A semiconductor capacitance type crash sensor has been developed for airbag systems of automobiles. The sensing device has a symmetric structure of glass-silicon-glass plates. The two glass plates sandwich the anisotropically etched silicon plate with two cantilever beams and a moveable electrode having a function of inertial mass. Thin metal films are sputtered on the glass plates as fixed electrodes, so that they face the moveable electrode. The crash acceleration of automobiles is detected by the difference of capacitances between the moveable electrode and the two fixed electrodes. The air gaps between the moveable electrode and the two fixed electrodes are four microns. Due to the squeeze-film effect of the air in the gaps, the moveable electrode has a large damping characteristic. To decrease the damping factor of this sensor, a new shape has been adopted for the moveable electrode. Many air grooves are made horizontally and vertically on both sides of the moveable electrode by anisotropic etching. As the air in the gaps can flow through the grooves, the damping factor became small. As a result, the crash sensor has a quick response, even though it operates at atmospheric pressure. Self-diagnosis function is required for high reliability of the airbag system. By applying a voltage between the moveable electrode and the fixed electrodes, electrostatic forces occur in the air gaps. Since a quasi-acceleration is obtained by this electrostatic force, active self-diagnosis within a short time has become possible for this sensor.
Semiconductor capacitance-type crash sensor for airbag systems
Aufprallsensor für Airbag-Systeme als Halbleiterkapazitätstyp
1992
10 Seiten, 10 Bilder, 9 Quellen
Aufsatz (Konferenz)
Englisch