Pneumatic tire

Abstract

To provide a pneumatic tire that enables improvement in performance of removing a stone in stone-biting.SOLUTION: The pneumatic tire comprises a tread part 1 extending in a tire circumferential direction to form an annular shape, where at least one main groove 11 extending in the tire circumferential direction is formed in the tread part 1. At least one protrusion 20 protruding from a groove bottom is arranged in the main groove 11. The protrusion 20 has an inside region Ain positioned inside and an outside region Aout positioned outside, in a planar view. At least one slit 21 is formed in the outside region Aout but the slit 21 is not formed in the inside region Ain.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a pneumatic tire suitable for retreading, and more particularly to a pneumatic tire that enables improved stone removal performance against stone entrapment. [Background technology]

[0002] When the tread portion of a pneumatic tire wears, the tread rubber layer is replaced. For pneumatic tires that are reused through retreading, measures to prevent stone entrapment are important. When stone entrapment occurs in a groove formed in the tread portion, the stone trapped in the groove gradually moves toward the groove bottom and eventually reaches the groove bottom. This phenomenon is called stone drilling. Once the stone reaches the groove bottom, it can cause cracks to form in the groove bottom. Furthermore, if a crack at the groove bottom reaches the belt layer and damages the belt layer, it can reduce the durability of the pneumatic tire or make it impossible to reuse the pneumatic tire through retreading.

[0003] In order to prevent cracks at the groove bottom due to stone entrapment, protrusions that protrude from the groove bottom are provided in the groove (see, for example, Patent Documents 1 to 3). By providing protrusions in the groove, it is possible to prevent stones from reaching the groove bottom and also to have the effect of expelling stones from the groove.

[0004] However, in recent years, retreading has begun to be carried out on small-sized pneumatic tires such as those used on small trucks.However, since the groove width of small-sized pneumatic tires is also smaller, there are restrictions on the shape and placement of the protrusions formed in the grooves to prevent stone entrapment, and the current situation is that sufficient stone removal performance is not necessarily achieved. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-264480 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-43619 [Patent Document 3] Patent No. 7104573 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a pneumatic tire that can improve stone removal performance against stone entrapment. [Means for solving the problem]

[0007] In order to achieve the above object, a pneumatic tire of the present invention includes a tread portion extending in a tire circumferential direction to form an annular shape, and at least one main groove extending in the tire circumferential direction is formed in the tread portion, At least one protrusion protruding from the groove bottom is arranged within the main groove, and the protrusion has an inner region located on the inside and an outer region located on the outside when viewed in a plane, and at least one slit is formed in the outer region while no slit exists in the inner region. [Effects of the Invention]

[0008] As a result of extensive research into protrusions formed in the grooves of the tread portion to prevent stone trapping, the inventor discovered that if a structure is adopted in which slits are formed only in the outer region of the protrusion, a difference in rigidity occurs between the outer region and the inner region, improving stone removal performance against stone trapping, and thus arrived at the present invention.

[0009] That is, in the present invention, at least one protrusion protruding from the groove bottom is disposed in the main groove, and the protrusion has an inner region located on the inside in a plan view and an outer region located on the outside, and at least one slit is formed in the outer region while no slit is present in the inner region, which creates a rigidity difference between the outer region and the inner region and allows displacement of stones caught in the main groove, thereby improving stone removal performance against stone trapping. As a result, cracks in the groove bottom due to stone trapping can be effectively suppressed, and ultimately damage to the belt layer caused by cracks in the groove bottom can be prevented.

[0010] In the present invention, it is preferable that a plurality of protrusions are arranged in the main groove so as to be aligned along the longitudinal direction of the main groove, thereby effectively improving stone removal performance against trapped stones.

[0011] In the present invention, it is preferable that the protrusion is spaced from at least one sidewall of the main groove, and a see-through portion is formed between the protrusion and at least one sidewall of the main groove. By providing the see-through portion, it is possible to avoid a decrease in drainage performance.

[0012] In the present invention, it is preferable that the depth h of the slits satisfies the relationship 0.2≦h / H≦1.0 with respect to the height H of the protrusions. When the depth h of the slits is within the above range, stone removal performance against trapped stones can be sufficiently improved.

[0013] In the present invention, the slits are preferably arranged so as to close within the protrusions along imaginary lines having a shape similar to the outer contours of the protrusions. By arranging the slits in this manner, the rigidity difference in the protrusions can be optimized, and stone removal performance against trapped stones can be effectively improved.

[0014] In the present invention, the slits are preferably arranged within an angular range of 90° or more around the center point of the protrusion. By arranging the slits within this angular range, the protrusions have an appropriate resilience, which can effectively improve stone removal when stones get caught.

[0015] In the present invention, it is preferable that the slit is annular, and the area S of the portion inside the outer contour of the slit and the area A of the portion inside the inner contour of the slit satisfy the relationship 0.25≦A / S≦0.9. This optimizes the rigidity difference in the protrusion, and effectively improves stone removal performance against trapped stones.

[0016] In the present invention, when a plurality of lug grooves extending in the tire width direction are formed in the tread portion, it is preferable that the above-mentioned protrusions are disposed in the lug grooves in addition to the main grooves. By disposing the protrusions as defined above in the lug grooves, stone removal performance in the lug grooves against stone entrapment can be improved. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a meridian cross-sectional view showing a pneumatic tire according to an embodiment of the present invention. [Figure 2] 2 is a plan view showing a protrusion formed in a groove of the pneumatic tire of FIG. 1. FIG. [Figure 3] 1. FIG. 4 is a plan view showing a modified example of a protrusion formed in a groove of the pneumatic tire of FIG. [Figure 4] 1A and 1B show an example of a protrusion, in which FIG. 1A is a plan view and FIG. 1B is a perspective view. [Figure 5] 10A and 10B show a modified example of the protrusion, in which FIG. 10A is a plan view and FIG. [Figure 6] 10A and 10B show a modified example of the protrusion, in which FIG. 10A is a plan view and FIG. [Figure 7] 10A and 10B show a modified example of the protrusion, in which FIG. 10A is a plan view and FIG. [Figure 8] 10A and 10B show a modified example of the protrusion, in which FIG. 10A is a plan view and FIG. [Figure 9] 9 is a cross-sectional view taken along the line IX-IX in FIG. 4. [Figure 10] 10A to 10C show modified examples of the protrusion, each of which is a plan view. [Figure 11]10A to 10C show modified examples of the protrusion, each of which is a plan view. [Figure 12] 10A to 10C show modified examples of the protrusion, each of which is a plan view. DETAILED DESCRIPTION OF THE INVENTION

[0018] The configuration of the present invention will be described in detail below with reference to the accompanying drawings. Fig. 1 shows a pneumatic tire according to an embodiment of the present invention, Fig. 2 shows protrusions formed in the grooves of the pneumatic tire, and Fig. 3 shows a modified example of the protrusions.

[0019] As shown in FIG. 1, the pneumatic tire of this embodiment includes a tread portion 1 extending circumferentially in a ring shape, a pair of sidewall portions 2, 2 arranged on both sides of the tread portion 1, and a pair of bead portions 3, 3 arranged radially inward of the sidewall portions 2.

[0020] A carcass layer 4 is mounted between the pair of bead portions 3, 3. This carcass layer 4 includes a plurality of reinforcing cords extending in the tire radial direction, and is folded back from the inside to the outside of the tire around a bead core 5 disposed in each bead portion 3. The reinforcing cords of the carcass layer 4 are preferably organic fiber cords such as nylon or polyester cords, or steel cords. A bead filler 6 made of a rubber composition and having a triangular cross section is disposed on the outer periphery of the bead core 5.

[0021] On the other hand, multiple belt layers 7 are embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1. These belt layers 7 include multiple reinforcing cords that are inclined with respect to the tire circumferential direction, and are arranged so that the reinforcing cords cross each other between the layers. In the belt layers 7, the inclination angle of the reinforcing cords with respect to the tire circumferential direction is set to a range of 10° to 40°, for example. Steel cords are preferably used as the reinforcing cords of the belt layers 7. At least one belt cover layer 8 is arranged on the outer peripheral side of the belt layer 7, with the aim of improving high-speed durability, and the reinforcing cords are arranged at an angle of, for example, 5° or less with respect to the tire circumferential direction. As the reinforcing cords of the belt cover layer 8, organic fiber cords such as nylon or aramid cords, or steel cords are preferably used.

[0022] The above-described tire internal structure is a typical example of a pneumatic tire, but is not limited to this.

[0023] In the pneumatic tire, as shown in FIGS. 1 and 2 , a plurality of main grooves 11 extending in the tire circumferential direction and a plurality of lug grooves 12 extending in the tire width direction are formed in the tread portion 1. At least one protrusion 20 protruding from the groove bottom is disposed in the main groove 11. More specifically, the plurality of protrusions 20 are disposed in the main groove 11 so as to be aligned along the longitudinal direction of the main groove 11. Similarly, at least one protrusion 20 protruding from the groove bottom is disposed in the lug groove 12. More specifically, the plurality of protrusions 20 are disposed in the main groove 12 so as to be aligned along the longitudinal direction of the lug groove 12. The shape of the protrusion 20 in a plan view is not particularly limited, and may be a circle ( FIG. 2 ), a polygon including a triangle or a rectangle ( FIG. 3 ), or an ellipse. The protrusion 20 may also have a cone shape such as a truncated cone. It is preferable that the protrusion 20 is lower than the tread surface of the tread portion 1.

[0024] 4(a) and (b) to 8(a) and (b) show various protrusions. The protrusion 20 has an inner region Ain located on the inside in a plan view and an outer region Aout located on the outside. In each figure, the inner region Ain and the outer region Aout are separated by an imaginary boundary line X. The inner region Ain is a region defined in the center of the protrusion 20 in a plan view, and has an area of ​​at least 25% of the area within the outer contour of the protrusion 20. At least one slit 21 is formed in the outer region Aout, while no slit 21 is present in the inner region Ain.

[0025] In the example of FIGS. 4(a) and 4(b), the protrusion 20 has a cylindrical shape, and a single slit 21 forming a ring shape is formed in the outer region Aout. In the example of FIGS. 5(a) and 5(b), the protrusion 20 has a cylindrical shape, and a plurality of slits 21 are formed in the outer region Aout, intermittently arranged in a ring shape along the circumferential direction. In the example of FIGS. 6(a) and 6(b), the protrusion 20 has a cylindrical shape, and a slit 21 having a ring-shaped portion and a radial portion is formed in the outer region Aout. In the example of FIGS. 7(a) and 7(b), the protrusion 20 has a cylindrical shape, and a plurality of slits 21 extending radially are formed in the outer region Aout. In the example of FIGS. 8(a) and 8(b), the protrusion 20 has a square pillar shape, and a single slit 21 forming a square ring shape is formed in the outer region Aout.

[0026] In the pneumatic tire described above, at least one protrusion 20 protruding from the groove bottom is disposed in the main groove 11. The protrusion 20 has an inner region Ain located on the inside and an outer region Aout located on the outside in a plan view. At least one slit 21 is formed in the outer region Aout, while no slit 21 is present in the inner region Ain. This creates a difference in rigidity between the outer region Aout and the inner region Ain, and the protrusion 20 elastically deforms in the outer region Aout, allowing for the displacement of stones trapped in the main groove 11, thereby improving stone removal performance against stone trapping. As a result, cracks in the groove bottom due to stone trapping are effectively suppressed, and damage to the belt layer 7 caused by cracks in the groove bottom can be prevented. This is significant for pneumatic tires that are subject to retreading.

[0027] In the pneumatic tire, it is preferable that a plurality of protrusions 20 are arranged in the main groove 11 so as to be aligned along the longitudinal direction of the main groove 11. This effectively improves stone removal performance against stone entrapment. For example, it is preferable that the number of protrusions 20 provided per 5 cm of groove length be 3 to 15.

[0028] 2 and 3, in the pneumatic tire, the protrusions 20 are preferably spaced apart from at least one sidewall (preferably both sidewalls) of the main groove 11, and a see-through portion 25 is formed between the protrusions 20 and the at least one sidewall (preferably both sidewalls). By providing the see-through portion 25, even when the protrusions 20 are provided in the main groove 11, a decrease in drainage performance can be avoided.

[0029] In the above pneumatic tire, as shown in Figure 9, it is preferable that the depth h of the slits 21 and the height H of the protrusions 20 satisfy the relationship 0.2 ≤ h / H ≤ 1.0. When the depth h of the slits 21 is within the above range, stone removal performance against trapped stones can be sufficiently improved. If the depth h of the slits 21 is less than 0.2H, the difference in rigidity between the outer region Aout and the inner region Ain becomes small, and the effect of improving stone removal performance decreases. In particular, it is preferable that the depth h of the slits 21 and the height H of the protrusions 20 satisfy the relationship 0.8 ≤ h / H ≤ 1.0.

[0030] In the above pneumatic tire, as shown in Figures 10(a) to 10(c), the slits 21 are preferably arranged so as to close within the protrusions 20 along imaginary lines Y having a shape similar to the outer contour of the protrusions 20. For example, if the outer contour of the protrusions 20 is circular, the imaginary line Y is also circular. By arranging the slits 21 in the above manner, the rigidity difference in the protrusions 20 can be optimized, and the stone removal performance against trapped stones can be effectively improved. The greater the total length of the slits 21 on the imaginary line Y, the greater the rigidity difference between the outer region Aout and the inner region Ain of the protrusions 20.

[0031] In the above pneumatic tire, as shown in FIGS. 11(a) to 11(c) and 12(a) to 12(c), the slits 21 are preferably arranged in an angular range of 90° or more around the center point O of the protrusion 20. In other words, the arrangement angle θ of the slits 21 around the center point O of the protrusion 20 is preferably 90° or more. When the slits 21 are arranged intermittently, the arrangement angle θ is the sum of the angles of all the slits 21. By arranging the slits 21 in the above angular range, the protrusion 20 is endowed with appropriate resilience, and stone removal performance against trapped stones can be effectively improved. In particular, it is desirable that the slits 21 be arranged in an angular range of 180° or more around the center point O of the protrusion 20.

[0032] In the above-described pneumatic tire, when the slit 21 is annular (see FIG. 4 ), it is preferable that the area S of the portion inside the outer contour line of the slit 21 (i.e., the inner edge of the portion of the protrusion 20 defined outside the slit 21) and the area A of the portion inside the inner contour line of the slit 21 (i.e., the outer edge of the portion of the protrusion 20 defined inside the slit 21) satisfy the relationship 0.25≦A / S≦0.9. This optimizes the rigidity difference in the protrusion 20, effectively improving stone removal performance against stone entrapment. If the area A is too small relative to the area S, the rigidity of the inner region Ain becomes insufficient. The groove width of the slit 21 is 0.3 mm or more, preferably 0.5 mm to 2.0 mm. If the groove width of the slit 21 is too small, the forming blade that forms the slit 21 during vulcanization becomes thin, making the forming blade more susceptible to damage.

[0033] In the above pneumatic tire, when a plurality of lug grooves 12 extending in the tire width direction are formed in the tread portion 1, it is preferable that the protrusions 20 with slits 21 are arranged in the lug grooves 12 as well as in the main grooves 11. By arranging the protrusions 20 with slits 21 in the lug grooves 12, it is possible to improve the stone removal performance of the lug grooves 12 in response to stone entrapment. When arranging the protrusions 20 with slits 21 in the lug grooves 12, the protrusions 20 can have the same structure as in the main grooves 11. However, arranging the protrusions 20 with slits 21 in the lug grooves 12 is optional. [Example]

[0034] A pneumatic tire with a tire size of 195 / 85R16 and a tread portion formed with multiple main grooves extending in the tire circumferential direction and multiple lug grooves extending in the tire width direction was fabricated. Multiple protrusions were arranged in the main grooves in a line along the longitudinal direction of the main grooves. Tires for Conventional Example and Examples 1 to 10 were fabricated with the following settings as shown in Table 1: presence or absence of see-through portions, protrusion shape, presence or absence of slits in the protrusions, ratio h / H of slit depth h to protrusion height H, slit shape, slit arrangement angle θ, ratio A / S of area S of the portion inside the outer contour line of the slit to area A of the portion inside the inner contour line of the slit, and presence or absence of protrusions in the lug grooves. When the slits were shaped radially, the radial slits were arranged at eight equally spaced locations around the protrusions. The structure of the protrusions in the lug grooves was the same as the structure of the convex portions in the main grooves.

[0035] These test tires were evaluated for wet performance and stone-trapping prevention performance by the following test methods, and the results are shown in Table 1.

[0036] Wet Performance: Each test tire was mounted on a 16x5 1 / 2J rim wheel and fitted to a test vehicle (2B light truck), the air pressure was set to 600kPa, and the braking distance from braking to a stop on a wet road from a speed of 40km / h was measured. The evaluation results were expressed as an index using the reciprocal of the measured value, with the conventional example being set at 100. The higher the index value, the better the wet performance.

[0037] Stone-trapping resistance: Each test tire was mounted on a 16x5 1 / 2J rim wheel and mounted on a test vehicle (2B light truck), the air pressure was set to 600kPa, and the vehicle was driven off-road for 10 hours and then on-road for 2 hours. After driving, the number of stones remaining in the grooves was counted. The evaluation results were expressed as an index using the reciprocal of the measurement value, with the conventional example being set at 100. The higher the index value, the better the stone-trapping prevention performance.

[0038] [Table 1]

[0039] As can be seen from Table 1, in comparison with the conventional tire, the tires of Examples 1 to 10 had good stone removal performance against trapped stones while adequately maintaining wet performance, and were excellent in stone trap prevention performance.

[0040] The present disclosure encompasses the following inventions [1] to [8]. Invention [1] is a pneumatic tire having a tread portion extending in a tire circumferential direction and forming an annular shape, and at least one main groove extending in the tire circumferential direction is formed in the tread portion, The pneumatic tire is characterized in that at least one protrusion protruding from the groove bottom is arranged in the main groove, the protrusion having an inner region located on the inside and an outer region located on the outside when viewed on a plane, and at least one slit is formed in the outer region while no slit exists in the inner region. Invention [2] is the pneumatic tire according to invention [1], characterized in that a plurality of the protrusions are arranged in the main groove so as to be aligned along the longitudinal direction of the main groove. Invention [3] is a pneumatic tire according to invention [1] or [2], characterized in that the protrusion is spaced from at least one side wall of the main groove, and a see-through portion is formed between the at least one side wall and the protrusion. Invention [4] is a pneumatic tire according to any one of inventions [1] to [3], characterized in that the depth h of the slit and the height H of the protrusion satisfy the relationship 0.2≦h / H≦1.0. Invention [5] is a pneumatic tire according to any one of inventions [1] to [4], characterized in that the slits are arranged so as to close within the protrusions along imaginary lines having a shape similar to the outer contours of the protrusions. Invention [6] is the pneumatic tire according to invention [5], characterized in that the slits are arranged within an angular range of 90° or more around the center point of the protrusion. Invention [7] is the pneumatic tire according to invention [5], characterized in that the slit is annular, and the area S of the portion inside the outer contour line of the slit and the area A of the portion inside the inner contour line of the slit satisfy the relationship 0.25≦A / S≦0.9. Invention [8] is a pneumatic tire according to any one of inventions [1] to [7], characterized in that a plurality of lug grooves extending in the tire width direction are formed in the tread portion, and the protrusions are arranged in the lug grooves in addition to the main grooves. [Explanation of symbols]

[0041] 1 Tread section 2 Sidewall 3 Bead section 4 carcass layers 5 bead core 6 Bead filler 7 Belt Layer 11 Main groove 12 Lug groove 20 protrusion 21 Slit 25 See-through part

Claims

1. A pneumatic tire having a tread portion extending in a tire circumferential direction and forming an annular shape, and at least one main groove extending in the tire circumferential direction formed in the tread portion, A pneumatic tire characterized in that at least one protrusion protruding from the groove bottom is arranged in the main groove, the protrusion having an inner region located on the inside and an outer region located on the outside in a plan view, at least one slit is formed in the outer region, while no slit exists in the inner region.

2. The pneumatic tire according to claim 1, wherein a plurality of the protrusions are arranged in the main groove so as to be aligned along the longitudinal direction of the main groove.

3. The pneumatic tire according to claim 1 or 2, wherein the protrusion is spaced from at least one sidewall of the main groove, and a see-through portion is formed between the at least one sidewall and the protrusion.

4. 3. The pneumatic tire according to claim 1, wherein the depth h of the slit and the height H of the protrusion satisfy the relationship 0.2≦h / H≦1.

0.

5. The pneumatic tire according to claim 1 or 2, wherein the slit is disposed so as to close within the protrusion along an imaginary line having a shape similar to an outer contour of the protrusion.

6. 6. The pneumatic tire according to claim 5, wherein the slits are provided within an angular range of 90 degrees or more around the center point of the protrusion.

7. 6. The pneumatic tire according to claim 5, wherein the slit is annular, and an area S of a portion of the slit that is inside an outer contour line and an area A of a portion of the slit that is inside an inner contour line satisfy the relationship 0.25≦A / S≦0.

9.

8. 3. The pneumatic tire according to claim 1, wherein a plurality of lug grooves extending in the tire width direction are formed in the tread portion, and the protrusions are arranged in the lug grooves in addition to the main grooves.

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