Thermal management systems for many consumers is considered a knowledge blind spot or do not care much about the point, some people have heard of thermal management, but most of them only know that thermal management in fuel vehicles, in fact, electric vehicles also have a thermal management system, and, thermal management system for electric vehicle electrical efficiency, energy consumption range and other aspects have a more important role, can directly affect the driver’s experience with the car.
A new generation of automotive thermal management needs
The role of the thermal management system of automobiles is getting more and more attention; in the early automotive research, there was no thermal management sub-sector, the main related ones were air conditioning systems to regulate the cabin temperature, cooling systems to help cool down the engine, etc. Later on, automobile consumers gradually raised the requirements of air conditioning comfort and energy saving, and cost reduction, and the country also gradually raised the requirements of fuel consumption and emission; moreover, in the automobile electric intelligence Under the wave of automotive electric intelligence, the rapid development of new energy vehicles, and new energy vehicles, such as range and safety issues are particularly prominent, automotive thermal management is increasingly important, so the future of thermal management industry demand for certainty.
Compared with the thermal management system of traditional vehicles, the thermal management system of new energy vehicles is more complex, and there are also higher requirements in terms of system efficiency and temperature control accuracy.
The thermal management system of traditional vehicles basically revolves around its power system, which mainly includes the engine cooling system and the air conditioning system that mainly uses the engine waste heat and power for heating/cooling.
Compared with the thermal management system of traditional vehicles, the thermal management system of new energy vehicles is separated from the traditional “three electric”, and there is no engine waste heat to use, relying more on PTC and heat pump, while the working characteristics of the battery also put forward higher requirements for the temperature control accuracy of the thermal management of new energy vehicles.
Development of thermal management system for new energy vehicles
(1) Battery thermal management
Battery thermal management is the core of the thermal management system of new energy vehicles. battery efficient working temperature range is narrow, the thermal management system is the key to maintaining battery performance and safety. power battery can fully play the performance of the temperature range is usually 0 ℃ ~ 40 ℃. temperature is too low, battery charging and discharging power performance decreases, the vehicle shows a lack of power and range reduction; the too high temperature will produce battery thermal runaway risk, threatening the safety of the vehicle. Safety.
The “barrel effect” of the battery requires uniform temperature control, and the power battery is composed of a large number of battery cells in series and parallel, and the overall voltage and capacity are easily affected by a “short” cell. To ensure the consistency of cell performance, the battery thermal management system usually requires a complex and elaborate cooling circuit and multiple temperature sensors to maintain the consistency of cell temperature.
With the increase of battery capacity and power, the efficient liquid cooling has become the main battery cooling method.
Liquid cooling uses coolant (or antifreeze, such as glycol, etc.) as the heat transfer medium, and its heat transfer coefficient is higher than that of air, so the heat transfer effect is better. The coolant flows through the fine flow channel inside the cooling plate to remove the heat from the cells.
The air-cooling system is more traditional and used in China, and is mainly divided into passive air-cooling system and active air-cooling system according to the type of technology. The air-cooling system is usually a simple structure.
Air-cooled systems are characterized by simple structure and low cost, but the effect of thermal management is relatively general, mainly used in the early passenger cars and buses, etc.
(2) The trend of air conditioning system
At present, there are two main types of air conditioning systems for new energy vehicles, PTC air conditioning and heat pump air conditioning.
PTC is the abbreviation of Positive Temperature Coefficient, which means positive temperature coefficient, refers to the semiconductor material or component with a large positive temperature coefficient, referred to as PTC thermistor. If the heat is not enough, the heat production can be increased by increasing the number of resistors or increasing the power.
PTC air conditioner has constant temperature heating characteristics, the principle is that the PTC heating element is charged with self-heating heating up the resistance value into the jump zone, the surface temperature of the PTC heating element will maintain a constant value, the temperature is only related to the Curie temperature of the PTC heating element and the applied voltage, and the ambient temperature is basically irrelevant. The type of PTC heater has a small thermal resistance, high heat transfer efficiency and long-term use of the advantages of low power decay, and better safety performance, that is, in case of fan failure stop, PTC heaters due to insufficient heat dissipation, its input power will automatically drop sharply, at this time the surface temperature of the heater to maintain the Curie temperature or so (generally at 250 ℃ up and down), so as not to produce such as electric heaters class Heater surface “red” phenomenon, the probability of safety accidents is low.
PTC is characterized by low cost, simple structure, fast heat, and low impact by the external environment, so from entry-level cars to high-end cars are commonly used.
The shortcomings of PTC air conditioning is obviously affect the vehicle range, because it needs to consume electricity to generate heat, so it directly affects the vehicle range, as the outside temperature decreases, the resistance value of the PTC decreases, the current through the resistance to generate heat, its heating energy efficiency ratio (COP) maximum value of no more than 1, that is, 1kW of electricity can produce a maximum of 1kW of heat, the test shows that when the winter driving open warm air, the whole process at least The higher the power, the greater the energy consumption, and the longer the time, the greater the energy consumption, and the winter range will be greatly affected, which is especially obvious in new energy vehicles with poor range.
When the heat pump system is heating/cooling, the low-temperature and low-pressure gaseous refrigerant is compressed into a high-temperature and high-pressure state in the compressor, and then the refrigerant flows into the internal/external heat exchanger, exerts heat to the air inside/outside of the car and turns into a high-pressure liquid state, then flows through the liquid storage and drying bottle to remove water and impurities, then transforms into a low-temperature and low-pressure gas-liquid mixture through the expansion valve, and finally changes into a low-temperature and low-pressure gas-liquid mixture through the external/internal heat exchanger from the outside/inside of the car. The air inside the car flows through the heat exchanger to absorb heat and warm up/exhaust heat and cool down to realize the heating/cooling function inside the car.
The heat pump air conditioning system can heat the interior of the car through heat pump technology, and its efficient heating energy efficiency ratio is in line with the development direction of new energy vehicles, and the heat pump air conditioning system is driven by an electric compressor, which has an independent energy supply method, and the heat pump air conditioning system has no significant impact on the operation of new energy vehicles, Then the thermal energy efficiency ratio COP (absorbed heat + consumed electricity)/consumed electricity) must be greater than 1, so that 1kW of electric power can achieve 1.5kW or even 2kW of heat.
The heat pump air conditioning system can improve the efficiency of the vehicle’s electric power utilization and change the phenomenon that the range of pure electric vehicles is greatly reduced in low-temperature environment. Energy-saving, new energy vehicles in the future may use heat pump air conditioning is the main.
The heat pump system can transfer heat from the low temperature to the high temperature, mainly by collecting heat from the outside environment, evaporating and absorbing heat, and liquefying and releasing heat. The main components are compressor, pump body, etc.
In addition, even with heat pump air conditioning, PTC is still difficult to be completely replaced in the short term because: 1) at present, it is difficult to meet the mandatory standards of defrosting and defogging by heat pump alone, PTC is still the standard for new energy vehicles; 2) PTC has cost advantages.
(3) Electric drive electric control system thermal management
Motor and electric control (inverter, charger, DCDC, etc.) is a major source of heat in new energy vehicles, and the motor winding and IGBT will generate a lot of heat under high power output and charging, and if the heat is not dissipated in time, the performance and life of electromagnetic and electronic components will be reduced under high temperature, which will eventually lead to the weakening of the performance of the whole vehicle and even cause downtime.
Similar to the traditional automobile engine cooling system, the mainstream motor cooling method is liquid-cooled, some high-performance cars use oil-cooled. in the high current, the motor internal consumption in the form of heat increased sharply. if the motor does not operate under high-current conditions to effectively cool, the motor’s internal temperature continues to rise, which will lead to a decline in motor efficiency. if the temperature is too high, it will cause internal ablation or even breakdown, resulting in motor damage. According to the type of medium, the motor cooling system is divided into air-cooled, water-cooled and oil-cooled. air-cooled, i.e. air-cooled, has limited heat dissipation capacity and is usually used for small electric vehicles with low power. water-cooled is the mainstream cooling method for motors at present, and the coolant takes away the heat by flowing through the motor shell. however, the heat of the rotor, winding, stator and other internal components has to be transferred through layers of components to the shell and the coolant heat exchange, which has a long transfer path, Oil is non-conductive, non-magnetic, good thermal conductivity, and can be used as a medium to directly cool the internal parts of the motor. oil cooling method requires the addition of an oil cooler to make the oil and coolant heat exchange. oil cooling system is complex, technically difficult, and costly, and is not used much except for Tesla.
The heat generating components of the electronic control system mainly come from the power components such as IGBT, etc. The pursuit of high power of the motor and the requirement of compact design of the electronic control system pose a higher challenge to the heat dissipation of the electronic control system, especially the power components; currently, the electronic control system and the motor are usually connected in series in a cooling circuit, and the heat is dissipated through a heat sink, the architecture is similar to that of the engine cooling system.
Value of thermal management system for new energy vehicles
The thermal management system of new energy vehicles is more complex than that of traditional vehicles, which also determines that the value of the thermal management system of new energy vehicles is higher, and the proportion of the total vehicle manufacturing cost will increase.
Overall, the overall sales of new energy vehicles will continue to grow in the future, and it is expected that the sales of new energy vehicles in the domestic market will reach 12 million units in 2025. The thermal management system with higher value will help the new energy vehicle thermal management market achieve rapid growth and increase in volume and price.
Under the background of carbon peak and carbon neutral, thermal management technology, as an important means to help enterprises to transform into green, will have a profound impact on the long-term trend of various industrial fields, and the thermal management industry will soon usher in new development opportunities.