Plastic closure cap for electric motor

#This invention relates to a fractional horsepower electric motor and more particularly to a plastic closure cap for such motor.

#Typically, a prior art electric motor of the fractional horsepower type, such as shown in U.S. Pat. No. 3,633,055, includes a stator housing forming a stator cavity in which a rotor having a shaft is rotatably mounted by a sleeve bearing fixedly secured in the stator housing. Axial movement of the shaft is normally limited by means fixed on the shaft which abuts against opposite ends of the sleeve bearing. Unless the parts of the motor are manufactured to very close tolerances and carefully assembled, there is usually some end play in the shaft, which in many motor applications is undesirable. Since fractional horsepower motors are manufactured in large quantities for various applications, only some of which require limited end play, it is prohibitively expensive to limit the amount of end play by the above-mentioned known technique.

#Further, an electric motor, particularly of the permanent magnet type, requires absence of foreign particles in the stator cavity. In the prior art, one method of preventing entrance of such particles was to close the end of the stator with a metal plate adhesively secured to the stator housing. However, such a construction is not entirely reliable in all applications as the adhesive may tend to dry up. Moreover, such a procedure is relatively expensive due to the high cost of forming metal parts, and the additional assembly step of applying the adhesive.

#FIG. 1 is a cross-sectional view of one embodiment of the plastic closure cap of the present invention installed on an electric motor;

#FIG. 2 is a perspective view of the closure shown in FIG. 1;

#FIG. 3 is an enlarged fragmentary cross-sectional view taken substantially along line 3--3 of FIG. 2; and

#Referring to FIG. 1, an electric motor 10 of the fractional horsepower, permanent magnet type, comprises a stator assembly 12, a rotor assembly 14, and a plastic closure cap 16 constructed in accordance with the present invention.

#In more detail, the stator 12 includes a pair of annular stator housings 18 and 20 containing field windings and each having a pair of electric wires 22 extending therefrom. The housing 18 is secured to the housing 20 which in turn is secured to a mounting or base plate 24 to form a stator cavity 26 in which the rotor 14 rotates. An axially inwardly bent sleeve portion 28 of the base plate 24 forms a support for an axially extending sleeve bearing 30.

#The rotor 14 has an elongated shaft 32 which is rotatably supported in the bearing 30, one end 33 of the shaft extending from the stator to receive various appliances, such as fans, pulleys, etc., and the other end 35 having a sheet metal hub 34 pressed thereon to which a tubular ceramic magnet 36 is fixedly secured. A plurality of washers or shims 44 are located between the hub 34 and the inner end of the bearing 30 to axially locate the shaft 32 in one direction. The plastic closure cap 16 of the present invention closes the open end of the cavity 26 to prevent foreign materials from contaminating the ceramic magnet 36, the stator windings or the bearing surfaces etc., and in addition it axially locates the shaft 32 in the opposite axial direction.