Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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PATENT
ATTORNEY DOCKET NO .: REX-1 6
TITLE OF THE TNVENTION
MEANS FOR SECURING A BEARING TO A SHAFT
BACKGROUND OF q~HE INVENTION
Where bearing structures, such as pillow blocks,
having either spherical or tapered roller bearings or ball
bearings, are used for supporting rotatable shaft members,
the inner race must be securely locked to the shaft for
the bearing structure and associated machinery to operate
properly and efficiently. If slippage occurs, the
generated forces will be borne by the race instead of the
balls or rollers in the bearings. Since lubrication is
not supplied to the interface between the shaft and inner
race, uch slippage results in undesirable metal-to-metal
sliding contact, with an associated heat buildup from the
friction generated, fretting corrosion, wear, and eventual
failure of some or all of the related elements. Many
methods have been used to secure the inner race to the
shaft. For example, the race may be shrunk or
press-fitted to the shaft, which provides a relatively
secure grip but requires extremely close tolerances, is
generally more expensive than other methods, and makes
removal of the fitted elements difficult. Another more
common method involves the use of set screws threaded
radially through the inner race to contact the shaft in an
interface fit, or threaded radially through an over-collar
and through an unthreaded hole in the ~nner race to
contact the shaft. An additional method involves the use
of a set screw threaded axially through a locking collart
to abut a tapered adapter sleeve and wedge the sleeve
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against the oppositely tapered outer surface of the inner
racet combined with radially disposed set screws in an
over-collar, as disclosed in U.S. Patent No. 3,957,319,
owned by the assignee of the present invention.
The use of set screws in any of the previously
described embodiments hac certain disadvantages. The
inner race is normally hardened in the raceway area, with
minimum resiliency to withstand the rotative and thrust
forces applied by the roller or ball bearing elements.
Thus, where set screws are threaded through the inner
race, any vibration is transmitted directly to the set
screws from the hardened race, leading to loosening of the
screws and slippage of the race. The screws may also
cause both axial and radial deflection of the inner race,
which can extend into the raceway area. Such deflection
in the raceway is undesirable, due to load concentration
and distortion and adverse vibration in the bearing
structure. Additionally, most radially disposed set
screws, which are threaded through an over-collar into an
~-nthreaded hole or gap formed in the inner race are easily
loosened from vibration or other movements generated
through operation of the machinery, and have a tendency to
"work" against the inner race, thus causing further
loosening and wear on the inner race.
SUMMARY OF THE INVENTION
It is, therefore, one of the principal objects
of the present invention to improve the performance of
roller or ball bearings by providing means for securing a
bearing to a shaft that securely locks the inner race to
the shaft for rotation therewith, while minimizing
vibratory effects which lead to loosening of the secured
race, and subsequent slippage.
Another object of the present invention is to
reduce distortion and lobbing in the inner raceway by
providing through cut slot means in selected areas of an
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axial extension of the inner race. The through cut slot
means minimizes deflection of the raceway caused by the
set screws.
A further object of the present invention is to
provide a bearing locking device which can easily be
substituted for existing conventional locking devices, has
fewer parts and is generally less expensive than
conventional means, and which is durable to provide
security in shaft-mounted bearings throughout a long
service life.
These and additional objects are attained by the
present invention, which relates to a means for securing a
bearing to a shaft, having an inner race with a raceway
disposed around the shaft for receiving the roller or ball
elements of the bearing. Extending axially from one or
both sides of the raceway is an extension or end portion,
which is also disposed around the shaft and has a
plurality of threaded holes therein, preferably disposed
within an arc of 180. Securing means are threaded
radially through the holes to contact the shaft and to
deflect the extension into contact therewith. Preferably,
the securing means comprises a plurality of set screws.
Means are provided to prevent or minimize deflection from
extending into the raceway itself. The means for
minimizing the deflection of the raceway caused by the
securing means is provided in the wall of the extension
between the raceway and the securing means. PreEerably,
the means for minimizing the deflection of the raceway
caused by the securing means comprises a through-cut slot
defined in the end portion between the raceway and the
securing means and extending in the circumferential
direction.
Various other objects and advantages of the
present invention will become apparent from the following
description, with reference to the accompanying drawings.
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BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a perspective view of the means for
securing a bearing to a shaft embodying the present
invention, a portion of the bearing housing having been
broken away;
Fig. 2 is an end elevational view of the present
invention secured to the shaft, the shaft being shown in
cross-section, and the broken lines in the lower portion
of the inner race illustrating the ends of a through-cut
slot;
Fig. 3 is a fragmentary, side elevational view
of the device shown in Fig. 2, further illustrating the
through-cut slot;
Fig. 4 is an end elevational view of another
embodiment of the present invention secured to the shaft,
the shaft being shown in cross-section, and the broken
lines in the lower portion of the inner race illustrating
a through-cut slot; and
Fig. 5 is in part a cross-sectional view of an
embodiment such as shown in Fig. 4.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Re~erring more specifically to the drawings, and
to Fig. 1 in particular, numeral 20 designates generally
the means for securing a bearing to a shaft embodying the
present invention. The invention includes an inner race
22 and an axial extension or end portion 23 which projects
beyond a housing 24 of a pillow block 26 on one end, or on
both ends, as shown here. Inner race 22 has a raceway
portion 25 for receiving a bearing of the ball-type, or a
roller-type as shown here. In bearing structures such as
pillow block 26, inner race 22 must be securely locked to
a shaft 35 (Fig. 2), while an outer race 28 is locked to
housing 24. Inner race 22 is then normally slipped over
the shaft, where it is locked to the shaft. The present
invention may be practiced with ball-type (not shown) or
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roller-type bearing elements 30, and in a variety of
bearing structures, pillow hlock 26, shown here, serving
as a general example. The extension is provided with a
plurality of threaded holes 34, such as the three shown in
the embodiment of Figs. 2 and 3, for receiving securing
means. ~referably, at least two set screws 36 comprise
the securing means. The set screws are disposed radially
and within an arc of less than one-hundred eighty degrees,
and the present invention may be practiced with a minimum
of two set screws, as in the embodiment of Figs. 4 and 5,
up to as many as are required, based on the size of the
assembly.
Either the entire extension of inner race 22 or
portions of the inner race in the set screw mounting area
are composed of a softer and more resilient metal than the
normally hardened metal forming a raceway 32 which
receives roller elements 30. In the embodiment shown in
Fig. 2 with three set screws, each screw applies tension
to the end portion of the inner race, which is transmitted
through the relatively softer metal to the additional
screws, tending to prevent loosening of the screws from
vibration or other effects. In addition, the holding
force is greatly increased. Thus, locking contact between
shaft 35 and the extended end portion is established
between the screws. Normally, the use of set screws
threaded radially through the inner race extension to
contact the shaft produces a desirable deflection of the
extension of the race, in that the deflection and
subsequent contact lock the elements together. The
deflection, however, if extensive, may extend into the
raceway area, leading to undesirable load concentration,
bearing structure distortion, and adverse vibration.
As embodied herein and shown for example in
Figs. 1-3, the means for preventing or minimizing the
deflection from extending into the raceway, comprises a
through-cut slot 38 provided in the wall of the extension
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of the inner race, between the set screw mounting area and
the raceway, for absorbing the force applied to the
extension. Slot 38 extends completely through the inner
race and partially around the circumference of extension
23 and preferably extends approximatelY 270 around the
circumference of the extension. ~he slot means prevents
stress concentration, and absorbs the force exerted on the
extension of the inner race and prevents or minimizes the
intrusion of the distortion into the raceway area, thereby
assuring that the raceway retains its original
configuration. As shown in Fig. 3, slot 38 is longitudlnally
bounded peripherally by the extension.
Modified forms of the present invention a~e
shown in Figs. 4 and 5. In Figs. 4 and 5, the extension
68 of inner race 69 is provided with two threaded holes
70, disposed approximately sixty-five degrees apart, for
receiving set screws 72. A through-cut slot 74 is
provided through the extension, between the set screw
mounting area and a raceway 75.
The entire extension of the inner race, or
portions thereof in the set screw mounting area is
softened as previously discussed, to permit it to be
distorted to facilitate the locking action. The extension
is deflected more when two set screws are used than when
three or more are used. However, the through-cut slot
prevents or minimizes the deflection from intruding into
the raceways. As in the previous embodiments, the
through-cut slot extends around the extension parallel to
the arc formed by the disposition of the set screws and
extends beyond the circumferential location of outermost
set screws.
In all the embodiments di~closed herein, a
through-cut slot is formed by drilling two holes 39 (Figs.
1, 3 and 5) radially through the extension and spaced
about 270 around the circumference thereof. Then a slot
is cut through the exten~ion in the 270 separation be-
tween the two radially drilled end-holes. The width of
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the slot preferably is less than the diameter of each of
the end-holes. Moreover, a slot preferably is included on
each side of the extension of the inner race. However, a
single through-cut slot on one side may allow sufficient
force to be placed on the set screws to secure the inner
race to the shaft in light-duty installations without
appreciable deflection encroaching on the raceway. Where
greater holding action is required, and greater force is
applied to the set screws, through-cut slots may be
included on both extensions of the inner race to ensure
that any deflection of the extensions will not cause
lobbing or will minimize its effect on the configuration
of the raceway.
Similarly, two or more set screws may be used,
depending on the particular installation. The set qcrews
are disposed within an arc of approximately 180, and the
preferred use of three screws will ensure tension on all
of the screws, improve the spring-locking action, and
increase resistance to vibration. The slot means
preferably extends through a wider arc than that of the
set screws to absorb the force applied to the inner race
extension by the set screws. Preferably, the slot means
extends over about a 270 arc around the circumference of
the extension.
In the use and operation of the present means
for securing a bearing to a shaft, the inner race is
slipped over the end of the shaft and, as tolerances are
normally quite close, tapped into position on the shaft.
The axial extension or extensions of the race include at
least two, and preferably three, threaded radial holes for
receiving suitable fastening means, such as set screws,
disposed within an arc of 180. The entire extension, or
portions thereof in the area of the threaded holes, are
composed of a relatively resilient metal to more easily
deflect toward the shaft and to transmit the tension
applied by a single set screw through the extension to the
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other set screws. This occurs with all of the set screws.
Moreover, as the screws are threaded radially through the
holes to contact the shaft, the extensi~n is forced into
locking contact with the shaft on the side opposite the
set screws. The locking contact thereby established, in
combination with the set screws, secures the inner race
and shaft together, preventing relative rotation
therebetween. Since the deflection caused in the
extension of the race must not intrude into the raceway
itself, through-cut slot means is provided between the set
screws and the raceway itself. The stress relief slot
preferably extends through an arc wider than that formed
by the set screws. The through-cut slots absorb the
applied force, thereby preventing or minimizing the
distortion from encroaching into the raceway.
While one embodiment of a means for securing a
bearing to a shaft and several modifications thereof have
been shown and described in detail herein, various changes
and other modifications may be made without departing from
the scope of the invention. It will be apparent to those
skilled in the art that various modifications and
variations can be made in the means for securing a bearing
to a shaft without departing from the scope or spirit of
the invention. Thus, it is intended that the present
invention cover the modifications and variations which
come within the scope of the appended claims and their
equivalents.
