Pneumatic tire with optimized crown and bead architectures

Abstract

A tire comprises, in the central part of its crown, at least one undulation (51) of the radially outermost crown layer, having a radial amplitude A at least equal to 1 mm. At least one bead comprises, aside from the radial carcass layer and the bead wire, a radial reinforcing element that is such that the axial distance between the radial reinforcing element and the axially innermost carcass layer is at least equal to 1 mm and at most equal to 12 mm at the point of the radial reinforcing element that is situated 30 mm from the radially innermost point of the bead wire, for a better trade-off between the stiffness of the undulating crown and of the bead.

Claims

1. A tire comprising: a crown comprising: a tread intended to come into contact with the ground via its tread surface having an axial width L, the tread comprising a tread central part having a width equal to 0.8*L, the tread central part comprising at least two circumferential grooves; and a crown reinforcement, radially on an inside of the tread, comprising at least one crown layer, each crown layer of the at least one crown layer being a layer of reinforcing elements, the crown reinforcement including a working reinforcement comprising at least one working crown layer, the reinforcing elements of each working crown layer being at least partially metallic, coated with an elastomeric material, and parallel to one another, and making, with a circumferential direction of the tire, an oriented angle of which an absolute value is at least equal to 15 and at most equal to 50, each crown layer of the at least one crown layer extending radially from a radially inner surface to a radially outer surface, a radially outermost crown layer vertically beneath the tread central part comprising at least one central undulation, with a radial amplitude A at least equal to 1 mm, each at least one central undulation of the radially outermost crown layer being such that the portion of a radially outer surface of the radially outermost crown layer in the central undulation is radially outside of those points of the radially outermost crown layer vertically beneath the bottom face of a circumferential groove closest to the central undulation; two beads intended to come into contact with a rim and two sidewalls connecting the crown to the beads, each bead having at least one bead wire comprising circumferential metal reinforcing elements, wherein each bead of the two beads comprises a radial reinforcing element; at least one carcass layer including an axially innermost carcass layer, the at least one carcass layer being radially inside of the crown reinforcement layer and connecting the two beads, the axially innermost carcass layer comprising textile reinforcing elements coated in an elastomeric material, the textile reinforcing elements being nonmetallic, being parallel to one another, and making, with a radial direction of the tire, an angle of which an absolute value is at most equal to 15; and a bead filler rubber, for each bead of the two beads, positioned between the carcass layer and the radial reinforcing element of each bead of the two beads, the radial reinforcing element of each bead of the two beads comprising textile reinforcing elements coated in an elastomeric material, the textile reinforcing elements being nonmetallic, being parallel to one another, and making, with the radial direction of the tire, an angle of which an absolute value is at most equal to 15, in each bead of the two beads a radially innermost point of the radial reinforcing element being at a radial distance at most equal to 20 mm from a radially innermost point of the at least one bead wire, and in each bead of the two beads a point of the radial reinforcing element being radially outside of, and at a radial distance at least equal to 40 mm from, the radially innermost point of the at least one bead wire, wherein an axial distance between the radial reinforcing element of each bead of the two beads and the axially innermost carcass layer is at least equal to 1 mm and at most equal to 12 mm at the point of the radial reinforcing element that is situated 30 mm from the radially innermost point of the at least one bead wire, wherein the bead filler rubber, for each bead of the two beads, has an axial thickness at least equal to 1 mm at the point of the radial reinforcing element that is situated 30 mm from the radially innermost point of the at least one bead wire, and wherein the bead filler rubber, for each bead of the two beads, comprises at least one rubber compound having a secant extension modulus MA10 at 10% strain, measured at 23 C. in accordance with standard ASTM D 412 at least equal to 5 MPa.

2. The tire according to claim 1, wherein one of the two beads is intended to be positioned on an exterior side of a vehicle to which the rim is attached, and, in the one of the two beads, the axial distance between the radial reinforcing element and the axially innermost carcass layer is at least equal to 3 mm and at most equal to 12 mm at the point of the radial reinforcing element that is situated 30 mm from the radially innermost point of the at least one bead wire.

3. The tire according to claim 1, wherein the at least one rubber compound is two rubber compounds, a first rubber compound of the two rubber compounds being radially on an inside of a second rubber compound of the two rubber compounds, and the first rubber compound having a secant extension modulus MA10 at 10% strain, measured at 23 C. in accordance with standard ASTM D 412 at least equal to the secant extension modulus MA10 at 10% strain, measured at 23 C. in accordance with standard ASTM D 412, of the second rubber compound.

4. The tire according to claim 1, wherein each bead of the two beads includes at least one bead reinforcement layer, comprising reinforcing elements, making with the radial direction, an angle comprised, in terms of absolute value, between 10 and 60, and being situated between the axially innermost carcass layer and the radial reinforcing element.

5. The tire according to claim 1, wherein the radial reinforcing element of each bead of the two beads is made up of a turned-back strand of the axially innermost carcass layer.

6. The tire according to claim 1, wherein axially innermost points of the radial reinforcing element of each bead of the two beads are axially on an inside of a respective axially outermost point of the at least one crown layer and on a same radius as the reinforcing elements of a radially innermost carcass layer of the at least one carcass layer.

7. The tire according to claim 1, wherein the radial reinforcing element is a second carcass layer connecting the two beads, the second carcass layer comprising nonmetallic textile reinforcing elements coated in an elastomeric material, which are parallel to one another and make, with a radial direction of the tire, an angle of which an absolute value is at most equal to 15.

8. The tire according to claim 7, wherein the two carcass layers are situated on a same radii for all points axially on an inside of axially outermost points of the at least one crown layer and radially on an outside of axially outermost points of the tire.

9. The tire according to claim 1, wherein the at least one central undulation of the radially outermost crown layer is such that, over at least 10% of the radially outer surface of the radially outermost crown layer vertically beneath the tread central part, a radial distance between the radially outer surface of the radially outermost crown layer and the tread surface at each at least one central undulation is at least 1 mm less than a radial distance between the radially outer surface of the radially outermost crown layer and the tread surface vertically beneath the bottom face of a circumferential groove closest to the respective central undulation.

10. The tire according to claim 1, wherein the part of the axially innermost carcass layer vertically beneath the tread central part is radially outside of all the points of the axially innermost carcass layer vertically beneath axial ends of the at least one crown layer.

11. The tire according to claim 1, wherein a minimum radial distance between the radially outer surface of the radially outermost crown layer and the tread surface is at most equal to a depth D of the circumferential groove closest to the at least one central undulation plus 2 mm and at least equal to the depth D of the circumferential groove closest to the at least one central undulation minus 2 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The features and other advantages of the invention will be understood better with the aid of FIGS. 1 to 9, said figures not being drawn to scale but in a simplified manner so as to make it easier to understand the invention:

(2) FIG. 1 shows a meridian half-section through the crown of a tyre according to the invention, having undulations. It illustrates the radial amplitude A of an undulation (51) of the radially outermost crown layer 5, the various radial distances do, d1, D, df, dc and a filler material, referred to as crown filler (6) suitable for creating an undulation, notably in the radially outermost crown layer.

(3) FIGS. 2 to 9 depict nonlimiting examples of the beads and sidewall according to the invention.

(4) A meridian section through the tyre is obtained by cutting the tyre on two meridian planes. This section is used to determine the various radial and axial distances mentioned.

(5) FIG. 1 depicts a portion of the crown of a tyre. It depicts a carcass layer 9, radially on the inside of the crown layer 3, comprising a working reinforcement 4 comprising, in this instance, two working layers 41 and 42, made up of reinforcing elements which are at least partially metallic, coated with an elastomeric material, parallel to one another and which make, with the circumferential direction (XX) of the tyre, an oriented angle of which the absolute value is at least equal to 15 and at most equal to 50, and a hooping layer 5. The tyre also comprises a tread 2, delimited by the tread surface 21 and the exterior lateral surfaces 26 and comprising cuts, which in this instance include two circumferential grooves 24 having widths at least equal to 6 mm. A circumferential groove may be made of a succession of cuts making a non-zero angle with the direction XX and connected to one another in such a way as to form a cut that is continuous over the entire circumference of the tyre.

(6) FIG. 1 shows how the width L of the tread is determined. The width L of the tread is determined on a tyre, mounted on a nominal rim and inflated to the nominal pressure. In the event of an obvious boundary between the tread surface and the rest of the tyre, the width of the tread is easily determined as a trivial matter by a person skilled in the art If the tread surface 21 is continuous with the exterior lateral surface 26 of the tyre, the axial limit of the tread passes through the point at which the angle between the tangent to the tread surface 21 and an axial direction YY is equal to 30. When, in a meridian plane, there are several points for which said angle is equal to 30, it is the radially outermost point that is adopted. The width of the tread is equal to the axial distance between the two axial limits of the tread surface on either side of the equatorial plane.

(7) FIG. 1 in particular illustrates undulations of all the layers of the crown reinforcement (3), including the working layers (41, 42) and the radially outermost crown layer (5) using a filler material (6) positioned between the carcass layer (9) and the radially innermost working layer (42). This filler material causes all of the crown layers 41, 42, 5 to undulate and therefore creates an undulation 51 in the hooping layer 5 that is the radially outermost of the crown layers.

(8) FIG. 1 also illustrates the following radial distances: D: the depth of a circumferential groove (24), which is the maximum radial distance between the tread surface (21) and the bottom face of the groove (not including retreading wells), dc: the radial distance between the radially outer surface (ROS) of the radially outermost crown layer (5) and the tread surface (21), which is the distance vertically beneath the radially innermost point of the bottom face of the circumferential groove (24), do: the radial distance between the radially outer surface (ROS) of the radially outermost crown layer (5) and the tread surface (21) at the undulation (51), d1: the minimum distance (d1) between the radially outer surface (ROS) of the radially outermost crown layer (5) of the crown reinforcement (3) and the bottom face of the circumferential grooves (24), df: the radial distance between the tread surface (21) and the radially outermost point of the wear indicator (11), A: the radial amplitude of the undulation measured for a given undulation between the radially outermost point of said undulation and the radially innermost point situated vertically beneath the closest circumferential groove 24.

(9) FIG. 2 depicts the beads and sidewalls of the same tyre, the asymmetry of which is connected with the direction of rotation of the tyre. The bead BE is positioned on the exterior side of the vehicle and the bead BI is positioned on the interior side of the vehicle. Special markings on the sidewall of the tyre allow the user to position the tyre correctly. The exterior bead needs to be stiffened because it is liable to be the most highly stressed under the most stress-inducing conditions, namely under high-speed cornering at the limits of grip of the tyre. Under such circumstances, the overload and the deformation are the greatest on the tyre that is on the exterior side of the vehicle and on the vehicle-exterior side of the tyre. Stiffening both beads may be beneficial in terms of behaviour, but this will come at a cost in terms of rolling resistance. In FIG. 2, the beads BE, BI comprise, aside from the carcass layer 9, a radial reinforcing element 95, possibly a second carcass layer, and a bead wire 92, in this instance of multi-linear cross section, therefore made up of at least two windings of elementary metal wires that are substantially parallel to at least one carcass layer. Only the exterior bead is such that the radial reinforcing element 95 is at a radial distance db at least equal to 1 mm and at most equal to 12 mm, at the point of the radial reinforcing element that is situated 30 mm from the radially innermost point of the bead wire, so as to generate a beam effect stiffening this bead. For tyres the sidewalls of which do not indicate a preferred direction of mounting, both of the beads would have the aforementioned feature present in the exterior bead (BE). The solution depicted shows a rubber compound, or filling rubber, referred to as bead filler 97, positioned between the carcass layer and the radial reinforcing element.

(10) The bead BI is a standard bead that is optimized if it is associated with a crown having no undulations in its crown layers. It notably performs well in terms of rolling resistance, because shearing between the carcass layer 9 and the carcass reinforcing element 95 is practically nil in bending.

(11) FIGS. 3 to 9 illustrate variants of the beads according to the invention, entirely nonlimitingly.

(12) FIG. 3 depicts a bead with a multi-linear bead wire having three windings of elementary metal wires substantially parallel to at least one carcass layer, the carcass layer 9, the radial reinforcing element 95 which in this instance is possibly a second carcass layer.

(13) FIG. 4 illustrates a bead in which the bead wire is a bead wire with a polygonal cross section and the radial reinforcing element 95 is made up of the turned-back strand of the carcass layer. The bead filler is made up of two filler rubbers 971 and 972. The first rubber compound 971 is radially on the inside of the second rubber compound 972, and the first rubber compound 971 has a secant extension modulus MA10 at 10% strain, measured at 23 C. in accordance with standard ASTM D 412 at least equal to the secant extension modulus MA10 at 10% strain, measured at 23 C. in accordance with standard ASTM D 412, of the second rubber compound 972. These two features are combined only for the purposes of illustration. For example, the feature whereby there are two different rubber compounds may be associated with bead wires that are multi-linear.

(14) FIG. 5 illustrates a bead in which the bead wire is a bead wire with a polygonal cross section and the radial reinforcing element 95 is made up of the turned-back strand of the carcass layer with a second carcass layer 91.

(15) FIG. 6 is a variant of FIG. 5, in which the carcass turned-back strand is in intimate contact with the carcass layer 9. In this configuration, since the second carcass layer 95 is also a carcass reinforcing element, the essential feature of the invention is present.

(16) FIG. 7 is a variant in which, since the carcass turned-back strand is too short, it is the second carcass layer that is the carcass reinforcing element used to stiffen the bead by creating a beam effect. The bead according to FIG. 7 also comprises a bead reinforcing layer 96. This bead reinforcing layer comprises reinforcing elements, making with the radial direction an angle which in terms of absolute value is comprised between 10 and 60. These reinforcing elements are situated between the carcass layer and the radial reinforcing element, particularly at the point on the radial reinforcing element that is situated 30 mm from the radially innermost point of the bead wire.

(17) FIG. 8 is a variant of FIG. 7 in which the second carcass layer is the radial reinforcing element 95 and is in intimate contact with the radially innermost carcass layer 9 on its interior part but satisfies the feature of the invention in the bending zone where stiffness is needed.

(18) FIG. 9 is another variant nonlimitingly illustrating the possibility of the bead comprising other types of reinforcer, here by way of example a textile reinforcer 98 in intimate contact with the carcass layer 9 in the lower part of the bead near the bead wire so as to improve the performance of the tyre in terms of the peeling of the carcass layer in the event of excessive brake temperature.

(19) Tests were conducted in order to compare various solutions: Tyres of type A, the beads of which each comprise two multi-linear bead wires clamping within the bead a single carcass layer. The crown layers of these tyres have no undulations. They are referred to in Table 1 as flat crown, soft bead. Tyres of type B, the beads of which comprise three multi-linear bead wires clamping within the bead two carcass layers as illustrated in FIG. 3. These beads are stiffened in comparison with the beads of the tyres of type A, by the insertion of a bead filler 97 positioned between the carcass layer and the radial reinforcing element, having an axial thickness equal to 5 mm. It is made up of a rubber compound having a secant extension modulus MA10 at 10% strain, measured at 23 C. in accordance with standard ASTM D 412 equal to 7 MPa. The crown layers of these tyres have no undulations. They are referred to in Table 1 as flat crown, stiff bead. Tyres of type C, the beads of which are identical to the beads of the tyres of type A, soft, and the crown layers of which have undulations. They are referred to in Table 1 as undulating crown, soft bead. Tyres of type D according to the invention, the beads of which are identical to the stiff beads of the tyres of type B, and the crown layers of which have undulations. They are referred to in Table 1 as undulating crown, stiff bead.

(20) The tyres of types A, B, C, D are available in 1 single size 305/30R20 intended to be fitted to the driven rear axleset of a passenger vehicle. The tyres of the front axleset of the vehicle are identical in the behaviour tests. They are not a variable of the experiment.

(21) The various components of the tyres A, B, C, D are identical in terms of nature and properties. The architecture, the properties of the reinforcing elements of the various reinforcing layers and the density thereof are identical. The rubber compounds for the various parts of the tyres are also identical with the exception of the bead filler (97) which is present only in tyres B and D and the crown fillers (6) capable of creating undulations in the crown layers, which are present only in tyres C and D.

(22) The tread patterns for tyres A, B, C, D are identical. The depths D of the grooves of the tread pattern are between 5 mm at the shoulders and 7 mm at the equator, for widths W that vary between 4 and 15 mm, the tread containing 4 circumferential grooves. The crown reinforcement is made up of two working layers, the reinforcing elements of which make an angle of + or 38 with the circumferential direction, and of a textile hooping layer, the reinforcing elements of which make an angle of near 0 with the circumferential direction.

(23) For tyres of type C and D, the radially outermost crown layer, the hooping layer 5, is undulated under the 5 ribs of the tread, making up more than 50% of its surface area. The undulations are made with the aid of crown filling rubbers (6) radially on the inside of the radially innermost working layer, said filling rubbers being situated more specifically between the carcass layer and the radially innermost crown layer. The undulations have radial amplitudes of 2 mm, meaning that the radial distances (du) between the radially outer surface (ROS) of the radially outermost crown layer (5) and the tread surface at the undulations (51) are 2 mm less than the radial distances (dc) between the radially outer surface (ROS) of the radially outermost crown layer (5) and the tread surface (21), these being the distances vertically beneath the radially innermost point of the bottom face of the circumferential grooves (24) closest to said undulations (51). The radial distance (d1) between the radially outer surface (ROS) of the radially outermost crown layer (5) and the bottom face of the circumferential grooves (24) is equal to 1.5 mm.

(24) The tyres were tested for rolling resistance and to assess behaviour, in terms of response time and subjective damping.

(25) The improvement of the invention in terms of rolling resistance was evaluated on a standard machine for measurements standardized in accordance with ISO 2850:2009.

(26) The response time was tested on a vehicle (Ferrari 488 GTB) by a professional driver trained for this test, on a straight of a motor racing circuit at a speed of 140 km/h. The driver applies a determined amount of steering lock in a very short given time and assesses the time lag between the steering wheel input and the lateral acceleration of the vehicle thus generated. The shorter the time lag, the better the performance. The measurement may also be conducted using accelerometers.

(27) The same measurements can be used to evaluate the damping, which is assessed subjectively by the driver who assesses the amplitude of the first oscillation, the number of oscillations, the time taken for the driver to stop perceiving oscillations about the intended path as a result of the step steering input the driver has applied. Good damping performance is associated with a low-amplitude first oscillation, a low number of oscillations felt, and a short time needed to stop perceiving the oscillations. These criteria are weighted on a score chart dependent on the vehicle and on the associated features that the manufacturer of said vehicle wishes to offer.

(28) TABLE-US-00001 TABLE 1 Response Subjective Rolling Tyre Crown Bead time damping resistance A flat soft 100 100 100 B flat stiff 102 109 94 C undulating soft 108 92 110 D invention undulating stiff 110 101 104

(29) Table 1 gives the performance of the tyres according to the various tests. Any performance higher than 100 is better than the performance of control tyre A considered by the manufacturer to be a reference.

(30) By only stiffening the bead and keeping the crown flat, tyre B is substantially equivalent to the control in terms of the response time which is essentially associated with the working of the crown. It is 9% better in damping because of the stiffness of the bead. However, the increase in bead thickness leads to a 6% drop-off in terms of rolling resistance.

(31) By only undulating the crown layers and keeping a soft bead, tyre C is 8% better in comparison with the control A in terms of response time. Tyre C is 8% worse in damping, because the interaction between the undulating crown and the bead leads to impaired performance. The undulating crown leads to a 10% improvement in rolling resistance.

(32) By undulating the crown layers and combining this with a stiff bead, tyre D according to the invention is 10% better in comparison with the control A in terms of response time. Tyre D is substantially equivalent to the control in terms of subjective damping, thanks to the interaction between the undulating crown and the stiff bead. The undulating crown provides a 4% improvement in rolling resistance, in spite of the bead thickness having been increased in comparison with the control A.

(33) Thus, only tyre D according to the invention provides an uncompromised improvement in performance over the control tyre A.