Patent Publication Number: US-9421986-B2

Title: Railroad car constant contact side bearing assembly

Description:
RELATED APPLICATION 
     This application is a divisional of U.S. patent application Ser. No. 13/507,144; filed on Jun. 7, 2012, now U.S. Pat. No. 8,813,655. 
    
    
     FIELD OF THE INVENTION DISCLOSURE 
     The present invention disclosure generally relates to railroad cars and, more specifically, to a constant contact side bearing assembly for a railroad car. 
     BACKGROUND 
     A typical railroad freight car includes a car body supported on a pair of wheeled trucks which are confined to roll on rails or tracks. Each truck includes a bolster extending essentially transversely of the car body longitudinal centerline. In the preponderance of freight cars, a pivotal connection is established between the bolster and railcar body by center bearing plates and bowls transversely centered on the car body underframe and the truck bolster. Accordingly, the truck is permitted to pivot on the center bearing plates under the car body. As the railcar moves between locations, the car body also tends to adversely roll from side to side. 
     Attempts have been made to control the adverse roll of the railcar body through use of side bearings positioned on the truck bolster outwardly of the center bearing plates. A “gap style” side bearing has been known to be used on slower moving tank/hopper railcars. Conventional “gap style” side bearings include a metal, i.e. steel, block or pad accommodated within an elongated open top pocket or recess defined on the truck bolster. An elongated and upstanding housing or cage, integrally formed with or secured, as by welding or the like, to an upper surface on the truck bolster defines the open top recess and inhibits sliding movement of the metal block relative to the bolster. As is known, a gap or vertical space is usually present between the upper surface of the “gap style” side bearing and the underside of the railcar body. 
     Other conventional “gap style” side bearings have included roller bearings carried for rolling movements within the elongated housing or carrier mounted on the upper surface of the railcar bolster. The roller extends above an uppermost extent of the housing or carrier and engages with an underside of the railcar body. Such side bearings are able to support the railcar body with respect to the bolster while at the same time permitting the bolster, and therefore the truck, freedom to rotate with respect to the car body as is necessary to accommodate normal truck movements along both straight and curved track. 
     Under certain dynamic conditions, coupled with lateral track irregularities, the railcar truck also tends to adversely oscillate or “hunt” in a yaw-like manner beneath the car body. The coned wheels of each truck travel a sinuous path along a tangent or straight track as they seek a centered position under the steering influence of the wheel conicity. As a result of such cyclic yawing, “hunting” can occur as the yawing becomes unstable due to lateral resonance developed between the car body and truck. Excessive “hunting” can result in premature wear of the wheeled truck components including the wheels, bolsters, and related equipment. Hunting can also furthermore cause damage to the lading being transported in the car body. 
     Track speeds of rail stock, including tank/hopper cars, continue to increase. Increased rail speeds translate into corresponding increases in the amount of hunting movements of the wheeled trucks. “Gap style” or those side bearings including roller bearings simply cannot and do not limit hunting movements of the wheeled trucks. As such, the truck components including the wheels, bolsters, and related equipment tend to experience premature wear. 
     The art has also contemplated constant contact side bearings for railcars. Constant contact railcar side bearings not only support a railcar body with respect to the bolster during relative rotational movements therebetween but additionally serve to dissipate energy through frictional engagement between the underside of the railcar body and a bearing element thereby limiting destructive truck hunting movements. Constant contact side bearings typically include a housing assembly including a base and a cap. The base usually has a cup-like configuration and includes at least two apertured flanges, extending in opposed radial directions relative to each other, permitting the base to be suitably fastened to the bolster. In one form, the cap is biased from the base and includes an upper surface for contacting and rubbing against a car body underside. The cap must be free to vertically move relative to the side bearing base. 
     Such constant contact side bearings furthermore include a spring. The purpose of such spring is to absorb, dissipate, and return energy imparted thereto during a work cycle of the side bearing assembly and resiliently position the upper surface of the cap, under a preload force, into frictional contact with the car body underframe. The spring for such side bearings can comprise either spring loaded steel elements or elastomeric blocks or a combination of both operably positioned between the side bearing base and the cap. An elastomeric block which has been found particularly beneficial is marketed and sold by the Assignee of the present invention under the tradename “TecsPak.” As will be appreciated, however, such an elastomeric block, by itself, lacks longitudinal stiffness and, thus, requires surrounding housing structure to provide added support and stiffness thereto. 
     There are several challenges presented in connection with the design of a constant contact side bearing assembly. First, and during the course of operation, the clearance between the base and cap of a constant contact side bearing housing assembly becomes enlarged due to abrasion and wear. Such wear is a critical detractor to side bearing assembly performance. That is, a gap or space between the base and cap of the side bearing housing assembly adversely permits longitudinal or horizontal shifting movements of the cap relative to the housing thereby reducing the energy absorption capability for the side bearing assembly—a critical operating criteria for the side bearing assembly. Of course, when the gap or space between the base and cap of the side bearing housing assembly reaches a critical limit, the side bearing assembly is no longer useful and will be condemned. 
     During operation of the railcar side bearing assembly, and while controlling any clearance or gap between the cap and housing of the side bearing assembly so as to limit horizontal shifting movements of the cap relative to the housing remains advantageous, the cap must remain able to vertically reciprocate relative to the housing. As will be appreciated, if the cap cannot vertically reciprocate during operation of the side bearing assembly, the primary purpose and function of the constant contact side bearing assembly will be lost. 
     Another design challenge involved with those constant contact side bearings using an elastomeric spring relates to the buildup of heat in proximity to the elastomeric spring. During operation of the railcar, frictional contact between the railcar body and the side bearing assembly results in the development of heat buildup. Unless such heat buildup can be controlled, the elastomeric spring will tend to soften and deform, thus, adversely affecting the operable performance of the constant contact side bearing assembly. 
     The frictional sliding relationship between the side bearing assembly and the related railcar component can create temperatures within the side bearing assembly that can exceed the heat deflection temperature of the elastomeric spring thus causing the elastomeric spring to deform. As used herein and throughout, the term “heat deflection temperature” means and refers to a temperature level at the which the elastomeric spring, regardless of its composition, tends to soften and deform. Deformation of the elastomeric spring can significantly reduce the ability of the elastomeric spring to apply a proper preload force and, thus, decreases vertical suspension characteristics of the side bearing assembly which, in turn, results in enhanced hunting of the wheeled truck. Enhanced hunting and/or unstable cyclic yawing of the truck increases the resultant translation/oscillation of the railcar leading to a further increase in the heat buildup and further deterioration of the elastomeric spring. 
     Thus, there is a continuing need and desire for a railcar constant contact side bearing assembly having components which are designed to optimize energy absorption and related performance criteria for the side bearing assembly while maintaining vertical reciprocity of the cap relative to the housing while furthermore inhibiting deterioration of an elastomeric spring resulting from localized heat. 
     SUMMARY 
     According to one aspect of this invention disclosure, there is provided a railroad car constant contact side bearing assembly including a housing and a plastic or non-metallic cap. The side bearing housing includes upstanding wall structure defining a central axis for the side bearing assembly. The non-metallic cap is arranged for generally coaxial movement relative to the housing an has a generally flat upper surface extending beyond the upper end of the housing wall structure. Moreover, the cap includes wall structure depending from the generally flat upper surface. The cap wall structure combines with the housing wall structure for guiding the cap for generally axial vertical movements. A spring biases the plastic cap into position and is accommodated within a cavity operably defined by the wall structures of the housing and cap. A metallic insert is maintained in operable association with the generally flat surface on the cap to slidably contact to with an underside of the railcar whereby allowing the side bearing assembly to establish a coefficient of friction ranging between about 0.4 and about 0.9 with the railcar during operation of the constant contact side bearing assembly. 
     Preferably, the insert maintained in operable association with the cap is formed from a metal material selected from the class of: steel and austempered ductile iron. In one form, the housing and said cap preferably define cooperating instrumentalities for guiding the cap for vertical reciprocatory movements relative to said housing and for maintaining a predetermined relation between the cap and the housing. 
     In this family of embodiments, the spring for the side bearing assembly includes an elastomeric member having first and second axially aligned ends. Preferably, the housing includes a base with generally horizontal flange portions extending in opposite directions and away from the central axis of the side bearing assembly, with each flange portion defining an aperture therein. Moreover, the housing preferably includes a post extending upwardly from the base for a predetermined distance. In this form, the insert on the cap includes a depending post generally aligned with the post of the housing for limiting reciprocatory movement of the cap toward the housing during operation of the railroad car constant contact side bearing assembly. 
     According to another aspect of this invention disclosure, there is provided a railroad car constant contact side bearing assembly adapted to be disposed intermediate a bolster and a car body of a railroad vehicle. In this family of embodiments, the side bearing assembly includes a cap having a generally planar upper surface configured to contact and slide along an underside of the car body and wall structure formed integral with and depending from the generally planar surface so as to define the cap with an open-bottom cavity. A spring is provided for continually urging the generally planar surface on the cap into sliding contact with the underside of the car body. A housing formed from high performance plastic has an open-top upstanding wall structure defining a non-metal sliding surface which guides and promotes vertical reciprocatory movements of the wall structure of the cap relative to the housing. The open-top wall structure of the housing and the open-bottom wall structure of the cap combine to define a cavity wherein the spring is accommodated. A metal skeleton is arranged in operable combination with the plastic housing. The skeleton preferably includes a base and wall structure extending upwardly from the base and embedded within and adding strength to the upstanding wall structure of the housing. The base of the metal skeleton defines two apertures on opposed sides of the side bearing assembly central axis for allowing fasteners to pass therethrough so as to allow the side bearing assembly to be secured to an upper surface of a bolster on said railcar. 
     In one form, the housing and cap of the side bearing assembly define cooperating instrumentalities for guiding the cap for vertical reciprocatory movements relative to the housing and for maintaining a predetermined relation between the cap and housing. Preferably, the wall structure of the skeleton includes at two vertically upright projections extending from and formed integral with the skeleton base. Each projection on the skeleton terminates at an upper end of the wall structure on the housing for limiting reciprocatory movement of the cap toward the housing during operation of said railroad car constant contact side bearing assembly. 
     In one embodiment, the spring is formed from a thermoplastic elastomer. As such, the the cap wall structure defines openings arranged toward an intersection of the generally planar surface and the wall structure so as to remain substantially unobstructed by the underside of said railcar body during operation of said side bearing assembly. The openings in the cap dissipate heat away from the spring during operation of said side bearing assembly. In a preferred form, the plastic housing also defines openings toward a bottom thereof and which are arranged in communication with the cavity defined by the side bearing assembly. The openings in the plastic housing and the openings in the cap define an air passage between the bottom of the housing and the openings in the cap to promote the dissipation of heat away from said elastomeric spring during operation of said side bearing assembly. 
     According to another aspect of this invention disclosure, there is provided a railroad car constant contact side bearing assembly adapted to be disposed intermediate a bolster and a car body of a railroad vehicle. The side bearing assembly includes a cap having a generally planar surface configured to contact and slide along an underside of the car body. The cap further includes wall structure formed integral with and depending from the generally planar surface so as to define an open-bottom cavity. A spring continually urges the generally planar surface on the cap into sliding contact with the underside of the car body. The side bearing assembly furthermore includes a housing formed from high performance plastic. The housing has an open-top cavity defined by upstanding wall structure. The housing wall structure defines a non-metal sliding surface which guides and promotes vertical reciprocatory movements of the wall structure of the cap relative to the housing. The open-top wall structure of the housing and the open-bottom wall structure of the cap combining to define a cavity wherein the spring is accommodated. In this embodiment, a metal skeleton is arranged in operable combination with the plastic housing. The skeleton includes a two-piece structure. Each skeletal piece includes a base and a projection extending upwardly from the base and embedded within and adding strength to a segment of the upstanding wall structure of the side bearing assembly housing. The base of each skeletal part defines an aperture for allowing a fastener to pass therethrough so as to allow the side bearing assembly to be secured to an upper surface of the bolster on the railcar. 
     Preferably, the housing and cap define cooperating instrumentalities for guiding the cap for vertical reciprocatory movements relative to the housing and for maintaining a predetermined relation between the cap and the housing. Moreover, the projection on each piece of the two-piece structure terminates at an upper end of the wall structure on the housing for limiting reciprocatory movement of the cap toward the housing during operation of the railroad car constant contact side bearing assembly. 
     In this embodiment, the spring is preferably formed from a thermoplastic elastomer. As such, the side bearing assembly cap defines openings arranged toward an intersection of the generally flat surface and the wall structure of the cap. The openings in the cap remain substantially unobstructed by the underside of the railcar body during operation of the side bearing assembly. Additionally, the openings in the cap are preferably arranged in communication with the open-bottom cavity defined by the cap to dissipate heat from the cavity during operation of the side bearing assembly. Also, the plastic housing preferably defines openings toward a bottom thereof which are arranged in communication with the cavity defined by the housing. Those openings in the plastic housing and the openings in the cap define an air passage between the bottom of the housing and the openings in the cap to promote the dissipation of heat away from said elastomeric spring during operation of the side bearing assembly. 
     According to yet another aspect, there is provided a railroad car constant contact side bearing assembly adapted to be disposed intermediate a bolster and a car body of a railroad vehicle. The side bearing assembly includes a plastic or non-metallic cap having a generally planar upper surface and wall structure depending from the generally planar upper surface. The wall structure of the cap defines an open-bottom cavity. A metallic insert is maintained in operable association with the generally flat surface on the cap to slidably contact with an underside of the railcar whereby allowing the side bearing assembly to establish a coefficient of friction ranging between about 0.4 to about 0.9 with the railcar during operation of the constant contact side bearing assembly. In one instance, the side bearing assembly furthermore includes a housing formed from high performance plastic and having an open-top upstanding wall structure defining a non-metal sliding surface which guides and promotes vertical reciprocatory movements of the wall structure of the cap relative to the housing. The open-top wall structure of the housing and the open-bottom wall structure of the cap combine to define a recess wherein a spring is accommodated for urging the cap toward an underside of the car body. A metal skeleton is arranged in operable combination with the plastic housing. The metal skeleton includes wall structure embedded within and adding strength to the upstanding wall structure of the housing. The metal skeleton defines two apertures for allowing fasteners to pass therethrough so as to allow the side bearing assembly to be secured to an upper surface of the bolster on the railcar. 
     Preferably, the insert that is maintained in operable association with the cap is formed from a metal material selected from the class of: steel and austempered ductile iron. Moreover, the housing and the cap define preferably define cooperating instrumentalities for guiding the cap for vertical reciprocatory movements relative to the housing and for maintaining a predetermined relation between the cap and the housing. 
     In one form, the spring includes an elastomeric member having first and second axially aligned ends. The metal skeleton of the side bearing assembly preferably includes an elongated base and a post extending upwardly from the base for a predetermined distance. The base preferably defines two apertures for allowing a fastener to pass through each aperture whereby securing the side bearing assembly to an upper surface of the bolster on the railcar. In one embodiment, the insert on the cap further includes a depending post generally aligned with the post of the skeleton for limiting reciprocatory movement of the cap toward the housing during operation of the railroad car constant contact side bearing assembly. 
     In one embodiment, the skeleton includes a two-piece structure. Each piece of the skeleton includes a base and a projection extending upwardly from the base and embedded within and adding strength to a segment of the upstanding wall structure of the housing. The base of each two piece structure defines an aperture for allowing a fastener to pass therethrough so as to allow the side bearing assembly to be secured to an upper surface of the bolster on said railcar. 
     Preferably, the spring for the side bearing assembly is formed from a thermoplastic elastomer. When the spring is formed from a thermoplastic elastomer, the side bearing assembly cap defines preferably openings arranged toward an intersection of the generally planar surface and the wall structure of the cap. The openings in the cap remain substantially unobstructed by the underside of the railcar body during operation of the side bearing assembly. Also, the openings in the cap are in communication with the open-bottom cavity defined by the cap to dissipate heat from the cavity during operation of the side bearing assembly. In a preferred form, the plastic housing defines openings toward a bottom thereof and which are arranged in communication with the open-top cavity defined by the housing. The openings in the plastic housing and the openings in the cap combine to define an air passage between the bottom of the housing and the openings in the cap to promote the dissipation of heat away from said elastomeric spring during operation of said side bearing assembly. 
     According to still another aspect, there is provided a railroad car constant contact side bearing assembly plastic cap including a generally flat surface with wall structure formed integral with and depending from the generally flat surface. The wall structure combines with an underside of the generally flat surface to define an open-bottom cavity for the cap. A metallic insert is maintained in operable association with the generally flat surface on the cap to slidably contact with an underside of a railcar whereby permitting the cap to establish a coefficient of friction ranging between about 0.4 and about 0.9 with the railcar. The side bearing cap further defines a plurality of openings for allowing air to pass into and from the open-bottom cavity. The openings are defined by the side bearing assembly cap in the vicinity of an intersection between the generally flat surface and the wall structure of the cap for allowing the dissipation of heat from said open-bottom cavity defined by the cap. 
     In this embodiment, the plurality of openings defined by the cap includes at least two openings which are generally aligned relative to each other. Preferably, the metallic insert is defined by a class of materials including: steel and austempered ductile iron. In one form, the metallic insert includes a generally centralized post depending from an underside of the generally flat surface on the cap. In a preferred form, at least an axial section of the cap wall structure depending from the generally flat surface on the cap has a generally cylindrical configuration. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top plan view of a portion of a railroad car wheeled truck including one form of a constant contact side bearing assembly embodying principals of this invention disclosure; 
         FIG. 2  is an enlarged top plan view of one form of constant contact side bearing assembly embodying principals and teachings of this invention disclosure; 
         FIG. 3  is an elevation view of the side bearing assembly illustrated in  FIG. 2 ; 
         FIG. 4  is a longitudinal sectional view of the side bearing assembly taken along line  4 - 4  of  FIG. 2 ; 
         FIG. 5  is a top plan view of one embodiment of a metal skeleton forming part of a housing of the side bearing assembly illustrated in  FIG. 2   
         FIG. 6  is a side elevational view of the metal skeleton shown in  FIG. 5 ; 
         FIG. 7  is an end view of the metal skeleton shown in  FIG. 5   
         FIG. 8  is an enlarged top plan view of another embodiment of constant contact side bearing assembly embodying principals and teachings of this invention disclosure; 
         FIG. 9  is an elevational view of the side bearing assembly shown in  FIG. 8 ; 
         FIG. 10  is a longitudinal sectional view of the side bearing assembly taken along line  10 - 10  of  FIG. 8 ; 
         FIG. 11  is a top plan view of one form of insert forming part of a cap used in operable combination with the side bearing assembly shown in  FIG. 8 ; 
         FIG. 12  is a side elevational view of the insert shown in  FIG. 11 ; 
         FIG. 13  is an end view of the insert shown in  FIG. 11 ; 
         FIG. 14  is an enlarged top plan view of another embodiment of constant contact side bearing assembly embodying principals and teachings of this invention disclosure; 
         FIG. 15  is an elevational view of the side bearing assembly shown in  FIG. 14 ; 
         FIG. 16  is a longitudinal sectional view of the side bearing assembly taken along line  16 - 16  of  FIG. 14 ; 
         FIG. 17  is an side elevational view of one form of a part of used in operable combination with the side bearing assembly illustrated in  FIG. 16 ; 
         FIG. 18  is a top plan view of the part illustrated in  FIG. 17 ; and 
         FIG. 19  is an end elevation of the part illustrated in  FIG. 17 . 
     
    
    
     DETAILED DESCRIPTION 
     While this invention disclosure is susceptible of embodiment in multiple forms, there is shown in the drawings and will hereinafter be described preferred embodiments of this invention disclosure, with the understanding the present disclosure is to be considered as setting forth exemplifications of the disclosure which are not intended to limit the disclosure to the specific embodiment illustrated and described. 
     Referring now to the drawings, wherein like reference numerals indicate like parts throughout the several views,  FIG. 1  shows a fragment of a railcar wheeled truck assembly, generally indicated by reference numeral  10 , for supporting and allowing a railcar body  12  defining a part of a railcar  13  ( FIG. 3 ) to ride along and over tracks T. Truck assembly  10  is of a conventional design and includes a side frame  14 , a bolster  16 , extending generally transversely relative to a longitudinal centerline  18  of the railcar body  12  ( FIG. 3 ), and a wheel set  20 . A conventional center bearing plate  22  is suitably mounted on the bolster  16  for pivotally supporting one end of the car body  12  ( FIG. 3 ). 
     A railroad car constant contact side bearing assembly embodying principals of this invention disclosure is generally indicated in  FIG. 1  by reference numeral  30  and is arranged in operable combination with each wheeled truck assembly  10 . More specifically, and as is conventional, the railroad car constant contact side bearing assembly  30  is mounted on an upper surface  17  ( FIGS. 2, 3 and 4 ) of the railcar bolster  16  on opposite lateral sides of the center bearing plate  22  ( FIG. 1 ) to limit hunting movements and oscillation of the wheeled truck assembly  10  as the railcar moves over the tracks T. 
     The aesthetic design of the side bearing assembly  30  shown in the drawings is merely for exemplary purposes. Whereas, the principals and teachings set forth below are equally applicable to side bearings having other forms and shapes from that illustrated for exemplary purposes. Turning to  FIGS. 2 and 3 , the railcar constant contact side bearing assembly  30  includes a housing or cage  40 , a cap  60  arranged for generally telescoping or vertical reciprocatory movements relative to the housing  40 , and a spring  100  ( FIG. 4 ). 
     In the embodiment shown in  FIGS. 2, 3 and 4 , housing  40  includes wall structure  44  extending upwardly from a base  46  to define an axis  47  for the side bearing assembly  30 . The housing wall structure  44  extends upwardly from the base  46  for a predetermined distance and defines an axis  47  for the side bearing assembly  30 . The interior surface  49  of housing wall structure  44  defines an open-top cavity or internal void  48 . 
     The housing base  46  is configured for suitable attachment to the upper surface  17  of the railcar bolster  16  as through any suitable means, i.e. threaded bolts or the like. In the illustrated embodiment, housing base  46  includes a pair of mounting flanges  50  and  50 ′ radially extending outwardly in opposed directions away from the side bearing assembly axis  47 . Each mounting flange  50 ,  50 ′ defines a bore or aperture  52 ,  52 ′ ( FIG. 4 ), respectively, for allowing a suitable fastener to extend therethrough whereby permitting the housing  40  to be fastened to the upper surface  17  of the bolster  16 . Preferably, the bores or apertures  52 ,  52 ′ are aligned relative to each other along a longitudinal axis  55  ( FIG. 2 ) such that, when housing  40  is secured to the bolster  16 , axis  55  extends generally parallel to the longitudinal axis  18  of car body  12  ( FIG. 1 ). 
     In the embodiment illustrated in  FIGS. 2, 3 and 4 , the cap or member  60  is preferably formed from a strong and rigid metal such as steel and the like and is adapted to telescopically move relative to the housing  40 . A top plate  62  of cap  60  has a generally planar or flat configuration for frictionally engaging and establishing metal-to-metal sliding contact with an underside  19  or surface of the railcar body  12  ( FIGS. 3 and 4 ). 
     When the side bearing assembly  30  is secured to the bolster  16 , the generally flat surface of top plate  62  is disposed above a terminal end of the upstanding wall structure  44  of the side bearing housing  40  for a predetermined distance. In the example shown, the normal distance between the top plate  62  of cap or member  60  and a top of the housing wall structure  44 , indicated by the distance “X” in  FIG. 3 , is determinative of the permissible compressive movement of the side bearing assembly  30  and such that after the underside  19  of the railcar body  12  contacts the housing structure  44 , the side bearing assembly  30  functions as a solid unit and prevents further rocking and relative movement between the bolster  16  and the railcar body  12 . 
     In the illustrated embodiment, cap  60  includes wall structure  64  depending from and, preferably, formed integral with the top plate  62  to define an open-bottom cavity  68 . At least a portion of the wall structure  64  of cap  60  is positioned within the housing  40  for generally vertical reciprocatory movements. Moreover, in a preferred embodiment, at least an axial section of the wall structure  64  of cap  60  has a generally cylindrical cross-sectional configuration. 
     As shown in  FIG. 2 , an outer surface  68 ′ of the wall structure  64  of cap  60  complements an inner surface  49 ′ defined by the wall structure  44  of the side bearing housing  40  Moreover, and as shown in  FIG. 8 , the open-top wall structure  44  of the side bearing housing  40  and the open-bottom wall structure  68  of cap  60  operably combine to surround the spring  100  and define a void  69  wherein spring  100  is accommodated. As will be appreciated, if the wall structure  44  of housing  40  is designed with other than a generally round cross-sectional configuration, the cross-sectional configuration of the wall structure  64  of cap  60  would similarly change and vice versa. 
     According to one aspect of this invention disclosure, and as illustrated in  FIG. 4 , the housing  40  is formed from a high performance plastic material to enhance vertical reciprocity of the cap  60  relative to the housing  40 . In this embodiment, housing  40  is formed from a non-metal, high performance plastic material of the type sold by DuPont™ under the tradename Zytel® under Model Nos. 75LG50HSL BK031, 70G33HS1L BK031, ST801AHS BK010, and HTNFE8200 BK431 and equivalents thereto. Besides being less weight than steel, forming the housing  40  from such non-metal, high performance plastic material has also shown lower wear rates between the sliding surfaces or contact areas with cap  60  which, in turn, increases the expectant life of the side bearing assembly  30 . 
     To add strength and rigidity thereto, a metal skeleton  70  is arranged in operable combination with and forms and integral part of housing  40 . Skeleton  70  is preferably formed from a strong and rigid metal material selected from the class of: steel and austempered ductile iron whereby enabling the wall structure of housing  40  to absorb the relatively high impact loads and forces directed thereagainst during operation of the side bearing assembly  30 . 
     In the form shown by way of example in  FIGS. 4, 5 and 6 , the skeleton  70  includes an elongated base  72  having a pair of mounting flanges  71  and  71 ″ radially extending outwardly in opposed directions relative to each other. Each mounting flange  71 ,  71 ′ defines a bore or aperture  74 ,  74 ′ ( FIG. 5 ), respectively, for allowing a suitable fastener to extend therethrough whereby permitting the housing  40  to be fastened to the upper surface  17  of the bolster  16 . Like the bores or apertures  52 ,  52 ′, the bores or apertures  74 ,  74 ′ in the metal skeleton  70  are aligned relative to each other along a longitudinal axis  75 . Moreover, the longitudinal spacing between the bores  74 ,  74 ′ defined by the skeleton  70  is equal to the longitudinal spacing between the bores  52 ,  52 ′ in the side bearing housing  40 . 
     Skeleton  70  of housing  40  furthermore includes wall structure  76  extending upwardly from the base  72  and embedded within and adding strength and rigidity to the plastic wall structure  44  of housing  40 . In the embodiment shown in  FIG. 4 , the wall structure  76  of skeleton  70  preferably extends upwardly from the base  72  and terminates at or adjacent to a terminal end of the wall structure  44  of housing  40 . Preferably, the wall structure  76  of skeleton  70  is formed integral with the base  72 . In one form, and for reasons discussed below, the wall structure  76  of skeleton  70  includes two radially spaced upstanding wall structures  77 ,  77 ′ which extend partially around the wall structure  44  of housing  40  a sufficient distance whereby enabling the wall structure  44  of housing  40  to absorb the relatively high impact forces and loads directed thereagainst during operation of the side bearing assembly  30 . 
     In the illustrated embodiment, and when the wall structure  44  of the side bearing housing  40  has a generally cylindrical cross-sectional configuration, the wall structure  76  of skeleton  70  will also have a generally arcuate or radiused configuration, in plan, on at least an inner surface  79  and preferably an outer surface  79 ′ of each wall structure  77 ,  77 ′. Preferably, the sides or surfaces  79 ,  79 ′ of each wall structure  77 ,  77 ′ are disposed in generally concentric relation relative to the wall structure  44  of housing  40 . Suffice it to say, in this embodiment of the invention disclosure, the outer surface  69 ′ of the metal cap  60  is separated from the inner surface  49 ′ of the housing  40  and from the inner surface  79  of the skeletal wall structure  76  by high performance plastic material to enhance vertical reciprocity of the cap  60  relative to the housing  40 . 
     In the embodiment shown in  FIGS. 4, 5 and 7 , the skeleton  70  furthermore defines cooperating instrumentalities  80  for maintaining the plastic housing  40  and skeleton  70  in operable association relative to each other. As will be appreciated, the exact shape and design of the cooperating instrumentalities  80  for maintaining the plastic housing  40  and skeleton  70  in operable association relative to each other can take a myriad of designs and configuration without detracting or departing from the spirit and scope of this invention disclosure. 
     In the embodiment illustrated by way of example in  FIGS. 4, 5 and 7 , the metal skeleton  70  is preferably provided with a plurality or series of grooves or channels  82 . Each groove or channel  82  preferably extends through and opens to each side of the skeleton  70 . As such, and when the non-metal housing  40  is formed about the skeleton  70 , plastic material flows into and through each groove or channel  82  in the skeleton  70  whereby maintaining the plastic housing  40  and skeleton  70  in operable association relative to each other. 
     Like the aesthetics of the side bearing housing design elected for exemplary purposes, the exact shape or form of the spring  100  can vary or be different from that illustrated without detracting or departing from either the spirit or scope of this invention disclosure. In the embodiment illustrated in  FIG. 4 , spring  100  is comprised of a formed and resiliently deformable thermoplastic elastomer member  110 . The purpose of the spring  100  is to position the top plate  62  of the cap relative to the housing  40  and to develop a predetermined preload or suspension force thereby urging the plate  62  of cap  60  toward and into frictional sliding engagement with the underside  19  of the car body  12 . The preload or suspension force on the cap or member  60  allows absorption of forces imparted to the side bearing assembly  30  when the car body  12  tends to roll, i.e., oscillate about a horizontal axis of car body  12  and furthermore inhibits hunting movements of the wheeled truck ( FIG. 1 ) relative to the car body  12 . 
     In the embodiment illustrated for exemplary purposes in  FIG. 4 , member  110  of spring  100  has a configuration suitable for accommodation between base  46  of the side bearing housing  40  and an underside of the plate  62  of cap or member  60 . Member  110 , illustrated by way of example in  FIG. 4 , preferably embodies the teachings set forth in coassigned U.S. Pat. No. 6,792,871 the applicable portions of which are incorporated herein by reference. In the illustrated embodiment, member  110  defines a generally centralized bore  112  opening to axially aligned ends of member  110 . It should be appreciated, however, member  110  could also be solidly configured. Suffice it to say, the thermoplastic member  110  preferably has an elastic strain to plastic strain ratio of about 1.5 to 1. Coassigned U.S. Pat. No. 4,198,037 to D. G. Anderson, the applicable portions of which are incorporated hereby by reference, better describes the composition and methodology for forming member  110 . 
     In the illustrated embodiment, a thermal insulator  120  is preferably arranged at one end of and is intended to operably protect the thermoplastic member  110  from the adverse affects of heat generated by the sliding frictional movements between the underside  19  of the railcar body  12  ( FIG. 3 ) and the planar surface  62  on the side bearing cap  60  during movements of the railcar between locations. Suffice it to say, and in the illustrated embodiment, the thermal insulator  120  is operably carried at one end of the thermoplastic member  110  and is preferably of the type disclosed in coassigned U.S. Pat. Nos. 6,092,470; 6,892,999; and 7,044,061; the applicable portions of which are incorporated herein by reference. 
     In the embodiment illustrated for exemplary purposes in  FIG. 4 , the base  46  of the side bearing assembly  40  supports that end of the spring  100  opposite from the thermal insulator  120 . Preferably, the skeleton  70  furthermore defines a spring guide or projection  78  centrally located on the base  74  of the skeleton  70 . In the illustrated embodiment, the spring guide  78  fits within the bore or recess  112  defined by member  110  whereby operably locating at least the lower end of the spring  100  within the side bearing assembly housing  40 . In the illustrated embodiment, the spring guide  78  defines a flat or stop  78 ′ at a distal end thereof. 
     In the embodiment illustrated in  FIG. 4 , the cap  60  also includes a spring guide  66  generally concentrically disposed within the cavity  68  defined by the cap  60  and which generally aligns with the spring guide or projection  78  on the base  72  of skeleton  70  when housing  40  and cap  60  are arranged in operable combination relative to each other. Preferably, spring guide  68  defines a flat or stop  68 ′ which, when housing  40  and cap  60  are arranged in operable combination relative to each other, is disposed in axially spaced but confronting relation relative to the stop  78  on the skeleton  70  of housing  70  to limit compression of the cap  60  relative to housing  40 . 
     During travel of railcar  13 , the wheeled truck naturally hunts or yaws about a vertical axis of the truck, thus, creating frictional sliding or oscillating movements at and along the interface of the top plate  62  of cap  60  and the underside of the car body  12  thereby creating significant and even excessive heat. When the heat at the interface of the side bearing assembly  30  and the underside  19  of the car body  12  exceeds the heat deflective temperature of the thermoplastic member  110 , deterioration, deformation and even melting of the thermoplastic member  110  can occur thus adversely affecting predetermined preload characteristics provided by the spring  100 . 
     Accordingly, the side bearing assembly  30  is preferably configured to promote dissipation of heat away from the elastomeric spring  100  thereby prolonging the usefulness of the side bearing assembly  30 . More specifically, and as shown in  FIGS. 3 and 4 , the wall structure  44  of the housing  40  preferably defines a pair of openings  45 ,  45 ′ disposed to opposed sides of the centerline  47  of the side bearing assembly  30  toward the bottom of the housing  40  adjacent to an intersection of the wall structure  44  and base  46 . The openings  45  extend from an interior of cavity  48  ( FIG. 4 ) to the exterior of the housing  40 . 
     In the illustrated embodiment, the radial spacing between the upstanding wall structures  77  and  77 ′ of the metal skeleton  70  are arranged relative to the openings  45 ,  45 ′ in the side bearing housing  40  such that the wall structures  77 ,  77 ′ do not obstruct or otherwise interfere with venting of heat from an interior of the spring cavity  69  and through the openings  45 ,  45 ′ in the housing  44 . Of course, rather than being radially spaced relative to each other, the wall structure  76  of the metal skeleton  70  could otherwise be designed with suitable openings disposed relative to the openings  45 ,  45 ′ in the side bearing housing  40  to readily permit venting of heat from an interior of the cavity  48  and through the openings  45 ,  45 ′ in the housing  44  without detracting or departing from the spirit and scope of this invention disclosure. 
     To furthermore promote the dissipation of heat from the side bearing assembly  30 , cap  60  is preferably configured to vent heat away from the spring  100 . As shown in  FIG. 2 , cap  60  is preferably configured with a pair of openings  67  and  67 ; arranged proximate to the intersection of the top plate  62  and wall structure  64 . At least a portion of each opening  67 ,  67 ′ is defined by the wall structure  64  of cap  60  whereby allowing the openings  67 ,  67 ′ to remain unobstructed by the underside  19  of the railcar body  12  during operation of the railcar side bearing assembly  30 . In a preferred form, the openings  67 ,  67 ′ are disposed to opposed sides of the centerline  47  of the side bearing assembly  30 . In the illustrated embodiment, the openings  67 ,  67 ′ are generally aligned along a line extending generally perpendicular or normal to the longitudinal axis  55  of the side bearing assembly  30  ( FIG. 2 ). In the illustrated embodiment, the openings  45 ,  45 ′ in the housing  40  communicate with and define an air passage with the openings  69 ,  69 ′ in the top cap  60  whereby promoting the dissipation of heat from the spring cavity  69 . As will be appreciated, the openings  45 ,  45 ′ along with  67 ,  67 ′ provide a particular advantage when a thermoplastic spring is used to resiliently urge the cap  60  against and into frictional sliding contact with an underside  15  of the railcar body  12  ( FIG. 2 ). 
     Returning to  FIG. 2 , the side bearing housing  40  and cap  60  furthermore preferably define cooperating instrumentalities, generally identified by reference numeral  130 . The purpose of the cooperating instrumentalities  130  is to guide cap  60  for vertical reciprocatory movements relative to the housing  40  and for maintaining a predetermined relation between cap  60  and the side bearing housing  40 . As will be appreciated, the cooperating instrumentalities  130  can take many forms and shapes for accomplishing the desired ends or purposes without detracting or departing from the spirit and scope of this invention disclosure. 
     In the embodiment shown in  FIG. 2 , the interior surface  49  of the side bearing housing  40  preferably defines a pair of vertically extending keyways or recesses  132  which, in the illustrated embodiment, are positioned in diametrically opposed relation from each other. Each keyway or recess  132  extends generally vertically along the side bearing housing  40  for a vertical distance which is sufficient to accommodate and guide vertical reciprocatory movements of the side bearing cap  60  during operation of the side bearing assembly  30 . 
     Preferably, in the embodiment illustrated in  FIG. 2 , the keyways  132  are formed integral with the housing  40  and are disposed in generally orthogonal relation with the longitudinal axis  55 . Moreover, and in a preferred form, cap  60  defines a pair of projections or keys  136  which are configured to mate with and slide along the keyway or recess  132  defined by the side bearing housing  40  whereby guiding cap or member  60  for vertical reciprocatory movements relative to the housing  40  while maintaining a predetermined relation between the housing  40  and cap  60  during operation of the side bearing assembly  30 . 
       FIGS. 8 through 10  illustrate an alternative form for the constant contact side bearing assembly of the present invention. This alternative form of the constant contact side bearing assembly is designated generally by reference numeral  230 . The elements of this alternative form of side bearing assembly that are functionally analogous to those components discussed above regarding side bearing assembly  30  are designated by reference numerals identical to those listed above with the exception this embodiment uses reference numerals in the 200 series. 
     Side bearing assembly  230  includes a housing or cage  240 , a cap  260  arranged for generally telescoping or vertical reciprocatory movements relative to the housing  240 , and a spring  300  ( FIG. 10 ). In this embodiment, the housing  240  is preferably formed of a strong and wear resistant metal material such as steel or the like. 
     In this embodiment, housing  240  includes wall structure  244  extending upwardly from a base  246  to define an axis  247  for side bearing assembly  230 . The wall structure  244  extends upwardly from base  246  for a predetermined distance. The wall structure  244  of the side bearing housing  40  defines an open-top cavity or internal void  248 . The housing base  246  includes radial flanges  250 ,  250 ′. As shown in  FIG. 10 , the mounting flanges  250 ,  250 ′ define bores or apertures  252 ,  252 ′, respectively, for allowing a suitable fastener to pass therethrough whereby permitting the housing  240  to be fastened to the upper surface  17  of bolster  16 . Preferably, the bores or apertures  252 ,  252 ′ are aligned relative to each other along a longitudinal axis  254  such that, when the side bearing assembly  230  is fastened to the bolster  16 , axis  245  extends generally parallel to the longitudinal axis  18  of the railcar body  12  ( FIG. 1 ). 
     Cap  260  is arranged in operable combination with and for vertical reciprocatory movements relative to housing  240  In this embodiment, however, and to enhance the vertical reciprocity of cap  260  relative to the housing  240 , cap  260  is formed from a non-metal, high performance plastic material of the type sold by DuPont™ under the tradename Zytel® under Model Nos. 75LG50HSL BK031, 70G33HS1L BK031, ST801AHS BK010, and HTNFE8200 BK431 and equivalents thereto. Besides being less weight than steel, forming the cap  260  from such non-metal, high performance plastic has also shown to offer lower wear rates between the sliding contact surfaces as compared to steel which, in turn, increases the expectant life of the side bearing assembly  230 . 
     As shown in  FIG. 10 , cap  260  is at least partially positioned within housing  240  for generally vertical reciprocatory movements and includes an upper generally flat surface  262 . When the side bearing assembly  230  is secured to the bolster  16 , the generally flat surface  262  of member  230  is disposed above a terminal end of the wall structure  244  of the side bearing housing  240  for a predetermined distance. In the example shown, the normal distance between surface  262  of member  260  and the top edge of the wall structure  244 , indicated by the distance “X” in  FIG. 9 , is determinative of the permissible compressive movement of the side bearing assembly  230  and such that after the underside  19  of the railcar body  12  contacts an upper edge of the housing structure  244 , the side bearing assembly  230  functions as a solid unit and will prevent further rocking and relative movement between the bolster  16  and the railcar body  12 . 
     As shown in  FIG. 10 , cap  260  furthermore includes wall structure  264  depending from and preferably formed integral with the generally flat or planar surface  262  of cap  260  to define an open-bottom cavity  268 . Preferably, at least an axial section of the wall structure  264  of cap  260  has a generally cylindrical configuration. As shown in  FIG. 11 , an outer surface  268 ′ on the wall structure  264  of cap  260  complements an inner surface  249 ′ defined by the wall structure  244  of the side bearing housing  240  The open-top wall structure  244  of the side bearing housing  240  and the open-bottom wall structure  268  of cap  260  operably combine relative to each other to surround the spring  300  and define a void  269  wherein spring  300  is accommodated. As will be appreciated, if the wall structure  244  of housing  240  is designed with other than a generally round cross-sectional configuration, the cross-sectional configuration of the wall structure  264  of cap  260  would similarly change and vice versa. 
     In the embodiment shown in  FIGS. 8 and 10 , the cap  260  furthermore includes an insert  270  that is maintained in operable association with and preferably generally centered on the upper generally flat surface  262  cap  260 . The insert  270  is preferably formed from a metal material selected from the class of: steel and austempered ductile iron. As shown in  FIG. 10 , the insert  270  is arranged in operable association with cap  260  so as to slidably interact and contact with the underside  19  of the car body  12 . In the embodiment illustrated by way of example, the insert  270  has a width of about 2 inches and a length of about 3.5 inches. 
     In the embodiment illustrated by way of example in  FIG. 10 , the insert  270  is furthermore preferably provided with an elongated upper and generally planar or flat surface or side  271  adapted to slidably and frictionally engage with an underside  19  of the railcar body  12  and a lower generally planar or flat surface or side  272 . In one form, the surfaces  271  and  272  are separated by about 0.375 inches. Suffice it to say, the insert  270  is engineered and designed whereby allowing the side bearing assembly  230  to establish a coefficient of friction ranging between about 0.4 and about 0.9 with the railcar  13  during operation of the constant contact side bearing assembly  230  so as to limit hunting movements and oscillation of the wheeled truck assembly  10  as the railcar moves over the tracks. 
     In the embodiment shown in  FIGS. 8, 10 and 11 , cap  260  and insert  270  define cooperating instrumentalities  280  for maintaining the cap  260  and insert  270  in operable association relative to each other. As will be appreciated, the exact shape and design of the cooperating instrumentalities  280  for maintaining the cap  260  and insert  270  in operable association relative to each other can take a myriad of designs and configuration without detracting or departing from the spirit and scope of this invention disclosure. 
     In the embodiment illustrated in  FIGS. 8, 10 and 11 , the cooperating instrumentalities  280  preferably includes a plurality or series of arcuate equally spaced grooves or channels  282 . Each groove or channel  282  preferably opens to both sides or surfaces  271  and  272  on the insert  270 . As such, and when the non-metal cap  260  is formed, plastic material comprising the cap  260  can flow into each groove or channel  282  whereby maintaining the top cap  260  and insert  270  in operable association relative to each other. 
     Like side bearing assembly  30  discussed above, in the embodiment of the side bearing assembly  230  illustrated in  FIG. 10 , spring  300  includes an elastomeric member  310  and is arranged in operable combination with housing  240  and cap  260  for absorbing, dissipating and returning energy imparted to the side bearing assembly  230 . Preferably, spring  300  is of the type described above regarding spring  100  and incorporated herein by reference. Spring  300  is arranged and accommodated within cavity  269  defined by housing  240  and cap  260 . Moreover, spring  300  can include a thermal insulator  320  of the type disclosed above and incorporated herein by reference. Like the configuration of the side bearing assembly, the exact shape or form of the spring  300  can vary or be different from that illustrated for exemplary purposes without detracting or departing from either the spirit or scope of this invention disclosure. 
     In the illustrated embodiment, member  310  of spring  300  has a configuration suitable for accommodation between base  246  of the side bearing housing  240  and an underside of the plate  262  of cap or member  260 . In the illustrated embodiment, member  310  defines a generally centralized bore  312  opening to axially aligned ends of member  310 . Suffice it to say, the thermoplastic member  310  preferably has an elastic strain to plastic strain ratio of about 1.5 to 1. 
     In the embodiment illustrated in  FIG. 10 , the base  246  of the side bearing assembly  240  supports that end of the spring  300  opposite from the thermal insulator  320 . Preferably, the base  246  of side bearing housing  240  defines a spring guide or projection  241  centrally located on the side bearing housing base  244 . In the illustrated embodiment, the spring guide  241  fits within the bore or recess  312  defined by the elastomeric member  310  whereby operably locating at least the lower end of the spring  300  within the side bearing assembly housing  340 . In the illustrated embodiment, the spring guide  241  defines a flat or stop  243  at a distal end thereof. 
     In the embodiment illustrated in  FIGS. 10 through 13 , insert  270  also includes a spring guide  278  which generally aligns with the spring guide or projection  241  on the base  246  of side bearing housing  240  when the housing  240  and cap  260  are arranged in operable combination relative to each other. Preferably, the spring guide  278  carried by insert  270  defines a flat or stop  279  which, when housing  240  and cap  260  are arranged in operable combination relative to each other, is disposed in axially spaced but confronting relation relative to the stop  243  on the side bearing housing  240  to limit compression of the cap  60  relative to housing  40 . 
     Side bearing assembly  230  is preferably configured to promote dissipation of heat away from the elastomeric spring  300  thereby prolonging the usefulness of the side bearing assembly  230 . As with the above described side bearing housing  40 , the wall structure  244  of the housing  240  is preferably configured to define a pair of openings  245 ,  245 ′ arranged to opposed sides of the side bearing assembly  30  toward the bottom of the housing  244  adjacent to an intersection of the wall structure  244  and the base  246  for venting heat from the spring cavity  269 . 
     Returning to  FIG. 8 , and to furthermore promote the dissipation of heat away from the spring  300 , cap  260  is preferably configured to vent heat away from the spring  400 . The plastic cap  260  is preferably configured with a pair of openings  267  and  267 ; arranged proximate to the intersection of the top plate  262  and wall structure  264 . At least a portion of each opening  267 ,  267 ′ is defined by the wall structure  264  of cap  60  whereby allowing the openings  267 ,  267 ′ to remain unobstructed by the underside  19  of the railcar body  12  during operation of the railcar side bearing assembly  30 . Suffice it to say, the openings  267 ,  267 ′ in cap  260  are substantially similar to the openings  67 ,  67 ′ in cap  60 . Preferably, the openings  245 ,  245 ′ in the side bearing housing  240  communicate and define an air passage with the openings  267 ,  267 ′ in the cap  60  whereby promoting the dissipation of heat from spring cavity  269 . 
     The side bearing housing  240  and cap  260  furthermore preferably define cooperating instrumentalities, generally identified by reference numeral  330 . The purpose of the cooperating instrumentalities  330  is to guide cap  260  for vertical reciprocatory movements relative to the housing  240  and for maintaining a predetermined relation between cap  60  and the side bearing housing  240 . The cooperating instrumentalities  330  can take many forms and shapes for accomplishing the desired ends or purposes without detracting or departing from the spirit and scope of this invention disclosure. 
     In the embodiment shown in  FIG. 8 , an interior surface  249  of the side bearing housing  240  preferably defines a pair of vertically extending keyways or recesses  332  which, in the illustrated embodiment, are positioned in diametrically opposed relation from each other. Each keyway or recess  332  extends generally vertically along the side bearing housing  240  for a vertical distance which is sufficient to accommodate and guide vertical reciprocatory movements of the side bearing cap  260  during operation of the side bearing assembly  230 . 
     Preferably, in the embodiment illustrated in  FIG. 8 , the keyways  332  are formed integral with the housing  240  and are disposed in generally orthogonal relation with the longitudinal axis  254 . Moreover, and in a preferred form, the plastic cap  260  defines a pair of radial projections or keys  336  which are configured to mate with and slide along the keyway or recess  332  defined by the side bearing housing  240  whereby guiding cap or member  260  for vertical reciprocatory movements relative to the housing  240  while maintaining a predetermined relation between the housing  240  and cap  260  during operation of the side bearing assembly  230 . 
       FIGS. 14 through 16  illustrate another alternative embodiment for the constant contact side bearing assembly of the present invention. The alternative form of constant contact side bearing assembly shown in  FIGS. 14 through 16  is designated generally by reference numeral  430 . The elements of this alternative form of side bearing assembly that are functionally analogous to those components discussed above regarding side bearing assembly  30  are designated by reference numerals identical to those listed above with the exception this embodiment uses reference numerals in the 400 series. 
     Side bearing assembly  430  includes a housing or cage  440 , a cap  460  arranged for generally telescoping or vertical reciprocatory movements relative to the housing  440 , and a spring  500  ( FIG. 16 ). In this embodiment, the housing  440  includes wall structure  444  having an interior surface  449  and extending upwardly from a base  446  to define an axis  447  for the side bearing assembly  430 . The housing wall structure  444  extends upwardly from the base  446  for a predetermined distance. The wall structure  444  of the side bearing housing  440  defines an open-top cavity or internal void  448 . In the illustrated embodiment, at least an axial section of the housing wall structure  444  has a generally cylindrical cross-sectional configuration. 
     The housing base  446  is configured for suitable attachment to the upper surface  17  of the railcar bolster  16  as through any suitable means, i.e. threaded bolts or the like. In the illustrated embodiment, housing base  446  includes a pair of mounting flanges  450  and  450 ′ radially extending outwardly in opposed directions away from the side bearing assembly axis  447 . Each mounting flange  450 ,  450 ′ defines a bore or aperture  452 ,  452 ′ ( FIG. 14 ), respectively, for allowing a suitable fastener to extend therethrough whereby permitting the housing  440  to be fastened to the upper surface  17  of the bolster  16 . Preferably, the bores or apertures  452 ,  452 ′ are aligned relative to each other along a longitudinal axis  455  ( FIG. 1 ) such that, when housing  440  is secured to the bolster  16 , axis  455  extends generally parallel to the longitudinal axis  18  of car body  12  ( FIG. 1 ). 
     According to this aspect of this invention disclosure, and as illustrated in  FIG. 14 , the housing  440  is formed from a high performance plastic material to enhance vertical reciprocity of the cap  460  relative to the housing  440 . In this embodiment, housing  440  is formed from a non-metal, high performance plastic material of the type sold by DuPont′ under the tradename Zytel® under Model Nos. 75LG50HSL BK031, 70G33HS1L BK031, ST801AHS BK010, and HTNFE8200 BK431 and equivalents thereto. Besides being less weight than steel, forming the housing  440  from such non-metal, high performance plastic material has also shown lower wear rates between the sliding surfaces or contact areas with cap  460  which, in turn, increases the expectant life of the side bearing assembly  430 . 
     To add strength and rigidity thereto, a metal skeleton  470  is arranged in operable combination with and forms and integral part of housing  440 . In the embodiment shown by way of example in  FIG. 14 , the skeleton  470  includes at least two separate and longitudinally spaced parts or pieces  470 ′ and  470 ″. 
     Preferably, the pieces  470 ′ and  470 ″ are substantially identical relative to each other to reduce manufacturing costs of the side bearing assembly  430 . Since the pieces  470 ′ and  470 ′ comprising the skeleton  470  are substantially identical, only part  470 ′ will be described in detail. In this embodiment, each skeletal piece comprising skeleton  470  is preferably formed from a strong and rigid metal material selected from the class of: steel and austempered ductile iron whereby enabling the wall structure  444  of housing  440  to absorb the relatively high impact loads and forces directed thereagainst during operation of the side bearing assembly  430 . As illustrated in  FIGS. 17, 18 and 19 , skeletal piece  470 ′ preferably has a generally L-shaped configuration and includes a base  471  defining a bore or aperture  474  toward one end thereof for allowing a suitable fastener to extend therethrough whereby permitting the housing  440  ( FIG. 18 ) to be fastened to the upper surface  17  of the bolster  16 . Notably, the bores or apertures  474  in the skeletal pieces  470 ′,  470 ″ are longitudinally aligned relative along axis  455  and relative to each other when the housing  440  is formed so as to facilitate securement of the side bearing assembly  430  to the to the upper surface  17  of the bolster  16 . Moreover, and when the plastic cap  460  is molded or otherwise formed about the skeletal pieces  470 ′,  470 ″, the longitudinal spacing between the bores or openings  474  in the skeletal pieces  470 ′,  470 ″ is equal to the longitudinal spacing between the bores  452 ,  452 ′ in the housing  440 . 
     Each skeletal piece furthermore includes generally vertical wall structure  476  extending upwardly from the base  471  and embedded within and adding strength and rigidity to the plastic wall structure  444  of housing  440 . In the embodiment shown in  FIG. 16 , the wall structure  476  of each part of skeleton  470  preferably extends upwardly from base  472  and terminates at or adjacent to a terminal end of the wall structure  444  of housing  440 . Preferably, the wall structure  476  of each skeletal piece is formed integral with the base  471 . In one form, the upstanding wall structure  476  of each skeletal piece  470 ′,  471 ″ will be arranged concentrically relative to the wall structure  44  of housing  440 . In this embodiment of the invention disclosure, each side or surface preferably has a generally arcuate or radiused configuration, in plan, which complements the configuration of the wall structure  444  of the side bearing housing  440 . The skeletal pieces or parts  470 ′,  470 ″ each have an inner surface  479  and an outer surface  479 . Suffice it to say, in this embodiment of the invention disclosure, the outer surface  469 ′ of the metal cap  460  is separated from the interior surface  449  of the housing  440  as well as the inner surface  479  of the each skeletal piece or part  470 ′,  470 ″ by high performance plastic material to enhance vertical reciprocity of the cap  460  relative to the housing  440 . 
     Each skeletal piece of skeleton  470  also defines cooperating instrumentalities  480  for maintaining the plastic housing  440  and skeleton  470  in operable association relative to each other. As will be appreciated, the exact shape and design of the cooperating instrumentalities  480  for maintaining the plastic housing  440  and skeleton  470  in operable association relative to each other can take a myriad of designs and configuration without detracting or departing from the spirit and scope of this invention disclosure. 
     In the embodiment illustrated by way of example in  FIG. 19 , the wall structure  476  of each skeletal piece of skeleton  470  is preferably provided with a plurality or series of openings  482 . Each opening  482  preferably opens to each generally vertical side  479 ,  479 ′ of the wall structure  476 . As such, and when the non-metal housing  40  is formed about the pieces or parts comprising skeleton  470 , plastic material flows into and through each opening  482  whereby maintaining the plastic housing  440  and the pieces or parts  470 ′,  470  of the metal skeleton  470  in operable association relative to each other. Of course, it will be appreciated, more than two parts each having a different design from each other could alternatively be used to form the metal skeleton  470  without detracting or departing from the spirit and scope of this invention disclosure. 
     Returning to  FIG. 16 , the cap  460  is arranged in operable combination with and for vertical reciprocal movement relative to housing  440 . Like that embodiment of the invention disclosure discussed above, and to enhance the vertical reciprocity of cap  460  relative to the housing  440 , cap  460  is preferably formed from a non-metal, high performance plastic material of the type sold by DuPont™ under the tradename Zytel® under Model Nos. 75LG50HSL BK031, 70G33HS1L BK031, ST801AHS BK010, and HTNFE8200 BK431 and equivalents thereto. 
     Suffice it to say, the plastic or non-metal cap  460  embodies many of the same features discussed above regarding cap  260 . The plastic cap  460  is positioned at least partially within the housing  440  for generally vertical movements and includes an upper generally flat surface  462 . When the side bearing assembly  430  is secured to the bolster  16 , the generally planar surface  462  of the side bearing assembly  430  is disposed above a terminal end of the upstanding wall structure  444  of the side bearing housing  440  for a predetermined distance. 
     As shown in  FIG. 16 , cap  460  includes wall structure  464  depending from and preferably formed integral with the generally flat or planar surface  462  to define an open-bottom cavity  468 . Preferably, at least an axial section of the wall structure  464  of cap  460  has a generally cylindrical configuration. As shown in  FIG. 14 , an outer surface on the wall structure  464  of cap  460  complements an inner surface defined by the wall structure  444  of the side bearing housing  440  The open-top wall structure  444  of the side bearing housing  240  and the open-bottom wall structure  468  of cap  460  operably combine relative to each other to surround the spring  500  and define a void  469  wherein spring  500  is accommodated. As will be appreciated, if the wall structure  444  of housing  440  is designed with other than a generally round cross-sectional configuration, the cross-sectional configuration of the wall structure  464  of cap  460  would similarly change and vice versa. 
     Moreover, the plastic cap  460  includes an insert  480  that is maintained in operable association with and preferably generally centered on the upper generally flat surface  462  of cap  460 . Insert  480  is preferably formed from a metal material selected from the class of: steel and austempered ductile iron. As shown in  FIG. 16 , insert  480  is arranged in operable association with cap  460  so as to slidably interact and contact with the underside  19  of the car body  12 . In the embodiment illustrated by way of example, the insert  470  is engineered and designed whereby allowing the side bearing assembly  430  to establish a coefficient of friction ranging between about 0.4 and about 0.9 with the railcar  13  during operation of the constant contact side bearing assembly  430  so as to limit hunting movements and oscillation of the wheeled truck assembly  10  as the railcar moves over the tracks. 
     In the embodiments shown in  FIGS. 14 and 16 , cap  460  and insert  480  preferably define cooperating instrumentalities  490  for maintaining cap  460  and insert  480  in operable association relative to each other. The exact shape and design of the cooperating instrumentalities  490  for maintaining cap  460  and insert  480  in operable association relative to each other are preferably similar to the cooperating instrumentalities  290  discussed above but can take a myriad of other designs without detracting or departing from the spirit and scope of this invention disclosure. 
     Like side bearing assembly  30  discussed above, in the embodiment of the side bearing assembly  430  illustrated in  FIG. 16 , spring  500  is arranged in operable combination with housing  440  and cap  460  for absorbing, dissipating and returning energy imparted to the side bearing assembly  430 . The spring  500  is preferably of the type described above regarding spring  100  and incorporated herein by reference. As shown, spring  500  is arranged and accommodated within the cavity  469  defined by housing  440  and cap  460 . Moreover, the spring  500  can include a thermal insulator  520  of the type disclosed above and incorporated herein by reference. Like the configuration of the side bearing assembly, the exact shape or form of the spring  500  can vary or be different from that illustrated for exemplary purposes without detracting or departing from either the spirit or scope of this invention disclosure. 
     In the illustrated embodiment, member  510  of spring  500  has a configuration suitable for accommodation between base  446  of the side bearing housing  440  and an underside of the plate  462  of cap or member  460 . In the illustrated embodiment, member  510  defines a generally centralized bore  512  opening to at least one end of member  510 . Suffice it to say, the thermoplastic member  510  preferably has an elastic strain to plastic strain ratio of about 1.5 to 1. 
     In the embodiment illustrated for exemplary purposes in  FIG. 16 , the base  446  of the side hearing assembly  440  supports that end of the spring  500  opposite from the thermal insulator  520 . In the embodiment illustrated in  FIG. 16 , the insert  480  associated with cap  460  also includes a spring guide  478  depending from the underside of the top plate  462  of the cap  460 . Preferably, the spring guide  488  carried by insert  480  is preferably designed to fit endwise and within the bore  512  in the spring member  510  whereby positively positioning the spring  500  with the cavity  469  defined by the side bearing assembly  430 . 
     Moreover, the side bearing assembly  430  is preferably configured to promote dissipation of heat away from the elastomeric spring  500  thereby prolonging the usefulness of the side bearing assembly  230 . As with the above described side bearing housing  40 , the wall structure  444  of the housing  440  preferably defines a pair of openings  445 ,  445 ′ ( FIGS. 15 and 16 , respectively) disposed to opposed sides of the side bearing assembly  430  toward the bottom of the housing  444  adjacent to an intersection of the wall structure  444  and the base  446  for venting heat from the spring cavity  469 . 
     Returning to  FIG. 14 , and to furthermore promote the dissipation of heat away from the spring  500 , cap  460  is preferably configured to vent heat away from the spring  500 . The plastic cap  460  is preferably configured with a pair of openings  467  and  467 ′; arranged proximate to the intersection of the top plate  462  and wall structure  464 . At least a portion of each opening  467 ,  467 ′ is defined by wall structure  464  of the cap  460  whereby allowing the openings  467 ,  467 ′ to remain unobstructed by the underside  19  of the railcar body  12  during operation of the railcar side bearing assembly  430 . Suffice it to say, the openings  467 ,  467 ′ in cap  260  are substantially similar to the openings  67 ,  67 ′ in cap  60 . Preferably, the openings  445 ,  445 ′ in the housing  440  communicate and define an air passage with the openings  467 ,  467 ′ in the cap  60  whereby promoting the dissipation of heat from cavity  269 . 
     The side bearing housing  440  and cap  460  furthermore preferably define cooperating instrumentalities, generally identified by reference numeral  530 . The purpose of the cooperating instrumentalities  530  is to guide cap  460  for vertical reciprocatory movements relative to the housing  440  and for maintaining a predetermined relation between cap  60  and the side bearing housing  440 . The cooperating instrumentalities  530  can take many forms and shapes for accomplishing the desired ends or purposes without detracting or departing from the spirit and scope of this invention disclosure. In the illustrated embodiment, the cooperating instrumentalities  530  are substantially similar to the instrumentalities  330  discussed above and incorporated herein by reference. 
     Regardless of the constant contact side bearing design, an important aspect of this invention disclosure relates to the ability to provide a non-metal material, preferably in the form of a high performance plastic material between the sliding surfaces on the side bearing housing and cap. This invention disclosure furthermore contemplates using a metal insert or skeleton in operable combination with that side bearing member formed from such non-metal, high performance plastic material whereby enabling the non-plastic member with sufficient strength and stiffness to withstand the relative high impact loads and forces directed against it during operation of the side bearing assembly. Moreover, and when such metal insert is used in operable combination with a plastic top cap design for the side bearing assembly, such construction allows the constant contact side bearing assembly to establish a coefficient of friction ranging between about 0.4 and about 0.9 with the railcar  13  during operation of the constant contact side bearing assembly so as to limit hunting movements and oscillation of the wheeled truck assembly as the railcar moves over the tracks. 
     From the foregoing, it will be observed that numerous modifications and variations can be made and effected without departing or detracting from the true spirit and novel concept of this invention disclosure. Moreover, it will be appreciated, the present disclosure is intended to set forth exemplifications which are not intended to limit the disclosure to the specific embodiments illustrated. Rather, this disclosure is intended to cover by the appended claims all such modifications and variations as fall within the spirit and scope of the claims.