Radial carcass tyre with apex reinforcement for trucks

The subject of the invention is a radial tire with apical reinforcement for a truck. The radial reinforcement is attached to at least one bead in each bead. In addition, the tire contains apical reinforcement formed by at least two sleepers called working, arranged and formed from reinforcement elements, parallel to each other in each sleeper and crossed one sleeper with the next creating with the circumferential direction of the tire angles maximum 40 ° in absolute value.

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U.S. Patent 4,688,615 describes the top reinforcement of a radial tire consisting of a first fiber deck and a second fiber deck formed from cables parallel to each other in each deck, crossing from one deck to the next in such a way that they form an angle with the tire's circular direction that could be between 5 and 60 °. Between these decks there is a third deck of circularly arranged cables. These ropes have a diameter almost equal to the diameter of the ropes of the first and second decks and are made of a material having tensile strength weaker than the material of which the ropes of the first and second decks are made, which gives the third deck the tensile strength and the least extensibility than any of crossed cable decks, this third deck is furthermore wider than the widest deck of cables laid at an angle.

French application FR 94/15 736, not yet published, relates to a tire as described above, and especially to Truck type tires, whose height ratio on the H rim on the maximum axial width S is at most 0.60. The said application recommends, in order to improve the durability of the top reinforcement of such a tire, as well as the correctness of its tread wear, the construction of the top reinforcement characterized by the presence of a sleeper arranged in this reinforcement, axially continuous, formed from metal unstretched reinforcement elements, forming an angle of at least the circumferential direction of the tire equal to 60 °, and the primer, made of metal elements oriented approximately parallel to the circumferential direction, located radially between two top working ties.

This design allows for better separation strength between working sleepers, as well as better fatigue strength of the reinforcement warp cables located below the apical reinforcement thus formed. The axial width of the additional sleeper with perimeter reinforcement elements may be smaller than the width of the working sleepers.

Operating temperatures in tires with a shape ratio of at least 0.5 are not insignificant, therefore the applicant's research has led to the search for a more effective solution from a thermal and economic point of view.

In order to improve the durability of the apical reinforcements and the underlying carcass below the tire, without the use of an apex formed from metal cables very strongly inclined in relation to the circumferential direction of the tire and radially above the reinforcement matrix, the present invention provides a more economical solution than presented in the above-mentioned French application .

Tire with radial carcass with apical reinforcement for a truck with an H / S shape ratio at least equal to 0.50, with apex reinforcement consisting of at least two apex sleepers made of unstretched metal cables, crossed one sleeper with another, forming with the circumferential direction angles α β contained between 10 ° and 45 ° with a width of L31 and L33 called the top ties called protective steel formed with metal elastic steel lines oriented with respect to the circumferential direction at an angle φ in the same direction as the angle β work primer lines radially outermost width L34 additional continuous foundation axially formed from metal oriented reinforcement elements essentially parallel to the circumferential direction, the sleeper is located above the working sleeper radially closest to the reinforcement matrix, with the sole occurrence of an apex sleeper formed of these metal elements forming with an circumferential direction greater than 45 °, that the axial width L34 of the protective undercoat is greater than the axial width L32 of the additional undercoat of metal steel elements that are below the axial width L33 of the radially outermost working undercoat, where the linear stiffness is expressed by the formula R = df / dc elongation per unit of additional sleeper width in relation to the sum of the linear elongations of all other vertex reinforcement sleepers and is between 0.35 and 0.70 F being the tensile force per unit of sleeper width, and ε relative extension of 0.5%.

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Advantageously, both from a technical and economical point of view, the value of this ratio is obtained by using, in the so-called additional sleeper, metal steel elements with a larger diameter as the diameter of the metal steel cables forming the working sleepers.

Non-stretchable cable is understood to mean a steel cable, for example, which has a relative elongation less than 0.5% measured at 25% of its breaking load.

Metal elements oriented more or less parallel to the circumferential direction are elements that with this direction create angles in the range + 2.5 °, -2.5 ° around 0 °.

The linear stiffness of the sleeper tensile strength from the reinforcement elements resulting from the tensile force acting in accordance with the direction of the lines per unit width of the sleeper, necessary to obtain a given relative elongation ε, can be expressed by the formula R = dF / dc, where R is the stiffness of the considered sleeper, dF / dc derivative tensile force in relation to the relative elongation, is equal to 0.5%, or by the formula R = 1 / p.dF / dc, where p is the distance between the elements of the said undercoat and df / dc derivative of the tensile force acting on the element in relation to the relative elongation.

As part of the above, the additional undercoat may be formed from continuous steel cables called semi-elastic cables, i.e. cables having relative elongation at break between 2% and 6%. These cables allow to obtain a level of stiffness capable of harmonious distribution of peripheral stress between the top working sleepers and the additional sleeper. Said cables are preferably so-called two-module, i.e. they have characteristics, tensile stress as a function of relative elongation, with small inclinations for small elongations and with approximately constant constant and large inclinations. The very low curing module, for elongations less than 2%, allows to increase the circumferential development of the additional undercoat during curing the tire.

The additional sleeper can also be formed from circumferentially oriented steel wire cut and cut so as to create sections much shorter than the perimeter length of the sleeper, the gaps between the sections are circumferentially shifted relative to each other. This method of construction allows to give the additional foundation the required rigidity, whatever it is.

The apical reinforcement, according to the invention, is preferably supplemented by a so-called protective apex, formed from metal elastic steel cables oriented in relation to the circumferential direction at an angle equal to the angle formed by the cables of the apex working primer located most radially outwards, and whose axial width is greater than the axial width of the additional undercoat made of metal steel elements, however, remaining smaller than the axial width of the working outermost radially.

The characteristics and advantages of the invention are illustrated in the embodiment in which the only figure schematically shows, in the meridian section, the apical reinforcement according to the invention.

The tire P, measuring 315/80 R 22.5, has a shape ratio H / S of 0.8, where H is the height of the tire P on its mounting rim and S is its maximum axial width. Said tire P contains reinforcement with a radial carcass 1, formed from one single base made of metal steel cables, fastened in each bead to at least one bead, forming a curl. Reinforcement 1 is crimped by apical reinforcement 3, formed radially from the inside out:

- from the first apex working layout: 31, formed from tough steel wire ropes, oriented at an angle of 22 °, and whose central part is parallel to the reinforcement matrix 1, the cables of the matrix foundation and the working foundation, respectively, are separated only by calendering thicknesses , the side parts are separated from the reinforcement matrix by a rubber prufil 2 so as to give this foundation a low curvature;

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- an additional undercoat 32 formed radially on the first working undercoat 31 formed of unstretched metal steel elements, each of which has a circumferential length roughly equal to 1/6 of the outer length of the undercoat 32, and said elements are oriented at an angle of 0 °;

- then from the second apex working undercoat 33 formed from metal lines identical to that in the first undercoat 31, and forming with the circumferential direction the angle β opposite to the angle ai, in the case shown, equal to the said angle a 22 ° (but may be different from the angle at);

- and finally from the last sleeper 34 made of elastic steel cables oriented in relation to the circumferential direction at an angle θ in the same direction as the angle β and equal to the said angle β (but can be different), the latter sleeper is a protective sleeper, and elastic cords are ropes with a relative elongation of at least 4% when broken.

The axial width L31 of the first working undercoat is equal to 226 mm, which is, for the tire in question, roughly equal to the tread width that is equal in the case under consideration to 235 mm. The axial width L33 of the second working layer 33 is smaller than the width L31 of the first working layer 31 by 204 mm. The axial width L32 of the additional sleeper 32 is 160 mm. The last protective apex 34, has a width L34 very slightly larger than the width L32 of the additional foundation, i.e. 170 mm.

Linear tensile stiffness per unit width of the working sleeper 31 or the working sleeper 33, identical in the present case, because they are formed from the same 9.28 unreinforced steel metal cables, 1.09 mm in diameter, unstretched and continuous over the entire width of the sleeper, lines located at the same distance of 1.8 mm, is higher than 4000 daN / mm at 0.5% relative elongation, and in the case under consideration equal to 5500 daN / mm. The same stiffness and measured under the same conditions, additional sleeper 32, formed from 27.23 unreinforced steel metal cables, with a diameter equal to 1-4 mm, and cut so as to obtain sections of cables whose circumferential length is approximately equal to 20% of the circumferential length of the sleeper, with rows of elements separated from each other by an interval of 2 mm, is then, with a relative elongation of 0.5%, equal to 5500 daN / mm

The tire presented above was tested, both on the test wheel under conditions simulating rolling on a vehicle under a load of 4,000 kg at inflation pressure

8.5 bar, for 5 ° drift and 80 km / h, as well as on the test vehicle, under a load greater than 4500 kg at 8.5 bar, with an average speed of 105 km / h, and the vehicle can be considered, that he was moving in a straight line. Temperature measurements in vehicle tests carried out at the tip of the working sleepers show a slight advantage in terms of operating temperature, but, on the contrary, an advantage of at least 100% in kilometer has been observed to break compared to a tire of ordinary construction, i.e. with compound vertex reinforcement from a backing made of strongly inclined lines, from two working sleepers made of slightly inclined lines crossed one backing in relation to the next, and with a protective backing made of elastic cords. The advantage in kilometers is also serious when turning on the test wheel and at 5 ° drift, since 80% has been achieved: 7800 km mileage for a tire according to the invention, while a conventional tire only reached 4430 km.

The additional sleeper 32 can also be formed of so-called two-module steel cables. Some elasticity of the undercoat 32 is only useful when shaping the tire in a vulcanization form, so a low modulus rope, e.g. at most 1000 daN / mm2 derived from 1% relative elongation, and a module greater than 8000 daN / mm2 for elongation may be used relative greater than 2%.

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