Patent ID: 6050128
Filing Date: 2000-04-18
Classification: F01N,Y02T

Abstract:
A method of testing a catalyst used in the exhaust stream of an internal combustion engine having a variable air/fuel ratio, while the engine is operating, with a first oxygen sensor mounted in the exhaust stream upstream of the catalyst and a second oxygen sensor mounted in an exhaust stream downstream of the catalyst, the method comprising the steps of:determining an engine temperature parameter;comparing the temperature parameter to a first predetermined temperature value;determining that engine RPM and load values are substantially constant;adjusting the air/fuel ratio to a predetermined lean value;waiting a predetermined first time interval;reading the first and second sensor outputs after the first time interval and storing as values AF1 and AF2, respectively, if the temperature parameter is greater than the first predetermined temperature value and the RPM and load values are generally constant;adjusting the air/fuel ratio to a predetermined rich value;waiting a predetermined second time interval;reading the first and second sensor output values after the second time interval and storing as values AF3 and AF4, respectively;again adjusting the air/fuel ratio to a predetermined lean value;determining a first difference between the first sensor output and AF1 and determining a second difference between the second sensor output and AF2;again adjusting the air/fuel ratio to a predetermined rich value if the first difference and the second difference are zero;determining a third difference between the first sensor output and AF3;setting a first time value to zero if the third difference is equal to zero;reading the second sensor output and storing as AF5;incrementing the first time value;comparing AF4 to AF5;saving the first 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 first time value to a predetermined minimum time value after the first time value is saved; andoutputting that the catalyst failed if the saved first time value is not greater than the predetermined minimum time value.