Patent Description:
The pneumatic tire has been the solution of choice for vehicular mobility for over a century. The pneumatic tire is a tensile structure. The pneumatic tire has at least four characteristics that make the pneumatic tire so dominate today. Pneumatic tires are efficient at carrying loads, because all of the tire structure is involved in carrying the load. Pneumatic tires are also desirable because they have low contact pressure, resulting in lower wear on roads due to the distribution of the load of the vehicle. Pneumatic tires also have low stiffness, which ensures a comfortable ride in a vehicle. The primary drawback to a pneumatic tire is that it requires compressed fluid. A conventional pneumatic tire is rendered useless after a complete loss of inflation pressure.

A tire designed to operate without inflation pressure may eliminate many of the problems and compromises associated with a pneumatic tire. Neither pressure maintenance nor pressure monitoring is required. Structurally supported tires such as solid tires or other elastomeric structures to date have not provided the levels of performance required from a conventional pneumatic tire. A structurally supported tire solution that delivers pneumatic tire-like performance would be a desirous improvement.

Non-pneumatic tires are typically defined by their load carrying efficiency. "Bottom loaders" are essentially rigid structures that carry a majority of the load in the portion of the structure below the hub. "Top loaders" are designed so that all of the structure is involved in carrying the load. Top loaders thus have a higher load carrying efficiency than bottom loaders, allowing a design that has less mass.

Thus an improved non-pneumatic tire is desired that has all the features of the pneumatic tires without the drawback of the need for air inflation is desired. It is also desired to have an improved non-pneumatic tire that has longer tread life as compared to a pneumatic tire of the same size.

<CIT> describes a non-pneumatic tire and wheel assembly in accordance with the preamble of claim <NUM>.

Further non-pneumatic tire and wheel assemblies are known from <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT> and <CIT>.

The invention relates to a non-pneumatic tire and wheel assembly in accordance with claim <NUM> and to a method in accordance with claim <NUM>.

The invention provides in a first preferred aspect a non-pneumatic tire and wheel assembly comprising: a wheel, a spoke ring structure having an inner ring that is mounted on an outer rim mounting surface of the wheel, wherein the spoke ring structure has a plurality of spoke members, and an outer tread ring mounted on the outer circumference of the spoke ring, wherein the wheel is axially recessed within the non-pneumatic tire and wheel assembly.

The invention provides in a second preferred aspect a non-pneumatic tire and wheel assembly comprising: a wheel, a spoke ring structure having an inner ring that is mounted on an outer rim mounting surface of the wheel, wherein the spoke ring structure has a plurality of spoke members, and an outer tread ring mounted on the outer circumference of the spoke ring, wherein at least one of the spoke members has an axially outer edge, wherein the axially outer edge is radiused.

"Aspect Ratio" means the ratio of a tire's section height to its section width.

"Axial" and "axially" means the lines or directions that are parallel to the axis of rotation of the tire.

"Circumferential" means lines or directions extending along the pewheeleter of the surface of the annular tread perpendicular to the axial direction; it can also refer to the direction of the sets of adjacent circular curves whose radii define the axial curvature of the tread as viewed in cross section.

"Radial" and "radially" mean directions radially toward or away from the axis of rotation of the tire.

Referring to <FIG>, a non-pneumatic tire and wheel assembly <NUM> of the present invention is shown. The non-pneumatic tire and wheel assembly <NUM> includes an outer annular tread ring <NUM>, a spoke ring structure <NUM>, and a wheel <NUM>. The outer annular tread ring <NUM> is preferably a one-piece annular structure that is formed of a polymer, rubber or other desired elastomer. The tread ring <NUM> may be molded and cured as a one-piece ring and is mounted on the outer periphery of the spoke ring structure <NUM>. The outer tread surface of the tread ring <NUM> may include tread elements such as ribs, blocks, lugs, grooves, and sipes as desired in order to improve the performance of the tire in various conditions. Preferably, a shear band <NUM> is provided, which is an annular structure that is located radially inward of the tread ring <NUM> between tread ring <NUM> and spoke ring structure <NUM> and functions to transfer the load from the bottom of the tire which is in contact with the ground to the spokes and to the hub, creating a top loading structure. The annular structure is called a shear band <NUM> because the preferred form of deformation is shear over bending.

A first embodiment of a shear band <NUM> is shown in <FIG>. The shear band <NUM> preferably includes a first, second and third reinforcement layer <NUM>, <NUM>, <NUM>. Each reinforcement layer <NUM>, <NUM>, <NUM> is preferably formed of a plurality of closely spaced parallel reinforcement cords. The parallel reinforcement cords may be formed from a calendared fabric so that the reinforcement cords are embedded in an elastomeric coating. Preferably, each reinforcement layer <NUM>, <NUM>, <NUM> is formed from spirally winding a single end cord. Preferably, the single end cord has multiple filaments.

The first and second reinforcement layers <NUM>, <NUM> are preferably the radially innermost reinforcement layers of the shear band <NUM>, and the second reinforcement layer <NUM> is located radially outward of the first reinforcement layer <NUM>. The third reinforcement layer <NUM> is located radially outward of the second reinforcement layer <NUM>. The preferably inextensible reinforcement cords of each layer <NUM>, <NUM>, <NUM> are preferably angled in the range of five degrees or less with respect to the tire equatorial plane. The reinforcing cords of the first and second reinforcement layers <NUM>, <NUM> may be suitable tire belt reinforcements, such as monofilaments or cords of steel, aramid, and/or other high modulus textiles. For example, the reinforcing cords may be steel cords of four wires of <NUM> diameter (<NUM> x <NUM>) or <NUM> diameter. In another example, the reinforcing cords may be steel cords of <NUM> wires, with five wires surrounding a central wire (<NUM> +<NUM>) construction.

The third reinforcement layer <NUM> is preferably separated from the second reinforcement layer <NUM> by a first shear layer <NUM>. The shear band <NUM> preferably further comprises a second shear layer <NUM> located radially outward of the third reinforcement layer <NUM>. The first and second shear layer <NUM>, <NUM> is preferably formed of an elastomer or rubber having a shear modulus in the range of <NUM> MPa to <NUM> MPa, or more preferably in the range of <NUM> MPa to <NUM> MPa. The shear modulus is defined using a pure shear deformation test, recording the stress and strain, and determining the slope of the resulting stress-strain curve.

The shear band <NUM> preferably further includes a first angled belt <NUM> and a second angled belt <NUM>. The first angled belt <NUM> is located radially outward of the second shear layer <NUM>, and the second angled belt <NUM> is located radially outward of the first angled belt <NUM>. The first and second angled belts <NUM>, <NUM> preferably each have parallel reinforcement cords that are embedded in an elastomeric coating. The parallel reinforcement cords are preferably angled in the range of <NUM> to <NUM> degrees with respect to the tire equatorial plane. Preferably, the angle of the parallel reinforcement cords is in the range of from <NUM> to <NUM> degrees. Preferably, the angle of the reinforcement cords of the first angled belt <NUM> is in the opposite direction of the angle of the reinforcement cords in the second angled belt <NUM>. It is additionally preferred that the reinforcement cords are inextensible.

The shear band <NUM> has an overall shear stiffness GA. The shear stiffness GA may be determined by measuring the deflection on a representative test specimen taken from the shear band <NUM>. The upper surface of the test specimen is subjected to a lateral shear force F. The test specimen is a representative sample taken from the shear band and having the same radial thickness as the shearband. The shear stiffness GA is then calculated from the following equation: GA=F*L/ΔX, where F is the shear load, L is the shear layer thickness, and ΔX is the shear deflection. It is preferred that GA be in the range of from <NUM>,<NUM> N to <NUM>,000N, and more preferably <NUM>,000N.

The shear band <NUM> has an overall bending stiffness El. The bending stiffness El may be determined from beam mechanics using the three point bending test. It represents the case of a beam resting on two roller supports and subjected to a concentrated load applied in the middle of the beam. The bending stiffness EI is determined from the following equation: EI = PL3/<NUM>* ΔX, where P is the load, L is the beam length, and ΔX is the deflection. It is preferred that EI be in the range of <NUM> E6 N-mm<NUM> plus or minus <NUM>%.

The non-pneumatic tire and wheel assembly <NUM> includes a spoke ring structure <NUM>. The spoke ring structure <NUM> has at least one layer of spoke rings <NUM>, and preferably at least two spoke rings <NUM>, <NUM>. <FIG> illustrates a non-pneumatic tire and wheel assembly having three spoke rings <NUM>, <NUM>, <NUM>, that are preferably axially adjacent.

Each spoke ring <NUM>, <NUM>, <NUM> may be an integrally formed ring or may be formed from a plurality of sectors 22a, 24a, 26a respectively that are assembled to form the ring. <FIG> illustrates a sector 22a used to form the spoke ring <NUM>. There are for example <NUM> sectors used to form the spoke ring <NUM>, although there may be more or less sectors to form the ring. As shown in <FIG>, the spoke ring <NUM> is the outboard spoke ring that faces axially outward when mounted on a vehicle. The spoke ring <NUM> has a plurality of preferably X shaped spokes formed from a first spoke member <NUM> that is joined to a second spoke member <NUM>. The first and second spoke member <NUM>, <NUM> are joined together at a junction <NUM> to form a preferably X-shaped spoke. The first and second spoke members <NUM>, <NUM> may be straight or curved. The number of spokes may vary, for example, from <NUM> to <NUM> depending upon the vehicle weight and desired spring rate. The outboard spoke ring has an axially outer edge <NUM> that is radiused. The outboard spoke ring <NUM> has an axially inner edge <NUM> that is not radiused and is straight in the radial direction. The outer tread ring <NUM> extends axially outward of the center disk <NUM> of the wheel, so that the wheel is recessed to reduce noise.

<FIG> illustrates a sector 26A of the inboard spoke ring <NUM>. The inboard spoke ring <NUM> is the same as the spoke ring <NUM>, except for the following differences. The axially outer edge <NUM> of the inboard spoke ring <NUM> is radiused, while the axially inner edge <NUM> is straight, or aligned with the radial direction.

<FIG> illustrates a sector of the middle spoke ring <NUM>. The middle spoke ring <NUM> is the same as the spoke ring <NUM>, except for the following differences. The axially outer edge <NUM> and axially inner edge <NUM> of the middle spoke ring <NUM> is straight or aligned with the radial direction. Additionally, as shown in <FIG>, the middle spoke ring is clocked so that it is not in alignment with the X spokes of spoke rings <NUM> or <NUM>.

Each spoke ring <NUM>, <NUM>, <NUM> has an inner portion <NUM> that is mounted on the wheel rim mounting surface <NUM>, and an outer portion <NUM> that is connected to the inner surface of the tread ring <NUM>. The inner portion <NUM> has an interference fit on the outer rim mounting surface <NUM> of the wheel <NUM>.

The radius R of the radiused outer edges may range from <NUM> to <NUM>. The scalloped or radiused outer edges allow the wheel to be recessed axially inward of the spoke and tread ring structure.

The spoke ring structures <NUM>, <NUM>, <NUM> are preferably made of a resilient and/or moldable polymeric material such as but not limited to, a thermoplastic elastomer, natural rubber, styrene butadiene rubber, polybutadiene rubber or EPDM rubber or a blend of two or more of these materials which can be utilized in either injection molding or compression molding. The material of the spoke ring structure is selected based upon one or more of the following material properties. The tensile (Young's) modulus of the spoke disk material is preferably in the range of <NUM> MPa to <NUM> MPa, and more preferably in the range of <NUM> MPa to <NUM> MPa.

Claim 1:
A non-pneumatic tire and wheel assembly comprising a wheel structure (<NUM>), a spoke ring structure (<NUM>) formed of one or more segments (22a, 24a, 26a) arranged to form an annular spoke ring, wherein the spoke ring structure (<NUM>) has a plurality of spoke members (<NUM>, <NUM>), and a radially outer tread ring (<NUM>) mounted on the outer circumference of the spoke ring structure (<NUM>), and wherein the spoke ring structure (<NUM>) is attached to a radially outer wheel structure mounting surface of the wheel structure (<NUM>) via an interference fit, characterized in that the assembly further comprises one or more of the following features:
(i) a radially inner portion of the spoke ring structure (<NUM>) has an axial width less than the axial width of a radially outer portion of the spoke ring structure (<NUM>);
(ii) the spoke structure (<NUM>) comprises a plurality of axially adjacent spoke rings (<NUM>, <NUM>, <NUM>);
(iii) each spoke member (<NUM>, <NUM>) has a radially inner portion and a radially outer portion, wherein the radially inner portion has an axial width less than the radially outer portion.