Device for pressure equalization in a closed volume

Abstract

Device (1) for pressure equalization of a closed volume (10) with its surroundings comprising: - a pressure equalization cylinder (2), with - an ambient fluid inlet (3) ; - an exhaust valve (15); - a fluid outlet (5) which is configured to be coupled to the closed volume (10), as well as - a movable piston (14) for dividing the pressure equalization cylinder (2) into a first volume (I) and a second volume (II); wherein - the ambient fluid inlet (3) is pneumatically coupled to the second volume (II), and - the fluid outlet (5) is coupled to the first volume (I), and - the outlet valve (15) is configured to allow, in a first position of the piston (14), an inflow of ambient fluid through the ambient fluid inlet (3) into the first volume (I) of the pressure equalization cylinder (2) and to prevent, in a second position of the piston (14).

Description

State of the art

[0001] The present invention relates to a device for pressure equalization in a closed volume. In particular, the present invention relates to such a device, which makes dehumidification measures simpler and more cost-effective. Electrochemical energy storage devices are required for electrically powered vehicles. These electrochemical energy storage devices are usually protected from external influences by a sealed housing. To equalize pressure differences resulting from temperature and air pressure changes inside and outside the housing, so-called pressure equalization elements (PEEs) are typically used. These sometimes include a membrane designed to retain liquids while allowing gases to pass through.

[0002] EP 2 290 729 A1 discloses an electrical energy storage device with a volume compensation device, in which a piston pre-tensioned by a spring in a pressure equalization cylinder releases a fluid outlet when the pressure within an electrochemical energy storage device rises and a predefined pressure is reached. In this way, fluid located in the storage housing can escape and the internal pressure can be reduced.

[0003] DE 10 2010 051 000 A1 discloses a battery with a battery housing for a vehicle, which is coupled to the environment via a pressure equalization element. The volume of the battery housing is hermetically sealed from the environment by a membrane within the pressure equalization element. However, deformation of the membrane allows adiabatic pressure equalization within the volume defined by the pressure equalization element.

[0004] US 3 514 341 A discloses a battery housing with a pressure equalization element and a pressure relief valve.

[0005] Pressure equalization elements are installed upstream of pressure equalization openings in housings, allowing gas exchange and thus pressure equalization. However, these pressure equalization elements do not provide an ideal moisture barrier. Therefore, it is common practice to include desiccants inside the housings as an additional dehumidification measure. These desiccants can be understood as moisture sinks, but they have only a limited capacity. Once this capacity is exhausted, the desiccant must be replaced. This requires opening the housing, which is costly and time-consuming. Another known pressure equalization measure involves pistons, which are arranged in a virtually fluid-tight manner within a cylindrical pressure equalization opening and thus provide limited pressure equalization.Particularly in vehicles, pistons are only able to compensate for limited alternating pressures due to the constraints regarding the available installation space.

[0006] It is therefore an object of the present invention to eliminate the aforementioned disadvantages of the prior art. Disclosure of the invention

[0007] The aforementioned problem is solved according to the invention by a device with the features of claim 1. Accordingly, a device for pressure equalization of a closed volume with its surroundings is proposed. The closed volume can, for example, be a housing for technical equipment. Particularly with rigid housings, it is necessary to perform pressure equalization as addressed by the present invention, since the operation of the technical equipment is often associated with heat generation. Especially with mobile closed volumes, the aspect of possible differences in altitude above sea level must also be considered. The present invention comprises a pressure equalization cylinder with an ambient fluid inlet through which ambient fluid can flow to establish pressure equalization with the surroundings. The pressure equalization cylinder includes an outlet valve.In the context of the present invention, a valve is generally understood to be a reversibly closable passage for fluid flow. Additionally, the pressure equalization cylinder has a fluid outlet designed to be coupled to the closed volume. In other words, the fluid outlet is an opening in the pressure equalization cylinder through which the cylinder can pneumatically communicate with the closed volume. Furthermore, a movable piston is provided in the pressure equalization cylinder to divide it into a first volume and a second volume. For this purpose, the movable piston is in fluid-tight contact with the inner wall surface of the pressure equalization cylinder. Due to the movable arrangement of the piston, the sum of the first and second volumes on both sides of the movable piston is always approximately equal.The ambient fluid inlet is pneumatically coupled to the second volume. In other words, ambient fluid is constantly entering and exiting the second volume. Apart from dynamic processes, ambient pressure always prevails in the second volume of the pressure equalization cylinder. The second fluid outlet of the pressure equalization cylinder is coupled to the first volume of the pressure equalization cylinder. In this way, a displacement of the piston caused by pressure differences can equalize the pressure via the second fluid outlet. According to the invention, and in contrast to the prior art, the outlet valve ensures that an overpressure prevailing in the first volume, which cannot be equalized by a mere displacement of the piston, does not lead to overpressure or even to the bursting of the pressure equalization cylinder or the closed volume.In other words, the outlet valve is configured to allow fluid to escape from the first volume towards the environment, at the latest when the movable piston exceeds a predefined operating range. In this way, the device according to the present invention provides a compact and self-contained unit that fulfills the underlying objective of the invention and does not require additional safeguards against moisture ingress. According to the invention, the outlet valve is configured to allow ambient fluid to flow into the first volume of the pressure equalization cylinder through the ambient fluid inlet in a first position of the piston and to prevent this in a second position of the piston. For example, an inflow of ambient fluid (ambient air) may be necessary in the first position to equalize a pressure differential between the environment and the first volume or the closed volume.It is accepted that, at least in small quantities, (humid) ambient air may penetrate the system, which then needs to be dehumidified. Therefore, the first position of the piston can correspond to an operating condition in which the piston is close to the limit of its ability to equalize the negative pressure within the closed volume. Additionally, the piston can be configured in a second position to prevent the inflow of ambient fluid through the ambient fluid inlet into the first volume. This is advantageous, for example, if the piston is capable of equalizing a negative pressure within the system by means of a further stroke. In such a situation, the invention can therefore prevent the ingress of potentially moisture-containing ambient fluid into the system.

[0008] The dependent claims relate to preferred embodiments of the invention.

[0009] Preferably, the device is configured to seal the first volume from the environment by closing the valve in a first operating state. In other words, the valve acts as a barrier against fluid flowing from the environment towards the first volume in at least one operating state. Simultaneously, in a second operating state, the device is configured to open the first volume towards the environment of the device, at least in one direction, by means of the outlet valve. This can occur, for example, when the pressure within the first volume of the pressure equalization cylinder is higher or significantly higher than the ambient pressure. While this results in the loss of air that was hermetically sealed within the system up to this point, and which may have been dried, the invention reliably prevents a major malfunction or even damage to the system due to internal overpressure.

[0010] In the first operating state, the ambient pressure can be higher than the ambient pressure in the second operating state, relative to the respective fluid pressure in the first volume. In other words, the pressure difference between the ambient pressure and the fluid pressure inside the volume is greater in the first operating state than the pressure difference between the ambient pressure and the simultaneous fluid pressure inside the volume during the second operating state. This prevents the ingress of moist ambient air in cases where there is a pressure gradient towards the first volume. It also prevents the system according to the invention from bursting, specifically the device and the enclosed volume.

[0011] Preferably, the piston can include a rolling diaphragm as part of the exhaust valve. The rolling diaphragm acts as the actuator of the exhaust valve, which (depending on the operating state) closes or opens an opening within the pressure equalization cylinder. The rolling diaphragm can serve both to guide and seal the piston within the pressure equalization cylinder and to reversibly close the second air outlet within the second volume. If a passage of the exhaust valve located in the second volume of the pressure equalization cylinder is not covered by the rolling diaphragm, fluid can flow in both directions.If the rolling diaphragm covers the passage of the outlet valve, fluid cannot escape from the second volume of the pressure equalization cylinder. However, a pressure differential predefined by the diaphragm in the direction of the second volume lifts the rolling diaphragm from the wall of the pressure equalization cylinder, allowing the fluid to enter the second volume through the passage of the outlet valve. This enables a simple, robust, and advantageous integration of functions in several respects.

[0012] Preferably, the device includes a pressure equalization element designed to prevent the passage of liquids from the direction of the ambient fluid inlet towards the enclosed volume. This pressure equalization element can, for example, be designed as a membrane (e.g., a textile membrane) such as those used in functional clothing. This largely prevents the ingress of liquids when fresh air flows into the system. Simultaneously, the pressure equalization element is designed to allow the passage of gases in the same direction. In this way, the pressure equalization element does not impede the necessary pressure equalization between the environment and the enclosed volume. While the pressure equalization element cannot guarantee 100% protection against moisture ingress, it supports the dehumidification function and is also maintenance-free and extremely durable.

[0013] Preferably, the device further comprises a filter arranged between the pressure equalization element and the enclosed volume. The filter can, in particular, include a desiccant. In other words, the filter has a moisture-absorbing capacity capable of removing moisture from a fluid flow passing through it. For the sake of completeness, it should be clarified that the desiccant can still also be located within the enclosed volume (e.g., a battery housing). The reduced air exchange with the environment achieved by the device according to the invention, and the resulting reduction in moisture ingress, also extend the service life of a desiccant located within the enclosed volume.However, arranging the desiccant within the device is particularly advantageous if the device is designed to be significantly more accessible than the interior of the enclosed volume. This makes replacing or maintaining the filter / desiccant less complex and therefore faster and more cost-effective. For example, the desiccant can be arranged in the form of a desiccant cartridge downstream of the pressure equalization element (PEE), which can be inserted into a removable section of the device via a screw connection. Placing the filter / desiccant within the device can offer a further advantage. If the filter is located in a channel element through which the oscillating liquid column flows, the repeated flow through the filter / desiccant leads to rapid and thorough dehumidification of the enclosed fluid.

[0014] Preferably, the part in which the filter / desiccant is provided can be opened reversibly in a fluid-tight manner. Screw connections, bayonet connections, plug connections, bonded connections, etc., are particularly suitable for this purpose. The filter can be provided as an insert in an openable channel element of the device, or it can encompass a portion of the channel. In the latter case, for example, a sealant provided within the channel element for reversible sealing can also be replaced simultaneously within a spare parts unit to prevent leaks and wear.

[0015] According to a further aspect of the present invention, an electrochemical storage unit comprising a housing and a device connected to the housing is proposed. The device is configured as described in detail above in connection with the first-mentioned aspect of the invention. The housing of the electrochemical storage unit is coupled to the fluid outlet of the device as a closed housing, as defined in the first-mentioned aspect of the invention. The electrochemical storage unit can, for example, comprise lithium-ion, lithium-polymer, nickel-metal hydride, nickel-cadmium cells, or similar components. The combinations of features and advantages described in connection with the first-mentioned aspect of the invention are correspondingly realized. Brief description of the drawings

[0016] Exemplary embodiments of the invention are described in detail below with reference to the accompanying drawings. The drawings show: Fig. 1 a schematic representation of a device on a battery housing as a closed volume; Fig. 2 the in Fig. 1 device presented in a second operating state; Fig. 3 the in Fig. 1 and Fig. 2 device shown in a third operating state; Fig. 4 those in the Fig. Device 1 to 3 shown in a fourth operating state; and Fig. 5 a schematic view of an embodiment of a device according to the invention. Embodiments of the invention

[0017] Fig. Figure 1 shows a battery 9 as an electrochemical energy storage device in a closed housing 10, which is connected via a hose 11 to a device according to the invention. The device comprises a pressure equalization cylinder 2, the underside of which has an opening as a fluid outlet 5 in the direction of the hose 11. A movable piston 14 is arranged inside the pressure equalization cylinder 2. A first volume I is arranged between the movable piston 14 and the fluid outlet 5, which contains a filter 13 with a desiccant. When the movable piston 14 moves, the fluid column arranged within the first volume I, i.e., within the hose 11, also moves through the filter 13 and releases moisture to it. A second volume II is arranged above the movable piston 14.In a section facing the upper end of the pressure equalization vessel 2, an outlet valve 15 is recessed into the side wall. An ambient fluid inlet 3 is provided at the upper head end of the pressure equalization cylinder 2, within which a pressure equalization element 16 with a diaphragm is arranged. The pressure equalization element 16 is configured to allow ambient gases to flow into the second volume II, while essentially retaining moisture within the ambient gases.

[0018] Fig. 2 shows the in Fig. Figure 1 shows the arrangement, with a second state 14' of the movable piston 14 depicted. The positions of the movable piston 14 shown represent opposite limits of a working range of the piston 14, in which the device can equalize pressure differences without any external fluid flowing into the closed volume 10. Above the state 14' of the movable piston 14, a second volume II is shown, into which the ambient fluid, represented by arrow P4, can flow in and out through the outlet valve 15. The fluid-tight sealing of the piston 14 reliably prevents any moisture introduced into the first volume I from entering the second volume II in this way.

[0019] Fig. 3 shows the one in Fig. The state shown in Figure 2 is reached after the ambient pressure has decreased significantly compared to the pressure inside the first volume I. The movable piston 14 has risen past the outlet valve 14 to an outer end of the pressure equalization cylinder 2. In the illustrated situation, the piston 14 closes the ambient fluid inlet 3 at the head end of the pressure equalization cylinder 2. Simultaneously, the outlet valve 15 (as indicated by arrow P5) is configured only to allow fluid to escape from the pressure equalization cylinder 2 into the environment, but to prevent ambient fluids from entering the interior of the pressure equalization cylinder 2. This change in the function of the outlet valve 15 can be implemented either purely mechanically or with the aid of suitable sensors / actuators. Overpressure and bursting of the closed volume 10 or the device according to the invention are effectively prevented by the provision of the outlet valve 15 as shown.

[0020] Fig. 4 shows the in Fig. Figure 3 shows the situation after the ambient pressure has increased relative to the pressure inside the pressure equalization cylinder 2 or the closed volume 10. The tendency of the ambient fluid to flow into the pressure equalization cylinder 2 has closed the outlet valve 15, as indicated by arrow P6. Pre-dried ambient fluid has flowed into the second volume II through the ambient fluid inlet 3 and the pressure equalization element 16, lowering the movable piston 14. In this way, the first volume I decreases accordingly. The closing of the outlet valve 15 can also be assisted either purely mechanically or by sensors / actuators. The figures described above schematically represent a particularly simple setup in which the device according to the invention is protected against overpressure within the closed volume.

[0021] Fig.Figure 5 shows a schematic representation of an alternative embodiment, which is additionally protected against high ambient pressure. A movable piston 14 is arranged inside the pressure equalization cylinder 2. This piston is fluid-tightly anchored to the inner wall of the pressure equalization cylinder 2 via a rolling diaphragm 19 embedded in the wall of the pressure equalization cylinder 2 at points 20. The piston 14, or the identical piston 14' shown in a lowered position, divides the volume of the pressure equalization cylinder 2 into a first volume I below the piston 14 or 14' and a second volume II above the piston 14 or 14'. Ambient fluid inlets 3 in an upper section of the pressure equalization cylinder 2 are designed to maintain the second volume II at ambient pressure at all times.The piston 14 is shown in an upper position in which the rolling diaphragm 19 prevents the escape of ambient fluid from an outlet valve 15 embedded in the side wall of the pressure equalization cylinder 2. The outlet valve 15 is released as soon as the piston 14, and thus the rolling diaphragm 19, has been moved downwards by a corresponding stroke, i.e., when the piston is in position 14'. A channel element 21 is connected to the outlet valve 15, and a pressure equalization element 16 is embedded in its end. A filter 13, containing a desiccant, is arranged downstream of the pressure equalization element 16. A further channel element 22 is connected to the filter 13 and is linked to a fluid outlet 5 at the bottom of the pressure equalization cylinder 2 and to a pipe leading towards a closed volume 10.To explain the functioning of the illustrated embodiment of the device according to the invention, the upper position of the movable piston 14 is considered first. This represents a first operating state, provided that the ambient pressure is greater than or equal to the internal pressure within the first volume. Ambient fluid flows through the ambient fluid inlets 3 into the second volume II. The pressure difference between the second volume II and the pipe 21 causes the outlet valve 15 to close via the rolling diaphragm 19. If the external pressure continues to increase or the pressure in the closed volume 10 continues to decrease, the piston 14 moves downwards in the pressure equalization cylinder 2 until it reaches position 14'.Although the movable piston 14' is thus almost at the end of its working range (the rolling diaphragm 19, like the base of the pressure equalization cylinder 2, would prevent further downward movement), the outlet valve 15 is no longer covered by the rolling diaphragm 19, so that ambient fluid can pass directly into the first volume I or the closed volume 10 through the ambient fluid inlets 3, the second volume II, the pipe 21, the pressure equalization element 16, the filter 13, and the pipe 22. Although the incoming fresh air is only simply purified of moisture by the pressure equalization element 16 and a simple flow through the filter 13, collapse of the closed volume 10 and of the device according to the invention is effectively prevented. If the pressure within the closed volume 10 subsequently rises, the pressure equalization element 16 and the filter 13 are then removed.As the ambient pressure decreases, the piston 14' rises within the pressure equalization cylinder 2 because the flow resistance through the filter 13, the pressure equalization element 16, and the pipes 21, 22 is greater than the flow resistance between the closed volume 10 and the first volume I. Additionally, the rolling diaphragm 19 soon closes the outlet valve 15, so that with a further increase in pressure inside the closed volume 10, the piston assumes position 14. If the pressure inside continues to rise, the piston 14 eventually reaches its upper end position. The rolling diaphragm 19 and the ambient fluid inlets 3 are positioned relative to each other such that the ambient fluid inlets 3 are never completely closed.In such a situation, if the fluid pressure inside the closed volume 10 continues to rise and presses on the rolling diaphragm 19 via the pipes 21, 22 and also via the outlet valve 15, the escape of air trapped in the system via the second volume II and the ambient fluid inlets 3 could still be ensured, provided the rolling diaphragm 19 is appropriately dimensioned, and a bursting of the closed volume 10 or the pressure equalization cylinder 2 could be effectively prevented.

[0022] The present invention enables, on the one hand, external access to the desiccant and, on the other hand, the relocation of the modular volume compensation system to allow for a compact high-voltage battery package. In preferred embodiments, constantly changing ambient pressure conditions result in an oscillating column of air that moves back and forth through the desiccant, extracting moisture from the air in the closed system. The device according to the invention implements a combination of features that are often referred to in the prior art as "internal" and "external" pressure compensation or "internal" and "external" pressure compensation elements. Advantageously, by connecting a desiccant cartridge downstream of the pressure compensation element, the service life of the desiccant is maximized.Ideally, external pressure equalization (in other words, the exchange with the ambient air) only occurs once the internal pressure equalization (i.e., the oscillating volume traversed by piston 14) has been fully utilized. This approach offers the following advantages: First, external pressure equalization keeps the required air volume for internal pressure equalization small. This prevents the internal pressure equalization system from having to compensate for extreme pressures. Second, internal pressure equalization reduces air exchange or ensures it is only required for extreme pressure differences. Third, the optional use of the desiccant cartridge downstream of the pressure equalization element (PEE) ensures that only dry air enters the battery as a closed volume. Fourth, the reduced air exchange extends the service life of the desiccant, thus increasing the overall lifespan.The service life of the desiccant is extended. In particular, the service life of the desiccant can be dimensioned so that it outlasts an electrochemical energy storage device.

[0023] It is evident to those skilled in the art that the fundamental functional descriptions given within this description can take on a wide variety of configurations in their technical implementation. The core of the invention is a permanent, reduced air exchange via the external pressure equalization element. To modify this element, a valve would have to be installed in the supply line, for example, which only opens when the piston reaches a corresponding end position. According to the invention, a reduction in air exchange is achieved through an internal pressure equalization element. Naturally, the pressure equalization element itself does not need to be included as part of the device according to the invention in order to benefit from an extended service life / operating period in conjunction with it. Furthermore, the invention allows the pressure equalization to be implemented externally and independently of the battery compartment.For example, a connection via a hose is possible. In particular, a filter medium or desiccant can be installed in a service-friendly position. Advantageously, several devices according to the invention can be arranged modularly at different dead volumes within a closed volume (e.g., battery housing). This reduces problems associated with the space requirements of electrochemical energy storage devices. Service intervals for maintenance or replacement of the filters / desiccants can be extended due to the reduced air exchange with the environment. In general, the present invention provides a solution in which the desiccant does not come into contact with humid ambient air during "normal" operating conditions.

Claims

[1] Device (1) for pressure equalization of a closed volume (10) with its surroundings, comprising: - a pressure compensation cylinder (2), with - an ambient fluid inlet (3); - an outlet valve (15); - a fluid outlet (5) which is arranged to be coupled to the closed volume (10), and - a displaceable piston (14) for dividing the pressure compensation cylinder (2) into a first volume (I) and a second volume (II); wherein - the ambient fluid inlet (3) is pneumatically coupled to the second volume (II), and - the fluid outlet (5) is coupled to the first volume (I), and - the outlet valve (15) is configured to allow ambient fluid to flow through the ambient fluid inlet (3) into the first volume (I) of the pressure compensation cylinder (2) in a first position of the piston (14) and to prevent it in a second position of the piston (14). [2] Device according to claim 1, wherein the device is arranged - in a first operating state, to seal the first volume (I) from the environment by closing the valve (15), and - in a second operating state, to open the first volume (I) towards the environment at least in one direction by means of the outlet valve (15). [3] Device according to claim 2, wherein in the first operating state the ambient pressure relative to a fluid pressure in the first volume (I) is higher than an ambient pressure in the second operating state relative to a fluid pressure in the first volume (I). [4] Device according to one of the preceding claims, wherein the piston (14) comprises a rolling diaphragm (19) as part of the outlet valve (15). [5] Device according to one of the preceding claims, wherein the outlet valve (15) comprises a controllable valve. [6] Device according to one of the preceding claims, further comprising a pressure compensation element (16) which is designed to prevent the passage of liquids from the direction of the ambient fluid inlet (3) in the direction of the closed volume (10), but to ensure the passage of gases in this direction. [7] Device according to claim 6 further comprising a filter (13), in particular comprising a drying agent, which is arranged between the pressure compensation element (16) and the closed volume. [8] Device according to claim 7, wherein the device can be opened reversibly in a fluid-tight manner for maintenance purposes of the filter (13), in particular for replacing a drying agent. [9] Electrochemical storage unit comprising a housing (10) and a device connected to the housing (10) according to one of the preceding claims 1 to 8, wherein the housing (10) of the electrochemical storage unit (9) is coupled as a closed housing (10) to the fluid outlet (5) of the device.

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