Device for measuring concentration/flow rate of a mixture drawn into an

Abstract

A device for measuring a flow rate of a mixture of evaporative fuel and air supplied to an internal combustion engine comprises a plurality of flowmeters arranged in a purging passage connecting between a canister and an intake passage of the engine for purging the mixture of evaporative fuel and air therethrough into the intake passage. The flowmeters have different output characteristics relative to concentration of the evaporative fuel in the mixture. At least one of the concentration of the evaporative fuel in the mixture and the volumetric flow rate of the mixture are detected based on outputs from the flowmeters. In an air-fuel ratio control system incorporating the above device, the weight per unit time of evaporative fuel supplied to the intake system is calculated from the detected concentration of the evaporative fuel and the detected volumetric flow rate of the mixture. The air-fuel ratio of a total air-fuel mixture supplied to the engine is corrected by the use of the ratio of the calculated weight per unit time of evaporative fuel supplied by purging to the intake system to weight per unit time of fuel supplied by injection to the engine.