JP2794986B2 - Fuel tank airtightness inspection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an airtightness inspection method for a fuel tank of an automobile.

[0002]

2. Description of the Related Art One of the methods for inspecting the airtightness of a hollow container is a method called a differential pressure type. This differential pressure type airtightness inspection method is based on the principle that a hollow container to be inspected and a reference container are simultaneously pressurized at a constant pressure and a leak defect of the hollow container is detected as a pressure difference between the hollow container and the reference container. It is said that compared to the pressure drop type that pressurizes a hollow container to a predetermined pressure and checks the pressure drop, the effects of compression heat and ambient temperature at the time of pressurization can be minimized. (Similar structures are disclosed, for example, in JP-A-58-92925).

[0003]

In the conventional differential pressure type airtightness inspection method as described above, a certain amount of leakage occurs in a large container such as a fuel tank of an automobile having a volume of several tens of liters. Even if it occurs, the generation of the differential pressure is extremely small, and there is a limit in improving the inspection accuracy when detecting a minute leak defect. Further, in order to accurately detect the above minute leak defect, it is necessary to wait until the differential pressure becomes large to some extent, and as a result, the inspection time becomes long.

On the other hand, the inspection accuracy can also be improved by increasing the pressure at the time of pressurizing the container. However, the increase in pressure causes deformation of the container itself, and there is naturally a limit to increasing the pressure.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and a leak defect found in a fuel tank airtightness inspection stage is not a fuel tank body but a gauge unit which is later assembled to the fuel tank body. Since the occurrence at the mounting part occupies most of the parts (for example, looseness due to insufficient tightening of the gauge unit, poor sealability of the seal member, etc.), the inspection time is made redundant and fuel consumption is reduced by focusing on the leakage defect around the gauge unit. An object of the present invention is to provide a method capable of accurately detecting a tank without causing deformation of the tank.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a method for checking the airtightness of a fuel tank provided with a gauge unit for detecting the amount of fuel in the fuel tank. Cover the exposed portion of the gauge unit with a chamber having a smaller capacity than the fuel tank and seal it tightly.
In parallel with simultaneously increasing the pressure to a predetermined pressure, the pressure in the chamber and the chamber reference container is simultaneously reduced to a predetermined degree of vacuum, and the difference between the fuel tank and the tank reference container is reduced.
Pressure, and the differential pressure between the chamber and the chamber reference container pieces
Detected separately, it is characterized by performing the airtightness of the suitability judgment on each.

[0007]

According to this structure, for example, the pressure is increased to a specified pressure.
If the damaged fuel tank itself has a leak defect,
Side pressure drops to the pressure on the tank reference container side.
A difference is generated, and this pressure difference is electrically taken out and set in advance.
By comparing with the reference value, the presence or absence of
The suitability of the fuel tank itself is determined.
You. Similarly, a gauge unit evacuated to the specified pressure
If there is a leak around the chamber, the pressure in the chamber will increase.
The pressure on the side of the reference container for the chamber.
By extracting the differential pressure electrically, the presence or absence of a leak defect,
Airtightness around the gauge unit covered by the chamber
No is determined. Then, by the negative pressure within this chamber using a smaller chamber capacity than the fuel tank, since the detected capacitance is significantly reduced as compared with the case where the fuel tank itself has a detection volume, Gejiyunittoma
Instead, the change in the differential pressure when a leak defect occurs is fast, and the leak defect can be specified in a short time.

[0008]

FIG. 1 shows an embodiment of the present invention, in which an airtightness inspection of a tank body 2 of a fuel tank 1 and an airtightness inspection around a gauge unit 3 mounted on the tank body 2 are performed in parallel. An example of the case of performing the operation is shown.

As shown in FIG. 1, in the fuel tank 1, various tubes 5, 6, 7 other than the fuel filler tube 4 are closed by a plug 8 during an airtightness inspection.
A pressurizing jig 10 connected to a leak tester 9 is attached to the fuel filler tube 4. A gauge unit (also referred to as a center unit) 3 unitized with tubes 6, 7 and the like around a gauge for detecting the amount of fuel in the fuel tank 1 has a cup-shaped smaller capacity than the tank body 2. Chamber 11 is covered.

[0010] Since the gauge unit 3 is intended to be attached to the tank main body 2 from the rear by a bolt coupling method as is well known, junction of the tank body 2 and the gauge unit 3
The chamber 11 connected to the leak tester 9 is covered so as to cover the entire exposed portion of the gauge unit 3 to the outside of the tank main body 2, and a space formed by the chamber 11 and the tank main body 2 is sealed.

The leak tester 9 is a device in which devices necessary for an airtightness inspection, for example, a pressure adjusting mechanism, a vacuum pump, a leak defect determination circuit unit, and a display device are integrated as one unit. Two reference containers 12, 13 are connected.

During the airtightness inspection, one of the reference containers 12 is evacuated to a predetermined degree of vacuum simultaneously with the inside of the chamber 11, and the other reference container 13 is pressurized to a predetermined pressure simultaneously with the inside of the tank body 2. .

Here, the capacity of the fuel tank 1 of a general automobile is 50 to 90 liters, whereas the capacity of the chamber 11 is set to about 2 to 3 liters.

At the time of the airtightness inspection, as shown in FIG. 1 and FIG. 2, the stopper 8, the pressing jig 10 and the chamber 1 are used.
1 are set at predetermined positions, and air pressure from a pressure source is introduced to pressurize the inside of the tank body 2 and the reference container 13 with a specified pressure (for example, 0.15 kg / cm ² ). At the same time, the chamber 11 and the reference container 12 are evacuated with a specified pressure (for example, 0.15 kg / cm ² ) to
And the inside of the reference container 12 is set to a negative pressure.

At this time, in order to prevent pulsation or the like in the tank body 2 and the reference containers 12 and 13 having a particularly large capacity, both the above-described pressurizing operation and the depressurizing operation are performed by the primary pressurization or the primary depressurization and the secondary pressurization. It should be performed in two stages of secondary depressurization, and after pressurizing or depressurizing to a specified pressure, a predetermined pressure is set to mutually balance the tank body 2 and the reference container 13, and the chamber 11 and the reference container 12. Is allowed to stand for the pressure stabilization time (balance time).

After the pressure stabilization time, the process proceeds to the detection and determination of the differential pressure. For example, if there is a leak defect in the tank body 2 pressurized to the specified pressure, the pressure on the tank body 2 drops and the reference container 13 A difference between the side pressure. The differential pressure is electrically extracted by a pressure sensor in the leak tester 9 and compared with a preset reference value,
It is determined whether or not there is a leak defect, that is, whether or not the airtightness of the tank body 2 is appropriate.

Similarly, if there is a leakage defect around the gauge unit 3 evacuated to a specified pressure, the pressure in the chamber 11 increases, and a difference is generated between the pressure in the chamber 11 and the pressure in the reference container 12. Is electrically taken out to determine whether there is a leak defect, that is, whether or not the airtightness around the gauge unit 3 covered with the chamber 11 is appropriate.

The result of the determination is displayed on the display of the leak tester 9 and printed together with the inspection data.

After the above judgment, the tank body 2, the chamber 11, and the reference containers 12, 13 are each returned to the atmospheric pressure, and then the chamber 11, the pressurizing jig 10 and the stopper 8 are removed, and the inspection is completed. Becomes

[0020] Here, leakage of V _L occurs in capacity assuming no temperature change and volume change V, the atmosphere from the fuel tank 1 of pressure P ₁ (atmospheric pressure P ₀₎ as shown in FIG. 3 Is assumed, the change ΔP in the pressure in the fuel tank 1 is ΔP = (V _L / V) · P ₀ ‥‥‥‥‥ (1)

As apparent from the above equation (1), the pressure change ΔP in the fuel tank 1 becomes larger as the capacity V of the fuel tank 1 becomes smaller, even when the same leak is detected.
Since the existing leak tester 9 determines the leak by detecting the pressure change ΔP, the detection accuracy of the leak defect improves as the value of ΔP increases.

Further, as shown in FIG. 4, when the leakage of _VL occurs in the chamber 11 having the capacity V _C (<V) and the internal pressure P ₂ (<P ₀ ), the pressure change ΔP in the chamber 11 Is simulated by the following equation.

ΔP = {(V _L · P ₀ ) / (V _C · P ₂ )} ·
P ₀ ‥‥‥‥‥ (2) In this equation (2), V _C <V,
Since P ₂ <P ₀ , even if the same amount of leakage as in the above equation (1) occurs, the generated pressure change ΔP is further increased.

As described above, in the present embodiment, the airtightness inspection around the gauge unit 3 and the airtightness inspection of the tank body 2 are not only independently performed, but also the leakage defect around the gauge unit 3 is performed. In order to make the inspection capacity for inspecting the fuel tank 1 significantly smaller than the capacity of the fuel tank 1, the apparent detection capacity is reduced by covering the chamber 11.
And the detection accuracy is greatly improved. According to the results of the experiment conducted by the inventor, the detection accuracy of the leak defect was improved up to 5 to 20 times as much as that of the conventional differential pressure type inspection method, although there was variation depending on the size of the fuel tank 1.

Further, in the conventional pressurized inspection method, there is a limit in increasing the pressurizing force because the fuel tank 1 may be deformed. Since the pressure inside the chamber 11 is negative, the apparent inspection pressure can be locally increased without causing deformation of the portion around the gauge unit 3, which also greatly increases the detection accuracy. improves.

[0026]

As described above, according to the present invention, the outer periphery of the fuel tank is covered with a chamber having a capacity smaller than that of the fuel tank so as to cover the exposed portion of the gauge unit to the outer periphery of the tank, and the fuel is sealed. Tanks and reference containers for tanks
Simultaneously with pressurizing to a predetermined pressure, the chamber and the chamber reference container are simultaneously depressurized to a predetermined degree of vacuum, and the difference between the fuel tank and the tank reference container is reduced.
Pressure, and the differential pressure between the chamber and the chamber reference container pieces
Detected separately, since it has to perform the airtightness of the suitability judgment on each difference pressure change between the chamber reference container by the capacity for detecting leakage by use of the chamber is greatly smaller Since the speed is faster, it is possible to accurately detect even small leak defects without causing deformation of the fuel tank and redundant inspection time, especially in the vicinity of the gauge unit where leak defects are likely to occur, shortening the inspection time In addition, the inspection accuracy is improved and the reliability of the inspection result is improved.

Further, since the fuel tank itself is pressurized in the same manner as in the prior art at the same time as the negative pressure in the chamber as described above, the inspection around the gauge unit and the inspection of the fuel tank itself are performed in parallel. Around the gauge unit
Apparent inspection pressure without deformation
The force can be locally increased, and the inspection accuracy and the reliability of the inspection result are further improved.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing one embodiment of the present invention.

FIG. 2 is a flowchart showing a processing procedure in FIG. 1;

FIG. 3 is an explanatory diagram of a pressure change when a leakage defect of a fuel tank is assumed.

FIG. 4 is an explanatory diagram of a pressure change when a leakage defect of a fuel tank equipped with a chamber is assumed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Fuel tank 2 ... Tank main body 3 ... Gauge unit 11 ... Chamber 12, 13 ... Reference container

Claims (1)

(57) [Claims] 1. A method for inspecting the airtightness of a fuel tank provided with a gauge unit for detecting an amount of fuel in a fuel tank, comprising: an outer portion of the fuel tank; Cover the chamber with a smaller volume than the fuel tank so as to cover it, and seal the fuel tank and the tank reference container simultaneously to a predetermined pressure.
In parallel with pressurize, on reducing the pressure and the chamber and the chamber for groups <br/> quasi vessel to simultaneously predetermined degree of vacuum, the pressure difference between the fuel tank and the tank for standard containers, and chamber and the chamber the pressure difference between the reference container is detected separately, their
A method for inspecting the airtightness of a fuel tank, comprising determining whether the airtightness is appropriate.