This invention relates to a centrifugal fan for sucking air from one of both sides defined along an axis of a revolving shaft of an electric motor and discharging it in a direction perpendicular to an axial direction of the revolving shaft, and more particularly a centrifugal fan exhibiting enhanced waterproof performance.
A prior art fails to develop a centrifugal fan called a sirocco fan which exhibits increased waterproof performance while being simplified in structure. For example, a centrifugal fan disclosed in Japanese Patent Application Laid-Open Publication No. 148484/1999 is so constructed that a stator which is required to exhibit waterproofness structure is covered with a resin mold.
However, techniques of covering the stator with the resin mold require much time and much cost for formation of the resin mold, to thereby fail to reduce manufacturing costs of the centrifugal fan.
The present invention has been made in view of the foregoing disadvantage of the prior art.
Accordingly, it is an object of the present invention to provide a centrifugal fan which is capable of exhibiting enhanced waterproof performance without using any resin mold while being simplified in structure.
It is another object of the present invention to provide a centrifugal fan which is capable of being simplified in structure and exhibiting waterproof performance.
It is a further object of the present invention to provide a centrifugal fan which is capable of permitting water collected in a casing to be discharged outwardly of the casing to a degree sufficient not to interfere with operation of the centrifugal fan even when accuracy at which the centrifugal fan is assembled is deteriorated.
It is still another object of the present invention to provide a centrifugal fan which is capable of exhibiting increased waterproof performance irrespective of a posture in which the centrifugal fan is mounted or operated.
In accordance with the present invention, a centrifugal fan is provided. The centrifugal fan includes an electric motor including a stator having a stator-side magnetic pole and a rotor rotated about a revolving shaft outside the stator. The rotor includes a cup-like member including a bottom wall fixed on the revolving shaft and a peripheral wall arranged so as to extend in an axial direction of the revolving shaft from an outer edge of the bottom wall, and a rotor-side magnetic pole fixed inside the peripheral wall of the cup-like member and arranged opposite to the stator-side magnetic pole of the stator. The centrifugal fan further includes an impeller including a fixed section fixed outside the cup-like member of the rotor of the electric motor, a blade support fixed on the fixed section and arranged so as to extend in a radial direction of the revolving shaft, and a plurality of blades fixed on the blade support so as to suck air on one axial side of the revolving shaft and discharge the air in the radial direction of the revolving shaft; and a casing including a first side wall provided with a suction port which is open to the one axial side of the revolving shaft, a second side wall positioned on the other axial side of the revolving shaft with respect to the first side wall and arranged so as to be spaced from the first side wall at a predetermined interval, and a peripheral wall arranged so as to connect the first side wall and second side wall to each other and form an air passage between the first side wall and the second side wall for guiding air discharged from the impeller to a discharge port which is open in a direction tangential to a direction of rotation of the impeller. The casing receives the electric motor and impeller therein. The term xe2x80x9cone axial sidexe2x80x9d of the revolving shaft used herein is intended to mean one of both sides defined along an axis of the revolving shaft of the motor. Also, the term xe2x80x9cthe other axial sidexe2x80x9d of the revolving shaft used herein is intended to mean the other of both sides defined along the axis of the revolving shaft.
In the centrifugal fan generally constructed as described above, the electric motor is arranged in the casing so that the stator is fixed on the second side wall and the cup-like member of the rotor permits the bottom wall to face the suction port of the first side wall. The second side wall of the casing and a wall of the blade support of the impeller have opposite surface portions arranged so as to be opposite to each other in the axial direction of the revolving shaft, respectively. The opposite surface portion of the second side wall of the casing and the opposite surface portion of the wall of the blade support of the impeller each are formed into a configuration which permits the opposite surface portions to cooperate with each other to provide a labyrinth structure which prevents water from intruding into a space defined between the cup-like member and the second wall from an outside in the radial direction of the revolving shaft. The blades are mounted on a surface portion of the blade support opposite to the opposite surface portion of the blade support.
Such construction of the present invention permits the centrifugal fan to exhibit satisfactory waterproof performance while being simplified in structure without increasing an overall size thereof and using any resin mold. Also, in the present invention, as described above, the labyrinth structure is arranged at a position at which the blades are mounted, to thereby increase a length of the labyrinth structure and permit a space defined inside the labyrinth structure to be effectively utilized for receiving parts thereon.
The labyrinth structure may be constructed in any desired manner. For example, it may be constructed in such a manner that the opposite surface portion of the second side wall is formed with a plurality of cylindrical projections in a manner to project toward the one axial side of the revolving shaft and be arranged concentrically with the revolving shaft, wherein the opposite surface portion of the impeller is integrally formed thereon with a plurality of cylindrical projections in a manner to project toward the other axial side of the revolving shaft, be concentric with the revolving shaft and alternate with the cylindrical projections of the second side walls in the radial direction of the revolving shaft. Such construction permits the cylindrical projections to cooperate with each other to define a gap passage therebetween which provides the labyrinth structure. Also, it facilitates an increase in length of the gap passage. Thus, the centrifugal fan of the present invention exhibits enhanced waterproof performance while being simplified in structure.
Irrespective of arrangement of the labyrinth structure described above, the centrifugal fan has a likelihood that water is gradually collected in the casing and then intrudes from an inlet of the labyrinth structure through the labyrinth structure into the motor. In order to avoid the problem, at least one of the first and second side walls may be formed at a portion thereof positioned outwardly in the radial direction of the revolving shaft as compared with the labyrinth structure with at least one drainage through-hole for outwardly discharging water collected in the casing. The drainage through-hole may be arranged so as to extend through the side wall in the axial direction. Such arrangement of the drainage through-hole, when water collected in the casing reaches a level of the drainage through-hole, permits the water to be outwardly discharged therethrough from the casing irrespective of a posture in the centrifugal fan is operated and/or operated. This prevents water connected in the casing from intruding through the labyrinth structure into the motor. Water at a level below the drainage through-hole is still remain in the casing. However, the water does not adversely affect operation of the centrifugal fan. The drainage through-hole may be arranged at the peripheral wall. This permits water collected in the casing to be naturally discharged therethrough from the casing. However, when the drainage through-hole of the peripheral wall has a large size, air discharged from the impeller is caused to positively leak therethrough, to thereby deteriorate air feed efficiency and generate noise. Thus, a size of the drainage through-hole and the number thereof are preferably limited to the minimum.
When it is possible to previously know a posture in which the centrifugal fan is operated, a position of the drainage through-hole may be determined depending on the posture. However, in the case of a general-purpose centrifugal fan, a posture in which it is mounted or operated is varied depending on a user. Thus, it is preferable that at least one of the first side wall and second side wall is formed with a plurality of drainage through-holes in a manner to be spaced from each other at intervals in a peripheral direction of the revolving shaft. Such arrangement of the through-holes permits water collected in the casing to be outwardly discharged from the drainage through-holes of the side wall without substantially considering a posture of operation of the centrifugal fan, to thereby enhance general-purpose properties of the centrifugal fan. In particular, in this instance, arrangement of one or more such drainage through-holes at both first side wall and second side wall substantially prevents intrusion of water into the electric motor irrespective of a posture of mounting and/or operation of the centrifugal fan. In this instance, the first side wall and second side wall each may be formed with at least one such drainage through-hole. This prevents intrusion of water into the motor irrespective of a posture of mounting and/or operation of the centrifugal fan.
For example, when the drainage through-hole is formed at the side wall of the casing, at least one of the first side wall and second side wall is formed with a plurality of drainage through-holes at a portion thereof positioned in an angular range except a predetermined angular range defined about the revolving shaft and including the discharge port when the first side wall is viewed from the one axial side of the revolving shaft. In this instance, the drainage through-holes may be arranged at portions of the first side wall and second side wall positioned in the predetermined angular range including the discharge port. However, when the centrifugal fan is operated in a posture which may possibly cause water to be collected in the casing under such conditions, water collected in the casing to a degree is permitted to be discharged from the discharge port, so that it is not required to form the drainage through-holes in the angular range. Thus, at least one drainage through-hole may be formed at a position which permits water collected in the casing to be discharged through the drainage through-hole when the centrifugal fan is operated or mounted in a posture which keeps water entering the casing through the suction port from being discharged through the discharge port. Thus, at least one of the first side wall, second side wall and peripheral wall may be formed with at least one drainage through-hole for discharging water in the casing when the centrifugal fan is operated or mounted in a posture which keeps water entering the casing through the suction port from being discharged through the discharge port.