EP2510850A1 - Low-noise waste air filter assembly - Google Patents

Abstract

The filter assembly (10) has an air guide rib (13) that is arranged at downstream side of an air filter (12) in circulating manner. The air guide rib is formed to guide exhaust air flow from the air filter to an air-permeable sound absorber (14) without leakage. The circulating air guide rib forms a contour pocket, where contour of the contour pocket is formed for retaining the air-permeable sound absorber such that the air is prevented to pass between the sound absorber and the air guide rib. An independent claim is included for a method for manufacturing a filter assembly.

Description

TECHNICAL AREA

Embodiments of the present invention relate to an apparatus and a method for cleaning or filtering an exhaust air stream by means of an air filter, such as. B. in household appliances, in particular, but not exclusively, vacuum cleaners, can be used.

STATE OF THE ART

For removing dust from an exhaust air flow of a household appliance, such. As a vacuum cleaner, are from the writings US Pat. No. 3,882,961 . JP 05317208 A and DE 10 2005 058 940 A1 , various filter arrangements known.

Such exhaust air filter assemblies often include an air or particulate filter disposed in a filter housing. Often, two or three filter stages are arranged in series in a filter assembly to maximize a quantity of dust collected by the filter assembly.

Known exhaust filter types include, for example, a foam filter, which is arranged directly in the exhaust air flow and in itself has a relatively large dust retention capacity. An electric and / or HEPA (High Efficiency Particulate Air Filter) capable of collecting very small particles of dust, especially particles smaller than 1 μm, can then be placed downstream of the foam filter. to retain or filter out of the exhaust air flow those residual dust that escaped the upstream foam filter.

In addition to filtering out the finest dust particles, it is also possible with known filter devices to improve the odor of the exhaust air of a vacuum cleaner. With, for example, when vacuuming dust recorded even microorganisms such. B. bacteria or house dust mites get into the dust filter of a vacuum cleaner, especially in the dust filter bag. A massive accumulation of all impurities in the Dust filter bag and possibly also in the after- or exhaust filter accelerates and enhances the growth and reproduction of mites and bacteria, as well as their excrement, whereby a moisture content in the filters can be disadvantageously increased with the additional formation of a warm, moist atmosphere. Due to the then accelerated decomposition processes, an unpleasant odor can develop, especially in the dust filter bag, which can pollute the ambient air when vacuuming. Multi-stage filter arrangements with particle and downstream odor filters, which are to prevent such unpleasant odor nuisance, are for example from WO 2000/066247 A1 , of the US 2001/0015132 A1 and the WO 2008/070963 A1 known. There filter arrangements are shown, which filter an exhaust air stream by means of a series arrangement of a fine dust or HEPA filter and a downstream carbon impregnated foam filter (active carbon filter) for odor absorption.

In addition to dust and odor nuisances it comes when blowing exhaust air by means of a motor-blower unit by downstream arranged to conventional filter arrangements often also considerable noise nuisance, which u. a. caused by diffuse Luftverwirbelungen or turbulent flow conditions in and after conventional filter arrangements. Especially in everyday activities such as vacuuming, it would be desirable to keep such noise levels as low as possible.

PRESENTATION OF THE INVENTION

It is therefore an object of the present invention, noise or noise in a Abluftausblasbereich especially in household appliances, such. As vacuum cleaners to reduce.

A realization of embodiments of the present invention is to arrange for an air or particulate filter, such as a HEPA filter, for noise reduction in the downstream direction of an exhaust air stream an air-permeable sound absorber, which is also intended to serve to calm a diffuse exhaust air flow and rectify if necessary. In this case, serve as an air-permeable sound absorber, for example, a sound-absorbing layer, which, for example, a sound-absorbing fleece or a sound-absorbing foam such. B. one Melamine resin foam, may have. In embodiments, the sound absorber takes over only a sound-absorbing and / or the exhaust air stream rectifying function. A particle and / or odor filtration by means of the sound-absorbing layer, however, is not provided. This can already be accomplished by the upstream air filter.

Embodiments therefore relate to a filter arrangement with a series arrangement of air filter and sound absorber, wherein the sound absorber downstream of the air filter, d. H. downstream of the exhaust air flow. To direct the exhaust air flow from the air filter in the downstream sound absorber, a circumferential air guide rib is provided in a transition region of the air filter to the sound absorber.

Embodiments of the present invention thereby include a filter assembly for cleaning an exhaust air stream by means of an air filter, the filter assembly having an air guide fin circumferentially disposed on a downstream side of the air filter configured to locate the exhaust air stream from the air filter to downstream in series with the air filter to conduct air-permeable sound absorber. As a result, a diffuse exhaust air flow from the air filter can be passed through the air duct in the air-permeable sound absorber to then flow through the sound absorber calms at its exit areas.

Preferably, the circulating Luftleitrippe be formed to conduct the exhaust air flow from the air filter, which may be, for example, a particle or HEPA filter leak-free to the air-permeable sound absorber, the sound absorber according to embodiments having a sound-absorbing layer, which, for example, a sound-absorbing Fleece or a sound-absorbing foam, such as. B. a melamine resin foam, may include.

According to exemplary embodiments, the circulating air guide rib can form a contour pocket whose contour is designed to accommodate the sound absorber without play, so that no exhaust air can flow between the sound absorber and the circulating air guide rib. This is particularly advantageous if a resiliently deformable foam is used as the sound absorber, which can take a clamping fit in the contour pocket. In such embodiments is also a simple exchange of the sound absorbing foam, if necessary. It is according to other embodiments also possible to glue side surfaces of the sound absorber with inner surfaces of the circumferential air guide rib in order to obtain a leak-free coupling of the air filter or air guide rib and sound absorber. As a result, a particularly hard-wearing, leak-free connection of the sound-absorbing foam to the circulating air guide rib becomes possible.

In preferred embodiments, the circumferential air guide rib has a lower height than the air-permeable sound absorber to be accommodated therein, so that side surfaces of the air-permeable sound absorber are only partially covered by the circulating air guide rib in the assembled state of the filter arrangement. Due to the protrude of the downstream sound absorber on the circumferential Luftleitrippe also not covered by the Luftleitrippe parts of the side surfaces of the air-permeable sound absorber can be used as a blowout, which can contribute to a particularly advantageous reduction of the Ausblasluftgeschwindigkeit and thus the reduction of the Ausblasgeräuschs.

Other embodiments also see a household appliance, such. As an air conditioner, but in particular a vacuum cleaner, with a filter assembly according to embodiments of the present invention.

Further embodiments and advantageous developments are the subject of the dependent claims, as well as the following detailed description of the accompanying figures.

According to the concept presented here, an air or particle filter via an air guide or air guide rib is airtight or leak-free with an air-permeable sound absorber, z. B. in the form of a sound-absorbing foam, coupled to reduce noise. Diffuse exhaust air can thus be passed leak-free on the air duct rib and then calm out of the exit areas of the air-permeable sound absorber. Thus, by embodiments of the present invention, unpleasant and annoying noises can be reduced in the blow-out area after a motor-blower unit.

Hereinafter, embodiments of the present invention will be explained with reference to the accompanying figures. Show it:

BRIEF DESCRIPTION OF THE FIGURES

Fig. 1

a schematic cross section through a filter assembly for cleaning an exhaust air stream, according to an embodiment of the present invention;

Fig. 2

an exploded view of the filter assembly according to Fig. 1 ;

Fig. 3

a perspective view of the filter assembly according to Fig. 1 and Fig. 2 ; and

Fig. 4

a vacuum cleaner with a filter assembly, according to an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

The Fig. 1 shows a schematic representation of a cross section through a filter assembly 10 for cleaning an exhaust air stream, which is indicated by the reference numeral 11, by means of an air filter 12th

The filter assembly 10 has an air guide rib 13 circumferentially disposed on a downstream side of the air filter 12 and configured to direct the exhaust air flow 11 from the air cleaner 12 to a downstream air-permeable sound absorber 14 in series with the air cleaner 12. In this case, "downstream" in the flow direction and "upstream" counter to the flow direction of the exhaust air flow 11.

The air filter 12 may be, for example, a particle or particulate filter in the form of a HEPA filter. HEPA filters can, for. As for filtering out viruses, respirable dusts, mite eggs and excretions, pollen, smoke particles, asbestos, bacteria, various toxic dusts, etc., are used from the exhaust air stream 11. Accordingly, some embodiments of the filter assembly 10 may be used, inter alia, in the medical field, such as in operating rooms, intensive care units and / or laboratories, as well as in clean rooms. For the selection of a filter class of the air filter 12, the respective application is crucial. Other embodiments of the filter assembly 10 may also be used for non-industrial applications, such as As household appliances, and in particular vacuum cleaner used. Vacuum cleaners generally comprise a motor-blower unit, by means of which the exhaust air stream 11 can be blown through the (downstream) filter assembly 10 to the outside. In connection with a vacuum cleaner, the air filter 12 may be, for example, a HEPA filter, an electric dust filter and / or a foam filter for odor absorption. Under the air filter 12 can therefore - depending on the purpose - also a combination of different air, particulate and / or odor filter are understood.

Seen in the direction of the exhaust air flow 11, d. H. Downstream of the air filter 12 is the air-permeable sound absorber 14. According to exemplary embodiments, the sound absorber 14 primarily serves to calm and / or rectify the exhaust air flow 11 diffusely emerging from the air filter 12, so that it is caused by the exhaust air flow 11 or with it associated Ausblasgeräusch can be reduced. The air-permeable sound absorber 14 may be a sound-absorbing or sound-reducing layer according to exemplary embodiments. This sound-absorbing or reducing layer 14 has no air cleaning function, but only serves mainly to calm and / or the rectification of the exhaust air flow 11 and thus the noise reduction. As a sound-absorbing material according to embodiments, for example, a sound-absorbing fleece or a sound-absorbing foam, such. As a melamine resin foam may be provided.

The circulating air guide rib 13 arranged in the transitional region between the air filter 12 and the sound absorber 14 is preferably designed to guide the exhaust air flow 11 from the air filter 12 without leakage to the air-permeable sound absorber, ie to the sound-absorbing layer 14. D. h., The sound-absorbing layer 14 is downstream of the air filter 12 through the air duct 13 quasi airtight or leak-free for noise reduction, which is to be understood that between side walls 15 of the sound absorber 14 and the rotating air duct 13 no originating from the air filter 12 To be able to flow through exhaust air. For this purpose, the circumferential air guide rib 13 in embodiments forms a contour pocket whose contour is formed to accommodate the air-permeable sound absorber 14 without play, so that between the sound absorber 14 and the circumferential air guide rib 13 no exhaust air can flow. The contour or the floor plan of the circumferential air guide rib 13 is thus adapted to a contour or a floor plan of the sound-absorbing layer 14. According to exemplary embodiments, the circumferential air guide rib 13 and the sound-absorbing layer 14 may have a substantially rectangular contour, corresponding to a cuboidal volume of the sound absorber 14 and / or of the air filter 12. Of course, with regard to the air filter 12, the circumferential air guide rib 13 and / or the sound-absorbing layer 14, other plans or contours, such as square or circular contours, conceivable.

In order to record the sound absorber 14 without play in the circumferential air guide rib 13, the inner dimensions of the circumferential air guide rib 13, for example, be slightly smaller than the outer dimensions of the sound absorber 14. In this way, the sound absorber 14 after its introduction into the contour of the circumferential air guide rib 13, or the frame formed by these, take a kind of press fit in this. In particular, in connection with an elastic, sound-absorbing foam 14 thus a clearance or leakage can be achieved. In addition or as an alternative to the clamping fit, the air-permeable sound absorber 14 can also be adhesively bonded to inner surfaces of the circumferential air guiding rib 13 at its side surfaces 15, as indicated by the reference numeral 16, in order to prevent the passage of exhaust air between the side walls 15 and the air guiding rib 13.

In a preferred embodiment, the (around the air filter 12 and the sound absorber 14) circulating air duct 13 has a lower height h ₁₃ , as the sound-absorbing therein sound absorber 14, so that the side surfaces 15 of the air-permeable sound absorber 14 in the assembled state of the filter assembly 10th only partially covered by the circumferential air guide rib 13, as shown in the Fig. 1 can be seen. D. h., The sound-absorbing, exhaust-permeable layer 14 is in the assembled state beyond a frame formed from the air duct 13, whereby the side surfaces 15 of the sound absorber 14, in addition to a downstream facing exhaust air outlet surface 18, as a Ausblasfläche and can be used, as in Fig. 1 is indicated by the obliquely away from the side surfaces 15 away arrows. This can advantageously contribute to a further reduction of a resistance formed by the sound absorber 14 and thus to a reduction of the air velocity and the Ausblasgeräuschs. According to an embodiment of the present invention For example, the sound-absorbing or reducing layer 14 may have a height h ₁₄ of about 20 mm. This means that according to a preferred embodiment, the height h _{13 of} the circulating air guide rib 13 is smaller than 20 mm, ie h ₁₃ <h ₁₄ . Preferably, in this embodiment, the height h _{13 is} less than half the height h ₁₄ , ie, h ₁₃ <10 mm, to provide sufficient lateral discharge area at the sound absorber 14.

Like it out Fig. 1 1, the filter assembly 10 includes a filter frame 17 for accommodating, in a mounted state, the filter assembly 10, the air filter 12 in a first (upstream) filter frame portion 17a facing the inflowing air, and for receiving, in the assembled state, the air-permeable one Sound absorber 14 in a second (downstream) filter frame portion 17b facing the outflowing air, wherein the second filter frame portion 17b has the circumferential Luftleitrippe 13 which is adapted to the exhaust air flow 11 of the first filter frame portion 17a arranged or arranged air filter 12 to the in the second filter frame portion 17 b can be arranged or arranged air-permeable sound absorber 14 to lead. The two filter frame sections 17a, 17b follow each other directly.

The upstream first filter frame portion 17 a is formed to completely accommodate the air filter 12 in itself. That is to say, a height h _17a of the frame formed by the first filter frame section 17a corresponds at least to a height h _{12 of} the air filter 12 to be accommodated in a positive fit. The side walls of the first filter frame section 17a thus preferably surround the side walls or surfaces of the air filter 12 completely. to ensure that the exhaust air flow 11 can be filtered by the air filter 12 completely and without leakage. In addition or alternatively, an adhesive connection between side surfaces of the air filter 12 and inner surfaces of the first filter frame portion 17a is conceivable in addition to a clamping seat of the air filter 12 in the first filter frame section 17a. In other words, the first filter frame portion 17a has a geometry adapted to a geometry of the air filter 12, so that in the assembled state side surfaces of the air filter 12 are completely surrounded by the first filter frame portion 17a.

The filter frame 17 formed from the sections 17a and 17b may be integrally formed according to one embodiment. For example, the filter frame 17 could be made of plastic by an injection molding process. In other words, the circumferential Luftleitrippe 13 can be integrally formed in the direction of the outflowing air, d. H. downstream, to the first filter frame portion 17a to be formed to form the immediately following second filter frame portion 17b.

A perspective exploded view of the filter assembly 10 is shown in FIG Fig. 2 shown.

The Fig. 2 11 shows the filter frame 17 having the first filter frame portion 17a in a lower (upstream) region and the second filter frame portion 17b with the circumferential air guide rib 13 for receiving the sound absorber 14 in an upper (downstream) region. On the first filter frame portion 17a may be laterally formed a projection 21 with two further, laterally projecting protrusions 22. The projections 22 can serve, for example, as gripping sections, by means of which the filter arrangement 10 can be introduced into or removed from a filter housing provided therefor.

As in the view of Fig. 2 1, the filter frame 17 between the first and second filter frame sections 17a and 17b may include an optional grid 23 for separating the downstream (and upstream) air cleaner 12 and the downstream (or downstream) sound absorber 14 from each other. The individual grid bars of the grid 23 may, for example, advantageously be configured as air guide ribs arranged in parallel in order to rectify the diffuse exhaust air flow 11 from the air filter 12 and / or to conduct it in a calm manner into the sound absorber 14. That is, from a diffuse or turbulent flow, a laminar flow can be effected by means of the grating 23, before the exhaust air flow 11 enters the sound absorber 14. Further, on the grid 23 downstream thorn-like projections 24 may be attached, by means of which the sound absorber 14, the z. B. may be in the form of a sound-absorbing foam, in addition to the circumferential air duct 13 can be fixed. When introducing the sound-absorbing foam 14 into the second filter frame portion 17b formed by the circulating air guide rib 13, the sound-absorbing foam 14 becomes upstream, that is, toward the first filter frame portion 17a, pressed to the grid 23, so that the spikes 24 can press into the foam body 14 in order to fix this in addition. The sound absorbing foam 14 and the air filter 12 may be in direct contact with the grid.

However, embodiments are also possible in which the air filter 12 and the sound absorber 14 are directly, i. without the grid 23, are arranged one after the other. In this case, air filter 12 and sound absorber 14 may be glued together, for example, wherein an exhaust air flow 11 is ensured.

Based on Fig. 2 Also, a method for manufacturing or mounting the low-noise filter assembly 10 is clear.

On the downstream side of a provided air filter 12, the circulating air guide rib 13 is arranged so as to guide the exhaust air flow 11 from the air filter 12 to an air-permeable sound absorber 14 which can then be arranged in series with the air filter 12 downstream. In the downstream of the air filter 12 arranged circumferential air guide rib 13 of the air-permeable sound absorber 14 is arranged.

In particular, in a first step, the filter frame 17 can be provided with the first section 17a facing the inflowing air and the second section 17b facing the outflowing air, the second section 17b having the circulating air guide rib 13, which is designed to control the exhaust air flow 11 from the air filter 12, which can be arranged in the first section 17a, to the sound absorber 14 which can be arranged in the second section 17b. In order to obtain the entire filter assembly 10, the air filter 12 is disposed in the first portion 17a of the filter frame 17, and the air-permeable sound absorber 14 is disposed in the second portion 17b of the filter frame 17. It is important on the one hand that both the air filter 12 play and thus leak-free in the first filter frame portion 17a and the air-permeable sound absorber 14 play and thus is arranged without leakage in the circumferential air guide rib 13, so that both between the air filter 12 and the first filter frame section 17a as well as between the sound absorber 14 and the circulating air duct 13 each exhaust air 11 can flow through. Second, it is advantageous if the sound absorber 14 protrudes beyond the circumferential air guide rib 13, in particular when the side surfaces 15 of the air-permeable sound absorber 14 also can be used as blow-out, whereby the exhaust air flow 11 distributed over a larger area and thus the blow-out and thus the noise can be reduced.

After mounting the filter assembly from their individual parts results in a mounted filter assembly 10, as exemplified in a perspective view in Fig. 3 is shown.

In one embodiment of the filter assembly 10, the z. B. can be used in the blow-out of a vacuum cleaner, the filter assembly 10, for example, a length I of about 160 mm, a width b of about 60 mm and a height h of about 45 mm. At a height h _{14 of} the sound-absorbing foam 14 of about 20 mm, this results in a possible height h _{12 of} the HEPA filter 12 of about 25 mm.

In the presentation of Fig. 3 can be easily seen that the air duct 13 has a lower height h ₁₃ than the sound absorber 14 located therein, so that the side surfaces 15 of the sound absorber 14 in addition to its downstream air outlet surface 18 can also contribute to the flow of calmed exhaust air flow 11 advantageous, as it Arrows in Fig. 3 is indicated.

For a better understanding of a possible placement of the filter assembly 10 in a vacuum cleaner, shows Fig. 4 an opened vacuum cleaner 40 with a motor-blower unit 41 and a Abluftstromauslass 42. Between the motor-blower unit 41 and the outlet 42 in the housing of the vacuum cleaner 40, the above-described filter assembly 10 is arranged in a designated filter housing to To filter an exhaust air flow from the motor-blower unit 41 to the outlet 42 quietly. For this purpose, the filter assembly 10 is in a housing (in Fig. 4 shown open), from which it can be removed by means of the frame portion 17 a located projections or tabs 22 or introduced into this.

Embodiments of the present invention thus also include a vacuum cleaner 40 with a filter device 10 according to embodiments.

According to the concept described here, an air-guiding rib 13 is located downstream of a blow-off air filter 12, which may comprise a HEPA filter, for example. This rib 13 may be integrally formed on the outflowing side of the filter 12. In turn, a sound-absorbing foam as a sound absorber 14 can be clamped airtight in this contour pocket formed thereby.

By means of embodiments of the present invention, diffuse exhaust air can be guided past the air guide rib 13 in a leak-free manner and thus flow out at the outlet regions 15, 18 of the foam-type sound absorber 14 in a calm manner.

The filter frame 17 may also be used for a ratio variant without foam according to some embodiments of the present invention.

Another advantage of the present invention can be seen in the simple, one-piece construction of the filter frame 17. Despite this simple structure, by embodiments of the present invention, a significant noise reduction in the blow-out area of a household appliance, such. As a vacuum cleaner take place.

In particular, by embodiments in which the downstream sound absorber 14 is above the frame portion 17b and the Luftleitrippe 13 also, the side surfaces 15 of the foam-like sound absorber 14 can be additionally used as a blow-off, which can contribute to a further reduction of the air velocity and the Ausblasgeräuschs.

LIST OF REFERENCE NUMBERS

10

A filter assembly

11

exhaust air flow

12

air filter

13

Luftleitrippe

14

sound absorber

15

Side surface of the air-permeable sound absorber 14

16

adhesive layer

17

filter frame

17a

first filter frame section

17b

second filter frame section

18

downstream air outlet surface of the sound absorber 14

21

Projection on the first filter frame section

22

Grab handle projection on the first filter frame section

23

grid

24

thorns

40

vacuum cleaner

41

Motor-fan unit

42

exhaust outlet

Claims (11)

Filter arrangement (10) for cleaning an exhaust air stream (11) by means of an air filter (12), in particular in a domestic appliance, comprising: an air guide fin (13) circumferentially disposed on a downstream side of the air filter (12) and adapted to move the exhaust air flow (11) from the air filter (12) to an air-permeable sound absorber (14) downstream of the air filter (12) to lead, wherein the encircling air guide rib (13) has a lower height than the air-permeable sound absorber (14) to be accommodated therein, so that side surfaces (15) of the air-permeable sound absorber (14) in the assembled state of the filter arrangement (10) only partially from the circulating air guide rib (13) are covered. Filter arrangement (10) according to claim 1, wherein the circulating air guide rib (13) is designed to guide the exhaust air flow (11) from the air filter (12) leak-free to the air-permeable sound absorber (14). Filter assembly (10) according to any one of the preceding claims, wherein the circumferential Luftleitrippe (13) forms a contour pocket whose contour is formed to receive the air-permeable sound absorber (14) without play, so that between the sound absorber (14) and the circulating air guide rib (13 ) can not flow through exhaust air. A filter assembly (10) according to any one of the preceding claims, comprising: a filter frame (17) for receiving, in an assembled state, the air filter (12) in an inflowing air facing first filter frame portion (17a) and for receiving, in the assembled state, the air-permeable sound absorber (14) facing in an outgoing air second filter frame portion (17b), wherein the second filter frame portion (17b) comprises the circumferential air guide rib (13) adapted to direct the exhaust air flow from the air filter (12) disposable in the first filter frame portion (17a) to the air-permeable sound absorber (14b) locatable in the second filter frame portion (17b) ). A filter assembly (10) according to claim 4, wherein the circulating air guide rib (13) is integrally formed in the direction of the outflowing air to the first filter frame portion (17a) to form the second filter frame portion (17b). A filter assembly (10) according to any one of claims 4 or 5, wherein the filter frame (17) between the first and the second filter frame portion has a grid (23) to separate the air filter (12) and the air-permeable sound absorber (14) from each other. A filter assembly (10) according to any one of claims 4 to 6, wherein the first filter frame portion (17a) has a geometry adapted to a geometry of the air filter (12) so that when mounted, side surfaces of the air filter (12) are completely separated from the first filter frame portion (17a ) are surrounded. Filter assembly (10) according to any one of the preceding claims, wherein the air filter (12) comprises a particulate filter, in particular a HEPA filter, and / or the sound absorber (14) comprises a sound-absorbing foam. Vacuum cleaner (40) with a filter arrangement (10) for cleaning an exhaust air flow according to one of the preceding claims. Method for producing a filter arrangement (10) for cleaning an exhaust air stream (11), comprising the following steps: Providing an air filter (12); Arranging, on a downstream side of the air filter (12), a circulating air guide rib (13) adapted to move the exhaust air flow (11) from the air filter (12) to an air-permeable one downstream of the air filter (12) To direct sound absorber (14), wherein the circumferential air guide rib (13) is arranged so that it has a lower height than the air-permeable sound absorber (14) to be accommodated therein, so that side surfaces (15) of the air-permeable sound absorber (14) in the assembled state only partially covered by the circulating air guide rib (13); and Arranging the air-permeable sound absorber (14) in the circumferential air guide rib (13). A method of manufacturing a filter assembly (10) according to claim 10, wherein arranging said circulating air duct (13) comprises providing a filter frame (17) having a first portion (17a) facing an inflowing air and a second portion (17b) facing an outflowing air. wherein the second section (17b) has the circulating air guide rib (13), which is designed to move the exhaust air flow (11) from the air filter (12) which can be arranged in the first section (17a) to that in the second section (17b). directable sound absorber (14), wherein the air filter (12) in the first portion (17a) of the air-permeable sound absorber (14) in the second portion (17b) of the filter frame are arranged.

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