Tire offering an advantageous performance compromise between snow grip and rolling resistance

Abstract

The invention relates to a tire (1) provided with a tread (10) comprising sculpture patterns distributed over a wheel revolution according to distribution pitches. Each sculpture pattern comprises at least one central block (140) provided with a blocking element (220). Said blocking element (220) comprises a blocking face (270), provided with a surface Sb and is backed by a face of the central sculpture block (140), called the free face (250) and provided with a surface Sf. Said tire (1) is characterized in that, for at least one central sculpture block (140), the ratio Sb / Sf is between 0.25 and 0.85, in that at least a first central sculpture block (140) on a first side of the equatorial plane (C) comprises a first blocking element (220) opposite a second blocking element (220) of a second central sculpture block (140) on a second side of the equatorial plane (C), and in that the first central sculpture block (140) comprises a blocking element (220) which touches the central groove (100) over a width L1 and the second central sculpture block (140) comprises another blocking element (220) which touches the central groove (100) by a width L2; the widths L1 and L2 being different. Abstract figure: Figure 5.

Description

Title of the invention: Tire offering an advantageous performance compromise between grip on snow and rolling resistance Technical field

[0001] The present invention relates to a tire for a motor vehicle, and more particularly an "all-season" tire optimized in rolling resistance, and intended to equip a passenger vehicle or a van.

[0002] As is known, a so-called "all-season" tire for a passenger vehicle or van offers a compromise in grip on snowy and wet ground while maintaining performance on dry ground. These tires are designed to drive safely all year round whatever the weather, while having improved rolling resistance performance compared to conventional designs.

[0003] As for their snow grip performance, these tires have generally received the 3PMSF (3 Peaks Mountain Snow Flake) winter regulatory certification, according to tire safety regulations such as UNECE (United Nations Economic Commission for Europe) R30 / R54 and RI 17 regulations, attesting to their proven performance in snow grip and wet ground.

[0004] This certification is indicated on one or both sidewalls of these types of tire by a distinctive logo representing a mountain with three emerging peaks including a snowflake (3 Pics Mountain Snow Flake: 3PMSF).

[0005] The invention also relates to multi-purpose tires which can be used in different weather conditions, and which have an “M+S” (Mud + Snow) marking on at least one of their sidewalls.

[0006] By grip, we mean both the grip characteristics of the tire in the direction transverse to the movement of the vehicle, such as cornering, and those of the tire in the direction longitudinal to the movement of the vehicle, i.e. the possibility of transmitting a braking or driving force to the ground. Definitions

[0007] In the following, the circumferential, axial and radial directions respectively designate a direction tangent to any circle centered on the axis of rotation of the tire, a direction parallel to the axis of rotation of the tire and a direction perpendicular to the axis of rotation of the tire.

[0008] By convention, a reference (O, XX', YY', ZZ'), the center O of which coincides with the center of the tire, the circumferential XX', axial YY', and radial ZZ' directions respectively designate a direction tangent to the rolling surface of the tire in the direction of rotation, a direction parallel to the axis of rotation of the tire, and a direction orthogonal to the axis of rotation of the tire.

[0009] By radially inner, respectively radially outer, is meant closer, respectively further from the axis of rotation of the tire.

[0010] By axially inner, respectively axially outer, is meant closer, respectively further from the equatorial plane of the tire, the equatorial plane of the tire being the plane passing through the middle of the tread of the tire and orthogonal to the axis of rotation of the tire. Generally speaking, a circumferential plane is a plane orthogonal to the axis of rotation of the tire.

[0011] A tire comprises a crown, intended to come into contact with the ground via a tread, the two axial ends of which are connected via two sidewalls with two beads ensuring the mechanical connection between the tire and the rim on which it is intended to be mounted.

[0012] By tread "rolling surface" is meant the surface which groups together all the points of the tire which will come into contact with the ground under normal rolling conditions. These points which will come into contact with the ground belong to the contact faces of the blocks. For a tire, the "usual conditions" of rolling are the conditions of use defined by the ETRTO (European Tire and Rim Technical Organization) standard. These conditions of use specify the reference inflation pressure corresponding to the load capacity of the tire indicated by its load index and its speed code. These conditions of use can also be called "nominal conditions" or "conditions of use".

[0013] The total width of the tread is the axial distance between the axial ends of the tread surface, distributed on either side of the equatorial plane of the tire. In practical terms, an axial end of the tread surface does not necessarily correspond to a clearly defined point. Knowing that the tread is delimited externally, on the one hand, by the tread surface and, on the other hand, by two connecting surfaces with two sidewalls connecting said tread to two beads intended to ensure the connection with a mounting rim, an axial end can then be defined mathematically as the orthogonal projection, on the tread, of a theoretical point of intersection between the tangent to the tread surface, in the axial end zone of the tread surface, and the tangent to the connecting surface, in the radially outer end zone of the connecting surface.The total width of the strip of . rolling corresponds substantially to the axial width of the contact surface when the tire is subjected to the recommended load and pressure conditions.

[0014] The tread is generally formed by the repetition of raised volumetric elements called sculpture patterns in the circumferential direction. Said sculpture patterns are separated from each other by cutouts. A sculpture pattern groups together a set of raised elements, from a first axial end of the tread to a second axial end. Most often a sculpture pattern is composed of two half-patterns: a first half-pattern is arranged on a first side of the equatorial plane, and extends into a second half-pattern arranged on a second side of said plane. The raised elements constituting the half-patterns of sculpture are called sculpture blocks.

[0015] Each half-pattern of the tread begins at an axial end and continues a curved profile to end at the center of the tread, giving the tread pattern an overall “V” shape, and defining a preferred rolling direction, oriented towards the center of the “V”. Each half-pattern of the tread is formed of juxtaposed tread blocks going from the edge to the center of the tread, so as to determine a central groove centered on the equatorial plane.

[0016] The pitch of a sculpture pattern is the distance measured on a circumference of the tire between a point of this pattern and the translated image of this point on the immediately following pattern, according to the direction of rotation of the tire when it has a preferred rolling direction.

[0017] A tread with a single sculpture pattern is called a single-pitch. But in general, the tread of a passenger vehicle tire is made up of a circumferential repetition of two or three sculpture patterns with pitch lengths between 20 mm and 50 mm. In general, two consecutive patterns are homothetic.

[0018] In order to increase the grip potential of a tread of a tire rolling on a snow-covered or water-covered road, it is known to provide this tread with a sculpture formed from a plurality of cutouts made more or less deeply in each sculpture pattern, said cutouts opening onto the rolling surface with the road.

[0019] By cutout is meant any recess made in the tread whether by removal of material once the tread has been vulcanized or by molding in a mold for molding said tread and comprising molding elements projecting from the molding surface of said mold, each molding element having a geometry identical to the geometry of the desired cutout. As a general rule, a cutout made in a tread is delimited by at least two walls of rubber facing each other, said walls being separated of an average distance representing the width of the cutout, the intersection of said walls with the rolling surface forming edges. There are several types of cutouts, for example: • grooves or furrows characterized by a width greater than approximately 10% of the thickness of the tread; • incisions of relatively small width compared to the thickness of the tread; under certain stress conditions, these incisions can close, at least partially, in contact with the road; the facing walls come into contact with each other at least over a more or less large part of the surfaces of said walls (the edges formed by an incision on the rolling surface are in contact which causes the incision to close). In general, the distance between the walls of material which delimit an incision is less than or equal to 2 mm and the depth is greater than or equal to 1 mm.

[0020] Certain cutouts may open into at least one other cutout. The trace of a cutout on the running surface of a tread follows a mean geometric profile determined as the geometric profile located at a mean distance from the edges formed by the walls of said cutout on the running surface. The mean axis of the trace of a cutout on the running surface corresponds to the straight line of least squares of the distances of the points of the mean profile of the trace of said cutout.

[0021] By making a plurality of cutouts opening onto the rolling surface, a plurality of rubber edges are created to cut the layer of water possibly present on the road, so as to keep the tire in contact with the ground and to create cavities possibly forming channels intended to collect and evacuate the water present in the contact zone of the tire with the road as soon as they are arranged so as to open outside the contact zone.

[0022] Each sculpture pattern is composed of sculpture blocks which are often in the form of a rectangular parallelepiped. This parallelepiped comprises two parallel faces which follow the curvature of the half-pattern to which they belong: these are the lateral faces; an axially external upstream face; a downstream, axially internal face; a face intended to be in contact with a rolling ground, and finally a face against the bottom of the sculpture.

[0023] By "leading face" is meant the lateral face of said block which first comes into contact with the roadway, in a preferred rolling direction of the tire. The leading faces of the blocks of a pattern extend only on the same side of the half-pattern. Thus, if the block assembly comprises only one block, the leading face of the block assembly extends on a lateral wall of this block. If the assembly block comprises several blocks, the leading face of the block set extends over several side walls of different blocks.

[0024] By "trailing face" is meant the lateral face of said block assembly which last comes into contact with the roadway, in a preferred rolling direction of the tire. The trailing face of the block assembly extends only on one side of the block assembly. Thus, if the block assembly comprises only one block, the trailing face of the block assembly extends on a side wall of this block. If the block assembly comprises several blocks, the trailing face of the block assembly extends on several side walls of different blocks. Prior art

[0025] An example of such a sculpture is found in US patent 1,452,099 which describes a tread provided with a plurality of regularly spaced transversely oriented incisions.

[0026] However, increasing the number of cutouts quickly leads to a significant reduction in the rigidity of the tread, which has an adverse effect on the performance of the tire or even on the grip performance. By rigidity of the tread, we mean the rigidity of the strip under the combined actions of compression forces and shear forces in the region affected by contact with the road. At the same time, the presence of numerous cutouts forming water evacuation channels induces a level of noise when driving on a dry road which is today considered to be a nuisance that we wish to reduce as much as possible, particularly on vehicles of recent design. This noise when driving is amplified by the cyclic movements of closing and opening of the cutouts associated with the friction of the walls of said cutouts when they are closed.

[0027] In patent FR 1 028 978, a solution to this problem is proposed consisting of providing the tread with a plurality of shallow circumferential incisions on the tread surface of the new tread so as to increase the flexibility of said tread only in the vicinity of the tread surface.

[0028] However, since the tire is intended, once mounted on a vehicle, to ensure good performance throughout the life of said tire (i.e. until wear of its tread corresponds at least to the permitted legal level), it is necessary to provide a tread whose sculpture ensures the durability of the grip performance on wet and snowy ground without degrading the rolling resistance.

[0029] Rolling resistance is another performance addressed in the invention. Rolling resistance is one of the forces that oppose the movement of the vehicle. The Rolling Resistance Coefficient (RRC) is the rolling resistance force related to the load carried by the tire. The coefficient is expressed in kilos per ton (kg / t). Rolling resistance is essentially linked to the deformation of the tire. For illustration, the beads associated with the sidewalls represent 20% to 30% of the rolling resistance of the tire, while the tread contributes 60% to 80%.

[0031] Reducing greenhouse gas emissions from transport is one of the major challenges facing vehicle manufacturers today. Tires are an important source of progress, through a reduction in rolling resistance, because this has a direct impact on the vehicle's fuel consumption. As an illustration, a 20% reduction in the rolling resistance of a passenger car tire saves approximately 3% of fuel per 100 km in the combined cycle.

[0032] The choice of tread plays a vital role in establishing a compromise between grip and rolling resistance.

[0033] The object of the present invention is to develop a tire with a tread which combines a very good level of grip on snowy and / or wet roads throughout the life of said tire, while having improved rolling resistance. Statement of the invention

[0034] According to the invention, a tire is proposed comprising a tread, intended to come into contact with a ground via a rolling surface: -the tread comprising raised elements organized in at least a first and a second sculpture pattern MA, MB, separated at least in part from each other by grooves and extending radially outwards from a bottom surface to the tread surface over a radial height H at least equal to 6 mm and at most equal to the radial thickness Hsre of the tread; -each sculpture pattern MA, MB comprising half-sculpture patterns MAI, MB1 arranged on a first side of the equatorial plane C passing through the center of the tread, then extending on a second side of said plane C to form other half-patterns MA2, MB2; - the tread pattern being obtained by repeating over one wheel revolution said tread patterns MA, MB according to respective pitches PA, PB with PA<=PB; -each half-pattern of sculpture MAI, MA2; MB1, MB2 comprising sculpture blocks extending from an axial end of the edges of the tread to the center of the tread so as to form a groove centered on the equatorial plane (C), the sculpture block of a half-pattern of sculpture the most axially inner being designated central sculpture block; -at least one central sculpture block comprising at least one blocking element consisting of a protuberance extending a face, called the free face, of said central sculpture block until it touches the central groove; said blocking element comprising at least one face, called the blocking face having a surface Sb and said free face having a surface Sf, said tire is characterized in that for at least one central tread block, the ratio Sb / Sf is between 0.25 and 0.85.

[0035] When designing a winter tire, the choice of tread is an essential step. In addition to the objective of the invention of achieving an advantageous compromise in rolling resistance and grip on snowy ground, it is also necessary to control the rolling noise generated by the tire.

[0036] For this, the tread pattern is designed from a basic pattern MA which comprises raised elements extending from a first axial end of the tread to a second axial end. This pattern is associated with a pitch PA. A second pattern MB with an associated pitch PB is deduced from MA by a homothety, at least as regards the geometric shape of the blocks. From the positioning of a first pattern on the crown of the tire, by moving a circumferential distance corresponding to the associated pitch, a second homothetic pattern is positioned after the first pattern. By running this algorithm over one wheel revolution, a tread is obtained composed of a succession of homothetic tread patterns. Two tread patterns may differ in their circumferential width, their incision density, and / or the associated pitch.According to the inventors, two to three tread patterns (MA, MB, MC) are enough to significantly reduce tire rolling noise. Beyond three patterns, the manufacturing cost of the tire curing mold becomes prohibitive.

[0037] In the case where the patterns and the sculpture steps are identical, we find ourselves in a single-step sculpture configuration which corresponds to the particular solution of the invention.

[0038] According to the inventors, two main types of emergences are distinguished which are caused by the impact of the sculpture patterns on the road: siren and beat. These are emergences whose acoustic power is much higher than the average power of the spectrum and to which the human ear is particularly sensitive.

[0039] The rhythm of the impacts of the sculpture on the ground at the entrance to the contact patch is determined by the order of succession of the patterns. If the patterns are all the same size, they follow one another at a perfectly regular rhythm. A single frequency will then be used, which will produce a sound resembling that of a "siren". Having several sizes of patterns makes it possible to scramble the sound signal emitted by the tire sculpture, that is to say to reduce the emergences, to tend towards white noise.

[0040] The succession of tread patterns is designed to reduce the whirring and the beating. Thus, the design of the sculpture from homothetic patterns makes it possible to control the noise level emitted by the tire while rolling.

[0041] This method of designing the tread sculpture makes it possible to control noise performance, therefore the principle of the invention is to position the central sculpture blocks in such a way as to attenuate their deformations and therefore to minimize the viscoelastic dissipation of the mixtures to achieve reduced rolling resistance compared to a tire of conventional design.

[0042] To achieve this result, at least one central sculpture block comprises two so-called free faces, an axially inner face and a leading face which are the potential support for a blocking element which corresponds to a volume protuberance attached to said free face.

[0043] Said blocking element comprises a face, called the blocking face, provided with a surface Sb and the free face is provided with a surface Sf. According to the inventors for at least one central sculpture block, the ratio Sb / Sf is between 0.25 and 0.85.

[0044] The blocking face is intended to be in contact with another sculpture block of the tread. If Sb is less than 0.25, contact cannot be established effectively and the blocking element deforms, and therefore degrades the rolling resistance. For values ​​of the Sb / sf ratio greater than 0.25, the blocking face has a sufficient surface area to ensure the blocking of two sculpture blocks in contact. If Sb / Sf is greater than 0.85, the snow performance is no longer sufficient because too little snow is stored in this area to allow effective snow / snow grip and the passage of the regulatory thresholds.

[0045] The main characteristic of the invention, namely the blocking of the central sculpture blocks, contributes to obtaining the tire of the invention characterized in that it achieves an excellent compromise of performance in grip on snow and rolling resistance, while having a rolling noise level in accordance with regulatory requirements, thanks to the optimized arrangement of the sculpture in patterns.

[0046] Other characteristics of the invention linked to the geometry of the sculpture patterns reinforce the technical solution in the performance compromise achieved.

[0047] Advantageously, at least a first central sculpture block on a first side of the equatorial plane comprises a first blocking element opposite a second blocking element of a second central sculpture block on a second side of the equatorial plane.

[0048] In this embodiment, the tread pattern is defined so as to arrange the blocking elements in symmetry with respect to the equatorial plane. In this way, the blocking elements are opposite each other with respect to the equatorial plane. This distribution of blocking elements makes it possible to maximize the contact surfaces between blocks and therefore allows a significant reduction in rolling resistance.

[0049] Advantageously, the distance Dbloc is between 0.1 mm and 2 mm, the distance Dbloc being the distance between a blocking face of a first blocking element of a first central block and another blocking face, positioned opposite relative to the equatorial plane, of a second blocking element of a second central block.

[0050] The distance Dbloc is greater than or equal to 0.1 mm to allow decoupling between the central blocks on either side of the plane C with a view to improving rolling noise. Beyond 2 mm, the distance Dbloc is too great to have sufficient clamping between the locking faces to avoid deformation of the tread blocks.

[0051] Still according to the previous embodiment, at least a first central sculpture block on a first side of the equatorial plane opposite a second central block on a second side of the equatorial plane, the first central sculpture block comprises a blocking element which touches the central groove over a width L1; the second central sculpture block comprises another blocking element which touches the central groove by a width L2; the widths L1 and L2 are different.

[0052] A central tread block is in the form of a rectangular parallelepiped. This parallelepiped comprises two parallel faces which follow the curvature of the half-pattern to which they belong: these are the lateral faces; an upstream, axially outer face; a downstream, axially inner face; a face intended to be in contact with a rolling surface, and finally a face against the bottom of the tread. When the tire is rotating around its axis and crushed by a carried load, so as to form a contact area on the rolling surface, the lateral face which first enters the contact area is the leading face, the other lateral face is the trailing face. The trailing face and the axially inner face are free faces potentially comprising a blocking element which comes to touch the central groove over a distance which represents the width L1 of the blocking element.A second central block on the other side of the equatorial plane and opposite the first touches as much. to it the central groove over a distance L2. According to the inventors, in general, the widths L1 and L2 are different, and serve as adjustment parameters to reduce the rolling noise of the tire.

[0053] Preferably, at least a first central sculpture block on a first side of the equatorial plane opposite a second central sculpture block on a second side of the equatorial plane, the first central sculpture block comprises a blocking element which touches the central groove over a length L1; the second central sculpture block comprises another blocking element which touches the central groove over a length L2; the lengths L1 and L2 are identical.

[0054] In this configuration, the two central blocks mentioned above on one side of the equatorial plane are symmetrical to those on the other side. The production of the sculpture becomes easier to achieve.

[0055] Still in a simplification approach, preferably, the widths (L1, L2) are proportional respectively to the widths of the first and second central blocks measured along the central groove. Indeed, the widths of the blocking elements are not identical to those of the central blocks.

[0056] Advantageously, the locking face of a locking element comprises undulations oriented along the central groove and / or in the radial direction, said radial direction being orthogonal to the axis of rotation of the tire.

[0057] In this configuration, we seek to facilitate contact between the blocking faces by warping them.

[0058] Advantageously, the distance Dbloc, between two blocking faces arranged opposite each other with respect to the equatorial plane, is variable in the radial direction, and is maximum at the radially inner end of the blocking faces.

[0059] Advantageously, a channel opening onto the central groove is arranged at the radially inner ends of a first and a second blocking element facing each other with respect to the equatorial plane. This second embodiment is illustrated in [Fig.4]-B.

[0060] The function of this channel is to evacuate the water present in the contact area to facilitate contact and therefore grip between the tire and the road.

[0061] Advantageously, a contact area being a surface on the ground resulting from the crushing of the tire while rolling, Gamma being the angle formed by an edge of a blocking face entering the contact area first in the direction of rolling of the tire, and a radial direction, Gamma is between 0° and 10°. This condition is necessary to preserve the wear of the tread blocks, the angle Gamma reflects the orientation of the blocking face as it passes through the contact area. By having a closed angle between 0° and 10°, the wear of the tread blocks is minimized.

[0062] Advantageously, the angle Delta formed by an edge of a blocking face entering the second into the contact area in the rolling direction of the tire, and a radial direction, is greater than the angle made by an edge of a free face entering the second into the contact area, and the radial direction. This condition makes it possible to avoid the retention of stones in the sculpture.

[0063] Advantageously, the Delta angle formed by an edge of a blocking face entering the second into the contact area in the rolling direction of the tire, and the radial direction in which the Delta angle is greater than 30°. When this condition is met, the sculpture is better protected against the retention of stones.

[0064] Advantageously, the central groove makes an average angle of between 30° and 55° with the circumferential direction.

[0065] Advantageously, each sculpture block comprises one or more incisions; an incision being a cutout on the rolling surface with a distance between the walls of material which delimit the incision, less than or equal to 2 mm and a depth greater than or equal to 1 mm.

[0066] Advantageously, the radially outer surface of a locking element is at a distance from the rolling surface greater than or equal to 2 mm, the distance being the maximum value of the radial projections of the points of the radially outer surface of the locking element on the rolling surface.

[0067] The traction of the tire of the invention on snowy ground is favored by the preceding characteristic which facilitates the gripping of the tire in the snow. The tire of the invention, by its sculpture and the material of the tread, passes the snow grip test required to have the 3MPSF certification indicated on at least one of its sidewalls.

[0068] The inventors have identified characteristics linked to the cutouts of the tread, to its volumetric and surface notch rates.

[0069] The overall volumetric notch rate TEV corresponds to the ratio of the volume of notches VE to the total volume VT of the tread, such that TEV=VE / VT. Advantageously, the overall volumetric notch rate TEV of the tread is between [20%; 40%], and preferably between [20%; 35%].

[0070] For grip performance on snowy ground, the notch rate has a rack effect to promote the grip of the tire in the snow. This rack effect is amplified with a directional sculpture comprising cutouts. According to the inventors, an overall notch rate TEV of between [20%, 40%] and preferably between [20%, 35%] is necessary to have grip performance on snow in accordance with expectations.

[0071] In addition, the volumetric notch rate also defines the volume of elastomeric material constituting the tread intended to be worn. The rate notch is therefore a sensitive parameter for determining the compromise of tire performance such as wear, grip, and noise.

[0072] In addition to the volumetric notch rate, the surface notch rate is another criterion for the desired performance compromise. The bandwidth rolling forms a ground contact area AC when rolling said tire, a part of the sculpture patterns also forms a contact surface SC on said area of AC contact. We define the surface notch rate TES of the tread as being the report, Preferably, TES is included in the interval [0.35; 0.6], and even more preferably TES is at least equal to 0.38, and even more preferably TES is at least equal to 0.4.

[0073] The inventors have identified other characteristics related to the pitch of the sculpture patterns to even better manage the compromise between grip and rolling noise of the tire.

[0074] Preferably, the ratio between the pitch PA of the first sculpture pattern MA divided by the pitch PB of the second pattern MB, PA / PB is at least equal to 0.60 and at most equal to 0.90.

[0075] The PA / PB ratio of the shortest PA pitch of the first sculpture pattern divided by the longest PB pitch of the second sculpture pattern is included in the interval [0.6; 0.9]. The smallest pitch and the longest pitch are in a ratio ideally equal to 0.85, or at least included in the interval [0.6; 0.9].

[0076] When the pitch ratio is less than 0.6, the gap between the two pitches becomes too large and results in too great a discontinuity in the arrangement of the sculpture patterns around the wheel.

[0077] Conversely, for a pitch ratio beyond 0.9, the distance between the sculpture patterns becomes too small, the sculpture of the tread becomes close to a single-pitch solution which is not satisfactory in terms of the level of noise generated.

[0078] In the design of a snow tire tread, the choice of tread material is an essential step. The chemical composition of the tread material is formulated to remain flexible at low temperatures, which increases grip on slippery ground (wet, snow and ice). Low temperature means a temperature below 7°C.

[0079] Advantageously, the composition of the rubber material of the tread has a glass transition temperature Tg of between -40°C and -10°C and preferably between -35°C and -15°C and a complex dynamic shear modulus G* measured at 60°C of between 0.5 MPa and 2 MPa, and preferably between 0.7 MPa and 1.7 MPa.

[0080] The grip of the tire on the ground obeys at least two physical phenomena: adhesion and indentation. For example, for wet ground, the tread pattern evacuates water from the ground to allow adhesion by bonding the dry rolling surface with the ground. At the same time, the flexibility of the tread material makes it possible to follow the roughness of the ground by indentation to grip the tire. The material must remain flexible and effective at temperatures below 7°C. According to the inventors, an elastomeric material with a glass transition temperature Tg between -40°C and -10°C and preferably between -35°C and -15°C and a complex dynamic shear modulus G* measured at 60°C between 0.5 MPa and 2 MPa, and preferably between 0.7 MPa and 1.7 MPa, gives the tread the appropriate physical properties to meet the desired performance compromises. Brief description of the drawings

[0081] The present invention will be better understood on reading the detailed description of embodiments taken as examples, in no way limiting and illustrated by the appended drawings in which:

[0082] [Fig.l] represents a view of the tire of the invention in a meridian plane representing in particular the profile and the height of the tread.

[0083] [Fig.2] shows a tread pattern MA which comprises two half-patterns MAI and MA2 positioned on either side of the equatorial plane C.

[0084] [Fig.3] shows a progress of the tread pattern with three tread patterns MA, MB and MC comprising respective half-patterns MAI, MA2, MB1, MB2, and MCI, MC2. The tread patterns differ in their geometry (widths, cutouts, pitches, etc.). The MA pattern is shown with a light gray background, and the MB pattern with a dark background, and the MC pattern with wavelets on its surface.

[0085] [Fig.4] shows two views [Fig.4]-A and [Fig.4]-B representing enlargements of sculpture blocks highlighting the principle of blocking elements to reduce sculpture deformations.

[0086] [Fig.5] is again an enlargement of a sculpture block showing a channel arranged in two blocking elements.

[0087] Finally [Fig.6] is an enlargement showing a central sculpture block with two blocking elements. Detailed description of the invention

[0088] The invention has been more particularly studied for a passenger car tire of standardized designation, according to the specification standard of the ETRTO (European Technical Organization for Rims and Tires), 235 / 65R16 115 / 113R. For this dimension a version of the tire in accordance with the invention with a tread comprising three sculpture patterns MA, MB, and MC with respective variable pitches PA, PB, and PC was produced.

[0089] In the various figures, identical or similar elements bear the same references. For the readability of the figures, the elements are referenced only once, sometimes on the 24G side, sometimes on the 24D side.

[0090] [Fig.l] gives a view in a meridian plane of the tire, of general reference 1, showing the height of the sculpture of the tread 10 which rests on the crown 25 comprising the crown layers (21, 22, 23), first a hooping layer 21 radially inside the tread, then two crossed layers (22, 23) representing the working layers, radially inside the hooping layer 21. The tire 1 also comprises a carcass reinforcement 70 consisting of reinforcements coated with rubber composition, and two beads 35 intended to be in contact with a rim. Said carcass reinforcement 70 connects the two beads 35, and comprises a main branch 31 which is wrapped around an annular reinforcing structure 33 to form a turn-up 32. The sidewalls 60 connect the beads 35 to the tread 10. In [Fig.3], the tread 10 which is shown, comes to cover the tire of [Fig.l] radially outside the hooping layer 21. .

[0091] In [Fig. 2], a first pattern MA of the tread sculpture is shown, composed of the half-patterns MAI, MA2, arranged on either side of the equatorial plane C. Each half-pattern comprises sculpture blocks 135 arranged from an axial edge (24G, 24D) then extend to the center of the tread according to a curved profile which gives a sculpture pattern a chevron shape. The tip of the chevron indicates the rolling direction 150 of the tire. The sculpture blocks 140 in the center of the tread touch a central groove 100 which is zigzag and circumferentially oriented. The sculpture blocks comprise incisions 160 from the rolling surface to a radial depth of 7 mm. We can also see the widths Ll, ​​and L2, of blocking elements distributed on either side of the equatorial plane C. The widths ALI, and AL2 are the curvilinear distances of the central blocks along their curved profile.

[0092] In [Fig. 3], a sequence of the tread pattern is shown showing the distribution of three tread patterns MA, MB, and MC, with respective pitches PA, PB, and PC. The arrangement of the tread patterns, i.e. the order of succession of the patterns MA, MB, and MC, results from an optimization of the rolling noise. As a general rule, the geometry of the tread patterns is in a homothetic relationship, with conventionally the pattern MA having the smallest width, and MC the largest width, and MB an intermediate width. However, the number of cutouts between two patterns may be different. Between the tread patterns (MA, MB, MC), the bottom of the tread 40 can be seen. The patterns rise radially outwardly from the bottom 40 towards the tread surface at a radial height which corresponds to the height of the tread pattern which varies slightly decreasing from the center towards the axial ends of the tread. Each tread pattern MA, MB, MC comprises two half-tread patterns respectively MAI, MA2, MB1, MB2, MCI, MC2, arranged in a chevron shape, on either side of the equatorial plane C on the tread with a preferred rolling direction 150.

[0093] By “edges” 24G, 24D of the tread 10, we mean the surfaces delimiting the boundaries between the tread 10 and the sidewalls 60. These two edges 24G, 24D are spaced apart from each other by a value W corresponding to the width of the tread 10.

[0094] To optimize the arrangement of the patterns, that is to say their succession over a wheel revolution so as to reduce the siren and beat noise, each sculpture pattern is associated with an elementary signal, for example a sinusoidal signal. For a complete wheel revolution, the associated signal is periodic and results from the summation of the elementary signals.

[0095] With the help of a numerical tool, the optimization of the initial arrangement with respect to the siren and beat noise is carried out by carrying out simulations on different possible arrangements. By a Fourier transformation of the signal associated with the arrangement, the signal spectrum is analyzed in the frequency domain. The criteria for stopping the optimization process are linked to the amplitude of the siren and beat emergences, as well as to their spread on the frequency axis.

[0096] At the end of this iterative approach, for the tire size studied, 235 / 65R16 115 / 113R, the total number of tread patterns is 76 on one wheel revolution, arranged according to the sequence: MC MA MC MC MA MA MA MA MB MA MC MC MC MB MC MA MC MA MB MC MA MA MB MA MC MA MA MB MB MB MB MA MA MB MC MB MB MB MB MC MC MA MC MB MB MA MA MB MB MA MB MC MB MC MB MA MB MB MA MB MC MB.

[0097] The circumference of the tire is equal to 2225 mm, and the tread width is 190 mm. The tread pattern of the manufactured tire comprises 3 tread patterns (MA, MB, MC) divided into 30 MA patterns, 25 MB patterns, and 21 MC patterns.

[0098] The following table summarizes the characteristics of the sculpture patterns (MA, MB, MC):

[0099] [Tables 1] Number of patterns Pitch (mm) Width of the solid (mm) Surface notch rate (%) Volumetric notch rate (%) MA pattern NA=30 25 18 40 24 MB pattern NB=25 29 22 39 24 MC pattern NC=21 36 26 39 24

[0100] The volumetric notch rate of each pattern (MA, MB, MC) corresponds to the ratio of the volume of the notches to the volume of said patterns (MA, MB, MC). The surface notch rate associated with a pattern (MA, MB, MC) is defined equivalently. By extrapolation, the overall volumetric notch rate, TEV, corresponds to the ratio of the notch volume VE to the total volume VT of the tread, such that TEV=VE / VT. The overall volumetric notch rate TEV of the tread of a tire of the invention is between [20%; 40%], and preferably between [20%; 35%].

[0101] The inventors defined the incision density of the sculpture patterns as being the ratio between the sum of the projected lengths (Lpx) of the incisions of a sculpture pattern (MA, MB, MC) in a circumferential direction on the product of the pitch (PA, PB, PC) of the sculpture pattern and the width (W) of the tread, the whole being multiplied by 1000, such that: SDA = * 100ΠSDg = SDC = * 1000 PA*W " PB*W ' PC*W

[0102] with (NA, NB, NC) the number of incisions of each sculpture pattern (MA, MB, MC), and Lpxi the projected length of the i-th incision of the pattern considered.

[0103] According to the inventors, in the definition of (SDA, SDB, SDC), the denominator corresponds to the surface area encompassing a tread pattern (MA, MB, MC), so that the incision density represents the amount of edge of a pattern (MA, MB, MC) on the encompassing surface. The higher the density, the more incisions the tire tread has, and consequently the higher its grip performance on wet and snowy ground.

[0104] The incision density (SDA, SDB, SDC) of each sculpture pattern (MA, MB, MC) is at least equal to 10 mm ', and at most equal to 70 mm '.

[0105] From the incision densities of the sculpture patterns, we can deduce the average incision density: SDmoy = SD A* PÆSDS* sVS*P£H-SD OiV

[0106] By construction, the average density of incisions SDmoy is at least equal to 10 mm and at most equal to 70 mm'.

[0107] From a practical point of view, the tread width is determined from a dynamically produced imprint. In order to obtain such an imprint, black ink is deposited on a portion of the tire tread and this inked portion is rolled over a sheet of paper at a certain forward speed. The conditions for producing such an imprint are at nominal pressure, for a load corresponding to 0.76 times the nominal load and at a forward speed of 100 mm / s. For example, for a tire of size 205 / 55R16 91V, the conditions for producing the imprint will be at a pressure of 2.5 bars and for a load of 480 daN.All the measurements for determining the incision density SD and the average incision density SDmoy are subsequently made from an imprint of the tread rolling on a support under the load, pressure and forward speed conditions as described above.

[0108] [Fig.4] with the two views 4-A, and 4-B shows a magnification of a portion of central sculpture blocks 140. View 4-A shows the axial end of a central block 140 without opposite showing the rolling surface 20, the groove 100, a locking element 220 in the axial extension in part of a free face 250 with locking edges 270.

[0109] As for view 4-B, it shows two central blocks 140 with blocking elements 220 facing each other, one opposite the other. When the tire rolls on ground, crushed by the load carried, the blocking faces come into contact and block the deformations of the sculpture.

[0110] [Fig.5] shows an embodiment of the invention where a channel 280 for evacuating water from the roadway is arranged between two blocking elements 220 and opens onto the furrow 100. The distance Dbloc is represented between the two blocking faces 270.

[0111] In [Fig.6], we can see a central sculpture block 140 comprising two blocking elements 220. A first blocking element 220 of the central sculpture block 140 is an outgrowth of a free lateral face 250 with a bold outline in the figure, of surface Sf. We also see a blocking face 270 also with a bold outline, and of surface Sb. A second blocking element 220 is located on an axially inner free face.

[0112] Finally, in [Fig.7], identical to [Fig.6], we show the angle Gamma between a leading edge and a radial direction, and the angle Delta between a trailing edge and a radial direction of a blocking face 270. When the tire is rotating around its axis and passes over a ground, the contact patch is the surface formed by the crushing of the tire due to the load carried. For a blocking face 270, the leading edge is the one that enters the contact patch first. The trailing edge is the last edge of the face 270 to pass into the contact patch.

[0113] As regards the tread material, its composition is grouped in table no. 2 below: [Tables 2] SBR Elastomer (Styrene Butadiene) BR Elastomer (Butadiene) Reinforcing filler Silica Antioxidant Sulphur Accelerator Plasticizer Mixture Tread 80 20 115 4.5 1.4 1.6 70

[0114] The tread compound of the tire of the invention used in this example is based on a styrene butadiene elastomer. Plasticizers (reinforcing resin) are included in the composition to facilitate the processability of the compounds. The compound also includes vulcanizing agents, sulfur, accelerator, and protective agents.

[0115] The associated mechanical and viscoelastic properties, measured at 23°C under a deformation amplitude of 10% are summarized in table no. 3:

[0116] [Tables3] G' (MPa) G" (MPa) Tan (ô)ma X Tg glass transiti on (°C) Mixture Tread 1.7 0.5 0.2 -31

[0117] The tire of the invention was tested to clearly highlight the performance provided by the invention. The results of these tests are compared with those obtained for a TL control tire.

[0118] The longitudinal grip tests on snowy ground, on wet ground, and rolling noise were carried out in accordance with the requirements of UNECE / RI 17 regulation.

[0119] For grip performance, the indicator T1 is that provided for by regulation UNECE / R117, corresponding to a tire of usual design which includes a tread pattern without the main characteristics of the invention. Said tread is made of a material suitable for winter use.

[0120] The control dimension T2 for the noise test is 235 / 65R16 115 R of a usual design with regard to the tread.

[0121] A tire P according to the invention is considered with a tread comprising a sculpture as described according to claim 1.

[0122] A result higher (respectively lower) than 100% means an improvement (respectively a deterioration) of the performance considered. The results obtained are summarized in table no. 4, below: [Tables 4] Longitudinal grip Snow According to UNECE / R117 Longitudinal grip on wet ground According to UNECE / R117 Rolling noise According to UNECE / R117 Rolling resistance (Kg / t) Tl 100 100 Not Applicable Not applicable T2 110 145 100 7.2 P 110 145 101 6.9

[0123] The tire of the invention achieves the desired performance shift without compromising on snow / wet grip and noise. The tread locking elements limit the deformation of the tread and therefore limit rolling resistance. The incisions and notches in the tread have made it possible to achieve the desired level of grip on snow and wet ground. Rolling noise is under control and remains at a level that complies with the approval thresholds of regulation RI 17.

Claims

1. Claims Tire (1) comprising a tread (10), intended to come into contact with a ground via a rolling surface (20): - the tread (10) comprising raised elements organized in at least a first and a second sculpture pattern (MA, MB), separated at least in part from each other by grooves (30) and extending radially outwards from a bottom surface (40) to the rolling surface (20) over a radial height H at least equal to 6 mm and at most equal to the radial thickness Hsre of the tread (10); - each sculpture pattern (MA, MB) comprising half-sculpture patterns (MAI, MB1) arranged on a first side of the equatorial plane (C ) passing through the center of the tread (10 ), then extending on a second side of said plane (C ) to form other half-patterns (MA2, MB2); - the tread pattern being obtained by repeating over one wheel revolution said tread patterns (MA, MB) according to respective pitches PA, PB with PA<=PB; - each half-pattern of sculpture (MAI, MA2; MB1, MB2) comprising sculpture blocks (135) extending from an axial end of the edge of the tread (24G, 24D) to the center of the tread (10) so as to form a groove (100) centered on the equatorial plane (C), the sculpture block of a half-pattern of sculpture the most axially inner being designated central sculpture block (140); - at least one central sculpture block (140) comprising at least one blocking element (220) consisting of a protuberance attached to a face (250), called the free face, of said central sculpture block (140) extending until it touches the central groove (100); - said blocking element (220) comprising at least one face, called blocking face (270) provided with a surface Sb and said free face (250) being provided with a surface Sf, said tire (1) being characterized in that, for at least one central tread block (140), the ratio Sb / Sf is between 0.25 and 0.85, in that at least one first central tread block (140) on a first side of the equatorial plane (C) comprises a first blocking element (220) opposite a second blocking element (220) of a second central tread block (140) on a second side of the equatorial plane (C), and in that the first central tread block (140) comprises a blocking element (220) which touches the central groove (100) over a width L1 and the second central tread block (140) comprises another ... blocking (220) which touches the central groove (100) with a width L2; the widths L1 and L2 being different.

2. Tire (1) according to claim 1, wherein the distance Dbloc is between 0.1 mm and 2 mm, the distance Dbloc being the distance between a blocking face (270) of a first blocking element (220) of a first central block (140) and another blocking face (270), positioned opposite relative to the equatorial plane (C) of a second blocking element (220) of a second central block (140).

3. A tire (1) according to one of claims 1 or 2, wherein the widths (L1, L2) are proportional respectively to the widths of the first and second central blocks measured along the central groove.

4. Tire (1) according to one of claims 1 to 3, in which the locking face (270) of a locking element (220) comprises undulations oriented along the central groove (100) and / or in the radial direction, said radial direction being orthogonal to the axis of rotation of the tire (1).

5. Tire (1) according to one of claims 2 to 4, in which the distance Dbloc, between two blocking faces (270) arranged opposite each other relative to the equatorial plane, is variable in the radial direction, and is maximum at the radially inner end of the blocking faces (270).

6. Tire (1) according to one of claims 1 to 5, in which a channel opening into the central groove (100) is arranged at the radially inner ends of a first and a second blocking element (220) facing each other relative to the equatorial plane (C).

7. Tire (1) according to one of claims 1 to 6, a contact area being a surface on the ground resulting from the crushing of the tire while rolling, the angle Gamma being the angle formed by an edge of a blocking face (270) entering the contact area first in the rolling direction (150) of the tire (1), and a radial direction in which the angle Gamma is between 0° and 10°

8. IV. Tire (1) according to claim 7, in which the angle Delta formed by an edge of a blocking face (270) entering the second into the contact area in the rolling direction (150) of the tire (1), and a radial direction, is greater than the angle Gamma made by an edge of a free face (250) entering the second into the contact area, and the radial direction.

9. A tire (1) according to claim 8, wherein the Delta angle is greater than 30°.

10. Tire (1) according to one of claims 1 to 9, in which the central groove (100) makes an average angle of between 30° and 55° with the circumferential direction.

11. A tire (1) according to one of claims 1 to 10, wherein each tread block (135) comprises one or more incisions (160), an incision (160) being a cutout on the rolling surface (20) with a distance between the walls of material which delimit the incision (160) of less than or equal to 2 mm and a depth of greater than or equal to 1 mm.

12. A tire (1) according to any one of claims 1 to 11, wherein the radially outer surface of a locking element (220) is at a distance from the rolling surface (20) greater than or equal to 2 mm, the distance being the maximum value of the radial projections of the points of the radially outer surface of the locking element (220) on the rolling surface.

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