Method and apparatus using a gas concentration sensor for accurately controlling an air fuel ratio in an internal combustion engine

Abstract

The present invention provides a method and apparatus using a gas concentration sensor for accurately controlling an air fuel ratio in an internal combustion engine, featuring in that before the fuel-vaporized gas purged from the canister enters into the intake manifold whereat the sensor detects the gas concentration of the purged gas, the sensor is adjusted so as to adjust a zero point (or zero output level) of the sensor output. In step of FIG. , a judgment is made as to whether the flow rate of air reaches a predetermined level. In step , processing for zero-point correction of the gas concentration sensor is performed. Specifically, in a state in which the purge valve is closed, concentration of purge gas is measured by use of the gas concentration sensor , and a sensor output S at that time is obtained. Subsequently, the sensor output S is compared with a correct sensor output S in order to obtain a difference &Dgr;S therebetween. Accordingly, during subsequent gas concentration measurement, a value S obtained through subtraction of the difference &Dgr;S from an obtained sensor output S is used as a correct sensor output. In step , a supply amount of purge gas, i.e., a concentration of the purge gas to be supplied is obtained. In subsequent step , the purge valve is driven in order to supply purge gas to the intake pipe in a required amount (A%).