Airbags | How do they work?

0:00 This would happen in a high-speed accident if there was no airbag, even if the driver fastened their seatbelt. It is a big engineering challenge to bring the human body to rest from a high speed in a time duration of 100 milliseconds without causing much harm to the body. Let's learn about this life-saving technology by understanding the mechanism of airbag inflation, which, interestingly, happens thanks to a chemical explosion. Seatbelts are supposed to hinder the movement of a human body. However, during accidents, such seatbelts exert huge force on your chest area and can cause internal organ injury. To avoid this huge force on the chest, modern seatbelts slightly release the seatbelt with the

0:46 help of a torsion bar. This action makes the upper body slightly move forward, but once the torsion bar is done with the belt release, the upper body's movement is arrested here. Let's pause here and analyze the physics of the accident in detail. Please note that the seatbelt arrests the motion of your upper body, excluding your neck and head. When only your upper body is arrested and the neck and head are not arrested, you can guess what will happen. The head goes in a perfect pendulum movement in a high-speed accident. The devastation can be horrific even with the seatbelt. This is why engineers came up with the idea of airbags. Airbags have a cushioning effect and at the same time prevent you from hitting the dashboard. The very first

1:33 attempt to inflate the airbag using a compressed air arrangement was a failure. This design had two main issues. One, the spring was not able to determine the crash accurately. Two, the compressed air was not able to fill the airbag fast enough to prevent damage from the crash. For these reasons, they were not commercially used. The founder of Joyson Safety Systems, Mr. Alan K. Breed, came up with some groundbreaking inventions to solve these issues. First, he improved the accuracy of the sensor using a ball-in-tube sensor. In this sensor, a steel ball is held in position with the help of a magnet. When a collision occurs, the car decelerates very quickly, but the ball gets separated from the magnet due to its inertia. The ball moves

2:22 forward to close the circuit and sends a signal to the inflator. The second and his biggest contribution was the use of chemical explosives instead of compressed air. Mr. Breed used a chemical called sodium azide for this purpose. The specialty of sodium azide is such that if this solid chemical is triggered by a temperature more than 300 degrees Celsius, it would rapidly and directly convert to a gaseous state. The 50 grams of sodium azide generated nearly 70 liters of nitrogen. This chemical is filled inside an airtight cylinder of the steering wheel. The electric signal sent by the ball sensor passes through a pyrotechnic device. It is a thin, resistant wire. When

3:08 the current passes through it, it generates a temperature of more than 300 degrees Celsius. This causes the sodium azide to explode and generate nitrogen gas very quickly. This is able to inflate the bag within 30 milliseconds. These two breakthroughs made airbags possible for commercial use. This patented design of Breed Corporation was released by Chrysler in their Dodge Daytona model cars in 1988. This was a massive success and all other car manufacturers started to implement similar airbag technologies. However, this design has two major drawbacks. First, the gas produced after the sodium

3:54 azide explosion is toxic. The sodium metal of the exhaust causes the trouble. Scientists were able to neutralize this issue by adding potassium nitrate and silicon dioxide. Do you remember the infamous Takata's 67 million airbag recall incident? This incident happened due to a notorious property of sodium azide. They absorb moisture content easily. If there is a leakage in the design stage or manufacturing, sodium azide will absorb moisture. After the moisture absorption, when triggered, the chemical will undergo violent explosions, causing the rupturing of airbags and shrapnel flying to the passengers. This is exactly what happened with Takata's airbags. Eventually, the company went bankrupt. To

4:42 avoid such unfortunate incidents, the addition of a drying agent will be helpful, and strict quality control measures are required for components like airbags. Nowadays, sodium azide is replaced by guanidine nitrate as a gas generator. It is less toxic than sodium azide and is less explosive. It is not sensitive to moisture. Now we need not worry about the explosion and harmful gases. Even after these two design changes, the electromechanical sensor-based airbags suffered from one more issue. They would occasionally get activated even when they fell in a pothole. The reason? The electrical switches do not provide information about the rate of deceleration, which is necessary to determine the severity of the crash. That means it can't distinguish between a pothole and a crash. This is

5:33 why, to detect the crash more accurately, nowadays, MEMS sensors are used with an advanced electronic control unit. This is a capacitance-based method, and the severity of the crash can easily be determined. ECU also takes input from the wheel speed sensors, gyroscopes, brake pressure sensors, and seat occupancy sensors. The algorithm determines when to trigger the gas generator and how much to inflate the airbag based on the severity of the crash. The igniter ignites the explosive within 2 milliseconds and fills the bag within 20 to 30 milliseconds. The airbag remains fully open for 100 milliseconds. Now the airbag is ready to cushion you.

6:19 The airbag spreads the impact force over a larger area. It not only inflates, but also deflates to slow you down during impact. While deflating, it gives more time to travel. You can see two vent holes in airbags. The air vents out from these holes and the airbag deflates to slow down your body. Do you know why the airbag will not work in some car models if you are not wearing the seatbelt? The speed of airbag inflation is huge, around 320 km per hour. During this inflation, if you hit the airbag, that will be more lethal. So don't forget to wear your seatbelt so that this beautiful airbag technology can work. Before

7:05 you leave, don't forget to be a member of the Lessix team. See you next time. Thank you.