On-line catalyst monitoring using a Kalman filter
View Patent ↗A method of non-intrusive monitoring of catalyst performance in an automotive exhaust system uses a model of catalytic converter operation emphasizing oxygen storage capacity dominance. Model parameters are identified using a recursive Kalman filtering technique. A catalyst diagnostic index is derived from at least one identified parameter, and the index is used to judge converter performance.
1. A method of on-line, non-intrusive monitoring of a catalytic converter, the method comprising:
modeling dynamic behavior of a catalytic converter using an oxygen storage dominant model;
identifying parameters in the model using a recursive Kalman filtering technique;
deriving a catalyst diagnostic index using said model parameters identified by said Kalman filtering technique; and
using the index to judge performance of the catalytic converter.
2. The method of claim 1 wherein the storage dominant model is described by an auto-regressive moving average equation.
3. The method of claim 2 wherein the preselected parameter comprises a pole of the auto-regressive moving average equation.
4. The method of claim 3 wherein the pole is directly related to a catalyst conversion rate.
5. The method of claim 3 wherein the pole comprises a dominant pole of the equation.
6. The method of claim 1 wherein the performance of the catalytic converter is judged acceptable whenever the index is less than a predetermined threshold value.
7. The method of claim 2 wherein the equation is
y ( k )= a 1 y ( k− 1)+ b 1 u ( k− 1)+ b 2 u ( k− 2)+. . . + b n u ( k−n )+ v ( k )
where
u represents the upstream relative equivalent air/fuel ratio which is input to the system or catalyst;
y represents the downstream relative equivalent air/fuel ratio which is the output from the system;
a 1 and b 1 , b 2 , . . . , b n are the coefficients of the model;
k is the discrete time step;
n represents the time delay step for the input; and
v is the measurement noise.
8. The method of claim 7 wherein the preselected parameter is a 1 , and the index is derived by taking the absolute value of a 1 .
9. The method of claim 7 wherein the absolute value of a 1 ranges in value from zero to one and wherein the performance of the catalytic converter is judged acceptable whenever the absolute value of a 1 is less than an experimentally determined threshold value between zero and one.
10. The method of claim 1 , wherein said using an oxygen storage dominant model includes using a linear model.