Abstract:
A method of forming a tire includes a) forming a carcass, the carcass comprising at least one carcass reinforcing ply, a pair of opposing sidewalls, and a pair of bead portions, b) placing a belt structure on the carcass, c) forming a tread stock, d) placing the tread stock on the belt structure, and e) curing the tire in a mold wherein the mold has at least one rib to form a groove on the radially outer surface of the tire. A tube is placed adjacent to or within the tread stock prior to the curing the tire, wherein the tube creates a buried groove in the cured tire. After wear of the tire tread to a preset level, the tube is exposed and opened during further wear to create increased grooving in the tread after the tire has experienced some tire wear.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a method of forming a pneumatic tire, and more particularly to forming a pneumatic tire wherein the tread is configured to provide a different tread pattern as the tire is worn.  
       BACKGROUND OF THE INVENTION  
       [0002]     Tire tread patterns are provided with numerous elements such as ribs and blocks, the elements being separated by circumferential and/or transverse grooves. The grooves provide means for water evacuation and form the biting edges of the tread elements.  
         [0003]     When a tire is new, the tread has a maximum tread height. This initial height may vary depending upon the intended use of the tire; a winter tire has an increased tread depth in comparison to an all season tire. Regardless of the initial tread depth, when the tire is new, the tread elements have an initial stiffness. The actual stiffness of the tread elements is dictated by the block size, shape, the presence of any siping, and the tread compound. As the tread is worn, the block height decreases while the tread element stiffness increases. As the tread stiffness increases, some desired tire characteristics, such as wet skid and wet handling, decrease. Hydroplaning characteristics also decrease with increased tread wear due to the reduced groove volume. It would be desirable, then, to better maintain a tire&#39;s performance characteristics as the tire wears.  
         [0004]     U.S. Pat. No. 6,408,910 discloses a method of manufacturing a tire to maintain a desired groove volume wherein the tire is manufactured with molds that create submerged grooves that appear when the tread is worn. However, such a tire is difficult to manufacture due to the necessity of removing the molds that create the submerged grooves, and use of this method is limited to forming only submerged grooves that contact the tread edges or open into grooves.  
       SUMMARY OF THE INVENTION  
       [0005]     Disclosed herein is a method of forming a pneumatic tire. The tire is designed to have a variable tread pattern, the tread pattern changing with wear, to achieve similar tread performance for the tire when both new and worn. The changing pattern optimizes the worn tire performance in an attempt to maintain the tire&#39;s wet performance characteristics.  
         [0006]     Disclosed herein is a method of manufacturing a tire. The tire has a carcass, a belt structure, and a tread. The tread has an evolving tread configuration wherein the tread configuration varies at different depths of the tread. The steps to manufacture the tire include a) forming a carcass, the carcass comprising at least one carcass reinforcing ply, a pair of opposing sidewalls, and a pair of opposing bead portions, b) placing a belt structure on the radially outer surface of the carcass, c) forming a tread stock, the tread stock having two opposing surfaces parallel to the length of the tread stock, d) placing the tread stock on the radially outer side of the belt structure, and e) curing the tire in a mold wherein the mold has at least one rib to form a groove on the radially outer surface of the tire. In accordance with the invention, a tube is placed adjacent to or within the tread stock prior to the curing the tire, wherein the tube creates a buried groove in the cured tire. After wear of the tire tread to a preset level, the tube is exposed and opened during further wear to create increased grooving in the tread after the tire has experienced some tire wear.  
         [0007]     In one aspect of the disclosed method, the tread stock is formed by extrusion and at least one groove is formed in the tread stock into which the tube is placed. The formed groove may extend along the longitudinal length of the stock, or it may be transverse to the longitudinal length of the tread stock. The formed groove may be continuous or it may be a discontinuous, short length groove or series of discontinuous short length grooves. For such a grooved extruded tread stock, the groove formed in the tread stock prior to curing is preferably not coincident with any groove formed on the radially outer surface of the cured tire.  
         [0008]     In another aspect of the invention, the tube placed in or adjacent to the tread is formed of a material that is not destroyed during vulcanization of the tire. The tube may be a continuous ring shaped tube extending the full circumference of the tire, a preformed open-ended tube of any length or at least one flexible cylinder of any length. The tube preferably has a thickness in the range of 0.10 to 5 mm. The tube may be formed from either a vinyl copolymer or a thermoplastic material. The tube may also be provided with a fill material that is released when the tube material is worn away during tread wear.  
         [0009]     In another aspect of the invention, the tube may have a preformed shape. Such a preformed shape may be selected from the group consisting of circular, elliptical, a two-dimensional curvilinear configuration, square, rectangular, trapezoidal, tetragonal, pentagonal, hexagonal, and polygonal.  
         [0010]     In another aspect of the manufacturing method, during curing of the tire, the tube is held in the desired position by needles extending from a tread mold surface, mold ribs extending from the tread mold surface, or sipe blades extending from the tread mold surface.  
         [0011]     In another aspect of the manufacturing method, an additional step of placing a cushion rubber on the belt structure prior to placing the tread stock on the radially outer surface of the belt structure may be performed.  
         [0012]     Also disclosed herein is a tire made by the disclosed manufacturing method and its variations.  
         [0013]     The disclosed tire has a carcass, a belt structure, and a tread. The tread has either at least one surface circumferential groove or at least one surface lateral groove, and an evolving tread configuration wherein the tread configuration varies at different depths of the tread. The tread has a buried groove, the buried groove not communicating with any surface groove. The tread is formed of at least one rubber matrix that is all cured at the same time and in the same mold as the remainder of the tire.  
         [0000]     Definitions  
         [0014]     The following definitions are controlling for the disclosed invention.  
         [0015]     “Annular” means formed like a ring.  
         [0016]     “Evolving tread configuration” means a tread configuration that varies at different depths, or wear levels, of the tread.  
         [0017]     “Inner” means toward the inside of the tire and “outer” means toward its exterior.  
         [0018]     “Lateral” means an axial direction.  
         [0019]     “Nonskid” means the depth of grooves in a tire tread.  
         [0020]     “Radial” and “radially” are used to mean directions radially toward or away from the axis of rotation of the tire.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]     The invention will be described by way of example and with reference to the accompanying drawings in which:  
         [0022]      FIG. 1  is a tire formed in accordance with the invention;  
         [0023]      FIG. 2  is an unworn tire tread;  
         [0024]      FIG. 3  is the tread of  FIG. 2 , following a defined amount of wear;  
         [0025]      FIG. 4  is a cross sectional view of a tread stock;  
         [0026]      FIGS. 5A-5B  are cross sectional view of tread stocks; and  
         [0027]      FIGS. 6-9  are alternative views of tread stocks. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0028]     The following language is of the best presently contemplated mode or modes of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims.  
         [0029]      FIG. 1  is a cross-sectional view of a pneumatic tire  10  that has been formed in accordance with the invention. The tire  10  has a carcass structure  12  comprising an innerliner  14 , at least one reinforcing ply  16  extending between a pair of opposing bead portions  18  and a pair of opposing sidewalls  20 . Radially outward of the carcass  12  is a belt package  22 . The belt package  22  conventionally has at least two plies  24  of crossed reinforcing cords. Radially outward of the crossed cord plies  24 , and part of the belt package  22 , there may be an overlay ply  26  of cords inclined substantially parallel to the circumferential direction of the tire  10 .  
         [0030]     A tire tread  28 , located on the radially outer surface of a tire  1 , is characteristically defined by a plurality of tread elements  30  in the form of blocks and/or ribs. Such tread elements  30  are formed by circumferentially extending and/or laterally extending grooves  32 . Located inward of the tread surface is at least one buried groove  34 . The buried groove  34  preferably has at least some portion extending in the circumferential direction. Additionally, preferably the buried groove  34 , when the tread  4  is at an unworn stage, does not communicate with any surface grooves  32  in the tread, i.e. it is isolated within a tread element  30  of the tire tread  28 ; a surface groove being defined as a groove that is present at the tread surface  36  when the tire  10  is at an unworn stage.  
         [0031]     In the tread of  FIG. 2 , at the unworn stage, the tread is defined by four circumferentially extending grooves, dividing the tread into five rows of tread elements. The tread element row  40  located on the tread centerline CL is a rib defined by circumferential grooves  42 ,  44 . The tread element rows  46 ,  48  bordering the center tread element row  40  are a plurality of blocks  50  formed by the circumferential rows  42 ,  44 ,  52 ,  54  and lateral grooves  56 .  
         [0032]     Axially outward of the outer circumferential rows  52 ,  54  are the axially outermost tread element rows  58 ,  60 . These rows  58 ,  60  have a plurality of quasi blocks  62 . The blocks  62  are formed by the circumferential grooves  52 ,  54  and inclined lateral grooves  64 ; however, the blocks  62  are connected at the axially inner edges by a connecting element  66 . The blocks  50 ,  62  and the connecting element  66  are also provided with sipes  68  to increase the number of biting edges in the tread.  
         [0033]     The tread of  FIG. 3  is the tread of  FIG. 2  after approximately 30 percent wear. The worn tread has an additional circumferential groove  34  that now divides the center tread element row  40  into two smaller width rows  70 ,  72 . The presence of the exposed groove  34  after a period of wear increases the wet performance characteristics of the tire. The tread has an evolving tread configuration wherein the tread configuration varies at different depths, or wear levels, of the tread. The tread with such a later exposed groove may be formed as described below.  
         [0034]     In a two-stage tire building process, the tire carcass  12  is assembled on a first stage tire building drum. The green carcass  12  comprises all of the elements of the tire excluding the belt package  22  and the tread  4 . The belt-tread package is formed separately on a second stage tire building machine. Plies  24 ,  26  of belt package material are positioned on the second stage drum, then a continuous strip of green rubber that will form the tread  4  is supplied as tread stock material. The continuous strip is cut to the necessary length, preferably at an angle, for splicing cut end to cut end to form a closed circle covering the belt package. The assembled belt-tread package is applied to the green tire carcass already assembled on the first stage tire building machine. The tire carcass is then “blown up” into a torodial shape within the belt-tread package and sent to a mold where the entire assembly is cured into the final tire. Examples of this process are disclosed in U.S. Pat. Nos. 5,141,587, 5,3544,404, 5,554,242, and 6,139,668.  
         [0035]      FIG. 4  illustrates a cross-sectional view of a tread stock  74  for the tread configuration of  FIGS. 2 and 3  useful for the present invention. The tread stock  74  has a predominately rectangular configuration, though the ends may be tapered more than illustrated. The tread stock  74  has a defined outer side  76  and a defined inner side  78 . The outer side  76  will be placed external to the belt package  22  and the tire carcass  12  on the green tire, and form the tread configuration of the cured tire. The inner side  78  is the side of the tread stock  74  that will be placed directly onto the belt package  22  or a tread base stock material  80 . In accordance with an embodiment of the invention, to form a wear-exposed groove  34  in a evolving tread configuration, at least one groove  82  is preformed in one side  76 ,  78  of the tread stock  74 . In the tread stock  74  of  FIG. 4 , the groove  82  is formed on the stock inner side  78 .  
         [0036]     The groove  82  in the tread stock  74  may be formed by extrusion or by removal of stock material to form the groove  82 . In forming the groove  82 , the groove  82  may be formed with a cross-sectional area greater than desired for the final cured buried groove  34 . Forming the groove  82  with a greater cross-sectional area by having either a greater width or a greater depth will compensate if there is limited flow of the tread stock  74  during curing resulting in a smaller cross-sectional area final cured buried groove  34 . Alternatively, the groove  82  may be formed to approximately the same dimensions as the cured buried groove  34 .  
         [0037]     Alternatively, if the tread compound  74  is subject to high flow during curing of the tire, either due to the tread compound or the selected tread configuration, the groove  82  may be maintained by insertion of an element  84  into the groove  82  that is not destroyed during curing or which maintains its integrity during cure completion, see  FIGS. 5A and 5B .  
         [0038]     As noted above, the groove  82  may be formed on the inner side  78  or the outer side  76  of the tread stock material  74 . When the groove  82  is formed on the inner side  78 , as illustrated, and the groove shape is maintained by the use of an insertion element  84  such as a tube, during molding of the tire, the tread stock material flows around the insertion element  84 , and the relative location of the insertion element  84  is not affected during molding. If the rubber flow during curing has the potential to move the insertion element  84  from the final desired location within the cured tire, mold means may be used to retain the insertion element  84  in the desired location. Such mold means includes needles extending from the tread mold, or groove ribs or sipe blades extending from the mold. If using needles, the needles are dimensional to provide the necessary retention of the insertion element  84 , but small enough to not alter the final tread configuration. If needles alone are used to retain the insertion element  84 , preferably, a set of needles is employed, one on each side of the insertion element  84 , with sets of needles located along the length of the insertion element  84  as needed. Such retention means will position the insertion means  84  from the top and/or sides, while the expansion of the tire during curing will hold the insertion means  84  from the underside.  
         [0039]     If the groove  82  and an insertion element  84  is located on the outer side  76  of the tread stock  74  to form the buried groove  34 , the tread rubber must flow around the insertion element  84  to complete encompass the insertion element  82 . For such an embodiment, in the final cured tire, the buried groove  34  will be relatively close to the tread surface  36 , such that the buried groove  34  becomes evident at an earlier state of tread wear, such as at 20 or 25% tread wear.  
         [0040]     The insertion element  84  is preferably a tube having any length—equal, less than, or greater than the circumferential length of the tire tread  28 . The tube may be formed as a continuous ring or have a defined length. The cross sectional configuration of the tube may vary and is likely dictated by the desired cross-sectional configuration of the buried groove. Possible cross-sectional configurations for the tube include, but are not limited to: circular, elliptical, or other two-dimensional curvilinear configuration; square, rectangular, trapezoidal, or other tetragonal shape; pentagonal, hexagonal, or other polygonal shape. The tube may be placed in the groove  82  following extrusion of the tread stock  74  or the tread stock  74  may be extruded over the tube resulting in the tread stock  74  as illustrated in  FIG. 5A . Alternatively, the tube may be placed between a pair of extruded layers  74 ,  80  of material, see  FIG. 5B ; the inner tread stock  80  may be of cushion rubber that assists in holding the tube in place during molding of the tire  10 . For such a dual tread stock configuration, the cushion rubber  80  may be placed first on the belt package  22  during tire building, followed by placement of the tube and the outer tread stock  74 .  
         [0041]     In one embodiment of the invention, the tube is formed from a material that is not destroyed during curing of the green tire, nor does the material interfere with the cured tire performance. The thickness of the tube material is selected to balance the above two goals and is based upon the type of material employed. Possible alternatives include, but are not limited to, a vinyl copolymer such as stiff copolymer of a starch and ethylene/vinyl alcohol or a thermoplastic material such as high molecular weight polyethylene.  
         [0042]     Alternatively, the tube may be formed from a fully or partially precured elastomeric tube. Ideally, the rubber polymer matrix forming the tube will be the same rubber polymer matrix as the adjacent tread component but having a greater parts per hundred rubber of reinforcement material (e.g. carbon black, silica) to yield a tube with a greater stiffness than the adjacent rubber. For example, the tube is formed of material wherein the reinforcement material loading is in the range of 80 to 130 parts per hundred rubber, preferably, in the range of 100 to 120 phr.  
         [0043]     The thickness of the tube, regardless of any precuring, is in the range of 0.10 to 5.0 mm. Preferably, the thickness of the tube is in the range of 0.50 to 3 mm. The greater tube thickness is more suited to formation of very large treads such as those used for radial medium trucks or off-road tires. For passenger vehicles, the tube thickness is in the range of 0.5 to 2 mm.  
         [0044]     In any of the above variations, the item  84  inserted into the groove  82  to maintain the configuration may be short length closed cylinders wherein the cylinders have a length less than the circumferential length of the tire tread. This alternative embodiment is most useful when forming the discontinuous grooves on the tread stock underside.  
         [0045]     In another embodiment, it may be desired to fill in the buried grooves  34  with a bio-degradable material or non-polluting material with a soluble link (e.g. sand bound together with a soluble glue). Examples of bio-degradable materials are disclosed in co-owned U.S. Patent Application 60/723,756, filed on Oct. 5, 2005, titled “Pneumatic Tire.” The fill material may be used when the tube is partially cured, and the bio-degradable material is partially employed to maintain a shape to the tube or cylinders and to prevent the tube material from flowing into and closing the buried groove  34  during curing of the tire  10 . The fill material also has the added benefit of providing stiffness to the tread when the tread rubber immediately above the filled tube has been worn low but has yet to be completely worn off the tread.  
         [0046]     The grooves  82  formed on the tread stock may be continuous as suggested in the tread embodiment of  FIG. 3 ; however, the grooves  82  may take any configuration desired, see  FIGS. 6-8 . Multiple grooves  82  may be formed in the longitudinal direction L of the tread stock  74 ,  FIG. 6 ; grooves  86  may be formed transverse to the longitudinal direction L of the tread stock  74 ,  FIG. 7 ; or the grooves may be a combination of both longitudinal  82  and transverse  86  grooves,  FIG. 8 . The grooves may also be a discontinuous series  88  formed on the inner side  78  of the tread stock  74 , see  FIG. 9 .  
         [0047]     In another method of manufacturing the tire, the tread stock  74  provided to the second stage tire being machine is not provided with any grooves  82 ,  86 ,  88  preformed therein. After the assembled belt-tread package is assembled onto the green tire carcass, a tube in the form of a ring is applied to the outer surface  76  of the green assembly. Due to the diameter of the tube ring, its position is maintained on the green tire. During molding of the tire, similar to a groove and insertion element located on the inner side  78  of the tread stock  74 , the rubber will flow around the tube ring, creating a buried groove  34  in the cured tire. This method of manufacturing does not require any change to the elements of a conventional green tire. All of the features regarding the tube as discussed above are also relevant and useful with the tube ring used in this method of manufacturing.