Accelerometers designed to include a low pass filter create the possibility of output signal distortion when these accelerometers are subjected to high-g, high frequency shocks that are beyond the dynamic range and bandwidth for which they were designed. These distortions are further aggravated by the presence of undamped resonaces within the accelerometer, the module into which it is mounted, and in the vehicle system in which it is used. Since the detection methodology was based on the deceleration of a large mass, early in the development it was typically defined that the frequency bandwidth of interest should be less than 400 Hz. This low bandwidth would reduce the need to perform extremely fast A/D conversions and mathematical calculations that would be needed to follow the higher frequency components of a crash signal. As airbags gained more field experience it became apparent that the force and timing of deployments needed to be controlled for a wider range of crash types in order to avoid possible injury to passengers. This requirement increased the need to monitor the accelerometer signal for longer periods of time than previously required. In developing these new algorithms, the rquirements for sensors added more of them outside of the central control module for two reasons. First, some types of crashes were difficult to detect within the short time frame required for deployment (offset pole crashes) and the solution was to provide a high-g 'precrash' sensor within the front of the vehicle. And second, the need for side impact detection required deployment decisions even faster that the frontal crashes (within appr. 5 ms). Both of these requirements moved accelerometers to 'satellite' positions closer to the perimeter of the vehicle where they are more likely to pick up impacts from small objects. The mechanism of signal distortion is applicable to all applications of accelerometers, not just to airbag systems, and can be an issue with low-g sensors used in ABS, suspension control, and vehicle stability as these accelerometers have less dynamic range than airbag sensors. Therefore a wider variety of shocks could cause overloading. There are a number of solutions to reduce this effect that require consideration by the accelerometer manufacturer, the module builder, and the final vehicle assembler.
Accelerometer overload considerations for automotive airbag applications
Betrachtungen zur Überbeanspruchung von Beschleunigungsmessern im Zusammenhang mit der Auslösung von Automobil-Airbags
2002
7 Seiten, 15 Bilder, 2 Quellen
Conference paper
English
Accelerometer Overload Considerations for Automotive Airbag Applications
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