Abstract:
A tire with improved resistance to sidewall damage such as splitting or puncture is provided. More particularly, the present invention provides a tire with tread features positioned along the sidewall in a manner that improves the protection of the sidewall against damage when contacting obstacles during operation of the tire.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a tire with improved resistance to sidewall damage such as splitting or puncture. More particularly, the present invention provides a tire with tread features positioned along the sidewall in a manner that improves the protection of the sidewall against damage when contacting obstacles during operation of the tire. 
     BACKGROUND OF THE INVENTION 
     Operating a tire in aggressive environments such as off road conditions provides challenges in protecting the tire from damage. Obstacles such as rocks, trees, and other features provide threats to the tire not only along the tread region but also along the sidewall. While the tread region is designed to be in contact with the ground surface and is therefore constructed from compositions intended for this purpose, the sidewalls are generally not designed to be ground contacting. Instead, the sidewalls of a tire typically include a relatively thin layer of rubber material that covers certain structural elements, such as e.g., the cords of a tire carcass, which extend between and through the sidewalls of the tire. This rubber material is conventionally created from a composition not designed for ground contact but rather for flexibility so that the sidewalls can withstand the repeated flexing of the tire that occurs as it rotates through the contact patch. In addition, this sidewall rubber is typically not as thick as the tread rubber. As such, the sidewalls generally have less resistance than the tread to splitting or other puncture damage that can occur when the tire is contacted with an obstacle along the ground surface. 
     Certain tires are intended for more rugged applications where encounters with obstacles that may split or otherwise damage the sidewall can be frequent. For example, for recreational and emergency off-road applications, tires may be subjected to repeated contact with obstacles that can split the sidewall and damage or even deflate a pneumatic tire. Of course, for such tires, it is generally desirable to increase their capability to resist sidewall damage such as splitting, puncture, rupture, or other sidewall damaging events caused by contact during tire use. 
     Features can be added along the sidewall to help resist certain sidewall damage. Lugs, blocks, and/or other tread features can be added about the sidewall to protect it from aggression by remaining between a dangerous obstacle and the sidewall as the tire interacts with the obstacle during operation. The addition of features along the sidewall adds material, complexity, and expense to a tire. Such features can also unfavorably reduce the flexibility of the sidewall. Therefore, it is desirable to optimize the size and positioning of such features particularly when not all portions of the sidewall necessarily need protection. Also, such features along the sidewall can significantly alter the appearance of the tire. Consequently, aesthetic concerns play a significant role in determining the shape and location of features added to the sidewall. 
     Accordingly, a tire with improved resistance to sidewall damage from obstacles encountered during tire operation is needed. More particularly, a tire with protective features positioned along the sidewall in a manner that improves resistance to splitting, puncture, and other potential damage would be useful. A tire having such features while also satisfying aesthetic considerations would also be particularly useful. 
     SUMMARY OF THE INVENTION 
     Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention. 
     In one exemplary embodiment, a tire having improved protection against obstacles damaging the sidewall is provided. The tire defines an equator and has tread blocks and tread grooves positioned along a shoulder of the tire. The tire includes a plurality of block-based tread features located along the sidewall of the tire. The block-based tread features are positioned along the tire based upon the radial position of the equator, LPN, and a first area in which an obstacle would move along the sidewall of the tire if the obstacle slipped off a tread block as the tire moved past the obstacle. A plurality of groove-based tread features are located along the sidewall of the tire. The groove-based tread features are positioned along the tire based upon the radial position of LPN, LPG, and a second area in which an obstacle would move along the sidewall of the tire if the obstacle slipped off a tread block as the tire moved past the obstacle. 
     In certain embodiments, the groove-based tread feature and the block-based tread feature each have a thickness in the range of about 3 mm to about 15 mm. The groove-based tread features can be positioned closer to the summit of the tire than the block-based features. The position of the block-based tread feature along the sidewall of the tire may be coextensive with a block-based contact region defined by the equator, LPN, and the first area. Similarly, the position of the groove-based tread feature along the sidewall of the tire may be coextensive with a groove-based contact region defined by the LPN, LPG, and the second area. The radial depth of the groove-based tread feature can extend beyond LPN, especially when the thickness of the groove-based tread feature is less than 3 mm. The radial depth of the block-based tread feature can also extend beyond the equator, especially when the thickness of the block-based tread feature is less than 3 mm. 
     Preferably, in certain embodiments, the distance along the radial direction between the top and the bottom of the groove-based feature is at least 10 mm. Similarly, the distance along the radial direction between the top and the bottom of the block-based feature is preferably at least 10 mm in certain embodiments. 
     The first area and second area can be determined using the following equations: 
             r   =           (       L   o     -     R   ⁢           ⁢   θ       )     2     +     H   o   2                     α   =     θ   +     arctan   ⁢       H   o         L   o     -     R   ⁢           ⁢   θ                   
where:
         R=radius of the tire   θ=the amount of the tire&#39;s rotation   L o =the initial horizontal position of the obstacle P 0  relative to the tire center O   H o =the initial vertical position of the obstacle P 0  relative to the tire center O   r=the radial coordinate of the obstacle   α=the angular coordinate of the obstacle
 
Alternatively, the first area and second area can be determined experimentally. LPN and LPG can be determined experimentally or can be determined by mathematical modeling.
       

     In certain embodiments, the groove-based features and the block-based features are staggered along the circumferential direction of the sidewall. In still other embodiments, the groove-based features and the block-based features may have different thicknesses. 
     In still another exemplary embodiment of the present invention, a tire having improved protection against obstacles damaging the sidewall is provided. The tire has an equator, a summit, and defines radial directions. The tire has tread blocks and tread grooves positioned along a shoulder of the tire. The tire comprises a plurality of block-based tread features located along the sidewall of the tire. The block-based features are positioned radially below respective tread blocks located along the shoulder of the tire. A plurality of groove-based tread features are located along the sidewall of the tire. The groove-based features are positioned radially below respective tread grooves located along the shoulder of the tire. The groove-based tread features are positioned closer to the summit of the tire than the block-based tread features. 
     These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which: 
         FIG. 1  illustrates an exemplary trace along the sidewall of a tire that is represented schematically. 
         FIGS. 2A through 2C  illustrate a sectional views of a tire schematic for purposes described in the specification below. 
         FIG. 3A  is a side view of an exemplary tire showing traces along the sidewall of the tire as well as a circles positioned at the equator, LPN, LPG, and the rim seating location as described below. 
         FIGS. 3B and 3C  are close-up views of a portion of the sidewall of the exemplary tire shown in  FIG. 3A . 
         FIG. 4  illustrates a portion of a representative sidewall for purposes of further describing an exemplary procedure for positioning tread features along the sidewall. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     For purposes of describing the invention, reference now will be made in detail to embodiments and aspects of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, from the teachings disclosed herein, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment, can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
     As used herein, the following terms are defined as follows: 
     Radial refers to directions perpendicular to the axis of rotation of the tire. 
     LPN refers to the radial position at which an obstacle would first contact the sidewall of the tire if the obstacle slipped off an edge of a tread block as the tire rotates along its path after making contact with the obstacle. 
     LPG refers to the radial position at which the obstacle would first contact the sidewall of the tire if the obstacle slipped off an edge of a tread groove as the tire rotates along its path after making contact with the obstacle. 
     Equator refers to the radial location along the sidewall at which the tire is widest as viewed in a cross section taken along a plane perpendicular to the circumferential direction of the tire. 
     Trace refers to the path a point of contact of an obstacle would make along the sidewall of a tire as the tire rotated past, and in a non-deforming contact with, the obstacle. 
     As a tire rolls along a surface during operation, the sidewall may come into contact with an obstacle capable of damaging the sidewall by splitting or puncturing. For purposes of describing the invention, assume that such an obstacle can be represented by a single point of contact that begins along the tread region of the tire and then moves along the tire sidewall as the tire rotates. As the tire rolls past such an obstacle, the point of contact with the obstacle will follow a path—referred to herein as a trace—along the sidewall of the tire. By way of example, assuming that the sidewall is flat and undamaged by contact with the obstacle, this trace can be characterized mathematically by the following equations: 
                     r   =           (       L   o     -     R   ⁢           ⁢   θ       )     2     +     H   o   2           ⁢     
     ⁢     α   =     θ   +     arctan   ⁢       H   o         L   o     -     R   ⁢           ⁢   θ                           (   1   )     &amp;     ⁢           ⁢     (   2   )                 
where:
         R=radius of the tire   θ=the amount of the tire&#39;s rotation   L o =the initial horizontal position of the obstacle P 0  relative to the tire center O   H o =the initial vertical position of the obstacle P 0  relative to the tire center O   r=the radial coordinate of the obstacle   α=the angular coordinate of the obstacle
 
Accordingly, as illustrated in  FIG. 1A , assuming an obstacle initially contacts tire  100  at point P 0  along the tread region  105 , trace T illustrates the path that the obstacle will make along the sidewall  110  of the tire  100  as calculated using equations 1 and 2. Equations 1 and 2 are provided by way of example. Other mathematical models may be used for determining the trace or such can be determined experimentally as well.
       

     One mode of sidewall splitting that can occur is when a tire initially rolls into contact with an obstacle and the tire subsequently slips off the obstacle. For example, as tire  100  encounters an obstacle in its path, initial contact may occur between tread region  105  and the obstacle. However, as tire  100  rotates, the tread region  105  may slip off the obstacle leading to undesired contact with the sidewall  110 . Accordingly, an important step in improving the resistance of sidewall  110  to damage is to determine where the obstacle will make contact with sidewall  110  when such a slip occurs. The location will likely be different depending upon whether the obstacle slips off the edge of a tread block or the edge of a tread groove. 
     Referring now to  FIG. 2A , point N represents the edge of a tread block  160  ( FIG. 3A ) and point G represents the edge of a tread groove  170  ( FIG. 3A ) within tread region  105 . If the obstacle slips off point N (i.e. an edge of a tread block  160 ), then LPN represents the radial position along sidewall  110  at which the obstacle will land or first make contact with sidewall  110 . If the obstacles slips off point G (i.e. an edge of a tread groove  170 ), then LPG represents the radial position along sidewall  110  at which the obstacle will first make contact with sidewall  110 . 
     The radial position of LPG or LPN can be determined mathematically or by experiment. For example,  FIGS. 2B and 2C  provide an exemplary illustration of a numerical method for determining LPN and LPG, respectively. First, beginning with  FIG. 2B , a straight line  10  is drawn that passes through point N and point G. Next, a straight line  20  is constructed tangent to the tire carcass  115  at the location where line  10  passes through carcass  115 . Straight line  30  is then drawn perpendicular to line  20  and through the point where lines  10  and  20  intersect. Length  40  represents the distance along sidewall  110  from point N to line  30 . Length  50  is equal to length  40  and represents the distance of LPN from line  30  along sidewall  110 . Similarly, the position of LPG can be determined as shown in  FIG. 2C . Length  60  represents the distance along sidewall  110  from point G to line  30 . Length  70  is equal to length  60  and represents the distance of LPG from line  30  along the sidewall  110 . 
     The final positions of LPG and LPN as calculated using the above technique may need to be adjusted based on the particular construction of the tire and/or the off-road conditions anticipated during its use. It has been determined that the final positions of LPN and LPG may be located at about −15 mm to +5 mm along sidewall  110  from the positions calculated using the technique shown in  FIGS. 2B and 2C . As previously stated, the positions of LPG and LPN can be determined by other methods as well. For example, experiments can be conducted to determine the actual location along sidewall  110  at which an obstacle makes contact after slipping off tread groove  170  or tread block  160 . 
       FIG. 3A  is a side view of tire  100  with sidewall  110  and tread region  105  shown in more detail. Using the calculation of LPN and LPG, circles  140  and  150  have been superimposed onto sidewall  110 . Circle  140  represents the circumferential position of LPN about the sidewall  110  of tire  100  while circle  150  represents the circumferential position of LPG about the sidewall  110 . LPG&#39;s circle  150  will always be located closer to the tread region  105  than LPN&#39;s circle  140 . Circle  130  represents the position of the equator of tire  110 . Circle  120  represents the location on tire  100  where a rim would be received. Tread region  105  of tire  100  also includes tread blocks  160  and tread grooves  170  along the tire shoulder as shown. Blocks and grooves having shapes and sizes other than as shown in  FIG. 3A  may also be used with the present invention as well. 
     Using equations 1 and 2 above, the traces for an obstacle slipping off the edges of a tread block  160  and a tread groove  170  have been calculated and superimposed onto sidewall  110 . More specifically, as shown in  FIGS. 3A  thru  3 C, trace  180  brackets a tread groove  170  between ends  175  and defines an area within which an obstacle would move if the obstacle started anywhere in the groove  170  as tire  100  rotates into contact with, and then past, the obstacle. Similarly, trace  190  brackets a tread block  160  with ends  165  and defines an area within which an obstacle would move if the obstacle started anywhere on the tread block  160  as the tire  100  rotates into contact with, and then past, the obstacle. More specifically, referring now to  FIG. 3B , if an obstacle slips off of tread groove  170  during operation, the obstacle will move between the curves of groove-based trace  180 . Similarly, referring to  FIG. 3C , if an obstacle slips off of tread block  160  during operation, the obstacle will move between the curves of block-based trace  190 . 
     Accordingly, traces  180  and  190  along with circles  120 ,  130 , and  140  assist in identifying one ore more contact regions of concern for splitting or puncture of sidewall  110  during operation of tire  100 . Consequently, these contact regions represent preferred locations for the consideration of adding protection such as the addition of tread features to sidewall  110 . Aesthetic considerations can also be applied using the identification of these contact regions. 
     For example, referring to  FIG. 3B , groove-based contact region  200  (represented by cross-hatching) denotes a preferred position for adding a tread feature to protect sidewall  110  against an obstacle that slips off of a groove  170 . Contact region  200  is bounded by trace  180 , LPN circle  140 , and LPG circle  150 . The thickness of the tread feature (i.e. the height of the tread feature above the surrounding sidewall  110 ) to be added at contact region  200  is determined by how much improvement in performance is desired. Normally, such a tread feature should be in the range of about 3 mm to about 15 mm in thickness. Thicker features will provide more protection but at increased cost in materials and the addition of weight to the tire. It may also generate excessive heat that may damage the tire during prolonged operations. Thinner features, i.e., less than 3 mm can also be used but it may be desirable to extend the bottom of the tread feature (line b) beyond LPN circle  140  to provide additional protection. Regardless, preferably the distance between top of the tread feature (line a) and the bottom of the tread feature (line b) should be at least about 10 mm along the radial direction and need not be precisely located at circles  140  and  150 , respectively. 
     Similarly, block-based contact region  210  (represented by cross-hatching) in  FIG. 3C  indicates a preferred position for adding a tread feature to protect against an obstacle that slips off of a tread block  160 . Region  210  is bounded by trace  190 , equator circle  130 , and LPN circle  140 . Again, the thickness of the tread feature is preferably in the range of about 3 mm to about 15 mm depending upon the amount of protection desired. Features less than 3 mm in thickness may require moving the bottom of the feature (line B) beyond the equator circle  130  so as to provide additional protection. Preferably the distance between the top of the tread feature (line A) and the bottom of the tread feature (line B) should be at least about 10 mm along the radial direction. 
     Depending upon the relative widths of tread blocks and grooves for a particular tire construction, the addition of tread features as described above may result in overlap. For example, if tread features are positioned coextensive with the contact region  210  for each of the tread blocks  160  on tire  100 , a continuous rib or ring will be formed on sidewall  110 . While such a feature may offer much protection to the sidewall  105 , a solid ring may not be satisfactory from an aesthetic perspective or from the standpoint of mud traction. It may also generate excessive heat that may damage the tire during prolonged operations. Accordingly, using information provided by identifying the contact regions as described above, tread features may be staggered or otherwise shaped and manipulated along the sidewall in order to optimize sidewall protection while also addressing other concerns such as aesthetics, mud traction, and heat generation. In addition, tread features may be positioned coextensive or somewhat offset from the contact regions while still providing sidewall protection based on knowing the location of the anticipated contact regions. 
       FIG. 4  represents a portion of a tire  400  having tread blocks  460  and tread grooves  470 . Also shown is trace  480  based on the edges of groove  470  and trace  490  based on the edges of block  460 . Using the methods described above, groove-based tread features  500  have been positioned radially below grooves  470  to protect sidewall  410  from obstacles slipping off the grooves. Similarly, block-based tread features  510  have been positioned radially below blocks  460  to protect sidewall  410  from obstacles slipping off the blocks. In order to improve aesthetic appeal, features  500  and  510  have been shaped and staggered as shown in  FIG. 4 . Other shapes and orientations may be applied. However, the positioning of such features is informed using the methods described herein. 
     While the present subject matter has been described in detail with respect to specific exemplary embodiments and methods thereof, it will be appreciated that those skilled in the art, upon attaining an understanding of the foregoing may readily produce alterations to, variations of, and equivalents to such embodiments. Accordingly, the scope of the present disclosure is by way of example rather than by way of limitation, and the subject disclosure does not preclude inclusion of such modifications, variations and/or additions to the present subject matter as would be readily apparent to one of ordinary skill in the art.