Abstract:
A testing assembly calculates stress levels along a cross section of a pneumatic tire. The cross section of the pneumatic tire includes its tire beads, sidewalls, and tread. The testing assembly includes a base and a plurality of mounts slidably secured to the base. Mounts secure each of the tire beads. The testing assembly also includes a platform that extends parallel across the testing assembly. The platform moves with respect to the base to simulate a tire under load. The platform does this by deforming the cross section of the tire as if it were under a load on a road. The method for using the testing assembly includes taking measurements of the cross section of the tire in an un-deflected state and a deflected state. Calculations between the two states identifies areas in the tire that stresses are damaging.

Description:
BACKGROUND ART 
     1. Field of the Invention 
     The invention relates to tires of a motor vehicle. More specifically, the invention relates to testing stress levels along a periphery of a vehicular tire. 
     2. Description of the Related Art 
     Tires for a motor vehicle serve an essential part of the safety of the motor vehicle. In particular, the tires are responsible for ensuring the motor vehicle handles properly. Not only do the tires have an integral part in the proper handling, i.e., proper acceleration, deceleration and cornering, they also affect the ride and fuel consumption of the motor vehicle. Therefore, the tire provides the operator of a motor vehicle with a comfortable and fuel efficient motor vehicle. 
     Testing of the tire is important when determining the various properties of the tire. A tire undergoes a deformation during each rotation. Any abnormal deformation of the tire causes excessive stresses to occur and may lead to premature failure. The higher stresses and abnormal deformation lead to higher thermal generation. The key design characteristics for preventing the abnormal deformations are that of the carcass line and the mold contour. The carcass line is defined by the carcass, an element of the tire. The carcass extends between and is connected to the tire beads. The carcass extends through a tread portion of the tire substantially close to the inner surface of the tire. The mold contour includes the outer surface defined by the two sidewalls and the tread of the tire. 
     These two design characteristics are important in minimizing the abnormal deformations and, thus, high stresses and excess thermal energy generated by the tire under deformation. It would be beneficial to have a relatively simple test that can be utilized to evaluate the stresses of a tire when it is deformed. Such a test would allow a designer of a tire the ability to modify a mold contour with respect to a carcass extending through a carcass line to minimize stresses and enhance the performance and reliability of the tire. 
     U.S. Pat. No. 2,251,803, issued to Pummill on Aug. 5, 1941, discloses a tire tester. The tire tester tests a tire casing for structural defects while in place on a vehicle wheel mounted to a vehicle. The testing device includes a roller which is recessed within a pit for placement of a vehicle tire thereon. The roller is connected to a motor for variably controlling the velocity of the tire. The testing device further includes contact mechanisms, such as bellows, interconnected to a pressure gauge by a tube. The bellows are placed on either side of the tire in contact with the tread of the tire. When the testing device is activated, the tire begins rotating. The tire tester is a dynamic testing system. The bellows follow the contours of the tire and indicate any structural defects in the tire up on the pressure gauge. 
     The above-cited reference discloses a testing apparatus that relates only to bias tires. Radial tires were yet to be invented when the patent application was filed, 1937. The contour of the bias tire carcass and carcass line the column bigger when its inflation pressure becomes higher. Conversely, a radial tire, properly designed, does not sustain any significant change when inflated at various pressures. The invariance of the length of the radial carcass line in the presence of very stiff steel belts under the tread justify the fact that a simple one-inch radial tire section can adequately represent the tire contour in-service. This is not the case for a bias tire. Therefore, the testing apparatus of the Pummill &#39;803 reference is required for a bias tire because the full casing must be inflated under pressure before it can be properly evaluated. 
     SUMMARY OF THE INVENTION 
     A testing assembly calculates stress levels along a cross section of a pneumatic tire having tire beads, sidewalls, and the tread. The testing assembly includes a base defining a base surface. A plurality of mounts are slidably secured to the base surface. Each of the tire beads are secured to each of the plurality of mounts. The tire beads are mounted thereto in a manner to simulate the mounting of a tire to a rim of a wheel. The testing assembly also includes a platform that extends parallel to the base surface. The platform is engagable with the tread of the tire and is movable with respect to the base. The movement of the platform simulates the tire under a load by deforming the tire. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Advantages of the invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
     FIG. 1 is a perspective view, partially cut away, of one embodiment of a testing assembly according to the invention, 
     FIG. 2 is a cross-sectional side view, partially cut away, of a tire identifying a carcass line; 
     FIG. 3 is a schematic representation of factors measured to calculate stress levels according to one embodiment of the inventive method; 
     FIG. 4 is a schematic representation, partially cut away, of a deflected carcass line, used in the inventive method to calculate stress levels. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, one embodiment of a testing assembly according to the invention is generally indicated at 10. As shown in FIG. 1, the testing assembly  10  is framed within an attaché case  12 . The attaché case  12  includes a handle  14  and a lid  16 . The testing assembly  10  is designed to be easily transported. It should, however, be known to those skilled in the art that the testing assembly  10  may have many different sizes, limiting its portability. Further, while it is sure that the testing assembly  10  measures through mechanical means, it should also be apparent to those skilled in the art that electronic measuring devices may be incorporated into the invention  10  without adding to the inventive concept disclosed herein. 
     The testing assembly  10  does not require an entire tire for the testing thereof. The testing assembly  10  only requires a cross section  18  of a tire. In the embodiment shown in FIG. 1, the tire cross section  18  is approximately one inch thick. A simple one inch cross section  18  is adequate to test the entire tire due to the construction of the tire. More specifically, the radial configuration of today&#39;s tires allows a cross section thereof to accurately depict how the entire tire is going to react to different stress levels. 
     The cross section  18  of the tire includes two tire beads  20 , two sidewalls  22  and tread  24 . (A tire bead  20  is best seen in FIG. 2.) The outer periphery of the tire cross section  18  is referred to as the mold contour  26 . The cross section also includes a carcass, best seen via a representation of a carcass line  28  in FIG.  2 . The cross section  18  includes all of the parts of the tire and, therefore, accurately represents the complete tire. 
     The testing assembly  10  includes a base  30 . The base  30  defines a base surface  32 . The base includes gradations  34  allowing the testing assembly  10  to accurately reflect a particular configuration of a rim for the wheel to which the tire is designed to the mounted. 
     The testing assembly also includes a plurality of mounts  36 ,  38 . Each of the mounts  36 ,  38  include rim simulating portions  40 ,  42  and air pressure simulating portions  44 ,  46 . The rim simulating portions  40 ,  42  of the mounts  36 ,  38  are designed to simulate a rim to which the tire would be mounted. Likewise, the air pressure simulating portions  44 ,  46  of the mounts  36 ,  38  simulate the pressure that would be applied to a tire to force the tire beads  20  into a rim of a wheel. The force is created by the mounts  36 ,  38  to retain the tire beads  20  therein. Each of the mounts  36 ,  38  are slidable along the base  30  and may be measured out along the gradations  34 . While any type of securing device may be used, the embodiment shown in FIG. 1 shows the bolt  48 ,  50  and wing nut  52 ,  54  combination. The air pressure simulating portions  44 ,  46  includes slots  56 ,  58  allowing the air pressure simulating portions  44 ,  46  to move with respect to the bolt  48 ,  50 . The rim simulation portions  40 ,  42  are movable along the base  30  using pegs (not shown) which are insertable into a plurality of holes  60 . 
     The testing assembly  10  also includes a platform  62 . The platform  62  extends between first and second ends  64 ,  66 . The first and second ends  64 ,  66  are housed within side portions  68 ,  70  of a frame  72  that is fixedly secured to the base  30 . The platform  62  includes a tread engagement portion  74  that is generally equidistant from the first and second ends  64 ,  66 . The tread engagement portion  74  has a width that is greater than the width of the rest of the platform  62 . The tread engagement portion  74  extends into a channel  76 . The channel  76  is a guide for the platform  62  as it is moved. The movement of the platform  62  is limited to one direction wherein the platform  62  remains parallel to the base  30  at all times. 
     The platform  62  includes a support plate  78  secured thereto. The support plate  78  includes bolts  80 ,  82 . The support plate  78  is fixedly secured to the platform  62  via a platform extension (not shown). The platform extension extends between the platform  62  and the support plate  78 . The platform extension slides within the channel  76 . The support plate  78  holds the bolts  80 ,  82  in place allowing the bolts  80 ,  82  to force the tread  24  into abutment with the platform  62 . The support plate  78  ensures the tread  24  remains in abutment with the platform  62  to simulate the tread  24  engaging a driving surface out which the tire would be rotating therealong. 
     The testing assembly  10  operates by securing the cross section  18  of the tire into the mounts  36 . The tread  24  of the cross section  18  is secured to the platform  62 . The platform  62  is slid within the frame  72  which, in turn, deforms the cross section  18 . The deformation of the cross section  18  represents the tire to which the cross section  18  was taken as it transitions from an un-deflected state to a deflected state. As the cross section  18  becomes more deflected, it represents the tire as the tire is losing air pressure. 
     By viewing the cross section  18  as it moves through various degrees of deflection, measurements of the cross section  18  may be made. From the measurements of the mold contour  26  and the carcass line  28 , determinations may be made as to where the tire will fail due to the high stress levels the tire will generate during normal operation under normal load. 
     Referring to FIGS. 2 through 4, the cross section  18  is shown schematically. Further, the carcass  28  defines a carcass line (also  28 ) as represented by a series of points, M, extending along the carcass line  28 . When the testing assembly  10  is used, a plot of the curves representing the carcass line  28  and the mold contour  26  are made. FIG. 2 represents such a plot. (Inner surface  84  of the cross section  18  is shown in FIG. 2 for purposes of orientation. The surface  84  does not have to be plotted.) 
     The plot set forth above is used as a tire configuration identifying a first condition. This first condition is the condition of the tire being un-deflected. At this point, parameters of the tire in the first condition are measured. Referring to FIG. 3, the measurements taken include the radius of curvature, r, of various points along the carcass line  28  and the distance, t, between the carcass line  28  and the mold contour  26 . 
     The cross section  18  of the tire is then reconfigured to a second condition. The second condition represents the tire in a deflected state. Referring to FIG. 4, the carcass line  28  is shown in such a deflected state. Again, measurements are taken of the carcass line  28  and the mold contour  26  and the relationship therebetween, as was done prior. The relationship between the radius of curvature of the carcass line and various points in its un-deflected and deflected states identifies the stress levels of the tire with respect to specific points on the carcass line  28 . Graphically, a stress map (not shown) may be generated to better articulate the relative stresses along the cross section  18 . The radius of curvature r for each point M of the carcass line  28  is defined by the line OM. The tire thickness t is measured along a perpendicular at each point M on the carcass line  28 . Therefore, the thickness t is defined by MA for each point M. Then, upon deflection of the cross section  18 , the radius of curvature becomes r′, as is represented in FIG.  4 . Even through deflection, all other parameters remain equal. From these measurements, the relative stress levels for a particular location along the tire cross section  18  may be calculated using the equation set forth below:        S   =     Bt                   (       1     r   ′       -     1   r       )                              
     wherein B is the bending moment at each of the points M along the carcass line  28 . In practical terms, bending moments at the various points M are not significantly different. Therefore, with a satisfactory approximation, a common value of 1 can be assigned to the bending moments and the above equation becomes:        S   =     t                     (       1     r   ′       -     1   r       )     .                              
     As the level of stress grows for a particular location along the carcass line  28  with respect to neighboring locations of the carcass line  28 , failure points in the tire can be identified. Once the failure points are identified, the mold contour  26  may be modified with respect to the carcass line  28  to reduce the relative stress level of that particular location to a level similar to that of its neighboring locations. The carcass  28  should not be modified if the carcass  28  defines a carcass line that follows the Purdy theory, which was first articulated in 1928. 
     The invention has been described in an illustrative manner. It is to be understood that the terminology, which has been used, is intended to be in the nature of words of description rather than of limitation. 
     Many modifications and variations of the invention are possible in light of the above teachings. Therefore, within the scope of the appended claims, the invention may be practiced other than as specifically described.