Thermal management information for the new energy industry

With the support of national policies and in the face of the depletion of traditional energy sources, new energy vehicles are developing more and more rapidly and becoming more mature. According to data from China Automobile News, at the end of 2022, new energy vehicles in China's auto market hit record highs. From January to November, the production and sales of new energy vehicles completed 6.253 million and 6.067 million, respectively, a year-on-year increase of 100%, and the market share reached 25%, both reaching record highs. As market demand continues to increase, higher requirements are also placed on product reliability. As the most critical component of new energy vehicles, the battery's durability and life are the issues users are most concerned about. The thermal management of the battery is one of the essential technologies that affect the battery's service life and low-temperature battery life.

New energy vehicle thermal management

1. Vehicle thermal management composition

The cooling system of new energy vehicles generally consists of three parts: battery cooling circulation system, motor electronically controlled cooling circulation system, and air conditioning warm air circulation system. The PHEV model also has an engine cooling circulation system. The battery circulation system mainly heats or cools the battery, the motor circulation system significantly cools the drive motor and CIDD (drive motor controller), and the air-conditioning heater system mainly heats or cools the passenger compartment. The main functional components involved include electronic water pumps, three-way solenoid valves, two-way solenoid valves, PTCs, heat exchangers, liquid-gas separators, radiators, expansion kettles, cooling pipelines, and various fixed brackets. The electronic water pump is used as the power source, the coolant is the medium, and the solenoid valve controls the flow direction so that the cooling medium flows through the radiator and the cooled body along the pipeline, thereby dissipating and cooling through heat exchange so that the working temperature of the functional parts is always maintained at Within an ideal operating range to maximize performance. Whether a pure electric or hybrid vehicle, the battery thermal management loop is independent of other systems. The main reason is that the normal operating temperature range of the battery pack is quite different from other systems. The operating temperature of the battery pack is generally not allowed to exceed 35°C. In comparison, the drive motor often works at around 55°C, and the engine operating temperature range is about 95°C, so each circuit must act independently.

2. Differences from traditional automotive thermal management

Thermal management of traditional automobiles is simple, without complex control and component systems. Its goal is only to ensure that the engine temperature always works within an ideal range and to provide the required heat for the passenger compartment to use the waste heat generated by the engine to ensure that No extra power is consumed. Significant differences exist in the system structure between new and traditional energy vehicles. The requirements for the arrangement and installation of system components on the entire vehicle have also increased, and the space requirements for the cabin are more significant. Different types of new energy vehicles have their characteristics. Other characteristics: for pure electric cars, there is no engine as the power source for coolant circulation, and there is no waste heat from the engine to be used. For hybrid vehicles, due to their particular control strategies, the machine cannot provide power for the circulation of coolant when it is not working, nor can it provide the required heat source for the passenger compartment in real time. Therefore, structurally, the thermal management systems of new energy vehicles are designed with an independent electronic water pump to provide power for the circulation of coolant. The warm air usually uses electric heating. A separate electric heating PTC is designed to heat the coolant. Recirculation to the hot water tank in the car to provide heat to the passenger compartment is currently the mainstream method; there is also a method to directly heat the air passing through the evaporation box and blow the heat into the car through a fan. This method involves the vehicle's safety, which is currently rarely used.

Types of battery thermal management systems

Different battery thermal management methods involve other parts numbers, structures, and layouts. Different types of thermal management systems are selected based on vehicle development costs, vehicle weight, and layout space requirements. Its main technical routes include the following five types:

1. Direct cooling type

Referred to as battery direct cooling technology, the natural cooling system has a built-in refrigeration evaporator inside the storm, connected to the air conditioning system through pipelines. When the battery needs to be cooled, a compressor sends the compressed refrigerant into the evaporator inside the storm and then takes the battery away. Internal heat achieves a cooling effect. The system has the advantages of a compact structure, good cooling effect, a small number of parts (only one inlet and one outlet refrigeration pipeline are required), and is lightweight. However, the disadvantages of this system are that it cannot heat the battery under sub-zero low-temperature conditions, the condensed water generated during the refrigeration process is not protected, and the temperature uniformity of the refrigerant is difficult to control. The refrigeration system has a short life and low reliability; refrigerant leakage often occurs. Leakage, insufficient refrigeration capacity, and other faults. This is the latest battery cooling technology with relatively low maturity. It has been applied in mass-produced models on the market, such as BYD and Tesla. It is a major technical route in the future.

2. Heat Sink water cooling type

The Heat sink cooling circuit is independent, consisting of a heat sink, an electronic water pump, a heater, etc., with antifreeze as the medium. The antifreeze comes out of the radiator, passes through the heater, then to the battery, and returns to the heat sink. This cycle cools and heats the battery. The system has the advantages of simple structure, low cost, and energy saving in the low-temperature environment all year round. However, the heat dissipation efficiency of this system is down. The water temperature is high in high-temperature climate environments in summer and cannot meet the operating conditions in high-temperature environments.

3. Direct cooling water cooling type

This system integrates direct and water cooling and bridges the air conditioning and water cooling systems through the battery cooler Chiller (a heat exchanger). This system avoids the shortcomings of the first two cooling methods and is currently one of the most commonly used battery thermal management systems. The system has more components than the first two. The system is more complex and requires a relatively large space to arrange details. The compressor has a heavy load during operation, which consumes much energy for the entire vehicle and could be better economical. In addition, when part of the air conditioning system fails, the cooling needs of the battery cannot be met to the maximum extent.

4. Water-cooled hybrid type

This system is based on the direct cooling water cooling system and adds a radiator water cooling system. The two are arranged in parallel circuits. Different circuits cool the battery under various conditions by controlling the solenoid valve. In low-temperature environments, only the radiator water cooling system works. When in a high-temperature environment, switch to a direct cooling water cooling system to work. Under harsh working conditions, the two systems can work simultaneously, and the battery can also obtain maximum cooling capacity, covering all use environments. This cooling system is highly complex, has high cost, requires high vehicle layout space, has complex system control strategies, and poses a challenge to stability and reliability. This system is also used in most hybrid PHEV models and has mature technology.

5. Air cooling type

This system directly leads the cold air from the passenger compartment, cooling to the battery through the duct, and uses the cold air to air-cool the battery. The advantages of this system are simple structure, controllable cold air temperature, and low system cost. However, it also has the disadvantages of the direct cooling system. The system has no heating function, and the condensed water generated on the battery surface is not easy to dry. There is a risk of corrosion and contamination inside the battery. This type of thermal management method is generally not recommended.

In summary, new energy vehicles will become mainstream in the market with the development of new energy vehicles, and the vehicle's core components will gradually change from engines to batteries. Due to the complex driving conditions of the car, such as high speed, low speed, acceleration, deceleration, etc., the battery will discharge at different rates, generating a large amount of heat accumulation. With the influence of time and space, the battery temperature will gradually increase. The cooling performance of power batteries directly affects the efficiency of the battery and the safety, and durability of the power battery. The battery temperature will affect many characteristic parameters, such as SOC, voltage resistance, capacity, charge and discharge efficiency life, etc. Therefore, cooling the battery when the temperature is too high and heating it when it is too low can ensure its performance and extended service life. With the popularization of new energy vehicles, battery thermal management technology will continue to improve and become more mature. Shortly, other better thermal management systems will appear to improve and overcome the shortcomings of existing thermal management systems. The development of battery thermal management technology will allow the battery to always work in an excellent environment, significantly contributing to the storm's service life. This will eventually promote the continuous development of my country's new energy industry.