Air-fuel ratio feedback control method for internal combustion engines

Claim 1

In a method of controlling the air-fuel ratio of a mixture being supplied to an internal combustion engine having an exhaust system, in a feedback manner responsive to an output signal from sensing means arranged in said exhaust system for sensing the concentration of a component in exhaust gases from said engine to produce as said output signal a normally fluctuating output signal indicative of the concentration of said component, the method including: comparing the value of said output signal with a predetermined reference value; and controlling the air-fuel ratio of said mixture to a desired value by means of at least one of proportional control applying a first correction value to correct the air-fuel ratio when said output signal changes from a rich side to a lean side or vice versa with respect to said predetermined reference value, and integral control applying a second correction value to correct the air-fuel ratio with a predetermined period so long as said output signal remains on the lean side or on the rich side with respect to said predetermined reference value, the improvement comprising the steps of: (1) sensing a rate of change in the value of said output signal; (2) determining a correcting amount in response to the sensed rate of change; and (3) increasing or decreasing said second correction value by means of said determined correcting amount, depending upon whether said output signal remains on the lean side or on the rich side with respect to said predetermined value.

Claim 6

A method as claimed in any of claims 1-4, wherein said correcting amount for correcting said second correction value is decreased when said output signal from said sensing means changes in a direction toward said predetermined reference value, and at the same time the rate of change sensed is larger than a second predetermined value.