Abstract:
A method of tire testing comprising applying a drive torque to a tire and a wheel assembly about an axis of rotation to drive the tire and wheel assembly and a rotatable drum with the tire in rolling contact with the rotatable drum; controlling a load pressure of the tire against the rotatable drum; and adjusting a lateral position of the tire across a surface of the rotatable drum.

Description:
BACKGROUND 
       [0001]    The present invention relates to a tire testing system that positions a rotating tire on a roadway simulator. More particularly, the present invention provides a lateral position control feature for a tire tread wear test machine. 
         [0002]    The testing of tires using a roadway simulator such as a drum or flat belt is known. During the testing, the tire is rotated against an outer surface of the roadway simulator that simulates various road pavements such as concrete or blacktop. The tire is typically mounted to a wheel assembly, the wheel assembly being forced toward the roadway simulator in order to apply radial loads upon the tire to simulate the weight of an automobile. 
         [0003]    The wheel assembly is mounted to an adjustable carriage for adjusting the axial position of the wheel assembly, and thus, when and with what force the tire contacts the roadway simulator. By varying the angular placement of the tire on the roadway simulator, tread wear, static and dynamic forces and moments, and other parameters required by specific testing practices can be measured. An example of a tire testing system can be seen in FIG. 1, taken from U.S. Pat. No. 5,481,907, the entirety of which is herein incorporated by reference. 
         [0004]      FIG. 1  illustrates a tire testing system  10  incorporating an adjustable wheel positioning assembly  12 . The adjustable wheel positioning assembly  12  is mounted and slides on rails  13  which in turn are fixed to a stationary frame  14 . The adjustable wheel positioning assembly  12  supports a wheel assembly  16  against a road wheel  18 . An outer perimeter surface  20  of the road wheel  18  contacts the tread of a tire  22  of the wheel assembly  16 . The outer surface  20  simulates various road surfaces such as black top or concrete. Tire radial loads are applied using a suitable servohydraulically controlled hydraulic actuator, attached to the adjustable wheel positioning assembly  12  and the frame  14 . The adjustable wheel positioning assembly  12  adjusts the position of the tire  22  on the outer surface  20 . In the embodiment illustrated, the adjustable wheel positioning assembly  12  adjusts the slip angle or steer of the tire  22 , which is the rotation of the tire  22  about an axis  24  in a direction indicated by double arrow  26 , the axis  24  being generally perpendicular to the contact patch of the tire  22  with the road surface  20 . In addition, the adjustable wheel positioning assembly  12  adjusts the camber angle of the tire  22  relative to the outer surface  20 . As illustrated, the camber angle is pivotal displacement of the tire  22  and axis  24  on the road wheel  18  to and away from the frame  14  in a direction indicated by double arrow  30 . 
         [0005]    The frame  14  includes suitable cross members  32  such that the frame  14  self-reacts all forces applied to the tire  22  by the system so that a special facility foundation is not required. A drive/braking unit  38  rotates or loads the roadwheel  18  through a drive belt  40  applying power or braking loads selectively to the roadwheel  18 . A direct drive or gear box would also be acceptable. A control system  44  having suitable analog and digital controls monitors system performance and provides command instructions to adjust speed of the roadwheel  18 , positioning of the tire  22  on the roadwheel  18  by the adjustable positioning of assembly  12 , and location of the adjustable wheel positioning assembly  12  on the frame  14 . An operator control center  48  connected to the control system  44  through signal lines  50  provides an interface for an operator. 
         [0006]    In a preferred embodiment, three additional adjustable tire positioning assemblies  52 ,  54  and  56  are provided to allow the system  10  to test four tires simultaneously. As illustrated, the adjustable wheel positioning assembly  52  is mounted to the frame  14  with slides, not shown, on a side opposite adjustable wheel positioning assembly  12 . The adjustable wheel positioning assembly  52  supports a wheel assembly  60  so that a tire  62  mounted thereto contacts the roadwheel  18 . The adjustable tire testing assemblies  54  and  56  are mounted to the frame  14  in a similar manner on opposite sides of a second roadwheel  64 . The second roadwheel  64  is rotated or loaded by a drive/braking unit  66  similar to drive/braking unit  38 . Flexible conduits  68 ,  70 ,  72  and  74  enclose data signal and control lines, not shown, allowing each of the adjustable tire testing assemblies  12 ,  52 ,  54  and  56 , respectively, to move relative to the frame  14 . 
         [0007]    The present invention provides an advantage over the design shown in  FIG. 1  by providing for lateral movement of the test tire over the surface of the road wheel. Moreover, one shortcoming of the illustrated design is the repeated use of the same circumferential surface area on the road wheel. 
       BRIEF DESCRIPTION 
       [0008]    The present invention is broadly directed to a tire wear test method including lateral motion control. More particularly, the invention is directed to a method of tire testing by applying a drive torque to a tire and a wheel assembly about an axis of rotation to drive the tire and wheel assembly against a rotatable drum while the tire is in rolling contact with the rotatable drum. The load pressure of the tire against the rotatable drum is controlled and the lateral position of the tire on the surface of the rotatable drum is varied. Preferably, the lateral position of the tire is varied in accord with a user-defined waveform. Advantageously, the surface of the drum can be formed by at least two different abrasive materials. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a perspective view of a prior art tire testing apparatus. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    A tire testing machine provides a simulated roadway surface coupled through suitable framework to a mounting for a rotating wheel and tire. The tire is capable of being moved under known loads into engagement with the simulated roadway, steered, and tilted in camber under positive control. The tire supporting framework is mounted relative to the roadway so that the camber loading axis and the steering axis define a plane and the steering axis remains in this plane while it is being loaded under camber. 
         [0011]    The present invention is directed to controlling the lateral position of a test tire with respect to the contact location with a test machine&#39;s road wheel. Prior art test machine carriages already perform many functions such as measuring and controlling the tire load (Fz), the slip angle (SA) of the tire and road wheel, the side force (Fy), braking or driving torque (My), and inclination angle (IA). In accord with the present invention the tire carriage is constructed to provide lateral tire motion relative to the road testing surface. More particularly, depending upon the width of the tire being tested and the width of the roadway surface, the lateral motion can be controlled such that the roadway surface is evenly used throughout the testing procedure. By controlling the position of the tire, the tire wear can be more uniformly and consistently generated since “tracks” or “grooves” are less likely to form on the abrasive surface. 
         [0012]    The present invention can further optimize use of the roadway surface by utilizing waveforms. This operating condition is advantageous because a linear ramp rate of the tire back and forth across the abrasive surface of the road wheel, does not necessarily optimize the usage of the surface. For example, the center portion of the roadway surface would experience the predominate wear. Accordingly, the lateral position control system has a digital control system which allows arbitrary waveforms to be defined with up to 1000 points and the amplitude and offset values to be independently controlled and saved. The attached graph illustrates a typical waveform that might be used for a tire with a fairly wide footprint width. The amplitude is lateral location of the center line of the tire contact region with respect to the road wheel. Therefore, 0% would be the center and +/−100% would be the extreme edges of the lateral motion. The period is the time required to complete one cycle, typically 5-10 minutes. In this case, the tire moves to the outer edge of the road wheel 10 times to prevent “tracks”, and then at the middle point of the period, it traverses to the inner edge of the road wheel and repeats the same process. Accordingly, a waveform having between 10 and 1000 waveform points can be employed. The cycle is continuously repeated until the wear test is completed. Variables such as the width of the tire footprint, the width of the abrasive surface, the total capability of the lateral motion, and even the width of the tire ribs all need to be considered to optimize the even usage or wear of the surface. 

 
         [0013]    By optimizing the shape of the waveform for the specific tread width of the test tire, excessive shoulder wear caused by testing a wide tire immediately after testing of narrower tires may be eliminated. Similarly, by properly controlling the lateral position of the tire to produce even usage of the entire roadway surface, the surface will need to be changed less often. 
         [0014]    The lateral position control aspect of the present invention also makes it possible to use two different abrasive surfaces on the same drum, such as a high micro content surface and a high macro surface, and spend a given percentage of the test time on each of the two surfaces. 
         [0015]    The tire wear testing machine of the present invention is similar in many ways to the apparatus of  FIG. 1 , is shown. However, the present machine includes an adjustable wheel positioning assembly that slides to bring a tire (not shown) into contact with a road wheel and includes means which permit controlled side-to-side movement of the wheel assembly relative to the wear surface. 
         [0016]    The present invention provides for several distinct advantages over the prior art. Unlike the prior art, the present invention controls the position of the tire and since it can also optimize the shape of the waveform used for the position control, the tire wear can be more uniformly and consistently generated since no “tracks” or “grooves” will be able to form on the abrasive surface. Moreover, by optimizing the shape of the waveform for the specific tread width of the test tire and the width of the roadway surface, the problem of excessive shoulder wear caused by testing a wide tire immediately after the testing of narrower tires will be eliminated. Also, by properly controlling the lateral position of the tire, the present invention produces even usage of the roadway surface. Due to even usage, the surface will not need to be changed as often, which will save both time and cost. Unlike the prior art, the lateral position control makes it possible to use two different abrasive surfaces on the same drum, such as a high micro content surface and a high macro surface, and spend a given percentage of the test time on each of the two surfaces. In addition, the lateral motion makes it possible to reproduce the actual behavior of tire motion associated with vehicle slipping laterally on the road. 
         [0017]    An exemplary embodiment has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the exemplary embodiment be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.