Method of assembling an electric motor

The method of assembling an electric motor which comprises forming an upper housing assembly by first forming a generally cylindrical shell, forming an end member with an axial tube, mounting the end member on the cylindrical shell with the tube extending axially inwardly, locating the shell radially in an accurate position with respect to the axis of the shell, fastening the end member to the shell to form an upper housing assembly, mounting a radial wall on a hollow shaft, accurately locating a stator on the radial wall so that the stator and the outer diameter of the shaft are in accurate concentric relationship, fixing the stator in this accurate position to form a lower housing assembly, telescoping the upper assembly over the shaft of the lower housing assembly and interposing bearings between the shaft and the tube so that the upper housing assembly is in accurate concentric relationship with the stator.

This invention relates to electric motors. 
BACKGROUND AND SUMMARY OF THE INVENTION 
In the manufacture of electric motors, a basic requirement for high 
efficiency and low noise is that the air gap between the rotor and stator 
be maintained within predetermined limits. However, assembly methods for 
motors often are such that the tolerances do not assure a precise final 
construction of the motor. 
Further in certain types of motors such as used for ceiling fans, it is 
required to have a conduit extending through the rotating shaft of the 
motor in order that wiring may be provided to controls and light fixtures 
suspended from the motor. 
Accordingly, among the objectives of the present invention are to provide 
an electric motor and a method of making and assembling the motor wherein 
the accumulation of tolerances which would detract from the efficiency and 
would produce noise are minimized; wherein the motor has a minimum number 
of parts and can be utilized for ceiling fan operations which require a 
hollow conduit through which wires may be provided. 
In accordance with the invention, the electric motor comprises a lower 
housing assembly and an upper housing assembly. The lower housing 
comprises a hollow stationary shaft, a bottom plate mounted on the shaft 
and a stator mounted on the bottom plate. The upper housing comprises a 
tube and an integral top plate and a rotor mounted on the plate. The tube 
of the upper housing assembly is telescoped over the shaft of the lower 
housing assembly and bearings between the tube and shaft rotatably support 
the rotor about the stator. 
The method of assembling an electric motor comprises forming an upper 
housing assembly by first forming a generally cylindrical shell, forming 
an end plate with an axial tube, mounting the end plate on said 
cylindrical shell with the tube extending axially inwardly, locating the 
shell radially in an accurate position with respect to the axis of the 
shell, fastening the end member to the shell to form an upper housing 
assembly, mounting a radial wall on a hollow shaft, accurately locating a 
stator on the radial wall in accurate concentric relationship between the 
stator and the outer diameter of the shaft, fixing the stator in this 
accurate position to form a lower housing assembly, telescoping the upper 
housing assembly over the shaft of said lower housing assembly and 
interposing bearings between the shaft and the tube so that the rotor is 
in accurate concentric relationship with the stator.

DESCRIPTION 
Referring to FIGS. 1-4, the motor embodying the invention comprises a lower 
housing assembly 20 and an upper housing assembly 21. The lower housing 
assembly 20 consists of a stationary hollow shaft 22 that has an accurate 
outer diameter provided by machining or grinding fixed to a radial wall or 
bottom plate 23 by flaring the lower end as at 24 and interposing adhesive 
25 between the flared end 24 and a corresponding surface of the wall 23. A 
stator 26 is accurately positioned in concentric relationship to the outer 
diameter of the shaft 22 and comprises a stator winding 27 fixed to the 
outer surface of an annular wall 28, the lower end of which extends into 
an upwardly facing groove 29 in wall 23. Sealing means 30 in the form of 
adhesive holds the annular wall 28 and, in turn, the stator 26 in accurate 
concentric relation with respect to the shaft 22. 
The upper housing assembly 21 comprises a tube 31 with an integral radial 
flange 32 defining a wall or top plate and a cylindrical shell 33 adhered 
as at 34 at its upper end to the periphery of the wall 32 in accurate 
concentric relationship to the inner diameter of the tube 31. The inner 
wall of the shell 33 is provided with a plurality of magnets 34 that 
define the rotor of the motor herein shown and described as a permanent 
magnet brushless d.c. motor. Although the construction is described with 
respect to such a motor it can also be utilized with respect to other type 
motors such as shaded pole motors. 
Sleeve bearings 35, 36 are interposed between the shaft 22 and the tube 31. 
Felt 37 impregnated with oil is provided between the bearings and a flat 
thrust washer 38 is provided between the lower bearing 36 and the hub 39 
of the member 23. Each bearing 35, 36 is provided with a flange 35a, 36a. 
Flange 36a engages the lower free end of tube 31. 
In operation, as the upper housing assembly 21 rotates relative to the 
lower housing, assembly 20 and the motor heats up, the oil passes 
downwardly from felt 37 and accumulates in the area 40 between the wall 
28, wall 23 and tube 31 to lubricate the thrust bearings. However, oil is 
prevented from leaking by the seal formed by the sealent 30 and the seal 
between the flange 24 and the member 23. 
Brackets 41 are provided at circumferentially spaced points on the 
periphery of shell 33 for mounting fan blades where the motor is to be 
utilized for a ceiling fan. The hollow shaft 22 provides a passage for 
wiring to extend downwardly to the controls and light fixtures (not shown) 
which may be mounted on the wall 23. The hollow shaft 22 also functions as 
a means of supporting the electric motor and controls, light fixtures 
mounted thereon. 
The upper housing assembly is assembled by utilizing a fixture 42 such as 
shown in FIG. 5. The shell 33 in the form of a rectangular blank rolled 
into a cylinder is first supported on the cylinder 43 of the fixture 42 
and the ends of the shell are welded to define an accurate cylinder (FIG. 
6). The top plate 32 with the tube 31 and bearings 35, 36 and felt 37 
thereon is positioned on the cylinder, the tube 31 being guided by a guide 
member 44 that is concentric with the outer diameter of the cylinder 43 of 
the fixture 42 and the top plate 32 is then welded on the shell 33 (FIG. 
7). Finally, brackets 41 are located on guide pins 45 accurately 
positioned with respect to cylinder 42 and guide 44 to accurately position 
them with respect to the shell 33 and they are then welded to the shell 33 
(FIG. 8). 
Referring to FIG. 9, the lower housing assembly 20 is assembled by mounting 
the tube 22 on the member 23 and then supporting it on a fixture 46 with a 
guide tube 47 engaging the accurately formed exterior of the tube 22. The 
fixture 46 also receives the stator 26. As the fixture 46 is moved along 
the shaft tube 22 the stator is held in concentric relationship to the 
outer diameter of the stator and guided axially of the shaft 22 to bring 
wall 28 into groove 29 into which the adhesive 30 has been placed. The 
fixture is held stationary until the adhesive sets. 
The upper and lower housing assemblies 20, 21 are then assembled by first 
placing the thrust washer in position on the hub, and then telescoping the 
upper housing assembly 21 and lower housing assembly 20 axially to bring 
them into assembled relationship.