KR20090116449A - Method for detecting leak of fuel tank - Google Patents

Abstract

PURPOSE: A fuel tank leakage sensing method of a vehicle is provided to accurately classify and determine the partial opening adherence of a purge valve and the vapor gas leakage of a fuel system. CONSTITUTION: A fuel tank leakage sensing method of a vehicle receives signals to diagnose the evaporative gas leakage of a fuel tank(101) and checks leakage diagnosis conditions(103). If it is satisfied with the leakage diagnosis condition, a canister close valve and a purge valve are closed and receive the fuel pressure(107). The fuel pressure is checked to reach a target value and air-fuel ratio is received in a regular interval if the fuel pressure does not reach the target value. The partial opening adherence of the purge valve is judged based on comparison result of the pre-set critical value and the operation value(125).

Description

How to detect fuel tank leaks in cars {METHOD FOR DETECTING LEAK OF FUEL TANK}

The present invention relates to a fuel tank leak detection method of an automobile, and more particularly, in the leakage detection of a fuel system, which is one of the items requiring failure diagnosis of all systems affecting the emission of the vehicle. The present invention relates to a method for accurately distinguishing and determining large-scale leakage and partial open fixation of a purge valve.

A general vehicle is a transport port that can travel freely on a road without a rail by using the power of an engine installed in a vehicle body, and has high maneuverability, adjustability, stability, and security.

Fuel used as a driving force for moving such automobiles is usually gasoline, which is mixed with air (or fuel only) by a fuel device and supplied to each cylinder.

With the recent development of the industry, the number of automobiles is rapidly growing, and the exhaust gas emitted from the automobiles is the main culprit of environmental pollution. In order to reduce such environmental pollution, each country is making efforts to reduce the amount of automobile emissions, and the automobile emission regulations (OBD-II), which is regulated in California, is being prepared.

In other words, it is to detect the leakage of fuel system, which is one of the items requiring failure diagnosis of all systems affecting the emission of vehicles, and it corresponds to the size of 0.5mm and 1.0mm diameter required by current regulation. To ensure that the engine controller accurately detects leaks.

A leak detection system of a typical fuel system generates a negative pressure in a fuel tank and measures the magnitude of the leakage according to the rate of change of the generated negative pressure. That is, the size of the leakage hole is calculated according to the rate of change of the pressure in the fuel tank due to the generation of fuel evaporation gas and the rate of change of the fuel tank pressure due to the negative pressure.

In the general fuel system leakage test method, as shown in FIGS. 1 and 2, when the canister shutoff valve 700 and the purge valve 800 are closed during idling of the engine 200, the pressure in the fuel tank 100 may be reduced. 2 is increased as shown in FIG. 2A by the generation of the boil-off gas, and the pressure change rate at this time is measured by the pressure sensor 900, and when the purge valve 800 is opened in this state, the fuel tank 100 A negative pressure is formed inside (B). When the purge valve 800 is closed again, the internal pressures of the fuel system, that is, the fuel tank 100, the connection line 600, the canister 300, the intake manifold line 500, and the like are transferred to the atmospheric pressure side as shown in (C). Will rise.

That is, the pressure change rate due to leakage in the fuel system is measured by the pressure sensor 900, and the pressure change due to the boil-off gas is measured. At this time, the initial fuel tank pressure change rate (A) is used as a compensation value when measuring the pressure change rate (C) due to leakage. For example, if the pressure in the fuel tank 100 increased in the initial pressure change rate (A) measurement step as shown in FIG. 2, this may be due to effects other than leakage (a large amount of boil-off gas, temperature rise in the fuel tank, etc.). Therefore, even if there is no leakage, an increase in the pressure in the fuel tank is expected in the pressure change rate (C) measurement step due to leakage. Therefore, the rate of change of pressure due to leakage (C)-the initial rate of change of pressure (A) is the rate of change of fuel tank pressure due to actual leakage.

At this time, if there is no change as shown in Figure 2 (C) there is no leakage in the fuel system.

The leak test method of this general fuel system is that when the coolant temperature is higher than a predetermined value, the fuel level controller is higher than a predetermined value, and the vehicle is stopped, the pressure in the fuel tank is closed when the canister shutoff valve is closed and the purge valve is opened. It is determined that large-scale leakage does not occur if it falls to the lower limit within the predetermined time at atmospheric pressure, and it is determined that there is a large-scale leakage if it does not fall below the lower limit at atmospheric pressure, and informs the driver of the result.

That is, when the canister shutoff valve 700 and the purge valve 800 are closed, the fuel tank is sealed and the fuel pressure in the sealed fuel tank is increased. However, when leakage occurs in the purge valve 800, the fuel pressure in the fuel tank is lowered. Based on this, the error of the purge valve is diagnosed.

However, when the purge valve is stuck in the partially open state, since the opening of the purge valve cannot be controlled afterwards, there is a problem that it is difficult to execute the leakage diagnosis for the evaporated gas described above. Therefore, a separate logic and device was needed to perform partial open fixation diagnostics for the purge valve prior to the evaporative gas leak diagnosis and then allow the purge valve to perform leakage for the evaporative gas in normal operation.

SUMMARY OF THE INVENTION The present invention has been made to solve this problem, and an object of the present invention is to accurately distinguish between partial open stuck of the purge valve and evaporation gas leakage of the fuel system based on the integral value of fuel pressure and air-fuel ratio in the fuel tank. It is an object of the present invention to provide a fuel tank leak detection method for a vehicle that can improve the reliability of the vehicle's leakage determination diagnosis.

Fuel tank leak detection method of a vehicle according to the present invention for achieving the above object,

a) receiving signals for diagnosing leakage of the boil-off gas in the fuel tank and checking whether the leakage diagnosis condition is satisfied;

b) receiving and storing fuel pressure after closing control of the canister shutoff valve and the purge valve when the leakage diagnosis condition is satisfied through the step a);

c) determining whether the fuel pressure of step b) has reached a predetermined target value and receiving an air-fuel ratio for a predetermined time at a predetermined cycle when the fuel pressure has not reached the target value;

d) calculating an integral value of the received air-fuel ratio and determining whether the purge valve is partially open based on a result of comparing the operation value with a preset threshold value.

Here, the leak diagnosis condition of step a),

Canister collection amount, fuel level, intake pressure, engine speed, air-fuel ratio, operating state information of the canister purge valve, diagnostic result information of the pressure sensor, diagnostic result information of the canister shutoff valve, wherein the canister collection amount Is 25% or less of the total collection amount, the fuel level is 20% or more and 80% or less of the total fuel amount, the intake pressure is 0.7 or less of atmospheric pressure, the engine speed is 1200 rpm or more, and the air-fuel ratio is -15 % To 19%, the operation state information of the canister purge valve is the maximum open state, characterized in that the diagnostic result information of the pressure sensor and the canister shutoff valve is normal.

In addition, the target value of step c) is characterized in that -20hPa.

In step d)

If the integral value of the air-fuel ratio is less than or equal to a preset threshold, determining that the purge valve is partially open and further, prohibiting leakage diagnosis of the evaporated gas;

In addition, in step d),

If the integral value of the air-fuel ratio is not equal to or less than a predetermined threshold value, and further comprising the step of determining the purge valve to be normal, and performing the leakage diagnosis of the evaporated gas after controlling the opening of the canister shutoff valve.

In the step c), when the fuel pressure reaches the target value, the purge valve further includes the step of controlling the opening of the canister shutoff valve after determining that it is normal, and further performing a diagnosis of leakage of the evaporated gas.

As described above, the fuel tank leak detection method of the vehicle according to the present invention, after the canister shutoff valve and the purge valve closed control based on the integral value of the fuel pressure and the air-fuel ratio received for a predetermined period of time the portion of the purge valve By accurately classifying and determining the stuck in the open state and the large-scale leakage of the fuel system, the effect of improving the reliability of the vehicle's leakage determination diagnosis is obtained.

DETAILED DESCRIPTION In order to fully understand the present invention, the operational advantages of the present invention, and the objects achieved by the practice of the present invention, reference should be made to the accompanying drawings that illustrate preferred embodiments of the present invention.

BEST MODE Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

3 is a schematic view showing a configuration of a vehicle fuel system to which a fuel tank leak diagnosis method according to the present invention is applied, and FIG. 4 is a flowchart illustrating a fuel tank leak detection process of a vehicle according to the present invention. That is, as shown in Figure 3, the leak detection device is a canister (2) for collecting the boil-off gas generated in the fuel tank (1), and the amount of sending the boil-off gas collected in the canister (2) to the engine A purge valve (3) for controlling the pressure, a canister shutoff valve (4) for blocking the atmospheric opening of the canister (2), a pressure sensor (5) for measuring the pressure in the fuel tank, and the pressure sensor (5). The purge valve (3), the canister shutoff valve (4), and the engine controller (6) for controlling the engine in accordance with the detection signal of the.

First, the engine controller 6 has the canister collection amount less than 25% of the total collection amount, the fuel level is 20% or more and 80% or less of the total fuel amount, the intake pressure is 0.7 or less of the atmospheric pressure, the engine The rotation speed is 1200 rpm or more, the air-fuel ratio is -15% or more and 19% or less, the operation state information of the canister purge valve is the maximum open state, and the canister shutoff when the diagnostic result information of the pressure sensor and the canister shutoff valve are normal, respectively. After controlling the valve 4 and the purge valve 3 to the closed state, the fuel pressure provided from the pressure sensor 5 in the fuel tank is received. At this time, the fuel pressure is reduced.

Then, in the engine controller 6, the fuel reduction amount is compared with the preset target value, and the purge valve 3 is determined when the fuel pressure reaches the preset target value as a result of the comparison. The engine controller 6 then controls the canister shutoff valve 4 to open and then diagnoses leakage to the evaporated gas.

However, the engine controller 6 receives the air-fuel ratio for a predetermined time and calculates the integral value for a predetermined time when the fuel reduction amount does not reach the target value or less, and when the calculated value is equal to or less than the preset threshold value, the purge valve 3 The diagnosis of leakage to the evaporated gas is stopped after the determination as partial open fixation.

In addition, the engine controller 6 determines that the purge valve 3 is normal when the calculated value is not equal to or less than a predetermined threshold value, and then controls the opening of the canister shutoff valve 4 and then leaks to the evaporation gas. Run diagnostics.

The target value and the threshold value are the result values obtained through a plurality of experiments, and are stored in advance in the engine controller 6 in order to maintain an optimum engine state.

A leak detection process of the fuel tank using the negative pressure described above will be described in more detail with reference to FIG. 4.

First, the engine controller 6, which has received signals corresponding to the leakage diagnosis condition of the boil-off gas supplied from the outside or the diagnosis of the partial open fastening of the purge valve 101, through step 103, Proceeding to step 105 if the partial open stuck diagnosis condition of the purge valve is satisfied.

At this time, the step 105 receives and stores the fuel pressure of the fuel tank after a predetermined set time (30 seconds) has elapsed in the closed control state of the canister shutoff valve 4 and the purge valve 3. (Step 107), it is then determined whether the received fuel pressure has reached a predetermined target value (-20 hPa) or less (step 109).

The engine controller 6 then determines that the purge valve 3 is normal when the fuel pressure reaches the target value (step 111) and controls the opening of the canister shutoff valve 4 (step 113). Run a leak diagnosis (step 115).

On the other hand, when the fuel pressure does not reach the target value below the target value in step 107, the engine controller 6 receives the air-fuel ratio for a predetermined time at a predetermined cycle through step 117, and then the predetermined time is If it has passed (step 119), the integral value of the received air-fuel ratio is calculated (step 121).

In addition, the engine controller 6 determines whether the operation value and the predetermined threshold value (500% * sec) or less in the step 121 is less than or equal to (step 123). If it is less than or equal to the set threshold value (500% * sec), it is determined that partial purging of the purge valve 3 is established (step 125). The engine controller 6 then stops leak diagnosis for the boil-off gas (step 127).

On the other hand, the partial open fixation determination result of the purge valve and the stop of the evaporative gas leakage diagnosis are visually and / or audibly displayed to the driver.

If the operation value and the predetermined threshold value (500% * sec) or less through the step 123 proceeds to the step 111.

As such, those skilled in the art to which the present invention pertains will understand that the present invention may be embodied in other specific forms without changing to the technical spirit or essential features of the present invention. Therefore, the above-described embodiments are to be understood in all respects as illustrative and not restrictive. The scope of the present invention is shown by the following claims rather than the above description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included in the scope of the present invention. .

1 is a view showing a fuel system constructed between a general fuel tank and an engine.

2 is a view for explaining a leak detection method of the boil-off gas using a general engine negative pressure.

3 is a view showing the configuration of a fuel system to which the fuel tank leak detection method according to the present invention is applied.

4 is a flowchart illustrating a fuel tank leak detection process according to the present invention.

<Explanation of symbols for the main parts of the drawings>

1: fuel tank 2: canister

3: purge valve 4: canister shutoff valve

5 pressure sensor 6 engine controller (ECU)

Claims (8)

a) receiving signals for diagnosing leakage of the boil-off gas in the fuel tank and checking whether the leakage diagnosis condition is satisfied; b) receiving the fuel pressure after a predetermined set time after the canister shutoff valve and the purge valve are closed controlled when the leakage diagnosis condition is satisfied through the step a); c) determining whether the fuel pressure of step b) has reached a preset target value and receiving an air-fuel ratio for a predetermined time at a predetermined period when the fuel pressure has not reached the target value; And d) calculating an integral value of the received air-fuel ratio and determining whether the purge valve is partially open or stuck based on a comparison result of the calculated value and a predetermined threshold value. . The method of claim 1, wherein the leak diagnosis condition of step a) is Canister collection amount, fuel level, intake pressure, engine speed, air-fuel ratio, operation status information of the canister purge valve, diagnostic result information of the pressure sensor, diagnostic result information of the canister shutoff valve, characterized in that . The method of claim 2, wherein the canister capture amount is 25% or less of the total collection amount, the fuel level is 20% or more and 80% or less of the total fuel amount, the intake pressure is 0.7 or less of the atmospheric pressure, the engine speed Is at least 1200 rpm, the air-fuel ratio is at least -15% and at most 19%, the operating state information of the canister purge valve is in the maximum open state, and the diagnostic result information of the pressure sensor and the canister shutoff valve are normal. Fuel tank leak detection method. The method of claim 1, wherein the target value of step c) is -20 hPa. The method of claim 1, wherein step d) If the integral value of the air-fuel ratio is less than a predetermined threshold value, the fuel tank leakage detection method of a vehicle characterized in that the diagnosis of the partial open fastening of the purge valve is prohibited after the leakage diagnosis for the evaporated gas. The method of claim 1, wherein step d) When the integral value of the air-fuel ratio is not equal to or less than a predetermined threshold value, after determining that the purge valve is normal, and controlling the opening of the canister shutoff valve, a leakage diagnosis of the evaporated gas is performed. 7. A method of detecting fuel tank leakage in a vehicle according to any one of claims 1, 5, and 6, wherein the threshold is 500% * sec. The method of claim 1, further comprising: when the fuel pressure reaches the target value in step c), after purging the valve to be normal, controlling the opening of the canister shutoff valve to perform a leak diagnosis on the evaporated gas. A fuel tank leak detection method for a vehicle.

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