Patent Application
20100132225
This invention relates to the field of snowshoes, and in particular snowshoes constructed of injection or compression molded materials such as polymers or composites.
A number of snowshoes in the commercial market place are made by injection molding of polymers. These snowshoes typically consist of a molded deck, which provides a surface for flotation on the snow, a surface for attaching traction elements to the bottom, and a structure to which a binding can be attached to hold the shoe or boot of the user. The deck of a snowshoe in this category usually is of injection molded plastic of thickness approximately 3-4 mm. Alternately the deck could consist of a fiber reinforced composite of appropriate thickness. Since snowshoes of this design do not rely on a peripheral structural frame for any of the structure of the snowshoe, the deck itself is typically rather rigid (flexural rigidity) so that the structure can support the flotation loads required by the snowshoe and the concentrated load inputs from the attachment to the user's foot, as well as supporting traction elements normally affixed to the snowshoe structure.
The molded snowshoe provides a surface in the area of the user's heel or rear portion of the foot on which the foot or heel can rest when bearing weight.
Materials from which molded snowshoes are produced are usually polymers, or reinforced polymers with moduli of elasticity of approximately 350,000 or higher.
The molded plastic snowshoes have exhibited some problems, primarily due to the stiffness and hardness of the deck. One issue has been noise; the molded snowshoe presents a relatively hard surface against which the heel of the user strikes upon contact with the terrain surface. This produces a sharp tapping noise with each step. This hard impact with each step also tends to be uncomfortable. Another problem is with traction. The typical molded snowshoe provides an essentially rigid support structure for any traction elements mounted on the underside of the snowshoe. This rigidity does not allow preferential pressure to be applied to the traction elements through direct weighting of the snowshoe at the point of the traction elements, allowing virtually no deformation of the snowshoe structure for adaptation to the terrain by directing force through those traction elements where it is needed. On uneven terrain, traction elements such as a heel cleat mounted on the deck beneath the user's heel may not come into any engaging contact with the snow or ice.
In the prior art, traditional snowshoes formed of wood frames and rawhide lacing for a decking surface provide a structure that has a good inherent level of sound deadening, since there was no heel strike on a hard surface. Similarly, snowshoes having frames formed of aluminum tubing supporting a stretched flexible decking avoid the situation of a sharp heel strike against a rigid surface, but these snowshoes can still exhibit a certain inherent level of noise particularly as the aluminum frame drags, due to the relatively low damping and the mass and modulus of electricity of the aluminum used for the frame. In addition, the decking material selected for an aluminum framed snowshoe further influences the noise generated by the shoe, with some decking materials providing less sound transmission and more sound dampening than others.
The difficult problem arises with conventional molded snowshoes, as outlined above, which are comprised in most of their area by polymeric materials that are hard and relatively rigid during use. These materials will generate a rather high level of noise when impacted by the boot heel and have limited sound damping characteristics, as well as having the comfort and traction stiffness problems outlined above.
The present invention addresses these problems as described below.
In the current invention a molded plastic or composite snowshoe has an open area at the vicinity of the heel strike, with a soft, pliable heel strike insert across this area. This material preferably supports a heel cleat at the bottom side, directly below the position of heel strike. The material in the soft region is one that is at or above its glass transition temperature during use, such as an elastomer. This dampens the sound and reduces sound transmission as compared to a conventional molded snowshoe.
The impact forces of the user's boot striking the deck of the snowshoe is determined by the materials and construction of the snowshoe. As noted above, traditional wood frame snowshoes with rawhide lacing provide a platform for the heel to strike with some degree of compliance due to this construction. This compliance reduces the impact forces compared to a rigid surfaces. Similarly, aluminum frame snowshoes with stretched, suspended plastic film or plastic coated fabric also provide a surface with some compliance, reducing the magnitude of impact loads that result when the user's boot contacts the snowshoe.
However, the category of snowshoes formed of molded plastic or composite materials is very different. The molded plastic structure is far more rigid, particularly in the region under the foot, than either of the previous constructions described. The typical construction of molded snowshoes employs materials having moduli of elasticity of around 350,000 psi or greater, in thicknesses of usually about 3 to 4 mm, resulting in a relatively rigid structure, and in particular, rigid against yielding distortion in the vertical direction in the region where the user's boot contacts the upper surface of the snowshoe. The invention solves this problem by providing a soft and flexible material, which may be an elastomeric material, across the open heel area in the region of contact from the heel of the user's boot. In this way the invention achieves the goal of combining the advantages of the molded plastic snowshoe with aspects of noise reduction, comfort and terrain conforming ability which are inherent in the previous types of construction outlined above.
In further explanation, traction for snowshoes on snow and ice surfaces is typically achieved by placing elements having shapes (e.g. a sharp blade like shape with teeth) suited for digging into the snow or ice surface on the lower side of the snowshoe in areas that contact the snow or ice. These elements can be mounted in various locations and can consist of various materials and shapes. The snowshoe's binding typically has a cleat or traction element, mounted under the ball or toe area of the foot. To generate traction, it is necessary to apply pressure to these elements so they can penetrate the surface of the snow or ice. It is known that traction elements can be arranged in portions of the snowshoe that are part of a rigid structure, or they can be located on a relatively flexible support structure such as on the underside of a coated fabric deck on certain constructions of snowshoes (as in U.S. Pat. No. 6,006,453, for example), or on the underside of a binding that is suspended from the snowshoe with various binding suspension systems that are currently employed in the field. An advantage of locating traction on a portion of the structure that is non-rigid with respect to the overall snowshoe structure is that the traction element can have pressure selectively applied to it by direct pressure on top of the snowshoe in the general location where this traction is located. However, the construction of molded snowshoes is such that the structure of the shoe is characterized by one relatively rigid plate or grid structure which precludes the mounting of traction in an area having flexibility. Thus the advantage described above of achieving enhanced traction by the application of pressure generally above the traction element cannot be achieved. The present invention overcomes this limitation by the inclusion of the soft region to which traction elements can be mounted, thus achieving the advantages of traction elements with preferential pressure application.
It is thus among the objects of the invention to combine the advantages of the plastic molded snowshoe with a soft strike feature which reduces noise, increases comfort and increases engagement with the terrain by traction elements. These and other objects, advantages and features of the invention will be apparent from the following description of a preferred embodiment, considered along with the accompanying drawings.
In the particular embodiment shown in
The soft strike insert 22 in one preferred form is injection molded of polyurethane, an elastomeric polymer, and is at or above its glass transition temperature in the environment of anticipated use (as contrasted to the molded body, which operates below its glass transition temperature). Alternative materials are natural rubber, styrene block copolymer elastomer, neoprene, and fabric coated neoprene, as well as other suitable elastomers. The insert may have a thickness range of about 2-4 mm depending on shape. The insert preferably is of durometer about 85 A, or a range of about 70 A to 85 A. This provides for elasticity, with the proper amount of softness and “give” when engaged by the user's shoe or boot (boot is used to mean either shoe or boot herein), and provides good sound damping. The insert 22 is located in the snowshoe generally where the heel and rear half to two-thirds of the user's boot will contact and rest on the upper surface of the snowshoe.
In a preferred embodiment the soft heel insert will deflect down relative to the snowshoe body at least about one-half inch when used by a person of about 160 pounds or more.
Also seen in
The above described preferred embodiments are intended to illustrate the principles of the invention, but not to limit its scope. Other embodiments and variations to these preferred embodiments will be apparent to those skilled in the art and may be made without departing from the spirit and scope of the invention as defined in the following claims.
