Airbag system using three-dimensional acceleration sensor

An airbag system comprising:

• a three-dimensional acceleration sensor having a support on which a stationary electrode is arranged, a central part fixed to said support, a single massive part acting as a movable electrode and a link member for interconnecting said central part and said massive part;
• said link member being comprised of a combination of diaphragms and beams which are operatively provided around said central part;
• and means for starting an airbag on the basis of an output of an arithmetic output unit of said three-dimensional acceleration sensor, wherein means is provided for sensing changed electrical capacitance between the stationary electrode and the single massive part at four positions thereof, and means is further provided for detecting applied acceleration in response to changes in sensed electrical capacitance at the four positions by addition and subtraction of changes in electrical capacitance values.