Passenger car tires

Abstract

The present invention relates to a passenger tire (1) with improved rolling resistance performance without compromising lateral drift stiffness. The bead (50) is provided with a packing layer (70) and the lateral reinforcing layer (60) is softened by using a low hysteresis material. The lateral drift stiffness is increased by managing the contact between the bead (50) and the mounting rim (100). The rim contact curve length LADC is measured in a first section located in the contact patch of at least one first bead. The rim contact curve length LCJ is measured in a second section located on the opposite side of the contact patch with respect to the axis of rotation of the tire of at least one second bead. The ratio of the difference between the lengths of the rim contact curves in the two sections, i.e. 100*(LADC-LCJ) / LCJ, is 30 or more.

Description

[Technical field]

[0001] The present invention relates to a tire for automobiles having improved performance in terms of rolling resistance without adversely affecting the lateral cornering stiffness, and is more particularly suitable for radial tires intended to be fitted on cars or vans. [Background technology]

[0002] By convention, in a reference system (O, XX', YY', ZZ') whose center O coincides with the center of the tire, the circumferential direction XX', the axial direction YY' and the radial direction ZZ' refer to the direction tangent to the tread surface in the direction of tire rotation, the direction parallel to the tire rotation axis and the direction perpendicular to the tire rotation axis, respectively.

[0003] Radially inner and radially outer mean closer to and farther from the axis of rotation of the tire, respectively.

[0004] Axial inner and axial outer mean closer to and farther from, respectively, the tire's equatorial plane, which is the plane passing through the center of the tire's tread and perpendicular to the tire's axis of rotation.

[0005] The construction of a tire is usually described by depicting its components in a meridian plane, that is, the plane containing the tire's axis of rotation.

[0006] The tire comprises a crown, intended to come into contact with the ground through the tread, and its two axial ends are connected through two sidewalls to two beads, which provide the mechanical connection between the tire and the rim on which it is intended to be mounted.

[0007] Radial tires also include a reinforcement consisting of a crown reinforcement radially inward of the tread and a carcass reinforcement radially inward of the crown reinforcement.

[0008] The crown reinforcement of a radial tire comprises a superposition of crown layers extending circumferentially radially outside the carcass reinforcement. Each crown layer is made up of mutually parallel reinforcements coated with a polymeric material of the elastomer or elastomeric compound type. The assembly made up of the crown reinforcement and the tread is called the crown.

[0009] The carcass reinforcement of a radial tire usually comprises at least one carcass layer made up of metallic or textile reinforcing elements coated with an elastomeric coating compound. The reinforcing elements are substantially parallel to each other and form an angle between 85° and 95° with respect to the circumferential direction. The carcass layer comprises a main part that connects two beads and is wound around an annular reinforcing structure at each bead. The annular reinforcing structure can be a bead wire with circumferential reinforcing elements, usually made of metal and surrounded by at least one elastomeric or textile material (not exhaustive). The carcass layer is wound around the annular structure from the inside to the outside of the tire, forming a turn-up with an end. The turn-up at each bead allows the carcass reinforcement layer to be anchored to the annular structure of the bead.

[0010] Each bead includes a filler layer extending radially outwardly from the annular reinforcing structure, the filler layer being comprised of at least one elastomeric filler compound, and the filler layer axially separates the main and turnup portions of the carcass reinforcement.

[0011] Each bead also comprises a protective layer extending radially inwardly on the sidewall and axially outwardly of the turn-up, the protective layer also being in at least partial contact with the flange of the rim via its axially outer surface, the protective layer being made of at least one protective elastomeric compound.

[0012] Finally, each bead comprises a lateral reinforcing layer positioned between the sidewall and the turnup of the carcass reinforcement, said outer lateral reinforcing layer being made of at least one elastomeric composition.

[0013] Each tire sidewall includes at least one sidewall layer made of an elastomeric compound and extending axially from the tire's exterior surface exposed to the atmosphere toward the tire's interior.

[0014] The term "radial cross section" or "radial section" is understood here to mean a cross section or section along a plane containing the axis of rotation of the tire.

[0015] Elastomeric compounds are understood to mean elastomeric materials obtained by mixing their various components. They conventionally comprise at least one diene elastomer of natural or synthetic rubber type, at least one reinforcing filler of carbon black type and / or silica type, a crosslinking system, usually based on sulfur, and an elastomer matrix containing a protective agent. In some applications, the elastomers may also comprise thermoplastics (TPEs).

[0016] The expression "composition based on" should be understood to mean a composition comprising compounds and / or reaction products of the various components used, some of these basic components being capable or intended to react, at least in part, with one another during the various stages of the preparation of the composition, in particular in the course of crosslinking or vulcanizing it.

[0017] The expression "per hundred parts by weight of elastomer" (or phr) is to be understood within the meaning of the present invention as meaning the percentage per hundred parts by weight of elastomer present in the compounded composition under consideration.

[0018] Elastomeric compounds can be characterized mechanically, especially after curing, by their dynamic properties, such as the dynamic shear modulus G* = (G'2 + G"2)1 / 2, where G' is the elastic shear modulus and G" is the viscous shear modulus, and the dynamic losses Tan δ = G" / G'. The dynamic shear modulus G* and the dynamic losses Tan δ are measured on a Metravib VA4000 viscometer according to standard ASTM D5992-96. A 4 mm thick, 400 mm cross-sectional area viscoelastic specimen subjected to a simple alternating sinusoidal shear stress at a frequency of 10 Hz and a temperature of 100°C is subjected to a viscoelastic shear stress of 10 Hz. 2 The response of a vulcanized elastomeric compound sample in the form of a cylindrical specimen is recorded. A strain amplitude sweep is performed from 0.1% to 50% (forward cycle) and then from 50% to 0.1% (return cycle). During the forward cycle, the maximum value of tan(δ) observed (Tan(δ) max (denoted as "") is shown.

[0019] "Handling" performance corresponds to the response of the vehicle / tire assembly to multiple driver-initiated stresses (steering, acceleration, braking, etc.). Handling is important for vehicle stability from a safety perspective, and also for driving pleasure.

[0020] Tyres play a key role during manoeuvring, as they are at the end of the chain and guarantee the transmission of forces between the vehicle and the ground in order to maintain the path defined by the driver.

[0021] When cornering, in order for a vehicle to stay on path, it must generate a force equal to (but opposite to) the centrifugal force tending to move the vehicle off the path. This lateral force must be generated by the vehicle's four tires to overcome the centrifugal force.

[0022] The deformation of the rubber blocks in contact with the ground generates lateral forces. The mechanism by which the tire deforms the rubber blocks while cornering is called drift. Drift is the angle between the direction of the wheels and the path the vehicle follows. This angle is not zero in order for the tire to deform the rubber blocks of the tread while cornering, and thus generate the necessary lateral forces.

[0023] Lateral cornering stiffness refers to the change in lateral force generated by a tire's contact patch as a function of the drift angle imparted to the tire when moving in a compressed manner due to the load it is supporting. Lateral cornering stiffness is expressed in Newtons per degree (N / °).

[0024] For small drift angles, i.e. less than 10°, the lateral force parallel to the axis of rotation of the tire is proportional to the drift angle. The lateral cornering stiffness is equal to this proportionality factor.

[0025] Lateral cornering stiffness is a very important physical variable which couples the tire to the vehicle and determines the quality of the vehicle's handling on the road.

[0026] Rolling resistance is another performance feature addressed in this invention. Rolling resistance is one of the forces that oppose the forward movement of a vehicle. The rolling resistance coefficient (C RR ) is the rolling resistance of the tire to the load it supports. This coefficient is expressed in kg / t.

[0027] Rolling resistance is essentially linked to the deformations of the tire. For instance, the beads in relation to the sidewalls represent 20% to 30% of the rolling resistance of a tire, while the tread contributes 60% to 80%.

[0028] In the present invention, the tire is most often mounted on a rim. It is selected in accordance with the specifications of the ETRTO (European Tire and Rim Technical Organisation) standard, which relates a recommended rim to a given tire size. In general, several rim widths may fit for one and the same tire size. The part of the rim that interacts with the tire within the context of the present invention exhibits rotational symmetry about the tire's axis of rotation. To describe the rim, it is sufficient to describe the generator profile in the meridian plane.

[0029] In the meridian plane, the rim comprises at least one flange located at one axial end and connected to a seat intended to receive the radially innermost surface of the bead. The flange of the rim, extending axially in a straight section, limits the movement of the bead during expansion.

[0030] The fit of the bead to the rim when inflated is also a performance that the invention influences. The performance regarding the fit of the bead consists in evaluating the function of correctly seating the bead of the tire on the rim when inflated. The radially innermost surface of the bead must have sufficient contact with the seat to avoid the leakage of the air used to inflate the tire. Generally, a contact pressure of at least 1.4 MPa is expected in this contact area. The air pressure causes the bead to be captured by the flange of the rim. The contact pressure on the flange must also be sufficient to prevent the tire from coming off the rim, especially during severe cornering at high speed. Observation means, in particular operating with radiography, for observing the bead attached to the rim make it possible to diagnose the quality of the attachment.

[0031] It is therefore possible to classify the two tyres in terms of their performance in terms of their fitment on the rim.

[0032] prior art Reducing greenhouse gas emissions in the transportation sector is one of the major challenges facing vehicle manufacturers today. Considerable progress has been made through tires by lowering rolling resistance, as this has a direct impact on a vehicle's fuel consumption. As an illustration, a 20% reduction in tire rolling resistance can result in a fuel saving of around 3% per 100 km in a combined cycle.

[0033] There remains a need to reduce the rolling resistance of passenger vehicle tires without adversely affecting vehicle handling characteristics.

[0034] It has already been proposed to improve the rolling resistance of passenger car tires by optimizing the beads. WO 2010 / 072736 notably teaches the use of an elastomeric composition having a low elastic modulus G' of about 15 MPa and a viscous modulus G" that is more than 20% lower than the elastic modulus, in order to obtain a significant reduction in rolling resistance.

[0035] WO 2010 / 072736 also recommends reducing the rolling resistance even further by optimizing the geometry of the layers of elastomeric compounds whose elastic and viscous moduli satisfy the above relationship, which may result in shorter and wider profiles of the layers of elastomeric compounds than in conventional tires, causing implementation difficulties.

[0036] French Patent No. 2 994 127 describes an improvement of WO 2010 / 072736 on the premise of adding a reinforcement within the bead, which is formed by a reinforcing material coated with an elastomeric compound.

[0037] The main drawback of this solution is the significant increase in industrial production costs due to the introduction of a new semi-finished product into the process of making tires. [Prior art documents] [Patent documents]

[0038] [Patent Document 1] International Publication No. 2010 / 072736 [Patent Document 2] French Patent No. 2994127 Summary of the Invention [Problem to be solved by the invention]

[0039] The inventors set themselves the objective of producing a tire that improves rolling resistance without adversely affecting vehicle handling, while still controlling associated manufacturing costs. [Means for solving the problem]

[0040] Disclosure of the Invention This object is achieved by a passenger vehicle tire comprising: a tyre comprising two beads intended to be attached to a rim, two sidewall layers connected to the beads, and a crown having a tread intended to come into contact with the ground, the crown having a first side connected to the radially outer end of one of the two sidewall layers and a second side connected to the radially outer end of the other of the two sidewall layers, The tires are at least one carcass reinforcement extending from the two beads through the sidewall layer to the crown, the carcass reinforcement having a plurality of carcass reinforcing elements and anchored to the two beads by turnups around the annular reinforcing structure to form a main portion and a turnup portion in each bead; The tires are a first layer of an elastomeric filler compound, the first layer occupying a volume at least partially contained between a main portion of the carcass reinforcement on the one hand and a radially outer portion of the annular reinforcing structure on the other hand, and extending radially outward from an axial line HH' tangent to the annular reinforcing structure at its radially innermost point to an end portion located at a perpendicular distance DRB; The tires are a second layer of elastomeric compound forming a lateral reinforcing layer, the second layer of elastomeric compound occupying a volume at least partially contained between the sidewall layer and the turn-up of the carcass reinforcement (53) and extending radially outward from an axial straight line HH' tangent to the annular reinforcing structure at a radially innermost point to an end located at a vertical distance DRL; The dynamic shear modulus and viscoelastic loss of the elastomeric compounds are measured at 100°C and 10% strain according to standard ASTM D5992-96; for each bead, a rim contact curve includes points on the tire that contact the rim, the rim contact curve connecting a first point M1 on the tire that is axially outermost and contacts the rim, and a second point M2 on the tire that also contacts the rim and is midway along the straight line joining the flange to the seat of the rim, the length of this rim contact curve being the curvilinear distance from point M1 to point M2 along the contact curve; The tires are The tire further comprises two sections in the vertical meridian plane of an inflated tire mounted on a rim and compressed against a hard, flat surface by a vertical load, the vertical load and inflation pressure being nominal values ​​of the ETRTO (European Tire and Rim Technical Organization) standard, the first section being located at the contact surface and the second section being located opposite the first section with respect to the axis of rotation of the tire; A rim contact curve length LADC is measured at least at the first bead in a first section located at the contact patch; A rim contact curve length LCJ is measured at least at a second bead in a second section located on the opposite side of the tire contact patch with respect to the tire axis of rotation; The ratio of the difference in the length of the rim contact curve in the two sections, i.e., 100*(LADC-LCJ) / LCJ, is 30 or more; The elastomeric compound constituting the second lateral layer of at least one bead has a viscoelastic loss Tan(δ)max of 0.100 or less.

[0041] For the tire of the invention, the combination of a rim contact change rate of 100*(LADC-LCJ) / LCJ of more than 30 and a hysteresis level Tan(δ)max of the elastomeric compound constituting the second lateral reinforcing layer of less than or equal to 0.100 results in a reduction of the rolling resistance of the tire without adversely affecting the handling of the vehicle on which the tire is mounted. The beads of such a tire achieve a balanced performance in terms of rolling resistance and lateral cornering stiffness due to the material properties and the geometric profile of the sidewall layer in the contact area with the rim. The production of such a tire does not require any specific process development or the introduction of new materials, so that the industrial production costs are the same as those of the prior art.

[0042] The rate of change in rim contact for the tire of the present invention is much greater than that found in prior art tires.

[0043] The rim contact curve represents all the points on the tire that are in contact with the rim at a given moment. For each bead, this rim contact curve extends from a first point M1 on the tire that is axially outermost and in contact with the rim, to a second point M2 on the tire that is also in contact with the rim and is located halfway along the straight line that connects the flange to the seat of the rim. The length of this rim contact curve is the curvilinear distance from point M1 to point M2 along the rim contact curve.

[0044] When an inflated tire mounted on a rim is compressed by the load it is supporting, the point on the tire that is in contact with the rim may change from one meridian to another, and therefore the length of the rim contact curve as defined above will also vary from meridian to meridian.

[0045] The present tire is designed, in comparison with prior art tires, so that the rim contact curve is as long as possible in the contact patch, and more specifically in the central meridian of the contact patch: in these conditions, the inventors presume, the contribution of the rim contact to the cornering stiffness is maximized.

[0046] In a meridian section of a pneumatic tire mounted on a rim and compressed under the load it bears, a first section of the tire can be seen passing through the centre of the contact patch. Contact patch is understood to mean all the points on the tire that are in contact with the ground on which the tire is compressed at a given moment. The point on the contact patch that lies on the vertical axis ZZ' is called the centre of the contact patch. On the opposite side of the contact patch with respect to the axis of rotation YY' of the tire, another section of the tire can also be seen, which defines as a whole a state of deformation similar to the inflated state, which shows rotational symmetry.

[0047] The rate of change of rim contact corresponds to the maximum change in rim contact length per wheel revolution.

[0048] According to the inventors, an essential step in designing the tire of the invention consists in modifying its external profile in the contact area with the rim. Various solutions are possible, for example increasing the axial thickness of the sidewall layer at its junction with the protective layer. Another solution consists in modifying the external profile so as to obtain a profile in the contact area with the same curvature as the rim flange. Yet another solution consists in inserting a compound cushion in the area of ​​the junction of the sidewall layer and the protective layer, at the flange of the rim. This compound cushion can preferably consist of the same compound as the sidewall layer, in order to keep the industrial production costs low. What is expected of this elastomeric compound cushion is in particular its elastic shear stiffness, which can advantageously be equal to the elastic shear stiffness of, for example, the sidewall layer.

[0049] According to the invention, the viscoelastic loss Tan(δ)max of the elastomeric compound constituting the second lateral reinforcing layer of at least one bead has a value less than or equal to 0.100.

[0050] The invention proposes the use of a second lateral layer with a viscoelastic loss of less than 0.100, with the aim of improving the rolling resistance, which second lateral reinforcing layer can be associated with a first infill layer with low viscoelastic loss or which is stiff or flexible.

[0051] The function of the second lateral reinforcing layer of the bead is to reinforce the infill layer in terms of shear stiffness. To transmit the torque of the vehicle to the wheel, the bead needs to have a sufficient level of stiffness to be effective. The second lateral reinforcing layer contributes to the stiffness of the bead in cooperation with the first infill layer.

[0052] The reduction of the rolling resistance of the bead is due to the reduction of the hysteresis of the elastomeric compound which has the largest volume and is subject to considerable strain. The compounds of the first and second layers of the bead are located respectively axially inward and outward of the turnup of the carcass reinforcement, which occupy the largest volume and are subject to strong bending, tension-compression and shear stresses.

[0053] In a first advantageous embodiment, the second lateral reinforcing layer of at least one bead has an elastic shear stiffness modulus lying in the range [1.5; 10] MPa, preferably in the range [1.5; 7] MPa.

[0054] This embodiment is intended to make the bead work with a flexible second lateral reinforcing layer, which typically has a shear modulus between 20 and 50 MPa. This embodiment has the advantage that it allows the use of elastomeric compounds that have both low viscoelastic losses, with a Tan(δ)max of less than 0.1, and an elastic shear modulus in the range [1.5;10] MPa. Given the consistency of these material properties, it is not particularly difficult to implement such compounds.

[0055] In a second advantageous embodiment of the invention, the viscoelastic loss Tan(δ)max of the elastomeric compound constituting the first filling layer of at least one bead has a value less than or equal to 0.100.

[0056] In this embodiment, the performance trade-off is weighted towards rolling resistance. This first filler layer has the largest volume in the bead. Its reduced hysteresis, combined with the low-loss second lateral reinforcing layer, translates into a noticeable reduction in the rolling resistance of the bead.

[0057] In other words, this embodiment contributes to lowering the rolling resistance of the bead and therefore the tire, while still having a vehicle handling level comparable to prior art tires, thanks to the rim contact variation ratio being maintained at a level above 30.

[0058] In a third embodiment, the elastic shear stiffness modulus of the elastomeric compound constituting the first filling layer of at least one bead is in the range of [1.5; 10] MPa, preferably in the range of [1.5; 7] MPa.

[0059] Another advantage of the invention related to this variant is that when carrying out a mountability test on the rim comparing the prior art tires with the present tire, the inventors noticed that the mountability of the present tire is better than some tires with rigid beads. This is because in the prior art tires, the compounds of the filler layer have an elastic stiffness modulus generally between 15 MPa and 50 MPa. The inventors hypothesize that the flexibility of the present tire with respect to the bead facilitates mounting due to its deformability, facilitating a better seating on the seat and against the rim flange. Furthermore, modifying the radially inner profile of the sidewall layer causes a decrease in the mountability on the rim in relation to the rigid beads. The use of a flexible elastomeric compound (G'<10 MPa) makes it possible to compensate for this decrease and obtain an adequate level of mountability.

[0060] Preferably, the ratio of the difference in rim contact curve lengths for the two sections, ie, 100*(LADC-LCJ) / LCJ, is 40 or more, preferably 50 or more, more preferably 70 or more.

[0061] The inventors have found that the lateral cornering stiffness of the tire of the present invention increases in the same sense as the rate of change of rim contact, where changing the outer profile of the sidewall layer facilitates bead mounting, but excessive ratios above 100 may impede mounting.

[0062] In addition to the primary features of the present invention, the inventors have identified measures related to the geometry of the bead compound layer to better address the performance tradeoffs of improved rolling resistance while maintaining good handling characteristics.

[0063] Advantageously, the radial distance DRB of the first infilling layer included between the main portion of the carcass reinforcement and the turn-up portion is less than or equal to 50% of the radial height H of the tire.

[0064] The height H of a tire is the perpendicular distance between a first line parallel to the tire's axis of rotation and tangent to the radially innermost point of the annular reinforcing structure, and a second line parallel to the tire's axis of rotation and passing through the radially outermost point of the tread. The radial height H is measured with the tire mounted on a rim and inflated to a set pressure in accordance with ETRTO (European Tyre and Rim Technical Organisation) standards.

[0065] Advantageously, the radial distance DRI, taken as the radial height of the radially innermost end of the lateral reinforcing layer positioned between the sidewall layer and the turn-up of the carcass reinforcement, is in the range [5%;25%] of the radial height H of the tyre.

[0066] More advantageously, the distance DRL, taken as the distance between the radially outer ends of the lateral reinforcing layers positioned between the sidewall layer and the turn-up of the carcass reinforcement, is greater than or equal to 25% of the radial height H of the tire.

[0067] It will be recalled that the distance DRL is the perpendicular distance from the radially outermost end of the end of the second lateral reinforcing layer to a line (HH') tangent to the annular reinforcing structure at its radially innermost point.

[0068] A second lateral reinforcing layer, included between the sidewall and the carcass reinforcement turnup, contributes to the stiffness of the bead in addition to the first filler layer, and according to the inventors, its positioning is adjusted with the lateral DRI and DRL to withstand bending and tensile-compressive stresses as the bead enters the ground.

[0069] In an advantageous embodiment of the invention, the turn-up portion of the carcass reinforcement contacts the main portion of the carcass reinforcement radially outwardly along the turn-up portion.

[0070] As mentioned above, the carcass reinforcement is formed of a reinforcement material coated between two layers of an elastomeric compound. The turn-up part of the carcass reinforcement is pressed against the main part of the carcass reinforcement, meaning that the turn-up part is in contact with the main arm of the carcass reinforcement. This contact is made along the axially outer surface of the coating of the carcass reinforcement.

[0071] In this configuration, the volume of the first filler layer is restricted to a strict minimum around the annular reinforcing structure, which is very advantageous in reducing the rolling resistance of the bead.

[0072] In another embodiment, the bead reinforcement is introduced axially on the axial inside of the sidewall, between the turn-up of the carcass reinforcement and the lateral reinforcing layer.

[0073] The reinforcement of the bead is formed by parallel reinforcements coated between two layers of an elastomeric compound. The addition of this semi-finished product results in additional production costs that must be compensated for.

[0074] In order to limit the impact of such a solution on the manufacturing costs, this embodiment can be combined with pressing of the turn-up parts of the carcass reinforcement against the main part of the carcass reinforcement.

[0075] Advantageously, the elastomeric compound constituting at least one of the first and second layers of at least one bead has a composition based on 100% polyisoprene natural rubber, or else a blend of natural rubber and polybutadiene, crosslinked system, reinforcing filler of carbon black N550 type, with a total content of between 50 and 75 phr.

[0076] Preferably, the elastomeric compound constituting the filling layer of at least one bead has the same composition as the elastomeric compound constituting the lateral outer reinforcing layers of the bead.

[0077] The rubber composition is preferably based on at least one diene elastomer, a reinforcing filler and a crosslinking system.

[0078] "Diene" elastomer (or equivalently rubber) is understood in a known manner to mean an elastomer (i.e. homopolymer or copolymer) that is at least partially derived from a diene monomer, i.e. a monomer having two conjugated or non-conjugated carbon-carbon double bonds. The diene elastomer used is preferably selected from the group consisting of polybutadiene (BR), natural rubber (NR), synthetic polyisoprene (IR), styrene-butadiene copolymer (SBR), butadiene-isoprene copolymer (BIR), styrene-isoprene copolymer (SIR), styrene-butadiene-isoprene copolymer (SBIR), and compositions of these elastomers.

[0079] A preferred embodiment is to use "isoprene" elastomers, i.e. homopolymers or copolymers of isoprene, in other words diene elastomers selected from the group consisting of natural rubber (NR), synthetic polyisoprene (IR), various isoprene copolymers, and compositions of these elastomers.

[0080] The isoprene elastomer is preferably natural rubber or a synthetic polyisoprene of the cis-1,4 type. Of these synthetic polyisoprenes, preferably polyisoprenes with a content (mol %) of cis-1,4 bonds of more than 90%, more preferably even more than 98%, are used. According to another preferred embodiment, the diene elastomer can consist entirely or partly of another diene elastomer, such as an SBR elastomer (E-SBR or S-SBR) used with or without blending with another elastomer, for example of the BR type.

[0081] The rubber composition may also contain all or some of the additives normally used in rubber matrices intended for the manufacture of tires, such as reinforcing fillers such as carbon black or inorganic fillers such as silica, coupling agents for inorganic fillers, anti-aging agents, antioxidants, plasticizers or extender oils, the latter whether aromatic or non-aromatic (in particular oils which, if aromatic at all, are very weak, for example of the naphthenic or paraffinic oil type, high or preferably low viscosity oils, MES oils or TDAE oils, oils with a high Tg above 30° C. These include, for example, plasticizing resins having a tackifier resin, agents which improve the workability (processability) of the composition in the raw state, tackifying resins, crosslinking systems based either on sulfur or on sulfur and / or peroxide donors, accelerators, vulcanization activators or retarders, anti-reversion agents, methylene acceptors or donors, such as HMT (hexamethylenetetramine) or H3M (hexamethoxymethylmelamine), reinforcing resins (such as resorcinol or bismaleimide), known adhesion promoter systems of the metal salt type, such as, in particular, cobalt or nickel salts.

[0082] The rubber compositions are produced in a suitable mixer using two successive preparation stages well known to those skilled in the art: a first stage of thermomechanical kneading or working at high temperature ("non-productive" stage), up to a maximum temperature between 110°C and 190°C, preferably between 130°C and 180°C, then a second stage of mechanical working at low temperature, typically below 110°C ("productive" stage), which is the finishing stage during which the crosslinking system is incorporated.

[0083] By way of example, the non-productive phase is carried out in a single thermomechanical step lasting a few minutes (for example between 2 and 10 minutes), during which all the necessary base components and other additives, except the crosslinking or vulcanization system, are introduced into a suitable mixer, such as a conventional internal mixer. After cooling the composition thus obtained, the vulcanization system is introduced into an open mixer, such as an open mill, kept at a low temperature (for example between 30°C and 100°C). The whole is then mixed for a few minutes (for example between 5 and 15 minutes) (productive phase).

[0084] The final composition thus obtained is then calendered or otherwise extruded, for example in the form of sheets or slabs for characterization, to form the outer bands used in tires according to the invention.

[0085] Vulcanization (or curing) can then be carried out in a known manner, generally at temperatures between 130° C. and 200° C., preferably under pressure, for a sufficient period of time which can vary, for example, between 5 and 90 minutes, depending in particular on the curing temperature, the vulcanization system employed, and the vulcanization kinetics of the composition in question.

[0086] Further details and advantageous features of the invention will become apparent in the following text from the description of an exemplary embodiment of the invention given with reference to a figure which depicts a meridian view of a tire design according to one embodiment of the invention, the figure not being drawn to scale for ease of understanding. [Brief description of the drawings]

[0087] [Figure 1] Shown is a meridian section of an inflated tire mounted on a rim and compressed under the load it supports: a first section at the contact patch and a second section facing the contact patch about the axis (YY') are visible. [Figure 2-A] Shows modifications to the outer profile of the tire to facilitate contact with the rim. [Figure 2-B] Shows modifications to the outer profile of the tire to facilitate contact with the rim. [Figure 2-C] FIG. 2 is an enlarged view of the first bead of the tire of the present invention mounted on a rim. [Figure 3-A] Determination of tire height H is shown. [Figure 3-B] 1 shows the main side of a bead according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0088] Detailed Description of the Invention The present invention is implemented in a passenger car tire of size 245 / 45R18 conforming to the ETRTO (European Tire and Rim Technical Organisation) specification. Such a tire is capable of supporting a load of 800 kg at an air pressure of 250 kPa.

[0089] In FIG. 1 , the tire 1 comprises a carcass reinforcement 90 made of a reinforcing material coated with a rubber composition, and two beads 50, each having an annular reinforcing structure 51 that holds the tire 1 on a rim 100. The carcass reinforcement 90 is anchored to each of the beads 50. The tire 1 also comprises a crown reinforcement 20, which comprises two working layers 21, 22 and a hooping layer 23. Each of the working layers 21 and 22 is reinforced with filamentary reinforcing elements that are parallel in each layer and cross from one layer to the other, forming an angle between 10° and 70° with the circumferential direction. The hooping layer 23 is arranged radially outside the crown reinforcement 20, this hooping layer 23 being formed of reinforcing elements oriented in the circumferential direction and wound in a spiral. The tread 10 is arranged radially on the hooping layer 23, this tread 10 providing the contact between the tire 1 and the ground 100. The tire 1 shown is a "tubeless" tire, which comprises an "inner liner" 95 made of a rubber composition impermeable to inflation gases and covering the inside surface of the tire. The tire is compressed against the ground 200 by a vertical load 250. Each bead 50 comprises a layer 80 of elastomeric compound positioned radially innermost and intended to be in contact with the rim 100, and a layer 70 of elastomeric filler compound positioned at least partially between the main portion 52 and the turnup portion 53 of the carcass layer 90. The bead 50 also includes a lateral reinforcing layer 60 on the axially outer side of the turn-up portion 53 and on the axially inner side of the sidewall 30 .

[0090] Further, in FIG. 1 , the mounting rim 100 extends axially on either side of the vertical axis OZ and, at least in the part bounded by the axis OZ, comprises at least one profile 105 having a seat 110 intended to receive an end of the tire, the seat 110 connecting to a straight portion 130 of the rim, which straight portion 130 is itself connected to a flange 120.

[0091] Figure 2-A shows the outer profile for a bead 50 of a tire 1 of the invention compared to that of a prior art tire. The bead 50 is depicted in cross section on the opposite side of the contact patch. The two profiles differ in the area of ​​the rim flange 120. Reference number 30 indicates the profile of the prior art tire, and reference number 35 indicates the changes in the profile made in the tire of the invention to facilitate contact with the rim 100.

[0092] Figure 2-B depicts the same as Figure 2-A, except that it shows the profile at the center of the contact patch that contacts the ground. In contrast to Figure 2-A, the tire is in contact with the entire rim flange 120. The rate of change of rim contact reveals this evolution in rim contact.

[0093] In the embodiment shown in FIG. 2-C, there is an elastomeric compound cushion 40 (a variation located at the radially inner end of the sidewall 30) intended to contact the rim flange 120. The compound cushion 40 is bounded radially inward by a curve that closely follows the profile of the rim flange 120. A first side of the elastomeric compound cushion 40 has a suitable geometry that anticipates contact with the curvature of the rim flange 120 so as to closely follow the curvature of the rim flange 120 upon contact, a second side of the elastomeric compound cushion continues on the outside of the sidewall in contact with the surrounding air, a third side of the elastomeric compound cushion 40 contacts the radially inner end of the sidewall, and finally a fourth side of the elastomeric compound cushion contacts the protective layer 80.

[0094] In Figure 2-C, the rim contact curve extends from a first point M1 on the tire, which is axially outermost and in contact with the rim, to a second point M2 on the tire, also in contact with the rim, which is midway along the straight line joining the flange 120 to the rim seat 110. The length of this rim contact curve is the distance along the rim contact curve that forms the curve from point M1 to point M2.

[0095] Figure 3-A illustrates the determination of the height H of a tire. The height H of a tire is the perpendicular distance between a first line parallel to the tire's axis of rotation and tangent to the radially innermost point of the annular reinforcing structure, and a second line parallel to the tire's axis of rotation and passing through the radially outermost point of the tread. The radial height H is measured with the tire mounted on a rim and inflated to a set pressure in accordance with ETRTO (European Tire and Rim Technical Organization) standards.

[0096] 3-B shows the geometric parameters of the bead according to the present invention. The height is defined from a straight line HH' that is tangent to the bead wire 51 at the radially innermost point.

[0097] DRI is the radial distance from the radially inner edge HH' of the lateral reinforcing layer 60. The radial distance DRI is equal to or less than 20% of the radial height H of the tire, and is 5 mm in the example shown.

[0098] DRL is the radial distance from the straight line HH' of the radially outer end of the lateral reinforcing layer 60. The radial distance DRL is equal to or greater than 25% of the radial height H of the tire, and is 38 mm in the example shown.

[0099] DRR is the radial distance from HH' of the end of the turnup of the carcass reinforcement 90. The radial distance DRR is equal to or greater than 10% of the radial height H of the tire, and is 20 mm in the example shown.

[0100] DRB is the radial distance from HH' for the radially outer end of the filler layer 70, which in the example shown is 28 mm.

[0101] Table 1 below shows the composition of the elastomeric compounds of the beads to which the invention pertains, listing the main compounds used and, for each, expressing the main component in phr (parts by weight per 100 parts by weight of elastomer).

[0102] [Table 1]

[0103] The compound used in this example of the invention is based on natural rubber elastomer and is reinforced with carbon black. A plasticizer (reinforcing resin) is incorporated in the composition to promote the processability of the compound. The compound also contains vulcanizing agents, sulfur, accelerators, and protective agents. The relevant mechanical and viscoelastic properties, measured at 23° C. under a strain amplitude of 10%, are summarized in Table 2.

[0104] [Table 2]

[0105] In the context of the present invention, the elastomeric compounds M1 and M2, having dynamic elastic shear moduli of 46 MPa and 48 MPa, respectively, are called stiff. Compound M3, having a viscoelastic loss equal to 0.1, is called low hysteresis.

[0106] To strongly highlight the performance offered by the present invention, a tire of the present invention, construction P1, was tested.

[0107] The results of these tires were compared to those of controls T1, T2 and T3.

[0108] The control T1 corresponds to a tire of conventional design and comprises a first filler layer located between the main part of the carcass layer and its turn-up. This first filler layer is made of compound M1. This tire also comprises a second lateral reinforcing layer arranged between the sidewall layer and the turn-up of the carcass reinforcement. This second lateral reinforcing layer comprises elastomeric compound M2. The profile of the sidewall layer has not been modified to facilitate contact with the rim, as is the case with tires according to the invention.

[0109] The rate of change in rim contact for the control tire T1 is conventionally set to 100, ie this rate of change in contact with the rim deviates by less than 30 from the tire according to the invention.

[0110] In the case of configuration T2, the filler layer and the second lateral reinforcing layer are made of the same elastomeric compound M3, but the profile of the sidewall is not modified to promote contact with the rim, in contrast to the tires of the invention.

[0111] With regard to the second variant T3, the first filling layer is made of compound M1 and the second lateral reinforcing layer comprises an elastomeric compound M2. The profile of the sidewall is modified to facilitate contact with the rim according to figures 2-A and 2-B.

[0112] The tire variant P1 according to the invention reproduces the specifications of the control T1, with the compound of the second filler layer being replaced by compound M3. After modifying the profile of the sidewall layer in the contact area with the rim as shown in Figures 2-A and 2-B, the change in the rim contact is 167.

[0113] A control tire and a construction according to the invention were tested to measure rolling resistance and lateral cornering stiffness. These same tires were also evaluated by a rim-mounting test.

[0114] Table 3 below summarizes the construction of the tested tires having beads with filler compounds but no lateral reinforcing layers.

[0115] [Table 3] (1) The term Nok means that the profile of the sidewall layer was not altered to promote contact with the rim, and the term Ok means that this profile was altered such that the rate of change of rim contact was greater than 30.

[0116] The rolling resistance tests were carried out in accordance with standard ISO 28580. For the tested tires, the result is the rolling resistance coefficient, which represents the ratio of the resistance force against the forward movement of the vehicle due to the tire's hysteresis divided by the supported load.

[0117] The lateral cornering stiffness was measured using a dedicated measuring instrument such as that sold by MTS.

[0118] The fitment test on the rim is based on breaking down the fitment into basic operations to give a comprehensive fitment result, in particular: passing the rim flange, pressing, going over the hump on the rim, placing the bead by compression, tightening under the rim seat, removing the bead, and dismantling. To carry out this test, a semi-automatic fitment machine or else a means such as an X-ray means is required.

[0119] The results obtained are summarized in Table 4 below, which also shows the percentage change in rim contact for each variant:

[0120] [Table 4]

[0121] Observing the results on tires confirms the principle of reducing the rolling resistance of tires by using beads with a flexible material such as compound M3 (T2), however, a reduction in cornering stiffness can also be observed at the same time.

[0122] Conversely, these results teach that the use of stiff beads, i.e. beads having a first filler layer and a second lateral reinforcing layer each made of elastomeric compounds (M1, M2), results in a significant deterioration in rolling resistance.

[0123] Control T3 teaches that modifying the profile of the sidewall layer to facilitate rim contact in conjunction with a stiff bead improves lateral cornering stiffness but deteriorates attachment to the rim.

[0124] Variant P1 shows an improvement in rolling resistance. The lateral cornering stiffness is reduced. The rate of change of the rim contact is at a level that allows the reduction in the lateral cornering stiffness to be suppressed. The relative flexibility of the bead in combination with the reduction in the shear stiffness of the compound M3 of the first filler layer aids the attachment to the rim.

[0125] Variants P1 have approximately the same level of lateral cornering stiffness as the control. Digital simulations are used to verify that the handling of these variants gives identical results to the control.

[0126] All the presented variants are produced without developing manufacturing processes and keep industrial production costs not significantly different from the usual costs.

[0127] Furthermore, the invention can be applied more generally to bead structures other than those described here, such as beads having a first filler layer and a second lateral reinforcing layer, even if the carcass reinforcement does not have a turn-up portion. [Explanation of symbols]

[0128] 1 Tire 10 Tread 20 Crown Reinforcement 21,22 Working Class 23 Hooping Layer 30 Profiles 40 Elastomer compound cushion 50 Beads 51 Annular reinforcement structure / bead wire 52 Main part of carcass layer 53 Carcass layer folded portion 60 Lateral reinforcement layer 70 Elastomer filler compound layer / first layer 80 Elastomer compound layer / protective layer 90 Carcass Reinforcement 95 Innerliner 100 Rims 105 Rim Profile 110 Seat area 120 Flange 130 Straight part of the rim 200 ground 250 Vertical Load O center YY' axis direction ZZ' Radial

Claims

1. A tire (1) for a passenger vehicle, comprising: A tire comprising two beads (50) intended to be attached to a rim, two sidewall layers (30) connected to said beads (50), and a crown (20) having a tread (10) intended to come into contact with the ground (200), said crown having a first side connected to the radially outer end of one of said two sidewall layers (30) and a second side connected to the radially outer end of the other of said two sidewall layers (30), The tire (1) comprises: at least one carcass reinforcement (90) extending from said two beads (50) through said sidewall layer (30) to said crown (20), said at least one carcass reinforcement (90) having a plurality of carcass reinforcing elements and anchored to said two beads (50) by turnups around an annular reinforcing structure (51) so as to form a main portion (52) and a turnup portion (53) in each of said beads; The tire (1) comprises: a first layer (70) of elastomeric filler compound, said first layer (70) of elastomeric filler compound occupying a volume at least partially contained between said main portion of said at least one carcass reinforcement on the one hand and a radially outer portion of said annular reinforcing structure (51) on the other hand, and extending radially outwardly from an axial straight line (HH') tangent to said annular reinforcing structure (51) at its radially innermost point to an end located at a vertical distance DRB; The tire (1) comprises: a second layer of elastomeric compound forming a lateral reinforcing layer (60), the second layer of elastomeric compound occupying a volume at least partially contained between said sidewall layer (30) and the turn-up of said at least one carcass reinforcement (53) and extending radially outward from an axial straight line HH' tangent to said annular reinforcing structure (51) at a radially innermost point to an end located at a vertical distance DRL; The dynamic shear modulus and viscoelastic loss of the elastomeric compound are measured at 100° C. and 10% strain according to standard ASTM D5992-96; For each of said beads (50), a rim contact curve includes a point on said tire (1) that is in contact with the rim (100), said rim contact curve connecting a first point M1 on said tire (1) that is axially outermost and in contact with the rim, and a second point M2 on said tire that is also in contact with the rim and is located midway between the straight line connecting the flange to the seat of the rim, said length of said rim contact curve being the curvilinear distance from said point M1 to said point M2 along said rim contact curve, The tire (1) comprises: and two sections in a vertical meridian plane of the inflated tire mounted on the rim and compressed against a hard flat surface by a vertical load (250), the vertical load and the inflation pressure being nominal values ​​of the ETRTO (European Tyre and Rim Technical Organisation) standard, a first section being located at the contact surface and a second section being located opposite the first section with respect to the axis of rotation of the tire; A length of the rim contact curve (LADC) is measured at least at a first bead in the first section located in the contact patch; The length of the rim contact curve LCJ is measured at least at a second bead in the second section located on the opposite side of the contact patch with respect to the axis of rotation of the tire; A tire (1) for passenger cars, characterized in that the ratio of the difference in the lengths of the rim contact curves in the two sections, i.e., 100*(LADC-LCJ) / LCJ, is greater than or equal to 30, and further characterized in that the viscoelastic loss Tan(δ)max of the elastomer compound constituting the lateral reinforcing layer (60) of at least one bead (50) has a value of less than or equal to 0.

100.

2. 2. Tyre (1) according to claim 1, wherein the lateral reinforcing layer (60) of the at least one bead (50) has an elastic shear stiffness modulus lying in the range [1.5; 10] MPa.

3. Tyre (1) according to claim 1, wherein the ratio of the difference in the lengths of the rim contact curves for the two sections, i.e. 100*(LADC-LCJ) / LCJ, is greater than or equal to 40.

4. 2. The tire (1) according to claim 1, wherein the radial distance DRB of the first layer (70) of elastomeric filler compound comprised between the main portion (52) and the turnup portion (53) of the at least one carcass reinforcement (90) is less than or equal to 50% of the radial height H of the tire (1).

5. 2. Tyre (1) according to claim 1, wherein a radial distance DRI is the radial height of a radially innermost end of said lateral reinforcing layer (60), said radial distance DRI being in the range [5%; 25%] of the radial height H of said tyre (1).

6. 2. Tyre (1) according to claim 1, wherein said vertical distance DRL is the distance of the radially outer ends of said lateral reinforcing layers, said vertical distance DRL being greater than or equal to 25% of the radial height H of said tyre (1).

7. 2. The tire (1) according to claim 1, wherein the turn-up portion (53) of the at least one carcass reinforcement (90) is in contact with the main portion (52) of the at least one carcass reinforcement (90) radially outwardly along the turn-up portion (53).

8. 2. Tyre (1) according to claim 1, characterized in that the reinforcement of the bead (50) is introduced axially externally, axially inside the sidewall (30), between the turn-up (53) of the at least one carcass reinforcement (90) and the lateral reinforcing layer (60).

9. 2. Tire (1) according to claim 1, wherein at least one of said first layer (70) and said lateral reinforcing layers (60) of elastomeric filler compound has a composition based on 100% polyisoprene natural rubber, or else a blend of natural rubber and polybutadiene, crosslinked system, reinforcing filler of carbon black N550 type, with a total content of between 50 and 75 phr.

10. 2. Tire (1) according to claim 1, characterized in that the elastomeric compound constituting the first layer (70) of elastomeric filler compound of the at least one bead (50) has the same composition as the elastomeric compound constituting the lateral reinforcing layer (60).

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