Diagnostic method and device for operating an internal combustion engine

An electronic control device for of an internal combustion engine comprising a catalytic converter, a first exhaust gas sensor that is disposed in such a way that it may be used in a lambda closed-loop control operation, and a second exhaust gas sensor that is disposed in such a way that it may be used in a trim closed-loop control operation, the electronic control device being communicatively coupled to the first and second exhaust sensors, the electronic control device comprising:

• a memory storing data and programs, the programs when executed:
• determines an HC quality value, which is representative of an oxygen storage capacity of the catalytic converter, in dependence upon a measuring signal of the second exhaust gas sensor,
• determines a NOx correction value by:
• comparing the measuring signal to one or more threshold values, each having a predetermined factor assigned thereto,
• determining durations during which the measuring signal crosses each of the one or more threshold values,
• for each determined duration, calculating a product of a determined air mass flow for the internal combustion engine and the factor assigned to the threshold value crossed during that duration, and
• summing the calculated products for the durations, and
• multiplies or adds the HC quality value and the NOx correction value to determine a NOx quality value.

A system for operating an internal combustion engine comprising:

• a catalytic converter,
• a control device,
• a first exhaust gas sensor that is disposed in such a way that it may be used in a lambda closed-loop control operation, and
• a second exhaust gas sensor that is disposed in such a way that it may he used in a trim closed-loop control operation,
• wherein the second exhaust gas sensor feeds a measuring signal to the control device which:
• determines an HC quality value that is representative of an oxygen storage capacity of the catalytic converter from the measuring signal by:
• increasing a forced excitation amplitude applied to an air-fuel ratio setpoint value,
• comparing an oscillation of the measuring signal generated by the second exhaust gas sensor with respect to a predefined reference value, and
• determining the HC quality value based on the results of the comparison,
• determines an NOx correction value by:
• comparing the measuring signal generated by the second exhaust gas sensor to one or more threshold values, each having a predetermined factor assigned thereto,
• determining durations during which the measuring signal crosses each of the one or more threshold values,
• for each determined duration, calculating a product of a determined air mass flow for the internal combustion engine and the factor assigned to the threshold value crossed during that duration, and
• summing the calculated products for the durations,
• multiplies or adds the HC quality value and the NOx correction value to determine an NOx quality value representing a level of current NOx emissions from the engine.