Abstract:
A system and method for assessing a health and functionality of a locomotive friction modifying system wherein the locomotive has a friction modifying applicator associated with a wheel of the locomotive for applying a friction modifying agent to a rail on which the wheel is traversing. The system and method comprise a sensor detecting a predetermined operational condition of the locomotive. The system and method also comprise a controller associated with the sensor and responsive to input from the sensor determining a per unit creep of an axle of the locomotive. The controller also determines a tractive effort of the axle of the locomotive and determines a friction modifying applicator state for the applicator associated with the axle. The controller further compares the determined per unit creep of the axle, the tractive effort of the axle and the state of the friction modifying applicator associated with the axle to a predetermined value indicative of the health and functionality of the locomotive friction modifying system. The controller provides an indication of the health and functionality of the locomotive friction modifying system.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims priority to U.S. Provisional Patent Application No. 60/391,743, filed on Jun. 26, 2002, the entire disclosure of which is incorporated herein by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The invention relates generally to railroad friction modifying systems. More particularly, the invention relates to systems and methods for automatically detecting the health and functionality of a locomotive friction modifying system, as well as components thereof.  
         DESCRIPTION OF THE PRIOR ART  
         [0003]    Locomotives used for heavy haul applications typically must produce high tractive efforts. The ability to produce these high tractive efforts depends on the available adhesion between the wheel and rail. Many rail conditions (especially wet), require an application of sand to improve the available adhesion. Therefore, locomotives typically have sandboxes on either end of the locomotives, and have nozzles to dispense this sand (both manually and automatically) to the rail on either side of the locomotive.  
           [0004]    [0004]FIG. 1 illustrates a typical prior art locomotive having a sanding system for applying sand to the rails. Sand is stored in a short hood sandbox  118  or a long hood sandbox  120 . The illustrated example includes eight sand nozzles  102 - 116 . Locomotive  122  has two trucks, front truck  124  and rear truck  126 . Additionally, front truck  124  has a front truck forward  30  and a front truck rear axle  132 . Rear truck  126  has a rear truck front axle  134  and a rear truck rear axle  136 . Front truck  124  has one nozzle in the front left  102 , one nozzle in the front right  104 , one nozzle in the rear left  106 , and one nozzle in the rear right  108 . The rear truck  126  similarly has one nozzle in the front left  110 , one nozzle in the front right  112 , one nozzle in the rear left  114 , and one nozzle in the rear right  116 . Chart  128  of FIG. 1 illustrates when each of the nozzles are active. For example, sand nozzle  114  is active in the reverse direction if “lead axle sand,” “auto sand,” or “trainline sand” is enabled. The sand function “lead axle” means sand is applied in front of the leading locomotive axle only and is enabled manually by the operator. The sand function “trainline” means sand is applied in front of both locomotives and is enabled manually by the operator. The sand function “automatic” means sand is applied in front of both locomotives automatically.  
           [0005]    [0005]FIG. 2 illustrates a prior art schematic diagram of the sanding system  200  of FIG. 1. The system  200  includes a compressed air reservoir  202 , one sandbox for each truck, front sandbox  204  and rear sandbox  206 , one manual air valve for each truck, valve  208  for the front truck  124  and valve  210  for the rear truck  126 . The system also includes two electrically controlled sand valves for each truck, valves  212  and  214  for the front truck and valves  216  and  218  for the rear truck. The system has two nozzles for each of these electrically controlled sand valves, nozzles  102  and  104  for the forward front truck valve  212 , nozzles  106  and  108  for the reverse front truck valve  214 , nozzles  110  and  112  for the forward rear truck valve  216 , and nozzles  114  and  116  for the reverse rear truck valve  218 . A locomotive control system  220  enables the appropriate sand valves based on the inputs from the operator or train lines, or when an adhesion control system determines that the rail conditions are poor and sanding will yield a higher tractive effort.  
           [0006]    In the prior art, the sandboxes are periodically inspected to determine sand level. Based on the periodic inspection, the sandboxes are filled if needed. If sand runs out between inspections, however, there is no indication to the operator. Similarly, if a valve is not functioning or if a sand nozzle or any of the piping is blocked, sand delivery is adversely affected. Such problems can result in a locomotive not producing enough tractive effort and may cause train stall and undue delays for a whole railroad system. In the prior art, such problems are detected only at an inspection time. This is true for other prior art friction modifying systems as well.  
         BRIEF DESCRIPTION OF THE INVENTION  
         [0007]    Therefore, there is a need for an improved system and method for automatically detecting the condition of a locomotive friction modifying system, as well as components thereof. Such a system and method monitors and assesses the effects of attempted friction modifying applications, for the purpose of friction enhancement/reduction control, so as to determine if a friction modifying agent actually was delivered to the desired wheel-rail interface.  
           [0008]    One aspect of the invention provides a system for assessing a health and functionality of a locomotive friction modifying system wherein the locomotive has a friction modifying applicator associated with a wheel of the locomotive for applying a friction modifying agent to a rail on which the wheel is traversing. The system comprises a sensor for detecting a predetermined operational condition of the locomotive. The system also comprises a controller associated with the sensor and responsive to input from the sensor for determining a per unit creep of an axle of the locomotive. The controller also determines a tractive effort of the axle of the locomotive and determines a friction modifying applicator state for the applicator associated with the axle. The controller further compares the determined per unit creep of the axle, the tractive effort of the axle and the state of the friction modifying applicator associated with the axle to a predetermined value indicative of the health and functionality of the locomotive friction modifying system. The controller provides an indication of the health and functionality of the locomotive friction modifying system.  
           [0009]    In another aspect of the invention, a method is provided for assessing health and functionality of a locomotive friction modifying system wherein the locomotive has a friction modifying applicator associated with a wheel supported on an axle of the locomotive for applying a friction modifying agent to the rail on which the wheel is traversing. The method comprises determining per unit creep of an axle of the locomotive, determining a tractive effort of the axle of the locomotive, and determining a friction modifying applicator state for the applicator associated with the axle. The method further comprises comparing the determined per unit creep of the axle, tractive effort of the axle, and state of the friction modifying applicator associated with the axle to a predetermined value indicative of the health and functionality of the locomotive friction modifying system. The method also provides an indication of the health and functionality of the locomotive friction modifying system. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is a schematic illustration of a prior art locomotive having a sanding system.  
         [0011]    [0011]FIG. 2 is a schematic further illustrating the sanding system of FIG. 1.  
         [0012]    [0012]FIG. 3 illustrates exemplary adhesion versus creep curves for different rail conditions.  
         [0013]    [0013]FIG. 4 illustrates exemplary friction/adhesion curves with and without sand applied in front of an axle during wet rail conditions.  
         [0014]    [0014]FIG. 5 is a graphic illustration of the effect of sand state change when the sand valve is moved from off to on at the wheel/rail interface and adhesion/creep changes.  
         [0015]    [0015]FIG. 6 is a graphic illustration of the effect of sand state change when the sand valve is moved from on to off at the wheel/rail interface and adhesion/creep changes.  
         [0016]    [0016]FIG. 7 is a relationship diagram illustrating relationships between (a) the tractive effort, (b) creep of axles ( 1 ,  3 ,  4 , and  6 ), and (c) sand valve command states on the health of sanding (front truck forward, front truck reverse, rear truck reverse and rear truck forward) and the sandboxes (front and rear).  
         [0017]    [0017]FIG. 8 is a logic diagram illustrating a sand health determination at an exemplary axle location (axle 1).  
         [0018]    [0018]FIG. 9 is a control state diagram for determining the health of a nozzle.  
         [0019]    [0019]FIG. 10 illustrates six sand health state integrators.  
         [0020]    [0020]FIG. 11 illustrates sand health update logic for an OFF to ON transition of the sanding system command.  
         [0021]    [0021]FIG. 12 illustrates sand health update logic for an ON to OFF transition of the sanding system command.  
     
    
     DETAILED DESCRIPTION  
       [0022]    Although the following detailed description is, for the most part, limited to sanding systems, it is to be understood that the systems and methods of the present invention apply equally well to other friction modifying agents such as, air, steam, water, lubricating fluid, or oil and includes agents that increase or decrease friction or remove another friction modifying agent.  
         [0023]    One way to assess the health of a locomotive sanding system is to recognize a change in friction that occurs when sand is introduced to the wheel/rail interface. FIG. 3 illustrates exemplary adhesion versus creep curves, identifying differences in friction or available adhesion for different potential rail conditions. As illustrated, curve  302  depicts the adhesion characteristics of dry sand that provides the highest level of adhesion for each level of per unit creep especially at per unit creep levels of less than 0.2. For per unit of creep levels of less than 0.05, wet sand as depicted by curve  304  provides a higher adhesion than a dry rail as shown by curve  306 . However, at per unit creep levels greater than 0.05, wet sand curve  304  has less adhesion than the dry rail curve  306 . For the situations where less adhesion is desirable, as is the case for connected railway cars or a locomotive rounding a curve in a track, oil as depicted by curve  308  provides the least amount of adhesion for per unit creep less than 0.1. Curve  310  illustrates the adhesion characteristics of water that also provides improved reduced friction as compared to a dry rail (curve  306 ) for per unit creep.  
         [0024]    [0024]FIG. 4 illustrates exemplary friction/adhesion curves that may exist with and without sand applied in front of an axle during wet rail conditions. Chart  400  illustrates two changes in the operating point of a wheel on a wet rail when sand is applied to the wet rail (curve  402 ) and when sand is removed from the rail (curve  404 ). For example, if sand is applied to a wet rail at point  406  on water curve  310 , curve  402  illustrates that the creep decreases to point  408 , a point on wet sand curve  304 . Similarly, if water is applied to a rail operating at point  408  on the wet sand curve  304 , the removal of the wet sand moves the creep from point  408  to point  406  on curve  310 , thereby indicating a significant increase in creep. FIG. 4 also illustrates optimal adhesion control system performance—creep is controlled such that maximum tractive effort is attained (assuming that the operator is calling for more tractive effort than what can be sustained by the rail conditions). In this illustration, a locomotive is applying 17,000 pounds of tractive effort. However, at point  406  the rail is wet and the wheels are experiencing a per unit creep of more than 0.14. Sand is applied immediately prior to the advancing wheel of the locomotive. As a result, at point  408  tractive effort is increased to 20,000 pounds and per unit creep is reduced to less than 0.03. If the sand is later removed, the operating point returns from point  408  to the prior operating point  406 . Creep is controlled such that maximum tractive effort is attained (assuming that the operator is calling for more tractive effort than what can be sustained by the rail conditions). Therefore, such a change can be observed by the adhesion control system only when the available adhesion at the wheel is utilized by the wheel and it typically happens at high tractive effort, low speed operating conditions. At other operating conditions the tractive effort versus creep characteristics change but not as dramatically.  
         [0025]    In order to detect the application of sand to the rail, it is not required to fully understand the precise nature of the change in adhesion curves as previously shown. Any change in the friction/creep characteristics associated with sand state changes signifies the effect of sand. For example, if the rail conditions were such that upon application of sand the available adhesion or friction was to be reduced, this would also be detectable. FIG. 5 summarizes certain conclusions that may be drawn from the changes in tractive effort and creep that occur when sand is successfully applied to the wheel/rail interface. FIG. 5 illustrates the effect of sand state change when the sand valve is moved from off to on at the wheel/rail interface and adhesion/creep changes. The change in tractive effort is the vertical axis  502  and is charted as a function of the change in percentage creep the horizontal axis  504 . As shown, where there is a positive change of tractive effort and positive change in creep or a negative change of tractive effort and negative change in creep, then there is weak evidence that sand is functional (weak evidence regions indicated as  506  and by the vertical lines). However, when there is a positive change in the tractive effort and a negative change in the creep (section  514 ), sand increases adhesion and there is strong evidence that the sand system is functional and delivering sand as required (strong evidence regions indicated by  514  and the horizontal lines). Similarly when there is a negative change in the tractive effort and a positive change in the creep (section  512 ) as when sand decreases adhesion, there is also strong evidence  510  that the sand system is functional. When the change in tractive effort and change in creep is small, whether each is positive and/or negative, this is evidence that the sand system is not functional as indicated by section  508  with the diagonal lines.  
         [0026]    Referring similarly to FIG. 6, the effect of sand state change when the sand valve is moved from on to off at the wheel/rail interface and adhesion/creep changes is illustrated. In this case, when there is a positive change in tractive effort and a negative change in creep, sand decreases adhesion (section  604 ) and there is strong evidence that the sand system is functional (indicated by  510 ). Similarly, when there is a negative change in tractive effort and a positive change in the creep, sand increases adhesion (section  602 ) and there is also strong evidence that the sand is functional (also indicated by  510 ). As with FIG. 5 above, when both the change in tractive effort and change in creep are either both positive or both negative, there is weak evidence  506  that the sand is functional. Additionally, when there is only a small change in both, whether positive or negative, then the sand system is not functional  508 .  
         [0027]    Analyzing the effect of adhesion/creep changes associated with manual, trainline, and/or automatic sand on each wheel, depending on the axle and direction of travel, provides an indication of the effectiveness of the sanding system. Such information can also be used to determine the state/health of the sandboxes, the sand valves, and/or the sand nozzles. Creep of an axle is the difference in speed of a wheel associated with the axle and the locomotive. Per unit creep is the ratio of creep to locomotive speed. Per unit creep of each axle “n” is calculated (sometimes identified herein as “creep_pu[n]”). The tractive effort of each axle (sometimes identified herein as “te[n]”) is obtained from torque produced by each motor and the knowledge of wheel diameter and gear ratio. These te and creep calculations and changes associated with a sanding state change are used to determine the health of the sanding components of each truck, in each direction and for each sandbox.  
         [0028]    Table 1, as provided at the end of the specification, provides a list of potential failure modes that correlates those modes to the sand nozzles affected by the failure modes. For example, if the front truck sandbox is closed (blocked), then nozzles  102 ,  104 ,  106 , and  108  are affected.  
         [0029]    Table 2, as provided at the end of the specification, identifies relationships between phenomena detected and the potential failure modes causing each detected phenomenon. For example, if axle 1 friction indicates no sand in the forward direction, then the reasons could be (a) the front truck manual air valve is closed, (b) the front truck forward sand solenoid valve is failed, or (c) the front truck sandbox is blocked.  
         [0030]    [0030]FIG. 7 is a relationship diagram illustrating relationships between (a) the tractive effort, (b) creep of axles ( 1 ,  3 ,  4 , and  6  which correspond to axles  130 ,  132 ,  134 , and  136 , respectively), and (c) sand valve command states on the health of sanding (front truck forward, front truck reverse, rear truck reverse and rear truck forward) and the sandboxes (front and rear). Sensor  446  detects input to the front truck forward system  702 . These inputs include the front truck forward command  710 , the tractive effort of axle 1 ( 718 ), and the per unit creep of axle 1 ( 726 ). Sensor  748  collects inputs to axle 3 for the front truck reverse system  704  including the front truck reverse command  712 , the tractive effort  720 , the per unit creep  728  for axle 3. Sensor  750  detects input to the rear truck forward system  706 . These inputs include the rear truck forward reverse  714 , the tractive effort of axle 6 ( 722 ), and the per unit creep of axle 6 ( 730 ). Sensor  752  collects inputs to axle 4 for the rear truck forward system  708  including the rear truck forward command  716 , the tractive effort  724 , and the per unit creep  732  for axle 4.  
         [0031]    The front truck forward system  702  analyzes the data and outputs the sand health for the front truck forward (FTF)  734 . The front truck reverse (FTR) system  704  analyzes the data and outputs the sand health for the front truck reverse  736 . Both of these are provided inputs to the front sandbox health determination system  754  that outputs the sand health front box  738 . Similarly, the rear truck reverse (RTR) system  706  analyzes the data and outputs the sand health for the rear truck reverse  740 . The rear truck forward (RTF) system  708  analyzes the data and outputs the sand health for the rear truck forward  742 . Both of these are provided inputs to the rear sandbox health determination system  756  that outputs the sand health rear box  744 .  
         [0032]    In FIG. 7, only an axle immediately following the sand nozzle is used since that axle experiences the greatest change, even though other axles may also experience the effect of sanding. A slight variation of this method would be the use of information from multiple axles and aggregate the information such as by using the average or mean of the information from multiple axles. FIG. 7 further assumes that a single nozzle failure (e.g., due to misalignment, blockage, etc.) is detected by the axle  1  torsional vibration.  
         [0033]    [0033]FIG. 8 is a logic diagram  800  illustrating a sand health determination at one exemplary axle nozzle location for the first axle, e.g., axle 1 of the front truck forward (FTF). The inputs are the tractive effort of the first axle  710 , per unit creep of the first axle  726 , and the command to the front truck forward sander  710 . The creep  726  and tractive effort  710  are filtered by a low pass filter (LPF) and the absolute value (ABS) is sampled synchronously with the sander command changes by sample and hold systems  804  and  802 , respectively. When the process is enabled (EN), the outputs include the previous creep values creep pre  816  and the previous tractive effort_pre  814  are integrated by creep integrator  808  and tractive effort integrator  806  to produce the delta creep  812  and the delta tractive effort  810 , e.g., the change of creep and tractive effort. These changes are input into the front truck forward state machine  702 . The front truck forward state machine  702  also receives the front truck forward command and new factor and generates the sand health front truck forward  734 . Similar processes are used for each of the other axle systems. The logic used here is shown and described for a six axle locomotive but it is contemplated that four or eight axle locomotives can similarly be controlled.  
         [0034]    [0034]FIG. 9 is a control state diagram  900  illustrating a determination of the health of one of the nozzle locations. The illustrated example depicts the front truck in the forward direction, i.e., first axle sanding system. These state machines control a set of sand health state integrators, which are illustrated in FIG. 10. The system starts in the OFF state  902 . When the front truck forward  710  is commanded from OFF to ON, the system changes state to the TOWARD ON  904 . Once time exceeds timer  1  ( 914 ) which has a predetermined time such as 5 seconds, then the system changes state to ON SAND CHECK  906 . Of course if the front truck forward command  710  is changed to the off state before the timer exceeds 5 seconds, the system returns to the OFF state  902 . The ON SAND CHECK  906  changes to ON state  908  when the new factor is less than 0.1 and the update sand health front truck forward  734  and the tractive effort and creep integrators as reset. When the front truck forward command  710  is changed to off and second timer  916  is started and the system changes to the TOWARD OFF  910  state. If the front truck forward command  710  is changed to on, the state changes back to the ON state  908 . If the time interval exceeds the predetermined value of the second timer  916 , then the system changes to OFF SAND CHECK state  912 . In the OFF SAND CHECK state  912  new factor is less than 0.1, the sand health front truck forward is updated and the tractive effort and creep integrators are reset and the state changes to the OFF state  902 . Similar state change diagrams apply to each of the other sand health systems.  
         [0035]    Six sand health state integrators are shown in FIG. 10. They are sand health front truck forward  734  integrator  1002 , sand health front truck reverse  736  integrator  1006 , sand health rear truck forward  742  integrator  1004 , sand health rear truck reverse  740  integrator  1008 , sand health front box  738  integrator  1010 , and sand health rear box  744  integrator  1012 . The appropriate integrators are enabled based on the sand health determination state diagram as illustrated in FIG. 9. These integrators are limited to values of +/−1. A “+1” value indicates that the health of the associated sanding system (for example the forward sander in the front truck) is completely healthy or functional. A “−1” value indicates that the sanding system is not functioning. A health state value of “0” indicates that there has not been enough information to determine the health of the system. Preferably, the integrators are always enabled and are incremented or decremented by the various state machines. As time progresses with no sand state changes, the health indicators slowly return to a value of 0 at a predetermined time constant (for example 10 hours). This is done so that if no sand state changes have happened recently, it is possible for the health of the sanding system to change (e.g., due to freezing, repairing, an addition of sand, and so on), and under this condition the health returns to an indication corresponding to unknown. If at any time the health has fallen below a predetermined level, the appropriate personnel (e.g., an operator, a designated maintainer, remote monitoring equipment or remote monitoring personnel) are preferably informed so that they can take appropriate action.  
         [0036]    [0036]FIG. 11 illustrates sand health update logic for an OFF to ON transition of the sanding system command. The thresholds and health increments are shown for exemplary purposes only. The sand health update logic uses percentage change in tractive effort and percentage change in creep when the sand logic command changes from OFF to ON. The logic uses a tractive effort change ratio and creep change ratio. The tractive effort change ratio is a ratio of the tractive effort change to the maximum value of tractive effort obtained around the command transition. An absolute minimum value of tractive effort is assumed to avoid a large per unit change calculation error caused by measurement errors. The previous tractive effort  814  and input along with the change in tractive effort  810  and compared with the maximum value at  1002 , which is shown for illustrative purposes as the value  5000 . This is compared with the minimum at  1110  and the current value of the tractive effort  1106  is output. Similarly, the ratio of creep change around the command transition is also calculated. The previous creep value  816  is input along with the change in creep  812  to a maximum determination function  1104 . This determination is input to the minimum value function  1112  and compared to a minimum value, shown in FIG. 11 as 0.1 for illustrative purposes. A current value of the creep  1108  is determined. The current values of the tractive effort  1106  and creep  1108  are compared to the changes in tractive effort and creep in table  1104  where a determination is made regarding the functional effectiveness of the sand system. As shown in FIG. 10, the ratio changes can be shown as regions in chart  1106  (Similar to previous FIG. 5). Each region can be classified as (a) strong evidence that the sand system is functional  510 , (b) weak evidence that the sand system is functional  506 , or (c) evidence that the sand system is determined to be nonfunctional  508 .  
         [0037]    Similarly, FIG. 12 illustrates sand health update logic for OFF to ON transition. The change in the tractive effort  810 , change in creep  812 , the current tractive effort value  1106  and the current creep value  1108  are determined as discussed above with regard to FIG. 11. In table  1102 , the health value is decremented or incremented based on the determination of the functional effectiveness. The chart  1204  is similar to FIG. 5 above showing graphically the various regions. In this process, three levels are determined and, based on these levels, the health values changed by a certain increment. While the system discloses using discrete increments, a continuous health value change is possible with this system.  
         [0038]    In addition to these effects, a single sand nozzle failure can cause a torsional vibration due to an unequal adhesion/friction coefficient between the left and right side wheel rail interface. The axle immediately following the failed sand nozzle typically encounters this phenomenon more than any other axle. Such torsional vibration causes resonance of the wheel/axle set at its natural frequency. This resonance can be detected by observing the frequency content in the torque or speed feedback of that axle and can directly indicate a nozzle health. Any change in resonance torque or speed immediately following a sand command state change is used to determine the health of the sand nozzles in front of the axle.  
         [0039]    When introducing elements of the present invention or the embodiment(s) thereof, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.  
         [0040]    As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.  
                                                                                                                             TABLE 1                           Relationship Between Failure Modes and Nozzles            Failure           Nozzle Affected            Mode #   Device   Condition   102   104   106   108   110   112   114   116                    1   Front Truck Manual   Closed   x   x   x   x                           Air Valve       2   Rear Truck Manual   Closed                   x   x   x   x           Air Valve       3   Front Truck Forward   Failed open or   x   x           Sand Solenoid Valve   closed       4   Front Truck Reverse   Failed open or           x   x           Sand Solenoid Valve   closed       5   Rear Truck Reverse   Failed open or                   x   x           Sand Solenoid Valve   closed       6   Rear Truck Forward   Failed open or                           x   x           Sand Solenoid Valve   closed       7   Front Truck Sand Box   Failed open or   x   x   x   x               closed       8   Rear Truck Sand Box   Failed open or                   x   x   x   x               closed       9   Front Truck Forward   Flow blocked or   x           Right Nozzle   poor alignment       10   Front Truck Forward   Flow blocked or       x           Left Nozzle   poor alignment       11   Front Truck Reverse   Flow blocked or           x           Right Nozzle   poor alignment       12   Front Truck Reverse   Flow blocked or               x           Left Nozzle   poor alignment       13   Reverse Truck Forward   Flow blocked or                   x           Right Nozzle   poor alignment       14   Reverse Truck Forward   Flow blocked or                       x           Left Nozzle   poor alignment       15   Reverse Truck Reverse   Flow blocked or                           x           Right Nozzle   poor alignment       16   Reverse Truck Reverse   Flow blocked or                               x           Left Nozzle   poor alignment                  
 
         [0041]    [0041]                                                   TABLE 2                           Relationship Between Phenomena Detected and Possible Failure Modes                Direction   Possible       Phenomina Detected   of Motion   Failure Modes            Axle 1 friction indicates no sand   fwd   1   3   7       Axle 3 friction indicates no sand   rev   1   4   7       Axle 4 friction indicates no sand   fwd   2   5   8       Axle 6 friction indicates no sand   rev   2   6   8       Axle 1 torsional vibration indicates   fwd   9   10       non-symmetrical sand       Axle 3 torsional vibration indicates   rev   11   12       non-symmetrical sand       Axle 4 torsional vibration indicates   fwd   13   14       non-symmetrical sand       Axle 6 torsional vibration indicates   rev   15   16       non-symmetrical sand