Exhaust system and method of estimating diesel particulate filter soot loading for same

Abstract

A method of estimating soot loading in a diesel particulate filter (DPF) in a vehicle exhaust system includes determining engine operating conditions of an engine in exhaust flow communication with the diesel particulate filter, and monitoring a pressure differential of the exhaust flow across the diesel particulate filter. The method includes estimating soot loading in the diesel particulate filter according to a pressure-based model using the monitored pressure differential when the engine operating conditions are within a predetermined first set of engine operating conditions, and estimating soot loading in the diesel particulate filter according to an engine-out soot model and a DPF soot loading model when the engine operating conditions are within a predetermined second set of operating conditions. The method includes updating the engine-out soot model based in part on a difference in estimated soot loading between the pressure-based model and the DPF soot loading model.

1 . A method of estimating soot loading in a diesel particulate filter (DPF) in a vehicle exhaust system, the method comprising:
 determining engine operating conditions of an engine in exhaust flow communication with the diesel particulate filter;   monitoring a pressure differential of the exhaust flow across the diesel particulate filter;   estimating soot loading in the diesel particulate filter according to a pressure-based model using the monitored pressure differential when the engine operating conditions are within a predetermined first set of engine operating conditions; wherein said estimating is performed by an electronic controller;   estimating soot loading in the diesel particulate filter according to an engine-out soot model and a DPF soot loading model when the engine operating conditions are within a predetermined second set of operating conditions; wherein said estimating is performed by the electronic controller; wherein said engine-out soot model and said DPF soot loading model are stored on the electronic controller; wherein the engine-out soot model is based on the monitored engine operating conditions and the diesel particulate soot loading model is based at least partially on the engine-out soot model;   updating the engine-out soot model based in part on a difference in estimated soot loading between the pressure-based model and the DPF soot loading model; wherein said updating the engine-out soot model is performed by the electronic controller in real time when the engine operating conditions are within the first set of engine operating conditions; and wherein said updating the engine-out soot model is performed by the electronic controller after a return to engine operating conditions within the first set of engine operating conditions after operation in the second set of engine operating conditions, and is based in part on a saved estimated soot rate loading value from an engine operating point in the first set of engine operating conditions prior to said operation in the second set of engine operating conditions.   
     
     
         2 . The method of  claim 1 , wherein the engine-out soot model includes a lookup table of stored engine-out soot rate values correlated with the engine operating conditions; and wherein said updating the engine-out soot model in real time is by updating the stored engine-out soot rate values for a predetermined number of engine operating points within a predetermined proximity to the engine operating point at which said difference is calculated. 
     
     
         3 . The method of  claim 2 , further comprising:
 measuring time of operation at each engine operating point;   calculating an estimated soot rate loading error; wherein the estimated soot rate loading error is said difference divided by a time of operation at the engine operating point at which said difference is calculated;   wherein said updating the engine-out soot model in real time is by distributing a respective portion of said estimated soot rate loading error to each of said stored engine-out soot rate values of the predetermined number of engine operating points in the predetermined proximity to the engine operating point at which said difference is calculated;   calculating a respective distance from each of the predetermined number of engine operating points to the engine operating point at which said difference is calculated; and   wherein each respective portion is in proportion to each respective distance.   
     
     
         4 . The method of  claim 1 , further comprising:
 measuring time of operation at each engine operating point during the second set of engine operating conditions;   calculating a respective distance from each of a predetermined number of engine operating points within a predetermined proximity to an engine operating point at which time is measured; and   distributing the measured time at each engine operating point during the second set of engine operating conditions to each of the predetermined number of engine operating points within the predetermined proximity to the engine operating point at which time is measured; wherein said distributing is in proportion to the calculated respective distance.   
     
     
         5 . The method of  claim 4 , further comprising:
 calculating a total time between a last engine operating point in the first set of engine operating conditions prior to operation in the second set of engine operating conditions and a first engine operating point in the first set of engine operating conditions after a return from the second set of engine operating conditions;   calculating a first difference between the estimated soot loading based on the pressure-based model and the estimated soot loading based on the DPF soot loading model, both measured at the first engine operating point in the first set of engine operating conditions after a return from the second set of engine operating conditions;   calculating a second difference between the estimated soot loading based on the pressure-based model and the estimated soot loading based on the DPF soot loading model, both measured at the last engine operating point in the first set of engine operating conditions prior to operation in the second set of engine operating conditions; wherein the estimated soot loading based on the pressure-based model at the last engine operating point in the first set of engine operating conditions prior to operation in the second set of engine operating conditions is said saved estimated soot loading value;   subtracting the second difference from the first difference to provide a soot loading increment error;   dividing the soot loading increment error by the total time to provide an average total soot rate error; and   wherein said updating after a return to engine operating conditions within the first set of engine operating conditions is by distributing the average total soot rate error to engine operating points in the second set of engine operating conditions in proportion to said distributed measured time.   
     
     
         6 . The method of  claim 4 , wherein the distributed measured time is saved in a time lookup table according to engine operating points within the second set of engine operating conditions, and further comprising:
 resetting the time lookup table to clear the distributed measured time following said updating after a return to engine operating conditions within the first set of engine operating conditions.   
     
     
         7 . The method of  claim 1 , wherein said monitoring engine operating conditions includes:
 monitoring engine speed; and   estimating injected fuel rate.   
     
     
         8 . A method of estimating engine-out soot rate in exhaust flow from an engine, wherein engine-out soot flows from the engine to a diesel particulate filter (DPF), the method comprising:
 determining engine operating conditions;   periodically determining via a controller whether a respective engine operating point in the engine operating conditions is within a first set of operating conditions or a second set of operating conditions;   updating stored engine-out soot rate estimates via the controller by distributing a difference between a DPF pressure-based model and a DPF soot loading model according to respective proximities of a predetermined number of corresponding engine operating points to the respective engine operating point if the respective engine operating point is within the first set of operating conditions; wherein the pressure-based model is based on a measured pressure differential across the DPF; wherein the DPF soot loading model is based in part on the stored engine-out soot rate estimates; and   updating the stored engine-out soot rate estimates via the controller by
 calculating an engine-out soot rate error based in part on a difference between the pressure-based model and the DPF soot loading model at (i) a final engine operating point within the first range of engine operating conditions immediately prior to one or more engine operating points within the second range of engine operating conditions, and at (ii) an initial engine operating point within the first range of engine operating conditions and subsequent to said one or more engine operating points within the second range of engine operating conditions; and 
 distributing the calculated engine-out soot rate error via the controller according to a pro-rata portion of time spent at each engine operating point in the second range of operating conditions to a total time between the final engine operating point and the initial engine operating point. 
   
     
     
         9 . The method of  claim 8 , wherein the engine-out soot model includes a lookup table of stored engine-out soot rate values correlated with the engine operating conditions. 
     
     
         10 . The method of  claim 8 , wherein the pro-rata portion of time spent at each engine operating point in the second set of engine operating conditions is saved in a time lookup table according to engine operating points within the second set of engine operating conditions, and further comprising:
 resetting the time lookup table to clear the pro-rata portion of time following said updating after a return to engine operating conditions within the first set of engine operating conditions.   
     
     
         11 . The method of  claim 8 , wherein said determining engine operating conditions includes:
 monitoring engine speed; and   estimating quantity of injected fuel quantity rate.   
     
     
         12 . An exhaust system for treating exhaust from an engine on a vehicle, the exhaust system comprising:
 a diesel particulate filter (DPF) in fluid communication with the engine;   a differential pressure measurement device operatively connected to the DPF and operable to provide a signal corresponding with a pressure differential across the DPF;   a controller in operative communication with the differential pressure measurement device to monitor the pressure differential and with the engine to monitor engine operating conditions; wherein the controller is configured to execute:
 a first stored algorithm that is a pressure-based model to provide an estimated soot loading in the DPF based on the pressure differential when engine operating conditions are within a first set of engine operating conditions; 
 a second stored algorithm that is a DPF soot loading model based on the engine operating conditions and on an engine-out soot model when the engine operating conditions are within a second set of engine operating conditions; and 
 a learning algorithm that updates the engine-out soot model based in part on a difference in estimated soot loading between the pressure-based model and the DPF soot loading model by updating the engine-out soot model (i) in real time when the engine operating conditions are within the first set of engine operating conditions, and (ii) after a return to engine operating conditions within the first set of engine operating conditions after operation in the second set of engine operating conditions; wherein updating after a return to engine operating conditions within the first set of engine operating conditions is based in part on a saved estimated soot rate loading value from an engine operating point in the first set of engine operating conditions prior to said operation in the second set of engine operating conditions. 
   
     
     
         13 . The exhaust system of  claim 12 , wherein the engine-out soot model includes a lookup table of stored engine-out soot rate values correlated with the engine operating conditions; and wherein said updating the engine-out soot model in real time is by updating the stored engine-out soot rate values for a predetermined number of engine operating points within a predetermined proximity to the engine operating point at which said difference is calculated. 
     
     
         14 . The exhaust system of  claim 12 , wherein the learning algorithm:
 measures time of operation at each engine operating point during the second set of engine operating conditions;   calculates a respective distance from each of a predetermined number of engine operating points within a predetermined proximity to an engine operating point at which time is measured; and   distributes the measured time at each engine operating point during the second set of engine operating conditions to each of the predetermined number of engine operating points within the predetermined proximity to the engine operating point at which time is measured and in proportion to the calculated respective distance.   
     
     
         15 . The exhaust system of  claim 14 , wherein the learning algorithm:
 calculates a total time between a last engine operating point in the first set of engine operating conditions prior to operation in the second set of engine operating conditions and a first engine operating point in the first set of engine operating conditions after a return from the second set of engine operating conditions;   calculates a first difference between the estimated soot loading based on the pressure-based model and the estimated soot loading based on the DPF soot loading model, both measured at the first engine operating point in the first set of engine operating conditions after a return from the second set of engine operating conditions;   calculates a second difference between the estimated soot loading based on the pressure-based model and the estimated soot loading based on the DPF soot loading model, both measured at the last engine operating point in the first set of engine operating conditions prior to operation in the second set of engine operating conditions; wherein the estimated soot loading based on the pressure-based model at the last engine operating point in the first set of engine operating conditions prior to operation in the second set of engine operating conditions is said saved estimated soot loading value;   calculates a soot loading increment error by subtracting the second difference from the first difference;   calculates an average total soot rate error by dividing the soot loading increment error by the total time; and   wherein said updating after a return to engine operating conditions within the first set of engine operating conditions is by distributing the average total soot rate error to engine operating points in the second set of engine operating conditions in proportion to the distributed measured time.   
     
     
         16 . The exhaust system of  claim 14 , wherein the learning algorithm includes a time lookup table, and wherein the distributed measured time is saved in the time lookup table according to engine operating points within the second set of engine operating conditions; and
 wherein the learning algorithm resets the time lookup table to clear the distributed measured time following said updating after a return to engine operating conditions within the first set of engine operating conditions.   
     
     
         17 . The exhaust system of  claim 12 , wherein the engine operating conditions include engine speed and injected fuel quantity rate.