TIRE HAVING OPTIMIZED PERFORMANCE IN TERMS OF ROLLING RESISTANCE WITHOUT IMPAIRING THE INDUSTRIAL PERFORMANCE

Abstract

The rolling resistance of a tire has been improved without degrading industrial performance. The sidewall (30) consists of two sub-layers. A first sub-layer (FE1) of thickness E1 and volume V1 provides the expected protection functions of a sidewall as the outer wall of the tire, and a second sub-layer of the sidewall (FE2) of thickness E2 and volume V2 is optimized at low hysteresis to improve rolling resistance. The ratio V1/(V1+V2) of the volumes of the two sub-layers (FE1, FE2) is less than or equal to 0.3. The elongation at break of the compound of FE1 is greater than or equal to 200% measured at a temperature of 100? C., and the viscoelastic loss of the compound of FE2, Tan(?)max, is less than or equal to 0.10.

Claims

1.-15. (canceled)

16. A tire (1) for a passenger vehicle comprising in a meridian plane: two beads (50) intended to be mounted on a rim, two sidewall layers (30) connected to the beads (50), a crown (20) comprising a tread (10), the crown (20) having a first side connected to a radially outer end of one of the two sidewall layers (30) and having a second side connected to a radially outer end of the other of the two sidewall layers (30); and at least one carcass reinforcement (90) extending from the two beads (50) to the crown (20), the at least one carcass reinforcement (90) comprising a plurality of carcass reinforcement elements and being anchored in the two beads (50) by a turn-up around an annular reinforcement structure (51), so as to form in each bead a main part (52) and a turn-up (53), wherein each sidewall layer (30) consists of two axially superposed sub-layers (FE1, FE2), a first sidewall sub-layer (FE1) delimited by a first axially outermost side constituting a lateral wall of the tire in contact with ambient air, and a second axially inner side defined such that the sidewall sub-layer (FE1) has an average axial thickness E1, and occupying a volume V1, and a second sidewall sub-layer (FE2), a first side of which coincides with the second axially inner side of the first sidewall sub-layer (FE1), and a second, axially inner side of which is at least partially in contact with the carcass reinforcement (50), the sidewall sub-layer (FE2) having an average axial thickness E2, and occupying a volume V2, wherein the thickness E1 of the first sidewall sub-layer (FE1) is greater than or equal to 0.7 mm, wherein a ratio V1/(V1+V2) is less than or equal to 0.3, wherein an elongation at break of an elastomer compound constituting the first sidewall sub-layer (FE1) is greater than or equal to 200% measured at a temperature of 100? C., and wherein a viscoelastic loss of the second sidewall sub-layer (FE2), Tan(?) max, is less than or equal to 0.10.

17. The tire (1) according to claim 16, wherein an elastic shear modulus of the second sidewall sub-layer FE2 is in a range [1.5; 10] MPa.

18. The tire (1) according to claim 16, each bead (50) comprising a filling layer (70) comprised at least in part between a main part of the carcass reinforcement (52), the turn-up (53) of the carcass reinforcement and a radially outer portion of the annular reinforcement structure, wherein an elastomer compound constituting the filling layer has a viscoelastic loss Tan(?)max of less than or equal to 0.1.

19. The tire according to claim 16, wherein each bead comprises a lateral reinforcement layer (60) consisting of an elastomer compound occupying a volume comprised at least in part between the second sidewall layer (30) and the turn-up (53) of the carcass reinforcement.

20. The tire (1) according to claim 19, wherein the lateral reinforcement layer (60) of each bead consists of an elastomer compound a viscoelastic loss Tan(?)max of which is less than or equal to 0.10.

21. The tire (1) according to claim 16, in each bead (50) a rim contact curve comprising points of the tire (1) in contact with the rim (100), the rim contact curve connecting a first point Ml of the tire positioned outermost axially, and in contact with the rim, and a second point M2 of the tire in contact with the rim and situated in a middle of a rectilinear portion (130) connecting a flange (120) to a seat (110) of the rim, the tire (1) further comprising two sections in a vertical meridian section of the tire when inflated, mounted on a rim, and compressed against the ground by a vertical load (250), where the vertical load and an inflation pressure are determined in a specification standard, a first section being located in a contact area and a second section being located on an opposite side to the first section in relation to an axis of rotation of the tire, in the first section located in the contact area, in at least a first bead, a length of the rim contact curve, LADC, being measured, and in the second section located opposite the contact area in relation to the axis of rotation of the tire, in at least a second bead, a length of the rim contact curve, LCJ, being measured, wherein a ratio of difference in the lengths of the rim contact curves of the two sections, 100*(LADC?LCJ)/LCJ, is greater than or equal to 30%.

22. The tire (1) according to claim 21, wherein the ratio of the difference in the lengths of the rim contact curves of the two sections, 100*(LADC?LCJ)/LCJ, is greater than or equal to 40%.

23. The tire (1) according to claim 16, a distance DRB being a radial distance from a radially outer end of the filling layer (70), wherein the distance DRB is less than or equal to 50% of a radial height H of the tire (1).

24. The tire (1) according to claim 19, a distance DRI being a radial distance from a radially inner end of the lateral reinforcement layer (60) to a straight line (HH), wherein the radial distance DRI is in a range [5%; 20%] of a radial height H of the tire (1).

25. The tire (1) according to claim 19, a distance DRL being a radial distance from a radially outer end of the lateral reinforcement layer (60) to a straight line (HH), wherein the radial distance DRL is greater than or equal to 25% of a radial height H of the tire (1).

26. The tire (1) according to claim 16, wherein the turn-up (53) of the carcass reinforcement (90) is pressed against the main part (52) of the carcass reinforcement (90) over its entire height radially externally.

27. The tire (1) according to claim 16, wherein the tire further comprises a reinforcement of the bead (50) axially externally to the turn-up (53) of the carcass reinforcement (90), and axially internally to the sidewall (30).

28. The tire (1) according to claim 19, wherein an elastomer compound constituting at least one layer among the filling layer (70), the lateral reinforcement layer (60), and the sidewall sub-layer (FE2) has a composition based on a diene elastomer, a crosslinking system, a reinforcing filler, and carbon black type N550, at an overall rate of between 50 and 75 phr.

29. The tire (1) according to claim 28, wherein an elastomer compound constituting the filling layer (70), an elastomer compound constituting the lateral reinforcement layer (60), and an elastomer compound constituting the sidewall sub-layer (FE2) have the same composition.

30. The tire (1) according to claim 16, wherein the two sidewall sub-layers (FE1, FE2) are manufactured by a co-extrusion process.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0101] Other details and advantageous features of the invention will emerge below from the description of the exemplary embodiments of the invention with reference to the figures which represent meridian views of diagrams of a tyre according to embodiments of the invention. In order to make them easier to understand, the figures are not shown to scale.

[0102] FIG. 1 comprises a view 1-A which shows a section of a tyre of the invention in a meridian plane, and a view 1-B which represents a magnification of a portion of the meridian view 1-A surrounded by a dashed circle showing the bead of a tyre of the invention.

[0103] FIGS. 2-A, 2-B, 2-C and 2-D show embodiments of the invention with modifications to the outer profile of the sidewall layers (FE1, FE2) to facilitate contact with the rim.

[0104] FIG. 3 shows a meridian section of the inflated tyre, mounted on a rim and compressed by a carried load. There can be seen a first section in the contact area and a second section opposite the contact area with respect to the axis (OY). This figure illustrates the determination of the rate of variation in contact with the rim.

[0105] FIGS. 4-A and 4-B show the visualization of the main dimensions of the bead of the tyre.

DETAILED DESCRIPTION OF THE INVENTION

[0106] The invention was implemented on a passenger vehicle tyre of size 245/45R18, according to the ETRTO (European Tyre and Rim Technical Organisation) specification standard. Such a tyre can carry a load of 800 kilos, inflated to a pressure of 250 kPa.

[0107] In FIG. 1-A, the tyre of general reference 1 comprises a carcass reinforcement 90 consisting of reinforcers coated with rubber composition, and two beads 50 in contact with a rim 100. A zone 49 delimited by a dotted circle defines one of the two beads 50 of the tyre, a magnification of which is proposed in FIG. 1-B. The carcass reinforcement 90 is anchored in each of the beads 50. The tyre further comprises a crown reinforcement 20 comprising two working layers 21, 22 and a hooping layer 23. Each of the working layers 21 and 22 is reinforced by filamentary reinforcing elements which are parallel in each layer and crossed from one layer to the other, making angles of 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 circumferentially oriented reinforcement elements wound in a spiral. A tread 10 is laid radially on the hooping layer 23; it is this tread 10 which ensures the contact of the tyre 1 with the ground. The tyre 1 depicted is a tubeless tyre: it comprises an inner liner 95 made from a rubber composition impermeable to the inflation gas, covering the inner surface of the tyre.

[0108] The sidewall layer 30 comprises two sub-layers (FE1, FE2). The first sub-layer FE1 is positioned axially externally so as to constitute the lateral wall of the tyre in contact with the ambient environment. The second sub-layer FE2 32 is in contact at least in part with the carcass reinforcement 90. In FIGS. 1-A and 1-B, the first sub-layer FE1 has a dark background, while the second sub-layer FE 2 has a hatched background.

[0109] The part of the rim 100 which interacts with the tyre in the context of the invention is axisymmetric with respect to the axis of rotation of the tyre.

[0110] In a meridian plane, the rim 100 comprises at least one flange 120 situated at an axial end, and connected to a seat 110 which is intended to receive a face of the bead situated radially innermost. A rectilinear portion 130 that connects the rim flange 120 to the seat 110 via fillets is located between the seat 110 and the flange 120. The flange 120 of the rim extended by the rectilinear portion 130 axially limits the movement of the beads during inflation.

[0111] The bead 50 comprises in part a carcass reinforcement 90 which comprises a main part 52, then winds around an annular reinforcement structure 51 to form a turn-up 53. A filling layer 70 is positioned between the main part 52 of the carcass reinforcement 90 and its turn-up 53. Depending on the embodiment, the bead 50 can comprise a lateral reinforcing layer 60, positioned axially outside the turn-up 53 and axially inside the sidewall layer 30. Axially innermost to the bead 50, a leaktight layer 95 constitutes the inner wall in contact with the internal inflation air.

[0112] Said bead 50 also comprises a protective layer 80 which is in axially external contact with a rectilinear portion 130 of the rim so as to limit the axial displacement of the bead. Said protective layer 80 also comprises a portion intended to be in contact with the rim on the rim seat 110. A sidewall layer 30 interacts with the bead 50 and forms an outer lateral wall.

[0113] FIG. 2-A shows the outer profiles of a bead 50 of a tyre according to a particular embodiment of the invention in comparison with that of a tyre of conventional design. The bead 50 is represented in a section opposite the contact area. The two profiles differ in an area at the rim flange 120. Reference 30 indicates the profile of a tyre of the prior art, and reference 35 shows the modification of the profile made on the tyre of the invention to facilitate contact with the rim 100.

[0114] In FIG. 2-B, we have the same representation as in FIG. 2-A, but the profiles are shown at the centre of the ground contact area. The tyre is in contact with the entire rim flange 120, unlike in FIG. 2-A. The rate of variation in rim contact reflects this change in the rim contact.

[0115] In another embodiment shown in FIG. 2-C, there is a cushion of elastomer compound 40 (modification located at the radially inner end of the sidewall 30), intended to be in contact with the rim flange 120. The cushion of compound 40 is delimited radially on the inside by a curve that closely follows the profile of the rim flange 120. A first side of the cushion of elastomer compound 40 has an appropriate geometric shape that anticipates contact with the curvature of the rim flange so as to closely follow the shape of the rim flange 120 upon contact, a second side of the cushion of elastomer compound extends an outer side of a sidewall in contact with the ambient air, a third side of the cushion of elastomer compound 40 is in contact with the radially inner end of the sidewall and finally a fourth side of the cushion of elastomer compound is in contact with the protective layer 80.

[0116] In FIG. 2-C, the rim contact curve extends from a first point M1 of the tyre positioned axially outermost, and in contact with the rim, and a second point M2 of the tyre also in contact with the rim and situated in the middle of the rectilinear portion connecting the flange 120 to the seat 110 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.

[0117] FIG. 2-D is a variant of the preceding embodiment characterized by the presence of a lateral reinforcement layer 60 of the bead 50, positioned axially externally to the turn-up 53 of the carcass reinforcement 90, and axially internally to the sidewall layer 30.

[0118] FIG. 3 is a view in the vertical plane of a tyre of the invention according to a preceding embodiment. The tyre is inflated, mounted on a rim 100 and compressed by the load carried 250 against the ground 200. There can be seen a first meridian section in the contact area and a second meridian section opposite the contact area. In the first section located in the contact area, in at least a first bead, the length of the rim contact curve 100, LADC, is measured. The length of the rim contact curve, LCJ, is also measured in the second section, in at least a second bead. The ratio of the difference in the lengths of the rim contact curves of the two sections, i.e. 100*(LADC?LCJ)/LCJ, is greater than or equal to 30%, and in this case is equal to 62%.

[0119] In FIG. 4-A, the determination of the height H is illustrated. The height H of the tyre is the normal distance between a first straight line HH parallel to the axis of rotation of the tyre and tangent to the radially innermost point of the annular reinforcement structure, and between a second straight line DD also parallel to the axis of rotation of the tyre and passing through the radially outermost point of the tread. The radial height H is measured on the tyre mounted on a rim and inflated to a reference pressure in accordance with the ETRTO (European Tyre and Rim Technical Organisation) specifications.

[0120] FIG. 4-B shows the geometrical parameters of the bead in connection with the invention. The heights are defined from the straight line HH, which is tangent to the bead wire 51 at its radially innermost point:

[0121] DRI is the radial distance with respect to HH from the radially inner end of the lateral reinforcement layer 60. The radial distance DRI is less than or equal to 20% of the radial height H of the tyre, and is equal to 5 mm in the example presented here;

[0122] DRL is the radial distance with respect to the straight line HH from the radially outer end of the lateral reinforcement layer 60. The radial distance DRL is greater than or equal to 25% of the radial height H of the tyre and is equal to 38 mm in the example presented here;

[0123] DRR is the radial distance with respect to HH from the end of the turn-up of the carcass reinforcement 90. The radial distance DRR being greater than or equal to 10% of the radial height H of the tyre and equal to 20 mm in the example presented here;

[0124] DRB is the radial distance with respect to HH from the radially outer end of the filling layer 70, and is 28 mm in the example presented here.

[0125] Table No. 1 below gives the compositions of elastomer compounds of a tyre of the invention. The main compounds used are listed by expressing for each the main ingredients expressed in phr (part by weight per hundred parts by weight of elastomer):

TABLE-US-00001 TABLE 1 Elastomer Reinforcing NR Elastomer filler - (Natural BR carbon Reinforcing rubber) (Butadiene) black Antioxidant Sulphur Accelerator resin Hardener M1 100 0 75 1.5 8.5 0.95 12 4.18 (N326) M2 100 0 75 2 7.5 0.97 12 6.8 (N326) M3 35 65 30 (N550) 1.3 8.0 4.75 0 0 10 (Silica) M4 35 65 48 5 1.4 1.4 18 0 (N550)

[0126] The compounds of the invention used in this example are based on natural rubber elastomer, or a blend of natural rubber and butadiene for compounds M3 and M4, reinforced with carbon black. Plasticizers (reinforcing resin) are incorporated into the composition to facilitate the processability of the compounds. The compounds also comprise vulcanization agents, sulphur, an accelerator, and protection agents.

[0127] The compound M4 which constitutes the first sidewall layer FE1 comprises an antioxidant at 5 phr and carbon black at 48 phr, so as to guarantee protection against attacks due to exposure to light and attack by ozone.

[0128] The associated mechanical and viscoelastic properties, measured at 23? C. under a deformation amplitude of 10%, are summarized in Table No. 2:

TABLE-US-00002 TABLE 2 G G Tan(?)max M1 46 7 0.2 M2 48 8 0.2 M3 2.47 0.06 0.03 M4 1.26 0.100 0.08

[0129] The elastomer compound M4 has a level of elongation at break of 300% measured at 100? C., whereas the level of elongation at break of the compound M3 is 80% also measured at 100? C.

[0130] Configurations of tyres of the invention were tested to clearly highlight the performance provided by the invention. The results of these tests were compared with those obtained on control tyres.

[0131] The control T1 in accordance with FIGS. 1-A and 1-B corresponds to a tyre of conventional design which comprises a filling layer constituted by the elastomer compound M1, a lateral bead reinforcement layer constituted by the elastomer compound M2, and the two sidewall sub-layers (FE1, FE2) consisting of the elastomer compound M4. The profile of the sidewall layer is of usual design, i.e. it has not been modified to facilitate contact with the rim.

[0132] A second control T2 reprises the specifications of T1, but the elastomer compounds of the two sidewall sub-layers consist of the same compound M3.

[0133] The first tyre P1 according to the invention reprises the specifications of the control T1, but the first sidewall sub-layer FE1 is composed of the compound M4 and the second sidewall sub-layer FE2 is composed of the compound M3.

[0134] In general, all the tyres according to the invention have the first sidewall layer FE1 consisting of the compound M4, and the second sidewall layer FE2 consisting of the compound M3.

[0135] The second tyre P2 according to the invention contains a filling layer consisting of the compound M3 and also contains a lateral reinforcement layer consisting of the compound M2.

[0136] The third tyre P3 according to the invention has the filling layer and the lateral reinforcement layer consisting of the same compound M3.

[0137] Finally, the fourth tyre P4 of the invention differs from P3 by the modification of the profile of the sidewall layer for a rate of variation of rim contact greater than 30%.

[0138] The configurations of the tyres P1, P2 and P3 of the invention are illustrated in FIG. 1-B. As regards the configuration P4, the illustrations can be observed in FIGS. 2-A, 2-B and 2-D.

[0139] The rate of variation of rim contact is 62% for P4, after a partial modification of the profile of the sidewall layer in the area of contact with the rim, as shown in FIGS. 2-A and 2-B.

[0140] Industrial performance is measured according to the scrap rate for sidewall moulding defects. None of the tyres of the invention P1, P2, P3 and P4 have moulding defects affecting the markings, and are satisfactory in industrial performance like T1. On the other hand, the control T2 with a single-layer sidewall consisting of the compound M3 leads to numerous rejects due to difficult demoulding.

[0141] The rolling resistance test was carried out in accordance with ISO 28580. For a tested tyre, the result is the rolling resistance coefficient, which represents the ratio of the resistance force to the forward travel of the vehicle by hysteresis of the tyres divided by the load carried.

[0142] The transverse slip stiffness measurements were carried out on dedicated measuring machines such as, for example, those marketed by MTS.

[0143] A result above (respectively below) 100% means an improvement (respectively a degradation) of the considered performance.

[0144] The results obtained are summarized in Table No. 3 below:

TABLE-US-00003 TABLE 3 Rolling Transverse slip resistance stiffness T1 100 100 T2 102 101 P1 102 100 P2 104 100 P3 112 98 P4 111 101

[0145] All the tyres of the invention achieve the desired compromise between rolling resistance and industrial performance. Rolling resistance is improved from 2% to 12% depending on the tested variants.

[0146] The transverse slip stiffness of the tyres was measured. Tyres P1 and P3 have a transverse slip stiffness of 100% and 98% respectively, without noticeably affecting the handling of the vehicle. Tyres P2 and P4 have superior or equal performance to the target sought.

[0147] All the variants of tyres according to the invention presented are produced without developing the processes and retain a usual industrial manufacturing cost.

[0148] Moreover, the invention can be generalized to other bead architectures than those described here, such as, for example, a bead having a first filling layer and a second lateral reinforcement layer, even though the carcass reinforcement does not comprise a turn-up.