DETROIT - In the march toward intelligent airbag systems, sensor technology is bringing up the rear.
Developers of the other key component in future systems - such as hybrid inflators that can tailor the airbag deployment to the severity of the crash - say their units are nearly ready for production. Some, such as AlliedSignal Automotive, already have signed production contracts to provide hybrid inflators for 1999- and 2000-model vehicles.
But sensor development has a ways to go. That is because future sensors will have to collect and analyze three or four times the amount of data they do now.
Current sensors concentrate on crash severity to determine whether to fire the airbag. But future sensors will also need to figure out seat belt status and occupant position, and decide whether to call for a low-power or high-power deployment, or no deployment at all. They also will have to decide whether to fire side airbags, sometimes several seconds after the front airbags have fired. And they will have to make the right decision 100 percent of the time.
'Those decisions are not always intuitive,' said Paul Witt, program manager of passenger safety systems with Siemens Automotive.
For example, Witt said, many times a properly belted front occupant reaches for the instrument panel.
'In a low-speed accident, maybe we don't fire because you would do more damage with the airbag,' Witt said.
Makers of airbag inflators have had a slightly easier time only because hybrid inflation systems have been under development since the 1970s, said John Musiol, manager of airbag core engineering for AlliedSignal Automotive in Sterling Heights, Mich.
Most hybrid inflators use a metal cylinder that stores a gas under pressure. A burner unit within the cylinder provides heat to rapidly expand the gas.
In an accident, the device punctures one end of the cylinder to start the gas flowing. The gas alone would be used in a low-powered inflation. In a more aggressive crash, the burner ignites to expand the gas, providing fuller and more rapid inflation of the airbag.
The hybrid inflator makes it easier to tailor inflation rates, said Musiol. Gas expansion can be controlled by having two burners that can be ignited at different stages.
A multistage inflator also helps by giving crash sensors more time, said Witt of Siemens. This is important in crashes that initially appear to the sensor as being minor, such as hitting a pole. In this scenario, the inflator would begin a low-power deployment. But after sensors had gathered more data and better read the crash severity - a process that would take only 10 to 15 milliseconds - it could trigger the burners to cause a full-power deployment.