NZ215005A - Heavy vehicle radial tyre: circumferential tread grooves castellated at tread surface and zig-zag at base - Google Patents

Description

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Pric: Complete Specification Filed :3Jr0on-.86 Class: (56QCUJ.96 3'OfXPftW.

Publication Date: P.O. Journal, No: .13915.

^•Z. PATEOT 0PM65 r L 31 JAN 1986 R bocA/ED o PATENTS FORM NO. 5 NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION "RADIAL TIRE FOR HEAVY VEHICLES" o -t, WE SUMITOMO RUBBER INDUSTRIES, LTD. of No. 1-1, Tsutsuicho 1-chome, Chuo-ku, Kobe-shi, Hyogo, Japan a Japanese company hereby declare the invention, for which-f/we pray that a patent may be granted to-me/us, and the method by which it is to be performed, to be particularly described in and by the following statement (followed by page I A.> ' r" ; -/'A ";i:" • J J ■ .' - /■ - la - 2,1 ~j u 0 5 The present invention relates to a radial tire for heavy vehicles having a tread pattern which reduces railway wear.

A radial tire for heavy vehicles usually has a carcass made of cord arranged approximately perpendicular to the equatorial plane of the tire and a steel cord belt layer arranged outside the crown of the carcass. This type of tire is superior in wear resistance, puncture resistance, and fuel saving to tires of cross-ply structure, and consequently it ha3 come into general use recently. This radial tire, however, has the following disadvantage. The tread is highly stiff as a whole because the stiff belt layer is arranged in the tire crown as mentioned above. On the other hand, the tread surface becomes uneven in stiffness due to the tread pattern, and this leads to uneven wear. In the case of radial tire for heavy vehicles, the common tread pattern is the rib pattern or rib-lug pattern that has the lengthwise grooves in the circumferential direction of the tire. In this case, the outside corner of the rib is less stiffer than other parts and hence is easier to wear.

In the case of a rib pattern as shown in Fig. 1, the rubber at the outside corner (P) of the rib is more mobile that the rubber at the other parts. Therefore, it is rubbed against the road surface and the ^ local wear takes place in the hatched area between one inside corner of the rib to the other inside corner of the rib. In order to increase the stiffness of the outside corner of the rib, and thereby to decrease the uneven wear of the outside corner of the rib, there has been proposed a tread pattern as shown in Fig. 2. In this tread pattern, the outside corner is removed and the lengthwise groove (G4) is composed of the groove components (Ga and Gc) parallel to the circumferential direction of the tire and the groove components (Gb and Gd) aslant by an angle (a) to the circumferential direction of the tire. This tread pattern ■'( *1 achieves the object of reducing uneven wear, but requires that the angle (a) for the slant groove components (Gb and Gd) should be increased for good grip performance. This, in turn, leads to heel-and-toe wear that occurs near the ridgeline of the slant groove component.

It is an object of this invention to provide a radial tire for heavy vehicles having a'tread pattern in which the lengthwise groove is composed of groove components in the circumferential direction, said tread pattern being less liable to railway wear and heel-and-toe wear than the conventional ones. k The gist of this invention resides in a radial pneumatic tire for heavy vehicles having a tread pattern which is defined by a plurality of grooves each continuous in the circumferential direction of the tire, each of said grooves being composed of groove components in the circumferential direction, with the walls at the tread surface thereof being parallel to the circumferential direction of the tire, and inclined groove components with the walls of the tread surface thereof being inclined 30° to 90° to the circumferential direction of the tire, connecting said groove components in the circumferential direction, said inclined groove component walls at the tread surface increasing in length to become a single zigzag groove as the tread wears out.

An example of this invention is described in more detail with reference to the accompanying drawing.

Fig. 3 is a partial plan view showing the tread pattern of the tire of this invention. The tread (T) is continubtis in the circumferential • \ u 1 ' i~ . cv.\ 'f -3 MAR 2987 ;v: © d-' r 1 - ' . ' ■ ^ 1 ,-*y- ' " ■■■■r- 4 ' ' ^ w *'■ 7 ■• ^ ' ■-... -•:■ : ,v| -3" 2 I 50 0 direction of the tire. There are three lengthwise grooves (G5, G6, G7), each composed of circumferential groove components (Ga, Gc) which run parallel to the circumferential direction of the tire and slant groove components (Gb, Gd) placed between said circumferential grooves components and connecting said circumferential grooves. The ridgeline of the slant groove component is aslant at an angle (a), which is 30° to 90°, to the circumferential direction of the tire, so that the grip performance is maintained.

The bottom (GA) of each lengthwise groove takes on a zigzag pattern that runs in the circumferential direction. As the tread wears, the zigzag pattern of the groove bottom appears. In other words, the ridgelines (a, b, c, d) is lost gradually as the tread wears, and at the same time, the new ridgeline (e) appears. This ridgeline (e) becomes longer as the tread wears more. Finally, there will be the ridgeline (e) only, and the zigzag pattern of the groove bottom appears.

The tire of this invention may be constructed such that the above-mentioned zigzag pattern appears in the last stage of tread wear or in the intermediate stage of tread wear. In other words, the tire of this invention is constructed such that the ridgelines of the slant groove components (Gb, Gd) which are liable to heel-and-toe wear become shorter as the tread wear proceeds. Therefore, the above-mentioned wear is reduced.

In the initial stage of wear, the lengthwise groove has such a pattern that the outside corner of the rib is partly removed; therefore, the railway wear is effectively prevented.

In the meantime, the tire of this invention may has thin widthwise grooves (2) which connect said lengthwise grooves to one another to improve the water drain effect. The tread pattern may be modified without departure from the scope of this invention.

(Effect of the invention) The lengthwise groove composed of circumferential groove components and aslant groove components prevent the railway wear, and the ridgeline structure that permits the zigzag pattern to appear at the intermediate or final stage of tread wear reduces heel-and-toe wear.

Brief Description of the Drawings: Figs. 1 and 2 are partial plan views of the conventional tire tread.

Fig. 3 is a partial plan view showing the tread of the tire of this invention.

G5, G6, G7 Lengthwise grooves Ga, Gc Circumferential groove components Gb, Gd Aslant groove components 215005

Claims (1)

1. WHAT WE CLAIM IS: (1) A radial pneumatic tire for heavy vehicles having a tread pattern which is defined by a plurality of grooves each continuous in the circumferential direction of the tire, each of said grooves being composed of groove components in the circumferential direction, with the walls at the tread surface thereof being parallel to the circumferential direction of the tire, and inclined groove components with the walls of the tread surface thereof being inclined 30° to 90° to the circumferential direction of the tire, connecting said groove components in the circumferential direction, said inclined groove component walls at the tread surface increasing in length to become a single zigzag groove as the tread wears out. (2) A radial tire substantially as herein described with reference to Figure 3 of the accompanying drawings. 'ffpjmon & CAficY •TTQRNEYS FOR THE APPLICANTS