GB2218057A

GB2218057A - Pneumatic tyre

Info

Publication number: GB2218057A
Application number: GB8908611A
Authority: GB
Inventors: David John Wall
Original assignee: Dunlop Ltd
Current assignee: Dunlop Ltd
Priority date: 1988-05-06
Filing date: 1989-04-17
Publication date: 1989-11-08
Also published as: GB8810783D0; GB8908611D0

Abstract

A cross-ply tyre of three-rib configuration has a tread width T which is less than 75% of the maximum sectional width W of the tyre. The central rib 7 is approximately twice as wide as the other ribs 6 and (8), Fig 2, and may be provided with isolated recesses (13) for drainage purposes. <IMAGE>

Description

PNEUMATIC TYRE This invention relates to a pneumatic tyre and in particular to a cross-ply pneumatic tyre intended for use on commercial vehicles.

In accordance with the invention, a pneumatic tyre comprises a cross-ply carcass, two sidewalls and a tread having three circumferentially-extending ribs, the central one of which is approximately twice as wide as each of the remaining ribs, and a ground contacting tread surface which extends sideways to form edges with the side surfaces of the tyre sidewalls, the overall ground contacting tread surface width between the edges being less than 75 of the maximum sectional width of the tyre in the normally inflated and unloaded state.

The central rib is preferably provided with isolated recesses which do not connect with a circumferential groove between tread ribs.

Each buttress region of the tyre, i.e. that region immediately radially inwards of a tread edge, may be convex or concave in cross-sectional profile.

Two embodiments of the invention will now be described by way of example only with reference to the accompanying drawings of which; Figure 1 is a partial cross-sectional view through the tread and buttress region of a tyre according to the first embodiment of the invention, Figure 2 is a plan view of part of the tread of the tyre shown in Figure 1, Figure 3 is a cross-section on line III-III of Figure 2, Figure 4 is an enlarged plan view of one of the tread recesses of the tyre shown in Figure 2, Figure 5 is a cross-section of a recess on the line V-V of figure 4, Figure 6 is a cross-sectional view of line VI-VI of the recess shown in Figure 4, and Figure 7 is a partial cross-sectional view through the tread and buttress region of a tyre according to a second embodiment of the invention.

The tyre of the first embodiment illustrated in Figures 1-6 has a conventional cross-ply carcass anchored in bead regions and as shown particularly in Figure 1 has two breaker plies 1,2 lying immediately outwards of the carcass (not shown), a tread 3 immediately radially outwards of the breaker plies and two buttress regions 4, one on each side of the tyre, extending radially inwards from the edge 5 of the tread 3 towards the mid-sectional line 0-0 of the tyre.

The tyre as illustrated is of size 11.00-20 and has a tread arc width T measured across the curvature of the tread of 178.6 mm. The maximum cross-sectional width W of the tyre is 252.7 mm. Thus the tread arc width T is 70.7% of the sectional width W.

As illustrated in Figure 2, the tread 3 comprises three ribs, 6,7 and 8 separated by two circumferentiallyextending zig-zag grooves 9 and 10. These grooves 9,10 each have a shape or configuration and dimensions such that the apices 11 of those parts of the tread rubber immediately adjacent the groove and extending transverseley thereof do not project far into the groove 9 or 10 and in particular do not extend across the groove to cross the imaginary circumferential line joining the corresponding projecting apices 12 formed on the other side of the groove. In other words a clear, truly circumferentially-extending channel is provided in the central portion of each groove 9,10.

As shown in Figure 3, the base width S of the clear channel is 8 mm, the surface width Q of the clear channel is 10 mm and the maximum transverse extent R of each groove 9,10 is 13 mm.

The central rib 7 is much wider than each of the other two ribs 6,8, one on each side of the central rib, and is approximately twice the width of each. In Figure 2 the arc length Y measured from the centre line of groove 9 to the centre line of groove 10 is 95 mm. The arc length X, measured from the centre line of a groove to the nearer tread edge is 41.8 mm.

The central rib 7 is also provided with a plurality of isolated recesses 13 having an approximate semicircular outline at the tread surface 14. These recesses 13 are arranged in four circumferentially-extending rows but are so arranged that no recess is in line in the transverse direction with another recess. Details of the shape and configuration of each recess are clearly shown in Figures 4,5 and 6. The maximum dimension of each recess in the circumferential direction measured at the tread surface is 8 mm. The maximum dimension in the transverse direction at the tread surface is 4 mm. The recesses are each tapered in form, having a smaller cross-sectional area at their bases.The sides 16,17 slope equally in a circumferential plane as shown on Figure 5 but in a transverse plane the straight side 18 closer to the mid-circumferential plane C-C of the tyre extends perpendicularly to the tread surface 14 as shown in Figure 6.

As can be seen in Figure 1, the outer crosssectional profile 19 of the buttress region 4 is convex, thus providing more support for the tyre shoulder region than a tyre having a substantially concave cross-sectional buttress profile.

As shown in Figure 1, the tyre tread surface is reinforced with two breaker layers 1,2. The radially inner layer 2 has a width of 340 mm in this size of tyre and the radially outer layer 1 has a width of 130 mm. Both these widths are measured around the curvature of each layer.

It is found that a tyre in accordance with the invention has substantially reduced tyre running temperatures at the tread edges and prolonged effective tyre life compared with prior art tyres. This is brought about by the reduced overall tread width which creates a substantially reduced tread gauge in the shoulder region which is inherently bigger than in the middle of the tread. Additionally, the use of a three rib configuration inherently produces stiffer ribs compared with the more conventional five rib configuration.

This additional stiffness restores in part the tread wear quality lost hy providing a generally narrow tread width Further, a convex buttress profile provides added support for the outer ribs 6,8 at the tread edges 5. This is especially advantageous when using a relatively narrow tread width. A water draining capability is provided for the relatively wide central rib by means of isolated recesses rather than extended grooves or slots which would otherwise reduce general tread stiffness.

The tyre shown on Figure 7 is substantially the same as that shown in Figure 1 but it is important to note that in this embodiment for appearance reasons, the buttress region 4 has a slightly concave crosssectional profile 20. This means that the support provided for outer ribs 6,8 at the tread edge 5 is less than that provided in the tyre of the first embodiment but since the degree of concavity is only slight, the support is still adequate. In addition the tread arc width T is 182.8 mm and the maximum section width W is 257.8 mm so that T is 70.9% of W. The dimensions X and Y are 42.4 mm and 98.0 mm respectively. The dimensions of P,Q and R, and the surface dimensions of the recesses are the same as for the tyre shown in Figure 1.

Claims

CLAIMS:

1. A pneumatic tyre comprising a cross-ply carcass, two sidewalls, and a tread having three circumferentiallyextending ribs, the central one of which is approximately twice as wide as each of the remaining ribs, and â ground-contacting tread surface which extends sideways to form edges with the side surfaces of the tyre sidewalls, the overall ground contacting tread surface width between the edges being less than 75 of the maximum sectional width of the tyre in the normally inflated and unloaded state.

2. A pneumatic tyre according to Claim 1 wherein the central rib is more than twice as wide as each of the remaining ribs.

3. A pneumatic tyre according to either one of the preceding claims wherein the central rib is provided with isolated recesses.

4. A pneumatic tyre according to Claim 3 wherein the isolated recesses are arranged in at least one circumferentially-extending row.

5. A pneumatic tyre according to any one of the preceding claims wherein the buttress region of the tyre has a convex cross-sectional profile.

6. A pneumatic tyre according to any one of the preceding claims wherein the three ribs are separated by two circumferentially-extending zig-zag grooves, the apices of the tread immediately adjacent each groove on one side thereof extending into the groove but not crossing the imaginary circunferential line joining the apices on the other side of the groove.

7. A pneumatic tyre according to Claim 6 wherein a clear truly circumferentially-extending channel is provided in the central portion of each groove.

8. A pneumatic tyre substantially as described herein with reference to Figures 1-6 of the accompanying drawings.

9. A pneumatic tyre substantially as described herein with reference to Figure 7 of the accompanying drawings.

10. A tread for a pneumatic tyre according to any one of the preceding claims.