tire

Abstract

To provide a tire which can adjust a balance between a dry performance and a wet performance.SOLUTION: A pneumatic tire 1 has major grooves 30 extending in a tire circumferential direction and a land part 20 defined by the major grooves 30 in a tread part 2 and has lug grooves 40 extending in a tire width direction at the land part 20. At least one end part 40A of the lug groove 40 opens to the major groove 30. A groove bottom width W2 of the lug groove 40 is wider than an opening width W1. A widening amount of the groove bottom width W2 relative to the opening width W1 of the lug groove 40 varies in a groove length direction.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a tire having lug grooves on the surface of a tread portion. [Background technology]

[0002] In general, in tires including pneumatic tires, a plurality of main grooves extending in the tire circumferential direction and a plurality of lug grooves extending in the tire width direction are formed on the surface of the tread portion, which is the contact surface, for the purpose of draining water between the surface of the tread portion and the road surface when traveling on a wet road surface. In this type of tire, if the area ratio of the main grooves or lug grooves to the surface of the tread portion is increased, the groove volume increases, improving wet performance such as steering stability and braking performance on wet road surfaces, while there is a concern that the dry performance such as steering stability and braking performance on dry road surfaces will decrease due to a relative decrease in the contact area. Patent Document 1 (FIG. 9) discloses a pneumatic tire provided with lug grooves having a cross-sectional shape in which the groove bottom width is wider than the contact surface opening width. In this pneumatic tire, both dry performance and wet performance are achieved by ensuring the contact area and groove volume of the tread portion. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 2774775 Summary of the Invention [Problem to be solved by the invention]

[0004] Meanwhile, there is a demand in the market for further improvement in the dry and wet performance of this type of tire, and a construction that allows adjustment of the balance between the dry performance and the wet performance is being sought.

[0005] The present invention has been made in view of the above, and has an object to provide a tire in which the balance between dry performance and wet performance can be adjusted. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems and achieve the object, the tire of the present invention has a plurality of main grooves extending circumferentially in the tread portion and land portions defined by the main grooves, and has lug grooves extending in the tire width direction in the land portions, at least one end of the lug groove opens into the main groove, and the groove bottom width of the lug groove is wider than the contact patch opening width, and the amount of widening of the groove bottom width relative to the contact patch opening width of the lug groove changes in the groove length direction.

[0007] In the tire, it is preferable that the lug groove has a groove bottom width wider at the center of the contact width than at the end portions of the contact width in the land portion.

[0008] In the tire, it is preferable that the lug groove has a maximum widening portion where the widening amount is maximum, located within a range of 20% to 80% of the contact width of the land portion.

[0009] In the tire, the lug groove preferably has a relationship between the groove length Wa of the widened region and the ground contact width Wb of the land portion within the range of 0.1≦(Wa / Wb)≦1.0.

[0010] In addition, in the above tire, it is preferable that the maximum widening portion of the lug groove, where the widening amount is maximum, is located at a depth of 50% or more of the maximum groove depth of the lug groove, and the relationship between the maximum widening amount ΔWmax of the lug groove at the maximum widening portion and the maximum groove depth H1 of the lug groove is within the range of 0.2≦(ΔWmax / H1)≦1.2.

[0011] In the tire, it is preferable that the relationship between the maximum groove depth H1 of the lug groove and the maximum groove depth Hg of the main groove is within the range of 0.5≦(H1 / Hg)≦1.0. Effect of the Invention

[0012] The tire of the present invention has lug grooves extending in the tire width direction in the land portion, at least one end of the lug groove opens into the main groove, and the groove bottom width of the lug groove is wider than the ground contact patch opening width, and the amount of widening of the groove bottom width relative to the ground contact patch opening width of the lug groove changes in the groove length direction.Therefore, by adjusting the position where the amount of widening is largest, the balance between dry performance and wet performance can be adjusted. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a meridian cross-sectional view showing a main part of a pneumatic tire according to this embodiment. [Diagram 2] FIG. 2 is a view taken along the line AA in FIG. [Diagram 3] FIG. 3 is a cross-sectional view taken along line BB in FIG. [Figure 4] FIG. 4 is a partially enlarged cross-sectional view showing the relationship between the groove depths of the main grooves and the lug grooves. [Diagram 5] FIG. 5 is a diagram showing a cross-sectional shape of a lug groove according to a modified example. [Figure 6] FIG. 6 is a plan view showing the shape of the groove bottom of a lug groove according to a modified example. [Figure 7] FIG. 7 is a plan view showing the shape of the groove bottom of the lug groove according to a modified example. [Figure 8] FIG. 8 is a plan view showing the shape of the groove bottom of the lug groove according to a modified example. [Figure 9] FIG. 9 is a plan view showing a shape in which the other end of the lug groove terminates within the land portion. [Figure 10] FIG. 10 is a plan view showing a shape in which the other end of the lug groove terminates within the land portion. [Figure 11] FIG. 11 is a table showing the results of a performance evaluation test of a pneumatic tire. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of a tire according to the present invention will be described in detail with reference to the drawings. The tire according to this embodiment is, for example, a pneumatic tire for vehicles. Note that the present invention is not limited to this embodiment. In addition, the components in the following embodiments include those that are replaceable and easily conceivable by a person skilled in the art, or those that are substantially the same.

[0015] FIG. 1 is a meridian cross-sectional view showing a main part of a pneumatic tire according to this embodiment. In the following description, the tire radial direction refers to a direction perpendicular to a rotation axis (not shown) of a pneumatic tire 1. Furthermore, the tire radial inner side refers to a side facing the rotation axis in the tire radial direction, and the tire radial outer side refers to a side away from the rotation axis in the tire radial direction. Furthermore, the tire circumferential direction refers to a direction around the rotation axis as a central axis. Furthermore, the tire width direction refers to a direction parallel to the rotation axis. Furthermore, the tire width direction inner side refers to a side facing the tire equatorial plane (tire equatorial line) CL in the tire width direction, and the tire width direction outer side refers to a side away from the tire equatorial plane CL in the tire width direction.

[0016] The tire equatorial plane CL is a plane that is perpendicular to the rotation axis of the pneumatic tire 1 and passes through the center of the tire width of the pneumatic tire 1. The tire width is the width in the tire width direction between the parts located at the outermost sides in the tire width direction, that is, the distance between the parts farthest from the tire equatorial plane CL in the tire width direction. The tire equatorial line is a line that is on the tire equatorial plane CL and runs along the tire circumferential direction of the pneumatic tire 1. The tire meridian section is a cross section obtained by cutting the tire with a plane that includes the tire rotation axis.

[0017] 1, a pneumatic tire 1 according to this embodiment has a tread portion 2 disposed on the outermost portion in the tire radial direction, and the tread portion 2 has a tread rubber layer 4 made of a rubber composition. The surface of the tread portion 2, i.e., the portion that comes into contact with the road surface when a vehicle (not shown) equipped with the pneumatic tire 1 is traveling, is formed as a tread surface (contact surface) 3, and the tread surface 3 constitutes a part of the contour of the pneumatic tire 1.

[0018] In the tread portion 2, a plurality of main grooves 30 extending in the tire circumferential direction are formed on the tread surface 3, and the plurality of main grooves 30 are aligned in the tire width direction. In addition, in the tread portion 2, a plurality of land portions 20 are formed, the ends of which in the tire width direction are partitioned by the main grooves 30. In this embodiment, three main grooves 30 are aligned in the tire width direction, and therefore, four rows of land portions 20 are aligned in the tire width direction via the main grooves 30. The four rows of land portions 20 are formed in a rib-like shape extending in the tire circumferential direction.

[0019] The main groove 30 is a longitudinal groove at least partially extending in the tire circumferential direction, and has a treadwear indicator (slip sign; not shown) therein that indicates the end of wear. The main groove 30 may extend linearly in the tire circumferential direction, or may be formed in a wave or zigzag shape by repeatedly oscillating in the tire width direction while extending in the tire circumferential direction. In the example of FIG. 1, the pneumatic tire 1 has one center main groove 31 provided in the center in the tire width direction (on the tire equatorial plane CL), and shoulder main grooves 32 provided on the tire width direction outer side (shoulder portion 5 side described later) of the center main groove 31. The pneumatic tire 1 also has two center land portions 21 arranged on either side of the center main groove 31, and shoulder land portions 22 arranged on the tire width direction outer side of the center land portions 21 on either side of the shoulder main groove 32. In the following description, when there is no need to distinguish between the center main groove 31 and the shoulder main groove 32, they are simply referred to as the main groove 30. Furthermore, when there is no need to distinguish between the center land portion 21 and the shoulder land portion 22, they will simply be referred to as land portion 20.

[0020] Shoulder portions 5 are located at both outer ends of the tread portion 2 in the tire width direction, and sidewall portions 8 are disposed on the tire radially inner sides of the shoulder portions 5. That is, the sidewall portions 8 are disposed on both sides of the tread portion 2 in the tire width direction.

[0021] Bead portions 10 are located on the inner side of the sidewall portions 8 in the tire radial direction. The bead portions 10 are disposed on both sides of the tire equatorial plane CL in the tire width direction, similar to the sidewall portions 8. Each bead portion 10 is provided with a bead core 11, and a bead filler 12 is provided on the outer side of the bead core 11 in the tire radial direction. The bead core 11 is an annular member formed by bundling bead wires, which are steel wires, into a circular ring shape, and the bead filler 12 is a rubber member disposed on the outer side of the bead core 11 in the tire radial direction.

[0022] The tread portion 2 is provided with a belt layer 14. The belt layer 14 is formed of a multi-layer structure in which a plurality of belts 60, 61 are laminated, and in this embodiment, two layers of belts 60, 61 are laminated. The belts 60, 61 constituting the belt layer 14 are formed by covering a plurality of belt cords made of steel or organic fiber materials such as polyester, rayon, and nylon with a coating rubber and rolling them. The two-layer belts 60, 61 have a belt angle, which is defined as the inclination angle of the belt cord in the tire width direction with respect to the tire circumferential direction, within a predetermined range (for example, 20° or more and 55° or less). The tread rubber layer 4 of the tread portion 2 is disposed on the tire radial direction outer side of the belt layer 14 in the tread portion 2.

[0023] A carcass layer 13 containing the cords of the radial ply is provided continuously on the inner side in the tire radial direction of the belt layer 14 and on the tire equatorial plane CL side of the sidewall portion 8. Therefore, the pneumatic tire 1 according to this embodiment is configured as a so-called radial tire. The carcass layer 13 has a single-layer structure consisting of one carcass ply, or a multi-layer structure consisting of a plurality of carcass plies stacked together, and is toroidally spanned between a pair of bead portions 10 arranged on both sides in the tire width direction to form the framework of the tire.

[0024] Specifically, the carcass layer 13 is disposed from one bead portion 10 to the other bead portion 10 of a pair of bead portions 10 located on both sides in the tire width direction, and is wound back along the bead core 11 at the bead portion 10 toward the outside in the tire width direction so as to envelop the bead core 11 and the bead filler 12. The bead filler 12 is a rubber material disposed in a space formed on the outside in the tire radial direction of the bead core 11 by folding back the carcass layer 13 at the bead portion 10 in this manner. The belt layer 14 is disposed on the outside in the tire radial direction of the portion of the carcass layer 13 that is stretched between the pair of bead portions 10 and that is located in the tread portion 2. The carcass ply of the carcass layer 13 is formed by covering a plurality of carcass cords made of steel or organic fiber material such as aramid, nylon, polyester, rayon, etc. with a coating rubber and rolling the covered cords. The carcass cords constituting the carcass ply are arranged in parallel at a certain angle to the tire circumferential direction while being aligned along the tire meridian direction.

[0025] In the bead portion 10, a rim cushion rubber 17 that constitutes the contact surface of the bead portion 10 with the rim flange is disposed on the inner side in the tire radial direction and the outer side in the tire width direction of the bead core 11 and the turned-up portion of the carcass layer 13. Also, an inner liner 16 is formed along the carcass layer 13 on the inner side of the carcass layer 13 or on the inner side of the carcass layer 13 in the pneumatic tire 1. The inner liner 16 forms a tire inner surface 18 that is the inner surface of the pneumatic tire 1.

[0026] FIG. 2 is a view taken along the line AA in FIG. 1. FIG. 3 is a cross-sectional view taken along the line BB in FIG. 2. FIG. 4 is a partially enlarged cross-sectional view showing the relationship between the groove depths of the main grooves and the lug grooves. FIG. 2 illustrates a land portion 20 (center land portion 21) of the multiple land portions 20, both sides of which in the tire width direction are partitioned by the main grooves 30. As shown in FIG. 2, the land portion 20 has multiple lug grooves 40 extending in the tire width direction, and these lug grooves 40 are formed side by side in the tire circumferential direction. The lug grooves 40 may extend linearly in the tire width direction, or may be formed in a wave or zigzag shape by repeatedly vibrating in the tire circumferential direction while extending in the tire width direction. The lug grooves 40 may extend linearly, wave-like, or zigzag along a direction inclined at a predetermined angle with respect to the tire width direction. In the example of FIG. 2, the lug grooves 40 have both ends 40A open to the two main grooves 30 that partition both sides of the land portion 20 in the tire width direction. As a result, the land portion 20 is divided into blocks by the two lug grooves 40. Note that at least one end 40A (one end) of the lug groove 40 needs to be open to the main groove 30, and the other end (other end) may terminate within the land portion 20. In this case, the land portion 20 is formed into a rib shape that is continuous in the tire circumferential direction without being divided in the tire circumferential direction. The configuration in which the other end of the lug groove 40 terminates within the land portion 20 will be described later.

[0027] The lug groove 40 is a groove portion that extends in the tire width direction and has a groove length of 30% to 100% of the ground contact width Wb of the land portion 20, and has an opening 41 that opens to the tread surface 3 and a groove bottom 42, as shown in FIG. 3. The lug groove 40 is formed in a cross-sectional shape in which the groove bottom width W2 of the groove bottom 42 is wider than the opening width (ground contact surface opening width) W1 in the tire circumferential direction of the opening 41. Furthermore, as shown in FIG. 2, the lug groove 40 is formed so that the widening amount of the groove bottom width W2 relative to the above-mentioned opening width W1 changes along the groove length direction of the lug groove 40. In this case, the widening amount is the difference value (W2-W1) between the groove bottom width W2 and the opening width W1. In addition, the groove bottom width W2 indicates the groove width of the lug groove 40 which is wider than the opening width W1. For example, in the case of a round bottom groove having a groove width longer than the groove bottom, the groove bottom width W2 includes the longest groove width in a depth region of 50% or more of the groove depth.

[0028] 2, the opening 41 is formed with an opening width W1 that is almost constant in the groove length direction. Specifically, "the opening width W1 is almost constant" means that the relationship between the minimum opening width W1min and the maximum opening width W1max is within the range of 0.8≦(W1min / W1max)≦1.0. This makes it possible to suppress a reduction in the contact area of ​​the tread portion 2 of the pneumatic tire 1, and thus to suppress a decrease in dry performance.

[0029] In contrast, the groove bottom 42 is formed such that the groove bottom width W2 is wider at the center than at the ends in the groove length direction. That is, in this embodiment, as shown in Fig. 2, the groove bottom width W2 is a maximum value (maximum groove width) W2max at the maximum widening part 42A in the center of the ground contact width Wb of the land portion 20, and the groove bottom width W2 continuously and monotonically decreases from this maximum widening part 42A to the end of the ground contact width Wb of the land portion 20 (the end part if it ends within the land portion 20).

[0030] As described above, the opening width W1 of the opening 41 is almost constant in the groove length direction, and the groove bottom width W2 of the groove bottom 42 is formed to be maximum at the maximum widening portion 42A. Therefore, the widening amount of the lug groove 40 becomes the maximum widening amount ΔWmax at the maximum widening portion 42A in the center of the ground contact width Wb of the land portion 20 as shown in FIG. 3, and the widening amount decreases monotonically toward the end of the ground contact width Wb of the land portion 20 (the end portion if it is terminated within the land portion 20). According to this configuration, the lug groove 40 is formed in a cross-sectional shape in which the groove bottom width W2 of the groove bottom 42 is wider than the opening width W1 of the opening 41, and the groove volume of the lug groove 40 is secured, thereby ensuring wet performance such as wet handling stability and wet braking performance (hereinafter simply referred to as wet performance). In addition, the lug grooves 40 are formed so that the width of the end side of the ground contact width Wb of the land portion 20 is smaller than that of the center, thereby increasing the edge rigidity of the land portion 20, and therefore the rigidity of the land portion is ensured, and dry performance such as dry handling stability and dry braking performance (hereinafter simply referred to as dry performance) can be improved. Furthermore, the lug grooves 40 are formed so that the width of the end side of the ground contact width Wb of the land portion 20 is smaller than that of the center, thereby suppressing sound leakage from the lug grooves 40, and therefore passing noise during vehicle travel can be reduced, and noise performance can be improved.

[0031] The center of the ground contact width Wb of the land portion 20 where the maximum widening portion 42A is provided refers to a peripheral region in the width direction including 50% of the ground contact width Wb, and preferably includes a range of 20% to 80% of the ground contact width Wb from the end of the land portion 20. In addition, as shown in FIG. 2, the relationship between the groove length Wa of the widening region 43, which is wider than the opening width W1 of the opening 41, and the ground contact width Wb of the land portion 20 is preferably within the range of 0.1≦(Wa / Wb)≦1.0, and more preferably within the range of 0.3≦(Wa / Wb)≦1.0. In this case, the widening region 43 refers to a region larger than the opening width W1 of the opening 41. According to this configuration, the groove volume of the lug groove 40 can be secured by increasing the widening region 43 of the lug groove 40, and wet performance can be secured when the vehicle runs on a wet road surface.

[0032] In addition, the maximum widening portion 42A of the lug groove 40 is preferably formed at a depth position of 50% or more of the maximum groove depth H1 of the lug groove 40. In the example of FIG. 3, the maximum widening portion 42A is formed at the groove bottom 42 of the lug groove 40, that is, at a depth position of 100% of the maximum groove depth H1. In this case, the relationship between the maximum widening amount ΔWmax of the lug groove 40 at the maximum widening portion 42A and the maximum groove depth H1 of the lug groove 40 is preferably within the range of 0.2≦(ΔWmax / H1)≦1.2. According to this configuration, it is possible to maintain the rigidity of the land portion 20 while ensuring the drainage performance of the lug groove 40. In addition, the angle θ between the perpendicular line 41A extending from the opening 41 to the groove bottom 42 and the wall surface 43A of the widening region 43 at the maximum widening portion 42A is preferably formed to be 5°≦θ≦30°. In this case, one maximum width increase amount (0.5×ΔWmax) in the maximum width increase portion 42A is set to be 0.5 mm or more and 7.0 mm or less.

[0033] 4, the relationship between the maximum groove depth H1 of the lug grooves 40 and the maximum groove depth Hg of the main groove 30 is preferably within the range of 0.5≦(H1 / Hg)≦1.0. With this configuration, the drainage of the lug grooves 40 can be ensured, and wet performance can be ensured.

[0034] In this embodiment, the ground contact width Wb of the land portion 20 is the width of the tread surface 3 of the land portion 20 in the tire width direction. For this reason, in the land portion 20 in which both sides in the tire width direction are defined by the main grooves 30, such as the center land portion 21, the ground contact width Wb is approximately the same as the maximum width of the land portion 20 in the tire width direction. In the shoulder land portion 22 in which only the inner side in the tire width direction is defined by the main grooves 30, although not shown in the figure, the ground contact width Wb is the distance in the tire width direction from the inner end of the land portion 20 in the tire width direction to the ground contact end T (see FIG. 1) located on the land portion 20.

[0035] The ground contact ends T here refer to both outermost ends in the tire width direction of the area of ​​the tread 3 that comes into contact with a flat plate when the pneumatic tire 1 is mounted on a specified rim, inflated to a specified internal pressure, and placed perpendicular to a flat plate in a stationary state and subjected to a load equivalent to a specified load, and are continuous in the tire circumferential direction. In this embodiment, when one side in the tire width direction is defined by the ground contact ends T, such as the shoulder land portion 22, the ground contact ends T are included in the ends of the land portion 20.

[0036] The above-mentioned specified rim is the "standard rim" specified by JATMA, the "design rim" specified by TRA, or the "measuring rim" specified by ETRTO. The specified internal pressure is the "maximum air pressure" specified by JATMA, the maximum value listed in the "tire load limits at various cold inflation pressures" specified by TRA, or the "inflation pressures" specified by ETRTO. The specified load is the "maximum load capacity" specified by JATMA, the maximum value of the "tire load limits at various cold inflation pressures" specified by TRA, or the "load capacity" specified by ETRTO.

[0037] When the pneumatic tire 1 according to the present embodiment is mounted on a vehicle, the pneumatic tire 1 is mounted on a rim wheel, and is inflated by filling the inside with air. When a vehicle equipped with the pneumatic tire 1 runs, the pneumatic tire 1 rotates while the lower tread surface 3 of the tread portion 2 contacts the road surface. When a vehicle equipped with the pneumatic tire 1 runs on a dry road surface, the vehicle runs by transmitting driving force and braking force to the road surface and generating turning force mainly by the frictional force between the tread surface 3 and the road surface. When running on a wet road surface, water between the tread surface 3 and the road surface enters the main groove 30 and the lug groove 40, and the vehicle runs while draining the water between the tread surface 3 and the road surface through the main groove 30 and the lug groove 40. This makes it easier for the tread surface 3 to contact the road surface, and the vehicle can run due to the frictional force between the tread surface 3 and the road surface.

[0038] Here, the lug grooves 40 are formed such that both ends 40A are open to the two main grooves 30 that divide the land portion 20 on both sides in the tire width direction, and the groove bottom width W2 of the groove bottom 42 is wider than the opening width W1 of the opening 41. This ensures the ground contact area and groove volume of the tread surface 3 of the land portion 20 (tread portion 2) where the lug grooves 40 are formed, so that both dry performance and wet performance can be achieved when the vehicle runs. Furthermore, the lug grooves 40 have an increase in the groove bottom width W2 relative to the opening width W1 that changes along the groove length direction of the lug grooves 40, so that one of the dry performance and the wet performance can be improved more than the other by adjusting the position where the increase in the groove length direction is large, and the balance between the dry performance and the wet performance can be adjusted.

[0039] In this embodiment, the lug groove 40 is formed so that the groove bottom width W2 is wider at the center than at the end of the ground contact width Wb of the land portion 20. That is, the widening amount of the lug groove 40 is maximum at the maximum widening portion 42A at the center of the ground contact width Wb of the land portion 20, and the widening amount monotonically decreases toward the end of the ground contact width Wb of the land portion 20. According to this configuration, the lug groove 40 can secure the groove volume of the lug groove 40 by widening the groove bottom width W2 at the center of the ground contact width Wb of the land portion 20, so that the wet performance when the vehicle runs on a wet road surface can be maintained. In addition, the lug groove 40 is formed so that the widening amount is smaller at the end side than at the center of the ground contact width Wb of the land portion 20, so that the edge rigidity of the land portion 20 can be increased, and the land portion rigidity can be secured to improve the dry performance when the vehicle runs on a dry road surface. Furthermore, since the lug grooves 40 are formed so that the amount of widening is smaller at the ends of the contact width Wb of the land portion 20 than at the center, sound leakage from the lug grooves 40 can be suppressed, thereby reducing passing noise when the vehicle is traveling and improving noise performance.

[0040] Here, the lug groove 40 is configured such that the maximum widening portion 42A, where the widening amount is maximum, is located within a range of 20% to 80% of the ground contact width Wb of the land portion 20 from the end of the land portion 20. That is, in this embodiment, the range of 20% to 80% of the ground contact width Wb of the land portion 20 is the center of the ground contact width Wb. Here, if the above-mentioned maximum widening portion 42A is provided in a range from the end of the land portion 20 that is less than 20% or greater than 80% of the ground contact width Wb of the land portion 20, the widening amount of the lug groove 40 at the end of the land portion 20 becomes large, so that the edge rigidity of the land portion 20 decreases, and there is a risk that the land portion rigidity becomes too low. In this case, there is a risk that the partial decrease in rigidity of the land portion 20 makes it difficult to ensure dry steering stability, mainly on dry road surfaces, when the vehicle is traveling.

[0041] On the other hand, when the maximum widening portion 42A of the lug groove 40 is located within a range of 20% to 80% of the ground contact width Wb of the land portion 20 from the end of the land portion 20, the widening amount is smaller on the end side (less than 20% of the ground contact width Wb of the land portion 20 from the end) than on the center of the ground contact width Wb of the land portion 20. This makes it possible to increase the edge rigidity of the land portion 20, thereby ensuring the rigidity of the land portion and improving the dry performance when the vehicle runs on a dry road surface. Furthermore, it is possible to suppress sound leakage from the lug groove 40, thereby reducing passing noise during vehicle running and improving noise performance.

[0042] In addition, the relationship between the groove length Wa of the widened region 43 of the lug groove 40, which is wider than the opening width W1 of the opening 41, and the ground contact width Wb of the land portion 20 is preferably within the range of 0.1≦(Wa / Wb)≦1.0, and more preferably within the range of 0.3≦(Wa / Wb)≦1.0. According to this configuration, by enlarging the widened region 43 of the lug groove 40, the groove volume of the lug groove 40 can be secured, and wet performance when the vehicle runs on a wet road surface can be secured.

[0043] That is, when the relationship between the groove length Wa of the widened region 43 and the ground contact width Wb of the land portion 20 is 0.1>(Wa / Wb), the groove volume of the lug groove 40 cannot be sufficiently secured, and there is a risk of the drainage performance of the lug groove 40 decreasing. In this case, there is a risk that the wet handling stability, mainly on wet road surfaces, during vehicle running will be difficult to ensure due to the decreased drainage performance of the lug groove 40.

[0044] On the other hand, when the relationship between the groove length Wa of the widened region 43 and the ground contact width Wb of the land portion 20 is within the range of 0.1≦(Wa / Wb)≦1.0, preferably 0.3≦(Wa / Wb)≦1.0, the widened region 43 of the lug groove 40 can be made large, so that a sufficient groove volume of the lug groove 40 can be secured. Therefore, wet performance when the vehicle runs on a wet road surface can be secured.

[0045] In addition, the lug groove 40 has a maximum widening portion 42A at which the widening amount is maximum, located at a depth of 50% or more of the maximum groove depth H1 of the lug groove 40, and the relationship between the maximum widening amount ΔWmax of the lug groove 40 at the maximum widening portion 42A and the maximum groove depth H1 of the lug groove 40 is within the range of 0.2≦(ΔWmax / H1)≦1.2. That is, the ratio (ΔWmax / H1) of the maximum widening amount ΔWmax to the maximum groove depth H1 of the lug groove 40 is set within the range of 20% to 120%. This numerical range is almost synonymous with the angle θ (see FIG. 3) between the perpendicular line 41A extending from the opening 41 to the groove bottom 42 and the wall surface 43A of the widening region 43 at the maximum widening portion 42A being formed within the range of 5°≦θ≦30°. With this configuration, it is possible to maintain the land portion rigidity (block rigidity) of the land portion 20 while ensuring the drainage of the lug groove 40.

[0046] That is, when the above-mentioned maximum widening portion 42A is located at a depth less than 50% of the maximum groove depth H1 of the lug groove 40, the groove volume of the lug groove 40 cannot be sufficiently secured, and the drainage of the lug groove 40 may be deteriorated. Also, when the relationship between the above-mentioned maximum widening amount ΔWmax and the maximum groove depth H1 is within the range of 0.2>(ΔWmax / H1), the groove volume of the lug groove 40 cannot be sufficiently secured, and the drainage of the lug groove 40 may be deteriorated. In this case, the drainage of the lug groove 40 may be deteriorated, and therefore it may be difficult to secure wet handling stability, mainly on wet road surfaces, when the vehicle is traveling.

[0047] Furthermore, when the relationship between the maximum widening amount ΔWmax and the maximum groove depth H1 is within the range of (ΔWmax / H1)>1.2, the maximum widening amount ΔWmax of the lug groove 40 becomes too large, which may reduce the rigidity of the land portion in the lug groove 40. In this case, the partial reduction in rigidity of the land portion 20 may make it difficult to ensure dry handling stability, mainly on dry road surfaces, when the vehicle is traveling.

[0048] On the other hand, when the above-mentioned maximum widening portion 42A is located at a depth of 50% or more of the maximum groove depth H1 of the lug groove 40 and the relationship between the maximum widening amount ΔWmax and the maximum groove depth H1 is within the range of 0.2≦(ΔWmax / H1)≦1.2, a sufficient groove volume of the lug groove 40 can be secured. Therefore, wet performance when the vehicle runs on a wet road surface can be maintained. In addition, since the maximum widening amount ΔWmax of the lug groove 40 can be prevented from becoming too large, a decrease in land portion rigidity can be prevented, and dry performance when the vehicle runs on a dry road surface can be secured.

[0049] Moreover, the relationship between the maximum groove depth H1 of the lug grooves 40 and the maximum groove depth Hg of the main groove 30 is within the range of 0.5≦(H1 / Hg)≦1.0. With this configuration, the groove volume of the lug grooves 40 can be secured, and the drainage performance of the lug grooves 40 can be secured.

[0050] That is, when the relationship between the maximum groove depth H1 of the lug grooves 40 and the maximum groove depth Hg of the main grooves 30 is 0.5>(H1 / Hg), the groove volume of the lug grooves 40 cannot be sufficiently ensured, and there is a risk of a decrease in the drainage performance of the lug grooves 40. In this case, there is a risk that the decrease in the drainage performance of the lug grooves 40 makes it difficult to ensure wet handling stability, mainly on wet road surfaces, when the vehicle is traveling.

[0051] On the other hand, when the relationship between the maximum groove depth H1 of the lug grooves 40 and the maximum groove depth Hg of the main grooves 30 is within the range of 0.5≦(H1 / Hg)≦1.0, it is possible to ensure a sufficient groove volume of the lug grooves 40. Therefore, it is possible to ensure wet performance when the vehicle runs on a wet road surface.

[0052] [Variations] In the above embodiment, the lug groove 40 is formed in a substantially trapezoidal cross section with the groove bottom width W2 of the groove bottom 42 being wider than the opening width W1 of the opening 41, but the cross section of the lug groove 40 is not limited thereto. FIG. 5 is a diagram showing the cross section of a lug groove according to a modified example. As shown in FIG. 5, the lug grooves 140-440 include rectangular upper groove portions 141-441 that open onto the tread surface 3, and lower groove portions 142-442 that are wider than the upper groove portions 141-441. The upper groove portions 141-441 are formed in a rectangular cross section and have an opening width W1. The lower groove portions 142-442 are connected to the upper groove portions 141-441, and each has a different cross section.

[0053] Specifically, the lower groove portion 142 of the lug groove 140 is formed in a substantially circular cross section, and the lug groove 140 is formed in a round-bottom groove shape. The lower groove portion 242 of the lug groove 240 is formed in an isosceles trapezoidal cross section, the lower groove portion 342 of the lug groove 340 is formed in a rectangular cross section, and the lower groove portion 442 of the lug groove 440 is formed in a trapezoidal cross section that is widened to one side. These lower groove portions 142-442 have maximum widening portions 142A-442A and are formed to a groove width (groove bottom width) W2 at the maximum widening portions 142A-442A. In this way, regardless of the shape into which the lug grooves 140-440 are formed, the maximum widening portions 142A-442A are formed at a depth position that is 50% or more of the maximum groove depth H1 of the lug grooves 140-440, and it is preferable that the relationship between the maximum widening amount ΔWmax of each lug groove 140-440 at the maximum widening portions 142A-442A and the maximum groove depth H1 of the lug groove 40 is within the range of 0.2≦(ΔWmax / H1)≦1.2.

[0054] In the above-mentioned embodiment, the shape of the groove bottom 42 of the lug groove 40 is such that the groove bottom width W2 is continuously (gradually) reduced in a curved manner from the maximum widening part 42A at the center of the ground contact width Wb to the end, but the shape of the groove bottom 42 is not limited to this. Figures 6 to 8 are plan views showing the shapes of the groove bottom of the lug groove according to the modified examples. In these modified examples, the openings 41 in the lug grooves 540 to 740 are the same as those described above, so the same reference numerals are used and the description is omitted.

[0055] The groove bottom 542 of the lug groove 540 may be shaped such that the groove bottom width W2 decreases stepwise (in a step-like manner) from the maximum widening portion 542A in the center of the ground contact width Wb toward the end 542B, as shown in FIG. 6. In this case, the groove width of the end 542B of the groove bottom 542 may be the same as the opening width W1, or may be formed larger than the opening width W1. Also, the groove bottom 642 of the lug groove 640 may be shaped such that the groove bottom width W2 decreases linearly from the maximum widening portion 642A in the center of the ground contact width Wb toward the end 642B, as shown in FIG. 7. In this case, the groove width W3 at both ends 642B may be the same, or one may be formed larger than the other. Also, the groove bottom 742 of the lug groove 740 may be shaped asymmetrically with respect to the center line 41B in the groove length direction of the opening 41 when decreasing from the maximum widening portion 742A in the center of the ground contact width Wb toward the end 742B, as shown in FIG. 8. In this case, it is preferable that the groove width W3 at both ends 742B is the same, and this groove width W3 may be the same as the opening width W1 or may be formed to be larger than the opening width W1.

[0056] In the above-described embodiment, the lug groove 40 is configured such that both ends 40A are open to the two main grooves 30 that define both sides of the land portion 20 in the tire width direction, but the other end 40B of the lug groove 40 may terminate within the land portion 20. FIG. 9 and FIG. 10 are plan views showing a shape in which the other end of the lug groove terminates within the land portion. Here, the other end 40B of the lug groove 40 is different from the above-described embodiment in that it terminates, and therefore the same configurations are given the same reference numerals and description is omitted. FIG. 9 illustrates a land portion 20 (center land portion 21) of the multiple land portions 20, both sides of which in the tire width direction are defined by the main grooves 30, and FIG. 10 illustrates a land portion 20 (shoulder land portion 22) of the multiple land portions 20, one side of which in the tire width direction is defined by the main groove 30.

[0057] As shown in FIG. 9 and FIG. 10, one end 40A of the lug groove 40 opens into the main groove 30, and the other end 40B terminates within the land portion 20. In the example of FIG. 9, the lug groove 40 has a maximum widening portion 42A at the position of the other end 40B, and the widening amount decreases monotonically in a linear manner from the maximum widening portion 42A toward the one end 40A. In this case, the widening amount may decrease in a curved manner. In the example of FIG. 10, the lug groove 40 has a maximum widening portion 42A at a position between the one end 40A and the other end 40B, and the widening amount decreases monotonically in a curved manner from the maximum widening portion 42A toward the one end 40A and the other end 40B. In this case, the widening amount may decrease linearly, or one may decrease linearly and the other may decrease in a curved manner. In the example of FIG. 10, the other end 40B of the lug groove 40 may terminate at the ground contact end T. In this case, the groove length of the lug groove 40 is formed to be 30% or more and 100% or less of the ground contact width Wb of the land portion 20. Even if the other end 40B terminates within the land portion 20, the lug groove 40 only needs to have the maximum widening portion 42A, where the widening amount is maximum, located within a range of 20% or more and 80% or less of the ground contact width Wb of the land portion 20 from the end of the land portion 20.

[0058] In addition, in the above-described embodiment, three main grooves 30 are formed, but the number of main grooves 30 may be other than three. The number of main grooves 30 formed in the tread portion 2 is preferably within the range of three to five.

[0059] [Example] 11 is a table showing the results of a performance evaluation test of a pneumatic tire. Hereinafter, a performance evaluation test conducted on the conventional pneumatic tire and the pneumatic tire 1 according to the present invention will be described for the above pneumatic tire 1. The performance evaluation test was conducted on dry braking performance, which is the braking performance on a dry road surface, as dry performance, wet braking performance, which is the braking performance on a wet road surface, as wet performance, and noise performance against passing noise during driving.

[0060] The performance evaluation test was carried out by mounting a pneumatic tire 1 having a tire nominal size of 255 / 35R19 as specified by JATMA on a JATMA standard rim wheel having a rim size of 19 x 9J, adjusting the air pressure to 260 kPa, mounting it on an evaluation vehicle (FF sedan passenger car) and running the evaluation vehicle.

[0061] The method of evaluation for each test item was as follows: for dry braking performance, an evaluation vehicle fitted with test tires was driven on a dry road surface on a test course at an initial speed of 100km / h, the braking distance was measured when braking, and the reciprocal of the measured distance was expressed as an index with the conventional example (described below) set at 100. The higher the value, the shorter the braking distance and the better the dry braking performance.

[0062] For wet braking performance, an evaluation vehicle fitted with the test tires was driven at an initial speed of 100km / h on a road surface that had been sprayed with water approximately 1mm deep on a test course, the braking distance when braking was measured, and the reciprocal of the measured distance was expressed as an index, with the conventional example (described below) being set at 100. The higher this value, the shorter the distance required for braking and the better the wet braking performance.

[0063] The noise performance was evaluated based on the loudness of the passing noise outside the vehicle measured according to the tire noise test method defined in ECE R117-02 (ECE Regulation No. 117 Revision 2). In this test, the test vehicle was started to run from well before the noise measurement section, the engine was stopped before the section, and the vehicle was coasted. The maximum noise value dB (noise value in the frequency range of 800 Hz to 1200 Hz) in the noise measurement section was measured at multiple speeds divided into 8 or more equal intervals within a speed range of ±10 km / h from the reference speed, and the average was taken as the passing noise outside the vehicle. The maximum noise value dB is the sound pressure dB(A) measured through an A-weighted frequency weighting circuit using a fixed microphone installed at the midpoint of the noise measurement section, 7.5 m to the side from the center line of the road and 1.2 m above the road surface. The passing noise is expressed as an index with the conventional example described later being 100, and the higher the value, the lower the sound pressure dB and the better the noise performance against passing noise.

[0064] The performance evaluation test was performed on 17 types of pneumatic tires, including a conventional pneumatic tire, which is an example of a conventional pneumatic tire, and Examples 1 to 16, which are the pneumatic tire 1 according to the present invention. Of these, in the conventional example, the groove bottom width W2 is increased relative to the opening width W1, but this amount of increase is constant and does not change in the groove length direction. In contrast, in the pneumatic tires 1 according to Examples 1 to 16, the amount of increase changes in the groove length direction of the lug groove 40.

[0065] In addition, the pneumatic tires 1 of Examples 1 to 16 each differ in the relationship of the position of the maximum widening portion 42A to the contact width Wb of the land portion 20, the relationship between the groove length Wa of the widened widening region 43 and the contact width Wb of the land portion, the relationship of the position of the maximum widening portion to the groove depth of the lug groove 40, the relationship between the maximum widening amount of the lug groove 40 and the groove depth of the lug groove 40, and the relationship between the groove depth of the lug groove 40 and the maximum groove depth Hg of the main groove 30.

[0066] As a result of carrying out a performance evaluation test using these pneumatic tires 1, as shown in FIG. 11, it was found that the pneumatic tires 1 according to the examples (Examples 2, 3, 6, 7, 9, 11, 12, 15, and 16) in which the above-mentioned relationships are within the specified ranges can improve the dry braking performance and noise performance while minimizing the deterioration of at least the wet braking performance compared to the conventional example. In particular, the relationship of the "maximum widening amount relative to the lug groove depth" is 13% in the conventional example, whereas in this embodiment it is up to 120% (Example 12), so that the wet braking performance can also be improved. In contrast, it was found that the pneumatic tires 1 according to the examples (Examples 1, 4, 5, 8, 10, 13, and 14) in which any of the above-mentioned relationships is outside the specified range have at least one of the wet braking performance, dry braking performance, and noise performance lower than the conventional example. In other words, the pneumatic tires 1 according to the examples in which the above-mentioned relationships are within the specified ranges can ensure the dry braking performance and noise performance while suppressing the deterioration of the wet braking performance.

[0067] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment. For example, in the present embodiment, a pneumatic tire is exemplified as a tire, but the present invention is not limited to this, and can of course be applied to a tire that is not filled with air, such as an airless tire. In addition, as the gas filled in the pneumatic tire exemplified in the present embodiment, in addition to normal air or air with an adjusted oxygen partial pressure, an inert gas such as nitrogen, argon, or helium can be used. [Explanation of symbols]

[0068] 1 Tire 2 Tread section 3. Tread surface (surface of the tread, contact surface) 5 Shoulder section 20 Land 21 Center Land Section 22 Shoulder Land Section 30 Main groove 31 Center main groove 32 Shoulder main groove 40, 140, 240, 340, 440, 540, 640, 740 Lug groove 40A, 40B end 41 Opening 42, 542, 642, 742 groove bottom 42A, 142A, 542A, 642A, 742A Maximum width 43 Widening Area 43A Wall CL Tire Equatorial Plane T ground end W1 Opening width (ground plane opening width) W2 Groove bottom width Wb Ground width

Claims

1. A tire having a plurality of main grooves extending in a tire circumferential direction in a tread portion, and a land portion defined by two adjacent main grooves, the land portion having lug grooves extending in a tire width direction, The lug groove has a groove length of 50% or more of the ground contact width of the land portion, one end of the lug groove opens into the main groove and the other end terminates within the land portion, and a groove bottom width including the longest groove width in a depth region of 50% or more of the maximum groove depth of the lug groove is wider than the ground contact opening width, The amount of widening of the groove bottom width relative to the ground contact opening width of the lug groove varies in the groove length direction, and a maximum widening portion where the amount of widening is maximum is located within a range of 20% to 80% of the ground contact width of the land portion from an end of the land portion, The lug groove has a maximum widening portion where the widening amount of the groove bottom width is maximum, the maximum widening portion being located at a depth of 50% or more of the maximum groove depth of the lug groove, A relationship between a maximum widening amount ΔWmax of the lug groove at the maximum widening portion and a maximum groove depth H1 of the lug groove is within a range of 0.2≦(ΔWmax / H1)≦1.

2. A tire characterized by:

2. The tire according to claim 1 , wherein the lug groove has the maximum widening portion at the position of the other end, and the widening amount monotonically decreases from the maximum widening portion toward the one end.

3. The tire according to claim 1, wherein the lug groove has the maximum widening portion at a position between the one end and the other end, and the widening amount monotonically decreases from the maximum widening portion toward the one end and the other end, respectively.

4. The tire according to any one of claims 1 to 3, wherein the lug groove has a relationship between a groove length Wa of the widened region and a ground contact width Wb of the land portion within a range of 0.1≦(Wa / Wb)≦1.

0.

5. The tire according to any one of claims 1 to 4, wherein a relationship between a maximum groove depth H1 of the lug groove and a maximum groove depth Hg of the main groove is within a range of 0.5≦(H1 / Hg)≦1.0.

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