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

Claim 2

A dual sensor type air-fuel ratio feedback control apparatus for an internal combustion engine, comprising: an engine load sensor; an engine speed sensor; means for determining a basic fuel injection quantity based on the outputs of the engine load and speed sensors; a first air-fuel ratio sensor disposed in an exhaust passage, at a location upstream of a catalytic converter, for producing an output indicative of the air-fuel ratio of the exhaust gases prevailing upstream of the catalytic converter; means for averaging the output of the first air-fuel ratio sensor; memory means, including a plurality of addresses and corresponding engine operational sub-regions, each address storing first and second slice level values; means for determining into which of the sub-regions the current engine operation falls; means for reading out the first slice level value which is stored at the address which corresponds to the determined sub-region; means for comparing a working slice level value, which is based on the first slice level value which is read out, with the averaged output of the first air-fuel ratio sensor and determining if the output of the first air-fuel ratio sensor traverses the working slice level value; means for deriving an air-fuel ratio feedback control correction factor for feedback control of the air-fuel ratio, based on a comparison of the averaged output of the first air-fuel ratio sensor and the working slice level; means for deriving a fuel injection amount by correcting the basic fuel injection quantity using the feedback control correction factor; a second air-fuel ratio sensor disposed in the exhaust passage at a location downstream of the catalytic converter for producing an output indicative of the air-fuel ratio of the exhaust gases prevailing downstream of the catalytic converter; means for selecting a sub-region based on a timing with which the output of the first air-fuel ratio sensor traverses the first slice level; means for reading out the first and second slice level values stored at the address of the selected sub-region; means for comparing the output of the second air-fuel ratio sensor with the second slice level; and means for updating the values of the first and second slice levels in accordance with the comparison of the output of the second air-fuel ratio sensor with the second slice level.

Claim 3

A dual sensor type air-fuel ratio feedback control apparatus for an internal combustion engine, comprising: an engine load sensor; an engine speed sensor; means for determining a basic fuel injection quantity based on the outputs of the engine load and speed sensors; a first air-fuel ratio sensor disposed in an exhaust passage at a location upstream of a catalytic converter for producing an output indicative of the air-fuel ratio of the exhaust gases prevailing upstream of the catalytic converter; means for averaging the output of the first air-fuel ratio sensor; memory means including a plurality of addresses and corresponding engine operational sub-regions, each address storing first and second slice level values; means for determining into which of the sub-regions the current engine operation falls; means for reading out the first slice level value which is stored at the address which corresponds to the determined sub-region; means for comparing a working slice level value, which is based on the first slice level value which is read out, with the averaged output of the first air-fuel ratio sensor, and determining if the output of the first air-fuel ratio sensor traverses the working slice level value; means for deriving an air-fuel ratio feedback control correction factor used for feedback control of the air-fuel ratio, based on the comparison of the averaged output of the first air-fuel ratio sensor and the working slice level; means for deriving a fuel injection amount by correcting the basic fuel injection quantity using the feedback control correction factor; a second air-fuel ratio sensor disposed in the exhaust passage at a location downstream of the catalytic converter for producing an output indicative of the air-fuel ratio of the exhaust gases prevailing downstream of the catalytic converter; means for determining if the engine operation continuously falls in the same sub-region for a predetermined time following the output of the first air-fuel ratio sensor traversing the working slice level; means for reading out the first and second slice level values stored at the address which corresponds to the sub-region selected on the basis of timing with which the first slice level is traversed by the output of the first air-fuel ratio sensor; means for comparing the output of the second air-fuel ratio sensor with the second slice level; means for updating the values of the first and second slice levels in accordance with the comparison of the output of second air-fuel ratio sensor with the second slice level; means for comparing the value of the updated first slice level with maximum and minimum values; means for indicating that the first air-fuel ratio sensor is undergoing degradation when the updated first slice level value is greater than the maximum value or less than the minimum value; and means for modifying the averaging of the output of the first air-fuel ratio sensor in accordance with the indication that the first sensor is undergoing degradation.

Claim 4

A dual sensor type air-fuel ratio feedback control apparatus for an internal combustion engine, comprising: an engine load sensor; an engine speed sensor; means for determining a basic fuel injection quantity based on the outputs of the engine load and speed sensors; a first air-fuel ratio sensor disposed in an exhaust passage at a location upstream of a catalytic converter for producing an output indicative of the air-fuel ratio of the exhaust gases prevailing upstream of the catalytic converter; means for averaging the output of the first air-fuel ratio sensor; memory means including a plurality of addresses and corresponding engine operational sub-regions, each address storing first and second slice level values; means for determining into which of the sub-regions the current engine operation falls; means for reading out the first slice level value which is stored at the address which corresponds to the determined sub-region; means for comparing a working slice level value, which is based on the first slice level value which is read out, with the averaged output of the first air-fuel ratio sensor, and determining if the output of the first air-fuel ratio sensor traverses the working slice level value; means for deriving an air-fuel ratio feedback control correction factor used for feedback control of the air-fuel ratio, based on the comparison of the averaged output of the first air-fuel ratio sensor and the working slice level; means for deriving a fuel injection amount by correcting the basic fuel injection quantity using the feedback control correction factor; a second air-fuel ratio sensor disposed in the exhaust passage at a location downstream of the catalytic converter for producing an output indicative of the air-fuel ratio of the exhaust gases prevailing downstream of the catalytic converter; means for determining if the engine operation continuously falls in the same sub-region for a predetermined time following the output of the first air-fuel ratio sensor traversing the working slice level; means for reading out the first and second slice level values stored at the address which corresponds to the sub-region selected on the basis of timing with which the first slice level is traversed by the output of the first air-fuel ratio sensor; means for comparing the output of the second air-fuel ratio sensor with the second slice level; means for updating the values of the first and second slice levels in accordance with the comparison of the output of second air-fuel ratio sensor with the second slice level; means for comparing the value of the updated first slice level with maximum and minimum values; means for indicating that the first air-fuel ratio sensor is undergoing degradation when the updated first slice level value is greater than the maximum value or less than the minimum value; and means for modifying the averaging of the output of the first air-fuel ratio sensor in accordance with the indication that the first sensor is undergoing degradation.

Claim 5

The air-fuel ratio feedback control apparatus as set forth in claim 2, wherein said first air-fuel ratio sensor is an O 2 sensor arranged just upstream of the catalytic converter, while said second air-fuel ratio sensor is an O 2 sensor arranged just downstream of the catalytic converter.