Title of Invention

"TYRE WITH RADIAL CARCASS REINFORCEMENT"

Abstract

Tyre with radial carcass reinforcement (1), having a crown reinforcement (3) comprising at least two working crown plies (31,33) made of inextensible cables, crossed from one ply to the other, characterized in that an additional ply (32), axially continuous and formed of undulating metallic elements orientated essentially parallel to the circumferential direction is positioned between the working plies (31,33).

Full Text

The invention concerns a tyre with radial carcass reinforcement anchored in each bead to at last one bead wire, and comprising a crown reinforcement consisting of at least two plies known as working plies, which are superimposed and formed of mutually parallel wires or cables in each ply and crossed from one ply to the other so that, relative to the circumferential direction of the tyre, they form angles whose absolute value can range between 10° and 60°. French patent application FR 2 744 955, which aims to lower the working temperature of a tyre with radial carcass reinforcement of the "Heavy Duty" type while providing a solution as effective as it is economical, recommends that to the said carcass reinforcement should be added a crown reinforcement comprising at least two working crown plies of inextensible cables, crossed from one ply to the other so as to make angles ranging from 10° to 45° relative to the circumferential direction, characterized in that an additional, axially continuous ply formed of metallic elements orientated essentially parallel to the circumferential direction is positioned radially between the working plies, the said additional ply having an axial width that could be at least equal to 1.05 times the axial width of the widest working crown ply. In the above context, the additional ply may be formed of continuous cables of the type known as semi-elastic, i.e. cables whose relative elongation at fracture is greater than 2%. These cables make it possible to obtain the level of rigidity required for a harmonious distribution of the circumferential tension between the working crown plies and the additional ply. The said cables are advantageously of the so-termed "double-modulus" type, i.e. their tensile stress/relative elongation curve has shallow slopes at low elongations and an essentially constant and steep slope at high elongations. The very low modulus before curing, for elongations smaller than 2%, makes it possible to increase the circumferential development of the additional ply during the curing of the tyre. The additional ply may also be formed of metallic steel cables, orientated circumferentially and cut so as to form sections of length much less than the circumferential length of the ply, the gaps between the sections being axially offset relative to one another. Such a structure is a simple way to confer the desired rigidity, whatever that may be, on the additional ply. The choice of elastic or cut cables for the reinforcement of the additional ply does not permit the said ply to have the best possible fatigue resistance, either because of reduced breaking strength of the elastic cables, or because of the presence of stress concentrations in the calendering mix of the cut cables. French patent application FR 97/0996 discloses that a better fatigue resistance of the additional ply comprising circumferential metallic reinforcement elements, combined with easier industrial production, can be obtained thanks to the use as reinforcement elements of metallic elements which undulate in the plane of the ply, positioned radially between the working plies, with the undulations of the reinforcement elements parallel to one another, in phase, and orientated parallel to the circumferential direction, such that the ratio of the linear rigidity of the additional ply to the sum of the linear rigidities of the other plies of the crown reinforcement is at most equal to 0.10. Granted the progress achieved in the durability of treads for "Heavy Duty" tyres and in the endurance of the carcass reinforcements, the endurance of the crown reinforcements needs to be improved from the standpoint of resistance to separation between the carcass reinforcement and the crown reinforcement, the resistance to separation between the working crown plies, and the fatigue resistance of the cables orientated circumferentially in the additional ply. The tyre with radial carcass reinforcement according to the present invention, which has a crown reinforcement comprising at least two working crown plies formed of inextensible metallic reinforcement elements crossed from one ply to the next, is characterized in that an additional ply, axially continuous and formed of reinforcement elements undulating in the plane of the ply, is positioned radially between the working plies, the said ply having an axial width L32 at least equal to 50% of the maximum axial width S0 of the carcass reinforcement, and with the undulations of the elements parallel to one another, in phase, and orientated parallel to the circumferential direction, such that the ratio a/λ of the amplitude a to the wavelength A, of the undulating elements decreases in the axial direction from the centre towards the edges of the said ply being a minimum at its edges. Undulating metallic elements whose mean direction is circumferential are elements whose undulations have axes with a direction relative to the circumferential direction ranging between angles of+5° and -5° about 0. The reinforcement elements undulating in the plane of the ply are preferably metallic, and better still, metallic steel cables which confer higher fatigue endurance and higher rigidity upon the additional ply. Whatever the material of which the reinforcement elements are made (cables or monofilaments), it is advantageous for their diameter to be larger than that of the reinforcement elements (generally metallic steel cables) of the plies of the crown reinforcement situated radially on either side of the said additional ply. Similarly, the ratio of amplitude a to wavelength λ of the undulations is preferably between 2% and 15%, the amplitude of a wave being by definition measured from crest to crest. The ratio a/λ between 2% and 15% makes it possible to have reinforcement elements which do not conflict with the shaping of the tyre blank in the vulcanization mould, while giving after vulcanization, fitting and inflation of the tyre the linear rigidity of the crown reinforcement required for the improvement of the said crown reinforcement's endurance. The additional ply may have an axial width at least equal to 1.05 times the axial width of the widest working crown ply. The additional ply of undulating circumferential elements, more particularly in the case of tyres with a shape ratio H/S at least equal to 0.50, may be used in combination with a first working crown ply whose meridian curvature is essentially equal to that of the underlying carcass reinforcement, so that it can be positioned parallel to the said carcass reinforcement without having to interpose shaping sections. The additional ply is then given essentially zero curvature by being separated from the first working ply by appropriate sections of essentially triangular shape. The crown reinforcement according to the invention is advantageously completed by a crown ply termed the protection ply, formed of rectilinear elastic metallic cables made of steel, orientated relative to the circumferential direction at an angle essentially equal to the angle formed by the cables of the radially outermost working crown ply, and whose axial width may be either smaller or greater than the mean width of the working plies. Accordingly, the present invention relates to tyre with radial carcass reinforcement, having a crown reinforcement which comprises at least two working crown plies formed of inextensible metallic reinforcement elements, which are crossed from one ply to the next forming angles between 10° and 60° relative to the circumferential direction, an additional ply, axially continuous and formed of metallic reinforcement elements of greater diameter than that of the reinforcement elements of the working plies located radially on either side of said additional ply, being positioned radially between the working plies, having an axial width L32 at least equal to 50% of the maximum axial width of the carcass reinforcement, characterized in that the reinforcement elements are made of steel and undulate in the plane of the ply, the undulations of the cables being parallel to each other, in phase, and orientated parallel to the circumferential direction, such that the ratio of the amplitude to the wavelength of the undulating elements decreases in the axial direction from the centre to the edges of the said ply, being a minimum at the said edges. The characteristics and advantages of the invention will be better understood from the description below, which refers to the drawing illustrating in a non-limiting way an embodiment of the invention, and in which: Fig. 1 represents a schematic meridian view of a crown reinforcement according to the invention, and Fig. 2 shows a stripped plan view of the said reinforcement. The tyre P of size 315/80 R 22.5 X, has a shape ratio H/S equal to 0.8, where H is the height of the tyre P on its mounting rim and S its maximum axial width. The said tyre P comprises a radial carcass reinforcement (1) anchored at each bead to at least one bead wire with a turn-up, and formed of a single ply of metallic cables. This carcass reinforcement (1) is hooped by a crown reinforcement (3) formed of the following, considered radially from the inside outwards: A first working crown ply (31) formed of 4 + 10 x 0.28 non-hooped inextensible metallic cables made of steel, the said cables having a diameter of 1.25 mm, being parallel to one another in the ply, and being spaced at intervals of 2.0 mm (measured perpendicularly to the said cables). They are orientated relative to the circumferential direction at an angle α between 10° and 60°, and equal to 22° in the case described. The said first ply is radially separated at its edges from the underlying carcass reinforcement (1) by rubber mix sections (3) of essentially triangular shape. Above the first working crown ply (31), an additional ply (32) formed of non-hooped 3 + 9 + 15 x 0.23 inextensible metallic steel cables with a diameter of 1.4 mm and spaced at intervals of 2 mm. Axially at the centre of the additional ply, the said cables have undulations with a crest-to-crest amplitude equal to 12 mm and a wavelength of 100 mm, i.e. approximately 1/30 of the circumferential length of the ply (33). In contrast, at the edges of the said ply (32), the amplitude a decreases down to 4 mm while the wavelength λ of the said undulations remains unchanged. The axial width of the additional ply (32) is subdivided into 9 equal strips of width 18 mm in the case described: a central strip, and on either side of the equatorial plane four lateral strips. The central strip is composed of cables with undulation amplitude a equal to l2 mm, while the two lateral strips nearest the central strip are formed of cables whose undulation amplitude is 10 mm, and so on outwards to the two lateral strips at the edges of the ply, where the amplitude a has become 4 mm after a decrease of 2 mm from one strip to the next. The said elements are orientated at 0°, i.e. the axes of their undulations are circumferential. Then, a second working crown ply (33) formed of metallic cables identical to those of the first ply (31), arranged at the same intervals and making relative to the circumferential direction an angle p, opposite to the angle a and in the case illustrated equal to the said angle a of 22° (but which may be different from the angle a). And finally, a last ply (34) of metallic steel cables of the so-termed elastic type, orientated relative to the circumferential direction at an angle γ in the same direction as the angle P and equal to the said angle P (though it could be different therefrom), this last ply being known as the protection ply and its so-termed elastic cables being cables whose relative elongation at fracture is at least 4%. The axial width L31 of the first working ply (31) is approximately equal to 0.71 times the maximum axial width S0 of the middle fibre of the carcass reinforcement (1), i.e. 226 mm, which for a tyre of the usual shape is essentially equal to the width of the tread, equal in the case considered to 235 mm. The axial width L33 of the second working ply (33) is smaller than the width L31 of the first working ply 31 by an amount equal to 0.07 S0 i.e. its width is 204 mm. The axial width L32 of the additional ply (32) is essentially equal to 162 mm, or approximately 0.51 S0. The last crown ply (34), known as the protection ply, has a width L34 at least equal to and in the case described very slightly greater than the width L32 of the additional ply (32), or 170 mm. Another tyre variant (not shown in the drawing) according to the invention has a first working crown ply (31) radially adjacent to and parallel with the carcass reinforcement (1), whose meridian curvature 1/r is essentially equal to the meridian curvature 1/r, of the underlying carcass reinforcement (1), the cables respectively of the carcass ply and the working ply being separated by a small and constant thickness of rubber mix. The axially external edges of the working ply (31) are then separated from the additional ply (32) of undulating circumferential cables by sections of triangular cross-section, the thickness of rubber between the ply (31) and the ply (32), measured at the level of the axially external edge of the ply (32), being essentially equal to 2 mm. WE CLAIM: 1. Tyre with radial carcass reinforcement (1), having a crown reinforcement (3) which comprises at least two working crown plies (31, 33) formed of inextensible metallic reinforcement elements, which are crossed from one ply to the next forming angles between 10° and 60° relative to the circumferential direction, an additional ply (32), axially continuous and formed of metallic reinforcement elements of greater diameter than that of the reinforcement elements of the working plies (31, 33) located radially on either side of said additional ply (32), being positioned radially between the working plies (31,33), having an axial width L32 at least equal to 50% of the maximum axial width of the carcass reinforcement (1), characterized in that the reinforcement elements are made of steel and undulate in the plane of the ply, the undulations of the cables being parallel to each other, in phase, and orientated parallel to the circumferential direction, such that the ratio of the amplitude to the wavelength of the undulating elements decreases in the axial direction from the centre to the edges of the said ply (32), being a minimum at the said edges. 2. Tyre as claimed in claim 1, wherein the ratio of the amplitude to the wavelength of the undulations of the reinforcement elements of the additional ply (32) is between 2% and 15%. 3. Tyre as claimed in claims 1 and 2, wherein the ratio of the amplitude of the undulations to their wavelength decreases progressively, from the centre of the ply (32) axially towards its edges. 4. Tyre as claimed in any of claims 1 to 3, wherein the first working crown ply (31) has a meridian curvature substantially equal to the meridian curvature of the underlying carcass reinforcement (1), so that it is positioned parallel to the said carcass reinforcement (1), sections (4) being interposed between the edges of the working ply (31) and the additional ply (32), the curvature of which being substantially zero. 5. Tyre as claimed in any of claims 1 to 4, wherein the crown reinforcement (3) also comprises a ply (34) known as the protection ply, situated radially above the last working ply (33), and, formed of elastic and rectilinear metallic cables made of steel orientated relative to the circumferential direction at an angle γ in the same direction as the angle p of the elements of the radially outermost working ply (33), the axial width 1,34 of the said ply being at least equal to the axial width L32 of the additional ply (32). 6. Tyre with radial carcass reinforcement (1), substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

Documents:

3172-del-1998-abstract.pdf

3172-del-1998-claims.pdf

3172-DEL-1998-Correspondence Others-(25-10-2011).pdf

3172-DEL-1998-Correspondence-Others-(28-09-2012).pdf

3172-del-1998-correspondence-others.pdf

3172-del-1998-correspondence-po.pdf

3172-del-1998-description (complete).pdf

3172-del-1998-drawings.pdf

3172-del-1998-form-1.pdf

3172-del-1998-form-13.pdf

3172-del-1998-form-19.pdf

3172-del-1998-form-2.pdf

3172-del-1998-form-3.pdf

3172-del-1998-form-4.pdf

3172-del-1998-form-6.pdf

3172-DEL-1998-GPA-(25-10-2011).pdf

3172-DEL-1998-GPA-(28-09-2012).pdf

3172-del-1998-gpa.pdf

3172-del-1998-pct-409.pdf

3172-del-1998-petition-137.pdf

3172-del-1998-petition-138.pdf

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