Abstract:
A long travel constant contact side bearing for railway cars provides better handling characteristics, achieving improved tracking and curving through use of various combinations of features. The side bearing comprises a base and a generally cylindrical wall section extending upwardly from the base. A cup-shaped cap comprises a generally circular top section and a generally cylindrical wall section extending downwardly therefrom. The cap extends into the wall section of the base. At least one coil spring is provided within the base and extends to the underside of the cap. The cup shaped cap includes a centrally located cut out section with an elastomer pad fitted within the cut out section. The cup shaped cap cylindrical wall sections can be coated with a lubricant or hardening substance.

Description:
BACKGROUND OF INVENTION 
     The present invention related to an improved side bearing for mounting on a railroad car truck bolster that allows long travel, substantial weight reduction, improved hunting and curving characteristics, longer service life and various ease of installation features. 
     In a typical railway freight train, such as that shown in  FIG. 1 , railway cars  12 ,  14  are connected end to end by couplers  16 ,  18 . Couplers  16 ,  18  are each received in draft sills  20 ,  22  of each respective car along with hydraulic cushioning or draft gear assemblies (unshown). Draft sills  20 ,  22  are provided at the ends of the railway car&#39;s center sill, and include center plates that rest in center plate bowls of railway car trucks  26 ,  28 . 
     As better shown in  FIG. 2 , each typical car truck  26  includes a pair of side frames  30 ,  32  supported on wheel sets  34 ,  36 . Bolster  38  extends between and is supported on springs  40  mounted on side frames. A bolster center plate  24  is provided having a central opening  42 . The bolster center plate bowl  24  received and supports a circular center plate of the draft sill  20 . Side bearing pads  60  are provided laterally to each side of center plate  24  on bolster  38 . Side frames  30 ,  32  comprise a top member  44 , compression member  46 , tension member  48 , column  50 , gib  52 , pedestal  54 , pedestal roof  56 , bearings  58  and bearing adapter  62 . 
     Constant contact side bearings are commonly used on railroad car trucks. They are typically located on the truck bolster, such as on side bearing pads  60 , but may be located elsewhere. Some prior designs have used a single helical spring mounted between a base and a cap. Others use multiple helical springs or elastomer elements. Exemplary known side bearing arrangements include U.S. Pat. No. 3,748,001 to Neumann et al and U.S. Pat. No. 4,130,066 to Mulcahy. 
     Typical side bearing arrangements are designed to control hunting of the railroad car. That is, as the semi-conical wheels of the railcar truck ride along a railroad track, a yaw axis motion is induced in the railroad car truck. As the truck yaws, part of the side bearing is made to slide across the underside the wear plate bolted to the railroad car body bolster. The resulting friction produces an opposing torque that acts to prevent this yaw motion. Another purpose of railroad car truck side bearings is to control or limit the roll motion of the car body. Most prior side bearing designs limited travel of the bearings to about 5/16″. The maximum travel of side bearings is specified by the Association of American Railroads (AAR) standards. Previous standards, such as M-948-77, limited travel to 5/16″ for many applications. 
     New standards have evolved requiring side bearings that have improved hunting, curving and other properties to further increase the safety and design of railcars. The most recent AAR standard is M-976 that now allows for longer travel side bearings and has several new requirements, such as new specifications for bearing preloads. Preload is defined as the force applied by the spring element when the constant contact side bearing is set at the prescribed height. 
     Under certain conditions, undesirable wear is caused to the railroad car body bolster due to contact with the side bearings. Further, undesirable wear may occur within the side bearing itself when two metallic components are moving in contact with each other. 
     SUMMARY OF THE INVENTION 
     There is a need for improved side bearings for railroad cars that can meet or exceed these new AAR standards, such as M-976 or Rule 88 of the AAR Office Manual, and M-948 for side bearings. 
     There also is a need for side bearings with better wear characteristics to increase service life. 
     There further is a need for side bearings that can be designed for a particular application by incorporating design features that prevent interchangeability of incorrect components for that application. 
     There also is a need for a side bearing having improved wear characteristics in contacting the freight car body bolster. 
     There also is a need for a standardized set of springs that can reduce parts inventories of various custom spring sizes. 
     The above and other advantages are achieved by various embodiments of the invention. 
     In exemplary embodiments, long travel can be achieved in a side bearing arrangement for railroad car trucks by a combination of features, including reduction of base and/or cap heights and/or reduction of the spring solid height to accommodate ⅝″ travel or more before the spring is fully compressed (solid) and before the base and cap bottom out. 
     In exemplary embodiments, substantial weight reduction is achieved by reducing sides and thicknesses of the base and cap in areas not needed for structural rigidity. 
     In exemplary embodiments, non-metallic inserts are provided in the flat top surface of the cap of the side bearing to reduce wear contact with the freight car body bolster. 
     In exemplary embodiments, non-metallic coatings are applied to the outer surface of the cap of the side bearing to reduce wear in the side bearing. 
     In exemplary embodiments, improved operation of the side bearing, including improved control and hunting characteristics, is achieved by careful control of longitudinal clearances between the cap and base. This has been found to be important to prevent excessive movement between the cap and base, as well as reduce associated impact forces, stresses and wear. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described with reference to the following drawings, wherein: 
         FIG. 1  is a schematic elevation of the coupled ends of two typical railroad cars; 
         FIG. 2  is a perspective view of a typical railway car truck for use with the present invention; 
         FIG. 3  is an exploded perspective view of an exemplary constant contact side bearing according to the invention; 
         FIG. 4  is a cross-sectional view of an exemplary constant contact side bearing according to the invention; 
         FIG. 4A  is a partial detailed view of the coil springs and spring base of an embodiment of the present invention; 
         FIG. 4B  is a cross-sectional view of an exemplary constant contact side bearing according to the present invention; 
         FIG. 5  is a perspective view of a spring base in accordance with an embodiment of the present invention; 
         FIG. 6  is a perspective view of a first exemplary constant contact side bearing base according to the invention; 
         FIG. 7  is a cross-sectional view of the first exemplary side bearing base; 
         FIG. 8  is a top view of the first exemplary side bearing base; 
         FIG. 9  is a perspective view of the exemplary side bearing cap with a non-metallic insert according to the invention, and 
         FIG. 10  is a perspective view of the exemplary side bearing cap without a non-metallic insert according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A first embodiment of a side bearing according to the invention will be described with reference to  FIGS. 3-10 . Side bearing assembly  100  has a major longitudinal axis coincident with the longitudinal axis of a railway car. That is, when the side bearing is mounted on railway truck bolster  38 , the major axis of the side bearing is perpendicular to the longitudinal axis of the bolster. Side bearing assembly  100  includes as main components, a base  110 , a cap  120 , and one or more resilient urging elements  130 , such as a spring or elastomer element, and spring base  131 . In the exemplary embodiment shown, there are provided two springs, outer spring  130 A, and inner spring  130 B that serve as the urging element, each of which may have a different spring constant to provide an overall combined load rating. 
     Base  110  is fixed to bolster  38  by suitable means. As shown, base  110  is bolted to bolster  38  by way of mounting bolts (not shown) passing through mounting holes  146  provided on base flanges  112 . 
     As best shown in  FIGS. 3 &amp; 4 , and  6 - 8 , base  110  has generally open cylindrical wall  116  that extends upwardly from base  110 . Wall  116  may include two openings  114 . Opening  114  serves as an opening for the head of a wrench used to tighten the bolts passing through bolt holes  146 . Opening  114  also serves to reduce weight of the base  110 . 
     To increase the travel length of the side bearing, walls  116  are reduced in total height by 5/16″ from prior designs, such as that used in U.S. Pat. No. 3,748,001. This helps to achieve greater travel of the spring before cap  120  and base  110  mate and prevent further travel. In an exemplary embodiment, base  110  has a total height of about 4.188 in. (+/−0.030), with walls  116  extending approximately 3.626 in. above flange  112 . 
     Referring to  FIGS. 3&amp;4  and  9 - 10 , cap  120  is cup-shaped and includes generally circular top section  119  downwardly extending general cylindrical side walls  121 , that enter base  110  open wall  116  in a telescoping fashion. As shown in  FIG. 4B , cap side walls  121  can include a protruding ridge  124  on side wall  121  that can be U or V shaped corresponding in location with opening  114  on an inner surface of base wall  116  to restrict or prohibit the rotation of cap  120  in base  110 . The downwardly extending side wall  121  of cap  120  extends into wall  116  of base  110  in such a fashion that even when the spring(s)  130  are at their free height or in an uncompressed condition, there is still provided an amount of overlap between side wall  121  and cylindrical wall  116 . 
     Cap  120  is further provided with a top contact surface  128 , lower stop edge  123 , and lower recessed spring support surface  127 . Preferably, all peripheral edges  129  are coped or rounded with a scoped or flat transition area  129 A extending from top contact surface  128  to edge  129 . This serves several purposes. It reduces weight of the cap. Moreover, by coping the corners, there is a better contact surface is made that abuts against a car body wear plate (unshown but located on the underside of a car body immediately above cap  120  in use). In particular, by having coped corners, it has been found that less gouging occurs on the car body wear plate when the cap slides and rotates in frictional engagement with the car body wear plate during use. To further assist in a better contact surface, top contact surface  128  is formed substantially flat, preferably within 0.010″ concave or 0.030″ convex to further improve wear characteristics. In particular, this bias reduces the chance of the edge “binding” against the wear plate and is easier to manufacture. 
     Further, in order to improve the wear of cap  120  top contact surface  128  against a freight car body bolster, top contact surface  128  includes a generally circular cut out section  119 . Circular cut out section or well  119  is usually about 0.187 inch in depth. Further, a generally circular elastomer or other suitable non-metallic pad  122  is received in cut out section  119 . Pad  122  is usually about 0.25 inch in thickness, so it typically protrudes from cut out section  119 . Notches  129  can be provided around the edges of cut out section  119  to aid in the insertion of a tool to remove and replace elastomer pad  122 . The actual depth of well  119  and the height of pad  122  are not critical; it is a part of the present invention that pad  122  protrudes above well  119 . 
     Non-metallic elastomer pad  122  can be of several compositions. One such composition is a combination of carbon, rubber and strengthening fiber that is mold formed. Other non-metallic elastomeric compounds also would be operative. 
     Further, side walls  121  of cap  120  can be coated with a lubricant to reduce the wear of cap  120  within walls  116  of base  110 . Such coating or sidewalls  121  can be a graphite lubricant impregnated into the metal surface or can be a hardening yet friction reducing coating such as titanium nitride. Similar coatings could be applied to the inside of walls  116  of base  110 . 
     To assist in providing long travel of the springs, cap  120  is shortened similar to that of base  110 . In an exemplary embodiment, cap  120  is shortened in height by 5/16″ over previous designs to allow further travel of spring(s)  130  before cap  120  and base  110  mate and prevent further travel. Cap  120  preferably has a total cap height of 3.875 in., with side wall  121  extending downward approximately 3.375 in. below lower support surface  127 . This allows the cap to insert farther onto base  110  before lower stop edge contacts the inside surface of base  110 . 
     As mentioned, the inventive side bearing cap  120  and base  110  can be used with one or more urging members, such as springs  130 . To achieve long travel of at least ⅝″, it is preferably to reduce the spring solid height from that used in prior designs. This is because prior spring designs would have gone solid before ⅝″ of travel was achieved. That is, the individual spring coils would have compressed against each other so that no further compression was possible. 
     Although two springs per side bearing are described in the embodiments, the invention is not limited to this and fewer, or even more, springs could be used. In fact, the number and size of springs may be tailored for a particular application. For example, lighter cars will use a softer spring rate and may use softer springs or fewer springs. Similarly, multi-unit articulated cars may use lighter or fewer springs because such cars use four side bearings instead of two per truck. As such, the load carrying capacity of each must be reduced. Also, it has been found that better performance can be achieved through use of substantially stiffer spring constants than previously used. This has been found to provide a suspension system with a slower reaction time, which has been found to achieve improved tracking and curving, without adversely affecting hunting. This has been found to result in reduced sensitivity to set-up height variations or component tolerances so as to achieve a more consistent preload on the truck system. This tends to equalize the loading and allow a railcar to stay more level, with less lean or roll both statically and dynamically. 
     To obtain longer fatigue life, the material used for base  110  and cap  120  can be Grade E steel or cast iron. To assist in longer service life, hardened wear surfaces are provided on the inside surfaces of base wall  116 . 
     Additionally, in an exemplary preferred embodiment, to prevent excessive movements and accelerated wear, reduced longitudinal clearances between cap  120  and base  110  are provided by reducing the tolerances from prior values. This can be achieved, for example, by more closely controlling the casting or other formation process of the cap  120  and base  110  side walls  116 . In a preferred embodiment, base  100  has a longitudinal distance of 7.000″ (+0.005/−0.015) between inside surfaces of side wall  116  and outside surfaces of side wall  121  of cap  120  have a longitudinal distance of 7.031″ (+0.000/−0.020). This results in a closely controlled combined longitudinal spatial gap having a minimum of 0.006″ and maximum of 0.046″. The minimum is achieved when base side wall  116  is at the maximum tolerance of 7.005″ and cap side walls  121  are at the minimum tolerance of 7.011.″ The maximum is achieved when the base side wall  116  are at the minimum tolerance of 6.985″ and the cap side walls  121  are at the maximum tolerance of 7.031.″ 
     Further, base  110  is seen to have a generally cylindrical opening  147  that is centrally located between flange  112 . As shown in  FIG. 5 , a spring base  149  is located in cylindrical opening  147 . Spring base  149  is generally circular, with two identical spring supports  151 ,  152  extending upwardly from a near center location. Spring supports  151 ,  152  are raised formed siding the inner support spring  130 A. These supports are located to reject springs not included in the correct group for the preload specified on the identification tab  153 . Spring base  149  is usually a fabricated steel component.