Method for operating an exhaust-gas catalytic converter of an internal combustion engine

1. A method for determining characteristic operating values of an exhaust-gas catalytic converter, the method comprising the step of:

arranging a lambda sensor downstream of an exhaust-gas catalytic converter of an internal combustion engine with at least one cylinder and an exhaust-gas tract;

receiving a measured signal from the lambda sensor;

determining a first characteristic value that is representative of the NOx concentration as a function of the measured signal, wherein the first characteristic value for the NOx concentration is a NOx factor that is determined from a first characteristic curve as a function of the measured signal from the lambda sensor, the first characteristic curve being constant in sections of the first characteristic curve based on comparisons of the measured signal with one or more first predefined threshold values that are lower than a reference signal value;

determining a second characteristic value that is representative of the HC concentration as a function of the measured signal, wherein the second characteristic value for the HC concentration is a HC factor that is determined from a second characteristic curve as a function of the measured signal from the lambda sensor, the second characteristic curve being constant in sections of the second characteristic curve based on comparisons of the measured signal with one or more second predefined threshold values that are higher than the reference signal value; and

detecting a fault condition of the catalytic converter based on at least one of the NOx factor and the HC factor.

2. The method as claimed in claim 1 ,

in which, in periods of time in which the relevant NOx factor is constant, the relevant NOx factor is multiplied by a mean value of an air-mass flow into the cylinders in order to obtain a measurement for the NOx emissions in the periods of time, and

in which the measurement for the NOx emission is determined from the sum of the NOx emissions in the periods of time.

3. The method as claimed in claim 1 ,

in which, in the periods of time in which the relevant HC factor is constant, the relevant HC factor is multiplied by mean values of the air-mass flow into the cylinders in order to obtain a measurement for the HC emissions in the periods of time, and

in which the measurement for the HC emission is determined from the sum of the HC emissions in the periods of time.

4. An arrangement for determining characteristic operating values of an exhaust-gas catalytic converter of an internal combustion engine comprising at least one cylinder and an exhaust-gas tract, the arrangement comprising:

an exhaust-gas catalytic converter and a lambda sensor arranged downstream of the exhaust-gas catalytic converter, and

a device being operable to:

determine a characteristic value as a function of a measured signal of the lambda sensor that is representative of the NOx concentration, wherein the first characteristic value for the NOx concentration is a NOx factor that is determined from a first characteristic curve as a function of the measured signal from the lambda sensor, the first characteristic curve being constant in sections of the first characteristic curve based on comparisons of the measured signal with one or more first predefined threshold values that are lower than a reference signal value, and

determine a second characteristic value that is representative of the HC concentration as a function of the measured signal, wherein the second characteristic value for the HC concentration is a HC factor that is determined from a second characteristic curve as a function of the measured signal from the lambda sensor, the second characteristic curve being constant in sections of the second characteristic curve based on comparisons of the measured signal with one or more second predefined threshold values that are higher than the reference signal value; and

detect a fault condition of the catalytic converter based on at least one of the NOx factor and the HC factor.

5. The arrangement as claimed in claim 4 ,

wherein, in periods of time in which the relevant NOx factor is constant, the relevant NOx factor is multiplied by a mean value of an air-mass flow into the cylinders in order to obtain a measurement for the NOx emissions in the periods of time, and

wherein the measurement for the NOx emission is determined from the sum of the NOx emissions in the periods of time.

6. The arrangement as claimed in claim 4 ,

wherein, in the periods of time in which the relevant HC factor is constant, the relevant HC factor is multiplied by mean values of the air-mass flow into the cylinders in order to obtain a measurement for the HC emissions in the periods of time, and

wherein the measurement for the HC emission is determined from the sum of the HC emissions in the periods of time.

7. The arrangement as claimed in claim 4 ,

wherein the measurement for the NOx emission is determined from the sum of the NOx emissions in the periods of time and further divided by a reference NOx emission value corresponding to a predefined permissible NOx emission limit.

8. The arrangement as claimed in claim 7 ,

wherein the measurement for the HC emission is determined from the sum of the HC emissions in the periods of time and further divided by a reference HC emission value corresponding to a predefined permissible HC emission limit.

9. The method as claimed in claim 1 ,

in which the measurement for the NOx emission is determined from the sum of the NOx emissions in the periods of time and further divided by a reference NOx emission value corresponding to a predefined permissible NOx emission limit.

10. The method as claimed in claim 9 ,

in which the measurement for the HC emission is determined from the sum of the HC emissions in the periods of time and further divided by a reference HC emission value corresponding to a predefined permissible HC emission limit.