1.  Field of the Invention
The present invention relates to a shaft seal part structure of a hydraulic shock absorber and an assembling method of the same. 
2.  Description of the Related Art
In a hydraulic shock absorber, for example, as described in Japanese Unexamined Utility Model Application Laid-Open No.  6-65638, an inner cylinder is arranged in an inner side of an outer cylinder.  A rod guide is arranged in an inner side of the inner cylinder.  An oil seal for sealing the inner cylinder and the rod guide is attached in a sealing manner to an inner side of the outer cylinder, and a piston rod is inserted to the inner cylinder via the oil seal and the rod guide. 
In the conventional art, the rod guide is attached to an upper end of the inner cylinder.  The oil seal which is inserted to an upper inner periphery of the outer cylinder is layered on the rod guide.  An upper end of the outer cylinder is bent inward according to a roll caulking.  The inner cylinder, the rod guide, and the oil seal are held in an inner portion of the outer cylinder by the bent portion.  At this time, an outer peripheral lip of the oil seal is in contact with an inner periphery of the outer cylinder so as to seal the outer cylinder. 
The conventional art mentioned above has the following problems. 
(1) Since the structure is made such that the outer peripheral lip of the oil seal is in contact with the inner periphery of the outer cylinder so as to seal the outer cylinder, it is necessary to make surface roughness of the outer periphery in the outer cylinder fine.  It is also necessary to finish the inner periphery of the outer cylinder to which the oil seal is inserted according to a cutting process or the like. 
(2) When inserting the oil seal to the outer cylinder, there is a risk that the outer peripheral lip of the oil seal is damaged because the outer diameter of the outer peripheral lip in the oil seal is larger than the inner diameter of the outer cylinder. 
An object of the present invention is, in a shaft seal part structure of a hydraulic shock absorber, to seal an outer cylinder to which an oil seal is inserted, without finishing an inner periphery of the outer cylinder and while avoiding the risk that damage is generated in an outer peripheral seal portion of the oil seal at a time of inserting the oil seal. 
According to the present invention, there is disclosed a shaft seal part structure of a hydraulic shock absorber in which an inner cylinder is arranged in an inner side of an outer cylinder, a rod guide is arranged in an inner side of the inner cylinder, an oil seal for sealing the inner cylinder and the rod guide is attached in a sealing manner to an inner side of the outer cylinder, and a piston rod is inserted to the inner cylinder via the oil seal and the rod guide. 
The oil seal is provided with a seal core having a doughnut-like horizontal portion and a tubular portion extending downward from an outer periphery thereof, layered on an upper portion of the inner cylinder via the rod guide. 
A diameter of an upper portion of the outer cylinder is reduced toward the tubular portion of the oil seal. 
The diameter reduced portion of the outer cylinder presses the tubular portion of the oil seal downward, thereby holding the inner cylinder, the rod guide, and the oil seal in an inner portion of the outer cylinder. 
According to the present invention, there is disclosed a method of assembling a shaft seal part structure of a hydraulic shock absorber in which an inner cylinder is arranged in an inner side of an outer cylinder, a rod guide is arranged in an inner side of the inner cylinder, an oil seal for sealing the inner cylinder and the rod guide is attached in a sealing manner to an inner side of the outer cylinder, and a piston rod is inserted to the inner cylinder via the oil seal and the rod guide. 
The inner cylinder is arranged in a coaxial manner in an inner side of the outer cylinder by using the oil seal provided with a seal core having a doughnut-like horizontal portion and a tubular portion extending downward from an outer periphery thereof. 
The rod guide and the oil seal are layered in an upper end of the inner cylinder. 
The diameter of an upper portion of the outer cylinder toward the tubular vertical portion of the oil seal is reduced so as to press the tubular portion of the oil downward by the diameter reduced portion. 
According to the present invention, a horizontal direction means a direction orthogonal to a center axis of a piston rod in a hydraulic shock absorber, and a vertical direction means a direction extending along the center axis of the piston rod.  An upward direction means a direction in which the piston rod moves out from the hydraulic shock absorber, and a downward direction means a direction in which the piston rod moves.