Battery housing and method for testing leak tightness

Abstract

The invention relates to a battery housing (3) for a traction battery (1), comprising at least two housing parts (4, 5) which surround an inner volume, connection elements (6) for connecting the housing parts (4, 5) in the region of an interface, and seal elements (7) for sealing the interface. The battery housing according to the invention is characterized in that at least one test volume (8) which is sealed off from the inner volume and from the surroundings via the seal elements (7) is formed in the region of the interface, said test volume having at least one test connection (11), wherein an electrically conductive and elastic element (9) which is permeable to gases is arranged in the test volume (8), said element having a width which is greater than the cross-section thereof in the unloaded state and which extends transversely to the extension direction of the test volume (8). According to a method, a pressure is applied to the test volume (8), and the leak tightness is tested using the time curve of the pressure.

Description

[0001] Battery casings and leak testing procedures

[0002] The invention relates to a battery housing for a traction battery according to the type defined in more detail in the preamble of claim 1. Furthermore, the invention relates to a method for leak testing of an assembled battery housing according to the invention.

[0003] Traction batteries for vehicles that provide electrical drive power for the at least partially electrically powered vehicle are known from the prior art. Such traction batteries are typically constructed from one or more battery modules, which are housed in a battery housing or battery case.

[0004] Traction battery housings are housed.

[0005] To manufacture the battery and, if necessary, maintain it, several housing components are always installed in the battery housing, typically at least two: a lower section that accommodates the battery modules and a cover that closes the housing. Interfaces are formed between these housing components, including flange surfaces, screw head supports, etc. These interfaces must be sealed against moisture penetration and potentially escaping gases, so the tightness of the housing interfaces is of particular safety relevance. The housing interfaces typically have sealing elements for this purpose.

[0006] During battery manufacturing with the battery housing, or during maintenance of the battery in the battery housing, it must be ensured that the housing is reliably sealed after production or maintenance. This is typically done by inspecting the interfaces. A common method for leak testing components is to pressurize them and observe how the pressure changes over time. If the pressure in the sealed volume drops, a leak exists. DE 40 34 106 A1 describes such a process for starter batteries.

[0007] However, such a leak test is unsuitable for practical use in traction battery housings, as for technical reasons, the battery may only be subjected to a relatively low overpressure of typically only 50 mbar. This makes it impossible to detect a pressure drop within a reasonable timeframe for production and maintenance.

[0008] In practice, a test gas, such as helium, is often introduced into the assembled and sealed battery casing at a low overpressure that is harmless to the battery. The interfaces are then scanned with a test gas detector equipped with a sniffer probe to detect safety-relevant leaks at the interfaces of the battery casing. This is comparatively complex and can still be implemented in production, but it represents a considerable effort for repeat leak testing after battery maintenance, during which the battery casing was opened.

[0009] A further problem with such battery housings is that both the lower and upper housing sections are typically designed as metallic trays or are otherwise electrically conductive or have an electrically conductive coating. A connection between these two parts of the housing therefore also serves to shield against electromagnetic fields, as these components form a Faraday cage. It is therefore important that these components are electrically connected to one another. This is often achieved by screwing the components together. However, modern manufacturing processes increasingly rely on simply gluing the housing parts of the battery housing, requiring additional measures to electrically contact the housing parts. This causes a corresponding amount of effort during assembly in terms of the required components and the required installation space.

[0010] DE 102020 107 043 A1 discloses a battery housing for a motor vehicle battery. This battery housing comprises two housing parts and, at the interface between these housing parts, an inner seal arranged between the interior of the housing and a screw connection, as well as an outer seal arranged at a distance from the inner seal, which is arranged between the exterior of the housing and the screw connection. Furthermore, tabs are described which enable electrical contact between the housing parts when they are connected.

[0011] The object of the present invention is to provide an improved battery housing that avoids these disadvantages and enables a simple and efficient leak test with simple electrical contact. Furthermore, the object of the present invention is to provide a method for leak testing such a battery.

[0012] According to the invention, this object is achieved by a battery housing having the features in claim 1, and in particular in the characterizing part of claim 1. Furthermore, a method according to claim 9 solves the problem. Advantageous embodiments and further developments of the battery housing and the method are set out in the subclaims dependent thereon.

[0013] The battery housing according to the invention provides a housing comprising at least two parts with an interface between the housing parts. The housing parts are connected to one another using sealants and / or adhesives. Sealing elements for sealing the interface, i.e. for sealing the internal volume of the battery housing from the external environment, are arranged in the region of the interface. According to the invention, at least one test volume is formed in the region of the interface, which is sealed by the sealing elements both from the internal volume and from the environment and has at least one test connection. A test volume is therefore provided which is sealed by the sealing elements both from the interior space and from the environment. This test volume can then be used to apply pressure to it.A comparatively high overpressure can be applied in the test volume area, as this pressure neither reaches the interior volume of the battery casing and the components mounted there, nor the surrounding area, provided everything is sealed. Since the test volume is located in the interface area, its total volume is much smaller than the interior volume of the battery. Therefore, the higher applied pressure cannot lead to technical damage to the battery, even if there is a leak to the interior of the battery.

[0014] The test volume can now be subjected to a comparatively high pressure and a conventional test medium, such as compressed air. The higher pressure makes it relatively easy and very quick to detect any pressure drop in the event of a leak, enabling efficient leak testing of this test volume. Since the test volume is sealed off by the sealing elements both from the interior volume of the battery housing and from the environment, this test volume enclosed in the interface area can be used to determine the tightness both from the interior volume of the battery housing and from the environment, provided no unexpected pressure drop occurs. This means that the tightness of the entire interface can be tested and verified very easily and efficiently using the test volume.This is possible in almost any workshop, as no special equipment is required and the test can be carried out quickly and conclusively due to the higher pressures that can be used in the test volume range.

[0015] In order to ensure electrical contact between the two housing parts, it is now also provided that an electrically conductive, elastic and gas-permeable element is introduced into the test volume. This is dimensioned such that, in its unloaded state, it has a width transverse to the direction of extension of the test volume that is greater than the extent of the cross-section of the test volume in this direction. The electrically conductive, elastic element therefore completely fills the test volume and projects beyond it at least minimally. This means that when the housing parts are placed on top of one another and connected, for example by gluing using an adhesive that forms the sealing element, it comes into contact with both the one and the other housing part and is elastically deformed in the process. Due to its elasticity and restoring force, it lies reliably against both housing parts and connects them electrically.

[0016] The elastic, electrically conductive element can be designed, for example, as a hose made of metal mesh, a spiral made of wire, a coil spring, or another type of structure, such as wire or metal mesh. This element is easily permeable to a test gas such as compressed air, is elastically deformable enough not to impede the sealing of the housing parts, and simultaneously ensures reliable contact with both housing parts, preferably over a large length in the direction of extension of the test volume, thus ensuring secure electrical contact between the housing parts. This ideally meets electromagnetic compatibility (EMC) requirements.

[0017] According to a very advantageous embodiment of the battery housing according to the invention, the interface can be designed to run all the way around the interior volume. According to a particularly advantageous embodiment of this development of the battery housing according to the invention, it can then be provided that the test volume is designed as a circumferential test volume which is interrupted by a seal transverse to the circumferential direction. The test volume therefore does not run completely around the circumference, but is interrupted by a corresponding seal, so that it essentially runs from the seal in one direction around the entire circumference to the opposite side of the seal. In this particularly advantageous development, a test connection can then be arranged on each of the two sides adjacent to the seal in the circumferential direction. The use of two test connections enables not only the actual leak test but also a test of the function of the test volume.If this allows gases to pass from one test port to the other, it is ensured that the test volume itself is not blocked. If the test volume then runs around the entire circumference, this ensures that the entire circumference is tested and not just a portion of it, potentially leading to a possible blockage of the test volume, meaning that the adjacent portion would remain untested in practice.

[0018] Another very advantageous embodiment of the battery housing according to the invention provides that the test volume is formed by two parallel material beads of a sealant and / or adhesive. Two parallel beads of a sealant and / or adhesive can be applied to a flange, which ideally forms the interface between the two housing parts, in order to, on the one hand, form the test volume and, on the other hand, reliably seal the structure between the two housing parts. For example, the outer bead can be a sealant and adhesive, which ensures both the sealing and the mechanical stabilization of the connection, whereas the inner bead, i.e. on the side of the interface facing the inner volume, is designed as a pure sealing bead.If necessary, the seal mentioned above can then be inserted between the material beads as a material bead running transversely to the other beads, preferably between the two test connections.

[0019] Alternatively, this seal can also be achieved by crossing the two material beads between the two test connections if the sealant and / or adhesive paths are accordingly formed from the same material during assembly of the battery housing.

[0020] According to a very advantageous embodiment of the battery housing according to the invention, the electrically conductive elastic element can, as already mentioned, be designed as a metal mesh, as a wire part, or as a spring element. According to a very advantageous further development, the metal mesh can be designed as a hose, as a roll wound transversely to its direction of extension, or as an element with a U- or S-shaped cross-section relative to the direction of extension. The use of a hose made of metal mesh or braid is particularly simple and efficient and is readily available on the market as a standard component. Alternatively, a roll wound transversely to its direction of extension could be used, i.e., a metal hose which is not circumferentially encircling but has a parting line in the circumferential direction.The entire circumference of the roll can be the same as that of a metal hose, but more material can also be used, so that the roll has more than one circumferential rotation. In this case, only a slight overlap of the two ends can be provided in the circumferential direction. Alternatively, a suitably shaped metal mesh can be used, which is preformed, for example, in a U-shape or S-shape and inserted into the test volume.

[0021] In addition to the use of such metal meshes, which could also be referred to as wire meshes or braids, the use of wire parts is also conceivable. These consist solely of bent wire and are designed, for example, as a spiral running in the direction of extension, and which exhibits a certain inherent elasticity due to the shape of the spiral. Spring elements would also be conceivable in principle, in particular, for example, a spiral spring that runs around the entire circumference of the interface and thus ensures good electrical contact. Other types of spring elements, such as spiral springs with protruding ends, would also be conceivable, so that these ends would lie between the flange planes of the two housing parts and, during assembly, are pressed together by the elasticity of the spring part in order to permanently contact the flanges of the interface.

[0022] A further very advantageous embodiment provides for the interface to be formed by two flanges of the housing parts, i.e. one flange per housing part. At least one of the flanges can have a groove for receiving the sealing elements and / or the electrically conductive, elastic and gas-permeable element. This facilitates their positioning, particularly when using material beads applied during assembly as a sealant and / or adhesive. A groove for the electrically conductive, elastic and gas-permeable element can ensure that this too remains in the desired area during assembly, for example in the middle of the test volume between the two sealing elements or material beads, in order to guarantee reliable functionality.A stable central positioning can prevent the penetration of sealant and / or adhesive between the elastic element and the material of the flange - at least over a large area - so that the electrical contact can be achieved easily and reliably without great assembly effort.

[0023] The inventive method for testing such a battery housing for leaks provides for the test volume to be connected directly or via an adapter volume to a pressure source and a pressure sensor, with the pressure profile at the pressure sensor being evaluated. By evaluating the pressure profile over time at the pressure sensor, the application of pressure can be detected. If the system is subsequently closed and the temperature remains approximately constant, the pressure should also remain constant. If, however, it drops significantly, a leak in the battery housing must be assumed.

[0024] A further very advantageous embodiment of the method according to the invention, when using two test connections, provides that the permeability of the test volume is tested via at least two test connections in advance, i.e. before the actual pressure test and evaluation of the pressure curve over time. This can be achieved, for example, by connecting an adaptation volume to both one test connection and the other test connection. If the pressure source is now switched on, the first adaptation volume fills first, followed by the test volume, and finally the second adaptation volume. If the pressure sensor is arranged in the second adaptation volume, the permeability of the test volume can thus already be determined when the pressure increases in the expected manner.If this does not happen despite the connection to the pressure source being open, one could immediately conclude that the test volume is faulty, making the test impossible. If, however, this is reliably possible, the test is carried out analogously to the setup described above, in which the pressure variation over time, preferably at the second adaptation volume, is evaluated accordingly. This pressure should remain constant for a certain period of time after the desired nominal pressure has been established, otherwise there is a leak in the test volume and thus in the seal of the battery housing.

[0025] The test can preferably be carried out with a test gas, but in principle also with a test liquid.

[0026] Further advantageous embodiments of the battery housing according to the invention and of the method also emerge from the exemplary embodiments which are described in more detail below with reference to the figures.

[0027] Showing:

[0028] Fig. 1 is a schematic representation of a battery with a battery housing in an embodiment according to the invention;

[0029] Fig. 2 is an enlargement of section II in Fig. 1 before assembly of the battery housing;

[0030] Fig. 3 is an enlargement of section II in Fig. 1 after assembly of the battery housing;

[0031] Fig. 4 shows a design of the sealing element and the test volume according to Fig. 2 in a plan view;

[0032] Fig. 5 is a schematic representation of a first possibility for pressure testing; and

[0033] Fig. 6 is a schematic representation of another possibility for pressure testing.

[0034] The illustration in Figure 1 schematically shows a battery 1 which is to be designed as a traction battery for providing electrical drive power in a vehicle. The battery 1 is designed as a so-called high-voltage battery and typically comprises a plurality of battery modules, each designated 2 here, which are arranged within a battery housing 3. The battery housing 3 comprises at least two housing parts 4, 5, which are designed here as a housing base 5 and a cover 4. They can be produced, for example, as deep-drawn parts made of sheet metal. Both housing parts 4, 5 have a flange 4', 5' which runs at least partially around the battery housing 3 in order to connect the housing parts 4, 5 to one another. This can be done, for example, by gluing.

[0035] The enlarged view in Figure 2 shows a possible embodiment in detail. The two housing parts 4, 5 each form the flange designated 4' and 5' respectively. On the outside of the lower flange 5', i.e. on the side facing away from the internal volume of the battery housing 3, an adhesive bead 6 is applied for firm bonding and additional sealing of the connection. In addition, on the side of the flange 5' facing the internal volume, another adhesive bead is arranged as a pure sealing element 7. Both elements 6, 7 can also be interchanged, or both can each perform both functions equally. For the sake of simplicity, they will therefore both be referred to below as the sealing element 6, 7, although this should not exclude an adhesive effect that is sufficient even for structurally load-bearing connections.The sealing elements 6, 7 are preferably produced during assembly by applying a pasty, preferably elastically curing sealing and adhesive material.

[0036] A free space remains between the two sealing elements 6, 7, which will later be used as the test volume 8. Before the other flange 4' of the upper housing section 4 is placed on the flange 5' of the lower housing section 5, an electrically conductive, elastic and gas-permeable element 9 is inserted into the area of ​​this later test volume 8. This element 9 can be designed in a variety of ways. A hose made of a metallic knit or braid is particularly preferred. After the two sealing elements 6, 7 have been applied to the lower flange 5' and the electrically conductive, elastic and gas-permeable element 9 has been placed between them in the later test volume 8, the upper housing section 4 is placed on top with its flange 4'. This attached state can be seen in the illustration in Figure 3.The sealing elements 6, 7 now seal and bond the two flanges 4' and 5' together to close the battery housing 3. They enclose the test volume 8 with the electrically conductive, elastic and gas-permeable element 9 arranged therein between the sealing elements 6, 7 and the two flanges 4, 5. The element 9 is elastically deformed into the plane of the page in the direction of the attached upper flange 4, i.e. transversely to the direction of extension of the test volume 8, as can be seen in the illustration in Figure 3, and thus lies securely on both the surface of the flange 5' and the surface of the flange 4. It thus electrically connects the two housing parts 4, 5 to one another and thus ensures good shielding against electromagnetic radiation.

[0037] Unlike the illustration in Figures 2 and 3, grooves for the sealing elements 6, 7 and / or the element 9 could be provided in the flange 5' and / or the flange 4', thus facilitating their positioning during assembly. Such grooves would preferably be circular segment-shaped.

[0038] In the two representations of Figures 2 and 3, a test connection 10 can also be seen in the upper flange 4', via which the test volume 8 can now be used in an extraordinary manner, which will be described in more detail later, to test the tightness of the battery housing 3.

[0039] In principle, a single test connection 10 is sufficient to test the test volume 8 surrounding the entire circumference of the battery housing. However, due to the application of the sealing elements 6, 7 as pasty adhesive and / or sealing beads during assembly, the test volume 8 may be interrupted at several points, for example, if pasty sealing material gets between the two beads of sealing material 6, 7. This can occur in particular if the element 9 is not continuous, but has only been inserted in individual sections distributed around the circumference, which would be possible in principle.

[0040] In order to counteract such a fault scenario, it can be provided that two test connections 10, 11 are provided. A plan view of a section of the flange 5' analogous to the illustration in Figure 2 is shown in Figure 4. This section of the flange 5' has the two test connections 10, 11, which could of course also be arranged in the flange 5' instead of being arranged in the flange 4'. The sealing element 6 runs at the top in the illustration in Figure 4, and the sealing element 7 runs at the bottom. The test volume 8 is to be designed to be circumferential here and to be partially filled by a circumferential element 9. A seal 12 is made from the sealing and adhesive material between the two test connections 10, 11 and divides the test volume 8 into a circumferential test volume 8 with two ends facing each other. The two test connections 10, 11 are arranged in the area of ​​the respective ends.This allows not only the tightness of the test volume 8 or the part of the test volume 8 which is connected to the respective test connection 10, 11 to be tested, but also the continuity of the test volume 8 to ensure that it is not blocked by sealing and / or adhesive material, so that an undetected leak could remain in the area not accessible from the respective test connection 10, 11.

[0041] A first simple variant of the leak test will now be described using the schematic representation in Figure 5. A pressure source 13 is connected via a valve device 14 to an adaptation volume 15, in the area of ​​which a pressure sensor 16 is arranged. In a design in which only one such test connection 10 exists, the test volume 8 is connected via the test connection 10. By opening the valve 14, first the adaptation volume 15 and then the test volume 8 are filled with the test medium, preferably compressed air. After the valve device 14 is shut off, the pressure determined via the pressure sensor 16 in the test volume 8 connected to the adaptation volume 15 or in the volume formed by these two volumes 8, 15 should remain constant, provided the ambient temperature remains constant.If this is the case, the tightness of the test volume 8, and thus ultimately also of the battery housing 3, can be reliably determined, since the test volume 8 is sealed both from the interior volume of the battery housing 3 and from its surroundings. If a leak were present, the pressure would drop as the test medium escapes either into the interior volume of the battery housing 3 or into the surroundings.

[0042] Figure 6 shows an alternative, improved variant of this method. Here, too, a pressure source 13 and a valve 14 are used. The test volume 8, which here is designed as a test channel surrounding one of the flanges 5', as explained, for example, in Figures 4 and 5, is pressurized via a first adaptation volume 15 and a test connection 10. A second adaptation volume 17, which has the pressure sensor 16, is then connected via the second test connection 11. When the valve 14 is opened, the first adaptation volume 15 is filled first before the test gas passes through the test volume 8 to the second adaptation volume 17. If there is a pressure increase at the pressure sensor 16 after the valve 14 is opened, it can be assumed that the test volume 8 is permeable.If this is arranged analogously to the description in Figure 4, it can be ensured that almost the entire circumference of the interface between the two housing parts 4, 5 of the battery housing 3 can be reliably tested. If this is the case, the valve device 14 is closed, and the temporal progression of the pressure is evaluated at the pressure sensor 16. Here, too, a constant pressure over a certain period of time, at constant temperature and ambient conditions, is an indication of tightness, while a pressure drop would, in turn, be an indication of a leak in the area of ​​the interface between the two housing parts 4, 5 or their flanges 4', 5'.

Claims

Battery housing (3) for a traction battery (1), with at least two housing parts (4, 5) enclosing an internal volume, with connecting elements (6) for connecting the housing parts (4, 5) in the region of an interface, and with sealing elements (6, 7) for sealing the interface, characterized in that in the region of the interface at least one test volume (8) is formed which is sealed by the sealing elements (6, 7) both from the internal volume and from the environment and which has at least one test connection (10, 11), wherein an electrically conductive elastic element (9) which is permeable to gases is arranged in the test volume (8), which element, in its unloaded state, has a width transverse to the direction of extension of the test volume (8) which is greater than the extension of the cross section of the test volume (8) in this direction.Battery housing (3) according to claim 1, characterized in that the interface is designed to extend circumferentially around the internal volume. Battery housing (3) according to claim 2, characterized in that the test volume (8) is designed as a circumferential test volume (8) which is interrupted transversely to the circumferential direction only by a seal (12), wherein a test connection (10, 11) is arranged adjacent to the seal (12) on each of the two sides in the circumferential direction. Battery housing (3) according to claim 1, 2 or 3, characterized in that the test volume (8) is formed between two parallel material beads of a sealant and / or adhesive. Battery housing (3) according to one of claims 1 to 4, characterized in that the electrically conductive elastic element (9) is made of metal mesh or braid, as a wire part or as a spring element. Battery housing (3) according to claim 5, characterized in that the metal mesh is designed as a hose, as a roll wound transversely to its direction of extension, or has a U- or S-shaped cross-section relative to the direction of extension. Battery housing (3) according to claim 6, characterized in that the wire part or the spring element has a spiral running in the direction of extension.Battery housing (3) according to one of claims 1 to 7, characterized in that the interface is formed by two flanges (4', 5') of the housing parts (4, 5), at least one of the flanges (4', 5') having a groove for receiving the sealing elements (6, 7) and / or the electrically conductive, elastic, and gas-permeable element (9). Method for leak testing an assembled battery housing (3) according to one of claims 1 to 8, characterized in that the test volume (8) is connected directly or via at least one adaptation volume (15, 17) to a pressure source (13) and a pressure sensor (16), wherein the temporal pressure profile at the pressure sensor (16) is evaluated after pressurization of the test volume (8). Method according to claim 9, characterized in that, if at least two test connections (10, 11) are present, the permeability of the test volume (8) between these test connections (10, 11) is tested in advance.

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