Deformable wheel with non-pneumatic load support and tread heating for lunar and Martian conditions

Abstract

The invention relates to a deformable, non-pneumatic load wheel (2) intended for use on a vehicle for driving in extreme conditions such as those found on the Moon and Mars, comprising a hub (4), a laminated strip (6) comprising a plurality of bushings assembled with interposed layers and a plurality of metal cables (8) connecting the hub to the laminated strip, the laminated strip being covered with at least one thermal insulation coating (20) made of at least one material having a thermal conductivity of less than 0.2 Wm - 1 K - 1, and the wheel further comprising means (22, 24, 26) for heating the interposed layers of the laminated strip.

Description

Background of the invention

[0001] The present invention relates to a deformable wheel with a non-pneumatic load support. More particularly, the invention relates to a wheel that supports a load with its structural components and that has performance capabilities suitable for equipping a vehicle intended to operate in extreme conditions such as those encountered on the Moon and Mars.

[0002] Pneumatic tires possess load-bearing capacity, road shock absorption, and power transmission capabilities (acceleration, braking, and changes of direction) that are particularly well-suited to many vehicles, including bicycles, motorcycles, cars, and trucks. The shock-absorbing capabilities of pneumatic tires are also useful in other applications, such as carts transporting medical equipment or sensitive electronics.

[0003] Alternatives to pneumatic tires exist. These include solid tires and pneumatic tires. However, these alternatives do not offer the same performance advantages as pneumatic tires. In particular, solid tires rely on compression of the part in contact with the ground to support the load. This type of tire can be heavy and rigid and lacks the shock absorption capacity of pneumatic tires. Even when made more elastic, conventional non-pneumatic wheels do not have the same load-bearing capacity or durability as pneumatic tires.

[0004] To remedy these drawbacks, US publication 7,418,988 proposes a structurally supported tire that includes an outer annular band and a plurality of spokes extending transversely and radially inward from the annular band to the wheel hub and intended to transmit in tension the load forces between the annular band and the hub.

[0005] The structurally supported wheel according to this invention does not have a cavity for containing pressurized air and therefore does not require a seal with the wheel rim to maintain internal air pressure. This structurally supported wheel thus does not require a tire in the conventional sense.

[0006] The spokes of this wheel act under tension to transmit load forces between the wheel and the rim, thus enabling it to support the mass of a vehicle. These support forces are generated by the tension of the spokes that are not connected to the portion of the rim in contact with the ground. The spokes also transmit the forces required for acceleration, braking, and cornering.

[0007] Whatever prior art alternatives exist for manufacturing non-pneumatic wheels, they generally do not provide complete satisfaction, especially when intended for use in extreme conditions such as those encountered on the Moon and Mars. Indeed, in such conditions, it is necessary for the wheel to deform significantly upon encountering an obstacle while generating a low and uniform contact pressure to allow the vehicle to remain mobile on soft ground like that found on the Moon and Mars.

[0008] Patent application EP22192685, filed on August 29, 2022, by the Applicant, describes a wheel that meets these needs, notably due to the presence of a laminated annular band comprising a plurality of concentric rings assembled with interposed layers, each composed of a material whose Young's modulus is 600,000 to 1,000 times lower than that of the rings, for example, an elastomeric material. Under an externally applied load, the portion of the laminated band in contact with the ground deforms, not into an essentially circular shape, but into a shape conforming to the ground surface while maintaining an essentially constant ring length. The wheel described in this patent application thus generates a low and uniform contact pressure on the ground.In this way, the vehicle equipped with such wheels can remain mobile (i.e., it does not get stuck in the sand) even on soft ground (like sand) such as that found on the Moon and on Mars.

[0009] The elastomer-based structure of the interlayers in the laminated strip of such a wheel has a minimum operating temperature between -140°C and -150°C, allowing the wheel to operate in most missions around the lunar south pole and at all latitudes on Mars (where the absolute minimum temperature is -120°C). However, this limitation can pose problems if the vehicle equipped with such wheels must travel to permanently shadowed regions (PSRs), such as the lunar poles, where temperatures are consistently between -220°C and -240°C.

[0010] The disclosure of document WO 2019 / 115905-A1 is also relevant to understanding the invention. Object and summary of the invention

[0011] The main purpose of the present invention is to overcome such drawbacks by proposing a deformable wheel structure with non-pneumatic load support that can be fitted to vehicles intended to travel in permanently shaded regions of the Moon where temperatures are constantly in the range of -220°C to -240°C.

[0012] According to the invention, this goal is achieved by means of a deformable wheel with a non-pneumatic load support intended to equip a vehicle for driving in extreme conditions such as those encountered on the Moon and on Mars, comprising: a hub, a laminated annular strip intended to be in contact with the ground, positioned around the concentric hub and comprising a plurality of concentric ferrules which are assembled with interposition of interposition layers each composed of a material whose Young's modulus is 600,000 to 1,000 times lower than that of the ferrules, and a plurality of metal cables radially connecting the hub to the laminated strip by being fixed, on the one hand by an external end to the laminated strip, and on the other hand by an internal end to the hub, and in which, according to the invention: the laminated strip is covered with at least one thermal insulation coating made of at least one material having a thermal conductivity of less than 0.2 Wm-1< K-1< , and the wheel further comprises means for heating the interposition layers of the laminated strip.

[0013] The wheel according to the invention is remarkable, in particular, because of the use of heating means for the interlayers of the laminated strip, which raise the temperature of these interlayers away from the glass transition temperature of the material from which they are made. Since the material composing these interlayers tends to generate heat when it deforms during rolling (due to rolling resistance), and since the heat generated is higher the closer the material's temperature gets to its glass transition temperature, this will have the effect of heating the wheel further, thus raising it even further away from this glass transition temperature.

[0014] Furthermore, the presence of a thermal insulation coating at the level of the laminated strip helps to limit the thermal conductivity between the lunar soil and the material composing the interposition layers of the laminated strip.

[0015] It follows that the wheel according to the invention is capable of withstanding temperatures of around -220°C to -240°C which are typically encountered in regions of the Moon which are permanently in shadow.

[0016] The means for heating the laminated strip may include rotating contacts to establish a rotating electrical connection between the wheel hub and the ferrules of the laminated strip.

[0017] In this case, the rotating contacts are preferably coupled to heated electric wires which are wound in the thickness of the ferrules of the laminated strip.

[0018] More specifically, the ferrules of the laminated strip can be made of composite material and the interposition layers can be composed of a hyperelastic elastomer, the electrical wires of the heating means of the laminated strip being embedded in the composite material during the manufacture of the ferrules in order to convey heat to the elastomer composing the interposition layers.

[0019] In this case, the electrical wires are advantageously positioned at the level of a neutral fiber in the circumferential direction of the composite material, being the fiber which does not undergo any variation in length, regardless of the bending deformation of the ferrule, in a plurality of loops spaced circumferentially from each other.

[0020] Preferably, the heating electric wires run inside a spring, one end of which is screwed on the laminated strip side onto a collar fixed to a ferrule of the laminated strip containing the heating electric wire, and the opposite end is fixed to the hub.

[0021] The thermal insulation coating can be made from one or more of the following materials: aramid synthetic fiber, fiberglass, polyvinyl acetate, and leather.

[0022] Preferably, the thermal insulation coating is covered under one inner face with a metallic coating to limit the transfer of thermal energy by radiation.

[0023] Preferably, the wheel also includes means for measuring the temperature of the interposition layers of the laminated strip.

[0024] Preferably, the wheel also includes means for measuring the deformations and stresses of the laminated strip in order to monitor the performance and lifespan of the laminated strip to compensate for any failure in the event of a mission far from a lunar base. Brief description of the drawings

[0025] Other features and advantages of the present invention will become apparent from the description below, with reference to the accompanying drawings, which illustrate an example of an embodiment without being limiting in any way. In the figures: there figure 1 is a schematic and perspective view of a wheel according to one embodiment of the invention; the figure 2 is a schematic, front view of the wheel of the figure 1 in elevation; the figure 3 is a cross-sectional view along III-III of the figure 2 ; and the figure 4shows an example of the ferrule of the laminated band of the wheel in which heated electrical wires are embedded. figure 5 is a view of a part of the spring inside which run the electric wires heating the interposition layers of the laminated strip. Detailed description of implementation methods

[0026] The invention relates to a deformable wheel with a non-pneumatic load support as shown in the figure 1 which is suitable for equipping a vehicle intended to operate in extreme conditions such as those encountered on the Moon and Mars.

[0027] Wheel 2 shown on the figure 1 comprises mainly a hub 4, a laminated annular strip 6 intended to be in contact with the ground, and a plurality of metal cables 8 radially connecting the hub to the laminated strip.

[0028] As depicted on the figures 2 And 4, the laminated strip 6 consists of a plurality of concentric ferrules 6a which are assembled together by sandwiching interposition layers 6b each composed of a material whose Young's modulus is 600000 to 1000 times lower than that of the ferrules.

[0029] The 6a ferrules can be metallic (for example, made of steel) or made of composite material.

[0030] As for the interposition layers 6b, they are advantageously made of a hyperelastic elastomer having a glass transition temperature below 120°C.

[0031] Thanks to this composition of the laminated strip 6, the portion of the laminated strip in contact with the ground deforms under an externally applied load, conforming to the ground surface while maintaining a virtually constant length of the rings 6a that compose it. The relative displacement of the rings of the laminated strip occurs through shearing in the interposed layers 6b.

[0032] As depicted in particular on the figure 1 The hub 4 of the wheel carries two discs 12, 14 which protrude radially outwards. These two discs 12, 14 are spaced apart along the axis XX of the wheel and each has an outer diameter against which the inner surface of the laminated strip 6 is able to come abut in order to limit deformations of the latter.

[0033] The cables 8 radially connect the laminated strip 6 to the hub 4. For this purpose, each cable 8 includes an outer end 8a which is fixed onto rods 16 which are themselves mounted against an outer surface of the laminated strip.

[0034] In this configuration, the outer ends 8a of the cables pass through all the ferrules 6a and interposition layers 6b of the laminated strip. Of course, it is also possible to have the outer ends 8a of the cables fixed to the inner surface of the laminated strip.

[0035] At their respective inner ends, the cables 8 are fixed to the hub 4 preferably by means of an elastic element 18 allowing modulation of the radial stiffness of the cables. Here too, the inner ends 8b of the cables pass through the hub in its thickness.

[0036] In the implementation of figures 1 to 3, the elastic elements 18 are leaf springs which each have an elongated plate shape and which are fixed in their center by rivets against an inner surface 4a of the hub.

[0037] In another embodiment not shown in the figures (but described in patent application EP22192685), the elastic elements can be in the form of U-shaped (i.e. 180°) folded blades forming springs that allow the radial stiffness of the cables to be modulated.

[0038] Each cable 8 is composed of an assembly of metallic wires (for example, steel) arranged in strands, themselves gathered around a metallic core. As an example, each cable has 6 or 7 strands, each composed of 7 to 61 metallic wires, the whole having an external diameter of between 0.2 mm and 5 mm.

[0039] Furthermore, each cable 8 can advantageously have a ratio between its mechanical stiffness in tension Kt and its mechanical stiffness in compression Kc which is between 50000 and 300000 (i.e. 5000 ≤ Kt / Kc ≤ 300000), and preferably between 25000 and 150000 (i.e. 25000 ≤ Kt / Kc ≤ 150000).

[0040] These mechanical stiffness values ​​Kt and Kc were obtained by following the recommendations of ISO 2408:2017 and ISO 17893:2004 standards (relating to the requirements of steel cables) and using a testing machine of the brand "INSTRON ®<", model 34TM-10.

[0041] In other words, the cables 8 exhibit a stiffness asymmetry with a tensile mechanical stiffness Kt that is significantly greater than their compressive mechanical stiffness Kc.

[0042] Furthermore, in the embodiment shown in the figure, the cables 8 have a particular distribution all around the axis XX of the wheel, with a first double row of n cables whose respective inner ends are positioned on the inner side of the wheel, and a second double row of m cables whose respective inner ends are positioned on the outer side of the wheel.

[0043] More specifically, for each double row of cables, the inner ends are mounted on the hub, positioned laterally between one of the two discs 12, 14 and the lateral edge (inner and outer) of the hub. The number n, m the cable length can be the same for each double row of cables.

[0044] Furthermore, as depicted on the figure 2 , each cable 8 is advantageously inclined with respect to a radial plane Pr at the hub 4 at an angle αbetween 0.1° and 45° (in absolute value), and preferably equal to 10° (in absolute value).

[0045] In particular, for the same row of cables, it can be advantageous to alternate the inclinations between adjacent cables (one of the cables would have an angle of inclination α positive - rated " α+ » on the figure 2 - and the adjacent cable would have an angle of inclination α negative - noted " α- » on the figure 2 ).

[0046] Similarly, as depicted on the figure 4 , each cable 8 is advantageously inclined with respect to a transverse plane Pt at the hub 4 at an angle β between 0.1° and 45° (in absolute value), and preferably equal to 10° (in absolute value).

[0047] In particular, for each of the two double rows of cables, it may be advantageous to ensure that all cables belonging to one of the two rows have an angle of inclinationβ positive (rated " β+ » on the figure 4 ) and all cables belonging to the other of the two rows have an angle of inclination β negative (noted " β- » on the figure 4 ).

[0048] These inclinations α , β Cables 8 allow the wheel's rigidity to be increased when it is subjected to lateral stress (for example in a turn) or when the vehicle equipped with such a wheel brakes.

[0049] According to the invention, the laminated strip 6 of the wheel 2 is covered with at least one thermal insulation coating 20 which is made of at least one material having a thermal conductivity of less than 0.2 Wm-1< K-1< , i.e. very low.

[0050] For example, this thermal insulation coating 20 can be made from one or more of the following materials: synthetic aramid fiber (including Kevlar ®), fiberglass, polyvinyl acetate, and leather.

[0051] Furthermore, to further reduce the effective thermal conductivity of the thermal insulation coating, it is advantageous to incorporate "pockets" or void openings within it. This can be achieved, for example, using a woven material.

[0052] Furthermore, thermal insulation coating 20 can be made by combining several materials, notably by stacking several layers of different materials. For example, thermal insulation coating 20 can be made by stacking a 3 to 5 mm thick layer of leather, an aluminum layer to limit radiation, a 5 to 10 mm thick layer of aramid fabric, and a 1 to 2 mm thick layer of polyvinyl acetate.

[0053] More generally, the thermal insulation coating 20 is advantageously covered under an inner face with a metallic coating (for example, a layer of aluminum) to limit the transfer of thermal energy by radiation.

[0054] According to the invention, the wheel 2 further includes means for heating the interposition layers 6b of the laminated strip.

[0055] These means for heating the interposition layers 6b of the laminated strip may include rotating contacts to establish a rotating electrical connection between the wheel hub 4 and the ferrules 6a of the laminated strip.

[0056] There figure 2shows an example of the implementation of such rotating contacts: a block of brushes 22 is attached to the vehicle equipped with the wheel 2 and supplied with electricity from it via power cables 23. This block of brushes 22 is in electrical contact with a ring 24 centered on the axis XX of the wheel and attached to the hub 4 of the wheel in order to ensure a transfer of the electrical supply to the ferrules 6a of the laminated strip via heated electrical wires 26 which are wound in the thickness of the ferrules 6a of the laminated strip.

[0057] In an advantageous way as shown on the figure 4, when the ferrules 6a of the laminated strip are made of composite material and the interposition layers 6b are composed of a hyperelastic elastomer, the electric heating wires 26 can be embedded in the composite material of one of the ferrules during its manufacture in order to convey heat to the hyperelastic elastomer composing the interposition layers 6b.

[0058] In this case, the heating electric wires 26 are preferably positioned at the level of a neutral fiber in the circumferential direction (i.e. the fiber which does not undergo any variation in length, regardless of the bending deformation of the ferrule) of the composite material in a plurality of loops 26a which are circumferentially spaced from each other.

[0059] Furthermore, as detailed on the figure 5, the heating electric wires 26 can advantageously run inside a spring 28, one end of which is screwed on the laminated strip side onto a collar 30 itself fixed onto the ferrule 6a of the laminated strip containing the heating electric wire, and an opposite end which is fixed to the hub.

[0060] Using such a spring to guide the heated electrical wires has many advantages, including the ability to guarantee the protection of the wires against possible contact with stones, and to allow a movement of several centimeters between the hub and the laminated strip.

[0061] According to another advantageous arrangement (not shown in the figures), means for measuring the temperature (for example thermocouples or other sensors of different types) of the interposition layers 6b of the laminated strip can be provided in order to control the heating power to be delivered to them to prevent their temperature from approaching the glass transition temperature of the material which composes them.

[0062] For example, the temperature of the interposition layers 6b of the laminated strip can be monitored using Bragg grating optical fibers (known in themselves) which are directly inserted into the thickness of the ferrules 6a.

[0063] The advantage of using Bragg grating optical fibers is that they also allow monitoring of deformations and deduction of the stresses experienced by the material composing the ferrules of the laminated strip.

[0064] Alternatively, temperature monitoring of the interposition layers 6b of the laminated strip can be achieved by means of a temperature probe, for example a platinum resistance thermometer (also called RTD probe for "Resistance Temperature Detector").

[0065] According to yet another advantageous arrangement (not shown in the figures), means can be provided for measuring the deformations and stresses of the laminated strip, for example using Bragg grating optical fibers.

[0066] It should be noted that the means for measuring the temperature of the interposition layers of the laminated strip and the means for measuring the deformations and stresses of the laminated strip can advantageously pass through the spring used to guide the heating electrical wires.

Claims

1. A deformable wheel (2) with non-pneumatic load bearing intended to equip a vehicle for driving in extreme conditions such as those encountered on the Moon and on Mars, comprising: a hub (4), a laminated annular strip (6) intended to be in contact with the ground, positioned around the hub which is concentric therewith and comprising a plurality of concentric ferrules (6a) that are assembled with the interposition of interposition layers (6b) each composed of a material the Young's modulus of which is 600000 to 1000 times lower than that of the ferrules, and a plurality of metal cables (8) radially connecting the hub to the laminated strip while being fastened, on the one hand by an outer end (8a) to the laminated strip (6), and on the other hand by an inner end (8b) to the hub (4), characterized in that: the laminated strip is covered with at least one thermal insulation coating (20) made of at least one material having a thermal conductivity of less than 0.2 Wm-1K-1, and the wheel further comprises means (22, 24, 26) for heating the interposition layers (6b) of the laminated strip.

2. The wheel according to claim 1, wherein the means for heating the laminated strip comprise rotating contacts (22, 24) for establishing a rotating electrical connection between the hub (4) of the wheel and the ferrules (6a) of the laminated strip (6).

3. The wheel according to claim 2, wherein the rotating contacts (22, 24) are coupled to electric heating wires (26) which are wound in the thickness of the ferrules of the laminated strip.

4. The wheel according to claim 3, wherein the ferrules (6a) of the laminated strip (6) are made of composite material and the interposition layers (6b) are composed of a hyperelastic elastomer, the electric wires (26) of the heating means of the laminated strip being embedded in the composite material during the manufacture of the ferrules in order to convey calories to the elastomer making up the interposition layers.

5. The wheel according to claim 4, wherein the electric wires (26) are positioned at a neutral fiber in the circumferential direction of the composite material, being the fiber which does not undergo any variation in length, regardless of the bending deformation of the ferrule, in a plurality of loops circumferentially spaced from each other.

6. The wheel according to any one of claims 3 to 5, wherein the electric heating wires (26) run inside a spring (28) one end of which is screwed on the side of the laminated strip onto a collar (30) fastened to a ferrule (6a) of the laminated strip containing the electric heating wire, and an opposite end is fastened to the hub.

7. The wheel according to any one of claims 1 to 6, wherein the thermal insulation coating (20) is made of one or more of the following materials: synthetic aramid fiber, fiberglass, polyvinyl acetate, and leather.

8. The wheel according to any one of claims 1 to 7, wherein the thermal insulation coating (20) is covered under an internal face with a metallic coating to limit the transfer of thermal energy by radiation.

9. The wheel according to any one of claims 1 to 8, further comprising means for measuring the temperature of the interposition layers of the laminated strip.

10. The wheel according to any one of claims 1 to 9, further comprising means for measuring the deformations and stresses of the laminated strip.

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