Research on thermal management system of Tesla electric vehicle

The automobile air conditioning circuit is divided into an air conditioning refrigeration circuit and an air conditioning heating circuit. The air conditioning refrigeration circuit is connected in parallel with the battery circuit through an electronic expansion valve + Chiller, while the air conditioning heating circuit is completely independent. When the cabin needs to be cooled: the compressor in the refrigeration circuit will start working and transport the high-pressure gaseous refrigerant (R134a, R1234yf, etc.) to the condenser to be converted into a high-pressure liquid refrigerant. The refrigerant is converted from gas to liquid at the outlet of the condenser to release heat. The heat is blown away by the electronic fan. After that, the refrigerant reaches the electronic expansion valve (10) through the three-way valve (9) for throttling, and is converted from liquid to gas at the evaporator (11), absorbing the heat from the surrounding environment and starting to cool. At the same time, the blower (24) close to the evaporator starts working and blows the cold air near the evaporator into the cabin for cooling. Finally, the refrigerant flows out of the evaporator and returns to the compressor through the three-way valve (12), completing the cycle. When the cabin needs to be heated: At this time, the W-PTC (water-cooled-PTC) in the heating circuit starts working, and the coolant starts from the electronic water pump, is heated by the W-PTC, and reaches the heater core, and blows hot air to the cabin from the heater core, and then returns to the electronic water pump through the water tank to complete the cycle.

2.1.2 Battery Thermal Management Circuit

Cooling path: electronic water pump 17 → battery water cooling plate 19 → Chiller 14 (right side) → low temperature water tank 15 → W-PTC 16 (off state) → electronic water pump 17; electronic expansion valve 13 (refrigerant circuit conduction) → Chiller 14 (left side)

Heating path: electronic water pump 17 → battery water cooling plate 19 → Chiller 14 (off state) → low temperature water tank 15 → W-PTC 16 (heating state) → electronic water pump 17

When the battery needs to be cooled: the car air conditioning refrigeration circuit starts working, and the right valve port of the three-way valve will open, the electronic expansion valve 13 adjusts the flow of refrigerant through the Chiller to reduce the Chiller temperature. At this time, the W-PTC is in a stopped state. At this time, the low-temperature coolant will flow from the electronic water pump through the water cooling plate to take away the heat generated by the battery, and then reach the Chiller and cool down again. After that, the coolant will return to the electronic water pump after passing through the water tank and the stopped W-PTC to complete the circuit cycle. When the battery needs to be heated: the three-way valve in the air conditioning circuit closes the right valve port, so that the heat exchanger Chiller maintains room temperature, and the heating component W-PTC in the circuit starts working; the coolant heated by the PTC starts from the electronic water pump, reaches the battery water cooling plate and heats the battery, then passes through the Chiller and water tank to reach the W-PTC and heats again, and finally returns to the electronic water pump to complete the circuit cycle;

2.1.3 Motor thermal management circuit

Cooling path: electronic water pump 6 → low temperature radiator 1 → DC/DC 2 → IPU 3 → motor 4 → expansion kettle 5 → electronic water pump 6

When the motor needs to be cooled, the high-temperature coolant starts from the electronic water pump and reaches the low-temperature radiator for cooling. The coolant with lower temperature then flows through the DC/DC, IPU, and motor and takes away the heat from the power components. The high-temperature coolant then returns to the electronic water pump through the water tank, completing the loop cycle.

2.2 Model S Thermal Management Solution

2.2.1 Function and composition

Tesla's first-generation thermal management technology route is applied to Mode S/X. Like domestic manufacturers, it divides the thermal management of the whole vehicle into three major management circuits: battery, motor and car air conditioning. Among them, the Model S circuit has four major functions: battery cooling, battery heating, cabin thermal management, and motor electronic control cooling. From the perspective of thermal functional components, the whole vehicle is a dual-energy system of battery cooler + air-cooled PTC (chiller + A-PTC), which can heat the cabin and battery pack by PTC and motor waste heat. The changes of the first-generation thermal management technology route relative to the general basic solution are mainly reflected in: First, the series connection of the motor thermal management circuit and the battery thermal management circuit is realized by adding a four-way valve, that is, the motor waste heat recovery function is introduced to realize the function of introducing the excess heat of the motor into the battery circuit; second, a combination of two sets of condensers + electronic fans is adopted, and its consideration is mainly to control the temperature of the cockpit of high-end vehicles and ensure comfort; third, its air conditioning and heating circuit uses an integrated A-PTC + evaporator.

Automobile air conditioning circuit analysis

Heating path: A-PTC (air-cooled PTC) 16 → blower 17 → cockpit

Refrigeration path: compressor 9 → condenser 10 (electronic fan 11) → condenser 12 (electronic fan 13) → thermal expansion valve 14 (open) → evaporator 15 → compressor 9

Automobile air conditioning is mainly used for cabin heating or cooling. When the cabin needs to be heated, the circuit does not circulate, the compressor does not work, the A-PTC is powered on and releases heat, and the blower (not shown in the circuit) close to the A-PTC blows the external air to the A-PTC, which blows the hot air into the cabin after heating. When the cabin needs to be cooled, the A-PTC does not work, the refrigerant reaches the evaporator through the compressor and blows out cold air to generate cooling capacity, passes through the stop valve (14), the evaporator and returns to the compressor, completing the cycle.

Battery Thermal Management Loop Analysis

Heating path: electronic water pump 25 → three-way valve 26 (left side closed, top side open) → electronic water pump 20 → W-PTC 21 (heating state) → battery 23 (battery water cooling plate 22) → four-way valve 3 (left and bottom sides closed) → electronic water pump 25

Cooling path: electronic water pump 25 → three-way valve 26 (left side open, top side closed) → Chiller 19 (heat exchange with the air conditioning refrigeration circuit for cooling, electronic expansion valve 18 is in the open state, controlling the flow of refrigerant) → electronic water pump 20 → W-PTC 21 (closed state) → battery 23 (battery water cooling plate 22) → four-way valve 3 (left and bottom sides closed) → electronic water pump 25

When the battery needs to be heated: the coolant starts from the electronic water pump, flows through the W-PTC through the water-cooled plate close to the battery, and finally passes through the four-way valve, water pump, and three-way valve and returns to the original electronic water pump to complete the circuit cycle. In addition, Model S can also adjust the four-way valve guide to connect the motor circuit and the battery circuit in series to achieve motor waste heat recovery. When the battery needs to be cooled: the water circuit starts from the battery cooler Chiller, flows through the electronic water pump and W-PTC (not working at this time) through the water-cooled plate to cool the battery; then flows through the four-way valve, electronic water pump, three-way valve and returns to the chiller to complete the circuit cycle.

Analysis of Motor Thermal Management Loop

Cooling: electronic water pump 5 → charger 6 → motor integrated reducer and inverter 7 → three-way valve 8 (left side open, bottom side closed) → low-temperature radiator 1 (electronic fan 2) → four-way valve 3 (upper and right side closed, left and bottom side open) → expansion kettle 4 → electronic water pump 5

The motor has a high temperature when it is working, and the main requirement is cooling. When the motor electronic control and charger need to be cooled, the coolant starts from the low-temperature radiator, flows through the four-way valve, the electronic water pump, passes through the power components and takes away the heat, and finally returns to the low-temperature radiator after the three-way valve to complete the cycle.

2.2.2 Value chain distribution

By disassembling the components used in different circuits, we estimate that the thermal management value of a single Model S is about 9,075 yuan (excluding hoses and sensors). Among them, the highest value is the air conditioning thermal management circuit using A-PTC, with a value of about 5,000 yuan and a cost share of about 55%; the battery thermal management circuit has a value of about 2,375 yuan, a cost share of about 25%; the motor thermal management circuit has a value of about 1,500 yuan, a cost share of about 16%; the cross circuit 1 has a value of about 390 yuan, a cost share of about 4%. There is no particularly novel thermal management technology in the Model S, but because it is positioned as a high-end model, it is equipped with dual condensers and the low-temperature radiator of the motor circuit is equipped with an electronic fan separately, rather than sharing it with the air conditioning circuit, so the comprehensive value of the thermal management system is relatively high.

2.3 Model X Thermal Management Solution

2.3.1 Function and composition

The thermal management circuit design of Tesla Model X is not much different from that of Model S. In terms of core technology, both mainly use four-way valves to connect the motor circuit and battery circuit in series and parallel.