Leakage diagnostic device for evaporated fuel treatment apparatus

A leakage diagnostic device for diagnosing leakage in an evaporated fuel treatment apparatus for purging and treating evaporated fuel generated in a fuel tank to an intake passage of an engine, wherein

• the evaporated fuel treatment apparatus comprises:
• a canister configured to trap the evaporated fuel generated in the fuel tank,
• the canister including an inlet port for introducing the evaporated fuel from the fuel tank into the canister, an outlet port for discharging the evaporated fuel from the canister, and an atmosphere port for introducing atmospheric air into the canister;
• a purge passage configured to guide the evaporated fuel trapped in the canister to the intake passage through the outlet port;
• a purge pump provided in the purge passage and configured to pressure-feed the evaporated fuel trapped in the canister to the intake passage through the purge passage;
• and
• an atmosphere passage configured to introduce atmospheric air into the canister through the atmosphere port,
• the leakage diagnostic device comprises:
• a first bypass passage connecting between the purge passage upstream of the purge pump and the atmosphere passage;
• a second bypass passage arranged in parallel with the first bypass passage between the purge passage upstream of the purge pump and the atmosphere passage, the second bypass passage having one end connected to the purge passage downstream of a first junction in which the first bypass passage and the purge passage are connected to each other and an other end connected to the atmosphere passage upstream of a junction in which the atmosphere passage and the first bypass passage are connected to each other;
• a reference orifice provided in the first bypass passage and configured to create a pressure difference between the purge passage and the atmosphere passage;
• a first communication switching unit configured to selectively switch between communication of the purge passage in the first junction and communication between the purge passage downstream of the first junction and the first bypass passage;
• a second communication switching unit configured to selectively switch between communication between the atmosphere passage and the second bypass passage in a second junction in which the atmosphere passage and the second bypass passage are connected to each other and communication of the atmosphere passage in the second junction;
• a pressure detecting unit configured to detect a passage pressure in the purge passage between the purge pump and the first junction;
• and
• a control unit configured to control the purge pump, the first communication switching unit, and the second communication switching unit, and diagnose the leakage based on the passage pressure detected, and
• the control unit is configured to:
• control the first communication switching unit and the second communication switching unit under a predetermined condition during operation of the purge pump to sequentially set a reference pressure measurement mode in which atmospheric air is pressure-fed into the intake passage through the reference orifice and the purge pump and a leakage measurement mode in which the evaporated fuel trapped in the canister is pressure-fed into the intake passage through the reference orifice and the purge pump;
• measure a reference pressure based on the passage pressure detected when the reference pressure measurement mode is set;
• measure a leakage pressure based on the passage pressure detected when the leakage measurement mode is set, and
• compare between the measured reference pressure and the measured leakage pressure to determine whether or not the leakage exists.