Introduction and cooling scheme of power vehicle battery pack
Power battery is the core of the electric vehicle, high temperature resistance and water resistance and freezing. Electric car does not move, the first time will think of the "core" (battery) out of the question, that in the summer heat, the power battery can be affected by the high temperature?
How to heat the electric vehicle power battery?
The working current of the power battery is large, the heat production is large, and the battery pack is in a relatively closed environment, which leads to the temperature rise of the battery. This is because of the electrolyte in the lithium battery, the electrolyte in the lithium battery internal charge conduction function, the battery which does not have the electrolyte is unable to charge and discharge the battery. Most of the lithium battery is flammable, volatile non aqueous solution composition, the composition of the system compared to aqueous electrolyte composition of the battery is higher than the energy and voltage output, in line with the higher energy needs of users. Because the non aqueous electrolyte is flammable, volatile, and infiltrated in the battery, it also forms the burning source of the battery. So the above two kinds of battery materials are not higher than the working temperature of 60 DEG C, but now the outdoor temperature is close to 40 degrees Celsius, while the battery itself will lead to great heat, working temperature of the battery rises, but if there is thermal runaway, the situation will be very dangerous. In order to avoid becoming "barbecue", to the battery cooling is particularly important.
There are two kinds of active and passive heat dissipation, and there is a big difference between the two. The cost of the passive system is relatively low, and the measures taken are relatively simple. Active system structure is relatively complex, and requires a greater additional power, but it is more effective heat management.
The different cooling effect of different heat transfer medium, air cooling and liquid cooling have advantages and disadvantages.
The main advantages of using liquid as the heat transfer medium are:
With high coefficient of heat transfer between the cell wall and the cooling speed; shortcomings: sealing requirements, quality is relatively large, repair and maintenance of complex water jacket, a heat exchanger, the structure is relatively complex.
In the practical application of electric bus, due to the large capacity, large size, relatively low power density, and therefore more use of wind cooling program. For ordinary passenger car battery, the power density is much higher. Accordingly, it will be more heat dissipation requirements, so the program is more common.
Different sensor of the battery pack will be determined according to the temperature measuring point and the demand. The temperature sensor will be placed in the most representative, the most temperature change position, such as the air inlet and outlet location and the battery pack in the middle area. Especially the maximum temperature and minimum temperature, and the heat accumulation in the center of the battery pack. This will help to control the temperature of the battery in a relatively safe environment, to avoid excessive heat and cold to the battery risk.
In addition, the effect of diaphragm is the battery, mainly in the narrow space will be separated from the battery board, to prevent contact poles caused by short circuit, it can guarantee the freedom of the ions in the electrolyte between the anode. So the diaphragm is the core material to ensure the safety and stability of lithium ion batteries.
Electrolyte is to cut off the source of combustion, the diaphragm is to improve the heat resistance, while the heat is sufficient to reduce the battery temperature, avoid excessive heat caused by excessive thermal control. If the battery temperature rises to 300 degrees, even if the diaphragm does not melt contraction, electrolyte, electrolyte and the positive and negative pole will occur strong chemical reaction, releasing gas, formation of internal pressure and explosion, so the critical cooling way for.
Cooling principle and introduction
Reflect the ability to block the heat transfer of the integrated parameters, when the heat transfer in the heat conduction inside the object, the resistance encountered called thermal resistance. For the heat flux through the cross-sectional area of the same, thermal resistance is L/ (k*A). Where L is the thickness of the plate, A is the cross-sectional area of the plate which is perpendicular to the heat flow direction, and K is the thermal conductivity of the plate material.