Patent ID: 7373929

Claim:
A fuel nature measuring device, for measuring the nature of fuel stored in a fuel tank of an internal combustion engine, the measuring device comprising: a measurement passage having an orifice therein; gas flow generating means for generating a gas flow in said measurement passage; differential pressure detecting means for detecting a differential pressure between opposite ends of said orifice; evaporated fuel concentration operating means for determining a concentration of evaporated fuel in the fuel tank based on the differential pressure detected when said opposite ends of said measurement passage communicates with said fuel tank and the fuel in the fuel tank flows in said measurement passage; temperature detecting means for determining a temperature of the fuel in said fuel tank; volatility calculation means for calculating a volatility of the fuel in said fuel tank as the fuel nature based on the concentration of the evaporated fuel determined by said evaporated fuel concentration operation means and the temperature determined by said temperature detecting means; and measurement passage switching means for switching between first and second concentration measurement states, the first concentration measurement state being configured such that said opposite ends of said measurement passage are opened to the atmosphere and the gas passed through said measurement passage is atmospheric air, the second concentration measurement state being i&-configured such that said opposite ends of said measurement passage communicate with said fuel tank through a gas phase portion of said fuel tank and the fuel flows in said fuel measurement passage is the fuel from the fuel tank, wherein said evaporated fuel concentration operating means determines the concentration of the evaporated fuel based on a difference in detected differential pressures across said measurement passage between said first and second concentration measurement states.