Abstract:
A tire having a pair of beads; a carcass ply having ends, each of the ends anchored to a respective one of the beads; at least one belt ply extending circumferentially around the tire and disposed radially outward of the carcass ply; and a tread layer disposed radially outward of the at least one belt ply and formed from a first tread compound. The tread layer has a plurality of tread ribs; at least one groove disposed between adjacent tread ribs; and a groove wall lining covering from the at least one groove. The groove wall lining is made from a second tread compound different than the first tread compound.

Description:
This application is a continuation-in-part of application application Ser. No. 09/013,452 filed on Jan. 26, 1998 now abandoned and which designated the U.S. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a vehicle tire. Specifically, the invention relates to a pneumatic vehicle tire having a groove wall lining that reduces the formation of anomalies causing subjective user dissatisfaction. 
     Tires, especially commercial vehicle tires, may be removed from service due to anomalies on the tread region. These anomalies are depressions in the tread rib or tread block. The anomalies can be caused by unequal normal stress distribution laterally across the rib or block. 
     The stress concentration occurs at the edges of the tread rib or block. The stress concentration at the edges of the tread rib or block is known as the edge effect. The central portion of the tread rib or block experiences a lower stress than the edges of the tread rib or block. The stress at the edge of the tread rib or block may be approximately twice as large as the stress at the central portion of the tread rib or block. The stress concentration at the edges of the tread rib or block typically causes anomalies to form at the edges of the tread rib or block. 
     Once an anomaly forms at the edge of the rib or block, the anomaly will propagate to the remainder of the rib or block; and often to adjacent ribs or blocks. The propagation of the anomaly occurs quickly as the tire continues to roll. 
     The decision to remove a tire is subjective and may depend on the location of the tire on the truck/trailer combination. Generally, a driver can feel an anomaly on a steering tire by the ride comfort and handling of the vehicle. In that case, the driver pulls the tire when uncomfortable with the ride and/or handling of the vehicle. However, if a tire having an anomaly is a drive tire or is located on the trailer, the driver may not sense any discomfort. The driver may, however, hear an increase in tire noise. If the driver does not sense discomfort or an increase in noise, the driver will pull the tire during a subsequent visual inspection of the vehicle. 
     The removal of a tire due to anomalies causing subjective user dissatisfaction is premature when considering the portions of the tire without the anomaly. The portions of the tire without the anomaly are capable of substantial additional service on the vehicle. Extending the time until the onset of an anomaly or decreasing the severity of the anomaly once found may extend the life of the tire. The extended life of the tire reduces the cost of purchase and installation of new tires. In the commercial trucking field, these potential cost savings are significant. 
     Thus, it is an object of the present invention to provide a tire with an improved tread portion which reduces the formation of anomalies causing subjective user dissatisfaction. 
     It is a further object of the present invention to provide a tread portion which eliminates the edge effect or exhibits a reduced edge effect, defined as the high normal stress value at the edges of a tread rib or block as compared to the center portion of a tread rib or block. 
     It is a further object of the present invention to provide a tread portion which more uniformly distributes normal stress laterally across a tread rib or block. 
     SUMMARY OF THE INVENTION 
     These and other objects of the present invention are accomplished in a first embodiment of the present invention by a tire having a pair of beads; a carcass ply having ends, each of the ends anchored to a respective one of the beads; at least one belt ply extending circumferentially around the tire and disposed radially outward of the carcass ply; and a tread layer disposed radially outward of the at least one belt ply and formed generally from a first tread compound. The tread portion has at least a pair of shoulder ribs and a plurality of tread ribs each having a defining circumferential groove on each side thereof with two walls and a base; and a groove lining defining the groove walls and base forming composite shoulder and tread ribs. The groove lining is made from a second tread compound different than the first tread compound. 
     The tread portion has a radial thickness and extends laterally beneath the base of each groove which is defined by the groove lining. The groove lining in the area of the groove base has a radial thickness which is between about 25 and 50 percent of the combined tread layer and groove lining thickness in this area. 
     The composite shoulder and tread ribs are formed with a lateral width of which the groove wall lining of each wall comprises between 15 and 30 percent. 
     The tread compound forming the groove lining has a modulus of elasticity which is 40 to 80 percent of the modulus of elasticity of the tread compound forming the tread portion. 
     The tread ribs may include sipes and the groove lining may include sipes. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects of the present invention will become apparent from the following description with reference to the accompanying drawings, wherein: 
     FIG. 1 is a perspective view of a tire having a tread portion of the present invention; 
     FIG. 2 is a perspective, cross-sectional view of a tire having a tread portion of the present invention; 
     FIG. 3 is a cross-sectional view of a tread portion of the present invention; 
     FIG. 4 is a partial cross-sectional view of the invention with a second embodiment of the decoupling rib structure; and 
     FIG. 5 is a partial sectional cross-section of the invention with a third embodiment of the decoupling rib structure. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     This application uses numerous phrases and terms of art. The phrase “mid-circumferential plane” refers to the plane passing through the center of the tread and being perpendicular to the axis of rotation of the tire. 
     The term “radial” refers to the direction perpendicular to the axis of rotation of the tire. 
     The term “axial” refers to the direction parallel to the axis of rotation of the tire. 
     The term “lateral” refers to the direction along the tread of the tire going from one sidewall of the tire to the other sidewall. 
     The term “groove” refers to an elongated void area in the tread that may extend circumferentially or laterally in a straight, curved of zig-zag manner. 
     The phrase “tread width” refers to the greatest axial distance across the main portion of the tread in constant contact with a road surface, as measured from a footprint of the tire, when the tire is mounted on a rim, subjected to a load, and inflated to a pressure corresponding to the load. All of the other tire dimensions are measured when the tire is mounted on a rim and inflated to a given pressure, but not subjected to a load. 
     The phrase “tread depth” refers to the radial extent, or height, of a tread block or rib on a tread portion of a tire. 
     The term “rib” refers to a continuous circumferential rib or a circumferential arrangement of rib blocks. 
     The term “tread portion” refers to a rubber crown area of the tire radially outside of any reinforcing layers of the tire for contacting a surface to support a vehicle. 
     The phrase “modulus of elasticity” refers to the modulus of elasticity measured at ten percent (10%) unit elongation. 
     A tire having a tread portion capable of reducing the formation of anomalies causing subjective user dissatisfaction will now be described with reference to FIGS. 1-5. 
     FIG. 1 is a perspective view of a tire  10  mounted on a rim R. The exterior features of tire  10  include sidewalls S and a tread portion TP having a tread width TW. The tread portion contacts a supporting surface when the rim is mounted on the axle of a vehicle and rotated about an axis of rotation A. Tread portion TP of tire  10  uses a unique design for the groove between adjacent ribs. The specific groove design is described in greater detail below. 
     FIG. 2 is a perspective, cross-sectional view of the exterior and interior features of tire  10  having tread portion TP. Tire  10  includes a pair of annular beads  11  on axially opposite sides of a midcircumferential plane M. Beads  11  securely mount tire  10  to rim R for use on a vehicle (not shown). Opposite ends of at least one carcass ply  13  anchor to beads  11 . The middle portion of carcass ply  13  forms part of sidewalls S and a crown portion C. Crown portion C extends between sidewalls S. At least one belt ply  15  is positioned radially outward of carcass ply  13 . Belt ply  15  includes reinforcing cords  17 . In commercial vehicle tires, reinforcing cords  17  are typically manufactured from steel. Sidewalls S include shoulder regions  19 . Tread portion TP occupies the radially outermost extent of crown portion C and is situated between shoulder regions  19 , and joins sidewalls S. 
     Tread portion TP contacts the ground during rolling movement of tire  10 . Tread portion TP may include conventional tire tread sculpture features, such as circumferential grooves  27 , shoulder grooves  30 , lateral grooves (not shown), and sipes  29  in a central portion and at an edge of tread ribs  21 , shoulder ribs  23 , and decoupling or sacrificial ribs  25  (see FIG.  1 ). Circumferential grooves  27  and shoulder grooves  30  can be straight grooves, or grooves having an undulating, or zig-zag, pattern. Circumferential grooves  27  separates adjacent tread ribs  21 . 
     In shoulder region  19 , tire  10  can include a shoulder rib  23  and a decoupling, or sacrificial, rib  25 . The desirability of a decoupling rib on a shoulder portion of a tire is discussed in U.S. Pat. No. 4,480,671 to Giron. 
     As seen in FIG. 3, tread portion TP has two components, a main component  31  and a groove lining  33 . Main component  31  is formed of a first tread compound and encompasses the majority of tread portion TP. Main component  31  is located laterally of tread portion TP and radially of belt ply  15  along line TC. Groove lining  33  occupies the remaining volume of tread portion TP and is formed from a second tread compound. 
     Tread portion TP as shown in FIG. 3, is formed to include a plurality of circumferential grooves  27  and a pair of shoulder grooves  30 . Each groove  27 ,  30  is defined by a bottom or base laterally separating a pair of radially extending walls. Between each pair of grooves  27  a tread rib  22  is formed while between the lateral most grooves  27  and shoulder grooves  30 , a pair of shoulder ribs  24  are formed. The walls of grooves  27  and  30 , defining tread ribs  22  and shoulder ribs  24 , along with each groove base are defined by groove lining  33  of the second tread compound. 
     As seen in FIG. 3, groove lining  33  completely lines grooves  27 , both in the lateral and in the radial directions. Groove lining  33  includes radial portions  35  which form opposing walls of groove  27 . Radial portions  35  of groove lining  33  can mirror the contour of the surface of the main component  31  along each groove  27 . Radial portions  35  have a lateral width w. A portion  37  of lining  33  extends across the base of groove  27  and connects with radial wall portions  35 . Lateral portion  37  has a thickness t in the area laterally across the base or bottom surface of groove  27 . 
     Groove lining  33  defines also at least the laterally inner walls of shoulder grooves  30 , as shown at  40 , along with the base of the groove and at least the radially innermost portion of the lateral outer walls thereof, as shown at  41 . The radial portion  40  is shaped as the main component  31  while radial portion  41  is formed in a circumferential cavity formed adjacent to base  37  and radially inwardly of the radial outer extremity of shoulder groove  30 . The circumferential cavity allows the laterally inner face of groove lining  33  over the lateral outer wall, as shown at  41 , and the uncoated portion of the remainder of the outer portion of the wall to extend along a mutual circumferential plane. Radial portion  40  of groove lining  33  has a lateral width w while the radial portion at  41  of groove lining  33  has a lateral width w′. Lateral widths w and w′, while not necessarily being equal in width, are preferably between 3 and 9 mm although they may be slightly larger or smaller. 
     Decoupling ribs  25  are formed between the lateral outer wall of shoulder groove  30  and the radially outer portion of shoulder  19  and are formed primarily of main component  31 . 
     The portion  21  of the tread ribs formed by the main component  31  along with groove lining  33  combine to form composite tread ribs  22 . Shoulder ribs portions  23  formed by the main component  31  along with groove lining  33  combine to form composite shoulder ribs  24 . Composite tread and shoulder ribs have a lateral width W. In the area of the base or bottom of grooves  27  and  30 , tread portion TP has a radial thickness T which is the combined radial thickness of main component  31  and groove lining  33  at base  37 . Typically thickness T is between 4 and 8 mm although the range can vary slightly at each extreme. In typical long haul commercial vehicles composite tread ribs  22  and composite shoulder ribs  24  have a lateral width W which is between approximately 28 and 43 mm although these limits may vary slightly in each direction. It is noted that composite tread ribs  22  and composite shoulder ribs  24  are not necessarily of equal lateral width. 
     In a second embodiment shown in FIG. 4, decoupling rib  25 ′ is formed between the lateral outer wall of groove  30 ′ and the radially outer portion of shoulder  19 . In this embodiment, the walls of shoulder grooves  30 ′ extend radially outward along a single plane. Groove lining  33  forms the entire surface of the lateral inner wall of the groove at a width w and the entire surface of the lateral outer wall at the width w′. Lining  33  extends across the bottom of groove  30 ′ at a radial thickness t. A radial thickness T is defined to included the thickness t combined with the radial thickness of main component  31  at the base of shoulder groove  30 ′. Decoupling rib  25 ′ is also formed primarily of main component  31 . 
     It is noted that while lateral widths w and w′ are within the same size range, they are normally not equal. Preferably width w is slightly wider than width w′ by about 1 mm. 
     In a third embodiment shown in FIG. 5, the radial and lateral outer circumference of main component  31  of tread portion TP is formed as a L-shaped shoulder  44 . Groove lining  33 , forms shoulder  44  and shoulder groove  30 ″. Radial portion  40 ″, which comprises the coating for the lateral inner wall of shoulder groove  30 ″, covers the lateral outer radial surface of shoulder rib  23 . Radial portion  40 ″ is formed at a width w. Decoupling rib  25 ″ is formed between the lateral outer wall of shoulder groove  30 ″ and the radial outer extend of shoulder  19 . A radial thickness t is defined by groove lining  33  between the bottom of shoulder groove  30 ″ and main component  31 . A radial thickness T is defined to include the radial thickness of groove lining  33  at the bottom of the groove and the radial thickness of main compound  31  below the bottom of shoulder groove  30 ″. 
     The tread depth of the decoupling ribs may be equal to or less than that of the shoulder ribs and the tread ribs. The particular tread design with which the instant invention is employed will determine the relative tread depth of these ribs. 
     The specific geometric and physical characteristics of the groove lining  33  and the main component  31 , and the relationships therebetween will now be discussed. 
     The modulus of elasticity E measures, among other characteristics, the hardness of a particular tread compound. The hardness of a particular tread compound can prove to be both beneficial and detrimental to the performance of a tire. For instance, a harder tread compound may be beneficial in terms of tread wear rate and rolling resistance when compared to a softer tread compound. However, the hard tread compound can be more susceptible to an edge effect and have less wet traction than the softer tread compound. 
     On the other hand, a softer tread compound may be less susceptible to the edge effect and have greater wet traction than a harder tread compound. However, the softer tread compound may have a greater tread wear rate and higher rolling resistance than the harder tread compound. 
     The present invention utilizes two tread compounds to take advantage of the benefits of both softer and harder tread compounds at specific locations on tread portion TP. 
     The modulus of elasticity for the two tread compounds is measured at ten percent (10%) unit elongation by the standard ASTM test. In a preferred embodiment, the modulus of elasticity (E 31 ) of the first tread compound for the main component  31  is within a range of approximately 4 to 8 mega Pascals (Mpa). The modulus of elasticity (E 33 ) of the second tread compound selected for use in the groove lining  33  should satisfy the following approximate ratio:            E   33       E   31       ≈     0.4                 to                 0.8                            
     In other words, the second tread compound used as groove lining  33  is softer than the first tread compound used as main component  31 . The preferred ratio between the modulus of elasticity (E 33 ) of the second tread compound used in groove lining  33  and the modulus of elasticity (E 31 ) of the first tread compound used in main portion  31  should be approximately 0.65. 
     Although FIGS. 1 and 2 show tire  10  as having a typical array of siping  29  at the edges of tread rib  21  (including groove lining  33 ), the present invention is also capable of use with a fewer number of sipes  29  on tread rib  21 , or with no sipes on tread rib  21 . Theoretically, the lower end of the ratio between the modulus of elasticity is more appropriate for a tire with a fewer number of sipes on the tread rib, or no sipes on the tread rib. Also, the upper end of the ratio between the moduli of elasticity is theoretically more appropriate for a tire with a greater number of sipes on the tread rib. 
     Also in the preferred embodiment, lateral width w of radial portions  35  and  40  and lateral width W of composite tread rib  22  and shoulder ribs  24  should satisfy the following approximate ratio:          w   W     ≈     0.15                 to                 0.3                            
     Preferably, the ratio between lateral width w of radial portion  35  and lateral width W of composite ribs  22  and  24  is approximately 0.2. In the preferred ratio, main component  31  encompasses at least 50 percent of the lateral width W of the composite ribs  22 ,  24 . In a long haul commercial vehicle tire, lateral width w of each radial portions  35  or  40  is preferably between approximately 6 and 9 mm, although these limits may be slightly larger or smaller. 
     To prevent the formation of cracks propagating from the base of grooves  27 , portion  37  of groove lining  33  should extend laterally across the bottom of groove  27  and  30 . In the preferred embodiment, radial thickness t of groove lining  33  over lateral portion  37  and radial thickness T of tread portion TP should satisfy the following approximate ratio:          t   T     ≈     0.25                 to                 0.5                            
     Preferably, the ratio between the radial thickness t of lateral portion  37  and radial thickness T of tread portion TP is approximately 0.4. In a long haul commercial vehicle tire, radial thickness t of lateral portion  37  is preferably between approximately 2 and 3.5 mm, although these limits may vary slightly in each direction. 
     It has also been found that radial thickness t of lateral portion  37  of groove lining  33  should also always be less than the lateral thickness w of lateral portion  37 . The desired ratio is for t to have a thickness which is between 22% to 58% of the thickness w. 
     An experiment was performed to determine the effectiveness of the present invention to reduce the formation of anomalies causing subjective user dissatisfaction. The experiment utilized tires that were identical in all aspects, save the groove wall lining. The tread portion of one set of tires lacked a groove wall lining. The tread portion of the other set of tires had a groove wall lining. The groove wall lining satisfied the parameters of the modulus of elasticity, thickness and lateral width described above. 
     The experiment established that the present invention reduced the formation of anomalies on the tread portion that causes subjective user dissatisfaction. Specifically, the experiment established that the stress concentration at the edges of the shoulder ribs and the tread ribs was reduced significantly. The normal stress distribution of a tire having the groove wall lining of the present invention was more uniform laterally across each rib of the tire. The experiment also established that tires having the groove wall lining of the present invention required a greater amount of use, or mileage, to exhibit an anomaly causing subjective driver discomfort. 
     Applicant also understands that the invention does not merely apply to new tires. For example, Applicant recognizes that the present invention can be applied to tread layers used with retreaded tires and to tire tread layers in strip form which are ultimately cured before or after mounting on a tire casing. 
     Applicant also recognizes that the present invention is not limited to commercial vehicle tires. For example, automobile tires can benefit from the present invention. 
     The above description is given in reference to the preferred embodiment of a tire having a tread portion for reducing the formation of anomalies causing subjective user dissatisfaction. However, it is understood that many variations are apparent to one of ordinary skill in the art from a reading of the disclosure of the invention. Such variations and modifications apparent to those skilled in the art are within the scope and spirit of the instant invention as defined by the following appended claims.