Lateral load tire testing system

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.

RELATED PATENT APPLICATIONS

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'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.

DETAILED DESCRIPTION OF THE INVENTION

With reference toFIG. 1, a lateral load tire testing system according to the concepts of the present invention is generally indicated by the numeral10. System10includes a frame11, which may include legs12and a header13that rests on top of the legs12. A motor14may be supported on frame11to drive a load assembly, generally indicated by the numeral15and described more completely below. Load assembly15may be provided within or adjacent frame11, and is used to apply a load to the tire T. The load assembly15may 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 assembly15may be used to dynamically load the tire T or simulate rolling conditions. To that end, load assembly15may include a rotatable load wheel16.

In the example shown, load wheel16may be rotatable about a center axis C at which a vertically extending plane V and a horizontally extending plane H intersect. The motor14may be connected to the load wheel by a suitable coupling (not shown) or directly drive the load wheel16to cause its rotation. A tire support assembly, generally indicated by the numeral20, is located radially outward of the load wheel16and configured to place a tire T in contact with the load assembly15. As shown, more than one tire support assembly20may be used with load assembly15to test more than one tire T at a time. In the example shown, a pair of tire support assemblies20are diametrically opposed, relative to load wheel16, and lie along the same horizontal plane H. In particular, the spindle21on 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 assembly20may be used. For sake of simplicity, the description will proceed with reference to only one tire support assembly20.

Turning toFIG. 2, tire support assembly20may be mounted on a subframe, generally indicated by the numeral25. The subframe25may pivot about a vertical pivot axis P that projects orthogonally from the horizontal plane H, where the tire T contacts the load wheel16. By pivoting the subframe25about this point, the machine10can 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 inFIG. 2and indicated by the reference letter TC. While only the tire T is shown in the cambered position TC, it will be appreciated that since the tire support assembly20is also mounted on the subframe25, its position will rotate as well. The tire support assembly20may be movable inward and outward relative to the load wheel16to adjust the loading on the tire T and remove the tire T from contact with the load wheel16at the conclusion of testing.

Tire support assembly20generally includes an arm22on which the spindle21is supported. Arm22may 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 arm22, as shown. In the example depicted inFIG. 3, the arm22is rotatably supported on a bearing portion24that rotates about an axis H extending through the center of the tire T and load wheel16. Any known actuator may be used to cause rotation of the arm22including, for example, a hydraulic cylinder26, as shown. In the example shown, hydraulic cylinder26is attached to the radial outward side of arm22relative to bearing portion24to provide the greatest leverage. Cylinder26is suitably attached to the arm22to allow the arm22to 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 frame23may 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. 3depicts the tire T rotated to a selected slip angle position indicated by the reference letter TS. 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 spindle21, as will be described more completely below.

With reference toFIGS. 1 and 2, it will be seen that a spindle housing27is supported on spindle frame23. The spindle housing27may be generally cylindrical in form and defines a cylindrical spindle bore28, best shown inFIG. 5. Spindle21is rotatably mounted within spindle bore28. The spindle housing27is a movable frame that responds to the loading of the tire T, as will be described more fully below. Relative movement between the spindle housing27and spindle frame23is detected to determine the force on tire T.

Spindle housing27includes a first support33that extends radially outward from spindle housing27. As best shown inFIG. 5, first support33may be provided with fastener receivers34used in attaching a load cell35to the spindle frame23. As shown, four first supports33may be provided and arranged in diametrically opposed pairs on the spindle housing27. Supports33advantageously provide rigidity, stability, and unity to spindle housing27improving the likelihood that accurate measurements may be obtained.

As best shown inFIG. 5, the centers36of first supports33are aligned with the spindle center S of the spindle along horizontal plane H (FIG. 2). In this way, the load wheel15, tire T, and load cells35all have centers aligned within horizontal plane H. By aligning these components straight line force measurements can be obtained. A second support38may extend downward from spindle frame23at a location corresponding to first support33. As in the case of first support33, more than one second support38may be provided, and be located opposite a corresponding first support33. Thus, in the example shown, four second supports38are arranged in pairs opposite four first supports33with a load cell35between each pair of supports33,38. The second support38is axially spaced such that the load cell35is received between the first and second supports33,38. Supports33,38are respectively attached to load cell35, such that, supports33,38are connected to each other by load cell35. Lateral loads on tire T cause movement of spindle frame23, which results in first support33moving relative to second support38. With the load cell35coupled to the supports33,38this movement results in a force being detected at load cell35. In this way the lateral load is directly transmitted to the load cell35via the spindle housing27and measured by load cell35without 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 inFIG. 8, second support38may have receivers39corresponding to those on the first supports33to facilitate the fastening of the load cells35thereto. As best shown inFIG. 4, suitable fasteners may run between the first and second supports33,38to fasten the first and second supports33,38together locking the movable spindle housing27to spindle frame23. Locking the spindle housing27to stationary spindle frame23may be desirable to avoid overloading of load cells35during camber testing.

Supports33,38are shown, for example, as having a generally rectangular form with flat inward faces37,39that extend generally parallel to each other. It will be appreciated that other support configurations may be used, as well.

With reference toFIG. 6, to ensure proper mounting of the load cells35, spacers40may be attached to one or more of the supports33,38. In setting up the load cells35, errant readings may be corrected by attaching a spacer40having a selected thickness42or grinding the spacer40until the appropriate reading is obtained.

To that end, readings from the load cells35may be electrically communicated along separate lines46to a junction box50that includes a switch51corresponding to each line46. As shown in the given example, there are four load cells35having four lines46running to four switches51at junction box50. Switches51may be used to separately view the signal produced by each load cell35to determine whether the proper support spacing has been provided or whether the load cell35is malfunctioning. For example, for a given load, load cells35each should provide the same signal. Therefore, if it is observed that one of the load cells35is producing a different signal, correction may be made by adjusting the spacer40until 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 switches51may be turned on and the signals from the load cells35combined and transmitted to a controller60along a single line61. Alternatively each load cell signal may be directly received and monitored by controller60. Controller60will be understood as generically referring to an instrument for receiving a signal from the load cell35. Controller60may simply display a force reading or provide further functions useful to the user. Thus, the type of controller60used is largely at the user's discretion. Consequently, a generic controller60is schematically represent inFIG. 1.

In operation, the lateral force tire testing system10of the present invention may move spindle frame23toward load wheel15to pre-load the tire T before testing. The load wheel15is rotated causing the tire T to rotate on spindle21. With the tire T aligned with load wheel15straight line performance of tire T may be observed at various speeds. To observe the tire T under steering conditions, the spindle frame23may be rotated about a horizontal axis to create a slip angle or steering angle, (tire TS) depicted inFIG. 3. Lateral forces likely to be generated during such testing would be observed by the load cells35. In particular, these forces would cause relative movement between spindle housing27and spindle frame23. Since these components each connect to load cells35, the relative movement would generate a corresponding force reading at load cell35. 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 TC(FIG. 3) relative to load wheel15. This may be achieved by rotating the subframe25supporting spindle frame23. With the camber angle α set, testing may proceed as described above. As mentioned, during camber testing, the spindle housing27may be locked to spindle frame23, as by fasteners coupling supports33,38to 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.