Patent ID: 7631900

Claim:
A pre-tensioner comprising: a cylinder; a piston that is slidably disposed in the cylinder and is connected to a coupling member; a cover that is coupled to the coupling member and is contractable to a fully contracted position; and a gas generator which generates gas to act on the piston, wherein the gas generator is actuated to generate gas and the piston is moved by gas pressure of the generated gas so as to pull the coupling member so that the coupling member contracts the cover toward the fully contracted position, wherein the cylinder is provided with an impact buffering zone which buffers impact exerted on the coupling member by absorbing kinetic energy of the piston during operation, the impact buffering zone being a tapered portion of the cylinder in which the piston slides through, the impact buffering zone of the cylinder being deformed by movement of the piston so as to buffer the impact on the coupling member, wherein the cylinder is provided with a pre-decelerating zone for decelerating the piston, the pre-decelerating zone comprising annular concavities separated a distance from the tapered portion of the impact buffering zone, and wherein the piston is configured to deform at least a portion of the impact buffering zone prior to the cover reaching the fully contracted position.