JP7610092B2 - tire - Google Patents

Description

The present invention relates to a tire having lug grooves on the surface of the tread portion.

In general, in tires including pneumatic tires, multiple main grooves extending in the tire circumferential direction and multiple 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 driving on a wet road surface. In this type of tire, if the area ratio of the main grooves and 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 (Figure 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.

Patent No. 2774775

However, there is a market demand for further improvements in the dry and wet performance of this type of tire, and constructions that can adjust the balance between dry and wet performance are being explored.

The present invention was made in consideration of the above, and aims to provide a tire that allows adjustment of the balance between dry performance and wet performance.

In order to solve the above problems and achieve the objectives, the tire according to the present invention has a plurality of main grooves extending in the tire circumferential direction 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 ground contact opening width, and the amount of widening of the groove bottom width relative to the ground contact opening width of the lug groove changes in the groove length direction.

In the above 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 of the contact width in the land portion.

In addition, in the above 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.

In addition, in the above tire, it is preferable that the relationship between the groove length Wa of the widened region and the ground contact width Wb of the land portion of the lug groove is within the range of 0.1≦(Wa/Wb)≦1.0.

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.

In addition, in the above 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.

The tire according to the present invention has lug grooves extending in the tire width direction on 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 opening width. The amount of widening of the groove bottom width relative to the ground contact opening width of the lug groove changes in the groove length direction. Therefore, by adjusting the position where the widening amount becomes larger, the balance between dry performance and wet performance can be adjusted.

FIG. 1 is a meridian cross-sectional view showing a main part of a pneumatic tire according to the present embodiment. FIG. 2 is a view taken along the line AA in FIG. FIG. 3 is a cross-sectional view taken along line BB of FIG. 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. 5 is a diagram showing a cross-sectional shape of a lug groove according to a modified example. FIG. 6 is a plan view showing the shape of the groove bottom of a lug groove according to a modified example. FIG. 7 is a plan view showing the shape of the groove bottom of a lug groove according to a modified example. FIG. 8 is a plan view showing the shape of the groove bottom of a lug groove according to a modified example. FIG. 9 is a plan view showing a shape in which the other end of the lug groove terminates within the land portion. FIG. 10 is a plan view showing a shape in which the other end of the lug groove terminates within the land portion. FIG. 11 is a table showing the results of the performance evaluation test of pneumatic tires.

Below, 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. Furthermore, the components in the following embodiment include those that are replaceable and easily conceivable by a person skilled in the art, or those that are substantially the same.

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

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 positions 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 of the tire cut by a plane that includes the tire rotation axis.

As shown in FIG. 1, the pneumatic tire 1 according to this embodiment has a tread portion 2 disposed on the radially outermost portion of the tire, 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) on which the pneumatic tire 1 is mounted is traveling, is formed as a tread surface (contact surface) 3, and the tread surface 3 constitutes part of the contour of the pneumatic tire 1.

The tread portion 2 has a plurality of main grooves 30 formed on the tread surface 3, which extend in the tire circumferential direction, and the plurality of main grooves 30 are aligned in the tire width direction. The tread portion 2 also has a plurality of land portions 20, the ends of which in the tire width direction are defined 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.

The main groove 30 is a longitudinal groove that extends at least partially in the tire circumferential direction and has a treadwear indicator (slip sign; not shown) inside 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.

Shoulder sections 5 are located at both outer ends of the tread section 2 in the tire width direction, and sidewall sections 8 are arranged on the tire radially inner side of the shoulder sections 5. In other words, the sidewall sections 8 are arranged on both sides of the tread section 2 in the tire width direction.

Bead portions 10 are located on the radially inner side of the sidewall portions 8. The bead portions 10 are arranged 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 radially outer side of the bead core 11. 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 arranged on the radially outer side of the bead core 11.

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 coating a plurality of belt cords made of steel or organic fiber materials such as polyester, rayon, and nylon with coating rubber and rolling them. The two-layer belts 60, 61 have a belt angle, defined as the inclination angle of the belt cord in the tire width direction relative to the tire circumferential direction, within a predetermined range (for example, 20° to 55°). The tread rubber layer 4 of the tread portion 2 is disposed on the tire radial outer side of the belt layer 14 in the tread portion 2.

A carcass layer 13 containing the cords of the radial ply is provided continuously on the inner side of the belt layer 14 in the tire radial direction 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 multiple 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 tire framework.

In detail, 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 around the bead core 11 at the bead portion 10 to wrap the bead core 11 and the bead filler 12. The bead filler 12 is a rubber material disposed in a space formed on the tire radial outer side of the bead core 11 by folding the carcass layer 13 at the bead portion 10 in this way. The belt layer 14 is disposed on the tire radial outer side of the portion of the carcass layer 13 located in the tread portion 2 that is stretched between the pair of bead portions 10 in this way. The carcass ply of the carcass layer 13 is formed by coating a plurality of carcass cords made of steel or organic fiber material such as aramid, nylon, polyester, rayon, etc. with coating rubber and rolling them. The carcass cords that make up the carcass ply are arranged in parallel at an angle to the tire circumferential direction, while aligning with the tire meridian direction.

In the bead portion 10, rim cushion rubber 17 is arranged on the tire radial inner side and tire width outer side of the bead core 11 and the turned-up portion of the carcass layer 13, which constitute the contact surface of the bead portion 10 with the rim flange. In addition, 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 the tire inner surface 18, which is the inner surface of the pneumatic tire 1.

2 is a view taken along the line A-A in FIG. 1. FIG. 3 is a cross-sectional view taken along the line B-B in FIG. 2. FIG. 4 is a partially enlarged cross-sectional view showing the relationship between the groove depths of the main groove and the lug groove. FIG. 2 illustrates a land portion 20 (center land portion 21) of the multiple land portions 20, the both sides of which in the tire width direction are partitioned by the main groove 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 in a line 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 oscillating in the tire circumferential direction while extending in the tire width direction. The lug grooves 40 may extend linearly, wave-shaped, 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 open into 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 in 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.

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 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. The groove bottom width W2 indicates the groove width of the lug groove 40 that is wider than the opening width W1. For example, in the case of a round-bottom groove that has a groove width longer than the groove bottom, the groove bottom width W2 includes the longest groove width in a depth region that is 50% or more of the groove depth.

As shown in FIG. 2, the opening 41 is formed with an opening width W1 that is almost constant in the groove length direction. Specifically, "almost constant opening width W1" 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.

In contrast, the groove bottom 42 is formed so that the groove bottom width W2 is wider in 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 portion 42A in the center of the ground contact width Wb of the land portion 20, and the groove bottom width W2 decreases continuously and monotonically from this maximum widening portion 42A to the end of the ground contact width Wb of the land portion 20 (the terminating portion if it terminates within the land portion 20).

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, as shown in FIG. 3, the widening amount of the lug groove 40 is 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, and the widening amount monotonically decreases toward the end of the ground contact width Wb of the land portion 20 (the end portion if it terminates 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, thereby ensuring the groove volume of the lug groove 40 and 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 portion 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 can be secured 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 portion 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 thus reducing passing noise during vehicle travel and improving noise performance.

The center of the ground contact width Wb of the land portion 20 where the maximum widening portion 42A is provided refers to the 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.

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 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 of the maximum widths (0.5 x ΔWmax) in the maximum width portion 42A is formed to be 0.5 mm or more and 7.0 mm or less.

As shown in FIG. 4, the relationship between the maximum groove depth H1 of the lug groove 40 and the maximum groove depth Hg of the main groove 30 is preferably within the range of 0.5≦(H1/Hg)≦1.0. This configuration ensures the drainage of the lug groove 40 and ensures wet performance.

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.

The ground contact ends T here refer to the outermost ends in the tire width direction of the area of the tread surface 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 a ground contact end T, such as the shoulder land portion 22, the ground contact end T is included in the end of the land portion 20.

The above-mentioned specified rim refers to the "standard rim" specified by JATMA, the "design rim" specified by TRA, or the "measuring rim" specified by ETRTO. The specified internal pressure refers to 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 refers to 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.

When the pneumatic tire 1 according to this 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 comes into contact with 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. In addition, 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 water between the tread surface 3 and the road surface is drained by these main grooves 30 and lug grooves 40 while running. 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.

Here, the lug grooves 40 are formed 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, 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) in which the lug grooves 40 are formed, making it possible to achieve both dry and wet performance when the vehicle is running. Furthermore, since the amount of widening of the groove bottom width W2 relative to the opening width W1 changes along the groove length direction of the lug groove 40, by adjusting the position in the groove length direction where the widening amount is large, one of the dry performance and the wet performance can be improved more than the other, and the balance between the dry performance and the wet performance can be adjusted.

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, the lug grooves 40 are formed so that the width of the contact width Wb of the land portion 20 is smaller at the ends than at the center, which can prevent sound leakage from the lug grooves 40, thereby reducing passing noise while the vehicle is running and improving noise performance.

Here, the lug groove 40 is configured so 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 to less than 20% or more 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, and the edge rigidity of the land portion 20 decreases, so 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 handling stability, mainly on dry road surfaces, when the vehicle is traveling.

In contrast, 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, sound leakage from the lug groove 40 can be suppressed, reducing passing noise while the vehicle is running and improving noise performance.

In addition, the relationship between the groove length Wa of the widened 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. With this configuration, by increasing 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.

In other words, if 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 the drainage performance of the lug groove 40 may be reduced. In this case, the reduced drainage performance of the lug groove 40 may make it difficult to ensure wet handling stability, mainly on wet road surfaces, when the vehicle is traveling.

In contrast, when the relationship between the groove length Wa of the widening 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 widening region 43 of the lug groove 40 can be made large, so that a sufficient groove volume of the lug groove 40 can be ensured. This ensures wet performance when the vehicle runs on a wet road surface.

In addition, the lug groove 40 has a maximum widening portion 42A 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 equivalent to 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°. This configuration makes it possible to maintain the land portion rigidity (block rigidity) of the land portion 20 while ensuring the drainage of the lug grooves 40.

That is, if 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 reduced. Also, if 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 reduced. In this case, the reduced drainage of the lug groove 40 may make it difficult to ensure wet handling stability, mainly on wet road surfaces, when the vehicle is traveling.

In addition, if 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, and there is a risk that the rigidity of the land portion of the lug groove 40 will decrease. In this case, there is a risk that it will be difficult to ensure dry handling stability, mainly on dry road surfaces, when the vehicle is traveling, due to a partial decrease in the rigidity of the land portion 20.

In contrast, 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. This makes it possible to maintain wet performance when the vehicle runs on a wet road surface. In addition, since the maximum widening amount ΔWmax of the lug groove 40 can be prevented from becoming too large, it is possible to prevent a decrease in land portion rigidity and ensure dry performance when the vehicle runs on a dry road surface.

The relationship between the maximum groove depth H1 of the lug groove 40 and the maximum groove depth Hg of the main groove 30 is within the range of 0.5≦(H1/Hg)≦1.0. This configuration ensures the groove volume of the lug groove 40 and ensures the drainage of the lug groove 40.

In other words, if 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 secured, and the drainage performance of the lug grooves 40 may be reduced. In this case, the reduced drainage performance of the lug grooves 40 may make it difficult to ensure wet handling stability, mainly on wet road surfaces, when the vehicle is traveling.

In contrast, when the relationship between the maximum groove depth H1 of the lug groove 40 and the maximum groove depth Hg of the main groove 30 is within the range of 0.5≦(H1/Hg)≦1.0, a sufficient groove volume of the lug groove 40 can be ensured. This ensures wet performance when the vehicle runs on a wet road surface.

[Modification]
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 to this. FIG. 5 is a diagram showing the cross section of the lug groove according to a modified example. As shown in FIG. 5, the lug grooves 140 to 440 include rectangular upper groove portions 141 to 441 that open onto the tread surface 3, and lower groove portions 142 to 442 that are wider than the upper groove portions 141 to 441. The upper groove portions 141 to 441 are formed in a rectangular cross section and have an opening width W1. The lower groove portions 142 to 442 are connected to the upper groove portions 141 to 441, and each has a different cross section.

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 on 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, no matter what shape the lug grooves 140-440 are formed in, 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 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 preferably within the range of 0.2≦(ΔWmax/H1)≦1.2.

In the above-described embodiment, the shape of the groove bottom 42 in the lug groove 40 is such that the groove bottom width W2 decreases continuously (gradually) in a curved line from the maximum widening portion 42A in the center of the contact width Wb toward 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 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.

As shown in FIG. 6, the groove bottom 542 of the lug groove 540 may have a shape in which the groove bottom width W2 decreases stepwise (in steps) from the maximum widening portion 542A in the center of the ground width Wb to the end 542B. 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, as shown in FIG. 7, the groove bottom 642 of the lug groove 640 may have a shape in which the groove bottom width W2 decreases linearly from the maximum widening portion 642A in the center of the ground width Wb to the end 642B. 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, as shown in FIG. 8, the groove bottom 742 of the lug groove 740 may have an asymmetric shape 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 width Wb to the end 742B. 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 larger than the opening width W1.

In the above 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. Figures 9 and 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 terminates, which is different from the above embodiment, so the same configuration is given the same reference numerals and description is omitted. Figure 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 Figure 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.

As shown in FIG. 9 and FIG. 10, the lug groove 40 has one end 40A that opens into the main groove 30, and the other end 40B that 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 linearly from this maximum widening portion 42A to 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 linearly from this maximum widening portion 42A to 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.

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. It is preferable that the number of main grooves 30 formed in the tread portion 2 is within the range of three to five.

[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 with respect to 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.

The performance evaluation test was carried out by mounting a pneumatic tire 1 with a tire nominal size of 255/35R19 as specified by JATMA on a JATMA standard rim wheel with a rim size of 19x9J, adjusting the air pressure to 260 kPa, mounting it on an evaluation vehicle (FF sedan passenger car) and running the evaluation vehicle.

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 100 km/h, 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 dry braking performance.

As for wet braking performance, an evaluation vehicle fitted with the test tires was driven at an initial speed of 100 km/h on a road surface that had been sprayed with water to a depth of approximately 1 mm on a test course, and the braking distance when braking was measured. 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.

Noise performance was evaluated based on the volume of the vehicle's external pass-by noise measured according to the tire noise test method stipulated 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 just 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 eight or more sections at approximately equal intervals within a speed range of ±10 km/h from the reference speed, and the average was taken as the vehicle's external pass-by noise. The maximum noise value dB was 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 of the centerline of the road and 1.2 m above the road surface. The pass-by noise measurement results are expressed as an index with the conventional example described below being 100, and the higher the value, the lower the sound pressure dB and the better the noise performance against pass-by noise.

The performance evaluation test was conducted 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 pneumatic tires 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.

In addition, the pneumatic tires 1 according to Examples 1 to 16 are different in the relationship of the position of the maximum widening portion 42A to the ground contact width Wb of the land portion 20, the relationship of the groove length Wa of the widened widening region 43 to the ground 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 of the maximum widening amount of the lug groove 40 to the groove depth of the lug groove 40, and the relationship of the groove depth of the lug groove 40 to the maximum groove depth Hg of the main groove 30.

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 prescribed ranges can improve dry braking performance and noise performance while minimizing the deterioration of at least wet braking performance compared to the conventional example. In particular, the relationship of the "maximum widening amount relative to lug groove depth" is 13% in the conventional example, whereas in this embodiment it is a maximum of 120% (Example 12), so that 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 prescribed 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 prescribed ranges can ensure dry braking performance and noise performance while suppressing the deterioration of wet braking performance.

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 used as an example of the tire, but the present invention is not limited to this, and can of course also be applied to tires that are not filled with air, such as airless tires. Furthermore, in addition to normal air or air with an adjusted oxygen partial pressure, inert gases such as nitrogen, argon, and helium can be used as the gas filled into the pneumatic tire exemplified in this embodiment.

1 Tire 2 Tread 3 Tread surface (surface of tread, contact surface)
5 Shoulder portion 20 Land portion 21 Center land portion 22 Shoulder land portion 30 Main groove 31 Center main groove 32 Shoulder main groove 40, 140, 240, 340, 440, 540, 640, 740 Lug groove 40A, 40B End portion 41 Opening 42, 542, 642, 742 Groove bottom 42A, 142A, 542A, 642A, 742A Maximum widening portion 43 Widening area 43A Wall surface CL Tire equatorial plane T Ground contact edge W1 Opening width (ground contact surface opening width)
W2 Groove bottom width Wb Ground contact width

Claims (5)

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: 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. 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. 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. 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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