Pneumatic tire

Abstract

To provide a pneumatic tire that easily realizes both of improvement of drainage performance and improvement of quietness.SOLUTION: A tire 1 includes a tread 10 having a ground plane 10a and one or more grooves 24. The one or more grooves 24 include one or more major grooves 24a, 24b, 24c including see-through parts 28a, 28b, 28c extending in the circumferential direction over the whole circumference in the circumferential direction. A void ratio of the tread 10 is 24% or more and 26% or less, and a see-through void ratio of the tread 10 is 20.5% or more and 21.5% or less.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to pneumatic tires.

Background Art

[0002] It is known that increasing the groove volume improves drainage performance. For example, Patent Document 1 discloses that the area ratio of the grooves is preferably 10% or more and 30% or less, and a tread pattern with an area ratio of 10% or more is disclosed to have excellent drainage performance. Further, from the viewpoint of drainage performance, it is disclosed that the area ratio is preferably 13% or more, and particularly preferably 15% or more.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Increasing the groove volume improves drainage performance. However, increasing the groove volume increases air resistance, increases vehicle exterior noise, and it is not easy to achieve both improved drainage performance and improved quietness. Therefore, an object of the present invention is to provide a pneumatic tire that can easily achieve both improved drainage performance and improved quietness.

Means for Solving the Problems

[0005] To solve the above problems, the pneumatic tire according to the present disclosure includes a tread having a ground contact surface and one or more grooves, the one or more grooves including one or more main grooves including a through-sheet portion extending in the circumferential direction over the entire circumference in the circumferential direction, the void ratio of the tread being 24% or more and 26% or less, and the through-sheet void ratio of the tread being 20.5% or more and 21.5% or less.

[0006] In the present disclosure, the void ratio of the tread is defined as (total groove area including sipes)÷(land area of the ground contact surface + total groove area including sipes) in a plan view when the entire circumference of the tread extending in the circumferential direction is unfolded in a strip shape so as to be located on a plane.

[0007] Also, in the present disclosure, the through-void ratio is defined as (area of the through-groove portion)÷(land area of the ground contact surface + total groove area including sipes) in a plan view when the entire circumference of the tread extending in the circumferential direction is unfolded in a strip shape so as to be located on a plane. Here, the through-groove portion (through portion) refers to a groove portion where no land portion exists when the circumferential groove is viewed in the tire circumferential direction. The through-groove portion (through portion) becomes zero when the circumferential groove extends in a zigzag manner or the like.

[0008] When the vehicle moves, a tire cavity resonance sound, that is, a noise whose sound pressure and frequency change depending on the width, depth, length of the longitudinal groove and the vehicle speed at the ground contact surface of the tire, is generated. According to the present disclosure, the void ratio of the tread is a value smaller than a general value. Therefore, since the groove region, which is the sound source of the cavity resonance sound, is smaller than that of a general tire, the cavity resonance sound can be reduced and the quietness can be improved.

[0009] Furthermore, since the through-void ratio of the tread is 20.5% or more and 21.5% or less, which is larger than a general value, the drainage performance is improved. Therefore, even if the void ratio of the tread is made smaller than a general value and the drainage performance is reduced, the reduction in the drainage performance can be offset by increasing the area of the through-void, and good drainage performance can be maintained. Thus, it is easy to simultaneously achieve both good drainage performance and good quietness, which are in a trade-off relationship with each other.

[0010] Also, the depth of the main groove may be 3 times or more and 3.6 times or less that of the tread wear indicator.

[0011] If the groove depth is shallow, the tire cavity resonance noise can be reduced, and the tread rubber can also be lightened, so the rolling resistance can be reduced and the fuel efficiency can be improved. However, if the groove depth is made shallow, there is a risk of deterioration in wear resistance. The inventor of the present application confirmed through tests that if the depth of the main groove is 3 times or more and 3.6 times or less that of the tread wear indicator, not only can the quietness be made good, but also the fuel efficiency can be improved, and moreover, the tire life is at a level without problems. Therefore, according to this configuration, not only can the quietness be made good, but also the fuel efficiency can be improved, and moreover, it is easy to achieve a level where the tire life has no problems.

[0012] Also, the depth of the main groove may be 3 times or more and 3.3 times or less that of the tread wear indicator.

[0013] According to this configuration, both quietness and life can be made good, and the fuel efficiency can also be reduced.

[0014] Also, the lateral rigidity may be 47% or more and 49% or less of the longitudinal rigidity.

[0015] The inventor of the present application confirmed through tests that when the lateral rigidity is 47% or more of the longitudinal rigidity, the side vibrations generated in the sidewall etc. can be effectively suppressed, and the quietness can be made excellent. Furthermore, the inventor of the present application confirmed by riding that if the lateral rigidity is increased too much, there is a risk of deterioration in ride comfort, but if the lateral rigidity is 49% or less of the longitudinal rigidity, it is difficult to confirm the influence on ride comfort. Therefore, according to this configuration, it is easy to realize a tire with excellent quietness and no problems in ride comfort.

[0016] In addition, three of the main grooves are provided in the tread, and are provided on the first side in the width direction rather than on the first side main groove provided at the end on the first side in the width direction among the three main grooves, and one or more first side sipes including an extending component in the width direction; and one or more second side sipes including an extending component in the width direction, which are provided on the second side in the width direction rather than on the second side main groove provided at the end on the second side in the width direction among the three main grooves, and all of the one or more first side sipes are arranged at intervals from the first side main groove, and all of the one or more second side sipes may be arranged at intervals from the second side main groove.

[0017] According to this configuration, there are no sipes communicating with the first side main groove and the second side main groove from the outside in the width direction. Therefore, pitch noise, that is, an annoying single-frequency noise generated when the circumferential intervals, that is, pitches, of the lateral grooves are arranged at equal intervals, can be reduced, and quietness can be further improved.

Advantages of the Invention

[0018] According to the pneumatic tire according to the present disclosure, it is easy to achieve both improvement in drainage performance and improvement in quietness.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0020] Hereinafter, embodiments according to the present disclosure will be described in detail with reference to the accompanying drawings. In the following, when a plurality of embodiments, modification examples, etc. are included, it is initially assumed that new embodiments can be constructed by appropriately combining their characteristic parts. Also, among the plurality of drawings, schematic diagrams are included, and the dimensional ratios such as vertical, horizontal, and height of each member between different drawings do not necessarily match.

[0021] In the present disclosure, the void ratio of the tread is defined as (total groove area including sipes)÷(groove area of the grounding surface + total groove area including sipes) in a plan view when the entire circumference of the tread extending in the circumferential direction is developed in a strip shape so as to be located on a plane. Also, the through-void ratio is defined as (area of the penetrating groove portion)÷(land area of the grounding surface + total groove area including sipes) in a plan view when the entire circumference of the tread extending in the circumferential direction is developed in a strip shape so as to be located on a plane. Here, the penetrating groove portion, that is, the through portion, is a groove portion where no land portion exists when the circumferential groove is viewed in the tire circumferential direction. The penetrating groove portion becomes zero when the circumferential groove extends in a zigzag shape or the like.

[0022] The longitudinal stiffness is obtained by measuring the longitudinal deflection amounts when loads of 110% and 90% of the reference load (480 kgf) are applied to the tire using a compression tester, taking the average value of the two as the longitudinal deflection amount, and dividing the reference load value by the longitudinal deflection amount. Also, the lateral stiffness is obtained by measuring the lateral deflection amount when a lateral force of 30% of the reference load is further applied to the tire while the reference load is applied to the tire, and dividing the value of the lateral force by the lateral deflection amount. Also, a sipe is a groove provided on the grounding surface and having a groove width of 1 mm or less.

[0023] In the following description, the width direction is the width direction of the pneumatic tire 1, the radial direction is the radial direction of the pneumatic tire 1, and the circumferential direction is the circumferential direction of the pneumatic tire 1. Also, among the components described below, components not described in the independent claims indicating the top-level concept are arbitrary components and not essential components. Further, the present disclosure is not limited to the following embodiments and their modifications, and various improvements and changes can be made within the scope of the matters described in the claims of the present application and their equivalent scope.

[0024] FIG. 1 is a 1 / 4 cross-sectional view including the width direction and the radial direction in the pneumatic tire 1 according to an embodiment of the present disclosure, and is a cross-sectional view on one side in the width direction and one side in the radial direction. As shown in FIG. 1, the pneumatic tire (hereinafter simply referred to as the tire) 1 includes a tread 10, a pair of shoulders 11, a pair of sidewalls 12, and a pair of beads 13.

[0025] The tread 10 is disposed at the center in the width direction and includes a ground contact surface 10a that contacts the road surface. The tread 10 includes, for example, the central portion in the width direction of the tread rubber 36 made of crosslinked rubber or the like. One or more grooves 24 are provided on the outer peripheral surface of the tread 10. The one or more grooves 24 serve to drain rainwater that has entered between the road surface and the tire 1 and ensure the ground contact area between the road surface and the tire 1.

[0026] The shoulders 11, the sidewalls 12, and the beads 13 are portions that form the side surface of the tire 1 and are provided on both sides in the width direction of the tire 1. The shoulders 11, the sidewalls 12, and the beads 13 extend radially inward from both ends in the width direction of the tread 10. The ground contact end E of the tire 1 may be defined as the boundary position between the tread 10 and the shoulder 11. The ground contact end E is both ends in the width direction of the portion that contacts the ground when the tire 1 is mounted on a regular rim, the internal pressure is adjusted to the regular internal pressure, and the regular load is applied. The regular rim and the like are defined in the same manner as the definition described in JP-A-2020-131965.

[0027] The shoulder 11 includes the outer end 36a in the width direction of the tread rubber 36. The shoulder 11 is the shoulder portion of the tire 1, which projects outward in the width direction from both ends in the width direction of the tread 10 and extends radially inward. The shoulder 11 is a portion that curves from the ground contact end E to the radially outer end of the sidewall 12 of the tire. The shoulder 11 is provided annularly along the circumferential direction, similar to the tread 10.

[0028] The sidewall 12 is a rubber layer between the shoulder 11 and the bead 13, and is the portion with the largest bending in the tire 1. The sidewall 12 extends radially inward from the shoulder 11 and is provided annularly along the circumferential direction. The sidewall 12 includes the portion that projects most outward in the width direction of the tire 1 and gently curves so as to be convex toward the outside.

[0029] The sidewall 12 protects the carcass 15 and plays a role in preventing its elongation. The sidewall 12 includes the outer portion in the width direction of the sidewall rubber 21 disposed on the radially outer side of the carcass 15 in the tire width direction. The sidewall rubber 21 is the portion that bends the most when the tire 1 functions as a cushion, and is usually composed of a flexible rubber having fatigue resistance. The radially outer end 21a of the sidewall rubber 21 is included in the shoulder 11. The tire 1 may have an annular rib on the side, and in that case, the annular rib may be defined as the boundary between the shoulder and the sidewall.

[0030] The bead 13 extends radially inward from the sidewall 12 and is formed annularly along the circumferential direction. The bead 13 is the portion fixed to the rim of the wheel and constitutes the inner peripheral portion of the tire 1. The bead 13 gently curves so as to be convex toward the inside and is located more inward in the width direction than the sidewall 12.

[0031] The bead 13 is surrounded by a rim strip rubber 19 with the carcass 15 interposed therebetween. The rim strip rubber 19 is disposed on the inner side in the tire radial direction of the tire 1 in such a manner that it wraps around from the inner side in the tire width direction of the bead 13 through the inner end in the tire radial direction to the outer side in the tire width direction. The rim strip rubber 19 contacts the inner surface of the rim on which the tire 1 is mounted. A rim line along the tire circumferential direction is provided on the outer surface on the outer side in the tire width direction of the rim strip rubber 19.

[0032] The bead 13 includes a bead core 26 and a bead filler 27. The bead core 26 and the bead filler 27 are provided on both sides in the width direction. The bead core 26 is a ring-shaped member in which bundled steel wires are coated with rubber. The bead core 26 is a member that serves to fix the air-filled tire 1 to the rim.

[0033] The bead filler 27 is disposed on the outer side in the radial direction than the bead core 26. The bead filler 27 has a tapered shape in which the thickness decreases as it extends from the inner side in the tire radial direction to the outer side in the tire radial direction. The bead filler 27 is provided to increase the rigidity of the peripheral portion of the bead 13 and ensure high maneuverability and stability. The bead filler 27 is composed of, for example, rubber having a higher hardness than the surrounding rubber members.

[0034] The tire 1 includes a carcass 15, a belt 16, a belt reinforcing member 17, and an inner liner 18. The carcass 15 is a cord layer coated with rubber. The carcass 15 includes carcass plies and forms a tire skeleton that withstands loads, impacts, air pressure, etc. The carcass 15 has a radial structure in which carcass cords extending in a direction orthogonal to the circumferential direction are arranged. The rubber layer that covers and protects the carcass 15 is generally composed of a plurality of rubber materials such as tread rubber 36 and sidewall rubber 21.

[0035] The carcass ply constituting the carcass 15 is spanned from the inner side in the width direction to the bead core 26 and folded back toward the sidewall 12 so as to wrap the bead core 26 and the bead filler 27. In the example shown in FIG. 1, the ply end 15E which is the end of the carcass ply is located on the sidewall 12. When the carcass 15 includes two carcass plies, generally, the ply end of the other carcass ply is located on the bead 13.

[0036] The belt 16 is disposed between the tread 10 and the carcass 15. The belt 16 is installed over the entire area where the belt 16 radially overlaps the tread 10 and a partial area of the shoulder 11 in the width direction. The belt 16 is a circumferentially tensioned reinforcing belt that tightly clamps the carcass 15 to increase the rigidity of the tread 10. The belt 16 is composed of, for example, a steel belt including steel cords and has a two-layer structure, and includes two steel belts 16a and 16b. However, the number of belts to be laminated is not limited to two, and instead of a steel belt, a belt including a tire cord using aramid fibers or the like may be used. Or, the belt may be composed of only one layer. By providing the belt 16, the rigidity of the tire 1 can be ensured and the grounding state between the tread 10 and the road surface can be made good.

[0037] The belt reinforcement 17 is disposed between the belt 16 and the tread 10. The belt reinforcement 17 has, for example, a two-layer structure and includes two cap plies 17a and 17b. The cap plies 17a and 17b are composed of, for example, an insulating organic fiber layer such as polyamide fiber and are covered with topping rubber. The belt reinforcement 17 is installed for purposes such as improving durability and reducing road noise during driving. Note that the number of cap plies to be laminated is not limited to two. The belt reinforcement 17 is disposed over the entire area where the belt reinforcement 17 radially overlaps the tread 10 and a partial area of the shoulder 11 in the width direction. The outer end 22 of the belt reinforcement 17 in the width direction extends outward in the width direction from the belt 16.

[0038] The inner liner 18 is a rubber layer for retaining air pressure and is attached to the inner surface of the carcass 15 between a pair of beads 13 on both sides in the width direction. The inner liner 18 is made of, for example, air permeation resistant rubber to prevent the air in the tire inner cavity from leaking to the outside. In the present embodiment, the inner liner 18 has a two-layer structure in which a first inner liner 18a and a second inner liner 18b are overlapped, and the first inner liner 18a is disposed on the tire inner cavity side of the second inner liner 18b. The inner liner 18 may be composed of a single layer.

[0039] The center portions in the width direction of the belt 16 and the belt reinforcing material 17 are included in the tread 10, and the outer end portions in the width direction of the belt 16 and the belt reinforcing material 17 are included in the shoulder 11. By appropriately selecting the materials constituting the above-described respective members, particularly by appropriately selecting the materials of the tread rubber 36, the sidewall rubber 21, the rim strip rubber 19, and the bead filler 27, the longitudinal rigidity and the lateral rigidity of the tire 1 can be easily adjusted. In the present embodiment, the lateral rigidity of the tire 1 is 47% or more and 49% or less of the longitudinal rigidity of the tire 1. Note that the lateral rigidity of the tire 1 may be less than 47% of the longitudinal rigidity of the tire 1 or may be greater than 49%.

[0040] FIG. 2 is a schematic front view when the tire 1 is viewed from the radially outer side. As shown in FIG. 2, three main grooves 24a, 24b, 24c are provided in the tread 10 of the tire 1. Each of the main grooves 24a, 24b, 24c is provided over the entire circumference in the circumferential direction.

[0041] The center in the width direction of the center main groove 24a is located substantially on the tire equatorial plane CL. Further, each of the first side main groove 24b provided at the end on the first side in the width direction and the second side main groove 24c provided at the end on the second side in the width direction is spaced apart from the center main groove 24a in the width direction. The groove center portions located at the centers in the width direction between the first end on the first side and the second end on the second side in the width direction in each of the main grooves 24a, 24b, 24c are included in the through-slot portions 28a, 28b, 28c of each of the main grooves 24a, 24b, 24c.

[0042] The void ratio of the tread 10 is 24% or more and 26% or less, and the through-slot void ratio of the tread 10 is 20.5% or more and 21.5% or less. As will be described later, the void ratio of the tread 10 is preferably 24.5% or more and preferably 25.5% or less. Further, the depth of each of the main grooves 24a, 24b, 24c is preferably 3 times or more and 3.6 times or less of the tread wear indicator (TWI), and more preferably 3 times or more and 3.3 times or less of the tread wear indicator.

[0043] The tire 1 includes a plurality of first side transverse grooves 70a and a plurality of first side sipes 71a on the outer side in the width direction than the first side main groove 24b. Each of the first side transverse grooves 70a and the first side sipes 71a extends in a direction having a width direction component. More specifically, in the present embodiment, each of the first side transverse grooves 70a and the first side sipes 71a extends in a direction inclined at an angle of 30° or less with respect to the width direction, and has a smooth curved shape or a linear shape in a plan view shown in FIG. 2. The plurality of first side transverse grooves 70a are substantially the same, are arranged at intervals in the circumferential direction, and are arranged at substantially equal intervals in the circumferential direction. Further, the plurality of first side sipes 71a are also substantially the same, are arranged at intervals in the circumferential direction, and are arranged at substantially equal intervals in the circumferential direction.

[0044] The first side sipe 71a is arranged at intervals in the circumferential direction between two adjacent first side transverse grooves 70a with respect to the circumferential direction. The first end on the inner side in the width direction of the first side sipe 71a is located radially inward of the first end on the inner side in the width direction of the first side transverse groove 70a. Further, the second end on the outer side in the width direction of the first side sipe 71a is located radially inward of the second end on the outer side in the width direction of the first side transverse groove 70a. All of the first side sipes 71a are arranged at intervals in the first side main groove 24b.

[0045] The tire 1 includes a plurality of second side transverse grooves 70b and a plurality of second side sipes 71b on the outer side in the width direction from the second side main groove 24c. Each of the second side transverse grooves 70b and the second side sipes 71b extends in a direction having a width direction component. More specifically, in the present embodiment, each of the second side transverse grooves 70b and the second side sipes 71b extends in a direction inclined at an angle of 30° or less with respect to the width direction, and has a smooth curved shape or a linear shape in a plan view shown in FIG. 2. The plurality of second side transverse grooves 70b are substantially the same, are arranged at intervals in the circumferential direction, and are arranged at substantially equal intervals in the circumferential direction. Also, the plurality of second side sipes 71b are substantially the same, are arranged at intervals in the circumferential direction, and are arranged at substantially equal intervals in the circumferential direction.

[0046] The second side sipes 71b are arranged at intervals in the circumferential direction between two adjacent second side transverse grooves 70b with respect to the circumferential direction, and are arranged at intervals in the circumferential direction on both of the two second side transverse grooves 70b. The first end on the inner side in the width direction of the second side sipes 71b is located on the inner side in the radial direction than the first end on the inner side in the width direction of the second side transverse grooves 70b. Also, the second end on the outer side in the width direction of the second side sipes 71b is located on the inner side in the radial direction than the second end on the outer side in the width direction of the second side transverse grooves 70b. All of the second side sipes 71b are arranged at intervals from the second side main groove 24c.

[0047] Next, the operation and effect of the tire 1 of the present disclosure will be described. The inventor of the present application has experimentally investigated the relationship between the void ratio, the through void ratio, and the lateral rigidity / longitudinal rigidity of the tread and the vehicle exterior noise, and has also experimentally investigated the relationship between the void ratio, the through void ratio, and the lateral rigidity / longitudinal rigidity of the tread and the drainage performance. Part of the test results are shown in Table 1.

[0048] Furthermore, the inventor of the present application has experimentally investigated the relationship between the groove depth of the main groove extending in the circumferential direction and the vehicle exterior noise, and has also experimentally investigated the relationship between the groove depth of the main groove extending in the circumferential direction and the wear resistance. Part of the test results are shown in Table 2. In each test, the reference shows the test results in an existing tire.

[0049]

Table 1

Table 2

[0050] (Method for Evaluating Exterior Noise) The exterior noise was measured with a noise meter attached to the outer surface of the vehicle body for the noise level radiated from the tire during the coasting running of the vehicle. The engine was turned off, the vehicle speed was set to 50 km / h, the air pressures of the front and rear wheels were set to 240 kPa, the load acting on the front wheels was 655 kgf, and the load acting on the rear wheels was 440 kgf. The exterior noise was measured under these conditions. By conducting the test with the engine turned off, the noise from the engine is not measured, and the evaluation of the exterior noise can be performed with high accuracy. The exterior noise was evaluated as the increase or decrease value with respect to the exterior noise of the reference (existing single tire).

[0051] (Method for Evaluating Drainage Performance) With the front and rear wheels mounted on the vehicle, each tire was rotated on a wet road surface with a water depth of 8 mm, and the speed at which the hydroplaning phenomenon occurred was measured. The drainage performance evaluation test was conducted under the conditions that the air pressures of the front and rear wheels were 240 kPa, the load acting on the front wheels was 690 kg, and the load acting on the rear wheels was 470 kgf. The drainage performance was evaluated as a relative value when the drainage performance of the reference (existing single tire) was set to 100.

[0052] Regarding the tire drainage performance, if the drainage performance is poor, the removal of water from within the contact surface with the road surface during running becomes insufficient, and the remaining water forms a water film between the road surface and the tread surface, resulting in the loss of ground contact with the road surface and causing the hydroplaning phenomenon. Therefore, as an index of drainage performance, the speed at which the hydroplaning phenomenon occurs was measured, and the slower the speed, the easier the hydroplaning phenomenon occurs, that is, the lower the drainage performance was evaluated.

[0053] (Method for Evaluating Abrasion Resistance) With the front and rear wheels mounted on the vehicle, the wear resistance was simulated and evaluated by the method of obtaining the running distance D (mm) until the tread contact surface wears by 1 mm in thickness from the following formula (1). For wear resistance, those with a larger D (mm) were evaluated as better. The simulation of wear resistance evaluation was carried out under the conditions that the air pressures of the front and rear wheels were 240 kPa, the load acting on the front wheel was 690 kg, and the load acting on the rear wheel was 470 kgf. Wear resistance was evaluated as a relative value when the wear resistance of the reference (existing one tire) was set to 100. In formula (1), D is the running distance, and Ceave is the average wear amount of the main groove. D (mm) = D / Ceave ··· (1)

[0054] [Consideration on Test Results] As shown in Table 1, as the void ratio was decreased, the quietness improved while the drainage performance decreased. However, as shown in the vehicle exterior noise evaluation and the drainage performance evaluation in the reference and Test 1, when the void ratio was decreased and at the same time the through-void ratio was increased, the quietness improved while the drainage performance did not decrease. That is, it was found that when the void ratio was decreased and at the same time the through-void ratio was increased, not only the effect of reducing the vehicle exterior noise could be promoted, but also the drainage performance could be brought to a level without problems.

[0055] The inventor of the present application found through a number of tests that when the void ratio of the tread is set to 24% or more and 26% or less and at the same time the through-void ratio of the tread is set to 20.5% or more and 21.5% or less, the vehicle exterior noise can be effectively reduced and the drainage performance can also be at a level without problems. In particular, when the void ratio of the tread is set to 24.5% or more and 25.5% or less and at the same time the through-void ratio of the tread is set to 20.5% or more and 21.5% or less, it was found that both the quietness and the drainage performance can be made good regardless of other factors such as the value of lateral rigidity / longitudinal rigidity [ % ].

[0056] Furthermore, as shown in Table 1, it has been confirmed that vehicle exterior noise can be effectively reduced when the lateral rigidity / longitudinal rigidity [%] is in the range of 48% or more and 52% or less. However, when the lateral rigidity / longitudinal rigidity [%] exceeds 49%, it becomes easier to significantly feel the shaking of the vehicle body based on the road surface condition, and it is easier to feel that the ride comfort has deteriorated. On the other hand, through a number of tests, it was confirmed that if the lateral rigidity / longitudinal rigidity [%] is in the range of 47% or more and 49% or less, not only can good quietness be achieved, but the ride comfort is also likely to be good. Furthermore, if the lateral rigidity / longitudinal rigidity [%] is in the range of 47.5% or more and 48.5% or less, not only can good quietness be achieved, but excellent ride comfort can also be realized.

[0057] As shown in Table 2, while the vehicle exterior noise decreases as the depth of the main groove becomes shallower, the wear resistance decreases. On the other hand, if the depth of the main groove is made shallower while maintaining the rubber thickness at the bottom of the groove, the volume of the entire tread rubber 36 becomes smaller. Therefore, since the tire 1 can be lightened, the rolling resistance becomes smaller and the fuel consumption can be reduced.

[0058] In the test results shown in Table 2, it was confirmed that if the depth of the main groove is 3.5 times the TWI (Tread Wear Indicator), the vehicle exterior noise can be reduced by 0.4 dB compared to the reference (the vehicle exterior noise of an existing single tire). When the depth of the main groove is made shallower to 3.0 times the TWI, the vehicle exterior noise can be significantly reduced by 1.1 dB compared to the reference, and it has been confirmed that a tire with extremely excellent quietness can be realized.

[0059] On the other hand, if the depth of the main groove is further made shallower to 2.7 times the TWI, the vehicle exterior noise can be further reduced, but the wear resistance becomes 90% or less of the reference, and the tire life deteriorates to a level that is not suitable as a product. Considering these viewpoints comprehensively, if the depth of the main groove is in the range of 3.0 times or more and 3.6 times or less of the TWI, a tire with excellent quietness, easy to achieve high fuel efficiency, and no problem with wear resistance can be realized.

[0060] In addition, when the depth of the main groove is set to be 3.0 times or more and 3.5 times or less the TWI, a tire with even better quietness and easier to achieve high fuel efficiency can be realized. When the depth of the main groove is set to be 3.0 times or more and 3.3 times or less the TWI, a tire that is particularly quiet, quiet, and easy to achieve high fuel efficiency can be realized. Further, when the depth of the main groove is set to be 3.5 times or more and 3.2 times or less the TWI, a tire with excellent quietness, easy to achieve high fuel efficiency, and good wear resistance can be realized. When the depth of the main groove is set to be 3.4 times or more and 3.2 times or less the TWI, a tire with even better quietness, better fuel efficiency, and good wear resistance can be realized.

[0061] [Essential configurations and preferred configurations of the present disclosure, and their functions and effects] The tire 1 according to the present disclosure includes a tread 10 having a ground contact surface 10a and one or more grooves 24. Further, the one or more grooves 24 include one or more main grooves 24a, 24b, 24c including through-sheath portions 28a, 28b, 28c extending in the circumferential direction over the entire circumference in the circumferential direction. And the void ratio of the tread 10 is 24% or more and 26% or less, and the through-sheath void ratio of the tread 10 is 20.5% or more and 21.5% or less.

[0062] According to the present disclosure, the void ratio of the tread 10 is smaller than a general value. Therefore, since the groove region, which is the sound source of the air column resonance sound, is smaller compared to a general tire, the air column resonance sound can be reduced and the quietness can be improved.

[0063] Furthermore, since the through-sheath void ratio of the tread is 20.5% or more and 21.5% or more, which is larger than a general value, the drainage performance is improved. Therefore, even if the void ratio of the tread is made smaller than a general value and the drainage performance is reduced, the reduction in the drainage performance can be offset by increasing the area of the through-sheath void, and good drainage performance can be maintained. Thus, it is easy to simultaneously realize both good drainage performance and good quietness, which are in a trade-off relationship with each other.

[0064] Further, the depth of the main grooves 24a, 24b, and 24c may be 3 times or more and 3.6 times or less that of the tread wear indicator.

[0065] According to this configuration, not only can the quietness be improved, but also the fuel efficiency can be enhanced, and moreover, the tire life can be easily maintained at a satisfactory level.

[0066] Further, the depth of the main grooves 24a, 24b, and 24c may be 3 times or more and 3.3 times or less that of the tread wear indicator.

[0067] According to this configuration, both the quietness and the life can be improved, and the fuel efficiency can also be reduced.

[0068] Further, the lateral rigidity may be 47% or more and 49% or less of the longitudinal rigidity.

[0069] According to this configuration, excellent quietness can be achieved, and it is easy to realize a tire with good ride comfort.

[0070] Further, three main grooves 24a, 24b, and 24c may be provided in the tread 10. Also, the tire 1 is provided on the first side in the width direction with respect to the first side main groove 24b provided at the end on the first side in the width direction among the three main grooves 24a, 24b, and 24c, and includes one or more first side sipes 71a including an extending component in the width direction. And the tire 1 is provided on the second side in the width direction with respect to the second side main groove 24c provided at the end on the second side in the width direction among the three main grooves 24a, 24b, and 24c, and may have one or more second side sipes 71b including an extending component in the width direction. And all of the one or more first side sipes 71a may be arranged at intervals from the first side main groove 24b, and all of the one or more second side sipes 71b may be arranged at intervals from the second side main groove 24c.

[0071] According to this configuration, there are no sipes communicating with the first side main groove 24b and the second side main groove 24c from the outside in the width direction. Therefore, pitch noise, that is, the annoying single-frequency noise generated when the circumferential intervals, that is, the pitches, of the lateral grooves 70a and 70b are arranged at equal intervals, can be reduced, and the quietness can be further improved.

Description of Symbols

[0072] 1 Tire, 10 Tread, 10a Ground Contact Surface, 11 Shoulder, 12 Sidewall, 13 Bead, 15 Carcass, 15E Ply End, 16 Belt, 16a, 16b Steel Belt, 17 Belt Reinforcement, 17a, 17b Cap Ply, 18 Inner Liner, 18a First Inner Liner, 18b Second Inner Liner, 19 Rim Strip Rubber, 21 Sidewall Rubber, 21a Radially Outer End of Sidewall Rubber, 22 Widthwise Outer End of Belt Reinforcement, 24 Groove, 24a Central Main Groove, 24b First Side Main Groove, 24c Second Side Main Groove, 26 Bead Core, 27 Bead Filler, 28a, 28b, 28c Through-Sheet Portion, 36 Tread Rubber, 36a Widthwise Outer End of Tread Rubber, 70a First Side Transverse Groove, 70b Second Side Transverse Groove, 71a First Side Sipe, 71b Second Side Sipe, CL Tire Equator Plane, E Ground Contact End.

Claims

Claim 1 A pneumatic tire comprising a ground contact surface and a tread having one or more grooves, wherein the one or more grooves include one or more main grooves each including a through-sheath portion extending in the circumferential direction over the entire circumference in the circumferential direction, the void ratio of the tread is 24% or more and 26% or less, and the through-sheath void ratio of the tread is 20.5% or more and 21.5% or less. Pneumatic tire. Claim 2 The pneumatic tire according to claim 1, wherein the depth of the main groove is 3 times or more and 3.6 times or less the tread wear indicator. Claim 3 The pneumatic tire according to claim 2, wherein the depth of the main groove is 3 times or more and 3.3 times or less the tread wear indicator. Claim 4 The pneumatic tire according to any one of claims 1 to 3, wherein the lateral rigidity is 47% or more and 49% or less the longitudinal rigidity. Claim 5 Three of the main grooves are provided in the tread, one or more first side sipes provided on the first side in the width direction and including an extending component in the width direction, on the first side in the width direction relative to a first side main groove provided at an end on the first side in the width direction among the three main grooves, and one or more second side sipes provided on the second side in the width direction and including an extending component in the width direction, on the second side in the width direction relative to a second side main groove provided at an end on the second side in the width direction among the three main grooves, all of the one or more first side sipes are arranged at intervals from the first side main groove, and all of the one or more second side sipes are arranged at intervals from the second side main groove. The pneumatic tire according to any one of claims 1 to 3.

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