Abstract:
A tire testing apparatus and method for measuring the local stiffness of a tire. The apparatus includes a force producing mechanism, a force measuring device, a force transmitting member, and a measuring device. The force transmitting member applies a force to a tire surface and the measuring device measures the distance of the displacement of the tire surface caused by the force. A tire testing method comprising mounting a tire on a tire testing apparatus to measure a local stiffness of the tire. The method further comprises inflating the tire, applying a force to a local area of the tire, monitoring the force, measuring a distance corresponding to the local deflection, and calculating a local stiffness.

Description:
FIELD OF INVENTION 
     The claimed invention is directed to an apparatus and method to measure tire stiffness. More particularly, the claimed invention is directed to an apparatus and method to measure local tire stiffness such as can be caused by variations in tire construction. 
     BACKGROUND 
     Tire manufacturers have used global run out probes or global non-contact lasers to measure global tire surface topography in order to sort or grade tires. For example, global tire surface topography compares an entire sidewall or an entire tread of a test tire to a computer model and provides an acceptable or unacceptable rating for the test tire. However, global tire surface topography techniques are not suitable to identify more discrete or local tire stiffnesses. Variations that occur between tire layers, between carcass or reinforcement ply cords, or within other tire components can produce local stiffness variations in body ply force from one location to another or between one cord to another along the sidewall or other surface of a tire. With variations, as well as certain others, global tire surface topography techniques are not suitable. 
     SUMMARY 
     A tire testing apparatus and method for measuring the local stiffness of a tire. The apparatus includes a force producing mechanism, a force measuring device, a force transmitting member, and a measuring device. The force transmitting member applies a force to a tire surface and the measuring device measures the distance of the displacement of the tire surface caused by the force. A tire testing method comprising mounting a tire on a tire testing apparatus to measure a local stiffness of the tire. The method further comprises inflating the tire, applying a force to a local area of the tire, monitoring the force, measuring a distance corresponding to the local deflection, and calculating a local stiffness. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings, embodiments of an apparatus and method for measuring local tire stiffness are illustrated that, together with the detailed description provided below, describe exemplary embodiments of the apparatus and method. It will be appreciated that the illustrated boundaries of elements in the drawings represent one example of the boundaries. One of ordinary skill in the art will appreciate that one element or step may be designed as multiple elements or steps or that multiple elements or steps may be designed as a single element or step. An element shown as an internal component of another element may be implemented as an external component and vice-versa. 
       Further, in the accompanying drawings and description that follow, like parts are indicated throughout the drawings and description with the same reference numerals, respectively. The figures are not drawn to scale and the proportions of certain parts have been exaggerated for convenience of illustration or to enhance understanding. 
         FIG. 1  illustrates a side view of a local stiffness measuring apparatus  100  and a tire T. 
         FIG. 2  illustrates a schematic  200  of the local stiffness measuring apparatus  100  and tire T, shown in  FIG. 1 , and various tire stiffness related parameters. 
         FIG. 3  illustrates a side view of another exemplary local stiffness measuring apparatus  300  and a tire T. 
         FIG. 4  is a side view of another exemplary local stiffness measuring apparatus  400  and a tire T. 
         FIG. 5  is a graph of the local deflection for the tire T. 
         FIG. 6  illustrates a graph of the root mean square or RMS of variation in tire deflection for tires tested with the local stiffness measuring apparatus  100  of  FIG. 1 . 
         FIG. 7  illustrates a flow chart of one embodiment of a method to determine local tire stiffness  700 . 
     
    
    
     DETAILED DESCRIPTION 
     The following includes definitions of selected terms employed herein. The definitions include various examples and/or forms of components that fall within the scope of a term and that may be used for implementation. The examples are not intended to be limiting. Both singular and plural forms of terms may be within the definitions. 
     “Axial” and “axially” refer to a direction that is parallel to the axis of rotation of a tire. 
     “Bead” refers to the part of the tire that contacts the wheel and defines a boundary of the sidewall. 
     “Body ply force” refers to the tensile force in the tire cords and various tire component layers that are part of the carcass ply, reinforcement ply, circumferential belt, tread, shoulders, sidewalls, bead portions of a tire, or the like, due to expansion of an uncured tire into a tire mold during curing and due to inflation pressure when a tire and wheel assembly is inflated. 
     “Circumferential” and “circumferentially” refer to a direction extending along the perimeter of the surface of the annular tread perpendicular to the axial direction. 
     “Equatorial plane” refers to the plane that is perpendicular to the tire&#39;s axis of rotation and passes through the center of the tire&#39;s tread. 
     “Lateral” refers to a direction along the tread of the tire going from one sidewall of a tire to the other sidewall, wherein the direction is parallel with the axis of rotation. 
     “Radial” and “radially” refer to a direction perpendicular to the axis of rotation of a tire. 
     “Sidewall” refers to that portion of the tire between the tread and the bead. 
     “Shoulder region” refers to the upper portion of each sidewall just below the edge of the tread. 
     “Tread” refers to that portion of the tire that comes into contact with the road under normal inflation and load. 
     The inventors have discovered or disclosed herein an apparatus and method that measures local stiffness in a tire.  FIG. 1  illustrates an exemplary local stiffness measuring apparatus  100 , connected to a computer system C, for testing the local stiffness in a tire T with a sidewall S. The apparatus measures local stiffness about the peripheral surfaces or inner surfaces of a tire T, e.g., an internal or external portion of a sidewall or a tread. The local stiffness measuring apparatus  100  connects at member  105  to a tire testing machine (not shown) that enables inflation of tire T to a specified pressure P and rotates the tire T at various speeds. 
     In the illustrated embodiment of  FIG. 1 , local stiffness measuring apparatus  100  includes a steel support structure comprising a lower plate  110 , an upper plate  115 , and connecting rods  120  that move freely through upper plate  115  as the tire deflects. In addition, local stiffness measuring apparatus  100  includes a contact probe  125 , a load cell  130 , a spring  135 , and a linear measurement device  140 . In an alternative embodiment (not shown), local stiffness measuring apparatus  100  further includes a wire  145  that attaches to the lower plate  110 . In yet another alternative embodiment (not shown), local stiffness measuring apparatus  100  includes linear measurement device  140  that comprises a laser that measures distance. In another alternative embodiment (not shown), the local stiffness measuring apparatus  100  comprises a contact probe  125 , a load cell  130 , a spring  135 , and a linear measurement device  140 . 
     In operation, the tire T is connected to a tire testing machine (not shown) and the contact probe  125  (e.g., a roller bearing) transfers a force F from the spring  135  to the sidewall S of the tire T as the load cell  130  measures the force F. The contact probe  125  can comprise a stationary end or a rotating end, such as a track wheel or wheel bearing, so the tire is not damaged as the apparatus  100  measures the tire. Force F is oriented in a direction perpendicular to the radial direction of the tire. Alternatively, the contact probe  125  of the local stiffness measuring apparatus  100  can be positioned such that the force on the tire is in a radial direction, a normal direction, a direction that is normal to the sidewall contact location of the contact prove, or some other direction relative to the sidewall of the tire. 
     In order to measure variation in tire stiffness K t , the force F applied to the tire T is a substantially constant force and measured by load cell  130 , shown in  FIG. 1 . The force F is set to a constant force by compressing spring  135  by an initial deflection X o  of the spring, where spring  135  has a spring constant K s  and force F is equal to the initial deflection X o  times the spring constant K s . Spring  135  is illustrated as a single helical spring, but could be substituted with two or more helical springs. In other embodiments (not shown), as one skilled in the art would know, spring  135  could be replaced by at least one of the following devices: a coil spring, a conical spring, a Belleville spring, a gas spring, an air cylinder, a block of known weight, and similar devices that can apply a substantially constant force. Alternatively, the force applied can vary wherein the force-deflection curve is known for the spring and the varying force and deflection are recorded by the computer system C as the tire rotates. 
     With continued reference to  FIG. 1 , force F produces a localized deflection X t  on sidewall S of tire T. Linear measurement device  140  measures a change in deflection of the spring ΔX s  that corresponds to the localized deflection X t  on sidewall S under force F at discrete positions by continuously measuring the linear movement of wire  145  connected to spring  135  as the tire rotates. As sidewall S deflects under the force F, the spring  135  compresses or expands and linear measurement device  140  measures the linear distance that the wire  145  moves, which is substantially similar to the localized deflection X t . The linear measurement device  140  may be a distance measuring device, a string pot linear measuring device, a linear variable displacement transducer, or the like. 
     Further, in the illustrated embodiment, the force F measured by load cell  130  and localized deflection X t  of rotating tire T measured by linear measurement device  140  are sent to the computer system C that calculates and records the local stiffness K t . Load cell  130  and linear measurement device  140  send measurements (e.g., force, deflection, and location) to computer system C while the tire rotates. The measurements are sent by at least one of the following data transmission techniques: hard wire transmission, wireless transmission, and the like (data transmission is represented by the dashed lines  150 ,  155  in  FIG. 1 ). Alternatively, the measurements from the load cell  130  and the linear measurement device  140  are sent to the computer system C at the end of the test in a batch transmission mode. If the hard wire transmission technique is selected, then dashed lines  150  and  155  in  FIG. 1  represent wires that the data is sent through to computer system C. Unless specifically stated otherwise, it is appreciated that throughout this detailed description, terms like computer system, computer, processing, computing, calculating, determining, displaying, or the like, refer to physical components, actions, and processes of a computer system, logic, processor, hardware and/or software, or a similar electronic device that manipulates and transforms data represented as physical (electronic) quantities. 
     In other embodiments (not shown), the local stiffness measuring apparatus  100  includes member  105  that does not connect to a tire testing machine, but attaches to at least one weight bearing device. Suitable weight bearing devices include, but are not limited to, a support stand that mounts to a floor, a wall, a ceiling, a structural beam, and other building structural components. In yet other embodiments (not shown), local stiffness measuring apparatus  100  can be configured to rotate at various speeds about a fixed structural support while the tire T is stationary and connected to a tire testing machine. In still other embodiments (not shown), local stiffness measuring apparatus  100  and the tire T can be configured to both rotate relative to a fixed structural support. In other embodiments (not shown), local stiffness measuring apparatus  100  or tire T can be configured horizontally, vertically, or at any angle relative to a fixed structural support. In addition, it should be understood that the local stiffness measuring apparatus  100  may include more or less structural components than what is shown in the illustrated embodiment. 
     Further, local stiffness measuring apparatus  100  may include a programmable logic controller PLC, computer control unit, or the like. In another embodiment, a control system may be at least one of the following: a computer, a programmable logic controller, a computer control unit, or the like. The control system or the programmable logic controller can store the measurements of the load cell  130 , the linear measurement device  140 , and the coordinates of the tire (X, Y, and Z coordinates) and then calculate and record the tire&#39;s local stiffness K t  as the tire testing machine rotates the tire. In yet other embodiments (not shown), programmable logic controller PLC or the like records and calculates various parameters, including: deflection, root mean square of variance for deflection, stiffness, stiffness variance, position coordinates, or other testing and statistical parameters. In other embodiments (not shown), programmable logic controller PLC can be programmed to rotate the tire or the tire testing machine and then record tire coordinates and measurements of the tire&#39;s local stiffness variation K t  at a specific location or range of locations specified in a coordinate system with X, Y, and Z coordinates, degrees of rotation, force, deflection, change in force, change in deflection, change in stiffness, or the like. In yet other embodiments (not shown), programmable logic controller PLC or the like can be programmed to calculate the local stiffness variation for a tire at a user specified or pre-programmed radial, lateral, or circumferential position relative to the tire&#39;s center of rotation, axis of rotation, equatorial plane, or the like. 
     In other embodiments, contact probe  125  of the local stiffness measuring apparatus  100  can be arranged to make contact with any of the peripheral surfaces, inner surfaces, or confine surfaces of the tire T, including at least one of the following: a bead region, a sidewall, a shoulder, a tread, an internal wall beneath the tread, an internal sidewall or shoulder, and the like. If a tire designer desires to measure an inner surface or confine surface of the tire T, then the tire T is not installed and inflated on the tire testing machine, but is held on its peripheral surface by a tire fixture (not shown) to allow access for the local stiffness measuring device  100 . In yet other embodiments (not shown), contact probe  125  may be any rolling, load bearing device that allows movement between a moving surface (of the tire) and itself, including at least one of the following: at least one roller pin, at least two roller bearings, and the like. 
     In an alternative embodiment (not shown), the local stiffness measuring apparatus  100  further includes a marking apparatus and system  160  that can mark a tire location according to a user specified parameter, e.g., stiffness that is outside a specified acceptable range. The marking system  160  can use at least one of the following marking materials: chalk, adhesive tape, paint, ink, dye, removable sticker, and the like. Further, the marking system  160  can apply to the tire T various marks in different shapes, or lines, and in various colors depending on the user specified parameter (e.g., a yellow dot can represent a portion of the tire that is below a user specified stiffness and a red dot can represent a portion of the tire that is above a user specified stiffness). In an alternative embodiment (not shown), the marking system  160  can apply to the tire T various marks that are removable or non-removable from the tire. 
       FIG. 2  shows a schematic diagram of portions of the apparatus  200  together with tire T and factors that determine local tire stiffness. The schematic depicts the tire T with a sidewall S that is at a pressure P and further illustrates related forces, distances, and spring constants for the tire T and the local stiffness measuring apparatus  100 . In the illustrated embodiment, the spring  135 , which has a spring constant K s  and an initial deflection X o , produces a constant force F against the contact probe  125  that then transfers this force to sidewall S as tire T is rotated by the tire machine (not shown). If the stiffness varies about the sidewall&#39;s periphery, then the deflection X t  of the tire T varies. The tire stiffness K t  is inversely proportional to the tire&#39;s deflection X t , i.e., K t =F/X t . As discussed above, the force F can be applied to various peripheral portions and inner portions of the tire T to determine the local tire stiffness K t  in different locations. 
       FIG. 3  illustrates a side view of another exemplary local stiffness measuring apparatus  300  and a tire T. The local stiffness measuring apparatus  300  is substantially the same as the local stiffness measuring apparatus  100  of  FIG. 1 , except the local stiffness measuring apparatus  300  includes a contact probe  325  that is at a position that is normal to the sidewall contact location of the contact probe. Alternatively (as illustrated in dashed lines), the local stiffness measuring apparatus  300  includes a contact probe  325   a - d  that can be positioned so the force on the tire is in a radial direction, a normal direction, a direction that is normal to the sidewall contact location of the contact prove, a lateral direction, or some other direction relative to the sidewall of the tire. In another embodiment (not shown), the contact probe  325  of the local stiffness measuring apparatus  300  is positioned such that the force on the tire is at an angle, relative to a normal N direction relative to the sidewall contact location of the contact probe, from about minus ninety degrees to about ninety degrees. In yet another embodiment (not shown), the contact probe  325  of the local stiffness measuring apparatus  300  is positioned from about a substantially radial angle to about a substantially lateral angle. 
       FIG. 4  is a side view of another exemplary local stiffness measuring apparatus  400  and a tire T. The local stiffness measuring apparatus  400  is substantially the same as the local stiffness measuring apparatus  100  of  FIG. 1  and the local stiffness measuring apparatus  300  of  FIG. 3 , except the linear measurement device  140  and the wire  145  are replaced with a linear measurement device  440  that comprises a laser linear measurement device. The linear measurement device  440  emits a laser, represented by a dashed line  445 , to measure the distance between the linear measurement device  440  and a lower plate  460 . In an alternative embodiment (not shown), linear measurement device  440  may be mounted on the lower plate  410  and measure the distance between the linear measurement device  440  and an upper plate  415 . 
       FIG. 5  shows a test graph of deflection of a sidewall S of a tire T connected to a local stiffness measuring apparatus. As shown in the graph, a repeating pattern forms with a maximum deflection MAX and a minimum deflection MIN. The graph illustrates that the tire T has about a 0.18 inch maximum deflection MAX at a sidewall location just beyond a half rotation and about a −0.20 inch minimum deflection MIN at a sidewall location just before a full rotation. Tire designers can use a graph of this type to determine an average deflection for a tire or to determine where a tire defect may exist. Further, tire designers can use this graph to evaluate tire designs and to evaluate manufacturing variability relative to a target tire design or relative to other manufactured tires. In addition, tire manufacturing facilities can measure a large population of tires and use statistical tools to sort, grade, group, or classify tires based on local stiffness measurements. 
       FIG. 6  shows an exemplary graph of root mean square of variation (“RMS”) in tire deflection for a batch of thirty-one tires tested (tire nos. 1-31 listed along the horizontal-axis of the graph) with the local stiffness measuring apparatus  100 , shown in  FIG. 1 . The tires in the graph are P225/60R15 tires having a maximum allowable inflation of 35 psi and a maximum allowable load of 1521 lbs that were inflated to 15 psi and loaded with 23 lbs of static load against the sidewall. For the thirty-one tires in the graph, the RMS in tire deflection varies from about 0.01 inch to about 0.12 inch. Twenty-eight tires have a RMS in tire deflection of about 0.09 inch or less, twenty-seven tires have a RMS in tire deflection of about 0.08 inch or less, twenty-five tires have a RMS in tire deflection of about 0.07 inch or less, twenty-one tires have a RMS in tire deflection of about 0.06 inch or less, and sixteen tires have a RMS in tire deflection of about 0.05 inch or less. 
     Tire manufacturers can use the RMS in tire deflection to grade tires, sort tires, group tires, or the like. For example, without limiting the scope of the invention, tire nos. 2, 7, 15, and 17 may be graded as an “acceptable” class of tires since the tires have a RMS in tire deflection less than 0.02 inch. Conversely, tire nos. 11, 27, 28 and 30 may be graded as a “non-acceptable” class since the tires have a RMS in tire deflection greater than 0.08 inch. Tire manufacturers may use the RMS in tire deflection as a manufacturing in-line or off-line testing technique and can develop varying acceptable and unacceptable standards. 
       FIG. 7  illustrates steps of a method  700  for measuring local tire stiffness. A tire is mounted on a tire testing machine at  705  and the tire testing machine inflates the tire to a testing pressure at  710 . After the tire is mounted and inflated, then the local stiffness measuring apparatus applies a force to the rotating tire. The force is monitored by a measurement device at  715  while a linear measuring device simultaneously or substantially simultaneously measures a distance corresponding to the deflection of the tire at the location of the applied force at  720 . During and after the tire test, the local tire stiffness is calculated at  725 . Optionally, further processing can be completed to sort, grade, classify, or group the tires at  730 . In an alternative embodiment (not shown), the method  700  can be modified to further include calculations of peak to peak differences, minimum to maximum differences, Fourier analysis, signal analysis, harmonic analysis, or the like. In yet another alternative method (not shown), the method  700  can be modified to further include a marking step where the tire is marked in at least one portion where the local stiffness of the tire satisfies at a pre-selected condition such as: exceeds a maximum stiffness, does not meet a minimum stiffness, falls within a user defined stiffness range, and the like. The marking step may occur during or after any of the previously mentioned method steps. 
     While various embodiments of the claimed invention are discussed and illustrated, and while these embodiments have been described in some detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to embodiments. Moreover, advantages and modifications other than those identified above will appear to those skilled in the art. Accordingly, other undisclosed embodiments that fall within the scope of the appended claims, either literally or equivalently, are hereby reserved.