HIGH-SPEED WARM-UP TIRES

Description

[0001] The present invention relates to a tire and a mold. By tire, we mean a band intended to form an internal cavity by cooperating with a support element of an assembled unit, this internal cavity being capable of being pressurized to a pressure greater than atmospheric pressure.

[0002] We know the state of the art of competition tires for motor racing vehicles and motor racing vehicles.

[0003] In car and motorcycle racing, drivers want tires that offer optimal performance, particularly grip, throughout their entire lifespan—from the start of the race or their installation on the vehicle until the finish or until they are changed. One of the key parameters for achieving this optimal performance is the tire temperature, which must reach a specific operating temperature to guarantee this performance.

[0004] Thus, in some races, prior to mounting them on the vehicle, the tire temperature is increased by heating, for example using heating devices consisting of heating blankets that are wrapped around the tires. Such heating devices are, on the one hand, expensive and cumbersome, and on the other hand, energy-intensive.

[0005] In other cases, no heating device is used, which leads to a delay in reaching the operating temperature and therefore achieving optimal performance.

[0006] The invention aims to enable optimal performance to be achieved in a more economical and ecological way, or more quickly in racing.

[0007] Thus, the invention relates to a tire for a motor vehicle or motorcycle for asphalt surfaces comprising a tread surface including one or more continuously smooth parts, in which the continuously smooth part(s) comprise: a plurality of hollows, each hollow of the plurality of hollows comprising a hollow bottom, a plurality of bumps, each bump of the plurality of bumps comprising a bump crest, The troughs of the plurality of troughs and the bumps of the plurality of bumps are arranged such that, when the continuously smooth part or parts roll on a ground, the average pressure at the crest of the bumps exerted on average by the ground on the crests of the bumps of the plurality of bumps is strictly greater than the average pressure at the bottom of the troughs exerted on average by the ground on the bottoms of the troughs of the plurality of troughs, the average pressure at the bottom of the troughs being non-zero, the pressure exerted by the ground on each trough of the plurality of troughs and on each bump of the plurality of bumps being measured in the contact area of ​​the continuously smooth part or parts of the tire, the tire rolling at a speed of 100 mm / sec under substantially zero drift and camber angles, the tire being inflated to a reference pressure of 1.6 bar and subjected to a reference load of 5000 N in the case of a motor vehicle tire,The tire is inflated to a reference pressure of 1.8 bar and subjected to a reference load of 1500 N in the case of a motorcycle tire.

[0008] Since the average pressure of the bumps is strictly greater than the average pressure of the hollows, the radial and tangential deformations imposed on the bumps are greater than those imposed on the tread surface of a prior art tire in which the equivalent average pressure is substantially uniform across the tread surface. By imposing relatively large deformations, local overpressures are created on the bumps, which heats the tire according to the invention. This rapidly increases the tire temperature, particularly during the initial moments of rolling.

[0009] Unlike prior art tires, whose smooth section(s) have a substantially constant transverse radius in the median plane and in each parasagittal plane, the grooves in said smooth section of the tire according to the invention have an average transverse radius strictly smaller than the average transverse radius of the bumps in said smooth section, the transverse radius being the radial distance between the axis of rotation and a point on said smooth section. The average transverse radius is, for each set of grooves and bumps, the arithmetic mean of the transverse radii of each set.

[0010] Thus, unlike prior art tires which are heated by external heating devices, the tire according to the invention heats itself by contact with the ground, thus enabling optimal performance to be achieved in an economical and ecological way, without resorting to costly, restrictive and energy-consuming external heating devices.

[0011] Furthermore, in the event that no external heating device is used, the invention allows the tire to reach its operating temperature more quickly compared to a prior art tire, and therefore allows the driver to have optimal performance more quickly during the course of the race.

[0012] State-of-the-art tires are known from US6540858B1, US9776456B2, FR3094270A1, US7762296B2, XP055939780 and JP2000198320A.

[0013] The invention does not characterize the overpressures usually observed on the axially outer parts of a tire. Indeed, due to the curvature of a tire, the axially outer parts generally form depressions because these parts typically have a smaller transverse radius than the axially central part. Thus, these axially outer parts, simply because they have depressions, cannot, for that reason alone, constitute bumps on the tire according to the invention. In the event that these axially outer parts were to form bumps, contrary to what is generally observed, and thus cause overpressures, then these axially outer parts would, of course, form bumps in accordance with the invention.

[0014] The invention applies equally to tires for motor vehicles and to tires for motorcycles.

[0015] The tire's intended use on asphalt surfaces, whether on a closed circuit or an open road, is essential to allow for the creation of localized overpressures over bumps. Indeed, loose surfaces, such as dirt, would not allow for the creation of significant overpressures. Therefore, tires designed for gravel rallying are not part of this invention. In particular, competition tires for gravel rallying are not part of this invention.

[0016] Of course, the invention applies to a tire both new and worn, whether fully or partially worn. Given the invention and its application, it is preferable to use it on a new tire.

[0017] Each continuously smooth part comprises a plurality of hollows and a plurality of bumps; that is, each continuously smooth part comprises at least two hollows and at least two bumps. Thus, depending on the embodiment, the continuous smooth part(s) as a whole will comprise more or fewer hollows and bumps. Depending on the orientation and arrangement of the hollows and bumps, there may be, for example, from 2 to 600 hollows and from 2 to 600 bumps on the continuous smooth part(s). In some embodiments where there is a reduced number of hollows and bumps, the continuous smooth part(s) as a whole comprises from 2 to 10 hollows and from 2 to 10 bumps. In other embodiments in which there is a high number of hollows and bumps, the continuously smooth part(s) comprise from 10 to 600 hollows and from 10 to 600 bumps.

[0018] A skilled technician will know how to adapt the bumps and dips according to the tread's properties, particularly its rigidity. Indeed, the more rigid the tread, the more difficult it is to flatten the tread and the greater the pressure at the bump peaks will be. Thus, in the case of a relatively rigid tread, a relatively small average amplitude between the bump peaks and the dip bottoms will be preferred to achieve sufficient pressure without it being unnecessarily excessive. Conversely, the more flexible the tread, the easier it is to flatten the tread and the less pressure will be at the bump peaks. Therefore, in the case of a relatively flexible tread, a larger average amplitude between the bump peaks and the dip bottoms will be preferred to achieve a higher desired pressure.

[0019] Preferably, although not an essential feature of the invention, tires will be chosen in which any contact area obtained under the conditions described above has at least 2 hollows and 2 bumps.

[0020] When two smooth sections of the running surface are at least partially joined and connected by a common smooth section, these connected sections will be considered as a single, continuously smooth section. Conversely, when two smooth sections of the running surface are completely separated by a non-smooth section, these two smooth sections will be considered as two distinct, continuously smooth sections.

[0021] A smooth area is a portion of the running surface that does not include any raised features, such as wear indicators or cutouts. Such wear indicators or cutouts, for example, create a discontinuity or an abrupt break in the curvature of the running surface.

[0022] The invention therefore applies to tires whose tread consists of a single smooth section, but also to tires whose tread comprises one or more smooth sections and one or more non-smooth sections. One or more such non-smooth sections may include raised features, for example, wear indicators, cutouts for water drainage or storage, cutouts molded with vents to allow the evacuation of air trapped between the tire's curing mold and the tread during the tire manufacturing process, or even molding burrs.In other words, each smooth part is devoid of these raised elements chosen from among wear indicators, cutouts for water drainage or storage, cutouts molded by vents allowing the evacuation of air trapped between the tire curing mold and the tread surface during the tire manufacturing process, or even molding burrs.

[0023] The hollows of the plurality of hollows in the tire do not have as their essential function the evacuation or storage of water, nor any essential function that can be associated with the evacuation of air trapped between the tire curing mold and the tread surface during the tire manufacturing process.

[0024] The tread is the part of the tire that makes contact with the ground during rolling. The tread area is the area of ​​revolution of a tire bounded by the axial ends of the tread. This area can be measured, for example, by taking a profile measurement. For a vehicle tire, the axial width of the tire can also be measured and multiplied by the maximum circumference measured in the tire's median plane.

[0025] In the case of a tire of the invention, the surface(s) formed by the continuously smooth part(s) is determined by calculating, on an uninflated and unloaded tire, the surface of each of this or these continuously smooth part(s), for example by imaging.

[0026] Each depression and each bump of the continuously smooth section(s) is defined relative to a mean surface of revolution whose axis of revolution substantially coincides with the axis of rotation of the tire, the mean surface of revolution being equidistant from the bottom of the depressions and the top of the bumps. Thus, any part radially outside the mean surface of revolution is a bump, while any part radially inside the mean surface of revolution is a depression. The continuously smooth section(s) may therefore also include one or more mean sections substantially coinciding with the mean surface of revolution.

[0027] The hollows and bumps can have various shapes. For example, some hollows and bumps may have a rounded profile. Others may have a profile with edges and / or straight sections, such as a trapezoidal profile, where the peaks of the bumps and the bottoms of the hollows are formed by roughly straight profiles.

[0028] The average pressure at the crest of a bump is equal to the arithmetic mean of the pressures measured at the crests of the bumps in the continuous smooth section(s). Similarly, the average pressure at the bottom of a hollow is equal to the arithmetic mean of the pressures measured in the bottoms of the hollows in the continuous smooth section(s). To measure the pressures at the crests of bumps and the bottoms of hollows in the continuous smooth section(s), methods known to those skilled in the art may be used, such as those described, for example, in WO2017109377, or those marketed by Tekscan, Inc. under the name TireScan CrossDrive System. Preferably, the ground used for the measurement should be flat, smooth, and rigid, as described, for example, in WO2017109377.

[0029] Alternatively, we could preferentially determine the average peak pressure by considering only the 25% highest measured pressures on the peaks of the bumps of the or each smooth part and determine the average trough pressure by considering only the 25% lowest measured pressures on the bottoms of the troughs of the or each smooth part.

[0030] To avoid edge effects, particularly where the continuously smooth section is at least partially bordered by the edges of the tire contact patch, pressures will be determined in a central zone of the contact patch of the continuously smooth section. This central zone has an axial width equal to 50% of the width of the continuously smooth section and is axially centered on the median plane of the continuously smooth section, and a length equal to 50% of the length of the continuously smooth section and is longitudinally centered on the transverse plane of the continuously smooth section.

[0031] The tire according to the invention has a substantially toroidal shape around an axis of revolution substantially coinciding with the axis of rotation of the tire. This axis of revolution defines three directions conventionally used by those skilled in the art: an axial direction, a circumferential direction, and a radial direction.

[0032] Axial direction refers to the direction substantially parallel to the axis of revolution of the tire, that is, the axis of rotation of the tire.

[0033] By circumferential direction, we mean the direction which is substantially perpendicular to both the axial direction and to a radius of the tire (in other words, tangent to a circle whose center is on the axis of rotation of the tire).

[0034] By radial direction, we mean the direction along a radius of the tire, that is to say any direction intersecting the axis of rotation of the tire and substantially perpendicular to this axis.

[0035] By median plane of the tire (denoted M), we mean the plane perpendicular to the axis of rotation of the tire which is located at mid-axial distance of the two ribs and passes through the axial midpoint of the crown reinforcement.

[0036] The equatorial circumferential surface of a tire, in a meridional cross-section, is defined as the surface passing through the tire's equator, perpendicular to the median plane and the radial direction. The tire's equator, in a meridional cross-section (a plane perpendicular to the circumferential direction and parallel to the radial and axial directions), is the axis parallel to the tire's axis of rotation and located equidistant between the outermost radial point of the tread intended to be in contact with the ground and the innermost radial point of the tire intended to be in contact with a support, such as a rim.

[0037] By meridian plane, we mean a plane parallel to and containing the axis of rotation of the tire and perpendicular to the circumferential direction.

[0038] Radially inside and radially outside refer to the area closest to and further from the tire's axis of rotation, respectively. Axially inside and axially outside refer to the area closer to and further from the tire's median plane, respectively.

[0039] The bead is the radial portion of the tire designed to allow the tire to be attached to a mounting surface, such as a wheel with a rim. Each bead is specifically designed to make contact with a hook on the rim, enabling it to be secured.

[0040] Any range of values ​​designated by the expression "between a and b" represents the range of values ​​from more than a to less than b (i.e., bounds a and b excluded) while any range of values ​​designated by the expression "from a to b" means the range of values ​​from a to b (i.e., including the strict bounds a and b).

[0041] Ideally, the tire is a competition tire. A competition tire sometimes has markings indicating that it is intended exclusively for competition use, for example "competition use only" or "for competition purpose only".

[0042] Most competition tires do not have homologation conforming to R30 UNECE, nor R117 UNECE and therefore do not have corresponding markings.

[0043] However, some competition tires, particularly some rally tires, have a homologation marking for the R30 UNECE without this allowing their use to be extended outside of competition.

[0044] The competition notably covers officially timed events and not free track driving, sometimes known as "track days" or "HDPE" (High Driving Performance Events), which covers officially untimed events.

[0045] In certain embodiments applicable to most racing tires in which the smooth parts are relatively large, the continuously smooth part or parts form at least 10%, preferably at least 20%, more preferably at least 30% and even more preferably at least 40% of the tread area.

[0046] Among the tires used in competition, particularly in circuit racing, tires are distinguished by their intended use depending on weather conditions. Thus, we distinguish, in particular, slick tires designed for use in dry conditions, intermediate tires designed for use on damp surfaces without rain, and wet tires designed for use on wet surfaces in rainy conditions.

[0047] In certain embodiments applicable to smooth tires, the continuously smooth portion or all continuously smooth portions together form at least 80%, preferably at least 90%, and more preferably at least 95% of the tread surface. In other words, the surface notch ratio of the tread surface is strictly less than 20%, preferably 10%, and more preferably 5%. Indeed, unlike intermediate and rain tires, which include a significant proportion of raised features, particularly cutouts for water evacuation or storage, smooth tires have few or no raised features.

[0048] In other embodiments applicable to intermediate tires, the continuously smooth portion or set of continuously smooth portions forms 80% to 99%, preferably 85% to 95%, of the tread surface. In other words, the surface notch ratio of the tread surface ranges from 1% to 20%, preferably 5% to 15%.

[0049] In other embodiments applicable to rain tires, the continuously smooth portion or set of continuously smooth portions forms 50% to 80%, preferably 70% to 80%, of the tread surface. In other words, the surface notch ratio of the tread surface ranges from 20% to 50%, preferably 20% to 30%.

[0050] To optimize tire heating, the ratio of average pressure at the peak of the bump to average pressure at the bottom of the hollow is greater than or equal to 1.5, preferably greater than or equal to 2.0 and more preferably greater than or equal to 2.5.

[0051] In order not to penalize the flattening of the tire too much and therefore the grip, the ratio of the average pressure at the crest of the bump to the average pressure at the bottom of the hollow is less than or equal to 14.0, preferably less than or equal to 10.0 and more preferably less than or equal to 7.0.

[0052] In embodiments where the bumps and depressions are geometrically characterized to optimize the compromise between tire heating and tire flattening, and therefore its grip, in a central portion of the tread surface with an axial width equal to 50% of the tread surface's axial width and axially centered on the tire's median plane, the average radial distance between the crest of each bump and the bottom of each depression ranges from 0.1 mm to 1.5 mm, preferably from 0.2 mm to 1.0 mm, and more preferably from 0.3 mm to 0.7 mm. Indeed, if the average radial distance is too small, the overpressure created on each bump allows the tire to heat up, but relatively slowly. If the average radial distance is too large, the overpressure is significant, but this can reduce the contact patch area and therefore the tire's grip.Furthermore, with an average radial distance that is too large, there is a risk of creating vibrations, which is undesirable.

[0053] The average radial distance is calculated by taking the difference between the arithmetic mean of the transverse radii of the vertex(s) of each bump in the central portion and the arithmetic mean of the transverse radii of the bottom(s) of each hollow in the central portion.

[0054] In certain embodiments, each depression in the plurality of depressions of said continuously smooth section and each bump in the plurality of bumps of said continuously smooth section extends axially over at least 50%, preferably at least 80%, and more preferably at least 90% of the axial width of said continuously smooth section. Thus, due to a relatively large axial coverage, the tire heats up over a relatively large axial width of the continuous smooth section(s), which contributes to achieving optimal performance over a large area of ​​the tread.

[0055] In some embodiments, the hollows of the plurality of hollows are distributed according to at least one repeating pattern of hollows over at least one portion of said continuously smooth part and / or the bumps of the plurality of bumps are distributed according to at least one repeating pattern of bumps over at least one portion of said continuously smooth part.

[0056] By pattern, we mean that the hollows or bumps are geometrically substantially identical, that is to say, of substantially identical dimensions and shapes regardless of their distribution relative to each other.

[0057] A repeating pattern is a set of geometrically similar depressions or bumps whose distribution relative to one another is organized, as opposed to random, on a continuously smooth surface. This distribution, although organized, is not necessarily constant and can therefore be variable. An example of a constant distribution is an arrangement in which the depressions and / or bumps are equidistant from each other in pairs. An example of a variable distribution is an arrangement in which the depressions and / or bumps are separated by a variable distance, for example, a distance that increases with the distance from the median plane of the tire.

[0058] The repeating pattern of hollows and the repeating pattern of bumps may be identical or different, preferably identical.

[0059] In one variant, the hollows of the plurality of hollows are distributed according to: a first repetitive pattern of hollows on a first portion of said continuously smooth part, and a second repetitive pattern of hollows, distinct from the first repetitive pattern of hollows, on a second portion of said continuously smooth part.

[0060] Similarly, in a variant, the bumps of the plurality of bumps are distributed according to: a first repetitive pattern of bumps on a first portion of said continuously smooth part, and a second repetitive pattern of bumps, distinct from the first repetitive pattern of bumps, on a second portion of said continuously smooth part.

[0061] In a preferred variant, the hollows of the plurality of hollows and the bumps of the plurality of bumps are distributed according to a single common repeating pattern over at least a portion of said continuously smooth part.

[0062] In other embodiments, the hollows of the plurality of hollows are randomly distributed over said continuously smooth part and / or the bumps of the plurality of bumps are randomly distributed over said continuously smooth part.

[0063] Advantageously, although not essential to the invention, the hollows of the plurality of hollows and the bumps of the plurality of bumps are arranged so as to form at least one undulating portion of said continuously smooth part.

[0064] By corrugated portion, we mean a portion of said continuously smooth part which includes bottoms and tops which alternate successively with each other so as to generate several changes in sign of curvature of the running surface.

[0065] In one variant, the continuously smooth portion consists of a wavy portion. In another variant, the continuously smooth portion comprises a wavy portion and a non-wavy portion. An example of a non-wavy portion is a flat portion or a portion with a constant sign of curvature, for example, a completely concave or completely convex portion.

[0066] In some embodiments, the undulating portion or portions comprise at least one repeating undulation of said continuously smooth surface, the repeating undulation or portions being oriented along a principal direction substantially parallel to the direction of translation from one hollow to another of the plurality of hollows of the undulating portion or to the direction of translation from one bump to another of the plurality of bumps of the undulating portion distributed according to the common repeating pattern.

[0067] A wave comprises several successive changes in the direction of curvature of said continuously smooth surface along the principal direction, each change in the direction of curvature being located on one and only one inflection point arranged along the principal direction between each crest of a bump and each bottom of a successive trough.

[0068] A repetitive undulation corresponds to an undulation between hollows and bumps of identical dimensions and shapes because the hollows and bumps define a common repetitive pattern.

[0069] The direction of the repetitive wave can be rectilinear or curvilinear. Due to its repetitive nature, the repetitive wave can also be characterized by a constant period.

[0070] In some variants, the wavy portion comprises a single repeating undulation. In other variants, the wavy portion comprises first and second repeating undulations with first and second principal directions that differ from each other.

[0071] In other embodiments, the undulating portion or portions comprise at least one random undulation of the continuously smooth surface. Such random undulation is particularly useful when the troughs of the plurality of troughs and the bumps of the plurality of bumps are not distributed according to a single common repeating pattern.

[0072] In preferred embodiments, the main direction of the or each repeating corrugation being substantially rectilinear, the main direction of the or each repeating corrugation makes an angle greater than or equal to 45°, preferably greater than or equal to 80° with the axial direction of the tire.

[0073] The angle considered is of course the smallest angle between the principal direction and the axial direction.

[0074] Since tire wear, especially in racing tires, is primarily linked to particularly high lateral forces, it is preferable for the corrugation direction to be as far removed as possible from these lateral forces (i.e., as far removed as possible from the tire's axial direction) to promote even tire wear. Furthermore, a corrugation direction too close to the tire's axial direction would result in a loss of the tire's initial drift stiffness.

[0075] In a variant of the preceding preferred embodiment, the continuously smooth portion comprises, on average, 0.10 to 0.40 pits and 0.10 to 0.40 bumps per cm along the circumferential direction of the continuously smooth surface. To determine the average number of pits and bumps per cm along the circumferential direction, the circumference of the tire is measured along the median plane of the tire, as well as the number of pits and bumps in the continuously smooth portion, and the preceding numbers are then expressed per centimeter of the measured circumference.

[0076] In some embodiments, the wave(s) preferably have a constant period. Preferably, to avoid any resonance problems, care is taken to ensure that the period of the wave(s) is not too close to the natural resonant period of the vehicle's suspension. In other, more complex embodiments, the wave(s) have a variable period.

[0077] Another object of the invention is the use, in competition or open track driving on asphalt surfaces, of a tire comprising a tread surface including one or more continuously smooth parts, in which the continuously smooth part(s) comprise: a plurality of depressions, each depression of the plurality of depressions comprising a depression bottom, a plurality of bumps, each bump of the plurality of bumps comprising a bump crest, the depressions of the plurality of depressions and the bumps of the plurality of bumps are arranged such that, when the or each continuously smooth part rolls on a ground, the average crest pressure exerted on average by the ground on the crests of the bumps of the plurality of bumps is strictly greater than the average depression bottom pressure exerted on average by the ground on the depression bottoms of the plurality of depressions, the average depression bottom pressure being non-zero, the pressure exerted by the ground on each depression of the plurality of depressions and on each bump of the plurality of bumps being measured in the contact area of ​​the or each continuously smooth part of the tire,The tire is rolling at a speed of 100 mm / sec under essentially zero drift and camber angles, the tire is inflated to a reference pressure of 1.6 bar and subjected to a reference load of 5000 N in the case of a motor vehicle tire, and the tire is inflated to a reference pressure of 1.8 bar and subjected to a reference load of 1500 N in the case of a motorcycle tire.

[0078] Whether in competition or free riding on a circuit, the use notably covers car or motorcycle competition or free riding on car or motorcycle circuits.

[0079] The competition notably covers officially timed events, while open track driving, sometimes known as "track days" or "HDPE" (High Driving Performance Events), covers officially untimed events.

[0080] Another object of the invention is a mold for manufacturing a tire as defined above, comprising a molding surface of the tread surface, including a continuously smooth molding portion of the or each continuously smooth portion of the tread surface, the or each continuously smooth molding portion comprising: a plurality of molding depressions of the bumps of the plurality of bumps of said continuously smooth part of the rolling surface, and a plurality of molding depressions of the plurality of depressions of said continuously smooth part of the rolling surface.

[0081] In particularly advantageous embodiments that facilitate the evacuation of air trapped between the tire mold and the tread surface during the tire manufacturing process, the mold includes a plurality of venting elements out of the mold of the air trapped between the molding surface and the tread surface when the tire is in the mold, each venting element of at least a portion of the venting elements opening radially into one of the molding recesses.

[0082] During tire molding, the mold surface first comes into contact with the tread surface via the mold ridges, and then with the tread surface via the mold cavities. Trapped air therefore concentrates primarily between the mold cavities and the tread surface in the form of air pockets. By positioning the venting elements so that they open into the mold cavities, we ensure that they will expel the trapped air.

[0083] In mold variants where the mold comprises a plurality of individual bearing surface molding elements capable of cooperating in pairs along parting lines, each parting line of at least some of the parting lines opens radially into one of the molding recesses. In these variants, the parting lines form the venting elements.

[0084] Optionally, and very advantageously, each mold cavity has at least one venting element, with at least some of the venting elements opening into said mold cavity. This ensures that the air trapped in each cavity is evacuated through a venting element.

[0085] In variants in which the mold comprises a plurality of individual molding elements of the bearing surface capable of cooperating two by two along parting planes, each molding cavity has a parting plane of at least a portion of the parting planes opening into said molding cavity.

[0086] The invention will be better understood upon reading the following description, given solely by way of non-limiting example and made with reference to the drawings in which: there figure 1 is a front view of a racing tire for a motor vehicle according to a first embodiment of the invention, the figure 2 is a photograph of a stack of several tires according to the first embodiment, the figure 3 is a schematic view of the tire of the figure 1 in the section plane III-III' of the figure 1 , there figure 4 is a detailed view of area IV of the figure 3 , THE figures 5, 6, 7 et 8 are schematic views of the tire of the figure 4 respectively in the section planes V-V', VI-VI', VII-VII' and VIII-VIII', the figure 9 is a schematic view illustrating the tire according to the first embodiment, the figure 10 is a schematic view of a mold according to the invention for molding the tire of figures 1 à 9 , THE figures 11, 12 And 13 are views similar to that of the figure 9 of tires respectively according to the second, third and fourth embodiments of the invention, the figure 14 is a detailed view of area XIV of the figure 13 , THE figures 15, 16 , 17 et 18 are views similar to that of the figure 9 of tires respectively according to fifth, sixth, seventh and eighth embodiments of the invention, and the figure 19 is a front view of a motorcycle racing tire according to an embodiment of the invention.

[0087] In the figures, we have represented a coordinate system X, Y, Z corresponding to the usual directions respectively axial (Y), radial (Z) and circumferential (X) of a tire.

[0088] We have represented on the figures 1 à 9 One or more racing tires 10 for asphalt surfaces according to the first embodiment of the invention. The tire 10 has a substantially toroidal shape around an axis of revolution R substantially parallel to the axial direction Y. The tire 10 is a racing tire and is intended for a motor vehicle and has the dimensions 30 / 68 R18. On the different figures 1 And 3 à 9Tire number 10 is shown in its new condition, meaning it has not yet been driven on. In the photograph of the figure 2 The tires are partially worn as they have been used in free rolling on a circuit with an asphalt surface.

[0089] With reference to the figure 1 The tire 10 comprises a vertex 12 with a tread 14 intended to make contact with the ground during rolling via a tread surface 16. The tread surface 16 is delimited by two axial ends 16A and 16B defining an axial width L of the tread surface. Here, L = 30 cm. The diameter in the median plane M of the unloaded and uninflated tire 10 is 68 cm. The area of ​​the tread surface 16 is 6406 cm².

[0090] The tire comprises two sidewalls 18 extending radially inward from the crown 12. The tire 10 further has two radially inward beads on the sidewalls 18 for securing the tire 10 to a mounting support, for example, a rim. Each sidewall 18 connects each bead to the crown 12.

[0091] The tread surface 16 of the tire 10 according to the first embodiment comprises a continuously smooth portion 20 and a plurality of non-smooth portions 22, here eight non-smooth portions 22 of which two are visible on the figure 1 In this case, each non-smooth part 22 includes a wear indicator 24 in the form of a well with a diameter of 2.5 mm and a depth of between 2 and 5 mm.

[0092] The or each continuously smooth part 20 forms, on the surface, at least 10%, preferably at least 20%, more preferably at least 30% and even more preferably at least 40% of the rolling surface 16.

[0093] In the case of a smooth tire comprising a single continuously smooth part 20, the continuously smooth part 20 forms, on the surface, at least 80%, preferably at least 90% and more preferably at least 95% of the tread surface 16. In this case, the continuously smooth part 20 forms, on the surface, more than 99% of the tread surface 16.

[0094] With reference to figures 1 , 2 , 3 And 9The continuously smooth portion 20 comprises a plurality of hollows 26 and a plurality of bumps 28. Each hollow 26 of the plurality of hollows comprises a bottom 30 corresponding to the portion of each hollow 26 having the smallest transverse radius RT, here RTI. Each bump 28 of the plurality of bumps comprises a peak 32 corresponding to the portion of each bump 28 having the largest transverse radius RT, here RTE.

[0095] Each hollow 26 of the plurality of hollows of the continuously smooth part 20 and each bump 28 of the plurality of bumps of the continuously smooth part 20 extends axially over at least 50%, preferably at least 80% and more preferably at least 90% and here over 100% of the axial width L of the continuously smooth part 20.

[0096] The hollows 26 of the plurality of hollows and the bumps 28 of the plurality of bumps are distributed according to a single common repeating pattern over at least a portion of the continuously smooth part 20, here over the entirety of the continuously smooth part 20. In this case, and as schematically represented on the figure 9 , the common repeating pattern is a band with axial width substantially equal to the axial width L of the rolling surface 16 and circumferential curvilinear length I equal to 26.7 mm.

[0097] The continuously smooth part 20 comprises from 2 to 600 hollows and from 2 to 600 bumps, here from 10 to 600 hollows and from 10 to 600 bumps on the continuously smooth part 20 and in this case 40 hollows and 40 bumps on the continuously smooth part 20. The continuously smooth part 20 comprises, on average, from 0.10 to 0.40 hollows and from 0.10 to 0.40 bumps per cm along the circumferential direction X of the continuously smooth surface 20, and here on average 0.18 hollows and 0.18 bumps per cm.

[0098] Thus, as can be seen in the photograph of the figure 2 and illustrated on the figure 3 , the hollows 26 of the plurality of hollows and the bumps 28 of the plurality of bumps are arranged so as to form a wavy portion 34 of the continuously smooth part 20. In this case, the continuously smooth part 20 includes the wavy portion 34 and here is constituted by the wavy portion 34.

[0099] Here, the corrugated portion 34 comprises a single repeating undulation 36 of the continuously smooth surface 20. The repeating undulation 36 is oriented along a principal direction D substantially parallel to the direction of translation from one trough 26 to another of the plurality of troughs in the corrugated portion 34, or to the direction of translation from one bump 28 to another of the plurality of bumps in the corrugated portion 34. The principal direction D of the repeating undulation 36 is rectilinear here and makes an angle A greater than or equal to 45°, preferably greater than or equal to 80°, here substantially equal to 90°, with the axial direction Y of the tire 10. The repeating undulation 36 exhibits a constant period here. On the figures 1 , 3 And 9 , we have schematically represented the inflection lines I of the repetitive undulation 36 delimiting each trough 26 and each bump 28.

[0100] As depicted on the figures 3 à 8 , the corrugated portion 34 of the continuously smooth part 20 is radially contained between a radially external surface of revolution Se whose axis of revolution substantially coincides with the axis of rotation R of the tire 10 and a radially internal surface of revolution Si whose axis of revolution substantially coincides with the axis of rotation R of the tire 10.

[0101] The radially external surface of revolution Se passes through the vertices 32 of the bumps 28 of the plurality of bumps in the continuously smooth part 20, and the radially internal surface of revolution Si passes through the bottoms 30 of the hollows 26 of the plurality of hollows in the continuously smooth part 20. On the figures 5 à 8 , we have represented the median plane M as well as the two para-sagittal planes P1 and P2 delimiting a central portion C having an axial width L / 2 equal to 50% of the axial width L of the rolling surface 16, the para-sagittal planes P1 and P2 being equidistant from the median plane M.

[0102] The average radial distance between the top 32 of each bump 28 and the bottom 30 of each hollow 26 of the continuously smooth part 20 ranges from 0.1 mm to 1.5 mm, preferably from 0.2 to 1.0 mm and more preferably from 0.3 mm to 0.7 mm and here is equal to 0.5 mm.

[0103] The hollows 26 of the plurality of hollows and the bumps 28 of the plurality of bumps are arranged such that, when the continuously smooth section 20 rolls on a surface, the average pressure Pb exerted by the surface on the crests 32 of the bumps 28 of the plurality of bumps, called the average crest pressure, is strictly greater than the average pressure Pc exerted by the surface on the bottoms 30 of the hollows 26 of the plurality of hollows, called the average bottom pressure. The pressures exerted by the surface on each hollow 26 of the plurality of hollows and on each bump 28 of the plurality of bumps are measured in the contact area of ​​the continuously smooth section 20 of the tire 10 inflated to a reference pressure of 1.6 bar and subjected to a reference load of 5000 N and rolling at a speed of 100 mm / sec under substantially zero drift and camber angles. In this case, Pb=3.0 bars and Pc=1.0 bar.Here, any contact area of ​​the tire 10 obtained under the previous conditions has at least 2 hollows and 2 bumps.

[0104] The ratio of the mean pressure at the crest of the hump Pb to the mean pressure at the bottom of the trough Pc is greater than or equal to 1.5, preferably 2.0 and more preferably 2.5 and less than or equal to 14.0, preferably less than or equal to 10.0 and more preferably less than or equal to 7.0. Here Pb / Pc=3.0.

[0105] We have represented on the figure 10 A mold 50 for manufacturing the tire 10 described above. The mold 50 includes a molding surface 52 complementary to the tread surface 16, comprising a continuously smooth molding portion 54 of the continuously smooth portion 20 and a non-smooth molding portion 56 of the non-smooth portions 22. The continuously smooth molding portion 54 includes a plurality of molding depressions 58 of the bumps 28 of the plurality of bumps and a plurality of molding depressions 60 of the depressions 26 of the plurality of depressions.

[0106] The mold 50 comprises a plurality of individual molding elements 62 of the rolling surface 16 suitable for cooperating two by two along parting planes 64.

[0107] The mold 50 includes a plurality of venting elements 66 for venting trapped air between the molding surface 52 and the rolling surface 16 when the tire 10 is in the mold 50. The plurality of venting elements 66 includes a portion of venting elements 66 comprising parting lines 64. Each parting line 64 opens radially onto one of the molding recesses 58, and each molding recess 58 has a parting line 64 opening into said molding recess 58. Alternatively, the plurality of venting elements 66 may include another portion of venting elements 66 comprising discharge channels formed in each of the individual elements 62 (not shown).

[0108] We will now describe competition tires for competition motor vehicles according to second to eighth embodiments with reference to figures 11 à 18 . Elements analogous to those described with reference to the first embodiment are designated by identical references.

[0109] In the second embodiment illustrated on the figure 11 and unlike the first embodiment, the repetitive undulation 36 is oriented along a principal direction D making an angle A substantially zero with the axial direction Y.

[0110] In the third embodiment illustrated on the figure 12 and unlike the first embodiment, the repetitive undulation 36 is oriented along a principal direction D making an angle A equal to 45° with the axial direction Y.

[0111] In the fourth embodiment illustrated on the figures 13 et 14 Unlike the first embodiment, the corrugated portion 34 comprises first and second repeating corrugations. The first repeating corrugation is, similarly to the first embodiment, oriented along a principal direction D1 making an angle of approximately 90° with the axial direction Y. The second repeating corrugation is, similarly to the second embodiment, oriented along a principal direction D2, different from the principal direction D1 and making an angle of approximately zero with the axial direction Y. Furthermore, in addition to the troughs 26 and the crests 28, the corrugated portion 34 comprises median portions 27 following a median surface of revolution whose axis of revolution is substantially coincident with the axis of rotation R of the tire 10, the median surface of revolution being substantially equidistant from the radially inner surface of revolution Si and the radially outer surface of revolution Se.

[0112] In the fifth embodiment illustrated on the figure 15 and unlike the first embodiment, the continuously smooth surface 20 comprises first, second and third wavy portions respectively designated by references 340, 342, 344.

[0113] The 26 hollows of the plurality of hollows are distributed according to a first, second, and third repeating pattern of hollows on each first, second, and third undulating portion 340, 342, and 344, respectively. The 28 bumps of the plurality of bumps are distributed according to a first, second, and third repeating pattern of bumps on each first, second, and third undulating portion 340, 342, and 344, identical respectively to each first, second, and third repeating pattern of hollows. Thus, the 26 hollows of the plurality of hollows and the 28 bumps of the plurality of bumps are distributed according to a common first, second, and third repeating pattern on each first, second, and third undulating portion 340, 342, 344, respectively, of the continuously smooth part 20.

[0114] Each first and third undulating portion 340, 344 comprises a repeating undulation 360, 364 oriented along a principal direction respectively D1, D3 making an angle substantially zero with the axial direction Y. The second undulating portion 342 comprises a repeating undulation 362 oriented along a principal direction D2 making an angle substantially equal to 90° with the axial direction Y.

[0115] In the sixth embodiment illustrated on the figure 16 and unlike the first embodiment, only the bumps 28 of the plurality of bumps are distributed according to a repeating pattern of bumps on the continuously smooth part 20. The hollows 26 of the plurality of hollows are distributed randomly on the continuously smooth part 20. The wavy portion 34 therefore includes a random undulation 37.

[0116] In the seventh embodiment illustrated on the figure 17 and unlike the first embodiment, each non-smooth part 22 includes not wear indicators but cutouts 23, in this case, cutouts molded by vents allowing the air trapped between the tire curing mold and the tread surface 16 to be evacuated during the tire manufacturing process.

[0117] In the eighth embodiment illustrated on the figure 18 Unlike the first embodiment, the running surface 16 comprises first, second, and third continuously smooth portions 200, 202, 204. The hollows 260, 262, 264 of the plurality of hollows and the bumps 280, 282, 284 of the plurality of bumps of each first, second, and third continuously smooth portion 200, 202, 204 are respectively arranged to form a first, second, and third corrugated portion 340, 342, 344 of each first, second, and third continuously smooth portion 200, 202, 204. Each first, second, and third corrugated portion 340, 342, 344 comprises respectively a repeating undulation 360, 362, and 364 oriented along a principal direction D1, D2, D3 respectively, making an angle substantially equal to 90° with the axial direction Y.

[0118] In addition, the running surface 16 includes non-smooth parts 22 comprising not wear indicators but cutouts 23, in this case, cutouts for water drainage or storage including here, circumferential cutouts.

[0119] On the figure 19 A schematic representation of a motorcycle racing tire 10 according to the invention, analogous to the motor vehicle racing tire 19 according to the first embodiment, is shown. In the case of the tire 10 of the figure 19 , the tire 10 is characterized as rolling at a speed of 100 mm / sec under angles of drift and camber that are substantially zero, the tire 10 being inflated to a reference pressure of 1.8 bars and subjected to a reference load of 1500 N.

[0120] In all the embodiments described above and in accordance with the invention, the tires are used in competition or in free riding on a circuit on an asphalt surface.

[0121] The invention is not limited to the embodiments described above.

Claims

1. Tyre (10) for a motor car or a motorbike for use on an asphalted surface, comprising a tread surface (16) comprising one or more continuously-smooth part(s) (20), the or each continuously-smooth part (20) comprises: - a plurality of recessed portions (26), each recessed portion (26) of the plurality of recessed portions comprising a recessed-portion bottom (30), - a plurality of raised portions (28), each raised portion (28) of the plurality of raised portions comprising a raised-portion top (32), characterized in that the recessed portions (26) of the pluralities of recessed portions and the raised portions (28) of the plurality of raised portions are arranged in such a way that, when the or each continuously-smooth part (20) rolls along a surface, the mean top-of-raised-portion pressure (Pb) exerted on average by that surface on the tops (32) of the raised portions (28) of the plurality of raised portions is strictly greater than the mean bottom-of-recessed-portion pressure (Pc) exerted on average by that surface on the bottoms (30) of the recessed portions (26) of the plurality of recessed portions, the mean bottom-of-recessed-portion pressure (Pc) being nonzero, the pressure exerted by that surface on each recessed portion (26) of the plurality of recessed portions and on each raised portion (28) of the plurality of raised portions being measured in the contact patch of the or each continuously-smooth part (20) of the tyre (10), the tyre (10) running at a speed equal to 100 mm / sec with substantially zero slip and camber angles, - the tyre (10) being inflated to a reference pressure equal to 1.6 bar, and subjected to a reference load equal to 5000 N in the case of a car tyre (10), - the tyre (10) being inflated to a reference pressure equal to 1.8 bar, and subjected to a reference load equal to 1500 N in the case of a motorbike tyre (10).

2. Tyre (10) according to the preceding claim, wherein the or each continuously-smooth part (20) forms, on the surface, at least 10%, preferably at least 20%, more preferentially at least 30% and more preferentially still at least 40% of the tread surface (16).

3. Tyre (10) according to either one of the preceding claims, wherein the continuously-smooth part or the collection of continuously-smooth parts forms, on the surface, at least 80%, preferably at least 90%, and more preferentially at least 95% of the tread surface (16).

4. Tyre (10) according to any one of the preceding claims, wherein the ratio of the mean top-of-raised-portion pressure (Pb) to the mean bottom-of-recessed-portion pressure (Pc) is greater than or equal to 1.5, preferably greater than or equal to 2.0 and more preferentially greater than or equal to 2.5.

5. Tyre (10) according to any one of the preceding claims, wherein the ratio of the mean top-of-raised-portion pressure (Pb) to the mean bottom-of-recessed-portion pressure (Pc) is less than or equal to 14.0, preferably less than or equal to 10.0 and more preferentially less than or equal to 7.0.

6. Tyre (10) according to any one of the preceding claims, wherein each recessed portion (26) of the plurality of recessed portions of said continuously-smooth part (20) and each raised portion (28) of the plurality of raised portions of said continuously-smooth part (20) extends axially over at least 50%, preferably at least 80%, and more preferentially at least 90% of the axial width (L) of said continuously-smooth part (20).

7. Tyre (10) according to any one of the preceding claims, wherein the recessed portions (26) of the plurality of recessed portions are distributed in at least one repeating pattern of recessed portions over at least a portion of said continuously-smooth part (20) and / or the raised portions (28) of the plurality of raised portions are distributed in at least one repeating pattern of raised portions over at least a portion of said continuously-smooth part (20).

8. Tyre (10) according to any one of the preceding claims, wherein the recessed portions (26) of the plurality of recessed portions and the raised portions (28) of the plurality of raised portions are distributed in a single common repeating pattern over at least a portion of said continuously-smooth part (20).

9. Tyre (10) according to any one of the preceding claims, wherein the recessed portions (26) of the plurality of recessed portions and the raised portions (28) of the plurality of raised portions are arranged in such a way as to form at least one undulating portion (34) of said continuously-smooth part (20).

10. Tyre (10) according to Claims 8 and 9 considered in combination, wherein the or each undulating portion (34) comprises at least one repeating undulation (36) of said continuously-smooth surface (20), the or each repeating undulation (36) being oriented in a main direction (D, D1, D2) substantially parallel to the direction of translation from one recessed portion (26) to another of the plurality of recessed portions of the undulating portion (34), or to the direction of translation from one raised portion (28) to another of the plurality of raised portions of the undulating portion (34), these recessed / raised portions being distributed in the common repeating pattern.

11. Tyre (10) according to the preceding claim, wherein, with the main direction (D, D1, D2) of the or each repeating undulation (36) being substantially rectilinear, the main direction (D, D1, D2) of the or each repeating undulation (36) makes an angle (A) greater than or equal to 45°, preferably greater than or equal to 80° with the axial direction (Y) of the tyre (10).

12. Use, in competition or free running on a racetrack, on an asphalted surface, of a motorcar or motorbike tyre (10) comprising a tread surface (16) comprising one or more continuously-smooth part(s) (20); the or each continuously-smooth part (20) comprises: - a plurality of recessed portions (26), each recessed portion (26) of the plurality of recessed portions comprising a recessed-portion bottom (30), - a plurality of raised portions (28), each raised portion (28) of the plurality of raised portions comprising a raised-portion top (32), the recessed portions (26) of the pluralities of recessed portions and the raised portions (28) of the plurality of raised portions are arranged in such a way that, when the or each continuously-smooth part (20) rolls along a surface, the mean top-of-raised-portion pressure (Pb) exerted on average by that surface on the tops (32) of the raised portions (28) of the plurality of raised portions is strictly greater than the mean bottom-of-recessed-portion pressure (Pc) exerted on average by that surface on the bottoms (30) of the recessed portions (26) of the plurality of recessed portions, the mean bottom-of-recessed-portion pressure (Pc) being nonzero, the pressure exerted by that surface on each recessed portion (26) of the plurality of recessed portions and on each raised portion (26) of the plurality of raised portions being measured in the contact patch of the or each continuously-smooth part (20) of the tyre (10), the tyre (10) running at a speed equal to 100 mm / sec with substantially zero slip and camber angles, - the tyre (10) being inflated to a reference pressure equal to 1.6 bar, and subjected to a reference load equal to 5000 N in the case of a car tyre (10), - the tyre (10) being inflated to a reference pressure equal to 1.8 bar, and subjected to a reference load equal to 1500 N in the case of a motorbike tyre (10).

13. Mould (50) for manufacturing a tyre (10) according to any one of Claims 1 to 11, comprising a moulding surface (52) for moulding the tread surface (16) comprising a continuously-smooth moulding part (54) for moulding the or each continuously-smooth part (20) of the tread surface (16); the or each continuously-smooth moulding part (54) comprises: - a plurality of recesses (58) for moulding the raised portions (28) of the plurality of raised portions of said continuously-smooth part (20) of the tread surface (16), and - a plurality of raised portions (60) for moulding the recessed portions (26) of the plurality of recessed portions of said continuously-smooth part (20) of the tread surface (16).

14. Mould (50) according to the preceding claim, comprising a plurality of venting elements (66) for venting from the mould any air that is trapped between the moulding surface (52) and the tread surface (16) when the tyre (10) is in the mould (50), each venting element (64) of at least part of the venting elements (66) opens radially into one of the moulding recesses (58).

15. Mould (50) according to the preceding claim, wherein each moulding recess (58) has at least one venting element (64) of at least part of the venting elements (66) opening into said moulding recess (58).