Patent Application
20210339571
This application claims priority pursuant to 35 U.S.C. 119(a) of Japan Patent Application No. 2020-080849, filed Apr. 30, 2020, which application is incorporated herein by reference in its entirety.
The present technology relates to a tire.
Of heavy duty tires, super low-aspect tires referred to as ultra wide-base tires are used for, for example, a garbage truck in some cases. For example, the garbage truck often performs stop-and-go operations in which acceleration and deceleration are repeatedly performed. Accordingly, when block-patterned super low-aspect tires considering drainage performance are employed for, for example, the garbage truck, heel and toe wear, in other words, uneven wear is easily generated. Meanwhile, the use of a rib pattern that allows ensuring rigidity in a tire circumferential direction to suppress heel and toe wear results in insufficient drainage performance and poor acceleration performance on wet road surfaces. Accordingly, the super low-aspect tire used for, for example, the garbage truck is desired to have the excellent acceleration performance on dry road surfaces and wet road surfaces.
Here, the improvement in acceleration performance on dry road surfaces can be achieved by increasing a ground contact area of the tire. Additionally, the improvement in acceleration performance on wet road surfaces can be achieved by increasing a groove area of the tire. Accordingly, the improvement in acceleration performance on dry road surfaces and the improvement in acceleration performance on wet road surfaces are in a negative correlation.
A heavy duty tire disclosed in Japan Patent No. 6110838 has lateral grooves curved in an S-shape. The heavy duty tire disclosed in Japan Patent No. 6110838 can exhibit high drainage performance and wear resistance performance.
However, the technology disclosed in Japan Patent No. 6110838 has room for improvement in improving uneven wear resistance performance while providing improved acceleration performance on dry road surfaces and improved acceleration performance on wet road surfaces in a compatible manner.
The present technology provides a tire that allows improving uneven wear resistance performance while providing improved acceleration performance on dry road surfaces and improved acceleration performance on wet road surfaces in a compatible manner.
A tire includes a tread portion that includes a center main groove, an outer main groove provided on an outer side in a tire width direction of the center main groove, and a lug groove extending in a direction intersecting with both main grooves. The center main groove has a zigzag shape in which a first linear portion and a second linear portion are alternately connected. The outer main groove has a zigzag shape in which a long linear portion and a short linear portion are alternately connected. The lug groove has a groove center line intersecting with the short linear portion in the zigzag shape of the outer main groove. A ratio (LC1/PDc) of a length (LC1) of the first linear portion to a length (PDc) of one period of the zigzag shape of the center main groove is 0.40 or more and 0.60 or less. A ratio (Ls1/PDs, Ld1/PDd) of a length (Ls1, Ld1) of the long linear portion to a length (PDs, PDd) of one period of the zigzag shape of the outer main groove is 0.45 or more and 0.75 or less. A ratio (PDs/PDc) of the length of the one period of the zigzag shape of the outer main groove to the length of the one period of the zigzag shape of the center main groove is 0.90 or more and 1.20 or less.
In order to solve the problems described above and achieve the object, a tire according to an aspect of the present technology includes a tread portion. The tread portion includes a center main groove, an outer main groove, and a lug groove. The center main groove is provided at a position closest to a tire equatorial plane and extends in a tire circumferential direction. The outer main groove is provided on an outer side in a tire width direction of the center main groove and extends in the tire circumferential direction. The lug groove extends in a direction intersecting with the center main groove and the outer main groove. The center main groove has a zigzag shape in which a first linear portion and a second linear portion having mutually different inclination angles in the tire width direction with respect to the tire circumferential direction are alternately connected. The outer main groove has a zigzag shape in which a long linear portion and a short linear portion having mutually different inclination angles in the tire width direction with respect to the tire circumferential direction and having different tire circumferential direction lengths are alternately connected. An extension line as an extension of a groove center line of the lug groove intersects with the short linear portion in the zigzag shape of the outer main groove. A ratio of a tire circumferential length of the first linear portion to a tire circumferential length of one period of the zigzag shape of the center main groove is 0.40 or more and 0.60 or less. A ratio of the tire circumferential length of the long linear portion to a tire circumferential length of one period of the zigzag shape of the outer main groove is 0.45 or more and 0.75 or less. A ratio of the tire circumferential length of the one period of the zigzag shape of the outer main groove to the tire circumferential length of the one period of the zigzag shape of the center main groove is 0.90 or more and 1.20 or less.
The following is preferred. The period of the zigzag shape of the outer main groove has a phase difference with the period of the zigzag shape of the center main groove. When the center main groove is adjacent to the outer main groove in the tire width direction, a ratio of a tire circumferential length corresponding to the phase difference to the tire circumferential length of the one period of the zigzag shape of the center main groove is 0.60 or more and 0.85 or less.
The following is preferred. The tire includes a plurality of the outer main grooves. A ratio of a tire circumferential length corresponding to a phase difference between the period of the zigzag shape of the outer main groove on the outer side in the tire width direction among the plurality of outer main grooves and the period of the zigzag shape of the center main groove to the tire circumferential length of the one period of the zigzag shape of the center main groove is 0.95 or more and 1.15 or less.
The following is preferred. The tire includes a plurality of the lug grooves and a plurality of the outer main grooves. Each of the plurality of lug grooves extends from the tire equatorial plane to each of the plurality of outer main grooves. A plurality of center blocks are defined by the plurality of lug grooves and a plurality of the center main grooves. A plurality of outer blocks are defined by the plurality of lug grooves and the plurality of outer main grooves. Each of the plurality of lug grooves between the plurality of outer blocks adjacent in the tire circumferential direction has an inclination angle with respect to the tire circumferential direction greater than an inclination angle of each of the plurality of lug grooves between the plurality of center blocks adjacent in the tire circumferential direction with respect to the tire circumferential direction.
The following is preferred. The inclination angle of each of the plurality of lug grooves between the plurality of center blocks adjacent in the tire circumferential direction with respect to the tire circumferential direction is 20 degrees or more and 60 degrees or less.
The following is preferred. The inclination angle of each of the plurality of lug grooves between the plurality of outer blocks adjacent in the tire circumferential direction with respect to the tire circumferential direction is 60 degrees or more and 89 degrees or less.
The following is preferred. When each of the plurality of outer blocks is a first outer block adjacent to each of the plurality of center blocks on the outer side in the tire width direction, a ratio of a tire width direction length of the first outer block to a tire width direction length of each of the plurality of center blocks is 0.80 or more and 1.00 or less. When each of the plurality of outer blocks is a second outer block located on the outer side in the tire width direction of the first outer block, a ratio of a tire width direction length of the second outer block to the tire width direction length of each of the plurality of center blocks is 0.90 or more and 1.10 or less.
The following is preferred. The tire includes a plurality of the lug grooves and a plurality of the outer main grooves. Each of the plurality of lug grooves extends from the tire equatorial plane to each of the plurality of outer main grooves. A plurality of center blocks are defined by the plurality of lug grooves and a plurality of the center main grooves. A first outer block and a second outer block on the outer side in the tire width direction of the first outer block are defined by the plurality of lug grooves and the plurality of outer main grooves. A ratio of a tire circumferential length of the first outer block to a tire circumferential length of each of the plurality of center blocks is 0.75 or more and 1.00 or less. A ratio of a tire circumferential length of the second outer block to the tire circumferential length of each of the plurality of center blocks is 0.65 or more and 0.85 or less.
The following is preferred. The tire circumferential length of the long linear portion in the zigzag shape of each of the plurality of outer main grooves is longer than the tire circumferential length of the first linear portion. The tire circumferential length of the long linear portion in the zigzag shape of each of the plurality of outer main grooves is longer than the tire circumferential length of the second linear portion. The tire circumferential length of the short linear portion in the zigzag shape of each of the plurality of outer main grooves is shorter than the tire circumferential length of the first linear portion. The tire circumferential length of the short linear portion in the zigzag shape of each of the plurality of outer main grooves is shorter than the tire circumferential length of the second linear portion. The tire circumferential length of the short linear portion is 15 mm or more. The tire circumferential length of the long linear portion is 45 mm or less.
The following is preferred. A ratio of a distance in the tire circumferential direction between a plurality of outer blocks adjacent in the tire circumferential direction across the lug groove to a distance in the tire circumferential direction between a plurality of center blocks adjacent in the tire circumferential direction across the lug groove is 0.60 or more and 1.10 or less.
The following is preferred. Each of a plurality of the lug grooves extends from the tire equatorial plane to a plurality of the outer main grooves on both sides in the tire width direction across the tire equatorial plane. A ratio of a tire circumferential length between an opening position of each of the plurality of lug grooves to each of the plurality of outer main grooves on one side across the tire equatorial plane and an opening position of each of the plurality of lug grooves to each of the plurality of outer main grooves on the other side across the tire equatorial plane to a width of the tread portion is 0.30 or more and 0.60 or less.
The following is preferred. A ratio of an amplitude of the zigzag shape of each of the plurality of outer main grooves in the tire width direction to an amplitude of the zigzag shape of each of the plurality of center main grooves in the tire width direction is 1.15 or more and 1.50 or less.
The following is preferred. The tire includes a plurality of the lug grooves and a plurality of the outer main grooves. A ratio of an area of a road contact surface of each of a plurality of outer blocks defined by the plurality of lug grooves and the plurality of outer main grooves to an area of a road contact surface of each of a plurality of center blocks defined by the plurality of lug grooves and a plurality of the center main grooves is 0.85 or more and 1.05 or less.
The following is preferred. Each of a plurality of the lug grooves extends from the tire equatorial plane to a plurality of the outer main grooves on both sides in the tire width direction across the tire equatorial plane. An inflection point is provided between each of the plurality of outer main grooves on one side with respect to the tire equatorial plane and each of the plurality of outer main grooves on the other side with respect to the tire equatorial plane. A direction of a curvature in the tire circumferential direction from each of the plurality of outer main grooves on the one side to the inflection point and a direction of a curvature in the tire circumferential direction from each of the plurality of outer main grooves on the other side to the inflection point are opposite.
The following is preferred. The tire includes a plurality of the outer main grooves. The plurality of outer main grooves have shapes similar to one another.
The tire according to an embodiment of the present technology can improve uneven wear resistance performance while providing improved acceleration performance on dry road surfaces and improved acceleration performance on wet road surfaces in a compatible manner.
Embodiments of the present technology are described in detail below with reference to the drawings. In the embodiments described below, identical or substantially similar components to those of other embodiments have identical reference signs, and descriptions of those components are either simplified or omitted. The present technology is not limited by the embodiment. Constituents of the embodiments include elements that are essentially identical or that can be substituted or easily conceived by one skilled in the art. Note that it is possible to combine the configurations described below as desired. Moreover, various omissions, substitutions, and changes to the configurations can be carried out within the scope of the present technology.
In the description below, the tire meridian cross-section is defined as a cross-section of the tire taken along a plane that includes a tire rotation axis (not illustrated). “Tire radial direction” refers to the direction orthogonal to the rotation axis (not illustrated) of the tire 1, the inner side in the tire radial direction refers to the side toward the tire rotation axis in the tire radial direction, and the outer side in the tire radial direction refers to the side away from the tire rotation axis in the tire radial direction. “Tire circumferential direction” refers to the circumferential direction with the tire rotation axis as the center axis. “Tire width direction” refers to the direction parallel with the tire rotation axis. “Inner side in the tire width direction” refers to the side toward a tire equatorial plane (tire equator line) CL in the tire width direction. “Outer side in the tire width direction” refers to the side away from the tire equatorial plane CL in the tire width direction. The tire equatorial plane CL is a plane that is orthogonal to the rotation axis of the tire 1 and passes through the center of the tire width of the tire 1. The position in the tire width direction of the tire equatorial plane CL matches the center line in the tire width direction, which is the center position of the tire 1 in the tire width direction. “Tire width” is the width in the tire width direction between portions located on the outermost in the tire width direction, or in other words, the distance between the portions that are the most distant from the tire equatorial plane CL in the tire width direction. “Tire equator line” refers to the line along the tire circumferential direction of the tire 1 that lies on the tire equatorial plane CL. In the present embodiment, the tire equator line and the tire equatorial plane are denoted by the identical reference sign CL.
As illustrated in
In
The end portions of the carcass layer 6 in the tire width direction are folded back around the pair of bead cores 51 from an inner side to an outer side in the tire width direction, and the carcass layer 6 is stretched in a toroidal shape in the tire circumferential direction to form the framework of the tire. The carcass layer 6 is made of coating rubber-covered carcass cords (not illustrated) disposed side by side with an angle with respect to the tire circumferential direction along the tire meridian direction at an angle with respect to the tire circumferential direction. The carcass cords are made of steel or organic fibers (polyester, rayon, nylon, or the like).
The belt layer 7 has a multilayer structure in which four layers of belts 71, 72, 73, 74 are layered, for example, and in the tread portion 2, is disposed on the outer side in the tire radial direction, which is the outer circumference, of the carcass layer 6, covering the carcass layer 6 in the tire circumferential direction. The belts 71, 72, 73, 74 are made of coating rubber-covered cords (not illustrated) disposed side by side at a predetermined angle with respect to the tire circumferential direction. The cords are made of steel or organic fibers (polyester, rayon, nylon, or the like).
The tread portion 2 is made of a rubber material (tread rubber) and is exposed on the outermost side of the tire 1 in the tire radial direction, with the surface thereof constituting the contour of the tire 1. A tread surface 21 is formed on an outer circumferential surface of the tread portion 2, in other words, on a road contact surface that comes into contact with a road surface when running. A plurality (six in the present embodiment) of circumferential main grooves 22A, 22B, 23 that extend in the tire circumferential direction are provided in the tread surface 21. A plurality (seven in the present embodiment) of land portions 20C, 20M1, 20M2, 20S defined by the plurality of circumferential main grooves 22A, 22B, 23, extending in the tire circumferential direction, and arranged in the tire width direction are provided in the tread surface 21. Note that a length TW in the tire width direction between tire ground contact edges T is a tread width.
The circumferential main grooves 22A are circumferential main grooves provided at positions closest to the tire equator line CL. The circumferential main groove 22B is the circumferential main groove that is second closest to the tire equator line CL. The circumferential main grooves 22B are circumferential main grooves provided on the outer side of the circumferential main grooves 22A in the tire width direction. The circumferential main grooves 23 are circumferential main grooves provided on the outer side of the circumferential main grooves 22B in the tire width direction. The circumferential main grooves 23 are circumferential main grooves closest to the tire ground contact edges T. “Main groove” refers to a groove on which a wear indicator must be provided as specified by JATMA (The Japan Automobile Tyre Manufacturers Association, Inc.).
The land portion 20C is provided between the adjacent circumferential main grooves 22A, 22A across the tire equator line CL. The land portion 20C is defined by the two circumferential main grooves 22A, 22A. The land portion 20M1 is provided between the circumferential main groove 22A and the circumferential main groove 22B. The land portion 20M1 is defined by the circumferential main groove 22A and the circumferential main groove 22B. The land portion 20M2 is provided between the circumferential main groove 22B and the circumferential main groove 23. The land portion 20M2 is defined by the circumferential main groove 22B and the circumferential main groove 23. The land portions 20S are provided on the outer side of the circumferential main grooves 23 in the tire width direction. In the following description, the circumferential main groove is simply referred to as “main groove” in some cases. In the following description, the circumferential main groove 22A is referred to as a center main groove, and the circumferential main groove 22B and the circumferential main groove 23 are referred to as outer main grooves in some cases.
The tread portion 2 will be described in detail below. In the following description, a groove depth is measured as the maximum value of a distance from the tread surface to the groove bottom when the tire is mounted on a specified rim, inflated to the specified internal pressure, and in an unloaded state. Additionally, in a configuration in which the grooves include an uneven portion or sipes on the groove bottom, the groove depth is measured excluding these portions.
As illustrated in
The lug grooves 24 extend from the tire equatorial plane CL to the circumferential main grooves 23 as the outer main grooves on both sides in the tire width direction across the tire equatorial plane CL. A tire circumferential length between a point P1, which is the opening position of the lug groove 24 to the circumferential main groove 23 on one side across the tire equatorial plane CL, and a point P2, which is the opening position of the lug groove 24 to the circumferential main groove 23 on the other side across the tire equatorial plane CL, in other words, the extension length of the lug groove 24 in the tire circumferential direction, is defined as a length L. A ratio L/TW of the length L to the tread width TW of the tread surface 21 is preferably 0.30 or more and 0.60 or less. When the ratio L/TW is less than 0.30, the strain of each block BK becomes excessive when a tire ground contact area is small, and dry performance is degraded, which is not preferred. When the ratio L/TW exceeds 0.60, the lug grooves 24 are divided when the tire ground contact area is small, and uneven wear resistance performance is degraded, which is not preferred. The ratio L/TW is more preferably 0.40 or more and 0.50 or less.
The land portion 20C includes the lug grooves 24 that connect to the circumferential main grooves 22A and the circumferential main grooves 22B to connect the circumferential main grooves 22A and the circumferential main grooves 22B. The land portions 20S are defined on the outer side in the tire width direction of the circumferential main grooves 23, and are disposed on the outermost side in the tire width direction of the tread portion 2. The land portion 20S includes lug grooves 30 on the edge portion on the outer side in the tire width direction. The lug grooves 30 are provided in the land portions 20S at a predetermined pitch in the tire circumferential direction. The end portion of the lug groove 30 on the side closer to the tire equatorial plane CL terminates in the land portion 205. The end portion of the lug groove 30 on the side farther from the tire equatorial plane CL extends beyond the tire ground contact edge T in the tire width direction and opens to the shoulder portion 3.
The tire ground contact edge T is defined as the maximum width position in the tire axial direction of the contact surface between the tire and a flat plate when the tire is mounted on a specified rim, inflated to the specified internal pressure, placed perpendicular to the flat plate in a static state without a load applied, and loaded with a load corresponding to the specified load.
“Specified rim” refers to a “standard rim” defined by JATMA, a “Design Rim” defined by TRA (The Tire and Rim Association, Inc.), or a “Measuring Rim” defined by ETRTO (The European Tyre and Rim Technical Organisation). Additionally, “specified internal pressure” refers to a “maximum air pressure” defined by JATMA, to the maximum value in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined by TRA, or to “INFLATION PRESSURES” defined by ETRTO. Additionally, “specified load” refers to a “maximum load capacity” defined by JATMA, the maximum value in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined by TRA, or “LOAD CAPACITY” defined by ETRTO.
As illustrated in
In the lug groove 24, a raised bottom portion 240 is provided between the blocks BK adjacent in the tire circumferential direction. The raised bottom portion 240 is a portion where the groove bottom is raised such that the groove depth becomes shallower than the other portion.
The tread portion 2 includes the plurality of the blocks BK. The respective blocks BK are defined by the plurality of main grooves 22A, 22B, 23 and the plurality of lug grooves 24. Each block BK includes at least one bend point K. Thus, the block BK has a bent shape projecting to the inside of the block BK in plan view. Each block BK may include a plurality of the bend points K.
The blocks BK1 are center blocks defined by the two circumferential main grooves 22A provided on both sides across the tire equatorial plane CL and the plurality of lug grooves 24. The blocks BK2, BK3 are outer blocks provided on the outer side of the blocks BK1 in the tire width direction. The block BK2 is adjacent to the block BK1. The block BK3 is adjacent to the block BK2. The block BK3 is closer to the tire ground contact edge T than the block BK2.
Here, a ratio Wb2/Wb1 of a tire width direction length Wb2 of the block BK2 to a tire width direction length Wb1 of the block BK1 is preferably 0.80 or more and 1.00 or less. A ratio Wb3/Wb1 of a tire width direction length Wb3 of the block BK3 to the tire width direction length Wb1 of the block BK1 is preferably 0.90 or more and 1.10 or less. The ratio Wb2/Wb1 and the ratio Wb3/Wb1 falling within the value ranges described above approximately equalize the tire width direction lengths of the respective blocks, and uneven wear resistance performance is improved.
The block BK1 as the center block, the block BK2 as a first outer block adjacent to the block BK1 in the outer side in the tire width direction, and the block BK3 as a second outer block on the outer side in the tire width direction further have tire circumferential lengths preferably in the following relationships. In other words, a ratio Wb5/Wb4 of a tire circumferential length Wb5 of the block BK2 as the first outer block to a tire circumferential length Wb4 of the block BK1 as the center block is preferably 0.75 or more and 1.00 or less. A ratio Wb6/Wb4 of a tire circumferential length Wb6 of the block BK3 as the second outer block to the tire circumferential length Wb4 of the block BK1 as the center block is preferably 0.65 or more and 0.85 or less. The ratio Wb5/Wb4 and the ratio Wb6/Wb4 falling within the value ranges described above improve uneven wear resistance performance.
Here, an area of a road contact surface of one block BK1 is denoted as SBK1, an area of a road contact surface of one block BK2 provided on the outer side in the tire width direction of the block BK1 is denoted as SBK2, and an area of a road contact surface of one block BK3 provided on the outer side in the tire width direction of the block BK2 is denoted as SBK3. In this case, both of an area ratio SBK2/SBK1 and an area ratio SBK3/SBK1 are preferably 0.85 or more and 1.05 or less. The area ratios of the blocks falling within the value range described above allows providing dry performance and wet performance in a compatible manner. The ratio SBK2/SBK1 and the ratio SBK3/SBK1 described above being less than 0.85 decreases the ground contact areas of the center blocks. This degrades dry performance, which is not preferred. The ratio SBK3/SBK1 and the ratio SBK3/SBK1 described above in excess of 1.05 degrades wet performance, which is not preferred. The ratio SBK2/SBK1 and the ratio SBK3/SBK1 described above are more preferably 0.90 or more and 1.00 or less.
As illustrated in
A groove center line 230 of the circumferential main groove 22B as the outer main groove has a zigzag shape in which long linear portions 22BL and short linear portions 22BS are alternately connected. The long linear portion 22BL and the short linear portion 22BS differ from one another in an inclination angle in the tire width direction with respect to the tire circumferential direction. A tire circumferential length of the long linear portion 22BL and a tire circumferential length of the short linear portion 22BS differ from one another. The tire circumferential length of the long linear portion 22BL is denoted as Ls1, and the tire circumferential length of the short linear portion 22BS is denoted as Ls2. A ratio Ls1/PDs of the tire circumferential length Ls1 of the long linear portion 22BL to a tire circumferential length PDs of one period of the zigzag shape of the circumferential main groove 22B as the outer main groove is preferably 0.45 or more and 0.65 or less. When the ratio Ls1/PDs is less than 0.45 or the ratio Ls1/PDs exceeds 0.65, the period of the zigzag shape of the circumferential main groove 22B is close to the period of the zigzag shape of the circumferential main groove 22A as the center main groove. This degrades uneven wear resistance performance, which is not preferred.
Similarly, a groove center line 210 of the circumferential main groove 23 as the outer main groove has a zigzag shape in which long linear portions 23L and short linear portions 23S are alternately connected. The circumferential main groove 22B and the circumferential main groove 23 preferably have mutually similar shapes.
The long linear portion 23L and the short linear portion 23S differ from one another in an inclination angle in the tire width direction with respect to the tire circumferential direction. The long linear portion 23L and the short linear portion 23S differ in a tire circumferential length. The tire circumferential length of the long linear portion 23L is denoted as Ld1, and the tire circumferential length of the short linear portion 23S is denoted as Ld2. A ratio Ld1/PDd of the tire circumferential length Ld1 of the long linear portion 23L to the tire circumferential length PDd of one period of the zigzag shape of the circumferential main groove 23 as the outer main groove is preferably 0.45 or more and 0.65 or less. When the ratio Ld1/PDd is less than 0.45 or the ratio Ld1/PDd exceeds 0.65, the period of the zigzag shape of the circumferential main groove 23 is close to a period of the zigzag shape of the circumferential main groove 22A as the center main groove. This degrades uneven wear resistance performance, which is not preferred.
As long as the ratio LC1/PDc is 0.40 or more and 0.60 or less and the ratio Ls1/PDs and the ratio Ld1/PDd are 0.45 or more and 0.65 or less, the circumferential main grooves having the zigzag shapes of two kinds of periods can be provided in the tread surface 21. As a result, uneven wear resistance performance can be improved.
A ratio PDs/PDc of the tire circumferential length PDs of one period of the zigzag shape of the circumferential main groove 22B as the outer main groove to the tire circumferential length PDc of one period of the zigzag shape of the circumferential main groove 22A as the center main groove is preferably 0.90 or more and 1.20 or less. When the ratio PDs/PDc is less than 0.90 or the ratio PDs/PDc exceeds 1.20, the period of the zigzag shape of the center main groove greatly differs from the period of the zigzag shape of the outer main groove. This degrades uneven wear resistance performance, which is not preferred.
A ratio PDd/PDc of the tire circumferential length PDd of one period of the zigzag shape of the circumferential main groove 23 as the outer main groove to the tire circumferential length PDc of one period of the zigzag shape of the circumferential main groove 22A as the center main groove is preferably 0.90 or more and 1.10 or less. When the ratio PDd/PDc is less than 0.90 or the ratio PDd/PDc exceeds 1.10, the period of the zigzag shape of the center main groove greatly differs from the period of the zigzag shape of the outer main groove. This degrades uneven wear resistance performance, which is not preferred.
As illustrated in
In addition, among the plurality of outer main grooves, there is a phase difference between the period of the zigzag shape of the circumferential main groove 23 as the outer main groove on the outer side in the tire width direction and the period of the zigzag shape of the circumferential main groove 22A as the center main groove. A ratio φ13/PDc of a tire circumferential length φ13 corresponding to this phase difference to the tire circumferential length PDc of one period of the zigzag shape of the circumferential main groove 22A is preferably 0.95 or more and 1.15 or less. When the ratio φ13/PDc is less than 0.95, the phase difference is small and uneven wear resistance performance is degraded, which is not preferred. When the ratio φ13/PDc exceeds 1.15, the phase difference is large and uneven wear resistance performance is degraded, which is not preferred.
Note that there is a phase difference between the period of the zigzag shape of the circumferential main groove 22B as the outer main groove and the period of the zigzag shape of the circumferential main groove 23 as the outer main groove. A tire circumferential length corresponding to this phase difference is φ23.
In
The tire circumferential length of the short linear portion 22BS is preferably 15 mm or more. The tire circumferential length of the long linear portion 22BL is preferably 45 or less. When the tire circumferential length of the short linear portion 22BS is less than 15 mm, a deviation from the tire circumferential length of the long linear portion 22BL is large. This degrades uneven wear resistance performance, which is not preferred. When the tire circumferential length of the long linear portion 22BL exceeds 45 mm, a deviation from the tire circumferential length of the short linear portion 22BS is large. This degrades uneven wear resistance performance, which is not preferred. Note that the tire circumferential length of the short linear portion 22BS is more preferably 20 mm or more. The tire circumferential length of the long linear portion 22BL is more preferably 40 mm or less.
Here, an amount of displacement in the tire width direction (tire width direction length) of the zigzag shape of the circumferential main groove 22A is defined as an amplitude PHDc. An amount of displacement in the tire width direction (tire width direction length) of the zigzag shape of the circumferential main groove 22B is defined as an amplitude PHDs. An amount of displacement in the tire width direction (tire width direction length) of the zigzag shape of the circumferential main groove 23 is defined as an amplitude PHDd. A ratio PHDs/PHDc of the amplitude PHDs to the amplitude PHDc is preferably 1.15 or more and 1.50 or less. When the ratio PHDs/PHDc is less than 1.15, the area of the blocks BK constituting the center land portion 20C is insufficient. This degrades dry performance, which is not preferred. When the ratio PHDs/PHDc exceeds 1.50, due to uneven shoulder land portions, uneven wear resistance performance is degraded, which is not preferred. Note that the ratio PHDs/PHDc is more preferably 1.25 or more and 1.40 or less.
A ratio PHDd/PHDc of the amplitude PHDd to the amplitude PHDc is preferably 0.90 or more and 1.20 or less. When the ratio PHDd/PHDc is less than 0.90, the area of the blocks BK constituting the center land portion 20C is insufficient. This degrades dry performance, which is not preferred. When the ratio PHDs/PHDc exceeds 1.20, due to uneven shoulder land portions, uneven wear resistance performance is degraded, which is not preferred. Note that the ratio PHDd/PHDc is more preferably 0.95 or more and 1.15 or less.
As illustrated in
In other words, the inclination angle of the lug groove 24 with respect to the tire circumferential direction between the plurality of blocks BK2 adjacent in the tire circumferential direction is greater than the inclination angle of the lug groove 24 with respect to the tire circumferential direction between the plurality of blocks BK1 adjacent in the tire circumferential direction. Also, the inclination angle of the lug groove 24 with respect to the tire circumferential direction between the plurality of blocks BK3 adjacent in the tire circumferential direction is greater than the inclination angle of the lug groove 24 with respect to the tire circumferential direction between the plurality of blocks BK1 adjacent in the tire circumferential direction.
An inclination angle θ1 of the lug groove 24 with respect to the tire circumferential direction between the blocks BK1 as the center blocks is preferably 20 degrees or more and 60 degrees or less. The inclination angle θ1 is an angle formed between an imaginary line VL1 and the tire circumferential direction. The imaginary line VL1 is a straight line connecting midpoints of opening positions of the lug groove 24 to the circumferential main grooves 22A between the blocks BK1. The inclination angle θ1 being less than 20 degrees degrades scratch resistance performance of the block BK1 (in other words, increases a possibility of a lack of a part of the block BK1), which is not preferred. The inclination angle θ1 in excess of 60 degrees degrades dry performance, which is not preferred. The inclination angle θ1 is more preferably 30 degrees or more and 50 degrees or less.
An inclination angle θ2 of the lug groove 24 with respect to the tire circumferential direction between the blocks BK2 as the outer blocks adjacent to the block BK1 is preferably 60 degrees or more and 85 degrees or lesss. The inclination angle θ2 is an angle formed between an imaginary line VL2 and the tire circumferential direction. The imaginary line VL2 is a straight line connecting a midpoint P3 of an opening position of the lug groove 24 to the circumferential main groove 22A and a midpoint P4 of an opening position of the lug groove 24 to the circumferential main groove 22B between the blocks BK2. The inclination angle θ2 being less than 60 degrees degrades uneven wear resistance performance, which is not preferred. The inclination angle θ2 in excess of 85 degrees degrades dry performance due to uneven block rigidity, which is not preferred. The inclination angle θ2 is more preferably 65 degrees or more and 80 degrees or less.
An inclination angle θ3 of the lug groove 24 with respect to the tire circumferential direction between the blocks BK3 as the outer blocks close to the tire ground contact edge T is preferably 60 degrees or more and 89 degrees or less. The inclination angle θ3 is an angle formed between an imaginary line VL3 and the tire circumferential direction. The imaginary line VL3 is a straight line connecting a midpoint P5 of an opening position of the lug grooves 24 to the circumferential main grooves 22B and a midpoint P6 of an opening position of the lug grooves 24 to the circumferential main groove 23 between the blocks BK3. The inclination angle θ3 being less than 60 degrees degrades uneven wear resistance performance, which is not preferred. The inclination angle θ3 in excess of 89 degrees degrades dry performance due to uneven block rigidity, which is not preferred. The inclination angle θ3 is more preferably 65 degrees or more and 85 degrees or less.
In this way, since the imaginary line VL intersects with the short linear portion 22BS, not the long linear portion 22BL, the long linear portion 22BL is located on the side surface of the block BK2 in the tire width direction. Since the long linear portion 22BL is located on the side surface of the block BK2 in the tire width direction, the area of the road contact surface of the block BK2 can be ensured. As a result, dry performance and uneven wear resistance performance are improved.
Similarly, since the imaginary line VL intersects with the short linear portion 23S, not the long linear portion 23L, the long linear portion 23L is located on the side surface of the block BK3 in the tire width direction. Since the long linear portion 23L is located on the side surface of the block BK3 in the tire width direction, the area of the road contact surface of the block BK3 can be ensured. As a result, dry performance and uneven wear resistance performance are improved.
Furthermore, as illustrated in
However, the inflection point P0 on the imaginary line VL may be at a position other than the position intersecting with the tire equatorial plane CL. Even when the inflection point P0 is at the position other than the position intersecting with the tire equatorial plane CL, the lug grooves 24 having the S-shape allow improving dry performance, wet performance, and uneven wear resistance performance.
An example of the cross-sectional shape of the main groove will be described with reference to
Here, angles of the groove walls on both sides of the main grooves 22A, 22B, 23 with respect to normal lines N of the tread surfaces are referred to as groove wall angles. The groove wall angles of the main grooves 22A, 22B, 23 are preferably 10 degrees or more and 35 degrees or less. When the groove wall angle is less than 10 degrees, dry performance is degraded. Accordingly, when the groove wall angle exceeds 35 degrees, wet performance is degraded, which is not preferred.
In
In
In
In
In
In
The angle difference between the angle α15 and the angle α25, which have been described with reference to
In
The angle difference between the angle α16 and the angle α26, which have been described with reference to
In
Additionally, in
Regarding the groove widths W11, W22, W20 described above, both of a ratio W22/W11 of the groove width W22 to the groove width W11 and a ratio W20/W11 of the groove width W20 to the groove width Wi are preferably 0.60 or more and 1.10 or less. The ratio W22/W11 or the ratio W20/W11 being less than 0.60 degrades wet performance, which is not preferred. The ratio W22/W11 or the ratio W20/W11 in excess of 1.10 degrades dry performance, which is not preferred.
Additionally, in
As illustrated in
The raised bottom portions 240 are provided in regions including the midpoints P11, P14, P23 of the lug grooves 24. In the present example, the groove depth of the lug groove 24 is equal to the groove depths of the main grooves 22A, 22B, 23. However, in the lug groove 24, the groove depth of the portion where the raised bottom portion 240 is provided is shallower than the groove depths of the main grooves 22A, 22B, 23. Note that a maximum value of a groove depth DR of the main groove 22A is 19.1 mm, for example.
Here, the groove depths of the main grooves 22A, 22B, 23 are denoted as DR. A ratio DS/DR of the groove depth DS to the groove depth DR is preferably 0.15 or more and 0.35 or less. The ratio DS/DR being smaller than 0.15 shallows the lug groove 24 and degrades wet performance, which is not preferred. The ratio DS/DR being greater than 0.35 deepens the lug groove 24, reduces block rigidity, and degrades uneven wear resistance performance, which are not preferred.
When the groove depths DR of the main grooves 22A, 22B, 23 are equal to the original groove depth of the lug grooves 24, similarly, the ratio of the groove depth DS to the original groove depth of the lug grooves 24 is preferably 0.15 or more and 0.35 or less.
As illustrated from
As described with reference to
Although the cross-sectional shapes of the main grooves 22A have been described with reference to
In the embodiment described above, the pneumatic tire has been described as an example of the tire as described above. However, the configuration is not limited thereto, and the configurations described in this embodiment can be optionally applied to other tires as well within the scope apparent to those skilled in the art. Examples of other tires include airless tires and solid tires.
In the present examples, performance tests for rolling resistance performance and snow traction performance were performed on a plurality of types of tires of different conditions (see from Table 1 to Table 10). In the performance tests, tires (heavy duty tires) with a size of 455/55R22.5 were mounted on 22.5 inches×14.00 inches rims, inflated to a standard maximum air pressure (900 kPa), and mounted on a drive shaft of a test vehicle (2-D, tractor head), and the actual vehicle evaluation was performed with a standard maximum load applied.
In the evaluation of dry performance, time required for a speed of the test vehicle to reach 40 km/h from 5 km/h was measured on a dry road surface and indexed. Results are expressed as index values with the result of Conventional Example being assigned the value of (100). Larger index values indicate excellent dry performance.
In the evaluation of wet performance, a time required for the speed of the test vehicle to reach 20 km/h from 5 km/h was measured on a wet asphalt road surface that had been sprayed to a water depth of 1 mm and indexed. Results are expressed as index values with the result of Conventional Example being assigned the value of (100). Larger index values indicate excellent wet performance.
In the evaluation of uneven wear resistance performance, an amount of heel and toe wear after the test vehicle traveled for 50000 km on a dry asphalt road surface was measured by market monitor and indexed. Results are expressed as index values with the result of Conventional Example being assigned the value of (100). The larger index values are, the smaller the amount of heel and toe wear is, and this indicates excellent uneven wear resistance performance.
All tires of Example 1 to Example 65 from Table 1 to Table 5 include a center main groove having a zigzag shape in which first linear portions and second linear portions having mutually different inclination angles in the tire width direction with respect to the tire circumferential direction are alternately connected and outer main grooves having a zigzag shape in which long linear portions and short linear portions having mutually different inclination angles in the tire width direction with respect to the tire circumferential direction and different tire circumferential lengths are alternately connected.
Additionally, in the tires of Examples 1 to 65, the ratio LC1/PDc is 0.40 or more and 0.60 or less, the ratio Ls1/PDs is 0.45 or more and 0.75 or less, and further the ratio PDs/PDc is 0.90 or more and 1.20 or less. In the tires of Example 1 to Example 65, the lug groove intersects with the short linear portion or intersects with the long linear portion, the ratio φ12/PDc is 0.60 or more and 0.85 or less or not, the ratio φ13/PDc is 0.95 or more and 1.15 or less or not, the inclination angle of the lug groove is larger in the land portion on the outer side than an inclination angle of the center land portion or not, the inclination angle θ1 is 20 degrees or more and 60 degrees or less or not, the inclination angle θ2 is 60 degrees or more and 89 degrees or less or not, the inclination angle θ3 is 60 degrees or more and 85 degrees or lesss or not, the ratio Wb2/Wb1 is 0.80 or more and 1.00 or less or not, the ratio Wb3/Wb1 is 0.90 or more and 1.10 or less or not, the ratio Wb5/Wb4 is 0.75 or more and 1.00 or less or not, the ratio Wb6/Wb4 is 0.65 or more and 0.85 or less or not, the tire circumferential lengths of the short linear portion and the long linear portion are 15 mm or more and 45 mm or less or not, the ratio W22/W11 is 0.60 or more and 1.10 or less or not, the ratio W20/W11 is 0.60 or more and 1.10 or less or not, the ratio L/TW is 0.30 or more and 0.60 or less or not, the ratio PHDs/PHDc is 1.15 or more and 1.50 or less or not, the ratio PHDd/PHDc is 0.90 or more and 1.20 or less or not, the ratio SBK2/SBK1 is 0.85 or more and 1.05 or less or not, the ratio SBK3/SBK1 is 0.85 or more and 1.05 or less or not, the lug groove shape is the S-shape or the linear shape, the outer main grooves have similar shapes or not (non-similar shapes), the outer opening lug groove is provided or not, the ratio Wrsh/W20 is 2.0 or more and 3.0 or less or not, the ratio DS/DR is 0.15 or more and 0.35 or less or not, the groove wall angle of the main groove is 10 degrees or more and 35 degrees or less or not, the bending is present in the groove wall or not, the block end portions are chamfered or not.
The tire of Conventional Example in Table 1 includes land portions defined by three straight main grooves and includes a center land portion having a road contact surface formed of square blocks. A tire of Comparative Example 1 in Table 1 has the ratio LC1/PDc of 0.40, the ratio Ls1/PDs of 0.80, and the ratio PDs/PDc of 1.20. A tire of Comparative Example 2 in Table 1 has the ratio LC1/PDc of 0.50, the ratio Ls1/PDs of 0.80, and the ratio PDs/PDc of 1.20. A tire of Comparative Example 3 in Table 1 has the ratio LC1/PDc of 0.60, the ratio Ls1/PDs of 0.80, and the ratio PDs/PDc of 1.20.
As shown in the test results from Table 1 to Table 10, it is seen that the tires of the respective Examples have excellent dry performance, wet performance, and uneven wear resistance performance.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-080849 | Apr 2020 | JP | national |
