GB2349366A - Tyre tread - Google Patents

Abstract

The tread comprises a block pattern having a circumferentially extending row of tread blocks (1) aligned substantially along the tyre circumferential centreline (C) to provide a central row of blocks, each central tread block (1) being defined on its axial left and right sides by circumferentially extending left-side and right-side grooves (LG,RG), characterised in that the depth profiles of the left-side and right-side grooves (LG,RG) are different.

Description

TYRE TREAD This invention relates to a tyre tread for a pneumatic tyre and particularly but not exclusively to a tread pattern for winter performance.

Tyres designed for winter performance commonly employ block-type tread patterns in which the block edges, particularly axially extending edges, contribute greatly to the transmission of tractive forces.

However the use of a block pattern, particularly in the centre of the tread, can lead to a reduction in the steering characteristics of the tyre.

It is therefore an object of the present invention to provide a tyre tread having good winter performance and good steering characteristics.

According to the invention a tyre tread comprises a block pattern having a circumferentially extending row of tread blocks aligned substantially along the tyre circumferential centreline to provide a central row of blocks, each central tread block being defined on its axial left and right sides by circumferentially extending left-side and right-side grooves, characterised in that the depth profiles of the left-side and right-side grooves are different.

By depth profile of the left-side groove and the right-side groove is meant the distribution or variation in depth along the longitudinal length of the groove, the depth of the groove at any point being the radial distance from the bottom of the groove to the tread surface.

Preferably the depth profiles of circumferentially adjacent left-side and right-side grooves of a circumferentially adjacent central tread block are the same as the depth profiles of respectively the right-side and left-side grooves such that the depth profile of alternate left-side groove and alternate right-side grooves are the same and those of adjacent left-side grooves and right-side grooves are different.

The depth profile may take the form of a reducing depth in the manner of a ramp over part or whole of the length or may take the form of a portion of full depth and a remaining portion of reduced constant depth.

Most preferably however the depth profile takes the form of a constant reduced depth over substantially the whole length of the groove and different constant reduced depth of left-side and right-side 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 is a schematic plan view of a tyre tread according to the invention; Figure 2 is a schematic sectional view taken along the lines A-A and D-D in Figure 1, Figure 3 is a schematic sectional view taken along the lines B-B and C-C in Figure 1; Figure 4 is a schematic section view taken along lines E-E and G-G in Figure 1; Figure 5 is a schematic section view taken along lines D-D and H-H in Figure 1; and Figures 6-9 show alternative groove depth profiles for left-side and right-side grooves in accordance with the invention.

Shown in Figure 1 is a plan view of a tyre tread of the invention.

The tread is a block-type winter tread pattern having a circumferentially extending row of tread blocks 1 disposed substantially along the tyre circumferential centreline C.

Each of the centre tread blocks 1 is defined by and delimited from axially adjacent tread blocks 2 by substantially circumferentially extending left-side grooves LG and right-side groove RG.

As can be seen alternate central tread blocks 1 have a substantially similar configuration whilst adjacent blocks have a mirror image relationship being lateral inversions of each other.

The remaining features of the tread pattern are seen to be symmetrical about the tread centreline C such that the overall pattern is directional having curved full-depth axial grooves AG configured in the form of a'V'-shape as seen in plan view.

Turning to the circumferentially extending grooves delimiting the central tread blocks.

Considering a first central tread block CB1, this is delimited from axially adjacent blocks by a leftside groove LG1 and a right-side groove RG1. Both of these grooves have a groove depth profile which is a constant reduced depth compared to the normal full pattern groove depth over the remainder of the tyre over the whole of their longitudinal length. Details of the groove shapes and groove depth profiles are presented in Figures 2-5.

Thus as shown in Figure 2, the left-side groove LG1 has a generally flat-bottomed'V'-shaped symmetrical profile perpendicularly across its width, with a depth ds equal to 50% of the full pattern depth D of the axial grooves AG. Since the full pattern depth D of this tyre is 10 mm the depth ds is 5 mm. As shown in Figure 4 the reduced depth ds is constant and extends substantially along the entire longitudinal length of the groove LG1 except for the ends where it is radius-blended with the full depth axial grooves AG.

The right-side groove RG1 as shown in Figures 3 and 5 has a similar shape and configuration to the leftside groove LG1 except that it has a greater depth dl then the depth ds. The depth dl of the groove RG1 is 70% of the full groove depth D of the axial grooves AG, thus in this embodiment dl is 7 mm..

Turning now to a circumferentially adjacent central block CB2. This is similarly delimited by a leftside groove LG2 and a right-side groove RG2.

However differently to the previous grooves LG1 and RG1, the groove depth profile of groove LG2 is as shown in Figures 3 and 5 whilst that of RG2 is as shown in Figures 2 and 4. Thus LG2 has the larger depth dl whilst the right-side groove RG2 has the smaller depth ds.

This configuration of the circumferential grooves defining the axial sides of the central blocks having reduced depth ensures that the central blocks have increased buttressing and therefore increased stability. Accordingly whilst both central blocks CB1 and CB2 have differential axial buttressing to the same degree, the buttressing is identical on alternate central blocks and reversed in adjacent blocks.

To illustrate the advantages of the present invention example tyres EX of size 195/65R15 having the previously discussed tread pattern of Figure 1 were tested in comparison to similar reference tyres REF wherein the left and right axial side grooves were both full depth at 10 mm.

The two sets of tyres were tested under the same conditions for steering/handling at sub-zero temperatures on both a dry road surface and a snow covered road surface and also tested for winter traction on a snow covered hill-climb track.

The steering/handling results on the dry and snowy road surfaces are shown in Tables 1 and 2 respectively whilst the traction results are shown in Table 3.

The results in Tables 1 and 2 are shown as in index from 1 to 10, and those of Table 3 as an index from 100 upwards, a higher figure representing a better performance.

TABLE 1

Example Reference Steering straight Response 7.5 6+ Feel 6.5 6.5 Progression 6.5 6 Power ON/OFF Straight 8 8 Stability Straight 7+ 7 Ridging 7.5 7.5 Transient 7-6. 5 Overall 7 6.5 Road conditions: Dry Temperature: 10 C TABLE 2

Example Reference Steering : straight Response 7 6+ Precision 7-6 Feel 7. 5 7+ Progression 7+ 7 Steering : curves Precision 7+ 7 Lateral Grip 8-8 Stability Curves 7+ 7+ Transient FT 7+ 7 Braking/Accel 7+ 7 Handling On Ice 7 7 On Loose Snow 7 7 Overall 7+ 7- ~ Road Conditions: Loose snow, packed snow, ice Temperature: Air :-4 C Snow :-2 C TABLE 3

Example 100 Reference 101 Conditions : Air temp-3 C Snow temp-2 C The test results shown in Tables 1-3 show that the overall steering and handling properties of the tyres of the invention were superior to those of the reference tyres whilst the winter traction properties of the two tyres were comparable.

Other depth distributions or variations in groove depths along the length of the right-and left-side grooves are possible in accordance with the invention.

For example the groove depth profile of the leftand right-side grooves may also take the form of a ramp 15,16 over a portion LR or the whole of the groove longitudinal length L as shown in Figure 6 and 7 respectively. Alternatively it may take the form of two or more portions of constant depth 17,18 connected by either a ramp 19 as shown in Figure 8 or a step in the form of a radially extending face 20 as shown in Figure 9. The ramps 15,16 and 19 shown in Figures 6,7 and 8 may comprise curved surfaces as alternatives to the plane or flat surfaces shown.

Whilst the cross-sectional shape of the left-side and right-side grooves has been described as flat bottomed'U'or'V', any shape of groove crosssection common-in-art may be used. The cross sectional shape may of course also vary along the longitudinal length of the side grooves.

Accordingly the present invention provides a tyre having good counter performance and good steering characteristics.

Claims (12)

1. CLAIMS 1. A tyre tread comprising a block pattern having a circumferentially extending row of tread blocks aligned substantially along the tyre circumferential centreline to provide a central row of blocks, each central tread block being defined on its axial left and right sides by circumferentially extending leftside and right-side grooves, characterised in that the depth profiles of the left-side and right-side grooves are different.
2. 2. A tyre tread according to claim 1, characterised in that the depth profiles of circumferentially adjacent left-side and right-side grooves of a circumferentially adjacent central tread block are the same depth profiles at respectively the right-side and left-side grooves such that the depth profile of alternate left-side groove and alternate right-side grooves are the same and those of adjacent left-side grooves and rightside grooves are different.
3. 3. A tyre tread according to either of claims 1 or 2, characterised in that the depth profile of the left-side grooves is such that at least a portion of the groove length has a reduced groove depth.
4. 4. A tyre tread according to either of claims 1 or 2, characterised in that the depth profile of the right-side groove is such that at least a portion of the groove length has a reduced groove depth.
5. 5. A tyre tread according to either of claims 3 or 4, characterised in that the portion of reduced groove depth has a constant groove depth.
6. 6. A tyre tread according to claim 5, characterised in that the portions of constant reduced groove depth of the left-side and right-side grooves have different reduced groove depths.
7. 7. A tyre tread according to claim 5 or 6, characterised in that the portions of reduced depth of the left-side and right-side grooves are different lengths of the groove.
8. 8. A tyre tread according to claim 6, characterised in that the left-side and right-side grooves have different constant depths over their whole length.
9. 9. A tyre according to any of claims 1 to 4 wherein the depth profile of the left-side groove and/or the right-side groove comprises a ramped portion.
10. 10. A tyre according to claims 1 to 4 wherein the depth profile of the left-side groove and/or the right-side groove comprises two or more portions of constant depth.
11. 11. A tyre according to claim 10 wherein at least two groove portions of constant depth are connected by a ramped portion (19).
12. 12. A tyre according to claim 10 or 11 wherein at least two groove portions of constant depth are connected by a stepped portion (20).