Tire

Abstract

A tire includes a tread having: a plurality of main grooves extending along the tire circumferential direction; and a plurality of ground contact portions separated by the main grooves. The tread is configured to include: a first rubber layer located on the inner side in the tire width direction; and a second rubber layer contacting the first rubber layer and located on the outer side in the tire width direction of the first rubber layer. In a cross-sectional view in the width direction, the boundary between the first rubber layer and the second rubber layer is inclined with respect to the tire radial direction, and one end of the boundary terminates at the groove wall on the inner side in the tire width direction of the main groove.

Description

Technical Field

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

[0002] In order to suppress uneven wear of a tire and improve the balance of various performances, a structure has been proposed in which a plurality of rubber materials are divided in the width direction to form a tread portion (for example, Patent Document 1).

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2012-116246 Summary of the Invention

[0006] Problems to be Solved by the Invention

[0007] According to the technique disclosed in Patent Document 1, uneven wear can be suppressed. However, since the boundaries between the plurality of rubbers forming the tread portion are in a direction perpendicular to the ground contact surface, there is a case where cracks are generated at the boundary portions between the rubbers due to concentration of strain during rolling.

[0008] The present invention has been made in view of the above problems, and an object thereof is to provide a pneumatic tire capable of suppressing cracks between rubbers at the boundary where the rubbers are joined to each other in a structure in which a tread portion is formed of a plurality of rubbers.

[0009] Solutions for Solving the Problems

[0010] As a structure of a tire for solving the above problems, the tire includes a tread having: a plurality of main grooves extending along the circumferential direction of the tire; and a plurality of ground contact portions divided by the main grooves. The tread is configured to include: a first rubber layer located on the inner side in the 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. In a cross-sectional view in the width direction, the boundary between the first rubber layer and the second rubber layer is inclined with respect to the tire radial direction, and one end of the boundary terminates at a groove wall on the inner side in the tire width direction of the main groove.

[0011] In addition, the above summary of the invention does not list all the essential features of the present invention, and each structure constituting the feature group can also be an invention. Brief Description of the Drawings

[0012] Figure 1 is a block diagram of a tire.

[0013] Figure 2is an enlarged cross-sectional view of the tread surface portion.

[0014] Figure 3 is an enlarged cross-sectional view of the intermediate ground portion.

[0015] Hereinafter, the present invention will be described in detail through embodiments of the invention. However, the following embodiments do not limit the invention described in the claims. In addition, the combinations of the features described in the embodiments are not necessarily all essential for the solution of the invention. Detailed Embodiment

[0016] [Basic Structure of Tire]

[0017] Figure 1 is a cross-sectional view in the width direction of the tire T of the present embodiment. In the following description, the directions indicated by the arrows such as Figure 1 are specified as the tire width direction and the tire (semi) radius direction. In addition, for the tire width direction, it is sometimes set as left and right when facing the paper surface with the tire center CL as the center. The tire center CL sides on the left and right are each called the inner side, and the opposite side is called the outer side.

[0018] 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 base rubber 24, a sidewall rubber 26, a base rubber 28, a tread rubber 30, and the like. The bead core 12, the carcass 14, and the belt 16 form the skeleton of the tire T. The bead filler 20, the rim cushion rubber 22, the inner liner 18, the belt base rubber 24, the sidewall rubber 26, the base rubber 28, and the tread rubber 30 are provided as thickening members for the skeleton to meet the performance requirements for each part of the tire T.

[0019] A pair of bead cores 12 are provided on the left and right of the tire T. The bead core 12 is formed into a ring shape by winding a bead cord a predetermined number of turns, and the bead cord is formed by layer twisting, double twisting, etc. of a steel wire rod. The contour shape of the bead core 12 is formed into a polygonal shape such as a quadrilateral or a hexagon, or a circular shape, etc.

[0020] The carcass 14 is folded back so as to roll up from the inner side to the outer side of the bead cores 12 provided on the left and right, and is provided so as to extend in a ring shape between the left and right bead cores 12, 12. The carcass 14 is constituted by overlapping one or more carcass plies, and the carcass cords forming each carcass ply extend in the tire radius direction. The rolled-up end of the carcass 14 sometimes terminates at a position inside the tire radius with respect to the maximum width portion of the tire T, sometimes terminates at a position outside the tire radius direction with respect to the maximum width portion of the tire T, or sometimes terminates in coincidence with the maximum width portion.

[0021] The belt 16 is provided at the crown portion of the carcass 14, that is, at a position corresponding to the tread surface of the tire T. The belt 16 is wound along the circumferential direction of the tire. The belt 16 is formed, for example, by overlapping one or more belt plies (in this embodiment, four belt plies 16a to 16d), and the belt cords forming each belt ply extend along the circumferential direction of the tire.

[0022] The bead filler 20 is arranged so as to fill the space formed between the carcass 14 wound around the bead core 12.

[0023] [Rubber structure of the tire]

[0024] The rim cushion rubber 22 extends a predetermined length along the outer side of the carcass 14 wound from the innermost side in the radial direction of the tire. Thereby, the close contact with the applicable rim when the tire T is assembled to the rim and the structure of the bead portion are protected.

[0025] The belt base rubber 24 is provided between the end portion side of the belt 16 protruding in the tire width direction and the carcass 14, and protects the structure of the end portion side of the belt 16.

[0026] The sidewall rubber 26 is adjacent to the rim cushion rubber 22, extends along the outer circumference of the carcass 14 toward the outer side in the radial direction, and covers the side portion of the belt base rubber 24.

[0027] The base rubber 28 extends in the tire width direction on the outer side in the radial direction of the belt 16, and is arranged so as to cover the left and right belt base rubbers 24, 24 and the sidewall rubbers 26, 26.

[0028] The tread rubber 30 is provided overlapping on the outer side in the radial direction of the base rubber 28, and together with the base rubber 28 forms the tread surface of the tire T. A predetermined tread pattern is formed on the tread rubber 30, and its surface becomes the ground contact surface of the tire T.

[0029] The inner liner 18 extends over the entire range between the rim cushion rubbers 22, 22 provided at the left and right bead portions, and covers the entire inner circumferential region of the carcass 14. The airtightness of the pneumatic tire is imparted by the inner liner 18.

[0030] [Structure of the tread surface]

[0031] As Figure 1 shown, the tread rubber 30 of this embodiment includes a plurality of (four in this embodiment) main grooves 40, 42, 44, 46 extending along the circumferential direction of the tire (circle) (hereinafter, sometimes referred to as main grooves 40 to 46) and a plurality of ground contact portions 50, 52, 54, 56, 58 (hereinafter, sometimes referred to as ground contact portions 50 to 58) divided by the main grooves 40 to 46.

[0032] The main grooves 40 to 46 are recesses provided with wear indicators indicating the usage limit of the tire T, and are the deepest recesses formed in the recesses of the tire T. In the following description, the main grooves 40 and 46 located on the outermost side in the tire width direction among the main grooves 40 to 46 are taken as the outermost grooves 40 and 46, and the main grooves 42 and 44 located on the inner side are taken as the inner grooves 42 and 44. In addition, the grounding portions 50 and 58 located on the outermost side in the tire width direction among the grounding portions 50 to 58 are taken as the shoulder grounding portions 50 and 58, and the grounding portion 54 located within the range including the tire center CL is taken as the center grounding portion 54. In addition, the grounding portions 52 between the shoulder grounding portion 50 and the center grounding portion 54 and the grounding portions 56 between the shoulder grounding portion 58 and the center grounding portion 54 are respectively referred to as the intermediate grounding portions 52 and 56.

[0033] The tread rubber 30 having the above-described tread pattern is configured to include a first rubber layer 32 located on the inner side in the tire width direction and second rubber layers 34, 34 that are in contact with the first rubber layer 32 and are located on the outer side in the tire width direction of the first rubber layer 32. The first rubber layer 32 and the second rubber layers 34 are made of rubbers having different characteristics. For example, the second rubber layers 34 are made of a rubber having better wear resistance than the first rubber layer 32, and can suppress uneven wear that is likely to occur at the tire shoulders of the tire T when the vehicle turns or the like.

[0034] Hereinafter, mainly with reference to Figure 2 the relationship between the first rubber layer 32 and the second rubber layers 34 will be described. In the tire T of this example, the tread pattern formed on the tread rubber 30 is symmetric about the tire center CL in the left-right direction (that is, a tire whose rotation direction is not specified), and therefore the right side portion of the tire center CL is used to describe the details thereof.

[0035] [Regarding the boundary]

[0036] Figure 2 is an enlarged cross-sectional view of the tread portion. As shown in this figure, for the tread rubber 30, in the cross-sectional view in the width direction, the boundary (interface) B between the first rubber layer 32 and the second rubber layers 34 extends in a manner inclined with respect to the tire radial direction. More specifically, the boundary B extends obliquely with respect to the tire radial direction and the width direction.

[0037] [Regarding the outer end of the boundary]

[0038] As this Figure 2As shown, the end Bto on the outer side in the tire width direction of the junction B reaches the inner groove wall 40wi in the tire width direction of the outermost groove 40 and terminates. By the end Bto terminating at the inner groove wall 40wi in the tire width direction of the outermost groove 40, the shoulder grounding 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 grounding portion 52 is formed by both the first rubber layer 32 and the second rubber layer 34. In addition, since the junction B is inclined, the first rubber layer 32 and the second rubber layer 34 are in contact with each other in the intermediate grounding portion 52 and are in a state of being laminated in the tire radial direction.

[0039] In this way, by inclining the junction B where the first rubber layer 32 and the second rubber layer 34 are joined in contact with each other, and causing the end Bto on the outer side in the tire width direction of this junction B to terminate at the inner groove wall 40wi of the outermost groove 40, the stress generated due to the friction with the road surface during tire rolling is dispersed, it is difficult for strain concentration to occur at the junction B, and it is possible to suppress cracks at the junction B of the first rubber layer 32 and the second rubber layer 34.

[0040] As Figure 2 shown by the arrow α in, the termination position of the end Bto of the junction B on the groove wall 40wi is preferably set within the range of 0% or more and 90% or less from the tread contact surface 30a of the outermost groove 40 to the groove bottom 40b. In this way, by setting the termination position of the end Bto of the junction B on the groove wall 40wi to a position that at least does not include the groove bottom 40b and has a predetermined distance from the groove bottom 40b, it is possible to suppress cracks at the bottom of the groove (groove bottom 40b) caused by strain concentration. In addition, the groove bottom 40b refers to the deepest position of the outermost groove 40 starting from the tread contact surface 30a. In addition, the 0% position corresponds to the position where the groove wall 40wi intersects the tread contact surface 30a.

[0041] [Regarding the inner end of the junction]

[0042] The end Bti on the inner side in the tire width direction of the junction B terminates at a position on the inner side in the tire width direction with respect to 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 of the outermost groove 40. In addition, the end Bti reaches the laminated interface between the base rubber 28 and the tread rubber 30, and it can also be said that the first rubber layer 32 and the second rubber layer 34 are divided and laminated in the width direction by the junction B. In addition, since the end Bti terminates at a position on the inner side in the tire width direction with respect to the width direction center Cx, the junction B extends in a manner that is inclined radially outward from the inner side to the outer side in the tire width direction as a whole. In addition, it can be said that the junction B has a length longer than half of the width direction dimension of the intermediate grounding portion 52 including this junction B. Here, as Figure 2As shown, the center Cx in the width direction coincides with the center of the width direction distance between the groove center part 40c of the outermost groove 40 and the groove center part 42c of the inner groove 42. In addition, the groove center parts 40c and 42c coincide with the center of the line segment connecting the opening ends of the openings on the tread ground contact surface 30a.

[0043] By setting the termination position of the end Bti of the boundary B within the above range, while the tire T is in use, the entire tread rubber 30 gradually wears, and the second rubber layer 34 is exposed again as the tread surface layer part, that is, as the tread ground contact surface. Therefore, the performance of the second rubber layer 34 can be gradually exerted on the tread end side. Specifically, by using a rubber with better abrasion resistance than the first rubber layer 32 as the second rubber layer 34, the second rubber layer 34 gradually appears in the area (shoulder area) on the tread end side where uneven wear is likely to occur in the tire width direction, and the area of the second rubber layer 34 with excellent abrasion resistance increases, thereby effectively suppressing uneven wear.

[0044] [Other preferred examples]

[0045] It is also possible to set the termination position of the end Bto of the boundary B on the groove wall 40wi within the range of 0% or more and 50% or less from the tread ground contact surface 30a to the groove bottom 40b. That is, by terminating at a shallower position from the ground contact surface in the outermost groove 40, the second rubber layer 34 in the range of the intermediate ground contact part 52 appears as the tread surface layer part from the early wear stage of the tread part during tire use. Therefore, by using a rubber with excellent abrasion 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 part.

[0046] In addition, it is also possible to set the termination position of the end Bto of the boundary B on the groove wall 40wi within the range of 0% or more and 30% or less from the tread ground contact surface 30a to the groove bottom. If set within this range, compared with the above example, the second rubber layer 34 in the range of the intermediate ground contact part 52 appears as the tread surface layer part from an earlier wear stage, and uneven wear can be suppressed from an earlier wear stage of the tread part.

[0047] Alternatively, the termination position of the end portion Bto of the junction B on the groove wall 40wi can be set within a range of more than 30% and less than 50% from the tread contact surface 30a to the groove bottom 40b. In this case, compared with the above examples, starting from a certain stage (delayed in time) of wear of the tread portion, the second rubber layer 34 within the range of the intermediate grounding portion 52 appears as the tread surface layer portion. Therefore, in the early stage of wear of the tread portion, after the performance of the first rubber layer 32 has dominantly played a role for a certain period, uneven wear at the tread end side can be suppressed.

[0048] It can be set such that the loss factor tanδ of the rubber composition forming the second rubber layer 34 at 60°C is larger than the loss factor tanδ of the rubber composition forming the first rubber layer 32 at 60°C. That is, for the rubber compositions forming the first rubber layer 32 and the second rubber layer 34, materials can be selected in such a way that the relationship tanδ of the material forming the first rubber layer 32 at 60°C < tanδ of the material forming the second rubber layer 34 at 60°C is satisfied.

[0049] Thereby, the wear at the tread end side is slowed down, and uneven wear can be suppressed. In addition, tanδ is calculated based on JIS K6254 and K6394, and is the result obtained from an experiment conducted using a testing machine conforming to K6272 and based on K6250.

[0050] As the rubber compositions forming the first rubber layer 32 and the second rubber layer 34, materials can be selected in such a way that the complex elastic modulus of the rubber composition forming the first rubber layer 32 is larger than the complex elastic modulus of the rubber composition forming the second rubber layer 34.

[0051] That is, it can be set in such a way that the relationship complex elastic modulus of the material forming the first rubber layer 32 > complex elastic modulus of the material forming the second rubber layer 34 is satisfied. By setting the characteristics of the materials of the first rubber layer 32 and the second rubber layer 34 as described above, the wear at the tread end side is slowed down, and uneven wear can be suppressed.

[0052] [Regarding the rubber ratio]

[0053] Figure 3 It is an enlarged view of the intermediate grounding portion 52 having the junction B. As shown in this figure, in the intermediate grounding portion 52 having the junction B between the first rubber layer 32 and the second rubber layer 34, the first rubber layer 32 and the second rubber layer 34 can be set such that, in terms of the area ratio in the cross-sectional view in the tire width direction, the first rubber layer 32 is, for example, 10% or more, 35% or more, 50% or more, 65% or more, etc.

[0054] As Figure 3As shown, the area ratio means the ratio of the areas of the first rubber layer 32 and the second rubber layer 34 in the area enclosed by the line segment f connecting the bottom 40b of the outermost groove 40 and the bottom 42b of the adjacent inner groove 42 and the contour shape of the intermediate grounding portion 52 with respect to the area of this region.

[0055] By setting the ratio of the rubber composition of the first rubber layer 32 included in the intermediate grounding portion 52 within the above range, even when the junction B bends in the intermediate grounding portion 52 during tire molding, the second rubber layer 34 can be gradually and appropriately exposed as the tread surface portion according to the use of the tire. In particular, it is possible to prevent a sharp change in performance caused by the second rubber layer 34 being exposed sharply from the early stage of use. In addition, by intentionally controlling the bending during tire molding, it is possible to intentionally achieve a change in performance at any stage of use.

[0056] In addition, as the upper limit of the ratio of the area of the rubber composition of the first rubber layer 32, it can be set to 95% or less, and more preferably 85% or less. By setting such an upper limit value, even when the junction B bends within the intermediate grounding portion 52 during molding, it is possible to suppress stress concentration caused by the junction B approaching perpendicularity.

[0057] As described above, the present invention has been illustrated by the embodiments, but the present invention is not limited by any of the above embodiments. For example, in the above embodiment, a tire T having four main grooves 40, 42, 44, 46 in the tread rubber 30 is employed, but it may also be a tire having three main grooves in which a 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 end sides, or a tire having five or more main grooves.

[0058] In addition, in the above embodiment, it is configured such that the tread rubber 30 is laminated on the base rubber 28 on the tread portion of the tire T, but the base rubber 28 is not an essential structure, and the tread rubber 30 may also be laminated on the belt 16. And, the inner end Bti of the junction B where the first rubber layer 32 and the second rubber layer 34 are joined is located on the interface when the tread rubber 30 is laminated on the belt 16.

[0059] In addition, in the above embodiment, the two rubber layers of the first rubber layer 32 and the second rubber layer 34 are arranged along the tire width direction to form the tread rubber 30, but the tread rubber 30 may also be formed using three or more rubber compositions. For example, if five main grooves are formed in the tread rubber, six grounding portions are divided by each main groove. And, for example, it is also possible to set the junction of the first rubber composition and the second rubber composition at the second grounding portion from the outer side in the tire width direction, and set the junction of the second rubber composition and the third rubber composition at the third grounding portion.

[0060] The present invention can also be described as follows. That is, the tire of the present invention has a tread, which has: a plurality of main grooves extending along the tire circumferential direction; and a plurality of grounding portions divided by the main grooves. The tread is configured to include: a first rubber layer located on the inner side in the 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. In a width direction cross-sectional view, the boundary between the first rubber layer and the second rubber layer is inclined with respect to the tire radial direction, and one end of the boundary terminates at the groove wall on the inner side in the tire width direction of the main groove.

[0061] Alternatively, one end of the boundary may terminate within a range of 0% or more and 90% or less from the tread ground contact surface to the groove bottom of the main groove.

[0062] Alternatively, the other end of the boundary may terminate at a position closer to the inner side in the width direction than the width direction center between the main groove where one end terminates and the main groove adjacent to the main groove on the inner side in the tire width direction of the main groove.

[0063] Alternatively, the tanδ at 60°C of the respective rubber compositions forming the first rubber layer and the second rubber layer satisfies the relationship that the tanδ at 60°C of the rubber composition forming the first rubber layer < the tanδ at 60°C of the rubber composition forming the second rubber layer.

[0064] As described above, according to the present invention, it is possible to effectively suppress the cracks between the rubber layers caused by strain concentration at the boundary.

[0065] In addition, by making the outer end of the boundary in the tire width direction terminate within a range of 0% or more and 90% or less from the tread ground contact surface to the groove bottom of the main groove, it is possible to effectively suppress the cracks between the rubber layers at the groove bottom caused by strain concentration.

[0066] In addition, by making the other end of the boundary terminate at a position closer to the inner side in the width direction than the width direction center between the main groove where one end terminates and the main groove adjacent to the main groove on the inner side in the tire width direction of the main groove, the range of the second rubber layer gradually expands due to the wear of the entire tread. Therefore, it is possible to mitigate the progress of wear at the tread end side and suppress uneven wear.

[0067] In addition, by making the tanδ at 60°C of the respective rubber compositions forming the first rubber layer and the second rubber layer satisfy the relationship that the tanδ at 60°C of the rubber composition forming the first rubber layer < the tanδ at 60°C of the rubber composition forming the second rubber layer, it is possible to further mitigate the wear at the tread end side and further effectively suppress uneven wear.

[0068] Explanation of Reference Signs

[0069] 28. Base rubber; 30. Tread rubber; 32. First rubber layer; 34. Second rubber layer; 40, 42, 44, 46. Main grooves; 50, 52, 54, 56, 58. Contact portions; B. Junction; Bto, Bti. Ends; 40wi. Groove wall; CL. Tire center; T. Tire.

Claims

1. A tire, characterized in that, the tire is a pneumatic tire and has a tread, the tread has: a plurality of main grooves extending along the circumferential direction of the tire; and a plurality of grounding portions divided by the main grooves, the tread includes: a first rubber layer located on the inner side in the tire width direction; and a second rubber layer contacting the first rubber layer and located on the outer side in the tire width direction of the first rubber layer, in a cross-sectional view in the width direction, the boundary between the first rubber layer and the second rubber layer is inclined with respect to the tire radial direction, and one end of the boundary terminates at the groove wall on the inner side in the tire width direction of the main groove, the other end of the boundary terminates at a position closer to the inner side in the width direction than the width direction center between the main groove at which the one end terminates and the main groove adjacent to the main groove on the inner side in the tire width direction of the main groove, taking the main groove at which the one end of the boundary terminates as the outer groove and the main groove adjacent to the inner side in the tire width direction of the outer groove as the inner groove, the intersection point of the boundary line between the first rubber layer and the second rubber layer and the center line of the grounding portion between the inner groove and the outer groove appears in the grounding portion surrounded by the virtual line connecting the bottom of the inner groove and the bottom of the outer groove and the tread surface.

2. The tire according to claim 1, characterized in that, the one end of the boundary terminates within a range of 0% or more and 90% or less from the tread contact surface to the bottom of the main groove.

3. The tire according to claim 1 or 2, characterized in that, the tanδ at 60°C of each rubber composition forming the first rubber layer and the second rubber layer satisfies the relationship that the tanδ at 60°C of the rubber composition forming the first rubber layer < the tanδ at 60°C of the rubber composition forming the second rubber layer.

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