Diagnostic device for an evaporative emission control system

A diagnostic device for an evaporative emission control system, comprising:

• a canister for adsorbing fuel vapor sent from a fuel tank of an internal combustion engine, a fuel vapor passage for connecting a space above a fuel level in the fuel tank to the canister, and a purge gas passage for connecting the canister to an intake air passage of the engine;
• a purge control valve for controlling the flow rate of purge gas from the canister flowing into the intake air passage through the purge gas passage;
• an atmospheric valve attached to the canister which opens when the internal pressure of the canister becomes lower than the atmospheric pressure by more than a predetermined amount, to thereby introduce atmosphere into the canister;
• a pressure detecting device for detecting the internal pressure of the canister;
• determining means for determining that the canister has failed if an increase in the internal pressure of the canister within a predetermined period after the purge control valve is closed is greater than a reference value during the operation of the engine;
• means for detecting the flow rate of the purge gas when the purge control valve is opened;
• and
• means for prohibiting the determination means from determining that the canister has failed when the flow rate of the purge gas is greater than a reference value.

A diagnostic device for an evaporative emission control system, comprising:

• a canister for adsorbing fuel vapor sent from a fuel tank of an internal combustion engine, a fuel vapor passage for connecting a space above a fuel level in the fuel tank to the canister, and a purge gas passage for connecting the canister to an intake air passage of the engine;
• a purge control valve for controlling the flow rate of purge gas from the canister flowing into the intake air passage through the purge gas passage;
• an atmospheric valve attached to the canister which opens when the internal pressure of the canister becomes lower than the atmospheric pressure by more than a predetermined amount, to thereby introduce atmosphere into the canister;
• a pressure detecting device for detecting the internal pressure of the canister;
• determining means for determining that the canister has failed if an increase in the internal pressure of the canister within a predetermined period after the purge control valve is closed is greater than a reference valve during the operation of the engine;
• means for detecting the flow rate of the purge gas when the purge control valve is opened;
• and
• means for setting said reference value according to the flow rate of the purge gas.

A diagnostic device for an evaporative emission control system, comprising:

• a canister for adsorbing fuel vapor sent from a fuel tank of an internal combustion engine, a fuel vapor passage for connecting a space above a fuel level in the fuel tank to the canister, and a purge gas passage for connecting the canister to an intake air passage of the engine;
• a purge control valve for controlling the flow rate of purge gas from the canister flowing into the intake air passage through the purge gas passage;
• a pressure detecting device for detecting the internal pressure of the canister;
• first determining means for determining that the canister has failed if an increase in the internal pressure of the canister within a predetermined period after the purge control valve is closed is greater than a first reference value during the operation of the engine;
• and
• second determining means for determining, when the first determining means has determined that the canister has failed, that the canister is normal if an increase in the internal pressure of the canister is greater than a second reference value within a predetermined period that starts when a predetermined time has lapsed after the first determining means has determined that the canister has failed.