Patent ID: 8292048

Claim:
An impact energy absorbing device configured for single-use occupant protection in a motor vehicle, comprising: a container containing a magneto-rheological medium, said container being formed with an opening and having a burst element covering said opening to prevent said magneto-rheological medium from unintentionally flowing out of said container; an outlet duct communicating with said opening and having a substantially rectangular cross-sectional area, said magneto-rheological medium being irreversibly forced out of said container through said opening into and through said outlet duct on being subjected to an external force of said impact sufficient to break said burst element; and a device sandwiching said outlet duct for generating a magnetic field and for influencing a flow resistance of said magneto-rheological medium when forced through said outlet duct, said device comprising two iron parts forming magnet poles disposed with a gap therebetween, wherein said outlet duct extends through said gap between said magnet poles and has a length L defined by the following formula: L ≥ V m ⁢ t v ( t a - t v ) . F where V m is a volume of the medium in the container; t v is a dwell time; t a is an impact time; and F is a cross-sectional area of said outlet duct.