IT202000012616A1 - FAN FOR AIR-GAS MIXING SYSTEMS IN BURNERS OF HEATING APPLIANCES - Google Patents

Description

Fan for air-gas mixing systems in burners of heating appliances

DESCRIPTION

The present invention relates to a fan for air-gas mixing systems in burners of heating appliances, having the characteristics stated in the preamble of the main claim no. 1 .

In the reference technical sector, heating appliances are known and widely used, such as gas boilers, provided with burners with premixing systems for the combustible air-gas mixture, these appliances being designed for heating domestic hot water and/or circulating in the space heating circuits.

Burners of this type are associated with a fan, in particular an electric fan, arranged to suck in or push a combustible mixture of air and gas, generated in a mixing device, in order to deliver this combustible mixture to the burner.

Only by way of application example is a centrifugal fan for masonry gas boilers.

These fans usually comprise an impeller housed in a casing or scroll provided with a motor support plate, an electric motor on whose shaft ? keyed the impeller, a motor support comprising a metal frame for mounting vibration damping elements, which is solidified to the plate, an electronic motor control card positioned near? of the motor, generally in a position above the motor itself, and a cap for protecting and containing the board-motor assembly.

The vibration damping elements, otherwise known by the term ? silent blocks?, are they fixed, for example with screws, to the aforementioned frame cos? to be placed between the motor and the motor support plate, in order to reduce the transmission of vibration to the fan structure.

One of the problems faced by the invention ? relating to the noise generated by the fan, during its operation, in particular to the additional noise generated by the cover cap of the motor electronic control card and substantially related to the system for fixing the cap to the fan. The box-shaped structure of the cap also tends to produce an amplification of the sound waves of the noise generated.

A known fastening system provides for the cap to be connected to a stationary body or frame of the rotary engine or to the engine support plate (typically made of sheet metal or die-cast), by means of additional fastening elements, such as screws or hooks.

Another known system provides for the cap to be connected to the aforementioned plate by couplings, normally metal, without the use of additional fastening elements.

In these systems, the function of contrasting the formation of noise emitted by the fan? delegated to the use of vibration dampers (for example in rubber or elastomers), placed between the motor body and the rigid structure of the fan body to which ? the protective cover of the electronic board is fixed.

In the case of couplings without the use of additional fastening elements, such as screws or hooks, the coupling between materials of different nature, i.e. generally of a plastic nature for the cap and of a metallic nature for the motor support or body of the fan, cause with the variation of the temperature thermal expansions of different entities, with consequent variation of the state of assembly. This differentiated expansion, related to the different nature of the materials, results in a variation of the tolerances and coupling clearances between the components, which can generate unexpected vibrations during fan operation with consequent generation of noise.

A purpose of the invention? that of making available a fan structurally and functionally designed to overcome the limits set forth with reference to known solutions, in particular aimed at releasing the protective cover of the motor control card from the vibrations generated by the motor during fan operation, thus avoiding additional noise generation mode.

Another purpose? that of making the fixing system of the cap to the fan independent of thermal expansion due to the temperatures reached in the conditions of use of the fan.

Yet another purpose? that of realizing the coupling of the cap to the fan without the need? of additional components or fasteners, for a consequent reduction of time and costs in the assembly process line.

These and other aims which will appear clearly hereinafter are achieved by the invention by means of a fan for air-gas mixing systems in burners of heating appliances, manufactured in accordance with the appended claims.

Further characteristics and advantages of the invention will become clearer from the detailed description which follows of a preferred embodiment thereof illustrated, by way of example and not of limitation, with reference to the attached drawings in which:

- figure 1 ? a perspective exploded view of an example of a fan made in accordance with the present invention,

- figures 1A and 1B are perspective views of a detail of the fan of figure 1,

- figure 2 ? a top plan view of the fan of figure 1 , - figure 3 ? a view corresponding to that of figure 2 of a detail of the fan of the invention,

- figure 4 is a perspective view of the fan detail shown in figure 3,

- figures 5 and 6 are perspective views of the detail of figure 3 shown in respective and distinct operative positions of a group of components of the fan,

- figures 7, 8 and 9 are partial views in section and on an enlarged scale of details of the fan of the previous figures,

- figure 10 ? a perspective view in partial section of the fan according to the invention,

- figure 1 1 ? a partial perspective view on an enlarged scale of a detail of figure 10.

With reference to the figures cited, with 1 ? indicated as a whole is a fan for air-gas mixing systems in burners of heating appliances, made in accordance with the invention.

The fan 1, of the centrifugal type, comprises an impeller 2 with the main axis of rotation indicated by X, which ? provided with a plurality of radial blades 2a and ? housed in a scroll or case 3 defining the conveyance duct of the fluid processed by the impeller between an axial suction zone and a tangential delivery zone.

The auger 3 comprises a main auger body 3a on which ? fixed, for example by means of screws, a closing plate 4 (in metal sheet or die-cast) which ? configured as an engine support plate.

With 5 ? marked a fan drive electric motor, on the 5th shaft of which ? the impeller 2 is keyed.

Does the fan also include? an engine support comprising a first metal frame 6, arranged to be integral with the plate 4 and on which ? the installation of vibration damping elements 7 is foreseen. Engine 5? therefore supported on the frame 6 with the interposition of the damping elements 7, configured for example as cylindrical silent-blocks of the type per se? conventional. With 8 ? indicated an electronic control board of the engine, positioned near? of the engine itself, preferably in a position above the engine, ie on the side axially opposite the frame 6 with respect to the engine. The electronic board 8 ? fixed, for example screwed, to a stationary part 5b of the motor 5. The part 5b pu? be made in the form of a collar solidified to the stator casing of the motor, from which a series of bridges 5c extend radially (three in number in the example described) bearing respective mushroom-shaped appendages 5d designed to be inserted into the respective bodies of the elements dampers.

With 9 ? a cooling fan is indicated which is intended to be fitted to the motor shaft 5a on the opposite side of the motor with respect to the impeller.

The fan 1 also comprises a cap 10 for protecting and containing the board-motor assembly, which has an open box-like shape with side walls 10a erected from a bottom wall 10b.

In one embodiment, the bottom wall 10b has a substantially quadrilateral perimetrical shape for the definition of four mutually connected side walls. With 10c ? indicated an opening passing through the cap 10, obtained in correspondence with the side walls, for the passage of a connector (not shown) of a power supply and data transmission cable to the electronic board 8.

The cap 10 ? conveniently made of a plastic material with electrical insulating characteristics.

In accordance with a main feature of the invention, the fan comprises a second frame 11 made of plastic material the same or compatible with the plastic material of the cap. Chassis 1 1 ? can be coupled to the metal frame 6 of the engine support and also includes? interconnection means and countermeans respectively provided on the cap 10 and on the second frame 11, which mutually cooperate to achieve the fixing of the cap to the fan by means of said second frame.

Through said interconnection means and counter-means, a coupling of the removable type is also achieved between the shell 10 and the second frame 11.

Said means and counter-means of interconnection are also configured to preferably achieve a snap fit coupling between the cap and the second frame.

In one embodiment, the interconnecting means and counter-means comprise a plurality of interconnecting means and counter-means. of openings 12 passing through the second frame 1 1 , and, respectively, a corresponding plurality? of interlocking appendages 13 protruding from the cap and obtained in such positions that each opening 12 is arranged for the insertion of a corresponding interlocking appendage 13, when the cap 10 is coupled to the frame 11 .

Each appendage 13 conveniently has at its end releases a notch formation 14 which can be snapped into the corresponding opening 12.

In one embodiment, the frame 11 has a thin-thickness base 11a with an open contour perimeter profile, on which three extended sides are identified as extensions of each other and with pairs of contiguous sides substantially orthogonal to each other , each side corresponding to a respective free edge of a corresponding side wall of the cap. In this configuration, on each of said sides of the base 11a there are provided a pair of openings 12 arranged in such a position as to be engaged by a corresponding pair of appendages 13 protruding from the free edge of the corresponding cap wall 10a, thus to make the coupling with snap joint between the shell 10 and the frame 1 1 . This coupling is then achieved by means of the overall engagement of six appendages 13 in the respective six openings 12. It is understood that a different number and positioning of apertures and corresponding appendages can? be provided, in order to ensure suitable fixing of the cap 10 on the frame 1 1 .

On the base 1 1 a there are appendices of columnar shape, all indicated with 20, similarly erected from the surface of the base facing the cap.

Said columnar appendices 20 are arranged along the sides of the base, particularly in correspondence with the openings 12, and are selected in number, shape and positioning suitable to allow their interaction, by contact, with the internal surfaces of the side walls of the cap, to create a state of tension suitable to ensure greater stability? of connection between the shell and the frame, in particular recovering the clearances of the coupling between the appendices 13 and the corresponding openings 12.

Said frame 11 also comprises means for coupling to the frame 6 to create a removable connection between the frames themselves.

The hooking means comprise at least one seat 15 on the frame 1 1 for the engagement of at least one portion 6a of the frame 6 and at least one tab 16 protruding from the frame 1 1 suitable for abutting said portion of the frame 6 so? to retain the frame 6 in the seat 15 and mutually constrain the frames. Conveniently, the coupling means perform a snap coupling between the frames 6 and 11. For this purpose, the at least one fin 16 has at its end releases a notch formation 16a which can abut against the portion 6a of frame 6, after elastic flexion of the flap, in the relative coupling movement between the frames.

In one embodiment, frame 6 is made of sheared and bent sheet metal and has a central annular plate delimited by a perimetric frame bearing three portions 6a with a substantially rectilinear profile, each pair of contiguous portions 6a joining in a corresponding frame section 6b, each section 6b carrying a respective hole 6c through hole arranged for the assembly of the corresponding cylindrical damper element 7. The edge of hole 6c can? be prepared for engagement in a counter-shaped groove 7a along the perimeter of the damper element.

Such a configuration provides that the three holes 6c are positioned with an angular pitch of 120? from each other (around the main axis coinciding with the X axis) and the portions 6a develop along the respective sides of a hypothetical equilateral triangular profile.

Chassis 6? solidified to the plate 4 by plastic deformation of a part of the central plate against a surface portion of the plate. Following their relative fixing, the frame frame bearing the portions 6a remains spaced from the plate 4, allowing the frame 11 to be hooked to the frame 6.

In the embodiment described here, in the frame 1 1 ? a pair of laterally opposite seats 15 is provided, each seat being delimited by surfaces 15a adapted to at least partially surround the corresponding portion 6a of the frame 6, in the relative coupling movement. 15b indicates reliefs protruding from the base and suitable for cooperating with the surfaces 15a, finding the portions 6a of the frame 6 in the condition of coupling with the frame 11. The frame 11 also has two pairs of fins 16, directed parallel to the base 11a, the tabs of each pair having different longitudinal extensions and such as to couple with the corresponding portion 6a, in different positions, to hook to said portion and hold it in the respective seat 15, thus binding the frames to each other ?other.

Each flap 16, with its own end? free notched, ? suitable for snap hooking and abutting the corresponding portion 6a of the frame 6. In the frame 11 there are also three gaps or recesses with a substantially semi-circular profile, indicated with 18, which are configured to surround, with limited coupling clearance , part of the lateral cylindrical skirts of the respective damping elements 7, in the reciprocal coupling movement of the frames 6 and 11 . The cutouts 18 enable the centering of the frame 11 with respect to the frame 6 in the relative hooking stage.

The conformation of the frame 1 1 described above ? conceived to allow the frame 11 to be hooked to the frame 6 in three distinct relative orientations, angularly arranged at 120? from each other (around the X axis). Figures 4 to 6 respectively show the three relative positionings between the configurable frames.

Thanks to the adjustability? of relative positioning, the assembly constituted by frame 1 1 , motor 5 (and its stationary part 5b), control board 8 and cap 10 can? be fixed to the auger 3 in three distinct positions oriented by 120? from each other, allowing the cover 10, and in particular its opening 10c for accessing the connection connector to the board, to be placed in three different positions relative to the delivery section of the fan, with the advantageous result of facilitating , during installation, the choice of positioning pi? suitable according to the overall dimensions and system requirements encountered on site.

It should be noted that the solution proposed by the invention deals with the problem of contrasting the onset of vibrations and the consequent additional noise generated by the protective cap of the electronic motor control card and substantially related to the system for fixing the cap to the fan. This additional noise component is added to other noise components that are emitted by the fan throughout its operating range, in particular it is added to a relevant component linked to the nature of the motor used, typically for example a single-phase brushless motor with permanent magnet , whose cause ? due to the tuning of the torque harmonics generated by the engine and the structural resonance frequencies of the mechanical components that make up the fan itself.

Below is a brief description of this problem and the technical solutions made available to remedy it.

To date, the single-phase brushless motor with permanent magnet installed on centrifugal fans is typically driven by an inverter device with a driving technique which provides for the supply to the motor of an electric voltage with a square wave profile.

With this control, the motor generates a torque with a spectrum characterized by a large number of harmonics. This feature, combined with the fact that the harmonics vary their amplitude and frequency as the speed varies? of the engine, causes a significant increase in the probability? to have the tuning of the harmonics of the engine torque with the frequencies of structural resonance of the components of the fan and this effect of tuning ? one of the causes of the acoustic noise emitted by the fan.

The problem? therefore that of significantly reducing the number of tunings between the harmonics of the couple and the resonant frequencies, since? such a reduction results in a reduction of sound emission and therefore in a lowering of the average noise level.

A solution that addresses this problem involves the supply to the motor by the inverter of a voltage with a sinusoidal profile. Such a solution allows to lower, even to cancel completely, the amplitude of all the harmonics of the engine torque higher than the first and therefore to reduce the probability? that there is tuning with structural resonance frequencies. With this driving technique, compared to that with square profile voltage, ? possible to considerably lower the average acoustic noise emitted by the fan along the entire operating range. Such a solution, which intervenes in the driving technique of the voltage with which the motor is powered, is not? suitable for completely eliminating the problem of the onset of additional noise related to the structure of the fan and in particular to the structural characteristics of the protective cap of the electronic control card and to the system for fixing the cap to the fan.

The present invention deals with this specific problem and achieves the proposed objects by achieving numerous advantages compared to known solutions. A first advantage consists in the fact that the provision, in accordance with the invention, of a fixing frame for the cap, made of the same material as the cap or in a material compatible with the material of the cap (conveniently a plastic material with insulating characteristics electrical) prevents the onset of different thermal expansions linked to the operating temperature of the fan, typically responsible for causing vibrations with the consequent generation of noise sound waves.

Another advantage? that the fixing frame of the cap ? hooked to the motor support plate and closure of the auger, which plate ? released from the vibrations triggered by the operation of the fan, thanks to the action of the vibration damping elements interposed between the motor and the plate, consequently also releasing the cap from the aforementioned vibrations.

Another plus? linked to the fact that the protective cap and containment of the electronic card ? bound to the frame, without additional fixing elements, for more than half? of the extension of the perimeter coupling profile, consequently effectively limiting the deformation subject to vibrations of the cap itself, this deformation being in fact able to cause the generation of sound waves.

The coupling of the cap to the frame without additional fastening elements (screws, hooks and similar means) is also advantageous in terms of cost and assembly time reduction along the fan production line, in addition to the fact that it does not require the use of tools.

Furthermore, the foreseen coupling between the shell and the frame in the assembly phase? elastic in nature (joint with snap coupling), therefore free of tensional efforts once the final coupling condition has been reached. Doesn't such a coupling present also? assembly conditions degradable over time and during the operating life of the fan.

Claims (10)

1 .Fan for air-gas mixing systems in burners of heating appliances including: - a fan impeller housed in an auger fitted with a motor support plate, - an engine on whose shaft ? the impeller is keyed, - an engine support comprising a first metal frame for mounting vibration damping elements, said first frame being integral with said plate, said engine being supported on the first frame with interposition of said vibration damping elements, -an electronic control board of the engine positioned near? of the engine, - a protective cap and containment of the card-motor assembly, characterized by the fact that said cap ? made of plastic material and by comprising a second frame in plastic material which can be coupled to the first metal frame and interconnection means and counter-means respectively provided on the cap and on the second frame, mutually cooperating for fixing the cap to the fan by means of the second frame . 2. Fan according to claim 1, wherein said interconnection means and counter-means realize a coupling of the removable type between the cap and the second frame. 3. A fan according to claim 1 or 2, wherein said interconnection means and countermeans are configured to provide a snap fit. 4. A fan according to claim 3, wherein said interconnection means and counter-means comprise a plurality of of through openings on the second frame and a respective plurality? of interlocking appendices protruding from said cap, each opening being arranged for the insertion of a respective interlocking appendage. 5. A fan according to claim 4, wherein each of said appendages has one end? free bearing a notch formation for hooking with snap fit into the corresponding opening of the second frame. 6. Fan according to one or more? of the preceding claims, wherein said second frame comprises means for coupling to the first frame to create a removable connection between said first and second frames. 7. Fan according to claim 6, wherein said hooking means comprise at least one seat on the second frame for engaging at least a portion of the first frame and at least one fin protruding from the second frame suitable for abutting said portion of the first frame so? to retain the first frame in the seat of the second frame and to mutually constrain said frames. 8. fan according to claim 7, wherein said coupling means perform a snap coupling between said first and second frames. 9. A fan according to claim 7 or 8, wherein the first and second frames have respective conformations such that the second frame is? likely to be coupled to the first frame in pi? of an oriented positioning relative to the first frame. 10. A fan according to claim 9, wherein three relative hooking positions are provided between the first and second frames, oriented at 120? from each other around a main axis of the first frame. 1 1 . Fan according to one or more? of the preceding claims, in which said cap ? made of electrical insulating material.