JPS60236807A - pneumatic tires - Google Patents

Abstract

PURPOSE:To improve wet grib properties and to decrease the occurrence of stone biting, by a method wherein the inclination angle of the inner wall of a longitudinal groove radially formed in a tread is set to a value which is given times as high as that of the outer wall thereof, and a platform is formed on the other wall. CONSTITUTION:Inclination angles alpha1 and alpha2 of inner walls A1 and A2, located closer to the equator surface of a tyre, of circumferential longitudinal grooves G1 and G2, formed in a tread part, with normal lines L1 and L2 of a tread surface are set to a value which is within a range of 1-7 times as high as inclination angles beta1 and beta2 of outer walls B1 and B2, positioned closer to a tread end, with normal lines L3 and L4. Further, platforms P are respectively formed on the outer wall B1 of the longitudinal groove G1 and the inner wall A2 of the longitudinal groove G2, and buffering projections 4 and 5 are provided on the other walls A1 and B2. The set position of the projections 4 and 5 is located in a level equal to that of the platform P, and the width thereof is set to 50-100% of the width of groove in a position where the platform is set. This constitution enables improvement of wet grip properties and decrease in the occurrence of stone biting.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pneumatic tire with improved wet grip properties and reduced stone bite.

In general, the basic groove shapes of conventional tires are a square shape, a tJ shape, and a bottom arc shape, as shown in cross-sectional views in FIGS. 1 to 3. With such a conventional groove shape, if a stone enters the inside of the groove G, it will be pushed inward by the flat sidewall of the groove due to the load applied to the tire, making it difficult for it to fall out.

This stone-grained condition not only reduces the original function of the groove, but also causes stress concentration at the contact area between the stone and the sidewall, which promotes the occurrence and growth of cracks inside the groove, which shortens the life of the tire. . Therefore, as a measure to prevent stone encroachment, a method has been proposed in which the cross-sectional expansion and softening of the groove is made into two or more steps as shown in Fig. 4 (a) (Japanese Patent Application Laid-Open No. 120302/1983).
However, with this method, when the tread wears down to a predetermined amount, the groove width becomes extremely narrow and the wet grip performance is significantly reduced.

Furthermore, as shown in Fig. 4(b), a method has been proposed in which the cross-sectional shape of the groove is made into a ■ shape and the inclination angle a of the side wall is made extremely large. This has the disadvantage that the contact area is reduced, resulting in a decrease in wear resistance, and stress concentration at the groove bottom is likely to occur.

It is an object of the present invention to eliminate such drawbacks and to propose a pneumatic tire that reduces stone-biting while maintaining wet grip performance from the early stage to the late stage of tire wear.

The present invention has a plurality of longitudinal grooves extending in the circumferential direction of the tire, and the inclination angle α of the inner wall of the longitudinal groove cross section located closer to the tire equatorial plane with respect to the normal to the tread surface is set to the outer side located closer to the trend end. Inclination angle β with respect to the normal of the wall tread surface
This is a pneumatic tire having a tread portion in which the range is more than 1 times and less than 7 times, and a platform is formed on either the inner wall or the outer wall.

An embodiment of the present invention will be described below based on one drawing.

In the figure, the trend part has two longitudinal grooves G1 and G2 extending in the tire circumferential direction, and the normal L1 to the tread surface of the inner IAI and A2 located closer to the tire equatorial plane C of the longitudinal groove cross section.
．． 1, α2 is the outer wall B1, B located closer to the tread end
2, with a range of 1 to 7 times. Although it is preferable to make the side walls combed in order to reduce stone trapping, increasing the inclination angle decreases the ground contact area, which is not preferable from the viewpoint of wear resistance and handling stability. Therefore, the inventor obtained the knowledge that the load on the side wall of the longitudinal groove is larger on the side wall closer to the tire equatorial plane, that is, the inner wall, than on the side wall closer to the tread throat end, that is, the outer wall. By increasing the size of the tread, stones are prevented from getting stuck, while by reducing the angle of inclination of the outer wall, the ground contact area of the tread portion is ensured. Note that the angle of inclination α of the inner wall is preferably in the range of 1.2 to 2 times the angle of inclination β of the outer wall. Furthermore, in the present invention, a platform P is formed on one side wall, and even if a stone enters the inside of the vertical groove, this platform P
This prevents the tire from entering the inside of the tire further, and prevents damage at the bottom of the groove, which is fatal to the life of the tire. This platform is preferably formed continuously in the circumferential direction of the tire, but may be configured to be partially intermittent.

Depth Dl from the vertical groove surface where the platform P is formed
is in the range of 30-70% of the longitudinal groove depth D2, and 30%
If it is shallower, the drainage performance will deteriorate early due to the progression of wear of the tread portion, while if it is deeper than 70%, prevention of stone encroachment will not be sufficient.

Next, in the present invention, it is preferable that a buffer protrusion 4.5 is formed on the side wall of the longitudinal groove opposite to that on which the platform is formed. This lff1 protrusion 4.5 is formed in the vertical groove at approximately the same depth as the plaque 1-bohm, and its width m is in the range of 50 to 100% of the vertical groove 1]z at the platform formation position. It is. This buffer protrusion 4.5 is
Even if a stone enters the vertical groove, it prevents the stone from entering further toward the bottom of the groove, thereby preventing stone encroachment.
Since the effective volume of the vertical grooves is hardly reduced, wet grip properties can be maintained. Buffer protrusion 4.
5 can be formed continuously in the tire circumferential direction, but
It is preferable from the viewpoint of drainage that the holes are formed intermittently as shown in FIG. In this case, the circumferential length n of the buffer protrusion 4.5 is required to be at least 5fi, and the buffer protrusion 4.5
It is preferable that the circumferential interval W is set to 3 times or less the circumferential length n of the collision point.

In the present invention, it is sufficient that at least one of the plurality of longitudinal grooves arranged in the tread portion satisfies the above-mentioned structural requirements, and as shown in the cross-sectional shape of FIGS. 8 and 9, no buffer protrusion is included. Of course, scales are applied to the longitudinal grooves.

As shown in Section E, in the pneumatic tire of the present invention, the side inclination angle of the side walls of the longitudinal groove of the tread portion is made larger on the inner wall and smaller on the outer wall, and a platform is formed on one side wall, so that the effective use of the tread portion is increased. Reduces stone bite without reducing ground contact area, and improves wet grip by 1m
Moreover, by forming the buffer protrusion opposite to the platform of the longitudinal groove side wall, stone encroachment can be more effectively prevented.

Examples Examples of the present invention include vertical grooves shown in FIGS. 5, 6, and 7 (Example 1), and vertical #1lG1 in FIG.
The vertical groove shape shown in Fig. 8 was used instead of G2 (Example 2)
, Furthermore, as a conventional example, instead of vertical 11G1 and G2 in FIG. 5, 1t! Tire size 7.5 for a tire with vertical groove shape (Comparative Example 1) whose specifications are shown in Table 1.
Prototype tires with OR16,14PR and internal pressure of 7.0kg/
- We attached it to a 4-ton vehicle and evaluated the stone bite test and wet grip by driving the vehicle.

In the stone-biting test, the number of stones remaining inside the vertical groove was calculated after driving at a speed of 50 km/h over a distance of 10 km, which is a combination of 4 km of gravel road and 6 km of paved road.

On the other hand, the wet grip property of the i-red part of the tire is 5.
Use one with 0% wear and sprinkle water on slippery roads.
The speed at which sideslip occurred while traveling on the road surface with a turning radius of 40 m was measured. The results of these seven measurements are shown in Table 1. From Table 1, it can be seen that all of the examples of the present invention are excellent in stone-biting prevention and wet and grip properties.

[Brief explanation of drawings]

Figures ff11 to tlsA (A) and (B) are cross-sectional shapes of conventional vertical grooves, Figures 5 and 6 are a partial front view and cross-sectional view of the right half of the tread portion of the tire of the present invention, respectively, and Figure 7. is an enlarged view of the vertical groove 01 in FIG. 6, and FIGS. 8 and 9 are cross-sectional views of other vertical grooves of the present invention. 4.5-・Buffer protrusion, A1, A2-Inner wall, B1, B
2-outer wall, r, - tire equatorial plane, G1, G2- longitudinal groove, L 1,], 2, L 3, T,, 4-) normal to red surface, P- platform, α1, α2- Side slope angle of inner wall, β1, B2 V4 slope angle of outer wall. Patent Applicant Sumitomo Rubber Industries Co., Ltd. Representative Patent Attorney Tadashi Naemura Figure 1 82m 311 Procedural Amendment (Nagi 1. Indication of the Case 1982 Kiri (2) No. 9361B No. 3, Person Making Amendment 4, Agent 5. 81 dimensions of the amendment order July 31, 1980 (dispatch date) 6. Number of inventions increased by the amendment None 7. Subject of the amendment

Claims (1)

[Claims] +11 The tire has a plurality of longitudinal grooves extending in the circumferential direction, and the inclination angle α of the inner wall of the longitudinal groove cross section located beyond the tire equatorial plane C with respect to the normal to the tread surface is The range is greater than 1 times and less than 7 times the inclination angle β with respect to the normal to the trend plane of the outer wall located closer to the end, and there is a platform on either the inner wall or the outer wall. A pneumatic tire with a tread formed with. (2) The vertical groove is provided with a buffer protrusion on the side wall opposite to where the platform is formed.
Pneumatic tires listed in section. (3) The buffer protrusion is formed in the vertical groove at approximately the same depth as the platform, and the width (m) of the wk street protrusion is in the range of 50 to 100% of the vertical groove width i at the platform formation position. A pneumatic tire according to claim 2. (4) The pneumatic tire according to claim 2, wherein the buffer projections are continuous or discontinuous in the tire circumferential direction.