Abstract: Fuel vapor is prevented from leaking to the outside during refueling, and even when an air space is formed in an upper portion of a fuel filler pipe, a diagnosis of leakage of fuel vapor can be performed with good accuracy. During refueling, fuel vapor is guided from a fuel tank 1 to a canister 3, and is absorbed by the canister 3. A change in the internal pressure of a fuel vapor path including the fuel tank 1, a fuel vapor pipe 4, and the canister 3 is detected by a pressure sensor 8, thereby performing a diagnosis of leakage of fuel vapor. An upper space 16 in the fuel tank 1 and an upper space 17 in a fuel filler pipe 2 communicate with each other through an airflow resistance pipe 12, and in order to restrict flow of fuel vapor from the fuel tank 1 through the airflow resistance pipe 12 into the fuel filler pipe 2 during refueling, the airflow resistance pipe 12 includes an orifice 13.

Abstract: Fuel vapor is prevented from leaking to the outside during refueling, and even when an air space is formed in an upper portion of a fuel filler pipe, a diagnosis of leakage of fuel vapor can be performed with good accuracy. During refueling, fuel vapor is guided from a fuel tank 1 to a canister 3, and is absorbed by the canister 3. A change in the internal pressure of a fuel vapor path including the fuel tank 1, a fuel vapor pipe 4, and the canister 3 is detected by a pressure sensor 8, thereby performing a diagnosis of leakage of fuel vapor. An upper space 16 in the fuel tank 1 and an upper space 17 in a fuel filler pipe 2 communicate with each other through an airflow resistance pipe 12, and in order to restrict flow of fuel vapor from the fuel tank 1 through the airflow resistance pipe 12 into the fuel filler pipe 2 during refueling, the airflow resistance pipe 12 includes an orifice 13.