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(11) | EP 0 927 673 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Friction shoe for freight car bogie |
| (57) A friction shoe is provided for use in a railway freight car bogie (10). A freight
car bogie (10) comprises two laterally spaced sideframes (12, 14) with a bolster (16)
extending transversely between said sideframes (12, 14). The bolster has two ends
(22, 24) each of which extends into an opening (30) in each sideframe and is supported
by a spring group (32) in each sideframe opening (30). A friction shoe (40) is provided
in a sloped pocket between each bolster end (22, 24) and a vertical face of the sideframe.
The friction shoes (40) are themselves comprised of a sloped wall (46), a vertical
rear wall (48) extending from a lower part of the rear wall (48) to a lower part of
the sloped wall (46), and side walls (52, 54). The friction shoe (40) of the present
invention is also comprised of a cast steel. |
[0001] The present invention relates to a damping or snubbing arrangement for a railway freight car bogie and, more particularly, to a single sloped wedge surface friction shoe for use in a variable damped railway freight car bogie snubbing interface between the bolster ends and the sideframe bolster pockets.
[0002] 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 bogie 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.
[0003] 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.
[0004] 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 two such friction shoe pockets formed by sloped surfaces facing laterally on each side of the bolster end. In the variable damped designed railway bogie, the bottom of the friction shoe is supported by a spring or spring group that extends to the sideframe spring support surface. This type of bogie is known as a variable damped bogie 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 bogies typically have a single sloped wedge surface extending for the entire lateral width of the friction shoe itself.
[0005] Such friction shoes for use in variable damped railway freight car bogies have traditionally 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) (23.41 kg/cm2) is about 0.177 and at a loading of about 500 per square inch (psi) (35.15 kg/cm2) 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 (44.5kJ for a 2.032 cm stroke) and about 21.8 for a 0.5 inch stroke (27.0 kJ for a 1.27 cm stroke).
[0006] A vertical wear plate is typically provided along the sideframe vertical face that contacts the vertical wall of the friction shoe.
[0007] As discussed in the two patents mentioned above, undesirable wear along a wall of the bolster friction shoe pocket may occur in such bogies 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.
[0008] 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 an 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 bogie.
[0009] 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 bogie. It is necessary to hold the friction shoe in the bolster during assembly or servicing of the bogie. 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 held 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.
[0010] Neither of these solutions address the real problem in such variable damped railway freight car bogies, namely the inherent hardness and abrasiveness of the cast iron friction shoe in the cast steel bolster friction shoe pocket.
[0011] The present invention provides a cast steel friction shoe for use in a snubbing arrangement with a railway freight car bogie bolster and sideframe interface.
[0012] According to one aspect of the present invention, there is provided a friction shoe for use in a railway freight car bogie 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, and wherein said friction shoe is comprised of cast steel.
[0013] 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 bogie 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 (23.41 kilograms per cm2) is about 0.194 and at a loading of 500 psi (35.15 kilograms per cm2) is about 0.211. Further, the energy dissipation in inch KIPS of the cast steel friction shoe of the present invention for a 0.8 inch stroke is 39.3 and for a 0.5 inch stroke is 23.9 (44.5 kJ for a 2.032 cm stroke and 27.0 kJ for a 1.27 cm stroke respectively). The performance improvements are clearly seen over the characteristics of a cast iron friction shoe mentioned above.
[0014] The reliability of the cast steel friction shoe when utilized in a traditional railway freight car bogie 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.
[0015] The cost of such railway freight car bogies utilizing such cast steel friction shoes will be lower as well over railway freight bogies 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 bogie utilizing the cast steel friction shoe will be extended as well.
[0016] According to another aspect of the present invention, there is provided a railway freight car bogie 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 position of said vertical 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, and 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 bolster sloped pocket having planar inner faces adjacent side walls of said friction shoe.
[0017] A preferred embodiment of the present invention will now be described by way of example only.
Figure 1 is a perspective view of a railway freight car bogie 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 bogie;
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 bogie;
Figure 4 is a side view of the friction shoe of the present invention; and
Figure 5 is a perspective view of the friction shoe of the present invention.
[0018] Referring now to Figure 1 of the drawings, a typical three piece railway freight car bogie is shown generally at 10. Railway freight car bogie 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.
[0019] 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.
[0020] 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 with 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.
[0021] 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.)
[0022] 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. 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.
[0023] While only a specific embodiment of the invention has been described and shown, it is apparent that various modifications can be made therein. It is, therefore, the intention in the appended claims to cover all such modifications and alterations as may fall within the scope of the invention as defined by the attached claims.
said friction shoe (40) comprising a vertical rear wall (48) extending for about the entire lateral width of the friction shoe
a sloped wall (46) extending downwardly at an acute angle from a top position of lateral junction with a top position of said vertical rear wall (48),
a bottom section (44) extending from and generally perpendicular to a lower portion of said vertical rear wall (48) to a lower portion of said sloped wall (46),
side walls (52, 54) each extending from outer edges of said vertical real wall (48), said sloped wall (46) and said bottom section (44),
and an internal support wall (56) extending from a generally laterally central intersection
with an inner surface of said vertical rear wall (48) to a generally laterally central
intersection with an inner surface of said sloped wall (46),
and wherein said friction shoe (40) is comprised of cast steel.
wherein the coefficient of friction of the cast steel material is about 0.194 at a loading of 333 pounds per square inch (23.41 kilograms per square centimetre).
when installed in a freight car bogie (10),
has an energy dissipation in inch-KIPS of about 39.4 for a 0.80 inch stroke (44.5 kJ for a 2.032 cm stroke).
when installed in a freight car bogie (10) has an energy dissipation in inch-KIPS of about 23.9 for a 0.50 inch stroke (27.0 kJ for a 1.27 cm stroke).
wherein said friction shoe (40) is comprised of an AISI/SAE Grade 1527 steel.
a vertical rear wall (48) extending for about the entire lateral width of the friction shoe,
a sloped wall (46) extending downwardly at an acute angle from a junction with a top portion of said vertical rear wall (48),
a bottom section (44) extending from and generally perpendicular to a lower portion of said vertical wall (48) to a lower portion of said sloped wall (46),
and at least one support wall (56) extending between an inner surface of said vertical
rear wall (48) and an inner surface of said sloped wall (46),
and wherein said friction shoe (40) is comprised of cast steel.
two laterally space sideframes (12, 14), a bolster (16) extending transversely between said sideframes (12, 14),
said bolster (16) having two ends (22, 24), each end extending into an opening in each sideframe (30),
a spring group (32) in each sideframe opening (30) to support said bolster end (22, 24) and a friction shoe (40) in each sloped pocket, said friction shoe (40) comprising a vertical rear wall (48) extending for about the entire lateral width of the friction shoe (40),
a sloped wall (46) extending downwardly at an acute angle from a top position of lateral junction with a top position of said vertical rear wall (48),
a bottom section (44) extending from and generally perpendicular to a lower portion of said vertical rear wall (48) to a lower portion of said sloped wall (46),
side walls (52, 54) each extending from outer edges of said vertical real wall (48), said sloped wall (46) and said bottom section (44),
and an internal support wall (56) extending from a generally laterally central intersection
with an inner surface of said vertical rear wall (48) to a generally laterally central
intersection with an inner surface of said sloped wall (46),
and wherein said friction shoe (40) 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.
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 (23.41 kilograms per square centimetre).
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 (35.15 kilograms per square centimetre).
wherein said friction shoe cast steel has an energy dissipation in inch-KIPS of about 39.4 for a 0.80 inch stroke (44.5 kJ for a 2.032 cm stroke).
wherein said friction shoe cast steel has an energy dissipation in inch-KIPS of about 23.9 for a 0.50 inch stroke (27.0 kJ for a 1.27 cm stroke).
wherein said friction shoe (40) is comprised of an AISI/SAE Grade 1527 steel.