NON-PNEUMATIC TIRE WITH GEODESIC PLY & BEAD
A non-pneumatic tire is described which includes a ground contacting annular tread portion, a shear band, and a reinforcement structure positioned radially inward of the tread. The reinforcement structure is formed from a plurality of strips, wherein each strip has a first end located radially outward of the shear band and a second end secured to a bead, wherein the plurality of strips do not extend completely across the annular tread portion.
The present invention relates generally to vehicle tires and non-pneumatic tires, and more particularly, to a non-pneumatic tire.
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.
The present invention will be better understood through reference to the following description and the appended drawings, in which:
The following terms are defined as follows for this description.
“Equatorial Plane” means a plane perpendicular to the axis of rotation of the tire passing through the centerline of the tire.
“Meridian Plane” means a plane parallel to the axis of rotation of the tire and extending radially outward from said axis.
“Hysteresis” means the dynamic loss tangent measured at 10 percent dynamic shear strain and at 25° C.
A non-pneumatic tire 100 of the present invention is shown in the enclosed figures. The non-pneumatic tire of the present invention includes a radially outer ground engaging tread 200, a shear band 300, and one or more reinforcement layer 400. The non-pneumatic tire of the present invention is designed to be a top loaded structure, so that the shear band 300 and the reinforcement layer 400 efficiently carries the load. The shear band 300 and the reinforcement layer 400 are designed so that the stiffness of the shear band is directly related to the spring rate of the tire. The reinforcement layer is designed to be a stiff structure that buckles or deforms in the tire footprint and does not compress or carry a compressive load. This allows the rest of structure not in the footprint area the ability to carry the load, resulting in a very load efficient structure. It is desired to minimize this load for the reason above and to allow the shearband to bend to overcome road obstacles. The approximate load distribution is such that approximately 95-100% of the load is carried by the shear band and the upper radial portion of the reinforcement layer 400, so that the lower portion of the reinforcement structure undergoing compression carries virtually zero of the load, and preferably less than 10%.
The tread portion 200 may be a conventional tread as desired, and may include grooves or a plurality of longitudinally oriented tread grooves forming essentially longitudinal tread ribs there between. Ribs may be further divided transversely or longitudinally to form a tread pattern adapted to the usage requirements of the particular vehicle application. Tread grooves may have any depth consistent with the intended use of the tire. The tire tread 200 may include elements such as ribs, blocks, lugs, grooves, and sipes as desired to improve the performance of the tire in various conditions.
The shear band 300 is preferably annular. A cross-sectional view of the shear band is shown in
It is additionally preferred that the outer lateral ends 302, 304 of the shear band be radiused in order to control the buckled shape of the sidewall and to reduce flexural stresses.
In the first reinforced elastomer layer 310, the reinforcement cords are oriented at an angle Φ in the range of 0 to about +/−10 degrees relative to the tire equatorial plane. In the second reinforced elastomer layer 320, the reinforcement cords are oriented at an angle φ in the range of 0 to about +/−10 degrees relative to the tire equatorial plane. Preferably, the angle Φ of the first layer is in the opposite direction of the angle φ of the reinforcement cords in the second layer. That is, an angle +Φ in the first reinforced elastomeric layer and an angle −φ in the second reinforced elastomeric layer.
The shear matrix 330 has a radial thickness in the range of about 0.10 inches to about 0.2 inches, more preferably about 0.15 inches. The shear matrix is preferably formed of an elastomer material having a shear modulus Gm in the range of 15 to 80 MPa, and more preferably in the range of 40 to 60 MPA.
The shear band has a shear stiffness GA. The shear stiffness GA may be determined by measuring the deflection on a representative test specimen taken from the shear band. The upper surface of the test specimen is subjected to a lateral force F as shown below. The test specimen is a representative sample taken from the shear matrix material, having the same radial thickness.
The shear stiffness GA is then calculated from the following equation:
The shear band has a bending stiffness EI. The bending stiffness EI may be determined from beam mechanics using the three point bending test subjected to a test specimen representative of the shear band. 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=PL3/48*ΔX, where P is the load, L is the beam length, and ΔX is the deflection.
It is desirable to maximize the bending stiffness of the shearband EI and minimize the shear band stiffness GA. The acceptable ratio of GA/EI would be between 0.01 and 20, with a preferred range between 0.01 and 5. EA is the extensible stiffness of the shear band, and it is determined experimentally by applying a tensile force and measuring the change in length. The ratio of the EA to EI of the shearband is acceptable in the range of 0.02 to 100 with a preferred range of 1 to 50. The shear band 300 preferably can withstand a maximum shear strain in the range of 15-30%.
The shear band 300 has a spring rate k that may be determined experimentally by exerting a downward force on a horizontal plate at the top of the shear band and measuring the amount of deflection as shown in
The non-pneumatic tire has an overall spring rate kt that is determined experimentally. The non-pneumatic tire is mounted upon a rim, and a load is applied to the center of the tire through the rim. The spring rate kt is determined from the slope of the Force versus deflection curve. The spring rate kt is preferably in the range of 500 to 1000 for small low speed vehicles such as lawn mowers.
The invention is not limited to the shear band structure disclosed herein, and may comprise any structure which has a GA/EI in the range of 0.01 to 20, or a EA/EI ratio in the range of 0.02 to 100, or a spring rate kt in the range of 500 to 1000, as well as any combinations thereof. More preferably, the shear band has a GA/EI ratio of 0.01 to 5, or an EA/EI ratio of 1 to 50 and any subcombinations thereof. The tire tread is preferably wrapped about the shear band and is preferably integrally molded to the shear band.
A first embodiment of the non-pneumatic tire of the present invention is shown in
As shown in
Preferably, the reinforced strips are oriented in the radial direction. It is preferred that tire ply be used as the reinforcement material for several reasons. First, tire ply is an ideal connecting structure for the non-pneumatic tire application because it is thin, and has a low bending stiffness with no resistance to compression or buckling. Tire ply has a high tensile stiffness and strength which is needed in the non-pneumatic tire application. Tire ply is also cheap, has a known durability, and is readily available.
As shown in
It is advantageous to locate the reinforcement layer radially outward of the shear band because it eliminates the tensile stress on the bond between the shear band and load carrying member or connecting structure. This advantage is especially important when the shear band and the play are dissimilar materials. The interface of the shear band and the connecting web is typically a point of failure due to the interface of dissimilar materials.
Alternatively, the reinforced ply strip may be continuously wound from one side of the tire to the other, forming a plurality of radial ply spokes as shown in
The reinforcement structure 400 need not be positioned radially outward of the shear band. The reinforcement structure may be positioned radially inward and underneath the shear band (not shown).
Alternatively, the first ends 402a,b of the reinforced strips 400 may be positioned between the reinforcement layers of the shear band, as shown in