Quick warm-up tires

Abstract

The present invention relates to a tire for use on asphalt pavements having a tread surface (16) having a continuously smooth portion (20). The or each continuously smooth portion (20) has a plurality of recesses (26) and a plurality of protrusions (28). The recesses (26) and protrusions (28) are arranged such that, when the continuously smooth portion (20) runs over a road surface, the average protrusion crest pressure exerted, on average, by the road surface on the crests (32) of the protrusions (28) is strictly greater than the average recession base pressure exerted, on average, by the road surface on the bases (30) of the recesses (26).

Description

[Technical field]

[0001] The present invention relates to a tire and a mould. A tire is understood to mean a casing intended to cooperate with the support elements of a wheel-tire assembly to form an internal cavity, said internal cavity being pressurizable up to a pressure above atmospheric pressure. [Background technology]

[0002] Racing tyres for racing cars and racing bikes are well known in the prior art.

[0003] In motorsport competitions, the driver of a car or motorbike wants to have a tire that provides optimal performance, especially grip, throughout its entire life, i.e. from the start of the race or when the tire is fitted to the vehicle, until the end or when the tire is replaced. One of the essential parameters for obtaining this optimal performance is the tire temperature, which must reach a value called the operating temperature that guarantees this optimal performance.

[0004] Therefore, in certain races, before mounting the tire on the vehicle, its temperature is increased by heating it, for example by using a heating device comprising a heated tire blanket that is wrapped around the tire. Such heating devices are on the one hand expensive and restrictive, and on the other hand energy consuming.

[0005] In other cases, the heating device is not used, which means a delay in reaching operating temperature and therefore optimum performance. Summary of the Invention [Problem to be solved by the invention]

[0006] The aim of the present invention is to make it possible to obtain optimum performance in a more economical and environmentally friendly way, or more quickly during a race. [Means for solving the problem]

[0007] Thus, one subject of the present invention is a tire for motor vehicles or motorcycles intended for use on asphalt roads, comprising a tread surface including one or more continuously smooth portions, the or each continuously smooth portion being: a plurality of recesses, each recess of the plurality of recesses comprising a recessed bottom; a plurality of protruding portions, each protruding portion of the plurality of protruding portions having a protruding apex; Equipped with the concaves of the plurality of concaves and the convexities of the plurality of convexities are arranged such that, when the or each successive smooth portion rolls along a road surface, an average convex-top pressure that the road surface exerts, on average, on the convex tops of the plurality of convexities is strictly greater than an average concave-bottom pressure that the road surface exerts, on average, on the concave bottoms of the plurality of concaves, so that the average concave-bottom pressure is non-zero; the pressure exerted by the road surface on each concave portion of the plurality of concave portions and on each convex portion of the plurality of convex portions is measured at the contact patch of the or each successive smooth portion of the tire when the tire is running at a speed equal to 100 mm / sec with a slip angle and a camber angle of substantially zero; - for automobile tyres, the tyre is inflated to a reference pressure equal to 1.6 bar and subjected to a reference load equal to 5000 N, - In the case of motorcycle tyres, the tyre is inflated to a reference pressure equal to 1.8 bar and subjected to a reference load equal to 1500 N.

[0008] Since the average pressure in the projections is strictly greater than that in the recesses, the radial and tangential deformations imposed on the projections are strictly greater than those imposed on the tread surface of a prior art tire, where the equivalent average pressure is substantially uniform over the entire tread surface. By imposing a relatively high level of deformation, local overpressures are created in the projections, thereby warming up the tire according to the invention. The temperature of the tire thus rises rapidly, especially during the first few hours of running.

[0009] Unlike prior art tires in which the smooth portion(s) have a substantially constant transverse radius in the median plane and in each parasagittal plane, the concaves of said smooth portions of a tire according to the invention have an average transverse radius strictly smaller than the average transverse radius of the convex portions of the smooth portion (the transverse radius being the radial distance between the axis of rotation and a point on the smooth portion), the average transverse radius being, for each pair of concaves and convexities, the arithmetic mean of the transverse radii of each pair.

[0010] Thus, unlike prior art tires which are heated by external heating devices, the tire according to the invention heats itself upon contact with the road surface, making it possible to obtain the expected optimum performance in an economical and environmentally friendly manner, since it does not require the use of expensive, restrictive and energy-consuming external heating devices.

[0011] Furthermore, without the use of an external heating device, the present invention allows the tire to reach its operating temperature more quickly than prior art tires, thus providing the driver or rider with the benefit of optimal performance more quickly during the course of a race.

[0012] The present invention is not characterized by the overpressures that are usually observed in the axially outermost shoulder portions of tires. In particular, due to the curvature of the tire, the axially outermost shoulder portions generally form concave portions, since they generally have a smaller transverse radius than the axially central portion. The mere fact that these axially outermost shoulder portions are subject to overpressure is therefore not sufficient for them to constitute, for this reason alone, a convex portion of the tire according to the invention. If, contrary to what is usually observed, these axially outermost shoulder portions form a convex portion and thus give rise to overpressure, then of course these axially outermost shoulder portions would form a convex portion according to the present invention.

[0013] The present invention applies to both automobile and motorcycle tires.

[0014] The tire's intended use on asphalt surfaces, whether on closed race tracks or on public roads, is an essential feature in order to be able to create local overpressures on bumps. In particular, on loose surfaces, such as mud, it would not be possible to create significant overpressures. Off-road rally tires therefore do not form part of the present invention. In particular, off-road rally competition tires do not form part of the present invention.

[0015] Naturally, the invention applies both to new tires and to tires that have been worn, whether completely or partially worn, although, in view of the invention and its applications, its use on new tires is preferred.

[0016] The or each continuously smooth portion comprises a plurality of depressions and a plurality of protrusions, i.e., the or each continuously smooth portion comprises at least two depressions and at least two protrusions. Thus, the continuously smooth portion or collection of continuously smooth portions may comprise a greater or lesser number of depressions and protrusions depending on the embodiment. Depending on the orientation and arrangement of the depressions and protrusions, for example, there may be from 2 to 600 depressions and from 2 to 600 protrusions across the continuously smooth portion or collection of continuously smooth portions. In certain embodiments with a smaller number of depressions and protrusions, the continuously smooth portion or collection of continuously smooth portions comprises from 2 to 10 depressions and from 2 to 10 protrusions. In other embodiments with a larger number of depressions and protrusions, the continuously smooth portion or collection of continuously smooth portions comprises from 10 to 600 depressions and from 10 to 600 protrusions.

[0017] A person skilled in the art will know how to adapt the peaks and valleys depending on the properties of the tread, in particular its stiffness. In particular, the harder the tread is, the less likely it is to flatten, and therefore the greater the overpressure on the peaks of the peaks. For a relatively stiff tread, the average amplitude between the peaks of the peaks and the bottoms of the valleys will therefore preferably be kept relatively small, so as to provide a sufficient overpressure without being unnecessarily excessive. In contrast, the softer the tread is, the more likely it is to flatten, and therefore the smaller the overpressure on the peaks of the peaks. For a relatively soft tread, the average amplitude between the peaks of the peaks and the bottoms of the valleys will therefore preferably be larger, the greater the desired overpressure.

[0018] Preferably, although this is not an essential feature of the invention, the tire is contemplated such that any contact patch obtained under the conditions described above will include at least two recesses and two protrusions.

[0019] If two smooth portions of the tread surface are at least partially in contact with each other and connected to each other at a common smooth portion, the connected smooth portions will be considered to be completely connected and form the same single continuous smooth portion. In contrast, if two smooth portions of the tread surface are completely disconnected from each other and separated from each other by a non-smooth portion, the two smooth portions will be considered to be two different continuous smooth portions.

[0020] A smooth portion is a portion of the tread surface that is devoid of any relief in the tread surface, in particular that is devoid of any tread wear indicators or grooves, such tread wear indicators or such grooves forming, for example, a discontinuity or abrupt break in the curvature of the tread surface.

[0021] The invention therefore applies to tires whose tread surface consists of a single smooth portion, and also to tires whose tread surface comprises one or more smooth portions and one or more non-smooth portions. One or such non-smooth portion(s) may comprise relief elements, such as, for example, tread wear indicators, grooves for removing or storing water, molded cuts in the form of vents for removing air trapped between the tire curing mold and the tread surface during the tire manufacturing process, or otherwise molding flash. In other words, each smooth portion is completely free of relief elements, such as, for example, tread wear indicators, grooves for removing or storing water, molded cuts in the form of vents for removing air trapped between the tire curing mold and the tread surface during the tire manufacturing process, or otherwise molding flash.

[0022] The recesses of the plurality of recesses of the tire do not have as their essential function the removal or retention of water, nor do they have as their essential function any function that may be associated with the removal of air trapped between the tire curing mold and the tread surface during the tire manufacturing process.

[0023] The tread surface is the part of the tire that is intended to come into contact with the road surface when the tire 10 is running. The surface area of ​​the tread surface is the amount of the rolling surface of the tire bounded by the axial edges of the tread surface. To measure this surface area, it is possible, for example, to make a profile record. In the case of automobile tires, it is also possible to measure the axial width of the tire and multiply this by the maximum circumference measured at the center plane of the tire.

[0024] In the case of a tire according to the invention, the surface area(s) formed by the or each consecutive smooth portion is determined by calculating, for an uninflated and unloaded tire, the surface area of ​​the or each of these consecutive smooth portions, e.g. using image processing.

[0025] Each concave and each protruding portion of the or each continuously smooth portion is defined relative to a mean plane of rotation of an axis of rotational symmetry substantially coinciding with the axis of rotation of the tire, the mean plane of rotation being equidistant from the bottom of the concave and the top of the protruding portion. Thus, any portion radially outside the mean plane of rotation is a convex portion, whereas any portion radially inside the mean plane of rotation is a concave portion. As a result, the or each continuously smooth portion may comprise one or more mean portions substantially coinciding with the mean plane of rotation.

[0026] The recesses or protrusions can have various shapes. Thus, it is possible to have recesses and protrusions with rounded profiles. It is also possible to have recesses and protrusions with profiles presenting sharp corners and / or straight lines, for example trapezoidal profiles, in which case the tops of the protrusions and the bottoms of the recesses are formed with substantially straight line profiles.

[0027] The average crest pressure is equal to the arithmetic mean of the pressures measured at the crests of the or each successive smooth section. Similarly, the average concave bottom pressure is equal to the arithmetic mean of the pressures measured at the bottoms of the concaves of the or each successive smooth section. To measure the pressures at the crests and bottoms of the concaves for the or each successive smooth section, means known to those skilled in the art can be used, for example as described in WO 2017 / 109377 or as sold by Tekscan Inc. under the name TireScan CrossDrive System. Preferably, the road surface used to perform the measurements is flat, smooth and rigid, in particular as described in WO 2017 / 109377.

[0028] It would also be possible, preferentially, to determine the average convex apex pressure by considering only the top 25% of the pressures measured at the apexes of the convex portions of the or each smooth portion, and to determine the average concave bottom pressure by considering only the bottom 25% of the pressures measured at the bottoms of the concave portions of the or each smooth portion.

[0029] To avoid edge effects, particularly when a continuously smooth portion is at least partially bounded by an edge of the tire's contact patch, the pressure is determined in a central region of the contact patch of the continuously smooth portion, the central region having an axial width equal to 50% of the width of the continuously smooth portion and axially centered on the central plane of the continuously smooth portion, and a length equal to 50% of the length of the continuously smooth portion and longitudinally centered on a cross-section of the continuously smooth portion.

[0030] The tyre according to the invention has a substantially toroidal shape about an axis of rotational symmetry substantially coinciding with the axis of rotation of the tyre, which axis of rotational symmetry defines three directions conventionally used by those skilled in the art: axial, circumferential and radial.

[0031] Axial means the axis of rotational symmetry of the tire, i.e. the direction substantially parallel to the axis of rotation of the tire.

[0032] Circumferential direction means a direction substantially perpendicular to both the axial direction and the radial direction of the tire (in other words, tangent to a circle about the axis of rotation of the tire).

[0033] Radial means any direction along the radius of the tire, i.e., any direction intersecting the axis of rotation of the tire and substantially perpendicular to that axis.

[0034] The median plane of the tire (denoted M) means the plane perpendicular to the axis of rotation of the tire, located axially midway between the two beads and passing through the axial center of the crown reinforcement.

[0035] By equatorial circumferential plane of a tire is meant the surface that, in a meridian section, passes through the tire's equator, perpendicular to the median plane and to the radial direction. The equator of a tire is the axis, in a meridian section (plane perpendicular to the circumferential direction and parallel to the radial and axial directions), parallel to the tire's axis of rotation and equidistant between the radially outermost point of the tread intended to be in contact with the road surface and the radially innermost point of the tire intended to be in contact with a support, for example the rim.

[0036] Meridian plane means the plane parallel to and containing the axis of rotation of the tire and perpendicular to the circumferential direction.

[0037] "Radially inner / inner" and "radially outer / outer" mean "closer to" and "farther from" the axis of rotation of the tire, respectively. "Axially inner / inner" and "Axially outer / outer" mean "closer to" and "farther from" the centerplane of the tire, respectively.

[0038] By bead is meant the radial portion of the tire intended to enable the tire to be mounted on a mounting support, for example on a wheel with a rim. Each bead is therefore intended in particular to come into contact with the flange of the rim enabling the mounting of the latter.

[0039] A range of values ​​indicated by the expression "between a and b" denotes a range of values ​​extending from greater than a to less than b (i.e. excluding the endpoints a and b), whereas a range of values ​​indicated by the expression "from a to b" means a range of values ​​extending from a to b (i.e. including the precise endpoints a and b).

[0040] Highly preferably, the tire is a racing tire. Racing tires may bear inscriptions designating exclusive racing use, such as "For racing purposes only" or "For racing use only".

[0041] Most racing tyres are not subject to certification according to UN / ECE Regulation No. 30 or UN / ECE Regulation No. 117 and therefore do not bear the corresponding markings.

[0042] Nevertheless, competition tyres, particularly certain rally tyres, although they do bear the UN / ECE Regulation No. 30 homologation markings, are not permitted for use outside of competition.

[0043] Competition specifically refers to events where an official timekeeping is held, but does not refer to free practice sessions on a race track, known as "Track Days" or "HDPE" (High Driving Performance Events), which are events where an official timekeeping is not held.

[0044] In some embodiments, applicable to most tires used in racing, in which the smooth portions are relatively large, the or each successive smooth portion forms at least 10% of the tread surface, preferably at least 20%, more preferentially at least 30% and even more preferentially at least 40% of the surface.

[0045] Among the tyres used in competitions, and in particular those used in competitions on race tracks, a distinction is made between them according to the weather conditions in which they are used: a distinction is thus made in particular between smooth tyres, known as "slicks", intended to be used in dry conditions, intermediate tyres, known as "intermediate", intended to be used when the track is wet but not raining, and rain tyres, known as "wet", intended to be used on rain-soaked tracks.

[0046] In a particular embodiment applicable to slick tires, the continuous smooth portion or the collection of continuous smooth portions forms at least 80%, preferably at least 90%, more preferentially at least 95% of the tread surface of the surface. In other words, the void area ratio of the tread surface is strictly less than 20%, preferably less than 10%, more preferentially less than 5%. In particular, unlike intermediate or rain tires, which have a significant proportion of relief elements, in particular grooves for removing or storing water, slick tires have few or no relief elements.

[0047] In another embodiment applicable to intermediate tires, the continuous smooth portion or collection of continuous smooth portions forms 80% to 99%, preferably 85% to 95%, of the tread surface, in other words, the void area percentage of the tread surface ranges from 1% to 20%, preferably 5% to 15%.

[0048] In yet another embodiment applicable to rain tires (wet), the continuous smooth portion or the collection of continuous smooth portions forms 50% to 89% of the tread surface, preferably 70% to 80% of the surface, in other words, the void area ratio of the tread surface is in the range of 20% to 50%, preferably 20% to 30%.

[0049] To optimize the warm-up of the tire, the ratio of the mean crest pressure to the mean concave basin pressure 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.

[0050] In order not to unduly penalize the tire profile and therefore the grip, the ratio of the average crest pressure to the average concave basal pressure 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.

[0051] In an embodiment in which the projections and recesses are geometrically characterized to optimize the trade-off between tire warm-up and tire flattening and therefore tire grip, the projections have an axial width equal to 50% of the axial width of the tread surface, and the average radial distance between the top of each projection and the bottom of each recess, in the central part of the tread surface axially centered on the central plane of the tire, is between 0.1 mm and 1.5 mm, preferably between 0.2 mm and 1.0 mm, more preferentially between 0.3 mm and 0.7 mm. In particular, if the average radial distance is too small, the overpressures created in the projections will certainly warm up the tire, but only relatively slowly. If the average radial distance is too large, the overpressure will be large, but the surface area of ​​the contact patch will be small, which may then reduce the tire's grip. Moreover, if the average radial distance is too large, there is a risk of causing vibrations, which is undesirable.

[0052] The average radial distance is calculated by taking the difference between the arithmetic mean of the transverse radii for the peak(s) of each protrusion in the central portion and the arithmetic mean of the transverse radii for the bottom(s) of each recess in the central portion.

[0053] In a particular embodiment, each recess of the plurality of recesses of a continuously smooth portion and each peak of the plurality of peaks of a continuously smooth portion extend axially over at least 50%, preferably at least 80%, more preferentially at least 90% of the axial width of the continuously smooth portion. Due to this relatively large axial extent, the tire is warmed up over a relatively large axial width of the or each continuously smooth portion, which contributes to obtaining optimal performance over a large area of ​​the tread surface.

[0054] In certain embodiments, the recesses of the plurality of recesses are distributed in at least one repeating pattern of recesses across at least a portion of the continuous smooth portion, and / or the protrusions of the plurality of protrusions are distributed in at least one repeating pattern of protrusions across at least a portion of the continuous smooth portion.

[0055] By pattern, it is meant that the depressions or protrusions are substantially geometrically identical, i.e. have substantially the same size and shape, whatever their distribution relative to one another.

[0056] A repeating pattern is a collection of geometrically substantially identical depressions or protrusions whose distribution relative to one another is structured, rather than random, across a continuous smooth section. Although the distribution is structured, it does not necessarily have to remain constant and therefore may be variable. An example of a constant distribution is an arrangement in which the depressions and / or protrusions are equidistant from one another in pairs. An example of a variable distribution is an arrangement in which the depressions and / or protrusions are spaced apart in pairs by a variable distance, for example increasing away from the center plane of the tire.

[0057] The repeating pattern of recesses and the repeating pattern of protrusions can be the same or different, but preferably are the same.

[0058] In one variation, the recesses of the plurality of recesses are a first repeating pattern of recesses over a first portion of the continuously smooth portion; and a second repeating pattern of recesses that differs from the first repeating pattern of recesses over a second portion of the continuously smooth portion; They are distributed in a grid.

[0059] Similarly, in one variation, the protrusions of the plurality of protrusions are a first repeating pattern of peaks over a first portion of the continuously smooth portion; and a second repeating pattern of protrusions that differs from the first repeating pattern of protrusions over a second portion of the continuously smooth portion; They are distributed in a grid.

[0060] In a preferred variation, the recesses of the plurality of recesses and the protrusions of the plurality of protrusions are distributed in a single common repeating pattern over at least a portion of the continuously smooth portion.

[0061] In another embodiment, the recesses of the plurality of recesses are randomly distributed throughout the continuous smooth portion and / or the protrusions of the plurality of protrusions are randomly distributed throughout the continuous smooth portion.

[0062] Advantageously, although this is not essential to the invention, the recesses of the plurality of recesses and the protrusions of the plurality of protrusions are arranged so as to form at least one undulation of a continuously smooth portion.

[0063] By undulations is meant continuously smooth portions having valleys (bottoms) and crests (peaks) which alternate with one another in a continuous manner to produce some changes in the sign of the curvature of the tread surface.

[0064] In one variation, the continuously smooth portion consists of undulating portions. In another variation, the continuously smooth portion comprises undulating portions and non-undulating portions. An example of a non-undulating portion is a planar portion or a portion that otherwise has a constant sign of curvature, such as a generally concave or generally convex portion.

[0065] In a particular embodiment, the or each undulating portion comprises at least one repeating undulation of a continuous smooth portion, the or each repeating undulation being oriented in a main direction substantially parallel to the direction of translation from one concave portion to another of the plurality of concave portions of the undulating portion or from one convex portion to another of the plurality of convex portions of the undulating portion, the concave portions / convex portions being distributed in a common repeating pattern.

[0066] The undulations include a plurality of successive points of change in the direction of curvature along a main direction of a continuously smooth surface, each point of change in the direction of curvature being located at a unique inflection point located along the main direction between each successive peak of a protrusion and each successive bottom of a recess.

[0067] Repeating undulations correspond to undulations between depressions and protrusions of the same shape and size through the fact that the depressions and protrusions define a common repeating pattern.

[0068] The direction of the repeating undulations can be linear or curvilinear. Due to their repeating nature, the repeating undulations can also be characterized by a regular period.

[0069] In a particular variation, the undulations comprise a single repeating undulation, hi another variation, the undulations comprise first and second repeating undulations having respective first and second main directions that are different from each other.

[0070] In another embodiment, the or each undulation comprises at least one random undulation of a continuously smooth surface, such random undulation being of particular use in cases where the concaves of the plurality of concaves and the convexities of the plurality of convexities are not distributed in a single common repeating pattern.

[0071] In a preferred embodiment, when the main direction of the or each repeating undulation is substantially straight, it forms an angle of at least 45°, preferably at least 80°, with the axial direction of the tyre.

[0072] The angle considered is of course the smallest angle between the main direction and the axial direction.

[0073] Since tire wear, especially that of racing tires, is essentially related to particularly high lateral loads, it is preferable to orient the undulations as close as possible to the direction of these lateral loads (i.e., as close as possible to the axial direction of the tire) in order to promote uniform tire wear. Furthermore, if the undulations are directed too close to the axial direction of the tire, this leads to a decrease in the initial cornering stiffness of the tire.

[0074] In one variation of the above preferred embodiment, the continuously smooth portion contains, on average, 0.10 to 0.40 recesses and 0.10 to 0.40 peaks per circumferential centimeter of the continuously smooth surface. To determine the average number of recesses and peaks per circumferential centimeter, the circumference of the tire at the center plane is measured along with the number of recesses and peaks in the continuously smooth portion and the numbers are proportionately proportional to the measured centimeter of circumference.

[0075] In a particular embodiment, the or each undulation has a constant period. Preferentially, care is taken that the period of the or each undulation is not too close to the natural resonance period of the vehicle suspension, to avoid any resonance problems. In another, more complex embodiment, the or each undulation has a variable period.

[0076] Another subject of the invention is the use, in racing or free running on race tracks with asphalt surfaces, of a tire having a tread surface including one or more continuously smooth portions, the or each continuously smooth portion being: a plurality of recesses, each recess of the plurality of recesses comprising a recessed bottom; a plurality of protruding portions, each protruding portion of the plurality of protruding portions having a protruding apex; Equipped with the concaves of the plurality of concaves and the convexities of the plurality of convexities are arranged such that, when the or each successive smooth portion rolls along a road surface, an average convex-top pressure that the road surface exerts, on average, on the convex tops of the plurality of convexities is strictly greater than an average concave-bottom pressure that the road surface exerts, on average, on the concave bottoms of the plurality of concaves, so that the average concave-bottom pressure is non-zero; the pressure exerted by the road surface on each concave portion of the plurality of concave portions and on each convex portion of the plurality of convex portions is measured at the contact patch of the or each successive smooth portion of the tire when the tire is running at a speed equal to 100 mm / sec with a slip angle and a camber angle of substantially zero; - for automobile tyres, the tyre is inflated to a reference pressure equal to 1.6 bar and subjected to a reference load equal to 5000 N, - In the case of motorcycle tyres, the tyre is inflated to a reference pressure equal to 1.8 bar and subjected to a reference load equal to 1500 N.

[0077] Whether for competitive use or for free riding on a race track, the use is particularly intended for automobile or motorbike competitive events or for free riding on a race track for automobiles or motorbikes.

[0078] Competition specifically covers events where official timekeeping is performed, but also covers events where free practice on a race track, known as "Track Days" or "HDPE" (High Driving Performance Events), is not officially timed.

[0079] Another subject of the invention is a mould for producing a tyre as defined above, comprising a moulding surface for moulding the tread surface, comprising a continuously smooth moulding portion for moulding the or each continuously smooth portion of the tread surface, the or each continuously smooth moulding portion being: - a plurality of recesses for forming a plurality of protrusions of a continuous smooth portion of the tread surface; a plurality of protrusions for molding recesses of a plurality of recesses in a continuous smooth portion of the tread surface;

[0080] In a particularly advantageous embodiment that facilitates removal of air trapped between the tire mold and the tread surface during the tire manufacturing process, the mold includes a plurality of vent elements for releasing air trapped between the molding surface and the tread surface from the mold when the tire is in the mold, with each vent element of at least a portion of the vent elements opening radially into one of the mold recesses.

[0081] During the molding of the tire in the mold, the molding surface first abuts against the tread surface through the convex mold portion and then through the mold recess. As a result, the trapped air is concentrated in the form of air pockets, mainly between the mold recess and the tread surface. By positioning the ventilation element so that it opens into the mold recess, the ventilation element can ensure that the trapped air can be removed.

[0082] In mold variations in which the mold comprises a plurality of cooperable individual tread surface molding elements paired along parting lines, at least some of the parting lines each open radially to one of the mold recesses. In these variations, the parting lines are used to form the ventilation elements.

[0083] Optionally, but very advantageously, each molded recess has at least one vent element of at least a portion of the vent element opening into the molded recess, thus ensuring that air trapped in each recess can be removed by the vent element.

[0084] In a variation of the mold in which the mold comprises a plurality of individual tread surface molding elements cooperable in pairs along parting lines, each molding recess has at least a portion of the parting lines opening into the molding recess.

[0085] The invention will be better understood on reading the following description, given purely by way of non-limiting example and with reference to the drawings in which: [Brief description of the drawings]

[0086] [Figure 1] FIG. 1 is a front view of a racing car tire according to a first embodiment of the present invention. [Diagram 2] 1 is a photograph of multiple tires stacked together according to the first embodiment. [Diagram 3] 2 is a schematic view of the tire of FIG. 1 in section III-III' of FIG. 1; [Figure 4] FIG. 4 is a detailed view of region IV in FIG. [Diagram 5] FIG. 5 is a schematic diagram of the tire in section V-V' of FIG. 4. [Figure 6] FIG. 6 is a schematic diagram of the tire in section VI-VI' of FIG. 4. [Figure 7] FIG. 7 is a schematic diagram of a tire cross section taken along line VII-VII' of FIG. 4. [Figure 8] FIG. 5 is a schematic view of the tire in section VIII-VIII' of FIG. 4. [Figure 9] 1 is a schematic diagram showing a tire according to a first embodiment. [Figure 10] FIG. 10 is a schematic representation of a mold according to the invention capable of molding the tires of FIGS. 1 to 9. [Figure 11] FIG. 10 is a view similar to FIG. 9 for a tire according to a second embodiment of the invention. [Figure 12] FIG. 10 is a view similar to FIG. 9 for a tire according to a third embodiment of the invention. [Figure 13] FIG. 10 is a view similar to FIG. 9 for a tire according to a fourth embodiment of the invention. [Figure 14] FIG. 14 is a detailed view of region XIV in FIG. [Figure 15] FIG. 10 is a view similar to FIG. 9 for a tire according to a fifth embodiment of the invention. [Figure 16] FIG. 10 is a view similar to FIG. 9 for a tire according to a sixth embodiment of the invention. [Figure 17] FIG. 10 is a view similar to FIG. 9 for a tire according to a seventh embodiment of the invention. [Figure 18]FIG. 10 is a view similar to FIG. 9 for a tire according to an eighth embodiment of the invention. [Figure 19] 1 is a front view of a racing bike tire according to a first embodiment of the present invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0087] The figure shows a coordinate system X, Y, Z corresponding to the conventional axial (Y), radial (Z) and circumferential (X) directions of the tire, respectively.

[0088] Figures 1 to 9 show one or more racing tires 10 for use on asphalt surfaces according to a first embodiment of the invention. The tire 10 has a substantially toroidal shape around an axis of rotational symmetry R substantially parallel to an axial direction Y. The tire 10 is a racing tire for automobiles and has the dimensions 30 / 68 R18. In the various figures (Figures 1 and 3 to 9), the tire 10 is shown as new, i.e. not yet run. In the photograph of Figure 2, the tire is partially worn, since it has been used for free running on a race track with an asphalt surface.

[0089] With reference to Figure 1, the tire 10 comprises a crown 12 including a tread 14 intended to come into contact with the road surface during running through a tread surface 16. The tread surface 16 is bounded by two axial ends 16A, 16B that define an axial width L of the tread surface. In this example, L = 30 cm. The diameter at the mid-plane M of the tire 10 in the unloaded and uninflated state is in this case equal to 68 cm. The area of ​​the tread surface 16 is 6406 cm 2 is equal to.

[0090] The tire comprises two sidewalls 18 extending radially inwards from the crown 12. The tire 10 further comprises, radially inwards from the sidewalls 18, two beads intended to enable the tire 10 to be fixed to a mounting support, for example a wheel rim. Each sidewall 18 connects a respective bead to the crown 12.

[0091] The tread surface 16 of the tire 10 according to the first embodiment comprises a continuous smooth portion 20 and a plurality of uneven portions 22, in this example eight uneven portions 22, two of which are visible in Figure 1. In this particular example, each uneven portion 22 comprises a tread wear indicator 24 in the form of a well having a diameter of 2.5 mm and a depth of between 2 mm and 5 mm.

[0092] The or each continuous smooth portion 20 forms at least 10% of the surface of the tread surface 16, preferably at least 20%, more preferably at least 30%, and even more preferably at least 40%.

[0093] In the case of a slick tire with a single continuous smooth portion 20, the continuous smooth portion 20 forms at least 80%, preferably at least 90%, and more preferably at least 95% of the surface of the tread surface 16. In this particular example, the continuous smooth portion 20 forms greater than 99% of the surface of the tread surface 16.

[0094] 1, 2, 3 and 9, the continuously smooth portion 20 comprises a plurality of recesses 26 and a plurality of protrusions 28. Each recess 26 of the plurality of recesses has a base 30 corresponding to the portion of each recess 26 having the smallest transverse radius RT, in this example RTI. Each protrusion 28 of the plurality of protrusions has an apex 32 corresponding to the portion of each protrusion 28 having the largest transverse radius RT, in this example RTE.

[0095] Each of the recesses 26 of the plurality of recesses in the continuously smooth portion 20, and each of the protrusions 28 of the plurality of protrusions in the continuously smooth portion 20, extends axially over at least 50%, preferably at least 80%, more preferentially at least 90%, and in this example over 100%, of the axial width L of the continuously smooth portion 20.

[0096] The recesses 26 of the plurality of recesses and the peaks 28 of the plurality of peaks are distributed in a single common repeating pattern throughout at least a portion of, and in this example throughout, the entire continuously smooth portion 20. In this particular example, the common repeating pattern is a strip having an axial width substantially equal to the axial width L of the tread surface 16 and a circumferential curvilinear length l equal to 26.7 mm, as shown diagrammatically in FIG.

[0097] The continuously smooth portion 20 comprises from 2 to 600 recesses and from 2 to 600 protrusions, in this example from 10 to 600 recesses and from 10 to 600 protrusions on the continuously smooth portion 20, in this particular example from 40 recesses and 40 protrusions on the continuously smooth portion 20. The continuously smooth portion 20 comprises on average from 0.10 to 0.40 recesses and 0.10 to 0.40 protrusions per cm in the circumferential direction X of the continuously smooth surface 20, in this case on average from 0.18 recesses and 0.18 protrusions per cm.

[0098] Thus, as can be seen in the photograph of Figure 2 and as shown in Figure 3, the recesses 26 of the plurality of recesses and the peaks 28 of the plurality of peaks are arranged to form undulations 34 of the continuously smooth portion 20. In this particular example, the continuously smooth portion 20 comprises, and in this case consists of, undulations 34.

[0099] Here, the undulation 34 comprises a single repeating undulation 36 of the continuous smooth surface 20. The repeating undulation 36 is oriented in a main direction D that is substantially parallel to the direction of translation from one concave 26 of the plurality of concaves of the undulation 34 to another concave or from one convex 28 of the plurality of convexities of the undulation 34 to another convex. The main direction D of the repeating undulation 36 is linear here and forms an angle A with the axial direction Y of the tire 10 of at least 45°, preferably at least 80°, in this example substantially 90°. The repeating undulation 36 here has a constant period. Figures 1, 3 and 9 show diagrammatically the inflection curve I of the repeating undulation 36 that separates each concave 26 and each convex 28.

[0100] As shown in Figures 3 to 8, the undulations 34 of the continuously smooth portion 20 are bounded radially between a radially outer surface of rotation Se, about an axis of rotational symmetry that substantially coincides with the axis of rotation R of the tire 10, and a radially inner surface of rotation Si, about an axis of rotational symmetry that substantially coincides with the axis of rotation R of the tire 10.

[0101] The radially outer plane of rotation Se passes through the tops 32 of the protrusions 28 of the plurality of protrusions of the continuously smooth portion 20, and the radially inner plane of rotation Si passes through the bottoms 30 of the recesses 26 of the plurality of recesses of the continuously smooth portion 20. Figures 5 to 8 show a central plane M and two parasagittal planes P1, P2 that define a central portion C having an axial width L / 2 equal to 50% of the axial width L of the tread surface 16, the parasagittal planes P1, P2 being equidistant from the central plane M.

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

[0103] The recesses 26 of the plurality of recesses and the peaks 28 of the plurality of peaks are arranged in such a way that when the continuously smooth portion 20 rolls along a road surface, the average pressure Pb exerted by the road surface on the peaks 32 of the peaks 28 of the plurality of peaks (called the average peak-peak pressure) is strictly greater than the average pressure Pc exerted by the road surface on the peaks 30 of the recesses 26 of the plurality of peaks (called the average peak-bottom pressure). The pressure exerted by the road surface on each recess 26 of the plurality of recesses and each peak 28 of the plurality of peaks is measured at the contact patch of the continuously smooth portion 20 of a tire 10 inflated to a reference pressure equal to 1.6 bar, subjected to a reference load equal to 5000 N, running at a speed equal to 100 mm / sec with substantially zero slip and camber angles. In this particular example, Pb=3.0 bar, Pc=1.0 bar. In this case, any contact patch obtained for the tire 10 under the above conditions will have at least two recesses and two protrusions.

[0104] The ratio of the average peak pressure Pb to the average bottom pressure Pc is 1.5 or more, preferably 2.0 or more, more preferably 2.5 or more, and 14.0 or less, preferably 10.0 or less, more preferably 7.0 or less. In this example, Pb / Pc=3.0.

[0105] 10 shows a mold 50 for manufacturing the tire 10 described above. The mold 50 has a molding surface 52 complementary to the tread surface 16, and has a continuously smooth molded portion 54 for molding the continuously smooth portion 20 and a non-smooth molded portion 56 for molding the non-smooth portion 22. The continuously smooth molded portion 54 has a plurality of recesses 58 for molding the protrusions 28 of the plurality of protrusions, and a plurality of protrusions 60 for molding the recesses 26 of the plurality of recesses.

[0106] The mold 50 includes a plurality of individual elements 62 for molding the tread surface 16, which may cooperate in pairs along parting lines 64.

[0107] Mold 50 includes a plurality of vent elements 66 for releasing air trapped between molding surface 52 and tread surface 16 from the mold when tire 10 is within mold 50. The plurality of vent elements 66 includes a portion of vent element 66 that includes parting lines 64. Each parting line 64 opens radially into one of the mold recesses 58, with each mold recess 58 having a parting line 64 that opens into that mold recess 58. It is also envisioned that the plurality of vent elements 66 includes a separate portion of vent element 66 that includes a vent tube (not shown) formed in each of the individual elements 62.

[0108] Racing tyres for racing cars according to second to eighth embodiments will now be described with reference to figures 11 to 18. Elements similar to those described with reference to the first embodiment are indicated with the same reference numbers.

[0109] In the second embodiment shown in FIG. 11, unlike the first embodiment, the repeated undulations 36 are oriented in a main direction D that forms an angle A with the axial direction Y of substantially zero.

[0110] In the third embodiment shown in FIG. 12, unlike the first embodiment, the undulations 36 are oriented in a main direction D which forms an angle A with the axial direction Y equal to 45°.

[0111] In the fourth embodiment shown in Figures 13 and 14, unlike the first embodiment, the undulating portion 34 comprises a first and a second repeating undulation. The first repeating undulation, like the first embodiment, faces a main direction D1 that forms an angle substantially equal to 90° with the axial direction Y. The second repeating undulation, like the second embodiment, faces a main direction D2 different from the main direction D1 that forms an angle substantially equal to zero with the axial direction Y. In addition to comprising the recesses 26 and the protrusions 28, the undulating portion 34 further comprises a rotational center plane 27 about an axis of rotational symmetry that substantially coincides with the rotational axis R of the tire 10, the rotational center plane being substantially equidistant from the radially inner rotational plane Si and the radially outer rotational plane Se.

[0112] In the fifth embodiment shown in FIG. 15, unlike the first embodiment, the continuously smooth surface 20 comprises first, second and third undulations, indicated by the reference numerals 340, 342 and 344 respectively.

[0113] The recesses 26 of the plurality of recesses are distributed in a first, second, and third repeating pattern of recesses over the first, second, and third undulating portions 340, 342, and 344, respectively. The protrusions 28 of the plurality of protrusions are distributed in a first, second, and third repeating pattern of protrusions over the first, second, and third undulating portions 340, 342, and 344, respectively, which repeating patterns are identical to the first, second, and third repeating patterns of recesses, respectively. Thus, the recesses 26 of the plurality of recesses and the protrusions 28 of the plurality of protrusions are distributed in a first, second, and third common repeating pattern over the first, second, and third undulating portions 340, 342, and 344 of the continuous smooth portion 20, respectively.

[0114] The first and third undulations 340, 344 each include repeating undulations 360, 364 that face a respective main direction D1, D3 that forms an angle substantially equal to zero with the axial direction Y. The second undulations 342 include repeating undulations 362 that face a main direction D2 that forms an angle substantially equal to 90° with the axial direction Y.

[0115] 16 , unlike the first embodiment, only the peaks 28 of the plurality of peaks are distributed in a repeating pattern of peaks over the continuously smooth portion 20. The valleys 26 of the plurality of valleys are randomly distributed over the continuously smooth portion 20. Thus, the undulating portion 34 comprises random undulations 37.

[0116] In the seventh embodiment shown in FIG. 17, unlike the first embodiment, each uneven portion 22 includes a discontinuity 23 rather than a tread wear indicator, in this example a molded in the form of a vent used to remove air trapped between the tire curing mold and the tread surface 16 during the tire building process.

[0117] In the eighth embodiment shown in FIG. 18, unlike the first embodiment, the tread surface 16 comprises first, second and third continuous smooth portions 200, 202, 204. The concave portions 260, 262, 264 of the plurality of concave portions and the convex portions 280, 282, 284 of the plurality of convex portions for each of the first, second and third continuous smooth portions 200, 202, 204 are respectively arranged to form first, second and third undulating portions 340, 342, 344 for each of the first, second and third continuous smooth portions 200, 202, 204. Each of the first, second and third undulating portions 340, 342, 344 comprises a respective repeating undulation 360, 362, 364, which are oriented in a respective main direction D1, D2, D3 that forms an angle substantially equal to 90° with the axial direction Y.

[0118] Additionally, the tread surface 16 includes textured portions 22 that include discontinuities 23 rather than tread wear indicators, in this example discontinuities for removing or retaining water, here circumferential discontinuities.

[0119] Figure 19 shows diagrammatically a racing bike tire 10 according to the invention, similar to a racing car tire 19 according to the first embodiment. In the case of the tire 10 of figure 19, the tire 10 is characterized by running at a speed equal to 100 mm / sec with substantially zero slip and camber angles, is inflated to a reference pressure equal to 1.8 bar and is subjected to a reference load equal to 1500 N.

[0120] Throughout all of the embodiments hereinabove described and in accordance with the present invention, the tire is used for racing or free running on race tracks with asphalt surfaces.

[0121] The present invention is not limited to the above-described embodiments. [Explanation of symbols]

[0122] 10. Competition tires 12 crowns 14 Tread 16 Tread surface 16A,B Axial ends of tread surface 18 Sidewall 20 Continuously smooth area 22 Non-smooth part 24 Tread Wear Indicator 26 Recess 28 Convex 30 bottom 32 Top I. Repeated undulation curve L Axial width of the tread surface M center plane R Tire rotation axis

Claims

1. A tire (10) for an automobile or motorcycle for use on asphalt surfaces, comprising a tread surface (16) including one or more continuously smooth portions (20), the or each continuously smooth portion (20) being: a plurality of recesses (26), each recess (26) of said plurality of recesses comprising a concave bottom (30); a plurality of projections (28), each projection (28) of said plurality of projections comprising a peak (32); The present invention is characterized by comprising: the recesses (26) of the plurality of recesses and the protrusions (28) of the plurality of protrusions are arranged such that, when the or each continuously smooth portion (20) rolls along a road surface, an average convex crest pressure (Pb) exerted by the road surface on the crests (32) of the protrusions (28) of the plurality of protrusions is strictly greater than an average concave bottom pressure (Pc) exerted by the road surface on the bottoms (30) of the recesses (26) of the plurality of recesses, and the average concave bottom pressure (Pc) is non-zero; a pressure exerted by the road surface on each recess (26) of the plurality of recesses and each protrusion (28) of the plurality of protrusions is measured at the contact patch of the or each successively smooth portion (20) of the tire (10) when the tire (10) is running at a speed equal to 100 mm / sec with a slip angle and a camber angle of substantially zero; in the case of a motor vehicle tire (10), said tire (10) is 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 motorcycle tire (10), said tire (10) is inflated to a reference pressure equal to 1.8 bar and subjected to a reference load equal to 1500 N.

2. 2. The tire (10) of claim 1, wherein the or each continuously smooth portion (20) forms, with respect to its surface, at least 10% of the tread surface (16).

3. 2. The tire (10) of claim 1, wherein the continuous smooth portion or collection of continuous smooth portions forms at least 80% of the surface of the tread surface (16).

4. The tire (10) of claim 1, wherein the ratio of the mean crest pressure (Pb) to the mean trough pressure (Pc) is greater than or equal to 1.

5.

5. 2. The tire (10) of claim 1, wherein the ratio of the mean crest pressure (Pb) to the mean trough pressure is less than or equal to 14.

0.

6. 2. The tire (10) of claim 1, wherein each concave portion (26) of the plurality of concave portions of the continuously smooth portion (20) and each convex portion (28) of the plurality of convex portions of the continuously smooth portion (20) extends axially over at least 50% of the axial width (L) of the continuously smooth portion (20).

7. 2. The tire (10) of claim 1, wherein the recesses (26) of the plurality of recesses are distributed in at least one repeating recess pattern across at least a portion of the continuously smooth portion (20), and / or the peaks (28) of the plurality of peaks are distributed in at least one repeating peak pattern across at least a portion of the continuously smooth portion (20).

8. 2. The tire (10) of claim 1, wherein the recesses (26) of the plurality of recesses and the peaks (28) of the plurality of peaks are distributed in a single common repeating pattern across at least a portion of the continuously smooth portion (20).

9. 1. Use of a motor vehicle or motorcycle tire (10) having a tread surface (16) including one or more continuously smooth portions (20) in racing or free riding on an asphalt race track, wherein the or each continuously smooth portion (20) comprises: a plurality of recesses (26), each recess (26) of said plurality of recesses comprising a concave bottom (30); a plurality of projections (28), each projection (28) of said plurality of projections comprising a peak (32); The present invention is characterized by comprising: the recesses (26) of the plurality of recesses and the protrusions (28) of the plurality of protrusions are arranged such that, when the or each continuously smooth portion (20) rolls along a road surface, an average convex crest pressure (Pb) exerted by the road surface on the crests (32) of the protrusions (28) of the plurality of protrusions is strictly greater than an average concave bottom pressure (Pc) exerted by the road surface on the bottoms (30) of the recesses (26) of the plurality of recesses, and the average concave bottom pressure (Pc) is non-zero; a pressure exerted by the road surface on each recess (26) of the plurality of recesses and each protrusion (26) of the plurality of protrusions is measured at the contact patch of the or each successively smooth portion (20) of the tire (10) when the tire (10) is running at a speed equal to 100 mm / sec with a slip angle and a camber angle of substantially zero; in the case of a motor vehicle tire (10), said tire (10) is 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 motorcycle tire (10), the use of said tire (10) when said tire (10) is inflated to a reference pressure equal to 1.8 bar and subjected to a reference load equal to 1500 N.

10. A mold (50) for manufacturing a tire (10) according to claim 1, comprising: a molding surface (52) for molding the tread surface (16) including a continuously smooth molding portion (54) for molding the or each continuously smooth portion (20) of the tread surface (16), wherein the or each continuously smooth molding portion (54) a plurality of recesses (58) for molding the protrusions (28) of the plurality of protrusions of the continuous smooth portion (20) of the tread surface (16); a plurality of protrusions (60) for molding the recesses (26) of the plurality of recesses of the continuous smooth portion (20) of the tread surface; A mold (50) comprising:

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