Dual sensor type air fuel ratio control system for internal combustion engine

In an internal combustion engine a method of controlling the air-fuel ratio comprising:

• sensing engine speed and engine load;
• sensing the air-fuel ratio at a location upstream of a catalytic converter using a second air-fuel ratio sensor;
• sensing the air-fuel ratio at a location downstream of a catalytic converter using a second air-fuel ration sensor;
• supplying fuel into the engine;
• using the air-fuel ratio sensed at the location upstream of the catalytic converter to determine a basic injection pulse width;
• determining an air-fuel ratio feedback control factor value based on the output of said first air-fuel ratio sensor by a table look up using a stored data table;
• determining an actual pulse width by correcting the basic pulse width using said air-fuel ration feedback control factor;
• modifying said air-fuel ratio feedback control factor using an adaptive update value which is read out of memory, in a first predetermined manner based on the instant engine speed and load, and updated based on the output of said second air-fuel ratio sensor;
• and
• inhibiting the updating of adaptive update value in the event that a data element obtained by the table look up from said stored data table contains a special zone signal indicates that the engine is operating in a predetermined zone of engine parameters.

An air fuel ratio control system for an engine, said control system comprising:

• an engine system comprising an engine, an exhaust gas conduit connected to said engine, and a catalystic converter disposed said exhaust gas conduit;
• a sensor group comprising an engine load sensor for sensing an engine load of said engine, and engine speed sensor for sensing an engine speed of said engine, an upstream air fuel ratio sensor disposed in said exhaust gas conduit at a position upstream of said catalytic converter, and a downstream air fuel ratio sensor disposed in said exhaust gas conduit at a position downstream of said catalytic converter;
• a fuel injecting means for supplying fuel to said engine in response to a control signal;
• and
• a control unit for producing said control signal in accordance with sensor output signals produced by said sensor group, said control unit comprising a controlling means for:
• producing said control signal representing a fuel supply quantity in accordance with a feedback correction quantity and a basic injection quantity which is determined by said engine load sensed by said engine load sensor and said engine speed sensed by said engine speed sensor;
• determining a feedback control factor by obtaining a value of said feedback control factor from a map of a feedback control factor data table in accordance with the output of said upstream air fuel ratio sensor;
• updating an adaptive variable in accordance with the output of said downstream air fuel ratio sensor;
• determining said feedback correction quantity in accordance with said feedback control factor and said adaptive variable, and
• inhibiting said adaptive variable from being updated in response to a special zone signal;
• wherein said control unit comprises a storage means comprising a feedback control factor memory for storing said map of said feedback control factor data table determined in accordance with the engine speed and a second variable which is one of the engine load and the basic injection quantity, said feedback control factor memory comprising a normal zone memory section for storing values of said feedback control factor in a predetermined normal zone determined by the engine speed and said second variable, and a special zone memory section for storing special values of said feedback control factor in a predetermined special zone determined by the engine speed and said second variable, said feedback control factor memory further storing said special zone signal in said map;
• wherein said storage means further comprises a normal learning memory which is subdivided into a plurality of memory sections each of which stores a collection of values of said adaptive variable in a unique one of a plurality of learning zones determined by the engine speed and said second variable, each of said learning zones being grater in area than said special zone.

An air fuel ratio control system for an engine, said control system comprising:

• an engine system comprising an engine, an exhaust gas conduit connected to said engine, and a catalytic converter disposed in said exhaust gas conduit;
• a sensor group comprising a sensor means for sensing first and second engine operating parameters of said engine, an upstream air fuel ratio sensor disposed in said exhaust gas conduit at a position upstream of said catalytic converter, and a downstream air fuel ratio sensor disposed in said exhaust gas conduit at a position downstream of said catalytic converter;
• a fuel injection means for supplying fuel to said engine in response to a control signal;
• and
• a control unit for producing said control signal in accordance with sensor output signals produced by said sensor group, said control unit comprising a controlling means for;
• producing said control signal representing a fuel supply quantity in accordance with a feedback correction quantity and a basic fuel quantity which is determined by the first and second engine operating parameters sensed by said sensor means;
• determining a feedback control factor by obtaining a value of said feedback control factor from a feedback control factor data table in accordance with an output of said upstream air fuel ratio sensor;
• updating an adaptive variable in accordance with an output of said downstream airfuel ratio sensor;
• determining said feedback correction quantity in accordance with said feedback control factor and said adaptive variable, and
• inhibiting said adaptive variable from being updated in response to a special zone signal;
• wherein said control unit comprises a storage means for storing said feedback control factor data table which contains values of said feedback control factor and said special zone signal.