| abstract |
A method and apparatus convert time-resolved sensor signals into transfer functions and/or cumulative transfer function signals which can be attained by computation means (34) such as by using Fast Fourier Transforms. A signal, as a means to assess catalyst performance such as a signal based on oxygen concentration (32, 42), or air-fuel ratio (32, 42), or hydrocarbon concentration (32, 42) in motor vehicule exhaust (28, 30, 36, 38, 40) in accordance with the present invention is in the time domain and has multiple components at different frequencies. The use of Fast Fourier Transforms isolates the various spectral densities which arise from different frequency components of the complex time domain signal. Cross spectral density function and power spectral density function are used to determine the transfer function. The analysis has been found to be substantially independent of operating conditions. The transfer function and cumulative transfer function have been found to be a precise indication of the catalyst performance. |