Exhaust system with bypass catalytic converter and diagnostics

A control method for engine exhaust gas purification and monitoring, comprising the steps of:

• enabling flow of the exhaust gas through a first catalytic converter via a first valve when an indication of exhaust gas temperature is above a predetermined temperature and enabling flow of the exhaust gas through a second catalytic converter when said exhaust gas temperature is below said predetermined temperature;
• providing a first ratio of transitions in outputs of exhaust gas oxygen sensors respectively positioned downstream and upstream of said first converter during said enablement of said first converter;
• providing a second ratio of transitions in outputs of exhaust gas oxygen sensors respectively positioned downstream and upstream of said second converter during said enablement of said second converter;
• indicating degraded operation of said first converter during a test cycle when said first ratio exceeds a first preselected ratio and indicating degraded operation of said second converter when both said second ratio exceeds a second preselected ratio and an indication of airflow inducted into the engine exceeds a preselected airflow;
• and
• indicating degraded performance of said valve when both said second ratio exceeds a second preselected ratio and an indication of airflow inducted into the engine is below said preselected airflow.

An engine exhaust purification and monitoring system, comprising:

• a first catalytic converter having an inlet coupled to the engine exhaust via a first electronically controlled valve;
• a second catalytic converter coupled to the engine exhaust via a second electronically controlled valve, said second catalytic converter having an outlet coupled to said first catalytic converter inlet downstream of said first valve;
• a first exhaust gas oxygen sensor coupled to the engine exhaust upstream of both said first converter and said second converter;
• a second exhaust gas oxygen sensor coupled to said second converter outlet;
• a third exhaust gas oxygen sensor coupled to an outlet of said first converter;
• a controller for enabling said second converter by closing said first valve and opening said second valve when an indication of exhaust gas temperature is below a predetermined value, said controller enabling said first converter by opening said first valve and closing said second valve when said exhaust gas temperature indication exceeds said predetermined value;
• and
• a monitor for providing an indication of degraded operation of said first converter from a ratio of transitions in output of said third sensor to said first sensor while said first converter is enabled, said monitor providing an indication of degraded operation of said second converter from a ratio of transitions in output of said second sensor to said first sensor while said second converter is enabled.

An electronic storage device containing a computer program to be executed by an engine controller which controls and monitors engine operation, comprising:

• enablement means for enabling flow of engine exhaust gas through a first catalytic converter via a valve when an indication of exhaust gas temperature is above a predetermined temperature and enabling flow of said exhaust gas through a second catalytic converter when said exhaust gas temperature is below the predetermined temperature;
• signal indicating means for deriving an indicating signal from transitions in output of an exhaust gas oxygen sensor positioned downstream of said second converter;
• converter indicating means for indicating degraded operation of said second converter when both said indicating signal indicates degraded operation and an indication of airflow inducted into the engine exceeds a preselected airflow;
• and
• valve indicating means for indicating degraded performance of said valve when both said indicating signal indicates degraded operation and an indication of inducted airflow is below said preselected airflow.