JP3002419B2 - Pneumatic tire - Google Patents

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 a reduction in 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 at a specific frequency becomes loud when the tire runs.

Conventionally, as a technique for reducing such pattern noise, a plurality of types of blocks having different circumferential lengths are used for the blocks, lugs, etc., or the circumferential widths of lateral grooves sandwiched between these blocks are made different. By doing so, tires that adopted the variable pitch method, which aims to disperse sound in a specific frequency region and prevent resonance,
For example, it has been proposed in Japanese Patent Application Laid-Open No. 2-127103.

[0004]

However, such a variable pitch method requires a rate of change of the circumferential length of the block in the tire circumferential direction, that is, the minimum circumferential length a of the block in order to exhibit the noise reduction effect. Since it is necessary to set a large ratio (b / a) to the circumferential length b of the largest block, the rigidity of the block is not uniform, the steering stability is reduced, and the force in the front-rear direction of the tire varies. There is a problem that the tractive force variation or the like as a component becomes large and the tire uniformity is also deteriorated.

The inventor of the present invention has presumed the use of a variable pitch technique having a pattern noise reduction effect, and as a result of intensive studies on improving steering stability and the like, as a result, the rate of change of land portions such as the blocks has been obtained. Based on restricting to a certain range in relation to the rate of change of the width of the tire in the circumferential direction of the lateral groove, noise dispersion is effectively improved, and steering rigidity is improved to a high level by minimizing the difference in rigidity of the block as much as possible. They have found what can be done and completed the present invention.

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

[0007]

According to the present invention, by providing a lateral groove extending in a direction intersecting in the tire circumferential direction on a tread surface, a land portion row in which the land portions sandwiched between the lateral grooves are arranged in the tire circumferential direction is formed. In addition, the land portion row is a variable-pitch pneumatic tire using three to five types of land portions having different tire circumferential lengths, and a tire circumferential length of a land portion having the shortest tire circumferential length. Assuming that the land portion length change rate BR represented by the ratio (Bll / Bss) of the length Bll of the longest land portion to the tire circumferential length Bll is 1.1 to 1.5.
In particular, the land portion length change rate BR is represented by the ratio (Gll / Gss) of the tire circumferential width Gss of the shortest lateral groove to the tire circumferential width Gll of the longest lateral groove. The ratio (GR / BR) to the lateral groove width change rate GR is 1.2 to 1.
5 is a pneumatic tire.

In the land portion row, the number of types of the circumferential length of the land portion in the tire circumferential direction and the number of types of the width of the lateral groove in the tire circumferential direction are the same, and the land portion has the same length as the tire circumferential length Bi. When the lateral grooves are arranged in the order of the tire circumferential width Gi, it is preferable that a lateral groove of the same order as the land portion is adjacent to one edge of the land portion in the tire circumferential direction.

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

[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 has a pair of bead portions 3 having a bead core 2, a sidewall portion 4 extending radially outward from each bead portion 3, and an outer end of the sidewall portion 4. In this example, the tire is formed as a flat tire for a passenger car having a flatness ratio H / WT, which is a ratio of a tire cross-sectional height H to a tire maximum width WT, of 80% or less, preferably 60% or less. You.

A carcass 6 that is folded back and locked around the bead core 2 from the tread portion 5 to the sidewall portion 4 from the tread portion 5 is bridged over the pneumatic tire 1, and the carcass 6 is outside the tread portion and the carcass 6. A tough belt layer 7 is wound inward of 5 to give the carcass 6 a hammer effect.

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

The belt layer 7 is formed of one or more belt plies 7A and 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, two inner and outer belt plies 7A and 7B. 7B is superposed in a different direction so that the belt cords cross each other between the plies. As the belt cord, similarly to 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 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. 10 are formed on the tread surface K to form land portions L1, L2 in which land portions sandwiched between the lateral grooves 10, for example, blocks 11, 12, etc., are arranged in the tire circumferential direction. A pattern or a block / rib pattern is formed. Note that FIG.
Indicates the difference in the circumferential length of the block, which is different from the actual measurement.

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

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

The lateral groove 10 has a tread surface K in the present embodiment within the range of the tread width TW.
The left and right lateral grooves 10A, 10B,... Extend from Eb inward in the tire axial direction and are interrupted near the tire equator C, and the depth of each lateral groove is constant. Each lateral groove 1
The inner ends of the tires 0A and 10B in the tire axial direction are the tire equators C, respectively.
May be interrupted at a position exceeding the distance, or may be formed as a continuous groove connecting the left and right tread edges Ea and Eb.

Further, a plurality of types of the lateral grooves 10A and 10B having different widths GW2 in the tire circumferential direction (hereinafter, simply referred to as "groove widths GW2") in each of the land portion rows L1 and L2, in this example, the block 11 are used. , 12 of which are the same as the number of types of tire circumferential length, and the groove width GW2
Has the following relationship when described using the reference numerals shown in FIG. Gll>Gl>Gm>Gs> Gss

Each of the land sections L1 has a tire circumferential length B11, B1, Bm, Bs,
Bss in the order of Bss (shown for the land portion row L1), and the lateral grooves 10A, 10B are arranged in the tire circumferential widths G11, G1, G
In the illustrated example, m, Gs, and Gss are arranged in this order, and horizontal grooves having the same order as the blocks 11A to 11E are arranged adjacent to one edge in the tire circumferential direction.

In this embodiment, each block has a width in the circumferential direction:... Bm, B1, B11, B1, Bm, Bs, Bss, B
The arrangement in which the circumferential length of the block increases and then decreases as s, Bm, Bl... is repeated, and the difference in circumferential width between adjacent blocks in the tire circumferential direction is kept constant.

The horizontal grooves 10A and 10B and the land row L2
FIG. 2 also shows an example of a configuration similar to the land row L1, but as is clear from FIG. 2, the land rows L1 and L2 are shifted from each other by one order, and the blocks 11 and 12 are respectively arranged. are doing. In the block, the largest circumferential length Bll and the smallest circumferential length Bss are not adjacent to each other, but may be skipped, for example, Bll and Bm, Bs and Bl may be adjacent to each other, Blocks of the same size may be continuous.

In this embodiment, the left and right tread surface portions K1, K
Each pattern shape of No. 2 forms a symmetrical pattern having a different phase in the circumferential direction, and will be described below using the left tread surface portion K1, especially the land portion row L1.

First, the blocks 11A-11 of the land row L1
E, the ratio (Bll / Bss) between the tire circumferential length Bss of the block 11E having the shortest tire circumferential length and the tire circumferential length Bll of the longest land portion 11A is defined as the land portion length change rate BR. In this embodiment, the land portion length change rate BR is set to 1.1 to 1.5. Further, as described above, it is preferable to make the difference in the length in the tire length direction 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 tends not to be reduced. 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 decrease, and the tire uniformity tends to deteriorate. More preferably, the land part length change rate BR is 1.15 to 15.
It is preferably 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 case of the block.

Next, in the transverse groove 10A, the ratio (Gll / Gss) of the tire circumferential width Gss of the shortest transverse groove to the tire circumferential width Gll of the longest transverse groove (Gll / Gss) is defined as the transverse groove width change rate GR. It goes without saying that the greater the lateral groove width change rate GR, the more effective the pattern noise reduction.

The ratio (GR / BR) between the land portion length change rate BR and the lateral groove width change rate GR is regulated in the range of 1.2 to 1.5. Thus, the land length change rate BR
The ratio (GR / BR) between the ratio (GR / BR) and the lateral groove width change rate GR is regulated based on a graph as shown in FIG. 3 obtained by examining the relationship between the ratio (GR / BR) and steering stability. ing.
The steering stability is indicated by an index on a 10-point scale, and the pattern noise is indicated by the difference between (GR / BR) = 1.

First, regarding the steering stability, the ratio (GR)
/ BR) was found to be significantly improved at 1.2 or more. This is based on the fact that the rigidity of the block and the like is made uniform by reducing the rate of change of the land portion, and the value almost reaches a plateau when the ratio exceeds 1.5.

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

It has been found that if the ratio (GR / BR) is within this range, the tire uniformity can maintain the standard level.

The ratio (GR / BR) is determined by the land row L1
However, it is desirable to adopt the same configuration for the land row L2, and in this example, the same configuration as the land row L1 is used. In addition, the circumferential length of the block,
The circumferential width of the lateral groove is determined by measuring the tire at an arbitrary circumferential cross section, and the cross section satisfies the regulation.

[0031]

EXAMPLES The tire size is 205 / 60R15 and the circumferential length according to the invention is B11, B1,
A radial tire having five types of blocks of Bm, Bs and Bss and five types of lateral grooves having a circumferential width of Gll, Gl, Gm, Gs and Gss and having a tread pattern of FIG.
A plurality of prototypes were manufactured according to the specifications shown in Table 1 (Example 1
3), outside the scope of the present invention, the ratio (GR / BR)
= 1 (conventional example), and the same ratio is 1.2 to 1.
The tires (Comparative Examples 1 and 2) outside the range of No. 5 were also prototyped, and a test for comparing the performance was performed. The central block circumferential length Bm and the circumferential width Gm of the lateral groove
The values of Bm = 23.41 mm and Gm = 4.68 mm were used. The test conditions are as follows.

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

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

C) Using a tire uniformity cornering tester, a tractive force variation (TFV), which is a component of the force in the front-rear direction of the tire, was measured at a speed of 80 km / h. The difference is displayed 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 described in a) above, the vehicle is driven on a dry asphalt road surface and a wet asphalt road surface of a tire test course, respectively. The results are displayed on a 10-point scale, with the example being 6 (reference). The larger the numerical value, the better, and the evaluation 8 reaches a fairly good level. Table 1 shows the test results.

[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 decreases, the steering stability is improved while maintaining the reduction of the pattern noise. It was confirmed that it could be done. Particularly, the evaluation index “8” of the steering stability indicates that the performance is remarkably improved.

In Comparative Example 1, the steering stability was not improved because (GR / BR) was small, and in Comparative Example 2, the steering stability could be increased, but the reduction in pattern noise could not be maintained.

The tire size is 205 / 60R15, and it has three types of blocks having circumferential lengths of B11, Bm, and Bss, and three types of lateral grooves having circumferential widths of G11, Gm, and Gss. A plurality of types of radial tires having the tread pattern of (1) and (2) were prototyped according to the specifications shown in Table 2 (Examples 4 and 5). Conventional tires) and tires having the same ratio outside the range of 1.2 to 1.5 (Comparative Examples 3 and 4) were also trial-produced, and a test for comparing the same performance as that of the example was performed. In addition, the values of Bm = 23.41 mm and Gm = 4.68 mm were used as the central block circumferential length Bm and the lateral width Gm of the lateral groove.

[0040]

[Table 2]

In Examples, the products of Examples 4 and 5 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.
Steering stability and tire uniformity can be improved while maintaining a reduction in pattern noise.

[Brief description of the drawings]

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

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

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

[Explanation of symbols]

 10 Side grooves 11, 12 Block L1, L2 Land row K Tread surface Ea, Eb Tread edge

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B60C 11/03 B60C 11/04 B60C 11/11

Claims (2)

(57) [Claims] 1. A land portion row in which a land portion sandwiched between the lateral grooves is formed in a tire circumferential direction by providing a lateral groove extending in a direction crossing the tire circumferential direction on a tread surface.
This land portion row is a variable-pitch pneumatic tire using three to five types of land portions having different tire circumferential lengths, and the tire circumferential length Bs of the land portion having the shortest tire circumferential length.
s and the length of the longest land portion in the tire circumferential direction B11 (B
ll / Bss), the land portion length change rate BR expressed as 1.1
And a ratio (Gll / Gss) of the land portion length change rate BR, the tire circumferential width Gss of the shortest lateral groove in the tire circumferential direction, and the tire circumferential width Gll of the longest lateral groove in the tire circumferential direction. A pneumatic tire characterized in that the ratio (GR / BR) to the lateral groove width change rate GR (GR) is in the range of 1.2 to 1.5. 2. The land portion row has the same number of types of tire circumferential lengths of the land portions and the number of types of tire circumferential widths of the lateral grooves, and the land portions have a tire circumferential length Bi. 2. The air according to claim 1, wherein when the lateral grooves are arranged in the order of the tire circumferential width Gi, one lateral edge of the land portion in the tire circumferential direction is adjacent to the lateral groove in the same order as the land portion. Containing tires.