Abstract:
A constant-contact load-bearing assembly for a railcar truck bolster and operable against a complementary body bolster bearing and biased to continuously contact the body-bolster bearing to transfer the lading and railcar weight forces, which assembly has an outer element of a first coefficient of friction, a second or inner element with a second and larger coefficient of friction and biasing apparatus to maintain the inner assembly pad element in contact with the body-bolster assembly at an empty-railcar condition to provide control of the railcar body at the empty or unloaded car status with the biasing apparatus compressible at a loaded railcar state to provide contact between the outer pad element and the body-bolster bearing pad for transfer of the railcar loads and forces over the range of operating loads between the empty-car state and the loaded to capacity state.

Description:
BACKGROUND OF THE INVENTION 
     Railway trucks generally include a truck bolster coupling a pair of side frames at their midpoints and include the wheels, axles, journal bearings, suspension systems and ancillary equipment. The railcars usually include a truck assemblies at either end of the railcar with the railcar body mounted on the truck bolsters at a body bolster. Railcars may broadly be classed into those with center-plate assemblies for the transfer of loads and control of car body and truck positions, and those with the load borne outboard of the center plate position. Both of these car types utilize side bearing assemblies between the car body bolster and the truck bolster, however, in the first noted railcar type the side bearings are utilized to avoid extreme displacement from car body roll, but in the second case the full weight of the railcar and lading is continuously borne by the side bearing assembly. 
     In general, the side bearing assemblies include an upper or body-bolster side bearing and a lower or truck-bolster side bearing, which upper and lower side bearings will be referred to as either a side bearing or side bearing assembly. In addition, the side bearings are usually paired, that is a first side bearing is provided between the truck bolster center and one of the side frames of the truck assembly and a second side bearing is provided equidistant to the first but between the truck bolster center and the other of the side frames. 
     In U.S. Pat. No. 4,030,424 to Garner et al., a rigid railway truck provides side bearing assemblies to bear the weight of the railcar, which bearing assembly is mounted over the spring assembly of the truck. This bearing assembly has a bearing guide which may be hollow or solid, but is illustrated with reinforcing ribs. A resilient support of an elastomeric member is mounted on the ribs and a bearing member is affixed atop the elastomer with a low friction bearing material on the bearing member. This laminate like bearing is provided in the disclosed truck on or over the side frame. 
     U.S. Pat. No. 5,024,166 to Alhborn et al. discloses a railcar truck assembly with the load borne outside the center plate region, however, the load is borne by leaf springs anchored outboard of the lateral cheeks but above the rails. 
     U.S. Pat. No. 4,434,720 to Mulcahy et al. teaches a multirate side bearing assembly for a railway truck with a center plate assembly, which carries and transfers most of the vertical load to the truck bolster and sideframes. In this apparatus, the side bearing is utilized to provide load support to a limited degree, but more importantly is utilized to damp car body-truck rocking motion. The apparatus includes alternative embodiments of laminate arrays of elastomers with intermediate solid plate-like structures. However, under an empty car condition it is considered that the bearing assemblies would support the weight of the railcar, at least in the static state. The second resilient device is mounted next to the first or empty-car resilient device, and this second device of greater compression and shear properties is fitted with wear plates at its top and bottom. The roll or yaw stiffness is generally provided by the second resilient device. At a loaded car state, the first resilient device is compressed, the second resilient device is contacted by the car body and the center plate contacts the truck bolster center-plate opening, which center plate is the primary force transfer mechanism in this car body and truck bolster arrangement. 
     U.S. Pat. No. 5,138,954 to Mulcahy discloses a railcar truck bolster with distal ends outboard of the truck side frames and having the car body weight at the side sills supported at these distal ends. The friction side bearings provide a combination pad with a major friction body of a relatively low friction material and at least one second friction body inserted in the low friction material, which second body is a relatively high friction material. The bearing embodiments illustrated and taught are in the form of an arcuate body to mate with a concave seat. These bearings will tilt in their seat to level themselves with the car body wear pad. This second friction body is dependent upon the first or low friction material for its relative position and maintenance of its base as the second friction body is only operable against the first friction body. 
     SUMMARY OF THE INVENTION 
     A constant-contact load-bearing assembly for a ligthweight railcar has a body-bolster bearing and a truck-bolster multi-element arrangement, which truck-bolster element is spring biased against the truck bolster and operable to continuously bear the car weight at either the loaded or empty state. The truck bolster load-bearing assembly has a first and outer element with a generally central passage therethrough. A second or inner element is provided in the central passage with a biasing spring in a recess in the truck bolster between the bolster and the inner element, which spring biases the inner element against the body-bolster side bearing. As a practical matter the body bolster most generally includes a wear pad to bear against the truck-bolster load-bearing assembly. At an empty-car state the wear pad abuts or contacts the truck-bolster bearing inner pad and the biasing spring supports the car body against contact with the truck bolster or side frame. At the loaded or partially loaded state, the railcar body bolster, and specifically the wear pad, compresses the truck-bolster inner pad and bias spring to contact the first or outer pad of polymeric material. This outer pad polymer does have a bulk modulus and is slightly compressible, but along with the similarly situated load-bearing assemblies, it will sustain the weight of the loaded railcar. The coefficient of friction of the outer pad polymer is substantially lower than the coefficient of friction of the inner pad material, which permits relatively unrestrained movement of the truck relative to the bolster especially during travel around curves. Although the inner pad is continuously biased against the wear pad, the primary load carrying function is accommodated by the outer pad, which load carrying function is understood to be related to the contact area of the truck-bolster outer pad with the body-bolster load bearing element. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     In the Figures of the drawing, like numerals refer to like components and in the drawing: 
     FIG. 1 is a plan view of the preferred embodiment of the truck-bolster load bearing assembly; 
     FIG. 2 is a cross-sectional view of the truck-bolster load bearing assembly of FIG. 1 taken along the line 2--2; 
     FIG. 3 is a cross-sectional view of the truck-bolster load bearing assembly of FIG. 1 taken along the line 3--3; 
     FIG. 4 is a plan view of an one-half of an exemplary truck bolster with the load bearing assembly in position; 
     FIG. 5 is an elevational view in the railcar longitudinal direction of the half-bolster of FIG. 4; 
     FIG. 6 is a plan view of an alternative load bearing arrangement; 
     FIG. 7 is a cross-sectional view of the load bearing arrangement of FIG. 6 taken along the line 7--7; and, 
     FIG. 8 is a front elevational view of one-half of a body bolster with an exemplary body-bolster load bearing pad. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A constant-contact, spring-biased, dual coefficient of friction load-bearing assembly or pad 10 for one side of a railcar truck bolster 12 with one end 13 in a side frame 15 is illustrated in FIGS. 4 and 5. More specifically, load-bearing assembly 10, hereafter load bearing 10, is shown in enlarged detail in FIGS. 1, 2 and 3. A complementary body-bolster load bearing or pad 14 is illustrated in FIG. 8 and downwardly extends from body bolster 16 on bottom 18 of railcar body 20. Body-bolster pad 14 is secured to lower end 22 of load bearing support 24. The illustration of FIG. 8 is merely exemplary of a body-bolster load bearing structure and position, as the figure includes a center plate structure, which is not utilized with the present invention. Body bolster 16 and truck bolster 12 are generally aligned and parallel in a railcar assembly. In such assembly body-bolster pad 14 and truck-bolster load bearing 10 are generally vertically aligned for contact between pad 14 and load bearing assembly 10. 
     Although a railcar is not illustrated, it is known to have a longitudinal axis, a railcar body, a first end, a second end and generally a truck assembly at each of the first and second ends. A typical three-piece railcar truck assembly (not shown) has first and second side frames 15 connected by truck bolster 12. The complete truck assembly would include axles, wheels, springs and ancillary components, but these elements are not included within the present invention. Truck bolster 12 is either matable with or coupled to body bolster 16, thus connecting the truck assembly with railcar body 20. 
     In FIG. 1, load-bearing assembly 10 is shown with an elliptical shape, but this shape is merely illustrative, not a limitation. Load-bearing assembly 10 has a first and outer pad 26 of a material with a relatively low coefficient of friction in comparison to the coefficient of friction for the material of second or inner pad 28. Steel pad 30, which is generally centrally located in first pad 26, may be a mild steel and has second or inner pad 28 nested therein with upper surfaces 32 and 36 approximately coplanar, as an illustration not a requisite. 
     Outer pad 26 in FIG. 1 provides a base or housing-like support for inner pad 28 and is noted with a significantly greater area of bearing or top surface 32 than the combined areas of surfaces 34 and 36. This difference in area between surfaces 32 and 34,36 is illustrated herein, but is not a requirement for operation of the invention. Second bearing surface 34 of inner pad 28 has a significantly smaller surface and contact area than surface 32. In the complementary or contacting relationship between body-bolster pad 14 and truck-bolster pad 10, the mating surfaces 14, 32 and 34 may not be in a perfect mated relationship even at a reference position, that is with the empty railcar at rest, but the interaction between the surfaces for either the empty railcar or loaded railcar state is not dependent upon perfect mating of these surfaces. 
     In the preferred embodiment, second or inner pad 28 is nested in steel pad 30, which is slidably positioned for reciprocation in throughport 40 of first pad 26. The clearance between pad 26 and pad 30 in throughport 40 should be a minimal amount, but adequate to allow for sliding of pad 26 in throughport 40. This collection of elements 26, 28 and 30 are mountable on upper surface 42 of truck bolster 12 as noted in FIG. 3. In this figure, truck bolster 12 has recess 44 in upper surface 42, and in cooperation with undercut 47 in lower surface 49 of first pad 26 they provide cavity 51 to receive a first Belleville spring 46 and a second Belleville spring 48 serially arranged against the bottom 50 of recess 44. Although only first and second Belleville springs 46 and 48 are shown in the Figure, it is known that more and different types of springs may be utilized or accommodated in cavity 51 to bias pads 30 and 28, as required. Upper surface 52 of first spring 46 is in contact with lower surface 54 of steel pad 30, which springs 46 and 48 cooperate to bias steel pad 30 and second pad 28 into contact with body-bolster pad 14. In this illustration, first pad 26 has second undercut or relief section 60 at the intersection of surface 32 and throughport 40 for ease of assembly, operation of steel pad 30 and to inhibit migration of lubricant from surface 32 to second bearing surface 34. 
     At a reference state, the illustrated configuration of FIG. 3 has upper surface 34 displaced above first-pad upper surface 32 by a distance x. This separation or travel distance is the compression or travel available for second or inner pad 28 and 30 to control and maintain contact with body-bolster pad 14, and thus railcar body 20 at the empty railcar state. At a full or lading bearing state for railcar body 20, second pad 28 and steel pad 30 will be compressed against the bias force of springs 46 and 48, which have a spring rate great enough to bear the weight of the empty railcar. Pads or surfaces 26 and 28 are slightly compressible, but the compressibility or deflection from the illustrated state is a minimal compression and will not be further considered. At the loaded railcar state, pads 26 and 28 are in contact with body-bolster pad 14, which pads are considered relatively incompressible and provide a surface area large enough to sustain the weight of a fully loaded railcar. 
     In operation, there are broadly speaking two operational modes: the empty-railcar state, wherein the load or force is the weight of the railcar; and, the loaded or lading-bearing state wherein the load or vertical force is the sum of the railcar and lading weights. The preferred embodiment of truck-bolster load bearing pad 10 has first pad 26 of a low-coefficient-of-friction material, such as a thermoplastic with additions of Teflon and silicon. A plurality of tests of this product have shown a coefficient of friction of 0.10 and lower, and this product has sustained its operability over a testing period, which has not been previously sustainable with other known high-polymer products. It is known that low coefficient of friction measurements are attainable on a surface by lubricating the surface with a compound such as oil, however, only recently has the above-noted thermoplastic compound been provided, which would maintain a low coefficient of friction surface during an operating period and under operational conditions. Oil is not generally utilized between pads 14 and 26,28 as it may be squeezed from between the contacting surfaces, thereby obviating its lubricity; it retains grit between the pads thereby potentially increasing the coefficients of friction therebetween; and, it may deteriorate some polymeric pad materials. 
     Second or inner pad 28 is a second material, such as a urethane product with a coefficient of friction between about 0.18 and 0.24, which coefficient is also sustainable during operational conditions and for extended operating periods, not merely for a single test. An alternative second pad material may have a coefficient of friction greater than 0.18. It is the ability to maintain their relative coefficients of friction that now enable the present load bearing assemblies to be assembled and tested for manufacture and use. These pads 26 and 28 contact body-bolster pad 14, which may be a hard material such as stainless steel or another hard polymer, and continuously abrade against this pad 14. The continuous wear between the pad surfaces and the entrapment of tramp materials between these surfaces has historically abused and eroded these surfaces and increased the coefficient of friction of each of the surfaces. As a consequence, no known continuous contact load bearing assembly has maintained the low coefficient of friction requisite to continuous long-term operation. 
     In an alternative embodiment, wear plate 62 may be provided on recess bottom 50 to contact Belleville spring 48, which thus avoids direct wear on the surface of bottom 50. Wear plate 62 may be of any hard wearing material. 
     In the alternative embodiment of FIGS. 6 and 7, load bearing assembly 70 has first pad 26 with passage 40. However, second pad 28 is directly nested in passage 40 and positioned against spring 46 in cavity 51. Second pad 28 may either a metal of an operable hard polymer. In addition, lower surface 54 in any of the embodiments may be hardened to inhibit wear between piston 30 and spring 46, as well as alternatively interposing a plate similar to plate 62 between surface 54 and spring 46. 
     The present invention provides a spring biased, constant-contact side-bearing assembly with a dual coefficient of friction pad surface from the utilization of separate materials for the empty or reference railcar state and the loaded or laden railcar state. The lower coefficient of friction material of pad surface 32 reduces the torsional resistance to turning between body-bolster pad 14 and truck bolster 12 to encourage ease of turning and cornering between a truck assembly and a railcar. Further, this constant-contact, dual-rate side bearing arrangement allows the introduction of a lower weight truck assembly and the elimination of the center plate assembly for the truck assembly, which is the predominant truck assembly structure presently in use in the United States. 
     Those skilled in the art will recognize that certain variations can be made in the illustrated embodiments. While only specific embodiments of the invention have been described and shown, it is apparent that various alterations and 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 true scope of the invention.