Wheels including non-pneumatic tires

Abstract

This invention provides a non-pneumatic tire comprising a thermoplastic elastomer pre-tensioned during the process of forming the non-pneumatic tire. This pre-tensioning is provided by a thermal method inherently available in the forming process. This results in a combination of efficient manufacturing and efficient pre-tensioning without adding the complexity of pre-tensioning mechanically.

Description

[0001] This application claims the benefit of U.S. Provisional Application No. 63 / 018,485, filed on April 30, 2020. Technical Field

[0002] This disclosure relates to non-pneumatic tires (NPTs) for use with on-road or off-road vehicles (e.g., automobiles, light and heavy trucks, all-terrain vehicles, zero-turn radius lawnmowers, military vehicles). Specifically, it relates to off-road vehicles that may require higher speeds and load capacities as well as high damage tolerance. Background Technology

[0003] Non-pneumatic tires (NPTs) have advantages over pneumatic tires. Unlike pneumatic tires, NPTs are not pressure vessels. They will not fail due to pressure loss.

[0004] NPT generates loads mechanically (by bending, tensioning, and / or compression of various design elements). On the other hand, pneumatic tires are pre-tensioned due to inflation pressure. Vertical loads can be counteracted by reducing the tension in pre-tensioned components (such as reinforcing layers). This kind of "release" of pretension can be more effective than causing structural deflection. These pre-tensioned layers can be thin and therefore lightweight. Thus, the load-bearing and speed capabilities of pneumatic tires can be enhanced.

[0005] Prior art discloses methods for adding pretension to NPT. For example, US2019 / 0009613 (owned by the current applicant) discloses a spoke design and a mechanical method for adding pretension to the spokes. As a result, load capacity and fatigue are improved. However, adding pretension via the disclosed mechanical method can be laborious.

[0006] NPT may require inefficient and / or expensive manufacturing methods. An example of prior art involving NPT manufacturing is US 9,004,901 (owned by the current applicant). It discloses a method for forming thermosetting polyurethane spokes and bonding said spokes to a rubber tread and a center hub. A mold is rotated, generating centrifugal force that allows the mold to fill. The liquid polyurethane then cures and hardens, and the NPT can be demolded. Operating such equipment and procedures can be expensive and may require the creation of new production processes.

[0007] US 9,751,270 (owned by the current applicant) discloses a thermoplastic molding process for forming NPT. Thermoplastic injection molding is a mature industry that reduces the cost of NPT. However, there is no disclosure regarding pre-tensioning in this prior art.

[0008] This disclosure bridges this gap by providing an NPT comprising a thermoplastic elastomer pre-tensioned during the process of forming the NPT. This pre-tensioning is provided by a thermal method inherently available in the molding process. Thus, the advantages of efficient manufacturing are combined with the efficiency of pre-tensioning without adding the complexity of pre-tensioning mechanically. Summary of the Invention

[0009] The aspects and advantages will be set forth in part in the description which follows, or may be apparent from the description, or may be learned by practice. The invention has a general application to vehicles using tires. Specifically, the application is particularly suitable for off-road vehicles that may require high speeds, high loads, and high energy absorption capabilities.

[0010] According to one aspect of the invention, a non-pneumatic tire is provided, comprising: a reinforcing annular beam; an annular support extending radially inward from the annular beam, the support comprising a thermoplastic elastomer; and a rim extending radially inward from the annular beam. The annular support has circumferential reinforcement such that the inner diameter surface does not deflect more than 2 mm. Furthermore, the annular support has a pre-strain of not less than 0.5%, which is generated by thermal shrinkage following the injection molding operation.

[0011] According to one aspect of the invention, a non-pneumatic tire is provided, comprising: a reinforcing annular beam; an annular support extending radially inward from the annular beam, the support comprising a thermoplastic elastomer; and a rim extending radially inward from the annular beam. The non-pneumatic tire has an initial tangential vertical stiffness that is at least twice the tangential vertical stiffness under design load.

[0012] According to one aspect of the invention, a non-pneumatic tire is provided, comprising: a reinforcing annular beam; an annular support extending radially inward from the annular beam, the support comprising a thermoplastic elastomer; and a rim extending radially inward from the annular beam. The reinforcing member of the annular beam has a compressive strength of not less than 0.5 MPa, and the reinforcing member is configured such that the annular beam is transversely isotropic in the RY plane.

[0013] According to one aspect of the invention, a process for forming an NPT (Non-Petrol Plate) is provided. The NPT has a tread portion having a tread pattern. A reinforcing annular beam extends radially inward from the tread. The annular beam and the tread are formed in a first process. An annular support member comprising a thermoplastic elastomer extends radially inward from the annular beam and is formed in a second process comprising thermoplastic injection molding. The second process includes a mold in which the annular beam and the tread are positioned. The mold supports only the tread pattern at an outer diameter limit.

[0014] These and other features, aspects, and advantages of the invention will become more readily understood with reference to the following description and the appended claims. The accompanying drawings, which are incorporated in and form a part of this specification, and together with the description, serve to explain the principles. Attached Figure Description

[0015] Referring to the accompanying drawings, the complete and feasible disclosure of the invention for those skilled in the art, including its best mode, is set forth in the specification, wherein:

[0016] The following detailed description of the embodiments is provided by way of example only, with reference to the accompanying drawings, in which:

[0017] Figure 1 This is an exemplary example of NPT.

[0018] Figure 2 This is an exemplary example of NPT and a graph showing the relationship between load and deflection in existing NPT techniques.

[0019] Figure 3 This is an exemplary example of a ring beam and a tire tread.

[0020] Figure 4a and Figure 4b This is the YZ cross-sectional view of the ring beam.

[0021] Figure 5 It is a 2D FE model of a ring beam subjected to pressure, as seen in thermoplastic injection molding.

[0022] Figure 6 This is an RY sectional view of a ring beam placed in a mold used for thermoplastic injection molding.

[0023] Figure 7a and Figure 7b This is a FEA simulation of the deflection of two ring beams under pressure, as seen in thermoplastic injection molding.

[0024] Figure 8a and Figure 8b The FEA simulation of two NPTs when loaded onto an off-road obstacle is shown.

[0025] Figure 9 The critical load of NPT with different numbers of reinforcement layers is shown.

[0026] Figure 10 The following are exemplary examples of thermoplastic wheel spokes, ring beams, and treads for NPT.

[0027] Figure 11a and Figure 11b The difference between the slender spoke distance and the linear distance between the spoke ends is shown.

[0028] Figure 12 This is a cross-sectional view of an exemplary NPT, showing the hub area.

[0029] Figure 13 The FEA simulation of two NPTs loaded to 4000N is shown.

[0030] Figure 14 An exemplary NPT with a load of 7000N is shown.

[0031] Figure 15 This is a FEA prediction of the relationship between load and deflection for four NPTs.

[0032] Figure 16 It is a FEA prediction of the tangential vertical stiffness of the three NPTs.

[0033] Figure 17 The FEA predictions for the relationship between contact surface length and deflection for the three NPTs are shown.

[0034] Figure 18 The FEA prediction for a single wheel spoke subjected to critical buckling load is shown.

[0035] Figure 19 An exemplary gate location for an exemplary NPT is shown.

[0036] It should be clearly understood that the specification and drawings are for illustrative purposes only and to aid understanding of specific embodiments. The specification and drawings are not intended to be, and should not be, limiting.

[0037] Terminology Definition

[0038] Unless otherwise stated, the following terms are defined for the purposes of this disclosure, wherein material properties refer to those properties at ambient temperature:

[0039] "Wheel hub" refers to any structure used to support the tire and can be attached to the axle.

[0040] When referring to thermoplastic elastomers, "modulus" means the Young's tensile modulus of elasticity as measured according to ISO 527-1:2019.

[0041] When referring to reinforced cords or cables, "modulus" refers to Young's tensile modulus as measured according to ASTM D2969. The tensile modulus can be calculated as the secant modulus at 0.5% strain.

[0042] When referring to reinforced cords or cables, "compressive strength" refers to the compressive stress required for failure under uniaxial compression, measured by... Journal of Composite MaterialsThe method disclosed in the article "Theoretical and experimental compressive strength of a glass fiber-vinyl ester pultruded composite" in Volume 49, Issue 6, pp. 739-748, is used to measure it.

[0043] When referring to rubber, "shear modulus" means the dynamic shear modulus measured at 10 Hz, 23°C, and 2% strain according to ASTM D5992–96 (2018). When referring to rubber, "elongation modulus" means the Young's modulus measured according to ASTM D 412.

[0044] The tire's "design load" is the tire's normal and expected operating load.

[0045] "Design contact length" is the contact length when the load is applied to the design load.

[0046] The relationship between tire vertical force, deflection, and area occupied can be measured according to SAE J2704. Detailed Implementation

[0047] This invention provides a non-pneumatic tire and a method for forming the same. For the purposes of describing the invention, reference will now be made in detail to embodiments and / or methods, one or more examples of which are illustrated in or by way of the accompanying drawings. Each example is provided in an illustrative rather than restrictive manner. Indeed, it will be apparent to those skilled in the art that various modifications and variations can be made to the invention without departing from its scope or spirit. For example, a feature or step illustrated or described as part of one embodiment may be used with another embodiment or step to produce yet another embodiment or method. Therefore, it is intended that the invention cover such modifications and variations as they fall within the scope of the appended claims and their equivalents.

[0048] Figure 1 An exemplary example of the NPT 100 is shown, measuring 26 × 10⁻¹². This is a common size for off-road applications. The tire defines a cylindrical coordinate system with a radial direction R, a circumferential direction θ, and an axial direction Y. A convenient Cartesian coordinate system places X as the tire's direction of travel, Y as the axial direction, and Z as the vertical direction.

[0049] The tire includes a tread portion 101, an annular beam 102 (which includes a reinforcement in the circumferential direction), an annular support portion 103 (which includes a thermoplastic elastomer), a rim portion 104, and a hub portion 105. In this embodiment, the annular support portion includes spokes extending in the radial direction, thereby connecting the inner surface of the annular beam to the rim without intersecting any spokes of the other spokes.

[0050] In this embodiment, the ring beam and tread are formed in the initial molding operation. The ring beam, together with the hub portion 105, is placed in a mold for a secondary molding operation, in which thermoplastic injection molding is used to form the spokes.

[0051] Prior art constructions (such as those described in US 9,004,901) use thermosetting polyurethane to form the spokes. The present application discloses a method for forming spokes using thermoplastic injection molding of a thermoplastic elastomer. Furthermore, this method can result in a non-stressed wheel spoke (NPT). This pre-stressing is due to the thermal shrinkage of the spokes, as they are constrained at radially inward and radially outward boundaries by the rim and annular beam, respectively.

[0052] Historically, the inventors were initially motivated by the superior economics of thermoplastic injection molding compared to rotational molding of thermoset polyurethane. Prototypes of a research tire in the size 24x12-12 were created, tested, and compared with existing tires that included thermoset polyurethane spokes. This size tire is commonly used in off-road vehicles such as all-terrain vehicles (ATVs) and zero-turn radius (ZTR) lawnmowers. The results were surprising—better than expected. These positive surprises included:

[0053] - Tire rolling resistance is reduced by 20%, even when the research tire uses the same tread and ring beam sections as existing technology tires.

[0054] - This produces a strongly nonlinear load-deflection curve. Compared to existing technologies, the current invention exhibits a higher initial slope in the load-deflection relationship, even though the tangent slope remains essentially constant under the design load. This is in... Figure 2 As shown in the diagram. Those skilled in tire design will recognize the value of such performance. Under a design load of 3000N, the exemplary NPT exhibits a deflection 4.5mm less (30%) than prior art tires. However, the tangential KZ of both NPTs at a design load FZ = 3000N is 160N / mm. The exemplary tire has a significantly higher initial KZ of 700N / mm. This initial KZ is more than four times higher than the KZ at the design load. Therefore, for the exemplary NPT, ride comfort is maintained.

[0055] This also reduces deformation and deflection.

[0056] The process for forming thermoplastic wheel spokes is relatively straightforward, even with anticipated significant challenges. Thermoplastic injection molding requires high pressure. Pressures of 28 MPa (4000 psi) or higher can occur near the gate. Even at locations not near the gate, the pressure at the end of mold filling can reach 100 psi (0.7 MPa).

[0057] 200 psi (1.4 MPa) or higher. For this reason, injection molding uses robust steel or aluminum molds, held together by clamping forces of several metric tons. Rubber (even reinforced rubber) is not used as the surface for injecting high-pressure plastics. However, Figure 1 The architecture of the NPT 100 clearly requires a large contact area between the radially inward surface of the annular beam 102 and the annular support 103, which includes the thermoplastic elastomer. The inventors hypothesized that high injection pressure would deform the annular beam and tread, resulting in poor thickness control of the thermoplastic elastomer. However, this was not the case. The process was stable and well-controlled.

[0058] After careful study, the inventors identified several process and product attributes necessary to produce better results. Each of these process and product attributes is disclosed below.

[0059] Reinforced ring beam with specific strengthening properties

[0060] Figure 3 An exemplary embodiment of the tread 101 and the annular beam 102 is shown. They are a molded part, formed in an initial molding operation. Figure 4a and Figure 4b The annular beam is further described below. In this embodiment, the annular beam is reinforced with a circumferential stiffener 301. In this embodiment, the stiffener comprises seven radially spaced layers. The beam comprises an elastic matrix material 302, which may include rubber. The spacing between the radial layers is approximately equal to the stiffener spacing in the axial direction. Therefore, the stiffener forms a transversely isotropic composite material in the RY section of the annular beam. If the inter-cord spacing in the radial direction is within + / - 33% of the inter-cord spacing in the axial direction, the resulting composite material is approximately transversely isotropic.

[0061] The reinforcement may comprise steel cable or any suitable high-stiffness and high-strength material. In this exemplary embodiment, the reinforcement comprises continuously pultruded glass monofilament. The inventors have found that this type of reinforcement can be particularly advantageous.

[0062] exist Journal of Composite MaterialsThe properties of continuously pultruded glass fiber monofilaments are disclosed in the article "Theoretical and experimental compressive strength of a glass fiber-vinylester pultruded composite" in Volume 49, Issue 6, pp. 739-748. This reinforcement exhibits high stiffness and strength under tension and compression. The properties of this reinforcement are advantageous for exemplary NPTs. These properties include:

[0063] Young's modulus E = 40 GPa

[0064] High modulus is advantageous because the exemplary ring beam is used as a pressure vessel during thermoplastic injection molding. High stiffness enables a more stable molding process.

[0065] - Compressive strength σc=1.1GPa

[0066] The off-road application of this exemplary model results in very high impact loads. Those skilled in the art of off-road tire design know that, for instantaneous events, dynamic loads can approach four times the design load. High compressive strength is a performance requirement.

[0067] -CTE=5×10 -6 mm / mm-C

[0068] Following the molding process, the annular beam anchors the radially outer ends of the spokes. The low CTE for the circumferential reinforcement results in an annular beam that does not shrink after demolding, even at high molding temperatures. Thermal pre-strain is generated in the thermoplastic spokes. The steel has a CTE of 12 × 10⁻⁶. -6 mm / mm-C, which is also an acceptable low value. For comparison, the thermoplastic elastomer used in the exemplary example has a CTE of 1.6 × 10⁻⁶. -4 mm / mm-C. When low CTE is combined with high modulus, a very efficient structure is obtained, which enables spoke pre-strain.

[0069] The inventors performed a 2D finite element analysis (FEA) to understand and quantify these effects.

[0070] Figure 5 This is a structured 2D FEA used for molding simulations to predict deflection in ring beams and tire treads. In this 2D plane strain model, stiffness is expressed per unit width. Therefore, the calculation of stiffness for stiffeners is normalized relative to a section with a thickness of 1 mm in the axial direction.

[0071] In a thermoplastic molding process, molten elastomer is injected into a mold, and an annular beam is positioned within the mold. In an exemplary embodiment, the annular beam is positioned such that its radially inward surface 201 serves as the outer diameter boundary of the mold cavity. A molding operation then forms at least a portion of the annular support 103 and at least a portion of the rim 104. A hub 105 may also be positioned in the same mold, and the molding operation may overmold the thermoplastic elastomer around the hub.

[0072] When the elastomer fills the mold and contacts the radially inward surface 201 of the annular beam, very high pressure is applied to surface 201. The annular beam includes a circumferential reinforcement 301 and a matrix material 302. The tread 101 contacts the rigid mold surface 400 on the outer diameter boundary 305 of the tread pattern. The tread groove walls 303 are freely deformable. The outer diameter boundary of the tread is constrained in the radial direction, but the tread is freely compressible. In other words, the presence of the tread pattern creates an air gap between the tread and the mold surface 400. Therefore, the rigidity of the annular beam in the circumferential direction becomes very important.

[0073] To cope with the pressure, the reinforcement generates tension T. This is necessary because the tread groove walls may deform. Since the tread may comprise rubber, its compressive stiffness will be relatively low compared to the injection pressure. Due to the Poisson effect, the blocks will compress and bulge. Rigid reinforcement is necessary to mitigate this undesirable effect.

[0074] Figure 6 An exemplary location of the annular beam and tread in the mold within the RY section is shown. Mold surface 401 is at the lateral boundary of the annular beam and tread. This section acts as a flow-blocking device, preventing the molten elastomer from flowing out of the mold cavity and around the annular beam. In this exemplary embodiment, mold surface 400 only constrains the outer diameter boundary 305 of the tread. In other words, combined with... Figure 5 The mold surfaces 400 and 401 can be smooth, and therefore can be low-cost. No support structures are required for the bottom 304 of the tread grooves or the sides 303 of the tread pattern.

[0075] Figure 7a and Figure 7b Figure 7a shows the deflection results (in mm) for the case of P = 0.7 MPa (100 psi). Figure 7a shows the deflection for the case without reinforcement. If an isotropic rubber with an elongation modulus of 7 MPa is used, the radial inner surface deflection is between 2.5 mm and 3.05 mm. This is excessive. Those skilled in the art of thermoplastic injection molding will recognize that the wall thickness is typically 3 mm. A mold surface with deflection up to the desired wall thickness will cause serious problems. Additionally, there is a circumferential variation in thickness of approximately 0.5 mm.

[0076] In comparison, Figure 7bThe results with reinforcement are shown. The deflection is approximately one-fifth of that described above. The inner surface deflection is now 0.50 mm to 0.62 mm. This level of deflection is controllable in thermoplastic injection molding processes.

[0077] Technicians in the field of mechanical engineering will realize that Figure 5 This is for pressure vessels with approximate soft treads and high-modulus stiffeners. Therefore, well-known formulas relating stiffener tension to internal pressure are applicable. Further application of the fundamental relationships between modulus, area, and strain can be used to create relationships between the desired maximum permissible radial deflection and other design parameters. This is given below:

[0078]

[0079] Where R = inner radius of the ring beam

[0080] P = Injection pressure at the inner radius

[0081] W = Width of the ring beam

[0082] A = Cross-section of the total reinforcing member

[0083] E = Young's modulus of the reinforcing component

[0084] ∈ = Circumferential strain of the reinforcing member

[0085] And radial deflection at R ∈ = inner radius

[0086] The inventors have discovered that the injection pressure P = 1 MPa (146 psi) is a representative pressure at the inner radius of the beam during the molding process. Furthermore, the inventors have determined that the acceptable value for the radial deflection R∈ at the inner radius can be as low as 2 mm. Substituting these values ​​into Equation (1):

[0087]

[0088] That is, the product of the ring beam width multiplied by the square of the radius R, divided by the Young's modulus of the stiffener and the total cross-sectional area of ​​the stiffener, should be less than 2 cubic millimeters per Newton. For a representative pressure P = 1 MPa, formula (2) simply gives the radial deflection of the inner radius of the ring beam in mm. In some cases, the acceptable value can be as low as 2 mm. In some cases, it can be 1.5 mm. In other cases, it can be 1.0 mm or even lower.

[0089] Formula (2) uses Newtons and millimeters. Therefore, stress is expressed in megapascals. Other unit systems should be converted to these units for formula (2) to be applicable.

[0090] The above analysis assumes that the stiffeners have a constant spacing in the axial direction for each stiffener layer. It also assumes that the stiffeners extend across the lateral boundaries of the annular beam. Designs inconsistent with the above do not depart from the intent of this application. The above formulas can still be used to approximate the deflection of the annular beam during injection molding operations.

[0091] The following procedure can also be used to directly measure the deflection of a ring beam at its inner radius under injection pressure:

[0092] - Place the ring beam in the thermoplastic injection mold.

[0093] - Measure the minimum radial distance from the mold body used to form the annular support to the radially inward boundary of the annular beam.

[0094] - Forming NPT by using a thermoplastic process to create a ring-shaped support.

[0095] - Cut the NPT ring beam and ring support at the location of the minimum radial distance.

[0096] - Measure the radial thickness of the thermoplastic elastomer used to form the annular support.

[0097] - Subtract the in-mold distance from the actual thickness. This is the amount of deflection of the inner diameter surface of the annular strip during the molding process.

[0098] As an exemplary example of formula (2), Figure 1 The NPT has a total reinforcing cross section A = 800 mm. 2 The reinforcing member has a modulus of 40,000 N / mm². 2 Therefore, EA = 3.2E + 07N. Where the inner radius is 300mm and the width W = 250mm, we get R ∈ = 0.7mm.

[0099] According to prior art US 7,201,194, two types of reinforcing layers are disclosed. Using the disclosed values ​​G = 5 MPa and E'film / G = 1000:1, the total EA = 2.5E + 0.6 N is obtained. Using R = 330 mm, as disclosed, and W = 250 mm, R ∈ = 10.5 mm. This is too high and would not be rigid enough for injection molding.

[0100] While efficient manufacturing processes require high tension circumferential stiffness, product performance necessitates high circumferential compressive strength. The inventors have discovered that multi-layered reinforcement also improves load-bearing capacity under off-road conditions, where very high impacts are frequently generated against objects with reverse curvature. This was also investigated using 2D plane strain (FEA).

[0101] Figure 8aAn NPT with two layers of glass monofilament reinforcement in a ring beam is shown. These layers are separated by an isotropic rubber layer. The NPT is loaded onto a surface with reverse curvature, the radius of which is equal to the radius of the NPT. At 14,500 N, the reinforcement layer buckles at the outer diameter limit of the ring beam. It becomes unstable. This could lead to failure either in the rubber matrix or in the reinforcement itself.

[0102] Figure 8b An NPT with three layers of reinforcement is shown. Currently, two adjacent layers exist at the outer diameter boundary of the ring beam. The structure remains stable under a load of 17,000 N.

[0103] "Critical load" is the load at which cord buckling begins to occur. Figure 9 The critical load is shown relative to the number of reinforcing layers. For 6 layers, the predicted critical load is 27,500 N. This represents a doubling of performance compared to 2 layers. The mechanism for this improvement could involve producing a transversely isotropic reinforced ring beam.

[0104] In the article in the Journal of Composites mentioned above, the critical buckling compressive stress of unidirectional composite materials is given as follows:

[0105]

[0106] Where σ c =Critical buckling stress

[0107] G 12 =Shear modulus in the plane to which stress is applied

[0108] G m =Matrix shear modulus

[0109] Vf = Volume fraction of fiber (or cord)

[0110] Assuming the unidirectional composite material is transversely isotropic, the critical buckling stress decreases when the composite material is not transversely isotropic. Therefore, Figure 4b The reinforcing pattern shown is exemplary. Therefore, the inventors have discovered that formulas commonly applied to so-called classic composite materials (fibers of carbon or glass with thermosetting resins, such as vinyl esters) also describe cord-rubber composite materials.

[0111] What may not be immediately apparent to those skilled in tire design is the assumption that cord-rubber composites might behave like classic composites of high-modulus resins and fibers. The excellent prototype performance in testing, along with these modeling results, confirms this.

[0112] The inventors have discovered that optimal performance is achieved when the inter-cord distance in the radial direction is within 33% of the inter-cord distance in the axial direction. In some cases, this may need to be 25%, and in others, 10%, and in still others, even less.

[0113] Furthermore, the inventors have discovered that, according to formula (3), a critical buckling stress of at least 5 MPa is required; in some cases, at least 8 MPa, and in others even higher.

[0114] The required cord volume fraction can be at least 0.15; in other cases, 0.25; in other cases, 0.35; and in other cases, even higher. The rubber matrix shear modulus can be at least 3 MPa, in some cases 5 MPa, and in some cases even higher.

[0115] Even without considering macroscopic buckling, the outer diameter reinforcement layer experiences high compressive stress. Therefore, the cord itself needs to have high compressive strength. A journal article discloses a method for measuring the compressive strength of a single cord or cable reinforcement. Using this method, continuously pultruded glass monofilaments can achieve a compressive strength of 1.1 GPa. The inventors have found that exemplary NPTs benefit from reinforcements with a compressive strength of at least 0.5 MPa; in other cases, 0.8 MPa; and exceeding 1.1 GPa in the most demanding applications. The same procedure described in the journal article can be used to measure the compressive strength of any cord or cable.

[0116] Creating a pre-tensioned non-pneumatic structure

[0117] Figure 10 This is an exemplary NPT. The annular support includes thermoplastic elastomer spokes 103 extending radially without intersecting with other spokes. An outer diameter boundary is adhered to an inner diameter boundary 201 of the annular beam. In an injection molding process, a uniform thickness 401 of thermoplastic elastomer is adhered to the inner diameter surface of the annular beam. The inner diameter boundary is adhered to an outer diameter boundary of the rim portion 104, which may include thermoplastic elastomer. The rim may be thicker and more rigid than the spokes. Therefore, this creates rigid, fixed boundaries at both ends for the spokes.

[0118] Figure 11a The RT cross-section of an exemplary NPT configured in a mold before demolding is shown. The spokes 103 extend from the radial outer boundary B (joining to the annular beam 102) to the radial inner boundary A (joining to the rim 102). The curvilinear distance Lc is the length of the spokes before demolding. In this representative example, the curvilinear distance Lc = Rα, where angle α is in radians. The distance L is the linear distance between point A and point B.

[0119] When the spokes cool after demolding, thermal shrinkage occurs and the stress-free length decreases. The degree of tensile pre-strain in the cold spokes involves the amount of thermal shrinkage and the difference between the spoke curvilinear distance and the linear distance. This can be approximated as follows:

[0120]

[0121] Wherein: S PS The pre-strain of the spokes is expressed as a percentage.

[0122] CTE is the coefficient of linear thermal expansion.

[0123] T H For the spoke temperature in the mold

[0124] T C ambient temperature

[0125] L C The length of the spoke curve in the mold

[0126] L is the distance between the radial boundaries of the spokes.

[0127] The associated spoke pretension is given below:

[0128]

[0129] Wherein: S PT Pre-tensioning the spokes

[0130] E S For spoke modulus

[0131] A S The cross-sectional area of ​​the spokes

[0132] Figure 11b It shows Figure 10 The exemplary post-molding geometry of the NPT. Due to the circumferential reinforcement of the annular beam 102, the inner radius R of the annular beam is [value missing] by using reinforcements with low CTE. B Relatively unchanged. Similarly, the inner radius R of rim 104 remains unchanged. R The size may remain relatively unchanged or even decrease slightly. Exemplary examples of wheel rim designs will be shown in the following sections.

[0133] The inventors have discovered that at least 0.5% of the spoke pre-strain S is required. PS To give the previously disclosed favorable load-flexural properties relationship; in some cases, a pre-strain of at least 1.0% is better; in others, a pre-strain of at least 1.5% is beneficial, and in still others, even more.

[0134] The actual spoke prestrain may vary according to formula (4), depending on other construction factors such as the CTE of the stiffeners. The actual prestrain can be measured by the following:

[0135] - Measure the actual spoke length from point A to point B (outer and inner diameter limits of the spokes) after molding.

[0136] - Mark the point used to measure the distance.

[0137] - Cut the spokes from the NPT.

[0138] -Measurement of stress-free spokes that have been removed from NPT

[0139] If the spokes are under tension in the molded tire, the stress-free length will be reduced. The amount of reduction divided by the length before removal gives the tire's pre-strain percentage.

[0140] against Figure 11a The simple geometry used for the in-mold spoke geometry is for illustrative purposes only. Any curved spoke geometry can be used. Standard computer-aided design tools make it possible to calculate the distance of any such curve.

[0141] Figure 12 An exemplary NPT RY cross-section is shown. The rim material 104 may include a thermoplastic elastomer, formed in the same operation as the spokes. Furthermore, the hub 105 may have a portion 501 extending in the axial direction. In some cases, the hub may extend 15% of the axial width of the rim; in others, the hub may extend 30%; and in still others, the hub may extend more than 50% of the axial width.

[0142] Utilizing a steel hub design that extends more than 50% of the rim's axial width, the rim R... B It may not change during the molding process. The steel has a high modulus and low CTE, which constrains the rim. If the hub extends 15% or less in the axial width of the rim, the rim R... B It may decrease when the tire cools. Since most of the rim consists of thermoplastic elastomer, R... B This is due to the high CTE, which reduces the prestress in the spokes. This can increase the prestress to a value greater than that given in formula (5).

[0143] This exemplary rim design specifically embodies a hub that is overmolded using the same thermoplastic elastomer used to form both the spokes and the rim. It may be low-cost, but it is highly effective in providing anchoring for the lower end of the spokes.

[0144] High modulus spokes with high buckling load

[0145] The advantages of spoke prestress can be amplified using other design parameters. For example, the inventors have found that spoke modulus and spoke thickness can significantly enhance positive performance. The effects of thermal shrinkage, along with these, were also investigated using 2D FEA. The cumulative effect of these design parameters is surprisingly good. "Tension-based" NPT can be transformed into hybrid NPT that supports the load through a combination of prestressing, compression, and tension.

[0146] Tire size 33x10-15 is typically used for larger utility vehicles (UTVs). The four versions shown below are modeled using this size. Each version has the same ring beam. The only differences relate to the design parameters in the table below.

[0147] Version Spoke pre-strain (%) Spoke thickness (mm) Spoke modulus (MPa) V1 0 4 45 V2 1 4 45 V3 1 5 90 V4 1 6 90

[0148] Figure 13 The deformation geometries of V1 and V2 are shown, their only difference being the spoke prestrain. Under a design load of 4000 N, a 1% spoke prestrain clearly results in V2 having lower flexural strength and less spoke deformation compared to V1.

[0149] Figure 14 Version V4 is shown at 4000 N and 7000 N. At 4000 N, the deflection is minimal—the spoke deformation is very small. At a load of 7000 N, the deflection is less than that of reference version V1 at a load of 4000 N. Although the spoke prestrain has not changed from version V2 to V4, the spoke pretension has been increased. The spoke modulus and spoke thickness have been increased, which results in a higher spoke pretension, as given in Equation (5).

[0150] Figure 15 The FEA predictions for the load-deflection relationship of V1, V2, V3, and V4 are shown.

[0151] -From V1 to V2, only the effect of the spoke pre-strain can be seen.

[0152] -From V2 to V3, we can see the effects of increasing both the spoke modulus and thickness.

[0153] -From V3 to V4, we can see the effect of further increasing the spoke thickness.

[0154] In a cumulative manner, pre-strain, modulus, and thickness can significantly increase the load-bearing capacity of exemplary NPTs. For example, V4 has less than 10 mm of deflection at a design load of 4000 N, while reference version V1 requires 30 mm of deflection.

[0155] The main effect of the aforementioned lever design is to increase the initial tangent KZ. Figure 15The relationship between the tangent KZ and deflection is shown for each of V1, V2, and V3. At low deflection, the tangent KZ of tires V2 and V3 is much higher than that of V1. At higher deflection, the tangent KZ becomes closer together.

[0156] The inventors have discovered that the tangent KZ at zero deflection can be at least twice the tangent KZ at the deflection required to generate the design load. In other cases, this can be at least three times; in other cases, it can be four times, and in still other cases, even more.

[0157] from Figure 14 It is evident that even under minimal deflection, the exemplary NPT can produce a long contact surface. Figure 17 The relationship between contact length and deflection is shown for V1, V2, and V3. V1 requires 31 mm of deflection to give a design load FZ = 4000 N. At this deflection, V1 produces a contact length of 135 mm. Therefore, the contact length divided by the vertical deflection is 4.3. Under the same load, V2 requires 22 mm of deflection and a contact length of 125 mm. This yields a ratio of 5.7. V3 requires 11 mm of deflection and a contact length of 110 mm, with a ratio of 10.0.

[0158] Those skilled in tire design will recognize the benefits of achieving a long contact patch with minimal flex. Traction (especially off-road traction) is strongly correlated with contact patch length. Exemplary NPTs combine low flex with a long contact patch. Therefore, low rolling resistance and improved durability can be combined with high traction performance.

[0159] The inventors have discovered that the ratio of tire deflection under design load to contact surface length under design load can be as high as 5. In other cases, it can be as high as 7; in other cases, it can be as high as 10, and in other cases, even higher.

[0160] After experimentation and modeling, the inventors understood that even moderately thick spokes could significantly contribute to load-bearing capacity. Technicians in the field of mechanical engineering are familiar with the Euler critical load used in compression bars.

[0161] The Euler critical buckling load formula for a compression member fixed at both ends is:

[0162]

[0163] For the case where a rectangular spoke cross-section is used as a compression bar:

[0164]

[0165] Wherein: F C For buckling load

[0166] E is the spoke modulus.

[0167] I is the moment of inertia of the spokes in the RT plane.

[0168] w is the width of the wheel spokes.

[0169] t is the thickness of the spokes

[0170] L is the distance from the intersection of the spokes and the ring beam to the intersection with the rim.

[0171] The inventors performed a 3D FEA on the spoke structure. Figure 18 The deformed geometry of a representative model is shown. The FEA results agree very well with Euler's formula. For example, given a spoke length of 100 mm, a width of 200 mm, and a modulus of 100 MPa:

[0172] thickness <![CDATA[F C FEA]]> <![CDATA[F C Euler critical 2.5mm 111N 102N 3.5 286 280 4.5 591 594

[0173] The results with 4.5mm thick spokes are quite surprising. Buckling requires a compressive force of almost 600N. (Reference) Figure 13 and Figure 14 Several spokes buckle radially inward from the contact surface. Therefore, the 600N buckling force per spoke is not negligible compared to the design load of 4000N.

[0174] The inventors have discovered that spoke buckling load can therefore be used as a design parameter in the development of an exemplary NPT that bears both tension load (tensioned spokes around the top of the tire, away from the contact area) and compression load (spokes in the contact area). This is Figure 14 One of the effects seen is that V4 has spokes with higher buckling loads.

[0175] The inventors have discovered that exemplary NPTs may have spokes with a critical buckling load of at least 10% of the design load; in other cases, at least 15% of the design load; in other cases, at least 20% of the design load; and in other cases, even higher.

[0176] To reduce the injection pressure exerted by the thermoplastic elastomer on the radially inward surface of the ring beam, the inventors have found it advantageous to position the gate near the rim portion of the exemplary NPT. This is in Figure 19 As shown, the gating gate 600 is located at or near a portion of the rim. An exemplary NPT may have a thermoplastic elastomer comprising at least a portion of the rim. In this case, the elastomer may be formed first as a portion of the rim before forming the annular support.

[0177] Mold flow analysis (MFA) has shown that injection pressure decreases as the thermoplastic material flows from the rim section through the annular support (which may include radially oriented spokes). Pressure can drop to as low as 2 MPa (290 psi) or even as low as 1 MPa (140 psi) as the material reaches the radially inward surface of the annular beam, even though injection pressure may be higher near gate 600.

[0178] Certain additional components are not described or shown because they are assumed to be within the capabilities of those skilled in the art. Furthermore, certain embodiments may be absent, may be missing, and / or may function without any components not specifically disclosed herein.

[0179] In some examples of implementations, any feature of any implementation discussed herein may be combined with any feature of any other implementation discussed herein.

[0180] While various implementations and examples have been presented, this is for illustrative purposes only and should not be construed as limiting. Various modifications and enhancements will become apparent to those skilled in the art. Features or steps described or illustrated as part of one embodiment may be combined with aspects of another embodiment to produce yet another embodiment.

[0181] As used herein, the terms "method" or "process" refer to one or more steps that may be performed in an order different from the order shown without departing from the scope of the invention. The order of any steps is exemplary and is not intended to limit the methods described herein to any particular order, nor is it intended to exclude the addition, omission, repetition, or simultaneous execution of steps.

[0182] Unless expressly excluded or otherwise limited, every document referenced herein (including any cross-references or related patents or applications) is hereby incorporated in its entirety. No reference to any document acknowledges it as prior art to any invention disclosed or claimed herein, or as teaching, indicating, or disclosing any such invention, alone or in combination with any other referenced document. Furthermore, in the event of any conflict between the meaning or definition of any term in this document and the meaning or definition of the same term in any document incorporated by reference, the meaning or definition given to the term in this document shall prevail.

Claims

1. A non-pneumatic tire, the non-pneumatic tire comprising: - A ring beam having an inner radius R, the ring beam including circumferential reinforcements with a modulus E. The circumferential reinforcing member has a total cross-sectional area A; -The annular support reinforcement is constrained to make... - An annular support member, the annular support member extending radially inward from the annular beam, the support member comprising a thermoplastic elastomer; - A rim that extends radially inward from the annular beam; as well as The annular support has a pre-strain of not less than 0.5%, which is generated by thermal shrinkage after the injection molding operation. The value of the pre-strain is calculated based on the following equation: Wherein: S PS For spoke pre-strain, expressed as a percentage CTE is the coefficient of linear thermal expansion. T H For the spoke temperature in the mold T C ambient temperature L C The length of the spoke curve in the mold L is the distance between the radial boundaries of the spokes. The modulus E refers to Young's tensile modulus of elasticity as measured according to ASTM D2969.

2. The non-pneumatic tire according to claim 1, wherein 3. The non-pneumatic tire according to claim 1, wherein the annular support has a pre-strain of not less than 1.5%.

4. The non-pneumatic tire according to claim 1, further comprising a tread pattern on the radial outer boundary of the annular beam.

5. The non-pneumatic tire according to claim 1, wherein the reinforcing member comprises continuously pultruded glass monofilament.

6. The non-pneumatic tire according to any one of claims 1 to 5, wherein the rim comprises the thermoplastic elastomer.

7. The non-pneumatic tire according to claim 6 further includes a wheel hub.

8. The non-pneumatic tire according to claim 7, wherein the axial width of the hub does not exceed 50% of the width of the rim.

9. The non-pneumatic tire of claim 8, wherein the axial width of the hub does not exceed 30% of the width of the rim.

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