Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
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FIELD OF THE INVENTION
This invention relates to railroad cars and
more particularly to side bearing units attached to a
bolster of each truck of the car to regulate independent
movement of a body of the car and impede truck hunting
5 associated with higher speed travel.
PRIOR ART
For sometime, side bearing units have been
used to regulate relative movement between a body of a
10 railroad car and trucks carrying ends of the car body
respectively. One such side bearing unit is disclosed
in U.S. Patent No. 3,712,691 and includes a housing
containing a pair of resilient cushions. The resilient
cushions in turn support a cap member having a down-
15 ward contoured projection which in part fits betweenthe cushions. A top wall of the cap frictionally en-
gages a bearing member attached to a bottom of the rail-
road car body.
A more recent railroad vehicle side bearing
20 unit is disclosed in U.S. Patent No. 3,910,655. This
unit includes a housing containing a block of resilient
material formed with an upper ~-shaped groove. A cap
fits over the block and has a central projection which
fits into the groove and radiused inner facing sidewalls.
25 When the cap is compressed by the weight of the car
body, deformation of the block is in part restricted by
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the cap sidewalls.
A still further side bearing unit is set
forth in U.S. Patent No. 4,~80,016. This unit
includes a base with a housing formed by upright
sidewalls and connecting end portions. Within the
housing are a pair of elastomeric blocks spaced
apart by a saddle block. An upper surface of the
saddle block has a cusp to separate a pair of roller
bearings. Each elastomeric block is formed with a
relatively soft lower portion and a stiff upper
portion having a top surface to engage a wear plate
affixed to the body of the railroad car. A fully
loaded car body compresses the elastomeric blocks
sufficiently so that the wear plate engages the
roller bearings. This engagement reduces frictional
restraints to relative movement between the bearing
unit and car body.
SUMMARY OF THE I~VE~TION
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In accordance with an embodiment of the
present invention there is provided a railroad side
bearing unit comprising: a one-piece elastomeric
device having a non-linear spring rate to provide an
exponentially increasing resistance to compression
and prepared to fit on a base plate of the unit, the
device having a center portion, the center portion
having sides outwardly radiating from a vertical
axis through the center of the device and tapering
horizontally inward from a midpoint of the device
respectively to join ends of the device, the sides
of the center portion and the ends being
substantially free of interference with the unit,
and the center portion having a top strip connecting
therewith, the ends each having an end wall
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vertically convex and hori~ontally concave and sides
tapering to proximately align with and join the
center portion sides, and a generally rectangular
cap formed with a bottom groove to receive the
elastomeric device strip and key the cap to the
elastomeric device, the cap having a top surface
prepared to engage with a wear plate of a railroad
car body and sides to fit closely adjacent to
complementary polygonal walls of the unit to prevent
substantia~ movement of the cap relative to the unit
in a twisting direction and a direction transverse
to the vertical axis of the elastomeric device, and
to limit movement of the cap and attached
elastomeric device to a direction substantially
parallel to the vertical axis and promote a transfer
of forces from the wear plate to the elastomeric
device to evenly compress the elastomeric device
over its entire middle portion to flex the device
sides and ends in a shear stress minimizing manner,
wherein compression of the elastomeric device
results in the exponentially increasing resistance
to such compression.
In accordance with a further embodiment of
the present invention there is provided a side
bearing unit for use with a railroad car, the side
bearing unit comprising: a base prepared for
attachment to a bolster of a truck of the car, a
housing carried on the base and including a pair of
spaced apart sidewalls connected by end walls to
~0 define a polygonal inner cavity with the walls
having inner surfaces formed with a ledge, a one-
piece elastomeric device carried on the base within
the housing cavity, the device having a center
portion, the center portion having sides outwardly
radiating from a vertical axis through the center of
the device and tapering horizontally inward to join
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ends of the device respectively, the sides and the
ends of the device being separated from the housing
wall inner surfaces to form a continuous clearance
space therebetween, the ends each having an end wall
vertically convex and horizontally concave and sides
tapering to proximately align with and join the
center portion sides, and a generally rectangular
cap disposed in the housing and integrally keyed to
the center portion of the elastomeric device, the
cap having a bottom surface positioned above the
wall ledge and a top surface positioned above a top
edge of the walls for engagement with a wear plate
attached to a bottom of a body of the railroad car
and sides fitting closely adjacent the wall inner
surfaces of the polygonal inner cavity of the
housing to promote movement of the cap in a
direction substantially parallel to the vertical
axis of the elastomeric device and limit movement of
the cap and attached elastomeric device in other
directions to maintain the device substantially free
from contact with the housing walls, wherein forces
may be transferred from the railroad car body to
provide movement of the cap with the nonparallel
movements being selectively regulated by
interference between the cap sides and the housing
walls with the parallel movements compressing the
device middle portion evenly to flex the device
sides and ends in a minimal shear stress manner with
the parallel movements limited in part by
interference of the cap bottom surface with the
ledge.
In accordance with a further embodiment of
the present invention there is provided a method of
making a railroad side bearing unit comprising the
steps of: providing a generally rectangular cap with
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a top surface for engaging a wear plate of a
railroad car; forming a keyway in the underside of
the cap; providing a block of thermoplastic
elastomer material having a selected transverse
configuration including sides and ends and a
selected initial free height, and forming the block
with an integral key at the top thereof for fitting
in the keyway of the cap; assembling the block with
the cap by locating the key of the block in the
keyway of the cap to thereby form an assembly;
applying to the assembly a force sufficient to
compress the block at least 30% of its initial free
height to permanently reduce the height and
permanently change the transverse shape of the block
such that the ends each are formed with an end wall
vertically convex and horizontally concave and
tapering to proximately align with and join the
sides and to permanently expand and lock the key of
the block into the keyway of the cap; removing the
force from the assembly; and providing a housing
adapted for attachment to a bolster of a truck of
the car, the housing being provided with a generally
rectangular cavity complementary to the generally
rectangular shape of the cap and fitting closely
with the cap to prevent substantial movement of the
cap relative to the housing in a twisting direction
and a direction transverse to the direction of
applying the force, the sides of the permanently
compressed block being separated from the housing to
form a continuous clearance space therebetween.
In accordance with a further embodiment of
the present invention there is provided a side
bearing unit for use with a railroad car,
comprising: a generally rectangular cap with a top
surface for engaging a wear plate of a railroad car,
with a keyway in the underside of the cap; a body of
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thermoplastic elastomeric material having a selected
transverse configuration including sides and ends
and axial free height with an integral key at the
top thereof for fitting in the keyway of the cap,
defined by axially compressing the body by an extent
equal to at least 30% of the initial free height to
permanently reduce the height and permanently change
the transverse shape of the body such that the ends
each are formed with an end wall vertically convex
and horizontally concave and tapering to proximately
align with and join the sides and to permanently
expand and lock the key of the block into the keyway
of the cap; a housing adapted for attachment to a
bolster of a truck of the car, including a generally
rectangular housing cavity defined by surrounding
side wall means, the sides of the permanently
compressed body being separated from the side wall
means to form a continuous clearance space
therebetween, and the side wall means of the
generally rectangular cavity fitting closely to the
generally rectangular cap to prevent relative
substantial movement of the cap relative to the
housing in a twisting direction and a direction
transverse to the direction of compressing the body,
and to thereby limit movement of the cap and
attached body in a direction substantially parallel
to the direction of compressing the body.
A side bearing unit of this invention has
a base which may be readily attached to a top wall
of a railroad car truck bolster. A housing,
attached to the base, includes a pair of space
sidewalls connected by end walls. The walls have an
inward projecting ledge forming a stop.
Within the housing is an elastomeric
device having a middle portion joined by end
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portions. The device is made of polymer material
and has non-linear compressive spring rate which
increases exponentially as the device is compressed.
An upper part of the middle portion of the
elastomeric device is integrally joined to a cap
which also fits within the hcusing above the wall
ledge. Sides of the cap fit closely adjacent to the
housing walls while a clearance space separates the
housing walls and sides of the elastomeric device.
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A top surface of the cap is positioned above
the housing to engage a wear plate attached to a bot-
tom of a body of the railroad car. The weight of the
car body acting through the cap compresses the eIasto-
5 meric device. A selective reserve space allows furthertravel of the cap before a bottom surface of the cap
engages the housing wall ledge.
The side bearing unit of this invention offers
several important advantages over known side bearing
10 units.
A first advantage is provided by joining the
cap and elastomeric device into a single integral unit.
Since the cap must be replaced periodically because of
wear, the elastomeric device also is replaced. The
15 elastomeric device is subject to failure because of
fatigue, environmental damage or both, yet the device
cannot be readily visually inspected. Therefore, re-
placing both the cap and elastomeric device at the same
time reduces the probability of inadvertent fail~re.
A second important advantage is provided by
the close fit between the cap and housing and the loose
fit between the elastomeric device and the housing.
This arrangement confines horizontal rotational movements
of the cap to minimize shearing forces acting on the
25 elastomeric device. Since the spring rate of the el-
astomeric device in shear is ~uite low, subjecting
the elastomeric device to excessive shear forces could
result in failure of the elastomeric device.
A last and most important advantage provided
30 by this side bearing unit is improved regulation of
independent rolling movement of the car body with re-
spect to the truck bolster. Such movements are dampened
by resisting such with an eIastomeric device having an
exponentially increasing spring rate. As the degree of
35 roll increases, the amount of resistance to such move-
ment increases even more. To insure that the eIastomeric
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device reacts in this desirous manner, the close fit
between the cap and the housing walls promotes linear
movement of the cap. The cap in turn being integrally
joined to the elastomeric device applies a compressive
5 force uniformly over a substantial length of the el-
astomeric device.
DESCRIPTION OF THE DRAWINGS
Fig. 1 is a plan view of a portion of a
railroad car truck which includes a side bearing unit
10 of this invention.
Fig. 2 is a detailed plan view of the side
bearing unit shown in Fig. 1.
Fig. 3 is an elevational view, partly in section,
as seen generally along the line 3-3 of Fig. 2.
Fig. 4 is a further elevational view, partly
in section, as seen generally along the line 4-4 of
Fig. 2.
Fig. 5 is a plan view of an existing side
bearing unit retrofitted with an elastomeric device and
20 top cap similar to that shown in Figs. 1-4.
Fig. 6 is a side elevational view of the side
bearing unit of Fig. 5.
Fig. 7 is an end elevational view of the side
bearing unit of Fig. 5.
DESCRIPTION OF THE
PREFERRED EMBODIMENT
In Fig. 1 a portion of a standard railroad
car truck 10 is seen generally and comprises a pair o
wheelsets with a part of one such wheelset shown and
30 designated 12. The wheeIset 12, as shown, has one axle
end 14 journaled in a bearing carri~d by a side frame
16. As is appreciated, the truck l0 includes a pair of
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such side frames which are connected by a transversely
positioned bolster partly shown and designated 18. An
end 20 of the bolster 18 is resiliently carried in a
window in the side'frame'16 in a known manner.
The bolster 18 further includes a center plate
22 and a pair of spaced recesses. One recess 24 is
shown and contains a side bearing unit 26. The bolster
center p~ate 22 connects with a body of the railroad
car (not shown). As is recognized, the railroad car
10 has two such trucks 10 with each supporting one e~d of
the car body. Therefore, the railroad car has four
side bearing units 26.
The side bearing unit 26 is shown in detail in
Figs. 2-4 and includes a base plate 28 formed with a
15 pair of apertures 30 to facilitate connecting the
unit 26 to the truck bolster 18. At~ached to the base
plate 28 is a housing 32 defined by sidewalls 34 joined
by end walls 36 to form an inner cavity 38. On an in-
ner surface 40 of each sidewall 34 is a horizontal
20 ledge 42. Likewise, on an inner surface 44 of each end
wall 36 is a horizontal ledge 46. The ledges 42, 46
connect to form a continuous stop 48. Adjacent to the
base plate 28 in each sidewall 34 and end wall is an
opening 50.
In the housing cavity 38 is an elastomeric
device 54. Uncompressed, the device 54 has a generally
rectangular cross-sectional configuration through a
center portion 56 of the device 54. The center portion
56 has a substantially flat top and bottom wall 58, 60
30 and radiused sidewalls 62, see Fig. 4. Joining the
elastomeric device center portion 56 are end portions
~; 64. Each end portion 64 has an end wall 66 which is
vertically convex and horizontally concave, see Figs.
3, 4. Sidewalls 68 of each end portion'64 taper out-
35 ward to join the'center portion sidewalls 62.' A clear-
ance space'70 separates the'side'and end walls 62, 66
and 68 of the eIastomeric device'54 from the inner sur-
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faces 40, 44 of the housing sidewalls 34 and end walls
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36. The elastomeric device 5~ further includes a key
shaped strip 72 joined to the device center portion 56.
The strip 72 fits in a keyway slot 74 in a bottom sur-
face 76 of a cap 78.
The preferred material from which to make the
elastomeric device 54 is a copolyester polymer sold
under the trademark HYTREL. The material is first
cast into a preformed block which is then annealed.
The annealed preformed block is then placed together
10 with the cap 78 and subjected to a compressive force
sufficient to reduce the size of the preform by at
least 30 percent of its cast size. This force is suf-
ficient to cause a flow of material into the cap slot
74 to form the strip 7Z. The elastomeric device 54 and
15 cap 78 are thus joined into an integral unit. U.S.
Patent No. 4,198,037 describes the above noted polymer
material and forming process and is herein incorporated
by reference to the extent applicable.
The overall height of the elastomeric device
20 54 and attached cap 78 is such that a top surface 80
of the cap 78 is positioned above a top edge 82 of the
housing sidewalls and end walls 34, 36. In an installed
state, a set of side bearing units 26 are fastened to
the bolster 18 with a body of the railroad having a
25 set of corresponding wear plates (not shown) attached
to a bottom of the car body. The wear plates engage the
cap top surface 80 of each unit 26 and compress each
elastomeric device 54 proximately 3/8in. As so compressed,
the bottom surface 76 of each cap 78 is positioned proxi-
30 mately 1/4in. above the housing stop 48 provided byledges 42, 46. Note that weight of the car body is
distributed equally between the centerplate 22 and the
set of side bearing units 26. Note further that sides
84 of the cap 78 are positioned in close proximity to
35 the inner surface 40, 44 of the ho~sing sidewalls 34 and
end walls 36.
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In Figs. 5, 6 and 7 is a further embodiment of
a side bearing unit 90. In this case the unit 90 is
formed by using a base 92 and attached housing 94 of an
existing side bearing unit. This preexisting struc-
5 ture is depicted by broken lines'. Attached to the base92 are a pair of spaced stop blocks 96. Within the
housing 94 and between the stop bIocks 96 is a further
elastomeric device 98 having the same general configura-
tion as the device 54 except for a concave shaped bot-
10 tom 100 which fits over a convex portion 102 in theunit base 92. Integrally joined to the elastomeric
device 98 is a further cap 104. Again the cap 104 may
be formed with a keyway shaped slot 106 to receive a
flow of polymer material to form a complimentary key
15 shaped strip 108.
In an uncompressed state the overall height
of the elastomeric device 98 and attached cap 104 is
such that a top surface 110 of the cap 104 is positioned
proximately 5/8in. above a top surface 112 of the stop
20 blocks 96. With a set of such units 90 attached to a
truck bolster, for example the bolster 18, the weight
of the body of the railroad car compresses the elasto-
meric device 98 of each unit 90. This compressive force
positions the top surface 110 of the cap 102 proximately
25 1/4in. above the top surface 112 of the stop blocks 96.
Note that like the unit 26, a clearance space 114 is
provided between the unit housing 94 and elastomeri~c
device 98 while sides 116 of the cap 104 are located
closely adjacent to sides 118 of the stop blocks 96 and
30 housing 94 to provide a relatively close fit therebe-
tween~
During travel of the railroad car, the truck
10 tends to hunt, i.e. yaw or oscillate about a vertical
axis of the truck.' Such hunting is inherent since the
35 wheelsets 12 have'¢onical shaped`rims which produce a
cyclical self-centering action as the wheelsets 12
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roll over a section of track.' Because of the frictional
engagement of the'unit cap top surface, for example top
surface 80 with the car body wear plate such oscillating
movements are impeded. The'frictional engagement be-
5 tween the cap top surface'80 and body wear plate is notof sufficient magnitude'to prevent reIative movement
between the car body and-truck bolster 18 which must
occur if the car is to travel safely about a curved
section of track.'
During such traveI, particularly at higher
speeds over a rough'section of roadbed when the car
body is empty, the car body tends to roll, i.e. oscil-
late about a horizontal axis of the car body, independent
of the bolster 18. This independent rolling action of
15 the car body is impeded by the further compression of
the elastomeric devices, for example devices 54 of the
units 26. As was noted earlier, the spring rate of the
device 54 is non-linear and increases exponentially as
the device 54 is compressed. Thus, a much greater force
20 is required to move the cap bottom surface 76 1/4in.
into contact with the stop ledge'48 than is required
to compress the device 54 3/8in. during initial load-
ing. This incrementially increasing spring rate tends
to dampen rolling action of the car body which is
25 limited to 1/2in. by interference of the respective
cap bottom surfaces 76 with the respective unit housing
ledge stops 4B.
To insure that device 54 maintains this desired
spring rate characteristic, movement of the cap 78 is
30 limited by its close fit with the housing sidewalls
34 and end walls 36. The integxal joining of the cap 78
and elastomeric device 54 promotes the even distribution
of forces transmitted by the car body wear plate to the
cap 78 over the entire'length of the device center por-
35 tion 56 to compress the'device'54. The clearance space70 about the'device'54 insures that these forces do not
place the'device'54 in shèar and unduly shorten its
useful life. As the device 54 is loaded and unloaded,
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heat is generated which may escape through the openings
50. When the cap 78 becomes sufficiently worn, the cap
78 and elastomeric device 54 are replaced as a unit
insuring continued high performance. It should be ap-
5 preciated that the side bearing unit 90 functions ina manner similar to the unit 26 to produce comparable
results.
While the invention has been described with
respect to various specific examples and embodiments, it
10 should be understood that the invention is not limited
thereto, and that it can be variously practiced within
the scope of the claims.
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