Securing Brake Shoes to Brake Beams in a Railroad Car Retarder

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

BACKGROUND OF THE INVENTION

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.

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.

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.

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.

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.

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.

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

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.

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.

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.

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

FIG. 1 is a top plan view of a prior art hydraulic retarder that has two shoes mounted on the face of one beam.

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.

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.

FIG. 4 is an enlarged vertical section, taken on line 4-4 of FIG. 2, showing a connecting bolt.

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.

FIG. 6 is an enlarged elevation showing the tongue and groove connection between adjacent brake shoes in the FIG. 2 embodiment.

FIG. 7 shows a conventional brake shoe modified to accommodate a square head bolt.

FIG. 7A is an enlarged sectional detail taken on line 7A-7A of FIG. 7.

FIG. 8 shows a square head bolt used with the improved connection arrangement.

FIG. 9 is a conventional brake shoe machined to accept prior art cam head connecting bolts.

FIG. 10 shows a conventional cam head bolt used with the FIG. 9 brake shoe.

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.

FIG. 12 is a sectional detail taken on line 12-12 of FIG. 11.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

In accordance with the improved embodiment of the invention shown in FIGS. 7, 7A 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.

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.

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.

In summary, the square head bolt 44 and the shoe 42 are the most cost effective way found to date to accomplish:

increasing the load bearing area which in turn lengthens the time for material to wear away causing the bolts to loosen;

permitting symmetric loading of the bolt head without incurring very high brake shoe machining costs;

increasing bolt torque which stretches the bolt further, increasing the time before the bolt becomes loose from material wear;

maintaining interchangeability with existing brake beams;

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);

avoiding contact with the passing railcar wheels; and

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).

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.

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.

Claims

1. A system for bolting brake shoes to brake beams in a railroad car retarder wherein the brake shoes have a generally inverted L-shaped cross section including a vertical web and a horizontal contact bar, and a vertical bolting face opposite the contract bar adapted to engage a mounting face on a connecting flange on the brake beam, the system comprising: elongate horizontally extending blind slots in the vertical web of the brake shoe, said slots extending linearly along the web and positioned in spaced relation, the slots having coplanar bottom surfaces and flat parallel opposing side faces lying in respective common planes, through bores in the slots extending perpendicular to the bottom surfaces and aligned with through bores in the connecting flange of the brake beam;a headed grade 8 bolt for each aligned pair of through bores, said bolts positioned with the bolt heads in the slots and having opposite parallel bolt head faces dimensioned to provide a close clearance fit with the side faces of the slot;said bolts having threaded shanks for receipt of nuts threaded on the ends thereof to engage the vertical outside face of the brake beam connecting flange;whereby the engagement of the bolt head faces with the side faces of the slots permits bolts to be tightened to grade 8 level and a uniform clamping torque to be applied to the bolts sufficient to prevent relative rubbing movement and loosening of the connection between the brake shoes and the brake beams in use.

2. The system as set forth in claim 1 wherein the headed bolts comprise square-head bolts.

3. The system as set forth in claim 1 wherein the blind slots comprise milled slots.

4. The system as set forth in claim 1 wherein the slots are milled to define semi-cylindrical ends joining the side faces of the slots.

5. The system as set forth in claim 1 wherein each brake shoe is attached to the end halves of adjacent brake beams.

6. The system as set forth in claim 1 wherein each brake shoe is attached to and runs coextensively with a brake beam.

7. The system as set forth in claim 6 wherein the adjacent ends of adjacent brake shoes are provided with a tongue and groove arrangement operable to provide restrictive engagement and transfer of loading applied as a result of uneven movement of adjacent brake beams.

8. The system as set forth in clam 6 wherein brake beams are tied together with a resilient connection.

9. The system as set forth in claim 8 wherein the resilient connection comprises a leaf spring arrangement.

10. The system as set forth in claim 9 wherein the leaf spring arrangement comprises: aligned recesses formed in the adjacent ends of the brake beams; and,a plurality of leaf spring layers positioned in the recesses and spanning the space between said brake beam ends.

11. An improved system for connecting brake shoes to brake beams in a railroad car retarder wherein the brake shoes have a generally inverted L-shaped cross section including a vertical web and a horizontal contact bar, and a vertical attachment face on the vertical web opposite the contract bar adapted to engage a mounting face on a connecting flange on the brake beam, the system comprising: a connection arrangement selected from the group consisting of (1) bolts extending through horizontal bores in the brake beam mounting face and threaded into tapped holes in the attachment face of the brake shoe, (2) pins extending through bores in the brake beam mounting face with a close clearance fit and into blind holes in the attachment face of the brake shoe with an interference fit, (3) pins extending through bores in the brake shoes with a close clearance fit and into holes in the brake beam with an interference fit; and (4) square-head bolts with bolt heads received in horizontal slots in the brake shoe web with a close clearance fit and bolt shanks extending through aligned pairs of through bores in said brake shoe attachment face and said brake beam connecting flange and nuts threaded on the bolts against the vertical outside face of the brake beam connecting flange;whereby the selected arrangement provides a fixed connection between the brake shoe and the brake beam adequate to prevent relative rubbing movement between the brake shoes and brake beams and loosening of the connections.

12. The system as set forth in claim 11 wherein each of said connection arrangements is installed from the field side of the retarder by one person.

13. The system as set forth in claim 11 wherein each brake shoe is attached to and runs coextensively with only one brake beam.

14. The system as set forth in claim 13 wherein the adjacent ends of adjacent brake shoes are provided with a tongue and groove arrangement operable to provide restrictive engagement and transfer of loading applied as a result of uneven movement of adjacent brake beams.

15. The system as set forth in claim 13 wherein adjacent brake beams are tied together with a resilient connection.

16. The system as set forth in claim 15 wherein the resilient connection comprises a leaf spring arrangement.

17. The system as set forth in claim 16 wherein the leaf spring arrangement comprises: aligned recesses formed in the adjacent ends of the brake beams; and,a plurality of leaf spring layers positioned in the recesses and spanning the space between said brake beam ends.

18. The system as set forth in claim 16 wherein the leaf spring layers are retained in operative position by a retarder system operating lever.

19. The system as set forth in claim 11 wherein the connection arrangement having bolts extending through horizontal bores in the brake beam mounting face and threaded into tapped holes in the attachment face of the brake shoe comprises horizontal bores providing a close clearance fit with the bolts.

20. The system as set forth in claim 11 wherein the connection arrangement having pins extending through bores in the brake beam and into blind holes in the brake shoe includes supplemental threaded bolts positioned between and in linear alignment with the pins to assure contact between the contact face on the brake shoe and the mounting face on the brake beam.

21. The system as set forth in claim 11 wherein the horizontal slots for receipt of the heads of the square-head bolts comprise milled slots having flat parallel opposing side faces providing the close clearance fit with opposite bolt head faces.

22. The system as set forth in claim 21 wherein the milled slots have a depth approximately equal to the thickness of the bolt heads in the axial direction.