JPH04215504A - Pneumatic radial tire - Google Patents

Abstract

PURPOSE:To improve controllability and rectilinear derivability in a pneumatic radial tire having a directional tread pattern by forming quasi main grooves on both sides of a main groove in the same direction as inclined sub-grooves at a predetermined inclination and setting a circumferential projected length of the tire larger than a circumferential ground contacting length of the ground contacting surface of the tire under the regular condition. CONSTITUTION:A directional pattern is formed of a straight main groove 1 in the circumferential direction of a tire and sub-grooves 2 inclined to designated rotational direction R of the tire in the opposite directions R toward ground contacting ends E. At least one quasi main groove 3 is formed respectively no both sides of the main groove 1 to be inclined in the same direction as the sub-groove by 3-30 deg. of an average inclination alpha to the circumferential direction of the tire. Also, the circumferential projected length L1 of the tire is set larger than the circumferential ground contacting length L2 of the ground contacting surface of the tire under the regular internal pressure and load.

Description

[Detailed description of the invention]

0001

FIELD OF THE INVENTION This invention relates to pneumatic radial tires having a directional tread pattern.

0002

BACKGROUND OF THE INVENTION Among the various performances that a pneumatic tire should have, drainage performance is one of the most important factors. This drainage performance is often influenced by the main grooves and sub-grooves that form the tread pattern. Conventionally, as shown in Fig. 4, as a tread pattern that takes drainage performance into consideration, a plurality of (four in the figure) main grooves 1 are provided in the tread that extend endlessly in parallel and straight along the circumferential direction of the tire. In addition, when providing a sub-groove 2 that intersects these main grooves 1 and extends to the left and right shoulder contact edges, the sub-groove 2 should be arranged in a direction opposite to the designated tire rotation direction from the center area of the tread toward the contact edge. A directional tread pattern that slopes is known.

Tires with this directional tread pattern have a plurality of main grooves 1 to enhance the water drainage effect in the front and back directions of the tire, and the directionality of the sub grooves 2 to improve water drainage to the sides of the tire. The water removal effect is increased to improve drainage performance. In order to improve drainage performance in this way, it is necessary to increase the number and groove width of the main grooves, and further increase the number and groove width of the sub-grooves connected to the main grooves, but as a result of these increases, the ground contact area of the block is reduced, and its rigidity is reduced, resulting in worsening of steering stability. In addition, especially when there are a large number of main grooves, when driving on a so-called rain groove road surface, which has many parallel grooves in the direction of travel for the purpose of drainage, the edge of the block may get stuck in the rain groove, making it difficult to turn the steering wheel. There is a problem in that the vehicle tends to be easily moved, causing so-called wandering, and the straight-line running performance (hereinafter referred to as straight-line running performance) is reduced.

0004

SUMMARY OF THE INVENTION An object of the present invention is to provide a pneumatic radial tire that has improved steering stability and straight running performance without impairing drainage performance.

[0005]

[Means for Solving the Problems] The present invention achieves the above object by providing only one main groove extending straight in the tire circumferential direction in the ground contact center region of the tread, and from the main groove to both ground contact areas respectively. A tire having a directional tread pattern in which a plurality of sub-grooves are provided that extend obliquely toward the end, and the inclination direction of the sub-grooves is inclined in the opposite direction to the specified tire rotation direction as the tire approaches the ground contact end. , 3 to 30 degrees to the tire circumferential direction on both sides of the main groove, respectively.
At least one semi-main groove is provided which is inclined in the same direction as the sub-groove at an average angle of It is characterized by being larger than the circumferential ground contact length L1.

[0006] In this way, the number of main grooves extending straight in the circumferential direction of the tire is limited to one in the center contact area, and semi-main grooves each having a specific length and angle are formed on both sides of the main groove. By arranging the blocks so as to be inclined in the same direction as the main groove, drainage performance is ensured even though there is only one main groove, and the block rigidity can be increased, thereby improving steering stability. Moreover, since there is only one main groove in the circumferential direction of the tire, it is possible to suppress the occurrence of wandering due to digging into the rain groove.

[0007] Hereinafter, the pneumatic radial tire of the present invention will be explained in detail with reference to the drawings. FIG. 1 is a plan view showing an example of the tread pattern of the tire of the present invention,
FIG. 2 is a front view of the same tire. 1 and 2, the tread surface T of the tire of the present invention has one main groove 1 extending straight in the tire circumferential direction within the ground contact center area C, and a main groove 1 extending straight from both sides of the main groove 1. Both grounding ends E,
A plurality of sub grooves 2 extending obliquely toward the E direction are arranged at predetermined intervals in the tire circumferential direction. The rotational direction of the tire is designated as arrow R, and the direction of inclination of the sub-groove 2 becomes opposite to the designated tire rotational direction R toward the ground contact edge E.

In such a directional tread pattern, at least one semi-main groove 3 is provided on each side of the main groove 1 at a predetermined interval in the tire circumferential direction, and at an angle of 3 to 30° to the tire circumferential direction. It is installed so as to be inclined in the same direction as the sub-groove 2 at an average angle α. Here, the average angle means that the tangent to the semi-main groove 3 at the end P of the center contact area of the semi-main groove 3 is around the tire circumference, as shown schematically in a part of the right half of the tire tread in Fig. 8. It is the average value of the angle α1 made with the tire circumferential direction and the angle α2 made with the tire circumferential direction by a straight line connecting the end P and the end Q on the ground contact side of the semi-main groove 3.

These quasi-main grooves 3 intersect with a plurality of minor grooves 2,
Both ends thereof are formed so as to be connected to the sub-groove 2. Furthermore, the length L2 of the semi-main groove 3 projected in the tire circumferential direction is:
It is formed to be larger than the ground contact length L1 of the tire under normal internal pressure and normal load (L2 > L1). As a result, the semi-main groove 3 always crosses the contact surface S of the tire, making it possible to increase its contribution to drainage performance. Moreover, by providing such a semi-main groove 3, the number of main grooves 1 can be reduced to the minimum of one. Therefore, the ground contact area of the block can be increased and the rigidity can be increased, so that steering stability can be improved. Furthermore, it is possible to suppress the occurrence of wandering due to the block edges digging into the rain grooves.

[0010] The average angle α of the semi-main groove with respect to the circumferential direction of the tire, which performs the above-mentioned action, must be within the range of 3° to 30°. By setting α to 3° or more, the rigidity of the block can be ensured to improve steering stability, and interference with rain grooves can be eliminated to improve straight running performance. Further, by setting the angle to 30° or less, it becomes possible to exhibit a drainage effect that can be substituted for the main groove.

Further, it is preferable that the groove width of the semi-main groove is set smaller than that of the main groove, but in particular, as shown in the figure, it is preferable that the width of the semi-main groove is gradually increased from the side of the ground contact center region where the ground contacts the ground first toward the ground contact end. good. With such a groove configuration, better drainage performance can be ensured. The main groove 1 is not particularly limited as long as it is within the central tread contact area, but preferably it is provided at a position slightly shifted toward the outside of the tire from the center of the tire when mounted on a vehicle, and is located outside the inside area. It is desirable to have an asymmetric tread pattern in which the number of quasi-main grooves 3 in the region is reduced. By creating such an asymmetrical tread pattern, the block rigidity in the outer region is made greater than in other regions, further improving handling stability, and the groove area ratio in the inner region is increased to ensure drainage performance. be able to.

[0012] The width of the main groove is usually 14 to 20 mm.
The groove depth is preferably in the range of 6 to 9 mm. Third
The figure shows a partial plan view of a tread pattern of another example of the present invention, and FIGS. 5 to 7 show partial plan views of a tread pattern of a comparative tire to be described later. [Example] Six types of conventional tires, tire sizes and tires of the present invention, all having the same tire size of 225/50ZR16, but with different tread patterns, main grooves, semi-main grooves, etc., as shown in the table, were used. , comparative tires A, B, and H were manufactured, respectively.

[0013] These six types of tires are each 16×7
Rim assembled on JJ rim, regular internal pressure 2.0kg/cm2
was filled and installed in a vehicle, and the drainage performance, steering stability, and straight running performance in a rain groove were evaluated using the following methods. The table shows the evaluation results based on the evaluation value of conventional tires (10
0). The larger the value of each of these indexes, the better the performance. Drainage performance: The vehicle was driven on a wet road and the speed at which hydroplaning occurred was measured. Steering stability: The steering stability during cornering while driving on a 2.5 km test course was scored by five test drivers using a 10-point scale, and the average value was used for evaluation. Rain Groove Straight Driving Performance: Sensory evaluation of handling performance when driving straight on a test course with rain grooves on the road surface was scored by five test drivers using a 10-point system, and the average value was used for evaluation.

[0014]

[Table 1] From Table 1, comparative tires A, B, and C all have improved steering stability and straight running performance compared to the conventional tires, but have significantly lower drainage performance. In contrast, Tires A and B of the present invention have drainage performance that is substantially the same as conventional tires, and have improved steering stability and straight-line running performance. It can be seen that this has a positive effect.

[0015]

[Effects of the Invention] As explained above, according to the present invention,
Strain-shaped main groove in the tire circumferential direction in the center area of contact with the ground.
Only main grooves are provided, and quasi-main grooves with specific lengths and angles are arranged at an angle on both sides of this main groove to ensure drainage performance and improve handling stability by increasing block rigidity. be able to. Furthermore, since there is only one main groove, it is possible to suppress the occurrence of wandering due to the block edge biting into the rain groove, and it is possible to improve straight running performance.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing an example of a tread pattern of a pneumatic radial tire of the present invention.

FIG. 2 is a front view of the pneumatic radial tire of the present invention shown in FIG. 1;

FIG. 3 is a plan view of a tread pattern of another embodiment of the pneumatic radial tire of the present invention.

FIG. 4 is a plan view of a tread pattern of a conventional tire.

5-7 are plan views of tread patterns of comparative tires, respectively.

FIG. 8 is a diagram for explaining the arrangement angle of the semi-main groove of the tire of the present invention.

[Explanation of symbols]

T Tread 1 Main groove 2 Sub-groove 3 Semi-main groove L1 Tire circumferential ground contact length L2 Projected length E of the semi-main groove in the tire circumferential direction
Grounding end S Grounding surface

Claims (1)

[Claims] [Claim 1] Providing only one main groove extending straight in the tire circumferential direction in the ground contact center region of the tread, and providing a plurality of sub grooves each extending diagonally from the main groove toward both ground contact ends, A tire having a directional tread pattern in which the direction of inclination of the minor grooves is inclined in the opposite direction to the specified tire rotation direction toward the ground contact edge, and in each side area of the main groove, a groove is provided with respect to the circumferential direction of the tire. At least one semi-main groove is provided that is inclined in the same direction as the sub-groove at an average angle of 3 to 30 degrees, and the projected length L2 of the semi-main groove in the tire circumferential direction is determined at the normal internal pressure and normal load. A pneumatic radial tire that is larger than the tire circumferential ground contact length L1 of the tire contact surface.