Patent Publication Number: US-2007095624-A1

Title: Saddle-type vehicle and steering damper for use in the same

Description:
RELATED APPLICATIONS  
      This application claims the benefit of priority under 35 USC 119 of Japanese patent application no. 2005-302288, filed on Oct. 17, 2005, which application is hereby incorporated by reference in its entirety.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a saddle-type vehicle such as a motorcycle and a steering damper for use in the same.  
      2. Description of Related Art  
      Riders of motorcycles sometimes feel uncomfortable or cannot steer smoothly during driving when vibrations from a road or the like are applied to the steering. Accordingly, to reduce vibrations, some motorcycles are equipped with a steering damper for improving steering operability, for example, between the body frame and the under bracket.  
      However, with this conventional technique, when the steering angle is large, an end of a piston rod projects greatly from a piston cylinder. To prevent interference between the great projection of the piston rod and components of the vehicle body, such as a cowling for covering the vehicle body, a large space is needed around the steering damper. This makes it difficult to design the layout of the vehicle components disposed around the steering damper.  
      To solve this problem, a motorcycle is proposed in which interference between the projection of the piston rod and the vehicle components is prevented by a curved structure of the steering damper (refer to JP-UM-A-1-175494).  
      However, since the motorcycle disclosed in JP-UM-A-1-175494 is constructed with a steering damper curved in an arc shape, the steering damper must be curved by pressing or the like at manufacture. This leads to the problems of increased man-hours and high manufacturing costs.  
     SUMMARY OF THE INVENTION  
      The present invention is made in light of such circumstances and provides a saddle-type vehicle and steering damper in which the layout of the components of the vehicle around the steering damper are easily designed and the steering damper is manufactured at reduced man-hours and cost.  
      A saddle-type vehicle according to the invention includes a body frame, an under bracket mounted to a steering shaft supported by the body frame and a steering damper that causes attenuation during steering. The steering damper includes a piston cylinder mounted to the body frame, a piston slidably disposed in the piston cylinder and causing attenuation during sliding in the piston cylinder, a first piston rod projecting from one end face of the piston to the outside of the piston cylinder, the projecting end being fixed to an longitudinal end of the under bracket of the body, and a second piston rod projecting from the other end face of the piston to the outside of the piston cylinder, the projecting end being fixed to the other longitudinal end of the under bracket of the body. The projection of the first piston rod and the projection of the second piston rod are in a line.  
      This arrangement prevents change of the positional relationship between the steering damper and the under bracket even when the steering is turned, which enables the steering load to be directed on a tangential line of the steering circle when the steering is turned. Therefore, the steering load is not changed according to the steering angle, allowing stable steering operation.  
      When the steering is turned in one direction, the first piston rod extends from the piston cylinder, and the second piston rod contracts into the piston cylinder by the amount of the extension of the first piston rod. On the other hand, when the steering is turned in the other direction, the second piston rod extends from the piston cylinder, and the first piston rod contracts into the piston cylinder by the amount of the extension of the second piston rod.  
      Accordingly, the entire length of the steering damper including the piston cylinder and the first and second piston rods is held at a fixed length whichever direction the steering is turned, thus preventing the piston rod from projecting greatly from the under bracket, unlike the conventional art. Thus interference between the first and second piston rods and vehicle components around the steering damper is prevented.  
      The piston cylinder and the first and second piston rods of the steering damper extend in a straight line between the first and second brackets. This arrangement eliminates the need for pressing the steering damper as in the conventional art.  
      According to an embodiment of the invention, the steering shaft is mounted to substantially the center of the under bracket, a pair of front forks are mounted to both ends of the under bracket with the steering shaft therebetween and the first and second piston rods are mounted to the under bracket at the same vehicle width as the pair of front forks. With this arrangement, even if the steering angle is at the maximum, interference between the steering damper and vehicle components around the steering damper is prevented.  
      According to an embodiment of the invention, the steering damper is disposed on the back of the under bracket. With this arrangement, the steering damper is disposed in the space on the back of the under bracket and facilitates the layout design of the steering damper.  
      According to an embodiment of the invention, the steering damper is disposed in parallel with the length of the under bracket. With this arrangement, the steering damper is disposed compactly in the space around the under bracket, further facilitating the layout design of the steering damper. Moreover, the right and left steering loads are balanced when the steering is turned.  
      The arrangement of a saddle-type vehicle and steering damper according to the invention prevents ends of the piston rod from projecting greatly from the under bracket, in contrast to conventional steering dampers, and facilitates the layout design of various vehicle components around the steering damper. Moreover, the need for pressing the steering damper is eliminated and thereby reduces man-hours and manufacturing costs of the steering damper.  
      Other features and advantages of the invention will be apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, various features of embodiments of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a side view of a motorcycle according to an embodiment of the invention.  
       FIG. 2  is an enlarged diagram of a front pipe, a head pipe and a steering damper of the motorcycle of  FIG. 1 .  
       FIG. 3  is a plan view of an under bracket and the steering damper, as viewed in the direction of arrow III-III in  FIG. 2 .  
       FIG. 4  is the plan view of  FIG. 3 , with the steering turned. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      The present invention is described in detail below according to an embodiment applied to a motorcycle with reference to  FIG. 1-4 . A motorcycle  1  includes right and left main pipes  10  (only one is shown), an engine  20 , and a steering damper  100 .  
      Main pipes  10  serve as the frame of the vehicle. Main pipes  10  each include an intermediate pipe  11  extending substantially horizontally in a front-back direction above engine  20 , a front pipe  12  welded at an upper end to a front end  11 A of intermediate pipe  11  and extending from front end  11 A downward in front of engine  20 , and a rear pipe  13  welded at an upper end to a rear end  11 C of intermediate pipe  11  and extending from the rear end downward on the back of engine  20 . A damper mounting frame  12 A projects from the front end lower part of front pipe  12 , to which steering damper  100  is mounted through a link  105 , to be described later. Front end  11 A of intermediate pipe  11  is located toward the front of engine brackets  13 A and  13 B of rear pipe  13 .  
      An engine bracket  10 A projects from the lower end of front pipe  12 . Engine bracket  10 A fixes a front cylinder  22  of engine  20 . Front pipe  12  is welded to right and left radiator brackets  92  (only one is shown), as indicated by the chain double-dashed lines of  FIGS. 3 and 4 , to which an upper radiator  90  is mounted. An engine bracket  11 B is disposed in the middle of the length of intermediate pipe  11 . Engine bracket  11 B extends from intermediate pipe  11  downward and between front cylinder  22  and rear cylinder  23  of engine  20 . The lower end of engine bracket  11 B is forked. Front cylinder  22  and rear cylinder  23  are fixed to the lower end of engine bracket  11 B.  
      Rear pipe  13  at the rear of main pipe  10 , as shown in  FIGS. 1 and 2 , extends downward from rear end  11 C of intermediate pipe  11  toward the back of a pivot shaft  41 , in the form of an arc. Rear pipe  13  includes upper engine bracket  13 A and lower engine bracket  13 B projecting from the lower end apart from each other. Upper engine bracket  13 A and lower engine bracket  13 B are fitted with an upper case  21 A and a lower case  21 B of engine  20 , respectively. Rear pipe  13  overlaps with front part  30 A of fuel tank  30  at the rear of engine  20  in side view. The upper part  13 C of rear pipe  13  is narrow in side view, while the lower part is wide in side view.  
      The lower part  13 D of rear pipe  13  is pivotally connected to the front end of a swing arm  40  with pivot shaft  41 . The rear end of swing arm  40  is rotatably connected to the steering shaft of a rear wheel  60 .  
      Main pipe  10  is bolted to a seat rail  24  extending rearward from upper part  13 C of rear pipe  13 . Lower part  13 D of rear pipe  13  is bolted to a backstay  25  extending obliquely to the upper rear in a curve. The upper end of backstay  25  is bolted to the middle of seat rail  24 . A shock absorber  26  is provided between the upper end of backstay  25  and the rear end of swing arm  40 .  
      A head pipe  14  is welded to the front end of intermediate pipe  11  of main pipe  10 . Head pipe  14  is rotatably fitted on a steering shaft  15  disposed to a handle  2 . Steering shaft  15  is fitted at the lower end with an under bracket  16 . Steering shaft  15  is supported in head pipe  14  constituting part of the frame. Head pipe  14  is fitted at the lower end with the under bracket  16 .  
      Referring to  FIG. 3 , under bracket  16  comprises a substantially oblong plate extending in a lateral direction. Under bracket  16  has a steering-shaft insertion hole  16 A in the middle in a longitudinal direction (substantially in the center). The lower end of steering shaft  15  is inserted and fixed in steering-shaft insertion hole  16 A. Under bracket  16  has front-fork insertion holes  16 B and  16 B at opposite ends in the longitudinal direction. The upper ends of right and left front forks  17  are inserted and fixed in front-fork insertion holes  16 B and  16 B. In other words, front forks  17  are mounted to opposite ends of under bracket  16  with steering shaft  15  therebetween. The lower ends of front forks  17  are rotatably connected to a front wheel  50 . Under bracket  16  has left support plates  16 C and  16 D and right support plates  16 C and  16 D projecting from both sides. Left support plates  16 C and  16 D hold a first bracket  18 , and right support plates  16 C and  16 D hold a second bracket  19 .  
      Steering damper  100  includes a piston cylinder  101 , a piston  102 , a first piston rod  103 , a second piston rod  104 , and a link  105 . As shown in  FIG. 3 , steering damper  100  is located on the back of under bracket  16  and substantially in parallel with the length of under bracket  16 .  
      Piston cylinder  101  extends axially in a straight line and is filled with liquid oil. Piston  102  is shaped like a disk and is slidably disposed in piston cylinder  101 . Piston  102  has an orifice (not shown), through which liquid oil circulates when piston  102  slides axially in piston cylinder  101 , thereby causing attenuation. Referring to  FIG. 3 , the left end face of piston  102  is indicated by numeral  102 A, and the right end face is indicated by numeral  102 B.  
      First piston rod  103  is in the form of a column extending axially in a straight line, whose trailing end is secured to end face  102 A of piston  102 . The leading end of first piston rod  103  extends axially in piston cylinder  101  to project to the outside of piston cylinder  101 , to which a damper mounting portion  103 A is fixed. Damper mounting portion  103 A is bolted to first bracket  18 .  
      Second piston rod  104  is also in the form of a column extending axially in a straight line, whose trailing end is secured to end face  102 B of piston  102 . The leading end of second piston rod  104  extends axially in piston cylinder  101  to project to the outside of piston cylinder  101 , to which a damper mounting portion  104 A is fixed. Damper mounting portion  104 A is bolted to second bracket  19 . The projections of first piston rod  103  and second piston rod  104  are in a line. As shown in  FIG. 3 , first piston rod  103  and second piston rod  104  are mounted to under bracket  16  with first and second brackets  18  and  19 , respectively, at the same vehicle width as the pair of front forks  17 .  
      As shown in  FIG. 3 , link  105  is a substantially oblong plate that is narrow in the middle of the length. A longitudinal end of link  105  is rotatably joined to damper mounting frame  12 A projecting from front pipe  12  with a pin  106 . The other longitudinal end of link  105  is rotatably joined to piston cylinder  101  with a pin  107 .  
      Engine  20  is preferably a V-four-cylinder engine. Engine  20  includes a crankcase  21  divided into upper and lower sections: upper case  21 A and lower case  21 B. Right and left front cylinders  22  (only one is shown) extend obliquely from the upper front of upper case  21 A to the upper front, and right and left rear cylinders  23  located on the back of front cylinder  22  extend obliquely from the top of upper case  21 A to the upper rear. Engine  20  is suspended from main pipes  10  by engine brackets  10 A,  11 B,  13 A, and  13 B.  
      A pump  31  for supplying fuel to engine  20  is disposed at the front of fuel tank  30  and in the vicinity of rear pipe  13 . An air cleaner  70  is disposed on intermediate pipe  11 . A battery  80  is disposed on intermediate pipe  11  between air cleaner  70  and fuel tank  30 . Upper radiator  90  and lower radiator  91  are disposed between engine  20  and front wheel  50 . Upper radiator  90  is fixed to radiator bracket  92  and welded to front pipe  12 , while lower radiator  91  is secured to crankcase  21 .  
      When motorcycle  1  is steered clockwise, e.g., along the arrow in  FIG. 4 , around steering shaft  15 , steering damper  100  is inclined in parallel with under bracket  16  through link  105 , while first piston rod  103  extends from piston cylinder  101 . Second piston rod  104  is contracted into piston cylinder  101  by an amount corresponding to the extension of first piston rod  103 .  
      When motorcycle  1  is steered counterclockwise ((not shown) about steering shaft  15 , steering damper  100  is inclined in parallel with under bracket  16  through link  105 , while second piston rod  104  extends from piston cylinder  101 . First piston rod  103  is contracted into piston cylinder  101  by an amount corresponding to the extension of second piston rod  104 .  
      The embodiment is constructed such that the projection of first piston rod  103  and the projection of second piston rod  104  are in a line. Accordingly, the entire length of steering damper  100  including piston cylinder  101  and first and second piston rods  103  and  104  can be held at a fixed length whichever direction (clockwise and counterclockwise) the steering is turned. This prevents the piston rod from projecting greatly from the under bracket, unlike the conventional art, to thereby prevent interference between first and second piston rods  103  and  104  and the various vehicle components around steering damper  100 , thus facilitating the layout design of the components.  
      The embodiment is constructed such that piston cylinder  101  of steering damper  100  and first and second piston rods  103  and  104  extend in a straight line between first and second brackets  18  and  19 . This eliminates the need for pressing the steering damper  100 , as in the conventional art, thereby reducing man-hours and manufacturing cost of steering damper  100 .  
      Furthermore, first and second piston rods  103  and  104  are mounted to under bracket  16  at the same vehicle width as the pair of front forks  17 . Accordingly, even if steering damper  100  is greatly turned as shown in  FIG. 4 , there is no interference between an end  16 E of under bracket  16  and radiator bracket  92  in the vicinity thereof, thus preventing damage of under bracket  16 .  
      The embodiment is constructed such that rear pipe  13  at the rear of main pipe  10  is curved into an arc shape. This prevents the load of engine  20  from being concentrated locally on the bent portion of the main pipe when rear pipe  13  is joined to crankcase  21 , thus allowing the load to be evenly applied to the entire main pipe  10  to thereby increase the rigidity of the main pipe.  
      Rear pipe  13  is joined to crankcase  21  via the back of pivot shaft  41 . Accordingly, the load of engine  20  transmitted to the rear of main pipe  10  is surely received by rear pipe  13 , in contrast to the conventional art in which the rear pipe extends from the rear end of the front pipe substantially vertically downward in a straight line to be joined to the crankcase. This also increases the rigidity of main pipe  10 , improving the performance and reliability of motorcycle  1 .  
      The invention has been described using motorcycle  1  as an example of a saddle-type vehicle. However, the invention is not limited to that, and may be applied to other saddle-type vehicles such as motor three wheelers and buggies.  
      The particular embodiments of the invention described in this document should be considered illustrative, rather than restrictive. Modification to the described embodiments may be made without departing from the spirit of the invention as defined by the following claims.