Diagnosis device for an engine

Abstract

A diagnosis system for an engine including an exhaust pipe, a hydrocarbon (HC) absorbent arranged within the exhaust pipe, an upstream air/fuel ratio sensor arranged upstream of the HC absorbent and detecting a wide range air/fuel ratio of an exhaust gas, a downstream air/fuel ratio sensor arranged downstream of the HC absorbent and detecting rich or lean with respect to stoichiometric air/fuel ratio of the exhaust gas, and a control unit, the control unit includes means for correcting an air/fuel ratio upstream of the HC absorbent, means for correcting an air/fuel ratio downstream of the HC absorbent, and means for predicting a HC absorbing amount of the HC absorbent, the means for correcting the air/fuel ratio upstream of the HC absorbent correcting and controlling an output value of the upstream air/fuel ratio sensor toward lean, the means for predicting the HC absorbing amount of the HC absorbent predicting an absorbing performance of the HC absorbent on the basis of a difference between an output value of the upstream air/fuel ratio sensor and a predetermined value C during a period from a timing where a temperature of the HC absorbent becomes higher than or equal to a predetermined value A and the output value of the upstream air/fuel ratio sensor is corrected and controlled toward lean to a timing where the temperature becomes lower than or equal to a predetermined value B.

What is claimed is:  
     
         1 . A diagnosis system for an engine including an exhaust pipe, a hydrocarbon (HC) absorbent arranged within said exhaust pipe, an upstream air/fuel ratio sensor arranged upstream of said HC absorbent and detecting a wide range air/fuel ratio of an exhaust gas, a downstream air/fuel ratio sensor arranged downstream of said HC absorbent and detecting rich or lean with respect to stoichiometric air/fuel ratio of the exhaust gas, and a control unit, characterized by 
 said control unit including means for correcting an air/fuel ratio upstream of said HC absorbent, means for correcting an air/fuel ratio downstream of said HC absorbent, and means for predicting a HC absorbing amount of said HC absorbent, said means for correcting the air/fuel ratio upstream of said HC absorbent correcting and controlling an output value of said upstream air/fuel ratio sensor toward lean, said means for predicting the HC absorbing amount of said HC absorbent predicting an absorbing performance of said HC absorbent on the basis of a difference between an output value of said upstream air/fuel ratio sensor and a predetermined value C during a period from a timing where a temperature of said HC absorbent becomes higher than or equal to a predetermined value A and the output value of said upstream air/fuel ratio sensor is corrected and controlled toward lean to a timing where the temperature becomes lower than or equal to a predetermined value B.    
     
     
         2 . A diagnosis system for an engine as set forth in  claim 1 , wherein said means for correcting the air/fuel ratio upstream of said HC absorbent corrects and controls the output value of said upstream air/fuel ratio sensor toward lean so that an output value of said downstream air/fuel ratio sensor becomes constant.  
     
     
         3 . A diagnosis system for an engine as set forth in  claim 1  or  2 , wherein said means for predicting the HC absorbing amount of said HC absorbent predicts the absorbing performance of said HC absorbent from a value derived by integrating a value calculated by multiplying a difference between the output value of said downstream air/fuel ratio sensor and said predetermined value C by an inflow air amount of the engine, over a predetermined period.  
     
     
         4 . A diagnosis system for an engine including an exhaust pipe, a hydrocarbon (HC) absorbent arranged within said exhaust pipe, a downstream air/fuel ratio sensor arranged downstream of said HC absorbent and detecting a wide range air/fuel ratio of an exhaust gas or detecting rich or lean with respect to stoichiometric air/fuel ratio of the exhaust gas, and a control unit, characterized by 
 said control unit including means for correcting an air/fuel ratio downstream of said HC absorbent and means for predicting a HC absorbing amount of said HC absorbent, said means for correcting the air/fuel ratio downstream of said HC absorbent correcting and controlling a correction value of an air/fuel ratio control of a fuel amount or air amount to be supplied to a combustion chamber of the engine toward lean, and said means for predicting the HC absorbing amount of said HC absorbent predicting an absorbing performance of said HC absorbent on the basis of a difference between an output value of said upstream air/fuel ratio sensor and a predetermined value C during a period from a timing where a temperature of said HC absorbent becomes higher than or equal to a predetermined value A and the correction amount of said air/fuel ratio control is corrected and controlled toward lean to a timing where the temperature becomes lower than or equal to a predetermined value E.    
     
     
         5 . A diagnosis system for an engine as set forth in  claim 4 , wherein said means for correcting the air/fuel ratio upstream of said HC absorbent corrects and controls the output value of said upstream air/fuel ratio sensor toward lean so that an output value of said downstream air/fuel ratio sensor becomes constant.  
     
     
         6 . A diagnosis system for an engine as set forth in any one  claims 1  to  5 , wherein said means for correcting the air/fuel ratio downstream of said HC absorbent includes means for measuring or predicting temperature of the HC absorbent.  
     
     
         7 . A diagnosis system for an engine as set forth in any one of  claims 1  to  6 , wherein said means for predicting the HC absorbing amount of said HC absorbent starts prediction of absorbing performance of said HC absorbent when rich condition of the output value of said downstream air/fuel ratio sensor is maintained for a predetermined period.  
     
     
         8 . A diagnosis system for an engine as set forth in any one of  claims 1  to  7 , wherein at least a catalytic converter or a nitrogen oxide (NO x ) catalyst is provided on downstream of said HC absorbent.  
     
     
         9 . A diagnosis system for an engine as set forth in any one of  claims 1  to  8 , wherein said control unit comprises means for making judgment of fatigue of said HC absorbent on the basis of an output signal of the means for predicting the HC absorbing amount of said HC absorbent, and means for announcing fatigue of said HC absorbent on the basis of the output signal of the means for making judgment of fatigue of said HC absorbent.