MONITORING DEVICE FOR MULTICYLINDERED INTERNAL-COMBUSTION ENGINE

摘要

A monitoring apparatus comprises a catalytic converter 43, an upstream air-fuel ratio sensor 55, and a downstream air-fuel ratio sensor 56; calculates a sub feedback amount to have an air-fuel ratio represented based on an output value of the downstream air-fuel ratio sensor coincide with a stoichiometric air-fuel ratio; and controls an fuel injection amount based on an output value of the upstream air-fuel ratio sensor and the sub feedback amount, in such a manner that an air-fuel ratio of a mixture supplied to an engine 10 coincides with the stoichiometric air-fuel ratio. Further, the monitoring apparatus updates a learning value of the sub feedback control amount such that the learning value comes closer to a steady-state component of the sub feedback control amount. The monitoring apparatus classifies a convergence state of the learning value into at least three states, and sets a changing speed of the learning value based on the classified state. The monitoring apparatus performs an abnormality determination based on a first parameter for abnormality determination based on the learning value. The monitoring apparatus allows or prohibits to perform the abnormality determination based on the set changing speed of the learning value (i.e., a convergence state of the learning value).