Note: Descriptions are shown in the official language in which they were submitted.
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BAC~GR~UND OF THE INVENTION
This invention relates to railroad cars and particularly
to articulated railroad cars and to side bearing units used
therewith. A side bearing unit is attached to the bolster of each
truck whereby regulating independent l..ove,..ent of the body of the
car and impeding truck hunting. Side bearing units have been used
to regulate movement between the body of a railroad car and the
trucks for a substantial period of time. These side bearing units
are of various designs and structure as based upon the type of car
they are associated with, the weight it carries, etc.
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Recently, a new type of railroad car has been put into
service which creates unique demands upon the side bearing
employed. These cars are generically known as articulated cars,
they are lightweight, of high technology design and offer a new
series of challenges for side bearings. For example, it has been
found that the connectors between the articulated cars are prone
to wear, whereby the male end of the articulated connector will
tend to settle and, in fact, lose as much as 3/8" in vertical
height. This results in lowering of the male end of the car body
relative to the side bearing. The drop in vertical height has the
potential of compressing a st~n~rd side bearing beyond its normal
limits of travel and thus render it useless for its designed
objective. For example, the weight of the entire car will be
carried by the side bearings and not by the center plate of the
bolster. A further ~em~n~ use for increased travel on articulated
cars has been found when the car is run through a super elevated
curve. Articulated cars with st~n~rd 5/16" travel constant
contact side bearings have been noted to derail while passing
through such a curve.
In articulated car applications, there is a necessity of
mounting the side bearings off the centerline of the bolster. This
may result in a twisting moment in the bolster, thus requiring
increased side bearing travel. Increased side bearing travel is
one of the situations which must be satisfied in articulated car
service. The side bearing of this invention addresses this problem
in a way in which no other side bearing has been designed to
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accomplish. It should be noted that side ~earings used today in
interchange must meet all of the requirements of the Association
of American Railroads M-948 Specification.
SU~MARY OF THE INVENTION
~ The side bearing unit of this invention is designed to
meet the unique d~m~n~c of articulated car service. Foremost in
the features is the ability to provide a full 5/8" travel from
installed height while experiencing only min;m~l increase in
resistant forces over the initial preload. The side bearing itself
includes a generally round top cap that has a flat center portion,
and side angled portions which extend into a downwardly depending
integrally formed side wall. The particular structure of the top
cap provide constant frictional control and tolerance to side
bearing arm misalignment. The bottom surface of the top cap
includes a first primary stop adjacent to the side wall and a
centrally located downwardly depending secondary solid stop, both
of which cooperate with a stop means provided in the housing as
hereafter discussed.
The housing itself includes a base portion suitable for
attachment to the top wall of a railroad car bolster. Also
included is an integrally formed outwardly extending side wall
which has a primary stop portion and a centrally located upwardly
extending secondary stop. As mentioned above, both of these stop
means cooperate with those located in the top cap to provide solid
positive stops in the event of a massive overload of the side
3 i;
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bearing unit. The center secondary stop is uniquely located
to prevent the top cap from being crushed inwardly should such
overload conditions take place.
The top cap and the housing cooperate whereby the
housing fits within the top cap to create an internal void.
This internal void is occupied by first and second thermo-
plastic elastomer springs which due to their design can be
folded and flexed a substantial amount without a rapid increase
in their resistive forces. The thermoplastic elastomer
material which is employed for the springs herein disclosed is
that specified in U.S. Patent No. 4,198,037 dated April 15,
1980 by David G. Anderson and U.S. Patent No. 4,566,678 dated
January 28, 1986 by David G. Anderson.
Lastly, a means is provided for connecting the top
cap and housing whereby a preload can be exerted on said first
and second thermoplastic elastomeric springs. The free height
of the side bearing is 3/8" higher than the 5-1/16" set-up
height, thus allowing the side bearing to exert an upward force
on the car body wear plate during severe car rocking. The
frictional control to resist truck hunting is thus not lost
during car rocking. However, the top cap is still free to move
with respect to the housing as an external force is exerted
thereon, either due to a drop in vertical height through wear
of the components in the articulated car, because of car
rocking, etc.
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DESCRIPTION OF THE DRAWINGS
Fig. 1 is a plan view of a portion of a railroad car
truck which includes a side bearing unit of this invention;
Fig. 2 is an elevational view in section, as seen
generally along the lines 2-2 of Fig. S;
, Fig. 3 is a simple graph showing the travel distance
; .
versus the increase in resistive forces of the side bearing unit;
Fig. 4 is a perspective view of the top cap;
Fig. 5 is a plan view of the side bearing unit ~rom the
top;
Fig. 6 is a sectional view as seen generally along the
lines 6-6 of Fig. S; and
Fig. 7 is a perspective view of the thermoplastic
elastomer spring as employed in the side bearing shown in Fig. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In Fig. 1 a portion of a railroad car truc~ 10 is seen
generally and comprises a wheel set, a part of which is shown and
designated 12. The wheel set 12 as shown in Fig. 1, has an axle
end 14 journaled in a bearing carried by a side frame 16. As is
appreciated, the truc~ 10 includes a pair of such side frames which
are connected by transversely positioned bolster partially shown
and designated 18. An end 20 of the bolster 18 is resiliently
carried in a window of the side frame 16 in a well-known manner.
A side bearing mount 24 is secured to the bolster 18 by
any suitable means and functions as the support for the side
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bearing unit 30. A conventional constant contact side bearing unit
26 is also supported by the side bearing mount 24.
The side bearing unit 30 shown in greater detail in Figs.
2, 4, 5 and 6 includes a round top cap 32, a housing 34 and first
and second thermoplastic elastomeric springs 36 and 38. The
generally round top cap 30 includes a top surface 40 which has a
center flat portion 42, plus a side angle portion 44. The center
flat portion 42 occupies approximately 21%, plus or minus 5%, of
the total top surface. The remainder being occupied by the angled
side portion which forms an angle 3S (Fig. 6) of about 3 degrees,
plus or minus 1 degree, with respect to said center flat portion.
The combination of the flat and tapered surfaces provide constant
frictional control and tolerance to misalignment of parts, etc.
during a normal functioning cycle. This provides for metal-to-
metal contact on the car body wear plates to control truc~ hunting
and to reduce the rock angle of the car. A downwardly depending
integrally formed side wall 46 drops down from said top surface 44.
A bottom surface 48 has a centrally located integrally formed
depending secondary solid stop 50 and a primary stop surface 52
which is adjacent said side wall 46 and extends a full 360 degrees
around said round top cap 30. The function of the primary and
secondary stops will hereafter be more fully explained.
A housing 54 includes a base portion 56 which is prepared
for attachment to the side bearing mount 24 via any suitable means.
The holes 58a and 58b are provided for this purpose. The housing
54 further includes an integrally formed upwardly extending side
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wall 60 which includes a primary stop portion 62 located at the top
edge 64 thereof. This primary stop portion 62 extends 360 degrees
around the housing and is designed to cooperate with the primary
stop 52 located on the bottom surface 48. Centrally located is an
integrally formed upwardly extending secondary stop 66 that
cooperates with the depending secondary stop 50 These stops
cooperate to prevent crushing in of the top surface 42 when the
primary stops have bottomed out and an extreme load is present.
As previously mentioned, the top surface has a 3 degree taper
whereby such crushing action is accentuated.
The housing 54 fits within the round top cap 30 whereby
creating an internal void 68. The first and second thermoplastic
elastomeric springs 36 and 38 are situated within this internal
void in a piggyback or one on top of the other position. Both
thermoplastic elastomeric springs are identical and therefore
description will be limited to one with the underst~n~; ng that it
is equally applicable to the other. By placing them in series, the
available travel of the side bearing can be doubled and the spring
rate cut in half. The two elastomeric springs are separated ~y a
plate 75 and both are mechanically locked to the plate by pins 77,
or any other suitable means, thus forming an elastomer spring
assembly. Referring to Fig. 7, it is apparent that the elastomeric
spring iS an open-ended hollow tube.
The thermoplastic elastomer spring 36, shown, for
example, in Fig. 6, is designed to fold and flex as it is subjected
to a wor~ cycle. The fold and flex are important in that during
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a normal wor~ cycle the slope o~ the force vs. travel curve of Fi~.
3 must remain as flat as possible. This is done by controlling the
contact surfaces or loaded areas, such as 80 and 82. As long as
these loaded areas do not increase or decrease during the operating
cycle, their existence will contribute or withdraw little from the
slope of the curve The combined effect of elastomer springs in
series, and fold or flex of the elastomer, and the generally
constant loaded areas result in the low spring rate or flat force
versus travel curve as in Fig. 3. This low spring rate is of great
importance in order to satisfy the unique de~ndc of articulated
cars. A high spring rate would result in possible derailment while
the car is traversing a super elevated curve or in the case of the
worn articulated connection as previously described.
As stated, the elastomeric spring is so designed so that
throughout its total travel from free height, it is folding and
flexing rather than compressing. The loaded area rem~i n.
essentially- the same throùghout its total travel. This is
accomplished by designing the pre-formed thermoplastic elastomeric
spring so that the outside diameter minus the inside diameter is
less than the solid height within the side bearing.
As will be hereafter discussed, a requirement of this
invention is that the round top cap 42 must be able to move
vertically with respect to the housing and yet sustain a preload
on the first and second thermoplastic elastomeric springs 36 and
38. The means for movably connecting 74 is shown in Figs. 4, 5 and
6. It includes a basically J-shaped slot 76, cut in the downwardlY
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.
depending integrally formed side wall 46, which cooperates with a
pin 78 (Fig. 6) secured to the upwardly extending side wall 60.
By this means the first and second thermoplastic elastomeric
springs 36 and 38 can be preloaded, the preload maintained and yet
the top cap can move vertically as it is subjected to external
forces during a wor~ cycle.
Referring now to the force versus travel graph shown in
Fig. 3. Because of the preload, the initial resistive force
recorded is naturally not zero. The resistive force, however,
increases only minim~lly with the addition of further external
force until the amount of travel passes beyond point 0.6". Because
of the nature of the curve of Fig. 3, the forces between car, the
side bearings and the truc~ remain generally constant if wear takes
place, if the cars are loaded or unloaded, or if the track is rough
or banked. Depending upon conditions the top cap 40 bottoms upon
the solid stops somewhere around 0.625" travel. The resistive
~orces then, go substantially straight up since it is a metal-
against-metal situation. Fig. 3 dramatically shows the results of
the particular combination of elements in the invention hereunder
consideration. Approximately a full 5/8" of travel is allowed from
installed height and yet the resistant forces do not become
elevated to the point where there is a danger of derailment or that
the threshold speed of truck hunting is greatly affected.
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While the invention has been described with respect to
various specific examples and embodiments, it should be understood
that the invention is~not limited hereto, and that it can be
variously practiced within the scope of the claims.
