Patent Application
20170259621
The subject matter of the present disclosure relates generally to a novel shape for the body ply, or carcass, of a tire including a wide-based single tire.
The body ply of a tire, also referred to sometimes as the carcass or carcass ply, extends from the bead portions, through both opposing sidewall portions, and the crown portion of the tire. One or more layers that include substantially inextensible materials referred to e.g., as cords are typically used in its construction. For a radial tire, these cords are typically oriented at greater than about 80 degrees as measured from an equatorial plane of the tire within the crown portion. In a pneumatic tire, the body ply helps constrain inflation pressure and determine the overall shape of the tire upon inflation. When the tire is inflated to a given pressure, the body ply will assume a particular shape or profile in the meridian plane that is referred to as the equilibrium curve.
Body ply design poses a challenge for all tires and particularly for wide-based single (WBS) tires, which are tires that typically have a relatively wide crown portion and may be used to replace a pair of tires each having a relatively narrow crown portion. All tires, particularly WBS tires, commonly have a difference in rigidity between the center of the tire and the shoulder portions. This difference can be particularly pronounced as compared with either of the dual conventional tires that a single WBS tire replaces. The difference in rigidity can lead to uneven growth of the tire as it is inflated including differences in growth along the crown portion where the tread is located. As a result, the tire can experience enhanced motion of the shoulders compared with the center when the tire is rolling, which can create issues such as groove bottom cracking in the tread and an enhanced sensitivity of the contact patch shape to load variations.
For a heavy truck tire, uneven inflation growth can also cause the tire to experience a break-in period (e.g., the first thousand miles or so) during initial use. During the break-in period, the rubber of the tire experiences viscoelastic relaxation due to the stresses created by uneven inflation growth. As a result, the shape or profile of the tire evolves in order to dissipate the stress. Such evolving shape impedes the ability to optimize the design of the tire for tread wear performance—resulting in a tread wear rate that is typically unacceptably high during the break-in period.
Conventionally, the equilibrium curves used for tire design and construction are based upon a traditional three-ply membrane model. Unfortunately, because of the large difference in rigidity between the center and the shoulder portions of the tire, particularly a WBS tire, this traditional model can yield a tire with uneven inflation growth. Again, this uneven inflation growth can create a flex point in shoulder of the tire, which can place large stresses on shoulder groove bottoms and reduce the rigidity of the shoulder portions relative to the center of the tire.
Previous attempts to achieve even inflation growth have focused on e.g., adding structural stiffness to the belt package in the crown portion so as to mechanically restrain unwanted inflation growth and/or adding rubber portions in an effort to shape inflation growth. Unfortunately, these approaches increase the cost of the tire as well as the mass of the tire. Increased mass can adversely affect tire performance such as rolling resistance.
Thus, a tire employing a body ply that provides for more uniform inflation growth would be useful. Having these features in a tire such as e.g., a WBS tire that can also prevent or deter e.g., groove bottom cracking in the tread, decrease sensitivity to load variations, reduce or eliminate the break-in effect, and/or provide other benefits would be useful. Achieving these advantageous benefits without increasing the mass or deleteriously affecting the rolling resistance or other performance criteria would be particularly beneficial. A method of creating or designing such a tire would also be useful.
Additional objects and advantages of the invention will be set forth in part in the following description, or may be apparent from the description, or may be learned through practice of the invention.
In one exemplary embodiment of the present invention, the present invention provides a tire defining a radial direction, an axial direction, and a tire centerline. The tire includes a pair of opposing bead portions; a pair of opposing sidewall portions connected with the opposing bead portions; and a crown portion connecting the opposing sidewall portions. At least one body ply extends between the bead portions and through the sidewall and crown portions, the body ply having a curve along a meridian plane, wherein s is the length in mm along the curve from the centerline of the tire.
This exemplary tire includes at least two belt plies positioned in the crown portion, each belt ply including belt ply reinforcement elements that are crossed with respect from one belt ply to the other belt ply, the reinforcement elements forming an angle ±α with respect to an equatorial plane of the tire having an absolute value of between 10° and 45°. For this tire, sM denote one-half of the maximum curvilinear width, along the axial direction, of the widest belt ply in the meridian plane of the at least two belt plies. A circumferential layer is provided that includes circumferential reinforcement elements and has a width along the axial direction which in some embodiments may exceed the axial width of each of the belt plies.
When a basis curve having three points of tangency p, d, and q is constructed for the body ply, along at least one side of the tire centerline the body ply has
i) a deviation D(s) from the basis curve in the range of −4.25 mm≦D(s)≦0.5 mm at a point P1=0.13 sq+0.87 sm−56.6 mm, and
ii) a deviation D(s) from the basis curve in the range of −0.5 mm≦D(s)≦1.25 mm at a point P2=0.8 sq+0.2 sm−13 mm; where sq is the length along the curve of the basis curve at which point q occurs.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:
from a reference curve
at a point s0.
For purposes of describing the invention, reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment, can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.
As used herein, the following definitions apply:
“Meridian plane” is a plane within which lies the axis of rotation of the tire.
The “center line” (C/L) of the tire is a line that bisects the tire, as viewed in the meridian plane, into two halves.
“Equatorial plane” is a plane perpendicular to the meridian plane that bisects the tire along its center line (C/L). As used herein, the equatorial plane EP includes the x-z plane of a Cartesian coordinate system.
The “crown portion” of the tire is the portion that extends along the axial direction A (which is the direction parallel to the axis of rotation of the tire) between the sidewall portions of the tire and includes the tread and components positioned radially inward of the tread. The crown portion and its components extend circumferentially around the tire.
“Body ply” or “carcass” or “carcass ply” is a ply that, as viewed in the meridian plane, extends between and from the bead portions on opposing sides of the tire, through the opposing sidewall portions, and across the crown portion of the tire. As used herein, a body ply has reinforcements such as e.g., cords that are at an angle of 10 degrees or less from the meridian plane.
“Belt ply” is a ply that, as viewed in the meridian plane, is located primarily in the crown portion, radially inward of the tread portion, and radially outward of the body ply. A belt ply does not extend past the shoulder portions of a tire.
“Equilibrium curve” or “curve of the body ply” refers to a model of the shape or geometry of a body ply as viewed in the meridian plane of the tire. The tire, including the body ply, will assume an equilibrium shape when mounted onto a wheel or rim and inflated. An equilibrium curve can be used e.g., to model the shape of the body ply in this equilibrium condition.
“Maximum sidewall pressure” means the maximum inflation pressure of the tire that is typically marked on the tire's sidewall.
The “radial direction” is perpendicular to the axis of rotation of the tire. A Cartesian coordinate system is also employed in the following description where the y-axis is parallel to the axis of rotation and the z-axis is parallel to the radial direction. The “circumferential direction” refers to rotations about the y axis.
“Section width” refers to the greatest overall width of the tire along the axial direction as viewed along a meridian plane, which typically occurs at the tire equator. “Section height” refers to the greatest overall height of the tire along the radial direction as viewed along a meridian plane and typically extends from the bottom of a bead portion to the top of the crown portion.
“Aspect ratio” is that ratio of the tire's section height to its section width.
Tires sizes are referred to herein according to conventions published and used by the Tire and Rim Association as will be understood by one of skill in the art.
The use of terms such as belt, bead, and/or ply herein and in the claims that follow does not limit the present invention to tires constructed from semi-finished products or tires formed from an intermediate that must be changed from a flat profile to a profile in the form of a torus.
At least one exemplary body ply H of the present invention extends between the bead portions 102, 104, passing through opposing sidewall portions 106, 108 and crown portion 110. The body ply contains cords or other reinforcement oriented at angles from the meridian plane typically of 10 degrees or less (i.e. 80 degrees or more from the equatorial plane EP). For example, such reinforcements for the body ply H may include materials that are nominally inextensible such as e.g., metal cable, aramid, glass fibers, and/or carbon fiber components.
A tread portion 124 is located in the crown portion 110 radially outward of the belt plies 112, 114, and 116. Tread portion 124 includes ribs 126 separated by grooves such as first groove 128 and 130 along each shoulder portion 132 and 134. It should be noted that the present invention is not limited to the particular size or appearance of tire 100 shown in
In one exemplary embodiment, tire 100 has an aspect ratio in the range of 50 to 80. In another exemplary embodiment, tire 100 has a section width in the range of 275 to 455 mm. In still another exemplary embodiment, tire 100 has a section width in the range of 445 to 455 mm. Other dimensions and physical configurations may be used as well.
As stated above, the present invention provides a tire having a more uniform inflation growth—i.e. the growth of the tire as it is inflated—across the entire body ply H of the tire. The extent of uniformity can be specified e.g., through the tire's inflation growth amplitude A, which is defined herein. The inventive tire's uniform inflation growth reduces load sensitivity, reduces or eliminates the break-in period, and/or decreases the propensity for cracking—particularly along one or more groove bottoms in the shoulder region e.g., grooves 128 and/or 130 of the tread portion 124 of tire 100.
In a typical tire manufacturing process, tires are cured in a mold where they take on their final geometry. Conventionally, the body ply is typically designed to be as close to equilibrium as possible in the mold for ease of manufacturing. For the present invention, an inventive body ply H (of which the body ply H in
As used herein, the term “inflation growth” can be quantified and understood more fully with reference to the difference between two curves. More particularly, assume that R is a reference curve denoting the shape of a body ply in the meridian plane, that X is another curve denoting the shape of another body ply in the meridian plane, and that DRX designates the deviation of curve X from curve R along a direction towards curve X from curve R that is normal to curve R at any given point. Assume also that curves R and X are coplanar and lie in the same y-r plane in the well-known polar, cylindrical coordinate system. Curves R and X can be specified in the Cartesian y-z plane because any y-r plane can be rotated into the y-z plane—i.e. the meridian plane as defined herein.
With reference to
and normal vector
Accordingly, the distance DRX(s0) between the curve R at the point R(s0) and curve X is defined in the following manner as illustrated in
Continuing with
and normal vector
Similarly, the interior surface I and exterior surface E of tire 100 can also be described by curves I(s1) and E(s2) with normal vectors {right arrow over (n)}i and {right arrow over (n)}E, respectively.
Using these definitions, in one exemplary method of the present invention, inflation growth can be measured between a very low pressure state (referred to herein as the “reference pressure”), e.g., 0.5 bar, and the desired design pressure of the tire (referred to herein as the “nominal pressure”—which could be e.g., the maximum sidewall pressure). Preferably, the reference pressure is high enough to seat a bead portion 102, 104 of tire 100 on a wheel rim but low enough to avoid otherwise changing the shape of tire 100. More particularly, to keep the boundary conditions unchanged between these two pressure states, for this exemplary method, the position of the bead portion 102, 104 of the tire 100 on the rim is fixed in the position it occupies at the nominal pressure. Such can be accomplished experimentally through the use of an internal bead support, for example, and can also be easily simulated or modeled with e.g., a computer using finite element analysis (FEA) or computer aided design programs.
Next, measurements of tire 100 are made that yield the curves I, E and/or C at any desired azimuth. For example, the curve C(s) for body ply H can be measured directly (e.g., by x-ray techniques) or obtained from a computer model by FEA. As illustrated in
Plot U of
For the production tire, a large peak in plot U occurs at approximately 142 mm along curve length s. As the tire is symmetrical, this means that the two peaks occurring at ±142 mm align closely with the position of the first shoulder groove 120 or 130 of the tread portion 124 and place the groove bottom under strong tensile extension, which greatly facilitates crack nucleation and propagation. This strong growth, coupled with the sharp decrease in growth at the edge of the tread band, acts to bend the crown portion 110 of the tire in the location of the groove 128 or 130. This introduces a hinge point into the crown of the tire at each such point so that the tire bends structurally rather than acting pneumatically—thereby reducing the tire's overall vertical rigidity. This hinge point occurs with or without the presence of a shoulder groove but is particularly problematic when it coincides with the location of a groove in the tread.
Additionally, because the degree of bending at this hinge point is a function of load, the tire's footprint experiences rapid evolution at the shoulders 132 and 134 relative to the center line C/L of the tire as the load changes. For example, at high loads the shoulders 132 and 134 have too much length in contact with the ground relative to the center. Conversely, at lower loads the shoulders 132 and 134 become too short relative to the center; they may even lose contact with the ground entirely at the lowest usage loads. This phenomenon, known as load sensitivity, is undesirable for the even and regular wear of the tread band and results in reduced removal mileage for the tire.
The present invention solves these and others problems by providing for a flat and stable inflation growth curve across the entire body ply H (e.g., from bead portion 102 to bead portion 104) as represented by the exemplary plot K in
For example, as also shown in
The exemplary inflation growth represented by plot K is obtained by providing a certain inventive geometry or curve for the exemplary body ply H (along one or both sides of the centerline C/L) of tire 100 as viewed in the meridian plane. The location of this inventive curve for body ply H is specified and claimed herein with reference to the deviation D from a “basis curve” (denoted as BC in the figures) that can be unambiguously constructed for any desired tire. More particularly, the basis curve BC can be unambiguously constructed from measurements of a physical specimen of an actual tire or constructed from one or more models of a tire such as e.g., a computer simulated model or a model from computer aided design (CAD)—as will be understood of one of skill in the art. As such, the basis curve BC is used herein to provide a clear reference for future measurements and for specification of the location of the body ply of the present invention.
Accordingly, “basis curve” or “basis curve BC” as used in this description and the claims that follow is defined and constructed as will now be set forth with reference to the exemplary profile of a hypothetical tire having a belt ply W and body ply H as shown in
As part of the method of constructing the basis curve BC for body ply H (or any other body ply for which a basis curve BC is to be constructed for reference), the shape of body ply H is determined using the shape body ply H assumes when the tire is mounted on the application wheel rim at a reference inflation pressure of 0.5 bar (designated e.g., as C(s)R in
Next, considering all belt plies (such as e.g., plies 112, 114, and 116 in
Using the definitions above, basis curve BC is constructed from two parts. Continuing with
To specify the second part J of basis curve BC, several additional points are now defined for this description and the claims that follow. First, let se be the parameter value for which body ply H takes on its minimum value in y, and let sz be the parameter value for which body ply H takes on its minimum value in z. The equator point e is defined as e=CR(se)=(ye, ze) and the point z is defined as z=CR(sz)=(yz, zz).
L is defined a vertical line passing through point e. Point h, which is h=(yh, zh), is the intersection between a horizontal line T passing through point z and line L. It should be noted that point h does not in general lie on body ply H. Define distance n as n=∥e−h∥ i.e., the Euclidean distance between points e and h.
Now an intermediate point f, not necessarily on the body ply H, is defined with respect to point h as f=(yh, zh+0.3*n). A horizontal line is constructed through point f and its point of intersection with body ply H is defined as point t, which occurs at parameter st so that t=CR(st). A circle C is constructed with a radius of 20 mm that is also tangent to the body ply at point t. The center of the circle is defined to be the point g located 20 mm from body ply H along the line defined by the normal to the body ply {right arrow over (n)}CR(st) at point t.
Accordingly, the second part of the basis curve BC includes a radial equilibrium curve J in a manner that can be readily determined in the following manner. As will be understood by one of skill in the art, a radial equilibrium curve is characterized by 2 parameters: rc, the center radius, and re, the equator radius. Here r is the usual cylindrical polar radial coordinate and is equal to z when in the y-z plane. The radial equilibrium curve can be described by a differential equation and can also be unambiguiously constructed starting from the center radius by calculating the tangent angle φ and curvature κ of the curve at each subsequent radius. The expressions for the tangent angle and curvature for a radial equilibrium curve are well known and are given as follows:
To uniquely determine the parameters rs and re of radial equilibrium curve J, a tri-tangency condition is imposed. First, radial equilibrium curve J must be tangent to arc A. The point of tangential intersection of these two curves will occur at a point p≠b in general. The point b is projected in a fashion perpendicular to the reference curve for body ply H onto the basis curve BC to obtain its equivalent. Typically the point p will intersect the arc laterally outward of point b, in which case this projection is unnecessary as it simply yields the original point b. The second requirement of tri-tangency is that the radial equilibrium curve J and the line L must be tangent to each other, which occurs at a point designated as point d in
Accordingly, basis curve BC is defined to be the union of the arc segment A from a to p with the radial equilibrium curve J between points p and q, i.e. basis curve BC=A∩J. The values of rc and re for the radial equilibrium curve can be determined by many means known to one of ordinary skill in the art. For example, one method would be to begin by taking rc=zb and re=ze and then iterating to find a solution.
Referring now to
By introducing a shifted parameter s′=s−sb, it can also be observed that the inventive new body ply H deviates in a systematic manner from conventional tires as the width of the tires change. As illustrated in
Additionally, with reference to
The use of the parameter s″ normalizes e.g., the deviation for tires of different tread widths, section widths and rim dimensions.
As shown in
Importantly, the inventive body ply H results in the desired uniform inflation growth G.
Returning to
Using equation 2 above and substituting for sb=sM−65 mm leads to following for points P1 and P2 along curve length s of body ply H where for its deviation D(s′) from basis curve BC:
P
1 occurs at s=0.13 sq+0.87 sm−56.6 (units in mm) Equation 4
P
2 occurs at s=0.8 sq+0.2 sm−13 (units in mm) Equation 5
By maintaining the deviation D(s) from basis curve BC at points P1 and P2 within a specified range, the desired uniform inflation growth G for the inventive body ply H can be obtained. More particularly, at point P1 the deviation D(s) from the basis curve should be maintained within a range of −4.25 mm≦D(s)≦−0.5 mm, and at point P2 the deviation D(s) from the basis curve should be maintained within a range of −0.5 mm≦D(s)≦1.25 mm. As used herein, the expression of a range of for D(s) includes the endpoints of the specified range.
By constructing a tire within an inventive body ply H having deviation D as specified, uniform inflation growth G from bead portion 102 to bead portion 104 is obtained. For obtaining the benefits of the invention, the magnitude of inflation growth G is not critical. Instead, the absence of peaks and valleys is important. Recalling that the value of the distance parameter at point t is st as set forth above, the maximum, minimum, and amplitude of inflation growth G over the region from −st to st at a given azimuthal angle θ is defined as follows:
G
max(θ)=maxs∈[−s
G
min(θ)=mins∈[−s
A(θ)=Gmax(θ)−Gmin(θ) Equation 8
Gmax(θ) is the maximum inflation growth G found between parameter points −st and st at a given angle θ. Similarly, Gmin(θ) is the minimum inflation growth found between parameter points −st and st at a given angle θ. A(θ) is the amplitude of the inflation growth at angle θ and is the difference between Gmax(θ) and Gmin(θ). This is illustrated in
Finite element calculations of inflation growth G are typically 2d axisymmetric simulations, predicting the same amplitude A at all azimuthal angles θ. For physical tire measurements, however, inflation growth G can vary from azimuth to azimuth around the tire. Accordingly, as used in the claims that follow, the final amplitude measurement is defined herein as an average of n≧4 evenly spaced azimuthal measurements in the following fashion:
Using equations 6, 7, and 9, the following results were calculated using the four conventional tires previously referenced as well as tires of the same size equipped with a body ply H of the present invention:
In one exemplary embodiment of the invention, when constructed with such a body ply H, tire 100 has an inflation growth amplitude A that is less than, or equal to, about 1.5 mm when the tire is inflated from a pressure of about 0.5 bar to about the maximum sidewall pressure.
The efficacy of the new invention was also demonstrated by a shoulder groove cracking simulation performed using the same four tire sizes. Specially prepared FEA models were generated for this purpose in which the mesh density was drastically increased along the shoulder groove bottoms (
The present invention also provides for an exemplary method of designing or constructing tire 100. Such method could be used to improve the body ply for an existing tire design or could be used in creating a new tire design. In either case, for this exemplary method, the designer would begin by creating a model of the tire that includes a reference curve representing the shape of the body ply along a meridian plane when the tire is inflated to a reference pressure, wherein s is a length in mm along the reference curve from a centerline of the tire. For an existing tire, the reference curve could be created as described above using existing CAD drawings or by using physical measurements of a specimen of the tire subjected, e.g., X-ray, laser profilometry, or other techniques. For a new tire design, the reference curve could be created from e.g., CAD models or other computer models of the tire. The reference pressure could be e.g., 0.5 bar or other pressures.
Next, a basis curve BC is constructed for the tire based upon the reference curve of the tire at the reference pressure. The basis curve BC is constructed e.g., as previously described.
Using the basis curve BC, a target reference curve (which can be described by R(s) as set forth above via equations 4 and 5) is created for the shape of the body ply along the meridian plane. This target reference curve is the desired curve or geometry for the new body ply—such as e.g., the exemplary body ply H discussed above—to be used in the tire.
The target reference curve is created by repositioning the reference curve to have a deviation D(s) from the basis curve BC that is in the range of −4.25 mm≦D(s)≦−0.5 mm at point P1 and in the range of −0.5 mm≦D(s)≦1.25 mm at a point P2, where P1 and P2 are located along the target reference curve as set forth in equations 4 and 5 above, respectively.
The target reference curve could be created by repositioning the reference curve on one or both sides of the tire centerline as well.
For an existing tire, the design would be changed to include the new shape of the body ply. This would include changes to manufacture the tire having the new body ply. For a newly designed tire, the design would include the new profile or curve for the body ply. Accordingly, the present invention includes tires constructed and manufactured having the new inventive body ply providing for uniform inflation growth G as described herein.
Certain tires are used to travel at highway speeds on relatively long trips. With improvements in wear performance and retreading of e.g., truck tires having an aspect ratio greater than 0.5, it can become important for the crown portion of the tire to also have good endurance. For example, the crown portion can experience shearing stresses between the shear layers. When coupled with a significant increase in temperature near the ends of certain layers in the crown during tire operation, it is possible for cracks to appear and propagate in the tire rubber located near such ends.
For this exemplary embodiment, tire 200 includes at least two belt plies 241 and 243 positioned in crown portion 210. Belt plies 241 and 243 each include belt ply reinforcement elements that are formed of non-wrapped elements such as e.g., metal cables that, for each belt ply, are continuous over the entire axial width of belt ply 241 and 243, respectively. These cables may form a positive or negative angle ±α (see
Belt ply 241, for this exemplary embodiment, has an axial width L241 that can be equal to 183 mm while belt ply 243 can have an axial width L243 of 172 mm. In another exemplary embodiment, belt plies 241 and 243 have a difference in axial width that is between 10 mm and 30 mm. As used herein, the axial width of a belt ply is measured along the axial direction A in a meridian plane of the tire (as used e.g., in
Tire 200 includes a circumferential layer 242 that includes circumferential reinforcement elements that may be continuous or variable over the entire axial width of circumferential layer 242. As used herein, circumferential reinforcement elements are reinforcement elements that form an angle α of about 0° from the equatorial plane EP (see
In addition, tire 200 of
While the present subject matter has been described in detail with respect to specific exemplary embodiments and methods thereof, it will be appreciated that those skilled in the art, upon attaining an understanding of the foregoing may readily produce alterations to, variations of, and equivalents to such embodiments. Accordingly, the scope of the present disclosure is by way of example rather than by way of limitation, and the subject disclosure does not preclude inclusion of such modifications, variations and/or additions to the present subject matter as would be readily apparent to one of ordinary skill in the art using the teachings disclosed herein.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2014/062893 | 10/29/2014 | WO | 00 |
