Elastomeric bearing

Details Elastomeric bearing Elastomeric bearing

1998-08-28

2001-05-01

Graham, Matthew C. (Department: 3613)

Spring devices

Vehicle

Elastomeric

C267S141000, C267S293000

Reexamination Certificate

active

06224047

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to elastomeric bearings and, more particularly, to an elastomeric side bearing for supporting a railway car body relative to a railway car truck bolster.
BACKGROUND OF THE INVENTION
A railway car conventionally includes a car body supported on the center plates of a pair of longitudinally spaced trucks. The conical-shaped wheels of the trucks engage the respective rails of a railway track. The trucks travel a generally sinuous path along the track as the respective wheels continuously seek a centered position on a respective rail. In traveling such a sinuous path, a railway truck tends to hunt, i.e., yaw or oscillate about a vertical axis of the truck. One side frame of a truck tends to move ahead of the other which, in turn, results in the flanges of the wheels striking and rubbing against the rails, first on one side, and then on the other. Such undesirable lateral oscillations may cause excessive wheel and track wear. In addition, unstable truck hunting responses can develop if the frequency of the cyclic motion approaches resonance.
Also, during travel of a railway car, a railway car body may have the tendency to rock, i.e., oscillate about a horizontal (or roll) axis of the railway car body, independent of the truck upon which the railway car body is mounted. As the trucks of a railway car negotiate their sinuous path of travel along a railway track, the car body may move laterally in concert with the cyclic lateral movement of the truck center plates. A loaded or heavy car may tolerate such lateral oscillation. However, an empty or light car body may rock from side to side which movement can become dangerous should the frequency of the rocking approach resonance.
Efforts to control truck hunting and car body rocking include the use of side bearings which are mounted to a truck bolster on opposite sides of the center plate. Conventional side bearings are configured to maintain frictional contact between a truck and a car body. As the truck yaws, an upper portion of a side bearing slides across the underside of the railway car body. The resulting friction produces an opposing torque which acts to prevent yaw motion. For example, see U.S. Pat. No. 4,712,487 to Carlson, U.S. Pat. No. 4,090,750 to Wiebe, and U.S. Pat. No. 3,762,339 to Dwyer.
One type of side bearing employs a tube form mount. Inner and outer concentric, annular members are employed. An annular elastomeric spring member is interposed between the inner and outer members. The elastomeric spring is bonded to the outer surface of the inner member and to the inner surface of the outer member such that the elastomeric spring operates in shear to resist relative axial movement between the inner and outer members. The bearing is mounted between the truck and car body such that relative displacement between the truck and the car body causes a corresponding relative axial displacement between the inner and outer members.
In order to satisfy close tolerances and achieve faster production rates, bearings as just described are preferably formed using a transfer or injection molding process. With reference to
FIG. 10
, a tube form mount type bearing
100
is shown. The bearing
100
as shown is mounted in a transfer or injection mold
110
by which it has been formed. The mold
110
includes an upper mold portion
102
including a transfer pot
103
which holds a pig of elastomeric material
140
. A plurality of gates or sprue passages
104
extend from the bottom of the transfer pot and communicate with the cavity defined between an inner annular member
120
and an outer annular member
130
. A lower mold portion
106
seals the lower end of the cavity. An intermediate mold portion
107
supports the outer member
130
in the mold
110
. The elastomeric material
140
is fed into the cavity by forcing a piston
108
downwardly as indicated by arrows
108
A into the transfer pot
103
. The elastomeric material
140
typically follows paths as indicated by the arrows
141
.
Notably, the sprue passages
104
are gated into the working section of the elastomeric member
142
. One significant problem experienced with formation of a bearing as described using the prior art method described with reference to
FIG. 10
is that at the openings
105
where the sprue passages
104
terminate and meet the elastomeric member
142
(commonly referred to as the sprue location sites), the elastomeric member
142
may develop undesirable performance characteristics which degrade the overall performance of the bearing
100
. More particularly, the sprue location site may be a point of crack initiation when the finished and cured part is repeatedly flexed in service. When the cured cull pad material in the transfer pot
103
is removed from the elastomeric member
142
, a portion of the elastomeric material
140
which has cured within the gate
104
may remain with the elastomeric member
142
as a nub or sprue. Typically, the nub or sprue must be removed. Often, when the nub or sprue is separated from the elastomeric member
142
, the removed portion tears down into the working body of the elastomeric member causing deep sprues and stress concentration which may result in a reduced flex life. Also, flow eddies at the sprue location sites may cause improper knit of the elastomeric material which likewise causes a stress concentration and may reduce the member's durability.
With reference to
FIG. 11
, as an alternative to terminating the sprues in the working body of the elastomeric member, it has been proposed to form a bearing
100
A including an elastomeric member
142
A having sprue risers
106
A. The upper mold portion
102
A is formed with transfer pot
103
A in the upper portion thereof and plurality of recesses
152
A in the lower face thereof so that the sprue passage openings
105
A, and thus the sprue location sites, are at the sprue risers
106
A and located above the working section of the elastomeric member
142
A. The stress concentrations of the sprue location sites are localized in the low stress riser
106
A so that their effect on the performance of the working body of the elastomeric member
142
is reduced. While this alternative improves on the method described above, it presents significant new problems. With reference to
FIG. 11A
, in service, the bearing
100
A is axially compressed between a contact plate
52
and a bolster (not shown). In doing so, the contact surface engages the top of the inner member
120
A and also the sprue riser
106
A. Chafing of the sprue riser or deflection of the sprue riser
106
A into the working body of the elastomeric member
142
A by the contact surface
52
may induce stress concentrations and initiate cracks in the elastomeric member. Also, the sprue riser may be unacceptably unattractive.
Accordingly, there exists a need for an elastomeric bearing having an elastomeric member formed by transfer or injection molding wherein the sprue location sites do not present stress concentration points in the working body of the elastomeric member. Further, there exists a need for a convenient and cost-effective method for forming such an elastomeric bearing. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.
SUMMARY OF THE INVENTION
In view of the above discussion, it is a first aspect in accordance with the present invention to provide an elastomeric bearing, and more particularly, an elastomeric side bearing having an elastomeric member formed by transfer or injection molding wherein the sprue location sites of the elastomeric member do not present stress concentration points in the working body of the elastomeric member. According to a further aspect, the invention provides such an elastomeric side bearing wherein the sprue location sites do not otherwise interfere with the operation or performance of the side bearing. The

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