas that has passed through the heat exchange channel  133  flows to the buffer tank  155 , whereby a rapid pressure change may be suppressed. The gas moving into the buffer tank  155  is recirculated by flowing to the first channel  131  and then passes through again the catalyst converter  154 . 
     The most dangerous matter in a battery fire in a vehicle is that re-ignition frequently occurs. Accordingly, when re-ignition occurs after a fire is extinguished at the battery pack  1 , that is, when the concentration of carbon monoxide detected by the main fire sensor  140  after primary fire suppression increases over a set concentration and it is determined that re-ignition has occurred, the gas generated in re-ignition is made pass through the catalyst converter  154  so that carbon monoxide in the gas is converted into carbon monoxide. 
     Because some of the extinguishing agent in the extinguishing agent tank  170  was used in the primary fire, carbon dioxide converted from carbon monoxide in flammable gas through the catalyst converter  154  may be supplied in to the battery pack  1  through the nozzle  172  as an extinguishing agent when re-ignition occurs (that is, a second fire occurs). 
     As a result, because flammable gas is not directly discharged out of a vehicle even though a fire occurs at a battery, it is possible to somewhat reduce the danger that a driver or passengers are poisoned by gas. Furthermore, when a battery fire occurs at an area with many people such as a school or a mart, it is possible to reduce a loss of lives including a driver or passengers which may be caused by flammable gas. 
     Hereafter, the general operation of the fire extinguishing system is described. 
     In  FIG.  3   , the arrows indicate an air flow path for pressure balancing of the battery pack. At normal times without a fire, the pressure balancing element  110  and the ventilation valve  120  of the fire extinguishing system are used to airflow and pressure balancing between the inside and the outside of the battery pack  1 . At normal times, the first valve  181 , the second valve  182 , and the fourth valve  184  are controlled to be closed, and the third valve  183  and the fifth valve  185  are controlled to be open. 
     Gas can flow in and out of the battery pack  1  through the pressure balancing element  110  and the ventilation valve  120  with the atmosphere port  123  and the connection port  124  of the ventilation valve  120  both open, and pressure is balanced inside and outside the battery pack  1  while gas flows in the direction of the arrows. 
     Because the connection port  124  is a port which is always open, gas (air) can flow even through the connection port  124  and the gas channel  130  connected thereto at normal times. In the instant state, oxygen may be continuously supplied also to the catalyst converter  154  through the first channel  131  of the gas channel  130 , and accordingly, oxygen to be used for an oxidation reaction may be stored in the oxidation catalyst in the catalyst converter  154 . 
     Because the third valve  183  provided in the connection channel  136  and the fifth valve  184  provided in the fourth channel  135  are open with the first valve  181  provided in the second channel  132  closed, the air that has passed through the catalyst converter  154  may be circulated sequentially through the connection channel  136  of the second channel  132 , the third channel  134 , the buffer tank  155 , and the fourth channel  135 . As described above, at normal times, air cannot approach the extinguishing agent tank  170  and continuously circulates through the catalyst converter  154 . 
       FIG.  11    is a flowchart showing the general operation process of the fire extinguishing system according to an exemplary embodiment of the present disclosure. It is exemplified that a plurality of (n) battery packs is mounted in a vehicle. 
     In a key-on state of a vehicle (S 11 ), the controller  160  monitors in real time whether a fire occurs at the battery packs  1  based on signals from the assistant fire sensor  150  and the main fire sensor  140  (S 12 -S 15 ). When a fire occurs at a battery pack  1 , gas is discharged from the battery pack with a fire. The gas discharged from the battery pack flows through the gas channel  130  after sequentially passing through the pressure balancing element  110  and the ventilation valve  120 . 
     In the present state, the controller  160  can recognize whether a fire has occurred at a battery pack  1  based on the main fire sensor  140  and can recognize the battery back  1  with a fire of all of the battery packs  1  based on a signal from the assistant fire sensor  150 . 
     A process of recognizing a battery pack with a fire is described. The controller  160 , performs real-time monitoring by reading out a signal value of the assistant fire sensor  150  provided for each battery pack  1 , that is, the value of a current flowing through the wire  153  of each assistant fire sensor  150 , and checks whether the current values X(n) of the wires  153  are a set value or less (S 12 -S 14 ). 
     Gas that was discharged from a battery pack  1  with a fire and has passed through the pressure balancing element  110  flows into the ventilation valve  120 . The gas flowing in the ventilation valve  120  pushes and moves the valve body  125  and the valve body  125  moves to the position for closing the atmosphere port  124  against the force of the spring  126  to prevent gas from being discharged to the atmosphere through the atmosphere port  124  (see  FIG.  7   ). 
     After the valve body  125  moves to the position for closing the atmosphere port  123 , the first magnet  151  and the second magnet  152  of the assistant fire sensor  150  are brought in contact with and attached to each other (see  FIG.  7   ), and in the instant case, the controller  160  can read out the value of a current flowing through the wire  153 . 
     The controller  160  determines that a fire has occurred at the corresponding battery pack  1  when the value of a current flowing through the wire  153  is the set value or less (or a variation of the value of a current is a predetermined amount or more). As a result, the controller  160  can recognize the battery pack  1  with a fire of all of the battery packs  1 . 
     The gas that has sequentially passed through the pressure balancing element  110  and the ventilation valve  120  after being discharged from the battery pack  1  flows to the first channel  131  of the gas channel  130  and then passes through the main fire sensor  140  provided in the first channel  131 . 
     The main fire sensor  140  can detect the concentration Z of a specific component, for example, carbon monoxide (CO) in the gas passing through the first channel  131  and outputs a signal based on the concentration of the specific component in the gas to the controller  160 . 
     Accordingly, the controller  160  checks whether the concentration Z of the specific component in the gas is a set concentration or more based on the signal from the main fire sensor  140  (S 15 ), and when the concentration is the set concentration or more, the controller  160  finally determines that a fire has occurred at the battery pack  1  (which is the n-th battery pack in  FIG.  10   ) at which fire was detected by the assistant fire sensor  150  (S 16 ). 
     Even though a current value which is a signal value of the assistant fire sensor  150  is the set value or less in step S 13 , as described above, it is finally determined that a fire has occurred at a corresponding battery pack  1  only when the concentration Z of carbon monoxide (CO) detected by the main fire sensor  140  is the set concentration of more in step S 15 , whereby a danger of misoperation is reduced. 
     Accordingly, when determining that a fire has occurred at the battery pack  1 , the controller  160  warns a driver and passengers of a fire by operating the warning device  200  (S 17 ), and performs control for suppressing the fire (S 18 ). 
       FIG.  12    is a flowchart illustrating an operation process in a primary battery fire by the fire extinguishing system according to an exemplary embodiment of the present disclosure and  FIG.  13    is view showing a gas flow path in a primary battery fire in the fire extinguishing system according to an exemplary embodiment of the present disclosure. Step S 15  in  FIG.  12    is a step that is the same as step S 15  in  FIG.  11   , some of the steps shown in  FIG.  11    are not shown in  FIG.  12   . 
     When a fire at a battery pack is not detected (Z&lt;set concentration) in step S 15 , control at normal times described above is performed, that is, the first valve  181 , the second valve  182 , and the fourth valve  184  are controlled to close and is configured to control the third valve  183  and the fifth valve  185  are controlled to open by the controller  160  (S 15 - 1 ). In the instant state, the internal pressure of the battery packs  1  are adjusted and oxygen may be supplied to the catalyst converter  154 . 
     However, when it is finally determined that a fire has occurred at a battery pack  1  (Z≥set concentration) in step S 15 , the third valve  183  and the fourth valve  184  are controlled to open, and the first valve  181 , the second valve  182 , and the fifth valve  185  are controlled to open by the controller  160  (S 18 - 1 ). 
     While high-temperature gas discharged from the battery pack  1  passes through the catalyst converter  154  in a fire, carbon monoxide in the gas is converted into carbon dioxide, and then the gas that has passed through the catalyst converter  154  passes through the heat exchange channel  133  in the extinguishing agent tank  170 . 
     While the gas passes through the heat exchange channel  133 , as described above, the pressure of the extinguishing agent tank  170  is increased by heat exchange between the gas and the liquid-state carbon dioxide in the extinguishing agent tank  170 . 
     As a result, the carbon dioxide in the extinguishing agent tank  170  is discharged to the outside by the high vapor pressure in the extinguishing agent tank  170 , and the carbon dioxide discharged outside is supplied to the nozzle  172  of the battery pack  1  with a fire through the extinguishing agent supply channel  171  (S 18 - 2 ). Therefore, the carbon dioxide which is an extinguishing agent is finally sprayed into the battery pack  1  through the nozzle  172 , whereby the fire at the battery pack is suppressed. 
     The gas that has passed through the catalyst converter  154  flows to the buffer tank  155  through the second channel  132 , the heat exchange channel  133 , and the third channel  134 , and then undergoes a recirculation process in which the gas flows back to the first channel  131  and the catalyst converter  154  from the buffer tank  155 . 
     An oxidation reaction is continuously generated in the catalyst converter  154  until a secondary fire (re-ignition) is detected, whereby carbon dioxide for suppressing a fire is produced and some of the produced carbon dioxide is kept in the buffer tank  155 . The carbon dioxide kept in the buffer tank  155  may be used as an extinguishing agent when a secondary fire occurs. 
     Next,  FIG.  14    is a flowchart illustrating an operation process in a secondary battery fire (re-combustion) of the fire extinguishing system according to an exemplary embodiment of the present disclosure.  FIG.  15    is view showing a gas flow path in a secondary battery fire in the fire extinguishing system according to an exemplary embodiment of the present disclosure. 
     The controller  160 , as shown in the flowchart of  FIG.  14   , performs control for suppressing a secondary fire (re-ignition) after the second valve  182  is opened (on) (S 21 ). The fact that the second valve  182  has opened once means that a first fire occurred. 
     When the second valve  182  is opened and a first fire is suppressed, the concentration of carbon monoxide (CO) detected by the main fire sensor  140  decreases to the set concentration, but when re-ignition occurs later, flammable gas is produced again from the battery pack  1 . 
     In the assistant fire sensor  150  in the ventilation valve  120 , when a primary fire is detected, the first magnet resistor  151  provided on the valve body  125  is attached to the second magnet resistor  152  provided on the internal surface of the valve housing  121 , and then, the two magnet resistors  151  and  152  maintain the attached state by magnetism. Accordingly, in the ventilation valve  120 , only the connection port  124  to which the first channel  131  is connected is maintained in the open state with the atmosphere port  123  closed. 
     If the concentration Z of carbon monoxide (CO) detected by the main fire sensor  140  becomes the set concentration or more (Z≥set concentration) in step S 22  after the second valve  182  is opened (S 21 ), the controller  160  determines re-ignition has occurred at the battery pack  1 . 
     In the present state, only the fourth valve  184  provided in the assistant supply channel  137  is controlled to open, and the first valve  181 , the second valve  182 , the third valve  183 , and the fifth valve  185  are controlled to close by the controller  160  (S 24 ). 
     As a result, when the fourth valve  182  is opened, the high-pressure carbon dioxide collected and kept in the buffer tank  155  when the primary fire occurred is supplied to the nozzle  172  of the battery pack  1  with a fire through the assistant supply channel  137  and then sprayed into the battery pack  1  through the nozzle  172 , whereby the secondary fire (re-ignition) is suppressed (S 25 ). 
     When the carbon dioxide kept in the buffer tank  155  is supplied to the battery pack  1  for fire suppression, the carbon dioxide in the heat exchange channel  133  and at the rear end portion of the third valve  183  is also supplied to the nozzle  172  through the buffer tank  155 . 
     Because the carbon dioxide which is supplied as an extinguishing agent in re-ignition, as described above, was converted from carbon monoxide in the flammable gas produced from the battery pack  1  by the catalyst converter  154 , as described above, carbon dioxide converted by the catalyst converter  154  is used at an extinguishing agent in re-ignition. 
     If re-ignition does not occur after a primary fire, the second valve  182  and the fourth valve  184  are controlled to maintain the closed state and the first valve  181 , the third valve  183 , and the fifth valve  185  are controlled to maintain the open state by the controller  160  (S 23 ). 
     To supply gas converted by the catalyst converter  154  by opening the fourth valve  184 , the controller  160  may be set to open the fourth valve  184  for a set time and then closes the fourth valve  184 . Thereafter, the controller  160  compares the concentration Z detected by the main fire sensor  140  with a set concentration, and may open again the fourth valve  184  for a set time only when the detected concentration is the set concentration or more. 
     It is possible to suppress re-ignition in the way of closing the fourth valve  184  after opening the fourth valve  184  and then checking the gas concentration. Furthermore, even if re-ignition is repeated later, fires may be suppressed in the same way (n-th fire suppression is performed). 
     The fire extinguishing system for a battery according to an exemplary embodiment of the present disclosure and a method of controlling the fire extinguishing system were described above. According to an exemplary embodiment of the present disclosure described above, it is possible to rapidly and accurately detect a fire that occurs at a battery in a vehicle and can effectively suppress the fire immediately after detecting. 
     According to an exemplary embodiment of the present disclosure, it is possible to supply an extinguishing agent in an extinguishing agent tank to a battery pack without a separate pressurizing unit such as a pump or a compressor by use of flammable gas, which is discharged from a battery pack when a fire occurs, as a thermal medium. Accordingly, it is possible to reduce the installation cost of the system and to suppress a fire even in a situation in which power cannot be supplied to drive a pump or a compressor. 
     Furthermore, it is possible to suppress a following fire using carbon dioxide, which was converted by the catalyst converter from carbon monoxide in flammable gas produced from a battery pack, as an extinguishing agent in re-ignition after a primary fire. 
     Furthermore, when one assistant fire sensor simply and inexpensively configured is provided for each battery pack and one main fire sensor (gas concentration measurement sensor) which is configured to measure a gas concentration is provided in the gas channel to which the battery packs are connected in the present disclosure, it is possible to detect a battery fire and recognize all battery packs with a fire using only the one expensive main fire sensor for the plurality of battery packs. 
     Because an inexpensive assistant fire sensor is used to recognize a battery pack with a fire and only one expensive main fire sensor is used to finally determine a battery pack with a fire, mis-detecting of a fire may be prevented and the manufacturing cost may be considerably reduced as compared with when an expensive gas concentration measurement sensor is provided for each battery pack, as in the related art. 
     Furthermore, because the fire extinguishing system of the present disclosure performs the function of a pressure balancing element, it is possible to balance the pressure inside and outside the battery pack without mounting several pressure balancing elements on the battery pack. 
     Furthermore, the term related to a control device such as “controller”, “control apparatus”, “control unit”, “control device”, “control module”, or “server”, etc refers to a hardware device including a memory and a processor configured to execute one or more steps interpreted as an algorithm structure. The memory stores algorithm steps, and the processor executes the algorithm steps to perform one or more processes of a method in accordance with various exemplary embodiments of the present disclosure. The control device according to exemplary embodiments of the present disclosure may be implemented through a nonvolatile memory configured to store algorithms for controlling operation of various components of a vehicle or data about software commands for executing the algorithms, and a processor configured to perform operation to be described above using the data stored in the memory. The memory and the processor may be individual chips. Alternatively, the memory and the processor may be integrated in a single chip. The processor may be implemented as one or more processors. The processor may include various logic circuits and operation circuits, may process data according to a program provided from the memory, and may generate a control signal according to the processing result. 
     The control device may be at least one microprocessor operated by a predetermined program which may include a series of commands for carrying out the method included in the aforementioned various exemplary embodiments of the present disclosure. 
     The aforementioned invention can also be embodied as computer readable codes on a computer readable recording medium. The computer readable recording medium is any data non-transitory storage device that can store data which may be thereafter read by a computer system and store and execute program instructions which may be thereafter read by a computer system. Examples of the computer readable recording medium include Hard Disk Drive (HDD), solid state disk (SSD), silicon disk drive (SDD), read-only memory (ROM), random-access memory (RAM), CD-ROMs, magnetic tapes, floppy discs, optical data non-transitory storage devices, etc and implementation as carrier waves (e.g., transmission over the Internet). Examples of the program instruction include machine language code such as those generated by a compiler, as well as high-level language code which may be executed by a computer using an interpreter or the like. 
     In various exemplary embodiments of the present disclosure, each operation described above may be performed by a control device, and the control device may be configured by a plurality of control devices, or an integrated single control device. 
     In various exemplary embodiments of the present disclosure, the control device may be implemented in a form of hardware or software, or may be implemented in a combination of hardware and software. 
     Furthermore, the terms such as “unit”, “module”, etc. included in the specification mean units for processing at least one function or operation, which may be implemented by hardware, software, or a combination thereof. 
     For convenience in explanation and accurate definition in the appended claims, the terms “upper”, “lower”, “inner”, “outer”, “up”, “down”, “upwards”, “downwards”, “front”, “rear”, “back”, “inside”, “outside”, “inwardly”, “outwardly”, “interior”, “exterior”, “internal”, “external”, “forwards”, and “backwards” are used to describe features of the exemplary embodiments with reference to the positions of such features as displayed in the figures. It will be further understood that the term “connect” or its derivatives refer both to direct and indirect connection. 
     The foregoing descriptions of specific exemplary embodiments of the present disclosure have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present disclosure to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and their practical application, to enable others skilled in the art to make and utilize various exemplary embodiments of the present disclosure, as well as various alternatives and modifications thereof. It is intended that the scope of the present disclosure be defined by the Claims appended hereto and their equivalents.