Method and device for controlling the functioning of a nitrogen oxide trap for an internal combustion engine running on a lean mixture

Abstract

A method in which a first oxygen sensor is disposed on an exhaust pipe upstream from a nitrogen oxide trap, and development of a meaningful signal representative of the signal supplied by the sensor is monitored. A substantial increase of the meaningful signal, which is obtained following a variation resulting from a motor being switched from running on a lean mixture to running on a rich mixture, from a first plate having an essentially constant level is used as an indicator to control an end of a purge process. The method can be applied to diesel engines.

1 - 10 . (canceled)  
   
   
       11 . A method for control of operation of a nitrogen oxides trap for an internal combustion engine running on a lean mixture, wherein purging of the nitrogen oxides trap is commanded periodically, and a first oxygen sensor is disposed in an exhaust pipe downstream from the nitrogen oxides trap, the method comprising: 
 observing evolution of a meaningful signal representative of a signal delivered by the first oxygen sensor;    using an increase of the meaningful signal from a first plateau of substantially constant level, reached following a variation subsequent to a changeover of the engine from running on a lean mixture to running on a rich mixture, as an indicator to command an end of purging.    
   
   
       12 . A method according to  claim 11 , wherein a second oxygen sensor disposed upstream from the nitrogen oxides trap is additionally used to deliver a reference signal, relative to which the evolution of the signal delivered by the first oxygen sensor is compared to deliver the meaningful signal.  
   
   
       13 . A method according to  claim 11 , wherein the increase of the meaningful signal is detected by applying filtering of a first derivative of the meaningful signal and by comparing the filtered first derivative with a predetermined threshold.  
   
   
       14 . A method according to  claim 12 , wherein the increase of the meaningful signal is detected by applying filtering of a first derivative of the meaningful signal and by comparing the filtered first derivative with a predetermined threshold.  
   
   
       15 . A method according to  claim 11 , wherein the increase of the meaningful signal is detected by applying filtering of a second derivative of the meaningful signal and observing passage of the filtered second derivative through zero in decreasing threshold.  
   
   
       16 . A method according to  claim 12 , wherein the increase of the meaningful signal is detected by applying filtering of a second derivative of the meaningful signal and observing passage of the filtered second derivative through zero in decreasing threshold.  
   
   
       17 . A method according to  claim 11 , wherein the increase of the meaningful signal is detected by taking a difference between an instantaneous value of the meaningful signal and a sliding mean of the meaningful signal, and by comparing the difference with a threshold.  
   
   
       18 . A method according to  claim 12 , wherein the increase of the meaningful signal is detected by taking a difference between an instantaneous value of the meaningful signal and a sliding mean of the meaningful signal, and by comparing the difference with a threshold.  
   
   
       19 . A method according to  claim 11 , wherein the increase of the meaningful signal, for a lambda sensor, is detected by comparing a voltage value delivered by the first oxygen sensor with a predetermined threshold.  
   
   
       20 . A method according to  claim 12 , wherein the increase of the meaningful signal, for a lambda sensor, is detected by comparing a voltage value delivered by the first oxygen sensor with a predetermined threshold.  
   
   
       21 . A method according to  claim 11 , wherein the first oxygen sensor is chosen from among sensors of a sensor of lambda type, proportional oxygen sensor, nitrogen oxides detector, in which the oxygen-concentration measuring function is used.  
   
   
       22 . A method according to  claim 12 , wherein the first oxygen sensor is chosen from among sensors of a sensor of lambda type, proportional oxygen sensor, nitrogen oxides detector, in which the oxygen-concentration measuring function is used.  
   
   
       23 . A method according to  claim 22 , wherein the first and second oxygen sensors are of different types.  
   
   
       24 . A device for control of an operation of a nitrogen oxides trap for an internal combustion engine running on a lean mixture, for use of the method according to  claim 11 , the engine being equipped with an exhaust line containing a nitrogen oxides trap, the device comprising: 
 a first oxygen sensor disposed on an exhaust line downstream from the nitrogen oxides trap; and    calculating means for determining an increase of a meaningful signal representative of the signal delivered by the first oxygen sensor from a first plateau of substantially constant level, reached following initiation of a purging operation, and using the increase as an indicator to command an end of purging.    
   
   
       25 . A device according to  claim 24 , further comprising a second oxygen sensor disposed upstream from the nitrogen oxides trap and connected to the calculating means to deliver a reference signal thereto.