Abstract:
An outsole ( 2 ) for footwear ( 1 ) comprises at least one protrusion ( 4 ) having a portion ( 8 ) configured for supporting the footwear against a ground surface (S). A traction-enhancing element ( 6 ) is connected to the protrusion ( 4 ) and selectively insertable between said portion ( 8 ) and the ground surface (S). The traction-enhancing element is attached to at least a portion of the protrusion and configured for bending between a first position and a second position; wherein the traction-enhancing element in the second position is between said portion and the ground surface. The movement of the traction-enhancing element between the first position and the second position is effected by a movement of the footwear predominantly along the ground surface.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to Norwegian patent application No. 20120984, filed on Sep. 3, 2012, the disclosure of which including the specification, the drawings, and the claims is hereby incorporated by reference in its entirety. 
       FIELD OF THE INVENTION 
       [0002]    This invention relates to traction surfaces. More specifically, the invention concerns a device for controlling the traction of a footwear outsole. 
       BACKGROUND OF THE INVENTION 
       [0003]    There are numerous examples of means and methods of improving the traction of footwear, in order to reduce the hazards associated with walking on sloping and/or slippery surfaces. 
         [0004]    The state of the art includes U.S. Pat. No. 4,160,331 A, describing a shoe having an outsole with a gripping surface. The gripping surface is applied to the outsole in separated, discrete bands within channels in the outsole and comprises a mixture of grit, such as silicon carbide, and an adhesive. The gripping surface is intended to prevent or curtail slipping by the wearer on smooth surfaces, such as ice or snow. 
         [0005]    The state of the art also includes US 2011/0192054 A1, describing a boot having an outsole with embedded traction enhancing studs. Each stud is partially embedded in the carrier portion of the outsole and projects from the carrier portion. 
         [0006]    The state of the art also includes CA 2 535 426 A1, describing an antiskid attachment for footwear. The attachment comprises of a multitude of skid-resisting elements positioned between the shoe outsole and the surface, and flexible linkage used to ensure appropriate positioning of the elements when walking and running. 
         [0007]    The state of the art also includes WO 2011/028114 A1, describing a sports shoe having an outsole provided with a grip enhancing structure and a detector arranged for detecting movement of the shoe. The grip enhancing structure is moveable between an increased gripping state and a decreased gripping state, in that a processor is arranged to move the grip enhancing structure between these states based on detected movements. 
         [0008]    The state of the art also includes US 2012/0066938, which describes shoe outsoles with removable and replaceable gripping pods for athletic or sport shoes. The gripping pods hold a supply of a substance that exhibits tackiness for enhancing friction between the outsole and the any hard floor. The tackiness-enhancing substance may be time-released or discharged from within the shoe sole onto the lower surface(s) of the outsole that make(s) contact with the smooth hard playing surface or may be in response to compression or shear forces acting on the sole during play to prolong the tacky properties and reduce slippage. 
         [0009]    The state of the art also includes GB 2113072 A, describing a flexible sole for use with hiking, running, or walking shoes comprising flexible protrusions extending from a support portion in a direction inclined toward the rear of the shoe. As the shoe is pressed against the ground under the weight of the user, the inclined protrusions flex elastically. As the protrusions flex along their length, the bottom surface of each protrusion in contact with the ground remains fixed relative to the ground due to frictional forces. The protrusions flex by forming a smaller angle with the bottom surface of the support portion. The result is that the support portion of the sole and the shoe attached to the sole move forward an additional distance relative to the point of contact between the protrusions and the ground. 
         [0010]    The state of the art also includes WO 2008/064862 A1, describing a profile structure for a running surface, in particular of a shoe, having at least one profile element which is arranged or can be arranged in the region of an associated depression on the running surface and can be pressed at least partially into the depression counter to elastic restoring forces. When the running surface is loaded or comes into contact with an underlying surface, the profile element is pressed at least partially into the depression and in the process rolls on the underlying surface by way of a rolling surface which is situated outside the depression. A propulsion force is generated in a propulsion direction which is directed substantially parallel to the running surface or to the underlying surface. 
         [0011]    One disadvantage with state of the art traction control devices for footwear is that the traction control devices are active, i.e. in operation, at all times, also when they are not needed. 
         [0012]    The applicant has devised and embodied this invention to overcome these shortcomings and to obtain further advantages. 
       SUMMARY OF THE INVENTION 
       [0013]    The invention is set forth and characterized in the main claim, while the dependent claims describe other characteristics of the invention. 
         [0014]    It is therefore provided an outsole for footwear, comprising at least one protrusion extending from the outsole and having a portion configured for supporting the footwear against a ground surface, characterized by a traction-enhancing element connected to the protrusion and selectively insertable between said portion and the ground surface when the portion is at least partially supported by the ground surface. 
         [0015]    In one embodiment, the traction-enhancing element is attached to at least a portion of the protrusion and configured for bending between a first position and a second position; wherein the traction-enhancing element in the second position is between said portion and the ground surface. In one embodiment, the movement of the traction-enhancing element between the first position and the second position is effected by a movement of the footwear predominantly along the ground surface. 
         [0016]    The traction-enhancing element is connected to the protrusion via an elastic connection, said connection being configured such that the traction-enhancing element returns to the first position when it is not subjected to external loads, the first position representing a state of equilibrium for the traction-enhancing device. 
         [0017]    The traction-enhancing element comprises a first side and a second side, configured such that the first side is generally not in contact with the ground surface when the traction-enhancing element is in the first position, but is at least partially in contact with the ground surface when the traction-enhancing element is in the second position. 
         [0018]    In one embodiment, the first side comprises a friction-enhancing material. The second side is generally flush with said portion when the traction-enhancing element is in the first position. In one embodiment, the traction-enhancing element comprises a lip made of an elastic material. In one embodiment, the material of the protrusion and the material of the lip are similar materials. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    These and other characteristics of the invention will become clear from the following description of preferential forms of embodiment, given as non-restrictive examples, with reference to the attached drawings, wherein: 
           [0020]      FIG. 1  is a schematic side view of a boot having an outsole with a gripping pattern in the form of a plurality of protrusions; 
           [0021]      FIG. 2   a  is plan view of an outsole having a plurality of protrusion, the figure also illustrating the traction enhancers according to the invention; 
           [0022]      FIG. 2   b  is a sectional side view as defined by the section line A-A in  FIG. 2   a;    
           [0023]      FIGS. 3   a - c  are principle sketches of a protrusion having traction enhancers and being supported by a surface, and illustrate the function of the traction enhancers in a static state ( FIG. 3   a ), upward slope ( FIG. 3   b ), and downward slope ( FIG. 3   c ), respectively; 
           [0024]      FIG. 4   a  and  FIG. 4   b  are schematic plan views of an outsole protrusion, illustrating two embodiments of the traction enhancer; 
           [0025]      FIG. 5   a  is a principle sketch of an outsole protrusion, being supported by a surface, the figure showing the traction enhancers in a static, inactive, state; 
           [0026]      FIG. 5   b  shows the outsole protrusion as illustrated in  FIG. 5   a , having been subjected to a movement along the surface, whereby the traction enhancer has been activated; 
           [0027]      FIG. 6  is a sketch of an alternative embodiment of the protrusion and traction enhancer; 
           [0028]      FIGS. 7   a - c  are principle sketches illustrating the traction enhancers when walking on a level surface ( FIG. 7   a ), a downhill slope ( FIG. 7   b ), and an uphill slope ( FIG. 7   c ), respectively; 
           [0029]      FIGS. 8   a  and  8   b  illustrate various outsole patterns; 
           [0030]      FIGS. 9   a - g  illustrate various possible geometries for the traction enhancers; 
           [0031]      FIG. 10   a  is a plan view of another variant of the invented outsole; 
           [0032]      FIG. 10   b  is a section drawing along section line CL-CL in  FIG. 10   a;    
           [0033]      FIG. 11   a  is a section drawing along section line B-B in  FIG. 10   a;    
           [0034]      FIG. 11   b  is a section drawing along section line C-C in  FIG. 10   a;    
           [0035]      FIG. 11   c  is a section drawing along section line D-D in  FIG. 10   a;    
           [0036]      FIG. 11   d  is a section drawing along section line E-E in  FIG. 10   a ; and 
           [0037]      FIG. 11   e  is a section drawing along section line G-G in  FIG. 10   a.    
       
    
    
     DETAILED DESCRIPTION 
       [0038]      FIG. 1  shows a boot  1  having an outsole  2 , and the outsole is furnished with protrusions  4  that support the user&#39;s weight and provide contact with the ground surface S. The term “outsole” generally refers to the bottom of the boot, that is, the part of the sole that comes in contact with ground when the boot is in use. The protrusions  4  may be in the form of ridges, knobs, etc., arranged in a suitable pattern, as are well known in the art. Although the following description uses the term “boot”, the invention shall not be restricted to a boot, but applies to any footwear in general. 
         [0039]    Referring now to  FIGS. 2   a  and  2   b , each protrusion  4  comprises traction-enhancing elements in the form of a “lip”  6  extending around the protrusion&#39;s periphery (illustrated as dotted lines in  FIG. 2   a ). The curved arrows in  FIG. 2   b  illustrate how the lips  6  may be bent down and around to the underside of the protrusion. This is also indicated in  FIGS. 7   a - c . The lip is made of an elastic material (e.g. rubber, thermoplastic polyurethanes (TPU), latex, PVC or any other known outsole material. The lip may be molded together with the protrusion, such that the two form one unitary element, or the lip may be connected (e.g. glued or vulcanized) to the protrusion after the protrusion has been made. 
         [0040]      FIG. 5   a , which is a schematic illustration of one protrusion  4 , shows how the lower surface  7  of the lip  6  is flush with the protrusion&#39;s ground-engaging surface  8 , and also how the lip has a width dimension w and a height dimension h. Typical dimensions for w and h may be in the order of 2 mm, but the invention shall not be limited to any such dimensions. The lip  6  comprises an upper side  12  and a lower side  13 . The lower side  13  typically comprises the lower surface  7 . The upper side  12  is generally not in contact with the ground surface S when the lip is inactive. However, the upper side  12  is at least partially in contact with the ground surface when the lip is bent down and under the protrusion ( FIG. 5   b ). 
         [0041]      FIGS. 4   a  and  4   b  illustrate two possible lip configurations:  FIG. 4   a  shows a plurality of discrete lip sections  6   a  arranged at intervals around the protrusion, while  FIG. 4   b  indicates how one lip  6   b  extends along each side of the protrusion. A number of conceivable lip cross-sections are shown in  FIGS. 9   a - g . Various protrusion patterns are illustrated in  FIGS. 8   a  and  8   b.    
         [0042]    Referring again to  FIG. 5   a , this figure illustrates a walking mode where there is no slipping between the outsole (i.e. each protrusion&#39;s ground-engaging surface  8 ) and the ground surface S. The static friction between the ground-engaging surface  8  and the ground S maintains a stationary (i.e. non-slipping) relationship between the boot and the ground. In this state, the lips  6  are inactive, inasmuch as that they do not carry the weight of the user and contribute little to the static friction between the outsole and the surface. This is the equilibrium position for the lip, i.e. the position which it attains when it is not subjected to external loads or mending moments causing it to deflect. 
         [0043]    In order for the outsole to start sliding (slipping) with respect to the ground, the static friction force must be overcome by an applied force. The maximum possible friction force between the ground-engaging surface and the ground before the boot starts slipping is a product of the coefficient of static friction and the normal force. This may be expressed as: 
         [0000]    
       
      
       f=μ 
       s 
       *F 
       n  
      
       
         
           
             where: f=the maximum possible friction force between the ground-engaging surface  8  and the ground S; 
             μ s =the coefficient of static friction (determined by empirically); 
             F n =the normal force 
           
         
       
     
         [0047]    The invention is based on the fact that the friction exerted by the lips  6  when they are deflected and bent down, underneath the protrusion, act in a direction opposite of the movement of the boot (i.e. the outsole and the protrusion  4 ). This is illustrated by FIG.  5   b . Here, the protrusion  4  has started to slide (indicted by the arrow M), whereby the lip  6  is forced to down and fold underneath the ground-engaging surface  8 . The movement M is induced by a force component in the positive or negative x-direction, and this x-force component may be due to accelerations in the x-direction or/and an inclined surface (uphill or downhill). 
         [0048]      FIG. 3   a  similarly illustrates a static situation on a level surface, where the lips  6  are not activated.  FIGS. 3   b  and  3   c  illustrates a downward and an uphill slope, respectively, where the protrusion  4  starts to move downwards (arrow M), thus activating the “forward” lip  6 , i.e. the lip that is facing towards the direction of motion (M). 
         [0049]    A fundamental principle behind the invention is that the lips  6  are activated when the protrusion  4  starts to slip. 
         [0050]      FIG. 6  illustrates a variant where the protrusion  4 ′ comprises a groove  9 . This enhances lip activation in that the groove allows for an initial rotation of the part of the protrusion where the lip is attached. The transition between the protrusion and the lip preferably has a radius R 2  to avoid stress and strain hot spots and material failure.  FIG. 6  also shows how the lip conveniently may be furnished with an enlarged (“mushroom-shaped”) outer portion  10 , and that the upper side  12  of the lip may comprise a friction material  11  which will come into contact with ground when the lip is activated. A similar friction material  11  is indicated in  FIGS. 9   e - g.    
         [0051]      FIGS. 10   a,b  and  11   a - e  illustrate another variant of the invented outsole. A number of peripheral protrusions  4   a  and central protrusions  4   b  are provided with respective traction-enhancing elements in the form of “lips”  6 ″ extending around the protrusion&#39;s periphery in a manner similar to that described above. 
         [0052]    Referring specifically to  FIG. 11   e , each lip  6 ″ comprises an upper side  12  and a lower side  13 . The upper side  12  is generally not in contact with the ground surface when the lip is inactive. However, the upper side  12  is at least partially in contact with the ground surface when the lip is bent down and under the protrusion ( FIG. 5   b ). The protrusion  4   a  comprises a groove  9  which enhances lip activation in that the groove allows for an initial rotation of the part of the protrusion where the lip is attached. 
         [0053]    Modifications and/or additions can be made to the element as described heretofore, but these shall remain within the field and scope of the invention. 
         [0054]    Although the invention has been described with reference to a protrusion  4  having a rectangular cross-section, as shown in  FIGS. 4   a  and  4   b , it should be understood that the invention is equally applicable to protrusions having non-rectangular cross-sections, e.g. as shown in  FIG. 2 . Circular, elliptical and polygonal cross-sections, etc. are other examples of non-rectangular cross-sections. Examples of such cross-sections are shown in  FIGS. 8   a  and  8   b.