JPH06344725A - Radial tire for heavy load - Google Patents

Abstract

PURPOSE:To reduce noise without deteriorating the running property on a wet road of a radial tire for heavy loads on the tread of which a plurality of longitudinal grooves extending along the circumferential direction of the tire and a plurality of ribs are provided by arranging the side walls of the longitudinal grooves in a zigzag pattern, and specifying the number of pitches of the zigzag and the depth between each mountain portion and each valley portion of the zigzag. CONSTITUTION:In a tire the tread 1 of which has a plurality of longitudinal grooves 3 provided thereon along the circumferential direction of the tire and a plurality of ribs 4 partitioned by the longitudinal grooves 3, the inclined faces of the walls 8 of the longitudinal grooves 3 are notched 7 to form a zigzag Z comprising alternate mountain and valley portions 11 and 12 in the circumferential direction of the tire. The number N of pitches of the zigzag Z in one complete turn of the tire is 200 to 700 and the depth (d) (the amplitude of the zigzag Z) between each mountain portion 11 and each valley portion 12 is set to the range of 1/2 to 1/5 of pitch length P. Thereby the resonance point of the characteristic frequency and excitation frequency of the tire is shifted out of a practical speed range toward a lower speed range so as to lower the noise level of the tire during running at high speeds.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heavy load radial tire for use in trucks, buses and the like, and more particularly to an improvement in noise reduction technology against tire noise.

[0002]

2. Description of the Related Art Conventionally, as a technique for reducing the noise of a tire of this type, a technique for dispersing noise generated by a tread pattern (referred to as pattern noise) over a wide frequency band has been provided. For example, Japanese Examined Patent Publication No. 3-23366 and Japanese Unexamined Patent Publication No. 58-2844 disclose two types of variable pitches for the pitch lengths of patterns arranged in the tire circumferential direction so that sounds in a specific frequency range are not concentrated. This prevents noise from increasing due to resonance.

Further, there has been proposed a means for suppressing the generation of air columnar resonance noise by changing the cross-sectional shape of the vertical groove from a normal U shape to a V shape and providing a plurality of stepped shelves on the groove wall.

Further, in the lug block pattern, the width of the lateral groove is reduced, the plane is passed through the tire rotation axis, the pitch is reduced, and the vibration force to the tire is reduced. Of the pattern noises, the noises related to tire vibration are reduced.

[0005]

However, the technique of using the pitch of the tread pattern as the variable pitch is effective in that the noise is reduced by dispersing the pattern noise over a wide frequency band. Since it is a technology that makes the tires different in the circumferential direction, it is necessary to give a large pitch length ratio in order to obtain the expected effect, which causes a difference in rigidity of the ribs and causes a problem that uneven wear easily occurs. is there. In addition, a means for suppressing the generation of air columnar resonance noise by changing the cross-sectional shape of the vertical groove from a normal U shape to a V shape and providing a plurality of stepwise shelves on the groove wall is a drum noise test which is an indoor noise test. However, it is smaller than other components of the pattern noise on the actual road surface, for example, vibration noise, and is not necessarily good for reducing the pattern noise. In addition, lugs or block patterns with a reduced width of the lateral groove have restrictions to secure traction or braking performance when traveling on wet roads, which is a contradictory matter, and they cannot be sufficiently dealt with, and it is a problem for recent environmental problems. It is hard to say that it is not always possible to sufficiently meet the regulatory requirements of.

An object of the present invention is to provide a heavy duty radial tire which can effectively reduce the noise of the tire.

[0007]

One of the causes of tire noise, particularly pattern noise, is generally an air column tube which is formed between a tire tread groove and a road surface when the tire is in contact with the road surface and rolls. It is believed to be due to formation. This is a concept that has been emphasized in a drum test of a tire alone, because a resonance sound having a frequency mainly determined by the length of the air column tube is often generated, which is a main factor of noise.

[0008] However, in actual road running, the roughness of the road surface has an influence, and as the tire rolls, the air column tube becomes more likely not to be formed, and the noise due to the air column tube formation is more of a pattern noise than the drum test which is an indoor noise test. It does not affect the level very much. Rather, when driving on actual roads, it is considered that the vibration generated by hitting the road surface intermittently at a number of times proportional to the number of pitches of the tires and the number of rotations of the tires during running may affect noise. To be

Therefore, the frequency of pattern noise is analyzed,
As a result of examining various heavy load radial tires with respect to the relationship between the noise level and the speed, for example, as shown in FIG. 6, the noise level peaks at a specific speed (the frequency at this time is 5
It corresponds to 00 to 700 Hz. ) Appeared. From these results, the tire has a certain natural frequency that affects noise, and exists in the sidewall portion near the tire ground contact portion, and probably near the tire ground contact portion, and the vibration frequency generated during running is equal to the natural frequency. It can be inferred that the peak value was created because they coincided with each other and entered the resonance state. In addition, it was confirmed by the frequency analysis of the noise of the vehicle exterior noise during actual road running that the frequencies that contributed to the noise level almost corresponded to this natural frequency. Therefore, it can be said that the tire noise depends on how to remove this resonance state.

Generally, between the vibration frequency ω and the natural frequency ω ₀ near the tire ground contact portion, the ratio e of the tire-side vibration amplitude e _t to the vibration amplitude e _P added from the pattern by the value ω / ω _{0 The t} / e _P , that is, the vibrational conductivity greatly changes, and at the resonance state of ω / ω ₀ = 1, the maximum of e _t / e _P is ω / ω ₀ > 2 ^1/2 , and e _t / e _P < It is known to be 1 (see FIG. 7). Therefore, the noise level at the time of resonance is lowered by passing through the resonance point at an extremely low speed, and at the practical speed range of the tire (vehicle), the resonance point (ω / ω ₀ =
By removing 1), noise can be reduced in the practical speed range.

On the other hand, the vibration frequency generated during running is proportional to the product of the number of rotations of the tire and the number of pitches of the zigzag forming the groove wall of the vertical groove of the tire tread, so that the number of pitches is different. For many heavy duty radial tires,
As a result of measuring the peak generation speed V _p (Km / h) where ω / ω ₀ = 1, as shown in FIG. 8, there is a constant relationship between the zigzag pitch number N and the peak generation speed V _p. I found it. FIG. 8 suggests that the peak generation speed V _P is determined not by the tire size but by the pattern pitch number N.

When this curve is expressed by an empirical formula, between the pitch number N and the peak velocity V _P ,

[Equation 1] Can be expressed by a simple relational expression.

This implies that the peak is always the natural frequency of a portion of the tire, probably the sidewall portion near the tire ground contact portion, and that value is f = 640 in the heavy load radial tire. However, this is an average value and actually lies between 500 and 700 Hz.

By the way, generally, tire noise has a small contribution to the vehicle exterior noise at low vehicle speeds, but in urban areas it often travels at a speed of around 40 to 50 km / h, so at least low from around 30 km / h. It is necessary to make noise.
That is, at least near 30 km / h, ω / ω ₀ is 1.0
It needs to be larger. Therefore, from FIG. 8, 3
20 to obtain a frequency of 640 Hz at 0 km / h
A pitch number of 0 to 300 is required. Furthermore ω / ω ₀
Approximately 350 pieces are required to ^achieve > 2 ^1/2 .

Further, since the viscoelastic body called rubber is used for the vibration of the tire including the vicinity of the side portion of the tire, there is always a vibration damping property, and the vibration is transmitted even at the resonance of ω / ω ₀ = 1. The rate does not become ∞, but is always finite (see Fig. 2). Therefore, even when ω / ω ₀ = 1 the resonance level becomes smaller as the excitation force becomes smaller. Therefore, not only increasing the number of pitches to increase ω / ω ₀ , but also reducing the amplitude of the zigzag of the crests and troughs in the groove wall,
The excitation force can be reduced and (ω / ω ₀ =
Even if the vibration transmissibility in 1) is the same, since the excitation force is small, the absolute value of vibration is small, and it is possible to further reduce noise.

However, the zigzag amplitude is 1 of the pitch length P.
When it is / 2 or more, the depth d (zigzag amplitude) between the peak and the valley is almost the same as that of the conventional tire, and the effect is low in terms of noise reduction. Further, the zigzag peak portion causes uneven wear, which is not preferable. In the past, when dealing with low noise in a straight tone with a small rib width in and out, lateral grooves, notches, sipes, etc. were used to deal with the contradictory issue of running on wet roads. Since this corresponds to increasing the amplitude of, the excitation force is also increasing. If this is an extremely shallow lateral groove, a short or shallow notch, or a thin sipe that closes when touching down, it is possible to reduce the vibration force, that is, noise, but in that case the running performance on a wet road is natural. You will not be able to exert it.

When the amplitude of the zigzag, that is, the depth d between the peak portion and the valley portion is ⅕ or less of the pitch length P of the zigzag, not only the wet road running performance becomes poor, but also
It seems to be slippery even on the surface, and it cannot be said to be a practical pattern.

According to the present invention, in a heavy-duty radial tire having a plurality of vertical grooves continuous in the tire circumferential direction on a tire tread and a plurality of ribs adjacent to the vertical grooves, the groove walls of the vertical grooves are mountain peaks. Sections and valleys are alternately arranged in the tire circumferential direction to form a zigzag shape, and the total number of pitches N included in one round of the zigzag tire is 200 to 700, and the depth between the peaks and the valleys is set. The radial tire for heavy loads is characterized in that the pitch d (amplitude of zigzag) is set to 1/2 to 1/5 of the pitch length P.

The above-mentioned zigzag can be formed on the groove walls of some of the vertical grooves, but in order to obtain sufficient braking and traction characteristics when traveling on a wet road and to reduce noise. Are preferably formed on the groove walls of all the vertical grooves.

[0020]

According to the present invention, in a heavy-duty radial tire having a plurality of vertical grooves continuous in the tire circumferential direction on the tire tread and a plurality of ribs adjacent to the vertical grooves, the groove walls of the vertical grooves are Sections and valleys are alternately arranged in the tire circumferential direction to form a zigzag shape, and the total pitch number N included in one round of the zigzag tire is 200 to 700, and the zigzag peaks and valleys are Depth of d (amplitude of zigzag)
Is a radial tire for heavy loads in which ½ to ⅕ of the pitch length P is set, the resonance point (ω / ω ₀ = 1) between the natural frequency of the tire and the vibration frequency is determined from the practical speed range. Since it can be removed by shifting to the low speed side, at the time of resonance,
The noise level of the tire at higher speeds can be reduced.

[0021]

1 is a schematic view of a rib pattern showing an embodiment of a heavy duty radial tire according to the present invention.
FIG. 3 is an enlarged view of a main part near the vertical groove of the tire, and FIG. 3 is a sectional view taken along the line AA in FIG.

In the figure, 1 is a tire tread portion, 2 is a shoulder ground contact end, and a vertical groove 3 is formed on the tire tread portion 1 so as to be continuous in the tire circumferential direction. Reference numeral 4 is a rib sandwiched between the vertical grooves 3 and 3, and 5 is a shoulder rib sandwiched between the vertical groove 3 and the shoulder ground contact end 2. Reference numeral 6 denotes a narrow groove provided in the tire circumferential direction on the shoulder ground contact end 2 side of the shoulder rib 5.

Reference numeral 7 is a notch formed in the inclined surface of the groove wall 8 of the vertical groove 3, thereby forming a zigzag Z in which the peaks 11 and the valleys 12 are alternately arranged in the tire circumferential direction. In this embodiment, in particular, the rib 4 and the shoulder rib 5 are cut from the opening end 9 of the vertical groove 3 to open in the tire tread portion 1 and cut toward the groove bottom 10 of the vertical groove 3. Is formed in a state in which the width of is increased.

Further, in this embodiment, the peak portion 11 and the valley portion 12 of the zigzag Z notch 7 facing each other across the vertical groove 3 are provided.
And face each other, forming a pair. P is the pitch of the notches 7, d is the depth of the notches 7 of the vertical grooves 3, that is, the depth d between the peaks 11 and the valleys 12 (amplitude of zigzag Z), H is the groove depth of the vertical grooves 3, TW indicates the developed width of the tire tread portion. The amplitude of the zigzag Z, that is, the depth d of the cut 7 is
The groove bottom does not have to be constant from the ground contact end of the tread portion, and may be different in the range of 1/2 to 1/5 of the pitch P.

By the way, noise levels corresponding to various traveling speeds were measured using the heavy load radial tires having the tread pattern and under various conditions shown in the following table.
All test tires had a rim size of 7.00 x 20, and the test conditions were that the tire alone had an air pressure of 7.0 kg / cm.
² , JASO-C6 in a drum test with a load of 2750 kg
The test was performed according to the 06 test method.

[0026]

[Table 1]

The results are shown in FIGS. 4 and 5. FIG. 4 is a diagram showing the relationship between the noise level (total sound pressure level OAL) dB (A) and the traveling speed V (km / h) for the conventional tire (comparative example), and FIG. 7 is a diagram showing a relationship between a noise level (total sound pressure level OAL) dB (A) and a traveling speed V (km / h) in the example of FIG.

From FIGS. 4 and 5, the conventional tire of the comparative example has a low noise level at low speed, but 40 to 50 km.
While the noise level is considerably increased at a normal speed of around / h or more, the noise level of the tire of this example is slightly higher than that of the comparative tire at a low speed of 30 km / h or less, but 40 to 50 km / h. It is recognized that the noise level is not so low in the low speed region even at the normal speed above and near, and the noise level is low as a whole, and the noise reduction effect is excellent.

The present invention is not limited to the above embodiments.

[0030]

As described above, the present invention provides a heavy-load radial tire having a plurality of vertical grooves continuous in the tire circumferential direction on the tire tread and a plurality of ribs adjacent to the vertical grooves. Is a zigzag shape in which peaks and valleys are alternately arranged in the tire circumferential direction, and the zigzag tire 1
The total number of pitches included in the circumference is 200 to 700, and the depth d (zigzag amplitude) between the crests and the troughs is 1/2 to 1/5 of the pitch length for heavy loads. Since it is a tire, it is possible to shift the resonance point (ω / ω ₀ = 1) between the natural frequency of the tire and the vibration frequency (ω / ω ₀ = 1) from the practical speed range to the low speed side, and remove the noise level at resonance. Since it can be lowered, tire noise can be effectively reduced without impairing running performance on a wet road.

[Brief description of drawings]

FIG. 1 is a schematic view of a rib pattern showing an embodiment of a heavy duty radial tire according to the present invention.

FIG. 2 is an enlarged view of a main part near a vertical groove of the tire.

3 is a cross-sectional view taken along the line AA in FIG.

FIG. 4 Noise level of conventional tire (comparative example)
It is a figure which shows the relationship between (OAL) (A) and traveling speed V.

FIG. 5 Noise level (OAL) for an embodiment of the present invention
It is a figure which shows the relationship between (A) and traveling speed V.

FIG. 6 Noise level (OAL) dB in a conventional tire
It is a figure which shows the relationship between (A) and traveling speed V.

FIG. 7 is a relationship diagram between ω / ω ₀ value and _et / e _P value.

FIG. 8 is a relationship diagram between a zigzag pitch number N and a peak generation speed V _p .

[Explanation of symbols]

 1 Tire Tread Part 2 Shoulder Ground Contact End 3 Vertical Groove 4 Rib 5 Shoulder Rib 8 Groove Wall Z Zigzag 11 Crest 12 Valley P Pitch Length d Depth

Claims (1)

[Claims] 1. A heavy-load radial tire having a plurality of vertical grooves continuous in the tire circumferential direction on a tire tread and a plurality of ribs adjacent to the vertical grooves, wherein a groove wall of the vertical grooves is provided.
The zigzag shape in which the crests and the troughs are alternately arranged in the tire circumferential direction is formed, and the total number of pitches N included in one round of the zigzag tire is 200 to 700, and the crests and the troughs of the zigzag are formed. A radial tire for heavy loads, characterized in that the depth d between them (amplitude of zigzag) is set to 1/2 to 1/5 of the pitch length P.