JP2018138430A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire which secures load support performance with a small diameter, and has such excellent durability and abrasion resistance as to prevent occurrence of a buckling phenomenon, saves a space, and has good traveling stability performance.SOLUTION: There is provided a pneumatic tire, where the total width SW of a tire, a cross-sectional height H1 of the tire and a bead diameter D satisfy an expression (1), an expression (2) and an expression (3), and when a grounded tread area is equally divided into four in a width direction, two areas in the center in a width direction out of the four areas that are equally divided into four are center areas, and areas on each end in the width direction are shoulder areas, a relationship between a groove area CA on the center area and a groove area SA of the shoulder area satisfies CA<SA. The expression (1): A≤480, the expression (2): [A=2×H1+D] and B≤1.0, the expression (3): [B=SW×(2×H1+D)×10] and 3≤C≤5.5, an expression (4): [C=W×(D+W)×10and W=0.427×SW+0.637×H1].SELECTED DRAWING: Figure 1

Description

  The present invention relates to a pneumatic tire.

  In recent years, a pneumatic tire (10 inches) having a relatively small diameter has been disclosed (see Non-Patent Document 1).

Michelin Technological Innovation in Challenge by Bicheldam 2011 by Michelin Berlin, Germany May 18-22, 2011 Press Kit 8-9

  The tire disclosed in Non-Patent Document 1 is said to exhibit on-road performance equivalent to that of a 14-inch diameter tire, as well as grip performance and brake performance, although having a small diameter as described above. . Here, the small vehicle to which the small-diameter tire is attached has an advantage that the turning radius of the vehicle required at the time of steering is small, and so-called small turning is effective. Further, by reducing the diameter of the tire, it is possible to save space and secure a wide area at the foot of the riding space. The small-diameter tire as described above has a small diameter and therefore has a low load supporting performance. For this reason, in order to improve load support performance while exhibiting space saving at a large rudder angle, it is necessary to expand dimensions such as tire width and bead diameter in an appropriate relationship. However, when expanding the tire width, a buckling phenomenon occurs in which the vicinity of the center in the width direction on the contact surface with the road surface is lifted, and the distortion may adversely affect the durability and wear resistance of the tire. .

  The present invention has been made in view of the above circumstances, and realizes a space saving with excellent durability and wear resistance in which buckling phenomenon hardly occurs while ensuring load supporting performance with a small diameter. An object of the present invention is to provide a pneumatic tire with improved running stability.

In order to solve the above-described problems and achieve the object, a pneumatic tire according to an aspect of the present invention has a total tire width SW, a tire cross-sectional height H1, and a bead diameter D expressed by the formula (1). When the tread region that satisfies Equation (2) and Equation (3) and is grounded is divided into four equal parts in the width direction, the center two regions in the width direction of the four divided regions are centered. When the region and the region at each end in the width direction are shoulder regions,
In the pneumatic tire, the relationship between the groove area CA of the center region and the groove area SA of the shoulder region satisfies CA <SA.
A ≦ 480 (1)
[A = 2 × H1 + D]
B ≦ 1.0 (2)
[B = SW × (2 × H1 + D) × 10 ⁻⁵ ]
3 ≦ C ≦ 5.5 (3)
[C = W ^1.39 × (D + W) × 10 ⁻⁵ , W = 0.427 × SW + 0.637 × H1]

  The material of the tread region is preferably a rubber or a resin having a loss tangent tan δ at a temperature of 60 ° C. of 0.05 or more and 0.20 or less, or a blend of rubber and resin.

  The ratio CA / SA of the groove area SA of the shoulder area to the groove area CA of the center area preferably satisfies 0 ≦ CA / SA ≦ 0.8.

  The shoulder region at each end in the width direction preferably has at least one circumferential main groove extending in the tire circumferential direction.

  The groove depth of the circumferential main groove in the center region is preferably smaller than the groove depth of the circumferential main groove in the shoulder region.

  The shoulder region has a lug groove at least partially extending in the tire width direction, and a ratio of the tire circumferential direction arrangement interval A to the circumferential contact length L of the lug groove is 0.3 ≦ A / L ≦ 0. 8 is desirable.

  It is desirable to further have a belt layer provided on the radially inner side of the center region and a reinforcing layer provided on the radially outer side of the belt layer.

  The reinforcing layer includes an under rubber provided radially outside the tread region and outside the belt layer, and the loss tangent tan δ at a temperature of 60 ° C. of the under rubber is a temperature of the cap rubber of the tread region of 60 ° C. It is desirable that the loss tangent tan δ at or below.

  It is desirable that at least a part has a lug groove extending in the tire width direction, and at least one corner of the tread block surrounded by the main groove and the lug groove is chamfered.

  The pneumatic tire is a tire whose rotational direction is specified, and a chamfering length La viewed from the tread surface of the tread block is 0 ≦ La / Lbk ≦ with respect to a tire circumferential direction length Lbk of the tread block. It is desirable to be 0.3.

  The pneumatic tire according to the present invention achieves load saving performance while maintaining a small diameter, and further realizes space saving with excellent durability and wear resistance, which is unlikely to cause a buckling phenomenon, and improves running stability performance. it can.

FIG. 1 is a meridional sectional view of a pneumatic tire according to an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view of a part of the pneumatic tire according to the embodiment of the present invention. FIG. 3 is a diagram illustrating an example of a tread region of the pneumatic tire according to the embodiment of the present invention. FIG. 4 is a diagram schematically showing a tread region of the pneumatic tire according to the embodiment of the present invention. FIG. 5 is a view for explaining the groove area ratio of the tread region of the pneumatic tire according to the embodiment of the present invention. FIG. 6 is a view showing another example of a cross-sectional view in which a part of the pneumatic tire according to the embodiment of the present invention is enlarged. FIG. 7 is a view showing another example of a sectional view in which a part of the pneumatic tire according to the embodiment of the present invention is enlarged. FIG. 8A is a view showing a cross section of the tread block when the pneumatic tire according to the embodiment of the present invention is cut along a plane parallel to the equator plane. FIG. 8B is an enlarged view showing a broken-line circle part of the tread block of FIG. 8A. FIG. 8C is a cross-sectional view illustrating another example of chamfering of a corner portion of the tread block. FIG. 9 is a diagram illustrating an example of a tread block in which chamfers are provided on both the corner portion on the road surface entering side and the kicking side.

  Embodiments of the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments. The constituent elements of this embodiment include those that can be easily replaced by those skilled in the art or those that are substantially the same. The components of the embodiments described below can be combined as appropriate. Some components may not be used. In addition, a plurality of modifications described in this embodiment can be arbitrarily combined within a range obvious to those skilled in the art.

  In the following description, an XYZ orthogonal coordinate system is set, and the positional relationship of each part will be described with reference to this XYZ orthogonal coordinate system. One direction in the horizontal plane is defined as the X-axis direction, a direction orthogonal to the X-axis direction in the horizontal plane is defined as the Y-axis direction, and a direction orthogonal to each of the X-axis direction and the Y-axis direction is defined as the Z-axis direction. Further, the rotation (inclination) directions around the X axis, the Y axis, and the Z axis are the θX, θY, and θZ directions, respectively.

(Pneumatic tire structure)
FIG. 1 is a cross-sectional view showing an example of a pneumatic tire 1 according to an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view of a part of the pneumatic tire 1 according to the embodiment of the present invention. FIG. 3 is a diagram illustrating an example of a tread region of the pneumatic tire 1 according to the embodiment of the present invention. In the following description, the pneumatic tire 1 is appropriately referred to as a tire 1.

  The tire 1 is rotatable about a central axis (rotating axis) AX. 1 and 2 each show a meridional section passing through the central axis AX of the tire 1. A center axis AX of the tire 1 is orthogonal to the equator plane CL of the tire 1.

  In the present embodiment, the center axis AX and the Y axis of the tire 1 are parallel. That is, in the present embodiment, the direction parallel to the central axis AX is the Y-axis direction. The Y-axis direction is the width direction of the tire 1 or the vehicle width direction. The equatorial plane CL passes through the center of the tire 1 with respect to the Y-axis direction. The θY direction is the rotation direction of the tire 1 (center axis AX). The X-axis direction and the Z-axis direction are radial directions with respect to the central axis AX. The road surface (ground) on which the tire 1 travels (rolls) is substantially parallel to the XY plane.

  In the following description, the rotation direction of the tire 1 (center axis AX) is appropriately referred to as the circumferential direction, the radial direction with respect to the center axis AX is appropriately referred to as the radial direction, and the direction parallel to the center axis AX is appropriately determined as the width. It is called direction.

  The tire 1 includes a carcass portion 2, a belt layer 3, a belt cover 4, a bead portion 5, a tread portion 6, an inner liner 7, and a sidewall portion 8.

  Each of the carcass part 2, the belt layer 3, and the belt cover 4 includes a cord. The cord is a reinforcing material. The cord may be referred to as a wire. Each of the layers including the reinforcing material such as the carcass portion 2, the belt layer 3, and the belt cover 4 may be referred to as a cord layer or a reinforcing material layer.

  The carcass portion 2 is a strength member that forms the skeleton of the tire 1. The carcass part 2 includes a cord. The cord of the carcass portion 2 may be referred to as a carcass cord. The carcass part 2 functions as a pressure vessel when the tire 1 is filled with air. The carcass part 2 is supported by the bead part 5. The bead portion 5 is disposed on each of one side and the other side of the carcass portion 2 with respect to the Y-axis direction. The carcass portion 2 is folded back at the bead portion 5. The carcass portion 2 includes one or more organic fiber carcass cords and rubber covering the carcass cords. The carcass portion 2 may include a polyester carcass cord, a nylon carcass cord, an aramid carcass cord, or a rayon carcass cord.

  The belt layer 3 is a strength member that maintains the shape of the tire 1. The belt layer 3 includes a cord. The cord of the belt layer 3 may be referred to as a belt cord. The belt layer 3 is disposed between the carcass portion 2 and the tread portion 6. The belt layer 3 includes, for example, a belt cord made of metal fiber such as steel and rubber covering the belt cord. The belt layer 3 may include two or more organic fiber belt cords. In the present embodiment, the belt layer 3 includes a first belt ply 3A and a second belt ply 3B. The first belt ply 3A and the second belt ply 3B are laminated so that the cord of the first belt ply 3A and the cord of the second belt ply 3B intersect.

  The belt cover 4 is a strength member that protects and reinforces the belt layer 3. The belt cover 4 includes a cord. The cord of the belt cover 4 may be referred to as a cover cord. The belt cover 4 is disposed outside the belt layer 3 with respect to the central axis AX of the tire 1. The belt cover 4 includes, for example, a cover cord made of metal fiber such as steel and rubber covering the cover cord. The belt cover 4 may include an organic fiber cover cord.

  The bead portion 5 fixes the tire 1 to the rim. The bead portion 5 has a bead 50. The bead 50 is a strength member that fixes both ends of the carcass portion 2. The bead 50 is a bundle of steel wires. The bead 50 may be a bundle of carbon steel. A hard rubber portion 51 is provided adjacent to the bead 50. The hard rubber portion 51 corresponds to a bead filler and has a function of increasing the casing rigidity of the entire tire.

  The tread portion 6 includes a center region Ce and shoulder regions Sh disposed on both sides of the center region Ce with respect to the Y-axis direction. The tread portion 6 protects the carcass portion 2. The tread portion 6 includes a grounding portion that comes into contact with the road surface.

  The tread portion 6 has a plurality of grooves 20 formed on the outer surface in the tire radial direction. The groove 20 includes main grooves 21 </ b> C and 21 </ b> S that extend in the circumferential direction of the tire 1, and lug grooves (lateral grooves) 22 that at least partially extend in the width direction of the tire 1. A land portion is provided around the groove 20. The land portion is provided between the groove 20 and the groove 20 adjacent to the groove 20. The tread portion 6 includes a plurality of land portions arranged between the grooves 20. Note that a grounding region surrounded by a broken line in FIG.

  The main grooves 21 </ b> C and 21 </ b> S are straight grooves extending in the circumferential direction of the tire 1. The main groove 21 </ b> C is provided in the center region Ce of the tread portion 6. The main groove 21 </ b> S is provided in the shoulder region Sh of the tread portion 6. Hereinafter, the main grooves 21C and 21S may be collectively referred to as the main groove 21. When the tire 1 is a competition tire, two or more main grooves 21 are provided. In this example, as shown in FIG. 2, the tire 1 has four main grooves 21. That is, the tire 1 has two main grooves 21C and two main grooves 21S.

  The main groove 21 has a tread wear indicator inside. The treadwear indicator indicates the wear limit of the tire 1. The main groove 21 has a width of 5.0 [mm] or more and may have a depth of 5.0 [mm] or more.

  At least a part of the lug groove 22 is provided in the width direction of the tire 1. At least a part of the lug groove 22 is provided in the shoulder region Sh of the tread portion 6. The shoulder region Sh is arranged on one side (+ Y side) and the other side (−Y side) of the center region Ce in the width direction (Y-axis direction). The lug groove 22 has a width of 1.5 [mm] or more. The lug groove 22 may have a depth of 4.0 [mm] or more, and may partially have a depth of less than 4.0 [mm].

  The inner liner 7 is a rubber layer having a high airtightness that is attached to the inner surface of the tire 1. The sidewall portion 8 protects the carcass portion 2. The sidewall portions 8 are disposed on one side and the other side of the tread portion 6 with respect to the Y-axis direction. The sidewall portion 8 includes sidewall rubbers disposed on one side and the other side of the tread portion 6 with respect to the Y-axis direction.

  In the present embodiment, the outer diameter of the tire is OD. The total width of the tire is SW. The tread ground contact width is W1.

  The outer diameter OD of the tire refers to the diameter of the tire 1 when the tire 1 is assembled to a rim, a prescribed internal pressure is filled, and no load is applied to the tire 1. The bead diameter D refers to the diameter of the portion in contact with the wheel rim that fits the tire 1.

  The tire cross-sectional height H1 is a half of the difference between the tire outer diameter OD and the bead diameter D when the tire 1 is assembled on the rim and filled with a specified internal pressure in an unloaded state.

(Tire shape)
In the pneumatic tire 1 according to the present embodiment, the total tire width SW, the tire cross-sectional height H1, and the bead diameter D satisfy the expressions (1), (2), and (3). . Unless otherwise specified, the unit of length is [mm].

A ≦ 480 (1)
[A = 2 × H1 + D]

B ≦ 1.0 (2)
[B = SW × (2 × H1 + D) × 10 ⁻⁵ ]

3 ≦ C ≦ 5.5 (3)
[C = W ^1.39 × (D + W) × 10 ⁻⁵ , W = 0.427 × SW + 0.637 × H1]

  When the total tire width SW, the tire cross-sectional height H1, and the bead diameter D satisfy the expressions (1), (2), and (3), the outer diameter of the pneumatic tire 1 is relatively large. It becomes a small pneumatic tire.

  Equation (1) defines the “outer diameter” of the tire in order to improve space saving. Equation (2) defines an upper limit of “width × outer diameter” in order to improve space saving when the vehicle is stationary and straight ahead.

  Formula (3) is a formula for ensuring the load capacity W of the tire. The value of C is a value that substantially matches the maximum load force [kN] of the tire. Formula (3) can increase the load carrying capacity by setting C to 3 or more, and by suppressing C to 5.5 or less, preferably 5 or less, an increase in rigidity is suppressed and steering stability is improved. Can be high. The load applied to measure the ground contact shape is assumed to be 0.75 times C defined by Equation (3). The unit of the applied load is [kN].

  The total width SW and the cross-sectional height H1 in Expression (2) are measured in a state where the rim is assembled at an internal pressure of 180 kPa. The rim width R of the rim to be assembled uses the measurement rim width Rm derived from the following equation (4) and Table 1 regarding the tire cross-section width W0 and the tire cross-section height H0 in the unloaded state where the rim is not assembled. It shall be. That is, after calculating the no-load flatness ratio F0 using the section width W0 and the section height H0 at no load, the corresponding coefficient K is obtained from Table 1.

  F0 = H0 / W0 (4)

  Then, the rim width R of the rim to be assembled is calculated by the following equation (5).

  R = K × W0 (5)

  The measurement rim width Rm is set in increments of 0.5 inches, such as 3.5 inches, 4.0 inches, and 4.5 inches, for example. Of the set measurement rim widths Rm, the rim closest to the rim width R of the rim to be assembled is selected.

(Tread area)
Here, the tread area | region which the pneumatic tire 1 by this Embodiment contacts is demonstrated. FIG. 4 is a diagram schematically showing a tread region of the pneumatic tire 1 according to the present embodiment. FIG. 5 is a view for explaining the groove area ratio of the tread region of the pneumatic tire 1 according to the present embodiment.

  In FIG. 4, the tread region of the pneumatic tire according to the present embodiment has a center region Ce located at a position passing through the equator plane CL and shoulder regions Sh located on both sides thereof. In the present embodiment, the center region Ce is a region obtained by combining two regions obtained by dividing the tread region into two equal parts along the equator plane CL and combining the two regions closer to the equator plane CL of the two divided regions. It is. The shoulder region Sh is a region located outside the center region Ce. That is, with respect to the tread grounding width W1, the center region Ce is the two regions at the center in the width direction among the four regions divided into four when the tread region to be grounded is divided into four equal parts in the width direction. The area | region Sh is an area | region of each edge part of the outer side, ie, the width direction.

  The tread region of the pneumatic tire according to the present embodiment has at least one circumferential main groove 21 extending in the circumferential direction of the tire 1 and lug grooves 22 at least partially extending in the width direction of the tire 1. Since the pneumatic main tire 21 has the circumferential main groove 21 in the center region Ce, it can ensure drainage.

  In FIG. 5, the area ratio of the tread region of the pneumatic tire according to the present embodiment is as follows. That is, when the tread region is divided into the center region Ce and the shoulder region Sh as described above with respect to the width direction, the relationship between the groove area CA of the center region Ce and the groove area SA of the shoulder region Sh is CA < It is preferable to satisfy SA. However, the groove area is a groove area including all grooves such as a main groove, a lug groove, a narrow groove, and a sipe.

  Further, the ratio CA / SA of the groove area CA of the center region Ce to the groove area SA of the shoulder region Sh preferably satisfies the following formula (6). However, the groove area is a groove area including all grooves such as a main groove, a lug groove, a narrow groove, and a sipe.

  0 ≦ CA / SA ≦ 0.8 (6)

  By making the groove area of the center region Ce smaller than the groove area of the shoulder region Sh, the out-of-plane bending rigidity of the tread portion can be secured and the buckling phenomenon can be suppressed. If the ratio CA / SA of the groove area CA to the groove area SA exceeds 0.8, the effect of suppressing the buckling phenomenon is not sufficient. More preferably, 0.3 ≦ CA / SA ≦ 0.7. In order to achieve both the suppression of the buckling phenomenon and the improvement of drainage, the groove area ratio of the entire ground plane is preferably 15% or more and 40% or less.

  A tire having a small outer diameter has a problem in that the risk of hydroplaning is increased because the contact length in the circumferential direction is shortened. Since the road surface non-contact area of the tread tends to be near the center in the tire width direction when entering the puddle, it is desirable to preferentially drain the tread center area Ce.

  In the pneumatic tire 1 of the present embodiment, the ratio CA / SA of the groove area CA of the center region Ce to the groove area SA of the shoulder region Sh satisfies the formula (6). For this reason, the groove area CA of the center region Ce is smaller than the groove area SA of the shoulder region Sh, and drainage efficiency can be increased. Further, it is preferable that a groove is provided in the center region Ce, and a ratio CA / SA of the groove area CA to the groove area SA is 0.05 ≦ CA / SA. Thereby, drainage efficiency can be raised more. Furthermore, the ratio CA / SA of the groove area CA to the groove area SA preferably satisfies 0.05 ≦ CA / SA ≦ 0.7. Thereby, the balance of a groove area improves more and drainage efficiency can be raised more.

  Here, the ratio CA / SA = 0 of the groove area CA with respect to the groove area SA means that there is no groove in the center region Ce. The pneumatic tire 1 desirably has a non-contact area of 10% or more of the total ground contact area in the shoulder region Sh when CA / SA = 0.

  It is desirable that the component of the main groove is larger than the components of grooves other than the main groove such as lug grooves, narrow grooves, and sipes in the entire contact surface of the tread. That is, it is desirable that the area ratio of only the main groove with respect to the entire ground contact surface of the tread is larger than the area ratio of all grooves other than the main groove with respect to the entire ground contact surface of the tread. Here, the area ratio of only the main groove to the entire ground contact surface of the tread is preferably 0.15 or more and 0.40 or less. Further, the area ratio of all grooves other than the main groove to the entire contact surface of the tread is more preferably 0.05 to 0.25.

  As shown in FIGS. 2 to 5, at least one circumferential main groove 21 is provided in the left and right shoulder regions Sh in the tire width direction cross section. If there is at least one circumferential main groove in the shoulder region Sh, the drainage of the entire tire 1 can be ensured. The width of the circumferential main groove 21 is preferably 2% or more and 10% or less of the maximum ground contact width. If the width of the circumferential main groove is less than 2% of the maximum contact width, sufficient drainage is not ensured. If the width of the circumferential main groove is greater than 10% of the maximum contact width, the block rigidity is lowered and cornering performance is deteriorated. When the maximum ground contact width is about 80% of the total width, when the total width is 145 [mm], the groove width is 2.3 [mm] or more and 11.6 [mm] or less, and the total width is 245 [mm]. mm] is a guideline for the groove width from 3.9 [mm] to 19.6 [mm]. Therefore, the practical range is sufficiently covered.

(Groove depth)
As shown in FIGS. 2 and 3, in the pneumatic tire 1, the circumferential main groove 21 provided in the shoulder region Sh has a depth of the circumferential main groove 21 provided in the center region Ce in the tire width direction cross section. It is smaller than the groove depth of the groove 21. By making the groove depth of the center region Ce shallower than the groove depth of the shoulder region Sh, it is possible to increase the tread surface bending rigidity of the center region Ce and suppress the buckling phenomenon.

  In the pneumatic tire 1, the circumferential main groove 21 in the center region Ce has a depth of 3% or less of the tire radius, and the radius of the curved surface between the groove bottom and the groove wall is 2 [mm] or more. Is preferable from the viewpoint of securing bending rigidity and running durability. For example, when the tire radius is 240 [mm], the depth of the circumferential main groove 21 is 240 * 0.03 = 7.2 [mm] or less.

  The tire 1 preferably satisfies 0.4 ≦ Cd / Sd ≦ 0.8 with respect to the groove depth (maximum) Cd of the center region Ce and the circumferential main groove depth (maximum) Sd of the shoulder region Sh.

  The pneumatic tire 1 has a lug groove 22 that extends from the contact width end portion of the shoulder region Sh toward the tire equator line. The lug groove 22 is provided in the ground contact area. The tire circumferential direction arrangement interval A of the lug grooves 22 is 0.3 ≦ A / L ≦ 0.8 in terms of the ratio of the contact length L. Here, the contact length L is the maximum contact length in the tire circumferential direction.

(Tread material)
The pneumatic tire 1 has a cap rubber 10 on the radially outer side from the belt layer 3. The material of the cap rubber 10 is a rubber or resin or a blend of rubber and resin having a loss tangent tan δ at a temperature of 60 ° C. of 0.05 or more (preferably 0.07 or more) and 0.20 or less. The loss tangent tan δ is given by loss elastic modulus / storage elastic modulus. A small-diameter tire has a shorter overall tire circumference and a greater tread contact frequency during rolling. Therefore, by using a material that suppresses heat generation, it is possible to prevent deterioration in durability due to heat generation of the tread due to frequent ground contact, and to improve tire durability. For the cap rubber 10, for example, a rubber composition made of natural rubber and SBR (styrene butadiene rubber) can be used.

(Reinforcing layer)
FIG. 6 is a view showing another example of a sectional view in which a part of the pneumatic tire 1 is enlarged. As shown in FIG. 6, the pneumatic tire 1 desirably has a reinforcing layer 4A on the outer side in the tire radial direction of the belt cover layer 4 in the center region Ce. The reinforcing layer 4 </ b> A is disposed on the outer side in the tire radial direction than the carcass portion 2 of the tire 1. The reinforcing layer 4A is made of a composite material obtained by combining organic fiber or metal fiber or a combination thereof and rubber or resin or a combination thereof. It is desirable to provide the reinforcing layer 4A at a position including the equator plane CL. The width W4A in the tire width direction of the reinforcing layer 4A is desirably ¼ or more and ½ or less of the ground contact width W1.

  Since the reinforcing layer 4A is disposed in the vicinity of the center region Ce, the pneumatic tire 1 can increase the out-of-plane bending rigidity of the center region Ce and can further suppress the buckling phenomenon. The material of the reinforcing layer 4A is preferably an organic fiber such as aramid, polyester, polyethylene, nylon, etc., in order to achieve a good road followability while suppressing the buckling phenomenon.

  The pneumatic tire 1 desirably has an under rubber having material characteristics different from the material of the cap rubber, on the outer side in the radial direction of the belt layer 3 and on the lower layer of the cap rubber 10 (inner side in the tire radial direction).

  FIG. 7 is a view showing another example of a sectional view in which a part of the pneumatic tire 1 is enlarged. As shown in FIG. 7, the pneumatic tire 1 has an under rubber 10 </ b> U on the radially outer side of the belt layer 3 and on the inner side of the cap rubber 10 in the tire radial direction. The material of the under rubber 10U is preferably such that the loss tangent tan δ at a temperature of 60 ° C. is lower than that of the cap rubber 10. For the under rubber 10U, for example, either natural rubber (NR) or a diene synthetic rubber, or a mixed system thereof can be used.

(Chamfered corner of tread block)
In the tread region, the tread block is formed by being surrounded by the main groove 21 and the lug groove 22. A chamfer may be provided on at least one of the corners of the tread block. FIG. 8A is a diagram showing a cross section of the tread block when the pneumatic tire 1 according to the present embodiment is cut along a plane parallel to the equator plane CL. In FIG. 8A, the tread block TB is exaggerated.

  In FIG. 8A, the pneumatic tire 1 rotates in the arrow Y1 direction. At this time, the tread block TB provided in the tread region of the pneumatic tire 1 has the corner portion C1 in contact with the road surface RM first, and then the corner portion C2 in contact with the road surface RM. Therefore, the corner of the tread block TB on the step-in side, that is, the road surface approaching side is the corner C1, and the corner of the road surface RM on the kicking side is the corner C2. In this example, chamfering is provided at a corner C1 in the tire circumferential direction of the tread block TB.

  FIG. 8B is an enlarged view showing a broken line circle HC portion of the tread block TB of FIG. 8A. FIG. 8B is a cross-sectional view of the tread block TB. As shown in FIG. 8B, the tread block TB has a chamfer at a corner C1 indicated by a one-dot chain line. For this reason, the circumferential length of the tread block TB in the circumferential direction M1 is shorter than the circumferential length Lbk of the tread block TB by the circumferential length La of the chamfer.

  In FIG. 8B, in this example, both the tread surface M1 and the groove wall surface M2 are flat surfaces. Due to the chamfering, a curved surface KM1 is formed between the tread surface M1 and the groove wall surface M2. For this reason, the tread block TB is connected to the groove wall surface M2 from the tread surface M1 through the curved surface KM1, and has a shape extending from the groove wall surface M2 to the groove bottom surface M3.

  The end of the curved surface KM1 on the groove wall surface M2 side is a point P1. The point P1 is a connection point between the curved surface KM1 and the groove wall surface M2. The length from the tread surface M1 to the point P1 is the chamfering depth Da of the tread block TB. The end of the curved surface KM1 on the tread surface M1 side is a point P2. A point P2 is a connection point between the curved surface KM1 and the tread surface M1. The length from the groove wall surface M2 to the point P2 is a circumferential length La of chamfering of the tread block TB.

  The tread block TB may have chamfering by a plane instead of chamfering by the curved surface KM1. FIG. 8C is a cross-sectional view showing another example of chamfering of the corner portion C1 of the tread block TB. As shown in FIG. 8C, the tread block TB has a chamfer at a corner C1 indicated by a one-dot chain line. Due to the chamfering, a flat surface HM1 is formed between the tread surface M1 and the groove wall surface M2. That is, the tread block TB is connected to the groove wall surface M2 through the flat surface HM1 from the tread surface M1, and has a shape extending from the groove wall surface M2 to the groove bottom surface M3.

  Here, the angle θM1 between the tread surface M1 and the plane HM1 is an angle larger than 90 degrees and smaller than 180 degrees, that is, an obtuse angle. Further, the angle θM2 between the groove wall surface M2 and the plane HM1 is larger than 90 degrees and smaller than 180 degrees, that is, an obtuse angle.

  In addition, the curved surface or flat surface which arises because rubber does not enter the corner of the molding die when manufacturing the tire 1 is not chamfering in this example. The chamfering in this example is a curved surface or a flat surface formed by the shape of the inner surface of the mold corresponding to the corner portion C1.

  The chamfering depth Da shown in FIGS. 8B and 8C is, for example, 15% to 70%, more preferably 25% to 70% of the groove depth DM. Further, in the case of chamfering by the plane HM1 shown in FIG. 8C, the angle θM formed by the virtual plane M4 obtained by extending the groove wall surface M2 and the plane HM1 is, for example, not less than 30 degrees and not more than 70 degrees.

  A tire having a small outer diameter has a larger tread block distortion at the time of rolling than a tire having a large outer diameter, so that the contact pressure tends to be uneven. Therefore, by providing chamfering at the corner C1 of the tread block TB, it is possible to improve grip performance on the DRY road surface and the WET road surface and to prevent uneven wear of the tread block TB. And if chamfering is provided in at least one of the corner part C1 of the tread block TB on the step-in side, that is, the road surface approaching side, and the corner part C2 of the road surface kicking side, the grip performance is improved and the tread block TB Uneven wear can be prevented.

  The smaller the outer diameter of the tire, the higher the road surface approaching side contact pressure during tire rotation. For this reason, it is desirable for the tread block TB to be chamfered at the corner C1 or C2 that is the corner in the circumferential direction.

  FIG. 9 is a diagram illustrating an example of a tread block TB in which chamfers are provided on both the corner portion on the road surface entering side and the kicking side. FIG. 9 is a diagram showing a cross section of the tread block when the pneumatic tire of the present embodiment is cut along a plane parallel to the equator plane CL.

  As shown in FIG. 9, the tread block TB has a chamfer at the corner C1 indicated by the alternate long and short dash line, and is a curved surface KM1. Further, the tread block TB has a chamfer at the corner portion C2 indicated by the alternate long and short dash line.

  In FIG. 9, in this example, the tread surface M1 and the groove wall surfaces M2 and M5 are all flat surfaces. Due to the chamfering, a curved surface KM1 is formed between the tread surface M1 and the groove wall surface M2. For this reason, the tread block TB is connected to the groove wall surface M2 from the tread surface M1 through the curved surface KM1, and has a shape extending from the groove wall surface M2 to the groove bottom surface M3. The end of the curved surface KM1 on the groove wall surface M2 side is a point P1. The point P1 is a connection point between the curved surface KM1 and the groove wall surface M2. The length from the tread surface M1 to the point P1 is the chamfering depth Da of the tread block TB. The end of the curved surface KM1 on the tread surface M1 side is a point P2. A point P2 is a connection point between the curved surface KM1 and the tread surface M1. The length from the groove wall surface M2 to the point P2 is the circumferential length La of the chamfering on the entry side to the road surface.

  Further, due to chamfering, a curved surface KM2 is formed between the tread surface M1 and the groove wall surface M5. Therefore, the tread block TB is connected to the groove wall surface M5 from the tread surface M1 through the curved surface KM2, and has a shape extending from the groove wall surface M5 to the groove bottom surface M6. The end of the curved surface KM2 on the groove wall surface M5 side is a point P3. Point P3 is a connection point between the curved surface KM2 and the groove wall surface M5. The end of the curved surface KM2 on the tread surface M1 side is a point P4. Point P4 is a connection point between curved surface KM2 and tread surface M1.

  Note that the tread block TB may have chamfering by the plane HM1 as in FIG. 8C instead of chamfering by the curved surfaces KM1 and KM2.

  Further, in the pneumatic tire 1, when the tire rotation direction is specified and at least one tread block TB is chamfered at a corner in the circumferential direction, the pneumatic tire 1 is viewed from the tread surface of the tread block TB. The circumferential length La of the chamfered tire is preferably 0 ≦ La / Lbk ≦ 0.3 with respect to the tire circumferential length Lbk of the tread block TB. Furthermore, it is more preferable that 0.01 ≦ La / Lbk ≦ 0.2. By setting the chamfer on the road surface entry side large, the contact surface pressure can be further optimized and uneven wear can be suppressed.

  A tire having a small outer diameter that satisfies the formula (1), the formula (2), and the formula (3) has a large distortion of the tread block TB at the time of rolling, so that the contact pressure to the road surface RM tends to be uneven. That is, in a tire having a small outer diameter, the contact pressure on the road surface entrance side of the tread block TB tends to increase when the tire rotates. For this reason, it is desirable that chamfering is provided at the corner C1 in the circumferential direction of the tread block TB. As in the present embodiment, by providing chamfers at the corners of the tread block TB, grip performance on the DRY road surface and the WET road surface can be improved, and uneven wear resistance can be prevented.

  In the tread block TB, it is possible to further optimize the contact surface pressure by setting the chamfer on the entry side to the road surface larger than the chamfer on the kicking side from the road surface, and on the DRY road surface and the WET road surface The grip performance can be further improved.

(Other)
The groove depth DM of the main groove 21 with respect to the tire outer diameter OD is, for example, not less than 0.008 and not more than 0.02.

  In order to increase the tread rigidity to improve the handling stability and suppress uneven wear, the pneumatic tire 1 desirably has at least one tread land portion (rib) that is continuous in the circumferential direction.

(Example)
In the examples, the evaluation tire was filled with an air pressure of 180 kPa, and performance evaluation was performed. An evaluation tire was assembled to a rim having a measurement rim width Rm. The actual vehicle test was evaluated with a vehicle capable of providing a steering angle of 90 degrees at the maximum. The test results are shown in Tables 2 and 3.

  In the space-saving test of the steered wheels, the volume of the wheel house required at the time of vehicle design was calculated, the reciprocal was taken, and the index was evaluated with an index where the conventional example (reference tire) was 100. The larger the index value, the better.

  The durability test was performed using a drum testing machine. While increasing the speed step of the drum tester, the distance traveled until the tire broke was evaluated by an index. The conventional example is set to 100, and the larger the index value, the better.

  The abrasion resistance test was performed by an actual vehicle abrasion test. The distance traveled to the wear limit was evaluated by an index. The conventional example is set to 100, and the larger the index value, the better.

  The WET handling stability test was evaluated using an index based on a conventional example of 100, traveling on a WET road surface (watering course with a water depth of 3 mm), taking the reciprocal of the lap time. The larger the index value, the better.

  In Tables 2 and 3, the tire outer diameter is 510 [mm], the tire total width is 145 [mm], the bead diameter is 12 inches, the groove area ratio CA / SA is “1”, and the loss tangent tan δ at a cap rubber temperature of 60 ° C. Is “0.5”, there is no under rubber, there is no main groove in the circumferential direction of the shoulder region Sh, and the ratio A / L of the tire circumferential direction arrangement interval A of the lug groove to the contact length L is “1.1”, the center region A tire having no Ce reinforcing layer, no chamfering at the corner of the tread block, and no designation of the rotation direction when mounted on the vehicle was used as a reference tire. In Tables 2 and 3, as described above, the air pressure is 180 kPa, and the ground shape is defined as a load obtained by multiplying C defined by Equation (3) by 0.75 (unit: [kN]). When measured, the main groove in the range included in the ground contact contour 9 with respect to the total ground contact area (that is, the sum of the groove area and the ground contact area) of the region surrounded by the ground contact contour 9 that is the outer edge of the ground contact region between the tire and the road surface. A tread groove shape in which the percentage of the groove area ratio was about 30% was used.

  As the tire of Comparative Example 1, the tire outer diameter is 480 [mm], the tire total width is 155 [mm], the bead diameter is 10 inches, the groove area ratio CA / SA is “1.2”, and the loss tangent of the cap rubber at a temperature of 60 ° C. tan δ is “0.5”, there is no under rubber, there is no circumferential main groove in the shoulder region Sh, the ratio A / L of the lug groove circumferential arrangement distance A to the ground contact length L is “1.1”, the center A tire having no reinforcing layer in the region Ce, no chamfering at the corner of the tread block, and no designation of the rotation direction when mounted on the vehicle was prepared.

  As a tire of Comparative Example 2, the tire outer diameter is 480 [mm], the total tire width is 155 [mm], the bead diameter is 10 inches, the groove area ratio CA / SA is “0.9”, and the loss tangent of the cap rubber at a temperature of 60 ° C. Tan δ is “0.2”, loss tangent tan δ at an under rubber temperature of 60 ° C. is “0.5”, there is no main groove in the circumferential direction of the shoulder region Sh, The tire was prepared with a ratio A / L of “1.1”, no reinforcing layer in the center region Ce, no chamfering at the corners of the tread block, and no designation of the rotation direction when mounted on the vehicle.

  As the tire of Comparative Example 3, the tire outer diameter 480 [mm], the tire total width 155 [mm], the bead diameter 10 inches, the groove area ratio CA / SA is “0.9”, and the loss tangent of the cap rubber at a temperature of 60 ° C. Tan δ is “0.8”, loss tangent tan δ at a temperature of 60 ° C. of the under rubber is “0.7”, there is no circumferential main groove in the shoulder region Sh, The tire was prepared with a ratio A / L of “1.1”, no reinforcing layer in the center region Ce, no chamfering at the corners of the tread block, and no designation of the rotation direction when mounted on the vehicle.

  As a tire of Comparative Example 4, the tire outer diameter is 480 [mm], the tire total width is 155 [mm], the bead diameter is 10 inches, the groove area ratio CA / SA is “0.9”, and the loss tangent of the cap rubber at a temperature of 60 ° C. Tan δ is “0.8”, loss tangent tan δ at a temperature of 60 ° C. of the under rubber is “0.7”, there is a circumferential main groove in the shoulder region Sh, and the groove depth of the center region Ce with respect to the groove depth of the shoulder region Sh The height ratio is “0.8”, the ratio A / L of the lug groove arrangement distance A to the contact length L is “0.8”, the center region Ce has a reinforcing layer, and the chamfered corners of the tread block There is a specification of the rotation direction when mounted on the vehicle, and a tire with a ratio La / Lbk of the chamfered tire circumferential direction length to the tire circumferential length Lbk of the tread block TB of “0.4” is prepared. did .

  According to Example 1 to Example 19, good results were obtained when the groove area ratio CA / SA was “0” or more and smaller than “1”. Moreover, when the groove area ratio CA / SA was “0.1” or more and “0.8” or “0.7”, good results were obtained. In particular, a better result was obtained when the groove area ratio CA / SA was “0.7”.

  According to Example 1 to Example 19, better results were obtained for tires with the under rubber 10U than tires without the under rubber 10U on the inner side in the tire radial direction of the cap rubber 10. Further, good results were obtained for a tire in which the loss tangent tan δ of the under rubber 10U at a temperature of 60 ° C. is equal to or less than the loss tangent tan δ of the cap rubber 10 at a temperature of 60 ° C. Further, when the shoulder region Sh has a circumferential main groove, and the ratio of the groove depth of the center region Ce to the groove depth of the shoulder region Sh is smaller than “1”, that is, the groove depth of the circumferential main groove of the center region Ce. Good results were obtained when the length was smaller than the depth of the circumferential main groove of the shoulder region Sh.

  According to Example 1 to Example 19, good results were obtained when the ratio A / L of the lug groove arrangement distance A of the lug groove to the contact length L was smaller than “1”. In addition, better results were obtained for the tire having the reinforcing layer 4A than the tire having no reinforcing layer 4A in the center region Ce.

  According to Example 1 to Example 19, good results were obtained for a tire with chamfering than a tire without chamfering of the tread block. In addition, when the rotation direction at the time of mounting on the vehicle is specified and the ratio La / Lbk of the chamfering length La on the road surface side to the tread block length Lbk is “0.3” or less, Good results were obtained. In addition, as in Comparative Example 4, when the ratio La / Lbk exceeds “0.3”, the ground contact area is reduced and the wear resistance is reduced.

  As described above, according to the pneumatic tire 1 of the embodiment, while maintaining a load supporting performance with a small diameter, further realizing a space saving that is excellent in durability and wear resistance in which a buckling phenomenon hardly occurs. In addition, driving stability can be improved.

DESCRIPTION OF SYMBOLS 1 Pneumatic tire 2 Carcass part 3 Belt layer 3A, 3B Belt ply 4 Belt cover 4A Reinforcing layer 5 Bead part 6 Tread part 7 Inner liner 8 Side wall part 9 Grounding contour 10 Cap rubber 10U Under rubber 20 Grooves 21, 21C, 21S Main groove 22 Lug groove 50 Bead 51 Hard rubber part Ce Center region CL Equatorial plane Sh Shoulder region

Claims (10)

A tread region in which the total width SW of the tire, the tire cross-sectional height H1, and the bead diameter D satisfy Expressions (1), (2), and (3) and is grounded is 4 in the width direction. When equally divided into four regions, the two regions in the center in the width direction are the center region, and the region at each end in the width direction is the shoulder region,
A pneumatic tire in which the relationship between the groove area CA of the center region and the groove area SA of the shoulder region satisfies CA <SA.
A ≦ 480 (1)
[A = 2 × H1 + D]
B ≦ 1.0 (2)
[B = SW × (2 × H1 + D) × 10 ⁻⁵ ]
3 ≦ C ≦ 5.5 (3)
[C = W ^1.39 × (D + W) × 10 ⁻⁵ , W = 0.427 × SW + 0.637 × H1]   2. The pneumatic tire according to claim 1, wherein the material of the tread region is a rubber or a resin having a loss tangent tan δ at a temperature of 60 ° C. of 0.05 or more and 0.20 or less, or a blend of rubber and resin. The ratio CA / SA of the groove area CA of the center area to the groove area SA of the shoulder area is:
0 ≤ CA / SA ≤ 0.8
The pneumatic tire according to claim 1 or 2, satisfying   The pneumatic tire according to any one of claims 1 to 3, wherein the shoulder region at each end in the width direction includes at least one circumferential main groove extending in the tire circumferential direction. .   The pneumatic tire according to any one of claims 1 to 4, wherein a groove depth of the circumferential main groove in the center region is smaller than a groove depth of the circumferential main groove in the shoulder region. The shoulder region has at least a lug groove extending in the tire width direction,
The pneumatic according to any one of claims 1 to 5, wherein a ratio between a tire circumferential arrangement interval A of the lug grooves and a circumferential contact length L is 0.3≤A / L≤0.8. tire.   The pneumatic tire according to any one of claims 1 to 6, further comprising a belt layer provided radially inside the center region and a reinforcing layer provided radially outside the belt layer. .   The reinforcing layer includes an under rubber provided radially outside the tread region and outside the belt layer, and the loss tangent tan δ at a temperature of 60 ° C. of the under rubber is a temperature of the cap rubber of the tread region of 60 ° C. The pneumatic tire according to claim 7, which is equal to or less than a loss tangent tan δ.   At least one part has a lug groove extending in the tire width direction, and at least one corner portion of the tread block surrounded by the circumferential main groove extending in the tire circumferential direction and the lug groove is chamfered. The pneumatic tire according to any one of claims 1 to 8. The pneumatic tire is a tire whose rotation direction is specified,
The pneumatic tire according to claim 8, wherein a chamfered length La of the tread block as viewed from the tread surface is 0 ≦ La / Lbk ≦ 0.3 with respect to a tire circumferential direction length Lbk of the tread block.

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