Fan construction and method of assembly

#This invention relates to a fan, and more specifically, to the structure of a fan particularly suited for use with electro-machinery.

#Electro-machinery such as an electric motor generates a sizeable amount of internal heat during operation, and it is common practice to provide the motor with a cooling fan. A fan is mounted on the motor drive shaft, and the fan turns with the shaft during operation and produces cooling air flow around the motor. One particular type of motor is referred to in the trade as a Totally Enclosed Fan Cooled (TEFC) motor, and it includes a fan mounted on the rotor shaft outside the motor housing or shell. The fan causes cooling air to flow around external cooling fins formed on the motor housing. The fan is typically made of a high strength plastic, and is produced by an injection molding process.

#A problem encountered in the manufacture of an injection molded fan is that the molds are quite expensive for the fan of a large size motor. Such a fan may have an outer diameter between one-two feet, for example. Since the cost of a mold increases approximately with the cube of its size, it will be apparent that the cost of a mold for a large one-piece fan may be quite high. This problem of relatively high cost of molding large parts is often exacerbated by the relatively low volume of large parts. If the volume is at least, for example, 10,000 to 15,000 parts per year, injection molding is economically feasible, but a low volume, large size part may be excessively expensive to produce when molding prior art designs for large motors.

#The invention may be better understood from the following detailed description taken in conjunction with the accompanying figures of the drawings wherein:

#FIG. 1 is a diagrammatic view of a machine including a fan constructed in accordance with the invention;

#FIG. 2 is an enlarged perspective view of a portion of a fan mounted on the shaft;

#While the following description makes reference to an electric motor, and while FIG. 1 shows one type of motor, it will be apparent that the invention is also applicable to other types of machinery. Further, while the following description relates to a radial flow fan, the invention is also applicable to other types of fans.

#With reference first to FIG. 1, a motor 10 includes a housing or shell 11 supported on a base 12. A rotor shaft 13 is rotatably mounted in the housing by suitable bearings 15, and at least one end 14 of the shaft extends out of the rearward end of the housing for coupling to a device to be driven. The housing 11 totally encloses the stator and the rotor of the motor (except for the ends of the shaft 13). In the example illustrated in FIG. 1, angularly spaced cooling fins 16 are formed on the outer periphery of the housing 11, but the motor may instead include a finless metal housing.

#Mounted on the other end 15 of the shaft 13 and rotatable with the shaft 15 is a radial flow fan 20 which produces a circulation of the air around the fins 16, for cooling purposes. As best shown in FIG. 2, the fan 20 is formed by a cylindrical hub 21 which is secured to the shaft 13, and by a plurality (only one illustrated in FIG. 2) of angularly spaced identical fan blades 22 which are attached to and extend radially outwardly from the hub 21. The fan 20 is enclosed within a fan shroud 17 which is attached to the motor housing 11. The shroud 17 includes air intake vents formed in the center area 18, and an air outlet passage 19 is formed between the shroud 17 and housing 11. Rotation of the fan blades 22 causes air to be drawn into the center of the fan through the intake vents, and to be expelled through the outlet passage 19 to the cooling fins 16. The hub and the blades are preferably made by an injection molding process utilizing a conventional thermo-plastic material of a type in common use in the industry. An example of a suitable material is polypropylene, and if static electricity is a problem, an electrically conductive polypropylene may be used. Of course, other suitable materials may be used.