System and method for monitoring a catalytic converter using adaptable indicator threshold

Claim 1

A method for monitoring efficiency of a catalytic converter in a vehicle having an internal combustion engine connected to the catalytic converter and controlled by an engine controller having a memory for storing a malfunction indicator threshold value, the vehicle including an upstream exhaust gas oxygen sensor between the engine and the converter for providing voltage signals to the controller indicative of excursions from a stoichiometric combustion mixture and a downstream exhaust gas oxygen sensor interposed the converter and atmosphere for providing voltage signals to the controller indicative of conversion efficiency of the converter, the method comprising: counting switches of the upstream sensor wherein a switch occurs when the voltage signal crosses a switching threshold; counting switches of the downstream sensor wherein a switch occurs when the voltage signal varies in excess of a switching level; determining a current value for the malfunction indicator after a predetermined number of switches of the upstream sensor have been observed, the current value being a ratio based on the switches of the upstream and downstream sensors; calculating a historical value for the malfunction indicator based on the current value; and modifying the predetermined malfunction indicator threshold value based on the historical value.

Claim 2

A method for monitoring efficiency of a catalytic converter in a vehicle having an internal combustion engine connected to the catalytic converter and controlled by an engine controller having a memory for storing a malfunction indicator threshold value, the vehicle including an upstream exhaust gas oxygen sensor between the engine and the converter for providing voltage signals to the controller indicative of excursions from a stoichiometric combustion mixture and a downstream exhaust gas oxygen sensor interposed the converter and atmosphere for providing voltage signals to the controller indicative of conversion efficiency of the converter, the method comprising: counting switches of the upstream sensor wherein a switch occurs when the voltage signal crosses a switching threshold; counting switches of the downstream sensor wherein a switch occurs when the voltage signal varies in excess of a switching level; determining a current value for the malfunction indicator after a predetermined number of switches of the upstream sensor have been observed, the current value being a ratio based on the switches of the upstream and downstream sensors; calculating a historical value for the malfunction indicator based on the current value; and modifying the predetermined malfunction indicator threshold value based on the historical value.

Claim 8

A system for monitoring performance of a catalytic converter in a vehicle having an internal combustion engine connected to the catalytic converter, the system comprising: a first exhaust gas sensor between the engine and the catalytic converter; a second exhaust gas sensor positioned downstream from the catalytic converter; and a controller having a memory with a predetermined threshold for a catalyst efficiency indicator, the controller being in communication with the first and second exhaust gas sensors for determining a current value of the catalyst efficiency indicator based on a ratio of observed transitions of the second exhaust gas sensor and observed transitions of the first exhaust gas sensor, modifying a historical value for the catalyst efficiency indicator based on the current value, calculating at least one statistical parameter based on the historical value, and adjusting the threshold for the catalyst efficiency indicator based on the at least one statistical parameter to produce a modified threshold.

Claim 9

A system for monitoring performance of a catalytic converter in a vehicle having an internal combustion engine connected to the catalytic converter, the system comprising: a first exhaust gas sensor between the engine and the catalytic converter; a second exhaust gas sensor positioned downstream from the catalytic converter; and a controller having a memory with a predetermined threshold for a catalyst efficiency indicator, the controller being in communication with the first and second exhaust gas sensors for determining a current value of the catalyst efficiency indicator based on a ratio of observed transitions of the second exhaust gas sensor and observed transitions of the first exhaust gas sensor, modifying a historical value for the catalyst efficiency indicator based on the current value, calculating at least one statistical parameter based on the historical value, and adjusting the threshold for the catalyst efficiency indicator based on the at least one statistical parameter to produce a modified threshold.