Patent Description:
In general, the present invention finds an application in the ventilation, conditioning, dehumidification, cooling or heating fields, and in all technical fields where fans provided with a housing are present, in particular fans of the centrifugal type.

Fans, i.e. pumps for air circulation, are noise sources when in operation. In fact, the impeller of a rotating fan propagates an acoustic field, due among other things to the interaction of the fan blades with the air and to the noise of the electric motor used to drive the impeller blades in rotation. This acoustic field propagates along the air paths both downstream and upstream of the fan, for example within a duct and in the environment where the fan is installed.

This acoustic field generated by the fan is obviously undesirable and it is thus a noise which propagates in the environment.

In many applications, it is desirable to acoustically attenuate or reduce an acoustic field or noise generated by a fan.

There are in the prior art some solutions for acoustically attenuating a noise generated by a fan and propagating in the environment along an air path.

Document <CIT>) refers to a fan equipped with a tube silencer, arranged in a space which is radially external to the fan.

Document <CIT>) refers to a fan equipped with means for damping a radial component of the airflow.

Document <CIT>) refers to a ventilation system equipped with acoustic resonators, configured for reducing a tone of the fan blade pass frequency.

Document <CIT>) refers to a fan comprising a casing which defines a cylindrical opening, in which a slot is obtained to release excess air from the casing, so as to reduce an irradiated noise.

Document <CIT>) relates to a centrifugal blower having an electric motor connected with an impeller, a casing surrounding the periphery of the impeller and having a bell-mouth-shaped suction opening on one surface, and a bell-mouth-shaped orifice concentric with the suction opening.

Document <CIT>) relates to a noise suppression apparatus including a resonator disposed on a sound transmission tube of a noise generation source and includes a chamber and a clapboard disposed in the chamber. A status indication unit generates a control signal and a thermoelectric component deforms in response to the control signal as the operational status of the noise generation source changes, so as to move the clapboard to change resonance volume of the resonator.

Document <CIT>) relates a blower with a casing equipped with a suction port, a centrifugal impeller disposed in the casing, a motor rotating a centrifugal impeller, and a first orifice plate and a second orifice plate disposed between the casing and an opening of an outline with intervals.

Document <CIT>) relates to a centrifugal fan including a casing that surrounds a periphery of an impeller, a bell-mouthed suction port on one side, and a bell-mouthed orifice that has an opening that is concentric with the suction port and has a diameter equal to or smaller than that of the suction port; a member closing a clearance portion between an end of the orifice and the casing is a noise absorbing structural material, and a space formed by the orifice is a rear air layer, thereby forming a resonance type noise absorbing structure.

Document <CIT>) relates to a fan shroud and barrel combination with built in silencers such as Helmholtz resonators. The resonator can be a hollow cavity in networks attached to an outer or inner barrel or shroud and tuned to reduce noise at predetermined noise frequency ranges within the airflow.

Document <CIT>) relates to a fan shroud having a double pipe structure composed of an inner pipe and an outer pipe and is divided into interference chambers by partition plates. Opening parts are equipped on the inner pipe <NUM> of respective interference chambers.

However, known solutions do not turn out to be fully effective in acoustically attenuating the acoustic field or noise generated by a fan, in particular in the case of a centrifugal fan.

Aim of the present invention is to solve some drawbacks of the prior art.

A particular aim of the present invention is to attenuate in a more effective manner an acoustic field or a noise generated by a fan.

A further particular aim of the present invention is to provide a fan incorporating an acoustic attenuation element, to reduce a noise generated by the fan impeller.

A further particular aim of the present invention is to provide a fan, in particular a centrifugal fan, having improved acoustic performances.

These and other aims are achieved by a fan as it appears from the features of the attached claims, which form an integral part of the present description.

An idea underlying the present invention is to provide a fan comprising an impeller and a housing encasing the impeller, wherein the housing comprises at least one inlet for fluid to the impeller and at least one outlet for fluid from the impeller. The housing further comprises at least one acoustic attenuation element associated with the at least one inlet, the acoustic attenuation element comprising at least one hollow lateral expansion arranged around the at least one inlet, the at least one hollow lateral expansion being open towards the at least one inlet and being closed towards a periphery of the at least one acoustic attenuation element, so as to be configured as an acoustic resonant cavity for noise generated by the impeller. The acoustic attenuation element further comprises at least one separation element in the at least one hollow lateral expansion, the at least one separation element being configured for defining at least one second separated volume within the at least one hollow lateral expansion.

The at least one separation element is configured for dissipating an acoustic field within the at least one hollow lateral expansion. The at least one separation element is configured for mechanically oscillating under the action of the acoustic field, so as to act as a selective mechanical damper in the frequency domain.

Advantageously, the fan according to the present invention provides a housing equipped with an acoustic attenuation element which attenuates in a more effective manner the acoustic field or noise generated by the fan.

Advantageously, the at least one separation element allows an acoustic attenuation on a wide range of frequencies to be developed, also allowing a tuning of attenuation effects.

Advantageously, the separated acoustic cavity defined by the at least one separation element contributes to an acoustic attenuation based on the development of standing waves, similar to that of resonators of the lambda/<NUM> type.

In particular, advantageously, the geometrical features of the separated acoustic cavity defined by the at least one separation element determine acoustic attenuation frequencies and intensities provided by the acoustic attenuation element of the fan according to the present invention.

Advantageously, the fan according to the present invention allows the propagation of the noise generated by the fan impeller to be reduced, so as to have improved acoustic performances with regard to users that are present in an environment in which the fan is installed.

The fan according to the present invention finds its advantageous application in all industrial machineries and/or household appliances in which a fan is present.

Further features and advantages will be more apparent from the following detailed description of non-limiting preferred embodiments of the present invention and from the dependent claims which outline preferred and particularly advantageous embodiments of the invention.

The invention is illustrated with reference to the following figures, given by way of non-limiting examples, in which:.

In the different figures, identical elements will be identified by identical reference numbers.

Moreover, in the figures, if there is a plurality of elements which are identical to each other, only one of them will be indicated with a reference number for clarity; the other identical elements, although not indicated with a suitable reference number, will have to be understood as encompassed by analogy.

<FIG> illustrates an embodiment of a fan <NUM>.

The fan <NUM> comprises an impeller <NUM> and a housing <NUM> encasing the impeller <NUM>. In addition to the impeller <NUM>, the fan <NUM> comprises known elements (an electric motor, power supply and control means, etc.) which allow the fan operation, but which are not described here in detail for conciseness.

The housing <NUM> comprises at least one inlet <NUM> for fluid to the impeller <NUM> and at least one outlet <NUM> for fluid coming from the impeller <NUM>.

<FIG> illustrates the fan <NUM> partially disassembled, so as to better display the impeller <NUM>.

In particular, the fan <NUM> is of the centrifugal type: the at least one inlet <NUM> is perpendicular to the at least one outlet <NUM> and the impeller <NUM> comprises a plurality of centrifugal blades.

The fan <NUM> is a mechanical device for moving the air or other gases in a direction which is typically at an angle with respect to the direction of the incoming fluid. Centrifugal fans provide a ducted housing, such as the housing <NUM>, to direct the outgoing air in a specific direction. The fan <NUM> is adapted to increase the speed and the volume of an airflow with the rotation of the impeller <NUM>.

In particular, the centrifugal fan <NUM> uses the kinetic energy of the impeller <NUM> to increase the volume of the airflow, which moves in turn, for example against the resistance caused by ducts. The centrifugal fan <NUM> radially moves the air, changing the direction (typically by <NUM>°) of the airflow between the inlet <NUM> and the outlet <NUM>. The centrifugal fan <NUM> has thus the at least one inlet <NUM>, in particular a pair of inlets <NUM>, which is perpendicular to the least one outlet <NUM> and the impeller <NUM> comprises a plurality of centrifugal blades.

<FIG> illustrates a cross-sectional view of the fan <NUM>, which makes the internal structure thereof visible.

The housing <NUM> further comprises at least one acoustic attenuation element <NUM>, associated with the at least one inlet <NUM>.

The acoustic attenuation element <NUM> comprises at least one hollow lateral expansion <NUM>, arranged around the at least one inlet <NUM>. In particular, the at least one hollow lateral expansion <NUM> is substantially ring-shaped and is arranged to surround the at least one inlet <NUM>.

The at least one hollow lateral expansion <NUM> is open towards the at least one inlet <NUM> and is closed towards a periphery of the at least one acoustic attenuation element <NUM>, so as to be configured as an acoustic resonant cavity for noise generated by the impeller <NUM>.

In particular, the at least one hollow lateral expansion develops at least partially on a plane which is orthogonal to a flow direction of the fluid to the impeller <NUM>, entering the inlet <NUM>.

In other words, for a centrifugal fan <NUM>, the inlet <NUM> is aligned to a main direction defined by the rotation axis of the impeller <NUM>, and the at least one hollow lateral expansion <NUM> is substantially transversal to the above main direction of the plurality of centrifugal blades.

In particular, since the fan <NUM> is preferably symmetrical, it comprises a pair of inlets <NUM>, symmetrically arranged on an axis of the impeller <NUM>; the at least one acoustic attenuation element <NUM> comprises at least two lateral expansions <NUM> respectively arranged around the pair of inlets <NUM>.

In the preferred embodiment of the fan <NUM>, the at least one hollow lateral expansion <NUM> develops, on a first length 306a, at least partially on a plane which is orthogonal to a flow direction of the fluid to the impeller <NUM>, a flow which is directed axially with respect to the at least one inlet <NUM>. Preferably, the at least one hollow lateral expansion <NUM> further comprises a bend 306b so as to develop further tangentially to the already-mentioned flow direction, at the periphery of the at least one acoustic attenuation element <NUM>.

In particular, the bent portion 306b of the at least one hollow lateral expansion <NUM> results folded on the body of the housing <NUM>.

In other words, the configuration comprising a hollow lateral expansion of the fan <NUM> further comprises a bend 306b, so as to result folded on the body <NUM> of the housing, allowing the compactness of the fan <NUM> equipped with the at least one acoustic attenuation element <NUM> according to the present invention to be maximized.

In the preferred embodiment of the fan <NUM>, the acoustic attenuation element <NUM> further comprises at least one second hollow lateral expansion <NUM>, which is juxtaposed to the first hollow lateral expansion <NUM> around the at least one inlet <NUM>.

The at least one second hollow lateral expansion <NUM> is open towards the at least one inlet <NUM> and is closed towards a periphery of the at least one acoustic attenuation element <NUM>, so as to be configured as a second acoustic resonant cavity for noise generated by the impeller <NUM>.

The presence of the at least one second hollow lateral expansion <NUM> allows the acoustic attenuation element <NUM> to attenuate in an even more effective manner the acoustic field or noise generated by the fan, being it moreover allowed to be configured for having tonal attenuation features which are different and complementary with respect to the at least one first hollow lateral expansion <NUM>, thus attenuating the noise in a wider range of frequencies.

In an alternative, both hollow lateral expansions <NUM> and <NUM> can comprise a respective bent portion, so as to result both folded on the body of the housing <NUM>.

<FIG> illustrates a detail of the acoustic attenuation element <NUM> of the fan <NUM>.

In this detail, it can be appreciated that the acoustic attenuation element <NUM> further comprises at least one separation element <NUM> and <NUM>, in the at least one hollow lateral expansion <NUM> and <NUM>, respectively.

The at least one separation element <NUM> or <NUM> is configured for defining at least one second separated volume <NUM> or <NUM>, within the at least one hollow lateral expansion <NUM> or <NUM> respectively.

In this respect, the at least one separation element <NUM> or <NUM> is configured for further dissipating an acoustic field within the at least one hollow lateral expansion <NUM> or <NUM>, respectively.

In particular, the at least one separation element <NUM> or <NUM> is configured for mechanically oscillating under the action of the acoustic field which propagates within the at least one hollow lateral expansion <NUM> or <NUM>, respectively, so as to act as a selective mechanical damper in the frequency domain.

The presence of the at least one separation element <NUM> or <NUM> allows the acoustic attenuation element <NUM> to attenuate in an even more effective manner the acoustic field or noise generated by the fan, thus attenuating in a more effective manner a noise, in a wider and selectable range of frequencies.

In particular, the at least one separation element <NUM> or <NUM> is configured for defining a hollow portion <NUM> or <NUM> which is separated and external to the respective at least one hollow lateral expansion <NUM> or <NUM>.

Moreover, preferably, the separation element <NUM> or <NUM> comprises at least one elastic membrane. In particular, the elastic membrane <NUM> or <NUM> is perimetrically constrained to walls of the respective hollow lateral expansion <NUM> or <NUM>.

The oscillating elastic membrane <NUM> or <NUM> is preferably made of a material characterized by a Young's modulus (modulus of elasticity) comprised between <NUM> MPa and <NUM> GPa and a density comprised between <NUM>/m3 and <NUM>/m3. The acoustic attenuation of the elastic membrane <NUM> or <NUM> is characterized by operating frequencies and amplitudes depending on the membrane geometry and on the mechanical features of the material it is made of.

The air cavity <NUM> or <NUM> behind the membrane <NUM> or <NUM> has a geometry depending on the cavity of the hollow lateral expansion <NUM> or <NUM> and on the position of the elastic membrane <NUM> or <NUM>. , The geometry of the air cavity <NUM> or <NUM> behind thus involves an additional stiffness contribution to the oscillating membrane <NUM> or <NUM>, with an effect which can change the range of frequencies and the intensity of attenuation.

The elastic membrane <NUM> or <NUM> located at the end of the acoustic cavities of the respective hollow lateral expansion <NUM> or <NUM>, is constrained to the walls of the cavity itself, separating the cavity in two portions. When the acoustic standing wave develops in the hollow lateral expansion <NUM> or <NUM>, it stresses the elastic membrane <NUM> or <NUM>, which will begin vibrating. Based on the elastic and geometrical features thereof, and on the position in which it is constrained in the cavity, these vibrations will occur at specific frequencies, whereat the suppression of the acoustic field is concentrated.

The position of the elastic membrane <NUM> or <NUM> within the cavity of the respective hollow lateral expansion <NUM> or <NUM> can affect the operating frequencies of the resonant mechanisms too. The position of the elastic membrane <NUM> or <NUM> can lead to the following effects, whose magnitude also depends on the features of the membrane itself:.

Within the acoustic cavities of the respective hollow lateral expansions <NUM> or <NUM> a standing wave is established; the effect of this phenomenon is a suppression at particular frequencies of the acoustic field which passes through the channel which the hollow lateral expansion <NUM> or <NUM> opens in. These frequencies are dependent on the geometrical features of the cavity and thus on the acoustic modes thereof.

The acoustic suppression effect at the vibration frequencies of the membrane <NUM> or <NUM> combines with the typical frequencies of the acoustic cavities <NUM>, <NUM> and <NUM>, <NUM> with a final result which leads to a more "broadband" response in terms of acoustic attenuation, i.e. concerning a wide range of frequencies. As a matter of fact, it can be observed how the combination of two resonators with a tuning at sufficiently close frequencies leads to an attenuation which not only has peaks at the two frequencies of the starting resonators, but which improves the attenuation in the range of frequencies comprised between those of the two resonators.

Through a correct tuning of the parameters being involved (geometrical features of the cavity <NUM> or <NUM> of the hollow lateral expansion, geometry of the elastic membrane <NUM> or <NUM>, material of the elastic membrane and position of the elastic membrane within the separated cavity <NUM> or <NUM>), the characteristics of the device attenuation can thus be controlled, and for the above-mentioned reasons the addition of the elastic membrane <NUM> or <NUM> provides more degrees of freedom in the design and greater performances with respect to versions with only an acoustic cavity.

It is to be understood that, in a further alternative, the fan <NUM> could provide only the separation element <NUM> or only the separation element <NUM>, remaining one of the cavities which is devoid of the respective second separated volume.

In a still further alternative, not represented, a fan according to the present invention can further comprise at least one second acoustic attenuation element, which is associated with the at least one outlet <NUM>. This second acoustic attenuation element comprises in turn at least one third hollow lateral expansion, arranged around the at least one outlet <NUM>. This at least one third hollow lateral expansion is open towards the at least one outlet <NUM> and is closed towards a periphery of the second acoustic attenuation element, so as to be configured as a further acoustic resonant cavity for noise generated by the impeller and propagated towards the at least one outlet <NUM>.

The second acoustic attenuation element further comprising at least one second separation element in the at least one third hollow lateral expansion. The second separation element is configured for defining at least one third separated volume within the third hollow lateral expansion, and it is thus configured for dissipating an acoustic field within said third hollow lateral expansion.

In general, the features described in connection with the separation elements <NUM> or <NUM> also apply to this at least one second separation element.

In this respect, the present invention provides the use of a second acoustic attenuation element associated with the outlet of the fan. This alternative turns out to be particularly effective in the case in which the fan does not let out in a closed duct for discharging fluid, but it discherges in an environment in which the fan itself is installed.

In an alternative, the fan of the present invention could comprise a single acoustic attenuation element associated only with the one or more outlets of the fan, without providing an acoustic attenuation element at the one or more inlets. This acoustic attenuation element associated only with the one or more outlets of the fan could have structural features which are similar to those described in connection with the embodiments of acoustic attenuation elements at the one or more inlets being disclosed here.

<FIG> exemplifies the acoustic performances of a fan according to the present invention.

The trend represented by the dotted line represents a noise spectrum between <NUM> and <NUM> for a fan of the traditional type, i.e. which is devoid of the at least one acoustic attenuation element according to the present invention.

The trend represented by the solid line represents instead a noise spectrum between <NUM> and <NUM>, for a fan according to the present invention equipped with at least one acoustic attenuation element, such as the already-described acoustic attenuation elements <NUM>.

As it is noted by comparing the two plots, the fan <NUM> according to the present invention allows the acoustic field or noise generated by the impeller and which propagates outside the fan to be attenuated in a more effective manner, in particular sharply attenuating it for frequencies above <NUM>.

The fan of the present invention has thus improved acoustic performances with regard to the users that are present in an environment in which the fan is installed.

Advantageously, the fan according to the present invention allows the propagation of a noise generated by its own impeller to be effectively attenuated.

Other examples of application can be: ventilation, conditioning, dehumidification, cooling or heating, and all technical fields where fans are present.

Considering the here-reported description, the person skilled in the art will be allowed to devise further changes and alternatives, in order to meet contingent and specific requirements.

It is thus evident that, where there are no technical incompatibilities which are apparent to the person skilled in the art, the configurations of specific elements described with reference to certain embodiments, will be allowed for use in other embodiments described here.

Claim 1:
Fan (<NUM>) comprising an impeller (<NUM>) and a housing (<NUM>) encasing said impeller (<NUM>), wherein said housing (<NUM>) comprises at least one inlet (<NUM>) for fluid to said impeller (<NUM>) and at least one outlet (<NUM>) for fluid from said impeller (<NUM>), wherein said housing (<NUM>) further comprises at least one acoustic attenuation element (<NUM>) associated with said at least one inlet (<NUM>), said acoustic attenuation element (<NUM>) comprising at least one hollow lateral expansion (<NUM>; <NUM>) arranged around said at least one inlet (<NUM>), said at least one hollow lateral expansion (<NUM>; <NUM>) being open towards said at least one inlet (<NUM>) and being closed towards a periphery of said at least one acoustic attenuation element (<NUM>), so as to be configured as an acoustic resonant cavity for noise generated by said impeller (<NUM>), wherein said acoustic attenuation element (<NUM>) further comprises at least one separation element (<NUM>; <NUM>) within said at least one hollow lateral expansion (<NUM>; <NUM>), said at least one separation element (<NUM>; <NUM>) being configured for defining at least one second separated volume (<NUM>; <NUM>) within said at least one hollow lateral expansion (<NUM>; <NUM>), said at least one separation element (<NUM>; <NUM>) being configured for dissipating an acoustic field within said at least one hollow lateral expansion (<NUM>; <NUM>), characterized in that said at least one separation element (<NUM>; <NUM>) is configured for mechanically oscillating under the action of said acoustic field, so as to act as a selective mechanical damper in the frequency domain.