KR100774684B1 - Pressure compensation method for leak diagnosis of vehicle fuel tank - Google Patents

Abstract

The present invention relates to a pressure compensation method for leak diagnosis of a fuel tank for a vehicle. More specifically, in the leak diagnosis of a fuel tank, the present pressure and the target when the inclination value changed when the tank pressure decreases have a constant slope. After calculating the pressure difference, the fuel tank for the vehicle, which adjusts the amount of opening of the PCSV so that the pressure difference maintains a constant pressure value, and reaches the target pressure, thereby allowing the pressure to be corrected for accurate diagnosis of the fuel tank. Pressure compensation method for the diagnosis of leaks.

To this end, the present invention includes the steps of checking the conditions for starting the leak diagnosis of the fuel tank; Determining whether the condition is satisfied in the step; Identifying an initial condition before starting diagnosis when the condition is satisfied at the step; Determining whether all the conditions are satisfied; Opening the PCSV and reducing the pressure in the tank when all the conditions are satisfied in the step; Calculating a pressure gradient in the step; Determining whether the variation range of the pressure gradient converges; Determining whether the pressure in the tank is equal to or less than a reference value in the step; Inputting a difference between a current pressure and a target pressure in the tank; Adjusting the opening amount of the PCSV according to the fuel amount and the pressure difference in the step; Determining whether the current pressure is equal to a target pressure; Determining whether the present pressure is greater than the allowable pressure when the present pressure is equal to the target pressure in the step; And performing a pressure calculation for leak diagnosis when the current pressure is greater than the allowable pressure in the step. The pressure correction method for leak diagnosis of a vehicle fuel tank is provided.

Description

Pressure correction method for leak diagnosis of fuel tank of vehicle

1 is a flow chart showing a pressure correction method for leak diagnosis of a vehicle fuel tank according to the present invention,

2 is a pressure graph and a purge valve duty signal in the fuel tank before and after applying the improvement logic.

3 is a block diagram showing an adsorption filtration device using a conventional canister,

4 is a flowchart illustrating a conventional fuel evaporation gas leak diagnosis method;

5 is an internal configuration diagram showing an embodiment of a conventional ROV,

Figure 6 is a block diagram showing another embodiment of a conventional ROV for KOBD diagnosis.

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

10: fuel tank 11: PCSV

12: ROV 13: canister

14 ECU 15 Inlet

16: purge side outlet 17: atmospheric side outlet

17a: pipe 18: air filter

19: shut-off valve (CCV) 20: fuel inlet

21: DTP sensor

The present invention relates to a pressure compensation method for leak diagnosis of a fuel tank for a vehicle. More specifically, in the leak diagnosis of a fuel tank, the present pressure and the target when the inclination value changed when the tank pressure decreases have a constant slope. After calculating the pressure difference, the fuel tank for the vehicle, which adjusts the amount of opening of the PCSV so that the pressure difference maintains a constant pressure value, and reaches the target pressure, thereby allowing the pressure to be corrected for accurate diagnosis of the fuel tank. Pressure compensation method for the diagnosis of leaks.

In general, the exhaust gas of an automobile is cranked from the exhaust gas discharged through the exhaust system after the mixture of fuel and air is combusted in the cylinder, the evaporation gas generated by evaporation of the fuel in the fuel tank, and the mixer or unburned gas in the combustion chamber. It can be divided into blow-by gas flowing into the case.

Among the above-mentioned emissions, fuel evaporation gas is more strongly regulated by the recently established North American ORVR regulations.

The apparatus currently employed for the control of such boil-off gas is an adsorption filtration method using a charcoal canister as shown in FIG. 3.

That is, when the engine is not driven and the gas evaporated from the fuel tank (or the carburetor) is absorbed and stored by the charcoal canister 13 and the engine is started and a certain driving condition is reached, the ECU 14 causes the purge control solenoid valve 11 ( The Purge Control Solenoid Valve (hereinafter referred to as PCSV) is opened to induce the evaporated gas stored in the canister 13 to the intake pipe by the intake negative pressure together with the outside air.

Here, the canister is described in more detail with reference to FIG. 3.

First, one side of the canister 13 is formed with an evaporation gas inlet 15 connected to the fuel tank 10 and the purge side outlet 16 connected to the PCSV side, and the upper side of the canister 13 is formed. Another outlet 17 connected to the side is formed.

In the canister 13, the evaporation gas generated from the fuel tank when the engine is not driven is introduced into the case through the evaporation gas inlet 15, and is adsorbed and stored on the surface of the activated carbon particles. It is discharged into the atmosphere through the filter 18.

In addition, when the ECU 14 opens the PCSV 11 under a constant driving condition after the engine is driven, the fresh air in which the boil-off gas adsorbed on the activated carbon flows through the air filter 18 and the air outlet 17 is introduced. It is separated and sent to the intake cylinder through the purge side outlet 16 and the PCSV 11 together with this atmosphere and burned in the combustion chamber.

In FIG. 3, a canister close valve 19 (hereinafter referred to as CCV) is a valve installed on a pipe 17a connecting between the air outlet 18 and the air outlet 18 of the canister 13.

The CCV 19 is normally open at all times when the engine is driven or not driven, but during the EVAP monitoring performed by the ECU 14 during driving, a short time (about 30 seconds) is controlled by the ECU 14. The bar is closed so that a negative pressure is formed in the fuel tank 10.

That is, during EVAP monitoring, the ECU 14 detects a leak of the fuel tank 10 according to the degree of resolving the negative pressure after forming a negative pressure in the fuel tank 10 while the PCSV 11 is opened. In this case, in order to form a negative pressure in the fuel tank 10, the air side should be closed, and the valve for immediately closing the air passage of the canister 13 when detecting the leak is the CCV 19.

On the other hand, the upper side of the fuel tank 10 is provided with a run-over valve (ROV 12) to stop the lubricator when the fuel tank 10 is filled with fuel when the fuel tank 10 is filled through the fuel inlet (20). At this time, the hole size formed inside the ROV 12 causes a difference in the pressure between the canister 13 and the fuel tank 10.

4 is a flow chart for the leak detection method of the fuel tank, the step of confirming the conditions for the leakage diagnosis of Table 1, and the initial conditions before the start of the diagnosis of Table 2 when it is satisfied after determining whether the conditions are satisfied at the same time Checking and determining whether all the above conditions are satisfied.

Subsequently, if all of the above conditions are met, opening the PCSV (25%), depressurizing the pressure in the tank, calculating the pressure gradient and determining whether the current pressure matches the target pressure; If the target pressure is met, it is determined whether the current pressure is greater than the allowable pressure, and if the above conditions are satisfied, calculation for leak diagnosis is performed.

However, in the prior art, EVAP monitoring is performed by the above method in order to cope with the North American EVAP regulation. In North America, there is no problem even with the conventional technology because there is a regulation such as ORVR in the fuel system, but KOBD (Korea On Board Diagnosis) ), ORVR is not applied and EVAP regulation must be satisfied.

That is, in the prior art, when the KOBD corresponds to the adsorption filtration method using the canister, EVAP diagnosis is not possible due to the ROV 12 of the existing specification as shown in FIG. 5.

This is because when the leak diagnosis of the conventional fuel tank in which the ROV 12 is not installed, a negative pressure is formed in the fuel tank 10 by closing the air passage connected to the canister 13 and opening the PCSV 11. Due to the installation of the ROV 12 (hole formed in the inside) at 10, it is formed lower than the desired fuel pressure.

Therefore, even in the prior art, in order to cope with the KOBD, a separate ROV must be added as shown in FIG. 6, resulting in a cost increase. In this case, in FIG. 6, the first ROV 101 is installed at an existing position and plays the same role, and the second ROV 102 is used for purging when diagnosing KOBD.

The present invention has been made in view of the above point, in order to diagnose the leak of the tank to open the purge valve to reduce the pressure in the tank, after determining whether the change of the pressure gradient converges, the target pressure is below the reference value It is an object of the present invention to provide a pressure compensation method for leak diagnosis of a fuel tank for a vehicle in which the duty amount of the PCSV is adjusted to reach the pressure, so that the pressure can be reduced to a pressure for accurate leak diagnosis of the tank.

In the present invention for achieving the above object in the pressure correction method for leak diagnosis of a vehicle fuel tank,

Step 1 of determining whether the condition is satisfied after checking the conditions for starting the leak diagnosis of the fuel tank; and 2 to determine whether the initial condition is satisfied after checking the initial condition before starting the diagnosis when the condition is satisfied in the first step. In step 2, if the initial conditions are satisfied in step 2, the PCSV is opened, the pressure in the tank is decompressed, and the pressure gradient is calculated to determine whether the variation of the pressure gradient converges, and the constant convergence in the third step. If the slope is determined to determine whether the pressure in the tank is less than the reference value step 4, if the pressure value is less than the reference value in step 4, after calculating the difference between the current pressure and the target pressure in the tank PCSV according to the fuel amount and pressure difference Step 5 for adjusting the opening amount of the and whether the current pressure has reached the target pressure in accordance with the PCSV opening amount control in the step 5 In step 6, the step 7 determines whether the present pressure is greater than the allowable pressure when the present pressure is equal to the target pressure in step 6 and the step 7 for diagnosing the leak when the present pressure is greater than the allowable pressure. Characterized in that it comprises the eight steps to perform the pressure calculation.

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

1 is a flowchart illustrating a pressure compensation method for leak diagnosis of a fuel tank for a vehicle according to the present invention, and FIG. 2 is a pressure graph and a purge valve duty signal in a fuel tank before and after applying improvement logic.

As described above, the fuel tank leak diagnosis method for automobiles opens the PCSV 11 to form a constant negative pressure in the fuel tank 10, and then closes the PCSV 11 after a certain time, and then lowers the pressure in the tank. This will slowly fill up.

However, since the ROV 12 is installed above the conventional fuel tank 10, the tank pressure is lowered to a steep slope slope than the desired target pressure, and when the PCSV 11 is closed, the slope increases to a gentle slope at a lower lowest point. .

The present invention obtains the difference between the present pressure and the target pressure when the inclination value changes when the tank pressure decreases, and then adjusts the opening amount of the PCSV 11 to maintain the constant pressure value. The main point is that by allowing the pressure to reach the target pressure, the pressure can be corrected for accurate diagnosis of the fuel tank 10.

First, as shown in Table 1, it is determined whether the conditions for starting the leak diagnosis are satisfied at the same time.

Next, if the above conditions are satisfied, the initial conditions before starting the diagnosis, that is, the evaporation amount, the offset and the pressure increase range, are checked.

Subsequently, if all the above conditions are satisfied, the PCSV 11 is opened (25%), the pressure in the tank is reduced, and the pressure gradient is calculated to determine whether the change range converges.

The meaning of the convergence of the change range is that when the EVAP system starts to lower the initial pressure by applying a duty to the PCSV 11, that is, when the negative pressure is formed, the pressure starts to decrease in a static state, and thus the pressure gradient becomes smaller and larger. The value increases, and this value has a constant slope after a certain time depending on the shape of the system.

That is, when the constant convergence slope is determined, it is determined whether the pressure value in the tank is, for example, -7 hPa or more.

If the double slop phenomenon is detected when the pressure value is higher than -7 hPa, it is due to various external factors in the system (temperature, fluctuation of the sensor value in an unstable state of fuel, etc.), and thus this is excluded.

The double slop is a phenomenon in which the inclination value at the time of reducing the pressure of the tank decreases initially and then rapidly increases from the time when the pressure calculation is completed.

When the pressure value is -7 hPa or less, the difference between the present pressure and the target pressure is calculated, and then the opening amount of the PCSV 11 is adjusted according to the fuel amount and the pressure difference.

When the present pressure reaches the target pressure, it is determined whether the present pressure is greater than the allowable pressure, and if so, pressure calculation is performed for the leak diagnosis.

Therefore, the present invention in such a method, by adjusting the opening amount of the PCSV (11) so that the pressure gradient has a constant range of change and the current pressure value reaches the target pressure value, without having to add one more ORV for KOBD diagnosis, The negative pressure can be formed at the pressure value, the pressure can be corrected to increase gradually when the PCSV 11 is closed, and the cost can be reduced because the ORV 12 is not added separately.

While the invention has been shown and described with respect to certain preferred embodiments thereof, the invention is not limited to these embodiments, and has been claimed by those of ordinary skill in the art to which the invention pertains. It includes all the various forms of embodiments that can be implemented without departing from the spirit.

As described above, according to the pressure compensation method for leak diagnosis of a vehicle fuel tank according to the present invention, the pressure gradient has a constant variation range and the current pressure value is the target pressure value without adding an ORV for KOBD diagnosis. By adjusting the PCSV opening amount to reach the negative pressure at the desired pressure value, the pressure can be corrected to increase when the PCSV is closed, and the cost can be reduced because there is no need to add an ORV.

Claims (1)

In the pressure correction method for leak diagnosis of a vehicle fuel tank, Checking a condition for starting a leak diagnosis of the fuel tank and determining whether the condition is satisfied; A second step of checking whether the initial condition is satisfied after checking the initial condition before starting the diagnosis when the condition is satisfied in the first step; A third step of determining whether the variation range of the pressure gradient converges by opening the PCSV, reducing the pressure in the tank, and calculating the pressure gradient when all the initial conditions are satisfied in the second stage; Determining whether the pressure in the tank is equal to or less than the reference value when the gradient that is constantly converged in the third step is determined; A fifth step of adjusting the opening amount of the PCSV according to the fuel amount and the pressure difference after calculating the difference between the present pressure and the target pressure in the tank when the pressure value is less than the reference value in the fourth step; Determining whether the current pressure reaches the target pressure according to the PCSV opening amount adjustment in step 5; Determining whether the present pressure is greater than the allowable pressure when the present pressure is equal to the target pressure in the sixth step; An eighth step of performing pressure calculation for leak diagnosis when the present pressure is greater than the allowable pressure in the seventh step; Pressure correction method for diagnosing the leak of the vehicle fuel tank comprising a.

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