Patent Description:
the first filter medium being arrangeable to surround the second filter medium.

Such a filter system is known from <CIT>.

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.

<CIT> 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 <NUM> and use of filter elements according to claim <NUM>. Advantageous embodiments are given in the subclaims and the description.

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

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

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

According to the invention, the outer filter element has an axial protrusion at the second end cap, which protrusion protrudes into the inner filter element, when the filter elements are arranged for filtering operation of the gas filter system. 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.

Further, according to the invention, the protrusion exhibits a radially outward facing sealing surface. In other words, a radially outward facing sealing surface is formed on the protrusion.

The fourth end cap of the inner filter element has a (second) sealing section for sealing abutment against the sealing surface of the protrusion. In this way, the two filter elements are sealed against each other at the second end. Since the second end cap of the outer filter element, which covers the inner filter element is closed, the filter elements, in particular the inner filter element, are also sealed towards an environment, such as an inlet side of the filter system.

The second sealing section may be an integral part of the fourth end cap. Typically, the second sealing section is made of a material, which is softer than the material of the protrusion. In particular, the sealing section or the fourth end cap in total can be made from polyurethane, preferably polyurethane foam. The protrusion can be made from rigid plastic.

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.

Preferably, the protrusion is integrally formed with a support tube of the outer filter element. In other words, the support tube closes the second end cap and forms the protrusion. The support tube stiffens the outer filter element. The support tube can be partially embedded in the second end cap.

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.

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 first end cap of the outer filter element and the third end cap of the inner filter element are sealed against each other. Gas flow between the filter elements from an environment such as an inlet side, or into the environment from between the filter elements is thereby prevented. This ensures that the gas flows through the two filter elements consecutively.

The first end cap may have a fourth sealing section for sealing abutment against the third end cap, preferably in the radial direction.

Alternatively, the third end cap may have a fourth sealing section for sealing abutment against the first end cap, preferably in the radial direction.

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 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.

The third end cap can be sealed against the collar or the central tube. In particular, the third sealing section of the third end cap may sealingly abut the collar or the central tube. In this way, the inside of the inner filter element can be conveniently sealed towards the housing.

It may be provided, that 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.

Preferably, the housing has a dome, which protrudes into the protrusion at the second end cap. The dome can provide guidance during mounting and in particular additional support to outer 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.

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 SO<NUM>, NOx and NH<NUM>.

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.

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

The filter system <NUM> further comprises an outer filter element <NUM>, see also <FIG>. The outer filter element <NUM> comprises a first filter medium <NUM>. The first medium <NUM> is contained between a first end cap <NUM> and a second end cap <NUM>. The first filter medium <NUM> surrounds a longitudinal axis <NUM> in a ciruclar manner. The first filter medium <NUM> can be made from pleated cellulose paper.

The filter system <NUM> further comprises an inner filter element <NUM>, see also <FIG>. The inner filter element <NUM> comprises a second filter medium <NUM>. The second medium <NUM> is contained between a third end cap <NUM> and a fourth end cap <NUM>. The second filter medium <NUM> also surrounds the longitudinal axis <NUM> in a ciruclar manner. The second filter medium <NUM> can contain activated carbon in order to achieve gas-adsorbing properties.

The inner filter element <NUM> is arranged inside the outer filter element <NUM>. Both filter elements <NUM>, <NUM> are arranged inside the housing <NUM>. Here, the first and second filter media <NUM>, <NUM> are concentric to one another and to the longitudinal axis <NUM>.

At a first end of the filter system <NUM>, the first end cap <NUM> is arranged to surround the third end cap <NUM>, see also <FIG>. The first end cap <NUM> and the third end cap <NUM> each have a central opening, see also <FIG> and <FIG>, respectively. The outlet <NUM> is in fluid communication with a clean side <NUM> within the inner filter element <NUM>, cf.

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

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

A central tube <NUM> of the housing <NUM> is held at the axial collar <NUM>. The central tube <NUM> extends through the opening of the third end cap <NUM> towards the fourth end cap <NUM>. The central tube <NUM> can be made from rigid plastic.

The outer filter element comprises a support tube <NUM>. The support tube extends from the first end cap <NUM> to the second end cap <NUM> on the inside of the first filter medium <NUM>. The support tube <NUM> may be partially embedded in the first and/or second end cap <NUM>, <NUM>. The support tube <NUM> can be made from rigid plastic.

At the second end, the support tube <NUM> sealingly closes the outer filter element <NUM>. At the second end cap <NUM>, the support tube <NUM> forms a closed protrusion <NUM>, see also <FIG>. The protrusion <NUM> extends into the clean side of the inner filter element <NUM> through a central opening in the fourth end cap <NUM> of the inner filter element <NUM>.

The fourth end cap <NUM> is sealed against the protrusion <NUM>. At the protrusion <NUM>, a sealing surface <NUM>, which faces radially outwardly is formed. A second sealing section <NUM> is formed at the opening of the fourth end cap <NUM>. Here, the fourth end cap <NUM> and the second sealing section <NUM> are integrally made from polyurethane foam. The second sealing section <NUM> sealingly abuts the sealing surface <NUM> of the protrusion <NUM> in the radial direction.

The central tube <NUM> of the housing <NUM> and the protrusion <NUM> of the outer filter element <NUM> overlap each other along the longitudinal axis <NUM>. The protrusion <NUM> may be tapered above the sealing surface <NUM> in order to extend into the central tube <NUM>.

The housing may have a dome <NUM>. Here, the dome <NUM> is formed at the second housing part <NUM>. The dome <NUM> extends towards the inside of the inner filter element <NUM>. In particular, the dome <NUM> extends into the protrusion <NUM> of the outer filter element <NUM>. More particularly, the dome <NUM> and the central tube <NUM> overlap each other along the longitudinal axis <NUM>.

A second embodiment of the gas filter system <NUM>', which is partially depicted in <FIG>, corresponds substantially to the first embodiment of the gas filter system <NUM>, cf. <FIG> and the description above. The filter system <NUM>' differs from the gas filter system <NUM> in that, in the second embodiment, the third endcap <NUM> is sealed against the central tube <NUM>. The third sealing section <NUM> sealingly abuts the central tube <NUM> in the radial direction, here slightly below the collar <NUM>.

A third embodiment of the gas filter system <NUM>", which is partially depicted in <FIG>, is also substantially identical to the first embodiment of the gas filter system <NUM>, cf.

In the third embodiment, the first end cap <NUM> of the outer filter element <NUM> is axially and radially sealed against the housing <NUM>. The first housing part <NUM> has a circumferential rib <NUM>, against which the first sealing section <NUM> of the first end cap <NUM> rests in the radial direction.

Claim 1:
Gas filter system (<NUM>; <NUM>'; <NUM>") comprising
- an outer filter element (<NUM>) having a first filter medium (<NUM>) arranged between a first end cap (<NUM>) and a second end cap (<NUM>); and
- an inner filter element (<NUM>) having a second filter medium (<NUM>) arranged between a third end cap (<NUM>) and a fourth end cap (<NUM>);
the first filter medium (<NUM>) being arrangeable to surround the second filter medium (<NUM>);
wherein the first, third and fourth end caps (<NUM>, <NUM>, <NUM>) are open;
wherein the outer filter element (<NUM>) is closed at the second end cap (<NUM>);
wherein the outer filter element (<NUM>) has an axial protrusion (<NUM>) at the second end cap (<NUM>), which protrusion (<NUM>) protrudes into the inner filter element (<NUM>) and which exhibits a radially outward facing sealing surface (<NUM>);
and wherein the forth end cap (<NUM>) of the inner filter element (<NUM>) has a second sealing section (<NUM>) for sealing abutment against the sealing surface (<NUM>) of the protrusion (<NUM>).