JPH04372833A - Method for inspecting airtightness of fuel tank - Google Patents

Abstract

PURPOSE:To enhance the detecting accuracy of leaking defect so that the minute leaking defect around a gage unit can be detected. CONSTITUTION:A chamber 11 having the capacity smaller than a fuel tank 1 is applied on the outer surface of the fuel tank 1 so as to cover the exposed part of a gage unit 3 at the outer surface of the tank, and the chamber is tightly sealed. The pressures in a tank main body 2 and a reference container 13 are compressed (b) at the same time to the specified pressure. The differential pressure between the tank main body 2 and the reference container 13 is detected, and the adequacy the airtightness of the tank main body 2 is judged. At the same time, the pressure in the chamber 11 and a reference container 12 is reduced to the specified vacuum degree. The differential pressure between the chamber 11 and the reference container 12 is detected, and the adequacy of the airtightness around the gage unit 3 is judged.

Description

[Detailed description of the invention]

0001

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

0002

2. Description of the Related Art There is a method called a differential pressure method as one of the airtightness testing methods for hollow containers. The basic principle of this differential pressure airtightness testing method is to pressurize the hollow container to be inspected and the reference container at a constant pressure at the same time, and detect any leakage defects in the hollow container as the pressure difference between the container and the reference container. Compared to the pressure drop method, which pressurizes a single hollow container to a predetermined pressure and examines the pressure drop, it is said to be able to minimize the effects of compression heat and ambient temperature during pressurization. (A similar structure is disclosed in, for example, Japanese Patent Application Laid-open No. 58-92925).

0003

[Problem to be Solved by the Invention] In the conventional differential pressure type airtightness testing method as described above, a certain degree of leakage occurs when the container is large, such as an automobile fuel tank with a capacity of several tens of liters. Even if a leak occurs, the differential pressure generated is extremely small, and there is a limit to the improvement in inspection accuracy when trying to detect a minute leak defect. Furthermore, in order to accurately detect the above-mentioned minute leak defect, it is necessary to wait until the differential pressure becomes large to a certain extent, resulting in a longer inspection time.

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

The present invention was made in view of the above-mentioned problems, and leakage defects discovered during the airtightness inspection stage of the fuel tank are caused not by the fuel tank itself but by the gauge unit that is later assembled into the fuel tank body. Since most of the leaks occur in the installed parts (for example, the gauge unit is loosened due to insufficient tightening, the sealing member has poor sealing performance, etc.), focusing on leakage defects around this gauge unit requires redundant inspection time and fuel It is an object of the present invention to provide a method that enables accurate detection without causing deformation of a tank.

[0006]

[Means for Solving the Problems] The present invention provides a method for testing the airtightness of a fuel tank equipped with a gauge unit for detecting the amount of fuel in the fuel tank. A chamber with a smaller capacity than the fuel tank is placed over the exposed part of the gauge unit to cover it and sealed, and this chamber and the reference container are simultaneously depressurized to a predetermined degree of vacuum, and the difference between the chamber and the reference container is It is characterized by detecting pressure and determining whether airtightness is appropriate.

[0007]

[Operation] According to this structure, by using a chamber with a smaller capacity than the fuel tank and creating a negative pressure inside this chamber, the detection capacity becomes significantly smaller than when the fuel tank itself is used as the detection capacity. When there is a leakage defect, the differential pressure changes quickly and the leakage defect can be identified in a short time.

[0008]

[Embodiment] Fig. 1 is a diagram showing an embodiment of the present invention, in which an airtightness test of a tank body 2 of a fuel tank 1 and an airtightness test around a gauge unit 3 attached to the tank body 2 are carried out simultaneously. An example of how to do this is shown below.

As shown in FIG. 1, in the fuel tank 1, various tubes 5, 6, and 7 other than the Fehr filler tube 4 are closed off by a plug 8 during an airtightness test.
A pressurizing jig 10 connected to a leak tester 9 is attached to the Fehl filler tube 4. In addition, a gauge unit (also called a center unit) 3, which is unitized with tubes 6, 7, etc. around a gauge for detecting the amount of fuel in the fuel tank 1, has a cup shape with a smaller capacity than the tank body 2. chamber 11 is covered.

As is well known, since the gauge unit 3 is attached to the tank body 2 later by a bolt connection method, it is not only possible to connect the tank body 2 and the gauge unit 3, but also to connect the gauge to the outside of the tank body 2. A chamber 11 connected to the leak tester 9 is placed over the entire exposed portion of the unit 3, and the space formed by the chamber 11 and the tank body 2 is sealed.

The leak tester 9 is composed of equipment necessary for airtightness testing, such as a pressure adjustment mechanism, a vacuum pump, a leak defect determination circuit, a display device, etc., all integrated into one unit. Two reference containers 12, 13 are connected.

During the airtightness test, one reference container 12 is evacuated to a predetermined degree of vacuum at the same time as the inside of the chamber 11, and the other reference container 13 is pressurized to a predetermined pressure at the same time as the inside of the tank body 2. .

[0013] Here, the capacity of the fuel tank 1 of a typical automobile is 50 to 90 liters, whereas the capacity of the chamber 11 is set to about 2 to 3 liters.

In the airtightness test, as shown in FIG. 2 as well as in FIG.
1 are set at predetermined positions, and then air pressure from a pressure source is introduced to pressurize the inside of the tank body 2 and the reference container 13 at a specified pressure (for example, 0.15 kg/cm 2 ). At the same time, the chamber 11 and the reference container 12 are kept at a specified pressure (
For example, the chamber 11 and the reference container 12 are evacuated to a negative pressure of 0.15 kg/cm2.

At this time, in order to prevent pulsations in the tank body 2 and the reference vessels 12 and 13, which have a particularly large capacity, both the pressurization operation and the depressurization operation are performed by primary pressurization, primary depressurization and secondary pressurization, or primary pressurization and secondary pressurization. The secondary depressurization shall be carried out in two stages, and after further pressurization or depressurization to a specified pressure, a predetermined step is taken to equilibrate the pressures between the tank body 2 and the reference container 13, and between the chamber 11 and the reference container 12. Let it stand still for the pressure stabilization time (balance time).

After this pressure stabilization time has elapsed, the process moves to differential pressure detection and judgment. For example, if there is a leakage defect in the tank body 2 that has been pressurized to a specified pressure, the pressure on the tank body 2 side will drop and the reference vessel 13 There will be a difference between the pressure on the side. By electrically extracting this differential pressure using the pressure sensor in the leak tester 9 and comparing it with a preset reference value,
The presence or absence of a leakage defect, that is, the suitability of the airtightness of the tank body 2 is determined.

Similarly, if there is a leakage defect around the gauge unit 3 that has been evacuated to a specified pressure, the pressure inside the chamber 11 will increase and a difference will occur between the pressure on the reference container 12 side and this differential pressure. By electrically taking out the leakage defect, it is determined whether there is a leakage defect, that is, whether the airtightness around the gauge unit 3 covered with the chamber 11 is adequate.

The above determination result is visually displayed on the display section of the leak tester 9 and is also printed together with the test data.

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

Here, as shown in FIG. 3, assuming that there is no temperature change or capacity change, assume that a leak of VL occurs from the fuel tank 1 of capacity V and internal pressure P1 into the atmosphere (atmospheric pressure P0). Assuming, the change in pressure ΔP in the fuel tank 1 is Δ
P=(VL/V)・P0 (1).

As is clear from the above equation (1), the pressure change ΔP within the fuel tank 1 increases 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 leakage by detecting the pressure change ΔP, the larger the value of ΔP, the higher the accuracy in detecting leak defects.

Further, as shown in FIG. 4, when a leak of VL occurs in the chamber 11 with a capacity VC (<V) and an internal pressure P2 (<P0), the pressure change ΔP in the chamber 11 is pseudo- It is expressed by the following formula.

[0023]ΔP={(VL・P0)/(VC・P2)
}・P0 ‥‥‥‥‥(2) In this equation (2), VC
Since <V and P2<P0, even if the same amount of leakage occurs as in equation (1) above, the change in pressure ΔP that occurs becomes even larger.

As described above, in this embodiment, not only the airtightness test around the gauge unit 3 and the airtightness test of the tank body 2 are carried out independently, but also leakage defects around the gauge unit 3 are carried out independently. In order to make the inspection capacity for inspecting the fuel tank 1 significantly smaller than the capacity of the fuel tank 1, the chamber 11 is placed over the chamber 11 to reduce its apparent detection capacity.
Since the capacitance of the sensor is no longer affected, detection accuracy is greatly improved. According to the results of experiments conducted by the present inventors, although there are variations depending on the size of the fuel tank 1, the accuracy of detecting leak defects was improved by 5 to 20 times compared to the conventional differential pressure type inspection method.

Furthermore, in the conventional pressurized inspection method, there was a limit to increasing the pressurizing force due to the risk of deformation of the fuel tank 1, but in the above embodiment, while pressurizing the inside of the tank body 2, Since the inside of the chamber 11 is kept under negative pressure, the apparent inspection pressure can be locally increased without causing deformation in the area around the gauge unit 3, which also greatly improves the detection accuracy. improves.

[0026]

As described above, according to the present invention, a chamber having a smaller capacity than the fuel tank is covered and sealed around the outer periphery of the fuel tank so as to cover the exposed portion of the gauge unit to the outer periphery of the tank. By simultaneously reducing the pressure in the chamber and reference container to a predetermined degree of vacuum, and then detecting the differential pressure between the chamber and reference container to determine whether airtightness is adequate, the capacity for leak detection has been greatly increased. By reducing the size of the fuel tank, the pressure difference between the reference container and the reference container changes quickly, so it is possible to eliminate minute leaks without causing deformation of the fuel tank or redundant inspection time, especially around the gauge unit where leakage defects are likely to occur. Even defects can be detected accurately, which reduces inspection time, improves inspection accuracy, and improves the reliability of inspection results.

[0027] Also, as mentioned above, while creating a negative pressure in the chamber, the fuel tank itself is pressurized as in the past, and the inspection around the gauge unit and the fuel tank itself can be carried out at the same time. This will further improve test accuracy and reliability of test results.

[Brief explanation of drawings]

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

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

FIG. 3 is an explanatory diagram of pressure changes assuming a leakage defect in the fuel tank.

FIG. 4 is an explanatory diagram of pressure changes assuming a leakage defect in a fuel tank equipped with a chamber.

[Explanation of symbols]

1...Fuel tank 2...tank body 3...Gauge unit 11...Chamber 12, 13...Reference container

Claims (1)

[Claims] Claim 1: A method for inspecting the airtightness of a fuel tank equipped with a gauge unit for detecting the amount of fuel in the fuel tank, comprising: attaching a portion of the gauge unit exposed to the outer periphery of the fuel tank to the outer periphery of the fuel tank; Cover it with a chamber with a smaller capacity than the fuel tank and seal it.
A fuel tank airtightness inspection method comprising simultaneously reducing the pressure in the chamber and the reference container to a predetermined degree of vacuum, and then detecting the differential pressure between the chamber and the reference container to determine whether the airtightness is adequate.