Emission control device of engine exhaust and control method exhaust emissions

A control device exhaust emission of the engine including: an adder (43) for adding a NOx reducing agent to exhaust gas of an engine (1); a first controller (61) for controlling the adder ( 43); yun second controller (51) configured to be in association with the engine (1), characterized eldispositivo that the first controller (61) detects an abnormality occurring in the feeding device (43) as a first anomaly, and time of occurrence of the first abnormality when the occurrence of this primeraanomalia is detected, sends the second controller (51) a control signal of motor to make unacantidad NOx emission of the engine (1) varies with respect to time of control normal addition, distintade the time of occurrence of the first fault, under the same engine operating conditions, andthe second controller (51) sets a control factor engine influences the composition of exhaust gas inthe time point emission from a cylinder, and detects an abnormality occurring in an engine part (12,36) to perform engine control factor as a second failure, and the time or na appearance segundaanomalia when the occurrence of the second abnormality is detected, sends to the first controller (61) a decontrol signal addition device to an addition amount of reducing agent by deadicion (43) device to vary from the a time of normal engine operation, other than the normal time abnormality aparicionde.