Abstract:
A snowshoe having a boot harness assembly includes one or more cam lock type buckles through which webbing straps are tightened. The cam lock buckle allows low friction pulling of the tail end of a strap for tightening, while providing a positive lock against slippage in the opposite direction. A particular configuration of cam lock buckle is disclosed by which friction in tightening the strap is reduced further.

Description:
BACKGROUND OF THE INVENTION 
     This invention concerns snowshoes and the manner in which snowshoes are secured to boots of users. Specifically the invention relates to use of a more effective, efficient and lower friction buckle with webbing straps in a snowshoe harness, and to a special design of buckle for achieving low friction tightening regardless of the environment of use. 
     Snowshoes have some form of harness assembly for securely engaging at least the toe end of a user&#39;s boot, normally also including a strap to extend around the heel. Examples of snowshoe harness assemblies are shown in U.S. Pat. Nos. 5,440,827, 5,687,491, 5,699,630, 5,901,471 and copending application Ser. No. 10,199, filed Jan. 21, 1998. A number of snowshoes have webbing type straps in the harness assemblies, formed usually of woven nylon, polyester or other synthetic fibers. These webbing straps are flat, relatively soft and flexible, and have a width of usually about ¾ inch. Most commonly, a ladder lock type buckle is used for engagement with the webbing straps to tighten the harness over a boot. Ladder lock buckles are common in many different contexts and are based on a type of frictional engagement of the strap, which enters through the bottom of the ladder lock buckle, then passes over a crossbar, doubling back and down under another sharply edged crossbar and extending forward as the tensioned portion of the strap, thus engaging the strap against itself beneath the second crossbar. Other buckles or latches have also been used, such as ratcheting buckles where movement of a lever in one direction advances the toothed strap by one tooth each stroke, and release is effected by an extreme movement of the lever. Such straps are relatively rigid, not webbing straps. The latches are not as quick to use as ladder lock buckles, but greater leverage can be achieved in tensioning the harness. 
     Ladder lock buckles suffer from the problem of high friction. When the tail end of the webbing strap is pulled to tighten the strap by advancing it through the ladder lock buckle, the sharp fold-back of the strap coupled with the usually somewhat ridged or textured surface of the woven strap, the rubbing against the crossbar, and the rubbing of the strap against itself provide considerable friction and require an objectionable degree of pulling force. Accordingly there is a need for a more easily used buckle for webbing straps, one that provides for much lighter pulling force to reach the tension desired in the tension portion of the strap, while also providing for positive locking engagement of the strap in the buckle, preventing slippage. 
     Cam lock buckles are well known in contexts other than snowshoes. Heavy metal cam lock buckles have been used for large straps for cargo restraint on a truck or trailer, and buckles based on the same principle have found many other uses. The cam lock buckles, sometimes known spring lever buckles, have a lever with teeth which engage against the webbing strap at such orientation and in such a manner that the greater the back-pulling force in the tensioned portion of the strap, the more the teeth engage into the strap and thus the more positive becomes the locking engagement. The back-pulling of the strap through tension causes the spring lever to tend to pivot more firmly toward the strap and a cross bar beneath the strap, the principle by which the tension causes the teeth to engage more positively into the strap. Some of these cam lock buckles have a generally nautilus-shaped hub, with varying radius and the teeth located at the area of greatest radius. Typically in these cam lock buckles the strap is doubled back over the same bar toward which the spring lever is biased, causing relatively high friction at this doubling over location, friction to be overcome when the strap is to be tightened. 
     SUMMARY OF THE INVENTION 
     In the invention a snowshoe has a harness with webbing straps, and for tightening the straps and harness on a user&#39;s boot, the strap or straps are fitted with at least one cam lock buckle. 
     The buckle is connected at one end to the harness and has a second end through which passes a webbing strap to be tightened, with the webbing strap being doubled back through the buckle to provide a tail of the strap for gripping and pulling to tighten the tension portion of the strap leading to the buckle. 
     The cam lock buckle or spring lever buckle has a spring loaded pivoted lever with engagement teeth on a lower or strap-facing side or edge positioned to engage against the tail of the webbing strap. The buckle includes a cross bar toward which the teeth of the lever are urged such that the tail of the strap passes between the teeth and the bar. In use of the strap and buckle, the webbing strap tail can be pulled through the second end of the buckle freely, forcing the lever to pivot away from the surface of the strap tail against the spring force while the tensioned portion of the webbing strap is pulled tighter to tighten the harness. When pulling force on the strap tail is discontinued, back-pulling force from the tensioned portion of the strap tends to draw the lever more tightly against the strap tail, biting the teeth into the surface of the strap more firmly and thus positively gripping the webbing strap in the buckle and preventing slipping. 
     In one preferred embodiment the buckle has a direction reversal pin or bar adjacent to and spaced from the spring loaded pivoted lever, between the lever and said one end of the buckle. The webbing strap passes around and over the reversal pin and doubles back such that the strap tail passes between the lever and the cross bar, the reversal pin having a low-friction surface relative to the webbing strap. By this construction, friction in tightening the strap is greatly reduced. 
     In another preferred embodiment the cam lock buckle is simpler, preferably all plastic with a plastic lever pivotally secured to a plastic frame or base. Teeth preferably comprising lateral ridges on the edge of the lever bite into the strap by spring force, engaging more tightly into the strap when the back-pulling force is present. 
     It is thus among the objects of the invention to improve the efficiency and ease of use of strap tightening buckles on snowshoes, as well as to provide a particular configuration of cam lock or spring lever buckle which provides for very low friction use. 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 
     FIG. 1 is a side view showing a snowshoe with a harness assembly and showing the use of a buckle in accordance with the invention. 
     FIG. 2 is a perspective view showing a particular embodiment of the buckle in greater detail, connected to a webbing strap. 
     FIG. 3 is a side elevation view partially in section showing the buckle and strap of FIG.  2 . 
     FIG. 4 is a plan view showing the buckle in accordance with the invention. 
     FIG. 5 is a side view showing another form of buckle according to the invention. 
     FIG. 6 is a side view showing another form of buckle for use with the invention. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 shows a snowshoe  10  of the general type disclosed in patents referenced above. The snowshoe  10  has a harness assembly  12  for securing a user&#39;s boot  14  to the snowshoe, the harness including left and right harness web portions  16  which are to be drawn toward one another for engaging the boot. Webbing straps  20  are used to draw the harness tight. Webbing straps are as defined above, flat flexible straps, usually woven of synthetic fibers but possibly of other non-rigid materials. 
     Typically in conventional harness arrangements the webbing straps would be engaged through ladder lock buckles, of the type having several rungs which the straps would travel over and under in such a way as to create a high friction against back-slippage of the straps. Nonetheless, some such slippage could occur. 
     In the snowshoe shown, a webbing straps  20  passes through buckles  22  of the invention. A first side  24  of the buckle is normally fixed in position, and this can be from a fixed length of webbing strap  25 , which is in turn secured to a part of the harness shell or web  16 , or this first end can be staked directly to the harness shell, as by riveting. At the second end  26  of the buckle, the strap  20  passes through the buckle forming a tail  20   a  of the strap, pulled by the user to tighten the webbing over the boot. A tension portion  20   b  of the strap pulls the harness shells toward one another to engage the boot. 
     FIG. 2 shows the buckle  22  of the invention in perspective. The strap  20  is shown entering the buckle from the bottom side, then passing up and over a direction reversal pin  30  which forms an important feature of this embodiment of the buckle of the invention. The pin, dowel or other crossbar  30 , having a low friction surface relative to the webbing strap, is located between the first and second ends  24  and  26  of the buckle, secured to the buckle&#39;s frame or base  31  and spaced back from a spring loaded locking lever  32  of the buckle. The strap  20  passes over the direction reversal pin or crossbar  30 , then forward through the second end of the buckle, passing between the spring loaded lever  32  and a stationary bar  34  (FIG. 3) against which the lever acts to engage the strap between. FIG. 3 shows the strap in cross section and its relationship to the buckle. FIG. 4 shows the buckle alone. 
     FIGS. 2,  3  and  4  show a buckle  22  construction that provides for direct staking to the harness, rather than providing for connection via a connecting strap  25  as in FIG.  1 . Either type of connection can be used, but FIGS. 2-4 show a hole  35  in the first end  24  of the buckle frame, for direct riveting to a snowshoe harness or other item. 
     As shown particularly in FIG. 3, the buckle  22  of the preferred embodiment has a cam lock engagement with the strap. The lever  32 , which preferably is of molded plastic, is pivoted at an axis comprising a metal pin  36 , and has a hub  38  preferably with a varying radius. One form of such varying radius is a spiral or nautilus shape in cross section, shown in FIG. 3, wherein strap engaging teeth  40  are at a maximum radius on the hub, but the hub radius tapers down smaller in the direction to the left, or clockwise as seen in the drawings. Thus, when the lever  32  is pivoted up, in a counterclockwise direction around the axis  36 , it opens a greater space between the hub  38  and the stationary cross bar  34 , allowing a strap to pass freely through. Such pivoting is against the force of a spring, a portion of which is shown at  45  in FIG. 4, but the strap&#39;s tail  20   a  is easily pulled to release the cam lock because such pulling force has a tendency to rotate the hub and lever in the counterclockwise direction (as viewed in the drawing), and even a small rotational movement will open the gap wider between the hub  38  and the cross bar  34 . 
     As in known cam lock or spring lever type buckles, the teeth  40  preferably are oriented obliquely in the direction of engaging the strap&#39;s surface to resist back-pulling by the tension section  20   b  of the strap, which tension urges the teeth more firmly into the strap, tending to rotate the lever clockwise in FIG.  3 . 
     An important feature of the buckle  22  as noted above, is the strap direction reversal pin or bar  30 . Prior similar cam lock buckles have been made without any such direction reversal pin, with the stationary cross bar  34  at the second end of the buckle being relied upon directly for reversal of the strap and to accept the pulling force of tightening the strap. This cross bar  34  on conventional such buckles typically is a flat, blade-like element, and a webbing strap which has lateral surface grooves o texture, as is typical, experiences a high degree of friction resistance to this pulling of the tail end. The greater the tension, the harder this strap bears against the edge of the cross bar  34 , and thus the greater resistance to tightening. The buckle of the invention overcomes this problem by providing a low friction surface on a pin or bar  30  which is spaced back from the strap engagement lever  32 , thus always providing a smooth transition in reversal of the strap, particularly during pulling of the strap&#39;s tail  20   a  to secure the strap tightly. 
     FIG. 5 shows another embodiment of a cam lock buckle  50 , based on a slightly different principle. The back-pulling tension in the tension portion  20   b  of the strap  20  in this embodiment has a tendency to rotate the buckle&#39;s lever  52  about an axis  53  in a direction (clockwise in FIG. 5) to engage the lever&#39;s teeth  54  more firmly into the strap, as above. In this embodiment, however, a wide and planar array of angled teeth  54  is relied on to engage into the surface of the strap, rather than a varying-radius pivoted hub having teeth on its surface as in FIGS. 2-4. The buckle  50  has comfortable thumb and finger gripping surfaces  56  and  58 . An anchoring strap  60  is shown engaged around a dowel  62  of the buckle. 
     FIG. 6 shows another embodiment of a cam lock buckle  65  which is advantageously used in the snowshoe attachment arrangement of the invention, as a substitute for the cam lock buckle  22  shown in FIGS. 1-4. The cam lock buckle  65  includes a frame or base  66  and a locking lever  68 , both of which preferably are formed from injection molded plastic. The lever  68  is pivoted on the frame  66  via an axis comprising a preferably metal pivot pin  70 , and is biased by a spring (not shown) in the clockwise direction relative to the frame as viewed in the side view of FIG.  6 . 
     In many respects the cam lock buckle  65  is typical of known cam lock buckles, particularly in its manner of operation. The cam lever  68  preferably has several ridges  72  for thumb gripping, and at its opposite end, at least one and preferably about three laterally extending ridges  74  are provided as teeth for engaging against the snowshoe strap  20 . The end of the lever having the ridges  74  is cam-shaped, so that its upper end  76  engages more closely toward a wall or crossbar  78  of the frame  66  than does its lower end  80 , the end of the buckle being seen in dashed lines in FIG.  6 . The strap is thus more and more tightly engaged between the lever  68  and the wall or crossbar  78  of the frame  66  as the tensioned part  20   b  of the strap is pulled more tightly. Conversely, when the strap tail  28   a  is pulled, this rotates the camming lever  68  in the counterclockwise direction, loosening the cam&#39;s force on the strap and allowing the strap tail to be pulled relatively easily. 
     As in other embodiments of buckles described above, the cam lock buckle  65  has a hole  82  in the tail end of the frame or base  66 , for anchoring to the snowshoe webbing or to an anchor strap. 
     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 this preferred embodiment will be apparent to those skilled in the art and may be made without departing from the spirit and scope of the invention.