Patent Publication Number: US-2007096376-A1

Title: Front fork

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a front fork of a motor cycle or the like.  
      2. Description of the Related Art  
      In a front fork, there is a structure in which an axle side tube is slidably fitted to a vehicle body side tube, and a damper cylinder having a bottom piece is provided in a standing manner in a bottom portion of the axle side tube.  
      As a fixing structure for the bottom piece, Japanese Patent Application Laid-open No. 2003-172392 (patent document 1) describes the followings. A lower end surface of a damper cylinder is brought into contact with a bottom portion (an axle bracket or the like) of the axle side tube. A bottom piece is inserted to an inner periphery of a lower end portion of the damper cylinder. The bottom piece is locked to a stopper ring in an inner periphery of a lower end of the damper cylinder. A bottom bolt engagedly inserted to the bottom portion of the axle side tube from an outer side is screwed with the bottom piece, whereby the damper cylinder is pulled and the lower end surface of the damper cylinder is fastened to the bottom surface of the axle side tube.  
      The structure described in the patent document 1 has the following problems.  
      (1) Since the damper cylinder is provided with a groove cross section for forming the stopper ring in addition to a real cross section sufficient for securing the necessary tensile strength of a front fork, it is difficult to make the thickness dimension of the damper cylinder thin.  
      (2) When the bottom portion of the axle side tube is formed by an aluminum alloy such as the axle bracket or the like, and the damper cylinder is formed of iron, it is necessary to make the surface pressure small which a lower end surface of the damper cylinder applies to the bottom surface of the axle side tube for preventing the lower end surface of the damper cylinder from eating into the bottom surface of the axle side tube. Accordingly, it is difficult to make the thickness dimension of the damper cylinder thin.  
      (3) Since the lower end surface of the damper cylinder is brought into contact with the bottom surface of the axle side tube, processes of finishing work relating to perpendicularity and surface roughness or the like of the lower end surface of the damper cylinder may be increased.  
     SUMMARY OF THE INVENTION  
      An object of the present invention is to simplify a finish of a lower end surface of a damper cylinder as well as making a thickness dimension of the damper cylinder thin, when forming the damper cylinder in a standing manner in a bottom portion of an axle side tube, in a front fork.  
      The present invention relates to a front fork structured such that an axle side tube is slidably fitted to a vehicle body side tube and a damper cylinder is provided in a standing manner in a bottom portion of the axle side tube. A bottom piece is inserted to an inner periphery of a lower end portion of the damper cylinder, and the lower end portion of the damper cylinder is fixed by caulking to an outer periphery of the bottom piece. A bottom bolt engagedly inserted to the bottom portion of the axle side tube from an outer side is screwed to the bottom piece, whereby a lower surface of the bottom piece is fastened to a bottom surface of the axle side tube. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The present invention will be more fully understood from the detailed description given below and from the accompanying drawings which should not be taken to be a limitation on the invention, but are for explanation and understanding only.  
      The drawings:  
       FIG. 1  is a sectional view showing a front fork;  
       FIG. 2  is an enlarged sectional view of a lower portion of the front fork in  FIG. 1 ;  
       FIG. 3  is an enlarged sectional view of a middle portion of the front fork in  FIG. 1 ;  
       FIG. 4  is an enlarged sectional view of an upper portion of the front fork in  FIG. 1 ;  
       FIGS. 5A and 5B  show a cap unit assembly, in which  FIG. 5A  is a sectional view and  FIG. 5B  is a bottom view;  
       FIGS. 6A and 6B  show a cap, in which  FIG. 6A  is a sectional view and  FIG. 6B  is a bottom view;  
       FIGS. 7A and 7B  show an adjuster main body, in which  FIG. 7A  is a front elevational view and  FIG. 7B  is a sectional view;  
       FIG. 8  is a sectional view showing an adjuster collar;  
       FIG. 9  is a plan view showing a slider;  
       FIGS. 10A and 10B  show a leaf spring, in which  FIG. 10A  is a plan view and  FIG. 10B  is a side elevational view;  
       FIG. 11  is a sectional view showing a damper unit assembly;  
       FIG. 12  is an enlarged view of a main portion in  FIG. 11 ; and  
       FIG. 13  is a sectional view showing a bottom valve unit assembly. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      A front fork  10  is structured, as shown in FIGS.  1  to  4 , such that a vehicle body side outer tube (a vehicle body side tube)  11  is slidably fitted to an axle side inner tube (an axle side tube)  12  so as to be inverted. A suspension spring  13  is placed between both the tubes  11  and  12 , and a single cylinder type damper  14  is incorporated in an erect manner.  
      A bush  15 , an oil seal  16  and a dust seal  17  with which an outer peripheral portion of the inner tube  12  is brought into slidable contact are fitted to an inner peripheral portion of a lower end of the outer tube  11 , and a bush  18  with which an inner peripheral portion of the outer tube  11  is brought into slidable contact is fitted to an outer peripheral portion of an upper end of the inner tube  12 .  
      The outer tube  11  is supported to a vehicle body side via an upper bracket  19 A and a lower bracket  19 B, and the inner tube  12  is coupled to an axle via an axle bracket  20 .  
      A lower end portion of a damper cylinder  21  of the damper  14  is attached to a bottom portion of the inner tube  12  so as to be provided in a standing manner. At this time, the damper cylinder  21  is fixedly held by a bottom bolt  24  engagedly inserted to the axle bracket  20  from an outer side via a bottom piece  51  mentioned below, in a manner mentioned below.  
      A cylinder portion  25 A of a cap  25  is inserted and screwed to an upper end portion of the outer tube  11  via an O-ring  26  in a liquid tight manner, and a spring load adjuster  28  is rotatably inserted to an inner periphery of a cover portion  25 B of the cap  25  via an O-ring  27  in a liquid tight manner. A base end portion of a piston rod  29  is screwed to an inner periphery of a lower end of the adjuster  28 , and is locked by a lock nut  30 . A leading end portion of the piston rod  29  is inserted to the damper cylinder  21 .  
      An oil lock collar  31  is fixed to an outer peripheral portion of an upper end of the damper cylinder  21  in an inner portion of the inner tube  12 , and a spring seat  32  is provided in an upper end portion of the oil lock collar  31 . On the other hand, a groove portion  25 C extending in an axial direction is provided in the inner portion of the outer tube  11  and in an inner periphery of the cylinder portion  25 A of the cap  25 , and a slider  33  prevented a rotation with respect to the groove portion  25 C of the cap  25  is screwed with an outer periphery of the adjuster  28 . The slider  33  supports an upper end of the suspension spring  13  via a spring collar  34 A, and the spring seat  32  supports a lower end of the suspension spring  13 . The slider  33  is moved upward and downward by rotationally operating the adjuster  28 , and an initial load of the suspension spring  13  can be set via the spring collar  34 A by extension. In this relation, a thread portion of the adjuster  28  and a thread portion of the slider  33  are set as inverse threads moving the slider  33  downward on the basis of a rightward rotation of the adjuster  28  and compressing the suspension spring  13 .  
      An oil reservoir chamber  35 A and a gas chamber  35 B are provided around an outer peripheral portion of the damper cylinder  21  in the inner portions of the outer tube  11  and the inner tube  12 . A gas sealed in the gas chamber  35 B structures a gas spring. A working fluid in the oil reservoir chamber  35 A contributes to adjustment of a spring constant of the gas chamber  35 B, lubrication of the slidable contact bushes  15  and  18  in the outer tube  11  and the inner tube  12 , and wetting of the oil seal  16  in the lower end portion of the inner tube  12 . Further, an elastic force of the suspension spring  13  and the gas spring absorbs an impact force which a vehicle receives from a road surface.  
      The damper  14  has a piston valve apparatus (an extension side damping force generating apparatus)  40 , and a bottom valve apparatus (a compression side damping force generating apparatus)  50 . The damper  14  suppresses a stretching vibration of the outer tube  11  and the inner tube  12  caused by the absorption of the suspension spring  13  and the gas spring, on the basis of damping forces generated by the piston valve apparatus  40  and the bottom valve apparatus  50 .  
      A rod guide  36  is fixed by caulking to an upper end opening portion of the damper cylinder  21 , and a bush  37  slidably guiding the piston rod  29  is press-fitted in to the rod guide  36 .  
      In this case, a rebound spring  38  which is compressed with respect to a piston holder  41  mentioned below at a time of being extended at the maximum so as to serve a buffering effect is held just below the rod guide  36  in an inner periphery of the damper cylinder  21 .  
      Further, an oil lock piece  39  held by a stopper ring  39 A is installed or fitted (or press-fitted) to the outer periphery of the piston rod  29 , and a buffering effect at the maximum compressing point is achieved by entering the oil lock piece  39  into to the oil lock collar  31  mentioned above at maximum compression.  
      A description will be given below of a damping mechanism of the front fork  10 .  
      Piston Valve Apparatus  40 :  
      The piston valve apparatus  40  is structured such that the piston holder  41  is installed to a leading end portion of the piston rod  29 , and the piston  42  and a valve stopper  41 C are installed by a nut  41 A screwed to the piston holder  41  and a valve stopper  41 B. The piston  42  is brought into slidable contact with the inner portion of the damper cylinder  21 , and sections the inner portion of the damper cylinder  21  into a piston side oil chamber  43 A in which the piston rod  29  is not received, and a rod side oil chamber  43 B in which the piston rod  29  is received. The piston  42  is provided with an extension side flow path  44  (not shown) which is provided with an extension side valve  44 A and can communicate the piston side oil chamber  43 A with the rod side oil chamber  43 B, and a compression side flow path  45  which is provided with a compression side valve (a check valve)  45 A and can communicate the piston side oil chamber  43 A with the rod side oil chamber  43 B.  
      Further, the piston valve apparatus  40  passes a damping force adjusting tube  47  fixed by caulking to a damping force adjusting rod  46  which is inserted and attached in a liquid tight manner to the adjuster  28  via an O-ring  46 A and is screwed so as to be operated from an external portion, through a hollow portion of the piston rod  29 . A flow path area of a bypass path  48  between the piston side oil chamber  43 A and the rod side oil chamber  43 B provided in the piston holder  41  can be adjusted by a needle  47 A in a leading end of the damping force adjusting tube  47 .  
      Accordingly, the oil in the piston side oil chamber  43 A passes through the compression side flow path  45 , opens the compression side valve  45 A and is introduced to the rod side oil chamber  43 B, when the front fork  10  is compressed.  
      Further, when the front fork  10  is extended, and a relative speed between the damper cylinder  21  and the piston rod  29  is low, oil in the rod side oil chamber  43 B is introduced to the piston side oil chamber  43 A through the bypass path  48  in which the needle  47 A exists, and the extension side damping force is generated on the basis of a throttle resistance by the needle  47 A therebetween. The damping force is adjusted on the basis of a position adjustment of the needle  47 A by the damping force adjusting rod  46 .  
      Further, when the front fork  10  is extended, and the relative speed between the damper cylinder  21  and the piston rod  29  is at a middle or high speed, oil in the rod side oil chamber  43 B is introduced to the piston side oil chamber  43 A while deflecting the extension side valve  44 A through the extension side flow path  44 , which generates an extension side damping force.  
      Bottom Valve Apparatus  50 :  
      The bottom valve apparatus  50  is structured such that a compression side valve  56 A, a valve housing  53  and a valve stopper  54  are held to a bottom piece  51  to which the damper cylinder  21  is fixed as mentioned above, by a bolt  52 . The valve stopper  54  holds an extension side valve (a check valve)  57 A and a spring  57 B with respect to the valve housing  53 . The valve housing  53  is sealed to an intermediate portion of the damper cylinder  21  in a liquid tight manner, and sections and forms a bottom valve chamber  55  in a lower side of the piston side oil chamber  43 A. The valve housing  53  is provided with a compression side flow path  56  which is provided with the compression side valve  56 A and can communicate the piston side oil chamber  43 A with the bottom valve chamber  55 , and an extension side flow path  57  (not shown) which is provided with the extension side valve  57 A and can communicate the piston side oil chamber  43 A with the bottom valve chamber  55 . The bottom valve chamber  55  can be communicated with the oil reservoir chamber  35 A provided around the outer portion of the damper cylinder  21  by an oil path  58  provided in the wall surface of the damper cylinder  21 .  
      Further, a bypass flow path  59  which can communicate the piston side oil chamber  43 A with the oil reservoir chamber  35 A while bypassing the compression side flow path  56  and the extension side flow path  57  is provided in the axle bracket  20  provided in the bottom portion of the inner tube  12 , the bottom bolt  24 , the bottom piece  51  and the bolt  52 . Further, a damping force adjusting rod  62  is inserted and screwed in a liquid tight manner to a cap  61  inserted to the axle bracket  20  in a liquid tight manner while gripping an O-ring  61 A, via an O-ring  63 . An area of a flow path of the bypass flow path  59  of the inner tube  12  can be adjusted by a leading end needle  62 A of the damping force adjusting rod  62 .  
      Accordingly, the oil at a volumetric capacity at which the piston rod  29  goes into the damper cylinder  21  is discharged to the oil reservoir chamber  35 A from the piston side oil chamber  43 A through the bypass flow path  59  or to the oil reservoir chamber  35 A through the compression side flow path  56 , the bottom valve chamber  55  and the oil path  58  in the wall surface of the damper cylinder  21 , when the front fork  10  is compressed. Where the relative speed between the damper cylinder  21  and the piston rod  29  is low, the compression side damping force is obtained on the basis of a throttle resistance caused by the needle  62 A provided in the bypass flow path  59 . The damping force is adjusted on the basis of a position adjustment of the needle  62 A by the damping force adjusting rod  62 . Further, where the relative speed between the damper cylinder  21  and the piston rod  29  is at a middle or high level, the oil passing through the compression side flow path  56  from the piston side oil chamber  43 A deflects the compression side valve  56 A so as to be introduced to the bottom valve chamber  55 , and generates the compression side damping force.  
      When the front fork  10  is extended, the oil at a volumetric capacity at which the piston rod  29  goes out of the damper cylinder  21  is flowed back to the piston side oil chamber  43 A from the oil reservoir chamber  35 A through the bottom valve chamber  55  and the extension side flow path  57 .  
      Accordingly, the front fork  10  executes a damping effect as mentioned below.  
      Compression Time:  
      When the front fork  10  is compressed, the compression side damping force is generated by the oil flowing through the compression side valve  56 A of the valve housing  53  or the needle  62 A, in the bottom valve apparatus  50 , and the damping force is generated at a very low level in the piston valve apparatus  40 .  
      Extension Time:  
      When the front fork  10  is extended, the extension side damping force is generated by the oil flowing through the extension side valve  44 A of the piston  42  or the needle  47 A, in the piston valve apparatus  40 , and the damping force is generated at a very low level in the bottom valve apparatus  50 .  
      The stretching vibration of the front fork  10  is suppressed by the compression side and extension side damping forces.  
      Accordingly, in the front fork  10 , there are structured (A) a mounting structure of the adjuster  28  provided in the cap  25 , in a spring load adjusting apparatus of the suspension spring  13 , and (B) a standing structure of the damper cylinder  21 .  
      (A) Mounting Structure of Adjuster  28   
      As a cap unit assembly  70  shown in  FIGS. 5A and 5B , the cap  25  can be inserted in a liquid tight manner to an upper end portion of the outer tube  11  via the O-ring  26  loaded to an outer peripheral annular groove of the cylinder portion  25 A, and the adjuster  28  is rotatably fitted in a liquid tight manner to an inner periphery of the cover portion  25 B of the cap  25  via the O-ring  27 . The damping force adjusting rod  46  is fitted and screwed in a liquid tight manner to an upper end inner periphery of the adjuster  28  via the O-ring  46 A, and the damping force adjusting tube  47  is fixed by caulking to the lower end portion of the damping force adjusting rod  46 . The slider  33  ( FIG. 9 ) is screwed to an outer periphery of the adjuster  28 . A convex portion  33 A protruding to an outer side in a diametrical direction of the slider  33  is engagedly inserted into the groove portion  25 C provided in the cylinder portion  25 A of the cap  25  ( FIGS. 6A and 6B ) and extending along an axial direction, and the slider  33  can move upward and downward in a rotation preventing state.  
      The adjuster  28  has an adjuster main body  80  ( FIGS. 7A and 7B ) which is rotatably inserted to an inner periphery of the cover portion  25 B of the cap  25 , and is structured such that an adjuster collar  90  ( FIG. 8 ) is press-fitted to an outer periphery of the adjuster collar main body  80  positioned within the cap  25 . The slider  33  is screwed with a screw  92  provided in an outer periphery of the adjuster collar  90 .  
      The adjuster  28  is structured such that a collar-shaped operating portion  81  is integrally formed with an upper end large-diameter outer peripheral portion  80 A of the adjuster main body  80  positioned in the outer side of the cover portion  25 B of the cap  25 . An outer peripheral annular groove  82  for the O-ring  27  is provided in an intermediate middle-diameter outer peripheral portion  80 B of the adjuster main body  80  inserted to the cover portion  25 B of the cap  25 . An approximately upper half portion of a lower end small-diameter outer peripheral portion  80 C of the adjuster main body  80  positioned within the cap  25  is set as a press-fitting portion  83  for the adjuster collar  90 . The adjuster main body  80  fits the O-ring  46 A of the damping force adjusting rod  46  to an upper end small-diameter inner peripheral portion  84  in a liquid tight manner, and screws the damping force adjusting rod  46  to a large-diameter thread portion  85  just below the upper end small-diameter inner peripheral portion  84 .  
      The adjuster  28  is structured such that a large-diameter collar portion  91  is provided in an upper end outer periphery of the adjuster collar  90  press-fitted to the press-fitting portion  83  of the adjuster main body  80 , and a thread  92  is formed just below the collar portion  91 .  
      The adjuster  28  is prevented from coming off in the following manner: the adjuster main body  80  is inserted to an inner periphery of the cover portion  25 B from an outer side of the cap  25 ; the intermediate middle-diameter outer peripheral portion  80 B is rotatably fitted to the inner periphery of the cover portion  25 B via the O-ring  27 ; the adjuster collar  90  is press-fitted to the press-fitting portion  83  of the adjuster main body  80  positioned in the inner portion of the cap  25 ; the upper and lower surfaces of the cover portion  25 B of the cap  25  are pinched by the collar-shaped operating portion  81  of the adjuster main body  80  and the collar portion  91  of the adjuster collar  90 .  
      In the adjuster  28 , the damping force adjusting rod  46  is inserted to the inner periphery of the adjuster main body  80  from an inner side of the cap  25 . The damping force adjusting rod  46  is rotatably fitted to the upper end small-diameter inner peripheral portion  84  of the adjuster main body  80  via the O-ring  46 A, and is screwed to the large-diameter thread portion  85 . Thereafter, in the adjuster  28 , a base end portion of the piston rod  29  of the damper cylinder  21  is screwed to the large-diameter thread portion  85  of the adjuster main body  80 . A washer  93  is pinched and locked between the lock nut  30  screwed to the piston rod  29  and the lower end surface of the adjuster main body  80  ( FIG. 4 ). The washer  93  has a larger diameter than the thread  92  of the adjuster collar  90 .  
      In the adjuster  28 , the collar portion  91  in the upper portion of the adjuster collar  90  is formed as an upper limit stopper  94 A of the slider  33 , and the washer  93  in the lower portion of the adjuster collar  90  is formed as a lower limit stopper  94 B.  
      Therefore, in accordance with the present embodiment, the following operations and effects can be achieved.  
      (a) The slider  33  is screwed to the adjuster collar  90  which is press-fitted to the adjuster main body  80  constituting the adjuster  28  at a certain press-fitting force which leads to a slip at a time when the upward and downward motion of the slider  33  is stopped. Accordingly, within the spring load adjustment range, rotation of the adjuster main body  80  is transmitted to the adjuster collar  90  by the press-fitted coupling force, and moves the slider  33  upward and downward. If the upward and downward motion of the slider  33  is stopped at an upper limit and a lower limit of the spring load adjustment range, the adjuster collar  90  slips with respect to the excessive rotation input to the adjuster main body  80  so as to prevent the adjuster  28  or the like from being broken. The press-fitting force does not disappear after the slip, and the normal spring load adjusting operation is executed within the spring load adjusting range.  
      (b) Since the upper limit stopper  94 A and the lower limit stopper  94 B for the slider  33  are provided in the upper and lower sides of the adjuster collar  90 , it is possible to securely stop the upward and downward motion of the slider  33  and to lead the adjuster collar  90  to the slip at the upper limit and the lower limit of the spring load adjusting range.  
      (c) The adjuster  28  is prevented from coming off by integrally forming the collar-shaped operating portion  81  in the adjuster main body  80  positioned in the outer side of the cap  25 , and pinching the cover portion  25 B of the cap  25  by the collar-shaped operating portion  81  and the adjuster collar  90 . Since the collar-shaped operating portion  81  is integrally formed in the adjuster main body  80 , it is possible to reduce a risk of coming off of the adjuster  28 , and it is possible to reduce a number of the parts, and assembly man hours.  
      (d) It is possible to securely receive a tensile load in an axial direction applied to the piston rod  29  of the damper cylinder  21  by the collar-shaped operating portion  81  integrally formed in the adjuster main body  80 , and therefore it is possible to prevent the adjuster  28  from falling away due to the excessive tensile input to the adjuster main body  80 .  
      Further, the adjuster  28  is structured such that an annular leaf spring  100  is interposed in an elastic compression state between the lower surface of the cover portion  25 B of the cap  25  and the upper surface of the collar portion  91  of the adjuster collar  90 . An annular concave portion  25 D positioning the leaf spring  100  in a radial direction along an outer edge of the leaf spring  100  is provided in the lower surface of the cover portion  25 B of the cap  25 . The leaf spring  100  is loaded to the annular concave portion  25 D of the cap  25 .  
      The leaf spring  100  is structured, as shown in  FIGS. 10A and 10B , such that a left piece  101  and a right piece  102  with respect to one diametrical line A of an annular disc are curved so as to form a circular arc in a side view, or bent so as to form an L shape with each other. The leaf spring  100  is loaded to the annular concave portion  25 D of the cap  25 , and brings a center curve convex portion of the circular arc, or a center bent convex portion of the L shape on the diametrical line A into pressure contact with an upper surface of the collar portion  91  of the adjuster collar  90 . In this case, the leaf spring  100  may be formed in a disc spring shape.  
      Therefore, in accordance with the present embodiment, the following operations and effects can be achieved.  
      (a) Since the leaf spring  100  is interposed between the lower surface of the cover portion  25 B of the cap  25  and the adjuster  28 , it is possible to absorb assembly play caused by a dimensional difference between the cap  25  and the adjuster  28  by elastic deformation of the leaf spring  100 . It is also possible to prevent unexpected rotation of the adjuster  28  due to the vibration by a frictional force which the leaf spring  100  applies to the adjuster  28 .  
      (b) In the structure using the leaf spring  100  mentioned in the item (a), the rotating operation force and the rotating operation position of the adjuster  28  are not affected by a friction and a viscous effect in the O-ring, and it is possible to improve rotating operability of the adjuster  28 .  
      (c) In the structure using the leaf spring  100  mentioned in the item (a), working man hours and assembly man hours are not so necessary as the O-ring, an assembling space can be made small, and it is possible to make the structure compact.  
      (B) Standing Structure of Damper Cylinder  21   
      A damper unit assembly  14 A shown in  FIG. 11  is structured by inserting the piston valve apparatus  40  of the piston rod  29  and others to the damper cylinder  21 , fixing the oil lock collar  31  as well as fixing the rod guide  36  by caulking to the upper end portion of the damper cylinder  21 , and fixing a bottom valve unit assembly  50 A to the lower end portion of the damper cylinder  21 . The bottom valve unit assembly  50 A is structured, as shown in  FIG. 13 , by screwing the bolt  52  to an upper thread of the bottom piece  51  and unit assembling the compression side valve  56 A, the valve housing  53 , the valve stopper  54 , the extension side valve (the check valve)  57 A and the spring  57 B between the bottom piece  51  and the bolt  52 .  
      In the damper unit assembly  14 A, the bottom piece  51  of the bottom valve unit assembly  50 A is inserted to the inner periphery of the lower end portion of the damper cylinder  21 , and the lower end portion of the damper cylinder  21  is fixed by caulking to the outer periphery of the bottom piece  51 . At this time, as shown in  FIGS. 12 and 13 , an annularly continuously formed concave groove  51 A is provided in the outer periphery of the intermediate portion of the bottom piece  51 , and a step  51 B (a step amount h) larger than a thickness t of the damper cylinder  21  is provided in the outer periphery of the lower end portion. Further, the lower end portion of the damper cylinder  21  is fixed by caulking to the concave groove  51 A of the bottom piece  51  at a caulking portion  21 A, and a lowest end portion of the damper cylinder  21  is fixed by caulking to the step  51 B of the bottom piece  51  at a caulking portion  21 B, whereby the lower end portion of the damper cylinder  21  is fixed by caulking to the outer periphery of the bottom piece  51 . The caulking portion  21 A is provided at a plurality of positions along the peripheral direction of the damper cylinder  21 , or may be continuously provided with an entire periphery of the damper cylinder  21 . The caulking portion  21 B is provided continuously in the entire periphery of the damper cylinder  21 .  
      The bottom bolt  24  locked into the axle bracket  20  from the outer side is screwed with the lower thread of the bottom piece  51  such that the damper unit assembly  14 A is inserted to the inner portion of the inner tube  12 , and the lower surface of the bottom piece  51  constituting the damper unit assembly  14 A is mounted on the bottom surface of the axle bracket  20 . The bottom bolt  24  is locked into a through hole provided in the bottom portion of the axle bracket  20  from the outer side via the seal member  23 . Accordingly, the lower surface of the bottom piece  51  is brought into pressure contact with the bottom surface of the axle bracket  20  so as to be fastened.  
      The axle bracket  20  may be made of an aluminum alloy, and the damper cylinder  21  may be made of an iron.  
      Therefore, in accordance with the present embodiment, the following operations and effects can be achieved.  
      (a) The lower end portion of the damper cylinder  21  is fixed by caulking to the outer periphery of the bottom piece  51 , and a groove for arranging the stopper ring in the damper cylinder  21  is not necessary. It is possible to make the thickness dimension of the damper cylinder  21  thinner at a degree at which the groove is not necessary. Accordingly, it is possible to reduce the weight and the cost of the front fork  10 .  
      (b) The bottom bolt  24  pulls the bottom piece  51  and fastens the lower surface of the bottom piece  51  to the bottom surface of the axle bracket  20 . Since there is absolutely no risk that the lower end surface of the damper cylinder  21  is brought into contact with the bottom surface of the axle bracket  20  so as to eat into the bottom surface, it is possible to make the thickness of the damper cylinder  21  thin. Accordingly, it is possible to reduce the weight and the cost of the front fork  10 .  
      (c) Since the lower end surface of the damper cylinder  21  is not brought into contact with the bottom surface of the axle bracket  20 , it is possible to simplify the finishing work regarding the perpendicularity, the surface roughness and others of the lower end surface of the damper cylinder  21 .  
      (d) The lower end portion of the damper cylinder  21  is fixed to the concave groove  51 A in the outer periphery of the intermediate portion of the bottom piece  51  by caulking, and the lowest end portion is fixed to the step  51 B in the outer periphery of the lower end portion of the bottom piece  51  by caulking, so that the lower end portion of the damper cylinder  21  can be firmly fixed to the outer periphery of the bottom piece  51 . Since the step  51 B of the bottom piece  51  to which the lowest end portion of the damper cylinder  21  is fixed by caulking is larger than the thickness of the damper cylinder  21 , the lowest end portion of the damper cylinder  21  fixed by caulking is received within the step  51 B, and does not interfere with the bottom surface of the axle bracket  20 .  
      As heretofore explained, embodiments of the present invention have been described in detail with reference to the drawings. However, the specific configurations of the present invention are not limited to the illustrated embodiments but those having a modification of the design within the range of the presently claimed invention are also included in the present invention. For example, the present invention can be also applied to a conventional front fork.  
      Although the invention has been illustrated and described with respect to several exemplary embodiments thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions and additions may be made to the present invention without departing from the spirit and scope thereof. Therefore, the present invention should not be understood as limited to the specific embodiment set out above, but should be understood to include all possible embodiments which can be encompassed within a scope of equivalents thereof with respect to the features set out in the appended claims.