How to evaluate the airtightness of a case

Abstract

To provide a method for evaluating the airtightness of a case, which can reduce measurement errors in the amount of pressure change inside the case due to dimensional tolerances of parts provided inside the case, and perform more accurate evaluation of the airtightness. [Solution] The method for evaluating the airtightness of a case of the present invention includes a pressure measurement process in which the gas inside the case is discharged to reduce the pressure inside the case and then the pressure inside the case is stabilized, followed by measuring the amount of pressure change inside the case; a discharged gas amount acquisition process in which the amount of discharged gas, which is the amount of gas discharged from inside the case, is acquired; a process in which the measured amount of pressure change is corrected based on the acquired amount of discharged gas; and an evaluation process in which the airtightness of the case is evaluated based on the corrected amount of pressure change.

Description

[Technical Field]

[0001] The present invention relates to a method for evaluating the airtightness of a case. [Background technology]

[0002] Patent Document 1 discloses a method for evaluating the airtightness of a battery pack case by evacuating the gas inside the case to reduce the pressure, stabilizing the pressure inside the case, measuring the amount of pressure change inside the case and the amount of deformation of the case, and then correcting the amount of pressure change using the amount of deformation of the case. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-117088 Summary of the Invention [Problem to be solved by the invention]

[0004] In the technique disclosed in Patent Document 1, there is room for improvement in the method of evaluating airtightness because measurement errors occur in the amount of pressure change inside the case due to dimensional tolerances of parts provided inside the battery pack case.

[0005] The present invention has been made in consideration of the above-mentioned problems, and its object is to provide a method for evaluating the airtightness of a case that reduces measurement errors in the amount of pressure change inside the case due to dimensional tolerances of parts installed inside the case, and enables more accurate evaluation of airtightness. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems and achieve the object, the method for evaluating the airtightness of a case according to the present invention is characterized by comprising a pressure measurement process for measuring the amount of pressure change inside the case after evacuating the gas inside the case to reduce the pressure inside the case and stabilizing the pressure inside the case, an exhaust gas amount acquisition process for acquiring the amount of gas exhausted from inside the case, a process for correcting the measured amount of pressure change based on the acquired amount of exhaust gas, and an evaluation process for evaluating the airtightness of the case based on the corrected amount of pressure change.

[0007] As a result, in the method for evaluating the airtightness of a case according to the present invention, it is possible to reduce measurement errors in the amount of pressure change inside the case caused by dimensional tolerances of parts installed inside the case, and perform a more accurate evaluation of the airtightness.

[0008] In the above, the amount of exhaust gas may be measured using a flow meter provided in an exhaust pipe of the vacuum pump when the vacuum pump is operated to exhaust gas from inside the case.

[0009] This allows the flow meter to measure the actual amount of gas being discharged when the vacuum pump is operated to discharge gas from the case. [Effects of the Invention]

[0010] The method for evaluating the airtightness of a case according to the present invention makes it possible to evaluate the airtightness of the case using the amount of pressure change inside the case corrected using the amount of gas discharged from inside the case. Therefore, the method for evaluating the airtightness of a case according to the present invention has the effect of reducing measurement errors in the amount of pressure change inside the case caused by dimensional tolerances of parts installed inside the case, and enabling a more accurate evaluation of airtightness. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram showing a schematic configuration of an evaluation device to which a method for evaluating the airtightness of a case according to an embodiment is applied. [Figure 2]FIG. 2 is a block diagram showing the configuration of the main part of the evaluation device according to the embodiment. [Figure 3] FIG. 3 is a block diagram illustrating an example of a functional configuration of a control device included in the evaluation device according to the embodiment. [Figure 4] FIG. 4 is a diagram showing an example of a method for calculating the amount of exhaust gas. [Figure 5] FIG. 5 is a flowchart showing an example of the flow of processing executed by the control device of the evaluation device according to the embodiment. [Figure 6] FIG. 6 is an explanatory diagram of the amount of change in volume inside a battery case when a first component and a second component that are the same components but have different dimensional tolerances are provided inside the battery case. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the method for evaluating the airtightness of a case according to the present invention will be described, although the present invention is not limited to this embodiment.

[0013] Fig. 1 is a diagram showing a schematic configuration of an evaluation device 1 to which a method for evaluating the airtightness of a case according to an embodiment is applied. Fig. 2 is a block diagram showing the configuration of a main part of the evaluation device 1 according to an embodiment. Fig. 3 is a block diagram showing an example of the functional configuration of a control device 13 included in the evaluation device 1 according to an embodiment.

[0014] 1, an evaluation device 1 according to the embodiment includes a leak tester 10, a master chamber 11, a vacuum pump 12, and a control device 13. The evaluation device 1 is a device that evaluates the airtightness of a battery case 40 of a battery pack 4 using the method for evaluating the airtightness of a case according to the embodiment. In this embodiment, the evaluation device 1 is used to evaluate the airtightness of the battery case 40 of the battery pack 4.

[0015] The battery pack 4 is mounted, for example, under the floor of the vehicle and supplies power to a motor that drives the vehicle. The battery pack 4 contains a flat, long, box-shaped battery case 40, which houses a plurality of battery modules (not shown), a battery ECU (Electronic Control Unit), a thermistor, and other components (not shown). Each battery module is formed by electrically connecting a plurality of batteries (battery cells), such as lithium-ion batteries. To grasp the status of each battery module, the battery ECU measures the voltage, current, temperature, and other parameters of each battery module and monitors the input and output to each battery module.

[0016] The battery case 40 includes a lower case having a box-like shape with an open top and an upper case having a box-like shape with an open bottom. The lower case is made of a light metal such as an aluminum alloy. The upper case is made of a resin, for example. The lower case and the upper case have flanges at the open ends thereof that overlap each other, and the flanges are fixed to each other by bolts or the like. One longitudinal end of the lower case (the front end when mounted on a vehicle) is provided with a plurality of connectors 41. These connectors 41 are, for example, female connectors. When evaluating the airtightness of the battery case 40, a jig manufactured using a male connector is attached to each of the connectors 41. This seals each connector 41.

[0017] The leak tester 10, the master chamber 11, and the vacuum pump 12 constitute a pressure measurement unit in the evaluation device 1. In the evaluation device 1, a pressure measurement process is performed using the leak tester 10, the master chamber 11, and the vacuum pump 12. The leak tester 10 is connected to the master chamber 11 via a pipe 20. The master chamber 11 is configured to be highly airtight. The leak tester 10 is also connected to the vacuum pump 12 via a pipe 21. One end of a pipe 22 that communicates with the pipe 20 via the leak tester 10 is connected to the leak tester 10. The other end of the pipe 22 is connected to a work connection jig 5. The work connection jig 5 is configured to be connected to a battery case 40, which is a work. In the present embodiment, as an example, the work connection jig 5 is connected to one longitudinal end of a lower case of the battery case 40. One end of a pipe 23 that communicates with the pipe 21 via the leak tester 10 is also connected to the leak tester 10. The other end of the pipe 22 is connected to the pipe 22. A flow meter 6 is provided in the exhaust pipe 70 of the vacuum pump 12.

[0018] Furthermore, valves, differential pressure sensors, and the like (not shown) are provided within the leak tester 10. When using the leak tester 10 or the like to test the airtightness (air leakage) of the battery case 40, the vacuum pump 12 is first operated to exhaust the air from the battery case 40 and the master chamber 11, thereby reducing the pressure within the battery case 40 and the master chamber 11. Next, the vacuum pump 12 is isolated from the battery case 40 and the master chamber 11, respectively, and the pressure within the battery case 40 and the master chamber 11 is stabilized. Next, the battery case 40 is isolated from the master chamber 11, and the test is held until the pressure within the battery case 40 stabilizes. Next, the differential pressure between the pressure within the battery case 40 and the pressure within the master chamber 11 is measured by a differential pressure sensor provided in the leak tester 10. The differential pressure measured by the differential pressure sensor is recognized as the amount of pressure change within the battery case 40.

[0019] Then, if the differential pressure is ΔP [Pa], the time taken for measuring the differential pressure by the differential pressure sensor is T [sec], and Ve is the equivalent internal volume [ml], the amount of air leaking from the battery case 40, Q [ml / min], can be calculated using the following equation (1):

[0020] Q=Ve×{ΔP / (1.012×105)}×(60 / T)···(1)

[0021] The equivalent internal volume Ve is a coefficient that takes into consideration the influence of pressure fluctuation factors (volume changes due to the internal pressure of the battery case 40 and the differential pressure sensor) in the entire measurement system, including the workpiece battery case 40 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.

[0022] The leak tester 10 is electrically connected to the control device 13 via wiring 30 so as to be able to communicate with each other. As shown in Fig. 2, 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 (Interface) 135. The CPU 131, the ROM 132, the RAM 133, the storage unit 134, and the input / output I / F 135 are connected to each other via a bus 136 so as to be able to communicate with each other.

[0023] The CPU 131 is a central processing unit that executes various programs and controls each part. That is, the CPU 131 reads the programs from the ROM 132 and executes the programs using the RAM 133 as a work area. As a result, the control device 13 functions as an exhaust gas amount acquisition unit 1301, a correction unit 1302, and an evaluation unit 1303 shown in FIG. 3. In this embodiment, various programs and various data are stored in the ROM 132. The storage unit 134 is configured by an HDD (Hard Disk Drive) or an SSD (Solid State Drive), and stores various programs and various data including an operating system.

[0024] The input / output I / F 135 is electrically connected to the leak tester 10, the vacuum pump 12, a user I / F 137, a flow meter 6, and the like. The user I / F 137 includes, for example, a display which is a display device (not shown) and a keyboard which is an input device (not shown). Note that the user I / F 137 is not shown in FIG. 1. Also, in FIG. 1, the control device 13 and the flow meter 6 are electrically connected to each other via a wiring 31 so as to be able to communicate with each other.

[0025] The control device 13 functions as a discharged gas amount acquisition unit 1301, a correction unit 1302, and an evaluation unit 1303 by the CPU 131 executing a program. The discharged gas amount acquisition unit 1301 performs a discharged gas amount acquisition step, the correction unit 1302 performs a correction step, and the evaluation unit 1303 performs an evaluation step. Specifically, as shown in FIG. 4 , the discharged gas amount acquisition unit 1301 acquires the amount of discharged gas as the total amount of gas discharged from the battery case 40 from the time T1 during which gas is discharged from the battery case 40 by the vacuum pump 12 and the amount of discharged gas per unit time measured by the flow meter 6. The correction unit 1302 corrects the amount of pressure change measured by the leak tester 10 based on the amount of gas discharged from the battery case 40 acquired by the discharged gas amount acquisition unit 1301. The evaluation unit 1303 evaluates the airtightness (air leakage) of the battery case 40 based on the amount of pressure change corrected by the correction unit 1302.

[0026] The correction unit 1302 calculates a corrected pressure change amount by subtracting a value obtained by multiplying the amount of gas discharged from the battery case 40 acquired by the discharged gas amount acquisition unit 1301 by a predetermined correction coefficient from the amount of pressure change (pressure fluctuation) measured by the leak tester 10. Specifically, if the amount of pressure change measured by the leak tester 10 is ΔP, the amount of gas discharged from the battery case 40 acquired by the discharged gas amount acquisition unit 1301 is L, the amount of corrected pressure change is ΔP', and the correction coefficient is α, the correction unit 1302 calculates the corrected pressure change amount ΔP' as ΔP' = ΔP - α × L. The correction coefficient α is determined by confirming the correlation between the amount of pressure change in the battery case 40 and the amount of gas discharged from the battery case 40 by, for example, measuring the actual battery case 40. This correction coefficient α is determined, for example, as the slope of a graph plotting data on the amount of pressure change inside the battery case 40 and the amount of gas discharged from the battery case 40, obtained by measuring the actual battery case 40.

[0027] The evaluation unit 1303 evaluates the airtightness (air leakage) of the battery case 40 by determining whether the corrected pressure change amount ΔP' is less than a preset specified value. Specifically, if the corrected pressure change amount ΔP' is less than the specified value, the evaluation unit 1303 evaluates that the airtightness of the battery case 40 is ensured. On the other hand, if the corrected pressure change amount ΔP' is equal to or greater than the specified value, the evaluation unit 1303 evaluates that the airtightness of the battery case 40 is not ensured.

[0028] Fig. 5 is a flowchart showing an example of the flow of processing executed by the control device 13 of the evaluation device 1 according to the embodiment. Next, the flow of control in the control device 13 will be described with reference to Fig. 5. The CPU 131 of the control device 13 starts executing a program when, for example, a switch (not shown) provided in the user I / F 137 is turned on. In this program, the CPU 131 performs a pressure measurement process in steps S1 to S4, a discharge gas amount acquisition process in step S5, a correction process in step S7, and an evaluation process in step S8 in the control flow shown in Fig. 5.

[0029] First, in step S1, the CPU 131 activates the vacuum pump 12 to exhaust the air in the battery case 40 and the air in the master chamber 11, thereby reducing the pressure inside the battery case 40 and the master chamber 11.

[0030] Next, in step S2, CPU 131 controls and closes valves (not shown) of leak tester 10 to isolate the interior of battery case 40 and the interior of master chamber 11 from vacuum pump 12. As a result, in step S2, the pressure in battery case 40 and the pressure in master chamber 11 are equalized (stabilized).

[0031] Next, in step S3, the CPU 131 controls and closes a valve (not shown) of the leak tester 10, disconnecting the interior of the battery case 40 from the interior of the master chamber 11, and waits until the pressure inside the battery case 40 stabilizes (reaches an equilibrium state). At this time, if there is an air leak in the battery case 40, the air inside the battery case 40 will escape from that leak point, causing the pressure inside the battery case 40 to decrease.

[0032] Next, in step S4, the CPU 131 measures the differential pressure between the pressure inside the battery case 40 and the pressure inside the master chamber 11, that is, the amount of pressure change ΔP (pressure change) inside the battery case 40, using the differential pressure sensor provided in the leak tester 10.

[0033] Next, in step S5, the CPU 131 operates the vacuum pump 12 to acquire the exhaust gas amount L, which is the amount of air exhausted from the battery case 40. Specifically, the CPU 131 acquires the exhaust gas amount L, which is the amount of air exhausted, measured by the flow meter 6 while the vacuum pump 12 is exhausting air from the battery case 40.

[0034] Next, in step S6, the CPU 131 completes the measurement of the pressure change amount ΔP and the acquisition of the amount of gas L discharged from the battery case 40.

[0035] Next, in step S7, the CPU 131 calculates a corrected amount of pressure change ΔP′ by subtracting the value obtained by multiplying the amount of exhaust gas L and the correction coefficient α from the amount of pressure change ΔP.

[0036] Next, in step S8, the CPU 131 determines whether the corrected pressure change amount ΔP′ is less than a preset specified value, and evaluates the airtightness of the battery case 40. When the processing in step S8 is completed, the execution of this program is terminated.

[0037] As described above, in the method for evaluating the airtightness of a case according to the embodiment, it is possible to evaluate the airtightness of the battery case 40 using the corrected pressure change amount ΔP' inside the battery case 40, which is corrected using the amount of gas L discharged from inside the battery case 40.

[0038] For example, as shown in FIGS. 6( a) and 6(b), a first component 81 and a second component 82, which are the same but have different dimensional tolerances, are provided in a battery case 40 of a battery pack 4. Note that in FIGS. 6(a) and 6(b), the difference in size between the first component 81 and the second component 82 is exaggerated to make it easier to understand the difference in dimensional tolerance between the first component 81 and the second component 82. By evacuating air from the battery case 40 in each of FIGS. 6(a) and 6(b) to reduce the pressure, the top plate 401 of the battery case 40 is deformed to be recessed, resulting in a change in volume within the battery case 40. In this case, if the amount of recession (deformation) of the top plate 401 is the same in FIGS. 6(a) and 6(b), the change in volume within the battery case 40 must take into account the respective volumes of the first component 81 and the second component 82 within the battery case 40, relative to the change in pressure ΔP within the battery case 40 before and after the deformation of the top plate 401. The measurement error in the amount of pressure change ΔP inside the battery case 40 between when the volumes of the first part 81 and the second part 82 inside the battery case 40 are taken into account and when they are not is directly reflected by the dimensional tolerances of the first part 81 and the second part 82. The amount of gas L discharged from inside the battery case 40 changes depending on the dimensional tolerances of the first part 81 and the second part 82, even if the amount of depression (amount of deformation) of the top plate 401 is the same.

[0039] Therefore, in the method for evaluating the airtightness of a case according to the embodiment, the airtightness of the battery case 40 is evaluated using a corrected pressure change amount ΔP' corrected using the amount of gas L discharged from inside the battery case 40. As a result, the method for evaluating the airtightness of a case according to the embodiment reduces measurement errors in the pressure change amount ΔP inside the battery case 40 caused by dimensional tolerances of the components inside the battery case 40, and enables more accurate evaluation of the airtightness of the battery pack 4. [Explanation of symbols]

[0040] 1 Evaluation device 4 Battery pack 5 Workpiece connection jig 6 Flow Meter 10 Leak Tester 11 Master Chamber 12 Vacuum pump 13 Control device 20, 21, 22, 23 Piping 30,31 Wiring 40 Battery case 41 Connector 70 Exhaust pipe 81 First Part 82 Second part 131 CPU 132 ROM 133 RAM 134 Storage section 135 Input / Output Interface 136 Bus 137 User Interface 401 Top plate 1301 Exhaust gas amount acquisition unit 1302 Correction Unit 1303 Evaluation Department

Claims

1. a pressure measurement step of evacuating the gas inside the case to reduce the pressure inside the case, stabilizing the pressure inside the case, and then measuring a pressure change amount inside the case; a discharged gas amount acquiring step of acquiring a discharged gas amount, which is the amount of the gas discharged from the case; correcting the measured amount of pressure change based on the acquired amount of exhaust gas; an evaluation step of evaluating the airtightness of the case based on the corrected amount of pressure change; A method for evaluating the airtightness of a case, comprising:

2. 2. The method for evaluating the airtightness of a case according to claim 1, wherein the amount of exhausted gas is measured using a flow meter provided in an exhaust pipe of the vacuum pump when the vacuum pump is operated to exhaust gas from inside the case.

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