GB2326386A - Tyre treads - Google Patents

Abstract

A tyre, particularly a truck tyre, has each of its main tread grooves GM1 - GM3 provided with an extension GE1 - GE3 radially inward of the main groove. The groove extension preferably has a maximum width between 50 and 95% of the width of the radially inner end of the main groove. The groove extensions may have stone ejectors (6, Figs 5, 6) in the form of discrete radially outwardly extending protrusions. Provision of such groove extensions avoids problems associated with regrooving partially worn truck tyres.

Description

IMPROVEMENTS TO TYRES The present invention relates to improvements to the ground contacting tread region of tyres and particularly but not exclusively to heavy duty tyres such as may be used on trucks or buses.

Truck tyre treads may be provided with circumferentially extending grooves defining tread ribs for steer axle applications, or further having axially extending grooves to divide such ribs into rows of blocks for drive axle applications. Tyres for on/off road special use may have a combination of both ribs and blocks in a so-called rib-lug configuration.

The new pattern depth of the tread grooves of such tyres varies depending both on the required rib or block stiffness for the type of application and the tyre manufacturer. However heavy duty tyres from many manufacturers are provided with sufficient thickness of tread rubber between the bottom of the original moulded tyre pattern and the top of the tread reinforcing belt or breaker to permit further rubber to be removed from the bottom of the grooves in the tread. Thus the practice of regrooving truck and bus tyres in the later part of tread life is well established.

Accordingly most heavy duty tyres are marked "Regroovable" and many manufacturers provide schedules indicating when regrooving should be carried out according to the remaining pattern depth, the maximum thickness of rubber which can safely be removed and a recommended regrooving pattern which normally corresponds closely to the original moulded pattern. Thus regrooving provides the tyre user with a valuable opportunity to extend the useful safe working life of a truck or bus tyre.

However certain problems with regrooving remain.

Initially it is necessary to check regularly the remaining pattern depth in order that the tyre be regrooved at the recommended time. This decision may be further complicated if the tread has been subject to irregular wear of any sort. Once it has been decided to regroove, the tyre must be removed from the vehicle, during which time the use of the vehicle is of course lost.

Finally the regrooving operation itself must be carried out with great care and in strict accordance with the manufacturer's instructions in order to ensure that a sufficient thickness of rubber is left over the belt or breaker. Removal of too much rubber which is particularly apt to occur when the tyre bead is irregularly worn or actual exposure of the belt or breaker fabric may result in failure of the tyre in subsequent use.

Accordingly it is an object of the present invention to provide a tyre which avoids the above-mentioned problems associated with regrooving.

According to the present invention there is provided a tyre having a ground contacting tread region having at least one main tread groove, wherein the main tread groove has a separate groove extension extending radially inward of the main groove and distinct from the main groove the groove extension having substantially constant depth.

By the main groove extension being distinct from the main groove is meant that the groove extension is clearly delineated or distinguishable from the main groove.

The main groove may also have a substantially constant depth.

Further the cross-sectional centrelines of the main groove and the groove extension may be coincident.

Preferably the width of the groove extension is between 50% and 90% of the width of the radially inward end of the main groove and its depth is preferably between 15% and 30% of the main groove depth.

Further aspects of the invention will become apparent from the following description by way of example only of one embodiment in conjunction with the following schematic diagrams in which: Figure 1 shows a portion of the tread of a tyre according to the present invention; and Figure 2 is a cross-section view taken along A A' in Figure 1; Figures 3 and 4 show other embodiments of the invention; Figure 5 shows an embodiment of the invention having stone ejectors; and Figure 6 is a cross-sectional view of the groove of Figure 5 taken along C-C' Shown in Figures 1 and 2 are details of a portion of a 275/70R22.5 truck tyre according to the present invention. The tread is provided with three main grooves GM1-GM3 which extend in a zig-zag manner circumferentially around the tyre to divide the tread into four ribs.

Each of the main groove has a common truncated Vshaped cross-section with a maximum depth DG of 14 mm and a maximum width WGT at the tread surface of also 14 mm. Both the maximum depth DG and the width WGT are constant around the entire circumference of the tread.

Each of the main groove GMl-GM3 is further provided with a groove extension GE1-GE3 respectively disposed radially inwardly of the bottom 2 of the main groove. The groove extension has a truncated V-shaped cross-section similar to the main groove and is located centrally with respect to it, i.e.

the radial centreline of the groove extension is coincident with the radial centreline GCL of the main groove and the width LW of the ledge 2 is the same on both sides of the groove extension.

The maximum width WE of the groove extension is less than the width WEB of the bottom of the main groove.

Preferably the maximum width WE of the groove extension is between 50% and 95% of the width of the bottom of the main groove, in this embodiment it is 78% of the width WGB. The maximum width WE of one groove extension may vary between 50% and 95% around the circumference of the tread.

The groove extensions GE1-GE3 are distinct from their respective main grooves by virtue of the portion 2 of the main groove bottom lying between and forming a ledge connecting the main groove sidewall 3 and the groove extension sidewall 4.

Thus according to the present invention the groove extension is distinguishable from the main groove by means of the ledge portion 2 of the bottom of the main groove separating them. Such a separating ledge is provided on both sides of the groove extension. The junctions of all of the abovementioned elements may, as shown, be radiused as is common in the art.

The maximum depth of the groove extension DE, measured between the portion 2 of the main groove bottom and the bottom of the groove extension, preferably lies in the range of 15% to 30% of the depth DG of the main groove. In this embodiment the maximum depth of the groove extension is 3.3 mm, i.e. 23.5% of the main groove depth.

In the above embodiment the grooye extension is disposed centrally with respect to the main groove so that they both follow exactly the same path around the tyre. However the groove extension may be arranged non-centrally so that it follows a different path. Figures 3 and 4 illustrate just two examples wherein the groove extension follows zigzag paths having respectively lesser and greater axial pitch displacements than their corresponding main groove.

The groove extensions whilst having substantially constant depth may be provided with such features such as raised rubber platforms acting as tread wear indicators or means for discouraging the trapping of small stones.

In an embodiment of the invention shown in Figures 5 and 6 the groove extensions are provided with stone ejectors 6 in the form of protrusions preferably having a part-spherical shape provided on the groove extension bottom 5. In a preferred embodiment these protrusions 6 have as shown a hemi-spherical shape disposed centrally with respect to the groove extension longitudinal and axial centrelines. In this embodiment the hemispheres have a radius of 2 mm.

Preferably the stone ejectors protrude to a height PH above the groove extension bottom of between 40% and 70%, most preferably 60%, of the depth DE of the groove extension. Also preferably the width PW of the protrusions, measured axially across the groove, is greater than 40% and most preferably is 60% of the width BW of the bottom of the groove extensions.

Preferably the stone ejectors 6 occupy a total volume of between 5 and 15%, most preferably 7.5% of the total volume of the groove extension.

According to the above invention there is provided a tyre having all the advantages of a regroovable tyre but which avoids the aforementioned problems associated with this practice.

Claims (15)

1. A tyre having a ground contacting tread region having at least one main tread groove (GM1-GM3), wherein the main tread groove (GM1-GM3) has a separate groove extension (GEl-. GE3) extending radially inward of the main groove and distinct from the main groove, the groove extension having substantially constant depth.

2. A tyre according to claim 1, wherein the main groove has substantially constant depth.

3. A tyre according either of claims 1 or 2, wherein the maximum width (WE) of the groove extension is at least 50% of the width (WG) of the radially inward end of the main groove.

4. A tyre in accordance with claim 3, wherein the maximum width (WE) of the groove extension is less than 95% of the width (WG) radially inward end of the main groove.

5. A tyre in accordance with any of claims 1 to 4, wherein the depth (DE) of the groove extension (GE1 GE3) is between 15% and 30% of the depth (DG) of the main groove (GM1-GM3).

6. A tyre according to either of claims 1 to 2, wherein the radially extending cross-sectional centreline (GCL) of the groove extension is coincident with that of the main groove.

7. A tyre according to any of claims 1 to 6, wherein the bottom of the groove extension (GE1-GE3) is provided with a plurality of discrete radially outwardly extending protrusions.

8. A tyre according to claim 7, wherein the protrusions have a part-spherical surface.

9. A tyre according to claim 8, wherein the protrusions have a hemi-spherical shape.

10. A tyre according to any of claims 7 to 9, wherein the protrusions extend from the bottom of the groove extension to a maximum height (PH) of between 40% and 70% of the depth (DE) of the groove extension.

11. A tyre in accordance with claim 10, wherein the protrusions extend to a maximum height of 60% of the depth (DE) of the groove extension.

12. A tyre according to any of claims 7 to 11, wherein the protrusions have a width (PW) in axial cross-section of the groove extension of greater than 40% of the width (BW) of the bottom of the groove extension.

13. A tyre according to claim 12, wherein the width of the protrusions is 50% of the width of the bottom groove extension.

14. A tyre according to any of claims 7 to 13, wherein the plurality of protrusions occupy a volume of between 5 and 15% of the total volume of the groove extension.

15. A tyre according to claim 14, wherein the protrusions occupy a volume of 7;51f; of the total volume of the groove extension.