Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INYENTION
In modern railway freight cars, conical wheels of the railway truck engage
cylindrical rail heads of the railway track. The rolling engagement of the
wheels on the track produces a steering action that can become unstable and
cause the railway truck to oscillate laterally about the track centerline and
yaw cyclically about a vertical axis as it continually seeks a centered
position on the track. This phenomenon is commonly referred to as truck
hunting. Hunting can cause or exacerbate lateral roll movement of the car
body about its longitudinal axis. Reference is made hereby to prior U.S.
patent No. 3,957,318 for further detailed explanation of railway vehicle truck
hunting phenomena, and such explanation is hereby incorporated herein and made
a part hereof by reference.
Railway truck side bearings have long been utilized to support rail car
bodies with respect to their trucks laterally outward of the truck
centerplates. Side bearings are necessary not only because of the tendency of
the car body to roll about its longitudinal axis, but in addition to support
the car body during negotiation of track curves.
Among many examples of railway truck side bearings are those which employ
elastomeric elements to provide some or all of the load bearing capacity
afforded by the bearing as well as hunting response restraint. Included among
known side bearings are those disclosed in U.S. patents 4,715,290, 3,707,927,
3,670,661, 4,434,720, 3,045,998, 3,895,206, 4,355,583, 4,030,424 and
5,386,783. The above-mentioned U.S. patent 3,957,318 is another example of a
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side bearing utilizing elastomeric bearing elements.
One type of modern side bearing in particular is characterized as a
constant contact side bearing, because the bearing assembly becomes engaged in
load bearing engagement between the railway truck and the car body during the
setup process when the car body is mounted on the truck. A constant contact
side bearing remains in 10ad bearing engagement, and preferably uniform load
bearing engagement, between the truck and the car body throughout the entire
range of car body motion relative to the truck. This includes, most notably,
the entire range of car body roll motion.
BRIEF SUMMARY OF THE INVENTION
The present invention contemplates a novel and improved constant contact
side bearing having improved vertical travel characteristics whereby improved
bearing load response in the normal bearing operating range is achieved.
The bearing of this invention preferably employs compliant bearing
assemblies of elastomeric elements bonded to rigid substrates. The bearing
assemblies are configured in a novel way to provide an extended vertical
travel or movement characteristic through reliance primarily on shear
deformation of the elastomeric bearing elements as the vertical height of the
bearing varies in response to changes in the vertical spacing between the
truck and the car body at the bearing location. The increased vertical travel
available with this side bearing allows for greater setup height tolerance or
variation and a controlled spring rate in the operating range.
By relying primarily on shear loading in the elastomeric bearing elements,
larger material strain can be tolerated with less permanent set or damage to
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the elastomeric material. The force-deflection characteristic of the novel
bearing can be customized by varying any of a variety of geometric, structural
or dimensional specifications. These may include the deformation
characteristics of the elastomeric elements, their section thicknesses, the
number of elastomer sections employed, the shape or geometry of unbonded
elastomeric surfaces, employment of multiple elastomeric materials of
differing deformation characteristics, and so forth.
The invention also contemplates use of elastomeric bearing elements such
as above characterized in conjunction with appropriate solid stops to limit
the maximum elastomer deformation which can occur in operation of the bearing.
The novel side bearing includes modular assemblies of elastomeric elements
bonded to rigid substrates such as steel in configurations to provide a
relatively lower stiffness or spring rate in response to vertical deformation
of the elastomeric elements in shear, while providing a relatively greater
stiffness or spring rate in the longitudinal direction as a response to
compressive deformation of the elastomeric elements. The longer vertical
travel for the bearing thus is achieved without compromising longitudinal
stiffness which is desirable for assisting in control of hunting.
Other variations to the novel side bearing can include employment of
tapered or other shapes for unbonded elastomer surfaces, and variation in the
shape of the substrates to which elastomeric elements are bonded.
It is, therefore, one object of the invention to provide a novel and
improved constant contact side bearing for a railway vehicle.
A further object of the invention is to provide a railway vehicle side
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bearing with extended vertical travel achieved through use of elastomeric
bearing assemblies.
Another object of the invention is to provide a constant contact side
bearing with a force-deflection characteristic achieved primarily through
deformation of elastomeric elements in vertical shear.
These and other objects and further advantages of the invention will be
more readily appreciated upon consideration of the following detailed
description, and the accompanying drawings, in which:
Fig. 1 is a sectioned side elevation of a side bearing of the present
invention taken on line I-I of Fig. 2;
Fig. 2 is a sectioned top plan view taken on line II-II of Fig. 1;
Fig. 3 is a sectioned side elevation of an alternative embodiment of the
invention;
Fig. 4 is a sectioned side elevation of a presently preferred embodiment
of the invention taken on line IV-IV of Fig. 5;
Fig. 5 is a sectioned top plan view taken on line V-V of Fig. 4;
Fig. 6 is a sectioned side elevation of another presently preferred
embodiment of the invention taken on line VI-VI of Fig. 7;
Fig. 7 is a sectioned top plan view taken on line VII-VII of Fig. 6;
Fig. 8 is a sectional side elevation of another embodiment of the
invention; and
Fig. 9 is a representation of a hypothetical force-deflectior, curve for a
side bearing of the present invention.
There is generally indicated at 10 in Figs. 1 and 2 a railway truck side
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bearing according to one embodiment of the instant invention and comprising a
rigid, unitary bearing housing 12 having a base portion 14 with mounting
flanges 16, and an upstanding, generally cylindrical perimeteral wall portion
18. Flanges 16 include through openings 20 to receive suitable fasteners such
as rivets or nut and bolt assemblies (not shown) for securing the side bearing
10 to a railway truck bolster (not shown) or comparable structure.
A bearing assembly 22 is received within the confines of perimeteral wall
18, the assembly 22 being comprised of plural, concentric elastomeric rings 24
and 26 having confronting cylindrical surfaces 28 and 30 thereof suitably
bonded to a rigid, cylindrical substrate 32 of steel, for example. The inner
cylindrical wall 34 of elastomeric element 26 is similarly bonded to a rigid
cylindrical substrate 36, and the radially outermost cylindrical wall 38 of
elastomeric element 24 is similarly bonded to the cylindrical inner surface 40
of bearing carrier wall portion 18.
As shown in Figs. 1 and 2, the plural elastomeric elements 24 and 26, as
well as the cylindrical substrate elements 32 and 36, are arranged in mutually
concentric relationship about axis X-X with respect to wall 18. Further, the
radially inner elastomeric element 26 is positioned to extend vertically above
the radially outer elastomeric element 24, and similarly substrate element 36
is positioned to extend vertically above substrate element 32. Additionally,
both of the substrate elements 32 and 36 extend above the uppermost extent of
either elastomeric element 24 or 26.
A vertical clearance 42 (Fig. 1) is provided between all elements of
bearing assembly 22 and the upper surface 44 of base 14 to permit a range of
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vertical motion for elements of bearing assembly 22 upon application of
downwardly directed loads L thereto.
From the above description it will be appreciated that when load L is
applied to the side bearing, rigid substrate element 36 will move downwardly
thereby deforming elastomeric element 26 in shear? rather than in compression,
as indicated by S in Fig. 1. In turn, the downward impetus exerted by this
shear deformation moves substrate element 32 vertically downward, thereby also
deforming elastomeric element 24 in shear as indicated by S' in Fig. 1.
The bonding of the elastomeric elements to the metal substrates, together
with reliance on shear deformation, allows a side bearing with lower stiffness
or spring rate in a vertical direction, while providing much greater stiffness
in the horizontal direction. In particular, with shear loading as described,
much larger strains in the elastomeric material can be sustained with less
permanent set or damage to the material. The shape of the force-deflection
curve for a side bearing such as disclosed in Figs. 1 and 2 may be readily
tailored to a specific application.
The overall force-deflection characteristic for the side bearing of Fig. 1
and 2 embodiments can be customized by such variations as the elastomeric
material selected, the geometry of the elastomeric elements, the number of
elastomeric elements used, and the shape of both the bonded and unbonded
elastomer surfaces.
Other variations to achieve different modes of bearing response may
include preloading the side bearing in various ways. For example, preloading
the elastomer in shear, tension, compression or torsion can assist in
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generating the initial stiffness of the bearing so that the shear loading
which the elastomer undergoes during setup will not have to generate as high a
force response in order to provide adequate performance. It is to be
appreciated that torsion is merely a special case of shear loading. The
loading conventionally referred to as shear is developed by applying equal and
opposite forces in planes parallel to the bonded interfaces between the
substrates and the elastomeric element, whereas torsion is developed by
applying equal and opposite torques to the substrate elements in planes
parallel to the bonded faces.
Fig. 9 illustrates a force-deflection characteristic for a non-preloaded
bearing with the values at the origin O of zero force and zero deflection
being the starting point for bearing installation and setup. By contrast, the
initial point for the force-deflection curve of a preloaded bearing would be
shifted upward along the vertical (force) axis.
Additional possible variations to influence bearing performance may
include the following, by way of example. In the Fig. I and 2 embodiment,
more elastomeric rings of smaller radial cross section would be expected to
provide a stiffer bearing than fewer rings of larger radial cross section. To
equalize shear strength among the elastomeric rings, the radial section of the
rings may be reduced and/or its vertical dimension increased as radius
increases. The vertical clearance of the individual rigid substrate elements
from the base or from the cap member may be individually varied to customize
the bottoming behavior of the bearing assembly. This can permit equalization
of the strain energy stored in each elastomeric element.
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Further, by changing the shape of the circular elastomeric elements in
plan view to an elongated or oval configuration, the bearing may exhibit
different stiffness characteristics in the lateral and longitudinal
directions. There also may be circumstances in which it would be desirable to
leave part of the volume between pairs of inner and outer substrate elements
empty, for such purposes as to avoid areas of stress concentration.
Other modes of preloading and other bearing assembly configurations such
as those described hereinbelow may also be employed for purposes of this
invention, so long as the bearing response to the generally vertical loading
evolved between the truck bolster and the car body at the bearing location is
primarily a response of shear deformation.
Still further variations and additional structural features of the
invention are illustrated by Fig. 3 in a side bearing generally indicated at
46 and having an elongated bearing carrier 48 similar to a conventional side
bearing housing or carrier. An assembly of plural elastomeric bearing
elements 50 bonded to intervening rigid substrate elements 52 provide load
bearing capacity which affords a range of vertical movement under loading L,
with bearing response principally occurring as shear deformation S of the
elastomeric elements 50. In these respects, bearing 46 is similar to the
bearing described above with reference to Figs 1 and 2; however, because it
can utilize a conventional bearing carrier 48, the bearing assembly of Fig. 3
can be retrofitted to existing side bearing hardware on freight car trucks.
Since the option of retrofitting the Fig. 3 bearing assembly requires that
they fit within the confines of a conventional bearing carrier 48, the bearing
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assembly must be configured accordingly. Hence, the elastomeric elements 50
are located only at opposed longitudinal ends of the bearing assembly. One or
more of the substrate elements 52 may include side portions 53 extending
longitudinally of the bearing assembly, but having no elastomeric material
bonded thereto. The side portions 53 on opposed lateral sides of the bearing
assembly therefore lie closely adjacent one another and move vertically with
respect to one another in response to loading L, but the bearing response
afforded by shearing S of the elastomeric elements 50 is confined to the
longitudinal end portions of the bearing assembly where the elastomeric
elements 50 are located.
Conventional side bearings also have commonly employed a solid stop
arrangement such as a roller 54 and a cap member 56. For purposes of the
present invention, cap member 56 is carried atop the bonded elastomer and
rigid substrate bearing assemblies to impart vertical loading thereto from a
car body (not shown). The maximum vertical deflection of the Fig. 3 side
bearing is limited to that deflection where a depending stop portion 58 of cap
member 56 engages roller 54. Of course, either the roller or a corresponding
solid bearing element, and/or cap member 56, may be incorporated in the Fig. 1
and 2 embodiment.
One presently preferred embodiment of the invention is shown in Figs. 4
and 5 as a bearing assembly 60 carried by a conventional side bearing cage or
housing 62 and including a longitudinally spaced pair of bonded elastomeric
bearing assemblies 647 and an intervening rigid bearing element such as roller
66. Each of assemblies 64 includes outer and inner rigid substrate elements
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12
68 and 70, respectively, each being preferably of a generally rectangular form
as shown in Fig. 5, but having rounded or radiused corners as shown at 72 and
74, for example. An intervening elastomeric element 76 is bonded to the
confronting surfaces 78 and 80 of substrate elements 68 and 70, respectively.
As shown in Fig. 4, one of the options mentioned hereinabove for customizing
bearing response is illustrated in Fig. 4 by the selected shaping or forming
of free (i.e. unbonded) surfaces of elastomeric element 76, for example as
indicated at 82 and 84.
Each of substrate elements 70 includes an opening 86 which receives a
downwardly projecting interlock portion 88 of a rigid cap 90. the cap 90
spans the longitudinally spaced bearing assemblies 64 and includes an
intervening depending portion 92 which is engageable with roller 66. This
provides a solid stop to limit vertically downward travel of cap 90 under
loadings L, thus also limiting deformation of elastomeric elements 76 in
shear.
Figs. 6 and 7 show another presently preferred embodiment of the invention
wherein an assembly of bearing elements 93 is carried by a conventional side
bearing housing or carrier 94. Assembly 93 comprises a bonded elastomer and
metal substrate bearing assembly 96 that is similar in many salient respects
to that described with reference to Figs. 4 and 5. As shown in Fig. 7,
however, bearing assembly 96 may be of a generally rectangular section form,
rather than generally square as in the Fig. 4 and 5 embodiment. In addition,
the cap or wear member 90 of the Fig. 4 and 5 embodiment is substituted in the
Fig. 6 and 7 embodiment by an integral wear member portion 98 of the bearing
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assembly 96.
The assembly 96 resides in bearing carrier 94 longitudinally adjacent to a
saddle member 100 having an upwardly projecting abutment 102 which confines
bearing assembly 96 between itself and the opposed end 104 of housing 94.
Between abutment 102 and the opposite end 106 of housing 94 there is confined
a roller element 108, which may roll freely within a range of longitudinal
movement between carrier end 106 and abutment 102.
Fig. 8 shows yet another embodiment of the invention in generally
schematic form as a bearing assembly 110 comprising a base portion 112 having
either a plurality of elastomeric elements, or a unitary ring-shaped
elastomeric element 114 as shown. A substrate element 116 includes a
peripheral side portion 118 and a top portion 120. A radially inwardly facing
wall portion 122 of the peripheral side portion 118 confronts the radially
outwardly facing wall 124 of base element 112, and elastomeric element 114 is
bonded to these surfaces.
The confronting wall portions 122 and 124 are angled outward from the
vertical by an angle A such that loading L produces shear deformations that
are not parallel to the confining walls 122 and 124. The result is a degree
of elastomeric compression in addition to the shear deformation under loading
L. The limit on angle A for practical purposes has not been determined,
although it will be clear that as angle A increases the deformation of the
elastomeric elements 114 in response to loading L is increasingly greater
compression and decreasing shear deformation. Since the novel bearing as
described operates primarily in reliance on the response from shear
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14
deformation of the elastomeric elements, the magnitude of angle A is to be
limited accordingly so that the bearing response is indeed primarily shear
response.
Bearings according to the present invention may be configured in
accordance with any described embodiment, and others not described. In
addition, any embodiment of the invention may be modified in accordance with
any of the alternative structures or modifications mentioned herein, as well
as others which would have the function of altering in some preferred way the
force-deflection response of the bearing upon deformation of the elastomeric
materials in shear under vertical loading.
A force-deflection curve for a hypothetical side bearing of the present
invention is illustrated in Fig. 9 as curve C representing the vertical
bearing deflection D under force F.
Origin O represents the free or unloaded state of the bearing extending to
its full free height. (As noted hereinabove, for a preloaded bearing, the
initial point O of curve C would be shifted upwardly along the vertical axis.)
Upon application of a force F directed vertically downward, the bearing
response is observed as a deflection D over an initial range of loading I
representing bearing installation and setup. The range of deflection R
represents the variation which occurs due to normal error or variation in
setup of the bearing. The functional characteristics of the bearing are such
that, in this region the slope of curve C flattens significantly.
Consequently, the variation V in force F over the entire setup range R of the
bearing is relatively small. This provides for greater uniformity of the
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bearing setup.
Beyond setup range R, the slope of the force-deflection characteristic
increases with each additional increment of deflection D. At a point S
representing the solid stop, which is the limit of vertical travel, force
increases with no additional vertical deflection.
The significance of flattening of the force-deflection characteristic in
setup range R may be appreciated by extrapolating that portion of the curve C
backward toward O deflection as indicated by extrapolation E. The deformation
behavior of the elastomeric bearing assemblies in the setup range R
corresponds to a hypothetical linear force-deflection characteristic which has
undergone a very large deflection D before reaching the setup force range V.
Thus, to achieve such a response in a purely linear elastomeric side
bearing would be a practical impossibility because the required range of
vertical deflection needed to reach setup force levels would be far greater
than the deflection available in the vertical space envelope for standard side
bearing applications. Due to other space limitations that must be observed in
conventional side bearing applications, one could not reduce the required
vertical space envelope by significantly increasing the number or size of
elastomeric bearing elements, for example to increase the mass of elastomer
undergoing shear.
Thus, by virtue of this invention, a side bearing force-deflection
characteristic that would be thought unavailable, due to the space limitations
that must be observed, is nevertheless achieved within those space limitations
and without sacrificing any favorable aspect of bearing performance that is
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16
offered by the force-deflection characteristic C within the setup range R of
the bearing.
It will be understood that the force-deflection characteristic of Fig. 9
is merely illustrative and not intended to limit the scope of the invention.
There may be many circumstances where the invention provides a different but
equally desirable force-deflection characteristic.
Nol:withstanding the description hereinabove of certain presently preferred
embodiments of the invention, it is to be understood that we have envisioned
and ant;icipated various alternative and modified embodiments. All such
alternative embodiments are intended to be included within the scope of the
invention as described. Elastomeric materials for the invention may be chosen
from a range of materials having suitable properties that they can be
subjected to the necessary deflections with minimal permanent set or
hysteresis, while generating the required load responses as described
hereinabove within the side bearing space limitations. Similarly, metallic
substrates may be selected from a variety of materials based on load bearing
capacit,y and the wear to which the material may be subjected. The bonding
techniques for producing the elastomer and metal substrate bearing assemblies
may be standard bonding methods or heretofore unknown bonding techniques.
