METHOD FOR DIAGNOSING FUNCTION OF REDUCTION NON-METHANIC HYDROCARBON IN SELECTIVE CATALYTIC REDUCTION SYSTEM

摘要

A non-methane hydrocarbon reduction function diagnostic method of a SCR system is provided to output a warning signal which means that error of NMHC reduction function is diagnosed when the reduced difference of the signals outputted from a lambda sensor of both front-end and rear-end of DDPF is less than the standard value. A non-methane hydrocarbon reduction function diagnostic method of a SCR system comprises the steps of: a first step(S307) which computes the oxygen concentration of a CDPF rear end and a CDPF front end through the signal received from the CDPF(Catalyzed Diesel Particulate matter Filter) front end lambda sensor and a CDPF rear end lambda sensor when the temperature of the SCR(Selective Catalytic Reduction) front end is greater than a certain temperature(S303); a second step(S309) which computes a non-methane hydrocarbon value of the CDPF rear end and CDPF front end by using the oxygen concentration; and a third step(S313) which outputs a warning signal when the value dividing the difference between the non-methane hydrocarbon value of the CDPF front end and the non-methane hydrocarbon value of the CDPF rear end with the non-methane hydrocarbon value of the CDPF front end is lower than a certain standard value(S311).