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Патент USA US2082379

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June 1, 1937.
, R_ J_ BRITTMN. JR
2,082,379
PRESS FITTING
Filed April 11, 1934
FIG. 3
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RICHARD J BB/TTA/N,JB.,
BY
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Patented June 1, 1937
2,082,379
UNITED STATES PATENT OFFICE_
2,082,379
PRESS FITTING
Richard J. Brittain, Jr., Bloom?eld, N. L, as
signor to General Motors Corporation, Detroit,
Mich., a corporation of Delaware
Application April 11, 1934, Serial No. 720,147
8 Claims.
This invention relates to press-?tting and com
prises all of the features and aspects of novelty
herein disclosed. An object of the invention is to
provide an improved method of press-?tting parts,
5 such as sleeves or the like on shafts.
Another
object is to provide improved means of avoiding
shaft failure, as when a hollow member is pressed
upon a rotatable shaft and transmits load thereto.
Another object is to provide an improved shaft
10 and sleeve combination. To these ends and also
to improve generally upon methods and devices
of this character, the invention further consists
in the various matters hereinafter described and
claimed.
15
In its broader aspects, the invention is not
necessarily limited to the speci?c constructionv
and method steps selected for illustration in the
accompanying drawing in which
Figs. 1 to 4 are sectional views indicating some
20 what diagrammatically certain forces and condi
‘ tions arising when sleeves and shafts are com
bined.
.
Fig. 5 is a sectional view of portions of the
improved shaft and sleeve combination, certain
25 small dimensions being exaggerated.
Fig. 6 is a sectional view with the sleeve pressed
on the shaft and showing certain conditions of
stress.
Fig. '7 is a sectional view of a modi?cation.
Fig. 8 is a sectional view of a sleeve.
30
When mounting bushings, bearing race rings
and the like upon shafts, it is common practice
to use press ?ts in order that such bushing or
ring may be securely held and supported. Some
times the bore of the bushing is provided with a
comparatively steep chamfer at one end to pro
vide a lead when pressing the bushing on the
shaft.
So far as I am aware, however, the bore
of the bushing or ring has been of uniform di
40 ameter or straight except at the chamfer and
the surface stresses due to the press ?t have been
substantially uniform along the shaft. In any
(01. 287-52)
point l8 where the chamfer begins and the
straight bore terminates.
Fig. 2 indicates a condition which occurs when
load is applied. For this load, there must be a
corresponding tension stress in the upper ?bres of 5
the shaft and a corresponding compression stress
in the lower ?bres, all as indicated by the arrows.
Both tension and compression stresses are maxi
mum at top and bottom in the line of the load
but are continually reversing as the shaft rotates. 10
Thus when the shaft turns 180°, the portion
initially having maximum tension stress comes
under maximum compressive stress and the por
tion initially having maximum compressive
stress comes under maximum tension stress. 15
These bending stresses are‘ to a great extent ,
localized in the plane where the straight bore l4
terminates because of the press ?t and the
abrupt termination of surface stress.
-
I
The condition of the loaded and rotating shaft 20
is further illustrated in exaggerated degree in
Fig. 3. For every load, the shaft has a corre
sponding de?ection or bending and the deflection
is concentrated at the point of greatest stress
which is at the bore termination. As the shaft 25
de?ects, the pressed-on race sleeve tends to in
dent the shaft at the lower side. Due to shaft
rotation, this tendency to indent is effective for
the entire circumference and a minute shoulder
20 forms on the shaft where the bore l4 ter- 30
minates. This indenting increases the effect of
stress localization produced by the press ?t. As
a result, the metal in the shaft is subjected to
gradual surface fatigue which progresses until
a circumferential surface crack starts in the shaft
where the bore l4 terminates or at the shoulder
20. This crack becomes a progressive fractvure
which ultimately results in shaft breakage.
Fig. 4 shows a shaft H0 with an enlarged por
tion H2 terminating with a sharp corner H8. 5%
The condition is directly comparable to that "
shown in the preceding ?gures, except that the'
event, there has been an abrupt termination of height of the enlargement H2 would be somewhat
the magnitude of the stress at the end of the less than the thickness of the race sleeve l2 to
45 bushing, and shaft failure under load has fre
produce the same effect.
,
In order to overcome the bad effects noted
quently occurred at this point. The condition is
above, the present invention provides exceedingly
illustrated in Fig. 1 wherein the numeral l0 rep
simple
means for preventing localized stress. In
resents a shaft, such as a railway axle, on which
Fig. 5, dimension A represents the inside diameter
is
pressed
the
inner
race
ring
or
sleeve
[2
of
a
50
_ of a sleeve 212 to be mounted with a press ?t on 50
roller bearing, the sleeve having a straight bore v a shaft 2| 0 of diameter B. The difference be
l4 extending to a steep chamfer IS. The arrows tween these diameters is determined by the de
indicate the substantially uniform pressure or sired amount of press ?t. Dimension C is the
stress between sleeve and shaft and it is apparent radial allowance for the press ?t and is exag
65 that the stress terminates very abruptly at the gerated in the drawing. In practice it would 55
2
10
15
20
25
2,082,370
frequently be only about two thousandths of an
the shaft and having its bore of uniform size, the
inch. If the sleeve bore were made to dimen
sion A for its entire length, the bad conditions
illustrated in Figs. 1 and 2 would occur. If the
bore were made to dimension A plus 2C, there
would be zero stress between the shaft and the
shaft having one portion of uniform size and
larger than the bore by the amount of the press
sleeve. In the actual construction shown, the
tially as described.
2. The combination with a shaft of a member
race bore has a straight portion 2“ meeting at
222 a slightly angled or tapered portion 224 which
has an axial length D and joins a chamfer 2".
When this sleeve M2 is pressed‘ on the shaft, the
conditions illustrated in Fig. 6 are secured. Here
the surface stress between the sleeve and the
shaft is indicated by the arrows. For a consider
able distance, the stress is uniform and maximum.
From the arrow 222 to the point 2l8, along a
distance corresponding to the dimension D of
Fig. 5, the stress gradually decreases and fades
out to zero. Thus there is no abrupt change
in surface stress as in Fig. l and the localized
tension' and compression stresses indicated in
Fig. 2 are avoided.
One effect of the internal taper and the press
?t is that the outer surface of the sleeve 2|2 will
become slightly tapered near the end as indicated
at 226. This external taper is less than dimen
fit, and another portion of the shaft being tapered
down and engaging the bore with decreasing
stress along the end portion thereof; substan
having an elongated bore tightly ?tting said shaft,
said member having the end portions of its bore 10
?ared for a substantial distance but slightly
enough to maintain contact with said shaft and
thereby gradually reduce the tightness of the ?t
of said member on said shaft.
3. The combination with a shaft of an inner 15
raceway member of a roller bearing thereon, said
inner raceway member having an axial bore with
radiused ends, the middle portion of the wall of
said bore having a press ?t on said shaft of from
.003" to .005" tight and said ?t decreasing grad
ually from an end of such middle portion for a
substantial distance to nothing at a radiused
end.
4. The combination with a shaft of an inner
raceway member of a roller bearing having an
elongated bore tightly ?tting said shaft, said
roller bearing because the rollers, of which one
is indicated at 228, usually terminate short of
raceway member having the end portions of its
bore ?ared a substantial distance but slightly
enough to maintain contact with said shaft and
sion C and does no harm even in the case of a
the end of the race sleeve and the usual cage, a
thereby gradually reduce the tightness of the ?t
portion of which is indicated at 230, overlies the
tapered end portion of the sleeve. The length of
of said member on said shaft.
5. The combination with a shaft, of a member
the internal taper or dimension D may be in
creased to any desired extent to get a more grad
35 ual change in stress when the length of the ex
ternal taper at 226 is of no consequence. It is
shaft, said member having an end portion of its
bore ?ared for a substantial distance but slightly
enough to maintain contact with said ‘shaft and
preferred to make dimension C slightly greater
thereby gradually reduce the tightness of the ?t
than the radial press ?t allowance in order to
of said member on said shaft.
6. The combination with a shaft, of an inner
raceway member of a roller hearing or the like 40
thereon, said inner raceway member having an
be sure and have the press ?t terminate or fade
40 out in the tapered portion.
Fig. 7 illustrates a modi?cation wherein the
same results are obtained in a different way.
is
having an elongated bore’ tightly ?tting said
The
ring or sleeve 3l2 has its bore wall initially
straight except for a chamfer SIB. The shaft ‘III
is straight from its end to the region of the arrow
322 and then tapers down or decreases in diam
eter so that the press ?t stress becomes zero at
axial bore with a chamfered end, the middle por
tion of the wall of said here having a tight ?t on
said shaft, and said ?t decreasing gradually from
the point 3I8. Dimension C is the radial allow
an end of said middle portion for a substantial 45
distance to nothing at a chamfered end.
7. The combination with a shaft, of an inner
raceway member of a roller bearing or the like
ance for the press ?t as before.
The exterior
having an elongated bore tightly ?tting said shaft,
end portion 326 of the sleeve will become tapered
said raceway member having an end portion of
its bore uniformly tapered for a substantial dis
tance but slightly enough to maintain contact
as well as the interior portion between points 3|.
and 322 because in those regions the sleeve has
less than maximum stretching ‘under the press
?t. Thus, paradoxically, the shaft becomes
55 stronger and less liable to failure by thinning it
down.
As indicated in Fig. 8, the sleeve 2| 2 of Figs. 5
and 6 may be provided with a chamfer “8 formed
by a radius merging smoothly with the tapered
60 surface 224.
I claim:
1. In a device of the‘ character described, a
shaft, a hollow member adapted to be pressed on
with said shaft and thereby gradually reduce the
tightness of the ?t of said member on said shaft.
8. The combination with a shaft member, of a
member having a bore tightly ?tting the shaft
member, one of said members being tapered
throughout an end portion of the region of ?t so
as to gradually reduce the grip of the member
on the shaft member from a maximum to a mini
mum adjacent the end of said region to avoid
abrupt changes in stress.
'
RICHARD J. BRI'I'TAIN, Jl.
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