ANDERSON, Austin, James (1362 Black River Drive, Mt. Pleasant, SC, 29466, US)
LEMASTER, Gregory, Adam (208 Register Street, Sanford, NC, 27330, US)
MCCONNAUGHEY, Charles, Bradley (118 Fairview Place, Greer, SC, 29651, US)
STRAUSS, Jason, Edward (109 Ragon Lane, Greenville, SC, 29609, US)
LUND, Mark, Henry (33 Fernwood Trail, Hilton Head, SC, 29928, US)
MICHELIN RECHERCHE ET TECHNIQUE S.A. (Route Louis-Braille 10, Granges-Paccot, CH-1763, CH)
THOMPSON, Ronald, Hobart (300 Gilderbrook Road, Greenville, SC, 29615, US)
ANDERSON, Austin, James (1362 Black River Drive, Mt. Pleasant, SC, 29466, US)
LEMASTER, Gregory, Adam (208 Register Street, Sanford, NC, 27330, US)
MCCONNAUGHEY, Charles, Bradley (118 Fairview Place, Greer, SC, 29651, US)
STRAUSS, Jason, Edward (109 Ragon Lane, Greenville, SC, 29609, US)
LUND, Mark, Henry (33 Fernwood Trail, Hilton Head, SC, 29928, US)
WHAT IS CLAIMED IS:
1. A shear band defining axial, radial, and circumferential directions, the shear band comprising: an outer member extending along the circumferential direction at a radial position R 2 ; an inner member extending along the circumferential direction at a radial position R 1 ; and a plurality of resilient, columnar elements connected with said outer and inner members and extending between said outer and inner members, wherein a ratio of Ri to R 2 is about 0.8 ≤ (Ri / R 2 ) < 1
2. A shear band as in claim 1, wherein said plurality of columnar elements are arranged into multiple, offset rows along the axial direction, said off-set rows being positioned about the circumferential direction between said outer and inner members.
3. A shear band as in claim 2, wherein each said columnar element is connected at an inner end with said inner member and is connected at an outer end with said outer member, and wherein said columnar element has a pivotal point of connection at either said inner end or said outer end.
4. A shear band as in claim 1, wherein each said columnar element is connected at an inner end with said inner member and is connected at an outer end with said outer member, and wherein said columnar element has a pivotal point of connection at either said inner end or said outer end. Attorney Docket No. : P50-0230-WO-PCT
5. A shear band as in claim 1, wherein said plurality of columnar elements each further comprise a plurality of inextensible strands generally oriented longitudinally along the radial direction.
6. A shear band as in claim 1, wherein said outer and said inner members comprise metal elements encircled along the circumferential direction.
7. A shear band as in claim 1, further comprising means for connecting said plurality of columnar elements to said outer member.
8. A shear band as in claim 7, further comprising means for connecting said plurality of columnar elements to said inner member.
9. A shear band as in claim 1, wherein said shear band has a shear efficiency of at least about 50 percent.
10. A wheel comprising the shear band of claim 1.
11. A wheel defining axial, radial, and circumferential directions, the wheel comprising: a hub; a shear band comprising an outer circumferential member, an inner circumferential member, a plurality of radially-oriented, flexible posts having an inner end connected with said inner circumferential member and an outer end connected with said outer circumferential member, wherein said flexible posts generally form axially-aligned rows spaced about the circumferential direction; and a plurality of support elements connecting said hub and said inner circumferential member of said shear band.
12. A wheel as in claim 11, wherein each of said plurality of flexible posts comprises multiple, inextensible filaments generally oriented longitudinally along the radial direction.
13. A wheel as in claim 12, wherein each of said plurality of flexible posts has a pivotal point of connection at either said inner end or said outer end.
14. A wheel as in claim 12, wherein said multiple inextensible filaments comprise metal wires generally oriented longitudinally along the radial direction.
15. A wheel as in claim 11, wherein each said post has a pivotal point of connection at either said inner end or said outer end.
16. A wheel as in claim 11, wherein said outer and said inner circumferential members comprise metal elements encircled along the circumferential direction.
17. A wheel as in claim 11, further comprising means for connecting said plurality of posts to said outer circumferential member. Attorney Docket No. : P50-0230-WO-PCT
18. A wheel as in claim 17, further comprising means for connecting said plurality of posts to said inner circumferential member.
19. A wheel as in claim 11, wherein said shear band has a shear efficiency of at least about 50 percent. |
PCT PATENT APPLICATION
TITLE
ELASTIC SHEAR BAND WITH COLUMNAR ELEMENTS
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention relates to a shear band that may be used as part of a structurally supported wheel. More particularly, a shear band constructed from resilient, columnar elements attached between members is provided. In certain embodiments, the shear band may be constructed entirely or substantially without elastomeric or polymer-based materials, which allows for applications in extreme environments.
BACKGROUND OF THE INVENTION
[0002] The use of structural elements to provide load support in a tire without the necessity of air pressure has been previously described. For example, U.S. Patent No. 6,769,465 provides a resilient tire that supports a load without internal air pressure. This tire includes a ground contacting tread portion, a reinforced annular band, and sidewall portions that extend radially inward from the tread portion. By way of further example, U.S. Patent No. 7,201,194 provides a structurally supported non-pneumatic tire that includes a ground contacting tread portion, a reinforced annular element disposed radially inward of the tread portion, and a plurality of web spokes extending transversely across and radially inward from the reinforced annular element and anchored in a wheel or hub. For each of these references, the constructions described are particularly amenable to the use of elastomeric materials including rubber and other polymeric materials. The use of such materials has certain
limitations, however. For example, extreme temperatures levels and large temperature fluctuations can make such elastomeric materials unsuitable for certain applications. Accordingly, constructions that can be created in whole or in part with non-elastomeric materials would be advantageous. Also, constructions from materials such as carbon-based elements, for example, may also result in reduced weight and lower material costs. These and other advantages are provided by certain exemplary embodiments of the present invention.
THE SUMMARY OF THE INVENTION
[0003] Objects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.
[0004] In one exemplary embodiment, the present invention includes a shear band defining axial, radial, and circumferential directions. The shear band includes an outer member extending along the circumferential direction at a radial position R 2 and an inner member extending along the circumferential direction at a radial position Ri A plurality of resilient, columnar elements are connected with the outer and inner members and extend between such members. Preferably, the ratio of Ri to R 2 is about 0.8 ≤ (Ri / R 2 ) < 1. The plurality of columnar elements are arranged into multiple rows along the axial direction with such being positioned about the circumferential direction between the outer and inner members. In variations of the invention, the columnar elements may be in axially-aligned rows, off-set rows, staggered rows, non-linear rows, or other variations and geometries. [0005] Each columnar element is connected at an inner end with the inner member and is connected at an outer end with the outer member. By way of example, the columnar elements may have a fixed or pivotal point of connection at either the inner end or the outer
end. Further, for this exemplary embodiment, the columnar elements may be connected directly to the outer and inner members, to another element that is in turn attached to the outer and inner members, or may be formed integrally with the outer and inner members, for example. The columnar elements may each comprise a plurality of inextensible strands generally oriented longitudinally along the radial direction. Alternatively, the columnar elements may be homogenous or a composite of materials.
[0006] In another exemplary embodiment, the present invention provides a wheel defining axial, radial, and circumferential directions. The wheel includes a hub, a shear band, and a plurality of support elements connecting the hub and the inner circumferential member of the shear band. The shear band is constructed from an outer circumferential member; an inner circumferential member; and a plurality of radially-oriented, flexible posts. Each post has an inner end connected with the inner circumferential member and an outer end connected with the outer circumferential member. The flexible posts generally form axially- aligned rows spaced about the circumferential direction. In certain embodiments, the shear band has a shear efficiency of at least about 50 percent.
[0007] These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:
[0009] Fig. IA is an exemplary embodiment of the present invention that includes a non- pneumatic wheel incorporating an embodiment of a shear band.
[0010] Fig. IB is a perspective view of a section of the exemplary shear band of Fig. IA. [0011] Fig. 2 is a schematic view of a shear band according to another exemplary embodiment of the present invention illustrating a "fixed-free" construction for the shear layer elements.
[0012] Fig. 3 is a schematic view of a shear band according to another exemplary embodiment of the present invention illustrating a "fixed- fixed" construction for the shear layer elements.
[0013] Fig. 4A is another exemplary embodiment of the present invention that includes a non-pneumatic wheel incorporating an embodiment of a shear band. [0014] Fig. 4B is a perspective view of a section of the exemplary shear band of Fig. 4A. [0015] Fig. 4C is a cross-sectional view of the exemplary shear band of Fig. 4A.
DETAILED DESCRIPTION
[0016] Objects and advantages of the invention will be set forth in the following description, or may be apparent from the description, or may be learned through practice of the invention. Repeat use of reference characters throughout the present specification and appended drawings is intended to represent same or analogous features or elements of the invention.
[0017] An exemplary embodiment of a wheel 10 according to the present invention is shown in Fig. IA with a portion of wheel 10 being shown in Fig. IB. Wheel 10 defines radial directions R, circumferential directions C (Fig. IA), and axial directions A (Fig. IB). Wheel 10 includes a hub 20 connected to a shear band 40 by multiple support elements 30.
Shear band 40 includes multiple columnar elements 70 that are spaced circumferentially
about shear band 40. Hub 20 provides for the connection of wheel 10 to a vehicle and may include a variety of configurations for connection as desired. For example, hub 20 may be provided with connecting lugs, holes, or other structure for attachment to a vehicle axle and is not limited to the particular configuration shown in Fig. 1. Support elements 30 connect hub 20 to shear band 40 and thereby transmit the load applied to hub 20. As with hub 20, support elements 30 may take on a variety of configurations and are not limited to the particular geometries and structure shown in Fig. 1. In addition, using the teachings disclosed herein, one of skill in the art will understand that tread or other features may be readily added to the outer circumferential surface 55.
[0018] Columnar elements 70 are positioned between an outer member 50 and an inner member 60. In one embodiment, for example, elements 50 and 60 may each be constructed from a metal element encircled as shown in Fig. 1. By way of further examples, steel as might be used in the construction of springs and/or carbon based filaments may also be utilized for the fabrication of members 50 and 60. Monofilament elongate composite elements of long glass fibers impregnated in a thermoset resin, as described in U.S. Patent No. 7,032,637, may also be useful in the construction of members 50 and 60. While elastomeric materials can also be used for outer and inner members 50 and 60, the utilization of non-elastomeric materials provides for extreme temperature applications such as a polar or lunar environment where elastomeric materials may become too rigid or brittle. For example, shear bands (including wheels incorporating such elements) capable of functioning at temperatures as low as 100 degrees Kelvin should be achievable where elastomeric constructions are avoided.
[0019] Focusing on Figs. IA and IB, for this particular exemplary embodiment, columnar elements 70 may be constructed from resilient, inextensible materials such as, for example, carbon-based filaments as well as elastomeric materials such as rubber or polymer-based
compositions. In addition, the present invention is not limited to columnar elements 70 that are circular in shape as shown in the figures. Instead, other shapes and geometries may be used depending upon the particular application intended. Although shown in Figs. IA and IB as unitary constructions with outer and inner members 50 and 60, a variety of constructions may be used to connect columnar elements 70 between members 50 and 60. For example, exemplary constructions may include adhesives, various types of fasteners, combinations thereof, and a variety of additional methods as will be understood by one of skill in the art using the teachings disclosed herein. Also, the present invention does not require that columnar elements 70 be attached directly to members 50 and 60. Instead, constructions where columnar elements 70 are attached to other components that connect with members 50 and 60 may be used, for example.
[0020] For the exemplary embodiment shown in Figs. IA and IB, columnar elements 70 are arranged in rows that are staggered or offset relative to axial directions A. However, the present invention includes multiple other arrangements of columnar elements 70 between members 50 and 60. For example, columnar elements 70 could be non-offset, random, aligned in rows that are either parallel or not parallel to axial directions A, and so forth. As will be discussed later, columnar elements 70 provide a shear layer during operation that may be achieved by multiple other geometries that are within the scope of the present invention. [0021] Although not limited thereto, the shear band of the present invention has particular application in the construction of wheels including, but not limited to, non-pneumatic tires and other wheels that do not require pneumatic pressure for structural support. For example, in a pneumatic tire, the ground contact pressure and stiffness are a direct result of the inflation pressure and are interrelated. However, a shear band of the present invention may be used to construct a wheel or tire that has stiffness properties and a ground contact pressure that are based on their structural components and, advantageously, may be specified
independent of one another. Wheel 10 provides an example of one such construction. In addition, and advantageously, because the present invention includes structures and geometries for a shear band construction that are not limited to elastomeric (e.g. rubber) or polymer-based materials, the present invention provides for the construction of a wheel that may be used in extreme temperature environments. As used herein, extreme temperature environments includes not only environments experiencing temperatures that would be unacceptable for elastomeric or polymer-based materials but also includes environments where large temperature fluctuations may occur.
[0022] Returning to Fig. IA, for example, the exemplary shear band 40 can generally be modeled as a circular beam that allows for shear where the top and bottom of the beams are comprised of the outer and inner members 50 and 60. The outer member 50 is longer circumferentially than the inner member 60 and both are relatively inextensible. Therefore, shearing of the columnar elements 70 between the outer and inner members 50 and 60 allows the shear band to deform to provide a greater contact area with the travel surface (e.g. ground).
[0023] More specifically, columnar elements 70 collectively act as a shear layer providing an effective shear modulus G eff . The relationship between this shear modulus G eff and the effective longitudinal tensile modulus E im of the outer and inner members 50 and 60 controls the deformation of the shear band 40 under an applied load. When the ratio E im / G eff is relatively low, deformation of the shear band under load approximates that of the homogeneous element and produces a non-uniform contact pressure with the travel surface. On the other hand, when the ratio E im / G eff is sufficiently high, deformation of the annular shear band under load is essentially by shear deformation of the shear layer (i.e. columnar elements 70) with little longitudinal extension or compression of the members 50 and 60.
Perfectly members 50 and 60 would provide the most efficient structure and maximize the
shear displacement in the shear layer. However, perfect inextensibility is only theoretical: As the extensibility of members 50 and 60 is increased, shear displacement will be reduced as will now be explained in conceptual terms below.
[0024] In the contact region, the inner member 60, located at a radius R 1 , is subjected to a tensile force. The outer member 50, located at a radius R 2 , is subjected to an equal but opposite compressive force. For the simple case where the outer and inner members 50 and 60 have equivalent circumferential stiffness, the outer member 50 will become longer by some strain, e, and the inner member 60 will become shorter by the some strain, -e. For a shear layer having a thickness h, this leads to a relationship for the Shear Efficiency of the bands, defined as: (1)
Shear Efficiency = (1 - e ( f?2 ^ + f?1 ))
It can be seen that for the perfectly inextensible members, the strain e will be zero and the Shear Efficiency will be 100%.
[0025] The value of the strain e can be approximated from the design variables by the equation below: (2)
8 R 2 E t
For example, assume we have a proposed design with the following values: h = 10 mm (radial distance between bands 50 and 60)
Ge ff = 4 N/mm2 (effective shear stiffness between the bands)
L = 100 mm (contact patch length necessary for design load)
R 2 = 200 mm (radial distance to outer member)
Ri = 190 mm (radial distance to inner member)
E = 20,000 N/mm2 (tensile modulus for both members 50 and 60) t = 0.5 mm (thickness for both members 50 and 60)
Calculating for e using E:
(10) (10O) 2 e = = 0.0025
8 (200)(20,000)(0.5)
The shear efficiency can then be calculated as:
(3)
0.0025 (190 + 200)
Shear efficiency = 1 = 0.9025
10
Thus, the efficiency in this case is approximately 90%.
[0026] The above analysis assumes that outer and inner members 50 and 60 have identical constructions. However, the thickness and/or the modulus of members 50 and 60 need not be the same. Using the principles disclosed herein, one skilled in the art can readily calculate the strains in members 50 and 60 and then calculate the shear efficiency, using the above approach. A Shear Efficiency of at least 50% should be maintained to avoid significant degradation of the contact pressure with the travel surface. Preferably, a Shear Efficiency of at least 75% should be maintained.
[0027] Accordingly, as sufficient Shear Efficiency is achieved, contact pressure with the travel surface becomes substantially uniform. In such case, an advantageous relationship is created allowing one to specify the values of shear modulus G eff and the shear layer thickness h for a given application:
(4)
P e ff * R 2 = G e ff * h
Where:
P eff = predetermined ground contact pressure
G eff = effective shear modulus of columnar elements 70 within members 50 and 60 h = thickness of the shear layer - i.e. radial height of columnar elements 70
R- 2 = radial position of the outer member 50
As one of skill in the art will appreciate using the teachings disclosed herein, the above relationship is useful in the design context because frequently P eff and R 2 are known - leaving the designer to optimize G eff and h for a given application.
[0028] The effective shear modulus (G eff ) behavior of the columnar elements 70 may be approximated using standard beam theory as will be understood by one of skill in the art. While the cross-sectional area of individual elements 70 may be varied within the scope of the present invention, the shear modulus G eff behavior can be divided into primarily two categories from the standpoint of standard beam theory: "fixed-free" and "fixed- fixed." Each category will now be described.
[0029] Fig. 2 schematically illustrates the fixed-free condition. As used herein, "fixed-free" refers to a beam model where only one end of the beam can transmit a bending moment. More specifically, posts or columnar elements 270 are fixed at end 290 to an inner extensible member 260. At the other end 280, columnar elements 270 are free or pivotable at the point of connection 300 to outer member 250. As shown in phantom in Fig. 2, when a force F is applied to shear band 240 as shown, columnar elements 270 experience a bending moment along ends 290 while ends 280 do not experience a reactionary moment. Assuming that the deflection v is small relative to the height h (along the radial direction R) of columnar elements 270, the strain experienced by post 270 becomes
(5)
γ = tan "1 (v/h) = v/h
Standard beam theory understood by one of skill in the art provides that deflection v can be calculated as follows:
(6) v = (P * h 3) / (3 * E * I) where: v = deflection
P = load per post = F / n, where n is the number of columnar elements 270 h = thickness of the shear layer - i.e. radial height of columnar elements 270
E = modulus of elasticity for columnar elements 270
I = moment of inertia
Accordingly, with the above, the shear modulus G e fr for the fixed- free post 270 as shown schematically in Fig. 2 can be approximated using the following equation:
(V)
Ge ff = (3 * E * I * n)/(h 2 * A) where A is the total area normal to the beams.
[0030] Fig. 3 schematically illustrates the fixed-fixed condition for post or columnar element 370. As used herein, "fixed-fixed" refers to a beam model where both ends of the beam can transmit a bending moment. More specifically, columnar elements 370 are fixed at both ends 380 and 390 to an outer and inner extensible member 350 and 360, respectively. As shown in phantom in Fig. 3, when a force F is applied to shear band 340 as shown, columnar elements 370 experience a bending moment along both ends 380 and 390. Again, as will be understood by one of skill in the art using standard beam theory, the deflection v of columnar element 370 is given by
(8) v = (P * h 3 ) / (12 * E * I)
Therefore, the shear modulus G eff for the fixed-fixed columnar element 370 as shown schematically in Fig. 3 can be approximated using the following equation:
(9)
Ge ff = (12 * E * I * n)/(h 2 * A)
[0031] Comparing equation 4 with equation 6, the fixed-free columnar elements 270 reduce Ge ff by a factor of 4 and necessarily concentrate the bending stress from force F at a fixed point. The fixed-fixed columnar element 370 distribute the bending stress from force F to both ends of columnar elements 370. This reduces the maximum moment by half and increases the stiffness of columnar elements 370 so as to increase G e ff and the contact pressure P e ff.
[0032] Another exemplary embodiment of a wheel 410 according to the present invention is shown in Fig. 4A with a portion of wheel 410 being shown in Fig. 4B and in cross-section in Fig. 4C. Wheel 410 defines radial directions R, circumferential directions C (Fig. 4A), and axial directions A (Fig. 4B). Wheel 410 includes a hub 420 connected to a shear band 440 by multiple support elements 430. Shear band 440 includes multiple columnar elements 470 that are spaced circumferentially about shear band 440. Hub 420 provides for the connection of wheel 410 to a vehicle and may include a variety of configurations for connection as desired. For example, hub 420 may be provided with connecting lugs, holes, or other structure for attachment to a vehicle axle and is not limited to the particular configuration shown in Fig. 4A. Support elements 430 connect hub 420 to shear band 440 and thereby transmit the load applied to hub 420. As with hub 420, support elements 430 may take on a variety of
configurations and are not limited to the particular geometries and structure shown in Fig. 4A. In addition, using the teachings disclosed herein, one of skill in the art will understand that tread or other features may be readily added to the outer circumferential surface 455. [0033] Columnar elements 470 are positioned between an outer member 450 and an inner member 460. Focusing on Figs. 4B and 4C, for this particular exemplary embodiment, columnar elements 470 are each constructed from a plurality of resilient, inextensible members 472 that are bundled together to create the columnar element 470. For example, inextensible members 472 may be constructed from steel wire that is bundled together as shown. In one exemplary embodiment, steel wire approximately 0.014" in diameter and about 1 inch in length was used in bundles of about forty individual wires to create columnar element 470. However, other resilient, inextensible materials may be used to construct columnar elements 470 as previously described.
[0034] For the exemplary embodiment of Figs. 4A through 4C, inextensible members 472 may be secured in place as columnar elements 472 by rivets 474 that extend through the inner and outer elements 450 and 460. Reinforcement plates 476 help secure and strengthen the position of rivets 474. Side rivets 478 help secure plates 476 to elements 450 and 460. As previously indicated, it should be understood that multiple other fasteners or techniques may be used to secure the position of columnar elements 472, and the present invention is not limited to the use of rivets 474 or plates 476. Columnar elements 470 are arranged in rows that are axially-aligned - i.e. parallel to axial directions A. However, the present invention includes multiple other arrangements of columnar elements 470 between elements 450 and 460 as indicated above.
[0035] Finally, it should be noted that advantages of the present invention are principally obtained where the relative radial distance between the inner and outer elements fall within a certain range. More specifically, preferably the following relationship is constructed:
(10)
0.8 < (Ri / R 2 ) < 1 where:
R 2 = radial position of the outer member (e.g. the distance to the outer element from the axis of rotation or focus of the radius defined by such element)
Ri = radial position of the inner member (e.g. the distance to the inner element from the axis of rotation or focus of the radius defined by such element) [0036] While the present subject matter has been described in detail with respect to specific embodiments thereof, it will be appreciated that those skilled in the art, upon attaining an understanding of the foregoing may readily produce alterations to, variations of, and equivalents to such embodiments. Accordingly, the scope of the present disclosure is by way of example rather than by way of limitation, and the subject disclosure does not preclude inclusion of such modifications, variations and/or additions to the present subject matter as would be readily apparent to one of ordinary skill in the art.
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