Pneumatic tire

Abstract

A pneumatic tire (1) has a tread (2) designated with respect to an assembly direction of a vehicle. The tread (2) has a central main groove (10), a plurality of V-shaped grooves (20) formed in the tire circumferential direction between the central main groove (10) and a ground end (E), and a middle rib (7) sandwiched by the central main groove (10) and the V-shaped grooves (20) and extending in the tire circumferential direction. The V-shaped groove (20) is composed of a longitudinal groove (21) and a lateral groove (22). In the pneumatic tire (1), the longitudinal groove (21) is connected to the lateral groove (22) of the other V-shaped groove (20) adjacent in the tire circumferential direction, whereby the plurality of V-shaped grooves (20) are communicated in the tire circumferential direction.

Description

Technical Field

[0001] The present invention relates to a pneumatic tire, and more specifically to a pneumatic tire whose mounting direction relative to a vehicle is specified. Background Technology

[0002] Previously, it was widely known that pneumatic tires with a directional tread pattern, which gave the grooves directionality and improved drainage, were available. For example, Patent Document 1 discloses a pneumatic tire with a directional tread pattern, suitable for racing in wet conditions at high speeds. The tire of Patent Document 1 has multiple main grooves extending along the tire circumference. By modifying the shape of the connecting portion of the serrated middle main groove and the middle transverse groove connected thereto, wet grip performance is maintained and handling stability is improved.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2017-121846 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] However, in high-performance rain tires, a crucial issue is achieving a high level of preheating performance that allows for rapid temperature rise of the tread while maintaining good hydroplaning resistance. It should be noted that conventional tires, including the one described in Patent Document 1, suffer from shortcomings in various performance aspects, resulting in issues such as poor road contact and low handling stability.

[0008] Methods for solving problems

[0009] One aspect of the present invention provides a pneumatic tire having a tread, specified relative to the vehicle's mounting direction, characterized in that the tread has: a central main groove extending circumferentially along the tire; multiple V-grooves formed circumferentially between the central main groove and the ground contact end of the tread; and a central rib sandwiched between the central main groove and the V-grooves, extending circumferentially along the tire, the V-grooves being composed of longitudinal grooves and transverse grooves, the longitudinal grooves extending circumferentially along the tire, the transverse grooves being inclined axially towards the tire than the longitudinal grooves and extending from a first connection portion with the longitudinal groove containing the apex of the V-shape to a position beyond the ground contact end, the longitudinal grooves connecting with the transverse grooves of other adjacent V-grooves in the tire circumferential direction to form a second connection portion, thereby connecting the multiple V-grooves circumferentially.

[0010] Another aspect of the invention provides a pneumatic tire with a tread. The pneumatic tire, with its mounting direction relative to the vehicle specified, is characterized in that, when the tread is divided into three equal parts from the equator to the ground contact point, each region is sequentially defined from the equator side as a central region, an intermediate region, and a shoulder region, the tread has: a circumferential groove formed in the central region and extending circumferentially along the tire; and a plurality of lateral grooves extending axially along the tire, at least from the intermediate region to a position beyond the ground contact point, wherein the void ratio in each of the central region and the intermediate region is at least 1.50 times the void ratio in the shoulder region.

[0011] Invention Effects

[0012] The pneumatic tire of the present invention can achieve a high degree of balance between excellent warming-up performance and anti-slip performance. Attached Figure Description

[0013] Figure 1 This is a perspective view of an inflatable tire as an example of an implementation method.

[0014] Figure 2 This is a perspective view of an inflatable tire as an example of an implementation method.

[0015] Figure 3 This is a top view of an inflatable tire as an example of an implementation method.

[0016] Figure 4 yes Figure 3 Enlarged view of part A in the image.

[0017] Figure 5 Is Figure 3 The sectional perspective view is obtained by cutting the tire along the BB line.

[0018] Figure 6 yes Figure 3 The enlarged view of part A in the diagram is a simplified representation of the groove shape.

[0019] Figure 7 This is a top view of the tread pattern of the pneumatic tire used in the comparative example.

[0020] Explanation of reference numerals in the attached figures:

[0021] 1 Pneumatic tire, 2 Tread, 3 Sidewall, 4 Bead, 5 Central rib, 6 Outer land, 7 Middle rib, 7a Minimum section, 7b Maximum section, 7c Widened section, 8 Shoulder tread block, 10 Central main groove, 11 Sipe, 20 V-groove, 21 Longitudinal groove, 22 Transverse groove, 22a Bend, 22b First section, 22c Second section, 23 First connecting section, 24 Second connecting section, 30 Second transverse groove, 31 Bend, 32 Conical section, CL Equator, E Ground contact end, Ce Central area, Me Intermediate area, Sh Shoulder area. Detailed Implementation

[0022] Hereinafter, an example embodiment of the pneumatic tire of the present invention will be described in detail with reference to the accompanying drawings. The embodiment described below is merely an example, and the present invention is not limited to the following embodiment. Furthermore, arrangements obtained by selectively combining the constituent elements of the embodiment described below are included in the present invention.

[0023] Figure 1 and Figure 2 This is a perspective view of an inflatable tire 1 as an example of an implementation method. Figure 3 This is a top view of pneumatic tire 1. Figures 1-3 As shown, the pneumatic tire 1 has a tread 2, which is the part in contact with the road surface. The tread 2 has a central main groove 10 extending along the tire circumference and a V-groove 20 formed in a V-shape when viewed from above. The central main groove 10 and the V-groove 20 improve the water drainage performance of the central region Ce and the intermediate region Me of the tread 2, which have a significant impact on the braking performance of the pneumatic tire 1, thereby improving its anti-slip performance. The void ratio in the central region Ce and the intermediate region Me of the tread 2 is more than 1.50 times that in the shoulder region Sh, as detailed later. As a result, handling stability on wet and slippery roads is improved.

[0024] The pneumatic tire 1 is a tire with a directional tread pattern that directs the grooves and is specified relative to the vehicle's mounting direction. The pneumatic tire 1 has a tread pattern (directional tread pattern) that is symmetrical about the equator CL. The equator CL is an imaginary line passing through the center of the tire's axial direction along the tire's circumference. The pneumatic tire 1 is a high-performance tire that balances excellent warm-up performance and anti-slip performance, providing good road contact (follow-the-road) contact and achieving excellent handling stability on wet surfaces. The pneumatic tire 1 is, for example, suitable for racing rain tires.

[0025] The tread 2 has two central main grooves 10 and a central rib 5 formed on the equator CL, sandwiched between the central main grooves 10. The central main grooves 10 are circumferential grooves extending parallel to each other along the tire circumference and are formed with the same width. The central rib 5 is a rib-shaped tread block divided by the two central main grooves 10, extending with a constant width along the tire circumference. The central main grooves 10 and the central rib 5 are preferably formed in a continuous ring shape along the tire circumference.

[0026] The tread 2 has outer land portions 6 separated from the central rib 5 by a central main groove 10. The outer land portions 6 are tread blocks wider than the central rib 5, and are disposed on the left and right sides of the tread 2. The tread 2 has a directional tread pattern arranged sequentially from the first contact end E side towards the second contact end E side, consisting of the first outer land portion 6, the first central main groove 10, the central rib 5, the second central main groove 10, and the second outer land portion 6. The first and second outer land portions 6 have the same width.

[0027] In this specification, the tread blocks 2 refer to the protrusions that project radially outwards from the tire, sometimes referred to as land sections in the tire industry. It should be noted that tread blocks that form a continuous ring shape along the tire's circumference are generally called ribs. Furthermore, the contact patch E is defined as the area (ground surface) of the tire that contacts a flat road surface when an unused pneumatic tire 1 is fitted onto a standard rim and inflated with air at standard internal pressure, and a specified load is applied. In the case of passenger car tires, the specified load is equivalent to 88% of the standard load.

[0028] Here, "standard rim" refers to the rim specified according to tire standards. For JATMA, it's "standard rim"; for TRA and ETRTO, it's "measuring rim". "Standard internal pressure" is "maximum air pressure" for JATMA, the maximum value recorded in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" for TRA, and "INFLATION PRESSURE" for ETRTO. For passenger car tires, the standard internal pressure is typically 180 kPa, but for tires listed as ExtraLoad or Reinforced, it's set to 220 kPa. "Standard load" is "maximum load capacity" for JATMA, the maximum value recorded in the table "TIRE LOAD LIMITS ATVARIOUS COLD INFLATION PRESSURES" for TRA, and "LOADCAPACITY" for ETRTO.

[0029] The pneumatic tire 1 includes a pair of sidewalls 3 and a pair of bead 4 that bulge outwards along the tire axial direction. The sidewalls 3 extend radially inwards from both ends of the tread 2, forming the sidewalls of the pneumatic tire 1. The boundary position between the tread 2 and the sidewalls 3 does not need to be particularly defined, but in this embodiment, for ease of explanation, the position of the outer end of the groove extending along the tire axial direction is defined as the boundary position between the tread 2 and the sidewalls 3. The bead 4 is the portion fixed to the rim of the wheel.

[0030] A pneumatic tire 1, for example, comprises a carcass, a belt layer, and a crown belt layer. The carcass is a layer of cords covered with rubber, forming the tire's skeleton that withstands loads, impacts, air pressure, etc. The carcass consists of two layers of carcass plies and has a radial structure in which the carcass cords are arranged in a direction orthogonal to the tire's circumference. An airtight layer, a rubber layer for maintaining air pressure, is usually provided on the inner side of the carcass. The belt layer is a reinforcing belt positioned between the rubber constituting the tread 2 and the carcass.

[0031] The pneumatic tire 1 is a tire whose assembly direction relative to the vehicle is specified; in other words, its main rotation direction is specified. Therefore, it can also have a display for indicating the main rotation direction. The display for indicating the main rotation direction can be text, markings, illustrations, etc., indicating the main rotation direction, the inside and outside of the tire, etc., and its structure is not particularly limited. The tire sidewall 3 may have a display called a sequence containing information such as size code, manufacturing date, and manufacturing location, but the sequence can also be used as a display for indicating the tire's assembly direction relative to the vehicle.

[0032] As described above, the tread 2 has two central main grooves 10, multiple V-grooves 20, and tread blocks (central ribs 5 and outer landmasses 6) separated by the central main grooves 10. Multiple V-grooves 20 are formed between the central main grooves 10 and the contact patch end E of the tread 2, i.e., on the outer landmasses 6, along the tire circumference. The tread 2 also has an intermediate rib 7, sandwiched between the central main grooves 10 and the V-grooves 20 and extending along the tire circumference. The intermediate rib 7 is a rib-shaped tread block divided by the central main grooves 10 and the V-grooves 20, extending along the tire circumference in the same manner as the central rib 5. It should be noted that the intermediate rib 7 forms part of the outer landmasses 6.

[0033] The central rib 5 and intermediate ribs 7 exhibit good road surface following and are easily movable, generating heat rapidly, thus greatly contributing to improved preheating performance. As a result, the pneumatic tire 1 achieves excellent handling stability even in the initial stages of driving. Furthermore, the tread 2 preferably has multiple sipes 11 formed at intervals along the tire circumference and traversing the central rib 5. Forming sipes 11 in the central rib 5 appropriately reduces the rib's rigidity, making it easier for the rib to move, and further enhancing the preheating performance. The intermediate ribs 7 have a shape where the width varies along the tire circumference, with alternating sections of decreasing width and increasing width. The intermediate ribs 7, particularly in the sections with decreasing width, have appropriately reduced rigidity, thus moving and generating heat as easily as the central rib 5.

[0034] The shape of the width variation of the intermediate rib 7 is caused by the shape of the V-groove 20, which will be described in detail later. The V-groove 20 is composed of a longitudinal groove 21 extending along the tire circumference and a transverse groove 22 that is inclined axially towards the tire than the longitudinal groove 21 and extends from a first connecting portion 23 containing the apex of the V to a position beyond the ground contact end E. Furthermore, the longitudinal groove 21 connects with the transverse grooves 22 of other adjacent V-grooves 20 in the tire circumference direction to form a second connecting portion 24, thereby connecting multiple V-grooves 20 in the tire circumference direction. By connecting multiple V-grooves 20 in the tire circumference direction, the intermediate rib 7 is formed into a ring shape while varying its width in the tire circumference direction.

[0035] Multiple V-grooves 20, connected circumferentially, divide the outer land portion 6 into a central rib 7 and shoulder tread blocks 8. Each shoulder tread block 8 is divided by two V-grooves 20 and is arranged in multiples circumferentially. These shoulder tread blocks 8, arranged circumferentially, can be of the same size or arranged with a variable spacing, the variable spacing varying the size of each block in a predetermined number of units. Similarly, the multiple V-grooves 20, arranged circumferentially, can be of the same size or formed with a variable spacing, the variable spacing varying the size of the grooves in a predetermined number of units.

[0036] V-grooves 20 are formed on the first and second outer land portions 6 such that the apexes of the V-shape (the apexes of the V-grooves 20) face the same direction. The plurality of V-grooves 20 on each outer land portion 6 have, for example, the same shape and the same size. Furthermore, the apexes of two V-grooves 20 formed on the left and right sides, separated by the equator CL, are arranged along the tire axis. The V-grooves 20 formed on the first outer land portion 6 and the V-grooves 20 formed on the second outer land portion 6 have a top-view shape that is symmetrical about the equator CL. That is, if one V-groove 20 is flipped about the equator CL, it overlaps with the other V-groove 20.

[0037] The tread 2 also has a second lateral groove 30, which enters from a position further outward along the tire axial direction than the contact end E between the longitudinal groove 21 and the lateral groove 22 of the V-groove 20, and terminates without connecting with the V-groove 20. The lateral grooves 30 are formed in the shoulder tread blocks 8 at constant or variable intervals along the tire circumference. For example, the lateral grooves 30 are formed on the contact end E at positions equidistant from the lateral grooves 22 of two adjacent V-grooves 20 in the tire circumference direction. The lateral grooves 30 are discontinuous and shorter grooves in the tire circumference direction, but they supplement the drainage function of the central main groove 10 and the V-groove 20, contributing to improved anti-slip performance. Additionally, appropriately reducing the rigidity of the shoulder tread blocks 8 also contributes to improved preheating performance.

[0038] The following is further reference. Figure 4 and Figure 5 The components of the tire tread pattern are explained in detail. Figure 4 yes Figure 3 Enlarged view of part A in the image. Figure 5 Is Figure 3 The sectional perspective view is obtained by cutting the tire along the BB line.

[0039] like Figures 3-5 As shown, two central main grooves 10, one central rib 5, and two intermediate ribs 7 are formed in the central region of the tread 2. In this specification, the area of ​​the tread 2 extending from the equator CL to the ground contact point E is divided into three equal parts, defined sequentially from the equator CL side as the central region Ce, the intermediate region Me, and the shoulder region Sh. The boundaries of each region are located at... Figure 3 As shown in the diagram. Figure 3 As shown, a portion of the intermediate rib 7 extends into the intermediate region Me, and the portion of the intermediate rib 7 with a reduced width is only located in the central region Ce.

[0040] By configuring a wide central main groove 10, a central rib 5 sandwiching the central main groove 10, and an intermediate rib 7 in the central area Ce of the tread 2, continuous contact surface in the tire circumferential direction is ensured and water drainage performance is improved. As a result, good braking performance on wet and slippery roads is achieved, and excellent anti-slip performance is realized. In addition, the central rib 5 and intermediate rib 7 are easier to move and heat up quickly compared to the shoulder tread blocks 8, thus improving preheating performance.

[0041] In the intermediate region Me of the tread 2, connecting portions 23 and 24 of V-grooves 20 are provided, and the groove area of ​​the intermediate region Me is increased in the same way as in the central region Ce. On the other hand, the groove area of ​​the shoulder region Sh of the tread 2 is smaller than that of the central region Ce and the intermediate region Me. In other words, the contact area of ​​the shoulder region Sh is larger than that of the central region Ce and the intermediate region Me. In this case, it is easier to ensure high cornering performance.

[0042] The clearance ratio in the central region Ce and the intermediate region Me is preferably 45% or more and 50% or less, as detailed later. Furthermore, the clearance ratio in the shoulder region Sh is preferably 25% or more and 35% or less. Here, clearance ratio refers to the ratio of the groove area of ​​each region to the total area of ​​all regions (ground contact area + groove area). If the clearance ratio of each region is within the above range, excellent preheating performance and anti-slip performance can be achieved more effectively.

[0043] [Central Main Slot 10]

[0044] The central main groove 10 extends straight along the tire circumference and is formed in a ring shape with a constant width and depth. The two central main grooves 10 may have different widths and depths, but from the viewpoint of improving the stability of water drainage performance of the left and right tires, it is preferable that they have the same width and depth. Furthermore, the two central main grooves 10 are formed at a position equidistant from the equator CL. The interval between the two central main grooves 10, which determines the width of the central rib 5, is preferably greater than the width of the central main groove 10; as a preferred example, it is at least 1.3 times and less than 1.5 times the groove width. In this case, for example, the improvement in braking performance on wet and slippery surfaces becomes more significant.

[0045] The width of the central main groove 10 is preferably 5.0% to 8.0% of the contact patch width of the tread 2 (the length along the tire axial direction from the first contact patch end E to the second contact patch end E), more preferably 5.5% to 7.0%. If the width of the central main groove 10 is within this range, it is easier to achieve both excellent grip and drainage performance. It should be noted that the groove width refers to the groove width at the groove opening; in other words, it refers to the groove width along the contact patch surface of the tread 2. Each groove, including the central main groove 10, has its groove walls inclined such that the groove width gradually decreases from the groove opening towards the groove bottom. The depth of the central main groove 10 is, for example, 5.5 mm to 6.5 mm.

[0046] [Central Rib 5]

[0047] The central rib 5 is a rib-shaped tread block that extends straight along the tire circumference and is formed in a ring shape with a constant width. The center of the central rib 5 in the width direction is preferably located on the equator CL. That is, the central rib 5 has a top-view shape that is symmetrical about the equator CL. The width of the central rib 5 is preferably 8.0% to 12.0% of the contact patch width of the tread 2, more preferably 9.0% to 10.0%. If the width of the central rib 5 is within this range, good braking performance can be ensured, and heat generation in the central region Ce can be promoted, resulting in excellent preheating performance. It should be noted that the width of the central rib 5 is preferably 1.3 times to 1.5 times the width of the central main groove 10.

[0048] A sipe 11 is formed in the central rib 5. The tread 2 has a plurality of sipes 11 formed at intervals in the tire circumferential direction and traversing the central rib 5. The sipes 11 appropriately reduce the rigidity of the central rib 5. In other words, the sipes 11 are preferably formed with dimensions and intervals that appropriately reduce the rigidity of the central rib 5. In this specification, a sipe refers to a fine-line groove, specifically a groove with a width of less than 1.5 mm. The V-grooves 20 and the transverse grooves 30 do not close their openings even when a large load is applied to the tread blocks, but the openings of the sipes close. Therefore, even though the central rib 5 has sipes 11 that traverse the rib, it can be said to be a continuous annular tread block in the tire circumferential direction.

[0049] The sipes 11 are formed vertically along the tire axial direction and connect to the two central main grooves 10. The sipes 11 are formed at constant or variable intervals in the tire circumferential direction. The intervals between the multiple sipes 11 can be greater than the width of the central rib 5, but are preferably set to be less than the width of the central rib 5. A preferred example of the intervals between the multiple sipes 11 is 70% or more and 95% or less, or 75% or more and 90% or less, the width of the central rib 5. The width of the sipes 11 is less than 1.5 mm, more preferably 0.5 mm or more and 1.2 mm or less. The depth of the sipes 11 is preferably shallower than the depth of the central main grooves 10, for example, 50% or more and 90% or less of the depth of the central main grooves 10. By forming the sipes 11 traversing the central rib 5 with this interval and size, the central rib 5 moves more easily, promoting heat generation, and the improvement in preheating performance becomes more significant.

[0050] [V-groove 20]

[0051] In the V-groove 20, the longitudinal groove 21, which extends mainly along the tire circumference, and the transverse groove 22, which is inclined axially towards the tire than the longitudinal groove 21, intersect near the central main groove 10, thus forming a V-shape in the outer land portion 6 when viewed from above. The longitudinal groove 21 connects to the transverse grooves 22 of other V-groove 20s. Thus, multiple V-groove 20s are connected in the tire circumference, forming a central rib 7 and a shoulder tread block 8 in the outer land portion 6. The transverse groove 22 extends from the intersection with the longitudinal groove 21, i.e., the first connecting portion 23, to a position beyond the contact end E. The V-groove 20 particularly improves the drainage performance of the intermediate area Me, greatly contributing to improved anti-slip performance.

[0052] In this embodiment, multiple adjacent transverse grooves 22 in the tire circumferential direction are connected by a connecting groove, i.e., a longitudinal groove 21, extending along the tire circumferential direction. The transverse grooves 22 and the connecting grooves (longitudinal grooves 21) form a V-shaped groove when viewed from above. A large recess (gap) is formed at the intersection of the longitudinal groove 21 and the transverse groove 22 at the apex of the V-shaped groove 20, i.e., the first connecting portion 23. Therefore, more water from the road surface can enter the first connecting portion 23, and the water between the road surface and the contact surface is effectively removed via the transverse grooves 22. In addition, some of the water entering the connecting portion 23 can flow along the tire circumferential direction through the longitudinal grooves 21 and be removed via the transverse grooves 22 of other V-shaped grooves 20. Furthermore, more water from the road surface can also enter at the intersection of the longitudinal groove 21 and the transverse grooves 22 of other V-shaped grooves 20, i.e., the second connecting portion 24, and this water is removed by the transverse grooves 22.

[0053] As described above, multiple V-grooves 20 are formed on the outer left and right land portions 6, with the apexes of the V-grooves 20 facing the same direction, at constant or variable intervals in the tire circumferential direction. The first connecting portions 23 of the multiple V-grooves 20 are arranged along the tire circumferential direction. The apexes of the multiple V-grooves 20 are positioned near the central main groove 10 on the same straight line (imaginary line α) along the tire circumferential direction. The width of the intermediate rib 7 is significantly reduced at a position slightly closer to the second connecting portion 24 than the apexes of the V-grooves 20, and gradually widens along the longitudinal groove 21, as detailed later.

[0054] The longitudinal grooves 21 are inclined axially toward the tire in a manner that gradually moves away from the central main groove 10 toward the second connecting portion 24. The inclination angle θ1 of the longitudinal grooves 21 relative to the imaginary line α that passes through the apex of the V and extends along the tire circumference is preferably 10° or more and 20° or less, more preferably 12° or more and 17° or less. If the inclination angle θ1 of the longitudinal grooves 21 is within this range, for example, the intermediate rib 7 can be moved easily, and excellent drainage performance can be ensured, thus more effectively balancing preheating performance and anti-slip performance.

[0055] The structure of the V-grooves 20 will now be described, with one designated as the "first V-grooves 20" and the other as the "second V-grooves 20" for each adjacent V-groove 20 in the tire circumferential direction. The longitudinal groove 21 of the first V-grooves 20 connects to the transverse groove 22 of the second V-grooves 20, forming a second connecting portion 24, thereby connecting the first and second V-grooves 20 in the tire circumferential direction. In this embodiment, the longitudinal groove 21 of the first V-grooves 20 is connected to the portion of the second V-grooves 20 near the first connecting portion 23. That is, the distance between the first connecting portion 23 and the second connecting portion 24 is shorter than the distance between the second connecting portion 24 and the grounding end E. In this case, the second connecting portion 24, with its larger groove area, is positioned axially inside the tire, improving drainage performance.

[0056] On the other hand, a short transverse groove 22 exists between the first connecting portion 23 and the second connecting portion 24, and the longitudinal grooves 21 of the first V-groove 20 and the second V-groove 20 are not on the same straight line. That is, each longitudinal groove 21 is connected by the shorter portion of the transverse groove 22, forming a serrated shape along the tire circumference. As a result, an intermediate rib 7 with concave and convex shapes is formed on the side of the V-groove 20. In the intermediate rib 7, there are multiple extremely narrow portions 7a and extremely wide portions 7b that are alternately arranged in the tire circumference, as will be described in detail later.

[0057] The longitudinal groove 21 extends straight from the first connecting portion 23 to the second connecting portion 24, forming a constant width and depth. The width of the longitudinal groove 21 is preferably less than the width of the central main groove 10; as a preferred example, it is more than 50% and less than 80% or more than 60% and less than 70% of the width of the central main groove 10. If the width of the longitudinal groove 21 is within this range, excellent grip and drainage performance can be easily ensured. The depth of the longitudinal groove 21 can be the same as the depth of the central main groove 10, or it can be more than 80% and less than 95% of the depth of the central main groove 10.

[0058] The transverse groove 22 extends from the first connecting portion 23, which is the intersection with the longitudinal groove 21, along both the tire circumferential and axial directions. The inclination angle θ2 of the transverse groove 22 relative to the imaginary line β passing through the apex of the V-groove 20 and extending along the tire axial direction is smaller than the inclination angle of the transverse groove 22 relative to the imaginary line α; the transverse groove 22 is more inclined axially than circumferentially. The inclination angle θ2 of the transverse groove 22 is preferably 30° or more and 43° or less, more preferably 33° or more and 40° or less. If the inclination angle θ2 of the transverse groove 22 is within this range, the improvement in drainage performance, for example, becomes more significant. It should be noted that the inclination angle θ2 refers to the inclination angle of the first portion 22b of the transverse groove 22.

[0059] The transverse groove 22 includes: a bent portion 22a; a first portion 22b extending straight from the first connecting portion 23 to the bent portion 22a; and a second portion 22c extending straight from the bent portion 22a to a position beyond the ground contact end E, and inclined axially towards the tire than the first portion 22b. The transverse groove 22 may be gently curved along its entire length, but from the viewpoint of improving drainage, it is preferable to have a first portion 22b and a second portion 22c extending in a straight line, with local bends at the boundaries of each portion. The inclination angle of the second portion 22c relative to the tire axial direction is smaller than the inclination angle θ2 of the first portion 22b, for example, 10° or more and 20° or less.

[0060] The second connecting portion 24 is formed in the first portion 22b of the transverse groove 22. The first portion 22b can be considered as the connecting groove between the longitudinal groove 21 and the second portion 22c, and is the connecting groove between the two longitudinal grooves 21. In this embodiment, the distance between the first connecting portion 23 and the second connecting portion 24 is shorter than the distance between the second connecting portion 24 and the bend 22a. In this case, the second connecting portion 24 with a large groove area is positioned in the intermediate region Me of the tread 2, making it easier to guide water into the transverse groove 22. In addition, from the viewpoint of improving the durability of the shoulder tread block 8, the bend 22a is preferably formed at a position away from the grounding end E. For example, the central portion of the second portion 22c in the longitudinal direction is located on the grounding end E.

[0061] The depth of the V-groove 20 in the first connecting portion 23 gradually decreases towards the apex of the V-groove 20. The apex of the V-groove 20 is positioned close to the central main groove 10, and the width of the intermediate rib 7 is significantly reduced near the apex. Therefore, by making the groove gradually shallower towards the apex, the durability of the intermediate rib 7 can be improved. In other words, the V-groove 20 is formed such that the further the first connecting portion 23 is from the apex, the wider and deeper it becomes. As a result, water entering through the first connecting portion 23 flows smoothly along the longitudinal groove 21 and the transverse groove 22, improving drainage performance.

[0062] [Middle Rib 7]

[0063] The intermediate rib 7 is a rib-shaped tread block extending along the tire circumference, formed on both sides of the central rib 5, sandwiched between the central main groove 10. The width of the central rib 5 is constant along the tire circumference, but the width of the intermediate rib 7 varies. The intermediate rib 7 has a shape in which a very small portion 7a and a very large portion 7b alternately repeat in the tire circumference. Additionally, the intermediate rib 7 has a widening portion 7c whose width gradually increases from the very small portion 7a to the very large portion 7b. The two intermediate ribs 7 have a top-view shape that is symmetrical about the equator CL; therefore, the very small portions 7a of the two intermediate ribs 7 are arranged along the tire axis (as are the very large portions 7b and the widening portions 7c).

[0064] The narrower portion of the intermediate rib 7, such as the smallest part 7a, has reduced rigidity and is easier to move, improving its road-following ability and making it more prone to heat generation. Therefore, the intermediate rib 7 greatly contributes to improved preheating performance. On the other hand, the intermediate rib 7 also has a width of 5.5 mm or more in the smallest part 7a, and the depth of the V-groove 20 gradually decreases towards the apex, or in other words, towards the smallest part 7a. This ensures the durability of the intermediate rib 7, excellent braking performance, and improved preheating performance.

[0065] The variation in the width of the intermediate rib 7 is caused by the shape of the V-groove 20. Therefore, the intermediate rib 7 extends straight along the edge of the central main groove 10 in the tire circumferential direction, while the intermediate rib 7 slopes axially along the edge of the V-groove 20, forming a serrated shape. In this specification, the width of the intermediate rib 7 refers to the length along the tire axial direction from the edge of the central main groove 10 to the edge of the V-groove 20 closest to the central main groove 10. It should be noted that the intermediate rib 7 has a triangular portion 7d that is approximately triangular in plan view between the longitudinal groove 21 of the first V-groove 20 and the transverse groove 22 of the second V-groove 20, but the triangular portion 7d is not counted as part of the width of the intermediate rib 7.

[0066] The intermediate rib 7 includes a minimum portion 7a, a widened portion 7c, and a maximum portion 7b arranged in the tire circumferential direction, and has a top view shape with a large unevenness formed along the edge of the V-groove 20. In this embodiment, the portion adjacent to the part whose groove depth gradually decreases towards the apex of the V-groove 20 in the tire axial direction is the minimum portion 7a, and the portion adjacent to the triangular portion 7d in the tire circumferential direction is the maximum portion 7b. The intermediate rib 7 extends gradually outward in the tire axial direction from the portion where the most concave minimum portion 7a is formed towards the triangular portion 7d along the edge of the V-groove 20. The width of the intermediate rib 7 at the minimum portion 7a is preferably 10% or more and 30% or less, more preferably 15% or more and 25% or less, of the width of the intermediate rib 7 at the maximum portion 7b. In this case, it is easy to ensure excellent braking performance and durability of the intermediate rib 7, and improve preheating performance.

[0067] [Second horizontal slot 30]

[0068] In the shoulder tread block 8, a second lateral groove 30 is formed between each of the two first lateral grooves 22. The lateral grooves 22 and 30 are alternately arranged in the tire circumferential direction, for example, from the intermediate region Me of the tread 2 across the shoulder region Sh and extending beyond the contact end E. The lateral groove 30 is a short groove that is not connected to the V-groove 20, but it improves drainage performance and appropriately reduces the rigidity of the shoulder tread block 8, and also helps to improve preheating performance.

[0069] Like the transverse groove 22, the transverse groove 30 also has a bend 31. The portion of the transverse groove 30 located axially outward of the bend 31 is inclined axially towards the tire compared to the portion located axially inward of the bend 31. The bend 31 is formed, for example, at the central portion along the length of the transverse groove 30. The end of the transverse groove 30 on the side of the central main groove 10 (axially inward end) between the longitudinal groove 21 and the transverse groove 22 of the V-groove 20 is formed into a top-view cone shape, and the groove depth gradually decreases towards the front end. In this case, drainage to the axially outward side of the tire becomes smoother.

[0070] The following is for reference Figure 6Detailed explanation of the void ratio in each region of tread 2. Figure 6 yes Figure 3 The enlarged view of part A in the diagram is a simplified representation of the groove shape.

[0071] Figure 6 and Figure 3 Similarly, the boundary positions of the central region Ce, the intermediate region Me, and the shoulder region Sh of the tread 2 are shown. As described above, each region of the tread 2 is a region that divides the tread 2 from the equator CL to the contact patch E into three equal parts, with the central region Ce, the intermediate region Me, and the shoulder region Sh sequentially from the equator CL side. Furthermore, the void ratio of each region refers to the ratio of the area of ​​the groove formed in each region to the total area of ​​the region. It should be noted that the groove includes a kerf, and the portion outside the contact patch with the road surface is defined as a void. Figure 6 The shaded areas are the ground surfaces, while the unshaded areas are grooves (gaps).

[0072] like Figure 6 As shown, in tread 2, the clearance ratio of the central region Ce and the intermediate region Me is significantly increased compared to the clearance ratio of the shoulder region Sh. In other words, the contact area of ​​the shoulder region Sh is significantly larger than that of the central region Ce and the intermediate region Me. By increasing the contact area by reducing the clearance ratio of the shoulder region Sh, and on the other hand increasing the clearance ratio of the central region Ce and the intermediate region Me, drainage performance is improved while maintaining cornering limit performance, and tread block heating is promoted. As a result, preheating performance and anti-slip performance are improved, and the improvement in handling stability on wet roads becomes significant.

[0073] Specifically, the clearance ratio in the central region Ce and the intermediate region Me is at least 1.50 times that in the shoulder region Sh, preferably at least 1.50 times and less than 1.80 times, or at least 1.50 times and less than 1.70 times, or at least 1.55 times and less than 1.65 times. In this case, compared with cases where this clearance ratio relationship is not met, the preheating performance and anti-slip performance are significantly improved.

[0074] The void ratio in both the central region Ce and the intermediate region Me is preferably 45% or more and 50% or less, more preferably 46% or more and 49% or less. In this case, the improvement in preheating performance and anti-slip performance is greater compared to cases where the void ratio in the central region Ce and the intermediate region Me deviates from this range. The connecting portions 23 and 24, where a central main groove 10 is formed in the central region Ce and a V-groove 20 is formed in the intermediate region Me, result in a higher void ratio and improved anti-slip performance. Furthermore, the higher void ratio leads to a suitable reduction in the rigidity of the patterned block, promoting heat generation in the patterned block, which in turn improves preheating performance.

[0075] The difference between the void ratio in the central region Ce and the void ratio in the intermediate region Me is preferably less than 1.5%. The void ratio in the central region Ce can be higher or lower than the void ratio in the intermediate region Me, but a small difference in void ratio is preferred. In this case, compared to cases where this void ratio relationship is not met, the improvement in preheating performance and anti-slip performance is greater. It should be noted that... Figure 6 In the tread pattern shown, if there is a sipe 11 in the central rib 5, the void ratio of the central region Ce is greater than that of the intermediate region Me. If no sipe 11 is formed, the void ratio of the central region Ce is less than that of the intermediate region Me.

[0076] The clearance ratio in the shoulder area Sh is preferably 25% or more and 35% or less, more preferably 27% or more and 33% or less, or 28% or more and 31% or less. In this case, compared to cases where the clearance ratio in the shoulder area Sh deviates from this range, excellent preheating performance and anti-slip performance are ensured, and grip performance on wet roads is improved, resulting in good cornering characteristics. Through the function of the V-groove 20 and the transverse groove 30, good drainage performance is ensured even with a lower clearance ratio, and the heating of the tread blocks is promoted.

[0077] As described above, the pneumatic tire 1 with the aforementioned structure achieves a high degree of balance between excellent preheating performance and anti-slip performance. In particular, the central rib 5 and intermediate rib 7 exhibit good road surface following and are easily movable, generating heat rapidly, thus greatly contributing to improved preheating performance and achieving excellent handling stability even in the initial stages of driving. Furthermore, the central main groove 10 and V-groove 20 improve drainage performance, significantly contributing to improved anti-slip performance. Additionally, by setting the clearance ratio in the central region Ce and the intermediate region Me to at least 1.50 times the clearance ratio in the shoulder region Sh, cornering limit performance is maintained, drainage performance is improved, and tread block heating is promoted. As a result, the improvement in handling stability on wet and slippery surfaces during the initial stages of driving becomes significant.

[0078] In the above embodiment, the central rib 5 and the intermediate rib 7 have good road surface following and are easy to move, and heat up quickly, thus greatly contributing to improved preheating performance and achieving excellent handling stability even in the initial stage of driving. Furthermore, the central main channel 10 and the V-shaped channel 20 improve drainage performance, greatly contributing to improved anti-slip performance.

[0079] It should be noted that the above embodiments can be appropriately modified within the scope of the present invention without affecting the purpose. For example, in the above embodiments, a plurality of sipes 11 are formed in the central rib 5, but it is also possible not to form sipes 11 in the central rib 5. Alternatively, a structure in which a central main groove is formed on the equator CL without forming the central rib 5 can also be considered. However, by forming the central rib 5 on the equator CL, it is easier to achieve both excellent grip and drainage performance. In addition, the central rib 5 promotes heat generation in the central region Ce, especially when sipes 11 are formed, the rigidity of the central rib 5 is appropriately reduced and the rib is easier to move, thus further promoting heat generation, and the improvement effect of preheating performance becomes more significant.

[0080] [Example]

[0081] The present invention will be further illustrated below by way of examples, but the present invention is not limited to the examples.

[0082] <Example 1>

[0083] Will have Figures 1-6 Tire T1 (tire size: 305 / 680R18) with the tread pattern shown was fitted to the front and rear four wheels of an actual vehicle. The temperature rise at the tread contact patch (tread surface) and the LAP time were evaluated during a test drive on a rainy track. The evaluation results, along with the clearance ratios of the central area Ce, intermediate area Me, and shoulder area Sh of the tread, are shown in Table 1. The temperature rise rate shown in Table 1 is a relative value with the temperature rise of tire R2 of Comparative Example 2 (described later) set to 100. The LAP time is a relative value with the LAP time of the vehicle equipped with tire R1 of Comparative Example 1 (described later) and tire R2 of Comparative Example 2 (described later) set to 100. Furthermore, the anti-skid performance was evaluated using the method described later.

[0084] The main specifications of tire T1 are as follows.

[0085] The porosity of Ce in the central region is 48.4%.

[0086] The void ratio of the intermediate zone Me: 47.3%

[0087] The clearance ratio of the shoulder area (Sh) is 30.1%.

[0088] Width of the central main channel: 17mm

[0089] V-groove width: 11mm

[0090] Width of central rib: 26mm

[0091] Width and spacing of the cutting grooves: 1.0mm, 20mm

[0092] [Evaluation of anti-slip performance]

[0093] On a road surface with a water depth of 8 mm, the speed at which slippage occurred during acceleration from 0 km / h (straight-line driving) was evaluated. The evaluation results shown in Table 1 are relative values ​​with the tire R1 value of Comparative Example 1 set to 100. The higher the value, the better the anti-slip performance.

[0094] <Comparative Example 1>

[0095] Will have Figure 7 Tire R1 with the tread pattern shown in (a) (the clearance ratio of each area of ​​the tread is shown in Table 1) was fitted to the front and rear four wheels of an actual vehicle for performance evaluation.

[0096] <Comparative Example 2>

[0097] Will have Figure 7 Tire R2 with the tread pattern shown in (b) (the clearance ratio of each area of ​​the tread is shown in Table 1) was fitted to the front and rear four wheels of an actual vehicle for performance evaluation.

[0098] [Table 1]※Please refer to “Temperature rise width” in Table 1 as “Tread surface temperature rise rate”.

[0099]

[0100] As shown in Table 1, it can be understood that tire T1 of Example 1 has a higher rate of temperature rise on the tread surface and superior preheating performance compared to tire R2 of Comparative Example 2. Furthermore, tire T1 of Example 1 exhibits superior anti-slip performance compared to tires R1 and R2 of Comparative Examples 1 and 2. The superior performance of tire T1 is significantly reflected in the LAP time. This can be understood as the LAP time with tire T1 being significantly shorter compared to the LAP time with tires R1 and R2, indicating that tire T1 possesses excellent handling stability on wet and slippery surfaces.

Claims

1. A pneumatic tire having a tread, specified relative to the mounting direction of a vehicle, wherein, The tread has: The central main groove extends along the circumference of the tire; V-grooves, having multiple grooves formed along the tire circumference between the central main groove and the contact patch end of the tread; and The middle rib, which is sandwiched between the central main groove and the V-groove, extends along the circumference of the tire. The V-groove is composed of a longitudinal groove and a transverse groove. The longitudinal groove extends circumferentially along the tire, and the transverse groove is inclined axially towards the tire than the longitudinal groove, extending from a first connection portion with the longitudinal groove containing the apex of the V to a position beyond the ground contact end. The longitudinal groove is connected to the transverse groove of the other V-grooves adjacent in the tire circumferential direction to form a second connection, thereby connecting the plurality of V-grooves in the tire circumferential direction.

2. The pneumatic tire according to claim 1, wherein, The first connecting portions of the plurality of V-grooves are arranged along the circumference of the tire. The longitudinal grooves are inclined axially toward the tire in a manner that gradually moves away from the central main groove toward the second connecting portion.

3. The pneumatic tire according to claim 2, wherein, The distance between the first connecting part and the second connecting part is shorter than the distance between the second connecting part and the grounding terminal.

4. The pneumatic tire according to any one of claims 1 to 3, wherein, The depth of the V-groove in the first connecting portion gradually decreases towards the apex of the V.

5. The pneumatic tire according to any one of claims 1 to 3, wherein, The intermediate rib has a shape that alternates between narrower and wider portions along the tire circumference.

6. The pneumatic tire according to any one of claims 1 to 3, wherein, The transverse groove includes: Bending section; The first part extends straight from the first connecting portion to the bent portion; and The second part extends straight from the bend beyond the grounding end, and is inclined axially toward the tire than the first part.

7. The pneumatic tire according to claim 6, wherein, The second connecting portion is formed in the first part of the transverse groove. The distance between the first connecting part and the second connecting part is shorter than the distance between the second connecting part and the bent part.

8. The pneumatic tire according to any one of claims 1 to 3, wherein, The tread has a second transverse groove that enters the V-groove between the longitudinal groove and the transverse groove from a position axially outer of the ground contact end, and terminates without connecting to the V-groove.

9. The pneumatic tire according to claim 8, wherein, The second transverse groove is formed into a cone shape when viewed from above at its end on the side of the central main groove, and the groove depth gradually becomes shallower towards the front end.

10. The pneumatic tire according to any one of claims 1 to 3, wherein, The tread has: The two central main channels; and The central rib, which is sandwiched between the central main grooves, is formed on the equator.

11. The pneumatic tire according to claim 10, wherein, The tread has multiple sipes that are spaced apart in the circumferential direction of the tire and traverse the central rib.

12. A pneumatic tire having a tread, specified relative to the vehicle's mounting direction, wherein, When the area of ​​the tire tread extending from the equator to the ground contact point is divided into three equal parts, defined sequentially from the equator side as the central area, the intermediate area, and the shoulder area,... The tread has: A circumferential groove is formed in the central region and extends circumferentially along the tire. as well as Multiple transverse grooves, which extend axially along the tire from at least the intermediate region to a position beyond the grounding end. The gap ratio in the central region and the intermediate region is more than 1.50 times that in the shoulder region.

13. The pneumatic tire according to claim 12, wherein, The plurality of adjacent transverse grooves in the tire circumferential direction are connected by connecting grooves extending along the tire circumferential direction. The transverse groove and the connecting groove form a V-shaped groove when viewed from above.

14. The pneumatic tire according to claim 13, wherein, The intersection of the transverse groove and the connecting groove exists in the intermediate region.

15. The pneumatic tire according to any one of claims 12 to 14, wherein, The void ratio in the central area and the intermediate area is between 45% and 50%.

16. The pneumatic tire according to any one of claims 12 to 14, wherein, The difference between the void ratio in the central region and the void ratio in the intermediate region is less than 1.5%.

17. The pneumatic tire according to any one of claims 12 to 14, wherein, The void ratio in the shoulder area is above 25% and below 35%.

Images