Since it was gradually adopted in civilian vehicles in the 1980s, airbags have become a very important passive safety equipment for automobiles. The number of airbags has become one of the references to measure the safety of vehicles. The structure and principles of airbags How? What conditions do airbags need to open? What are the disadvantages? What should be paid attention to during use? The following will explain to you one by one.
Principle and structure of airbag
Airbags are part of the "Assisted Restraint System" (SRS), which is mainly used to prevent injuries caused by collisions between occupants and components in the car during a car collision. It usually appears as an auxiliary safety device for seat belts. collective effect. The protection principle of the airbag is: when the car is subjected to a certain collision force, the airbag system will trigger a chemical reaction similar to the explosion of a small amount of explosives. The parts can be placed in time before the collision. When the human body contacts the airbag, the airbag begins to exhaust through the air holes on the surface of the airbag, thereby playing a cushioning role, reducing the impact force on the body, and finally reducing the occupant injury.
Schematic diagram of the airbag system structure of a common car model
Commonly used automobile airbag systems are composed of collision sensors, control modules (ECUs), gas generators, and airbags. The following describes each of these main components one by one.
Airbag system sensor
Airbag sensors are generally called collision sensors. According to different uses, collision sensors are divided into trigger collision sensors and guard collision sensors. Triggered collision sensor is also called collision intensity sensor, which is used to detect the acceleration change during collision, and transmits the collision signal to the airbag computer as the trigger signal of the airbag computer; the protective collision sensor is also called the safety collision sensor, which is connected with the trigger collision sensor It is used in series to prevent accidental explosion of the airbag.
According to different structures, collision sensors can also be divided into electromechanical collision sensors, electronic collision sensors, and mechanical collision sensors. The protective collision sensor generally adopts an electronic structure, and the trigger collision sensor generally adopts an electromechanical combined structure or a mechanical structure. The electromechanical combined collision sensor uses mechanical movement (rolling or turning) to control the action of electrical contacts, and then the opening and closing of the contacts to control the turning on and off of the airbag circuit. The common ball and eccentric hammer types Impact sensor. Electronic collision sensors do not have electrical contacts, and there are currently two types of resistance strain and piezoelectric effect. Commonly used in mechanical collision sensors is the mercury switch type, which uses the conductive characteristics of mercury to control the turning on and off of the airbag circuit.
The airbag collision sensors installed above the front longitudinal beam of the engine compartment are mostly electromechanical
Control module (ECU)
For early cars, there are usually multiple trigger collision sensors, and the installation location is generally in the front and middle of the body, such as the inside of the fender on both sides of the body, under the headlight bracket, and the sides of the engine radiator bracket. With the development of collision sensor manufacturing technology, some cars will trigger the collision sensor to be installed in the airbag system ECU. The protective collision sensors are generally assembled with the airbag system ECU, most of which are installed under the center console in the cockpit. The ECU is the core component of the airbag system and is mostly installed under the center console in the cockpit.
Most airbag control modules (ECU) are installed in the middle of the body near the stop
Schematic diagram of a typical airbag system control circuit
During vehicle driving, the sensor system continuously sends speed change (or acceleration) information to the control device. The airbag control module (ECU) analyzes and judges this information. If the measured acceleration, speed change, or other indicators exceed the predetermined value ( That is, a collision actually occurred), the capsule control module issues an ignition command to the gas generator.
The gas generator
The gas generator is mainly used to generate a large amount of gas to fill the airbag in a short time (about 30ms). The gas generated must be harmless to the human body, and the temperature must not be too high. At the same time, the gas generator must be highly reliable. Sex and stability. At present, there are three types of gas generators: compressed gas type, pyrotechnic type and mixed type. The hybrid gas generator is a combination of compressed gas type and pyrotechnic type. It is also a gas generator widely used at present.
Modules (back) containing gas generators and air bags are generally not allowed to be disassembled
Sodium nitride or ammonium nitrate are stored in the gas generator. When the car is violently hit during high-speed driving, these substances will quickly decompose and produce a large amount of gas (non-toxic and odorless nitrogen accounts for more than 70%), filling the airbag. The newer airbags incorporate devices that can be staged to inflate or release pressure in order to prevent the huge pressure from a sudden burst from hurting the human body. Hierarchical explosion device, that is, the gas generator is detonated in two stages, the first stage produces about 40% of the gas volume, which is far below the maximum pressure, which buffers the movement of the human head, and the second stage explosion produces residual gas. And reach the maximum pressure. The gradual pressure release method is to open a pressure relief hole or an adjustable pressure hole in the airbag bag. When the pressure reaches the set limit at the beginning, the pressure can be released instantly to avoid excessive damage to the passengers.
Cushion airbag
The airbag is generally made of polyphthalamide fabric with good crack resistance. It is a semi-hard polymer material that can withstand greater pressure; after vulcanization treatment, the impact force of the airbag when inflating and expanding can be reduced. To seal the gas, the airbag is coated with a coating material. The size, shape, and air leakage performance of the airbag are important factors in determining the protective effect of the airbag, and must be determined according to the actual situation of different cars. When the airbag is at rest, it is folded into a bag and placed between the upper part of the gas generator and the airbag trim cover. The surface of the airbag trim cover is molded with a light mark to tear the trim cover when the airbag is inflated and reduce the resistance to rush out of the trim cover . The back or top of the airbag is provided with an exhaust hole. When the driver presses on the airbag, the airbag is exhausted from the exhaust hole after being compressed.
In addition, the airbag system has a backup power supply. The backup power supply circuit is composed of a power supply control circuit and a number of capacitors. When the car crashes and the battery and generator are disconnected from the airbag system, the backup power supply can maintain the airbag system power supply for a certain period of time (generally 6 seconds).
In order to ensure that the steering wheel has a sufficient turning angle without damaging the connection harness of the airbag assembly, a spiral harness is used between the steering wheel and the steering column, that is, the harness is installed in the spiral spring (the spiral harness is also called a spiral spring, Hairspring or hairspring).
Airbag initiation conditions
In order to ensure that the airbags are opened at the appropriate time, automobile manufacturers have stipulated the detonation conditions of the airbags. Only when these conditions are met, the airbags will explode. Although in some traffic accidents, the occupants in the car are hit by blood, even in danger of life, and the vehicle is close to scrapping, but if the conditions for the explosion of the airbag are not met, the airbag will not be opened.
Airbag deployment requires proper speed and collision angle. Theoretically, the airbag can only be opened when the vehicle hits a fixed object at a position between about 60 ° right and left, and the speed is higher than 30 km / h. The speed mentioned here is not the speed we usually understand in the sense, but the speed of the vehicle in the laboratory with a relatively rigid fixed obstacle collision. The actual speed of the car in the collision must be equivalent to this test speed to open the airbag.
In the crash test, they all hit a rigid object, and the actual collision speed must be equivalent to the predetermined speed before the airbag will open.
The main load-bearing parts of a car during a collision are the passenger cabin frame and the body longitudinal beam. In order to buffer the impact force during a collision, the front of the body is mostly designed with a collision buffer, and the stiffness of the body is also announced unevenly. In some accidents, such as a rear-end collision accident between a car and a truck without rear guards, or a rollover accident after a car crashes into the guardrail, or a side collision of the body, etc. Such accidents often do not have a direct impact on the front of the body , Mainly due to the collision between the upper part and the side of the body. The stiffness of the body part of the collision is very small. Although the cabin is greatly deformed, causing occupants to be injured or killed, but because the collision part is wrong, sometimes the airbag cannot be opened.
Airbags have defects
As one of the effective measures to improve the safety of automobiles, airbags have been paid more and more attention. In some actual collision accidents, it has been proved that airbags have the effect of reducing occupant casualties, but some problems existed. The problems in the use of airbags are:
The airbag may be opened at a very low speed. When the car is running at a very low speed and a collision accident occurs, the occupant and the driver can wear a seat belt, and the airbag does not need to be deployed for protection at all. If the airbag is deployed at this time, it will cause unnecessary waste, and may even increase the collision injury due to the deployment of the airbag.
The activation of the airbag will cause injury to the occupants. When the airbag system is activated, the airbag cover will be opened, and the airbag will be deployed and inflated in an instant, which may cause shock to the occupant; the hot gas generated will also burn the occupant and the driver. According to calculations, if the car travels at a speed of 60km / h, the sudden impact will stop the vehicle within 0.2 seconds, and the airbag will pop up at a speed of about 300km / h, and the resulting impact force is about 180 kg It is difficult to bear the weak parts of the human body such as the head and neck.
When the passenger deviates from the seat or no one or child is seated on the seat, the activation of the airbag system not only does not provide the protection it deserves, but may also cause some damage to the occupant.
The front passenger airbag that can be turned off is still very practical
Use of airbags
Because the airbag system has certain risks, and it needs to be used correctly to play the role of the SRS system, therefore, for vehicles equipped with airbags, some matters need to be paid attention to in daily use. In the case of ensuring the correct driving posture, the driver should move the seat as far as possible, so that there is enough space for the airbag to fully play its protective role after accidental expansion, and the driver must wear a seat belt. Children under the age of 12 should sit in the back row of the car and buckle up the seat belt. Never put the child in the front row. The huge impact of the airbag when it detonates may even be fatal for them!
For models with airbags, the rear child safety seat fixtures should be more fully utilized
summary:
Although the current car manufacturers promote airbags as an important selling point, airbags are a double-edged sword that does not compromise. When you use them reasonably, they can play a good role in protection, but the airbag cannot be opened Or unreasonable use may have side effects. Again, all safety equipment is auxiliary, and only safe driving is the most important guarantee to ensure safety.
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