FIELD OF THE INVENTION
The present invention relates generally to vehicle tires and non-pneumatic tires, and more particularly, to a non-pneumatic tire.
BACKGROUND OF THE INVENTION
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.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be better understood through reference to the following description and the appended drawings, in which:
FIG. 1 is a perspective view of a first embodiment of a non-pneumatic tire of the present invention;
FIG. 2 is a cross-sectional perspective view of the non-pneumatic tire of FIG. 1;
FIG. 3 is an exploded view of non-pneumatic tire of FIG. 1;
FIG. 4 is a perspective view of the spoke loop structure of the present invention;
FIG. 5 is a front view of the spoke loop structure of the present invention;
FIG. 6 is a front perspective view of the wheel of the present invention;
FIG. 7 is a rear perspective view of the wheel of the present invention;
FIG. 8A is a front view of an alternate embodiment of a spoke loop structure having a single set of loops, while FIG. 8B is a close-up view of the spoke loops, and FIG. 8C is variation of FIG. 8A with more loops;
FIG. 9 is a cross-sectional view of the spoke loop structure illustrating the shear band;
FIG. 10A illustrates a perspective view of a strip of elastomer with parallel reinforcement cords while FIG. 10B illustrates different orientations of the reinforcement cords for the strip of elastomer; and
FIG. 10C illustrates a front view of the nonpneumatic tire with only a single spoke loop (the others removed for clarity reasons) with the associated parts labeled.
DEFINITIONS
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.
DETAILED DESCRIPTION OF THE INVENTION
The non-pneumatic tire 100 of the present invention is shown in FIGS. 1-5. The nonpneumatic tire of the present invention includes a spoke loop structure 400 having a plurality of spoke loops 420. The spoke loop structure 400 further includes a radially outer ground engaging tread 200 and shear band 300. The tread 200 may be conventional in design, and include the various elements known to those skilled in the art of tread design such as ribs, blocks, lugs, grooves, and sipes as desired to improve the performance of the tire in various conditions. The design of the shear band 300 allows the non-pneumatic tire of the present invention to be a top loaded structure, so that the shear band 300 and the spoke loops efficiently carry the load. The shear band 300 and the spoke loops 420 are designed so that the stiffness of the spoke loops 420 is directly related to the spring rate of the tire. The spoke loops 420 are designed to be structures that buckle or deform in the tire footprint yet are unable to carry a compressive load. This allows the rest of the loops not in the footprint area the ability to carry the load. Since there are more spoke loops outside of the footprint than inside the footprint, the load per spoke loop would be small enabling smaller loops to carry the tire load which gives a very load efficient structure. It is desired to minimize this compressive load on the spokes for the reasons set forth above and to allow the shear band to bend to overcome road obstacles. The approximate load distribution is such that approximately 90-100% of the load is carried by the shear band and the upper spokes, so that the lower spokes carry virtually zero of the load, and preferably less than 10%.
Shear Band
The shear band 300 is preferably annular, and is shown in cross-section in FIG. 9, and is preferably located radially inward of the tire tread 200. The shear band 300 includes a first and second reinforced elastomer layer 310,320 separated by a shear matrix 330 of elastomer. Each inextensible layer 310,320 may be formed of parallel inextensible reinforcement cords 311,321 embedded in an elastomeric coating. The reinforcement cords 311,321 may be steel, aramid, or other inextensible structure. In the first reinforced elastomer layer 310, the reinforcement cords 311 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 321 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 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 G in the range of 2.5 to 40 MPa, and more preferably in the range of 20 to 40 MPA. The shear band has a shear stiffness GA and a bending stiffness EI. 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 an ideal 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 shear band is acceptable in the range of 0.02 to 100 with an ideal range of 1 to 50.
In an alternative embodiment, the shear band may comprise any structure which has the above described ratios of GA/EI and EA/EI. The tire tread is preferably wrapped about the shear band and is preferably integrally molded to the shear band.
Spoke Loop Structure
The spoke loop structure 400 functions to carry the load transmitted from the shear layer. The spoke loops 420 are primarily loaded in tension and shear and cannot carry any compression load. FIG. 4 illustrates an exemplary spoke loop structure 400 having four circumferentially aligned sets of loops 420 which are spaced apart in the axial direction. However, the spoke loop structure may have only a single row of loops or multiple rows. As shown in FIG. 5, each loop 420 extends inward towards the wheel 500 from an outer annular ring 410. Preferably, each loop 420 is V shaped or triangular in shape. Each loop has a first side 421 and a second side 423. In one embodiment, the loops are not oriented in the radial direction. In another embodiment, the sides of the spoke loops are primarily oriented in the radial direction. The orientation of the loops with respect to the radial direction may thus be varied. As shown in FIG. 8C, increasing the number of loops also changes the angle of the loop side with respect to the radial direction.
The radial height of each loop 420 is in the range of 75% to 100% of the nominal radial distance between the inner surface of the shear band and the inner radius R of the pins plus the thickness of the flexible loop shown in FIG. 11. More preferably in the range of 80% to 90%. The circumferential spacing of the loops 420 may vary as desired, and the circumferential gap spacing between loops may be reduced to increase the number of loops 420. Each loop 420 has radially outer ends 422,424 which are secured to the outer annular ring 410, which is bonded to the shear band and outer tread structure. Preferably, the radially outer ends 422,424 are integrally formed with the shear band and tread outer structure.
The spoke loop structure may comprise a single row of spoke loops (not shown), wherein the axial width of each spoke loop may be equal to or less than the axial width of the tire. As shown in FIG. 4, the spoke loop structure may have multiple rows of circumferentially aligned spoke loops. Alternatively, the loops in each set may not be circumferentially aligned.
As shown in FIG. 8B, the loops 420 are preferably formed of a flexible strip 430, preferably a flexible strip of rubber or elastomer, and more preferably, a reinforced elastomer strip with parallel reinforcement cords 426 such as nylon or polyester cords. The reinforcement cords 426 are aligned parallel with respect to each other, and thus when formed in the loop are not radially oriented when assembled. The orientation of the cords 426 in each strip are typically oriented in a direction parallel with the longitudinal axis of the strip, however the cords may also be oriented at an angle θ in the range of −60 to +60 degrees, and more preferably −45 to +45 degrees with respect to the strip longitudinal axis L. The strip width is typically 0.3 to 2 inches but may vary as desired. The thickness of the strip or flexible loop is typically 0.04 to 0.25 inches but may vary.
As shown in FIG. 2, each loop 420 of the spoke loop structure is secured to a wheel 500 via locking members, which in this example is a bolt 510 in combination with nuts 508 which are secured to the threaded ends of bolt 510. The locking member may also be a clamp, spring loaded clip, pin or other mechanical locking means known to those skilled in the art. As shown in FIG. 6, the wheel 500 includes a plurality of circumferential partitions 520,530 located between outer ends 515 and 516. As shown in FIG. 2, the circumferential partitions 520,530 together with the wheel rim inner surface 514 function to keep the spoke loops separated from each other in discrete compartments, as well as to prevent axial motion of each spoke loop. Each bolt 510 extends axially across the wheel 500 from a first side 515 to a second side 516, and through as aligned holes of each circumferential partition. Each bolt also is received in an axially aligned row of the spoke loops in order to secure each spoke loop to the rim between two circumferential partitions.
The locking members also function to pretension the spoke loops. The length of strip used to form each loop may also be varied in order to achieve the desired loop pretension. In order to tune the nonpneumatic tire for desired performance characteristics, the spring rate may be varied across the axial width of the tire by varying the stiffness of the cords selected for a set of loops, or by the cord angle orientation. Each loop set may use a different type of cord or different angle of cords in order to have the desired spring rate of the loops in a given set.
Each loop preferably has an axial width A that is substantially less than the axial width AW of the non-pneumatic tire. The axial width A of each loop is preferably in the range of 5-20% of the tire's axial width AW, and more preferably 5-10% AW. If more than one set of loops are utilized, than the axial thickness of each loop may vary or be the same.
Each spoke loop structure 400 has a spring rate SR which may be determined experimentally by measuring the deflection under a known load, as shown in FIG. 12. One method for determining the spoke loop structure spring rate k is to mount the spoke loop structure to a hub and attaching the outer ring of the spoke loop structure to a rigid test fixture. A downward force is applied to the hub, and the displacement of the hub is recorded. The spring rate k is determined from the slope of the force deflection curve as shown in FIG. 13. It is preferred that the spoke loop structure spring rate be greater than the spring rate of the shear band. It is preferred that the spoke loop structure spring rate be in the range of 4 to 12 times greater than the spring rate of the shear band, and more preferably in the range of 6 to 10 times greater than the spring rate of the shear band.
If more than one row of spoke loops is used, each row may have the same spring rate or a different spring rate. The spring rate of the non-pneumatic tire may be adjusted by increasing the number of spoke loop structures as shown in FIG. 8. Alternatively, the spring rate of each row of spoke loops may be different by varying the geometry of the spoke loop structure or changing the material.
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 present invention as defined by the following appended claims.
Patent Application
20210061012
