JPH07179104A - Pneumatic tire - Google Patents

Abstract

PURPOSE:To provide a pneumatic tire capable of reducing rolling resistance and passing noises, improving snow travelling and being used as one for electric car in all seasons. CONSTITUTION:A ratio K (=S1/S) between the area S of a grounding area 7 and the area S1 of the total tread groove area 9 positioned therein is 20 to 32%, lateral edge density (alpha) in the grounding area 7 is 0.065 to 0.085mm/mm<2> and a pattern repeating unit N is 30 to 60 pieces.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire capable of reducing rolling resistance, improving snow running performance, and reducing passing noise (pattern noise).

[0002]

2. Description of the Related Art In recent years, there have been a large number of all-season tires that run on, for example, a shallow snow road while maintaining high-speed running performance. In order to improve drainage performance and snowy road running performance, this tire has a larger groove volume compared to normal tires and a large number of sipings, and adopts a block pattern with a high tread groove area ratio, that is, a sea ratio is doing.

On the other hand, in recent years, electric vehicles have made remarkable progress from the viewpoint of environmental protection. As tires used in such electric vehicles, the traveling distance per charge is increased.
It is desired to reduce rolling resistance.

[0004]

As a result of repeated research to meet the above-mentioned demand, the inventor has found that in order to reduce the rolling resistance, it is more effective to increase the internal pressure and to deal with the pattern. I got it.

In order to reduce rolling resistance, it is necessary to form a pattern having high compression rigidity, that is, a pattern having a small number of tread grooves is advantageous, and passing volume noise is also reduced by reducing the volume ratio of the grooves. I knew what I could do. In particular, tire noise is an essential requirement for an electric vehicle that is quieter than a gasoline vehicle.

[0006] However, the reduction in groove volume, as its antithetic performance, results in deterioration of running performance on wet road surfaces and snow.

As a result of repeated research to develop a tire that can satisfy the above-mentioned trade-off requirements, the inventor regulates the sea ratio on the tread surface, the lateral edge density, and the number of repeated tread patterns within a fixed range. As a result, they have found that both reduction of rolling resistance and improvement of snow running performance can be achieved, and that passing noise can be reduced, and the present invention has been completed.

An object of the present invention is to provide a pneumatic tire which can be suitably used as an all-season tire for an electric vehicle by reducing rolling resistance, improving snow running performance, and reducing passing noise. I am trying.

[0009]

SUMMARY OF THE INVENTION The present invention is formed by a main groove extending in the tire circumferential direction, a lateral groove arranged in a direction intersecting with the main groove, and a lateral groove consisting of substantially widthless siping. In the normal state in which the tread groove is provided and the rim is assembled to the regular rim and the regular internal pressure and the regular load are added, the tire axial direction outer edge of the tread surface comes into contact with the outer circumferential edge of the tire in the axial direction. The sea ratio K (= S1), which is the ratio of the ground contact area S of the ground contact area, which is the area, to the total sum S1 of the areas of the tread grooves located in this ground contact area.
/ S) is 20% or more and 32% or less, and of the two groove walls that sandwich each tread groove included in the ground contact area, the length measured in the tire axial direction of the groove wall that comes into contact with the ground after the tire rolls. The lateral edge density α (= A / S), which is the ratio of the total length A of the above to the ground contact area S, is 0.065 mm /
The pneumatic tire has a tread groove of at least mm ² and no more than 0.085 mm / mm ² , and the tread groove is formed by repeating a tread pattern of 30 to 60 in the circumferential direction.

It is more preferable that the sea ratio K is 20% or more and 32% or less, and that the lateral edge density (mm / mm ² ) is α, which satisfies the following formula (1). K ≦ 3.5α + 6 (1)

[0011]

It is known that increasing the internal pressure is effective for reducing the rolling resistance. Further, the graph of FIG. 5 shows the relationship of the contribution ratio to the reduction of rolling resistance between the tread portion and the other portion when the internal pressure is changed. Although the rolling resistance coefficient (RRC) decreases, the contribution of energy loss in the tread portion becomes large. The rolling resistance coefficient (RRC) is represented by {rolling resistance (kg) / measured load (kg)} × 10 ⁴ .

On the other hand, under the internal pressure of a normal tire of about 2.0 kgf / cm ² , the tire has a majority of energy loss due to bending deformation, while the internal pressure is 3.5 kgf / cm, for example. ^When it becomes ² , as shown in FIG. 6, both the longitudinal rigidity and the lateral rigidity of the tread portion increase. That is, a tread pattern with few tread grooves is advantageous for reducing rolling resistance. The numerical values circled in the graph of FIG. 6 indicate the rolling resistance coefficient (RRC) in units of 10 ⁻⁴ .

Reducing the area ratio of the tread groove is also effective for reducing pattern noise such as air column resonance noise, especially in the case of an electric vehicle in which the engine produces less noise than a gasoline vehicle. In particular, the reduction of tire noise can greatly contribute to the noise suppression of the entire vehicle.

Therefore, in the case of a high-speed running tire, conventionally, the area ratio of the tread groove is kept within a minimum range where drainage can be secured and abrasion resistance is maintained, so that the lateral edge component is not increased. Although the pattern configuration has been the mainstream, the reduction of the groove area ratio impairs the running performance on a wet road surface and the running performance on snow.

For this reason, in a snow tire intended for running on snow, the area ratio of the groove portions is increased, the lateral edge density is increased, and the drainage performance and the grip force on snow are improved.

However, in the present invention, in order to achieve both high speed running performance and snow running performance, the sea ratio K (= S1), which is the ratio of the total area S1 of the tread grooves located in the ground contact area, / S) and the lateral edge density α are both regulated with respect to the upper limit and the lower limit thereof, thereby achieving both reduction of rolling resistance and improvement of snow running performance.

The sea ratio K is set to 20% or more and 32% or less. If the value of K is less than 20%, the grip force during running on snow is insufficient and the traction performance is poor, and the groove area is insufficient, so the drainage performance is reduced and the grip force and braking force on wet road surfaces are insufficient. If it exceeds 32%, the compression resistance of the tread portion becomes insufficient, the rolling resistance increases, and the passing noise such as pattern noise generated during running becomes large.

On the other hand, when the lateral edge density α of the above construction is 0.065 mm / mm ² or more and 0.085 mm / mm ² or less, running performance on snow, especially gripping power on snow is insufficient,
If it exceeds 0.085 mm / mm ² , the compression resistance of the tread portion becomes insufficient, resulting in an increase in rolling resistance and passing noise.

In the prior art, the sea ratio K is 28 to 31% for high speed tires and 35 to 42% for snow running tires. The conventional tire sea ratio K is adopted up to a low ratio. This can be achieved by adopting a novel structure which has never existed before, in which both the sea ratio K and the lateral edge density α are regulated.

In addition, the tread pattern is repeated 30 times.
It is set to be not less than 60 and not more than 60. If the number of repeated tread patterns is less than 30, the passing noise cannot be dispersed and the quietness is inferior. On the other hand, if the number exceeds 60, the compression resistance of the tread is insufficient, rolling resistance increases and the passing noise becomes large. Because.

As described above, according to the present invention, the above-mentioned components are organically combined and integrated to reduce rolling resistance, improve energy utilization efficiency during traveling, and reduce passing noise such as pattern noise. As well as
It is possible to improve grip performance when traveling on snow and improve snow traveling performance.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. 1 and 2, a pneumatic tire 1 includes a tread portion 12 having a tread surface 2 as an outer peripheral surface and a sidewall portion 13 extending from both ends thereof inward in a tire radial direction.
And a bead portion 14 located at the tire radial inner end of the sidewall portion 13. Further, in the pneumatic tire 1, a carcass 16 is formed by folding back the bead core 15 of the bead portion 14 from the tread portion 12 through the sidewall portion 13 toward the outer side in the tire axial direction, and the tread portion 1
2 and the belt layer 17 disposed on the outer side in the radial direction of the carcass 16.

In the present embodiment, the carcass 16 has at least one carcass cord of radial arrangement or semi-radial arrangement inclined at an angle of 70 to 90 ° with respect to the tire equator C. An organic fiber cord made of nylon, polyester aromatic polyamide or the like is used as the carcass cord, which is composed of a single carcass ply.

In the present embodiment, the belt layer 17 is composed of two belt plies, and each belt ply is made of an organic fiber such as nylon, polyester, aromatic polyamide or a steel cord, and the belt cord is inclined with respect to the tire equator C. And they are installed side by side.

In the present embodiment, the tread portion 12 is shown in FIG.
As shown in FIG. 2, the two main grooves 3 and 3 extending in the circumferential direction on both sides of the tire equator C sandwich the tread portion 12 from the central rib 21 including the tire equator C to the tread edge E. It is divided into two outer rims 22, 22.

Further, the outer rim 22 is provided with a plurality of lateral grooves 4 which are arranged in a direction intersecting with the main groove 3 and which are composed of an inner lateral groove 4A connected to the main groove 3 and an outer lateral groove 4B opened at the tread edge E. To be done. Further, the central rib 21 and the outer rib 22 are provided with a plurality of sipings 5 ... Arranged to intersect with the main groove 3. The width of the groove is 0.2 for siping.
It is formed as ~ 2.0 mm. Therefore, the tread groove 6 is formed in the tread portion 12 by these main groove 3, lateral groove 4, ..., Siping 5.

In the normal state in which the pneumatic tire 1 is assembled to the regular rim J, and the regular internal pressure and the regular load are applied, the outer circumferential edge of the tread surface 2 is in contact with the outer circumferential edge of the tire. A region between M and M is a ground region 7, and a sea ratio K (= S1 / S) which is a ratio of a ground area S of the ground region 7 and a total area of tread grooves 6 located in the ground region 7. Is 20% or more and 32% or less.

Further, the lateral edge density α is regulated as follows. The lateral edge density α means that the tread groove 6 included in the ground contact area 7, that is, the main groove 3, the lateral groove 4 and the siping 5 sandwiches the groove walls 9A and 9B on both sides, respectively, and contacts the ground later with the tire rolling. The ratio A / S of the total length A of the length of the side groove wall 9A (schematically shown in FIG. 4) measured in the tire axial direction (lateral direction) and the ground contact area S is shown.

A block pattern is formed and siping 5 is performed so that the lateral edge density α (= A / S) is 0.065 mm / mm ² or more and 0.085 mm / mm ² or less.
... is arranged.

In this embodiment, when the sea ratio K and the lateral edge density (mm / mm ² ) are α, the following equation (1) is satisfied. K ≦ 3.5α + 6 Here, if the value of K is larger than the line of (3.5α + 6) that is a function of the lateral edge density α, the sea ratio is relatively high with respect to the lateral edge density.
Especially in the region where the lateral edge density is relatively high,
The ground contact area will be reduced, and sufficient steering stability will not be ensured.

Further, the tread surface 2 is formed with a tread pattern in which repeating patterns are arranged in the circumferential direction, and the number of repeating units N of the pattern is 30 or more and 6 or more.
The range is 0 or less. In the conventional normal tire, the repeating unit N is greatly reduced as compared with the case where the repeating unit N is 60 to 80, thereby reducing rolling resistance and reducing noise. The deterioration of running performance is compensated by the regulation of the lateral edge density.

FIG. 3 shows another example of the tread pattern. In this example, one central groove 3A extending in the circumferential direction on the equator C of the tire and longitudinal grooves 3B arranged on both sides thereof which are intermittent in the circumferential direction.
Forming a tread groove 6 by a main groove 3 composed of a plurality of horizontal grooves 4 connected to the vertical groove 3B, and a plurality of sipings 5 arranged on ribs formed on both sides of the central groove 3A. There is.

Also in this example, the sea ratio K, the lateral edge density α, and the number of times the pattern is repeated in the circumferential direction are all restricted within the above-mentioned ranges.

[0034]

[Specific example] Tire size is 185 / 65R14 86S
And a tire having the configuration shown in FIG. 1 (Example 1,
2) was prototyped and the performance of Example 1 was investigated. A tire having the same tire size and the conventional pattern shown in FIG. 8 (conventional example) was also tested and its performance was compared.

The test was conducted as follows. 1) Rolling resistance It was measured using a rolling resistance tester and shown by an index with the conventional example being 100. The smaller the value, the less rolling resistance the better.

2) Riding comfort While mounted on an actual vehicle, the test course was circulated, the driver's feeling was used for judgment, and the index was set as 100 for the conventional example. The larger the value, the better.

3) Pattern noise In a test course consisting of a smooth asphalt road surface, a microphone was installed at the right ear of the driver of a vehicle equipped with each test tire, and 40, 60, 80, 100 km /
The sound pressure level at each speed of H was measured, the overall value was averaged, and the noise level result in the sensory evaluation was also taken into consideration. The larger the value, the better.

4) Dry performance While running the test vehicle on a test course composed of a dry road surface, the vehicle is allowed to run straight, and stability, responsiveness,
Sensory evaluation of the convergence and ground contact property at the time of lane change was performed, and the result was displayed as an index with the conventional example being 100. The larger the value, the better.

5) Wet performance The test vehicle was run on a test course with a wet road surface, and the same test as in Section 4 was performed and evaluated. The test results are shown in Table 1.

[0040]

[Table 1]

[0041]

As described above, the pneumatic tire of the present invention is
Since the sea ratio of the tread pattern, the lateral edge density, and the number of repeated patterns are regulated at the upper and lower limits as described above, rolling resistance can be reduced and passing noise such as pattern noise can be reduced and snow running performance can be improved. Therefore, it can be suitably used as an all-season tire for an electric vehicle, which requires low rolling resistance.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is a developed plan view showing the tread pattern.

FIG. 3 is a developed plan view showing another tread pattern.

FIG. 4 is a cross-sectional view showing a state when traveling on snow.

FIG. 5 is a graph showing the relationship between tire internal pressure and rolling resistance.

FIG. 6 is a graph showing a relationship between lateral rigidity and vertical rigidity of a tread portion and rolling resistance.

FIG. 7 is a graph showing the range of the configuration of the present application in the relationship between the lateral edge density and the sea ratio.

FIG. 8 is a developed plan view showing a tread pattern of a conventional tire.

[Explanation of symbols]

 2 tread surface 3 main groove 4 lateral groove 5 siping 6 tread groove 7 grounding area 9 groove wall J regular rim M grounding outer edge

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B60C 11/12 D 8408-3D G10K 11/16 8408-3D B60C 11/06 B G10K 11/16 C

Claims (2)

[Claims] 1. A tire having a main groove extending in a tire circumferential direction, a lateral groove arranged in a direction intersecting with the main groove, and a tread groove formed by a lateral groove made of substantially widthless siping. , In the normal state where the rim is assembled to the regular rim and the regular internal pressure and the regular load are applied, the contact area of the contact area, which is the area between the contact outer edges of the contact surface where the tread surface contacts the tire, extends in the circumferential direction. The sea ratio K (=, which is the ratio of S to the total sum S1 of the areas of the tread grooves located in this ground contact area
S1 / S) is 20% or more and 32% or less, and of the groove walls sandwiching each tread groove included in the ground contact area, the length measured in the tire axial direction of the groove wall that comes into contact with the ground after the tire rolls. The lateral edge density α (= A / S), which is the ratio of the total length A of the heights to the contact area S, is 0.065.
mm / mm ² or more and a 0.085 mm / mm ² or less, yet tread grooves circumferentially repeated with repeating units of 30 or more and 60 or less pneumatic tire comprising formed by the tread pattern. 2. The sea ratio K is 20% or more and 32% or less, and the lateral edge density (mm / mm ² ) is α.
The pneumatic tire according to claim 1, wherein the following expression (1) is satisfied. K ≦ 3.5α + 6 (1)