TECHNICAL FIELD

The presently disclosed invention is generally directed to precured treads for application to a tire carcass and retreaded tires derived therefrom.

BACKGROUND

Precured treads are designed to include an undertread below the grooves to provide sufficient strength and integrity to the precured tread for proper handling during retreading operations, for stability in placement on the tire carcass being recapped, and to maintain the designed groove width as the retreaded tire is put in an envelope and cured. Furthermore, this undertread is often of at least a minimum thickness to ensure that the tread does not rip or tear when handled or when the bottom side of the tread is abraded in preparation for bonding to a tire carcass. The undertread of the procured tire becomes part of the total undertread of the newly retreaded tire, and, generally, an equivalent amount of the original undertread is removed from the tire being retreaded to accommodate the new undertread thickness of the precured tread to maintain the desired total undertread thickness in the finished tire.

In an effort to reduce the thickness and weight of the new precured tread, which reduces waste as less tread is removed from the used tire during the retreading process, it would be advantageous to reduce the undertread of the precured tread while maintaining the tread stability and rigidity by increasing the strength and rigidity of the groove bottom itself. A thinner undertread on the precured tread would allow more of the original undertread to be retained on the tire being retreaded. The net result would be a retreaded tire with the same skid depth and undertread thickness as before, but with significantly less new rubber being spent. Furthermore, a tread having a reduced undertread would be better able to

accommodate a used tire from which an insufficient amount of undertread was removed prior to application of the new precured tread. Otherwise, the effective or net undertread thickness of the retreaded tire may be thicker than desired, which may reduce tire performance.

Furthermore, during tire operation, there is the possibility that cracks may form and propagate along a groove bottom, such as where the groove side intersects the groove bottom. This arises, at least in part, due to the cycle deflection of the tire as the tire tread repeatedly rotates through the tire footprint during tire operation. Benefits may therefore be realized by a pre-cured tread having a more rigid groove bottom that prevents the formation of these cracks. A retread method that employs such a tread would allow undertread reduction by reinforcing the groove bottom while maintaining skid depth.

SUMMARY

A tire tread is provided that includes opposing top and bottom tread faces delineating a tread thickness coextensive therewith. The bottom tread face is configured to attach to an annular tire carcass. Opposing lateral sides define a tread width along which adjacent tread elements assume a tread sculpture. One or more grooves are provided on the top tread face with each groove terminating at a predetermined offset distance from the tread bottom face at a groove bottom and bounded by a pair of opposing side walls defining a groove width. The tread also includes an undertread having a predetermined undertread thickness bounded by the groove bottom and the bottom tread face. One or more indentations are integral with the undertread, and each indentation includes a recessed area of predetermined depth in the undertread. The recessed area has a perimetrical extent with at least one tapering wall coextensive therewith. The indentations are arranged along a length of the groove such that consecutive indentations are separated by a predetermined distance.

In some embodiments of the presently disclosed invention, the tire tread also includes a landing between adjacent indentations separated by the predetermined distance. Each landing may be coextensive with the groove bottom. A series of indentations may be integral with the undertread. Each indentation may incorporate a predetermined geometry selected from at least one of an ellipse and a polygon.

In additional embodiments of the presently disclosed invention, the tire tread includes at least one of: a distance between antipodal points of an elliptical indentation that delineates an outermost length of the indentation relative to the groove bottom; adjacent antipodal points of adjacent elliptical indentations separated by the predetermined distance that delineates an extent of each landing; a conjugate diameter of an elliptical indentation delineated by the groove width; adjacent extents of adjacent polygonal indentations separated by the predetermined distance; and one or more polygonal indentations, at least one of which includes a pair of sides that are equal and coextensive with the opposing groove side walls. Consecutive landings may have consistent parameters as determined by the predetermined distance.

Methods are also provided for increasing effective skid depth while reducing undertread. Some embodiments of such methods include providing a tire tread as presently disclosed herein. Such a tire tread may be a pre-cured tire tread. The exemplary methods presently disclosed herein may also include providing an annular tire carcass having an annular tread- receiving portion and arranging at least one layer of bonding material between the tire tread and the tire carcass. The tire tread may be applied to the tire carcass, such that the undertread with the one or more indentations extends into a thickness of the layer of bonding material.

A retreaded tire assembly is also provided that includes a tire as presently disclosed herein and an annular tire carcass having an annular tread-receiving portion. At least one layer of a bonding material may be between the tire tread and the tire carcass.

A kit is also provided for increasing effective skid depth of a retreaded tire. The kit includes an annular tire carcass having an annular tread-receiving portion and one or more tire treads as presently taught herein. The one or more tire treads are selected from a plurality of tire treads each having a tread sculpture of similar configuration to a tread sculpture of the tire carcass.

Other aspects of the presently disclosed apparatus will become readily apparent from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The nature and various advantages of the present invention will become more apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout, and in which:

FIG. 1 shows a cross-sectional view taken laterally across a retreaded tire as known in the art.

FIG. 2 shows a cross-sectional view of an exemplary tire tread separated from a tire carcass.

FIG. 3 shows a front cross-sectional perspective view of the exemplary tread of FIG. 2 taken along line 3-3.

FIG. 4 shows a top plan view of the exemplary tread shown in FIGS. 2 and 3 having lateral and longitudinal grooves with protrusions extending into the tread.

FIGS. 5, 6 and 7 show top partial views of exemplary undertreads, with each exemplary undertread having a number of protruding strengthening members forming a stone ejector arrangement. FIG. 8 shows a top partial view of an exemplary tread having strengthening members arranged along a length of a groove bottom and extending from opposing sides of the groove in an alternating arrangement.

FIG. 9 shows a front sectional view of the tread of FIG. 8 along line 9-9, showing tapering strengthening members protruding from the groove bottom and from opposing sides of the groove.

FIGS. 10 and 11 show top partial views of exemplary undertreads, with each exemplary undertread having a number of radiused areas forming a stone ejector

arrangement.

FIGS. 12 and 13 show a cross-section of the exemplary undertread of FIG. 10 taken along respective lines 12-12 and 13-13, showing a non-linear groove bottom and a constant undertread thickness.

FIG. 14 shows a front cross-sectional perspective view of the exemplary tread of FIG.

10.

DETAILED DESCRIPTION

Particular embodiments of the presently disclosed invention provide one or more exemplary tire treads, at least one tire incorporating at least one such tread and one or more methods for forming such tires. A tire tread as disclosed herein may include a new tire tread that is molded prior to application to a tire carcass, such as to form a retreaded tire, or molded with the tire during new tire manufacture. The presently disclosed invention provides strengthening members (also referred to herein as "stiffening members") having protrusions extending into a groove arranged within a tread from the bottom of a groove. By the addition of strengthening members along the groove bottom, at least locally the tread is stiffer or stronger in the area of the grooves. This allows reduction of the thickness of the tread underneath the grooves (the "undertread") without significant reduction in the stiffness of the tread, including portions of the tread proximate the groove bottom. By reducing the undertread, a higher percentage of tread is maintained above the undertread for use during the normal wear life of the tread. By maintaining the stiffness of the tread, proper handling of the tread is maintained without risk of tearing. By providing strengthening members along the groove bottom, crack initiation and/or propagation along a groove bottom may be avoided or significantly reduced during tire operation. Furthermore, by arranging stiffening members along the groove bottom, any peaking or raising of the reduced thickness undertread is generally avoided, or at least significantly reduced (relative a reduced thickness undertread not including strengthening members) during curing operations, where otherwise the bonding layer (e.g., the bonding layer identified as element 22 in FIG. 1) would push the undertread upwards into the depth of the groove (e.g., the groove identified as element 16 in FIG. 1).

Particular embodiments of methods of forming a retreaded tire include applying a tire tread to a tire carcass. The tire carcass generally includes a pair of beads, a pair of sidewalls, body plies, and a belt package if the tire is a radial tire (otherwise, if not including a belt package, the tire is a biased ply tire). The body plies and belt package generally have plies of rubber containing strands of reinforcements. When retreading a tire, a used tire carcass is provided, which generally includes a cured tire having at least a portion of the old tread removed so that a new tread may be attached to the tire carcass to form a retreaded tire. Commonly, at least a portion of the old tread is removed to a desired depth by performing a buffing or abrading operation. The old tread may be complete or partially removed. When forming a new tire, in lieu of a retreaded tire, a new tire carcass may be provided, where such tire carcass is generally uncured.

Particular embodiments of methods of forming a tire tread include forming a tread thickness bounded by a top side (also referred to as a ground-engaging side of the tread, configured to engage a surface upon which the tire operates during vehicle operation), a bottom side (configured for attachment to a tire carcass), opposing lateral sides and a groove extending into the tread thickness from the tread top side and terminating within a thickness of the tread at a groove bottom. The groove has a width defined by a pair of opposing sides and a groove bottom spaced from the bottom side of the tread by an undertread thickness. It is understood that the groove may be any type of groove having a groove bottom, where the groove is characterized as having any desired size, shape and geometry that may be employed in any desired tire tread.

The tread may be formed to further include a plurality of strengthening members forming protrusions extending into the groove from the groove bottom and from at least one side of the pair of opposing groove sides, the plurality of strengthening members being arranged along a length of the groove. For example, when retreading a tire, the tread may be molded and cured according to any known method and operation of retreading, which includes molding and curing the tread prior to applying the tread to the tire carcass to provide a precured tire tread. By further example, when the tire being formed is a new tire, the tread may be molded and cured according to any known method or operation of forming a new tire, which includes molding and curing the tread while attached to the tire carcass.

The strengthening members may be arranged in any one or more grooves, where such grooves may be longitudinal and/or lateral grooves. The strengthening members may also extend partially or fully across the groove width, and in any path or direction. In particular embodiments, for example, each strengthening member extends from one or both sides of a groove. Furthermore, the strengthening members may form any desired shape. For example, in particular embodiments, the cross-sectional shape of the strengthening members (e.g., as taken in a plane extending in a direction of the tread thickness and either in a direction of the tread length or width) may be block-shaped, polygonal, arcuate, rounded or any other shape as desired. The size, shape and direction of extension may vary amongst any plurality of strengthening members along the length of any groove or between different grooves within the tire tread. The strengthening members increase the stiffness of the tread so that the thickness of the tread arranged under the groove, that is, between the groove and the bottom side of the tread, which is referred to as the undertread, may be of a reduced thickness.

By providing a reduced thickness undertread, a higher percentage of the tread thickness is arranged at or above the bottom of the groove bottom, which places a higher percentage of the tread within the useable portion of the tread. The overall tread thickness may also shrink with the reduction in undertread thickness. In providing a reduced undertread, any reduction from a normal undertread thickness is possible. For example, in some exemplary embodiments, the undertread may be reduced to have a thickness less than 1 mm. Of course other reductions are contemplated. It is also understood, however, that the strengthening members may be used in any tread, whether or not being characterized as being a reduced thickness, normal thickness or even increased thickness tread or as having a reduced thickness, normal thickness or increased thickness undertread, as it is understood that the strengthening members can be useful for any such tread to provide additional strength and/or reduce or eliminate cracking, for example.

In some embodiments of a tire tread having a plurality of strengthening members arranged within a groove, the tire tread includes a thickness of the tread extending from the groove bottom to form a protruding portion of the bottom side arranged below the groove bottom such that adjacent portions of the bottom side located adjacent the protruding portion are recessed within the tread thickness from an outer surface of the protruding portion. Such embodiments are shown and described in co-owned and co-pending PCT Application No. PCT/US2013/034736 entitled TIRE TREADS WITH REDUCED UNDERTREAD

THICKNESS, filed 30 March 2013 and claiming priority to co-owned and co-pending PCT Application No. US2013/032467 filed 15 March 2013 and co-owned U.S. Appl. No.

61/618,267 filed 30 March 2012, the entire disclosures of which are all incorporated by reference herein.

Some embodiments of the presently disclosed invention may include a applying the tread to a tire carcass where a layer of bonding material is arranged between the tire tread and the tire carcass. During retreading operations, the tire tread (i.e. , the "retread") is arranged upon the tire carcass. When the tire tread is a strip of tread, such as when molded in a flat mold, for example, the tread is wrapped around the tire carcass. When the tire tread is an annular tread band, the tread band is positioned around the tire carcass, where the tire carcass is arranged within a central opening of the tread band. When applying the tread to the tire, bonding material may be employed to attach or improve attachment of the tread to the tire carcass. For example, the bonding material may comprise any elastomeric or polymeric material, such as natural or synthetic rubber, which is curable and promotes bonding by way of cross-linking. By further example, bonding material comprising an adhesive may be arranged between the tread and the tire carcass. In particular embodiments, in performing the assembling, the bonding layer may be an uncured bonding material. It is appreciated that the bonding layer may comprise any bonding material known to one of ordinary skill used for bonding the pre-cured tire tread to a tire carcass.

Further embodiments of the presently disclosed invention include curing the tread to the tire carcass. The retread curing process is performed generally within a curing vessel (e.g., an autoclave), although it is appreciated that any known method for curing the tread to the tire carcass may be employed. The curing vessel generally includes a curing chamber providing a controlled environment in which the tire-membrane assembly is cured. Generally during the curing process, the chamber is pressurized to a desired pressure and heated to a desired temperature based upon a recipe or formula. In performing the step of curing, some embodiments of the presently disclosed invention include placing the sealed fluid chamber of the tire-membrane assembly under substantial vacuum. This generally occurs at the beginning of the curing process, before pressure and heat is applied to the tire-membrane assembly in a curing chamber of a curing vessel. As used herein, "vacuum" or "under vacuum" means providing a fluid pressure equal to zero psia (pounds per square inch absolute). Now referring to the figures, wherein like numbers represent like elements, and with particular reference to FIG. 1, a prior art tread 10' is shown in a cross-sectional view extending laterally across the tread. The tread 10' is shown as having a top side 12 and a bottom side 14 (each of which may also be referred to as top and bottom faces, respectfully) and a thickness T' extending therebetween. The tread also includes a plurality of grooves 16, such as longitudinal grooves 16i _ong and optional lateral grooves (not shown), extending from top side 12 towards bottom side 14. Grooves 16 terminate at a groove bottom 17b offset a distance T'is from the tread bottom side 14 to define an undertread having a thickness T'is. Typically, the prior art undertread thickness T'is is in a range from about 2.5 to about 4.5 mm. Grooves 16 also have a width defined by opposing sides 17a.

A skid depth Di6 is defined by the difference between thickness T' between top side 12 and bottom side 14 and thickness T'is of undertread 18. Skid depth Di6 is the thickness of useful tread contained within the pre-cured retread, that is, a thickness designed to be available for wearing during vehicle operation. Tread 10' also extends between opposing lateral sides 19, which may be coextensive with a tire carcass 20. Tread 10' is transferred to and bonded with tire carcass 20 along at least a portion of bottom side 14, either directly or by use of a bonding material 22, such as a layer of bonding rubber or adhesive, arranged between the tread and the tire carcass. In some embodiments, carcass 20 may be of similar original tread design to a pre-cured tread sculpture such as tread 10'. In other embodiments, carcass 20 may be of different tread design to the pre-cured tread sculpture being applied thereto.

With reference to FIGS. 2-4, an exemplary embodiment of the presently disclosed invention is shown. In particular, an exemplary tread 10 is shown having a top side (or face) 12, a bottom side (or face) 14 and a thickness T extending therebetween. A plurality of grooves, generally indicated as 16, is shown that include lateral grooves 16i _at and longitudinal grooves 16i _ong extending into the tread thickness from top side 12 towards bottom side 14. Longitudinal and lateral grooves 16i _ong , 16i _a t are shown to extend longitudinally (that is, in a lengthwise direction) along a linear path, although is it understood that each may extend lengthwise along any desired path, which includes any curvilinear path or non- linear path. As best shown in FIGS. 3-4 in a particular embodiment, longitudinal grooves 16i _on g extend along a linear path while lateral grooves 16i _at extend along a non-linear path. Furthermore, the lateral and longitudinal grooves may extend along continuous or discontinuous path. Grooves 16 also terminate at a groove bottom 17b, offset a distance from tread bottom side 14 to define an undertread having a thickness Tig. Undertread thickness Tig is thinner than an undertread thickness of tread 10' of FIG. 1 due at least to the addition of strengthening members 24 arranged along the groove bottom 17b to provide sufficient rigidity and strength to improve handling of the tread, to maintain dimensional stability of the tread, and to prevent tearing of the tread during the retreading process, such as when the tread is handled, transported, and applied to the tire carcass. For example, in particular embodiments, with the addition of strengthening members 24 as presently described herein, undertread thickness Tig is reduced 1 to 3 mm to approximately 1.5 mm or less, which at least equals a 40 to 67% decrease in the undertread thickness relative to a typical undertread thickness of 2.5 to 4.5 mm. In other embodiments, undertread thickness Tig is reduced to approximately 1.0 mm or less, which at least equals a 60% to 78% decrease in the undertread thickness relative to typical undertread thicknesses. In these exemplary embodiments, which include applications for truck tires, the typical overall tread thickness T is generally 12 to 30 mm. Therefore, a prior art undertread typically consumes 8% to 15% of a 30 mm thick tread and 21% to 38% of a 12 mm thick tread. However, when reducing the undertread thickness, the undertread may consume less than 8% of the tread thickness. For example, when reducing the undertread thickness from 2.5 mm to 1.5 mm, whereby a 12 mm thick tread becomes an 11 mm thick tread, the reduced undertread consumes no more than 14% (that is, 14% or less) of the thinner tread. Furthermore, when reducing the undertread thickness from 2.5 mm to 1.0 mm, and the 12 mm thick tread becomes a 10.5 mm thick tread, the reduced undertread consumes no more than 10% (that is, 10% or less) of the thinner tread. Performing similar calculations on a 30 mm thick tread for the same reduction in undertread, the reduced undertread consumes no more than 5% (that is, 5% or less) of the thinner tread (when reducing the undertread thickness to 1.5 mm) and 4% (that is, 4% or less) of the thinner tread (when reducing the undertread thickness to 1.0 mm)

With continued reference to FIGS. 2-4, strengthening members 24 include protrusions extending upwardly or outwardly from groove bottom 17b into a corresponding groove 16 by a distance T2 . Distance T2 is also referred to as a thickness of each strengthening member 24. Strengthening members 24 also have a width W24. In the exemplary embodiment shown, strengthening members extend across a full width Wi6 of each groove measured at the groove bottom and from each side 17a. In other embodiments, strengthening members 24 may extend fully or partially between opposing sides 17a and across the groove width Wi6- It is understood that the strengthening members 24 are sufficiently sized, oriented and spaced to provide a sufficiently resilient and strong tread that resists tearing and improves tread stability during the retreading process. Strengthening members also provide an effective skid depth Di6 that is closer to the total tread height T than treads provided in the prior art. For example, when employing strengthening members, the undertread thickness Tig is less than 2 mm. In some embodiments, Tig is at or about 1.5 mm or less, or at or about 1 mm or less. In such instances, in particular embodiments, strengthening members 24 have a thickness T24 of about 4 mm or less, which is below the groove depth that commonly remains when a tire is removed from service. Width W2 and frequency must be sufficient to give adequate stiffness to the groove.

In addition to strengthening the tread, the strengthening members may also operate as wear bars useful for determining the amount of useful tread remaining. For example, the height of the strengthening members may be preselected to become exposed to the top surface of the tread when an intended thickness of the tread remains in the normal life of the tread. Furthermore, strengthening members may operate as stone ejectors to assist in discharging any unwanted material from the groove, such as stones or other foreign matter, or noise suppressors for reducing the noise generation of the tread during tire operation. When operating as noise suppressors, strengthening members extend at least halfway through the depth or height of the groove and/or at least halfway across the groove width. In some embodiments, the strengthening members, when operating as noise suppressors, extend substantially the full depth or height of the groove and/or substantially across the groove width. It is understood, however, that any prior art wear bars, stone ejectors and noise suppressors are not configured or arranged in sufficient frequency to operate as the strengthening members described herein, and not taught for use in conjunction with thin undertread tire treads to solve the problems described herein that may arise during retreading operations. Accordingly, while the strengthening members may be configured to operate as wear bars, stone ejectors and/or noise suppressors, strengthening members may or may not operate as such and may be arranged within a groove in addition to other wear bars, stone ejectors and/or noise suppressors separately provided for their intended purpose.

With specific reference to FIGS. 3-4, strengthening members are shown in further detail according to a particular embodiment. In particular, the strengthening members 24 are shown spaced along groove bottom 17b, extending across the full width of the groove and from each side 17a. Strengthening members 24 are shown spaced along the groove bottom 17b by a distance S24, such that the strengthening members are separated by a distance Δ2 . Spacing S2 may comprise any desired spacing sufficient to provide strengthening or stiffening properties as desired for the particular tread design and use. For example, in particular embodiments, spacing S2 is at or about 10 mm or less, although greater spacings may be employed (such as when, for example, employing strengthening members having greater widths W24) for this and any other embodiments discussed or contemplated herein. It can also be said that the strengthening members are arranged in an array, at least along each tread element. Accordingly, the spacing may be constant along a length of the groove, or may be variable as desired. Nevertheless, the spacing is sufficient to provide a desired stiffness for the undertread thickness reduction. With regard to the distance of separation Δ24 between adjacent strengthening members 24, it is understood that such distance may be any distance desired. It is also understood that in certain embodiments, separation distance Δ24 may be equal to zero.

In some embodiments, an arrangement of strengthening members may be quantified by comparing the void defined by each groove without the presence of any strengthening members with the amount of volume the strengthening members consume within the groove. This comparison of volumes is often referred to as a void volume ratio. For example, in particular embodiments, for a length of the groove, the volume of the groove between the groove bottom and the top of the tallest strengthening member (the height of a strengthening member equals distance T24, shown in FIGS. 1 and 9) is at least 25% filled with

strengthening members. In other words, the ratio of strengthening member volume to total groove void as measured below the tallest strengthening member is 1:3. In other

embodiments, the volume of the groove between the groove bottom and the top of the tallest strengthening member is at least 20% and at least 40% filled with strengthening members.

With continued reference to FIGS. 3-4, strengthening members 24 are shown to include rectangular cubes. As such, the sides of each strengthening member 24 generally extend normal to the groove bottom, but may be tapered or inclined such that the sides of the strengthening members intersect the bottom groove at an angle other than 90 degrees. A tapered arrangement may reduce stress concentrations that may form along the sides of the strengthening members at the groove bottom. Furthermore, the strengthening members extend laterally, normal to a longitudinal centerline of the tread. It can also be said that the strengthening members are arranged in an array, at least along each tread element 28 or rib 29. It is understood, however, that strengthening members may comprise any shape and extend from either or both groove sides 17a, extend across the groove width fully or partially, and may extend across the groove width Wi6 in any direction. In particular exemplary embodiments, a plurality of strengthening members 24 having a width of approximately 8 mm spaced are arranged every 10 mm or less (S24) to form an arrangement of strengthening members along a length of a groove.

It is understood that strengthening members may form any desired shape and arrangement along a length of a groove. With reference to FIGS. 5-7, a variety of groove and strengthening member arrangements are illustrated.

In the exemplary embodiment illustrated in FIG. 5, strengthening members 24 extend into the groove 16 from opposing sides 17a in an alternating arrangement along a length of the groove. Each strengthening member 24 has a width W2 less than the groove width W16. In particular embodiments, width W2 is greater than one-half (1/2), or at least three-quarters (3/4), of the groove width Wi6 as measured along the groove bottom (or, in other words, at least ½ or ¾ the width Wi6 of the groove bottom) - such as when the groove width varies with the depth of the groove, such as is shown in the FIGURES. In other variations, W24 extends fully across a width Wi6 of the groove, such as is shown in FIGS. 2-4 by example. As can be appreciated from this figure, the strengthening members 24 form rectangular cubes having a rounded terminal end. Further, the length dimension L ₂ 4 and spacing S24 are such that there is space or void arranged between the strengthening members 24. In particular exemplary embodiments, a plurality of strengthening members 24 having a width of approximately 8 mm spaced are arranged every 5 mm or less (S24) to form an arrangement of strengthening members along a length of a groove.

In the exemplary embodiment illustrated in FIG. 6, strengthening members 24 extend diagonally across the groove width Wi6 (that is, in a direction not perpendicular to the length of the groove or biased relative a widthwise direction of the groove) in an alternating arrangement. Strengthening members 24 are also shown connected to form a continuous arrangement of alternating strengthening members extending lengthwise along a length of the groove 16. In the embodiment shown, the lengthwise extending of the continuous arrangement of strengthening members extends along a zigzag path, although it is understood such path may comprise any non-linear or curvilinear path. In the embodiment shown, strengthening members 24 extend from both opposing sides 17a diagonally across the groove, although strengthening members may only extend from one of the sides 17a while still extending lengthwise in a continuous, alternating path. Distance S24 represents the length of each strengthening member of the continuous arrangement of strengthening members as the length of each such member extends to and from opposing sides 17a of a corresponding groove 16. The continuous arrangement of strengthening members can also be described as a continuous strengthening member having alternating segments extending between opposing sides 17a of a groove 16. In other variations, a plurality of strengthening members comprising any shape maybe disconnected (that is, spaced apart) while remaining biased to the groove widthwise direction. In particular exemplary embodiments, a plurality of strengthening members 24 having a width of approximately 8 mm spaced are arranged every 10 mm or less (S24) to form an arrangement of strengthening members along a length of a groove.

In another exemplary embodiment illustrated in FIG. 7, strengthening members 24 are arranged to form a continuous arrangement of strengthening members extending lengthwise along a length of the groove 16, whereby the continuous arrangement forms a network or web of crisscrossing strengthening members. For example, it could be said that the continuous arrangement shown comprises the alternating zigzag arrangement of FIG. 6 overlaid with a second alternating zigzag arrangement shifted lengthwise such that the first and second zigzag arrangements are mirror images of each other as referenced from a longitudinal centerline of the grove. The arrangement of strengthening members 24 shown can also be described as comprising "X" shaped or diamond-shaped strengthening members

interconnected to form a continuous arrangement of strengthening members. It is understood that any shaped strengthening members 24 may be used to form a network or web of intersecting or crisscrossing strengthening members. Furthermore, the "X" or diamond- shaped strengthening members 24 may be disconnected, whereby such strengthening members may be separated and spaced apart in lieu of being connected in a continuous arrangement. It is understood that the embodiment of FIG. 7 is a variation of the continuous arrangement of strengthening members shown in FIG. 6. In particular exemplary

embodiments, a plurality of strengthening members 24 having a width of approximately 8 mm spaced are arranged every 10 mm or less (S24) to form an arrangement of strengthening members along a length of a groove.

Yet another exemplary embodiment is illustrated in FIGS. 8 and 9, whereby strengthening members 24 taper in depth or thickness. Furthermore, strengthening members 24 are spaced apart along a length of the groove and extend alternatively from opposing groove sides 17a to form an alternating, spaced apart arrangement, and groove bottoms 17b within the grooves 16 may alternate. In the aspect illustrated in FIGS. 8-9, the design is similar to the aspect shown in FIG. 6 with the strengthening members 24 and groove bottoms 17b being inverted. In this arrangement, the strengthening members 24 form a tetrahedron, or are pyramidal in shape, extending from alternating sidewalls 17a. The strengthening members are arranged such that the arrangement of groove bottom 17b between the strengthening members 24 forms a reduced groove 26 along the groove bottom zigzagging sideways along a length of the major groove 16. This reduced groove 26 has a width W26, which is shown to be constant but may be variable in other variations. It can be said that the arrangement of strengthening members in FIG. 5 also provide a reduced groove 26. In the embodiment of FIGS. 8 and 9, strengthening member width W2 is greater than one -half (1/2) of the groove width Wi6 and may also be at least equal to three-quarter (3/4) of groove width Wi6 or equal to such groove width as measured along the groove bottom. This embodiment is especially advantageous, because it provides the needed rigidity while maintaining a continuous, full depth groove bottom.

Referring specifically to FIG. 9, each strengthening member 24 is shown as having a gradually sloped profile between sides 17a of groove 16. According to the aspect illustrated, each strengthening member 24 has the greatest thickness T2 at sidewalls 17a and tapers to groove bottom 17b as it approaches the opposite side. As shown in FIG. 8, strengthening member thickness T ₂ may also taper along the length of strengthening member 24, such as from the vertex of the tetrahedron whereby each strengthening member decreases in thickness in each lengthwise direction of the groove.

The arrangement described above provides a tire tread 10 having grooves 16 that define a tread design. The grooves 16 extend from top side 12 towards bottom side 14 of tread 10 and include tapering sides 17a and a groove bottom 17b arranged at the full depth of the groove. A series of protrusions 24 extend from undertread 18 into grooves 16, providing a web of connectors, thereby allowing for a thin undertread 18 at other points. In this arrangement, a skid depth Di6 is nearly equal to tread thickness T. Strengthening members 24 arranged along groove bottom 17b provide stability, strength and rigidity to a reduced thickness undertread 18 during the de-molding of the pre-cured tread, as the bottom side of the tread is abraded for improved adhesion, and during the handling of the tread during the retreading process, which resists tearing and maintains dimensional stability during the retread process. Furthermore, in any newly formed tire or in any retreaded tire, using the tread designs described herein optimizes resistance to the formation of cracks within the grooves, and in particular longitudinal grooves, during tire operation. This increases the durability of the tire and the tread.

The performance of the strengthening members has been evaluated according to certain tests to confirm the benefits of the strengthening members. In particular, the performance of the tread generally represented by FIGS. 8 and 9 was evaluated, treads having a reduced thickness with strengthening members generally described in FIGS. 8 and 9 were evaluated against treads having prior art undertread thicknesses without strengthening members. (For the test, the continuous arrangement of strengthening members formed an alternating arrangement comprising a winding, curvilinear arrangement as opposed to the linear-segmented, zig-zag arrangement shown in the FIG 8.) Specifically, reduced undertread-thickness treads were characterized as having an overall thickness T of 11 mm and an undertread thickness Tig of 1.0 to 1.4 mm, with the height of the strengthening members 24 being 4 mm and being spaced a distance Δ2 of 10 mm. The prior art tread (with reference to FIG. 1) had an overall thickness T' of 13 mm and an undertread thickness T'is of 3.5 mm. Testing included verifying the durability of the reduced undertread-thickness treads as they were processed and used to form a retreaded tire. Furthermore, the retreaded tires were inspected to ascertain whether any peaking of bonding layer material (e.g. , see element 22 in FIG. 1) occurred, where peaking would cause excessive bonding layer material to accumulate beneath the undertread (e.g. , see element 18 in FIG. 1) and therefore push the undertread upwards and further into the groove to reduce the overall depth of the groove. Finally, the retreaded tires were run under common conditions to ascertain the performance of the reduced-thickness undertread tires with regard to crack initiation and propagation along the groove bottom and with regard to tread operating temperature and tire rolling resistance. In conclusion, while maintaining the same groove depth between the different tire treads while also removing 21 % weight in the reduced undertread-thickness tread by reducing the thickness of the undertread, no noticeable bonding layer peaking was observed in the reduced undertread-thickness tires, which would have been expected to peak without use of the strengthening members. Furthermore, no noticeable cracking was observed along the groove bottoms for those reduced undertread-thickness treads employing the strengthening members. Finally, the operating temperature of the reduced-thickness undertread tires ran

approximately 12% cooler across the tread (from shoulder to center), and exhibited a 4.5% reduction in rolling resistance. Therefore, by reducing the undertread thickness to reduce the weight of the tread without reducing the depth of any groove, the reduced undertread- thickness tread was able to avoid issues normally arising when reducing the thickness of the undertread, such as peaking and cracking.

In other embodiments of the inventive treads discussed above, strategically located indentations, rather than protrusions, are integrated with the undertread and groove bottom to form a full depth of the skid at a minimal undertread thickness. As with other treads, tread 10 has a top side 12 and a bottom side 14 defining a tread thickness T and may include any other desired feature, including void features. For example, the tread may include any combination of lateral grooves and longitudinal grooves extending longitudinally along any linear or nonlinear path of any design as discussed above. In the embodiments shown, however, a plurality of grooves 16 comprising longitudinal grooves 16i _ong are shown extending into the tread thickness from the top side 12 towards the bottom side 14. Each groove 16i _on g terminates at a groove bottom 17b from which undertread 18 having a thickness Tig extends to bottom side 14.

With reference to the exemplary embodiments of FIGS. 10 and 11, a variation of the tread shown in FIG. 2 is shown, where tread 10 instead includes an undertread 18 having one or more indentations 100 incorporated therein. In an exemplary embodiment as shown in FIGS. 10, 12, 13 and 14, each indentation 100 may assume a generally elliptical geometry with a distance between antipodal points delineating an outermost length Li ₀ o of indentation 100 along groove bottom 17b and relative to groove sides 17a. A predetermined distance D between adjacent antipodal points (e.g., adjacent pairs of antipodal points 100a, 100b and 100c, lOOd of FIG. 10) delineates an extent of a landing 102 between adjacent indentations 100 with landings 102 being coextensive with groove bottom 17b. In embodiments where each indentation 100 assumes a generally elliptical shape, the conjugate diameter (e.g., the smallest distance across the ellipse) may be delineated by a groove width Wi ₇ bounded by opposing groove side walls 17a. As further shown in FIG. 12, each indentation 100 has a perimetrical extent 101 for a recessed area 100b as further described hereinbelow.

In some exemplary embodiments, each indentation 100 may assume an alternative generally symmetric geometry such that a distance D between adjacent indentations 100 remains constant. In the exemplary embodiment of FIG. 11, for example, each indentation 100 assumes a generally octagonal configuration wherein extents lOOe are equal and delineate a perimetrical extent of a landing 102 between adjacent indentations 100. Landings 102 remain coextensive with groove bottom 17b. In such embodiments, each indentation may have sides lOOf that are equal and coextensive with opposing groove side walls 17a. Also, remaining sides lOOg may be equal and, together with sides lOOf and extents lOOe, determine a perimetrical extent for a recessed area as further described hereinbelow.

Although elliptical and octagonal geometries are shown herein, it is understood that indentations 100 may assume a variety of geometries, including but not limited to regular and irregular polygonal configurations.

Each indentation 100 desirably incorporates a recessed area 100b whereby perimetrical extent 101 delineates a fully open recess at a crest of the recessed area.

Recessed area 100b may have one or more walls 105 (e.g., one wall if the recessed area is generally conical or multiple walls if the recessed area is generally polygonal). Walls 105 of recessed area 100b may generally taper inwardly from perimetrical extent 101 adjacent landings 102 toward undertread 18 (e.g., as shown in FIG.12). Each recessed area desirably has a predetermined depth Uis into undertread 18 wherein the depth is determined by an extent between perimetrical extent 101 and undertread 18 having thickness Tig.

Predetermined depth Uis accommodates a maximum skid depth thickness for optimized wear of the tread with minimal undertread thickness. Such performance is attained while retaining the stability of the tread, for example during brushing of bottom side 14 and during building and curing processes as known in the art of retreading.

In the presently disclosed embodiments, consecutive landings 102 have consistent parameters as determined by predetermined distance D. In some embodiments, distance D may be from about 2mm to about 4mm inclusive. In some embodiments, distance D may be at or about 3mm + 0.25mm. For some embodiments of the presently disclosed invention, each indentation may have a length Lioo from about 12 mm to about 18 mm. In some embodiments, each indentation may have a length Lioo at or about 15mm + 0.50mm. For some embodiments, depth Uis of recessed area 100b may be from about 1mm to about 3mm. In other embodiments, depth Uis may be at or about 2mm + 0.25mm. It is understood that, for the aforementioned parameters, it is desirable to retain consistency for each recessed area 100b and landing 102. A person of ordinary skill would contemplate such consistency as providing a full depth of the skid at a minimal undertread thickness (e.g., an undertread thickness less than about 1mm). Such consistency also enhances the aesthetic appearance of the groove pattern while providing sufficient reinforcement prior to, during and after a retreading process. It is understood, however, that parameters may be adjusted between adjacent indentations 100 to accommodate tread stability requirements for certain tread designs. For example, one landing 100 may be defined by a distance D of 2.5mm while an adjacent landing 102 may be defined by a distance D of about 3.0mm, and these distances may be alternating between adjacent indentations. Similarly, one recessed area 100b may have a depth of about 2.0mm while an adjacent recessed area 100b may have a depth of about 1.75mm, and these depths may be alternating. A person of ordinary skill would contemplate parametrical variances as being amenable to the practice of the presently disclosed invention.

By arranging at least a portion of undertread 18 with indentations 100, the useful wear portion of skid depth Di6 of the tread can be increased. The skid depth is the thickness of useful tread 10 contained within the precured retread, that is, the thickness designed for wearing during vehicle operation. By arranging undertread 18 with recessed areas 100b having a depth Uis that forms a full depth of the skid, the skid depth of the tread is increased over the prior art tread of FIG. 1 to thereby increase the wear life of the tread. In particular embodiments, skid depth Di6 may be increased by more than 1 mm, or alternatively more than 1.5 mm over the prior art tread depth. In particular embodiments, the skid depth is increased between 2 and 4 mm. Smaller or larger increases are contemplated. The undertread thickness Tig is decreased commensurately (e.g., to a thickness less than about lmm) without compromising tread integrity and performance. In operation, bottom side 14 presses onto the transfer surface of the carcass without additional preparation of the carcass. Thus, the exemplary treads herein are readily used on a carcass and readily integratable into current retreading operations without requiring variance to same.

The presently disclosed process reduces both tread weight and thickness by utilizing maximum skid depth without compromising the integrity of the tread. The presently disclosed invention enhances the attributes of existing retread tires by employing a pre-cured tread of reduced thickness and increasing the usable skid depth via groove bottom geometry. Advantage is taken of all usable material of the tire, with the effect that less material is required in the undertread. Costs attributable to buffing processes are inherently reduced, and the amount of new rubber required for the pre-cured tread is similarly reduced.

It is understood that the presently disclosed methods may be employed on tires that have never been retread. It is further understood that the presently disclosed methods are contemplated for use on tires that have previously been subject to one or more retread processes, either as disclosed herein or according to one or more other amenable retreading methods. The presently disclosed invention may be utilized in association with retreaded heavy duty truck or trailer tires and any other tire type, including but not limited to light truck, off-road, ATV, bus, aircraft, agricultural, mining, bicycle, motorcycle and passenger vehicle tires.

The terms "comprising," "including," and "having" and their equivalent terms, as used in the claims and specification herein, shall be considered as indicating an open group that may include other elements not specified. The terms "a," "an," and the singular forms of words shall be taken to include the plural form of the same words, such that the terms mean that one or more of something is provided. The terms "at least one" and "one or more" are used interchangeably. The term "single" shall be used to indicate that one and only one of something is intended. Similarly, other specific integer values, such as "two," are used when a specific number of things is intended. Ranges that are described as being "between a and b" are inclusive of the values for "a" and "b".

As used herein, a "user" or an "operator" may be a single user or operator or multiple users and operators (for example, multiple users sharing use of one or more devices incorporating the presently disclosed invention). As used herein, the term "process" or "method" may include one or more steps performed at least by one user or operator. Any sequence of steps is exemplary and is not intended to limit methods described herein to any particular sequence, nor is it intended to preclude adding steps, omitting steps, repeating steps or performing steps simultaneously.

The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as "40 mm" is intended to mean "about 40 mm."

Every document cited herein, including any cross-referenced or related patent or application is hereby incorporated herein by reference in its entirety unless expressly excluded or otherwise limited. The citation of any document is not an admission that it is prior art with respect to any invention disclosed or claimed herein or that it alone, or in any combination with any other reference or references, teaches, suggests or discloses any such invention. Further, to the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern.

While particular embodiments of the disclosed apparatus have been illustrated and described, it will be understood that various changes, additions and modifications can be made without departing from the spirit and scope of the present disclosure. Accordingly, no limitation should be imposed on the scope of the presently disclosed invention, except as set forth in the accompanying claims.