Car Safety Systems: Active, Passive, Airbags

Active Safety Systems

Active safety systems aim to prevent accidents, ensuring vehicle operation is as safe as possible on the road or in any situation. They contribute to the vehicle's active safety in addition to factors that increase running safety (such as suspension, steering, and brakes). This also includes the design of the body, which takes into account driver visibility, and seats manufactured properly to fit the body and avoid fatigue.

Passive Safety Systems

Passive safety systems condition the manufacture of all components of the passenger compartment so that, in the event of an accident, they reduce damage to passengers or prevent injuries. Active systems are engaged at the time of an accident (e.g., ABS, airbags), while passive systems are always acting (e.g., seatbelts, chassis structure).

Seatbelt Pretensioners

A pretensioner is a device integrated into the seatbelt winding cartridge. In case of a vehicle collision, it quickly retracts the belt to remove slack and retrieve the elongation that occurs due to body movement, keeping the passenger firmly coupled to the seat support.

Types of Pretensioners

• Mechanical Pretensioning: Acts through the belt buckle and is governed by a mechanical deceleration sensor.
• Pyrotechnic Pretensioning: Also acts through the belt buckle but is commanded by an electronic deceleration sensor (built into or triggering the airbag electronic module).
• Mechanical Winder Pretensioner: Deceleration control is handled by a mechanical sensor acting on the winder.
• Pyrotechnic Tape Pretensioner: Commanded by an electronic deceleration sensor acting on the winder.

The tension of the belt is obtained automatically and quickly, whether the device is located in the belt buckle or the automatic belt winder.

Airbag Systems

Airbags are a passive safety system consisting of an air cushion in front of the driver and passenger. In case of a collision, they inflate rapidly to protect occupants. The driver's airbag is typically housed in the steering wheel, and the passenger airbag is in the dashboard.

Airbags are effective when a frontal collision occurs, typically above a certain speed threshold (e.g., more than 18 km/h). They are controlled by an electronic control unit equipped with calibrated deceleration sensors that detect the impact and activate an electric detonator. This, in turn, causes a chemical reaction of a compound that produces nitrogen gas to inflate the cushion. The control unit has a specific location for the sensors to ensure they are positioned correctly. It also has a fault memory.

The steering wheel cushion stays in a closed housing, with the inflation device located behind it, activated electronically. The passenger-side cushion stays properly folded in the dashboard, and its activation system is very similar to the steering wheel type.

One type of mechanical sensor mechanism involves the airbag being enclosed in the steering wheel box, positioned above the inflation device. This device consists of an aluminum case enclosing a sensor supported by an articulated steel ball. When there is strong deceleration, the inertia force applied to the ball overcomes a weighted spring, releasing a hammer that hits a fulminate, producing a chemical compound. The resulting inflation pressure breaks through a lid with a crack and releases the cushion, which deflates within milliseconds after the impact.