Air-fuel ratio control system for internal combustion engines and exhaust system temperature-estimating device applicable thereto

An air-fuel ratio control system for an internal combustion engine having an exhaust passage, and a catalytic converter arranged in said exhaust passage, comprising:

• exhaust gas amount-calculating means for calculating an exhaust gas amount indicative of an amount of exhaust gases supplied to said catalytic converter;
• forcible oscillating means for forcibly oscillating an air-fuel ratio of a mixture supplied to said engine at predetermined frequency and a predetermined amplitude;
• oscillation-changing means for changing at least one of said predetermined frequency and said predetermined amplitude at a predetermined rate of change;
• and
• change rate-setting means for setting a predetermined rate of change of said at least one of said predetermined frequency and said predetermined amplitude in dependence on said exhaust gas amount.

An air-fuel ratio control system for an internal combustion engine having an exhaust passage, a catalytic converter arranged in said exhaust passage, and an oxygen sensor arranged in said exhaust passage at a location upstream of said catalytic converter, comprising:

• maximum oxygen storage amount-calculating means for calculating a maximum oxygen storage amount indicative of the maximum amount of oxygen that can be stored in said catalytic converter;
• air-fuel ratio feedback control means for calculating an air-fuel ratio feedback control amount, based on an output from said oxygen sensor and a feedback control constant;
• control amount-changing means for changing said air-fuel ratio feedback control constant at a predetermined rate of change;
• and
• change rate-setting means for setting said predetermined rate of change of said feedback control constant, based on said maximum oxygen storage amount.

An air-fuel ratio control system for an internal combustion engine having an exhaust passage, a catalytic converter arranged in said exhaust passage, and an oxygen. sensor arranged in said exhaust passage at a location upstream of said catalytic converter, comprising:

• exhaust gas amount-calculating means for calculating an exhaust gas amount indicative of an amount of exhaust gases supplied to said catalytic converter;
• air-fuel ratio feedback control means for calculating an air-fuel ratio feedback control amount, based on an output from said oxygen sensor and a feedback control constant;
• control amount-changing means for changing said air-fuel ratio feedback control constant at a predetermined rate of change;
• and
• change rate-setting means for setting said predetermined rate of change of said feedback control constant, based on said exhaust gas amount.

An air-fuel ratio control system for an internal combustion engine having an exhaust passage, and a catalytic converter arranged in said exhaust passage, comprising:

• maximum oxygen storage amount-calculating means for calculating a maximum oxygen storage amount indicative of the maximum amount of oxygen that can be stored in said catalytic converter;
• exhaust gas amount-calculating means for calculating an exhaust gas amount indicative of an amount of exhaust gases supplied to said catalytic converter;
• forcible oscillating means for forcibly oscillating an air-fuel ratio of a mixture supplied to said engine at a predetermined frequency and a predetermined amplitude;
• and
• setting means for setting said predetermined frequency and said predetermined amplitude, in dependence on said maximum oxygen storage amount and said exhaust gas amount.

An air-fuel ratio control system for an internal combustion engine having an exhaust passage, a catalytic converter arranged in said exhaust passage, and an oxygen sensor arranged in said exhaust passage at a location upstream of said catalytic converter, comprising:

• control amount-calculating means for calculating an air-fuel ratio feedback control amount, based on a predetermined Proportional term when a predetermined delay time period elapses after said output from said oxygen sensor is inverted.
• maximum oxygen storage amount-calculating means for calculating a maximum oxygen storage amount indicative of the maximum amount of oxygen that can be stored in said-catalytic converter;
• exhaust gas amount-calculating means for calculating an exhaust gas amount indicative of an amount of exhaust gases supplied to said catalytic converter;
• and
• setting means for setting said predetermined proportional term and said predetermined delay time period, in dependence on said maximum oxygen storage amount and said exhaust gas amount.

An air-fuel ratio control system for an internal combustion engine having an exhaust passage, and a catalytic converter arranged in said exhaust passage, comprising:

• oxygen amount-calculating means for calculating an amount of oxygen stored in said catalytic converter;
• maximum oxygen storage amount-calculating means for calculating a maximum oxygen storage amount indicative of the maximum amount of oxygen that can be stored in said catalytic converter;
• air-fuel ratio control means for controlling an air-fuel ratio of a mixture supplied to said engine such that said amount of oxygen stored in said catalytic converter falls within a predetermined range within said maximum oxygen storage amount;
• and
• changing means for changing said predetermined range in dependence on operating conditions of said engine.

An air-fuel ratio control system for an internal combustion engine having a cylinder block, an exhaust passage extending from said cylinder block, and a catalytic converter arranged in said exhaust passage, comprising:

• an oxygen sensor arranged in said exhaust passage at a location upstream of said catalytic converter;
• control amount-calculating means for calculating an air-fuel ratio feedback control amount, based on an output from said oxygen sensor;
• air-fuel ratio control means for controlling an air-fuel ratio of a mixture supplied to said engine based on said air-fuel ratio feedback control amount;
• first air-fuel ratio-estimating means for estimating an air-fuel ratio of exhaust gases in said exhaust passage at a location immediately downstream of said cylinder block from an amount of variation of said air-fuel ratio feedback control amount relative to an average value of said air-fuel ratio feedback control amount;
• and
• second air-fuel ratio-estimating means for estimating an air-fuel ratio of exhaust gases in said exhaust passage at a location immediately upstream of said catalytic converter from an averaged air-fuel ratio obtained by averaging said air-fuel ratio of said exhaust gases at said location immediately downstream of said cylinder block by the use of a predetermined averaging time constant.

An air-fuel ratio control system for an internal combustion engine having an exhaust passage, and a catalytic converter arranged in said exhaust passage, comprising:

• an oxygen sensor arranged in said exhaust passage at a location upstream of said catalytic converter;
• control amount-calculating means for calculating an air-fuel ratio feedback control amount, based on an output from said oxygen sensor;
• air-fuel ratio control means for controlling an air-fuel ratio of a mixture supplied to said engine, based on said air-fuel ratio-feedback control amount;
• first averaging means for averaging said air-fuel ratio feedback control amount by a first averaging time constant;
• second averaging means for averaging said air-fuel ratio feedback control amount by a second averaging time constant;
• and
• air-fuel ratio-calculating means for calculating an air-fuel ratio of exhaust gases at a location immediately upstream of said catalytic converter, based on an output from said first averaging means and an output from said second averaging means.

In an exhaust system temperature-estimating device for an internal combustion engine having an exhaust passage, including steady condition temperature-calculating means for calculating a steady condition temperature of said exhaust passage in a steady condition of said engine, based on operating conditions of said engine at least including load on said engine, follow-up speed-calculating means for calculating a follow-up speed of said temperature of said exhaust system relative to said steady condition temperature, and exhaust system temperature-estimating means for estimating temperature of said exhaust system, based on said steady condition temperature and said follow-up speed,

• the improvement comprising:
• intake air temperature-detecting means for detecting intake air temperature of said engine;
• vehicle speed-detecting means for detecting speed of a vehicle on which said engine is installed;
• and
• correcting means for correcting said steady condition temperature and/or said follow-up speed, based on said intake air temperature and said vehicle speed.