Abstract:
Embodiments of suspension units for a wheel such as a dirigible wheel for a vehicle such as a motorcycle wherein the dampers at the opposite sides of the wheel each dampen only a compression or an expansion stroke respectively. This offers greater control and simplifies the construction.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates to a suspension system for a vehicle and more particularly to a suspension arrangement for a dirigible wheel for, by way of example, a steered wheel of a vehicle such as motorcycle type of vehicle, although the application for the invention is not so limited, as those skilled in the art will readily recognize.  
         [0002]     The front wheel of a motorcycle is conventionally dirigibly journalled by a front fork made up of a pair of left and right front fork members each of which is double acting to dampen the movement of the vehicle body attitude due to irregularities on a road surface. Such a front fork is disclosed for example in Japanese Published Application Hei 10-119868 and as shown, for example in  FIG. 1 , hereof comprises a conventional, ordinary front fork, indicated generally by the reference numeral  11 . A pair of symmetric, left and right front fork damping members  12   a  and  12   b  are interconnected via a bracket  13  to the lower end of a steering shaft  14 . Handlebars (not shown) are connected, in a known manner, to the steering shaft  14 , which is suitably journalled for dirigible movement by the front part of a vehicle body (not shown). A front wheel (not shown) is supported for free rotation via a wheel shaft (not shown) fixed to brackets  15  formed at the lower ends of the front fork damping members  12   a  and  12   b . Thus and as well known in the art, the front wheel is steered via the steering shaft  14  and the front fork  11  using the handlebars.  
         [0003]     In this conventional prior art structure, each of the front fork damping members  12   a  and  12   b  is of the same construction comprised of concentric outer and inner cylinders  16  and  17  each configured and constructed to be double acting. The interior of the inner cylinders  16 ,  17  is divided by a respective piston  18  into an upper, compression side oil chamber C and a lower, expansion side oil chamber D. The pistons  18  are held in a fixed axial position relative to the steering shaft  14  by means of a respective piston rod  19  in any suitable manner.  
         [0004]     The compression side oil chamber C experiences compressive action in compression stroke, while the expansion side oil chamber D receives compressive action in expansion stroke. Each piston  18  has a mechanism for producing damping force and a base valve  21  having a mechanism for producing damping force is disposed at the lower end of the respective inner cylinder  16  and  17  coaxially with its respective piston  18 .  
         [0005]     The damping action of the prior art construction will flow be described by reference to  FIGS. 2A and 2B  that are partial, enlarged views of the piston  18  shown in  FIG. 1 . The damping action with the left and right damping members  12   a  and  12   b , is the same, as has been noted. The arrows show the direction of oil flow.  FIG. 2A  shows the compression stroke and  FIG. 2B  shows the flow during the expansion stroke.  
         [0006]     Each piston  18  is formed a first passage  22  and a second passage  23  for providing fluid communication between a respective compression side oil chamber C and a respective expansion side oil chamber D. At the expansion chamber side opening of the each first passage  22  is provided a respective compression valve  24  capable of opening during compression stroke of the piston rod  19 , while at the compression chamber side opening of the second passage  23  is provided a respective expansion valve  25  capable of opening during the expansion stroke.  
         [0007]     As best seen in  FIGS. 2A and 2B , the lower end portion of each of the piston rods  19  is formed an axial, in-shaft passage  26  in fluid communication with the compression side oil chamber C and an upper passage  27  for fluid communication between the in-shaft passage  26  and the expansion side oil chamber D. Consequently, the compression side oil chamber C and the expansion side oil chamber D are in fluid communication via the in-shaft passages  26  and  27 .  
         [0008]     Also, a respective damping force regulation valve  28  is positioned in the interior of the respective piston rod  18  for axial movement. At the lower end of the damping force regulation valve  28 , a conical needle  29  is positioned inside the in-shaft passage  26 . Movement of the needle  29  back and forth, regulates the amount of oil flowing through the in-shaft passage  26  so as to regulate damping force in particular in low speed range during the expansion stroke.  
         [0009]     As shown in  FIG. 2A , during a compression stroke, the pressure in the expansion side oil chamber D lowers as the piston  18  is pushed down. Consequently, the oil in the pressure in the compression side oil chamber C pushes the compression valve  24  open and oil flows through the first passage  22  into the expansion side oil chamber D, and at the same time, moves through the in-shaft passage  26  and the passage  27  into the expansion side oil chamber D. Here, as resistance is small, little damping force is produced.  
         [0010]     At this time, as the piston rod  19  is inserted into the inner cylinder  17 , the pressure in the entire interior of the cylinder increases corresponding to the inserted volume of the piston rod  19 . Consequently, the amount of oil flowing from the compression side oil chamber C to the expansion side oil chamber D corresponds to an amount derived from the difference between the cross-sectional area of the inner cylinder  17  less the cross-sectional area of the piston rod  19 .  
         [0011]     As shown in  FIG. 2B , during an expansion stroke, as the piston  18  is pulled tip, the pressure of the expansion side oil chamber D rises, while the pressure of the compression side oil chamber C lowers. Consequently, the oil in the expansion side oil chamber D pushes open the expansion time valve  25  to move through the second passage  23  into the compression side oil chamber C, and also moves front the passage  27  through the in-shaft passage  26  into the compression side oil chamber C, and this resistance produces expansion damping force.  
         [0012]     Again, at this time, the amount of oil flowing from the expansion side oil chamber D into the compression side oil chamber C, as the pressure in the expansion side oil chamber D lowers is equal to cross-sectional area of the inner cylinder  17  minus the cross-sectional area of the piston rod  18 .  
         [0013]     Referring now to  FIGS. 3A and 3B , these show the actions of the base valve  21  with the flow directions being indicated by the arrows.  FIG. 3A  shows the compression stroke while  FIG. 3B  illustrates the expansion stroke. Thus these figures correspond to  FIGS. 2A and 2B .  
         [0014]     As has been noted, the base valves  21  are provided at the lower end portion of the respective inner cylinders  17 . They serve the function of accommodating the fluid displaced due to the cross sectional area of the piston rod  19 , by either receiving this fluid or replacing it depending on whether compression or expansion are occurring.  
         [0015]     In each of these base valves  21 , a third passage  31  and a fourth passage  32  are formed to provide fluid communication between the respective compression oil chamber C and the respective outer cylinder  16  through a hole  33  provided in the respective inner cylinder  17 . A compression valve  34  is provided at the lower opening of each of the third passage  31  that opens during the compression stroke. In a similar manner, the compression opening of the fourth passage  32  is provided an expansion valve  35  that opens during the expansion stroke.  
         [0016]     Also an in-shaft passage  36  is axially formed in each of the base valves  21 , to provide fluid communication between the compression side oil chamber C and the fore-end of the respective inner cylinder  17 , and also a respective passage  37  is formed to provide fluid communication between the in-shaft passage  36  and the respective outer cylinder  16 . Into each of these passage  37 , a respective conical needle  38  is movably supported for regulating damping force. By moving the position of the needles  38  back and forth, the amount of oil flowing through the passages  37  via the needles  38  is regulated so as to regulate damping force.  
         [0017]     As shown in  FIG. 3A  in a compression stroke, the excessive oil corresponding to the inserted volume of the piston rod  18  that does not flow into the expansion side oil chamber D in  FIG. 2A  flows to the in-shaft passage  36  and also pushes open the compression valve  34  disposed in the third passage  31 . The oil having passed into the in-shaft passage  36  flows from the needle  38  through the passage  37  into the outer cylinder  16 . The oil having passed from the compression valve  34  flows through the hole  33  of the inner cylinder  17  to the outer cylinder  16 . By this resistance, compression damping force is produced.  
         [0018]     As shown in  FIG. 3B , during an expansion stroke, the oil corresponding to the displaced volume of the piston rod  18  flows from the outer cylinder  16  through the hole  33  of the inner cylinder  17  and, while pushing open the expansion valve  35 , into the compression side oil chamber C. Here, resistance is small and no significant damping force is produced.  
         [0019]     As a result, as the piston  18  moves axially in the inner cylinder  17  due to irregularities on the road surface, damping forces during expansion and compression are produced Damping force characteristics are set so that damping forces matching the road surface conditions may be obtained to realize operability and ride comfort the user desires.  
         [0020]     Thus with the prior art, hydraulic damping mechanism is obtained in each of the left and right front fork members, and both compression side damping force and expansion side damping force are produced and regulated in each of the front fork members. That is, the conventional left and right front fork members are the same in construction and operation. Basically, damping forces on the both compression and the expansion are respectively regulated to be the same on both sides. In other words, each of left and right front fork members are double acting.  
         [0021]     This has been the practice because it was generally assumed that to do otherwise would adversely affect maneuverability due to left and right imbalance in damping force. Consequently, conventional front fork members have been of a pair of double acting devices that are the same in construction.  
         [0022]     However, proving mechanisms for producing and regulating the compression side and expansion side damping forces respectively likewise on each of the left and right front fork members makes the respective front fork members complicated and expensive This results in addition of structures in excess. That is, providing damping force producing mechanisms for both compression and expansion sides respectively on both left and right front fork members of a single front fork is not the most efficient or effective. Excess damping forces are sometimes produced, causing inefficient production of damping force.  
         [0023]     In addition the conventional hydraulic damping mechanism described above the oil acting for providing compression side damping force is used only in amount corresponding to the cross-sectional area of the piston rod  18  and therefore small in flow rate and does not provide sufficient compression side damping force relative to the cross-sectional area of the entire inner cylinder  17 . Consequently, the compression side damping force is inadequate.  
         [0024]     In addition recent vehicles of light weight and high output such as of sports models, require high stabilized maneuverability. This can be accomplished by increasing compression damping force and at the same time to improve responsiveness in the expansion side damping. It is further required to obtain damping forces in compression stroke and expansion stroke while quickly to responding to switching between these strokes. Such requirements of high performance are difficult to meet using the front fork based on the conventional, double acting hydraulic damping mechanism.  
       SUMMARY OF THE INVENTION  
       [0025]     The inventor hereof has discovered that the previously believed theory of using identical paired double acting hydraulic mechanisms really is not required for stability. In fact performance and stability can in fact be obtained by employing paired, oppositely acting single hydraulic mechanisms on the opposite sides of the front fork.  
         [0026]     Therefore it is a principal object of the invention to provide a wheel suspension for a vehicle having dampers provided on opposite sides of the wheel rotational axis, one of which acts to only dampen movement on compression and the other of which operates only to dampen movement on expansion.  
         [0027]     In accordance with another feature of the invention the suspended wheel is supported for dirigible movement. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0028]      FIG. 1  is a front elevational view, with portions broken away, of a conventional prior art front wheel suspension for a motorcycle.  
         [0029]      FIGS. 2A and 2B  are enlarged views showing the flow through the piston valves of each shock absorber during a compression stroke and the following expansion stroke.  
         [0030]      FIGS. 3A and 3B  are enlarged views showing the flow through the base valves of each shock absorber during a compression stroke and the following expansion stroke.  
         [0031]      FIG. 4  is a front elevational view, with portions broken away, in part similar to  FIG. 1 , but showing an embodiment of the invention.  
         [0032]      FIGS. 5A and 5B  are enlarged views, in part similar to  FIGS. 2A and 2B , but showing the flow in the left and right shock absorbers, respectively, of this embodiment during a compression stroke.  
         [0033]      FIGS. 6A and 6B  are enlarged views, in part similar to  FIGS. 2A and 2B , but showing the flow in the left and right shock absorbers during an expansion stroke.  
         [0034]      FIG. 7  is a view in part similar to those of  FIGS. 2A and 2B  and  3 A and  3 B, but showing a different embodiment. 
     
    
     DETAILED DESCRIPTION  
       [0035]     Referring now in detail to the illustrated embodiments of the invention and initially to  FIG. 4 , like the prior art construction the front wheel (not shown) is dirigibly supported for steering movement by a steering shaft  14  that supports handlebars (not shown) provided in the front part of an associated vehicle body (not shown). At the fore-end of a front fork, indicated generally by the reference numeral  51 , a front wheel (not shown) is rotatably supported through a wheel shaft (not shown). Thus, the front wheel is steered through the steering shaft  14  and the front fork  51  using the handlebars.  
         [0036]     Unlike the prior art, the suspension comprises left and right damper units, each indicated by the respective reference numerals  52  and  53 . Each of the damper units  52  and  53  is comprised of coaxial outer cylinders  54  and inner cylinders  55 .  
         [0037]     Each damper unit  52  and  53  also includes a piston rod  56  axially movable in its inner cylinder  55 . A piston  57  is fixed to the lower end of each of the piston rods  56  and divides the interior of the inner cylinder  55  into a contraction side oil chamber C on the lower side of the piston  57  and the extension side oil chamber D on the back face side of the piston  57 . The contraction side oil chamber C receives compressive action in contraction stroke, while the extension side oil chamber D receives compressive action in extension stroke.  
         [0038]     Now the difference between the damper units  52  and  53 , will be described. In the left hand damper unit  52 , a hole  58  is formed in the inner cylinder  55  that is open toward the outer cylinder  54 . This provides communication between the interior of the inner cylinder  55  and the annular space between both cylinders  54  and  55  on the back face side of the piston  57 , of the inner cylinder  55 . On the other hand, a hole  59  that is open toward the outer cylinder  54  (to make communication between the interior of the inner cylinder  55  and the annular space between both cylinders  54  and  55 ) is formed in part of the side face, on the front face side of the piston  57 , of the inner cylinder  55  of the other (right side in the figure) front fork member  53 .  
         [0039]      FIGS. 5A and 5B  are partial, enlarged views of the left damper member  52 , that produces the contraction side damping force through the use of the hole  58 , formed in part of the inner cylinder  55  on the back face side of the piston  57  and opening toward the outer cylinder  55 . The arrow indicates the oil flow direction.  FIG. 5A  shows the contraction stroke, while  FIG. 5B  illustrates the extension stroke.  
         [0040]     Continuing to refer to these figures ( 5 A and  5 B), a first passage  61  and a second passage  62  are formed through the piston  57  for providing fluid communication between the contraction side oil chamber C and the extension side oil chamber D. At the opening facing the extension side oil chamber D of the first passage  61 , a contraction valve  63  is provided which opens during the contraction stroke of the piston rod  56 . Likewise, at the opening facing the contraction side oil chamber C of the second passage  62 , an extension valve  64  is provided which opens during the extension stroke of the piston rod  56 . The contraction valve  63  and the extension valve  64  for example be either single or plural plate valves made of for example annular, thin plate springs, to be pushed open with oil flow. Further, an in-shaft passage  65  for permitting fluid communication with the contraction side oil chamber C is formed along the center axis direction of the piston  57 .  
         [0041]     A damping force regulating valve  66  is inserted to be axially movable in the axis of the piston rod  56 . A needle  67  of a conical shape is formed at the fore-end of the damping force regulating valve  66 . The needle  67  is placed to be movable back and forth between a position for fully closing the base end side opening of the in-shaft passage  65  and a position for fully opening it. The oil having entered the in-shaft passage  65  during contraction stroke is controlled with the needle  67  and flows into the extension side oil chamber D. By adjusting the position of the needle  67 , oil flow rate is controlled and damping force is regulated. Adjusting the position of the needle  67  to control the flow rate may be done with an adjusting section (not shown) provided on the base (upper) end of the damping force regulating valve  66 .  
         [0042]     As has been noted, in part of the inner cylinder  55  on the back face side of the piston  57 , the hole  58  is formed which leads to the outer cylinder  54 . When the piston rod  56  is inserted in the compressing direction (down in the figure), in response to hitting a bump or the like, oil in an amount corresponding to the inserted portion of the piston rod  56  flows through the hole  58  into the space defined between the outer cylinder  54  and the inner cylinder  55 , as indicated by the flow arrow.  
         [0043]     Considering this condition, the contraction side damping force producing mechanism of the front fork member  52  will be described in detail and referring primarily to  FIG. 5A . When the front fork member  52  comes to a compressed state as the wheel is pushed up with a bump on the road surface, both of the cylinders  54 ,  55  move toward the base end (upward in the figure). As a result, the piston  57  is relatively pushed down. At this time, pressure in the contraction side oil chamber C increases. Consequently, oil flows up in the figure, and the contraction valve  63  is pushed open. When the contraction valve  63  opens, oil flows through the first passage  61  into the extension side oil chamber D. At this time, damping force is produced with the passage resistance of the contraction valve  63 . Further, when the pressure in the contraction side oil chamber C increases, part of oil flows from the in-shaft passage  65  through the needle  67  and a passage hole  68  into the extension side oil chamber D. In normal and low speed drive, oil flows through the in-shaft passage  65  into the extension side oil chamber D. As the drive speed increases, oil pushes open the contraction valve  63 , so that increased or greater damping force is produced.  
         [0044]     In addition, as the piston rod  56  is inserted into the inner cylinder  55  during the contraction stroke, an amount of oil in the extension side oil chamber D corresponding to the inserted volume of the piston rod  56  becomes excessive. This excessive oil flows through the hole  58  into the outer cylinder  54 . Thus, the pressure in the extension side oil chamber D is prevented from rising and the oil flow through the contraction valve  63  is made smooth, so that sufficient damping force is produced during contraction. Therefore, oil in the contraction side oil chamber C in an amount corresponding to the entire cross-sectional area of the inner cylinder  55  (S 1  in the figure) contributes to producing damping force during contraction, so that sufficient damping force during contraction is obtained efficiently.  
         [0045]     Continuing to refer to the action of the left damper  52 , during the extension stroke when the piston  57  moves in the opposite direction as shown in  FIG. 5B , the pressure in the contraction side oil chamber C decreases. During this time, oil flows down in this figure, pushes open the extension valve  64 , and flows through the second passage  62  into the contraction side oil chamber C. The resistance of the extension valve  64  is so small that no damping force is produced. At this time, the deficit amount of oil corresponding to the drawn out volume of the piston rod  56  (the volume corresponding to S 2  in the figure) is supplied from the outer cylinder into the inner cylinder  59  through the hole  58 .  
         [0046]     Now the operation of the right damper  53  will be described by reference to  FIGS. 6A and 6B  during the same conditions shown in  FIGS. 5A and 5B , respectively. These  FIGS. 6A and 6B  are enlarged views of the front fork member  53 , on the side producing extension side damping force. The piston rod  56  and the piston  57  are of the same construction as those of the other front fork damping member  52 .  
         [0047]     As the piston  57  is pushed down in the figure during contraction stroke, the pressure in the extension side oil chamber D decreases. Consequently, as shown in  FIG. 6A , oil flows up in the figure, pushes open a contraction valve  69 , and flows through the first passage  61  into the extension side oil chamber D. During this time, the resistance of the contraction valve  69  is very small, so that no damping force is produced.  
         [0048]     At this time, the excess amount of oil in the contraction side oil chamber C due to the compressive action of the piston  57  flows through the hole  59  near the fore-end of the inner cylinder  55  into the outer cylinder  54 .  
         [0049]     During the extension stroke, as the pressure in the extension side oil chamber D rises, oil flows as shown in  FIG. 6B , and pushes open an extension valve  71 , and flows through the second passage  62  into the contraction side oil chamber C. During this time, damping force is produced with the passage resistance of the extension valve  71 . In addition, as the pressure in the extension side oil chamber D rises, part of oil flows through the passage hole  68 , the needle  67 , and the in-shaft passage  65  into the contraction side oil chamber C.  
         [0050]     As the piston  57  is drawn out during the extension stroke, the volume of the contraction side oil chamber C increases, so that make up oil is required. For the short amount required, the oil accumulated in the space between the outer cylinder  54  and the inner cylinder  55  flows through the hole  59  into the inner cylinder  55 . This prevents oil flowing into the contraction side oil chamber C from running short and falling in pressure. Moreover, as no valves like those in the conventional constitution are present, oil flows easily and smoothly, so that sufficient damping force during extension is produced.  
         [0051]     Thus, by appropriately adjusting the valves and needles of the left and right front fork members  52 ,  53  respectively to produce damping force during contraction with one member and produce damping force during extension with the other, both the front fork members  52 ,  53  become simple in constitution. Along with it, as oil flow is simplified, oil flows smoothly and efficiently to produce appropriate damping force, so that smooth maneuverability is provided.  
         [0052]     In addition, as no base valves or the like for producing damping force need be provided and the length of the fore-end portion of the front fork damper members  52  and  53  may be shortened. Therefore, it is possible to provide sufficient stroke by making the inner cylinder  55  part long enough.  
         [0053]      FIG. 7  illustrates a different compression damper element that could be used rather than the construction shown in  FIGS. 5A and 6A . This unit is identified by the reference numeral  52   a  and except as will be noted, is the same as the previously described embodiment. For that reason, components that have substantially the same construction and operation are identified by the same reference numerals.  
         [0054]     In essence, the front fork member incorporates a one-way valve  81  that opens up during extension stroke provided at the fore-end portion of the inner cylinder  55 .  
         [0055]     This one-way valve  81  remains in closed state due to the internal pressure in the contraction side oil chamber C during contraction stroke. However the one-way valve  81  opens up during extension stroke for adding an oil supply passage to the contraction side oil chamber C to compensate for the low pressure during extension stroke thus making it possible to prevent a shortage of oil acting during contraction stroke from running low and further improve responsiveness of damping force.  
         [0056]     Thus from the foregoing description it should be readily apparent from the foregoing description that the described embodiments utilizing separately constructed dampers for respective compression and expansion damping father than like constructed dampers that each functions to dampen the movement in both directions a less expensive and better acting damper arrangement results without sacrificing handling or performance. Of course those skilled in the art will readily understand that the foregoing description is of exemplary of acceptable constructions and various changes and modifications may be made without departing from the spirit and scope of the invention, as defined by the appended claims.