Patent ID: 8903628
Filing Date: 2014-12-02
Classification: F02D,F02P,Y02T

Abstract:
1. A diagnostic method for a multicylinder internal combustion engine for detecting a rotational fluctuation between cylinders during lean-burn operation of the engine and determining an occurrence of a malfunction pertaining to air-fuel ratio in a given cylinder based on the detected rotational fluctuation, the method comprising: determining that the malfunction pertaining to the air-fuel ratio has occurred when a degree of the rotational fluctuation is equal to or more than a first determination value; determining that the malfunction pertaining to the air-fuel ratio has not occurred when the degree of the rotational fluctuation is equal to or less than a second determination value that is smaller than the first determination value; and changing a mode of engine control to increase the degree of the rotational fluctuation when the degree of the rotational fluctuation is smaller than the first determination value and greater than the second determination value, so that: a difference between a torque generated in the given cylinder and a torque generated in another cylinder becomes greater, a control for the given cylinder and that for the another cylinder are different, and the torques are increased, wherein, after changing the mode of engine control, determining if the malfunction pertaining to the air-fuel ratio has occurred based on the increased degree of the rotational fluctuation.