TYRE TREAD

Abstract: A tyre having a tread pattern having a plurality of generally elliptically shaped grooves (237;340) disposed such that one axis is substantially perpendicular to the mid-circumferential centerplane (CP) and the other axis is disposed closely adjacent the tread edge (214,215).

Description: This is a divisional application derived from EP Application 83630047.5, now EP-B-89306. This invention relates to tyres of the type described in the preamble to claim 1. Such a tire is described in FR-A-2 383 029. It is well known in the tyre industry that the choice of a particular tread design involves trade-off between specific type performance characteristics. For example, a tread pattern which has good wet traction or snow traction is generally obtained at the expense of dry road traction, tread wear, rolling resistance, ride and noise level, and a tread pattern which has good tread wear and low rolling resistance is generally obtained at the expense of wet and snow traction. In the prior art when improved wet traction or improved hydroplaning performance was desired, the void volume in the tread area of the tyre was simply increased by either enlarging the width of the grooves or by increasing the depth of the non-skid of the tread or by doing both. However, increasing the void volume in this manner generally results in a reduction in performance in dry traction, handling, tread wear and/or an increase in noise level. There is disclosed in the characterizing portion of claim 1 a particular groove shape arrangement whereby acceptable levels of wet traction and hydroplaning characteristics of a type are maintained while also maintaining or improving other performance characteristics such as rolling resistance, tread wear, noise levels, traction and handling. Figure 1 is a fragmentary plan view of a portion of a tread of a tyre made in accordance with the invention described in EP patent 89306 from which the present invention has been divided out. Figures 2 and 3 illustrate two forms of the tread for a tyre made in accordance with the present invention. Referring to figure 1, there is illustrated a fragmentary plan view of a tread 12 for a pneumatic tyre made in accordance with the invention of parent case EP-B-89306. The tread pattern illustrated in figure 1 is particularly adapted for passenger pneumatic tyres and more particularly to pneumatic tyres having a carcass structure of the radial type construction and having a belt reinforcing ply structure disposed radially outwardly of the carcass ply structure in the tread region of the tyre. For the purposes of this invention, a radial type tyre is a tyre wherein the cords of the carcass reinforcing ply structure are disposed at an angle from about 75° to 90° with respect to the mid-circumferential centerplane CP of the tyre. The tread is provided with a set of grooves 16 disposed about the entire circumference of the tyre which extend from each of the axially opposed tread edges 14,15 respectively and extend axially across a portion of the tread 12. The grooves 16 each have a cross-sectional width such that when in the footprint of the tyre the grooves 16 do not close up at the tread surface. Preferably, the grooves 16 each have a substantially constant width. The center line of each groove 16 generally follows a portion of a path formed by an ellipse having an axis A and an axis B. The axis A is disposed substantially perpendicular to the mid-circumferential centerplane CP of the tyre 10 and the axis B of the ellipse is disposed substantially parallel to the mid-circumferential centerplane and closely adjacent to the tread edge 14 or 15 from which any particular groove 16 extends. The axis B of each groove 16 is disposed from the tread edge 14 or 15 from which it extends a distance no greater than about one-eighth the tread width TW. Preferably, the axis B is disposed axially inward of the tread edge toward the mid-circumferential centerplane CP. In the particular embodiment illustrated, the axis B lies substantially along its respective tread edge. The length L of the axis B ranges from approximately 50% to 120% of the tread width TW and preferably from about 70% to 100%, the length L of the particular embodiment illustrated is approximately 80% of the tread width TW. For the purposes of this invention, the tread width TW of a tyre is the maximum axial width of the tread 12 measured perpendicular to the mid-circumferential centerplane CP of the tyre as determined from the footprint of the tyre when the tyre is inflated to design inflation pressure and at rated load. The grooves 16 extend axially across the tread 12 at a distance of at least 25% of the tread width TW and preferably a distance of at least 35% and not greater than 75% of the tread width TW, preferably no greater than 45% of the tread width TW so as to provide a continuous circumferentially extending rib in the central portion of the tyre. The axially innermost point of the center line of each of the grooves 16 is disposed from the tread edge from which it starts a distance d of approximately 45% of the tread width TW, forming circumferentially continuous extending rib 30. Rib 30 contributes to reducing the noise level of the tyre. The axis A of circumferentially adjacent elliptical grooves 16 which extend from the same tread edge are spaced circumferentially apart a distance approximately equal to the length of the axis B. Each elliptically shaped groove 16 has a pair of ends 19,21 which open up into tread edge 14,15 respectively. Each groove 16 extends from end 19 across the tread 12 to end 21 of the same groove in a substantially continuous manner. Each groove 16 comprises a pair of branches 20 which extends from openings 19,21 to a common point 17 where they coincide. The center line of each branch 20 of each groove 16 is substantially tangent to the center line of the branch 20 of the next circumferentially adjacent groove 16 thereby making the adjacent branches 20 substantially mutually tangent to each other. Accordingly, circumferentially adjacent branch 20 merges into a single groove having substantially the same longitudinal direction at or near the point at which they merge. The mutual tangency of the adjacent branch contributes to minimize the turbulence of any fluid that may be present in this area. The provision of substantially elliptically shaped grooves provides for efficient water removal from the footprint of the tyre by minimizing any turbulence the fluid may experience as it proceeds from the center portion of the tread to the tread edge. The systematic placement of the circumferentially adjacent grooves 16 about the tyre maximizes the use of the available void area required to remove fluid from the footprint of the tyre. Accordingly, a tread pattern designed in accordance with the present invention provides for efficient removal of any fluid that may be present in the footprint of the tyre while also providing other performance characteristics such as dry traction, noise levels and low rolling resistance. A second set of elliptically shaped grooves 22 is provided, each groove 22 following a path which is substantially identical to the elliptical path which grooves 16 follow. The axis C of each groove 22 has a length LC and is parallel to the mid-circumferential centerplane of the tyre and preferably lies substantially in the same plane as the axis B of the elliptically shaped grooves 16. The axis D of each groove 22 is substantially perpendicular to the mid-circumferential centerplane of the tyre 10 and is preferably parallel to the axis A of groove 16. The first and second set of elliptically shaped grooves 16,22 respectively, combine to form a family of elliptically shaped grooves. The elliptically shaped grooves 16,22 are substantially identical to each other but are displaced at different positions circumferentially about the tyre; preferably the elliptically shaped grooves 16 and 22 are disposed about the tyre such that the axis D of each groove 22 is disposed approximately midway between the axes A of circumferentially adjacent grooves 16. The tread 12 is provided with sufficient grooves such that the amount of void area present in the tread will be able to handle any water or fluid present in the footprint of the tyre. Accordingly, the tread portion 12 is provided with a sufficient number of grooves having a predetermined shape and configuration so that the net to gross ratio of the thread in the footprint of the tyre is at least 50% and preferably no greater than 70%. For the purposes of this invention, the net to gross of the tread is the ratio of the total area of the tread which comes into contact with the road surface to the total footprint area of the tread. The grooves in the tread 12 are disposed such that from about six to fourteen branches of the elliptically shaped grooves are present in the footprint of the tyre from each of the tread edges. Referring further to figure 2, the elliptically shaped grooves which extend from tread edge 214 if allowed to continue would intersect the grooves which start from the opposed tread edge 215. The dotted lines indicate the path which the center line of the elliptically shaped grooves would follow if allowed to extend past the intersection of the elliptically shaped grooves which start from the opposed tread edge. The branches 230 of the grooves follow an elliptical path from the tread edge to a termination point 233, which is spaced from the tread edge from which it starts a distance D2 no less than about 30% of the tread width TW, preferably a distance of at least 40% of the tread width TW. The termination point 233 of each branch 230 is spaced from the summit 235 of the elliptical path which center line grooves follow an axial distance D3 which is no greater than about one-fourth of the tread width TW. For the purpose of this invention, the summit 235 of the elliptical path is the point at which the elliptical path is spaced furthest from the tread edge from which is starts. From the termination point 233 at which the center line of branch 230 of grooves depart from the elliptical path, a groove 237 extends across the tread to connect with a corresponding branch of an elliptically shaped groove starting from the opposed tread edge. Each of the generally straight grooves 237 is oriented such that it forms an angle with the mid-circumferential centerplane of the tyre and is no greater than about 60°C. Referring now to figure 3, there is illustrated another modified form of the present invention wherein some of the elliptically shaped grooves 337 which extend from one tread edge interconnect with elliptically shaped grooves starting from the opposed tread edge and are connected by a network of grooves 340 which form an angle no greater than approximately 60° with respect to the mid-circumferential centerplane, preferably each groove 340 is substantially straight. While certain representative embodiments and details have been shown for the purposes of illustrating the invention, it will be apparent to those skilled in the art that various changes and modifications can be made. For example, the repeating design cycle of the tread of a tyre made in accordance with the present invention may be varied about the tyre (also known in the tyre industry as pitching of the tread design).

Claims: A tyre comprising a ground-engaging tread portion having a pair of axially opposed tread edges (214,215) said ground-engaging tread having a first set of circumferentially adjacent grooves (230,337) extending g from each of said respective tread edges across the axial width of said tread a distance (D₂) of at least 30 % of the tread width (TW), each of said grooves of said first set having a pair of ends at said tread edge (214,215) and a pair of circumferentially spaced branches (230',337'), one of said branches extending from each of said ends to a termination point (233), said branches of said grooves generally following a portion of an elliptical path having one axis (A) generally perpendicular to the mid-circumferential centerplane (CP) of the tyre and a second axis (B) which is substantially parallel to the mid-circumferential centerplane (CP) of the tyre, said second axis (B) of each said groove being spaced from the tread edge (214,215) from which the grooves start a distance not greater than one-eighth of the tread-width (TW), said termination point (233) of each of said branches (230',337') being spaced from the summit point (235) at which the path of said ellipse is spaced furthest from said tread edge from which said grooves start, an axial distance (D₃) no greater than about one-eighth of the tread width (TW), characterized in that said grooves (230,337) are disposed about said tyre such that each branch (230',337') of said grooves (230,337) is substantially tangent to the branch of the next circumferentially adjacent groove in the area of the tread portion adjacent to the tread edge (214,215), both branches (230',337') of one groove (230,337) follows the path of one ellipse, said tread portion has a second set of circumferentially adjacent grooves extending from each of said respective tread edges across the axial width of said tread having a configuration substantially identical to that of said first set of grooves, and both said sets of grooves on either side of the mid-circumferential centerplane (CP) are arranged symmetrically with respect thereto. A tyre according to claim 1, characterized by said tread portion having a net to gross of at least 50 %. A tyre according to claim 1, characterized by said grooves (230) of said first set of circumferentially adjacent grooves following alternately two different sized elliptical paths. A tyre according to claim 1, characterized by said grooves (230) of said second set of circumferentially adjacent grooves following alternately two different sized elliptical paths. A tyre according to claim 1, characterized by a connecting groove (237) extending across the tread from the termination point (233) of each of said grooves to connect with a corresponding groove starting from the opposed tread edge (214,215). A tyre according to claim 2, characterized by some of the grooves (337) which extend from one tread edge interconnecting with grooves starting from the opposed tread edge are connected by a network of connecting grooves (340). A tyre according to claim 5 or 6, characterized by said connecting grooves (237;340) being oriented at an angle (α) of not greater than about 60° with the mid-circumferential centerplane (CP) of the tyre.

Inventors: FONTAINE,JEAN FRANCOIS LEON
Applicants: THE GOODYEAR TIRE & RUBBER COMPANY
Application year: 1983
Main classification: B60C11
IPC codes: B60C11