Canister purge system and method for diagnosing purge valve thereof

A method for diagnosing a purge valve of a canister purge system includes (a) determining whether a purge valve, which is installed on a purge pipe connecting a canister with an intake system of an engine, is open and whether a purge pump is running, wherein the purge pump is configured to pump evaporative emission captured in the canister toward the intake system, and (b) determining 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.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean Patent Application No. 10-2017-0172294, filed on Dec. 14, 2017, which is incorporated herein by reference in its entirety.

FIELD

The present disclosure relates to a canister purge system provided in a vehicle and a method for diagnosing a purge valve thereof.

BACKGROUND

The statements in this section merely provide background information related disclosure and may not constitute prior art.

A canister purge system mounted in a vehicle connects a fuel tank with a canister through a fuel tank vapor line, captures evaporative emission evaporated from the fuel tank through the canister, and opens a purge control solenoid valve (PCSV) (hereinafter, referred to as “a purge valve”) mounted on a purge pipe connecting the canister with an intake system of an engine under the purge control condition of the engine that the negative pressure of the engine is sufficiently formed, thereby returning the evaporative emission to the intake system.

However, we have discovered that engines have been developed and used with negative pressure relatively insufficient to transfer the evaporative emission, which is captured in the canister, to an intake system of an engine only by using the negative pressure of the engine, similarly to an engine such as TGDI HEV. Accordingly, an active canister purge system is applied to a vehicle, which is equipped with the types of engines having insufficient negative pressure, with a purge pump which forcibly pumps the evaporative emission captured in the canister and transfers the evaporative emission to the intake system of the engine.

SUMMARY

The present disclosure relates to a canister purge system improved to effectively diagnose whether a close stuck occurs in a purge valve and a method for diagnosing a purge valve of the canister purge system.

According to an aspect of the present disclosure, a method for diagnosing a purge valve of a canister purge system includes (a) determining whether a purge valve, which is installed on a purge pipe connecting a canister with an intake system of an engine, is open and whether a purge pump is running, wherein the purge pump is used to pump evaporative emission captured in the canister toward the intake system, and (b) determining 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.

Preferably, the upstream pressure is measured by using a first pressure sensor installed to be positioned at a front end of the purge pump, and the downstream pressure is measured by using a second pressure sensor installed to be positioned at a rear end of the purge pump.

Preferably, step (b) includes (b1) determining whether the downstream pressure exceeds first reference pressure which is preset, (b2) determining whether the upstream pressure exceeds 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.

Preferably, 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.

Preferably, 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.

Preferably, the second reference pressure is set to be a lower value such that a revolution per minute (RPM) of the purge pump is increased.

Preferably, the step (b) 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.

Preferably, 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 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.

The step (b) 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. According to an aspect of the present disclosure, a canister purge system includes 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 determining 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.

Preferably, the canister purge system further includes a first pressure sensor installed on the fuel tank vapor line to be interposed between the purge pump and the canister and measuring 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 measuring the downstream pressure.

Preferably, 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.

Preferably, 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.

Preferably, 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.

Preferably, the second reference pressure is set to be a lower value such that a RPM of the purge pump is increased.

Preferably, 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.

Preferably, 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 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.

Preferably, 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.

As described above, the present disclosure relates to the canister purge system and the method for diagnosing a purge valve of the canister purge system, which may effectively diagnose whether the purge valve is the close stuck state, and the degree of the close stuck, by using a pressure value provided from the pressure sensors installed at both ends of the purge pump.

DETAILED DESCRIPTION

In the following description of elements according to the present disclosure, the terms ‘first’, ‘second’, ‘A’, ‘B’, ‘(a)’, and ‘(b)’ may be used. The terms are used only to distinguish relevant elements from other elements, and the nature, the order, or the sequence of the relevant elements is not limited to the terms. In addition, unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meanings as those generally understood by those skilled in the art to which the present disclosure pertains. Such terms as those defined in a generally used dictionary are to be interpreted as having meanings equal to the contextual meanings in the relevant field of art, and are not to be interpreted as having ideal or excessively formal meanings unless clearly defined as having such in the present application.

FIG. 1is a schematic view illustrating a canister purge system, andFIG. 2is a graph illustrating the variation in the front pressure and the rear pressure of a purge pump when the purge valve is in a normal state.

Hereinafter, a description will be made regarding the schematic configuration of an active canister purge system1to which a method for diagnosing a purge valve of the canister purge system is applicable, according to an exemplary form of the present disclosure.

Referring toFIG. 1, the active canister purge system1may include a fuel tank10storing fuel, a canister20capturing evaporative emission produced as the fuel stored in the fuel tank10is evaporated, a fuel tank vapor line30connecting the fuel tank10with the canister20, a canister close valve40opening the canister20to introduce external air into the canister20, a purge pipe50connecting the canister20with an intake system130of the engine120, a purge valve60installed on the purge pipe50such that the movement of the evaporative emission is allowed or blocked, a purge pump70forcibly pumping the evaporative gas captured in the canister20to the intake system130, a first pressure sensor80installed at one point of the purge pipe50, which is interposed between the canister20and the purge pump70, such that upstream pressure Pu of the purge pump70is measured, a second pressure sensor90installed at another point of the purge pipe50, which is interposed between the purge pump70and the purge valve60, such that downstream pressure Pd of the purge pump70is measured, an oxygen sensor100installed in an exhaust manifold of the engine120to measure an air-fuel ratio (A/F) by detecting an oxygen concentration included in the exhaust gas, and a controller110which controls the overall driving of the active canister purge system1.

When a specific purge control condition is satisfied, the controller110may perform a purge control such that the purge valve60is open while being run and thus may transfer the evaporation emission captured in the canister20to the intake system130. The purge control condition is not limited thereto, and the controller110may perform the purge control of the canister20when determining that the purge of the canister20is desired, by totally taking into consideration temperature information of a coolant and engine control information, which are received from various sensors.

In the purge control of the canister20, the evaporative emission captured in the canister20is discharged from the canister20by the negative pressure forcibly applied by the purge pump70and then transferred to the intake system130through the purge valve60. Accordingly, as illustrated inFIG. 2, in the purge control of the canister20, the upstream pressure Pu of the purge pump70becomes lowered than the air pressure by the negative pressure provided from the purge pump70and then constantly maintained. The downstream pressure Pd of the purge pump70becomes slightly higher than the air pressure by the evaporative emission compressed in the purge pump70and then constantly maintained.

FIG. 3is a flowchart illustrating a method for diagnosing the purge valve of the canister purge system, according to an exemplary form of the present disclosure,FIG. 4is a graph illustrating the variation in the upstream pressure and the downstream pressure of the purge pump when the purge valve is in a high-level close stuck state, andFIG. 5is a graph illustrating the variation in the upstream pressure and the downstream pressure of the purge pump when the purge valve is in a middle-level close stuck state.

When the purge valve60is in the close stuck state, even if the purge valve60is open, the evaporative emission is stagnant without passing through the purge valve60. According to an exemplary form of the present disclosure, the method for diagnosing the purge valve of the canister purge system is to diagnose whether the purge valve60is in the close stuck state.

First, the controller110may determine whether the purge control of the canister20is performed (S20) when the engine120is running (S10). To this end, the controller110may determine whether the purge valve60is open and whether the purge pump70is running. The controller110may determine that the purge control of the canister20is performed when the purge valve60is open while the purge pump70is running. In addition, the controller110may not perform the diagnosis of the purge valve60(S45) by determining that the purge control of the canister20is not performed when the purge valve60is in a close state, when the purge pump70is stopped, or when the purge valve is in the close state while the purge pump70is being stopped.

Then, the controller110starts diagnosing the purge valve60when the purge control of the canister20is performed (S30). For example, the controller110checks whether the purge pump70is running under a specific normal condition, receives the upstream pressure Pu of the purge pump70from a first pressure sensor80, and receives the downstream pressure of the purge pump70from a second pressure sensor90.

Thereafter, the controller110determines whether the purge valve60is in the close stuck state by using the upstream pressure Pu and the downstream pressure Pd of the purge pump70which are received from the first and second pressure sensors80and90(S40).

The controller110determines whether the downstream pressure Pd of the purge pump70is equal to or greater than specific first reference pressure P1(S41).

Preferably, the first reference pressure P1is the downstream pressure Pd of the purge pump70when the purge pump70is running under the normal condition, in the state that the purge valve60, which is in a normal state that the close stuck does not occur, is open. As illustrated inFIG. 2, in this case, the first reference pressure P1becomes slightly higher than the air pressure. For example, the first reference pressure P1may be 2 kPa.

The close stuck of the purge pump70may be classified into a high level and a middle level depending on the close degree of the purge valve60. The high-level close stuck refers to that the purge valve60is fully closed and thus the evaporative emission is stagnant in the purge pipe50without passing through the purge valve60. The middle-level close stuck refers to that the purge valve60is partially closed and thus the flow resistance of the evaporative emission is increased from a normal value even if the evaporative emission passes through the purge valve60.

As illustrated inFIG. 4, when the purge valve60is in the high-level close stuck state, the upstream pressure Pu of the purge pump70is decreased to be lower than the air pressure at the initial stage of the purge control of the canister20, but is recovered to the air pressure after specific time (ΔT) elapses as the evaporative emission is stagnant without passing through the purge valve60and thus the negative pressure is not normally provided from the purge pump70. In addition, in this case, after the downstream pressure Pd of the purge pump70is increased to be higher than the downstream pressure Pd of the purge pump70, which is made when the purge valve60is in the normal state, that is, the first reference pressure P1, as the evaporative emission stagnant without passing through the purge valve60is compressed. Then, the downstream pressure Pd of the purge pump70is constantly maintained.

As illustrate inFIG. 5, when the purge valve60is in the middle-level close stuck state, the upstream pressure Pu of the purge pump70is constantly maintained after being decreased to be lower than the air pressure by the negative pressure provided from the purge pump70. In this case, the downstream pressure Pd of the purge pump70may be constantly maintained after being increased to be higher than the downstream pressure Pd of the purge pump70, which is made when the purge valve60is in the normal state, as the purge valve60is partially closed and thus the flow resistance of the evaporative emission is increased, and to be lower than the downstream pressure Pd of the purge pump70which is made when the purge valve60is in the high-level close stuck.

The controller110does not perform the diagnosis of the purge valve60based on the determination that the purge valve60is in the normal state, when the downstream pressure Pd of the purge valve60is equal to or less than the first reference pressure P1(S45).

The controller110determines whether the purge valve60is in the high-level close stuck state or the middle-level close stuck state, based on the determination that the purge valve60is in the close stuck state, when the down pressure Pd of the purge pump70exceeds the first reference pressure P1. To this end, the controller110determines whether the upstream pressure Pu of the purge pump70exceeds a specific second reference pressure P2(S43).

Preferably, the second reference pressure P2is the upstream pressure Pu of the purge pump70when the purge pump70is running under the normal condition, in the state that the purge valve60, which is a normal state that the close stuck does not occur, is open. As illustrated inFIG. 2, in this case, the second reference pressure P2is lower than the air pressure. It is preferred that the second reference pressure P2is lowered as the revolution per minute (RPM) of the purge pump70is increased. This is based on that the negative pressure provided from the purge pump70is increased as the RPM of the purge pump70is increased. For example, the second reference pressure P2may be −5 kPa when the RPM of the purge pump70is 50,000 RPM, and may be −7 kPa when the RPM of the purge pump70may be 70,000 RPM.

The controller110may determine that the purge valve60is in the high-level close stuck state (S47) when the upstream pressure Pu of the purge pump70exceeds the second reference pressure P2. This is determined based on that the upstream pressure Pu of the purge pump70is maintained to the air pressure as the negative pressure is not normally provided from the purge pump70when the purge valve60is in the high-level close stuck state. However, even though the purge valve60is in the high-level close stuck state, the upstream pressure Pu of the purge pump70is lower than the air pressure during a specific time (ΔT) at the initial stage of the purge control of the canister20. Accordingly, it is preferred that the controller110preferably compares the upstream pressure Pu of the purge pump70and the second reference pressure P2after specific reference time elapses from a time point of starting the purge control. In this case, it is preferred that a reference time is set to be longer than the specific time (ΔT) spent until the upstream pressure Pu of the purge pump70is decreased to be lower than the air pressure and recovered to the air pressure at the initial stage of the purge control of the canister20.

The controller110may determine that the purge valve60is in the middle-level close stuck state (S49) when the upstream pressure Pu of the purge pump70is equal to or less than the second reference pressure P2. This is determined based on that the upstream pressure Pu of the purge pump70is decreased to pressure approximate to pressure, which is made when the purge valve60is in the normal state, as the negative pressure is provided from the purge pump70, when the purge valve60is in the middle-level close stuck state.

According to an exemplary form of the present disclosure, in the method for diagnosing the purge valve of the canister purge system, the diagnosing may be effectively performed regarding whether the purge valve60is in the close stuck state and the occurrence degree of the close stuck by using the pressure values provided from the pressure sensors80and90mounted at both ends of the purge pump70.

Hereinabove, although the present disclosure has been described with reference to exemplary forms and the accompanying drawings, the present disclosure is not limited thereto, but may be variously modified and altered by those skilled in the art to which the present disclosure pertains without departing from the spirit and scope of the present disclosure claimed in the following claims.

Therefore, forms of the present disclosure are not intended to limit the technical spirit of the present disclosure, but provided only for the illustrative purpose. The scope of protection of the present disclosure should be construed by the attached claims, and all equivalents thereof should be construed as being included within the scope of the present disclosure.