Bumper airbag with multiple chambers

An inflatable multi-chambered bumper airbag system for a motor vehicle having a bumper comprising:

• a housing mounted inboard of the bumper and having a door flush with the outer surface of the bumper;
• a folded, non-inflated bumper airbag mounted in the housing behind the door, the airbag comprising a main chamber and a first outer chamber, said first outer chamber comprising a concentric chamber circumferentially disposed around said main chamber, said first outer chamber being separated from said main chamber by a seam of frangible thread;
• at least one sensor mounted on the vehicle for sensing an imminent collision with an object and generating a signal therefor;
• a control unit having a microprocessor having an algorithm stored therein for processing the signal from the sensor and generating a firing signal at a predetermined time before the collision occurs;
• and
• an inflator responsive to the firing signal and operatively connected to the main chamber for supplying sufficient inflation fluid to the main chamber to inflate said main chamber to a predetermined maximum inflation pressure, whereby the main chamber inflates, bursts through the door and forms an inflated cushion barrier extending at least partway across the vehicle;
• wherein said seam of frangible thread separating said main chamber from said first outer chamber comprises a seam of thread having sufficient strength to withstand said maximum inflation pressure without rupturing, said seam of thread adapted to rupture at a predetermined pressure above said maximum inflation pressure, such that upon impact between said main chamber and an object, said main chamber is overpressurized above said maximum inflation pressure causing said seam of frangible thread to rupture thereby inflating said first outer chamber.

A method for fabricating a multi-chambered bumper airbag to be inflated to a maximum inflation pressure comprising the steps of:

• a) providing a first fabric member having a first perimeter;
• b) providing a second fabric member having a second perimeter;
• c) positioning the first and second fabric members so that the first and second perimeters align;
• d) sewing a first frangible seam inboard of the perimeters for binding the first and second fabric members together to define a main chamber circumscribed by the first frangible seam, said first frangible seam having sufficient strength to withstand said maximum inflation pressure without rupturing and adapted to rupture at a predetermined pressure above said maximum inflation pressure;
• e) sewing a second frangible seam radially outward from the first frangible seam for binding the first and second fabric members and to define a second chamber concentric with the main chamber;
• f) sewing a non-frangible seam adjacent the first and second perimeter for joining the first and second fabric members and forming a third chamber concentric with the second chamber;
• and
• g) mounting a gas inlet valve through the first fabric member.