Wheel, in particular for extraterrestrial vehicle, comprising an airless tyre and an optimised rim

Abstract

The present invention relates to a mounted assembly (10) for a vehicle comprising a rim (100) and an airless tyre (1) mounted on the rim (100), the airless tyre (1) comprising, radially from the inside to the outside, a supporting structure (2) secured to an outer surface (101) of the rim (100), a shear strip (3) secured to the supporting structure (2) and a tread (4) secured to the shear strip (3). The outer surface (101) of the rim (100) comprises a plurality of consecutive patterns (102) distributed circumferentially along the perimeter of the outer surface (101) of the rim (100).

Description

[0001] DESCRIPTION

[0002] TITLE: Wheel, particularly for an extraterrestrial vehicle, comprising an airless tire and an optimized rim

[0003] Technical field of the invention

[0004] The present invention relates to the field of wheels comprising an airless tire, 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.

[0005] The present invention relates more particularly to the rim of such an airless tire.

[0006] State of the prior art

[0007] A conventional tyre subjected to the internal pressure of an inflation gas, generally air, or a conventional solid or airless tyre, 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.

[0008] 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".

[0009] In the following, the circumferential or longitudinal direction means the direction of rotation of the tire, the axial or transverse direction means a 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.

[0010] The term "inner" element means the part closer to the axis of rotation of the tire compared to an "outer" element.

[0011] An airless tire generally comprises, radially from the inside to the outside:

[0012] - a carcass made up of structural elements and intended to cooperate with a rim or a hub; and

[0013] - a tread integral with the carcass and intended to transmit rolling forces to said carcass, to be worn and to guarantee the grip of the tire with the ground.

[0014] The carcass comprises, radially from the inside to the outside:

[0015] - a supporting structure, intended to structurally carry at least part of the load applied to the tire and secured to the rim or hub; and

[0016] - a shear strip, intended to transmit rolling forces by shear to the supporting structure and to contribute at least in part to carrying the load.

[0017] 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.

[0018] However, the load-bearing structure does not usually delineate a sealed internal cavity 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.

[0019] The shear band comprises, radially from the inside to the outside:

[0020] - a first radially inner membrane,

[0021] - a shear layer consisting of one or more shear elements, and - a second radially outer membrane intended to receive the tread and connected to the radially inner membrane by the shear layer.

[0022] Generally, the first and second membranes have a modulus of elasticity in circumferential extension often significantly higher 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.

[0023] The shear layer of polymeric material is made, for example, of a polymeric material, such as a natural rubber or a synthetic rubber, or 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.

[0024] Finally, the tread, which is the radially outer component of the tire, is most often made of a polymeric material, such as natural rubber or synthetic rubber.

[0025] 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.

[0026] However, increasing the load capacity of these airless tires requires: - either increasing the thickness of the structural elements of the carcass, which implies an increase in the stresses in these structural elements. Indeed, an increase in the thickness of a structural element, intended to work in bending, such as for example, a radius of a load-bearing structure, will lead to an increase in bending stresses.

[0027] - or to increase the number of structural elements of the carcass, distributed around the rim. However, in the event of heavy load, contact between the structural elements may appear.

[0028] Thus, when the airless tire is subjected to a strong vertical load, an interpenetration of the spokes of the supporting structure is observed at the junction with the rim, i.e. an overlap of the spokes of the supporting structure in the initial unloaded state, which is not acceptable.

[0029] It is therefore not possible to increase the number of spokes beyond a certain quantity without modifying the rest of the structure and while guaranteeing suitable mechanical operation.

[0030] Subsequently, there is a need to address the above-mentioned drawbacks.

[0031] Statement of the invention

[0032] The inventors aim to design an airless tire capable of supporting loads between 5 daN and 200 daN per wheel, in particular by choosing an appropriate rim.

[0033] Another objective is to design an airless tire capable of rolling in an 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 rolling in a terrestrial environment and on soils of various types, which may be sandy or stony.

[0034] The present invention relates to a mounted assembly or wheel for a vehicle comprising a rim and an airless tire mounted on said rim, the airless tire comprising, radially from the inside to the outside, a supporting structure secured to an outer surface of the rim, a shear band secured to the supporting structure and a tread secured to the shear band, the supporting structure comprising a plurality of spokes regularly distributed circumferentially.

[0035] The outer surface of the rim comprises a plurality of successive patterns distributed circumferentially around the perimeter of the outer surface of the rim.

[0036] The outer surface of the rim is corrugated, so it is not cylindrical, unlike the cylindrical outer surface of existing wheel rims.

[0037] Such patterns make it possible to increase the number of spokes in the supporting structure, i.e. to densify it without the risk of the spokes overlapping each other in the initial unloaded state, in order to support high loads, between 5 daN and 200 daN per wheel, and without increasing the maximum stress in the overall structure, i.e. of the carcass beyond a threshold value depending on the material.

[0038] By "successive patterns" we mean a succession of patterns along the perimeter of the outer surface of the rim.

[0039] The term "rim" means a structure for connecting to the vehicle and centrally supporting the tire. The rim comprises, in a known manner, a fixing hub intended to be fixed to the vehicle and at least one outer ferrule delimiting the outer surface of the rim. The fixing hub is connected to the outer ferrule by a connecting structure, for example one or two radial flanges.

[0040] Each pattern of a plurality of patterns successively comprises circumferentially a convex shape, a concave shape and a substantially planar anchoring section.

[0041] By "concave" we mean a shape that curves towards the inside of the tire.

[0042] By "convex" we mean a shape that curves outward from the tire, as opposed to concave.

[0043] Advantageously, the patterns of a plurality of patterns are identical to each other and are regularly distributed around the perimeter of the outer surface of the rim. For example, each pattern extends over an angular sector of an angle between 5° and 15°.

[0044] Advantageously, the anchoring section of a pattern of the outer surface of the rim cooperates with a first inner end of a spoke of the supporting structure.

[0045] 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.

[0046] Preferably, the first inner end of each spoke of the supporting structure is tangential to the anchoring section of a corresponding pattern of the outer surface of the rim.

[0047] For example, the anchor section of one pattern of the outer surface of the rim connects tangentially at each of its ends to the straight sections of adjacent patterns.

[0048] For example, the anchoring section of a pattern of the outer surface of the rim forms with a cylindrical geometry passing through two ends of each pattern, an angle between 5° and 30°, preferably equal to 10°.

[0049] Alternatively, one could provide that the convex shape is located between the anchoring section and the concave shape.

[0050] For example, the number of patterns on the outer surface of the rim is equal to the number of spokes in the supporting structure.

[0051] In other words, the number of patterns corresponds to the number of anchor sections.

[0052] Preferably, the spokes of the supporting structure are distributed circumferentially at a regular pitch and extend radially between the outer surface of the rim and the shear band.

[0053] For example, the shear band comprises, radially from the inside to the outside, an inner shear membrane, a shear structure consisting of a plurality of circumferentially distributed shear elements and an outer shear membrane. Advantageously, the shear elements of the shear structure are circumferentially distributed at a regular pitch and extend radially between the inner shear membrane and the outer shear membrane.

[0054] In a non-limiting manner, each shear element comprises two opposing curvatures.

[0055] For example, and in no way limiting, the internal shear membranes and the external shear membranes of the shear band are cylindrical.

[0056] Alternatively, it could be provided that the radially inner membrane and / or the radially outer membrane of the shear band comprises a plurality of successive patterns distributed circumferentially over the circumferential perimeter of the corresponding shear membrane.

[0057] Each pattern comprising at least one concave shape, at least one convex shape and an anchoring section cooperating with a shear element.

[0058] 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

[0059] - 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.

[0060] 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. To enable an airless tire to run in an extraterrestrial environment that may vary between very low temperatures and very high temperatures, typically in the range [-243°C; 130°C], and on soils of various types, which may 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 as 20°C, and at very low temperature, taken as -196°C.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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 components of an airless tire simplifies manufacturing and allows for easier adhesion between the different components.

[0066] Brief description of the drawings

[0067] 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:

[0068] [Fig. 1] represents an overall perspective view of a wheel comprising an airless tire according to a first embodiment of the invention;

[0069] [Fig.2] illustrates a front view of the wheel of Figure 1;

[0070] [Fig.2A] represents a detail of Figure 2; and

[0071] [Fig.2B] represents a detail of Figure 2A.

[0072] Detailed description of at least one embodiment

[0073] In the following description, the terms "circumferential", "axial" and "radial" are defined with respect to the axis of rotation XI - XI of the tire 1. The "circumferential" direction designates a direction of a plane perpendicular to the axis of rotation X l -Xl tangent to the tread of the tire 1, the "axial" direction is the direction of the axis of rotation Xl -X l of the tire 1 and a "radial" direction designates a direction perpendicular to the axis of rotation Xl -Xl of the tire 1.

[0074] Figure 1 is a perspective overview of a mounted assembly or wheel 10 comprising a rim 100 and an airless tire 1 mounted on said rim 100.

[0075] By “rim” is meant a structure connecting to the vehicle and centrally supporting the tire 1.

[0076] 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.

[0077] 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 shear band 3 secured to the supporting structure 2 and a tread 4 secured to the shear band 3.

[0078] The supporting structure 2 is constituted, here, of a plurality of spokes 21 regularly distributed circumferentially.

[0079] The spokes 21 of the supporting structure 2 are integral with the outer surface 101 of the rim 100.

[0080] In a non-limiting manner, the spokes 21 each here comprise an internal end 21 a 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 21 b and an external end 21 c secured to the shear band 3 by screw means or by rivets (not shown).

[0081] 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. The shear strip 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.

[0082] 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.

[0083] In a non-limiting manner, each shear element 32a comprises two opposing curvatures.

[0084] The supporting structure 2 is made of a thermoplastic polymer material, said to be high-performance.

[0085] The material constituting at least the supporting structure 2 has the following mechanical characteristics, measured according to ASTM D638 standard of ASTM (“American Society for Testing and Materials”) International:

[0086] - 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

[0087] - 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.

[0088] As illustrated in detail in Figure 2A, the rim 100 comprises an outer surface 101 comprising a plurality of successive patterns 102 distributed circumferentially around the perimeter of the outer surface 101 of the rim 100.

[0089] In other words, the perimeter of the outer surface 101 of the rim 100 is not circular, unlike the perimeter of the outer surface of the rim of existing wheels. Such patterns 102 make it possible to increase the number of spokes 21 of the supporting structure 2, that is to say to densify it without the risk of the spokes 21 overlapping each other in the initial unloaded state.

[0090] By “successive patterns” is meant a succession of patterns along the perimeter of the outer surface 101 of the rim 100.

[0091] The patterns 102 of a plurality of patterns are here identical to each other and are regularly distributed around the perimeter of the outer surface 101 of the rim 100.

[0092] As illustrated in Figure 2B, each pattern 102 of the outer surface 101 of the rim 100 successively comprises a convex shape 102a, a concave shape 102b and a substantially planar anchoring section 102c.

[0093] As illustrated in Figure 2B, the anchoring section 102c of the outer surface 101 of the rim 100 cooperates with a first internal end 21a of a spoke 21 of the supporting structure 2.

[0094] By "concave" we mean a shape that curves towards the inside of the tire.

[0095] By "convex" we mean a shape that curves outward from the tire, as opposed to concave.

[0096] The patterns of the outer surface 101 of the corresponding rim 100 are periodic, that is to say they are distributed according to a constant pitch.

[0097] The anchor section 102c is made so as to connect tangentially at each of its ends to the straight sections of the adjacent patterns.

[0098] The anchoring section 102c of each pattern 102 forms with a cylindrical geometry C, passing through the two ends 102d, 102e of each pattern 102, an angle a of between 5° and 30°, preferably equal to 10°.

[0099] Each pattern 102 extends over an angular sector of angle P between 5° and 15°, preferably between 8° and 10°. The angle P is formed between two straight lines each passing through an end 102d, 102e and the center XC 1 -XC 1 of the corresponding cylindrical geometry C l.

[0100] In the example illustrated, and in a non-limiting manner, the internal shear membranes 31 and the external shear membranes 33 of the shear band 3 are cylindrical.

[0101] Alternatively, it could be provided that the radially inner membrane 31 and / or the radially outer membrane 33 of the shear band 3 comprises a plurality of successive patterns distributed circumferentially over the circumferential perimeter of the corresponding shear membrane. Each pattern comprising at least one concave shape, at least one convex shape and an anchoring section cooperating with a shear element 32a.

[0102] Such an optimized rim allows to increase the number of spokes of the supporting structure, in order to support a greater vertical load on the airless tire.

Claims

CLAIMS 1. Mounted assembly (10) for a vehicle comprising a rim (100) and an airless tire (1) mounted on said rim (100), the airless tire (1) comprising, radially from the inside to the outside, a supporting structure (2) secured to an outer surface (101) of the rim (100), a shear band (3) integral with the supporting structure (2) and a tread (4) integral with the shear band (3), the supporting structure (2) comprising a plurality of spokes (21) regularly distributed circumferentially, characterized in that the outer surface (101) of the rim (100) is corrugated and not cylindrical and comprises a plurality of successive patterns (102) distributed circumferentially on the perimeter of the outer surface (101) of the rim (100), each pattern (102) of a plurality of patterns successively comprises circumferentially a convex shape (102a), a concave shape (102b) and a substantially planar anchoring section (102c).

2. Mounted assembly (10) according to claim 1, in which the patterns (102) of a plurality of patterns are identical to each other and are regularly distributed around the perimeter of the outer surface. (101) of the rim (100).

3. Mounted assembly (10) according to claim 1 or 2, in which each pattern (102) extends over an angular sector of angle (P) between 5° and 15°.

4. Mounted assembly (10) according to any one of the preceding claims, in which the anchoring section (102c) of a pattern (102) of the outer surface (101) of the rim (100) cooperates with a first internal end (21a) of a spoke (21) of the supporting structure (2).

5. Mounted assembly (10) according to claim 4, in which the first internal end (21a) of each spoke (21) of the supporting structure (2) is tangential to the anchoring section (102c) of a pattern (102) corresponding to the outer surface (101) of the rim (100).

6. Mounted assembly (10) according to any one of the preceding claims, in which the anchoring section (102c) of a pattern (102) of the outer surface (101) of the rim (100) connects tangentially at each of its ends to the straight sections of the adjacent patterns.

7. Mounted assembly (10) according to any one of the preceding claims, in which the anchoring section (102c) of a pattern (102) of the outer surface (101) of the rim (100) forms with a cylindrical geometry (C) passing through two ends (102d, 102e) of each pattern (102), an angle (a) of between 5° and 30°, preferably equal to 10°.

8. Mounted assembly (10) according to any one of the preceding claims, in which the number of patterns (102) of the outer surface (101) of the rim (100) is equal to the number of spokes (21) of the supporting structure (2).

9. Mounted assembly (10) according to any one of the preceding claims, in which the spokes (21) of the supporting structure (2) are distributed circumferentially according to a regular pitch and extend radially between the outer surface (101) of the rim (100) and the shear band (3).

10. Mounted assembly (10) according to any one of the preceding claims, in which the supporting structure (2), the shear strip (3) and the tread (4) are each made of the same material.

11. Mounted assembly (10) according to any one of the preceding claims, in which the supporting structure (2), the shear band (3) and the tread (4) 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.

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