Airless tyre for an extraterrestrial vehicle capable of travelling at very low temperatures

Abstract

The present invention relates to an airless tyre (1) for a vehicle capable of travelling in an extraterrestrial environment at very low temperatures and on a plurality of different surfaces. Such an airless tyre (1) comprises, radially from the inside to the outside, a supporting structure (2), which is intended to co-operate with a rim or a hub (3), a shear band (4) and a tread (6). According to the invention, the at least one constituent material of the support structure (2), of the shear band (4) and of the tread (6) has a Young's modulus E, measured at a temperature of 20°C, that is at least equal to 1 GPa and at most equal to 6 GPa and, measured at a temperature of -196°C, that is at least equal to 1.2 GPa and at most equal to 9 GPa and a maximum tensile stress Sm, measured at a temperature of 20°C, that is at least equal to 25 MPa and at most equal to 150 MPa and, measured at a temperature of -196°C, that is at least equal to 40 MPa and at most equal to 260 MPa, these mechanical characteristics being measured according to standard ASTM D638.

Description

Airless tire for extraterrestrial vehicles that can operate at very low temperatures

[0001] The present invention relates to an airless tire, intended to equip an extraterrestrial exploration vehicle, intended to move, for example, on the moon or on the planet Mars, in an atmosphere which can reach very low temperatures, typically in the range [-243°C; +53°C], as measured at the South Pole of the moon.

[0002] A conventional tire, subjected to the internal pressure of an inflation gas, generally air, or a classic solid tire 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.

[0003] Metal wheels have been made to equip extraterrestrial vehicles. But such metal wheels have the disadvantages of having a non-linear vertical rigidity, that is to say constant over a restricted operating range and evolving rapidly until a break in rigidity when the maximum load is reached, of having a high mass and of having limited endurance, which is penalizing for long use.

[0004] Furthermore, 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". Such an airless tire has been described, by way of examples, in documents WO 2003018332A1, FR 2964597, WO 2012102932A1, WO 2018101937A1, WO 2018102303A1, WO 2018102560A1, WO 2018125186A1.

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

[0006] An airless tire generally comprises, radially from the inside to the outside: - a supporting structure, intended to structurally carry at least part of the load and to cooperate with a rim or a hub, - a shear strip, intended to transmit rolling forces to the supporting structure by shear and to contribute at least in part to carrying the load, -and a tread, designed to transmit rolling forces to the shear band, to be worn and to guarantee the grip of the tire on the ground.

[0007] The supporting structure comprises, radially from the inside to the outside, means for connection to a rim or hub, radial elements or spokes, and means for connection to a shear band. However, the supporting structure does not generally delimit 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 to a rim or hub.

[0008] The shear band comprises, in a known embodiment, radially from the inside to the outside: -a first inner membrane, - a shear layer made up of one or more polymeric materials, - a second outer membrane.

[0009] In the embodiment described above, 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 one another occurs by shear in the shear layer. In a preferred embodiment, the inner and outer membranes respectively comprise superimposed layers of reinforcements coated in a polymeric material.

[0010] The shear layer of polymeric material consists, for example, of a polymeric material, such as a natural rubber or a rubber synthetic, or polyurethane. Typically, the shear layer material 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.

[0011] 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 load-bearing structure consisting of highly resistant polyresin spokes and a hub made of two reinforced steel parts.

[0012] However, in very low temperature applications, the usual polymeric materials used in an airless tire are incompatible with the specified temperature range. In addition, the usual polymeric materials used, in particular, for the shear band, have rigidity levels that will generate high contact pressures, involving a risk of the tire sinking into soft ground (as on the moon), and generate high rolling resistance, involving high energy consumption, which is detrimental to the energy autonomy of the extraterrestrial vehicle.

[0013] The inventors set themselves the objective of designing an airless tire, as previously described, capable of running in an extraterrestrial environment, at very low temperatures, typically in the range [-243°C; +53°C], and on soils of various types, which may be sandy or stony.

[0014] This objective has been achieved by 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, a shear band and a tread, -the shear band comprising, radially from the inside to the outside, a radially inner membrane, a shear structure and a radially outer membrane, - the supporting structure, the shear band and the tread each being made of at least one material, - at least one material constituting the supporting structure, the shear band and the tread having the following mechanical characteristics, measured according to 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, - 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.

[0015] To enable an airless tire to roll in an extraterrestrial environment that can reach very low temperatures, typically in the range [- 243°C; +53°C], and on soils of various types, which can be sandy or stony, the inventors were led to select materials having, essentially, a Young's modulus in traction E and a maximum tensile stress Sm included in specific ranges both at room temperature, taken equal to 20°C, and at very low temperature, taken equal to -196°C.

[0016] 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 specimen, 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 specimen 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 specimen is equal to 500 mm / min. The Young's modulus in tension E is a tangent modulus measured at low strain.

[0017] The Young's modulus in traction E conditions the rigidities and the load capacity of the airless tire, at the target operating temperatures. The maximum tensile stress Sm conditions the endurance of the airless tire, at the target operating temperatures.

[0018] 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 16 and 160 daN, and is intended to be mounted on a vehicle that can typically travel up to a maximum speed of 20 km / h.

[0019] Preferably, the at least one material constituting the supporting structure, the shear band and the tread is a high-performance thermoplastic polymeric material. This type of material, which performs very well at room temperature, is known to retain good mechanical properties, in terms of mechanical strength and rigidity, at high temperatures, typically at least equal to 150°C. 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.

[0020] According to a first advantageous embodiment, the at least one material constituting the supporting structure, the shear band and the tread is a polyaryletherketone (PAEK). The generic term “polyaryletherketones” (PAEK) designates a family of technical polymers with high thermomechanical properties, in particular at high temperature. A polyaryletherketone, such as, for example, the Victrex AM200™ material, marketed by the company Victrex®, is, in particular, easy to process and has good mechanical characteristics at very low temperature, as shown in Table 1 of this document.

[0021] According to a second advantageous embodiment, the at least one material constituting the supporting structure, the shear band and the tread is a polyetheretherketone (PEEK). A polyetheretherketone is a thermoplastic polymeric material belonging to the family of polyaryletherketones. A polyetheretherketone, such as, for example, the materials Victrex CT 100™ and Victrex 450G™, marketed by the company Victrex®, have the required mechanical characteristics, in particular at cryogenic temperatures.

[0022] According to a third advantageous embodiment, the at least one material constituting the supporting structure, the shear band and the tread is a polyimide (PI). A polyimide, such as, for example, the Aurum PL500A™ material, has excellent mechanical characteristics at cryogenic temperatures, but is more difficult to process than a polyetheretherketone, such as the Victrex CT 100™ material.

[0023] According to a fourth advantageous embodiment, at least one material constituting the supporting structure, the shear band and the tread is a polyetherimide (PEI). A polyetherimide such as, for example, the Ultem 1010™ material, has mechanical properties comparable to those of a polyetheretherketone, such as the Victrex CT 100™ material, but with a lower elongation at break. It has the advantage of being more economical.

[0024] Preferably, the load-bearing structure, the shear band and the tread are each made of the same material. An identical material for all the components of an airless tire simplifies manufacturing and allows for easier adhesion between the different components.

[0025] Even more preferably, the shear structure is constituted by a plurality of shear elements distributed circumferentially. 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.

[0026] A second object of the invention is a wheel comprising an airless tire as previously described, mounted on a rim.

[0027] The invention also relates to a method for manufacturing an airless tire as previously described and comprising, radially from the inside to the outside, a supporting structure, a shear band and a tread made of at least one high-performance thermoplastic polymeric material.

[0028] A first method for manufacturing an airless tire uses injection technology. Such an injection manufacturing method consists of injecting the material(s) constituting the airless tire into a mold.

[0029] A second method for manufacturing an airless tire uses additive manufacturing technology. An additive manufacturing method uses a three-dimensional printing machine that deposits a malleable printing material in successive layers, using a nozzle. Such a three-dimensional printing machine generally comprises a chamber that forms an enclosure delimited by a wall, and inside which is a plate intended to support a part being printed, as well as a nozzle for supplying the material constituting said part. To be able to generate the shape of the part, drive systems are provided comprising an elevator for moving either the plate or the nozzle vertically, and translation tables crossed relative to each other for horizontally controlling either the plate or the nozzle responsible for delivering the material constituting the part.

[0030] A first variant of the manufacturing process using injection technology or additive manufacturing technology includes a single manufacturing step of the tire consisting of a single part.

[0031] A second variant of the manufacturing process using injection technology or additive manufacturing technology successively comprises a step of manufacturing elementary parts, constituting the airless tire, and a step of assembling said elementary parts.

[0032] Preferably, the manufacturing method, comprising a step of manufacturing elementary parts, comprises a step of assembling the elementary parts by rivets.

[0033] According to a first variant of the step of assembling the elementary parts by rivets, the manufacturing method comprises a step of assembling the elementary parts by metal rivets, preferably made of stainless steel or aluminum.

[0034] According to a second variant of the step of assembling the elementary parts by rivets, the manufacturing method comprises a step of assembling the elementary parts by rivets made of thermoplastic polymer materials.

[0035] According to a first embodiment of the step of assembling the elementary parts by rivets made of thermoplastic polymeric materials, the method of manufacturing includes a step of assembling elementary parts by rivets in unitary thermoplastic polymer materials, heated by thermal or electrical conduction or by ultrasonic heating, and crushed.

[0036] According to a second embodiment of the step of assembling the elementary parts by rivets made of thermoplastic polymer materials, the manufacturing method comprises a step of assembling the elementary parts by rivets made of thermoplastic polymer materials grouped into plates, heated by thermal or electrical conduction or by ultrasonic heating, and crushed.

[0037] Advantageously, the manufacturing method, comprising a step of manufacturing elementary parts, comprises a step of assembling the elementary parts by gluing.

[0038] According to a first variant of the step of assembling the elementary parts by gluing, the manufacturing method comprises a step of assembling the elementary parts by gluing using a thermoplastic adhesive of the same nature as the high-performance thermoplastic material of one of the two elementary parts intended to be assembled together.

[0039] According to a second variant of the step of assembling the elementary parts by gluing, the manufacturing method comprises a step of assembling the elementary parts by gluing using a polymeric glue, preferably an epoxy glue.

[0040] An example of an airless tire according to the invention is illustrated in Figure 1.

[0041] Figure 1 is an overall perspective view of 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 or a hub 3, a shear band 4 and a tread 6. The shear band 4 comprises, radially from the inside to the outside, a radially inner membrane 41, a shear structure 40 and a radially outer membrane 42. In the embodiment shown, the shear structure 40 is constituted by a plurality of shear elements 5 distributed circumferentially. The supporting structure 2, the shear band 4 and the tread 6 are each constituted by a material unique high-performance thermoplastic polymer, identical for each of the previously mentioned components. In this case, the airless tire 1 is obtained by a manufacturing process using additive manufacturing technology.

[0042] The inventors studied several high-performance thermoplastic polymeric materials, the mechanical properties of which, satisfying the criteria of the invention, are presented in Table 1 below: [Table 1]

[0043] Victrex CT 100™ material, PEEK type, is considered particularly interesting for the production of an airless tire, intended to equip an extraterrestrial exploration vehicle, planned to move, for example, on the moon or on the planet Mars, down to very low temperatures which can reach, for example, -243°C. This material has the advantage of having both a high Young's modulus in tension E (7 GPa), guaranteeing satisfactory rigidity, and a high maximum tensile stress Sm (252 MPa), guaranteeing satisfactory endurance, at very low temperatures (-196°C).

Claims

Airless pneumatic tire (1) for a vehicle, comprising, radially from the inside to the outside, a supporting structure (2), intended to cooperate with a rim or a hub (3), a shear band (4) and a tread (6), - the shear band (4) comprising, radially from the inside to the outside, a radially inner membrane (41), a shear structure (40) and a radially outer membrane (42), -the supporting structure (2), the shear band (4) and the tread (6) each being made of at least one material, characterized in that the at least one material constituting the supporting structure (2), the shear band (4) and the tread (6) has the following mechanical characteristics, measured according to ASTM D638 standard ("American Society for Testing and Materials") International: - 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, -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. Airless tire (1) according to claim 1, wherein the at least one material constituting the supporting structure (2), the shear band (4) and the tread (6) is a high-performance thermoplastic polymeric material. Airless tire (1) according to claim 2, wherein the at least one material constituting the supporting structure (2), the shear band (4) and the tread (6) is a polyaryletherketone (PAEK). Airless tire (1) according to claim 3, wherein the at least one material constituting the supporting structure (2), the shear band (4) and the tread (6) is a polyetheretherketone (PEEK). Airless tire (1) according to claim 2, wherein the at least one material constituting the supporting structure (2), the shear band (4) and the tread (6) is a polyimide (PI). Airless tire (1) according to claim 2, wherein the at least one material constituting the supporting structure (2), the shear band (4) and the tread (6) is a polyetherimide (PEI). An airless tire (1) according to any one of claims 1 to 6, wherein the supporting structure (2), the shear band (4) and the tread (6) are each made of the same material.An airless tire (1) according to any one of claims 1 to 7, wherein the shear structure (40) is constituted by a plurality of circumferentially distributed shear elements (5). A wheel comprising an airless tire according to any one of claims 1 to 8 mounted on a rim. A method of manufacturing an airless tire (1) according to any one of claims 2 to 8, implementing additive manufacturing technology. Manufacturing method according to claim 10, comprising a single step of manufacturing the tire consisting of a unitary part. Manufacturing method according to claim 10, successively comprising a step of manufacturing elementary parts, constituting the airless tire, and a step of assembling said elementary parts. Manufacturing method according to claim 12, comprising a step of assembling the elementary parts by rivets. Manufacturing method according to claim 13, comprising a step of assembling the elementary parts by rivets made of thermoplastic polymeric materials. Manufacturing method according to claim 14, comprising a step of assembling the elementary parts by rivets made of unitary thermoplastic polymeric materials, heated by thermal or electrical conduction or by ultrasonic heating, and crushed.Manufacturing method according to claim 14, comprising a step of assembling the elementary parts by rivets made of thermoplastic polymeric materials grouped into plates, heated by thermal or electrical conduction or by ultrasonic heating, and crushed.

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