pneumatic tires

Abstract

To provide a pneumatic tire which can restrain a shoulder part from being eccentrically wore and accident from being generated.SOLUTION: A pneumatic tire comprises a carcass which is provided between a pair of bead parts, a belt layer which is laminated on the outside of the carcass in a radial direction of a tire and a cushion rubber which intervenes between an end part of the belt layer and the carcass. The cushion rubber contains a boundary surface which extends from a position on the outer side in an axial direction of the tire than the outermost end of the belt layer toward the inside in the axial direction of the tire and the inside of the radial direction of the tire, an inside rubber which is positioned on the inside of the boundary surface in the axial direction of the tire, and an outside rubber which is positioned on the outside of the boundary surface in the axial direction of the tire. Modulus at 100% extension is higher in an order of a cap rubber which forms an external surface of a tread, the inside rubber, and the outside rubber.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a pneumatic tire in which a cushion rubber is interposed between an end portion of a belt layer and a carcass. [Background technology]

[0002] Patent Document 1 describes a pneumatic tire with cushion rubber interposed between the end of a belt layer and the carcass. In this tire, a reinforcing rubber with a higher hardness than the cushion rubber is arranged axially outward of the cushion rubber, thereby preventing failure in the shoulder portion of the tread. However, depending on the physical properties of the tread rubber, the force acting on the shoulder portion during tire rolling may not be sufficiently dispersed, which may result in uneven wear in which the shoulder portion wears out earlier than the center portion, or failure such as separation due to strain concentration at the end of the belt layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-026111 Summary of the Invention [Problem to be solved by the invention]

[0004] The present disclosure has been made in consideration of the above-described circumstances, and has an object to provide a pneumatic tire that can suppress uneven wear and failure in the shoulder portion. [Means for solving the problem]

[0005] The pneumatic tire of the present disclosure includes: a pair of bead portions; a pair of sidewalls extending radially outward from each of the pair of bead portions; a tread connected to each of the pair of sidewalls at an outer end in the tire radial direction; a carcass provided between the pair of bead portions; a belt layer laminated on the outer side of the carcass in the tire radial direction; a cushion rubber interposed between the end of the belt layer and the carcass, the cushion rubber includes an interface extending from a position axially outward of an outermost end of the belt layer toward the axially inward and radially inward of the tire, an inner rubber positioned axially inward of the interface, and an outer rubber positioned axially outward of the interface, The modulus at 100% elongation is highest in the cap rubber forming the outer surface of the tread, followed by the inner rubber and the outer rubber in that order. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is a half cross-sectional view taken along the tire meridian plane, schematically illustrating an example of a pneumatic tire according to the present disclosure. [Figure 2] Enlarged view of the main part of Figure 1 DETAILED DESCRIPTION OF THE INVENTION

[0007] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a pneumatic tire according to the present disclosure will be described with reference to the drawings.

[0008] The pneumatic tire T shown in Figures 1 and 2 includes a pair of bead portions 1, a pair of sidewalls 2 extending radially outward from each of the pair of bead portions 1, a tread 3 continuing to the radially outer ends of each of the pair of sidewalls 2, a carcass 4 provided between the pair of bead portions 1, a belt layer 5 laminated on the radially outer side of the carcass 4, and cushion rubber 6 interposed between the end of the belt layer 5 and the carcass 4.

[0009] Here, the tire radial direction is the direction along the diameter of the tire T, and corresponds to the up-down direction in the drawings. In Figures 1 and 2, the upper side is the outer side in the tire radial direction, and the lower side is the inner side in the tire radial direction. The tire axial direction is the direction parallel to the rotation axis of the tire T, and corresponds to the left-right direction in the drawings. The side closer to the tire equatorial plane TC (left side in Figures 1 and 2) is the inner side in the tire axial direction, and the side away from the tire equatorial plane TC (right side in Figures 1 and 2) is the outer side in the tire axial direction. The tire circumferential direction is the direction around the rotation axis of the tire T.

[0010] An annular bead core 1a is embedded in the bead portion 1. The bead core 1a is formed by covering a bundle of steel wires or the like with rubber. A bead filler 1b is disposed radially outward of the bead core 1a. The bead filler 1b is formed of rubber with a triangular cross section that extends radially outward from the bead core 1a. A rim strip rubber 11 that forms the outer surface of the bead portion 1 is provided axially outward of the bead core 1a and bead filler 1b.

[0011] The carcass 4 extends in a toroidal shape, straddling the pair of bead portions 1. The carcass 4 is wound up (i.e., turned up) from the inside to the outside in the axial direction of the tire, sandwiching the bead cores 1a and bead fillers 1b. In other words, the carcass 4 has a main body portion extending from the tread 3 through the sidewalls 2 to the bead portions 1, and is provided with a series of wound-up portions located axially outward of the bead cores 1a and bead fillers 1b. Axially outward of the carcass 4 is provided a sidewall rubber 12 that forms the outer surface of the sidewalls 2.

[0012] The carcass 4 is composed of a carcass ply formed by rubber-coating carcass cords. Metals such as steel, or organic fibers such as polyester, rayon, nylon, and aramid are preferably used as materials for the carcass cords. The carcass cords are aligned in a direction substantially perpendicular to the tire circumferential direction (for example, a direction at an angle of 75 to 90 degrees with respect to the tire circumferential direction). In this embodiment, an example is shown in which the carcass 4 is composed of one carcass ply, but two or more carcass plies may be used. An inner liner 14 is disposed on the inner surface of the tire along the carcass 4.

[0013] The belt layer 5 is composed of a plurality of belt plies formed by rubber-coating belt cords. Steel is preferably used as the material for the belt cords. In this embodiment, an example is shown in which the belt layer 5 is composed of four belt plies 51 to 54. Among these, the belt plies 52 and 53 functioning as working belts have belt cords aligned at an inclination angle of 20 to 30 degrees with respect to the tire circumferential direction, and the belt cords are arranged so that they cross each other in opposite directions between the plies. Note that the number of belt plies constituting the belt layer 5 is not limited to this.

[0014] A tread rubber 13 is provided on the outer side of the belt layer 5 in the tire radial direction. The tread rubber 13 is provided with grooves including circumferential grooves 15, and a tread pattern is formed in accordance with the required tire performance and usage conditions. The tread rubber 13 has a cap rubber 13a that forms the outer surface of the tread 3, and a base rubber 13b that is laminated on the inner side of the cap rubber 13a in the tire radial direction. In this embodiment, a SWOT (sidewall on tread) structure is adopted in which the outer ends of the sidewall rubbers 12 in the tire radial direction are placed on the sides of the tread rubber 13.

[0015] The cushion rubber 6 is arranged on what is called a buttress. The buttress corresponds to the radially outer portion of the sidewall 2 and is a portion that does not come into contact with the ground during normal running on flat paved roads. The cushion rubber 6 is sandwiched between the end of the belt layer 5 and the carcass 4, protrudes axially outward from the belt layer 5, and contacts the end of the belt layer 5 (more specifically, the end of the belt ply 52 including the outermost end 5E described below) from the radially inner side of the tire. A pair of cushion rubbers 6 are provided on either side of the tire equatorial plane TC. That is, a similar cushion rubber 6 is arranged on the buttress on the side not shown in FIG. 1.

[0016] The cushion rubber 6 has a crescent (or trapezoid) cross section and is formed in an annular shape along the tire circumferential direction. An axially inner end 6a of the cushion rubber 6 corresponds to the point where the belt layer 5 starts to separate from the carcass 4. An axially outer end 6b of the cushion rubber 6 corresponds to the point where the sidewall rubber 12 starts to separate from the carcass 4. The thickness of the cushion rubber 6 gradually increases from the inner end 6a toward the outer side in the tire axial direction, and also gradually increases from the outer end 6b toward the inner side in the tire axial direction. The thickness of the cushion rubber 6 is measured along the normal direction to the outer peripheral surface of the carcass 4.

[0017] As shown enlarged in Fig. 2, the cushion rubber 6 includes an interface 6c, an inner rubber 61 located axially inward of the interface 6c, and an outer rubber 62 located axially outward of the interface 6c. The interface 6c extends axially inward and radially inward from a position P1 that is axially more outer than the outermost end 5E of the belt layer 5. The outermost end 5E of the belt layer 5 is the axially outer end of the belt ply 52, which is the widest of the belt plies 51 to 54. The interface 6c extends from a position P1 on the outer peripheral surface of the cushion rubber 6 to a position P2 on the inner peripheral surface, dividing the cushion rubber 6. In this embodiment, the cushion rubber 6 is composed of two layers: the inner rubber 61 and the outer rubber 62.

[0018] In this tire T, the modulus at 100% elongation (hereinafter sometimes simply referred to as "modulus") increases in the order of cap rubber 13a, inner rubber 61, and outer rubber 62. That is, the modulus of cap rubber 13a is greater than that of inner rubber 61, which is greater than that of outer rubber 62. The modulus (M100) is determined as the tensile stress at 100% elongation by a tensile test (using a No. 3 dumbbell) at 25°C in accordance with JIS K6251.

[0019] By satisfying the above modulus relationship, the force acting on the shoulder portion during tire rolling can be appropriately distributed to promote uniform contact pressure and suppress uneven wear in the shoulder portion. At the same time, the interface 6c of the cushion rubber 6 extends from a position P1 axially outward of the outermost end 5E toward the axially and radially inward direction of the tire, thereby mitigating strain acting on the end of the belt layer 5 and suppressing the occurrence of failures such as separation. On the other hand, if the position P1 of the interface 6c is at the end of the belt layer 5 or further axially inward, there is a concern that failures may occur due to strain concentration at the interface 6c (and the end of the belt layer 5).

[0020] From the viewpoint of keeping the strain energy density of the shoulder portion low, it is preferable to ensure a sufficient difference in modulus between the cap rubber 13a and the outer rubber 62. Specifically, the difference between the modulus of the cap rubber 13a and the outer rubber 62 is preferably 1.5 MPa or more, and more preferably 2.0 MPa or more. The difference in modulus between the cap rubber 13a and the inner rubber 61 is, for example, 1.0 MPa or more. The difference in modulus between the inner rubber 61 and the outer rubber 62 is, for example, 0.8 MPa or more. The modulus of the cap rubber 13a is, for example, 2.7 to 3.7 MPa. The modulus of the inner rubber 61 is, for example, 2.5 to 3.3 MPa. The modulus of the outer rubber 62 is, for example, 1.2 to 2.2 MPa.

[0021] From the viewpoint of ensuring that the modulus of the inner rubber 61 is appropriately large, it is preferable that the modulus of the inner rubber 61 is larger than that of the base rubber 13b. The difference in modulus between the inner rubber 61 and the base rubber 13b is, for example, 1.0 MPa or more. Furthermore, from the viewpoint of ensuring that the modulus of the outer rubber 62 is appropriately small, it is preferable that the modulus of the outer rubber 62 is smaller than that of the sidewall rubber 12. The difference in modulus between the sidewall rubber 12 and the outer rubber 62 is, for example, 0.4 MPa or more. Furthermore, it is preferable that the modulus of the base rubber 13b is larger than that of the sidewall rubber 12. In this embodiment, an example is shown in which the moduli increase in the order of cap rubber 13a, inner rubber 61, base rubber 13b, sidewall rubber 12, and outer rubber 62.

[0022] In this embodiment, a pad rubber 7 is provided at the end of the belt layer 5. The pad rubber 7 is interposed between the widest belt ply 52 among the belt plies 51 to 54 and the belt ply 53 laminated on the tire radially outer side thereof. The pad rubber 7 is not in contact with the cushion rubber 6 and is provided as a separate member from the cushion rubber 6. The pad rubber 7 has a crescent (or trapezoid) cross section and is formed in an annular shape along the tire circumferential direction. The modulus of the pad rubber 7 is greater than the modulus of the cap rubber 13a. By providing such pad rubber 7, the effect of reducing strain acting on the end of the belt layer 5 is obtained.

[0023] The interface 6c preferably extends at an angle θ1 of 80±5 degrees relative to the tire radial direction. If this angle θ1 is 75 degrees or more, it is easy to ensure adhesive strength at the interface 6c against radial forces acting on the shoulder portion. Furthermore, if the angle θ1 is 85 degrees or less, it is convenient to ensure an appropriate volume of the inner rubber 61. The interface 6c is preferably inclined axially inward with respect to a normal L1 to the outer peripheral surface of the cushion rubber 6 that passes through position P1.

[0024] Considering an imaginary line L2 connecting the outermost end 5E of the belt layer 5 and the position P1 of the interface 6c on the outer peripheral surface of the cushion rubber 6, the interface 6c preferably extends at an angle θ2 of 30±10 degrees relative to the imaginary line L2, and more preferably at an angle θ2 of 30±5 degrees. By setting this angle θ2 to 20 degrees or more, it is easy to ensure adhesive strength at the interface 6c against forces acting on the shoulder portion in the tire radial direction. Furthermore, by setting the angle θ2 to 40 degrees or less, it is convenient to ensure an appropriate volume for the inner rubber 61.

[0025] The position P1 of the interface 6c on the outer peripheral surface of the cushion rubber 6 is preferably 3 to 10 mm apart axially outward from the outermost end 5E of the belt layer 5 along the outer peripheral surface of the cushion rubber 6 (the interface between the cushion rubber 6 and the base rubber 13b). A distance of 3 mm or more between them is advantageous in preventing failures caused by strain concentration at the end of the belt layer 5 or the interface 6c. Furthermore, a distance of 10 mm or less between them is advantageous in ensuring an appropriate volume of the outer rubber 62.

[0026] It is preferable that the position P1 of the interface 6c on the outer peripheral surface of the cushion rubber 6 is located on a straight line L3 that passes through the tread edge TE and extends in the tire radial direction, or is located axially outward of the straight line L3. With this configuration, the position P1 of the interface 6c is located at an appropriate distance from the end of the belt layer 5, which is convenient for preventing failures caused by strain concentration at the end of the belt layer 5 or the interface 6c.

[0027] In the present embodiment, an example has been shown in which the interface 6c extends linearly in a cross section taken along the tire meridian plane, but this is not limiting and the interface 6c may be gently curved. In this case, the inclination angle and other parameters of the interface 6c described above are determined based on a straight line connecting a position P1 on the outer circumferential surface of the cushion rubber 6 and a position P2 on the inner circumferential surface. Furthermore, it is preferable that such a curved interface 6c extends in an arc shape that is convex outward in the tire radial direction in a cross section taken along the tire meridian plane.

[0028] Unless otherwise specified, the shapes and dimensions described in this specification are based on a tire mounted on a standard rim, inflated to the standard internal pressure, and in a normal, unloaded state. A standard rim is a rim specified for each tire by the standard system, including the standard on which the tire is based, such as a "standard rim" in JATMA or a "measuring rim" in TRA or ETRTO. The standard internal pressure is the air pressure specified for each tire by the standard system, including the standard on which the tire is based, such as the "maximum air pressure" in JATMA, the maximum value listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" table in TRA, or the "INFLATION PRESSURE" in ETRTO.

[0029] As described above, the pneumatic tire T of this embodiment includes a pair of bead portions 1, a pair of sidewalls 2 extending radially outward from each of the pair of bead portions 1, a tread 3 connected to the radially outer ends of each of the pair of sidewalls 2, a carcass 4 provided between the pair of bead portions 1, a belt layer 5 laminated on the radially outer side of the carcass 4, and a cushion rubber 6 interposed between an end of the belt layer 5 and the carcass 4. The cushion rubber 6 includes an interface 6c extending axially inward and radially inward from a position P1 axially outward of the outermost end 5E of the belt layer 5, an inner rubber 61 located axially inward of the interface 6c, and an outer rubber 62 located axially outward of the interface 6c. The moduli at 100% elongation are highest in the order of the cap rubber 13a forming the outer surface of the tread 3, the inner rubber 61, and the outer rubber 62. This configuration appropriately distributes the force acting on the shoulders of the tread 3, promoting uniform ground pressure and suppressing uneven wear in the shoulders. It also reduces strain acting on the ends of the belt layer 5, suppressing breakdowns such as separation in the shoulders.

[0030] It is preferable that the difference between the modulus at 100% elongation of the cap rubber 13a and the modulus at 100% elongation of the outer rubber 62 be 1.5 MPa or more. This enhances the strain relaxation effect of the cushion rubber 6, keeps the strain energy density of the shoulder portion low, and improves the improvement effect.

[0031] In order to ensure that the modulus of the inner rubber 61 is appropriately large, it is preferable that the modulus of the inner rubber 61 at 100% elongation is larger than the modulus at 100% elongation of the base rubber 13b laminated on the tire radially inner side of the cap rubber 13a.

[0032] In order to ensure that the modulus of the outer rubber 62 is appropriately small, the modulus of the outer rubber 62 at 100% elongation is preferably smaller than the modulus of the sidewall rubber 12 forming the outer surface of the sidewall 2 at 100% elongation.

[0033] The interface 6c preferably extends at an angle θ1 of 80±5 degrees relative to the tire radial direction. This configuration makes it easy to ensure adhesive strength at the interface 6c against radial forces acting on the shoulder portion of the tire, and is also advantageous in ensuring an appropriate volume of the inner rubber 61.

[0034] When considering an imaginary straight line L2 connecting the outermost end 5E of the belt layer 5 and the position P1 of the interface 6c on the outer peripheral surface of the cushion rubber 6, it is preferable that the interface 6c extends at an angle θ2 of 30±10 degrees with respect to the imaginary straight line L2. This configuration makes it easy to ensure adhesive strength at the interface 6c against radial forces acting on the shoulder portion of the tire, and is also convenient for ensuring an appropriate volume of the inner rubber 61.

[0035] The pneumatic tire T exhibits the above-described effects and can suppress uneven wear and breakdowns in the shoulder portion, and is therefore particularly useful as a heavy-duty pneumatic tire used on heavy vehicles such as trucks, buses, industrial vehicles, construction vehicles, etc. However, without being limited thereto, the pneumatic tire of the present disclosure can be employed as various tires used on passenger cars, light trucks, etc.

[0036] The pneumatic tire of the present disclosure is not limited to the above-described embodiment, and various improvements and modifications are possible within the scope of the spirit thereof. [Explanation of symbols]

[0037] 1 Bead section 2 Sidewall 3 Tread 4. Carcass 5 Belt Layer 5E Outermost edge 6 Cushion rubber 6c interface 12 Sidewall rubber 13a Cap rubber 13b base rubber 61 Inner rubber 62 Outer rubber L2 Imaginary line

Claims

1. a pair of bead portions; a pair of sidewalls extending radially outward from each of the pair of bead portions; a tread connected to each of the pair of sidewalls at an outer end in the tire radial direction; a carcass provided between the pair of bead portions; a belt layer laminated on the outer side of the carcass in the tire radial direction; a cushion rubber interposed between the end of the belt layer and the carcass, the cushion rubber includes an interface extending from a position axially outward of an outermost end of the belt layer toward the axially inward and radially inward of the tire, an inner rubber positioned axially inward of the interface, and an outer rubber positioned axially outward of the interface, a cap rubber forming an outer surface of the tread has a modulus at 100% elongation that is highest in the order of the cap rubber, the inner rubber, and the outer rubber; The position of the interface on the outer peripheral surface of the cushion rubber is 3 to 10 mm axially outward from the outermost end of the belt layer along the outer peripheral surface of the cushion rubber, and is located on a straight line extending radially of the tire through the tread edge or axially outward of the straight line.

2. A pneumatic tire as described in claim 1, wherein the difference between the modulus at 100% elongation of the cap rubber and the modulus at 100% elongation of the outer rubber, determined as the tensile stress at 100% elongation in a tensile test at 25°C (using No. 3 dumbbells) in accordance with JIS K6251, is 1.5 MPa or more.

3. 3. The pneumatic tire according to claim 1, wherein the modulus at 100% elongation of the inner rubber is greater than the modulus at 100% elongation of a base rubber laminated on the inner side of the cap rubber in the tire radial direction.

4. 4. The pneumatic tire according to claim 1, wherein the modulus at 100% elongation of the outer rubber is smaller than the modulus at 100% elongation of a sidewall rubber forming an outer surface of the sidewall.

5. The pneumatic tire according to any one of claims 1 to 4, wherein the interface extends at an angle of 80±5 degrees relative to the tire radial direction.

6. The pneumatic tire according to any one of claims 1 to 5, wherein, when a virtual line connecting an outermost end of the belt layer and a position of the interface on the outer peripheral surface of the cushion rubber is considered, the interface extends at an angle of 30±10 degrees with respect to the virtual line.

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