Leak detection of emission control system

An apparatus for detecting a leak in an evaporative emission control system for an internal combustion engine including a fuel tank, a canister for collecting fuel vapors from the fuel tank and having a fresh air inlet, and a purge control valve disposed between the canister and an intake pipe for controlling flow of the fuel vapors from the canister to the intake pipe together with fresh air drawn into the canister through the fresh air inlet such that a fuel vapor flow passage is provided which extends from the fuel tank to the purge control valve by way of the canister, the apparatus comprising:

• means for defining an atmospheric vent in communication with the open air;
• a motor driven air pump having an outlet;
• a directional control valve capable of connecting said fresh air vent selectively to one of said atmospheric vent and said outlet of said air pump;
• a bypass conduit providing communication between said fresh air inlet and said outlet of said air pump while bypassing said directional control valve, said bypass conduit having a reference orifice;
• judgment level determining means for detecting, when said air pump is ON and said directional control valve connects said fresh air inlet to said atmospheric vent, for thereby allowing air from said air pump to pass through said reference orifice of said bypass conduit and thereafter be released to the open air through said directional control valve, a first current through said air pump and determining said first current as a judgment level;
• leak level measuring means for measuring, at a measurement timing after lapse of a predetermined time from establishment of a condition in which said air pump is ON and said directional control valve connects said fresh air inlet to said outlet of said air pump so that air from said air pump passes through said directional control valve and said fresh air inlet of said canister and is supplied to said fuel vapor flow passage, a second current through said air pump and determining said second current as a leak level;
• leak judging means for comparing said leak level with said judgment level and judging if a leak is present in said fuel vapor flow passage;
• fuel temperature detecting means for detecting a temperature of fuel in said fuel tank;
• and
• measurement timing variable determining means for determining said measurement timing variably on the basis of said temperature of fuel.

A method of detecting a leak in an evaporative emission control system including a fuel vapor flow passage which extends from a fuel tank to a purge control valve by way of a canister, a device for defining an atmospheric vent in communication with the open air, a motor driven air pump having an outlet, a directional control valve for connecting the fresh air vent selectively to one of the atmospheric vent and the outlet of the air pump, and a bypass conduit providing communication between a fresh air inlet of the canister and the outlet of the air pump while bypassing the directional control valve, the bypass conduit having a reference orifice, the method comprising:

• detecting a first current through said air pump when said air pump is ON and said directional control valve is in a position of connecting said fresh air inlet to said atmospheric vent;
• detecting a second current through said air pump after lapse of a predetermined time from establishment of a condition in which air pump is ON and said directional control valve is in a position of connecting said fresh air inlet to said outlet of said air pump;
• comparing said second current with said first current and judging if a leak is present in said fuel vapor flow passage;
• detecting a temperature of fuel in said fuel tank;
• and
• determining said predetermined time variably on the basis of said temperature of fuel.

A method of detecting a leak in an evaporative emission control system for an internal combustion engine including a fuel tank, a canister for collecting fuel vapors from the fuel tank and having a fresh air inlet, a purge control valve disposed between the canister and an intake pipe for controlling flow of the fuel vapors from the canister to the intake pipe together with fresh air drawn into the canister through the fresh air inlet such that a fuel vapor flow passage is provided which extends from the fuel tank to the purge control valve by way of the canister, means for defining an atmospheric vent in communication with the open air, a motor driven air pump having an outlet, a directional control valve capable of connecting the fresh air vent selectively to one of the atmospheric vent and the outlet of the air pump, a bypass conduit providing communication between the fresh air inlet and the outlet of the air pump while bypassing the directional control valve, the bypass conduit having a reference orifice, the method comprising:

• detecting, when said air pump is ON and said directional control valve connects said fresh air inlet to said atmospheric vent, for thereby allowing air firm said air pump to pass through said reference orifice of said bypass conduit and thereafter be released to the open air through said directional control valve, a first current through said air pump and determining said first current as a judgment level;
• measuring, at a measurement timing after lapse of a predetermined time from establishment of a condition in which said air pump is ON and said directional control valve connects said fresh air inlet to said outlet of said air pump so that air from said air pump passes through said directional control valve and said fresh air inlet of said canister and is supplied to said fuel vapor flow passage, a second current through said air pump and determining said second current as a leak level;
• comparing said leak level with said judgment level and judging if a leak is present in said fuel vapor flow passage;
• detecting a temperature of fuel in said fuel tank;
• and
• determining said measurement timing variably on the basis of said temperature of fuel.