Pretensioner and pretensioner manufacturing method

Abstract

A pretensioner is provided, of which the cylinder, including a restriction portion, can be inexpensively formed, the cylinder having the restriction portion for positioning a gas generation unit to be mounted to a cylinder, and a pretensioner manufacturing method for manufacturing such a pretensioner is provided. In the pretensioner, since the cylinder is molded by forging, an inexpensive material compared with a stainless pipe member can be used for the molding. In addition, since the positioning portion can be molded during forging-molding for molding the entire cylinder, cost can be reduced even in this regard.

1 . A pretensioner manufacturing method for manufacturing a pretensioner that increases tension of a webbing belt configuring a seatbelt device by increased internal pressure of a cylinder upon activation of a gas generation unit, the cylinder being formed into a cylindrical shape open at both ends, the gas generation unit being mounted to the cylinder from one of the open ends of the cylinder, the method comprising a cylinder manufacturing process that forms the cylinder, the process including:
 forming, by forging-molding of a metal-block molding material, a cylindrical body, an inner circumferential portion of which a node portion is integrally formed and which is open at both ends, the cylindrical body corresponding to the cylinder, and the node portion corresponding to a restriction portion which is integrally on a inner circumferential portion of the cylinder and interferes, inside the cylinder, with the gas generation unit mounted to the cylinder so as to restrict relative displacement of the gas generation unit with respect to the cylinder.   
     
     
         2 . The pretensioner manufacturing method of  claim 1 , wherein in the forming of the cylindrical body:
 accommodating the metal-block molding material in a die which has a bottom portion and whose one end is opened; and   forging-molding the metal-block molding material which is accommodated in the die by a punch member disposed coaxially with respect to the die being inserted into the die.   
     
     
         3 . The pretensioner manufacturing method of  claim 1 , wherein the process further includes forming a through hole in the node portion. 
     
     
         4 . The pretensioner manufacturing method of  claim 2 , wherein the process further includes forming a through hole in the node portion. 
     
     
         5 . The pretensioner manufacturing method of  claim 2 , wherein a core portion is protrusively provided toward the opened one end of the die from a center of the bottom portion of the die. 
     
     
         6 . The pretensioner manufacturing method of  claim 4 , wherein a core portion is protrusively provided toward the opened one end of the die from a center of the bottom portion of the die. 
     
     
         7 . The pretensioner manufacturing method of  claim 3 , wherein
 the node portion divides the inside of the cylinder into one end side and another end side of the cylinder, and   as the through-hole, a non-circular through hole, whose inner circumferential shape is smaller than that of the cylindrical body, is formed in the node portion, whereby the restriction portion restricts relative rotation of the gas generation unit with respect to the cylinder about an axis whose direction is a penetrating direction of the cylinder due to a portion of the gas generation unit being fitted in the through hole.