Airless tires for extraterrestrial vehicles capable of travelling at cryogenic temperatures

Abstract

The subject of the present invention is an airless tire (1) for vehicles capable of traveling on various types of ground in extraterrestrial environments at extremely low temperatures. Such an airless tire (1) comprises, from radially inside to outside, a support structure (2) intended to cooperate with a rim or hub (3), a shear band (4) and a tread (6). According to the invention, at least one material forming the support structure (2), the shear band (4) and the tread (6) has a tensile Young's modulus E, measured at a temperature equal to 20° C., of at least 1 GPa and at most 6 GPa, a tensile Young's modulus E, measured at a temperature equal to −196° C., of at least 1.2 GPa and at most 9 GPa, a maximum tensile stress Sm, measured at a temperature equal to 20° C., of at least 25 MPa and at most 150 MPa, and a maximum tensile stress Sm, measured at a temperature equal to −196° C., of at least 40 MPa and at most 260 MPa, these mechanical properties being measured according to the ASTM D638 standard.

Description

[Technical Field]

[0001] The subject of the present invention is an airless tire intended to be fitted to extraterrestrial exploration vehicles intended to move around in environments that can reach extremely low temperatures, for example on the Moon or Mars, in the range [-243°C; +53°C], as typically measured at the lunar south pole. [Background technology]

[0002] Conventional tires, which are subjected to an internal pressure of an inflation gas, typically air, or the usual rubber-based materials of conventional solid tires, have mechanical properties that are not compatible with use in environments that can reach extremely low temperatures, also known as cryogenic temperatures, and therefore are not suitable for such applications.

[0003] Metal wheels have been manufactured for attachment to extraterrestrial vehicles, however, such metal wheels suffer from the drawbacks of nonlinear vertical stiffness, i.e., constant over a limited operating range but changing rapidly until failure when a maximum load is reached, high mass, and limited durability, which adversely affect long-term use.

[0004] Furthermore, as an alternative to conventional tires, airless tires, or more generally tires that do not use inflation gas, are known, which support loads with structural components and have performance aspects comparable to those of conventional tires. Airless tires mounted on a hub or rim are sometimes called "non-pneumatic elastic wheels." Such airless tires are described, by way of example, in International Publication No. 2003018332 A1, French Patent No. 2964597, International Publication No. 2012102932 A1, International Publication No. 2018101937 A1, International Publication No. 2018102303 A1, International Publication No. 2018102560 A1, and International Publication No. 2018125186 A1.

[0005] In the following text, circumferential or longitudinal direction refers to the direction of rotation of the tire, axial or lateral direction refers to the direction parallel to the tire's axis of rotation, and radial direction refers to the direction perpendicular to the tire's axis of rotation. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2003018332 [Patent Document 2] French Patent No. 2964597 [Patent Document 3] International Publication No. 2012102932 [Patent Document 4] International Publication No. 2018101937 [Patent Document 5] International Publication No. 2018102303 [Patent Document 6] International Publication No. 2018102560 [Patent Document 7] International Publication No. 2018125186 Summary of the Invention

[0007] Airless tires generally have the following characteristics: - a support structure intended to cooperate with the rim or hub to at least partially structurally support the load; - shear bands intended to transmit running forces to the supporting structure by shear and contribute at least partially to the support of the load; - a tread intended to transmit the rolling forces to the shear zone and to wear down to ensure the tire's grip on the ground; Includes.

[0008] The support structure includes, from radially inner to outer, a connection means to the rim or hub, radial elements or spokes, and a connection means to the shear band. However, the support structure does not generally define a sealed internal cavity intended to contain pressurized gas as in conventional tires. Therefore, a non-pneumatic tire does not need to have a sealed connection to the rim or hub.

[0009] In known embodiments, the shear bands extend radially from inner to outer: - a first inner membrane; a shear layer formed from one or more polymeric materials; - a second outer membrane; Includes.

[0010] In the above-described embodiments, the first and second membranes have circumferential tensile elastic modulus that is often substantially higher than the shear elastic modulus of the shear layer formed from the polymeric material, so that the membranes stretch very little under the application of load, even if the tire flattens during operation. The relative movement of the membranes relative to each other occurs due to shear at the shear layer. In a preferred embodiment, the inner and outer membranes each include superposed layers of reinforcement coated with polymeric material.

[0011] The shear layer may be formed of a polymeric material, such as natural or synthetic rubber, or polyurethane, for example. Typically, the shear layer material has a shear modulus at least equal to 3 MPa and at most equal to 20 MPa, which facilitates flattening of the shear bands under load.

[0012] For several years, Michelin North America has been selling a mounted assembly consisting of an airless tire and wheel as described above under the name MICHELIN® TWEEL®. This technical solution mainly comprises a tread, a shear band, a support structure made of very strong spokes made of polyresin, and a hub made of two pieces of reinforced steel.

[0013] However, for cryogenic applications, the usual polymeric materials from which airless tires are made are not suitable for the specified temperature range. Furthermore, the usual polymeric materials used, especially in shear zones, have a stiffness level that results in high ground pressure, i.e., the risk of the tire sinking into loose ground (such as the lunar surface), and high rolling resistance, i.e., high energy consumption, which negatively impacts the energy autonomy of extraterrestrial vehicles.

[0014] The inventors set themselves the goal of designing an airless tire as described above that can run on a variety of ground types, which may be sandy or stony, in an extraterrestrial environment at extremely low temperatures, typically in the range of [-243°C; +53°C].

[0015] The object is to provide an airless tire for a vehicle, comprising, from radially inner to outer, a support structure intended to cooperate with a rim or hub, a shear band and a tread, The shear band includes, from radially inner to radially outer, a radial inner membrane, a shear structure, and a radial outer membrane; - the support structure, the shear band and the tread are each formed from at least one material; - the material of at least one of the support structure, shear zone and tread is measured in accordance with ASTM (American Society for Testing and Materials) International Standard ASTM D638; - a Young's modulus in tension E, measured at a temperature equal to 20 ° C, of ​​at least 1 GPa and at most 6 GPa, and a Young's modulus in tension E, measured at a temperature equal to -196 ° C, of ​​at least 1.2 GPa and at most 9 GPa, - a maximum tensile stress Sm, measured at a temperature equal to 20 ° C, of ​​at least 25 MPa and at most 150 MPa, and a maximum tensile stress Sm, measured at a temperature equal to -196 ° C, of ​​at least 40 MPa and at most 260 MPa, This was achieved by an airless tire with the following mechanical properties:

[0016] The inventors have chosen a material that has a tensile Young's modulus E and a maximum tensile stress Sm within a specific range both at ambient temperatures, which are essentially taken to be equal to 20°C, and at cryogenic temperatures, which are taken to be equal to -196°C, in order to enable the airless tire to run on various types of ground, which may be sandy or stony, in an extraterrestrial environment that may reach cryogenic temperatures, typically in the range of [-243°C; +53°C].

[0017] The tensile Young's modulus E and the maximum tensile stress Sm are measured on the basis of a "stress-elongation" tensile curve established on the basis of tensile tests carried out on standard specimens according to the ASTM D638 standard ("Standard Test Method for Tensile Properties of Plastics") prepared by ASTM (American Society for Testing and Materials) International. The standard specimen has a length equal to 84 mm and a thickness equal to 2 mm, including a narrowing with 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 tensile Young's modulus E is the tangent modulus measured at low deformation.

[0018] The tensile Young's modulus E determines the stiffness and load-bearing capacity of the airless tire at the target operating temperature, and the maximum tensile stress Sm determines the durability of the airless tire at the target operating temperature.

[0019] As a result, the inventors have selected materials whose mechanical properties allow them to guarantee a satisfactory compromise between load-bearing capacity and durability required for an airless tire under the intended conditions of use, which should be able to withstand loads typically between 16 and 160 daN and which are intended to be fitted to vehicles capable of moving at a maximum speed typically equal to 20 km / h.

[0020] At least one material forming the support structure, the shear bands and the tread is preferably a high-performance thermoplastic polymeric material. Materials of this type, which exhibit high performance at ambient temperatures, have been found to maintain good mechanical properties in terms of mechanical strength and stiffness at elevated temperatures, typically at least equal to 150°C. Surprisingly, as a background to the present invention, the inventors have also demonstrated that such high-performance thermoplastic polymeric materials can achieve a satisfactory compromise between high structural stiffness, high durability and low mass for airless tires even at very low cryogenic temperatures, as demonstrated by measurements carried out at -196°C.

[0021] According to a first advantageous embodiment, at least one material forming the support structure, the shear bands and the tread is polyaryletherketone (PAEK). The generic term "polyaryletherketone" (PAEK) refers to a family of technical polymers that have high thermomechanical properties, especially at high temperatures. As shown in Table 1 herein, polyaryletherketones, such as the material Victrex AM200™ sold by the company Victrex®, are particularly easy to apply and have good mechanical properties at very low temperatures.

[0022] According to a second advantageous embodiment, at least one material forming the support structure, the shear bands and the tread is polyetheretherketone (PEEK), a thermoplastic polymeric material belonging to the polyaryletherketone family. Polyetheretherketones, such as the materials Victrex CT100™ and Victrex 450G™ sold by the company Victrex®, have the required mechanical properties, especially at cryogenic temperatures.

[0023] According to a third advantageous embodiment, at least one material forming the support structure, the shear bands and the tread is a polyimide (PI), which has excellent mechanical properties at cryogenic temperatures, but is more difficult to employ than polyetheretherketones, such as the material Victrex CT100.

[0024] According to a fourth advantageous embodiment, at least one material forming the support structure, shear bands and tread is polyetherimide (PEI). Polyetherimides, such as the Ultem 1010™ material, have mechanical properties comparable to polyetheretherketones, such as the Victrex CT100™ material, but have a lower elongation at break. Polyetherimides (PEI) have the advantage of being more economical.

[0025] Preferably, the support structure, shear bands, and tread are each formed from the same material, as having all components of an airless tire made from the same material simplifies manufacturing and facilitates adhesion between the different components.

[0026] Preferably, the shear structure is formed from multiple circumferentially distributed shear elements. Such discrete shear structures have the advantage of being lighter than continuous shear structures, and their stiffness can be more precisely optimized.

[0027] A second subject of the invention is a wheel comprising an airless tire such as described above mounted on a rim.

[0028] A further subject of the present invention is a method for manufacturing an airless tire comprising, from radially inner to outer, a support structure, shear bands and a tread formed from at least one high performance thermoplastic polymeric material as described above.

[0029] The first method of manufacturing airless tires employs injection molding technology, where the material from which the airless tire is made is injected into a mold.

[0030] A second method for producing airless tires employs additive manufacturing techniques. Additive manufacturing employs a 3D printer that deposits a malleable printing material in successive layers through a nozzle. Such 3D printers generally include a chamber forming an enclosure bounded by walls, inside which is located a platform for supporting the printing piece and a nozzle for supplying the material that forms such a printing piece. To enable the formation of the part's shape, a drive system is provided that includes a lift for vertically moving the platform or nozzle and intersecting translational-displacement stages for horizontally manipulating the platform or nozzle intended to supply the material that forms the part.

[0031] A first variant of the manufacturing method, employing injection molding or additive manufacturing techniques, involves a single step of manufacturing a tire formed from a single piece.

[0032] A second variant of the manufacturing method, using injection molding or additive manufacturing techniques, comprises successive steps of manufacturing the elementary pieces that make up the airless tire and joining these pieces together.

[0033] Preferably, the manufacturing method including the step of manufacturing the pieces includes the step of joining the pieces together by rivets.

[0034] According to a first variant of the step of joining the pieces together by rivets, the manufacturing method comprises a step of joining the pieces together by metal rivets, preferably made of stainless steel or aluminium.

[0035] According to a second variant of the step of joining the pieces together by rivets, the manufacturing method comprises a step of joining the pieces together by rivets made of a thermoplastic polymeric material.

[0036] According to a first embodiment of the step of joining the pieces together with a rivet formed from a thermoplastic polymer material, the manufacturing method includes the step of joining the pieces together with a single rivet formed from a thermoplastic polymer material that has been heated and compressed by thermal conduction, electrical conduction or ultrasonic heating.

[0037] According to a second embodiment of the step of joining the pieces together with rivets made of thermoplastic polymer material, the manufacturing method includes a step of joining the pieces together with rivets made of thermoplastic polymer material that has been heated and compressed together into a plate by thermal conduction, electrical conduction or ultrasonic heating.

[0038] Advantageously, the manufacturing method comprising the step of manufacturing the pieces comprises the step of joining the pieces together by adhesive bonding.

[0039] According to a first variant of the step of joining the pieces together by adhesive bonding, the manufacturing method includes a step of joining the pieces together by adhesive bonding using a thermoplastic adhesive of the same type as the high-performance thermoplastic material of one of the two pieces to be joined together.

[0040] According to a second variant of the step of joining the pieces together by adhesive bonding, the manufacturing method comprises a step of joining the pieces together by adhesive bonding using a polymeric adhesive, preferably an epoxy adhesive. DETAILED DESCRIPTION OF THE INVENTION

[0041] FIG. 1 shows an example of an airless tire according to the present invention.

[0042] 1 is a perspective overall view of an airless tire for vehicles 1, comprising, from radially inside to outside, a support structure 2 intended to cooperate with a rim or hub 3, a shear band 4, and a tread 6. The shear band 4 comprises, from radially inside to 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 formed from a plurality of circumferentially distributed shear elements 5. The support structure 2, the shear band 4, and the tread 6 are each formed from a single high-performance thermoplastic polymeric material, which is the same for each of the aforementioned components. In this case, the airless tire 1 is obtained by a manufacturing method employing additive manufacturing techniques.

[0043] The inventors have investigated several high performance thermoplastic polymeric materials, the mechanical properties of which, according to the criteria of the present invention, are shown in Table 1 below. [Table 1] TIFF2026503390000002.tif118157

[0044] The PEEK-type material Victrex CT100™ is considered particularly advantageous for producing airless tires for fitting extraterrestrial vehicles intended to roam on the Moon or Mars down to extremely low temperatures that can reach, for example, −243° C. This material has the advantage of having both a high tensile Young's modulus (7 GPa) at extremely low temperatures (−196° C.), which ensures a satisfactory stiffness, and a high maximum tensile stress Sm (252 MPa), which ensures a satisfactory durability. [Explanation of symbols]

[0045] 1. Airless tires 4 Shear zone 5 Shear elements 6 Tread 40 Shear structure 42 Radial adventitia

Claims

1. A pneumatic tire (1) for a vehicle, comprising, from radially inside to outside, a support structure (2) intended to cooperate with a rim or hub (3), a shear band (4) and a tread (6), - said shear band (4) comprises, from radially inside to outside, a radially inner membrane (41), a shear structure (40) and a radially outer membrane (42); - said support structure (2), said shear band (4) and said tread (6) are each made of at least one material; the at least one material forming the support structure (2), the shear band (4) and the tread (6) has a surface roughness measured in accordance with ASTM (American Society for Testing and Materials) International Standard ASTM D638; a tensile Young's modulus E measured at a temperature equal to -20°C of at least equal to 1 GPa and at most equal to 6 GPa, and a tensile Young's modulus E measured at a temperature equal to -196°C of 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., of at least 25 MPa and at most 150 MPa, and a maximum tensile stress Sm, measured at a temperature equal to −196° C., of at least 40 MPa and at most 260 MPa, The airless tire (1) is characterized by having the following mechanical properties.

2. the at least one material forming the support structure (2), the shear band (4) and the tread (6) is a high performance thermoplastic polymeric material; An airless tire (1) according to claim 1.

3. the at least one material forming the support structure (2), the shear band (4) and the tread (6) is polyaryletherketone (PAEK); An airless tire (1) according to claim 2.

4. the at least one material forming the support structure (2), the shear band (4) and the tread (6) is polyetheretherketone (PEEK); An airless tire (1) according to claim 3.

5. the at least one material forming the support structure (2), the shear band (4) and the tread (6) is polyimide (PI); An airless tire (1) according to claim 2.

6. the at least one material forming the support structure (2), the shear band (4) and the tread (6) is polyetherimide (PEI); An airless tire (1) according to claim 2.

7. the support structure (2), the shear band (4) and the tread (6) are each formed from the same material; An airless tire (1) according to any one of claims 1 to 6.

8. The shear structure (40) is formed from a plurality of circumferentially distributed shear elements (5), An airless tire (1) according to any one of claims 1 to 7.

9. 9. An airless tire according to claim 1 mounted on a rim. A wheel characterized by:

10. A method for manufacturing an airless tire (1) according to any one of claims 2 to 8, employing additive manufacturing techniques. A manufacturing method characterized by:

11. a single step of producing a tire formed from a single piece; The method of claim 10.

12. The method includes a step of manufacturing pieces that constitute the airless tire and a step of joining the pieces to each other, The method of claim 10.

13. joining the pieces together with rivets; The method of claim 12.

14. joining the pieces together with rivets formed of a thermoplastic polymeric material; The method of claim 13.

15. joining the pieces together with a single rivet formed of a thermoplastic polymeric material that has been heated and compressed by thermal conduction, electrical conduction, or ultrasonic heating; The method of claim 14.

16. joining the pieces together with rivets formed of thermoplastic polymer material heated and compressed together into a plate by thermal conduction, electrical conduction, or ultrasonic heating; The method of claim 14.

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