Research on thermal management system of Tesla electric vehicle

1. Thermal management functional architecture and trends of new energy vehicles

The purpose of the technical iteration of the thermal management system of new energy vehicles is to achieve internal matching of the heat and cooling requirements of each circuit, optimize energy consumption, reduce battery energy consumption and realize cooling and heating functions; the thermal management circuit of pure electric vehicles mainly includes automobile air-conditioning circuit (cockpit thermal management circuit), battery thermal management circuit, and motor thermal management circuit. Among them, the air-conditioning heating circuit can generate heat through PTC or heat pump, and the air-conditioning refrigeration circuit can generate cooling; the battery thermal management circuit can generate heat, but in different situations, it needs to be cooled and heated; the motor thermal management circuit can generate heat and mainly needs to be cooled. If we divide each circuit according to the supply and demand of heat and cooling: heat supplier: air-conditioning heating circuit, battery thermal management circuit, motor (or electric drive) thermal management circuit; cooling supplier: air-conditioning refrigeration circuit; heat demander: cockpit, battery thermal management circuit; cooling demander: cockpit, battery thermal management circuit, motor thermal management circuit.

Upgrading the thermal management system can improve the range of new energy vehicles and the driving experience of car owners. 1) Efficient thermal management technology can reduce the energy consumption of the whole vehicle and improve the range without increasing the capacity of the power battery. At the same time, the car air-conditioning system can maintain a constant temperature in the car cabin by adjusting the PTC power or the heat pump power, so that passengers feel a comfortable temperature; 2) By analyzing the differences in the thermal management circuit structure and the increase and decrease in the number of parts, the value of the thermal management system of new energy vehicles can reach 5,000-10,000 yuan (including heat pumps), which is significantly higher than the value of traditional fuel vehicles, which is generally no more than 2,500 yuan. With the upgrade of thermal management technology, degree of integration, refrigerant media and other solutions, it is expected to drive the value of thermal management vehicles to increase.

By analyzing and combing the history of iterative changes in thermal management technology solutions, we found that the industry has two major characteristics in the accelerated growth period: First, the current mainstream domestic OEMs have completed the realization of basic thermal management functions, but thermal management technology is still innovating and iterating. By combing the technical routes of strong OEMs such as Tesla and Toyota and thermal management manufacturers such as Sanhua and Yinlun, we believe that the technical iteration direction of heat pump air conditioning and integrated control is clear. At present, the motor thermal management, battery thermal management and cabin thermal management of leading OEMs have all derived second-generation and third-generation technologies, and each generation of technology has higher requirements for software and hardware integration. Taking the active liquid cooling technology of motor thermal management as an example, in order to quickly cool the motor, the on-board computer needs to adjust the coolant flow in the loop according to the preset program, and can decide whether to connect the battery circuit and the motor circuit in series through a four-way valve according to the heat of the battery pack to achieve more efficient integrated thermal management control. We believe that the technical trend of thermal management solutions for new energy vehicles is to achieve optimal energy consumption within each thermal management circuit by integrating or changing the connection method of each circuit, and to minimize dependence on battery energy consumption.

Second, the OEMs lead the development of thermal management solutions, with significant customization features; there is no clear guidance on thermal management technology routes at the policy level; by sorting out the policies of regulatory departments such as the Ministry of Industry and Information Technology and the State Administration for Market Regulation, we found that national policies have few technical guidance and mainly focus on new energy vehicles and battery safety. At present, many national departments have successively issued policies to prevent and control the spontaneous combustion and explosion of batteries under extreme conditions. However, there are no guidance requirements for specific thermal management technology routes. Taking heat pump technology as an example, Europe and other countries currently prohibit the use of R134a due to environmental protection requirements, but have not determined further refrigerant routes in the future (CO2 or R1234yf).

In terms of thermal management technology, Tesla has iterated three versions of technology routes in the four models of Model S/X/3/Y; it has strong technical accumulation in motor waste heat recovery, large integrated control valves, motor blocking technology, vehicle thermal management calibration and intelligent thermal management algorithms. By comparing the technical differences between Tesla and domestic OEMs, we believe that Tesla's third-generation technology represented by Model Y has outstanding advantages in energy consumption management and thermal control. In contrast, domestic OEMs and thermal management manufacturers are still in the stage of motor waste heat recovery (Tesla's first-generation technology). In 2021, the penetration rate of heat pumps was only about 20%, and solutions such as large-scale integrated control and intelligent thermal management algorithms have not yet been mass-produced.

Tesla Model Y is the epitome of thermal management technology for new energy vehicles. From 2010 to 2019, new energy pure electric thermal management technology was still in the stage of realizing basic functions, and the technology was still frequently iterating (integration). At the same time, technical trends such as refrigerant technology upgrades have not yet been clarified, and the industry competition pattern has not yet been fully finalized (each supplier gradually expanded the remaining links of thermal management products based on their own advantageous products). In 2020, Tesla Model Y opened up a new benchmark for thermal management solutions for new energy vehicles. In 2021, BYD and Huawei followed up to launch new and efficient solutions. The analysis of its technical route is helpful to sort out the technical development path and predict the technical trends in advance: 1) Technical feature 1: large integrated eight-way valve. Dynamically combine the heat pump air conditioning system with the motor and battery thermal management circuit to realize motor waste heat recovery, reduce pipeline usage, save energy and reduce costs; 2) Technical feature 2: multifunctional heat pump using R1234yf refrigerant. The R1234yf-based heat pump recovers waste heat in the thermal management loop, and is supplemented by a low-voltage heater and refrigerant recirculation technology, which enhances the heating capacity and heating efficiency of the thermal management loop in low-temperature environments, improves battery life, and improves the owner experience; 3) Technical feature three: motor oil cooling. In the Model 3 system, Tesla added an oil cooling module to assist cooling, greatly improving thermal management efficiency and meeting the cooling requirements of high-power operation of the motor.

2. New Energy Vehicle Thermal Management 1.0 Technical Architecture

Core point: In order to better understand Tesla's technological iteration and highly integrated thermal management technology, we first introduce the most basic new energy pure electric thermal management circuit. Generally speaking, the thermal management system of new energy pure electric vehicles can be divided into automotive air-conditioning circuit, battery thermal management circuit and motor thermal management circuit. Among them, the battery heat pipe circuit operating temperature generally needs to be maintained at 20-35°C. This circuit can generate heat, and there are cooling and heating requirements in summer and winter respectively; the operating temperature of the automotive air-conditioning circuit is generally 18-30°C, which can be used for heating and cooling; the normal operating temperature of the motor thermal management circuit can reach up to 60-80°C. This circuit can generate heat and only has cooling requirements.

2.1 Functional principle and structural composition

In the basic thermal management architecture, the three major circuits of air conditioning, battery and motor are connected in parallel and independent of each other, and the coolant will not flow across the circuit. Taking the first-generation thermal management circuit of a domestic new power car company as an example, the motor circuit is connected in parallel on the outside of the entire thermal management circuit; the battery circuit and the car air conditioning circuit are connected in parallel, and the heat exchange between the refrigerant and the coolant is carried out through the chiller; inside the car air conditioning circuit, the cooling and heating function circuits are connected in parallel.

2.1.1 Passenger compartment air conditioning circuit

Refrigeration path: electric compressor 7 → condenser 8 (electronic fan 24) → three-way valve 9 → electronic expansion valve 10 → evaporator 11 → three-way valve 12 → compressor 7

Heating path: electronic water pump 20 → W-PTC 21 → heater core 22 → expansion kettle 23 → electronic water pump 20