Abstract:
A lateral load testing system for testing a tire mounted on a rotatable spindle, the tire tester including a load assembly, a spindle frame having a support extending therefrom, a spindle housing defining a spindle bore adapted to rotatably receive the spindle, the spindle housing having a support opposite the support on the spindle frame, and a load cell located between the supports, where each support is attached to the load cell. The load cell is in electrical communication with a controller. The spindle frame is moveable to cause the tire to engage the load assembly, whereby lateral forces generated between the load wheel and tire are measured by the load cell and communicated to the controller.

Description:
RELATED PATENT APPLICATIONS 
   None. 
   TECHNICAL FIELD 
   In general, the present invention relates to a tire testing machine. In particular, the present invention relates to a tire testing machine that measures lateral forces on a tire during simulated operating conditions including steering and camber of the tire. 
   BACKGROUND OF THE INVENTION 
   Tire testing machines are used to measure forces generated between a tire and a testing surface, which often is a rotating wheel or drum, to evaluate tire performance, failure and endurance. While these machines are often used to evaluate uniformity of the tire, they may also be used to simulate road conditions and test reaction forces at the tire. For example, tire testing machines have been developed to measure lateral forces on the tire generated by steering and camber of the tire. These machines are useful in evaluating steering, camber, belt edge separation, and slip angle characteristics of the tire, among others. 
   Existing devices that measure lateral forces require complex calibration making it difficult to obtain reliable results in a consistent fashion. In particular, one existing design includes a tire mounted on a spindle that is rotatable within a bearing. Lubricating pockets are provided all along the length of the bearing to maintain the lubricating film. A load cell is provided around the spindle and measure variations in the loads created within the film. Changes in the film thickness resulting from operation of the testing machine and friction within the bearing causes errors in the forces read by the load cell. The presence of the lubrication pockets inherently causes changes in the film thickness along the length of the bearing and, thus, complex equations have been developed to eliminate these errors and attempt to ascertain a true force from the load cells. While meaningful measurements can be taken with this machine, zeroing of the machine to eliminate the aforementioned errors is time consuming and complicated. 
   Another known system, referred to as a “piezo-quartz” system, uses piezo-electric gauges to measure loads. In this design the piezo gauges are located around the spindle hub. Since the piezo-electric response requires periodic release of force on the cell to allow it to recharge, the system is not practical for long term force measurements. Also, for a given load, since the system&#39;s signal deteriorates with time. As a result of this drift, the piezo quartz system lacks the precision necessary for many testing applications. Consequently, there is a need for a simpler, more reliable lateral force tire testing machine. 
   SUMMARY OF THE INVENTION 
   In view of the foregoing, it is one object of the present invention to provide a more reliable lateral force tire testing machine. 
   It is another object of the present invention to provide a lateral force tire testing machine that includes a movable spindle assembly frame supported by load cells mounted to a rigid stationary frame. 
   In light of at least one of the foregoing objects, the present invention provides a lateral load tire testing system for testing a tire mounted on a rotatable spindle, the system including, a load assembly, a tire support assembly configured to place the tire in contact with the load assembly, wherein the tire support assembly includes a spindle frame and a spindle housing, the spindle frame having a support extending therefrom, the spindle housing defining a spindle bore adapted to rotatably receive the spindle, the spindle housing having a support opposite the support on the spindle frame, and a load cell located between and attached to the supports, the load cell being adapted to measure forces resulting from relative axial movement between the supports, the load cell being in electrical communication with a controller, whereby lateral forces are measured by the load cell and communicated to the controller. 
   The present invention further comprising a lateral load tire testing system for measuring lateral forces on a tire, the system includes, a load assembly engagable with the tire, a tire support assembly including, a spindle housing having a pair of first supports extending radially outward therefrom, a spindle adapted to support the tire, the spindle being rotatably supported on the spindle housing, a spindle frame having a pair of second supports extending outward therefrom opposite the first supports, wherein the first supports and second supports are coupled to each other, such that, the spindle frame supports the spindle housing yet allows the spindle housing to move axially relative to the spindle frame, and a pair of load cells supported by the first and second supports and adapted to detect forces at the tire from relative axial movement of the first and second supports. 
   The present invention further provides a method of measuring lateral loads on a tire including, providing a load assembly and a spindle located adjacent to the load assembly, the spindle being adapted to rotatably support the tire and selectively engage the tire with the load wheel, supporting the spindle in a spindle housing that is attached to a spindle frame yet movable axially relative thereto, and coupling a load cell to the spindle housing and spindle frame measuring axial loads generated by movement of the spindle housing relative to the spindle frame to determine lateral forces on the tire. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a complete understanding of the objects, techniques and structure of the invention, reference should be made to the following detailed description and accompanying drawings wherein: 
       FIG. 1  is a front elevational view of a tire testing machine according to the concepts of the present invention; 
       FIG. 2  is an enlarged top plan view of a tire testing machine according to the concepts of the present invention as might be seen along line  3 — 3  in  FIG. 2 ; 
       FIG. 3  is an enlarged top plan view similar to  FIG. 3  showing the tire in a rotated position to simulate steering; 
       FIG. 4  is a top plan view of a force measurement assembly according to the concepts of the present invention depicting a plurality of load cells mounted on a stationary frame; 
       FIG. 5  is an end elevational view of the force measurement assembly as might be seen along line  5 — 5  in  FIG. 4 ; 
       FIG. 6  is a side elevational view of the force measurement assembly as might be seen along line  6 — 6  in  FIG. 4 ; 
       FIG. 7  is an end elevational view as might be seen along line  7 — 7  in  FIG. 6 ; and 
       FIG. 8  is a front elevational view of a spindle support frame according to the concepts of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   With reference to  FIG. 1 , a lateral load tire testing system according to the concepts of the present invention is generally indicated by the numeral  10 . System  10  includes a frame  11 , which may include legs  12  and a header  13  that rests on top of the legs  12 . A motor  14  may be supported on frame  11  to drive a load assembly, generally indicated by the numeral  15  and described more completely below. Load assembly  15  may be provided within or adjacent frame  11 , and is used to apply a load to the tire T. The load assembly  15  may simply include a stationary surface, such as a plate (not shown) for applying static loads to the tire T and measuring the results of those loads. Also, as shown, a moving load assembly  15  may be used to dynamically load the tire T or simulate rolling conditions. To that end, load assembly  15  may include a rotatable load wheel  16 . 
   In the example shown, load wheel  16  may be rotatable about a center axis C at which a vertically extending plane V and a horizontally extending plane H intersect. The motor  14  may be connected to the load wheel by a suitable coupling (not shown) or directly drive the load wheel  16  to cause its rotation. A tire support assembly, generally indicated by the numeral  20 , is located radially outward of the load wheel  16  and configured to place a tire T in contact with the load assembly  15 . As shown, more than one tire support assembly  20  may be used with load assembly  15  to test more than one tire T at a time. In the example shown, a pair of tire support assemblies  20  are diametrically opposed, relative to load wheel  16 , and lie along the same horizontal plane H. In particular, the spindle  21  on which the tire T is mounted has a spindle center S that lies in the horizontal plane H of load wheel center C. It will also be appreciated that only a single tire support assembly  20  may be used. For sake of simplicity, the description will proceed with reference to only one tire support assembly  20 . 
   Turning to  FIG. 2 , tire support assembly  20  may be mounted on a subframe, generally indicated by the numeral  25 . The subframe  25  may pivot about a vertical pivot axis P that projects orthogonally from the horizontal plane H, where the tire T contacts the load wheel  16 . By pivoting the subframe  25  about this point, the machine  10  can test the tire T at a selected camber angle α. For purposes of illustration, a cambered position of the tire T is depicted in broken lines in  FIG. 2  and indicated by the reference letter T C . While only the tire T is shown in the cambered position T C , it will be appreciated that since the tire support assembly  20  is also mounted on the subframe  25 , its position will rotate as well. The tire support assembly  20  may be movable inward and outward relative to the load wheel  16  to adjust the loading on the tire T and remove the tire T from contact with the load wheel  16  at the conclusion of testing. 
   Tire support assembly  20  generally includes an arm  22  on which the spindle  21  is supported. Arm  22  may be made rotatable to allow variation in the slip angle of the tire T. Rotation of the tire T may be effected by any number of methods available within the art including rotation of the entire arm  22 , as shown. In the example depicted in  FIG. 3 , the arm  22  is rotatably supported on a bearing portion  24  that rotates about an axis H extending through the center of the tire T and load wheel  16 . Any known actuator may be used to cause rotation of the arm  22  including, for example, a hydraulic cylinder  26 , as shown. In the example shown, hydraulic cylinder  26  is attached to the radial outward side of arm  22  relative to bearing portion  24  to provide the greatest leverage. Cylinder  26  is suitably attached to the arm  22  to allow the arm  22  to be moved through the desired slip angle range and held at a selected slip angle or reciprocated for continuous steering movements. As the tire T is loaded, any variation in the slip angle may be measured, or spindle frame  23  may be rotated to a selected position to provide a selected slip angle to measure loads for that selected slip angle. Finally, the tire T may be rotated through a selected angular range in a reciprocal fashion to perform endurance testing of the tire T under steering conditions. In each case, rotation of the tire T is about an axis extending through pivot axis P and within plane H.  FIG. 3  depicts the tire T rotated to a selected slip angle position indicated by the reference letter T S . It will be appreciated that the tire T may be rotated through any angular position or range, as desired by the user. Forces resulting from such movements may be measured directly at the spindle  21 , as will be described more completely below. 
   With reference to  FIGS. 1 and 2 , it will be seen that a spindle housing  27  is supported on spindle frame  23 . The spindle housing  27  may be generally cylindrical in form and defines a cylindrical spindle bore  28 , best shown in  FIG. 5 . Spindle  21  is rotatably mounted within spindle bore  28 . The spindle housing  27  is a movable frame that responds to the loading of the tire T, as will be described more fully below. Relative movement between the spindle housing  27  and spindle frame  23  is detected to determine the force on tire T. 
   Spindle housing  27  includes a first support  33  that extends radially outward from spindle housing  27 . As best shown in  FIG. 5 , first support  33  may be provided with fastener receivers  34  used in attaching a load cell  35  to the spindle frame  23 . As shown, four first supports  33  may be provided and arranged in diametrically opposed pairs on the spindle housing  27 . Supports  33  advantageously provide rigidity, stability, and unity to spindle housing  27  improving the likelihood that accurate measurements may be obtained. 
   As best shown in  FIG. 5 , the centers  36  of first supports  33  are aligned with the spindle center S of the spindle along horizontal plane H ( FIG. 2 ). In this way, the load wheel  15 , tire T, and load cells  35  all have centers aligned within horizontal plane H. By aligning these components straight line force measurements can be obtained. A second support  38  may extend downward from spindle frame  23  at a location corresponding to first support  33 . As in the case of first support  33 , more than one second support  38  may be provided, and be located opposite a corresponding first support  33 . Thus, in the example shown, four second supports  38  are arranged in pairs opposite four first supports  33  with a load cell  35  between each pair of supports  33 ,  38 . The second support  38  is axially spaced such that the load cell  35  is received between the first and second supports  33 ,  38 . Supports  33 ,  38  are respectively attached to load cell  35 , such that, supports  33 ,  38  are connected to each other by load cell  35 . Lateral loads on tire T cause movement of spindle frame  23 , which results in first support  33  moving relative to second support  38 . With the load cell  35  coupled to the supports  33 ,  38  this movement results in a force being detected at load cell  35 . In this way the lateral load is directly transmitted to the load cell  35  via the spindle housing  27  and measured by load cell  35  without the frictional influences found in prior art devices. As a result of this direct measurement, more reliable and precise force measurements are obtained. 
   As best shown in  FIG. 8 , second support  38  may have receivers  39  corresponding to those on the first supports  33  to facilitate the fastening of the load cells  35  thereto. As best shown in  FIG. 4 , suitable fasteners may run between the first and second supports  33 ,  38  to fasten the first and second supports  33 ,  38  together locking the movable spindle housing  27  to spindle frame  23 . Locking the spindle housing  27  to stationary spindle frame  23  may be desirable to avoid overloading of load cells  35  during camber testing. 
   Supports  33 ,  38  are shown, for example, as having a generally rectangular form with flat inward faces  37 ,  39  that extend generally parallel to each other. It will be appreciated that other support configurations may be used, as well. 
   With reference to  FIG. 6 , to ensure proper mounting of the load cells  35 , spacers  40  may be attached to one or more of the supports  33 ,  38 . In setting up the load cells  35 , errant readings may be corrected by attaching a spacer  40  having a selected thickness  42  or grinding the spacer  40  until the appropriate reading is obtained. 
   To that end, readings from the load cells  35  may be electrically communicated along separate lines  46  to a junction box  50  that includes a switch  51  corresponding to each line  46 . As shown in the given example, there are four load cells  35  having four lines  46  running to four switches  51  at junction box  50 . Switches  51  may be used to separately view the signal produced by each load cell  35  to determine whether the proper support spacing has been provided or whether the load cell  35  is malfunctioning. For example, for a given load, load cells  35  each should provide the same signal. Therefore, if it is observed that one of the load cells  35  is producing a different signal, correction may be made by adjusting the spacer  40  until the load cell output matches that of the other cells. Once all of the cells have been calibrated and determined to be functioning properly, all of the switches  51  may be turned on and the signals from the load cells  35  combined and transmitted to a controller  60  along a single line  61 . Alternatively each load cell signal may be directly received and monitored by controller  60 . Controller  60  will be understood as generically referring to an instrument for receiving a signal from the load cell  35 . Controller  60  may simply display a force reading or provide further functions useful to the user. Thus, the type of controller  60  used is largely at the user&#39;s discretion. Consequently, a generic controller  60  is schematically represent in  FIG. 1 . 
   In operation, the lateral force tire testing system  10  of the present invention may move spindle frame  23  toward load wheel  15  to pre-load the tire T before testing. The load wheel  15  is rotated causing the tire T to rotate on spindle  21 . With the tire T aligned with load wheel  15  straight line performance of tire T may be observed at various speeds. To observe the tire T under steering conditions, the spindle frame  23  may be rotated about a horizontal axis to create a slip angle or steering angle, (tire T S ) depicted in  FIG. 3 . Lateral forces likely to be generated during such testing would be observed by the load cells  35 . In particular, these forces would cause relative movement between spindle housing  27  and spindle frame  23 . Since these components each connect to load cells  35 , the relative movement would generate a corresponding force reading at load cell  35 . These forces may be monitored continuously as a variety of steering conditions are made including a fixed slip angle or cyclical movement of the tire T through positive and negative slip angles measured relative to a vertical plane passing through the tire T. Also, as mentioned previously, changes in the slid angle in response to a given load may be measured. Therefore, slip angle and load measurements may be made independently of each other or combined during movement of the tire T through a range of slip angles. 
   Similarly, camber angle testing may be performed by rotating the tire T about a pivot axis P to a position T C  ( FIG. 3 ) relative to load wheel  15 . This may be achieved by rotating the subframe  25  supporting spindle frame  23 . With the camber angle α set, testing may proceed as described above. As mentioned, during camber testing, the spindle housing  27  may be locked to spindle frame  23 , as by fasteners coupling supports  33 ,  38  to each other, to reduce the likelihood of load cell overload. 
   In light of the foregoing, it should thus be evident that a lateral load tire testing system according to the concepts of the present invention substantially improves the art. While, in accordance with the patent statutes, only the preferred embodiment of the present invention has been described in detail hereinabove, the present invention is not to be limited thereto or thereby. It will be appreciated that various modifications may be made to the above-described embodiment without departing from the spirit of the invention. Therefore, to appreciate the scope of the invention, reference should be made to the following claims.