How much do you know about the hidden safety technology of pure electric vehicles?

Posted 2022-08-03 00:00:00 +0000 UTC

Because it involves a lot of electrical safety problems, many safety protection measures need to be designed. If you know very little about pure electric vehicles in the past few years, you must have reached the standard of passing line now. For example, we will pay attention to whether a new car comes from the pure electric platform, because the pure electric vehicle not only cancels the fuel, but also changes the transmission mechanism. According to different driving modes, some parts are even cancelled directly, and new mechanisms such as charging system and driving motor are added, which make the pure electric vehicle need to be redesigned in the platform stage. Once we have an understanding of pure electric vehicles, we can further explore the safety technologies that are not easy to be detected in pure electric vehicles. Because of the high risk of fire and the difficulty of putting out the fire, pure electric vehicles pay much attention to the electrical safety. The 7 items listed below are the common guidance methods for the layout of high-voltage system of electric vehicles: for example, collision high-voltage power-off protection, one of the characteristics of this technology is that it occurs very fast. Take the pi4 platform design as an example, after the collision, the PSS can disconnect the high-voltage main relay within 30ms to ensure the high-voltage safety. Based on these requirements, there are many technologies that we will not feel directly in our daily life. Collision high-voltage power-off technology will cut off the electrical connection of the main circuit of the high-voltage system when the vehicle collides and the power battery manager detects that the collision signal is greater than a certain limit value, at the same time, it will inform the drive motor controller to activate the active discharge, thus blocking the short-circuit danger. In addition, the anti overcharge system is secretly protecting us. For example, a CID (current interrupt device) mechanical device is installed on the cell. When the internal pressure of the cell exceeds the set value (and the BMS battery management system fails), the CID will automatically pop open, disconnect the series circuit between the cell and the cell, and forcibly terminate the charging process. Therefore, in this case, do not think it must be equipment failure, or the active power-off protection adopted by the equipment to prevent overcharge. The basic principle of this technology is to use the internal pressure rise caused by overcharge (because the electrolyte is vaporized), so as to push the CID flip sheet to turn off the circuit to prevent the battery overcharge. The basic working principle of electric drive control system pure electric vehicle is to output electric energy through the power battery, the motor controller drives the motor to run to generate power, and then transmits the power to the driving wheel through the deceleration mechanism. In the last paragraph, we mainly introduced the battery safety technology, of course, the electric drive technology also contains mystery. We know that the electric drive system mainly includes high-performance power motor, power electronic control unit, reducer and other parts. According to the current development trend, integration has become a hot spot. Taking ZF mstars rear suspension as an example, this 150KW electric drive EVD module includes motor, transmission, differential and power electronic module, which is applicable to pure electric and system, and can replace the drive or non drive rear axle system with independent suspension. The integration of the electric drive system can effectively reduce the volume of the electric drive system (easy to layout), reduce the total mass of the system (conducive to lightweight). One of the technical highlights in the mstars system of ZF mstars rear suspension is the rear wheel active steering system AKC, which is a set of wire controlled active steering system that can cooperate with the front wheel steering system to achieve four-wheel steering. Specifically, it can help reduce the turning radius of the vehicle when driving at low speed; reduce the body sway when driving at high speed, and improve stability and safety. Because of the complexity of the structure and the high requirement of the safety capability of the integrated drive system, multiple protections need to be set. For example, aion LX adopts dynamic monitoring, safety monitoring platform, temperature control protection and other links to ensure system safety. We always focus on the body materials in the body safety design. In fact, the body structure design is also very important. However, we seldom see this part, and the impact process is very intense. Unlike safety belts, airbags, headrests, etc., which can give us the most direct safety protection experience, it is easy to ignore their safety contributions. Why is structural design important? Let's take the egg as an example. Three eggs can support a Book nearly half a meter high without breaking, because the eggshell fully mobilizes the structure of each place to bear the force, and reduces the stress concentration as far as possible, leading to local fracture. The body structure of carbon fiber monomer shell is built by the force principle of egg. In the design of pure electric vehicle body, the best practice is to get rid of the traditional load-carrying structure and adopt the frame floor + load-carrying body structure. For example, es8, etc. This kind of body is similar to the half load body structure, and the purpose is to protect the battery pack located on the floor. Weilai es8 also adopts integrated hollow door sill, which can strengthen the ability of anti-collision. This kind of structure is rare in the traditional body. The crash safety performance of pure electric vehicle should consider not only the safety of passengers, but also the safety of battery system. In addition to the battery pack, the protection of high-voltage components is particularly important. Tesla Model 3 uses a method to remove some high-voltage devices from the front compartment for energy absorption and integrate them into the upper rear part of the battery pack. When the high-voltage device is placed in this position, it will be protected by the frame floor structure in case of collision, and the battery pack shell in case of bottom scraping. High voltage components shall be arranged in non collapse energy absorption area as far as possible. This integrated design of Tesla Model 3 makes full use of the space under the rear seats. Yaston summarizes the safety protection measures that our consumers pay most attention to, such as air bag, ADAS protection technology (such as AEB, LDW, BSD, etc.), which are very important, but pure electric vehicles need to design many safety protection measures because they involve a lot of electrical safety problems. These technologies may not be as dazzling as ADAS, or even many people can't call them names, but it's just a little accumulation that ensures enough security.

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