KR20020061029A - Evaperative system leak check by underpressure after engine stop - Google Patents

Abstract

PURPOSE: A method for detecting leakage of fuel system using negative pressure after stop of engine is provided to measure change of pressure in a tank due to leakage without restriction by time. CONSTITUTION: A method comprises the steps of: a first closed circuit forming step(10) intercepting a line connected from a fuel tank to an atmosphere side line and an intake manifold to form a closed circuit of a fuel system during operation of an engine; a negative pressure generating step(20) opening the line between the intake manifold of the engine and the fuel tank to generate negative pressure in the fuel tank; a negative pressure maintaining step(30) maintaining negative pressure when the negative pressure in the fuel tank reaches fixed value; a first pressure fluctuation measuring step(40) measuring fluctuation of pressure in the fuel system with closed circuit after the engine stops while the negative pressure in the fuel tank is maintained; a fuel system open circuit forming step(50) opening the atmosphere side line to make pressure in the fuel tank into atmosphere pressure; a second closed circuit forming step(60) intercepting the line connected with the atmosphere side line and the intake manifold to form the closed circuit of the fuel system; a second pressure fluctuation measuring step(70) measuring fluctuation of pressure due to generation of evaporative gas in the fuel tank; and a leakage detecting step(80) detecting leakage by calculating changing rate in the first and the second pressure fluctuation measuring steps.

Description

Fuel system leak detection method using negative pressure after engine stop {EVAPERATIVE SYSTEM LEAK CHECK BY UNDERPRESSURE AFTER ENGINE STOP}

The present invention relates to a fuel system leak detection method using negative pressure after the engine is stopped, and in particular, for the leakage detection of the fuel system, which is one of the items requiring failure diagnosis of all systems affecting the increase of the exhaust gas of the vehicle, The present invention relates to a fuel system leak detection method using a negative pressure after an engine stop to diagnose a leakage of the fuel system by measuring a change in pressure in the fuel tank when the engine stops after generating a constant negative pressure in the fuel tank when the engine is driven.

In general, gasoline vapors generated from fuel systems such as fuel tanks, or boil-off gas, are discharged into the atmosphere in vehicles equipped with gasoline engines. Because this gas is a hydrocarbon, it pollutes the atmosphere. The fuel evaporation gas emission control device was developed to prevent such air pollution. The emission suppression apparatus is introduced in various ways, but as shown in FIG. 1, the boil-off gas in the fuel tank 100 is guided into the canister 300 to be adsorbed to the activated carbon, and the combustion chamber is operated according to the operation of the engine 200. Sending and burning is common.

At this time, the emission suppression device is configured to only suck the boil-off gas generated in the fuel tank 100 to the canister 300, but is sucked into the combustion chamber and burned according to the negative pressure generated when the engine 200 intakes fuel. It was difficult to properly check whether the boil-off gas leaked from the connection line 600 and the intake manifold side line 500 provided between the fuel tank 100 and the engine 200.

This problem could be somewhat solved with the introduction of a test method for checking whether or not the leakage of the evaporated gas in recent years, the leak test method according to the prior art as shown in Figs. 1 and 2 idling of the engine 200 When the shut-off valve 700 and the purge valve 800 are closed at the time, the pressure in the fuel tank 100 increases as shown in FIG. 2A due to the generation of the boil-off gas, and the pressure change rate at this time is the pressure detection sensor ( When the measurement is performed at 900 and the purge valve 800 is opened in this state, a negative pressure is formed in the fuel tank 100 as shown in (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 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 has risen in the initial pressure change rate (A) measurement step as shown in FIG. 2A, this may be due to effects other than leakage (a large amount of evaporation 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) becomes the rate of change of pressure due to actual leakage.

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

However, the leak test method according to the related art stops when the engine is out of the idle section. Therefore, there is a problem that the accuracy of leakage is low because it is diagnosed whether or not leakage in a limited condition in a short time.

In addition, since the fuel in the fuel tank 100 flows while the engine 200 is being driven, it is difficult to accurately measure the pressure change.

The present invention has been invented to solve the problems of the prior art as described above, the technical problem of the present invention by generating a negative pressure in the fuel system during the operation of the engine after stopping the engine by detecting the leakage, the leakage without time constraints It is to provide a means to measure the pressure change in the tank caused by the result and to obtain accurate diagnosis results.

1 is a schematic view showing a fuel system constructed between a fuel tank and an engine;

2 is a view for explaining a leak detection method using a negative pressure during engine driving according to the prior art.

3 is a schematic block diagram for explaining a fuel system leak detection method according to the present invention.

4 is a view for explaining a fuel system leak detection method according to the present invention.

5 is a graph for explaining a fuel system leak detection method according to the present invention.

Figure 6 is a view for explaining a diagnostic method for the leakage of large diameter and the opening of the fuel inlet plug in the fuel system leak detection method according to the present invention.

7A and 7B are graphs showing changes in primary and secondary pressures in section b of FIG.

8 is a flow chart for explaining fuel system leak detection according to the present invention.

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

10: first closed loop configuration step 20: negative pressure generation step in the fuel tank

30: maintaining the negative pressure in the tank 40: measuring the first pressure change

50: fuel system open circuit configuration step 60: secondary closed circuit configuration step

70: second pressure change measurement step 80: leak detection step

100: fuel tank 200: engine

300: canister 400: atmospheric line

500: intake manifold line 600: connection line

700: shut off valve 800: purge valve

900: pressure sensor

The present invention for solving the above technical problem is a primary closed circuit configuration step of constituting a closed circuit of the fuel system by cutting off the line connected to the atmosphere and intake manifold from the fuel tank during operation of the engine: configuring the closed circuit of the fuel system A negative pressure generation step in the fuel tank which generates a negative pressure in the fuel tank by opening a line between the intake manifold and the fuel tank of the engine when the closed circuit is configured in the step; A negative pressure maintaining step for maintaining the pressure when the negative pressure in the fuel tank reaches a predetermined value in the negative pressure generating step in the fuel tank; A first pressure change measuring step of measuring a pressure change in the fuel system in a closed loop configuration when the engine is stopped while the negative pressure in the fuel tank is maintained; When the pressure change is first measured in the first pressure change measurement step, a fuel system open circuit configuration step of opening a line connected to the atmosphere to make the pressure in the fuel tank to atmospheric pressure; A second closed circuit configuration step of forming a closed circuit of the fuel system by cutting off a line connected to the atmosphere and the intake manifold from the fuel tank while the pressure in the fuel tank is at atmospheric pressure; A secondary pressure change measuring step of measuring a pressure change under the influence of the generation of boil-off gas in the fuel tank in a state where the secondary closed circuit of the fuel system is configured; It provides a fuel system leak detection method using the negative pressure after the engine stop, characterized in that it comprises a leak detection step of calculating the pressure change rate of the first pressure change measurement step and the second pressure change measurement step to detect the leak.

When described in detail with reference to the accompanying drawings a preferred embodiment of the present invention having the above characteristics as follows.

In the accompanying drawings, Figure 1 is a schematic diagram showing a fuel system configured between the fuel tank and the engine, Figure 3 is a schematic block diagram illustrating a fuel system leak detection method according to the present invention, Figure 4 is 5 is a view illustrating a fuel system leak detection method, FIG. 5 is a graph illustrating a fuel system leak detection method according to the present invention, and FIG. 6 is a large diameter leak and fuel in the fuel system leak detection method according to the present invention. A diagram for explaining a diagnosis method for opening the inlet stopper.

As shown in the accompanying drawings, the present invention is the fuel tank 100, the atmosphere side line 400 and the intake manifold line 500, such as the primary closed circuit configuration step of making the interior of the fuel tank to atmospheric pressure ( 10) and the negative pressure generating step 20 in the fuel tank generating negative pressure in the fuel tank in the state where the first closed circuit is configured, and the negative pressure maintaining step 30 in the fuel tank maintaining the negative pressure in the fuel tank in the negative pressure generated state (30). ), And a primary pressure change measuring step 40 of measuring a pressure change in the fuel system when the engine 200 is stopped while the negative pressure is maintained, and a fuel system open circuit that makes the fuel tank at atmospheric pressure when the pressure change is measured. Configuration step 50, the secondary closed circuit configuration step 60 to configure the closed loop again in the atmospheric pressure state of the fuel tank, and the secondary pressure change measurement step 70 to measure the secondary pressure change if the secondary closed circuit is configured With the first pressure change It is composed of a leak detection step 80 to detect the leak by calculating the pressure change rate of the measurement step 40 and the first pressure change measurement step 70.

When the process of detecting the leakage of the fuel system according to the present invention configured as described above is as follows.

During operation of the engine 200, the pressure in the fuel tank 100 is at atmospheric pressure as shown in FIG. In this state, the shutoff valve 700 installed in the atmosphere line 400 connected to the atmosphere side from the fuel tank 100 and the purge installed in the intake manifold line 500 through the canister 300 from the fuel tank 100. Each valve 800 is closed to form a closed circuit of the fuel system.

That is, the fuel tank 100, the connection line 600 for connecting the fuel tank 100 and the canister 300, the atmosphere line 400 for connecting the atmosphere side from the canister 300, the canister ( The fuel system formed by the intake manifold line 500 connecting the intake manifold of the engine 200 and the engine 200 is shut off while the shutoff valve 700 and the purge valve 800 are shut off. It constitutes a closed circuit. This step is the primary closed-loop configuration step 10.

In this state, the purge valve 800 which is closing the line between the intake manifold of the engine 200 and the fuel tank 100 is opened to generate a negative pressure in the fuel tank 100. That is, when the purge valve 800 is opened in a closed circuit as shown in section a of FIG. 4, negative pressure is generated in the fuel tank 100 by the suction action of the engine 200. This step is the negative pressure generation step 20 in the fuel tank.

When a negative pressure is generated in the fuel tank 100 in this manner, the purge valve 800 is opened and the shutoff valve 700 maintains the closed state to maintain the negative pressure in the fuel tank 100. This step is the negative pressure maintaining step 30 in the fuel tank.

In this state, when the start key is turned off and the purge valve 800 is closed, the engine 200 is stopped so that negative pressure no longer occurs. As such, when the engine 200 is stopped and the purge valve 800 is closed, a pressure change occurs in a leaky fuel system. That is, when the shutoff valve 700 and the purge valve 800 are closed in the state where the negative pressure is generated, the pressure in the fuel system gradually approaches the atmospheric pressure.

In this state, the pressure change is measured using the pressure sensor 900 installed in the connection line 600 connecting the fuel tank 100 and the canister 300.

That is, the pressure change in the fuel system having the pressure change as in section b of FIG. 4 is measured. This step is the first pressure change measurement step 40.

In this case, as shown in FIG. 5, when the negative pressure increases in the b section of FIG. 4 to the atmospheric pressure, the increase speed line is steeply inclined in the case of leakage of 1.0 mm, but leakage or leakage of 0.3 mm or less If not, the line is in a loose state. In addition, as shown in FIG. 7A, the first and second pressure changes in the case of generating a large amount of boil-off gas in section b are different from each other in the case of A: leakage and B: no leakage. As shown in the figure, the first and second pressure changes in the absence of evaporation gas are different from each other in the case of A: leakage and B: no leakage.

As such, the detection of the leakage and the magnitude of the leakage of the fuel system is determined by the primary pressure increase rate measured in section b of FIG. 4, and the increase rate is affected by the amount of evaporation gas generated or the temperature change in the fuel system as well as the leakage. For this reason, it is necessary to measure the pressure change in the fuel system at atmospheric pressure. See FIGS. 7A and 7B)

To this end, when the measurement of the pressure is completed in the first pressure change measurement step 40, as shown in Figure 4 constitutes an open circuit of the fuel system. That is, when the shutoff valve 700 installed in the atmospheric line 400 is opened, the fuel system is opened so that the pressure in the fuel tank 100 is at atmospheric pressure. This step is the fuel system open circuit construction step 50.

As shown in FIG. 4, the shutoff valve 700 is closed again to form a closed circuit of the fuel system in the state in which the shutoff valve 700 is opened to make the fuel system at atmospheric pressure as described above. This step is the secondary closed loop configuration step 60.

As such, when the shutoff valve 700 is closed in the atmospheric pressure of the fuel system to form a closed circuit of the fuel system, as shown in section c of FIG. The pressure change can be seen.

That is, when the shutoff valve 700 is closed while the fuel system is at atmospheric pressure, the pressure in the fuel system is increased by the boil-off gas of the fuel. At this time, the pressure change is detected by the pressure sensor 900.

This step is a secondary pressure change measuring step 70 for measuring the pressure in the fuel system with the shutoff valve 700 closed.

In the same process as described above, after defining the magnitude of the primary leakage according to the magnitude of the pressure change rate measured in the first pressure change measurement step 40, the coefficient according to the magnitude of the pressure change rate measured in the secondary pressure change measurement step 70 Calculate the final leakage and leakage size by multiplying by the basic leakage size.

That is, it can be calculated by the coefficient defined by the basic leakage size × secondary pressure change rate defined by the leakage size = primary pressure change rate.

Therefore, it is possible to measure the leakage and the leakage size in the fuel system.

At this time, as shown in Figure 8 looks at the process of detecting and warning the leakage in the fuel system in the control unit of the engine as follows.

That is, the controller measures the primary leak size defined in the primary pressure change rate measured in the primary pressure change measurement step 40 and the secondary pressure change measurement step 70 measured by the second pressure change measurement step 70 to detect leakage in the fuel system. Multiply the coefficient defined according to the differential pressure change rate (S71).

If the calculated leak size is greater than 0.5 mm, (S72) detects the leakage of the fuel system (S73), if the number of leak detection is two or more times (S74), activates the warning light (S75).

On the other hand, if the pressure in the fuel tank 100 does not fall below a certain pressure in section a of FIG. 4, that is, as shown in FIG. 6, the fuel tank in the state in which the purge valve 800 is opened and the shutoff valve 700 is closed. If the pressure in the 100 does not fall below a certain pressure, the diagnosis is caused by a large leak and the opening of a fuel injection port (not shown).

As described above, when the inside of the fuel system is kept below atmospheric pressure during the operation of the engine 200, and when the engine 200 is stopped, the change in the negative pressure formed during the driving of the engine 200 is measured to determine whether or not the leakage and the leakage size in the fuel system are measured. By diagnosing, leaks can be accurately detected without time constraints.

In the fuel system leak detection method using the negative pressure after the engine stop according to the present invention by generating a negative pressure in the fuel system while the engine is running, by stopping the engine to measure the pressure change in the fuel system to detect the leak, the leakage without time constraints The accurate diagnosis results can be obtained by measuring the pressure change in the tank caused by the engine, and since the diagnosis is carried out after the engine stops, the diagnosis can be performed at all times without the minimum diagnosis due to various engine conditions, and the diagnosis is reduced by reducing several prerequisites for the diagnosis. The program can be simplified, and the engine can be shut down and there is no flow of fuel, thus providing the effect of performing a diagnosis in a stable state.

Claims (1)

Primary closed-loop configuration, which shuts off the lines from the fuel tank to the atmosphere and intake manifolds during engine operation to form a closed loop of the fuel system: A negative pressure generation step in the fuel tank for generating negative pressure in the fuel tank by opening a line between the intake manifold of the engine and the fuel tank when the closed circuit is configured in the closed circuit of the fuel system; A negative pressure maintaining step in the fuel tank for maintaining the pressure when the negative pressure in the fuel tank reaches a predetermined value in the negative pressure generating step in the fuel tank; A first pressure change measuring step of measuring a pressure change in the fuel system in a closed loop configuration when the engine is stopped while the negative pressure in the fuel tank is maintained; When the pressure change is first measured in the first pressure change measurement step, a fuel system open circuit configuration step of opening a line connected to the atmosphere to make the pressure in the fuel tank to atmospheric pressure; A second closed circuit configuration step of forming a closed circuit of the fuel system by cutting off a line connected to the atmosphere and the intake manifold from the fuel tank while the pressure in the fuel tank is at atmospheric pressure; A secondary pressure change measuring step of measuring a pressure change under the influence of the generation of boil-off gas in the fuel tank in a state where the secondary closed circuit of the fuel system is configured; Leak detection step of detecting the leakage by calculating the pressure change rate of the first pressure change measurement step and the second pressure change measurement step; Fuel system leak detection method using the negative pressure after the engine stop, characterized in that consisting of.