Abstract:
A steering damper system for motorcycles provided for generating an adjustable damping force for restraining the shaking of the steering system at the time of disturbance. The system includes a cross member laid between the front portions of the mainframes branching to the left and right from the head pipe and extending to the rear, and a steering damper mounted at the center of the cross member. A sector gear projects forward from the housing, and the teeth thereof are inserted through the opening formed on the head pipe, and are engaged with the drive gear integrally mounted around the steering stem rotatably supported within the head pipe. The resulting steering damper provides the desired adjustable damping force without adversely increasing the inertia of the steering system.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2001-157068, filed on May 25, 2001, the entire contents thereof are hereby incorporated by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a steering damper system for motorcycles provided for generating a damping force to restrain shaking of the steering system at the time of disturbance, and more specifically, to a steering damper system in which a damping force is adjustable.  
           [0004]    2. Description of Background Art  
           [0005]    A steering damper system which generates a damping force to prevent shaking of the steering system caused by kickback, or the like, at the time of disturbance, is known (for example, U.S. Pat. No. 2,593,461). A steering damper system in which a damping force is adjustable so as to generate a precise damping force, and a system in which a damping force is generated only when needed, are also known. For example, there is the system that controls the damping force based on the steering angle and the traveling speed (Japanese Patent Laid-Open No.64888/1988). There is another system that controls the damping force based on the variation of the load exerted on the front wheel (Japanese Patent Publication No.74023/1995).  
           [0006]    The steering damper of the aforementioned related art is relatively heavy. When it is disposed in the steering system, inertia increases at the time when the vehicle is turned by an amount corresponding to the weight of the steering damper added thereto. However, in a steering system, it is desirable to prevent this increase in inertia, and thus provide a steering system that has the same inertia as those without a steering damper. Further, it is desirable to provide an installation structure for the damper that does not impair the appearance of the vehicle body while maintaining enough operating space for the damper needed for the steering operation. Also, since it may be difficult to do maintenance on a steering damper if mounted in a tight space, it is also desirable that the structure for the steering damper be such that maintenance can be done easily.  
         SUMMARY AND OBJECTS OF THE INVENTION  
         [0007]    The object of the present invention is to realize the requirements outlined above. Accordingly, the present invention relates to a steering damper system for vehicles and includes a pair of left and right mainframes branching to the left and right from the head pipe located at the front end and extending rearward along the vehicle body. It includes a steering system for steering a front wheel rotatably supported on the head pipe and a steering damper for providing a damping force to the steering system. The pair of left and right mainframes are connected by a cross member in the vicinity of the head pipe, the steering damper is disposed on the cross member, and the operating section of the steering damper and the steering system are connected by a connecting member.  
           [0008]    According to a second aspect of the steering damper system of the present invention, the cross member is detachably secured on the pair of left and right mainframes.  
           [0009]    According to a third aspect of the steering damper system of the present invention, the cross member is secured on or under the pair of left and right mainframes.  
           [0010]    The steering damper is installed in the vicinity of head pipe by connecting the pair of left and right mainframes by a cross member in the vicinity of the head pipe. A damping force may be generated by the steering damper when the vehicle is turned. The steering damper is disposed on the cross member via the connecting member. Therefore, inertia occurring at the time of steering may be maintained at the same level as in conventional steering systems not having a damper. This is due to the fact that, even though the steering damper is a heavy part, it does not have to be disposed in the steering system. With this invention, a good vehicle appearance is maintained, because the damper is disposed in a space between the left and right mainframes.  
           [0011]    Also, according to the present invention, the cross member and the steering damper may be removed easily and at the same time, because the cross member is detachably secured on the pair of left and right mainframes. Therefore, since maintenance work need not be done in a small space, maintenance of the steering damper is facilitated.  
           [0012]    Further, according to the present invention, the cross member is secured on or under the pair of left and right mainframes. Thus, the steering damper and the cross member may be attached and detached from above or from below the vehicle body, further facilitating maintenance of the steering damper.  
           [0013]    Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:  
         [0015]    [0015]FIG. 1 is a schematic perspective view of the motorcycle to which the present invention is applied;  
         [0016]    [0016]FIG. 2 is a partially exploded side view of the front portion of the vehicle body according to the present invention;  
         [0017]    [0017]FIG. 3 is a plan view of the same part;  
         [0018]    [0018]FIG. 4 is a drawing showing a schematic structure of the steering damper; and  
         [0019]    [0019]FIG. 5 is a drawing of the second embodiment corresponding to FIG. 2; 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]    Referring now to the drawings, the first embodiment will be described. FIG. 1 is a schematic perspective view of the motorcycle to which the present invention is applied; FIG. 2 is a partially exploded side view of the front portion of the vehicle body; FIG. 3 is a plan view of the same part; and FIG. 4 is a drawing showing a schematic structure of the steering damper.  
         [0021]    In FIG. 1, the upper portion of a front fork  2  supporting a front wheel  1  at the lower end thereof is connected to the front portion of a vehicle body frame  3 , and is rotatable by a handle  4 . A fuel tank  5  is supported on the vehicle body frame  3 . Shown also are a seat  6 , rear cowl  7 , a rear swing arm  8 , and a rear wheel  9 .  
         [0022]    The steering damper will be described below. As shown in FIGS. 2 and 3, the steering damper  10  is disposed at the central portion of a cross member  12  laid between the front portions of the mainframes  3 ,  3 . Mainframes  3 ,  3  branch to the left and right in the vicinity of the upper bracket  11  on which the handle (not shown) is mounted.  
         [0023]    In this embodiment, a housing  10   a  for accommodating the operating portion of the steering damper  10  and the cross member  12  are integrally formed of cast metal, or the like. The cross member  12  is formed into a plate shape laterally extending from the housing  10   a , and the respective ends of the extended portion are secured to the stepped recesses  13  formed on the upper portion of the mainframe  3  with bolts  14  from above the vehicle body. The cross member  12  also serves as a reinforcing member at the front portion of the mainframe  3 .  
         [0024]    At the front portion of the steering damper  10 , a sector gear  15  projects from the housing  10   a  forwardly of the vehicle body, and engages with the drive gear  16 . The drive gear  16  is integrally mounted around the upper portion of a steering stem  17 . Steering stem  17  passes through the head pipe  18  in the vertical direction, and is rotatably supported by the bearings  19 ,  20  at the top and bottom of the head pipe  18 .  
         [0025]    The upper and lower ends of the steering stem  17  is secured to the upper bracket  11  and the lower bracket  21  located at the upper and lower ends of the head pipe  18 . The lower bracket  21  is placed substantially in parallel with the upper bracket  11 , and supports the front fork  2  together with the upper bracket  11 .  
         [0026]    Therefore, the handle  4 , the upper bracket  11 , the steering stem  17 , the lower bracket  21 , and the front fork  2  constitute a steering system. When the handle  4  is turned, the upper bracket  11 , the steering stem  17 , the lower bracket  21  and the front fork  2  turn integrally to steer the front wheel  1 . During the turning operation, the drive gear  16  also turns integrally with the steering stem  17 .  
         [0027]    The head pipe  18  is a tubular member connecting the front end portions of the left and right mainframes  3 ,  3  with each other to constitute the front end portion of the vehicle body frame. The head pipe is formed with an opening  22  at the location corresponding to the drive gear  16 , through which the teeth of the sector gear  15  inserted into the head pipe  18  engage the drive gear  16 .  
         [0028]    [0028]FIG. 4 illustrates a structure of the steering damper  10  schematically, showing that a fan-shaped liquid chamber  30  fanning out toward the front is provided within the steering damper  10 . Also shown is a shaft  31 , rotatably provided at the position corresponding to the linchpin of the fan. The portion of the sector gear  15  located within the housing  10   a  corresponding to the linchpin of the fan is connected to the shaft  31 , so that the sector gear  15  and the shaft  31  rotate as a single unit. The shaft  31  is also provided integrally with a wing-shaped portion  32  extending forward for dividing the liquid chamber  30 . The liquid chamber  30  is thus divided into two chambers, the right liquid chamber  33  and the left liquid chamber  34 .  
         [0029]    The tip of the wing-shaped portion  32  is formed with a sliding surface, and is brought into sliding contact with the inner surface of the arc-shaped wall  35  of the liquid chamber  30 . The right liquid chamber  33  and the left liquid chamber  34  are filled with uncompressible liquid such as oil, or the like, and are connected by a bypass channel  36 . An adjustable valve  37  is provided at the central portion of the bypass channel  36 . The adjustable valve  37  comprises a throttling passage for generating a damping force, and throttle may be varied by changing the sectional area of the throttling passage. However, the adjustable valve  37  employed here is not limited to the type described above. Alternatively, various other known adjustable valves may be employed.  
         [0030]    By constructing the steering damper system comprising the steering damper  10  in the manner described above, when the steering stem  17  is turned, the drive gear  16  turns the sector gear  15  and the integrally connected shaft  31 . As a consequence, the wing-shaped portion  32 , which is integrally connected to shaft  31 , is turned in the liquid chamber  30 . The winged-shaped portion  32  moves (as shown in phantom) to vary the volume balance between the right liquid chamber  33  and the left liquid chamber  34 . Liquid moves the by-pass channel  36  in accordance with variations in volume balance.  
         [0031]    Accordingly, when the prescribed conditions are met, such as may be caused by a disturbance or the like, the adjustable valve  37  is throttled. The movement of liquid in the by-pass channel  36  generates a damping force and restrains turning of the shaft  31 , and further restrains turning of steering stem  17  via the sector gear  15  and the drive gear  16 , thereby controlling the turning operation of the vehicle against adverse disturbances. Under normal conditions, the adjustable valve  37  is not throttled, thus enabling free movement of liquid in the by-pass channel  36  and smooth turning.  
         [0032]    Throttling of the adjustable valve  37  is controlled by a controlling system  38 . The controlling system  38  is constructed of a microcomputer, or the like. In this embodiment, it controls throttling of the adjustable valve  37  based on the detected signals of the angular speed sensor  39  and a moment sensor  40 . In other words, the value of the angular speed and the rotated direction of the steering stem  17  are obtained by the angular speed detected by the angular speed sensor  39 , and the direction of rotating torque applied on the steering stem  17  from the moment detected by the moment sensor  40  is detected. When these values meet the prescribed conditions, the throttle of the adjustable valve  37  is varied to adjust the damping force, thus controlling turning of the steering system  17  when kickback or another disturbance occurs. However, the elements employed by the controlling system  38  are not limited to those described above. Various known elements such as a speed of travel or a load on the front wheel may be employed as alternatives or in addition to the elements described above.  
         [0033]    The operation of this embodiment will now be described. As is clear in FIGS. 2 and 3, the steering damper  10  is located at the midsection of the cross member  12  provided between the left and right mainframe  3 ,  3 . Further, it is disposed outside the steering system, and not within or combined with the steering system. Therefore, when mounting the steering damper  10 , the only changes that must be made to the steering system are that of providing a drive gear  16  around the steering stem  17 , and forming an opening  22  on the head pipe  18 .  
         [0034]    Therefore, even when the steering damper  10  is mounted, only a small amount of weight is added as compared to the steering systems of the related art. Therefore, since inertia of the steering system changes little even when the steering damper  10  is mounted, the steering system of the present invention operates with the essentially same inertia conditions as conventional steering systems having no steering damper mounted thereon.  
         [0035]    In order to perform maintenance of steering damper  10 , the cross member  12  must simply be detached from the mainframes  3 ,  3  by removing the bolts  14 . Thus, the steering damper  10  and the cross member  12  can be removed together, allowing maintenance to be performed separately from the vehicle body. Therefore, since maintaining the damper in a small space is unnecessary, the maintainability is improved.  
         [0036]    In addition, the cross member  10  is secured on the pair of left and right mainframes  3 ,  3 , and the steering damper  10  and the cross member  12  may be attached and detached from above the vehicle body. This further facilitates maintenance of the steering damper  10 .  
         [0037]    The second embodiment will now be described. In this embodiment, the mounting position of the steering damper  10  is inverted upside down, but otherwise is the same as the former embodiment. The common parts are only shown by identical numerals, and will not be described below. FIG. 6 is a drawing corresponding to FIG. 2, in which the cross member  12  is mounted on the lower surfaces of the left and right mainframes  3 ,  3  from below the vehicle body, and the steering damper  10  is mounted on the cross member  12 . Therefore, the drive gear  16  and the opening  22  are provided on the lower position of the steering stem  17  and the head pipe  18  respectively.  
         [0038]    In this arrangement, since the space below the front portion of the mainframe  3  may be effectively utilized, the space behind the head pipe  18  increases. Also, the steering damper  10  and the cross member  12  may be attached and detached from below the vehicle body, thereby facilitating maintenance of the steering damper  10  as in the case of the former embodiment. In addition, since the steering damper  10  cannot be seen from above, a good appearance may be maintained.  
         [0039]    The present invention is not limited to the embodiments described so far, and various modifications or applications may be made within the principle of the same invention. For example, it is also possible to provide the housing  10   a  of the steering damper  10  and the cross member  12  separately and mount the housing  10   a  detachably to the cross member  12  with bolts, or the like. In this case, when performing maintenance of the steering damper  10 , either it may be removed together with the cross member  12  from the mainframe  3  as in the former embodiment, or only the steering damper  10  may be attached or detached for maintenance without detaching the cross member  12 .  
         [0040]    Though the steering damper  10  and the steering stem  17  are connected by the sector gear  15  and the drive gear  16  in the aforementioned embodiments, the invention is not limited thereto. Turning of the steering stem  17  may be transmitted to the steering damper by any appropriate means, such as a link structure, or a lever structure.  
         [0041]    The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.