Airbag

An airbag, also known as a supplemental inflatable restraint, is a critical vehicle safety system.

It consists of a flexible fabric cushion, an inflation module, and an impact sensor. The primary goal of the system is to provide soft cushioning for occupants during a collision. By doing this, the airbag creates an energy-absorbing surface. This surface sits between the person and hard interior parts like the steering wheel, instrument panel, or windshield. It helps reduce injuries caused by the occupant flailing against the vehicle's interior during a crash.

The mechanism of deployment relies on a complex chain of electronic and chemical events. First, crash sensors in the vehicle detect an impact. These sensors send data regarding the collision type, angle, and severity to the airbag electronic controller unit (ECU). The ECU then runs a crash algorithm to determine if the impact meets specific deployment criteria. If the criteria are met, the ECU triggers firing circuits. Most traditional modules use a pyrotechnic process, which is a chemical reaction, to inflate the bag in milliseconds. Newer side-impact modules may instead use compressed-air cylinders to achieve inflation.

Modern vehicles utilize a wide variety of airbag configurations to protect different parts of the body. A single car may contain up to ten different airbag modules. These include driver and passenger frontal airbags, as well as side-curtain airbags. Other types include seat-mounted, door-mounted, and pillar-mounted modules for side impacts. There are also specialized designs like knee bolsters, inflatable seat belts, and even pedestrian airbag modules.

Each type is placed strategically to address specific collision directions and occupant positions.

The history of the airbag spans over a century of engineering. The earliest origins trace back to a 1919 patent by two dentists, Arthur Parrott and Harold Round. In 1952, American industrial engineer John W. Hetrick filed a patent for an automobile airbag. Hetrick used his experience with United States Navy torpedoes to develop his design.

Although his invention was valuable, he struggled to find investment. Later, in 1964, Japanese engineer Yasuzaburou Kobori developed an airbag system that used explosives for inflation. A major breakthrough occurred in 1967 when Allen K. Breed invented a ball-in-tube sensor. This electromechanical sensor could trigger deployment in under 30 milliseconds using sodium azide.

Commercial adoption of airbags evolved through several distinct phases. In the early 1970s, General Motors offered the Air Cushion Restraint System (ACRS) in certain fleet vehicles. These early systems included a driver-side airbag and a passenger-side cushion that protected both the torso and knees.

However, GM discontinued the option in 1977 due to low consumer interest. By the late 1980s and early 1990s, the industry saw much broader adoption. Chrysler became the first U.S. automaker to make driver-side airbags standard in 1988. By 1991, U.S. legislation required airbags in most new passenger vehicles sold after 1997.

It is important to distinguish between different types of vehicle safety. Airbags are classified as "passive" restraints because they require no action from the occupant to work. In contrast, seat belts are "active" restraints because a person must manually buckle them.

This does not mean airbags are an alternative to seat belts. Instead, they are designed as supplemental systems to work alongside them. This distinction is different from "active safety" and "passive safety" in general engineering. Active safety refers to systems like anti-lock brakes that prevent crashes, while passive safety refers to systems that minimize injury once a crash occurs.

Today, the airbag is a standard component of global automotive safety. The transition from seeing airbags as seat-belt replacements to seeing them as supplemental systems has improved occupant protection. For example, Mercedes-Benz introduced an integrated system in 1981 that tensioned seat belts and deployed airbags simultaneously.

This integrated approach ensures that both the belt and the bag work together to manage the energy of a collision. As technology continues to advance, these systems remain a fundamental part of vehicle design.