Patent Application
20050072507
The present invention relates to a tire construction, which utilizes characteristics of the elastomeric tire shell construction without requiring internal pneumatic pressure as the primary performance determinant, the shell having an effectively homogeneous composition and providing a closed toroidal structure. The shell provides an anisotropic or isotropic assembly when mounted in a wheel rim.
Vehicle tires, especially those for automobiles, motorcycles, bicycles and other vehicles, generally comprise a pressure-containing shell. The shell is seated in a sealing manner onto a wheel rim in order to convert an open chamber in the tire interior into a pressure-retaining closed chamber. The tire supports the load by inflation pressure placing the unloaded shell portion into tension. To provide the pressure-retaining characteristics but to minimize weight, the tire sidewalls tend to be thinner than the radially outward road or other surface engaging tread portion. The road engaging surface is provided with tread features designed to allow good control under various road conditions or for a particular environment, while attempting to provide reduced road noise, or other characteristics.
Traditionally, pneumatic tires of the prior art are built up in layers of rubber compounds and incorporate polymeric or metallic fiber materials to provide strength. A metallic bead element is built up in the tire in the rim seat region in a manner to establish and maintain the pneumatic-pressure retaining seal upon which operation depends. These tires are formed from materials in the solid state that remain in the solid state throughout the fabrication process. This general tire construction is complex to manufacture, and the characteristics of the rubber compounds and ultimate solid state layers are difficult to control. Problems in the manufacturing process or design of the tire to perform a given duty cycle can lead to tire failure. Due to the reliance upon inflation pressure, any failure can in turn result in significant problems in handling of the vehicle and dangerous operating conditions, let alone rendering the tire inoperative.
Problems also exist with respect to the high deflection of the tire tread, increasing the rolling resistance and reducing the performance characteristics with respect to mileage or wear of this type of tire design. Further, with the inflation pressure impacting upon deflection and rolling resistance, the tire design can't be optimized. Attempts have been made to provide highly fuel efficient tires for use with vehicles having engines, such as in European Patent No. 0 119 152, wherein specific dimensional and physical characteristics provide decreased rolling resistance, but the pneumatic tire is still reliant upon inflation pressure for operation.
In the alternative, some tires known early in the automotive industry were formed as solid hard rubber designs. These tires exhibited virtually no resilience, and were useful only on large diameter, narrow width rims, similar to buggy wheels. Such tires and rims are entirely impractical on modern vehicles. But there have been attempts to get around the problems associated with pneumatic tires, and based upon compression loading for support and not inflation pressure.
In fact, it may be noted that tire technologies may be generally classified on a pair of spectra. One of the spectra represents the type of engineered structure, and runs from pneumatic or tensional systems in which the tires operate under high inflation pressures (up to 10 atmospheres or so), through hybrid tension/compression systems to pure compressional systems in which there is no inflation pressure in the tire. Examples of hybrid tension/compression systems include “run flat” tire technologies. These tires are able to run after inflation pressure is lost. In general, such attempts have utilized a mass of rubber provided along the inside of the sidewall portions to support tire loads during running under flat conditions, which are commonly limited to about 200 miles at speeds not to exceed about 50 mph. This results in an increase in tire weight, and creates additional heat, running under flat conditions as well as normal conditions. This in turn can result in degradation of the tire and failure. Other approaches have attempted to use high rigidity materials to provide structural integrity after loss of pneumatic pressure, or filling the tire with an elastic material having some degree of rigidity to support the tire load when the tire air pressure is lost. Such attempts have not provided a satisfactory solution to the problem of losing inflation pressure in pneumatically pressurized tire constructions. Other systems, such as shown in U.S. Pat. No. 5,027,876 or U.S. Pat. No. 3,961,657 have been proposed as alternatives. An example of a compression based tire technology is shown in U.S. Pat. No. 5,743,316.
The other spectrum represents the type of materials used in the fabrication. At one extreme, the materials used to construct the tire are solid and remain in the solid state throughout the fabrication, such as in typical pneumatic tires. Alternatively, the tire is formed from solid and liquid materials or purely from liquid materials, which are solidified during processing. Examples of solid and liquid phase processing are shown in of U.S. Pat. No. 5,254,405 and European Patent No. 0 374 081 A2. Although various alternative strategies have been attempted to provide desired tire characteristics, no tire design heretofore has provided the desired characteristics in a simple and cost-effective configuration.
It is, therefore, an unmet need of the prior art to provide a tire construction having a design which does not rely only upon internal pneumatic pressurization for proper operation. There is also a need to provide a tire design which has very low rolling resistance and yet performs in a manner similar to typical pneumatic tires. A further need is found in providing a tire design which allows for a simplified and repeatable manufacturing process to provide proper operational characteristics in all operating conditions and applications.
The present invention is therefore directed at a tire design and method of manufacturing which avoids the problems associated with prior tire designs, and allows for proper operational characteristics in all operating conditions. The invention is further directed at providing a compression tire construction which is engineered such that the normal rolling resistance of the tire is reduced significantly relative to a tension tire, even if the tension tire were inflated to a very high inflation pressure. These advantages, and others, are provided by a tire for mounting on a wheel rim, which comprises a homogeneous toroidal body having a pair of spaced-apart radially extending sidewalls and a cross member. Each sidewall has a first and a second end and an internal face and an external face, with the second end of each of the sidewalls integrally merging into the cross member. A set of rim-engaging surfaces at the first end of each of the sidewalls allows effective mounting to conventional tire rims. At least one road-engaging surface on an external surface of the cross member may be provided with appropriate tread characteristics to facilitate proper performance of the tire. In an embodiment, an annular chamber is defined by the internal faces of the sidewalls and an internal top wall on the cross member opposite the at least one road-engaging surface. The chamber may be formed by forming the tire into a closed torus shape, or providing the rim-engaging surfaces as independent lobe-like portions being separable when the tire is not mounted on the rim, but being compressed into engagement when the tire is mounted in the rim, thereby closing the annular chamber. The rim may also be used to close the chamber to form a closed toroid, which is placed into compression under load.
In another embodiment, a homogenous body is formed as a generally flat member who is folded or shaped into a form for engagement with the tire rim. Circumferential and/or radial anisotropy is built into the structure for distribution of loading stresses upon mounting on the rim. The compression tire of the invention is designed such that it can be engineered for a particular application in a manner such that its normal rolling resistance is reduced significantly, such as compared to a typical pressurized tire construction. The design can be optimized for a particular application, to reduce rolling resistance while maintaining other desired attributes in operational characteristics. Methods of manufacturing are also set forth according to the invention.
The present invention will be best understood when reference is made to the detailed description of the invention and the accompanying drawings, wherein identical parts are identified by identical reference numbers and wherein:
A first embodiment tire 10 of the present invention is shown with a section thereof in perspective view in
The sidewalls 16 are notably distinct from known tire sidewalls because the external face 24 has a concave sculpted curvature and the internal sidewall face 20 is provided with a sculpted concave curvature when viewed from within the annular chamber 18. These opposing curvatures result in the sidewalls 16 having a thickness which varies radially inwardly or outwardly. Conventional tires typically have convex external sidewall surfaces and concave internal sidewall surfaces with a generally constant wall thickness, and are inflated to support the vehicle with internal pressure.
As will be described with reference to further embodiments of the invention, the tire may include anisotropic features both radially and circumferentially to facilitate distribution of stress and accommodating a given duty cycle as required. Anisotropic refers to providing properties in portions of the tire having different values when measured along different directions within the tire. As seen in
As will be hereinafter described, the tires according to the invention may be manufactured using liquid phase processing techniques, producing a homogenous tire body. Anisotropy may be provided in the tire design by formation of reinforcing structures circumferentially and/or radially within the inside surface of the toroidal structure. Such reinforcing structures may be formed integrally with the tire during molding, casting, etc., or the reinforcing structures may be formed and adhered to the inside surfaces if desired. The reinforcing structures may also be provided on other embodiments of the invention, and again may be a series of alternating ridges and grooves which extend circumferentially and/or radially within the closed toroidal structure of the tire. The shapes of the alternating ridge and groove structures may be of any desired configuration.
At the radially outward end of the tire 10, the cross member 13 and its external road-engaging surface 14 has a convex curvature across the width, effectively forming a crown which may be depressed against the road surface upon loading. Inside the annular chamber 18, the internal top wall face 20 of the cross member is concavely curved when viewed from the annular chamber, so that this portion of the tire has a generally constant thickness. Of course, it will be well known to put road-engaging tread features 26, such as dimples, holes, grooves and the like onto the external road-engaging surface 14 to edges thereof, but it is the general thickness of the cross member 13 and not the localized thickness thereof which is generally constant.
At the radially inwardly end of each sidewall 16, a number of rim-engaging surfaces 12 are provided. First, a concave groove 28 is sized and positioned around the circumference to allow the tire 10 to be seated in a rim with an inwardly-projecting seating surface. Second, a lobe-like thickened portion 30 is situated on each sidewall 16, with each of the portions 30 having a convexly curved outer surface 32. While a slight separation 34 is shown between the sidewalls 16 in
It will also be recognized that this possible hybrid tensional-compressional system may be manufactured using a purely liquid phase manufacturing scheme. The tire 10 according to the invention may be manufactured by any suitable manufacturing method, but contemplates a purely liquid phase spin casting manufacturing process to provide significant cost advantages as well as manufacturing control. The invention also contemplates the use of homogenous elastomeric materials, such as urethanes, polyurethanes, composites of polyethylurethane elastomeric particles, rubber compounds, thermoplastic elastomers or combinations thereof, either in mixture or in a laminated construction. The ability to spin cast tires 10 using a homogenous material such as polyurethane, may provide the ability to form a non-porous outer tread or skin with the material becoming increasingly porous downwardly from the tread to the inner surface. The tire 10 then functions as anisotropic assembly, which is capable of carrying the load in compression. The ability to cast tire 10 and form tire 10 in a liquid phase manufacturing process insures consistency in the manufacturing process and materials used to form tire 10. This type of manufacturing process provides a high degree of control over the characteristics of the material produced by the manufacturing process, while drastically reducing the cost of investment in the manufacturing process. The control over the material properties as well as shape and design of the tire 10 therefore allow a great amount of flexibility to the designer for implementing tires 10 according to the invention for a variety of different and varying applications. Thus, the design of tire 10 as shown in this embodiment is only representative of the types of designs possible in accordance with the invention. Depending upon the duty cycle for which the tire 10 is designed, the characteristics of the sidewalls 16 may be modified to support the vehicle load under compression. In all designs, the tire 10 may be configured to fit in association with a standard vehicle rim, whether associated with a bicycle, passenger vehicle, heavy vehicle or the like. In the embodiment shown in
In a second embodiment, a tire 110 is similar to the first embodiment. A section of the second embodiment tire 110 is shown in
The sidewalls 16 are notably distinct from known tire sidewalls because the external face 24 has a concave curvature and the internal sidewall face 20 is concave when viewed from within the annular chamber 118. These opposing curvatures result in the sidewalls 16 having a thickness which varies as one moves radially inwardly or outwardly. Conventional tires typically have convex external sidewall surfaces and concave internal sidewall surfaces with a generally constant wall thickness.
At the radially outward end of the tire 110, the external road-engaging surface 14 has a convex curvature across the width, effectively forming a crown, which may be depressed upon loading. Inside the annular chamber 118, the internal top wall face 20 is concavely curved when viewed from the annular chamber, so that this portion of the tire has a generally constant thickness. Of course, it will be well known to put road-engaging features 26, such as dimples, cylindrical holes, grooves and the like onto the external road-engaging surface 14, but it is the general thickness of the tire and not the localized thickness which is generally constant.
At the radially inwardly end of each sidewall 16, a number of rim-engaging surfaces 112 are provided. First, a concave groove 28 is sized and positioned around the circumference to allow the tire 110 to be seated in a rim with an inwardly-projecting seating surface. Second, the sidewalls 16 are conjoined by a lobe-like thickened portion 130 formed at the base of each sidewall 16, with the portion 130 having a convexly curved outer surface 32. As the tire 110 is mounted in a rim, the act of compressively fitting the tire into the rim will accomplish two goals: the lobe-like portion 130 will be compressed between radially-extending sides of the rim, and the convexly curved outer surface 32 will conform compressively into engagement with the internal surfaces of the rim. Annular chamber 118 is a closed air-retaining chamber whether the tire 110 is mounted or not. The design of the tire 110 provides an anisotropic assembly with structurally stable sidewalls 16 even in the absence of any positive pressurization beyond ambient in the annular chamber 118. Also similar to the previous embodiment, the annular chamber 118 may be pressurized with air if desired, to modify the load bearing or handling characteristics of the tire if desired.
Turning to
Thereafter, stress may be normalized at different locations of the tire design for finalizing a design for a given duty cycle. In the examples as shown in
In Table 2, tread design data and tire design data are set forth for known pneumatic tires and non-pneumatic tires according to the invention.
Physical characteristics of pneumatic tires for use with power bikes are shown, along with tire design data and performance characteristics. It is noted for example with the MT model tire produced by Specialized, the tire has a stiffness index SSR at a 150 lb. load, of 193.0 LB/IN, yielding a rolling resistance index WC of 9.7125 FT-LBS. For the non-pneumatic tires according to the present invention, examples 1-4 are shown having varying tread and tire design characteristics, but in each case, providing performance characteristics which are greatly improved over the pneumatic tires shown in Table 2. In each of the examples 1-4, it is noted that relatively high stiffness indexes (SSR) are provided in the tire designs, yielding a rolling resistance index (WC) which is significantly reduced. Although certain of the known pneumatic tires have reasonably good rolling resistance indexes (WC), being similar to that achieved in the tire designs according to the invention, it should be apparent that the tire design according to the invention produces lower rolling resistance generally, and significant improvements for certain tire designs. Further, as previously mentioned, rolling resistance may be further reduced by introducing pneumatic pressure to the annular chamber formed in the closed torus tire design according to the invention.
A tires rolling resistance is generally effected by its environment as well as by the engineering of the tire, wherein tread compression characteristics, tread bending characteristics, as well as the material from which the tire is made, each will have an impact upon rolling resistance. It is known in pneumatic tires, that a worn out tire can have up to a 15% lower rolling resistance than a new tire due to lower traction and weight. Therefore, reducing mass and increasing inflation pressure directly reduces rolling resistance in a pneumatic tire. For a passenger tire, a typical range of rolling resistance measured in pounds drag/pounds load is between 10 to 25, whereas a light truck type of vehicle may have a rolling resistance in the range of 7 to 15 and a medium truck a rolling resistance in the range of 5 to 10. In the present invention, the design of the tire as well as the ability to make it from a homogenous material such as a urethane, provide significantly reduced rolling characteristics in the tires. With respect to the material, it is generally known that the higher the hysteresis losses within the material due to vibration, the higher the rolling resistance. Therefore, the stress and strain of the compound has been quantified in terms of loss modulus G11 and storage modulus G1. The angular phase lag of strain behind stress is defined as tan ∂ or G11/G1 and is the basic parameter for expressing energy losses relative to energy stored between 1500 and 2500 PSI for low amplitude vibrations at 60 HZ and room temperature.
The coefficient of rolling resistance of a tire is defined as the drag force divided by the vertical load and is related to power loss as follows:
Power losses of tires have been measured on various rubber compounds to vary by approximately 1.5 times. Rolling resistance is thus also affected by the materials used in the tire construction, and the ability to use a low loss material in the construction of the tire according to the invention facilitates engineering the tire with a much reduced rolling resistance as compared to pneumatic tire constructions.
Experiments with urethane compounds when comparing them to rubber show the chemical bonds to be 4-6 times stronger with tan ∂'s one fourth of those for rubber. This could be due to the molecular structure and bond length differences, where rubber is a linear double-ionic bond structure and urethane is a three-dimensional double or triple, covalent bond structure. This increases packing and shortens urethane bond lengths.
Utilizing the work of compression as an index for the design/compound integral. The following data was generated for 700-20 bicycle tires.
These data indicate that the tires according to the present invention as shown in Examples A and B can be engineered using stronger, lighter and cheaper materials in much more effective design configuration. Approximately a 34.5% reduction in rolling resistance and 17.25% in fuel economy may be achievable. At the current petroleum prices, it should be evident that significant fuel cost savings would be accomplished.
As previously briefly described, the tire 10, 110 of the present invention need not be laid down in plies like the conventional pneumatic tire. Instead, the tire 10, 110 is homogeneous, and may be formed from a variety of techniques known for forming elastomeric materials, such as compression or injection molding, spin casting or extrusion. Likewise, the manufacturing process can utilize either solid or liquid phase manufacturing, allowing rapid dispersion of the elastomeric materials, and a simplified and cost effective manufacturing process. The tire 10, 110 may be formed from a variety of known elastomeric materials, including, for illustration rather than limitation, natural rubber, modified rubbers, urethanes, polyurethanes or other suitable elastomeric materials for a particular application. A further embodiment of the tire of the present invention is shown in
Turning to
The tire 10, 110 of the present invention may be useful in any known application where a pneumatic tire is currently the preferred technology. Since the tire of the present invention is not dependent upon pneumatic pressurization to maintain its structural stability, the tire acts as a “runs flat” tire and provides safety beyond that known in the conventional pneumatic tire. It also provides advantages in remote operations or in high hazard situations, such as on military vehicles, where a pneumatic tire simply poses a great risk. In one set of applications, the tire of the present invention may be used on a situation where the ratio of the height of the tire as measured radially is less than 10% or so of the diameter of the wheel rim, as in a bicycle tire. In another set of applications, the tire of the present invention may be used on a situation where the ratio of the height of the tire is in the range of from about 20 to about 60% of the diameter of the wheel rim, as in an automobile tire.
The operational characteristics of the tire 10, 110 are effectively identical once the tire is mounted in a proper rim, and those characteristics are largely determined by the sidewalls 16, the cross member 13 and the annular chamber 18. These operational characteristics are illustrated in a series of figures numbered 3 through 8. These figures exemplify how the imposition of a weight load on the tire 10, 110 causes resilient deformation of the tire and distortion of the cross sectional shape of the annular chamber, in a manner which is comparable to a pneumatic tire.
The present invention provides a tire design which improves performance characteristics in operation, including extended mobility, and lower rolling resistance. The shape of the tire provides a rim interfering design, which in conjunction with the materials allow for energy resolution.
“This application is a continuation of copending application application Ser. No. 09/849,854 filed on May 4, 2001.”
| Number | Date | Country | |
|---|---|---|---|
| Parent | 09849854 | May 2001 | US |
| Child | 10910778 | Aug 2004 | US |
