Abstract:
A ski boot molded to be relatively stiff in a lateral direction but independently flexible in the forward-backward direction, characterized by molded elastomeric hinges and corrugations.

Description:
BACKGROUND 
     A ski boot performs better if it is relatively stiff latterally, but has some independent flexibility in a forward-backward direction. Numerous designs are known wherein two separately molded sections are joined by pinned hinges, usually with a common hinge axis that approximately corresponds to the skier&#39;s ankle joints. Means to constrain the forward-backward motion about the hinges may depend on constraining hardware or simply on the way the boot sections are molded so that one section presses into the other. Many other designs do not use hinges, but then additional flexibility in the forward-backward direction usually leads to additional flexibility in the latteral direction. 
     It is the object of this invention to make a ski boot that can be molded and ascembled with minimum expense and hardware, and still retain the advantages of a flexible hinged boot with latteral stiffness. It is a further object to make a boot that is easy to put on and take off, and that will fit a variety of foot shapes without specially shaped liners. 
    
    
     BRIEF DISCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of a ski boot showing the hinges and corrugations. 
     FIG. 2 shows a hinge portion of the ski boot of FIG. 1. 
     FIG. 3 shows a corrugated portion of the ski boot of FIG. 1. 
    
    
     DESCRIPTION OF THE INVENTION 
     In common with many ski boots the subject boot has a foot-holding section and a leg-holding section. As shown in FIG. I, these respective sections, 1 and 2, are uniquely connected by integrally molded elastomeric hinges, 3. These hinges are molded to make them flex along a common axis that approximately coincides with the axis of the skier&#39;s ankle joints. As shown in FIG. 2, a view of a cross section taken nearly horizontally thru the boot at hinge hight, these hinges are relatively thick (see dimension t) in line with this axis (a), preferably as thick or thicker than they are in the horizontal forward-backward dimension (h). This said foreward-backward dimension (h) does not include the thinner molded corrugated section 5 shown extending around the front of the boot from hinge to hinge. The thickness (t) of the hinges in line with the axis (a) provides the boot with the desired latteral stiffness. The desired forward-backward flexibility is dependent on the internal stiffness of the hinges and the stiffness contributed by the molded corrugations 5. 
     In common with most ski boots, means are provided to hold the skier&#39;s foot, heel, and lower leg so they can not move loosely within the boot. However instead of a usual slit front, FIG. I shows how molded corrugations 6 can be provided to make the boot flexible enough to accomodate the width of a foot, and flexible enough to be drawn snugly around the foot by buckle 7. FIG. 3, a view of a section taken nearly vertically thru the foot-holding section, shows another view of the corrugations 6. The buckle 7 is symbolized by arrows in FIG. 3. It is preferred to make the corrugations 6 relatively stiff and to arrange for the buckle 7 to have the leverage and strength to tighten the front of the boot across the skier&#39;s foot. On the other hand, it is more economical to eliminate the need for this buckle 7 if the thickness, shape, and elasticity of corrugations 6 can be set so that the skier can force his foot into the boot and a satisfactory degree of snugness continues to hold the foot. 
     A preferred means for holding the skier&#39;s heel in position is the internal strap 8 with an extension passing through the shell of the boot to an external buckle 9. 
     All of the boot except the buckles, strap, and the rear flexible snow guard 10 can be molded in one piece, but there is an advantage to molding the heel-holding section 4 separately. It facillitates the installation and fastening of one end of strap 8. Moreover, grooves can be molded into section 1 and/or section 4 so that when section 4 is fitted into position in section 1 an internal passageway is properly located for the extension of strap 8 to reach the hole in the shell of the boot. This passageway functions as a guide for the extension of strap 8 and it tends to keep snow and water out of the boot. When section 4 is separately molded it also facillitates the molding of section 1, by making it easier to withdraw the mold from inside section 1. 
     An elastomeric polymer with good physical properties that do not change apreciably when cold is a preferred material of construction. For instance du Pont&#39;s &#34;Adiprene&#34; urethane will remain flexible and tough, and is well suited to make such ski boots. This polymer can be formulated to be relatively hard and stiff as compared to most rubber materials, but it still can be stretched or elongated several times its normal length when cold; therefore it can be considered flexible even though it seems relatively stiff. 
     It will be apparent that for a given polymer formulation a variation in boot shell thickness or shape will affect the stress/strain characteristics or the performance of the boot. Thickness in the hinges contributes to latteral stiffness but has relatively little effect on the forward-backward stiffness. When the boot is flexed forward it is the molded corrugations 5 that are strained the most. These corrugations are shaped to accomodate this strain. As can be seen from FIG. 1, the molded corrugations 5 extend around the front of the boot from hinge to hinge, with the corrugations substantially focusing or pointing toward the axis of the hinges. When the skier leans back the corrugations 5 and all material in front of the hinge axis is stressed and strained in tension, and all material behind the axis is stressed and strained in compression.