JPH0930213A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve operational stability and at the same time reduce tire pattern noise by specifying the range of the ratio of the rate of change of the length of a tire flat portion, which is represented by the ratio of the shortest length to the longest length of the flat portion in the circumferential direction, to the rate of change of a translot width, which is represented by the ratio of the shortest width to the longest width of the translot of the tire in the circumferential direction. SOLUTION: Among blocks 11A to 11E of a flat portion L1, it is preferable to define the ratio of the tire circumferential length or the shortest block 11E tire circumferential length Bss to the tire circumferential length B11 of the longest flat portion 11A as a flat portion length rate of change BR and set the flat portion rate of change to approximately 1.1 to 1.5. Regarding a translot 10A, the ratio of the tire circumferential width Gss, which has the narrowest tire circumferential width, to the widest tire circumferential width G11 of the longest translot is defined as a translot width rate of change GR. The ratio of the fiat portion length rate of change BR to the translot width rate of change GR (GR/BR) is regulated within the range of 1.2 to 1.5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire capable of improving steering stability while maintaining reduction of pattern noise.

[0002]

2. Description of the Related Art A pneumatic tire having a tread pattern in which land portions such as blocks and lugs are arranged at a constant pitch is liable to generate so-called pattern noise, in which sound of a specific frequency becomes loud when the tire is running.

Conventionally, as a method for reducing such pattern noise, a plurality of types of blocks having different circumferential lengths are used for the blocks, lugs, or the lateral widths of the lateral grooves sandwiched between these blocks are made different. As a result, tires that employ the variable pitch method, which aims to disperse the sound in a specific frequency range and prevent resonance,
For example, it is proposed by Japanese Patent Laid-Open No. 2-127103.

[0004]

However, in order to exert the noise reducing effect, such a variable pitch method has a rate of change in the tire circumferential direction length of the block, that is, the tire circumferential direction length a of the minimum block. Since it is necessary to set a large ratio (b / a) to the maximum block circumferential length b, etc., the block rigidity becomes non-uniform, the steering stability is reduced, and the tire longitudinal force fluctuations occur. There is a problem that the tractive force variation, which is a component, becomes large, and the tire uniformity is deteriorated.

The present inventor has conducted extensive studies on the point of improving steering stability on the assumption that a variable pitch method having a pattern noise reducing effect is adopted, and as a result, the rate of change of the land portion such as the block is calculated as follows. Basically, it is regulated within a certain range in relation to the rate of change in the width of the lateral groove in the tire circumferential direction, while effectively distributing noise, while minimizing the difference in block rigidity to improve steering stability to a high level. The inventors have discovered what is possible and have completed the present invention.

[0006] That is, an object of the present invention is to provide a pneumatic tire capable of improving steering stability while reducing pattern noise.

[0007]

According to the present invention, a lateral groove extending in a direction intersecting with a tire circumferential direction is provided on a tread surface to form a land portion row in which land portions sandwiched by the lateral groove are arranged in the tire circumferential direction. Along with this, the land portion row is a variable-pitch pneumatic tire using a plurality of types of land portions having different tire circumferential lengths, and the tire circumferential length Bss of the land portion having the shortest tire circumferential length. And the land portion length change rate BR represented by a ratio (Bll / Bss) to the tire circumferential direction length Bll of the longest land portion is the tire circumferential direction width Gss of the lateral groove having the shortest tire circumferential direction width, The ratio (GR / BR) to the lateral groove width change rate GR represented by the ratio of the longest lateral groove to the tire circumferential width Gll (Gll / Gss) is set to a range of 1.2 to 1.5. It is a pneumatic tire that does.

In the land portion row, the number of types of tire circumferential direction lengths of the land portions is the same as the number of types of lateral groove tire circumferential direction widths, and the land portions are of tire circumferential length Bi. When the lateral grooves are arranged in this order, and when the lateral grooves are arranged in the order of the tire circumferential width Gi, it is desirable that the lateral groove of the same rank as the land portion is adjacent to one edge of the land portion in the tire circumferential direction.

According to the results of experiments conducted by the present inventors, the rate of change BR of the land portion length is a ratio (GR / B) to the rate of change of the lateral groove width GR.
By controlling R) in the range of 1.2 to 1.5, it is possible to minimize the unevenness of the rigidity of each land portion, improve the steering stability in a so-called peak, and specify Pattern noise can be reduced by distributing the sound in the frequency domain.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, a pneumatic tire 1 connects a pair of bead portions 3 each having a bead core 2, a sidewall portion 4 extending from each bead portion 3 outward in the tire radial direction, and an outer end of the sidewall portion 4 connected to each other. It is formed as a flat tire for passenger cars having a tread portion 5 and a flatness ratio H / WT, which is a ratio of the tire cross-sectional height H to the tire maximum width WT, is 80% or less, preferably 60% or less in this example. It

Further, a carcass 6 which is folded around the bead core 2 from the tread portion 5 to the side wall portion 4 and is locked is bridged over the pneumatic tire 1, and at the outside of the carcass 6 and the tread portion. A tough belt layer 7 is wound around the inside of the carcass 5 to impart a hoop effect to the carcass 6.

The carcass 6 is composed of one or more carcass plies having a so-called radial or semi-radial structure in which the carcass cords are arranged at an angle of 60 to 90 degrees with respect to the tire equator C, and the carcass cords are steel or nylon, An organic fiber cord such as rayon or polyester is adopted.

The belt layer 7 is formed by one or more, in this example, two belt plies 7A, 7B in which belt cords are arranged at an angle of 30 degrees or less with respect to the tire equator C, and in this example, each ply 7A, 7B is piled up in different directions so that the belt cords cross each other between the plies. As the belt cord, as with the carcass cord, an organic fiber cord such as nylon, polyester or rayon or a metal cord such as steel is used.

As shown in the developed tread pattern in FIG. 2, the tread surface K of the tread portion 5 has a longitudinal groove 9 extending in the tire circumferential direction and a lateral groove extending in a direction intersecting with the longitudinal groove 9 in this embodiment. By forming a tread groove including 10 and a land portion row L1 and L2 in which the land portion sandwiched by the lateral groove 10, for example, blocks 11 and 12, are arranged in the tire circumferential direction on the tread surface K. A pattern or block / rib pattern is formed. Note that FIG.
Shows the difference in the circumferential length of the block in an emphasized manner, which is different from the actual measurement.

The land portion rows L1 and L2 are a plurality of types such as 3 to 5 types having different tire circumferential lengths in this example, and 5 types of blocks 11A to 11E and 12A to 12E in this example.
Together with these blocks 11A-1
A variable pitch in which 1E and 12A to 12E are arranged in the order of the length in the tire circumferential direction is used. In addition, if it demonstrates using the code | symbol shown in FIG. 2, the circumferential direction length of each block will have the following relationships. Bll>Bl>Bm>Bs> Bss

Next, in the present embodiment, the vertical grooves 9 are composed of a total of four internal grooves 9A, 9A passing on both sides of the tire equator C, and external vertical grooves 9B, 9B arranged outside thereof. The vertical grooves 9A and 9B have a groove width GW1 on the tread surface K, respectively.
Although the groove is formed to be 3% or more and 5 mm or more of the tread width TW and the groove depth is substantially constant over the entire circumference of the tire in this example, it may be bent.

The lateral groove 10 has a tread width TW, and in this example, the tread surface K is formed on the left and right tread edges Ea,
The lateral grooves 10A, 10B, ... Extend from Eb toward the inner side in the tire axial direction and are interrupted near the tire equator C, and the groove depth of each lateral groove is constant. Each lateral groove 1
The inner ends of the tires 0A and 10B in the axial direction are the tire equator C, respectively.
It may be interrupted at a position in the vicinity of over, or may be formed as a continuous groove connecting the left and right tread edges Ea and Eb.

Further, the lateral grooves 10A, 10B are a plurality of types having different widths GW2 (hereinafter simply referred to as "groove width GW2") in the tire circumferential direction in the respective land portion rows L1, L2. , 12 in the circumferential direction of the tire in the same number of types, and the groove width GW2
Will have the following relationship if explained using the symbols shown in FIG. Gll>Gl>Gm>Gs> Gss

In addition, each of the land portion rows L1 has tire circumferential lengths Bll, Bl, Bm, Bs, at the tread circumferential portion.
They are arranged in the order of Bss (shown for the land portion row L1), and the lateral grooves 10A and 10B are provided in the tire circumferential widths Gll, Gl, G.
An example is shown in which m, Gs, and Gss are arranged in this order, and lateral grooves of the same order as the blocks are arranged side by side on one edge in the tire circumferential direction of each block 11A to 11E.

In this example, the width of each block in the circumferential direction is ... Bm, Bl, Bll, Bl, Bm, Bs, Bss, B.
s, Bm, Bl ... The block circumferential length increases and then decreases, and the circumferential width difference between adjacent blocks in the tire circumferential direction is made constant.

The lateral grooves 10A, 10B and the land portion row L2
Also, an example of a configuration similar to that of the land portion row L1 is illustrated, but as is clear from FIG. 2, the land portion rows L1 and L2 are shifted one order from each other and the blocks 11 and 12 are arranged respectively. are doing. In the block, the block Bll having the maximum length in the circumferential direction and the block Bss having the minimum circumferential length are not adjacent to each other, but one block, for example, Bll and Bm or Bs and Bl may be adjacent to each other. Further, blocks having the same size may be continuous.

In this example, the left and right tread surface portions K1, K
The respective pattern shapes of No. 2 are symmetrical patterns having different phases in the circumferential direction, and will be described below using the left tread surface portion K1, particularly the land portion row L1.

First, the blocks 11A-11 of the land row L1
Of the E, the ratio (Bll / Bss) between the tire circumferential length Bss of the block 11E having the shortest tire circumferential length and the longest tire circumferential length Bll of the land portion 11A is defined as a land length change rate BR. In the present embodiment, it is desirable that the land portion length change rate BR is set to about 1.1 to 1.5 as a preferable range. Further, as described above, it is preferable to make the difference in the tire length direction length between the blocks uniform.

When the land portion length change rate BR is smaller than the value of 1.1, the rigidity of the block 11 tends to be uniform, but the pattern noise reduction tends to be unmaintainable. The land length change rate BR is 1.
When the value is larger than 5, the rigidity of the block 11 becomes uneven, the steering stability tends to be deteriorated, and the tire uniformity tends to be deteriorated. More preferably, the land length change rate BR is 1.15.
It is preferable that the width is about 1.25, and the difference in width in the tire circumferential direction between adjacent lateral grooves in one unit is uniform, as in the above block.

Next, in the lateral groove 10A, the ratio (Gll / Gss) between the tire circumferential width Gss of the lateral groove having the shortest width in the tire circumferential direction and the tire circumferential width Gll of the longest lateral groove is defined as the lateral groove width change rate GR. Needless to say, the larger the lateral groove width change rate GR, the more effective the pattern noise is in reducing.

The ratio (GR / BR) between the land length change rate BR and the lateral groove width change rate GR is regulated within the range of 1.2 to 1.5. In this way, the land length change rate BR
The ratio (GR / BR) between the horizontal groove width change rate GR and the lateral groove width change rate GR is regulated based on the graph shown in FIG. 3 which is the result of examining the relationship between the ratio (GR / BR) and steering stability. ing.
The steering stability is indicated by an index of 10 grades, and the pattern noise is indicated by the difference based on (GR / BR) = 1.

First, regarding the steering stability, the ratio (GR
It has been found that / BR) is significantly improved when 1.2 or more. This is based on the fact that the rigidity of the blocks and the like is made uniform by reducing the rate of change of the land portion, and reaches a level when the ratio exceeds 1.5.

For pattern noise, the ratio (G
It can be understood that R / BR) can be reduced when it is 1.5 or less, and conversely, when it exceeds 1.5, the change in the block length becomes small and the pattern noise reduction effect cannot be obtained. Therefore, in order to improve the steering stability while maintaining the reduction of pattern noise, the ratio (GR / BR) is set to 1.2 to 1.5.
Must be within the range.

It has been found that when the ratio (GR / BR) is within this range, the tire uniformity can be maintained at the standard level.

The above-mentioned ratio (GR / BR) is the land line L1.
However, it is desirable to employ the same configuration for the land portion row L2 as well, and in this example, the same configuration as the land portion row L1 is adopted, and the circumferential length of the block,
The width of the lateral groove in the circumferential direction is determined by measuring it on an arbitrary circumferential cross section of the tire, and it suffices to satisfy the regulation at the cross section.

[0031]

EXAMPLES Tire size is 205 / 60R15 and circumferential lengths according to the invention are Bll, Bl, Bm, B.
Five types of blocks, s and Bss, and a circumferential width of Gll,
A plurality of radial tires having five types of lateral grooves of Gl, Gm, Gs, and Gss and having the tread pattern of FIG. 1 were prototyped according to the specifications shown in Table 1 (Examples 1 to 3).
A tire (conventional example) having a ratio (GR / BR) of 1 and a tire having a ratio outside the range of 1.2 to 1.5 (comparative examples 1 and 2), which are outside the configuration of the present invention, are also included. And made a prototype,
Tests were performed to compare performance. For the central block circumferential length Bm and the lateral groove circumferential width Gm, values of Bm = 23.41 mm and Gm = 4.68 mm were used. The test conditions are as follows.

B) Pattern noise After the test tire was mounted on a 15 × 6-JJ aluminum wheel rim at an internal pressure of 200 Kpa (the front and rear are the same), 2500c
The vehicle was mounted on four wheels of a rear-wheel-drive vehicle of c, and was run by one person on a smooth road surface at a speed of 80 km / h. At this time,
Overall noise level dB on the right side of the driver's window
(A) was measured and the deviation from the conventional example was displayed.

B) Road noise Under the same conditions as above, the road noise was measured by running on a rough road surface of dry asphalt at a speed of 50 km / h and using a road noise measuring instrument during steady running. In addition, the sound pressure level difference based on the conventional example is displayed.

C) A tire uniformity cornering tester was used to measure the tractive force variation (TFV), which is a fluctuation component of the force in the longitudinal direction of the tire, at a speed of 80 km / h. The difference is based on the conventional example. The smaller the value, the smaller the fluctuation component before and after the tire, and the better the tire uniformity.

D) Driving stability (DRY, WET) and ride comfort Under the same conditions as the pattern noise test of the above-mentioned a), the tire was run on the dry asphalt road surface and the wet asphalt road surface of the tire test course, respectively, and it was judged by the driver's sensory evaluation. The example is displayed in 10-level evaluation with 6 (reference). The larger the numerical value is, the better, and the evaluation 8 reaches a considerably good level. The test results are shown in Table 1.

[0036]

[Table 1]

As a result of the test, in Examples 1 to 3, although the pattern noise tends to increase as the block length change rate BR becomes smaller, the steering stability is improved while maintaining the reduction of the pattern noise. It was confirmed that it was possible. In particular, the steering stability evaluation index "8" indicates that the performance is remarkably improved.

In Comparative Example 1, since (GR / BR) is small, the steering stability is not improved, and in Comparative Example 2, the steering stability can be increased, but the reduction of the pattern noise cannot be maintained.

The tire size is 205 / 60R15, and there are three types of blocks having a circumferential length of Bll, Bm, and Bss and three types of lateral grooves having a circumferential width of Gll, Gm, and Gss. A plurality of radial tires having the tread pattern of No. 1 were prototyped according to the specifications shown in Table 2 (Examples 4 and 5), and the tires which are outside the configuration of the present invention and have the ratio (GR / BR) = 1 ( Conventional examples) and tires having the same ratio outside the range of 1.2 to 1.5 (Comparative Examples 3 and 4) were also prototyped, and a test for comparing the same performance as that of the example was performed. For the central block circumferential length Bm and the lateral groove circumferential width Gm, values of Bm = 23.41 mm and Gm = 4.68 mm were used.

[0040]

[Table 2]

Also in Examples, Examples 4 and 5, which are the products of the present invention, obtained better results than the conventional examples and Comparative Examples 3 and 4.

[0042]

As described above, the pneumatic tire of the present invention has the following features.
It is possible to improve steering stability and tire uniformity while maintaining reduction of pattern noise.

[Brief description of drawings]

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

FIG. 2 is a plan view showing a developed tread pattern of the pneumatic tire of the present invention.

FIG. 3 is a diagram showing a relationship between a ratio (GR / BR) and steering stability.

[Explanation of symbols]

 10 Transverse grooves 11, 12 Blocks L1, L2 Land line row K Tread surface Ea, Eb Tread edge

Claims (2)

[Claims] 1. A tread surface is provided with a lateral groove extending in a direction intersecting with a tire circumferential direction to form a land portion row in which land portions sandwiched by the lateral groove are arranged in the tire circumferential direction. A variable pitch pneumatic tire using a plurality of types of land portions having different tire circumferential lengths, wherein the tire circumferential length Bs of the land portion having the shortest tire circumferential length is Bs.
The ratio of s to the longest tire circumferential length Bll of the land (B
11 / Bss) is the land portion length change rate BR, which is the tire circumferential width Gss of the lateral groove having the shortest tire circumferential width.
To the width Gll of the longest lateral groove in the tire circumferential direction (Gll
/ Gss) Ratio of lateral groove width change rate GR (GR /
A pneumatic tire having a BR) of 1.2 to 1.5. 2. The land portion row has the same number of types of tire circumferential direction lengths of the land portions and the same number of types of lateral groove tire circumferential direction widths, and the land portions have tire circumferential direction lengths Bi. 2. The air according to claim 1, wherein when the lateral grooves are arranged in the order of the tire circumferential width Gi, the lateral groove having the same rank as the land portion is adjacent to one edge of the land portion in the tire circumferential direction. Included tires.