Radial tyre

Abstract: A heavy duty radial tyre comprising a tread region reinforced by a belt comprising at least three breaker plies (1-3) of strips of fabric comprising parallel metallic cords in which the cords of the radially innermost first ply (1) and those of the third ply (3) are inclined at a relatively small angle (∝1,∝3) with respect to the equatorial direction (CE) of the tyre, characterised in that the cords of the second ply (2), disposed radially between the first and third plies, are the only cords inclined at an inclination angle (∝2) with respect to the equatorial direction in the range 40-85°, and in that the cords of the first and third plies are inclined in opposite directions to each other and have inclination angles (∝1,∝3) in the range 5 to 40°.

Description: The present invention relates to radial tyres and in particular but not exclusively to heavy duty tyres for vehicles such as trucks or buses. Such heavy duty tyres have relatively flat ground contacting tread regions reinforced by a breaker strip assembly or belt which is dedicated to maintaining a consistent contact between the tyre and road surface under all conditions. Such reinforcing breaker strip assemblies normally comprise three or more plies of fabric each consisting of rubber coated metallic cords laid parallel to each other and inclined with respect to the equatorial direction of the tyre. Often a narrower fourth ply sometimes termed a "slave" ply is arranged radially outside the three main belt plies. This fourth ply has the function of protecting the main breaker strip assembly both in service and particularly in subsequent retreading operations. In a conventional arrangement the cords of the radially innermost first ply are inclined at a relatively large angle with respect to the equatorial direction of the tyre whilst the cords of the adjacent second and third plies are inclined at relatively small angles with respect to the tyre equatorial direction and in the opposite directions to each other. Accordingly crossing angles of the cords of the radially innermost three plies form a triangulated structure which together with the stiffness of the cords themselves provides an effective breaker belt of high rigidity in the longitudinal and axial directions of the belt thus keeping the tyre tread flat on the road surface. Furthermore in belt design it is desirable to stagger the ply endings in the edge regions of the belt by employing plies of differing widths. This gives a progressive reduction in stiffness and minimises stress concentration at the belt edge. Accordingly the conventional design for truck tyre belts is for the widest ply to be the inner of the two low angles plies and the innermost high angle ply and the other low angle ply to be of similar widths. The belt may optionally include a radially outermost and narrowest fourth ply of low angle cords. Conventionally the metallic cords of the belt plies used in heavy duty tyres comprise steel wires which are surface coated with brass to promote adhesion to their rubber coating. In the cutting of the belt plies from the fabric sheet the metallic cords are cut at an acute angle to the cord direction resulting in cut faces which are both sharp and devoid of brass coating. Despite the stress level of the belt edges being minimised the factors of sharp cut ends, poor adhesion and the concentration of stress at the cut face combine the promote the breakdown of adhesion and cutting of the rubber at the belt edge. This so called "belt ply looseness" is a common cause of premature tyre failure. Previous attempts to solve the problem of edging rubber looseness include for example the disclosure of document FR-A-2358998 which describes a belt for truck tyres comprising a narrow high angle ply sandwiched between an inner wide low angle ply and an outer wide low angle ply. However the two low angle plies have cords lying in the same direction so that in combination with the oppositely inclined high angle cords they do not form a triangulated structure. Accordingly such a non-triangulated belt is not so effective in reinforcing the tyre tread region. It is therefore an object of the present invention to provide a triangulated belt for a heavy duty tyre which is improved in belt ply looseness. According to the present invention a heavy duty radial tyre comprises a ground contacting tread region reinforced by a belt comprising at least three plies of fabric comprising parallel steel cords in which the cords of the radially innermost first ply and the cords of the third ply are inclined at a relatively small angle to the equatorial direction of the tyre characterised in that the cords of the second ply, disposed radially between the first and third plies, are the only cords inclined at an inclination angle with respect to the equatorial direction in the range 40°-85° and in that the cords of the first and third plies are inclined in opposite directions to each other and have inclination angles in the range 5° to 40°. Preferably the inclination angle of the cords of the second ply is in the range 65° to 75° and the inclination angles of the cords of the first and third plies are in the range 15° to 25°. Most preferably the cords of the second ply are at 67° and those of the first and third plies are at 18°. Whilst the first, second and third plies may have different widths in any configuration, most preferably the innermost first ply is the widest and the adjacent second ply is the narrowest. In the case that the second ply is narrowest or narrower than the third ply then preferably there is provided immediately adjacent to each edge of the second ply a rubber strip extending axially outwardly at least as far as the edge of the third ply and having a thickness such that the lateral regions of the third ply are supported. Further aspects of the invention will become apparent on reading the following description given by way of example only of an embodiment of the invention taken in conjunction with the following Figures in which: Figure 1 is a schematic diagram showing the cross section of a truck tyre tread region according to the present invention; Figures 2-5 are schematic diagrams showing the possible relative belt cord directions according to the present invention; Figures 6-11 are schematic diagrams showing alternative arrangements of breaker strip widths according to the present invention; and Figure 12 shows a variant embodiment of the second ply. Figure 1 shows a half cross-section of the tread region of a 385/65R22.5 truck tyre in accordance with the present invention. The tyre has an overall tread width TW of 290mm. The tread region is reinforced by a breaker strip assembly 5 comprising in the radially inward towards outward direction four plies 1-4 of steel cord fabric. This breaker strip assembly 5 is disposed radially outside a carcass ply comprising radially extending reinforcing steel cords 7. The overall widths BW1-BW4 in the axial direction of the tyre of the four breaker strips are respectively 280, 245, 260 and 195mm. Accordingly the breaker strips are arranged according to width such that BW1>BW3>BW2>BW4. This arrangement of the main breaker strips 1-3 is shown schematically in Figure 6. All four breaker strips 1-4 comprise steel cord fabric comprising cut steel cords laid parallel to each other and embedded in rubber. The cords of the main plies 1-3 are inclined with respect to the circumferential equator CE of the tyre at angles of ∝1, ∝2 and ∝3 respectively. These angles have values of 18°, 67° and 18° respectively. Breaker plies 1 and 2 have their cords inclined in the same direction with respect to the circumferential equator CE whereas the cords of breaker ply 3 are oppositely inclined to the circumferential equator CE. This arrangement of the inclinations α1, α2 and α3 of the three main breaker plies 1-3 in relation to the tyre circumferential equator CE and the radially disposed carcass ply cords 7 is shown in Figure 2. The cords of the fourth strip ply 4 are inclined also at 18° in the same direction as the third ply 3. The truck tyre shown in Figure 1 additionally has in the breaker strip assembly a rubber strip 6 positioned on the radial outside of the first ply 1 adjacent to the axial outer edge of the second ply 2. This rubber strip 6 thus provides support for the axial outer portion of the third ply 3 which is radially adjacent to the second ply 2. The truck tyre breaker strip assembly 5 shown in Figure 1 and described above has been tested and shown to exhibit improved resistance to belt ply looseness. Alternative arrangements of ply cords directions and breaker strip widths are shown in Figures 3-5 and Figures 6-11 respectively. These arrangements also provide improved edging rubber looseness characteristics for the heavy duty tyre. Figures 6 to 11 show alternative arrangements for breaker strip widths. In Figure 6, the second ply is the narrowest and the first ply is the widest. In Figure 7, the first ply is the narrowest and the third ply is the widest. In Figure 8, the first ply is the widest and the third ply is the narrowest. In Figure 9, the second ply is the widest and the third ply is the narrowest. In Figure 10, the second ply is the widest and the first ply is the narrowest. In Figure 11, the second ply is the narrowest and the third ply is the widest. Figures 1 to 11 show a tyre in which the second ply is made in one piece. Figure 12 shows an arrangement of breaker strips 1, 2, 3, which is similar to the arrangement of Figure 6 in which the second ply is constituted of 2 parts 2a and 2b disposed on either side of the circumferential equator CE and separated by a rubber strip 9. The cords of the two parts 2a and 2b are parallel with each other. This arrangement of the second ply 2 may be applied to the various arrangements shown in Figures 6 to 11.

Claims: A heavy duty radial tyre comprising a tread region reinforced by a belt comprising at least three breaker plies (1-3) of strips of fabric comprising parallel metallic cords in which the cords of the radially innermost first ply (1) and those of the third ply (3) are inclined at a relatively small angle (∝1,∝3) with respect to the equatorial direction (CE) of the tyre, characterised in that the cords of the second ply (2), disposed radially between the first and third plies, are the only cords inclined at an inclination angle (∝2) with respect to the equatorial direction in the range 40-85°, and in that the cords of the first and third plies are inclined in opposite directions to each other and have inclination angles (∝1,∝3) in the range 5 to 40°. A radial tyre according to claim 1, characterised in that the inclination angle (∝2) of the cords of the second ply (2) is in the range 65 to 75° and the inclination angles (∝1,∝3) of the cords of the first and third plies (1 and 3) are in the range 15 to 25°. A radial tyre according to claim 1, characterised in that the inclination angle (∝2) of the cords of the second ply (2) is 67° and the inclination angles (∝1,∝3) of the cords of the first and third plies are 18°. A tyre according to any one of claims 1 to 3, characterised in that the cords of the second and third plies (2 and 3) are inclined in the same direction. A tyre according to any one of claims 1 to 3, characterised in that the cords of the first and second plies (1 and 2) are inclined in the same direction. A tyre according to any one of claims 1 to 5, characterised in that the second ply (2) is made of two parts (2a,2b). A tyre according to any of claims 1 to 6, characterised in that the second ply (2) is narrower than the third ply (3) and immediately adjacent to each axially outer edge of the second ply (2) is provided a rubber strip (6) extending axially outwardly at least as far as the edge of the radially outer wider third ply (3) and having sufficient thickness in the radial direction to support the axially outer lateral regions of the third ply (3). A tyre according to any one of claims 1 to 7, characterised in that the first ply (1) is the narrowest and in that the third ply (3) is the widest. A tyre according to any one of claims 1 to 6, characterised in that the first ply (1) is the widest and third ply (3) is the narrowest. A tyre according to any one of claims 1 to 6, characterised in that the second ply (2) is the widest and the third ply (3) is the narrowest. A tyre according to any one of claims 1 to 6, characterised in that the second ply (2) is the widest and the first ply (1) is the narrowest. A tyre according to any one of claims 1 to 7, characterised in that the second ply (2) is the narrowest and the first ply (1) is the widest. A tyre according to any one of claims 1 to 7, characterised in that the second ply (2) is the narrowest and the third ply (3) is the widest.

Inventors: GAUDIN YVES, GAUDIN, YVES
Applicants: DUNLOP SA, DUNLOP FRANCE SA
Application year: 1995
Main classification: B60C9
IPC codes: B60C9