On-board vehicle diagnostic of an oxidation catalyst

Abstract

There is presented a method for monitoring an oxidation catalyst in an exhaust line of an internal combustion engine, wherein a catalyst diagnostic event comprises a test cycle during which a conversion capability of the oxidation catalyst is determined based on the exotherm generated by post-injection of fuel. The diagnostic event may only be initiated when the temperature of the oxidation catalyst lies within a predetermined temperature range.

1 . A method for monitoring an oxidation catalyst in an exhaust line of an internal combustion engine, wherein a catalyst diagnostic event comprises a test cycle during which a conversion capability of said oxidation catalyst is determined based on an exotherm generated by post-injection of fuel,
 wherein said diagnostic event may only be initiated when the temperature of said oxidation catalyst lies within a predetermined temperature range,   and wherein a post-injection event and an exotherm monitoring period that lasts, after said post-injection event, until essentially all of the heat stored in said oxidation catalyst has been evacuated.   
     
     
         2 . A method according to  claim 1 , wherein the exotherm is evaluated by measuring the temperature of exhaust gases exiting said oxidation catalyst during said exotherm monitoring period. 
     
     
         3 . A method according to  claim 2 , wherein said oxidation catalyst has an outlet, and wherein said exotherm monitoring period ends when the exhaust gas temperature at the catalyst outlet (T out ) and a model catalyst-out exhaust gas temperature T out-mod  are substantially equal. 
     
     
         4 . A method according to  claim 2 , wherein said exotherm monitoring period ends when a difference between the exhaust gas temperature at the catalyst outlet (T out ) and a model catalyst-out exhaust gas temperature T out-mod  drops below a predetermined threshold. 
     
     
         5 . A method according to  claim 2 , wherein said exotherm monitoring period ends with the expiry of a calibrated timer. 
     
     
         6 . A method according to  claim 1 , wherein said predetermined temperature range is selected to correspond to a transition zone of the conversion efficiency for a reference oxidation catalyst with given ageing. 
     
     
         7 . A method according to  claim 1 , wherein said predetermined temperature range has an upper temperature limit selected to correspond to a conversion efficiency of no more than 90% for an aged, reference oxidation catalyst. 
     
     
         8 . A method according to  claim 1 , wherein said predetermined temperature range has lower and upper temperature limits that are selected to correspond to a conversion efficiency of about 40 to 80%, respectively, for an aged, reference oxidation catalyst. 
     
     
         9 . A method according to  claim 1 , wherein the lower temperature of said predetermined temperature range is selected to at least correspond to a predetermined conversion efficiency of a functional, reference oxidation catalyst. 
     
     
         10 . A method according to  claim 1 , wherein said diagnostic event is performed when the engine is not operated in a DPF regeneration mode. 
     
     
         11 . A method according to  claim 1 , wherein said diagnostic event is cancelled in case the temperature of said oxidation catalyst exits said predetermined temperature range. 
     
     
         12 . A method according to  claim 1 , wherein said diagnostic event is cancelled in case the temperature of said oxidation catalyst exits said predetermined temperature range during the performance of said post-injection event. 
     
     
         13 . A method according to  claim 1 , wherein the oxidation catalyst temperature is monitored by means of a multi-slice model, and said diagnostic event may only be triggered and/or performed when the respective temperatures of all of said slices lie within said predetermined temperature range. 
     
     
         14 . A method according to  claim 1 , wherein during said diagnostic cycle engine parameters are set to minimize the amount of HC in the engine-out exhaust gases, except for said post injection event. 
     
     
         15 . A method according to  claim 1 , wherein an alert signal is triggered when the conversion efficiency drops below a conversion efficiency alert threshold. 
     
     
         16 . A method according to  claim 1 , wherein said predetermined temperature range has lower and upper temperature limits that are selected to correspond to a conversion efficiency of about 40 to 60%, respectively, for an aged, reference oxidation catalyst. 
     
     
         17 . A method according to  claim 9 , wherein said predetermined conversion efficiency is of at least 50%.