What is thermal management of electric vehicles? The development direction of thermal management technology

"Thermal management" is unfamiliar and indifferent to most traditional car consumers. However, in the era of pure electric vehicles, due to the high cost of batteries, battery energy consumption has become the focus of car companies and users. The importance of thermal management has been highlighted.

The vehicle's thermal management system, whether it is regulating the cabin temperature or keeping the battery warm, will have a direct impact on energy consumption and battery life. In the winter tests conducted by media organizations, the quality of thermal management can be intuitively reflected in the rate of battery life achieved and the proportion of increased energy consumption.

What is a thermal management system

Let's first explain what a thermal management system is and what a good thermal management system is.

From the user's perspective, the main functions of thermal management systems in the electric vehicle era are reflected in two aspects: internal and external. The internal function is to keep the temperature inside the car warm in winter and cool in summer, such as heating the seats and steering wheel, or turning on the air conditioner in advance, etc. In the process of quickly adjusting the cabin temperature, how much time it takes to reach the specified temperature and how much energy it takes are critical to find a balance; the external function is to ensure that the battery is at a suitable working temperature - not too hot, which will cause thermal runaway and fire; nor too cold, because when the battery temperature is too low, energy release is hindered, and the actual use is affected by a significant reduction in driving range.

Thermal management is more important in winter because preventing thermal runaway has been fully considered in battery design. However, in winter, how to spend less energy to keep the battery at the optimal operating temperature is the key issue that thermal management needs to solve.

It can be seen from this that the thermal management system of electric vehicles is not just the air-conditioning system of fuel vehicles. It also needs some in-depth iterations on this basis. It needs to be coordinated and optimized with the electronic and electrical architecture, powertrain, braking system, etc. Therefore, there are many tricks and details involved.

How to manage heat

● Traditional method: PTC heating

In traditional designs, electric vehicles are equipped with additional heat source components, such as PTC, to provide heat sources for the passenger compartment and the battery. PTC refers to a positive temperature coefficient thermistor, and the resistance of this component is positively correlated with temperature. In other words, when the ambient temperature drops, the resistance of the PTC will also decrease. In this way, when the power is turned on at a constant voltage, the resistance decreases, resulting in an increase in current, and the heat generated by the power will increase accordingly, achieving a heating effect.

There are two options for PTC heating, water heating and air heating. The difference between the two is the heating medium. Water heating heats the coolant through PTC and then exchanges heat with the radiator; air heating directly exchanges heat with PTC and finally blows out warm air.

● Tesla's heat pump system

In addition to traditional methods, thermal management engineers are also actively trying new solutions. For example, Tesla's solution. I have a friend who is a novice electric car user. She asked me what is so good about Tesla? In fact, Tesla has many technical innovations in electric cars, and thermal management around the heat pump system is one of them.

The heat pump is equivalent to a heat "carrier". It can absorb the heat of low-temperature "objects", such as the cold air outside, transfer it to the working fluid, and then compress the working fluid to increase its temperature. Finally, the high-temperature working fluid exchanges heat with the air inside the car through the condenser to achieve the function of warm air. - It should be noted that this technology itself is not the first of its kind by Tesla. In the early days of electric vehicle development, traditional car companies have already applied heat pump systems to cars and spent 5-8 years to verify product technology.

Heat pump technology has four core components: electric compressor, reversing valve, heat exchanger and electronic expansion valve. Here comes the point. In traditional design, the reversing valve is four-way, and the heat source is the outside air. Tesla's innovation lies in integrating more heat sources and developing an eight-way valve as the "dispatcher" of the thermal management system on the vehicle. Tesla fans affectionately call it "octopus".

Tesla's improved heat pump system essentially combines two parts:

One is the ambient heat that traditional heat pump systems rely on;

The second is the waste heat generated by the power battery system, drive system (including motors and traditional systems) and power electronics. Tesla's thermal management relies on an eight-way reversing valve to perform complex heat extraction on the above two sources of heat, and to move heat more efficiently, which can not only heat up the interior of the car very quickly, but also effectively save energy and reduce consumption, and improve the overall efficiency of the heat pump air conditioner.

Moreover, the working method of Tesla's heat pump system can also improve efficiency through continuously updated algorithms.

The development direction of thermal management technology

What further breakthroughs can be achieved in thermal management technology?

Because the essence of thermal management is to balance the cabin temperature and battery energy consumption, the direction of thermal management technology development should still revolve around "thermal coupling" technology. Simply put, it is to consider at the vehicle level and the overall situation: how to integrate and utilize energy coupling, including: energy gradient utilization, and through system component structure integration and system central integrated control to transfer energy to the required location; in addition, it can also be based on intelligent control of intelligent architecture.

Technological breakthroughs mainly revolve around the interaction of three types of energy:

1) Active heating energy: It uses both traditional PTC heating and motors to heat the battery, using loads in combination to create heat;

2) Passive utilization of environmental energy and waste heat from batteries and motors: Effectively utilize environmental energy and waste heat from motors and batteries through a heat pump system

3) Leverage external grid energy: Take advantage of the grid connection and further leverage (mainly) the grid of home charging stations to preheat the vehicle battery in advance, allowing the battery to reach the optimal state when the vehicle is in use.

In general, the new generation of thermal management systems integrates three types of energy: air, cooling medium, and electrical energy, and then utilizes mechanical energy transfer between systems to maximize energy utilization.

Summary: One of the most important purposes of electric vehicle thermal management is to continuously improve the winter performance of electric vehicles. Some time ago, the temperature dropped across China, and the low-temperature performance of electric vehicles was criticized again. However, I believe that with the development of thermal management systems and battery technology, electric vehicles in the future will be fully adapted to low temperatures.