(19)
(11)EP 3 346 105 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
10.06.2020 Bulletin 2020/24

(21)Application number: 18157694.3

(22)Date of filing:  05.04.2012
(51)International Patent Classification (IPC): 
F01N 3/20(2006.01)
F01N 11/00(2006.01)
F01N 3/10(2006.01)

(54)

SYSTEM, METHOD, AND APPARATUS FOR AFTERTREATMENT SYSTEM MONITORING

SYSTEM, VERFAHREN UND VORRICHTUNG ZUR ÜBERWACHUNG EINES NACHBEHANDLUNGSSYSTEMS

SYSTÈME, PROCÉDÉ, ET APPAREIL POUR SURVEILLANCE DE SYSTÈME DE POST-TRAITEMENT


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

(30)Priority: 05.04.2011 US 201161472177 P

(43)Date of publication of application:
11.07.2018 Bulletin 2018/28

(62)Application number of the earlier application in accordance with Art. 76 EPC:
12767966.0 / 2694785

(73)Proprietor: Cummins Emission Solutions, Inc.
Columbus, IN 47201 (US)

(72)Inventors:
  • WEI, Xi
    Asbury, Iowa 52002 (US)
  • EVERARD, David S.
    Columbus, Indiana 46201 (US)
  • QI, Baohua
    marietta, GA 30062 (US)
  • MCDANIEL, Mickey R.
    Greenwood, Indiana 46143 (US)
  • HODZEN, Edmund P.
    Greenwood, Indiana 46143 (US)
  • LI, Guoqiang
    Greenwood, Indiana 46143 (US)

(74)Representative: Pinnington, Giles Oliver 
Marks & Clerk LLP 1 New York Street
Manchester M1 4HD
Manchester M1 4HD (GB)


(56)References cited: : 
WO-A2-2008/014072
US-A1- 2010 180 576
US-A1- 2010 043 400
  
      
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description

    BACKGROUND



    [0001] The technical field generally relates to methods relating to aftertreatment systems for internal combustion engines. The introduction of aftertreatment systems into the exhaust systems of internal combustion engines introduces a number of related challenges and drawbacks.

    [0002] In one example, a NOx reduction system provides a capability to reduce NOx emissions from the engine. However, it is desirable to detect whether the NOx reduction system is properly or sufficiently reducing NOx gases. One method to determine whether the NOx reduction system is operating properly is to put a NOx sensor downstream of the NOx reduction system. However, in certain engine operating conditions, the system will be operating properly, yet the engine will be producing enough NOx that the NOx sensor detects NOx output and the system may appear to be in a failed condition. At certain engine operating conditions, the engine may be producing a small amount of NOx such that even a failed NOx reduction system is capable of converting virtually all of the presented NOx and the system may appear to be operating properly.

    [0003] Certain systems for aftertreatment rely upon an active component (e.g. a selective reduction catalyst (SCR) component), upon a reagent (e.g. urea to provide NH3 to the SCR component), and/or upon a reagent delivery system (e.g. a reagent injector). Certain failures of these systems produce failures that are difficult to detect, and/or difficult to identify a source of the failure. For example, it is challenging to distinguish between a failed catalyst on the SCR component, a failed reagent (e.g. a urea reagent container erroneously or improperly filled with water), and a failed reagent delivery system.

    [0004] Certain systems for aftertreatment rely upon having both upstream and downstream NOx measurement of the reduction catalyst to determine if the catalyst NOx conversion has degraded. Certain systems for aftertreatment rely upon inlet NOx determinations and reductant injection rate determinations that have high accuracy and precision to determine if the catalyst NOx conversion efficiency has degraded.

    [0005] US2010/043400 and US2010180576 relate to methods for controlling catalyst diagnostic tests in selective catalytic reduction systems . WO2008/014072 relates to a method and apparatus for monitoring urea injection systems in exhaust after-treatment systems.

    [0006] Therefore, further technological developments are desirable in this area.

    SUMMARY



    [0007] One embodiment is a unique method for determining a NOx reduction system failure. In particular, the present invention relates to a method of determining a fault value for a NOx reduction system NOx conversion capability in response to a comparison of averaged values of an expected NOx calculation over a period of time or execution cycles and an average number of values of a NOx sensor reading over the period of time or execution cycles.

    BRIEF DESCRIPTION OF THE DRAWINGS



    [0008] 

    Fig. 1 is a schematic flow diagram of a procedure for detecting a reductant fluid quality error.

    Fig. 2A illustrates an exemplary timeline for detecting a reductant fluid refill event.

    Fig. 2B illustrates a second exemplary timeline for detecting a reductant fluid refill event.

    Fig. 3 illustrates a timeline for detecting a reductant fluid quality error.

    Fig. 4 illustrates exemplary deNOx efficiency and deNH3 efficiency values plotted against ANR for a NOx reduction system.

    Fig. 5 illustrates an epsilon (ε) value plotted against ANR for a NOx reduction system.

    Fig. 6 depicts an exemplary behavior table for a NOx reduction system diagnostic procedure.

    Fig. 7 is a schematic flow diagram of a procedure for determining an average deNOx efficiency.

    Fig. 8 is a schematic flow diagram of a procedure for determining an averaged ε value.

    Fig. 9 is a schematic flow diagram of a procedure for monitoring a NOx reduction system NOx conversion amount according to the present invention.

    Fig. 10 provides an illustrative estimated NOx, high NOx threshold, and low NOx threshold value.

    Fig. 11 provides an illustrative estimated NOx, high NOx threshold, and low NOx threshold value, with a NOx value plotted on a logarithmic axis.

    Fig. 12 depicts an exemplary behavior table for a NOx reduction system monitoring procedure.

    Figures 1 to 8 depict reference procedures.


    DESCRIPTION



    [0009] Referencing Fig. 1, an example procedure 100 not according to the claimed invention for performing a reductant fluid quality check is depicted. The procedure 100 includes an operation 102 to determine whether a refill event is detected. If the refill event is detected, at operation 104 a urea quantity accumulator value is cleared (e.g. reset to zero) and a latching abort command is cleared, allowing the reductant fluid quality check to proceed. The latching abort command indicates that, once the abort command is set, the abort command value is held at the same value until updated by another operation.

    [0010] In response to the refill event not being detected, the procedure 100 bypasses operation 104 to continuation 106, and the procedure further includes an operation 108 to determine whether abort conditions are met. In response to the abort conditions being met, the check includes an operation to clear the urea quantity accumulator, clear the latch abort command, and exit the check. Example operations to determine whether the abort conditions are met include checking the latching abort command, and checking whether a fault is present. Example faults that cause the reductant fluid quality check to abort include a temperature sensor fault, a NOx sensor fault, a reductant injector fault, and/or a reductant tank level fault. Additionally or alternatively, any fault in the system that renders an engine-out NOx estimate, a reduction catalyst NOx conversion efficiency estimate, and/or an injected amount of reductant (relative to a commanded amount of reductant) to be sufficiently uncertain is a fault that can be utilized to abort the reductant fluid quality check.

    [0011] The reductant fluid quality check continues, when no abort condition is met, by an operation 112 to increment a urea quantity accumulator (or reductant quantity accumulator) according to an amount of urea being injected. The procedure 100 includes an operation 112 to compare the output of the urea quantity accumulator, the urea quantity, to a low test threshold, and if the urea quantity is less than the low test threshold the current execution cycle of the reductant fluid quality check is exited through continuation 128. If the urea quantity is greater than the low test threshold, the test is continued with an operation 116 to compare the urea quantity to a high test threshold.

    [0012] In response to the urea quantity being greater than the high test threshold, the procedure 100 includes an operation 124 to determine whether the urea quality check can be determined to be a PASS value. The operation 124 is determined to be a PASS value when no NOx exceedance is observed. If the operation 124 is determined to be a PASS value, the procedure 100 includes an operation 126 to clear any urea quality error before proceeding to continuation 128 and exiting.

    [0013] In response to the urea quantity being lower than the high test threshold, the procedure 100 includes an operation 120 to determine whether the check can be determined to be a FAIL value. If the check is determined to be a FAIL value, the procedure includes an operation 122 to set a urea quality error (or reductant fluid quality error), if present. An example operation 120 determines the check to be a FAIL value when a NOx exceedance is observed.

    [0014] Referencing Figs. 2A and 2B, illustrative data demonstrating an operation to detect a refill event is depicted. The curve 202a illustrate the state of the key switch 208, with a high vertical position indicating an "ON" key switch and a low vertical position indicating an "OFF" key switch. The curve 204a indicates the output of the urea tank level 206 (or reductant tank level), for example from a urea tank level sensor.

    [0015] The exemplary operation not according to the present invention includes a detection in response to a fill-up during a key off event (or other controller shutdown event wherein, during the period of the shutdown, a signal from a reductant tank level sensor is unavailable) illustrated in the top timeline. At a first time 210 the urea tank level is shown to be low at a time when a key switch is turned off. In the example of the upper timeline, the signal from the urea tank level is unavailable while the keyswitch remains off. The signal is resumed at a second time 212, and when the urea tank level is determined to be high, a refill event is detected.

    [0016] The difference between the low and the high tank levels that is required to determine that a refill event has occurred may be any amount, including any minimally significant amount up to an amount requiring that the tank be substantially filled with new reductant fluid before a refill event is detected. For example, the refill event may detect top-off events where a minor but significant amount of urea is added, only events from a threshold low level to ensure that most of the present urea is newly added urea, or events where a specified percentage of the entire capacity of the urea tank is added (e.g. 10%, 20%, 50%, or other value). One of skill in the art will recognize that requiring more complete refills improves the reliability of a given reductant fluid quality check to properly determine the NOx reduction capacity of the replacement reductant fluid, but it will also reduce the number of opportunities to perform a reductant fluid quality check, as partial fill-ups of insufficient size to trigger a refill detection will extend the time period between checks.

    [0017] Referencing Fig. 2B illustrative data demonstrates an exemplary operation to detect a refill event. In the operations of the lower timeline, while the key switch remains on and the urea tank level signal remains active, a fill up event occurs at the time period 214. In certain exemplary operations, when a urea tank level increase is detected, an initial urea tank level and a final urea tank level are determined according to when the tank level rise begins and ends, and/or according to when the tank level rise begins and a tank level decrease begins. According to the difference between the final and initial urea tank levels, a refill event may be detected. The amount of rise determined to be a refill event is determined under similar considerations for an exemplary operation utilizing Fig. 2B or Fig. 2A.

    [0018] Referencing Fig. 3, example operations of a reductant fluid quality check procedure not according to the present invention are shown on a timeline of illustrative data 300. The upper data timeline indicates the "DEF" tank level (diesel exhaust fluid), which may be a level of any reductant fluid. The lower timeline indicates an asterisk 318, 320 at each reductant fluid quality check result. Certain ones of the reductant fluid quality check results are utilized, and certain others of the reductant fluid quality check result are ignored. At the bounded times 302, 304 in the upper timeline, a refill event is detected due to the rise in the DEF tank level.

    [0019] Referencing the lower timeline, test data points occurring before the DEF tank refill event are ignored and the test results are not used to set or clear a reductant fluid quality error. After the DEF tank refill event, the test data points are likewise ignored until an amount of reductant is injected that exceeds the low test threshold - occurring at time 306 in the illustration. The test continues until the high test threshold amount of reductant is injected, occurring at time 308 in the illustration. The test point 318 that occurs between the times 306, 308 is utilized, and since a sufficient SCR conversion efficiency 322 is demonstrated reductant fluid quality error is cleared, reset, decremented, or other actions are taken consistent with a passed check on the NOx reduction system. In the example procedure, test values occurring later than the high test threshold may be ignored, or may be utilized to clear or decrement a reductant fluid quality error. In one form, test values occurring later than the high test threshold are not utilized to increment or set the reductant fluid quality error.

    [0020] Further in Fig. 3, a second DEF tank refill event occurs between times 314, 316. The low test threshold amount of urea injected is passed at time 310 in the example, and the high test threshold amount of urea injected is passed at time 312 in the example. A test value 320 indicates that a NOx exceedance event occurred. The test value 320 occurs before the high test threshold is reached, and a reductant fluid quality error is set or incremented, or other actions are taken consistent with a failed check on the NOx reduction system. In the example of Fig. 3, the two test values occurring after the high test threshold is reached are not utilized.

    [0021] An example procedure for determining whether an aftertreatment deNOx system failure is present and for determining the source of the deNOx system failure is described following. The example procedure for determining the deNOx system failure and source may be combined with other procedures to eliminate potential causes for system failure and/or performance degradation.

    [0022] The exemplary procedure includes determining a deNOx efficiency within a temperature and exhaust flow range where the deNOx efficiency has a reduced sensitivity to variation and uncertainty in the sensing values. The procedure includes determining a normalized deNOx efficiency, which includes a ratio between measured deNOx efficiency and expected deNOx efficiency, such as shown in Equation 1. The normalized deNOx efficiency is calculated for the data points with an ammonia to NOx ratio (ANR) higher than a stoichiometric ANR (6).



    [0023] It has been found that at ANR values above the β value, the deNOx efficiency is not sensitive to ANR, which reduces the noise introduced from NOx reduction catalyst inlet NOx sensing error (or modeled inlet NOx error) and urea dosing error. Accordingly, the normalized deNOx efficiency can be more indicative of the effects of the NOx reduction catalyst and the reductant fluid quality, while helping decouple the effects of inlet NOx determination errors and reductant injection rate errors. Referencing Fig. 4, simulated illustrative data is shown illustrating the deNOx efficiency behavior of various operating curves. The curves 416, 418, 420, and 424 illustrate example deNOx efficiency values as a function of the ANR, and illustrate that the deNOx efficiency rises linearly with the ANR over a period of operating points below the β value, begins a non-linear transition region around the β value, at flattens at high ANR values to a value which is not responsive to the ANR at high ANR values. The values 422 represent a number of possible curves that may be determined for a given system, similar to the curves 416, 418, etc.

    [0024] Referencing again Fig. 4, the curves 406, 408, 410, 414 illustrate example deNH3 efficiency curves corresponding to the deNOx efficiency curves 416, 418, 420, 424. The curves for deNOx efficiency and deNH3 efficiency meet at the β value, or at the stoichiometric point. The values 412 represent a number of possible curves that may be determined for a given system, similar to the curves 406, 408, etc. The curves 406, 408, 410, 414 are illustrated to provide a fuller understanding of the catalyst activity in the system.

    [0025] For the data points with ANR less than β, the procedure includes determining an ε value. The ε value is defined as the ratio between dosing commands and NOx removed in the catalyst (see Equation 2). In the example of Equation 2, the ε value is a mass balance ratio. For example, as depicted in the illustrative data of Fig. 5, while the deNOx efficiency is insensitive to ANR at high ANR values - specifically above β - the ε value becomes relatively insensitive to ANR at low values of ANR. The curves 504 depicts the ε value as a function of ANR. As depicted in the illustrative data of Fig. 4, the ε value becomes relatively insensitive to ANR at low values of ANR, specifically below β.



    [0026] When evaluated in the regions where it is insensitive to ANR, the normalized deNOx efficiency is more sensitive to catalyst deNOx efficiency deterioration, and decouples engine-out NOx determinations and urea injector errors. Generally, a deteriorated deNOx efficiency will move downward in the curves, for example from operating curve 416 to operating curve 418. When evaluated in the regions where it is insensitive to ANR, the ε value is more sensitive to urea delivery, and decouples catalyst deNOx efficiency deterioration.

    [0027] Referencing Fig. 6, an example logic description to utilize the normalized deNOx efficiency and the ε value is illustrated. In the example of Fig. 6, where both the deNOx efficiency and the ε value indicate a component failure, the failure is attributable to any of the deNOx catalyst, the reductant dosing system, or the reductant fluid quality. Where both of the deNOx efficiency and the ε value indicate a PASS, then no component failure is indicated. Where the ε value indicates a component failure and the deNOx efficiency indicates a PASS, the component failure is narrowed to the reductant dosing system or the reductant fluid quality. Where the ε value indicates a PASS and the deNOx efficiency indicates a component failure, the component failure is narrowed to the deNOx catalyst or the reductant fluid quality.

    [0028] Referencing Fig. 6, an illustrative component failure logic 600 is depicted. The component failure logic 600 is helpful to reduce maintenance costs and failure diagnostic time, as well as to separate coupled issues in diagnosing a failed component. Alternatively or additionally, the information from Fig. 6 can be utilized with other information available in the system to further determine which component is failed. For example, if a catalyst temperature excursion is observed immediately before a failure, it may be determined to be more likely to be a failed catalyst than a reductant fluid quality failure. A technician may manually check a reductant fluid quality or a reductant doser system. In one form, a fault present in the reductant doser system, a reductant tank level that is observed to drop as expected over time, results from an active diagnostic performed on the reductant dosing system, and/or any other information available in the system may be utilized with the information from Fig. 6 to determine which component of a NOx reduction aftertreatment system has failed.

    [0029] In the example component failure logic 600 of Fig. 6, a first column 602 depicts an ε based failure determination, for example according to Equation 2 and the nominal operations depicted in Fig. 5 or similar information calibrated for a particular system. A second column 604 depicts a normalized deNOx efficiency based failure determination, for example according to Equation 1 and the deNOx efficiency curves depicted in Fig. 4 or similar information calibrated for a particular system. In the example logic 600, where the ε indicates a failure and the normalized deNOx efficiency indicates a failure, the failure is determined to be one of the catalyst, the dosing injector, or the reductant quality, although the diagnostic differences of the ε and normalized deNOx efficiency do not separate these component failures. Where the ε indicates a failure, but the normalized deNOx efficiency does not indicate a failure, the catalyst is understood to be working properly and the component failure is narrowed to a dosing injector or the reductant quality. Where the ε indicates a pass and the normalized deNOx efficiency indicates a failure, the component failure is understood to be either the catalyst or the reductant quality. Where both the ε and the normalized deNOx efficiency indicate a pass, the system is understood to be working correctly. The output of the logic 600 can be combined with other information, for example a reductant quality check such as depicted in Fig. 1, to further narrow the diagnosis of any failure.

    [0030] Another example procedure is described for diagnosing whether reductant fluid is proper, diluted, replaced, or otherwise improper. The procedure includes an operation to determine whether a tank refill event is detected. An example operation includes interpreting a reductant tank level value, for example from a tank level sensor, and in response to the reductant tank level value determining the reductant tank is recently filled. The procedure further includes determining a tank refill event in response to the reductant tank level value. In response to the tank refill event, the procedure includes an operation to clear a reductant accumulator value and proceeding with a reductant fluid quality check. The operation also clears an abort latch, such that a check at operation will indicate that abort conditions are not met for the purpose of checking a new urea tank, although other abort conditions may be otherwise met.

    [0031] The procedure further includes determining a NOx emissions amount, for example determined from reductant dosing commands, inlet and outlet NOx levels for a reductant catalyst, an estimated temperature for the reductant catalyst, and an exhaust flow rate for an engine providing the exhaust treated by the reductant catalyst. The inlet and outlet NOx level values may be determined from a sensor, and the inlet NOx level may alternatively or additionally be determined from a model. The reductant catalyst temperature may be determined from an inlet sensor, outlet sensor, a mid-brick sensor, and/or from a weighted average of available sensors or a modeled value based upon exhaust and/or turbine outlet temperatures.

    [0032] The exemplary procedure further includes determining a NOx exceedance event in response to the NOx emissions amount. In response to the NOx exceedance event occurring within a predetermined period after the tank refill event, a reductant fluid quality failure is detected. In certain exemplary procedures, determining the NOx exceedance event includes accumulating a reductant injected amount during a period of the reductant fluid quality check. In response to the reductant injected amount being lower than a low test threshold, the reductant fluid quality check is exited without conclusion. In response to the reductant injected amount being greater than a high test threshold, the procedure includes an operation to clear any reductant fluid quality error if a NOx exceedance is not detected. In response to the reductant injected amount being greater than the low test threshold but less than the high test threshold, the procedure includes an operation to set a reductant fluid quality error if a NOx exceedane is detected, and to clear a reductant fluid quality error if the NOx exceedance is not detected.

    [0033] The detection of the NOx exceedance includes determining that a threshold amount of NOx is being emitted from the system, where the threshold amount of NOx is a selected amount of NOx. Exemplary and non-limiting threshold amounts of NOx include an amount exceeding an emissions target, an amount exceeding a short-term emissions target, an amount exceeding any other NOx target value, and/or an amount exceeding any selected target with an added or subtracted estimated margin of error. The margin of error may be added, for example, to ensure that a given NOx emissions level is actually greater than the NOx target value. The margin of error may be subtracted, for example, to ensure that a given NOx emissions level does not exceed the NOx target value before a reductant fluid quality error is set. The margin of error is a value that may be updated over time, for example to the uncertainty of a NOx estimate at current operating conditions of the system.

    [0034] Referencing Fig. 7, an example procedure 700 for monitoring an aftertreatment system not according to the present invention is illustrated. The procedure 700 includes an operation 702 to check whether abort conditions for the procedure are met. Exemplary abort conditions include a fault in a hardware component and/or sensor related to the aftertreatment system, a transient operating condition being present, and a reductant dosing system that is presently available to dose (e.g. no conditions are present that prevent the dosing system from providing reductant during the monitoring procedure). The transient operating condition can be a transient exhaust temperature, exhaust flow, and/or engine-out NOx level value. In certain procedures, the presence of steady state operating conditions, or the lack of transient operating conditions, allows the monitoring procedure to proceed. Where abort conditions are present, the procedure includes an operation 704 to reset a counter (a samples taken counter) and an efficiency accumulator.

    [0035] The procedure 700 further includes an operation 706 to determine whether screening conditions are present. Example screening conditions include determining that an SCR catalyst temperature is within an operating range, determining that an exhaust flow value or a catalyst space velocity is in an operating range, determining that a dosing command is not presently restricted or limited, and/or that a NOx sensor output is operating within a high confidence regime. Example conditions for the NOx sensor output to operate in a high confidence regime include the NOx sensor output value being within a rational range, the NOx sensor value being lower than a threshold value (e.g. not near the top of the operating range such that it might become unreliable during the test), that ambient air pressure is within a normal range, that an NH3 slip estimate is within a normal range, and/or that an NO2 slip estimate is within a normal range. In certain procedures, some test screening or testing abort conditions may be characterized as an abort condition or a screening condition. Generally, where a condition should be absent it is characterized as an abort condition for the test to proceed, and where a condition should be present it is characterized as a screening condition for the test to proceed, but such characterizations are not limiting to any particular procedure, and certain conditions may be an abort condition in certain procedures and a screening condition in certain procedures.

    [0036] The procedure 700 includes an operation 708 to determine whether the present ANR is greater than the β value. The β value is a stoichiometric value of ANR, or a value near stoichiometric wherein the variability in the deNOx efficiency as a function of the ANR is acceptably low. Where the ANR is below the β value, the procedure 700 exits the current execution cycle through continuations 712, 716. Where the ANR is above the β value, the procedure 700 continues with an operation 710 to calculate and accumulate a normalized efficiency value, for example as in Equation 1. The operation 700 to accumulate the normalized efficiency value includes any operation enabling the averaging of a number of normalized efficiency values, including storing a number of efficiency values in a memory buffer, utilizing a filtered or weighted averaged efficiency value that captures historical efficiency value information over a number of efficiency value points, and similar operations understood in the art.

    [0037] The procedure 700 further includes an operation 714 to determine whether a sufficient number of efficiency value samples have been taken. The operation 714 to determine whether a sufficient number of samples have been taken includes determining whether a predetermined number of samples have been taken, determining whether enough samples have been taken to provide a given statistical confidence in the average of the samples, and/or may further include weighting of the confidence increment provided by each of the samples in response to the particular reliability of a given sample and determining whether the accumulated confidence exceeds a threshold value.

    [0038] Where the procedure 700 has not resulted in a sufficient number of samples, the procedure 700 exits the current execution cycle through the continuation 716. Where the procedure 700 has provided sufficient samples, the procedure 700 includes an operation 718 to calculate an averaged efficiency. The operation 718 to calculate the averaged efficiency includes an operation to determine a statistically significant average - for example a mean or median average, an operation to utilize a moving average as the average, and/or an operation to utilize a filtered value as an average. Any other averaging operations understood in the art are contemplated herein. The procedure includes an operation 720 to clear the efficiency accumulator, which may further include resetting any filters, moving averages, or other information history parameters.

    [0039] Referencing Fig. 8, an exemplary procedure 800 not in accordance with the present invention for monitoring an aftertreatment system is illustrated. The procedure 800 includes an operation 802 to check whether abort conditions for the procedure are met. Exemplary abort conditions include a fault in a hardware component and/or sensor related to the aftertreatment system, a transient operating condition being present, and a reductant dosing system that is presently available to dose (e.g. no conditions are present that prevent the dosing system from providing reductant during the monitoring procedure). The transient operating condition can be a transient exhaust temperature, exhaust flow, and/or engine-out NOx level value. In certain procedures, the presence of steady state operating conditions, or the lack of transient operating conditions, allows the monitoring procedure to proceed. Where abort conditions are present, the procedure includes an operation to reset a counter (a samples taken counter) and an ε accumulator.

    [0040] The procedure 800 further includes an operation 806 to determine whether screening conditions are met. The abort conditions and screening conditions of the procedure 800 are similar to but need not be the same as the abort conditions and screening conditions of the procedure 700. For example, procedure 800 utilizes values of ANR below β, and determines values of ε rather than normalized deNOx efficiency. The criteria, operating ranges of sensors, and operating margin within the operating range of sensors and hardware components, to determine whether ε can be reliably determined and an ε-based test successfully completed can differ from the same parameters for a deNOx efficiency based test.

    [0041] The procedure 800 includes an operation 808 to determine whether the present ANR is less than the β value. The β value is a stoichiometric value of ANR, or a value near stoichiometric wherein below the β value the variability in the ε as a function of the ANR is acceptably low. Where the ANR is above the β value, the procedure exits the current execution cycle through the continuations 816, 818. Where the ANR is below the β value, the procedure 800 continues with an operation 810 to calculate and accumulate an ε value, for example as in Equation 2. The operation 810 to accumulate the ε value includes any operation enabling the averaging of a number of ε values, including storing a number of ε values in a memory buffer, utilizing a filtered or weighted averaged ε value that captures historical ε value information over a number of ε value points, and similar operations understood in the art.

    [0042] The procedure 800 further includes an operation 812 to determine whether a sufficient number of ε value samples have been taken. The operation to determine whether a sufficient number of samples have been taken includes determining whether a predetermined number of samples have been taken, determining whether enough samples have been taken to provide a given statistical confidence in the average of the samples, and/or may further include weighting of the confidence increment provided by each of the samples in response to the particular reliability of a given sample.

    [0043] Where the procedure 800 has not resulted in a sufficient number of samples, the procedure exits the current execution cycle. Where the procedure 800 has provided sufficient samples, the procedure 800 includes an operation 814 to calculate an averaged ε value. The operation 814 to calculate the averaged ε value includes an operation to determine a statistically significant average - for example a mean or median average, an operation to utilize a moving average as the average, and/or an operation to utilize a filtered value as an average. Any other averaging operations understood in the art are contemplated herein. The procedure includes an operation 820 to clear the ε accumulator, which may further include resetting any filters, moving averages, or other information history parameters.

    [0044] Another exemplary set of procedures includes a procedure for monitoring a NOx reduction catalyst conversion capability. In certain exemplary procedures, the procedure is operable with a NOx sensor downstream of the NOx reduction catalyst, and no NOx sensor upstream of the NOx reductions catalyst. The procedure may be useful in a system having an upstream NOx sensor, for example as a backup diagnostic for the NOx reduction catalyst if the upstream NOx sensor is failed or suspect. The procedure includes an operation to determine an expected NOx emissions value - the NOx emissions value being a NOx emissions value downstream of the NOx reduction catalyst (e.g. "tailpipe" NOx). An exemplary expected NOx emissions value is described with reference to Figs. 10 and 11 following, wherein the diagonal line 1010, 1110 is utilized as the expected NOx emissions value.

    [0045] The procedure further includes determining that a present engine out NOx amount is lower than a NOx catalyst threshold capability value and greater than a failed NOx catalyst threshold capability value. The NOx catalyst threshold capability value is a NOx amount where a fully capable NOx catalyst experiences a decreasing NOx conversion capability due to high quantity of NOx passing through the catalyst. The failed NOx catalyst threshold capability value is a NOx amount where a severely degraded NOx catalyst will nevertheless exhibit a very high NOx conversion due to the low quantity of NOx passing through the catalyst. Additionally or alternatively, the high and low NOx threshold values are further bounded by a region wherein a NOx model is determined to be reliable. Exemplary high and low NOx threshold values are described with reference to Figs. 10 and 11 following. Fig. 10 depicts test cell data 1000 taken for a particular system run through a predetermined load schedule, and Fig. 11 depicts test cell data 1100 for a similar system run through a different predetermined load schedule. The data includes the engine out NOx output 1002, 1102 as a function of the fuel mass over charge mass 1004. The left vertical line 1006 is selected according to the low NOx threshold value, and the right vertical line 1008 is selected according to the high NOx threshold value. The example thresholds 1006, 1008 are non-limiting.

    [0046] The procedure includes determining the present engine out NOx amount in response to engine fueling, engine torque, and/or a present engine speed. Additionally or alternatively, the procedure includes determining the present engine out NOx amount in response to an intake manifold pressure and one or more timing values of injected fuel (or spark timing for a spark-ignition engine). Any engine out NOx model understood in the art is contemplated herein.

    [0047] In one example, the low NOx value 1006 (e.g. the failed NOx catalyst threshold capability value) is determined at a low value of a fuel mass-flow to charge mass-flow ratio, and the high NOx value 1008 (e.g. the NOx catalyst threshold capability value) is determined at a high value of the fuel mass-flow to charge mass-flow ratio. When the observed fuel mass-flow to charge mass-flow ratio is between the low value and the high value, the procedure to monitor the NOx reduction catalyst proceeds. In a further procedure, an estimated NOx value for the engine is determined from a calibration line 1010, 1110 between the low value and the high value that bounds an observed engine out NOx amount, or that bounds a majority of observed engine out NOx amount data points.

    [0048] Referencing Fig. 10, a plot 1000 of engine-out NOx amounts as a function of fuel mass-flow to charge mass-flow ratios are illustrated. The data points in Fig. 10 are taken from a test cell for a particular engine, and are representative of the type of data that an operator can readily determine for a given system. In the embodiment of Fig. 10, the left vertical line 1006 is taken as the low value of a fuel mass-flow to charge mass-flow ratio, and the right vertical line 1008 is taken as the high value of a fuel mass-flow to charge mass-flow ratio. The low and high values may be determined according to the quality of the model, for example selecting logical bounding points for reliable data, and/or according to the engine-out NOx amounts that are treatable by a properly functioning NOx reduction catalyst (for the high value) and the engine-out NOx amounts that would be treatable even for a failed or degraded NOx reduction catalyst (for the low value). The diagonal line 1010 between the high and low values, in one form, is the engine-out NOx amount estimate to be utilized in a procedure such as the procedure described in the section referencing Fig. 9.

    [0049] The procedure further includes an operation to perform a screening step, wherein a number of screening parameters are checked, and the operation to monitor the NOx reduction catalyst NOx conversion capability is continued if the screening parameters pass. Exemplary and non-limiting screening parameters include the NOx reduction catalyst within a proper operational temperature, an exhaust flow of the engine being within a specified range, a rate of change of the NOx reduction catalyst temperature being lower than a threshold value, a reductant injection command value not being limited by a system constraint (i.e. the control system for the reductant injection determination is commanding a reductant injection amount that is estimated to be sufficient to convert a designed amount of NOx), the downstream NOx sensor value is reading within a specified range and does not have a fault, the rate of change of the NOx sensor value is below a threshold value, an ambient pressure is within a specified range, an estimated NH3 slip amount is within a range or below a threshold, and an estimated NO2 slip amount is within a range or below a threshold value. Additional screening parameters include a determination that the engine is at steady state operation, that an engine speed rate of change is below a threshold value, and/or that an engine fueling or torque value rate of change is below a threshold value.

    [0050] The determination of ranges for each screening parameter depends upon the hardware present in the system, the NOx amount that is considered for the system (e.g. due to relevant emissions limits, etc.), and is a mechanical step for one of skill in the art having the benefit of the disclosures herein. Each range and limit for the screening parameters is selected to ensure that the NOx reduction catalyst is operating under nominal conditions wherein a properly operating catalyst should be expected to succeed and a sufficiently degraded or failed catalyst should be expected to provide insufficient NOx reduction.

    [0051] An exemplary procedure includes determining an averaged expected NOx value and an averaged measured NOx value from the NOx sensor downstream of the NOx reduction catalyst, and determining whether the NOx reduction capability is failed in response to the averaged measured NOx values. The averaged NOx values may be averages of a number of values stored in a buffer, a filtered value of each parameter (with the same or distinct time constants), moving averages of the NOx values, or values determined from other averaging mechanisms known in the art. The threshold to determine a failed NOx conversion capability is selectable according to the specific parameters of the contemplated system, and may be a difference of 20%, 30%, 50%, or greater NOx amounts. In certain embodiments, the difference may be a ratio difference of observed:expected NOx (e.g. 1.2:1), an absolute value of NOx (e.g. 10 g/hr), and/or a difference in selected units (e.g. 0.5 g/hp-hr difference).

    [0052] Another exemplary procedure includes determining whether an engine-out NOx regime is in a low, nominal, or high output region. For example, referencing Fig. 10, the low region may be left of the left vertical line 1006, the nominal region may be between the vertical lines 1006, 1008, and the high region may be to the right of the right vertical line 1008. The exemplary procedure further includes determining whether the observed NOx amount is higher or lower than the expected NOx amount. Referencing Fig. 12, an exemplary response table 1200 is illustrated for the exemplary procedure.

    [0053] In response to the observed tailpipe NOx amount being lower 1208 than the expected NOx amount, in the low engine-out NOx regime 1202 the procedure in region 1212 includes blocking the monitor from passing the NOx reduction capability, or blocks the monitor from clearing a NOx reduction capability fault. In the region 1212, an example procedure in certain embodiments does not determine the NOx reduction capability is failed. In response to the observed tailpipe NOx amount being lower 1208 than the expected NOx amount, in the nominal engine-out NOx regime 1204, the procedure in region 1214 determines the NOx reduction capability is passed or allows the monitor to clear a NOx reduction capability fault. In response observed tailpipe NOx amount being lower 1208 than the expected NOx amount, in the high engine out NOx region 1206, the example procedure in the region 1216 determines the NOx sensor to be in error or to fail a sensor rationality check.

    [0054] In response to the observed tailpipe NOx amount being higher 1210 than the expected NOx amount, in the low engine-out NOx regime 1202 the procedure in region 1218 determines the NOx sensor to be in error or to fail a sensor rationality check. In response to the observed tailpipe NOx amount being higher 1210 than the expected NOx amount, in the nominal engine-out NOx regime 1204, the procedure in region 1220 determines the NOx reduction capability is failed or allows the monitor to set a NOx reduction capability fault. In response observed tailpipe NOx amount being higher 1210 than the expected NOx amount, in the high engine out NOx region 1206, the example procedure in the region 1222 excludes the operations from affecting any sensor or system failures, and/or from allowing faults to be set or cleared.

    [0055] Referencing Fig. 9, a schematic flow diagram illustrates a procedure 900 for monitoring a NOx reduction system according to the present invention. The procedure 900 includes an operation 916 to determine whether an engine fuel flow 902 and an engine mass flow 904 are below threshold values to perform a monitoring check of the NOx reduction system. The procedure 900 further includes an operation 918 to determine whether the rate of change of the engine fuel flow 902 and the engine mass flow 904 are below threshold values to perform the monitoring check of the NOx reduction system. The threshold values for the engine fuel flow 902 and engine mass flow 904, and the rates of change thereof, may be set for any reason, including without limitation controlling the test to occur within certain power or emissions limits, within certain catalyst space velocity limits, and/or within certain exhaust temperature limits. The outputs of the operations 916, 918 are input as logical values to an AND block 926. The procedure 900 further includes an operation 922 to determine whether a value of a

    is between a high and low threshold. The value

    may be determined according to any method; a lookup table utilizing fuel massflow 902 and charge massflow 904 is consistent with the depiction in the example. The procedure 900 further includes operations to determine whether data screening parameters 920 have values indicating the monitor should be performed.

    [0056] In response to all of the logical values for the determining operations entering the AND block 926 being TRUE, the procedure 900 includes an enable operation 928 for each of the operations 932, 934. The procedure 900 further includes an operation 912 to determine an expected NOx emissions value 914. The example operation 912 utilizes an engine speed 916, an engine torque 918, and a weighting factor 910. The weighting factor 910 may be determined in response to various engine operation conditions, including at least an EGR fraction, a charge temperature, the timing of fueling, and/or a fuel rail pressure. Additionally or alternatively, any NOx model to determine an expected NOx emissions value is contemplated herein.

    [0057] The procedure 900 further includes, in response to the enabling operation 928, calculating an average value of the expected NOx tailpipe a first operation 932 to calculate an average of a number of values of an expected NOx calculation over a period of time or execution cycles, and a second operation 934 to calculate an average of a number of values of a NOx sensor reading 930 over the period of time or execution cycles. The NOx sensor reading is interpreted from a NOx sensor positioned downstream of the NOx reduction catalyst of the NOx reduction system. The procedure 900 further includes an operation 936 to compare the averaged values, and an operation 938 to determine a fault value (increment, set, decrement, and/or clear) in response to the comparison.

    [0058] An example set of embodiments is a method including determining whether a urea refill event is detected, and in response to the refill event being detected, clearing a urea quantity accumulator value and clearing a latching abort command. The method includes determining whether urea fluid quality check abort conditions are met, and in response to the abort conditions being met, clearing the urea quantity accumulator, clearing the latching abort command, and exiting the urea fluid quality check. The method further includes, in response to the abort conditions not being met, incrementing the urea quantity accumulator according to an amount of urea being injected. The method further includes comparing the accumulated urea quantity to a low test threshold, and in response to the accumulated urea quantity being less than the low test threshold, exiting the current execution cycle of the reductant fluid quality check. The method further includes, in response to the accumulated urea quantity being greater than the low test threshold, comparing the accumulated urea quantity to a high test threshold, and in response to the urea quantity being greater than the high test threshold, determining whether a NOx exceedance for NOx emissions amount is observed and clearing a urea quality error in response to the NOx exceedance not being observed.

    [0059] Certain further embodiments of the example method are described following. An example method includes in response to the accumulated urea quantity being less than the high test threshold, determining whether the a NOx exceedance is observed and setting a urea quality error in response to the NOx exceedance being observed and clearing the urea quality error in response to the NOx exceedance not being observed. An example method includes determining an averaged ε value including ANR/deNOx η values taken at ammonia-to-NOx ratio (ANR) values below a β value, wherein β is approximately a stoichiometric ANR value, determining an averaged deNOx η value comprising deNOx η values taken above the β value, and in response to the averaged ε value and the averaged deNOx η value, determining whether a NOx reduction system is in a PASS or FAIL state. An example method further includes determining the state of the NOx reduction system in response to the averaged ε value and the averaged deNOx η value comprises determining the NOx reduction system is in a PASS state in response to the averaged ε value and the averaged deNOx η value both indicating a passing value. Additionally or alternatively, the method includes determining the state of the NOx reduction system in response to the averaged ε value and the averaged deNOx η value by determining the NOx reduction system is in a failed state, with the failure being at least one of a urea injector and the urea in response to the averaged ε value indicating a failing value and the averaged deNOx η value indicating a passing value. In certain embodiments, the method includes determining the failure to be a urea injector in response to the urea fluid quality error being one of cleared and not set.

    [0060] An example method includes determining the state of the NOx reduction system in response to the averaged ε value and the averaged deNOx η value by determining the NOx reduction system is in a failed state, with the failure being at least one of a NOx reduction catalyst and the urea in response to the averaged ε value indicating a failing value and the averaged deNOx η value indicating a passing value. In certain embodiments, the method further includes determining the failure to be a NOx reduction catalyst in response to the urea fluid quality error being one of cleared and not set. In certain embodiments, the averaged deNOx η value includes a normalized deNOx η value. An example method includes each ε value determined for the averaged ε value being determined according any one of the terms selected from the equation:

    where NH3_in is the NH3 concentration into the deNOx catalyst, wherein NOx_in is the NOx concentration into the deNOx catalyst, wherein the NOx_out is the NOx concentration out of the deNOx catalyst.

    [0061] An example method includes each deNOx η value determined for the averaged deNOx η value being determined according to the equation:

    where ηNormalized is the deNOx η value, and wherein ηnominal is an expected deNOx efficiency.

    [0062] As such, according to an embodiment of the present invention, there is provided a method including determining whether an engine fuel massflow and an engine charge massflow have values below threshold values, determining whether the engine fuel massflow and an engine charge massflow have rates of change below threshold values, determining whether a NOx reduction system monitor operation can be performed, and determining whether a value of a ratio of the engine fuel mass flow to the engine charge mass flow

    is between a high and low threshold. The method further includes, in response to all of the logical values for the determining operations being TRUE, calculating an average of a number of values of an expected NOx calculation over a period of time or execution cycles, and calculating an average of a number of values of a NOx sensor reading over the period of time or execution cycles. The method includes comparing the averaged values and determining a fault value for a NOx reduction system NOx conversion capability in response to the comparing.

    [0063] Certain further embodiments of the method are described following. An example method includes calculating an average of a number of values of an expected NOx calculation over a period of time or execution cycles by operating a NOx reduction model of the NOx reduction system. An example method includes calculating an average of a number of values of an expected NOx calculation over a period of time comprises using lookup values from a predetermined function of engine out NOx values as a function of the values for the ratio of the engine fuel mass flow to the engine charge mass flow (

    values. In certain further embodiments, the method includes the high and low thresholds of the

    being validated operating ranges for the predetermined function, and/or the predetermined function being a linear increasing function with



    [0064] Also described herein is a method including determining an averaged ε value comprising ANR/deNOx η values taken at ammonia-to-NOx ratio (ANR) values below a β value, where β is approximately a stoichiometric ANR value for a NOx reduction system fluidly coupled to the exhaust of an internal combustion engine, determining an averaged deNOx η value being deNOx η values taken above the β value, and in response to the averaged ε value and the averaged deNOx η value, determining whether the NOx reduction system is in a PASS or FAIL state. In certain embodiments, the method includes determining the state of the NOx reduction system in response to the averaged ε value and the averaged deNOx η value by determining that the NOx reduction system is in a PASS state in response to the averaged ε value and the averaged deNOx η value both indicating a passing value. Additionally or alternatively, the method includes determining the state of the NOx reduction system in response to the averaged ε value and the averaged deNOx η value by determining the NOx reduction system is in a failed state, with the failure being at least one of a urea injector and a urea fluid quality, in response to the averaged ε value indicating a failing value and the averaged deNOx η value indicating a passing value, where the urea is a reductant fluid for the NOx reduction system and the urea injector is operationally coupled to the exhaust at a position upstream of a selective reduction catalyst. In certain further embodiments, the method includes determining the failure to be the urea injector in response to a urea fluid quality check passing the urea fluid quality.

    [0065] In certain procedures, the method includes determining the state of the NOx reduction system in response to the averaged ε value and the averaged deNOx η value by determining the NOx reduction system is in a failed state, with the failure being at least one of a NOx reduction catalyst and the urea, in response to the averaged ε value indicating a failing value and the averaged deNOx η value indicating a passing value. In certain procedures, the method includes determining the failure to be a NOx reduction catalyst in response to the urea fluid quality check passing the urea fluid quality. Additionally or alternatively, the averaged deNOx η value is a normalized deNOx η value.

    [0066] In certain procedures, the method includes each ε value determined for the averaged ε value to be determined according any one of the terms selected from the equation:

    where NH3_in is the NH3 concentration into the deNOx catalyst, wherein NOx_in is the NOx concentration into the deNOx catalyst, wherein the NOx_out is the NOx concentration out of the deNOx catalyst. In certain embodiments, the method includes each deNOx η value determined for the averaged deNOx η value to be determined according to the equation:

    where ηNormalized is the deNOx η value, and wherein ηnominal is an expected deNOx efficiency.

    [0067] Also described herein but not claimed is a system including an internal combustion engine having an exhaust, a NOx reduction system having a selective catalytic reduction (SCR) catalyst, and a reductant injector operationally coupled to the exhaust at a position upstream of the SCR catalyst and receiving reductant from a reductant source. The system includes a means for determining a failure in one of the reductant injector, the SCR catalyst, and the reductant. In certain configurationss, the system includes the means for determining a failure further including a means for distinguishing a failure source between the reductant injector, the SCR catalyst, and the reductant. In still further configurations, the system includes the means for determining a reductant failure including means for detecting a reductant source refill event, and accumulating an amount of reductant injected over a period of time following the reductant source refill event. In certain further configurations, the system includes the means for determining a failure of the reductant injector in response to: a failed ε value, a passed normalized deNOx efficiency value, and the determining the failure of the reductant determines that the reductant is not failed. Additionally or alternatively, the system includes a means for determining a failure of the SCR catalyst in response to: a passed ε value, a failed normalized deNOx efficiency value, and the determining the failure of the reductant determines that the reductant is not failed.

    [0068] Also described herein but not claimed is a system including an internal combustion engine having an exhaust, a NOx reduction system having a selective catalytic reduction (SCR) catalyst, a reductant injector operationally coupled to the exhaust at a position upstream of the SCR catalyst and receiving reductant from a reductant source, and a means for determining a failure in the NOx reduction system in response to an engine-out NOx amount and a NOx measurement at a position downstream of the SCR catalyst. In certain configurations, the means for determining a failure in the NOx reduction system determines the NOx reduction system is passed in response to the engine-out NOx amount in a middle range and the NOx measurement in a low range. Additionally or alternatively, the means for determining a failure in the NOx reduction system determines the NOx reduction system is failed in response to the engine-out NOx amount in a middle range and the NOx measurement in a high range. In certain configurations, the means for determining a failure in the NOx reduction system determines a NOx sensor providing the NOx measurement is failed in response to the engine-out NOx amount in a high range and the NOx measurement in a low range. In certain configurations, the means for determining a failure in the NOx reduction system determines a NOx sensor providing the NOx measurement is failed in response to the engine-out NOx amount in a low range and the NOx measurement in a high range.

    [0069] 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 certain exemplary embodiments have been shown and described and that all changes and modifications that come within the scope of the claims are desired to be protected. Any subject matter not falling within the scope of the claims is for reference only. In reading the claims, it is intended that when words such as "a," "an," "at least one," or "at least one portion" are used there is no intention to limit the claim to only one item unless specifically stated to the contrary in the claim. When the language "at least a portion" and/or "a portion" is used the item can include a portion and/or the entire item unless specifically stated to the contrary.


    Claims

    1. A method (900), comprising:

    determining (916) whether an engine fuel massflow (902) and an engine charge massflow (904) have values below threshold values;

    determining (918) whether the engine fuel massflow and an engine charge massflow have rates of change below threshold values;

    determining (926) whether a NOx reduction system monitor operation can be performed;

    determining (922) whether a value of a ratio of the engine fuel massflow to the engine charge massflow is between a high and low threshold; and

    in response to all logical values for the determining operations being TRUE, calculating an average of a number of values of an expected NOx calculation (932) over a period of time or execution cycles, and calculating an average of a number of values of a NOx sensor reading (930) over the period of time or execution cycles;

    comparing (936) the averaged values; and

    determining (938) a fault value for a NOx reduction system NOx conversion capability in response to the comparing.


     
    2. The method of claim 1, wherein the calculating an average of a number of values of an expected NOx calculation (932) over a period of time or execution cycles comprises operating a NOx reduction model of the NOx reduction system.
     
    3. The method of claim 1, wherein the calculating an average of a number of values of an expected NOx calculation (932) over a period of time comprises using lookup values from a predetermined function of engine out NOx values as a function of the values for the ratio of the engine fuel massflow to the engine charge massflow.
     


    Ansprüche

    1. Verfahren (900), umfassend:

    das Bestimmen (916), ob ein Motorkraftstoff-Mengenfluss (902) und ein Motorladung-Mengenfluss (904) Werte aufweisen, die unter Schwellenwerten liegen,

    das Bestimmen (918), ob der Motorkraftstoff-Mengenfluss und ein Motorladung-Mengenfluss Änderungsraten aufweisen, die unter Schwellenwerten liegen,

    das Bestimmen (926), ob ein NOx-Reduktionssystem-Kontrollvorgang ausgeführt werden kann,

    das Bestimmen (922), ob ein Wert eines Verhältnisses des Motorkraftstoff-Mengenflusses zum Motorladung-Mengenfluss zwischen einem hohen und einem niedrigen Schwellenwert liegt, und

    als Reaktion darauf, dass alle Logikwerte der Bestimmungsvorgänge RICHTIG sind, Berechnen eines Mittelwerts einer Anzahl von Werten einer erwarteten NOx-Berechnung (932) über eine Zeitspanne oder Ausführungszyklen, und Berechnen eines Mittelwerts einer Anzahl von Werten des Ablesens (930) eines NOx-Sensors über die Zeitspanne oder die Ausführungszyklen,

    das Vergleichen (936) der gemittelten Werte, und

    das Bestimmen (938) eines Fehlerwertes einer NOx-Umsetzungsfähigkeit für das NOx-Reduktionssystem als Reaktion auf das Vergleichen.


     
    2. Verfahren nach Anspruch 1, wobei das Berechnen eines Mittelwerts einer Anzahl von Werten einer erwarteten NOx-Berechnung (932) über eine Zeitspanne oder Ausführungszyklen, das Durchführen eines NOx-Reduktionsmodells des NOx-Reduktionssystems umfasst.
     
    3. Verfahren nach Anpruch 1, wobei das Berechnen eines Mittelwerts einer Anzahl von Werten einer erwarteten NOx-Berchnung (932) über eine Zeitspanne, das Verwenden von Nachschlagewerten aus einer vorbestimmten Funktion von Motor-Aus-NOx-Werten als eine Funktion der Werte für das Verhältnis von Motorkraftstoff-Mengenfluss zu Motorladung-Mengenfluss umfasst.
     


    Revendications

    1. Procédé (900), comprenant :

    déterminer (916) si un débit massique de carburant de moteur (902) et un débit massique de charge de moteur (904) ont des valeurs inférieures à des valeurs de seuil ;

    déterminer (918) si le débit massique de carburant du moteur et un débit massique de charge du moteur ont des taux de variation inférieurs à des valeurs de seuil ;

    déterminer (926) si une opération de surveillance du système de réduction des NOx peut être effectuée ;

    déterminer (922) si une valeur d'un rapport du débit massique de carburant du moteur au débit massique de charge du moteur est comprise entre un seuil haut et bas ; et

    en réponse à toutes les valeurs logiques pour les opérations de détermination étant VRAIES, calculer une moyenne d'un certain nombre de valeurs d'un calcul de NOx attendu (932) sur une période de temps ou des cycles d'exécution, et calculer une moyenne d'un certain nombre de valeurs d'une lecture (930) du capteur NOx sur la période de temps ou les cycles d'exécution ;

    comparer (936) les valeurs moyennes ; et

    déterminer (938) une valeur de défaut pour une capacité de conversion de NOx du système de réduction de NOx en réponse à la comparaison.


     
    2. Procédé selon la revendication 1, dans lequel le calcul d'une moyenne d'un certain nombre de valeurs d'un calcul de NOx attendu (932) sur une période de temps ou des cycles d'exécution comprend l'exploitation d'un modèle de réduction de NOx du système de réduction de NOx.
     
    3. Procédé selon la revendication 1, dans lequel le calcul d'une moyenne d'un certain nombre de valeurs d'un calcul de NOx attendu (932) sur une période de temps comprend l'utilisation de valeurs de recherche à partir d'une fonction prédéterminée de valeurs NOx de sortie moteur en fonction des valeurs du rapport entre le débit massique de carburant de moteur et le débit massique de charge de moteur.
     




    Drawing
































    Cited references

    REFERENCES CITED IN THE DESCRIPTION



    This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

    Patent documents cited in the description