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Fan assemblyRelated Patent Categories: Pumps, Motor Driven, Motor Within Rotary Pumping Member, Armature Within Pumping Member, Stator Within ArmatureFan assembly description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070014675, Fan assembly. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention generally relates to an electrically powered fan assembly used to blow air. [0003] 2. Description of the Related Art [0004] Conventionally, a centrifugal type fan assembly, taking air in an axial direction and exhausting the air in a radial direction, has the following configuration. Specifically, the conventional fan assembly includes an impeller having a plurality of blades arranged in a circumferential direction centered about a center axis, and a substantially cup-shaped portion arranged at the middle of the impeller into which a substantially cylindrical yoke made of magnetic material is press-fitted. In addition, a field magnet is attached to an inner side surface of the yoke. By virtue of this configuration, the impeller is rotatably supported around the center axis. The blades of the impeller are arranged on radially outer positions of the cup-shaped portion, and the cup-shaped portion and the blades are unitarily formed of synthetic resin, both of which are connected via a joint portion. By virtue of this configuration, a circular space is provided between the plurality of blades and the outer side surface of the cup-shaped portion. [0005] In terms of a centrifugal fan assembly, it may be preferable to enlarge the space provided at an inner side of the plurality of blades (in other words, the space between radially inner end portions of the blades and the outer side surface of the cup-shaped portion, to which the yoke is press-fitted, is made wider). With the wider space, the fan assembly may take more air therein, which results in improved blower efficiency of the fan assembly. However, upon making a diameter of the yoke smaller to enlarge the space, a magnetic circuit will be decreased in size. As a result, the motor efficiency is degraded. Upon making a diameter of the circular space bigger while fixing an outer diameter of the impeller, a blade-area will be decreased in size, which results in degraded blower efficiency. Upon making a diameter of the circular space bigger while keeping the blade-area of the impeller constant, the impeller will be enlarged. [0006] In order to enlarge the circular space without expanding the outer diameter of the impeller or degrading the blower efficiency, it is preferable to omit the cup shaped portion of the impeller covering the outer side surface of the yoke. [0007] In publicly available examples, a portion of the outer side surface around the opening of the permanent-magnet rotor having a cylindrical shape whose top is covered, and an inner side surface of the cylindrical portion provided at a middle of the impeller are fixed by, for example, press-fitting, bonding, and crimp-fixing. In another publicly available example, a flange portion is provided around the outer side surface of the opening of the permanent-magnet rotor, and the flange portion is fixed to the base plate of the centrifugal fan by crimp-fixing. [0008] However, in case that the permanent-magnet rotor and the cylindrical portion arranged at the middle portion of the impeller are press-fitted or bonded, an axial length of an affixing area at which the outer side surface of the permanent-magnet rotor is abutted against the impeller is short. Therefore, the impeller may not be fixed securely to the permanent-magnet rotor by press-fitting or bonding. For crimp-fixing, forming the engaging portion and crimping processes are required, which may deteriorate the work efficiency. [0009] Furthermore, the cup shaped portion of the impeller, which is made of resin, may be broken or cracked by the stress generated upon press-fitting the permanent magnet rotator (i.e., the cylindrical yoke made of metallic material with the field magnet attached to the inner side surface thereof) into the cup-shaped portion. Especially in a large-size fan, it is highly probable that the impeller is damaged or cracked. On the other hand, if the press-fit pressure is reduced, the permanent-magnet rotor may not be securely fixed to the impeller. As a result, the permanent-magnet rotor may detach from the impeller. [0010] In case that such a fan assembly is utilized in a low temperature environment, the impeller made of resin shrinks more than the yoke made of metallic material does, which results in breaking or cracking of the attaching portion of the impeller and the yoke. SUMMARY OF THE INVENTION [0011] In order to overcome the problems described above, preferred embodiments of the present invention provide an impeller portion securely fixed to the yoke while improving the blower efficiency of a fan assembly, and the breaking or the cracking of the impeller portion caused by thermal deformation is prevented. [0012] According to one preferred embodiment of the present invention, a fan assembly includes a yoke having a cylindrical shape whose top is covered and an impeller portion attached to the outer surface or around the bottom opening of the yoke. The impeller portion and the yoke are fixed by insert molding, and the two members are securely fixed to each other while the outer side surface of the yoke is exposed. In the fan assembly mentioned above, an outer side surface of the yoke may be exposed to outside air of the fan assembly. As a result, the impeller portion and the yoke are securely fixed while improving the blower efficiency of the fan assembly. [0013] A fan assembly according to another preferred embodiment of the present invention further includes a flange portion extending radially outwardly from the bottom opening of the yoke, and an impeller portion attached to the outer surface or a bottom portion around the opening of the yoke. In addition, a portion of the impeller portion may be formed concurrently with the insert molding for fixing the circular portion and the yoke. Upon forming the impeller portion, each of a plurality of weld lines passes between the two adjacent affixing portions. According to another preferred embodiment of the present invention, a plurality of gate marks are arranged on a portion of the discoid circular portion which is attached to the flange portion. By virtue of the configurations mentioned above, damages or cracks of the impeller portion caused by thermal deformation may be prevented. [0014] It should be understood that in the explanation of the present invention, when positional relationships among and orientations of the different components are described as being up/down or left/right, positional relationships and orientations that are in the drawings are indicated, however, positional relationships among and orientations of the components once having been assembled into an actual device are not indicated. [0015] Other features, elements, processes, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS [0016] FIG. 1 is a cross sectional view illustrating a configuration of a fan assembly according to a first preferred embodiment of the present invention. [0017] FIG. 2 is a bottom plan view illustrating a yoke and a circular portion. [0018] FIG. 3 is a plan view illustrating the yoke and the circular portion. [0019] FIG. 4 is a partial sectional view illustrating a yoke and a circular portion. [0020] FIG. 5 is a partial sectional view illustrating a yoke and a circular portion. [0021] FIG. 6 is a bottom plan view illustrating a yoke and a circular portion. Continue reading about Fan assembly... Full patent description for Fan assembly Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Fan assembly patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. 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