FUNCTIONAL TESTING OF A LEAK DETECTION DEVICE FOR THE SEAL TESTING OF A TEST FILLED WITH A LIQUID

Description

[0001] The invention relates to a device and a method for functional testing of a leak detection device for the leak test of a test object filled with a liquid.

[0002] It is known to perform leak detection on a test specimen filled with a liquid, such as a battery, to test its tightness. Typically, with such test specimens, no gas present within the specimen is available as a test gas, and the specimen cannot or should not be actively filled with a separate test gas. This is the case, for example, with batteries filled with electrolyte fluids, such as an electrolyte-filled lithium-ion battery, where the electrolyte contains dimethyl carbonate as a key component.

[0003] Leak detection of such test specimens is based on the principle of detecting, using a detector, any liquid particles within the specimen that leak out through a leak. For leak testing, the specimen is placed in a vacuum chamber. Any liquid that has leaked from the specimen is continuously extracted from the chamber by a vacuum pump and fed to a suitable sensor.

[0004] In the refrigeration and air conditioning industry, it is common practice to test components filled with liquid refrigerant – such as heat exchangers – for leaks. A special feature of these components is that the liquid refrigerant is contained within the component under positive pressure to maintain its liquid phase. To leak test such components, a sniffer probe is guided along the areas of the component being tested. This probe draws in refrigerant escaping from a leak into the atmosphere, which then evaporates, and feeds it to a gas detector. The sniffer probe draws in air from the surrounding area and detects any escaping leakage gas. This gas is selectively detected by a sensor and distinguished from the components of the air being drawn in.

[0005] For a test object filled with a liquid whose internal pressure is lower than the atmospheric pressure in the external environment (e.g., an internal pressure in the range of approximately 50–500 mbar), the sniffer leak detection method is not applicable because no leakage gas escapes to the outside in the event of a leak. For example, in batteries filled with a liquid electrolyte with a low vapor pressure and operating under negative pressure, air from the external environment enters the test object in the event of a leak. The leak cannot be detected using a sniffer probe.

[0006] Conventional calibration devices or leak test devices cannot be used to verify the functionality of a leak detection device of the type described above. Conventional leak test devices are based on the principle of storing the test fluid in a reservoir and drawing it out of the reservoir through a capillary or membrane. However, the leak detection device in question requires a test fluid with a low vapor pressure of less than 500 mbar at room temperature. For example, the solvent ethylene acetate has a vapor pressure of 103 mbar at 20°C. Such test fluids cannot be introduced into the detection system in sufficient quantity through a capillary or membrane via a pressure differential.

[0007] Against this background, the invention is based on the objective of providing an improved test leak device and an improved method for functional testing of a leak detection device for the leak test of a test object filled with a liquid.

[0008] Examples of leak detection devices whose function can be tested with the test leak device and the method according to the invention are given in DE 20 2019 005 500 U1 and DE 10 2019 121 462 A1.

[0009] The test leakage device according to the invention is defined by the features of claim 1.

[0010] According to the invention, a reservoir is filled with a test fluid that has a vapor pressure of less than 500 mbar at room temperature. The reservoir has an outlet for the test fluid. The special feature of the device according to the invention is that a pump, designed to pump the test fluid from the reservoir, interacts with the reservoir in such a way that the test fluid exits the reservoir in liquid form through the outlet. With the aid of the pump, it is possible to supply even liquids with low vapor pressure to the leak detection device in sufficient quantity per pumping operation.

[0011] The pump can, for example, be a micro-dosing pump designed to deliver a flow rate of less than 100 µl, and preferably less than 100 nl, of the test fluid from the outlet per pumping cycle. The test leak device, the pump, and / or the outlet can be designed to deliver the test fluid as a spray mist from the outlet. The pump can include a piezoelectric fluid metering device for metering the flow rate to be delivered by the pump per pumping cycle.

[0012] According to the invention, the test object is a battery. The liquid within the test object and / or the test liquid is an electrolyte or a single component of an electrolyte.

[0013] The method according to the invention is defined by the features of claim 6. Accordingly, the test chamber of the leak detection device is first pressurized to a pressure lower than atmospheric pressure. Subsequently, a predetermined quantity of a test fluid, which has a vapor pressure of less than 500 mbar at room temperature, is introduced into the test chamber. The introduced quantity of the test fluid is then transported to a detector of the leak detection device and detected by the detector. The test fluid can be supplied to the detector in the form of vaporized molecular particles. Vaporization typically occurs after the test fluid exits the outlet of the test leak device. Typically, the test fluid evaporates at the outlet of the leak channel or outlet channels that form the outlet from the reservoir.

[0014] Preferably, the pump is designed to deliver a predetermined quantity of the test fluid from the outlet per delivery cycle, for example, in the form of one pump stroke. The amount of test fluid delivered per cycle should be less than 100 µl and preferably less than 100 nl. The test fluid may be in diluted form.

[0015] The test fluid can be dispensed as a spray from the outlet. Alternatively, it is conceivable that the test fluid evaporates after leaving the reservoir through the outlet and thus exists in gaseous form outside the reservoir.

[0016] The pump can be positioned between the reservoir and the outlet of the test leak device and is connected to the reservoir and the outlet via a fluid conductor.

[0017] It is conceivable that no carrier gas is supplied to the test chamber from the outside, for example, from a carrier gas source connected to the test chamber or taken from the surrounding environment. In this case, no gas flow is produced that is guided along the surface of the test specimen. Instead, the parts or particles of the test liquid, along with residual gas components, are extracted from the test chamber and fed to the detector. A carrier gas is not required in this process.

[0018] The test chamber can be designed as a rigid chamber with rigid walls. Alternatively, it can be designed as a foil chamber, characterized by having at least one flexible wall section that is drawn against the test specimen during evacuation, thus reducing the chamber's volume. Furthermore, foil chambers, especially those with walls made entirely of flexible foil, offer the advantage that the walls drawn against the test specimen support it, which is particularly beneficial for flexible specimens.

[0019] The detector features a sensor that selectively detects the parts or particles of the liquid to be detected, thereby distinguishing them from other parts or gases. The components of the leaked liquid can be in liquid form and fed to the detector. The detector must be capable of analyzing liquids and selectively detecting the liquid contained in the test specimen. The leaked liquid and the test liquid can be fed to the detector, for example, in the form of a mist or aerosol.

[0020] Alternatively, it can be provided that the liquid evaporates upon escaping from a leak in the test specimen, and the escaping liquid, in its vaporized form (i.e., in the gaseous phase), is fed to the detector. The detector must then be designed as a gas detector and be capable of analyzing gases and selectively distinguishing the liquid in the test specimen, in its gaseous phase, from other gases. Crucially, the liquid contained in the test specimen only undergoes the transition from the liquid to its gaseous phase upon leaving the test specimen, i.e., outside the test specimen or in the opening or channel of the leak. Therefore, no gas present in the test specimen is used as a test gas, because the liquid within the test specimen remains in liquid form, even if the liquid escapes through a leak and evaporates in the process.

[0021] The detector for the parts of the liquid to be detected can be a gas detector, such as a mass spectrometer, a gas chromatograph, an infrared radiation absorption detector, or a detector with chemical sensors or semiconductor sensors.

[0022] Preferably, the gas flow transporting the liquid components is only fed to the detector once a pressure limit is reached in the test chamber or in the connecting line between the test chamber and the vacuum pump that evacuates the test chamber. This pressure limit can be between approximately 2 mbar and 50 mbar and is preferably less than 20 mbar.

[0023] The vacuum pump, preferably a diaphragm pump, can be connected to the test chamber and / or to the gas line connecting the vacuum pump and the test chamber via a valve. At the start of the test chamber evacuation, the valve is closed. Upon reaching the pressure limit, the valve opens, and a partial flow reaches the detector, while the remaining main gas flow continues to be extracted by the diaphragm pump. In this way, particularly when using a diaphragm vacuum pump, an accumulation of the liquid components escaping from a leak is achieved, unlike in a conventional carrier gas method. Upon reaching the pressure limit, the accumulated liquid components are fed to the detector.

[0024] Advantageously, the test specimen is purged with a purge gas in the test chamber to remove any liquid adhering to it before the functional test is performed. Preferably, the purge of the test specimen with purge gas takes place before the actual leak detection or the functional test, e.g., before evacuating the test chamber.

[0025] It is conceivable that the components of the test fluid accumulate within the test chamber or in the connecting line during a period of time before the test fluid is supplied to the detector for analysis.

[0026] An embodiment of the invention is explained in more detail below with reference to the figures. They show: Fig. 1 is a block diagram of an embodiment of the leak detection device, and Fig. 2 is a block diagram of an embodiment of the test leak device.

[0027] In this embodiment, a test specimen 14 filled with a liquid 12 is contained in a test chamber 16. The test specimen 14 is a battery filled with a liquid electrolyte. In the present embodiments, the test chamber 16 is a conventional rigid test chamber.

[0028] The test chamber 16 is equipped with a vacuum connection 22 to which a vacuum pump 24 is connected, enabling the test chamber 16 to be evacuated. For this purpose, the vacuum pump 24 comprises at least one vacuum pump in the form of a diaphragm pump. The test chamber 16 and the vacuum pump 24 are connected to each other via a gas-conducting connecting line 26, allowing the vacuum pump 24 to extract gas from the test chamber 16 through this connecting line.

[0029] A detector 28 for analyzing and detecting components of the liquid 12 is connected to the connecting line 26 between the vacuum pump 24 and the test chamber 16. In both embodiments, the detector 28 is a selective gas detector, for example, in the form of a mass spectrometer, whose sensor selectively detects molecular particles of the liquid 12 and can distinguish them from other gases. The detector 28 is part of a mass spectrometric vacuum system 20, which includes a backing pump 19 and a high-vacuum pump 18 for evacuating the mass spectrometer 28.

[0030] The detector 28 is connected to the connecting line 26 via a gas-conducting detection line 21. The detection line 21 is equipped with a throttle 38 for throttling the gas flow branched off from the connecting line 26 and with a valve V2 for selectively closing the detection line 21. To measure the pressure within the connecting line 26, it is connected to a pressure sensor 17 via a gas-conducting connection.

[0031] Parts of the liquid 12 escape from a leak in the test specimen 14 and enter the test chamber 16. When the liquid 12 escapes from the test specimen 14, it can evaporate, so that the escaped parts of the liquid 12 may be in gaseous form.

[0032] The detector 28 is operated as a mass spectrometer in the vacuum system 20 at a pressure that is lower than the pressure inside the test chamber 16 and lower than the pressure at the connection point 40 between the connecting line 26 and the detection line 21. However, the diaphragm pump 24 used according to the invention for evacuating the test chamber 16 does not generate a high vacuum inside the test chamber 16. Rather, the diaphragm pump 24 generates a pressure in the range of a few millibars. The diaphragm pump 24 extracts any residual gas components remaining in the test chamber 16. In addition, when a pressure in the range of approximately 10 mbar is reached inside the test chamber 16, gas components desorb from the walls of the test chamber, which are also extracted by the diaphragm pump 24. These gas components, i.e.,Residual gas components from the test chamber 16 and gas components desorbing from its walls absorb portions of the liquid 12 that enter the test chamber 16 through a leak from the test specimen 14. These portions of the liquid 12 are then fed to the detector 28.

[0033] The vacuum pressure inside test chamber 16 is a few millibars after evacuation. At this pressure, the diffusion of the liquid 12 components that have escaped and evaporated from the test specimen 14 is still sluggish. The transport of these components to the detector 28 is accelerated by the gas components, without the need for a carrier gas to be supplied to test chamber 16 from the outside.

[0034] The functionality of the leak detection device is verified by the Fig. 2 The test leak device shown is tested. The leak detection device can also be calibrated using the test leak device. The test leak device has a reservoir 102 filled with a test fluid 104. In this embodiment, the test fluid is the solvent dimethyl carbonate. A pump 100 pumps the test fluid 104 from the reservoir 102 to the outlet 106 and out of the outlet 106.

[0035] Pump 100 delivers the test fluid 104 in liquid form from outlet 106. Depending on the pressure conditions in the test chamber 16, the test fluid exiting outlet 106 may form an aerosol in the form of a spray mist or evaporate and transition into the gaseous phase. The portions of the test fluid exiting outlet 106 are transported to detector 28 and analyzed by it. The measured detection signal is then correlated with the known, predetermined quantity of test fluid, thus calibrating detector 28.

[0036] It is conceivable that the liquid components that escaped from outlet 106 accumulate within test chamber 16 or within connecting line 26 before the escaped components of the test liquid 104 are fed to detector 20. For this to occur, it is conceivable that a [missing word - likely "connection point"] is located between connection point 40 and diaphragm pump 24. Fig. 1A valve (not shown) is provided which closes when sufficient vacuum pressure is reached within the test chamber 16 to cause the accumulation of the escaped liquid components within the test chamber 16 or in the connecting line 26 between the test chamber 16 and the valve (not shown) before detection takes place. Valve V2 can be opened for detection. During the accumulation phase, valve V2 can be either closed or open.

Claims

1. A test leak device for functional testing of a leak detection device for the leak test of a test specimen (14) filled with a liquid (12), wherein the test specimen (14) is a battery having an internal pressure that is lower than atmospheric pressure, characterized in that the test leak device comprises: a reservoir (102) filled with a test liquid (104), wherein the test liquid (104) has a vapor pressure of less than 500 mbar at room temperature, and the reservoir (102) comprises an outlet (106), wherein the liquid (12) is an electrolyte or solvent and / or the test liquid (104) is an electrolyte or solvent, and a pump (100) cooperating with the reservoir (102) and configured to convey the test liquid (104) from the reservoir (102) in such a way that the test liquid (104) escapes from the pump (100) through the outlet (106) in liquid form from the reservoir (102).

2. The test leak device according to claim 1, characterized in that the pump (100) is a micro-metering pump configured to deliver a flow rate of less than 100 µl and preferably less than 100 nl of the test liquid (104) from the outlet (106) per conveying operation.

3. The test leak device according to claim 1 or 2, characterized in that the test leak device, the pump (100) and / or the outlet (106) are configured to convey the test liquid (104) from the outlet (106) as spray mist.

4. The test leak device according to any one of the preceding claims, characterized in that the pump (100) comprises a piezo liquid metering device for metering the flow rate to be delivered by the pump (100) per conveying operation.

5. A method for functional testing of a leak detection device for the leak test of a test specimen (14) filled with a liquid (12), wherein the test specimen (14) is a battery having an internal pressure that is lower than atmospheric pressure, characterized in that the method comprises the following steps: evacuating a test chamber (16) of the leak detection device to a pressure lower than atmospheric pressure, delivering a predetermined amount of a test liquid (104), which has a vapor pressure of less than 500 mbar at room temperature, into the test chamber, wherein the liquid (12) is an electrolyte or solvent and / or the test liquid (104) is an electrolyte or solvent, transporting the delivered amount of test liquid (104) to a detector (28) of the leak detection device, and detecting the transported amount of test liquid (104) by means of the detector (28) for testing its functionality.

6. The method according to claim 5, characterized in that the test liquid (104) is delivered by means of a test leak device according to any one of claims 1-5.

7. The method according to any one of the preceding claims, characterized in that a flow rate of less than 100 µl and preferably less than 100 nl of the test liquid (104) is conveyed from the outlet (106) per conveying operation.

8. The method according to any one of the preceding claims, characterized in that the test liquid (104) is conveyed from the outlet (106) as spray mist.

9. The method according to any one of the preceding claims, characterized in that the test liquid (104) is drawn from the test chamber (16) together with residual gas components and / or together with gas components desorbing from a wall of the test chamber (16) and is supplied to the detector (28) without a separate carrier gas being supplied to the test chamber (16) from the outside.

10. The method according to any one of the preceding claims, characterized in that the detector (28) is a gas detector, such as a mass spectrometer, a gas chromatograph, an infrared absorption detector, or a detector with chemical or semiconductor sensors.

11. The method according to any one of the preceding claims, characterized in that the detector (28) is operated in a vacuum system with a lower pressure than the pressure within the test chamber (16).

12. The method according to any one of the preceding claims, characterized in that the test liquid (104) in the test chamber (16) or in the connecting line is accumulated during a period of time before the test liquid (104) is detected by means of the detector (28).

13. The method according to any one of the preceding claims, characterized in that the test liquid (104) is only supplied to the detector (28) if a predetermined pressure limit value is reached in the test chamber (16), wherein the pressure limit value is preferably in the range between 2-100 mbar or is less than 20 mbar.