Air-fuel ratio control unit for engine

Claim 1

An air-fuel ratio control unit for a V-type engine, comprising: means for calculating a basic fuel injection time on the basis of an intake air amount detected by an air flow sensor and for generating a fuel feeding instruction signal to an injector installed in an air intake pipe; air-fuel ratio feedback correction means for correcting a fuel injection time of said injector in such a manner that said engine is operated at a theoretical air-fuel ratio, on the basis of output information form O 2 sensors installed respectively on left and right exhaust banks; learning means for storing a learned value representing a deviation of the basic fuel injection time for each of the exhaust banks from a mean fuel injection time; and means for, in case one of said O 2 sensors becomes in any abnormal state, correcting the fuel injection time on the basis of the output information from another O 2 sensor operating in a normal state, and the learned values stored in said learning means at a time when both of said O 2 sensors were in a normal state.

Claim 4

A method of controlling an air-fuel ratio for an engine installed with at least two exhaust banks each having an O 2 sensor, comprising the steps of: calculating a basic fuel injection time on the basis of an amount of intake air detected by an air flow sensor; calculating a fuel injection time of an injector on the basis of an output information from said each O 2 sensor; calculating a mean fuel injection time for said each O 2 sensor; storing a learned value for said each O 2 sensor on the basis of the basic fuel time and the means fuel injection time; and correcting, in case one of said O 2 sensors becomes in any abnormal state, the fuel injection time on the basis of the output information from the other O 2 sensor performing its normal operation and the learned values stored at the time when both the O 2 sensors performed normal operations.

Claim 5

A method of controlling an air-fuel ratio for an engine installed with at least two exhaust banks each having an O 2 sensor, comprising the steps of: calculating a basic fuel injection time on the basis of an amount of intake air detected by an air flow sensor; calculating a fuel injection time of an injector on the basis of an output information from said each O 2 sensor; calculating a mean fuel injection time for said each O 2 sensor; storing a learned value for said each O 2 sensor on the basis of the basic fuel time and the means fuel injection time; and correcting, in case one of said O 2 sensors becomes in any abnormal state, the fuel injection time on the basis of the output information from the other O 2 sensor performing its normal operation and the learned values stored at the time when both the O 2 sensors performed normal operations.