Non-pneumatic tire having curved spokes and method for manufacturing the same

Abstract

This disclosure relates to a non-pneumatic tire having curved steel spokes and a method for manufacturing the same. [Solution] The non-pneumatic tire includes a lower ring having a first diameter and an upper ring having a second diameter greater than the first diameter. The upper ring is substantially coaxial with the lower ring. The non-pneumatic tire further includes a plurality of curved steel spokes extending between the lower ring and the upper ring. Each of the plurality of curved steel spokes has a 0.2% yield strength of at least 1300 MPa, a tensile strength of at least 1400 MPa, and a hardness of at least 50 HRC.

Description

Technical Field

[0001] The present disclosure relates to a non-pneumatic tire having curved spokes and a method of manufacturing the same. More specifically, the present disclosure relates to a non-pneumatic tire having curved steel spokes and a method of manufacturing the same.

Summary of the Invention

Problems to be Solved by the Invention

[0002] Various tire structures have been developed that enable a tire to travel in a non-inflated or under-inflated state. Non-pneumatic tires do not require inflation, but "run-flat tires" can continue to operate at a relatively high speed for a long time after a puncture and the complete or partial loss of pressurized air. Non-pneumatic tires may include a plurality of spokes, a webbing, or other support structures that connect an inner ring to an outer ring.

[0003] In one embodiment, a method for manufacturing a non-pneumatic tire includes providing a rolled sheet of steel having a carbon content of 0.20% to 0.60%. The sheet has a thickness of 1.5 mm to 7 mm. The method further includes unwinding the rolled sheet of steel and tailor-rolling the sheet of steel such that the thickness of the sheet changes periodically between a minimum thickness and a maximum thickness along its length. The minimum thickness is at least 1.2 mm and the maximum thickness is 4.5 mm or less. The method also includes cutting the sheet into blanks having one or more thick portions and one or more thin portions of steel. The length of each blank is equal to the width of the sheet. The method further includes rotating each blank by 90 degrees and roll-forming each blank so as to form a curve along the width of the blank, having one or more thick portions and one or more thin portions parallel along the length of the blank. The method also includes heating each blank to a temperature of 950°C to 1400°C for 2 to 10 seconds, and cooling each blank to a temperature of less than 200°C within 10 seconds. The method further includes cutting each blank into a plurality of steel spokes having a width of 80 mm to 400 mm. The method also includes providing a lower ring and an upper ring, and arranging a plurality of steel spokes between the lower ring and the upper ring.

[0004] In another embodiment, the non-pneumatic tire includes a lower ring having a first diameter and an upper ring having a second diameter greater than the first diameter. The upper ring is substantially coaxial with the lower ring. The non-pneumatic tire further includes a plurality of curved steel spokes extending between the lower ring and the upper ring. Each of the plurality of curved steel spokes has a 0.2% yield strength of at least 1300 MPa, a tensile strength of at least 1400 MPa, and a hardness of at least 50 HRC.

[0005] In yet another embodiment, a method for manufacturing spokes for non-pneumatic tires includes providing a rolled sheet of steel having a carbon content of 0.28% to 0.50%, unwinding the rolled sheet of steel, and roll-forming the steel sheet to form a curve along its width. The method also includes heating the steel sheet to a temperature of 950°C to 1400°C for 2 to 10 seconds, and cooling the steel sheet to a temperature of less than 200°C within 10 seconds. The method further includes cutting steel spokes from the steel sheet, the steel spokes having a width of 80 mm to 400 mm. [Brief explanation of the drawing]

[0006] The attached drawings illustrate structures illustrating exemplary embodiments of the claimed invention, along with the detailed description provided below. Similar elements are identified by the same reference numeral. It should be understood that elements shown as single components may be replaced by multiple components, and elements shown as multiple components may be replaced by single components. The drawings are not to exact scale, and the proportions of certain elements may be exaggerated for illustrative purposes.

[0007] [Figure 1] Figure 1 is a front view of one embodiment of a non-pneumatic tire. [Figure 2] Figure 2 is a flowchart showing one embodiment of a method for manufacturing spokes for non-pneumatic tires. [Figure 3] Figure 3 is a diagram illustrating the method shown in the flowchart of Figure 2. [Figure 4] Figure 4 is a flowchart illustrating an alternative embodiment of a method for fabricating spokes for non-pneumatic tires. [Figure 5] Figure 5 is a diagram illustrating the method shown in the flowchart of Figure 4. [Modes for carrying out the invention]

[0008] The following includes definitions of optional terms used herein. These definitions include various examples and / or forms of components that fall within the scope of the terms and may be used for implementation. The examples are not intended to be limiting. Both singular and plural forms of the terms may fall within the scope of the definitions.

[0009] "Axial" and "in the axial direction" refer to the direction parallel to the tire's axis of rotation.

[0010] "Circumferential" and "circumferentially" refer to the direction that extends along the outer circumference of the tread surface, perpendicular to the axial direction.

[0011] "Radial" and "radially" refer to the direction perpendicular to the tire's axis of rotation.

[0012] As used herein, "tread" refers to the portion of the tire that is in contact with the road or ground under normal inflation and load conditions.

[0013] While common tire components are described using similar terminology in the following description, it should be understood that, naturally, the terms have slightly different implications, and therefore, those skilled in the art will not consider any of the following terms to be purely interchangeable with other terms used to describe common tire components.

[0014] In this specification, direction is given with respect to the tire's axis of rotation. The terms “upward” and “towards” refer to the general direction toward the tire's tread, while “downward” and “towards” refer to the general direction toward the tire's axis of rotation. Therefore, when relative directional terms such as “upper” and “lower” or “top” and “bottom” are used in relation to elements, the “upper” or “top” element is spaced further away from the tread than the “lower” or “bottom” element. Additionally, when relative directional terms such as “up” or “down” are used in relation to elements, an element “above” another element is closer to the tread than the other element.

[0015] The terms "inward" and "inward" refer to the general direction toward the tire's equatorial plane, while "outward" and "outward" refer to the general direction toward the tire's sidewall, away from the tire's equatorial plane. Therefore, when relative directional terms such as "internal" and "external" are used in relation to elements, "internal" elements are spaced further away from the tire's equatorial plane than "external" elements.

[0016] Figure 1 is a front view of one embodiment of a non-pneumatic tire 100. The non-pneumatic tire 100 includes a lower ring 130 having a first diameter and an upper ring 140 having a second diameter larger than the first diameter. The upper ring 140 is coaxial with the lower ring 130. The lower ring 130 can engage with a vehicle hub (not shown) for mounting the non-pneumatic tire 100 to a vehicle.

[0017] The spokes 200 extend between the lower ring 130 and the upper ring 140, connecting the lower ring 130 to the upper ring 140. In the illustrated embodiment, the spokes 200 are curved. In an alternative embodiment, the spokes may have a more pronounced curve, such as being substantially C-shaped. In yet another alternative embodiment, the spokes may have any desired shape. For example, the spokes may be substantially V-shaped or meandering. In yet another alternative embodiment, the non-pneumatic tire may include two or more spokes of different shapes. For example, the non-pneumatic tire may include C-shaped spokes alternating with V-shaped spokes along the circumferential direction of the non-pneumatic tire. In yet another alternative embodiment, the spokes may be replaced by webbing or other support structures.

[0018] A circumferential tread 210 is attached to the upper ring 140. The circumferential tread 210 may be made of rubber or other elastomer material and may include tread elements (not shown) such as grooves, ribs, blocks, lugs, sipes, studs, or any other desired elements. In alternative embodiments, the tread layer may be omitted, and the tread elements may be formed directly on the upper ring.

[0019] Other components of the non-pneumatic tire 100 can be made from a variety of materials. The lower ring 130 or upper ring 140 can be made from elastomer material, plastic, composite material, or metal. The spokes 200 can also be made from elastomer material, plastic, composite material, or metal. In alternative embodiments, the lower ring, upper ring, or tread band can be made from any desired material. Specific materials can be selected for specific components to provide a non-pneumatic tire with desired performance characteristics.

[0020] In some embodiments, it is desirable to construct spokes from very high-strength steel. However, forming very high-strength steel into curved shapes (such as a constant radius) is difficult because steel tends to return to its original shape after being bent. This property is sometimes called "springback" of steel. This tendency becomes increasingly strong as the strength of the steel increases. Forming ultra-high-strength steel requires much higher pressing force than conventional steel and therefore necessitates the use of specialized high-tonnage presses or roll forming equipment. Because such specialized equipment is required, processing costs increase considerably, and therefore the number of companies capable of producing such parts may be limited.

[0021] Extremely high-strength steel, due to its springback tendency, is often overbent beyond the desired shape, then slackens and returns to the desired shape. In practice, the slackening is often inconsistent across different coils of steel, resulting in insufficient dimensional control. Therefore, overbent steel components often have to be readjusted. The forming process also has to be adjusted to compensate for differences in springback between coils. Residual stresses from the forming process can also vary due to the forming and readjustment processes, leading to inconsistencies in fatigue durability.

[0022] One known solution to this problem is to use a hot forming grade of steel, which can be formed at high temperature and then quenched to form a martensitic structure with the required mechanical properties. An example of a hot forming grade of steel is the Usibor grade of press hardening steel from ArcelorMittal. This steel can only be used in a hot stamping process in which individual flat blanks are heated to approximately 950 °C and then rapidly stamped in a die and rapidly cooled to less than 200 °C while under pressure in the die to form individual spokes. This process is very slow and expensive due to the high temperature and complexity of the cooling system required for the die.

[0023] Another known solution is to form the steel into a low strength structure and then increase the strength by using a heat treatment process to change the crystal structure of the steel to martensite or bainite. With conventional steels classified as high strength with an ultimate tensile strength of approximately 400 - 600 MPa, it is possible to roll form bends or C-shapes in a continuous cross-section and achieve consistent results. Adjustments to compensate for slight differences in strength between coils can be made using a laser measurement system and direct feedback to tighten or loosen the forming rolls. This process can be carried out from a coil of steel as a continuous process. The formed channels can then be cut into individual components or cut as longer lengths. For practical reasons, handling lengths exceeding 4 m or 5 m becomes very difficult.

[0024] Existing processes that roll steel and then heat treat the rolled steel can cause thermal distortion of the component as the component is gradually heated and residual stresses are relieved. The rapid cooling to "harden" the microstructure can then induce further residual stresses, which can cause distortion or lead to early fatigue failure due to residual tensile stress concentration in local areas. Taking measures such as clamping and supporting the component to prevent distortion can be successful, but this is expensive and impractical for mass production.

[0025] An improved solution to the springback problem is disclosed herein. In this improved solution, the component is rapidly heated using induction heating and then rapidly cooled by water cooling or quenching. The process of rapidly heating and cooling the component within seconds creates a bainite structure in the steel. The rapid heating and rapid cooling - or flash treatment - reduces the opportunity for thermal distortion or residual stresses to occur. In one test using 4140 steel components, the flash process described above resulted in a significant increase in strength as shown in Table 1 compared to the conventional process.

Table 1

[0026] Figure 2 is a flowchart showing one embodiment of such a method 300 for manufacturing a spoke for a non-pneumatic tire. The method 300 includes providing a heat-treatable rolled sheet (310). The sheet has a thickness of 1.5 mm to 7 mm. In one embodiment, the width of the sheet is 1.5 m or less.

[0027] In one embodiment, the heat-treatable steel is 4130 steel. In an alternative embodiment, the heat-treatable steel may be 4140 or 4150 steel. The heat-treatable steel may have a carbon content of 0.28% to 0.50%. In an alternative embodiment, the heat-treatable steel may have a carbon content of 0.20% to 0.55%. In another alternative embodiment, the heat-treatable steel may have a carbon content of 0.20% to 0.60%. The heat-treatable steel may also have a manganese content of 0.40% to 1.0%.

[0028] Although the disclosed process is described for very high-strength steel, it should be understood that other steel options, such as 1080 steel, may also be used. Therefore, in alternative embodiments, the process may be used for steels with a carbon content of 0.001% to 4.0%. Additionally, the method may be used for steels with a manganese content of 0.30% to 1.0%.

[0029] The rolled sheet is unwound and then roll-formed to impart a curve, bend, or other shape along its width. The roll-forming process can form any desired spoke shape on the strip (320). In one embodiment, an arc is formed within the strip, defined by a single radius. In an alternative embodiment, a curve is formed in the strip, defined by multiple radii. In yet another alternative embodiment, a V-shaped bend is formed in the strip. It should be understood that multiple arcs or bends may be formed in the strip.

[0030] Next, the strip is optionally preheated. In one embodiment, the strip is preheated to a temperature of 450°C to 650°C. Preheating can be performed in an electric furnace or a gas furnace. The preheating step may also be omitted.

[0031] Next, the strip is heated to a temperature of 950°C to 1400°C (330). The strip may be heated to this temperature for 2 to 10 seconds. This is therefore sometimes referred to as a rapid heating step. The heating step may be carried out in a heating unit. Examples of heating units include, but are not limited to, electric resistance heaters, fluidized beds, electric furnaces, plasma furnaces, microwave ovens, open-environment propane combustors, gas combustion units, solid fuels, high-temperature salt baths, torches, induction heaters, and any combination thereof.

[0032] The strip is heated to a temperature of 950°C to 1400°C and then cooled to a temperature of less than 200°C (340). The strip can be cooled to this temperature in less than 10 seconds. Therefore, this step is sometimes called a rapid cooling step. In one embodiment, the strip is cooled by quenching it in a quenching agent. Exemplary quenching agents include, but are not limited to, water, aqueous solutions containing water, oil, brine solutions, air, and powders.

[0033] After the strip is rapidly heated and then rapidly cooled, it is cut into multiple steel spokes (350). In one embodiment, each spoke has a width of 80 mm to 400 mm. However, it should be understood that the strip can be cut to any desired width.

[0034] After the strips have been cut, any finishing process may be applied. For example, at least one edge of a spoke may be machined (360). The machining process may impart a rounded edge or a chamfered edge. Alternatively, machining may impart a square corner or any geometric shape to the edge. As another example, one or more surfaces may be peened by a shot peening or laser peening process, for example (370). Those skilled in the art will understand that other known finishing processes may be applied to each spoke.

[0035] Spokes obtained from this process have been shown to have a tensile strength of at least 1400 MPa, a 0.2% yield strength of at least 1300 MPa, and a hardness of at least 50 HRC. These properties can be modified by adjusting any number of steps in the flash process.

[0036] In another embodiment, a non-pneumatic tire includes a lower ring having a first diameter and an upper ring having a second diameter greater than the first diameter. The tire manufacturer may then position the lower and upper rings coaxially and have a plurality of steel spokes extending between the lower and upper rings. The plurality of spokes may be attached to the lower and upper rings by welding or brazing processes. Alternatively, the plurality of spokes may be connected to the lower and upper rings by pins, adhesives, or other fasteners. For example, the plurality of spokes may be hinged to one or both of the lower and upper rings. In one known embodiment, one or more of the upper and lower rings may have slots for receiving spokes.

[0037] When the spokes are assembled to the upper and lower rings, each spoke may extend axially across the entire width of the lower and upper rings. Alternatively, one or more spokes may extend less than the entire width of the lower and upper rings. In certain embodiments, two or more rows of spokes may extend axially across the entire upper and lower rings. When two or more rows of spokes are used, spokes in adjacent rows may bend in opposite directions. Alternatively, when two or more rows of spokes are used, spokes in adjacent rows may bend in the same direction.

[0038] Next, the elastomer tread can be extended around the upper ring. The resulting non-pneumatic tire may be similar to the non-pneumatic tire 100 shown in Figure 1.

[0039] Figure 3 is an illustration of a method (400) for manufacturing spokes. This method is substantially the same as method 300 shown in the flowchart of Figure 2. As seen in this figure, method 400 includes providing a steel coil (410). The steel coil may have the same properties as described above with respect to Figure 2. The steel is then roll-formed (420), rapidly heated (430), and quenched (440). Next, the steel is cut to the desired spoke length (450).

[0040] Figure 4 is a flowchart illustrating an alternative embodiment of method 500 for producing spokes for non-pneumatic tires. Method 500 includes providing a heat-treatable rolled sheet (510). The sheet has a thickness of 1.5 mm to 7 mm. In one embodiment, the width of the sheet is 2.0 m or less.

[0041] In one embodiment, the heat-treatable steel is 4130 steel. In an alternative embodiment, the heat-treatable steel may be 4140 or 4150 steel. The heat-treatable steel may have a carbon content of 0.28% to 0.50%. In an alternative embodiment, the heat-treatable steel may have a carbon content of 0.20% to 0.55%. In another alternative embodiment, the heat-treatable steel may have a carbon content of 0.20% to 0.60%. The heat-treatable steel may also have a manganese content of 0.40% to 1.0%.

[0042] Although the disclosed process is described for very high-strength steel, it should be understood that other steel options, such as 1080 steel, may also be used. Therefore, in alternative embodiments, the process may be used for steels with a carbon content of 0.001% to 4.0%. Additionally, the method may be used for steels with a manganese content of 0.30% to 1.0%.

[0043] The rolled steel sheet is unwound and then tailor-rolled (520). The tailor-rolling process provides a continuous thickness transition between a minimum and maximum thickness. In one embodiment, the steel sheet is tailor-rolled such that its thickness periodically changes along its length between a minimum thickness of 1.2 mm and a maximum thickness of 4.5 mm.

[0044] Next, the steel sheet is cut into blanks, which include one or more thicker sections and one or more thinner sections of steel (530). The blanks may be cut so that their length is equal to the width of the coil. After each blank is cut, it is rotated 90 degrees (540).

[0045] Next, the rotated blank is roll-formed to impart curves, bends, or other shapes along its width. The roll-forming process can form any desired spoke shape on the blank (550). In one embodiment, an arc is formed on the blank, defined by a single radius. In an alternative embodiment, a curve is formed on the blank, defined by multiple radii. In yet another alternative embodiment, a V-shaped bend is formed on the blank. It should be understood that multiple arcs or bends can be formed on the blank.

[0046] Next, the blank is optionally preheated. In one embodiment, the blank is preheated to a temperature of 450°C to 650°C. Preheating can be carried out in an electric furnace or a gas furnace. The preheating step may also be omitted.

[0047] Next, the blank is heated to a temperature of 950°C to 1400°C (560). The blank may be heated to this temperature for 2 to 10 seconds. This is therefore sometimes referred to as a rapid heating step. The heating step may be carried out in a heating unit. Exemplary heating units include, but are not limited to, electric resistance heaters, fluidized beds, electric furnaces, plasma furnaces, microwave ovens, open-environment propane combustors, gas combustion units, solid fuels, high-temperature salt baths, torches, induction heaters, and any combination thereof.

[0048] The blank is heated to a temperature of 950°C to 1400°C and then cooled to a temperature of less than 200°C (570). The blank can be cooled to this temperature within 10 seconds. Therefore, this step is sometimes called a rapid cooling step. In one embodiment, the blank is cooled by quenching it in a quenching material. Examples of quenching materials include, but are not limited to, water, aqueous solutions containing water, oil, brine solutions, air, and powders.

[0049] The blank is rapidly heated and then rapidly cooled before being cut into multiple steel spokes (580). In one embodiment, each spoke has a width of 80 mm to 400 mm. However, it should be understood that the blank can be cut to any desired width.

[0050] Due to tailor rolling and rotation of the blanks prior to the roll forming process, each blank has a thickness that varies along its length. In one embodiment, the thickness varies from a minimum thickness of 1.2 mm to a maximum thickness of 4.5 mm.

[0051] After the blank has been cut, any finishing process may be applied. For example, at least one edge of a spoke may be machined (590). The machining process may impart a rounded edge or a chamfered edge. Alternatively, machining may impart a square corner or any geometric shape to the edge. As another example, one or more surfaces may be peened by a shot peening or laser peening process, for example (595). Those skilled in the art will understand that other known finishing processes may be applied to each spoke.

[0052] Spokes obtained from this process have been shown to have a tensile stress of at least 1400 MPa, a 0.2% yield strength of at least 1300 MPa, and a hardness of at least 50 HRC. These properties can be modified by adjusting any number of steps in the flash process.

[0053] In another embodiment, a non-pneumatic tire includes a lower ring having a first diameter and an upper ring having a second diameter greater than the first diameter. The tire manufacturer may then position the lower and upper rings coaxially and have a plurality of steel spokes extending between the lower and upper rings. The plurality of spokes may be attached to the lower and upper rings by welding or brazing processes. Alternatively, the plurality of spokes may be connected to the lower and upper rings by pins, adhesives, or other fasteners. For example, the plurality of spokes may be hinged to one or both of the lower and upper rings. In one known embodiment, one or more of the upper and lower rings may have slots for receiving spokes.

[0054] When the spokes are assembled to the upper and lower rings, each spoke may extend axially across the entire width of the lower and upper rings. Alternatively, one or more spokes may extend less than the entire width of the lower and upper rings. In certain embodiments, two or more rows of spokes may extend axially across the entire upper and lower rings. When two or more rows of spokes are used, spokes in adjacent rows may bend in opposite directions. Alternatively, when two or more rows of spokes are used, spokes in adjacent rows may bend in the same direction.

[0055] Next, the elastomer tread can be extended around the upper ring. The resulting non-pneumatic tire may be similar to the non-pneumatic tire 100 shown in Figure 1. It should be understood that method 500 in Figure 4 is merely illustrative. In alternative embodiments, certain steps may be omitted. For example, the strip may be cut into a blank without performing a tailor rolling process.

[0056] Figure 5 is an illustration of a method (600) for manufacturing spokes. This method is substantially the same as method 500 shown in the flowchart of Figure 4. As seen in this figure, method 600 includes providing (610) a steel coil. The steel coil may have the same properties as described above with respect to Figure 4. The steel coil is tailor-rolled (620), cut (630), and rotated (640). The steel coil is then roll-formed (650), rapidly heated (660), and quenched (670). Next, the steel coil is cut to the desired spoke length (680).

[0057] The terms “includes” or “including” are intended to be inclusive, as they are interpreted when used as transitional terms in a patent claim, to the extent that they are used herein or in the claims. Furthermore, the terms “or” are intended to mean “A or B, or both” to the extent that they are used (e.g., A or B). When the applicants intend to indicate “only A or B but not both,” the term “only A or B but not both” is used. Thus, the use of the term “or” herein is inclusive, not exclusive. See Bryan A. Garner, A Dictionary of Modern Legal Usage 624 (2d. Ed. 1995). Additionally, the terms “in” or “into” are intended to mean “on” or “onto” to the extent that they are used herein or in the claims. Furthermore, to the extent that the term “connect” is used herein or in the claims, it is intended to mean not only “directly connected to,” but also “indirectly connected to,” such as by connecting through one or more other components.

[0058] Although this application has been illustrated by the description of its embodiments, and these embodiments have been described in considerable detail, it is not the applicant's intention to limit the scope of the appended claims to such detail or to restrict them in any way. Additional advantages and modifications will be readily apparent to those skilled in the art. Therefore, the broader embodiments of this application are not limited to the specific details, representative apparatus and methods, and examples illustrated and described. For this reason, deviations from such details may be made without departing from the spirit or scope of the applicant's general inventive concept.

Claims

1. Non-pneumatic tires, A lower ring having a first diameter, An upper ring having a second diameter larger than the first diameter, and substantially coaxial with the lower ring, It comprises a plurality of curved steel spokes extending between the lower ring and the upper ring, A non-pneumatic tire in which each of the plurality of curved steel spokes has a 0.2% yield strength of at least 1300 MPa, a tensile strength of at least 1400 MPa, and a hardness of at least 50 HRC.

2. The non-pneumatic tire according to claim 1, wherein each of the plurality of curved steel spokes has a carbon content of 0.28% to 0.50%.

3. The non-pneumatic tire according to claim 1, wherein at least one of the plurality of curved steel spokes has a variable thickness.

4. The non-pneumatic tire according to claim 3, wherein at least one of the plurality of curved steel spokes having variable thickness has a minimum thickness of 1.2 mm and a maximum thickness of 4.5 mm.

5. The non-pneumatic tire according to claim 1, wherein each of the plurality of curved steel spokes has a rounded edge.

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