PNEUMATIC RADIAL TYRE

Abstract: A pneumatic radial tyre for trucks or buses which is resis­ tant to stone trapping comprises a tread having in its central part a central zig-zag longitudinal groove (G1) extending con­ tinuously in the circumferential direction of the tvre and pro­ viding in the sidewall of the groove (G1) points at which the sidewall changes direction characterised by a plurality of plat­ forms (P) formed one at each point (E) of change of direction and protruding from the sidewalls of the central longitudinal groove (G1), the depth (L4) of the platforms (P) from the tread surface to the platform (P) being in the range of 40 to 80% of the depth (L5) of the central longitudinal grooves (G1), the circumferential length (L2) of the platform (P) being in the range of 15 to 40% of the zigzag pitch (L1) of the central longitudinal groove (G1) and the width (L6) of the platforms (P) being in the ranges to 20% of the width (L3) of the central longitudinal groove (G1). The tyre may also have side zigzag grooves in which similar platforms (Q) are provided.

Description: This invention relates to a pneumatic radial tyre and more particularly to a pneumatic radial tyre for trucks or buses. In such tyres, stone entrapment in the tread grooves is liable to occur under dirt running. If the tyre runs continuously with entrapped stones, the stones often inflict cracks and other injuries to the tread. Stone trapping in the tyre tread under dirt road running is known to occur most in the zigzag longitudinal groove extending along the central part of the tread in the circumferential direction of the tyre and the frequency of stone trapping is particular high in the zigzag edge portions. This may be logically explained by a postulate that the stone is forced toward the direction of the tyre rotation owing to the friction of the stone with road surface, and this movement of the stone is stopped at the zigzag edge portion, accordingly the stone is trapped in the zigzag edge portion. As a countermeasure for this problem there have been attempts to widen the tread groove or, as exemplified in EP-A-0069464 which corresponds to the preamble of claim 1, to give a staircase-form to the tread groove walls in order to prevent the tread grooves from stone trapping and to cause any trapped stones to be ejected from the tread groove. Previous attempts, however, have the disadvantage that wear resistance is sacrificed and the wet grip property is reduced because of the tread grooves gradually decreasing in width as the tread wears down. An object of the present invention is to provide a pneumatic radial tyre in which stone entrapment in the tread grooves is suppressed without sacrifice of wet grip and wear resistance. This object is achieved by the features of claim 1. The tyre may also have lateral grooves extending from the projecting points of the sidewalls of the central groove to the projecting points of the sidewalls or the side grooves. Further aspects of the present invention will be apparent from the following description, by way of example only, of one embodiment in conjunction with the attached diagrammatic drawings in which:- Fig.1. is a plan view of the tread portion of a tyre according to the present invention: Fig.2. is a cross sectional view taken along the A-A line of Fig.1. and Fig.3. is a cross sectional view taken along the B-B line of Fig.1. The tread shown comprises a zigzag longitudinal groove G1 extending in the circumferential direction of the tyre along the equatorial plane C thereof. Two zigzag side longitudinal grooves G2 and G3 are disposed one on either side of the central longitudinal groove G1. The side grooves G2 and G3 also extend in the circumferential direction of the tyre similarly to the central groove G1. The central groove G1 and side grooves G2 and G3 are interconnected by spaced apart laterally extending grooves g. A plurality of first platforms P are formed at the points E where the sidewalls of the zigzag groove G1 change direction. The platforms P are of specified dimensions and are formed only on the zigzag edge portions (re-entrant points E), where the tread enters the groove G₁. The depth L4 of the first platforms P from the tread surface to the platforms P is in the range of 40 to 80% of the depth L5 of the central longitudinal groove G1, and the length L2 of the platforms P in the circumferential direction of the tyre is in the range of 15 to 40% of the zigzag pitch L1 of the central longitudinal groove G1. Furthermore the width L6 of the platforms P is in the range of 5 to 20% of the width L3 of the central longitudinal groove G1. These combinations of dimensions provide the resistance to stone trapping in the centre groove G1. The side grooves G2 and G3 have second platforms Q formed intermittently on the zigzag edge portions of the sidewalls. These platforms Q are at the projecting points extending into the adjacent tread, where the sidewalls forms an obtuse angle and thus alternately appear on the opposite sides of the sidewalls. This construction aims at preventing the side longitudinal grooves from stone trapping and maintaining wet grip property at the same time. The second platforms Q may be similar to the first platforms P. This invention can be applied effectively to all types of tread patterns, for example, rib pattern, rib block pattern, rib-lug pattern and the like, wherever there is a central longitudinal groove extending along the equatorial plane C of the tyre.

Claims: A pneumatic radial tyre, comprising a tread provided in its central part (with a plurality of zigzag longitudinal grooves (G₁,G₂,G₃) continuously in the circumferential direction of the tyre and provided with platforms (P,Q) protruding from the sidewalls thereof, the opposed sidewalls having projecting points, which extend into the adjacent tyre tread and re-entrant points (E), said longitudinal grooves including a first groove (G₁) provided with a plurality of first platforms (P) of uniform width (L6) located at points (E) at which the first groove (G1) changes direction, the depth (L4) of the first platforms (P) from the tread surface to the first platforms (P) being in the range of 40 to 80% of the depth (L5) of the first longitudinal grooves, characterized in that said first groove is a central groove (G1) extending along the tyre equator (C), two side grooves (G2, G3) are located one on each side of the central groove (G1), said central groove (G1) and said side grooves (G2, G3) are interconnected by lateral grooves (g), said first platforms (P) are disposed only at said re-entrant points (E) of the groove sidewalls, said first platforms (P) are circumferentially spaced separate platforms of uniform height, the circumferential length (L2) of the first platforms (P) are in the range of 15 to 40% of the zig zag Pitch (L1) of the central groove (G1), the width (L6) of the first platforms (P) are in the range of 5 to 20% of the width (L3) of the central groove (G1), each of said side grooves (G2, G3) is provided with a plurality of circumferentially spaced second platforms (Q) located one at each point at which the side groove (G2, G3) changes direction, but only at the projecting points, which extend into the adjacent tyre tread. A radial tyre according to claim 1 wherein the lateral grooves (g) extend from the projecting points of the sidewalls of the central groove (G1) to the projecting points of the sidewalls of the side grooves (G2, G3).

Inventors: KOYAMA, TOSHIO, TAKEUCHI, AKIHIRO
Applicants: SUMITOMO RUBBER INDUSTRIES LIMITED
Application year: 1986
Main classification: B60C11
IPC codes: B60C11, B29D30