Abstract:
A pneumatic tire with an improved balance between noise reduction and hydroplaning resistance as the tread wears. The tread of the pneumatic tire includes skewed tread blocks having walls that, as the tread wears, change the character of the lateral and circumferential channels in the tire footprint to better optimize noise reduction and hydroplaning resistance.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention generally relates to pneumatic tires and, more particularly, to a pneumatic tire characterized by a pattern arrangement with tread blocks having a road-contacting surface that changes its geometrical appearance as the tire wears.  
       BACKGROUND OF THE INVENTION  
       [0002]     Conventional tires include a tread with a tread pattern that, when the tire is loaded, defines a footprint providing a frictional engagement with the road. The tread pattern is segmented into a plurality of raised blocks defined and separated by intersecting circumferential and transverse grooves. The grooves are necessary to provide flexibility and water removal while the blocks determine the control, acceleration and braking characteristics of the tire. The circumferential grooves are positioned such that the raised blocks are arranged in columns that extend circumferentially about the tire circumference.  
         [0003]     The block dimensions, the number of ribs, and the inclination angle of the transverse grooves cooperate in determining the overall performance of the pneumatic tire. In particular, these factors determine the amount of tread that contacts the road, and hence the traction and control of the vehicle riding on the tires. The nonskid or groove depth determines the ability of the intersecting circumferential and transverse grooves to channel water.  
         [0004]     In a new condition, tread patterns are designed with compromises between various design parameters in order to optimize performance. As a tire wears, the parameter choices that optimized performance of the tire&#39;s tread pattern in the unworn state may not be optimal at reduced groove depths. For example, a new tire construction may be designed with a tread pattern having raised blocks in which noise reduction, due to the high nonskid, is a controlling factor. However, blocks that provide a balanced tire behavior in the new condition may not exhibit optimized noise reduction and hydroplaning control in a worn condition as the groove depth diminishes. As the tread wears, the noise created by contact between the road-contacting surfaces of the tread blocks and the road diminishes. However, worn tires with conventional blocks are significantly more susceptible to hydroplaning than new tires.  
         [0005]     For these and other reasons, it would be desirable to provide a pneumatic tire that addresses these and other deficiencies of conventional pneumatic tires.  
       SUMMARY OF THE INVENTION  
       [0006]     In one embodiment of the present invention, a pneumatic tire comprises a carcass having an axis of rotation and a tread disposed radially outward of the carcass. The tread includes an equatorial plane bisecting the tread perpendicular to the axis of rotation, a plurality of grooves, and a plurality of raised tread blocks located between the grooves. Each of the tread blocks has a road-contacting surface and at least one wall extending from the road-contacting surface so as to border at least one of the grooves. The at least one wall is oriented with a first angular orientation relative to the equatorial plane at a first groove depth below the road-contacting surface and with a second angular orientation relative to the equatorial plane at a second groove depth that differs from the first angular orientation.  
         [0007]     In another aspect, a method is provided for adjusting the water removal characteristics of a tire tread with tread wear. The tire tread has an equatorial plane, a plurality of grooves, and a plurality of tread blocks located between the grooves. Each of the tread blocks has a road-contacting surface and at least one wall extending from the road-contacting surface so as to border at least one of the grooves. The method includes orienting the at least one wall with a first angular orientation relative to the equatorial plane at a first groove depth and orienting the at least one wall with a second angular orientation differing from the first angular orientation at a second groove depth less than or shallower than the first groove depth.  
         [0008]     By virtue of the foregoing, there is provided an improved pneumatic tire that addresses various deficiencies of conventional pneumatic tires. The pneumatic tire of the present invention includes tread blocks with skewed walls. The pattern arrangement of tread blocks produces a footprint that is optimized for noise reduction and/or irregular wear in the new condition. In a worn condition, the pattern arrangement of tread blocks is optimized to produce a footprint that improves the balance between noise reduction and hydroplaning performance. The metamorphosis between these two states is produced by changing the angular orientation of at least one wall of, preferably, each tread block in at least one tread rib relative to the tire&#39;s equatorial plane.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an embodiment of the invention and, together with a general description of the invention given above, and the detailed description given below, serve to explain the invention.  
         [0010]      FIG. 1  is a cross-sectional view of a tire in accordance with the present invention;  
         [0011]      FIG. 2  is an enlarged fragmentary view of the tread of the tire of  FIG. 1 ;  
         [0012]      FIG. 3  is a diagrammatic view of a footprint of the tire having tread blocks in accordance with an alternative embodiment of the invention in which the tread has a first groove depth;  
         [0013]      FIG. 4  is a diagrammatic view of a tire footprint similar to  FIG. 3  in which the tread has a second groove depth; and  
         [0014]      FIGS. 5, 6  and  7  are views of tread blocks for tires constructed in accordance with alternative embodiments of the present invention. 
     
    
     DEFINITIONS  
       [0015]     “Apex” means an elastomeric filler located radially above the bead core and between the plies and the turnup ply.  
         [0016]     “Axial” and “axially” mean the lines or directions that are parallel to the axis of rotation of the tire.  
         [0017]     “Bead” means that part of the tire comprising an annular tensile member wrapped by ply cords and shaped to fit the design rim, with or without other reinforcement elements such as flippers, chippers, apexes, toe guards and chafers.  
         [0018]     “Carcass” means the tire structure apart from the belt structure, tread, undertread, and sidewall rubber over the plies, but including the beads.  
         [0019]     “Circumferential” means circular lines or directions extending along the surface of the sidewall perpendicular to the axial direction.  
         [0020]     “Cord” means one of the reinforcement strands of which the plies in the tire are comprised.  
         [0021]     “Cut belt or cut breaker reinforcing structure” means at least two cut layers of plies of parallel cords, woven or unwoven, underlying the tread, unanchored to the bead, and having both left and right cord angles in the range from 10 degrees to 33 degrees with respect to the equatorial plane of the tire.  
         [0022]     “Equatorial plane (EP)” means the plane perpendicular to the tire&#39;s axis of rotation and passing through the center of its tread.  
         [0023]     “Footprint” means the contact patch or area of contact of the tire tread with a flat surface at zero speed and under design load and pressure.  
         [0024]     “Groove” means an elongated void area in a tread that may extend circumferentially or laterally about the tread in a straight, curved, or zigzag manner.  
         [0025]     “Hydroplaning” refers to a condition wherein a tire in motion loses traction during wet pavement conditions because the tire is not in contact with the surface. The tire is in contact only with a film of liquid on the surface.  
         [0026]     “Lateral” means a direction parallel to the axial direction, as in across the width of the tread or crown region.  
         [0027]     “Lateral edge” means the axially outermost edge of the tread as defined by a plane parallel to the equatorial plane and intersecting the outer ends of the axially outermost traction lugs at the radial height of the inner tread surface.  
         [0028]     “Leading” refers to a portion or part of the tread that contacts the ground first, with respect to a series of such parts or portions, during rotation of the tire in the direction of travel.  
         [0029]     “Nonskid” means depth of grooves in a tire tread.  
         [0030]     “Normal inflation pressure” refers to the specific design inflation pressure and load assigned by the appropriate standards organization for the service condition for the tire.  
         [0031]     “Normal load” refers to the specific design inflation pressure and load assigned by the appropriate standards organization for the service condition for the tire.  
         [0032]     “Pneumatic tire” means a laminated mechanical device of generally toroidal shape, usually an open-torus having beads and a tread and made of rubber, chemicals, fabric and steel or other materials.  
         [0033]     “Radial” and “radially” mean directions radially toward or away from the axis of rotation of the tire.  
         [0034]     “Rib” means a circumferentially extending strip of rubber on the tread which is defined by at least one circumferential groove.  
         [0035]     “Shoulder” means the upper portion of sidewall just below the tread edge.  
         [0036]     “Sidewall” means that portion of a tire between the tread and the bead area.  
         [0037]     “Tire design load” is the base or reference load assigned to a tire at a specific inflation pressure and service condition; other load-pressure relationships applicable to the tire are based upon that base or reference load.  
         [0038]     “Tread” means a molded rubber component which, when bonded to a tire casing, includes that portion of the tire that comes into contact with the road when the tire is normally inflated and under normal load.  
         [0039]     “Tread width” means the arc length of the road contacting tread surface in the axial direction, that is, in a plane parallel to the axis of rotation of the tire.  
         [0040]     “Turn-up ply” refers to an end of a carcass ply that wraps around one bead only.  
       DETAILED DESCRIPTION  
       [0041]     With reference to the  FIG. 1 , a pneumatic tire  10  of the present invention includes a road-contacting tread  12  extending between lateral edges  14 ,  16 , a pair of sidewalls  18  each extending from one of the lateral edges  14 ,  16 , respectively, a shoulder  20  defined at the juncture between each sidewall  18  and tread  12 , and a carcass  22  defining a support structure for tire  10 . The tread  12  and sidewalls  18  are comprised of a suitable material, such as a natural or synthetic rubber compound, selected in accordance with engineering standards that are widely known in the tire art. Tire  10  has a mid-circumferential or equatorial plane  36  bisecting tire  10  midway between lateral edges  14 ,  16 . Generally, the tire  10  includes an axis of rotation  11  that orthogonally intersects the equatorial plane  39 .  
         [0042]     The carcass  22  includes a pair of beads  24  each having an annular inextensible tensile member  26  and an apex  28 . Each of the sidewalls  18  is terminated by a corresponding one of the beads  24 , which provide support for the tire  10  and seal air in the tire  10 . The carcass  22  further includes at least one composite ply structure  30  having opposite turn-up ply ends  32  each wrapped about one of the beads  24 . Tire  10  further includes a belt package  34  typically characterized by a plurality of individual cut belt plies and/or spiral wound belt layers. The construction of the belt package  34  varies according to the tire construction. The plies of the ply structure  30  and the belt package  34  generally consist of cord reinforced elastomeric material in which the cords are steel wire or polyamide filaments and the elastomer is a vulcanized rubber material. The cord reinforced elastomeric material constituting the ply structure  30  and belt package  34  are encased in and bonded to a suitable material, such as a natural or synthetic rubber compound, selected in accordance with engineering standards that are widely known in the tire art.  
         [0043]     A set of tires  10  is placed on a vehicle, such as an automobile. When each tire  10  is mounted on a rim and placed on the vehicle, the tread  12  protects the carcass  22  and belt package  34  while providing traction for the tire  10  on the road surface. Tire  10  contains an inflation fluid, like nitrogen, air, or another gas or gas mixture, that sustains the vehicle load. A liner  40 , which may be formed of, for example, halobutyl rubber, defines an air impervious chamber for containing the air pressure when the tire  10  is inflated.  
         [0044]     With reference to  FIGS. 1 and 2 , the tread  12  is partitioned into a plurality of raised tread blocks  42  located between a plurality of continuous circumferential grooves  44  and a plurality of transverse or lateral grooves  46  that are inscribed with an intersecting relationship into the tread  12 . Preferably, the circumferential grooves  44  are substantially parallel to one another so that the tread blocks  42  are arranged in three ribs, indicated generally at  51 ,  53 ,  55 , that extend circumferentially about the tire  10 . Adjacent ribs  51 ,  53 ,  55  are separated from each other by one of the circumferential grooves  44 .  
         [0045]     Each of the lateral grooves  46  either extends between adjacent circumferential grooves  44  or between a circumferential groove  44  and one of the lateral edges  14 ,  16 . The lateral grooves  46  extend across the width (i.e., axial dimension) of the tire  10  transversely relative to the equatorial plane  39 . Each block  42  is individually separated from an adjacent block  42  in the same rib  51 ,  53 ,  55  by one of the lateral grooves  46 .  
         [0046]     The circumferential and lateral grooves  44 ,  46  represent elongated void areas in tread  12 . The blocks  42  project outwardly from a base surface  35  of the tread  12  that is defined as a curved surface containing the bases of the individual grooves  44 ,  46 . The nonskid is represented by a distance or depth measured from a road contacting surface  38  of each tread block  42  to the base surface  35 . When driving on wet roads, the lateral grooves  44  transfer a continuous flow of water transversely or laterally out of the footprint of the tread  12  for expulsion through the shoulders  20 . The presence of the lateral grooves  46  alleviates the build up of water back pressure in front of the tread  12  and assists in maintaining rubber contact between the tread  12  and the road surface.  
         [0047]     Each tread block  42  includes a radially outermost, road-contacting surface  38  that contacts the road surface when periodically within the boundary of the tire footprint as tire  10  rotates. Each of the tread blocks  42  has a dimension in the circumferential direction of the tire  10  and a shorter dimension in the transverse direction of tire  10  that may be the same or differ from the circumferential direction. The tread blocks  42  may be provided with sipes (not shown). Each road-contacting surface  38  is bounded by corners  50 ,  52 ,  54 ,  56  defined by the intersection between surface  38  and a corresponding one of walls  58 ,  60 ,  62 ,  64  that extend from surface  38  to base surface  35 .  
         [0048]     When viewed in a direction orthogonal to the axis of rotation  11  of tire  10 , each of the tread blocks  42  has a polygonal cross-sectional profile. In alternative embodiments, the cross-sectional profile may be a quadrilateral, a trapezoid, or a parallelogram. The cross-sectional profile may have other polygonal shapes, such as triangular or pentagonal, or may be circular or another smooth curve defining a non-polygonal shape. The cross-sectional profile may change along the height of the tread blocks  42 . For example, the number of sides may change from four to three along the height of each of the tread blocks  42 .  
         [0049]     Due to the change in angular orientation, the four walls  58 ,  60 ,  62 ,  64  of tread block  42  spiral along the depth of grooves  44 ,  46 . The spiral angle of each wall  58 ,  60 ,  62 ,  64  is equal to the difference in the angular orientation of the corresponding corners  50 ,  52 ,  54 ,  56  and the angular orientation of the four walls  58 ,  60 ,  62 ,  64  at their intersection with base surface  35 . In alternative embodiments, less than all four walls  58 ,  60 ,  62 ,  64  of tread block  42  may spiral toward the base surface  35 . The spiral angle may differ among the individual walls  58 ,  60 ,  62 ,  64  so that the corresponding corners  50 ,  52 ,  54 ,  56  have a different inclination change per unit groove depth (i.e., inclination change per unit block height). Different walls  58 ,  60 ,  62 ,  64  may also rotate in different directions, as indicated in  FIG. 7 . In addition, the change in angular inclination of corners any or all of the walls  58 ,  60 ,  62 ,  64  may occur over the full extent of the groove depth or may occur over only a portion of the groove depth. The change in angular orientation may be gradual or smooth or, alternatively, may be more abruptly or drastic.  
         [0050]     With continued reference to  FIGS. 1 and 2 , each of the tread blocks  42  has corners  50 ,  52 ,  54 ,  56  that are defined at the road-contacting surface  38  by the intersection of a corresponding one of a plurality of walls  58 ,  60 ,  62 ,  64  with surface  38 . Corners  50  and  52  lead and trail, respectively, the tread block  42  in a circumferential direction. However, the invention is not so limited as the corners  50 ,  52 ,  54 ,  56  may be rounded or radiused instead of linear. The lateral grooves  46  change direction across the discontinuity defined by each of the circumferential grooves  44  so that the path to the shoulder  20  is non-linear. Corner  50  of one tread block  42  is generally parallel to corner  52  of the adjacent tread block  42  in each of the ribs  51 ,  53 ,  55 .  
         [0051]     The nonskid of tread  12  is defined by the groove depth or radial distance, d 1 , measured from the road-contacting surface  38  to the base surface  35 , as shown in  FIG. 1 . For simplicity and clarity, the depth of the nonskid is assumed to be identical and uniform across the width of the tread  12 , although the invention is not so limited.  
         [0052]     For example, lateral grooves  46  may have a position-dependent depth that varies across the width of the tread  12 . Each of the corners  50 ,  52 ,  54 ,  56  is oriented at a first angle relative to equatorial plane  39 . However, the angular orientation of the walls  58 ,  60 ,  62 ,  64  relative to equatorial plane  39  changes as a function of the groove depth between the road-contacting surface  38  and the base surface  35 .  
         [0053]     In use, the depth of grooves  44 ,  46  will decrease as the tread  12  wears. As the grooves  44 ,  46  become shallower, the corners  50 ,  52 ,  54 ,  56  approach the base surface  35 . As a result, the road-contacting surface  38  is at a different resultant height above the base surface  35  and, hence, cuts through a different plane of the original tread block  42 . As this occurs, the angular orientation of each of the corners  50 ,  52 ,  54 ,  56  changes relative to the equatorial plane  39 .  
         [0054]     With reference to  FIGS. 3 and 4 , footprints are shown for a tread, similar to tread  12 , patterned with tread blocks, similar to tread blocks  42 , in accordance with an alternative embodiment of the invention. The footprint of the tread represents the area of contact or contact patch  37  of the road-contacting surface of each tread block with a flat surface, such as a road surface, at zero speed and under design load and pressure. The footprint is circumscribed by an elliptical edge  48 .  
         [0055]     The footprint of  FIG. 3  is illustrated with the tread at a first groove depth, which may be the original groove depth d 1  in the new or unused condition or may be a worn depth shallower than the original groove depth. The footprint includes channels  45  representative of circumferential grooves, similar to circumferential grooves  44  ( FIG. 2 ), and channels  47  representative of lateral grooves, similar to lateral grooves  46  ( FIG. 2 ). Channels  45 ,  47  define the open areas between the contact patches  37 . The channels  47  in the footprint are inclined or angled diagonally relative to the equatorial plane  39 . Channels  47  are partially obstructed and have a pronounced zig-zag appearance as the corners  54 ,  56  of walls  62 ,  64  are not coplanar with the equatorial plane  39  but instead are oriented at the first angle relative to the equatorial plane  39 .  
         [0056]     Each contact patch  37  is bounded by edges  150 ,  152 ,  154 ,  156 . It is apparent from  FIG. 3  that, although each contact patch  37  is a polygon of four sides or a quadrilateral, the inclination angle of each of the edges  150 ,  152 ,  154 ,  156  relative to the equatorial plane  39  differs as a function of a row  151 ,  153 ,  155  in which the contact patch  37  belongs. Contact patches  37  in the central row  153  are parallelograms with edges  150 ,  152  parallel and edges  154 ,  156  parallel. Contact patches  37  in the peripheral rows  151 ,  155  are trapezoids with only edges  150 ,  152  parallel. Edges  154 ,  156  of contact patches  37  in the peripheral rows  151 ,  155  also differ in inclination angle relative to the equatorial plane  39 . The orientation of edges  150 ,  152 ,  154 ,  156  corresponds to, and is a mirror image of, the orientation of the corners of the tread blocks on the tread.  
         [0057]     With reference to  FIG. 4 , a footprint is shown with the tread at a second groove depth that is shallower than the first groove depth for the footprint shown in  FIG. 3 . This represents a condition with greater tread wear than at the first groove depth, so that contact patches  37   a  differ from contact patches  37  ( FIG. 3 ) in appearance and may also differ in contact area. Channels  45   a ,  47   a  represent the transformation of channels  45 ,  47 , respectively, from their arrangement at the first groove depth shown in  FIG. 3  to their new arrangement at the second groove depth shown in  FIG. 4 . Adjacent channels  45   a  have less prominent changes in direction diagonally across the width of the footprint. For purposes of illustration only, lateral channels  47   a  are depicted as being aligned nearly linear or linear diagonally across the width of the tread. In addition, the circumferential channels  45   a  are less obstructed than channels  45  ( FIG. 3 ) because of less prominent changes in direction. As a result, the network of channels  45   a ,  47   a  at the second groove depth presents a lateral path with lower flow resistance, as compared with the first groove depth as shown in  FIG. 3 , which makes channels  45   a ,  47   a  more effective and efficient for expelling water out of the tire footprint for expulsion through the shoulders  20  ( FIG. 1 ) when driving on wet roads. Hence, the tread in the reduced nonskid condition of  FIG. 4  has an improved hydroplaning performance, as compared with a conventional tire in which the footprint of the worn tread would be substantially identical to the footprint shown in  FIG. 3 .  
         [0058]     The transformation from channels  45 ,  47  ( FIG. 4 ) to channels  45   a ,  47   a  occurs because the edges  150 ,  152 ,  154 ,  156  of the contact patches  37   a  have a different angular orientation or inclination angle relative to the equatorial plane  39  at the second groove depth as compared with their orientation at the first groove depth ( FIG. 3 ). The change in orientation results from the change in angular orientation of the corners of the road-contacting surfaces of the tread blocks relative to the equatorial plane  39 . As is apparent, the contact patches  37   a  are all approximately shaped as parallelograms. Hence, the walls of the tread blocks defining the contact patches  37 ,  37   a  at the two different groove depths are configured to provide the footprints shown in  FIGS. 3 and 4  at the different groove depths.  
         [0059]     With reference to  FIG. 5 , which like reference numerals refer to like features in  FIGS. 1 and 2  and in accordance with an alternative embodiment of the present invention, a representative tread block  101 , similar to tread block  42  ( FIG. 2 ), has four walls that change orientation with groove depth, but in an opposite rotational sense from the tread blocks  42  of  FIG. 2 . Corners  100 ,  102 ,  104 ,  106 , which are arranged about the periphery of the rectangular road-contacting surface  108 , are defined by an intersection between surface  108  and corresponding walls  110 ,  112 ,  114 ,  116 , respectively, extending to the base of an adjacent groove.  
         [0060]      FIG. 6  shows a representative tread block  71 , similar to tread block  42 , having a single wall that changes orientation with groove depth. Corners  70 ,  72 ,  74 ,  76 , which are arranged about the periphery of the rectangular road-contacting surface  38 , are defined by an intersection between surface  38  and a corresponding wall extending to the base of an adjacent groove, of which only a wall  78  is visible in  FIG. 6 . The hidden walls (not shown) are inclined at a constant inclination angle relative to the equatorial plane  39  ( FIG. 2 ) and approximately equal to the inclination angle of the corresponding corners  70 ,  72 ,  74 ,  76 . Wall  78 , in contrast, changes its inclination angle relative to the equatorial plane  39  as a function of groove depth, similar to walls  58 ,  60 ,  62 ,  64  ( FIG. 5 ).  
         [0061]     Wall  78  may bound one of the circumferential grooves  44  ( FIG. 2 ) or one of the lateral grooves  46  ( FIG. 2 ). If wall  78  were bounding one side of one of the circumferential grooves  44 , the inclination of the portion of channel  45  adjacent to wall  78  defined by groove  44  in the tire footprint would change as the tread  12  wears. Similarly, if wall  78  bounds one side of one of the lateral grooves  46 , the inclination of the channel  47  defined by groove  46  in the tire footprint would change as the tread  12  wears.  
         [0062]      FIG. 7  shows a representative tread block  81 , similar to tread block  42 , having two walls that change orientation with groove depth. Corners  80 ,  82 ,  84 ,  86 , which are arranged about the periphery of the rectangular road-contacting surface  38 , are defined by an intersection between surface  38  and a corresponding wall extending to the base of an adjacent groove, of which only walls  88  and  90  are visible in  FIG. 7 . The non-visible walls (not shown) are inclined at a constant inclination angle relative to the equatorial plane  39  ( FIG. 2 ) and approximately equal to the inclination angle of the corresponding corners  82  and  86 . Walls  88  and  90 , in contrast, change their inclination angle relative to the equatorial plane  39  as a function of groove depth, similar to walls  58 ,  60 ,  62 ,  64  ( FIG. 5 ). The inclination angle of wall  90  changes in an opposite rotational sense to the inclination angle of wall  88 . In other words, wall  90  effectively creates an undercut beneath the road-contacting surface  38  proximate to corner  84 .  
         [0063]     While the invention has been illustrated by a description of various embodiments and while these embodiments have been described in considerable detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Thus, the invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicants&#39; general inventive concept.