HOUSEHOLD APPLIANCE WITH A SOUND ATTENUATOR

CROSS REFERENCE TO RELATED APPLICATIONS

Applicant claims priority under 35 U.S.C. § 119 of European Application No. 21189382.1 filed Aug. 3, 2021, the disclosure of which is incorporated by reference.

BACKGROUND OF THE INVENTION
1. Field of the Invention

The invention relates to a household appliance, in particular to a floor processing device, with a device housing, a blower arranged in the device housing, an outlet opening formed in the direction of flow behind the blower in the device housing, a flow channel that connects the outlet opening with the blower in terms of flow, and a sound attenuator allocated to the flow channel for attenuating sound arising from the operation of the household appliance.

2. Description of the Related Art

Household appliances of the aforementioned kind are known in prior art. For example, these include floor processing devices, in particular suction cleaning devices, with a blower for vacuuming dust and dirt from a surface to be cleaned. The suction material is usually transferred into a suction chamber by means of the blower, and there accumulated, while air cleaned by a filter flows to a blower, and finally to the outlet opening.

The operation of the blower and rotation of blower blades associated therewith produce soundwaves, which invariably become audible to the user during operation of the household appliance. In order to reduce the background noise associated therewith to a point where the user does not find it to be annoying, silencers that are introduced into the device housing of the household appliance are known in prior art.

Also known in prior art, for example in the field of pipe silencers for air ducts, is to equip flow channels from inside with a perforated support structure, which carries an acoustic foam or a nonwoven. This resultantly increases the pressure loss, so that suction material could no longer be removed as well from a surface to be cleaned relative to a suction cleaning device, for example as would be the case without such a silencer. In order to balance out the negative effect on the efficiency of the silencer, the suction cleaning device would have to be equipped with a more powerful blower or drive motor.

SUMMARY OF THE INVENTION

Proceeding from the aforementioned prior art, the object of the invention is to design a household appliance with a sound attenuator that has the smallest possible construction volume given a simultaneously optimal sound attenuation.

In order to achieve this object, it is proposed that the sound attenuator have a plurality of sound-absorbing wall elements, which together comprise at least a section of the flow channel, wherein the wall elements have a wall surface that is curved in relation to a direction of a longitudinal extension of the flow channel, and are positioned relative to each other in such a way that a flow path formed between opposing wall surfaces is curved.

According to the invention, the flow channel is curved in design at least in relation to a section along its longitudinal extension, so that the airflow guided in the flow channel hits the sound-absorbing wall elements multiple times in the direction of flow, and there can be at least partially absorbed. As a result, the flow channel is provided with sound-absorbing wall elements from the inside on the one hand, and the multiple reflections of the airflow on wall elements lead to an increased overall absorption level on the other. The essential idea of the invention is to give the flow channel as curved a design as possible, and not make it rectilinear or angular. The pressure losses are kept as low as possible, for example as opposed to abrupt (not continuous) changes in direction of the flow channel. As a consequence, a change in direction occurs along a curved flow path according to the invention. A free flow cross section between the opposing wall surfaces of the flow channel especially preferably has a specific minimum size, which is dimensioned as a function of the volume flow of the airflow guided in the flow channel. The free flow cross section should optimally have at least a quantity corresponding to 0.96 times the quantity of the volume flow², i.e., 0.96×Q², wherein Q is the quantity of the volume flow. Relative to the sound-absorbing property of the wall elements, the latter should ideally absorb 100 percent of the sound energy. Since this is rarely possible in practice, the sound attenuator should reach at least a sound absorption of 50 percent overall relative to the sound component to be attenuated.

In addition, it is proposed that the flow path have an s-shaped design, so that there are at least two changes in direction of the flow path within the flow channel. As a consequence, the flow path has at least two essentially opposite changes in direction for the airflow guided within the flow channel, wherein the shape of the flow path is here denoted as s-shaped. However, it goes without saying that other curved shapes having at least two opposite changes in direction, in particular essentially 180° changes, lie within the framework of the invention, for example a z-shape of the flow channel. Changes in direction of 145° to 180° can also optimally achieve the inventive effect. The deflections in the direction of the flow path can basically lie at any point of the flow channel, and be interrupted by straight flow channel sections. In addition, it is possible that not only the sound-absorbing wall elements contribute to the s-shape of the flow path, but also wall areas that essentially have a sound-reflecting design. Given a mixed configuration of predominantly sound-absorbing and predominantly sound-reflecting and straight and curved wall areas, it is essential that the flow channel have at least one section that contains curved and sound-absorbing wall elements, and thus forces a curved routing for the flow path, given a simultaneous, at least sectional absorption property of the curved wall elements.

Furthermore, it is proposed that the flow channel have a constant flow cross section between the opposing wall elements along the flow path. According to this configuration, the distance between the opposing wall elements remains constant, wherein the curved wall surfaces of the wall elements run parallel to each other, following the curvature. As a result, the flow cross section along the flow path likewise remains constant, preferably proceeding from the blower up to the outlet opening of the flow channel. As explained above, the flow cross section is ideally larger than a minimum flow cross section, which is measured as at least 0.96×volume flow².

A special embodiment proposes that the sound attenuator have a support body for receiving the sound-absorbing wall elements. According to this configuration, the sound attenuator is preferably modular in design, specifically comprised of a support body and a plurality of sound-absorbing wall elements that can be connected with the support body. The sound-absorbing wall elements can especially preferably be separably connected with the support body, thereby also enabling a later exchange. During production of the household appliance, the sound attenuator can initially be assembled out of the support body and sound-absorbing wall elements before installing the sound attenuator into the household appliance. This embodiment also makes it possible to individually equip the support body with wall elements depending on the type of respective household appliance, so that an individual sound attenuator can be manufactured for each household appliance. For example, the sound-absorbing wall elements can be adjusted to the respective sound emission spectrum of the household appliance. The support body especially preferably provides slots, which are universally suitable for different wall elements. For example, the wall elements can vary with respect to a material composition and/or wall thickness of the sound-absorbing material. For example, the support body itself consists of a hard plastic, such as ABS (acrylonitrile-butadiene-styrene) or PP (polypropylene). Only in conjunction with the received sound-absorbing wall elements does the support body comprise a complete sound attenuator. The flow paths of the flow channel are thus interactively formed by the surfaces of the sound-absorbing wall elements on the one hand, and by the surfaces of the support body on the other. Inside of the household appliance, the support body is arranged between an air outlet of the blower or a motor-blower unit and the outlet opening of the device housing. In addition, an outer surface of the support body preferably abuts from inside against the device housing of the household appliance. The support body can be fixed on the device housing, for example by a screw connection, clamped connection, plug connection or similar fixing method. The sound-absorbing wall elements are placed in the support body airtight, so that the airflow guided within the support body cannot exit the flow path through any openings or cracks between the material of the support body and the material of the wall elements.

In addition, it can be provided that the support body have a support body wall in a partial area of the support body, wherein the support body wall and the wall elements placed in the support body form a flow channel section closed airtight to the outside, which is airtightly connected with the blower on the one hand and the outlet opening of the device housing on the other. This configuration effectively prevents the airflow or sound guided in the airflow from taking a short circuit around the support body or at least partial areas of the support body. According to a special design of the invention, the support body wall of the support body can be such relative to an air outlet of the blower that the airflow exiting the blower is divided into two flow components which flow separately from each other within the support body to the outlet opening of the device housing. In this regard, two partial flow channels can arise within the support body, which each run s-shaped and subsequently empty in a shared air outlet of the support body. In particular, the support body wall can be orthogonal to an outflow direction of the airflow exiting the blower, so that a first deflection in the direction of the guided airflow in the flow path is already achieved during inflow into the support body. As the airflow enters into the support body, a 90° deflection and bifurcation of the airflow entering into the support body can thus essentially already be achieved, for example. The two partial airflows then run toward each other in a direction of flow behind the support body wall in a 180° deflection, and can be again deflected by 90° by a wall element with a curved design, so that the partial airflows then flow toward the outlet opening of the device housing parallel to each other, but preferably separated further apart from each other.

The wall elements of the sound attenuator are preferably comprised of an open-pored foam. In particular, the wall elements can be fabricated out of melamine resin foam or polyurethane foam. These materials have proven themselves to be especially effective in practice for absorbing common sound frequencies in household appliances, in particular sound frequencies caused by a blower.

In addition, the wall elements preferably have a wall thickness that corresponds to at least one fourth of a wavelength of a sound component to be attenuated. The wall thickness of the wall element determines the cutoff frequency, the so-called “cut-on frequency”, starting at which sound components are absorbed. The sound velocity of a resonance mode of the sound has an amplitude of 0 at a reflecting partial area of the wall element. Proceeding therefrom, the sound velocity then runs in the direction of the opposing wall element in a sinusoidal oscillation with the wavelength λ. To enable the sound-absorbing material of the wall element to exert its effect, the wall thickness of the wall element must correspond to at least one fourth of the wavelength λ of the respective sound component. The nearest peak of the amplitude of the sound velocity can thus still be located within the absorbing material, thereby effectively reducing the sound energy.

It is further proposed that the wall elements have an airtight closing wall on their outwardly facing exterior side facing away from the guided airflow. As a result, the airflow cannot flow completely through the otherwise open-pored material of the wall elements, with the guided air rather remaining within the flow channel instead. As a consequence, the respective wall element has an insulation layer that prevents both air and sound from exiting the flow channel.

Finally, it is proposed that the flow channel have a sound reducing wall, wherein a wall plane of the sound reducing wall is oriented parallel to the flow path, and wherein the sound reducing wall is centrally arranged between the opposing wall surfaces of the flow channel relative to a direction orthogonal to the longitudinal extension of the flow channel. The sound reducing wall is likewise designed to reduce the sound energy of the resonant sound components in the respective flow channel section that contains the sound reducing wall. The sound reducing wall is centrally arranged in the flow channel between the opposing wall surfaces of the flow channel, so that the plane of the sound reducing wall lies precisely where the fast amplitude of the sound velocity has a maximum. As a consequence, the sound reducing wall is spaced apart from the inner wall of the flow channel, and essentially lies centrally within an opening cross section of the flow channel. As a result, the sound-absorbing sound reducing wall is located precisely where an especially large amount of sound energy is guided in the airflow. Since the sound-reducing wall additionally runs parallel to the main direction of flow of the airflow in the flow channel, the airflow is not significantly impeded, so that the suction power of the blower or household appliance remains as high as possible. In other words, the sound-reducing wall is arranged within the flow channel in such a way that the airflow conveyed by the blower can flow within the flow channel to the outlet opening with the least possible pressure loss, while the sound generated by the blower is optimally reduced. The sound-reducing wall is oriented parallel to the direction of the airflow, while the soundwaves form between the opposing inner walls of the flow channel, i.e., transversely thereto. As a result, the airflow generated by the blower can flow through the flow channel with as little pressure loss as possible, and penetrate through the material of the sound-reducing wall. At the same time, an optimal acoustic absorption takes place by means of the sound-reducing wall arranged in the maximum of the sound velocity. The partial airflows flowing separately before reaching the sound-reducing wall can possibly be once again blended together through the sound-reducing wall, so that the airflow as a whole can flow through the flow channel with the least possible pressure loss. This increases the efficiency of the sound attenuator, i.e., the ratio between sound reduction and pressure loss.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and features of the invention will become apparent from the following detailed description considered in connection with the accompanying drawings. It is to be understood, however, that the drawings are designed as an illustration only and not as a definition of the limits of the invention.

In the drawings,

FIG. 1 is a household appliance according to the invention;

FIG. 2 is a schematic diagram of a flow channel with curved wall elements;

FIG. 3 is a longitudinal section of a flow channel with a sound attenuator, which has a support body and wall elements placed therein;

FIG. 4 is a cross section of the flow channel according to FIG. 3;

FIG. 5 is a wall element according to a first embodiment;

FIG. 6 is a wall element according to another embodiment;

FIG. 7 is a wall element according to another embodiment;

FIG. 8 is a wall element according to another embodiment; and

FIG. 9 is a support body for mounting wall elements.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows an example of a possible embodiment of a household appliance 1 according to the invention, which is here designed as a floor processing device. The household appliance 1 here involves a vacuum cleaner to be manually operated by a user. The household appliance 1 has a base device 18 and an attachment 19 detachably connected with the base device 18. For example, the attachment 19 here involves a suction nozzle with a suction mouth 20 and a floor processing element 21 allocated to the suction mouth 20. The base device 18 of the household appliance 1 has a device housing 2, in which a suction material chamber 17 and a blower 3 are located, among other things. A flow channel 5 connects an outlet side of the blower 3 with an outlet opening 4. The blower 3 is used to suck suction material into the suction material chamber 17, wherein suction material located on a surface to be cleaned can be sucked through the suction mouth 20 of the attachment 19 and into the suction material chamber 17 of the base device 18. While the suction material remains within the suction material chamber 17, purified air flows through the blower 3 and flow channel 5 to the outlet opening 4 of the household appliance 1.

The base device 18 of the household appliance 1 further has a handle 23 with a grip 22. A switch 24 is arranged on the grip 22, with which a user can set a specific operating mode of the household appliance 1, for example an intensity stage of the blower and/or a speed of the floor processing element 21 of the attachment 19.

Operating the blower 3 generates noise, which is carried via the flow channel 5 to the outlet opening 4 and into the environment of the household appliance 1. In order to design the household appliance 1 in such a way as to make application comfortable to a user, the household appliance 1 has a sound attenuator 6 shown in greater detail with respect to the additional figures (see in particular FIG. 3). The sound frequencies emitted by the blower 3 depend on various parameters, for example a speed of a motor shaft of the blower 3. A so-called blade passing frequency of the blower 3 is of particular interest, which is determined by the speed of the motor shaft on the one hand, and by the number of blower blades of the blower 3 on the other. Therefore, the sound attenuator 6 is configured in particular in such a way as to absorb the characteristic sound frequencies of the blower 3 of the household appliance that arise at specific power levels of the blower 3.

The principle underlying the invention will now be explained in greater detail based on FIG. 2. One essential aspect of the invention is the geometric design of the flow channel 5 or sound attenuator 6, so as to be able to absorb sound components propagating within the flow channel 5 as best as possible. Therefore, the flow channel 5 is designed by means of a plurality of curved wall elements 7, 8, 9 of the sound attenuator 6 in such a way that a flow path 11 formed between the wall elements 7, 8, 9 is curved, the sound components hit a wall surface 10 of the wall elements 7, 8, 9 as often as possible while passing the flow path 11, and the energy of the sound components is further reduced with each reflection on the wall element 7, 8, 9. The component of sound energy absorbed by the material of the wall element 7, 8, 9 rises with the number of reflections (viewed in absolute terms).

The wall elements 7, 8, 9 are foam elements comprised of an open-pored, acoustically effective foam, for example melamine resin foam or polyurethane foam. On the side facing away from the flow path 11, the wall elements 7, 8, 9 have an exterior side 14 (not shown on FIG. 2) comprised of a sound-attenuating material, so that the soundwaves entering into the pores of the wall elements 7, 8, 9 cannot leave the wall elements 7, 8, 9 on the rear side, i.e., via the exterior side 14, with the unabsorbed components of the soundwaves instead being reflected back into the flow path 11, so as to then in turn enter into an opposing wall element 7, 8, 9. The wall elements 7, 8, 9 have a specific wall thickness d. The wall thickness d determines the depth of the absorbing material of the respective wall element 7, 8, 9 from the flow path 11 in the direction toward the sound-attenuating, i.e., reflecting exterior side 14 of the wall element 7, 8, 9. The wall thickness d of the wall element 7, 8, 9 differs for various entry angles of the sound. In order for the wall element 7, 8, 9 or its absorbing material to be able to optimally absorb a soundwave with a defined frequency, it is necessary that the wall thickness d be at least as large as one fourth of the wavelength of the respective sound component. As a result, a first maximum of the sound velocity of the respective sound component nearest the wall element 7, 8, 9 lies within the absorbing material of the wall element 7, 8, 9. The sound velocity of a soundwave standing between opposing wall elements 7, 8, 9 has an amplitude of 9 on the reflecting inner wall of the exterior side 14 of the wall element 7, 8, 9, and continues as a standing sinusoidal wave to an opposing wall element 7, 8, 9, namely likewise up to the inner wall of the sound-reflecting exterior side 14 of the wall element 7, 8, 9. What is essential is that the amplitude peak nearest the exterior side 14 still lie within the absorbing material of the wall element 7, 8, 9, so that as much sound energy as possible is absorbed within the pores of the material, and does not get back into the flow path 11.

In addition, it is recommended that a minimum flow cross section be established for the free flow cross section of the flow path 11 between the wall elements 7, 8, 9. In practice, the minimum flow cross section should measure at least 0.96×volume flow²relative to the amount of the volume flow squared. This minimum flow cross section is preferably constant along the flow path 11, i.e., if possible from the blower 3 up to the outlet opening 4 in the device housing 2. As a result, the pressure loss within the flow channel 5 can be kept small, and an efficiency indicating the ratio between the sound reduction and pressure loss can be improved to more than 2:1 or even above that.

The wall elements 7, 8, 9 are held in the device housing 2 of the household appliance 1 by means of a support body 12. The support body 12 is shown on FIG. 9. The individual wall elements 7, 8, 9 are visible on FIGS. 5 to 7. The wall elements 7, 8, 9 as well as a sound reducing wall 15 also shown on FIG. 8 are inserted or plugged into corresponding receptacles of the support body 12, namely in such a way that no crevices or cracks arise between which air can escape from the sound attenuator 6. The support body 12 is fabricated out of a stiff plastic, such as ABS or PP.

As further shown on FIG. 3, the support body 12 in the flow channel 5 is arranged on the outlet side of the blower 3, namely between the blower 3 and the outlet opening 4. For example, the exterior side of the support body 12 here hits against the interior side of the device housing 2, and for example is fixed on the device housing 2, in particular by a screw connection, plug connection, latching connection or the like. Together with the wall elements 7, 8, 9 and the sound reducing wall 15 yet to be described later in detail, the support body 12 forms an installation module, which can be installed as a whole into the device housing 2 of the household appliance 1. The support body 12 comprises both its own walls, for example the support body wall 13 that acts as a flow-conducting contour, along with retaining elements for the wall elements 7, 8, 9 placed in the support body 12 as well as the sound reducing wall 15. Since the wall surfaces 10 of the wall elements 7, 8, 9 also have flow-conducting functions, only the support body 12 having completely all elements 7, 8, 9 as well as the sound reducing wall 15 fully forms the flow path 11 of the respective section of the flow channel 5.

As shown on FIG. 3, the outlet air of the blower 3 coming from the outlet opening of the blower 3 is divided into two separate flow paths 11, which at opposing marginal edges of the support body wall 13 flow in opposite directions around the support body wall 13, namely in a downward direction and an upward direction relative to the image plane on FIG. 3. The direction of the respective two flow paths 11 is here deflected by 180°, which is caused by the deflection of the outlet flow around the marginal edges of the support body wall 13. The flow paths 11 subsequently flow through between the wall elements 7, 8, 9, specifically a first flow path 11 between the wall element 8 and wall element 7, and a second flow path 11 between the wall element 9 and wall element 7. The wall element 7 is essentially inserted centrally into the support body wall 13, and in relation to the longitudinal section on FIG. 3 is shaped like a roughly isosceles triangle with concave lateral surfaces. The wall element 7 is shown in detail on FIG. 5. The wall element 7 continues the curvature of the support body wall 13 with its concave wall surfaces 10, and forms a flow path 11 running with essentially a constant opening cross section with the opposing wall element 8 or wall element 9. A tip of the wall element 7 here seamlessly adjoins the sound reducing wall 15, which is likewise placed in the support body 12 and shown in greater detail on FIG. 8.

After passing the wall element 7 between the wall element 8 and sound-reducing wall 15 on the one hand and the wall element 9 and sound-reducing wall 15 on the other, the flow paths 11 continue to flow, wherein the flow paths 11 then initially run parallel to a wall plane 16 of the sound-reducing wall 15, and then flow further around the respective curved wall element 8, 9, so that a flow deflection again arises. As a consequence, the flow paths 11 in the sound attenuator 6 essentially complete an s-shape or z-shape overall. The curved progression of the respective flow paths 11 leads to a maximum number of interactions between the guided airflow and the absorbing material of the wall elements 7, 8, 9. The sound-reducing wall 15 also has a sound-absorbing material, namely preferably a fiber-reinforced nonwoven, for example which is here reinforced to 30% (relative to the volume) with glass fibers or carbon fibers. For example, a wall thickness of the sound-reducing wall 15 measures less than 4 mm. The sound-reducing wall 15 can be air-permeable in design, so that the air components from the flow paths 11 running parallel to the wall plane 16 of the sound-reducing wall 15 can potentially intersect. As a result, the pressure loss within the flow channel 15 is kept as low as possible, so that the overall efficiency of the sound attenuator 6 (sound reduction:pressure loss) becomes as high as possible. Between the wall plane 16 of the sound-reducing wall 15 and the wall element 8 or wall element 9, the flow paths 11 each have a width that roughly corresponds to one fourth of the wavelength of a sound component to be attenuated. As a result, the central plane of the sound-reducing wall 15 lies in the peak of the sound velocity of a resonance mode (of the dominant sound component).

FIG. 4 shows a cross section through the flow channel 5 with the sound attenuator 6. The viewing direction therein is oriented parallel to the wall plane 16 of the sound-reducing wall 15 in the direction of the blower 3. Visible are the flow paths 11 running parallel on both sides of the sound-reducing wall 15, which come from the direction of the central wall element 7. As evident in particular from FIG. 3 as well as the shape of the wall elements 7, 8, 9 according to FIGS. 5 to 7, it is essential that the flow path 11 be as curved as possible in design, and not angular, for example. This ensures that the pressure losses caused within the flow channel 5 are kept as low as possible. In addition, the sound reduction effect due to the curvature and material of the absorbing wall elements 7, 8, 9 as well as the material of the absorbing sound-reducing wall 15 is increased, so that the efficiency of the sound attenuator 6 is as high as possible.

Although only a few embodiments of the present invention have been shown and described, it is to be understood that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention.

LIST OF REFERENCES

1 Household appliance d Wall thickness

2 Device housing

3 Blower

4 Outlet opening

5 Flow channel

6 Sound attenuator

7 Wall element

8 Wall element

9 Wall element

10 Wall surface

11 Flow path

12 Support body

13 Support body wall

14 Exterior side

15 Sound-reducing wall

16 Wall plane

17 Suction material chamber

18 Base device

19 Attachment

20 Suction mouth

21 Floor processing element

22 Grip

23 Handle

24 Switch

HOUSEHOLD APPLIANCE WITH A SOUND ATTENUATOR

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CPC

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Priority Claims (1)