Vaporized-fuel processing system

A vaporized-fuel processing system comprising:

• an absorbing device for absorbing vaporized fuel generated in a fuel tank;
• an air-communication valve of a normally-opened type provided in the absorbing device for cutting off supply of atmospheric air into the absorbing device when the air-communication valve is closed;
• a purge control valve of a normally-closed and an electromagnetic type provided in a purge pipe which connects the absorbing device to an intake-air passage of an engine, the vaporized fuel of the absorbing device is purged into the intake-air passage when the purge control valve is opened upon receiving electric power;
• a throttle valve provided in the intake-air passage for controlling an amount of intake air to be supplied into the engine;
• a supercharging device provided in the intake-air passage at an upstream side of the throttle valve for supercharging the intake air;
• a first and a second purge passage branched out from the purge pipe at a downstream side of the purge control valve, the first purge passage being connected to the intake-air passage at a downstream side of the throttle valve, and the second purge passage being connected to the intake-air passage at an upstream side of the supercharging device;
• a first check valve provided in the first purge passage, the first check valve being opened by negative pressure generated in the intake-air passage at the downstream side of the throttle valve;
• an ejector and a second check valve provided in the second purge passage, the ejector being operated by the intake air supercharged by the supercharging device and the second check valve being opened by an operation of the ejector;
• a pressure sensor for detecting an in-tank pressure, which corresponds to a pressure of a space including the fuel tank, the absorbing device, a connecting pipe between the fuel tank and the absorbing device;
• a determination unit for determining whether an upstream-side pressure of the throttle valve, which corresponds to a pressure of the intake air in the intake-air passage at the upstream side of the throttle valve, is at an atmospheric pressure, at a positive pressure with respect to the atmospheric pressure or at a negative pressure with respect to the atmospheric pressure, the determination unit further determining whether a downstream-side pressure of the throttle valve, which corresponds to a pressure of the intake air in the intake-air passage at the downstream side of the throttle valve, is at the atmospheric pressure, at the positive pressure or at the negative pressure;
• and
• a diagnosing unit for diagnosing an abnormal condition for the purge control valve whether the purge control valve is fixed to its valve opened position,
• wherein the diagnosing unit determines that the purge control valve is fixed to the valve opened position when the in-tank pressure is detected in a condition that the air-communication valve is closed and no electric power is supplied to the purge control valve and when such detected in-tank pressure is lower than a predetermined pressure,
• wherein the diagnostic unit further diagnoses abnormal conditions of the purge control valve, the first check valve and the second check valve, in order to identify which of the valves is not normally operated and whether such a valve is fixed to its valve opened position or to its valve closed position,
• wherein a diagnosing process of the diagnostic unit is carried out based on determination result of the determination unit and a change of the in-tank pressure detected by the pressure sensor, in a condition that the air-communication valve is closed and the purge control valve is opened.