Engine comprising a catalytic converter with failsafe operation

Abstract

The invention proposes an engine ( 11 ) comprising a catalytic converter ( 12 c ), a first probe ( 120 ) able to deliver a first signal (Vsp) proportional to the oxygen content of an exhaust gas and installed upstream of the converter, a second oxygen probe ( 130 ) downstream of the converter and able to provide a second signal (Vsb), and means ( 13 ) for making a diagnosis regarding the operating condition of the converter, characterized in that: the second oxygen probe ( 130 ) is of the on/off type and the means ( 13 ) are designed to convert the first signal (Vsp) into a third signal (Vspb) of the on/off type and to make the diagnosis on the basis of the second and third signals (Vsb, Vspb).

1 . An engine comprising a catalytic converter, a first probe capable of delivering a first signal (Vsp) proportional to an oxygen content in an exhaust gas and installed upstream of the converter, a second oxygen probe downstream of the converter and capable of supplying a second signal (Vsb), and means for making a diagnosis regarding an operating status of the converter, characterized in that:
 the second oxygen probe is of the on/off type, and   the means are designed to convert the first signal (Vsp) into a third signal (Vspb) of the on/off type and to make the diagnosis on the basis of the second and third signals (Vsb, Vspb).   
   
   
       2 . The engine as claimed in  claim 1 , characterized in that the signal conversion means comprise a probe model dependent on the first signal. 
   
   
       3 . The engine as claimed in  claim 2 , characterized in that the model is designed so that the third signal it supplies is in the form of a square wave with predetermined upper and lower values. 
   
   
       4 . The engine as claimed in  claim 3 , characterized in that the model is designed so that the third signal it supplies switches from the upper value to the lower value, and vice versa, when the first signal crosses a first predetermined threshold value, one of the upper and lower values being substantially equal to the first threshold value. 
   
   
       5 . The engine as claimed in  claim 1 , characterized in that the means are also designed to control the temperature (Ttip) of an oxygen-content-sensitive element in the second probe. 
   
   
       6 . The engine as claimed in  claim 5 , characterized in that the control means are designed to decrease the temperature down to a predetermined temperature value ranging between 400 and 500° C., before the means for making the diagnosis make use of the second and third signals. 
   
   
       7 . A method of monitoring the operating status of a catalytic converter of an engine, characterized in that it comprises the following steps:
 obtaining, from a first probe, a first signal (Vsp) proportional to an oxygen content in a gas and situated upstream of the converter,   obtaining a second signal (Vsb) from a second probe of the on/off type installed downstream of the converter,   converting the first signal into a third signal (Vspb) of the on/off type, and   making a diagnosis regarding the converter operating status on the basis of the second and third signals.   
   
   
       8 . The method as claimed in  claim 7 , characterized in that, in the step of making the diagnosis, a diagnostic criterion (Cdiag) is determined on the basis of an area (A) of a difference between the second and third signals. 
   
   
       9 . The method as claimed in  claim 8 , characterized in that, in the step of making the diagnosis, the diagnostic criterion is compared against three predetermined threshold values (S 1   diag , S 2   diag , S 3   diag ) that respectively define three ranges of values corresponding to three different converter operating statuses. 
   
   
       10 . The method as claimed in  claim 7 , characterized in that it comprises a step in which the running of the diagnostic step is governed by whether the first and/or second signal meets at least one predetermined criterion. 
   
   
       11 . The method as claimed in  claim 8 , characterized in that the diagnostic criterion is of the following form: 
     
       
         
           
             
               C 
                
               
                   
               
                
               diag 
             
             = 
             
               
                 ∫ 
                 
                   t 
                    
                   
                       
                   
                    
                   1 
                 
                 
                   t 
                    
                   
                       
                   
                    
                   2 
                 
               
                
               
                 
                   Dgaz 
                   3.6 
                 
                  
                 
                   ( 
                   
                     Vspb 
                     - 
                     Vsb 
                   
                   ) 
                 
                  
                 
                     
                 
                  
                 
                    
                   t 
                 
               
             
           
         
       
     
     where cdiag, t 1 , t 2  and Dgaz respectively denote the diagnostic criterion used, two predetermined moments in time and a rate of flow of exhaust gas through the catalytic converter.