Abstract:
A snowshoe of molded plastic material has a tail section with greater flexibility than the main body section, thereby allowing the tail to give and deform as the snowshoe tail is engaged against the terrain during the gait of the user. At the same time, the tail is stiff enough to provide flotation needed when the full weight of the user is on one snowshoe fully engaged against terrain, such as soft snow.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention concerns snowshoes, especially molded plastic or composite snowshoes, and relates to improvements in the comfort and convenience of use of snowshoes. 
         [0002]    Snowshoes are designed to provide enhanced flotation for a person walking over snow and ice surfaces, and to this end the snowshoes place on the user&#39;s foot a structure having a surface area larger than that of the foot. A snowshoe has larger dimensions in both length and width than a person&#39;s foot, and the lengthwise dimension is increased both forward of and behind the user&#39;s foot in order to keep a proper load balance on the snowshoe during use. Thus, the tail of a typical snowshoe extends substantially back from the heel of the user&#39;s foot. For this reason, walking with a snowshoe attached to the foot disrupts the normal gait of the user. 
         [0003]    The snowshoe thus acts as a relatively long extension to the foot. Especially when considering this extension in the rearward direction, the portion of the user&#39;s gait where the heel of the foot would normally contact the ground, and the following motion of the user&#39;s foot and lower body extremities, are greatly affected. The extended length at the rear of the snowshoe comes into contact with the terrain surface earliest, and in a location far to the rear of the user&#39;s normal heel strike. The snowshoe then rotates about this rear point and produces unnatural rotation and leverage against the user&#39;s lower extremities during the portions of the gait cycle that follow, as the snowshoe rotates into full contact with the terrain. 
         [0004]    It is an object of this invention to minimize the negative and unnatural effects presented by the presence of a snowshoe on a user&#39;s foot, and particularly to address issues associated with the extended length to the rear and the effects of the modified heel strike and subsequent gait-related motions. 
         [0005]    The effect of a snowshoe on the natural gait of the user can be minimized by shortening the length of the snowshoe, particularly rear of the boot. This, however, has the negative effect of reducing the flotation area of the shoe, and as noted, proper load balance requires that the design include extensions both fore and aft of the user&#39;s foot. 
         [0006]    Another approach that has been proposed has been to construct the tail of the snowshoe with an upwardly angled or curving shape. An example of this is a Tubbs snowshoe that can be seen on the website tubbssnowshoes.com. In this way the tail of the snowshoe is less disruptive to the gait of the user than in the case of relative flat tail portion of the same length. Although such an upward curve will somewhat decrease the flotation in this portion of the snowshoe, it will not have as negative an effect as shortening the snowshoe. 
       SUMMARY OF THE INVENTION 
       [0007]    In the invention, the tail of the snowshoe is substantially more flexible than the central portion of the snowshoe. In this manner, the snowshoe tail deforms and bends during the heel strike portion of the gait, when the tail of the snowshoe first contacts the ground. With the heel portion bending and accommodating the gait in this way, the user is able to walk in a way that more approaches the user&#39;s normal gait without snowshoes. In addition and as another benefit, the flexibility and bending of the tail reduce the impact load associated with the heel strike portion of the gait, especially on relatively rigid terrain such as ice or crusted snow. 
         [0008]    It is thus a primary object of the invention to provide a substantially more flexible tail in the snowshoe than typical of previous snowshoes, more flexible than the central portion of the snowshoe, so that the snowshoe tail will deform and bend during the heel strike portion of the gait, when the tail of the snowshoe contacts the ground. 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. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a perspective view showing a snowshoe of the invention in use and showing the snowshoe tail flexing. 
           [0010]      FIG. 2  is a bottom plan view of a molded snowshoe body according to the invention. 
           [0011]      FIG. 3  is a perspective view showing the bottom of the snowshoe body. 
           [0012]      FIG. 4  is an elevation view showing the snowshoe of the invention with its tail flexing and showing angularity of the tail with respect to the central section of the snowshoe. 
           [0013]      FIG. 5  is a perspective view showing a portion of the bottom of a snowshoe with a flexible tail pursuant to the invention. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0014]    In the drawings,  FIG. 1  shows a snowshoe  10  having a molded snowshoe body  12  of plastic material supporting a boot binding  14 . The boot binding is secured to the snowshoe in a known manner that permits pivoting of the binding and the attached user&#39;s boot  16  in the pitch direction, which can be via a pivot connection (not specifically shown) at  18 . 
         [0015]    In  FIG. 1  the user is taking a step, and the snowshoe has just been brought into contact with the terrain. The tail  20  of the snowshoe first makes contact with the terrain, and typically just after this has occurred the user has lowered the boot heel  22  against the snowshoe deck as shown. As the user puts his weight through the heel against the snowshoe deck, the tail section  20  of the snowshoe  10  of the invention flexes to accommodate the user&#39;s gait, thus bending the snowshoe tail  20  upwardly in relation to the central section  24  of the snowshoe body. This makes the use of the snowshoe much more comfortable by effectively shortening the rear extension of the snowshoe during this portion of the gait. When the user brings the snowshoe to rest fully against the terrain, however, the tail section  20  still has sufficient stiffness to provide the flotation needed. 
         [0016]      FIGS. 2 and 3  show the underside of the snowshoe body  24 . The tail section  20  preferably is rounded generally as shown, or blunt and somewhat curved. The body  24  is formed of molded plastic material, one example being polypropylene, with flexural modulus of about 1000-1750 MPa (depending on formulation). Another example is nylon, with flexural modulus in the range of about 1000-3000 MPa, depending on the specific nylon and the moisture level. In one preferred form of the invention the entire snowshoe body  24  can be formed of a rather flexible material but with at least a central region or section  26 , and optionally part of a forward or nose section  28 , reinforced with metal rails  30  secured to the bottom side of a snowshoe body. These are traction rails as well, with traction teeth  31  as shown. In addition, the snowshoe body can include integrally formed ridges, i.e. elongated bosses or ribs  32  and  34  as indicated. The ridges  32  are at the edges of the snowshoe and extend or curl downwardly from the deck. The ridges  34  preferably are sinuous as shown, following the metal rails, and there can be a pair of these ridges  34  along each metal rail  30 . The metal rails and integral reinforcing ridges add rigidity to the main body or central section, i.e. the length of the snowshoe body through which the rails extend. In this way at least the central section  26  is relatively stiff in flexure, while the tail section  20  is not reinforced by metal rails and has little or no strengthening via integrally molded features.  FIGS. 2 and 3  show the outer ridges  32  extending somewhat into the tail section but tapering down to zero height before the rear end of the tail, which is a preferred embodiment, but the configuration of the tail can vary so long as the stiffness is as defined herein. In addition, if needed, this tail section  20  can be of thinner material than the stiffer main body portion. Sufficient stiffness must be maintained in the tail section such that when the user stands flat on a level snow surface, the flexural deformation of the tail section are relatively small, and sufficient to significantly compromise the flotation afforded by the snowshoe. 
         [0017]      FIG. 4  is a side elevation view, somewhat schematic, showing the snowshoe body  12  of the invention with a load pressed on the snowshoe by the user following contact of the rear tip  20   a  of the tail portion  20  with the terrain surface. The load applied by the weight of the user is indicated by the arrow  38 . Note that the flexible tail section is that portion of the molded body behind the metal rails  30 , which give the central body portion most of its stiffness. In  FIG. 4 , the snowshoe body is, of course, restrained at the central section  26  by the connection of the binding (not shown in  FIG. 4 ) to the snowshoe body; this prevents the force  38  from simply pushing the central and upper portion of the snowshoe body down flatly against the terrain. Thus, with the force applied approximately at the location of the arrow  38 , the flexible tail section  20  behind that point flexes, bending in a curve, the geometry of which depends on the stiffness along the length of the tail section  20  (i.e. the tail section may vary in strength through its length, as by a tapering thickness or other features). 
         [0018]    The line  40  in  FIG. 4  represents not necessarily the terrain, but a parallel to the snowshoe tail section at the rear tip  20   a . This is a tagent line at the tip  20   a  if the entire profile of the tail section  20  is assumed to be a curve. The line  42  in  FIG. 4  is parallel to the central or main body section  26  of the snowshoe body. Thus, the angle alpha in  FIG. 4  represents the change in angle of the tail section tip  20   a  due to bending by forced contact of the tip  20   a  with the terrain during the user&#39;s gait. In a preferred embodiment of the invention, this angle is at least about 20°, and more preferably in the range of about 30° to 45°. This assumes the user is within the weight range for which the particular snowshoe is designed. 
         [0019]    One model of TSL snowshoe will flex somewhat in the tail when nearly all a user&#39;s weight is pushed down through the heel, with the snowshoe generally in the configuration shown in  FIG. 4 . However, the tail section of the TSL snowshoe is roughly two or three times as stiff as that of the invention, and the bend that forms in the TSL snowshoe actually extends from the center portion of the snowshoe, forward of the heel strike area, back to the tip of the heel. The TSL snowshoe has a fairly uniform stiffness throughout its length, and when forced to bend, the snowshoe body actually bends through a much greater portion of its length than merely the tail. In addition, the geometry of the TSL snowshoe is different, with a tail section that narrows in a sharp taper and has a tab extending back at its rear tip. 
         [0020]    The flexible tail portion  20  may have a length, for example, of about five or six inches in a snowshoe having an overall length of 24 inches. Thus, it may be about 21%-25% of the length of the snowshoe; tail length preferably changes with snowshoe length. More broadly, the tail may occupy a length of about 20% to 30% of the overall snowshoe. The bendability of the tail section  20  can be expressed as a function of bending moment applied to the tail section. In a preferred embodiment the tail section will bend through an angle alpha of at least about 30° with the application of about 200-250 inch pounds (22.6-28.25 newton-meters) to the tail section. This would be the case, for example, if a force at the arrow  38  is about 40-50 pounds (for an approximately 180 pound person) and the tail section  20  is about five inches in length. Approximately commensurate with the above bending characteristics, the tail section should generally have a bending modulus in an approximate range as described above to perform in the manner desired. 
         [0021]    The bendable tail section  20  allows deflection during the heel strike portion of the user&#39;s gait in a manner that reduces the effective length of the heel portion or rear deck of the snowshoe and reduces the impact forces associated with the heel strike against the snowshoe. This results in a lower moment exerting pressure on the user&#39;s knee. Walking with these snowshoes is more comfortable. 
         [0022]    The flexibility of the tail section can be realized in several different ways. One way is to simply mold the tail section in a relatively thin dimension, e.g. approximately 3 mm to 4 mm, with no stiffening elements either integrally molded into the tail section or attached (such as metal rails) to that section. As another example, the softer tail section can be achieved by modifying structural elements molded into the snowshoe body design such that the flexural stiffness in the tail section is greatly reduced. For example, transverse grooves can be provided in sections of the tail structure having significant depth, thus flexibilizing these regions. Another way of forming the flexible tail section is to construct the tail section  20  from a more flexible material than the central section  26 . This option requires either co-molding with different materials, or a separately molded tail section, attached mechanically to the central section, such as by mechanical fasteners, possibly with metal strips extending across the joint. 
         [0023]      FIG. 5  is a bottom perspective view showing a portion of the snowshoe of the invention. The flexible tail section is shown at  20 . Stiffening rails are shown at  30 , with cleats or teeth  45  in vertical walls or flanges  47  for traction. These rails are of an L shaped cross section and have base sides or flanges  46  that provide for attachment of the stiffening rails to the molded snowshoe body  12 , with fasteners  48  such as rivets.  FIG. 5  shows rear cleats  50  and  52  secured to the snowshoe at a position where the user&#39;s heel will strike against the snowshoe deck after the snowshoe tail  20  comes into contact with terrain. Although a single heel cleat could be provided, two spaced apart cleats  50  and  52  are included on this snowshoe. The snowshoe has a boot binding  14 , a portion of which is visible in  FIG. 5 , including a toe cleat structure  54 . The binding pivots about pivot connections  18  on each side, one side being visible in  FIG. 5 . 
         [0024]    The stiffening rails  30  preferably are sinuous in shape, as best seen in  FIGS. 2 ,  3  and  5 . They generally follow the contour of the snowshoe body  12  near the peripheral edge, and may include two reverse curves as shown, i.e. four curves through the length of a rail. In addition the rails  30  curve upwardly as they extend into the nose section  28  as seen in  FIG. 3 . The sinuous shape improves traction. These rails can be formed of stainless steel or a powder coated steel protected from corrosion. In one preferred form the rails are steel, about 1.2 to 1.5 mm thick, with a vertical flange of about 15 to 30 mm and a horizontal flange of about 4 to 18 mm. The horizontal flange can vary in width, wider at fastener points as shown in FIGS.  2 ,  3  and  5 . 
         [0025]    Also, a preferred embodiment of the snowshoe of the invention will have a nominal decking thickness of about 3.5 mm, and a maximum height of about 21 mm from bottom to top at side edges ridges or ribs  32 , in the main body section where the height increases. These ribs preferably enter the tail section as shown, but the thickness of the ribs tapers to zero about midway back into the tail. The stiffness of the tail, i.e. resistance to bending, preferably is about 1300 lb-in 2 to about 2000 lb-in 2 , at least at a point immediately behind the metal rails  30  which begins the tail section. Stiffness preferably lessens somewhat toward the end of the tail. The stiffness (as resistance to bending) of the tail is calculated as EI, where I is a function of dimension of an approximately rectangular cross section (basically bh 3 /12, with b and h representing base dimension and height dimension), in a fourth power (in 4 ), and E is Young&#39;s modulus or modulus of elasticity of a material, in psi. With a molded deck formed of polypropylene of Young&#39;s modulus about 218,000 psi, for example, the stiffness EI at the forward end of the tail is about 1310 pound-in 2 . By comparison the TSL snowshoe mentioned above has a stiffness of about 6550 (essentially constant through the snowshoe length) and an MSR snowshoe has a deck stiffness of about 4200, including in the tail. 
         [0026]    The steel rails  30  greatly stiffen the center region of the snowshoe. There, the stiffness is essentially the stiffness of the metal traction rails plus that of the molded deck material with its molded-in ribs. The stiffness of the molded deck, however, is much less than that of the rails. 
         [0027]    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.