AIR-FUEL RATIO CONTROLLING METHOD FOR FUEL SUPPLY MEANS USED IN INTERNAL-COMBUSTION ENGINE

PURPOSE:To improve the exhaust-gas purifying characteristics of an engine, by executing open-loop control of the fuel supply rate instead of feedback control of the same in case that the fuel supply rate is higher than a reference value, and varying the above reference value according to the temperature of cooling water. CONSTITUTION:In operation of an engine 4, judgement is made at first by a control circuit 16 whether activation of an O2-sensor 14 is completed. In case that the judgement is YES, judgement is made whether the temperature TW of cooling water detected by a water-temperature sensor 12 is higher than a feedback control starting temperature TW01. In case of TW>=TW01, a reference value Tr corresponding to the temperature TW is searched from a map. Here, the above reference value Tr is set at either of two prescribed values Tr1, Tr2 by using a prescribed water temperature TW02 (>TW01) as a threshold value. Then, judgement is made whether the calculated fuel injection period TOUT is greater than said reference value Tr. In case of TOUT>Tr, an injector 15 is controlled by way of open-loop control instead of feedback control.