Method for evaluating airtightness of housing

Abstract

The invention provides a method for evaluating the airtightness of a housing, which can reduce the measurement error of the pressure change amount in the housing caused by the dimensional tolerance of components arranged in the housing, and can more accurately evaluate the airtightness. This method for evaluating the airtightness of a case comprises: a pressure measurement step for discharging gas in the case, decompressing the inside of the case, stabilizing the pressure in the case, and then measuring the amount of change in the pressure in the case; a discharged gas amount acquisition step for acquiring a discharged gas amount, which is the amount of gas discharged from the inside of the housing; a correction step for correcting the measured pressure change amount on the basis of the acquired exhaust gas amount; and an evaluation step for evaluating the airtightness of the case on the basis of the corrected pressure change amount.

Description

Technical Field

[0001] This invention relates to a method for evaluating the airtightness of a casing. Background Technology

[0002] Patent document 1 discloses the following method: the gas inside the battery pack casing is discharged to reduce the pressure, and after the pressure inside the casing is stabilized, the pressure change inside the casing is measured and the deformation of the casing is measured. The airtightness of the casing is evaluated based on the pressure change corrected by the deformation of the casing.

[0003] Existing technical documents

[0004] Patent Document 1: Japanese Patent Application Publication No. 2021-117088 Summary of the Invention

[0005] The problem that the invention aims to solve

[0006] In the technology disclosed in Patent Document 1, there is a measurement error in the amount of pressure change inside the housing caused by the dimensional tolerance of the components installed inside the housing of the battery pack, so there is room for improvement in the method of evaluating airtightness.

[0007] The present invention was made in view of the above-mentioned problems, and its purpose is to provide a method for evaluating the airtightness of a housing, which can reduce the measurement error of the pressure change in the housing caused by the dimensional tolerance of the components installed in the housing, and make a more accurate evaluation of the airtightness.

[0008] Methods for solving problems

[0009] To address the aforementioned issues and achieve the objective, the method for evaluating the airtightness of a housing according to the present invention is characterized by comprising: a pressure measurement step, wherein gas is discharged from the housing to reduce the pressure inside the housing, and after the pressure inside the housing is stabilized, the pressure change inside the housing is measured; a gas discharge amount acquisition step, wherein the amount of gas discharged from the housing is acquired; a correction step, wherein the measured pressure change is corrected based on the acquired gas discharge amount; and an evaluation step, wherein the airtightness of the housing is evaluated based on the corrected pressure change.

[0010] Therefore, in the airtightness evaluation method of the housing of the present invention, the measurement error of the pressure change in the housing caused by the dimensional tolerance of the components installed in the housing can be reduced, and a more accurate airtightness evaluation can be performed.

[0011] Alternatively, as described above, the amount of gas discharged can be measured using a flow meter installed in the exhaust pipe of the vacuum pump while the vacuum pump is operating and gas is being discharged from the housing.

[0012] Therefore, the actual amount of gas discharged when the vacuum pump is working and gas is being discharged from the housing can be measured by a flow meter.

[0013] Invention Effects

[0014] In the airtightness evaluation method of the housing of the present invention, the airtightness of the housing can be evaluated using the pressure change within the housing after correction for the amount of gas discharged from the housing. Therefore, the airtightness evaluation method of the housing of the present invention has the following effect: it can reduce the measurement error of the pressure change within the housing caused by the dimensional tolerance of the components installed within the housing, and perform a more accurate airtightness evaluation. Attached Figure Description

[0015] Figure 1 This is a diagram showing the schematic structure of an evaluation device for evaluating the airtightness of a housing according to an application implementation method.

[0016] Figure 2 This is a block diagram showing the structure of the main parts of the evaluation device for the implementation method.

[0017] Figure 3 This is a block diagram illustrating an example of the functional structure of the control device included in the evaluation device of the implementation method.

[0018] Figure 4 This is a diagram illustrating an example of a method for calculating the amount of gas discharged.

[0019] Figure 5 This is a flowchart illustrating an example of the processing flow performed by the control device of the evaluation apparatus of the embodiment.

[0020] Figure 6 This is an explanatory diagram regarding the volume change within a battery casing when a first and a second component, which are identical but have different dimensional tolerances, are provided inside the battery casing. Detailed Implementation

[0021] The following describes an embodiment of the method for evaluating the airtightness of the housing according to the present invention. However, the present invention is not limited to this embodiment.

[0022] Figure 1 This is a diagram showing the schematic structure of the evaluation device 1, which is an evaluation method for evaluating the airtightness of the housing in an application implementation. Figure 2 This is a block diagram showing the structure of the main parts of the evaluation device 1 in the implementation method. Figure 3 This is a block diagram illustrating an example of the functional structure of the control device 13 included in the evaluation device 1 of the embodiment.

[0023] like Figure 1As shown, the evaluation device 1 of this embodiment includes a leak tester 10, a main chamber 11, a vacuum pump 12, and a control device 13. The evaluation device 1 is an apparatus for evaluating the airtightness of the battery casing 40 of the battery pack 4 using the airtightness evaluation method of the casing of this embodiment. In this embodiment, the evaluation device 1 is used to evaluate the airtightness of the battery casing 40 of the battery pack 4.

[0024] Battery pack 4 is mounted, for example, under the floor of the vehicle, supplying power to the motor that powers the vehicle. Within battery pack 4, a flat, elongated, box-shaped battery casing 40 houses multiple battery modules (not shown), a battery ECU (Electronic Control Unit) (not shown), a thermistor, etc. Each battery module is, for example, composed of multiple lithium-ion batteries (battery cells) electrically connected to each other. The battery ECU measures the voltage, current, and temperature of each battery module to monitor its status and inputs / outputs.

[0025] The battery housing 40 has a box-shaped lower housing open on the upper side and a box-shaped upper housing open on the lower side. The lower housing is made of a light metal, such as aluminum alloy. The upper housing is made of resin, for example. The flanges at the open ends of the lower and upper housings overlap each other and are fixed together by bolts or the like. A plurality of connectors 41 are provided at one end of the lower housing in the longitudinal direction (the front end in the vehicle-mounted state). These connectors 41 are, for example, female connectors. When evaluating the airtightness of the battery housing 40, clamps, for example, made using male connectors, are installed on each of these connectors 41. Thus, each connector 41 is sealed.

[0026] Leak tester 10, main chamber 11, and vacuum pump 12 constitute the pressure measuring unit in evaluation device 1. In evaluation device 1, the pressure measuring process is performed using leak tester 10, main chamber 11, and vacuum pump 12. Leak tester 10 is connected to main chamber 11 via piping 20. Main chamber 11 has a highly airtight structure. Leak tester 10 is also connected to vacuum pump 12 via piping 21. One end of piping 22, which communicates with piping 20, is connected to leak tester 10. The other end of piping 22 is connected to workpiece connecting fixture 5. Workpiece connecting fixture 5 is configured to connect to battery casing 40, which is the workpiece. In this embodiment, as an example, workpiece connecting fixture 5 is connected to one end of the lower casing of battery casing 40 along its length. Leak tester 10 is also connected to one end of piping 23, which communicates with piping 21. The other end of piping 23 is connected to piping 22. A flow meter 6 is installed in the exhaust pipe 70 of the vacuum pump 12.

[0027] Additionally, a valve (not shown) and a differential pressure sensor are installed within the leak tester 10. When checking the airtightness (air leakage) of the battery casing 40 using the leak tester 10, the vacuum pump 12 first operates to expel air from the battery casing 40 and the main chamber 11, thus reducing the pressure inside the battery casing 40 and the main chamber 11. Next, the vacuum pump 12 is disconnected from both the battery casing 40 and the main chamber 11, stabilizing the pressure within both chambers. Then, the battery casing 40 is disconnected from the main chamber 11, and the system remains idle until the pressure inside the battery casing 40 stabilizes. The differential pressure between the battery casing 40 and the main chamber 11 is then measured by the differential pressure sensor installed in the leak tester 10. The differential pressure measured by the differential pressure sensor is recorded as the pressure change within the battery casing 40.

[0028] Furthermore, with the differential pressure set to ΔP [Pa], the differential pressure sensor measurement time for the differential pressure set to T [sec], and Ve set to the equivalent internal volume [ml], the air leakage Q [ml / min] from the battery casing 40 can be calculated using the following equation (1).

[0029] Q=Ve×{ΔP / (1.012×105)}×(60 / T)····(1)

[0030] Furthermore, the equivalent internal volume Ve is a coefficient that takes into account the effects of pressure variation factors (volume changes caused by the internal pressure of the battery housing 40 and the differential pressure sensor) of the entire measurement system, including the battery housing 40 as a workpiece and the leak tester 10. This equivalent internal volume Ve is measured, for example, by a dedicated measuring unit provided in the leak tester 10.

[0031] Leakage tester 10 is electrically connected to control device 13 via wiring 30 in a communicative manner. For example... Figure 2 As shown, the control device 13 includes a CPU (Central Processing Unit) 131, a ROM (Read Only Memory) 132, a RAM (Random Access Memory) 133, a storage unit 134, and an input / output (I / F) 135. The CPU 131, ROM 132, RAM 133, storage unit 134, and I / F 135 are connected to each other via a bus 136 in a manner that enables communication.

[0032] CPU 131 is the central processing unit, executing various programs and controlling various components. Specifically, CPU 131 reads programs from ROM 132 and uses RAM 133 as the operating area to execute the programs. Thus, control device 13 acts as... Figure 3 The exhaust gas volume acquisition unit 1301, correction unit 1302, and evaluation unit 1303 shown in the diagram function as follows. In this embodiment, the ROM 132 stores various programs and various data. The storage unit 134 is composed of an HDD (Hard Disk Drive) or SSD (Solid State Drive), etc., and stores various programs including the operating system and various data.

[0033] The input / output I / F 135 is electrically connected to a leak tester 10, a vacuum pump 12, a user I / F 137, and a flow meter 6, etc. The user I / F 137 includes, for example, a display (not shown) and a keyboard (not shown) as input devices. Additionally, in... Figure 1 The illustration of user I / F 137 has been omitted. Additionally, in... Figure 1 In the middle, the control device 13 and the flow meter 6 are electrically connected in a communicative manner via wiring 31.

[0034] The control device 13 functions as an exhaust gas quantity acquisition unit 1301, a correction unit 1302, and an evaluation unit 1303 by executing a program via the CPU 131. The exhaust gas quantity acquisition unit 1301 performs an exhaust gas quantity acquisition process, the correction unit 1302 performs a correction process, and the evaluation unit 1303 performs an evaluation process. Specifically, as follows... Figure 4 As shown, the exhaust gas acquisition unit 1301 acquires the exhaust gas volume as the total amount of gas exhausted from the battery housing 40 based on the time T1 during which gas is exhausted from the battery housing 40 by the vacuum pump 12 and the exhaust gas volume per unit time measured by the flow meter 6. The correction unit 1302 corrects the pressure change measured by the leak tester 10 based on the exhaust gas volume acquired by the exhaust gas acquisition unit 1301. The evaluation unit 1303 evaluates the airtightness (air leakage) of the battery housing 40 based on the pressure change corrected by the correction unit 1302.

[0035] In the correction unit 1302, the pressure change (pressure fluctuation) measured from the leak tester 10 is subtracted from the amount of gas discharged from the battery casing 40 obtained by the gas discharge acquisition unit 1301 multiplied by a predetermined correction factor. This yields the corrected pressure change, or the corrected pressure change. Specifically, when the pressure change measured by the leak tester 10 is set as ΔP, the amount of gas discharged from the gas discharge acquisition unit 1301 is set as L, the corrected pressure change is set as ΔP', and the correction factor is set as α, the correction unit 1302 calculates the corrected pressure change ΔP' as ΔP' = ΔP - α × L. The correction factor α is determined by confirming the correlation between the pressure change within the battery casing 40 and the amount of gas discharged from the battery casing 40 through measurements of an actual battery casing 40. The correction factor α is, for example, determined by the slope of a plotted curve obtained from actual measurements using the battery housing 40, which plots the pressure change within the battery housing 40 and the amount of gas discharged from the battery housing 40.

[0036] In the evaluation unit 1303, the airtightness (air leakage) of the battery casing 40 is evaluated by determining whether the corrected pressure change ΔP' is less than a preset predetermined value. Specifically, if the corrected pressure change ΔP' is less than the predetermined value, the evaluation unit 1303 evaluates that the airtightness of the battery casing 40 is ensured. On the other hand, if the corrected pressure change ΔP' is greater than or equal to the predetermined value, the evaluation unit 1303 evaluates that the airtightness of the battery casing 40 is not ensured.

[0037] Figure 5 This is a flowchart illustrating an example of the processing flow performed by the control device 13 of the evaluation device 1 in the embodiment. Next, using Figure 5 The control flow in control device 13 will be described. For example, when a switch (not shown) set in user I / F 137 is turned on, the CPU 131 of control device 13 begins program execution. In this program, the CPU 131... Figure 5 In the control flow shown, the pressure measurement process is performed in steps S1 to S4, the exhaust gas volume acquisition process is performed in step S5, the correction process is performed in step S7, and the evaluation process is performed in step S8.

[0038] First, in step S1, the CPU 131 activates the vacuum pump 12 to expel the air inside the battery housing 40 and the main chamber 11, thereby reducing the pressure inside the battery housing 40 and the main chamber 11.

[0039] Next, in step S2, the CPU 131 controls the valve (not shown) of the leak tester 10 to close, disconnecting the battery housing 40 and the main chamber 11 from the vacuum pump 12. Thus, in step S2, the pressure inside the battery housing 40 and the pressure inside the main chamber 11 are made equal (stabilized).

[0040] Next, in step S3, the CPU 131 controls the valve (not shown) of the leak tester 10 to close, disconnecting the battery housing 40 from the main chamber 11, and waits until the pressure inside the battery housing 40 stabilizes (becomes in an equilibrium state). At this time, if there is an air leak in the battery housing 40, the air inside the battery housing 40 leaks from that location, thereby reducing the pressure inside the battery housing 40.

[0041] Next, in step S4, the CPU 131 measures the pressure difference between the pressure inside the battery casing 40 and the pressure inside the main chamber 11, i.e., the pressure change ΔP (pressure change) inside the battery casing 40, using the differential pressure sensor of the leak tester 10.

[0042] Next, in step S5, the CPU 131 activates the vacuum pump 12 to obtain the amount of air discharged from the battery casing 40, i.e., the discharged gas volume L. Specifically, the CPU 131 obtains the amount of air discharged, i.e., the discharged gas volume L, measured by the flow meter 6 during the process of venting air from the battery casing 40 using the vacuum pump 12.

[0043] Next, in step S6, the CPU 131 completes the measurement of the pressure change ΔP and the acquisition of the amount of gas L discharged from the battery casing 40.

[0044] Next, in step S7, CPU 131 calculates the corrected pressure change ΔP' by subtracting the value obtained by multiplying the discharged gas volume L by the correction coefficient α from the pressure change ΔP.

[0045] Next, in step S8, the CPU 131 determines whether the corrected pressure change ΔP' is less than a preset value and evaluates the airtightness of the battery casing 40. When the processing in step S8 is completed, the execution of this program ends.

[0046] In the above-described method for evaluating the airtightness of the housing in the embodiment, the airtightness of the battery housing 40 can be evaluated using the corrected pressure change ΔP' within the battery housing 40 after being corrected by the amount of gas discharged from the battery housing 40 L.

[0047] For example, such as Figure 6 (a) and Figure 6As shown in (b), a first component 81 and a second component 82, which are identical but have different dimensional tolerances, are provided inside the battery casing 40 of the battery pack 4. Furthermore, in Figure 6 (a) and Figure 6 In (b), to easily understand the difference in dimensional tolerances between the first component 81 and the second component 82, the dimensional difference between the first component 81 and the second component 82 is exaggerated. Furthermore, because from... Figure 6 (a) and Figure 6 (b) Air is expelled from each of the battery casings 40, reducing pressure, and the top plate 401 of the battery casing 40 deforms in a concave manner, causing a volume change within the battery casing 40. At this time, in Figure 6 (a) and Figure 6 In (b), when the amount of indentation (deformation) of the top plate 401 is the same, for the pressure change ΔP inside the battery casing 40 before and after the deformation of the top plate 401, it is necessary to consider the volumes of the first component 81 and the second component 82 occupying within the battery casing 40 in the volume change within the battery casing 40. The measurement error of the pressure change ΔP inside the battery casing 40 when the volumes of the first component 81 and the second component 82 within the battery casing 40 are not considered, and when they are considered, directly reflects the dimensional tolerances of the first component 81 and the second component 82. Furthermore, even if the amount of indentation (deformation) of the top plate 401 is the same, the amount of gas discharged from the battery casing 40, L, varies according to the dimensional tolerances of the first component 81 and the second component 82.

[0048] Therefore, in the airtightness evaluation method of the casing according to the embodiment, the airtightness of the battery casing 40 is evaluated using the corrected pressure change ΔP', which is corrected by the amount of gas discharged from the battery casing 40. Thus, the airtightness evaluation method of the casing according to the embodiment can reduce the measurement error of the pressure change ΔP within the battery casing 40 caused by the dimensional tolerances of the components within the battery casing 40, and perform a more accurate evaluation of the airtightness of the battery pack 4.

[0049] Explanation of reference numerals in the attached figures

[0050] 1 Evaluation device 4 Battery pack 5 Workpiece connecting fixture 6 Flow meter 10 Leak tester 11 Main chamber 12 Vacuum pump 13 Control device 20, 21, 22, 23 Piping 30, 31 Wiring 40 Battery housing 41 Connector 70 Exhaust pipe 81 First component 82 Second component 131 CPU 132 ROM 133 RAM 134 Storage unit 135 Input / output (I / F) 136 Bus 137 User I / F 401 Top plate 1301 Exhaust gas volume acquisition unit 1302 Correction unit 1303 Evaluation unit

Claims

1. A method for evaluating the airtightness of a shell, characterized in that, include: In the pressure measurement process, the gas inside the housing is discharged to reduce the pressure inside the housing. After the pressure inside the housing is stabilized, the pressure change inside the housing is measured. The process of obtaining the amount of discharged gas involves obtaining the amount of discharged gas as the amount of gas discharged from the housing. The correction process involves correcting the measured pressure change based on the obtained amount of discharged gas. as well as The evaluation process assesses the airtightness of the housing based on the corrected pressure change.

2. The method for evaluating the airtightness of the shell according to claim 1, characterized in that, During the operation of the vacuum pump, which is discharging gas from the housing, the amount of gas discharged is measured using a flow meter located in the exhaust pipe of the vacuum pump.

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