EP1479917A1 - Fan - Google Patents

Abstract

A fan (1) comprising an impeller (2), a casing (4) that is disposed so as to enclose the impeller (2), and amotor (3) for rotating the impeller (2) relatively to the casing (4), the fan having a rotational axis,wherein the impeller (2) includes a disk portion (22) and a plurality of blades (21) that is arranged on thedisk portion, optionally the impeller also includes a disk like shroud (123), the casing (4) includes aside wall (40a) that is opposed to outer peripheral end portions (212) of the blades (21) with a gap and that ishaving an outlet (43), a first end plate (40b) that constitutes an upper wall of the casing, and a secondend plate (40c) that constitutes a lower wall of the casing (4), both of the first and second end platesbeing provided with an aperture (41,42) including areas around the rotational axis.

Description

BACKGROUND OF THEINVENTION1. Field of the Invention
• The present invention relates to a fan for supplying fuel gas to a combustion apparatussuch as a boiler. More specifically, the present invention relates to an improvement of acasing, an impeller and a motor of a fan for cost reduction, safety and low-noise operation.
2. Description of the Prior Art
• A fan is used for supplying fuel gas to a combustion apparatus such as a boiler. Thereis one type of the fan that is described in Japanese unexamined patent publication No. H07-224796.This publication discloses a centrifugal fan that has an impeller having a plurality ofblades and a gas inlet in upper part of the impeller as shown in the Figures of this publication,a motor for rotating the impeller to generate a gas flow from the gas inlet to the outercircumference of the impeller and a casing that encloses the periphery of the impeller.
• It is not easy to construct the casing and the motor with no gaps between them in sucha centrifugal blower fan. In this case, it may be difficult to prevent the gas to be suppliedfrom leaking out of the fan through the gaps between the casing and the motor. If a sealingpart, such as O-ring, is used, the number of the parts for constructing the fan will beincreasing.
• In addition, an opening that is provided to the upper part of the casing of thecentrifugal fan as an inlet of the gas is just a hole having a substantially circular shape.Therefore, the centrifugal fan has an advantage of a static pressure higher than other type fanssuch as an axial fan or a laminar flow fan, but has a disadvantage of making noise due to aturbulent flow or a vortex generated in the casing.
• In addition, when using the centrifugal fan for supplying fuel gas to a combustionapparatus such as a boiler, there is a risk of fire due to a spark generated by the motor. A DCmotor having a mechanical commutator is called as DS brush motor. And because of themechanical commutation, the DS brush motor usually generates sparks during its rotating. Sowhen using a DC brush motor for supplying fuel gas to a combustion apparatus as a gas flowgenerating fan , many efforts and much cost may be required in order to avoid the burning risk. On the other hand a DC motor having a electrical commutation control is called as DCbrushless motor. Because of electrical commutation, the DC brushless motor may notgenerates a spark at its commutation. However if the DS brushless motor is used forsupplying fuel gas, it is necessary to insure that no spark is generated when the motor isrotating.
SUMMARY OF THE INVENTION
• A first object of the present invention is to provide a fan that can prevent a gas to besupplied from leaking out of the fan from other than the outlet of the fan.
• A second object of the present invention is to provide a fan that can suppress a noisecaused by the fan rotation with maintaining better static pressure and better flow quantity thanbefore.
• A third object of the present invention is to provide a fan that can supply fuel gas to acombustion apparatus such as a boiler more safely than before. These objects are solved bymeans of a fan having the characteristics as cited in the independent claims; preferredembodiments are defined by dependent subclaims.
• According to the present invention, inlet openings are formed on both ends of a casingin the axial direction of a fan, so that an air pressure inside the casing is always lower thanthat of the outside. By this structure, a supplied gas inside the casing does not leak into theoutside of the fan.
• In addition, the motor part of the fan may be molded by a resin or the like so that thegas does not leak externally through the inside of the motor.
• Thus, the process for attaching a seal member that was necessary conventionally canbe eliminated, so that workability can be improved. Furthermore, it is possible to provide theproduct at a low cost because the seal member is not necessary to be attached.
• Also in the present invention, a flow duct cylinder can be provided to the inlet openingof the casing and is extended to an opening of a shroud of the impeller. This flow ductcylinder suppresses generation of a circulation and a turbulent flow of the gas inside thecasing so that a noise caused by the circulation and the flow can be reduced. In addition, bysuppressing generation of a turbulent flow, the static pressure and the flow quantitycharacteristics are also improved.
• In addition, according to the present invention, the motor can be a DC brushless motorso that the brush and the commutator can be eliminated. Thus, a spark that might be generated between them at commutation does not appear, so there is little risk that the fuel gascatches fire by motor rotation. Accordingly, the fuel gas can be supplied safely.
• Furthermore, in a preferred embodiment the motor part of the fan is molded by a resinor the like, so as to prevent adhesion of dust or water to a part inside the motor such as anelectric contact that may cause a short circuit or a spark other than sparks caused by thecommutation. Therefore, the risk that the fuel gas catches fire from the short circuit portionor others can be reduced substantially.
BRIEF DESCRIPTION OF THE DRAWINGS
• Fig. 1 is a cross section of a fan and an enlarged view of a main portion according to afirst embodiment of the present invention.
• Fig. 2 is a cross section of the fan according to the first embodiment of the presentinvention and an enlarged view of a main portion.
• Fig. 3 is a plane view of the fan according to the first embodiment of the presentinvention.
• Fig. 4 is a bottom view of the fan according to the first embodiment of the presentinvention.
• Fig. 5 is a perspective view of an impeller that is cut out from the fan according to thefirst embodiment of the present invention.
• Fig. 6 is a cross section of a motor of the fan according to the first embodiment of thepresent invention.
• Fig. 7 is a cross section of a fan according to a second embodiment of the presentinvention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
• An embodiment of a fan according to the present invention will be described withreference to the attached drawings.
• Note that all descriptions about direction in the explanation just indicate directions onthe drawings and do not restrict directions in a real embodiment unless otherwise specified.
• Fig. 1 is a cross section and an enlarged view of a main portion indicating a fanaccording to a first embodiment.
• Thefan 1 includes animpeller 2, amotor 3 and acasing 4. Theimpeller 2 ispositioned in thecasing 4, and themotor 3 rotates theimpeller 2 relatively to thecasing 4.
• Theimpeller 2 includes adisk portion 22 and a plurality ofblades 21 that are arrangedalong a circumference of a circle on thedisk portion 22. Theimpeller 2 is attached to arotation shaft 36 of themotor 3 at the rotation center of theimpeller 2.
• Thecasing 4 comprises aside wall 40a that faces an outerperipheral end portion 21aof theblade 21 without contact, afirst end plate 40b as an upper wall that is positioned at theupper end of thecasing 4 and asecond end plate 40c as a lower wall that is positioned at thelower end of thecasing 4. A circularfirst aperture 41 serving as an inlet is formed in thefirstend plate 40b at a center area including the rotational axis of theimpeller 2. In addition thediameter of thefirst Aperture 41 is substantially the same as the one defined by the innercircumferential ends 21b of theblades 21. Thesecond end plate 40c is provided with asecond aperture (42), serving in the shown embodiment as an inlet at a periphery of therotation center axis of theimpeller 2.
• Fig. 5 is a perspective view of theimpeller 2 that is divided into two after removingthefirst end plate 40b. Thedisc portion 22 is provided with a plurality of small holes,defining passageways having definite section. Thus suction is provided in the vicinity of thesecond aperture. The passageways may be formed in various ways and are provided in theshown embodiment to be holes with diameters varying with the respective distance to therotation center axis of theimpeller 2.
• Theside wall 40a includes a circular peripheral wall and a linear wall portion that iscontinuous from the circular peripheral wall in the tangent direction thereof as shown in Figs.3 and 4. Anoutlet 43 is provided to the extended end portion of the linear wall portion. Notethat theperipheral wall 40a may have an equiangular spiral shape in which a radius of a partof the curved surface in the cylindrical shape of theside wall 40a increases gradually in therotational direction of theimpeller 2. In this case, it is preferable that theside wall 40a hasthe maximum radius portion of theside wall 40a and the minimum radius portion of thesidewall 40a, and there is an opening to make theoutlet 43 between the maximum radius portionof theside wall 40a and the minimum radius portion of theside wall 40a.
• Fig. 6 is a cross section of themotor 3. Themotor 3 includes arotor magnet 31, astator 33 having a plurality ofcoils 32, acircuit board 34 having a driving circuit forcontrolling supply of electricity to thecoil 32, amotor housing 35, anoutput shaft 36 and abearing 37. Note it is better for thisbearing 37 to be enclosed by rubber or to be sealed thesame. Therubber member 38 reduces communication between the inside of themotor 3 andthe inside of thecasing 4.
• Thismotor 3 is a DC brushless motor, in which the driving circuit controls excitationof thecoil 32 instead of a brush and a commutator. Therefore, a spark is not generated in theDC brushless motor though it can be generated between a brush and a commutator whenexciting the coil. In addition, rotation efficiency of the brushless motor is high because thereis little loss of rotation energy due to friction compared with the brush motor that includes abrush and a commutator that contact each other and slide during rotation. Furthermore, a lifeof themotor 3 can be elongated because there is no abrasion between a brush and acommutator. In addition, there is no sliding noise due to a brush and a commutator, sorotation noise can be reduced. Furthermore, excitation of thecoil 32 is controlled by theelectric signal in the DC brushless motor, so it is possible to perform a fine control inaccordance with the change of torque and rotation speed.
• An operation of the fan according to this embodiment is as follows. First, themotor 3and theimpeller 2 that is attached to themotor 3 start to rotate relatively to thecasing 4.Then, gas at the inner circumferential portion of theimpeller blade 21 is led in the outercircumferential direction of theimpeller blade 21 by a centrifugal force. Thus, there is anegative pressure to a barometric pressure outside thecasing 4 at the vicinity of the innercircumferential portion of theimpeller 21 . On the other hand, the gas is compressed at thevicinity of the outer circumferential portion of theimpeller 21, where higher pressure isgenerated than a barometric pressure outside thecasing 4. Thus, gas outside the casing is ledinto thecasing 4 through thefirst aperture 41 of thecasing 4 that is open to the innercircumferential portion of theimpeller blade 21. In addition, the gas is discharged externallythrough theoutlet 43 of thecasing 4 that is open to the outer circumferential portion of theimpeller blade 21.
• In addition, thesecond aperture 42 of thecasing 4 is opposed to the surface of thediskportion 22 of theimpeller 2 on which the blades are not arranged. Inside thecasing 4, there isthe highest pressure at the outer circumferential portion. Theoutlet 43 is open to the outercircumferential portion and is at a pressure substantially the same as the barometric pressureoutside. Since a definite passageway is provided in thedisc portion 22 gas can be sucked fromthe area surrounding thesecond aperture 42. As a result, the entire inside of thecasing 4 is ata lower pressure than the outer circumferential portion, so the vicinity of thesecond aperture42 is at a lower pressure than the barometric pressure outside. Therefore, the gas does notleak externally from the inside of the casing.
• Note thatauxiliary blades 24 can be arranged along a circumference of a circle on thesurface of thedisk portion 22 of theimpeller 2 on which the blade are not arranged as shown in Fig. 2. By this structure, the pressure at the vicinity of thesecond aperture 42 in thecasing4 is further decreased, so that leakage of the gas externally can be prevented stably.Furthermore, thisauxiliary blade 24 can work as a rib for reinforcing theimpeller 2 because itis provided at the inner circumferential side with reference to theblade 21.
• In addition, the fan can be used as a fan for supplying fuel gas to a combustionapparatus such as a boiler in this embodiment. The fuel gas can be fire by a spark. Therefore,it is necessary to prevent the fan from generating a spark or being a cause of fire, and toprevent the fuel gas from leaking externally.
• First, by making the inside of thecasing 4 always negative pressure with reference tothe barometric pressure outside as described above, so as to prevent the gas from leakingexternally.
• In addition, by using a brushless motor, generation of a spark from a contact between abrush and a commutator can be suppressed. Furthermore, the stator 33 and thecircuit board34 of this motor are molded 38 by a resin having insulating properties. Thismold resin 38 ispreferably a synthetic resin, a natural resin, a rubber, a vinyl or a plastic. Since themotor 3 ismolded, it will not happen that dust is deposited on thecircuit board 34, and a short circuit isformed on thecircuit board 34. In addition, it is also possible to prevent an electricconnection portion such as a contact between thecoil 32 and thecircuit board 34 is broken bya vibration of themotor 3 or the device.
• In addition, theimpeller 2 is made of a resin that contains a conductive material asconductive filler. The conductive filler may be particles of a metal such as copper, a copperalloy, silver, nickel or a low melting point alloy, metal oxide particles such as zinc oxide, tinoxide or indium oxide, conductive polymer particles such as various types of carbon black,polypyrrole or polyaniline, a polymer particles coated with a metal, particles of copper orsilver coated with a rare metal, metal fibers, or carbon fibers. Collision of gas molecules orparticles that are contained in the gas always occurs on the surface of theimpeller blade 21, sostatic electricity can be easily accumulated. Therefore, by containing theimpeller blade 21 ofa conductive material, electrification of the static electricity can be prevented.
• Note that it is desirable in this embodiment that thecasing 4 is made of aluminum bydie casting. Aluminum has a good conductivity of electricity and is also improved in itsmechanical strength by the die casting process. Therefore, thecasing 4 is always conductiveso that electrification of the static electricity can be prevented, sufficient strength is obtainedby die casting, and fine machining of thecasing 4 can be performed.
• In addition, thecasing 4 can be made of a resin by molding so as to produce it at a lowcost. Furthermore, if it is formed integrally with themold resin 38 of themotor 3, leakage ofgas through the inside of themotor 3 externally can be prevented stably.
• Fig. 7 is a cross section showing a fan according to the second embodiment.
• The fan 101 includes animpeller 102, amotor 103 and acasing 104. Theimpeller102 is positioned in thecasing 104, and themotor 103 rotates theimpeller 102 relatively tothecasing 104.
• Theimpeller 102 includes adisk portion 122 and a plurality of blades 121 arrangedalong a circumference of a circle on the surface of thedisk portion 122. Theimpeller 102 isattached to arotation shaft 136 of themotor 103 at the rotation center portion. In addition, adisk-like shroud 123 having a circular hole 123a at the center thereof is provided at the upperend portion of the blade 121. In addition, anouter rim end 123b of theshroud 123 isextended longer than the outer circumferential end 121b of the blade 121 to the outercircumference. Whereby a gas flow from theouter rim end 123b to the circular hole 123amay be decreased, because an opening between theouter rim end 123b and an inner side wallof thecasing 104 is made be narrower. Therefore a noise due to a back flow, a turbulent flowor the vortex flow of the gas can be suppressed in the upper area of theshroud 123.
• Thecasing 104 comprises aside wall 140a that is opposed to the outerperipheral endportion 121 a of the blade 121 without contact, afirst end plate 140b as an upper wall that ispositioned at the upper side of thecasing 104, asecond end plate 140c as an lower wall that ispositioned at the lower side of thecasing 104 and a cylinder-like wind tunnel 145. A circularfirst aperture 141 is formed in thefirst end plate 140b at a center area including the rotationalaxis of theimpeller 2. In addition, amotor 103 is attached on thelower wall 140c of thecasing. Theside wall 140a has an equiangular spiral shape in which a radius of a part of thecurved surface in the cylindrical shape of theside wall 140a increases gradually in the rotationdirection of theimpeller 102, having the same shape as theside wall 40a shown in Fig. 3.Theside wall 140a has the maximum radius portion of theside wall 140a and the minimumradius portion of theside wall 140a, and there is an opening to make the outlet 143 betweenthe maximum radius portion of theside wall 140a and the minimum radius portion of thesidewall 140a. Thewind tunnel 145 is provided so that the upper end thereof is attached closelyon the lower side of theupper wall 140b at the position where the circular opening of thewind tunnel 145 is aligned with thefirst inlet hole 141, and the lower end of thewind tunnel145 is extending to the same position or below the upper end of the center hole 123a of theshroud 123.
• Themotor 103 has the same structure as themotor 3 described in the firstembodiment.
• An operation of the fan in the second embodiment is as follows. First, themotor 103and theimpeller 102 that is attached to themotor 103 start to rotate relatively to thecasing104. Then, the gas at the inner circumferential portion of the impeller blade 121 is led in theouter circumferential direction of the impeller blade 121 by its rotation. And a negativepressure comparing with a barometric pressure outside thecasing 104 is generated at thevicinity of the inner circumferential portion of theimpeller 102. On the other hand, the gas iscompressed at the vicinity of the outer circumferential portion of the impeller 121, wherehigher pressure is generated than a barometric pressure outside thecasing 104. Thus, the gasoutside thecasing 104 is led into thecasing 104 through thefirst aperture 141 of thecasing104 that is open to the inner circumferential portion of theimpeller 102 through thewindtunnel 145. Thewind tunnel 145 is open at the circular hole 123a of theshroud 123. As aresult, a noise due to a back flow, a turbulent flow or a vortex flow of the gas can besuppressed. In addition, an external air can be led into thecasing 104 efficiently and can bedischarged smoothly from the portion. Preferably the lower end of thewind tunnel 145 isextending to below the top end of the center hole 123a of theshroud 123. In this case, acylindrical gap between the outer circumferential surface of thewind tunnel 145 and the innercircumferential portion 123a of theshroud 123 is formed. The narrower the cylindrical gapis, the less a gas flow from theouter rim end 123b to the circular hole 123a may be, becauseof the labyrinth effect. Therefore a noise due to a back flow, a turbulent flow or the vortexflow of the gas can be more suppressed in the upper area of theshroud 123.
• An outercircumferential end 123b of theshroud 123 is extended longer than theoutercircumferential end 121a of the blade 121 to the outer circumference. Therefore, the gasis prevented from flowing into the upper portion of theshroud 123 to form a circulating flow.Thus, the gas that is led into the outer circumferential portion of the impeller blade 121 isdischarged to the outside of thecasing 104 through the outlet 143 of thecasing 104 that isopen to the outer circumferential portion of the impeller blade 121.
• Note that the first and the second embodiments described above are just examples ofvarious embodiments of the present invention, and they can be modified or corrected in thescope of the present invention. For example, a space may be provided at the innercircumferential portion of the impeller for housing the motor so as to realize a compact size.A material of the impeller or the casing, a shape and a position of the first and/or secondaperture or the outlet, a shape of the impeller blade, and others can be determined freely. In addition, it is determined freely whether or not there is the shroud or the wind tunnel that iscontinuous to the first aperture in the first embodiment, or a structure of the motor andwhether or not there is the second aperture in the second embodiment.

Claims (11)

1. A fan (1; 101) comprising an impeller (2; 102), a casing (4; 104) that is disposedso as to enclose the impeller (2; 102), and a motor (3; 103) for rotating the impeller(2; 102) relatively to the casing (4; 104), the fan having a rotational axis, whereinthe impeller (2) includes a disk portion (22) and a plurality of blades (21) that isarranged on the disk portion (22), optionally the impeller also includes a disk likeshroud (123),
   the casing (4) includes a side wall (40a) that is opposed to outer peripheral endportions (21a) of the blades (21) with a gap and that is having an outlet (43), a firstend plate (40b) that constitutes an upper wall of the casing (4), and a second endplate (40c) that constitutes a lower wall of the casing (4),
   at least one, in particular both of the first and second end plates (40b) beingprovided with an aperture (41, 42) including areas around the rotational axis.
2. The fan according to claim 1, wherein means are provided, forming definitepassageway in the disc portion (22).
3. The fan according to claim 1 or 2, wherein the disk portion (22) is positioned so asto be opposed to the second end plate (40c), and a plurality of auxiliary blades (24)is attached onto the lower surface of the disk portion (22) in a radial patterncentered at the rotational axis, for generating gas flows to radial directions.
4. The fan according to claim 1, 2 or 3, wherein the second inlet hole (42) and/or saidmeans forming definite passage way in the disc portion includes a plurality ofsmall holes that is formed around the rotational axis.
5. A fan (101) comprising an impeller (102), a casing (104) that is disposed so as toenclose the impeller (102), and a motor (103) for rotating the impeller (102) relatively to the casing (104), the fan having a rotational axis, wherein the impeller(102) comprises a disk portion (122), a plurality of blades (121) that is arranged onthe disk portion, and a disk-like shroud (123) having a center hole (123a) at thecenter thereof, the casing (104) comprises a side wall (140a) that is opposed to anouter peripheral end portion (121a) of the blades (121) with gaps, a first end plate(140b) that constitutes an upper of the casing (104) and have a wind tunnel (145)having a cylindrical shape, and a second end plate (140c) that constitutes a lowerwall of the casing (104), the first end plate (140b) has a first inlet hole (141)including areas around the rotational axis, and the wind tunnel (145) is attached onthe lower side of the first end plate (140b) at the position where the circularopening of the wind tunnel (145) is aligned with the first inlet hole (141), the sidewall (140a) is provided with an outlet (143).
6. The fan according to claim 5, wherein a radius of an outer rim end (123b) of theshroud is larger than a distance between the blade outer circumferential end (121 a)and the rotation shaft.
7. The fan according to any one of claims 1 to 6, wherein the lower end of the windtunnel (145) is extending to the same position or below the upper end of the centerhole (123a) of the shroud (123).
8. The fan according to any one of claims 1 to 6, wherein the motor (3, 103) is abrushless motor that includes a stator (33) having one or more coils (32), a rotormagnet (31) that rotates with being opposed to the stator, and a circuit board (34)having a driving circuit for controlling excitation of the coil (32).
9. The fan according to any one of claims 1 to 8, wherein the motor (3, 103) ismolded by a mold material (38) that has insulating properties.
10. The fan according to any one of claims 1 to 9, wherein the impeller (2, 102) hasconductivity.
11. The fan according to any one of claims 1 to 10, wherein the casing (4, 104) ismade of aluminum by die casting.

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