WO2025052235A1

WO2025052235A1 - Tyre for vehicle wheels

Info

Publication number: WO2025052235A1
Application number: PCT/IB2024/058519
Authority: WO
Inventors: Roberto Bolzoni; Diego Ettore Speziari
Original assignee: Pirelli SpA; Pirelli Tyre SpA
Current assignee: Pirelli and C SpA; Pirelli Tyre SpA
Priority date: 2023-09-05
Filing date: 2024-09-02
Publication date: 2025-03-13
Anticipated expiration: 2026-03-05

Abstract

A tyre (1) for vehicle wheels comprises a tread band (2) which extends between a first axial end (4a) and a second axial end. There are defined on the tread band a plurality of first grooves (10) which are arranged in succession along a first shoulder region (7), a plurality of second grooves (20) which are arranged in succession along a second shoulder region (8), and a plurality of third grooves (30). Each third groove extends from a respective first end (31) which is defined between an equatorial plane (X) and a first axial end (4a) of the tread band as far as a respective second end (32) which is defined between the equatorial plane (X) and a second axial end (4b) of the tread band. Furthermore, each third groove is inclined at an angle (A) between 8° and 30° with respect to a circumferential direction defined on the tread band (2).

Description

Tyre for vehicle wheels

DESCRIPTION

The present invention relates to a tyre for vehicle wheels, in particular for wheels of high-performance motor cars.

In order to obtain adequate road-holding even on a wet road surface, tyres have a tread band which is provided with grooves and possibly notches, having various configuration and geometry, which delimit portions of tread band which are intended for contact with the ground, called blocks.

The overall configuration of the tread band which is defined by the group of grooves, notches and/or blocks represents the tread pattern of the tyre.

The main function of the grooves and notches is to allow the discharge of the water present between the surface of the tyre and the road surface during mutual contact, preventing the hydrostatic pressure resulting from the impact of the water against the advancing tyre from causing even partial lifting of the tyre off the road surface and the consequent loss of control of the vehicle (a phenomenon known as "aquaplaning").

The grooves and notches formed on the tread band may further have an influence on the traction performances of the tyre and on the performances of directionality and stability of the tyre in the different driving phases of the vehicle, such as, for example, during acceleration or braking or on bends.

The term "tread surface" is intended to be the radially external surface portion of the tread band which is intended to come into contact with the road surface when the tyre is caused to roll on a road surface.

The term "tread pattern" is intended to be the overall configuration of the tread band as defined by the assembly of the grooves and blocks.

In accordance with the configuration of the tread pattern, there may be defined on a tyre a preferential rolling direction.

In this case, the tyre is referred to as being "directional" and it is configured to be mounted on the vehicle so that the tyre, during travel of the vehicle in a forward direction, is rotated in the preferential rolling direction.

The tread pattern may further not be symmetrical with respect to the equatorial plane of the tyre, instead having a differentiated configuration between the external region of the tyre, which is intended to be directed towards the exterior when the tyre is mounted on the vehicle, and the opposite internal region of the tyre, which is nearer the centre plane of the vehicle. It is thereby possible to configure each portion of tread band in a more selective manner in relation to the different stresses and requirements which can affect the external regions and internal regions of the tread band during travel on the road surface, respectively.

A tyre having a tread pattern of the type briefly described above is referred to as being "asymmetrical".

The term "footprint area" is intended to be the portion of tread band which is instantaneously in contact with the road surface during the rolling movement of the tyre. Under real conditions, the footprint area is a function of different parameters, including the inflation pressure of the tyre, the load to which it is subjected, the road surface and the driving conditions, for which reference values can, however, be defined.

The term "equatorial plane" of the tyre is intended to be a plane which is perpendicular to the rotation axis of the tyre and which subdivides the tyre into two portions which are substantially identical apart from asymmetries of the tread pattern. The term "radial plane" of the tyre is intended to be any plane comprising the rotation axis of the tyre.

The term "axial direction" is intended to be a direction which is parallel with the rotation axis of the tyre.

The term "circumferential" direction is intended to be a direction which is generally directed in the rotation direction of the tyre.

The term "groove" is intended to be a recess which is formed in a tread band portion and which preferably has a width greater than or equal to 1.5 mm, more preferably greater than or equal to 3 mm. Preferably, a groove has a depth greater than 3 mm. A groove is preferably developed in a main longitudinal direction. This direction may have a linear progression which can be substantially rectilinear or may have a progression with successive rectilinear portions with a different orientation (broken line progression) or a curvilinear progression with constant or variable radii of curvature or a mixed linear progression with rectilinear portions and curvilinear portions.

The term "width" of a groove or a portion thereof is intended to be the dimension parallel with the tread surface and perpendicular to the main longitudinal extent of the groove or portion thereof.

Two grooves are "intersecting" when they are open one into the other so as to be in fluid communication.

Therefore, it may be noted that two grooves are defined to be "intersecting" both when the two grooves cross each other and when one groove terminates in the other groove.

In other words, a groove is "intersected" by another groove both when a groove extends through the other groove and when one end of a groove is open in the other groove.

The term "longitudinal extent" of a groove is intended to be the extent of the length of the groove measured in the development direction thereof on the tread surface, independently of the positioning or orientation thereof on the tread surface.

The term "circumferential extent" of a groove or a portion thereof is intended to be the extent of the length of the groove or the portion thereof when measured in the circumferential direction of the tyre. In other words, the circumferential extent of a groove or a portion thereof represents the extent of the orthogonal projection of the groove in the circumferential direction of the tyre.

Similarly, the term "axial extent" of a groove or a portion thereof is intended to be the extent of the length of the groove or the portion thereof when measured in the axial direction of the tyre.

A groove is referred to as being "transverse" when it extends in a direction which is inclined by an acute angle greater than at least 5° with respect to the circumferential direction.

The inclination of a direction, for example, a longitudinal direction of a groove, with respect to a circumferential direction which is identified on the tread band is defined by the acute angle formed by the direction with the circumferential direction. As an extreme case, a direction which extends parallel with the axis of the tyre will have an inclination of 90° with respect to the circumferential direction.

The inclination of a groove with respect to the circumferential direction which is identified on the tread band is defined by the acute angle formed by a straight line which passes through the ends of the groove with the circumferential direction.

The inclination of a portion of a groove with respect to the circumferential direction which is identified on the tread band is defined by the acute angle formed by a straight line which passes through the ends of the portion of the groove with the circumferential direction.

If the groove or the portion thereof are rectilinear, the inclination of the groove or the portion thereof coincides with the inclination of the longitudinal direction of the groove or the portion thereof, respectively.

Conversely, when the groove or the portion thereof does not have a rectilinear progression, the inclination of the groove or the portion thereof does not coincide (or may coincide only partially) with the inclination of the longitudinal direction thereof. A groove maintains an "inclination of the same sign" when, if considered on a Cartesian plane positioned on the tread band (tangentially thereto) with the axis of the ordinate parallel with the circumferential direction and the axis of the abscissa parallel with the axis of the tyre, each portion of the groove has an ascending progression or each portion of the groove has a descending progression.

In other words, a groove maintains an inclination of the same sign when the progression thereof can be represented, in the Cartesian plane defined above, by an increasing monotone function or by a decreasing monotone function.

Two grooves have an inclination "of the same sign" or are inclined "concordantly" when the progression thereof is, for both, ascending or descending when they are considered in a Cartesian plane which is positioned on the tread band (tangentially thereto) with the axis of the ordinate parallel with the circumferential direction and the axis of the abscissa parallel with the axis of the tyre.

Consequently, two grooves have an inclination "of opposite signs" or are inclined "discordantly" when, if considered in the Cartesian plane defined above, the progression thereof is ascending for one groove and descending for the other one. Two grooves or two groove portions are "axially aligned" or aligned in the axial direction of the tyre when the respective projections in the equatorial plane overlap each other over at least 80% of the longitudinal extent of the two grooves or groove portions.

Two grooves or two groove portions are "substantially parallel" when they extend at the same angle of inclination with respect to the circumferential direction or when the respective inclination angles with respect to the circumferential direction differ at a maximum by 10°, preferably at a maximum by 5°.

Two grooves or two groove portions are "substantially perpendicular" when they are inclined relative to each other at an angle of 90° with a maximum tolerance of 10°, preferably with a maximum tolerance of 5°.

A plurality of grooves is arranged "in succession" along the circumferential development of the tread band or a portion thereof when each of the grooves is spaced circumferentially apart from a similar groove by a predetermined extent, which is not necessarily constant and which may vary up to 50%, preferably up to 30%, of this predetermined extent.

The term "void-to-rubber ratio" is intended to be the ratio between the total surface of the grooves and the notches contained in a predetermined portion of the tread pattern of the tyre which is intended for rest on the ground (where applicable, of the entire tread pattern) and the total surface of the predetermined portion of tread pattern (where applicable, of the entire tread pattern).

EP 1930185, JP 2020125085 and JP 2016002886 disclose respective examples of tyres, on the tread band of which there is defined at least one circumferential groove having a helical or partially helical configuration.

The Applicant has preliminarily observed that, during travel on a wet road surface, a relevant portion of the water present in the footprint area of the tyre can be thrown into the air in the form of thin sprays and droplets which can substantially limit the visibility of the vehicles which are following behind.

The Applicant has further observed that this phenomenon is particularly amplified in the case of vehicles which are travelling at high speeds and with great dimensions of the tyres, so much so as to become one of the main safety problems in the case of motor races taking place under wet road conditions.

By way of example, the Applicant has verified that, in a racing vehicle, the quantity of water which can be discharged by the footprint area and which can therefore be sprayed into the air by each individual tyre is in the order of several tens of litres per second.

The Applicant has further ascertained that many motor races, in the case of travel on wet surfaces, are particularly conditioned by the poor visibility of the drivers of the vehicles, causing substantial problems of safety which can lead to measures for limiting the race or even the suspension thereof.

On the other hand, the Applicant has observed that this phenomenon is a direct consequence of the discharge action of the water carried out by the tread band which, specifically for this purpose, has on its surface grooves with different shapes and dimensions. As already set out above, in fact, an adequate capacity for discharging water present in a footprint area is necessary in order to be able to obtain during travel of the vehicle on a wet road surface an appropriate road-holding and particularly to avoid aquaplaning phenomena.

Therefore, the Applicant has felt the need to provide a tyre with a tread pattern which is configured to obtain optimum performance levels in terms of road-holding on wet road surfaces even under conditions of extreme stresses, as in the case of use in motor cars with high performance levels and in motor-racing competitions and which, at the same time, is configured so as to improve the visibility of the vehicles following behind.

To comply with this requirement, the Applicant has observed that a large portion of the water which is discharged by the wheels of a vehicle and thrown in the opposite direction to the direction of travel is mainly constituted by the fraction of water discharged by the circumferential grooves which are formed on the tread band.

The Applicant has particularly verified that the presence of the circumferential grooves, as a result of the high capacity thereof for discharging the water, also brings about sprays of water which are generally longer and higher, limiting the visibility for the following vehicles even at relatively great distances.

In some cases, furthermore, for example, at high speeds, some of the water present in the circumferential grooves carries out more than half a revolution of the wheel before being discharged by the tread band. In these cases, the water is in fact thrown in front, in the direction of travel of the vehicle, so as to fall on the road surface in front of the vehicle itself, with the evident undesirable result of increasing the quantity of water present on the road surface involved in the rolling of the tyre.

While evaluating these aspects, therefore, the Applicant has perceived that, in order to improve the visibility of the vehicles which follow without compromising the necessary capacity for discharging the water, the tread pattern of a tyre would have to be configured so as to define not only the quantity of water to be discharged by the footprint area by means of the grooves, but also the direction in which the discharged water would have to be discharged by the grooves themselves.

Finally, the Applicant has found that a tyre, on the tread band of which there are formed grooves which extend between the two opposite shoulder regions which are axially opposite and inclined with respect to the circumferential direction at a suitable angle, allows effective discharge of the water present in the footprint area, particularly the water present in the central region of the tread band, mainly towards one side of the tyre, avoiding both long sprays of water being thrown directly behind the vehicle and the possibility that some of the discharged water may be brought in front of the vehicle itself.

In particular, in a first aspect thereof, the invention relates to a tyre for vehicle wheels comprising a tread band which extends between a first axial end and a second axial end.

Preferably, there is defined on said tread band a first shoulder region which is delimited in an axially outer position by said first axial end.

Preferably, there is defined on said tread band a second shoulder region which is delimited in an axially outer position by said second axial end.

Preferably, there is defined on said tread band a central region which is interposed between said first shoulder region and said second shoulder region.

Preferably, said central region extends so as to straddle an equatorial plane of said tread band.

Preferably, a plurality of first grooves is defined on said tread band.

Preferably, said first grooves are arranged in succession along the circumferential development of said first shoulder region.

Preferably, each first groove extends transversely from said first axial end towards said central region.

Preferably, each first groove is in a position spaced apart from said second axial end. Preferably, a plurality of second grooves is defined on said tread band.

Preferably, said second grooves are arranged in succession along the circumferential development of said second shoulder region.

Preferably, each second groove extends transversely from said second axial end towards said central region.

Preferably, each second groove is in a position spaced apart from said first axial end. Preferably, a plurality of third grooves is defined on said tread band.

Preferably, each of said third grooves extends from a respective first end as far as a respective second end.

Preferably, said first end is defined between said equatorial plane and said first axial end.

Preferably, said second end is defined between said equatorial plane and said second axial end.

Preferably, each of said third grooves is inclined at an angle between 8° and 30° with respect to a circumferential direction of said tread band.

The Applicant considers that, as a result of these characteristics, and particularly the special configuration of the third grooves, the tyre according to the present invention when driven on a wet road surface, including under high-speed conditions, discharges a relevant fraction of the water which is discharged from the footprint area towards one side of the wheel and not directly in the direction counter to the travel direction of the vehicle.

In this manner, there is substantially reduced the area behind the vehicle having a poor or zero visibility, increasing the driving safety of the drivers of the vehicles which are positioned behind the vehicle under travel conditions on a wet road surface, including at high speeds. The Applicant further considers that the provision of the first and second grooves allows rapid discharge of the water in the shoulder regions, while maintaining in these regions adequate rigidity of the tread band, which allows to effectively counteract the tangential stresses with a strong axial component, which are generated during the vehicle's cornering phase.

In the above-mentioned aspect, the present invention may have at least one of the additional features indicated below.

Preferably, each of said third grooves maintains an inclination of the same sign between said first end and said second end with respect to a circumferential direction of the tread band.

Preferably, in each of said third grooves, said first end is spaced apart from said second end by a predetermined circumferential extent which is not zero.

In some embodiments, each third groove of said plurality is intersected by at least one first groove, more preferably by at least two first grooves, even more preferably by at least three first grooves and in a very preferred manner by at least four first grooves.

In this manner, each third groove is in fluid communication with at least one first groove (or at least two, three or four first grooves, respectively) so as to facilitate and accelerate the outflow of the water from the central region of the tread band until it is discharged out of the tyre in the region of the first axial end of the tread band, also using one or more first grooves. These first grooves, also for this purpose, pass through the first shoulder region in order to open at the first axial end.

In some embodiments, each third groove of said plurality is intersected by at least one second groove, more preferably by at least two second grooves, even more preferably by at least three second grooves and in a very preferred manner by at least four second grooves.

In this manner, each third groove is in fluid communication with at least one second groove (or at least two, three or four second grooves, respectively) so as to facilitate and accelerate the outflow of the water from the central region of the tread band until it is discharged out of the tyre in the region of the second axial end of the tread band, also using one or more second grooves. These second grooves, also for this purpose, pass through the second shoulder region in order to open at the second axial end.

In some embodiments, said first end of each third groove is spaced apart from said first axial end by an extent between 15% and 30% of the width of said tread band. In some embodiments, said second end of each third groove is spaced apart from said second axial end by an extent between 15% and 30% of the width of said tread band.

In some embodiments, said third grooves of said plurality are substantially mutually identical.

In some embodiments, said third grooves of said plurality are substantially mutually parallel.

In some embodiments, each third groove of said plurality has a circumferential extent less than the circumferential length of said tread band, preferably less than 70% of the circumferential length of said tread band.

Preferably, each third groove of said plurality has a circumferential extent greater than 20% of the circumferential length of said tread band, and more preferably has a circumferential extent between 30% and 50% of the circumferential length of said tread band.

In some embodiments, in each third groove of said plurality, said first end is spaced apart from said second end by a circumferential extent greater than 25% of the circumferential length of said tread band.

In some embodiments, said plurality of third grooves are formed by a number of third grooves greater than 3, preferably greater than 5, more preferably greater than 9. In some embodiments, said plurality of third grooves are formed by a number of third grooves less than 20, more preferably less than 15.

In some embodiments, each radial plane of said tyre intersects with at least three of said third grooves at said tread band.

In some embodiments, each radial plane intersects with no more than five third grooves at said tread band.

In some embodiments, each third groove of said plurality has a width between 5 mm and 15 mm, preferably between 8 mm and 12 mm.

In some embodiments, each third groove of said plurality has a depth greater than 3 mm, preferably less than 8 mm. Preferably, each third groove of said plurality has a depth between 3 mm and 6 mm.

In some embodiments, each third groove comprises a first end portion at said first end, a second end portion at said second end and a central portion which is interposed between said first end portion and said second end portion. Preferably, said central portion is substantially rectilinear.

Preferably, said central portions of said third grooves are substantially mutually parallel.

Preferably, said central portion constitutes at least 70%, more preferably at least 80% and even more preferably at least 90% of the longitudinal extent of said third groove.

In some embodiments, said central portion of each of said third grooves is inclined with respect to said circumferential direction at an angle between 8° and 30°, more preferably between 10° and 20°, even more preferably between 10° and 15°.

In some embodiments, said first end portion extends in a substantially circumferential direction.

In some embodiments, said first end portion constitutes no more than 10%, more preferably no more than 5% of the longitudinal extent of said third groove.

In some embodiments, said second end portion extends in a substantially circumferential direction.

In some embodiments, said second end portion constitutes no more than 10%, more preferably no more than 5% of the longitudinal extent of said third groove.

In some embodiments, each first groove intersects with at least one of said third grooves.

In some embodiments, each second groove intersects with at least one of said third grooves.

In some embodiments, each first groove is inclined at an angle between 70° and 85° with respect to said circumferential direction.

In some embodiments, each first groove is inclined with respect to said circumferential direction in a manner concordant with respect to said third grooves. In some embodiments, each second groove is inclined at an angle between 70° and 85° with respect to said circumferential direction.

In some embodiments, each second groove is inclined with respect to said circumferential direction in a manner discordant with respect to said third grooves. In some embodiments, each second groove is inclined with respect to said circumferential direction in a manner discordant with respect to said first grooves. In some embodiments, each second groove is substantially perpendicular to said third grooves.

In some embodiments, said central portion of each third groove comprises a first side wall which joins said third groove to a tread surface at the side proximal to said first axial end, and a second side wall which joins said third groove to said tread surface at the side proximal to the second axial end. Preferably, said first side wall is inclined with respect to a radial direction at a greater angle than said second side wall. Preferably, said first side wall is inclined with respect to a radial direction at an angle between 30° and 40°.

Preferably, said second side wall is inclined with respect to a radial direction at an angle between 10° and 20°.

In some embodiments, said plurality of first grooves comprise a plurality of first short grooves.

In some embodiments, said plurality of first grooves comprise a plurality of first long grooves.

Preferably, said first long grooves have a longitudinal extent greater than said first short grooves.

Preferably, each first short groove intersects with a single third groove.

Preferably, each first short groove terminates in said single third groove.

Preferably, each first long groove intersects with at least two third grooves, more preferably with three third grooves.

Preferably, each first long groove terminates in one of said third grooves.

Preferably, each first long groove extends at most as far as said equatorial plane, more preferably extends substantially as far as said equatorial plane.

In some embodiments, each first long groove is interposed between two first short grooves.

In some embodiments, said plurality of first grooves comprise a plurality of first intermediate grooves.

Preferably, said first intermediate grooves have a longitudinal extent greater than said first short grooves.

Preferably, said first intermediate grooves have a longitudinal extent less than said first long grooves.

Preferably, each first intermediate groove intersects with at least two third grooves, more preferably two third grooves.

Preferably, each first intermediate groove terminates in one of said third grooves.

In some embodiments, each first intermediate groove is interposed between two first short grooves.

In some embodiments, each first short groove is interposed between a first long groove and a first intermediate groove.

In some embodiments, said plurality of second grooves comprise a plurality of second short grooves.

In some embodiments, said plurality of second grooves comprise a plurality of second long grooves.

Preferably, said second long grooves have a longitudinal extent greater than said second short grooves.

Preferably, each second short groove intersects with a single third groove.

Preferably, each second short groove terminates in said single third groove.

Preferably, each second long groove intersects with at least two third grooves, more preferably three third grooves.

Preferably, each second long groove terminates in one of said third grooves.

Preferably, each second long groove extends at most as far as said equatorial plane, more preferably extends substantially as far as said equatorial plane.

In some embodiments, each second long groove is interposed between two second short grooves.

In some embodiments, said plurality of second grooves comprise a plurality of second intermediate grooves.

Preferably, said second intermediate grooves have a longitudinal extent greater than said second short grooves.

Preferably, said second intermediate grooves have a longitudinal extent less than said second long grooves.

Preferably, each second intermediate groove intersects with at least two third grooves, more preferably three third grooves.

Preferably, each second intermediate groove terminates in one of said third grooves. In some embodiments, each second intermediate groove is interposed between two second short grooves.

In some embodiments, each second short groove is interposed between a second long groove and a second intermediate groove.

In some embodiments, each first short groove is axially aligned with a corresponding second long groove or a second intermediate groove.

In some embodiments, each first long groove is axially aligned with a corresponding second short groove.

In some embodiments, each first intermediate groove is axially aligned with a corresponding second short groove.

In some embodiments, said equatorial plane divides said tread band into an external region of tread band, which is proximal to the exterior of the vehicle when the tyre is mounted on said vehicle, and an internal region of tread band, which is axially opposite said external region. Preferably, said first shoulder region is defined in said external region of tread band. In some embodiments, when said tyre is mounted on a vehicle and is rotated in a preferential rolling direction during travel of said vehicle, said second end enters the footprint area before said first end.

In some embodiments, said tread band has no circumferential grooves.

In some embodiments, said tread band does not have any grooves which extend between said first shoulder region and said second shoulder region and which are inclined in a discordant manner with respect to said third grooves.

In some embodiments, further grooves are not present on said tread band other than said first grooves, said second grooves and said third grooves.

In some embodiments, the void-to-rubber ratio of said tread band is between 0.30 and 0.35.

The features and advantages of the invention will be better appreciated from the detailed description of a preferred exemplary embodiment thereof, which is illustrated by way of non-limiting example with reference to the appended drawings, in which:

- Figure 1 is a perspective view of a tyre for wheels of vehicles according to the present invention,

- Figure 2 is a front view of the tyre of Figure 1, and

- Figure 3 is a schematic view, drawn to an enlarged scale, of a significant portion of the tread band of the tyre of Figure 1 developed in a plane,

- Figure 4 is a schematic sectioned view in a transverse plane of the tread band of the tyre of Figure 1,

- Figure 5 is a schematic view of a tyre realized according to the prior art.

With reference to the appended Figures 1 to 4, there is generally designated 1 a tyre for wheels of vehicles realized according to the present invention.

The tyre 1 comprises a tyre structure which is conventional per se and which is not illustrated in the appended Figures and a tread band 2 on which there is defined a tread surface 3 which is arranged in a radially external position with respect to the tread band 2 and which is intended for contact with a road surface.

The tyre 1 has a conventional, generically toroidal form which develops about a rotation axis, defining on the tread surface 3 an axial direction Y which is parallel therewith and which is passed through by an equatorial plane X which is perpendicular to the rotation axis and which defines on the tread surface 3 a circumferential direction which is parallel therewith. The tyre 1 is preferably arranged to be mounted on a high-performance car, for example, on a racing vehicle, and may have a nominal section width of approximately 305 mm with a rim diameter of 18 inches.

The tread band 2 extends axially between a first axial end 4a and a second axial end 4b, defining a width L of approximately 300 mm, which is intended for contact with the road surface under standard conditions of use.

The equatorial plane X divides the tread band 2 into an external region 5 of tread band which is intended to be proximal to the exterior of the vehicle when the tyre is mounted on the vehicle and an internal region 6 of tread band which is axially opposite the external region 5.

There are further defined on the tread band 2 a first shoulder region 7 which is delimited in an axially outer position by the first axial end 4a, a second shoulder region 8 which is delimited in an axially outer position by the second axial end 4b, and a central region 9 which is interposed between the first shoulder region 7 and the second shoulder region 8.

The first shoulder region 7 and the second shoulder region 8 extend axially over approximately from 20% to 25% of the width L of the tread band in a substantially symmetrical manner with respect to the central region 9 which in turn extends symmetrically so as to straddle the equatorial plane X.

The first shoulder region 7 is defined in the external region 5 of the tread band 2 while the second shoulder region 8 is defined in the internal region 6 of the tread band 2.

There are defined on the tread band 2 a plurality of first grooves 10 which are arranged in succession along the circumferential development of the first shoulder region 7, a plurality of second grooves 20 which are arranged in succession along the circumferential development of the second shoulder region 8 and a plurality of third grooves 30, which are arranged in succession along the circumferential development of the central region 9.

No other groove is present on the tread band 2, therefore the tread pattern of the tyre is completely defined by the first grooves 10, the second grooves 20 and the third grooves 30.

Each first groove 10 extends transversely from the first axial end 4a towards the equatorial plane X, in a substantially rectilinear longitudinal direction which is inclined with respect to the circumferential direction at an angle C of approximately 75°. Similarly, each second groove 20 extends transversely from the second axial end 4b towards the equatorial plane X in a substantially rectilinear longitudinal direction which is inclined with respect to the circumferential direction at an angle D of approximately 75° with an opposite sign with respect to the inclination of the first grooves 10.

Each first groove 10 and each second groove 20 has a depth P between 3 and 6 mm and a width between 10 mm and 20 mm with a slightly tapered progression from the axial end towards the equatorial plane X.

The third grooves 30 are substantially mutually identical and parallel and each of them extends from a respective first end 31, which is defined in the external region 5, to a second end 32, which is defined in the internal region 6.

Each third groove 30 is inclined with respect to the circumferential direction at an angle A (defined as the acute angle between the circumferential direction and the direction of the straight line passing through the first end 31 and the second end 32 of the third groove 30) of approximately 12°-13° with an opposite sign with respect to the second grooves 20 and the same sign with respect to the first grooves 10.

In particular, there are defined on each third groove 30 a first end portion 33 comprising the first end 31, a second end portion 34 comprising the second end 32 and a central portion 35 which is interposed between the first end portion 33 and the second end portion 34.

The first end portion 33 and the second end portion 34 extend substantially parallel with the circumferential direction and in mutually opposite directions, thereby delimiting the central region 9 from the first shoulder region 7 and the second shoulder region 8.

The first end portion 33 and the second end portion 34 have a longitudinal extent which does not exceed 5% of the total longitudinal extent of the third groove 30.

The central portion 35 forms the main portion of the longitudinal extent of the third groove 30 and extends in a substantially rectilinear longitudinal direction which is inclined at an angle B of approximately 13°-14° with respect to the circumferential direction.

The central portion 35 has a substantially constant width of approximately 10 mm while the first end portion 33 and the second end portion 34 have a width tapering towards the first end 31 and the second end 32, respectively.

The depth of the third groove 30 is between 3 and 6 mm, for example, constant in the central portion 35 while, in the first end portion 33 and second end portion 34, the depth decreases until substantially disappearing at the first end 31 and second end 32, respectively.

Preferably, the third grooves 30 have a depth P which is substantially identical to that of the first grooves 10 and second grooves 20.

Each third groove 30 has a circumferential extent of approximately 40% of the circumferential length of the tread band 2.

The third grooves 30 provided on the tread band 2 number 11 in total and are arranged in such a manner that each radial plane of the tyre 1 intersects with at least four third grooves 30, in particular five third grooves 30, in the region of the first or second end portions 33, 34, and four third grooves 30 in the region of the central portions 35.

Each third groove 30 is further preferably shaped in an asymmetrical manner in order to act counter to the lateral forces on bends. More specifically, as can better be seen in Figure 4, the normal section along the longitudinal axis of each central portion 35 has an inclination, with respect to a radial direction which is defined on the tread band and which passes through the central portion 35, which is greater at the external side with respect to the internal side.

In particular, the central portion 35 of each third groove 30 comprises a first side wall 36 which joins the third groove 30 to the tread surface 3 at the proximal side with respect to the first axial end 4a, and a second side wall 37 which joins the third groove to the tread surface 3 at the proximal side with respect to the second axial end 4b.

The first wall 36 is inclined with respect to a radial direction at an angle E between 30° and 40°, for example, 35°, while the second wall 37 is inclined with respect to a radial direction at an angle G between 10° and 20°, for example, 15°.

In this manner, during travel around a bend section, the presence of the more inclined angle at the external side assists the block present at that location to withstand the increase in the lateral forces resulting from the transfer of load as a result of the effect of this travel in a curvilinear direction.

The first grooves 10 are formed by first short grooves 11, first intermediate grooves 12 and first long grooves 13, preferably alternating with each other along the circumferential development of the tread band according to the following pattern which is repeated in succession: first short groove, first intermediate groove, first short groove and first long groove.

Each first short groove 11 intersects with a single third groove 30, in particular the nearest one with respect to the first axial end 4a, terminating therein. Each first intermediate groove 12, which is longitudinally more extensive than the first short grooves, intersects with two third grooves 30, terminating in the third groove 30 furthest away from the first axial end 4a and passing through the third groove 30 nearest the first axial end 4a.

Each first long groove 13, which is longitudinally more extensive than the first intermediate grooves 12, intersects with three third grooves 30, terminating in the third groove 30 furthest away from the first axial end 4a and passing through the third grooves 30 nearest the first axial end 4a.

In particular, each first long groove 13 extends through the external region 5 of the tread band 2 as far as the equatorial plane X.

The second grooves 20 are formed in a similar manner in the region of the internal region 6 of the tread band 2.

Therefore, the second grooves 20 are formed by second short grooves 21, second intermediate grooves 22 and second long grooves 23, preferably alternating with each other along the circumferential development of the tread band according to the following pattern which is repeated in succession : second short groove, second intermediate groove, second short groove and second long groove.

Each second short groove 21 intersects with a single third groove 30, in particular the nearest one with respect to the second axial end 4b, terminating therein.

Each second intermediate groove 22, which is longitudinally more extensive than the second short grooves 21, intersects with three third grooves 30, terminating in the third groove 30 furthest away from the second axial end 4b and passing through the third grooves 30 nearest the second axial end 4b.

Each second long groove 23, which is longitudinally more extensive than the second intermediate grooves 22, intersects with three third grooves 30, terminating in the third groove 30 furthest away from the second axial end 4b and passing through the third grooves 30 nearest the second axial end 4b.

In particular, each second long groove 23 extends through the internal region 6 of the tread band 2 as far as the equatorial plane X.

The first grooves 10 and second grooves 20 are arranged along the external region 5 and the internal region 6 of the tread band 2, respectively, in such a manner that each first short groove 11 is axially aligned with a corresponding second long groove 23 or a second intermediate groove 22 and similarly in such a manner that each second short groove 21 is axially aligned with a corresponding first long groove 13 or a first intermediate groove 12. The tread pattern of the tyre 1, as defined by the groove configuration described above, defines on the tread band a void-to-rubber ratio of approximately 0.33.

The characteristics of the tread pattern illustrated above make the tyre 1 a directional and asymmetrical tyre so as to define both a preferential rolling direction, which is designated F in the Figures and which is used during the normal forward travel of the vehicle, and a specific assembly position on the vehicle (that is to say, on the right side or left side).

In particular, there is provision for the tyre to be mounted on the vehicle in such a manner that, when it is rotated in the preferential rolling direction, the second end 32 of each third groove 30 enters the footprint area before the respective first end 31.

In this manner, the water discharged from the central region 9 of the tread band 2 through the third grooves 30 is conveyed, for a large part, towards the first axial end 4a of the tyre 1.

In this manner, any sprays of water resulting from the travel on a wet surface are directed towards the exterior of the vehicle laterally with respect to the travel direction and not directly behind the vehicle so as to improve the visibility of any additional cars which follow the vehicle on which the tyres 1 are mounted.

Furthermore, as a result of the characteristics described above in detail and illustrated in the appended Figures, the tyre 1 also has optimum characteristics of both longitudinal and axial rigidity which allow high levels of road-holding, traction and steerability to be obtained both on a wet road surface and on a dry one.

EXAMPLE

The characteristics and performance levels of the tyre 1 described above have been calculated and compared with those of a tyre 100 which is schematically illustrated in Figure 5 and realized, still by the Applicant, according to the prior art.

The tyre 100 has the same dimensions and is made from the same elastomer compound as the tyre 1 and is currently used in racing cars under moderately wet road surface conditions (so-called "intermediate" tyre).

The tread pattern of the tyre 100 comprises only blind grooves which extend from the central region of the tread band towards the opposite axial ends of the tread band.

The comparison has been carried out using appropriate mathematical models which are prepared by the Applicant and which have allowed calculation of the most relevant parameters of the two tyres in the definition of the behaviour thereof on the road both on a dry surface and on a wet surface.

In particular, for both tyres there have been calculated:

- the longitudinal rigidity, that is to say, the resistance of the tread band to the tangential stresses which are directed parallel with the circumferential direction, which is calculated at successive axially aligned locations of the tread band,

- the lateral rigidity, that is to say, the resistance of the tread band to the tangential stresses which are directed parallel with the rotation axis of the tyre, which is calculated at successive axially aligned locations of the tread band,

- the ratio between longitudinal rigidity and lateral rigidity, which is also calculated at successive axially aligned locations of the tread band.

The calculations carried out have shown how the rigidity characteristics of the tyre of the invention allow adequate performance levels in terms of road-holding to be achieved.

In particular, the models show how, in the tyre of the invention, the ratio between longitudinal rigidity and lateral rigidity is substantially constant along the crosssection of the tread band, exhibiting optimum homogeneity in terms of rigidity in the various portions of tread band, which is generally indicative of an advantageously balanced behaviour on the road.

The Applicant has further carried out simulations of the behaviour of the two tyres under aquaplaning conditions.

In particular, for each tyre, there has been calculated the force discharged to the ground in the footprint area when the tyre is driven at predefined speeds of 70 km/h and 80 km/h with a load of 600 kg on a road surface on which 3 mm of water is present. This force was then placed in relation to the force discharged to the ground under dry conditions by the respective tyre, thereby obtaining for each tyre a percentage of residual force.

The results of the calculations and the simulations have shown how the tyre 1 realized according to the present invention has a behaviour on a wet surface which is far greater than the tyre 100.

In fact, at the lower speed (70 km/h), the tyre of the invention shows a percentage of residual force of approximately double the percentage of residual force of the comparison tyre while, at the higher speed (80 km/h), the percentage of residual force of the tyre of the invention is even greater than about 10 times the percentage of residual force of the comparison tyre. The simulation therefore demonstrates how the tyre of the invention allows maintenance of the individual road-holding characteristics on a wet surface in a much more effective manner than the comparison tyre.

Claims

1. Tyre (1) for vehicle wheels comprising a tread band (2) which extends between a first axial end (4a) and a second axial end (4b) and on which there are defined:

- a first shoulder region (7) which is delimited in an axially outer position by said first axial end (4a),

- a second shoulder region (8) which is delimited in an axially outer position by said second axial end (4b);

- a central region (9) which is interposed between said first shoulder region (7) and said second shoulder region (8) and which extends so as to straddle an equatorial plane (X) of said tread band (2);

- a plurality of first grooves (10) which are arranged in succession along the circumferential development of said first shoulder region (7), each first groove (10) extending transversely from said first axial end (4a) towards said central region (9) in a position spaced apart from said second axial end (4b),

- a plurality of second grooves (20) which are arranged in succession along the circumferential development of said second shoulder region (8), each second groove (20) extending transversely from said second axial end (4b) towards said central region (9) in a position spaced apart from said first axial end (4a),

- a plurality of third grooves (30), each of said third grooves: i. extending from a respective first end (31) which is defined between said equatorial plane (X) and said first axial end (4a) as far as a respective second end (32) which is defined between said equatorial plane (X) and said second axial end (4b), and ii. being inclined at an angle (A) between 8° and 30° with respect to a circumferential direction of said tread band (2).

2. Tyre according to claim 1, wherein each third groove (30) of said plurality is intersected by at least one first groove (10).

3. Tyre according to claim 1 or 2, wherein each third groove (30) of said plurality is intersected by at least one second groove (20).

4. Tyre according to any one of the preceding claims, wherein each third groove (30) of said plurality has a circumferential extent less than the circumferential length of said tread band (2).

5. Tyre according to any one of the preceding claims, wherein each third groove (30) of said plurality has a circumferential extent greater than 20% of the circumferential length of said tread band (2).

6. Tyre according to any one of the preceding claims, wherein, in each third groove (30) of said plurality, said first end (31) is spaced apart from said second end (32) by a circumferential extent greater than 25% of the circumferential length of said tread band (2).

7. Tyre according to any one of the preceding claims, wherein each radial plane of said tyre (1) intersects with at least three of said third grooves (30) at said tread band (2).

8. Tyre according to any one of the preceding claims, wherein each radial plane of said tyre (1) intersects with no more than five third grooves (30) at said tread band (2).

9. Tyre according to any one of the preceding claims, wherein each third groove (30) comprises a first end portion (33) at said first end (31), a second end portion (34) at said second end (32) and a central portion (35) which is interposed between said first end portion (33) and said second end portion (34), wherein said central portion (35) is substantially rectilinear and constitutes at least 70% of the longitudinal extent of said third groove (30).

10. Tyre according to claim 9, wherein said central portion (35) of each of said third grooves (30) is inclined with respect to said circumferential direction at an angle (B) between 8° and 30°.

11. Tyre according to claim 9 or 10, wherein said central portion (35) of each third groove (30) comprises a first side wall (36) which joins said third groove (30) to a tread surface (3) at the side proximal to said first axial end (4a), and a second side wall (37) which joins said third groove (30) to said tread surface (3) at the side proximal to the second axial end (4b), said first side wall (36) being inclined with respect to a radial direction at a greater angle than said second side wall (37).

12. Tyre according to any one of the preceding claims, wherein each first groove (10) intersects with at least one of said third grooves (30).

13. Tyre according to any one of the preceding claims, wherein each second groove (20) intersects with at least one of said third grooves (30).

14. Tyre according to any one of the preceding claims, wherein each first groove (10) is inclined with respect to said circumferential direction in a manner concordant with respect to said third grooves (30).

15. Tyre according to any one of the preceding claims, wherein each second groove (20) is inclined with respect to said circumferential direction in a manner discordant with respect to said third grooves (30) and/or with respect to said first grooves (10).

16. Tyre according to any one of the preceding claims, wherein said plurality of first grooves (10) comprise a plurality of first short grooves (11) and a plurality of first long grooves (13), said first long grooves (13) having a longitudinal extent greater than said first short grooves (11).

17. Tyre according to claim 16, wherein each first short groove (11) intersects with a single third groove (30).

18. Tyre according to claim 16 or 17, wherein each first long groove (13) intersects with at least two third grooves (30).

19. Tyre according to any one of claims 16 to 18, wherein each first long groove (13) extends substantially as far as said equatorial plane (X).

20. Tyre according to any one of claims 16 to 19, wherein each first long groove (13) is interposed between two first short grooves (11).

21. Tyre according to any one of the preceding claims, wherein said plurality of second grooves (20) comprise a plurality of second short grooves (21) and a plurality of second long grooves (23), said second long grooves (23) having a longitudinal extent greater than said second short grooves (21).

22. Tyre according to claim 21, wherein each second short groove (21) intersects with a single third groove (30).

23. Tyre according to claim 21 or 22, wherein each second long groove (23) intersects with at least two third grooves (30).

24. Tyre according to any one of claims 21 to 23, wherein each second long groove (23) extends substantially as far as said equatorial plane (X).

25. Tyre according to any one of the preceding claims, wherein said equatorial plane (X) divides said tread band (2) into an external region (5) of tread band, which is proximal to the exterior of the vehicle when the tyre is mounted on said vehicle, and an internal region (6) of tread band, which is axially opposite said external region (5), and wherein said first shoulder region (7) is defined in said external region (5) of tread band.

26. Tyre according to claim 25, wherein, when said tyre (1) is mounted on a vehicle and is caused to rotate in a preferential rolling direction (F) during travel of said vehicle, said second end (32) enters footprint area before said first end (31).

27. Tyre according to any one of the preceding claims, wherein each of said third grooves (30) maintains an inclination of the same sign between said first end (31) and said second end (32) with respect to a circumferential direction of said tread band (2).