Measuring and testing – With fluid pressure – Leakage
Reexamination Certificate
1999-11-23
2001-11-13
Larkin, Daniel S. (Department: 2856)
Measuring and testing
With fluid pressure
Leakage
C073S040000, C073S049700
Reexamination Certificate
active
06314794
ABSTRACT:
The present invention relates to checking motor vehicle heat exchangers for leaks, for the purpose of enabling heat exchangers that have leaks greater than a predetermined threshold to be discarded.
The invention can be applied to any motor vehicle heat exchanger, including radiators for cooling the engine, radiators for heating the vehicle cabin, air-air coolers for turbocharged engines, oil coolers, gasoline coolers, and in general any heat exchanger as used in a motor vehicle.
BACKGROUND OF THE INVENTION
At present, motor vehicle heat exchangers are leak-tested using various possible methods, which are selected as a function of the type of leak that is being looked for.
A first method consists in immersing the heat exchanger in a liquid such as water, in putting the air in its internal cavity under pressure, and then looking for the appearance of bubbles leaving the heat exchanger and passing through the liquid. The quality of the results achieved depends significantly on the attention of the operator. Parts that have been tested need subsequently to be dried, thereby lengthening the inspection cycle. The operations performed are not traceable.
In a second method, a determined excess pressure is established inside the internal cavity; the heat exchanger is closed and the rate at which its internal pressure varies over time is measured. If it has a leak, then the pressure drops, and by measuring the pressure drop it is possible to deduce the magnitude of the leak. That method is of limited sensitivity. A test time of about 30 seconds is required for testing a part whose inside volume is one liter and to obtain sensitivity of a few cubic centimeters per minute. The result also depends on variations in temperature and in the volume of the heat exchanger.
In a third method, a helium test is used. For this purpose, the heat exchanger for testing is placed in a leakproof enclosure connected to a helium leak detector, and the heat exchanger is connected to pressurization apparatus of the kind shown in FIG.
1
. Air pressure of the order of 2×10
3
hPa to 10×10
3
hPa, depending on the type of heat exchanger, is then established inside the internal cavity of the heat exchanger, and major leaks are looked for by measuring variation in the internal pressure of the heat exchanger. If there is no major leak, the pressure inside the heat exchanger is returned to atmospheric pressure, and then the inside air is evacuated to a low pressure, e.g. about 10 hPa, after which helium is introduced into the inside cavity of the heat exchanger up to a pressure of about 10
3
hPa. Major leaks are then looked for by using a helium leak detector to detect the temporary presence of helium around the motor vehicle heat exchanger in the leakproof test chamber. Detection must be performed for helium concentrations that are much greater than the natural concentration of helium in the air. Thereafter, helium pressure of about 2×10
3
hPa to 10×10
3
hPa is established inside the heat exchanger and small leaks are looked for by detecting the presence of helium, if any, around the motor vehicle heat exchanger in the test chamber, again at a level that is significantly greater than the natural concentration of helium in the air. Thereafter the pressure inside the internal cavity of the heat exchanger is reduced to below atmospheric pressure, the heat exchanger is disconnected, and it is withdrawn from the test chamber.
Amongst the above-mentioned methods, the helium test is the most reliable, the most accurate, and the most sensitive. Nevertheless, it suffers from various drawbacks. Firstly, it is necessary to supply the helium tracer gas, at concentrations generally of the order of 10% to 100%, and this gas is consumed. That considerably increases the cost of the test. Thereafter, after massive exposure to helium, it is necessary to leave the machine unoccupied for as long as it takes to enable it to be depolluted. Also, the test is not entirely reliable since it often leads to acceptable parts being wrongly rejected. What happens is that when a defective heat exchanger having leaks is tested, helium escapes into the test chamber. After the defective heat exchanger has been withdrawn, residual helium can remain in the test chamber, thereby disturbing subsequent leak measurements on another heat exchanger, and giving the impression that said other heat exchanger also leaks.
OBJECTS AND SUMMARY OF THE INVENTION
The problem posed by the present invention is to design a novel method and novel apparatus for leak-testing motor vehicle heat exchangers, with sensitivity that is as good as that of a conventional helium test, while avoiding the drawbacks of the cost of consuming helium, while avoiding the time the machine is out of action so as to be depolluted after being massively exposed to helium, and while avoiding erroneous rejects that can result from residual helium being detected.
To achieve these objects, and others, the invention provides a method of leak-testing motor vehicle heat exchangers, such a heat exchanger comprising a peripheral wall surrounding an internal cavity, the method comprising a step during which an appropriate pressure of air is established inside the internal cavity of the heat exchanger, an appropriate vacuum is established around the peripheral wall of the heat exchanger, and the concentration of helium around the peripheral wall of the heat exchanger is detected by means of a helium leak detector. The helium leak detector thus measures leakage from the heat exchanger by means of the natural concentration of helium present in the compressed air.
In a practical implementation, the heat exchanger is placed in a leakproof test chamber connected to the helium leak detector and connected to a pump unit for establishing said appropriate vacuum, and the internal cavity of the heat exchanger is connected to an air pressurization device for establishing said appropriate air pressure.
Advantageously, to further improve the reliability with which leaks are detected, the leakproof test chamber prevents leakproofing of a quality that is significantly better than the quality of the leakproofing to be tested on a heat exchanger.
Also, the appropriate air pressure is about 6×10
3
hPa, and the pressure of air in the appropriate vacuum is less than 10
−2
Pa, approximately. These values are given by way of indication, and depend on the required sensitivity, on the rate of testing, and on the volume of the test chamber.
Advantageously, apparatus of the invention for detecting motor vehicle heat exchanger leaks via the peripheral wall surrounding an internal cavity, comprises:
a leakproof test chamber connected to a pump unit and shaped so as to be capable of receiving and containing a heat exchanger under test;
a pressurization device and leakproof connection means to the internal cavity of the heat exchanger;
a helium leak detector connected to the leakproof test chamber;
the pressurization device being fed with air and being adapted to produce an appropriate air pressure inside the internal cavity of the heat exchanger; and
the pump unit being adapted to establish a pressure of air inside the leakproof test chamber that is less than a pressure of about 10
−2
Pa.
In practice, the pressurization device can comprise:
a source of compressed air producing, at its outlet, compressed air at an appropriate pressure;
a compressed air feed pipe connected to the outlet of the source of compressed air and provided with an inlet valve and with an outlet endpiece connectable to the heat exchanger under test; and
an air exhaust pipe fitted with an air exhaust valve and adapted to put the internal cavity of the heat exchanger selectively into communication with the outside atmosphere.
It is thus possible to use a pressurization device whose structure is particularly simple and of low cost.
To establish a vacuum around the heat exchanger under test, the leakproof test chamber can be connected to the pump unit by a pump pipe fitted with a stop valve and with a branch conne
Alcatel
Larkin Daniel S.
Sughrue Mion Zinn Macpeak & Seas, PLLC
Wiggins David J.
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