JP7378435B2 - Pneumatic tire with optimized crown and tread pattern structure - Google Patents

Description

The present invention relates to a tire intended for installation on a passenger vehicle, and more particularly to the crown of such a tire.

Because tires have a geometry that exhibits rotational symmetry about an axis of rotation, tire geometry is generally described in a meridian plane that includes the tire's axis of rotation. For a given meridional plane, the radial, axial, and circumferential directions refer to the direction perpendicular to the axis of rotation of the tire, the direction parallel to the axis of rotation of the tire, and the direction perpendicular to the meridional plane, respectively. A median circumferential plane, called the equatorial plane, divides the tire into two substantially symmetrical semi-torus shapes, and the tire may exhibit asymmetries in the tread or structure related to manufacturing accuracy or sizing. .

In the following text, the expressions "radially inward of" and "radially outward of" mean "closer in the radial direction to the axis of rotation of the tire than" and "radially closer than..." respectively. "away from the axis of rotation of the tire in a direction". The expressions "axially inward of" and "axially outward of" mean "axially closer to the equatorial plane than..." and "axially further away from the equatorial plane than..." respectively. It means "there". The "radial distance" is the distance to the axis of rotation of the tire, and the "axial distance" is the distance to the equatorial plane of the tire. "Radial thickness" is measured in the radial direction and "axial width" is measured in the axial direction.

The tire comprises a crown with a tread intended for contact with the road surface via the tread surface, two beads intended for contact with the rim, and two sidewalls connecting the crown to the beads. Furthermore, the tire comprises a carcass reinforcement arranged radially inside the crown and comprising at least one carcass layer connecting the two beads.

The tread of a tire is radially bounded by two peripheral surfaces, the radially outermost surface of which is the tread surface, and the radially innermost surface is called the tread pattern bottom surface. The tread pattern base, or bottom surface, is defined as the surface of the tread surface that is radially translated inwardly by a radial distance equal to the depth of the tread pattern. This depth typically decreases gradually over the outermost axial circumference of the tread, called the shoulder.

In addition, the tire tread is axially delimited on two sides. The tread is also comprised of one or more rubber compounds. The expression "rubber compound" means a rubber composition comprising at least an elastomer and a filler.

The crown includes at least one crown reinforcement radially inward of the tread. The crown reinforcement comprises at least one working reinforcement with at least one working layer made up of mutually parallel reinforcement elements forming an angle of 15° to 50° with the circumferential direction. The crown reinforcement may also include a hoop reinforcement consisting of at least one hooping layer made up of reinforcing elements forming an angle between 0° and 10° with the circumferential direction, but does not necessarily include hoop reinforcement. The bodies are usually radially outward of the working layer.

For any layer of reinforcement elements, be it a crown reinforcement, working reinforcement, or other reinforcement, a continuous surface called the radial outer surface (ROS) of that layer is located at the radially outermost point of each reinforcement element with respect to each meridian. pass through. For any layer of reinforcing elements for a crown reinforcement, working reinforcement, or other reinforcement, a continuous surface called the radially inner surface (RIS) of that layer is located at the radially innermost point of each reinforcing element with respect to each meridian. pass through. The radial distance between the layer of reinforcing element and any other point is measured without taking in the radial thickness of that layer from either of these surfaces. From the radially outer surface ROS to this point if the other measurement point is radially outside the reinforcing element layer, or from the radially inner surface RIS if the other measurement point is radially inside the reinforcing element layer The radial distance from to this measurement point is measured in each case. This makes it possible to consider consistent radial distances from meridian to meridian without having to take into account possible local variations associated with the cross-sectional shape of the reinforcing element consisting of layers.

The tread is notched to provide good grip on wet roads. A cut means either a well, a groove, a sipe, or a circumferential fallow, which forms a spatial opening in the tread surface.

The sipes or grooves have two characteristic principal dimensions on the tread surface, a width W and a length L0, such that the length L0 is at least equal to twice the width W. Thus, a sipe or groove determines its length Lo and is bounded by at least two major sides connected by a bottom surface, the two major sides being separated by a non-zero distance called the width W of the sipe or groove. are separated from each other.

The depth of the cut is the maximum radial distance between the tread surface and the bottom of the cut. The maximum value of the cutting depth is called the tread pattern depth D.

A fallow is essentially a circumferential groove, the sides of which can vary locally in orientation by approximately ±45° to the circumferential direction, meaning that all patterns belonging to a fallow can be found over the entire surface of the tread. , forming a substantially circumferential and substantially continuous set, ie exhibiting a discontinuity in length of less than 10% compared to the length of the pattern.

Circumferential fallow delimits the ribs. The rib is comprised of a tread pattern element comprised between an axial edge of the tire and an adjacent axially outermost circumferential fallow, i.e. between two adjacent circumferential fallows. .

In the following text, the expression "vertically below" means "for each meridian, radially inward within the boundaries of the axial coordinates bounded by." Therefore, "points in the working layer vertically below Farrow" refer to the set of points in the working layer that are radially inside the groove within the axial coordinate boundaries bounded by Farrow for each meridian. .

In the following text, the expression "vertically above" means "for each meridian, radially outward within the boundaries of the axial coordinates bounded by." Thus, "the portion of the tread vertically above the relief" refers to the set of points of the tread that are radially outward of the relief within the axial coordinate boundaries bounded by the relief, for each meridian.

Tires must meet a number of performance criteria related to phenomena such as wear, grip on different types of road surfaces, rolling resistance, and dynamic behavior. These performance criteria can sometimes result in solutions that compromise other criteria. Therefore, in order to obtain good grip performance on dry roads, the rubber compound of the tread must be dissipative and soft. In contrast, in order to obtain a tire that performs well in terms of behavior, in particular in terms of dynamic response to lateral loads of the vehicle and thus loads along the axis of rotation of the tire, the tire must be sufficiently high, especially under lateral loads. It is necessary to have a certain level of rigidity. For a given size, the stiffness of a tire depends on the stiffness of its various elements: tread, crown reinforcement, sidewalls, and beads. Treads have traditionally been made by stiffening the rubber compound, resulting in a loss of grip on dry surfaces, or decreasing the depth of the tread pattern, resulting in a loss of grip on wet surfaces, or by reducing the depth of the tread pattern, resulting in loss of grip on wet surfaces. Stiffness is increased by either decreasing the groove-to-rubber ratio.

To alleviate this problem, tire manufacturers have improved their rubber compounds, especially by stiffening them with fibers, as described, for example, in documents FR 3,014,442 and FR 2,984,230. has been changed.

French Patent No. 3014442 French Patent No. 2984230

These solutions are not always satisfactory. Reducing the depth of the tread pattern limits performance both in terms of wear and wet grip. Hardening the rubber compound limits the ability for wet and dry grip and also increases tire noise while driving. Reducing the void volume of the tread pattern reduces grip ability on wet roads, especially when standing water is deep. Also, to ensure the durability of the tire, it is important to maintain a certain thickness of the rubber compound between the bottom surface of the notch, groove or fallow and the reinforcing element of the radially outermost crown layer.

Thus, the use of specific rubber compounds that are very soft and exhibit high levels of grip to create all or part of the tread cannot be done without compromising other performance aspects. I can't.

Accordingly, a primary objective of the present invention is to be able to use tread rubber compounds that are "soft" or exhibit low levels of stiffness to improve performance and take advantage of their associated properties. These rubber compounds can, for example, be highly hysteretic to enhance dry grip performance, or, by contrast, have very low hysteresis to facilitate flattening to further improve rolling resistance. These low stiffness rubber compounds can be placed throughout the tread or over limited portions thereof, so as not to adversely affect other performance aspects such as wear or behavior. This objective was achieved without changing its performance in terms of wear and crown durability, while complying with national standards for rolling resistance.

This purpose is
- A tread intended to come into contact with the road surface via a tread surface provided with grooves, the grooves opening into the tread surface and forming a space bounded by two main side surfaces connected at the bottom surface. a tread having a width W defined by the average distance between the two side surfaces and a depth D defined by the maximum radial distance between the tread surface and the bottom surface;
- at least one groove that is a main groove and has a width W equal to at least 1 mm and a depth D equal to at least 4 mm;
- at least one main groove is substantially circumferential, referred to as a circumferential fallow;
- at least two ribs;
A passenger car tire comprising:
- The tire also comprises a crown reinforcement with at least one layer of reinforcing elements, represented by a crown layer, radially inside the tread;
- at least one layer of reinforcing elements extends radially from a radially inner surface (RIS) to a radially outer surface (ROS);
- The radially outermost crown layer has at least one undulation vertically below the rib,
- At least one undulation in the radially outermost crown layer is such that the radially outermost crown layer portion of the undulation is located at a point in the radially outermost crown layer that is vertically below the bottom center of the circumferential fallow that is closest to the undulation. It is located radially outward,
- at least one undulation in the radially outermost crown layer extends over at least 10% of the radially outer surface (ROS) of the crown layer, and the undulations in the radially outermost crown layer extend over at least 10% of the radially outer surface (ROS) of the radially outermost crown layer and the tread surface; The radial distance (du) between the radial outer surface (ROS) of the radially outermost crown layer and the tread surface, where the directional distance (du) is the distance vertically below the center of the bottom surface of the circumferential fallow closest to the relief. dc) is at least 1.5 mm smaller than
- the minimum radial distance (du) between the radially outer surface (ROS) of the radially outermost crown layer of the crown reinforcement and the tread surface is at most equal to the depth of the nearest circumferential fallow D + 2 mm and at a minimum is equal to the depth of the nearest circumferential fallow D-2mm,
- the part of the tread vertically above the at least one undulation in the radially outermost crown layer comprises at least 30% of the rubber compound M, the dynamic shear modulus G ^* of which is 10% of 10Hz at 40°C; A peak-to-peak strain of equal to 3.25 MPa was achieved by a passenger car tire.

A point on the layer of a reinforcing element is determined if the radial distance between that point and a point on the same crown layer that is vertically below the radially innermost point of the bottom of the nearest main groove exceeds 1 mm. , belongs to the relief in its crown layer. If there are two or more closest main grooves, the test for belonging to an undulation will be performed by considering the main groove that maximizes the radial distance in question. To calculate the radial distance, consider the points of similar reinforcement elements: two points on the neutral axis, two radially outermost points of the reinforcement element and two radially innermost points of the reinforcement element. become.

The properties of the rubber compounds are determined with a viscosity analyzer (Metravib VA40000) according to ASTM standard D 5992-96. A sample of the vulcanized composition, preferably with a thickness of 4 mm and a cross-sectional area of 400 mm, is subjected to a simple alternating sinusoidal shear stress at a frequency of 10 Hz during a temperature sweep from 0 °C to 100 °C under a fixed stress of 0.7 MPa. The response of the cylindrical specimen is recorded. The dynamic shear modulus G ^* is measured at 10% peak-to-peak strain at a given temperature of 40° C. and 10 Hz, also according to ASTM standard D 5992-96. Using the same procedure, the shear modulus G ^* is measured at 90° C., 10 Hz, and under a stress of 0.7 MPa.

In order to improve certain performance aspects, for example dry grip, rubber compounds known to those skilled in the art can be used for specific applications such as motor racing competitions, but these rubber compounds are completely unsuitable for use in passenger cars, even sports cars. Not suitable. This is because passenger cars must comply with specific performance specifications set by environmental standards, such as maximum rolling resistance, minimum wear, durability, grip, and behavior performance. Specifically, these vehicles drive on public roads under driving conditions with different wet surfaces and wet grips than closed competition circuits for very short and ultimately limited mileage. , must be able to run. The owners of these vehicles do not have a team to change the tires in case of rain and after one hour of driving when these tires are worn out. There are design parameters for tires according to the invention, such as the presence of grooves or circumferential fallow in the tread, the ability to cover thousands of kilometers with the tire, and thus sufficient tread pattern depth. Preferably, the grooves and circumferential fallow in the tire constitute a void ratio in the new tread that is at least equal to 10%. Void ratio is measured as the ratio of the volume of voids formed by all cuts in the tread to the tread volume radially outward of the bottom surface of the tread pattern in which the voids are included.

The rubber compound may have poor wear performance due to a low tread pattern height or a normal tread pattern height that does not compensate for the low stiffness of the rubber compound, or a combination of a normal tread pattern height and a low stiffness of the rubber compound. It exhibits low stiffness over a temperature range that is unusable for passenger car tires according to the prior art, even though behavioral performance is unduly compromised due to the combination of If this low rigidity is accompanied by large hysteresis, performance regarding rolling resistance will also be impaired. Therefore, the use of these rubber compounds is itself problematic.

Dynamic shear elasticity at 40°C measured at 10% peak-to-peak strain of 10Hz and equal to a maximum of 3.25 MPa, preferably equal to a maximum of 3 MPa, preferably equal to a maximum of 2.5 MPa Rubber compounds with a modulus G ^* are greatly affected with regard to behavior with tread pattern height, such as exists for example for passenger cars.

Dynamic shear at 90 °C, measured at 90 °C, 10 Hz, under a stress of 0.7 MPa, equal to a maximum of 1 MPa, preferably equal to a maximum of 0.75 MPa, preferably equal to a maximum of 0.5 MPa Rubber compounds with a modulus of elasticity G ^* are highly adversely affected with respect to wear.

The present invention, i.e., by combining the undulations in the radially outermost crown layer with a lower stiffness rubber compound vertically above the undulations, it is possible to use a lower stiffness rubber compound, regardless of the relevant properties aimed at. Become. If this rubber compound of the tread, combined with its low stiffness, has good performance with respect to wear but high rolling resistance, the volume of this rubber compound and the shear height of this rubber compound within the tread are reduced. This makes it possible to use it. Further, according to the present invention, it is possible to find an acceptable rolling resistance value. Similarly, due to the high dry grip combined with the low stiffness of this rubber compound, performance degradation in terms of behavior or wear can be overcome by the present invention.

One of the characteristics characterizing the grip force is the tanδ0 hysteresis value, which represents the tanδ value measured at a temperature of 0° C., 10 Hz, and a stress of 0.7 MPa. A preferred embodiment of the invention is therefore that the rubber compound M has a tan δ0 value of at least equal to 0.5, preferably at least equal to 0.6.

The undulation must necessarily affect the radially outermost layer of the reinforcing element of the crown. The present invention affects behavior, wear and rolling resistance by reducing the volume of rubber compound in the tread vertically above the undulations. The other crown layers and carcass reinforcements may be contoured or non-contoured. To be perceptible, the undulations must affect at least 10% of the surface of the radially outermost crown layer, and the amplitude of the undulations, which can reduce the thickness of the rubber compound, must be at least 1.5 mm. Must be equal. A vertically downward undulation of a single rib of the tread is sufficient for this purpose. The undulations may, for example, be central and symmetrical about the median circumferential surface.

This solution can have advantages with respect to uneven wear or with respect to the axial thrust value depending on the direction of the axial thrust depending on the camber angle of the vehicle. Nevertheless, this single undulation can be located evenly under either rib, in particular under one of the radially outermost ribs. Such a selection can be made by considering the directional or axially symmetrical aspects of the tire and the camber angle of the vehicle for which the tire is intended.

Similarly, the undulations need to be properly positioned relative to the tread pattern depth D for optimal functionality. The minimum radial distance (du) between the radially outer surface (ROS) of the radially outermost crown layer of the crown reinforcement (3) and the tread surface is at most the depth of the nearest circumferential groove (24). equal to D+2 mm and at a minimum equal to the depth of the nearest circumferential groove (24) D-2 mm. For positions too far radially inward, the undulations cannot solve the problem, since the height of the rubber compound vertically above the undulations cannot be sufficiently reduced. If the undulations are positioned too far outward in the radial direction, wear may expose the crown layer and cause durability problems, or a larger portion of the tread may be made thinner to improve rolling resistance. However, this solution is not optimal.

Furthermore, the passenger car tire preferably has a tread pattern depth of at least 6 mm and at most equal to 10 mm. This depth is the maximum depth of the grooves and circumferential fallow in the tread. This depth is typically measured near the tire's equatorial plane. These values are current compromises that include wear, rolling resistance and behavior aspects, among other performance aspects.

The present solution maintains so far that the crown layer is laid on a substantially cylindrical formwork and has a regular curvature with no inflection points in the meridional plane, thus solving problems related to behavior. This goes against the traditional tire manufacturing method. Creating a substantially torus-shaped undulation beneath a rib that is itself toroidal is advantageous from the point of view of ease of manufacture and productivity. Specifically, tooling for manufacturing tires prior to curing typically takes advantage of the tire's axial symmetry, and by creating undulations with the same axial symmetry, standard tire manufacturing methods are It becomes possible to use it.

Relief layers of reinforcing elements subjected to compressive loads are contrary to recommendations to prevent buckling of the structure. Specifically, creating a discontinuity in the radius of curvature creates additional stress, which may result in buckling. However, in tires the loading is very localized, which means that one part of the crown is in compression while another part of the crown is in tension, on a much smaller scale than the undulation scale. Therefore, the undulations created within the scope of the present invention do not impair the durability of the tire.

Due to these undulations, it is no longer intended to improve the rolling resistance and behavior, but with low stiffness, i.e. at 40 °C and 10 Hz, in order to improve the behavior and allowable rolling resistance and increase dry grip. A tread rubber compound with a dynamic shear modulus G ^* at 10% peak-to-peak strain of at most equal to 3.25 MPa, at most 3 MPa, preferably at most 2.5 MPa is used at least vertically above the relief. It becomes possible to do so.

Depending on the desired performance profile and its evolution over time, the rubber compound vertically above the undulations in the radially outermost crown layer may be wholly or partially a rubber compound M with low stiffness and good dry grip. It can be assumed that there is. Preferably, the tread surface has this rubber compound in new condition.

The distance (du) is reduced by creating at least one undulation in the radially outermost crown layer, such that the undulation or the undulating portion of the crown layer is the closest to the undulation in the crown layer vertically below the circumferential fallow. It is arranged to be located radially outward of the undulating portion. It is not a problem to consider a crown layer to be contoured if it is not contoured but meets the criteria of reducing the distance du by reducing the tread pattern depth in a given area. This feature is further known in particular in passenger car tires, where the depth of the tread pattern is smaller at the outer axial edge of the tire, known as the shoulder, than at the nearest circumferential fall. In tires according to the prior art, in the part of the shoulder where the radial distance (du) decreases, the radially outermost crown layer is at the same radius or the part of the same crown layer vertically below the nearest circumferential fallow. radially inside.

The invention also works where the one or more undulations are positioned on one or more portions of one or more shoulders of the tire.

The air gap downward distance (d1) is preferably maintained in the main groove and the circumferential fallow. Grooves or sipes are less sensitive to punctures and impacts from obstacles. They are protected by a rubber compound that gives them their technical characteristics of shallow depth or narrow grooves.

Vertically below the undulations in the radially outermost crown layer, all or part of the other crown layers can be undulated, and the carcass layer can also be undulated depending on the desired structural rigidity of the crown. The radially outermost crown layer must be undulating, with an appropriate thickness of burial placed between it and the radially adjacent crown layer, typically the working layer. By using an embedded rubber compound, it can be the only relief layer. However, two, three or all of the crown layers can also be contoured in this way. A protective layer or hooping layer is optional in the tire and does not affect the advantage of the solution.

10% of the radially outer surface of the radially outermost crown layer is considered to have a measurable performance improvement in the 10% of the tread surface where the rubber compound improves in terms of dry grip. , a radial distance equal to at least 1.5 mm from the radially innermost point of the crown layer vertically below the nearest main groove is sufficient.

The amplitude of this undulation must be at least equal to 1.5 mm to have a significant effect on the tire scale. Thus, over at least 10% of the radially outer surface (ROS) of the crown layer having one or more undulations, the radial distance (du) between the radially outer surface (ROS) of the radially outermost crown layer and the tread surface ) is at least greater than the radial distance (dc) between the radially outer surface (ROS) of the radially outermost crown layer and the tread surface, which is the distance vertically below the bottom center of the main groove closest to the undulations. 1.5mm smaller.

In order to increase the stiffness of the crown and increase the bond between the undulations and the rubber compound M located vertically below the undulation(s), a preferred solution is to use a plurality of crown layers, a radially outermost crown layer and a In contrast, the radially adjacent crown layers, or all of the crown layers, are undulating, in other words they overlap each other substantially over the entire width of the crown, except for the last 3 centimeters at the axial ends. It is at a certain distance. This is because these axial ends are optionally subjected to a debonding process of the rubber compound.

The optimal solution takes into account tire characteristics and possibly vehicle characteristics. Optimization can be performed depending on tire orientation, tire asymmetry, and vehicle camber angle.

Preferably, over at least 10%, preferably at least 20%, and at most 85% of the radially outer surface (ROS) of the radially outermost crown layer, the radially outer surface (ROS) of the radially outermost crown layer and the tread surface The radial distance between the radial outer surface (ROS) of the radially outermost crown layer and the tread surface, where the radial distance (du) between is the distance vertically below the bottom center of the main groove closest to the undulations. distance (dc) by at least 1.5 mm, preferably 2 mm. The design parameters that allow adjustment of the performance aspects of grip, wear, rolling resistance and behavior are:
- The range of the contact surface formed by the low-stiffness, high-grip rubber compound M, as well as the range of undulations in the radially outermost crown layer (the void ratio of the tread pattern is almost never less than 10% or 15%, with the knowledge that it would limit it to a maximum of 85% (100% - 15%). The wider the range of undulations or the more vertically downwardly undulating ribs, the greater the advantage of using a rubber compound in terms of grip and the less its negative impact in terms of rolling resistance. It is therefore possible to adjust the number of undulations and the proportion of low stiffness, high grip rubber compound M depending on the desired performance with respect to dry grip, rolling resistance and dynamic behavior.
- The amplitude of the undulation equal to at least 1.5 mm, but limited to 5 mm due to the radius of curvature imposed on the rigid and therefore less deformable metal working layer (which makes the rolling resistance and dynamic behavior (This makes it possible to adjust the shear force of the tread rubber compound.)

A single rib may represent 15% of the axial width of the radially outermost working layer. It is common to have 3, 4 or 5 ribs, with the fallow corresponding to about 20% of this width.

Therefore, a preferred solution is to provide a radially outer surface (ROS) of the radially outermost crown layer over at least 10%, preferably at least 20% and at most 85% of the radially outer surface (ROS) of the radially outermost crown layer. The radial outer surface (ROS) of the radially outermost crown layer and the tread surface, where the radial distance (du) between by at most 5 mm, preferably at most 3 mm, than the radial distance (dc) between.

In order to obtain optimal performance with respect to punctures and impacts of the crown without penalizing rolling resistance, it is necessary to The radial distance (d1) is at least equal to 1 mm and at most 5 mm, preferably at least equal to 2 mm and at most 4 mm. Below the lower limit, the tire may prove too sensitive to shocks. If the upper limit is exceeded, the rolling resistance of the tire becomes disadvantageous.

Advantageously, the tread, e.g. the main groove of the tread, is provided with at least one wear indicator and the minimum radial distance (du) between the radially outer surface (ROS) of the radially outermost layer of the crown reinforcement and the tread surface. ) is advantageously at least equal to the radial distance (df) between the tread surface and the radially outermost point of the wear indicator. Specifically, the wear indicator allows the user to check tire wear before the radially outermost reinforcing elements of the crown reinforcement begin to appear on the tread surface. This is very important.

Advantageously, all parts of the tread, as well as all parts of the tread surface vertically above the undulations in the radially outermost crown layer (5), are coated with at least 50%, in order to optimize the properties of the rubber compound M. Preferably it comprises 75%, more preferably 100% of rubber compound M.

In a preferred embodiment of the invention, the part of the tread that is radially outward of the wear indicator is composed 100% of rubber compound M in order to take advantage of the properties of rubber compound M until the tire is removed due to wear. .

In order to maximize the advantages of the solution, the undulations of the radially outermost working layer are advantageously located vertically below all ribs of the tread surface.

One preferred solution is to undulate the radially outermost working layer in order to obtain a performance advantage that is commensurate with the increased manufacturing overhead implied by the step of undulating the radially outermost working layer. exists only vertically below the rib of the tread surface that is closest in the axial direction on either side of this surface with respect to the median circumferential surface.

Preferably, the depth D of the main groove is at least equal to 6 mm and at most equal to 10 mm. Tread pattern depths of 6 to 10 mm allow for a good compromise between the performance aspects of wear and rolling resistance in many passenger car tires.

If the radially outermost layer of the reinforcing element of the crown reinforcement is a hooping layer, the radially outermost layer of the reinforcing element of the crown reinforcement is a woven fabric, preferably of the aliphatic polyamide or aromatic polyamide type, of the aliphatic polyamide type. It is advantageous to provide reinforcing elements made of a type comprising a combination of aromatic polyamides and aromatic polyamides, of a type of polyethylene terephthalate or of a type of rayon, these reinforcing elements being parallel to each other and extending in the circumferential direction of the tire (XX' ) forms an angle B equal to maximum 10° in absolute value.

One preferred solution is that at least one potting rubber compound with a radial thickness equal to at least 0.3 mm is positioned vertically below any undulation in the radially outermost crown layer. be. The purpose of this is to allow the crown layer to undulate during manufacturing and curing. These potting rubber compounds can be present all around the tire or placed in specific parts of the tire, as desired. It is possible to lay down a plurality of potting rubber compounds vertically below one or more undulations with different radius values having different properties depending on the tire specification. When a single potting rubber compound is laid, its maximum thickness is, for a given relief, between the radially outermost point of the radially outer surface of the radially outermost crown layer in the relief and the circumferential point closest to the relief. It is approximately equal to the radial distance between the radially outer surface of the radially outermost crown layer located vertically below the center of the bottom surface of the fallow.

If the tread is formed from one or more rubber compounds, the potting rubber compound must have a maximum dynamic loss tan δ1 measured at a temperature of 23° C. and 10 Hz in the radial direction of the bottom surface of the main groove or circumferential fallow. at most equal to, and preferably 30% less than, the maximum dynamic loss tan δ2 of the least hysteretic rubber compound of the outer tread, measured under a stress of 0.7 MPa at a temperature of 23° C. and 10 Hz. It's advantageous. For a potting rubber compound with the same hysteresis, an improvement in rolling resistance is achieved simply by reducing the shear stress loads to which this rubber compound is subjected. Because the potting rubber compound is not subject to the same stresses as the rubber compound from which the tread is made, its properties can be modified to further improve rolling resistance. A 30% reduction in hysteresis leads to a significant improvement with the present invention. The rubber compound with the smallest hysteresis in the tread is the rubber compound that forms the radially outer part of the bottom surface of the tread pattern, and its maximum value of tan δ1 measured under a stress of 0.7 MPa at a temperature of 23°C and 10 Hz. is the smallest of all the rubber compounds that make up the radially outer portion of the bottom of the tread pattern.

Response of a sample of a crosslinked composition (preferably a cylindrical specimen with a thickness of 4 mm and a cross-sectional area of 400 mm) subjected to a simple alternating sinusoidal shear stress at a frequency of 10 Hz and 23 °C according to ASTM Standard D 5992-96 is recorded. A peak-to-peak distortion amplitude sweep is performed from 0.1% to 100% (outward cycle) and then from 100% to 0.1% (return cycle). This result that is utilized is the loss factor (tan(δ)). For the return cycle, the maximum observed value of tan(δ) (tan(δ)max at 23°C) is shown.

The crown reinforcement is preferably constructed of a hooping layer and a working reinforcement with two working layers having opposite angles, as in many current crown constructions.

The features and other advantages of the invention will be better understood with the help of Figures 1 to 4, which are not to scale and have been simplified to make the invention easier to understand. It is depicted as

1 is a partial view of a tire, in particular a structure and tread with grooves and circumferential fallow; FIG. 2 shows a meridional section through the crown of a tire according to the invention, with different radial distances du, d1, D, df, dc and suitable embeddings for creating undulations in the radially outermost crown layer, working layer or hooping layer; This undulation is provided with a low-rigidity rubber compound M vertically above it. shows a meridional section through the crown of a tire according to the invention, with different radial distances du, d1, D, df, dc suitable for creating undulations in the radially outermost crown reinforcement, working layer and hooping layer; An embedding rubber compound (6) is described, the undulations comprising a low stiffness rubber compound M 100% vertically above it and in the part of the tread radially outward of the wear indicator. illustrating a meridional section through the crown of a tire according to the invention, illustrating the different radial distances du, d1, D, df, dc and the undulations in the radially outermost crown reinforcement, working layer or hooping layer, This undulation comprises a low stiffness rubber compound M vertically above it and 100% in the part of the tread radially outward of the wear indicator. These undulations form during the lamination of the different layers of carcass reinforcing elements and crown reinforcing elements before curing or during curing of the tire with a tread volume suitable for creating this type of undulations. It is formed without the use of potting rubber using manufacturing tools designed for this purpose.

FIG. 1 is a perspective view of a portion of the crown of a tire. A Cartesian reference system (XX', YY', ZZ') is associated with each meridian plane. The tire has a tread 2 intended to come into contact with the road surface via a tread surface 21. Arranged in the tread are grooves 24 with a width W, which may vary from groove to groove, and circumferential fallows 25 delimiting the ribs 26. The tire also comprises a crown reinforcement 3 with a working reinforcement 4 and, in this case, for example a hoop reinforcement 5 . The working reinforcement comprises at least one working layer, in this case for example two working layers 41 and 42, each comprising reinforcing elements (411 for the crown layer 41) parallel to each other. Also shown is the radially outer surface (ROS) of the radially outermost working layer (41).

FIG. 2 schematically shows a meridional section through the crown of a tire according to the invention. It particularly illustrates the carcass layer 1 and the undulations (512) of the radially outermost crown layer (5) and the potting rubber compound (6) positioned vertically below the undulations over the entire width of the ribs 26. do. Figure 2 also shows the following radial distances:
D: Groove depth, which is the maximum radial distance between the tread surface (21) and the groove bottom (243).
dc: radial distance between the radially outer surface (ROS) of the radially outermost crown layer (5) and the tread surface (21), which is the bottom surface of the main groove (24) closest to the undulations (512); (243) is measured vertically downward from the radially innermost point.
- du: the minimum radial distance between the radially outer surface (ROS) of the radially outermost crown layer (5) of the crown reinforcement and the tread surface (21).
- df: radial distance between the tread surface (21) and the radially outermost point of the wear indicator (7).
- d1: the minimum distance between the radially outer surface (ROS) of the radially outermost crown layer (5) and the bottom surface (243) of the circumferential fallow (25).

FIG. 3 schematically shows a meridional section through the crown of a tire according to the invention. This is particularly true of the undulations in the crown reinforcement, which consists of two working layers (41 and 42) and, in this case, the radially outermost crown layer, the hooping layer (5), and the vertical alignment of each rib of the tread. The potting rubber compound (6) is shown disposed below the radially outermost working layer (42) vertically below the undulations.

FIG. 4 schematically shows a meridional section through the crown of a tire according to the invention. This, without the use of an embedding rubber compound (6), allows the undulations in the carcass reinforcement, the undulations in the crown reinforcement, which is composed of two working layers (41 and 42), and in this case the radially outermost The undulations in the hooping layer (5), which is the crown layer, are particularly illustrated.

A meridional section through the tire is obtained by cutting the tire in two meridional planes. This cross-section is used to determine the various radial distances, the center of the groove base, and the center of the circumferential fallow.

The present invention was implemented on a tire A of size 305/30ZR20 intended for mounting on a passenger car. The groove depth D of the tread pattern is between 5 mm at the shoulder and 7 mm at the equator, the width W varies between 4 and 15 mm, and the tread includes four circumferential furrows. . The crown reinforcement consists of two working layers whose reinforcing elements form an angle of ±38° with the circumferential direction and a fabric hooping layer whose reinforcing elements form an angle of ±3° with the circumferential direction. The radially outermost crown layer, the hooping layer 5, is undulating under the five ribs of the tread, occupying more than 50% of its surface area. This undulation is created using a potting rubber compound placed radially inward of the radially innermost working layer, the potting rubber compound being arranged more specifically between the carcass layer and the radially innermost crown layer. It is located between. The undulations have an amplitude of 2 mm, i.e. the radial distance (du) between the radially outer surface (ROS) of the radially outermost crown layer (5) and the tread surface in the undulations (512) 2 mm less than the radial distance (dc) between the radial outer surface (ROS) of the outer crown layer (5) and the tread surface (21), these are the circumferential fallows (24) closest to the undulations (512) is the vertically downward distance from the radially innermost point of the bottom surface of The radial distance between the radially outer surface (ROS) of the radially outermost crown layer (5) and the bottom surface (243) of the circumferential fallow (25) is equal to 1.5 mm. The tread is composed of a single rubber compound CC1 with the following characteristics:
- G ^* is measured at 10% peak-to-peak strain of 10 Hz at 40°C and is equal to 2.3 MPa.
- The dynamic shear modulus G ^* was measured at 90°C, 10 Hz, and a stress of 0.7 MPa and is equal to 0.45 MPa.
- tan δ is measured at a temperature of 0° C., 10 Hz, and a stress of 0.7 MPa and is equal to 0.58.

Tire A was compared to tires B and C of the same size having the same characteristics except for:
- Tire B has a flat crown layer and a tread composed of a single rubber compound CC2.
- Tire C has a flat crown layer and a tread composed of a single rubber compound CC1 similar to tire A.

Rubber compound CC2 is not relevant to the present invention, but is a rubber compound suitable for use in treads and has the following properties:
- G ^* is measured at 10% peak-to-peak strain of 10 Hz at 40°C and is equal to 3.3 MPa.
- The dynamic shear modulus G ^* was measured at 90°C, 10 Hz, and under a stress of 0.7 MPa and is equal to 1.05 MPa.
- tan δ is measured at a temperature of 0° C., 10 Hz, and a stress of 0.7 MPa and is equal to 0.48.

The potting rubber compound used to create the undulations of tire A has a dynamic loss tan δ1 measured at a temperature of 23 °C, 10 Hz, and a stress of 0.7 MPa, which is equal to 60% less than the dynamic losses of the rubber compound CC1 from which the tread is made.

The performance aspects of the tire according to the invention can be seen in the table below, with a reference value of 100. A rating of greater than 100 means that the performance of the tire of the present invention is superior to that of the control. A better performance in terms of rolling resistance, thus a rating of over 100, means that the rolling resistance of the tire of the invention is less than that of the control. A dry grip of over 100 means that it takes less time to complete one lap of the test circuit than a control tire.

表１：本発明の性能

Table 1: Performance of the present invention

It is an object of the present invention to enable the use of "soft" or low stiffness rubber compounds in the tread. Prior art tire B serves as a control without a contoured crown layer or low stiffness rubber compound in the tread.

It is evident in Tire C that the use of a prescribed low stiffness rubber compound in a tread based on a flat structure results in unacceptable performance in all performance aspects of rolling resistance, wear and behavior compared to the control Tire B. A decrease occurs and only the dry grip improves. Considering the size for sports applications and its high rolling resistance value, the deterioration in rolling resistance is such that Tire C is no longer acceptable with respect to environmental standards.

The present invention not only makes it possible to improve any deterioration caused by the use of the low stiffness rubber compound CC1, as is evident in tire A, but surprisingly, through the combination of the structure and the low stiffness rubber compound, It makes it possible to improve the dry grip provided a priori by the rubber compound CC1 by a further 25%.

The improvement of the invention with respect to rolling resistance was evaluated on a standard machine for standardized measurements according to ISO 2850:2009.

The behavior was evaluated at 3 bar pressure and high temperature by measuring the characteristic Dz of the Pacijka tire behavior model, which is well known to those skilled in the art.

The tires were also tested on a winding circuit on a sports-type vehicle, which can generate significant lateral loads. A professional driver trained to evaluate tires compares tire A according to the invention with tire B according to the prior art according to a rigorous testing process under the same temperature and road conditions and without knowing the characteristics of the tire being tested. The measurements were repeated in comparison with Tire C. The driver assigned a score to the tire. In all the tests carried out, tire A according to the invention outperformed tires B and C in terms of vehicle behavior, road holding, on dry roads and in terms of grip.

Wear was evaluated in tests where vehicles of the same type followed each other on a given lap circuit representative of a customer's application. The vehicle is driven by a professional driver trained to evaluate the tires in the same type of driving style, under the same temperature and road conditions, without knowledge of the characteristics of the tire being tested, and according to a rigorous testing process; The measurements were repeated. After each test day, the remaining tread pattern height was measured. The wear shown here corresponds to an improvement in post-rolling wear corresponding to 30% of tire life.

Claims (10)

A tire (1) for a passenger car,
A tread (2) intended to contact the road surface via a tread surface (21) provided with grooves (24), said grooves (24) opening into said tread surface (21) and forming a bottom surface ( A space defined by two main side surfaces (241, 242) connected by a tread surface (243) is formed, and a width W defined by the average distance between the two side surfaces (241, 242) and the tread surface (21 ) and a depth D defined by the maximum radial distance between said bottom surface (243);
at least one groove (24) which is a main groove, called a circumferential fallow and is substantially circumferential, with a width W equal to at least 1 mm and a depth D equal to at least 4 mm;
at least two ribs (26);
Equipped with
Said tire (1) also comprises a crown reinforcement (3) with at least one layer of reinforcing elements (41, 42, 5), represented by a crown layer, radially inside said tread (2);
said at least one layer of reinforcing elements (41, 42, 5) extending radially from a radially inner surface (RIS) to a radially outer surface (ROS);
In the tire (1),
the radially outermost crown layer (5) comprises at least one undulation (512) vertically below the rib (26);
The at least one undulation (512) in the radially outermost crown layer (5) is such that the radially outermost crown layer portion (5) of the undulation (512) is located at the periphery closest to the undulation (512). located radially outward of a point of the radially outermost crown layer that is vertically below the center of the bottom surface (243) of the direction fallow (24);
The at least one undulation (512) in the radially outermost crown layer (5) extends over at least 10% of the radially outer surface (ROS) of the radially outermost crown layer (5). The radial distance (du) between the radial outer surface (ROS) of at least 1.5 mm greater than the radial distance (dc) between the radially outer surface (ROS) of the radially outermost crown layer (5) and the tread surface (21), which is a vertically downward distance of It has become smaller,
The minimum radial distance (du) between the radially outer surface (ROS) of the radially outermost crown layer (5) of the crown reinforcement (3) and the tread surface (21) is at most equal to the depth D + 2 mm of the nearest circumferential fallow (24) and at least equal to the depth D - 2 mm of said nearest circumferential fallow (24);
The portion of the tread that is vertically above at least one undulation in the radially outermost crown layer comprises at least 30% of a rubber compound M, the dynamic shear modulus G ^* of which is 10 at 10Hz at 40°C. % peak-to-peak strain equal to a maximum of 3.25 MPa,
A tire characterized by: Said rubber compound M has a dynamic shear modulus G ^* at most equal to 3 MPa when measured at 10% peak-to-peak strain of 10 Hz at 40°C.
The tire according to claim 1. said rubber compound M has a dynamic shear modulus G ^* at most equal to 1 MPa when measured at 90° C., 10 Hz and under a stress of 0.7 MPa;
The tire according to claim 1 or 2. The rubber compound M has a tan δ value of at least equal to 0.5, where tan δ is the tan δ value measured at a temperature of 0° C., 10 Hz, and a stress of 0.7 MPa.
The tire according to any one of claims 1 to 3. said radially outer surface of said radially outermost crown layer (5) over at least 10%, preferably at least 20% and at most 85% of said radially outer surface (ROS) of said radially outermost crown layer (5); The radial distance (du) between (ROS) and the tread surface (21) is the distance vertically below the center of the bottom surface (243) of the nearest circumferential fallow (24). at least 1.5 mm less than the radial distance (dc) between the radially outer surface (ROS) of the outermost crown layer (5) and the tread surface (21);
The tire according to any one of claims 1 to 4. said radially outer surface of said radially outermost crown layer (5) over at least 10%, preferably at least 20% and at most 85% of said radially outer surface (ROS) of said radially outermost crown layer (5); The radial distance (du) between (ROS) and the tread surface (21) is the distance vertically below the center of the bottom surface (243) of the nearest circumferential fallow (24). at most 5 mm less than the radial distance (dc) between the radially outer surface (ROS) of the outermost crown layer (5) and the tread surface (21);
The tire according to any one of claims 1 to 5. The radial distance (d1) between the radially outer surface (ROS) of the radially outermost crown layer (5) and the bottom surface (243) of the circumferential fallow (24) is at least equal to 1 mm and at most is equal to 5mm,
The tire according to any one of claims 1 to 6. At least one main groove (24) of said tread (2) comprises at least one wear indicator (7) and said radially outer surface of said radially outermost crown layer (5) of said crown reinforcement (3). The minimum radial distance (du) between the tread surface (ROS) and the tread surface (821) is the minimum radial distance (du) between the tread surface (21) and the radially outermost point (71) of the wear indicator (7). at least equal to the radial distance (df);
The tire according to any one of claims 1 to 7. the depth D of the main groove (24) is equal to 10 mm at most;
The tire according to any one of claims 1 to 8. at least one potting rubber compound (6) having a radial thickness equal to at least 0.3 mm is positioned vertically below said undulations (512) in said radially outermost crown layer (5);
The tire according to any one of claims 1 to 9.

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