Determining Three-Way Catalyst Age Using Differential Lambda Signal Response

The duration over which a three way catalyst (TWC) maintains proper functionality during lambda excursions is critically impacted by aging, which affects its oxygen storage capacity (OSC). As such, emissions control strategies, which strive to maintain post TWC air-to-fuel ratios at the stoichiometric value, will benefit from an accurate estimation of TWC age. To this end, this investigation examines a method of TWC age estimation suitable for real-world transient operation. Experimental results are harvested from an instrumented test vehicle equipped with a two-brick TWC during operation on a chassis dynamometer. Four differently aged TWCs are instrumented with wideband and switch-type Lambda sensors upstream (Pre TWC location), and downstream (Mid location) of first catalyst brick. The lambda measurements are utilized to create an age dependent time parameter,τ which is found to be predominantly a function of exhaust flow with lesser dependencies on both exhaust gas and catalyst brick temperatures. The proposed method for age estimation can distinguish between TWC of different ages during fuel cut events within a defined range of exhaust flows. Future compensation of exhaust gas temperature impacts on τ is expected to increase the confidence level of the TWC age estimation.