JPH04193610A - Pneumatic radial tire - Google Patents

Abstract

PURPOSE:To produce a large cornering force while maintaining wet water drainage property of a tire by making shallow the depth of multiple circumferential grooves, which are formed on a tread ground-contact surface portion and extended in circumferential direction of a tire, gradually to the outer side of a vehicle with the tire provided on the vehicle. CONSTITUTION:A circumferential narrow groove 2 is provided at the center of a tread ground-contact surface portion 1, and also two circumferential wide grooves 3 and two circumferential intermediate grooves 4 are provided. On the other hand, multiple lateral grooves 5 are formed between the circumferential wide grooves 3 and tread ends. In addition, slant grooves 6, which are extended from the circumferential wide grooves 3 to the circumferential narrow grooves 2 and end without reaching at the circumferential narrow grooves 2, are formed. Accordingly, a row of 2nd blocks 7 and a row of shoulder blocks 8 are formed. In this case, the depth of the circumferential grooves 2 to 4 is made shallow gradually from the internal side to the external side of a tire which is mounted on a vehicle.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention relates to a high-performance pneumatic radial tire for passenger cars, and in particular, to a tire that greatly improves steering stability when the vehicle turns at high speed. .

(Prior art) In conventional passenger car tires, in order to achieve both wear resistance and wet drainage performance, the groove depth of the circumferential grooves formed in the tread surface is set to be symmetrical with respect to the tire's equatorial plane. This is generally true for so-called asymmetric patterns as well.

(Problem to be Solved by the Invention) Incidentally, with the appearance of vehicles with high dynamic performance in recent years, it has become important for tires to generate high cornering force while reducing self-lining torque as much as possible. ing.

In other words, high cornering force improves the tire's road grip, while self-lining torque is a force that tries to return the tire to a straight running condition, and acts to offset the cornering force, so it is It is important to reduce the self-lining torque as much as possible, especially in order to improve steering stability during high-speed turning.

The force generated by the tire, especially its ridges, is generated based on the cornering force that is generated based on its rigidity and acts as a lifting force against the road surface, and the deformation reaction force of the ridges, etc., and is generated based on the tire's original shape. Self-lining torque acts as a force to return the cornering force to the state of Conventional general tires have not taken such special consideration, and therefore have had the problem of insufficient cornering force during high-speed turning.

Therefore, it is possible to increase the rigidity of the ridges located at the outer tread edge by removing the circumferential groove from the outer tread edge of the vehicle when the tire is mounted on the vehicle. According to this, it has been proposed that
A natural consequence of omitting the circumferential groove was another problem in that the wet drainage of the tire was greatly reduced.

This invention was made by focusing on the problems of the prior art, and it is possible to solve the problem of the ridges which are subjected to a large road reaction force when the vehicle turns without reducing the number of required circumferential grooves. To provide a pneumatic radial tire that can generate a sufficiently large cornering force while ensuring wet drainage performance of the tire by increasing the rigidity of the tire.

(Means for Solving the Problems) This invention provides that when a vehicle turns, most of the force acting on the tire is an external force in the tread width direction directed from the outside to the inside of the turn. The depth and shallowness of the extending groove does not have much effect on the stiffness of the ridge, but the stiffness is rather greatly affected by the depth and shallowness of the circumferential groove. As shown in the partial cross-sectional view of the tire in the tread width direction in Fig. 3, the ridges defined by the circumferential grooves a are less rigid due to the road reaction force during cornering. The pneumatic radial tire of the present invention has been developed by focusing on the fact that the tire located on the outer side of the turn will be deformed more greatly. The groove depth of the circumferential groove is made gradually shallower toward the outside of the vehicle when the tire is mounted on the vehicle.

More preferably, the groove depth of the shallowest circumferential groove is
The range is 0.8 to 0.3 times that of the deepest circumferential groove.

(Function) In this pneumatic radial tire, the depth of the circumferential groove is made shallower on the outer side of the turn, where the road surface reaction force acting on the tire is greater when the vehicle turns, and the depth of the circumferential groove is made shallower on the ridges, for example, on the road surface of the block. By increasing the rigidity against reaction force, it is possible to sufficiently increase the drag force by the block and generate high cornering force, while at the same time suppressing deformation of the block and advantageously reducing self-lining torque. .

That is, in the tire according to the invention, as shown in a partial cross-sectional view in the tread width direction in FIG. Since each of the grooves al+at has a considerably shallower groove depth than the circumferential groove a of the conventional tire shown in a similar cross-sectional view in FIG. 1(b), each block l)l+t12+b: l will exhibit a form similar to that of an integrally molded body, and the thickness of the tread rubber can be made thinner by the shallower groove depth, greatly increasing the rigidity of the block l) I+ bz, bz. However, in the conventional tire shown in FIG. 1(b), all of the circumferential grooves a have a deep groove depth, so each block b is It shows a mutually independent form that is almost completely separated from block b, and at the same time, it is necessary to increase the tread rubber thickness according to the groove depth, so it is impossible to bring about high block rigidity. Therefore, while conventional tires cannot sufficiently increase cornering force and are forced to generate large self-lining torque, the invented tire generates high cornering force and still has no ability to generate self-aligning torque. It can be significantly reduced.

By the way, here, since there is no reduction in the number of circumferential grooves, sufficient wet drainage performance can be ensured by them. If circumferential grooves alone cannot provide the necessary and sufficient wet drainage, it is recommended to provide grooves in the tread width direction, which have less effect on ridge stiffness, or to improve the existing tread width. This can be countered by increasing the depth of the directional grooves.

Here, the groove depth of the shallowest circumferential groove is preferably in the range of 0.8 to 0.3 times the groove depth of the deepest circumferential groove.

In other words, if it exceeds 0.8 times, the ridge rigidity cannot be increased as expected, and if it is less than 0.3 times, the groove volume becomes too small and it is impossible to ensure wet performance. It is.

(Example) Embodiments of the present invention will be described below based on the drawings.

FIG. 2(a) shows a tread pattern of an embodiment of the present invention as seen from the front when the tire is mounted on a vehicle, and FIG. 2(b) shows the tread pattern of the tire shown in FIG. 2(a). FIG. 3 is a cross-sectional view in the tread width direction.

Note that the internal reinforcement structure of the tire is the same as that of a -C radial tire, so illustration thereof is omitted.

Here, in a tire with a size of 225150VR16 and a tread surface width of 186 mm, the tread surface portion 1
4.5, extending linearly in the circumferential direction of the tire,
A single circumferential narrow groove 2 having a groove width of ffIm is provided, and a circumferential groove 2 is located at a predetermined interval from this circumferential narrow groove 2 toward the trend end side, and is line symmetrical with respect to the circumferential narrow groove 2. Two straight circumferential thick grooves 3 with a groove width of 9.5 mm, forming a
In addition, from these circumferential thick grooves 3, two grooves with a groove width of 7.0 m are spaced at a predetermined interval on the tread end side and are symmetrical with respect to the circumferential narrow grooves 2. A straight circumferential intermediate groove 4 is provided, and a ``H'' shape is formed between each circumferential thick groove 3 and the tread edge, and 7.0. A plurality of width direction grooves 5 having a groove width of mm are formed at predetermined intervals in the tire circumferential direction, and each of these circumferential direction thick grooves 3 is formed at predetermined intervals in the tire circumferential direction.
By forming an inclined groove 6 that extends from the circumferential groove 2 in the direction of the circumferential groove 2, faces diagonally downward when viewed from the front of the tire in the mounting position, and ends without reaching the circumferential groove 2, the circumferential groove 3 When the second block row 7 and the shoulder block row 8 are formed between the circumferential intermediate groove 4 and between the intermediate groove 4 and the tread end, the groove depth of each circumferential groove is determined as follows: The installed tire is gradually made shallower from the inside to the outside of the vehicle, and toward the right side as shown in the figure.

That is, in the case shown in FIG. 2(b), the depths are 8.0 am and 7.0 m toward the outside of the vehicle.
m, 5.8 m, 4.8 m, and 3.0 m.

Note that all of the width direction grooves 5 in this example have a depth of 6.0 wn.

Although the present invention has been described above based on the illustrated example, it goes without saying that the present invention can be applied not only to the illustrated tread pattern but also to various other patterns.

[Comparative example]

Below are the invented tires, conventional tires, and comparison tires.
A comparative test regarding maximum cornering force, maximum self-lining torque, and rate of occurrence of hydroplaning phenomenon will be explained.

◎Test tire - Invention tire Tire with the tread pattern shown in Figure 2 and having the various dimensions described above - Conventional tire - Conventional tire with the tread pattern shown in Figure 2, groove depth of all circumferential grooves 8 A tire similar to the invention tire/comparison tire except that it was set to 0-.The tire had the tread pattern shown in Figure 2, and the groove depth of each widthwise groove was equal to the depth of the adjacent circumferential groove at both ends. Same tire as the invention tire, except that they are the same as each other ◎Test method The cornering force and self-lining torque were evaluated by measuring each with a bench cornering characteristic measuring machine, and the speed at which the hydroplaning phenomenon occurred was measured using the actual vehicle. The vehicle was evaluated by driving in a straight line on a road surface with a water depth of 5IIIl and measuring the speed at which the driving acceleration decreased.

◎Test results The results of these tests are shown in the table below using indices.

The larger the index value is, the better the results are. Cornering force is larger as the index value is larger, self-lining torque is smaller as the index value is larger, and the speed at which the hydroplaning phenomenon occurs is determined by the index value. The larger the value, the higher the value.

According to this table, in the invented tire, the groove depth of the circumferential groove is shallower than that of the conventional tire, so the rate at which the hydroplaning phenomenon occurs is somewhat lower than that of the conventional tire. It is clear that the maximum cornering force can be made considerably greater than with conventional tires, and in addition, the maximum self-lining torque can be made considerably smaller than with conventional tires.

(Effects of the Invention) Thus, according to the present invention, a plurality of circumferential grooves are formed such that the depth of the grooves becomes gradually shallower toward the outside of the vehicle when the tire is mounted on a vehicle. By increasing the rigidity of the tread land area, which is subject to large road reaction forces, it is possible to ensure the wet drainage performance of the tire and still generate a sufficiently large cornering force. The steering stability during turning can be greatly improved.

[Brief explanation of the drawing]

FIG. 1 is a partial cross-sectional view illustrating the tread width direction cross section of an inventive tire and a conventional tire. FIG. 2 is a tread pattern and a tread width direction cross section showing an embodiment of the present invention. FIG. 2 is a partial cross-sectional view in the tread width direction showing a deformed state of the tire due to road reaction force. ■...Tread surface part 2...Circumferential narrow groove 3.
... Circumferential thick groove 4... Circumferential intermediate groove 5...
Width direction groove 7.8...Block row Figure 1 (a) (b)

Claims (1)

[Claims] 1. The groove depth of the plurality of circumferential grooves formed on the tread surface and extending in the tire circumferential direction becomes gradually shallower toward the outside of the vehicle under the mounting position of the tire on the vehicle. Pneumatic radial tire.