JP2702758B2 - Pneumatic tire - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a pneumatic tire, and more particularly to a pneumatic tire having a block pattern employing a pitch variation.

[Conventional technology]

Conventionally, in order to reduce the pattern noise generated during running of the pneumatic tire, the zigzag interval of the vertical groove of the tread portion,
By making the pitch such as the length in the circumferential direction of the block different at the circumferential position (hereinafter referred to as “irregular pitch”), the frequency of noise generated by pattern elements such as grooves, blocks, etc. is dispersed, so that the sound is unpleasant. The pitch variation method for preventing the occurrence of pits is adopted.

[Problems to be solved by the invention]

However, a tire having such an irregular pitch is excellent in terms of reducing noise of the tire, but particularly in a block pattern tire in which blocks are arranged in the tire circumferential direction, according to the size of the pitch,
By changing the length of the block in the tire circumferential direction,
As a result, the rigidity of each block fluctuates, and the pattern rigidity changes in the circumferential direction. As a result, vibrations occur during tire running.

The present invention provides a pneumatic tire capable of improving the uniformity of a tire, suppressing generation of vibration, uneven wear, and the like, without reducing the noise reduction effect, in a tire having the irregular pitch block pattern. The main purpose is.

[Means for solving the problem]

The present invention includes a plurality of blocks defined by a lateral groove intersecting with the tire circumferential direction and a vertical groove intersecting with the tire axial direction, and is a length in a tire circumferential direction between centers of the lateral grooves adjacent to each other with the block interposed therebetween. A pneumatic tire having a block pattern with a changed block pitch Pi, wherein the blocks form a plurality of block rows arranged side by side in the tire circumferential direction, and at least one block row is engraved with siping. And a sipe effective length K which is a sum of effective lengths of the sipes provided in the respective blocks with the sipe in the block axial direction in the tire axial direction. The ratio K / Ymax to the maximum block width Ymax, which is the maximum length in the tire axial direction, is determined by the block pitch Pi of the sipe-equipped block and each block in the block row. The pneumatic tire has a square to fourth power of a pitch ratio Pi / Pm, which is a ratio of the block pitch of the block with the Ip to the average length Pm.

[Action]

The circumferential rigidity Kp of the block B defined by the horizontal groove and the vertical groove is expressed by the following equation.

Kp = F / Z = 1 / (1 / Km + 1 / Ks) = 1 / (H 3 / 3EI + H / AG) ...... (1) where, F: force in the tire circumferential direction applied to the block B Z: According to the force F deformation of the block B Km: block B the bending stiffness Ks: shear stiffness H of the block B: lateral groove depth E: tread rubber modulus I: geometrical moment of inertia of the block ^{B (= X 3 · Y /} 3) a : Area of block B = XYG: Shear modulus of block B X: Length of block B in tire circumferential direction Y: Length of block B in tire axial direction

As described above, the circumferential rigidity Kp of the block B changes depending on the sizes X and Y of the block B. On the other hand, in a tire to which an irregular pitch in which the block pitch Pi, which is the length in the tire circumferential direction between the lateral grooves sandwiching the block B, is changed depending on the position in the circumferential direction of the block B, is applied, The circumferential length X also changes according to the block pitch Pi, and has a circumferential rigidity Kp corresponding to the circumferential length X of each block B.

Therefore, while the tire is rolling, the grounding block B
The circumferential force of the tire generated on the tire varies depending on the size of the tire. This traction-based variation (hereinafter referred to as “TFV”) appears as a vibration phenomenon that occurs while the vehicle is running.

In general, when using a pitch variation using three or more different block pitches P ₁ , P ₂ , and P ₃ , a pitch Pmin is arranged next to the longest block pitch Pmax to avoid a sudden change in circumferential rigidity. There is little to do. However, it is inevitable that the fluctuation of the circumferential rigidity appears as a fluctuation of the circumferential force within one circumference of the tire and has a certain period during the rolling of the tire, since the irregular pitch is employed.

On the other hand, the circumferential rigidity of the block can be expressed as an empirical equation such as the following equation (2) as a result of analyzing various experiments in the case of a block with a sipe in which the block B is processed with siping.

Kpa = Kp [1- (K / Ymax) (0.233Hs / H-0.048)] ... (2) where Kpa: circumferential rigidity of block after adding siping Hs: siping depth Ymax: with sipes The maximum block width K, which is the maximum length of the block in the tire axial direction, is the effective sipe length, which is the sum of the effective lengths of the sipe in the tire axial direction in each block in a block row composed of blocks with sipes.

In the above equation (1), when the pitch ratio (Pi / Pm), which is the ratio between the block pitch of the block Bi and the average length Pm of the various block pitches Pi employed, increases, the circumferential rigidity of the block increases. In the above equation (2), when the siping is provided in the block, it can be seen that as (K / Ymax) increases, the circumferential rigidity of the block decreases.

Accordingly, if the sipe effective length K is larger as the pitch ratio is larger (than the average), and conversely, the sipe effective length K is smaller as the pitch ratio is smaller (than the average). Changes in rigidity can be reduced.

The present inventors use the parameter (K / Ymax) of the equation (2) as a guideline for the sipe effective length K, and do not simply make this equal to the pitch ratio (Pi / Pm). When the pitch ratio is related to the power, the larger the pitch ratio is 1, the larger the nonlinearity (K / Ymax) becomes, and the smaller the pitch ratio is smaller than 1 (K / Yma).
It was found that x) could be reduced nonlinearly.

However, (K / Ymax) is 4 times the pitch ratio (Pi / Pm).
Beyond the power, the siping becomes longer pitch B block
Causes excessive noise due to wear, tread breakage, new noise generation due to siping, and simply setting (K / Ymax) equal to the first power of (Pi / Pm) will result in circumferential variations due to pitch variations. The rigidity cannot be made sufficiently uniform.

Thus, in the present invention, as a range for achieving uniform tire circumferential rigidity without impairing the other performance,
(K / Ymax) is limited to the second to fourth power of the pitch ratio (Pi / Pm).

〔Example〕

 An embodiment of the present invention will be described below with reference to the drawings.

1 and 2, a tire 1 has a tread 2
Are divided by a mechanism 3 that intersects the tire circumferential direction and a vertical groove 4 that intersects the tire axial direction and extends in the tire circumferential direction in this example.
… Block pitch Pi, which is the length in the tire circumferential direction between the centers
However, in this example, five types of block pitches P ₁ , P ₂ ,
Blocks B ₁ to P ₃ , P ₄ , P ₅ (5 pitch variations)
B ₅ (referred to collectively as block Bi) are arranged side by side in the tire circumferential direction and randomly to form a block row.

When the blocks Bi have different block pitches PA and PB on both side surfaces in the tire axial direction as shown in FIG. 3, the block pitch Pi is defined as an average value.

Further, in this example, as shown in an enlarged view in FIG. 3, a siping 6 extending at an angle θ with respect to the tire axial direction and extending inward of the block Bi with respect to both side surfaces of the block Bi as a base point. Each siping 6 is provided and has a length Lj (j is the number of sipings in the block Bi).

Therefore, the effective sipe length K which is the sum of the effective lengths Kj = Lj · cos θ in the axial direction of the siping 6 of each block Bi is ΣKj
Is obtained as

Further, in the tire 1 of the present invention, the sipe effective length K
The ratio K / Ymax between the block Bi and the maximum block width Ymax, which is the maximum length of the block Bi in the tire axial direction, is determined as the square to fourth power of the pitch ratio Pi / Pm of the block Bi. The pitch ratio Pi / Pm is, as described above, the block pitch Pi of the block Bi.
When the average value Pm of the block pitch P ₁ to P ₅ of each block [=
(P ₁ + P ₂ + P ₃ + P ₄ + P ₅ ) / 5], and the ratio K / Ymax in each block Bi is set as follows.

When Pi / Pm ≧ 1: (Pi / Pm) ² ≦ K / Ymax ≦ (Pi / Pm) ^{4 When} Pi / Pm ≦ 1: (Pi / Pm) ⁴ ≦ K / Ymax ≦ (Pi / Pm) ² Thus, in the present invention, as the block pitch with respect to the average value of the block pitch increases,
As a measure for increasing the effective length of the sipe, by setting the effective length K of the sipe to the maximum width Ymax of the block within the above range, problems such as abrasion, tread breakage, and generation of new noise due to the addition of siping may occur. Instead, the uniformity of the circumferential rigidity of the block is achieved.

In addition, the block Bi with a sipe in which the siping 6 is engraved can be only the blocks P ₃ and P ₄ in which the block pitch Pi is larger than the average value Pm in each block. The ratio Hs / H is 0.
It is desirably 2 to 1.0, more preferably 0.4 to 0.8. By setting Hs / H in such a range, the effect of making the circumferential rigidity of the block uniform can be more effectively exerted. If the Hs / H is less than 0.2, the rigidity of the block tends to be hard to decrease.On the contrary, if it exceeds 1.0, the rigidity of the block becomes too small. The above effect may be reduced in some cases.

In addition, the type of irregular pitch, the angle of siping,
The number, shape, and row of blocks into which sipings are placed can be freely set, and can be arbitrarily selected according to the category of tire to be applied, the purpose of use, and the like. Further, the present invention can be applied to both a radial tire and a bias tire.

〔Concrete example〕

A tire having a tire size of 185 / 70R14 was prototyped according to the specifications shown in FIG. 1 and Table 1 and the distribution of circumferential rigidity was examined. The results are shown in Table 1.

In the first embodiment, siping is processed on all blocks, and in the second embodiment, siping is processed only on blocks larger than the average value.

[Effects of the Invention] The pneumatic tire of the present invention causes problems such as abrasion, tread breakage, and generation of new noise due to the addition of siping, despite having an irregular pitch block pattern to reduce tire noise. The rigidity in the circumferential direction can be made substantially uniform without any problem, and the generation of vibrations due to the unevenness in the circumferential rigidity can be effectively improved without reducing the effect of noise reduction.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a developed view illustrating a block pattern according to an embodiment of the present invention, FIG. 2 is a perspective view illustrating a block, and FIG. 3 is a plan view illustrating another block. is there. 2 ... tread part, 3 ... horizontal groove, 4 ... vertical groove, 6 ... siping, Bi ... block, K ... effective sipe length, Pi ... block pitch, Ymax ... maximum block width.

Claims (2)

(57) [Claims] 1. A tire having a plurality of blocks defined by a lateral groove intersecting a tire circumferential direction and a vertical groove intersecting a tire axial direction, and having a length in a tire circumferential direction between the centers of the lateral grooves adjacent to each other with the block interposed therebetween. A pneumatic tire having a block pattern in which a certain block pitch Pi is changed, wherein the blocks form a plurality of block rows arranged side by side in the tire circumferential direction, and at least one block row has a siping. And a sipe effective length K, which is a sum of effective lengths in the tire axial direction of sipes provided in each of the sipe blocks in the block row, and a block with the sipe. The ratio K / Ymax to the block maximum width Ymax, which is the maximum length in the tire axial direction, is the block pitch Pi of the block with the sipe, and Pitch ratio is the ratio between the average length Pm block pitch of blocks with sipes, a pneumatic tire has a square to 4 square of Pi / Pm. 2. The pneumatic tire according to claim 1, wherein the block with a sipe is a block in which the block pitch Pi of each block is longer than the average length Pm of the block pitch Pi of each block.