In recent years, with the rapid development of electric vehicles, how to solve the safety problems brought by electric vehicles has become a new topic and difficulty in the automotive industry. Since people have a process of cognition of new things, it is inevitable that there will be doubts and distrust at the beginning. Therefore, any safety accidents involving electric vehicles will lead to public doubts about the safety of electric vehicles and hinder the safety of electric vehicles. Development and popularization.
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In fact, the fire accidents caused by collision or spontaneous combustion of traditional fuel vehicles have occurred many times every year in the world, and there are also many serious casualties, which will not cause widespread public concern and doubt. The public is so sensitive to the safety accidents of electric vehicles. In addition to electric vehicles, accidents are often accompanied by "special effects" such as fire, sound, light, and smoke. The important reason is that the "battery" is a high-energy carrier. Fear. The cell phone battery is exploding, and there are still things that hurt or even kill people. What about the huge electric car battery?
Electric vehicles (including hybrid vehicles) have many similarities to traditional fuel vehicles, with some differences. There is basically no difference in its operating conditions, use environment, body structure, internal and external modeling, etc. The biggest difference lies in the driving mode and the source of energy. Because of the introduction of electric drives, there are risks such as "shock" and "short circuit" because of the presence of high energy carriers, there is a risk of fire and explosion caused by instantaneous energy release (obviously not what we expect). Because of the stability of the chemical battery itself, there are many risks beyond the “traditional†perception of people.
New things are always fragile. They have to withstand all kinds of suspicions, let alone vehicles that are closely related to personal safety. People who are willing to make their own lives to try and accept unreliable and unsafe products, I think it is a minority. . Therefore, whether it is national-level regulations and standards, or enterprise-level product and technology research and development, we must be people-oriented, effectively solve product risks and hidden dangers, eliminate people's doubts, and promote the development of new energy vehicles. We, there is no reason to take immature and unreliable products, to fool the public and consumers, to serve the personal interests of enterprises or individuals. The safety elements of the power battery will be analyzed in detail from the parameters of the power battery.
First, the composition of the power battery system
As one of the power sources or power sources of electric vehicles, power battery systems are usually composed of a cell, a battery management system (BMS), a cooling system, a harness, a housing, and a structural member. Mechanicalparts) and other related components, as shown below:
It can be seen that the composition of the power battery system is quite complicated, including chemical objects such as batteries, complex electronic and electrical systems and thermal management systems, as well as traditional mechanical components, which involve a very wide range of specialties. Many, coupled with the harsh operating environment, are also facing a wide range of security risks.
Second, the safety risks faced by the power battery system
The safety risks faced by power battery systems are mainly related to the characteristics of internal components and external use and operating environment, which constitute the main challenge of product safety design.
1) Will the battery fire and explode?
The battery used in the power battery system has a very high energy density. Taking lithium iron phosphate batteries as an example, the energy density can reach 120Wh/kg, which is converted into joules. The 1 kilogram lithium iron phosphate battery contains 120×3600 joules = 0.43MJ. . So how much energy does the TNT explosive release? 1 gram of TNT explosive can release 4,184 joules of energy. Converted, 1 kilogram of lithium iron phosphate battery contains the equivalent of 103 grams of TNT.
A pure electric vehicle usually uses a battery weight of several hundred kilograms, calculated on a 100 kilogram battery, and the total energy is equivalent to 10 kilograms of TNT explosives. Who is changing, my heart will be hairy, will this thing be unstable, will it catch fire, or even explode?
2) Will there be an electric shock accident?
In order to improve the driving efficiency of the whole vehicle, the DC output voltage of the power battery is usually above 100V, sometimes as high as 400V or more. Anyone with certain electrical knowledge knows that the DC voltage exceeds 60V, which is a dangerous voltage.
Every year, electric shocks caused by electric leakage from electrical appliances, electric wires, electrical equipment, etc., occur a lot, and they are often seen in the media. When I was a child, I was shocked by the bare 220V wire, and the taste was unforgettable. Then, people also have reason to doubt that the high-voltage live parts inside the electric car will leak electricity and cause electric shock accidents.
3) Can you withstand all kinds of harsh environments?
The operation and use environment of the vehicle is very complicated. It has to withstand the test of high temperature and high humidity, as well as the toughness of the plateau. There are flat pavements and rugged non-paved pavements. It has extremely dry areas and needs to be frequent. Wading place.
During the driving process, the vehicle must undergo a high and low temperature cycle test. It must experience the corrosive climate along the coast. It must undergo heavy rain baptism and large water immersion to withstand various shocks, vibrations, falls, and even collisions and tumbling. So, in the face of these objective environments, can the power battery system be tested without serious safety risks?
4) Can you withstand various abuses?
When the product sales volume is large enough, the use of the product always exceeds the specified limit or some unexpected situation, which is unavoidable. Taking a mobile phone as an example, when the charging protection fails, the mobile phone battery may catch fire or explode due to overcharging. If the cell phone battery is pierced by a sharp metal, an explosion may occur.
Then, can the electric vehicle's power battery system withstand similar abuse tests without causing safety accidents? These abuses are caused by both humans and the objective environment.
5) What should I do if the battery management system fails?
The power battery system has a complex management and control system that collects various operating parameters of the entire power battery pack for calculation, diagnosis, communication, and switch control. The more intelligent the system, the more serious the consequences will be when it fails.
For example, if a battery inside the power battery pack is overheated, the thermal management system fails, and the battery has a risk of thermal runaway. What if the temperature sensor is broken at this time? The software program cannot judge and issue the cutoff command normally. What should I do? Or what should I do if the switch that should be disconnected is not properly disconnected? Will the risk spread and cause serious safety accidents?
Third, the goal of power battery safety design
The safety design of the power battery system basically revolves around the above-mentioned internal component composition and possible safety risks, determines reasonable goals and frameworks, and guides specific product development work.
1) Chemical safety
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