tire

Abstract

To provide a tire that can be reduced in vehicle exterior noise and improved in performance in removing soil from a shoulder lug groove.SOLUTION: In a tire, a main groove 10 extending in a tire circumferential direction and a plurality of shoulder lug grooves 25 extending in a tire width direction are formed in a tread part, where one end of each shoulder lug groove 25 communicates with the main groove 10 and the other end thereof is positioned outside in the tire width direction with respect to a grounding end E of the tread part. Each shoulder lug groove 25 has a bottom-up part 51 at a site adjacent to the main groove 10 and also has a slope part 52 in which a groove depth of the shoulder lug groove 25 gradually increases from the bottom-up part 51 toward outside in the tire width direction. Groove depths Da and Db of the shoulder lug groove 25 at a start point A and an end point B of the slope part 52 satisfy a relational expression of 1.5≤Db / Da≤2.0, and a length Ls in the tire width direction of the slope part 52 with respect to a distance L in the tire width direction from the main groove 10 to the grounding end E satisfies a relational expression of 0.5≤Ls / L≤0.8.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a tire having a plurality of shoulder lug grooves extending in the tire width direction in the tread portion, and more specifically, to a tire that enables reduction of external noise and improvement of soil discharge performance from the shoulder lug grooves. [Background technology]

[0002] In recent years, regulations on external noise emitted from vehicles have been strengthened. Some of this external noise is also generated when tires roll on the road surface. In particular, tires for sports utility vehicles (SUVs) and the like tend to have a block-based tread pattern including multiple main grooves extending in the tire circumferential direction and multiple lug grooves extending in the tire width direction in the tread portion, which tends to increase the external noise.

[0003] In addition, tires mounted on sport utility vehicles and the like are required to have excellent off-road performance, but have the drawback that the off-road performance is reduced when soil gets stuck in the lug grooves during off-road driving. Therefore, there is a demand for improving soil discharge from the lug grooves.

[0004] It has been proposed to provide projections or bottom-raised portions in the shoulder lug grooves of tires (see, for example, Patent Documents 1 to 3). However, these projections and bottom-raised portions do not improve soil discharge from the shoulder lug grooves. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2007-1484 A [Patent Document 2] JP 2016-37277 A [Patent Document 3] JP 2016-55816 A Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a tire which enables reduction in external noise and improvement in soil discharge from shoulder lug grooves. [Means for solving the problem]

[0007] In order to achieve the above object, a tire of the present invention has a tread portion extending in a circumferential direction of the tire to form an annular shape, and the tread portion is formed with a main groove extending in the tire circumferential direction and a plurality of shoulder lug grooves extending in the tire width direction, and each shoulder lug groove has one end connected to the main groove and the other end located outward in the tire width direction from a ground contact edge of the tread portion, Each shoulder lug groove has a bottom-raised portion adjacent to the main groove, and a slope portion in which the groove depth of the shoulder lug groove gradually increases from the bottom-raised portion toward the outside in the tire width direction, the groove depths Da, Db of the shoulder lug groove at a start point A and an end point B of the slope portion satisfy the relationship of 1.5≦Db / Da≦2.0, and the length Ls of the slope portion in the tire width direction with respect to the distance L in the tire width direction from the main groove to the ground contact edge satisfies the relationship of 0.5≦Ls / L≦0.8. Effect of the Invention

[0008] In the present invention, the shoulder lug grooves that communicate with the main grooves have bottom-raised portions formed at their adjacent portions, which suppress the air column resonance sound generated in the main grooves from propagating through the shoulder lug grooves to the outside of the tire, thereby reducing noise outside the vehicle. In addition, each shoulder lug groove has a slope portion in which the groove depth of the shoulder lug groove gradually increases from the bottom-raised portion toward the outside in the tire width direction, so that soil or mud that has entered the shoulder lug grooves moves toward the outside in the tire width direction when compressed, making it easier to discharge from the shoulder lug grooves. This reduces noise outside the vehicle and improves soil discharge from the shoulder lug grooves.

[0009] In the present invention, it is preferable that the distance La in the tire width direction from the main groove to the start point A of the slope portion satisfies the relationship of 0.05≦La / L≦0.2 with respect to the distance L in the tire width direction from the main groove to the ground contact edge, and the distance Lb in the tire width direction from the main groove to the end point B of the slope portion satisfies the relationship of 0.55≦Lb / L≦1.0 with respect to the distance L in the tire width direction from the main groove to the ground contact edge. By specifying the positions of the start point A and end point B of the slope portion in this way and sufficiently securing the raised bottom portion adjacent to the main groove, it is possible to enhance the effect of reducing external noise and the effect of improving soil dischargeability.

[0010] In the present invention, it is preferable that the groove width of each shoulder lug groove expands toward the outside in the tire width direction in at least a portion of the longitudinal direction of the shoulder lug groove, the length Lx in the tire width direction from the main groove to the widening start position of each shoulder lug groove satisfies the relationship 0≦Lx / L≦0.2 with respect to the distance L in the tire width direction from the main groove to the ground edge, and the minimum width Wmin and maximum width Wmax of each shoulder lug groove satisfy the relationship 1.5≦Wmax / Wmin≦2.0. By expanding the groove width of each shoulder lug groove toward the outside in the tire width direction in this manner, soil discharge from the shoulder lug groove can be effectively improved.

[0011] It is preferable that the groove depth change rate X calculated from Db / Da and the groove width change rate Y calculated from Wmax / Wmin satisfy the relationship 1.0≦X / Y≦1.2, which can effectively improve soil discharge from the shoulder lug grooves.

[0012] In the present invention, it is preferable that the groove wall angle of the shoulder lug groove with respect to the normal direction of the tread surface of the tread portion gradually decreases toward the outer side in the tire width direction in the region corresponding to the slope portion, and the groove wall angle of the shoulder lug groove is in the range of 0° to 10°, thereby effectively improving soil discharge from the shoulder lug groove.

[0013] In the present invention, it is preferable that a circumferential auxiliary groove is formed in the tread portion, extending in the tire circumferential direction and intersecting with the shoulder lug groove, and the circumferential auxiliary groove is located between the start point A and the end point B of the slope portion. This makes it possible to effectively improve soil discharge from the shoulder lug groove.

[0014] The groove width of the circumferential auxiliary groove is preferably in the range of 30% to 60% of the groove width of the shoulder lug groove at the opening position to the main groove, which can effectively improve the soil discharge from the shoulder lug groove without reducing the effect of improving external noise.

[0015] The tire of the present invention is preferably a pneumatic tire, but may be a non-pneumatic tire. In the case of a pneumatic tire, the inside of the tire can be filled with air, an inert gas such as nitrogen, or other gases.

[0016] In the present invention, the ground contact edge of the tread portion is the outermost end in the axial direction of the tire ground contact area of ​​the tread portion formed when the tire is mounted on a standard rim, inflated to the standard internal pressure (in the case of a pneumatic tire), placed vertically on a flat surface, and subjected to a standard load. The "standard rim" is a rim that is determined for each tire by the standard system including the standard on which the tire is based, for example, the standard rim for JATMA, the "Design Rim" for TRA, or the "Measuring Rim" for ETRTO. The "standard internal pressure" is the air pressure that corresponds to the maximum load capacity determined for each tire by each standard in the standard system including the standard on which the tire is based. The "standard load" is a load that corresponds to 88% of the maximum load capacity determined for each tire by each standard in the standard system including the standard on which the tire is based. [Brief description 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. [Diagram 2] FIG. 2 is a development view showing a tread pattern of the pneumatic tire of FIG. [Diagram 3] FIG. 4 is a cross-sectional view showing a shoulder land portion in which shoulder lug grooves are formed. [Figure 4] FIG. 4 is a plan view showing a shoulder land portion in which shoulder lug grooves are formed. [Diagram 5] 5 is a cross-sectional view taken along the line VV in FIG. 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings, in which: Figures 1 to 5 show a pneumatic tire according to an embodiment of the present invention.

[0019] As shown in FIG. 1, the pneumatic tire of this embodiment includes a tread portion 1 extending circumferentially around the tire to form an annular shape, a pair of sidewall portions 2, 2 arranged on either side 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 fitted between a 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 arranged in each bead portion 3. A bead filler 6 made of a rubber composition having a triangular cross section is arranged on the outer periphery of the bead core 5.

[0021] On the other hand, a plurality of 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 a plurality of reinforcing cords 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, for example, a range of 10° to 40°. As the reinforcing cords of the belt layers 7, steel cords are preferably used. On the outer peripheral side of the belt layers 7, at least one belt cover layer 8 is arranged in which reinforcing cords are arranged at an angle of, for example, 5° or less with respect to the tire circumferential direction for the purpose of improving high-speed durability. As the reinforcing cords of the belt cover layer 8, organic fiber cords such as nylon and aramid are preferably used.

[0022] It should be noted that the above-described tire internal structure shows a typical example of a pneumatic tire, but is not limited thereto.

[0023] As shown in FIG. 2, four main grooves 10 extending in the tire circumferential direction are formed in the tread portion 1. The main grooves 10 have a groove width in the range of 8 mm to 20 mm, a groove depth in the range of 6 mm to 10 mm, and are grooves equipped with wear indicators. These main grooves 10 define five rows of land portions 11 to 15 in the tread portion 1. More specifically, the shoulder land portion 11 is disposed in a shoulder region on one side in the width direction of the tread portion 1, the shoulder land portion 15 is disposed in a shoulder region on the other side in the width direction of the tread portion 1, the center land portion 13 is disposed on the tire equator, the intermediate land portion 12 is disposed between the center land portion 13 and the shoulder land portion 11, and the intermediate land portion 14 is disposed between the center land portion 13 and the shoulder land portion 15.

[0024] In the shoulder land portion 11, a plurality of shoulder lug grooves 21 extending in the tire width direction, a plurality of sipes 31 extending in the tire width direction, and a circumferential auxiliary groove 41 extending in the tire circumferential direction and intersecting with the shoulder lug grooves 21 are formed. The shoulder lug groove 21 is configured such that one end on the inner side in the tire width direction terminates within the shoulder land portion 11 without communicating with the main groove 10, while the other end is located outside in the tire width direction from the ground contact edge E of the tread portion 1. The circumferential auxiliary groove 41 is a groove having a groove width in the range of 1 mm to 3 mm and a groove depth of 1 mm to 5 mm.

[0025] A plurality of lug grooves 22 extending in the tire width direction and a plurality of sipes 32 extending in the tire width direction are formed in the intermediate land portion 12. These lug grooves 22 and sipes 32 cross the intermediate land portion 12 and are bent so as to be convex toward one side in the tire circumferential direction.

[0026] A plurality of lug grooves 23 extending in the tire width direction and a plurality of sipes 33 extending in the tire width direction are formed in the center land portion 13. The lug grooves 23 have closed ends that terminate within the center land portion 13 and open ends that open into the main grooves 10, and the open ends are alternately arranged on both sides of the center land portion 13 along the tire circumferential direction.

[0027] A plurality of lug grooves 24 extending in the tire width direction and a plurality of sipes 34 extending in the tire width direction are formed in the intermediate land portion 14. The lug grooves 24 have a closed end that terminates within the intermediate land portion 14 and an open end that opens into the main groove 10, and the open end is disposed on the outer side of the intermediate land portion 14 in the tire width direction.

[0028] The shoulder land portion 15 is formed with a plurality of shoulder lug grooves 25 extending in the tire width direction, a plurality of sipes 35 extending in the tire width direction, and a circumferential auxiliary groove 45 extending in the tire circumferential direction and intersecting with the shoulder lug grooves 25. The shoulder lug groove 25 is configured such that one end on the inner side in the tire width direction communicates with the main groove 10, while the other end is located outside in the tire width direction with respect to the ground contact edge E of the tread portion 1. The circumferential auxiliary groove 45 has a groove width in the range of 1 mm to 3 mm and a groove depth of 1 mm to 5 mm.

[0029] In the above pneumatic tire, as shown in Fig. 3 and Fig. 4, each shoulder lug groove 25 has a bottom-raised portion 51 adjacent to the main groove 10, and has a slope portion 52 in which the groove depth of the shoulder lug groove 25 gradually increases from the bottom-raised portion 51 toward the outside in the tire width direction. The groove depth of each shoulder lug groove 25 is minimum at the bottom-raised portion 51 and maximum at the ground contact end. The groove depth of each shoulder lug groove 25 is constant on the bottom-raised portion 51. The groove depths Da, Db of the shoulder lug groove 25 at the start point A and end point B of the slope portion 52 satisfy the relationship of 1.5 ≦ Db / Da ≦ 2.0, and the length Ls of the slope portion 52 in the tire width direction is set to satisfy the relationship of 0.5 ≦ Ls / L ≦ 0.8 with respect to the distance L in the tire width direction from the main groove 10 to the ground contact end E. When the slope portion 52 is smoothly connected to the raised bottom portions 51 and the groove bottoms of the shoulder lug grooves 25 located on both sides thereof, the start point A and the end point B are the intersections of an extension of the slope portion 52 and an extension of the raised bottom portion 51 and the groove bottoms of the shoulder lug grooves 25. When the intersections of a straight line passing through the start point A and the end point B of the slope portion 52, perpendicular to the ground surface of the tread portion 1, and the ground surface are respectively designated as points A' and B', the groove depths Da and Db of the shoulder lug grooves 25 are the distances between the start point A and point A' and the distances between the end point B and point B', respectively.

[0030] In the above-described pneumatic tire, the bottom-raised portion 51 is formed at a portion of the shoulder lug groove 25 that communicates with the main groove 10 and that is adjacent to the main groove 10, so that the air column resonance sound generated in the main groove 10 is prevented from propagating to the outside of the tire through the shoulder lug groove 25, thereby reducing noise outside the vehicle. Also, each shoulder lug groove 25 is formed with a slope portion 52 in which the groove depth of the shoulder lug groove 25 gradually increases from the bottom-raised portion 51 toward the outside in the tire width direction, so that soil or mud that has entered the shoulder lug groove 25 moves to the outside in the tire width direction when compressed, and is easily discharged from the shoulder lug groove 25. This reduces noise outside the vehicle and improves soil discharge from the shoulder lug groove 25.

[0031] If the ratio Db / Da of the groove depths Da, Db of the shoulder lug grooves 25 is less than 1.5, the effect of reducing external noise and the effect of improving soil discharge will be insufficient, and conversely, if it is greater than 2.0, there is a risk of impairing the traction performance and drainage performance based on the shoulder lug grooves 25. In addition, if the ratio Ls / L of the length Ls of the slope portion 52 in the tire width direction is outside the above range, the effect of improving soil discharge will be insufficient.

[0032] The slope portion 52 is preferably a flat surface, but may be a curved surface. The slope portion 52 may have slight undulations or irregularities along the longitudinal direction of the shoulder lug groove 25, but excessive undulations or irregularities may reduce the effect of improving soil discharge. Therefore, the height of the undulations or irregularities in the slope portion 52 is preferably 0.5 mm or less. A protrusion may be provided in the shoulder lug groove 25 as long as it is located outside the slope portion 52 in the tire width direction.

[0033] 4, it is preferable that the distance La in the tire width direction from the main groove 10 to the start point A of the slope portion 52 satisfies the relationship of 0.05≦La / L≦0.2 with respect to the distance L in the tire width direction from the main groove 10 to the ground contact end E, and that the distance Lb in the tire width direction from the main groove 10 to the end point B of the slope portion 52 satisfies the relationship of 0.55≦Lb / L≦1.0 with respect to the distance L in the tire width direction from the main groove 10 to the ground contact end E. By specifying the positions of the start point A and end point B of the slope portion 52 in this way and sufficiently securing the raised bottom portion 51 adjacent to the main groove 10, it is possible to enhance the effect of reducing external noise and the effect of improving soil dischargeability.

[0034] Here, if the ratio La / L, which is the distance La in the tire width direction from the main groove 10 to the start point A of the slope section 52, is smaller than 0.05, the effect of reducing external noise is reduced, and conversely, if it is larger than 0.2, the effect of improving soil dischargeability is reduced. On the other hand, if the ratio Lb / L, which is the distance Lb in the tire width direction from the main groove 10 to the end point B of the slope section 52, is outside the above range, the effect of improving soil dischargeability is reduced. For example, a preferable combination is La / L=0.1 and Lb / L=0.7.

[0035] 4, it is preferable that the groove width of each shoulder lug groove 25 expands toward the outside in the tire width direction in at least a portion of the longitudinal direction of the shoulder lug groove 25, the length Lx in the tire width direction from the main groove 10 to the widening start position of each shoulder lug groove 25 satisfies the relationship 0≦Lx / L≦0.2 with respect to the distance L in the tire width direction from the main groove 10 to the ground edge E, and the minimum width Wmin and maximum width Wmax of each shoulder lug groove 25 satisfy the relationship 1.5≦Wmax / Wmin≦2.0. By expanding the groove width of each shoulder lug groove 25 toward the outside in the tire width direction in this manner, soil discharge from the shoulder lug groove 25 can be effectively improved.

[0036] Here, if the ratio Lx / L of the length Lx in the tire width direction from the main groove 10 to the width start position of each shoulder lug groove 25 is greater than 0.2, the improvement effect on the soil discharge property will decrease. Also, if the ratio Wmax / Wmin of the minimum width Wmin to the maximum width Wmax of each shoulder lug groove 25 is less than 1.5, the improvement effect on the soil discharge property will decrease. Conversely, if it is greater than 2.0, the change in groove width is too large, which may cause a decrease in the drainage performance based on the shoulder lug groove 25 and a decrease in the rigidity of the shoulder land portion 15, etc.

[0037] In the above pneumatic tire, it is preferable that the groove depth change rate X calculated from Db / Da and the groove width change rate Y calculated from Wmax / Wmin satisfy the relationship of 1.0 ≦ X / Y ≦ 1.2. Thereby, the soil discharge property from the shoulder lug groove 25 can be effectively improved. Here, if the ratio X / Y of the groove depth change rate X to the groove width change rate Y is out of the above range, the improvement effect on the soil discharge property will decrease. In particular, by setting 1.0 < X / Y ≦ 1.2, the improvement effect on the soil discharge property can be enhanced.

[0038] In the above pneumatic tire, as shown in FIG. 5, the groove wall angle θ of the shoulder lug groove 25 with respect to the normal direction of the tread surface of the tread portion 1 gradually decreases toward the outside in the tire width direction in the region corresponding to the slope portion 52 (that is, the region between the start point A and the end point B), and it is preferable that the groove wall angle θ of the shoulder lug groove 25 is in the range of 0° to 10°. Thereby, the soil discharge property from the shoulder lug groove 25 can be effectively improved. That is, when the groove wall angle θ of the shoulder lug groove 25 gradually decreases toward the outside in the tire width direction, the cross-sectional area of the shoulder lug groove 25 gradually increases toward the outside in the tire width direction, so the soil discharge property is improved. For example, the groove wall angle θ of the shoulder lug groove 25 can be set to 5° at the position of the start point A of the slope portion 52 and 0° at the position of the end point B of the slope portion 52.

[0039] In the above pneumatic tire, a circumferential auxiliary groove 45 is formed in the tread portion 1, extending in the tire circumferential direction and intersecting with the shoulder lug grooves 25, and the circumferential auxiliary groove 45 is preferably located between the start point A and the end point B of the slope portion 52. This effectively improves soil discharge from the shoulder lug grooves 25. That is, soil and mud stuck in the shoulder lug grooves 25 move along the slope portion 52, so the presence of the circumferential auxiliary groove 45 between the start point A and the end point B of the slope portion 52 makes it easier for the soil and mud to be discharged. In particular, it is preferable that the circumferential auxiliary groove 45 is located closer to the end point B of the slope portion 52 than the start point A, thereby improving soil discharge.

[0040] The groove width of the circumferential auxiliary groove 45 is preferably in the range of 30% to 60% of the groove width of the shoulder lug groove 25 at the opening position to the main groove 10. This makes it possible to effectively improve soil discharge from the shoulder lug groove 25 without reducing the effect of improving external noise. If the groove width of the circumferential auxiliary groove 45 is less than 30% of the groove width of the shoulder lug groove 25 at the opening position to the main groove 10, the effect of improving soil discharge is reduced, and conversely, if it is more than 60%, it becomes a factor that worsens external noise.

[0041] In the above-described embodiment, a specific structure is applied to the shoulder lug grooves formed in the shoulder land portion on one side in the tire width direction in the tread portion. However, in the present invention, the above-mentioned structure can be applied to the shoulder lug grooves on at least one side in the tread portion, and can also be applied to the shoulder lug grooves on both sides in the tread portion. EXAMPLES

[0042] In a pneumatic tire having a tire size of 265 / 65R17 112H, a tread portion, a pair of sidewall portions, and a pair of bead portions, and having the tread pattern shown in FIG. 2, Comparative Examples 1 to 4 and Examples 1 to 6 The company manufactured tires for the following models:

[0043] Comparative Examples 1 to 4 and Examples 1 to6 In the above, the presence or absence of bottom-up portions, the presence or absence of slope portions, the groove depth change rate X of the shoulder lug grooves (X=Db / Da), the ratio Ls / L of the length of the slope portion, the ratio La / L of the start point of the slope portion, the ratio Lb / L of the end point of the slope portion, the groove width change rate Y (Y=Wmax / Wmin), the ratio X / Y, the groove wall angle θ of the shoulder lug grooves, the presence or absence of a circumferential auxiliary groove, the position of the circumferential auxiliary groove, and the groove width ratio of the circumferential auxiliary groove (the ratio to the groove width at the opening position of the shoulder lug groove to the main groove) were set as shown in Table 1. Regarding the groove wall angle θ of the shoulder lug grooves, "5→0" means that the groove wall angle θ of the shoulder lug grooves is 5° at the position of the start point A of the slope portion and 0° at the position of the end point B of the slope portion. Regarding the position of the circumferential auxiliary groove, "between AB" means that the circumferential auxiliary groove is located between the start point A and the end point B of the slope portion.

[0044] These test tires were evaluated for soil discharge performance and exterior noise performance by the following test methods, and the results are shown in Table 1.

[0045] Soil removal ability: Each test tire was mounted on a wheel with a rim size of 17×8J and mounted on a test vehicle (SUV) with an engine displacement of 2700cc, the air pressure was set to 230kPa, and a sensory evaluation was carried out by a test driver on an off-road test course. That is, the off-road running performance was evaluated as an index of soil dischargeability. The evaluation results were shown as an index with Comparative Example 1 being 100. The higher the index value, the better the soil dischargeability.

[0046] Exterior noise performance: Each test tire was mounted on a wheel with a rim size of 17x8J and mounted on a test vehicle (SUV) with an engine displacement of 2700cc, the air pressure was set to 230kPa, and the vehicle exterior noise [db] was measured under the conditions of ECE R51.03. The evaluation results were expressed as an index using the reciprocal of the measured value, with Comparative Example 1 being set at 100. The higher the index value, the better the vehicle exterior noise performance.

[0047] [Table 1]

[0048] As can be seen from Table 1, Examples 1 to 6 In comparison with Comparative Example 1, the tire reduced external noise and improved soil discharge, providing excellent off-road running performance. On the other hand, in the tire of Comparative Example 2, the groove depth change rate X (X=Db / Da) of the shoulder lug groove was too small, so the effect of improving soil discharge and the effect of reducing external noise were insufficient. In the tire of Comparative Example 3, the ratio Ls / L relating to the length of the slope portion was too small, so the effect of improving soil discharge was insufficient. In the tire of Comparative Example 4, the ratio Ls / L relating to the length of the slope portion was too large, so the effect of improving soil discharge was insufficient.

[0049] The present disclosure includes the following inventions [1] to [7]. Invention [1] is a tire having a tread portion extending in a circumferential direction of the tire and forming an annular shape, in which a main groove extending in the tire circumferential direction and a plurality of shoulder lug grooves extending in the tire width direction are formed in the tread portion, and one end of each shoulder lug groove is connected to the main groove and the other end is located on the outer side in the tire width direction than the ground contact edge of the tread portion, Each shoulder lug groove has a bottom-raised portion adjacent to the main groove, and a slope portion in which the groove depth of the shoulder lug groove gradually increases from the bottom-raised portion toward the outside in the tire width direction, the groove depths Da, Db of the shoulder lug groove at a start point A and an end point B of the slope portion satisfy the relationship of 1.5≦Db / Da≦2.0, and the length Ls of the slope portion in the tire width direction with respect to the distance L in the tire width direction from the main groove to the ground contact edge satisfies the relationship of 0.5≦Ls / L≦0.8. Invention [2] is the tire according to invention [1], characterized in that the distance La in the tire width direction from the main groove to the start point A of the slope portion satisfies the relationship of 0.05≦La / L≦0.2 with respect to the distance L in the tire width direction from the main groove to the ground contact edge, and the distance Lb in the tire width direction from the main groove to the end point B of the slope portion satisfies the relationship of 0.55≦Lb / L≦1.0 with respect to the distance L in the tire width direction from the main groove to the ground contact edge. Invention [3] is a tire according to invention [1] or [2], characterized in that the groove width of each shoulder lug groove expands outward in the tire width direction in at least a portion of the longitudinal direction of the shoulder lug groove, the length Lx in the tire width direction from the main groove to the widening start position of each shoulder lug groove satisfies the relationship 0≦Lx / L≦0.2 with respect to the distance L in the tire width direction from the main groove to the ground contact edge, and the minimum width Wmin and maximum width Wmax of each shoulder lug groove satisfy the relationship 1.5≦Wmax / Wmin≦2.0. Invention [4] is the tire according to invention [3], characterized in that the groove depth change rate X calculated from Db / Da and the groove width change rate Y calculated from Wmax / Wmin satisfy the relationship 1.0≦X / Y≦1.2. Invention [5] is a tire according to any one of inventions [1] to [4], characterized in that the groove wall angle of the shoulder lug groove with respect to the normal direction of the tread surface of the tread portion gradually decreases toward the outside in the tire width direction in the region corresponding to the slope portion, and the groove wall angle of the shoulder lug groove is in the range of 0° to 10°. Invention [6] is the tire according to any one of inventions [1] to [5], characterized in that a circumferential auxiliary groove is formed in the tread portion extending in the tire circumferential direction and intersecting the shoulder lug groove, and the circumferential auxiliary groove is located between a start point A and an end point B of the slope portion. Invention [7] is the tire according to invention [6], characterized in that the groove width of the circumferential auxiliary groove is in the range of 30% to 60% of the groove width of the shoulder lug groove at the opening position into the main groove. [Explanation of symbols]

[0050] 1 Tread section 2 Sidewall 3 Bead section 10 Main groove 11,12,13,14,15 Land 21,22,23,24,25 Lug groove 31, 32, 33, 34, 35 Sipe 41,45 Circumferential auxiliary groove 51 Bottom raising part 52 Slope section E Ground end

Claims

1. A tire having a tread portion extending in a circumferential direction of the tire and forming an annular shape, in which a main groove extending in the tire circumferential direction and a plurality of shoulder lug grooves extending in the tire width direction are formed in the tread portion, one end of each shoulder lug groove communicates with the main groove and the other end is located outward in the tire width direction from a ground contact edge of the tread portion, a shoulder lug groove having a bottom-raised portion adjacent to the main groove and a slope portion in which the groove depth of the shoulder lug groove gradually increases from the bottom-raised portion toward the outside in the tire width direction, the groove depth of the shoulder lug groove is constant on the bottom-raised portion, groove depths Da, Db of the shoulder lug groove at a start point A and an end point B of the slope portion satisfy a relationship of 1.5≦Db / Da≦2.0, and a length Ls of the slope portion in the tire width direction with respect to a distance L in the tire width direction from the main groove to the ground contact edge satisfies a relationship of 0.5≦Ls / L≦0.

8.

2. 2. The tire according to claim 1, wherein a distance La in the tire width direction from the main groove to a start point A of the slope portion and a distance L in the tire width direction from the main groove to the ground contact end satisfy a relationship of 0.05≦La / L≦0.2, and a distance Lb in the tire width direction from the main groove to an end point B of the slope portion and a distance L in the tire width direction from the main groove to the ground contact end satisfy a relationship of 0.55≦Lb / L≦1.

0.

3. 3. The tire according to claim 1, wherein the groove width of each shoulder lug groove expands outward in the tire width direction in at least a portion of the longitudinal direction of the shoulder lug groove, the length Lx in the tire width direction from the main groove to the widening start position of each shoulder lug groove satisfies the relationship 0≦Lx / L≦0.2 with respect to the distance L in the tire width direction from the main groove to the ground contact edge, and the minimum width Wmin and maximum width Wmax of each shoulder lug groove satisfy the relationship 1.5≦Wmax / Wmin≦2.

0.

4. 4. The tire according to claim 3, wherein a groove depth change rate X calculated from Db / Da and a groove width change rate Y calculated from Wmax / Wmin satisfy the relationship 1.0≦X / Y≦1.

2.

5. The tire according to claim 1 or 2, characterized in that a groove wall angle of the shoulder lug groove with respect to a normal direction of the tread surface of the tread portion gradually decreases toward the outer side in the tire width direction in an area corresponding to the slope portion, and the groove wall angle of the shoulder lug groove is in a range of 0° to 10°.

6. 3. The tire according to claim 1, wherein a circumferential auxiliary groove is formed in the tread portion so as to extend in the tire circumferential direction and intersect with the shoulder lug grooves, and the circumferential auxiliary groove is located between a start point A and an end point B of the slope portion.

7. The tire according to claim 6, characterized in that the groove width of the circumferential auxiliary groove is in the range of 30% to 60% of the groove width of the shoulder lug groove at an opening position into the main groove.

8. A tire having a tread portion extending in a circumferential direction of the tire to form an annular shape, in which a main groove extending in the circumferential direction of the tire and a plurality of shoulder lug grooves extending in the width direction of the tire are formed in the tread portion, one end of each shoulder lug groove communicates with the main groove and the other end is located outward in the width direction of the tire than the ground contact edge of the tread portion, each shoulder lug groove has a bottom-raised portion adjacent to the main groove, and a slope portion in which the groove depth of the shoulder lug groove gradually increases from the bottom-raised portion toward the outside in the tire width direction, the groove depths Da, Db of the shoulder lug groove at a start point A and an end point B of the slope portion satisfy a relationship of 1.5≦Db / Da≦2.0, and the length Ls of the slope portion in the tire width direction satisfies a relationship of 0.5≦Ls / L≦0.8 with respect to the distance L in the tire width direction from the main groove to the ground contact edge, A tire characterized in that a groove wall angle of the shoulder lug groove with respect to a normal direction of the tread surface of the tread portion gradually decreases toward the outer side in the tire width direction in an area corresponding to the slope portion, and the groove wall angle of the shoulder lug groove is in the range of 0° to 10°.

9. A tire having a tread portion extending in a circumferential direction of the tire to form an annular shape, in which a main groove extending in the circumferential direction of the tire and a plurality of shoulder lug grooves extending in the width direction of the tire are formed in the tread portion, one end of each shoulder lug groove communicates with the main groove and the other end is located outward in the width direction of the tire than the ground contact edge of the tread portion, each shoulder lug groove has a bottom-raised portion adjacent to the main groove, and a slope portion in which the groove depth of the shoulder lug groove gradually increases from the bottom-raised portion toward the outside in the tire width direction, the groove depths Da, Db of the shoulder lug groove at a start point A and an end point B of the slope portion satisfy a relationship of 1.5≦Db / Da≦2.0, and the length Ls of the slope portion in the tire width direction satisfies a relationship of 0.5≦Ls / L≦0.8 with respect to the distance L in the tire width direction from the main groove to the ground contact edge, a circumferential auxiliary groove is formed in the tread portion, extending in the tire circumferential direction and intersecting with the shoulder lug grooves, and the circumferential auxiliary groove is located between a start point A and an end point B of the slope portion.

10. A tire having a tread portion extending circumferentially to form an annular shape, in which a main groove extending circumferentially and a plurality of shoulder lug grooves extending widthwise of the tire are formed in the tread portion, one end of each shoulder lug groove being connected to the main groove while the other end is located outward in the tire width direction from the ground contact edge of the tread portion, each shoulder lug groove has a bottom-raised portion adjacent to the main groove, and a slope portion in which the groove depth of the shoulder lug groove gradually increases from the bottom-raised portion toward the outside in the tire width direction, the groove depths Da, Db of the shoulder lug groove at a start point A and an end point B of the slope portion satisfy a relationship of 1.5≦Db / Da≦2.0, and the length Ls of the slope portion in the tire width direction satisfies a relationship of 0.5≦Ls / L≦0.8 with respect to the distance L in the tire width direction from the main groove to the ground contact edge, A tire characterized in that the groove width of the circumferential auxiliary groove is in the range of 30% to 60% of the groove width of the shoulder lug groove at an opening position into the main groove.

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