JP5350854B2 - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce columnar resonance sound caused by a circumferential groove at a wide frequency band area while maintaining a freedom degree of design of a tread pattern. <P>SOLUTION: The pneumatic tire includes at least one peripheral groove extended along a tread circumferential line, and a branch groove having one end opened to the peripheral groove and the other end completed in a land part on a tread step surface of the tire. A recessed and projecting part is provided on at least a part of a groove wall surface partitioning the branch groove, and a ratio of a surface area of the groove wall surface with respect to a projected area of the groove wall surface is increased. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a pneumatic tire with reduced tire noise, and more particularly to a pneumatic tire with reduced air column resonance caused by circumferential grooves formed on a tread surface.

  With the recent quietness of vehicles, the proportion of tire noise in automobile noise has become relatively large, so reducing tire noise has become a major issue. Among these, tire noise around 1000 Hz is a major factor of noise outside the vehicle, and an immediate countermeasure is desired for this noise from the viewpoint of environmental problems.

By the way, in a general passenger car, tire noise belonging to a frequency band of 800 to 2000 Hz is caused by resonance of air columns defined by circumferential grooves formed in a tread and a road surface in a tire contact surface, so-called air pressure. It is known to occur by column resonance.
In other words, when a tire having a circumferential groove is in contact with the ground, a tube having the same length as the contact length is formed between the groove wall of the circumferential groove and the contact surface. Noise called sound is generated. The frequency f ₀ of the air column resonance sound is defined as L, where the speed of sound is c, the length of the tube, that is, the length of the circumferential groove and the opening end correction amount is added.
f ₀ = c / 2L
It is a constant frequency represented by The opening end correction amount is normally obtained by experiment, and when the tube is cylindrical, it is obtained by multiplying the radius inside the tube by a constant.

  This air column resonance sound has a high peak and a wide frequency band, and is one of the main factors that cause a direct sound due to tires among noises. In addition, human hearing is sensitive in a frequency band around 1000 Hz, as indicated by a frequency correction characteristic called A characteristic that reflects human auditory sensitivity characteristics, and this reduction in air column resonance is quiet in the passenger compartment. It is very effective for improving the performance and reducing the noise near the road.

で表されることが分かっている。 In order to suppress such air column resonance, Patent Document 1 discloses that at least one circumferential groove extending along a tread circumferential line and one end of the tire tread are opened in the circumferential groove. There has been proposed a pneumatic tire including a branch groove that functions as a so-called side branch type resonator, the other end of which ends in the land. As shown in FIG. 1 (a), when the length of the side branch type resonator 5 opening in the circumferential groove 2 is l and the speed of sound is c, the frequency f to be reduced is:

It is known that

で表されることが分かっている。 Further, Patent Document 2 proposes to reduce air column resonance by using a so-called Helmholtz resonator, which is composed of a narrow groove portion having a small cross-sectional area and an air chamber portion having a large cross-sectional area. Yes.
In this case, as shown in FIG. 1 (b), the length of the narrow groove portion plus the opening end correction amount is l, the cross sectional area of the narrow groove portion is S, the volume of the air chamber portion is V, and the sound velocity is c. Then, the frequency f to be reduced is

It is known that

で表されることが分かっている。 Alternatively, instead of the Helmholtz type resonator as described above, as shown in FIG. 1C, pipes having different cross-sectional areas having constant cross-sectional areas S ₁ and S ₂ in their length directions are provided. A connected stepped tube resonator can also be applied. In this case, if the length of each pipe line plus the opening end correction amount is l ₁ , l ₂ and the sound velocity is c, the resonance frequency f is

It is known that

International Publication No. 2004/1037737 Pamphlet Japanese Patent Laid-Open No. 5-338411

  However, when the above-described resonator is used, a very large sound reduction effect is obtained at the resonance frequency of the resonator, but a sound reduction effect is hardly obtained at frequencies other than the resonance frequency. Therefore, in order to obtain a sound reduction effect over a wide frequency band, it is necessary to design a tread pattern so that a plurality of types of resonators having different resonance frequencies enter the ground plane at the same time. In other words, a plurality of types of resonators are usually disposed in the ground plane having a width of about 100 mm to 200 mm, which is a great limitation in designing the tread pattern.

  SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a pneumatic tire in which air column resonance noise caused by a circumferential groove is reduced over a wide band while maintaining the freedom of tread pattern design in consideration of the above facts. .

The gist of the present invention is as follows.
[1] Air having at least one circumferential groove extending along a tread circumference and a branch groove having one end opened in the circumferential groove and the other end ending in the land portion on the tread surface of the tire. In entering tires,
Providing at least a portion of the groove wall surface that divides the branch groove ,
Groove wall surface having irregularities, the surface area of the pneumatic tire, characterized in der Rukoto more than three times the projected area of the groove wall surface.

[2] The pneumatic tire according to the above [1], wherein the groove wall surface having irregularities has a surface area of 20 times or less of a projected area of the groove wall surface.

[3] The branch groove includes a narrow groove portion located on one end side of the branch groove and an air chamber portion located on the other end side of the branch groove and having a cross-sectional area larger than the cross-sectional area of the narrow groove portion. The pneumatic tire according to [1] or [2], wherein the pneumatic tire is a Helmholtz resonator .

  ADVANTAGE OF THE INVENTION According to this invention, the pneumatic tire which reduced the air column resonance sound resulting from the circumferential groove | channel over a wide band can be provided, maintaining the freedom degree of tread pattern design.

It is a schematic diagram of various resonators. It is one Example of the tread pattern of the pneumatic tire of this invention. It is a figure for demonstrating the unevenness | corrugation provided in a branch groove. It is another Example of the tread pattern of the pneumatic tire of this invention. It is another Example of the tread pattern of the pneumatic tire of this invention. It is a figure which shows the tread pattern of a reference example tire. It is a figure which shows the measurement result of the reference example tire contrast level of an example tire and a conventional example tire. It is a figure which shows the measurement result of the reference example tire contrast level of an example tire and a conventional example tire.

Hereinafter, the present invention will be described in detail with reference to the drawings.
FIG. 2 shows an example of a tread pattern of the pneumatic tire of the present invention. The tread tread surface 1 is provided with two pairs of circumferential grooves 2 that are positioned symmetrically with respect to the tire equatorial plane CL and extend along the tread circumferential line. Of these circumferential grooves 2, a pair of circumferential grooves 2 located close to the tire equatorial plane CL are located in the land portion 4 on the opposite side of the land portion where the tire equatorial plane CL exists. A plurality of branch grooves 5 that extend, have one end opened in the circumferential groove 2 and the other end ends in the land portion 4 are provided so as to extend in a straight line downward in the figure, and these branches Each of the grooves 5 is formed independently of the other circumferential grooves 2 and the lateral grooves 6.

  As described above, a conventional resonator using a branch groove can reduce only the sound near the resonance frequency and hardly reduce the sound in other frequency bands. Therefore, in order to obtain a sound pressure level reduction effect in a wide frequency band, it is possible to design a tread pattern so that a plurality of types of resonators having different resonance frequencies, that is, resonators having different sizes, enter the ground plane at the same time. Conceivable. However, a plurality of types of resonators are usually placed in the tire ground contact surface having a width of about 100 mm to 200 mm, and a great restriction on the design of the tread pattern has to be provided. Therefore, as a result of extensive studies by the present inventors, it has been found that it is effective to increase the surface roughness of the resonator (increase the ratio of the surface area to the cross-sectional area of the resonator). Therefore, as shown in FIG. 3, the sound pressure level can be reduced in a wide frequency band including the resonance frequency by providing fine irregularities on the groove wall surface defining the branch groove 5 to increase the surface area of the groove wall surface. I came up with it. As a result, it is not necessary to design the tread pattern so that a plurality of types of resonators having different resonance frequencies enter the ground plane at the same time, and the design freedom of the tread pattern can be increased.

  Moreover, although it is suitable to provide this unevenness over the entire groove wall surface of the branch groove 5 in order to reduce the sound pressure level, it may be provided partially. In the case of partial provision, in particular, in the case of a Helmholtz type resonator composed of a narrow groove portion and an air chamber portion, it is preferable to provide it in a portion close to the circumferential groove 2 of the resonator. This is because the particle velocity in the resonator is higher on the entrance side of the narrow groove and lower in the air chamber. Therefore, it is possible to effectively enhance the attenuation characteristics of the resonator by providing irregularities in the narrow groove portion where the particle velocity is high to increase the surface area, and as a result, it is possible to attenuate the sound pressure level in a wide band. Because.

となる（ｎ＝７）。また、溝壁面の投影面積は、７つ全ての凸状部材１０を覆うような、図中Ｐで表される部分の面積であり

となる。 In the example of FIG. 3, seven cubic convex members 10 having a width W ₁ , a height h, and a depth d are arranged on the groove wall with a width W ₂ arranged. When unevenness is provided in this way, the surface area of the groove wall surface is

(N = 7). Further, the projected area of the groove wall surface is an area of a portion represented by P in the figure so as to cover all seven convex members 10.

It becomes.

Moreover, it is preferable that the groove | channel wall surface which has an unevenness | corrugation is 1.5 times or more of the projection area of a groove | channel wall surface.
This is because, when the surface area of the groove wall surface having irregularities is less than 1.5 times the projected area of the groove wall surface, the increase in the surface area is small, and there is a possibility that the sound pressure level cannot be sufficiently reduced in a wide frequency band. Because.

Moreover, it is preferable that the groove | channel wall surface which has an unevenness | corrugation is 20 times or less of the projected area of a groove | channel wall surface.
As a comprehensive evaluation of the air column resonance band, when a partial overall value of 1/3 octave band center frequency 800-1000-1250 Hz band is used, there is a significant difference when an effect of 0.3 dB or more is obtained. Consider it as a threshold. As a result of the experiment, it was confirmed that an effect of 0.3 dB or more can be obtained when the groove wall surface having irregularities has a surface area of 1.5 times to 20 times the projected area of the groove wall surface.

When the convex member 10 as shown in FIG. 3 is provided on the groove wall surface of the branch groove, the longitudinal direction (direction of depth d) of the convex member 10 can be the depth direction of the branch groove. The longitudinal direction (the direction of depth d) of the convex member 10 can also be the longitudinal direction of the branch groove.
Moreover, although the unevenness | corrugation provided in a groove wall surface was demonstrated to the example of the plate-shaped convex member 10, a groove | channel wall surface can also be formed in an unevenness | corrugation by providing a dice type or a bowl-shaped convex member.
Furthermore, although the example which provides the convex-shaped member 10 in the groove wall surface of a branch groove was demonstrated, a groove wall surface can also be formed in an unevenness | corrugation by providing a recessed part.

4 and 5 show other examples of the tread pattern of the pneumatic tire of the present invention.
FIG. 4 shows a tread pattern having side branch type resonators. A tread tread surface 1 is provided with a plurality of circumferential grooves 2 extending along the tread circumferential line, in the illustrated example, four circumferential grooves 2. Among the grooves 2, one end is opened to the circumferential groove 2 in the vicinity of the tire equatorial plane CL and the circumferential groove 2 sandwiching the land portion on the opposite side of the tire equatorial plane CL, and the other end Are provided with a plurality of branch grooves 5 bent at an acute angle that terminate in the land portion.
Concavities and convexities are provided on at least a part of the groove wall surface defining the branch groove 5.

In the pneumatic tire having the tread pattern shown in FIG. 5, the tread tread surface 1 is provided with a plurality of circumferential grooves 2 extending along the tread circumferential line, in the illustrated example, four of the circumferential grooves 2. The circumferential groove 2 in the vicinity of the tire equator plane CL and the circumferential groove 2 sandwiching the land portion on the opposite side of the tire equator plane CL, one end opens in the circumferential groove 2 and the other end ends in the land portion. A helm-hot-type branch groove 5 comprising a narrow groove portion and an air chamber portion is provided.
Concavities and convexities are provided on at least a part of the groove wall surface defining the branch groove 5.

であるが、例えば、溝壁面に多数の凹凸が設けられている場合、ｎが十分に大きくなるので、ｎ＝ｎ−１と近似できる。さらに、奥行きｄが幅Ｗ_１、Ｗ_２および高さｈに対して十分に大きい場合（ｄ＞＞Ｗ_１，Ｗ_２，ｈ）、Ｗ_１ｈの項は無視できる。そこで、Ｗ_１＝Ｗ_２＝０．３ｍｍ、ｈ＝０．９ｍｍとすると、上記（３）式は、下記（４）式のように変形でき、

投影面積に対する表面積の割合は４となる。 Here, the ratio of the surface area to the projected area (surface area / projected area) is specifically calculated using the above formulas (1) and (2). Surface area / projected area is

However, for example, when a large number of irregularities are provided on the groove wall surface, n is sufficiently large, so that it can be approximated as n = n−1. Further, when the depth d is sufficiently large with respect to the widths W ₁ and W ₂ and the height h (d >> W ₁ , W ₂ , h), the term W ₁ h can be ignored. Therefore, when W ₁ = W ₂ = 0.3 mm and h = 0.9 mm, the above equation (3) can be transformed into the following equation (4):

The ratio of the surface area to the projected area is 4.

A pneumatic tire, a conventional tire, and a reference tire according to the present invention were prototyped according to specifications described later, and performance was evaluated.
The conventional tire 1 has a tread pattern shown in FIG. 4, and each branch groove 5 has a length of 85 mm and a cross section of 4 mm × 4 mm.
The conventional tire 2 has the tread pattern shown in FIG. 5, the narrow groove portion has a width of 2 mm, a depth of 2 mm, and a length of 10 mm, and the air chamber portion has a volume of 1000 mm ³ .
Example tire 1, and Reference Example tires 1-2, the groove wall surfaces defining the respective branch grooves 5, except that there is provided a fine irregularities as shown in FIG. 3 is the same as Conventional Example tire 1.
Invention Example Tire 2 has the tread pattern shown in FIG. 5, the width of the narrow groove portion is 2 mm, the depth is 3 mm, the length is 10 mm, and the volume of the air chamber portion is 1000 mm ^3. in is provided with fine irregularities as shown in FIG. Since the cross-sectional area of the narrow groove portion is reduced by about 2 mm ² due to fine unevenness, the resonance frequency is about 1000 Hz, which is substantially the same as that of the conventional tire 2.
The reference tire is a conventional tire having the tread pattern shown in FIG. 6 and having no branching groove that acts as a resonator for reducing tire noise, and has a widthwise groove 3 that connects between adjacent circumferential grooves 2. .
Table 1 shows the dimensions of the branch grooves and the irregularities provided in the branch grooves of each prototype tire. The sound reduction effect compared with the reference tire is also shown.

  Each prototype tire (tire size: 195 / 65R15) was assembled on a 15 × 6J rim to form a tire wheel, and the tire internal pressure was adjusted to 210 kPa. The tire side sound when running with an indoor drum tester at 80 km / h with a load of 4 kN was measured under the conditions defined in the JASO C606 standard, and each band was measured by 1/3 octave band analysis. evaluated. Further, as a comprehensive evaluation of the air column resonance band, a partial overall value of a 1/3 octave band center frequency 800-1000-1250 Hz band was used.

In FIG. 7, the measurement result of the reference | standard tire relative sound pressure level of the invention example tire 1 and the conventional example tire 1 is shown. When the sound pressure level (SPL: Sound Pressure Level) is greater than 0, it indicates that the sound pressure level is improved compared to the reference tire, and when the sound pressure level is less than 0, the sound pressure level is deteriorated.
The conventional tire 1 can obtain a high sound reduction effect (about 2.2 dB) in the 1000 Hz band, but does not have much sound reduction effect in other frequency bands.
Inventive tire 1 has a sound reduction effect in the 1000 Hz band, which is inferior to that of conventional tire 1, but a sound reduction effect of 0.4 dB or more was confirmed in the frequency band of 630 Hz to 1250 Hz.
Therefore, as shown in Table 1, the partial overall value of the 1/3 octave band center frequency 800-1000-1250 Hz band is 0.7 dB lower than that of the conventional tire 1 and 0. It was 9 dB decrease.
Further, in Reference Example Tires 1 and 2 in which the surface area / projection area was changed from that of Invention Example Tire 1, a sound reduction effect of 0.3 dB and 0.2 dB was confirmed, respectively.

In FIG. 8, the measurement result of the reference tire relative sound pressure level of the invention example tire 2 and the conventional example tire 2 is shown.
The conventional tire 2 can obtain a high sound reduction effect (about 1.8 dB) in the 1000 Hz band, but does not have much sound reduction effect in other frequency bands.
Inventive tire 2 was found to have a sound reduction effect of 0.4 dB or more in the frequency band of 630 Hz to 1600 Hz, although the noise reduction effect in the 1000 Hz band was inferior to that of conventional tire 2.
Therefore, as shown in Table 1, the partial overall value of the 1/3 octave band center frequency 800-1000-1250 Hz band is 1.1 dB lower than that of the reference tire, the conventional tire 2 is 1. It was 5 dB decrease.

  As described above, by providing irregularities on the groove wall surface of the branch groove that opens to the circumferential groove, a pneumatic tire that reduces air column resonance noise caused by the circumferential groove in a wide band while maintaining the freedom of tread pattern design. Can be provided.

1 tread surface 2 circumferential groove 3 width groove 5 branch groove 6 lateral groove 10 convex member

Claims (3)

In a pneumatic tire comprising at least one circumferential groove extending along a tread circumferential line and a branch groove having one end opened in the circumferential groove and the other end ending in a land portion on a tread surface of the tire. ,
Providing at least a portion of the groove wall surface that divides the branch groove ,
Groove wall surface having irregularities, the surface area of the pneumatic tire, characterized in der Rukoto more than three times the projected area of the groove wall surface. Groove wall surface having irregularities, the surface area, the pneumatic tire according to claim 1, characterized in that not more than 20 times the projected area of the groove wall surface. The Helmholtz type is composed of a narrow groove portion located on one end side of the branch groove and an air chamber portion located on the other end side of the branch groove and having a cross-sectional area larger than the cross-sectional area of the narrow groove portion. The pneumatic tire according to claim 1, wherein the pneumatic tire is a resonator.

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