Abstract:
This invention relates to a hub mounted shock absorber suitable for use in the wheels of in-line skates or other small wheel transportation devices such as scooters, street skis, etc. and to in-line skates utilizing wheels with such hub mounted shock absorbers. The hub mounted shock absorbers include an outer tube with an elastomer, preferably a low durometer elastomer between the outer tube and the axle of the wheel. The elastomer is prefereably sandwiched between the inner and outer tube with the axle passing through the inner tube. Openings may be selectively provided in the outer tube to further reduce the stiffness of the elastomer and flexure or other appropriate mechanism may be included which result in minimum stiffness for the shock absorber in the vertical direction only. A modified hub design to accommodate the hub mounted shock absorber without changing the overall size of the wheel and a novel tire for the wheel to achieve the same objective, and to also increase wheel stiffness are also provided.

Description:
RELATED APPLICATIONS 
     This application claims priority from provisional application No. 60/170,032, filed Dec. 10, 1999. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to shock absorber systems for use in the wheels of inline skates and other small-wheeled transport devices. 
     BACKGROUND OF THE INVENTION 
     While inline skating has enjoyed significant success, with current technology, an almost perfectly smooth pavement is still required to fully enjoy this activity. This has limited inline skating to well-maintained parks and recreational areas. Roads that feel perfectly comfortable to users on cars and bikes leave inline skaters shaken and frustrated. 
     One reason for this problem is that existing inline skates do not contain any shock absorbing system, relying only on the elasticity of the tire on each wheel to perform this function. While a number of shock absorbing systems have been proposed over the years for inline skates, these have involved modifying the skate itself by adding heavy and bulky springs, dampers, and the like to the skate truck or frame. However, none of these systems are currently being commercially used, primarily because the weight and complexity they add to the skate are not offset by the advantages they provide. The reliance on tire resiliency to absorb road variations also is disadvantageous in that it requires the use of tires which have some softness and resiliency, for example a durometer in the 65-75 range. However, such softer tires result in more tire deformation as it contacts the road surface, requiring the user to exert more energy, and thus limiting the speed attainable with the skate. A harder tire, for example a tire with a durometer in the 85-100, range would provide a faster skate, while requiring the use of less energy by the skater. The absence of an effective shock absorber system on inline skates also results in vibration passing into a user&#39;s feet and legs; even on relatively smooth pavements, these vibrations contribute to skater fatigue over time. 
     Problems similar to those described above exist for other transport devices, particularly ones having small wheels similar to those of inline skates. Such transport devices could include scooters, street skis, some skateboards, and the like. 
     A need therefore exists for an improved shock absorbing system for use in inline skates and related transportation devices which does not result in any appreciable increase in either weight or bulk for the device, and is relatively simple and inexpensive, while still being capable of absorbing a substantial portion of road vibration without reliance on the tires of the wheels, so as to facilitate a smoother ride on all surfaces while permitting harder, faster tires to be utilized. 
     SUMMARY OF THE INVENTION 
     In accordance with the above, this invention provides an inline skate or related transportation device having a plurality of wheels, each of which includes a non-rotating hub inside a rotating tire, with the hub for at least one of the wheels having a shock absorber therein. For preferred embodiments, all of the wheels of the skate or other device have the shock absorber either formed or mounted therein. For preferred embodiments, each of the hubs has an axle passing therethrough, and each shock absorber includes an outer tube and an elastomer, preferably a low durometer elastomer, between the outer tube and the axle. The outer tube may have an array of holes formed in at least a portion thereof which the elastomer may partially pass through. The sizes of the holes in the outer tube may be selected to achieve a desired stiffness for the shock absorber. The shock absorber also preferably includes an inner tube through which the axle passes, the elastomer being sandwiched between the inner and outer tubes. 
     For preferred embodiments, the shock absorber includes a mechanism which inhibits movement in rotational degrees of freedom and at least reduces movement in all translational degrees of freedom except vertical, there being a reduced stiffness for the shock absorbers in the vertical degree of freedom. To achieve this objective, the elastomer may be mounted within a flexural mechanism, flexure for such mechanism having minimum stiffness in the vertical direction. A replaceable tire may also be provided on each wheel, which tire is preferably of an ultra-hard material. 
     The invention also includes a wheel for an inline skate or other small wheeled transport device which includes a shock absorber positioned in its hub. The shock absorber may for example include an elastomer, preferably a low durometer elastomer, positioned between an outer tube of the shock absorber and an axial channel of the hub. Holes may be formed in at least a portion of the outer tube, as indicated above, and an inner tube in the axial channel may also be provided, the elastomer being sandwiched between the inner and outer tubes. The shock absorber may also include a mechanism which inhibits movement in rotational degrees of freedom and at least significantly reduces movement in all translational degrees of freedom except vertical, there being a reduced stiffness for the shock absorber in the vertical degree of freedom, the elastomer for example being mounted within a flexure assembly of the type indicated above. The outer tube may also have a shoulder at each end thereof, with a roller bearing being mounted on each shoulder, the hub being attached to the shock absorber through the bearings. The wheel may also include a replaceable tire, which tire preferably has an ultra-hard outer layer of a plastic material over a core of an even harder plastic material. The outer and inner layers of the tire preferably have different appearances so that wear through of the outer layer may be easily seen. The tire may be sufficiently elastic to be fitted over a rotatable rim portion of the wheel, or a two-part rim may be provided along with components for normally holding the two parts together with the tire mounted thereon, the components permitting separation of the parts for tire replacement. 
     The invention also includes a hub mounted shock absorber of the type indicated above which, at a minimum, includes an outer tube with an elastomer, preferably a low durometer elastomer, mounted in the tube and having an axial channel formed therethrough. A hole array may be formed in the outer tube, as indicated above, and an inner tube may also be provided in the axial channel, as may the mechanism indicated above which inhibits movement in rotational degrees of freedom and at least significantly reduces movement in all translational degrees of freedom except vertical. 
     Finally, the invention includes a replaceable tire for an inline skate wheel, or wheel of another small-wheeled transportation device, which tire includes an ultra-hard outer layer of a plastic material over a core of an even harder plastic material, which materials may have a different appearance. 
     The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention as illustrated in the accompanying drawings, common elements having the same reference numeral in each of the drawings. 
    
    
     IN THE DRAWINGS 
     FIG. 1 is a perspective view of an inline skate of a type in which the teachings of this invention might be employed; 
     FIG. 2 is an exploded perspective view of an exemplary prior art wheel used in a skate of the type shown in FIG. 1; 
     FIGS. 3A and 3B are an exploded perspective view and an assembled perspective view, respectively, of a hub mountable shock absorber for a first embodiment of the invention; 
     FIGS. 4A and 4B are an exploded perspective view and an assembled perspective view, respectively, of a shock absorber for a second embodiment of the invention incorporating a flexural mechanism; 
     FIG. 4C is a diagrammatic perspective view of a flexural mechanism suitable for use in the second embodiment of FIGS. 4A and 4B; 
     FIGS. 4D and 4E are diagrammatic representations of a shock absorber utilizing a flexural mechanism of the type shown in FIG. 4A when both unloaded and loaded or deformed, respectively; 
     FIGS. 4F,  4 H,  4 J, and  4 L are diagrammatic representations of four alternative flexural mechanisms in shock absorbers in their unloaded state, and FIGS. 4G,  4 I,  4 K and  4 M are diagrammatic representations, respectively, of the same four shock absorbers when loaded. 
     FIG. 5A is a cutaway perspective view of a first embodiment of a tire suitable for use in practicing the teachings of this invention; 
     FIGS. 5B,  5 C and  5 D are cross-sectional views of the tire shown in FIG.  5 A and of two alternative tire embodiments, respectively; and 
     FIGS. 6A and 6B are exploded perspective views of wheels for a first embodiment of the invention and a second embodiment of the invention, respectively, the wheel in FIG. 6A being shown with flexure hub mounted shock absorber of FIG. 4B, the wheel in FIG. 6B being shown with a non-flexure hub mounted shocker absorber which include the array of damping holes of FIG.  3 B. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows an illustrative inline skate  10  which includes a boot  12  mounted to a frame or trunk  14  containing a track  16  formed by a pair of side rails  18 . A plurality of wheels  20  are mounted in track  16 , four such wheels being shown in FIG.  1 . Each wheel is attached to rails  18  by an axial screw  22  which passes through both suitable openings in rails  18  and through the center or axis of each wheel. As is discussed later, a nut is provided for each screw  22  to hold the corresponding wheel in track  16 , while permitting easy removal of the wheels when required. A standard braking mechanism  24  is also provided for the skate. 
     FIG. 2 shows a wheel  20  for an illustrative existing inline skate, the wheel including a plastic injection molded hub  26  around which urethane rubber tire  28  is molded. The durometer of tire  28  for existing skates can typically vary from 65 A-85 A. A spacer  30  having a pair of shoulders  32  passes through a center channel in hub  26  and has a roller bearing  34  mounted on each shoulder  32 . Axial screw  22  passes through a center channel in spacer  30  and, in conjunction with nut  36 , secures wheel  20  in track  16  in skate frame or trunk  14 . Roller bearings  34  are snugly fitted in hub housing  26  and facilitate the rotation of the hub and tire  28  about a stationary spacer  30  and screw  22 . Wheels  20  may be of several standard diameters, for example 72 mm, 76 mm and 80 mm. 
     As indicated above, the prior art wheel of FIG. 2 relies only on the elasticity of tire  28  to absorb shock. This is disadvantageous for two reasons. First, tire  28  is not an effective shock absorber, limiting the terrain on which the skates can be enjoyably used, and causing vibration from the skates to be applied to the user&#39;s legs, significantly contributing to user fatigue. Second, in order to absorb at least some shock, tire  28  must be formed of a relatively low durometer material, for example a material having a durometer of 65 A-85 A, resulting in greater tire deformation in use and therefore increasing user effort and decreasing optimum skate speed. 
     In accordance with the teachings of this invention, the above problems are overcome by providing a shock absorber which is mountable in a modified hub  26 , the hub mounted shock absorber being designed to absorb significantly more shock than can be absorbed by tires  28 . Further, since tires  28  are no longer required to function as the primary shock absorber for the skate, a harder, higher durometer tire  28  may be utilized. 
     FIGS. 3A and 3B show a hub mounted shock absorber  40  in accordance with a first embodiment of the invention. For this shock absorber, spacer  30  is replaced by a slightly larger outer tube  42  having shoulders  44  formed thereon which perform substantially the same function as the shoulders  32 , namely to support a pair of roller bearings, which roller bearings are substantially the same as the roller bearings  34 , and in particular have balls which are at least as large as those for the bearing  34 , but which have a larger inner diameter so as to be able to snugly fit on shoulders  44 . An inner tube  46  is also provided having an inner diameter sized to permit screw  22  to fit therethrough. An elastomer tube  48  is sandwiched between outer tube  42  and inner tube  46 . Tube  48  is preferably formed of a low durometer elastomer material, for example a material having a durometer of 25 A-45 A; however, while this durometer range for the elastomer of tube  48  is preferable, it is not a limitation on the invention. The portion of outer tube  42  between shoulders  44  has a plurality of holes or openings  50  formed therein, which holes are shown as being circular in the FIGS. 3A and 3B and have a diameter of ⅜″ for an illustrative embodiment. The holes effectively reduce the stiffness of elastomer tube  48  by permitting the elastomer to partially pass through the holes under load. The existence of holes  50 , and the ability of the elastomer of tube  48  to pass or squeeze therethrough, provides additional damping. By choosing the correct diameter/size for the holes  50 , the damping and elasticity of the shock absorber can be controlled. 
     One problem with the shock absorber of FIG. 3A is that it provides reduced stiffness, not only in the vertical direction (the Z direction in FIG.  4 C), but also in the other two lateral directions (X and Y in FIG. 4C) and in the three rotational directions α,β, and φ of FIG.  4 C. The reduced stiffness in all of the lateral and rotational directions other than the vertical Z direction can cause undesirable wobble of the skate wheel. It is therefore desirable that the hub mounted shock absorber  40  be designed so as to provide relatively high stiffness in all rotational directions and added stiffness in all lateral directions except the Z direction, while providing significantly reduced stiffness in the Z or vertical direction. 
     One possible embodiment that incorporates an anti-wobble feature within the shock absorber system is to modify the damper holes  50 . The shape and location of holes  50  may vary and, in particular, holes may be positioned to provide reduced stiffness only in the vertical direction, with greater stiffness in other directions to reduce wobble. As discussed later, such configurations would require a key, flat or other orientation component for the shock absorber. 
     FIGS. 4A-4M illustrate a shock absorber  40 ′ for an alternative embodiment of the invention which also provides this anti-wobble functionality. In particular, in place of inner tube  46 , a flexural spring mechanism  52  is provided, which mechanism includes an outer structure  54  which can be divided into two sections by a pair of slits  56 U,  56 L extending along its length. Flexural mechanism  52  also includes an inner tube  57  which is connected to each section of outer structure  54  by a corresponding flexible wing  58 . The upper and lower spaces  60 U and  60 L, respectively, between wings  58  and adjacent portions of outer structure  54  are filled with a molded elastomer  62  which is preferably of the same low durometer material as elastomer tube  48 . Holes  50  may be provided in outer tube  42 , but if this is done, corresponding holes are also required in outer structure  54  so that the elastomer can pass through corresponding holes in both outer structure  54  and tube  42  to reduce stiffness. Where, as will be discussed shortly, there is relative movement between tube  42  and structure  54 , holes  50  may need to be slightly larger than the holes in structure  54  so as to maintain the alignment. 
     FIGS. 4D,  4 E illustrate the operation of the embodiment shown in FIGS. 4A-4C. For this embodiment, wings  58  provide significant stiffness to movement in the X direction and to rotation in the φ direction about the Z axis. Wings  58  being fixed to the walls of structure  54  also provide significant stiffness against movement in the Y direction, and the fixed relationship between inner tube  57  and outer tube  54  inhibits movement in the β direction around the X axis. Finally, the manner in which the flexure works, as shown in FIGS. 4D-4E provides significant stiffness on the a direction about the X axis. However, when a load is applied which moves the wheel up against its axle, flexure mechanism  52  deforms, with the lower sidewalls of outer tube  54  coming together to close the lower slot  56 L and the upper walls of tube  54  moving apart to enlarge the upper slot  56 U; or, as illustrated in FIG. 4E, slots  56  may be eliminated for the slightly modified embodiment. The reverse occurs for flexural mechanism  52  when a force is applied which would lower the wheel relative to its axle (i.e., a rut is hit in the pavement). To achieve the flexure shown in FIG. 4E, the material of flexural mechanism  52  should be of a plastic, metal or other suitable material having spring-like properties. FIGS. 4F,  4 H,  4 J and  4 L show four alternative flexural mechanisms which might be used in lieu of flexural mechanism  52  with the mechanisms in their unflexed positions, while FIGS. 4G,  4 I,  4 K and  4 M, respectively, show these four flexural mechanisms in their flexed position under load. However, the particular flexural mechanisms shown in the FIGS. 4A-4M are by way of illustration only, and other flexural mechanisms capable of providing substantial stiffness in five dimensions, with controlled reduced stiffness in a single lateral direction could also be utilized. 
     One potential problem with the shock absorber  40 ′ of FIGS. 4A-4M is that the design is no longer axially symmetric, and a feature may be necessary to assure the shock absorber is properly oriented in the wheel so that the reduced stiffness direction is in fact the Z or vertical direction. A variety of key ways or other orientation mechanisms known in the art could be utilized for this function. One example of an orienting mechanism is shown in the FIGS. 4C wherein inner tube  57  has a flat side which mates with a corresponding flat on axle screw  22 . Flats may also be provided on the corresponding openings in rails  18  to assure proper orientation. 
     Since, as indicated earlier, outer tube  42 ,  42 ′ will almost certainly be larger than spacer  30  for a conventional inline skate, a larger bearing  34  is also needed, and thus a larger bore in wheel hub  26 . Thus, while conventional wheels-use a metric bearing with an 8 mm bore, 22 mm outer diameter and a 7 mm thickness, shoulders  44  of the shock absorber will be designed to permit use of a larger commercially available metric bearing, for example one with dimensions of 20 mm bore, 37 mm outer diameter and 9 mm thickness, the increased thickness being a function of available commercial bearings with the required bore size. Commercial bearings having other larger bore sizes could also be utilized. 
     Further, since it is desirable that the overall size of the wheel not change so that the wheel can be used in existing inline skate designs, and can be retrofitted to existing skates, the increased hub size can result in a reduced size for tire  28 . These smaller tires can also be made harder, since they are no longer the main shock absorbing mechanism. 
     One potential drawback with the smaller tires is wear. Even though the harder rubber, whether natural or artificial, or other plastic material utilized for the tire will make the tire more wear resistant, the reduction in the volume of rubber for the tire will reduce the wear life of the wheel. In order to allow the cost of wheels to remain substantially unchanged for the consumer, one option is for the overall wheel design to be changed, with only the tire needing to be replaced when worn, rather than the entire wheel. Thus, the hub can become reusable, as it is not generally damaged by wear or use. 
     The replaceable rubber/plastic tires can be formed in a variety of O-ring like shapes, one such shape being shown in a cutaway perspective view in FIG.  5 A and in the cross-section of FIG.  5 B. Two alternative shapes are shown in cross-sectional views  5 C and  5 D. 
     In order to signal the user that it is time to change the tire on a wheel due to wear, the tire can be manufactured using a two-layer construction, as shown in FIG. 5, with the outer layer  72  being of an ultra hard or stiff rubber or other plastic material, for example a material having a durometer of 85 A-90 A, an inner layer  74 , which does not need to normally contact the surface being ridden on, being of an even harder plastic material, for example a material with a durometer in the 95 A-100 A range. However, these suggested ranges are by way of examples only, and other ranges of hardness/stiffness for the tire layers are also possible, or a single layer tire could be utilized. One advantage of the two-layer tire shown in the Figures is that the layers  72 ,  74  can be formed to have a different appearance, for example being formed of different colors, so that when a tire wears through outer layer  72 , exposure of inner layer  74  is easily seen, alerting the user that a tire change is required. The difference in appearance can result from a different color, hue, texture or other easily discernible difference. 
     The new wheel design with the replaceable tire concept and the shock absorber  40 ,  40 ′ requires some complementary changes in hub design. In addition to enlarging the opening in the center of the hub to accommodate shock absorber  40 ,  40 ′, the hub may need to be designed as either a one-piece hub or a two-piece hub depending on whether the tire used is sufficiently elastic so as to be easily removed from the hub when worn, perhaps by use of a special tool or tools, and a new tire stretched to fit on the hub as a replacement. FIG. 6A illustrates a wheel of this type, including an axial shock absorber unit  40 ′ and a pair of enlarged bearings  34 ′. The hub  26 ′ for this wheel  20 ′ has an enlarged center opening  80 , sized to snugly accommodate shock absorber  40 ′, bearings  34 ′ and a rim over which tire  70  may be stretched to fit. A cut away is shown in tire  70  to illustrate inner layer  74 . 
     However, because of the high durometer rubber/plastic preferably used for tire  70 , the tires will normally be too stiff to be sufficiently stretchable to fit over the rim of hub  26 ′, and will probably be substantially unstretchable. Therefore, a two piece hub as shown in FIG. 6B is normally required. This hub has a main body  82  on which tire  70  is fitted and is held in place by a hub cap  84  attached to main body  82  by hub screws  86 . Once assembled, the hub of FIG. 6B functions substantially the same as that of FIG.  6 A. 
     The embodiments illustrated in FIG.  6 A and FIG. 6B do not suggest that different combinations of the technologies and devices are not possible and have not been developed. For example, the two piece hub is as compatible with a flexural shock absorber  40 ′ as with a non-flexural shock absorber system  40 . Also, while for the embodiment of FIGS. 3A,  3 B, an inner tube  46  is shown, and the use of an inner tube is preferred, this is not a limitation on the invention, and the shock absorber  40  could be designed without such tube. 
     A hub-mounted shock absorber for an inline skate is thus provided which permits enhanced enjoyment and comfort for inline skating, even on less than perfect skating surfaces and which, by facilitating the use of harder/stiffer tires, enhances both skater efficiency and speed. While the discussion above has been with respect to inline skates and wheels for such skates, and this is the currently preferred application for the invention, wheels employing the shock absorber teachings of the invention could be used on other wheeled transportation devices, including, but not limited to, scooters, street skis, some skateboards and the like. Further, while specific shock absorber, wheel and tire designs have been disclosed for implementing this concept, these designs are being provided by way of illustration only and the foregoing in other changes in form and detail may be made in the invention by one skilled in the art while still remaining within the spirit and scope of the invention, which is to be defined only by the appended claims.