Tyre tread

Abstract: A tyre having a ground contacting tread comprising tread grooves which divide the tread into a plurality of tread pattern elements provided on its radially outer surface with a radially outwardly projecting ridge (5) disposed on an edge of the pattern element and at least one radially inwardly projecting small groove extending to the projecting ridge which facilitates the dispersal of trapped air in the moulding and vulcanisation operation of the tyre manufacturing process.

Description: This invention relates to tyres and particularly to aspects of the design of the tread region of the tyre which can facilitate dispersal of trapped air in the moulding and vulcanising operation of the tyre manufacturing process. A problem which commonly arises in the moulding of elastomeric articles such as tyres is the trapping of air between the surfaces of the article and the mould. Such trapped air prevents the elastomeric article from contacting the mould surface and thus locally reduces conductive heat transfer effecting the vulcanisation in an uncontrolled way and spoils the finished surface appearance. In the tyre art such resultant blemishes are termed "bareness". In tyres having block-type tread patterns, bareness on the top surface of the blocks can be a particular problem due to their relatively flat surface. To help prevent bareness on tyres, tyre moulds are commonly vented by means of holes of very small diameter provided through the mould wall. Such vent holes allow trapped air to escape but suffer the disadvantage that rubber can also flow into the hole resulting in bristle-like projections or 'spue-pips' covering the surface of the moulded tyre. Such spue-pips detract from the visual appearance of the tyre and are normally removed by rotating the tyre against a trimming knife held to the tyre surface. However such removal of spue-pips in the tyre tread region presents a particular problem because of the potential damage which can be done to the salient features of the tread pattern. It has also been proposed in DE-A-3709427 to provide on the radially outer surface of tread pattern elements a radially outwardly projecting ridge extending circumferentially of the tyre. Accordingly the present invention provides a tyre as set out in claim 1. Preferably a plurality of small grooves are provided. The combination of small grooves in the surface of a tread pattern element which communicate with a raised ridge on the edges of the element has proven effective in dispersing on moulding trapped air from the tread region without the need for venting. Preferably the surface of the pattern element is criss-crossed by a plurality of such intersecting small grooves. Sipes or knife-cuts may also be provided in the pattern element and may also be wholly contained within one or more of the small grooves. Further aspects of the present invention will become apparent from the following description by way of example only of one embodiment in conjunction with the following drawings in which: Figure 1 shows a scrap plan view of a tyre tread according to the invention; Figure 2 shows a partial radial cross-section through the tread of Figure 1 along the line X-X; Figure 3 shows further details of one of the tread blocks of the tyre tread of Figure 1;; Figure 4 shows a scrap radial cross-section of the tread block of Figure 3 taken along section A-A; and Figure 5 shows a scrap radial cross-section of the tread block of Figure 3 taken along section B-B. Shown in Figure 1 is a plan view of a block-type tyre tread pattern comprising pattern elements or blocks 1 defined by circumferential straight grooves 2 and axially extending straight grooves 3. As shown in Figures 3-5, each of the pattern elements 1 has on its radially outer surface a criss-cross pattern of radially inwardly extending small grooves 4 which extend to join or communicate with a radially outwardly projecting ridge 5 which extends on the outer surface of the block around the whole of the block edge. In this embodiment the criss-cross pattern of small grooves 4 comprises a first plurality of circumferentially extending grooves 4C and a second plurality of axially extending grooves 4A, each of the grooves 4C of the first plurality intersecting with each of those 4A of the second plurality. It can be clearly seen that each of the grooves 4C of the first plurality is parallel and equally spaced from adjacent grooves as are the axial grooves 4A of the second plurality. The grooves intersect at right angles. The width w and depth d of the small grooves is 0.7 mm. These dimension may lie in the range of 0.3-1.5 mm. Similarly the width wr and height hr of the ridge 5 are also 0.7 mm and again may lie in the range 0.3-1.5 mm. The cross-sectional shape of the small grooves 4 and the edge ridge 5 may take any form and is not restricted to the round bottomed and round topped sections shown. As also shown in Figures 3-5 the block may have a very narrow groove/knife cut 6 commonly known as a sipe. Such sipes may be provided as shown wholly within the narrow grooves 4 and extend radially inwards to a depth ds which may lie in the range of 50% to 95% of the full pattern depth PD. Whilst the above embodiment has the small groove criss-crossing the block surface in a regular pattern other configurations of a single or multiple groove communicating with a raised rib at the block edge are possible within the invention and will provide enhanced dispersion of trapped air in the moulding operation. For example the small grooves within a plurality may not be parallel or equi-spaced and the small grooves may intersect at different angles other than right angles.

Claims: A tyre having a ground contacting tread comprising tread grooves dividing the tread into a plurality of pattern elements (1) having edges wherein at least one pattern element (1) is provided on its radially outer surface with a radially outwardly projecting ridge (5) disposed on an edge of the pattern element (1) characterised in that the projecting ridge (5) is disposed on all edges of the pattern element and at least one radially inwardly projecting small groove (4) having a width and a depth in the range of 0.3 to 1.5 mm which extends to the projecting ridge (5). A tyre according to claim 1, characterised in that the pattern element (1) is provided with at least two such radially inwardly projecting small grooves (4A, 4C) . A tyre according to claim 2, characterised in that the pattern element (1) is provided with a first plurality (4A) of radially inwardly projecting small grooves each of which intersects with each of a second plurality (4C) of radially inwardly projecting small grooves. A tyre according to claim 3, characterised in that each of the small grooves of the first and second pluralities (4A,4C) of small grooves are mutually parallel. A tyre according to either of claims 3 or 4, characterised in that within the first and second pluralities of small grooves the small grooves are equi-spaced from adjacent grooves in that plurality. A tyre according to any of claims 2 to 5, characterised in that the small grooves intersect at a right angle. A tyre according to any of claims 1 to 6, characterised in that the small grooves have a width (w) in the range of 0.3 to 1.5 mm. A tyre according to any of claims 1 to 7, characterised in that the small grooves have a depth (d) in the range of 0.3 to 1.5 mm. A tyre according to any of claims 1 to 8, characterised in that the radially outwardly projecting ridge has a width (wr) in the range 0.3 to 1.5 mm. A tyre according to any of claims 1 to 9, characterised in that the radially outwardly projecting ridge has a height (hr) in the range 0.3 to 1.5 mm. A tyre according to any of claims 1 to 10, characterised in that the pattern element is a circumferentially extending rib. A tyre according to any of claims 1 to 10, characterised in that the pattern element is an axially extending rib. A tyre according to any of claims 1 to 10, characterised in that the pattern element is a block. A tyre according to any of claims 1 to 13, characterised in that the pattern element is further provided with at least one sipe (6). A tyre according to claim 14, characterised in that the sipe (6) is formed wholly within one or more of the small grooves (4).

Inventors: MARRIOTT PETER ROBERT, MARRIOTT, PETER ROBERT
Applicants: SUMITOMO RUBBER IND, SUMITOMO RUBBER INDUSTRIES LTD.
Application year: 1999
Main classification: B60C11
IPC codes: B60C11