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. A slit 21 crossing the protrusion 20 is formed in the protrusion 20. The protrusion 20 has a plurality of divided pieces 22 divided by the slit 21.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 bottom of the groove is arranged within the main groove, a slit is formed in the protrusion that crosses the protrusion, and the protrusion has multiple divided pieces separated by the slit. [Effects of the Invention]

[0008] As a result of extensive research into protrusions formed in the grooves of the tread portion to prevent stone entrapment, the inventor discovered that if the protrusion has a structure with multiple segments separated by slits, when a stone trapped in the groove comes into contact with the protrusion, each segment will collapse and return, improving stone removal performance against stone entrapment, which led to 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 a slit is formed in the protrusion, and the protrusion has multiple segments divided by the slits, so that when a stone caught in the main groove comes into contact with the protrusion, each segment moves in a downward and upward direction, 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 protrusion has two divided pieces separated by a slit, and these two divided pieces are preferably configured as symmetrical polyhedrons and have the same volume. By having the divided structure of the protrusion as described above, each divided piece can effectively collapse and return, thereby improving the effect of stone removal against trapped stones.

[0014] In the present invention, the slits are preferably arranged so that the straight line connecting both ends of the slit is parallel to the tire width direction. By having the above-described divided structure of the protrusion, the collapse and return of each divided piece can be effectively exhibited, thereby enhancing the effect of improving stone removal against stone entrapment.

[0015] 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]

[0016] [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] 10A and 10B show a modified example of the protrusion, in which FIG. 10A is a plan view and FIG. [Figure 10] 10A and 10B show a modified example of the protrusion, in which FIG. 10A is a plan view and FIG. [Figure 11] 10A and 10B show a modified example of the protrusion, in which FIG. 10A is a plan view and FIG. [Figure 12] FIG. 12 is a cross-sectional view taken along the line XII-XII in FIG. 4. DETAILED DESCRIPTION OF THE INVENTION

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] The above-described tire internal structure is a typical example of a pneumatic tire, but is not limited to this.

[0022] 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 is disposed in the main groove 11, protruding from the groove bottom. 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 is disposed in the lug groove 12, protruding from the groove bottom. 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 or 3 ), a polygon including a triangle or a rectangle, 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.

[0023] 4(a) and (b) to 11(a) and (b) show various protrusions. A slit 21 is formed in the protrusion 20, crossing the protrusion 20. Therefore, the protrusion 20 has a plurality of divided pieces 22 separated by the slits 21.

[0024] In the example of FIGS. 4(a) and 4(b), the protrusion 20 has a cylindrical shape, a linear slit 21 is formed across the protrusion 20, and the protrusion 20 is divided by the slit 21 into two divided pieces 22. In the example of FIGS. 5(a) and 5(b), the protrusion 20 has a cylindrical shape, a wavy slit 21 is formed across the protrusion 20, and the protrusion 20 is divided by the slit 21 into two divided pieces 22. In the example of FIGS. 6(a) and 6(b), the protrusion 20 has a square prism shape, a linear slit 21 is formed across the protrusion 20, and the protrusion 20 is divided by the slit 21 into two divided pieces 22. In the example of FIGS. 7(a) and 7(b), the protrusion 20 has a square prism shape, a bent slit 21 is formed across the protrusion 20, and the protrusion 20 is divided by the slit 21 into two divided pieces 22. In the example of FIGS. 8( a) and 8(b), the protrusion 20 has a rectangular prism shape, a linear slit 21 is formed diagonally across the protrusion 20, and the protrusion 20 is divided by the slit 21 into two segments 22. In the example of FIGS. 9(a) and 9(b), the protrusion 20 has a cylindrical shape, a cross-shaped slit 21 is formed across the protrusion 20, and the protrusion 20 is divided by the slit 21 into four segments 22. In the example of FIGS. 10(a) and 10(b), the protrusion 20 has a cylindrical shape, a linear slit 21 is formed across the protrusion 20 at a position off-center from the protrusion 20, and the protrusion 20 is divided by the slit 21 into two segments 22. In the example of FIGS. 11(a) and 11(b), the protrusion 20 has a cylindrical shape, an arc-shaped slit 21 is formed across the protrusion 20, and the protrusion 20 is divided by the slit 21 into two segments 22.

[0025] In the pneumatic tire described above, at least one protrusion 20 protruding from the groove bottom is disposed in the main groove 11, and a slit 21 is formed in the protrusion 20, and the protrusion 20 has a plurality of segments 22 separated by the slits 21. When a stone trapped in the main groove 11 comes into contact with the protrusion 20, each segment 22 collapses and returns, displacing the stone 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.

[0026] 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.

[0027] 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.

[0028] In the above pneumatic tire, as shown in Figure 12, it is preferable that the depth h of the slit 21 and the height H of the protrusion 20 satisfy the relationship 0.2 ≦ h / H ≦ 1.0. By having the depth h of the slit 21 within the above range, stone removal performance against stone entrapment can be sufficiently improved. If the depth h of the slit 21 is less than 0.2H, when a stone entrapped in the main groove 11 comes into contact with the protrusion 20, each divided piece 22 is less likely to collapse and return, reducing the effect of improving stone removal performance. In particular, it is preferable that the depth h of the slit 21 and the height H of the protrusion 20 satisfy the relationship 0.8 ≦ h / H ≦ 1.0.

[0029] In the pneumatic tire described above, the protrusion 20 has two segments 22 separated by a slit, and these two segments 22 are preferably configured as polyhedrons with symmetrical shapes and have the same volume. Examples of this configuration are shown in FIGS. 4(a), (b) to 8(a), (b). More specifically, in FIGS. 4(a), (b) to 8(a), (b), the pair of segments 22, 22 are configured as polyhedrons that are point-symmetric about the center point of the top surface of the protrusion 20. The protrusion 20 having the above-described divided structure effectively allows each segment 22 to collapse and return, thereby improving the effect of stone removal against stone entrapment. The volume of the segment 22 is the volume from the top surface of the protrusion 20 to the bottom position of the slit 21. The two segments 22 having the same volume means that the volume of one segment 22 is in the range of 90% to 110% of the volume of the other segment 22.

[0030] In the above-described pneumatic tire, as shown in Figures 2 and 3, the slits 21 are preferably arranged so that the straight line connecting both ends of the slits 21 is parallel to the tire width direction Tw. By having the above-described divided structure of the protrusions 20, the collapse and return of each divided piece 22 can be effectively achieved, thereby enhancing the effect of improving stone removal performance against stone entrapment. Note that, when the slits 21 are wavy (see Figure 5) or have a curved shape (see Figure 7), the slits 21 may be arranged so that a straight line L connecting both ends of the slits 21 is found on the groove width center line of the slits 21 and this straight line L is parallel to the tire width direction Tw. "The straight line connecting both ends of the slits 21 being parallel to the tire width direction Tw" means that the angle of this straight line with respect to the tire width direction Tw is 10° or less.

[0031] 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]

[0032] In a pneumatic tire having a tire size of 195 / 85R16 and having multiple main grooves extending in the tire circumferential direction and multiple lug grooves extending in the tire width direction in the tread portion, multiple protrusions were arranged in the main grooves so as to be aligned along the longitudinal direction of the main grooves, and tires of Conventional Example and Examples 1 to 10 were manufactured with the presence or absence of see-through portions, the shape of the protrusions, the presence or absence of slits in the protrusions, the ratio h / H of the slit depth h to the protrusion height H, the shape of the slits, the arrangement direction of the slits, and the presence or absence of protrusions in the lug grooves set as shown in Table 1. The structure of the protrusions in the lug grooves was the same as the structure of the convex portions in the main grooves. Regarding the arrangement direction of the slits, when the straight line connecting both ends of the slit is parallel to the tire circumferential direction, it is indicated as the "circumferential direction," and when the straight line connecting both ends of the slit is parallel to the tire width direction, it is indicated as the "width direction."

[0033] 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.

[0034] 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.

[0035] 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.

[0036] [Table 1]

[0037] 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.

[0038] The present disclosure includes the following inventions [1] to [7]. 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, This pneumatic tire is characterized in that at least one protrusion protruding from the groove bottom is arranged in the main groove, a slit is formed in the protrusion that crosses the protrusion, and the protrusion has multiple divided pieces separated by the slit. 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 protrusion has two divided pieces separated by the slit, and the two divided pieces are formed of polyhedrons having symmetrical shapes and have equal volumes. Invention [6] is a pneumatic tire according to any one of inventions [1] to [5], characterized in that the slits are arranged so that the straight line connecting both ends of the slits is parallel to the tire width direction. Invention [7] is a pneumatic tire according to any one of inventions [1] to [6], 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]

[0039] 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 22 Split piece 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 a groove bottom is arranged in the main groove, a slit is formed in the protrusion that crosses the protrusion, and the protrusion has a plurality of divided pieces separated by the slit.

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. 3. The pneumatic tire according to claim 1, wherein the protrusion has two divided pieces separated by the slit, and the two divided pieces are formed as polyhedrons having symmetrical shapes and have equal volumes.

6. 3. The pneumatic tire according to claim 1, wherein the slit is arranged so that a straight line connecting both ends of the slit is parallel to the tire width direction.

7. 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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