Patent Publication Number: US-9849933-B2

Title: Front suspension structure for saddle riding type vehicle

Description:
FIELD OF THE INVENTION 
     This application relates to a front suspension structure for a saddle riding type vehicle. 
     BACKGROUND OF THE INVENTION 
     One example of a conventional front suspension structure for a saddle riding type vehicle is disclosed in Japanese Patent Laid-Open No. Hei 4-169386 (“JP &#39;386”). This structure supports a steering shaft link, which steerably supports a front fork, and a vehicle body frame by front and rear end portions of an upper arm portion and a lower arm portion each extending longitudinally. The steering shaft link is disposed on the inside in a radial direction of the front fork. 
     SUMMARY OF THE INVENTION 
     One problem with the aforementioned structure of JP &#39;386 is that, when the front end portions of the upper and lower arm portions are supported by the steering shaft link on the inside in the radial direction of the front fork (head pipe) (a type in which the head pipe rotates), the positions at which the front end portions of the upper and lower arm portions are supported are inevitably the upper and lower end portions of the steering shaft link which end portions project above and below the head pipe. Therefore, a degree of freedom of the position at which the arm portion is supported is lowered. 
     Therefore, one objective of the present invention is to increase a degree of freedom of the position at which an arm portion is supported in a front suspension structure for a saddle riding type vehicle which structure supports a steering member by the arm portion rocking vertically. 
     To achieve this objective, one aspect of the present invention includes a head pipe ( 12 ) radially internally supporting a shaft portion ( 13   b ) forming a steering axis (C 3 ) such that the shaft portion ( 13   b ) is rotatable about the steering axis (C 3 ); a front fork ( 19 ) connected to a lower end portion of the shaft portion ( 13   b ) on a lower side of the head pipe ( 12 ), the front fork ( 19 ) supporting an axle ( 9   a ) of a steering wheel ( 9 ); and a link member ( 15 ) having one end portion connected rotatably on an upper side of a turning member ( 13 ) having the shaft portion ( 13   b ), and having another end portion connected rotatably on a side of handlebars ( 8 ); the head pipe ( 12 ) being disposed so as to be separated frontward from a vehicle body frame ( 1 ); a rocking arm ( 16 ) having a front end portion rockably supported by the head pipe ( 12 ), and having a rear end portion rockably supported by the vehicle body frame ( 1 ). Accordingly, the front end portion of the rocking arm is supported by the head pipe on the outside in the radial direction of the shaft portion forming the steering axis. Thus, the position at which the rocking arm is supported can be set arbitrarily. Hence, a degree of freedom of the position at which the arm portion is supported can be increased. In addition, because a turning system of the turning member and the like and a rocking system of the rocking arm and the like are separated from each other, the turning system is not readily affected by rocking. 
     According to a second aspect of the present invention, the rocking arm ( 16 ) includes an upper arm portion ( 17 ) and a lower arm portion ( 18 ) vertically separated from each other, the head pipe ( 12 ) is inclined such that an upper side of the head pipe ( 12 ) is located more rearward than a lower side of the head pipe ( 12 ) as viewed from a side, a front end portion ( 17   a ) of the upper arm portion ( 17 ) is in front of the steering axis (C 3 ) and is supported by a front upper portion of the head pipe ( 12 ), and a front end portion ( 18   a ) of the lower arm portion ( 18 ) is in a rear of the steering axis (C 3 ) and is supported by a rear lower portion of the head pipe ( 12 ). Accordingly, spaces of the front upper portion and the rear lower portion of the head pipe which spaces are created by the inclination of the head pipe can be utilized effectively as spaces for supporting the respective front end portions of the upper and lower arm portions. It is therefore possible to make the front suspension structure compact and thus shorten an overall length of the front suspension structure. In addition, because the respective front end portions of the upper and lower arm portions are distributed longitudinally, the concentration of force on one part can be prevented. 
     According to a third aspect of the present invention, the front end portion ( 17   a ) of the upper arm portion ( 17 ) and the front end portion ( 18   a ) of the lower arm portion ( 18 ) are rockably supported via coupling members ( 34   a ,  36   a ), respectively, the coupling members ( 34   a ,  36   a ) penetrating connecting portions ( 12   a ,  12   b ) of the head pipe ( 12 ) and extending along a vehicle width direction. Accordingly, the upper and lower arm portions can be supported by the respective coupling members so as to avoid the head pipe. Therefore the respective front end portions of the upper and lower arm portions can be supported with high rigidity. 
     According to a fourth aspect of the present invention, the front end portion ( 17   a ) of the upper arm portion ( 17 ) and the front end portion ( 18   a ) of the lower arm portion ( 18 ) are connected respectively to connecting portions ( 12   a ,  12   b ) of the head pipe ( 12 ) rockably about coupling axes (C 9 , C 11 ) along the vehicle width direction, and at least one of the coupling axes (C 9 , C 11 ) is disposed between an upper end and a lower end of the head pipe ( 12 ) as viewed from the side. Accordingly, the respective front end portions of the upper and lower arm portions can be supported on the head pipe compactly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be described with reference to the accompanying drawings, wherein: 
         FIG. 1  is a left side view of a front portion of a vehicle body of a motorcycle according to an embodiment of the present invention. 
         FIG. 2  is a left side view of a front wheel suspension device of the motorcycle. 
         FIG. 3  is a perspective view of the front wheel suspension device as viewed from an upper left front. 
         FIG. 4  is a top view of the front wheel suspension device. 
         FIG. 5  is a sectional view including a section along a rotation axis of the front wheel suspension device and a horizontal section of a left link member. 
         FIG. 6  is a sectional view including a section along a first coupling axis of an upper arm portion of the front wheel suspension device and a section along a second coupling axis. 
         FIG. 7  is a sectional view including a section along a third coupling axis of a lower arm portion of the front wheel suspension device, a section along a fourth coupling axis, and a section along a central axis of a connecting portion for connecting a front lower end portion of a cushion unit. 
         FIG. 8  is a sectional view including a section of a connecting portion of an upper end portion of a front fork of the front wheel suspension device along the longitudinal direction of a head pipe and a section along a central axis of a front wheel axle. 
         FIG. 9  is a left side view showing various axes of the front wheel suspension device and the like. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An embodiment of the present invention will hereinafter be described with reference to the drawings. Incidentally, directions such as a forward direction, a rearward direction, a left direction, a right direction, and the like in the following description are identical with directions in a vehicle to be described in the following unless otherwise specified. In addition, an arrow FR indicating the forward direction of the vehicle, an arrow LH indicating the left direction of the vehicle, an arrow UP indicating the upward direction of the vehicle, and a lateral center line CL of the vehicle are shown in appropriate positions in the drawings to be used in the following description. 
       FIG. 1  shows a front portion of a vehicle body of a motorcycle as an example of a saddle riding type vehicle. Referring to  FIG. 1 , a vehicle body frame  1  of the motorcycle has a front block  2  as a front end portion of the vehicle body frame  1  which front block  2  supports a front wheel suspension device  10 . 
     A pair of left and right main frames  3  extends rearward and downward from the rear of the front block  2 , and a pair of left and right sub-frames  3   a  extends rearward from the rear of the front block  2 . The left and right main frames  3  are connected to a pivot frame  4  that supports a rear wheel suspension device not shown in the figures. A horizontally opposed engine  5 , for example, is mounted below the front block  2 , the left and right main frames  3 , and the left and right sub-frames  3   a . A fuel tank  6  is disposed on the front block  2  and the left and right main frames  3 . The front portion of the vehicle body of the motorcycle is covered by a front cowl  7  made of a synthetic resin. 
     Referring also to  FIG. 2  and  FIG. 3 , the front block  2  has a V-shape projecting forward and upward as viewed from the side. Connecting portions  2   b  to which rear end portions  17   b  of an upper arm portion  17  to be described later are connected are formed in a front upper end portion of the front block  2 . Connecting portions  2   c  to which rear end portions  18   b  of a lower arm portion  18  to be described later are connected are formed in the vicinity of a vertical center of the front block  2 . 
     Supporting portions  2   d  supporting a left side portion and a right side portion of the engine  5  are formed in a front lower end portion of the front block  2 . 
     The front wheel suspension device  10  includes a supporting portion  2   a , a handlebar post  11 , a head pipe  12 , a turning member  13 , a rotary member  14 , link members  15 , a rocking arm  16 , a front fork  19 , and a cushion unit  20 . 
     Referring also to  FIG. 8  and  FIG. 9 , the front fork  19  is disposed below the head pipe  12 . The front fork  19  has an upper end portion connected to a shaft portion  13   b  of the turning member  13 , and has a lower end portion supporting a front wheel axle  9   a  of the front wheel  9  as a steered wheel. 
     The front fork  19  integrally has a pair of left and right arm portions  19   a  extending vertically and a cross member  19   b  coupling upper end portions of the left and right arm portions  19   a  to each other. The elements of the front fork  19  are each an integral part made of aluminum, for example. These elements are joined by welding to be integral with each other. 
     The left and right arm portions  19   a  are arranged on both of the left side and the right side of the front wheel  9 . The cross member  19   b  is curved to the inside in a vehicle width direction in such a manner as to be along a tread surface at an upper end position of the front wheel  9 , and is disposed between the upper end portions of the left and right arm portions  19   a . The left and right end portions of the cross member  19   b  are joined to the upper end portions of the left and right arm portions  19   a.    
     A connecting portion  19   c  to which the shaft portion  13   b  of the turning member  13  is connected is formed in an upper end portion of the cross member  19   b . An insertion hole  19   h  opening in a direction in which the shaft portion  13   b  of the turning member  13  extends is formed in the connecting portion of the cross member  19   b . The shaft portion  13   b  of the turning member  13  has a maximum diameter at a lower end portion thereof. The shaft portion  13   b  is inserted into the insertion hole  19   h  from an upper end portion of the shaft portion  13   b , and a lower end portion of the shaft portion  13   b  and the connecting portion  19   c  are joined to each other by welding in a state in which the lower end portion of the shaft portion  13   b  is located in the insertion hole  19   h , whereby the upper end portion of the front fork  19  is fixedly connected to the shaft portion  13   b  of the turning member  13 . 
     Incidentally, a symbol  13   g  in the figures denotes a ball bearing retained in an inner circumference of a lower end portion of the head pipe  12 . 
     Connecting portions  19   d  to which the front wheel axle  9   a  is connected are formed in lower end portions of the left and right arm portions  19   a . An insertion hole  9   h  opening in the vehicle width direction is formed in the connecting portions  19   d  of the left and right arm portions  19   a . In a state of a hub portion  9   d  of a wheel  9   c  of the front wheel  9  being held between the connecting portions  19   d  of the left and right arm portions  19   a , a bolt  9   b  is passed through the insertion holes  9   h  and an inner circumference of the hub portion  9   d  of the wheel  9   c , and is screwed and fastened to one end of the front wheel axle  9   a . An outer circumference of the front wheel axle  9   a  is provided with a pair of left and right side collars  9   j , a pair of left and right ball bearings  9   g  adjacent to the insides of the left and right side collars  9   j , and a center collar  9   i  for securing a distance between the left and right ball bearings  9   g . Both end portions in the vehicle width direction of the front wheel axle  9   a  are fixedly supported by the lower end portion of the front fork  19 , and the wheel  9   c  of the front wheel  9  is rotatably supported by a center in the vehicle width direction of the front wheel axle  9   a  via the left and right ball bearings  9   g.    
     Incidentally, a symbol  21   a  denotes a brake rotor whose inner rotor is fixed to both of a left end and a right end of the hub portion  9   d . A symbol C 1  in the figures denotes the central axis of the front wheel axle  9   a . A symbol C 1 L in the figures denotes a perpendicular from the central axis C 1  to a ground G. A symbol T in the figures denotes a trail. 
     A brake caliper  21  is supported in the rear of the lower portion (left and right arm portions  19   a ) of the front fork  19 . A front fender  22  is supported on the upper portion (cross member  19   b ) of the front fork  19  via a bolt not shown in the figures. 
     Referring also to  FIG. 2 ,  FIG. 3 , and  FIG. 9 , the supporting portion  2   a  is provided on a longitudinal center of the upper end portion of the front block  2  so as to be inclined rearward with respect to a vertical direction as viewed from the side. The supporting portion  2   a  is for example provided integrally with the upper front end portion of the front block  2  made of aluminum. An upper portion of the supporting portion  2   a  rotatably (steerably) supports the handlebar post  11 , and a lower portion of the supporting portion  2   a  rockably supports a rear upper end portion  20   b  of the cushion unit  20 . 
     Specifically, a shaft portion  11   a  of the handlebar post  11  is inserted into an inner circumference of the upper portion of the supporting portion  2   a , and the supporting portion  2   a  rotatably (steerably) supports the shaft portion  11   a . A ball bearing not shown in the figures is retained in the inner circumference of the supporting portion  2   a . An upper end portion of the shaft portion  11   a  projects above the supporting portion  2   a . This projecting portion fixedly supports a holder  11   b  of the handlebar post  11 . A pair of left and right connecting portions  2   e  to which the rear upper end portion  20   b  of the cushion unit  20  is connected is formed in both sides in the vehicle width direction of the lower portion of the supporting portion  2   a.    
     Incidentally, a symbol C 2  in the figures denotes the central axis of the shaft portion  11   a . The central axis C 2  may hereinafter be referred to as a steering axis. The shaft portion  11   a  of the handlebar post  11  forms the steering axis C 2 . 
     Referring to  FIG. 5 , the handlebar post  11  forms a V-shape projecting rearward as viewed in a direction along the steering axis C 2 . A laterally central portion of the handlebars  8  is fixedly supported on the holder  11   b  of the handlebar post  11 . Referring to  FIG. 2 , the shaft portion  11   a  of the handlebar post  11  is rotatably supported by the supporting portion  2   a , and thereby the handlebars  8  above the supporting portion  2   a  are supported by the handlebar post  11  rotatably (steerably) about the shaft portion  11   a  (steering axis C 2 ). Connecting portions  11   c  to which a left second ball joint  43  and a right second ball joint  43  to be described later are connected are formed in a left end portion and a right end portion of the handlebar post  11 . 
     Referring also to  FIG. 2 ,  FIG. 8 , and  FIG. 9 , the head pipe  12  is disposed so as to be separated frontward from the steering axis C 2 . The head pipe  12  is inclined such that an upper side of the head pipe  12  is located more rearward than a lower side of the head pipe  12  as viewed from the side. Specifically, the head pipe  12  forms a cylindrical shape, and is disposed in front of the supporting portion  2   a  (front block  2 ) so as to be inclined rearward with respect to the vertical direction. The head pipe  12  radially internally supports the shaft portion  13   b  of the turning member  13  rotatably (steerably) about the central axis C 3  of the shaft portion  13   b . A connecting portion  12   a  to which the front end portion  17   a  of the upper arm portion  17  is connected is formed in front of the steering axis C 3  and in the front upper portion of the head pipe  12  so as to project forward and upward. A connecting portion  12   b  to which the front end portion  18   a  of the lower arm portion  18  is connected is formed in the rear of the steering axis C 3  and in the rear lower portion of the head pipe  12  so as to project rearward and downward. 
     Incidentally, the central axis C 3  of the shaft portion  13   b  coincides with the central axis of the head pipe  12 . The central axis C 3  may hereinafter be referred to as a steering axis (turning axis). The angle of the steering axis C 3  to the vertical direction is a “caster angle.” The steering axis C 3  is offset (separate) frontward from the steering axis C 2 , and forms the shape of a straight line inclined such that an upper side of the straight line is located more rearward than a lower side of the straight line as viewed from the side. The steering axis C 3  and the steering axis C 2  are parallel to each other in a 1G state in which the load of a vehicle weight is applied to the front wheel suspension device  10  in the figures (which state may hereinafter be referred to simply as a “1G state”). 
     Referring also to  FIG. 2  and  FIG. 5 , the turning member  13  is rotatably supported by the head pipe  12 , and is steered about the steering axis C 3  integrally with the front wheel  9 . The turning member  13  includes an upper portion  13   a  and the shaft portion  13   b . The upper portion  13   a  has a C-shape whose front portion projects frontward as viewed from the side. The shaft portion  13   b  extends along the direction in which the head pipe  12  extends. 
     A lower end portion of the upper portion  13   a  forms a C-shape opening to the rear as viewed from a direction along the steering axis C 3 . An insertion hole  13   h  into which a positioning pin  13   c  is inserted is formed in a front lower end portion of the upper portion  13   a . An insertion hole  30   h  opening in the vehicle width direction is formed in a rear lower end portion of the upper portion  13   a . In a state of the pin  13   c  being inserted in the insertion hole  13   h , a bolt  30   a  is passed through the insertion hole  30   h , and is screwed and fastened to a nut  30   b , whereby the lower end portion of the upper portion  13   a  is fastened and fixed to the upper end portion of the shaft portion  13   b.    
     Referring also to  FIG. 2 ,  FIG. 4 ,  FIG. 5 , and  FIG. 9 , a cylindrical journaling portion  13   d  extending in the vehicle width direction is formed in an upper end portion of the upper portion  13   a . The journaling portion  13   d  is disposed on the upper side of the left and right link members  15  as viewed from the side. The journaling portion  13   d  supports the rotary member  14  such that the rotary member  14  is rotatable coaxially with the journaling portion  13   d.    
     Incidentally, a symbol C 4  in the figures denotes the central axis of the journaling portion  13   d . The central axis C 4  may hereinafter be referred to as a rotation axis. 
     The rotary member  14  is disposed between front end portions of the left and right link members  15  and the turning member  13 . The rotary member  14  is disposed in the vicinities of front ends of the left and right link members  15  and between the left and right link members  15 . The rotary member  14  is disposed on the upper side of the left and right link members  15 . 
     Referring to  FIG. 4 , the rotary member  14  extends in the vehicle width direction so as to have a width equal to that of the handlebar post  11  as viewed from above. The rotary member  14  includes: a main body portion  14   f  located in a front portion of the rotary member  14 ; and a pair of left and right extending portions  14   b  extending rearward with a predetermined interval therebetween on the inside in the vehicle width direction of the main body portion  14   f . Connecting portions  14   a  to which a left first ball joint  40  and a right first ball joint  40  to be described later are connected are formed in a left end portion and a right end portion of the main body portion  14   f.    
     Referring also to  FIG. 5 , an insertion hole  31   h  opening in the vehicle width direction is formed in the left and right extending portions  14   b  of the rotary member  14 . In a state of the cylindrical journaling portion  13   d  being held between the left and right extending portions  14   b , a bolt  31   a  is inserted through the insertion holes  31   h  and an inner circumference of the journaling portion  13   d , and a nut  31   b  is screwed and fastened to a projecting portion of the bolt  31   a . An outer circumference of the bolt  31   a  is provided with a pair of left and right side collars  31   j , a pair of left and right ball bearings  31   g  adjacent to the insides of the left and right side collars  31   j , and a center collar  31   i  for securing a distance between the left and right ball bearings  31   g . The journaling portion  13   d  of the turning member  13  supports the rotary member  14  rotatably about the rotation axis C 4  via the left and right ball bearings  31   g.    
     Referring also to  FIG. 2 ,  FIG. 4 , and  FIG. 5 , the link members  15  are provided as a pair of left and right members on both sides in the vehicle width direction. As viewed from above, the left and right link members  15  extend linearly in the forward-rearward direction of the vehicle, and are arranged in parallel with each other in the vehicle width direction. The front end portions of the left and right link members  15  are connected rotatably about a first axis C 5  to be described later on the side of the turning member  13 , and rear end portions of the left and right link members  15  are connected rotatably about a second axis C 6  to be described later on the side of the handlebars  8 . 
     Specifically, the front end portions of the left and right link members  15  are connected with a pair of left and right first ball joints  40  provided on both sides in the vehicle width direction. The rear end portions of the left and right link members  15  are connected with a pair of left and right second ball joints  43  provided on both sides in the vehicle width direction. The front end portions of the left and right link members  15  are rotatably connected to the left and right connecting portions  14   a  of the rotary member  14  via the left and right first ball joints  40 , and the rear end portions of the left and right link members  15  are rotatably connected to the left and right connecting portions  11   c  of the handlebar post  11  via the left and right second ball joints  43 . 
     The left and right first ball joints  40  each include a first ball stud  41  and a first socket  42 . 
     The left and right first ball studs  41  each include a spherical ball portion  41   a  and a stud portion  41   b  projecting upward from the ball portion  41   a . The left and right ball portions  41   a  are slidably retained within the left and right first sockets  42 . The left and right stud portions  41   b  extend linearly in the upward-downward direction of the vehicle. 
     The left and right first sockets  42  each include a first upper socket  42   a  and a first lower socket  42   b . The ball portion  41   a  is slidably retained between the first upper socket  42   a  and the first lower socket  42   b.    
     An insertion hole  14   h  opening in the upward-downward direction of the vehicle is formed in the left and right connecting portions  14   a  of the rotary member  14 . Screw portions of upper end portions of the left and right stud portions  41   b  are inserted into the left and right insertion holes  14   h , and a nut  32  is screwed and fastened to the upward projecting portions of the screw portions, whereby the left and right stud portions  41   b  are fastened and fixed to the left and right connecting portions  14   a  of the rotary member  14 . 
     Incidentally, a symbol C 5  in the figures denotes the central axis of the left and right stud portions  41   b . The central axis C 5  may hereinafter be referred to as a first axis. The first axis C 5  is a straight line extending in the upward-downward direction of the vehicle. In addition, a symbol C 7  in the figures denotes the center of the left and right ball portions  41   a . The center C 7  of the left and right ball portions  41   a  are a center of rotation of the left and right first ball joints  40 . 
     The left and right second ball joints  43  each include a second ball stud  44  and a second socket  45 . 
     The left and right second ball studs  44  each include a spherical ball portion  44   a  and a stud portion  44   b  projecting upward from the ball portion  44   a . The left and right ball portions  44   a  are slidably retained within the left and right second sockets  45 . The left and right stud portions  44   b  are parallel with the left and right stud portions  41   b , and extend linearly in the upward-downward direction of the vehicle. 
     The left and right second sockets  45  each include a second upper socket  45   a  and a second lower socket  45   b . The ball portion  44   a  is slidably retained between the second upper socket  45   a  and the second lower socket  45   b.    
     An insertion hole  11   h  opening in the upward-downward direction of the vehicle is formed in the left and right connecting portions  11   c  of the handlebar post  11 . Screw portions of upper end portions of the left and right stud portions  44   b  are inserted into the left and right insertion holes  11   h , and a nut  32  is screwed and fastened to the upward projecting portions of the screw portions, whereby the left and right stud portions  44   b  are fastened and fixed to the left and right connecting portions  11   c  of the handlebar post  11 . 
     Incidentally, a symbol C 6  in the figures denotes the central axis of the left and right stud portions  44   b . The central axis C 6  may hereinafter be referred to as a second axis. The second axis C 6  is a straight line that is parallel with the first axis C 5  and which extends in the upward-downward direction of the vehicle. In addition, a symbol C 8  in the figures denotes the center of the left and right ball portions  44   a . The center C 8  of the left and right ball portions  44   a  is a center of rotation of the left and right second ball joints  43 . 
     The front end portions of the left and right link members  15  are connected to rear end portions  42   r  of the left and right first lower sockets  42   b , and the rear end portions of the left and right link members  15  are connected to front end portions  45   f  of the left and right second lower sockets  45   b . Specifically, the left and right link members  15  are fixed by using a lock nut  33  in a state in which screw portions  15   a  of the front end portions of the left and right link members  15  are screwed into the rear end portions  42   r  of the left and right first lower sockets  42   b  by a predetermined amount, and the left and right link members  15  are fixed by using a lock nut  33  in a state in which screw portions  15   b  of the rear end portions of the left and right link members  15  are screwed into the front end portions  45   f  of the left and right second lower sockets  45   b  by a predetermined amount. Distances between the front and rear connecting portions for the left and right link members  15  can be adjusted by loosening the lock nuts  33  and increasing or decreasing amounts of screwing of the front screw portions  15   a  and the rear screw portions  15   b  into the left and right first lower sockets  42   b  and the left and right second lower sockets  45   b , respectively. 
     The left and right link members  15  form parallel links together with the rotary member  14  and the handlebar post  11  as viewed in the direction along the steering axis C 2  and the steering axis C 3 . Therefore, the front wheel  9  can be turned at the same angle as the steering angle of the handlebars  8 . In addition, the left and right link members  15  linearly interlock the steering operation of the handlebars  8  with the steering operation of the turning member  13 . 
     Referring also to  FIG. 2 ,  FIG. 3 , and  FIG. 9 , the front end portion of the rocking arm  16  is rockably supported by the head pipe  12 , and the rear end portion of the rocking arm  16  is rockably supported by the front block  2 . The rocking arm  16  has a pair of upper and lower arm portions  17  and  18 . The upper and lower arm portions  17  and  18  are arranged in juxtaposition to each other in the upward-downward direction of the vehicle, and extend along the forward-rearward direction of the vehicle. 
     The front and rear end portions  17   a  and  17   b  of the upper arm portion  17  of the rocking arm  16  are respectively arranged in front of the front and rear end portions  18   a  and  18   b  of the lower arm portion  18  of the rocking arm  16 . The front end portions  17   a  of the upper arm portion  17  of the rocking arm  16  are supported in front of the steering axis C 3 , and the front end portions  18   a  of the lower arm portion  18  of the rocking arm  16  are supported in the rear of the steering axis C 3 . The front end portions  17   a  of the upper arm portion  17  of the rocking arm  16  are disposed below an upper end of the head pipe  12 , and the front end portions  18   a  of the lower arm portion  18  are disposed in the vicinity of a lower end of the head pipe  12 . 
     Referring also to  FIG. 6 , the front end portions  17   a  of the upper arm portion  17  are rockably supported via a bolt  34   a  as a coupling member that penetrates the connecting portion  12   a  of the head pipe  12  and which extends along the vehicle width direction. The rear end portions  17   b  of the upper arm portion  17  are rockably supported via a bolt  35   a  as a coupling member that penetrates the connecting portions  2   b  of the front block  2  and which extends along the vehicle width direction. 
     The upper arm portion  17  integrally includes a pair of left and right arm main bodies  17   c  extending longitudinally and a cross member  17   d  coupling the rear end portions  17   b  of the left and right arm main bodies  17   c  to each other. The elements of the upper arm portion  17  are each an integral part made of aluminum, for example. These elements are joined by welding to be integral with each other. 
     The left and right arm main bodies  17   c  are arranged on both of the left and right sides of an upper portion of the head pipe  12 . The left and right arm main bodies  17   c  are curved to the inside in the vehicle width direction in such a manner as to be along an outer wall surface of the upper portion of the head pipe  12 . 
     The cross member  17   d  extends in the vehicle width direction in the rear of the upper portion of the head pipe  12 . Both of end portions of the cross member  17   d  are joined to the rear end portions  17   b  of the left and right arm main bodies  17   c.    
     An insertion hole  34   h  opening in the vehicle width direction is formed in the front end portions  17   a  of the left and right arm main bodies  17   c . In a state of the connecting portion  12   a  of the head pipe  12  being held between the front end portions  17   a  of the left and right arm main bodies  17   c , the bolt  34   a  is passed through the insertion holes  34   h  and an inner circumference of the connecting portion  12   a , and is screwed and fastened to a nut  34   b . An outer circumference of the bolt  34   a  is provided with a pair of left and right side collars  34   j  for supporting a pair of left and right needle bearings  34   m , a center collar  34   i  for securing a distance between the left and right side collars  34   j , and a ball bearing  34   g  receiving a thrust via the right side collar  34   j  and the center collar  34   i . The front end portions  17   a  of the upper arm portion  17  are rockably supported by the connecting portion  12   a  via the left and right side collars  34   j , the center collar  34   i , and the ball bearing  34   g.    
     Incidentally, a symbol C 9  in the figures denotes the central axis of the bolt  34   a . The central axis C 9  may hereinafter be referred to as a first coupling axis. The first coupling axis C 9  is disposed between the upper end and the lower end of the head pipe  12  as viewed from the side. 
     An insertion hole  35   h  opening in the vehicle width direction is formed in the left and right connecting portions  2   b  of the front block  2 . An adjusting collar  35   k  for adjusting a lateral gap is provided in the left connecting portion  2   b  of the front block  2 . In a state of the rear end portions  17   b  of the upper arm portion  17  (the rear end portions  17   b  of the left and right arm main bodies  17   c  and the cross member  17   d ) being held between the left and right connecting portions  2   b  of the front block  2 , the bolt  35   a  is passed through the insertion holes  35   h  and inner circumferences of the rear end portions  17   b  of the upper arm portion  17 , and is screwed and fastened to a nut  35   b . An outer circumference of the bolt  35   a  is provided with a pair of left and right side collars  35   j  for supporting a pair of left and right needle bearings  35   m , a center collar  35   i  for securing a distance between the left and right side collars  35   j , and a ball bearing  35   g  receiving a thrust via the right side collar  35   j  and the center collar  35   i . The rear end portions  17   b  of the upper arm portion  17  are rockably supported by the left and right connecting portions  2   b  via the left and right side collars  35   j , the center collar  35   i , and the ball bearing  35   g.    
     Incidentally, a symbol C 10  in the figures denotes the central axis of the bolt  35   a . The central axis C 10  may hereinafter be referred to as a second coupling axis. 
     Referring also to  FIG. 7 , the front end portions  18   a  of the lower arm portion  18  are rockably supported via a bolt  36   a  as a coupling member that penetrates the connecting portion  12   b  of the head pipe  12  and which extends along the vehicle width direction. The rear end portions  18   b  of the lower arm portion  18  are rockably supported via a bolt  37   a  as a coupling member that penetrates the connecting portions  2   c  of the front block  2  and which extends along the vehicle width direction. Connecting portions  18   e  to which a front lower end portion  20   a  of the cushion unit  20  is connected are formed in a front lower portion of the lower arm portion  18 . 
     The lower arm portion  18  integrally includes a pair of left and right arm main bodies  18   c  extending longitudinally and a cross member  18   d  coupling the rear end portions  18   b  of the left and right arm main bodies  18   c  to each other. The elements of the lower arm portion  18  are each an integral part made of aluminum, for example. These elements are joined by welding to be integral with each other. The longitudinal length of the lower arm portion  18  is larger than the longitudinal length of the upper arm portion  17 . Referring to  FIG. 2 , as viewed from the side, a length W 2  of a second segment connecting a third coupling axis C 11  to a fourth coupling axis C 12  is larger than a length W 1  of a first segment connecting the first coupling axis C 9  to the second coupling axis C 10  (W 2 &gt;W 1 ). 
     The left and right arm main bodies  18   c  are arranged on both of the left and right sides of a lower portion of the cushion unit  20 . The left and right arm main bodies  18   c  are curved to the inside in the vehicle width direction in such a manner as to be along an outer circumferential surface of the lower portion of the cushion unit  20  (spring  20   f  to be described later). Spaces  18   s  curved to the inside in the vehicle width direction are formed within the left and right arm main bodies  18   c.    
     The cross member  18   d  extends in the vehicle width direction in the rear of the lower portion of the cushion unit  20 . Both of end portions of the cross member  18   d  are joined to the rear end portions  18   b  of the left and right arm main bodies  18   c.    
     An insertion hole  36   h  opening in the vehicle width direction is formed in the front end portions  18   a  of the left and right arm main bodies  18   c . In a state of the connecting portion  12   b  of the head pipe  12  being held between the front end portions  18   a  of the left and right arm main bodies  18   c , a bolt  36   a  is passed through the insertion holes  36   h  and an inner circumference of the connecting portion  12   b , and is screwed and fastened to a nut  36   b . An outer circumference of the bolt  36   a  is provided with a pair of left and right side collars  36   j  for supporting a pair of left and right needle bearings  36   m , a center collar  36   i  for securing a distance between the left and right side collars  36   j , and a ball bearing  36   g  receiving a thrust via the right side collar  36   j  and the center collar  36   i . The front end portions  18   a  of the lower arm portion  18  are rockably supported by the connecting portion  12   b  via the left and right side collars  36   j , the center collar  36   i , and the ball bearing  36   g.    
     Incidentally, a symbol C 11  in the figures denotes the central axis of the bolt  36   a . The central axis C 11  may hereinafter be referred to as a third coupling axis. The third coupling axis C 11  is disposed between the upper end and the lower end of the head pipe  12  as viewed from the side. 
     An insertion hole  37   h  opening in the vehicle width direction is formed in the left and right connecting portions  2   c  of the front block  2 . An adjusting collar  37   k  for adjusting a lateral gap is provided to the left connecting portion  2   c  of the front block  2 . In a state of the rear end portions  18   b  of the lower arm portion  18  (the rear end portions  18   b  of the left and right arm main bodies  18   c  and the cross member  18   d ) being held between the left and right connecting portions  2   c  of the front block  2 , a bolt  37   a  is passed through the insertion holes  37   h  and inner circumferences of the rear end portions  18   b  of the lower arm portion  18 , and is screwed and fastened to a nut  37   b . An outer circumference of the bolt  37   a  is provided with a pair of left and right side collars  37   j  for supporting a pair of left and right needle bearings  37   m , a center collar  37   i  for securing a distance between the left and right side collars  37   j , and a ball bearing  37   g  receiving a thrust via the right side collar  37   j  and the center collar  37   i . The rear end portions  18   b  of the lower arm portion  18  are rockably supported by the left and right connecting portions  2   c  via the left and right side collars  37   j , the center collar  37   i , and the ball bearing  37   g.    
     Incidentally, a symbol C 12  in the figures denotes the central axis of the bolt  37   a . The central axis C 12  may hereinafter be referred to as a fourth coupling axis. 
     In addition, as viewed from the side in  FIG. 2 , a bead shape  12   e  is formed between the connecting portion  12   a  and the connecting portion  12   b  of the head pipe  12 . The bead shape  12   e  is formed along a segment connecting the first coupling axis C 9  to the third coupling axis C 11 . 
     In addition, a symbol AX 1  in the figures denotes a first straight line passing through the first coupling axis C 9  and the second coupling axis C 10  as viewed from the side. A symbol AX 2  in the figures denotes a second straight line passing through the third coupling axis C 11  and the fourth coupling axis C 12  as viewed from the side. 
     In the 1G state in the figures, the first straight line AX 1  of the upper arm portion  17  and the second straight line AX 2  of the lower arm portion  18  are parallel with each other. 
     Referring also to  FIG. 2 ,  FIG. 6 ,  FIG. 7 , and  FIG. 9 , the front lower end portion  20   a  of the cushion unit  20  is rockably connected to the lower arm portion  18 , and the rear upper end portion  20   b  of the cushion unit  20  is rockably connected to the supporting portion  2   a . The cushion unit  20  provides a cushioning action by making the front lower end portion  20   a  perform a stroke as the lower arm portion  18  rocks. 
     The cushion unit  20  includes a damper  20   e  and a spring  20   f.    
     The damper  20   e  is a rod type damper inclined such that an upper side of the damper is located more rearward than a lower side of the damper as viewed from the side. 
     The spring  20   f  is a coil spring wound around the damper  20   e.    
     The cushion unit  20  expands and contracts by performing a stroke along the central axis C 15  of the cushion unit  20 , and thereby provides a predetermined cushioning action. The central axis C 15  may hereinafter be referred to as a stroke axis. 
     Referring also to  FIG. 2  and  FIG. 9 , the front lower end portion  20   a  of the cushion unit  20  is supported in front of a middle point Pm of the segment connecting the third coupling axis C 11  to the fourth coupling axis C 12  as viewed from the side, and the rear upper end portion  20   b  of the cushion unit  20  is supported in the rear of the second coupling axis C 10  as viewed from the side. 
     The front lower end portion  20   a  of the cushion unit  20  is located in front of the longitudinal middle position of the lower arm portion  18 . The front lower end portion  20   a  of the cushion unit  20  is located in front of the middle point Pm of the segment connecting the third coupling axis C 11  to the fourth coupling axis C 12  as viewed from the side, and is located below the segment. 
     The rear upper end portion  20   b  of the cushion unit  20  is located in the vicinity of a lower end of the shaft portion  11   a  of the handlebar post  11  forming the steering axis C 2 , and in the rear of and below the steering axis C 2  as viewed from the side. The rear upper end portion  20   b  of the cushion unit  20  is located in the rear of the rear end portions  17   b  of the upper arm portion  17 . 
     The rear upper end portion  20   b  of the cushion unit  20  is disposed in the rear of the fourth coupling axis C 12  as viewed from the side. Specifically, the rear upper end portion  20   b  of the cushion unit  20  is located above and in the rear of the rear end portions  18   b  of the lower arm portion  18 . 
     Referring to  FIG. 7 , an insertion hole  39   h  opening in the vehicle width direction is formed in the left and right connecting portions  18   e  of the lower arm portion  18 . In a state of the front lower end portion  20   a  of the cushion unit being held between the left and right connecting portions  18   e  of the lower arm portion  18 , a bolt  39   a  is inserted through the insertion holes  39   h  and an inner circumference of the front lower end portion  20   a  of the cushion unit, and a nut  39   b  is screwed and fastened to the projecting portion of the bolt  39   a . An outer circumference of the bolt  39   a  is provided with a collar  39   j  for supporting a needle bearing  39   m . The front lower end portion  20   a  of the cushion unit  20  is rockably supported by the left and right connecting portions  18   e  via the collar  39   j.    
     Incidentally, a symbol C 13  in the figures denotes the central axis of the bolt  39   a.    
     Referring to  FIG. 6 , an insertion hole  38   h  opening in the vehicle width direction is formed in the left and right connecting portions  2   e  of the supporting portion  2   a . In a state of the rear upper end portion  20   b  of the cushion unit being held between the left and right connecting portions  2   e  of the supporting portion  2   a , a bolt  38   a  is inserted through the insertion holes  38   h  and an inner circumference of the rear upper end portion  20   b  of the cushion unit, and a nut  38   b  is screwed and fastened to the projecting portion of the bolt  38   a . An outer circumference of the bolt  38   a  is provided with a collar  38   j  for supporting a needle bearing  38   m . The rear upper end portion  20   b  of the cushion unit  20  is rockably supported by the left and right connecting portions  2   e  via the collar  38   j.    
     Incidentally, a symbol C 14  in the figures denotes the central axis of the bolt  38   a.    
       FIG. 1  and  FIG. 9  show the 1G state in which the load of the vehicle weight is applied to the front wheel suspension device  10 . 
     When front wheel braking or the like displaces the front wheel  9  relatively upward from this state, the rocking arm  16  rocks upward, and thus the front fork  19  and the head pipe  12  are displaced upward. At this time, the lower arm portion  18  rotates backward in a right-handed direction (clockwise direction) about the fourth coupling axis C 12 . Then, the lower arm portion  18  displaces the front lower end portion  20   a  of the cushion unit  20  upward, and thus compresses the cushion unit  20 . 
     When the head pipe  12  is displaced upward, the turning member  13  is also integrally displaced in accordance with the displacement of the head pipe  12 . At this time, the rotary member  14  is displaced with respect to the handlebar post  11 , and the angle of the steering axis C 3  to the steering axis C 2  is changed. However, this change is accommodated by the rocking of the left and right first ball joints  40  and the left and right second ball joints  43  and the rotation of the rotary member  14 . 
     On the other hand, when acceleration or the like displaces the front wheel  9  relatively downward from the 1G state, the rocking arm  16  rocks downward, and thus the front fork  19  and the head pipe  12  are displaced downward. At this time, the lower arm portion  18  rotates forward in a left-handed direction (counterclockwise direction) about the fourth coupling axis C 12 . Then, the lower arm portion  18  displaces the front lower end portion  20   a  of the cushion unit  20  downward, and thus extends the cushion unit  20 . 
     When the head pipe  12  is displaced downward, the turning member  13  is also integrally displaced in accordance with the displacement of the head pipe  12 . At this time, the rotary member  14  is displaced with respect to the handlebar post  11 , and the angle of the steering axis C 3  to the steering axis C 2  is changed. However, this change is accommodated by the rocking of the left and right first ball joints  40  and the left and right second ball joints  43  and the rotation of the rotary member  14 . 
     As described above, the foregoing embodiment is a front suspension structure for a saddle riding type vehicle, the front suspension structure including: a head pipe  12  radially internally supporting a shaft portion  13   b  forming a steering axis C 3  such that the shaft portion  13   b  is rotatable about the steering axis C 3 ; a front fork  19  connected to a lower end portion of the shaft portion  13   b  on a lower side of the head pipe  12 , the front fork  19  supporting an axle  9   a  of a steering wheel  9 ; a link  15  having one end portion connected rotatably on an upper side of a turning member  13  having the shaft portion  13   b , and having another end portion connected rotatably on a side of handlebars  8 ; the head pipe  12  being disposed so as to be separated frontward from a vehicle body frame  1 ; a rocking arm  16  having a front end portion rockably supported by the head pipe  12 , and having a rear end portion rockably supported by the vehicle body frame  1 . 
     According to this constitution, the front end portion of the rocking arm  16  is supported by the head pipe  12  on the outside in the radial direction of the shaft portion  13   b  forming the steering axis C 3 . Thus, the position at which the rocking arm  16  is supported can be set arbitrarily. Hence, a degree of freedom of the position at which the arm portion is supported can be increased. In addition, because a turning system of the turning member  13  and the like and a rocking system of the rocking arm  16  and the like are separated from each other, the turning system is not readily affected by rocking. 
     In addition, in the foregoing embodiment, the rocking arm  16  includes an upper arm portion  17  and a lower arm portion  18  vertically separated from each other, the head pipe  12  is inclined such that an upper side of the head pipe  12  is located more rearward than a lower side of the head pipe  12  as viewed from a side, a front end portion  17   a  of the upper arm portion  17  is in front of the steering axis C 3  and is supported by a front upper portion of the head pipe  12 , and a front end portion  18   a  of the lower arm portion  18  is in a rear of the steering axis C 3  and is supported by a rear lower portion of the head pipe  12 . Thus, spaces of the front upper portion and the rear lower portion of the head pipe  12  which spaces are created by the inclination of the head pipe  12  can be utilized effectively as spaces for supporting the respective front end portions  17   a  and  18   a  of the upper and lower arm portions  17  and  18 . It is therefore possible to make the front suspension structure compact and thus shorten an overall length of the front suspension structure. In addition, because the respective front end portions  17   a  and  18   a  of the upper and lower arm portions  17  and  18  are distributed longitudinally, the concentration of force on one part can be prevented. 
     In addition, in the foregoing embodiment, the front end portion  17   a  of the upper arm portion  17  and the front end portion  18   a  of the lower arm portion  18  are rockably supported via coupling members  34   a  and  36   a , respectively, the coupling members  34   a  and  36   a  penetrating connecting portions  12   a  and  12   b  of the head pipe  12  and extending along a vehicle width direction. Thus, the upper and lower arm portions  17  and  18  can be supported by the respective coupling members so as to avoid the head pipe  12 . Therefore the respective front end portions  17   a  and  18   a  of the upper and lower arm portions  17  and  18  can be supported with high rigidity. 
     In addition, in the foregoing embodiment, the front end portion  17   a  of the upper arm portion  17  and the front end portion  18   a  of the lower arm portion  18  are connected respectively to connecting portions  12   a  and  12   b  of the head pipe  12  rockably about coupling axes C 9  and C 11  along the vehicle width direction, and at least one of the coupling axes C 9  and C 11  is disposed between an upper end and a lower end of the head pipe  12  as viewed from the side. Thus, the respective front end portions  17   a  and  18   a  of the upper and lower arm portions  17  and  18  can be supported on the head pipe  12  compactly. 
     It is to be noted that the foregoing embodiment has been described by citing an example in which the first straight line AX 1  of the upper arm portion  17  and the second straight line AX 2  of the lower arm portion  18  are parallel with each other in the 1G state. However, the present invention is not limited to this. 
     For example, rearward extension parts of the first straight line AX 1  of the upper arm portion  17  and the second straight line AX 2  of the lower arm portion  18  may intersect each other such that the first straight line AX 1  of the upper arm portion  17  and the second straight line AX 2  of the lower arm portion  18  are separated from each other more toward the front in the 1G state. For such an intersection arrangement, for example, it is preferable to shift the vertical position of the second coupling axis C 10  downward or shift the vertical position of the fourth coupling axis C 12  upward as viewed from the side. 
     In addition, frontward extension parts of the first straight line AX 1  of the upper arm portion  17  and the second straight line AX 2  of the lower arm portion  18  may intersect each other such that the first straight line AX 1  of the upper arm portion  17  and the second straight line AX 2  of the lower arm portion  18  are separated from each other more toward the rear in the 1G state. For such an intersection arrangement, for example, it is preferable to shift the vertical position of the second coupling axis C 10  upward or shift the vertical position of the fourth coupling axis C 12  downward as viewed from the side. 
     In addition, the foregoing embodiment has been described by citing an example in which the steering axis C 3  is separated frontward from the steering axis C 2  and the steering axis C 3  and the steering axis C 2  are parallel with each other in the 1G state. However, the present invention is not limited to this. For example, the steering axis C 3  may be separated frontward from the steering axis C 2 , and the steering axis C 3  and the steering axis C 2  may intersect each other. That is, it suffices for the steering axis C 3  to be separated frontward from the steering axis C 2 . 
     In addition, the foregoing embodiment has been described by citing an example in which the first axis C 5  is a straight line extending in the upward-downward direction of the vehicle and the second axis C 6  is a straight line that is parallel with the first axis C 5  and which extends in the upward-downward direction of the vehicle. However, the present invention is not limited to this. For example, the first axis C 5  may be a straight line along a direction intersecting the vehicle width direction, and the second rocking straight line C 6  may be a straight line that is along a direction intersecting the vehicle width direction and which is different from the first axis C 5 . 
     In addition, the foregoing embodiment has been described by citing an example in which each of the first coupling axis C 9  and the third coupling axis C 11  is disposed between the upper end and the lower end of the head pipe  12  as viewed from the side. However, the present invention is not limited to this. For example, only the first coupling axis C 9  may be disposed between the upper end and the lower end of the head pipe  12  as viewed from the side, or only the third coupling axis C 11  may be disposed between the upper end and the lower end of the head pipe  12  as viewed from the side. That is, it suffices for at least one of the first coupling axis C 9  and the third coupling axis C 11  to be disposed between the upper end and the lower end of the head pipe  12  as viewed from the side. 
     It is to be noted that the present invention is not limited to the foregoing embodiment. For example, the saddle riding type vehicle described above includes vehicles in general that drivers ride astride vehicle bodies thereof. The saddle riding type vehicle described above includes not only motorcycles (including motor-assisted bicycles and motor scooter type vehicles) but also three-wheeled vehicles (including vehicles having two front wheels and one rear wheel as well as vehicles having one front wheel and two rear wheels). 
     In addition, the present invention may be applied to vehicles having a longitudinally mounted engine other than a horizontally opposed engine and vehicles having a laterally mounted engine with a crankshaft along the vehicle width direction. The present invention may also be applied to constitutions in which a cushion unit or a cushion arm is supported by an engine as a vehicle body. 
     The constitution in the foregoing embodiment is an example of the present invention, and is susceptible of various changes without departing from the spirit of the present invention by replacing a constituent element in the embodiment with a well-known constituent element, for example.