JPS6226105A - Pneumatic radial tire for passenger car - Google Patents

Abstract

PURPOSE:To improve a wet skid characteristic, by forming main grooves at both sides of a center rib, while connecting an interval between these main grooves with curved subgrooves where an angle with the circumferential direction is gradually decreased toward a tread center, setting a groove ratio down to the specified value, and forming four corners of a block to be formed into smoothness. CONSTITUTION:Main groove 11A-11C are parallelly installed at both sides of the center rib 12 set up on a tire tread center line (m), and the main groove 11A adjacent to this center rib 12 is formed into a curve proximate to straightness. And, an interval between these main grooves 11A-11C is connected with a curved subgroove 13 where an angle theta with a tread center is gradually decreased toward the center (m), while it is extendedly installed up to a tire breadthwise grounding end 14. And, a groove ratio of a tire tread should be set to 40+ or -5%, while four corners of blocks 15A-15C to be formed with these main grooves 11A-11C and the subgroove 13 are formed into smoothness. With this constitution, a wet skid characteristic is improved and, what is more, a pattern noise is reducible.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a pneumatic radial tire for passenger cars that has improved wet skid characteristics without impairing handling stability and further reduces pattern noise.

[Prior art]

BACKGROUND ART In recent years, as vehicles, especially passenger cars, have become more sophisticated, the structure of tires has changed from bias tires to radial tires, and the shape of radial tires has also become flatter. By flattening the tire, the ground contact width of the tire tread becomes wider, which increases the cornering force, and as a result, the compression stability of the vehicle improves. However, on the other hand, as the tire becomes flatter, the tire contact length tends to gradually become shorter, resulting in a decrease in wet skid characteristics.

In general, tire design factors that affect wet skid characteristics include the trend pattern formed on the tire tread, the material of the tread rubber in the trend section, the tire structure, and the shape of the tire. Among these, it is known that the influence of the tread pattern is noticeable on the wet skid characteristics of tires used for high-speed driving, which aims to improve the performance of tires, especially high-speed performance and handling stability. .

In other words, at high speeds, the tire's wet skid characteristics are purely determined by the tire's water drainage performance, rather than by the material of the trend rubber or by external factors (for example, the condition of the road surface, i.e., differences in the friction coefficient of the road surface). It turns out. It is clear that trend patterns have a direct impact on tire drainage performance.

Therefore, many studies have been conducted on improving the trend pattern of pneumatic radial tires. For example, as shown in Japanese Unexamined Patent Publication No. 55-140604, an invention related to tire trends has been made. Since they are connected and not curved, they have the disadvantage that water that has entered the grooves cannot be smoothly sent out to the sub-grooves. In addition, Japanese Utility Model Application Publication No. 18033/1983 describes an idea regarding an asymmetric tire, but in this idea,
Since there is no center rib in the center of the tire tread and the pattern is asymmetrical, the tire lacks the ability to quickly separate water to the left and right in the width direction of the tire in front of the tire tread while driving. Furthermore, in the invention related to a tire pattern with high wet skid resistance disclosed in Japanese Patent Application Laid-Open No. 60-45404, water that has entered the groove adjacent to the center rib smoothly flows into the sub-groove provided in the width direction of the tire. The drawback is that it is difficult to introduce.

On the other hand, the trailing throat pattern is also one of the causes of pattern noise. Incidentally, in recent years, the mainstream of flat tires has mainly been those having a block-based tread pattern.

Although this block-based tread pattern improves the steering stability of the flat tire, it has a negative effect on pattern noise. Therefore, it is desired to improve the handling stability and wet skid characteristics of a block-based tread pattern without worsening pattern noise.

[Purpose of the invention]

An object of the present invention is to provide a pneumatic radial tire for passenger cars that improves wet skid characteristics without impairing handling stability and further reduces pattern noise by making various improvements to the block-based tread pattern. do.

[Structure of the invention]

Therefore, in the present invention, a center rib is provided in the center of the tire tread in an annular manner in the tire circumferential direction, and a plurality of main grooves are arranged in an annular manner in the tire circumferential direction on the left and right sides of the center rib. The main grooves adjacent to the center rib are formed in a nearly straight curved shape, and these main grooves are connected transversely by curved sub-grooves, and the angle of the sub-grooves with respect to the tire circumferential direction is adjusted to match the tire tread. The groove ratio on the tire tread is 40% ± 5%, gradually becoming smaller as it approaches the center.
The present invention further provides a pneumatic radial tire for a passenger car, characterized in that the four corners of each block formed by each of the main grooves and each sub-groove are formed smoothly.

Hereinafter, the configuration of the present invention will be explained in detail with reference to the drawings.

FIG. 1 is an explanatory half-sectional perspective view of an example of a pneumatic radial tire for a passenger car according to the present invention, in which the tread and throat patterns of the tread are omitted. In this figure, a pair of left and right bead portions 1
, 1, a carcass layer 4 having a cord angle of substantially 90° with respect to the tire circumferential direction EE' is arranged.

Further, two belt layers 5 are arranged on the carcass cover 4 in the tread portion 3 over almost the entire area of the tread portion 3. Further, on this belt layer 5, a belt cover layer 6 is disposed over almost the entire tread portion 3. This belt cover layer 6 is provided to improve high-speed durability and does not necessarily need to be provided. In addition, 2
7 represents a sidewall portion, 7 represents a shoulder portion, and 8 represents a tire tread surface. Note that the tread pattern formed on the tire tread surface 8 is omitted in FIG. 1.

The carcass layer 4 has at least one layer, and its cord is made of nylon, polyester, aramid (
Chemical fibers such as aromatic polyamide fibers are generally used.

The cord constituting the heald layer 5 may be one that is normally used for tires, preferably nylon or polyester cord, and cords such as mata, steel, aramid, etc.
Cords such as throat and rayon can be used.

Nylon is generally used as the cord for the belt cover layer 6. The cord angle is in the tire circumferential direction EE'
It is substantially O'' (parallel) to the

In the present invention, a trend pattern as shown in FIGS. 2 and 3 is formed on the tire tread 8 of the pneumatic radial tire shown in FIG.

FIG. 2 is a perspective view of an example of a pneumatic radial tire for a passenger car according to the present invention.

Moreover, FIG. 3 is a plan view showing an example of the tire tread of the pneumatic radial tire for a passenger car of the present invention. In this FIG. 3, m indicates the center line of the tire tread in the tire circumferential direction, and IIA, 11B.

11C is a main groove provided annularly in the tire circumferential direction EE'. Further, 12 is a center rib provided annularly in the tire circumferential direction EE' at the center of the tire tread. Reference numerals 13 denote sub-grooves extending from the center of the tire tread to the tire widthwise grounding end 14, and the angles of these subgrooves 13 with respect to the tire circumferential direction are θ at the center of the tire tread and θ at the tire widthwise grounding end 14. It is ゛. 15A, 15B
, 15C is a block formed with 7" grooves 13 in each of the main holes 111A, IIB, and IIC.

The tire having the Torad 7 pattern shown in FIG. 3 satisfies the following requirements (1) to (6).

(1) A center rib 12 is provided annularly in the tire circumferential direction EE'' at the center of the tire tread.

This makes it possible to quickly separate water to the left and right in the width direction of the tire in front of the tire tread while the vehicle is running.

(2) Plural main grooves 11A on the left and right sides of the center rib 12
.

11B and IIC are arranged annularly in the tire circumferential direction EE', and among these main grooves, the main groove 118 adjacent to the center rib 12 is formed in a nearly straight curved shape.

The main grooves 11B and IIC are straight grooves. In this way, by providing multiple straight main grooves,
This is because the see-through effect on the tire tread, that is, the ability to see from the front of the tire tread to the rear of the tire tread through these straight grooves, makes it easier for water that enters from the front of the tire tread to escape to the rear of the tire tread while driving. be.

In addition, by forming the main groove 118 adjacent to the center rib 12 in a nearly straight curved shape, water that has entered the main groove 11A can be easily sent to the sub-groove 13.

(3) These main grooves 11A, IIB, II
A curved sub-groove 13 connects C in a transverse manner.

This allows the main groove 11A to be removed from the front of the tire tread when driving.
, IIB, and IIC pass through the sub-groove 13 and reach part of both shoulders of the tire (tire widthwise contact edge 14).
) will be easily drained away.

Furthermore, by forming the sub-grooves 13 in a curved shape, the flow of water in the cross areas where the main grooves 11A, IIB, IIC and the sub-grooves 13 intersect, especially the flow of water to the outside in the tire width direction, is improved. This makes it possible.

This sub-groove 13 is defined by the tire circumferential center line m of the tire tread.
It is preferable that they be arranged symmetrically with respect to . As a result, water that is separated to the left and right in the tire width direction by the center rib 12 during running is removed from the tire width direction ground contact edge 14.
This is because the effect of quickly ejecting in the direction of , that is, in the direction of a part of the shoulder is exhibited.

In addition, the sub groove 13 is connected to the main all, IIB, II
It is preferable that the groove depth is approximately the same as C. This is because the sub-groove 13 is also given sufficient drainage performance, and in particular, it becomes easy to drain water that has entered into a part of both shoulders.

(4) The angle of the sub-groove 13 with respect to the tire circumferential direction EE' is gradually reduced as it approaches the center of the tire tread.

In order to more quickly expel water entering from the main groove near the center rib 12, for example, the main groove 11A, toward a part of the shoulder, the sub-groove 13 near the center lip 12 is formed at a small angle with respect to the tire circumferential direction EE''. For example, θ=20°~4
It was set to 5°. However, the tire circumferential direction EE' of sub a13
If all angles with respect to the tread rubber are set to this angle θ, the lateral rigidity of the tread rubber will decrease. Therefore, the angle of the sub'a13 is gradually increased as it approaches a part of the shoulder, for example, θ'=50° to 80°.

(5) The groove ratio of the tire tread was set to 40% ± 5%.

If no trend pattern is formed on the tire tread, the groove ratio is zero. In this case, the drainage effect of the grooves due to water entering the tire tread while the vehicle is running is zero.

Therefore, generally speaking, the higher the groove ratio, the higher the water drainage effect. In other words, the water entrance path becomes larger or the number of water entrance paths increases.

However, when the groove ratio is increased, the size of each block forming the tread pattern becomes smaller. This also reduces the moment of inertia of each block.
Dry driving stability deteriorates.

Therefore, in order to satisfy each of these contradictory conditions, as a result of tests, it was found that it is best to set the groove ratio to 40%±5%.

In order to improve drainage, it is recommended to set the groove ratio to 45%, and in order to increase the moment of inertia of each block, that is, to improve steering stability, it is recommended to set the groove ratio to 35%. Based on test confirmation that it is appropriate to do so.

Therefore, in the present invention, the groove ratio is set to 40%=5%.

Note that the sizes of the blocks arranged in the circumferential direction of the tire are different from each other in order to reduce pattern noise.

(6) Each block 15A, 15 formed by each main groove 11A, IIB, IIC and each sub-groove 13
B, The four corners of 15C were formed smoothly.

As shown in Figure 4, which is an enlarged view of a part of Figure 3,
Four corners a of each block 15A, 15B, 15C,
b, c, and d are rounded and formed smoothly.

In this way, by forming the four corners a, b, c, and d smoothly, water that has entered each groove can be quickly discharged from the tread surface, improving water flow and reducing pattern noise. can be reduced.

Next, the results of a pattern noise test and a wet skid characteristic test using actual vehicles will be shown for the tires of the present invention, Comparative Tire 1, Comparative Tire 2, and Comparative Tire 3 having the following specifications.

The tire sizes are 205/60R, respectively.
It is 15.

(81 Tire of the present invention.

A tire having a tread pattern shown in FIG. The curved sub-grooves 13 are arranged in an arc shape having the same curvature. The angle that the tangent line of this sub-groove 13 makes with the tire circumferential direction EE'' is
It gradually became smaller as it approached the center of the tire tread (
25° to 40° for block L5A, 35° to 55° for block 15B, and 55° to 65° for block 15C.
). Groove ratio 41%.

Four corners a of each Brosoku Quest 58, 15B, 15C,
b, c.

d is round.

The specifications of the pattern are shown in Table 1 below.

(Leaving space below) Table 1 (b) Comparative tire 1° The angle between the tangent of the sub-groove 13 and the tire circumferential direction BE' is gradually decreased as it approaches the center of the tire tread in the range of 35° to 75°. and each block 1
Four corners a, b of 5A, 15B, 15G.

It is the same as the tire of the present invention described above except that C and d are not rounded.

(C) Comparative Tire 2 The same as Comparative Tire 1 above, except that the 2° sub-grooves 13 were linear approximately perpendicular to the main grooves 11A, IIB, and IIC.

-(d) Comparative Tire 3° The sub-groove 13 is linear, and the angle with the tire circumferential direction EE' is changed stepwise to 45° and 60° from the center of the tire tread to a part of the shoulder, respectively. °, 75
The tire is the same as Comparative Tire 1 above, except that the tire is set to have an angle of .degree.

Pan noise: Conducted based on the tire noise test method of JASOC606-81.

The test conditions were rim 6J x 15, air pressure P = 2.0kg/
cnl, load W = 350 kg (a value equivalent to about 1/4 of the vehicle weight).

The test results are expressed as an index in FIG. From FIG. 5, it can be seen that the tire of the present invention is superior to Comparative Tire 1, Comparative Tire 2, and Comparative Tire 3 in terms of pattern noise.

Wet skid: A wet road with a water depth of 7 to 8 mm is provided on a part of a dry road surface with a radius of 100 m, and the lateral acceleration on the wet road during steady circular turns is measured at each speed when the vehicle is running. This was done by determining the speed at which the maximum lateral acceleration is generated (critical speed; the higher the speed, the less likely hydroplaning will occur).

Test conditions are rim 6J x 15, air pressure P = 2.0kg
/cn! It is.

The test results are expressed as an index in FIG. From FIG. 6, it can be seen that the tire of the present invention is superior to Comparative Tire 1, Comparative Tire 2, and Comparative Tire 3 in terms of wet skid characteristics.

In the tire of the present invention, the curved sub-grooves 13 are arranged in an arc shape having the same curvature, but the main grooves, including the tire circumferential meandering main groove 118 adjacent to the center lip 12, are connected. Each sub? The planar shape of l113 does not have to be an arcuate shape with the same curvature, but can be any curved shape.

In any case, the sub groove 1 closest to the center of the tire tread
3, the tangent line of the sub-groove 13 is in the tire circumferential direction EE.
' The angle between the two ends is 20° to 45°, and the angle at sub a13 closest to the shoulder portion is required to be 50° to 80°.

〔Effect of the invention〕

As explained above, according to the present invention, since the shape and arrangement of the plurality of main grooves in the tread pattern and the sub-grooves connecting these main grooves are appropriately determined, wet-wetting stability can be improved without impairing the stability. It has become possible to improve skid characteristics and further reduce pattern noise.

The tire of the present invention can be advantageously used as a pneumatic radial tire for high-performance passenger cars with an aspect ratio of 60 or less.

[Brief explanation of drawings]

FIG. 1 is a half-section perspective explanatory view of an example of a pneumatic radial tire for a passenger car of the present invention, with the tread pattern of the tread omitted; FIG. 2 is a perspective view of an example of the pneumatic radial tire for a passenger car of the present invention; FIG. 3 is a plan view showing an example of the tire tread of the pneumatic radial tire for passenger cars of the present invention, FIG. 4 is a partially enlarged explanatory view of FIG. 3, and FIG. 5 is a diagram of the tire of the present invention and a comparative tire. FIG. 6 is an explanatory diagram showing a comparison of pattern noise, and FIG. 6 is an explanatory diagram showing a comparison of the sea urchin 7 toss performance between the tire of the present invention and a comparative tire. 1...Bead part, 2...Side wall part, 3...
・Trend part, 4... Carcass layer, 5... Belt layer, 6... Belt cover single layer, 7... Shoulder part, 8
...Tire tread, 118, IIB, IIC...
・Main groove, 12... Center rib, 13... Sub groove,
14... Tire width direction ground contact end, 15A, 15B
, 15C...block.

Claims (1)

[Claims] A center rib is provided in the center of the tire tread in an annular shape in the tire circumferential direction, and a plurality of main grooves are arranged in an annular shape in the tire circumferential direction on the left and right sides of the center rib, and of these main grooves, one adjacent to the center rib is provided. The main grooves are formed in a nearly straight curved shape, and these main grooves are connected transversely by curved sub-grooves, and the angle of the sub-grooves with respect to the tire circumferential direction is gradually decreased as it approaches the center of the tire tread. A pneumatic radial tire for a passenger car, characterized in that the groove ratio of the tire tread is 40%±5%, and the four corners of each block formed by each of the main grooves and each sub-groove are formed smoothly. .