Method and device for controlling and/or monitoring the function of a secondary air supply in an emission control system

Abstract

In a method and device for controlling and/or monitoring the function of a secondary air supply in an emission control system of an internal combustion engine, the emission control system includes at least two catalytic converters situated in succession in an exhaust duct, it being possible for the second catalytic converter to be implemented as a combination of catalytic converter and particulate filter. For a secondary air diagnosis and for secondary air control, a two-point lambda probe is situated, with respect to a direction of flow of exhaust gas, downstream of the first catalytic converter. Measures are applied for compensating tolerance and aging effects of the two-point lambda probe. This results in particular in cost advantages in emission control systems for fulfilling stricter emission requirements. In particular, this makes it possible to operate the particulate filter in optimized fashion.

What is claimed is: 
     
         1 . A method for at least one of controlling and monitoring a function of a secondary air supply in an emission control system of an internal combustion engine, the emission control system, in its central section, including a first catalytic converter and a second catalytic converter situated in an exhaust duct in succession, a first lambda probe being situated, with respect to a direction of flow of exhaust gas, downstream of an engine block and upstream of the first catalytic converter, an exhaust gas probe being situated upstream of the second catalytic converter, air being introducible between the first and second catalytic converters by the secondary air supply for an optimized operation of the second catalytic converter, wherein a two-point lambda probe is situated downstream of the first catalytic converter and of the secondary air supply, the method comprising:
 using the two-point lambda probe for at least one of a secondary air diagnosis and a secondary air control; and   applying to the two-point lambda probe measures that compensate tolerance and aging effects.   
     
     
         2 . The method of  claim 1 , wherein:
 at least one particulate filter is situated downstream of the first catalytic converter and the secondary air supply or is part of the second catalytic converter; and   the at least one of the secondary air diagnosis and the secondary air control is performed using the secondary air supply and the two-point lambda probe for the a least one particulate filter.   
     
     
         3 . The method of  claim 1 , wherein the applying of the measures includes adapting an offset of a probe characteristic of the two-point lambda probe by an adjustment at high excess air while the internal combustion engine is running or is at a standstill. 
     
     
         4 . The method of  claim 3 , wherein the applying of the measures includes applying a correction of a temperature-related shift of the probe characteristic with the aid of an active measurement of a sensor element temperature while the internal combustion engine is running or is at a standstill. 
     
     
         5 . The method of  claim 3 , wherein the applying of the measures further includes applying a correction of a calculation of a lambda value, thereby taking into account a current exhaust-gas composition and a varying cross sensitivity vis-à-vis different exhaust-gas components. 
     
     
         6 . The method of  claim 1 , wherein the applying of the measures includes shifting a lambda-one point of a probe characteristic of the two-point lambda probe via a tracking control of the second two-point lambda probe. 
     
     
         7 . The method of  claim 6 , wherein the applying of the measures includes applying a correction of a temperature-related shift of the probe characteristic with the aid of an active measurement of a sensor element temperature while the internal combustion engine is running or is at a standstill. 
     
     
         8 . The method of  claim 1 , wherein the applying of the measures includes:
 adapting an offset of a probe characteristic of the two-point lambda probe by an adjustment at high excess air while the internal combustion engine is running or is at a standstill;   shifting a lambda-one point of the probe characteristic via a tracking control of the second two-point lambda probe;   applying a correction of a temperature-related shift of the probe characteristic with the aid of an active measurement of a sensor element temperature while the internal combustion engine is running or is at a standstill; and   applying a correction of a calculation of a lambda value, thereby taking into account a current exhaust-gas composition and a varying cross sensitivity vis-à-vis different exhaust-gas components.   
     
     
         9 . The method of  claim 1 , wherein the internal combustion engine is part of a vehicle. 
     
     
         10 . An emission control system of an internal combustion engine, the emission control system comprising:
 an engine control unit that includes a least one of a storage device and a comparator unit; and   in a central section of the emission control system:
 a first catalytic converter situated in an exhaust duct; 
 a second catalytic converter situated in the exhaust duct in sequence with the first catalytic converter; 
 a lambda probe that is situated, with respect to a direction of flow of exhaust gas, downstream of an engine block and upstream of the first catalytic converter and that is configured to supply signals to the engine control unit; 
 an exhaust-gas probe that is downstream of the first catalytic converter and of the second catalytic converter; 
 a secondary air supply configured to introduce air between the first and second catalytic converters for optimized operation of the second catalytic converter; and 
 a two-point lambda probe that is situated downstream of the first catalytic converter and of the secondary air supply and is configured to supply signals to the engine control unit; 
   wherein the engine control unit is configured to:
 perform a catalytic converter diagnosis; 
 use the signals from the two-point lambda probe to perform at least one of a secondary air diagnosis and a secondary air control of the secondary air supply; and 
 apply to the two-point lambda probe measures that compensate tolerance and aging effects of the two-point lambda probe. 
   
     
     
         11 . The device of  claim 10 , wherein at least one of the emission control system further comprises a particulate filter downstream of the first catalytic converter and of the secondary air supply. 
     
     
         12 . The device of  claim 10 , wherein the second catalytic converter includes a particulate filter.