| 摘要 |
PURPOSE:To make it possible to prevent engine failure due to the extreme control of air fuel ratio, by limiting the control of air-fuel ratio in a predetermined range around the mean value of the integration value of air-fuel ratio feedback. CONSTITUTION:A comparator CP delivers a signal L or H in accordance with a lean or ritch signal from an air fuel ratio sensor 35, a counter CT1 carries out adding operating each time when the signal L or H is reversed, and the mean value C1 thereof is delivered from a register REG. A data selector DS normally changes the output period of a frequency divider DIV in accordance with the output of the comparator CP, for performing the feedback control of the valve opening time of a fuel supply valve in accordance with an intake air amount. However, the valve opening time is cripped on a limiter LM1 or LM2 to its lowermost or uppermost value even if the output of the comparator CP is held at H or L level due to any reason so that the control of valve opening time is limited thereabove. Accordingly, the engine failure due to the extreme control of air-fuel ratio is prevented. |
