GB2329161A

GB2329161A - Vehicle tyre treads

Info

Publication number: GB2329161A
Application number: GB9719440A
Authority: GB
Inventors: Peter Robert Marriott
Original assignee: Sumitomo Rubber Industries Ltd
Current assignee: Sumitomo Rubber Industries Ltd
Priority date: 1997-09-13
Filing date: 1997-09-13
Publication date: 1999-03-17
Also published as: GB9719440D0

Abstract

In a tyre for generating reduced noise a ground contacting tyre tread has at least one circumferentially extending tread groove, the tread groove being defined by opposing groove sidewalls (3,4) extending radially inwardly from the tread surface to the groove base (9), characterised by a groove base extension (5) formed in one groove sidewall (3) at the groove base and extending axially outwardly of the groove. The groove may have groove base extensions provided alternately in opposing groove sidewalls.

Description

IMPROVEMENTS TO VEHICLE TYRES This invention relates to a vehicle tyre having a ground contacting tread which is particularly adapted to be quiet in running without impairing performance in wet conditions.

The problem of tyre generated noise is the subject of increasingly stricter legislation concerned with reducing overall noise levels generated by moving vehicles. Thus the problem of minimising tyre generated or so-called "pass-by" noise is becoming an increasingly important aspect of tyre design.

In order for tyres to perform well under all conditions it is normal for the ground contacting tread region to be provided with grooves. In wet conditions such grooves assist in clearing bulk water from the contact area between the tyre tread and the road surface and thus help prevent aquaplaning and therefore prevent loss of steering control of the vehicle.

Conventional tyre tread pattern design for good wet performance has employed circumferentially continuous grooves which are often relatively wide and deep. However a serious problem with such continuous grooves running in dry conditions is noise generated by the so-called "organ-pipe phenomenon" by which resonance occurs in the airspace formed by the groove of the moving tyre and the road surface which acts like a musical pipe.

The particular problem with continuous circumferential grooves is that the length of the organ-pipe' in the tyre contact area is sufficiently great to generate frequencies which are close to those most troublesome to a driver and which also tend to reinforce other resonances occurring between the tyre and the road surface.

In previous attempts to reduce the organ-pipe' phenomenon, protuberances or constrictions have been placed in the circumferential grooves in order to suppress or disturb the resonance. Such groove modifications have not only failed to mitigate the tyre noise problem but have also shown a detrimental effect on the wet performance of the tyre by impeding the flow of water through the grooves.

Accordingly it is an object of the present invention to overcome the above-mentioned problems and provide a tyre having a low noise tread pattern without impaired wet performance.

According to one aspect of the present invention a tyre having a ground contacting tyre tread has at least one circumferentially extending tread groove, the tread groove being defined by opposing groove sidewalls extending radially inwardly from the tread surface to the groove bottom, wherein a groove base extension is formed in one groove sidewall at the groove bottom and extends axially outwardly of the groove.

Further aspect of the invention will become apparent from the following description by way of example only of embodiments of the invention in conjunction with the following drawings, in which: Figure 1 shows a plan view of a single tread groove according to the invention; Figure 2 shows a section taken along AA in Figure 1; Figure 3 shows a section taken along BB in Figure 1; Figure 4 shows a section taken along CC in Figure 1; Figure 5 shows a plan view of a second tread groove according to the invention; Figure 6 shows a section taken along A'A' in Figure 5; Figure 7 shows a section taken along B'B' in Figure 5; and Figure 8 shows a cross-section of another tread groove according to the invention.

Shown in Figures 1, 2, 3 and 4 is a portion of a first U'-shaped tread groove 1 according to the invention. The groove is defined by two opposing parallel radially extending groove sidewalls 3 and 4 and a groove base or bottom 9. The groove sidewalls are provided, in adjacent repeating pattern elements or pitches P1 and P2, with groove bottom or base extension 5 and 6 respectively. Thus groove base extensions 5,6 are provided one per pitch on alternate opposing groove sidewalls around the circumference of the tread.

The groove base extensions 5,6 extend outward axially of their respective sidewall by a distance EGW of less than 50% of the maximum width W of the circumferential groove 1. The radial height d of the groove base extension is also less then 50% of the depth D of the circumferential groove.

Preferably the axial width EGW and the radial height d of the groove base extensions are less than 40% of the respective width W and depth D of the circumferential groove.

As shown in Figure 1 the groove base extensions may be formed having their axial width EGW increasing progressively to each a maximum in the central region of the pitch P1,P2 and thus to either circumferential side of the central region the axial width may progressively taper to zero as indicated by the broken lines 7 and 8, and shown in Figure 4.

In a second embodiment of the invention shown in Figures 5-7, a circumferentially extending U'- shaped groove 10 is provided with two groove base extensions 11,12 per pitch P1,P2 of the tread pattern. The groove base extensions in this embodiment have a generally round cross-sectional shape as shown in Figure 7 and extend axially outwardly of the groove lo normally to the groove sidewall for a distance of less than 50% of the groove width. Similarly to the previous embodiment the radial height d of the groove base extension 11,12 is less than 50%, and preferably less than 40%, of the radial depth D of the circumferential groove 10.

However in this second embodiment the groove base extension 11,12 is opened to the tread surface 14 by means of a narrow groove 13. The width NW of the narrow groove 13 is small in comparison to the dimension of the groove base extension and small compared to the width of the circumferential groove such that when the narrow groove enters the contact region between the tyre and the road surface the narrow groove closes. For example where a circumferential groove 10 of 8 mm width is provided a suitable width NW for the narrow groove 13 would be 1 mm. Preferably the width NW of the narrow groove is between 5 and 15% of the width W of the circumferential groove.

Whilst both of the above described embodiments have U'-shaped circumferential grooves the groove base extensions of the present invention may be applied to other shaped grooves such as a V'-shaped groove shown in Figure 8. In the case of a V'-shaped groove the axial width EGW of the groove base extension is preferably less than 50% and more preferably less than 40% of the maximum groove width W which is at the tread surface. Accordingly dependent on the inclination of the groove sidewalls 32,33 the groove base extension may or may not extend axially beyond the radial projection of a point P at the intersection of the groove sidewall 32 with the tread surface 31 which projection is indicated by the broken line in Figure 8.

Thus the provision of a groove base extension in accordance with the invention introduces an intermittent increase in the volume of the circumferential groove around the tyre tread periphery and thus disturbs the air resonance to reduce the organ-pipe effect without impeding the water clearance through the groove. In fact the invention has shown to improve water clearance due to the increased groove volume. Accordingly tyre noise is reduced without impairing wet performance.

Claims

1. A tyre having a ground contacting tyre tread having at least one circumferentially extending tread groove, the tread groove being defined by opposing groove sidewalls extending radially inwardly from the tread surface to the groove base, characterised by a groove base extension formed in one groove sidewall at the groove base and extending axially outwardly of the groove.

2. A tyre according to claim 1, characterised in that groove base extensions are formed in the opposing groove sidewalls.

3. A tyre according to claim 2, characterised in that in the tread groove circumferential direction the groove base extensions are provided alternately on opposing groove sidewalls.

4. A tyre according to any of claims 1 to 3, characterised in that the tread groove sidewall extend radially and axially inwardly to define a V' -shaped groove.

5. A tyre according to claim 4, characterised in that the groove bottom extensions extend axially outwardly of the groove bottom beyond the radial inward projection of the point P of intersection of the groove sidewall and the tread surface.

6. A tyre according to any of claims 1 to 5, characterised in that the axial width EGW of the groove bottom extension is less than 50% of the axial width W of the circumferential groove.

7. A tyre according to any of claims 1 to 5, characterised in that the groove bottom extensions are connected to the tread surface by grooves having a width NW smaller than the width W of the circumferentially extending tread groove.

8. A tyre in accordance with claim 7, characterised in that the width NW of the groove is between 5 and 15% of the width W of the circumferentially extending grooves.

9. A tyre in accordance with any of claims 1 to 8, characterised in that the tyre tread is divided circumferentially into a plurality of repeated pattern elements or pitches and each pattern element or pitch is provided with at least one groove bottom extension.

10. A tyre in accordance with any one of claims 1 to 9, characterised in that the circumferentially extending groove is a straight groove.