Technical field

The present invention refers to a gas filter system comprising

- an outer filter element having a first filter medium arranged between a first end cap and a second end cap;

- an inner filter element having a second filter medium arranged between a third end cap and a fourth end cap; the first, second and third end caps being open, the inner filter element being closed at the fourth end cap, the first filter medium being arrangeable to surround the second filter medium.

Background

Such a filter system is known from DE 10 2018 215603 A1 .

In some applications, it is required to filter a gas flow with two filter elements. Typically, the gas flows through a first filter element and then, the prefiltered gas flows through a second filter element. The filter elements can be arranged in a common housing. This kind of filter systems is for instance used to filter combustion air for large combustion engines, such as for trucks, construction vehicles or the like. Another application is the filtration of air for fuel cells.

DE 10 2018 215 603 A1 discloses a gas filter system with a first filter element which surrounds a second filter element. At a first axial end, open end caps of the two filter elements are associated with an outlet for clean air. At a second axial end, the first (outer) filter element has an open end cap and the second (inner) filter element has a closed end cap. The closed end cap of the inner filter element is arranged to close the opening in the end cap of the outer filter element at the second axial end.

It is an object of the invention to provide a gas filter system with improved sealing between two filter elements, which are adapted for joint use. This is achieved by a gas filter system according to claim 1 and use of filter elements according to claim 15. Advantageous embodiments are given in the subclaims and the description.

Disclosure of the invention

In accordance with the invention, a gas filter system is provided. The gas filter system comprises

- an outer filter element having a first filter medium arranged between a first end cap and a second end cap; and

- an inner filter element having a second filter medium arranged between a third end cap and a fourth end cap.

The first, second and third end caps are open. The first, second and third end caps generally have a central opening.

The inner filter element is closed at the fourth end cap. The fourth end cap may be a monolithic closed end cap. Alternatively, a closing means may be permanently affixed to the inner filter element for sealing of the fourth end cap.

The first filter medium is arrangeable to surround the second filter medium. The filter media may be hollow-cylindrical or conical, preferably with an essentially circular or oval cross section. The filter media each surround a longitudinal axis. In particular, the filter media may be arranged concentric to a common longitudinal axis. Indications of directions such as radial or axial refer to the longitudinal axis of the filter system. In principle, the first and third end caps are associated with a first axial end; the second and fourth end caps are associated with a second axial end. The end caps cover the filter media in axial direction and in a sectional view will typically have the same geometrical shape as the filter media, e.g. circular or ring-shaped.

During use of the gas filter system, a gas flow is typically first directed through the first filter medium of the outer filter element and then through the second filter medium of the inner filter element. According to the invention, when the outer filter element is arranged around the inner filter element for use of the gas filter system, the first end cap of the outer filter element surrounds the third end cap of the second filter element, and the second end cap of the outer filter element surrounds the fourth end cap of the inner filter element. In other words, the first and third end caps are arranged on the same axial height along the longitudinal axis. Likewise, the second and fourth end caps are arranged on the same axial height along the longitudinal axis. In this mounted state, the first and third end caps are sealed against each other, preferably in the radial direction, and the second and fourth end caps are sealed against each other, preferably in the radial direction. By sealing of the first and third end caps against each other, an intermediate space between the first and second filter media is sealed at the first end. By sealing of the second and fourth end caps against each other, an intermediate space between the first and second filter media is sealed at the second end. Therefore, gas to be filtered must flow through the two filter media consecutively. The end caps being arranged on the same axial height must not necessarily mean that the filter bellows have the same height. For example, in case of a shorter inner filter element the third end cap may comprise an axial extension or collar for abutment against the first end cap of the outer filter element.

The first end cap of the outer filter element can have a first sealing section for sealing abutment against a housing, preferably in the radial direction. Alternatively or additionally, the first sealing section may provide axial sealing abutment against the housing. The first sealing section may be an integral part of the first end cap.

In general, sealing sections described within the context of this invention are softer than the counter-part against which they shall seal. In particular, a respective sealing section can be made from polyurethane, preferably polyurethane foam. The respective counter-part can be made from rigid plastic.

The first end cap of the outer filter element can have a second sealing section for sealing abutment against the third end cap of the inner filter element, preferably in the radial direction. The second sealing section may be an integral part of the first end cap. Preferably, the first end cap - with the first and/or second sealing section - is a monolithic foam part. If the first end cap has the (soft) second sealing section, the third end cap is generally made from a harder material such as rigid plastic and can be glued to the second filter medium.

Alternatively, the third end cap of the inner filter element can have a second sealing section for sealing abutment against the first end cap of the outer filter element, preferably in the radial direction. The second sealing section may be an integral part of the third end cap. In this case, the second end cap may be a, preferably monolithic, foam part. Then, the first end cap is generally made from a harder material such as rigid plastic and can be glued to the first filter medium.

The second end cap of the outer filter element can have a third sealing section for sealing abutment against the fourth end cap of the inner filter element, preferably in the radial direction. Preferably, the third end cap - with the third sealing section - is a monolithic foam part. If the second end cap has the (soft) third sealing section, the fourth end cap is generally made from a harder material such as rigid plastic and can be glued to the second filter medium.

Alternatively, the fourth end cap of the inner filter element can have a third sealing section for sealing abutment against the second end cap of the outer filter element, preferably in the radial direction. The third sealing section may be an integral part of the fourth end cap. In this case, the fourth end cap may be a, preferably monolithic, foam part. Then, the second end cap is generally made from a harder material such as rigid plastic and can be glued to the first filter medium.

End caps, which have at least one sealing section, can be made from polyurethane, in particular polyurethane foam. End caps, against which a sealing section abuts, can be made from rigid plastic. The plastic end caps can be glued to the respective filter medium. The second end cap can have at least one support leg for axial support of the outer filter element against a housing. The support leg can be integrally made with the second end cap.

Preferably, the gas filter system further comprises a housing, in which the inner and outer filter elements are arrangeable. In a mounted state, the filter elements are arranged inside the housing. Typically, the housing comprises a first housing part associated with the first end and a second housing part associated with the second end. An inlet may be formed at the first or second housing part. An outlet is preferably formed at the first housing part. The outlet may be in fluid communication with a clean side inside the inner filter element.

The inner filter element has an axial protrusion at the fourth end cap, which protrusion protrudes into an inner hollow space of the inner filter element. Preferably, the protrusion is integrally formed with the fourth end cap. Alternatively, the protrusion may constitute a closing means for the fourth end cap.

The housing may have a central tube, which extends into the inner filter element at the third end cap in a mounted state of the filter system. The central tube provides guidance to the inner filter element and support to the second filter medium.

The central tube can be held at an axial collar of the housing. This is advantageous for manufacturing the filter housing. A snap fit may be provided between the collar and the central tube.

Preferably, the protrusion and the central tube overlap each other in the axial direction. Mutual guidance and support between the central tube and the inner filter element can be achieved in this way. This can also facilitate mounting of the filter system. In particular, the protrusion may engage into the central tube. In other words, the central tube can surround the protrusion radially outwardly. Preferably, the housing has a dome, which protrudes into the protrusion at the fourth end cap. The dome can provide guidance during mounting and in particular additional support to inner filter element during use of the filter system.

It may further be provided, that the dome and the central tube overlap each other in the axial direction. Undesired movement of the filter elements during operation can be effectively reduced with this design. Upon heavy vibration, the central tube can bear against the dome via the protrusion, which is arranged between the central tube and the dome.

If the first filter element and/or the second filter element have/has a rotational symmetric shape it may be advantageous to add a feature which enables installation in a defined position. The protrusion, the central tube and preferably also the dome may have a corresponding protrusion or indentation in the radial direction. In this way the inner filter element and preferably also the cover may be mounted in a defined rotational position. Likewise, the second end cap and the fourth end cap may have a protrusion or indentation in order to define the relative position of the inner and outer filter element in circumferential direction. Additionally or alternatively, the second end cap and an inner wall of the housing may have a corresponding protrusion and indentation.

The first or the second filter medium, in particular the second filter medium of the inner filter element, can have gas-adsorbing properties and preferably contains activated carbon. Typical harmful gases are SO2, NOx and NH3.

The first or the second filter medium, in particular the first filter medium of the outer filter element, can be made with cellulose.

The first and/or the second filter medium may be pleated.

The invention also relates to the use of an outer filter element and/or an inner filter element in a gas filter system according to the invention, as described above. The gas filter system may be used for cathode air filtration of a fuel cell in an electric vehicle.

Brief description of drawings

Other advantages and features of the invention will be appreciated from the following description of embodiments of the invention with reference to the figures of the drawing, which show significant details, and from the claims. The individual features, as described above or explained below, may each be implemented individually or implemented together in any useful combination in variants of the invention.

Fig. 1 shows a gas filter system according to the invention, the gas filter system comprising an outer filter element, an inner filter element and a housing, in a schematic sectional view;

Fig. 2 shows the outer filter element of the gas filter system of Fig. 1 , in a schematic sectional view;

Fig. 3 shows the inner filter element of the gas filter system of Fig. 1 , in a schematic sectional view;

Fig. 4 shows a first end of the filter system of Fig. 1 in an enlarged view;

Fig. 5 shows a second end of the filter system of Fig. 1 in an enlarged view.

Detailed description

Figure 1 shows a gas filter system 10. The filter system 10 comprises a housing 12. The housing has a first housing part 14 and a second housing part 16, which are attachable to each other. An inlet 18 allows gas to enter the housing 12. Here, the inlet is formed at the first housing part 14. An outlet 19 for filtered gas is also formed at the first housing part 14. The housing parts 14, 16 can be made from metal and/or rigid plastic.

The filter system 10 further comprises an outer filter element 20, see also Figure 2. The outer filter element 20 comprises a first filter medium 22. The first medium 22 is contained between a first end cap 24 and a second end cap 26. The first filter medium 22 surrounds a longitudinal axis 28 in a ciruclar manner. The first filter medium 22 can be made from pleated cellulose paper. The filter system 10 further comprises an inner filter element 30, see also Figure 3. The inner filter element 30 comprises a second filter medium 32. The second medium 32 is contained between a third end cap 34 and a fourth end cap 36. The second filter medium 32 also surrounds the longitudinal axis 28 in a ciruclar manner. The second filter medium 32 can be pleated and can contain activated carbon in order to achieve gas-adsorbing properties.

The inner filter element 30 is arranged inside the outer filter element 20. Both filter elements 20, 30 are arranged inside the housing 12. Here, the first and second filter media 22, 32 are concentric to one another and to the longitudinal axis 28.

At a first end of the filter system 10, the first end cap 24 is arranged to surround the third end cap 34, see also Figure 4. The first end cap 24 and the third end cap 34 each have a central opening, see also Figures 2 and 3, respectively. The outlet 19 is in fluid communication with a clean side 40 within the inner filter element 30, cf. Figure 1 .

The first end cap 24 of the outer filter element 20 is axially and/or radially sealed against the housing 12. A first sealing section 42 axially protrudes form the first end cap 24. The first sealing section 42 abuts the first housing part 14 in the axial and in the radial direction. The first housing part 14 has a circumferential rib 44, against which the first sealing section 42 of the first end cap 24 rests in the radial direction.

The first end cap 24 and the third end cap 34 are sealed against each other. In the depicted embodiment, a radial sealing is established. The first end cap 24 has a second sealing section 46. The second sealing section 46 sealingly abuts the third end cap 34 in the radial direction.

In the depicted embodiment, the first end cap 24 with the first sealing section 42 and the second sealing section 46 is integrally made from polyurethane foam. In other words, the first end cap 24 with its sealing sections 42, 46 is a monolitic part. The third end cap 34 is made from rigid plastic and glued to the second filter medium 32.

A central tube 48 of the housing 12 is held at an axial collar 50, cf. Figures 1 and 4. The collar 50 axially protrudes into the housing 12 at the outlet 19. The central tube 48 extends through the opening of the third end cap 34 towards the fourth end cap 36. The central tube 48 can be made from rigid plastic.

At a second end of the filter system 10, the second end cap 26 is arranged to surround the fourth end cap 36, see also Figure 5. The second end cap 26 has a central opening, see also Figure 2. The fourth end cap 36 is closed, see also Figure 3. In the depicted embodiment, the fourth end cap 36 is a monolitic closed end cap. The fourth end cap 36 can be made from rigid plastic and is preferably glued to the second filter medium 32.

The second end cap 26 and the fourth end cap 36 are sealed against each other. In the depicted embodiment, a radial sealing is established. The second end cap 26 has a third sealing section 52. The third sealing section 52 sealingly abuts the fourth end cap 36 in the radial direction. The second end cap 26 with the third sealing section 52 can be integrally made from polyurethane foam. In other words, the second end cap 26 with its sealing section 52 is a monolitic part.

In its central area (radially within the second filter medium 32), the fourth end cap 36 forms a protrusion 54, see Figures 1 , 3 and 5. The protrusion 54 extendes into the inner filter element 30 in the axial direction towards the third end cap 34.

The central tube 48 of the housing 12 and the protrusion 54 of the inner filter element 30 overlap each other along the longitudinal axis 28. The protrusion 54 may be tapered in order to extend into the central tube 48.

The housing 12 may have a dome 56. Here, the dome 56 is formed at the second housing part 16, which can be a removable cover. The dome 56 extends towards the inside of the inner filter element 30. In particular, the dome 56 extends into the pro- trusion 54 of the inner filter element 30. More particularly, as the protrusion 54 protrudes into the central tube 48, the dome 56, the protrusion 54 and the central tube 48 overlap each other along the longitudinal axis 28.

Reference Numbers

Gas filter system 10

Housing 12

First housing part 14

Second housing part 16

Inlet 18

Outlet 19

Outer filter element 20

First filter medium 22

First end cap 24

Second end cap 26

Longitudinal axis 28

Inner filter element 30

Second filter medium 32

Third end cap 34

Fourth end cap 36

Clean side 40

First sealing section 42

Rib 44

Second sealing section 46

Central tube 48

Collar 50

Third sealing section 52

Protrusion 54

Dome 56