tire

Abstract

To provide a pneumatic tire which can suppress cracking between rubbers at a boundary where the rubbers are joined to each other in a configuration that a tread part is formed of a plurality of rubbers.SOLUTION: A tire has a tread having a plurality of main grooves extending in a tire circumferential direction, and a plurality of land parts partitioned by the main grooves, in which the tread includes a first rubber layer positioned inside in a tire width direction and a second rubber layer that is brought into contact with the first rubber layer and is positioned outside in a tire width direction of the first rubber layer, in a cross section view in the width direction, a boundary between the first rubber layer and the second rubber layer is inclined in a tire radial direction, and one end at the boundary terminates at a groove wall inside in the tire width direction in the main grooves.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a tire, and more particularly to a tire capable of suppressing uneven wear on a shoulder side of the tire and improving the tire life. [Background technology]

[0002] 2. Description of the Related Art In order to suppress uneven wear occurring in tires and improve the balance of various performance characteristics, a structure has been proposed in which a tread portion is formed by dividing a plurality of rubber materials in the width direction (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2012-116246 A Summary of the Invention [Problem to be solved by the invention]

[0004] The technology disclosed in Patent Document 1 can suppress uneven wear, but since the boundaries between the multiple rubbers that form the tread are perpendicular to the tread surface, concentration of strain during rolling can sometimes cause cracks to form at the boundaries between the rubbers. The present invention has been made in consideration of the above-mentioned problems, and aims to provide a pneumatic tire that can suppress cracks between rubbers at the boundaries where the rubbers are joined in a structure in which the tread portion is formed from multiple rubbers. [Means for solving the problem]

[0005] As a tire configuration for solving the above-mentioned problems, there is provided a pneumatic tire having a tread having a plurality of main grooves extending in a tire circumferential direction and a plurality of land portions defined by the main grooves, the tread including a first rubber layer located on the inner side in a tire width direction, and a second rubber layer in contact with the first rubber layer and located on the outer side in the tire width direction of the first rubber layer, the second rubber layer forms a contact surface of the tire together with the first rubber layer and extends so as to form a part of a tire side surface, and in a cross-sectional view in the width direction, a boundary between the first rubber layer and the second rubber layer is formed. but , inclined with respect to the tire radial direction, The above One end of the boundary is a groove wall on the inner side in the tire width direction of the main groove. The range is 0% to 90% from the tread contact surface to the bottom of the main groove. End with The other end portion terminates inward in the tire width direction of a center in the tire width direction of a land portion sandwiched between the main groove in which the one end portion terminates and a main groove adjacent to the main groove in which the one end portion terminates on the inner side in the tire width direction, and further inward in the tire radial direction of a line segment connecting the groove bottom of the main groove in which the one end portion terminates and the groove bottom of the main groove adjacent to the main groove in which the one end portion terminates on the inner side in the tire width direction, and the boundary intersects with a widthwise center line of the land portion on the outer side in the tire radial direction of a line segment connecting the groove bottom of the main groove in which the one end portion terminates and the groove bottom of the main groove adjacent to the main groove in which the one end portion terminates on the inner side in the tire width direction. The composition was as follows. According to this configuration, the concentration of strain at the boundary is alleviated, and cracks occurring between the rubber layers starting from the boundary can be suppressed.

[0006] It should be noted that the above summary of the invention does not list all of the necessary features of the present invention, and each of the configurations that make up the group of features can also be an invention. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a block diagram of a tire. [Diagram 2] FIG. [Diagram 3] FIG.

[0008] The present invention will be described in detail below through embodiments of the invention. However, the following embodiments do not limit the invention according to the claims, and not all of the combinations of features described in the embodiments are necessarily essential to the solution of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] [Basic tire structure] Fig. 1 is a cross-sectional view in the width direction of a tire T according to this embodiment. In the following description, the directions indicated by the arrows in Fig. 1 are specified as the tire width direction and the tire (semi)radial direction. The tire width direction is defined as the left and right sides of the paper with the tire center CL as the center, and the left and right tire center CL sides are sometimes referred to as the inner side and the opposite side as the outer side.

[0010] The tire T includes a bead core 12 formed mainly of a cord member, a carcass 14, a belt 16 (belt layer), an inner liner 18 formed mainly of a rubber member, a bead filler 20, a rim cushion rubber 22, a belt under rubber 24, a side rubber 26, a base rubber 28, and a tread rubber 30. The bead core 12, the carcass 14, and the belt 16 form the framework of the tire T. The bead filler 20, the rim cushion rubber 22, the inner liner 18, the belt under rubber 24, the side rubber 26, the base rubber 28, and the tread rubber 30 are provided as filler members for the framework to satisfy the performance required for each part of the tire T.

[0011] A pair of bead cores 12 are provided on the left and right sides of the tire T. The bead cores 12 are formed into a ring shape by winding a bead cord, which is formed by, for example, twisting a steel wire in layers or multiple twists, a predetermined number of times. The contour shape of the bead cores 12 is formed into, for example, a polygonal shape such as a rectangle or a hexagon, or a circle.

[0012] The carcass 14 is folded up from the inside to the outside of the bead cores 12 provided on the left and right sides, and is provided so as to extend in a toroidal shape between the left and right bead cores 12. The carcass 14 is formed, for example, by overlapping one or more carcass plies, and carcass cords forming each carcass ply extend in the tire radial direction. The end of the wound up carcass 14 may terminate radially inward of the maximum width part of the tire T, may terminate radially outward of the tire, or may terminate coinciding with the maximum width part.

[0013] The belt 16 is provided at a crown portion of the carcass 14, i.e., at a position corresponding to a tread portion of the tire T. The belt 16 is wound around the tire in the circumferential direction. The belt 16 is formed, for example, by stacking one or more belt plies (four belt plies 16a to 16d in this embodiment), and belt cords forming each belt ply extend in the circumferential direction of the tire.

[0014] The bead filler 20 is disposed so as to fill a space formed between the carcass 14 wound around the bead core 12 .

[0015] [Tire rubber composition] The rim cushion rubber 22 extends a predetermined length along the outside of the carcass 14 wound up from the innermost side in the tire radial direction of the carcass 14. This ensures adhesion to an applicable rim when the tire T is mounted on the rim, and protects the structure of the bead portion.

[0016] The belt under-rubber 24 is provided between the end side of the belt 16 protruding in the tire width direction and the carcass 14, and protects the structure of the end side of the belt 16.

[0017] The side rubber 26 is adjacent to the rim cushion rubber 22 , extends radially outward along the outer periphery of the carcass 14 , and covers the sides of the belt under rubber 24 .

[0018] The base rubber 28 extends in the tire width direction on the outer side of the belt 16 in the tire radial direction, and is provided so as to cover the left and right belt under-rubbers 24;24 and the side rubbers 26;26.

[0019] The tread rubber 30 is provided overlapping the radially outer side of the base rubber 28, and together with the base rubber 28 constitutes a tread portion of the tire T. A predetermined tread pattern is formed in the tread rubber 30, and its surface becomes the contact surface of the tire T.

[0020] The inner liner 18 extends between the rim cushion rubbers 22, 22 provided on the left and right bead portions, and covers the entire inner periphery of the carcass 14. The inner liner 18 provides airtightness as a pneumatic tire.

[0021] [Tread structure] As shown in FIG. 1, the tread rubber 30 of this embodiment has a plurality of (four in this embodiment) main grooves 40; 42; 44; 46 (hereinafter sometimes referred to as main grooves 40-46) extending in the circumferential direction of the tire (circle), and a plurality of land portions 50; 52; 54; 56; 58 (hereinafter sometimes referred to as land portions 50-58) partitioned by the main grooves 40-46.

[0022] The main grooves 40-46 are recesses in which a wear indicator indicating the usage limit of the tire T is set, and refer to the deepest recesses among the recesses formed in the tire T. In the following description, the main groove 40;46 located at the outermost side in the tire width direction among the main grooves 40-46 is referred to as the outermost groove 40;46, and the main groove 42;44 located on the inner side is referred to as the inner groove 42;44. In addition, among the land portions 50-58, the land portion 50:58 located at the outermost side in the tire width direction is referred to as the shoulder land portion 50;58, and the land portion 54 located in the range including the tire center CL is referred to as the center land portion 54. In addition, the land portion 52;56 between the shoulder land portion 50 and the center land portion 54 and between the shoulder land portion 58 and the center land portion 54 are referred to as the intermediate land portion 52;56, respectively.

[0023] The tread rubber 30 having the above tread pattern is configured to include a first rubber layer 32 located on the inner side in the tire width direction, and a second rubber layer 34, 34 that is in contact with the first rubber layer 32 and located on the outer side of the first rubber layer 32 in the tire width direction. The first rubber layer 32 and the second rubber layer 34 are made of rubber having different properties. For example, the second rubber layer 34 is made of rubber having better abrasion resistance than the first rubber layer 32, and uneven wear that tends to occur in the shoulder portion of the tire T when the vehicle is cornering, etc., can be suppressed.

[0024] The relationship between the first rubber layer 32 and the second rubber layer 34 will be described below mainly with reference to FIG. 2. However, since in the tire T of this example, the tread pattern formed in the tread rubber 30 is symmetrical on either side of the tire center CL (i.e., a tire with no restrictions on the direction of rotation), the details will be described using the right side of the tire center CL.

[0025] [About the boundary] 2 is an enlarged cross-sectional view of the tread portion. As shown in the figure, in a cross-sectional view in the width direction, the tread rubber 30 extends such that a boundary (boundary surface) B between the first rubber layer 32 and the second rubber layer 34 is inclined with respect to the tire radial direction. More specifically, the boundary B extends with an inclination with respect to the tire radial direction and width direction.

[0026] [About the outer edge of the boundary] As shown in the figure, the end Bto on the outer side in the tire width direction at the boundary B reaches and terminates at the groove wall 40wi on the inner side in the tire width direction of the outermost groove 40. Since the end Bto terminates at the groove wall 40wi on the inner side in the tire width direction of the outermost groove 40, the shoulder land portion 50 located on the outer side in the width direction of the outermost groove 40 is formed only by the second rubber layer 34. On the other hand, the intermediate land portion 52 is formed of two types of rubber, the first rubber layer 32 and the second rubber layer 34. In addition, since the boundary B is inclined, the first rubber layer 32 and the second rubber layer 34 are in contact with each other at the intermediate land portion 52 and are stacked in the tire radial direction.

[0027] In this way, by inclining the boundary B where the first rubber layer 32 and the second rubber layer 34 are in contact with and joined to each other, and terminating the outer end Bto of the boundary B in the tire width direction at the inner groove wall 40wi of the outermost groove 40, the stress generated by friction with the road surface when the tire rolls is dispersed, making it difficult for strain to concentrate at the boundary B, and suppressing cracks between the first rubber layer 32 and the second rubber layer 34 starting from the boundary B.

[0028] As shown by the arrow α in FIG. 2, the end position of the boundary B at the groove wall 40wi is preferably set in a range of 0% to 90% from the tread contact surface 30a of the outermost groove 40 to the groove bottom 40b. In this way, by setting the end position of the boundary B at the groove wall 40wi at a position that does not include at least the groove bottom 40b and keeping a predetermined distance from the groove bottom 40b, it is possible to suppress cracks at the groove bottom (groove bottom 40b) due to strain concentration. The groove bottom 40b refers to the deepest position from the tread contact surface 30a in the outermost groove 40. The 0% position corresponds to the position where the groove wall 40wi and the tread contact surface 30a intersect.

[0029] [About the inner edge of the boundary] The end Bti on the inner side in the tire width direction of the boundary B terminates on the inner side in the tire width direction than the width direction center Cx between the outermost groove 40 and the inner groove 42 adjacent to the outermost groove 40 on the inner side in the tire width direction. The end Bti reaches the lamination boundary surface between the base rubber 28 and the tread rubber 30, and it can be said that the first rubber layer 32 and the second rubber layer 34 are separated and laminated from each other in the width direction by the boundary B. In addition, since the end Bti terminates on the inner side in the tire width direction than the width direction center Cx, the boundary B extends so as to incline radially outward from the inner side toward the outer side in the tire width direction as a whole. In addition, it can be said that the boundary B has a length longer than half the width direction dimension of the intermediate land portion 52 including the boundary B. Here, as shown in FIG. 2, the width direction center Cx coincides with the center of the width direction distance between the groove center portion 40c of the outermost groove 40 and the groove center portion 42c of the inner groove 42. Further, the groove central portions 40c and 42c coincide with the centers of the line segments connecting the opening ends that open to the tread ground contact surface 30a.

[0030] By setting the end position of the end Bti of the boundary B within the above-mentioned range, the entire tread rubber 30 gradually wears as the tire T is used, and the second rubber layer 34 is newly exposed as the tread surface layer, i.e., the tread contact surface. Therefore, the performance of the second rubber layer 34 can be gradually exhibited on the tread end side. Specifically, by using a rubber having better wear resistance than the first rubber layer 32 as the second rubber layer 34, the second rubber layer 34 is gradually exposed in the region (shoulder region) on the tread end side where uneven wear is likely to occur in the tire width direction, and the region of the second rubber layer 34 having excellent wear resistance increases, so that uneven wear can be effectively suppressed.

[0031] [Other preferred examples] The end Bto of the boundary B may be set to a range of 0% to 50% from the tread contact surface 30a to the groove bottom 40b. That is, by terminating the outermost groove 40 at a shallow position from the tread surface, the second rubber layer 34 in the range of the intermediate land portion 52 appears as the tread surface layer from the early wear stage of the tread portion when the tire is used. Therefore, by using a rubber with excellent wear resistance as the second rubber layer 34, the wear rate at the tread end side gradually slows down, and uneven wear can be suppressed from the early wear stage of the tread portion.

[0032] Also, the end position of the boundary B at the groove wall 40wi may be set in a range of 0% to 30% from the tread contact surface 30a to the groove bottom. By setting it in this range, the second rubber layer 34 in the range of the intermediate land portion 52 appears as the tread surface layer portion from an earlier wear stage compared to the above example, and uneven wear of the tread portion can be suppressed from an earlier wear stage.

[0033] Also, the end position Bto of the boundary B on the groove wall 40wi may be set in a range of 30% to 50% from the tread ground contact surface 30a to the groove bottom 40b. In this case, the second rubber layer 34 in the range of the intermediate land portion 52 appears as the tread surface layer portion at a stage (later in time) when the wear of the tread portion has progressed to a certain extent in comparison with each of the above-mentioned examples. Therefore, in the early stage of wear of the tread portion, uneven wear on the tread end side can be suppressed after the performance of the first rubber layer 32 is predominantly exerted for a certain period of time.

[0034] It is preferable to set the loss tangent tan δ at 60° C. of the rubber composition forming the second rubber layer 34 to be larger than the loss tangent tan δ at 60° C. of the rubber composition forming the first rubber layer 32. In other words, it is preferable to select materials for the rubber compositions forming the first rubber layer 32 and the second rubber layer 34 so that the relationship of tan δ at 60° C. of the material forming the first rubber layer 32 < the material forming the second rubber layer 34 is satisfied. This makes it possible to slow down wear at the tread edge side and suppress uneven wear. Note that tan δ is calculated based on the results obtained from a test performed based on K6250 using a testing machine conforming to JIS K6272, and based on K6254 and K6394.

[0035] As the rubber compositions forming the first rubber layer 32 and the second rubber layer 34, it is preferable to select materials such that the complex modulus of the rubber composition forming the first rubber layer 32 is greater than the complex modulus of the rubber composition forming the second rubber layer 34. That is, it is preferable to satisfy the relationship that the complex modulus of the material forming the first rubber layer 32 is greater than the complex modulus of the material forming the second rubber layer 34. By setting the characteristics of the materials of the first rubber layer 32 and the second rubber layer 34 as described above, wear on the tread end side is slowed down, and uneven wear can be suppressed.

[0036] [About rubber ratio] 3 is an enlarged view of an intermediate land portion 52 having a boundary B. As shown in the drawing, in the intermediate land portion 52 having a boundary B between the first rubber layer 32 and the second rubber layer 34, the first rubber layer 32 may occupy, for example, 10% or more, 35% or more, 50% or more, 65% or more, in terms of area ratio in a cross-sectional view in the tire width direction, between the first rubber layer 32 and the second rubber layer 34.

[0037] As shown in FIG. 3, the area ratio refers to the ratio of the area of ​​the first rubber layer 32 and the second rubber layer 34 to the area of ​​the area surrounded by a line segment f connecting the groove bottom 40b of the outermost groove 40 and the groove bottom 42b of the adjacent inner groove 42 and the contour shape of the intermediate land portion 52 (the portion shown in gray in the figure).

[0038] By setting the ratio of the rubber composition of the first rubber layer 32 contained in the intermediate land portion 52 within the above range, even if the boundary B is curved in the intermediate land portion 52 during tire molding, the second rubber layer 34 can be gradually and appropriately exposed as the tread surface layer portion as the tire is used. In particular, it is possible to prevent a sudden change in performance due to a sudden exposure of the second rubber layer 34 from the early stage of use. Also, by intentionally controlling the curvature during tire molding, it is possible to intentionally realize a change in performance at any stage of use.

[0039] The upper limit of the area ratio of the rubber composition of the first rubber layer 32 is preferably 95% or less, more preferably 85% or less. By setting such an upper limit, even if the boundary B curves within the intermediate land portion 52 during molding, stress concentration caused by the boundary B approaching vertical can be suppressed.

[0040] Although the present invention has been described above through the embodiments, the present invention is not limited to the above embodiments. For example, in the above embodiments, the tire T has four main grooves 40, 42, 44, 46 in the tread rubber 30, but the tire may have three main grooves, in which one main groove is formed near the center including the tire center CL and one main groove is formed on each of the left and right tread ends, or may have five or more main grooves.

[0041] In the above embodiment, the tread rubber 30 is laminated on the base rubber 28 in the tread portion of the tire T, but the base rubber 28 is not an essential component, and the tread rubber 30 may be laminated on the belt 16. The inner end Bti of the boundary B where the first rubber layer 32 and the second rubber layer 34 are joined is located on the boundary surface when the tread rubber 30 is laminated on the belt 16.

[0042] In the above embodiment, the tread rubber 30 is formed by arranging two types of rubber, the first rubber layer 32 and the second rubber layer 34, in the tire width direction, but the tread rubber 30 may be formed from three or more types of rubber compositions. For example, if five main grooves are formed in the tread rubber, six land portions are partitioned by each main groove. It is also possible to set the boundary between the first and second types of rubber compositions in the second land portion from the outer side in the tire width direction, and to set the boundary between the second and third types of rubber compositions in the third land portion.

[0043] As described above, according to the present invention, cracks between rubber layers caused by strain concentration at the boundary can be effectively suppressed. In addition, by terminating the outer end of the boundary in the tire width direction within a range of 0% to 90% from the tread contact surface to the bottom of the main groove, cracks between the rubber layers at the bottom of the groove due to strain concentration can be effectively suppressed. In addition, since the other end of the boundary terminates widthwise inward of the widthwise center between the main groove where the one end terminates and the main groove adjacent to that main groove on the tire widthwise inner side, the range of the second rubber layer gradually expands as the entire tread wears, so that the progress of wear on the tread end side can be slowed down and uneven wear can be suppressed. In addition, by having the tan δ at 60°C of the rubber compositions forming the first rubber layer and the second rubber layer satisfy the relationship of rubber composition forming the first rubber layer < rubber composition forming the second rubber layer, wear on the tread end side can be further slowed and uneven wear can be more effectively suppressed. [Explanation of symbols]

[0044] 28 base rubber, 30 tread rubber, 32 first rubber layer, 34 second rubber layer, 40:42:44:46 Main ditch, 50:52:54:56:58 Land section, B boundary, end Bto:Bti end, 40wi groove wall, CL tire center, T tire.

Claims

1. A plurality of main grooves extending in a tire circumferential direction; A plurality of land portions defined by the main groove; A pneumatic tire having a tread having The tread is a first rubber layer located on an inner side in a tire width direction; and a second rubber layer in contact with the first rubber layer and located on an outer side in the tire width direction of the first rubber layer, the second rubber layer forms a contact surface of the tire together with the first rubber layer and extends to form a part of a tire side surface, In cross section in the width direction, a boundary between the first rubber layer and the second rubber layer is inclined with respect to a tire radial direction, One end of the boundary terminates in a range of 0% to 90% from the tread ground contact surface of the groove wall on the inner side in the tire width direction of the main groove to the groove bottom of the main groove, the other end portion terminates inward in the tire width direction from a center in the tire width direction of a land portion sandwiched between the main groove in which the one end portion terminates and a main groove adjacent to the main groove in which the one end portion terminates on the inner side in the tire width direction, and terminates radially inward from a line segment connecting a groove bottom of the main groove in which the one end portion terminates and a groove bottom of a main groove adjacent to the main groove on the inner side in the tire width direction, the boundary intersects with the widthwise centerline of the land portion radially outward of a line segment connecting a groove bottom of the main groove where the one end portion terminates and a groove bottom of a main groove adjacent to the main groove where the one end portion terminates on the inner side in the tire width direction.

2. A tire as described in claim 1, characterized in that the main groove in which the one end terminates is located at the outermost position in the tire width direction among the multiple main grooves.

3. 3. The tire according to claim 1, wherein a tan δ at 60° C. of each of the rubber compositions forming the first rubber layer and the second rubber layer satisfies the relationship: rubber composition forming the first rubber layer < rubber composition forming the second rubber layer.

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