JPH09156317A - Pneumatic radial tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To hold high-degree wet performance related to hydroplaning as well as to achieve further noise reduction. SOLUTION: Related to a ground length L (mm) and a maximum ground width W (mm) at the tread-width center of the outside contour of the ground tread of a tire having numerous pairs of diverging main grooves inclined in the same direction, each being open at an edge and having a deflected part, a length L1 (mm) obtained when a line dividing the width of the inclined main groove into two from the tread-width center to the deflected part is projected onto the equatorial plane of the tire is L1>=L. Also, with the use of a ground length L0.8 (mm) at a position of 0.8 times the maximum ground width W (mm), the length La (mm) of an arc extending in the cross direction of the tread between the tread-width center and the deflected part on the groove-width dividing line equals α×(W/2)±5mm, with α=-0.175+0.875 (L0.8 /L). The inclination angle 61 of the groove-width dividing line to the circumference of the tread, within the arc length La (mm), is 0 deg.<θ1<=tan<-1> (La/L), and the inclination angle θ2 of the groove-width dividing line to the circumference of the tread, from the deflected part to the edge, is tan<-1> (La/L)<θ2<=θ1+45 deg..

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a pair of beads, a pair of sidewalls, and a tread portion continuous toroidally on both sidewalls, and a radial carcass for reinforcing these parts, and an outer periphery of the carcass. The present invention relates to a pneumatic radial tire having a belt for reinforcing the tread portion, and more particularly to a pneumatic radial tire having both high hydroplaning resistance and excellent low noise characteristics.

[0002]

2. Description of the Related Art One of the main functions of a tread pattern provided on the tread surface of a pneumatic tire used for a vehicle traveling at a relatively high speed is a drainage function when rolling on a wet road surface. This function is a hydroplaning phenomenon. It is important to secure the safe running of the vehicle as it affects the vehicle. Naturally, the pattern is also an important factor in terms of commerciality, and therefore various patterns have been developed in consideration of both drainage function and appearance. Among them, a pattern in which a straight groove is provided in the tread portion along the circumference of the tread occupies the mainstream, and a pattern in which the groove volume of the straight groove is increased is typical in order to realize an advantageous drainage property.

[0003]

When it is desired to improve the drainage performance by using the tread pattern, it is effective to make the groove straight and further increase the volume of the groove, but on the other hand, noise is originally generated. On the other hand, since the amount of air passing through the inside of the disadvantageous straight groove also increases, it is inevitable that the vibration energy of the air in the groove increases and, as a result, the noise level deteriorates.

Therefore, an object of the present invention is to provide a pneumatic radial tire having a tread pattern which can achieve both excellent hydroplaning resistance by ensuring sufficient drainage and further low noise characteristics. To do.

[0005]

In order to achieve the above-mentioned object, the pneumatic radial tire according to the present invention is the pneumatic tire described in the beginning, wherein the tread portions are paired from the width center of the tread to both side edges. It has a large number of pairs of same-direction tilted main grooves that open at the edges and bend and expand in the middle toward the end, and are obtained by mounting a tire on a compatible rim and applying a normal load to a tire filled with normal internal pressure. Regarding the contact length L (mm) and maximum contact width W (mm) of the outer contour of the contact tread surface on the tire equatorial surface, the width bisecting line of the inclined main groove from the center of the tread width to the bend is to the tire equatorial surface. Projected length L1 (mm)
Satisfies L1 ≧ L, and the arc length La (mm) in the tread width direction between the center of the tread width and the bent portion on the groove width bisector is:
Using the contact length L _0.8 (mm) at a position where 0.8 times the maximum contact width W (mm) is evenly distributed from the tire equatorial plane to both sides, α
= -0.175 + 0.875 (L _0.8 / L), L
a = α × (W / 2) ± 5 mm is satisfied, and the inclination angle θ1 of the groove width bisecting line within the arc length La with respect to the tread circumference is 0 °.
<Θ1 ≦ tan ⁻¹ (La / L) is satisfied, and the inclination angle θ2 of the groove width bisector from the refraction portion to the end edge with respect to the tread circumference.
Is characterized in that tan ⁻¹ (La / L) <θ2 ≦ θ1 + 45 ° is satisfied.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below based on an embodiment shown in FIG. FIG. 1 is a development view of a tread surface of an example tire, and shows the length along the circumference of the tread edge according to the convention in accordance with the circumference length of the width center. In FIG. 1, reference numerals 2 and 3 denote inclined main grooves that are straight and inclined with respect to the tire equatorial plane E, and the inclined main grooves 2 and 3 are treads 1 of a tread portion (not shown) and have a width center E thereof. That is, the tire equatorial plane E forms a pair toward both end edges TE and extends divergently toward the end, and even after once refracting at a position P during the extension, the tire also extends in a divergent shape, and a shoulder portion (not shown) at the edge TE. ) Or a buttress portion (not shown).

A large number of pairs of inclined main grooves 2 and 3 which are paired with each other are arranged on the tread surface 1 in the same inclined direction. On the tire equatorial plane E, a large number of pairs of inclined main grooves 2 and 3 in the illustrated example are staggered alternately. A tire provided with this kind of tread pattern is usually provided with an indication for designating a rotation direction when mounted on a vehicle, and this rotation direction is indicated by a mark X in FIG.

After assembling a tire having a large number of pairs of inclined main grooves 2 and 3 to its compatible rim and filling the tire with a regular internal pressure, a regular load is applied to the tire as necessary to obtain the ground contact shape of the tread. At this time, unless there is a special reason, the tire is not provided with a camber angle or the like, and a load is applied to the tire perpendicular to the surface plate. The compatible rim, regular internal pressure and regular load are JATMA YEAR BOOK or TRA or ET.
The applicable rim of the corresponding tire described in RTO, the applied internal pressure, and the load commensurate with this internal pressure.

FIG. 2 shows the outer contour of the tread surface (the groove portion is represented by an inserted line) in the above ground contact shape. In FIG. 2, the reference sign W indicates the maximum contact width, and the reference sign L indicates the contact length on the tire equatorial plane E. Then, regarding the maximum ground contact width W and the ground contact length L, the inclined grooves 2 and 3 satisfy the relationship described below. Maximum contact width W and contact length L here
Both use millimeters (mm), and all units for width and length described later are millimeters (mm).

First, the length L1 obtained by projecting the width bisecting lines C ₂ and C ₃ of the inclined main grooves 2 and 3 from the tread width center E to the bending portion P on the tire equatorial plane E satisfies L1 ≧ L. And The length L1 is shown in FIG. 3 which is a development view of the width bisector C ₂ of the inclined main groove 2.
Was described. Of course, the width bisector C ₂ and the length L 1 shown in FIG.
Represents the length of the arc. Although the width bisector C ₃ of the inclined main groove 3 is similar, the illustration thereof is omitted, but the description about the inclined main groove 2 also applies to the inclined main groove 3. The width of the bending portion P is 2 for convenience.
It is treated as a refraction point P on the line segments C ₂ and C ₃ .

Next, the arc length La in the width direction of the tread 1 between the center E of the tread width and the inflection point P is La = α × (W / 2) ±
It should satisfy 5 mm. However, the coefficient α is α =-
0.175 + 0.875 (L _0.8 / L), length L
_As shown in FIG. 2, _0.8 is the end contact length at a position where 0.8 times the maximum contact width W is equally distributed from the tire equatorial plane E to both sides.

Next, when the intersection of the width bisector C ₂ and the tire equatorial plane E is designated as point Q and the intersection of the width bisector C ₂ and the edge extension line is designated as point R, points Q and The inclination angle θ1 with respect to the circumference of the tread 1 of the width bisecting line C ₂ sandwiched between P and 0 is 0 ° <θ
1 ≦ tan ⁻¹ (La / L) is satisfied, and the inclination angle θ2 of the width bisecting line C ₂ −1 sandwiched between the points P and R with respect to the circumference of the tread 1 is tan ⁻¹ ( La / L) <θ2
It is necessary to satisfy ≦ θ1 + 45 °.

[0013] example shown in FIG. 3 forms a width-half line C _2, C ₂ -1 is straight, therefore point Q, the inclination angle θ1 at the point P each position, but represents .theta.2, these widths The bisector does not necessarily have to be straight and can be curved. In that case, the inclination angles θ1 and θ2 are different at each position. This is the same width half line C _3, C ₃ -1.

Hydroplaning means that when a tire rolls on a wet road surface covered with a water film of a certain thickness at a considerable speed, the hydrodynamic pressure (hydrodynamic pressure) under the ground contact tread of the tire. This is a phenomenon in which water enters a wedge shape from the tire traveling direction in the ground contact tread, particularly in the central area of the tread width where the dynamic water pressure is highest, and this wedge-shaped water lifts the tire. Therefore, when discussing the wet performance of tires, it is necessary to take up the rate of occurrence of this hydroplaning phenomenon.

Among the factors that affect the generation speed,
It is no exaggeration to say that the element that is controllable and that contributes the most is the tread pattern, and that the drainage performance of the pattern determines the hydroplaning performance.
Therefore, by setting the projected length L1 of the width bisectors C ₂ and C ₃ of the inclined main grooves ₂ and ₃ to be the ground contact length L or more, the inclined main grooves 2 and 3 are formed at the stepping end of the rolling tire tread 1. When the central end (point Q) is located, the inclined main grooves 2 and 3 uniformly penetrate the ground contact surface from the stepping end to the kicking end, and exert a large back pressure on the water flowing from the stepping end. Since the refraction portion (refraction point) P to be caused is located outside the ground plane, the water in the grooves 2 and 3 can be efficiently drained regardless of the thickness of the water film (depth of water).

Further, the pressure applied to the tire rolling on the wet road surface from water is roughly classified into a tread central area where the hydraulic pressure is high and both side areas where the dynamic pressure is low. The branching position of the dynamic water pressure changes depending on the ground contact shape of the tread, and depends on the value of the ratio L _0.8 / L of the end ground contact length L _{0.8 to} the ground contact length L and the maximum ground contact width W. Therefore, this branch position is represented by the circumference of the tread 1 passing through the point P, and the arc length La between this circumference and the width center E of the tread 1 is set to the value of the ratio L _0.8 / L described above. If set as a function of the maximum ground contact width W, highly efficient drainage corresponding to high and low dynamic water pressure becomes possible.

Regarding the tilt angle θ1, the angle θ1 is 0 °.
While increasing the noise level by making the inclined main grooves 2 and 3 exceeding the upper limit, the upper limit of the angle θ1 is set to tan ⁻¹ (La / L), so that the width bisecting line C ₂ existing in both side regions of the tread 1 is
-1, the water flowing in the main groove part of C ₃ -1 is the width 2 of the central region
It is possible to prevent an increase in the amount of water that flows into the main groove portions of the dividing lines C ₂ and C ₃ to be drained, and this and the width 2 dividing lines of the inclined main grooves 2 and 3 Length L1 of C ₂ and C ₃
≧ L can be linked to improve drainage. If the angle θ1 exceeds tan ⁻¹ (La / L), a phenomenon occurs in which water flowing in the main groove portions existing in both side regions is drawn into the main groove portion in the central region where the hydrodynamic pressure is high, which is not possible.

Regarding the inclination angle θ2, refraction is performed at an angle θ2 exceeding tan ⁻¹ (La / L) at the branch position where the water flow path flowing into the inclined main grooves 2 and 3 from the stepped end side is touched first. By this, the flow of water in the main grooves 2 and 3 is forcibly created to be discharged to the outside of the tread 1, and the amount of water flowing into the groove portion in the central region of the inclination angle θ1 is suppressed, and the flowing water in the groove portion in the central region is suppressed. It can be quickly discharged to the outside of the tread 1. This means that the air flow related to noise becomes smooth and the effect of noise reduction can be obtained at the same time.

Here, when θ2 ≦ tan ⁻¹ (La / L), the running water in the groove portion in the central region cannot be quickly discharged to the outside of the tread 1, and when θ2> θ1 + 45 °, the degree of bending is too large. Therefore, the smooth flow of the flowing water is obstructed at the branch position, and at the same time, this also acts on the air flow, which causes deterioration of the noise level, which is not possible.

The above-mentioned arc length La and inclination angle θ1,
Each range of θ2 was determined by an experiment according to the L ₉ orthogonal array based on the experimental design method. As factors, the length La, the angle θ1, and the angle θ2 were taken and set to 3 levels respectively. The tire size used in the experiment is 225 / 50R16.
The maximum contact width W of this tire was 180 mm and the contact length L was 110 mm. Fig. 4 ~
As shown in FIG.

FIG. 4 is a diagram showing the relationship between the index value of the hydroplaning (referred to as HP) generation speed (vertical axis) and the arc length from the width center of the tread 1 (horizontal axis). In this experimental example, the range where the arc length is 41.08 to 51.08 mm (hatched portion) is the suitable range for maintaining the HP generation rate at a high level. Median value of this shaded area (46.08 mm, HP
The generation rate index 100) is calculated by using the coefficient α by the general formula La ′.
= Α × (W / 2), the arc length La including the shaded portion is La = α × (W / 2) ± 5 mm
It is. The ± 5 mm for including the shaded portion is a value for absorbing a slight difference between sizes obtained in another experiment and an experimental error. The coefficient α is also a general expression,
By introducing the contact length L _0.8 , α = −0.17
It can be represented by 5 + 0.875 (L _0.8 / L). The value of L _0.8 / L in this experiment is 0.785,
Therefore, the value of α is 0.512.

FIG. 5 shows the index value of the HP generation rate (vertical axis).
And a tilt angle θ1 (horizontal axis).
From Fig. 5, the arc length L determined by α × (W / 2) ± 5 mm
In relation to a, the inclination angle θ1 that satisfies the HP generation rate index of around 100 or more needs to be 20 to 24.4 ° or less, and the upper limit value is generally θ1 ≦ tan ⁻¹ (La / L). It can be expressed by a formula, and it is 0 to reduce the noise level.
° <θ1 must be satisfied. The shaded area in FIG. 5 indicates the range of ± 5 mm, and its meaning is as described above.

FIG. 6 shows the index value of the HP generation rate (vertical axis).
And a tilt angle θ2 (horizontal axis).
From Fig. 6, the arc length L determined by α × (W / 2) ± 5 mm
In relation to a, the inclination angle θ2 that satisfies the HP generation rate index of about 100 or more exceeds 20 to 24.4 °, and 65
It was found that it was necessary to be ˜69.4 ° or less, and if this is expressed as a general formula, tan ⁻¹ (La / L)
It can be represented by <θ2 ≦ θ1 + 45 °, and the shaded portion indicates the range of ± 5 mm, and the meaning is as described above.

The above-mentioned arc length La and inclination angle θ1,
When set to θ2, low noise performance is achieved regardless of the tire type or size, without applying straight grooves along the circumference of the tire tread and without increasing groove volume so as to impair the noise level. Excellent wet performance can be realized at the same time.

[0025]

【Example】

[Example 1] A radial ply tire for passenger cars having a size of 225 / 50R16, a radial carcass made of two plies of 1500D / 2 polyester cord plies, and a belt having two layers of twisted structure 1x5 steel cord intersections. Layer, and one layer of 12 as a wide cap layer around the layer
Nylon cord winding layer of 60D / 2 and 1 layer of 1260D / 2 as a narrow layer layer covering both end portions of the cap layer.
And a nylon cord winding layer.

The tread pattern is shown in Table 1 according to FIG. For the performance evaluation of Example 1, a conventional tire having a tread pattern whose tread pattern is shown in FIG. 8 as in FIG. 1 was prepared. This tire was the same as that of Example 1 except that the tread 11 had six straight grooves 12, 13, and 14. In addition, the negative ratio described in the item of Table 1 is
The ratio (%) of the groove area to the total surface area of the tread 1 in the actual development of the tread.

[0027]

[Table 1]

First of all, regarding the wet resistance, after both tires were installed in a compatible rim 7.5JJ × 16, the tires were filled with a normal internal pressure of 2.2 kgf / cm ² and each of them was separately mounted on a test road surface with a water depth of 10 mm. The superiority or inferiority was evaluated by measuring the hydroplaning generation speed when traveling straight on. The measurement result is represented by an index with the conventional example being 100, and the larger the value, the better. Next, the noise level (d
In B / A), the above tire and rim assembly was evaluated by a tabletop noise measuring drum, and the measurement result is represented by an index with the conventional example being 100, and the smaller the value, the better. The results are summarized in the lower part of Table 1.

[Embodiment 2] Embodiment 2 is a tire having the same size and structure as Embodiment 1 and having the tread pattern shown in FIG. 7, and this pattern is formed in the vicinity of the bending portion P of each of the inclined main grooves 2 and 3. It has both side inclined grooves 4 and 5 extending to the edge TE and opening. The patterns of comparative tires for Example 2 are shown in FIGS. Comparative Examples 1 and 2 have treads 21, 3
1, the inclined main grooves 22, 23, 32, 3 similar to those of the second embodiment
3 as well as the both side inclined grooves 24, 25, 34, 3 similarly.
The tire having No. 5 and the other parts except this pattern is matched with the second embodiment. The specifications of the patterns of these tires are shown in Table 2, a comparative test was conducted under the same conditions as the tires of Example 1 and the conventional example, and the test results are summarized in the same manner as in Example 1 and the conventional example. It is shown in the lower part and the plot of the test results is also shown in FIG.

[0030]

[Table 2]

From the results of the wet performance and the noise level shown in Tables 1 and 2, Example 1 has the same wet performance related to hydroplaning as compared with the conventional tire having the same air volume in the groove by adjusting the negative ratio. It was found that the noise level was remarkably improved by maintaining
In comparison with Comparative Examples 1 and 2 which deviate from the characteristic requirements of the present invention, both of the wet performance and the noise level occupy a superior position.

[0032]

According to the present invention, it is possible to solve the important problem that it has been difficult to achieve both the anti-wetting performance, which depends on the hydroplaning resistance, and the low noise performance, thereby making it possible to solve the wet road surface. It is possible to provide a pneumatic radial tire capable of ensuring safe running in a quiet environment and quiet and comfortable running.

[Brief description of the drawings]

FIG. 1 is a pattern development view of an embodiment according to the present invention.

FIG. 2 is an explanatory diagram of a ground contact outer contour of a tire tread according to the present invention.

FIG. 3 is a development view of a width bisector of the inclined main groove shown in FIG.

FIG. 4 is a diagram illustrating the relationship between the arc length to the refraction portion and the HP generation rate.

FIG. 5 is a diagram illustrating a relationship between a tilt angle θ1 and an HP generation speed.

FIG. 6 is a diagram illustrating a relationship between a tilt angle θ2 and an HP generation speed.

FIG. 7 is a pattern development view of another embodiment according to the present invention.

FIG. 8 is a development view of a conventional pattern.

9 is a development view of a comparative example pattern with respect to the pattern shown in FIG. 7. FIG.

FIG. 10 is a development view of another comparative example pattern with respect to the pattern shown in FIG. 7.

FIG. 11 is a plot diagram illustrating the relationship between wettability and noise level.

[Explanation of symbols]

1 tread 2,3 inclined main grooves 4 and 5 inclined grooves _{C 2, C 3, C 2} -1, the maximum C ₃ -1 groove width half line P refracting portion (inflection point) TE tread edge E tire equatorial plane W contact width L ground length L _0.8 0.8 W position of the ground length L1 groove width half line C _2, C ₃ of the projection length θ1 of the tire equatorial plane, .theta.2 inclined relative to the tread surface circumferential groove width 2 Bunsen Angle X Rotation direction

Claims (1)

[Claims] 1. A radial carcass comprising a pair of beads and a pair of sidewalls, and a tread part continuous toroidally on both sidewalls, and a radial carcass that reinforces these parts, and the tread part is reinforced at the outer periphery of the carcass. In a pneumatic radial tire equipped with a belt, the treads form a pair facing the end edges on both sides from the width center of the tread, and bend and extend once in the middle toward the end of the tread. The outer contour of the ground contact tread obtained by applying a regular load to a tire that has a main groove and is assembled to a compatible rim and filled with regular internal pressure.
Regarding the ground contact length (L (mm)) and maximum ground contact width (W (mm)) on the tire equatorial plane, the length of the sloping main groove width bisector from the center of the tread width to the bend is projected on the tire equatorial plane. (L1 (mm)) satisfies L1 ≧ L, and the arc length (La (mm)) in the tread width direction between the center of the tread width and the bent portion on the groove width bisector is the maximum. Ground width (W (m
m)) 0.8 times the tire equatorial plane to both sides, and using the contact length (L _0.8 (mm)) at the position, α = -0.175 + 0.875 (L _0.8 / L) , La = α × (W / 2) ± 5 mm, and the inclination angle (θ1) of the groove width bisector with respect to the tread circumference within the arc length (La (mm)) is 0 ° <θ1 ≦ tan ^-1 (La / L) and the inclination angle (θ2) of the groove width bisector from the refraction part to the edge with respect to the tread circumference should satisfy tan ^-1 (La / L) <θ2 ≦ θ1 + 45 ° Pneumatic radial tire featuring.