Method for diagnosing exhaust gas probes and/or catalytic converters

Abstract

New operating phases of internal combustion engines, such as coasting in which the internal combustion engine is decoupled from the rest of the drive section, continuously decrease the number of phases in which there is an overrun mode of an internal combustion engine in which diagnoses of catalytic converters and exhaust gas probes are carried out. Also, a method wherein the diagnosis of the at least one exhaust gas probe and/or the at least one catalytic converter carried out during the coasting mode and, in particular, when the cylinder bank is switched off.

1 . A method for diagnosing exhaust gas probes and/or catalytic converters having at least one catalytic converter which is arranged in an exhaust gas duct of an internal combustion engine and an exhaust gas probe which is arranged in the exhaust gas duct, the function of which exhaust gas probe is checked, wherein the diagnosis of the at least one exhaust gas probe and/or of the at least one catalytic converter is carried out during the coasting mode. 
     
     
         2 . The method for diagnosing exhaust gas probes as claimed in  claim 1 , wherein in a first diagnostic section the cylinders which are assigned to a first exhaust gas section are switched off. 
     
     
         3 . The method for diagnosing exhaust gas probes as claimed in  claim 2 , wherein in a first phase in the first diagnostic section the lambda value of a first exhaust gas section is set to a predetermined value, in a second phase for generating a sudden change in the lambda value the cylinders which are assigned to the first exhaust gas section are firstly switched off, in a third phase this state is maintained over a certain time period, and subsequently in a fourth phase the cylinders which are assigned to the first exhaust gas section are switched on again with a defined lambda value. 
     
     
         4 . The method for diagnosing exhaust gas probes as claimed in  claim 2 , wherein in a second diagnostic section the cylinders which are assigned to a second exhaust gas section are switched off. 
     
     
         5 . The method for diagnosing exhaust gas probes as claimed in  claim 4 , wherein in a first phase in the second diagnostic section the lambda value of a second exhaust gas section is set to a predetermined value, in a second phase for generating a sudden change in the lambda value the cylinders which are assigned to the second exhaust gas section are firstly switched off, in a third phase this state is maintained over a certain time period, and subsequently in a fourth phase the cylinders which are assigned to the second exhaust gas section are switched on again with a defined lambda value. 
     
     
         6 . The method for diagnosing exhaust gas probes as claimed in  claim 4 , wherein the diagnosis is interrupted when the coasting mode ends, and the cylinders which are assigned to the first or second exhaust gas section are switched on again, and when the coasting mode is re-entered that diagnostic section which was interrupted when the coasting mode ended is started. 
     
     
         7 . The method for diagnosing exhaust gas probes as claimed in  claim 3 , wherein at an exhaust gas probe which is arranged downstream of a catalytic converter in the first or second exhaust gas section, the time period which the exhaust gas probe requires in the second phase ( 6 ,  16 ) to detect the sudden change in the lambda value at the changeover from the rich mixture to the lean mixture is measured. 
     
     
         8 . The method for diagnosing exhaust gas probes as claimed in  claim 3 , wherein at an exhaust gas probe which is arranged downstream of a catalytic converter in the first or second exhaust gas section it is measured in the third phase whether the exhaust gas probe exceeds a predefined voltage threshold given an infinite lambda value. 
     
     
         9 . The method for diagnosing exhaust gas probes as claimed in  claim 3 , wherein at an exhaust gas probe which is arranged downstream of a catalytic converter in the first or second exhaust gas section, the time period which the exhaust gas probe requires in the fourth phase to detect the sudden change in the lambda value at the changeover from the lean mixture to the rich mixture is measured. 
     
     
         10 . The method for diagnosing exhaust gas probes as claimed in  claim 3 , wherein at an exhaust gas probe which is arranged upstream of a catalytic converter in the first or second exhaust gas section it is measured in the third phase whether the exhaust gas probe exceeds a predefined voltage threshold given an infinite lambda value. 
     
     
         11 . The method for diagnosing exhaust gas probes as claimed in  claim 3 , wherein in the first phase a lambda value of 1 is set at the exhaust gas probe which is arranged downstream of the catalytic converter. 
     
     
         12 . The method for diagnosing exhaust gas probes as claimed in  claim 3 , wherein in a second diagnostic section the cylinders which are assigned to a second exhaust gas section are switched off. 
     
     
         13 . The method for diagnosing exhaust gas probes as claimed in  claim 12 , wherein in a first phase in the second diagnostic section the lambda value of a second exhaust gas section is set to a predetermined value, in a second phase for generating a sudden change in the lambda value the cylinders which are assigned to the second exhaust gas section are firstly switched off, in a third phase this state is maintained over a certain time period, and subsequently in a fourth phase the cylinders which are assigned to the second exhaust gas section are switched on again with a defined lambda value. 
     
     
         14 . The method for diagnosing exhaust gas probes as claimed in  claim 13 , wherein the diagnosis is interrupted when the coasting mode ends, and the cylinders which are assigned to the first or second exhaust gas section are switched on again, and when the coasting mode is re-entered that diagnostic section which was interrupted when the coasting mode ended is started. 
     
     
         15 . The method for diagnosing exhaust gas probes as claimed in  claim 14 , wherein at an exhaust gas probe which is arranged downstream of a catalytic converter in the first or second exhaust gas section, the time period which the exhaust gas probe requires in the second phase to detect the sudden change in the lambda value at the changeover from the rich mixture to the lean mixture is measured. 
     
     
         16 . The method for diagnosing exhaust gas probes as claimed in  claim 15 , wherein at an exhaust gas probe which is arranged downstream of a catalytic converter in the first or second exhaust gas section it is measured in the third phase whether the exhaust gas probe exceeds a predefined voltage threshold given an infinite lambda value. 
     
     
         17 . The method for diagnosing exhaust gas probes as claimed in  claim 16 , wherein at an exhaust gas probe which is arranged downstream of a catalytic converter in the first or second exhaust gas section, the time period which the exhaust gas probe requires in the fourth phase to detect the sudden change in the lambda value at the changeover from the lean mixture to the rich mixture is measured. 
     
     
         18 . The method for diagnosing exhaust gas probes as claimed in  claim 17 , wherein at an exhaust gas probe which is arranged upstream of a catalytic converter in the first or second exhaust gas section it is measured in the third phase whether the exhaust gas probe exceeds a predefined voltage threshold given an infinite lambda value. 
     
     
         19 . The method for diagnosing exhaust gas probes as claimed in  claim 18 , wherein in the first phase a lambda value of 1 is set at the exhaust gas probe which is arranged downstream of the catalytic converter.