JP2022089630A - Pneumatic tire - Google Patents

Abstract

To improve wear performance while maintaining wet performance.SOLUTION: On a tread 16, provided are three main grooves of a center main groove 28 A, and a pair of shoulder main grooves 28B and 28C positioned on both sides of the center main groove. Void ratio VR is 26.5 to 28.5%, the Void ratio VR being ratio SB/SA of area SB of a non-grounded part in a tread surface 16A to area SA of the tread surface 16A between ground ends TE and TE. Groove depth DG of each main groove 28 is 79 to 85% of distance DX from an outer surface of an outermost layer 26 of a plurality of reinforcing layers under a groove of each main groove 28 to the tread surface 16A.SELECTED DRAWING: Figure 2

Description

Embodiments of the present invention relate to pneumatic tires.

Pneumatic tires are required to have high grip performance (that is, wet performance) on wet road surfaces, and for example, the wet performance can be improved by blending tread rubber forming a tread surface.

It should be noted that Patent Documents 1 and 2 disclose that the relationship between the groove depth of the main groove provided in the tread and the rubber thickness under the groove is specified in a heavy-duty pneumatic tire such as a truck or a bus.

Japanese Unexamined Patent Publication No. 2019-059340 Japanese Unexamined Patent Publication No. 2017-071275

When the wet performance is improved by blending the tread rubber as described above, the wear performance is generally lowered as a trade-off. Therefore, it is required to improve the wear performance by the tread pattern while maintaining the wet performance improved by the tread rubber compounding.

In view of the above points, it is an object of the present invention to provide a pneumatic tire capable of improving wear performance while maintaining wet performance.

The pneumatic tire according to the embodiment of the present invention has three main grooves, a center main groove and a pair of shoulder main grooves located on both sides of the center main groove in the tire width direction, as main grooves extending in the tire circumferential direction. In a pneumatic tire in which a groove is provided in the tread, the void ratio, which is the ratio of the area of the non-grounded portion in the tread surface between the grounded ends to the area of the tread surface between the grounded ends in the tread, is 26.5% or more. It is 28.5% or less, and the groove depth of each of the three main grooves is 79% or more and 85% of the distance from the outer surface of the outermost layer of the plurality of reinforcing layers under the groove of each main groove to the tread surface. It is characterized by the following.

According to the pneumatic tire according to the present embodiment, by defining the void ratio and the groove depth ratio of the main groove in the tread pattern, it is possible to improve the wear performance while maintaining the wet performance.

A development view showing a tread pattern of a pneumatic tire according to an embodiment. Cross section of the same pneumatic tire Partially enlarged cross-sectional view of FIG.

Hereinafter, embodiments will be described with reference to the drawings.

Unless otherwise specified, each shape, dimension, etc. in the present specification is a tire in a normal state with no load, in which a pneumatic tire (hereinafter, may be simply referred to as a tire) is attached to a regular rim and filled with a regular internal pressure. Is. A regular rim is a rim defined for each tire in the standard system including the standard on which the tire is based. For example, "standard rim" in the JATTA standard, "Design Rim" in the TRA standard, or "Design Rim" in the ETRTO standard. Measuring Rim ". The regular internal pressure is the air pressure defined for each tire in the standard system including the standard on which the tire is based. For example, the "maximum air pressure" in the JATTA standard and the table "TIRE LOAD LIMITS AT VARIOUS COLD" in the TRA standard. "Maximum value" described in "INFLATION PRESSURES" or "INFLATION PRESSURE" in the ETRTO standard.

The pneumatic tire 10 according to one embodiment is a passenger car tire, and as shown in FIG. 2, a pair of left and right beads 12 and 12 fixed to a rim and a pair of bead 12 and 12 in the tire radial direction, respectively. It has a pair of left and right sidewalls 14 and 14 connected to the outside, and a tread 16 extending between the pair of sidewalls 14 and 14 to form a ground plane.

In the figure, reference numeral CL indicates a tire equatorial plane corresponding to the center in the tire width direction. In the present specification, the tire width direction means a direction parallel to the tire rotation axis, and is indicated by reference numeral WD in the figure. The inside of the WD in the tire width direction is a direction approaching the tire equatorial plane CL, and the outside of the WD in the tire width direction is a direction away from the tire equatorial plane CL. The tire radial direction refers to a direction perpendicular to the tire rotation axis, and is indicated by the reference numeral RD in the figure. The inside of the tire radial direction RD is a direction approaching the tire rotation axis, and the tire radial direction RD outside is a direction away from the tire rotation axis. The tire circumferential direction refers to the direction of rotation about the tire rotation axis, and is indicated by the reference numeral CD in the figure.

In the present embodiment, a general tire structure can be adopted except for the tread pattern, and the tire structure is not particularly limited. In the example shown in FIG. 2, the pneumatic tire 10 has a pair of bead cores 18 and 18, a carcass ply 20 spanned between the pair of bead cores 18 and 18, and a tire radial RD of the crown portion of the carcass ply 20. A belt 22 arranged on the outside and a tread rubber 24 provided on the outer peripheral side of the belt 22 are provided.

The bead core 18 is an annular member composed of bead wires and extending over the entire circumference in the tire circumferential direction, and is embedded in the bead 12. The carcass ply 20 is formed by covering an array of fiber cords arranged along the meridian direction with topping rubber, and both ends thereof are folded back and locked around the bead core 18. The belt 22 is formed by covering an array of belt cords inclined at a predetermined angle with respect to the tire circumferential direction with topping rubber, and a plurality of layers (two layers in the figure) are provided on the outer peripheral side of the carcass ply 20 in the tread 16. ing. In the example of FIG. 2, a belt reinforcing layer 26 including an organic fiber cord extending substantially parallel to the tire circumferential direction is provided on the outer peripheral side of the belt 22. In the present embodiment, the belt 22 and the belt reinforcing layer 26 are collectively referred to as a “reinforcing layer”, and the “outermost layer of the reinforcing layer” is the belt reinforcing layer 26 in the example of FIG. 2, but the belt reinforcing layer 26 If there is no belt 22, it is the outermost layer of the belt 22.

In FIGS. 1 and 2, reference numeral TE indicates a grounded end of the tread 16. The ground contact end TE is the tire width direction WD of the tread surface that touches the road surface when the tire is rim-assembled on the regular rim, the tire is placed vertically on a flat road surface with the regular internal pressure charged, and the road surface is grounded when a regular load is applied. Refers to the outermost position. The normal load is the load defined for each tire in the standard system including the standard on which the tire is based. For example, the maximum load capacity in the JATTA standard, the maximum value described in the above table in the TRA standard, and ETRTO. Although it is "LOAD CAPACITY" in the standard, when the tire is for a passenger car, the load is equivalent to 88% of the above load.

The pneumatic tire 10 shown in FIGS. 1 and 2 is a tire whose mounting direction to a vehicle is designated, and a side surface to be mounted on the outside and a side surface to be mounted on the inside are designated when the tire is mounted on the vehicle. There is. Therefore, for example, the side portion of the pneumatic tire 10 is provided with a display for designating the mounting direction on the vehicle. In the figure, the side indicated by the reference numeral OUT faces the outside (outside the vehicle mounting) in the vehicle mounting posture, and the side indicated by the reference numeral IN faces the inside (inside the vehicle mounting) in the vehicle mounting posture.

As shown in FIGS. 1 and 2, three main grooves 28 extending in the tire circumferential direction CD are provided on the surface of the tread 16 (that is, the tread surface 16A) at intervals in the tire width direction WD. Specifically, a center main groove 28A located at the center of the tire width direction WD in the tread 16 and a pair of shoulder main grooves 28B and 28C located on both sides of the center main groove 28A in the tire width direction WD are provided. There is. In this example, all of these main grooves 28 have a straight shape extending parallel to the tire circumferential direction CD. The main groove 28 is generally a circumferential groove having a groove width (opening width) of 5 mm or more.

The tread 16 is divided into four land portions 30 by three main grooves 28. That is, the left and right center land portions 30A and 30B sandwiched between the center main groove 28A and the pair of shoulder main grooves 28B and 28C, respectively, and the shoulder main grooves 28B and 28C are located outside the WD in the tire width direction and touch the ground. Left and right shoulder land portions 30C and 30D including the end TE are provided.

Each land portion 30 is provided with a lateral groove 32 and / or a sipe 34 extending in a direction intersecting the tire circumferential direction CD. Here, the sipe 34 means a narrow groove having a groove width of 1.5 mm or less (preferably 0.4 to 1.2 mm). The horizontal groove 32 means a groove having a groove width of more than 1.5 mm (usually a groove width of 2 mm or more).

In this example, the center land portion 30A of the vehicle mounting inner IN extends from the first lateral groove 32A extending from the outer edge of the WD in the tire width direction and terminating in the center land portion 30A, and extending from the inner edge of the WD in the tire width direction. First sipes 34A terminating within the center land portion 30A are alternately provided on the tire circumferential direction CD. An inclined surface 33 extending in a reverse taper shape is provided at the opening of the first lateral groove 32A to the tread surface 16A. An inclined surface 35 extending in a reverse taper shape is also provided at the opening of the first sipe 34A to the tread surface 16A.

A second sipe 34B extending at an angle with respect to the tire width direction WD and crossing the center land portion 30B is provided on the center land portion 30B of the vehicle mounting outer OUT at intervals in the tire circumferential direction CD. .. The second sipe 34B is provided with an inclined surface 35 extending in a reverse taper shape at the opening to the tread surface 16A, and one without the inclined surface 35 is provided alternately in the tire circumferential direction CD. ing.

The second lateral groove 32B and the third lateral groove 32B and the third lateral groove 32B extending at the shoulder land portion 30C of the vehicle mounting inner IN in an inclined manner with respect to the tire width direction WD and crossing the shoulder land portion 30C at least within a range up to the ground contact end TE. Sipe 34C and sipe 34C are alternately provided on the tire circumferential direction CD. The end of the second lateral groove 32B on the shoulder main groove 28B side is formed as a sipe, and the opening to the tread surface 16A is provided with an inclined surface 33 extending in a reverse taper shape.

A third lateral groove 32C extending at an angle with respect to the tire width direction WD and crossing the shoulder land portion 30D is provided on the shoulder land portion 30D of the vehicle mounting outer OUT at intervals in the tire circumferential direction CD. There is. The third lateral groove 32C is formed with an end portion on the shoulder main groove 28C side as a sipe, and an inclined surface 33 extending in a reverse taper shape is provided at an opening to the tread surface 16A.

In this embodiment, the void ratio of the tread surface 16A is set to 26.5% or more and 28.5% or less. While the conventional general void ratio is about 33%, by setting the void ratio small in this way, the contact pressure can be lowered to make it difficult to wear, and the wear performance can be improved.

Here, the void ratio of the tread surface 16A means the ratio of the area of the non-grounded portion in the tread surface 16A between the grounded ends TE and TE to the area of the tread surface 16A between the grounded ends TE and TE on both sides. That is, it is the ratio of the area of the non-grounded portion in the region between the grounded ends TE and TE. Specifically, the area of the tread surface 16A from the ground contact end TE of the vehicle mounting inner IN to the ground contact end TE of the vehicle mounting outer OUT (total area of the ground contact portion and the non-ground contact portion over the entire circumference of the tire circumferential CD). Is SA, the area of the non-grounded portion on the tread surface 16A from the grounding end TE of the vehicle mounting inner IN to the grounding end TE of the vehicle mounting outer OUT is SB, the void ratio is VR, and VR = (SB / SA) ×. It is represented by 100. Here, the area of the non-grounded portion is the sum of the opening areas of the main groove 28, the lateral groove 32, and the sipe 34, and the opening area of the lateral groove 32 and the sipe 34 includes the portion expanded by the inclined surfaces 33, 35. Is done.

In the present embodiment, each groove depth DG of the three main grooves 28 is 79% of the distance DX from the outer surface of the outermost layer of the plurality of reinforcing layers under the groove of each main groove 28 to the tread surface 16A. It is set to 85% or more and 85% or less.

In this way, the ratio of the groove depth DG to the distance DX (hereinafter, this ratio is referred to as the groove depth ratio GR; GR = (DG / DX) × 100) is set to 79% or more and 85% or less. By setting the groove depth ratio to be larger than the standard groove depth ratio, the groove depth DG of the main groove 28 can be increased while suppressing the thickness of the tread rubber 24, and the wear life can be extended. Further, since the wet performance is improved by increasing the groove depth DG of the main groove 28, it is possible to suppress the deterioration of the wet performance due to the setting of the void ratio VR small. Further, since the thickness of the tread rubber 24 can be suppressed, deterioration of rolling resistance due to an increase in tire mass can be suppressed. Therefore, in combination with the above setting of the void ratio VR, it is possible to improve the wear performance while maintaining the wet performance and suppressing the increase in the tire mass. The groove depth ratio GR is more preferably 80% or more and 84% or less.

Here, as shown in FIG. 3, the groove depth DG of the main groove 28 is a distance in the tire radial direction RD from the bottom 29 of the main groove 28 to the opening surface of the main groove 28, and is a TWI (tread wear indicator). Refers to the maximum depth of the main groove 28 excluding the portion provided with the tread. The size of the groove depth DG is not particularly limited because it varies depending on the tire size, and may be, for example, 7 to 10 mm.

The distance DX is the distance in the tire radial direction RD from the outer surface of the outermost layer (belt reinforcing layer 26 in this example) of the reinforcing layer directly under the main groove 28 to the tread surface 16A (opening surface of the main groove 28). be. The distance DX is represented by DX = DG + TG, where the thickness of the rubber at the bottom of the main groove 28 is TG. Here, the groove bottom rubber thickness TG is the thickness of the rubber existing below the main groove 28 in the tire radial direction RD, and is the outermost layer of the bottom portion 29 of the main groove 28 and the reinforcing layer immediately below the bottom portion 29 (belt reinforcement in this example). It is the distance in the tire radial direction RD from the outer surface of the layer 26).

In this embodiment, also between the ground contact ends TE and TE of the tread 16, the region located in the vehicle mounting inner IN from the tire equatorial plane CL is located in the inner region 36 and the vehicle mounting outer OUT from the tire equatorial plane CL. When the region to be tired is the outer region 38, the void ratio VR1 in the outer region 38 is set to be smaller than the void ratio VR2 in the inner region 36 (that is, VR1 <VR2).

By reducing the void ratio at the vehicle-mounted outer OUT in this way, the following effects are achieved. For example, among passenger cars, in a vehicle having a high vehicle height such as a minivan, a high load is likely to be applied to the outside of the tire mounted on the vehicle when turning. On the other hand, by reducing the void ratio VR1 at the vehicle mounting outer OUT as described above, the ratio of the land portion becomes large, so that a high load can be shared over a wider area and the ground contact pressure is lowered. It can be made less likely to wear.

Here, the void ratio VR1 of the outer region 38 is the non-grounded region in the outer region 38 with respect to the area of the tread surface 16A of the outer region 38, which is the region from the tire equatorial plane CL to the grounded end TE of the vehicle mounting outer OUT. The ratio of the area of the part. Further, the void ratio VR2 of the inner region 36 is a non-grounded portion in the inner region 36 with respect to the area of the tread surface 16A of the inner region 36 which is a region from the tire equatorial plane CL to the grounding end TE of the vehicle mounting inner IN. The ratio of the area of.

The values of these void ratios VR1 and VR2 are not particularly limited, but VR1 may be 24% or more and 27% or less, or 25% or more and 26% or less. Further, VR2 may be 27% or more and 30% or less, and may be 28% or more and 29% or less. Further, the difference between VR2 and VR1 (VR2-VR1) is not particularly limited, but may be 2% or more and 6% or less, or 2% or more and 4% or less.

In this embodiment, the center main groove 28A is unevenly distributed in the vehicle mounting inner IN rather than the tire equatorial surface CL. Specifically, the center main groove 28A is entirely provided in the inner region 36 and does not exist in the outer region 38. Therefore, since the three main grooves 28 are present in the inner region 36 and one in the outer region 38, the void ratio VR1 in the outer region 38 can be reduced more effectively.

The tread pattern shown in FIG. 1 is only a preferable example, and the present embodiment can be applied to various tread patterns satisfying the void ratio VR and the groove depth ratio GR. For example, various changes can be made to the configuration such as the arrangement of sipes and lateral grooves in each land area, and the configuration such as the position of the main groove.

In order to confirm the effect of improving the performance of the tire according to the embodiment, the pneumatic radial tires (tire size: 205 / 60R16 92H) of Examples 1 to 3 and Comparative Examples 1 to 3 were prototyped, and each tire was 16 × 6. It was mounted on a 0.0 rim, filled with an internal pressure of 240 kPa, and mounted on a minivan to evaluate wet performance and wear performance.

Each prototype tire has the tread pattern shown in FIG. 1 above, and is set to the void ratio VR as shown in Table 1 by changing the groove width of the main groove 28, the groove width of the lateral groove 32, and the like. At the same time, the thickness of the tread rubber 24 was kept constant, and the groove depth DG of the main groove 28 was changed to set the groove depth ratio GR as shown in Table 1. Other configurations are common to Examples 1 to 3 and Comparative Examples 1 to 3.

Each evaluation method is as follows.
-Wet performance: The tire was run on a circuit surface wet with water, the handleability was evaluated by a sensory evaluation by a driver, and the handleability evaluation of the tire of Comparative Example 1 was set as an index of 100. The larger the value, the better the wet performance.
-Abrasion performance: The remaining groove depth of the main groove after traveling 9000 km on an asphalt road without tire rotation was measured, and the tire was expressed as an index with the remaining groove depth of the tire of Comparative Example 1 as 100. The larger the value, the better the wear performance.

The results are as shown in Table 1, and in Comparative Example 1 in which the void ratio VR and the groove depth ratio GR are out of the specified range, the examples in which the void ratio VR and the groove depth ratio GR are both within the specified range are shown. When it was 1 to 3, the wear performance was improved while maintaining or improving the excellent wet performance due to the tread rubber compounding. Further, since the distance DX was constant and the dread rubber thickness was constant, the tire mass was also maintained. On the other hand, in Comparative Example 2, although the groove depth ratio GR was within the specified range, the void ratio VR was outside the specified range, so that the effect of improving the wear performance was insufficient. In Comparative Example 3, although the void ratio VR was within the specified range, the groove depth ratio GR was outside the specified range, so that the effect of improving the wear performance was insufficient and the wet performance was also inferior.

Although some embodiments have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and variations thereof are included in the scope of the invention described in the claims and the equivalent scope thereof, as are included in the scope and gist of the invention.

10 ... Pneumatic tire, 16 ... Tread, 16A ... Tread surface, 26 ... Belt reinforcement layer, 28 ... Main groove, 28A ... Center main groove, 28B, 28C ... Shoulder main groove, 36 ... Inner area, 38 ... Outer area, CL ... tire equatorial plane, CD ... tire circumferential direction, WD ... tire width direction, IN ... vehicle mounting inside, OUT ... vehicle mounting outside, TE ... grounding end, DG ... groove depth, DX ... tread from the outer surface of the outermost layer Distance to the surface

Claims (3)

In a pneumatic tire in which three main grooves are provided on the tread as main grooves extending in the tire circumferential direction, a center main groove and a pair of shoulder main grooves located on both sides of the center main groove in the tire width direction.
The void ratio, which is the ratio of the area of the non-grounded portion in the tread surface between the grounded ends to the area of the tread surface between the grounded ends in the tread, is 26.5% or more and 28.5% or less.
A pneumatic tire in which the groove depth of each of the three main grooves is 79% or more and 85% or less of the distance from the outer surface of the outermost layer of the plurality of reinforcing layers under the groove of each main groove to the tread surface. The pneumatic tire is specified to be mounted on a vehicle, and between the ground ends of the tread, an inner region located inside the vehicle mounting on the tire equatorial plane and an outer region located outside the vehicle mounting on the tire equatorial plane. The pneumatic tire according to claim 1, wherein the tire comprises a region and the void ratio in the outer region is smaller than the void ratio in the inner region. The pneumatic tire according to claim 2, wherein the center main groove is unevenly distributed inside the vehicle mounting on the tire equatorial plane.

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