JP2000177323A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simultaneously improve both the uneven wear resistance and wear resistance by setting, in a plurality of stepped land parts of a tread, the down margin of one stepped land part small, compared with the other down margin, and setting the surface width of one stepped land part large, compared with the other surface width. SOLUTION: In respect to the down margins from the edges of the treads of a plurality of stepped land parts 20, 21, 22 to the down surfaces 20s, 21s, 22c thereof and the tire rotating directional down surface widths, the down margin of one stepped land part 20 is set small, compared with the down margins of the other stepped land parts 21, 22, between two groups of one stepped land part 2O and the other stepped land parts 21, 22. The two groups satisfy the relation that the surface 20s width of the one stepped land part 20 is large, compared with the surface 21s, 22s widths of the other stepped land parts 21, 22. According to this, the magnitude of the braking force in the stepped land part 20 can be made substantially equal to those of the stepped land parts 21, 22, and the wear resistance in slits 10, 11 can be held equally to slits 12-15.

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 to an improvement in uneven wear resistance and wear resistance of tread rubber of the tire. The present invention relates to a pneumatic tire that achieves both improved performance.

[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, a pair of grooves, a pair of grooves and a narrow cut, a pair of narrow cuts, and the like are provided in the tread rubber of the tread portion continuously extending in the circumferential direction of the tread. A groove or narrow notch has been proposed to provide a tire in which a plurality of stepped land portions having a stepped surface from a tread are formed in a tread portion, separated from a tread rubber land portion, and this proposal significantly contributes to uneven wear improvement. I have.

[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. The function is to concentrate the circumferential shear force in the opposite direction, that is, the braking force, on the step land portion, and to make the step land portion a sacrificial wear portion. As a result, it is possible to prevent or minimize the occurrence of local wear caused by the braking force, that is, uneven wear such as river wear, which has occurred on the circumferential groove edge having no step land portion. . As is clear from the above, the step land portion has the most significant effect when provided between a pair of straight grooves or narrow notches, and is next provided when provided between a pair of zigzag grooves or narrow notches. It is effective.

In order to prevent uneven wear, it is sufficient to apply a braking force as large as possible to the surface of the stepped land portion. The magnitude of the braking force is determined by the step allowance from the tread to the surface of the stepped land portion. Increases almost linearly until a certain value is reached, so that the step allowance from the tread to the surface of the stepped land is set as large as possible within the range of the braking force increase.

[0006]

However, both the frequency of loading / unloading and the frequency of starting acceleration / stopping are low, and the time ratio of so-called steady running, that is, straight running or close to straight running of the vehicle, is extremely large. As a pneumatic tire to be mounted on a vehicle having a low steady-state running time, the above-mentioned stepped land portion exhibits remarkably excellent uneven wear resistance, for example, a vehicle such as a local truck, a route bus, a luggage delivery truck, etc. As described above, the ratio of the steady traveling time as described above is relatively small, and the ratio of the non-steady traveling time is rather large. In this case, the ratio of the turning traveling necessarily increases, and the frequency of the lateral input to the tire is large. It has been found that a tire provided with the above-described stepped land portion as a tire to be mounted on a running vehicle cannot obtain sufficient wear resistance.

[0007] Originally, the above-mentioned river wear uneven wear,
This kind of uneven wear is a symptom that appears remarkably in the above-mentioned running mainly in steady running.Therefore, in the conventional stepped land portion, the specifications as the circumferential uneven wear sacrifice portion of the tread portion are the most important. Consideration has been given to the specifications in the tire rotation axis direction (lateral direction), and almost no consideration has been given mainly to the lateral rigidity. Land work around the stepped land (ribs, blocks, lugs, etc.)
It tends to decrease compared to the amount of wear work. Here, the work of wear is a value obtained by multiplying the product of the contact pressure per unit area (kgf / mm ² ) and the amount of slip (mm) by a constant.

As a result, the surface of the step land portion of the tire which has traveled to some extent protrudes from the tread forming the land portion.
Phenomenon is seen. The protrusion of the step land portion is disadvantageous not only in terms of wear resistance but also in terms of uneven wear resistance. Also, under such tire usage conditions where the lateral input is severe, uneven wear due to the circumferential drag component of the tread portion, which is captured as a result of the braking force action, is unlikely to occur, so the uneven wear sacrificed part originally at the stepped land portion It is unavoidable that the opportunity to play the role of 少 な く 少 な く 定 常 定 常 定 常 定 常 定 常 定 常 定 常 定 常 定 常 定 常 定 常 定 常 定 常 定 常 定 常 定 常 定 常 定 常 定 常 定 常. That is the current situation.

On the other hand, if the surface width of all the stepped land portions is greatly increased and the lateral rigidity of the stepped land portions is improved,
While it is advantageous to improve wear resistance under tire usage conditions where lateral input is severe, the volume ratio occupying the tread rubber of the step land portion as an uneven wear sacrifice part greatly increases and controls the wear resistance, Since the actual volume ratio of the land portion excluding the stepped land portion is greatly reduced, the required abrasion resistance (wear life of the tread rubber) cannot be ensured under straight running or running conditions close to straight running. With.

Therefore, the invention described in claims 1 to 5 of the present invention suppresses the occurrence of uneven wear under running conditions of straight running or nearly straight running, and the wear resistance of the tread rubber under running conditions where lateral input is severe. It is an object of the present invention to provide a versatile pneumatic tire in which both uneven wear resistance and wear resistance are simultaneously improved for use under two running conditions.

[0011]

In order to achieve the above object, according to the first aspect of the present invention, there is provided a tread rubber having a pair of grooves or narrow cuts extending continuously in a tread surface circumferential direction. It is provided with a plurality of stepped land portions which are separated from the land portion and have a stepped surface from the tread surface, and the stepped land portion has an uneven wear in which the surface is in sliding contact with the road surface under rolling load of the tire. In the pneumatic tire formed with the sacrificial portion, regarding the step allowance and the surface width of the step land portion from the tread surface to the step surface, between the plurality of step land portions, a step of one step land portion is provided. The falling margin is smaller than that of the other step land, and the surface width of one step land has a wider relationship than the surface width of the other step land. It is a pneumatic tire.

According to the first aspect of the present invention, as in the second aspect of the invention, the step allowance at both the one step land portion and the other step land portion is 0.1 to 3.
0 mm, and the step surface width in both the one step land portion and the other step land portion is 5.0 to 30.
It is suitable to be within the range of 0 mm.

Further, in a state where one step land portion and the other step land portion are separated from each other,
The step allowance of the one step land portion is 0.1 to 1.5 mm
And the step allowance of the other step land portion is in the range of 0.5 to 3.0 mm, and the surface width of one step land portion is 10. 0-3
It is suitable that it is within the range of 0.0 mm and the surface width of the other stepped land is within the range of 5.0 to 15.0 mm.

Here, in particular, the step allowance and the surface width of the step land portion are set to 1998 JATMAYEAR BOOK.
Assume that the tire is mounted on the applicable rim for each type of tire described in the JATMA standard, and the tire and the rim are measured with a tire filled with the maximum air pressure specified by the JATMA standard. The applicable rim is JAT
Includes standard and acceptable rims as described in the MA standard.

Regarding the arrangement of the one step land portion and the other step land portion on the tread portion, there are two cases depending on the type of the tire. As described above, a tire having one or more of the one step land portions in the tread portion central region and one or more of the other step land portions in both side regions of the tread portion central region is provided.

Next, in the second aspect, as in the fifth aspect of the present invention, one or more of the other stepped land portions are provided in a tread portion central region, and one or more of the other step land portions are provided in both side regions of the tread portion central region. It is assumed that the tire has one or more of the one step land portions.

Here, the tread portion center region is defined as a 1/30 divided tread width on each side of the tire equatorial plane.
A region where the three widths are equally divided is referred to, and the both side regions of the tread portion are regions located on both sides of the central region and having a width of 1/3 of the tread width. In the case where the tread portion is a round shoulder or a chamfered shoulder, the distance between the intersections of the extension line of the buttress and the extension line of the tread contour line in the tire cross section is defined as the tread width.

[0018]

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,
2 is a development view of the tread of the pneumatic tire shown in FIG. 1, FIG. 3 is an enlarged sectional view taken along line III-III of the development view of the tread shown in FIG. 2, and FIG. Of tread development
FIG. 5 is an enlarged sectional view taken along the line IV-IV, and FIG. 5 is an enlarged sectional view taken along the line V-V of the development view of the tread shown in FIG.
FIG. 4 is an enlarged cross-sectional view of a pneumatic tire having a stepped land portion different from the tire shown in FIG. 1, taken along the line IV-IV shown in FIG. 2.

Referring to 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.
In order to reinforce the treads 2, 3, a carcass 5 extending between bead cores 4 embedded in each bead portion 3 and a belt 6 for reinforcing the tread portion 1 are provided. It has rubber 7. The carcass 5 has one or more ply, the illustrated example has a rubber-coated ply of one ply of radially arranged steel cords, and the belt 6 has two or more layers, and the illustrated example has four steel cord layers.

Referring to FIG. 1 to FIG.
Has a pair of grooves or narrow notches 10 and 11 extending continuously in the circumferential direction of the tread surface 1t, a pair of narrow notches or grooves 12 and 13 and a pair of narrow notches or grooves 14 and 15 and has a tread. Part 1 comprises a pair of grooves or narrow cuts 10,
11, a stepped land portion 20 separated from the land portions 7L ₁ and 7L ₂ of the tread rubber 7 and having a stepped surface 20s from the tread surface 1t, and a pair of narrow cuts or grooves 12 and 13
And a stepped land portion 21 separated from the land portions 7L ₁ and 7L ₃ of the tread rubber 7 and having a stepped surface 21s from the tread surface 1t, and a pair of narrow cuts or grooves 14 and 1
5, a plurality of (three in the illustrated example) step land portions are provided with a step land portion 22 which is separated from the land portions 7L ₂ and 7L ₄ of the tread rubber 7 and has a stepped surface 22s from the tread surface 1t.

The surface 2 of each of the stepped portions 20, 21, and 22
0s, 21s, and 22s are in contact with the road surface under the rolling load of the tire, and the shear force inevitably generated between the tread surface 1t and the circumferential direction of the tire traveling in the circumferential direction. In other words, it is subjected to the action of the braking force and makes sliding contact with the road surface, so that the step land portion 20,
21 and 22 are other land parts 7L ₁ , 7L ₂ , 7L ₃ , 7L
_It plays the role of an uneven wear sacrificed part that takes over the uneven wear that would occur in ₄ .

Here, in FIGS. 3 to 5, the step allowance d of the plurality of step land portions 20, 21, 22 from the edge of the tread surface 1t to the step surfaces 20s, 21s, 22s.
₂₀ (mm), d ₂₁ (mm), d ₂₂ (mm), and the step surface 20s, 21s, and 22 width w in the tire rotation axis direction
Regarding ₂₀ (mm), w ₂₁ (mm) and w ₂₂ (mm), it is divided into two groups, one step land part 20 and the other step land parts 21 and 22, and between these two groups, ,
The step allowance d ₂₀ (mm) of one step land part 20 is the step allowance d ₂₁ (mm), d _{22 of the} other step land parts 21 and _22.
(Mm) and one of the step land portions 20
Surface 20s width w ₂₀ (mm) of the other step land portion 21,
22 surface 21s, 22 width w ₂₁ (mm), w ₂₂ (mm)
Satisfies the relationship of being wider than.

In order to further clarify these interrelationships, rewriting is as follows.
₂₀ (mm) <d ₂₁ (mm), d ₂₀ (mm) <d ₂₂ (m
m), and for the surface width w of the step land portion, w ₂₀ (m
m)> w ₂₁ (mm) and w ₂₀ (mm)> w ₂₂ (mm). Usually, d ₂₁ (mm) =
d ₂₂ (mm) or d ₂₁ (mm) ≒ d ₂₂ (mm), w
₂₁ (mm) = w ₂₂ (mm) or w ₂₁ (mm) ≒ w ₂₂ (m
m), and in a special case, d ₂₁ (mm) ≠ d ₂₂ (m
m), w ₂₁ (mm) ≠ w ₂₂ (mm).

FIG. 7 is a diagram summarizing the results of the research, showing the relationship between the step allowance d of the stepped land portion and the braking force, and the relationship between the surface width w of the stepped land portion and the braking force. From FIG. 8 shown as a diagram, the drop allowance d
The braking force simply increases while increasing from zero to a certain value dmax, and when the step-down margin d is increased beyond the value dmax, the braking force drops sharply from its maximum value BFmax, On the other hand, when the surface width w of the step portion is increased from a value close to zero, the braking force increases while showing a saturating tendency. These facts imply that the magnitude of the braking force generated on the stepped land is the value dmax
This means that it can be easily controlled by a combination of the following step margin d and the step land portion surface width w.

Using this matter as another research result, the work load in the circumferential direction of the tread portion on the stepped land portion is used as a parameter.
The correlation between the step allowance d and the surface width w of the step land portion was summarized, and the diagram shown in FIG. 9 was obtained. It can be seen from the diagram shown in FIG. 9 that there are countless combinations of the step allowance d and the surface width w of the step land portion for imposing the same circumferential wear work on the step land portion.

FIG. 10 is a graph showing the relationship between the surface width w of the stepped land portion and the rigidity in the lateral direction (the tire rotation axis direction) of the stepped land portion with the stepping margin d of the stepped land portion constant.
It has been found that increasing the surface width w increases the lateral stiffness of the step land substantially linearly.

Considering the diagrams shown in FIGS. 7 to 10 together, the surface width w ₂₀ (mm) of the step land portion of the step land portion 20 is considered.
To the surface widths w ₂₁ (mm) and w of the step land portions 21 and 22
₂₂ (mm) wider, instead a stepped land 20
Stage down the generations d ₂₀ (mm), the stage down cash d ₂₁ of the stepped land portion 21, 22 (mm), very smaller than d ₂₂ (mm), the stepped land portion 20, and the magnitude of the braking force, the circumferential The amount of work in the direction of wear
Can be almost the same as those of 1, 22
As a result, the uneven wear resistance of the pair of grooves or narrow cuts 10 and 11 is improved by the pair of narrow cuts or grooves 12 and 13.
And the pair of narrow cuts or grooves 14 and 15 can be held as high as the uneven wear resistance.

On the other hand, the surface width of the step land portion 20 is set to w ₂₀
(Mm) to the surface width w ₂₁ (m
m) and w ₂₂ (mm), the lateral rigidity of the stepped land portion 20 can be made higher than the lateral rigidity of the stepped land portions 21 and 22. On the other hand, the one step land portion 20 sufficiently opposes and less escapes, and as a result, under the action of the side force, at least the step land portion 20 is aligned with the land portions 7L ₁ and 7L _{2 around} it. Wear moderately,
Unlike the conventional tire, there is no problem that the step land portion protrudes, and an appropriate step allowance can be secured, and excellent uneven wear resistance can be maintained.

Therefore, one step land portion 20 is disposed in the region of action of the large side force, and the other step land portions 21 and 22 are disposed in the region of action of the smaller side force. Land part 2
The protrusions 1 and 22 are suppressed, and the original uneven wear suppressing function of the step land portions 21 and 22 can be sufficiently exhibited. Further, the total width of the step land portions 20, 21 and 22 (w ₂₀ + w ₂₁ +)
w ₂₂ ) does not need to be so wide and tread rubber 7
Can also be kept superior.

As described above, one of the steps 20
And the other stepped land portions 21 and 22 have been described. However, it is divided into three or more groups. For example, one stepped land portion 20 is divided into the first stepped land portion 20 and the other stepped land portion. The parts 21 and 22 are the second step land part 21 and the third step land part 2
1 and the first step land 20 and the second step land 2
1 and the first stepped land 20 and the third stepped land 2
2, the second stepped land 21 and the third stepped land 2
2, the step d margin and the width w
It is possible to satisfy the relationship. Of course, it is possible to provide a fourth or more step land portion.

The tires shown in FIGS. 1 to 5 have a step-down margin d ₂₀ (mm) and d ₂₁ having a mutual relationship as described in detail above.
(Mm), d ₂₂ (mm) and surface width w ₂₀ (mm), w ₂₁
(Mm), steps ₂₂ and 21 having w ₂₂ (mm)
As shown in FIG. 1, the tread portion 1 central region R in which the width １ ／ W obtained by equally dividing the tread width W, which is the distance between both tread ends TE, into three equal parts is equally distributed on both sides of the tire equatorial plane E.
c (indicated by Rcd in the developed view of FIG. 2) has one step land portion 20 and is a region Rs on both sides of the tread portion 1 having a width of 1 / 3W.
(Indicated by Rsd in the developed view of FIG. 2), each has the other stepped land portions 21 and 22. This tire has a feature that the tread rubber 7 has excellent uneven wear resistance under use conditions of performing unsteady running in which relatively large side force is generated relatively frequently, and has excellent wear resistance under steady running. Have.

Although not shown, a tire having one or more stepped land portions 21 or 22 in the central region Rc of the tread portion 1 and a stepped land portion 20 in each of both side regions Rs may be used. The contact pressure distribution has a so-called butterfly-shaped distribution, and mainly under operating conditions where steady running is performed,
It is suitable as a tire having both excellent uneven wear resistance and excellent wear resistance. The above-described tire is suitable for both a tire having a butterfly-type distribution and a tire having a so-called barrel-type distribution.

The above is a description of the step land portion distribution under extreme use conditions.
I mentioned about the minutes, ₂₀(Mm), d
_{twenty one}(Mm), d_{twenty two}(Mm) and the surface width w₂₀(Mm), w
_{twenty one}(Mm), w_{twenty two}(Mm) as described below.
If set within a positive value range, it can be used under almost all conditions.
The best balance between uneven wear resistance and wear resistance.
Tires that can be used.

First, both the one step land portion 20 and the other step land portions 21 and 22 have a step allowance d ₂₀ (mm), d
₂₁ (mm) and d ₂₂ (mm) are in the range of 0.1 to 3.0 mm, and the surface widths w ₂₀ (mm) and w ₂₁ (m
m), w ₂₂ (mm) is in the range of 5.0～30.0Mm, is that.

Step allowance d ₂₀ (mm), d ₂₁ (mm),
If d ₂₂ (mm) exceeds 3.0 mm, the surface of the steps 20, 21, and 22 on the ground contact surface of the tire under rolling with a load may be deprived of contact with the road surface. It should be noted that the lower limit has a value close to zero because the step-down margins d ₂₀ (mm), d ₂₁ (mm), and d ₂₂ (mm) tend to increase as the vehicle travels straight or nearly straight. 0.1 mm) is sufficient.

Surface widths w ₂₀ (mm), w ₂₁ (mm), w ₂₂
When (mm) is less than 5.0 mm, the braking force is too small, and the uneven wear resistance is reduced. In addition, the lateral rigidity is too small. If it exceeds, the lateral rigidity of the step land portion increases, but the portion of the tread rubber 7 that hardly contributes to the wear resistance in the straight running or almost straight running is excessively increased, and the wear life of the tread rubber 7 is reduced. Therefore, neither is possible.

Step allowance d ₂₀ (mm), d ₂₁ (mm),
d ₂₂ (mm), surface width w ₂₀ (mm), w ₂₁ (mm),
When w ₂₂ (mm) is divided into one step land portion 20 and the other step land portions 21 and 22, the step allowance d ₂₀ (mm) of the step land portion 20 is 0.1 to 1.5 mm. Within the range,
Step allowance d ₂₁ (mm), d for step land portions 21 and 22
₂₂ (mm) is suitable in the range of 0.5 to 3.0 mm.
The surface width w ₂₀ (mm) of the step land portion 20 is 10.0
The surface widths w ₂₁ (mm) and w ₂₂ (mm) of the stepped land portions 21 and ₂₂ are 5.0 to 15.
A range of 0 mm is suitable.

The step land portion 21 shown in FIG. 6 is a modified example of the step land portion 21 shown in FIG. 4, and has a chamfered portion 21p on the groove 13 side which is wider than the width of the narrow cut groove 12. Surface width w ₂₁ (m of the step land portion 21 having the chamfered portion 21p
m), as shown, the reference on the chamfered portion 21p side is the lower end of the chamfered portion 21p. Since this kind of tire has the opportunity to run on a road surface where gravel is scattered or scattered,
There is a case where pebbles may bite into the groove 13, and therefore, a chamfered portion 21 for making it difficult for foreign matters such as pebbles to bite into the groove 13.
p. A chamfered portion similar to the chamfered portion 21p is also provided on the opposing step land portion 22.

As described above, a pair of grooves or narrow cuts 1
0, 11 and a pair of narrow cuts or grooves 12 and 13
And the pair of narrow notches or grooves 14 and 15 are straight, but may be zigzag with small amplitude. The symbol S ₁ shown in FIG. 2 is a long sipe, and the symbol S ₂
Is a very short sipe. Land portion 7L _1, 7L ₂ is a rib as a whole, is divided into a block shape by sipes S _1.

[0040]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A radial ply tire for trucks and buses, the size of which is 295 / 75R22.5 (tubeless tire). The carcass 5 has one ply according to FIGS. 1 to 3 and FIGS. The belt 6 is composed of four rubber-coated teal cord layers.

The tread portion 1 has one step land portion 20 in the central region Rc and one step land portion 21 and 22 in both side regions Rs, and the step allowance d ₂₀ of the step land portion ₂₀ is 0.5 mm, surface width w ₂₀ is 20 mm, and step land portion 2
The drop allowances d ₂₁ and d ₂₂ of 1, ₂₂ are 2.5 mm,
The surface widths w ₂₁ and w ₂₂ are 5.0 mm based on the lower end of the chamfer. Also, the depth D of the pair of grooves or the narrow cuts 10, 11
₁ (see FIG. 3) is 14.5 mm, and has a depth D _{2 of} a pair of narrow notches or grooves 12 and 13 (see FIG. 4) and a depth D _{3 of} a pair of narrow notches or grooves 14 and 15. (FIG. 5
Reference) is 14.5 mm.

As a comparative object of the example, a comparative example tire having a tread pattern whose tread pattern is shown in FIG. 11 was prepared. The tread portion of the comparative example tire has a central region Rc.
(Rcd region in the developed view), two circumferential straight grooves 30,
31 and both side regions Rs (Rcd region in the developed view)
A step land portion 34 separated by a pair of narrow cuts 32 and grooves 33 and a step land portion 37 separated by a pair of narrow cuts 35 and grooves 36. Have the same specifications, and the descent allowance d is 2.5
mm and the surface width w based on the lower end of the chamfered portion is 9.0 mm. All other configurations and specifications other than those described above were matched to the examples.

The above example tires and comparative example tires:
The tread portion does not have a stepped land portion, and the same circumferential straight grooves 30 and 31 as the comparative example tire are each two (total of four).
The comparative tire and the conventional tire having substantially the same tread pattern were subjected to a field test by users under the following two different use conditions.

(1) A user who has a remarkable degree of uneven wear, and a river wear along a groove or a narrow notch spreads on a land portion, and finally the land portion often experiences the most significant uneven wear called a rib punch. (2) A user who has a certain degree of uneven wear but does not reach significant uneven wear such as a rib punch.

A summary of the test results is described below. The user test result (expressed as an index) described in (1).
The greater the value, the better); the distance traveled before removal due to tread rubber wear (indexed);
It is 115 against 0, and the conventional tire stops at 75.
The content is that uneven wear hardly occurs in the example tire,
On the other hand, in the comparative example tire, significant rib punch was generated in the tread central region, and early wear occurred in both side regions. If the degree of uneven wear progresses to a certain extent,
Normally, the tire is rejected. When the tread rubber thickness (depth of a groove or the like) used until reaching the rejection limit, the tire of Example is 11 compared to the tire of Comparative Example 100.
5. The number of tires in the conventional example is 60.

The user test results described in the item (2) (expressed as an index; the larger the value, the better); the tires of the example have almost no uneven wear like the comparative tire, and the running distance per 1 mm of tread rubber wear. The index of abrasion resistance is 100 in both cases. The wear resistance of the conventional tire was limited to 85. Incidentally, the stepped land portion 20 of the tread portion 1 a central region Rc of Example tire, stage down cash d ₂₀ becomes almost zero, rather than the uneven wear sacrificial portion, one of the ribs (full land portion)
It has been found that this greatly contributes to the improvement of wear resistance.

[0047]

According to the first to fifth aspects of the present invention, in a use condition mainly including straight running or steady running close to straight running, occurrence of uneven wear is suppressed to extend the usable limit distance. The tread rubber can improve the uneven wear resistance and abrasion resistance under running conditions mainly in unsteady running where the lateral input is severe, and the tread rubber can be used under two different running conditions. It is possible to provide a versatile and long-life pneumatic tire having both improved wear resistance and wear resistance.

[Brief description of the drawings]

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

FIG. 2 is a developed view of a tread of the tire shown in FIG. 1;

FIG. 3 is a sectional view taken along the line III-III shown in FIG. 2;

4 is a sectional view taken along the line IV-IV shown in FIG.

FIG. 5 is a sectional view taken along the line VV shown in FIG. 2;

FIG. 6 is a sectional view of a modification of the step land portion shown in FIG.

FIG. 7 is a diagram showing a relationship between a step allowance at a stepped land portion and a braking force.

FIG. 8 is a diagram showing a relationship between a surface width of a stepped land portion and a braking force.

FIG. 9 is a graph showing the relationship between the step allowance and the surface width of the step land portion.

FIG. 10 is a diagram showing a relationship between a surface width of a stepped land portion and lateral rigidity.

FIG. 11 is a development view of a tread of a comparative example tire.

[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 grooves 12, 13 pair of narrow cuts and grooves 14 , 15 A pair of narrow notches and grooves 20 One step land part 20s Step land part surface 21, 22 The other step land part 21s, 22s Step land part surface 21p Bevel E Tire equatorial plane TE Tread end Rc Tread central area Rs developed width d ₂₀ of the developed width Rsd side regions of the tread side regions Rcd central region, d _21, d ₂₂ stage edge cash w ₂₀ of the stepped land portion, w _21, w ₂₂ surface width of the stepped land portion S ₁ long sipe S ₂ short sipes

Claims (5)

[Claims] The tread portion includes a pair of step land portions that are separated from the tread rubber land portion by a pair of grooves or narrow cuts extending continuously in a tread surface circumferential direction and have a stepped surface from the tread surface, The step land portion is a pneumatic tire, the surface of which forms an uneven wear sacrifice portion that makes a sliding contact with a road surface under rolling load of the tire, wherein the surface of the step land portion is stepped down from a tread surface. Regarding the step allowance and the surface width, the step allowance of one step land is smaller than the step allowance of the other step land, and A pneumatic tire, wherein the surface width of the step land portion has a wider relationship than the surface width of the other step land portion. 2. A step allowance in both the one step land portion and the other step land portion is within a range of 0.1 to 3.0 mm, and the step allowance in both the one step land portion and the other step land portion is provided. The tire according to claim 1, wherein the step surface width is in a range of 5.0 to 30.0 mm. 3. A step allowance of said one step land portion is 0.
1 to 1.5 mm, the step allowance of the other step land portion is in the range of 0.5 to 3.0 mm, and the surface width of the step land portion is one of the step land portions. The tire according to claim 1, wherein the surface width is in a range of 10.0 to 30.0 mm, and the surface width of the other step land portion is in a range of 5.0 to 15.0 mm. 4. The tread portion central region has one or more of the one step land portions, and the tread portion central region has at least one of the other step land portions on both side regions thereof. A tire according to any one of the preceding claims. 5. The tread portion central region has at least one other step land portion, and the tread portion central region has at least one of the one step land portions on both side regions thereof. A tire according to any one of the preceding claims.