Patent ID: 6915213

Claim:
An air-fuel ratio computing apparatus, comprising: a linear air-fuel ratio sensor provided to an exhaust pipe of an engine, for measuring an air-fuel ratio of exhaust gas emitted from the engine; and an electronic control unit for repeatedly performing filter processing on the air-fuel ratio measured by the linear air-fuel ratio sensor, using a formula Vf ( n )=(1 −G )× Vf ( n −1)+ G×V ( n ), where V(n) represents a voltage value corresponding to the air-fuel ratio measured by the linear air-fuel ratio sensor, Vf(n−1) represents a previous computed value from the filter processing, G(0≦G≦1) represents a filter gain expressing a computational ratio of V(n) and Vf(n−1), and Vf(n) represents a current computed value of the filter processing, wherein, in a case where a temperature of the linear air-fuel ratio sensor is below a predetermined temperature, the electronic control unit cuts off a pump current to the linear air-fuel ratio sensor, performs the filter processing with the filter gain G set to a first predetermined value, and transforms a computed value from the filter processing into a theoretical air-fuel ratio voltage; and in a case where the temperature of the linear air-fuel ratio sensor rises to or above the predetermined temperature, the electronic control unit performs the filter processing with the filter gain G set to a second predetermined value that is smaller than the first predetermined value, and computes an air-fuel ratio from the difference between a computed value from the filter processing and the theoretical air-fuel ratio voltage.