Crash sensors that hear.

Siemens VDO Automotive (Troy, MI; www.usa.siemensvdo.com; Troy, MI) has developed a sensor that speeds vehicle crash detection by "hearing" the impact, rather than measuring deceleration. The Crash Impact Sound Sensor [CISS] mounts to a vehicle's chassis where it monitors noise vibrations. When a crash occurs, the sensor registers the sound wave variations caused by the deformation of steel chassis components and alerts reactive safety devices like air bags and seat belt pretensioners. Derrick Zechmair, vice president, Restraints, Safety Electronics, Siemens VDO Automotive, says this method provides faster, more precise results than the accelerometers normally deployed, in part because as crumple-zone engineering has become more sophisticated at slowing impact forces, measuring rapid deceleration has become more difficult. Sound wave signals, however, are unaffected. "As soon as the deformation of metal occurs the signal is transmitted, so it is available earlier on in a crash than deceleration data," explains Zechmair. This allows automakers to shave vital milliseconds off of the deployment time of safety measures.

The sensors are essentially modified versions of existing designs so they can be cost-effectively mass produced using proven chip manufacturing technologies. Further reducing cost, the first generation of the sensors, which will debut on an unnamed European passenger car in 2007, are designed to replace the two accelerometers commonly mounted in the front bumper area with one combined unit. The second generation, which should appear as early as 2008, does away with the bumper sensors altogether and is integrated with the airbag control unit.--KEW