JP2012162142A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire for reducing generation of road noise, while securing maneuvering stability and riding comfort performance.SOLUTION: In this pneumatic tire, the thinnest part of the tire is positioned in a height of the ratio of 0.6-0.8 from a bottom part of a bead part to a height up to a top part of a tread part from the bottom part of the bead part between an end part of a breaker and a maximum width part of the tire, a thickness of the thinnest part is the ratio of 0.7-0.9 to a thickness in the maximum width part, a thickness in an upper end part of the bead apex uniformly increases so as to become the ratio of 1.3-1.8 to the thickness in the thinnest part toward the upper end part of the bead apex from the thinnest part, a thickness of the bead apex also uniformly increases toward a lower end part from the upper end part of the bead apex, and the thickness of the bead apex in the lower end part is the ratio of 1.3-1.8 to a thickness in a central part.

Description

  The present invention relates to a pneumatic tire, and more particularly to a pneumatic tire that can reduce the generation of road noise while ensuring steering stability performance and riding comfort performance.

  A running pneumatic tire (hereinafter also simply referred to as “tire”) generates road noise based on a resonance frequency having a peak of 250 to 315 Hz, and greatly affects the quietness of the vehicle. For this reason, various proposals have been made on methods for reducing the occurrence of road noise in tires (for example, Patent Document 1).

Japanese Patent Laid-Open No. 2002-301912

  However, in these conventional techniques, although the generation of road noise is reduced, there is a possibility that the steering stability performance and the riding comfort performance are deteriorated.

  That is, since the generation of road noise can be reduced by suppressing the vibration of the tire against the input from the road surface, it is generally advantageous that the rigidity of the tire (particularly the tread portion) is low. On the other hand, steering stability is improved by increasing the cornering power by quickly transmitting the force applied to the tire to the steering wheel by input from the road surface, so that the tire (especially the tread portion) is generally more rigid. It is advantageous.

  Specific means for reducing the occurrence of road noise include, for example, increasing the tread gauge, softening the tread rubber, widening the breaker width, loosening the breaker angle, and increasing the rigidity of the bead apex. However, it has been confirmed that steering stability is reduced when the gauge of the tread portion is increased, the tread rubber is softened, and the breaker angle is reduced. In the case of widening the breaker width and increasing the rigidity of the bead apex, it has been confirmed that the riding comfort performance is lowered although the steering stability is not lowered.

  In this way, under the conventional technology, there is generally a trade-off between the reduction in road noise generation and the handling stability and riding comfort performance. It has been desired to provide a pneumatic tire with reduced noise generation.

The invention described in claim 1
The thinnest portion of the tire is 0.6 to 0. 0 from the bottom portion of the bead portion with respect to the height from the bottom portion of the bead portion to the top portion of the tread portion between the end portion of the breaker and the maximum width portion of the tire. The thickness of the thinnest portion is a ratio of 0.7 to 0.9 with respect to the thickness of the maximum width portion.
From the thinnest part toward the upper end of the bead apex, the thickness at the upper end of the bead apex is in a ratio of 1.3 to 1.8 with respect to the thickness at the thinnest part. Has increased uniformly,
Further, the thickness of the bead apex increases uniformly from the upper end portion of the bead apex to the lower end portion, and the thickness of the bead apex at the lower end portion is 1 with respect to the thickness at the central portion. A pneumatic tire characterized by a ratio of 3 to 1.8.

The invention described in claim 2
2. The pneumatic tire according to claim 1, wherein a thickness at the thinnest portion and a thickness at an upper end portion of the bead apex have variations within ± 0.6 mm, respectively. .

The invention according to claim 3
The breaker is a breaker configured by laminating two layers of belts made of steel cord,
The pneumatic tire according to claim 1 or 2, wherein the carcass ply is a carcass ply composed of one or more layers of plies made using an organic fiber cord.

  According to the present invention, it is possible to provide a pneumatic tire in which generation of road noise is reduced while securing steering stability performance and riding comfort performance.

It is a figure showing typically the section of the tire concerning one embodiment of the present invention. It is a figure which shows the change of the thickness of the side part of the tire which concerns on one embodiment of this invention. It is a figure which shows the result of having measured the sound pressure level in each frequency of the noise at the time of carrying out an actual vehicle test of the tire of one Example of this invention and a conventional product at 60 km / h. It is a figure which shows the result of having measured the sound pressure level in each frequency of the noise at the time of carrying out an actual vehicle test of the tire of one Example of this invention and a conventional product at 100 km / h.

  Hereinafter, the present invention will be described based on embodiments with reference to the drawings.

  First, the structure of the tire according to the present embodiment will be described with reference to FIG. FIG. 1 is a diagram schematically showing a cross section of a tire according to the present embodiment, which is symmetrical with respect to a center line CL. In FIG. 1, 10 is a tread portion, 20 is a shoulder portion, 30 is a sidewall portion, and 40 is a bead portion. Reference numeral 23 denotes a boundary portion between the shoulder portion 20 and the sidewall portion 30, and a denotes the thickness of the thinnest portion of the tire. Reference numeral 31 denotes a maximum width portion where the tire width is maximum. Further, 34 is a boundary portion between the sidewall portion 30 and the bead portion 40, and b indicates the thickness at the upper end portion of the bead apex 41. Here, each thickness is a thickness when measured perpendicular to the carcass 50.

  As shown in FIG. 1, the tire according to the present embodiment includes a pair of left and right shoulder portions 20, sidewall portions 30 and bead portions 40, and a tread portion 10 that spans both sidewall portions 30. .

  The tread portion 10 is provided with a tread rubber 11 and a breaker 12, and the breaker 12 is formed by laminating two belts having a topping rubber topped on a steel cord.

  The bead section 40 is provided with a bead apex 41 and a bead core 42. In addition, 411 is the upper end part of the bead apex 41, 412 is the center part (thickness c), and 413 is the lower end part (thickness d). Here, each thickness is the thickness of the bead apex 41 when measured perpendicular to the carcass 50.

  Between the pair of left and right bead cores 42, a carcass ply 50 is provided that is composed of at least one ply in which a topping rubber is topped on an organic fiber cord. The end portion of the carcass ply 50 is locked by being attached to the outer surface of the carcass ply 50 after being folded back by the folding portion 501 so as to wrap the bead core 42 and the bead apex 41 from the inside to the outside. Reference numeral 502 denotes an upper end portion of the folded portion.

  During the running of the tire, the largest distortion occurs at the center of the bend, and this becomes the starting point of the road noise peak. Therefore, the present inventor can reduce the peak sound pressure by shifting the noise around 250 Hz in the low frequency direction when the thinnest part is provided at the center of the bend to reduce the rigidity. Considering that the generation of road noise is reduced, the preferred position of the thinnest part and its thickness a were examined.

  As a result, as shown in FIG. 1, the section height (height from the bottom of the bead portion 40 to the top of the tread portion 10) is set to 1 between the end portion of the breaker 12 and the maximum width portion 31 of the tire. In this case, a position of 0.6 to 0.8 from the bottom of the bead portion 40 is preferable as the thinnest portion, and the thickness a in the thinnest portion is set to 0. It was found that it was most effective when the ratio was set to 7 to 0.9.

  Further, when the thickness of the sidewall portion 30 is gradually increased from the thinnest portion toward the upper end portion 411 of the bead apex, the inventor resonates by causing the vibration starting points to be dispersed and generating road noise. The experiment was conducted on the assumption that the frequency can be dispersed from the 250 Hz band, which tends to have a peak, to a lower frequency band, and the generation of road noise can be further reduced.

  As a result, the thickness is uniformly increased from the thinnest portion a toward the upper end portion 411 of the bead apex, and finally, the thickness b at the upper end portion 411 of the bead apex becomes the thickness at the thinnest portion. It was found that it was most effective when the ratio was set to 1.3 to 1.8 (b / a) with respect to a.

  At this time, it is preferable that the thickness at the thinnest portion and the thickness at the upper end portion of the bead apex are controlled to be within ± 0.6 mm, respectively. That is, if the variation is within ± 0.6 mm, the thickness at the thinnest portion is a ratio of 0.7 to 0.9 with respect to the thickness at the maximum width portion, and at the upper end of the bead apex. As long as the thickness is 1.3 to 1.8 with respect to the thickness of the thinnest part, it was found that the effect of the present invention is exhibited (see FIG. 2).

  Further, the present inventor, in the bead apex 41 having high rigidity, when the thickness of the bead apex is gradually increased from the upper end portion 411 toward the lower end portion 413, the resonance frequency at which road noise is generated in a high frequency band. The experiment was conducted on the assumption that the generation of road noise could be reduced from the 315 Hz band to the higher frequency band.

  As a result, the thickness of the bead apex 41 is uniformly increased from the upper end portion 411 to the lower end portion 413 of the bead apex 41, and finally, the thickness d of the bead apex 41 at the lower end portion 413 is the bead at the center portion. It was found that it was most effective when the ratio was set to a ratio (d / c) of 1.3 to 1.8 with respect to the thickness c of the apex 41.

  As described above, in the present embodiment, the generation of road noise can be effectively reduced. On the other hand, in the present embodiment, since the rigidity of the tread portion is not particularly changed, the behavior of the cornering power is not lowered, and the same steering stability performance and riding comfort performance as in the conventional case can be sufficiently ensured.

  Furthermore, in the present embodiment, since the distribution of the total thickness in the tire is simple, it is difficult for the rubber after molding to flow, and the occurrence of variations in the manufacturing process and the finishing process can be reduced. As a result, a stable quality tire can be provided.

  Using tires to which the above-described embodiments are applied as examples and conventional tires as comparative examples, each tire was mounted on a passenger car, and road noise, steering stability, and ride comfort performance were evaluated under the following test conditions.

1. Tire (1) size and pattern used for test Example: P195 / 65R15 89S Integrity
Comparative Example: P195 / 65R15 89S INTEGRITY
(All rims are 6.0J)

(2) Thickness and ratio of each part About each tire of an Example and a comparative example, the height from the bottom part of the bead part 40 to the thinnest part with respect to the height (h1) from the bottom part of the bead part 40 to the top part of the tread part 10 Ratio (h2 / h1), thickness a at the thinnest portion, thickness b at the upper end of the bead apex, bead apex thickness c at the central portion, bead apex thickness d at the lower end portion Were measured to determine (b / a) and (d / c). The results are shown in Table 1.

2. Test conditions Vehicles used for the test: Toyota Prius (model: NHW20)
Load: 1 person riding Tire pressure: 230 / 220kPa
Road surface: In-house road noise measurement road Traveling speed: 60 km / h and 100 km / h

3. Road noise 60 km / h and 100 km / h steady running were performed, and road noise in each case was measured. Specifically, the noise level dB (A) of the overall (OA) was measured at the front seat and the rear seat in the vehicle. The results are shown in Table 2 and Table 3. Table 2 shows the measurement results in the case of steady running at 60 km / h, and Table 3 shows the measurement results in the case of steady running at 100 km / h.

  In addition, with respect to the sound in the vehicle at the position of the right ear of the driver's seat, FIG. 3 shows the measurement results at 60 km / h when the sound pressure level at each frequency is measured, and FIG. 4 shows the measurement results at 100 km / h. . In each figure, the horizontal axis represents the frequency (Hz), and the vertical axis represents the sound pressure level (dB) in the A characteristic. Moreover, a dotted line is an Example and a dashed-dotted line is a conventional product.

  From Table 2, at 60 km / h, the noise level decreased by 1.4 dB (71.3 dB → 69.9 dB) at the front seat and decreased by 1.3 dB (71.6 dB → 70.3 dB) at the rear seat. I understand that. Similarly, from Table 3, at 100 km / h, the noise level decreases by 0.9 dB (74.3 dB → 73.4 dB) at the front seat and 1.0 dB (74.1 dB → 73.1 dB) at the rear seat. It turns out that it has fallen.

  This reduction of the 1 dB noise level is a significant difference, and it can be seen that applying the present invention provides a significant improvement effect on the generation of road noise.

  3 and 4, it can be seen that the sound pressure level in the example is lower than that in the comparative example in the band around 250 Hz at any speed, and the generation of road noise is reduced.

4). Steering stability and riding comfort performance Steering stability and riding comfort performance during actual driving were also evaluated by sensory evaluation of the driver.

  As a result of the measurement, it was confirmed that both the steering stability and the ride comfort performance were in the same level or higher in the example than in the comparative example.

  From the above, it can be seen that by applying the present invention, it is possible to provide a pneumatic tire with reduced generation of road noise while ensuring steering stability performance and riding comfort performance.

  While the present invention has been described based on the embodiments, the present invention is not limited to the above embodiments. Various modifications can be made to the above-described embodiment within the same and equivalent scope as the present invention.

DESCRIPTION OF SYMBOLS 10 Tread part 11 Tread rubber 12 Breaker 20 Shoulder part 23 Boundary part 30 of shoulder part and sidewall part Sidewall part 31 Maximum width part 34 Boundary part of sidewall part and bead part 40 Bead part 41 Bead apex 411 Bead apex Upper end portion 412 Central portion of bead apex 413 Lower end portion of bead apex 42 Bead core 50 Carcass ply 501 Folded portion 502 Upper end portion of folded portion a Thickness of thinnest portion of tire b Thickness at upper end portion of bead apex c The thickness of the bead apex at the center of the bead apex d The thickness of the bead apex at the lower end of the bead apex

2. Test conditions Vehicles used for the test: Toyota Prius (registered trademark) (Model: NHW20)
Load: 1 person riding Tire pressure: 230 / 220kPa
Road surface: In-house road noise measurement road Traveling speed: 60 km / h and 100 km / h

Claims (3)

The thinnest portion of the tire is 0.6 to 0. 0 from the bottom portion of the bead portion with respect to the height from the bottom portion of the bead portion to the top portion of the tread portion between the end portion of the breaker and the maximum width portion of the tire. The thickness of the thinnest portion is a ratio of 0.7 to 0.9 with respect to the thickness of the maximum width portion.
From the thinnest part toward the upper end of the bead apex, the thickness at the upper end of the bead apex is in a ratio of 1.3 to 1.8 with respect to the thickness at the thinnest part. Has increased uniformly,
Further, the thickness of the bead apex increases uniformly from the upper end portion of the bead apex to the lower end portion, and the thickness of the bead apex at the lower end portion is 1 with respect to the thickness at the central portion. A pneumatic tire having a ratio of 3 to 1.8.   2. The pneumatic tire according to claim 1, wherein a thickness of the thinnest portion and a thickness of an upper end portion of the bead apex have variations within ± 0.6 mm, respectively. The breaker is a breaker configured by laminating two layers of belts made of steel cord,
The pneumatic tire according to claim 1 or 2, wherein the carcass ply is a carcass ply composed of one or more layers of plies produced using an organic fiber cord.

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