FILTER ARRANGEMENT

Technical Field

The invention relates to a filter arrangement for cleaning the intake air to fuel cells.

State of the Art

Fuel cells, in particular PEM fuel cells, require an intake air which is free from corrosive elements for an optimum efficiency and a long durability. Corrosive elements are particulate and gaseous particles. Inscribed particles or abrasion particles from an upstream arranged system component such as air conveyance equipment or corrosive gases may accumulate in the fuel cell and may derogate the optimal function of several parts such as gas channels, gas diffusion layers, catalysts or membrane electrode assemblies. The corrosive elements may cause an early wastage of these components. To prevent entrainment of particles into the fuel cell, the fuel cell intake air is cleaned by means of a filter. However, the available design space is limited, especially with compact fuel cells.

Explanation of the Invention

The object of the present invention is to provide a filter arrangement for cleaning fuel cell intake air, such that it has a compact design and is inexpensive to manufacture.

This object is achieved with the features of Claim 1. The subclaims refer to advantageous embodiments.

To achieve this object, a filter arrangement for cleaning fuel cell intake area is composed, comprising at least one filter which has at least two layers of a first filter medium and at least one additional layer of a second filter medium, whereby the second filter medium is embedded between the first filter media, and the first filter media are connected to the mutually opposing edge sections, and comprising a housing which includes at least one top part and one bottom part, whereby the top part and the bottom part each have a flange and the edge sections of the filter are arranged between the flanges.

In the case of fuel cells, in particular with PEM and DMFC fuel cells, for example, the intake air must be filtered. Fuel cells for mobile use in particular have a compact design and under some circumstances the filter may be provided only in difficultly accessible locations. The inventive filter can be installed especially easily due to its design. The filter may be arranged according to this invention in the area of the air conveyance equipment, in other words, upstream and/or downstream from the air conveyance equipment, which may be designed as a pump or compressor. The filter arrangement is preferably situated upstream from an air humidifier. An air humidifier is necessary to humidify the intake air of the fuel cell to prevent the membrane from drying out, which would result in a voltage drop.

The edge sections of the first filter media are secured by a friction-locking and/or form-fitting and/or integrally bonded connection. A separate connection of the first filter media may be omitted, in particular if the filter arranged in the housing is not designed to be replaceable. The filter and the housing together form a preassembly unit, whereby in the case of a friction-locking and/or form- fitting connection in particular, replacement of the filter is possible. The edge sections arranged between the flanges at the same time seal the housing. It is

advantageous here that the filter arrangement is a single component, the filter layers of which are fixedly tied into the housing. This makes assembly especially simple, because only the air guides need be connected. The filter arrangement is also lightweight, so no additional fastening of the housing is necessary.

The flanges may be joined together in a friction-locking and/or form-fitting manner. Friction-locking and/or form-fitting connections can be established inexpensively by using simple tools and no assembly aids are necessary. The connections can be released nondestructively, so that replacement of the filter is simplified.

The flange and the edge sections may be bonded together in an integrally bonded manner. In the case of integrally bonded connections, unintentional release of the flange due to the influence of force is prevented. The connection that is integrally bonded, in particular by adhesive gluing, may be designed to be airtight. Then the filter is replaced by replacing the gas housing with the filter enclosed in it, which is advantageous especially in difficultly accessible locations.

The flange and the edge sections may be welded together. No particular shapes or contours of the flange are required for welding and the tolerance requirements are low.

The top part and the bottom part may be designed as injection-molded parts or as turning workpieces. The top part and the bottom part are each made of an inexpensive plastic such as Acrylonitrile-Butadiene-Styrol (ABS). Injection molding is a simple and inexpensive production process. The top part and the bottom part may be also designed as deep-drawn pieces.

The filter may be secured in the housing in such a way that an air space formed between the top part and the filter and/or between the bottom part and the filter.

The air space causes a distribution of the air current, resulting in a uniform oncoming flow against the filter. In addition, it is especially advantageous that the air spaces have a sound-absorbing effect, so that the noise emitted by the air conveying equipment can be dampened. The filter arrangement therefore at 5 the same time forms a device for suppressing sound. The sound suppression may additionally be improved if porous media such as nonwoven are arranged in the air spaces or if several chambers interconnected by a passage are provided in the air spaces.

o The first filter medium may be made of a nonwoven, whereby the first filter medium is designed as a coarse filter or a fine filter and the second filter is designed as a fine filter. The first filter medium is facing the uncleaned intake air side and the second filter medium is facing the cleaned intake air side. Nonwovens are inexpensive and can be produced by a variety of methods. The 5 nonwoven is preferably made of a plastic such as polyester, polyolefin or polyacrylonitrile. The first filter medium may also be formed from several layers of nonwoven made of different plastics. Due to the different production processes, different properties can be imparted to the nonwovens, e.g., the suitability for filtration of solid and liquid particles, so-called aerosols, of various 0 sizes as well as filtration of certain chemical constituents. The nonwoven may be furnished with ion exchange resins, for example, to be able to filter basic or acidic gases, e.g., NH ₃ or SO ₂ , depending on the properties of the resins. The second filter medium may be formed by activated carbon. The second filter medium is formed by activated carbon as an adsorption filter or an absorption 5 filter, whereby the activated carbon is suitable for filtration of a wide variety of chemical constituents as well as particles. Several layers of activated carbon may be provided. However, activated carbon is fine-grained and free-flowing, so that a means of securing it between the first filter media, which are made of nonwoven, for example, is especially advantageous. Other sorbents may also 0 be provided either alone or in combination as a second filter medium. These may also be active through physisorption or chemisorption. For example, an impregnated carbon, silica gel, alumina or an ion exchanger would also be

conceivable. The remaining filter arrangement may additionally have upstream and/or downstream particulate filters. The filter media may be designed as punched items. The punched items are particularly simple to fabricate. Production may be continuous if punched blanks of the second filter medium are arranged between sheets of the first filter medium and then punched blanks from the first filter media are produced. When punching out the first filter media, welding using the same mold may also be performed at the same time. If the second filter medium consists of activated carbon, it may be necessary to secure the activated carbon in the form of a block by using an adhesive. It may be advantageous here that the amount of adhesive may be especially low because the activated carbon punched blank is secured between the first filter media. Due to the reduced adhesive content, the freely accessible specific surface area of the activated carbon punched blank and the sorption performance is improved. The amount of adhesive in the activated carbon punched blank may be reduced to less than 50 wt%.

Brief Description of the Drawing

A few exemplary embodiments are explained in greater detail below with reference to the figures. The figures show, each in schematic diagrams:

Figure 1 the inventive filter arrangement;

Figure 2 an inventive filter;

Figure 3 a filter arrangement whose housing parts are joined in an integrally bonded manner;

Figure 4 a filter arrangement;

Figure 5 a filter arrangement whose housing parts are joined together in a form-fitting and friction-locked manner;

Figure 6 a filter arrangement whose housing parts are joined together in a form-fitting and friction-locked manner and have additional sealing elements;

Figure 7 a filter arrangement whose housing parts are joined together in a form-fitting and friction-locked manner and have additional sealing elements.

Embodiment of the Invention

Figure 1 shows a filter arrangement 7 for cleaning the fuel cell intake air from the fuel cell 19, whereby the filter arrangement 7 is arranged in the intake air stream of the fuel cell 19. If, in particular with PEM fuel cells, a humidifier 20 is provided in the intake air stream, the filter arrangement 7 may be arranged in front of the humidifier 20 to supply the humidifier 20 with cleaned intake air. Thereby the filter arrangement 7 may be provided in front of and/or behind air conveyance equipment 21 to convey the intake air stream.

Figure 2 shows a filter 1 which is arranged in the filter arrangement. The filter 1 is formed from two layers of a first filter medium 2, 3, a layer of a second filter medium 4 being arranged between the first filter media 2, 3, resulting in a sandwich-type design of the filter 1. The filter media 2, 3, 4 are designed to be fiat, with the first filter media 2, 3 having a larger area than the second filter medium. Therefore, the edge sections 5, 6 of the first filter media 2, 3 overlap. These opposing edge sections 5, 6 are joined together. In this embodiment, the edge sections 5, 6 are joined together in an integrally bonded manner by means of ultrasonic welding. In other embodiments, the edge sections 5, 6 may be joined together by hot-melt punching or by gluing. The first filter media 2, 3 are made of a polyester or polypropylene nonwoven and form a preliminary filter and a final filter of the filter 1. The second filter medium is made of activated carbon, with the particles being bonded to one another by an adhesive. The activated carbon blank is then in the form of a pressed blank, which can be shaped by punching. To produce the second filter medium 4, activated carbon is arranged on a carrier made of a nonwoven in a first step. In the next step, the carriers are arranged one above the other with activated carbon and laminated together, with the carriers facing away from one another

and forming the two main sides. In this embodiment, two of the laminated carrier-activated carbon-carrier layers are arranged one above the other, with one activated carbon layer being provided for filtration of acidic gases and another activated carbon layer being provided for filtration of basic gases.

In this embodiment, all three filter media 2, 3, 4 are designed as punched blanks. The filter 1 can be produced in a continuous process in which the punched blanks of the second filter medium 4 are arranged continuously between the layers of the first filter medium 2, 3. Then the first filter media 2, 3, with the second filter medium arranged between them, are punched out; simultaneously with this punching operation, the edge sections 5, 6 of the first filter media 2, 3 are integrally bonded. The filter 1 is arranged in the intake air stream of a fuel cell.

Figure 3 shows a filter arrangement 7 which consists of a housing 8 that holds a filter 1 according to Figure 2. The housing 8 has a top part 9 and a bottom part 10, which are made of plastic by injection molding. Flanges 11 , 12 provided on the top part 9 and the bottom part 10 can be used to bring the top part 9 and the bottom part 10 into contact. According to this embodiment, at the right of the line of symmetry, the filter 1 is arranged between the top part 9 and the bottom part 10 so that the edge sections 5, 6 of the first filter media 2, 3 are placed between the flanges 11 , 12 and secured there. In the other embodiment which is shown at the left of the line of symmetry, the edge sections 5, 6 of the first filter media 2, 3 are held in a groove formed by the flanges 11 , 12 in a form-fitting manner. The top part 9 and the bottom part 10 are designed as deep-drawn parts and have an enlarged cross section in the direction of the flanges 11 , 12 to facilitate their manufacture. In this embodiment, the flange 11 , 12 and the edge sections 5, 6 are integrally bonded together. The filter is secured in the housing in such a way that an air space remains between the top part and the filter and/or between the bottom part and the filter.

To produce the filter arrangement 7, a top part 9 and a bottom part 10 as well as two first filter media 2, 3 and one second filter medium 4 are arranged one above the other and in one operation the edge sections 5, 6 and the flanges 11 , 12 are welded together so that only a single welding operation is necessary to produce a filter arrangement 7. The filter arrangement 7 and the filter 1 in this embodiment have a rectangular essentially square cross section to utilize to the best possible extent the insulation space available. The filter arrangement 7 is also arranged in the intake airstream of a fuel cell.

Figure 4 shows a filter arrangement 7 according to Figure 3 in which the flanges 11 , 12 are not yet joined together. The flange 11 of the top part 9 has a web 14 running around the circumference on the side facing the flange 12 of the bottom part 10, ensuring contact between the flanges 11 , 12. The surface pressure is the greatest here owing to the small area of the web 14 and this area can be welded especially well. Due to the web 14, good penetration of the edge sections 5, 6 is also made possible, so that the connection has an improved imperviousness. .

Figure 5 shows a filter arrangement 7 according to Figure 3, whereby the flanges 11 , 12 in this embodiment are joined together in a form-fitting and friction-locking manner. The flange 11 of the top part 9 engages into the inside circumference of the flange 12 of the bottom part 10. A form-fitting element designed as a bulge 16 is provided on the outside circumference of the flange 11 and engages in a form-fitting manner with a congruently designed groove 15 and, owing to the slight radial pretension, engages in a friction-locked manner via the edge sections 5, 6 of the filter 1 , said groove being arranged on the inside circumference of the flange 12. In other embodiments, two or more form- fitting elements may also be provided. The housing 8 is sealed by the edge sections 5, 6 which are arranged so they are pressed between the flanges 11 , 12. The housing 8 can be opened and closed again for replacing the filter 1.

Figure 6 shows two other embodiments of a filter arrangement according to Figure 5, whereby an additional sealing element is arranged between the flanges 11 , 12. In the embodiment shown at the left of the line of symmetry, an O-ring 17 is arranged between the flanges 11 and 12 as an additional sealing element. An O-ring may be provided when special demands are made of the imperviousness and the housing must at the same time be easy to open. In the embodiment shown at the right of the line of symmetry, a sealing compound 18 is provided as an additional sealing element, this sealing compound being injected into the gap between the flanges 11 , 12. A sealing compound may be provided when special demands are made of the imperviousness and the tolerance requirements are low. If the edge sections are made of a nonwoven made of plastic, then the imperviousness may decline over time due to an irreversible deformation of the nonwoven.

Figure 7 shows two embodiments of a filter arrangement 7 according to Figure 6 whereby the form-fitting connection is designed as a snap fastener and is established directly between the flanges 11 , 12. Therefore, the top part 9 and the bottom part 10 are to be specially installed. In these embodiments, the bulge 16 of the flange 11 engages directly in the groove 15 of the flange 12. To improve the imperviousness, an O-ring 17 is provided at the left of the line of symmetry in this embodiment and a sealing compound 18 is provided at the right of the line of symmetry in this embodiment.