Linear tension damping device

Claim 1

In a motor vehicle provided with a restraint system haviNg a lap belt extending over and across a seat portion of the seat; a shoulder strap having one end anchored to the lap belt and having another end; a linear tension damping device comprising an elongate cylinder with an inner wall defining a bore, said elongate cylinder being closed at one end by an end plug which is anchored to said another end of said shoulder strap and said cylinder being reduced in diameter at an opposite end to provide a reduced diameter annular projection; a first piston axially slidable in said cylinder and axially dividing said bore into first and second compartments; a piston rod secured at one end to said first piston and extending from the same through said first compartment and through said reduced diameter annular projection externally of said bore, said piston rod terminating and being pivotally secured to a reinforced inner body portion of the vehicle; a second piston slidable in said second compartment and axially dividing said second compartment to provide at a side thereof opposing to said first piston a first subcompartment and at the opposite side of said second piston a second subcompartment; an annular seal member sealingly engaging with said wall of said elongate cylinder defining said bore and sealingly and slidably engaging with said piston rod to close said first compartment; said first piston having a plurality of axial passages extending therethrough; an incompressible liquid filling said first compartment said passages of said first piston and said first subcompartment; a compressed gas filling said second subcompartment; a valve disc having an aperture and disposed in said first subcompartment, said valve disc seating on an axial end of said first piston which faces said first subcompartment to close said passages of said first piston; an adjustor extending through said aperture of said valve disc and threadedly engaging into said piston from said axial end of said first piston to bias said valve against said axial end of said piston; and at least one shearing pin extending through said reduced diameter annular projection and through said piston rod to lock movement of said piston rod relative to said elongate cylinder, said shearing pin being constructed such that relative axial movement of said piston rod relative to said cylinder is prevented unless a predetermined magnitude of tension is applied on said lap belt.