Claims
- 1. In a railway truck assembly having a pair of elongated, laterally spaced metal side frames each having a longitudinally central open area and an elongated metal bolster having the ends thereof extending at least into said open areas, respectively, and supported therein by upwardly extending spring arrangements carried by said side frames with the upper ends thereof in engagement with the undersurfaces of said ends of said bolster, respectively, to support said bolster for movement relative to said side frames, wherein each end of said bolster has opposed downwardly open and open ended pockets with sloping inner surface means converging downwardly with respect to each other and each of said side frames has at the longitudinally spaced ends of said open area thereof essentially vertically extending first surfaces spaced outwardly of the open end of the one of said pockets adjacent thereto, a friction assembly comprising:
- a metal friction member adapted to be disposed at least partially within a given one of said pockets adjacent a respective one of said first surfaces with a vertically extending second surface thereof in slidable engagement with said one of said first surfaces, said friction member having a surface extending in spaced confronting relatioship to the said sloping inner surface means of said one of said pockets to provide a pair of spaced confronting surfaces;
- an elastomeric means comprised of a pair of laterally spaced elastomeric portions located between said pair of spaced confronting surfaces with each of said portions having a pair of spaced exterior surfaces which are engageable, respectively, with said pair of spaced confronting surfaces;
- at least one of said exterior surfaces of said elastomeric means being slidable with respect to the one of said pair of spaced confronting surfaces in engagement therewith;
- helical coil spring means engageable with said friction assembly;
- means for supporting said helical coil spring means with respect to said friction assembly in a manner to maintain said friction assembly in continuously biased engagement with the respective said first surface and inner surface means;
- said elastomeric means having an elastic characteristic that said vertically extending second surface of said friction member is in stationary engagement with the respective said first surface during an initial extent of relative movement of said bolster with respect to said side frames in either one of opposite vertical directions and in sliding engagement with said first surface cooperable therewith after said initial extent, with said initial extent being of relatively constant magnitude throughout repeated cycles of said relative movement in said opposite directions and said continuously biased engagement being maintained at a relatively uniform magnitude of bias during the transition from said stationary engagement to said sliding engagement.
- 2. The friction assembly as claimed in claim 1 wherein the other of said exterior surfaces of said elastomeric means is mechanically restrained with respect to the respective said spaced confronting surfaces in engagement therewith.
- 3. The friction assembly as claimed in claim 2 wherein said other exterior surface is mechanically interlocked with said respective spaced confronting surface.
- 4. The friction assembly as claimed in claim 3 wherein said elastomeric means includes laterally projecting portions and such bolster includes laterally spaced portions which are engageable by said laterally projecting portions to limit the magnitude of lateral movement of said friction assembly with respect thereto.
- 5. The friction assembly as claimed in claim 2 wherein said other exterior surfaces is confined by abutment means with respect to said respective spaced confronting surface.
- 6. The friction assembly as claimed in claim 1 wherein said elastomeric means includes laterally projecting portions and such bolster includes laterally spaced portions which are engageable by said laterally projecting portions to limit the magnitude of lateral movement of said friction assembly with respect thereto.
- 7. The friction assembly as claimed in claim 1 wherein said spaced confronting surfaces are generally parallel surfaces.
- 8. The friction assembly as claimed in claim 7 wherein said generally parallel surfaces are generally planer parallel surfaces.
- 9. The friction assembly as claimed in claim 1 wherein said friction means includes a pair of laterally spaced friction members and said vertically extending second surfaces thereof form a respective pair of laterally spaced surfaces which diverge laterally from said pocket with said laterally spaced surfaces engaging respective laterally spaced portions of the respective said first surface.
- 10. The friction assembly as claimed in claim 9 wherein said elastomeric means includes a pair of elastomeric means engaging the respective said friction members.
- 11. The friction assembly as claimed in claim 1 wherein each said sloping pocket surface means and each respective said first surface comprise a pair of laterally spaced surface portions which converge laterally outwardly toward the intervening friction means and elastomeric means.
- 12. The friction assembly as claimed in claim 1 wherein said friction means comprises a body member having laterally spaced wing portions and an intervening retention spring portion, said wing portions having a pair of laterally spaced surfaces which confront respective laterally spaced surface portions of said sloping surface means to receive and retain respective laterally spaced portions of said elastomeric means therebetween.
- 13. The friction assembly as set forth in claim 12 wherein said pairs of elastomeric portions are cooperable with such pockets, respectively, for lateral restraint of said body members within the respective said pockets.
- 14. The friction assembly as set forth in claim 13 wherein said body members additionally include abutment means which are cooperable with the respective said elastomeric portions to mechanically restrain said elastomeric portions with respect to said wing portions.
- 15. The friction assembly as set forth in claim 14 wherein said elastomeric portions include lip portions which overlie a laterally outer extent of each respective one of said wing portions for further mechanical restraint of said elastomeric portions with respect to said wing portions.
- 16. The friction assembly as claimed in claim 1 wherein said at least one of said exterior surfaces is both of said exterior surfaces of said elastomeric means.
- 17. The friction assembly as set forth in claim 1 wherein said helical coil spring means is supported by a retention spring support portion of such a bolster.
- 18. The friction assembly as set forth in claim 1 wherein said helical coil spring means is supported by a retention spring support portion of such a side frame.
- 19. In a railway truck assembly the combination comprising:
- a pair of laterally spaced elongated, upstanding rigid axle supported structures, each having a generally longitudinally central open area;
- a rigid car body support structure having portions thereof extending within said open areas;
- generally vertically extending spring arrangements carried by said axle supported structures and engaging undersurfaces of said portions of said car body support structure, respectively to support said car body support structure for relative movement with respect to said axle supported structures;
- each said portion having pockets which open downwardly and outwardly toward the longitudinal ends of said axle supported structure, said pockets including sloping surfaces which converge toward a point generally longitudinally centrally of said axle supported structure;
- said axle supported structures having essentially vertically extending first surface means located outwardly adjacent said open end of a respective one of said pockets and each said vertically extending first surface means comprising a pair of laterally adjacent first surfaces which diverge from the respective said pocket;
- metal friction shoe means supported adjacent said laterally adjacent first surfaces, each said friction shoe means including a pair of laterally adjacent vertically extending second surface portions which are maintained in complementary slideable engagement with said laterally adjacent first surfaces, respectively;
- each said friction shoe means having a surface extending generally in spaced confronting relationship to said sloping surface of the respective said pocket to provide a respective pair of spaced confronting surfaces;
- helical coil spring means engageable in biased engagement with downwardly facing surfaces of said friction shoe means and supported with respect thereto to maintain said friction shoe means in biased engagement within said pockets, respectively;
- elastomeric means located between said pairs of spaced confronting surfaces with spaced exterior surfaces thereof engaging said pairs of spaced confronting surfaces, respectively, at least one of said exterior surfaces of each said elastomeric means being slideable with respect to the one of said pair of spaced confronting surfaces in engagement therewith; and
- each said helical coil spring means exerting a biasing force on the respective said friction shoe means with said biasing force being maintained at a substantially uniform magnitude when the respective said friction shoe means is stationary relative to the respective said laterally adjacent first surfaces.
- 20. The combination as set forth in claim 19 wherein said shoe means includes a pair of laterally adjacent friction shoes, each said shoe having one of said pair of laterally adjacent surface portions.
- 21. The combination as set forth in claim 19 wherein said biasing force is maintained at a substantially uniform magnitude with respect to the force of said biased engagement.
- 22. The combination as set forth in claim 21 wherein said shoe means includes a pair of laterally adjacent friction shoes, each said shoe having one of said pair of laterally adjacent surface portions.
- 23. In a railway truck assembly having a pair of elongated, laterally spaced metal side frames each having a longitudinally central open area and an elongated metal bolster having the ends thereof extending at least into said open areas, respectively, and supported therein by partially compressed spring arrangements supported by said side frames and having the upper end portions thereof in engagement with the undersurfaces of said ends of said bolster, respectively, to support said bolster for movement relative to said side frames, wherein each end of said bolster has opposed downwardly open and open ended pockets with sloping inner surface means that converge downwardly with respect to each other and each of said side frames has at each of the longitudinally spaced ends of said open area an essentially vertically extending first surface located outwardly adjacent the open end of the respective one of said pockets adjacent thereto and forming a given included angle with the respective sloping inner surface means, a friction assembly comprising:
- a metal friction means located in a given one of said pockets and adjacent the respective one of said first surfaces with a vertically extending second surface thereof in slidable engagement with such a first surface, said friction means having laterally spaced surface means extending in spaced confronting relationship to the respective sloping inner surface means of such a pocket to provide respective, laterally spaced pairs of confronting surfaces;
- elastomeric means located between said pairs of confronting surfaces with spaced exterior surfaces of said elastomeric means being engageable with the respective said confronting surfaces;
- at least one of said exterior surfaces of said elastomeric means being slidable with respect to the one of said confronting surfaces in engagement therewith;
- helical coil spring means engageable with said friction means in a manner to bias said friction means into engagement with the respective first surface to maintain a normal force therebetween and to bias said elastomeric means into engagement with the respective sloping inner surface;
- said elastomeric means being deformable in a manner to control and limit said normal force to maintain said second surface in stationary engagement with such a first surface during an initial portion of relative movement of said bolster with respect to said side frames.
- 24. The friction assembly as set forth in claim 23 wherein the ratio of the shear modulus to the compression modulus of said elastomeric means is greater than M Tan a where a is such an included angle and M is the coefficient of friction between said elastomeric means and said metal friction means.
- 25. A railway truck assembly comprising:
- a pair of elongated, laterally spaced upstanding rigid side frames each having an elongated opening with opposed, longitudinally spaced and essentially vertically extending first surfaces;
- an elongated rigid bolster having longitudinal end portions thereof located intermediate said vertical first surfaces, respectively;
- upwardly extending spring arrangements carried by said side frames with the upper ends thereof in engagement with the undersurfaces of said bolster to support said bolster for movement relative to said side frames;
- each said end portion of said bolster having a pair of pocket means which open outwardly toward the respective said vertical first surfaces and downwardly, each said pocket means including sloping inner surfaces which diverge downwardly with respect to said vertical first surfaces, respectively;
- friction assemblies received within said pocket means with each said friction assembly comprising a rigid friction member and an elastomeric means;
- each said rigid friction member having an essentially vertically extending second surface disposed in slideable engagement with the respective said vertical first surface, and another surface extending generally in spaced essentially parallel and coextensive relationship with the respective said sloping inner surface to provide pairs of spaced confronting surfaces;
- said elastomeric means being located between said pairs of spaced confronting surfaces with spaced exterior surfaces thereof in engagement with said pairs of spaced confronting surfaces, respectively;
- helical coil spring means engageable in biased engagement with said friction assemblies and supported with respect thereto for biasing said friction assemblies into engagement with said vertical first surfaces and said sloping inner surfaces, respectively;
- said elastomeric means being resiliently deformable to permit relative movement between the respective said rigid friction member and said bolster in engagement therewith and to provide the sole direct connection between the respective said rigid friction member and said bolster throughout such relative movement therebetween;
- at least one of said exterior surfaces of each said elastomeric means being slideable with respect to the one of said pair of spaced confronting surfaces in engagement therewith; and
- said elastomeric means being deformable under loading imposed thereon by said bolster and the respective said rigid friction member in a mnner to permit a range of vertical movement of said friction member with respect to said bolster and to maintain said vertically extending second surfaces of said friction member in stationery engagement with said first surfaces, respectively, during relative movement of said bolster with respect to said side frames which includes movement in either of one of opposite vertical directions until such movement in either of said opposite vertical directions is of an extent that at least one of said friction members slides over the one of said first surfaces cooperable therewith, with said extent being relatively constant throughout repeated cycles of said movement in said opposite vertical directions.
- 26. A railway truck assembly as set forth in claim 25 wherein said range of vertical movement is at least one-half inch
- 27. A railway truck assembly as set forth in claim 25 wherein said elastomeric means is deformable primarily in shear under such loading.
- 28. A railway truck assembly as set forth in claim 25 wherein said relative movement further includes relative lateral movement in either one of opposed, generally horizontal directions and said extent for such relative lateral movement is different from the said extent for relative vertical movement.
- 29. A railway truck assembly as set forth in claim 25 wherein said relative movement further includes relative rotational movement in either one of opposite rotary directions and said extent for such relative rotational movement is different from the said extent for relative vertical movement.
- 30. A railway truck assembly as set forth in claim 25 wherein both of said spaced exterior surfaces of said elastomeric means are slidable with respect to the one of said pair of spaced confronting surfaces in engagement therewith.
- 31. A railway truck assembly as set forth in claim 25 wherein the other of said spaced exterior surfaces of siad elastomeric means is restrained from sliding movement with respect to the one of said pair of spaced confronting surfaces in engagement therewith.
- 32. A railways truck assembly as set forth in claim 25 wherein said sloping inner surfaces and the respective said first surfaces form an included angle in the range of approximately 30.degree. to approximately 50.degree..
- 33. A railway truck assembly as set forth in claim 25 wherein said helical coil spring means is supported by said bolster.
- 34. A railway truck assembly as set forth in claim 25 wherein said helical coil spring means is supported by said side frames.
- 35. A railway truck assembly as set forth in claim 25 wherein all of said friction means are slideable simultaneously over the respective said vertical first surfaces cooperable therewith.
- 36. The railway truck assembly as set forth in claim 25 wherein said at least one of said exterior surfaces is both of said exterior surfaces of each of said elastomeric means.
- 37. The railway truck assembly as set forth in claim 25 wherein said sole direct connection is the sole operative connection between said rigid friction member and said bolster throughout such relative movement therebetween.
- 38. A railway truck assembly comprising:
- a pair of laterally spaced rigid first structures adapted to be supported by railway truck wheels;
- an elongated rigid second structure adapted to support a car body and having longitudinal ends thereof located adjacent said first structures, respectively;
- spring arrangements extending generally vertically between said first and second structures, respectively, to support said second structure for movement relative to said first structures;
- each said longitudinal end having a portion which is cooperable with an adjacent portion of the respective said first structure to form a friction assembly retention means;
- in each said retention means, one of said portions including a wear surface and the other of said portions including an open ended pocket which opens toward the respective said wear surface and includes a sloping inner surface which diverges generally vertically from the respective said wear surface;
- friction assemblies retained by said retention means with each said friction assembly comprising a rigid friction means and an elastomeric means;
- said rigid friction means having respective first surfaces disposed in slideable engagement with said wear surfaces, repectively, and respective second surfaces extending generally in spaced essentially parallel and coextensive relationship with respect to said sloping surfaces, respectively, to provide pairs of spaced confronting surfaces;
- said elastomeric means being located between said pairs of spaced confronting surfaces with spaced exterior surfaces thereof engageable with said pairs of spaced confronting surfaces, respectively, to provide the sole direct connection between said rigid friction means and said second structure;
- helical coil spring means engageable with each said rigid friction means and supported with respect thereto in a manner to compressively deform said elastomeric means between the respective said pairs of spaced confronting surfaces and to maintain said friction assemblies in biased engagement with the respective said wear surfaces and sloping surfaces;
- at least one of said exterior surfaces of each of said elastomeric means being slideable with respect to the one of said pair of spaced confronting surfaces in engagement therewith;
- said elastomeric means, when compressively deformed between said respective pairs of spaced confronting surfaces, being further deformable in a manner to permit a range of vertical movement of said rigid friction means with respect to said pocket and to maintain said first surfaces of said rigid friction means in stationary engagement with said wear surfaces, respectively, during an initial extent of relative movement between said first and second structures which includes vertical movement in either one of opposite vertical directions and in sliding engagement on said wear surfaces engaged therewith after said initial extent, with said initial extent being of relatively constant magnitude throughout repeated cycles of said vertical movement in each of said opposite vertical directions.
- 39. A railway truck assembly as set forth in claim 38 wherein each said pocket is included in said portion of said second structure.
- 40. The railway truck assembly as set forth in claim 38 wherein each said pocket is included in said portion of said first structure.
- 41. In a railway truck assembly having a pair of elongated, laterally spaced rigid side frames each having a longitudinally central open area and elongated rigid bolster with longitudinal ends that extend into the open areas, respectively, and are supported therein for movement relative to the side frames by spring arrangements carried by the side frames, and wherein each longitudinal end of the bolster and adjacent portions of the side frames, respectively, provide friction assembly retention means including downwardly open and open ended pockets and essentially vertically extending wear surfaces spaced outwardly of the open ends of the respective pockets to accommodate friction assemblies which are received at least partially within each respective pocket and in engagement with each respective wear surface, the combination comprising:
- a rigid friction means adapted to be disposed in a given one of such pockets with a first surface thereof in slideable engagement with the respective one of such wear surfaces and with a second surface thereof extending in spaced confronting relationship to an inner surface means of the pocket to provide a pair of spaced confronting surfaces;
- an elastomeric means located between said pair of spaced confronting surfaces with a pair of spaced exterior sufaces of said elastomeric means being engageable with the respective said pair of spaced confronting surfaces;
- at least one of said exterior surfaces of said elastomeric means being slideable with respect to the one of said pair of spaced confronting surfaces in engagement therewith;
- helical coil spring means supported with respect to said rigid friction means and engageable with a downwardly facing surface thereof to maintain said rigid friction means in biased engagement with such a wear surface and to maintain said elastomeric means in biased engagement with said pair of spaced confronting surfaces; and
- means for laterally restraining mutually engaged portions of the other of said exterior surfaces of said elastomeric means and the one of said spaced confronting surfaces engaged therewith in a manner to transmit relative lateral shear forces in a given lateral direction between said elastomeric means and said respective one of said spaced confronting surfaces.
- 42. The combination as set forth in claim 41 wherein said means for laterally restraining is operative within the lateral periphery of said elastomeric means.
- 43. The combination as set forth in claim 42 wherein said means for lateral restraining is operative solely within the lateral periphery of said elastomeric means.
- 44. The combination as set forth in claim 42 wherein said means for laterally restraining includes mechanically interfering means having respective, mutually engaged surface portions which support such relative lateral shear.
- 45. The combination as set forth in claim 44 wherein said other of said exterior surfaces and the respective one of said spaced confronting surfaces in engagement therewith include intermeshing projections and depressions disposed within the lateral periphery of said other of said exterior surfaces.
- 46. The combination as set forth in claim 41 wherein said elastomeric means further includes laterally projecting portions which are engageable with respective laterally spaced portions of such a pocket to limit the magnitude of lateral movement of said elastomeric means with respect thereto.
- 47. The combination as set forth in claim 46 wherein said laterally projecting portions overlie respective laterally outer portions of said friction means intermediate said friction means and laterally adjacent side wall portions of such a pocket.
- 48. A railway truck assembly comprising:
- a pair of elongated, laterally spaced upstanding rigid side frames each having an elongated opening with opposed longitudinally spaced and essentially vertically extending first surfaces;
- an elongated rigid bolster having longitudinal end portions thereof located intermediate said vertical first surfaces, respectively;
- upwardly extending spring arrangements carried by said side frames with the upper ends thereof in engagement with undersurfaces of said bolster to support said bolster for movement relative to said side frames;
- each said end portion of said bolster having pocket means which open outwardly toward the respective said vertical first surfaces and downwardly and each said pocket means including a sloping inner surface which diverges downwardly with respect to the respective said vertical first surface;
- friction assemblies received within said pocket means with each said friction assembly comprising a rigid friction member and an elastomeric means;
- each said rigid friction member having an essentially vertically extending second surface disposed in slideable engagement with the respective said vertical first surface, and another surface extending generally in spaced essentially parallel and coextensive ralationship with the respective said sloping inner surface; to provide pairs of spaced confronting surfaces;
- said elastomeric means being located between said pairs of spaced confronting surfaces and having spaced exterior surfaces thereof in engagement with said pairs of spaced confronting surfaces, respectively;
- helical coil spring means engageable in biased engagement with said friction assemblies and supported with respect thereto for biasing said friction assemblies into engagement with said vertical first surfaces and said sloping inner surfaces, respectively;
- said elastomeric means being resiliently deformable to accommodate relative movement between the respective said rigid friction member and said bolster and to provide the sole direct connection between said rigid friction member and said bolster throughout such relative movement therebetween;
- said elastomeric means providing at least one of a pair of mutually engaged, relatively slideable surfaces to further accommodate such relative movement between the respective said rigid friction member and bolster;
- said elastomeric means being deformable under loading imposed thereon by said bolster and the respective said rigid friction member in a manner to permit a range of vertical movement of said friction member with respect to said bolster and to maintain said vertically extending second surfaces of said friction member in stationary engagement with said first surfaces, respectively, during relative movement of said bolster with respect to said side frames which includes movement in either one of opposite vertical directions until such movement in either one of said opposite vertical directions is of an extent that at least one of said friction members slides over the one of said first surfaces cooperable therewith, with said extent being relatively constant throughout repeated cycles of said movement in said opposite vertical directions.
- 49. The railway truck assembly as set forth in claim 48 wherein said sole direct connection is the sole operative connection between said rigid friction member and said bolster throughout such relative movement therebetween.
BACKGROUND OF THE INVENTION
This application is a continuation-in-part of application Ser. No. 741,299, filed June 4, 1985, which is a continuation-in-part of application Ser. No. 467,565, filed Feb. 17, 1983, which is a continuation-in-part of application Ser. No. 278,755, filed June 29, 1981, all now abandoned.
In the railway industry it has been common practice to support the opposite ends of a freight car body on spaced-apart, wheeled truck assemblies for traverse of standard gauge railway track. The standard wheeled truck assembly is generally referred to as a three-piece truck because its principal structural members are a pair of spaced side frames which extend generally longitudinally of the opposite sides of the freight car body, respectively, and an elongated bolster which extends transversely of the freight car body. The side frames of each such truck are supported on plural wheel and axle sets, commonly two sets, which are spaced apart along the track. The longitudinal ends of the bolster are received in openings in the opposed side frames, respectively, and are supported therein by a suspension system including respective spring sets to permit movement of the bolster relative to each of the opposed side frames. In various configurations of spring sets the springs extend between a spring seat on the side frame and a respective undersurface of the bolster spaced above the spring seat. The freight car body is supported adjacent its longitudinal ends by respective central portions of the bolsters in the respective spaced truck assemblies.
Such support of a freight car body permits the freight car body to rock laterally with respect to the longitudinal axis of the bolsters, that is, transversely of the track as the freight car travels over normal track. Normal track is frequently non-uniform due to such causes as differential track settlement resulting from non-uniform ballast or foundation under the railway ties, excess rail wear, and/or rail misalignment. Thus, under normal operating conditions the wheel movements in the truck assemblies may be such that energy imparted to the truck suspension system will cause the car body to bounce or sway. With the commonly used spring suspension system a car body has a natural resonant frequency of sway and bounce and, if the track surface and alignment are such as to cause the car body to sway or bounce at its resonant frequency, the truck wheels can become unloaded; that is, the forces between the wheels and rail can be significantly reduced and in the extreme can become nil and the wheels are lifted from the rail. Frequently, as a freight car body sways, the wheels on opposite sides of the car body may be alternately unloaded. Any wheel unloading substantially increases the risk of derailment.
The most common expedient presently being employed to dissipate the energy imparted to the suspension system of a truck assembly is a friction assembly utilizing a rigid metal friction wedge or friction shoe to damp relative motion between the bolster and the side frames. The use of rigid friction shoes or wedges is so common that practically all the freight cars built in the past 40 years have bolsters with opposed pockets formed in the longitudinal ends thereof for receiving friction shoes. U.S. Pat. No. 3,461,815 illustrates a more recent design of a friction assembly with shoe members received within bolster pockets. The respective side frames are provided with replaceable wear plates outwardly adjacent the open ends of the bolster pockets so that opposed friction shoes at each end of the bolster engage the opposed rigid side frame wear surfaces. Such friction wedges and wear plates, which are normally cast steel members, tend to "stick" or resist sliding movement until the force applied to the friction wedge reaches a magnitude which is sufficient to overcome the static friction force existing between the engaged surfaces of the wedge and the wear surface. Once such static friction force is overcome, the friction wedges suddenly breakaway and slide with respect to the respective adjacent wear surfaces. This "stick-slip" frictional action provides dynamic friction damping of the relative movement between the bolster and side frame; however, such a damping system has adverse consequences due to the abrupt nature of the "stick-slip" action. For example, in an empty car the force required to cause sliding of a wedge or the break away friction force of the combined suspension groups can approach the weight of the empty car body so that the benefit of the respective spring group is effectively nullified and the car body is in effect directly coupled to the side frames and wheel sets. When such effective coupling occurs, the force inputs to the bolsters and side frames can cause structural fatigue problems. The "stick-slip" effect occurs prior to overcoming the friction between the engaged friction surfaces, regardless of the direction of the impending motion between a bolster and side frame. That is, vertical or lateral forces, or a combination thereof can be imposed between the bolster and side frames as a freight car travels over typical railway track.
Rigid friction wedges must fit up in the bolster pockets and for such purpose the inner inclined surfaces of the bolster pocket is provided with an outwardly spherically convex or crowned surface to provide a centering force reaction between the bolster surface and the back or sloped surface or face of the friction wedge. This more or less centered reaction between the bolster pocket and wedge is necessary to provide a uniform pressure between the opposed wedge face and the column wear plate as the bolster rotates about either its vertical or longitudinal axis relative to the side frame. If the contact interface, that is the reaction resultant between the sloping inner surface of the bolster and the surface of the wedge, is over to one side of the bolster pocket or near the top or bottom of the sloped surface of the bolster pocket, the friction generating pressure between the wedge surface and the column wear plate will vary accordingly to the location of the contact interface. The "as cast" surfaces of the bolster pockets and the wedges are sufficiently imprecise when assembled new, even when within specified tolerances, to cause serious friction damping variations and even bolster-side frame lock up. Additionally, the softer nonheat treated pocket surfaces wear sufficiently in a short period of service to permit the crown of the wedge to literally wear into the bolster surface causing bolster pocket reactions to transfer readily to the wedge. Such "camming" behavior between the wedge, bolster pocket and column wear plate causes accelerated wear and high strains resulting in potential early failure and replacement or repair of each or all of these aforementioned related truck components.
Another type of friction wedge utilizes spaced winged surfaces. Rigid, constant, load, friction, winged shoe wedges similar to the embodiment showing sloped portions or surfaces on either side of a central spring retaining cavity, also require crowned surfaces on the slopes to insure that the reactions from the bolster slope interaction occur near the center of the sloped surface area. The degenerative wear implications follow the same pattern as the earlier discussed variable load rigid friction wedges.
The inventor in this application has previously developed elastomeric materials for use as friction elements as shown and described in U.S. Pat. No. 4,230,047, now Reissue Patent No. 31,784, and U.S. Pat. No. 4,295,429, which are incorporated herein in their entirety by reference for a better understanding of the present invention. The elastomeric friction elements disclosed in the identified patents offer improved damping for all modes of relative bolster to side frame motion; however, the use of friction elements made entirely of an elastomeric materials may not provide the most desirable modes of operation. Specifically, the elastomeric elements as decribed in the identified patents are confined by the surfaces of the column wear plate, bolster and spring biased follower such that the elastomeric elements are simultaneously placed in normal compression and shear with respect to all the confining surfaces. As the bolster moves in various modes, such elastomeric elements will deform and move, that is, slide partially relative to all of their confining surfaces, and with sufficient movement of the bolster with respect to the side frames, the elastomeric element will slide bodily in its deformed condition with respect to the column wear surface. Under operating conditions, non-uniform pressures will occur on the various confined surfaces of the elastomeric elements that will cause the elastomeric elements to deform, bunch up, or compress in the areas of highest pressure, especially along the column wear surface where the elastomeric elements are required to slide appreciable distances. Such deformation can overstrain portions of an elastomeric element thus causing those portions to take a permanent set and/or lose some of their resiliency or fail structurally. When the resiliency of an elastomeric element loses uniformity, its ability to operate as described in the identified patents may be substantially impaired. In addition, under repeated high force levels applied to an elastomeric element, the elastomer may well become overheated which also effects the elasticity of the element. Under extreme operating temperature the elastomer can experience a modulus of elasticity or stiffness reduction of such magnitude that relative motion between the bolster and side frame results primarily in deformation of the elastomeric element with minimal sliding and without generating any substantial frictional restraint at the column guide wear surfaces. Under these conditions, the elastomeric friction element will not operate as described in the identified patents. When excessive deformation of the elastomeric element occurs without sliding at the column wear plate, there is insufficient friction generated by the elastomeric element to provide the desired damping of the bolster motion. Also, overstraining and overheating thereof can cause deterioration of an elastomeric friction element.
Mechanical factors also can adversely affect the friction force produced by an elastomeric element as shown in the identified patents. For example, the friction generating metal surfaces, that is, the wear surfaces on the columns which mate with the elastomeric member, are generally not machined or precision surfaces. The steel wear plates are usually bolted or welded to the side frames and, as a result, the edges of countersunk fastener receiving holes, fastener heads and/or weld fillets may well be encountered by the surface of the elastomeric element as it moves on the wear plate surfaces. Any of these conditions can cause excessively high friction and localized shear forces which may result in gouging or accelerated wear on the elastomeric friction generating surface.
In addition to rigid or elastomeric friction elements, hydraulic snubbers have been used to dissipate the energy input to a railway truck assembly; however, such snubbers do not rely upon friction to dissipate energy. Such snubbers are mentioned herein only to emphasize that control of the force inputs to a truck assembly requires the conversion of a sufficient amount of the input energy into heat energy and thereafter dissipation of the heat energy to the atmosphere.
The present invention in one form is a composite elastomeric friction element of a structure which permits the elastomer portion to be selected primarily with reference to its intended control function. Preferably, the elastomeric friction element consists of a block or mass of elastomeric material which is received in a bolster pocket located adjacent to a column guide wear surface, and a rigid metal member which is engageable with the elastomer and the column guide wear surface. With such a metal member, the portion of the elastomeric mass adjacent to the metal member is generally uniformly loaded both in shear and compression, and the metal member distributes the applied loading along the adjacent portion of the elastomeric mass. Further, a metal member can provide improved abrasion and wear resistance with respect to an imperfect column wear surface as compared to an elastomeric element directly engaging such an imperfect column wear surface. By isolating the elastomeric portion from the friction surface, the effects described above are significantly reduced and the elastomer deformation capabilites are distributed more uniformly over the entire elastomer volume. The elastomeric element thus can furnish a more optimum control of the relative motion between a bolster and the side frames of the truck by resilient deformation of the elastomer mass and further response characteristics prior to or concurrently with static friction break when sliding movement occurs between the friction element metal face and the column wear surfaces.
An additional preferred embodiment of the present invention resides in locating an elastomeric mass or element for controlling the relative motion of a bolster relative to column wear surfaces in spaced rleationship to the engaged column guide friction surfaces whereby the stress and heat effects arising at the engaged friction surfaces are additionally isolated from the elastomeric mass. Specifically, the elastomeric element is located between the inner surface of a bolster pocket and the member which biases a friction surface into engagement with a column wear surface. Such further spacing of the elastomeric element from the stress and heat generating friction surfaces permits the elastomeric material to be selected essentially on the basis of its elastic control capabilites since the problems associated with non-uniform stress and heat generation are substantially reduced or eliminated. Further, such location of the elastomeric element permits the elastomeric element to be geometrically and dimensionally optimized and reduced to the most economical volume.
Accordingly, a principal object of this invention is to provide a new and improved resilient elastomeric element for controlling relative motion between a bolster and side frame wear surfaces.
Another object of this invention is to provide a new and improved friction element for controlling relative motion between a bolster and side frame wear surfaces in which the elastomer provides more optimum bolster pocket load transfer to the friction element assembly with resulting more uniform wedge pressures on the column faces with less friction face wear, and the volume of a reslient elastomeric mass is essentially determined solely by the deformation properties of the elastomeric mass.
Another object of this invention is to obtain a new and improved friction assembly for a railway truck in which an elastomeric member provides an improved bolster pocket load transfer to the friction wedge to minimize bolster pocket wear.
Another object of this invention is to obtain a new and improved friction assembly for a railway truck in which an elastomeric member provides an improved bolster pocket load transfer to the friction wedge wherein relatively uniform pressures are exerted on the friction surfaces of the side frame columns.
Another object of this invention is to provide a new and improved friction element having a resilient elastomeric portion of a selected minimum mass which is sufficient to control the relative motion between a bolster and side frame wear surfaces.
Still another major object of this invention is to provide a friction element having a resilent elastomeric portion spaced from the engaged column guide friction surfaces.
Another object of this invention is to provide a friction element in which a metal friction face and a spring biased follower element may be combined in a single piece that can be cast or made from the same material.
Still another object of the invention is to provide a friction element which includes a resilient elastomeric portion of optimal mass and geometry determined solely on the basis of the resilient deformation properties of the elastomeric mass.
Yet another object of the invention is to provide a friction element including a resilient elastomeric portion which provides for maximum area of surface contact with one bolster pocket wall opposed to the column guide wear surface.
Another object of the invention is to provide a friction assembly which is adaptable to the geometry of a standard three-piece truck and within the limits of that geometry is able to provide improved modes of dynamic damping response including resilient flexibility in three dimensions.
A more specific object of the invention is to provide a composite friction element having rigid and elastomeric portions which fulfills the objects hereinabove set forth.
US Referenced Citations (12)
Foreign Referenced Citations (1)
| Number |
Date |
Country |
| 1178123 |
Nov 1984 |
CAX |
Continuation in Parts (3)
|
Number |
Date |
Country |
| Parent |
741299 |
Jun 1985 |
|
| Parent |
467565 |
Feb 1983 |
|
| Parent |
278755 |
Jun 1981 |
|
Patent Grant
4915031
