| 摘要 |
A method and apparatus for controlling an air-to-fuel ratio of an internal combustion engine in which the air-to-fuel ratio is maintained within a predetermined control width or range even if one or more of the sensors which detect the conditions of the engine necessary to compute the desired air-to-fuel ratio fail. An air flow sensor produces an output signal having a frequency determined in accordance with the air flow rate into the engine, an oxygen sensor disposed in the exhaust manifold of the engine detects whether the air-to-fuel is lean or rich, and a coolant temperature sensor detects the coolant temperature of the engine. Transitions in the output from the oxygen sensor are used to control the integrating direction of an integrator circuit composed of an up/down counter. A predetermined number of integration values are averaged to compute upper and lower limits of the controlled ratio. To perform the integration, a timer is started by output pulses from the air flow rate sensor after having been preset with a digital value determined in accordance with the outputs of the air flow rate sensor and the coolant sensor. Clock pulses for the timer are supplied from a frequency divider, the frequency division ratio of which is set by the integration value if the integration value falls within the control width or range, and by upper and lower limits if the integration value is outside of the control range. |
