Electronic Crash Sensors for Restraint Systems 901136
Crash sensors are used for crash detection and initiation of squibs in Airbag and Seat Belt Tensioner Systems. A new single point electronic sensor has been developed that incorporates a dual piezoelectric accelerometer to measure the deceleration in the passenger compartment. This concept achieves the required fail safe operation without a mechanical safing switch. A conventional microcomputer and sophisticated crash discrimination algorithms are used to reach the deployment decision. Supplementary functions include monitoring of squib and wiring harness integrity and storing of fault codes as well as a “crash journal” in a non-volatile memory.
INFLATABLE RESTRAINT SYSTEMS, commonly called “AIRBAGs”, are designed to protect the occupants in automobile accidents against severe injuries. The life saving potential of such an air cushion becomes evident if one realizes that the impact of a body moving at 30 miles per hour corresponds to a free fall from a 10 m high diving tower.
The concepts of inflatable passive restraint systems have been developing over the last three decades as a supplement to seat belts. The mandatory requirement for passive restraint systems on 1990 cars in the United States has stirred renewed interest in these systems and may finally provide the breakthrough for their widespread use.
An airbag system includes acceleration sensors which detect a crash pulse. The sensor information is processed and initiates the airbag' s gas generator. The bag itself is inflated in about 30 ms by rapidly expanding nitrogen gas and cushions the occupants momentum as he moves forward. The bag is deflated through vents to provide controlled occupant deceleration and to avoid occupant rebound.
The velocity change in the passenger compartment during the first few milliseconds of a crash is small, so that precise crash discrimination criteria are difficult to obtain by a single central sensor. Most airbag systems in use today therefore use several mechanically integrating sensors mounted in the crush zone in addition to a central passenger compartment sensor. These systems however are costly to install and the sensor function cannot be tested during the operation of the car.
The all-electronic crash sensor presented in this paper has solved the problem of “single point sensing” and performs continuous self testing during the operation of the car. Its design is the result of a ten year evolution and experience with electronic crash sensing. The acceleration signal rather than the velocity is used to extract the information for the crash discrimination. Sophisticated microcomputer algorithms are applied to evaluate the acceleration signal. The sensor response is programmable and can be calibrated to each vehicle type. The calibration for each vehicle structure is optimized using computer simulation techniques applied to the crash data measured at the sensor's final location in the passenger compartment.