JP2018138435A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire which secures load support performance with a small diameter, and achieves improvement of operation stability performance on a dry road surface and a wet road surface.SOLUTION: There is provided a tire 1 that is a pneumatic tire of which an inside and an outside at the time of vehicle mounting are specified, where the total width SW of the 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 divided into two of an inside area and an outside area at the time of vehicle mounting with a tire meridian as a borderline, a relationship of a groove area IA of the inside area and a groove area OA of the outside area satisfies OA<IA. 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, and [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. In addition, tires with a small diameter are likely to be degraded in running performance due to a decrease in contact length. In particular, a decrease in steering stability performance on a dry road surface and a wet road surface is a serious problem from the viewpoint of safety.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a pneumatic tire capable of improving the steering stability performance on a dry road surface and a wet road surface while ensuring load supporting performance while having a small diameter. And

In order to solve the above-described problems and achieve the object, a pneumatic tire according to an aspect of the present invention is a pneumatic tire in which an inner side and an outer side at the time of mounting on a vehicle are designated, The tread area where the cross-sectional height H1 and the bead diameter D satisfy Expression (1), Expression (2), and Expression (3) and is grounded is defined as the inner area when the vehicle is mounted with the tire meridian as a boundary. When the outer area is divided into two, the relationship between the groove area IA of the inner area and the groove area OA of the outer area satisfies OA <IA.
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 resin having a loss tangent tan δ at a temperature of 60 ° C. of 0.20 or less, or a blend of rubber and resin.

  It is desirable that the relationship between the groove area IA of the inner region and the groove area OA of the outer region satisfies 0.2 ≦ OA / IA ≦ 0.8.

  The inner region preferably has at least one circumferential main groove extending in the tire circumferential direction.

  The groove depth of the circumferential main groove in the inner region is desirably larger than the groove depth of the circumferential main groove in the outer region.

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

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

  The pneumatic tire is a tire whose rotation direction is designated, and the length of the chamfering seen from the tread surface of the tread block is different between the entry side to the road surface and the kicking side from the road surface when the tire rolls, It is desirable that the ratio of the chamfering length on the kicking side from the road surface to the chamfering length on the entry side to the road surface is smaller than 1.

  The pneumatic tire according to the present invention can improve the steering stability performance on the dry road surface and the wet road surface while ensuring the load supporting performance while having a small diameter.

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. 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. The center region Ce is two regions in the center in the width direction among the four regions divided into four when the tread region to be grounded is divided into four in the width direction, and the shoulder region Sh is outside, that is, in the width direction. It is a region at each end. The tread portion 6 includes an outer region OUT on the outer side in the vehicle width direction and an inner region IN on the inner side in the vehicle width when the tire 1 is mounted on the left and right regions with the equator plane CL of the tire 1 as a boundary. Including. 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 ½ 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.

(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 F0 using the tire cross-section width W0 and the tire cross-section height H0 when no load is applied, 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 includes the outer region OUT on the outer side in the vehicle width direction when the tire 1 is mounted on the vehicle, and the vehicle width. And an inner region IN on the inner side in the direction. That is, with respect to the tread contact width W1, the outer region OUT is a region outside the vehicle width direction when the tire 1 is mounted on the vehicle, and the inner region IN is a region inside the vehicle width direction when the tire 1 is mounted on the vehicle.

  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 outer region OUT and the inner region IN as described above with respect to the width direction, the relationship between the groove area IA of the inner region IN and the groove area OA of the outer region OUT is OA < It is preferable to satisfy IA. 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 OA / IA of the groove area OA of the outer region OUT to the groove area IA of the inner region IN 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.

  0.2 ≦ OA / IA ≦ 0.8 (6)

  If the ratio OA / IA of the groove area OA of the outer area OUT to the groove area IA of the inner area IN is less than 0.2, the steering stability performance on the wet road surface deteriorates due to the reduced drainage performance when turning the vehicle, and the ratio OA If / IA exceeds 0.8, the block rigidity cannot be sufficiently secured, and the steering stability performance is deteriorated. Preferably, 0.4 ≦ OA / IA ≦ 0.7. In order to achieve both the steering stability performance on the dry road surface and the steering stability performance on the wet road surface, the groove area ratio of the entire ground surface is preferably 10% or more and 35% or less.

  As shown in FIGS. 2 to 5, in the tire width direction cross section, the inner region IN has at least one circumferential main groove 21. If there is at least one circumferential main groove in the inner region IN, 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 outer region OUT has a depth of the circumferential main groove 21 provided in the inner region IN in the tire width direction cross section. It is larger than the groove depth of the groove 21. Therefore, the groove depth of the outer region OUT is smaller than the groove depth of the inner region IN. By making the groove depth of the outer region OUT shallower than the groove depth of the inner region IN, it is possible to increase the block rigidity of the outer region OUT, which is important during turning, and to improve the steering stability performance.

  In the pneumatic tire 1, the depth of the circumferential main groove 21 in the outer region OUT is preferably 3% or less of the tire radius. 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. Note that 0.4 ≦ Od / Id ≦ 0.8 regarding the maximum value Id of the circumferential main groove in the inner region IN and the maximum value Od of the circumferential main groove in the outer region OUT. It is preferable to satisfy.

(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 4 </ b> A on the outer side in the tire radial direction of the belt cover layer 4. The pneumatic tire 1 is not limited to the case where the reinforcing layer 4A is provided in both the inner region IN and the outer region OUT as shown in FIG. It is desirable to have the reinforcing layer 4A. 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.

  By arranging the reinforcing layer 4A in the vicinity of the center region Ce, the pneumatic tire 1 can improve the steering stability by increasing the in-plane bending rigidity of the ground contact region and increasing the cornering force. 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. Since the contact surface pressure tends to be biased in the small outer diameter tire, the block defined by the lug groove 22 can be chamfered in the circumferential direction to further improve the steering stability performance on the dry road surface and the wet road surface. it can. 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, the steering stability performance can be improved by providing a chamfer at the corner C1 of the tread block TB. And if a chamfer is provided in at least one of the corner C1 on the tread block TB stepping side, that is, the road surface approaching side, and the corner C2 on the road kicking side, the steering stability performance can be improved.

  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 length from the tread surface M1 to the point P3 is the chamfering depth Db of the tread block TB. 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. By providing chamfers at the corners of the tread block TB as in the present embodiment, it is possible to improve the steering stability performance on the dry road surface and the wet road surface.

  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 kick side from the road surface, and on the dry road surface and the wet road surface The steering stability performance can be further improved.

  The relationship between the circumferential length La of the chamfer on the road surface entrance side and the circumferential length Lb of the chamfer on the kicking side is more preferably Lb / La ≦ 0.8. However, Lb = 0, that is, chamfering may not be provided. Further, in at least one tread block TB, the relationship between the chamfering depth Da on the road surface entering side and the kicking side Db preferably satisfies Db / Da <1.

(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. The ratio of the circumferential length La of the chamfered corner C1 on the road surface entrance side to the circumferential length TBL of the tread block TB is, for example, 0.05 or more and 0.40 or less. The ratio of the circumferential length Lb of the chamfered corner C2 to the circumferential length TBL of the tread block TB is, for example, 0.03 or more and 0.35 or less.

(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 test on the stability performance on wet roads was evaluated using an index with a conventional example of 100, running on a watering course (water depth 3 mm), taking the reciprocal of the lap time. The larger the index value, the better. The test of the driving stability performance on the dry road surface was evaluated by an index with a conventional example being 100 by sensory evaluation by a driver. The larger the index value, the better.

  In Tables 2 and 3, the tire outer diameter 510 [mm], the tire total width 145 [mm], the bead diameter 12 inches, the groove area ratio OA / IA 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 circumferential main groove in the inner region IN, there is no reinforcing layer in the outer region OUT, there is no designation of the rotation direction when mounted on the vehicle, the tread block corner A tire without chamfering 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.

  The tire of Comparative Example 1 has a tire outer diameter of 480 [mm], a tire total width of 155 [mm], a bead diameter of 10 inches, a groove area ratio OA / IA of “1.1”, and a loss tangent of 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 inner region IN, there is no reinforcing layer in the outer region OUT, there is no designation of the rotation direction when mounted on the vehicle, and the tread block corner Tires without chamfering were 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 OA / IA 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 of the under rubber at 60 ° C. is “0.5”, there is no circumferential main groove in the inner region IN, and there is no reinforcing layer in the outer region OUT. A tire with no designation of the direction of rotation and no chamfering at the corner of the tread block was prepared.

  As the tire of Comparative Example 3, the tire outer diameter is 480 [mm], the tire total width is 155 [mm], the bead diameter is 10 inches, the groove area ratio OA / IA 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 inner region IN, and there is no reinforcing layer in the outer region OUT. A tire with no designation of the direction of rotation and no chamfering at the corner of the tread block was prepared.

  The tire of Comparative Example 4 has a tire outer diameter of 480 [mm], a tire total width of 155 [mm], a bead diameter of 10 inches, a groove area ratio OA / IA of “0.1”, and a 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 “0.1”, there is no circumferential main groove in the inner region IN, and there is no reinforcing layer in the outer region OUT. A tire with no designation of the direction of rotation and no chamfering at the corner of the tread block was prepared.

  The tire of Comparative Example 5 has a tire outer diameter of 480 [mm], a tire total width of 155 [mm], a bead diameter of 10 inches, a groove area ratio OA / IA of “0.6”, and a 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 “0.1”, there is a circumferential main groove in the inner region IN, and the groove depth in the inner region IN with respect to the groove depth in the outer region OUT The thickness ratio is “1.2”, the outer region OUT has a reinforcing layer, the tread block corners are chamfered, the direction of rotation at the time of mounting on the vehicle is specified, and the tire circumferential length of the tread block TB A tire with a ratio La / Lbk of the chamfered length in the circumferential direction of the tire to Lbk of “0.4” was prepared.

  According to Example 1 to Example 14, good results were obtained when the groove area ratio OA / IA was “0.2” or more and “0.8” or less. In addition, particularly good results were obtained when the groove area ratio OA / IA was not less than “0.4” and not more than “0.7”.

  According to Example 1 to Example 14, good results were obtained for a tire having the under rubber 10U rather than a tire having no under rubber 10U inside the cap rubber 10 in the tire radial direction. 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.

  According to Example 1 to Example 14, when the ratio of the groove depth of the circumferential main groove of the inner region IN to the groove depth of the circumferential main groove of the outer region OUT is larger than “1”, that is, the inner region IN Good results were obtained when the groove depth of the circumferential main groove was smaller than the groove depth of the circumferential main groove of the outer region OUT. In addition, better results were obtained for the tire having the reinforcing layer 4A than the tire having no reinforcing layer 4A in at least the outer region OUT.

  According to Example 1 to Example 14, 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.

  As described above, according to the pneumatic tire 1 of the embodiment, it is possible to improve the steering stability performance on the dry road surface and the wet road surface while ensuring the load supporting performance even though the diameter is small.

DESCRIPTION OF SYMBOLS 1 Pneumatic tire 2 Carcass part 3 Belt layer 3A, 3B Belt ply 4 Belt cover 4A Reinforcement 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 IN Inner region Sh Shoulder region OUT Outer region

Claims (9)

In a pneumatic tire in which an inner side and an outer side are specified when the vehicle is mounted, the total tire width SW, the tire cross-sectional height H1, and the bead diameter D are expressed by the formulas (1), (2), and ( 3) and the tread area to be grounded is divided into two areas, an inner area and an outer area when the vehicle is mounted, with the tire meridian as a boundary, and the groove area IA of the inner area and the groove area of the outer area A pneumatic tire whose relationship with OA satisfies OA <IA.
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 pneumatic tire according to claim 1 or 2, wherein a relationship between a groove area IA of the inner region and a groove area OA of the outer region satisfies 0.2 ≦ OA / IA ≦ 0.8.   The pneumatic tire according to any one of claims 1 to 3, wherein the inner region has at least one circumferential main groove extending in a 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 inner region is larger than a groove depth of the circumferential main groove in the outer region.   The pneumatic tire according to any one of claims 1 to 5, further comprising a belt layer provided radially inward of the outer region and a reinforcing layer provided radially outward 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. The pneumatic tire according to claim 6, which is equal to or less than a loss tangent tan δ.   The chamfer is provided on at least one of the corners of the tread block that has at least a part of the lug groove extending in the tire width direction and is surrounded by the circumferential main groove and the lug groove. The pneumatic tire according to any one of 7. 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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