One of the biggest problems caused by vehicles using fossil fuel, such as gasoline and diesel oil, is the creation of air pollution. A technology of using a secondary battery, which can be charged and discharged, as a power source for vehicles has attracted considerable attention as one method of solving the abovementioned problem. As a result, electric vehicles (EV), which are operated using only a battery, and hybrid electric vehicles (HEV), which jointly use a battery and a conventional engine, have been developed. Some electric vehicles and hybrid electric vehicles are now being commercially used.
A hybrid electric vehicle (HEV) is configured to have a structure in which a middle or large-sized battery pack based on secondary batteries which can be charged and discharged and an engine based on gasoline and diesel oil are jointly used, and the battery pack or the engine is controlled to be operated according to traveling conditions of the vehicle, etc. That is, in order to minimize the use of fuel while improving operational efficiency, the engine or the battery pack is selectively operated according to running conditions of the vehicle. For example, when the vehicle runs at a normal speed or moves downward along an incline, only the battery pack is used without using the engine. On the other hand, when the vehicle runs at an accelerated speed or moves upward along an incline, the engine based on fuel is mainly operated. At this time, kinetic energy generated during operation of the engine is converted into electric energy, with which the battery pack is charged.
A nickel-metal hydride (Ni-MH) secondary battery or a lithium secondary battery has been mainly used as the power source for electric vehicles (EV) and hybrid electric vehicles (HEV). High output and large capacity are needed for such a secondary battery to be used as the power source for the electric vehicles (EV) and the hybrid electric vehicles (HEV). To this end, a plurality of small-sized secondary batteries (unit cells) is connected in series or in parallel to each other to constitute a battery module, and a plurality of battery modules is connected in parallel or in series to each other to constitute a battery pack.
However, a larger amount of heat is generated from such a high-output, large-capacity secondary battery during charge and discharge of the secondary battery. If heat generated from the unit cells during charge and discharge of the unit cells is not effectively removed from the unit cells, the heat accumulates in the unit cells with the result that deterioration of the unit cells is caused.
For this reason, a battery pack for vehicles, which is a high-output, large-capacity battery including a plurality of middle or large-sized battery modules, needs a cooling system to cool battery cells or battery modules mounted therein.
In connection with this case, a cooling technology using a liquid refrigerant to cool the battery cells or the battery module within a short time has attracted considerable attention, and the demand of a battery pack for vehicles adopting such a cooling technology has increased.
In the battery pack adopting the cooling technology using the liquid refrigerant, however, refrigerant channels are provided between battery cells or battery modules stacked in a pack case, or the refrigerant channels contact an additional thermal conduction member disposed in the pack case. For this reason, it is necessary to provide various joints and connection members for connection between the refrigerant channels. In addition, for the battery pack for vehicles, which is continuously affected by vibration for a long time, connections between the refrigerant channels and the joints may be broken when the liquid refrigerant flows along the refrigerant channels provided in an inner space of the battery pack with the result that leakage of the refrigerant may occur.
In a case in which the leaked liquid refrigerant contact bus bars, wires, and connectors disposed in the inner space of the battery pack, an insulation breakdown or a short circuit may be caused with the result that the vehicle may catch a fire.
Furthermore, connection members for fixing the refrigerant channels are disposed in the inner space of the pack case with the result that a manufacturing process of the battery pack is complicated, and component maintenance cost is increased.
Therefore, there is a high necessity for a battery pack having excellent safety against leakage of a refrigerant.