Abstract:
A motorcycle fork blade ( 21 A or  21 B) wherein a spring ( 50 ) is longitudinally captured between a leg and a fixture on an elongate member ( 33 ) so that the fixture and spring ( 50 ) are maintained within a lower tube during a normal range of travel of the blade so as to minimize binding or damage to the spring. Another aspect is a height adjuster featuring a threaded stud accommodated within a bore of a stanchion tube endplug ( 36 ) and carrying a fixture for engaging the spring ( 50 ). The invention also includes a shock absorber reservoir assembly ( 220 ), and a gas-filed bladder ( 240 ) on the extension side of a shock absorber ( 200 ) to provide volume compensation.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application claims priority of commonly owned U.S. patent application Ser. No. 60/112,838 entitled “Motorcycle Suspension” filed Dec. 18, 1998; and Ser. No. 60/114,040 entitled “Motorcycle Suspension Components” filed Dec. 29, 1998. U.S. patent application Ser. Nos. 60/112,838 and 60/114,040 are incorporated by reference in their entireties herein as if set forth at length. 
    
    
     BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     This invention relates to motorcycles, and more particularly to telescopic motorcycle forks and to reservoirs for height-adjustable motorcycle shock absorbers. 
     (2) Description of the Related Art 
     The dominant class of front suspension for motorcycles is the telescopic fork. Each of a left blade and a right blade of the fork includes telescoping members which extend and compress responsive to loads between the motorcycle frame and the front wheel. Each blade includes one or more springs which provide the necessary static compression resistance and hydraulic valving components which provide damping (shock absorption). Many telescoping forks have a height adjustment feature allowing adjustment of the static blade extension for a given static load. Although the art is extremely developed, there remains room for various combinations of enhanced performance and simplified manufacture. 
     Many shock absorbers (rear or front) include external reservoirs which receive hydraulic fluid from the shock absorber as it is compressed and return such fluid to the shock absorber as it is extended. The reservoirs may be gas-pressurized (such as by introduction of air). When air is introduced to the reservoir, it will tend to drive some of the hydraulic fluid back into the shock absorber thereby extending the shock absorber and increasing static ride height. Withdrawal of air similarly lowers ride height. 
     Valving of the fluid flow between the reservoir and shock absorber will affect the shock absorption characteristics. A user-adjustable valve or valves may be provided. The size of the reservoir, along with desired access for air introduction and valve adjustment are among factors which render reservoirs difficult to conceal so as to reduce visual clutter. 
     Although there is a well developed art in shock absorber reservoirs, there remains room to provide a reservoir having various combinations of improved performance, simplified manufacture, and aesthetic appeal. 
     BRIEF SUMMARY OF THE INVENTION 
     In one aspect, the invention is directed to a motorcycle fork blade including a leg for engaging a front wheel axle, a lower tube extending upward from the leg and an upper tube telescopically surrounding the lower tube. An upper endplug extension with an upper end portion of the upper tube. An elongate member depends from the endplug. A spring is longitudinally captured between the leg and a fixture on the elongate member so that the fixture and spring are maintained within the lower tube during a normal range of travel of the blade so as to minimize possibility for binding of or damage to the spring. 
     In another aspect the invention is directed a height adjuster featuring a threaded stud accommodated within a bore of a stanchion tube endplug and carrying a fixture for engaging a main spring of the blade. 
     In another aspect the invention is directed to a shock absorber reservoir assembly. 
     In another aspect the invention is directed to use of a gas-filled bladder on the extension side of a shock absorber to provide volume compensation. 
    
    
     The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 a semi-schematic view of a motorcycle. 
     FIGS. 2-5 are front, top, side, and oblique views of a motorcycle fork according to principles of the invention. 
     FIG. 6 is a front cross-sectional view of the fork of FIG. 3, taken along line  6 — 6 . 
     FIG. 7 is a side cross-sectional view of the fork of FIG. 2, taken along line  7 — 7 . 
     FIG. 8 is an enlarged cut-away view of a stanchion tube area of the fork of FIG. 7 with slider tube features omitted to show detail. 
     FIG. 9 is a view of a reservoir according to principles of the invention. 
     FIG. 10 is a partial longitudinal sectional view of the reservoir of FIG. 9, taken along line  10 — 10 . 
     FIG. 11 is a plan view of a valve plate of the reservoir of FIG.  9 . 
     FIG. 12 is a longitudinal cross-sectional view of the plate of FIG. 11, taken along line  12 — 12 . 
     FIG. 13 is a plan view of a valve washer of the reservoir of FIG.  9 . 
     FIG. 14 is a longitudinal cross-sectional view of the washer of FIG. 12, taken along line  14 — 14 . 
     FIG. 15 is a view of a motorcycle rear shock absorber. 
     FIG. 16 is a longitudinal cross-sectional view of the shock absorber of FIG. 15 taken along line  16 — 16 . 
    
    
     Like reference numbers and designations in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     FIG. 1 shows a motorcycle  10  having a frame  11  and front and rear wheels  12 A and  12 B, the latter carried on a suspension arm  13 . A wide variety of motorcycle constructions exit. FIGS. 2-5 are front, top, side, and oblique views of a motorcycle fork assembly  20  in accordance with the invention. The fork assembly  20  includes left and right blades  21 A and  21 B held by upper and lower triple clamps  22 A and  22 B. A central stem  23  extends between the upper and lower clamps offset behind the blades. When installed on the motorcycle, the stem is pivotally carried within a head tube (not shown) of the motorcycle for rotation about a stem axis  24  for steering the motorcycle. Each blade  21 A,  21 B extends along a central longitudinal blade axis  25 A;  25 B from a lower end  26  to an upper end  27 . A lower portion of the blade is formed by a leg  28 A;  28 B (FIG. 6) having a transverse compartment or bore  29 A;  29 B along an axle axis  30  for receiving a front wheel axle  31  of the motorcycle. Above the bore  29 A;  29 B, at least one blade is preferably provided with features  32  (FIG. 6) for mounting a disk brake caliper (the opposite blade optionally lacking such features). Secured to the leg proximate an upper end thereof and extending thereabove along the blade axis is a first tube or slider  33  (FIG.  7 ). Surrounding the first tube in telescoping relation is a second tube or stanchion  34  extending upward to a plug  36  at the blade&#39;s upper end  27 . 
     Centrally depending from a wide upper portion or head  37  (FIG. 8) of the plug  36  which is threaded into the stanchion  34 , a tubular collar  38  bounds a central longitudinal bore or compartment  35  of the plug and has an internally threaded distal end flange  39 . Extending upward into the bore and in threaded engagement with the distal end flange is a height adjustment stud  40  having an upper end or head bearing a hex socket  41  and a lower end  42  secured to the upper end of a push tube or rod  44  by an adapter  43 . In the exemplary embodiment, the adapter  33  includes an upper sleeve portion surrounding the stud lower end  42  and welded thereto through apertures in such sleeve portion. The adapter further includes a lower cylindrical portion depending from a flange which separates it from the sleeve portion. The cylindrical portion is secured the upper end of the push rod  44  via welding, force fit, threaded engagement, or the like. The lower end of the push tube  44  bears a spring top piece or cover/cap  46  (FIG. 7) having a central portion extending upward into the push tube and a lower portion extending radially outward therefrom into contact or near contact with the inner surface of the slider  33 . The central portion of the cover  46  is secured in the push tube lower end via welding, force fit, threaded engagement, or the like. The underside of the cover  46  has an annular shoulder for engaging a main spring  50  normally held in compression between the cover  46  and the upper end of the leg. 
     The blade has a normal range of motion between relatively extended and compressed fully topped-out and fully bottomed-out conditions. An exemplary normal range is about 5 inches (13 cm). Movement beyond the normal range would typically be associated with disassembly of or damage to the blade. Within a midrange of extension of the blade, the main spring  50  bears substantially the entire static load or longitudinal compression force applied to the blade. Preferably throughout the entire normal range of motion, but at least throughout a primary midrange portion (e.g. about 3-4 inches (8-10 cm)) thereof in which the blade reciprocates under typical riding conditions, the cover  46  (or at least a lower spring-engaging portion thereof) remains within the slider  33  so that the main spring  50  remains entirely within the slider. This avoids potential problems associated with the main spring encountering telescoping surfaces and, potentially, being caught on such surfaces (e.g., contacting the telescoping end of the inner of two telescoping tubes) to cause binding. The construction is also compatible with the height adjustment feature described below. 
     The cover  46  includes a central longitudinal passage or aperture  48  which allows fluid communication between the interior of the push tube  44  and a first space  52  defined by that portion of the interior of the slider  33  below the cover  46 . Apertures in the push tube  44  permit communication between its interior and a second space  54  largely defined by an interior of the slider  33  above the cap and an interior of the stanchion  34  within and above an annular piston  60  secured to the upper end of the slider. Details of an exemplary piston  60  are disclosed in the first numbered embodiment in co-pending provisional patent application Ser. No. 60/112,838 entitled “Motorcycle Suspension”. The piston  60  provides fluid valving between the second space  54  identified above and a third space  56  formed by the annular space radially between the tubes  33  and  34  and longitudinally between the piston  60  and a bearing/bushing/seal assembly  62  held within the tube  34  near its lower end. Details of other components such as seals, retainers, and the construction of the piston  60  may be as identified in the first embodiment of the Ser. No. 60/112,838 application. The primary compression valving is provided by the piston  60  between the second and third spaces identified above with some additional flow resistance being presented by the aperture  48  within the cover  46 . In a bottoming-out portion of the normal range of travel (extending to the fully bottomed-out position at the compressed extreme of the blade&#39;s range of travel) the piston  60  engages a bottom-out spring  70  to compress the bottom-out spring between the piston  60  and the underside of the head of the plug  36  to increase resistance to compression above that provided by the main spring  50  alone. In a topping-out portion of the normal range of travel (extending to the fully topped-out position at the extended extreme of the blade&#39;s range of travel) a flange or spring stop  72  secured between the piston  60  and the upper end of the tube  32  engages a top-out spring  74  to compress the top-out spring between the spring stop and the bushing  62  to resist further extension of the blade against any force from the main spring and from inertia. In the exemplary embodiment, the bottoming-out portion is about 1 inch (2.5 cm) while the topping-out portion includes the entire normal range of motion. This topping-out portion is facilitated by providing the top-out spring  74  with a much lower spring constant than the main spring  50 . Much shorter top-out ranges (e.g. 1 inch (2.5 cm)) are possible. 
     Static height adjustment of the blade is achieved by placing a hex key (not shown) into the central compartment  35  of the plug  36  and engaging the hex socket of the stud  40  to rotate the stud  40  to either raise or lower the stud within the compartment. This correspondingly raises or lowers the tube  44  and cover  46  to respectively lower or raise the static position of the stanchion  34  relative to the slider  33  and thus lower or raise the front end of the motorcycle. Advantageously the threaded portion of the stud has a length of about 2 inches (5 cm) to provide a nearly coextensive range of height adjustment. Within an exemplary 5 inch (13 cm) normal range of motion, an exemplary initial static position is 2 inches (5 cm) from the fully topped-out condition. The stud  40  may initially be at its highest position (e.g. with its hex socket just flush or slightly subflush to the upper surface of the plug  36 ). Lowering of the stud via rotation would raise the static position. If a large static load is placed upon the motorcycle or if the main spring sags over time, the static position would drop and the stud may be moved from its highest position sufficiently to restore the static height to a desired value. 
     The foregoing construction can provide a height adjustable front fork which is convenient to manufacture, has a valve providing a large blow-off area and corresponding large flow rate under compression and which is resistant to binding so as to provide smooth operation throughout its range of motion. 
     FIGS. 9-14 show details of a reservoir  120  for an adjustable air shock absorber such as may be featured on the rear suspension of a motorcycle. A reservoir body  122  is preferably unitarily formed as a single shot impact extrusion of an aluminum alloy. Within a main bore of the body encircled by a sidewall portion  123  (FIG.  10 ), there is an internal floating piston  124  carrying an elastomeric piston O-ring  126  and a PTFE/brass bushing  128  in outwardly facing annular pockets. The piston  124  separates the bore into proximal and distal spaces or volumes  129 A and  129 B. The distal end of the reservoir body is sealed by a fixed endcap  130  bearing an elastomeric endcap O-ring  132  and secured in place by a retainer ring  134 . Optionally, the piston  124  may be replaced by a bladder or the like and the endcap  130  may be formed as a plug (as shown) or as a cover. 
     The endcap  130  has an internally threaded bore  136  into which a Schrader valve  137  is mounted to permit selective air pressurization of the distal space  129 B. The proximal space  129 A is normally filled with hydraulic fluid and is communication with the shock absorber (not shown) via a hydraulic line (not shown) threaded into a transverse aperture or port  140 . This can permit mounting of the reservoir remote from the shock absorber. The port  140  is in communication with an annular space  141  separated from the space  129 A by an apertured valve plate  150  having rebound flow orifices  152  and a central orifice through which an apertured bolt  156  extends to threadingly engage a nipple or sleeve  158  depending from an upper web  160  of the body  122 . A valve plate or washer  166  normally blocks the orifices  152 . When the shock absorber is under compression, fluid flows through the port  140  into the annular space  141  and therefrom through lateral apertures  170  in the sleeve  158  and downward through the central aperture in the bolt  156  to the space  129 A causing a downward movement of the piston  124  compressing the air in the space  129 B. Under compression, the washer  166  contacts the plate  150  to seal the orifices  152 . Under rebound (extension), there is a reverse of such flow combined with flow through the orifices  152  as the pressure difference between the spaces  129 A and  141  moves the washer  166  out of engagement with the plate  150  compressing a spring  180 . 
     Low speed compression damping is typically associated with motion of the unsprung motorcycle mass. Exemplary low speed oscillations are in the range of 2 Hz+/−1 Hz. High speed compression damping is typically associated with the unsprung mass and involves typical frequencies of 10 Hz+/−5 Hz. To provide adjustment for low speed compression resistance, a needle  182  is threadingly engaged to the body  122  proximate the base or proximal end of the sleeve  158 . At the upper end of the needle, an adjustment knob  184  is screwed in place and is rotatable by user to rotate the needle  182  and thereby raise and lower the needle. Raising and lowering of the needle varies the degree to which the lower end of the needle blocks flow through the apertures  170  (i.e., the percentage of cross-sectional flow area blocked by the needle, from zero to total) and, thereby, regulates the compression stiffness of the shock absorber. A detent mechanism may include a spring loaded ball  185  in a compartment  186  of a neck portion of the body  122  to allow the knob  184  to be rotated in discrete increments and maintain its position until further adjusted by the user. 
     The exemplary embodiment  120  provides a reservoir assembly which is convenient to manufacture allowing the body  122  to be formed of a single impact extrusion with minor additional machining such as for the port  140 , aperture  170 , compartment  186 , pocket for the ring  134 , and the various threaded areas. Such a manufacture also provides a clean appearance as distinguished from multi-component reservoir bodies. Such a reservoir may be advantageously utilized with a variety of shock absorber constructions and in non-motorcycle applications such as automobiles and bicycles. 
     FIG. 15 shows a shock absorber  200  extending along an axis  201  from an upper clevis rod end  202  to a lower eyelet  204 . The clevis rod and lower eyelet each define apertures carrying associated elastomeric spacer  206  and elastomeric bushing  207  for respectively securing the shock absorber to the frame and the rear suspension arm of the motorcycle. Depending from the clevis rod end  202 , a threaded clevis rod shaft  208  is engaged to an internally threaded bore of a shaft adapter  210  and locked in place via a clevis nut  212  tightened into engagement with a rim at the upper end of the adapter. The clevis nut may be backed off and the clevis rod rotated about the axis  201  relative to the adapter  210  and the nut then retightened to provide a static length adjustment for the shock absorber and thereby a static height adjustment for the rear suspension. Depending from the adapter  210  are a central piston shaft  214  and an external housing tube  216 . Concentrically within the housing tube  216  and extending through an aperture in a web  217  at a lower end of the housing, an inner tube  218  extends upward from the lower eyelet  204 . The upper end of the inner tube  218  carries an assembly  220  surrounding the shaft  224  and acting both as bearing to permit relative longitudinal movement of the shaft and inner tube while maintaining them co-axial and as a seal to prevent escape of hydraulic fluid within the interior of the inner tube  218 . 
     The assembly  220  also includes a flange  222  extending outward toward an interior surface of the housing tube  216  and having an underside engaged to an upper portion of a main spring  224  to compress the main spring between such underside and an upper surface the housing tube flange  217  to resist extension of the shock absorber. At its lower end, the shaft  214  carries a piston assembly  226 . Near its upper end, the shaft  214  carries an elastomeric bottom-out bumper  227 . The piston assembly seals with the internal surface of the inner tube  218  and divides the internal volume of the inner tube into an upper or extension portion  228  and a lower or compression portion  230 . The piston assembly defines appropriate apertures and valving mechanisms to permit flow of hydraulic fluid between the extension and compression portions as the shock absorber is extended and compressed so as to provide appropriate damping. A wide variety of piston assembly structures may be utilized. 
     As the shock absorber is compressed, the combined free volume of the extension and compression portions is decreased by the volume of shaft  214  introduced into the interior of the inner tube  218  by the compression movement. During an extension movement the combined volume is increased by the volume of shaft which exits the interior. Since the hydraulic fluid is essentially incompressible, a volume compensation is provided. This may be done by mixing a gas with the fluid or by providing a reservoir. In the shock absorber  200 , compensation is provided in the form of an annular gas-filled bladder member  240  located on the extension side of the shock absorber within the extension volume  228 . In the exemplary embodiment the bladder member  240  is formed of an annular cylinder of closed cell microcellular urethane foam. Exemplary material is available from Rogers Corporation of Rogers, Connecticut. Upon compression, the gas within the cells is compressed so as to maintain the required free volume for the hydraulic fluid. Upon extension, the gas expands. The presence of the bladder member  240  provides a relatively light extension stroke. Specifically, the piston assembly permits sufficient fluid flow from the extension volume to the compression volume so that the pressure within the extension volume decreases, causing the bladder member to expand, which in turn relieves the pressure decrease and thus the resistance to extension. In the absence of compensation provided by the bladder member, there would be greater resistance to the extension caused by the pressure decrease. 
     To avoid damage to the bladder member  240  upon topping out, a sleeve  242  extends within the bladder member and at its upper end supports a washer  243  which in turn supports an elastomeric top-out bumper  244 . Upon topping out the sleeve  242  transfers compression load from the piston to the bumper and in turn to the assembly  220 , sparing the bladder member  240  all or much of this compressive load which might otherwise be sufficient to rupture the cells. 
     Exemplary material for the clevis rod and the shaft is steel. Exemplary material for the eyelet/inner tube, shaft adapter, and housing tube is aluminum. 
     One or more embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, modifications may be made to accommodate the environment of existing motorcycle or suspension elements to which the principles of the invention are being applied. Accordingly, other embodiments are within the scope of the following claims.