Method for operating an internal combustion engine and device for implementing the method

Abstract

A method for operating an internal combustion engine and a device for implementing the method may allow a catalytic converter diagnosis with a high degree of accuracy. At least one catalytic converter is positioned in the exhaust-gas region of the internal combustion engine, and a lambda sensor, which is configured as broadband lambda sensor, is positioned downstream from the catalytic converter or downstream from a section of the catalytic converter. The catalytic converter diagnosis is based on the evaluation of a measure for the oxygen storage capacity of the catalytic converter/within the catalytic converter. An at least approximately empty/filled oxygen reservoir of the catalytic converter is assumed. A change in the lambda setpoint value of the internal combustion engine to an excess air factor lambda that is greater than 1/less than 1 follows. Subsequently, a first change of the lambda signal is detected initially. Determined is a measure for the oxygen stored/discharged following the first change of the lambda signal. The determination of the stored/discharged oxygen is terminated if either a second change in the lambda signal is detected or if the measure of oxygen exceeds a threshold value.

1 . A method for operating an internal combustion engine, at least one catalytic converter arranged in an exhaust-gas region of the internal combustion engine, a lambda sensor arranged as a broadband lambda sensor and arranged downstream from one of (a) the catalytic converter and (b) a section of the catalytic converter, comprising: 
 performing a catalytic converter diagnosis based on a measure for an oxygen storage capacity at least one of (a) of and (b) within the catalytic converter based on an oxygen reservoir of the catalytic converter that is at least approximately one of (a) empty and (b) full, and in which a change in a lambda setpoint value of the internal combustion engine to an excess air lambda that is one of (a) greater than 1 and (b) less than 1 is implemented;    detecting a first change in a lambda signal provided by the broadband lambda sensor;    ascertaining an oxygen stored/discharged after the first change; and    terminating ascertaining of the stored/discharged oxygen when either: (a) a second change of the lambda signal is determined; or (b) a predefined measure of oxygen was stored/discharged.    
   
   
       2 . The method according to  claim 1 , wherein the change of the lambda signal is determined from a gradient of the lambda signal.  
   
   
       3 . The method according to  claim 2 , wherein the change is detected when the gradient exceeds a predefined gradient threshold value for a predefined time period.  
   
   
       4 . The method according to  claim 2 , wherein the change is detected when the gradient has a maximum.  
   
   
       5 . The method according to  claim 2 , wherein the change is detected when the gradient has exceeded a maximum and subsequently falls below a gradient threshold value.  
   
   
       6 . The method according to  claim 1 , further comprising low-pass filtering of the lambda signal provided by the lambda sensor.  
   
   
       7 . The method according to  claim 1 , wherein the oxygen is determined from an integral over time, which is a function of a diagnosis lambda predefined during the diagnosis, and of an air signal, which is provided by an air detection, which detects combustion air provided to the internal combustion engine.  
   
   
       8 . The method according to  claim 7 , wherein the air signal is buffer-stored for a delay time that corresponds to a gas propagation time before the broadband lambda sensor is reached.  
   
   
       9 . The method according to  claim 8 , wherein the delay time is a function of at least one of (a) the air signal and (b) a load of the internal combustion engine.  
   
   
       10 . The method according to  claim 1 , wherein one of (a) the oxygen reservoir of the catalytic converter and (b) a section of the catalytic converter is at least approximately completely one of (a) filled and (b) emptied prior to the catalytic converter diagnosis by specifying a combustion lambda that is one of (a) greater than 1 and (b) less than 1.  
   
   
       11 . The method according to  claim 10 , wherein the combustion lambda that is one of (a) greater than 1 and (b) less than 1 is specified within the framework of normal operation of the internal combustion engine.  
   
   
       12 . The method according to  claim 1 , wherein the catalytic converter diagnosis is implemented following a deceleration fuel-cutoff phase of the internal combustion engine by which the oxygen reservoir of the catalytic converter is at least approximately filled.  
   
   
       13 . The method according to  claim 1 , wherein the evaluation of the stored/discharged oxygen is implemented as a function of at least one of (a) a catalytic converter temperature, (b) an exhaust gas temperature and (b) an exhaust gas mass flow.  
   
   
       14 . A device for operating an internal combustion engine, comprising: 
 a control device configured to perform a method, at least one catalytic converter arranged in an exhaust-gas region of the internal combustion engine, a lambda sensor arranged as a broadband lambda sensor and arranged downstream from one of (a) the catalytic converter and (b) a section of the catalytic converter, the method including: 
 performing a catalytic converter diagnosis based on a measure for an oxygen storage capacity at least one of (a) of and (b) within the catalytic converter based on an oxygen reservoir of the catalytic converter that is at least approximately one of (a) empty and (b) full, and in which a change in a lambda setpoint value of the internal combustion engine to an excess air lambda that is one of (a) greater than 1 and (b) less than 1 is implemented;  
 detecting a first change in a lambda signal provided by the broadband lambda sensor;  
 ascertaining an oxygen stored/discharged after the first change; and  
 terminating ascertaining of the stored/discharged oxygen when either: (a) a second change of the lambda signal is determined; or (b) a predefined measure of oxygen was stored/discharged.  
   
   
   
       15 . The device according to  claim 14 , wherein the control unit includes: 
 a diagnostic controller adapted to change the lambda setpoint value;    a change determination adapted to process the lambda signal; and    an integrator adapted to determine a measure for the stored/discharged oxygen.