System and method for diagnosing the selective catalytic reduction system of a motor vehicle

Abstract

A system and method for diagnosing selective catalytic reduction system of a motor vehicle, the system including an internal combustion engine connected by an exhaust manifold to, successively, an assembly including a nitrogen oxide catalyst and a particle filter and a selective catalytic reduction system, a mechanism draining mass of ammonia stored in the selective catalytic reduction system, a mechanism controlling draining, and a mechanism injecting urea positioned upstream of the selective catalytic reduction system, a mechanism measuring quantity of ammonia at an outlet of the selective catalytic reduction system, a system determining maximum mass of ammonia stored in the selective catalytic reduction system, and a comparison mechanism configured to transmit a fault signal based on a result of a comparison between the maximum mass of ammonia stored in the selective catalytic reduction system and a threshold.

1 - 10 . (canceled) 
     
     
         11 : A system for diagnosing selective catalytic reduction system of a motor vehicle including an internal combustion engine connected via an exhaust manifold successively to an assembly including a nitrous oxide catalyst and a particulate filter, and a selective catalytic reduction system, the system comprising:
 a means for evacuation of ammonia mass stored in the selective catalytic reduction system;   a urea injection means arranged upstream of the selective catalytic reduction system;   a means for control of the evacuation and injection;   a means for measuring quantity of ammonia at an outlet from the selective catalytic reduction system;   a system for determining maximum mass of ammonia stored in the selective catalytic reduction system;   a means for comparing a value determined for the maximum mass of ammonia stored in the selective catalytic reduction system with a threshold, and to emit a fault signal as a function of the comparison result.   
     
     
         12 : The system as claimed in  claim 11 , wherein the means for determining the maximum mass of ammonia stored in the selective catalytic reduction system comprises:
 a means for modeling the selective catalytic reduction system, and to estimate levels of ammonia and nitrous oxides downstream of the selective catalytic reduction system via a model;   a means for determining a level of ammonia at the outlet from the selective catalytic reduction system as a function of the signal received from the measurement means;   a calculation means configured to determine a difference between the level of ammonia measured at the outlet from the selective catalytic reduction system and modeled values for levels of ammonia and nitrous oxides downstream of the selective catalytic reduction system, to determine a new value for the maximum mass of ammonia stored in the selective catalytic reduction system if the difference is positive, and to transmit the new value for the maximum mass of ammonia stored in the selective catalytic reduction system to the means for modeling the selective catalytic reduction system to determine new values until the difference is zero;   the calculation means configured to emit the maximum mass of ammonia stored in the selective catalytic reduction system when the difference is zero.   
     
     
         13 : The system as claimed in  claim 11 , wherein the fault signal for the selective catalytic reduction system assumes a first value if the value determined for the maximum mass of ammonia stored in the selective catalytic reduction system is less than a threshold, while it assumes a second value if that is not the case. 
     
     
         14 : The system as claimed in  claim 12 , wherein the means for modeling the selective catalytic reduction system is configured to estimate the ammonia level downstream of the selective catalytic reduction system via a model, as a function of the ratio between the nitrogen dioxide and the nitrous oxides downstream of the exhaust manifold, temperature upstream of the selective catalytic reduction system, the mass of urea injected upstream of the selective catalytic reduction system, the maximum mass of ammonia stored in the selective catalytic reduction system, exhaust gas flow, the level of ammonia upstream of the selective catalytic reduction system, and the level of nitrous oxides upstream of the selective catalytic reduction system. 
     
     
         15 : The system as claimed in  claim 14 , wherein the means for modeling the selective catalytic reduction system is configured to determine the ratio between nitrogen dioxide and nitrogen monoxide downstream of the exhaust manifold, as a function of temperature upstream of the assembly of the particulate filter and the catalyst, exhaust gas flow of the internal combustion engine, and level of nitrous oxides downstream of the exhaust manifold. 
     
     
         16 : A method for diagnosing a selective catalytic reduction system of a motor vehicle including an internal combustion engine connected via an exhaust manifold successively to an assembly including a nitrous oxide catalyst and a particulate filter, and a selective catalytic reduction system, the method comprising:
 evacuation of ammonia mass stored in the selective catalytic reduction system;   injection, upstream of the selective catalytic reduction system, of a mass of urea greater than a maximum mass which can be stored by the selective catalytic reduction system;   determination of the maximum mass of ammonia stored in the selective catalytic reduction system; and   emission of a fault signal as a function of a result of comparison of a value determined for the maximum mass of ammonia stored in the selective catalytic reduction system with a threshold.   
     
     
         17 : The method as claimed in  claim 16 , wherein the maximum mass of ammonia stored in the selective catalytic reduction system is determined by performing:
 initialization of a model with a saved value for the maximum mass which can be stored in the selective catalytic reduction system;   estimation of levels of ammonia and nitrous oxides downstream of the selective catalytic reduction system via a model;   measurement of an ammonia level at the outlet from the selective catalytic reduction system;   determination of a difference between the ammonia level at the outlet from the selective catalytic reduction system and the modeled values for the levels of ammonia and nitrous oxides downstream of the selective catalytic reduction system; and   if the difference is positive, determination of a new value for the maximum mass of ammonia stored in the selective catalytic reduction system, and determination of new values for the levels of ammonia and nitrous oxides downstream of the selective catalytic reduction system via the model until the difference is zero;   when the difference is zero, a value of the maximum mass stored in the selective catalytic reduction system is emitted.   
     
     
         18 : The method as claimed in  claim 16 , wherein if the value determined for the maximum mass of ammonia stored in the selective catalytic reduction system is less than a threshold, a fault signal assuming a first value is emitted for the selective catalytic reduction system, while it assumes a second value if this is not the case. 
     
     
         19 : The method as claimed in  claim 17 , wherein the levels of ammonia and nitrous oxides downstream of the selective catalytic reduction system are estimated via a model, as a function of the ratio between the quantity of nitrogen monoxide and nitrogen dioxide downstream of the exhaust manifold, the temperature upstream of the selective catalytic reduction system, the mass of urea injected upstream of the selective catalytic reduction system, the maximum mass of ammonia stored in the selective catalytic reduction system, exhaust gas flow, the level of ammonia upstream of the selective catalytic reduction system, and the level of nitrous oxides upstream of the selective catalytic reduction system. 
     
     
         20 : The method as claimed in  claim 19 , wherein the ratio between the nitrogen monoxide and the nitrogen dioxide downstream of the exhaust manifold is determined as a function of the temperature upstream of the assembly of the particulate filter and the catalyst, exhaust gas flow from the internal combustion engine, and the level of nitrous oxides downstream of the exhaust manifold.