Tyre with extended service life for heavy vehicles
By designing stepped progressive cuts in the middle part of the tread of heavy-duty vehicle tires and optimizing the thickness of the middle layer, the problem of needing to be re-grooved after tire wear is solved, the service life is extended, and the durability and grip of the crown are improved.
Patent Information
- Application Number
- CN202380046782.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2022-06-16
- Filing Date
- 2023-06-13
- Publication Date
- 2025-01-24
AI Technical Summary
After the wear reaches a certain level of wear, existing heavy-duty vehicle tires need to be re-engraved to extend their service life, but many users fail to effectively utilize this possibility, resulting in the tire wear potential being unexplored and the operating cost is not optimized.
By designing a stepped progressive cut in the middle part of the tread, consisting of a wide radially inner first part and a narrow second part, the minimum thickness of the middle layer between the bottom of the cut and the crown reinforcement is set to 2mm to 4mm to meet the specific thickness and width relationships to replace the tire regrooving process.
The service life of the tire is extended, without user intervention to re -engraved the groove, reducing the risk of tire crown enhanced parts to attack, improving the durability of the tire crown, and optimizing the grip and wear characteristics of the tire.
Smart Images
Figure CN119365348A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a tyre for heavy vehicles and more particularly to a tread crown of said tyre. Background Art
[0002] In the following, the circumferential or longitudinal direction is the direction of rotation of the tyre, the axial or transverse direction is the direction parallel to the axis of rotation of the tyre and the radial direction is the direction perpendicular to the axis of rotation of the tyre.
[0003] The crown of the tire comprises, radially from the outside towards the inside, a tread of rubber material, an intermediate layer also made of rubber material and a crown reinforcement having at least one crown layer comprising reinforcements embedded in rubber material.
[0004] The tread is the peripheral portion of the tire that is intended to grip the ground and to wear when it comes into contact with the ground through the tread surface. The tread generally comprises a tread pattern consisting of cuts separating raised elements and thus delimited by two walls of rubber material. These cuts may be circumferential, axial or inclined. Conventionally, the circumferential cuts form an average angle at most equal to 30°, the inclined cuts form an average angle between 30° and 70°, and the axial cuts form an average angle at least equal to 70°, relative to the circumferential direction of the tire.
[0005] The intermediate layer, radially inside the tread and in contact therewith, provides a mechanical connection between the tread and the crown reinforcement. In particular, it protects the crown reinforcement from external attacks, more particularly from mechanical attacks resulting from foreign bodies penetrating the tread.
[0006] The crown reinforcement comprises at least one crown layer, most often a radial superposition of crown layers, extending circumferentially radially inside the intermediate layer and in contact therewith, and radially outside the carcass reinforcement providing the overall reinforcement of the tire. The crown layer comprises a reinforcement, most often a metallic reinforcement in the case of tires for heavy vehicles, and coated with a rubber material.
[0007] In the crown layer, a distinction is generally made between a protective layer, which constitutes the radially outermost protective reinforcement, and a working layer, which constitutes the working reinforcement radially between the protective reinforcement and the carcass reinforcement. The crown reinforcement may also comprise a hoop reinforcement radially on the inside of the working reinforcement, between two working layers of working reinforcement or radially on the outside of the working reinforcement.
[0008] The protective reinforcement, which comprises at least one protective layer, essentially protects the working reinforcement from mechanical or physicochemical attacks that may propagate radially towards the interior of the tire through the tread. The protective layers generally comprise elastic metal reinforcements which are parallel to one another and form an angle at least equal to 10° with the circumferential direction. The elastic metal reinforcements are characterized by a structural elongation As of at least 1% and a total elongation at break At of at least 4%. Furthermore, the elastic metal reinforcement has a tensile modulus of elasticity at most equal to 150 GPa, generally between 40 GPa and 150 GPa. According to ISO 6892 of 1984, these mechanical properties are inferred from curves representing the variation of the tensile force (in N) applied to the metal reinforcement with its relative elongation (in %), known as force-elongation curves.
[0009] Working reinforcement (which usually includes at least two working layers) has the function of buckling tire and giving tire rigidity and road maintenance. Working reinforcement absorbs inflation mechanical stress and mechanical stress caused by running, the inflation mechanical stress is generated by tire inflation pressure and transmitted by carcass reinforcement, the mechanical stress caused by running is generated by tire running on the ground and transmitted by tread. Working reinforcement also needs to withstand oxidation, impact and perforation by its inherent design and the inherent design of protective reinforcement. Working layer usually includes two inextensible metal reinforcements, the inextensible metal reinforcements are parallel to each other and form an angle of at most 60°, preferably at least 15° and at most 45° with the circumferential direction. The inextensible metal reinforcement is characterized in that, under a tensile force equal to 10% of the breaking force Fm, the total elongation At is at most equal to 0.2%. In addition, the tensile elastic modulus of inextensible metal reinforcement is usually between 150GPa and 200GPa. These mechanical properties are also inferred from the force-elongation curve as described above.
[0010] The function of the hoop reinforcement comprising at least one hoop layer is to absorb at least part of the inflation mechanical stresses and thus reduce the inflation mechanical stresses transmitted to the working reinforcement. It contributes to strengthening the crown reinforcement, thereby improving the durability of the crown reinforcement compared to a crown reinforcement without a hoop. The hoop layer comprises metal reinforcements parallel to each other and forming an angle with the circumferential direction of at most 10°, preferably at most 5°, even more preferably equal to 0°.
[0011] The crown of the above-mentioned tire is connected at the two axial ends to two sidewalls, which are themselves respectively connected to two beads providing the mechanical connection between the tire and the rim on which it is intended to be mounted.
[0012] In a known manner, tyres for heavy vehicles are usually regroovable. After a certain level of wear on the tyre, the user can actually regroove it, i.e. remove a certain thickness of rubber material from the tread radially towards the inside, usually manually, starting from the bottom of a circumferential or transverse cut in the tread. This regrooving operation allows the cut to be recreated at the end of the life of the tyre, which prolongs the service life of the tyre.
[0013] This regrooving is still possible if the thickness of the rubber material between the bottom of the deepest tread cut and the crown reinforcement is sufficient (generally at least equal to 5 mm). The thickness of said rubber material radially inside the deepest cut consists of the superposition of the thickness of the tread portion and the thickness of the intermediate layer. In order to limit the regrooving depth (which is generally between 2 and 4 mm) and to leave a sufficient residual thickness of rubber material between the bottom of the recut groove and the crown reinforcement, a regrooving indicator is generally installed at the bottom of the cut to guide the user in the regrooving operation and prevent him from cutting too deep and reaching the crown reinforcement, which would be detrimental to the life of the tire.
[0014] However, many users do not take advantage of this regrooving possibility, which leads to a partial exploitation of the tyre's wear potential and to non-optimal costs for operating the tyre. Summary of the invention
[0015] The aim that the inventors have therefore set themselves is to propose a tyre for heavy vehicles having a prolonged service life without the need for regrooving, while maintaining a satisfactory level of durability of the tyre crown.
[0016] The invention relates to a tire for heavy vehicles, said tire comprising, radially from the outside towards the inside, a tread, an intermediate layer and a crown reinforcement:
[0017] - the tread intended to come into contact with the ground through the tread surface has an axial width and comprises an arrangement of raised elements made of rubber material and of the cuts separating them,
[0018] - the tread comprises a central portion having an axial width at most equal to 80% of the axial width of the tread and separating the two lateral portions,
[0019] - the middle portion comprises at least one cutout,
[0020] - at least one incision has a depth measured perpendicularly to the tread surface between the tread surface and the bottom of the incision,
[0021] - the intermediate layer comprises rubber material and has a minimum thickness measured between the bottom of the cutout and the crown reinforcement,
[0022] - the crown reinforcement comprises at least one crown layer comprising reinforcements embedded in rubber material,
[0023] at least one of the cutouts of the intermediate portion has a wide radially inner first portion extending radially outwards from the bottom of the cutout to a height at least equal to 0.2 times the depth of the cutout and having an average width greater than 2 mm,
[0024] at least one of the cutouts of the intermediate portion has a narrow second portion extending radially outwards from the radially inner first portion to a height at least equal to 4 mm and at most equal to the difference between the depth of the cutout and the depth of the wide first portion, and having an average width at most equal to 2 mm,
[0025] - the intermediate layer has a minimum thickness, measured between the bottom of the cutout and the crown reinforcement, of at least 2 mm and at most 4 mm,
[0026] - The minimum thickness of the intermediate layer and the average width of the first portion in the wide radial direction of at least one cutout of the intermediate portion satisfy the relationship: Ei 3 / W1<=12mm 2 , Ei and W1 are expressed in mm.
[0027] The invention essentially proposes to replace the usual regrooving possibilities of the tire by using a greater tread depth (and therefore a greater tread thickness) by reducing the amount of material available between the bottom of the cut and the crown reinforcement to a minimum thickness of between 2 and 4 mm, thus allowing maximum use of the tire without requiring specific intervention by the user.
[0028] The invention therefore proposes to have, at least in the middle portion of the tread, stepped progressive cuts with a maximum depth and each comprising a wide radially inner first portion and a narrow second portion, the narrow second portion being radially outside the wide first portion. The wide first portion extends radially outwards from the bottom of the cut to a height at least equal to 0.2 times the depth of the cut and has an average width greater than 2 mm; it is therefore a groove-like portion. The narrow second portion extends radially outwards from the radially inner first portion to a height at least equal to 4 mm and at most equal to the difference between the depth of the cut and the depth of the wide first portion, and has an average width at most equal to 2 mm; it is therefore a sipe-type portion that, when the tire is new, may (but not necessarily) open onto the tread surface.
[0029] Thus, this stepped progressive cut allows the bottom of the cut to come into contact with a foreign object (e.g. a stone) only at the end of the tire life when the tread reaches a significant level of wear. This arrangement therefore minimizes the risk of the bottom of the cut being attacked and, therefore, the risk of cracking of the underlying intermediate layer that could occur due to a foreign object being retained in the cut for a long period of time.
[0030] The minimum value of the minimum thickness of the intermediate layer measured perpendicularly to the bottom of the cutout is equal to 2 mm, thus ensuring satisfactory durability of the crown reinforcement since it is not directly exposed to risks of attack when the tire is completely worn out.
[0031] The minimum thickness of the intermediate layer, measured perpendicularly to the bottom of the cut, has a maximum value equal to 4 mm, making it possible to limit the contribution of the intermediate layer to the mass of the tyre.
[0032] According to the present invention, the minimum thickness of the intermediate layer and the average width of the first portion in the wide radial direction of at least one cutout of the intermediate portion satisfy the relationship: 3 / W1<=12mm 2 , Ei and W1 are expressed in mm.
[0033] This relationship defines an optimized design domain that links the minimum thickness of the intermediate layer measured perpendicularly to the bottom of the cut to the average width of the wide radially inner first portion of the cut. The minimum thickness of the intermediate layer determines the protection of the crown reinforcement from external attacks. The average width of the wide radially inner first portion defines the width of the cut for complete tread wear and limits the size of foreign bodies caught by the cut and able to generate cracks at the bottom of the cut.
[0034] According to a particular embodiment of the invention, the intermediate layer comprises a central portion separating two lateral portions of said intermediate layer, having an axial width at most equal to the axial width of the central portion of the tread and comprising a rubber material of a chemical composition different from that of the rubber material of the two lateral portions of said intermediate layer.
[0035] The middle portion of the intermediate layer, radially inside the middle portion of the tread, operates at a lower temperature than the lateral portions of the intermediate layer due to the smaller shear deformation, but is exposed to a greater risk of being attacked due to the higher ground contact pressure. Conversely, the lateral portions of the intermediate layer operate at a higher temperature, but are less exposed to attacks. It is therefore advantageous to have different rubber compounds between the middle portion and the lateral portions of the intermediate layer: the rubber material in the middle portion of the intermediate layer exhibits greater hysteresis and is more resistant to attacks, the rubber material in the lateral portions of the intermediate layer exhibits less hysteresis and is less resistant to attacks.
[0036] Advantageously, at least one of the cutouts of the intermediate portion has a radially inner first portion extending radially outwards from the bottom of the cutout to a height at most equal to 0.6 times the depth of the cutout.
[0037] Beyond 0.6 times the depth of the cut, the height of the narrow second portion extending radially outwards from the radially inner first portion becomes too small for this second portion to perform the function of blocking the relative material element defining it. This blocking effectively limits the deformation of the tread, which on the one hand consumes less energy and limits the rolling resistance, and on the other hand gives the tread rigidity, thus facilitating its wear resistance.
[0038] According to a particular embodiment, at least one of the cutouts of the intermediate portion has a wide radially outer third portion radially outside the narrow second portion, opening towards the tread surface and having a width measured thereon at least equal to 2 mm.
[0039] In other words, the radially outermost third portion is a groove. Therefore, the stepped progressive cut is composed of a groove portion, a sipe portion and a groove portion respectively from the outside to the inside in the radial direction. This arrangement can adjust the grip level on wet ground under different tread wear conditions. BRIEF DESCRIPTION OF THE DRAWINGS
[0040] By way of illustration, not drawn to scale Figures 1 to 5 The features of the present invention are described as follows:
[0041] - Figure 1 : Partial meridian half-section of a tire according to the invention with reduced minimum thickness of the intermediate layer,
[0042] - Figure 2 : A cross-sectional view of a cutout of the middle portion of a tire of the prior art with a conventional minimum thickness of the intermediate layer,
[0043] - Figure 3 : a cross-sectional view of a stepped progressive cutout of the middle portion of a tire with a reduced minimum thickness of the intermediate layer according to a first embodiment of the invention,
[0044] - Figure 4 : a cross-sectional view of a stepped progressive cutout of the middle portion of a tire with a reduced minimum thickness of the intermediate layer according to a second embodiment of the invention,
[0045] - Figure 5 : The design range of the present invention that links the average width of the incision at the end of tread wear to the minimum thickness of the intermediate layer perpendicular to the incision. DETAILED DESCRIPTION
[0046] Figure 1is a partial meridian half-section in the YZ plane of a tire with a reduced minimum thickness of the intermediate layer according to the invention. Figure 1 Only the axial width divided by 2 is shown. Similarly, elements that are symmetrical with respect to the median circumferential plane XZ of the tyre are shown only once. The meridian half-section is partial, since only the portion radially located outside the straight line passing through the maximum axial width of the tyre is shown. The tyre 1 for heavy vehicles comprises, radially from the outside towards the inside, a tread 2, an intermediate layer 3 and a crown reinforcement 4. The tread 2, intended to come into contact with the ground via a tread surface 20, has an axial width Lt and comprises an arrangement of raised elements 21 made of rubber material and of incisions 22 separating them. The tread 2 comprises a middle portion 23 having an axial width Lm at most equal to 80% of the axial width Lt of the tread 2 and separating two lateral portions 24. The middle portion 23 comprises four incisions 22, at Figure 1 Only two of them are shown in the meridian semi-section of . Each incision 22 has a depth H measured perpendicular to the tread surface 20 between the tread surface 20 and the bottom 220 of the incision. The intermediate layer 3 comprises a rubber material and has a minimum thickness Ei measured between the bottom 220 of the incision and the crown reinforcement 4. In the embodiment shown, the intermediate layer 3 with a substantially constant thickness Ei comprises an intermediate portion 31 separating two lateral portions 32 of the intermediate layer 3, an axial width Lim at most equal to the axial width Lm of the middle portion 23 of the tread, and a rubber material having a chemical composition different from that of the rubber material of the two lateral portions 32 of the intermediate layer 3. The crown reinforcement 4 comprises four crown layers 41, which comprise a reinforcement embedded in a rubber material and, in the embodiment shown, radially from the inside to the outside, consist of a first working layer, a hoop layer, a second working layer and a protective layer. The crown reinforcement is radially located on the outside of the carcass reinforcement shown in dotted lines. According to the invention, each cutout 22 of the middle portion 23 has a wide radially inner first portion 221 and a narrow second portion 222, wherein the wide radially inner first portion 221 extends radially outward from the bottom 220 of the cutout, and the narrow second portion 222 extends radially outward from the radially inner first portion 221, and the minimum thickness Ei of the intermediate layer 3 measured between the bottom 220 of the cutout and the crown reinforcement 4 is at least equal to 2 mm and at most equal to 4 mm.
[0047] Figure 2is a cross-sectional view of a cut of a tire of the prior art with a typical minimum thickness of the intermediate layer. The cut 22 in the middle portion of the tread 2, delimited by two raised elements 21, has a depth H measured perpendicularly to the tread surface 20 between the tread surface 20 and the bottom 220 of the cut: it is a simple cut formed by a single cavity. The intermediate layer 3 comprises rubber material and has a minimum thickness Ei measured between the bottom 220 of the cut and the crown reinforcement 4. For tires of the prior art, the typical minimum thickness Ei is usually at least equal to 5 mm, to allow the tread to be regrooved when it reaches complete wear.
[0048] Figure 3 2 is a cross-sectional view of a stepped progressive cut in the middle portion of a tire with a reduced minimum thickness of an intermediate layer according to a first embodiment of the invention. The cut 22 in the middle portion of the tread 2, delimited by two raised elements 21, has a depth H measured perpendicular to the tread surface 20 between the tread surface 20 and the bottom 220 of the cut. According to this first embodiment of the invention, the cut 22 has a wide radially inner first portion 221, extending radially outwards from the bottom 220 of the cut to a height H1 at least equal to 0.2 times the depth H of the cut 22, and having an average width W1 greater than 2 mm. In addition, the cut 22 has a narrow second portion 222, extending radially outwards from the radially inner first portion 221 to a height H2 at least equal to 4 mm and equal to the difference between the depth H of the cut 22 and the depth H1 of the wide first portion 221, and having an average width W2 at most equal to 2 mm. Finally, the intermediate layer 3 has a minimum thickness Ei at least equal to 2 mm and at most equal to 4 mm, measured between the bottom 220 of the cut and the crown reinforcement 4. Thus, in this first embodiment of the invention, the stepped progressive cut 22, comprising two stages: a radially inner stage of the groove type and a radially outer stage of the sipe type, combined with a reduced minimum thickness Ei of at least 2 mm and at most equal to 4 mm, measured between the bottom 220 of the cut and the crown reinforcement 4, makes it possible to increase the depth H of the cut 22 by typically 1 to 3 mm, and thus by 1 to 3 mm, of the thickness of the material to be worn, compared to the prior art.
[0049] Figure 4: is a cross-sectional view of a stepped progressive cut in the middle portion of a tire according to a second embodiment of the invention. This second embodiment differs from the first embodiment by a narrow second portion 222 extending radially outwards from the radially inner first portion 221 to a height H2 strictly less than the difference between the depth H of the cut 22 and the depth H1 of the wide first portion 221, and by a wide radially outer third portion 223, radially outside the narrow second portion 222, opening onto the tread surface 20 and having a width W3 measured on the tread surface 20 at least equal to 2 mm. Thus, in this second embodiment of the invention, the stepped progressive cut 22 comprises three stages: a radially inner groove type stage, a radially intermediate sipe type stage and a radially outer groove type stage. As previously mentioned, this stepped progressive cut 22 is combined with a reduced minimum thickness Ei measured between the bottom 220 of the cut and the crown reinforcement 4, at least equal to 2 mm and at most equal to 4 mm.
[0050] Figure 5 The design definition domain according to the present invention that relates the average width W1 of the incision 22 at the end of tread wear (i.e. the average width W1 of the wide first portion 221) to the minimum thickness Ei of the intermediate layer 3 perpendicular to the incision 22 is shown. According to the present invention, the following relationship is satisfied: Ei 3 / W1<=12mm 2 , Ei and W1 are expressed in mm. The design domain of the present invention is the shaded portion of the graph.
[0051] The inventors have studied the invention more specifically for a tyre of size 315 / 80R22.5, intended to equip the steering axles of heavy vehicles and having a load capacity of 4000 kg, with an inflation pressure equal to 8.5 bar.
[0052] Table 1 below shows the characteristics of a 315 / 80R 22.5 tyre (I) according to the invention compared with a prior art reference tyre 315 / 80R 22.5 Michelin XMULTID (R):
[0053] [Table 1]
[0054]
Claims
1. A tire (1) for a heavy vehicle, said tire (1) comprising, radially from the outside to the inside, a tread (2), an intermediate layer (3) and a crown reinforcement (4): - a tread (2) intended to come into contact with the ground through a tread surface (20) having an axial width (Lt) and comprising an arrangement of raised elements (21) made of rubber material and of cutouts (22) separating the raised elements, - the tread (2) comprises a central portion (23) having an axial width (Lm) at most equal to 80% of the axial width (Lt) of the tread (2) and separating two lateral portions (24), - said intermediate portion (23) comprises at least one cutout (22), - the at least one incision (22) has a depth (H) measured perpendicularly to the tread surface (20) between the tread surface (20) and the bottom (220) of the incision, - said intermediate layer (3) comprises rubber material and has a minimum thickness (Ei) measured between the bottom of the cutout (220) and the crown reinforcement (4), - the crown reinforcement (4) comprises at least one crown layer (41) comprising a reinforcement embedded in a rubber material, - It is characterized by At least one of the cutouts (22) of the middle portion (23) has a wide radially inner first portion (221), the wide radially inner first portion (221) extending radially outward from the bottom (220) of the cutout to a height (H1) at least equal to 0.2 times the depth (H) of the cutout (22) and having an average width (W1) greater than 2 mm, and at least one of the cutouts (22) of the middle portion (23) has a narrow second portion (222), the narrow second portion (222) extending radially outward from the radially inner first portion (221) to a height (H2) at least The intermediate layer (3) has a minimum thickness (Ei) equal to 2 mm and at most equal to the difference between the depth (H) of the cut (22) and the depth (H1) of the wide first portion (221), and has an average width (W2) equal to 2 mm, the minimum thickness (Ei) of the intermediate layer (3) measured between the bottom (220) of the cut and the crown reinforcement (4) is at least equal to 2 mm and at most equal to 4 mm, and the minimum thickness (Ei) of the intermediate layer (3) and the average width (W1) of the wide radially inner first portion (221) of at least one cut (22) of the intermediate portion (23) satisfy the relationship: Ei 3 / W1<=12mm 2 , Ei and W1 are expressed in mm.
2. The tire (1) according to claim 1, wherein: The intermediate layer (3) comprises a middle portion (31) which separates two lateral portions (32) of the intermediate layer (3), has an axial width (Lim) at most equal to the axial width (Lm) of the middle portion (23) of the tread, and contains a rubber material having a chemical composition different from that of the rubber material of the two lateral portions (32) of the intermediate layer (3).
3. The tire (1) according to any one of claims 1 or 2, wherein: At least one cutout (22) of the intermediate portion (23) has a radially inner first portion (221), the radially inner first portion (221) extending radially outward from the bottom (220) of the cutout to a height (H1) at most equal to 0.6 times the depth (H) of the cutout (22).
4. The tire (1) according to any one of claims 1 to 3, wherein: At least one cutout (22) of the intermediate portion (23) has a wide radially outer third portion (223) which is radially located on the outside of the narrow second portion (222), opens onto the tread surface (20) and has a width (W3) measured on the tread surface (20) of at least 2 mm.