Search Results

A common practice to improve vehicle fuel economy is to employ a fuel cut-off strategy on deceleration. This practice exposes the TWC exhaust catalyst to varying concentrations of oxygen depending on the vehicle control strategy. Since it is well known that exposure to oxygen at high temperature is deleterious to long term catalyst durability, it is important to understand the impact of oxygen concentration and temperature on catalyst performance. Simulated fuel cut agings at about 1%, 3%, and 9% oxygen concentration were compared to a full fuel cut aging (21% oxygen concentration). It was found that even small concentrations of oxygen at high temperature damaged catalyst performance. Deactivation increased with increasing oxygen concentration and increasing temperature.

On-Board Diagnostics for emissions-related components require the monitoring of the catalytic converter performance. Currently, the dual Exhaust Gas Oxygen (EGO) sensor method is the only proven method for monitoring the catalyst performance for hydrocarbons (HC). The premise for using the dual oxygen sensor method is that a catalyst with good oxygen storage capacity (OSC) will perform better than a catalyst with lower OSC. A statistical relationship has been developed to correlate HC performance with changes in OSC. The current algorithms are susceptible to false illumination of the Malfunction Indication Light (MIL) due to: 1. The accuracy with which the diagnostic algorithm can predict a catalyst malfunction condition, and 2. The precision with which the algorithm can consistently predict a malfunction. A new algorithm has been developed that provides a significant improvement in correlation between the EGO sensor signals and hydrocarbon emissions.