Abstract:
An elastomeric bearing. The bearing which may be used to support a railway car body includes first and second members and an elastomeric member interposed in a cavity defined between the first and second members. The second member has a recess formed therein which communicates with the cavity. The elastomeric member includes a working section positioned in the cavity and a non-working section integral with the working section and disposed in the recess. The non-working section serves as a sprue location site during the molding process to avoid locating surface defects associated with the sprue in the working section.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to elastomeric bearings and, more particularly, to an elastomeric side bearing for supporting a railway car body relative to a railway car truck bolster. 
     BACKGROUND OF THE INVENTION 
     A railway car conventionally includes a car body supported on the center plates of a pair of longitudinally spaced trucks. The conical-shaped wheels of the trucks engage the respective rails of a railway track. The trucks travel a generally sinuous path along the track as the respective wheels continuously seek a centered position on a respective rail. In traveling such a sinuous path, a railway truck tends to hunt, i.e., yaw or oscillate about a vertical axis of the truck. One side frame of a truck tends to move ahead of the other which, in turn, results in the flanges of the wheels striking and rubbing against the rails, first on one side, and then on the other. Such undesirable lateral oscillations may cause excessive wheel and track wear. In addition, unstable truck hunting responses can develop if the frequency of the cyclic motion approaches resonance. 
     Also, during travel of a railway car, a railway car body may have the tendency to rock, i.e., oscillate about a horizontal (or roll) axis of the railway car body, independent of the truck upon which the railway car body is mounted. As the trucks of a railway car negotiate their sinuous path of travel along a railway track, the car body may move laterally in concert with the cyclic lateral movement of the truck center plates. A loaded or heavy car may tolerate such lateral oscillation. However, an empty or light car body may rock from side to side which movement can become dangerous should the frequency of the rocking approach resonance. 
     Efforts to control truck hunting and car body rocking include the use of side bearings which are mounted to a truck bolster on opposite sides of the center plate. Conventional side bearings are configured to maintain frictional contact between a truck and a car body. As the truck yaws, an upper portion of a side bearing slides across the underside of the railway car body. The resulting friction produces an opposing torque which acts to prevent yaw motion. For example, see U.S. Pat. No. 4,712,487 to Carlson, U.S. Pat. No. 4,090,750 to Wiebe, and U.S. Pat. No. 3,762,339 to Dwyer. 
     One type of side bearing employs a tube form mount. Inner and outer concentric, annular members are employed. An annular elastomeric spring member is interposed between the inner and outer members. The elastomeric spring is bonded to the outer surface of the inner member and to the inner surface of the outer member such that the elastomeric spring operates in shear to resist relative axial movement between the inner and outer members. The bearing is mounted between the truck and car body such that relative displacement between the truck and the car body causes a corresponding relative axial displacement between the inner and outer members. 
     In order to satisfy close tolerances and achieve faster production rates, bearings as just described are preferably formed using a transfer or injection molding process. With reference to FIG. 10, a tube form mount type bearing  100  is shown. The bearing  100  as shown is mounted in a transfer or injection mold  110  by which it has been formed. The mold  110  includes an upper mold portion  102  including a transfer pot  103  which holds a pig of elastomeric material  140 . A plurality of gates or sprue passages  104  extend from the bottom of the transfer pot and communicate with the cavity defined between an inner annular member  120  and an outer annular member  130 . A lower mold portion  106  seals the lower end of the cavity. An intermediate mold portion  107  supports the outer member  130  in the mold  110 . The elastomeric material  140  is fed into the cavity by forcing a piston  108  downwardly as indicated by arrows  108 A into the transfer pot  103 . The elastomeric material  140  typically follows paths as indicated by the arrows  141 . 
     Notably, the sprue passages  104  are gated into the working section of the elastomeric member  142 . One significant problem experienced with formation of a bearing as described using the prior art method described with reference to FIG. 10 is that at the openings  105  where the sprue passages  104  terminate and meet the elastomeric member  142  (commonly referred to as the sprue location sites), the elastomeric member  142  may develop undesirable performance characteristics which degrade the overall performance of the bearing  100 . More particularly, the sprue location site may be a point of crack initiation when the finished and cured part is repeatedly flexed in service. When the cured cull pad material in the transfer pot  103  is removed from the elastomeric member  142 , a portion of the elastomeric material  140  which has cured within the gate  104  may remain with the elastomeric member  142  as a nub or sprue. Typically, the nub or sprue must be removed. Often, when the nub or sprue is separated from the elastomeric member  142 , the removed portion tears down into the working body of the elastomeric member causing deep sprues and stress concentration which may result in a reduced flex life. Also, flow eddies at the sprue location sites may cause improper knit of the elastomeric material which likewise causes a stress concentration and may reduce the member&#39;s durability. 
     With reference to FIG. 11, as an alternative to terminating the sprues in the working body of the elastomeric member, it has been proposed to form a bearing  100 A including an elastomeric member  142 A having sprue risers  106 A. The upper mold portion  102 A is formed with transfer pot  103 A in the upper portion thereof and plurality of recesses  152 A in the lower face thereof so that the sprue passage openings  105 A, and thus the sprue location sites, are at the sprue risers  106 A and located above the working section of the elastomeric member  142 A. The stress concentrations of the sprue location sites are localized in the low stress riser  106 A so that their effect on the performance of the working body of the elastomeric member  142  is reduced. While this alternative improves on the method described above, it presents significant new problems. With reference to FIG. 11A, in service, the bearing  100 A is axially compressed between a contact plate  52  and a bolster (not shown). In doing so, the contact surface engages the top of the inner member  120 A and also the sprue riser  106 A. Chafing of the sprue riser or deflection of the sprue riser  106 A into the working body of the elastomeric member  142 A by the contact surface  52  may induce stress concentrations and initiate cracks in the elastomeric member. Also, the sprue riser may be unacceptably unattractive. 
     Accordingly, there exists a need for an elastomeric bearing having an elastomeric member formed by transfer or injection molding wherein the sprue location sites do not present stress concentration points in the working body of the elastomeric member. Further, there exists a need for a convenient and cost-effective method for forming such an elastomeric bearing. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter. 
     SUMMARY OF THE INVENTION 
     In view of the above discussion, it is a first aspect in accordance with the present invention to provide an elastomeric bearing, and more particularly, an elastomeric side bearing having an elastomeric member formed by transfer or injection molding wherein the sprue location sites of the elastomeric member do not present stress concentration points in the working body of the elastomeric member. According to a further aspect, the invention provides such an elastomeric side bearing wherein the sprue location sites do not otherwise interfere with the operation or performance of the side bearing. The present invention provides a convenient and cost effective method for forming such a bearing. 
     According to the present invention, the elastomeric bearing includes a rigid first member having a first surface and a rigid second member having a second surface opposing the first surface. The first surface and the second surface define a mold cavity therebetween. A recess or kerf is formed in the second surface and communicates with the mold cavity. An elastomeric member is interposed between the first and second members and is secured to each of the first surface and the second surface preferably by hot vulcanized bonding. The elastomeric member includes a working section disposed in the mold cavity. The working section operates as a spring in shear to resist relative axial movement of the first and second members. The elastomeric member also has a non-working section integrally formed with the working section and disposed in the recess. A sprue location site is defined at the non-working section. 
     Preferably, the bearing includes a plurality of recesses formed in the second surface and spaced apart from one another, and the second member includes an end face adjoining the second surface along a corner, the recess or recesses being formed in the corner. In such a case, the non-working section of the elastomeric member preferably does not extend outwardly from the first member beyond the second surface or the end face. According to a preferred embodiment, the first member is an outer member and the second member is an inner member. 
     The present invention is further directed to an advantageous transfer or injection molding method for forming an elastomeric bearing such as a side bearing. The method includes providing a first member having a first surface and a second member having a second surface opposing the first surface. The first surface and the second surface define a mold cavity therebetween. A recess is formed in the second surface and communicates with the mold cavity. A transfer mold member is provided having a gate passage defined herein, the gate passage having a gate opening. The mold member is positioned such that the gate opening is disposed adjacent the recess. A supply of elastomeric material is fed through the gate passage, through the gate opening and into the recess to fill the mold cavity. 
     The first and second members provided according to the method are preferably constructed as described above. Preferably, the mold cavity is configured to form an elastomeric member having a working section and a non-working section, the non-working working section being disposed in the recess following the step of feeding the elastomeric material. According to a preferred embodiment, the first member is an inner member and the second member is an outer member. The outer member may include a substantially rigid outer casing of the formed bearing. 
     The side bearing and method of the present invention overcome the shortcomings of the aforedescribed methods. More particularly, the sprue location sites are positioned at the non-working sections where they do not adversely affect the performance of the bearing. In this manner, manufacture of the bearing is facilitated and the performance of the bearing is enhanced by locating defects associated with the mold gates outside of the working body of the elastomeric member. 
     The foregoing and other aspects will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing figures. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
     FIG. 1 is a perspective view of a conventional railway car truck; 
     FIG. 2 is an enlarged, partial, forward-looking, elevational view of the railway car assembly having a side bearing assembly according an embodiment of the present invention disposed between the car body and truck bolster; 
     FIG. 3 is a cross-sectional side view of the side bearing of FIG. 2 taken along the line  3 — 3  of FIG. 4; 
     FIG. 4 is a top plan view of the side bearing of FIG. 3; 
     FIG. 5 is a bottom plan view of the side bearing of FIG. 3; 
     FIG. 6 is a cross-sectional side view of the side bearing of FIG. 3 mounted in a mold; 
     FIG. 7 is an enlarged, perspective, partial view of an inner member forming part of the side bearing of FIG. 3; 
     FIG. 8 is a cross-sectional side view of the inner member of FIG. 7; 
     FIG. 9 is a partial, elevational view taken along the line  9 — 9  of FIG. 8; 
     FIG. 10 is a cross-sectional side view of a bearing mounted in a mold for forming the same according to the prior art; 
     FIG. 11 is a cross-sectional side view of another bearing mounted in a mold for forming the same according to the prior art; and 
     FIG. 11A is an enlarged, partial, cross-sectional side view of the bearing of FIG. 11 axially compressed between a contact plate and a bolster (not shown). 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. 
     Referring now to FIG. 1, a railway car truck  10  including side bearings according to an embodiment of the present invention is illustrated. The illustrated truck  10  includes a bolster  12  extending between opposing side frames  14 ,  16 . The ends  14 A,  14 B,  16 A,  16 B of each respective side frame  14 ,  16  are connected to respective wheelsets  18 ,  20 . Each wheelset  18 ,  20  includes a respective axle  18 A,  20 A with two wheels  18 B,  20 B mounted thereto, as illustrated. Bearings  21  are connected to the journal ends of the respective axles  18 A,  20 A outside of the wheels  18 B,  20 B, as illustrated. The opposing ends  22 ,  24  of the bolster  12  are received in respective window openings  30 ,  32  of the side frames  14 ,  16 . The side frames  14 ,  16  support the bolster  12  through respective spring assemblies  34 ,  36  which are configured to reduce dynamic forces produced as the truck  10  travels along a track, thereby providing a smooth ride. 
     As is known to those skilled in the art, a railway car body is connected to a centerplate  38  of the bolster  12  via a kingpin which allows the car body to pivot on the truck  10  as the truck travels along a curved section of track. A pair of side bearings  200 ,  201 , according to the present invention are provided on respective sides of the centerplate  38 , as illustrated. Each side bearing  200 ,  201  is securely mounted to the bolster  12  and maintains constant frictional contact with a railway car body, typically via wear plates mounted to the underside of the railway car body. The frictional contact, however, is not of sufficient magnitude to prevent relative movement between the car body and the truck bolster  12 . 
     Referring now to FIG. 2, a partial frontal elevational view of a truck bolster  12  having a side bearing  200  mounted thereto, according to the present invention, is illustrated. A car frame  50  and body (not shown) supported by the bolster  12  via the centerplate  38  and side bearings  200 ,  201  are positioned on opposite sides of the centerplate  38 . It is noted that only the side bearing  200  is illustrated in FIG. 2. A wear plate  52  is connected to the car frame  50 , as illustrated, for frictional engagement with the top (or upper) portion of the side bearing  200 . The side bearing  200  is mounted to the bolster  12  via suitable mounting means, for example, a plurality of bolts or studs with nuts. 
     With reference to FIGS. 3-5, the side bearing  200  according to the present invention is shown in greater detail. The side bearing  200  includes an inner annular member  220  and a concentric outer annular member  230 . The inner and outer members  220 ,  230  are rigid and preferably formed of metal, such as steel. The inner member  220  includes a cavity  225  formed therein. An annular elastomeric member  242  is disposed between the inner member  220  and the outer member  230  and is bonded to each of the outer surface  222  of the inner member  220  and the inner surface  232  of the outer member  230 . 
     The elastomeric member  242  is preferably formed of a natural or synthetic rubber or a blend thereof. The elastomeric member  242  preferably is of a hardness of between about 40 and 65 Durometer Shore A. However, any other suitable hardness may be utilized. 
     The elastomeric member  242  includes a working body section  245  extending about its circumference and extending axially through dimension S (see FIG.  3 ). By “working body section” it is meant that this portion of the elastomeric member  242  serves as a spring, which in this case is operating in shear, which resists relative axial movement between the inner member  220  and the outer member  230 . 
     The bearing  200  is characterized in that the inner member  220  has kerfs or recesses  228  formed therein about its upper edge  226  and the elastomeric member  242  includes non-working sections  244  disposed in the recesses  228 . The recesses  228  and the non-working sections  244  are spaced apart about the circumference of the bearing  200  (see FIG.  4 ). The non-working sections  244  extend axially through dimension R. By “non-working section” it is meant that these portions of the elastomeric member  242  provide substantially no or only de minimis resistance to relative axial movement between the inner and outer members  220 ,  230  through their intended range of relative motion. As shown, there are eight (8) of the non-working sections, however, more or fewer may be provided. Sprues or nubs  246  of elastomeric material project from the non-working sections  244  and may optionally be removed. As will be appreciated by the skilled artisan upon review of FIGS. 3-5, the non-working sections  244  will be substantially free of shear stress when the inner member  220  and the outer member  230  are axially displaced relative to each other at least as far as axially aligning their respective upper faces  224 ,  234 . Accordingly, the non-working sections  244  do not adversely affect the performance of the bearing  200 . To the contrary, the non-working sections  244  facilitate the manufacture of the bearing  200  and, in fact, enhance the performance of the bearing by locating defects associated with the transfer mold gates outside of the working body section  245 , as discussed in more detail below. 
     The bearing  200  may be formed by the following method according to the present invention. With reference FIG. 6, the bearing  200  is shown mounted in a mold  210 . Initially, the inner member  220  and the outer member  230  are mounted relative to mold pieces  206 ,  207  as shown. A pin  206 A of the base mold piece  206  and a hole  223  (FIGS. 3,  5 ) formed in the inner member  220  serve to positively orient the inner member  220  and the base mold piece  206  with respect to one another. Positive alignment may be achieved by other means as well, for example, the lower opening of the cavity  225  may be hex-shaped, octogaon shaped, or include a key with a mating piece being formed on the mold base piece  206 . The shape of the base piece  206  defines the shape of the lower face of the elastomeric member  242  once formed. 
     With reference to FIGS. 7-9, the inner member  220  has formed therein a plurality of circumferentially spaced apart recesses or kerfs  228 . The inner member  220  has an upper face  224  which joins the outer surface  222  along a circumferential extending corner  226 . The corner  226  is preferably continuously uniform except at the locations of the kerfs  228 . The inner member  220 , including the kerfs  228 , is preferably formed by casting. Alternatively, the recesses  228 , as well as the inner member  220 , may be formed by machining. 
     Preferably, the recesses  228  are smoothly rounded as shown in FIG.  9 . The recesses  228  are preferably spaced apart between about 30 degrees and 60 degrees about the circumference of the inner member  220 . Preferably also, each recess  228  has a length L in the range of between about 0.25 inch (6.3 mm) and 0.75 inch (19.0 mm) (FIG.  8 ). The width W (FIG. 9) of each recess  228  is preferably between about 0.12 inch (3.05 mm) and 0.5 inch (12.7 mm). The depth D (FIG. 9) of each recess  228  is preferably between about 0.25 inch (6.3 mm) and 0.75 inch (19 mm). Preferably, each recess  228  forms an angle A (FIG. 8) with respect to the outer surface  222  of between about 15 degrees and 45 degrees. 
     Again referring to FIG. 6, the upper mold portion  202  includes a plurality of sprue passages or gate passages  204  having spacing and locations corresponding to the spacing and locations of the plurality of recesses  228 . The upper mold portion  202  is placed over the inner member  220  and the outer member  230  as shown. More particularly, the upper mold portion  202  is placed such that gate openings  205  of the respective gate passages  204  are positioned at each recess  228  as shown. To ensure proper alignment, the mold  210  is configured such that the upper mold portion  202  and the base mold piece  206  are positively oriented with respect to one another via the intermediate mold piece  207  and appropriate locator pins (not shown) or other suitable locator mechanisms. The inner member is oriented with respect to the base mold piece  206  by the hole  223  and pin  206 A. Accordingly, positive alignment between the inner member  220  and the upper mold portion  202 , and thereby the recesses  228  and the gate openings  204 , is ensured. 
     The transfer pot  203  of the upper mold portion  202  is filled with a pig of uncured elastomeric material  240 . A piston  208  is driven in the direction indicated by the arrows  208 A. The elastomeric material  240  under heat and pressure is thereby forced through the gate passages  204 . The elastomeric material  240  enters the mold cavity  209  at the gate openings  205 , enters the respective recesses  228 , flows into the cavity  209  and fills the cavity. The recesses  228  are also filled with elastomeric material  240  forming the sprue risers  244 . Notably, the gate openings  205  are located such that the effective sprue risers are positioned at or within the recesses  228  and therefore within the envelope of the inner member  220  and entirely within the non-working section. 
     The elastomeric material is vulcanized bonded via suitable beat and pressure to the outer surface  222  of the inner member and to the inner surface  232  of the outer member. Once the elastomeric material has sufficiently cured, the cull pad of cured elastomer  240  and the upper mold piece  202  are removed thus breaking the sprues at the sprue openings  205 . If desired, the portions of sprues  246  (see FIG. 4) which remain following removal of the upper mold portion  202  may be removed. Finally, the outer member  230  is swaged (radially and plastically compressed) to statically pre-load the elastomeric member  242 . 
     As discussed above, by the provision of recesses  228 , the imperfections associated with the sprue location sites (i.e., where the gate openings  205  meet the elastomeric member  242 ) are substantially isolated from the working body section  245  (FIG.  3 ). If the sprues  246  remain, deflection thereof by a contact plate or the like will not present a problem. If the sprues  246  are removed, either during removal of the transfer pot  202  or as a separate step thereafter, and the removed portion tears into the non-working body section  244 , the effective performance of the bearing  200  will not be significantly degraded. Moreover, poor knit of the elastomeric material in the non-working sections  244  will not significantly adversely affect the performance of the elastomeric member  242 . Additionally, the non-working sections  244  of the elastomeric member  242  are not unattractive or obtrusive. 
     It will be appreciated that mold configurations other than those shown herein may be employed. Further, it will be appreciated that different constructions and arrangements of the inner member  220  and the outer member  230  may be used. Recesses may be formed in the outer member  230  in addition to or in place of the recesses  228  in the inner member  220 . In such case, the transfer pot would be provided with corresponding gate passages and openings and the formed bearing would have non-working elastomeric sections in these recesses. 
     The foregoing is illustrative of the present invention and is not to be construed as limiting thereof. Although a few exemplary embodiments of this invention have been described, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures. Therefore, it is to be understood that the foregoing is illustrative of the present invention and is not to be construed as limited to the specific embodiments disclosed, and that modifications to the disclosed embodiments, as well as other embodiments, are intended to be included within the scope of the appended claims. The invention is defined by the following claims, with equivalents of the claims to be included therein.