Device and Method for Estimating Ideal Air-Fuel Ratio in Internal Combustion Engine, Method of Estimating Oxygen Storage Capacity of Catalyst, Internal Combustion Engine Device and Motorcycle Incorporating Internal Combustion Engine Device

An ideal air-fuel ratio estimating device comprising:

• a first air-fuel ratio sensor which is attached to an exhaust gas passage of an internal combustion engine such that the first air-fuel ratio sensor is positioned upstream of a catalyst provided in the exhaust gas passage, and outputs a value changing in proportion to a change in an air-fuel ratio of an air-fuel mixture of the internal combustion engine;
• a second air-fuel ratio sensor which is attached to the exhaust gas passage such that the second air-fuel ratio sensor is positioned downstream of the catalyst and outputs a value changing steeply when the air-fuel ratio of the air-fuel mixture is close to the ideal air-fuel ratio;
• and
• a control unit for estimating that the output value of the first air-fuel ratio sensor in a state in which the second air-fuel ratio sensor continues to output the value which is close to a value corresponding to the ideal air-fuel ratio, is an output value corresponding to the ideal air-fuel ratio.

An internal combustion engine device comprising:

• an internal combustion engine;
• a catalyst provided in an exhaust gas passage of the internal combustion engine to purify an exhaust gas generated in the internal combustion engine;
• an upstream air-fuel ratio sensor attached to the exhaust gas passage such that the upstream air-fuel ratio sensor is positioned upstream of the catalyst;
• a downstream air-fuel ratio sensor attached to the exhaust gas passage such that the downstream air-fuel ratio sensor is positioned downstream of the catalyst;
• and
• a control unit which receives an output of the upstream air-fuel ratio sensor and an output of the downstream air-fuel ratio sensor, detects a state in which the catalyst does not store or release oxygen based on the output of the downstream air-fuel ratio sensor, and decides as an estimated ideal air-fuel ratio an air-fuel ratio detected by the upstream air-fuel ratio sensor when the state in which the catalyst does not store or release oxygen is detected.