ITMI992514A1 - TIRE FOR HIGH PERFORMANCE CARS - Google Patents

Description

DESCRIPTION of the invention entitled: "Tire for high performance cars"

Description

The invention refers to a tire for motor vehicles, especially a radial carcass tire for medium and high class cars that require tires capable of high performance. In particular, the invention relates to the tread pattern of the aforesaid tires.

A radial tire, in its most general form, comprises a carcass structure including a central portion of the crown and two axially opposite sides ending in a pair of beads for anchoring to a rim of a wheel, a belt structure coaxially associated with the carcass structure and a tread band, coaxially extended around the belt structure.

In the thickness of the tread band a relief pattern is obtained formed by a plurality of transversal and longitudinal grooves, which generally give rise to a plurality of cords and / or blocks distributed according to various configurations.

The characteristics required of the tires of the invention, in consideration of the high speed of the vehicle, are mainly a high directional stability, excellent grip qualities both in straight and cornering, both on dry and wet ground, quietness and good resistance. to wear.

Obtaining all these characteristics at the same time on the same tire is a difficult problem as each of them requires measures that are negative in relation to the other characteristics.

As regards directional stability and wear resistance, the difficulty of fully satisfying the aforementioned requirements is essentially related to the difficulty of limiting the mobility of the blocks (meaning by this term the portions of the tread band delimited between pairs of consecutive grooves both in the direction axial and circumferential) present on the tread band in the presence of high stresses and their degradation as the latter heat up during use.

In known type tires, in fact, the blocks present on the tread band, during the running of the tire, are subjected to a whole series of thermomechanical stresses, mainly due to the frictional heating of the compound and to the compression and shear stresses, which tend flexing and deforming the blocks by modifying their geometry: there is almost invariably a deterioration in the performance of the tire after a certain wear of the tread band, the more rapid and irregular the more the driving is carried out in “at the limit” conditions.

One way to try to overcome this difficulty consists in minimizing the number of blocks and strengthening their structure by assigning to the tread pattern a high value of the full / empty ratio: tires of this type are already known in the art.

An example of this known technique is described in the patent W09825776 which refers to a tire comprising a tread band without circumferential grooves but provided with transversal grooves differently oriented, respectively inclined according to both axial and circumferential directions in the central zone, astride the plane equatorial, and with an axial course in the shoulder areas, to define a tread pattern of a directional type, that is, having a preferential direction of rotation.

The presence of transversal grooves is necessary to guarantee the traction of the tire and their effectiveness with regard to traction is the greater the more the inclination of the aforementioned grooves approaches the axial direction: on the other hand, this axial inclination is penalizing as regards the capacity. drainage of water collected under the footprint area and as regards the directional stability of the tire, especially at high speeds.

In fact, these treads, due to the absence of circumferential grooves, have a strong sensitivity to the aquaplaning phenomenon, which cannot be tolerated in the tires of the invention in consideration of the expected performance. Circumferential grooves are therefore also necessary.

On the other hand, even these grooves, with the increased performance required of the tires in terms of power and speed, denote a series of problems, specifically in radial carcass tires.

In the first place, the structural resistance of the belt is generally limited due to the fact that, in correspondence with said grooves, where the thickness of the tread evidently is reduced to the minimum value, the belt has a preferential deformation zone, that is a "hinge". This hinge, when the tire is heavily engaged in drift, triggers a type of stress that causes the dynamic yielding of the belt structure, with relative deterioration of the road holding and of the behavioral qualities of the tire in general, and therefore of the vehicle at high speed.

In addition to this, while the vehicle is moving in a curve, the contact with the ground flexes the outer edge of the circumferential grooves, with reference to the direction of travel, lowering it radially inwards and moving it axially inwards, narrowing the groove and exposing the internal edge of the latter to a cyclic tangential stress that is repeated at each wheel revolution causing a typical irregular and premature wear, known as “sawtooth wear”.

This wear changes the optimal profile of the tire in the meridian plane, in a straight section, with negative effects on the directional stability and on the comfort of the tire.

In addition, this modification of the tire profile is not constant, and therefore predictable and compensable with suitable geometries of the vulcanization mold: in fact, the extent and speed of propagation of this wear vary with the variation of the speed of the vehicle, and therefore of the centrifugal force applied to the portion of the crown below the impression area, and with the residual depth of the groove.

The state of the art does not offer teachings to completely solve the problem of producing a tire for vehicles with high and very high performance at the same time capable of minimizing and uniform wear of the tread band during the rolling of the tire, of offering high directional stability and to improve aquaplaning resistance by offering excellent road holding both in straight and in curves both on dry roads and on wet roads, all without worsening but rather improving the characteristics of low rolling resistance, good running smoothness and good driving behavior in any driving condition.

The Applicant has now understood that the problem could be brilliantly solved with a tread band having a plurality of transverse grooves, inclined with respect to both axial and circumferential directions at least in the central portion of said band, in combination with a plurality of circumferential grooves, at least one of which is intersected by at least part of said transverse grooves, and has a V-shaped cross section of greater width and depth less than that of the transverse grooves which intersect it.

The Applicant has found that the effectiveness of the intuited solution was strongly conditioned by the value of the ratios between the homologous geometric dimensions of said transverse grooves and of the intersected circumferential grooves, which are therefore critical with respect to the invention.

The Applicant has then found that the preferred solution consisted in arranging in the central area of the tread said plurality of transverse grooves distributed in two axially opposite and circumferentially intercalated series. More particularly, in the central area of the aforementioned tread band these transverse grooves are distributed in groups; more specifically, each series comprises groups of three grooves, parallel to each other, of different length, alternating with groups of three grooves, parallel to each other, of different length, belonging to the opposite series.

In each group the grooves have decreasing length in the same direction of rotation of the tire and such that the largest groove has a length from three to four times greater than that of the shortest groove.

The Applicant has also understood that it was possible to optimize the solution found by giving the central area of the tread band particular geometric characteristics which vary along the axial development of said area, so as to obtain a synergistic effect with the characteristics of the adjacent shoulder areas, designed to improve all the performances offered by the tire in operation.

In a first aspect, the invention then relates to a tire for vehicle wheels comprising: a carcass structure including a central portion of the crown and two axially opposite sides ending in a pair of beads for anchoring the tire to a corresponding rim of a wheel, a belt structure, coaxially associated with the carcass structure and a tread band, extending coaxially around the belt structure, printed with a relief design on which two axially opposed shoulder areas are defined, each delimited between a pair of circumferential shoulder grooves, respectively axially external and axially internal, said shoulder zones comprising a plurality of transverse grooves inclined with respect to the circumferential direction of the tire, and a central zone delimited between the axially internal grooves of said pair of circumferential shoulder grooves, comprising and at least two intermediate circumferential grooves, and a plurality of transversal grooves inclined with respect to the circumferential direction, intersecting at least one of said intermediate grooves, characterized in that at least the intermediate circumferential groove intersected by said plurality of transverse grooves has, on the cross section with a radial plane, a V-shaped profile, with the vertex in a radially internal position, of greater width and less depth than those of the straight section of said transverse grooves.

Preferably the value of the ratio between the depth of said V-shaped groove and that of the transverse grooves that intersect it is comprised between 0.35 and 0.82, while the value of the ratio between the width of said V-groove and that of the transverse grooves that intersect it is between 1, 5 and 5

Even more preferably, the width of said V-shaped groove is comprised between 10 and 15 mm while the depth of said V-shaped groove is comprised between 3 and 7 mm.

As regards the shape of said V-shaped section, the angle a of inclination of the sides of said groove with respect to the axial direction is preferably comprised between 35 ° and 55 °. Preferably, said transverse grooves have a U-shaped cross-section and the areas of the cross-section of the V-groove and of the cross-section of the U-shaped grooves are equal to each other.

Preferably, said transverse U-shaped grooves have a width of between 3 and 10 mm and a depth of between 7 and 8.5 mm.

Even more preferably, the transverse grooves of said central zone comprise two series of grooves, respectively inclined on opposite sides with respect to the axial direction, according to an inclination angle with respect to the circumferential direction comprised between 30 ° and 60 °, and preferably substantially equal to 45 °; each of said series comprises a circumferential succession of groups of grooves interspersed with groups of grooves of the other series. Preferably, in each series said groups of grooves comprise three grooves parallel to each other.

In accordance with a preferred configuration, advantageous for improving the traction and silence qualities of the tire, the transverse shoulder grooves are perpendicular to the equatorial plane of the tire and are circumferentially offset with those of the opposite shoulder.

Further characteristics and advantages will become clearer from the following description of two preferred embodiments of a tire according to the invention, made with reference to the attached drawings, provided only by way of non-limiting example, of which: Figure 1 shows a development in plan of the drawing obtained in the tread band of a tire according to the invention, in a first embodiment, figure 2 shows a partial view of the tire, in particular of the crown portion of said tire, in cross section along line A, B, C, D, E, F of figure 1

Figure 3 shows a detail of the straight sections of a groove and a recess of the tread pattern of the tire of Figure 1, compared to each other; Figure 4 shows a plan development of the pattern obtained in the tread band of the tire of the invention , in a second embodiment, figure 5 shows a partial view of the tire of figure 4, in particular of the crown portion of said tire, in cross section along the line A, B, C, D.

Figure 1 illustrates as a whole the tread pattern of a tire for high-performance vehicles according to the invention, in particular a tire with asymmetrical pattern intended to be mounted on the vehicle with a preferential orientation with respect to which an external side and an external side are defined on the tire. internal side, or vehicle side.

The tire traditionally comprises a carcass structure which includes at least one reinforcement ply whose opposite side flaps are associated with corresponding bead cores. The opposite areas of the tire each comprising a bead core with the relative filling form the so-called beads, intended for anchoring the tire on a corresponding mounting rim of a vehicle wheel.

Coaxially associated with the carcass structure is a belt structure comprising one or more reinforcement strips each made by means of a layer of compound incorporating a plurality of textile or metal cords.

A tread band is applied to the belt structure within which the design shown in the aforementioned figure 1 is obtained.

All the elements described up to now are not illustrated as they are now well known to the person skilled in the art and substantially irrelevant with respect to the invention.

In a first preferred embodiment, the design according to the invention (Figure 1) is divided into three zones and precisely into two axially opposed shoulder zones S1 and S2, each delimited between a pair of circumferential shoulder grooves, respectively axially external (1, 3) and axially internal (2, 4) and a central zone M delimited between the axially internal grooves (2, 4) of said pair of circumferential shoulder grooves. It is known that the shoulders of the tire are the end portions of the tread which form the connection between the substantially flat portion of the crown and the sidewalls of the tire.

The axially external shoulder grooves, also better known as disconnection grooves, define the width W of the tread and separate the crown portion, i.e. the area normally in contact with the ground in different driving situations, from the tire sides: the distance w between said grooves 2 and 4 it defines the width of the central zone M, preferably between 45% and 65% of W. On the internal shoulder S2 the axially internal groove 4 is preferably adjacent to the external groove 3, i.e. this shoulder has no further circumferential grooves; vice versa, on the external shoulder S, a circumferentially continuous notch 19 adjacent to the internal groove 2 is preferably provided.

It is hereby specified that all the measures indicated below refer to new tires, mounted on the recommended rim and inflated to their operating pressure; in particular, the drawing of figure 1 refers to a tire measuring 225/40 ZR 18.

The external shoulder grooves 1 and 3 have the same depth, equal to 1.5 mm, and the same width, equal to 4 mm, while the internal grooves, in accordance with the asymmetry of the tread pattern, are different from each other; in particular they have a different width, equal to 2.5 mm for the groove 4, and of a greater value, equal to 8 mm for the groove 2.

However, the aforesaid grooves can also be identical to each other and, in any case, their width is preferably between 1.5 and 12 mm, while their depth is preferably between 1.5 and 8.5 mm. As illustrated in Figure 1, these grooves are preferably straight.

Each shoulder region comprises a plurality of transverse shoulder grooves 5, 6 substantially perpendicular to the circumferential direction of the tire: the grooves 5 have a width of 6.2 mm, the grooves 6 have a width of 4.8 mm.

The task of developing the maximum traction of the tire is entrusted to said transverse grooves: in this context, the inclination β of said grooves with respect to the axial direction is preferably included in a neighborhood of plus or minus 30 °.

In the example illustrated, the hollows 5 narrow to about two thirds of their development, proceeding axially outwards, assuming a width of 3 mm; both transverse grooves 5 and 6 have a constant depth, equal to 8 mm. More generally, their width is preferably between 2 and 10 mm, and their depth is preferably the same in correspondence with the corresponding internal groove, between 4 and 10 mm, decreasing in an axial direction towards the outside.

In the illustrated embodiment the recesses 5 open on both shoulder grooves 3 and 4 while the recesses 6 are blind on their axially internal end. Furthermore, each shoulder also comprises a plurality of lamellae (notches having a width not exceeding 1 mm) circumferentially intercalated with the transverse grooves and substantially parallel to said grooves. The lamellae 11 interspersed with the recesses 5 open on both grooves 3 and 4 and can also extend beyond the aforementioned groove 4, those (12) interspersed with the recesses 6, similarly to these, are blind on their axially internal end. It is hereby specified that this fact does not exclude the possibility, both for the recesses and for the lamellae of each shoulder, to open on both shoulder grooves or to have one or both blind ends.

In a preferred embodiment, the lamellae 11 open axially outwards into a cavity 13 having a width not greater than the maximum width of the recesses 5, and preferably coaxial with said lamellae.

Conveniently, as can be seen in the embodiment illustrated in Figure 1, the transverse grooves of one shoulder are circumferentially scaled with those of the opposite shoulder by a length equal to approximately 50% of the pitch of said transverse grooves. In this regard, it should be remembered that in the tire the tread pattern generally comprises an axial portion which is repeated identical to itself for a predetermined number of times along the circumferential extension of the tire. The circumferential development of said portion constitutes the step of the drawing. Generally, a tread pattern comprises a circumferentially variable pitch “p” according to an alternation of pitches (sequence of steps) of different (two or more) lengths, for example a long wheelbase and a short wheelbase.

The circumferential distance between two adjacent homologous transverse grooves constitutes the pitch "p" of the design according to the invention, which provides for pitches of length between 27 mm and 40 mm for circumferential developments of the tire, measured along the equatorial plane on the external surface of the tread band, between 1850 and 2200 mm. The central zone M comprises two intermediate circumferential grooves 7, 8 preferably located on opposite sides of the equatorial plane X-X, and a plurality of central transverse grooves, inclined with respect to the circumferential direction, part of which intersecting one of said intermediate grooves, the groove 7 in the illustrated case.

In the illustrated embodiment, the aforementioned plurality of grooves comprises two distinct series of transverse grooves, mutually oriented in the opposite direction with respect to the circumferential direction of the tire and preferably perpendicular to each other. The first series comprises notches 9, which follow each other in a circumferential direction all parallel to each other, extending from the internal shoulder groove 4 towards the equatorial plane.

These grooves all flow into the aforementioned groove 4 and follow each other circumferentially in groups of three, where the first groove (9a) of the group ends in the circumferential groove 7, the second groove (9b) crosses said groove 7 and stops at a distance from this groove substantially equal to the distance between groove 7 and groove 4, the third groove (9c) crosses groove 7 and stops substantially at the equatorial plane.

All the recesses 9 face the recesses 5 of which they form the extension in an axially internal direction and are inclined according to an angle γ equal to 45 ° with respect to the circumferential direction.

In the preferred embodiment illustrated, the recesses 5 and 9 are straight and are joined together by means of a curvilinear portion, preferably in the shape of a circle, with a radius of curvature between 30 and 60 mm.

The second series comprises grooves 10 which follow each other in a circumferential direction, all parallel to each other, extending between said pair of intermediate grooves 7 and 8, also oriented at 45 ° with respect to the circumferential direction, but in the opposite direction with respect to the grooves 9 of the first series.

In the illustrated drawing, said hollows also follow one another circumferentially in groups of three, interspersed with the groups of hollows of the first series; in each group the hollows have substantially different lengths according to a ratio of 1: 2: 3. The longer recess (10c) flows into the circumferential groove 7, the other two (10a, 10b) are blind recesses whose ends facing the groove 7 are aligned on a straight line parallel to the axis of the recesses 9 spaced from the facing recess of a section d, not less than 5 mm.

The opposite ends, facing the groove 8, are aligned along a circumferential straight line parallel to said groove 8 and spaced from it by a portion d2 also not less than 5 mm.

Alternatively, as will be seen with reference to the embodiment of Figure 4, all or at least some of the ends of the grooves 10 facing the groove 8 can lead into this groove. From the axially external edge of the groove 8, notches 14 branch off inclined like the grooves 10 and preferably also coaxial with said grooves of which they constitute the extension towards the outer side of the tread. In this case the ratio between the lengths of said grooves is approximately equal to 2: 3: 4. Preferably, the aforesaid grooves have an increasing width proceeding towards the inner edge of the tread, the one on the vehicle side.

It is hereby specified that the number of recesses in each group of each series can be comprised between 1 and 5, preferably equal to 3, and that their orientation with respect to the circumferential direction is preferably comprised between 30 ° and 60 °. Furthermore, the value of the angle between the axes of said recesses 9 and 10 can vary by more or less 15 ° with respect to the aforementioned perpendicular orientation.

It is hereby specified that the previous description of the tread pattern is not intended to be in any way limiting as the number of dimensions and positions of the aforementioned transverse grooves may vary from what is indicated, within the values specified above.

Between the inner shoulder groove 2 and the axially outer edge of the groove 8, in order to favor the comfort of the tire during travel, there is advantageously provided a further circumferentially continuous and rectilinear groove 18, twin of the groove 19, which divides the corresponding cord in two narrower cords placed side by side.

In the preferred embodiment illustrated in Figure 1, lamellae 17, coaxial with said recesses, extend from the blind ends of at least part of the recesses 9 and 10, extending away from the recess until they meet the last recess of the opposite group before of the adjacent circumferential groove.

Figure 2 illustrates the straight section of the tread of Figure 1, according to the section plane of track ABCDEF and, after the explanations already provided, it is not such as to require further clarifications.

Figure 3 illustrates the straight section R-R of the grooves 7, 8 and that Q-Q of a groove 9 superimposed on each other in the same plane, bringing the respective axes and their profiles in correspondence with each other in correspondence with the radially external surface of the tread. The groove 7 has a V-shaped section with the rounded vertex facing radially towards the inside, a width 1s equal to 13 mm, preferably between 10 and 15 mm and a depth h equal to 6 mm, preferably between 3 and 7 mm .

Conversely, the recess 9 has a U-shaped section with a width li equal to 10 mm, preferably between 3 and 10 mm and a depth H equal to 8 mm, preferably between 8.5 and 7 mm. Preferably the two straight sections have the same area A whose value is expressed in mm2.

The recesses 10 also preferably have a U-shaped cross section with a width and depth equal to or less than those of the recesses 9.

The value of the angle a between the slope of the sides of the groove and the axial direction is equal to 45 °, preferably between 35 ° and 55 °: in this context, the sides of the V-shaped grooves can have a different slope from each other. other. The intermediate circumferential grooves are also preferably continuous and straight.

Figure 4 illustrates the tire of the invention in a variant of embodiment with respect to that of Figure 1 intended for tires of greater size, ie with greater tread width. In particular, the drawing refers to a tire size 265/35 ZR 18. The measurements indicated refer for example to the equipment of the PORSCHE 996 car where the larger tires are mounted on the rear, drive axle.

The two drawings have many common characteristics so that the homologous elements in the two drawings maintain the same numerical reference and the following description will highlight only the differences.

It is hereby specified that the drawings described are not limiting with respect to the size of the tire since both drawings can be obtained on the tread of both tires.

In the first place, the central zone comprises a third, central circumferential groove 20, substantially identical to the grooves 7 and 8 and interposed between the two: this groove can be in correspondence with the equatorial plane but the Applicant has preferred to arrange it on the same side, with respect to said plane, of the inner side of the tire so as to differentiate the value of the ratio of the voids to the total between the different areas of the tread pattern. In particular, the drawing of figure 1 shows the following values of the aforementioned ratio: shoulder S1 = 0.107, shoulder S2 = 0.193, center M = 0.356. In the drawing of figure 4 the values of said ratio on the shoulders remain substantially unchanged while on the central part M the value increases to 0.433.

In any case, the values of said void ratio on the total are preferably between 0.1 and 0.2 for the shoulder areas and between 0.25 and 0.45 in the center area for all tires according to the invention.

As regards the lengths of the grooves 10, the three grooves of each group are, in this embodiment, preferably in the mutual ratio 2: 3: 4 and extend so as to intersect at least the pair of adjacent circumferential grooves 8 and 20.

Furthermore, at least part of the lamellae 17 extend until they intersect the circumferential groove opposite to the recess to which they belong.

As for the shoulders, the difference basically lies in the type and number of lamellae. On the outer shoulder of the tire, between two circumferentially adjacent transverse grooves, in relation to the different length of the pattern pitch, there may be more than one siping 12. The sipes are also blind and their ends facing the equatorial plane. they are on the same line that aligns the ends of the grooves.

Also on the vehicle side shoulder between two circumferentially adjacent transverse grooves, in relation to the different pitch length of the pattern, there may be more than one lamella 11 and the aforesaid lamellae extend beyond the circumferential groove 4 without however flowing into the groove 7. When then the slats 11 are arranged in pairs on the same block defined between two transverse grooves 5, none of them constitutes an extension of the notch 13 but this notch is circumferentially spaced with said pair of slats.

Figure 5 illustrates the straight section of the tread of Figure 4, according to the section plane of the ABCD track and, after the explanations already provided, it is not such as to require further clarifications.

The present invention allows to obtain multiple advantages.

The presence of the large circumferential V-shaped grooves on the central portion of the tire crown provides excellent water drainage under the footprint area, ensuring continuous contact between the tire and the road even at high vehicle speeds or in the presence of high thicknesses. 'water. Their V-section first of all solves the known problem of the hinge effect, minimized by the presence of a greater thickness of rubber between the bottom of the groove and the surface of the radially outermost belt layer. The absence of hinges along the circumferential development of the tread results in high characteristics of non-deformability of the tread and of the underlying belt structure in the transverse direction that allow it to effectively resist the stresses acting on the footprint area during the running of the tire when cornering.

Their V-section also solves the problem of sawtooth wear on the edges of the circumferential grooves. In fact, the slope of the flanks of these grooves generates massive edges on the corresponding beads or blocks that delimit the groove, which cannot flex under the thrust of the tangential forces in the axial direction produced on the footprint area during cornering due to the force centrifuge.

Water drainage is also ensured by the presence of the plurality of transverse grooves distributed over the entire width of the tread. These grooves, due to their inclined orientation on the circumferential direction, are not the most effective solution for the disposal of water, which the circumferential grooves provide, but they can have a considerable depth, as they do not generate hinge effects on the tread, so they behave as a water catchment basin awaiting disposal.

In other words, it can be said that the tire of the invention has two channeling systems for water drainage combined with each other, and precisely a deep system, consisting of transverse grooves, for collecting the water taken from the area of footprint and a surface system, consisting of circumferential grooves for quick disposal of the water collected from both systems. Critical elements of this double system of ducts are the values of the reciprocal dimensional ratios indicated above.

The asymmetrical nature of the illustrated tread patterns entrusts the greatest effort in terms of traction and water disposal to the center line of the tread arranged on the side of the vehicle, which therefore has a more empty pattern than the axially opposite part which is entrusted with the task of providing maximum wear resistance: in order to maintain good aquaplaning qualities, the internal shoulder groove, located on the outer side of the tread, has a greater width than the corresponding internal shoulder groove, located on the inner side of the tread. Advantageously, it has been found that increasing the width of this groove, while increasing the area of the gaps in the outer shoulder area, helps to improve road holding when cornering, particularly on wet ground.

A further advantage of the invention derives from the fact that the design of the tread band has a high value of the full / empty ratio. This feature results in low values of specific pressures in the imprint area and therefore modest deformations of the design blocks with consequent lower noise development.

Advantageously, the shoulders of the tire, where the higher specific pressure is exerted during travel, have a lower total of voids than the central area, that is, they are more massive than the center, with a considerable advantage in terms of running silence. An advantageous improvement in tire comfort is obtained, without compromising the longitudinal stiffness of the tread, i.e. the directional stability of the vehicle, and the overall value of the solids, by means of the pair of thin twin grooves, with a width between that of the sipes and that of the internal shoulder groove, on the outer side of the tread, arranged on opposite sides of said groove.

Finally, the fact of having defined in the central zone M a system of transverse grooves which never intersect each other, leads to an extreme capacity of reaction of the tread to the forces of external stresses.

To clarify this aspect, reference will be made to the drawings described above, with particular attention to the orientation of all the recesses both between them and relative to the equatorial plane.

Having said this, it should be noted that in the conditions of rolling when cornering, the tire is subjected to stresses resulting from the vector composition of a force in the direction of travel and a force perpendicular to the equatorial plane, necessary to balance the centrifugal force.

These resulting stresses have a direction on the tire which depends both on the strength characteristics of the compound forming the tread and on the prevalence of one of the two forces directed respectively in the direction of travel and in the transverse direction.

In accordance with the invention, the plurality of full, oblique portions of tread delimited between the pairs of adjacent and parallel transverse grooves constitutes a network of "struts" suitable for discharging the aforementioned resulting stresses along their own axis and since these portions oblique are substantially orthogonal to the oblique portions delimited by the grooves of the opposite group the whole system of struts contributes to elastically counteract the stresses acting on the tire. Once the person skilled in the art has understood the invention as previously described, he will now also be able to make all those choices, variants and modifications of the variables associated with the invention necessary to solve the specific technical problem faced by him; in particular, it will not have any difficulty in varying the axial position of the circumferential grooves and the inclination of the transverse grooves to convert the asymmetrical designs described and illustrated here into symmetrical or directional designs in relation to the particular type of use of the vehicle that is to be equipped with the tires of the invention.

It should again be noted that the descriptions of the aforementioned tread designs should not be construed in a limiting sense for the invention, constituting only a particular example among the various possible embodiments.

Claims (26)

R I V E N D I C A Z I O N I 1. Vehicle wheel tire comprising: a carcass structure including a central portion of the crown and two axially opposite sides ending in a pair of beads for anchoring the tire to a corresponding rim of a wheel; a belt structure, coaxially associated with the carcass structure; - a tread band, coaxially extended around the belt structure, printed with a relief design on which are defined: - two axially opposite shoulder areas, each delimited between a pair of circumferential shoulder grooves, respectively axially external and axially internal, said shoulder areas comprising a plurality of transversal grooves inclined with respect to the circumferential direction of the tire, - a central area delimited between the axially internal grooves of said pair of circumferential shoulder grooves, comprising at least two intermediate circumferential grooves, and a plurality of transverse grooves inclined with respect to the circumferential direction, intersecting at least one of said intermediate grooves, characterized in that at least the intermediate circumferential groove intersected by said plurality of transverse grooves has, on the straight section with a radial plane, a V-shaped profile with the vertex in a radially internal position, of greater width and less depth than those of said transverse grooves . 2. Tire as in claim 1, characterized in that the value of the ratio between the depth (h) of said V-groove and that (H) of the transverse grooves that intersect it is comprised between 0.35 and 0.82. 3. Tire as in claim 1 characterized in that the value of the ratio between the width (ls) of said V-groove and that (li) of the transverse grooves that intersect it is comprised between 1.5 and 5. 4. Tire as in claim 1, characterized in that the width (ls) of said V-groove is comprised between 10 mm and 15 mm. 5. Tire as in claim 1 characterized in that the depth (h) of said V-groove is comprised between 3 mm and 7 mm. 6. Tire as in claim 1 characterized in that the area (A) of the cross section of the V-groove and that of the cross section of the transverse grooves which intersect it are equal to each other. 7. Tire as in claim 1, characterized in that the angle a of inclination of the sides of the V-groove with respect to the axial direction is comprised between 35 ° and 55 °. 8. Tire as in claim 1 characterized in that said transverse grooves have a U-shaped cross section. 9. Tire as in claim 1, characterized in that said transverse grooves have a width (l) comprised between 3 mm and 10 mm and a depth (H) comprised between 7 mm and 8.5 mm. 10. Tire as in claim 1, characterized in that the transverse grooves of said central zone comprise two series of grooves, respectively inclined on opposite sides with respect to the axial direction. 11. Tire as in claim 10, characterized in that the angle of inclination γ of said transverse grooves with respect to the circumferential direction is comprised between 30 ° and 60 °. 12. Tire as in claim 11 characterized by the fact that the angle of inclination of said grooves of the first series with respect to said grooves of the second series is between 75 ° and 105 °. 13. Tire as in claim 10 characterized in that each of said series comprises a circumferential succession of groups of grooves interspersed with groups of grooves of the other series. 14. Tire as in claim 13 characterized in that said groups of grooves comprise three grooves parallel to each other in each series. 15. Tire as in claim 13 characterized in that the ends of the grooves of one group are aligned along a straight line parallel to the grooves of the opposite group. 16. Tire as in claim 1 characterized in that the tread comprises three circumferential V-shaped grooves. 17. Tire as in claim 10 characterized in that at least part of the grooves of each series pass through two adjacent circumferential grooves. 18. Tire as in claim 10 characterized in that the grooves of the same group differ from each other in length. 19. Tire as in claim 1 characterized by the fact that the angle of inclination β of the transverse grooves of the shoulder area with respect to the axial direction is between 60 ° and 120 ° 20. Tire as in claim 1 characterized in that the transverse grooves of the shoulder region have a depth of between 4 mm and 10 mm. 21. Tire as in claim 1 characterized in that the transverse grooves of the shoulder region have a maximum width between 2 mm and 10 mm. 22. Tire as in claim 19 characterized in that the grooves of at least one shoulder area are straight and oriented perpendicular to the equatorial plane. 23. Tire as in claim 1 characterized in that the grooves of at least one shoulder region are joined to the adjacent transverse grooves of the central region with a curvilinear portion having a radius of curvature between 30 and 60 mm. 24. Tire as in claim 1, characterized in that the value of the void area / total area ratio on said shoulder areas is between 0.1 and 0.2. 25. Tire as in claim 1 characterized in that the value of the void area / total area ratio on said center area is between 0.25 and 0.45. 26. Pre-molded tread band for covering worn tires characterized in that it comprises a relief pattern according to one of the preceding claims.