Seat belts are set to fix passengers' body to avoid collision occur. They are mainly divided into two points type and three points type. Two points type seat belt only fixes waist of passengers, but not the upper part of the body. General it is not used in front seats. Three points type seat belt, based on in two points type, is added a strap across to shoulder to fix the upper body. The fixing strap has three fixed points, and it can fix the upper body of passengers, improving security.
Pre-tightening seat belts: at the moment of car collisions occur, and before passengers move forward, it will first pull the belt, and immediately binds passengers tightly on the seat, and then locks the belt to prevent passengers leaning forward, effectively protecting passengers' safety. Apart from the usual retractable function of common seat belts, there are also pre-tensioning device and control device. Their function is to strengthen passengers' constraining force within about 0.1s, fix passengers in the seat, and reduce the possibility of injury furthest when the vehicle speed is drastically changed. Thus seat belts can also be attributed to the active safety system.
Air bags (SRS)
When strong collision occurs in the front-end of vehicles, the airbag will instantly "jump out" from steering wheel, padding between the steering wheel and the driver, to prevent the driver's head and chest from impacting to the steering wheel or the instrument plate these hard objects. (Airbag will not "jump out" without judging the strength of the collision. It has requirements on the stress and contact area of front collision. Generally, it will react and work to the front collision with speed above 40 km per hour).
Work process: when the sensor detects the intensity of the crash, it will send out signals; according to the signal indication, the gas generator produces ignition action, lights solid fuels and generates gases (mostly nitrogen) to inflate the air bag, expanding the air bag rapidly. After the air bag expands, it immediately discourages to prevent passengers from secondary damage by rebound. But it is important to note that airbag bursts out with a short period of time. Generally speaking, they will burst out only on severe impacts, and cannot recover. Its protection is much less than that of a seat belt from a realistic point of view. And if you are not using a seat belt, once the accident happens, the air bags will not help. Thus airbags can really play their role with seat belts.
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