Is the car airbag a protective umbrella or a death warrant?

What is an airbag?

Safety Airbag refers to a passive safety device that inflates to protect passengers before a secondary collision occurs in a car crash. As an auxiliary device of the seat belt's occupant restraint device, the airbag is also called the Supplemental Restraint System (SRS). It is used in conjunction with the seat belt to provide effective anti-collision protection for passengers. In the event of a car collision, the car airbag can reduce the rate of head injuries by 25% and the rate of facial injuries by about 80%.

The airbag is mainly composed of airbag sensors, anti-collision airbags and electronic control devices.

Working principle of airbag: When a car collides during driving, the airbag sensor first receives the impact signal. As long as the specified intensity is reached, the sensor will be activated and send a signal to the electronic controller. After receiving the signal, the electronic controller compares it with the original stored signal. If the airbag deployment condition is met, the drive circuit sends a start signal to the gas generator in the airbag assembly. After receiving the signal, the gas generator ignites the gas generator to produce a large amount of gas, which enters the airbag after filtering and cooling, so that the airbag breaks through the cushion in a very short time and quickly deploys, forming an elastic air cushion in front of the driver or passenger, and leaks and shrinks in time to absorb the impact energy, thereby effectively protecting the human head and chest from injury or reducing the degree of injury.

"Recalls are permanent, but vehicles are changing"

In 2004, the gas generator of the driver's side airbag of a 2001 Honda Accord sedan in Alabama, USA, ruptured, causing the metal pieces inside to explode and injuring the driver.

In November 2008, Honda recalled 4,000 vehicles due to air bag defects.

In May 2009, an 18-year-old American girl died when she collided with another car while picking up her brother from school. After investigation, it was confirmed that the metal piece ejected from the airbag after it was deployed pierced her carotid artery, causing her to bleed to death. In the same year, Honda announced the recall of 500,000 vehicles with airbag hazards.

In 2013, Toyota, Honda, Nissan and Mazda recalled 3.4 million vehicles worldwide, and BMW subsequently announced a global recall of 220,000 vehicles.

In 2014, Toyota announced a global recall of 2.27 million vehicles, Honda, Nissan and Mazda recalled 2.95 million vehicles worldwide, bringing the total number of recalls to 10.5 million vehicles. BMW and Volkswagen also continued to recall additional models.

In 2016, Mitsubishi Motors Sales (China) Co., Ltd. filed a recall plan with the General Administration of Quality Supervision, Inspection and Quarantine, to recall some imported Mitsubishi Pajero vehicles, involving 23,195 vehicles in mainland China.

In September 2017, 22 automobile brands issued recall notices in China involving multiple models, involving a total of 9,688,938 vehicles.

In June 2019, due to safety hazards posed by Takata airbags, the U.S. National Transportation Safety Administration asked General Motors to replace the airbag inflators installed in more than 6 million trucks and SUVs.

In September 2019, a total of more than 30 domestic vehicle manufacturers will recall 20 million vehicles with airbag hazards, including more than 4.86 million vehicles from Volkswagen, 2.53 million vehicles from General Motors, 454,000 vehicles from Toyota, as well as Changan Ford, BMW Brilliance and many other automakers. Among them, Toyota said that about 440,000 vehicles were recalled due to Takata airbag problems.

In October 2019, Volkswagen and Porsche announced that they would recall about 227,000 vehicles. The reason for the recall was problems with the airbags and seat belt pretensioners, and the solution was to update the software of the airbag control unit.

What are the problems with the airbags that led to the massive recall? 

Looking at the airbag problems over the years, there are three types: First, the airbag fails to deploy after a collision; second, the airbag deploys automatically when there is no collision; third, the airbag deploys after a collision, but the impact force is too strong, causing secondary injuries to the driver and passengers.

What kind of deep problems are hidden behind these surface phenomena? Is the airbag sensor, anti-collision airbag or electronic control unit fault the culprit?

According to the general rules of automobile collision accidents, the entire collision process lasts about 200ms from the beginning to the end of the collision. If it is a frontal collision accident, then within 20~50ms after the accident, the vehicle's deceleration will reach the deployment threshold set in the airbag ignition algorithm. At this time, the airbag system control device will issue an ignition command and the airbag will deploy.

In this process, airbag sensors, anti-collision airbags and electronic control devices all play an important role. Any problem in any link will lead to abnormal operation of the airbag. However, according to the data of airbag recall events in the past 15 years, we can know that the latter two are the main causes.

Airbag sensor problem

The airbags of most cars are installed directly in front of the driver and passengers, such as the steering wheel of the driver's seat, the front passenger panel, the windshield area, etc. The corresponding sensors will only activate the airbag driving device when they collect impact signals at a position approximately 60° to the left and right of the front of the vehicle. In other words, side impacts or impacts on the upper part of the body cannot be detected.

Side impact accidents are one of the most dangerous types of all traffic accidents. Germany has done a statistics earlier, and found that one-third of the people who died in traffic accidents each year were from side impact accidents. Therefore, in recent years, many high-end models have begun to be equipped with multi-directional airbags and multi-directional airbag sensors.

Anti-collision airbag problem

The problem with anti-collision airbags themselves is a hot spot for car recalls . In the past 10 years, as the world's second largest airbag manufacturer, Takata's problematic airbags have caused more than 100 deaths and injuries worldwide, involving recalls of up to 200 million vehicles, and are even called "death airbags" by the industry.

Why do safety airbags become death airbags?

This also depends on the working principle of the airbag. The airbag relies on the explosion reaction of chemical substances to cause gas expansion. Then these gases will fill the airbag in a short time, and the deployed airbag will protect the driver and passengers. However, the explosion of this chemical substance needs to be controllable. Once it gets out of control, it will cause secondary damage. Takata uses ammonium nitrate, an extremely unstable and cheap blasting material that easily blends with water at high temperatures. This material will slowly change from tablets to powder over time, temperature, humidity and other factors. At the same time, there is also the situation of excessive use of sodium azide (NaN3) and potassium nitrate (KNO3), which will lead to uncontrollable explosions, causing abnormal pressure rise in the gas generator in the airbag, and the metal filter cover is damaged by the strong airflow impact, splashing out fragments containing metal filter cover and glass, causing injuries or even death. Therefore, except for Takata, other airbag manufacturers all use guanidine nitrate, which is relatively more expensive.

Electronic control unit problems

The airbag electronic control device generally consists of two parts, namely the hardware part and the software part. As the main component of the hardware, the electronic control unit plays the role of the central nervous system. Its microcomputer can use algorithms such as neural networks to classify collision accidents, and make appropriate responses based on information such as severity and collision location, and correctly open the airbag through the driver.

No matter which component in the electronic control device has a design error or operating failure, it may cause the airbag to work abnormally. For example, Continental had a large-scale airbag recall in the early years, and the main reason was the airbag sensor control system.

The fate of active recalls and passive recalls is very different

Voluntary recall - Continental AG

In 2016, without receiving any relevant complaints, Continental AG proactively reported to the US National Highway Traffic Safety Administration (NHTSA) that its airbag control units had hidden dangers, which could cause the airbags to fail to deploy in a collision or to deploy suddenly without warning. According to statistics, a total of 5 million cars were equipped with these problematic airbags, involving brands including Honda, Chrysler, Mercedes-Benz and three other automakers.

It is reported that the recalled vehicles all use the airbag safety control system produced by Continental. These airbags were manufactured according to a set of ISO international standards, but there was no unified international standard for the electronic control unit of the airbags at that time. The lack of standards, the proactive admission of problems, and the method of recalling vehicles one after another won the understanding of customers. Therefore, Continental's airbag division continues to operate to this day and has achieved good results in the field of electric vehicles.

Passive recall - Takata in Japan

As one of the four major airbag suppliers, Takata has more than 100 years of R&D and production experience, and its business scope covers major car brands in the world. If you pick a car on the road, the airbag system may be provided by Takata. Honda, Toyota, Nissan, BMW, Mercedes-Benz, Tesla, domestic Geely, etc., all cars you can imagine are using Takata airbags.