1.  Field of the Invention
The present invention relates to a cover structure of a seat belt pretensioner configured to connect a seat belt to a pretensioner main body by a connecting member of a wire or the like and cover the connecting member by a containing cover. 
2.  Background Art
There is known a seat belt pretensioner for constraining a passenger by pulling a seat belt in order to protect the passenger in rapid deceleration of a vehicle or the like.  There is a seat belt pretensioner configured to protect a wire connecting a seat belt to a pretensioner main body against dust by covering the wire by a cover in a bellows-like shape (refer to, for example, JP-A-2001-225722 (pages 3 through 4, FIG.  2)). 
Meanwhile, there is a seat belt pretensioner which does not use a cover in a bellows-like shape as a cover for protection (refer to, for example, JP-A-8-164821 (pages 4 through 5, FIG.  1)). 
A detailed explanation will be given of JP-A-2001-225722, mentioned above, in reference to the following drawings. 
FIGS.  11A and 11B are side views showing a seat belt pretensioner of a related art, FIG.  11A shows a state before crushing a cover in a bellows-like shape, and FIG.  11B shows a state of crushing the cover in the bellows-like shape. 
A seat belt pretensioner 100 is arranged at a side of a seat cushion (not illustrated), the seat belt pretensioner 100 is connected with a buckle 102 via a wire 101 and the wire 101 is covered by a cover 103 in a bellows-like shape. 
According to the seat belt pretensioner 100, a tension force is generated at the seat belt pretensioner 100 by being made to react with a deceleration degree of a vehicle in a state of connecting a tongue 105 of a seat belt 104 to the buckle 102. 
The buckle 102 is moved down by pulling the wire 101 in an arrow mark direction by the tension force of the seat belt pretensioner 100 and the tongue 105 is moved down integrally with the buckle 102. 
The passenger is constrained by the seat belt 104 by pulling the seat belt 104 by moving down the tongue 105. 
Meanwhile, according to the seat belt pretensioner 100, the cover 103 in the bellows-like shape is crushed as shown by FIG.  11B by moving down the buckle by pulling the wire 101 by a moving amount L1 from a normal portion p1 to a constraining portion p2.  A length in crushing the cover 103 in the bellows-like shape, that is, a minimum length is designated by notation L2. 
By using the cover 103 in the bellows-like shape in this way, even when the cover 103 is crushed, a length of the cover 103 remains by the amount of L2. 
Therefore, a total length L3 of the cover 103 in normal time becomes a length configured by adding the moving amount L1 of the buckle 102 and the minimum length L2 of the cover 103.  Thereby, the length of the cover 103 in normal time is prolonged and the buckle 102 and the tongue 105 are arranged at comparatively high positions. 
Therefore, there is a concern that the buckle 102 and the tongue 105 are projected to an upper side of the seat cushion.  When the buckle 102 and the tongue 105 are projected to the upper side of the seat cushion, the buckle 102 and the tongue 105 touch the passenger in a state in which the passenger is seated on a seat and seat comfort cannot be maintained excellently. 
In addition thereto, when the seat belt pretensioner 100 of this type is attached to a side of a center pillar, for example, the seat belt pretensioner 100 is disposed at a vicinity of a reclining operating lever of a seat back. 
Therefore, when the buckle 102 and the tongue 105 are projected to the upper side of the seat cushion, the seat belt pretensioner constitutes a hindrance against operation of the reclining operating lever. 
Next, a detailed explanation will be given of a seat belt pretensioner of JP-A-8-164821 in reference to FIG.  12. 
FIG.  12 is a sectional view showing a seat belt pretensioner of a related art, showing a seat belt pretensioner which does not use a cover in a bellows-like shape. 
A seat belt pretensioner 110 is provided with a constituent member of a pretensioner at inside of a casing 111 substantially in a V-like shape and a cover 114 is formed by containing a single cover member 113 in an opening space 112 formed by the casing 111. 
The seat belt pretensioner 110 is for pulling a buckle 116 into a containing portion 117 at inside of the single cover member 113 by pulling a wire 115 in an arrow mark direction. 
The single cover member 113 is provided with a lip portion 118 at a front end thereof and the containing portion 117 is closed by bringing the lip portion 118 into contact with an outer periphery of the buckle 116 to thereby prevent dust or the like from invading inside of the containing portion 117. 
According to the seat belt pretensioner 110, since a cover in a bellows-like shape is not used, a total length of the cover 114 can be shortened by restraining the length of the cover 114 only to an amount of moving the buckle 116. 
However, the cover 114 only closes the containing portion 117 by bringing the lip portion 118 of the single cover member 113 into contact with the outer periphery of the buckle 116 and therefore, when a tongue (not illustrated) is inserted into the buckle 116 for constraining a passenger by a seat belt, the buckle 116 is inclined to the cover 114 and the lip portion 118 is separated from the buckle 116. 
Whereby, there is a concern that the containing portion 117 is opened and dust or the like invades the containing portion 117. 
In addition thereto, the cover 114 of the seat belt pretensioner 110 needs to form the lip portion 118 at the single cover member 113 in order to form the opening space 112 by utilizing a portion of the casing 111, contain the single cover member 113 in the opening space 112 and close the containing portion 117 of the single cover member 113. 
Therefore, the constituent members of the cover 114 are increased, which constitutes a hindrance against a reduction in cost.