KR102767295B1 - CNG Leakage Diagnostic Method for CNG Vehicles - Google Patents

Abstract

A method for diagnosing a CNG leak in a CNG vehicle that uses CNG as fuel is disclosed. The method for diagnosing a CNG leak in a CNG vehicle according to the present invention comprises the steps of: (a) checking whether a state of a pressure sensor measuring a pressure of a CNG fuel tank storing CNG in an ignition-on state, the pressure of the CNG fuel tank measured by the pressure sensor, and the outside temperature satisfy set diagnosis entry conditions; (b) checking the open/close state of a fuel cutoff valve at the time of condition satisfaction when the set conditions are satisfied; And (c) a step for diagnosing a CNG leakage by applying another diagnostic routine set in advance according to the open/closed state of the fuel shut-off valve; Including, in step (c), if the fuel shut-off valve is closed, the CNG leakage is diagnosed according to the first diagnostic routine, if the fuel shut-off valve is open, it is additionally checked whether the engine is in a fuel-cut state in which the fuel supply is cut off, and if the engine is in a fuel-cut state, the CNG leakage is diagnosed according to the second diagnostic routine, and if the engine is in a normal operating state in which the CNG is normally injected, the CNG leakage is diagnosed according to the third diagnostic routine.

Description

CNG Leakage Diagnostic Method for CNG Vehicles

The present invention relates to a CNG leak diagnosis method, and more particularly, to a CNG leak diagnosis method of a CNG vehicle applied to a CNG vehicle that uses CNG (Compressed Natural Gas) as fuel.

In a CNG mono-fuel system that uses CNG (Compressed Natural Gas) as the sole fuel, or a CNG bi-fuel system that uses either CNG or gasoline as fuel, the fuel CNG is stored in a CNG fuel tank. In this case, diagnosing CNG fuel leakage due to damage to the CNG fuel tank is called 'leakage diagnosis'.

In the past, when diagnosing a leak in a CNG fuel tank in a CNG mono fuel system or a CNG bi-fuel system, a method of using the measured value of a pressure sensor that detects the pressure of the CNG fuel tank was generally adopted. This is a method of diagnosing a leak by considering the pressure change inside the CNG fuel tank measured by the pressure sensor, or more precisely, the degree of pressure reduction.

However, the conventional leak diagnosis method that only considers the degree of pressure drop in the CNG fuel tank has a disadvantage in that it is likely to misdiagnose in situations where the CNG injection amount required increases rapidly, such as rapid acceleration or high-rpm driving. This is because when the CNG injection amount is large, the pressure in the CNG fuel tank decreases significantly in a short period of time, and the conventional leak diagnosis method did not take such situations into account.

Korean Patent Publication No. 2009-0013362 (Published on February 5, 2009)

The technical problem to be solved by the present invention is to provide a CNG leak diagnosis method for a CNG vehicle, which can implement a more accurate leak diagnosis by considering not only the pressure fluctuation of a CNG fuel tank but also the operating status of various electronically controlled components (CNG injector, fuel shut-off valve), and can greatly reduce the misdiagnosis rate and improve the reliability of the leak diagnosis performance.

According to an embodiment of the present invention as a means of solving the problem,

A method for diagnosing CNG leakage in a CNG vehicle that uses CNG as fuel,

(a) a step for checking the status of a pressure sensor that measures the pressure of a CNG fuel tank storing CNG in an ignition-on state, the pressure of the CNG fuel tank measured by the pressure sensor, and whether the outside temperature satisfies the set diagnostic entry conditions;

(b) a step for checking the open/close status of the fuel shutoff valve at the time when the set conditions are satisfied; and

(c) a step of diagnosing CNG leakage by applying a different diagnostic routine set in advance according to the open/closed state of the fuel shut-off valve; including,

In step (c) above,

If the fuel shutoff valve is closed, diagnose CNG leakage according to the first diagnostic routine.

If the fuel shut-off valve is open, the engine is checked to see if the fuel supply is cut off and the engine is in a fuel-cut state. If the engine is in a fuel-cut state, the CNG leakage is diagnosed according to a second diagnostic routine. If the engine is in a normal operating state in which the CNG is normally injected, the CNG leakage is diagnosed according to a third diagnostic routine.

In the step (a) of the leak diagnosis method according to an embodiment of the present invention, if the pressure sensor is normal, the pressure of the CNG fuel tank is within a set pressure range, and the outside temperature is within a set temperature range, it can be determined that the diagnosis entry conditions are satisfied.

And the above first diagnostic routine is,

(c1-1) A step of measuring the pressure of the CNG fuel tank at the time when the fuel shut-off valve is confirmed to be closed and storing it as a reference value;

(c1-2) A step of checking the open/close status of the fuel shut-off valve again after the set time has elapsed, and if the fuel shut-off valve is closed, measuring the pressure of the CNG fuel tank;

(c1-3) A step of comparing the measured pressure value of the CNG fuel tank with the reference value, and if the measured pressure value of the CNG fuel tank is lower than the reference value, deriving the difference between the reference value and the measured pressure value of the CNG fuel tank as a difference value 1 and storing it;

(c1-4) A step of deriving a difference value 2 using the same routine as (c1-2) and (c1-3) above and comparing it with the difference value 1 to make a final determination as to whether there is a CNG leak; may be configured.

In the above step (c1-4), specifically, if the difference value 2 is greater than the difference value 1, a final judgment can be made that there is a CNG leak.

And the second diagnostic routine is,

(c2-1) A step of measuring the pressure of the CNG fuel tank at the time when it is confirmed that the engine fuel cut has occurred and storing it as a reference value;

(c2-2) After the set time has elapsed, a step of checking again whether the engine fuel is cut, and if the engine fuel is cut, measuring the pressure of the CNG fuel tank;

(c2-3) A step for making a final judgment on whether or not there is a CNG leak by comparing the difference between the reference value and the measured CNG fuel tank pressure value with a set threshold value; may be configured.

Here, if the difference between the above-mentioned reference value and the measured CNG fuel tank pressure value is greater than the set threshold value, a final judgment can be made that there is a CNG leak.

In addition, the third diagnostic routine for diagnosing a CNG leak under normal engine operation conditions in which CNG is normally injected can determine whether a CNG leak has occurred by using the pressure change in the CNG fuel tank according to the fuel supply and the accumulated amount of CNG fuel injected into the engine through the CNG injector.

Specifically, the third diagnostic routine is:

(c3-1) A step of measuring the pressure of a CNG fuel tank at a time when it is confirmed that there is no engine fuel cut, converting the measured pressure value of the CNG fuel tank into the fuel amount (unit: Kg) of the CNG fuel tank, and storing it as a reference fuel amount (unit: Kg);

(c3-2) A step of calculating the amount of CNG fuel (unit: kg) injected into the engine through the CNG injector per second for a set time from the time point at which the above standard fuel amount (unit: kg) is stored, and accumulating the amount of CNG fuel calculated per second to obtain the total amount of fuel injected (unit: kg) for the set time;

(c3-3) A step of re-measuring the pressure of the CNG fuel tank immediately after the set time has elapsed from the time point at which the standard fuel amount (unit: Kg) is stored, and converting the measured pressure value of the CNG fuel tank into the fuel amount of the CNG fuel tank (unit: Kg); and

(c3-4) A step of comparing the difference between the reference fuel amount and the fuel amount in the CNG fuel tank immediately after the set time obtained in step (c3-3) with the total fuel injection amount to make a final determination on whether or not there is a CNG leak may be included.

At this time, in the step (c3-4), if the difference between the reference fuel amount and the fuel amount in the CNG fuel tank immediately after the set time has elapsed minus the total fuel injection amount ((reference fuel amount - fuel amount in the CNG fuel tank immediately after the set time has elapsed) - total fuel injection amount) is greater than the set threshold value, a final judgment can be made that there is a CNG leak.

According to a method for diagnosing a CNG leak in a CNG vehicle according to an embodiment of the present invention, a CNG leak can be diagnosed more accurately by considering not only the pressure fluctuation of a CNG fuel tank but also the operating status of an electronically controlled CNG injector and a fuel shutoff valve, and the reliability of the leak diagnosis performance can be improved by greatly reducing the rate of misdiagnosis due to the high accuracy of the diagnosis.

FIG. 1 is a system schematic diagram schematically illustrating a CNG mono fuel system to which a CNG leak diagnosis method according to an embodiment of the present invention is applied.
FIGS. 2 and 3 are flowcharts showing a method for diagnosing CNG leakage in a CNG vehicle according to an embodiment of the present invention.

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

The terminology used in the following specification is only used to describe specific embodiments and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. It should be understood that the terms "comprises" or "has" as used herein specify that a feature, number, step, operation, component, part or combination thereof described in the specification is present, but do not exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts or combinations thereof.

Additionally, while the terms first, second, etc. may be used to describe various components, the components should not be limited by the terms. The terms are used only to distinguish one component from another.

In addition, terms such as “part,” “unit,” and “module” described in the specification mean a unit that processes at least one function or operation, which may be implemented by hardware, software, or a combination of hardware and software.

In describing with reference to the attached drawings, identical components will be given the same reference numerals and redundant descriptions thereof will be omitted. In addition, when describing the present invention, if it is determined that a detailed description of a related known technology may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted.

A CNG leak diagnosis method according to an embodiment of the present invention is applied to a CNG mono fuel system that uses CNG (Compressed Natural Gas) as a sole fuel or a CNG bi-fuel system that uses both CNG and gasoline, and can implement high diagnosis accuracy by considering not only the pressure fluctuation of a CNG fuel tank but also the operating status of a CNG injector and a fuel shut-off valve in leak diagnosis.

Before examining a CNG leak diagnosis method according to an embodiment of the present invention, the configuration of a CNG mono fuel system to which the CNG leak diagnosis method is applied will be briefly examined with reference to FIG. 1.

For reference, the drawing illustrates a CNG mono fuel system as an example, but as mentioned above, it should be clearly stated that the CNG leak diagnosis method according to the embodiment of the present invention can also be applied to a CNG Bi-fuel system that uses both CNG and gasoline as fuel.

Figure 1 is a system schematic diagram of a CNG mono fuel system to which a CNG leak diagnosis method according to an embodiment of the present invention is applied.

Referring to FIG. 1, a CNG mono fuel system (1) to which a CNG leak diagnosis method according to an embodiment of the present invention is applied includes a CNG fuel tank (10) of a predetermined capacity for storing CNG as fuel in a high-pressure state (maximum of about 200 bar), a fuel distributor (not shown) for distributing CNG as fuel supplied to the CNG fuel tank (10) to an intake manifold at an appropriate ratio according to an engine load state, and a CNG injector (50) for injecting the fuel distributed through the fuel distributor into each combustion chamber of an engine intake manifold.

CNG stored in a CNG fuel tank (10) can be supplied to the CNG injector (50) or its supply can be cut off depending on the opening and closing operation of the fuel cut-off valve (20) arranged between the CNG fuel tank (10) and the fuel distributor, and the CNG passing through the fuel cut-off valve (20) can be supplied to the CNG injector (50) by reducing the pressure to an appropriate level by the fuel pressure regulator (40) installed between the fuel cut-off valve (20) and the CNG injector (50).

A pressure sensor (12) is installed in the CNG fuel tank (10) to measure the high pressure fuel pressure stored in the CNG fuel tank (10) and provide it in real time to the controller (60). The controller (60) controls the CNG injector (50) so that fuel injection can be performed at the optimal injection amount and injection timing according to the current engine driving conditions based on the information on the fuel pressure provided by the pressure sensor (12) and other information input through the CAN communication line.

The fuel shut-off valve (20) may be an electronic valve and is controlled by the controller (60). For example, the controller (60) may control the fuel shut-off valve (20) to open in response to a driver's ignition On request, and the controller (60) may control the fuel shut-off valve (20) to close in response to a direct ignition Off request by the driver or an automatic ignition Off request by the ISG (Idle Stop & Go) or SSC (Start Stop Coasting) function.

In Fig. 1, reference numeral 30 indicates a fuel filter that filters out foreign substances contained in CNG, which is fuel supplied from a CNG fuel tank (10) to a CNG injector (50), when a fuel cutoff valve (20) is opened, and reference numeral 15 indicates a check valve that restricts reverse movement of fuel (CNG) supplied to a CNG fuel tank.

A CNG leakage diagnosis method according to an embodiment of the present invention is a method for diagnosing a CNG leakage by applying it to a CNG mono fuel system briefly discussed above. Unlike the conventional method of diagnosing a leakage by considering only the degree of pressure drop in a CNG fuel tank, the present invention proposes a method for diagnosing a CNG leakage by considering the operating status of an electronically controlled CNG injector and fuel cutoff valve.

According to a CNG leak diagnosis method according to an embodiment of the present invention, a leak is diagnosed by considering not only the pressure fluctuation of a CNG fuel tank (10) but also the operating status of an electronically controlled CNG injector and fuel shutoff valve, thereby enabling a more accurate diagnosis of a CNG leak, and the reliability of the leak diagnosis performance is improved by greatly reducing the rate of misdiagnosis due to the highly accurate diagnosis.

A method for diagnosing a CNG leak in a CNG vehicle according to an embodiment of the present invention will be examined in detail with reference to the flowcharts of FIGS. 2 and 3.

FIGS. 2 and 3 are flowcharts sequentially showing a CNG leak diagnosis process of a CNG vehicle according to an embodiment of the present invention. The step-by-step execution entity of the leak diagnosis process to be described hereinafter is the controller (60), and therefore, the leak diagnosis process will be examined from the perspective of the controller (60), which is the execution entity. However, for the convenience of explanation, the configuration illustrated in FIG. 1 will be described by referring to the same drawing reference numerals.

Referring to FIGS. 2 and 3, the controller (60) first checks whether the state of the pressure sensor (12) that measures the pressure of the CNG fuel tank (10) storing CNG with the engine started, the pressure of the CNG fuel tank (10) measured by the pressure sensor (12), and the outside temperature satisfy the set diagnosis entry conditions (S100). Then, if the conditions are satisfied, the CNG leak diagnosis is performed according to a pre-determined sequence.

At step S100, the controller (60) can specifically determine that the diagnosis entry conditions are satisfied if the signal fed back from the pressure sensor (12) for the transmitted inspection signal is a normal signal, the pressure of the CNG fuel tank (10) is within the set pressure range, and the outside temperature is within the set temperature range.

Here, the set pressure range can be set to 5 to 150 bar based on a fuel tank (10) having a pressure of 200 bar when the fuel is fully charged, and the outside temperature can be set to a temperature range in which the outside temperature does not affect the pressure fluctuation of the fuel, preferably, to about -5 to 50 degrees, considering the pressure fluctuation due to the expansion or contraction of the fuel. Of course, the mentioned values are only preferred examples and are not limited to the values.

If the controller (60) determines that the internal and external environmental conditions satisfy the aforementioned set conditions (pressure sensor normal & CNG fuel tank pressure within the set pressure range & outside temperature within the set temperature range) as a result of the condition check through step S100, it then checks the open/close status of the fuel shutoff valve (20) (S200). Then, depending on the confirmed open/close status of the fuel shutoff valve (20), it performs a leak diagnosis by applying another diagnostic routine that has been input in advance (S300).

To this end, the controller (60) may be equipped with a diagnostic processor that has diagnostic logic inputted therein that can perform diagnosis by applying a diagnostic routine differently depending on whether the fuel shutoff valve (20) is open or not. At this time, the diagnostic logic inputted into the diagnostic processor may be specifically programmed to perform diagnosis by distinguishing situations depending on whether the fuel shutoff valve (20) is closed or open, and whether fuel is cut even when it is open.

At step S300, the controller (60) can diagnose a CNG leak according to the first diagnostic routine if the fuel shutoff valve (20) is closed. Then, if the fuel shutoff valve (20) is open, it is checked whether the engine is in a fuel-cut state where the fuel supply is cut off. If the engine is in a fuel-cut state, the controller can diagnose a CNG leak according to the second diagnostic routine. If the engine is in a normal operating state where the CNG is normally injected, the controller can diagnose a CNG leak according to the third diagnostic routine.

Let us examine in more detail each of the diagnostic routines (first to third diagnostic routines) that are applied differently depending on the open/close status of the fuel shutoff valve (20) and whether engine fuel is cut.

First, let's look at the first diagnostic routine.

Diagnostic Routine 1

The controller (60) selects the first diagnostic routine if the fuel shutoff valve (20) is confirmed to be closed as a result of checking the status of the fuel shutoff valve (20) through step S200, and can diagnose CNG leakage according to the diagnostic routine. If the first diagnostic routine is selected, the controller (60) first measures the pressure of the CNG fuel tank (10) using the pressure sensor (12) at the time when the fuel shutoff valve (20) is confirmed to be closed, and stores the measured value as a reference value (S302).

Next, after the set time has elapsed, the controller (60) checks again the open/close status of the fuel shutoff valve (20), and if the fuel shutoff valve (20) is still closed, i.e., if the fuel shutoff valve (20) is maintained in a closed state, a measurement command is applied to the pressure sensor (12) to measure the pressure of the CNG fuel tank (10) once again (S304). If the fuel shutoff valve (20) is open when checked again, the process is forcibly terminated at that stage without proceeding any further.

The first diagnostic routine diagnoses CNG leakage due to tank damage while the fuel shutoff valve (20) is closed, i.e., the CNG fuel tank (10) is completely sealed. Since a situation may arise where the fuel shutoff valve (20) opens in the middle and pressure fluctuations in the fuel tank (10) occur, which may be incorrectly diagnosed as a fuel leakage, the status of the fuel shutoff valve (20) is checked frequently during the diagnosis, and if it switches to the open state, the diagnosis is terminated.

When step S304 (pressure measurement of CNG fuel tank) is completed, the next step S306 is entered. In step S306, the controller (60) compares the pressure value of the CNG fuel tank (10) measured in step S304 with the reference value in step S302, and if the pressure value measured in step S304 is lower than the reference value, the difference between the reference value and the pressure value measured in step S304 (reference value - pressure value in step S304) is stored as a difference value 1 (S306).

The controller (60) derives the difference value 2 with the same routine as the above-described steps S304 and S306 (corresponding to steps S304' and S306' in the drawing), and compares the derived difference value 2 with the difference value 1 to make a final determination as to whether there is a CNG leak (S308). In step S308, the controller (60) can make a final determination as to whether there is a CNG leak, specifically, if the difference value 2 derived through steps S304' to S306' is greater than the immediately preceding difference value 1.

If fuel leaks due to damage to the fuel tank (10), the pressure of the CNG fuel tank (10) continuously decreases during the diagnosis process. Therefore, in this case, the pressure of the fuel tank (10) cannot but be lower at the time when the difference value 2 is derived than at the time when the difference value 1 is derived. Considering this, at step S308, the controller (60) makes a final judgment of a CNG leak if the difference value 2 is greater than the previous difference value 1.

Next, let's look at the second diagnostic routine.

Second diagnostic routine

As a result of checking the state (open/closed state) of the fuel shut-off valve (20) at step S200, if it is confirmed that the fuel shut-off valve (20) is open, the controller (60) additionally checks whether the engine fuel cut state is in operation (S210). If it is confirmed that the engine fuel cut state is in operation, the second diagnostic routine can be selected and CNG leakage can be diagnosed according to the diagnostic routine.

For reference, engine fuel cut during driving can be performed by the controller (60) according to an automatic start-off request by the ISG (Idle Stop & Go) function or the SSC (Start Stop Coasting) function.

If the second diagnostic routine is selected, the controller (60) first measures the pressure of the CNG fuel tank (10) using the pressure sensor (12) at the time when it is confirmed that the engine fuel cut has occurred and stores the measured value as a reference value (S312). Then, after the set time has elapsed, the controller (60) checks again whether the engine fuel cut has occurred and, if it is still in the fuel cut state, sends a measurement command to the pressure sensor (12) to measure the pressure of the CNG fuel tank (10) again (S314).

If, upon recheck, it is determined that the fuel cut state has been interrupted (when the engine is restarted in response to a driver acceleration request), the process switches to step S322, which will be described later. This is because the second diagnostic routine is a diagnostic routine that is performed on the condition that the fuel cutoff valve (20) is open but the fuel distributor has cut off the fuel supply to the intake manifold.

When step S314 (pressure measurement of CNG fuel tank) is completed, the next step S316 is entered. In step S316, the controller (60) reads the reference value from step S312, calculates the difference between the CNG fuel tank pressure values measured in step S314, and compares the difference with a set threshold value to make a final judgment on whether or not there is a CNG leak. Specifically, if the calculated difference is greater than or equal to the set threshold value, a final judgment can be made on a CNG leak.

Next, let's look at the third diagnostic routine.

3rd diagnostic routine

In step S210, if the controller (60) additionally checks whether the engine is in a fuel-cut state while driving, and if it is not in a fuel-cut state while driving (if the result is 'NO' in step S210 in the process), i.e., if the engine is in a normal operating state in which CNG is normally injected into the engine cylinder, the controller (60) can select the third diagnostic routine and diagnose a CNG leak according to the diagnostic routine.

Here, the third diagnostic routine for diagnosing a CNG leak in a normal engine operation state in which CNG is normally injected can determine whether a CNG leak has occurred by using the pressure change of the CNG fuel tank (10) according to the fuel supply, more precisely, the pressure decrease of the CNG fuel tank for a set time, and the fuel injection amount injected into the engine through the CNG injector (50) for the set time.

Let's take a closer look at the third diagnostic routine.

At step S210, when it is confirmed that the engine is not in a fuel cut state (the engine is operating normally), the controller (60) measures the pressure of the CNG fuel tank (10) using the pressure sensor (12), converts the measured pressure value of the CNG fuel tank (10) into the fuel amount (unit: kg) of the CNG fuel tank, and stores it as the reference fuel amount (unit: kg) (S322).

Next, the controller (60) calculates the CNG fuel amount (unit: kg) injected into the engine cylinder through the CNG injector (50) per second for a set time from the time the standard fuel amount (unit: kg) is stored, and accumulates the CNG fuel amount calculated per second to obtain the total fuel injection amount (unit: kg) for the set time (S324).

In addition, the controller (60) re-measures the pressure of the CNG fuel tank (10) by applying a measurement command to the pressure sensor (12) immediately after the set time has elapsed from the time of storing the reference fuel amount (unit: Kg), and converts the measured pressure value of the CNG fuel tank (10) into the fuel amount of the CNG fuel tank (unit: Kg) (S326).

When the total fuel injection amount during the set time and the fuel amount in the CNG fuel tank immediately after the set time has elapsed are respectively obtained through steps S324 and S326, the controller (60) finally compares the difference between the reference fuel amount obtained in step S322 and the fuel amount in the CNG fuel tank immediately after the set time has elapsed obtained in step S326 with the total fuel injection amount to make a final determination as to whether or not there is a CNG leak (S328).

In step S328, the controller (60) can specifically determine a CNG leak if the difference between the reference fuel amount obtained in step S322 and the fuel amount in the CNG fuel tank immediately after the set time has elapsed obtained in step S326 minus the total fuel injection amount obtained in step S324 ((reference fuel amount - fuel amount in the CNG fuel tank immediately after the set time has elapsed) - total fuel injection amount) is greater than or equal to the set threshold value.

If there is no fuel leak in the middle of the fuel supply process, the flow rate of the fuel supplied by the fuel tank (10) for engine operation and the flow rate of the fuel injected into the cylinder through the CNG injector (50) must be the same. In other words, if the flow rate of the fuel injected into the cylinder is smaller than the flow rate of the fuel supplied from the fuel tank (10), it means that the fuel leaked in the middle. The third diagnostic logic diagnoses whether or not there is a CNG leak by taking this into consideration.

In converting the measured pressure values in steps S322 and S326 of the third diagnostic logic into the fuel amount (unit: kg) of the CNG fuel tank, the following [Calculation Formula 1] can be used.

[Calculation formula 1]

CNG fuel quantity (Kg) = CNG standard mole (100% methane, 100 bar, 273 K, 100 L) * mole correction value based on CNG fuel tank capacity * mole correction value based on CNG fuel tank pressure * mole correction value based on outside temperature * mole Kg conversion constant

Here, each correction value can be calculated based on the ideal gas equation. The ideal gas equation is an equation that describes the relationship between pressure (P), volume (V), and temperature (T) (PV = nRT, n = PV/RT → mole number = (pressure * volume) / (gas constant * temperature)

Specifically, the mole correction value based on the CNG fuel tank capacity (volume, V) is a value for correction when the capacity is changed based on the mole number that natural gas has in a tank of a specific capacity (100 Liter), and data values obtained through experiments can be used. The mole correction value based on the CNG fuel tank pressure (P) is a value for correction when the pressure is changed based on the mole number that natural gas has at a specific pressure (100 bar), and data values obtained through experiments can also be used for this.

And the mole number correction value based on the outside temperature (T) is a value for correction when the temperature changes based on the mole number that natural gas has at a specific temperature (absolute temperature 270 K). Data values obtained through experiments can be used, and the mole number Kg conversion constant is used to convert 16.04 g, which is the amount of 1 mole of a substance, to Kg.

Meanwhile, the total fuel injection amount (unit: Kg) during the set time in the above step S324 can be obtained using [Calculation Formula 2] and [Calculation Formula 3] below.

[Calculation formula 2]

Fuel injection per second (Kg/s) = ((CNG injector fuel injection volume per engine revolution (%) / time per revolution (s)) * conversion factor for volume per mass (g/%) * correction factor according to engine temperature and filling rate * 3.6 (g/s to Kg/h) ) /1000

[Calculation formula 3]

Fuel injection amount accumulated value (Kg) = Fuel injection amount per second (kg/s) value accumulated for the set time according to [Calculation formula 2]

Here, the fuel injection volume (%) of the CNG injector per engine rotation is a value calculated by setting the injection volume based on the maximum injection time of the injector as 100% and calculating the fuel injection volume based on the injection time, and the volume conversion coefficient per mass is a coefficient for converting the fuel injection volume into mass and may be a preset value.

And the filling rate is the air filling rate inside the engine, and can be determined by a filling rate map (preliminary input data map) that stores pre-experimental values obtained based on the angle of the throttle valve and the engine speed.

According to the embodiments of the present invention discussed above, by diagnosing CNG leakage through various diagnostic routines that consider not only the pressure fluctuation of a CNG fuel tank but also the operating status of an electronically controlled CNG injector and fuel shutoff valve, CNG leakage can be diagnosed more accurately, and the reliability of leakage diagnosis performance can be greatly improved because the rate of misdiagnosis is greatly reduced by the high-accuracy diagnosis.

In the above detailed description of the present invention, only specific embodiments thereof have been described. However, it should be understood that the present invention is not limited to the specific forms mentioned in the detailed description, but rather should be understood to include modifications, equivalents, and alternatives within the spirit and scope of the present invention as defined by the appended claims.

1: CNG mono fuel system
10: CNG fuel tank
12 : Pressure sensor
20: Fuel shutoff valve
30 : Fuel filter
40 : Regulator
50 : CNG Injector
60 : Controller

Claims (9)

A method for diagnosing CNG leakage in a CNG vehicle that uses CNG as fuel,
(a) a step for checking the status of a pressure sensor that measures the pressure of a CNG fuel tank storing CNG in an ignition-on state, the pressure of the CNG fuel tank measured by the pressure sensor, and whether the outside temperature satisfies the set diagnostic entry conditions;
(b) a step for checking the open/close status of the fuel shutoff valve at the time when the set conditions are satisfied; and
(c) a step of diagnosing CNG leakage by applying a different diagnostic routine set in advance according to the open/closed state of the fuel shut-off valve; including,
In step (c) above,
If the fuel shutoff valve is closed, diagnose CNG leakage according to the first diagnostic routine.
A method for diagnosing a CNG leak in a CNG vehicle, characterized in that if the fuel shut-off valve is open, the engine is in a fuel-cut state in which the fuel supply is cut off, and if the engine is in a fuel-cut state, the CNG leak is diagnosed according to a second diagnostic routine, and if the engine is in a normal operating state in which the CNG is normally injected, the CNG leak is diagnosed according to a third diagnostic routine.
In paragraph 1,
In step (a) above,
The above pressure sensor is normal,
The pressure of the above CNG fuel tank is within the set pressure range,
If the above outside temperature is within the set temperature range,
A method for diagnosing a CNG leak in a CNG vehicle, characterized in that it is determined that the above diagnostic entry conditions are satisfied.
In paragraph 1,
The first diagnostic routine is,
(c1-1) A step of measuring the pressure of the CNG fuel tank at the time when the fuel shut-off valve is confirmed to be closed and storing it as a reference value;
(c1-2) A step of checking the open/close status of the fuel shut-off valve again after the set time has elapsed, and if the fuel shut-off valve is closed, measuring the pressure of the CNG fuel tank;
(c1-3) A step of comparing the measured pressure value of the CNG fuel tank with the reference value, and if the measured pressure value of the CNG fuel tank is lower than the reference value, deriving the difference between the reference value and the measured pressure value of the CNG fuel tank as a difference value 1 and storing it;
(c1-4) A method for diagnosing a CNG leak in a CNG vehicle, characterized by including a step of deriving a difference value 2 using the same routine as (c1-2) and (c1-3) above, and comparing it with the difference value 1 to make a final determination as to whether a CNG leak exists.
In the third paragraph,
In the above step (c1-4),
A method for diagnosing a CNG leak in a CNG vehicle, characterized in that if the difference value 2 is greater than the difference value 1, a final judgment is made that there is a CNG leak.
In paragraph 1,
The above second diagnostic routine is,
(c2-1) A step of measuring the pressure of the CNG fuel tank at the time when it is confirmed that the engine fuel cut has occurred and storing it as a reference value;
(c2-2) After the set time has elapsed, a step of checking again whether the engine fuel is cut, and if the engine fuel is cut, measuring the pressure of the CNG fuel tank;
(c2-3) A method for diagnosing a CNG leak in a CNG vehicle, characterized by including a step of making a final determination on whether or not a CNG leak exists by comparing the difference between the reference value and the measured CNG fuel tank pressure value with a set threshold value.
In paragraph 5,
In the above step (c2-3),
A method for diagnosing a CNG leak in a CNG vehicle, characterized in that if the difference between the above-mentioned reference value and the measured CNG fuel tank pressure value is greater than or equal to the set threshold value, a final judgment is made as to a CNG leak.
In paragraph 1,
The third diagnostic routine, which diagnoses CNG leakage under normal engine operation conditions in which CNG is injected normally,
A method for diagnosing a CNG leak in a CNG vehicle, characterized in that the presence or absence of a CNG leak is determined by using the pressure change in a CNG fuel tank according to fuel supply and the accumulated amount of CNG fuel injected into an engine through a CNG injector.
In paragraph 7,
The third diagnostic routine above is,
(c3-1) A step of measuring the pressure of a CNG fuel tank at a time when it is confirmed that there is no engine fuel cut, converting the measured pressure value of the CNG fuel tank into the fuel amount (unit: Kg) of the CNG fuel tank, and storing it as a reference fuel amount (unit: Kg);
(c3-2) A step of calculating the amount of CNG fuel (unit: kg) injected into the engine through the CNG injector per second for a set time from the time point at which the above standard fuel amount (unit: kg) is stored, and accumulating the amount of CNG fuel calculated per second to obtain the total amount of fuel injected (unit: kg) for the set time;
(c3-3) A step of re-measuring the pressure of the CNG fuel tank immediately after the set time has elapsed from the time point at which the standard fuel amount (unit: Kg) is stored, and converting the measured pressure value of the CNG fuel tank into the fuel amount of the CNG fuel tank (unit: Kg); and
(c3-4) A method for diagnosing a CNG leak in a CNG vehicle, characterized by including a step of making a final judgment on whether or not a CNG leak occurs by comparing the difference between the reference fuel amount and the fuel amount in the CNG fuel tank immediately after the set time obtained in step (c3-3) with the total fuel injection amount.
In Article 8,
In the above step (c3-4),
A method for diagnosing a CNG leak in a CNG vehicle, characterized in that if the difference between the reference fuel amount and the fuel amount in the CNG fuel tank immediately after the set time has elapsed minus the total fuel injection amount ((reference fuel amount - fuel amount in the CNG fuel tank immediately after the set time has elapsed) - total fuel injection amount) is greater than the set threshold value, a final judgment is made that there is a CNG leak.

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