GB1602723A

GB1602723A - Tyres

Info

Publication number: GB1602723A
Application number: GB1652577A
Authority: GB
Original assignee: Dunlop Ltd
Current assignee: Dunlop Ltd
Priority date: 1978-04-18
Filing date: 1978-04-18
Publication date: 1981-11-18

Description

(54) IMPROVEMENTS IN OR RELATING TO TYRES (71) We, DUNLOP LIMITED, a British Company of Dunlop House, Ryder Street, St.

James's. London S.W. 1. do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement: This invention relates to tyres and in particular to high performance tyres for use under arduous conditions.

Tyres used in car rallies and the like have to be capable of withstanding cuts and impacts from sharp rocks when the tyres are used on unmetalled roads.

To this end it has been proposed to reinforce the sidewalls of the tyre with a steel reinforcement. However this can only extend over a portion of the sidewall otherwise the tyre carcass is too stiff and produces a harsh ride. Previous tyres have therefore left a vulnerable band in the upper sidewall region of the tyre between the sidewall reinforcement and the breaker of the tyre.

However if rubber in the shoulder region of the tyre is increased by axially extending the tread portion the tyre will run at a high temperature when used on metalled roads due to the flexure of the rubber in the upper sidewall region and will be unable to penetrate mud and snow when used on unmetalled roads due to the broad contact area of the tread.

It is an object of the present invention to provide a tyre in which the above disadvantages are obviated or mitigated.

According to the present invention there is provided a tyre comprising a carcass formed of at least one ply each cord of which lies in a radial or substantially radial plane . a pair of bead portions, a pair of sidewalls at least one of which is reinforced by a ply of steel cords additional to the carcass ply or plies. a breaker assembly positioned adjacent said carcass and extending on each side of the mid-circumferential plane of the tyre. a tread portion extending over said breaker assembly and terminating at each side of the tyre, and two rubber reinforcing layers, one on each side of the tyre extending from said tread portion towards the mid-point of the respective sidewall, a rebate being provided at each side of the tread portion, the base of the rebate presenting a substantially axially-extending circumferential surface.

The term "radial or substantially radial" is used to indicate that each cord in the carcass ply crosses the mid-circumferential plane of the tyre at the range 80" to 90".

Preferably a part of each rubber reinforcing layer is formed into a buttress portion having a radially-extending surface.

The axial width of said tread portion may be equal to, or greater than, the width of said breaker assembly.

Preferably each ply of steel cords extends radially outwards from adjacent the respective bead portion.

An embodiment of the invention, a rally tyre size 195/70 SR 13, will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is a section through a portion of the tyre; Figure 2 is a view in the direction of arrow II of Figure 1.

Referring now to the drawings a tyre 10 has a carcass 12 formed from a pair of plies 14. The cords 16 of the plies 14 are arranged to cross the mid-circumferential plane C of the tyre at an anglegwhich is in the range 80 to 900. The cords 14 are wrapped around a bead portion 18 which comprises a bead core 20 and a rubber filler 22 of triangular cross-section.

A breaker assembly 24 is positioned radially outwards of the carcass 12 and extends equally on each side of the mid-circumferential plane C. A reinforcing ply 26 made of steel cords is positioned in the tyre sidewall outwardly of the carcass 12. The ply 26 extends radially outwardly from a circumferential line coincident with the apex of the filler 22 and has a maximum radial width "b" of 90 mm but is preferably of the order of 60 mm.

The cords of the reinforcing ply 26 are preferably formed from three strands each strand having three filaments of 0.15 mm diameter (i.e.

a3 x 3 x 0. 15 cord). The cords of the ply 26 are arranged with a bias angle in the range 60 - 80 , preferably 68", in an opposite sense to the bias of the cords of the outermost carcass ply.

A clinch strip 28 is positioned in the lower sidewall of the tyre and the tyre carcass 12 covered with a layer of tread rubber 30 which overlaps the radially outermost edge of the reinforcement strip 26 by up to 12 mm. The tyre also comprises, on each side of the tread, a rubber reinforcing layer 41. formed from an extruded strip, which includes (a) a buttress portion 38, overlapping the radially inner edge of the tread strip 33, and (b) an outer sidewall portion, overlapping the reinforcing ply 26, the outer sidewall portion extending to the radially outer edge of the clinch strip 28.

The rubber layer 30 is shaped in a mould to obtain the required profile and, as can be seen in Figure 1. the tyre is formed with the tread portion 32 and a shoulder region 36. At each side of the tyre tread there is a circumferentially-extending rebate 34 which has a substantially radiallyextending wall 35 and a substantially axiallyextending base surface 37.

The rebate base surface 37 extends into the buttress portion 38 which is formed with a radially extending surface 40 substantially parallel to the mid-circumferential plane C. The surface 40 is arranged axially outwardly of the adjacent sidewall so that those parts of the carcass in each sidewall are protected from vertical impacts.

The height h of the rebate 34, measured in a radial direction. should be small, and should be no greater than the tread depth. The base 37 of the rebate 34 may have a pattern of grooves or slots.

The axial width w of the tread portion 32 is preferably the same as the width of the breaker assembly 24, but may. as illustrated, be more.

The arrangement of the rebate 34 ensures that the contact pressure in mud or snow is maintained at an adequate level by the use of a narrow tread portion whilst providing adequate protection against cuts and punctures between the edge of the breaker 24 and the upper edge of the reinforcing ply 26. The bulk of rubber in the shoulder region 36 is reduced so that the tyre does not overheat when run on tarmac and it is believed that the axially outer edge of the rebate 34 provides increased grip when the tyre is moving in an axial direction across the surface.

WHAT WE CLAIM IS:- 1. A tyre comprising a carcass formed of at least one ply. each cord of which lies in a radial or substantially radial plane . a pair of bead portions, a pair of sidewalls. at least one of which is reinforced by a ply of steel cords additional to the carcass ply or plies, a breaker assembly positioned adjacent said carcass and extending on each side of the mid-circumferential plane of the tyre, a tread portion extending over said breaker assembly and terminating at each side of the tyre, and two rubber reinforcing layers, one on each side of the tyre extending from said tread portion toward the mid-point of the respective sidewall, a rebate being provided at each side of the tread portion, the base of the rebate presenting a substantially axially-extending circumferential surface.

2. A tyre according to claim 1 wherein a part of each rubber reinforcing layer is formed into a buttress portion having a radially extending surface.

3. A tyre according to claim 1 or 2 wherein the axial width of the tread portion is equal to the width of said breaker assembly.

4. A tyre according to claim 1 or2 wherein the axial width of the tread portion is greater than the width of the breaker.

5. A tyre according to any one of the preceding claims wherein said ply of steel cords extends radially outwards from adjacent the respective bead portion.

6. A tyre according to claim 4 or 5 wherein the bead portion comprises a rubber filler and said ply of steel cords extends radially outwards from a circumferential line coincident with the filler apex.

7. A tyre according to any one of claims 4,5 or 6 wherein the cords of said ply of steel cords have a bias angle in the range 60 - 80".

8. A tyre according to any one of claims 4,5 or 6 wherein the cords of said ply of steel cords have a bias angle of 68".

9. A tyre according to any one of claims 5-9 wherein the rubber reinforcing layer overlaps the ply of steel cords reinforcing the respective sidewall of the tyre.

10. A tyre according to any of the preceding claims wherein the radial height of the rebate is no greater than the tread depth.

11. A tyre according to any one of the preceding claims wherein the base of the rebate has a pattern of grooves or slots.

12. A tyre substantially as described herein with reference to. and as illustrated in. the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. covered with a layer of tread rubber 30 which overlaps the radially outermost edge of the reinforcement strip 26 by up to 12 mm. The tyre also comprises, on each side of the tread, a rubber reinforcing layer 41. formed from an extruded strip, which includes (a) a buttress portion 38, overlapping the radially inner edge of the tread strip 33, and (b) an outer sidewall portion, overlapping the reinforcing ply 26, the outer sidewall portion extending to the radially outer edge of the clinch strip 28. The rubber layer 30 is shaped in a mould to obtain the required profile and, as can be seen in Figure 1. the tyre is formed with the tread portion 32 and a shoulder region 36. At each side of the tyre tread there is a circumferentially-extending rebate 34 which has a substantially radiallyextending wall 35 and a substantially axiallyextending base surface 37. The rebate base surface 37 extends into the buttress portion 38 which is formed with a radially extending surface 40 substantially parallel to the mid-circumferential plane C. The surface 40 is arranged axially outwardly of the adjacent sidewall so that those parts of the carcass in each sidewall are protected from vertical impacts. The height h of the rebate 34, measured in a radial direction. should be small, and should be no greater than the tread depth. The base 37 of the rebate 34 may have a pattern of grooves or slots. The axial width w of the tread portion 32 is preferably the same as the width of the breaker assembly 24, but may. as illustrated, be more. The arrangement of the rebate 34 ensures that the contact pressure in mud or snow is maintained at an adequate level by the use of a narrow tread portion whilst providing adequate protection against cuts and punctures between the edge of the breaker 24 and the upper edge of the reinforcing ply 26. The bulk of rubber in the shoulder region 36 is reduced so that the tyre does not overheat when run on tarmac and it is believed that the axially outer edge of the rebate 34 provides increased grip when the tyre is moving in an axial direction across the surface. WHAT WE CLAIM IS:-

1. A tyre comprising a carcass formed of at least one ply. each cord of which lies in a radial or substantially radial plane . a pair of bead portions, a pair of sidewalls. at least one of which is reinforced by a ply of steel cords additional to the carcass ply or plies, a breaker assembly positioned adjacent said carcass and extending on each side of the mid-circumferential plane of the tyre, a tread portion extending over said breaker assembly and terminating at each side of the tyre, and two rubber reinforcing layers, one on each side of the tyre extending from said tread portion toward the mid-point of the respective sidewall, a rebate being provided at each side of the tread portion, the base of the rebate presenting a substantially axially-extending circumferential surface.