Apparatus for detecting malfunction in evaporated fuel purge system used in internal combustion engine

An apparatus for detecting a malfunction in an evaporated fuel purge system, said evaporated fuel purge system including a vapor passage, a canister for absorbing fuel vapor fed from a fuel tank to the canister via the vapor passage, and a purge passage for connecting the canister to an intake passage of an internal combustion engine, the fuel vapor being fed from the canister to the intake passage via the purge passage when the engine is operating under a prescribed operating condition, said apparatus comprising:

• a first control valve that is turned ON and OFF to control a flow of fuel vapor in the purge passage between the canister and the intake passage;
• a second control valve that is turned ON and OFF to control a flow of air from the atmosphere to the canister via the inlet opening of the canister;
• valve control means for turning OFF the second control valve and for simultaneously turning ON the first control valve so as to subject the purge passage to a negative pressure of the intake passage, and for detecting whether a pressure of the system reaches a prescribed first negative pressure, and for turning OFF the first and second control valves after said first negative pressure is reached in said system;
• detection means for detecting whether a pressure of the system changes from said first negative pressure to a prescribed second negative pressure after the first and second control valves are turned OFF, so as to detect whether the pressure of the system is substantially stable;
• and
• discrimination means for sensing pressures of the system when said detection means detects said second negative pressure has been reached and when a prescribed time period has elapsed since said detection of said detection means, wherein said discrimination means operates to determine whether a malfunction has occurred in said system in accordance with a pressure change rate derived form said sensed pressures of the system.

An apparatus for detecting a malfunction in an evaporated fuel purge system, said evaporated fuel purge system including a vapor passage, a canister for absorbing fuel vapor fed from a fuel tank to the canister via the vapor passage, a purge passage for connecting the canister to an intake passage of an internal combustion engine, a purge control valve being opened to feed the fuel vapor from the canister to the intake passage via the purge passage when the engine is operating under a prescribed operating condition, and a pressure control check valve for controlling a flow of fuel vapor fed from the fuel tank to the canister via the vapor passage, said apparatus comprising:

• a bypass passage for connecting the fuel tank to the canister, said bypass passage being connected to the vapor passage and passing around the pressure control check valve;
• a bypass control valve for controlling a flow of fuel vapor fed from the fuel tank to the canister via said bypass passage;
• pressure detecting means for sensing a pressure of a first portion of the system having the purge control valve, the purge passage, the canister, and the vapor passage between the canister and the pressure control check valve, and for sensing a pressure of a second portion of the system having the fuel tank, and the vapor passage between the fuel tank and the pressure control check valve;
• discrimination means for detecting whether a malfunction has occurred in said first portion in accordance with the pressure of said first portion sensed by said pressure detecting means, and for detecting whether a malfunction has occurred in said second portion in accordance with the pressure of the second portion sensed by said pressure detecting means;
• and
• valve control means for selectively turning ON and OFF said purge control valve and said bypass control valve when said system having said first portion and said second portion is diagnosed, and for switching said pressure detecting means to a first condition when a pressure of the second portion of the system is sensed, and for switching said pressure detecting means to a second condition when a pressure of the first portion of the system is sensed.

An apparatus for detecting a malfunction in an evaporated fuel purge system, said evaporated fuel purge system including a vapor passage, a canister for absorbing fuel vapor fed from a fuel tank to the canister via the vapor passage, a purge passage for connecting the canister to an intake passage of an internal combustion engine, the fuel vapor being fed from the canister to the intake passage via the purge passage when the engine is operating under a prescribed operating condition, and a check valve for controlling a flow of fuel vapor from the fuel tank to the canister via the vapor passage, said apparatus comprising:

• a pressure control check valve provided in the vapor passage and mechanically opened when a pressure of the vapor passage is higher than a prescribed positive pressure;
• a bypass control valve provided in a bypass passage, connected to the vapor passage and passing around said pressure control check valve, said bypass control valve being turned ON and OFF to control a flow of fuel vapor from the fuel tank to the canister;
• a first control valve that is turned ON and OFF to control a flow of fuel vapor in the purge passage between the canister and the intake passage;
• a second control valve which is turned ON and OFF to control a flow of air from the atmosphere into the canister via an air inlet opening of the canister;
• valve control means for turning OFF the second control valve and for turning ON the first control valve so as to subject the purge passage, the canister, and the vapor passage to a negative pressure of the intake passage, for detecting whether a pressure of the system reaches a prescribed first negative pressure, and for turning OFF both the first control valve and the second control valve after said first negative pressure is reached in said system;
• detection means for detecting whether or not a pressure of the system changes from said first negative pressure to a prescribed second negative pressure after the first and second control valves are turned OFF, so as to detect whether the pressure of the system is substantially stable;
• discrimination means for sensing pressures of the system when said detection means detects the pressure of the system as reaching said second negative pressure and when a prescribed time period has elapsed since said detection of said detection means, and for detecting whether a malfunction has occurred in said system, in accordance with a pressure change rate derived from said sensed pressures of the system;
• and
• means for subjecting the canister, the bypass passage and the fuel tank to the atmospheric pressure via the air inlet opening of the canister, by turning ON said second control valve and said bypass control valve after said discrimination means detects that a malfunction has occurred in said system.

An apparatus for detecting a malfunction in an evaporated fuel purge system, said evaporated fuel purge system including a vapor passage, a canister for absorbing fuel vapor fed from a fuel tank to the canister via the vapor passage, and a purge passage for connecting the canister to an intake passage of an internal combustion engine, the fuel vapor being fed from the canister to the intake passage via the purge passage when the engine is operating under a prescribed operating condition, said apparatus comprising:

• a pressure control check valve provided in the vapor passage for controlling a flow of fuel vapor from the fuel tank to the canister via the vapor passage;
• cold start detection means for detecting whether the engine is in a cold start condition;
• flag setting means for setting a cold start detection flag when the cold start condition of the engine is detected by said cold start detection means;
• valve control means for turning OFF the pressure control check valve, when the cold start detection flag is set, so as to close the vapor passage between the fuel tank and the pressure control check valve during a prescribed time period;
• pressure detection means for sensing a pressure of the vapor passage between the fuel tank and the pressure control check valve;
• and
• discrimination means for detecting whether a malfunction has occurred in said system, said discrimination means detecting that a malfunction has occurred in said system if the cold start flag is set and the pressure of the vapor passage sensed by said pressure detection means is not smaller than a prescribed negative pressure after the prescribed time period has elapsed since the vapor passage is closed by the pressure control check valve.

An apparatus for detecting a malfunction in an evaporated fuel purge system, said evaporated fuel purge system including a vapor passage, a canister for absorbing fuel vapor fed from a fuel tank to the canister via the vapor passage, and a purge passage for connecting the canister to an intake passage of an internal combustion engine, the fuel vapor being fed from the canister to the intake passage via the purge passage when the engine is operating under a prescribed operating condition, said apparatus comprising:

• a pressure control check valve provided in the vapor passage for controlling a flow of fuel vapor from the fuel tank to the canister via the vapor passage;
• a fuel temperature sensor for sensing a temperature of fuel of the fuel tank;
• valve control means for turning OFF the pressure control check valve to close the vapor passage between the fuel tank and the pressure control check valve during a prescribed time period;
• pressure detection means for sensing a pressure of the vapor passage between the fuel tank and the pressure control check valve when the vapor passage is closed;
• fuel temperature detection means for detecting whether a difference between a fuel temperature of the fuel tank sensed at a previous engine stop and a fuel temperature of the fuel tank sensed at a current engine start is greater than a prescribed value;
• and
• discrimination means for detection whether a malfunction has occurred in said system, said discrimination means detecting that a malfunction has occurred in said system if it is detected that said fuel temperature difference is greater than the prescribed value and the pressure of the vapor passage sensed by said pressure detection means is not smaller than a prescribed negative pressure.