Pneumatic tire having tread blocks with skewed walls

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.

FIELD OF THE INVENTION

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

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.

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.

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'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.

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

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.

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.

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's equatorial plane.

DEFINITIONS

“Apex” means an elastomeric filler located radially above the bead core and between the plies and the turnup ply.

“Axial” and “axially” mean the lines or directions that are parallel to the axis of rotation of the tire.

“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.

“Carcass” means the tire structure apart from the belt structure, tread, undertread, and sidewall rubber over the plies, but including the beads.

“Circumferential” means circular lines or directions extending along the surface of the sidewall perpendicular to the axial direction.

“Cord” means one of the reinforcement strands of which the plies in the tire are comprised.

“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.

“Equatorial plane (EP)” means the plane perpendicular to the tire's axis of rotation and passing through the center of its tread.

“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.

“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.

“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.

“Lateral” means a direction parallel to the axial direction, as in across the width of the tread or crown region.

“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.

“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.

“Nonskid” means depth of grooves in a tire tread.

“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.

“Normal load” refers to the specific design inflation pressure and load assigned by the appropriate standards organization for the service condition for the tire.

“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.

“Radial” and “radially” mean directions radially toward or away from the axis of rotation of the tire.

“Rib” means a circumferentially extending strip of rubber on the tread which is defined by at least one circumferential groove.

“Shoulder” means the upper portion of sidewall just below the tread edge.

“Sidewall” means that portion of a tire between the tread and the bead area.

“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.

“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.

“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.

“Turn-up ply” refers to an end of a carcass ply that wraps around one bead only.

DETAILED DESCRIPTION

With reference to theFIG. 1, a pneumatic tire10of the present invention includes a road-contacting tread12extending between lateral edges14,16, a pair of sidewalls18each extending from one of the lateral edges14,16, respectively, a shoulder20defined at the juncture between each sidewall18and tread12, and a carcass22defining a support structure for tire10. The tread12and sidewalls18are 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. Tire10has a mid-circumferential or equatorial plane36bisecting tire10midway between lateral edges14,16. Generally, the tire10includes an axis of rotation11that orthogonally intersects the equatorial plane39.

The carcass22includes a pair of beads24each having an annular inextensible tensile member26and an apex28. Each of the sidewalls18is terminated by a corresponding one of the beads24, which provide support for the tire10and seal air in the tire10. The carcass22further includes at least one composite ply structure30having opposite turn-up ply ends32each wrapped about one of the beads24. Tire10further includes a belt package34typically characterized by a plurality of individual cut belt plies and/or spiral wound belt layers. The construction of the belt package34varies according to the tire construction. The plies of the ply structure30and the belt package34generally 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 structure30and belt package34are 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.

A set of tires10is placed on a vehicle, such as an automobile. When each tire10is mounted on a rim and placed on the vehicle, the tread12protects the carcass22and belt package34while providing traction for the tire10on the road surface. Tire10contains an inflation fluid, like nitrogen, air, or another gas or gas mixture, that sustains the vehicle load. A liner40, which may be formed of, for example, halobutyl rubber, defines an air impervious chamber for containing the air pressure when the tire10is inflated.

With reference toFIGS. 1 and 2, the tread12is partitioned into a plurality of raised tread blocks42located between a plurality of continuous circumferential grooves44and a plurality of transverse or lateral grooves46that are inscribed with an intersecting relationship into the tread12. Preferably, the circumferential grooves44are substantially parallel to one another so that the tread blocks42are arranged in three ribs, indicated generally at51,53,55, that extend circumferentially about the tire10. Adjacent ribs51,53,55are separated from each other by one of the circumferential grooves44.

Each of the lateral grooves46either extends between adjacent circumferential grooves44or between a circumferential groove44and one of the lateral edges14,16. The lateral grooves46extend across the width (i.e., axial dimension) of the tire10transversely relative to the equatorial plane39. Each block42is individually separated from an adjacent block42in the same rib51,53,55by one of the lateral grooves46.

The circumferential and lateral grooves44,46represent elongated void areas in tread12. The blocks42project outwardly from a base surface35of the tread12that is defined as a curved surface containing the bases of the individual grooves44,46. The nonskid is represented by a distance or depth measured from a road contacting surface38of each tread block42to the base surface35. When driving on wet roads, the lateral grooves44transfer a continuous flow of water transversely or laterally out of the footprint of the tread12for expulsion through the shoulders20. The presence of the lateral grooves46alleviates the build up of water back pressure in front of the tread12and assists in maintaining rubber contact between the tread12and the road surface.

Each tread block42includes a radially outermost, road-contacting surface38that contacts the road surface when periodically within the boundary of the tire footprint as tire10rotates. Each of the tread blocks42has a dimension in the circumferential direction of the tire10and a shorter dimension in the transverse direction of tire10that may be the same or differ from the circumferential direction. The tread blocks42may be provided with sipes (not shown). Each road-contacting surface38is bounded by corners50,52,54,56defined by the intersection between surface38and a corresponding one of walls58,60,62,64that extend from surface38to base surface35.

When viewed in a direction orthogonal to the axis of rotation11of tire10, each of the tread blocks42has 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 blocks42. For example, the number of sides may change from four to three along the height of each of the tread blocks42.

Due to the change in angular orientation, the four walls58,60,62,64of tread block42spiral along the depth of grooves44,46. The spiral angle of each wall58,60,62,64is equal to the difference in the angular orientation of the corresponding corners50,52,54,56and the angular orientation of the four walls58,60,62,64at their intersection with base surface35. In alternative embodiments, less than all four walls58,60,62,64of tread block42may spiral toward the base surface35. The spiral angle may differ among the individual walls58,60,62,64so that the corresponding corners50,52,54,56have a different inclination change per unit groove depth (i.e., inclination change per unit block height). Different walls58,60,62,64may also rotate in different directions, as indicated inFIG. 7. In addition, the change in angular inclination of corners any or all of the walls58,60,62,64may 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.

With continued reference toFIGS. 1 and 2, each of the tread blocks42has corners50,52,54,56that are defined at the road-contacting surface38by the intersection of a corresponding one of a plurality of walls58,60,62,64with surface38. Corners50and52lead and trail, respectively, the tread block42in a circumferential direction. However, the invention is not so limited as the corners50,52,54,56may be rounded or radiused instead of linear. The lateral grooves46change direction across the discontinuity defined by each of the circumferential grooves44so that the path to the shoulder20is non-linear. Corner50of one tread block42is generally parallel to corner52of the adjacent tread block42in each of the ribs51,53,55.

The nonskid of tread12is defined by the groove depth or radial distance, d1, measured from the road-contacting surface38to the base surface35, as shown inFIG. 1. For simplicity and clarity, the depth of the nonskid is assumed to be identical and uniform across the width of the tread12, although the invention is not so limited.

For example, lateral grooves46may have a position-dependent depth that varies across the width of the tread12. Each of the corners50,52,54,56is oriented at a first angle relative to equatorial plane39. However, the angular orientation of the walls58,60,62,64relative to equatorial plane39changes as a function of the groove depth between the road-contacting surface38and the base surface35.

In use, the depth of grooves44,46will decrease as the tread12wears. As the grooves44,46become shallower, the corners50,52,54,56approach the base surface35. As a result, the road-contacting surface38is at a different resultant height above the base surface35and, hence, cuts through a different plane of the original tread block42. As this occurs, the angular orientation of each of the corners50,52,54,56changes relative to the equatorial plane39.

With reference toFIGS. 3 and 4, footprints are shown for a tread, similar to tread12, patterned with tread blocks, similar to tread blocks42, in accordance with an alternative embodiment of the invention. The footprint of the tread represents the area of contact or contact patch37of 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 edge48.

The footprint ofFIG. 3is illustrated with the tread at a first groove depth, which may be the original groove depth d1in the new or unused condition or may be a worn depth shallower than the original groove depth. The footprint includes channels45representative of circumferential grooves, similar to circumferential grooves44(FIG. 2), and channels47representative of lateral grooves, similar to lateral grooves46(FIG. 2). Channels45,47define the open areas between the contact patches37. The channels47in the footprint are inclined or angled diagonally relative to the equatorial plane39. Channels47are partially obstructed and have a pronounced zig-zag appearance as the corners54,56of walls62,64are not coplanar with the equatorial plane39but instead are oriented at the first angle relative to the equatorial plane39.

Each contact patch37is bounded by edges150,152,154,156. It is apparent fromFIG. 3that, although each contact patch37is a polygon of four sides or a quadrilateral, the inclination angle of each of the edges150,152,154,156relative to the equatorial plane39differs as a function of a row151,153,155in which the contact patch37belongs. Contact patches37in the central row153are parallelograms with edges150,152parallel and edges154,156parallel. Contact patches37in the peripheral rows151,155are trapezoids with only edges150,152parallel. Edges154,156of contact patches37in the peripheral rows151,155also differ in inclination angle relative to the equatorial plane39. The orientation of edges150,152,154,156corresponds to, and is a mirror image of, the orientation of the corners of the tread blocks on the tread.

With reference toFIG. 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 inFIG. 3. This represents a condition with greater tread wear than at the first groove depth, so that contact patches37adiffer from contact patches37(FIG. 3) in appearance and may also differ in contact area. Channels45a,47arepresent the transformation of channels45,47, respectively, from their arrangement at the first groove depth shown inFIG. 3to their new arrangement at the second groove depth shown inFIG. 4. Adjacent channels45ahave less prominent changes in direction diagonally across the width of the footprint. For purposes of illustration only, lateral channels47aare depicted as being aligned nearly linear or linear diagonally across the width of the tread. In addition, the circumferential channels45aare less obstructed than channels45(FIG. 3) because of less prominent changes in direction. As a result, the network of channels45a,47aat the second groove depth presents a lateral path with lower flow resistance, as compared with the first groove depth as shown inFIG. 3, which makes channels45a,47amore effective and efficient for expelling water out of the tire footprint for expulsion through the shoulders20(FIG. 1) when driving on wet roads. Hence, the tread in the reduced nonskid condition ofFIG. 4has 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 inFIG. 3.

The transformation from channels45,47(FIG. 4) to channels45a,47aoccurs because the edges150,152,154,156of the contact patches37ahave a different angular orientation or inclination angle relative to the equatorial plane39at 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 plane39. As is apparent, the contact patches37aare all approximately shaped as parallelograms. Hence, the walls of the tread blocks defining the contact patches37,37aat the two different groove depths are configured to provide the footprints shown inFIGS. 3 and 4at the different groove depths.

With reference toFIG. 5, which like reference numerals refer to like features inFIGS. 1 and 2and in accordance with an alternative embodiment of the present invention, a representative tread block101, similar to tread block42(FIG. 2), has four walls that change orientation with groove depth, but in an opposite rotational sense from the tread blocks42ofFIG. 2. Corners100,102,104,106, which are arranged about the periphery of the rectangular road-contacting surface108, are defined by an intersection between surface108and corresponding walls110,112,114,116, respectively, extending to the base of an adjacent groove.

FIG. 6shows a representative tread block71, similar to tread block42, having a single wall that changes orientation with groove depth. Corners70,72,74,76, which are arranged about the periphery of the rectangular road-contacting surface38, are defined by an intersection between surface38and a corresponding wall extending to the base of an adjacent groove, of which only a wall78is visible inFIG. 6. The hidden walls (not shown) are inclined at a constant inclination angle relative to the equatorial plane39(FIG. 2) and approximately equal to the inclination angle of the corresponding corners70,72,74,76. Wall78, in contrast, changes its inclination angle relative to the equatorial plane39as a function of groove depth, similar to walls58,60,62,64(FIG. 5).

Wall78may bound one of the circumferential grooves44(FIG. 2) or one of the lateral grooves46(FIG. 2). If wall78were bounding one side of one of the circumferential grooves44, the inclination of the portion of channel45adjacent to wall78defined by groove44in the tire footprint would change as the tread12wears. Similarly, if wall78bounds one side of one of the lateral grooves46, the inclination of the channel47defined by groove46in the tire footprint would change as the tread12wears.

FIG. 7shows a representative tread block81, similar to tread block42, having two walls that change orientation with groove depth. Corners80,82,84,86, which are arranged about the periphery of the rectangular road-contacting surface38, are defined by an intersection between surface38and a corresponding wall extending to the base of an adjacent groove, of which only walls88and90are visible inFIG. 7. The non-visible walls (not shown) are inclined at a constant inclination angle relative to the equatorial plane39(FIG. 2) and approximately equal to the inclination angle of the corresponding corners82and86. Walls88and90, in contrast, change their inclination angle relative to the equatorial plane39as a function of groove depth, similar to walls58,60,62,64(FIG. 5). The inclination angle of wall90changes in an opposite rotational sense to the inclination angle of wall88. In other words, wall90effectively creates an undercut beneath the road-contacting surface38proximate to corner84.