Abstract: A collision detecting method for detecting a collision of a vehicle on the basis of an acceleration signal produced by an acceleration sensor. A reduction in the amount of speed of the vehicle due to the collision from an acceleration signal is estimated by an acceleration signal from the acceleration sensor and by a rate of time variation in the acceleration signal, and the collision of the vehicle is detected when the amount of deceleration exceeds a predetermined value. In addition, the collision of the vehicle is detected, when an integration value resulting from an integration of the acceleration signal over a first period of time exceeds a predetermined value, and when a differentiation value of the acceleration signal exceeds a predetermined value. The collision detecting method can be used to operate a collision safety device (such as, an air bag system and a belt retracting system) within an extremely short time after occurrence of the collision.

Abstract: In a collision determining circuit designed to operate an air bag system or a belt retracting system based on an acceleration detected by an acceleration sensor in a vehicle, an acceleration signal output by an electric acceleration sensor is integrated in a passenger inertial speed calculation device to calculate a passenger inertial speed. At the same time, a power of the acceleration signal, filtered in a filter in a frequency range of 100 to 200 Hz, is calculated in a power calculation device. When at least one of the passenger inertial speed and the power exceeds a reference value, a starting signal generating circuit outputs a starting signal to ignite a squib for inflating the air bag system or for activating the belt retracting system. This ensures that even if the vehicle collides angularly against an obstacle, the starting signal can be properly produced without delay.