Abnormality determination method for purge system and abnormality determination system for purge system

1 . An abnormality determination method for a purge system, the purge system including a vapor passage connected to a fuel tank, a canister configured to collect vaporized fuel transmitted from the fuel tank through the vapor passage, a purge passage including a purge pump that supplies the vaporized fuel absorbed in the canister to an internal combustion engine, and an outside air introduction passage allowing the canister to communicate with outside air and to which an outside air shutoff valve is attached, the abnormality determination method being for determining an abnormality in the vapor passage or the purge passage in the purge system, the abnormality determination method comprising:

determining a first value of a physical quantity by closing the outside air shutoff valve while the purge pump is driven at a first speed,

classifying the physical parameter into a first range in which it is determined that there is no abnormality in the vapor passage and the purge passage or a second range in which it is determined that there is a possibility of an abnormality in the vapor passage or the purge passage, with a first threshold value as a boundary between the first range and the second range;

opening the outside air shutoff valve,

when the physical parameter is in the second range, determining a second value of the physical quantity by closing the outside air shutoff valve while the purge pump is driven at a second speed higher than the first speed;

classifying the second value into a third range in which it is determined that there is no abnormality in the vapor passage and the purge passage or a fourth range in which it is determined that there is an abnormality in the vapor passage or the purge passage, with a second threshold value as a boundary between the third range and the fourth range; and

determining that there is a clog in the vapor passage or the purge passage when the second value is in the fourth range.

2 . The abnormality determination method for the purge system according to claim 1 , wherein

the physical quantity is a volume that is determined based on a flow rate of the purge pump until a prescribed time elapses after the outside air shutoff valve is closed while the purge pump is driven, and a difference between the pressure of a portion of the purge passage that is closer to the canister than to the purge pump before the outside air shutoff valve is closed and the pressure after the prescribed time elapses since the outside air shutoff valve is closed, and

the abnormality determination method further comprises:

determining that the first value is in the second range when the first value is smaller than the first threshold value; and

determining that the second value is in the fourth range when the second value is smaller than the second threshold value.

3 . The abnormality determination method for the purge system according to claim 2 , wherein

the volume is calculated based on a ratio of the flow rate to the difference in pressure.

4 . The abnormality determination method for the purge system according to claim 1 , wherein

the physical quantity is the pressure of a portion of the purge passage that is closer to the canister than to the purge pump after a prescribed time elapses since the outside air shutoff valve is closed while the purge pump is driven, and

the abnormality determination method further comprises:

determining that the first value is in the second range when the first value is smaller than the first threshold value; and

determining that the second value is included in the fourth range when the second value is smaller than the second threshold value.

5 . The abnormally determination method for the purge system according to claim 4 , further comprising:

determining that there is an abnormality in the vapor passage or the purge passage when the pressure reaches a prescribed lower limit value before the prescribed time elapses since the outside air shutoff valve is closed.

6 . The abnormality determination method for the purge system according to claim 1 , wherein

the physical quantity is a decrease rate of the pressure of a portion of the purge passage that is closer to the canister than to the purge pump after the outside air shutoff valve is closed while the purge pump is driven, and

the abnormality determination method further comprises:

determining that the first value is in the second range when the first value is larger than the first threshold value; and

determining that the second value is in the fourth range when the second value is larger than the second threshold value.

7 . The abnormality determination method for the purge system according to claim 1 , further comprising:

in a case where the internal combustion engine is mounted on a vehicle, determining the first value by closing the outside air shutoff valve when the internal combustion engine is driven and the vehicle is stopped, or when the internal combustion engine is driven and the vehicle is traveling.

8 . The abnormality determination method for the purge system according to claim 1 , further comprising:

prohibiting the determination of the first value when a fluctuation of the level of the fuel in the fuel tank is equal to or larger than a prescribed upper limit value.

9 . The abnormality determination method for the purge system according to claim 1 , further comprising:

setting the first threshold value and the second threshold value to be smaller as an amount of the fuel in the fuel tank increases.

10 . An abnormality determination system for a purge system, the purge system including a vapor passage connected to a fuel tank, a canister configured to collect vaporized fuel transmitted from the fuel tank through the vapor passage, a purge passage including a purge pump that supplies the vaporized fuel absorbed in the canister to an internal combustion engine, and an outside air introduction passage allowing the canister to communicate with outside air and to which an outside air shutoff valve is attached, the abnormality determination system being for determining an abnormality in the vapor passage or the purge passage in the purge system, comprising:

a controller configured for:

determining a first value of a physical quantity by closing the outside air shutoff valve while the purge pump is driven at a first speed,

classifying the physical parameter into a first range in which it is determined that there is no abnormality in the vapor passage and the purge passage or a second-range in which it is determined that there is a possibility of an abnormality in the vapor passage or the purge passage, with a first threshold value as a boundary between the first range and the second range,

opening the outside air shutoff valve,

when the physical parameter is in the second range, determining a second value of the physical quantity by closing the outside air shutoff valve while the purge pump is driven at a second speed higher than the first speed,

classifying the second value into a third range in which it is determined that there is no abnormality in the vapor passage and the purge passage or a fourth range in which it is determined that there is an abnormality in the vapor passage or the purge passage, with a second threshold value as a boundary between the third range and the fourth range, and

determining that there is a clog in the vapor passage or the purge passage when the second value is in the fourth range.