Non-pneumatic tires

Abstract

The present invention provides a non-pneumatic tire comprising a thermoplastic elastomer that is pre-tensioned during the tire forming process. The pre-tension is provided by thermal means naturally available during the forming process. This results in efficient manufacturing combined with the efficiency of pre-tensioning without the complexity of mechanically adding pre-tensioning.

Description

[0001] This application claims the benefit of U.S. Provisional Application No. 63 / 018,491, filed on April 30, 2020. Technical Field

[0002] The present disclosure relates to non-pneumatic tires (NPTs) for on-road or off-road vehicles (e.g., automobiles, light and heavy trucks, all-terrain vehicles, zero-turn radius mowers, military vehicles), and in particular to off-road vehicles that may require higher speed and load capacity as well as high damage tolerance. Background Art

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

[0004] NPT generates loads through mechanical means (bending, tensioning, and / or compression of various design elements). Pneumatic tires, on the other hand, are pre-tensioned due to inflation pressure. Vertical loads can be counteracted by reducing tension in pre-tensioning components (such as reinforcing layers). This "releasing" of pre-tensioning can be more effective than inducing structural deflection. These pre-tensioning layers can be thin and therefore lightweight. Consequently, the load and speed capabilities of a pneumatic tire 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] NPTs can require inefficient and / or expensive manufacturing methods. An example of prior art related to NPT manufacturing is US 9,004,901 (owned by the current applicant). This discloses a method for forming thermosetting polyurethane spokes and bonding them to a rubber tread and a center hub. The mold rotates, creating centrifugal forces that allow the mold to fill. The liquid polyurethane then cures and hardens, and the NPT can be demolded. Such equipment and procedures can be expensive to operate 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 can reduce the cost of NPT. However, there is no disclosure in this prior art regarding pre-tensioning.

[0008] The present disclosure bridges this gap by providing an NPT that includes a thermoplastic elastomer that is pre-tensioned during the process of forming the NPT. The pre-tension is provided by thermal means that are naturally available during the forming process. Thus, the advantages of efficient manufacturing are combined with the efficiency of pre-tensioning without the complexity of adding pre-tensioning through mechanical means. Summary of the Invention

[0009] Various aspects and advantages will be set forth in part in the following description or will be obvious from the description or may be learned through practice. The present invention has general application to vehicles using tires. Specifically, it is particularly suitable for off-road vehicles that may require high speeds and high loads as well as high energy absorption capabilities.

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

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

[0012] According to one aspect of the present invention, a non-pneumatic tire is provided, comprising: a reinforcing annular beam; an annular support member extending radially inward from the annular beam, the support member 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 is configured such that the annular beam is transversely isotropic in the RY plane.

[0013] According to one aspect of the present invention, a process for forming an NPT is provided. The NPT includes 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 the tread pattern only at the outer diameter limit.

[0014] These and other features, aspects and advantages of the present invention will become better understood with reference to the following description.The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments and, together with the description, serve to explain the principles. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] A complete and enabling disclosure of the present invention, including the best mode thereof, to one of ordinary skill in the art is set forth in the specification with reference to the accompanying drawings, wherein:

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

[0017] Figure 1 is an illustrative example of NPT.

[0018] Figure 2 is a graph of load versus deflection for an illustrative example of an NPT and a prior art NPT.

[0019] Figure 3 are illustrative examples of annular beams and treads.

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

[0021] Figure 5 2D FE model of a circular beam under compression as seen in thermoplastic injection molding.

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

[0023] Figure 7a and Figure 7b is an FEA simulation of the deflection of two annular beams when subjected to pressure as seen in thermoplastic injection molding.

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

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

[0026] Figure 10 Shown are the thermoplastic spokes, annular beam, and tread of an exemplary embodiment of NPT.

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

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

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

[0030] Figure 14 An exemplary NPT loaded to 7000N is shown.

[0031] Figure 15 This is an FEA prediction of the load-deflection relationship for four NPTs.

[0032] Figure 16 is the FEA prediction of the tangential perpendicular stiffness of the three NPTs.

[0033] Figure 17 Shown are FEA predictions of the contact patch length versus deflection for three NPTs.

[0034] Figure 18 Shown are FEA predictions for a single spoke subjected to critical buckling load.

[0035] Figure 19 Example gate locations for an example NPT are shown.

[0036] It should be expressly understood that the description and drawings are for the purpose of illustrating specific embodiments only and are provided to aid understanding, and are not intended to be and should not be limiting.

[0037] Definition of terms

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

[0039] "Hub" refers to any structure used to support the tire and capable of being attached to the axle.

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

[0041] When referring to a reinforcing cord or cable, "modulus" refers to Young's tensile modulus of elasticity measured in accordance with ASTM D 2969. The tensile modulus can be calculated as the secant modulus at a strain of 0.5%.

[0042] When referring to reinforcing cords or cables, "compressive strength" means the compressive stress at failure in uniaxial compression, measured by Journal of Composite MaterialsThe compressive strength of a glass fiber-vinyl ester is measured by the method disclosed in the article "Theoretical and experimental compressive strength of a glass fiber-vinyl ester pultruded composite", Vol. 49, No. 6, pp. 739-748.

[0043] When referring to rubber, "shear modulus" refers to 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" refers to the Young's modulus measured according to ASTM D412.

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

[0045] The "design contact length" is the contact length when loaded to the design load.

[0046] Measurement of tire vertical force versus deflection and footprint may be performed in accordance with SAE J2704. DETAILED DESCRIPTION

[0047] The present invention provides a non-pneumatic tire and a method of 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 the accompanying drawings. Each example is provided by way of illustration and not limitation. Indeed, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit. For example, features or steps illustrated or described as part of one embodiment may be used with another embodiment or step to produce yet another embodiment or method. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.

[0048] Figure 1 An illustrative example of an NPT 100 is shown, measuring 26x10-12. This is a common size for off-road applications. The tire defines a cylindrical coordinate system having a radial direction R, a circumferential direction θ, and an axial direction Y. A convenient Cartesian coordinate system has X as the direction of travel of the tire, 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 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, connecting the inner surface of the annular beam to the rim without intersecting any of the other spokes.

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

[0051] Prior art constructions, such as that described in US Pat. No. 9,004,901, use thermoset polyurethane to form the spokes. The current application discloses a method for forming the spokes using thermoplastic injection molding of a thermoplastic elastomer. Furthermore, this method results in an NPT with pre-tensioned spokes. This pre-tensioning is due to thermal contraction of the spokes as they are constrained at their radially inward and radially outward limits by the rim and annular beam, respectively.

[0052] Historically, the inventors were primarily motivated by the superior economics of thermoplastic injection molding compared to rotational molding of thermoset polyurethane. A prototype of a research tire in the 24x12-12 size was produced, tested, and compared to a prior art tire that included thermoset polyurethane spokes. Tires of this size are typically used for off-road vehicles, such as all-terrain vehicles (ATVs) and zero-turn radius (ZTR) lawn mowers. The results were surprising—better than expected. These positive surprises included:

[0053] - Tire rolling resistance was reduced by 20%, even though the research tire used the same tread and annular beam sections as the prior art tire.

[0054] - A strong nonlinear load-deflection curve is generated. Compared with the prior art, the initial slope of the load-deflection relationship of the current invention is higher, even though the slope of the tangent line at the design load is essentially unchanged. This is Figure 2 . Those skilled in the art of tire design will recognize the value of such performance. At a design load of 3000N, the deflection of the exemplary NPT is 4.5mm (30% less) than that of the prior art tire. However, the tangent KZ at the design load FZ=3000N for both NPTs is 160N / mm. The exemplary tire has a much higher initial KZ of 700N / mm. The initial KZ is more than 4 times higher than the KZ at the design load. Therefore, for the exemplary NPT, ride comfort is maintained,

[0055] At the same time, deformation and deflection are reduced.

[0056] - The process for forming the thermoplastic spokes is relatively easy, even though significant problems are anticipated. Thermoplastic injection molding requires high pressures. 28 MPa can occur in the area near the injection gate.

[0057] (4000 psi) or higher. Even at locations not near the injection gate, the pressure at the end of mold filling can be 100 psi (0.7 MPa), 200 psi (1.4 MPa) or higher. For this reason, injection molding uses strong steel or aluminum molds that are held together by several metric tons of clamping force. Rubber (even reinforced rubber) is not used as a surface for injecting high-pressure plastic. 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 comprises a thermoplastic elastomer. The inventors hypothesized that high injection pressures would deform the annular beam and tread, resulting in poor control of the thermoplastic elastomer thickness. However, this was not the case. The process was stable and well-controlled.

[0058] After careful research, the inventors determined that a variety of process and product attributes were necessary to produce better results. Each of these process and product attributes is disclosed below.

[0059] Reinforced ring beam with specific reinforcement properties

[0060] Figure 3 An exemplary embodiment of the tread 101 and the annular beam 102 is shown. They are one molded component, formed in the initial molding operation. Figure 4a and Figure 4b The annular beam is further described in [ 1 ]. In this embodiment, the annular beam is reinforced with a circumferential reinforcement 301. In this embodiment, the reinforcement comprises seven radially spaced layers. The beam comprises an elastomeric matrix material 302, which may comprise rubber. The spacing of the radial layers is approximately equal to the spacing of the reinforcements in the axial direction. Thus, the reinforcement forms a transversely isotropic composite material in the RY section of the annular beam. If the intercord spacing in the radial direction is within + / - 33% of the intercord spacing in the axial direction, the resulting composite material is approximately transversely isotropic.

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

[0062] exist Journal of Composite MaterialsThe article "Theoretical and Experimental Compressive Strength of a Glass Fiber-Vinylester Pultruded Composite," published in the journal IEEE Trans. Composites, Vol. 49, No. 6, pp. 739-748, discloses the properties of continuously pultruded glass fiber monofilaments. The reinforcement exhibits high stiffness and strength in both tension and compression. The properties of the reinforcement are advantageous for exemplary NPTs. These properties include:

[0063] -Young's modulus E=40GPa

[0064] A high modulus is advantageous because the exemplary example annular beam acts as a pressure vessel during the thermoplastic injection molding process. High stiffness enables a more stable molding process.

[0065] -Compressive strength σc=1.1GPa

[0066] The off-road use of the exemplary embodiment results in very high impact loads. Those skilled in the art of off-road tire design know that for transient events, dynamic loads can approach 4 times the design load. High compressive strength is a performance requirement.

[0067] -CTE=5×10 -6 mm / mm-C

[0068] After the molding process, the annular beam anchors the radially outer ends of the spokes. The low CTE of the circumferential reinforcement results in an annular beam that does not shrink after demolding, even at high molding temperatures. Thermal pre-strain is created in the thermoplastic spokes. Steel has a CTE of 12×10 -6 mm / mm-C, which is also an acceptably low value. By comparison, the thermoplastic elastomer used in the exemplary examples has a CTE of 1.6×10 -4 mm / mm-C. When low CTE is combined with high modulus, a very efficient structure results, enabling spoke pre-straining to occur.

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

[0070] Figure 5 This is a structural 2D FEA simulation used to predict deflection in the annular beam and tread. In this 2D plane strain model, stiffness is expressed per unit width. Therefore, the stiffness calculations for the reinforcement are normalized relative to a cross-section with a thickness of 1 mm in the axial direction.

[0071] During the thermoplastic molding process, molten elastomer is injected into the mold in which the annular beam is already positioned. In the exemplary embodiment, the annular beam is positioned so that the radially inward surface 201 serves as the outer diameter limit of the mold cavity. The molding operation then forms at least a portion of the annular support 103 and at least a portion of the rim 104. The 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 that surface. The annular beam comprises circumferential reinforcement 301 and matrix material 302. The tread 101 contacts the rigid mold surface 400 at the outer diameter limit 305 of the tread pattern. The tread groove walls 303 are free to deform. The outer diameter limit of the tread is constrained in the radial direction, but the tread is free to compress. In other words, the presence of the tread pattern creates an air gap between the tread and the mold surface 400. Therefore, the circumferential rigidity of the annular beam becomes very important.

[0073] To counteract the pressure, the reinforcement generates a tensile force, T. This is necessary because the tread groove walls may deform. Since the tread may be made of rubber, its compressive stiffness will be 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 position of the annular beam and tread in the mold in the RY section is shown. Mold surface 401 is at the lateral limit of the annular beam and tread. This section acts as a shutoff device to prevent 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 limit 305 of the tread. In other words, in combination Figure 5 , mold surfaces 400 and 401 can be smooth and therefore can be low cost.No support structure for tread groove bottom 304 or tread pattern side 303 is required.

[0075] Figure 7a and Figure 7b The deflection results (in mm) for the case where P = 0.7 MPa (100 psi) are shown in 7a. The deflection for the case without reinforcement is shown. If an isotropic rubber with an elongation modulus of 7 MPa is used, the deflection of the radial inner surface is between 2.5 mm and 3.05 mm. This is too large. Those skilled in the art of thermoplastic injection molding will recognize that wall thicknesses of 3 mm are typical. Having a defined mold surface that deflects as much as the desired wall thickness will create serious problems. In addition, there is a circumferential variation in thickness of about 0.5 mm.

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

[0077] Those skilled in the art of mechanical engineering will recognize that Figure 5 This approximates a pressure vessel in the case of a soft tread and high-modulus reinforcements. Therefore, the well-known formula relating reinforcement tension to internal pressure applies. Further use of the basic relationship between modulus, area, and strain can be added to create a relationship between the desired maximum allowable radial deflection and other design parameters. This is given below:

[0078]

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

[0080] P = injection pressure at inner radius

[0081] W = width of ring beam

[0082] A = total reinforcement cross section

[0083] E = Young's modulus of the reinforcement

[0084] ∈=circumferential strain of reinforcement

[0085] and R∈ = radial deflection at the inner radius

[0086] The inventors have found that injection pressure P = 1 MPa (146 psi) is a representative pressure at the inner radius of the beam during the molding process. In addition, the inventors have determined that the radial deflection R at the inner radius ∈ Acceptable values can be as low as 2 mm. Substituting these into equation (1):

[0087]

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

[0089] Formula (2) is in Newtons and millimeters. Therefore, the stress is in MPa. Other unit systems should be converted to these units in order to apply Formula (2).

[0090] The above analysis assumes that the reinforcements are spaced at a constant distance in the axial direction for each of the reinforcement layers. It also assumes that the reinforcement layers extend across the lateral limits of the ring beam. Designs that deviate from this do not depart from the intent of this application. The above formula can still be used to approximate the deflection of the ring beam during the injection molding operation.

[0091] The deflection of the annular beam at the inner radius under injection pressure can also be measured directly using the following procedure:

[0092] -Placing 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 limit of the annular beam

[0094] -NPT is formed by forming an annular support using a thermoplastic process

[0095] - Cutting the NPT annular beam and annular support at the location of said minimum radial distance.

[0096] -Measurement of 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 the inner diameter surface of the annular band flexes during the molding process.

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

[0099] According to the prior art US 7,201,194, 2 reinforcement layers are disclosed. Using the disclosed values of G = 5 MPa, and E'film / G = 1000:1, a total EA = 2.5E+06N is obtained. Using R = 330 mm, as disclosed, and W = 250 mm, R ∈ = 10.5 mm. This is too high and will not be rigid enough for injection molding.

[0100] While high tensile circumferential stiffness is required for efficient production processes, high circumferential compressive strength is required for product performance. The inventors have discovered that multi-layer reinforcements also improve load-carrying capacity in off-road conditions, where very high impacts on objects with reverse curvature are common. 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 an inverse curvature, the radius of which is equal to the radius of the NPT. At 14,500 N, the reinforcement layer at the outer diameter limit of the ring beam buckles. It becomes unstable, potentially leading to failure in the rubber matrix or in the reinforcement itself.

[0102] Figure 8b The NPT is shown with 3 layers of reinforcement. Now, there are 2 adjacent layers at the outer diameter limit of the ring beam. Under a load of 17,000N, the structure remains stable.

[0103] The "critical load" is the load at which cord buckling begins to occur. Figure 9 The critical load is shown in relation to the number of reinforcement layers. For 6 layers, the predicted critical load is 27,500 N. This represents a doubling of the performance of 2 layers. The mechanism of this improvement may involve the creation of a transversely isotropic reinforced ring beam.

[0104] In the above-referenced article in the Journal of Composites, the critical buckling compressive stress for unidirectional composites is given by:

[0105]

[0106] where σ c = critical buckling stress

[0107] G 12 = shear modulus in the plane of applied stress

[0108] G m = Matrix shear modulus

[0109] Vf = fiber (or cord) volume fraction

[0110] Assume that the unidirectional composite material is transversely isotropic. When the composite material is not transversely isotropic, the critical buckling stress decreases. Therefore, Figure 4b The reinforcement patterns shown in are exemplary. Thus, the inventors have found that the formulas usually applied to so-called classical composite materials (fibers of carbon or glass with a thermosetting resin such as vinyl ester) also describe cord-rubber composite materials.

[0111] It is not obvious to those skilled in the art of tire design that a cord-rubber composite could behave like a classic composite of a high modulus resin and fiber. The excellent prototype performance in testing and these modeling results suggest that this is indeed the case.

[0112] The inventors have found that performance is best when the distance between the cords in the radial direction is within 33% of the distance between the cords in the axial direction. In some cases, this may need to be 25%, and in some cases, 10%, and in some cases even less.

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

[0114] The desired cord volume fraction may 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 may be at least 3 MPa, in some cases 5 MPa, and in some cases even higher.

[0115] Even without considering macrobuckling, the outer diameter reinforcement layer is subject to high compressive stresses. Therefore, the cord itself needs to have high compressive strength. The journal article discloses a method for measuring the compressive strength of single cord or cable reinforcements. Using this method, continuously pultruded glass monofilaments can have 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 in the most severe applications, exceeding 1.1 GPa. The same procedure described in the journal article can be used to measure the compressive strength of any cord or cable.

[0116] Creating pre-tensioned, non-inflatable structures

[0117] Figure 10 is an exemplary NPT. The annular support member includes thermoplastic elastomer spokes 103 extending in a radial direction without intersecting other spokes in the wheel. The outer diameter limit is adhered to the inner diameter limit 201 of the annular beam. During the injection molding process, a uniform thickness 401 of thermoplastic elastomer is adhered to the inner diameter surface of the annular beam. The inner diameter limit is adhered to the outer diameter limit of the rim portion 104, which may comprise thermoplastic elastomer. The rim can be thicker and more rigid than the spokes. This creates a rigid, fixed boundary for the spokes.

[0118] Figure 11a The RT cross-section of an exemplary NPT as configured in a mold prior to demolding is shown. Spoke 103 extends from a radially outer limit B (joined to annular beam 102) to a radially inner limit A (joined to rim 102). Curvilinear distance Lc is the length of the spoke prior to demolding. In this representative example, curvilinear distance Lc = Rα, where angle α is measured in radians. Distance L is the linear distance between points A and B.

[0119] When the spoke cools after demolding, thermal contraction occurs and the stress-free length decreases. The degree of tensile prestrain in the cold spoke is related to the amount of thermal contraction and the difference between the spoke's curvilinear distance and its linear distance. This can be approximated as follows:

[0120]

[0121] Where: S PS is the spoke prestrain in percentage.

[0122] CTE is the coefficient of linear thermal expansion

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

[0124] T C is the ambient temperature

[0125] L C is the spoke curve length in the mold

[0126] L is the distance between the radial limits of the spokes

[0127] The associated spoke pretension is given by:

[0128]

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

[0130] E S is the spoke modulus

[0131] A S is the cross-sectional area of the spoke

[0132] Figure 11b Shown Figure 10 Due to the circumferential reinforcement of the annular beam 102, the inner radius R of the annular beam is reduced by using a low CTE reinforcement. B Similarly, the inner radius R of the rim 104 is R Relatively unchanged or perhaps even slightly smaller. Illustrative examples of rim designs are shown in the following sections.

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

[0134] The actual spoke pre-strain may vary according to equation (4), depending on other construction factors such as the CTE of the reinforcement. The true pre-strain can be measured as follows:

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

[0136] -Mark the point from which this distance was measured.

[0137] -Cut the spokes from the NPT.

[0138] -Measure the stress-free spoke removed from the NPT

[0139] If the spokes are under tension in the molded tire, the unstressed length will decrease. The amount of this decrease 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 illustration purposes only. Any curvilinear spoke geometry may be used. Standard computer-aided design tools enable calculation of any such curvilinear distance.

[0141] Figure 12 An exemplary NPTRY cross-section is shown. Rim material 104 may comprise a thermoplastic elastomer formed in the same operation as the spokes. Furthermore, 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 other cases, the hub may extend 30%; and in other cases, the hub may extend more than 50% of the axial width.

[0142] Utilizing a steel hub design that extends over 50% of the rim's axial width, the rim R B May not change during the molding operation. Steel has a high modulus and low CTE, which constrains the rim. If the hub extends 15% or less across the axial width of the rim, the rim R B May decrease as the tire cools. Since the majority of the rim consists of thermoplastic elastomer, R B This can increase the amount of prestrain in the spokes to values greater than those given in equation (5).

[0143] This exemplary rim design embodies a hub that is overmolded with the same thermoplastic elastomer used to form the spokes and rim. It may be low-cost but very effective in providing anchoring for the lower ends of the spokes.

[0144] High modulus spokes with high buckling loads

[0145] The advantages of spoke prestrain can be amplified by other design parameters. For example, the inventors have discovered that spoke modulus and spoke thickness can significantly impact forward performance. These factors, along with the effects of thermal shrinkage, were also investigated using 2D FEA. The cumulative impact of these design parameters is surprising. It is possible to transform a "tension-based" NPT into a hybrid NPT that supports loads through a combination of pretension, compression, and tension.

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

[0147] Version Spoke prestrain (%) 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 deformed geometries of V1 and V2 are shown, with their only difference being the spoke pre-strain. Under the design load of 4000N, the 1% spoke pre-strain clearly results in V2 having lower deflection and less spoke deformation than 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 the 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 increased. The spoke modulus and spoke thickness have increased, which results in a higher spoke pretension, as given in Equation (5).

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

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

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

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

[0154] In a cumulative manner, prestrain, modulus, and thickness can greatly increase the load carrying capacity of the exemplary NPT. For example, V4 has a deflection of less than 10 mm at a design load of 4000 N, while the reference version V1 requires a deflection of 30 mm.

[0155] The main effect of the above design levers is to increase the initial tangent KZ. Figure 15The relationship between the tangent line KZ and the deflection is shown for each of V1, V2 and V3 in FIG. At low deflection, the tangent line KZ of tires V2 and V3 is much higher than that of V1. At greater deflection, the tangent lines KZ become closer.

[0156] The inventors have found that the tangent line KZ at zero deflection can be at least 2 times the tangent line KZ at the deflection required to produce the design load. In other cases, this can be at least 3 times; in other cases, this can be 4 times, and in other cases, even more.

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

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

[0159] The inventors have found that the ratio of tire deflection at design load to contact patch length at 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 have understood that even moderately thick spokes can contribute significantly to load carrying capacity.Those skilled in the art of mechanical engineering are familiar with the Euler critical load for compression rods.

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

[0162]

[0163] For the case of rectangular spoke cross-sections as compression bars:

[0164]

[0165] Among them: F C Buckling load

[0166] E is the spoke modulus

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

[0168] w is the spoke width

[0169] t is the spoke thickness

[0170] L is the distance from the intersection of the spoke and the annular beam to the intersection with the rim

[0171] The inventors performed 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 for the 4.5mm thick spokes were quite surprising. Buckling required almost 600N of compression. Figure 13 and Figure 14 , several spokes buckle radially inward from the contact surface. Therefore, compared with the design load of 4000N, the buckling force of 600N per spoke cannot be ignored.

[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 carries both tension loads (tension spokes around the top of the tire, away from the contact area) and compression loads (spokes in the contact area). Figure 14 One of the effects seen in the , where the V4 has spokes with higher buckling loads.

[0175] The inventors have discovered that exemplary NPTs can have spokes with critical buckling loads that are 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] In order to reduce the injection pressure exerted by the thermoplastic elastomer on the radially inward surface of the annular beam, the inventors have discovered that it is advantageous to locate the injection gate near the rim portion of the exemplary NPT. Figure 19 , where the injection 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 first be formed into 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 portion through the annular support (which may include radially oriented spokes). By the time the material reaches the radially inward surface of the annular beam, the pressure may drop to 2 MPa (290 psi), or even as low as 1 MPa (140 psi), even though the injection pressure near gate 600 may be higher.

[0178] Certain additional elements that may be required for the operation of some embodiments are not described or shown because they are assumed to be within the capabilities of one of ordinary skill in the art. Furthermore, certain embodiments may not be present, may be absent, and / or may function without any element not specifically disclosed herein.

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

[0180] Although various embodiments 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 illustrated or described as part of one embodiment may be used in combination with aspects of another embodiment to produce yet further embodiments.

[0181] As used herein, the term "method" or "process" refers to one or more steps that can be performed in an order different from that 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 of steps, the omission of steps, the repetition of steps, or the simultaneous performance of steps.

[0182] Unless expressly excluded or otherwise limited, each document cited herein (including any cross-referenced or related patents or applications) is hereby incorporated by reference in its entirety. The citation of any document does not constitute an admission that it is prior art to any invention disclosed or claimed herein, or that it alone or in combination with any other referenced document or documents teaches, suggests, or discloses any such invention. In addition, to the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern.

Claims

1. A non-pneumatic tire, comprising: - an annular beam having an inner radius R, said annular beam comprising a circumferential reinforcement; an annular support extending radially inwardly from the annular beam, the annular support comprising a thermoplastic elastomer, the annular support having a pre-strain of not less than 0.5%, the pre-strain resulting from thermal contraction following an injection molding operation; - a rim extending radially inwardly from the annular support; and The non-pneumatic tire has an initial tangential perpendicular stiffness that is at least twice the tangential perpendicular stiffness at a design load.

2. The non-pneumatic tire of claim 1, wherein the initial tangential perpendicular stiffness is at least three times the tangential perpendicular stiffness at the design load. 3 . The non-pneumatic tire according to claim 1 , wherein a ratio of a contact patch length under a design load to a tire deflection under the design load is not less than 5. 4 . The non-pneumatic tire according to claim 3 , wherein a ratio of the contact patch length under a design load to the tire deflection under the design load is not less than 7.

5. The non-pneumatic tire according to any one of claims 1 to 4, wherein the annular support comprises spokes extending in the radial direction, thereby connecting the annular beam to the rim without intersecting any of the other spokes.

6. The non-pneumatic tire of claim 5, wherein the critical buckling load of the spoke is at least 10% of the design load.

7. The non-pneumatic tire of claim 6, wherein the critical buckling load of the spoke is at least 15% of a design load.

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