Method for controlling airbag deployment

A method for controlling the deployment of an air bag based on the actual mass of an occupant secured to a passenger seat by a seat belt, the method comprising the steps of:

• measuring a total downward force on a seat contributed by a seat occupant;
• measuring a vertical component of force contributed by seat belt tension;
• and
• subtracting the vertical component of force from the total downward force to determine a weight, and hence an actual mass, of the seat occupant;
• and
• deploying the air bag in crash situations as a function of the actual mass.

A seat weight sensing system for controlling the activation of an airbag fitted to a seat of a vehicle and having an airbag control module, the seat weight sensing system comprising:

• a weight sensor associated with the seat and capable of measuring a total downward force on the seat contributed by a seat occupant and seat belt tension;
• a seat belt associated with the seat;
• a member for coupling a portion of the seat belt to an anchor piece on the vehicle adjacent to the seat;
• a strain gauge disposed on the member to detect deflection of the member caused by tension on the seat belt;
• a seat belt tension sensor module coupled to the strain gauge and operative to convert a voltage outputted by the strain gauge to a load value corresponding to the amount of vertical force exerted by seat belt tension on the anchor piece;
• and
• a seat weight module coupled to said seat belt tension sensor module, said seat weight sensor and the airbag control module, said seat weight module operative to subtract the load value from the total downward force on the seat contributed by a seat occupant and seat belt tension to determine a weight, and hence an actual mass, on the seat.