JP4925660B2 - tire - Google Patents

Description

  The present invention relates to a tire in which tire noise, in particular, air column resonance noise having a frequency of approximately 800 to 1400 Hz is effectively reduced without reducing the wear resistance of the tire.

  With the recent quietness of vehicles, the ratio of tire noise to automobile noise has become relatively large, so reducing tire noise has become a major issue. Among them, tire noise around 1000 Hz, which is easily heard by humans, is a main factor of noise outside the vehicle, and this noise is expected to be promptly taken from the viewpoint of environmental problems.

  By the way, the tire noise of about 800 to 1400 Hz may be generated by air column resonance caused by resonance of the air column defined by the circumferential groove and the road surface in the ground contact surface of the tire. In general, it is known that a reduction in the groove volume of the circumferential groove is effective for suppressing such air column resonance.

  However, since the reduction of the groove volume of the circumferential groove on the one hand requires a decrease in the drainage performance of the tire, and consequently the wet performance, for example, in Patent Document 1, tire noise is reduced without a decrease in the wet performance. For this purpose, one wide circumferential groove having a groove width of 25 to 70 mm is provided in the central area of the tread, and the tread grounding edge is opened on both sides of the wide circumferential groove, but the circumferential direction There has been proposed a pneumatic tire that is provided with a lateral groove that does not open in the groove and has a groove width of 5 to 15% of that of the wide circumferential groove.

  However, in this proposed tire, because of the presence of the wide circumferential groove, a large reduction in the tread contact area cannot be denied, and a large step in the contact pressure in the tread width direction is unavoidable, especially on dry road surfaces. There is a problem that it is difficult to achieve both steering stability and limit grip characteristics.

In order to solve this problem, the applicant of Patent Document 2 described in Japanese Patent Application Laid-Open No. H10-228867 while effectively suppressing a decrease in wet performance while sufficiently satisfying the handling stability on the dry road surface and the limit grip characteristics. A design method of pneumatic tire and tire tread pattern with greatly reduced column resonance noise was proposed.
JP-A-6-143932 International Publication No. 2004/1037737 Pamphlet

This pneumatic tire has at least one circumferential groove provided on the tread tread surface, one end of which is opened in the circumferential groove, and the other end which is terminated in the land portion. It is formed independently of the transverse sub-grooves that open to the groove and the tread grounding edge, and each of these transverse grooves and circumferential grooves is filled with the highest air pressure and maximum load capacity when mounted on the tire rim. In a tire posture loaded with a mass equivalent to the groove width, the groove walls do not come into contact with each other, and each lateral groove has an arrangement mode in which one or more are always completely included in the ground plane, Further, the width of the lateral groove in the ground plane is regulated.
By optimizing the setting of the lateral grooves in this way, it has become possible to greatly reduce the air column resonance noise of the tire while effectively suppressing a decrease in wet performance.

  However, in order to satisfy the setting of the lateral groove proposed here, it is necessary to allow extension suitable for the condition of the lateral groove, and in particular, when one end of the lateral groove is held in the land part, the rigidity in the land part is made uniform. It is difficult to ensure the initial wear resistance.

  Therefore, the present invention aims to propose a method for avoiding a decrease in wear resistance performance in a tire in which tire noise is effectively reduced by suppressing air column resonance sound having a frequency of 800 to 1400 Hz. Is.

  The inventors have found that, in order to equalize the rigidity of the land portion when arranging the lateral grooves advantageous for reducing the air column resonance noise of the tire, it is effective to arrange the grooves other than the lateral grooves, particularly sipes. The headline and the present invention have been completed.

That is, the present invention provides a tread tread with two or more circumferential grooves continuous in the circumferential direction, and at least one circumferential groove has one end opened in the circumferential groove and the other end terminated in the land portion. The lateral grooves of the book are formed independently of the other circumferential grooves and the other lateral grooves that open to the tread grounding edge. Under the tire posture where the weight corresponding to the maximum load capacity is loaded, the groove width is set so that the groove walls do not contact each other in the ground plane, and each lateral groove is always at least one in the ground plane. In addition, the length of each lateral groove portion in which the width of the lateral groove is 30% or more of the groove width of the peripheral groove in the ground plane The tire is 40% or more of the extension length of the circumferential groove,
At least one sipe extending within the land portion starting from the transverse groove is provided for each transverse groove, and in the extended length region of at least 1 mm of the sipe, the depth is 40% or less of the circumferential groove depth, and the width is The tire is 1 mm or less.

  Here, the applicable rim refers to the rim specified in the following standards, the maximum air pressure refers to the air pressure defined in accordance with the maximum load capacity in the following standards, and the maximum load capacity refers to the following The maximum mass allowed to be loaded on a tire by standard.

  The standard is determined by an industrial standard effective in the region where the tire is produced or used. For example, “THE TIRE AND RIM ASSOCIARION INC. YEAR BOOK” is in the United States, “European Tire and Rim Technical Organization is a Japanese tire in Japan” .

  The tread surface means that the tire is attached to the applicable rim, filled with the maximum air pressure, placed vertically on the flat plate, and brought into contact with the flat plate when a mass corresponding to the maximum load capacity is loaded thereon. The surface area of the tread rubber.

  Furthermore, the sipe is a narrow groove having a groove width of 2 mm or less, and is formed with a constant groove width regardless of the pitch length of the tread pattern.

  According to the present invention, it is possible to effectively reduce tire generated noise, particularly air column resonance, while ensuring excellent wear resistance in a tread.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a development view of a tread pattern schematically showing an embodiment of the present invention.
In addition, since the internal reinforcement structure of a tire is the same as that of a general radial tire, illustration is abbreviate | omitted.

  In the figure, reference numeral 1 denotes a tread surface. The tread surface 1 is provided with three circumferential grooves 2, 3 and 4 continuously extending along a tire equator line C in a straight line or zigzag pattern. 3 and 4 and both tread ends E define four rows of land portions 5, 6, 7 and 8.

  Of these land portions 5, 6, 7 and 8, the land portions 6 and 7 extend from the circumferential grooves 3 and 4 located close to the tire equator line C to the circumferential grooves 2 and 3, respectively. In the illustrated example, a plurality of lateral grooves 9 having one end opened in the circumferential groove 3 or 4 and the other end ending in the land portion 6 or 7 are provided to extend downward in the illustrated example. The sub-groove 10 and the lateral grooves 11 and 12 provided in the other circumferential grooves 2 or other land portions are completely independent from each other.

  The lateral groove 9 extends inclining with respect to the tire equator line C, and the inclination angle gradually decreases from one end on the circumferential groove side to the other end on the land portion side. The angle with respect to the tire equator line C need not be particularly limited.

  Furthermore, in this tire, when the tread pattern as described above is formed, the tire is assembled to the applicable rim, filled with the maximum air pressure, and loaded with a mass corresponding to the maximum load capacity. As apparent from the footprint shown in FIG. 2, the groove width of the lateral groove 9 as well as the circumferential grooves 3 and 4 is set to have a width dimension in which the groove walls do not contact each other. 9 is arranged so that one or more of the grooves 9 are always completely included in the grounding surface, and the groove width of the lateral grooves 9 is 30% or more of the groove width of the circumferential groove 3 or 4 in the grounding surface. The length of the lateral groove portion, that is, the total length 1 of the lateral groove 9 is 40% or more of the extending length L of the circumferential groove 3 or 4 in the ground plane as shown in FIG.

  Here, as shown in FIG. 2, the total length 1 of the lateral groove 9 is the central axial length of the lateral groove 9, and is the length of the curve when it is a curve, and the length of a straight line when it is a straight line.

  According to the tire configured in this way, as described above, the driving stability on the dry road surface and the limit grip characteristic can be achieved at the same time under the formation of a plurality of lateral grooves and the like. In addition, the air column resonance frequency of each of the circumferential grooves 3 and 4 can be made different while ensuring the wet performance. For example, the resonance frequency of the circumferential grooves 3 and 4 is equivalent to that of the circumferential groove 2. Thus, the peak level of the air column resonance noise can be effectively reduced, and at the same time, white noise can be greatly promoted.

That is, the air column resonance sound is generated by the air column partitioned by the circumferential groove and the road surface in the ground contact surface based on the vibration of each part of the tire during rolling. The frequency f ₀ of the air column resonance sound in this case is v, the sound speed is v, the circumferential contact length of the tread surface, in other words, When the circumferential groove length included therein is L,
f ₀ = v / 2L
It is represented by

Further, such air column resonance, in the tire tread pattern, when a plurality of circumferential grooves continuously extending in the tread circumferential direction are communicated with each other by a lateral groove extending across the circumferential groove, Only air column resonances with one specific frequency will occur.
Note that the width, depth, and number of circumferential grooves greatly affect the sound pressure level of the resonance rather than the resonance frequency.

Therefore, when the influence of the horizontal groove on the resonance phenomenon of the circumferential groove was examined, when the horizontal groove was terminated in the middle of the land portion, when the length of the horizontal groove in the ground plane was 1 and the speed of sound was v,
f = (2n−1) × v / 4l
n: vibration order (n = 1, 3, 5...)
It has become clear that sound is absorbed at the frequency f represented by
Therefore, when the sound absorption frequency is brought close to approximately 800 to 1400 Hz, which is the air column resonance frequency of the circumferential groove, the resonance noise can be reduced.

It was also found that the width, depth, and number of the lateral grooves also have a great influence on the sound absorption capacity rather than the vibration absorption frequency.
By the way, the air column resonance frequency changes between approximately 800 to 1400 Hz depending on the contact length of the tread surface. Therefore, in order to bring the sound absorption frequency close to these frequencies, it is included in the contact surface. It is necessary that the ratio of the extending length of the lateral groove to the circumferential groove length is 40% or more, more preferably 40% or more and 90% or less.
That is, if the ratio is less than 40%, the sound absorption frequency and the air column resonance frequency region are greatly different, and it is difficult to effectively reduce the resonance noise.

In order for the horizontal groove to sufficiently exhibit such a sound absorbing function, the groove walls of the horizontal groove do not contact each other in the ground plane, and one or more horizontal grooves that open to a predetermined circumferential groove must be in contact with the ground plane. It is always necessary to be completely contained within.
In this case, the extension length of the lateral groove is limited to the length of the portion whose groove width is 30% or more of the groove width of the circumferential groove. This is because the groove width is narrow and the groove volume is small, so that a sufficient sound absorbing effect cannot be obtained.

  Furthermore, any one of the other lateral groove opened at the tread ground edge, and the other lateral groove opened at the other circumferential groove, with the lateral groove having one end opened in a specific circumferential groove and the other end terminated in the land portion. By controlling the resonance frequency of the specific circumferential groove, it is possible to effectively disperse the resonance frequency of the plurality of circumferential grooves at the time of tire load rolling, As a result, the noise peak level can be reduced and white noise can be greatly promoted as compared with the case where air column resonance is generated with only one specific frequency.

  As described above, when the other end of the lateral groove is terminated in the middle of the land portion to reduce air column resonance, the land portion around the other end of the closed lateral groove is compared with the other land portion. As described above, the rigidity becomes high and a difference in rigidity occurs in the same land portion, and in particular, the initial wear resistance is adversely affected. This becomes more remarkable as the inclination angle of the lateral groove with respect to the tire equator line increases.

Here, in order to make the land part rigidity uniform, the aim was to improve the initial wear resistance by inserting a sipe into an arbitrary part of the transverse groove that was terminated in the middle of the land part.
That is, as shown in FIG. 1, at least one sipe extending in the land portion land portion 6 or 7 starting from the horizontal groove 9 is provided for each horizontal groove, and in the illustrated example, two sipes 13 and 14 for each horizontal groove 9 are provided. It is important to provide it. With this sipe, the sipe is appropriately introduced for each block-like land portion divided by the horizontal groove 9 to eliminate the rigidity step in each block-like land portion, and thus in the land portion.

  Note that the sipe extends from the lateral groove 9 as the starting point, as in the sipe 13, and from the circumferential groove 2 or 3 as the end point, and the sipe extends from the lateral groove 9 as the starting point, as in the sipe 14, to the end point. Although the number thereof may be arbitrary, about 1 to 8 for each lateral groove 9 is preferable. In other words, if the number exceeds 8, the land portion rigidity is excessively lowered, so 8 or less is appropriate from the viewpoint of avoiding this.

  Furthermore, it is important that the sipe 13 and 14 have a depth of 40% or less of the circumferential groove depth and a width of 1 mm or less in the extended length region of at least 1 mm. First, the restriction on the depth and the width is applied to the extension length region of at least 1 mm in order to obtain the sound absorption effect by making the lateral groove 9 independent of the extension length of at least 1 mm of the sipe. It suffices if there is a portion in the area that complies with the above-mentioned depth and width regulations.

  Next, the sipe depth in the area is set to 40% or less of the circumferential groove depth and the sipe width is set to 1 mm or less. This is to prevent the above-described effect of reducing the air column resonance from decreasing. That is, by forming a sipe with a sipe depth of 40% or less of the circumferential groove depth and a sipe width of 1 mm or less, the sound absorption effect in the lateral groove is prevented from being reduced by the presence of the sipe. be able to.

  Based on the pattern shown in FIG. 1, a tire having a tread pattern with various specifications shown in Table 1 and having a size of 225/55 R17 is assembled to a rim of 7JJ-17, and 230 kPa is installed there. With the internal pressure applied and a load of 5.25 kN applied, the air column resonance noise level and initial wear were evaluated. The depth of the circumferential groove was all 8 mm.

Here, the air column resonance noise level measures the sound pressure reduction effect of the air column resonance sound (1000 Hz) in accordance with JASO C606 standard from speed 40 to 100 km / h in 10 km / h increments. The measurement results are shown in Table 1 according to the following classification.
X: 0 dB or more Δ: less than 0 to −1 dB
○: Less than −1 to −2 dB
A: Less than -2 dB

In addition, the initial wearability is determined by attaching the test tire to a front-wheel drive vehicle with a displacement of 3000 cc and running on a general road for 5000 km with two passengers. The amount of difference in level with the land portion was measured and evaluated by its maximum value. The evaluation results were indexed with the level difference of the conventional example as 100 and displayed in Table 1 according to the following classification.
X: over 110 Δ: over 100-110
○: Over 90 to 100
A: 90 or less

It is an expanded view of the tread pattern which shows embodiment of this invention. It is a figure which shows the footprint of the tire of FIG.

Explanation of symbols

1 tread surface 2 circumferential groove 3 circumferential groove 4 circumferential groove 5 land part 6 land part 7 land part 8 land part 9 lateral groove 13 sipe 14 sipe

Claims (1)

Two or more circumferential grooves continuous in the circumferential direction are provided on the tread surface, and at least one of the circumferential grooves has one end opened in the circumferential groove and the other end terminated in the land portion. The circumferential grooves and other lateral grooves that open to the tread ground edge are formed independently from each other. Under the tire posture loaded with a mass equivalent to, the groove width is set so that the groove walls do not contact each other in the grounding surface, and each lateral groove is always completely included in the grounding surface. Further, the extension length of each lateral groove portion in which the groove width of the lateral groove is 30% or more of the groove width of the peripheral groove in the ground plane is defined as the extension length of the peripheral groove in the ground plane. Tires with 40% or more of
At least one sipe extending within the land portion starting from the transverse groove is provided for each transverse groove, and in the extended length region of at least 1 mm of the sipe, the depth is 40% or less of the circumferential groove depth, and the width is A tire characterized by being 1 mm or less.

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