Abnormality detection apparatus for preventing fuel gas emission

Abstract

When a diagnosis execution condition is established, a canister closure valve is closed, thereafter, a purge control valve is opened, a purge control valve is closed in a state where negative pressure is introduced into an evaporated gas system to thereby maintain the evaporated gas system in a hermetically-sealed state and the hermetically-sealed state is continued until abnormality diagnosis is finished. Time period for maintaining the evaporated gas system in the hermetically-sealed state is divided into three time periods of a pressure change determining time period at a first time, an awaiting time period and a pressure change determining time period at a second time. After determining a pressure change amount DPT1 of the evaporated gas system in the pressure change determining time period at the first time, the evaporated gas system is successively maintained in the hermetically-sealed state, after the predetermined awaiting time period has elapsed, the pressure change determination at the second time is carried out by which a pressure change amount DPT2 of the evaporated gas system is determined. Further, presence or absence of leakage of the evaporated gas system is diagnosed by comparing the pressure change amount DPT1 at the first time with the pressure change amount DPT2 at the second time.