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

Abstract

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 allow a tire to run in a non-inflated or under-inflated state. Non-pneumatic tires do not require inflation, while "run-flat tires" can continue to operate at a relatively high speed for an extended period after a puncture and the complete or partial loss of pressurized air. Non-pneumatic tires may include a plurality of spokes, webbing, or other support structures that connect an inner ring to an outer ring.

[0003] In one embodiment, a method of 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 unrolling the rolled sheet of steel and tailor-rolling the steel sheet such that the thickness of the sheet varies 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 including one or more thick portions of the steel and one or more thin portions. The length of each blank is equal to the width of the sheet. The method further includes rotating each blank 90 degrees and roll-forming each blank to form a curve along the width of the blank in a state having one or more thick portions and one or more thin portions parallel to 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, a non-pneumatic tire includes a lower ring having a first diameter and an upper ring having a second diameter larger 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 of manufacturing a spoke for a non-pneumatic tire 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 sheet of steel to form a curve along its width. The method also includes heating the sheet of steel to a temperature of 950°C to 1400°C for 2 to 10 seconds and cooling the sheet of steel to a temperature of less than 200°C within 10 seconds. The method further includes cutting a steel spoke from the sheet of steel, the steel spoke having a width of 80 mm to 400 mm.

Brief Description of the Drawings

[0006] In the accompanying drawings, structures that illustrate exemplary embodiments of the claimed invention are illustrated, along with the detailed description provided below. Like elements are identified by the same reference numerals. It should be understood that an element shown as a single component may be replaced by a number of components, and an element shown as a number of components may be replaced by a single component. The drawings are not to scale, and the ratios of certain elements may be exaggerated for illustration.

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

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

[0009] "Axial" and "axially" refer to a direction parallel to the rotational axis of the tire.

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

[0011] "Radial" and "radially" refer to a direction perpendicular to the rotational axis of the tire.

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

[0013] Similar terms used in the following description are used to describe general tire components. However, it should be understood that since the terms have somewhat different implications, those skilled in the art will not consider any of the following terms to be purely interchangeable with other terms used to describe general tire components.

[0014] In this specification, directions are described with reference to the rotational axis of the tire. The terms "upward" and "upwardly" refer to the general direction towards the tread of the tire, and "downward" and "downwardly" refer to the general direction towards the rotational axis of the tire. Thus, when relative direction terms such as "upper" and "lower" or "top" and "bottom" are used in relation to an element, the "upper" or "top" element is spaced closer to the tread than the "lower" or "bottom" element. Additionally, when relative direction terms such as "above" or "below" are used in relation to an element, an element "above" another element is closer to the tread than the other element.

[0015] The terms "inward" and "inwardly" refer to the general direction toward the equatorial plane of the tire, and "outward" and "outwardly" refer to the general direction away from the equatorial plane of the tire and toward the sidewall of the tire. Thus, when relative directional terms such as "inner" and "outer" are used in relation to an element, the "inner" element is spaced closer to the equatorial plane of the tire than the "outer" element.

[0016] FIG. 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 that is larger than the first diameter. The upper ring 140 is coaxial with the lower ring 130. The lower ring 130 can engage a vehicle hub (not shown) for attaching the non-pneumatic tire 100 to a vehicle.

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

[0018] A circumferential tread 210 is attached to the upper ring 140. The circumferential tread 210 may be composed of rubber or other elastomeric material and may include tread elements (not shown) such as grooves, ribs, blocks, lugs, sipes, studs, or any other desired element. 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 the upper ring 140 can be made from an elastomeric material, plastic, composite material, or metal. The spokes 200 can also be made of an elastomeric material, plastic, composite material, or metal. In alternative embodiments, the lower ring, upper ring, or tread band can be made of any desired material. Specific materials can be selected for specific components to provide a non-pneumatic tire having desired performance characteristics.

[0020] In some embodiments, it is desirable to construct the spokes from very high-strength steel. However, it is difficult to form very high-strength steel into a curved shape (such as a constant radius) because steel has a tendency to return to its previous shape after being bent. This property is sometimes referred to as the "springback" of steel. This tendency becomes stronger as the strength of the steel increases. Forming ultra-high-strength steel requires a much higher pressing force than conventional steel and thus requires the use of specialized high-tonnage presses or roll forming equipment. Since such special equipment is required, the processing cost increases significantly, and thus the number of companies capable of producing such parts may be limited.

[0021] Very high-strength steel is often bent excessively beyond the desired shape due to its springback tendency and then relaxed back to the desired shape. In practice, the relaxation is often inconsistent between different coils of steel, resulting in insufficient dimensional control. Thus, steel components that are bent excessively often have to be readjusted. The forming operation also has to be adjusted to compensate for the differences in springback between the coils. Residual stresses from the forming process can also vary due to the forming process and the readjustment process, causing 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 an elevated temperature and then quenched to form a martensitic structure with the required mechanical properties. An example of a hot-forming grade of steel is Usibor grade press-hardened 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 the 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 coils 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 components as the components are gradually heated and the 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 components to prevent distortion may 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 chance of thermal distortion or residual stress occurring. 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. 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 can be 4140 or 4150 steel. The heat - treatable steel can have a carbon content of 0.28% - 0.50%. In an alternative embodiment, the heat - treatable steel can have a carbon content of 0.20% - 0.55%. In another alternative embodiment, the heat - treatable steel can have a carbon content of 0.20% - 0.60%. The heat - treatable steel can also have a manganese content of 0.40% - 1.0%.

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

[0029] The rolled sheet is unrolled and then roll - formed to impart curvature, bend, or other shapes along its width. The roll - forming process can form any desired spoke shape in the strip (320). In one embodiment, an arc is formed within the strip and the arc is defined by a single radius. In an alternative embodiment, a curved portion is formed in the strip and the curved portion is defined by multiple radii. In 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] The strip is then optionally pre - heated. In one embodiment, the strip is pre - heated to a temperature of 450°C - 650°C. The pre - heating can be performed in an electric furnace or a gas furnace. Also, the pre - heating step may 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. Thus, this may be referred to as a rapid heating step. The heating step may be performed within 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 burners, gas combustion units, solid fuels, high temperature salt baths, torches, induction heaters, and any combination thereof.

[0032] After the strip is heated to a temperature of 950°C to 1400°C, it is cooled to a temperature below 200°C (340). The strip can be cooled to this temperature within 10 seconds. Thus, this step may be referred to as a rapid cooling step. In one embodiment, the strip is cooled by quenching the strip in a quenching agent. Exemplary quenching agents include, but are not limited to, water, aqueous solutions containing water, oils, brine solutions, air, and powders.

[0033] After the strip is rapidly heated and then rapidly cooled, the strip is cut into a plurality of 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 strip is cut, any finishing process may be applied. For example, at least one edge of the spoke can be machined (360). The machining process can impart a rounded edge or a chamfered edge. Alternatively, the machining can impart a square corner or any geometric shape to the edge. As another example, one or more surfaces can be peened, such as by a shot peening or laser peening process (370). Those skilled in the art will understand that other known finishing processes may be applied to each spoke.

[0035] The 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 altered by adjusting any number of steps in the flash process.

[0036] 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. Next, the tire manufacturer can arrange the lower and upper rings so that they are coaxial and extend a plurality of steel spokes between the lower and upper rings. The plurality of spokes can be attached to the lower and upper rings by a welding or brazing process. Alternatively, the plurality of spokes can be connected to the lower and upper rings by pins, adhesives, or other fasteners. For example, the plurality of spokes can be hingedly connected to one or both of the lower and upper rings. In one known embodiment, one or more of the upper and lower rings can have slots for receiving the spokes.

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

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

[0039] Figure 3 is a drawing of a method (400) for making a spoke. This method is substantially the same as method 300 shown in the flowchart of Figure 2. As can be 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 showing an alternative embodiment of a method 500 for making a spoke for a non-pneumatic tire. 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 can be 4140 or 4150 steel. The heat-treatable steel can have a carbon content of 0.28% to 0.50%. In an alternative embodiment, the heat-treatable steel can have a carbon content of 0.20% to 0.55%. In another alternative embodiment, the heat-treatable steel can have a carbon content of 0.20% to 0.60%. The heat-treatable steel can also have a manganese content of 0.40% to 1.0%.

[0042] Although the disclosed process is described for very high-strength steels, it should be understood that other steel options such as 1080 steel may be used. Thus, in alternative embodiments, the process can be used with steels having a carbon content of 0.001% to 4.0%. Additionally, the method can be used with steels having 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 imparts a continuous thickness transition between a minimum thickness and a maximum thickness. In one embodiment, the steel sheet is tailor - rolled such that its thickness varies periodically 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 that include one or more thick portions of the steel and one or more thin portions (530). The blanks can be cut such that their length is equal to the width of the coil. Each blank is rotated 90 degrees after being cut (540).

[0045] Next, the rotated blank is 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 blank (550). In one embodiment, an arc is formed on the blank, and the arc is defined by a single radius. In an alternative embodiment, a curve is formed on the blank, and the curve is defined by multiple radii. In 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 pre - heated. In one embodiment, the blank is pre - heated to a temperature of 450 °C to 650 °C. The pre - heating can be performed in an electric furnace or a gas furnace. Also, the pre - heating step can be omitted.

[0047] Next, the blank is heated to a temperature of 950 °C to 1400 °C (560). The blank can be heated at this temperature for 2 to 10 seconds. Thus, this is sometimes referred to as a rapid heating step. The heating step can be performed within 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 burners, 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 below 200°C (570). The blank can be cooled to this temperature within 10 seconds. Thus, this step may be referred to as a rapid cooling step. In one embodiment, the blank is cooled by quenching the blank in a quenching material. Exemplary quenching materials include, but are not limited to, water, aqueous solutions, oils, brine solutions, air, and powders.

[0049] After the blank is rapidly heated and then rapidly cooled, it is cut into a plurality of 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 the tailoring rolling and rotation of the blank 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 is cut, any finishing process can be applied. For example, at least one edge of the spoke can be machined (590). The machining process can impart a rounded edge or a chamfered edge. Alternatively, the machining can impart a square corner or any geometric shape to the edge. As another example, one or more surfaces can be peened, such as by a shot peening or laser peening process (595). It will be understood by those skilled in the art that other known finishing processes may be applied to each spoke.

[0052] The 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 altered by adjusting any number of steps in the flash process.

[0053] In another embodiment, the non-pneumatic tire includes a lower ring having a first diameter and an upper ring having a second diameter that is larger than the first diameter. Next, the tire manufacturer may arrange the lower ring and the upper ring so that they are coaxial and extend a plurality of steel spokes between the lower ring and the upper ring. The plurality of spokes may be attached to the lower ring and the upper ring by a welding or brazing process. 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 hingedly connected to one or both of the lower ring and the upper ring. In one known embodiment, one or more of the upper ring and the lower ring may have slots for receiving the spokes.

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

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

[0056] FIG. 5 is a drawing of a method (600) for making a spoke. This method is substantially the same as method 500 shown in the flowchart of FIG. 4. As can be seen in this figure, method 600 includes providing a steel coil (610). The steel coil may have the same characteristics as described above with respect to FIG. 4. The steel coil is tailor rolled (620), cut (630), and rotated (640). Next, the steel coil is 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 in the same manner as the term "comprising" as construed when used as a transitional term in a claim within the scope in which the term is used in this specification or the claims. Further, in the scope in which the term "or" is used (e.g., A or B), it is intended to mean "A or B, or both." Where the Applicants intend to indicate "only A or B but not both," the term "only A or B but not both" is used. Accordingly, the use of the term "or" in this specification is not exclusive but inclusive. See Bryan A. Garner, A Dictionary of Modern Legal Usage 624 (2d Ed. 1995). Also, the terms "in" or "into" are intended to additionally mean "on" or "onto" within the scope in which the terms are used in this specification or the claims. Further, in the scope in which the term "connect" is used in this specification or the claims, it is intended to mean not only "directly connected to" but also "indirectly connected to" such as connected through one or more other components.

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

Claims

1. A method for manufacturing a non-pneumatic tire, the method comprising: providing a rolled steel sheet having a carbon content of 0.20% to 0.60%, the sheet having a thickness of 1.5 mm to 7 mm; unrolling the rolled steel sheet; tailor-rolling the steel sheet such that the thickness of the sheet varies periodically between a minimum thickness and a maximum thickness along its length, wherein the minimum thickness is at least 1.2 mm, and the maximum thickness is 4.5 mm or less; cutting the sheet into blanks each including one or more thick portions and one or more thin portions of the steel, each blank having a length equal to the width of the sheet; rotating each blank by 90 degrees; roll-forming each blank to form a curve along the width of the blank in a state where the blank has one or more thick portions and one or more thin portions parallel to the length of the blank; heating each blank to a temperature of 950°C to 1400°C for 2 to 10 seconds; cooling each blank to a temperature of less than 200°C within 10 seconds; cutting each blank into a plurality of steel spokes having a width of 80 mm to 400 mm; providing a lower ring and an upper ring; and arranging the plurality of steel spokes between the lower ring and the upper ring.

2. The method according to claim 1, wherein the step of heating each blank includes heating each blank using a heating unit selected from the group consisting of an electric resistance heater, a fluidized bed, an electric furnace, a plasma furnace, a microwave oven, an open environment propane burner, a gas combustion unit, solid fuel, a high temperature salt bath, a torch, an induction heater, and any combination thereof.

3. The method according to claim 1, wherein the step of cooling each blank includes rapidly quenching the blank with a quenching material selected from the group consisting of water, an aqueous solution containing water, oil, a brine solution, air, and powder.

4. The method according to claim 1, further comprising the step of machining at least one edge of each of the plurality of steel spokes.

5. The method according to claim 1, further comprising preheating each blank to a temperature of 450°C to 650°C before heating each blank to a temperature of 950°C to 1400°C, wherein the preheating of the blank to a temperature of 450°C to 650°C is performed using one of an electric furnace and a gas furnace.

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