Rear motor bearing for worm gear drive motors

An electric motor, such as a motor for operating a worm drive, has a rear bearing and rear bearing support in the form of a sleeve bearing which is received within a rearwardly facing axial opening formed in the end of the motor armature shaft. The bearing receives one end of a non-rotating pin which has its opposite end secured to the rear end wall of the motor and thus supports the armature shaft on the end wall. Minor misalignments are provided for by aligning movements of the bearing support pin accompanied by slight bending of the end wall of the motor case. In another embodiment, the pin is provided with a spherical end received within a conforming or mating recess and providing for pivotal aligning movement of the bearing support pin with respect to the motor case. The bearing may also be shouldered or flanged so that thrust forces on the shaft are transmitted to an adjacent shoulder on the bearing support pin.

BACKGROUND OF THE INVENTION 
The rear bearings for most worm gear electric drive motors, such as used in 
large quantity in the automotive field for operating window lifts, sun 
roofs, seat positioners, mirrors, and the like, are generally designed for 
loads that greatly exceed the actual requirements of such drive motors. 
Therefore, the bearing supports and bearings are overrated and result in 
an unnecessary increase in the cost of production of electric drive motors 
for worm drive assemblies. 
A further cost factor, typical of worm drives, is the fact that the rear 
motor bearing must provide a self-aligning function. Since the 
self-aligning bearing itself must be free to move within the rear motor 
case or housing, complementary semi-spherical surfaces are provided for 
the common sleeve-type bearing which surfaces must be matched respectively 
in the bearing support end wall, thereby increasing the production cost. 
Also, since the bearing must be free to move or align itself, a retainer 
is required since it is not possible simply to press fit the bearing into 
place in the motor case. 
A need therefor exists for a dependable, easy-to-fabricate, low cost, and 
adequate bearing support for the rear bearings for worm drive motors or 
similar motors which represent a cost savings, which is easier and less 
expensive to make, of less complexity, and with inherent self-alignment 
capability. 
SUMMARY OF THE INVENTION 
The above objects are accomplished, in this invention, by providing a 
low-cost bearing which is received, such as by press fitting, into an 
axial recess centrally formed in the rear end of the armature shaft, and 
bearing receives a non-rotating shaft in the form of a pin secured to the 
rear or end wall of the motor case. Since the case is formed of drawn 
metal, the shaft or pin can deflect slightly, in response to misalignment, 
accompanied by limited elastic deformation or bending of the rear motor 
wall. 
In one modified form of the invention, the stationery bearing support pin, 
forming a bearing shaft, may be provided with a spherical head received 
and retained within a semi-spherical recess in the case rear wall. The 
spherical head permits the pin to be slightly rotated within the recess, 
as necessary, to compensate for alignment. In another modification, the 
sleeve bearing is provided with a flanged outer end providing for thrust 
loadings. 
The rear bearing loading, in an electric motor worm drive, is defined by a 
force that is applied orthoganally to the axis of the armature shaft. This 
force is the result of the separation force which occurs between the worm 
drive on the armature shaft and the large output gear. In such drives, 
axial thrust is mainly carried by a thrust bearing in the motor front 
case. 
The separation force between the worm and the gear is a function of the 
worm thrust and the gear tooth design. The actual bearing loading is 
relatively low, since the force is applied through a lever arm which 
represents the fixed spacing between the worm drive at the output gear, on 
the one hand, and the thrust bearing, on the other hand. This lever arm is 
generally short compared to the lever arm between the thrust bearing and 
the rear bearing, usually by a factor of about 1 to 3. 
The maximum loading, for any installation, can be calculated for any 
pressure and speed, and the life of the bearing can be predicted. The 
concept of utilizing a bearing mounted within the recess in the armature 
shaft, and piloted on a non-rotating stub pin-like shaft, provides more 
than adequate service life for intermittent operating automotive and motor 
vehicle worm gear installations or other low loaded rear bearing-type 
motors. 
It is accordingly an important object of this invention to provide a lower 
cost rear bearing support for worm drive motors. 
A still further object of the invention is the provision of a rear bearing 
support, for an electric motor, in which a bearing is received within and 
secured to the armature shaft of the motor, and which bearing is piloted 
on a stationery support shaft carried on the motor rear case. 
Another object of the invention is the provision of a rear bearing support, 
as outlined above, in which the bearing piloting shaft can move to 
compensate for misalignment through the bending of the motor case wall or 
through a pivotal connection between the wall and the support pin. 
A further advantage of the invention resides in the fact that since the 
rear support bearing material is recessed within the armature shaft, the 
overall length of the drive motor may be correspondingly shortened, thus 
further reducing material costs and providing a capability of fitting the 
motor into smaller spaces. 
Other objects and advantages of the invention will be apparent from the 
following description, the accompanying drawings and the appended claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring first to FIG. 1 of the drawings which illustrates a prior art 
electric motor worm drive, a motor casing or housing 10 supports internal 
permanent field magnets 11 or other suitable magnet means, and a rotating 
armature 12. The armature 12 has an output shaft 13 carried through a 
thrust bearing 15 mounted in a Wear housing 16 for the bull gear or large 
gear 18 of the worm drive. The shaft 13 is provided with threads 20 which 
engage the threads of the gear 18 when the armature is rotated. 
The rear bearing of the motor includes a self-aligning semi-spherical 
bearing 25 mounted within a rear extension 26 of the motor housing 10 and 
retained in place within the extension 26 by a retainer ring 28. The rear 
end 30 of the motor armature shaft is retained and supported within the 
bearing 25. 
Typically, the bearing design is far in excess of the needs of a rear 
bearing support for a worm drive motor since the rear bearing load 
requirements are only those which can be transmitted to the bearing by the 
separation force between the drive worm or threads 20 and the gear 18. The 
axial trust is carried by the bearing 15. 
The bearing arrangement of this invention not only reduces the cost, but 
also reduces the overall length which is necessary for the motor housing 
10 as shown in the fragmentary sectional view of FIG. 2. In FIG. 2, a 
metal motor housing case 35, which may be a deep drawn case, is formed 
with a rear wall 36. The armature shaft 40 (FIG. 4) has a rear end which 
is provided with an axially aligned cylindrical recess. The recess opens 
toward and faces the case end wall 36. 
A cylindrical sleeve bearing 50 is press fitted within the recess 44 and 
therefore is formed with an outer surface which forms a close interference 
fit with the shaft 40. 
The inside surface of the bearing 50 is piloted on one end of a 
shaft-supporting shaft or pin 52. The pin is relatively fixed or 
non-rotating, and the opposite end of the pin 52 is secured to the end 
wall 36 by any suitable attachment means, such as by radial riveting of 
the pin head, as shown at 34. The pin may be shouldered at 60 to form a 
stop against the inside wall of the case, thereby supporting the pin 52 in 
relatively fixed relation on the case, with the extended or free end 
thereof received within the bearing 50. 
In most applications, a suitable sleeve bearing, one formed of DU material 
that is a PTFE/lead composite, designed and developed to be used a dry 
self-lubricating bearing material. If desired, auxiliary lubrication may 
be provided by a suitable felt or other means located within the spacing 
62 located at the inner end of the recess 44 and the adjacent inner end of 
the bearing 50. Under suitable circumstances, other generally 
self-lubricating bearing materials may be used, such as sintered bronze. 
Also, small ball-type bearings may also be used. 
Among the many advantages resides in the fact that overall motor length has 
been reduced, commensurate with the elimination of the length which had 
been occupied by the conventional self-aligning bearing as illustrated at 
25 in FIG. 1. Further, the design of the case 35 is simplified as compared 
to that of the case 10 since there is no need to form a shaped bearing 
support recess which would permit self-aligning movement of the bearing. 
In the embodiment as shown in FIG. 2, limited aligning movements of the 
shaft supporting pin 52 are accomplished by small deflections of the motor 
rear wall 36 in response to alignment requirements for the pin. 
The assembly cost may also be reduced as well, since automated machinery 
may be used to provide the armature recess, to insert the sleeve bearing, 
and to insert and fix the supporting pin 52 within the end wall. 
Optionally, the modification as illustrated in FIG. 3 may be used for 
providing for self-alignment of the support pin where case deflection is 
not required or is not feasible. In that case, a pin 52A is provided with 
an integral spherical end 66 received within the conforming interior of a 
mating protrusion 68 formed on the rear wall of the case 36. In this 
manner, the pin 52A is captured and supported on the wall 36a while 
permitting limited self-aligning movement with respect to the rear wall. 
The shaft and bearing assembly of this invention may be modified, as shown 
in FIG. 4, to permit the armature shaft 40 to carry thrust. For this 
purpose, the sleeve bearing 50 may be modified as shown at 50a in FIG. 4 
with a generally radially extending flange 50b. The flange 50b is 
positioned at the end of the shaft 40 so that it may run in thrust 
abutment with the collar or shoulder 60 of the pin 52. 
While the forms of apparatus herein described constitute preferred 
embodiments of this invention, it is to be understood that the invention 
is not limited to these precise forms of apparatus, and that changes may 
be made therein without departing from the scope of the invention which is 
defined in the appended claims.