Title of Invention

A TYRE COMPRISING A RADIAL CARCASS REINFORCEMENT SURMOUNTED BY A CROWN REINFORCEMENT

Abstract

In order to improve the endurance of the crown reinforcement (3) ofa tyre, the HIS form ratio of which is at most 0.6, the latter is formed radially from the inside to the outside by a triangulation ply (31) of metal cables oriented at at least 60°, two working crown plies (32, 34) formed of inextensible metal cables oriented at angles of between 10° and 45°, between which there is inserted a first additional ply (33) of metallic elements which are oriented substantially parallel to the circumferential direction of the tyre, a second additional ply (36) being arranged, on either side of the tyre, radially above the outermost working ply (34) and substantially centred on the end of the first additional ply (33).

Full Text

The invention relates to a tyre with radial carcass reinforcement anchored in each bead to at least one bead wire, and comprising a crown reinforcement formed 5by at least two so-called working plies, superposed and made of wires or cables which are parallel to each other in each ply and are crossed from one to the next, forming angles of at most 40° in absolute value with the circumferential direction of the tyre. 10 More particularly, it relates to a "heavy vehicle"-type tyre, the ratio of the height above rim H to the maximum axial width S of which is at most 0.60, and which is intended to be fitted on a medium- or high- IStonnage vehicle, such as a lorry, bus, trailer, etc. It is very widely known to use in a tyre crown reinforcements composed firstly of so-called working plies formed of cables forming a certain angle with the 20circumferential direction, and secondly of additional plies formed of cables oriented substantially circum-ferentially. Such an example of a structure is illustrated and described in US Patent 3,677,319, the working plies being formed of metallic elements 25oriented at angles of between 18° and 75°, whereas the additional plies are formed of textile cables oriented at 0°. Such a structure makes it possible to reconcile the contradictory qualities which are to be obtained by the tyre: road-holding of the vehicle and comfort, wear 30resistance and rolling resistance, for example. The additional textile plies may be arranged either beneath or on top of or between the plies of metal cables, the width of the textile assembly being between 25 and 75% of the width of the metallic structure. French Patent 2,419,185 teaches that the type of tyre in question, with a low H/S ratio, although it has numerous advantages, also has a certain number of disadvantages, such as poor adhesion of the equatorial lOzone of the tread or localisation of high pressures in the region of the edges of the tread, due to the shortening of the area of contact in the longitudinal direction of the tyre. In order to overcome these disadvantages, the cited French Patent recommends 15arranging between the carcass reinforcement and the radially inner working ply, in two zones distant from the equatorial plane, two limiting blocks each formed of two superposed plies of inextensible cables, crossed from one ply to the other, forming opposed angles with 2 0the circumferential direction which are at most equal in absolute value to half the smallest angle used in the working plies, and other than 0°. In order to improve the endurance of the crown 25reinforcement of the "heavy-vehicle" tyre of form ratio of at most 0.6, the two solutions mentioned above have not been completely satisfactory, as the problem of endurance set by the tyre of the type in question becomes very complicated: the lack of endurance relates 30both to the lack of resistance to separation between crown ply ends and to the lack of fatigue strength of the cables of the portion of carcass reinforcement the meridian profile of which is parallel to the profile of the crown reinforcement, and also to the lack of Sresistance to separation between the carcass reinforcement and crown reinforcement. In order to improve said endurance, Application WO 96/20095, in the name of the Applicant, describes a lOcrown reinforcement comprising at least two working crown plies of inextensible cables, crossed from one ply to the next, forming angles of between 10° and 45° with the circumferential direction, said plies having widths at least equal to 80% of the maximum axial width 15S0 of the carcass reinforcement, and characterised in that an axially continuous ply formed of inextensible metal cables forming with the circumferential direction an angle of at least 60° and the axial width of which is at least equal to the axial width of the shortest 2 0working crown ply is arranged firstly between the carcass reinforcement and the working ply radially closest to the axis of rotation, and secondly an additional ply formed of metallic elements oriented substantially parallel to the circumferential 25direction, the axial width of said ply being at least equal to 0.7 SQ, and its modulus of elasticity upon traction being at most equal to the modulus of the same name of the most extensible working ply, is arranged between the two working crown plies. 30 Despite the progress made, such a tyre of H/S form ratio of at most 0.45 (H being the height of the tyre on its mounting rim and S its maximum axial width), intended to replace the set of two dual wheels on a Sdriving axle, has to be improved from the point of view of overall endurance in order positively to bear comparison with said assembly, and in particular has to be improved as far as resistance to separation between the carcass reinforcement and crown reinforcement, and lOfatigue strength of the circumferentially oriented cables of the additional ply, are concerned. It might have been logical to think that a modification of structure would have to affect the two regions in ISwhich are located the ends of the ply of cables oriented with an angle of at least 60° and of the first working ply, and that one possible solution capable of solving the double problem set would have been to increase the width of the ply of circumferential 20cables. To the great surprise of the inventor, although in fact it proved necessary to increase the number of circumferential cables, this increase does not have to be effected by widening the ply of circumferential cables but by the addition of a second 25additional ply of circumferential cables, of low axial width, arranged radially above the second working ply, that is to say in the extension, respectively on either side of the crown reinforcement, of the radially outermost ply of elastic cables, referred to as protective ply, and by covering the ends of the ply of circumferential cables. Thus the tyre according to the invention, comprising a Sradial carcass reinforcement surmounted by a crown reinforcement comprising at least two working crown plies of inextensible cables, crossed from one ply to the next, forming angles of between 10° and 45° with the circumferential direction, said plies having widths at lOleast equal to 80% of the maximum axial width SQ of the carcass reinforcement, and, arranged, firstly, between the carcass reinforcement and the working ply radially closest to the axis of rotation, an axially continuous ply formed of inextensible metal cables forming with 15the circumferential direction an angle of at least 60° and the axial width of which is at least equal to the axial width of the shortest working crown ply, and, secondly, arranged between the two working crown plies, a first additional ply formed of metallic elements 20oriented substantially parallel to the circumferential direction, the axial width of said ply being at least equal to 0.7 SQ, and the modulus of elasticity upon traction of which is at most equal to the modulus of the same name of the most extensible working ply, is 25characterised in that there is arranged, radially above the radially outermost working crown ply and on either side of the tyre, a second additional ply formed of metallic elements oriented substantially parallel to the circumferential direction, of low width and such 30that it radially covers the end of the first additional ply of circumferential cables which is arranged between the two working plies. "Inextensible cable" is to be understood to mean a Bcable, for example of steel, which has a relative elongation of less than 0.2% at 10% of the breaking load. Wires or cables oriented substantially parallel to the lOcircumferential direction are wires or cables which form angles within the range +2.5°, -2.5° around 0° with said direction. A modulus of elasticity upon traction of a ply of 15cables results from the tensile stress, exerted in the direction of the cables, necessary to obtain a given relative elongation 8, said modulus being a tangent modulus. "Elasticity modulus of the additional ply which is at most equal to the modulus of the same name 20of the most extensible working ply" is to be understood to mean that the tangent modulus of the additional ply, whatever the relative elongation, is at most equal to the tangent modulus of the most extensible working ply whatever the relative elongation, the most extensible 25ply being the ply which, for each value of tensile stress, has a relative elongation greater than that of the other ply for the same stress. Advantageously, the modulus of the second additional 30ply is equal to that of the first additional ply, and will be such that it is low for a relative elongation of between 0% and 0.4%, and at most equal to the greatest modulus of elasticity upon traction of the most extensible working ply, for relative elongations Sgreater than 0.4%. Within the above framework, the additional plies can be formed of so-called elastic cables, having a curve of tensile stress as a function of the relative elongation lOwhich has shallow gradients for the slight elongations and a substantially constant and steep gradient for the greater elongations. The additional plies may also be formed of cables oriented circumferentially and cut so as to form sections of a length very much less than the IBcircumference of the least long ply, but preferably greater than 0.1 times said circumference, the cuts between sections being axially offset relative to each other. Such an embodiment makes it possible to impart to the additional plies a given modulus, whatever it 2 0may be, in simple manner. The second additional ply has its width substantially centred on the end of the first additional ply, such that its own ends are axially distant from the end of 25the first additional ply by at least 10 mm, a low width of ply being a width of between 15 and 50 mm. It is advantageous for said second additional ply axially to extend the radially outermost ply, referred to as protective ply, generally formed of so-called elastic 3 0cables forming an angle of the same direction and substantially of the same value as the angle of the subjacent working ply with the circumferential direction, said extension being produced by leaving only a gap of low width ( The characteristics and advantages of the invention will be better understood with the aid of the following lOdescription which relates to the drawings, which illustrate examples of embodiment in non-limitative manner, and in which: Figure 1 shows a diagram, viewed in meridian section, of a crown reinforcement according to the invention. Figure 2 shows the crown reinforcement of Figure 1, in plan view and in a partial section. yre P, of dimension 495/45 R 22.5 X, has an H/S form ratio of 0.45, H being the height of the tyre P on its mounting rim and S its maximum axial width. Said tyre P comprises a radial carcass reinforcement (1) 25anchored in each bead to at least one bead wire, forming an upturn, and formed by a single ply of metal cables. This carcass reinforcement (1) is hooped by a crown reinforcement (3), formed radially from the inside to the outside by a first ply (31) of inextensible metal cables oriented relative to the circumferential direction by an angle 5 of 65°, the object of said ply being to absorb a major part of the axial compression forces to which the radial carcass reinforcement (1) may be subjected, radially above and covering the preceding so-called triangulation ply, by a first working ply (32) formed of inextensible metal cables oriented by an angle a, equal to 18° in the case illustrated, surmounting the first working ply (32), by a first additional ply (33) formed of inextensible metallic elements of a circumferential length substantially equal to 1/6 of the circumferential length of the ply (33) , said elements being oriented at 0°, then by a second working ply (34) formed of metal cables identical to those of the first working ply (32), and forming an angle P, opposed to the angle a and, in the case illustrated, equal to said angle a of 18° (but possibly being different from said angle a), with the circumferential direction, then by a final ply of so-called elastic cables oriented relative to the circumferential direction by an angle y of the same direction as the angle p and equal to said angle p (but possibly being different from said angle), this final ply being a protective ply, and finally, on either side of the tyre, by a second additional ply (36) formed of inextensible metallic elements of circumferential length substantially equal to 1/6 of the circumferential length of the ply (33), said elements being oriented at 0°, that is to say, of elements identical to those of the first additional ply (33) . The axial width L32 of the first working ply (32) is ISequal to 0.87 times the maximum axial width SQ of the centre section of the carcass reinforcement (1), namely 416 mm, which, for a tyre of conventional shape, is substantially less than the width Li of the tread, which is equal in the case in question to 430 mm. The axial 20width L34 of the second working ply (34) is equal to 0.8 times the axial width SQ, namely 400 mm. The triangulation ply (31) has an axial width L31 equal to the arithmetical mean of the widths of the two working plies (32) and (34), and in this case to 408 mm. As 25for the axial width L33 of the additional ply (33), which is at least equal to 0.7 SQ, it is equal to 350 mm, which represents 0.73 SQ- In fact, the width L33 of the additional ply (33) is less than the width L32 (L34) of the least wide working ply, without, however, 30being too low so as to contribute effectively to the reduction of the operating temperatures of the tyre close to the ends of the working crown plies, which are the regions most adversely affected by the heating and the separation between plies. The final crown ply 5(35), referred to as a protective ply, has a width L35 which is less than the previous ones, namely 32 0 mm. As for the width L36 of the ply (36), it is, in the example cited, 25 mm and such that its circumferential axis of symmetry is radially above the end of the first lOadditional ply (33). The gap between the axially inner end of the ply (36) and the end of the so-called protective ply (35) is then 2.5 mm. The elastic modulus of traction of the working ply (32) 15or of the working ply (34), which in this case are identical, since they are formed by the same hooped 27.23 metal cables which are inextensible and continuous over the entire width of the ply, said cables being arranged with the same pitch, that is to 2 0say with the same space between cables, is equal to 5300 daN/mm2 at 0.4% relative elongation. The modulus, of the same name and measured under the same conditions, of the so-called triangulation ply (31), formed of hooped 9.23 metal cables, is equal to 256925 daN/mm2. As for the two additional plies (33) and (36), they are formed of hooped 27.23 metal cables, and cut so as to have sections of cables the circumferential length of which is equal to 1/6 of the circumferential length of the first, least long, ply 30(33), which imparts to the two plies a common tangent modulus of elasticity upon traction of 3310 daN/mm2 for a relative elongation of 0.4%. The additional plies (33) and (36) may also be formed 5of so-called elastic bimodular cables, that is to say, cables having relative elongations at rupture greater than 2.5% and tensile force-relative elongation curves having two parts having substantially different gradients, such as the curve (17) shown in Figure 2 of lOPatent FR 1 188 486. Since reduced elasticity of the plies (33) and (36) is useful only during the shaping of the tyre in the vulcanisation mould, a cable having a low modulus from the origin to 0.4% relative elongation and a modulus for instance greater than 1514000 daN/mm^ for the greater relative elongations makes it possible readily to obtain plies of cables oriented substantially at 0° having, above 0.4% relative elongation, a modulus of 5200 daN/mm2. 2 0The tyre described above was tested, as far as endurance was concerned, compared with a control tyre as described in the international application referred to above. Under identical loading conditions (variable load, increasing by stages from 5800 kg onwards) and 25pressure conditions (regulated inflation pressure of 10 bar), the control tyres covered 11,500 km on a test drum (average of two results) whilst the tyres according to the invention covered 31,900 km (average of 5 results), which represents a very significant 3 0improvement, given the severity of the test. claims 1. A tyre P comprising a radial carcass reinforcement (1) surmounted by a crown reinforcement (3) comprising Sat least two working crown plies (32, 34) of inextensible cables, crossed from one ply (32) to the next (34), forming angles (a, p) of between 10° and 45° with the circumferential direction, said plies having widths L32, L34 at least equal to 80% of the maximum lOaxial width SQ of the carcass reinforcement (1) and, arranged, firstly, between the carcass reinforcement (1) and the working ply (32) radially closest to the axis of rotation, an axially continuous ply (31) formed of inextensible metal cables forming with the IBcircumferential direction an angle 8 of at least 60° and the axial width L31 of which is at least equal to the axial width L32/ L34 of the shortest working crown ply (32, 34), and, secondly, arranged between the two working crown plies (32) and (34), a first additional 20ply (33) formed of metallic elements oriented substantially parallel to the circumferential direction, the axial width L33 of said ply being at least equal to 0.7 SQ, and the modulus of elasticity upon traction of which is at most equal to the modulus 25of the same name of the most extensible working ply (33, 34), characterised in that there is arranged, radially above the radially outermost working crown ply (34) and on either side of the tyre P, a second additional ply (36) formed of metallic elements 3 0oriented substantially parallel to the circumferential direction, of low width Lgg and such that it radially covers the end of the first additional ply (33) of circumferential cables which is arranged between the two working plies (32, 34). 5 2. A tyre P according to Claim 1, characterised in that the modulus of elasticity upon traction of the second additional ply (36) is equal to the modulus of the same name of the first additional ply (33). 10 3. A tyre P according to Claim 2, characterised in that the common modulus of the additional plies (33, 36) is low for a relative elongation of between 0% and 0.4%, and at most equal to the greatest modulus of ISelasticity upon traction of the most extensible working ply, for relative elongations greater than 0.4%. 4. A tyre P according to Claim 3, characterised in that the additional plies (33, 36) are formed of so- 20called elastic cables, having a curve of tensile stress as a function of the relative elongation which has shallow gradients for the slight elongations of between 0 and 0.4% and a steep and substantially constant gradient for the greater elongations. 25 5. A tyre P according to Claim 3, characterised in that the additional plies are formed of cables oriented circumferentially and cut so as to form sections of a length very much less than the circumference of the least long ply (33), the cuts between sections being axially offset relative to each other. 6, A tyre P according to one of Claims 1 to 5, Bcharacterised in that the second additional ply (36) has its width L36 substantially centred on the end of the first additional ply (33) , such that its own ends are axially distant from the end of the first additional ply (33) by at least 10 mm. 10 7. A tyre P according to one of Claims 1 to 6, characterised in that the crown reinforcement (3) furthermore comprises, radially furthest to the outside, a so-called protective ply (35), formed of ISelastic cables forming an angle of the same direction and substantially of the same value as the angle of the subjacent working ply (34) with the circumferential direction, and in that the second additional ply (36) has a width of between 15 and 50 mm, said additional 20ply (36) axially extending the protective ply (35), and said extension being produced leaving only a gap of less than 5 mm between the axially inner end of the additional ply (36) and the axially outer end of the ply (35) of elastic cables. 8, A tyre P, substantially as herein described, with reference to the accompanying drawings.

Documents:

361-mas-1998-abstract.pdf

361-mas-1998-claims filed.pdf

361-mas-1998-claims granted.pdf

361-mas-1998-correspondnece-others.pdf

361-mas-1998-correspondnece-po.pdf

361-mas-1998-description(complete)filed.pdf

361-mas-1998-description(complete)granted.pdf

361-mas-1998-drawings.pdf

361-mas-1998-form 1.pdf

361-mas-1998-form 26.pdf

361-mas-1998-form 3.pdf

361-mas-1998-form 4.pdf

abs-361-mas-1998.jpg