Air-fuel ratio sensor for an internal combustion engine and an air-fuel ratio control apparatus using the same

An air-fuel ratio sensor for sensing an air-fuel ratio of air-fuel mixture supplied to an internal combustion engine, said air-fuel ratio sensor comprising:

• a sensing portion, exposed to exhaust gas from the engine, for producing an output voltage in response to the concentration of remaining oxygen included in the exhaust gas, said sensing portion having a temperature dependent output characteristic of a step change portion changing stepwise in the vicinity of stoichiometric air-fuel ratio of a mixture and a portion changing linearly with respect to an air-fuel ratio of a mixture on either side of said stoichiometric air-fuel ratio;
• and
• a microprocessor circuit, which has stored therein a table of reference voltage versus temperature of said sensing portion, for detecting a temperature of said sensing portion, determining a reference voltage by retrieving said table on the basis of said detected temperature, obtaining a voltage deviation between said output voltage of said sensing portion and said reference voltage, and identifying an actual air-fuel ratio on the said of said voltage deviation.

An air-fuel ratio sensor according to claim 3, wherein said microprocessor circuit in performing said detecting function detects an internal resistance of the solid electrolyte part, and identifies said temperature of said sensing portion on the basis of said detected internal resistance.

An air-fuel ratio control apparatus for an internal combustion engine, comprising:

• a sensing portion, exposed to exhaust gas from the engine, for producing an output voltage in response to the concentration of remaining oxygen included in the exhaust gas, said sensing portion having a temperature dependent output characteristic of a step change portion changing stepwise in the vicinity of stoichiometric air-fuel ratio of a mixture and a portion changing linearly with respect to an air-fuel ratio of a mixture on either side of said stoichiometric air-fuel ratio;
• and
• a microprocessor circuit, which has stored therein a table of reference voltage versus temperature of said sensing portion for detecting a temperature of said sensing portion, determining a reference voltage by retrieving said table on the basis of said detected temperature, obtaining a voltage deviation between said output voltage of said sensing portion and said reference voltage, comparing said voltage deviation with a target air-fuel ratio preset for an air-fuel ratio control of the fuel mixture to generate a control deviation, and producing a fuel control signal in accordance with said control deviation.