SHEAR BAND ASSEMBLY AND RESILIENT WHEEL

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 mechanical shear modules spaced apart at circumferential intervals is provided. In certain embodiments, the shear band may be constructed entirely or substantially without elastomeric or polymer-based materials, which allows for application in extreme environments.

[0002] United States Patents 6,769,465 and 7,201 ,194, which are commonly owned by the applicant of the present invention, relate to a structurally supported resilient tire that supports a load without internal air pressure. This structurally supported tire includes a reinforced annular band comprising a shear layer, a first membrane adhered to the radially inward extent of the shear layer, and a second membrane adhered to the radially outward extent of the shear layer. As disclosed, this annular band has specific desirable properties, including the virtue of obtaining a large ground contacting area with a relatively low, uniform contact pressure. The membranes have a high tensile and compression modulus in the circumferential direction. When the annular bland is deflected by an applied load against a flat surface, the relative displacement of the two membranes occurs substantially by a shear deformation of the shear layer. The shear modulus of the shear layer is sufficiently lower than the tensile modulus of the membranes to permit this result. However, this configuration has limitations related to the operating conditions of the tire and specifically the permissible operating temperature range of the shear layer.

SUMMARY OF THE INVENTION

[0003] A shear band assembly has been developed for use in non-pneumatic tires and having advantageous uses in other non-tire related technologies. An example of the shear band assembly is constructed from metallic components or members, combined in a specific manner to create desired performance characteristics. These performances include large displacements, with the ability to obtain large contact

areas with relatively low contact pressures. These performances are obtained while staying within the elastic yield points of industrially available metallic components. In a particular embodiment, a shear band is described relative to the axial, radial, circumferential directions, and an axis of rotation. The shear band comprises an outer member extending along the circumferential direction and at a first radial distance from the axis of rotation, an inner member extending along the circumferential direction and at a second radial distance measured from the axis of rotation, wherein the second radial distance is less than the first radial distance. A plurality of shear modules is spaced apart at circumferential intervals, interposed between the inner and outer members, and inter-connected to the outer and inner members. The shear modules permit a relative displacement in the circumferential direction of the outer and inner members.

[0004] In a more specific embodiment of the shear band, each of said shear modules comprises an outer end spring retainer attached to either the inner or outer members, an inner end spring retainer attached to the opposing inner or outer members, and at least one spring interposed in a circumferential orientation between the inner end and outer end spring retainers.

[0005] The invention further includes the use of the shear band in a wheel comprising a hub rotatable about an axis of rotation, a shear band comprising an inextensible, outer circumferential member extending along the circumferential direction at a radial position R ₀ , an inextensible, inner circumferential member extending along the circumferential direction at a radial position R,, wherein a ratio of R ₁ to R ₀ is about 0.8 ≤ (R, / R ₀ ) < 1. A plurality of shear modules spaced apart at circumferential intervals and inter-connected to the outer and inner members and interposed between these members. The shear modules permit a relative displacement in the circumferential direction of the outer and inner members. A plurality of support elements connecting the hub and the inner circumferential member of the shear band.

[0006] The shear band assembly obtains the functionality of the elastomeric annular band described in the references without the use of the elastomeric design elements. In the example disclosed herein, metallic elements are used. Metals typically are more resistant to large changes in temperature and typically have much

lower loss of energy due to hysteresis than elastomers. Thus, the ability to eliminate elastomeric materials can improve the range of acceptable temperatures in which such a resilient tire can operate. Additionally, the hysteretic loss, or rolling resistance, of such a resulting resilient tire can be reduced.

DESCRIPTION OF THE DRAWINGS

[0007] Fig. 1 is a cross section view of one module used in the design of a metallic annular band.

[0001] Fig. 2 is a cross section view of an elastomeric shear layer subjected to a shear displacement.

[0008] Fig. 3 shows a complete metallic annular band, comprised of a plurality of the modules shown in Fig. 1.

[0009] Fig. 4 is a close-up view of one of the modules.

DETAILED DESCRIPTION

[0010] Figure 2 is a schematic view of a section of an annual band having an eiastomeric shear layer. The horizontal direction shown in the figure corresponds to the circumferential direction around the complete annular band. The axial direction corresponds to the axis of rotation of the annular band, oriented perpendicular to the plane of Fig. 1 and 2. The vertical direction shown in the figures corresponds to the radial direction of an annular band. When the membranes are displaced horizontally relative to each other, that displacement is accommodated by a shear displacement Y in the shear layer. With reference to Fig. 2, the shear stress in the shear layer is defined as:

X = G - Y (1) where: τ = shear stress, in N/mm2 γ = shear angle, in radians G = shear modulus of the elastomeric shear layer material, in N/mm ² .

[0011] Figure 1 is a schematic diagram of a portion of the shear band assembly

comprising two annular components, or members, 10 and 20 that are interconnected by a plurality of shear modules 100. Each of the shear modules 100 comprises two springs and hardware to connect the ends of the two springs 37 to the annular metallic members 10 and 20. By way of comparison of the instant shear band assembly to the elastomeric shear band for the tire, each of the membranes of the elastomeric shear band is replaced by the annular members 10 and 20 and the shear layer is replaced by the plurality of shear modules 100. As used herein, the application of springs permits any type of device having a force versus displacement behavior, for which some non-limiting examples are coil springs, torsion springs, bending element or leaf springs.

[0012] The physical operating mechanism of the shear band assembly is similar to that of the elastomeric shear band. Application of a horizontal force F to the outer or inner element causes the annular members 10 and 20 to undergo a relative horizontal displacement that is resisted by the horizontally oriented springs 37 of the shear modules 100.

[0013] For each of the shear modules as shown in Fig. 1 , the force relative to the horizontal displacement can be calculated from the following equation:

F = 2K- Y- h (2) τ = F / b (3) where:

K = spring constant of each of the springs, in N/mm,

Y = relative angular displacement of inner element from outer element, in radians h = vertical distance between extreme top side of outer element and extreme bottom side of inner element, in mm b = horizontal (axial) width of the shear module, in mm τ = stress on top face of inner element, in N/mm ² , for a unit axial depth of the band.

The factor 2K in Equation 2 is the total spring constant and arises due to the two springs 37, each having a spring constant K, acting in parallel. Thus, the total spring constant is the sum of spring constants of the individual springs 37. Alternatively, a

single spring or more than two springs could be employed. The annular width b of the shear module is obtained by dividing the circumference of the annular band by the number of shear module elements.

[0014] In the elastomeric shear layer shown in Fig. 2, a homogeneous, elastomeric material separates and is adhered to the two inextensible membranes. The elastomeric material is homogeneous and isotropic having a shear modulus G. In order to choose the design parameters of the shear module, it is advantageous to express an equivalent shear modulus Ge of the shear module, relative to the shear modulus G of an elastomeric shear layer.

[0015] Equations 1 and 2 for the stress at the top face of the element 10 are set equal to each other. Furthermore, a condition is imposed for equal values of the shear angles for the case of the metallic shear module and the isotropic elastomeric shear layer. After substitution of Equation 2 to describe the force developed in the shear band assembly, an equivalent shear modulus Ge for the shear module is obtained:

Ge = (2 K- h) / b (4) where:

Ge = equivalent shear modulus of the shear module, for a unit axial depth of the band, in N/mm.

[0016] Finally, to account for the axial width of the band, the equivalent shear modulus Ge, as defined above, is divided by the axial width W of each shear module:

Ge' = Ge / W= (2 K- h) / (b'W) (5) where:

VV = axial width of shear module, in mm.

Ge' = equivalent shear modulus of shear module, in N/mm ² .

Thus, the designer of the shear modules chooses design variables h, K, b, and W in order to obtain the desired equivalent shear modulus.

[0017] Figures 3 and 4 provide a description of one example of the shear band assembly where all of the elements are metallic fabrications. The elements 10 and 20 are flat metal stock having the desired axial width W. The details of the shear

module are shown in Fig. 4 and correspond to the schematic view shown in Fig. 1. The outer half of the shear module 100 comprises section of square stock 30 attached to an outer end spring retainer 32 and to the outer element 20. Multiple pieces are used simply for convenience of fabrication. The outer end spring retainer 32 holds the outer ends of the springs 37 in position. The spring retainer 32 has a U- shaped opening where the vertical legs 35 serve to retain outer ends of the springs 37.

[0018] The inner half of the shear module 100 is centered in the U-shaped opening and comprises another section of square stock acting as an inner end spring retainer 40 attached to the inner element 10. The inner end spring retainer 40 serves to retain the inner ends of the springs 37 in position. Thus, a horizontal displacement of the inner and outer elements 10 and 20 causes a force to develop in each of the springs 37. The complete assembly of the shear band is shown in Fig. 3. In the present embodiment, the inner member 10 and outer member 20 are attached to the shear modules 100 with nuts and bolts. Additionally, numerous other means for attaching spring retaining members 32 and 40 to the outer and inner members 10 and 20 may be used such as, for example, riveting, welding, gluing or any type of adhesive bonding, and embedding or molding. It is also noted that the orientation of the parts of the shear module 100 may easily be reversed. That is to say, the U- shaped opening of the outer end spring retainer 32 may be reversed from the embodiment shown herein to face in a radially outward direction. Using the teachings disclosed herein, one of skill in the art will understand that numerous other variations are within the spirit and scope of the present invention.

[0019] Returning to Fig. 1 and Fig. 4, it will be understood from the figures and description provided above that outer member 20 is longer circumferentially than the inner member 10. If the members are made of metallic elements, then both are relatively inextensible or even rigid. Accordingly, in operation under an applied load to a wheel, the shear modules 100 between the members 10 and 20 allow the shear band to deform and provide a greater contact area with the travel surface (e.g. ground).

[0020] More specifically, the relationship between the effective shear modulus Ge and the effective longitudinal tensile modulus E _ιm of the inner and outer members 10

and 20 controls the deformation of the shear band under an applied load. When the ratio of E, _m /Ge is relatively low, deformation of the shear band under load approximates that of the homogeneous member and produces a non-uniform contact pressure with the travel surface. However, when the ratio E, _m / Ge is sufficiently high, deformation of the annular shear band under load is essentially by shear deformation of the shear layer (i.e., shear modules 100) with little longitudinal extension or compression of the inextensible members 10 and 20. Perfectly inextensible members 10 and 20 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 10 and 20 is increased, shear displacement will be reduced as will now be explained in conceptual terms below.

[0021] In the contact region, the inner member 10, located at a radius R1 , is subjected to a tensile force. The outer member 20, located at a radius R2, is subjected to an equal but opposite compressive force. For the simple case where the inner and outer members 10 and 20 have equivalent circumferential stiffness, the inner member 10 will become longer by some strain, e, and the outer member 20 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 members, defined as: u - _h )

Shear Efficiency = (1)

It can be seen that for the perfectly inextensible members, the strain e will be zero and the Shear Efficiency will be 100%.

[0022] The value of the strain e can be approximated from the design variables by the equation below:

Ge _ff L ² _{e s} _ ₍ 2)

8 R2 E t

For example, assume a proposed design with the following values: h = 10 mm (radial distance between members 10 and 20)

Geff = 4 N/mm ² (effective shear stiffness of the shear module 100)

L = 100 mm (contact patch length necessary for design load)

R2 = 200 mm (radial distance to outer member 10)

R1 = 190 mm (radial distance to inner member 20)

E = 20,000 N/mm2 (tensile modulus for both members 10 and 20) t = 0.5 mm (thickness for both members 10 and 20)

Calculating for e using Equation (2):

(1O) (IOO) ² e a _ = 0.0025

8 (200)(20,000)(0.5)

The shear efficiency can then be calculated as:

0.0025 (190 + 200)

Shear efficiency = 1 = 0.9025 (3)

10

Thus, the efficiency in this case is approximately 90%.

[0023] The above analysis assumes that inner and outer members 10 and 20 have identical constructions. However, the thickness and/or the modulus of members 10 and 20 need not be the same. Using the principles disclosed herein, one skilled in the art can readily calculate the strains in members 10 and 20 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.

[0024] 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 Ge and the shear layer thickness h for a given application:

Pe _ff ^* Ro = Ge ^* h (4)

Where:

Peff = predetermined ground contact pressure

Ge = effective shear modulus of the modules 100 h = thickness of the shear layer - i.e. radial height of modules 100

R ₀ = radial position of the outer member 20

[0025] 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 _β ff and R ₀ are known - leaving the designer to optimize Ge and h for a given application.

[0026] Accordingly, the shear band disclosed herein may be combined with other structural members to form a resilient wheel capable of supporting loads in a manner similar to a pneumatic tire. One example of such a wheel comprises the present mechanical shear band, a hub ratable about an axis of rotation, and a plurality of support elements connecting the hub and the inner member 10 of the shear band.

[0027] Applicants understand that many other variations are apparent to one of ordinary skill in the art from a reading of the above specification. These variations and other variations are within the spirit and scope of the instant invention as defined by the following appended claims.