Patent Publication Number: US-7721535-B2

Title: Method for modifying trigger level for adsorber regeneration

Description:
RELATED APPLICATIONS 
   The present application is a continuation of PCT Patent Application No. PCT/US2005/019850 filed Jun. 6, 2005, which claims the benefit of U.S. Provisional Patent Application No. 60/578,015 filed Jun. 8, 2004, and entitled METHOD FOR MODIFYING TRIGGER LEVEL FOR ADSORBER REGENERATION, each of which is incorporated herein by reference. 

   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   The U.S. Government has certain rights in the present invention as provided by the terms of contract no. DE-FC05-97OR22533 awarded by the U.S. Department of Energy. 

   BACKGROUND 
   The present invention relates generally to the regeneration of a nitrogen-oxygen compound (NOx) adsorber catalyst. More particularly, the present invention relates to a method of controlling the frequency of NO x  adsorber regeneration cycles by modifying a regeneration-triggering variable based on an engine operating condition. 
   Environmental concerns have led to increasingly stricter regulation of engine emissions by governmental agencies. The reduction of NO x  in exhaust emissions from internal combustion engines has become increasingly important in order to meet governmental regulations. It is widely recognized that this trend of stricter government regulation will continue. 
   Traditional in-cylinder emission reduction techniques such as exhaust gas recirculation and injection rate shaping, by themselves will not be able to achieve the desired low emission levels. Scientists and engineers recognize that aftertreatment technologies will have to be used, and will have to be further developed in order to meet the future low emission requirements of the diesel engine. Abatement of NO x  on motor vehicles may be achieved through the use of catalytic technology that converts the NOx species to diatomic nitrogen (N 2 ) using a reductant as shown in the following equation: 
   
     
       
       
           
           
       
     
   
   Removal of NO x  through the use of NO x  adsorber catalysts requires that a hydrocarbon reductant be provided to the catalyst to convert the NO x . Typically, on-board fuel (e.g., diesel fuel) is used as the reductant. Fuel is injected into the exhaust stream for reaction with NO x  on the catalyst. 
   Therefore, a need exists for further technological advancements in emission control systems for internal combustion engines. The present invention is directed toward meeting this need. 
   SUMMARY 
   One aspect of the present invention contemplates a method comprising: operating an internal combustion engine including an after-treatment system having a NO x  adsorber catalyst, the engine includes an engine operating condition threshold value for triggering a regeneration of the NO x  adsorber catalyst; determining a change in the NO x  adsorber catalyst; and adjusting the engine operating condition threshold value for triggering a regeneration of the NO x  adsorber catalyst based upon the determining act. 
   Another aspect of the present invention contemplates a method comprising: operating a diesel engine having an after-treatment system including a NO x  adsorber catalyst; triggering a NO x  adsorber catalyst regeneration cycle based on a fuel consumption threshold value; determining the decrease in the NO x  adsorber catalyst efficiency over a plurality of the NO x  adsorber catalyst regeneration cycles; and modifying the fuel consumption threshold value in response to the determining act. 
   Yet another aspect of the present invention contemplates a system comprising: a diesel engine that consumes a fuel and produces an exhaust gas; a NO x  adsorber in fluid communication with the exhaust gas for adsorbing at least a portion of the exhaust gas; a first value to trigger a first regeneration cycle of the NO x  adsorber; a control system to determine the decline in absorbtion efficiency of the NO x  adsorber and to output a second value corresponding to the decline in absorbtion efficiency of the NO x  adsorber; and a control to calculate a third value based upon the first value and the second value, the third value triggers a second regeneration cycle of the NO x  adsorber, in each of the regeneration cycles a reductant is delivered to the NO x  adsorber. 
   A further aspect of the present invention contemplates a method comprising: operating a vehicle including an internal combustion engine, the internal combustion engine including an after-treatment system with an adsorber catalyst; determining if the internal combustion engine has a load greater than a first threshold; determining if the internal combustion engine is participating in an aggressive driving situation; and regenerating the adsorber catalyst only when the engine is not participating in an aggressive driving situation nor subject to a load greater than the first threshold. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a flow chart illustrating an algorithm disclosing one embodiment of the present invention. 
       FIG. 2  is a schematic illustration of a system comprising another embodiment of the present invention. 
       FIG. 3  is a flow chart illustrating one embodiment of an algorithm to control the system depicted in  FIG. 2 . 
       FIG. 4  is a schematic illustration of a system comprising another embodiment of the present invention. 
       FIG. 5  is a flow chart illustrating one embodiment of an algorithm to control the system depicted in  FIG. 4 . 
       FIG. 6  is a flow chart illustrating one embodiment of an algorithm that prevents regeneration when engine-operating conditions are undesirable. 
   

   DESCRIPTION OF THE SELECTED EMBODIMENTS 
   For the purposes of promoting understanding of the principles of the invention, reference will be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is hereby intended and alterations and modifications in the illustrated device, and further applications of the principles of the present invention as illustrated herein being contemplated as would normally occur to one skilled in the art to which the invention relates. 
   The present application recognizes that one of the more complex problems in regenerating NO x  adsorber catalysts by periodically injecting reductants is that the adsorption efficiency of the catalyst deteriorates over time. As this occurs, the amount of NO x  adsorbed decreases after each regeneration cycle. Soon the injection timing and the amount of reductant injected may not properly track the amount of NO x  adsorbed on the catalyst. This failure to properly track the regeneration needs of the NO x  adsorber catalyst leads to increased NO x  emissions due to the failure of the NO x  adsorber to adsorb. Furthermore, reductant is wasted as amounts are released when unneeded. The present application provides methods to maintain the performance of the system as the catalyst deteriorates. 
   Referring to  FIG. 1 , there is illustrated an algorithm  10  that generally describes one method of the present invention. Trigger modification algorithm  10  begins at block  11  with determining an engine operating condition. The present invention preferably utilizes the amount of fuel consumed as the engine operating condition. However, other engine operating conditions may be used, including the number of engine cycles or engine air mass flow. At block  12  a decision is made whether the engine operating condition has met the regeneration triggering value. If the regeneration triggering value has not been met, then the algorithm returns to determining an engine operating condition in block  11 . If the engine operating condition has reached the regeneration triggering value, then a regeneration of the adsorber is indicated at block  13 . 
   After the adsorber is regenerated, the deterioration of adsorber efficiency is determined at block  14 . The deterioration of the adsorber efficiency may be determined by utilizing an open-loop empirical data table including a deterioration schedule residing in a controller or using a pair of sensors to provide a closed-loop assessment of the adsorber condition. In one form of the present invention the pair of sensors are oxygen sensors, however in another form the pair of sensors are NO x  sensors The NO x  sensors look at a direct measurement of the NO x . At block  15 , this adsorber efficiency is compared to a minimal threshold value. If the minimal threshold value is satisfied, then the algorithm ends. If not, the algorithm moves on to block  16  where the regeneration triggering value is modified based on the amount of deterioration of the adsorber. The algorithm then uses the new regeneration triggering value upon returning to the beginning of the algorithm at block  11 . 
   Referring to  FIG. 2 , there is illustrated a schematic diagram of one embodiment of the present invention. Engine  20  is connected to a fuel source  21  that provides fuel to be combusted inside engine  20 . The engine illustrated is purely schematic and no intention is made to limit the engine based on the figure. The engine can, but is not limited to an inline or V-engine with one or a plurality of cylinders, and can be a spark ignition or a compression ignition engine. Further, the engine can be gaseous or liquid fueled. Exhaust gas exits the engine at exhaust gas outlet  22  and passes through exhaust pipe  24  to NO x  adsorber  23  before continuing through the exhaust pipe  24  to the ambient atmosphere. The housing including the NO x  adsorber  23  includes an inlet  31  and an outlet  32 . Reductant is applied from reductant providing source  25  and injected into the exhaust gas pipe  24  through injector  26 . In a preferred form, the source of reductant is the fuel source  21 , which is coupled in flow communication with the injector  26 . In another form of the present application the reductant is delivered directly in-cylinder by the engine fuel injection system. Further, the present application contemplates that other methods known to one skilled in the art of providing the reductant to the inlet  31  of NO x  adsorber  23 . 
   An inlet oxygen sensor  27  measures the oxygen content of the exhaust gas at inlet  31  and an outlet oxygen sensor  28  measures the oxygen content of the exhaust gas at outlet  32 . Controller  29  receives an input corresponding to the amount of fuel consumed by engine  20  from fuel source  21 . A signal from fuel source  21  to controller  29  is used in determining the amount of fuel consumed. In one form of the present application the amount of fuel consumed is calculated. Preferably, but without limiting the present application the amount of fuel consumed is a summation of discrete values. Moreover, outputs from first oxygen sensor  27  and second oxygen sensor  28  are input into the controller  29 . Controller  29  then determines the time for supplying reductant and the amount of reductant to be supplied through injector  26  to NO x  adsorber inlet  31 . Controller  29  then sends an output signal to the reductant providing source  25 . While, the present application has been described in terms of two oxygen sensors it is also contemplated to utilize the output from a pair of NO x  sensors. 
   Reductant providing source  25  may further include a pump to provide a pressurized amount of reductant to injector  26 . In one form the system includes an auxiliary pump to pressurize the reductant. As discussed above in another form of the present invention the reductant is delivered in cylinder by the engine fuel injection system. The reductant providing source can be the fuel source  21  that can be placed in fluid flow communication with injector  26 . Further, other methods known to one skilled in the art for supplying reductant to the NO x  adsorber are contemplated herein. If inputs from first oxygen sensor  27  and second oxygen sensor  28  indicate that the efficiency of the adsorber has dropped below a minimum level then an output signal is sent to display  30  to indicate that the catalyst has malfunctioned. A malfunction may result in further activities such as a desulfurizing event or replacement of the catalyst. 
   Referring to  FIG. 3 , there is illustrated one embodiment of a trigger modification algorithm  34  for controlling the system set forth in  FIG. 2 . Algorithm  34  begins at block  35  by determining the present fuel consumption of the engine. The present fuel consumption value of the engine is depicted in  FIG. 3  as symbol F n . Block  36  then determines if at least one regeneration cycle has been performed. The number of regeneration cycles is indicated in  FIG. 3  as symbol b. If there has not been at least one regeneration cycle performed, then the algorithm moves to block  37 . At block  37 , the present fuel consumption value is compared to the regeneration triggering fuel consumption value. The regeneration triggering fuel consumption value is depicted in  FIG. 3  as symbol F t . If the fuel consumption value is greater than or equal to the regeneration triggering fuel consumption value, then adsorber regeneration is indicated at block  38 . If the present fuel consumption value is less than the regeneration triggering fuel consumption value, then the control system returns to determine a new present fuel consumption value. 
   After regeneration of NO x  adsorber  23  at block  38 , inputs from the first oxygen sensor  27  and second oxygen sensor  28  allow the controller to determine a first characteristic across the sensors. In one form of the invention the first characteristic is delay time, however other characteristics are contemplated herein. This is symbolized in block  39  as D n . The algorithm then moves to block  40  and determines if the actual delay time is less than or equal to a minimum delay time threshold value symbolized as D o . If the actual delay time is less than or equal to this minimum delay time threshold value, then a desulfation event is begun as indicated by block  41 . After the desulfation event at block  41 , the algorithm then moves to block  42  and determines the actual delay time across the oxygen sensors again. At block  43  the algorithm determines if the actual delay time across the oxygen sensors is still less than or equal to the minimum delay time threshold value. If true, a catalyst malfunction/failure signal is indicated at block  44 . The algorithm ends after the failure signal is made. 
   In contrast, if the delay across the sensors is determined at block  40  or  43  to be greater than the minimum delay time threshold value D o  then the algorithm proceeds to block  45  to calculate the percent difference. The percent difference is calculated by first subtracting the actual delay time from a predetermined base delay time and then dividing that difference by the predetermined base delay time. This value is then multiplied by one hundred to determine the percent difference. The predetermined base delay time corresponds to the delay time across a fresh NO x  adsorber. At block  46 , the algorithm then calculates the modified fuel consumption trigger value. The modified fuel consumption trigger value is symbolized as F ideal . F ideal  is a function of a scalable constant a 1 , the regeneration triggering fuel consumption value F t  and the percent difference. The scalable constant a 1  is derived empirically for each class of engines and for each particular adsorber. 
   After F ideal  is calculated in block  46 , the algorithm returns to block  35 , and the present fuel consumption is determined again. The number of regeneration cycles now is at least one, because one regeneration cycle has occurred. Therefore, the algorithm moves to block  47  where the present fuel consumption is now compared to see if it is greater than or equal to the modified fuel consumption trigger value. This is depicted at block  47  as F n  is greater than or equal to F ideal . If true, then adsorber regeneration is indicated and the algorithm passes to block  38 . If not, the algorithm returns and the fuel consumption value is determined again at block  35 . 
   Referring to  FIG. 4 , there is illustrated a schematic of another embodiment of the present invention. The reader will note that like feature numbers will be utilized to describe the features that were described previously. As discussed above, the reductant can also be delivered directly in-cylinder. Engine  20  produces exhaust gas containing contaminants such as NO x  that exit engine outlet  22  and pass through NO x  adsorber  23 . Reductant providing source  25  provides reductant to be injected into exhaust pipe  24  to help regenerate the NO x  adsorber catalyst in the NO x  adsorber  23 . 
   Controller  56  includes an empirically determined table of constants to modify the predetermined fuel trigger value in accordance to the number of regeneration cycles already performed. Once the controller determines a regeneration cycle is indicated, an output signal is sent to reductant providing source  25  to inject reductant into exhaust gas pipe line  24  through the use of injector  26 . As discussed above, the reductant providing source can be the fuel source  21 , which will be, placed in fluid flow communication with injector  26 . If controller  56  determines that the number of regeneration cycles performed indicates that the efficiency of NO x  adsorber  23  has likely dropped below a predetermined minimum threshold, then an output signal is sent to display  30  to indicate the failure of NO x  adsorber  23 . 
   Referring to  FIG. 5 , there is illustrated one embodiment of trigger modification algorithm  62  for controlling the system set forth in  FIG. 4 . Algorithm  62  begins at block  63  by determining the present fuel consumption of the engine. The present fuel consumption of the engine is symbolized as F n . The algorithm then moves to block  64  to determine if at least one regeneration cycle has been performed. The number of regeneration cycles is symbolized in  FIG. 5  as b. If there has not been at least one regeneration cycle, then the algorithm passes to block  65  where the present fuel consumption value is compared to the regeneration triggering fuel consumption value. The regeneration triggering fuel consumption value is symbolized in  FIG. 5  as F t . If the present fuel consumption value does meet the regeneration triggering fuel consumption value, then adsorber regeneration is indicated at block  66 . If the condition is not satisfied, the algorithm returns to block  63  to determine the present fuel consumption value. 
   After adsorber regeneration is indicated and performed, the algorithm determines the empirically derived modification constant at block  67 . The empirically derived modification constant is symbolized as a 2 . The empirically derived modification constants are provided from the controller  56  which includes a table of modification constants. The algorithm then proceeds next to block  68  where the modified fuel consumption trigger value is determined. The modified fuel consumption trigger value is symbolized in  FIG. 5  as F ideal . F ideal  is a function of empirically derived modification constant a 2  and regeneration triggering fuel consumption value F t . After the modified fuel consumption trigger value is calculated, the algorithm moves to block  69  where the modified fuel consumption trigger value is compared to a minimum fuel trigger value. The minimum fuel trigger value is depicted symbolically as F o . In one form the minimum fuel trigger valve is a fixed value or one that is obtained from a look-up table. In a preferred form the minimum fuel trigger values are empirically based and populate a table. 
   The algorithm moves to block  70  when the modified fuel consumption trigger value is less than or equal to the minimum fuel trigger value F o . Block  70  indicates beginning a desulfation event. After this desulfation event has occurred, the algorithm then moves to block  72  where the comparison between the modified fuel consumption trigger value and the minimum fuel trigger value is performed once again. When block  72  determines that the modified fuel consumption trigger value is still less than the minimum fuel trigger value F o  then the algorithm moves to block  73  to signal a catalyst failure to the display  30 . Alternatively, the algorithm returns to block  63  to determine the present fuel consumption value when either block  69  or  72  indicates that the valve for F ideal  is greater than the minimum fuel trigger value F o . 
   Upon return to block  64 , the number of regeneration cycles is now at least one and the algorithm moves to block  74 . At block  74 , the present fuel consumption value is compared to the modified fuel consumption trigger value F ideal . If the present fuel consumption value is greater than or equal to the modified fuel consumption trigger value, adsorber regeneration is indicated at block  66 . If not, the algorithm returns to block  63 . 
   While the description above depicts a few embodiments of the invention, they are not considered illustrative of all potential embodiments of the present invention. For example, the NO x  adsorber catalyst may consist of various alkali metals and precious metals and may contain some oxygen storage chemicals such as ceria. The oxygen sensors can be a switching type around stoichiometric, a wide range heated oxygen sensor (HEGO, WEGO) or a NO x  sensor with an oxygen sensing signal. Any sensor that can detect changes in the air fuel ratio are envisioned. 
   Referring to  FIG. 6 , there is illustrated one embodiment of an algorithm to postpone adsorber regeneration until an undesired operating condition has passed. The undesired operating condition may be, for example engine load or aggressive driving maneuvers. At block  77 , an accumulation monitor continuously sums a mass based on a signal that is proportional to a species of concern, preferably fuel consumption. In some embodiments, the accumulation value is modified depending upon the level of deterioration in the catalyst. When the accumulation monitor reaches a threshold, a flag is set to determine if regeneration will be clear of the undesired engine operating condition. To insure fuel efficiency is maximized in aggressive driving situations, the engine load is monitored. Block  78  signals clearance to regenerate only when the engine load is below a predetermined value. In addition, at block  79 , the algorithm checks for an aggressive driving situation and will not signal clearance to regenerate unless the aggressive drive situation is dampened. Blocks  78  and  79  will return indefinitely until their respective conditions are satisfied. Block  80  will then begin adsorber regeneration only when blocks  78  or  79  provide clearance signals. 
   While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected. It should be understood that while the use of the word preferable, preferably or preferred in the description above indicates that the feature so described may be more desirable, it nonetheless may not be necessary and embodiments lacking the same may be contemplated as within the scope of the invention. Further, when the language “at least a portion” and/or “a portion” is used the item may include a portion and/or the entire item unless specifically stated to the contrary.