Abstract:
A suspension system for a motorcycle, comprising a motorcycle main frame, a swing arm pivotally mounted to the motorcycle main frame about a pivot axis, and an air-bag suspension system. The air-bag suspension system includes at least one air-bag constructed of an elastomeric material. The air-bag is housed within a housing assembly and is secured at one end to a piston located within the housing assembly and at its other end to an upper plate or end cap of the housing assembly. The housing assembly is attached to a shock absorber, and the shock absorber is attached at its forward end to the cross member plate of the motorcycle main frame and is pivotally attached at its rearward end to the lower transverse cross member of the swing arm.

Description:
CROSS REFERENCES TO CO-PENDING APPLICATIONS  
         [0001]    None.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    This invention relates generally to motorcycles, more particularly, to motorcycle suspension systems.  
           [0004]    2. Description of the Prior Art  
           [0005]    Harley-Davidson is a well known motorcycle manufacturer that manufactures a popular suspension system for its motorcycles under the trademark SOFTAIL®. The SOFTAIL® suspension system has no visible suspension components and thus mimics the desirable appearance of the Harley-Davidson “hard tail” frame in which the connecting arms of the rear wheel are rigidly fixed to the frame. The SOFTAIL® suspension system, which incorporates a swing arm and shock absorbers, dampens the effect of the rear wheel attachment, thereby affording an advantage over the “hard tail” frame by providing some suspension cushioning that improves the handling and riding comfort of the motorcycle.  
           [0006]    In the SOFTAIL® suspension system, the swing arm pivotally attaches to the struts of the motorcycle main frame, thus enabling the rear wheel to arcuately move independently of the frame. The swing arm includes a pair of wheel mounts located on a wheel axis spaced to receive the rear wheel. The swing arm further includes pairs of arms extending from each of the wheel mounts and connectors connecting each pair of arms. Each connector is joined to the other connector by an upper transverse cross member and a lower transverse cross member. An intermediate transverse cross member extends through the connectors and through the frame struts of the motorcycle main frame. The swing arm is pivotal about this intermediate transverse cross member. The connectors have the same general size and shape as the frame struts of the main frame. Each connector is positioned adjacent and inside the corresponding frame struts so that they are hidden from view.  
           [0007]    The standard or stock SOFTAIL® suspension system uses two shock absorbers mounted in parallel relationship with the motorcycle main frame. One end of each shock absorber is attached to the main frame and the other end is connected to a projection extending forwardly from the lower transverse cross member of the swing arm. The projection is adapted to receive a bolt or pin which connects the shock absorber to the projection. The main frame of the motorcycle hides the projection and shock absorbers from view, thereby retaining the aesthetic appearance of the desirable Harley-Davidson “hard tail” frame.  
           [0008]    As mentioned previously, the SOFTAIL® suspension system affords an advantage over the “hard tail” frame by providing some suspension cushioning that improves the handling and riding comfort of the motorcycle. However, as discussed in U.S. Pat. No. 5,487,443 (hereinafter the &#39;443 patent), significant disadvantages remain. For example, the ride remains too harsh and uncomfortable because of the very short travel of the shock absorbers.  
           [0009]    As mentioned in the &#39;443 patent, the maximum vertical movement of the rear wheel relative to the main frame is limited to two inches in either vertical direction before the swing arm contacts the main frame. The shock absorbers have an even smaller maximum travel of 1.5 inches, 0.75 inch in either direction from a center position. The result is that while the rear wheel may travel two inches in one direction from its centered position, the shock absorbers can only travel a distance of 0.75 inch. This limited distance of travel of the shock absorbers results in a hard, uncomfortable ride because all of the shock absorption must occur within this narrow range of movement.  
           [0010]    Further, the short distance of travel mandates continual and rapid changes of the shock absorber shafts according to the movement of the wheel. Often, these directional changes of the shock absorber shafts cannot occur as fast as is necessary to create a smoother ride due to the inherent reluctance of the shock absorber shafts to rapidly change directions. As discussed in the &#39;443 patent, this inherent reluctance to rapid directional change is due to the relatively large momentum forces involved, the inertial drag caused by the movement of the oil or gas within the shock absorbers, and the friction resistance caused by the seals and O-rings.  
           [0011]    There have been previous attempts to improve the SOFTAIL® suspension system, but these attempts have had little success. For example, it has been attempted to increase the travel distance of the shock absorbers. This solution, however, offers only a modest improvement to the ride of the motorcycle because it does nothing for the responsiveness of the shock absorbers. Additionally, the range of movement of the swing arm is limited by the motorcycle frame, and therefore, the amount of travel of the shock absorbers is also limited. Any further increases in the shock absorber travel require modification to the motorcycle main frame, which is very undesirable. Other attempts have been made to improve the responsiveness of the shock absorbers; however, these attempts are hindered by the drag and friction forces discussed above.  
           [0012]    In addition to the problems associated with the ride and handling of the standard or stock SOFTAIL® suspension system, many motorcycle enthusiasts attempt to lower the rear of the motorcycle for aesthetic reasons, believing it improves the appearance of the motorcycle. Special kits are sold to allow the frame to be lowered; however, the lowering of the rear of the motorcycle reduces the stroke on the suspension, as discussed above, resulting in a rougher ride.  
           [0013]    Therefore, there remains a need for a motorcycle suspension system that maintains the aesthetic appearance of the SOFTAIL® frame while improving the ride, comfort and load adjustability of the motorcycle. There also remains a need for a motorcycle suspension system that enables the rear of the motorcycle to be raised and lowered when desired for aesthetic purposes and for load bearing capacity.  
         SUMMARY OF THE INVENTION  
         [0014]    A suspension system for a motorcycle, comprising a motorcycle main frame, a swing arm pivotally mounted to the motorcycle main frame about a pivot axis, and an air-bag suspension system. The swing arm has a pair of wheel mounts located on a wheel axis spaced to receive the rear wheel. The swing arm further includes pairs of arms extending from each of the wheel mounts and connectors connecting each pair of arms. Each connector is joined to the other connector by an upper transverse cross member and a lower transverse cross member. An intermediate transverse cross member extends along the swing arm pivot axis and through the connectors and is secured to the struts of the motorcycle main frame.  
           [0015]    The air-bag suspension system includes at least one air-bag constructed of an elastomeric material. The air-bag is housed within a housing assembly and is secured at one end to a piston located within the housing assembly and at its other end to an upper plate or end cap of the housing assembly. The housing assembly is attached to a shock absorber, and the shock absorber is attached at its forward end to the cross member plate of the motorcycle main frame and is pivotally attached at its rearward end to the lower transverse cross member of the swing arm.  
           [0016]    In operation, when the rear wheel is caused to move upwardly or downwardly, the swing arm will also move arcuately upwardly or downwardly. The movement of the swing arm will pull or push the air-bag forwardly or rearwardly as the case may be. If the rear wheel is caused to move upwardly with respect to the main frame, the shock absorber is extended, causing the rear suspension to be compressed and lowering the rear end of the motorcycle. The rearward movement of the air-bag relative to the stationary motorcycle main frame causes the air-bag to compress, thus dampening the effect of the movement of the rear wheel. If the rear wheel is caused to move downwardly with respect to the main frame, the shock absorber is compressed, causing the rear suspension to be extended and raising the rear end of the motorcycle. The forward movement of the air-bag relative to the stationary motorcycle main frame causes the air-bag to stretch, thus dampening the effect of the movement of the rear wheel.  
           [0017]    In the preferred embodiment, the air pressure in the air-bag is adjustable on the move by the use of a power switch operably connected to a small compressor mounted on the motorcycle.  
           [0018]    It is an object of the present invention to provide an improved suspension system for a Harley-Davidson SOFTAIL® motorcycle.  
           [0019]    It is another object of the present invention to provide an improved suspension system for a Harley-Davidson SOFTAIL® motorcycle without having to modify the motorcycle main frame or swing arm.  
           [0020]    It is yet another object of the present invention to provide a way to easily adjust the stiffness of a motorcycle&#39;s ride while on the move to accommodate different loads.  
           [0021]    It is still a further object of the present invention to enable the ride height of the motorcycle to be adjustable.  
           [0022]    It is still a further object of the present invention to permit the frame of a motorcycle to be lowered when the motorcycle is stopped or when traveling at low speeds for appearance purposes and to be able to quickly raise the frame once again when traveling at faster speeds to reduce road hop.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]    Other objects of the present invention and many of the attendant advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, in which like reference numerals designate like parts throughout the figures thereof and wherein:  
         [0024]    [0024]FIG. 1 illustrates an isometric view of an air-bag suspension system, the present invention;  
         [0025]    [0025]FIG. 2 illustrates a cross-sectional view of the air-bag suspension system where the shock absorber is extended;  
         [0026]    [0026]FIG. 3 illustrates a cross-sectional view of the air-bag suspension system where the shock absorber is at mid-stroke;  
         [0027]    [0027]FIG. 4 illustrates a cross-sectional view of the air-bag suspension system where the shock absorber is compressed; and,  
         [0028]    [0028]FIG. 5 is a graph comparing the air-bag suspension system to a stock SOFTAIL® suspension system and illustrates the range of adjustment allowed by the air-bag suspension system.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0029]    [0029]FIG. 1 illustrates an isometric view of an air-bag suspension system  10 , the present invention. The air-bag suspension system  10  is comprised of a shock absorber  12 , a housing assembly  24 , a main frame mounting assembly  26 , and an air-bag assembly  40  (FIGS.  2 - 4 ). The shock absorber  12  incorporates a swing arm mount  14 , a push rod  16 , and a standard hydraulic assembly  18 . The housing assembly  24  is comprised of an outer body member  22  having an inturned annular flange  28  at one end thereof and a mount  62  at the opposite end thereof, and an upper plate  20  (acting as an end cap and also serving as a component of the air-bag assembly  40 , later described in detail) which bears against the inturned annular flange  28 . The mount  62  secures the outer body member  22  to the hydraulic assembly  18 . A pressure regulator knob  32  is incorporated into the hydraulic assembly  18  for adjusting the hydraulic assembly  18 . The main frame mounting assembly  26  extends from the hydraulic assembly  18  and includes a threaded rod  34  and two identical bushings  36  and  38  with identical metal bushing caps  37  and  39  (illustrated in FIGS.  2 - 4 ). The housing assembly  24  contains the air-bag assembly  40  which compresses and thereby dampens the shock absorber  12 , as will be described in detail in connection with FIGS.  2 - 4 . A pair of identical air-bag suspension systems  10  replace the stock SOFTAIL® suspension system. The swing arm pivotally attaches to the swing arm mounts  14  of the identical air-bag suspension system  10 , and the main frame mounting assemblies  26  of the identical air-bag suspension systems  10  rigidly attach to the cross member plate of the motorcycle main frame using the two identical bushings  36  and  38  and their respective identical bushing caps  37  and  39  (FIGS.  2 - 4 ), which sandwich the cross member plate and are secured by a nut  66  (FIGS.  2 - 4 ) thus enabling the rear wheel to arcuately move independently of the frame.  
         [0030]    [0030]FIG. 2 illustrates a cross sectional view of the air-bag suspension system  10  where the shock absorber  12  is extended. When the shock absorber  12  is extended, the rear suspension is compressed and the motorcycle rear end will be fully lowered. The air-bag assembly  40  provides the means to control the travel of the shock absorber  12 . The air-bag assembly  40  will now be described in detail. The air-bag assembly  40  is comprised of an air-bag  44  formed of an elastomeric material, a piston  60  having a lower air-bag flange  46 , a retaining ring  58 , a lower seal  56 , a lower air-bag flange clamp  48 , an air hose fitting  30 , an air hose  42 , the upper plate  20 , which as previously mentioned bears against the inturned annular flange  28  of the outer body member  22  and acts as an end cap for the housing assembly  24 , the upper plate or end cap  20  having an upper air-bag flange  50 , an upper seal  54 , and an upper air-bag flange clamp  52 . The air-bag  44  is internally secured to piston  60  at lower air-bag flange  46  by lower air-bag flange clamp  48 , and air-bag  44  is externally secured to upper plate  20  at upper air-bag flange  50  by upper air-bag flange clamp  52 , creating an expandable and retractable air pocket  64  which communicates with an aperture extending through the upper plate  20 . Air hose fitting  30  is attached at the aperture and allows air from air hose  42  created by an onboard compressor and regulator to enter air pocket  64 . When the shock absorber  12  is extended and the rear suspension is compressed, piston  60  makes intimate contact with upper plate  20 , limiting the extension of the shock absorber  12 . In this fully lowered position, the rider will have a rigid-feeling suspension, similar to that of a “hard tail” with very little to no cushion.  
         [0031]    Push rod  16  and hydraulic assembly  18  constitute a typical shock absorber or hydraulic dampener when combined. Retaining ring  58  secures piston  60  to the push rod  16  of the shock absorber  12 . The lower seal  56 , which is encased and fixed within piston  60 , prevents the air inside air-bag  44  from leaking into or out of air pocket  64 . Upper seal  54  slidingly engages push rod  16  and also prevents the air inside air-bag  44  from leaking into or out of air pocket  64  when the piston  60  and push rod  16  make forward or reverse travel. The travel will be further described in detail with reference to FIG. 3 and FIG. 4.  
         [0032]    [0032]FIG. 3 illustrates a cross sectional view of the air-bag suspension system  10  where the shock absorber  12  is at mid-stroke, where all numerals correspond to those elements previously described. When the shock absorber  12  is at mid-stroke, the rear suspension is partially extended and the motorcycle rear end will be half way between the fully lowered and fully raised position. In order to reach the mid-stroke position, an onboard compressor introduces air into air-bag  44  through air hose  42  and air hose fitting  30 . When the air is introduced into air-bag  44 , air-bag  44  expands and piston  60  travels away from upper plate  20 , compressing the shock absorber  12 . In this half way position the rider will have a more cushioned ride than that of the fully lowered position.  
         [0033]    [0033]FIG. 4 illustrates a cross sectional view of the air-bag suspension system  10  where the shock absorber  12  is compressed, where all numerals correspond to those elements previously described. When the shock absorber  12  is compressed, the rear suspension is extended and the motorcycle rear end will be in the fully raised position. In order to reach the fully raised position, an onboard compressor introduces air into air-bag  44  through air hose  42  and air hose fitting  30 . When the air is introduced into air-bag  44 , air-bag  44  expands and piston  60  travels away from upper plate  20 , compressing the shock absorber  12 . In this fully raised position the rider will have a higher load capacity which allows the rider to accommodate a passenger or a heavy baggage load without compromising comfort or handling.  
         [0034]    [0034]FIG. 5 is a graph comparing the air-bag suspension system to a stock SOFTAIL® suspension system and illustrates the range of adjustment allowed by the air-bag suspension system. The horizontal axis represents the travel of the shock absorbers, with “0.0” indicating the shock absorbers in the fully compressed position as shown in FIG. 4, and “1.5” indicating the shock absorbers in the fully extended position as shown in FIG. 2.  
         [0035]    The vertical axis represents the supporting force provided by the spring elements of the suspension system. In the case of the stock SOFTAIL® suspension system, the spring elements consist of the coiled-wire springs, whereas in the case of the air-bag suspension system of the invention, these spring elements consist of inflatable air-bags.  
         [0036]    The line marked by “squares” illustrates the stock SOFTAIL® suspension system, having an initial pre-load of approximately 600 lbs. and a constant spring rate of 980 lbs. per inch. These properties are “factory set,” and do not allow the suspension system to be tailored to the riding conditions and/or the rider&#39;s preferences.  
         [0037]    The curve marked by “triangles” illustrates the air-bag suspension at its minimal setting of 0 psi., which allows the shock absorber to easily extend, thereby lowering the frame.  
         [0038]    The curve marked with “diamonds” illustrates the air-bag suspension at its maximum initial setting of 150 psi., which compresses the shock absorber with an initial pre-load of approximately 700 lbs., thereby raising the frame.  
         [0039]    As the motorcycle is burdened by the rider(s) and cargo, the additional weight causes the shock absorber to extend and the air-bag to compress. As the air-bag compresses, the volume of air inside is reduced exponentially in relation to the stroke. This action increases the pressure inside the air-bag exponentially, thus increasing the supporting force exponentially as well. This characteristic provides a truly progressive suspension without the complexity of a mechanical linkage, as found on many other motorcycles.  
         [0040]    The area between the two curves represents the indefinitely adjustable range of the air-bag suspension. This allows the suspension to be tailored to the riding conditions and/or the rider&#39;s preferences.  
       Mode of Operation  
       [0041]    With additional reference to FIGS.  2 - 4 , the mode of operation is now described. When all air pressure is released from air-bag  44 , the shock absorber  12  is extended, compressing the rear suspension, collapsing air-bag  44 , causing piston  60  to make contact with the interior of end cap  20  and lowering the rear end of the motorcycle to its lowest ride height (FIG. 2).  
         [0042]    As pressurized air is introduced into the air-bag  44 , piston  60  travels away from end cap  20  and toward the hydraulic assembly  18 . Shock absorber  12  begins compressing and the rear suspension begins extending and raising the rear end of the motorcycle. FIG. 3 illustrates this mid-stroke position.  
         [0043]    As even more pressurized air is introduced into the air-bag  44 , near its maximum capacity, piston  60  travels further toward the hydraulic assembly  18 , but no contact is made. Shock absorber  12  is now fully compressed and the rear suspension is fully extended, raising the rear end of the motorcycle to its highest ride height (FIG. 4).  
         [0044]    In accordance with the graph shown in FIG. 5 it can be seen that the air-bag suspension system  10  offers an arcuate range of travel and adjustment compared to that of a stock SOFTAIL® suspension system.  
         [0045]    Various modifications can be made to the present invention without departing from the apparent scope hereof.