IMPROVED FRICTION SHOE FOR FREIGHT CAR TRUCK

SABOT DE FRICTION AMELIORE POUR WAGON DE MARCHANDISES

English Abstract

A friction shoe is provided for use in a railway freight car truck. A freight
car truck
comprises two laterally spaced sideframes with a bolster extending
transversely between said
sideframes. The bolster has two ends each of which extends into an opening in
each sideframe
and is supported by a spring group in each sideframe opening. A friction shoe
is provided in a
sloped pocket between each bolster end and a vertical face of the sideframe.
The friction
shoes are themselves comprised of a sloped wall, a vertical rear wall
extending from a lower
part of the rear wall to a lower part of the sloped wall, and side wall. The
friction shoe
provides damping for the bolster supported on each spring group. The friction
shoe of the
present invention is also comprised of a cast steel.

Claims

WHAT IS CLAIMED IS:

1. A friction shoe for use in a railway freight car truck,
said friction shoe comprising a vertical rear wall extending for about the
entire
lateral width of the friction shoe,
a sloped wall extending downwardly at an acute angle from a top position of
lateral junction with a top position of said vertical rear wall,
a bottom section extending from and generally perpendicular to a lower portion
of said vertical rear wall to a lower portion of said sloped wall,
side walls each extending from outer edges of said vertical real wall, said
sloped
wall and said bottom section,
and an internal support wall extending from a generally laterally central
intersection with an inner surface of said vertical rear wall to a generally
laterally central
intersection with an inner surface of said sloped wall,
an wherein said friction shoe is comprised of cast steel.

2. The friction shoe of claim 1
wherein the coefficient of friction of the cast steel material is about 0.194
at a
loading of 333 pounds per square inch.

3. The friction shoe of claim 1 wherein the coefficient of friction of the
cast steel
material is about 0.21 at a loading of 500 pounds per square inch.

4. The friction shoe of claim 1
when installed in a freight car truck,
has an energy dissipation in inch-KIPS of about 39.4 for a 0.80 inch stroke.

5. The friction shoe of claim 1
when installed in a freight car truck, has an energy dissipation in inch-KIPS
of
about 23.9 for a 0.50 inch stroke.

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6. The friction shoe of claim 1
wherein said friction shoe is comprised of an AISI/SAE Grade 1527 steel.

7. A railway freight car truck comprising
two laterally spaced sideframes, a bolster extending transversely between said
sideframes,
said bolster having two ends, each end extending into an opening in each
sideframe.
a spring group in each sideframe opening to support said bolster end
and a friction shoe in each sloped pocket, said friction shoe comprising a
vertical rear wall
extending for about the entire lateral width of the friction shoe,
a sloped wall extending downwardly at an acute angle from a top position of
lateral junction with a top position of said vertical rear wall,
a bottom section extending from and generally perpendicular to a lower portion
of said vertical rear wall to a lower portion of said sloped wall,
side walls each extending from outer edges of said vertical real wall, said
sloped
wall and said bottom section,
and an internal support wall extending from a generally laterally central
intersection with an inner surface of said vertical rear wall to a generally
laterally central
intersection with an inner surface of said sloped wall,
an wherein said friction shoe is comprised of cast steel,
two sloped pockets in each bolster end,
each of said sloped pockets comprising a sloping wedge wall, a first lateral
wall
depending from said sloping wedge wall, a second lateral wall spaced from said
first lateral
wall and depending from said sloping wedge wall, each of said first and second
lateral walls of
said bolster sloped pocket having planar inner faces adjacent side walls of
said friction shoe.

8. The railway freight car truck of claim 7

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wherein said friction shoe cast steel has a coefficient of friction of the
cast
steel material is about 0.194 at a loading of 333 pounds per square inch.

9. The railway freight car truck of claim 7
wherein said friction shoe cast steel has a coefficient of friction of the
cast
steel material is about 0.211 at a loading of 500 pounds per square inch.

10. The railway freight car truck of claim 7
wherein said friction shoe cast steel has an energy dissipation in inch-KIPS
of
about 39.4 for a 0.80 inch stroke.

11. The railway freight car truck of claim 7
wherein said friction shoe has an energy dissipation in inch-KIPS of
about 23.9 for a 0.50 inch stroke.

12. The railway freight car truck of class 7
wherein said friction shoe is comprised of an AISI/SAE Grade 1527 steel.

13. A friction shoe for use in a railway freight car truck, said friction shoe
comprising
a vertical rear wall extending for about the entire lateral width of the
friction shoe,
a sloped wall extending downwardly at an acute angle from a top position of
lateral junction with a top position of said vertical rear wall,
a bottom section extending from and generally perpendicular to a lower portion
of
said vertical rear wall to a lower portion of said sloped wall,
side walls each extending from outer edges of said vertical rear wall, said
sloped
wall and said bottom section,
and an internal support wall extending vertically from a generally laterally
central
intersection with an inner surface of said vertical rear wall to a generally
laterally central
intersection with an inner surface of said sloped wall,

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said internal support wall extending downwardly to an intersection with an
inner
surface of said bottom section,
and wherein said friction shoe is comprised of cast steel of a Brinell
hardness of
418-512.

14. A railway freight car truck comprising
two laterally spaced sideframes, a bolster extending transversely between said
sideframes,
said bolster having two ends, each end extending into an opening in each
sideframe,
a spring group in each sideframe opening to support said bolster end and a
friction
shoe in each sloped pocket, said friction shoe comprising a vertical rear wall
extending
for about the entire lateral width of the friction shoe,
a sloped wall extending downwardly at an acute angle from a top position of
lateral junction with a top position of said vertical rear wall,
a bottom section extending from and generally perpendicular to a lower portion
of
said vertical rear wall to a lower portion of said sloped wall,
side walls each extending from outer edges of said vertical rear wall, said
sloped
wall and said bottom section,
and an internal support wall extending from a generally laterally central
intersection with an inner surface of said vertical rear wall to a generally
laterally central
intersection with an inner surface of said sloped wall,
said internal support wall extending downwardly to an intersection with an
inner
surface of said bottom section,
and wherein said friction shoe is comprised of cast steel of a Brinell
hardness of
418-512,
two sloped pockets in each bolster end,
each of said sloped pockets comprising a sloping wedge wall, a first lateral
wall
depending from said sloping wedge wall, a second lateral wall spaced from said
first

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lateral wall and depending from said sloping wedge wall, each of said first
and second
lateral walls of said bolster sloped pocket having planer inner faces adjacent
side walls of
said friction shoe.

15. The railway freight car truck of claim 14
wherein said friction shoe cast steel has a coefficient of friction of the
cast steel
material of about 0.194 at a loading of 333 pounds per square inch.

16. The railway freight car truck of claim 14
wherein said friction shoe cast steel has a coefficient of friction of the
cast steel
material of about 0.211 at a loading of 500 pounds per square inch.

11

Description

CA 02327975 2000-12-11
6173-CIP - Hawthorne et al.
IIVVIPROVED FRICTION SHOE FOR FREIGHT CAR TRUCK
BACKGROUND OF THE I1VVENT'ION
_ The present invention is a continuation-in-part of pending U.S. patent
application serial
number 08/999,084, which application is hereby incorporated by reference.
The present invention relates to a damping or snubbing arrangement for a
railway
freight car truck and, more particularly, to a single sloped wedge surface
friction shoe for use
in a variable damped railway freight car truck snubbing interface between the
bolster ends and
the sideframe bolster pockets.
As set forth to some degree in U.S. Patent Nos. 4,426,934 and 4,637,319, a
typical
three piece railway freight car truck in service today comprises two laterally
spaced sideframes
that are typically of an integral cast steel construction, and a bolster
extending transversely
between such sideframes. The bolster is also typically of an integral cast
steel construction.
The ends of the bolster are supported on spring groups with the weight of the
freight car itself
supported on the center plate and side bearings of the bolster top surface.
The axle and wheel
sets are received in pedestal jaws of the longitudinally aligned sideframe
ends.
As the railway freight car travels down the railroad track, the car is
subjected to typical
vertical and horizontal component forces that cause the bolster to travel
vertically within the
sideframe bolster openings. Such motion is absorbed by the spring groups
within the
sideframe openings. The lower ends of the springs are supported on the spring
group support
surface of the sideframe with the upper ends of the springs supporting the
lower edge of the
bolster ends.
It is necessary to provide snubbing or damping for the bolster so that the
motion of the
bolster is restricted. Such damping is provided by friction shoes that are
located in a so-called
friction shoe pockets formed at the outer ends of the bolster. Each end of the
bolster includes
,:;,,,r
y.,w L.
'1 '~ two such friction shoe pockets formed by sloped surfaces facing
laterally on each side of the
bolster end. In the variable damped designed railway truck, the bottom of the
friction shoe is
supported by a spring or spring group that extends to the sideframe spring
support surface.


CA 02327975 2000-12-11
This type of truck is known as a variable damped truck because the compression
force from
the shoe supporting spring varies during relative vertical motion between the
bolster and the
sideframe. The friction shoes in such variable damped trucks typically have a
single sloped
wedge surface extending for the entire lateral width of the friction shoe
itself.
Such friction shoes for use in variable damped railway freight car trucks have
~cadidonally been comprised of cast iron. The austempered ductile cast iron
used in such
friction shoes is typically produced with a Brinell hardness of 331-385. The
coefficient of
friction of such cast iron shoes at a loading of 333 pounds per square inch
(psi) is about 0.177
and at a loading of about 500 per square inch (psi) is about 0.206. The energy
dissipation of
such cast iron friction shoes in inch-KIPS is about 37.2 for a 0.8 inch stroke
and about 21.8
for a 0.5 inch stroke.
A vertical wear plate is typically provided along the sideframe vertical face
that
contacts the vertical wall of the friction shoe.
As discussed in the two patents mentioned above, undesirable wear along a wall
of the
bolster friction shoe pocket may occur in such trucks as the cast iron
friction shoe rubs against
the wall during relative movement between the bolster and sideframe. Such wear
may
eventually create a condition causing the friction shoe to wear in and hang up
or lock up
thereby restricting the damped motion of the bolster on the spring group. Such
lock up causes
the tremendous forces associated from the wheels and axles supporting a loaded
railway freight
car to be transmitted from the sideframes through the friction shoe directly
to the sloped
surface of the bolster pocket. This condition can lead to excessive stress
conditions, the
formation of fatigue cracks, and eventual failure of the bolster end
structure.
One arrangement to address this problem is set forth in U.S. Patent No.
4,426,934 and
comprises a wear plate positioned within the bolster friction shoe pocket. The
purpose of this
wear plate would be to protect the sloped surface of the bolster friction shoe
pocket as well as
the two lateral walls of such pocket. Such arrangement has not been readily
accepted and is
difficult to install, as such wear plates traditionally become loose in
service and can create a
"~' condition which may result in further malfunctioning of the railway
freight car truck.
2


CA 02327975 2000-12-11
Another solution is set forth in U.S. Patent No. 4,637,319 to mainly address
gouging
caused by such cast iron friction shoes. Such shoes include a pin hole to
allow assembly of the
railway freight car truck. It is necessary to hold the friction shoe in the
bolster during
assembly or servicing of the truck. A support pin is extended through the pin
holes in the
bolster friction shoe pocket and through the friction shoe itself to allow the
friction shoe to be
field in position. In service, the pin is removed and the shoe moves
vertically in its typical
snubbing fashion. However, the shoe wears into the outward bolster pocket wall
by the
movement of the edges of the pin hole of the friction shoe across the bolster
outer pocket. A
protrusion tracking the outside of the pin hole edges is formed in the pocket
wall to eventually
lock up the friction shoe. U.S. Patent No. 4,637,319 provides solution to this
problem by.
providing a recess along the outer bolster friction shoe pocket to thereby
allow the friction
shoe movement without wear by the accompanying pin hole in the friction shoe
itself.
Neither of these solutions address the real problem in such variable damped
railway
freight car trucks, namely the inherent hardness and abrasiveness of the cast
iron friction shoe
in the cast steel bolster friction shoe pocket.
SUMMARY OF THE INVENTION
The present invention provides an improved cast steel friction shoe for use in
a
snubbing arrangement with a railway freight car truck bolster and sideframe
interface.
The cast steel friction shoe of the present invention is particularly adapted
for use in a
variable damped friction snubbing arrangement and railway freight car truck
utilizing a
variable damped friction shoe arrangement between the bolster end and the
sideframe.
Performance of the cast steel friction shoe of the present invention is
improved over that of a
cast iron shoe as the coefficient of friction of the cast steel. friction shoe
at a loading of 333 psi
is about 0.194 and at a loading of 500 psi is about 0.211. Further, the energy
dissipation in
inch IMPS of the cast steel friction shoe of the present invention for a 0.8
inch stroke is 39.4
and for a 0.5 inch stroke is 23.9. The performance improvements are clearly
seen over the
characteristics of a cast iron friction shoe mentioned above.
3


CA 02327975 2000-12-11
The reliability of the cast steel friction shoe when utilized in a traditional
railway
freight car truck will also be improved. The cast steel friction shoe will not
inordinately wear
into the cast steel bolster pocket leading to the lock up of the friction shoe
and even failure of
the bolster itself. Improved safety of railway freight cars utilizing such
cast steel shoes will be
readily apparent.
The cost of such railway freight car trucks utilizing such cast steel friction
shoes will
be lower as well over railway freight trucks required to use a pocket wear
plate to protect the
sloped surface of the bolster from the inherent hardness of a cast iron
friction shoe. It is
obvious that the life cycle of the above railway freight car truck utilizing
the cast steel friction
shoe will be extended as well.
It is a primary object of the present invention to provide an improved
friction shoe of
cast steel to provide improved performance in a railway freight car truck.
IN ~ Ditawuvcs:
~ Figure 1 is a perspective view of a railway freight car truck having a
bolster received
between two laterally spaced sideframes;
Figure 2 is an exploded view of the bolster end and sideframe receiving pocket
of a
variable damped railway freight car truck;
Figure 3 is an end view and partial cross section of a bolster end received in
a
sideframe opening of a variable damp railway freight car truck;
Figure 4 is a side view of the improved friction shoe of the present
invention; and
Figure 5 is a perspective view of the improved friction shoe of the present
invention.
::
4


CA 02327975 2000-12-11
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to Figure 1 of the drawings, a typical three piece railway
freight car
truck is shown generally at 10. Railway freight car truck 10 is comprised of
cast steel
sideframes 12 and 14 that are identical and are laterally spaced from each
other. Axle wheel
sets 18 and 20 are received in pedestal end openings 26 and 28 of sideframe 12
and similar
pedestal end openings of sideframe 14. With the end 22 of bolster 16 extending
into and
received in sideframe opening 30, a similar end 24 of bolster 16 extends into
a similar opening
in sideframe 14. Support springs 32 extend upwardly from spring group support
section 34 of
sideframe 12. A similar spring group extends upwardly from sideframe 14 to
support bolster
end 24.
Referring now to Figures 2 and 3, a detailed view of bolster end 22 supported
on
spring group 32 extending upwardly from sideframe spring support section 34 is
shown.
Friction shoe 40 is seen supported by a spring group 42 which itself extends
upwardly from
sideframe spring group support section 34. The vertical face 48 of friction
shoe 40 contacts
wear plate 60 which is usually bolted and welded to a receiving section of
sideframe 12. It
can be readily seen that the forces from spring group 42 vary with the
vertical placement of
bolster 16 and associated friction shoe 40:
Referring now to Figures 4 and 5, a detailed view of friction shoe 40 is
provided.
Friction shoe 40 is comprised of a cast steel material, and is usually a
unitary structure.
However, for weight savings, a large portion of friction shoe 40 is hollow
with appropriate
strengthening walls and support ribs. Friction shoe 40 is seen to comprise a
generally vertical
wall 48 that extends about the entire width of friction shoe 40. A bottom
section 44 extends
transversely from an intersection with vertical wall 48. Sloped face 46
extends downwardly
from intersection width vertical wall 48 at an acute angle thereof. The
preferred angle is
usually 32 degrees. Sloped face 46 also extends about the entire width of
friction shoe 40.
The lower edge of sloped face 46 intersects with bottom wall 44.
The typical material for friction shoe 40 is an AISI/SAE Grade 1527 cast
steel. The
chemistry of such steel is as follows : carbon about .27 % and manganese about
1.6 % with a
Brinell hardness of 418-512.)
5


CA 02327975 2000-12-11
Internal rib 56 generally extends from a laterally central vertical
intersection with rear
wall 48 to again a generally vertical intersection with the inner surface of
sloped face 46.
Further, as seen in Figures 4 and 5, internal rib 56, extends upwardly from an
intersection
with bottom wall 44 to the upper intersection between vertical wall 48 and
sloped face 46. In
order to save weight, typically an internal section 58 of internal support rib
56 is generally
provided as a hollow structure. Further, sidewall 52 and 54 extend between the
lateral edges
of rear wall 48 and sloped wall 46 to provide additional structure and
strength. Sidewalls 52
and 54 also include hollow internal sections for weight savings.
6

Representative Drawing