Lun 21 Apr, 2008 2:03 pm
Asta ar trebui mutata la "Dictionar" insa acolo nu citeste nimeni 😠
Triggering conditions
Airbags system.Air bags are typically designed to deploy in frontal and near-frontal collisions, which are comparable to hitting a solid barrier at approximately 13-23 km/h (8-14 mph). Roughly speaking, a 23 km/h (14 mph) barrier collision is equivalent to striking a parked car of similar size across the full front of each vehicle at about 45 km/h (28 mph). This is because the parked car absorbs some of the energy of the crash, and is pushed by the striking vehicle. Unlike crash tests into barriers, real-world crashes typically occur at angles, and the crash forces usually are not evenly distributed across the front of the vehicle. Consequently, the relative speed between a striking and struck vehicle required to deploy the air bag in a real-world crash can be much higher than an equivalent barrier crash.
Because air bag sensors measure deceleration, vehicle speed and damage are not good indicators of whether an air bag should have deployed. Occasionally, air bags can deploy due to the vehicle's undercarriage violently striking a low object protruding above the roadway surface. Despite the lack of visible front-end damage, high deceleration forces may occur in this type of crash, resulting in the deployment of the air bag.
The air bag sensor is a MEMS accelerometer, which is a small integrated circuit chip with integrated micromechanical elements. The microscopic mechanical element moves in response to rapid deceleration, and this motion causes a change in capacitance, which is detected by the electronics on the chip, which then sends a signal to fire the airbag. The most common MEMS accelerometer in use is the ADXL-50 by Analog Devices, but there are other MEMS manufacturers as well.
There was some work initially in mercury switches but they did not work well. Before MEMS, the primary system used to deploy air bags was called a "rolamite". A rolamite is a mechanical device, consisting of a roller suspended within a tensioned band. As a result of the particular geometry and material properties used, the roller is free to translate with little friction or hysteresis. This device was developed at Sandia National Laboratories. The rolamite and similar macro-mechanical devices were used in air bags until the mid-1990s when they were universally replaced with MEMS.
Nearly all air bags are designed to automatically deploy in the event of a vehicle fire when temperatures reach 150-200 °C (300-400 °F). This safety feature, often termed auto-ignition, helps to ensure that such temperatures do not cause an explosion of the entire air bag module.
Today, air bag triggering algorithms are becoming much more complex. They try to reduce unnecessary deployments (for example, at low speed, no shocks should trigger the air bag to help reduce damage to the car interior in conditions where the seat belt would be an adequate safety device) and to adapt the deployment speed to the crash conditions. The algorithms are considered as valuable intellectual property. Experimental algorithms may take into account such factors as the weight of the occupant, the seat location, seatbelt use, and even attempt to determine if a baby seat is present.
Wikipedia.