Note: Descriptions are shown in the official language in which they were submitted.
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RAILWAY TRUCK WITH EQUALIZER BEAM MOUNTED DISC BRAKE CALIPER
RELATED APPLICATIONS
This application claims the benefit of priority of U.S. Provisional
Application No. 60/179,229
filed January 31, 2000, and U.S. Provisional Application No. 60/183,198 filed
February 17,
2000, the disclosures of which are incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to improved brake assemblies for
railway freight car
trucks. More specifically, but without restriction to the particular use which
is shown and
described, this invention relates to the improved mounting of disc brake
assemblies to the
freight car truck.
2. Description of the Related Art
It is well known in the art to use disc brake assemblies as the braking
mechanism for railway
trucks, including passenger and freight car trucks. It is also known in the
art that the disc
brake assemblies include brake discs, disc brake calipers, and brake pads. In
use, the brake
discs are typically mounted on the truck wheel axle assembly, either directly
to the axle or
through the wheel. Under either mounting, the brake discs are unsprung. That
is, the brake
discs do not move relative to the wheel axle assembly.
The disc brake calipers are conventionally mounted on the truck frame and
releasably engage
the brake discs. Attached to the disc brake calipers are the brake pads which,
in operation,
contact the brake discs to provide a braking force to the wheels. Passenger
and freight car
trucks feature a primary suspension between the wheel axle assembly and the
truck frame that
allows relative vertical motion between the wheel axle assembly and the truck
frame and
accompanying disc brake calipers. Thus, the disc brake calipers are sprung
relative to the
wheel axle assembly and brake discs.
On passenger car trucks, this relative motion between the sprung brake
calipers and unsprung
brake discs has been limited by several design factors: loaded tare weight
ratio is small on
passenger trucks to minimize deflections due to static load change; the disc
brake calipers
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conventionally have been located longitudinally inboard of the axle thereby
limiting the
deflection due to truck frame pitching; and a secondary suspension has been
located between
the truck frame and bolster to absorb the majority of vertical suspension
deflection, thereby
allowing the primary suspension to be stiffer. Taken together, these passenger
car truck
design factors have limited primary spring deflection sufficiently to
accommodate sprung
brake calipers and unsprung brake discs and has not resulted in the problems
encountered by
freight car trucks, discussed below.
As stated above, when a freight truck frame is mounted on a primary
suspension, such as a
primary spring, the disc brake caliper is sprung relative to the brake discs.
During freight car
operation, the sprung mounting of the caliper has resulted in an undesirable
amount of
relative vertical motion between the unsprung brake disc and the sprung brake
caliper due to
various conditions, such as, freight load, dynamic bounce and truck frame
pitching. This
undesirable relative vertical motion is amplified during high-speed operation
of freight cars,
which use softer primary springs to ensure safe operation and acceptable ride
quality over
existing track. The use of soft springs creates large spring deflections,
which has been shown
to create two common problems. First, the brake pads, which are part of the
caliper assembly,
can edge partially off of the disc, thereby reducing braking efficiency.
Second, the brake pad
reaction forces are transmitted through the brake caliper assembly to the
truck frame. These
reaction forces result in a pitching moment in the truck frame, which can
unload individual
primary springs. When the truck frame pitching is severe, individual springs
may completely
unload creating the possibility of unseating of the springs, or even losing
springs from th-;,
truck assembly.
The present invention overcomes the aforementioned problems of excessive
motion between
the brake disc and caliper, and potential spring unloading.
SUMMARY OF THE INVENTION
The present invention is directed at eliminating the known problems associated
with relative
motion between the brake disc and caliper due to load conditions and other
dynamic forces
which develop during high speed freight car operation. The invention achieves
these
objectives by providing a disc brake assembly wherein the brake caliper is
mounted to the
equalizer beam, which is unsprung relative to the wheel axle assembly. With
this
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construction, both the brake disc and brake caliper are unsprung members, and
unsprung
relative to each other. Because these members are unsprung, the relative
displacement
between the brake disc and calipEr due to load variation, dynamic bounce, and
braking
induced pitching is essentially eliminated. Moreover, the possibility of
primary spring
unloading is also eliminated.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described in relation to the accompanying drawings. In
the drawings,
the following figures have the following general nature:
Fig. 1 is a partial side view of a prior art truck assembly.
Fig. 2 is a partial top view of the prior art truck assembly of Fig. 1.
Fig. 3 is a partial side view of another prior art truck assembly.
Fig. 4 is a partial top view of the prior art truck assembly of Fig. 3.
Fig. 5 is a partial side view of the truck assembly of the present invention.
Fig. 6 is a partial top view of the invention of Fig. S.
Fig. 7 is an isometric view of a pair of equalizer beams of the present
invention connected to
a pair of disc brake mounting beams.
DESCRIPTION OF THE INVENTION
Refernng to the drawings wherein like numerals indicate like elements, there
is shown in
Figs. 1-4 prior art truck assemblies which illustrate the sprung mounting of a
disc brake
caliper relative to the brake disc. As illustrated, the truck assemblies 10
and 11, as shown in
Figs. 1 and 3, respectively, include truck brake discs 12 and 13 which are
mounted on the
axle assembly, either directly to the axle 14, as depicted in Figs. I and 2,
or through the wheel
16, as depicted in Figs. 3 and 4. Under either mounting, the brake discs are
unsprung and
therefore do not move relative to the wheel assembly. The truck assemblies
also include disc
brake calipers 18 and 19 which are mounted to the truck frame 20 and 21. The
truck frame,
in turn, is mounted to the wheel axle assembly 22 and 23 via a primary
suspension. With this
arrangement, the disc brake calipers are sprung, or move vertically relative
to the wheel
assembly during operation. It has been shown that, during operation, these
prior art
assemblies, wherein the caliper is sprung relative to the discs, have resulted
in undesirable
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relative vertical motion between the unsprung disc and the sprung caliper due
to load
conditions, dynamic bounce and truck frame pitching. In some instances, for
truck
assemblies that use soft primary springs, the relative vertical motion can be
such that the
brake pads will edge partially off the disc, thereby reducing braking
efficiency, and can be so
extreme the primary springs can unseat or be lost from the truck assembly.
Refernng to Figs. 5 and 6, the present invention is depicted and overcomes the
problems of
relative motion between the brake disc and caliper. As depicted in an
exemplary
embodiment, the present invention includes the truck assembly 40, which
incorporates the
inventive disc brake assembly, described below. The truck assembly 40 further
includes
wheel axle sets 42, comprising flanged railway wheels 44, spaced transversely
from each
other, and joined by a transversely extending axle 46. Mounted to the wheels
44 are the
brake discs 48. It should be understood by those skilled in the art that the
present invention
may be used with brake discs mounted to the wheels or to the axles. Truck
frame 50 is
supported on the wheel sets through equalizer beams 64 and primary springs 65.
As
conventional, the truck frame 50 is longitudinally elongated and defines
longitudinally
spaced, downwardly opening pedestal jaws 52. The pedestal jaws define an inner
pedestal
leg 54 and an outer pedestal leg 56. Mounted between the inner and outer
pedestal legs,
within the opening of the pedestal jaws, are axleboxes 58 which rotatably
receive the axles 46
through journal bearings. The axleboxes 58 are retained between the inner and
outer pedestal
legs via tie bars 60.
The truck 40 further comprises a disc brake caliper 62, which is mounted to an
equalizer
beam 64 via a mounting bracket 66. It will be understood by those skilled in
the art that the
mounting of the disc brake caliper 62 via the mounting bracket 66 may be
accomplished by
numerous methods of attachment, including the use of bolts, rivets, weld, or
other suitable
methods. Attached to the disc brake caliper 62 are brake pads 68 which; in
operation, engage
the brake discs 48 of the railcar wheels. In an exemplary embodiment, the
equalizer beam 64
extends between the wheel sets and longitudinally beyond the axleboxes through
an opening
or core hole 70 in the outer pedestal leg 56 of the pedestal jaw 52. It should
be understood by
those skilled in the art that other designs of the equalizer beam are
possible. Removable filler
blocks 72 are located on all four inner pedestal legs to allow assembly and/or
disassembly of
the extended equalizer beam 64. On single equalizer beam truck designs the
equalizer beams
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extend longitudinally between axleboxes and are transversely located on the
journal
centerlines passing between the inside and outside faces of the inner pedestal
legs, one on
each side of the truck. The filler blocks 72 are removable solid blocks
fastened between the
inside and outside faces of a split pedestal leg after the equalizer beam is
installed to
5 structurally replace material removed from the split pedestal leg to permit
assembly/disassembly of the equalizer beam into the truck frame. Typically,
filler blocks are
required at one end of each of the truck frame and are secured by rivets on
threaded fasteners.
Due to the extended length of the equalizer beam, to mount the disc brake
calipers in the
present invention, the filler blocks are required at all four inner pedestal
legs to facilitate
installation and removal of the equalizer beams.
Referring to Fig. 7, an alternative embodiment of the invention includes the
use of disc brake
mounting beams 80 which connect to and traverse opposing equalizer beams 64 to
provide an
alternative disc brake caliper mounting arrangement. The disc brake mounting
beam, at its
end, is pivotally mounted to a corresponding end of the equalizer beam 64. The
mounting
may be accomplished through the use of elastomeric bushings 82 or other
similar methods of
mounting which allow limited relative angular motion of the two equalizer
beams on opposite
sides of the truck. With this construction, the disc brake calipers may be
mounted to the disc
brake mounting beam 80.
Significantly, as assembled, the brake disc and caliper, and accompanying
brake pads, are
unsprung members. This unique assembly significantly, if not completely,
eliminates the
relative displacement between the brake disc and caliper due to load
variation, dynamic
bounce, and braking-induced pitching. In addition, the possibility of primary
spring
unloading is eliminated.
It should be understood that variations of the embodiments are possible
without being outside
the scope of the present invention. Therefore, to particularly point out and
distinctly claim
the subject matter regarded as the invention, the following claims conclude
the specification.
