JP3371038B2 - Pneumatic tire - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire having a high hydroplaning generation speed when traveling on a wet road. 2. Description of the Related Art Pneumatic tires, especially pneumatic tires for passenger cars, have been developed to have a higher speed, and a tire having a radial structure in which a base portion of a tread is reinforced by a non-extensible belt layer is generally used. . And, in terms of shape, the tire cross section is flattened, and the flatness ratio (the ratio of the cross section height to the tire width) is 0.1.
About 6 tires are commonly used, and even ultra-flat tires of 0.3 are emerging. [0003] When the cross section of the tire becomes flat, the width of the tire becomes wider, and the tread width is set wider accordingly. In such a tire, in addition to the high-speed running on a dry road, the steering stability is improved. It is known that the drainage property of the ground contact surface is deteriorated, so that it is easy to slip on a wet road, especially when traveling at a high speed. To improve drainage property, a plurality of circumferential grooves (4 to 6) are provided. Japanese Patent Laid-Open Publication No. Sho 55-140604 proposes a tread structure in which the grooves are divided into independent blocks by, for example, inclined lug grooves extending in a V-shape, and the ratio of the groove group to the entire tread, that is, the negative ratio is specified. Have been. [0004] The above-mentioned specification of the negative ratio is a compromise product in consideration of the adverse effect on the steering stability and the like of the tread rigidity, which is reduced by the increase in the proportion occupied by the groove group. It is not a practical solution. According to the inventor's diligent studies, the tread of a flat tire having a large tread width is formed by a remarkably flat shape, so that the ground contact shape becomes substantially rectangular. Drainage to the side occurs at a relatively low speed as far as hydroplaning is concerned, in terms of the amount of grooves normally arranged on the tread, and the amount of drainage from the structural surface such as grooves versus blocks (land portions) provided on the tread. Some improvements have been found to have limitations. An object of the present invention is to solve the problem of improving the critical speed at which hydroplaning occurs during running on a wet road from the aspect of the tread shape, and to provide a tire in which uneven wear which is a concern in this case is suppressed. . According to the present invention, there is provided a tire having a pair of side walls and a tread extending between the two side walls, the tread being made of a plurality of different rubbers. The rim is filled with air pressure corresponding to the design normal load specified in the JATMA standard, and when a load of 80% of the design normal load is applied, the contact shape at the point of 80% of the contact width symmetrical to the center of the contact surface is Rubber that has a rectangular ratio of 75 to 85% of the maximum contact length at the center of contact and that is equivalent to 30 to 70% of the contact width. This is a pneumatic tire characterized by having a. In order to specify the rectangular shape of the contact shape, the air pressure corresponding to the design normal load is filled based on the JATMA standard, and the contact shape when the tire is loaded to 80% of the design normal load is targeted. , Based on the conditions according to the actual use of the tire. The tire according to the present invention has a shape in which the rectangular ratio of the ground contact shape is remarkably out of the rectangle of 75 to 85%. This means that the central portion of the tread has a round shape protruding outward in the radial direction of the tire, and the necessary range in that case is the above numerical range specified as the rectangular ratio of the ground contact shape. 85% of the upper limit of this range
When the ratio exceeds 1, the effect of improving the hydroplaning is small, and when it is less than 75%, the occurrence of uneven wear becomes remarkable. When the tread has a rounded shape as described above, the movement of the center of the tread in the tread surface becomes large, so that the tread is relatively easily worn out. However, the tread corresponds to 30 to 70% of the tread width. Since rubber having excellent wear resistance compared to both sides is arranged, early wear of the tread central portion, which is concerned by the rectangularity, can be advantageously prevented. In this case, if it is 30% or less, it is difficult to make the wear amount uniform, and only the central portion of the tread tends to remain. On the other hand, if it exceeds 70%, it will adversely affect the feeling when driving on dry or wet roads. An embodiment will be described below with reference to the drawings. FIG. 1 is a cross-sectional view of a tire showing one embodiment of the present invention, and FIG. 2 is a diagram showing a grounded shape of the tire. In the present invention, the tire 1 has only an outer contour on the right half with respect to the equatorial plane O, and detailed illustration is omitted.
This is basically a known shape in which a tread 3 is continuous across the wheels 2, 2 and both side walls. In the tire 1 shown in FIG. 1, a carcass 5 is arranged from one bead ring 4 buried at the tip of a side wall to the other bead ring (not shown). A non-extensible belt layer is arranged between the tread 3 and the tread 3 for reinforcement. The carcass 5 is composed of one or a plurality of plies (usually two plies) in which fiber codes such as polyester and rayon are arranged in a direction substantially perpendicular to the equatorial plane of the tire.
And the belt layer 6 is formed by applying a metal code such as steel to the equatorial plane O from 15 to
Plural layers (usually two) of layers inclined at an angle of 35 °
Auxiliary layer formed by circumferentially spirally winding a rubberized strip in which a plurality of heat-shrinkable fiber codes such as nylon are arranged on the outer periphery of the layers so that the codes cross each other. Structures can be applied. [0010] Tire 1 fills the air pressure corresponding to the design regular load specified in JAYMA standards set in use the rim, grounded type C _A when loaded with 80% of the load of design conventional load, peripheral through its center The rectangular ratio defined by the ratio of the average contact length y on the left and right at the point F at 80% of the contact width W symmetrical to the central circumference line P with respect to the maximum contact length Y on the line P is in the range of 75 to 85% Yes, and the contact width W is 30 ~
Tread central portion 7, which corresponds to 70% the width Z is assumed consisting of rubber G _C which is excellent in rubber G _S versus the wear resistance of both sides 8. [0011] The rubber G _C located in the middle portion 7 of the tread in Figure 1, an example in which between arranged with the same width in the thickness direction reaches the belt layer, toward the belt layer from the surface position of the other tread or provided flared Te, also conversely, can be provided by narrowing the width direction of the belt layer, and further the side rubber G _S arranged in concave shape, the area of the recess of the center portion The center rubber G _C is provided with a required thickness (however, 60% or more of the total tread thickness), or the center rubber is provided with a wide base portion in a convex shape and placed on the left and right base portions. it is also possible depending on the intended use of the tire to provide a pair of side rubber G _S. [0012] To confirm the effect of the tire according to the present invention,
The tire of the embodiment shown in FIG. 1 and the rectangular ratio are the same as the tire of the embodiment, but have the same radial structure of 60R14 size and the block type tread, but Comparative Example 1 using a single rubber for the tread, rectangle Rate and the hydroplaning generation speed during straight running with the actual vehicle between the tire of Comparative Example 2 using a single rubber tread and the tire of Example 1 and the tire of Comparative Example 1 An uneven wear test was carried out by running a 20,000-kilometer actual vehicle, and evaluated. The test tire was assembled on a 6 J rim and filled with 1.9 kgf / Cm ² of internal pressure.
The hydroplaning test was performed on a special road with a water pool with a depth of 10 mm on the way, and the uneven wear test was performed on a special road containing a winding course of asphalt pavement.
The vehicle ran at an average speed of 0 km / h. Table 1 shows the details of the test tires and the test results. [Table 1] Thus, the rectangular ratio of the contact surface of the tire is 75
The center of the tread, which is in the range of .about.85% and which corresponds to 30.about.70% of the contact width, is made of rubber having excellent abrasion resistance compared to rubber on both sides. The speed is high, and uneven wear, which is a concern in this case, can be advantageously suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a tire according to an embodiment of the present invention. FIG. 2 is a diagram showing a contact shape of the tire according to the embodiment. [Description of Signs] 1 Tire 2 Sidewall 3 Tread 7 Center of tread C _A Ground type G _C Rubber at center of tread G _S Rubber at side of tread W Ground width Y Maximum ground length y 80% of ground width Contact length at

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B60C 11/00, 3/04, 9/08

Claims (1)

(57) [Claims] [Claim 1] A pair of side walls and both side walls
The tread is continuous across the tires, and the tread is made of a plurality of different rubbers. The tire is assembled on the rim to be used and filled with air pressure corresponding to the design working load specified in the JATMA standard. % When the load is applied, the average contact length at the 80% point of the contact width symmetrical to the center of the contact surface is a rectangular ratio of 75 to 85% of the maximum contact length at the contact center, and the contact width 30 ~
A pneumatic tire characterized in that rubber having better wear resistance than rubber on both sides is disposed at the center of a tread corresponding to 70%.