Importance

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Abstract

A first velocity change value V1 is derived by integrating the deviation of a detected vehicle deceleration from a first deceleration reference value, e.g., 1 g, and a second velocity change value V2 is derived by integrating the deviation of the detected vehicle deceleration from a second deceleration reference value, e.g., 6 g. When the velocity change values V1 and V2 have reached a first velocity threshold value TH1 and a second velocity threshold value TH2, respectively, an inflator is ignited to make it discharge compressed gas into an air bag. When the time t elapsed since the first velocity change value V1 has become positive is within a first time reference value t1 and the first velocity change value V1 does not reach the first velocity threshold value TH1, a second velocity threshold value TH2 is Updated to become TH3. The second velocity threshold value TH3 thus updated is greater than the preceding threshold value TH2. In updating the second velocity threshold value TH2, the ratio of the first velocity change value V1 to the second velocity change value V2 is calculated. When this ratio has satisfied a predetermined condition K, the second velocity threshold value TH2 is updated.

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First Claim