System for determining deterioration of catalysts of internal combustion engines

A catalyst deterioration-determining system for determining deterioration of catalyst means of an internal combustion engine having:

• an exhaust passage;
• catalyst means arranged in said exhaust passage;
• a first oxygen concentration sensor arranged in said exhaust passage upstream of said catalyst means, for sensing concentration of oxygen contained in exhaust gases emitted from said engine;
• first determining means for comparing an output from said first oxygen concentration sensor with a first predetermined reference value and determining, from a result of said comparison, whether the air-fuel ratio of a mixture supplied to said engine is richer or leaner than a stoichiometric air-fuel ratio;
• a second oxygen concentration sensor arranged in said exhaust passage downstream of said catalyst means for sensing concentration of oxygen contained in said exhaust gases;
• second determining means for comparing an output from said second oxygen concentration sensor with a second predetermined reference value and determining, from a result of said comparison, whether the air-fuel ratio of said mixture supplied to said engine is richer or leaner than said stoichiometric air-fuel ratio;
• air-fuel ratio control means responsive to an output from said second determining means for calculating an air-fuel ratio correction value and controlling the air-fuel ratio of said mixture by means of the calculated air-fuel ratio correction value;
• and
• operating condition detecting means for detecting operating conditions of said engine,
• said catalyst deterioration-determining system comprising:
• inversion time period measuring means for calculating a time period based upon the time an inversion occurs in an output from said first determining means to the time an inversion occurs in said output from said second determining means, after said air-fuel ratio control means causes an inversion in the value of the air-fuel ratio of said mixture with respect to said stoichiometric air-fuel ratio in response to said output from said second determining means, when it is detected by said operating condition detecting means that said engine is in a predetermined operating condition;
• and
• deterioration determining means for comparing said time period calculated by said inversion time period measuring means with a predetermined time period and determining that said catalyst means is deteriorated, when said calculated time period is shorter than said predetermined time period.

A catalyst deterioration-determining system for determining deterioration of catalyst means of an internal combustion engine having:

• an exhaust passage;
• catalyst means arranged in said exhaust passage;
• a first oxygen concentration sensor arranged in said exhaust passage upstream of said catalyst means, for sensing concentration of oxygen contained in exhaust gases emitted from said engine;
• a second oxygen concentration sensor arranged in said exhaust passage downstream of said catalyst means for sensing concentration of oxygen contained in said exhaust gases;
• and
• first air-fuel ratio control means responsive to an output from said first oxygen concentration sensor and an output from said second oxygen concentration sensor for controlling the air-fuel ratio of a mixture supplied to said engine by means of an air-fuel ratio correction value;
• said catalyst deterioration-determining system comprising:
• second air-fuel ratio control means responsive to said output from said second oxygen concentration sensor for controlling the air-fuel ratio of said mixture by means of said air-fuel ratio correction value;
• operating condition determining means for determining whether said engine is in a predetermined operating condition;
• changeover means for effecting changeover from said first air-fuel ratio control means to said second air-fuel ratio control means for controlling the air-fuel ratio of said mixture, when said engine is determined to be in said predetermined operating condition;
• inversion determining means for determining whether said output from said second oxygen concentration sensor has been inverted from a leaner side to a richer side or vice versa with respect to a stoichiometric air-fuel ratio;
• first time period measuring means for measuring a first time period elapsed from the time said second air-fuel ratio control means causes a change in the value of said air-fuel ratio correction value from said richer side to said leaner side with respect to said stoichiometric air-fuel ratio to the time said output from said second oxygen concentration sensor is inverted from said richer side to said leaner side with respect to said stoichiometric air-fuel ratio, after said changeover has been effected;
• second time period measuring means for measuring a second time period elapsed from the time said second air-fuel ratio control means causes a change in the value of said air-fuel ratio correction value from said leaner side to said richer side with respect to said stoichiometric air-fuel ratio to the time said output from said second oxygen concentration sensor is inverted from said leaner side to said richer side with respect to said stoichiometric air-fuel ratio, after said changeover has been effected;
• deterioration determining means for comparing the sum of said first and second time periods measured by said first and second time period measuring means or an average value thereof with a predetermined time period and determining that said catalyst means is deteriorated, when the sum or said average value is shorter than said predetermined time period.

A catalyst deterioration-determining system for determining deterioration of catalyst of an internal combustion engine having:

• an exhaust passage;
• catalyst means arranged in said exhaust passage;
• a first oxygen concentration sensor arranged in said exhaust passage upstream of said catalyst means, for sensing concentration of oxygen contained in exhaust gases emitted from said engine;
• a second oxygen concentration sensor arranged in said exhaust passage downstream of said catalyst means, for sensing concentration of oxygen contained in said exhaust gases;
• and
• first air-fuel ratio control means responsive to an output from said first oxygen concentration sensor and an output from said second oxygen concentration sensor, for controlling the air-fuel ratio of a mixture supplied to said engine by means of a first air-fuel ratio correction value;
• said catalyst deterioration determining system comprising:
• second air-fuel ratio control means responsive to said output from said second oxygen concentration sensor, for controlling the air-fuel ratio of said mixture by means of a second air-fuel ratio correction value;
• operating condition determining means for determining whether said engine is in a predetermined operating condition;
• changeover means for effecting changeover from said first air-fuel ratio control means to said second air-fuel ratio controlling means for controlling the air-fuel ratio of said mixture, when said engine is determined to be in said predetermined operating condition;
• deterioration determining means for determining whether said catalyst means is deteriorated, based on said output from said second oxygen concentration sensor which is output when the air-fuel ratio of said mixture is controlled by said second air-fuel ratio control means.