Fuel vapor treatment system with leak diagnosing

A fuel vapor treatment system comprising:

• adsorbing means for temporarily adsorbing fuel vapor evaporated from a fuel tank;
• fresh air introducing means for selectively introducing and stopping fresh air into the adsorbing means;
• purging means for regulating fuel vapor flows from the adsorbing means to an air intake system of an internal combustion engine by introducing fresh air into the adsorbing means via the fresh air introducing means and allowing the fresh air and fuel vapor to be drawn into the air intake system through the purging means;
• pressure detecting dmeans for detecting purge line pressure inside the purging means;
• and
• leak diagnosis control means for closing the purging means and the fresh air introducing means to close off a portion of the fuel vapor treatment system between the air intake system and the adsorbing means after determining engine operation is stopped, for calculating a purge line pressure decreasing rate at which the purge line pressure decreases in accordance with a temperature decrease occurring after the engine is stopped, and for conducting a leak diagnosis to determine a leakage state of the purging means based on the purge line pressure decreasing rate of the purge line pressure.

A method for diagnosing a fuel vapor treatment system having a canister disposed between a fuel tank and an air intake system of an internal combustion engine with a purge line that leads from the canister to the air intake system and a fresh air introducing port that allow fresh air and fuel vapor to be drawn into the air intake system, the method comprising:

• detecting pressure inside a purge line pressure within the purge line of the fuel vapor treatment system having a fuel tank fluidly connected to an intake passage of an internal combustion engine with a canister that is configured to adsorb fuel vapor from the fuel tank;
• closing a purge control valve and a fresh air introducing port on/off valve to close off the purge line after determining engine operation is stopped;
• calculating a purge line pressure decreasing rate at which the purge line pressure decreases in accordance with a temperature decrease occurring after the engine is stopped;
• and
• conducting a failure diagnosis on the fuel vapor treatment system to determine a leakage state of the purge line based on the purge line pressure decreasing rate of the purge line pressure.