PNEUMATIC TIRE

Abstract: A pneumatic tire (10) has a preferred cross-sectional shape which acts in concert with a preferred tread structure to provide varying performance characteristics under varying operating conditions. The tread (11) has a directional tread pattern, with the net-to-gross ratio being higher in a central portion (CP) of the tread than in the laterally outer portions (OP₁,OP₂). The stiffness of the block elements (64,65,66,67,68,69,70,71) of the tread also varies across the width of the tread.

Description: The present invention relates generally to pneumatic tires, and more specifically to pneumatic tires intended for use both on and off of paved surfaces. French patent FR-A-1 051 025 discloses a tread for a pneumatic, semi-pneumatic or solid tire providing an improved grip on roads and more specifically on ice and snow covered surfaces, according to the preamble of claim 1. A very popular class of motor vehicles are those which the owner can use both for commuting over paved highways and for recreational use in off-highway situations. Such vehicles often take the form of pick-up trucks or small general purpose motor vehicles. It is quite common for such on/off road vehicles to have four wheel drive capability. Such vehicles present a special challenge to a tire engineer because the performance characteristics desired for highway use are tradeoffs with the performance requirements for off-road use. For example, mud traction versus treadwear, off-road handling versus on-road handling, and wet traction versus dry traction. Furthermore, when an on/off road all purpose vehicle is used for commuting about town it is seldom loaded to its full weight capacity, whereas when the same vehicle is packed with recreational equipment for off-road use the tires are subjected to much greater loads. A tire should have the capacity to provide adequate treadwear, mud traction, sand traction, on road handling, off road handling, wet traction and dry traction when used with small general purpose motor vehicles and trucks. The invention as claimed is intended to provide such a tire. To acquaint persons skilled in the tire art with the invention a presently preferred embodiment illustrative of the best mode now contemplated for the practice of the invention is described herein making reference to the attached drawings forming a part of the specification and in which drawings: Fig. 1 is a perspective view of a tire according to the preferred embodiment of the invention; Fig. 2 is a front elevation view of the tire shown in Fig. 1; Fig. 3 is a cross-sectional view of said tire taken along a plane that includes the axis of rotation of the tire looking in the direction of arrows 3-3 of Fig. 2; and Fig. 4 is an enlarged fragmentary view of a portion of the tread of said tire looking towards the axis of rotation of the tire. A tire 10 according to a preferred embodiment of the invention comprises a ground engaging tread 11 extending circumferentially about the axis of rotation of the tire and having a pair of lateral edges TE₁, TE₂. A sidewall portion 13,14 extends radially inwardly from each lateral edge of the tread. As used herein , and in the claims, the terms "radial" and "radially" are understood to refer to directions that are perpendicular to the axis of rotation of the tire, and the terms "lateral", "laterally", "axial" and "axially" are understood to refer to directions going from one sidewall of the tire towards the other sidewall of the tire. As shown in Fig. 3, a tire according to a preferred embodiment of the invention has at least one carcass ply 17,18 of side-by-side cables which intersect the mid-circumferential plane M of the tire at 75° to 90° with respect to said plane. As used herein and in the claims, the "mid-circumferential plane" of a tire is understood to refer to a plane that is perpendicular to the axis of rotation of the tire and is located midway between the sidewalls 13,14 of the tire when the tire is mounted upon its specified rim and inflated to its specified inflation pressure but not subjected to a load. The specified rim and inflation pressure can be determined from any of the following sources: (a) indicia molded onto a sidewall of the tire by the tire manufacturer; (b) specification or sales literature available from the tire manufacturer; (c) the YEARBOOK OF THE TIRE AND RIM ASSOCIATION for the year in which the tire is manufactured; or (d) the YEARBOOK OF THE EUROPEAN TYRE AND RIM TECHNICAL ORGANIZATION for the year in which the tire is manufactured. In a preferred embodiment the reinforcing cables of the carcass plies 17,18 comprise a non-metallic material such as nylon, aramid, or most preferably polyester. Preferably each of the carcass plies 17,18 is folded axially and radially outwardly about a pair of axially spaced apart substantially inextensible annular bead cores 20,21. However, it is felt that the invention may be practiced with any suitable number of carcass plies folded in any suitable manner about bead cores in accordance with good engineering practice, and that if desired the carcass plies could be reinforced with metallic cables. At least one belt ply 19,20 of side-by-side cables is disposed radially outwardly of the carcass ply, or plies, 17,18 in a crown portion of the tire. In the preferred embodiment the belt plies are reinforced by metallic cables, but it is understood that the belt plies may be reinforced by cables of any suitable material such as aramid. A ground engaging tread 11 is disposed radially outwardly of the belt ply, or plies, 19,20 and extends circumferentially about the tire. The tread 11 has a pair of lateral edges TE₁, TE₂ with a sidewall portion 13,14 extending radially inwardly from each of said lateral edges. It is believed that the good performance characteristics of a tire according to the invention are attributable at least in part to the cross-sectional shape of the tire. All of the tire dimensions used herein and in the claims are understood to refer to a tire having a tread that has not yet been used on a vehicle but which has been mounted on its specified rim and inflated to its specified inflation pressure while not being subjected to any load. That is to say, the invention applies both to new tires and retreaded tires. Definitions of the terms used herein and in the claims for describing the cross-sectional shape of a tire according to the invention are set forth below with reference to Fig. 3. "Section height" (SH) refers to the radially measured distance from the nominal bead diameter of the tire to the maximum diameter of the tire. "Maximum section width" (SD) refers to the greatest axial distance between the axially outer surfaces of the tire sidewalls 13,14 exclusive of indicia or ornamentation on the sidewalls. "Aspect ratio" refers to the ratio of section height SH to maximum section width SD, or put another way SH SD . "Tread radius" (TR) refers to the radius of curvature, having its center on the mid-circumferential plane M of the tire, which is followed by the radially outer surfaces of the block elements 6,64,66,68,70 of the tread. "Tread arc width" (TAW) refers to the maximum axial distance across the tread measured along the curvature of the radially outer surfaces of the block elements. It is further understood that the tread arc width of a tire according to a preferred embodiment of the present invention extends between the axially outermost extents TE₁, TE₂ of the axially outermost extending block elements 60,70 on each side of the mid-circumferential plane M of a tire. A tire in accordance with the present invention has an aspect ratio SH SD in the range of 0.60 to 0.95, preferably in the range of 0.60 to 0.80. For example, a tire of size 31 X 10.50 R15 has a section height SH of about 7.7 inches, and a maximum section width SD of about 10.5 inches and an aspect ratio of about 0.73. A tire in accordance with the present invention has a ratio of tread radius to maximum section width TR SD in the range of 1.0 to 2.4, preferably in the range of 1.2 to 2.2. For example, a tire of size 31 X 10.50 R15 has a tread radius TR of about 18.4 inches, a maximum section width SD of about 10.5 inches and the ratio TR SD is about 1.8. A tire in accordance with the present invention has a ratio of tread radius to tread arc width TR TAW in the range of 1.4 to 2.8. For example, a tire of size 31 X 10.50 R15 inches, a tread arc width TAW of about 8.3 inches and the ratio TR TAW is about 2.2. It is not believed that any one of the dimensional ratios set forth above is critical when considered alone, but rather that in combination these parameters along with other features of the invention that will be disclosed herein cooperate to provide a pneumatic tire having a desirable portfolio of performance characteristics. The tread 11 of a tire according to the invention has first and second straight grooves 40,41 therein which extend circumferentially about the tire. As used herein and in the claims, a circumferentially extending "straight groove" is understood to refer to any groove for which the groove edges at the outer surface of the tread are disposed such that a plane which is perpendicular to the axis rotation of the tire could be located between said groove edges without intersecting any edge of the groove at any point around the circumference of the tire. That is to say, the groove edges do not need to be parallel to one another in order for a circumferentially extending groove to be a straight groove. In the preferred embodiment both said first and second straight grooves 40,41 have centerlines 46,47 that follow paths which are parallel to the mid-circumferential plane M. One of said straight circumferentially extending grooves 40,41 is disposed on each side of the mid-circumferential plane M of the tire and is spaced from said mid-circumferential plane by a distance as indicated at 42 and 43 in Fig. 4, in the range of 10% to 25% of the tread arc width TAW. The width of the straight circumferentially extending grooves 40,41 at the radially outer surface of the tread measured perpendicular to the mid-circumferential plane is preferably in the range of 6% to 9% of the tread arc width TAW, and most preferably in the range of 7% to 8% of the tread arc width. The width of these straight grooves 40,41 needs to be sufficient to allow for evacuation of water from the footprint of the tire when the tire is operated on a wet surface. A circumferentially extending central groove 44 is disposed axially between said first and second circumferentially extending straight grooves 40,41. Preferably, the central groove 44 intersects the mid-circumferential plane M of the tire. While in the preferred embodiment the central groove 44 meets the definition of a straight groove as used herein, (see line M in Fig. 4 that represents the mid-circumferential plane), it is preferred that the central groove have a centerline as represented by dashed line 45 that follows a zig-zag path. As used herein and in the claims, "zig-zag" is understood to refer to a line, path or groove which has adjacent segments that are oriented at angles other than 0° with respect to one another. Most preferably every other segment of the zig-zag path followed by the centerline 45 of the central groove 44 is parallel to the mid-circumferential plane M of the tire. However, it is understood that a tire according to the invention could have a central groove with a zig-zag centerline and not meet the definition of a straight groove used herein. A plurality of circumferentially extending zig-zag grooves 50, each of which extends laterally across the tread 11 from one tread edge TE₁, to the other tread edge TE₂, are disposed circumferentially about the tire. Preferably the number of laterally extending zig-zag grooves 50 is in the range of thirty-seven to fifty-seven with the exact number depending upon the size of the tire. For example, a tire of size 31 x 10.50 R15 has about 46 laterally extending zig-zag grooves in its tread portion. It is preferred that the centerlines 51 of each of the laterally extending zig-zag grooves 50 follow substantially identical paths across the tread and that said centerlines 51 be substantially symmetrical with respect to the mid-circumferential plane M of the tire. In a preferred embodiment each laterally extending zig-zag groove 50 has a centerline 51 which follows a path with every other segment of said path being oriented substantially perpendicular to the mid-circumferential plane M of the tire. It is especially preferred that the segments 52 of each laterally extending zig-zag groove 50 which intersect a lateral edge TE₁, TE₂ of the tread be oriented perpendicular to the mid-circumferential plane M in order that good tractive forces are generated near the tread edges when the tire is operated in mud or sand. The width of the laterally extending grooves needs to be sufficiently large to allow the evacuation of water or mud from the footprint of the tire. It is preferred to have either the width of the laterally extending grooves or the circumferential spacing between next adjacent laterally extending grooves, or both the groove width and circumferential spacing vary about the tire. These variations accommodate what is known in the tire art as pitching to help obtain desirable noise generation characteristics for a tire when it is used on a vehicle. The circumferentially and laterally extending grooves 40,41,44,50 cooperate with one another to define four circumferentially extending arrays 60,61,62,63 of block elements 64,65,66,67,68,69,70,71. Circumferentially aligned block elements 66,68; 67,69 of the two axially centermost arrays 61,62 cooperate with one another to present a "V" formation. In a preferred embodiment of the invention the circumferentially aligned block elements 64,66; 65,67; 68,70; 69,71 of the arrays 60,61;62,63 on the same side of the mid-circumferential plane M cooperate with one another to present "V" formations pointing in the opposite circumferential direction from the "V" formation presented by the axially centermost arrays. Such a tread design is referred to in the tire art as being a directional design. As used herein and in the claims a "directional" tread design is understood to be a tread design which operates differently when the tire is rotated in one direction from the way the tire operates when it is rotated in the opposite direction. A tire according to the preferred embodiment illustrated in the drawings is intended to rotate in the direction indicated by arrow 80 in Figs. 1 and 4 when a vehicle on which the tire is mounted is going forward. Preferably, for each of the block elements 66,67,68,69 in the two axially centermost arrays 61,62 a straight line extending from the axially outermost point on the leading edge of the block element to the axially innermost point on said leading edge is oriented at an angle β, α in the range of 30° to 65°, preferably 35° to 60°, with respect to the mid-circumferential plane M of the tire. As used herein and in the claims, the "leading edge" of a block element in a directional tread design is the edge of the block element that will enter a tire footprint first when the tire rotates in the preferred direction. As can be seen in Fig. 4, the angles β, α are the average angles at which the leading edge of a block element are inclined. In a preferred embodiment of the invention each of the block elements has a radially outer surface and the axial extent of the radially outer surfaces of circumferentially adjacent block elements 64,65; 66,67; 68,69; 70,71 in each circumferentially extending array 60,61,62,63 alternate between wide and narrow widths. For the two axially centermost arrays 61,62, the axial extent 94 of the radially outer surfaces of the wide block elements 66,69 is in the range of 14% to 20% of the tread arc width TAW and the axial extent 95 of the narrow block elements 67,68 is less than that of the circumferentially adjacent wide block elements and is in the range of 10% to 16% of the tread arc width TAW. For the two axially outermost arrays 60,63 the axial extent 92 of the radially outer surfaces of the wide block elements 65,70 is equal to the distance from the respective tread edge TE₁, TE₂ to the nearest straight circumferential groove 40,41, and the axial extent 93 of the radially outer surfaces of the narrow block elements 64,71 extends from the respective straight circumferential groove 40,41 for 60% to 90% of the axial extent 92 of said wide block elements 65,70 of the same array 60,63. As a result of this preferred arrangement of the blocks in the axially outermost arrays 60,63 the leading edges of the wide block elements 65,70 near the tread edges TE₁, TE₂ can exert extra traction when the tire is operated in mud or sand. The number of block elements in each of the circumferentially extending arrays 60,61,62,63 is in the range of 36 to 56 depending upon the size of the tire. Preferably, for each block element, the radially measured distance X from a radially outermost surface of the block element to the radially innermost extent of any groove 40,41,44 that is adjacent to the block element is in the range of 4% to 11% of the section height SH of the tire. Another important feature of a tire according to a preferred embodiment of the invention is the variation in stiffness between the block elements. This variation in stiffness can be represented by the varying ratios of circumferential length to axial width of the block elements. The ratio of the circumferential extent 96 to the axial extent 94 of each wide block element 66,69 of the two axially centermost arrays 61,62 is preferably in the range of 0.9 to 2.1. The ratio of the circumferential extent 96 to the axial extent 95 of each of the narrow block elements 67,68 of the two axially centermost arrays 61,62 is in the range of 1.0 to 2.4. The ratio of the circumferential extent 90 to the axial extent 92 of the wide block elements 65,70 of the two axially outermost arrays 60,63 is in the range of 0.4 to 1.5. The ratio of the circumferential extent 91 to the axial extent 93 of the narrow block elements 64,71 of the two axially outermost arrays 60,63 is in the range of 0.7 to 1.9. In the preferred embodiment is that the tread is divided into three zones OP₁ CP, OP₂ across its width. The central zone CP extends between the centerlines 46,47 of the two straight circumferential grooves 40,41. The laterally outer zones OP₁, OP₂ each extend from a tread edge TE₁, TE₂ to the centerline 46,47 of the nearest straight circumferential groove 40,41. Preferably, the net-to-gross ratio of the tread in the central zone CP is greater, most preferably at least 5% greater, than the net-to-gross ratio of the laterally outer zones OP₁, OP₂ of the tread. Most preferably, the net-to-gross ratio of the tread in the central zone CP is in the range of 0.4 to 0.5. For example, a tire of size 31 X 10.50 R15 can have a net-to-gross ratio in the central zone CP of about 0.46 and a net-to-gross ratio in the laterally outer zones OP₁, OP₂ of about 0.42, such that the net-to-gross ratio in the central zone CP is about 9% greater than the net-to-gross ratio in the outer zones OP₁, OP₂. As used herein and in the claims, "net-to-gross ratio" is understood to refer to the area of a tread that is actually in contact with the ground in a static footprint of a tire as a percentage of the total area of the footprint when the tire is mounted on its specified rim, inflated to specified inflation pressure and subjected to the tire's inflated load at said inflation pressure. It is an advantage of a tire according to the invention that due to its cross-sectional shape and preferred tread geometry, the tire will operate to provide preferred performance characteristics at different operating loads and in different operating conditions. For example, when the tire is mounted upon a small all-purpose vehicle and operated on a paved roadway at everyday commuting loads, which are far less than the tires rated load, the central portion CP of the tread is almost exclusively in contact with the roadway. The higher net-to-gross ratio of this central portion of the tread provides good treadwear and on-highway handling. When the tire is operated under higher loads and/or off-the-road the laterally outer zones OP₁, OP₂ of the tread also come into operation to provide greater traction in mud or sand and improve off-highway handling. The varying stiffness of the block elements across the tread also contributes to the performance characteristics of the tire under varying operating conditions.

Claims: 1. A pneumatic tyre (10) comprising a tread (11) extending circumferentially about the axis of rotation of the tyre and having a pair of lateral edges (TE₁, TE₂) with a sidewall portion (13,14) extending radially inwardly from each lateral edge of the tread, said tyre having an aspect ratio (SH/SD) in the range of 0.60 to 0.95, said tread (11) having first and second straight grooves (40,41) therein which extend circumferentially about the tyre, one of said straight circumferentially extending grooves being disposed on each side of the mid-circumferential plane (M) of the tyre, a circumferentially extending groove 45 being disposed axially between said first and second circumferentially extending straight grooves (40,41), a plurality of laterally extending zigzag grooves (51) each of which extends across the tread being disposed circumferentially about the tyre, said circumferentially and laterally extending grooves (40,41,45,51) cooperating with one another to define four circumferentially extending arrays (60,61,62,63) of block elements (64,65,66,67,68,69) circumferentially aligned block elements (66,67,68,69) of the centermost arrays (61,62) cooperating with one another to present a directional tread design, characterized by: the tyre having a ratio of tread radius (TR) to maximum section width (SD) in the range of 1.0 to 2.4, and a ratio of tread radius (TR) to tread arc width (TAW) in the range of 1.4 to 2.8; each of said straight circumferentially extending grooves (40,41) being spaced from said mid-circumferential plane (M) by a distance (42,43) in the range of 10% to 25% of the tread arc width (TAW); and the portion (CP) of the tread that is disposed between the centerlines of said circumferentially extending straight grooves (40,41) having a net-to-gross ration that is greater that the net-to-gross ratio of the portions (OP₁, OP₂) of the tread that are disposed axially outwardly of the centerlines of said circumferentially extending straight grooves (40,41). 2. A pneumatic tire (10) according to claim 1 characterized by said block elements (64,65,66,67,68,69,70,71) having radially outer surfaces, the axial extent of the radially outer surfaces of circumferentially adjacent block elements in each circumferentially extending array (60,61,62,63) alternating between wide and narrow widths. 3. A pneumatic tire (10) according to claim 2 characterized by the axial extent (94) of the radially outer surfaces of the wide block elements (66,69) of the two axially centermost arrays (61,62) being in the range of 14% to 20% of the tread arc width (TAW) and the axial extent (95) of the narrow block elements (67,68) being less than that of the circumferentially adjacent wide block elements (66,69) and being in the range of 10% to 16% of the tread arc width (TAW). 4. A pneumatic tire (10) according to claim 2 or 3 characterized by the axial extent (92) of the radially outer surfaces of the wide block elements (65,70) of the two axially outermost arrays (60,63) being equal to the distance from a tread edge (TE₁, TE₂) to the nearest straight circumferential groove (40,41) and the axial extent (93) of the radially outer surfaces of the narrow block elements (64,71) extending from said straight circumferential groove (40,41) for 60% to 90% of the axial extent (92) of said wide block elements (65,70) of the same array (60,63). 5. A pneumatic tire (10) according to any of the preceding claims characterized by a straight line extending from the axially outermost point on a leading edge of each of the block elements (66,67,68,69) in said two axially centermost arrays (61,62) to the axially innermost point on said leading edge being oriented at an angle (α,β) of 30° to 65° with respect to the mid-circumferential plane (M) of the tire. 6. A pneumatic tire (10) according to any of the preceding claims characterized by the number of block elements (64,65,66,67,68,69,70,71) in each of said circumferentially extending arrays (60,61,62,63) being in the range of 36 to 56. 7. A pneumatic tire (10) according to any one of claims 2 to 6 characterized by the ratio of the circumferential extent (96) to the axial extent (94) of the radially outer surface of each wide block element (66,69) of said two axially centermost arrays (61,62) being in the range of 0.9 to 2.1. 8. A pneumatic tire (10) according to any one of claims 2 to 7 characterized by the ratio of the circumferential extent (96) to the axial extent (95) of the radially outer surface of each narrow block element (67,68) of said two axially centermost arrays (61,62) being in the range of 1.0 to 2.4. 9. A pneumatic tire (10) according to any one of claims 2 to 8 characterized by the ratio of the circumferential extent (90) to the axial extent (92) of the radially outer surface of each wide block element (65,70) of the two axially outermost arrays (60,63) being in the range of 0.4 to 1.5. 10. A pneumatic tire (10) according to any one of claims 2 to 9 characterized by the ratio of the circumferential extent (91) to the axial extent (93) of the radially outer surfaces of the narrow block elements (64,71) of the two axially outermost arrays (60,63) being in the range of 0.7 to 1.9.

Inventors: GALANTE, RICHARD LOUIS, GOERGEN, RENE, HITZKY, LEO JOSEPH, HOPKINS, WILLIAM MICHAEL, KOLOWSKI, MICHAEL ALOIS, MILLER, FREDERICK WILLIAM, WAIBEL, TERRY JOHN, Goergen, René
Applicants: THE GOODYEAR TIRE & RUBBER COMPANY
Application year: 1988
Main classification: B60C11
IPC codes: B60C11, B60C3, B60C9