Air-fuel ratio control system for internal combustion engines

Claim 1

In an air-fuel ratio control system for an internal combustion engine having at least one combustion chamber, an intake passage having an inner surface, fuel injection means arranged in said intake passage, and an exhaust passage, the air-fuel ratio control system including fuel supply amount-calculating means for calculating an amount of fuel to be supplied to said engine in response to the rotational speed of said engine and a parameter indicative of load on said engine, direct supply ratio-calculating means for calculating a direct supply ratio defined as a ratio of a fuel amount directly drawn into said combustion chamber during intake stroke in a present cycle of said engine to the whole fuel amount injected in the same cycle, carry-off ratio-calculating means for calculating a carry-off ratio defined as a ratio of a fuel amount carried off said inner surface of said intake passage and drawn into said combustion chamber during intake passage in the present cycle to the whole fuel amount which adhered to said inner surface of said intake passage in an immediately preceding cycle, air-fuel ratio-detecting means arranged in said exhaust passage for detecting an air-fuel ratio in exhaust gases from said engine, feedback correction value-setting means for setting a feedback correction value to a value such that the air-fuel ratio detected by said air-fuel ratio-detecting means becomes equal to a desired value, and fuel supply amount-correcting means for correcting said amount of fuel calculated by said fuel supply amount-calculating means by said direct supply ratio, said carry-off ratio, and said feedback correction value, wherein an amount of fuel corrected by said fuel supply amount-correcting means is injected by said fuel injection means into said intake passage, the improvement wherein said feedback correction value-setting means includes control speed-setting means for setting a control speed at which said feedback correction value is corrected, based upon at least one of said direct supply ratio and said carry-off ratio.