RADIAL PLY TYRE

Abstract: A radial ply tyre having a tread reinforcement comprising three groups of layers. The first (51), radially inner, group comprises two bias cut layers; the second group (52), wider than the first, 0 degree layers; and the third (53), radially outer group, narrower than the first, more 0 degree layers. A fourth group of bias cut layers may be positioned between the second and third groups. The tread reinforcement is intended to enable the tyre to have the necessary high speed characteristics, to prevent the onset of standing waves from the tyre shoulder region and to prevent uneven tread wear.

Description: RADIAL PLY TYRE This invention relates to a radial ply pneumatic tyre. More particularly it relates to a radial ply tyre intended to bear heavy loads under high inflation pressure, e.g. as used on aircraft. In the present specification by "radial-ply tyre" is meant one having a carcass comprising one or more plies of parallel cords which cross the mid-circumferential plane of the tyre at an angle in the range of 70 degrees - 90 degrees. If the angle is not 90 degrees the plies are so arranged that the cords in one ply cross the mid-circumferential plane at the opposite bias to the cords in the adjacent ply. A radial-ply tyre for use on aircraft has to meet stringent requirements. The tyre has to be provided with a tread reinforcement which, acting with the carcass and the beads, meets the load-bearing requirements for the given overall weight, size and aspect ratio dependent on the actual type of aircraft for which the tyre is intended to be fitted. The tyre also has to have adequate high speed performance; for example, the tyre operating temperature must not be excessively high, otherwise internal damage may occur. The onset of standing waves which are often initiated in the tyre shoulder region must, be prevented. The tread reinforcement must be constructed to cause the generation of a cornering force necessary to give the tyre adequate cornering stability and also be such as to prevent the excessive increase in the diameter of the centre of the tread of the tyre due to high inflation pressure and centrifugal forces which could otherwise lead to rapid and uneven tread wear. It is an object of the present invention to provide a tyre having a construction which meets the above-mentioned operating requirements as far as possible. Thus in accordance with the invention a pneumatic radial ply tyre comprises a tread, a radial ply carcass anchored to at least one bead core in each bead region of the tyre and a tread reinforcement comprising three groups of layers of cord reinforcing fabric; the first, radially inner, group comprising at least two layers of parallel cords extending at a bias angle lying in the range lδ degrees to 60 degrees, each layer being at opposite bias to the adjacent layer and the width of the irst group of layers being less than the contact width of the tyre tread under the scheduled load and inflation pressure of the tyre; a second group of layers, positioned radially outwards of the first group, and comprising at least two layers of parallel cords extending substantially parallel to the mid-circumference of the tyre, and the width of the second group of layers being greater than the width of the first group of layers; and a third group of layers τ positioned radially outwards of the second group, comprising at least two layers of parallel cords extending substantially parallel to the mid-circumference of the tyre and having a width which is substantially less than the width of the second group of layers. Preferably the carcass comprises more than one ply the bias angle of each being less than 90 degrees and typically lying in the range 75 degrees to 85 degrees. A preferred value is 84 degrees but this depends on the speed requirement and aspect ratio of the tyre. Preferably the bias angle of the cords of the layers in the first group is 45 degrees. Preferably also the width of the first group is between 70% and 90% of the tread contact width under the scheduled load and inflation pressure. The first group of layers in the tread reinforcement serves to generate the cornering force and cornering stability necessary for optimum tyre performance. Preferably the width of the second group of layers is at least 1.03 times that of the first group of layers. Preferably also, the width of the second group is no greater than 1.20 times the tread contact width under the scheduled load and inflation pressure. The second group of layers is intended to enhance the speed performance of the tyre by reducing the onset of standing waves being initiated from the tyre shoulder regions particularly at the higher speed range of operation of the tyre. Preferably the third group of layers has a width within the range 40% to 70% of the width of the second group. The third group restricts the excessive stretch of the crown portion of the reinforcement ensuing from the high inflation pressure and centrifugal forces at high speeds, thus helping prevent rapid and uneven tread wear in the centre region of the tyre tread. A fourth group of layers may also be provided, compris¬ ing at least two layers of parallel cords crossing the mid- circumference of the tyre at an angle in the range 15 degrees to 60 degrees, each layer being at opposite bias to the adjacent layer in the group, and positioned between the second and third groups of layers. Preferably the width of this fourth group of layers is not greater than the width of the third group. A group of layers may comprise separate rubberised fabric plies each wrapped once around the carcass circumference but may also comprise one ply or a small number of plies wrapped more than once around the carcass circumference. The cords of the carcass ply, and of the second and third group of layers may be either aromatic polyamide, aliphatic polyamide or a mixture of aromatic and aliphatic polyamide fibres. The cords of the first group of layers, and fourth group, if present, may be either steel, aliphatic polyamide, aromatic polyamide or a mixture of aromatic and aliphatic polyamide fibres. Two embodiments of the invention will now be described in more detail by way of example only, reference being made to the accompanying drawings of which: Figure 1 shows half of a cross-section through an aircraft tyre according to the first embodiment, and Figure 2 shows half of a cross-section through an aircraft tyre according to the second embodiment. The aircraft tyre illustrated in Figure 1 is of size 30 x 11.5R14.5, has an aspect ratio of 67%, and comprises a tread 1, a radial carcass reinforcement 2 anchored in each tyre bead region 3 around a bead core 4, and a tread reinforcement 5 lying radially outwards of and encircling the carcass reinforce- ent 2. In the Figures line A indicates the mid-circumferential plane of the tyre. The carcass reinforcement 2 comprises three plies of aliphatic polyamide cords of 4/188 tex laid at 78 ends per decimetre. The cords in each ply lie parallel to each other and have a finished bias angle of 84 degrees. The bias angle of one ply is opposite"to the bias angle of the adjacent ply. The tread reinforcement 5 comprises three groups of plies 51, 52 and 53. The first group 51 lies radially inwards of the other two groups 52 and 53, and comprises two plies of aliphatic polyamide cords of 4/188 tex laid at 78 e.p.d. The bias angle of the plies is 45 degrees, and the bias angle of one ply is opposite to that of the other ply so the cords in one ply cross the cords in the other ply at 90 degrees. The width of the radially inner ply is 220 mm (Twice AE in Figure 1) and the width of the radially outer ply is 206 mm (Twice AD) . The tread contact width of the tyre under a scheduled load of 11,350 kg. (25000 lb) and inflation pressure of 18.61 bar (270 lb/in 2 ) is 247 mm. Thus the inner ply width is 89% of the tread contact width and the outer ply width is 83.4% of the tread contact width under these conditions. Under a greater scheduled load of 14605 kg (32170 lb) and greater inflation pressure of 25.16 bar (365 lb/in 2 ) the tread contact width increases to 248 mm. Thus the inner ply width is 88.7% of the tread contact width and the outer ply width is 83.1% of the tread contact width under this greater load and pressure condition. The second group 52 is positioned radially outwards of the first group and comprises five separate plies each comprising parallel cords lying substantially parallel i.e. within a tolerance of - 3 degrees, to the mid-circumference of the tyre. The cords are the same as the cords of the first group. The plies are all of the same width, i.e. 228 mm. (Twice AC) and this is 1.036 times-the width of the wider ply in the first group and 91.5% of the tread contact width of the tyre under its scheduled load of 11.350 kg (25000 lb) and inflation pressure of 18.61 bar (270 lb/in 2 ). The third group lies radially outwards of the second group and comprises three separate plies of parallel cords lying substantially parallel i.e. within a tolerance of - 3 degrees, to the mid-circumference of the tyre. The cords are the same as the cords in the first and second groups of plies. The width of the three plies in the third group is 130 mm. (Twice AB) i.e. 58% of the width of the second group. The second embodiment of the invention, a radial aircraft tyre having half of its tread reinforcement illustrated in Figure 2 comprises a tread 21, carcass reinforcement 22 and bead regions 23 containing bead cores 24 which are all the same as the tyre illustrated in Figure 1. The tread reinforcement 25 of the tyre shown in Figure 2 is similar to the tread reinforcement of the tyre shown in Figure 1 but comprising, in addition to the three groups of plies 251, 252 and 253 which correspond respectively to groups 51, 52 and 53, having the same structure and arrangement, a fourth group of plies 254, positioned between the second and third groups. The fourth group comprises two separate plies each having a bias angle of 45 degrees, the cords in one ply crossing the cords in the other ply at an angle of 90 degrees. The cords are the same as the cords in the other plies in the tread reinforcement. The width of the radially inner ply is 130 mm. (i.e. equal to the width of the third group) and the width of the radially inner~ply is 124 mm. (Twice AF in Figure 2).

Claims: CLAIMS: 1. A radial ply tyre comprising a tread, a radial ply carcass anchored to at least one bead core in each bead region of the tyre and a tread reinforcement characterised by comprising three groups of layers of cord reinforcing fabric; — * the first, radially inner, group comprising at least two layers of parallel cords extending at a bias angle lying in the range 15 degrees to 60 degrees, each layer being at opposite bias to the adjacent layer, and the width of the first group of layers being less than the contact width of the tyre tread under the scheduled load and inflation pressure of the tyre; a second group of layers, positioned radially outwards of the first group, and comprising at least two layers of parallel cords extending substantially parallel to the mid-circumference of the tyre, and the width of the second group of layers being greater than the width of the first group of layers; and a third group of layers, positioned radially outwards of the second group, comprising at least two layers of parallel cords extending substantially parallel to the mid-circumference of the tyre and having a width which is substantially less than the width of the second group of layers. 2. A radial ply tyre according to Claim 1 characterised in that the carcass comprises more than one ply having a bias angle in the range 75 degrees - 85 degrees. 3. A radial ply tyre according to Claim 1 or Claim 2 characterised in that the bias angle of the carcass ply is 84 degrees and the aspect ratio of the tyre is 67%. 4. A radial ply tyre according to any one of Claims 1, 2 and 3 characterised in that the bias angle of the cords in the layers in the first group is 45 degrees. 5. A radial ply tyre according to any one of the preceding claims characterised in that the width of the first group is between 70% and 90% of the tread contact width of the tyre under the scheduled load and inflation pressure. 6. A radial ply tyre according to any one of the preceding claims characterised in that the width of the second group is at least 1.03 times that of the first group. 7. A radial ply tyre according to any one of the preceding claims characterised in that the width of the second group -is no greater than 1.20 times the tread contact width under the scheduled load and inflation pressure. 8. A radial ply tyre according to any one of the preceding claims characterised in that the width of the third group of plies lies within the range 40% - 70% of the width of the second group. 9. A radial ply tyre according to any one of the preceding claims characterised by comprising a fourth group of plies comprising at least two layers of parallel cords crossing the mid-circumfrence of the tyre at an angle in the range 1.5 degrees to 60 degrees, each layer being at opposite bias to the adjacent layer in the group, and positioned between the second and third group of layers. 10. A radial ply tyre according to Claim 8 characterised in that said angle is 45 degrees. 11. A radial ply tyre according to Claim 8 or Claim 9 characterised in that the width of the fourth group of layers is no greater than the width of the third group. 12. A radial ply tyre according to any one of the preceding claims characterised in that a group of layers comprises separate rubberised fabric plies each wrapped once around the carcass circumference. 13. A radial ply tyre, according to any one of Claims 1-11 characterised in that a group of layers comprises one ply, or a small number of plies, wrapped more than once around the carcass circumference. 14. A radial ply tyre according to any one of the preceding claims characterised in that the cords of the carcass ply and of the second and third group of layers comprise either aromatic polyamide, aliphatic polyamide or a mixture of aromatic and aliphatic polyamide fibres. 15. A radial ply tyre according to any one of the preceding claims characterised in that the cords of the first group of layers and the fourth group of layers, if present, comprise either steel, aliphatic polyamide, aromatic polyamide or a mixture of aromatic and aliphatic polyamide fibres. 16. A radial ply tyre substantially as described herein with reference to, and as illustrated in, Figure 1 of the accompanying drawings. 17. A radial ply tyre substantially as described herein with reference to, and as illustrated in, Figure 2 of the accompanying drawings.

Inventors: BARLOW STEPHEN, PANIKKAR THARAMEL PADMANABHA K, BARLOW, STEPHEN, PANIKKAR, THARAMEL, PADMANABHA, KRISHNA
Applicants: DUNLOP LTD, DUNLOP LIMITED
Application year: 1988
Main classification: B60C9
IPC codes: B60C9, B60C19