Airless tire with optimized shear strips

Abstract

The present invention relates to an airless tire, and more particularly seeks to optimize the mass and stiffness of its shear strips, comprising a radially inner membrane (41) and a shear structure made up of a number of shear elements (5), a radially outer membrane (42) positioned at an average radial distance H from the radially inner membrane (41). According to the present invention, any shear element (5) of the number of shear elements comprises a main portion (50) having a non-radial generatrix (G) with a radially inner end (I1) positioned at a distance d1 from the radially inner membrane (41) and a radially outer end (I2) positioned at a distance d2 from the radially outer membrane (42) in any circumferential plane (XZ), the generatrix (G) of the main portion (50) of the shear element (5) having a curve length L at least equal to 1.25*(H-(d1+d2)).

Description

[Technical field]

[0001] The present invention is directed to airless tires for vehicles, and more particularly to shear strips therein. [Background technology]

[0002] Conventional tires, which are subjected to an internal pressure of an inflation gas, generally air, are a preferred choice for vehicles due to their capabilities in terms of load, force transmission between the ground and the vehicle, and shock absorption. However, conventional tires have an inherent risk that when impacted or rolled over a perforated object, they are prone to a more or less sudden loss of pressure, resulting in the vehicle becoming stuck.

[0003] To eliminate this risk of pressure loss, alternative solutions to conventional tires have been developed, such as solid tires. Solid tires support loads through compression of their structure, but do not offer the performance advantages of conventional tires discussed above. In particular, solid tires are generally heavy and stiff, and therefore have poor shock absorption capabilities. Furthermore, they often have low load capacity and high heat generation during use, resulting in a short lifespan. As a result, the use of solid tires is limited to specific vehicles, such as, as a non-exhaustive example, transport machinery.

[0004] Airless tires, or more generally tires without inflation gas, are another known alternative solution that supports loads thanks to their structural components and has performance comparable to that of conventional tires. Airless tires mounted on a hub or rim are sometimes called "non-pneumatic elastic wheels".

[0005] Such airless tires are described, for example, in the documents WO 2003 / 018332, FR 2 964597, WO 2012 / 102932, WO 2018 / 101937, WO 2018 / 102303, WO 2018 / 102560 and WO 2018 / 125186.

[0006] Hereinafter, circumferential or longitudinal direction refers to the direction of rotation of the tire, axial or lateral direction refers to the direction parallel to the axis of rotation of the tire, and radial direction refers to the direction perpendicular to the axis of rotation of the tire.

[0007] Airless tires generally have the following features: a support structure intended to structurally support at least a portion of the load and to cooperate with the rim or the hub; - shear strips intended to transmit the rolling forces by shear to the support structure and to contribute at least partially to the bearing of the load, a tread intended to transmit the rolling forces to the shear strips to undergo wear and ensure the adhesion of the tire to the ground; Equipped with.

[0008] The support structure comprises, for example radially outwardly, connection means to the rim or hub, radial elements or spokes, and connection means to the shear strips. However, the support structure generally does not define an internal sealed cavity intended to contain gas under pressure, as in conventional tires. As a result, pneumatic tires do not require a sealed connection to the rim or hub.

[0009] In one known embodiment, the shear strips extend radially outwardly, - the first inner membrane, - a shear layer comprising one or more polymeric materials; - a second outer membrane, The shear layer directly contacts the first and second membranes.

[0010] In the above described embodiment, the first and second membranes often have a circumferential elongation modulus significantly higher than the shear modulus of the polymeric shear layer, so that the membranes do not stretch significantly when the tire flattens as it rolls under an applied load. The relative movement between the membranes occurs due to shear in the shear layer. The membrane preferably includes a laminated reinforcing layer coated with a polymeric material.

[0011] The polymeric shear layer may be made of a polymeric material such as, for example, natural or synthetic rubber or polyurethane, etc. For example, the shear layer material may have a shear modulus at least equal to 3 MPa and at most equal to 20 MPa, which tends to flatten the shear strips under load.

[0012] For many years, Michelin North America has been selling a complete solution in the form of an assembly consisting of the above-mentioned airless tire and wheel under the product name MICHELIN® TWEEL®. This technical solution mainly consists of the tread, the shear strip or "shear band", the support structure consisting of very strong polyresin spokes, and the hub consisting of two reinforcing steel parts.

[0013] The shear strips of the prior art airless tires generally have two main drawbacks: they are generally heavy and the contact pressure with the ground is generated in a relatively narrow range. High contact pressures can therefore only be generated by shear strips with a very large mass, which is neither mechanically feasible nor economically acceptable. Furthermore, the use of such shear strips is practically limited to airless tires that operate at low pressures and high speeds, such as passenger cars, or at high pressures and low speeds, such as utility vehicles of the Bobcat type. Moreover, in applications with strict environmental constraints (e.g., very low temperatures), the shear levels of the shear strips required to generate low contact pressures are difficult to achieve with shear layers made of normal polymeric materials. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] International Publication No. 2003 / 018332 [Patent Document 2] French Patent Application Publication No. 2964597 [Patent Document 3] International Publication No. 2012 / 102932 [Patent Document 4] International Publication No. 2018 / 101937 [Patent Document 5] International Publication No. 2018 / 102303 [Patent Document 6] International Publication No. 2018 / 102560 [Patent Document 7] International Publication No. 2018 / 125186 Summary of the Invention [Problem to be solved by the invention]

[0015] The inventors aimed to propose an airless tire comprising a shear strip that has a reduced mass compared to prior art shear strips and a shear stiffness adapted to achieve a target medium ground pressure level for a given load carrying capacity of the tire. [Means for solving the problem]

[0016] The object is achieved by an airless tire for vehicles comprising, radially outwardly, a support structure intended to cooperate with a rim or hub, a shear strip and a tread, the shear strip comprises, radially outwardly, a radially inner membrane, a shear structure, and a radially outer membrane positioned at an average radial distance H from the radially inner membrane; The shear structure is made up of a number of shear elements distributed in the circumferential direction; any shear element of the plurality of shear elements includes a main portion having a non-radial generatrix with a radially inner end positioned at a distance d1 from a radially inner membrane and a radially outer end positioned at a distance d2 from a radially outer membrane in any circumferential plane perpendicular to the rotational axis of the tire; and - the generating line of the main part of the shear element has a curve length L at least equal to 1.25*(H-(d1+d2)).

[0017] The shear strip of the airless tire according to the invention essentially comprises a circumferential distribution of a plurality of shear elements distributed with a pitch that is not necessarily constant. Typically, the plurality of shear elements is a set of shear elements, most often including all of the shear elements, but sometimes including only a portion of the shear elements. This discrete shear structure allows an open structure of the shear strip, for example ensuring a summit mass of the airless tire that is quite close to the summit mass of a conventional tire. By convention, the summit of the tire is the main part of the tire that is radially outside the support structure in the case of an airless tire and radially outside the carcass reinforcement in the case of a conventional tire.

[0018] The shear strip includes, radially outwardly, a radially inner membrane, a shear structure, and a radially outer membrane positioned an average radial distance H from the radially inner membrane. By definition, the average radial distance H between the radially inner membrane and the radially outer membrane is an average value around the circumference of the tire.

[0019] In any circumferential plane perpendicular to the tire's axis of rotation, any of the shear elements, i.e. any basic pattern, has a circumferential cross section with a center line, called a generatrix, that is not radial, but curvilinear in shape. This generatrix extends between a radially inner end position at a distance d1 from the radially inner membrane and a radially outer end position at a distance d2 from the radially outer membrane. This implies that the radially inner end and the radially outer end are not necessarily positioned on the radially inner and radially outer membranes, respectively, and as a result there may be transition zones that serve as interfaces between the main part of the shear element and the radially inner and radially outer membranes. It is further noted that the shape of the generatrix is ​​an open curve, not a curve that closes on itself. For example, the generatrix cannot have a closed circular shape. The distances d1 and d2 are not necessarily constant in the axial direction of the tire, i.e. they may vary within the axial width of the shear strip.

[0020] According to the invention, this generatrix must have a curve length L, measured along it between its radially inner and outer ends, equal to at least 1.25 times the shortest distance between its two ends (equal to H-(d1+d2)). Such a generatrix thus has a non-zero mean curvature, ensuring the geometric flexibility of the shear element.

[0021] Such a generatrix shape allows the optimization of the stresses occurring in the shear elements during rolling. Indeed, compared to simple structures such as vertical beams, this generatrix shape makes it possible, for a given average radial membrane distance H, to either increase the effective working length of the shear elements or to make the interfaces with the radially inner and outer membranes sufficiently thick so as to move the maximum values ​​of stresses and deformations to the center of the shear elements rather than to the level of these interfaces.

[0022] Furthermore, in combination with the thickness characteristics of the shear element and the elastic modulus of the material(s) that make up the shear element, the shape of the busbar makes it possible to optimize the mechanical stiffness characteristics of the shear strip in order to obtain a ground pressure distribution and value suitable for the use of the vehicle concerned.

[0023] On the other hand, the overall bending stiffness of the shear strip must be high enough to prevent buckling of the shear strip upon contact with the ground, which is ensured mainly by the radially inner and radially outer membranes.

[0024] On the other hand, the overall shear stiffness of the shear strip must also be adapted to guarantee the required average pressure level, especially in the contact area. This overall shear stiffness is provided mainly by the shear structures between the radially inner and the radially outer membranes. Under the action of the rolling forces, this overall shearing of the shear strip generates a local deflection in each shear element, leading to a deformation of that shear element.

[0025] The first embodiment of the invention allows the design of a shear strip for this tire that generates a high contact pressure with a similar apex mass to that of conventional tires. The optimization of the shear strip in terms of the overall shear stiffness is achieved by matching the elastic modulus of the material(s) constituting the shear element with the generatrix curve length, the latter being high enough that the stresses and deformations induced in the material(s) constituting the shear element correspond to the rupture resistance and / or fatigue limit properties of the material. The circumferential distribution of several shear elements according to the invention allows a defined material volume to be obtained between the radially inner and radially outer membranes, allowing high contact pressures to be achieved at high rolling speeds. This allows the range of use of current pneumatic tires to be extended.

[0026] The second embodiment of the present invention allows for the design of highly flexible shear strips that are compatible with stringent environmental constraints, such as the extremely low temperatures encountered in extraterrestrial environments, by adapting the generatrix length of the shear elements such that the stresses and deformations induced in the constituent material(s) are sufficient to accommodate the fracture resistance and / or fatigue limit properties of the constituent materials.

[0027] The distance d1 from the radially inner end of the generatrix to the radially inner membrane is advantageously equal to at most 0.5 times the average radial distance H between the radially inner and radially outer membranes.

[0028] Also, the distance d1 from the radially inner end of the generating line to the radially inner membrane is advantageously equal to 0. This means that there is no transition zone forming an interface between the main part of the shear element and the radially inner membrane.

[0029] The distance d2 from the radially outer end of the generatrix to the radially outer membrane is advantageously equal to at most 0.5 times the average radial distance H between the radially inner and the radially outer membranes.

[0030] The distance d2 from the radially outer end of the generating line to the radially outer membrane is also advantageously equal to 0. This means that there is no transition zone forming an interface between the main part of the shear element and the radially outer membrane.

[0031] The tangent to the generatrix at the radially inner end advantageously makes an angle A1 with the radial direction of the pneumatic tyre that is at least equal to 45°.

[0032] Also, the tangent to the generatrix at the radially outer end advantageously makes an angle A2 with the radial direction of the pneumatic tyre that is at least equal to 45°.

[0033] Advantageously, the generatrices of the main parts of any shear element have a shape with one reversal of curvature direction, such as an S-shape.

[0034] Also, the main portion of any shear element has a thickness E0 that is advantageously not constant. This variation in thickness makes it possible to optimize the distribution of stresses and deformations in this shear element. The thickness E0 measured in a given circumferential plane may also vary between two different circumferential planes, i.e. in the axial direction of the tire.

[0035] The shear elements are preferably distributed circumferentially with a constant pitch.

[0036] Also, any shear element is preferably made of a material having an tensile modulus at 4% elongation at least equal to 20 MPa, preferably at least equal to 30 MPa, said tensile modulus being measured statically.

[0037] The generatrix shape of the shear elements has the consequence that the stresses generated by the shear in the shear strip resulting from the rolling forces are low enough to allow the use of materials with a higher modulus of elasticity than the elastomeric materials routinely used in the conventional tire field.

[0038] The use of a material with a high modulus of elasticity makes it possible to reduce the effective cross section of the shear element in the circumferential plane to reduce the weight of the shear strip or to stiffen the rolling strip in such a way as to increase the ground pressure. Features of the present invention are illustrated generally, and not to scale, in Figures 1-5. [Brief description of the drawings]

[0039] [Figure 1] 1 is an overall view of an airless tire according to the present invention. [Diagram 2] FIG. 2 shows a circumferential cross section of a shear element according to a first embodiment (d1 and d2 are non-zero). [Diagram 3] FIG. 13 is a circumferential cross-section of the main part of a shear element according to a first embodiment (d1 and d2 are non-zero). [Figure 4] FIG. 13 is a circumferential cross-section of a shear element according to a second embodiment (d1 and d2 are zero). [Diagram 5] FIG. 13 is a circumferential cross-section of the main part of a shear element according to a second embodiment (d1 and d2 are zero). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040] Figure 1 shows a general view of an airless tire 1 according to the invention. This airless tire 1 comprises, radially outwardly, a support structure 2 intended to cooperate with a rim or hub 3, a shear strip 4 and a tread 6. The shear strip 4 comprises, radially outwardly, a radially inner membrane 41, a shear structure 40 and a radially outer membrane 42. The shear structure 40 consists of a number of shear elements 5 distributed in the circumferential direction. Each shear element 5 of the number of shear elements has a non-radial generatrix with a radially inner end I1 and a radially outer end I2.

[0041] 2 is a circumferential view of a shear element 5 according to a first embodiment (d1 and d2 are not zero). The shear element 5 comprises a main part 50 having a non-radial generatrix G with a radially inner end I1 positioned at a distance d1 from the radially inner membrane 41 and a radially outer end I2 positioned at a distance d2 from the radially outer membrane 42 in any circumferential plane XZ perpendicular to the tire's rotation axis, the generatrix G of the main part 50 of the shear element 5 having a curve length L at least equal to 1.25*(H-(d1+d2)), H being the average radial distance between the radially inner membrane 41 and the radially outer membrane 42. In the illustrated embodiment, the distance d1 from the radially inner end I1 of the generatrix G to the radially inner membrane 41, as well as the distance d2 from the radially outer end I2 of the generatrix G to the radially outer membrane 42, are less than 0.5 times the average radial distance H and are not zero. Furthermore, the tangent T1 to the generatrix G at the radially inner end I1 makes an angle A1 with the radial direction ZZ' of the pneumatic tire 1 that is at least equal to 45° and even close to 90°. Similarly, the tangent T2 to the generatrix G at the radially outer end I2 makes an angle A2 with the radial direction ZZ' of the pneumatic tire 1 that is at least equal to 45° and even close to 90°. Finally, the generatrix G of the main portion 50 of the shear element 5 has an S-shape, the main portion 50 of the shear element 5 having a constant thickness E0.

[0042] 3 shows a circumferential section of a main part of a shear strip 4 according to a first embodiment (d1 and d2 are not zero). The shear strip 4 comprises radially outwardly a radially inner membrane 41, a shear structure 40 and a radially outer membrane 42. The shear elements 5 are of the type described with reference to FIG.

[0043] 4 is a circumferential section of a shear element 5 according to a second embodiment (d1 and d2 are zero). This shear element 5 differs from the one in FIG. 2 by the shape of the generatrix G with a more pronounced curvature, by a longer generatrix length G and by a smaller thickness of the main part. Furthermore, the distance d1 from the radially inner end I1 of the generatrix G to the radially inner membrane 41 and the distance d2 from the radially outer end I2 of the generatrix G to the radially outer membrane 42 are zero. In other words, the main part 50 is a direct interface with the radially inner membrane 41 and with the radially outer membrane 42.

[0044] 5 shows a circumferential section of a main part of a shear strip 4 according to a second embodiment (d1 and d2 are zero). As mentioned above, the shear strip 4 comprises radially outwardly a radially inner membrane 41, a shear structure 40 and a radially outer membrane 42. The shear elements 5 are of the type described with reference to FIG.

[0045] The inventors have investigated the invention in more detail in two different embodiments R1 and R2.

[0046] The first embodiment R1 concerns an airless tire intended to replace the reference tire of dimensions 235 / 65 R16 LI / SI 121R, intended to equip van-type vehicles, as specified by the European standard European Tyre and Rim Technical Organisation (ETRTO) in the Standards Manual 2020. In the case of R1, the elongation modulus at 4% elongation of the material constituting the shear element is 150 MPa, which corresponds for example to a thermoplastic elastomer (TPE).

[0047] A second embodiment R2 concerns an airless tire intended to equip vehicles adapted to travel in extreme environments at very low temperatures, with an outer diameter equal to 800 mm and a total width equal to 300 mm. In the case of R2, the elongation modulus at -200°C, at 4% elongation of the material constituting the shear element, is equal to 5800 MPa, corresponding for example to thermoplastics of the polyetheretherketone (PEEK) type or to polyimides.

[0048] The following table 1 specifies the characteristics of each of the two embodiments R1 and R2: [Table 1]

[0049] According to numerical simulations carried out by the inventors using finite element calculation software, the average ground pressure generated at the shear strip of a tire according to the first embodiment R1 is equal to 5 bar when the mass of the shear strip is equal to 8.7 kg.

[0050] According to numerical simulations carried out by the inventors using finite element calculation software, the average contact pressure generated at the shear strip of the tire according to the second embodiment R2 is equal to 0.075 bar. [Explanation of symbols]

[0051] 5 Shear elements 41 Radial inner membrane 42 Radial outer membrane 50 Main parts A1 Angle between tangent T1 and the radial direction A2 Angle between tangent T2 and the radial direction d1 Distance from the radially inner membrane to the radially inner end d2 Distance from the radially outer membrane to the radially outer end E0 Thickness of main part G non-radial generatrix H is the average radial distance between the radially inner and radially outer membranes I1 Radial inner end I2 Radial outer end L Curve length of non-radial generatrix T1 Tangent at the radial inner end T2 Tangent at the radial outer end X circumferential direction Y-axis direction Z radial direction

Claims

1. A pneumatic tire (1) for a vehicle comprising, radially outwardly, a support structure (2) intended to cooperate with a rim or hub (3), shear strips (4) and a tread (6), The shear strip (4) comprises, radially outwardly, a radially inner membrane (41), a shear structure (40), and a radially outer membrane (42) positioned at an average radial distance H from the radially inner membrane (41); The shear structure (40) comprises a plurality of shear elements (5) distributed in the circumferential direction, 1. An airless tire (1), characterized in that any shear element (5) of the plurality of shear elements includes a main portion (50) having a non-radial generatrix (G) with a radially inner end (I1) positioned at a distance d1 from the radially inner membrane (41) and a radially outer end (I2) positioned at a distance d2 from the radially outer membrane (42) in any circumferential plane (XZ) perpendicular to the rotation axis of the airless tire, and that the generatrix (G) of the main portion (50) of the shear element (5) has a curve length L at least equal to 1.25*(H-(d1+d2)).

2. 2. An airless tire (1) according to claim 1, wherein the distance d1 from the radially inner end (I1) of the generatrix (G) to the radially inner membrane (41) is at most equal to 0.5 times the average radial distance H between the radially inner membrane (41) and the radially outer membrane (42).

3. 3. An airless tyre (1) according to claim 1 or 2, wherein the distance d1 from the radially inner end (I1) of the generatrix (G) to the radially inner membrane (41) is equal to 0.

4. 3. An airless tyre (1) according to claim 1 or 2, wherein the distance d2 from the radially outer end (12) of the generatrix (G) to the radially outer membrane (42) is at most equal to 0.5 times the average radial distance H between the radially inner membrane (41) and the radially outer membrane (42).

5. 3. An airless tyre (1) according to claim 1 or 2, wherein the distance d2 from the radially outer end (I2) of the generatrix (G) to the radially outer membrane (42) is equal to 0.

6. 3. The airless tire (1) according to claim 1 or 2, wherein a tangent (T1) to the generatrix (G) at the radially inner end (I1) forms an angle A1 at least equal to 45° with a radial direction (ZZ') of the airless tire (1).

7. 3. The airless tyre (1) according to claim 1 or 2, wherein a tangent (T2) to the generatrix (G) at the radially outer end (I2) forms an angle A2 at least equal to 45° with a radial direction (ZZ') of the airless tyre (1).

8. 3. An airless tyre (1) according to claim 1 or 2, wherein the generatrices (G) of the main portions (50) of any shearing element (5) have a shape with one reversal of curvature direction.

9. 3. An airless tyre (1) according to claim 1 or 2, wherein the main portion (50) of any shear element (5) has a non-constant thickness E0.

10. 3. An airless tyre (1) according to claim 1 or 2, wherein the shearing elements (5) are distributed in the circumferential direction with a constant pitch.

11. 3. An airless tire (1) according to claim 1 or 2, wherein any shear element (5) of said plurality of shear elements is made of a material having an elongation modulus at 4% elongation at least equal to 20 MPa.

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