Exhaust System, Operating Method And Control Strategy In Internal Combustion Engine

Abstract

An exhaust system for an internal combustion engine includes an exhaust filter positioned within an exhaust conduit, and having a first and a second NOx sensing mechanism positioned upstream and downstream the exhaust filter. An electronic control unit is coupled with the NOx sensing mechanisms and generates a signal indicative of a soot loading state of the exhaust filter responsive to a difference in species composition of the sensed NOx upstream and downstream the exhaust filter. Related methodology and control strategy are also disclosed.

What is claimed is: 
     
         1 . A method of operating an exhaust system for an internal combustion engine comprising the steps of:
 conveying exhaust produced via operation of the internal combustion engine in a downstream direction through an exhaust filter of the exhaust system;   trapping soot in the exhaust within the exhaust filter;   sensing NOx in the exhaust upstream the exhaust filter;   sensing NOx in the exhaust downstream the exhaust filter; and   determining a soot loading state of the exhaust filter responsive to a difference in species composition of the sensed NOx upstream and downstream the exhaust filter.   
     
     
         2 . The method of  claim 1  wherein the difference in species composition includes a difference in a ratio of NO to NO 2 . 
     
     
         3 . The method of  claim 2  wherein the step of determining includes determining the soot loading state of the exhaust filter based at least in part on an amount of NO2 deoxidized to NO within the exhaust filter as indicated by the difference in the ratio. 
     
     
         4 . The method of  claim 3  wherein:
 the steps of sensing include receiving data from an upstream sensing mechanism having differing sensitivity to NO versus NO 2 , and a downstream sensing mechanism also having the differing sensitivity; and 
 the step of determining further includes a step of comparing the data from the upstream sensing mechanism with the data from the downstream sensing mechanism. 
 
     
     
         5 . The method of  claim 4  wherein the step of determining further includes determining a relative soot loading state of the exhaust filter, and further comprising a step of commanding regeneration of the exhaust filter based at least in part on the determined relative soot loading state. 
     
     
         6 . The method of  claim 3  further comprising the steps of:
 receiving data indicative of exhaust temperature; and 
 receiving data indicative of exhaust flow rate; 
 wherein the step of determining further includes determining the soot loading state responsive to the exhaust temperature and the exhaust flow rate. 
 
     
     
         7 . The method of  claim 3  further comprising a step of decreasing the ratio of NO to NO 2  via an oxidation catalyst located upstream the exhaust filter in the exhaust system. 
     
     
         8 . The method of  claim 7  further comprising the steps of receiving data indicative of an engine-out ratio of NO to NO 2 , and determining the amount of NO 2  deoxidized responsive to the engine-out ratio, and wherein the step of determining the soot loading state further includes a step of determining an amount of the trapped soot based on the amount of NO 2  deoxidized. 
     
     
         9 . An exhaust system for an internal combustion engine comprising:
 an exhaust conduit configured to couple with an exhaust manifold of the internal combustion engine;   an exhaust filter positioned within the exhaust conduit and configured to trap soot in exhaust from the internal combustion engine conveyed through the exhaust conduit;   a first NOx sensing mechanism configured to sense NOx in the exhaust upstream the exhaust filter;   a second NOx sensing mechanism configured to sense NOx in the exhaust downstream the exhaust filter;   an electronic control unit coupled with the first and second NOx sensing mechanisms, and configured to generate a signal indicative of a soot loading state of the exhaust filter responsive to a difference in species composition of the sensed NOx upstream and downstream the exhaust filter.   
     
     
         10 . The exhaust system of  claim 9  further comprising a regeneration device coupled with the exhaust filter and controllably coupled with the electronic control unit, and wherein the electronic control unit is configured to command regeneration of the exhaust filter via the regeneration device, responsive to the signal. 
     
     
         11 . The exhaust system of  claim 10  further comprising a diesel oxidation catalyst positioned within the exhaust conduit upstream the exhaust filter, and wherein the exhaust filter is free of catalyst. 
     
     
         12 . The exhaust system of  claim 11  wherein the first NOx sensing mechanism is positioned downstream the diesel oxidation catalyst. 
     
     
         13 . The exhaust system of  claim 11  wherein the first NOx sensing mechanism is positioned upstream the diesel oxidation catalyst. 
     
     
         14 . The exhaust system of  claim 10  wherein each of the first and second sensing mechanisms has differing sensitivity to NO versus NO 2 , and the difference in species composition includes a difference in a ratio of NO to NO 2  in the exhaust. 
     
     
         15 . The exhaust system of  claim 14  wherein the signal is indicative of an amount of NO 2  deoxidized to NO within the exhaust filter, and the electronic control unit is further configured to determine an amount of the trapped soot based on the amount of NO 2  deoxidized. 
     
     
         16 . The exhaust system of  claim 14  wherein the electronic control unit is configured to receive data indicative of a temperature of the exhaust, and data indicative of an exhaust flow rate, and further configured to determine the amount of the trapped soot responsive to the exhaust temperature and the exhaust flow rate. 
     
     
         17 . A control system for an exhaust filter in an internal combustion engine system comprising:
 a first NOx sensing mechanism configured to sense NOx in the exhaust at a first location upstream the exhaust filter in an exhaust conduit configured to connect with an exhaust manifold of the internal combustion engine;   a second NOx sensing mechanism configured to sense NOx in the exhaust at a second location downstream the exhaust filter in the exhaust conduit;   an electronic control unit coupled with the first and second NOx sensing mechanisms, and configured to generate a signal indicative of a soot loading state of the exhaust filter responsive to a difference in species composition of the sensed NOx upstream and downstream the exhaust filter.   
     
     
         18 . The control system of  claim 17  wherein each of the first and second NOx sensing mechanisms has differing sensitivity to NO versus NO 2 . 
     
     
         19 . The control system of  claim 18  further comprising an exhaust temperature monitoring mechanism, and an exhaust flow rate monitoring mechanism, and the electronic control unit is further configured to generate the signal responsive to data from the first and second NOx sensing mechanisms, and responsive to data from the exhaust temperature and exhaust flow rate monitoring mechanisms.