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; and

- an inner filter element having a second filter medium arranged between a third end cap and a 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 or US 5,415,677 A.

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 a 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.

The filter described in US 5,415,677 A comprises a primary and a secondary air filter element. At a rear end, the primary and the secondary air filter element are each closed by an end cap. At a front end, open end caps are provided at the primary and at the secondary filter elements. Annular gaskets are disposed at the open end caps in order to seal the primary and secondary filter element against a canister, in which the filter elements are arranged.

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, third and fourth end caps are open. The first, third and fourth 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 a circular or oval cross section. The filter media each surround a longitudinal axis. In particular, the filter media may be arranged concentric to the common longitudinal axis. Indications of directions such as radial or axial refer to the longitudinal axis. 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. 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 outer filter element is sealed against the inner filter element between the second end cap and the fourth end cap, preferably in the radial direction. 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 fourth end cap of the inner filter element can have a (second) sealing section for sealing abutment against the outer filter element, preferably in the radial direction. Alternatively or additionally, the second sealing section may provide axial sealing. The second sealing section may be an integral part of the fourth end cap. Preferably, the fourth end cap - with the second sealing section - is a monolithic foam part.

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 respect- tive counter-part can be made from rigid plastic.

The second end cap of the outer filter element can be a monolithic closed end cap. The monolithic closed end cap can be made of rigid plastic and is preferably glued to the first filter medium.

Alternatively, a closing means may be permanently affixed to the outer filter element for sealing of the second end cap. The monolithic closed end cap can be made of rigid plastic. Preferably, the outer filter element has a support tube. The support tube stiffens the outer filter element. The support tube can be partially embedded in the first and/or second end cap. The support tube can be made of rigid plastic.

Particularly preferably, the support tube has a radially inward facing end face, which end face closes the outer filter element at the second end cap. Thus, the support tube is used in a dual function as a stiffening means and as a closing means. By providing the closed end face, manufacturing of the second end cap can be facilitated, as less material is required. In particular, the second end cap can be made of polyurethane, preferably polyurethane foam, which might be directly molded to the first filter medium and preferably the support tube.

In a mounted state, the fourth end cap can be sealed against the support tube. In particular, the second sealing section may sealingly abut the support tube. The support tube may have an annular sealing strip for sealing abutment of the second sealing section. This facilitates sealing of the outer and inner filter elements between the second and fourth end caps. Preferably, the sealing strip of the support tube has a radially inward facing sealing surface. Radial sealing tolerates slight axial displacement of the inner filter element relative to the outer filter element.

The outer filter element has an axial protrusion at the second end cap, which protrusion protrudes into the inner filter element. The protrusion provides guidance between the filter elements, in particular during mounting. The protrusion typically protrudes beyond the fourth end cap of the inner filter element in the axial direction. The protrusion can be formed at the monolithic second end cap or at the end face of the support tube.

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

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.

Preferably, the housing has a dome, which protrudes into the protrusion. The dome can provide guidance during mounting and in particular additional support to outer filter element during use of the filter system.

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 outer 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. 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.

At least two of an inner wall of the housing, the second end cap, the fourth end cap, the protrusion, the central tube and the dome can have a projection-receiver arrangement which provides for defined installation in circumferential direction. For example, a radially inward directed projection on the housing wall could project into a recess on the outer circumference of the second end cap.

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 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 second filter medium 32 near 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.

A first sealing section 42 axially protrudes form the first end cap 24. The first sealing section 42 sealingly abuts the first housing part 14 in the axial direction. Here, the first end cap 24 with the first sealing section 42 is integrally made from polyurethane foam.

A third sealing section 44 axially protrudes from the third end cap 34. The third sealing section 44 sealingly abuts the first housing part 14 in the radial direction. In particular, the third sealing section sealingly rests against a collar 46, which axially protrudes into the housing 12 at the outlet 19. Here, the third end cap 34 and the third sealing section 44 are integrally made from polyurethane foam.

A central tube 48 of the housing 12 is held at the axial collar 46. 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.

The outer filter element comprises a support tube 50, see Figures 1 , 2, 4 and also Figure 5. The support tube extends from the first end cap 24 to the second end cap 26 on the inside of the first filter medium 22. The support tube 50 can be made from rigid plastic.

The support tube 50 may be partially embedded in the first and/or second end cap 24, 26. In particular, the second end cap 26 is in sealing contact with the support tube 50. Here, the second end cap 26 is made from polyurethane foam and can be molded to the first filter medium 22 and the support tube 50, in order to obtain a permanent connection. At the second end, the support tube 50 has a closed end face 52. The closed end face 52 spans a central area radially inside the first filter medium 22. In this way, the outer filter element 20 is closed at the second end cap 26 by the end face 52 of the support tube 50.

Radially within the second filter medium 32, the closed end face 52 of the support tube 50 forms a protrusion 54, see Figures 1 , 2 and 5. The protrusion 54 extends into the inner filter element 30 through a central opening in the fourth end cap 36.

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 central tube 48 may surround the protrusion 54.

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 protrusion 54 of the outer filter element 30. More particularly, the dome 56, the protrusion 54 and the central tube 48 overlap each other along the longitudinal axis 28.

The fourth end cap 36 is sealed against the outer filter element 20, cf. Figures 1 and 5. In the depicted embodiment, a radial sealing is established. The fourth end cap 36, at its outer perimeter, has a second sealing section 58, see also Figure 3. The fourth end cap 36 with the second sealing section 58 can be integrally made from polyurethane foam. In other words, the fourth end cap 36 with its sealing section 58 is a monolitic part.

The fourth sealing section 58 sealingly abuts an annular sealing strip 60 (see also Figure 2) of the support tube 50 in the radial direction. Here, the sealing strip 60 is formed on the same axial height as the second end cap 26. This allows the second end cap 26 and the fourth end cap 36 to seal against the sealing strip 60 from radially outside or inside, respectively. 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

Third sealing section 44

Collar 46

Central tube 48

Support tube 50

End face 52

Protrusion 54

Dome 56

Second sealing section 58

Sealing strip 60