JP2012086663A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire, in which anti-uneven wear performance is improved.SOLUTION: The pneumatic tire includes a carcass toroidally extended between a pair of bead core and serves as a frame, and a belt and a tread rubber positioned on the outer side in a tire radial direction of the carcass. In the pneumatic tire, the modulus of compressive elasticity in a tread center region of the tread rubber is higher than that in a tread shoulder region of the tread rubber.

Description

  The present invention relates to a pneumatic tire having improved uneven wear resistance, and more particularly to a side-reinforced run-flat tire.

There are various forms of uneven wear that occurs in the tread portion of a pneumatic tire. For example, center wear in which only the crown center is worn early is often observed on the rear drive shaft, and is caused by wear of the center portion because the load is applied vertically. Further, the river wear in which the rib edge continuously wears on the circumference at an early stage is likely to occur when a lateral force is applied, such as when a sharp curve is frequently cut.
In order to suppress such uneven wear, various methods have been conventionally proposed. For example, a plurality of dents extending in the tire circumferential direction and wide in the tire circumferential direction from the both ends in the longitudinal direction toward the central portion are arranged in series in the tire circumferential direction with intervals in the tire circumferential direction. Thus, a technique for suppressing center wear has been proposed (Patent Document 1). Moreover, the technique which suppresses riverware by changing the density, length, and inclination | tilt angle of the sipe of a tread pattern by a center part and a shoulder part is proposed (patent document 2).

JP 2010-116112 A JP 2010-149761 A

However, the present inventor has found that there is room for further improvement regarding so-called drag wear caused by the difference in tire diameter. In particular, in the side-reinforced run-flat tire, the problem of drag wear is remarkable, and an immediate countermeasure has been demanded.
Therefore, an object of the present invention is to provide a pneumatic tire with improved uneven wear resistance.

The gist of the present invention is as follows.
(1) In a pneumatic tire having a carcass extending in a toroidal shape between a pair of bead cores and having a belt and a tread rubber on the outer side in the tire radial direction of the carcass,
A pneumatic tire characterized in that the compression elastic modulus of the tread rubber in the tread center region is higher than the compression elastic modulus of the tread rubber in the tread shoulder region.

(2) The tread rubber is formed from a cap rubber layer constituting a tread surface, and a base rubber layer located on the inner side in the tire radial direction of the cap rubber layer,
The pneumatic tire according to (1) above, wherein the compression elastic modulus of the base rubber layer in the tread center region is higher than the compression elastic modulus of the base rubber layer in the tread shoulder region.

(3) A cap rubber layer that constitutes the tread tread, and a base rubber layer that is located on the inner side in the tire radial direction of the cap rubber layer and has a compression elastic modulus lower than the compression elastic modulus of the cap rubber layer; Formed from
The pneumatic tire according to (1) or (2) above, wherein the thickness of the base rubber layer in the tread center region is thinner than the thickness of the base rubber layer in the tread shoulder region.

(4) In the land portion of the tread center region, a plurality of grooves extending inclined with respect to the tire circumferential direction are formed,
The length of the land portion of the tread center region of 1 pitch in the developed view of the tread pattern is shorter than the length of the land portion of the tread shoulder region. Pneumatic tire.

(5) The pneumatic tire according to any one of the above (1) to (4) is a run flat tire in which a reinforcing rubber layer having a crescent cross section is disposed on the inner peripheral side of the carcass in a sidewall portion. A pneumatic tire characterized by being.

  According to the present invention, a pneumatic tire with improved uneven wear resistance can be provided.

It is a width direction sectional view of the pneumatic tire of the present invention. It is a figure for demonstrating the diameter difference of a tire. It is a width direction sectional view of the pneumatic tire of the present invention. It is a width direction sectional view of the pneumatic tire of the present invention. It is a development view of the tread pattern of the pneumatic tire of the present invention. It is a width direction sectional view of the pneumatic tire of the present invention. It is an expanded view of the tread pattern of an invention example tire and a comparative example tire.

Hereinafter, the pneumatic tire of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a cross-sectional view in the width direction of the pneumatic tire of the present invention. The pneumatic tire 10 of the present invention has a carcass 2 extending in a toroidal shape between a pair of bead cores 1 as a skeleton, and a belt 3 including two inclined belt layers 3a and 3b on the outer side in the tire radial direction of the carcass 2. A tread rubber 6 is arranged. The inclined belt layers 3a and 3b are formed by covering a plurality of cords extending in a direction oblique to the tire equatorial plane CL and intersecting each other with rubber.
The bead core 1, the carcass 2 and the belt 3 are not limited to the illustrated example. For example, the carcass can be composed of two carcass plies, or the belt can comprise a circumferential belt layer.

Here, it is important that the compression elastic modulus of the tread rubber 6 in the tread center region Tcent is higher than the compression elastic modulus of the tread rubber 6 in the tread shoulder region Tsho.
The tread center region Tcent refers to a region of 40% of the tread contact width W centered on the tire equatorial plane CL, and the tread shoulder region Tsho refers to both the tread center region Tcent and the tread contact end E on the outer side in the tire width direction. Refers to an area.
The tread contact width W means that the pneumatic tire is mounted on a standard rim specified by JATMA, filled with air pressure corresponding to the maximum load capacity at the applicable size, and corresponds to the maximum load capacity at the applicable size. This means the width in the tread width direction where the tread tread when the load is applied contacts the road surface. In addition, when TRA standard and ETRTO standard are applied in a use place or a manufacturing place, it follows each standard.

  Here, the compression modulus is a value calculated according to the following method. That is, a rubber test piece is filled in a cavity of a metal jig having a cylindrical cavity with a diameter of 14 mm and a height of 28 mm, for example, steel, without gaps, and this jig is set in a compression tester. The load W is applied to the upper and lower surfaces of the rubber test piece at a speed of 0.6 mm / min. The amount of displacement of the rubber test piece at this time is measured with a laser displacement meter, and the compression modulus is determined from the relationship between the load W and the displacement. Is calculated.

Hereinafter, the operation of the present invention will be described.
Generally, in the tire shape at the time of internal pressure filling, since there is a diameter difference between the tread center region Tcent and the tread shoulder region Tsho, so-called drag wear occurs. As shown in FIG. 2, the circumference of the tread center region Tcent is longer by the length d than the circumference of the tread shoulder region Tsho while the tire rotates once. However, since the tread center region Tcent and the tread shoulder region Tsho travel the same distance during one rotation of the tire, the tread rubber in the tread shoulder region Tsho slides relative to the road surface in order to correct the circumference difference d. , Drag wear occurs. This drag wear appears in the tread center region Tcent for the drive wheel, and appears in the tread shoulder region Tsho for the idle wheel.

Therefore, the present inventor diligently studied to reduce drag wear by reducing the difference in diameter between the tread center region Tcent and the tread shoulder region Tsho, and determined the compression elastic modulus of the tread rubber 6 in the tread center region Tcent. The inventors have conceived that the tread shoulder region Tsho is higher than the compression elastic modulus of the tread rubber 6.
When the compression elastic modulus of the tread rubber 6 in the tread center region Tcent is increased, the compression of the tread rubber 6 in the tire radial direction is reduced at the time of load rolling. Then, the elongation in the tire circumferential direction of the tread rubber 6 is reduced. On the other hand, if the compression elastic modulus of the tread rubber 6 in the tread shoulder region Tsho is reduced, the compression of the tread rubber 6 in the tire radial direction increases during load rolling. Then, the elongation in the tire circumferential direction of the tread rubber 6 increases. As described above, the tread rubber 6 has a small elongation in the tire circumferential direction in the tread center region Tcent, and the tread rubber region 6 has a large elongation in the tire circumferential direction in the tread shoulder region Tsho. Wear is suppressed.

The present inventor has conceived the following two methods as a specific method for imparting a tire width direction distribution to the compression elastic modulus of the tread rubber described above. These methods can be used alone or in combination.
As a first method, as shown in FIG. 3, the tread rubber 6 is formed from a cap rubber layer 6C constituting the tread surface and a base rubber layer 6B located inside the cap rubber layer 6C in the tire radial direction. Then, the compression elastic modulus of the base rubber layer 6B in the tread center region Tcent is set to be higher than the compression elastic modulus of the base rubber layer 6B in the tread shoulder region Tsho. Accordingly, when the tread rubber 6 including the base rubber layer 6B and the cap rubber layer 6C is viewed as a whole, the compression elastic modulus Etc of the tread rubber 6 in the tread center region Tcent is the compression elasticity of the tread rubber 6 in the tread shoulder region Tsho. Higher than the rate Ets. Incidentally, the cap rubber layer 6C constituting the tread surface is designed with a rubber friction coefficient or the like in order to improve the wear resistance performance, and the high durability performance is maintained by not changing the cap rubber layer 6C. Can do.
In the case where the tread rubber 6 is composed of three or more tread rubber layers, a plurality of tread rubber layers positioned on the inner side in the tire radial direction of the cap rubber layer without changing the cap rubber layer constituting the tread surface. The effect of the present invention can be achieved by imparting a tire width direction distribution to the compression modulus.

As a second method, as shown in FIG. 4, the tread rubber 6 is formed of a cap rubber layer 6C and a base rubber layer 6B, and the thickness Dc of the base rubber layer 6B in the tread center region Tcent is determined by the tread shoulder. The thickness is set to be thinner than the thickness Ds of the base rubber layer 6B in the region Tsho. In such a cap / base structure, generally, a rubber having a high compression elastic modulus is used for the cap rubber layer 6C in order to improve durability, and a low compression elastic modulus is used for the base rubber layer 6B for low heat generation. This rubber is also used in the present invention. In the tread center region Tcent, if the thickness of the base rubber layer 6B having a low compression elastic modulus is reduced, the tread rubber gauge (rubber gauge from the belt to the tread surface) does not change, so the thickness of the cap rubber layer 6C having a high compression elastic modulus is Will increase. As a result, in the tread center region Tcent, the compression elastic modulus of the entire tread rubber including the base rubber layer 6B and the cap rubber layer 6C can be increased. Similarly, in the tread shoulder region Tsho, the compression elastic modulus of the entire tread rubber including the base rubber layer 6B and the cap rubber layer 6C can be reduced by increasing the thickness of the base rubber layer 6B having a low compression elastic modulus. .
The thickness Dc of the base rubber layer 6B in the tread center region Tcent means an average value of the thickness of the base rubber layer 6B in the tread center region Tcent, and the thickness Ds of the base rubber layer 6B in the tread shoulder region Tsho. Means the average thickness of the base rubber layer 6B in the tread shoulder region Tsho.
In FIG. 4, the thickness of the base rubber layer 6B gradually increases from the tire equatorial plane CL toward the tread ground contact edge E, but may vary with a step from the tread center region Tcent to the tread shoulder region Tsho. .

FIG. 5 is a development view of the tread pattern of the pneumatic tire of the present invention. A plurality of lug grooves 7 extending in the tire width direction are formed in the land portion of the tread center region Tcent, and the land portion is partitioned into blocks 8 by these lug grooves 7. Here, the tire circumferential direction length Lc of the land portion (block 8) of the tread center region Tcent is shorter than the tire circumferential direction length Ls of the land portion of the tread shoulder region Tsho at one pitch in the development view of the tread pattern. Is preferred.
Since the lug groove 7 is closed by the adjacent block 8 at the time of tire load rolling, the contact length becomes the sum of the tire circumferential direction length Lc of the grounded block 8. Then, since the circumferential length of the tread center region Tcent is reduced by the groove width of the lug groove 7, the circumferential length difference d described above can be corrected.
As shown in the example, it is preferable that the land portion of the tread center region Tcent is divided into blocks 8 by the lug grooves 7, and the land portion of the tread shoulder region Tsho is a rib-shaped land portion, but also in the tread shoulder region Tsho A lug groove may be provided so that the density of the lug grooves in the tread shoulder region Tsho is lower than the density of the lug grooves in the tread center region Tcent.
In the illustrated example, the case where the lug groove 7 extending in the tire width direction is formed has been described. However, it may be a groove extending obliquely with respect to the tire circumferential direction, that is, a groove other than the groove extending in the tire circumferential direction. Thus, the effects of the present invention are exhibited.

As shown in FIG. 6, the present invention is preferably applied to a run-flat tire in which a reinforcing rubber layer 4 having a crescent-shaped cross section is disposed on the inner peripheral side of the carcass 2 in the sidewall portion. In the side reinforcing type run-flat tire, when the internal pressure is filled, the reinforcing rubber layer 4 bears the internal pressure. Therefore, the diameter growth of the tread shoulder region Tsho is small and the diameter growth of the tread center region Tcent is large. Therefore, the difference in diameter between the tread center region Tcent and the tread shoulder region Tsho is large, and the above-described problem of drag wear has remarkably appeared.
It should be noted that the crescent-shaped cross section is understood in a broad sense and includes not only regular and irregular crescent-shaped cross sections but also, for example, arcuate cross sections.

Examples of the present invention will be described below, but the present invention is not limited thereto.
Invention example tires and comparative example tires were prototyped and the shear force difference was measured.
Inventive tires 1-9 and comparative tires 1-5 (tire size: 245/40 R18) employ a cap / base structure and have the specifications shown in Table 1. The ratio of the compression elastic modulus of the cap rubber 6C to the compression elastic modulus of the base rubber 6B in the tread center region Tcent is 3.
Invention example tires 10-12 and comparative example tires 6-7 (tire size: 245/40 R18) are side-reinforced run-flat tires, adopt a cap / base structure, and have the specifications shown in Table 2. Yes.
In each of the inventive tires, the compression elastic modulus of the tread rubber in the tread center region is higher than the compression elastic modulus of the tread rubber in the tread shoulder region.
In Tables 1 and 2, Etc, Ets, Ec, Es, Er, Dc, and Ds are as follows.
Etc: Compression elastic modulus of the tread rubber in the tread center region Tcent Ets: Compression elastic modulus of the tread rubber in the tread shoulder region Tsho Ec: Compression elastic modulus of the base rubber layer 6B in the tread center region Tcent Es: Base rubber in the tread shoulder region Tsho Compression elastic modulus Er of layer 6B: Compression elastic modulus Dc of reinforcing rubber layer 4: Thickness of base rubber layer 6B in tread center region Tcent Ds: Thickness of base rubber layer 6B in tread shoulder region Tsho

  For each test tire, the shear force in the tread center region Tcent and the tread shoulder region Tsho was measured by the method disclosed in Japanese Patent Laid-Open No. 7-63658, and the differences are shown in Tables 1 and 2. A small shear force difference indicates a low drag wear.

  From Table 1, it can be seen that the inventive example tire has a reduced difference in shear force relative to the comparative example tire. That is, it can be confirmed that the uneven wear resistance is improved by the present invention.

1 bead core 2 carcass 3a inclined belt layer 3b inclined belt layer 4 reinforcing rubber layer 6 tread rubber 6C cap rubber layer 6B base rubber layer 10 pneumatic tire Tcent tread center area Tsho tread shoulder area

Claims (5)

In a pneumatic tire having a carcass extending in a toroidal shape between a pair of bead cores and having a belt and a tread rubber on the outer side in the tire radial direction of the carcass,
A pneumatic tire characterized in that the compression elastic modulus of the tread rubber in the tread center region is higher than the compression elastic modulus of the tread rubber in the tread shoulder region. The tread rubber is formed from a cap rubber layer constituting a tread surface, and a base rubber layer located on the inner side in the tire radial direction of the cap rubber layer,
The pneumatic tire according to claim 1, wherein the compression elastic modulus of the base rubber layer in the tread center region is higher than the compression elastic modulus of the base rubber layer in the tread shoulder region. The tread rubber is formed from a cap rubber layer that constitutes a tread surface, and a base rubber layer that is located on the inner side in the tire radial direction of the cap rubber layer and has a compression elastic modulus lower than that of the cap rubber layer. ,
The pneumatic tire according to claim 1 or 2, wherein the thickness of the base rubber layer in the tread center region is thinner than the thickness of the base rubber layer in the tread shoulder region. In the land portion of the tread center region, a plurality of grooves extending inclined with respect to the tire circumferential direction are formed,
The pneumatic tire according to any one of claims 1 to 3, wherein the length of the land portion of the tread center region of 1 pitch in a developed view of the tread pattern is shorter than the length of the land portion of the tread shoulder region. .   The pneumatic tire according to any one of claims 1 to 4, wherein the pneumatic tire is a run flat tire in which a reinforcing rubber layer having a crescent cross section is disposed on an inner peripheral side of the carcass in a sidewall portion. Pneumatic tire.

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