CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to International Application No. PCT/US2015/053343, filed September 30, 2015 with the U.S. Patent Office (acting as a Receiving Office), and which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

[0002] This invention relates to tire treads, and more specifically, to the arrangement and formation of sipes within a tire tread.

Description of the Related Art

[0003] Sipes are commonly employed in tire treads. Sipes form very narrow grooves or slits within a thickness of the tire tread and are configured to close or remain closed at some instance within a footprint during tire operation. A footprint refers to the area of contact between a tire and a ground surface. In certain instances, to generate an interlocking effect between opposing tread surfaces between which the sipe is arranged (that is, between opposing sides of the tread forming the sipe), the opposing sides or surfaces undulate in both a depthwise direction and a lengthwise direction of the sipe. This interlocking can improve tread wear, but may degrade rolling resistance. Therefore, there is a need to both improve tread wear and reduce rolling resistance.

SUMMARY OF THE INVENTION

[0004] Particular embodiments of the present invention include tire treads having a plurality of sipes where at least one of the opposing sides of the sipe thickness includes a plurality of projections and a method for forming the same.

[0005] Particular embodiments of a tire tread having a plurality of sipes includes a tire tread comprising a length extending in a lengthwise direction, the lengthwise direction being a circumferential direction when the tread is arranged on a tire, a width extending in a lateral direction, the lateral direction being perpendicular to the lengthwise direction, and a thickness extending in a depthwise direction from an outer, ground-engaging side of the tread, the depthwise direction being perpendicular to both the lengthwise direction and the widthwise direction of the tread. The plurality of sipes each have a length extending at least partially in a direction of the tread length or width, a height extending at least partially in a direction of the tread depth and perpendicular to the tread length, and a thickness. Each sipe is arranged between opposing surfaces of the tread within the tread thickness. Further, at least one of opposing sides of the sipe thickness includes a plurality of projections, the plurality of projections being spaced apart. In certain instances, each projection has a height measuring 0.025 to 0.375 millimeters.

[0006] In particular embodiments a method for forming the tire tread having a plurality of sipes includes a step of molding each of a plurality of sipes using a sipe-molding member. Each sipe-molding member has a length configured within the tread to extend at least partially in a direction of the tread length or width, a height configured within the tread to extend at least partially in a direction of the tread depth and perpendicular to the tread length, and a thickness. Each sipe-molding member is arranged between opposing surfaces of the tread within the tread thickness. At least one of opposing sides of the sipe-molding member thickness includes a plurality of projections being spaced apart. In certain instances, each projection has a height measuring 0.025 to 0.375 millimeters. The method for forming the tire tread having a plurality of sipes further includes removing the sipe-molding member and leaving a sipe remaining within the tread. The sipe has a void shaped as the sipe-molding member and a plurality of projections corresponding to the plurality of projections arranged along the sipe-molding member.

[0007] The foregoing and other embodiments, objects, features, and advantages of the invention will be apparent from the following more detailed descriptions of particular embodiments of the invention, as illustrated in the accompanying drawings wherein like reference numbers represent like parts of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 is a partial perspective view of a tire tread showing a plurality of tread blocks including a sipe, where one tread block is shown in a partial cutaway to better show the details of a sipe, in accordance with an embodiment of the invention.

[0009] FIG. 2 is an enlarged view of Section 2 from FIG. 1.

[0010] FIG. 3 is a side view of the sipe shown in FIGS. 1 and 2.

[0011] FIG. 4 is a sectional view of the sipe shown in FIG. 3 taken along line 3-3.

[0012] FIG. 5 is a perspective view of a sipe-mold member for forming the sipe in FIG. 1, in accordance with an exemplary embodiment of the invention.

[0013] FIG. 6 is a sectional view of the sipe-mold member shown in FIG. 5 taken along line 6-6.

[0014] FIG. 7 is a perspective view of a sipe, in accordance with another embodiment of the invention.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

[0015] The present invention includes tire treads, tires including such treads, and methods for forming tire treads, where any such tread includes a sipe having the surface geometry described herein.

[0016] With regard to the tire treads described herein, it is appreciated that each such tread includes a length, width, and thickness. The length extends in a lengthwise direction. As the tread may be formed with the tire, or separately for later installation on the tire, such as during retreading operations, for example, the lengthwise direction of the tread is a circumferential (that is, annular) direction when the tread is arranged on a tire. The width extends in a lateral direction, the lateral direction being perpendicular to the lengthwise direction, while the thickness extends in a depthwise direction from an outer, ground- engaging side of the tread, the depthwise direction being perpendicular to both the lengthwise direction and the widthwise direction of the tread.

[0017] The purpose of this invention is to introduce a surface geometry to supplement any undulation or undulating of the sipe thickness, for the purpose of increasing the surface friction between, and improved interlocking between, opposing sides of the tread between which the sipe is arranged. In turn, improvements in wear, dry braking and rolling resistance may be achieved. Additionally, because the new surface geometry increases the rigidity of the sipe-forming mold member, a wider sipe-forming area along said mold member may be increased and/or the thickness of the sipe-forming area may be reduced, each of which can lead to further improvements in wear, dry braking and rolling resistance.

[0018] It is appreciated that the surface geometry described herein may be applied to any sipe known to one of ordinary skill in the art, or obvious variation thereof. For example, with reference to an exemplary embodiment shown in FIG. 1, a partial perspective view of a tire tread 10 is shown having a plurality of tread blocks 12 each including a sipe 14. One sipe 14 is shown in greater particularity in a partial cutaway of a particular tread block 12, which is then shown in an enlarged view in FIG. 2. As shown, tread 10 includes a plurality of sipes 14 each having a length L14 extending at least partially in a direction of the tread length L1 ₀ or width W1 ₀ , a height H14 extending at least partially in a direction of the tread depth T1 ₀ and perpendicular to the tread length, and a thickness T14. As best seen in FIG. 1, each sipe 14 is arranged between opposing sides or surfaces 16 of the tread within the tread thickness.

[0019] It is appreciated that the sipe may form a planar or contoured sipe. In other words, the body of the sipe may be planar or contoured. A planar sipe may also be referred to as a straight sipe. A contoured sipe is non-planar, where the thickness extends in a direction of the sipe length and/or height along any desired non-linear path, which may be a curvilinear path or an undulating path, for example. In an exemplary embodiment, as can be seen in FIGS. 1-2, the sipe thickness T14 (forming a body of the sipe) undulates back and forth along a first path PI in a direction of the tread length L1 ₀ as the sipe extends in a direction of the sipe height H14, which is also the direction of the tread depth T1 ₀ in the embodiment shown. In other variations, the first path undulates back and forth in a direction of the tread length L1 ₀ while the first path extends a direction of the sipe length L14, which, in the embodiment shown, would be in the direction of the tread width Wio- Of course, because the sipe 14 may be formed in any arrangement within the tread, the sipe length and width may extend at least partially in any direction of the tread length or width. Because the undulating thickness does not pertain to or operate as any surface geometry, the undulating thickness of the sipe can be referred to as an undulating body. When, as noted above, a sipe more generally is planar or contoured in form, it can be said that the body of the sipe is planar or contoured.

[0020] The first path can be described as being a non-linear, undulating path, as the first path forms a plurality of undulations. In the embodiment shown, the undulating path is curvilinear, although in other variations, the undulating path may comprise a series of line segments, such as to form a stepped or zig-zagging undulating path. In certain embodiments, the plurality of undulations have a period greater than the spacing between the plurality of projections (discussed further below) and/or an amplitude of greater than the amplitude of each of the plurality of projections.

[0021] As it is appreciated that the surface geometry described herein may be applied to any sipe known to one of ordinary skill in the art, or any obvious variation thereof, in particular variations of the sipes described herein, a sipe (and its thickness or body) may not undulate at all and remain planar or may undulate in one or more directions. For example, a sipe (and its thickness or body) may not only undulate back and forth as the sipe extends in a particular direction, the sipe (and its thickness or body) may also undulate back and forth as the sipe extends in another direction. In extending in the second direction, it can be said that the sipe (and its thickness or body) undulates along a second path (a second non-linear, undulating path) in a second direction. For example, with reference to FIG. 7, a sipe 14 is shown that undulates as the sipe extends in both a direction of the sipe height H14 (via nonlinear, undulating path PI) and a direction of the sipe length L _i4 (via non-linear, undulating path P2). In this embodiment, the two directions are perpendicular to each other. Still, in other embodiments, the two directions may be biased to each other by an angle other than 90 degrees (perpendicular). It is noted that in FIG. 7, a prior art sipe is shown without the surface geometry discussed herein for the purpose of simplifying the figure. Accordingly, any surface geometry described herein, such as the surface geometry shown in FIGS. 1-6, may be applied to the sipe of FIG. 7.

[0022] As to the surface geometry for application to any desired sipe, and therefore for application to one or both of the opposing tread sides or surfaces between which the sipe is arranged and defined, the resulting geometry provides surface geometry features comprising a plurality of projections and/or recesses that form a or non-planar or contoured surface, much like a textured surface, such that opposing sides of the tread between which the sipe is arranged observe increased friction when relative movement between the two sides is attempted during tire operation. In applying the surface geometry to the sipe, the surface geometry is also applied to the plurality of undulations, or, in other words, the sipe body. It is appreciated that spaced apart projections form an interstitial space arranged between the projections, the interstitial space being a recess relative to the projections. Of course, the opposite is true as well, where spaced apart recesses form an interstitial space arranged between the recesses, the interstitial space being a projection relative to the recesses. Therefore, projections and recesses are used with reference to each other, and not as to how each is formed along a surface. Additionally, it is noted that a projection of the sipe is associated with a corresponding recess on one of the opposing sides or surfaces, and vice versa. In certain embodiments, the surface geometry features are formed such that surface geometry features arranged on the opposing sides generally interlock, such as when the opposing sides are mirrored opposites of each other, for example.

[0023] With reference to FIGS. 1 and 2, surface geometry features comprising a plurality of projections 18 and corresponding recesses 20 is shown along one of the opposing sides or surfaces 16 of the tread 10 between which the sipe is arranged and defined. The plurality of projections 18 and recesses 20 are spaced along the length L14 and height H14 of the sipe. In the variation shown, the projections and recesses are uniformly spaced apart, although it is appreciated that in other variations, the projections and/or recesses may be uniformly or non- uniformly spaced apart as desired. While the arrangement of projections 18 and recesses 20 is shown to form a generally smooth or rounded contoured surface, it is contemplated that more defined projections and/or recesses may be provided such that the surface is not smoothly contoured, such as where the projections form cylinders, rectangles, or pointed cones, for example. In particular embodiments, the smoothly or rounded contoured surface shown in FIG. 2 comprising a plurality of uniformly spaced projections 18 and recesses 20 represented by a function of f(x,y) = A*sin(B*x)*sin(C*y), at least along portions thereof, where A, B, and C are scaling factors. In particular, B and C control the period or spacing between protrusions and recesses, while A controls projection amplitude and recess depth with B and C. The surface generated by this function, which is also represented in the figures, generates an egg crate-like surface. The smooth or rounded contoured is also described as extending along an undulating path in two perpendicular directions at particular locations. Accordingly, by varying A, B, and C as desired, the surface geometry described herein may be obtained by one of ordinary skill using said formula. In particular embodiments, with particular reference to FIGS. 3 and 4 (showing the embodiment of FIGS. 1 and 2 in closer detail), the plurality of projections 18 are spaced apart from the middle of one projection to the middle of an adjacent projection, or from peak to peak and have a height (also referred to as an amplitude) measuring 0.025 to 0.375 millimeters (mm) or 0.025 to 0.25 mm in other variations. The height or amplitude is measured from the base or bottom of the projection. In certain embodiments, the plurality of projections are spaced apart by a distance that is less than twice the amplitude A _P1 of the first path PI, when the sipe thickness undulates. Twice the amplitude means the amplitude multiplied by two (2), where the amplitude or height is measured from the base or bottom of the projection. In more particular variations, the projections and recesses are arranged along an undulating path forming a plurality of undulations having a period (which is a spacing from the middle of one projection to the middle of an adjacent projection, or from peak to peak) of 0.1 to 3.0 mm, 0.1 to 2.0 mm, or 0.1 to 1.0 mm, and an amplitude of 0.025 to 0.375 mm or 0.025 to 0.250 mm in other variations. In such embodiments, twice the amplitude measures the distance between opposing peaks along the undulation within a single period. It is appreciated that the undulations may be formed along the surface without impacting the other side of the sipe, or the sipe thickness may undulate along the undulating path, such that where a projection is formed on one side of the sipe, a recess is formed opposite the projection on the other side of the sipe.

[0024] With reference to FIGS. 3 and 4, the tread shown in FIGS. 1 and 2 is provided in a side view and partial sectional view, respectively, to better show the undulating surface geometry features, namely, projections 18 and recesses 20. The amplitude As and period Ps are shown for the undulating path forming the projections 18 and recesses 20 along the sipe or adjacent tread surface, relative the undulating path PI along which the sipe thickness or sipe body extends. The amplitude and period of undulating path PI is represented as A _P1 and Ppi, respectively. An arrangement of projections and recesses can also be described as being arranged in an alternating projection-recess arrangement along the length and height of the sipe, such that the opposing sides of the tread are arranged in a mating configuration. Additionally, an arrangement of projections and recesses can be described as being arranged in an alternating arrangement within a plurality of rows, where adjacent rows are shifted relative to each other such that each projection in any row is arranged adjacent to a recess in each adjacent row (columns). This is seen in FIGS. 3 and 4, but can also be observed in FIGS. 2, 4, and 5.

[0025] It is appreciated that any sipe described herein may be formed by any known method for forming sipes in treads. For example, a method for forming a tire tread comprises molding any such sipe into a tire tread. In particular embodiments, a method for forming a tire tread comprises a step of molding each of a plurality of sipes using a sipe-molding member. The sipe-molding member includes a portion having the same shape as any particular sipe described herein, where such portion of the sipe-forming member is a solid form of the sipe, which is a void. In particular embodiments, for example, and with reference to FIGS. 5 and 6, a sipe-molding member 30 has a length L ₃₀ configured within the tread to extend at least partially in a direction of the tread length or width, a height H ₃₀ configured within the tread to extend at least partially in a direction of the tread depth and perpendicular to the tread length, and a thickness T30. Each sipe-molding member is arranged within the tread thickness, between opposing surfaces or sides of the tread within the tread thickness. The sipe-molding member thickness T30 undulates back and forth along a first path PI as the sipe-molding member extends in a direction of the sipe-molding member height H30 (or length L30). In particular embodiments, the first path PI forms a plurality of undulations 32 and has a period Ppi greater than the spacing (referred to as period Ps in the embodiment shown) between each of the plurality of projections and an amplitude Api of greater than the amplitude (referred to as amplitude As in the embodiment shown) of each of the plurality of projections. At least one of the opposing sides 34 of the sipe-molding member thickness T30 along one or more of the plurality undulations 32 includes a plurality of projections 36, for the purpose of forming the plurality of surface geometry projections along the resulting sipe, the plurality of projections being spaced apart by a distance less than the period Ppi of the first path PI and each having a height that is less than twice the amplitude A _P1 of the first path and measuring 0.025 to 0.375 millimeters. Twice the amplitude means the amplitude multiplied by two (2), where the height is measured from the base or bottom of the projection. Further steps of such methods includes removing the sipe-molding member, which leaves a sipe remaining within the tread, the sipe having a void shaped as the sipe- molding member and a plurality of projections corresponding to the plurality of projections arranged along the sipe-molding member.

[0026] It is appreciated that any other feature of the sipes described herein are incorporated into the sipe-molding member to form a sipe of like form. With reference to FIG. 6, for example, in certain embodiments, both of the opposing sides 34 of the sipe- molding member thickness T30 along one or more of the plurality undulations 32 include a plurality of projections 36, the plurality of projections being spaced apart by a distance less than the period of the first path and each having a height that is less than twice the amplitude of the first path and measuring 0.025 to 0.375 millimeters. Furthermore, in other embodiments, such as is shown in FIGS. 5 and 6, for example, one or more of the opposing sides 34 of the sipe-molding member thickness T30 along one or more of the plurality undulations 32 include a plurality of recesses 38, the plurality of recesses being spaced apart by a distance less than the period of the first path and each having a depth relative an adjacent projection that is less than twice the amplitude of the first path and measuring 0.025 to 0.375 millimeters. In certain variations, the projections and recesses are arranged in an alternating projection-recess arrangement along the length and height of the sipe-molding member, such that the opposing sides of the tread are arranged in a mating configuration. In other variations, the projections and recesses are arranged in an alternating arrangement within a plurality of rows, where adjacent rows are shifted relative to each other such that each projection in any row is arranged adjacent to a recess in each adjacent row. In yet other variations, the projections and recesses are formed by the thickness of the sipe-molding member undulating back and forth along a non-linear, undulating path as the sipe-molding member extends in the direction of the sipe height or length, the non-linear, undulating path forming a plurality of undulations and having a period of 0.1 to 3.0 millimeters and an amplitude of 0.025 to 0.375 millimeters.

[0027] It is appreciated that the sipe-molding member may comprise any form desired by one of ordinary skill, for use in any known molding apparatus. For example, in certain instances, such as is shown in one exemplary embodiment in FIGS. 5-6, a sipe-molding member 30 includes a thick sipe-molding portion 40 surrounding at least a portion of a thin sipe-molding portion 42. In this embodiment, both the thick and thin portions include the surface geometry, in addition to the sipe thickness undulating in a direction of the sipe thickness or width. In other variations, only the thin portion includes the surface geometry discussed herein while the thick portion only undulates, or vice versa. It is apparent that the thick sipe-molding portion is thicker than the thin sipe-molding portion. In different variations, the thick-molding portion may partially or fully surround the thin sipe-molding portion, in different variations.

[0028] Particular embodiments of this invention were tested to determine an improvement in a friction coefficient by applying a shear to two opposing rubber surfaces being treated with certain variations of the surface geometry described herein and without (smooth). In different tests, the opposing rubber surfaces either had surface geometry characterized as having projections of 0.3 mm amplitudes or 0.05 mm amplitudes or no surface geometry (smooth). All other characteristics of the tread surfaces remained constant. As a result, the samples having sipes characterized as having a surface geometry with projections of 0.3 mm amplitude observed a 60% increase in the measured friction coefficient as compared to surfaces having a surface geometry with projections of 0.05 mm amplitude. Moreover, surfaces characterized as having a surface geometry with projections of 0.3 mm amplitude observed a 70% increase in the measured friction coefficient as compared to surfaces having no surface geometry (smooth surfaces). These results were unexpected.

[0029] In other tests, a tread sample comprising five (5) rectangular tread blocks arranged side-by-side in a linear array, the tread blocks being separated by sipes, was tested to determine any improvement in tread stiffness. In each case, different tread samples having different sipe designs were tested in a friction-measurement machine, which applied a shear force in one side-by-side direction of the array, across the tread blocks and under compression such that the tread blocks pushed against one another in the side -by-side direction. In different samples, sipes were characterized as having the surface geometry described herein and shown in the figures, where for different samples the projections had either an amplitude of 0.3 mm or of 0.05 mm with the same, constant spacing. Each of these were compared to samples having sipes without the surface geometry described herein (that is, sipes having a smooth surface). All other characteristics of the tread samples were maintained between the samples as a constant. As a result, the samples having sipes characterized as having a surface geometry with projections of 0.3 mm amplitude observed a 19% increase in rigidity in the side-by-side direction as compared to samples having sipes characterized as having a surface geometry with projections of 0.05 mm amplitude. These results were unexpected.

[0030] It is appreciated that any tread discussed herein may be arranged along an annular pneumatic tire, or may be formed separately from a tire as a tire component for later installation on a tire carcass, in accordance with any technique or process known to one of ordinary skill in the art. For example, the treads discussed and referenced herein may be molded with a new, original tire, or may be formed as a retread for later installation upon a used tire carcass during retreading operations. Therefore, when referencing the tire tread, a longitudinal direction of the tire tread is synonymous with a circumferential direction of the tire when the tread is installed on a tire. Likewise, a direction of the tread width is synonymous with an axial direction of the tire or a direction of the tire width when the tread is installed on a tire. Finally, a direction of the tread thickness is synonymous with a radial direction of the tire when the tread is installed on a tire. It is understood that the inventive tread may be employed by any known tire, which may comprise a pneumatic or non- pneumatic tire, for example.

[0031] It is appreciated that any of the tread features discussed herein may be formed into a tire tread by any desired method, which may comprise any manual or automated process. For example, the treads may be molded, where any or all discontinuities therein may be molded with the tread or later cut into the tread using any manual or automated process. It is also appreciated that any one or both of the pair of opposing discontinuities may be originally formed along, and in fluid communication with, the outer, ground-engaging side of the tread, or may be submerged below the outer, ground-engaging side of the tread, to later form a tread element after a thickness of the tread has been worn or otherwise removed during the life of the tire.