Lean air-fuel control using stoichiometric air-fuel sensors

An air-fuel ratio control means for an internal combustion engine, said air-fuel ratio control means including:

• stoichiometric sensing means for providing an output in response to a stoichiometric condition so that it can be determined whether a sensed air-fuel ratio is rich or lean of stoichiometry;
• reference means for providing a desired air-fuel ratio;
• fuel metering means for injecting fuel into the internal combustion engine;
• adjustment means coupled to said stoichiometric sensing means, said reference means, and said fuel metering means for establishing a base air-fuel ratio, pulsing the air-fuel ratio at least two unequal pulses to determine the offset, within a braketed error, of the base air-fuel ratio from a stoichiometric air-fuel ratio, and adjusting the base air-fuel ratio toward the desired air-fuel ratio of the offset of the base air-fuel from the stoichiometric air-fuel ratio is not the same as the offset of the desired air-fuel ratio from the stoichiometric air-fuel ratio, said adjustment means including:
• a first gating means for establishing a difference in air-fuel ratio magnitude between two air-fuel ratio pulses;
• a second gating means for applying a first calculated air-fuel ratio which determines the air-fuel ratio magnitude during a first air-fuel ratio pulse and for applying a second calculated air-fuel ratio which determines the air-fuel ratio magnitude during a second air-fuel ratio pulse, the first air-fuel ratio value being such that when it is subtracted from the desired air-fuel ratio magnitude the resulting air-fuel ratio will be lean of stoichiometric air-fuel ratio and the second air-fuel ratio value being such that when it is subtracted from the desired air-fuel ratio magnitude the resulting air-fuel ratio will be rich of a stoichiometric air-fuel ratio;
• a clock means for periodically activating said second gating means;
• an output means for producing a first output when the two air-fuel ratio magnitude pulses do not cross a stoichiometric air-fuel ratio magnitude and for producing a second output when the two air-fuel ratio magnitude pulses both cross a stoichiometric air-fuel ratio magnitude;
• and
• offset means receiving an input from said output means and coupled to said fuel metering means for causing an increase in the richness of the base air-fuel ratio magnitude in response to said first output and for causing a decrease in the richness of the base air-fuel ratio magnitude in response to said second output.

A method for controlling the air-fuel ratio for an internal combustion engine including the steps of:

• sensing the base air-fuel ratio of the exhaust gas of the internal combustion engine;
• pulsing the base air-fuel ratio to increase the richness to the air-fuel ratio;
• sensing the value of the pulsed air-fuel mixture with respect to a stoichiometric air-fuel mixture;
• and
• adjusting the base air-fuel mixture so that if both the stored base and the pulsed air-fuel mixture values are lean of stoichiometry, the air-fuel mixture is made richer, if both the stored base and the pulsed air-fuel mixture values are rich of stoichiometry the air-fuel mixture is made leaner, if the stored and the pulsed value of the air-fuel mixture are on opposite sides of stoichiometry then no change is made in the air-fuel mixture.