EP4230873A1 - Geräuschreduzierte gebläsemittel und deren verwendung in elektrowerkzeugen und vorrichtungen - Google Patents

Geräuschreduzierte gebläsemittel und deren verwendung in elektrowerkzeugen und vorrichtungen Download PDF

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Publication number
EP4230873A1
EP4230873A1 EP22158036.8A EP22158036A EP4230873A1 EP 4230873 A1 EP4230873 A1 EP 4230873A1 EP 22158036 A EP22158036 A EP 22158036A EP 4230873 A1 EP4230873 A1 EP 4230873A1
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EP
European Patent Office
Prior art keywords
resonators
resonator
air
blower means
housing
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP22158036.8A
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English (en)
French (fr)
Inventor
Yohko Aoki
Jens Rohlfing
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Original Assignee
Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Publication date
Application filed by Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV filed Critical Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Priority to EP22158036.8A priority Critical patent/EP4230873A1/de
Publication of EP4230873A1 publication Critical patent/EP4230873A1/de
Pending legal-status Critical Current

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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
    • F04D29/00—Details, component parts, or accessories
    • F04D29/66—Combating cavitation, whirls, noise, vibration or the like; Balancing
    • F04D29/661—Combating cavitation, whirls, noise, vibration or the like; Balancing especially adapted for elastic fluid pumps
    • F04D29/663—Sound attenuation
    • F04D29/665—Sound attenuation by means of resonance chambers or interference
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
    • F04D25/00—Pumping installations or systems
    • F04D25/02—Units comprising pumps and their driving means
    • F04D25/08—Units comprising pumps and their driving means the working fluid being air, e.g. for ventilation

Definitions

  • noise reduced blower means comprising a housing, at least one air intake opening, at least one air exhaust opening, a fan disposed in the housing and drivingly coupled to an electric motor for generating a flow of air through said at least one air intake opening into the housing and through said at least one air exhaust opening out of the housing, noise reduction means including at least one acoustic resonator which has a wall defining a resonator cavity and a resonator opening, said resonator opening being in fluid communication with said resonator cavity and said flow of air.
  • noise reduction means including at least one acoustic resonator which has a wall defining a resonator cavity and a resonator opening, said resonator opening being in fluid communication with said resonator cavity and said flow of air.
  • This disclosure also relates to the use of noise reduced blower means in electric power tools and devices.
  • a ventilation device such as a fan to draw cooling air into the housing through the air intake opening, and exhaust the cooling air having absorbed heat in the housing out of the housing through the air exhaust opening.
  • a ventilation opening may be an air intake and an air exhaust opening at the same time.
  • the area of the ventilation openings is determined by the requirement from the cooling system and the geometry is controlled in terms of the safety issue and structural strength. But the sound emission through the ventilation is not considered.
  • the total noise emission of such an electric power tool or device which is usually generated by the motor, gear, fan etc. inside the tool or device, may be transmitted from the inside to the outside of the housing of the tool or device via three different paths:
  • An additional noise source is flow noise; i.e. aeroacoustics noise, which is generated due to the air flow through the ventilation openings.
  • flow noise i.e. aeroacoustics noise
  • aeroacoustics noise which is generated due to the air flow through the ventilation openings.
  • the direct airborne sound transmission via the ventilation openings dominates the overall sound emissions for the electric power tools and devices.
  • blower means of the kind defined in the pre-characterizing part of claim 1 are disclosed in JP5029593B2 .
  • Such blower means include a funnel-shaped Helmholtz resonator which is positioned in a duct which extends between an air intake opening and a fan. In operation the fan sucks air into the duct via the air intake opening. The air sucked into the duct via the air intake opening flows past the resonator and its opening before it reaches the fan. The resonator is arranged adjacent to the air intake opening and is closed except for its opening that faces the fan. As a result the sound emission from the air intake opening is reduced.
  • An object of the invention is to provide noise reduced blower means of the kind defined in the pre-characterizing part of claim 1 which noise reduced blower means reduce the noise emission through the air exhaust opening especially in cases where airborne sound transmission through the air exhaust opening dominates the overall sound emission from the housing.
  • noise reduced blower means are characterized in that there is a plurality of air exhaust openings and a plurality of resonators each of which is disposed adjacent to a respective one of said air exhaust openings.
  • the resonators are spaced from each other and the air exhaust openings are defined by the resonators.
  • the resonators each may be of the Helmholtz resonator type or the Lambda quarter resonator type, or the resonators may consist of a combination of the afore-mentioned types of resonators.
  • the air exhaust openings each may be covered partially by a portion of the wall of the respective resonator.
  • two or more resonators of the plurality of resonators may be tuned to different frequencies.
  • Acoustically absorptive material may be placed in the cavity and/or the neck of the resonators. Acoustically absorptive material may also be placed around the neck of the resonators.
  • the acoustically absorptive material may be in the form of one or more surface layers.
  • Noise reduced blower means reduce the direct sound transmission via the ventilation openings by a composition of a purposely designed air path, opening geometries and acoustic resonators in the vicinity of ventilation openings.
  • the acoustic resonator dissipates the sound energy into heat, and the noise emission from the power tool or device via the opening is reduced. This is particularly effective in cases where airborne sound transmission via the ventilation openings dominates the overall sound emissions of the electric tools and devices.
  • the resonators When the resonators are placed inside the housing the sound pressure levels inside the housing are reduced, and hence less sound is transmitted through the housing wall and less sound is transmitted through the ventilation openings. This is the conventional method.
  • This invention is applicable to electric power tool and devices producing a tonal noise at the fixed frequency, which is transmitted to the outside by means of airborne sound transmission via the ventilation openings.
  • An example is a motor driven by PWM (Pulse-Width Modulation signal).
  • PWM Pulse-Width Modulation signal
  • the motor during each active PWM cycle causes the impulse torque, which generates the noise at PWM driven frequency.
  • the conventional methods of solving the noise generation due to the PWM problem are:
  • the PWM cycle frequency is limited due to the power loss of the electronic components.
  • the oscillation of the PWM signal frequency is effective to reduce the peak amplitude of the tonal components, which is closely related to the annoyance due to sound.
  • the above mentioned methods reduce the generation of tonal noise components.
  • the invention disclosed herein does not reduce noise generation but reduces the sound transmission of tonal noise components via the ventilation openings.
  • An acoustic resonator is a particularly useful measure to suppress pure tones at a constant frequency.
  • the maximum sound mitigation by a resonator is achieved at the resonator resonance frequency which is determined by its geometry and the characteristics of the surrounding fluid. The larger the resonator is the lower the resonance frequency is.
  • the required dimensions of the acoustic resonators is in the range of a few centimeters, which is small enough to be installed, even in handheld electric power tools and devices.
  • blower means of a power tool or device comprise a housing 1 which includes a plurality of air exhaust openings 2 having the shape of slits and being referred to hereinafter also as ventilation openings or ventilation slits.
  • a fan which is not shown in the drawings is disposed in the housing and drivingly coupled to an electric motor for generating a flow of cooling air through an air intake opening (not shown) into the housing 1 and through the air exhaust openings 2 out of the housing 1.
  • the flow of cooling air serves to absorb heat inside the housing and transfer the heat out of the housing via the air exhaust openings 2.
  • the blower means further include noise reduction means which include a plurality of acoustic resonators 3 each of which is disposed adjacent to a respective one of the air exhaust openings 2.
  • the resonators 3 are arranged along the direction of the air flow such that the resonators 3 do not disturb the flow.
  • the air flow is indicated by an array of parallel arrows.
  • the resonators 3 are spaced from each other so that the walls of the resonators 3 form a short duct which contributes to the sound reduction over a wide frequency range.
  • the opening 4 of each acoustic resonator 3 is placed in the direction of the flow, i.e. normal incidence flow, and thus the resonators whistle under more limited conditions compared to the situation with a grazing flow.
  • the opening 4 of the resonators 3 points either in the upstream direction of the air flow as shown in Figures 1(a) and 2(a) or in the downstream direction of the air flow as shown in Figures 1(b) and 2(b) .
  • a resonator 3 can be installed inside or outside of the housing between adjacent ventilation openings 2 which may have the shape of slits.
  • an acoustic resonator 3 can be rotated 90 degrees and lie on the outer surface of the housing 1 next to every opening 2.
  • the resonant frequency of a resonator 3 can be adjusted by modifying the length of the resonator ( Fig.3 (b) ), or the volume of the resonator cavity ( Fig. 3(c) ).
  • the resonator structure is extended to the openings to form a cover over the ventilation openings 4 such that (i) the sound is not directly transmitted from the noise source through the ventilation openings 2, and (ii) the air flow is not along the opening sideways. It is important to assure that the opening area of the resonator neck is at least as big as the ventilation opening 2 in order to keep the flow rate (pressure loss) similar to that of a prior art device having no resonators at the ventilation openings of the housing.
  • An advantage of the invention is that it is not only applicable to large installments but also to small handheld electrical power tools and devices with limited space due to compact house dimensions.
  • the resonators 3 shown in Fig. 1 to Fig. 3 are composed with a narrow neck. This kind of resonators is referred to as a Helmholtz resonator.
  • the basic parameters of a Helmholtz resonator are the mass of air enclosed in the neck, and the volume of the attached cavity.
  • the shape of the cavity is of lesser importance. Therefore, the shape of a resonator is not confined to be cuboidal.
  • the resonators 3 can also be designed as quarter wavelength resonators which have a simple tube like geometry and no dedicated neck (see Fig. 4 (a) ).
  • the resonant frequency of the quarter wavelength resonator is determined by the length of the cavity.
  • a resonator As a resonator is designed to tackle a single frequency, sound mitigation will occur only in a narrow frequency range.
  • the bandwidth over which a resonator is effective is determined by the internal loss of the resonator system. This issue of limited bandwidth could be partly overcome by using two or more resonators 3 tuned to slightly different frequencies.
  • the placement of acoustically absorptive material in the resonator cavity or, especially, in the neck can broaden the bandwidth at the expense of peak performance at the resonance frequency.
  • the placement of the absorptive material around the neck further reduces the risk of aero-acoustic self-noise, i.e. whistling.
  • an experimental demonstrator test rig has been designed in order to perform acoustic tests on small sample plates.
  • the floor and walls of the test rig casing are made from 30 mm thick acrylic glass.
  • the inner dimensions of casing are 297 mm ⁇ 210 mm ⁇ 252 mm, which gives an inner volume of about 0.016 m 3 .
  • a duct of 100 mm outer diameter is connected to conduct air flow into the demonstrator with the flow rate between 3L/s and 35L/s.
  • the primary sound source inside the casing is an in-house design miniature hexahedron loudspeaker with monopole like radiation characteristics. For the experiments, a white noise signal with controlled amplitude is used as input to the loudspeaker.
  • a dummy head with a binaural recording system is used for measuring the sound pressure levels (SPLs).
  • SPLs sound pressure levels
  • a dummy head is placed next to the demonstrator with 300 mm distance from the side and the top face of the demonstrator in order to avoid the interaction with the flow from the demonstrator.
  • the top of the demonstrator casing is covered by a 15 mm thick aluminum mounting plate, in which a sample plate with the grid of 10x1 rectangular apertures with dimensions of 3 mm ⁇ 30 mm, which gives the total ventilation opening area of 900 mm 2 .
  • the ventilation slit geometries are modified by attaching Helmholtz resonators 3 whose resonant frequency is tuned to 6.8 kHz.
  • Figure 8 shows the measured air-borne noise emission of the test set-up with a primary loudspeaker without air flow.
  • the results show that the Helmholtz resonator arrangement can reduce the radiated sound through the ventilation opening by more than 10dB in 1/3 rd octave band around the resonant frequency of the resonators at 6.8 kHz ( Fig. 8 ) It was found that the orientation of the resonators (upstream or downstream) has no significant effect on the performance. The modest broad band frequency reduction is achieved due to the higher impedance of a duct, formed by the wall pair of acoustic resonators.
  • Figure 9 shows the measured flow noise for a flow rate of 8 L/s without a primary loudspeaker.
  • the results show that the installation of the resonators considerably increases the aero-acoustic self-noise in the entire frequency range up to 7 kHz. This is because the resonators distort the flow.
  • the results show that for the acoustic self-noise the direction of the acoustic resonator does make a difference.
  • the resonators should be arranged with the openings in downstream direction.
  • Fig. 10 shows the reduction of the volume flow rate for constant fan RPM of a blower.
  • the results show that the flow resistance of the ventilation opening increases due to the resonator arrangement. This is because the resonator walls form a short duct, which compared to the prior art configuration in which no resonators are arranged at the air exhaust openings, increases the friction losses.
  • the maximum reduction of the flow rate is about 2.5% which are tolerable in most applications.
  • the resonator arrangement with the opening facing in the downstream direction also shows lower reductions in the flow rate, with a maximum reduction of 1.5 %.
  • the invention has positive effects on the airborne noise.
  • the modified opening with resonators 3 reduces the total noise significantly around the tuned resonance frequency of the acoustic resonators and also provides modest reduction over a wide frequency range ( Fig. 8 )
  • the invention can be used for the ventilation of any product, provided (1) air-borne noise transmission through ventilation openings is the dominant contributor to the noise emissions, and (2) the noise emissions include a tonal component at the fixed frequency.
  • this invention can be applied to the following power tools:
  • the following devices can also be an application, provided a fan rotates at the constant r.p.m., and generates a tonal fan noise.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Soundproofing, Sound Blocking, And Sound Damping (AREA)
EP22158036.8A 2022-02-22 2022-02-22 Geräuschreduzierte gebläsemittel und deren verwendung in elektrowerkzeugen und vorrichtungen Pending EP4230873A1 (de)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP22158036.8A EP4230873A1 (de) 2022-02-22 2022-02-22 Geräuschreduzierte gebläsemittel und deren verwendung in elektrowerkzeugen und vorrichtungen

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
EP22158036.8A EP4230873A1 (de) 2022-02-22 2022-02-22 Geräuschreduzierte gebläsemittel und deren verwendung in elektrowerkzeugen und vorrichtungen

Publications (1)

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EP4230873A1 true EP4230873A1 (de) 2023-08-23

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EP22158036.8A Pending EP4230873A1 (de) 2022-02-22 2022-02-22 Geräuschreduzierte gebläsemittel und deren verwendung in elektrowerkzeugen und vorrichtungen

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5029593B2 (de) 1972-06-09 1975-09-25
US5869792A (en) * 1995-12-04 1999-02-09 Vibron Limited Reactive acoustic silencer
JPH1193670A (ja) * 1997-09-19 1999-04-06 Hitachi Constr Mach Co Ltd ファンシュラウド
US20200045845A1 (en) * 2018-08-01 2020-02-06 Winstron Corp. Fan system and sound suppression method thereof

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5029593B2 (de) 1972-06-09 1975-09-25
US5869792A (en) * 1995-12-04 1999-02-09 Vibron Limited Reactive acoustic silencer
JPH1193670A (ja) * 1997-09-19 1999-04-06 Hitachi Constr Mach Co Ltd ファンシュラウド
US20200045845A1 (en) * 2018-08-01 2020-02-06 Winstron Corp. Fan system and sound suppression method thereof

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