NZ215750A - Radial tyre: crown tread surface to groove wall area ratio small relative to shoulder tread ratio - Google Patents

Description

© 2 1 5750 © Priority Oate(s): . ./.Q .

Compla:o Specification Filed: Closs: . &6f?.Q(/?.{Aj.l.

Pub.-;r :.n 03-.c: 2 .9 APR 1988 * * * P.O. J. 'vc: Patents Form No. 5 NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION "A PNEUMATIC RADIAL TIRE OF IMPROVED DRIVING COMFORT FOR A HEAVY DUTY VEHICLE" •i/WE, SUMITOMO RUBBER INDUSTRIES, LTD. a Japanese company of 1-1 Tsutsuicho 1-chome, Chuo-ku, Kobe-shi, Hyogo-ken Japan hereby declare the invention, for which i/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 T A.} ssssfer ( 215750 / fl PNEUMATIC RADIAL TIRE OF IMPROVED DRIVING COMFORT FOR A HEAVY DUTY VEHICLE BACKGROUND OF THE INVENTION This invention relates to a pneumatic radial tire of improved driving comfort for a heavy duty vehicle, and can be applied in tires having such a type of tread pattern as a rib pattern, a block pattern, a block-rib pattern, a lug pattern and the like.

Generally, in a radial ply tire for heavy duty vehicles, a carcass ply is composed of at least one rubberized ply layer containing steel cords embedded therein and arranged at an angle o of 90 with respect to an equatorial line of the tire, and both ends of the said carcass ply are turned up around a pair of bead core, and a belt is superimposed about said carcass for stiff reinforcement beneath a tread and is composed of a plurality of rubberized ply layers each containing steel cords embedded therein. Such carcass construction can stand the severe traveling under high load. However, it is generally inferior in the driving comfort due to the said rigid belt construction.

On the other hand, with the development of the express highway networks and the arrangement and pavement of roads, necessity for long time driving in this type of vehicle is increasing, and requirements to alleviate the driver from fatigue by improving the driving comfort is increasing. What affects this ^ driving comfort includes the uniformity of tire and, in particular, RFV (radial force variation ). The waveform of this RFV generally well corresponds to RRO ( radial run out ), i.e., the variations of the tire surface in radial direction. This is 1 I 215750 shown in Fig .7, Therefore, attempts have been made to improve 1 the uniformity of the tire through the improvement of RRQ in the % v I past years, but this method is used to correct the uniformity by i cutting off the part of the tire, while it may possible that the complicated work results and adverse effect is given to other characteristics of the tire.

O BRIEF SUMMARY OF THE INVENTION An object of the present invention is to provide a radial tire of improved driving comfort for heavy duty vehicles by improving the uniformity of the tire by the betterment of tread patterns without being affected excessively by RRO.

BRIEF DESCRIPTION OF THE DRAWINGS Fig.l and Fig.6 are plan views showing the tread pattern according to the present invention: Fig.1(a) is a perspective view of the block shown in Fig.l; Fig.2 is a graph showing the shape coefficients at each section of the tread; Fig.3, 4 and 5 are plan views showing the tread patterns of comparative examples; Fig.7 is a graph showing the wave shapes of RFV and RRO; and Fig.8 is a graph showing the relation between RFV and RRO.

DETAILED DESCRIPTION The present invention relates to a pneumatic radial tire of improved driving comfort for a heavy duty vehicle, characterized in that a tread crown section having a width corresponding to about 20% to 35% of the distance between the right and left edges of the tread from the equatorial line of the tire has a shape 2 " vw.. 2157 coefficient, defined by a below equation, being small as compared to a shape coefficient of a shoulder section.

Loaded area (AL) Shape coefficient (F) = Free surface area (AF) where, Loaded area (AL) : Effective ground contact area.

Free surface area (AF): Total area of side wall of blocks or ribs.

An embodiment according to the present invention will be explained as follows with reference to the figures.

In the figures, the tread section is divided into the crown o section (CR) and the shoulder sections (SH) by a pair of longitudinal grooves (G1 and G2) extending in the circumferential direction of the tire and disposed at a position of about 30% of the distance between the right and left ends (TE and TE) of the tread from the equator plane (C). The crown section (CR) is provided with the narrow longitudinal grooves (gl and g2).

Between both narrow longitudinal grooves (gl and g2), and between the narrow longitudinal groove (gl, g2) and said longitudinal grooves (Gl, G2), the grooves are respectively connected by subgrooves (m, n), and blocks (A) of an approximate rhombic-form are formed on the crown section (CR). ^ The shoulder section (SH) is provided with wide transverse grooves (L) which connect the longitudinal grooves (Gl and G2) with the tread end section.

In the above mentioned tread pattern, the loaded areas (AL) of the crown sections (CR) is defined as a portion actually contacting the ground surface during driving, namely, the total surface area of the blocks (A), shown in Fig.1(a), included in one round of a tire. 2157 Likewise, the loaded area (AL) of the shoulder section (SH) are calculated in the same manner.

Fig.2 shows a graph of the shape coefficient (F) ( = AL/AF ) with respect to various tread patterns illustrated in Fig.l and Fig.3 - 6. In the figure, the shape coefficient (F) of the crown section (CR) of the embodiments 1 and 2 according to the present invention are almost constant and are about 50% of the shoulder section (SH).

The test tires of the embodiments 1 of the present invention, and the comparative example 1 and 2 were manufactured in the size 10.00 R20. The relation between RFV and RRO were 2 measured under the internal pressure of 7.25 kg/cm , the load of 2700 kg, and the graph shown in Fig. 8 was obtained. As a result, the value of RFV/RRO of the comparative example is about 80 kg/mm, while that of the embodiment is about 60 kg/mm. This means that the embodiment of the present invention has large RRO but the effect of RFV, i.e., the performance of the driving comfort is small.

(Effect of the Invention) As described above, because the shape coefficients of the crown section and shoulder section of the tread are set in the specified range, the effect of RFV, i.e., the effect of RRO on the performance of the driving comfort is alleviated, and it is possible to improve the performance of the driving comfort. 4 0

Claims (6)

WHAT WE CLAIM IS: SI5750

1. A pneumatic radial tire for heavy duty vehicles, comprising a tread provided with plural tread elements defining a tread pattern thereon so that each of a crown section and two shoulder sections thereof is provided with at least one tread element, wherein said crown section is defined between boundaries at 20 to 35% of the overall width of the tread from the equatorial line of the tire and said shoulder sections are defined as the remaining portions of the tread, characterized in that a shape coefficient of the or each element in the crown section is smaller than a shape coefficient of the or each element in each shoulder section, wherein Shape coefficient = Loaded area Free area Ground contacting area of tread element Total area of side walls of tread element

2. A pneumatic radial tire according to claim 1 wherein the crown section is provided with plural tread elements which are arranged in the circumferential direction of the tire and are substantially constant in shape coefficient.

3. A pneumatic radial tire according to claim 1, wherein the or each shape coefficient in the crown section is in the range of 303 to 70% of the or each ^khape coefficient in the shoulder sections.

4. A pneumatic radial tire according to claim 1, - 5 - o 1 r; k r« V 1 t) I w wherein the or each shape coefficient in the crown section is less than 0.

5.

3. A pneumatic radial tire according to claim 1, wherein the tread is reinforced by a belt disposed between the tread and a radial tire carcass.

6. A radial tire substantially as herein described with reference to Figures 1 and 1 (a) or Figure 6 of the accompanying drawings. SUMITOMO RUBBER INDUSTRIES, LTD leys CAREY ~L .Vv^ i' 1 1983 i