JP2000238508A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a pneumatic tire which excels in asymmetric abrasion resistance and lasts long in a steady state by providing a stepped land portion in a central range and both side ranges, while the stepped land portion of the central range has a larger step-down margin than that of the both side ranges. SOLUTION: A tread portion 1 has, in a central range Rc, a pair of circumferential center grooves 10, 11 which extend continuously in the circumferential direction with respect to a tread surface 1t, while having, in the both ranges Rs, pairs of circumferential shouldered grooves 12, 13 and 14, 15, respectively. In the tread portion 1, the central range Re has a stepped land portion 20, the surface of which is stepped down from the tread surface 1t, while the both side ranges Rs having stepped land portions 21, 22, the surface of which are stepped down from the tread surface It. A step-down margin of the stepped land portion 20 in the central range Rc is larger than that of the stepped land potions 21, 22 in both side ranges Rs. Thereby asymmetric abrasion resistance is improved and a tread rubber 7 can obtain a sufficiently longer life.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire, and more particularly to a radial ply tire for small trucks, trucks, and buses, and more particularly, exhibits excellent uneven wear resistance until the end of tread rubber wear. Related to pneumatic tires.

[0002]

2. Description of the Related Art A radial ply tire (hereinafter referred to as a pneumatic tire or tire) used for a vehicle having a relatively large gross weight called a heavy vehicle such as a small truck, a truck, a bus, or the like, extends along a tread surface of a tread portion. Generally, the tread portion is provided with a circumferential groove extending continuously around the tread portion. In a pneumatic tire having such a circumferential groove in the tread portion, a river wear or a rail way is provided along the circumferential groove edge. Irregular wear called abrasion occurs to some extent, and sometimes such uneven wear progresses to cause uneven wear defects called rib punches in the tread rubber land portion between the circumferential grooves adjacent to each other. Such uneven wear not only significantly shortens the wear life of the tread rubber, but also significantly impairs steering stability and vibration riding comfort of the vehicle. It is also known that tires with straight circumferential grooves are most disadvantageous for uneven wear.

In order to improve this kind of uneven wear, Japanese Patent Laid-Open No.
In the -169305 publication, in the tread rubber of the tread portion, a pair of grooves extending continuously in the tread surface circumferential direction, a pair of grooves and a narrow cut, a pair of narrow cuts, and the like are provided. A tire in which one or more rows of stepped land portions having a stepped surface from the tread surface and separated from the tread rubber land portion are formed in the tread portion has been proposed.
This proposal has significantly contributed to the improvement of uneven wear.

[0004] The function of the stepped land portion is to bring the surface of the stepped land portion into sliding contact with the road surface within the contact surface of the tread portion of the tire that rolls under a load, thereby changing the traveling direction of the vehicle. Concentrates the circumferential shear force in the opposite direction, the so-called braking force, on the stepped land, greatly reduces the braking force acting on the circumferential groove edge, and actively wears the stepped land, The function is to make it a wear sacrificial part. As a result, it is possible to prevent the occurrence of local wear due to the braking force generated on the circumferential groove edge portion having no step land portion, that is, to prevent the occurrence of uneven wear such as river wear, or to make it small. Become.

As is apparent from the above description, the step land portion is most effective when provided between a pair of straight grooves or straight narrow cuts (the former), and a pair of zigzag grooves or zigzag shapes is most effective. There is also a case (the latter) provided between the narrow cuts, but in the latter tire, the effect as an uneven wear sacrificial portion is reduced by the amount that the step land portion is inclined with respect to a plane parallel to the tire equatorial plane. Since the water draining effect on a wet road surface covered with a relatively thick water film is reduced, the former tire is often used.

[0006]

However, the use conditions of tires by users vary widely, and when roughly classified, the use conditions are, for example, frequently used on expressways, so that the ratio of straight running is low. Remarkably high steady driving conditions (the former) such as intercity trucks and high-speed buses, and the use of ordinary trucks such as delivery trucks (local trucks) and route buses, etc., and the ratio of straight traveling is not so high. It can be divided into so-called unsteady running conditions (the latter), in which the ratio of turning running is large.

On the other hand, as the degree of sliding contact between the surface and the road surface of the stepped land increases, the function of preventing the occurrence of uneven wear at the circumferential groove edge increases as the uneven wear sacrificial portion. The degree of sliding contact between the step land portion and the contact pressure between the tread rubber land portion forming the tread surface and the road surface increases as the contact pressure between the step land portion surface and the road surface becomes smaller. Accordingly, there has not been a tire which sufficiently conforms to both the former use condition and the latter use condition with respect to uneven wear resistance. This is because there is a significant difference between the contact pressure distribution state on the tread surface of the tire mounted on the vehicle traveling straight and the contact pressure distribution state on the tread surface of the tire mounted on the turning vehicle. This is also true of the contact pressure on the land surface.

However, if the step allowance from the tread of the step land portion is set to be extremely large, the braking force is drastically reduced along with the remarkable decrease in the contact pressure at a certain step allowance, and the step force is reduced. Since the wear work amount (a value proportional to the braking force × the amount of slip) rapidly decreases, the step land portion does not function as an uneven wear sacrifice portion, so that uneven wear starting from the circumferential groove edge cannot be suppressed. On the other hand, even if the step allowance of the step land part is set extremely small,
The work of wear at the step land portion becomes small, which causes uneven wear. In any case, severe uneven wear occurs under the above-mentioned steady running conditions.

Accordingly, the invention according to claims 1 to 3 of the present invention is an air-conditioner having excellent uneven wear resistance and a long wear life of tread rubber when used under a steady running condition mainly in a straight running of a vehicle. It is an object to provide a tire containing the tire.

[0010]

In order to achieve the above object, according to the first aspect of the present invention, a tread portion and a pair of sidewall portions are formed between bead cores embedded in a pair of bead portions. It has a radial carcass of at least one ply to reinforce and a belt to reinforce the tread portion, and is separated from the tread rubber land portion by a pair of grooves extending continuously in the tread surface circumferential direction on the tread portion, and descends from the tread surface. A pneumatic tire comprising a plurality of rows of stepped land portions having a surface, the stepped land portions forming an uneven wear sacrifice portion whose surface is in sliding contact with a road surface under rolling load of the tire. The tread portion has at least one row of stepped land portions in a central region thereof, and at least one row of stepped land portions in each region of both side regions of the central region. Below the step land A pneumatic tire characterized by having a cash d _C down larger stages than compared to Redirecting a d _S.

The "groove" of the pair of grooves described in claim 1 includes not only a groove generally called but also a narrow cut groove close to a sipe. According to this definition, the pair of grooves described in claim 1 , A pair of grooves, a pair of grooves and narrow notches, and a pair of narrow notches.

The central region of the tread portion refers to a region in which 1/3 of the tread width is equally divided on both sides of the tire equatorial plane, and both side regions of the central region are 1/3 of the tread width. Refers to an area where the width is applied to both sides of the central area. In a tire with a tread portion having a round shoulder, a distance between intersections of an extension of a contour of both tread edges and an extension of a contour of each buttress portion in a tire cross section is referred to as a tread width.

The invention described in claim 1 is, in effect, similar to the invention described in claim 2, in that the step d in the central region is d.
_It is suitable that the value of the ratio d _C / d _S of _C to the step allowance d _S of the step land portion on both side regions is in the range of 1.2 to 50.0.

In practicing the invention described in claims 1 and 2, preferably, the step d _c in the central region is 0.3 to 5.0 mm, as in the invention described in claim 3. It is within the range, and the descent allowance d _S of the step land on both sides is 0.1
範 囲 3.0 mm.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a cross-sectional view of a plane including a rotation axis of the pneumatic tire of the present invention,
FIG. 2 is an enlarged cross-sectional view of a pair of grooves and a stepped land portion in the tread portion center region of the tire shown in FIG. 1, and FIG. 3 is a pair of grooves and a stepped portion of a tread portion both side region of the tire shown in FIG. It is an expanded sectional view with a land part.

In FIG. 1, the pneumatic tire has a tread portion 1 and a pair of sidewall portions 2 and bead portions 3 connected to both sides of the tread portion 1.
A carcass 5 extending between the bead cores 4 embedded in each bead portion 3 to reinforce the tread portion 1 and a belt 6 for reinforcing the tread portion 1 are provided. It has a tread rubber 7. The carcass 5 has a rubber-coated ply of one or more plies, the illustrated example has a one-ply radially arranged steel cord, and the belt 6
Has two or more layers, and the illustrated example has four steel cord layers.

The tread portion 1 has a pair of circumferential central grooves 10, 11 extending continuously in the circumferential direction of the tread surface 1t in the central region Rc (described below), and both side regions Rs of the central region Rc.
And a pair of circumferential shoulder grooves 12 and 13 and a pair of circumferential shoulder grooves 14 and 15. Groove 10 in the illustrated example,
11, 12, 13, 14, and 15 are all straight grooves.

In FIG. 1, the central region R of the tread 1
c is a (1/3) × W area in which 1/3 of the width W of the tread 1t is equally divided on both sides of the tire equatorial plane E, and each of the two side areas Rs is a central area Rc and a tread edge. (1/3) × W area extending from the TE edge. Tread end T of a tire whose tread portion 1 is a round shoulder as shown in the illustrated example
E is, as shown in the cross-sectional view of FIG. 1, an intersection of an extension of the end contour of the tread surface and an extension of the buttress contour.

Here, in FIG. 1 to FIG.
Reference numeral 1 denotes a pair of circumferential central grooves 10 and 1 in the central region Rc.
1. Land portion 7L of tread rubber 7₁, 7L_TwoAway from
Step land having a step surface 20s descending from the tread 1t
In the region 20 and each region of both side regions Rs, a pair of circumferential
The land 7 of the tread rubber 7 is formed by the shoulder grooves 12 and 13.
L ₁, 7L_ThreeFrom the tread 1t
Step 21 having a surface 21s and a pair of circumferential shoulders
Land portion 7L of tread rubber 7 by grooves 14 and 15_Two, 7L
_FourFrom the tread surface 1t.
And a step land portion 22 having the same.

Here, the tread portion 1 has at least one row in the central area Rc.
In each of the regions s, one or more rows, in the illustrated example, one row of the step land portion 21,
22 and the step land portions 20, 21, 22
Shall form an uneven wear sacrifice portion in which the surfaces 20s, 21s, and 22s come into sliding contact with the road surface under the rolling load of a pneumatic tire (hereinafter referred to as a tire).

Referring to FIG. 2 and FIG. 3, a step allowance d from the tread 1t of the stepped land portion 20 in the central region Rc.
_C (mm) represents the step land portions 21 and 2 in both side regions Rs.
2 is made larger than the step allowance d _S (mm) from the tread surface 1t.

Here, first, the tread portion 1 of the tire in which a vertical load is applied to the tire rotation axis shows a contact pressure distribution shown in a diagram in FIG. This contact pressure distribution curve is a distribution curve immediately below the load, but shows a similar tendency in the contact length direction. That is, the ground pressure is highest in the central region Rc,
In both side regions Rs, tread surface 1t end TE from both ends of central region Rc
It has a chevron distribution that decreases toward. In particular, at the time of high-speed running of the vehicle, the centrifugal force acting on the tread portion 1 causes the central portion of the tread portion 1 to protrude, so that the contact pressure distribution tends to be even higher.

Next, with respect to a boundary between a region where the step land portions 20, 21 and 22 are in sliding contact (hatched portion) and a region where no sliding contact is made (open portion), the contact pressure of the tread portion 1 ( a kgf / cm ^2), as can be seen from FIG 5 representing the relationship between the stage down cash d (mm), the ground contact pressure of the tread portion 1 is increased, the surface 20 of the stepped land portion 20, 21, 22
In order for s, 21s, and 22s to make sliding contact, it is necessary to increase the step allowance d (mm).

For example, the contact pressure Pkgf / cm^TwoWhen the border
Upper point B_PStep d equivalent to _P(Mm) but slip
It is the minimum value required for contact, and the contact pressure Pkgf / cm^TwoThan
High contact pressure Qkgf / cm^Two, The point B on the boundary line_QEquivalent to
Step down d_Q(Mm) is required for sliding contact
It is the minimum value, and as is clear from the figure, d_Q(Mm)>
 d_P(Mm).

As is clear from the description given with reference to FIGS. 4 and 5, the step allowance d _C (mm) of the step land portion 20 located in the central region Rc is changed to the step land located in both side regions Rs. By making the step ds (mm) larger than the step descent (d _S (mm)) of the sections 21 and 22, the stepped land sections 20, 21, and 22 effectively function as uneven wear sacrifice sections in straight running or near straight running. As a result, the land portions 7L ₁ of the pair of grooves 10 and 11 extend over the entire tread surface 1t of the tread portion ₁ .
7L ₂ side groove edge land portion 7L _1, 7 a pair of grooves 12, 13
Land portions 7L ₂ , 7 of the L ₃ side groove edge and the pair of grooves 14, 15
L ₄ side groove edges each uneven wear occurs is suppressed to improve the uneven wear resistance, the wear life of the tread rubber 7 is sufficiently long.

Actually, the step allowance d of the step land portion 20
_C (mm), the step allowance d of the step land portions 21 and 22
The value of the ratio d _C / d _S to _S (mm) is 1.2 to 5
0.0. It is not possible for the value of the ratio d _C / d _S to be less than 1.2 or more than 50.0 because the ratio deviates from the actual condition of the contact pressure distribution of the tread portion 1.

Also, the step-down allowance d_C(Mm), d_S(M
Looking at m) individually, the drop-down allowance d _CIs 0.3 to 5.0
mm, and the step-down allowance d_SIs 0.1 to 3.0
mm. In addition, the descent allowance d_C
Is smaller than 0.3 mm,_SIs 0.1
mm, both of which are compared with the ground pressure in FIG.
Belongs to a non-sliding area below the indicated boundary,
Step down d_CIs more than 5.0mm
Teenage d_SIs over 3.0mm, both are too large,
In contrast to the contact pressure, there is no sliding contact.
It is impossible.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A radial ply tire for trucks and buses having a size of 315 / 80R22.5 (tubeless tire). The internal configuration, groove configuration and stepped land configuration are all in accordance with FIG. Rubber coated ply of radially arranged steel cord, belt 6
Consists of four rubber-coated teal cord layers. In order to accurately verify the effects of the step allowances d _C and d _S , a pair of grooves 1
0, 11, a pair of grooves 12, 13 and a pair of grooves 14, 15
Except for the step land portions 20, 21, and 22, the tread portion 1 had no pattern. Groove depth D _1, D ₂ of each groove 10-15 was 25 mm.

In addition to the example tires, a conventional example tire and a comparative example tire were prepared. The drop allowance d _C and d _S of each tire are described below. Except for the step-down margins d _C and d _S , all were the same.

Example tires, conventional tires, and comparative tires were used as test tires, and these tires were mounted on trucks mainly driven on European highways, and allowed to run on the road.
Changes in the steps d _C and d _S of the steps 20, 21 and 22 were frequently recorded.

The results of the recording are summarized by the running distance at which the step allowance d _{C is} approximately 0 (zero) mm. The tire of the conventional example is about 40,000 km, the tire of the comparative example is about 20,000 km, and the center area Rc is about The step land portion completely disappeared, lost its function as the uneven wear sacrifice portion, and caused uneven wear in the central region Rc during the subsequent traveling, and the tire had a short wear life. On the other hand, even after the tire of Example 1 traveled about 100,000 km, the step allowance d _C was maintained at about 1.0 to 1.5 mm, and almost no uneven wear was found. 7
Had a sufficient wear life. The stage down generations d _S of both sides area Rs had to be sufficiently retained any of the tire.

[0032]

According to the invention described in the first to third aspects of the invention, the tread exhibits excellent uneven wear resistance mainly under running conditions mainly in straight running or running close to straight running. It is possible to provide a long-life pneumatic tire that can significantly improve the wear life of rubber.

[Brief description of the drawings]

FIG. 1 is a sectional view of a pneumatic tire according to an embodiment of the present invention.

FIG. 2 is an enlarged sectional view of a main part of the tire shown in FIG.

FIG. 3 is an enlarged sectional view of another main part of the tire shown in FIG.

FIG. 4 is a ground pressure distribution diagram of a tread portion.

FIG. 5 is a graph showing the relationship between the contact pressure and the step allowance for the boundary between the sliding contact area and the non-sliding contact area.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 tread portion 1 t tread 2 sidewall portion 3 bead portion 4 bead core 5 carcass 6 belt 7 tread rubber 7 L ₁ , 7 L ₂ , 7 L ₃ , 7 L ₄ land portion 10, 11 pair of circumferential central grooves 12, 13 pair of circumferential directions Shoulder grooves 14, 15 A pair of circumferential central grooves 20 Step land portions 21, 22 in the central region Step land portions 20s, 21s, 22s in both side regions Step land surface E Tire equatorial plane TE Tread end W Tread width Rc Tread center the depth at which Rs tread side regions d _C central region stages down cash D ₁ of the stage decreases cash d _S side regions stepped land portion of the stepped land portion, D ₂ a pair of grooves

Claims (3)

[Claims] 1. A tread portion including one or more plies of a radial carcass for reinforcing a tread portion and a pair of sidewall portions, and a belt for reinforcing the tread portion, between the bead cores embedded in the pair of bead portions. A plurality of rows of step land portions separated from the tread rubber land portion by a pair of grooves continuously extending in the tread surface circumferential direction and having a step surface from the tread surface, and the step land portion has a surface of the tire. In a pneumatic tire having an uneven wear sacrifice portion which is in sliding contact with a road surface under a rolling load, a tread portion includes at least one row of stepped land portions in a central region thereof,
And a least one row of the stepped land portion in the region of both side regions of the central region, the stepped land portion of the central region, down larger stage than compared to cost down stage of the stepped land portion of each side region (d _S) A pneumatic tire, characterized in that the pneumatic tire has a cost (d _C ). 2. The ratio (d _C ) of the step margin (d _C ) of the central area to the step margin (d _S ) of the step land portion on both sides of the area
2. The tire according to claim 1, wherein the value of / d _S ) is in the range of 1.2 to 50.0. 3. The step allowance (d _C ) in the central area is 0.3.
3. The tire according to claim 1, wherein the tire falls within a range of about 5.0 mm, and a step allowance (d _S ) of a step land portion on both sides of the tire falls within a range of 0.1 to 3.0 mm. 4.