NZ216077A

NZ216077A - Heavy vehicle radial tyre: shoulder tread outer half has less groove volume than inner half

Info

Publication number: NZ216077A
Application number: NZ21607786A
Authority: NZ
Inventors: Takeuchi Akihiro
Original assignee: Sumitomo Rubber Ind
Priority date: 1985-05-11
Filing date: 1986-05-07
Publication date: 1988-04-29
Also published as: DE3615666A1; AU591121B2; JPS61185601U; AU5720986A

Description

Pr.V : //- 5."S^T Cv:r.p!eto r-, -. ,• , : , 7:^"^ CUr*: ..^O^//^/ •" " P, - CH Date: 2 9APRW88.'] P.O. Jo .t:V»|. NO: 2 16077 jf€'M t! \ '7nAY»%6: V*L Patents Form No. 5 NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION "A RADIAL TIRE FOR TRUCKS OR BUSES" %/WE, SUMITOMO RUBBER INDUSTRIES, LTD., of 1-1, Tsutsuicho 1-chome, Chuo-ku, Kobe-shi, Hyogo-ken, Japan, a Japanese company hereby declare the invention, for which 3t/we pray that a patent may be granted to iW8</us, and the method by which it is to be performed, to be particularly described in and by the following statement:- _ 1 _ (followed by pag6 1 A.), 2 1 60 A RADIAL TIRE FOR TRUCKS OR BUSES BACKGROUND OF THE INVENTION The present invention relates to a radial tire for trucks or buses, Nhich can suppress the temperature rise at the both ends of the belt layer and can reduce the uneven wear of the tread.

Usually, the radial tire for trucks or buses has a belt layer consisting of four plies each containing steel cords arranged at a snail angle with respect to the circumferential direction of the tire and disposed outside the crown portion of the carcass, the carcass is constructed of steel cords arranged in the radial direction of the tire, with both ends thereof turned up around the bead core. In the tire of this structure, the ends of the belt layer are apt to separate fro* rubber due to incomplete adhesion between the steel cords and rubber. This separation damage is accelerated by tenperature rise caused by repeated deformation under high load traveling.

In a conventional practice to prevent this trouble, the tread shoulder portion has been provided with a number of grooves to increase the area of the tread surface and radiation of heat. This, however, considerably reduces the stiffness of the tread shoulder portion, resulting in uneven wear in this part.

BRIEF SUMMARY OF THE INVENTION It is an object of the present invention to provide a radial tire for trucks or buses which can prevent not only the separation damage at the ends of the belt layer but also uneven wear at the tread shoulder portion.

V'lShf>-;<rvr.' ^ _ 2 16077 BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a partial plan view showing the tread of the tire of this invention; Figs. 2(a), 2(b), and 2 (c) are partial sectional views showing the tread shoulder portion; and Fig. 3 is a graph showing the relation between running speed and tenperature rise at the tread shoulder portion.

DETAILED DESCRIPTION According to the present invention, there is provided a radial tire for trucks or buses, having a tread divided into two shoulder rib and one center rib by two nain longitudinal grooves each extending circunferentially at 15 to 40% distance of the tread width froa the tread edge, characterized in that the inner half portion of the said shoulder rib is provided with blocks in order that the groove volune (Va) in the outer half portion of the shoulder rib is equal to or saaller than the groove voluae (Vb) in the said inner half portion of the shoulder rib.

Description will be now directed to an eabodiaent of the invention with reference to the accompanying drawings.

In the figures, the tread is provided with two longitudinal main grooves (G1 and G2) running in the circumferential direction of the tire. The distance between the center line (gl, g2) of the longitudinal nain groove (Gl. G2) and the tread edge TE is set within a range from 15 to 40% of the tread width TW. The longitudinal main grooves (Gl and G2) divide the tread into the shoulder ribs (Rs and Rs) and the center rib Rc, and the center rib Rc has a central groove Rc along the equator C of the tire.

The above mentioned shoulder rib Rs is divided into the outer shoulder rib Rsl which is outer half portion of the 2 16077 shoulder rib Rs and the inner shoulder rib Rs2 which is inner half portion of the shoulder rib Rs by it's center line Dv.

Usually, in order to reduce the damage at the ends of the belt layer, it is necessary to increase the surface area of the tread shoulder portion and to increase the radiation of heat.

However, increasing the groove voluae to Beet this requireiient leads to a decrease in stiffness of the tread, which in turn causes severe uneven wear.

According to the present invention, the groove voluae Va in the outer shoulder rib Rsl where severe uneven wear takes place is saaller than the groove voluae Vb in the inner shoulder rib Rs2. This arrangeaent satisfies the contradictory requireaents, i.e., radiation of heat and resistance to uneven wear at the ends of the breaker.

In this invention. the above Mentioned the tread edge TE is defined as the nost acute inflection point of the contour of the shoulder portion as shown in Fig. 2 (a) to Fig. 2 (c).

EXAMPLE Three kinds of radial tires (size 10.00R20) for trucks or buses were produced in accordance with the tread pattern shown in Fig. 1, with the voluae of the groove (2) changed as following Table. They were examined for relationship between the running speed and temperature rise at the shoulder portion. The results are shown in Fig. 3. 2 160 Va aa3 Vb mm1 Exaaple 1 1980 2180 Control Exaaple 1 2200 0 Control Exaaple 2 1980 1800 As apparent froa Fig. 3, the tire of this invention is superior in heat radiation.

The tires were also exaained for uneven wear. The results are given below.

I ndex Exaaple 1 100 Control Exaaple 1 120 Control Exaaple 2 100 The greater the index, the aore inferior the uneven wear.

(Effect of the invention) As described above, according to the present invention, the groove voluae in the outer half portion of the shoulder rib is equal to or saaller than that in the inner half portion. This effectively increase heat radiation without causing uneven wear, as a result the damage at both ends of the belt layer is effectively reduced. 4

Claims

WHAT WE CLAIM IS:- 216077 (1) A radial tire for trucks or buses, having a tread divided into two shoulder ribs and one central rib by two longitudinal grooves each extending circumferentially within 15 to 40% distance of the tread width from the tread edge, characterized in that the shoulder ribs are divided into blocks by grooves wherein the groove volume (Va) in the outer half portion of each shoulder rib is smaller than the groove volume (Vb) in the inner half portion of each shoulder rib. (2) A radial tire substantially as hereindescribed with reference to Example 1 of the Table. (3) A radial tire substantially as hereindescribed with reference to Figures 1 and 2 of the accompanying drawings. SUMITOMO RUBBER INDUSTRIES, LTD By Their Attorneys BALDWIN, SON & CAREY