Method to monitor pressure drop across a selective catalyst reducer for engine and exhaust airflow diagnostics

Abstract

A method to diagnose exhaust system malfunction in an electronically controlled internal combustion engine having an exhaust system and including a Selective Catalyst Reducer (SCR) is disclosed. The method may comprise determining ambient barometric pressure; determining a baseline curve of exhaust flow; and monitoring said exhaust flow rate for changes in exhaust flow rate compared to change of exhaust pressure across the SCR to diagnose exhaust system malfunction.

1 . A method to diagnose exhaust system malfunction in an electronically controlled internal combustion engine having an exhaust system and including a Selective Catalyst Reducer (SCR) with an inlet and an outlet, comprising:
 determining ambient barometric pressure;   determining a baseline curve of exhaust flow;   monitoring said exhaust flow rate for changes in exhaust flow rate compared to change of exhaust pressure across said SCR to diagnose exhaust system malfunction.   
     
     
         2 . The method of  claim 1 , wherein said baseline exhaust flow rate is determined by determining exhaust flow rate pressure at said SCR inlet and determining a baseline of exhaust flow rate versus change of pressure across the SCR. 
     
     
         3 . The method of  claim 1 , wherein said baseline curve of exhaust flow is determined at a first operating engine cycle and stored in memory for use during said engine life. 
     
     
         4 . The method of  claim 1 , wherein said baseline curve of exhaust flow is a predetermined value stored in memory in said electronic controller. 
     
     
         5 . The method of  claim 1 , wherein a shift of the baseline curve of exhaust flow rate versus change of pressure across the SCR over time is indicative of at least one of an exhaust leak, exhaust flow rate sensor malfunction, exhaust pressure sensor malfunction, or error in engine calculated exhaust flow. 
     
     
         6 . The method of  claim 1 , wherein determination of engine airflow rate is made based upon said baseline curve of exhaust flow. 
     
     
         7 . The method of  claim 1 , wherein each exhaust system failure is stored in said electronic controller memory. 
     
     
         8 . The method of  claim 1 , wherein said exhaust system further includes a diesel particulate filter (DPF) having an inlet and an outlet, said DPF outlet in fluid communication with said SCR inlet; said SCR inlet having a pressure sensor to generate data signals to said electronic controller indicative of exhaust flow pressure at said SCR inlet. 
     
     
         9 . The method of  claim 1 , wherein said barometric pressure is the pressure of the exhaust flow at the SCR outlet. 
     
     
         10 . The method of  claim 1 , wherein said change of pressure is determined by comparing the exhaust flow pressure at said SCR inlet to the ambient barometric pressure. 
     
     
         11 . A computer recordable medium configured to determine exhaust system malfunction in an electronically controlled internal combustion engine having an exhaust system and including a Selective Catalyst Reducer (SCR) with an inlet and an outlet, comprising:
 determining ambient barometric pressure;   determining a baseline curve of exhaust flow;   monitoring said exhaust flow rate for changes in exhaust flow rate compared to change of exhaust pressure across said SCR to diagnose exhaust system failure.