U.S. patent application number 12/751299 was filed with the patent office on 2010-10-07 for securing brake shoes to brake beams in a railroad car retarder.
This patent application is currently assigned to AAA Sales & Engineering, Inc.. Invention is credited to Thomas J. Heyden.
Application Number | 20100252372 12/751299 |
Document ID | / |
Family ID | 42814315 |
Filed Date | 2010-10-07 |
United States Patent
Application |
20100252372 |
Kind Code |
A1 |
Heyden; Thomas J. |
October 7, 2010 |
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.
Inventors: |
Heyden; Thomas J.;
(Arlington Heights, IL) |
Correspondence
Address: |
ANDRUS, SCEALES, STARKE & SAWALL, LLP
100 EAST WISCONSIN AVENUE, SUITE 1100
MILWAUKEE
WI
53202
US
|
Assignee: |
AAA Sales & Engineering,
Inc.
Oak Creek
WI
|
Family ID: |
42814315 |
Appl. No.: |
12/751299 |
Filed: |
March 31, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61166101 |
Apr 2, 2009 |
|
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|
Current U.S.
Class: |
188/62 ;
188/219.1 |
Current CPC
Class: |
B61K 7/02 20130101 |
Class at
Publication: |
188/62 ;
188/219.1 |
International
Class: |
B61K 7/02 20060101
B61K007/02; B61H 13/36 20060101 B61H013/36 |
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.
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 7A-7A
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, 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.
[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.
* * * * *