Abstract:
A method for predicting an exhaust gas temperature. The method includes detecting a plurality of exhaust gas temperatures and applying a weight value to the detected plurality of exhaust gas temperatures to determine a plurality of weighted temperature values. The weight value applied to at least one detected exhaust gas temperature may be different than the weight value applied to at least one other detected exhaust gas temperature. The method also includes determining an estimated temperature corresponding to the plurality of weighted temperature values and the applied weight value. The estimated temperature may be used to determine a set-point for the storage or absorption of a reductant by a catalyst. Moreover, the estimated temperature may allow for an adjustment to the reductant being stored on the catalyst if the storage capacity of the catalyst may be changing based on a predicted change in exhaust gas temperature.

Description:
BACKGROUND 
       [0001]    Combustion engines may employ emission controls or systems that are configured to reduce the amount of nitrogen oxides (NO x ), such as nitrogen dioxide, present in the engine&#39;s exhaust gas. One aspect of controlling such emissions may include the use of a NOx particulate filter (NPF) that has a Selective Catalytic Reduction (SCR) system and a particulate filter, such as a diesel particulate filter (DPF). The particulate filter is configured to remove particulate matter, such as soot, from the exhaust gas. The SCR typically uses a SCR catalyst, which, in some designs, may be coated on the particulate filter, and a reductant to convert NOx in the exhaust gas into nitrogen gas and water. Typically, the reductant is injected or dosed into the exhaust gas before the exhaust gas enters the NPF. The reductant may be a liquid or gas, such as, for example, ammonia (NH 3 ), among others. At least a portion of the reductant that is injected into the exhaust stream is absorbed onto the SCR catalyst where, with the assistance of the catalyst, the reductant reacts with the NO x  in the exhaust gas to form water vapor and nitrogen. In order for NO x  to be converted into nitrogen and water vapor, the SCR catalyst may be required to store an adequate amount of reductant. 
         [0002]    The amount of reductant that the SCR catalyst is able to store or absorb may decrease as the temperature of the exhaust gases that encounter or are around the SCR catalyst increase. Accordingly, a set-point may be established, and adjusted during vehicle operation, that indicates the reductant storage capacity of the SCR catalyst. Moreover, such a set-point may be established in an attempt to prevent excessive amounts of reductant from being present in the exhaust gas stream, such as excessive amounts due to a reduction in the SCR catalyst&#39;s reductant storage capacity and/or through reductant dosing levels. The presence of excess reductant in the exhaust gas due to the reduced storage capacity of the SCR catalyst may result in, or increase the probability of, reductant slipping through the after-treatment system and wasting the reductant. 
         [0003]    During certain operating conditions, the temperature of the exhaust gas may be elevated relatively rapidly. For example, a relatively quick and significant increase in engine load may result in a relative quick elevation in exhaust gas temperatures. Yet, such rapid elevation in temperature(s) may not allow for the time necessary for consumption of the stored reductant, an associated adjustment in the quantity of reductant that is to be stored on the SCR catalyst and/or an adjustment to the quantity of reductant that is being injected into the exhaust gas stream. In such situations, the decrease in the reductant storage capacity of the SCR catalyst may result in the presence of excess reductant in the exhaust gas that may, at least potentially, slip out of the after-treatment system wasting the reductant. 
       BRIEF SUMMARY 
       [0004]    According to certain embodiments, a method is provided for predicting an exhaust gas temperature. The method includes detecting a plurality of exhaust gas temperatures and applying, by a control unit, a weight value to the detected plurality of exhaust gas temperatures to determine a plurality of weighted temperature values. The weight value applied to at least one detected exhaust gas temperature may be different than the weight value applied to at least one other detected exhaust gas temperature. The method also includes determining an estimated temperature corresponding to the plurality of weighted temperature values and the applied weight value. 
         [0005]    Additionally, according to certain embodiments, a method is provided for predicting an exhaust gas temperature. The method includes detecting a plurality of exhaust gas temperatures and applying a weight value to the detected plurality of exhaust gas temperatures to determine a plurality of weighted temperature values. The weight value applied to at least one detected exhaust gas temperature may be different than the weight value applied to at least one other detected exhaust gas temperature. Further, the weight value may be based at least in part on the location of the detected exhaust gas temperature. The method further includes determining, by a control unit, an estimated temperature using a first summed value representative of the plurality of weighted temperature values and a second summed value representative of the weight values that were applied to the detected plurality of sensed temperatures. 
     
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
         [0006]      FIG. 1  illustrates an engine operably connected to an exemplary after-treatment system. 
           [0007]      FIG. 2  is an exemplary algorithm or control logic for estimating a set-point for the amount of reductant to be stored on the SCR catalyst based on a predicted exhaust gas temperature. 
           [0008]      FIG. 3  illustrates an engine operably connected to an exemplary after-treatment system. 
       
    
    
     DETAILED DESCRIPTION 
       [0009]      FIG. 1  illustrates an engine  10  operably connected to an after-treatment system  12 . The illustrated after-treatment system  12  includes a diesel oxidation catalyst (DOC)  14 , an injector  16  for injecting reductant, such as NH 3 , into the flow of an exhaust gas, a mixer  18  for mixing the injected reductant and exhaust gas, and a NPF  20  having an SCR system. The SCR system of the NPF  20  may include an SCR catalyst that is used in the conversion of NO x  into nitrogen and water vapor. 
         [0010]    The reductant may be supplied to the injector  16  from a storage tank  22  via a pump  24 . The amount of reductant injected or dosed into the exhaust gas stream may be controlled through the operation of pump  24  and/or the injector  16 , either or both of which may be controlled by a control unit, such as, for example, an electronic control unit (ECU)  26 . 
         [0011]    As illustrated, in  FIG. 1 , according to certain embodiments, a first temperature sensor  28   a  may be positioned at or around the inlet of the DOC  14 . Additionally, a second and a third temperature sensor  28   b,    28   c  may be positioned at or around the inlet and outlet, respectively, of the NPF  20 . While  FIG. 1  illustrates three temperature sensors, according to certain embodiments, additional temperature sensors may be employed, including, for example, a temperature sensor at or around the outlets of the engine  10  and/or DOC  14 , or the inlet or outlet of the mixer  18 , among others. Further the temperature sensors  28   a - c  in  FIG. 1  may also be repositioned, such as, for example, the first senor  28   a  being moved closer to the exhaust gas outlet of the engine  10 . 
         [0012]      FIG. 2  is an exemplary algorithm or control logic  200  for estimating a set-point for the amount of reductant to be stored on the SCR catalyst based on a predicted exhaust gas temperature. The logic  200  may be performed by a control unit, such as, for example, by the 
         [0013]    ECU  10 . At step  202 , a plurality of sensed temperature values are provided. For example, the temperature sensors  28   a - c  discussed above with respect to  FIG. 1  may provide signals, such as voltages, to the ECU  26  that are indicative of the temperature of the exhaust gas at those sensed locations in the after-treatment system  12 . The ECU  26  may be configured to determine the sensed temperature based on the information provided by the temperature sensors  28   a - c.    
         [0014]    More specifically, according to the embodiment of an after-treatment system  12  illustrated in  FIG. 1 , a first sensed temperature (“V_T_DOCin_CAN”), such as that provided by the first temperature sensor  28   a  that corresponds to a temperature at or around the inlet of the DOC  14  may be provided to and/or determined by the ECU  26  at step  202 . Second and third sensed temperatures (“V_T_NPFin_CAN” and “V_T_NPFOut_CAN”), such as those provided by the second and third temperature sensors  28   b,    28   c  at or around an inlet and outlet, respectively, of the NPF  20  may also be provided to and/or determined by the ECU  26  at step  202 . 
         [0015]    Although  FIG. 2  illustrates the use of three sensed temperatures, a variety of other sensed temperatures, such as those previously discussed, may be used and/or included at step  202 . For example,  FIG. 3  illustrates an after-treatment system  12 ′ that has a diesel particulate filter (DPF)  15  upstream of the injector  16  and an SCR catalyst  19  downstream of the mixer  18 . As also shown, the after-treatment system  12 ′ includes a five temperature sensors  30   a - e  positioned at various locations along the after-treatment system  12 ′. Thus, according to certain embodiments, some or all of the temperature sensors  30   a - e  may provide information to the ECU  26  that is used at step  202  in determining the set-point for the reductant storage level. 
         [0016]    At step  204 , the logic  200  may assign a total weight value to the temperatures provided at step  202 . The total weight value assigned to each sensed temperature may depend on a variety of different factors. For example, the weight given to a temperature may be based on the location of the sensed temperature relative to the location of the SCR catalyst, the proximity of the sensed temperature to the engine  10  and/or the various thermal inertias within the after-treatment exhaust system  12 . Such location based weighing may be used in an attempt to predict or estimate a future temperature of the exhaust gas that will be delivered to and/or encounter the SCR catalyst. 
         [0017]    For example, in the embodiment illustrated in  FIG. 2 , the sensed temperature at or around the inlet of the DOC  14  may be given a total weight value of 2 (“C_FAC_NPTTEMPStrDOCIn_AT NO=2”), while the downstream sensed temperatures at or around the inlet and outlets of the NPF  20  may be given total weight values of 1 (“C_FAC_NPTTEMPStrNPFIn_AT NO=1” and “C_FAC_NPTTEMPStrNPFOut_AT NO=1”). By giving a larger total weight value to a sensed temperature that is furthest upstream of the SCR catalyst and/or in closer proximity to the engine  10 , the logic  200  may be attempting to predict or estimate the temperature of the exhaust gas that will be, but may not have yet been, delivered to the SCR catalyst. 
         [0018]    Such a prediction of the temperature of the exhaust gas that the SCR catalyst will be encountering may allow the ECU  26  to determine whether the set-point for the amount of reductant to be stored on the SCR catalyst should be adjusted and/or whether to adjust the amount of reductant being injected into the exhaust gas stream by the injector  16 . Moreover, such prediction of temperature, such as a prediction of a temperature increase, may provide the ECU  26  the opportunity, if necessary, to adjust the reductant storage set-point of the SCR catalyst and allow for time to reduce the quantity of reductant stored on the SCR catalyst before the SCR catalyst encounters the elevated exhaust gas temperatures. Such adjustments in the amount of reductant being stored by the SCR catalyst may allow for time to prevent the release of excess reductant associated with a temperature related decrease in reductant storage capacity of the SCR catalyst, and thereby minimize or prevent the presence of excess reductant that may otherwise slip out of the after-treatment system and also reducing the waste of reductant. 
         [0019]    According to certain embodiments, the total weight value given to the sensed temperatures may be a fixed value. However, according to other embodiments, the total weight value may be variable, such as, for example, based on operating conditions of the engine  10  and/or ambient conditions, among other factors. For example, the total weight value given to sensed temperatures may increase or decrease. Additionally, the total weight value associated with one or more sensed temperatures may increase or decrease regardless of whether the total weight value for other sensed temperatures increase, decrease, or remain the same. For example, during normal, steady operating conditions, the total weight value for the temperature sensed at or around the inlet of the DOC  14  may be similar to, or less than, the total weight value given to the temperatures sensed at or around the inlet or outlet of the NPF  20 . However, the total weight value of the sensed temperature at or around the inlet of the DOC  14  may subsequently be increased as the engine load increases, such as when the vehicle associated with the engine changes from traveling on a relatively flat surface to climbing a relatively step incline. Additionally, while idling during cold starts, the total weight value for the temperature at or around outlet of the NPF  20  may increase as the temperature of the engine coolant increases while the total weight value for the temperature at or around the inlet of the DOC  14  remains the same. 
         [0020]    At step  206 , the total weight values from step  204  are applied to the temperatures provided at step  202 . For example, if the sensed temperature at the inlet of the DOC  14  is 200° Celsius and the total weight value for that temperature is 2, then step  206  returns a weighted temperature value of 400° Celsius for that sensed temperature. Similarly, if the sensed temperatures at the inlet and outlets of the NPF  20  are 150° Celsius and 100 ° Celsius, respectively, and the total weight values for each of those temperatures is 1, then the weighted temperature values returned at step  206  for those sensed temperatures are 150° Celsius and 100° Celsius. At step  208 , the weighted temperature values obtained at step  206  are summed together. Thus, in the present example, step  208  returns a total weighted temperature value of 650° Celsius. Further, at step  210 , the total weight values applied to the sensed temperatures are summed together. Therefore, in the present example, as total weight values of 2, 1, and 1 were applied, step  210  provides a total weight value of 4. 
         [0021]    At step  212 , the total weighted temperature value from step  208  is divided by the total weight value from step  210  to provide an estimated temperature. Thus, in the present example, the total weighted temperature value of 650° Celsius is divided by a total weight value of 4 to provide an estimated temperature of 162.5° Celsius. 
         [0022]    However, during certain operating conditions, the temperature sensed upstream of, and away from, the SCR catalyst, such as the temperature sensed at or around the inlet of the DOC  14 , may be lower than the actual temperatures being encountered by the SCR catalyst. In such an event, predicting the exhaust gas temperature using the sensed exhaust gas temperature at such an upstream location, and/or giving relatively significant weight to such a sensed temperature, may result in the prediction of an exhaust gas temperature that is lower than the actual temperatures of the exhaust gases that will be encountering the SCR catalyst. Moreover, the resulting low temperature estimation may result in the ECU  26  increasing the set-point for the amount of reductant to be stored on the SCR catalyst and/or increasing the quantity of reductant dosed into the exhaust gas stream by the injector  16 . However, such increases in the set-point and/or dosing levels based on a low exhaust gas temperature prediction may result in, based on the actual higher temperatures experience by the SCR catalyst, the SCR catalyst not being able to absorb and/or consume the increased level of reductant. In such a situation, the amount of reductant that may either actually or potentially slip through the after-treatment system  12 ,  12 ′ may increase. 
         [0023]    To avoid the potential for slippage/wastage of reductant based on low temperature predictions, according to certain embodiments, the logic  200  is configured to compare the estimated temperature from step  212  with the temperature of the exhaust gases that are encountering the SCR catalyst. Thus, at step  214 , the inlet and outlet exhaust gas temperatures that are encountering the SCR catalyst are added together. For example, according to the embodiment illustrated in  FIG. 3 , the temperatures sensed by a fourth and fifth temperature sensors  30   d,    30   e  may be added together, while the second and third temperature sensors  28   b,    28   c  for the embodiment shown in  FIG. 1  may be added together. With respect to the embodiment of  FIG. 1 , following the previously discussed example, if the inlet and outlet sensed temperatures are 150° Celsius and 100° Celsius, respectively, then step  214  would provide a summed temperature value of 250° Celsius. At step  216 , the summed temperature value from  214  would be divided to provide an average temperature. For example, using the previous example in which two temperatures provided a summed temperature value of 250° Celsius at step  214 , step  216  would return an average temperature of 125° Celsiu. 
         [0024]    At step  218 , the average temperature (“V_T NPFAvg_ATNO”) from step  216  is compared to the estimated temperature from step  212 . According to certain embodiments, step  218  would be configured to select the larger of either the average temperature or the estimated temperature to use in establishing the set-point for the quantity of reductant to be stored on the SCR catalyst. For example, using the previously discussed example, if the larger temperature (“V_T_NPFStr_ATNO”) is to be selected, step  218  would select the estimated temperature of 162.5° Celsius over the average temperature of 125° Celsius. 
         [0025]    At step  220 , the selected temperature may be used by the ECU  26  to determine the set-point (“V_T_NPFStr_ATNO”) for the storage of reductant on the SCR catalyst. According to certain embodiments, the temperature selected at step  218  may be used with a look-up table, chart, or other data that is accessible to the ECU  26  to establish the reductant storage set-point value. Thus, if the temperature of the exhaust gas is predicted to increase, using a reductant storage set-point value based on the predicted higher exhaust gas temperature may allow for reductant storage level of the SCR catalyst to be reduced accordingly so that if and when the exhaust gas temperature encountering the SCR catalyst does increase, the potential for excess reductant that may slip through the after-treatment system  12 ,  12 ′ is minimized or eliminated.