Airless tire, especially for extraterrestrial vehicles, including an optimized shear band

Abstract

The present invention relates to an airless tire (1) for a vehicle, comprising, radially from the inside to the outside, a supporting structure (2), intended to cooperate with a rim (100) of a wheel (10), a shear band (3) integral with the supporting structure (2) and a tread (4) integral with the shear band (3), the shear band (3) comprising, radially from the inside to the outside, an internal shear membrane (31), a shear structure (32) constituted by a plurality of shear elements (32a) distributed circumferentially and an external shear membrane (33). The inner shear membrane (31) and the outer shear membrane (33) of the shear band (3) comprise a plurality of successive patterns (34, 35) distributed circumferentially over the circumferential perimeter of the corresponding shear membrane (33, 34). Figure for abstract: Fig 2

Description

Title of the invention: Airless tire, in particular for extraterrestrial vehicles, comprising an optimized shear band Technical field of the invention

[0001] The present invention relates to the field of airless tires, in particular intended to equip an extraterrestrial exploration vehicle, in particular intended to move, for example, on the moon or on the planet Mars, in an environment subject to very strong temperature variations, which can reach very low temperatures down to -243°C and very high temperatures up to +130°C. Such a thermal gradient is notably measured at the South Pole of the moon.

[0002] The present invention relates more particularly to the shear band of such an airless tire. State of the prior art

[0003] A conventional tire subjected to the internal pressure of an inflation gas, generally air, or a conventional airless or solid tire, not subjected to the internal pressure of an inflation gas, are not suitable for such use, because the usual rubber-based materials from which they are made have mechanical properties incompatible with use in an environment which can reach very low temperatures, also called cryogenic temperatures.

[0004] It is known to have, as an alternative technical solution to a conventional tire, an airless tire, or more generally a tire without inflation gas, which carries the load thanks to structural components and which has performances comparable to those of a conventional tire. An airless tire, mounted on a hub, or a rim, is sometimes called a "non-pneumatic elastic wheel".

[0005] In the following, the circumferential or longitudinal direction designates the direction of rotation of the tire, the axial or transverse direction designates a direction parallel to the axis of rotation of the tire and the radial direction designates a direction perpendicular to the axis of rotation of the tire.

[0006] The term “inner” element means the part closer to the axis of rotation of the tire compared to an “outer” element.

[0007] An airless tire generally comprises, radially from the inside to the outside:

[0008] - a carcass made up of structural elements and intended to cooperate with a rim or hub; and

[0009] - a tread secured to the carcass and intended to transmit to said carcass, rolling forces, to be worn and to guarantee the grip of the tire with the ground.

[0010] The carcass comprises, radially from the inside to the outside:

[0011] - a supporting structure, intended to structurally support at least in part the load applied to the tire and secured to the rim or hub; and

[0012] - a shear band, intended to transmit by shear the forces of rolling to the supporting structure and to contribute at least in part to carrying the load.

[0013] The supporting structure comprises, radially from the inside to the outside, means of connection with a rim or a hub, radial elements or spokes, and means of connection with the shear band.

[0014] However, the supporting structure does not generally define a sealed internal cavity intended to contain a pressurized gas, as in a conventional tire. Therefore, an airless tire does not need to have a sealed connection with respect to a rim or a hub.

[0015] The shear band comprises, radially from the inside to the outside:

[0016] - a first radially inner membrane,

[0017] - a shear layer consisting of one or more shear elements, And

[0018] - a second radially outer membrane intended to receive the strip of rolling and connected to the radially inner membrane by the shear layer.

[0019] Generally, the first and second membranes have a modulus of elasticity in circumferential extension often substantially greater than the modulus of elasticity in shear of the shear layer of polymeric material, such that, under the applied load, the membranes do not elongate or elongate only slightly when the tire is flattened while rolling. The relative displacement of the membranes relative to each other occurs by shear in the shear layer. For example, the membranes, respectively inner and outer, comprise a layer or a superposition of layers of reinforcements coated in a polymeric material.

[0020] The shear layer of polymeric material is made, for example, of a polymeric material, such as a natural rubber or a synthetic rubber, or of a polyurethane. Typically, the material of the shear layer has a shear modulus of at least 3 MPa and at most 20 MPa, which allows for easier flattening of the shear band under load.

[0021] Finally, the tread, which is the radially outer component of the tire, is most often made of a polymeric material, such as a ca- natural or synthetic rubber.

[0022] For several years, Michelin North America has marketed a mounted assembly, consisting of an airless tire, as previously described, and a wheel, under the name MICHELIN® TWEEL®. This technical solution mainly comprises a tread, a shear-band, a supporting structure, consisting of highly resistant polyresin spokes and a hub consisting of two reinforced steel parts.

[0023] However, the shear bands of a state-of-the-art airless tire have two main disadvantages, which are a generally high mass and a generation of ground contact pressures within a relatively restricted range of values.

[0024] Thus, high contact pressures can only be generated by a shear band having a very high mass, which is neither mechanically viable nor economically acceptable.

[0025] Furthermore, the high rigidity levels of the shear band will generate high contact pressures, involving a risk of the tire sinking into soft ground, particularly as on the moon, and generate high rolling resistance, generating high energy consumption, which is detrimental to the energy autonomy of the extraterrestrial vehicle.

[0026] Thus, in applications having severe environmental constraints, in particular in applications at very low temperatures, the shear levels of the shear band, necessary to generate low contact pressures, are difficult to achieve with a shear layer constituted by the usual polymeric materials.

[0027] Finally, by increasing the load applied to the tire, for example between 50 daN and 100 daN per wheel, it has been found that the constituent elements of the tire overlap, and in particular the shear elements, which is not acceptable.

[0028] Subsequently, there is a need to remedy the aforementioned drawbacks. Statement of the invention

[0029] The inventors aim to design an airless tire with improved flattening in order to improve the traction of the airless tire while being able to withstand loads of between 5 daN and 200 daN per wheel, in particular by the choice of an appropriate shear band.

[0030] The invention aims in particular to increase the length of the contact area at iso load and at iso maximum stresses in the overall structure.

[0031] Another objective is to design an airless tire that can run in a extraterrestrial environment, at very low temperatures, typically in the range [-243°C; +130°C]. The tire according to the invention can also be adapted for driving in a terrestrial environment and on various types of ground, which may be sandy or stony.

[0032] The present invention relates to an airless tire for a vehicle, comprising, radially from the inside to the outside, a supporting structure intended to cooperate with a rim or a hub of a wheel, a shear band secured to the supporting structure and a tread secured to the shear band.

[0033] The shear band comprises, radially from the inside to the outside, a radially inner or internal shear membrane, a shear structure constituted by a plurality of circumferentially distributed shear elements and a radially outer or external shear membrane.

[0034] The internal shear membrane and / or the external shear membrane of the shear band comprises a plurality of successive patterns distributed circumferentially over the circumferential perimeter of the corresponding shear membrane.

[0035] In other words, the respective perimeters of the inner shear membrane and the outer shear membrane of the shear band are not circular, unlike the respective perimeters of the inner shear membrane and the outer shear membrane of the shear band of existing airless tires.

[0036] Such patterns make it possible to increase the length of the corresponding shear membrane compared to a shear membrane of circular circumferential perimeter.

[0037] In fact, we constant a length of the corresponding shear membrane increased by 0.01% to 5% compared to a shear membrane of circular circumferential perimeter.

[0038] Thus, when the wheel goes flat, the patterns will allow the corrugated inner and outer shear membranes respectively to elongate in the circumferential direction and therefore increase the circumferential length of the contact with the ground, and thus reduce the average contact pressure of the tire on the ground.

[0039] By "successive patterns" is meant a succession of patterns along the perimeter of the corresponding shear membrane.

[0040] Thanks to the particular structure of the shear band, the average contact pressure with the ground is minimized by maximizing the contact surface with the ground, which makes it possible to improve the traction of the airless tire while being able to withstand high loads, between 5 daN and 200 daN per wheel, and without increase the maximum stress in the overall structure, i.e. of the carcass beyond a threshold value dependent on the material.

[0041] Such a shear band also promotes the flattening of the tire on the ground.

[0042] Such a discrete shear structure has the advantage of being lighter than a continuous shear structure. In addition, its rigidities can be more finely optimized.

[0043] The shear band according to the invention makes it possible to minimize the average pressure of contact with the ground, between 0.10 bar and 0.15 bar, preferably 0.12 bar, for a wheel width of 300 mm, an average diameter between 800 mm and 900 mm, and a load of 100 daN, by maximizing the contact surface with the ground, which makes it possible to improve the traction of the tire.

[0044] Finally, such a shear band also has the advantage of being particularly light compared to known shear bands.

[0045] Furthermore, the corrugated shape of one or both membranes of the shear band in combination with the modulus of elasticity of the material(s) constituting the corresponding membrane makes it possible to optimize the mechanical rigidity characteristics of the shear band, with a view to obtaining the distribution and the value of the contact pressures with the ground, adapted to the use of the vehicle concerned.

[0046] Advantageously, the patterns of a plurality of patterns are identical to each other and are regularly distributed over the circumferential perimeter of the corresponding shear membrane.

[0047] For example, each pattern extends over an angular sector of angle between 5° and 15°, preferably between 8° and 10°.

[0048] Preferably, each pattern of a plurality of patterns comprises a substantially planar anchoring section, at least one concave shape and at least one convex shape.

[0049] By "concave" is meant a shape curved towards the inside of the tire.

[0050] By "convex" is meant a shape curved towards the outside of the tire, opposite to concave.

[0051] Advantageously, the anchoring section of the internal shear membrane cooperates, preferably tangentially, with a first internal end of a shear element of the shear structure and the supporting structure.

[0052] Advantageously, the anchoring section of the external shear membrane cooperates, preferably tangentially, with a second external end of a shear element of the shear structure and the tread.

[0053] For example, the anchor section of a pattern connects tangentially at each of its ends to straight sections of adjacent patterns.

[0054] For example, the anchoring section forms with a cylindrical geometry passing through two ends of each pattern, an angle between 5° and 30°.

[0055] According to one embodiment, each pattern of the internal shear membrane successively comprises circumferentially the substantially planar anchoring section, the concave shape and the convex shape.

[0056] According to one embodiment, each pattern of the external shear membrane successively comprises circumferentially the substantially planar anchoring section, the concave shape and the convex shape.

[0057] Alternatively, it could be provided that the convex shape is located between the anchoring section and the concave shape.

[0058] In the case where the inner shear membrane and the outer shear membrane of the shear band each comprise a plurality of patterns, the plurality of patterns of the inner shear membrane is parallel to the plurality of patterns of the outer shear membrane.

[0059] For example, the concave shape of each pattern of the inner shear membrane is radially opposite the concave shape of each pattern of the outer shear membrane and the convex shape of each pattern of the inner shear membrane is radially opposite the convex shape of each pattern of the outer shear membrane.

[0060] Alternatively, provision could be made to have an angular offset of the patterns of the internal shear membrane relative to the patterns of the external shear membrane.

[0061] It could also be provided that the patterns of the internal shear membrane are different from the patterns of the external shear membrane.

[0062] Alternatively, it could also be provided that the plurality of patterns of the internal shear membrane forms a mirror image, with respect to the average surface of the shear structure, of the plurality of patterns of the external shear membrane.

[0063] For example, the concave shape of each pattern of the inner shear membrane is radially opposite the convex shape of each pattern of the outer shear membrane and the convex shape of each pattern of the inner shear membrane is radially opposite the concave shape of each pattern of the outer shear membrane.

[0064] For example, the number of patterns is equal to the number of shear elements of the shear structure.

[0065] Each pattern comprises at least one convex portion, at least one concave portion and a single anchoring section.

[0066] In other words, the number of patterns corresponds to the number of sections anchoring.

[0067] Advantageously, the shear elements of the shear structure are distributed circumferentially at a regular pitch and extend radially between the internal shear membrane and the external shear membrane.

[0068] In a non-limiting manner, each shear element comprises two opposite curvatures.

[0069] Preferably, the supporting structure, the shear band and the tread are each made of at least one material, preferably thermoplastic, having the following mechanical characteristics, measured according to the ASTM D638 standard of the ASTM (“American Society for Testing and Materials”) International: - a Young's modulus in tension E, measured at a temperature equal to 20°C, at least equal to 1 GPa and at most equal to 6 GPa, and, measured at a temperature equal to -196°C, at least equal to 1.2 GPa and at most equal to 9 GPa, and - a maximum tensile stress Sm, measured at a temperature equal to 20°C, at least equal to 25 MPa and at most equal to 150 MPa, and, measured at a temperature equal to -196°C, at least equal to 40 MPa and at most equal to 260 MPa.

[0070] Such an airless tire is intended to equip an extraterrestrial vehicle and is capable of withstanding strong temperature gradients ranging from -243°C to +130°C.

[0071] To enable an airless tire to run in an extraterrestrial environment that can vary between very low temperatures and very high temperatures, typically in the range [-243°C; 130°C], and on soils of various types, which can be sandy or stony, the Applicant has selected materials having, essentially, a Young's modulus in tension E and a maximum tensile stress Sm within specific ranges both at room temperature, taken equal to 20°C, and at very low temperature, taken equal to -196°C.

[0072] The Young's modulus in tension E and the maximum tensile stress Sm are measured on a tensile curve "stress - elongation", established from a tensile test carried out on a standardized test piece, in accordance with the ASTM D638 standard ("Standard Test Method for Tensile Properties of Plastics"), developed by ASTM ("American Society for Testing and Materials") International. The standardized test piece has a length equal to 84 mm and a thickness equal to 2 mm, and includes a necking having a length equal to 25 mm and a width equal to 4 mm. The tensile speed applied to the test piece is equal to 500 mm / min. The Young's modulus in tension E is a tangent modulus measured at low deformation.

[0073] The Young's modulus in tension E conditions the rigidities and the load capacity of the airless tire, at the target operating temperatures. The maximum tensile stress Sm determines the endurance of the airless tire, at the target operating temperatures.

[0074] Consequently, the inventors have chosen materials whose aforementioned mechanical characteristics make it possible to guarantee a satisfactory compromise between the load capacity and the endurance required for the airless tire under the intended conditions of use. The airless tire must be capable of carrying a load typically between 5 daN and 200 daN, and is intended to be mounted on a vehicle which can typically travel up to a maximum speed of 20 km / h.

[0075] In the context of the present invention, the inventors have demonstrated, surprisingly, that such a high-performance thermoplastic polymeric material also makes it possible to achieve a satisfactory compromise between high structural rigidity, high endurance and low mass of the airless tire, at very low cryogenic temperatures, as shown by measurements carried out at -196°C.

[0076] According to a preferred embodiment, the supporting structure, the shear band and the tread are each made of the same material. An identical material for all the constituents of an airless tire simplifies manufacturing and allows for easier adhesion between the different constituents.

[0077] For example, the supporting structure consists of a plurality of spokes regularly distributed circumferentially. In a non-limiting manner, the spokes each comprise an internal end secured to the rim, for example by fixing means, such as screw means (screws / nuts) or by rivets, a concave portion and an external end secured to the shear band by screw means or by rivets. By way of non-limiting example, said fixing means could be configured to fix both a spoke of the tire and the rim.

[0078] According to a second aspect, the invention relates to a wheel comprising an airless tire as described previously mounted on a rim. Brief description of the drawings

[0079] Other aims, characteristics and advantages of the invention will appear on reading the following description, given solely by way of non-limiting example, and made with reference to the appended drawings in which:

[0080] [Fig.l] represents an overall perspective view of a wheel comprising an airless tire according to one embodiment of the invention;

[0081] [Fig.2] illustrates a front view of the wheel of [Fig.l], illustrating the flattening of the tire;

[0082] [Fig.2A] represents a detail of [Fig.2];

[0083] [Fig.2B] represents a detail of [Fig.2A];

[0084] [Fig.2C] represents a detail of [Fig.2A];

[0085] [Fig.3] represents a graph comparing the contact area of ​​the tire with the ground of the tire according to the invention compared to a known airless tire whose perimeter of the inner and outer membranes of the shear band is circular;

[0086] [Fig.4] represents a graph comparing the stresses in the corrugated external and internal shear membranes, respectively, as well as in the shear elements of the tire according to the invention; and

[0087] [Fig.5] represents a table summarizing, for a wheel width of 300mm, under a load of 100 daN, the measured wheel area length, the average contact pressure, the deflection corresponding to the radial crushing of the tire and various maximum stresses.

[0088] Detailed description of at least one embodiment

[0089] In the following description, the terms “circumferential”, “axial” and “radial” are defined relative to the axis of rotation XI-XI of the tire 1.

[0090] The “circumferential” direction designates a direction of a plane perpendicular to the axis of rotation XI-XI tangent to the tread of the tire 1, the “axial” direction is the direction of the axis of rotation XI-XI of the tire 1 and a “radial” direction designates a direction perpendicular to the axis of rotation XI-XI of the tire 1.

[0091] [Fig.l] is an overall perspective view of a mounted assembly or wheel 10 comprising a rim 100 and an airless tire 1 mounted on said rim 100.

[0092] By “rim” is meant a structure for connection with the vehicle and central support of the tire 1.

[0093] The airless tire 1 is intended to equip an extraterrestrial vehicle and is capable of withstanding strong temperature gradients ranging from -243°C to +130°C.

[0094] The airless tire 1 comprises, radially from the inside to the outside, a supporting structure 2, intended to cooperate with the rim 100 or a hub, a strip of shear 3 secured to the supporting structure 2 and a tread 4 secured to the shear strip 3.

[0095] The supporting structure 2 is constituted, here, of a plurality of spokes 21 regularly distributed circumferentially.

[0096] In a non-limiting manner, the spokes 21 each comprise here an internal end 21a secured to the rim 100, for example by fixing means (not shown), such as screw means (screws / nuts) or by rivets (not shown), a concave portion 21b and an external end 21c secured to the shear band 3 by screw means or by rivets (not shown).

[0097] By way of non-limiting example, said fixing means could be configured to fix both a spoke 21 of the tire 1 and the rim 100.

[0098] The shear band 3 comprises, radially from the inside to the outside, a radially inner membrane 31, integral with the supporting structure 2, a shear structure 32 and a radially outer membrane 33.

[0099] As illustrated, the shear structure 32 is constituted by a plurality of shear elements 32a, here distributed circumferentially according to a regular pitch and extending radially between the radially inner membrane or internal shear membrane 31 and the radially outer membrane or external shear membrane 33.

[0100] In a non-limiting manner, each shear element 32a comprises two opposite curvatures.

[0101] The supporting structure 2 is made of a thermoplastic polymer material, said to be high-performance.

[0102] The material constituting at least the supporting structure 2 has the following mechanical characteristics, measured according to the ASTM D638 standard of ASTM (“American Society for Testing and Materials”) International: - a Young's modulus in tension E, measured at a temperature equal to 20°C, at least equal to 1 GPa and at most equal to 6 GPa, and, measured at a temperature equal to -196°C, at least equal to 1.2 GPa and at most equal to 9 GPa, and - a maximum tensile stress Sm, measured at a temperature equal to 20°C, at least equal to 25 MPa and at most equal to 150 MPa, and, measured at a temperature equal to -196°C, at least equal to 40 MPa and at most equal to 260 MPa.

[0103] As illustrated in detail in Figures 2A, 2B and 2C, the radially inner membrane 31 and the radially outer membrane 33 of the shear band 3 comprise a plurality of successive patterns 34, 35, visible respectively in Figures 2B and 2C, distributed circumferentially over the circumferential perimeter of the corresponding shear membrane.

[0104] In other words, the respective perimeters of the radially inner membrane 31 and the radially outer membrane 33 of the shear band 3 are not circular, unlike the respective perimeters of the radially inner and radially outer membranes of the shear band of existing tires.

[0105] Such patterns 34, 35 make it possible to increase the length of the corresponding shear membrane relative to a shear membrane of circular circumferential perimeter. Indeed, a length of the corresponding shear membrane is observed to be increased by 0.01% to 5% relative to a shear membrane of circular circumferential perimeter.

[0106] Thus, when the wheel 10 goes flat, the patterns 34, 35 will allow the corrugated inner and outer shear membranes respectively to lengthen in the circumferential direction and therefore to increase the circumferential length of contact with the ground, and thus to reduce the average contact pressure of the tire on the ground.

[0107] Generally, the radially inner membrane 31 and / or the radially outer membrane 33 of the shear band 3 comprises a plurality of successive patterns 34, 35 distributed circumferentially over the circumferential perimeter of the corresponding shear membrane.

[0108] By “successive patterns” is meant a succession of patterns along the perimeter of the corresponding shear membrane.

[0109] The patterns 34, 35 of a plurality of patterns are here identical to each other and are regularly distributed over the circumferential perimeter of the corresponding shear membrane.

[0110] As illustrated in [Fig.2B], each internal pattern 34 of the internal shear membrane 31 successively comprises a substantially planar anchoring section 34a, a concave shape 34b and a convex shape 34c.

[0111] As illustrated in [Fig.2C], each external pattern 35 of the external shear membrane 33 successively comprises a substantially planar anchoring section 35a, a concave shape 35b and a convex shape 35c.

[0112] Generally, each pattern 34, 35 of a plurality of patterns comprises a substantially planar anchoring section 34a, 35a, at least one concave shape 34b, 35b and at least one convex shape 34c, 35c.

[0113] As illustrated in [Fig.2B], the anchoring section 34a of the internal shear membrane 34 cooperates with a first internal end 32b of a shear element 32a of the shear structure 32 and the supporting structure 2.

[0114] As illustrated in [Fig.2C], the anchoring section 35a of the external shear membrane 33 cooperates with a second external end 32c of an element shear 32a of the shear structure 32 and the tread 4.

[0115] By “concave” is meant a shape curved towards the inside of the tire.

[0116] By “convex” is meant a shape curved towards the outside of the tire, opposite to concave.

[0117] The patterns of the corresponding shear membrane are periodic, i.e. they have a constant pitch.

[0118] The anchoring section 34a, 35a is made so as to connect tangentially at each of its ends to the straight sections of the adjacent patterns.

[0119] The anchoring section 34a of each internal pattern 34 forms with a cylindrical geometry C1, passing through the two ends 34d, 34e of each internal pattern 34, an angle a of between 5° and 30°.

[0120] The anchoring section 35a of each external pattern 35 forms with a cylindrical geometry C2, passing through the two ends 35d, 35e of each external pattern 35, an angle a of between 5° and 20°.

[0121] Each pattern 34, 35 extends over an angular sector of angle [3 between 5° and 15°, preferably between 8° and 10°. The angle [3 is formed between two straight lines each passing through an end 34d, 34e; 35d, 35e and the center XC1-XC1; XC2-XC2 of the corresponding cylindrical geometry C1; C2.

[0122] As illustrated, the inner membrane 31 and the outer membrane 33 of the shear band 3 each comprise a plurality of patterns 34, 35.

[0123] In the example illustrated, and in a non-limiting manner, the concave shape 34b of the pattern 34 of the inner membrane 31 is radially opposite the concave shape 35b of the pattern 35 of the outer membrane 33 and the convex shape 34c of the pattern 34 of the inner membrane 31 is radially opposite the convex shape 35c of the pattern 35 of the outer membrane 33.

[0124] In other words, the plurality of patterns 35 of the outer membrane 33 is parallel to the plurality of patterns 34 of the inner membrane 31.

[0125] Alternatively, an angular offset could be provided between the patterns 34 of the inner membrane 31 and the patterns 35 of the outer membrane 33.

[0126] It could also be provided that the plurality of patterns 34 of the inner shear membrane 31 forms a mirror image, with respect to an average surface of the shear structure 32, of the plurality of patterns 35 of the outer shear membrane 33.

[0127] Figures 3 and 4 illustrate two graphs showing the gains obtained for an airless tire whose shear band comprises corrugated outer and inner shear membranes respectively, with reference to [Fig.2A], compared to a known airless tire whose perimeter of the inner and outer membranes respectively of the shear band is circular.

[0128] It can be seen that, according to the invention, the circumferential length of the contact area of ​​the tire with the ground is increased by 80% compared to the circumferential length of the contact area of ​​a known tire. In this example, the circumferential length of the contact area of ​​the tire 1 according to the invention is equal to 90mm and the circumferential length of the contact area of ​​a known tire is 50mm.

[0129] It is also noted that the stresses in the corrugated external and internal shear membranes, respectively, as well as in the shear elements 32 of the shear structure 32 of the tire 1 according to the invention are less than or equal to the stresses in the shear membranes of the known airless tire.

[0130] To read the graph on the stress levels, note that 1 daN / mm2 is equal to 1 bar which is equal to 0.1 MPa.

[0131] [Fig.5] represents a table summarizing, for a wheel width of 300 mm, an average diameter of the external shear membrane 33 of 840 mm, and an average diameter of the internal shear membrane 31 of 720 mm, under a load of 100 daN, the measured circumferential contact area length, the average contact pressure, the deflection corresponding to the radial crushing of the tire and different maximum stresses compared to a control, that is to say to a tire comprising shear membranes of circular perimeter.

[0132] In the tire according to the invention, a deflection greater than the indicator is observed with a greater circumferential length of contact area, which makes it possible to reduce the ground pressure.

[0133] Such an optimized shear band makes it possible to reduce the rigidity of the shear band without increasing the maximum stress generated in the shear band and thus to obtain the lowest possible average contact pressure of the tire with the ground.

[0134] Such a shear band also promotes the flattening of the tire on the ground.

[0135] In addition, the fact of not increasing the maximum stress makes it possible not to degrade the endurance compared to known tires.

Claims

Claims

1. Airless tire (1) for a vehicle, comprising, radially from the inside to the outside, a supporting structure (2), intended to cooperate with a rim (100) of a wheel (10), a shear band (3) secured to the supporting structure (2) and a tread (4) secured to the shear band (3), the shear band (3) comprising, radially from the inside to the outside, an internal shear membrane (31), a shear structure (32) constituted by a plurality of shear elements (32a) distributed circumferentially and an external shear membrane (33), characterized in that the internal shear membrane (31) and / or the external shear membrane (33) of the shear band (3) comprises a plurality of successive patterns (34, 35) distributed circumferentially on the circumferential perimeter of the corresponding shear membrane (33, 34).

2. A tire (1) according to claim 1, wherein the patterns (34, 35) of a plurality of patterns are identical to each other and are regularly distributed over the circumferential perimeter of the corresponding shear membrane (31, 33).

3. A tire (1) according to claim 1 or 2, wherein each pattern (34, 35) extends over an angular sector of angle (|3) between 5° and 15°.

4. A tire (1) according to any preceding claim, wherein each pattern (34, 35) of a plurality of patterns comprises a substantially planar anchoring section (34a, 35a), at least one concave shape (34b, 35b) and at least one convex shape (34c, 35c).

5. A tire (1) according to claim 4, wherein the anchoring section (34a) of the internal shear membrane (34) cooperates with a first internal end (32b) of a shear element (32a) of the shear structure (32) and the supporting structure (2).

6. A tire (1) according to claim 4 or 5, wherein the anchoring section (35a) of the external shear membrane (33) cooperates with a second external end (32c) of a shear element (32a) of the shear structure (32) and the tread (4).

7. A tire (1) according to any one of claims 4 to 6, wherein the anchoring section (34a, 35a) of a pattern (34, 35) connects tangentially at each of its ends to the straight sections adjacent patterns.

8. Tire (1) according to any one of claims 4 to 7, in which the anchoring section (34a, 35a) forms with a cylindrical geometry (C) passing through two ends (34d, 34e; 35d, 35e) of each pattern (34, 35), an angle (a) of between 5° and 20°.

9. A tire (1) according to any one of claims 4 to 8, wherein each pattern (34) of the internal shear membrane (31) successively comprises circumferentially the substantially planar anchoring section (34a), the concave shape (34b) and the convex shape (34c).

10. A tire (1) according to any one of claims 4 to 9, wherein each pattern (35) of the external shear membrane (33) successively comprises circumferentially the substantially planar anchoring section (35a), the concave shape (35b) and the convex shape (35c).

11. A tire (1) according to any one of claims 4 to 10, wherein the concave shape (34b) of each pattern (34) of the internal shear membrane (31) is radially opposite the concave shape (35b) of each pattern (35) of the external shear membrane (33) and the convex shape (34c) of each pattern (34) of the internal shear membrane (31) is radially opposite the convex shape (35c) of each pattern (35) of the external shear membrane (33).

12. A tire (1) according to any preceding claim, wherein the number of patterns (34, 35) is equal to the number of shear elements (32a) of the shear structure (32).

13. A tire (1) according to any preceding claim, wherein the shear elements (32a) of the shear structure (32) are circumferentially distributed at a regular pitch and extend radially between the inner shear membrane (31) and the outer shear membrane.

14. A tire (1) according to any preceding claim, wherein the supporting structure (2), the shear band (3) and the tread (4) are each made of the same material.

15. A tire (1) according to any one of the preceding claims, wherein the supporting structure (2), the shear band (3) and the tread (4) are each made of at least one material, preferably thermoplastic, having the characteristics following mechanical properties, measured according to ASTM D638 of the ASTM (American Society for Testing and Materials) International: - a Young's modulus in tension E, measured at a temperature equal to 20°C, at least equal to 1 GPa and at most equal to 6 GPa, and, measured at a temperature equal to -196°C, at least equal to 1.2 GPa and at most equal to 9 GPa, and - a maximum tensile stress Sm, measured at a temperature equal to 20°C, at least equal to 25 MPa and at most equal to 150 MPa, and, measured at a temperature equal to -196°C, at least equal to 40 MPa and at most equal to 260 MPa.

16. A wheel (10) comprising an airless tire (1) according to any preceding claim mounted on a rim (100).

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