Abstract:
A method of controlling a fuel injector is provided. Engine speed is monitored. Engine torque output is monitored. It is determined if the engine speed is within one of a plurality of predefined engine speed ranges. It is determined if the engine torque output is within one of a plurality of predefined engine torque output ranges. One of a plurality of injector coking factors is assigned based on the determined predefined engine speed range and the determined predefined engine torque output range. A total injector coking factor is calculated based upon total operating time within each of the plurality of injector coking factors. A duration of a fuel injection is increased based upon the calculated total injector coking factor.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates to a method of controlling a fuel injector. More particularly, the disclosure relates to a method of controlling a fuel injector that determines coking of a fuel injector and adjusts a fuel injection based on an estimated coking amount. 
       BACKGROUND 
       [0002]    Fuel systems for modern diesel engines operate at ever increasing fuel injection pressures. One way to achieve these high fuel injection pressures is to utilize a hydraulically intensified fuel injection system. Such a system may utilize a high-pressure common rail system that provides fuel to each individual injector from a high-pressure accumulator, oftentimes referred to as the “rail” or “common rail.” The injector also receives a high-pressure hydraulic fluid, such as fuel, engine oil, or other fluid, that is utilized to drive a piston, or other pressure intensifying system, to increase the pressure of the fuel that leaves the injector to the pressures required by modern diesel engines. As fuel injectors operate, the nozzle openings may be reduced from combustion effects in a process often referred to as “coking.” As the nozzle opening of the fuel injector is reduced, a volume of fuel provided to a cylinder during a fuel injection event may be less than the expected injection volume, because less fuel is capable of passing through the reduced diameter nozzle opening. Therefore, as precise control of fuel injection becomes more important with more stringent emission standards, a need exists for a way to control fuel injection that corrects for coking of fuel injectors. 
       SUMMARY 
       [0003]    According to one process, a method of controlling a fuel injector is provided. Engine speed is monitored. Engine torque output is monitored. It is determined if the engine speed is within one of a plurality of predefined engine speed ranges. It is determined if the engine torque output is within one of a plurality of predefined engine torque output ranges. One of a plurality of injector coking factors is assigned based on the determined predefined engine speed range and the determined predefined engine torque output range. A total injector coking factor is calculated based upon total operating time within each of the plurality of injector coking factors. A duration of a fuel injection is increased based upon the calculated total injector coking factor. 
         [0004]    According to another process, a method of controlling a fuel injector is provided. At least one of engine torque output and engine speed is monitored. It is determined if at least one of the monitored engine torque output and engine speed is within one of a first predefined range, a second predefined range, and a third predefined range. An amount of time within one of the first predefined range, the second predefined range, and the third predefined range is monitored. A first injector coking factor is assigned if the amount of time within the first predefined range exceeds a first preset time limit. A second injector coking factor is assigned if the amount of time within the second predefined range exceeds a second preset time limit. A third injector coking factor is assigned if the amount of time within the third predefined range exceeds a third preset time limit. A total injector coking factor is calculated based upon total operating time within each of the first injector coking factor, the second injector coking factor, and the third injector coking factor. A duration of a fuel injection is increased based upon the calculated total injector coking factor. 
         [0005]    According to a further process, a method of controlling a fuel injector is provided. Engine torque output is monitored. Engine speed is monitored. One of a plurality of coking factors is assigned based upon the monitored engine torque output and the monitored engine speed. An engine operating time at each assigned one of the plurality of coking factors is determined A total injector coking factor is calculated. The calculated total injector coking factor is compared to a predetermined maximum coking factor. A duration of a fuel injection is increased based upon one of the calculated total injector coking factor and the predetermined maximum coking factor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a schematic view of a control system for determining an injector coking factor for a first engine operating range for an internal combustion engine with coking correction. 
           [0007]      FIG. 2  is a schematic view of a control system for determining an injector coking factor for a second engine operating range for an internal combustion engine with coking correction. 
           [0008]      FIG. 3  is a schematic view of a control system for determining an injector coking factor for a third engine operating range for an internal combustion engine with coking correction. 
           [0009]      FIG. 4  is a schematic view of a control system for determining an injector coking factor for a fourth engine operating range for an internal combustion engine with coking correction. 
           [0010]      FIG. 5  is a schematic view of a control diagram for a fuel injector with coking correction. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]      FIG. 1  shows a schematic control diagram  10  for determining an injector coking factor for a first engine operating range. An engine speed indication  12  is compared to a first stored engine speed value  14  by a first comparator  16 . The first comparator  16  determines if the engine speed indication  12  is less than the first stored engine speed value  14 . Similarly, an engine torque output  18  is compared to a first stored engine torque output  20  by a second comparator  22 . The second comparator  22  determines if the engine torque output  18  is less than the first stored engine torque output  20 . The operation of the engine below the first stored engine speed value  14  and the first stored engine torque output  20  indicates that the engine is operating in a first operating output range A, as indicated by block  34 . 
         [0012]    A first timer loop  24  and a second timer loop  26  are also provided in the control diagram  10 . The first timer loop  24  is utilized to track an amount of time that has passed since the last time the engine was operating in output range A  34 . If the amount of time indicated by the first timer loop  24  exceeds a preset value, the first timer loop  24  is reset. Resetting the first timer loop  24  allows a more stable injector coking factor to be calculated, as certain transient operations in other output ranges may be ignored. 
         [0013]    The second timer loop  26  is used to determine a total amount of operating time of the engine in output range A  34 . The second timer loop  26  evaluates whether the engine was previously operating in output range B  28 , output range C  30 , or output range D  32 . If the engine had been operating in one of the other output ranges,  28 ,  30 ,  32 , the second timer loop  26  does not begin to count until the first timer loop  24  has reset, indicating that the engine has operated within output range A  34  for a sufficient period. 
         [0014]    It has been found that engine operations within output range A  34  causes a negligible amount of injector coking. Therefore, operating range A  34  does not require a calculation of a coking correction amount; instead, an operating range A output  36  is calculated that simply indicates that the engine had been within operating range A for a period of time. 
         [0015]      FIG. 2  shows a schematic control diagram  100  for determining an injector coking factor for a second engine operating range. The engine speed indication  12  is compared to a second stored engine speed value  38  by a third comparator  40 . The third comparator  40  determines if the engine speed indication  12  is greater than the second stored engine speed value  38 . The engine speed indication  12  is also compared to a third stored engine speed value  42  by a fourth comparator  44 . The fourth comparator  44  determines if the engine speed indication  12  is less than the third stored engine speed value  42 . 
         [0016]    Similarly, the engine torque output  18  is compared to a second stored engine torque output  46  by a fifth comparator  48 . The fifth comparator  48  determines if the engine torque output  18  is greater than the second stored engine torque output  46 . The engine torque output  18  is also compared to a third stored engine torque output  50  by a sixth comparator  52 . The sixth comparator  52  determines if the engine torque output  18  is less than the third stored engine torque output  50 . The operation of the engine between the second and third stored engine speeds  38 ,  42  and between the second and third stored engine torque outputs  46 ,  50  indicate that the engine is operating in a second operating output range B, as indicated by block  28 . 
         [0017]    A third timer loop  54  and a fourth timer loop  56  are also provided in the control diagram  100 . The third timer loop  54  is utilized to track an amount of time that has passed since the last time the engine was operating in output range B  28 . If the amount of time indicated by the third timer loop  54  exceeds a preset value, the third timer loop  54  is reset. Resetting the third timer loop  54  allows a more stable injector coking factor to be calculated, as certain limited duration transient operations in other output ranges may be ignored. 
         [0018]    The fourth timer loop  56  is used to determine a total amount of operating time of the engine in output range B  28 . The fourth timer loop  56  evaluates whether the engine was previously operating in output range A  34 , output range C  30 , or output range D  32 . If the engine had been operating in one of the other output ranges  30 ,  32 ,  34 , the fourth timer loop  56  does not begin to count until the third timer loop  54  has reset, indicating that the engine has operated within output range B  28  for a sufficient period. 
         [0019]    Once the engine has been determined to be operating within output range B  28 , a coking factor  58  is determined based on the engine speed  12  and the engine torque output  18 . The coking factor  58  is based on stored information that estimates a rate of injector coking that takes place while the engine operates within output range B  28 . The coking factor  58  may be based on empirical data gathered during engine testing, or may be in the form of an engine model. The coking factor  58  is multiplied by the time that the fourth timer loop  56  indicates the engine is operating within output range B  28  to provide a coking amount  60  for the operation with output range B  28 . 
         [0020]      FIG. 3  shows a schematic control diagram  200  for determining an injector coking factor for a third engine operating range. The engine speed indication  12  is compared to a fourth stored engine speed value  62  by a seventh comparator  64 . The seventh comparator  64  determines if the engine speed indication  12  is more than the fourth stored engine speed value  62 . The engine speed indication  12  is also compared to a fifth stored engine speed value  66  by an eighth comparator  68 . The eighth comparator  68  determines if the engine speed indication  12  is less than the fifth stored engine speed value  66 . 
         [0021]    Similarly, the engine torque output  18  is compared to a fourth stored engine torque output  70  by a ninth comparator  72 . The ninth comparator  72  determines if the engine torque output  18  is greater than the fourth stored engine torque output  70 . The engine torque output  18  is also compared to a fifth stored engine torque output  74  by a tenth comparator  76 . The tenth comparator  76  determines if the engine torque output  18  is less than the fifth stored engine torque output  74 . The operation of the engine between the fourth and fifth stored engine speeds  62 ,  66  and between the fourth and fifth stored engine torque outputs  70 ,  74  indicate that the engine is operating in a third operating output range C, as indicated by block  30 . 
         [0022]    A fifth timer loop  78  and a sixth timer loop  80  are also provided in the control diagram  200 . The fifth timer loop  78  is utilized to track an amount of time that has passed since the last time the engine was operating in output range C  30 . If the amount of time indicated by the fifth timer loop  78  exceeds a preset value, the fifth timer loop  78  is reset. Resetting the fifth timer loop  78  allows a more stable injector coking factor to be calculated, as certain limited duration transient operations in other output ranges may be ignored. 
         [0023]    The sixth timer loop  80  is used to determine a total amount of operating time of the engine in output range C  30 . The sixth timer loop  80  evaluates whether the engine was previously operating in output range A  34 , output range B  28 , or output range D  32 . If the engine had been operating in one of the other output ranges  28 ,  32 ,  34 , the sixth timer loop  80  does not begin to count until the fifth timer loop  78  has reset, indicating that the engine has operated within output range C  30  for a sufficient period. 
         [0024]    Once the engine has been determined to be operating within output range C  30 , a coking factor  82  is determined based on the engine speed  12  and the engine torque output  18 . The coking factor  82  is based on stored information that estimates a rate of injector coking that takes place while the engine operates within output range C  30 . The coking factor  82  may be based on empirical data gathered during engine testing, or may be in the form of an engine model. The coking factor  82  is multiplied by the time that the sixth timer loop  80  indicates the engine is operating within output range C  30  to provide a coking amount  84  for the operation with output range C  30 . 
         [0025]      FIG. 4  shows a schematic control diagram  300  for determining an injector coking factor for a fourth engine operating range. The engine speed indication  12  is compared to a sixth stored engine speed value  86  by an eleventh comparator  88 . The eleventh comparator  88  determines if the engine speed indication  12  is more than the sixth stored engine speed value  86 . 
         [0026]    Similarly, the engine torque output  18  is compared to a sixth stored engine torque output  90  by a twelfth comparator  92 . The twelfth comparator  92  determines if the engine torque output  18  is greater than the sixth stored engine torque output  90 . The operation of the engine above the sixth stored engine speed  86  and the sixth stored engine torque output  90  indicates that the engine is operating in a fourth operating output range D, as indicated by block  32 . 
         [0027]    A seventh timer loop  94  and an eighth timer loop  96  are also provided in the control diagram  300 . The seventh timer loop  94  is utilized to track an amount of time that has passed since the last time the engine was operating in output range D  32 . If the amount of time indicated by the seventh timer loop  94  exceeds a preset value, the seventh timer loop  94  is reset. Resetting the seventh timer loop  94  allows a more stable injector coking factor to be calculated, as certain limited duration transient operations in other output ranges may be ignored. 
         [0028]    The eighth timer loop  96  is used to determine a total amount of operating time of the engine in output range D  32 . The eighth timer loop  96  evaluates whether the engine was previously operating in output range A  34 , output range B  28 , or output range C  30 . If the engine had been operating in one of the other output ranges  28 ,  30 ,  34 , the eighth timer loop  96  does not begin to count until the seventh timer loop  94  has reset, indicating that the engine has operated within output range D  32  for a sufficient period. 
         [0029]    Once the engine has been determined to be operating within output range D  32 , a coking factor  98  is determined based on the engine speed  12  and the engine torque output  18 . The coking factor  98  is based on stored information that estimates a rate of injector coking that takes place while the engine operates within output range D  32 . The coking factor  98  may be based on empirical data gathered during engine testing, or may be in the form of an engine model. The coking factor  98  is multiplied by the time that the eighth timer loop  96  indicates the engine is operating within output range D  32  to provide a coking amount  99  for the operation with output range D  32 . 
         [0030]    Thus, in summary,  FIGS. 1-4  depict that four different operating ranges, output ranges A-D  28 - 34 , are determined based on observed engine speed  12  and engine torque output  18 . Once the operating range is determined, an amount of time the engine operates within that range is measured. The control logic allows for only one operating range to be active at any given time. Additionally, in order to prevent transient operations of the engine from having too great an effect on the determined operating range, the control logic requires that the determined operating range to remain active for a predefined period before the control logic switches from the preceding determined operating range. For example, if output range B  28  was active and the logic now determines that the engine is operating in output range C  30 , a set amount of time within operating range C  30  must occur before the logic changes the coking amount  60  from the operating range B  28  to the coking amount  84  of the operating range C  30 . Thus, according to one embodiment, only one of the four operating ranges is active at any given time, and the engine must operate within an operating range for a preset amount of time before that operating range is recognized as the active operating range. 
         [0031]    Turning now to  FIG. 5 , a schematic control diagram for a fuel injector with coking correction  400  is shown. The coking amount  60  for the operation within output range B  28 , the coking amount  84  for the operation within output range C  30 , and the coking amount  99  for the operation within output range F  32  are added together to create a sum of the coking amounts  60 ,  84 ,  99 , as shown at block  402 . The sum of the coking amounts  60 ,  84 ,  99  are compared to a maximum coking amount limit and a minimum coking amount limit at block  404 . If the sum of the coking amounts is more than the maximum coking amount limit, the sum of the coking amounts  60 ,  84 ,  99  is reduced to the maximum coking amount limit. The lesser of the sum of the coking amounts  60 ,  84 ,  99  and the maximum coking amount limit is then set as the coking factor sum  406  indicating the total amount of coking of the fuel injector. 
         [0032]    The schematic control diagram  400  additionally compares a total running time of the engine  408  to a stored minimum engine running time for coking correction  410  with a comparator  416 . If the total running time of the engine  408  is less than the stored minimum running time for coking correction  410 , no coking correction occurs, as the injectors are not likely to have sufficient coking to warrant a change in fuel injection parameters. 
         [0033]    The coking factor sum  406  is also compared to a preceding coking factor sum  412  by subtracting the preceding coking factor sum  412  from the coking factor sum  406  to determine a coking differential  418 . The coking differential  418  is compared to a stored minimum coking differential  414  by comparator  420 . If the coking differential  418  is less than the minimum coking differential  414 , no additional coking correction occurs, as the amount of coking that has occurred since the last coking correction was made is insignificant. 
         [0034]    If the total running time of the engine  408  and the coking differential  418  are sufficient, the coking factor sum  406  is provided to a fuel injector duration modifier  426 . The fuel injector duration modifier  426  contains data based on the coking factor sum  406  to indicate a correction to the duration of a fuel injection event based on the coking factor sum  406  and the total running time of the engine  408 . The fuel injector duration modifier  426  may contain data based upon empirical data generated during engine testing, or may be model based. 
         [0035]    The fuel injector duration modifier  426  output is compared to a stored maximum injector duration  428  by a comparator  429 . If the output of the fuel injector duration modifier  426  is more than the stored maximum injection duration, comparator  429  reduces the output of the fuel injector duration modifier  426  to the stored maximum injection duration  428 . The output of the comparator  429  is then provided as the modified injector duration  430 . 
         [0036]    It is contemplated that the stored maximum injector duration  428  may be based on a variety of factors, such as a maximum amount of time fuel injection can occur to allow combustion timing to remain as desired, the maximum amount of time fuel injection can occur to meet an emissions threshold, or the maximum amount of time fuel injection can occur based upon the engine speed or the engine torque output. 
         [0037]    Experimental data has shown that injector coking may reach a maximum coking amount of about 7% reduction in fluid flow through the nozzle openings of the injector. Thus, the maximum injection duration  428  may be based upon an injection duration required to increase the flow of the injection by about 7%, in order to compensate for the reduction in flow from coking.