Canister purge system and method for diagnosing purge valve thereof

1. A method for diagnosing a purge valve of a canister purge system including a controller, the method comprising:

(a) determining, by the controller, whether a purge valve, which is installed on a purge pipe connecting a canister with an intake system of an engine, is open while a purge pump is running, wherein the purge pump is used to pump evaporative emission captured in the canister toward the intake system and installed on the purge pipe arranged between the canister and the purge valve, where the controller is electrically connected to the purge valve and the purge pump; and

(b) when the purge valve is open while the purge pump is running, determining, by the controller, whether the purge valve is in a close stuck state, based on an upstream pressure and a downstream pressure of the purge pipe, wherein the upstream pressure is measured on a portion of the purge pipe between the purge pump and the canister, and the downstream pressure is measured on a portion of the purge pipe between the purge pump and the purge valve.

2. The method of claim 1 , wherein the upstream pressure is measured by using a first pressure sensor installed to be positioned at a front end of the purge pump, and

wherein the downstream pressure is measured by using a second pressure sensor installed to be positioned at a rear end of the purge pump.

3. The method of claim 1 , wherein the determining of whether the purge valve is in the close stuck state includes:

(b1) determining whether the downstream pressure exceeds a first reference pressure which is preset;

(b2) determining whether the upstream pressure exceeds a second reference pressure, which is preset, when the downstream pressure exceeds the first reference pressure; and

(b3) determining that the purge valve is in a high-level close stuck state, when the upstream pressure exceeds the second reference pressure.

4. The method of claim 3 , wherein the second reference pressure is the upstream pressure made when the purge pump is running under a normal condition, in a state that the purge valve in a normal state is open.

5. The method of claim 4 , wherein the determining of whether the purge valve is in the close stuck state further includes:

(b4) determining that the purge valve is in a middle-level close stuck state when it is determined that the upstream pressure is equal to or less than the second reference pressure.

6. The method of claim 5 , wherein the high-level close stuck state is a state that close stuck occurs in the purge valve such that flow of the evaporative emission is blocked by the purge valve; and

wherein the middle-level close stuck state is a state that the close stuck partially occurs in the purge valve such that the evaporative emission is allowed to pass through the purge valve and a flow resistance of the evaporative emission is more increased as compared to a flow resistance when the purge valve is in a normal state.

7. The method of claim 3 , wherein the determining of whether the upstream pressure exceeds the second reference pressure is performed by comparing the second reference pressure and an upstream pressure measured after a specified reference time elapses from a time point at which the purge valve is open.

8. A canister purge system comprising:

a purge valve installed on a fuel tank vapor line connecting a canister with an intake system of an engine to transfer evaporative emission captured in the canister to the intake system of the engine and allowing or blocking a flow of the evaporative emission through the fuel tank vapor line;

a purge pump installed on the fuel tank vapor line to pump the evaporative emission from the canister to the intake system; and

a controller configured to determine whether the purge valve is in a close stuck state, based on upstream pressure and downstream pressure of the purge pump, when the purge valve is open while the purge pump is running.

9. The canister purge system of claim 8 , further comprising:

a first pressure sensor installed on the fuel tank vapor line to be interposed between the purge pump and the canister and configured to measure the upstream pressure; and

a second pressure sensor installed on the fuel tank vapor line to be interposed between the purge pump and the purge valve and configured to measure the downstream pressure.

10. The canister purge system of claim 8 , wherein the controller determines that the purge valve is in a high-level close stuck state when the downstream pressure exceeds first reference pressure, which is preset, and the upstream pressure exceeds second reference pressure which is preset.

11. The canister purge system of claim 10 , wherein the first reference pressure is the downstream pressure made when the purge pump is running under a normal condition, in a state that the purge valve in a normal state is open.

12. The canister purge system of claim 10 , wherein the second reference pressure is the upstream pressure made when the purge pump is running under a normal condition, in a state that the purge valve in a normal state is open.

13. The canister purge system of claim 12 , wherein the second reference pressure is set to be a lower value such that a revolution per minute (RPM) of the purge pump is increased.

14. The canister purge system of claim 10 , wherein the controller determines that the purge valve is in a middle-level close stuck state, when the downstream pressure exceeds the first reference pressure and the upstream pressure is equal to or less than the second reference pressure.

15. The canister purge system of claim 14 , wherein the high-level close stuck state is a state that close stuck occurs in the purge valve such that a flow of the evaporative emission is blocked by the purge valve; and

wherein the middle-level close stuck state is a state that the close stuck partially occurs in the purge valve such that the evaporative emission is allowed to pass through the purge valve and a flow resistance of the evaporative emission is more increased as compared to a flow resistance when the purge valve is in a normal state.

16. The canister purge system of claim 10 , wherein the controller compares, with the second reference pressure, an upstream pressure measured after a specified reference time elapses from a time point at which the purge valve is open.