Abstract:
A method for determining the condition of a transmission fluid filter and controlling an operator indicator to alert the operator that the fluid filter requires replacement is disclosed. The method includes monitoring a fluid pressure switch, determining an operating mode of the transmission, determining whether the operating mode of the transmission is changing, activating a timer if the operating mode is changing, recording the time, comparing the time to a predefined time threshold, determining whether the recorded time is greater than the predefined threshold, and activating the operator indicator to indicate that the fluid filter requires replacement if the recorded time is greater than the predefined threshold.

Description:
TECHNICAL FIELD 
     The invention relates to a method for monitoring and diagnosing the status of a vehicle fluid filter, especially, fluids under pressure. 
     BACKGROUND 
     Road vehicles that have powertrains require lubricating fluids to continuously operate. More specifically, the engine and especially, the automatic transmission, require lubricating fluids or oils to maintain their operation and extend their useful life. Additionally, these fluids are passed through filters to remove contaminants and metal shavings caused by normal operation of the powertrain. The lubricating fluids and filters need to be replaced on regular intervals during the life of the vehicle. Generally, the change interval for replacing the engine lubricating fluid and filter is different from the change interval for replacing the transmission lubricating fluid and filter. Often the vehicle owner or operator is unaware of when these lubricating fluids and filters require replacement. As a result, many times the fluids and filters go without replacement. Alternatively, the fluids and filters are replaced unnecessarily. If a filter is not changed at its required interval, damage can occur especially in the transmission. A plugged or clogged transmission filter can increase the pressure in the main case of the transmission causing damage. 
     Thus, there is a need for a method for determining the status of the fluid filters, especially, the transmission filter. The method should alert the vehicle operator or owner that the fluid filter needs to be replaced. Moreover, the method should also check for hardware faults in the fluid filter monitoring system. 
     SUMMARY 
     In an aspect of the present invention, a method is provided for determining the condition of a transmission fluid filter and controlling an operator indicator to alert the operator that the fluid filter requires replacement. The method includes monitoring a fluid pressure switch, determining an operating mode of the transmission, determining whether the operating mode of the transmission is changing, activating a timer if the operating mode is changing, recording the time, comparing the time to a predefined time threshold, determining whether the recorded time is greater than the predefined threshold, and activating the operator indicator to indicate that the fluid filter requires replacement if the recorded time is greater than the predefined threshold. 
     In still another aspect of the present invention, the method includes determining whether the fluid pressure switch is cycling between an on and an off state. 
     In still another aspect of the present invention, the method includes activating a cycling timer to record the number of times the pressure switch cycles. 
     In still another aspect of the present invention, the method includes comparing the number of cycles to a predefined cycle threshold. 
     In yet another aspect of the present invention, the method includes activating the operator indicator to indicate that the fluid filter requires replacement if the recorded cycles is greater than the predefined cycle threshold. 
     In yet another aspect of the present invention, the method includes determining whether the torque converter of the transmission is operating. 
     In yet another aspect of the present invention, the method includes determining whether the lockup clutch of the transmission is operating. 
     In yet another aspect of the present invention, determining an operating mode further comprises determining whether the ignition is on and the engine is off. 
     The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view through the filter status detection device, wherein the detection device is in a first position, in accordance with an embodiment of the present invention; 
         FIG. 2  is a cross-sectional view through the filter status detection device, wherein the detection device is in a second position, in accordance with an embodiment of the present invention; 
         FIG. 3  is a flowchart illustrating a method for evaluating the status of the fluid filter using the detection device at ignition on and engine off, in accordance with an embodiment of the present invention; 
         FIGS. 4 and 5  are flowcharts illustrating methods for evaluating the status of the fluid filter during the transition between operating states, in accordance with an embodiment of the present invention; 
         FIG. 6  is a flowchart illustrating method for evaluating the drive cycle timers, in accordance with an embodiment of the present invention; 
         FIGS. 7 and 8  are flowcharts illustrating a method for evaluating the fluid filter at engine shutdown, in accordance with an embodiment of the present invention; and 
         FIG. 9  is a flowchart illustrating a method for handling a request from the vehicle operator to clear codes, in accordance with an embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings, wherein like reference numbers refer to like components, in  FIG. 1  a filter status detection device  10  is illustrated. Device  10  includes a valve  12  housed within a cavity  14 . Valve  12  is movable from a first position, shown in  FIG. 1 , to a second position, shown in  FIG. 2 . Valve  12  preferably includes a first land  16  and a second land  18  connected by an intermediate shaft portion  19 . First and second lands  16 ,  18  have the same diameter that is larger than the diameter of intermediate shaft portion  19 . Cavity  14  has a first inlet port  20 , a second inlet port  22 , an exhaust port  24 , a switch port  26 , and an activation port  28 . Fluid enters cavity  14  through first inlet port  20  at an inlet pressure equal to the inlet pressure of a fluid filter (i.e. a transmission oil filter), and through second inlet port  22  at an outlet pressure equal to the exit pressure of the filter. Fluid entering first inlet port  20  impinges upon valve  12 , tending to push valve  12  away from first inlet port  20  and toward second inlet port  22 , while fluid entering second inlet port  22  impinges upon the valve  12 , tending to push valve  12  toward first inlet port  20  and away from second inlet port  22 . A spring  30  having a spring constant equivalent to the desired allowable pressure drop biases valve  12  toward first inlet port  20 . 
     If the fluid pressure of the fluid entering first inlet port  20  is greater than the fluid pressure of the fluid entering second inlet port  22  by enough to overcome the force of spring  30 , valve  12  will move toward second inlet port  22  to the second position shown in  FIG. 2 . In the second position, activation port  28  is uncovered and fluid is allowed to enter cavity  14 . Fluid flows through activation port  28  at a steady predetermined control pressure, for example 100 psi. Fluid from activation port  28  then travels around intermediate shaft portion  19  of valve  12  through switch port  26  to activate a fluid pressure switch  32  indicating an undesirable drop in fluid pressure due to a plugged filter. The first land  16  of the valve  12  blocks fluid that has entered cavity  14  through first inlet port  20  from reaching switch  32 , thereby allowing even greater control of the force at which fluid influences switch  32 . Additionally, using varying diameter portions first land  16  and intermediate shaft portion  19  also causes a hysteresis effect within cavity  14 , such that once valve  12  moves toward second inlet port  22  and beyond a half-way position, the valve hysteresis effect will cause valve  12  to quickly move the rest of the way to the second position, shown in  FIG. 2 . The hysteresis effect will further cause valve  12  to remain in the second position until the pressure drop across the filter is sufficiently reduced. It can thus be seen that the hysteresis effect produced by the use of varying diameter portions of first land  16  and intermediate shaft portion  19  provides stability within device  10  by preventing valve  12  from cycling between the first and second positions. 
     In addition to detecting a plugged filter, device  10  of the present invention provides novel diagnostic capabilities, especially, in vehicles having a logic valve that selectively activates a lockup clutch  34 . When the lockup clutch is engaged, a vehicle torque converter clutch is pressurized. Conversely, when the lockup clutch  34  is disengaged, the torque converter clutch is exhausted. Preferably, second inlet port  22  is coupled to the lockup clutch (not shown), such that fluid pressurizes cavity  14  through second inlet port  22  only when the lockup clutch  34  is engaged. When a vehicle engine is started, typically the lockup clutch  34  is disengaged. Thus, fluid enters cavity  14  through first inlet port  20 , but not through second inlet port  22 , causing valve  12  to move to the second position, thereby activating switch  32 . If switch  32  does not activate upon engine start, which indicates to a vehicle controller  36  that either valve  12  is stuck in the first position, or switch  32  is malfunctioning. When the controller  36  activates the logic valve to engage the lockup clutch  34 , fluid should pressurize cavity  14  through second inlet port  22 , thereby moving valve  12  toward first inlet port  20  and deactivating switch  32  as activation port  28  is blocked by second land  18 . If switch  32  does not turn off, that indicates to the vehicle controller  36  either that valve  12  is stuck in the second position, the filter is plugged, or there is some problem with the connection between second inlet port  22  and the lockup clutch  34 . Failure of valve  12  to move from the first position to the second position when the lockup clutch is disengaged may also indicate a problem with a vehicle fluid pump  38 . Specifically, if the fluid pump  38  has not primed, or has lost its prime, fluid within device  10  will not be pressurized, and minimal fluid will enter cavity  14 . Thus, if the lockup clutch  34  is disengaged to prevent fluid from entering cavity  14  through second inlet port  22 , but the fluid pump  38  is not working properly such that fluid does not enter cavity  14  through first inlet port  20 , valve  12  will remain in the first position. It can thus be seen that the present invention provides diagnostic capabilities beyond detection of a plugged filter. 
     The present invention provides a method for determining whether the pressure switch and filter status detection device  10  is functioning properly at ignition on and engine off. Further, methods are provided for evaluating the filter pressure switch and detection device  10  when the valve of detection device  10  is transitioning from position one to position two and from position two to position one. Moreover, the methods of the present invention provide an indication to the operator of the vehicle that the switch  32  and detection device  10  are not functioning properly or that the fluid filter requires replacement. The operator is notified of a malfunctioning filter pressure switch and detection device  10  or the need for filter replacement by illuminating a warning light or activating an audible alarm. 
     Referring now to  FIG. 3 , a flowchart illustrating a method  40  for evaluating the status of the fluid filter using pressure switch  32  and device  10  is provided, in accordance with an embodiment of the present invention. At block  42 , the switch  32  is evaluated at key on and engine off. If the ignition is on, at block  44 , then the method determines whether the engine is on, at block  46 . If the ignition is off, then the method returns to block  42 . If the engine is off the transmission control module is powered on, as represented by block  48 . If the engine is on, then the method returns to block  42 . At block  50 , the pressure switch is monitored. If the output of the pressure switch is zero or low, then a first timer Tpass is started, as represented by block  54 . If the output of the pressure switch is one or high, then a second timer Tfail is started, as represented by block  56 . At block  58 , Tfail is compared to a predefined time threshold Tfailthreshold. If Tfail is greater than Tfailthreshold, then a diagnostic troubleshooting code is set and the operator of the vehicle is notified that the pressure switch  32  and device  10  are malfunctioning, as represented by block  60 . If Tfail is less than Tfailthreshold, then Tfail is compared again to Tfailthreshold, as represented by block  58 . At block  62 , Tpass is compared to a predefined Tpassthreshold. If Tpass is greater than Tpassthreshold, then pressure switch  32  and device  10  pass the diagnostic test, as represented by block  64 . If Tpass is less than Tpassthreshold, then Tpass is compared again to Tpassthreshold, as represented by block  62 . The diagnostic routine ends at block  66 . 
     Referring now to  FIGS. 4 and 5 , flowcharts illustrating a method  80  and  200  for evaluating the status of the fluid filter using pressure switch  32  and device  10  during the transition between four different operating states is provided, in accordance with an embodiment of the present invention. The four operating states are: (1) initialization at engine start and pressure switch off and device  10  in position one; (2) torque converter operating and pressure switch on and device  10  in position two; (3) lockup clutch operating and pressure switch off and device  10  in position one; and (4) lockup clutch operating and pressure switch on and device  10  in position two. Method  80  evaluates the pressure switch output as the vehicle and device  10  transitions between states. 
     More specifically, method  80  is initiated at block  82 . At block  84 , the output of the pressure switch is monitored. The transmission mode and operating state is determined, at block  86 . The method determines the transmission mode and operating state by monitoring, for example, the transmission fluid temperature, torque converter slip, and/or the application of the lockup clutch. At blocks  88 , the method determines whether detection device  10  is transitioning between operating states. If the method determines that device  10  is not transitioning to state two, then a clear timer (TokCLR) and a cycle timer (Tcycle 1 ) are cleared or set to zero and a timer (Tfail) is started and Tfail is set to zero, as represented by blocks  93  and  94 . At block  96 , the method determines whether the switch is cycling between on and off or a high and low voltage state or vice versa. If the switch is not cycling, then Tfail is compared to a Tfailthreshold, as represented by block  98 . The Tfailthreshold is a calibratable amount of time that varies based on transmission operating conditions, such as transmission fluid temperature. For example, the method will access a lookup table that correlates a time threshold for a given transmission fluid temperature. If Tfail is greater than Tfailthreshold, then a diagnostic code indicating that the pressure switch has failed in State  1  (SWITCH_ST 1 ) is set and a customer indicator is activated indicating that the pressure switch or device  10  requires servicing, as represented by block  100 . However, if Tfail is not greater than Tfailthreshold, then diagnostic method  80  returns to block  82  until a diagnostic code has been set or the engine has been shutdown, as represented by block  102 . If at block  96 , it is determined that the pressure switch is cycling between a high and low voltage level or vice versa, then a cycling counter is set to zero (C=0) and incremented each time the switch cycles between off and on (or high and low or vice versa), as represented by block  104 . At block  106 , C is compared to a Cfailthreshold, which is a predefined number of cycles. If C is determined to be greater than Cfailthreshold, then a diagnostic code indicating the pressure switch has failed in State  1  (SWITCH_ST 1 ) is set and a customer indicator is activated indicating that the pressure switch and/or device  10  is malfunctioning and requires servicing, as represented by block  100 . Diagnostic method  80  returns to block  82  until a diagnostic code has been set or the engine has been shutdown, as represented by block  102   
     However, if the method determines that device  10  is transitioning to state two, then a cycle timer (Tcycle 1  is initialized or set to zero) and a clear timer (TokCLR is initialized or set to zero), as represented by block  90 . At block  92 , Tcycle 1  is compared to a predefined threshold (Tcyclelthreshold). The Tcyclelthreshold is a calibratable amount of time. If Tcycle 1  is greater than Tcyclelthreshold, then a converter mode drive cycle flag is set (CM D/C), as represented by block  95 . However, if at block  92 , Tcycle 1  is not greater than Tcyclelthreshold, then TokCLR is compared to a predefined threshold (TokCLRthreshold), as represented by block  97 . If TokCLR is greater than TokCLRthreshold, then a Tfail timer is set to zero (Tfail=0) and a cycling counter is set to zero (C=0), as represented by block  99 . However, if at block  97 , TokCLR is not greater than TokCLR threshold, then diagnostic method  80  returns to block  82  until a diagnostic code has been set or the engine has been shutdown, as represented by block  102 . 
     Referring now to  FIG. 5 , a flowchart illustrating method  200  for evaluating the status of the fluid filter using pressure switch  32  and device  10  during a transition between operating states is provided, in accordance with an embodiment of the present invention. More specifically, method  200  is initiated at block  202 . At block  204 , the output of the pressure switch is monitored. The transmission mode and operating state is determined, at block  206 . At blocks  208 , the method determines whether detection device  10  is transitioning to state three. The method determines the transmission mode and operating state by monitoring, for example, the transmission fluid temperature, torque converter slip, and/or the application of the lockup clutch. If the method determines that device  10  is not transitioning to state three, then a clear timer (TokCLR 2 ) and a cycle timer (Tcycle 2 ) are cleared or set to zero and a timer (Tfail) is initialized and set to zero, as represented by blocks  209  and  210 . At block  212 , the method determines whether the switch is cycling between on and off or high and low voltage level or vice versa. If the switch is not cycling, then Tfail is compared to a Tfailthreshold, as represented by block  214 . If Tfail is greater than Tfailthreshold then the drive cycle timers are initialized, a fluid filter plugged flag is set and the vehicle, and specifically, the transmission is inhibited from operating normally, as represented by blocks  216 ,  218  and  219 . Inhibiting normal operation of the transmission, for example, is limiting the number of gears the operator is allowed to access. For example, the operator may only be allowed to use reverse gears and 1 st  gear through 4 th  gear out of a gear range of reverse gear to 6 th  gear. However, if Tfail is not greater than Tfailthreshold, then diagnostic method  200  returns to block  202  until a diagnostic code has been set or the engine has been shutdown, as represented by block  220 . If at block  212 , it is determined that the pressure switch is cycling, then a cycling counter is set to zero (C=0) and incremented each time the switch cycles between off and on (or a high and low voltage state or vice versa), as represented by block  222 . At block  224 , C is compared to a Cfailthreshold, which is a predefined number of cycles. If C is determined to be greater than Cfailthreshold, then the drive cycle timers are initialized, a fluid filter plugged flag is set and the vehicle, and specifically, the transmission is inhibited from operating normally, as represented by blocks  216 ,  218  and  219 . However, if C is not greater than Cfailthreshold, then diagnostic method  200  returns to block  202  until a diagnostic code has been set or the engine has been shutdown, as represented by block  220 . 
     However, if the method determines that device  10  is transitioning to state three, then a cycle timer (Tcycle 2  is initialized and set to zero) and a clear timer (TokCLR 2  is initialized and set to zero), as represented by block  226 . At block  228 , Tcycle 2  is compared to a predefined threshold (Tcycle 2 threshold). If Tcycle 2  is greater than Tcycle 2 threshold, then a lockup drive cycle mode (LU D/C) flag is set, as represented by block  230 . However, if at block  228 , Tcycle 2  is not greater than Tcycle 2 threshold, then TokCLR 2  is compared to a predefined threshold (TokCLR 2 threshold), as represented by block  232 . If TokCLR 2  is greater than TokCLR 2 threshold, then a Tfail timer is set to zero (Tfail=0) and a cycling counter is set to zero (C=0), as represented by block  234 . However, if at block  232 , TokCLR 2  is not greater than TokCLR 2 threshold, then diagnostic method  200  returns to block  202  until a diagnostic code has been set or the engine has been shutdown, as represented by block  220 . 
     Referring now to  FIG. 6 , a flowchart illustrating a method  300  for evaluating the drive cycle timers is provided, in accordance with an embodiment of the present invention. Method  300  is initiated at block  302 . At block  304 , the method determines whether the engine has been turned on (e.g. by monitoring the ignition switch and/or engine speed). If it is determined that the engine has been turned on, then a pair of drive cycle timers are started and initialized to zero (Tcurr and Tcumu), as represented by block  306 . Tcurr records the time of the current drive cycle and Tcumu records the cumulative time from one drive cycle to the next. At block  308 , Tcurr is compared to a predefined current drive cycle threshold (Tcurrthreshold). If Tcurr is greater than Tcurrthreshold, then a diagnostic code (Filter plugged) is set and a customer indicator is activated indicating that the fluid filter requires maintenance or changing, as represented by block  310 . At block  311 , the transmission is inhibited from operating normally. However, if at block  308 , Tcurr is not greater than Tcurrthreshold, then Tcumu is compared to a predefined cumulative drive cycle threshold (Tcumuthreshold), as represented by block  312 . If Tcumu is greater than Tcumuthreshold, then a diagnostic code (Filter plugged) is set and a customer indicator is activated indicating that the fluid filter requires maintenance or changing, as represented by block  310 . At block  311 , the transmission is inhibited from operating normally. If Tcumu is not greater than Tcumuthreshold, then the method terminates at block  314 . 
     Referring now to  FIGS. 7 and 8 , a flowchart illustrating a method  400  for evaluating the fluid filter using the pressure switch and device  10  at engine shutdown is provided, in accordance with an embodiment of the present invention. Method  400  is initiated at block  402 . At block  404 , the method determines the transmission mode and whether the engine is off. The method determines the transmission mode and the status of the engine by monitoring engine speed, transmission input speed, transmission output shaft speed and turbine speed and compares the monitored values to a threshold value. If the monitored values exceed the predefined threshold values then the engine is judged to be operating. If the engine has not been shutdown then method terminates, as represented by blocks  405 ,  407  (of  FIG. 8) and 424  (of  FIG. 8 ). However, if the engine has been shutdown then the output of the pressure switch is monitored, at block  408 . At block  410 , timer (Tfail 1 ) is initialized and set to zero. 
     Tfail 1  is compared to a Tfail 1 threshold, as represented by block  412 . If Tfail  1  is greater than Tfail 1 threshold, then the fluid filter is determined to be functioning properly, the switch has not failed in state  1  (SWITCH_ST 1 =OK), the Tcumu timer is cleared or set to zero and a code clear counter CC_Cnt is cleared or set to zero, at block  416 . At block  418 , a diagnostic code indicating the pressure switch has failed in state  2  (SWITCH_ST 2 ) is set and a customer indicator is activated indicating that the pressure switch requires maintenance. The method terminates thereafter, as represented by blocks  420 ,  422  (of  FIG. 8) and 424  (of  FIG. 8 ). 
     However, if at block  412  it is determined that Tfail 1  is not greater than Tfail 1 threshold, then the pressure switch output is determined, at block  426 . If the output of the pressure switch is not zero or at a high voltage level, then the method terminates, as represented by blocks  428 ,  430  (of  FIG. 8) and 424  (of  FIG. 8 ). However, if the output of the pressure switch is zero or at a low voltage level, then the method determines whether the plugged filter flag has been set (see  FIG. 5 , block  218 ), as represented by block  432 . If the plugged filter flag has been set, then the method determines if the converter mode drive cycle flag (CM D/C flag) has been set, as represented by block  434 . If the CM D/C flag has been set, then the method determines that the pressure switch has not failed in state  1  (SWITCH_ST 1 =ok), as represented by block  436 . If the CM D/C flag has not been set, then the method does not determine that the pressure switch has not failed in state  1 . At block  438 , the method determines that the pressure switch has not failed in state  2  (SWITCH_ST 2 =ok) and a diagnostic code is set and a customer indicator is activated indicating that the fluid filter requires maintenance. The method terminates thereafter, as represented by blocks  420 ,  422  (of  FIG. 8) and 424  (of  FIG. 8 ). 
     However, if at block  432  the method determines that the plugged filter flag has not been set, then the method determines if the lockup drive cycle flag (LU D/C flag) has been set, as represented by block  440 . If the lockup drive cycle flag (LU D/C flag) has been set, then at block  442  the method clears the current and cumulative drive timers (Tcurr and Tcumu). As represented by blocks  444 ,  446  (of  FIG. 8) and 448  (of  FIG. 8 ), a drive cycle counter (D/C Cnt) is initialized and incremented, see  FIG. 8 . At block  450  of  FIG. 8 , D/C Cnt is compared to a predefined drive cycle counter threshold (Cntthreshold). If D/C Cnt is greater than Cntthreshold, then the method clears the code clear counter (CC_Cnt) and the drive cycle counter (D/C Cnt), as represented by block  452 . However, if D/C Cnt is not greater than Cntthreshold then the method does not clear the CC_Cnt and D/C Cnt, as represented by block  450 . At block  454 , the filter is determined to be functioning properly and does not require maintenance. At block  456 , the method determines whether the converter mode drive cycle flag (CM D/C flag) has been set. If the method determines that the CM D/C flag has been set, then it is determined that the pressure switch has not failed in state  1  (SWITCH_ST 1 =ok), as represented by block  458 . However, if the method determines that the converter mode flag (CM D/C flag) has not been set, then SWITCH_ST 1  is not determined to be functioning properly, as represented by block  456 . At block  460 , the method determines that the pressure switch has not failed in state  2  (SWITCH_ST 2 =ok). The method terminates thereafter, as represented by block  424 . 
     However, if at block  440  of  FIG. 7  the method determines that the drive cycle lockup flag (LU D/C flag) has not been set, then the method at block  441  jumps to block  462  (of  FIG. 8 ) and continues to block  456 , as described above. 
     Referring now to  FIG. 9 , a flowchart illustrating a method  500  for handling a request from the vehicle operator to clear codes is provided, in accordance with an embodiment of the present invention. Method  500  is initiated at block  502 . At block  504 , the method recalls the drive cycle timer (Tcumu). At block  506 , the method compares Tcumu to a predefined cumulative drive cycle time threshold (Tcumuthresh). If Tcumu is determined not to be greater than Tcumuthresh, then the method clears the diagnostic codes, as represented by block  506  and  514 . 
     However, if Tcumu is determined to be greater than Tcumuthresh, then the method compares the clear code count (CC_cnt) with a predefined threshold (CC_CntThreshold), as represented by block  508 . If CC_cnt is determined to be greater than CC_CntThreshold, then the method does not allow the operator to clear the diagnostic codes or shutoff the indicator lamp and maintains inhibiting the transmission (i.e. reduced gear shift range), as represented by blocks  508  and  509 . The method terminates there after at block  516 . 
     However, if CC_cnt is determined not to be greater than CC_CntThreshold, then the method provides additional drive time without inhibiting transmission operation to allow the operator of the vehicle to get to a service station or maintenance area where the vehicle can be serviced, as represented by block  510 . At block  512 , CC_cnt is set to zero or initialized and then incremented. At block  514 , the diagnostic codes are cleared and the method terminates at block  516 . 
     While the best modes for carrying out the invention have been described in detail, it is to be understood that the terminology used is intended to be in the nature of words and description rather than of limitation. Those familiar with the art to which this invention relates will recognize that many modifications of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced in a substantially equivalent way other than as specifically described herein.