Apparatus for controlling air/fuel ratio for internal combustion engine

Claim 1

Apparatus for controlling air-fuel ratio of an air-fuel mixture to be supplied to an internal combustion engine having an intake passage, an exhaust passage, and an exhaust gas recirculation passage for recirculating exhaust gasses in said exhaust passage to said intake passage therethrough, said apparatus comprising: (a) means for sensing rotational speed of said engine; (b) means for sensing intake pressure in said intake passage; (c) means for sensing atmospheric pressure; (d) means for enabling and disabling exhaust gas recirculation through said exhaust gas recirculation passage in accordance with operating condition of said engine; (e) means for determining required amount of fuel in accordance with said sensed rotational speed and said sensed intake pressure; (f) means for determining, when the exhaust gas recirculation is enabled, a first correction value in accordance with said sensed rotational speed, said sensed intake pressure and said sensed atmospheric pressure, said first correction factor being used for correcting fuel amount so as to compensate for the decrease of fuel due to the performance of exhaust gas recirculation and also to compensate for the change in atmospheric pressure; (g) means for determining, when the exhaust gas recirculation is disabled, a second correction value in accordance with said atmospheric pressure, said second correction factor being used so as to compensate for the change in atmospheric pressure; (h) means for correcting said required amount of fuel by said first correction value and said second correction value when the exhaust gas recirculation is enabled and disabled respectively; and (i) means for supplying said engine with said corrected amount of fuel.