Wednesday, March 25, 2009

Occupant Classification Systems Enhance Airbag Effectiveness

Imagine walking into a clothing retailer and finding that all of the clothes on the racks are the same size. Unless that size happened to be yours, this would not be a good thing. Now imagine going next door to another clothier to find the same scenario. This example may be somewhat extreme, but it's essentially the scenario we faced as a driver or passenger of a vehicle with airbags prior to 2004.

Airbags became required equipment on all U.S. automobiles in the 1990s, and there has been much documentation regarding their effectiveness in reducing driver and passenger fatalities. Statistics show a significant reduction in driver and passenger fatalities has resulted from the added safety afforded by airbags in a collision. But at the same time, traditional airbags have been shown to be dangerous to small children when deployed at full force.

Like your clothing store, one-size-fits-all is not the best application for effective airbag safety and is one of the main motivators in the development of Occupant Classification Systems. An Occupant Classification Systems (OCS) can use various kinds of sensors to detect the size and/or position of an occupant in a passenger seat. An OCS eliminates the need for manual on/off switches for airbags found in many cars and trucks in the early 2000s because they use sophisticated computer technology to identify whether an adult or a child is in the seat.

Occupant Classification Systems are a great example of the kind of "smart" technology that is increasingly finding its way into our vehicles. An OCS senses the passenger's size, if a seat belt is being used, and even the location of the seat (pushed forward or pulled back). Some systems can distinguish an empty seat from a seat holding a book bag, child seat or even a small adult from a large adult. And by using dual- or variable-stage airbags, the force adapted to help protect the occupant.

There are many benefits to having an occupant classification system and "smart" airbags in your car. They pose less of a threat to children and small adults, and they allow drivers more options for seating their passengers. Once the onboard computer knows the passenger's size and seating location, the car's dual or variable-stage airbags come into play. The size of the occupant in the passenger's seat will determine the type of airbag deployment. Dual-stage airbags can deploy at full force, partial force or not at all depending upon the inputs they receive. Variable-stage airbags have even more deployment force settings. Preventing an airbag from deploying at full force can greatly reduce, or even eliminate, the possibility of injuring a smaller passenger.

A very popular OCS is made by Delphi. The system is comprised of a pressure sensor, a silicone-filled "bladder" in the seat and an electronic control unit (ECU). When someone sits in the seat, the pressure sensor sends applied force to the ECU. The ECU then sends that data to the airbag, which has its own control unit. Based on this information, the vehicle's computer turns the passenger airbag on or off and regulates it force.

Historically, the most common way of detecting an occupant in a seat is with weight or pressure sensors, but new technologies are being developed. Capacitive systems measure the amount of electrical coupling found in the seat. Some experimental systems take optical images of passengers to determine whether a child or adult is sitting in the seat and use that information to turn the airbags on or off accordingly. Others go so far as to detect physiological factors like respiration and heartbeats of passengers to tell the airbags what to do. And even though vehicles equipped with occupant classification systems significantly reduce risks, it's always safest to keep small children in the back seat according to CDC (Centers for Disease Control and Prevention, National Center for Injury Prevention and Control) research.

Delphi Corporation is a leading innovator of automobile safety equipment and technology. To learn about Delphi's safety advancements, visit

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