Abstract:
A constant contact spring bearing for use with a railway car truck bolster is provided. Greater design flexibility and installation tolerances are available because a longer travel spring, with potentially lower spring load rate and stress rate, may be used. The present invention facilitates the establishment of loadings that may be expected to fall reliably within set-up tolerances from unit to unit. Instead of mounting the spring bearing on the surface of the truck bolster top member, the present invention provides a recess in the truck bolster to receive the spring, allowing for use of longer springs. With longer travel springs available for use, a spring may be selected with a lower load rate and a lower stress rate.

Description:
FIELD OF THE INVENTION 
     The present invention relates to side bearings for truck bolsters, and more particularly, to improved constant contact type side bearings mountable on a truck bolster to contact the underside of a railcar body. 
     BACKGROUND OF THE INVENTION 
     The usual freight railcar comprises a car body supported on at least one, and usually two, wheeled trucks that are confined to roll on rails. Each truck includes a truck bolster that extends essentially transversely of the car body longitudinal center line and pivotally supports the car body. In the preponderance of freight cars in domestic use, the pivotal connection is made by center bearing plates and center plate bowls transversely centered on the car body underframe and the truck bolster. Accordingly, the truck may turn or pivot on the center plate under the car body and, under certain dynamic conditions and car speeds during operation, the truck may tend to adversely oscillate or &#34;hunt&#34; in a yaw-like manner beneath the car body. Also, the car body is subject to adversely roll from side to side during operation. Side bearings positioned on the truck bolster outwardly of the center plate bowl are commonly employed to control both such adverse conditions by frictionally retarding oscillations and cushioning and limiting the extent of the rolling motions. 
     Constant contact type side bearings usually include a base that is fastened to the top of the bolster and a cap that is biased upward from the base so as to contact bearing pads on the car body underframe. The cap must be free to move vertically with respect to the base, and during the course of operation, the clearance between those parts will be enlarged due to abrasion and wear. Various examples of prior art side bearings are provided in the art, including: U.S. Pat. No. 3,748,001 (1973) to Neumann et al.; U.S. Pat. No. 3,897,737 (1975) to Davis; and U.S. Pat. No. 4,130,066 (1978) to Mulcahy. 
     Other side bearing structures are shown, for example, in U.S. Pat. No. 4,434,720 (1984) to Mulcahy et al. and in U.S. Pat. No. 5,138,954 (1992) to Mulcahy. 
     Various structures have been suggested for use as side bearings. Prior art side bearings have frequently used coil springs mounted on the upper surface of a top member of a truck bolster. The coil springs used in the prior art side bearings have had a relatively large spring rate, that is, the load per unit deflection, to support the weight of the car. With such high spring rates, great care was necessary in installation of the springs, or the two side bearings could exert an uneven load on the bottom of the railcar, putting the railcar out of balance. For example, if a bearing spring with a spring rate of 4,000 pounds per inch (lb/in) was used, a variation in placement of the bearings that deflected one spring one tenth of an inch more than the other spring would result in 400 pounds of additional force being exerted on one side of the car than on the other side. Accordingly, it was necessary to ensure that both springs were properly deflected at rest to assure balanced loading of the railcar by the springs. Thus, the prior art presents problems of a low tolerance for error in placement of the side bearings, as well as the problem of non-uniform or unbalanced loading of the railcar if the side bearings fell outside of those close tolerances. 
     In addition, many of the springs used in the prior art side bearings have had a relatively high stress rate, so that at the loaded height of the spring, the spring was under significant stress, tending to fatigue the spring and decrease its useful life. 
     SUMMARY OF THE INVENTION 
     The present invention allows for greater flexibility in side bearing design, and in particular, greater flexibility in the choice of springs used in side bearings. It also allows for greater tolerances in the placement of side bearings without sacrificing uniform or balanced loading of the railcar body by the side bearings. The invention facilitates the establishment of loadings that may be expected to fall reliably within set-up tolerances from unit to unit. It also reduces the stress on the springs to improve the useful life of the bearing. 
     The present invention provides a constant contact side bearing that allows for use of a lower spring rate so that a difference between specified nominal set-up height and actual installed set-up height results in a smaller difference between desired and actual loading of the railcar by the springs. Lower stress rates may also be used to improve the useful life of the bearing. The present invention allows for use of springs with lower spring rates by increasing the lengths of the springs, and by providing a suitable housing for the longer travel springs without adding substantially to the structure of the truck bolster. 
     In one aspect, the present invention provides, in a railway truck of the type having a pair of side frames and a truck bolster extending between the side frames, wherein the truck bolster includes a top member, a bottom member spaced from the top member and an interior between the top member and the bottom member, the improvement wherein the truck bolster includes a spring supported within the interior of the truck bolster. The spring extends from an interior end in the interior of the truck bolster to an exterior end outside of the truck bolster. 
     In another aspect, the present invention provides a side bearing for use with a railway truck of the type having a pair of side frames and a truck bolster extending between the side frames for supporting a railroad car body. The side bearing comprises a housing support, a vertical member extending from one side of the housing support to an end, a spring support at the end of the vertical member and a spring. The spring has a lower end on the spring support and an upper end extending past the housing support. 
     In another aspect the present invention provides in a railway truck of the type having a pair of side frames and a truck bolster extending between the side frames, the improvement wherein the truck bolster comprises an apertured top member, a bottom member spaced from the top member, a pair of spring housings within the interior of the truck bolster. Each spring housing has an open upper end and includes a spring support within the interior of the truck bolster and aligned with the aperture of the top member of the bolster and a vertical member extending from the spring support to the top member of the truck bolster. The truck bolster also has a spring within each spring housing. Each spring has an interior end on the spring support within the interior of the truck bolster within the spring housing and an exterior end extending out of the aperture in the top member of the truck bolster. A bearing surface is on the exterior end of each of the springs for bearing against a portion of a railroad car body. 
     In another aspect the present invention provides in a railway truck of the type having a pair of side frames and a truck bolster extending between the side frames, the improvement wherein the truck bolster comprises a top member with a pair of recesses defining spring housings. Each recess includes a spring support and a vertical member extending between the spring support and the top member of the truck bolster. A spring is within each recess. Each spring has an interior end on the spring support and an exterior end extending beyond the top member of the truck bolster on the exterior of the truck bolster. A bearing surface is on the exterior end of the spring for contacting a portion of a railroad car body. 
     In another aspect the present invention provides in a railway truck of the type having a pair of side frames and a truck bolster extending between the side frames, wherein the truck bolster includes a top member, a bottom member spaced from the top member and an interior between the top member and the bottom member, the improvement wherein the truck bolster comprises a spring supported within the interior of the truck bolster. The spring extends from an interior end in the interior of the truck bolster to an exterior end. An end cap is on the exterior end of the spring. The end cap has a bearing surface outside of the truck bolster. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a prior art railroad car truck with two side bearings on its bolster. 
     FIG. 2 is a top plan view of a portion of the prior art truck bolster and side bearing of FIG. 1. 
     FIG. 3 is a partial cross-section taken along line 3--3 of FIG. 2, showing part of the side bearing in cross section. 
     FIG. 4 is a top plan view of a portion of a truck bolster with a side bearing of the present invention. 
     FIG. 5 is a cross-section taken along line 5--5 of FIG. 4. 
     FIG. 6 is a cross-section taken along line 6--6 of FIG. 4. 
     FIG. 7 is a top plan view of a portion of a truck bolster with another embodiment of the side bearing of the present invention. 
     FIG. 8 is a cross-section taken along line 8--8 of FIG. 7. 
     FIG. 9 is a cross-section of an alternative embodiment of a side bearing and portion of a truck bolster. 
     FIG. 10 is a cross-section of an alternative embodiment of a side bearing and portion of a truck bolster. 
     FIG. 11 is a cross-section of an alternative embodiment of a side bearing and portion of a truck bolster. 
     FIG. 12 is a cross-section of an alternative embodiment of a side bearing and truck bolster. 
     FIG. 13 is a cross-section of an alternative embodiment of a side bearing and truck bolster. 
     FIG. 14 is a cross-section of an alternative embodiment of a side bearing and truck bolster. 
    
    
     DETAILED DESCRIPTION 
     In FIGS. 1-3, a prior art side bearing, generally designated 10, is shown on a truck bolster, generally designated 12. Two such side bearings are provided on each truck bolster 10, spaced from and outboard from the center plate 14 of the truck bolster. Each such prior art side bearing generally includes a base housing 16 to be mounted by bolts, for example, on the top member 18 of the truck bolster 12. One or more springs 20 are mounted within the base housing 16, covered by an end cap 22. The cap and base are typically made of high tensile steel, and the cap is generally positioned to move vertically on the base. Typically, the end cap comprises a top bearing surface 24 that frictionally engages a bearing pad that is mounted on the underside of a car body part such as a body bolster (not shown). 
     Coil springs used in such prior art side bearings have been limited: the potential loaded length of the spring depends upon the distance between the top member 18 of the truck bolster 12 and the bearing pad of the railcar body to be supported; possible spring rates to provide the desired load or pre-load have also been limited by the types of springs available, and the types of springs available have been limited by the lengths of the springs. As illustrated in FIG. 3, each spring bearing may include more than one spring of different characteristics, to achieve proper loading of the railcar under different circumstances. The bearing shown in FIGS. 2-3 is described more fully in U.S. Pat. No. 4,130,066 (1978) issued to Mulcahy and assigned to Amsted Industries Incorporated. Other styles of bearings have been used in the prior art. 
     In the side bearing 100 of the present invention, illustrated in FIGS. 4-14, lower usable spring load and stress rates are achieved by increasing the lengths of the springs 102 that can be used while still supplying the desired load to the car body. To increase the length of the spring 102, a recess 104 is formed in the top member of the truck bolster, so that the spring is seated below the top member or compression member 106 of the truck bolster 108, within the interior 110 of the truck bolster. 
     In the first illustrated embodiment of FIGS. 4-6, two recesses 104 are formed in the truck bolster, each comprising an interior base or spring support 112, comprising a plate in the illustrated embodiments, within the interior 110 of the truck bolster. The top member 106 of the truck bolster 108 has a pair of rectangular apertures 114 vertically aligned with the interior base plates 112. The springs 102 may rest on the base spring support plates 112 and extend through the apertures 114 to the exterior of the bolster 108. 
     In the first illustrated embodiment, each side bearing 100 has a pair of springs 102 sitting side by side on the support plates 112, with parallel axes of elongation. Each of the illustrated springs 102 is a coil spring, although it should be understood that other types of springs, such as elastomeric springs, may be used, are within the scope of the invention, and are included in the term &#34;spring&#34; as used in this patent. In addition, it should be understood that it is not necessary to use two side-by-side springs in each side bearing; a single spring could be used, as shown in FIGS. 7-8, or multiple springs could be used, in a side by side arrangement as shown in FIGS. 4-6, or in a co-axial arrangement as well (not shown). 
     On the exterior of the illustrated truck bolster 108, a single end cap 116 rests on the upper exterior ends 117 of the pair of springs 102 in each side bearing. Each illustrated end cap 116 has a top bearing surface 118 to frictionally engage the bearing pad on the underside of the railroad car body and side walls 119 extending downward from the top bearing surface 118. It should be understood that end caps as shown in the illustrated embodiments are not necessary, and that other forms of bearing surfaces may be used with the present invention. In the case of a polymer spring, for example, the upper surface of the polymer could be the bearing surface; alternatively, a metal bearing surface could be joined to a polymer spring. 
     In the illustrated embodiment, the side bearings 100 are located outboard of the center 120 of the truck bolster and inboard of the side frames and outboard ends 123 of the truck bolster 108 of the railway truck. As shown in FIGS. 4 and 7, the side frames would be mounted at the positions designated 122 inboard of the ends 123 of the bolster, in the manner shown in FIG. 1. 
     The interior base plates 112 may be positioned in the interior of the truck bolster, that is, the space between the top member 106 of the truck bolster 108 and its bottom or tension member 124. The bottom member 124 of the truck bolster may comprise the interior base plate or spring support 112. The interior base plates 112 provide interior support for the lower interior ends 125 of the springs 102, and any shape that will provide this support will suffice. 
     The interior base plates or spring supports 112 may be suspended from the top member 106 of the truck bolster 108 as shown in FIGS. 4-6. As there shown, in each side bearing of the first illustrated embodiment, a housing support plate 126 surrounds the rectangular aperture 114 and rests on the upper surface 127 of the top member 106 of the bolster 108. In the first illustrated embodiment, vertical members or walls 128 are integral with and depend downward from the inner opening 129 of the horizontal housing support plate 126 to the interior base plate 112. 
     Alternatively, the vertical members or walls 128 and interior base plate 112 could be cast as integral parts of the truck bolster without a separate annular plate, as shown in the embodiment of FIGS. 7-8, where like numbers have been used to indicate parts equivalent to those of the embodiment of FIGS. 4-6. In this embodiment, a single coil spring 102 is shown in the bearing. 
     On the upper surface 127 of the top member 106 of the bolster 108, the side bearings 100 may include exterior housings 130 extending upward from the bolster. These exterior housings 130 may comprise vertical sidewalls 132 that may be integral with the horizontal support plate 126, as shown in FIGS. 4-6, or that may be integral with the top member 106 of the bolster 108 as shown in FIGS. 7-8, or that may be separate annular housings secured to the top member 106 of the bolster 108 or to the horizontal support and the top member of the bolster by bolts or otherwise. 
     The exterior housing sidewalls 132 may be on the interior of the end cap 116 side walls 119, as shown in the embodiment of FIGS. 4-6, or on the exterior of the end cap 116 side walls 119 as shown in the embodiments of FIGS. 9-12. Alternatively, the side bearing may omit an exterior housing and the end cap 116 side walls 119 may extend into the interior of the recess 104, as shown in the embodiments of FIGS. 13-14. In the embodiments of FIGS. 9-14, the same numbers have been used for like parts as in the embodiments of FIGS. 4-8. 
     As shown in FIGS. 12-14, the side bearing may include means for limiting non-vertical movement of the end cap 116. For example, there may be a wedge 140 disposed between the sidewalls 119 of the end cap 116 and the sidewalls 132 of the exterior housing 130, with one or the other of the sidewalls 132, 119 sloped to match the sloped face 142 of the wedge 140. The side bearing may include biasing means 144, such as a coil spring, to push the wedge 140 upward as shown in the embodiment of FIG. 14, instead of or in addition to a spring acting on the end cap 116. 
     The wedge 140 in this instance is a self adjustable spacing member. As set forth in U.S. Pat. No. 5,086,707 issued in 1992 to Charles P. Spencer and Terry L. Pitchford entitled &#34;Self Adjusting Constant Contact Side Bearing for Railcars&#34;, the entire disclosure of which is incorporated by reference herein, the vertical movement of the end cap with respect to the housing may cause the clearance between these elements to increase because of wear and abrasion. And pivotal movement of the truck beneath a car body will apply large frictional forces to the end cap in a generally longitudinal direction of the car body tending to wear the longitudinal ends of the cap and housing. As longitudinal wear occurs the cap becomes free to move longitudinally and thus, the ability to dampen oscillations (hunting) of the truck is reduced. Also, the longitudinal forces tend to cant or tilt the cap with respect to the base and that tendency increases as the clearance between the cap and base becomes enlarged through wear. When the cap becomes canted, the ability to dampen oscillations and cushion roll will be further hindered. This problem is addressed in the embodiments illustrated in FIGS. 12-14, wherein the wedge 140 acts as a shim to limit or prevent undesirable non-vertical movement between the end cap and the exterior housing. The illustrated wedges eliminate play between the end caps and the sidewalls, that is, they eliminate non-vertical movement in a generally longitudinal direction along the car body. It should be understood that other means for limiting non-vertical movement may also be employed, including all those disclosed in U.S. Pat. No. 5,086,707, for example. It may be desirable to construct devices similar to those described in that patent using ball bearings and grooves instead of rollers. 
     The depending vertical walls 128 and support plates 112 illustrated in FIGS. 4-10 define recessed spring housings 150, and it may not be necessary to provide such housings, or housings of the form shown in the illustrated embodiments. It should also be understood that it is not necessary that the vertical walls of such housings extend around the full perimeter of the support plate; the interior support plate could be suspended from its corners, for example. If the bottom member of the bolster is used as the interior support for the springs, it may not be necessary to include any housing for the spring, as shown in the embodiment of FIG. 12. Two springs 102 could also be provided to act against the end cap 116 without placing them in separate housings 150, as shown in the embodiment of FIG. 13. In using the bottom member of the bolster as the base for the spring, it may be desirable to provide some structure to limit lateral movement of the spring within the interior of the bolster, but such a lateral limit need not be in the form of vertical walls 128 or a housing 150 as shown in FIGS. 4-10. For example, as shown in the embodiment of FIG. 11, an annular positioning ring 200 could be used either on the bottom member 124 of the bolster or on an interior support plate (not shown), to surround the outer diameter of the bottom end 125 of the spring 102, or an upstanding element could extend through the interior of the spring (not shown); either structure would comprise a vertical member that limits lateral movement of the spring. In addition, the recessed spring housing 150 could be cylindrical, for example, if a single coil spring were used. 
     The benefits of the present invention may be seen from a comparison of the properties of commercially available types of springs. Comparing three springs made by American Steel Foundries of Hammond, Ind., designated as 11-1-05016, 11-1-05016-A, and 11-1-05016-B: 
     
         ______________________________________   11-1-05016 11-1-05016-A                        11-1-05016-B______________________________________Load Rate  4193         2627      2262(lb/in)Stress Rate     85615        50798     43175(psi/in)Free      5.410        8.000     8.000Height(in)Solid     3.880        5.500     6.200Height(in)Travel (in)     1.530        2.500     1.800______________________________________ 
    
     Thus, for desired load of, for example, 4066 lbs. per spring, the calculated travel for each of the three springs would be 0.9697 inches, 1.5477 inches, and 1.797 inches, respectively and the calculated stresses at those deflections would be 83021.841 psi, 78623.777 psi, and 77608.111 psi, respectively. And while the prior art space limitations may not have permitted use of springs with a solid height as great as 5.5 or 6.2 inches, using the present invention allows for use of these springs, with their lower spring load rates and lower stress rates. With the lower spring load rates, there are greater tolerances in setting the bearings: an imbalance of 0.1 inch in height for a bearing with spring 11-1-05016, there would be a difference of 419 pounds of force, while that same imbalance with spring 11-1-05016-A would amount to a difference of 262 pounds of force. These springs and the values of their spring load and stress rates, free heights, solid heights and travel are given for purposes of illustration only, to demonstrate that use of a longer travel spring with a lower spring load and stress rate may be beneficial, and that the present invention offers the beneficial advantage of use of longer travel springs with lower spring load and stress rates. 
     In actual service, side bearings&#39; load rates may be expected to range from about 500 lb./in. to about 10,000 lb./in. The current invention allows for a lower spring rate with a potentially higher ultimate capacity. 
     It may be desirable in some instances to use multiple springs, such as concentric springs with different characteristics, or springs of other construction, such as polymer springs or Bellville washers, for example, alone or in addition to or instead of coil springs. For a polymer spring, it may be desirable to fill the entire recess with the polymer to limit lateral movement. 
     The exterior housing 130 and end cap 116 may be made of the same materials as currently used in the art for side bearing end caps, such as hardened steel. The interior support 112 and vertical walls 128 may be also be made of steel of the same type used to make the bolster 108. The horizontal plate 126 or surface suspending the bearing may be welded to the bolster if desired. 
     While only specific embodiments of the invention have been described, it is apparent that various alternatives and modifications can be made thereto. Those skilled in the art will recognize that certain modifications can be made in these illustrative embodiments. It is, therefore, the intention in the appended claims to cover all such modifications and alternatives as may fall within the true scope of the invention.