Abstract:
Several embodiments of a system for connecting brake shoes to brake beams in a railroad car retarder all provide enhanced connecting joint tightness that reduces premature connecting joint loosening, reduces maintenance, and reduces failure of connecting bolts or equivalent connecting pins.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application relates to and claims priority from U.S. Provisional Application Ser. No. 61/166,101, filed on Apr. 2, 2009. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention pertains to rail car retarders used in railroad classification yards and, more particularly, to improved arrangements for attaching the brake shoes to the brake beams in a pneumatic retarder. 
         [0003]    Railroad car retarders are used in classification yards to regulate the speed of freight cars being arranged to make up a train or to be temporarily side tracked. Many types of hydraulic, pneumatic and mechanical systems are used to operate retarders. They all typically operate by clamping the railroad car wheels between a pair of parallel brake shoes positioned on each side of both track rails where they can be moved toward one another to clamp therebetween the wheels of a rolling freight car entering the retarder. The brake shoes are typically spring-biased or moved by gravity to open and are closed by the operating system to effect a braking force on the car wheels as the car enters the retarder and forces the brake shoes apart. 
         [0004]    In a typical pneumatic retarder, the brake shoes which may have a length of 75 in. (about 2 m) are made of steel or iron and are typically bolted to heavy cast steel brake beams of the same length. The beams are incorporated into the powered operating linkage which causes the brake shoes of each pair to be moved toward one another and into contact with opposite sides of the railroad car wheel. 
         [0005]    On pneumatic retarders, it is known to attach a brake shoe to the adjacent end halves of two brake beams, such that the brake shoes tie the beams together. In hydraulic retarders, brake shoes are mounted by attaching each brake shoe to a separate brake beam. The shoes are typically attached to the beams with bolted connections, using nuts threaded on the bolts. Tying the brake beams together with the brake shoes is a cost effective means for turning the beams/shoes into one long indeterminate beam. Thus, the force of multiple cylinders and actuating levers acts against any one car wheel. This reduces the cost of the cylinders and levers. 
         [0006]    Because the massive brake beams and correspondingly heavy linkage arrangements which connect and operate them cannot be made to move identically in use, conventional wisdom has dictated that by tying adjacent brake beams with the brake shoes, more uniformity in operation could be attained. It has been found, however, that the tightly bolted brake shoes cannot effectively force the beams to move identically. This is because the force imposed on the brake beams by the operating system and the massive construction of the beams is too great. As a result, it is beam movement that controls with the result that bolts get worn, stretched and loosened in operation. In addition, the braking action of the brake shoes against the rolling car wheels causes a primarily vertical cyclic loading, compounding the loading on the bolts. 
         [0007]    In an attempt to rectify the foregoing problem, retarders have been built with a single brake shoe mounted on a brake beam of equal length or two shoes mounted on the face of one beam, such that a single shoe spanning and connected to end halves of adjacent beams was eliminated and thus no direct connection between adjacent brake beams. With this arrangement, the forces at each brake beam support are much larger and there is therefore more wear of the operating linkage. 
         [0008]    Bolting one brake shoe directly to one beam eliminates many of the loads on the bolts. However, when this is done on hydraulic retarders, it has lead to another problem commonly referred to as “slamming” which is the heavy repeating brake shoe engagement generated sequentially as a car passes from brake beam to brake beam. This puts very high impact loads on several parts of the linkage, causing wear and cracking. In addition, the bolted connections in this arrangement are still subject to extremely high vertical cyclic loads and are subject to loosening and failure. 
       SUMMARY OF THE INVENTION 
       [0009]    In accordance with the subject invention, several related solutions to bolt loosening and failure in both types of retarders have been found. In one embodiment, in which the brake shoe spans adjacent end halves of two brake beams, the bolts that connect the brake shoe to the beams are supplemented with large hardened pins which become the main load carrying elements. The bolts function to help seat the pins by drawing the brake shoe and brake beam together and to hold the assembly in place. 
         [0010]    In the other embodiment, in which one brake shoe is attached to and spans the length of a single brake beam, a tongue and groove arrangement on the ends of adjacent brake shoes permits the lead brake shoe, when actuated, to engage and begin to lift the adjacent following shoe to get it moving in the correct direction. This arrangement also reduces considerably the sequential slamming in prior art retarders of this design. The large hardened pins of the embodiment discussed above are also used in this arrangement. 
         [0011]    Although some improvement in the decreased bolt loosening has been achieved in both of the foregoing embodiments utilizing pins to carry the main loads, unacceptable bolt loosening and failure continues to be encountered. A significant cause of this continued problem appears to be in the inability of the installer to torque the bolts connecting the brake shoes to the brake beams to their full theoretical loads. This is believed to be primarily due to the continued use in the industry of so called “cam head” bolts in which a round shank bolt has an offset round bolt head. The offset bolt head seats in an offset round blind bore surrounding the bore in the brake shoe to provide the opposing force when the bolt is tightened. The offset head exposes the head/shank connection to very high shear forces during tightening. It also causes the bolt head to climb out of its counterbore. 
         [0012]    This problem has been overcome by utilizing a square head bolt with the head being carried in an elongated slot in the brake shoe. Alternate connecting arrangements also provide improvements over the prior art. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a top plan view of a prior art hydraulic retarder that has two shoes mounted on the face of one beam. 
           [0014]      FIG. 2  is an enlarged detail showing a retarder shoe/beam detail and additionally showing an embodiment of the invention using supplemental load-isolating connecting pins. 
           [0015]      FIG. 3  is an enlarged vertical section through the interconnected brake shoe and brake beam, taken on line  3 - 3  of  FIG. 2 , showing a hardened connecting pin. 
           [0016]      FIG. 4  is an enlarged vertical section, taken on line  4 - 4  of  FIG. 2 , showing a connecting bolt. 
           [0017]      FIG. 5  is a detail similar to  FIG. 2  showing the connection between the brake shoe and the brake beam in an alternate embodiment of the invention. 
           [0018]      FIG. 6  is an enlarged elevation showing the tongue and groove connection between adjacent brake shoes in the  FIG. 2  embodiment. 
           [0019]      FIG. 7  shows a conventional brake shoe modified to accommodate a square head bolt. 
           [0020]      FIG. 7A  is an enlarged sectional detail taken on line  7 A- 7 A of  FIG. 7 . 
           [0021]      FIG. 8  shows a square head bolt used with the improved connection arrangement. 
           [0022]      FIG. 9  is a conventional brake shoe machined to accept prior art cam head connecting bolts. 
           [0023]      FIG. 10  shows a conventional cam head bolt used with the  FIG. 9  brake shoe. 
           [0024]      FIG. 11  is a top plan view of a retarder section of the type shown in  FIG. 5 , including a resilient connection between adjacent brake beam ends. 
           [0025]      FIG. 12  is a sectional detail taken on line  12 - 12  of  FIG. 11 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0026]    Referring to  FIG. 1 , a railroad car retarder  10  is shown mounted along a section of track  11  comprising a pair of conventional rails  12 . Track  11  continues in both directions from the retarder with rail cars entering the retarder from one direction, being slowed by the braking action of the retarder, and existing the other end. Each retarder  10  includes linear series of pairs of parallel brake shoes  13  on opposite sides of and parallel to each of the rails  12 . The brake shoes are attached to and carried by brake beams  14 , which position the brake shoes above the tops of the rails  12  such that, when moved toward one another, the brake shoes engage the sides of the car wheels to effect a braking or retarding of the moving rail car, as is well known in the art. 
         [0027]    Referring also to  FIG. 2 , there is shown one of a pair of brake shoe assemblies  13  for one track  11  of a retarder. The partial assembly of  FIG. 2  shows two adjacent brake beams  14  to which are attached three brake shoes  13 . Complete attachment of only the center brake shoe  13  to one half of each of the adjacent brake beams  14  is shown. It will be understood, however, that additional brake beams and brake shoes extend in opposite directions from the partial assembly shown. In addition, the counteracting brake shoes for the other side of the rail  12  are not shown, but may be clearly seen in  FIG. 1 . 
         [0028]    Each brake shoe  13  is of the same length as a brake beam  14 . However, in the arrangement shown, the brake shoe  13  spans one-half of each of the adjacent brake beams  14  and is connected thereto to tie the brake beams together. Referring also to  FIG. 4 , each brake shoe  13  includes a vertical web  17  and a horizontal braking contact bar  18 . The brake shoe  13  is attached by the vertical web  17  to a connecting flange  20  on the brake beam  14  using bolts  21 . Each bolt  21  extends through a bore  22  in the connecting flange  20  and is threaded into a tapped hole  23  in the vertical web  17  of the brake shoe  13 . In the brake beam arrangement shown in  FIG. 2 , each of the brake beams  14  has three bolts  21  connecting the ends of adjacent brake beams  14  to the single brake shoe  13 . This arrangement allows an increase in bolt diameter since the bolts can be installed from the field side of the retarder and do not have to go over the rail during installation. 
         [0029]    Because of the heavy, massive retarder construction comprising the brake shoes  13 , brake beams  14  and operating linkage  15 , some dimensional variation is inevitable and it is not possible to assure that adjacent brake beams  14  will move in an identical manner and to identical positions as they are activated to accomplish the braking function. In addition, shifting of the underlying foundation causes misalignment between brake beams. Tying adjacent brake beams  14  together with a brake shoe  13  will not always assure that the beams move identically, but rather will more likely cause the bolts to stretch and wear and, in some cases, eventually loosen or fail. In addition, of course, massive cyclical forces are imposed on the brake shoes  13  by contact with the rolling car wheels. Many conventional connecting bolts  37  simply cannot handle these forces for longer periods and are, therefore, the points where the retarder typically fails. In prior art retarders, such as those using cam head connecting bolts, as will be discussed below with respect to  FIGS. 9 and 10 , overstressed and loosened bolts must often be replaced weekly. The consequence of non-replacement of the bolts is shortening of the life or failure of the brake shoes. This represents a great expense and, in the worse case, can result in disconnection of a brake shoe and damage the system or derailment of cars. 
         [0030]    In accordance with one embodiment of the present invention, hardened pins  24  are used to carry the primary operating loads on the retarder rather than the bolts  21 . Referring to  FIGS. 2 and 3 , the brake shoe  13  is connected to the pair of adjacent brake beams  14  with three pins  24 . Each pin  24  is installed with a close clearance fit in a pin bore  25  extending through the connecting flange  20  of the brake beam  14  and an interference fit in a blind hole  26  in the vertical web  17  of the brake shoe  13 . Each pin  24  includes a tapered end  27  to facilitate insertion, compensate for slight misalignment of the bores  25  and  26 , and maintain the close fit. Preferably, the pins  24  are not inserted completely into the brake shoes  13  and, in particular, the pins do not bottom in the blind holes  26  such that, if necessary, bolts  21  can be used to draw the vertical web  17  of the brake shoe into contact with the connecting flange  20  of the brake beam. 
         [0031]    It is also important to note the hardened pins  24  (as well as the bolted embodiments discussed below) are in linear alignment with the bores  22  in the brake beam  14 . This permits direct match up of replacement brake shoes of the prior art with modified hole patterns to accommodate the connecting pins  24 . 
         [0032]    Referring briefly also to  FIG. 6 , the manner in which the hardened pins  24  interconnect the brake shoes to the brake beams may be reversed. In this embodiment, the blind hole  26  in the vertical web of the brake shoe is replaced with a through bore that receives the pin with a close clearance fit. In this situation, the pin  24  is reversed and it is inserted in the opposite direction through the clearance fit bore and into a press fit in the pin bore  25  of the brake beam connecting flange  20 . There are two hardened pins  24  connecting the right end of the center brake shoe  13  to the brake beam  14  on the right. There is only a single pin  24  connecting the left end of the brake shoe to the brake beam on the left. With respect to the single pin  24  connecting to the left brake beam, the blind hole  28  in the left end of the brake shoe  13  is formed as a slot to be longer by a small amount, in the linear direction of the shoe, than the diameter of the blind holes  26  for the other two pins (attaching the right brake beam). The elongation of the blind slot  28  need be only about 0.020 inch (about 0.5 mm). This will assure that, in installation, the brake shoe will interfere with the pin before the brake shoe forces one or more of the connecting bolts  21  against the side of the through bores  22  in the brake beam connecting flange. The interference fit of the pins  24  in the bores  25  and the close clearance fit of pins  24  in bores  26  prevents the brake shoe from rubbing on the face of the brake beam as a result of the primarily vertical cyclical loadings imposed by the moving car wheels. 
         [0033]    The pins are readily accessible for easy replacement, if necessary. In use, however, the pins will carry most of the load that would otherwise be carried by the bolts. The bolts  21  thus function primarily to prevent the brake shoe  13  from falling off the pins  24 . 
         [0034]    Referring now to  FIGS. 5 and 6 , there is shown an alternate embodiment for attaching the brake shoes to the brake beams. In this embodiment, a brake shoe is attached along its full length to a brake beam of the same length. In other words, there is no direct tying of adjacent brake beams with a brake shoe. Nevertheless, contact between adjacent brake shoes is provided, in use, as will be described below. 
         [0035]    As is best seen in  FIG. 5 , a right brake beam  30  has attached to it a right brake shoe  31 , both of which are of equal length. Similarly, a left brake beam  32  has attached to it an equal length left brake shoe  33 . Thus, there is initial separation and no direct contact between the right beam and shoe assembly  30 ,  31  and the left beam and shoe assembly  32 ,  33 . However, each brake shoe  31 ,  33  has an axially extending tongue  34  formed on one end and a groove  35  formed on the other end, as shown in  FIG. 6 . The brake shoes  31  and  33  are mounted to their respective brake beams  30  and  32  such that the tongue  34  of one shoe is received in the groove  35  of the other. However, substantial clearance is provided between the tongue and groove as is best seen in  FIG. 6 . In the longitudinal direction, a spacing of about 0.50 inch (about 13 mm) may be provided. In the vertical direction, a much smaller clearance of 0.06 inch (about 1.5 mm) may be provided. 
         [0036]    Each brake shoe  31  or  33  is attached to its respective brake beam  30  or  32  with six connecting bolts  21  as described with respect to the previous embodiment. In addition, a pair of hardened pins  24  may also be used to connect the shoe to the beam, as previously described with respect to the embodiment shown in  FIG. 3 . 
         [0037]    The vertical clearance between the tongue of the right brake shoe  31  and the groove of the left brake shoe  33  compensates for minor misalignment between adjacent brake beams. However, during braking operation, the tongue  34  of the right brake shoe  31  will engage the groove  35  in the left brake shoe  33  to begin to lift the left brake shoe  33  in the direction to which its brake beam  32  will force it to move. The upward component of brake shoe movement results from a slight arc (upwardly and outwardly) through which the brake shoe moves by virtue of the typical beam and linkage construction. In addition, by removing the rigid connection between adjacent brake beams by not tying them together with a brake shoe, the loadings on the bolted connections are reduced considerably. However, it is still desirable to utilize the hardened pins  24  in addition to the bolts for the reasons discussed above with respect to the first described embodiment. 
         [0038]    Referring first to  FIGS. 9 and 10 , a brake shoe  36  machined to receive a cam head bolt  37  is shown. The brake shoe includes through bores  38  for receipt of the cam head bolt shank  40  which also passes through aligned bores in the brake beam to which it is connected by threading a nut (not shown) thereon, all in a manner well known in the industry. The cam head bolt  37  seats in an oversize offset blind bore  41  surrounding the through bore  38 . 
         [0039]    It has been found that cam head bolts  37  cannot be fully tightened to the grade 8 levels for which they are designed, i.e. 650 ft./lbs. Instead, because of the inherent offset loads applied to the offset cam head in tightening, these bolts can only be torqued to about 475 ft./lbs. without failure. 
         [0040]    In accordance with the improved embodiment of the invention shown in  FIGS. 7 ,  7 A and  8 , a brake beam  42  has a modified bolt hole pattern which includes conventional through bores  43  for receipt of a bolt shank. In this embodiment, however, the prior art cam head bolt  37  has been replaced with a square head bolt  44  which is received in a milled slot  45  that surrounds the through bore  43 . As with the prior art embodiment, the bolt head  46  is retained in the slot  45  to permit a nut  49  to be threaded on the shank, but in this case to a full grade 8 torque limit of 650 ft./lbs. 
         [0041]    As indicated above, the cam head bolt  37  cannot be tightened to a full grade 8 level because of the asymmetrical shape of the head, resulting in an uneven load distribution in both tension and shear. By using a square head bolt  44 , the bolt can be fully and uniformly tightened to a grade 8 level. The increase in torque results in an increased stretching of the bolt which, in turn, will keep the bolt tighter for a longer period of time. The milled slot  45  should preferably be at least as deep as the height of the bolt head  46 , but may be somewhat shallower, as shown, thereby allowing the bolt head  46  to protrude just slightly out of the slot  45 . This is to assure that only as much of the brake shoe is machined away as needed in order to avoid weakening the shoe. 
         [0042]    Cutting complicated shapes into the face of the brake shoe  42  to restrain the bolt head is not cost effective. By utilizing the milled slot  45 , the pattern of through bores  43  may be maintained in their position in the brake shoe, thereby permitting the retrofitting of new brake shoes onto existing brake beams. Using a square head bolt  44 , instead of a hex head bolt, provides a larger interface with the milled slot  45  and allows for greater clearance between the bolt head and the slot, while permitting a looser tolerance on both parts. More specifically, the opposite bolt head faces  48  provide increased contact surface areas with the side faces  50  of the milled slots  45 . This substantially increases the load bearing area and permits the loads to be uniformly applied to maximize torque capacity and eliminate the uneven load distribution created with the prior art use of cam head bolts. 
         [0043]    In summary, the square head bolt  44  and the shoe  42  are the most cost effective way found to date to accomplish: 
         [0044]    increasing the load bearing area which in turn lengthens the time for material to wear away causing the bolts to loosen; 
         [0045]    permitting symmetric loading of the bolt head without incurring very high brake shoe machining costs; 
         [0046]    increasing bolt torque which stretches the bolt further, increasing the time before the bolt becomes loose from material wear; 
         [0047]    maintaining interchangeability with existing brake beams; 
         [0048]    maintaining the ease of inserting the bolt over the head of the running rail (most conventional bolts will not pass over the head of the running rail with the beam bolt holes in their current position); 
         [0049]    avoiding contact with the passing railcar wheels; and 
         [0050]    avoiding a reduction in the head of the brake shoe (the use of conventional bolts would result in a need to move the beam holes upward and remove material from the brake shoe head in order to maintain the ability to replace shoes and bolts for maintenance). 
         [0051]    Referring now to  FIGS. 11-12 , there is shown a modified arrangement of the  FIG. 5  retarder in which adjacent brake beams  30  and  32  are tied together with a resilient connection  51 . The resilient connection helps to transfer the load from one brake beam to the next as a rail car proceeds through the retarder. In this way, the phenomenon of “slamming” in retarders where there is no connection between the brake beams or the brake shoes can be minimized or eliminated. This resilient connection also restores the indeterminate beam, thereby keeping the operating lever forces low. 
         [0052]    The resilient connection comprises a multi-layer leaf spring  52  that is seated in adjacent pockets or recesses  53  formed in adjacent ends of the brake beams. The leafs of the spring  52  are positioned on edge such that the planes of the leaves are vertically disposed and extend in the linear direction of the retarder. Although three spring leafs  54  are shown, any suitable number may be used. The recesses  53  are formed in a bottom edge of the brake beams  30 ,  32  and are enclosed and held in place by the upper face  55  of an operating lever  56  for the retarder.