Patent Publication Number: US-2023141930-A1

Title: Thermal Chain Determination Method and Thermal Chain Detection System for Battery Pack

Description:
TECHNICAL FIELD 
     The present invention relates to a thermal chain determination method and a thermal chain detection system for a battery pack. 
     BACKGROUND 
     In a battery pack containing a plurality of battery cells, when an abnormality such as an internal short circuit occurs in one battery cell, heat generated by this battery cell may cause heat generated by another battery cell, which may lead to a thermal chain (thermal runaway). Vehicles such as electric vehicles and hybrid vehicles on which a battery pack is mounted are required to include a system for detecting the thermal chain (thermal runaway) early and accurately in view of safety. 
     However, for example, when detecting the thermal chain by detecting a temperature, the thermal chain cannot be detected quickly since there is a time lag from an occurrence of an abnormality in one battery cell to a temperature rise inside the battery pack due to the thermal chain. 
     Regarding the above problem, JP2011-060755A discloses a system that detects a pressure in a battery pack and detects a thermal chain (thermal runaway) based on a change in the pressure in the battery pack. With this system, the thermal chain is detected based on the pressure, and thus the problem of time lag can be solved. 
     SUMMARY 
     In recent years, there is an increasing number of battery packs including a cooling system using a gas refrigerant and an exhaust gas passage for battery cells that couples the battery cells and the outside of a battery pack. In such a battery pack, when the refrigerant gas leaks into the battery pack, the pressure in the battery pack rises regardless of the thermal chain. Further, the pressure in the battery pack may change regardless of the thermal chain due to an influence of the exhaust gas passage coupled to the outside of the battery pack as well. For such a battery pack including a pressure contributing component that contributes to a pressure change in the battery pack, it is not possible to accurately detect the occurrence of the thermal chain by only detecting the pressure in the battery pack as in the technique described in JP2011-060755A, and there is a risk of erroneously detecting the thermal chain. 
     The present invention is made in view of the above problems, and an object of the present invention is to provide a thermal chain determination method and a thermal chain detection system for a battery pack that are capable of quickly and accurately detecting an occurrence of thermal chain. 
     A thermal chain determination method for a battery pack according to one embodiment of the present invention is a thermal chain determination method for a battery pack, the battery pack including a plurality of cells inside the battery pack, a pressure contributing component contributing to a change in a pressure in the battery pack, at least one pressure sensor configured to detect the pressure in the battery pack, and at least one voltage sensor configured to detect a voltage of the cells, the method including, detecting the pressure in the battery pack by the pressure sensor, detecting the voltage of the cells by the voltage sensor, determining that the pressure in the battery pack is abnormal when an amount of change or a rate of change in the detected pressure in the battery pack is larger than a predetermined value, determining that the voltage of the cells is abnormal when an amount of change or a rate of change in the detected voltage of the cells is larger than a predetermined value, or when an absolute value of the voltage of the cells is smaller than a predetermined value, and determining that a thermal chain occurs when both the pressure in the battery pack and the voltage of the cells are abnormal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic configuration diagram showing a main configuration of a thermal chain detection system for a battery pack according to a first embodiment of the present invention; 
         FIG.  2    is a block diagram showing a control configuration of the thermal chain detection system; 
         FIG.  3    is a timing chart showing a thermal chain detection method; 
         FIG.  4    is a flowchart showing the thermal chain detection method; 
         FIG.  5    is a schematic configuration diagram showing a main configuration of a thermal chain detection system for a battery pack according to a second embodiment of the present invention; and 
         FIG.  6    is a block diagram showing a control configuration of the thermal chain detection system according to the second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments of the present invention are described with reference to the drawings and the like. 
     First Embodiment 
       FIG.  1    is a schematic configuration diagram of a thermal chain detection system  100  for a battery pack (hereinafter, referred to as thermal chain detection system) according to the first embodiment of the present invention. The thermal chain detection system  100  is mounted on a vehicle such as an electric vehicle or a hybrid vehicle. 
     As shown in  FIG.  1   , the thermal chain detection system  100  includes a battery pack  1 , a plurality of battery modules  10  housed in the battery pack  1 , a refrigerant gas passage  20  that cools the battery modules  10 , a plurality of pressure sensors  30  that detect a pressure in the battery pack  1 , a controller  40 , and the like.  FIG.  1    is a cross-sectional view of the battery pack  1  as viewed from an upper surface direction. An upper surface of the battery pack  1  is covered with a cover portion although not shown. That is, the battery pack  1  is a so-called closed-type battery pack. 
     Each of the battery modules  10  is a cell stack (cells) formed by stacking a plurality of unit cells (not shown). The battery pack  1  houses the plurality of battery modules  10 . The unit cells in the first embodiment are lithium ion secondary batteries, and are not necessarily limited thereto. Although not shown, the battery modules  10  are electrically connected to an external load by a lead wire or the like, and the battery modules  10  are also electrically connected to each other by a lead wire or the like. The number and an arrangement of the battery modules  10  in the battery pack  1  are optional and are not limited to those shown in  FIG.  1   . 
     The refrigerant gas passage  20  is a passage through which a refrigerant gas for cooling the battery modules  10  circulates and passes through each battery module  10 . When the refrigerant gas leaks into the battery pack  1  from the refrigerant gas passage  20 , the pressure in the battery pack  1  increases. That is, the refrigerant gas passage  20  is a pressure contributing component that contributes to a pressure change in the battery pack  1 . In addition, the shape and the arrangement of the refrigerant gas passage  20  are not limited to those of  FIG.  1    as long as the refrigerant gas passage  20  is capable of cooling the battery pack  1 . 
     The pressure sensors  30  include a first pressure sensor  30   a  and a second pressure sensor  30   b  and detect a pressure P in the battery pack  1 . The pressure sensors  30  are provided below a shielding plate  31  made of a metal plate or the like, and pressure measuring units of the pressure sensors  30  are directed at a bottom direction of the battery pack  1 . By covering the pressure sensors  30  with the shielding plate  31  in this way, the pressure sensors  30  are protected by the shielding plate  31  even when a thermal chain, which will be described later, occurs in the battery pack and a high-temperature and high-pressure gas is ejected from the cells. That is, since the pressure sensors  30  are provided at a position where the pressure sensors  30  would not be affected by the thermal chain when the thermal chain occurs, the pressure sensors  30  operate normally even when the thermal chain occurs. The pressure P detected by the pressure sensors  30  is transmitted to the controller  40  described later. 
     The controller  40  is constituted by a computer including a central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM), and an input and output interface (I/O interface), and performs an integrated control of the thermal chain detection system  100 . The controller  40  may also be constituted by a plurality of microcomputers. The controller  40  controls the thermal chain detection system  100  by executing a specific program. The controller  40  executes, for example, a thermal chain detection control described later. 
     The controller  40  includes a battery controller (LBC)  41  and a vehicle control module (VCM)  42 . The LBC  41  and the VCM  42  are connected to each other in a communicable manner by a CAN that is a communication line or the like. 
     The LBC  41  is provided in the battery pack  1  and is electrically connected to each battery module  10 . The LBC  41  includes a plurality of voltage sensors that measure a voltage V of the cells of the battery modules  10  (hereinafter, referred to as voltage of the battery modules  10  or cell voltage). The cell voltage V acquired by the LBC is transmitted to the VCM  42 . 
     The VCM  42  controls an entire system of the vehicle on which the thermal chain detection system  100  is mounted. As will be described later, the VCM  42  determines, for example, whether the acquired pressure P in the battery pack  1  and the cell voltage V are abnormal, and determines whether the thermal chain occurs in the battery pack  1 . 
     In a battery pack housing a plurality of cells like the battery pack  1 , when an abnormality such as an internal short circuit occurs in one cell, heat generated by this cell may cause heat generated by another cell, which may lead to the thermal chain (thermal runaway). Therefore, vehicles on which a battery pack is mounted are required to include a system for detecting the thermal chain (thermal runaway) early and accurately in view of safety (for example, EVS-GTR or the like). 
     However, for example, when the thermal chain is detected by detecting a temperature, the thermal chain cannot be detected quickly since there is a time lag from an occurrence of an abnormality in one cell to a temperature rise in the battery pack due to the thermal chain. 
     In a system that detects a pressure in a battery pack and detects the thermal chain based on a change in the pressure in the battery pack, the problem of time lag may be solved. However, in a battery pack that includes a cooling system (refrigerant gas passage  20 ) using a gas refrigerant as in the first embodiment, when a refrigerant gas leaks into the battery pack, the pressure inside the battery pack rises regardless of the thermal chain. Further, for example, in a battery pack that includes a gas discharge passage for discharge an exhaust gas of battery cells that couples the battery cells and the outside of the battery pack, the pressure in the battery pack may change regardless of the thermal chain due to an influence of the gas discharge passage coupled to the outside of the battery pack as well. For such a battery pack including the pressure contributing component that contributes to the pressure change in the battery pack, it is not possible to accurately detect the occurrence of the thermal chain by only detecting the pressure in the battery pack, and there is a risk of erroneously detecting the thermal chain. 
     Therefore, in the first embodiment, when both the pressure P in the battery pack  1  and the cell voltage V in the battery pack are abnormal, it is determined that the thermal chain occurs. Therefore, even when the pressure P in the battery pack  1  becomes abnormal due to the pressure contributing component that contributes to the pressure change in the battery pack, such as the refrigerant gas passage  20 , it is not determined that the thermal chain occurs unless the voltage V of the battery module  10  is abnormal. Further, since the occurrence of the thermal chain is determined based on the pressure P and the voltage V, the thermal chain can be detected quickly. That is, the occurrence of the thermal chain can be detected quickly and accurately. 
     In addition, with improvement in safety of cells in recent years, there are many cases where no thermal chain is caused even when the cell voltage is abnormal due to the internal short circuit or the like, except that there is a risk of erroneously detecting the thermal chain by only detecting the cell voltage. In response to the above problem, in the first embodiment, it is determined that the thermal chain occurs only when both the pressure P in the battery pack  1  and the cell voltage V are abnormal, and thus the erroneous detection is prevented. 
       FIG.  2    is a block diagram showing a control configuration of the thermal chain detection system  100 . 
     As shown in  FIG.  2   , the thermal chain detection system  100  includes a voltage detection unit  11 B and a pressure detection unit  12 B in the battery pack  1 , a cell voltage abnormality determination unit  21 B, a pressure abnormality determination unit  22 B, a running state determination unit  23 B and a thermal chain occurrence determination unit  24 B that are a part of the VCM  42 , and a display unit  31 B. 
     The voltage detection unit  11 B is constituted by the LBC  41  including the voltage sensors for measuring the cell voltage V of the battery modules  10 . The cell voltage V detected by the LBC  41  is input to the cell voltage abnormality determination unit  21 B of the VCM  42  at predetermined time intervals or at all times. 
     The pressure detection unit  12 B is constituted by the first and second pressure sensors  30   a  and  30   b  that detect the pressure P in the battery pack  1 . A pressure P 1  detected by the first pressure sensor  30   a  is input to a first pressure abnormality determination unit  221 B and a pressure P 2  detected by the second pressure sensor  30   b  is input to a second pressure abnormality determination unit  222 B of the VCM  42  at predetermined time intervals or at all times, respectively. 
     The cell voltage abnormality determination unit  21 B determines whether the cell voltage V input from the voltage detection unit  11 B is abnormal. Specifically, the cell voltage abnormality determination unit  21 B determines whether an amount of change or a rate of change ΔV (hereinafter, referred to as the amount (rate) of change ΔV) in the cell voltage V input at the predetermined time intervals or at all times is larger than a predetermined value ΔV th , and whether an absolute value of the cell voltage V is smaller than a predetermined value Vth. When the amount (rate) of change ΔV is larger than the predetermined value ΔV th , or when the absolute value of the cell voltage V is smaller than the predetermined value V th , the cell voltage abnormality determination unit  21 B determines that the cell voltage V is abnormal. The predetermined value ΔV th  here is, for example, a value of the amount (rate) of change in the voltage by which the cells can be regarded as being over-discharged. Similarly, the predetermined value V th  is a value by which the cells can be regarded as being over-discharged when the absolute value of the cell voltage V is smaller than the V th . The predetermined value ΔV th  or V th  can be set in advance based on experiments, common technical knowledge and the like. 
     The cell voltage abnormality determination unit  21 B determines that the cell voltage V is abnormal even when the internal short circuit is detected based on the input cell voltage V, when the cell voltage V is an invalid value, or when communication between the LBC  41  and the VCM  42  is poor. When the internal short circuit in one cell is detected, the cell is in an over-discharged state. When an abnormality occurs in the cells due to the thermal chain and an abnormality such as damage occurs in the voltage sensors, the cell voltage V is an invalid value. When an abnormality occurs in the cells due to the thermal chain and an abnormality such as damage occurs in the LBC  41  or the communication line CAN or the like between the LBC  41  and the VCM  42 , the communication between the LBC  41  and VCM  42  is poor. In such a case, the cell voltage abnormality determination unit  21 B determines that the cell voltage V is abnormal by regarding the amount (rate) of change ΔV in the cell voltage V as larger than the predetermined value ΔV th , or regarding the absolute value of the cell voltage V as smaller than the predetermined value V th . 
     The cell voltage abnormality determination unit  21 B determines that the cell voltage V is abnormal when at least one cell voltage V of the battery modules  10  is abnormal. For example, when it is assumed that the cell voltage V is determined to be abnormal only when values of all the voltage sensors of the LBC  41  are abnormal, there is a risk that the abnormality in the cell voltage V is not detected when a part of the voltage sensors of LBC  41  are faulty, or when a part of the cell voltages are not detected accurately for a certain reason. In such a case, there is a risk that the occurrence of the thermal chain cannot be detected. In response to the above problem, in the first embodiment, since it is determined that the cell voltage V is abnormal when at least one cell voltage V is abnormal, the thermal chain can also be detected when a part of the voltage sensors are faulty. 
     Since the VCM  42  including the cell voltage abnormality determination unit  21 B is provided outside the battery pack  1 , the VCM  42  is not affected by the high-temperature and high-pressure gas ejected from the cells even when the thermal chain occurs. Therefore, even when the abnormality such as damage occurs in the voltage detection unit  11 B (LBC  41 ) or the communication line between the LBC  41  and the VCM  42  due to the high-temperature and high-pressure gas during the thermal chain, the VCM  42  can detect the poor communication with the LBC  41 . That is, for example, even when the LBC  41  or the like is damaged due to the thermal chain, the VCM  42  can detect the abnormality of the cell voltage V. 
     When the cell voltage abnormality determination unit  21 B determines that the cell voltage V is abnormal, a signal indicating that the cell voltage is abnormal is input from the cell voltage abnormality determination unit  21 B to the thermal chain occurrence determination unit  24 B. 
     The pressure abnormality determination unit  22 B is constituted by the first pressure abnormality determination unit  221 B and the second pressure abnormality determination unit  222 B, and determines whether the pressure P in the battery pack  1  input from the pressure detection unit  12 B is abnormal. 
     The pressure P 1  detected by the first pressure sensor  30   a  is input to the first pressure abnormality determination unit  221 B and the pressure P 2  detected by the second pressure sensor  30   b  is input to the second pressure abnormality determination unit  222 B at the predetermined time intervals or at all times, respectively. 
     The first pressure abnormality determination unit  221 B and the second pressure abnormality determination unit  222 B determine whether amounts of change or rates of change ΔP (hereinafter, referred to as the amount (rate) of change ΔP) of the pressures P 1  and P 2  that are input at the predetermined time intervals or all the times are larger than a predetermined value ΔP th . The predetermined value ΔP th  here is a value corresponding to, for example, the amount of change or the rate of change in the pressure when the thermal chain occurs, and can be set in advance based on experiments, common technical knowledge and the like. The first pressure abnormality determination unit  221 B and the second pressure abnormality determination unit  222 B respectively determine that the pressures P 1  and P 2  are abnormal when the amounts (rates) of change ΔP of the input pressures P 1  and P 2  are larger than the predetermined value ΔP th . When the first pressure abnormality determination unit  221 B or the second pressure abnormality determination unit  222 B determines that the pressure is abnormal, a signal indicating that the pressure P in the battery pack  1  is abnormal is input from the pressure abnormality determination unit  22 B to the thermal chain occurrence determination unit  24 B. 
     In this way, when at least one of the first pressure abnormality determination unit  221 B and the second pressure abnormality determination unit  222 B determines that the pressure is abnormal, the signal indicating that the pressure P is abnormal is input to the thermal chain occurrence determination unit  24 B. Therefore, even when one of the pressure sensors  30   a  and  30   b  is faulty, or when the pressure is not detected accurately for a certain reason, the abnormality of the pressure P in the battery pack  1  can be detected. Therefore, the thermal chain also can be detected when one of the pressure sensors  30   a  and  30   b  is faulty. 
     The running state determination unit  23 B determines whether the vehicle is in a running state or a stopped state based on an accelerator operation of a driver or the like. A determination result of the running state determination unit  23 B is input to the thermal chain occurrence determination unit  24 B. 
     When receiving the signals indicating abnormality occurrence from both the cell voltage abnormality determination unit  21 B and the pressure abnormality determination unit  22 B, the thermal chain occurrence determination unit  24 B determines that the thermal chain occurs. That is, the thermal chain occurrence determination unit  24 B determines that the thermal chain occurs only when both the pressure P in the battery pack and the cell voltage V are abnormal. The signal indicating abnormality occurrence input from the pressure abnormality determination unit  22 B here is a signal indicating abnormality occurrence input from either or both of the first pressure abnormality determination unit  221 B and the second pressure abnormality determination unit  222 B. Therefore, the thermal chain occurrence determination unit  24 B determines that the thermal chain occurs when the cell voltage V and at least one of the pressures P 1  and P 2  in the battery pack are abnormal. 
     When the thermal chain occurrence determination unit  24 B determines that the thermal chain occurs, a warning command is transmitted from the thermal chain occurrence determination unit  24 B to the display unit  31 B. In this case, the thermal chain occurrence determination unit  24 B transmits the warning command to the display unit  31 B together with a determination result input from the running state determination unit  23 B. 
     The display unit  31 B is, for example, a meter display provided on a dashboard of the vehicle, or the like. When receiving the warning command from the thermal chain occurrence determination unit  24 B, the display unit  31 B notifies the occurrence of the thermal chain of and issues a warning to occupants and the like. When the determination result of the running state determination unit  23 B is the running state of the vehicle, the display unit  31 B displays on a display, for example, the notification of the occurrence of the thermal chain and a warning urging to stop the vehicle and retreat to a safe place outside the vehicle to the occupants and the like. When the determination result of the running state determination unit  23 B is the stopped state of the vehicle, the display unit  31 B displays on the display, for example, the notification of the occurrence of the thermal chain and a warning urging to retreat to a safe place outside the vehicle to the occupants and the like. A method for notifying the occurrence of the thermal chain and warning is not limited to the display on the display, and may be performed by, for example, a voice of a speaker. 
     As described above, since the thermal chain detection system  100  detects the occurrence of the thermal chain based on the pressure P in the battery pack  1  and the cell voltage V, the thermal chain can be detected quickly. Further, it is determined that the thermal chain occurs when both the pressure P in the battery pack  1  and the cell voltage V are abnormal, and thus the erroneous detection on the occurrence of the thermal chain can be prevented. 
       FIG.  3    is a timing chart showing a thermal chain detection method. 
     When the vehicle on which the thermal chain detection system  100  is mounted (hereinafter, simply referred to as the vehicle) is running, the cell voltage V is equal to or larger than the predetermined value V th  from a time point t0 to a time point t1, and the amounts (rates) of change ΔP 1  and ΔP 2  of the pressures P 1  and P 2  detected by the first pressure sensor  30   a  and the second pressure sensor  30   b  are both equal to or less than the predetermined value ΔPth. In such a case, the cell voltage abnormality determination unit  21 B, the pressure abnormality determination unit  22 B, and the thermal chain occurrence determination unit  24 B all maintain abnormality flags (0: normal, 1: abnormal) at 0 (normal). 
     When the cell voltage V lowers below the predetermined value V th  that is a criteria for over-discharging at the time point t 1 , the cell voltage abnormality determination unit  21 B sets the abnormality flag of the cell voltage to 1 (abnormal) at a time point t 2  immediately after the time point t 1 . A reason why the abnormality flag is set to 1 (abnormal) at the time point t 2  instead of the time point t 1  is to avoid determining the cell voltage V as abnormal when the cell voltage V momentarily lowers below the predetermined value V th  for a certain reason. In other word, when the cell voltage V returns to the predetermined value V th  or more between the time point t 1  and the time point t 2 , the cell voltage abnormality determination unit  21 B maintains the abnormality flag at 0 (normal). 
     When the abnormality flag is set to 1 (abnormal) at the time point t 2 , the cell voltage abnormality determination unit  21 B maintains the abnormality flag at 1 (abnormal) while the cell voltage V is lower than the predetermined value V th . 
     The cell voltage abnormality determination unit  21 B also sets the abnormality flag of the cell voltage to 1 (abnormal) when the internal short circuit is detected based on the cell voltage V, the cell voltage V is an invalid value, or the communication between the LBC  41  and the VCM  42  is poor. 
     At a time point t 3 , when the amount (rate) of change ΔP 1  of the pressure P 1  detected by the first pressure sensor  30   a  exceeds the predetermined value ΔP th , the first pressure abnormality determination unit  221 B sets the abnormality flag of the pressure P 1  to 1 (abnormal) at a time point t 4  after a predetermined time from the time point t 3 . The predetermined time here is a time during which the pressure in the battery pack  1  can be confirmed to be not changed accidentally only for a short time, and can be set in advance by experiments or the like. The erroneous detection of pressure abnormality is prevented by setting the abnormality flag to 1 (abnormal) at the time point t 4  after the predetermined time from the time point t 3 . 
     The thermal chain occurrence determination unit  24 B sets the abnormality flag to 1 (abnormal) when the abnormality flags of the cell voltage abnormality determination unit  21 B and the first pressure abnormality determination unit  221 B become 1 (abnormal) at the time point t 4 . That is, the thermal chain is detected. 
     The abnormality flag becomes 0 at a time point t 5  after the amount (rate) of change ΔP 1  of the pressure P 1  detected by the first pressure sensor  30   a  exceeds the predetermined value ΔP th , and then the amount (rate) of change ΔP 1  decreases to a negative value (the pressure decreases). That is, after the time point t 5 , the amount (rate) of change ΔP 1  of the pressure P 1  is equal to or less than the predetermined value ΔP th . On the other hand, the first pressure abnormality determination unit  221 B maintains the abnormality flag at 1 (abnormal) and continues an abnormality determination state for a predetermined time even when the amount (rate) of change ΔP 1  of the pressure P 1  becomes equal to or less than the predetermined value ΔP th  after the abnormality flag is set to 1 (abnormal) at the time point t 4 . That is, the abnormality flag is maintained at 1 (abnormal) even after t 5 . In this way, the pressure abnormality determination unit  22 B (the first pressure abnormality determination unit  221 B) continues the pressure abnormality determination state for a predetermined time even when the amount (rate) of change ΔP in the pressure P in the battery pack  1  becomes equal to or less than the predetermined value P th  after the pressure P in the battery pack  1  is determined to be abnormal. Therefore, the thermal chain also can be detected when the pressure P in the battery pack  1  is reduced in a short time after the thermal chain occurs. The predetermined time here is a time during which it can be confirmed that no thermal chain occurs, and can be set in advance by experiments or the like. 
     When the abnormality flag of the thermal chain occurrence determination unit  24 B becomes 1 (abnormal) at the time point t 4 , the notification of the occurrence of the thermal chain and the warning urging to stop the vehicle and retreat to a safe place outside the vehicle to the occupants and the like are performed at the same time by display on the meter display or the like. 
     When the vehicle is in the stopped state at the time point t 5 , the display on the meter display or the like is switched to the notification of the occurrence of the thermal chain and the warning urging to retreat to a safe place outside the vehicle to the occupants and the like. 
     Although the case where the amount (rate) of change ΔP 1  of the pressure P 1  detected by the first pressure sensor  30   a  exceeds the predetermined value ΔP th  is described in  FIG.  3   , the same thermal chain detection method can be used when the amount (rate) of change ΔP 2  of the pressure P 2  detected by the second pressure sensor  30   b  exceeds the predetermined value ΔP th . That is, when the amount (rate) of change ΔP 2  of the pressure P 2  exceeds the predetermined value ΔP th , the second pressure abnormality determination unit  222 B sets the abnormality flag to 1 (abnormal). When the abnormality flags of the cell voltage abnormality determination unit  21 B and the second pressure abnormality determination unit  222 B become 1 (abnormal), the thermal chain occurrence determination unit  24 B sets the abnormality flag to 1 (abnormal) and the thermal chain is detected. 
     Although the case where the absolute value of the cell voltage V lowers below the predetermined value V th  is described in  FIG.  3   , when the amount (rate) of change ΔV of the cell voltage V is larger than the predetermined value ΔV th , the cell voltage abnormality determination unit  21 B similarly sets the abnormality flag to 1 (abnormal). Further, as described above, when the internal short circuit is detected based on the cell voltage V, when the cell voltage V is an invalid value, or when the communication between the LBC  41  and the VCM  42  is poor, the cell voltage abnormality determination unit  21 B sets the abnormality flag to 1 (abnormal) by regarding the amount (rate) of change ΔV in the cell voltage V as larger than the predetermined value ΔV th , or regarding the absolute value of the cell voltage V as smaller than the predetermined value V th . 
       FIG.  4    is a flowchart showing the thermal chain detection method of the battery pack  1 . All of the following controls are repeatedly executed by the controller  40  at predetermined time intervals. 
     When the thermal chain detection system  100  is activated, for example, by pressing an ignition switch of the vehicle, the controller  40  starts a thermal chain detection control. From the start to the end of the thermal chain detection control, the controller  40  constantly acquires the pressures P 1  and P 2  in the battery pack  1  detected by the first and second pressure sensors  30   a  and  30   b , the cell voltage V detected by the voltage sensors of the LBC  41 , and information on the running state of the vehicle, or acquire these information at predetermined time intervals. 
     In step S 101 , the controller  40  determines whether the pressure P in the battery pack  1  is abnormal. The controller  40  determines whether the amount (rate) of change ΔP 1  of the pressure P 1  detected by the first pressure sensor  30   a  and the amount (rate) of change ΔP 2  of the pressure P 2  detected by the second pressure sensor  30   b  are larger than the predetermined value ΔP th . Then, the controller  40  determines that the pressure P in the battery pack  1  is abnormal when either or both of the amount (rate) of change ΔP 1  of the pressure P 1  and the amount (rate) of change ΔP 2  of the pressure P 2  are larger than the predetermined value ΔP th . The controller  40  determines that the pressure P is abnormal when the pressure P in the battery pack  1  is abnormal within a predetermined time. That is, when the amount (rate) of change ΔP of the pressure P in the battery pack  1  becomes larger than the predetermined value ΔP th , the controller  40  determines that the pressure P is abnormal within the predetermined time even when the amount (rate) of change ΔP of the pressure P subsequently becomes equal to or less than the predetermined value ΔP th . 
     When the pressure P in the battery pack  1  is abnormal, the controller  40  executes step S 102 . On the other hand, when the pressure P in the battery pack  1  is not abnormal, the controller  40  determines that no thermal chain occurs and ends the thermal chain detection control. 
     In step S 102 , the controller  40  determines whether the cell voltage V is abnormal. When the amount of change or the rate of change ΔV of the cell voltage V detected by the voltage sensors of the LBC  41  is larger than the predetermined value ΔV th , or the absolute value of the cell voltage V is smaller than the predetermined value V th , the controller  40  determines that the cell voltage V is abnormal. The controller  40  may determine the abnormality of the cell voltage V based on both the amount (rate) of change ΔV of the cell voltage V and the absolute value of the cell voltage V, and may determine the abnormality of the cell voltage V based on one of the amount (rate) of change ΔV and the absolute value. Further, the controller  40  determines that the cell voltage V is abnormal when at least one cell voltage V detected by the voltage sensors of the LBC  41  is abnormal. When the cell voltage V is abnormal, the controller  40  determines that the occurrence of the thermal chain is detected, and executes step S 103 . On the other hand, when the cell voltage V is not abnormal, the controller  40  determines that no thermal chain occurs and ends the thermal chain detection control. 
     In step S 103 , the controller  40  determines whether the vehicle is in the stopped state based on the accelerator operation of the driver or the like. When the vehicle is in the running state, the controller  40  executes step S 104 . On the other hand, when the vehicle is in the stopped state, the controller  40  executes step S 105 . 
     When the vehicle is in the running state, in step S 104 , the controller  40  executes the notification of the occurrence of the thermal chain and the warning urging to stop the vehicle and retreat to a safe place outside the vehicle to the occupants and the like. The notification and the warning are executed by display on the meter display or the like. When the notification and the warning are executed, the controller  40  returns to step S 103 . In step S 103 , when the vehicle is still in the running state, the notification of the occurrence of the thermal chain and the warning urging to stop the vehicle and retreat to a safe place outside the vehicle are continued. On the other hand, when the vehicle is in the stopped state, the controller  40  executes step S 105 . 
     When the vehicle is in the stopped state in step S 103 , the controller  40  executes in step S 105  the notification of the occurrence of the thermal chain and the warning urging to retreat to a safe place outside the vehicle to the occupants and the like. The notification and the warning are executed by display on the meter display or the like. When the notification and the warning are executed, the controller  40  ends the thermal chain detection control. 
     According to the thermal chain determination method and the thermal chain detection system  100  for the battery pack  1  of the first embodiment described above, the following effects can be achieved. 
     According to the thermal chain determination method for the battery pack  1 , it is determined that the pressure P in the battery pack  1  is abnormal when the amount of change or the rate of change ΔP of the pressure P in the battery pack  1  is larger than the predetermined value ΔP th . When the amount of change or the rate of change ΔV of the cell voltage V is larger than the predetermined value ΔV th , or when the absolute value of the cell voltage V is smaller than the predetermined value V th , it is determined that the cell voltage V is abnormal. Then, it is determined that the thermal chain occurs when both the pressure P in the battery pack  1  and the cell voltage V are abnormal. As a result, even when the pressure P in the battery pack  1  becomes abnormal due to the pressure contributing component that contributes to the pressure change in the battery pack  1 , such as the refrigerant gas passage  20 , it is not determined that the thermal chain occurs unless the voltage V of the battery module  10  is abnormal. Therefore, when the pressure P in the battery pack  1  changes regardless of the thermal chain, the erroneous detection of the occurrence of the thermal chain is prevented. Further, since the occurrence of the thermal chain is determined based on the pressure P in the battery pack  1  and the cell voltage V, the thermal chain can be detected quickly. That is, the occurrence of the thermal chain can be detected quickly and accurately. 
     Since it is determined that the thermal chain occurs when both the pressure P in the battery pack  1  and the cell voltage V are abnormal, the erroneous detection of the occurrence of the thermal chain is prevented when the cell voltage V is abnormal due to the internal short circuit or the like and the thermal chain does not occur. 
     According to the thermal chain determination method for the battery pack  1 , the battery pack  1  includes a plurality of pressure sensors  30   a  and  30   b . When the amount of change or the rate of change ΔP of the pressure in the battery pack  1  detected by at least one of the pressure sensors  30  is larger than the predetermined value ΔP th , it is determined that the pressure P in the battery pack  1  is abnormal. As a result, even when a part of the pressure sensors  30  are faulty, or when the value of the pressure P by a part of the pressure sensors  30  is not detected accurately for a certain reason, the abnormality of the pressure P in the battery pack  1  can be detected. Therefore, the thermal chain also can be detected when a part of the pressure sensors  30  are faulty. 
     According to the thermal chain determination method for the battery pack  1 , the battery pack  1  includes a plurality of voltage sensors that detect the voltage V of different cells. In addition, when the amount of change or the rate of change ΔV of the cell voltage V detected by at least one of the voltage sensor is larger than the predetermined value ΔV th , or when the absolute value of the cell voltage V is smaller than the predetermined value V th , it is determined that the cell voltage V is abnormal. As a result, even when a part of the voltage sensors are faulty, or when the value of the voltage V by a part of the voltage sensors is not detected accurately for a certain reason, the abnormality of the cell voltage V can be detected. Therefore, the thermal chain also can be detected when a part of the voltage sensors are faulty. 
     According to the thermal chain determination method for the battery pack  1 , even when the amount of change or the rate of change ΔP of the pressure P in the battery pack  1  becomes equal to or less than the predetermined value ΔP th  after the pressure P in the battery pack  1  is determined to be abnormal, the pressure abnormality determination state is continued for the predetermined time. Therefore, the thermal chain also can be detected when the pressure P in the battery pack  1  is reduced in a short time after the thermal chain occurs. 
     According to the thermal chain determination method for the battery pack  1 , it is determined that the cell voltage V is abnormal in any one of the cases where the internal short circuit is detected based on the cell voltage V detected by the voltage sensor, where the cell voltage V detected by the voltage sensor is an invalid value, or where the communication between the battery controller (LBC)  41  and the vehicle controller (VCM)  42  is poor. That is, in these cases, it can be regarded that the amount of change or the rate of change ΔV of the cell voltage V is larger than the predetermined value ΔV th , or the absolute value of the cell voltage V is smaller than the predetermined value V th . Therefore, the thermal chain can be detected more accurately in various scenes by determining that the cell voltage V is abnormal in such a case. 
     According to the thermal chain detection system  100  for the battery pack  1 , the controller  40  determines that the thermal chain occurs when both the pressure P in the battery pack  1  and the cell voltage V are abnormal. Therefore, when the pressure P in the battery pack  1  changes regardless of the thermal chain, the erroneous detection of the occurrence of the thermal chain is prevented. Further, since the occurrence of the thermal chain is determined based on the pressure P in the battery pack  1  and the cell voltage V, the thermal chain can be detected quickly. That is, the occurrence of the thermal chain can be detected quickly and accurately. 
     According to the thermal chain detection system  100  for the battery pack  1 , the controller  40  determines that the cell voltage V is abnormal in any one of the cases where the internal short circuit is detected, where the cell voltage V is an invalid value, or where the communication between the battery controller (LBC)  41  and the vehicle controller (VCM)  42  is poor. That is, in these cases, it can be regarded that the amount of change or the rate of change ΔV of the cell voltage V is larger than the predetermined value ΔV th , or the absolute value of the cell voltage V is smaller than the predetermined value V th . Therefore, the thermal chain can be detected more accurately in various scenes by determining that the cell voltage V is abnormal in such a case. 
     According to the thermal chain detection system  100  for the battery pack  1 , the pressure sensors  30  are provided at a position where the pressure sensors  30  would not be affected by the thermal chain in the battery pack  1  when the thermal chain occurs in the battery pack  1 . Therefore, even when the thermal chain occurs in the battery pack  1 , the pressure sensors  30  operate normally and can detect the change in the pressure P in the battery pack  1 . 
     According to the thermal chain detection system  100  for the battery pack  1 , the voltage sensors are provided in the battery pack  1 , and the vehicle controller (VCM)  42  is provided outside the battery pack  1 . As a result, even when the thermal chain occurs, the VCM  42  provided outside the battery pack  1  is not affected by the high-temperature and high-pressure gas ejected from the cells. Therefore, even when the abnormality such as damage occurs in the voltage detection unit  11 B (LBC  41 ) or the communication line between the LBC  41  and the VCM  42  due to the high-temperature and high-pressure gas during the thermal chain, the VCM  42  can detect failure of communication with the LBC  41  and detect the abnormality in the cell voltage V. Therefore, for example, even when the voltage detection unit  11 B (LBC  41 ) or the like is damaged by the thermal chain, the thermal chain can be detected. 
     Although the first embodiment has a configuration provided with two pressure sensors  30   a  and  30   b , the number of pressure sensors  30  is optional and is not limited to two. It is preferable to provide a plurality of pressure sensors  30 , and the configuration may be provided with only one pressure sensor  30 . In such a case as well, it is determined that the thermal chain occurs when both the pressure P in the battery pack  1  and the cell voltage V are abnormal, and thus the erroneous detection of the occurrence of the thermal chain can be prevented. Further, for example, the configuration may be provided with three or more pressure sensors  30 . In such a case, when the amount (rate) of change ΔP of the pressure P detected by at least one of the pressure sensors  30  is larger than the predetermined value ΔP th , it is determined that the pressure P in the battery pack  1  is abnormal. 
     As in the first embodiment, the pressure sensors  30  are preferably provided at a position where the pressure sensors  30  would not be affected by the thermal chain even when the thermal chain occurs. Alternatively, the present invention is not necessarily limited thereto, and the pressure sensors  30  may be provided anywhere in the battery pack  1 . 
     In the first embodiment, the battery pack  1  is a closed-type battery pack. Alternatively, the present invention is not limited thereto, and the battery pack  1  may be an open-type battery pack whose upper portion is not covered with a cover portion. 
     In the first embodiment, the cell voltage abnormality determination unit  21 B and the pressure abnormality determination unit  22 B transmit a signal to the thermal chain occurrence determination unit  24 B only in the case of the abnormality. Alternatively, the present invention is not limited thereto, and the cell voltage abnormality determination unit  21 B and the pressure abnormality determination unit  22 B may transmit a result of abnormality determination (that is, a signal indicating abnormality or normality). In this case, when determination results of the cell voltage abnormality determination unit  21 B and the pressure abnormality determination unit  22 B are both abnormal, the thermal chain occurrence determination unit  24 B determines that the thermal chain occurs. 
     Second Embodiment 
     A thermal chain detection system  200  for a battery pack according to the second embodiment will be described with reference to  FIGS.  5  and  6   . The same elements as those in the first embodiment are denoted by the same reference numerals, and descriptions thereof will be omitted. 
       FIG.  5    is a schematic configuration diagram of the thermal chain detection system  200  according to the second embodiment. The second embodiment is different from the first embodiment in that a battery pack  2  is an open-type, a pressure contributing component is a gas discharge passage  50 , and the like. 
     As shown in  FIG.  5   , the thermal chain detection system  200  includes the battery pack  2 , the battery modules  10  in the battery pack  2 , the gas discharge passage  50  through which an exhaust gas from cells constituting the battery module  10  flows, the controller  40 , and the like.  FIG.  5    is a cross-sectional view of the battery pack  2  as viewed from an upper surface direction, and an upper surface of the battery pack  2  is not covered. That is, the battery pack  2  is a so-called open-type battery pack. 
     The gas discharge passage  50  is a passage for discharging the exhaust gas of the cells, and is coupled to the battery modules  10  (cells) and the outside of the battery pack  2 . An upstream end portion  51  of the gas discharge passage  50  is closed, and the exhaust gas from the cells flows toward a downstream end portion  52  of the gas discharge passage  50 . The gas discharge passage  50  is coupled to one of the cells in the battery pack  2 , and the gas discharge passage  50  downstream of the portion coupled to the cell is provided with a pressure sensor  30  that detects the pressure of the battery pack  2 . In this way, since the gas discharge passage  50  is coupled to one of the cells and the pressure sensor  30  is downstream of the coupling portion, it is not necessary to provide the pressure sensor  30  for each cell, and the number of the pressure sensors can be reduced. 
     Similar to the first embodiment, the arrangement and the number of the battery modules  10  (cells) in the battery pack  2  are optional and are not limited to those in  FIG.  5   . 
     When there is a variation in the arrangement of the battery modules  10  (cells) in the battery pack  2 , the position of the gas discharge passage  50  coupled to the cells also varies. However, in this case, a position variation absorption structure such as a bellows may be provided at a part of the gas discharge passage  50  to widen a movable range of the gas discharge passage  50 . That is, the degree of freedom in layout of the battery modules  10  can be increased by providing the position variation absorption structure at the gas discharge passage  50 . 
     Here, it is easier to detect a change in the pressure when the pressure sensor  30  is provided at a position closer to the battery modules  10  (cells) downstream of the coupling portion of the gas discharge passage  50 . On the other hand, when the pressure sensor  30  is exposed to the high-temperature and high-pressure gas ejected from the cells when the thermal chain occurs, there is a risk of a defect such as a failure. Therefore, considering relations between a detection capability of the device and a pressure resistance and a heat resistance of the device, the pressure sensor  30  is arranged at a most appropriate position determined by tests, experiments and the like. 
     As the change in the pressure in the gas discharge passage  50  is more remarkable, the pressure sensor  30  detects the change in the pressure more easily. However, when the pressure in the gas discharge passage  50  is excessively high, the gas discharge passage  50  may be damaged. Therefore, considering the relation between the detection capability of the pressure sensor  30  and the pressure resistance of the gas discharge passage  50 , an internal hydraulic diameter of the gas discharge passage  50  is adjusted to a most appropriate value determined by tests, experiments and the like. 
     The downstream end portion  52  of the gas discharge passage  50  is closed by an air-permeable membrane (not shown) that adjusts the pressure in the gas discharge passage  50 . The air-permeable membrane is a pressure adjusting mechanism that adjusts the pressure in the gas discharge passage  50  by making air permeable or impermeable by a pressure difference between the inside and outside of the gas discharge passage  50 . However, as in the case where the thermal chain occurs, when the pressure in the gas discharge passage  50  suddenly becomes high, the air-permeable membrane is deviated from the gas discharge passage  50  and is blown off. Further, the pressure adjusting mechanism is not limited to the air-permeable membrane, and may be any known member as long as the pressure in the gas discharge passage  50  can be adjusted. 
     The pressure P in the battery pack  2  detected by the pressure sensor  30  is transmitted to the LBC  41 . 
     The controller  40  includes the LBC  41  and the VCM  42 , and the LBC  41  and the VCM  42  are connected to each other in a communicable manner with the CAN that is a communication line or the like. In the second embodiment, since the battery pack  2  is an open-type, even when the LBC  41  and VCM  42  are arranged in the battery pack  2 , the LBC  41  and the VCM  42  are not easily affected by the high-temperature and high-pressure gas ejected from the cells when the thermal chain occurs. Therefore, both the LBC  41  and the VCM  42  are provided in the battery pack  2 . As a result, the thermal chain detection system  100  is made compact. 
     The LBC  41  includes a plurality of voltage sensors (not shown) for measuring the cell voltage V of the battery modules  10 . In addition, the LBC  41  determines whether the pressure P in the battery pack  2  received from the pressure sensor  30  and the voltage V of the battery modules  10  (cells) acquired by the voltage sensor are abnormal. 
     The VCM  42  controls an entire system of a vehicle. For example, the VCM  42  determines whether the thermal chain occurs in the battery pack  2  and transmits a command for displaying a notification of the occurrence of the thermal chain and a warning to the display unit  31 B. 
       FIG.  6    is a block diagram showing a control configuration of the thermal chain detection system  200  for the battery pack according to the second embodiment. 
     As shown in  FIG.  6   , the thermal chain detection system  200  includes the voltage detection unit  11 B, the pressure detection unit  12 B, the cell voltage abnormality determination unit  21 B, the pressure abnormality determination unit  22 B, the running state determination unit  23 B and the thermal chain occurrence determination unit  24 B in the battery pack  2 , and the display unit  31 B. In the second embodiment, the voltage detection unit  11 B, the cell voltage abnormality determination unit  21 B and the pressure abnormality determination unit  22 B constitute a part of the LBC  41 , and the running state determination unit  23 B and the thermal chain occurrence determination unit  24 B constitute a part of the VCM  42 . 
     The voltage detection unit  11 B includes voltage sensors for measuring the cell voltage V of the cells, which are included in the LBC  41 . The cell voltage V detected by the voltage sensors is input to the cell voltage abnormality determination unit  21 B at predetermined time intervals or at all times. 
     The pressure detection unit  12 B is constituted by the pressure sensor  30  that detects the pressure P in the battery pack  2 . The pressure P in the battery pack  2  detected by the pressure sensor  30  is input to the pressure abnormality determination unit  22 B of the LBC  41  at predetermined time intervals or at all times. 
     The cell voltage abnormality determination unit  21 B determines whether the cell voltage V input from the voltage detection unit  11 B is abnormal. The specific determination method is the same as that of the first embodiment and the like, and thus the descriptions are omitted. 
     When the cell voltage abnormality determination unit  21 B determines that the cell voltage V is abnormal, a signal indicating that the cell voltage is abnormal is input from the cell voltage abnormality determination unit  21 B to the thermal chain occurrence determination unit  24 B. 
     The pressure abnormality determination unit  22 B determines whether the pressure P in the battery pack  2  input from the pressure detection unit  12 B is abnormal. The specific determination method is the same as that of the first embodiment, and thus the descriptions are omitted. 
     When the pressure P in the battery pack  2  becomes high, the air-permeable membrane (pressure adjusting mechanism) that closes the downstream end portion  52  of the gas discharge passage  50  is deviated, and the pressure P is almost constant after the pressure in the gas discharge flow path  50  is reduced. Therefore, even when the amount (rate) of change ΔP of the pressure P in the battery pack  2  becomes equal to or less than the predetermined value ΔP th  after the pressure P in the battery pack  2  is determined to be abnormal, the pressure abnormality determination unit  22 B continues a pressure abnormality determination state for a predetermined time. As a result, even when the ΔP lowers below the predetermined value ΔP th  due to an action of the pressure adjusting mechanism after the amount (rate) of change ΔP of the pressure P in the battery pack  2  becomes larger than the predetermined value ΔP th , the pressure P can be detected as abnormal. 
     The running state determination unit  23 B determines whether the vehicle is in a running state or a stopped state based on an accelerator operation of a driver or the like. A determination result of the running state determination unit  23 B is input to the thermal chain occurrence determination unit  24 B. 
     When receiving input signals indicating abnormality occurrence from both the cell voltage abnormality determination unit  21 B and the pressure abnormality determination unit  22 B, the thermal chain occurrence determination unit  24 B determines that the thermal chain occurs, and transmits a warning command to the display unit  31 B. Similar to the first embodiment, in this case, the thermal chain occurrence determination unit  24 B transmits the warning command to the display unit  31 B together with the determination result input from the running state determination unit  23 B. 
     When receiving the warning command from the thermal chain occurrence determination unit  24 B, the display unit  31 B notifies the occurrence of the thermal chain of and issues a warning to occupants and the like. A method for notifying and warning is the same as that of the first embodiment, and thus the descriptions are omitted. 
     According to the thermal chain determination method and the thermal chain detection system  200  for the battery pack  2  of the second embodiment described above, the following effects can be further achieved. 
     According to the thermal chain determination method for the battery pack  2 , even when the amount of change or the rate of change ΔP of the pressure P becomes equal to or less than the predetermined value ΔP th  after the pressure P in the battery pack  2  is determined to be abnormal, the pressure abnormality determination state is continued for a predetermined time. As a result, even when the amount of change or the rate of change ΔP of the pressure P in the battery pack  2  becomes equal to or less than the predetermined value ΔP th  due to an action of the pressure adjusting mechanism or the like after the amount of change or the rate of change ΔP of the pressure P in the battery pack  2  becomes larger than the predetermined value ΔP th , the pressure P can be detected as abnormal. That is, the thermal chain can be detected accurately. 
     According to the thermal chain detection system  200 , the gas discharge passage  50  that couples the battery modules  10  (cells) and the outside of the battery pack  2  is provided, and the gas discharge passage  50  includes the pressure adjusting mechanism that adjusts the pressure in the gas discharge passage  50 . As a result, even when the pressure in the gas discharge passage  50  changes regardless of the thermal chain, the pressure in the gas discharge passage  50  is adjusted by the pressure adjusting mechanism, and thus an erroneous detection on the thermal chain can be further prevented. 
     According to the thermal chain detection system  200 , the gas discharge passage  50  is coupled to one of the battery modules  10  (cells) in the battery pack  2 , and only one pressure sensor  30  is provided downstream of the portion where the gas discharge flow path  50  is coupled to the battery modules. In this way, since the gas discharge passage  50  is coupled to one of the cells, it is not necessary to provide the pressure sensor  30  for each cell, and only one pressure sensor  30  is provided downstream of the coupling portion. That is, the number of members of the thermal chain detection system  200  can be reduced. 
     According to the thermal chain detection system  200 , the battery pack  2  is an open-type battery pack, and the voltage sensors (LBC  41 ) and the controller  40  (LBC  41  and VCM  42 ) are provided inside the battery pack  2 . In this way, since the voltage sensors (LBC  41 ) and the controller  40  (LBC  41  and VCM  42 ) are both provided in the battery pack  2 , the thermal chain detection system  200  is made compact. 
     The cell voltage abnormality determination unit  21 B and the pressure abnormality determination unit  22 B are provided in the VCM  42  according to the first embodiment and in the LBC  41  according to the second embodiment. Alternatively, the present invention is not limited thereto, and a function distribution in the controller  40 , that is, functions distributed to the LBC  41  and the VCM  42  are optional. 
     Further, although the LBC  41  includes voltage sensors in any of the embodiments, the LBC  41  may be separated from the voltage sensors and transmits the cell voltage V detected by the voltage sensors to the controller  40 . 
     The pressure contributing component that contributes to the pressure change in the battery packs  1  and  2  is the refrigerant gas passage  20  according to the first embodiment and is the gas discharge passage  50  according to the second embodiment. Alternatively, the present invention is not limited thereto, and the pressure contributing component may be any component that contributes to the pressure change in the battery packs  1  and  2 . In addition, the gas discharge passage  50  may be further provided in the battery pack  1  and the refrigerant gas passage  20  may be further provided in the battery pack  2 . 
     Although the embodiments of the present invention have been described above, the above-mentioned embodiments are merely a part of application examples of the present invention, and does not mean that the technical scope of the present invention is limited to the specific configurations of the above-mentioned embodiments. 
     Each of the embodiments described above has been described as a single embodiment, and may be appropriately combined.