ITMI992516A1 - TIRE FOR VEHICLES AND HIGH AND MEDIUM PERFORMANCE - Google Patents

Description

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

Description

The invention refers to a tire for medium and high performance cars and, more particularly, to a tire with characteristics particularly, but not exclusively, suitable for use on winding roads and on dry roads.

A 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 the rim of a wheel, a belt structure coaxially associated with the structure of carcass and a tread band extending coaxially around the belt structure.

Generally the tread band comprises a relief design formed by a plurality of transverse and longitudinal grooves originating, as a whole, a plurality of blocks distributed according to different types of configurations, for example along a central area extending across the equatorial plane and in at least two areas of shoulder extended in axially opposite position with respect to the central area.

During the rolling of the tire, the blocks present on the tread band are subjected to a complex of thermo-mechanical stresses, the stronger the more severe the conditions of use that cause changes in their geometry and, in more or less rapid times, a decay tire performance.

In particular, during travel, contact with the ground causes a bending of the trailing edge of the tire blocks, said edge lowering radially towards the inside and moving in the opposite direction to travel, causes a narrowing of the groove that separates it from the next block. . This fact exposes the leading edge of the latter to a tangential stress that is repeated cyclically with each revolution of the wheel causing a typical irregular and premature wear, known as "sawtooth wear".

Tires that try to minimize the number of blocks and strengthen their structure are already known in the art.

For example, the patent WO 98/25776 refers to a tire comprising a tread band provided with transversal grooves distributed in three distinct areas, a central area straddling the equatorial plane and two shoulder areas, to define a directional tread pattern, that is, having a preferential direction of rotation.

Each transverse recess comprises a first portion extended in a shoulder region in a direction perpendicular to the equatorial plane and a second obliquely extended portion in the equatorial zone.

The transverse grooves are circumferentially distributed with a “p” pitch and extend alternately from opposing shoulder areas.

More specifically, in the aforementioned tread band these transverse grooves are distributed in groups; more specifically, the tread band comprises a first group of three grooves, parallel to each other, repeated circumferentially with a step "P" to the left of the equatorial plane and alternating with a second group of three grooves, parallel to each other, and repeated with an identical step " P ”to the right of the equatorial plane.

In each group the grooves have decreasing length in the direction of advancement of the tire and such that one of the grooves crosses the equatorial plane while the remaining two grooves are interrupted near the equatorial plane, at a different distance from the latter.

The configuration of the transverse grooves is such as to originate, in the spaces between the alternating groups, a central bead which is circumferentially extended in a continuous zigzag and a plurality of transverse ribs that branch off from the central cord and extend obliquely to the right and left of the equatorial plane. in the opposite direction to the rolling direction of the tire.

The state of the art does not completely solve the problem of making a tire provided with a tread pattern that can be indifferently symmetrical or asymmetrical or directional and that is at the same time able to minimize and uniform wear of the tread band during rolling. of the tire, and to improve and standardize the longitudinal and transverse stiffness in order to ensure effective stability both in straight lines and in curves on dry roads, all without worsening the characteristics of reduced rolling resistance, sufficient smooth running and good driveability even on non-dry terrain, for example on wet roads or in the presence of snow.

The tire described in the patent WO 98/25776 has transversal grooves extending with continuity and high density from the shoulder areas up to the area straddling the equatorial plane, thereby giving rise to a plurality of narrow and long-limbed blocks, obliquely arranged with respect to at the equatorial plane, excessively deformable. In this way, irregular wear of the elastomeric material delimiting these grooves may arise, in particular in the conditions of rolling the tire in a straight line on dry roads or in any case in conditions in which the stresses acting along the equatorial plane are significantly greater than those acting perpendicularly. to that floor.

The Applicant has perceived that a better solution to the above problem could be achieved by resorting to a tread band substantially devoid of blocks, and divided into at least five zones: a central zone straddling the equatorial plane, two intermediate zones arranged on the sides of the central zone and two shoulder zones, arranged in an axially external position with respect to said intermediate zones.

The Applicant has found that a preferred solution consists in providing each intermediate zone, at a predetermined distance from the equatorial zone, with a plurality of transverse grooves, arranged in axially opposite groups and at a predetermined mutual distance, so that, in the spaces between said grooves, define a continuous circumferential bead having a typically "zigzag" configuration.

The Applicant has perceived that it is possible to optimize the solution found by giving the central area of the tread band particular geometric characteristics not present in the other areas (intermediate and / or shoulder) and / or in any case a design different from that of the intermediate and / or shoulder areas. shoulder in order to obtain a synergistic effect capable of improving or integrating the performances offered by the designs of these areas.

Furthermore, the Applicant has found it particularly advantageous to differentiate the density of the transverse grooves possessed by the shoulder areas and by the intermediate areas contiguous to them, so as to distribute the grooves of the intermediate areas according to a circumferentially repeated module with a pitch different from that of the distribution of said hollows in the shoulder areas.

In a first aspect, the invention 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 said tire to a corresponding rim of a wheel;

- a belt structure, coaxially associated with said carcass structure;

- a tread band, coaxially extended around said belt structure, printed with a relief design comprising:

- a central zone (E), located astride the equatorial plane (Y-Y) of said tire and extending between two central planes (a-a) substantially parallel to said equatorial plane;

- two intermediate zones (F), each of which extending between one side of said central zone (E) and an intermediate plane (b-b) substantially parallel to said equatorial plane (Y-Y);

- two shoulder zones (G), each of which extending between the axially outermost side of one of said intermediate zones (F) and an axially external plane (c-c), substantially parallel to said equatorial plane (Y-Y) and placed in correspondence of the lateral edge of said tread band, said intermediate (F) and shoulder (G) zones comprising a plurality of transverse grooves,

characterized in that each intermediate zone (F) comprises two series of pairs of transverse grooves, first and second series respectively, the pairs of said first series being consecutively alternated for the entire circumferential length of the tire with the pairs of said second series, each pair being formed by two distinct recesses at least partially parallel, the recesses of each pair of said first series being inclined according to a predetermined angle a with respect to the recesses of each pair of said second series, said recesses of said first series starting from axially opposite parts of said intermediate zones and ending with ends inside the latter with respect to the grooves of said second series, said internal ends of a pair of a given series being at a predetermined distance from the groove of the pair of the other series closest to said ends, said predetermined distance circumferentially originating a continuous bead ext so in a “zigzag” pattern from which continuous oblique portions branch off alternately from opposite sides, each delimited by the hollows of one of these pairs.

Advantageously, each intermediate zone comprises a continuous "zigzag" bead and a plurality of continuous, ie full, portions of elastomeric material which branch off transversely from both parts of each "zigzag" bead. These characteristics determine in each intermediate zone a resistant structure both in the longitudinal direction and in the transversal direction capable of reacting elastically to the stresses acting on the tread band during the rolling of the tire.

In particular, it should be noted that the mutual configuration of the two series of pairs of transverse grooves is such that it is possible to pass from one side to the other of each intermediate zone (i.e. from plane a-a to plane b-b, or vice versa) without intersecting any groove. In this way, therefore, large transversal areas of said intermediate areas are obtained which give the tread band particularly favorable characteristics of non-deformability for resisting the stresses acting on curves during the rolling of the tire.

In a preferred embodiment of the invention, each pair of grooves has a groove having a longer length than the other. Therefore, for greater simplicity of description, in the continuation of the present treatment, where reference is made to the aforementioned preferred embodiment, the transverse grooves of each pair will be indicated as long groove and short groove. Furthermore, the two ends of each transversal notch will be respectively indicated as the terminal end and the starting end both in the case in which a notch is being considered in a position inside the intermediate zone, and in the case in which an opposite notch is being considered.

Preferably the terminal ends of the long grooves of a pair of grooves belonging to a given series are aligned with the terminal ends of the short grooves of a consecutive pair of grooves belonging to the other series, and vice versa.

Even more preferably, the pairs of grooves belonging to a given series comprise blind-shaped grooves.

Here and in the rest of this description, as well as in the attached claims, the term "blind recess" means a recess surrounded by continuous walls without any way of entry and / or exit to the recess itself.

Preferably the recesses of said series of pairs have the same shape and, even more preferably, said shape is of the elliptical type.

The transversal grooves of the intermediate zones and the contiguous ones possessed by the shoulder zones may be offset or not from each other.

In a preferred embodiment, the pairs of transverse grooves of the series closest to the shoulder region, adjacent to the intermediate region to which said pairs belong, are connected consecutively with the transverse grooves possessed by said shoulder region.

In accordance with a particularly preferred embodiment, since it is capable of conferring advantageous traction qualities to the tire of the invention, the transverse shoulder grooves are arranged perpendicular to the equatorial plane of the tire.

Even more preferably, the succession of a pair of transversal grooves respectively of the first and second series gives rise in the intermediate zone to a module which is circumferentially repeated with a pitch double with respect to the pitch of the transversal grooves present in the shoulder region.

Advantageously, the difference between said steps (ie between the step in the shoulder areas and the step in the intermediate areas) creates a discontinuity in the fronts of the tread along the footprint area which, advantageously, improves the silence of the tire.

Preferably, the central area of the tread band straddling the equatorial plane comprises two circumferential grooves delimiting a central bead inside them. Alternatively, said central area comprises a single circumferential groove, preferably of the straight type.

Advantageously, said one or more central grooves favor the drainage of water during the rolling of the tire on wet roads, avoiding the formation of a film of water between the tire and the road.

In a second aspect, the invention refers to a pre-molded tread band for covering worn tires comprising:

a central zone (E), located astride the equatorial plane (Y-Y) of said tire and extending between two central planes (a-a) substantially parallel to said equatorial plane;

- two intermediate zones (F), each of which extending between one side of said central zone (E) and an intermediate plane (b-b) substantially parallel to said equatorial plane (Y-Y);

- two shoulder zones (G), each of which extending between the axially outermost side of one of said intermediate zones (F) and an axially external plane (c-c), substantially parallel to said equatorial plane (Y-Y) and placed in correspondence of the lateral edge of said tread band, said intermediate (F) and shoulder (G) zones comprising a plurality of transverse grooves,

characterized in that each intermediate zone (F) comprises two series of pairs of transverse grooves, first and second series respectively, the pairs of said first series being consecutively alternated for the entire circumferential length of the tire with the pairs of said second series, each pair being formed by two distinct recesses at least partially parallel, the recesses of each pair of said first series being inclined according to a predetermined angle a with respect to the recesses of each pair of said second series, said recesses of said first series starting from axially opposite parts of said intermediate zones and ending with ends inside the latter with respect to the grooves of said second series, said internal ends of a pair of a given series being at a predetermined distance from the groove of the pair of the other series closest to said ends, said predetermined distance circumferentially originating a continuous bead ext so in a “zigzag” pattern from which continuous oblique portions branch off alternately from opposite sides, each delimited by the hollows of one of these pairs.

Preferably, the transverse grooves of said intermediate zones have an elliptical type configuration; even more preferably the major axes of said ellipses form a predetermined angle a between them between 80 ° and 100 °.

In a preferred embodiment, the major axes of the ellipses corresponding to the transverse grooves of the pairs of grooves of said first series form an angle γ comprised between 35 ° and 55 ° with respect to a plane parallel to the equatorial plane Y-Y.

Preferably, the grooves of each pair have a different length and each of the terminal ends of the grooves of a pair of a given series is aligned with as many terminal ends of the grooves of an axially opposite pair of the other series. More specifically, the terminal ends of the longest grooves of the first series are aligned with the terminal ends of the shorter axially opposite grooves, i.e. belonging to the second series and, similarly, the terminal ends of the shorter grooves of the first series are aligned with the terminal ends of the longest grooves belonging to the second series. .

Conveniently, the tread band is characterized by the fact that all the transverse grooves with starting ends close to the central zone have a blind shape. Preferably, the tread band according to the invention has a ratio between the width of the central zone and the width (W) of the tread band between 0.10 and 0.20, and a ratio between the width of an intermediate zone (L0) and the width of the tread band itself between 0.17 and 0.30.

Preferably the two intermediate zones have the same width.

In a further preferred embodiment of the invention, each intermediate area of the tread band has a full / empty ratio between 0.75 and 0.90.

Brief description of the figures

Further characteristics and advantages will become clearer from the following description of a preferred embodiment example of a tire according to the invention, made by way of non-limiting example with reference to the attached drawings, in which:

Figure I shows a cross-sectional view of a tire according to the invention, in particular of a tire intended to be mounted on the front wheel of a vehicle,

figure 2 shows a partial plan development of the tread band of the tire of figure 1,

figure 3 shows a partial plan development of a tread band according to a further embodiment of the tire of the invention,

Figure 4 illustrates some details of the partial plan view of Figure 2.

Detailed description of the preferred embodiments

With reference to Figures 1 and 2, 1 generally indicates a tire for high performance vehicles according to the invention, in particular a tire intended to be mounted on the front axle of a motor vehicle.

The tire I comprises a carcass structure 2, including a central portion of crown 3 and two sides 4, 5, said carcass structure 2 being provided with a reinforcing ply 2a whose opposite ends 2b, 2c are folded around corresponding cores 6, 7.

An elastomeric filling 8 is applied to the radially external perimeter edge of the bead cores 6, 7, arranged at the radially internal ends of said sides 4, 5, occupying the space defined between the reinforcement ply 2a and the corresponding ends 2b, 2c of the reinforcement cloth 2a.

As is known, the opposite areas of the tire 1, each comprising a bead core 6, 7 and the filling 8, form the so-called beads, globally indicated with 9 and 10, intended for anchoring the tire 1 on a corresponding mounting rim 11 of the wheel of a vehicle.

A belt structure 12 is coaxially associated with the aforesaid carcass structure 2 comprising one or more reinforcement strips 13 made by means of textile or metal cords incorporated in a given compound.

In a known way, a tread band 14 is applied to the belt structure 12 in the thickness of which a pattern illustrated in more detail in Figure 2 is carved.

Below, for simplicity of description, the tread band 14 of figure 2 will be detailed only in its part arranged to the left of the equatorial plane Y-Y since the part located to the right of said plane is the same as that on the left after overturning by 180 °. and subsequent predetermined offset in the circumferential direction.

The tread band 14 is divided into a plurality of zones, namely:

- a central zone E arranged over the equatorial plane Y-Y and between two central planes a-a, substantially parallel to the equatorial plane Y-Y,

- two intermediate zones F, each of which extends between one side of the zone E, i.e. between a plane a-a, and an intermediate plane b-b substantially parallel to said equatorial plane Y-Y,

- two shoulder areas G, each of which is delimited between a side of the intermediate area F, that is, between a plane b-b, and an axially external plane c-c substantially parallel to said equatorial plane Y-Y and placed in correspondence with the lateral edge of said tread band.

In the illustrated embodiment, the central area E comprises a central bead 15 with a width between 12 and 20 mm and two longitudinal grooves 16 arranged respectively on one side and the other of said bead 15.

Advantageously, the bead 15 gives the tire 1 an appropriate longitudinal stability during rolling and the two longitudinal grooves 16 favor the expulsion of water in driving conditions on wet roads.

The central zone E extends over the equatorial plane Y-Y for a portion equal to at least 10% of the axial width W of the tread band 14, measured between the planes c-c arranged in correspondence with the lateral edges of said tread band.

It should be noted that the aforementioned conformation of the central zone E must not be understood in a limiting sense for the invention, in fact constituting an example among various possible embodiments.

In the intermediate zones F the tread band 14 comprises a plurality of transverse grooves, preferably of an elongated elliptical shape, according to a configuration comprising two series of pairs of grooves repeated circumferentially.

More specifically, each intermediate zone F comprises a first series of pairs of grooves 17 and a second series of pairs of grooves 18 consecutively arranged along the circumferential direction, said second series being axially opposed to said first series along the entire circumferential development.

In the embodiment indicated in Figure 2, each pair of said series is formed by two distinct recesses, one long and one short, at least partially parallel to each other. Furthermore, the recesses of said second pairs 18 are of the blind type.

Conveniently, as shown in Figure 2, in each pair 17, 18 the longitudinal axis of the short recess has a length between 30% and 70% of the length of the long recess. In addition, the distance "1" between the long groove and the short groove of each pair is between 15 mm and 40 mm, said distance being measured perpendicular to the longitudinal axis of each groove.

The recesses of the pair 17 form, with respect to the direction of the equatorial plane Y-Y, an angle γ comprised between 35 ° and 55 °. In addition, the longitudinal axes of the recesses of the pairs 17 of the first series form, with the longitudinal axis of the recess of the pair 18 closer to the recesses of said couples 17, a predetermined angle a between 80 ° and 100 °. Preferably a is equal to 90 °.

More specifically, all the transverse recesses of the pairs 17 of the first series start from the axial planes b-b of separation with the shoulder areas G and end with ends 19, 20 at a distance "d" from the longitudinal axis of the respective long recesses of the pairs 18 of the second series.

In turn, all the transverse grooves of the pairs 18 of the second series start from parts of the intermediate zone F axially opposite to the pairs 17 of the first series and end with ends 21, 22 at a distance "d" from the longitudinal axis of the respective long grooves of the 17 pairs of the first series. Conveniently, this distance "d" is between 5 mm and 25 mm.

The starting ends of the recesses of the pairs 18 are aligned on the same plane whose distance "D" from the equatorial plane Y-Y is between 14mm and 32mm.

In the example shown in Figure 2 all the terminal ends 19, 20, 21, 22 of the recesses of the first 17 and second 18 pairs are aligned on two distinct planes substantially parallel to the equatorial plane Y-Y, and more precisely:

- all the ends 19 of the long recesses of the pairs 17 and all the ends 22 of the short recesses of the second pairs 18 are aligned on the same plane whose distance D! from the equatorial plane Y-Y is between 22 mm and 82 mm;

- all the ends 20 of the short grooves of the first pairs 17 and all the ends 21 of the long grooves of the pairs 18 are aligned on the same plane whose distance D2 from! equatorial plane Y-Y is between 30 mm and 95 mm.

Conveniently, all the transverse grooves of said pairs 17, 18 have a width between 3.5 mm and 10 mm and a maximum depth between 5 mm and 10 mm. The tread band 14 comprises further transversal grooves in the shoulder regions G each of said grooves comprising at least a straight portion 24 which forms, with respect to the equatorial plane Y-Y, an angle of not less than 85 °, preferably equal to 90 °.

More in detail, each transverse shoulder notch is formed by two sections 23 and 24, the first (23) about 8 mm wide and between 5 mm and 10 mm deep and the second (24) about 4 mm wide and 1 mm deep and 6 mm. Furthermore, the ratio between the lengths of said two portions 23, 24 is comprised between 30% and 50%.

Advantageously, it has been found that the reduction in width of the shoulder recess 23, 24 (in passing from the portion 24 to the portion 23 in the axial direction approaching the equatorial plane Y-Y), resulting in an increase in the area of the solids in the shoulder area, it contributes to improving the road holding in curves of the tire according to the invention. In the embodiment illustrated in Figure 2, the portions 23 of the shoulder recesses are connected by means of a curvilinear portion to the aforementioned transverse recesses of the pairs 17 of the first series belonging to the intermediate zone F. Preferably, this connecting portion is an arc of a circle with a radius included between 30 mm and 60 mm.

As can be seen from Figure 2, the design of the tread band 14 in the shoulder areas G is mainly identified by a plurality of transverse grooves 23, 24 repeated circumferentially with a step "p". Similarly, the aforementioned connecting sections, which connect the recesses of the shoulder areas G with the transverse recesses of the pairs 17 of the intermediate areas F, are repeated circumferentially with the same pitch "p".

The design of the intermediate zones F, as mentioned, is identified by pairs of transverse grooves 17, 18 which alternate along the circumferential direction, originating a module that is repeated, along the circumferential development of the tread, with a pitch "P" different from the step “p” of the transverse shoulder grooves. In the preferred embodiment illustrated in Figure 2, the pitch "P" has a substantially double value with respect to the pitch "p". For the sake of simplicity, a tread band with a single pitch "p" has been described, but it is clear that the above is also valid for tread bands with a circumferentially variable pitch "p" according to a predetermined law, for example with alternating pitches "p" of two different lengths, respectively a long wheelbase and a short wheelbase.

The preferred embodiments of the present invention provide pitches "p" ranging from 25 mm to 50 mm when the circumferential development of the tire, measured along the equatorial plane at the outermost point of the tread band, is between 1750 mm and 2200 mm.

Conveniently, in each shoulder area G the tread band 14 of the tire 1 comprises a longitudinal notch 25, also called "disconnection groove", and a longitudinal incision 26.

The notch 25 and the incision 26 are extended circumferentially in a substantially perpendicular direction to the transverse shoulder grooves 23, 24.

The longitudinal notch 25 has a depth of about 2 mm and a width of about 3 mm, while the longitudinal incision 26 has a width of about 1.5 mm and a depth between 3 mm and 7 mm.

Advantageously, said incisions and notches increase the wet grip.

Conveniently, in each shoulder region G the tire 1 further comprises a plurality of transverse notches 27 interposed between two consecutive transverse shoulder grooves 23, 24.

These notches 27 have a depth of about 4 mm and a width of about 3 mm and extend axially along a section between the longitudinal notch 25 and the longitudinal incision 26.

Advantageously, the use of said notches helps to reduce the noise of the tire.

Figure 3 illustrates a further embodiment of the invention concerning a detail of a tire 28 of the directional type, i.e. provided with an overall design having a predetermined rolling direction (in Figure 3 indicated by the arrow R) and two intermediate portions F and shoulder G of the tread band, placed on the sides of the equatorial plane Y-Y, which mirror each other on one side and on the other of said equatorial plane. The two halves of the tread band 28 comprise the same design features already described above, therefore the elements of the tire 28 structurally or functionally equivalent to those previously illustrated with reference to the tire 1 shown in Figures 1 and 2 will be indicated with the same reference numbers. reference and will not be described further.

As can be seen in the embodiment illustrated in Figure 3, the intermediate areas F and shoulder G of the tread band 28, in addition to being specular with respect to the equatorial plane Y-Y, are also out of phase with each other in the circumferential direction for a value equal to approximately 50% of the pitch "p" of the transverse shoulder grooves.

Defined with L the width of each shoulder area G and with W the width of the tread band measured between the planes c-c, the preferred embodiments of the tire according to the invention provide for a LAV ratio preferably between 0.10 and 0.28.

These preferential values of said ratio, as well as the aforementioned intervals relating to the dimensional quantities described, relate to tires having measures 185 / 60R14 or 225 / 50R16 or 255 / 45R18.

The present invention allows the achievement of a plurality of advantages.

A first advantage consists, for example, in the fact that having defined in the two intermediate areas F a system of transverse grooves that never intersect each other, gives the tread band a high reaction capacity against external stress forces.

In order to better clarify this aspect, reference is now made to a tread band 14 of the tire 1 illustrated in Figure 4 which is entirely the same as Figure 2 except for some further references introduced to explain the above.

The intermediate zones F of the tread band 1 comprise a particular design whose geometric characteristics depend, among other things, on the distance "1" between the two grooves of the same pair (17, 18), on the particular shape of the space between two grooves of the same pair, from the distance "d" between the two pairs of transversal grooves 17,18 distributed in a pitch "P", as well as from the orientation of all the pairs both between them and relative to the equatorial plane Y-Y. These characteristics determine in each intermediate zone F the formation of a "zigzag" bead extended throughout the circumferential development as well as a plurality of continuous portions of elastomeric material which branch off obliquely from both sides of said "zigzag" bead.

This configuration is represented schematically in figure 4 in which, for greater clarity, both the circumferential "zigzag" bead 29 and the oblique portions 30, 31 that branch off from it have been represented with dashed lines.

The two "zig-zag" beads 29 and the oblique portions 30, 31 are formed by continuous parts of elastomeric material which allow to oppose the stresses exerted by the ground on the tire during rolling. '

Having said all this, it is known that in the conditions of rolling on curves a tire is subjected to stresses resulting from the vector composition of a force acting in the direction of travel and of 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 resistance characteristics of the compound used in the tread band and on the prevalence of one of the two forces directed in the direction of travel or in the transverse direction.

In accordance with the invention, the plurality of oblique portions 30, 31 arranged as shown in Figure 4 constitute "struts" designed to discharge the aforementioned resulting stresses along their axis. Furthermore, since the oblique portions are connected to the "zigzag" beads 29, also these beads will contribute with their resistance to elastically balancing the stresses acting on the tire.

In particular, if the resultant of the stresses is directed in the direction of the arrow "f 'in figure 4, the active" struts "will be those relating to the plurality of portions 30 equally oriented in the direction of said resultant within the two intermediate zones F .

As a result of this ability to elastically resist transverse forces, the tire according to the invention lends itself favorably to use along winding paths.

Furthermore, as can be seen from figure 4, from each section of the broken line constituting the "zigzag" circumferential bead 29, alternatively, first an oblique portion 30 and then an oblique portion 31 branch off, in a direction substantially perpendicular to the portion 30, so such that the two portions, substantially of equal size, confer a substantial uniform rigidity both in the transverse and longitudinal directions to each intermediate zone F.

Advantageously, the uniform stiffness of the two intermediate zones F combined with the absence of isolated blocks significantly contributes to minimizing the wear of the tread band and to uniform said phenomena in order to avoid irregular wear of said band.

A further advantage of the tire according to the invention consists in the fact that, thanks to the alternate distribution of the pairs of transverse grooves of the first and second series belonging to said intermediate zones and to the high density of the transverse grooves in the shoulder areas, the number of grooves cross sections present in the footprint area during the rolling of the tire is advantageously kept constant. This aspect translates into an optimization of the distribution of pressures in the footprint area during the rolling of the tire.

A further advantage of the present invention consists in the fact that the design of the tread band has a high solids / voids ratio.

In fact, as can be seen from figure 4, the high solids / voids ratio is determined not only by the presence of the continuous beads of "zigzag" elastomeric material 29 and of the oblique portions 30, 31 which branch off obliquely from them, but also by the presence of longitudinal seams 33, 34 included between the starting ends of the recesses of the pairs 18 of the second series of the intermediate zones F and the planes a-a separating the intermediate zones F from the central zone E.

Preferably the width "T" of the beads 33, 34 is comprised between 3 mm and 21 mm.

The presence of the continuous seams 33, 34 causes the portion of the intermediate zone F closest to the central zone E to have a greater stiffness than the stiffness possessed by the remaining intermediate zone F contiguous to the shoulder zone G.

Furthermore, the high solids / voids ratio, with values between 0.65 and 0.85, results in low values of the specific pressures in the footprint area and low deformability of the tread band in this area with consequent advantageous attenuation of the noise of the tire. of the invention.

In particular, the tire according to the invention, having transversal grooves of the intermediate zones F isolated from each other and separated from the equatorial plane Y-Y through the central zone E, has a lower deformability relative to known tires equipped with transversal grooves directed from the shoulder regions. up close to the equatorial plane, and sometimes beyond the latter. Therefore, thanks to a more massive tread band than known tires, the present tire is advantageously endowed not only with a lower noise level, but also with a lower rolling resistance.

A further advantage of the present tire consists in the excellent driving performance which can be obtained even in the presence of snow-covered roads. In fact, according to one of the preferential embodiments according to the aforementioned invention, said tire comprises a tread band provided in the intermediate areas with a plurality of transversal blind-shaped grooves capable of capturing and retaining snow by replacing friction with rubber. snow the snow-snow friction being the latter, as is well known, far superior to the former.

Once the person skilled in the art has understood the invention as described above, he will now be able to make all those choices, variants and modifications of the variables associated with the invention necessary to solve the specific technical problem he has faced, i.e. to privilege a specific behavioral aspect (for example the mileage with respect to silence, increasing the depth of the inclined grooves, or the traction with respect to wear, increasing the depth and / or width of the transverse grooves, etc.) in relation to the severity of the exercise of the particular type of use of the vehicle to be equipped with the tires of the invention.

Claims (25)

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 said tire to a corresponding rim of a wheel; - a belt structure, coaxially associated with said carcass structure; - a tread band, coaxially extended around said belt structure, printed with a relief design comprising: - a central zone (E), located astride the equatorial plane (Y-Y) of said tire and extending between two central planes (a-a) substantially parallel to said equatorial plane; - two intermediate zones (F), each of which extending between one side of said central zone (E) and an intermediate plane (b-b) substantially parallel to said equatorial plane (Y-Y); - two shoulder zones (G), each of which extending between the axially outermost side of one of said intermediate zones (F) and an axially external plane (c-c), substantially parallel to said equatorial plane (Y-Y) and placed in correspondence of the lateral edge of said tread band, said intermediate (F) and shoulder (G) zones comprising a plurality of transverse grooves, characterized in that each intermediate zone (F) comprises two series of pairs of transverse grooves, first and second respectively series, the pairs of said first series being consecutively alternated for the entire circumferential length of the tire with the pairs of said second series, each pair being formed by two distinct grooves at least partially parallel, the grooves of each pair of said first series being inclined according to a predetermined angle (a) with respect to the recesses of each pair of said second series, said recesses of said first series starting from d to axially opposite parts of said intermediate zones and ending with ends inside the latter with respect to the grooves of said second series, said internal ends of a pair of a given series being at a predetermined distance from the groove of the pair of the other closest series at said ends, said predetermined distance originating circumferentially a continuous bead extended in a "zigzag" shape from which continuous oblique portions branch off alternately from opposite sides, each delimited by the hollows of one of said pairs. 2. Tire as in claim 1, characterized in that the transverse grooves of said intermediate zone are delimited in length by substantially rectilinear walls and are parallel to each other. 3. Tire as in claim 1, characterized in that said predetermined angle et is comprised between 80 ° and 100 °. 4. Tire as in claim 3, characterized in that the grooves of the pairs of said first series form, with respect to a plane parallel to the equatorial plane, an angle y comprised between 35 ° and 55 °. 5. Tire as in claim 1, characterized by the fact that each of said pairs comprises a groove of greater length than the other. 6. Tire as in claim 5, characterized by the fact that the short groove of each pair has a length between 30% and 70% of the long one. 7. Tire as in claim 1, characterized in that the terminal ends of the long grooves of one pair are aligned with the terminal ends of the short grooves of the other pair and vice versa. 8. Tire as in claim 7, characterized in that the terminal ends of the long grooves of the pairs of the first series and the terminal ends of the short grooves of the pairs of the second series are aligned on a circumferential plane whose distance (D,) relative to equatorial plane is respectively between 22 mm and 82 mm. 9. Tire as in claim 7, characterized in that the terminal ends of the short grooves of the pairs of the first series and the terminal ends of the long grooves of the pairs of the second series are aligned on a circumferential plane whose distance (D2) relative to the plane equatorial is between 30 mm and 95 mm. 10. Tire as in claim 1, characterized in that the grooves of the pairs of the second series are extended towards the inside of the intermediate zone starting from a plane whose distance (D) from the equatorial plane of the tire is between 14 mm and 32 mm. 3 1. Pneumatic as in claim 1 characterized in that the grooves of the pairs of the second series are of the blind type. 12. Tire as in claim 1, characterized by the fact that the predetermined distance between the inner ends of a pair and the longitudinal axis of the nearest groove of the axially opposed torque is constant throughout the circumferential development. 13. Tire as in claim 1, characterized in that the transverse grooves of the intermediate zone have a depth of between 5 mm and 10 mm. 14. Tire as in claim 1, characterized in that the transverse grooves of the intermediate zone have a width of between 3.5 mm and 10 mm. 15. Tire as in claim 1, characterized by the fact that the grooves of the pairs of the first series of the intermediate zone and the transverse grooves of the shoulder zone are straight and joined together by a curvilinear section with a radius of curvature between 30 mm and 60 mm mm. 16. Tire as in claim 1, characterized in that the transverse grooves of the shoulder area comprise a section perpendicular to the equatorial plane. 17. Tire as in claim 1, characterized in that the pitch of the transverse grooves of the intermediate zone is double that of the transverse shoulder grooves. 18. Tire as in claim 1, characterized in that the transverse grooves of the shoulder area have a depth of between 5 mm and 10 mm. 19. Tire as in claim 1, characterized in that the transverse grooves of the shoulder region have a width of between 3.5 mm and 10 mm. 20. Tire as in claim 1, characterized in that the ratio between the width (L0) of each intermediate zone (F) and the width (W) of the tread band is between 0.17 and 0.30. 21. Tire as in claim 1 characterized in that the ratio between the width of the central region (E) and the width (W) of the tread band is between 0.10 and 0.20. 22. Tire as in claim 1, characterized in that said central zone (E) comprises two circumferential grooves delimiting a central bead inside them. 23. Tire as in claim 1, characterized in that the portion of the tread band on the left of the equatorial plane rotated by 180 ° constitutes the portion on the right. 24. Tire as in claim 1, characterized in that the portion of the tread band to the left of the equatorial plane mirrors the portion on the right. 25. Pre-molded tread band for covering worn tires characterized in that it comprises a tread pattern according to any one of the preceding claims.