Bearings – Rotary bearing – Antifriction bearing
Reexamination Certificate
2002-05-29
2004-09-21
Footland, Lenard A. (Department: 3682)
Bearings
Rotary bearing
Antifriction bearing
Reexamination Certificate
active
06793398
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to collapsible spacers adapted to be placed between a pair of bearings mounted on an axle or spindle or the like for use as a bearing preloading element, and more particularly to a multi-convoluted collapsible spacer having a low spring rate.
2. Description of the Prior Art
Typically, drive shafts in many applications are rotatably mounted within a gear housing through tapered roller bearings. For example, as illustrated in
FIG. 1
, a pinion shaft
102
driven by an internal combustion engine through a transmission, is rotatably supported in a differential carrier
104
that forms part of a vehicular drive axle. The pinion shaft
102
has at its inner end a beveled pinion gear
110
, which meshes with a beveled ring gear
112
in the carrier
104
. The ring gear
112
in turn is connected to a differential mechanism (not shown). Here, the mesh of the pinion gear
110
and the ring gear
112
must be proper, lest the differential mechanism will generate excessive noise and wear rapidly. As shown in
FIG. 1
, the pinion shaft
102
rotates within the differential carrier
104
on inner and outer tapered roller bearings
106
and
108
, respectively, which are mounted in opposition to each other along an axis x of rotation.
Typically, the bearings
106
and
108
are set to a condition of preload, so as to impart rigidity to the shaft
102
(rigidity in the sense that the shaft
102
will rotate in the carrier
104
without any radial or axial play) and eliminate all axial and radial free motion between the shaft
102
and the carrier
104
, while still allowing rotation with minimum friction within the carrier
104
, thus achieving the proper mesh. However, too much preload will cause the bearings
106
and
108
to overheat and fail prematurely. On the other hand, too little preload may cause the bearings to acquire end play, and this likewise decreases the life of the bearings and introduces radial and axial play into the shaft
102
.
The pinion shaft
102
extends through a tubular extension
114
on the carrier
104
, the axis of which coincides with the axis x. The shaft
102
adjacent to the beveled pinion gear
110
possesses an inner bearing seat
116
around which the inner bearing
106
fits and an outer seat
118
around which the outer bearing
108
fits. The outer seat
118
is considerably longer than the inner seat
116
and terminates at a shoulder
120
, which is located between the two seats
116
and
118
. At its outer end, the pinion shaft
102
is provided with threads
122
over which a nut
124
is threaded. Indeed, the nut
124
is turned down against the shaft
102
to clamp the bearings
106
and
108
between a drive flange
126
and the pinion gear
110
. The extent to which the nut
124
is turned determines the setting for the bearings
106
and
108
.
The nut
124
serves to preload the bearings
106
and
108
by advancing the outer bearing
108
over an outer bearing seat
118
on the pinion shaft
102
. Initially, before adjustment, the bearings
106
and
108
exist in a state of end play in which the pinion shaft
102
can move both axially and radially with respect to the differential carrier
104
and, of course, rotate as well. As the nut
124
is turned down over the thread
122
at the end of the shaft
102
, it forces the outer bearing
108
along the outer bearing seat
118
of the pinion shaft
102
. After a short distance the outer bearing
108
encounters a convoluted collapsible spacer
128
, which now becomes snugly lodged between the outer bearing
108
and the shoulder
120
at the end of the seat
118
. As the advancement continues, still while the bearings
106
and
108
are in a condition of endplay, the spacer
128
collapses. In time, the rollers of the two bearings
106
and
108
seat against the raceways of their respective cups and cones. This represents a condition of zero endplay—a condition in which the shaft
102
cannot shift axially or radially with respect to the housing
102
. But some preload is usually desired to insure adequate rigidity or stiffness in the pinion shaft
102
and desired performance from the gears
110
and
112
. Hence, the preload setting for the bearings
106
and
108
.
The convoluted collapsible spacers for use as a bearing preloading elements are well known to those skilled in the art. Conventionally, the collapsible spacers have a substantially unitary thickness, and are made of a relatively thin strip of metal that is formed into a band and is then further formed so as to be convoluted or undulating in cross section, and are adapted for being compressed to a yield point of the material from which the spacers are made and which will thereafter compress under a substantially constant load for a substantial distance.
The dash line in the
FIG. 2
depicts a graph M showing an axial load F applied upon the conventional collapsible spacer
128
as a function of an axial deformation &dgr; of the spacer, and illustrates graphically the manner in which the conventional spacer performs when it is compressed. Such a spacer, when compressed in the axial direction, will first deform resiliently, like a spring, with the force required to effect the compression increasing substantially linearly with the amount of compression (section A-B′ of the graph M, as indicated by line
130
). At a certain amount of compression, a yield strength (or an elastic limit) of the material of the spacer will be reached (point B′ of the graph M), and the spacer will thereafter start to undergo plastic deformation and offer substantially constant resistance to deformation up to a point where the spacer commences to flatten out section (from point B′ of the graph M on, as indicated by line
132
). If at point C′ of the graph M, for example, the axial load applied upon the conventional collapsible spacer is released (e.g. by turned the nut
124
up over the thread
122
of the shaft
102
as shown in FIG.
1
), the spacer will expand in the axial direction substantially linearly (section C′-D′ of the graph M, as indicated by line
34
).
However, the conventional convoluted collapsible spacers have a relatively high spring rate, thus the low amount of “spring back”. The term “spring back” herein refers to a specific resilient deformation of the collapsible spacer in the direction of the expansion thereof when the axial load applied thereupon is released. As a result, they are very sensitive to wear, and are prone to significant change in the bearing preload during the operation that negatively affects bearing life and pinion position.
Thus, there is a need for a convoluted collapsible spacer having a low spring rate, hence less sensitivity to wear and maladjustment.
SUMMARY OF THE INVENTION
The present invention provides a novel low spring rate multi-convoluted collapsible spacer adapted for use as a bearing preloading element. The multi-convoluted collapsible spacer in accordance with the present invention comprises a substantially tubular body compressible in an axial direction thereof from a predetermined free length to a substantially shorter length. The tubular body includes a yielding zone and an elastic zone adjacent to said yielding zone. Each of the yielding and elastic zones has at least one convolution curved in the same radial direction and interconnected with a central convolution curved in the opposite radial direction to the convolutions of the yielding and elastic zones.
Preferably, each of the yielding zone and the elastic zone of the collapsible spacer of the present invention has one convex convolution interconnected with the central concave convolution.
Moreover, in accordance with the present invention, the tubular body of the collapsible spacer of the present invention has a substantially variable thickness in the axial direction. More specifically, an average thickness of the body of the collapsible spacer in the elastic zone is substantially greater than an average th
Ballinger Patrick J.
Knight Nolan James
Nahrwold Thomas Lee
Sullivan Robert William
Footland Lenard A.
Liniak Berenato & White
Torque-Traction Technologies Inc.
LandOfFree
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