Piston return stop device for tensioning device of seat belt

A seat belt tensioning device comprising:

• cylinder means having an inner wall and at one end a fluid thrust developing means,
• force movable means disposed inside said cylinder and thrustable in a first direction away from said one end in response to fluid thrust upon operation of said developing means,
• said force movable means including a first movable member which is in fluid tight movable contact with said inner wall and a second movable member of which one end is formed into a radially reduced tapered portion with a surface which inclines outwardly toward the other end of said cylinder means, and a breakable member for connecting said first movable member and said second movable member,
• the other end of said second movable member of said force movable means being connectable to a seat belt,
• said second movable member being slidable relative to said first movable member,
• said breakable member being breakable by a seat belt tension force greater than said fluid thrust by a predetermined amount, and
• radially extending return stop means disposed within said first movable member of said force movable means so as to move therewith in said first direction and so as to be slidable in the radial direction of said first movable member when pushed by said tapered portion,
• said stop means having at least one sharp outer radial end in contact with said inner wall so that when seat belt tension force exceeds said fluid thrust by said predetermined amount, said breakable member of said force movable means is broken to stop said second movable member from moving in said first direction and said return stop means is pushed radially by said tapered portion being moved in the reverse direction opposite to said first direction due to said greater amount of seat belt tension force to cause said sharp end of said return stop means to cut into said inner wall and assuredly prevent movement then of said first movable member of said force movable means in said reverse direction notwithstanding said greater seat belt tension force from that reverse direction.

A seat belt tensioning device comprising:

• cylinder means having an inner wall and at one end a fluid thrust developing means,
• force movable means disposed inside said cylinder and thrustable in a first direction away from said one end in response to fluid thrust upon operation of said developing means,
• said force movable means having opposite ends and being in fluid tight movable contact with said inner wall and having adjacent its end opposite said one end a radially reduced tapered portion with a surface which inclines outwardly toward said opposite end,
• the other end of said force movable means being connectable to a seat belt, and
• radially extending return stop means slidably disposed on said tapered portion between said cylinder means and said tapered portion for movement with said force movable means in said first direction and slidable in the radial direction of said cylinder means when pushed outwardly by said tapered portion surface,
• said stop means having at least one sharp outer radial end in contact with said inner wall so that when seat belt tension force is greater than said fluid thrust by a predetermined amount, at least part of said force movable means stops moving in said first direction and said return stop means is pushed outwardly by said tapered portion being moved in the reverse direction opposite to said first direction due to said greater amount of seat belt tension force to cause said sharp end of said return stop means to cut into said inner wall and assuredly prevent movement then of said force movable means in said reverse direction notwithstanding said greater seat belt tension force from that reverse direction,
• said return stop means comprising a plurality of stopper members respectively disposed in radial guide grooves in said force movable means each having an inner end in sliding contact with said tapered portion surface and a sharp outer end in contact with said inner wall.