Deformable wheel with non-inflatable load bearing and tread heating for lunar and Mars environments

Abstract

The invention relates to a deformable wheel (2) with a non-inflatable load-bearing, intended to be equipped with vehicles running in extreme environments such as those encountered on the moon and Mars, the invention relates to a deformable wheel comprising a hub (4), a laminate strip (6) comprising a plurality of ferrules assembled by inserting an insertion layer, the laminate 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 a plurality of metal cables (8) connecting the hub to the laminate strip, the thermal insulation coating being 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 (22, 24, 26) for heating the insert layer of the laminate strip.

Description

Background Art

[0001] The present invention relates to non-pneumatic load-bearing deformable wheels. More particularly, the present invention relates to a wheel that is load-bearing through its structural components and has performance capabilities suitable for fitting to a vehicle intended to travel in extreme environments such as those encountered on the Moon and Mars.

[0002] Pneumatic wheels have load-bearing, road-shock absorbing, and force-transmitting (acceleration, stopping, and direction-changing) capabilities that are particularly useful for many vehicles, including bicycles, motorcycles, cars, and trucks. The shock-absorbing capabilities of pneumatic tires are also useful in other applications, such as carts carrying medical equipment or sensitive electronic materials.

[0003] There are alternatives to pneumatic wheels. For example, solid tires and spring-loaded tires can be mentioned. However, these alternatives do not have the performance advantages of pneumatic wheels. In particular, solid tires rely on compression of the portion in contact with the ground to bear weight. This type of tire can be heavy and hard and does not have the shock-absorbing ability of a pneumatic wheel. While being made more resilient, conventional non-pneumatic wheels do not have the load-bearing or durability of a pneumatic wheel.

[0004] To overcome these drawbacks, US 7,418,988 provides a structural support tire comprising an outer annular strip and a plurality of spokes extending laterally and radially inwardly from the annular strip to the wheel hub and intended to transfer load forces between the annular strip and the hub under tension.

[0005] The structural support wheel of the present invention does not include a cavity intended for containing compressed air and therefore does not need to have a seal with the wheel rim to maintain internal air pressure. Therefore, such a structural support wheel does not require a tire in the sense in which it is understood.

[0006] The spokes of this wheel transmit the load forces between the wheel and the annular strip under tension, in particular allowing the mass of the vehicle to be carried. The load-bearing force is generated by the tension of the spokes that are not connected to the part of the annular strip that is in contact with the ground. The spokes also transmit the forces required for acceleration, stopping and turning.

[0007] Regardless of the alternatives known in the prior art for producing non-pneumatic wheels, the latter are generally not entirely satisfactory, especially when they are intended to travel in extreme environments such as those encountered on the Moon and Mars. Indeed, in such environments, the wheels must be able to deform significantly when passing obstacles and at the same time generate a low and uniform contact pressure to allow the vehicle to keep moving on soft terrain such as that encountered on the Moon and Mars.

[0008] Patent application EP22192685 filed by the applicant on August 29, 2022 discloses a wheel that allows to meet the above needs, in particular due to the presence of a laminated annular strip comprising a plurality of concentric rings, which are assembled by inserting an insert layer, each insert layer being made of a material having a Young's modulus 600000 to 1000 times lower than that of the ring (for example made of an elastomeric material). In the case of a load applied from the outside, the portion of the laminated strip in contact with the ground is deformed, but not substantially circular, but in a shape conforming to the surface of the ground, while keeping the length of the ring substantially constant. Therefore, the wheel according to the present patent application allows to generate a low and uniform contact pressure on the ground. In this way, a vehicle equipped with such a wheel can remain mobile (that is to say without sinking into the sand) even on soft ground (such as sand) encountered on the moon and Mars.

[0009] The elastomer-based structure of the intervening layer of the laminated strips of such a wheel has a minimum operating temperature between -140°C and -150°C, which allows the wheel to operate in most missions around the lunar south pole on the one hand, and on all latitudes on Mars, where the absolute minimum temperature is -120°C, on the other hand. However, such limitations can cause problems if a vehicle equipped with such a wheel has to travel to permanently shaded regions (or PSRs), such as the lunar poles, where the temperature is permanently between -220°C and -240°C. Summary of the invention

[0010] The main purpose of the present invention is to overcome such drawbacks by proposing a deformable wheel structure with non-pneumatic load-bearing that can equip vehicles intended to travel in permanently shaded areas of the Moon where the temperature is permanently between -220°C and -240°C.

[0011] According to the present invention, this object is achieved by a deformable wheel with non-pneumatic load-bearing, which is intended to be equipped for vehicles traveling in extreme environments such as those encountered on the moon and Mars, and which comprises:

[0012] Wheel hub,

[0013] a laminated annular strip intended to come into contact with the ground, positioned around the hub concentric therewith and comprising a plurality of concentric rings assembled by inserting interposing layers each consisting of a material having a Young's modulus 600,000 to 1,000 times lower than that of the rings, and

[0014] a plurality of metal cables which, while being fastened, radially connect the hub to the laminated strip, on the one hand by the outer ends to the laminated strip and on the other hand by the inner ends to the hub,

[0015] And wherein, according to the present invention:

[0016] The laminated strip is covered with at least one thermal insulation coating, which is composed of a thermal insulation layer having a thermal conductivity of less than 0.2 Wm -1 K -1 of at least one material with a thermal conductivity of

[0017] The wheel also comprises means for heating the intervening layer of the laminate strip.

[0018] The wheel according to the invention is remarkable in particular due to the use of means for heating the intervening layers of the laminated strips, allowing the temperature of these intervening layers to be removed from the glass transition temperature of the material constituting them. Considering that the material constituting these intervening layers tends to generate heat on its own when deforming in operation (due to the running resistance), and that the heat generated as the temperature of the material approaches its glass transition temperature or even higher, this will have the effect of heating the wheel even more, removing it even further from this glass transition temperature.

[0019] Furthermore, the presence of a thermal barrier coating on the laminated strips allows limiting the thermal conductivity between the lunar ground and the material constituting the intervening layer of the laminated strips.

[0020] The wheel according to the invention is therefore able to withstand the temperatures of -220°C to -240°C typically encountered in the permanently shadowed regions of the Moon.

[0021] The means for heating the laminate strip may include a rotary contact for establishing a rotary electrical connection between the wheel hub and the collar of the laminate strip.

[0022] In this case, the rotating contact is preferably coupled to a heating wire which is wound in the thickness direction of the ferrule of the laminated strip.

[0023] More particularly, the collar of the laminated strip may be made of a composite material and the insert layer may be composed of a superelastic elastomer, the heating wire of the heating device of the laminated strip being embedded in the composite material during the manufacture of the collar so as to transfer heat to the elastomer constituting the insert layer.

[0024] In this case, the heating wire is advantageously positioned at the neutral fiber in the circumferential direction of the composite material in a plurality of rings circumferentially spaced apart from one another.

[0025] Preferably, the heating wire extends within a spring which has one end screwed onto a collar on one side of the laminate strip, the collar being fastened to a ferrule of the laminate strip containing the heating wire, and the opposite end being fastened to the hub.

[0026] The thermal insulation coating may be made of one or more of the following materials: synthetic aramid fiber, glass fiber, polyvinyl acetate and leather.

[0027] Preferably, the thermal barrier coating is covered with a metallic coating below the inner face to limit the transfer of thermal energy by radiation.

[0028] Also preferably, the wheel further comprises means for measuring the temperature of the intervening layer of the laminate strip.

[0029] More preferably, the wheel also comprises means for measuring deformations and stresses of the laminate strip in order to monitor the performance and service life of the laminate strip, compensating for any failure in the event of a mission away from a lunar base. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Other features and advantages of the invention will emerge from the following description given with reference to the accompanying drawings, which illustrate exemplary embodiments of the invention without any limiting character. In the drawings:

[0031] Figure 1 is a schematic perspective view of a wheel according to one embodiment of the present invention;

[0032] Figure 2 yes Figure 1 a schematic diagram of a front view of a wheel in a perspective view;

[0033] Figure 3 is along Figure 2 A cross-sectional view taken along line III-III of ; and

[0034] Figure 4 An example of a ferrule of a laminated strip of a wheel with an embedded heating wire is shown;

[0035] Figure 5 is a partial view of a spring within which a wire heating insert layer of laminated strips extends. DETAILED DESCRIPTION

[0036] The present invention relates to Figure 1 The illustrated deformable wheels have non-pneumatic load bearings suitable for assembling vehicles intended to travel in extreme environments such as those encountered on the Moon and Mars.

[0037] Figure 1 The wheel 2 shown mainly comprises a hub 4, a laminated annular strip 6 intended to come into contact with the ground, and a plurality of metal cables 8 radially connecting the hub to the laminated strip.

[0038] like Figure 2 and Figure 4As shown, the laminated strip 6 is composed of a plurality of concentric ferrules 6a assembled together by sandwiching intervening layers 6b, each intervening layer being composed of a material having a Young's modulus 600,000 to 1,000 times lower than that of the ferrules.

[0039] The ferrule 6a may be metallic (eg made of steel) or made of a composite material.

[0040] As for the intervening layers 6b, they are advantageously made of a superelastic elastomer having a glass transition temperature below 120°C.

[0041] By such a configuration of the laminated strip 6, the portion of the laminated strip in contact with the ground deforms under the load applied from the outside, but assumes a shape conforming to the surface of the ground, while keeping the length of the loop 6a constituting it substantially constant. By shearing in the intervening layer 6b, a relative movement of the loops of the laminated strip occurs.

[0042] like Figure 1 As shown, the hub 4 of the wheel carries two discs 12, 14 projecting radially outwards. These two discs 12, 14 are spaced from each other along the axis XX of the wheel and each has an outer diameter against which the inner surface of the laminate strip 6 can abut so as to limit its deformation.

[0043] The cables 8 connect the laminate strip 6 radially to the hub 4. To this end, each cable 8 comprises an outer end 8a fastened to a rod 16 which is itself mounted against the outer surface of the laminate strip.

[0044] In this configuration, the outer end 8a of the cable passes through all the ferrules 6a and the intervening layer 6b of the laminate strip. Of course, it is conceivable that the outer end 8a of the cable is fastened to the inner surface of the laminate strip.

[0045] At their respective inner ends, the cables 8 are fastened to the hub 4, preferably by means of elastic members 18, thereby allowing adjustment of the radial stiffness of the cables. Here, too, the inner ends 8b of the cables pass through the hub in the thickness direction of the hub.

[0046] exist Figures 1 to 3 In the embodiment of , the elastic members 18 are leaf springs each having the shape of an elongated plate and fastened at the center thereof against the inner surface 4a of the hub by a rivet.

[0047] In another embodiment not shown in the drawings (but described in patent application EP22192685), the elastic member may be in the form of a leaf folded into a U shape (ie folded at 180°) forming a spring allowing adjustment of the radial stiffness of the cable.

[0048] Each cable 8 is composed of an assembly of metal wires (for example made of steel), which is composed of strands, which are assembled around a metal core. For example, each cable includes 6 or 7 strands, each of which is composed of 7 to 61 metal wires, and the assembly has an outer diameter between 0.2 mm and 5 mm.

[0049] Furthermore, each cable 8 may advantageously have a ratio between its tensile mechanical stiffness Kt and its compressive mechanical stiffness Kc between 50,000 and 300,000 (ie 5,000≤Kt / Kc≤300,000), and preferably between 25,000 and 150,000 (ie 25,000≤Kt / Kc≤150,000).

[0050] These mechanical stiffness values ​​Kt and Kc are obtained by following the recommendations of ISO 2408:2017 and ISO 17893:2004 (covering requirements for steel cables) and by using the brand The test machine model is 34TM-10.

[0051] In other words, the cable 8 has a stiffness asymmetry, with its tensile mechanical stiffness Kt being significantly greater than its compressive mechanical stiffness Kc.

[0052] Furthermore, in the embodiment of the figures, the cables 8 have a particular distribution all around the axis XX of the wheel, with a first double row n a cable (whose corresponding inner end is located on the inner side of the wheel) and a second double row m The inner ends of the cables are located outside the wheel.

[0053] More specifically, for each double row cable, the inner end is mounted on the hub by being positioned transversely between one of the two disks 12, 14 and the transverse (inner and outer) edges of the hub. n , m Can be the same.

[0054] In addition, if Figure 2 As shown, each cable 8 is advantageously inclined at an angle of α , this angle (absolute value) is between 0.1° and 45° and is preferably equal to 10° (absolute value).

[0055] In particular, for cables of the same row, it may be advantageous to provide alternating inclinations between adjacent cables (one of the cables will have an inclination in the Figure 2 Marked as " α+” Positive tilt angle α , and adjacent cables will have Figure 2 Marked as " α-” Negative tilt angle α).

[0056] Similarly, if Figure 4 As shown, each cable 8 is advantageously inclined at an angle relative to a plane Pt transverse to the hub 4. β , this angle is between 0.1° and 45° (absolute value) and is preferably equal to 10° (absolute value).

[0057] In particular, for each of the two double-row cables, it may be advantageous to provide that all cables belonging to one of the two rows have a positive tilt angle β (exist Figure 4 In the expression " β+” ), and all cables belonging to the other of the two rows have a negative tilt angle β (exist Figure 4 In the expression " β-” ).

[0058] These inclinations of the cables 8 occur when the wheel is subjected to lateral stresses (for example in a bend) or when a vehicle equipped with such a wheel is braked. α , β Allows to increase the rigidity of the wheel.

[0059] According to the invention, the laminate strip 6 of the wheel 2 is covered with at least one thermal insulation coating 20 consisting of a thermal insulation layer having a thermal conductivity of less than 0.2 Wm -1 K -1 The thermal conductivity of the material is very low (i.e., very low thermal conductivity).

[0060] For example, the thermal insulation coating 20 may be made of one or more of the following materials: synthetic aramid fibers (particularly ), fiberglass, polyvinyl acetate and leather.

[0061] Furthermore, in order to further reduce the effective thermal conductivity of the heat-insulating coating, it is advantageous to provide it with "pockets" or vacuum openings on the inside. This is achieved, for example, by means of a textile material.

[0062] In addition, the heat-insulating coating 20 can be made by assembling several materials, in particular by stacking several layers of different materials. For example, the heat-insulating coating 20 can be made by stacking a 3 to 5 mm thick leather layer, an aluminum layer for limiting radiation, a 5 to 10 mm thick aramid fabric layer, and a 1 to 2 mm thick polyvinyl acetate layer.

[0063] More generally, the thermal barrier coating 20 is advantageously covered below the inner face with a metal coating, for example an aluminum layer, in order to limit the transfer of thermal energy by radiation.

[0064] Still according to the invention, the wheel 2 also comprises means for heating the intervening layer 6b of the laminate strip.

[0065] These means for heating the intervening layer 6b of the laminate strip may comprise rotating contacts for establishing a rotating electrical connection between the hub 4 of the wheel and the collar 6a of the laminate strip.

[0066] Figure 2 An example of a specific implementation of such a rotary contact is shown: a brush block 22 is fixed to a vehicle equipped with a wheel 2 and is powered from the latter via an electric power cable 23. This brush block 22 makes electrical contact with a ring 24 centered on the axis XX of the wheel and fixed to the hub 4 of the wheel so as to ensure that the power supply is transmitted to the collar 6a of the laminated strip via a heating wire 26 wound in the thickness direction of the collar 6a of the laminated strip.

[0067] Advantageously, if Figure 4 As shown, when the collar 6a of the laminated strip is made of a composite material and the insert layer 6b is composed of a superelastic elastomer, the heating wire 26 can be embedded in the composite material of one of the collars during manufacturing to transfer heat to the superelastic elastomer constituting the insert layer 6b.

[0068] In this case, the heating wires 26 are preferably positioned at neutral fibers (that is, fibers that do not undergo any length changes regardless of bending deformation of the ferrule) along the circumferential direction of the composite material in a plurality of loops 26a circumferentially spaced from each other.

[0069] In addition, if Figure 5 As shown in detail in , the heating wire 26 can advantageously extend within a spring 28, one end of which is screwed to a collar 30 on one side of the laminate strip, the collar itself being fastened to the collar 6a of the laminate strip containing the heating wire, and the opposite end of the spring being fastened to the hub.

[0070] The use of such springs for routing the heating wire has many advantages, in particular ensuring protection of the heating wire from possible contact with the stone and allowing a movement of a few centimetres between the hub and the laminate strip.

[0071] According to another advantageous arrangement (not shown in the figures), means for measuring the temperature of the insert layer 6b of the laminated strip (for example, a thermocouple or other sensor of different types) can be provided in order to control the heating power delivered thereto, thereby preventing the temperature of the insert layer from approaching the glass transition temperature of the material constituting the insert layer.

[0072] For example, the temperature of the insertion layer 6b of the laminated strip may be monitored using a Bragg grating optical fiber (known per se) inserted directly into the thickness of the ferrule 6a.

[0073] An advantage of using Bragg grating fibres is that they also allow deformations to be monitored and the stresses experienced by the material constituting the ferrule of the laminated strip to be deduced.

[0074] Alternatively, monitoring the temperature of the intervening layer 6b of the laminated strip may be achieved by means of a temperature probe, for example a platinum resistance thermometer (also called an RTD probe, for “resistance temperature detector”).

[0075] According to a further advantageous arrangement (not shown in the figures), means for measuring deformations and stresses of the laminate strips may be provided, for example using Bragg grating optical fibres.

[0076] It should be noted that the means for measuring the temperature of the intervening layer of the laminated strip and the means for measuring the deformation and stress of the laminated strip can advantageously pass through the spring for routing the heating wire.

Claims

1. A deformable wheel (2) with non-pneumatic load-bearing, the deformable wheel (2) being intended to be equipped on a vehicle travelling in extreme environments such as those encountered on the moon and Mars, the deformable wheel (2) comprising: Wheel hub (4), a laminated annular strip (6) intended to come into contact with the ground, positioned around the hub concentric therewith and comprising a plurality of concentric rings (6a) assembled by inserting the insert layers (6b), the insert layers (6b) each consisting of a material having a Young's modulus 600,000 to 1,000 times lower than that of the rings, and a plurality of metal cables (8) which, while being fastened, radially connect the hub to the laminated strip, on the one hand to the laminated strip (6) via outer ends (8a) and on the other hand to the hub (4) via inner ends (8b), Features: The laminated strip is covered with at least one thermal insulation coating (20) composed of a thermal insulation layer having a thermal conductivity of less than 0.2 Wm -1 K -1 of at least one material with a thermal conductivity of The wheel also comprises means (22, 24, 26) for heating the intervening layer (6b) of the laminate strip.

2. A wheel according to claim 1, wherein the means for heating the laminate strip comprises rotary contacts (22, 24) for establishing a rotary electrical connection between the hub (4) of the wheel and the collar (6a) of the laminate strip (6).

3. The wheel according to claim 2, wherein the rotating contacts (22, 24) are coupled to a heating wire (26) which is wound in the thickness direction of the ferrule of the laminated strip.

4. A wheel according to claim 3, wherein the collar (6a) of the laminated strip (6) is made of a composite material and the inserted layer (6b) is composed of a superelastic elastomer, the heating wire (26) of the heating device of the laminated strip being embedded in the composite material during the manufacture of the collar so as to transfer heat to the elastomer constituting the inserted layer.

5. The wheel according to claim 4, wherein the heating wires (26) are positioned at neutral fibers along the circumferential direction of the composite material in a plurality of rings circumferentially spaced from each other.

6. A wheel according to any one of claims 3 to 5, wherein the heating wire (26) extends inside a spring (28), one end of the spring (28) being screwed onto a collar (30) on one side of the laminate strip, the collar (30) being fastened to a collar (6a) of the laminate strip containing the heating wire, and the opposite end being fastened to the hub.

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

8. A wheel according to any one of claims 1 to 7, wherein the thermal barrier coating (20) is covered with a metal coating underneath the inner face to limit the transfer of thermal energy by radiation.

9. A wheel according to any one of claims 1 to 8, further comprising means for measuring the temperature of the intervening layer of the laminate strip.

10. A wheel according to any one of claims 1 to 9, further comprising means for measuring the deformation and stress of the laminate strip.

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