Patent Publication Number: US-2005121881-A1

Title: Ski core

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
      This application also claims the benefit of Provisional Application No. 60/527,508, filed Dec. 5, 2003, the benefit of which is hereby claimed under 35 U.S.C. § 119. 
    
    
     FIELD OF THE INVENTION  
      The present invention relates to snow skis and, in particular, to snow ski cores having spatially varying material properties.  
     BACKGROUND OF THE INVENTION  
      Snow skiing, including downhill skiing, cross-country skiing, and telemark skiing, is a popular and well-established winter sport in the United States and around the world. In recent years, snowboarding has also become very popular as an option to conventional downhill skiing. The design of skis and snowboards has evolved and continues to evolve to enhance the user&#39;s fun, safety, and capabilities in practicing the sport. For example, the planform shape, length, and edge design of skis have undergone continuing innovation and improvement. Also, the use of modern materials, including polymers and composite materials, has increased the ski artisan&#39;s options for designing skis that are sufficiently strong, flexible, and lightweight.  
      Skis and snowboards, sometimes referred to as gliding boards, are typically constructed with a wood core having a structural outer layer—for example fiberglass—laminated or otherwise attached to the core. Sometimes a synthetic core material may be used rather than wood—for example, a polymeric foam or honeycomb material, composite material, or the like. The structural outer layer may be formed from a reinforcing material—such as an epoxy fiberglass, molded polymer, or metal—and is disposed generally about the core material to achieve a ski that exhibits the desired strength, weight, flexion, and torsion characteristics. The reinforcing material may be formed from other materials, such as graphite, carbon, or the like. The base element or bottom portion of the ski, i.e., the portion that glides on the snow, is typically constructed of a sintered polyethylene material and may be laminated or molded to the bottom of the ski. Edges, typically made of metal such as steel or titanium, are secured to the lateral side edges, approximately coplanar with the bottom surface of the base element.  
      The structural outer layer may comprise upper and lower portions having sidewalls disposed therebetween wherein the upper and lower portions are bonded to the core and sidewalls, or the upper portion of the structural layer may be cap-shaped to include integral sidewalls and attach directly to the lower portion to form a box-beam type structure. The former method is commonly called “sandwich laminated construction”; the latter method is commonly called “cap construction” or “monocoque construction.” Generally, cap construction provides certain aesthetic and structural advantages over sandwich laminated construction. Typically, a protective and/or decorative outer layer—that may be, for example, a transparent polyurethane—is attached over the top of the ski.  
      The performance, ease of use, and the feel of a ski in particular snow conditions are determined by certain physical properties of the ski. The length of a ski, its torsional and flexion properties, its weight and, in particular, its swing weight, its shape, the position and shape of the edges and the like, can all affect the user&#39;s experience using the ski. It will be appreciated that the selection of these various physical parameters involves design tradeoffs. For example, longer skis generally provide greater directional stability and generally provide a more stable gliding surface, but they are generally more difficult to use because they are more unwieldy to maneuver and have greater moment of inertia about the user&#39;s axis, i.e., a greater swing weight. In conventional skis, the swing weight may be reduced by shortening the length of the skis or by making the skis lighter. The length of the skis is important, however, for achieving good directional stability and a comfortable glide over the snow. For given materials, the minimum weight is typically limited by the need to provide sufficient strength and flexion in the ski. The swing weight of skis relates to how much energy or work is required to turn the skis about a pivot point—generally, the user&#39;s foot. It is therefore desirable to have a low swing weight to minimize the work associated with maneuvering the skis.  
      There remains a need for a ski having improved swing weight properties while maintaining desirable length, glide, strength, and flexibility characteristics.  
     SUMMARY OF THE INVENTION  
      A ski generally includes a forward shovel portion, a rearward heel portion, and a middle waist portion. The waist portion includes a binding mechanism for attaching to the user&#39;s boots and directly supports the user. The shovel and heel portions are disposed further away from the user and the pivot axis for the skis and, therefore, the weight in these sections contributes disproportionately to the swing weight of the ski. The present invention is directed to a gliding board, such as a ski and a core therefor, having relatively low-density shovel and heel portions and relatively high-density center sections.  
      In an embodiment of the invention, the core is made from laminated wood sections—for example, falcatta shovel and heel core sections and fir or aspen core sections in the waist portion.  
      In an embodiment of the invention, the core is made with a plurality of elongate members, each member having relatively low-density front and rearward sections and relatively high-density center sections, the elongate members being joined, for example, by bonding.  
      In an embodiment of the invention, the elongate members are formed by joining the low-density sections to the high-density section using finger joints and wherein the finger joints of adjacent elongate members are staggered.  
      In an embodiment of the invention, at least one elongate bamboo stringer is also attached to the elongate wood members to enhance the strength of the core. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:  
       FIG. 1  is a plan view of a ski made in accordance with the present invention;  
       FIG. 2  is a front cross-sectional view of the ski shown in  FIG. 1 , taken along cut  2 - 2 ;  
       FIG. 3  is a plan view of a core blank for the ski shown in  FIG. 1 ; and  
       FIG. 4  is a plan view of an alternate core blank for a ski according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      Refer now to the figures, wherein like numbers indicate like parts throughout the various figures.  FIG. 1  shows a plan view of a snow ski  100  made in accordance with the present invention. The present invention provides a ski having a relatively low swing weight and is therefore particularly suited for snow skis used for backcountry skiing, such as cross-country and telemark skiing. It will be readily appreciated, however, that the present invention may also be utilized for all forms of skiing, including alpine skiing, snowboarding, and the like. The ski  100  shown in  FIG. 1  includes a relatively wide front shovel section  102 , a tapered waist section  104 , and a relatively wide rearward heel section  106 . The waist section  104  is adapted to receive a binding (not shown) for securing a user&#39;s boot to the ski  100 . The tapered planform shown in  FIG. 1  provides well-known performance advantages, particularly for turning. However, other planforms are also known and may alternatively be utilized, including, for example, skis wherein the shovel, waist, and heel sections all share a common, constant width.  
      A front cross-sectional view of the ski  100  through line  2 - 2  of  FIG. 1  is shown in  FIG. 2 . In this embodiment, the ski  100  is formed utilizing a cap construction, including a central core  110 , that is substantially enclosed between a lower structural panel  116  and an upper structural cap  118 . The lower structural panel  116  and upper structural cap  118  may typically be formed from a fiberglass matrix and epoxy. A conventional base element  120 , which may be made from a suitable ski base material such as P-Tex®, is affixed to the ski  100  beneath the lower structural panel  116 . Ski edges  122  are disposed on either side of the ski  100  and may be made from any suitable material, and are commonly made of steel or titanium. A decorative and/or protective layer  124  is affixed to the upper structural cap  1118 , generally laminated thereto.  
      In the present invention, the core  110  of the present invention is made from a plurality of materials to achieve design goals including suitable strength, light weight, and flexibility. In the currently preferred embodiment, the core  110  is made from a plurality of laminated longitudinal members, including laminated wood longitudinal members  112  and a central bamboo member  114 . The outboard wooden members  112  are multi-component or composite members, as discussed below.  
       FIG. 3  shows a plan view of a core blank  130  from which the core  110  shown in  FIG. 2  may be produced. The core blank  130  of  FIG. 3  includes four laminated longitudinal members  112  and an optional central bamboo member  114 . In the disclosed embodiment, each of the laminated longitudinal members  112  may be approximately square in cross-section. The laminated longitudinal members  112  of the disclosed core blank  130  may each include three sections—a forward or shovel portion  132 , a center or waist portion  134 , and a rearward or heel portion  136 . The shovel portions  132  and the heel portions  136  are preferably made from a lighter, less dense wood, such as falcatta. Falcatta is a particularly suitable wood because of its light weight, workability, and tolerance to moisture. The waist portions  134  are preferably made from a relatively sturdier, more dense wood, such as fir or aspen.  
      The shovel portions  132  are joined to the waist portions  134  using a finger joint  140  and a suitable adhesive to form a longitudinal member  112 . Although finger-type joints  140  are currently preferred due to their strength and ease of production, it will be readily appreciated by the artisan that other joining arrangements may alternatively be utilized, including, for example, scarf joints, three-dimensional finger joints, and joints made utilizing joining hardware such as plates, pegs, and the like.  
      The longitudinal members  112  are formed and multiple longitudinal members  112  are placed side-by-side and jointed together, preferably by laminating, to complete a core blank  130 . As shown in  FIG. 3 , an optional bamboo member  114  may be incorporated into the core blank  130 . In the preferred embodiment, a single bamboo member  114  is disposed centrally in the core blank  130  and may be similarly formed with finger joints  140  to achieve the desired length. The bamboo member  114  may alternatively be formed as a single unitary member. It is also contemplated that more than one bamboo member  114  may be utilized—for example, narrow bamboo members may be interposed between each of the longitudinal members  112 .  
      The finger joints  140  may be staged or staggered as shown in  FIG. 3 . The staggering may be conveniently accomplished by merely shifting adjacent longitudinal members  112  longitudinally to achieve a desired staggering. Alternatively, the various longitudinal members  112  may be formed with different finger joint  140  locations and assembled to achieve a desired layout of staggered joints. It will be appreciated that staggering the finger joints  140  such that portions of the more dense waist portions  134  overlap portions of the less dense shovel portions  132  and heel portions  136  will produce a more gradual longitudinal variation in the aggregate material properties, such as the flexibility and strength of the resulting core  10 . Clearly, the length and position of the relatively dense waist portions  134  are strategically selected to achieve the desired strength for the load-carrying portions of the ski  100 .  
      The broken line  150  shown in  FIG. 3  on the core blank  130  is an exemplary outline of a ski core  110  that may be cut from the core blank  130 . It will be appreciated that the denser waist portions  134  are located near the center of the ski  100 —the portion of the ski that must directly support the user&#39;s weight. The lighter, less dense shovel portions  132  and heel portions  136  are disposed at locations of the ski  100  that are furthest away from the user. Therefore, the overall weight of the ski may be reduced by utilizing a less dense core material for portions of the core  110 . It will be readily apparent to the artisan that by using a less dense material at the ends of the ski, the swing weight of the ski is preferentially reduced, thereby reducing the torque that must be applied by a user to rotate the ski  100  during use.  
      It will also be appreciated that the optional bamboo section  114  increases the overall strength of the core  110  and therefore the ski  100 . In particular, bamboo has a very good strength-to-weight ratio that is similar to that of steel. The bamboo section  114 , therefore, will enhance the responsiveness of the ski  100  and its ability to withstand the forces exerted during use, and may permit the upper structural cap  118  and lower structural panel  116  to be of lighter construction. In particular, the bamboo section  114  advantageously provides additional support for the relatively low-density portions  132 ,  136  of the core  130 .  
      A plan view of an alternative ski core blank  230  is shown in  FIG. 4 , wherein a shovel portion  232 , waist portion  234 , and a heel portion  236  are each formed as unitary sections that are joined together with finger joints  240 . The shovel portion  232  and heel portion  236  are preferably formed from a relatively less dense material, such as a low-density wood or foam, and the waist portion  234  is formed from a relatively high-density material such as a higher-density wood or foam. In this embodiment, there is no reinforcing bamboo section and the fabrication step of joining separate elongate portions may be eliminated. It will also be appreciated that, although the finger joints  240  are shown as transverse and perpendicular to the longitudinal axis of the blank, the finger joints  240  may be alternatively shaped and/or oriented. For example, the finger joints  240  may be angled or cut along a generally V-shaped profile. Of course, the core blank  230  may alternatively be sectioned down the middle and a bamboo member or other reinforcing member interposed therebetween.  
      Although the preferred embodiment is shown in the context of a ski made using cap construction techniques, the invention is equally applicable to other ski construction techniques, such as sandwich laminated construction. Alternatively, the invention may be practiced by first constructing the structural box beam comprising the lower structural panel  116  and upper structural cap  118  ( FIG. 2 ) and injecting different density foams to form the waist, heel, and shovel core portions in situ, allowing the foams to set.  
      It will also be appreciated by one skilled in the art that other suitable materials may be used to form a ski core having a relatively higher-density waist section and relatively lower-density heel and/or shovel sections. For example, a variety of polymeric foams are known in the art that are suitable for ski cores. It is contemplated by the present invention, for example, that the ski core may be formed from one or more polymeric foams, such as polyurethane foam or a phenolic foam, and wherein the shovel and heel sections of the core are made (at least in part) from a lower-density foam and the waist section of the core is made from a higher-density foam or, alternatively, that portions of the ski core may be formed in whole or in part from relatively low-density foam materials and the waist section formed from a relatively dense wood.  
      It will be readily appreciated that, although the preferred embodiments discussed above utilizes a less dense core material for both the shovel portion  132  and the heel portion  136  of the ski  100 , it is contemplated by the present invention that alternatively, only the shovel portion  132  or only the heel portion  136  may be constructed utilizing the lower-density material, or that the shovel portion  132  may include a low-density material that is different from a low-density material used for the heel portion  136 .  
      Similarly, it is contemplated that the reinforcing bamboo center member  114  ( FIG. 3 ) alternatively may be made from a different material having desirable strength, flexibility, and weight properties, including, for example, a metal member or a denser wood member.  
      Referring again to  FIG. 2 , it will be apparent that the core  110  may be produced by forming a plurality of variable-density, elongate members  112  by joining a section of relatively low-density first material, such as shovel portion  132  ( FIG. 3 ), to the front of a section of relatively high-density second material, such as waist portion  134 , and joining another section of the relatively low-density first material, such as heel portion  136 , to the back of the section of the waist portion  134 , then forming a core blank  130  by laminating the plurality of variable-density, elongate members  112  together. The core  110  is then formed by cutting or otherwise shaping the core blank  130  to a desired core shape. The reinforcing elongate bamboo member  114  is preferably also included in the core blank  130 , as shown.  
      While the preferred embodiment of the invention has been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.