Patent ID: 6131439
Filing Date: 2000-10-17
Classification: F01N,Y02T

Abstract:
A method of testing a catalyst used in an exhaust stream of an internal combustion engine having a variable air/fuel ratio, while the engine is operating after a start-up, with the engine having a first oxygen sensor mounted in the exhaust stream upstream of the catalyst and a second oxygen sensor mounted in the exhaust stream downstream of the catalyst, the method comprising the steps of:operating the engine with a lean air/fuel ratio;determining an engine temperature parameter;comparing the temperature parameter to a first predetermined temperature value;comparing a time since engine start-up to a first predetermined time value;reading the outputs of the first and the second sensors if the temperature parameter is less than the first predetermined temperature value and the time since start-up is less than the first predetermined time value;computing a difference between the output from the first sensor and the output from the second sensor;recalibrating one of the first and second sensors if the difference is less than a predetermined difference value and the outputs are not equal;determining a second engine temperature parameter;comparing the second temperature parameter to a second predetermined temperature value;determining that engine RPM and load values are substantially constant;adjusting the air/fuel ratio to a predetermined rich value if the temperature parameter is greater than the first predetermined temperature value and the RPM and load values are generally constant;waiting a predetermined rich time interval;reading the first and second sensor output values after the rich time interval and storing as values AF3 and AF4, respectively;adjusting the air/fuel ratio to a predetermined lean value;again adjusting the air/fuel ratio to a predetermined rich value;determining an upstream difference between the first sensor output and AF3;setting a second time value to zero if the upstream difference is equal to zero;reading the second sensor output and storing as AF5;incrementing the second time value;comparing AF4 to AF5;saving the second time value if AF4 equals AF5;returning to the step of, reading the second sensor output and storing as AF5, if AF4 is not equal to AF5;comparing the second time value to a predetermined minimum time value after the second time value is saved; andoutputting that the catalyst failed if the saved second time value is not greater than the predetermined minimum time value.