Method and apparatus for detecting abnormal state of evaporative emission-control system

A method of detecting an abnormal state of an evaporative emission-control system in which a fuel-vapor evaporated from the fuel tank is temporarily trapped in a canister when an internal combustion engine is stopped or in an idle state, the trapped fuel-vapor is purged from the canister by a vacuum in a air-intake passage of the engine, and the purged fuel-vapor is mixed with an air-fuel mixture to be burned in a combustion chamber when a vehicle is running in a predetermined driving condition, comprising the steps of:

• detecting an amount of fuel-vapor trapped in the canister, wherein the detection of the amount of fuel-vapor trapped in the canister is carried out by counting the time period for which fuel-vapor flows into the canister;
• purging the fuel-vapor trapped in the canister and mixing the purged fuel-vapor with the air-fuel mixture in an air-intake passage;
• detecting a concentration of a vapor-laden air from the canister when the purging is executed;
• and
• determining the occurrence of an abnormal state of the evaporative emission-control system when the amount of fuel-vapor trapped in the canister is more than a predetermined amount, purging of the fuel-vapor trapped in the canister is executed, and the detected concentration of a vapor-laden air is smaller than the calculated concentration of a vapor-laden air in accordance with the amount of fuel-vapor trapped in the canister.

An apparatus for detecting an abnormal state of an evaporative emission-control system in which a fuel-vapor evaporated from the fuel tank is temporarily trapped in a canister when an internal combustion engine is stopped or in an idle state, the trapped fuel-vapor is purged from the canister by a vacuum in a air-intake passage of the engine, and the purged fuel-vapor is mixed with an air-fuel mixture to be burned in a combustion chamber when a vehicle is running in a predetermined driving condition, comprising:

• means for detecting an amount of fuel-vapor trapped in the canister, wherein the detection of the amount of fuel-vapor trapped in the canister is carried out by counting the time period for which fuel-vapor flows into the canister;
• means for purging the fuel-vapor trapped in the canister and mixing the purged fuel-vapor with the air-fuel mixture in an air-intake passage;
• means for detecting a concentration of a vapor-laden air from the canister when the purging is executed;
• and
• means for determining the occurrence of an abnormal state of the evaporative emission-control system when the amount of fuel-vapor trapped in the canister is more than a predetermined amount, purging of the fuel-vapor trapped in the canister is executed, and a change of the concentration of the vapor-laden air from the canister before and after the purging is less than a predetermined value.

An apparatus for detecting an abnormal state of an evaporative emission-control system in which a fuel-vapor evaporated from the fuel tank is temporarily trapped in a canister when an internal combustion engine is stopped or in an idle state, the trapped fuel-vapor is purged from the canister by a vacuum in a air-intake passage of the engine, and the purged fuel-vapor is mixed with an air-fuel mixture to be burned in a combustion chamber when a vehicle is running in a predetermined driving condition, comprising:

• means for detecting an amount of fuel-vapor trapped in the canister, wherein the detection of the amount of fuel-vapor trapped in the canister is carried out by counting the time period for which the fuel-vapor flows into the canister;
• means for purging the fuel-vapor trapped in the canister and mixing the purged fuel-vapor with the air-fuel mixture in an air-intake passage;
• means for detecting a concentration of a vapor-laden air from the canister when the purging is executed;
• and
• means for determining the occurrence of an abnormal state of the evaporative emission-control system when the amount of fuel-vapor trapped in the canister is more than a predetermined amount, purging of the fuel vapor trapped in the canister is executed, and the detected concentration of a vapor-laden air is smaller than the calculated concentration of a vapor-laden air in accordance with the amount of fuel-vapor trapped in the canister.