Inflatable Restraint System Design Considerations

In a vehicle crash event, the inflatable restraint system functions in considerably less than 100 milliseconds. The state and rate of deployment at any given time during the crash event determines the system effectiveness across the range of occupant seating conditions and vehicle crash situations. The inflatable restraint system which includes the inflator and bag assembly, diagnostic module, crash and safing sensors, is designed to perform in concert with other vehicle subsystems, such as the vehicle structure, steering control system, instrument panel, seat belts, and the seats. This paper examines these critical interrelationships that are considered in order to achieve occupant protection in a vehicle equipped with an inflatable restraint system.

The diagnostic module and sensors play a key role in the overall system integrity and the design of such products is accomplished using “world class” techniques to provide very long life under all environmental conditions. The safety critical nature of the system usually means a safing sensor is used, which continuously monitors firing circuits and driver warning in the event of a detected system malfunction. The redundancy of the firing energy source and internal diagnostics are discussed.

System considerations in the design of a crash sensor include the number of sensors and operational logic in the sensing system, as well as the location and calibration of sensors. These design characteristics, which may vary substantially for different vehicles, are determined through the use of mathematical models of sensor performance and actual crash data. The design of the sensor mechanism provides a sensor response curve which maximizes the ability to differentiate crash events from non-crash events. The sensor design should allow engineers as much freedom as possible to “shape” this response curve for different applications.