Note: Descriptions are shown in the official language in which they were submitted.
~6)48945
BACKGROUND OF TB INVENTION
Single cylinder truck-mounted brake systems for
rail cars have been in use for some time with varying de-
grees of success. One such system is shown in U.S. Patent
No. 3,780,837 issued to HaYdu.
While such prior art devices have achieved a mea-
sure of success, various problems and drawbacks have been
noted. The brake beams of these systems are usually heavy
section castings which include integral means for mounting
brake shoes, brake cylinders, parking brake linkages and
related equipment. The large size of these beams is made
necessary by the location on the beams of the points at
which the braking force is applied to the beams by the brake
cylinder. Usually, the pivot points for the linkages in-
terconnecting the parallel beams and the brake cylinder are
located well inboard of the location at which braking force
is transferred from the beam to the rail car wheels. This
results in the generation of high bending moment stresses
in the beams, which must be absorbed by heavy crossections.
Clearly, the large beam size results in increased component
weight and cost, plus reduced operating efficiency. More-
over, the use of integral brake heads requires beam removal
should the brake heads become worn due to wear of the brake
shoes.
Prior art systems have also been criticized be-
cause of the rather large amount of pressurized fluid re-
:1~4~945
quired to stroke their long stroke actuators, especiallythose actuators having no provision for slack adjustment.
Provision of long stroke capability is desirable to permit
the use of thicker, longer lasting brake shoes. Where
slack adjustment is provided, it frequently adjusts only for
increases in brake shoe clearance due to wear but not for
decreases due to shoe or wheel replacement.
Another drawback of prior art systems of this
type has concerned the manual or parking brake system.
Frequently, as in older parallel beam systems, the parking
brakes are applied through a linkage mounted on one side of
the truck, to provide clearance with the central portions of
the truck and bolster. Due to the off-center mounting of
the parking brake linkage, the brakes tend to be applied
first on the side nearer the linkage mount and then, if at
all, on the side further from the linkage mount. Due to
the point of force application, high stresses are induced
in the beams, which must be of a heavy crossection. The
off-center mounting may result in application of insufficient
braking force in cases where contact is made only on one
side. Furthermore, crewmen checking a car to ensure park-
ing brake application may mistakenly conclude that the brake
has not been applied after looking at the shoes and wheels
on the side opposite the linkage mount.
OBJECTS OF THE INVE~TION
An object of the invention is to provide a par-
allel beam brake rigging having light-weight tubular brake
89~5
beams and unique actuating and connecting linkages which
minimize bending moments in the beams.
Another object of the invention is to provide for
such a brake rigging a fluid pressure actuated brake cy-
linder having a mechanical slack adjuster which automati-
cally adjusts the clearance between the brake shoe and wheel
to provide a constant clearance prior to each brake appli-
catio~irrespective of brake shoe or wheel wear or replace-
ment of brake shoes or wheels.
A further object of the invention is to provide
an actuator for such a brake rigging which is mounted to
one of the beams itself and includes means for manually
stroking the actuator to apply parking brakes just as dur-
ing normal application, whereby uniform parking brake ap-
plication is achieved at all wheels on both sides of the
rail car truck.
Still another object of the invention is to pro-
vide a parking brake actuable by cable from a remote lo-
cation to provide uniform parking brake application at all
wheels.
Another object of the invention is to provide a
brake beam with a light-weight central section to which are
attached replaceable brake heads.
Yet another object of the invention is to provide
a simple spherical joint for connecting push rods to brake
beams.
The above objects of the invention are intended
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8945
to be only exemplary; thus, other advantages achieved and
problems solved by the disclosed invention may be apparent
to those skilled in the art; however, the scope of the in-
vention is to be limited only by the appended claims.
.
SUMMARY OF THE INVE~TIO~
The above objects and other advantages are
achieved by the invention which comprises in one of its
embodiments a cylinder housing having a bore therein with
a piston slidably mounted in the bore for alternate move-
ment in a force applying and force releasing direction. Apush rod is also slidably mounted within the bore for trans-
mitting force applied to the piston in the force applying
direction. An axially extending bore located in the push
rod houses a lead screw which is mounted for rotation there-
in. Connected to the piston and the push rod are means for
preventing movement of the push rod beyond a preselected
distance in the force releasing direction in response to
release of force acting on the piston. Means are also pro-
vided for preventing rotation of the lead screw into the
push rod in the force applying direction unless the piston
has moved a distance less than the preselected distance
and simultaneously the push rod has transmitted a prede-
termined force in the force applying direction. When these
conditions are met, rotation of the lead screw into the
push rod is permitted in the force applying direction.
Means are also provided for preventing rotation of the lead
screw in the force applying direction after the piston has
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1~)4894S
moved a distance equal to or greater than the preselected
distance and, finally, for withdrawing the lead screw from
the push rod in the force releasing direction when the with-
drawing means has stopped further movement of the push rod
in the force releasing direction and the piston has not yet
completed its motion in the force releasing direction.
The brake rigging according to the invention is
especially suited for use in a four-wheel type of vehicle
truck having a transverse axis, a longitudinal axis perpen-
dicular to the transverse axis and a bolster disposed so
that its axis coincides with the transverse axis of the
truck. The brake rigging includes two brake beams which
extend in spaced, substantially parallel relation to the
transverse axis of the truck and are guidably supported on
the truck for bodily movement longitudinally thereof. one
of the brake beams comprises a tubular central section to
which are mounted a pair of brake shoe carrying heads, each
of which includes an integral pivot means. A pair of bell
crank levers are pivoted on these pivot means for rotation
thereabout. The other brake beam also includes a tubular
central section and a second pair of brake shoe carrying
heads attached thereto. A pair of push rods are connected
between the bell cranks on one beam and the brake shoe car-
rying heads on the other beam. Finally, a fluid pressure
operable, double-acting brake actuator is mounted to the
remaining arms of the bell crank levers for producing the
necessary brake actuating forces. Unique spherical joints
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48945
for connecting the push rods to the bell cranks and the
brake shoe heads on the opposite brake beam are also pro-
vided.
BRIEF DESCRIPTIO~ OF THE DRAWINGS
FIG. 1 shows a plan view of a parallel beam rail
car brake apparatus according to the invention indicating
the orientation of the various elements of the invention
relative to the axles, wheels and bolster of a standard
rail car.
FIG. 2 shows a view taken along line 2-2 of FIG.
1.
FIG. 3 shows a view taken along line 3-3 of FIG.
1.
FIG. 4 shows a perspective view of one end of
the primary brake beam according to the invention indicating
the mode of attachment of the brake application bell cranks
and the brake shoes.
FIG. 5 shows a section view indicating the weld
geometry for the joint between the tubular central portions
of the brake beams according to the invention and the cast
brake heads according to the invention.
FIG. 6A shows an exploded view of the spherical
joint used to connect the brake applying bell cranks to
the push rod running between the brake beams. FIGS. 6B
and 6C shows schematically the manner in which the spherical
joint is assembled.
FIG, 7 shows a perspective view of one end of the
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8945
secondary brake beam according to the invention indicating
a portion of the geometry of the spherical joint connecting
the push rod to the brake head.
FIG. 8 shows an exploded view of the spherical
joint connecting the push rod to the brake head at the
secondary brake beam.
FIG. 9 shows an elevation view, partially in sec-
tion, of the brake cylinder and slack adjustor according to
the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
There follows a detailed description of the pre-
ferred embodiments of the invention, reference being had to
the accompanying drawings in which like reference numerals
identify like elements of structure in each of the several
Figures.
With reference to Figures 1-3, the overall geom-
etry and operation of the brake apparatus according to the
invention may be understood. Conventional rail car wheel
and axle assemblies 2 and 4 are partially illustrated.
Located between and parallel with rail and axle assemblies
2 and 4 and on opposite sides of truck bolster 10 are a
master beam 6 and a secondary beam 8. Beams 6 and 8 are
movably mounted in conventional side frame members 12 and
14 in the usual manner, as will be more fully discussed
hereafter. Master beam 6 comprises a central tubular por-
tion 16 having a pair of cast brake heads 18 welded thereto
at either end. Brake heads 18 include integral, outwardly
~104~945
projecting guide feet 19 which are sliably received in
slots located in side frame members 12 and 14 in the usual
manner, as will be appreciated by those skilled in the art.
Secondary beam 8 comprises a central tubular portion 20 to
which are welded cast brake heads 22. Brake heads 22 also
include outwardly projecting guide feet 23 which are like-
wise slidably received in side frame members 12 and 14.
Circumferential welds 24 and 26 join tubular portions 16
and 18 to cast brake head portions 20 and 22. Finally,
conventional composition brake shoes 28 are attached to
brake heads 18 and 22.
A pair of bell cranks 30 are pivotally mounted to
brake heads 18 of master beam 6. Each bell crank 30 in-
cludes a braking force receiving arm 32 and a braking force
transferring arm 34 mounted for unitary rotation about pivot
36. Arms 34 are sized to be as short as practical so that
pivot point 36 may be located as close as possible to the
outboard ends of master beam 6. This location of pivot
points 36 ensures that the optimum force will be transferred
from the actuator to brake heads on both beams, while a
minimum amount of bending stress will be generated in master
beam 6. The closer pivot points 36 are to the middle of
master beam 6, the greater are the bending stresses in use
and the heavier must be the tubular crossection.
A pneumatically driven brake cylinder 38, in-
cluding a double-acting slack adjustor 40, is pivotally
connected to arms 32 at pivots 42 and 44. Additional de-
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:1~4~3~45
tails of brake cylinder 38 and slack adjustor 40 will be
discussed with regard to Figure 9. An armored cable 46 is
provided for manually actuating brake cylinder 38. To this
end, a crank arm 48 is pivoted to the housing of slack ad-
justor 40 and brake cylinder 38 at pivot 50 and operatively
connected to cable 46 at cable attachment point 52. A
laterally extending bracket 54 attached to the housing of
slack adjustor 40 secures the outer sheath of armored cable
46 to prevent its movement during manual actuation of the
brakes. The other end of cable 46 (not shown) is attached
to a conveniently located actuator (not shown).
A pair of push rods 56 are pivotally connected to
arms 34 at spherical pivot joints 58, discussed in greater
detail with respect to Figures4 and 6. The opposite ends
of push rods 56 are joined to secondary beam 8 at spherical
pivot joints 60 located on brake heads 22, just in-board
of brake heads 28, as discussed with respect to FIGS. 7 and
8. Pivot joints 60 are located so that when the brakes are
actuated, push rods 56 will assume a position virtually
perpendicular to both master beam 6 and secondary beam 8 to
ensure transmission of optimum braking force to the rail
car wheels. That is, spherical joint 58 is located slightly
outboard of spherical joint 60 when the brakes are in their
illustrated, retracted position so that as bell cranks 30
rotate, push rods 56 tend to move to a position perpendic-
ular to brake beams 6 and 8.
During operation, pneumatic pressure is applied
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~04~3945
to brake cylinder 38, causing pivots 42 and 44 to move a-
part and rotate bell cranks 30 about pivots 36. As bell
cranks 30 rotate, brake heads 28 mounted on secondary beam
8 will first move into contact with wheels 4, due to force
transmitted by push rods 56. After contact is established
at wheels 4, continued expansion of brake cylinder 38 will
cause bell cranks 30 to pivot about spherical joints 58 and
thus move brake heads 28 of master beam 6 into contact with
wheels 2. Thus, the braking force is applied equally at
all wheels at both ends of each braking beam. During manual
application of the brakes, brake cylinder 38 functions
identically so that equal braking force is applied at all
wheels during manual brake application as well.
The unique geometry of the brake rigging permits
substantial simplification of the brake beams. Because
push rods 56 join secondary beam 8 at spherical joints 60
located just inboard of brake heads 28, very low bending
stresses are induced during operation. Also, axial loading
of the weld joint 26 is minimized. Thus, tubular section
20 may be quite small, such as three inch steel tubing.
The design flexibility of a geometrically complex brake head
is retained due to the use of cast brake heads, while final
beam assembly is simplified due to the use of circumfer-
ential welds 26. Primary beam 6 is also greatly simplified
compared to prior art cast beams; however, the location of
pivot points 36 on the primary beam necessitates the use
of a larger tubular section 16, which may be six to eight
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1848945
inch steel tubing. By making arms 34 as short as possible
consistent with the required movement of the brake heads
28 and the stroke capabilities of the actuator, the bending
stress in the primary beam may be minimized.
FIG. 4 shows a perspective view of cast brake
head 18 and a portion of central tubular portion 16 of the
primary brake beam 6. Brake head 18 comprises a unitary
steel casting having a circular cylindrical inboard end por-
tion 62 which includes a male weld preparation 64 adapted
to mate with central tubular portion 16. See also Figure
5. End portion 62 includes a longitudinal slot 66 located
approximately mid-way in the body of portion 62. Bores 68
are located in portion 62 to receive pivots 36 on which bell
cranks 30 are mounted. Slot 66 extends sufficiently toward
the outboard end of brake head 18 to permit brake force
application arm 34 to move therethrough to transfer brake
application force to push rods 56.
At the outboard end of brake head 18, cylindrical
inboard end portion 62 fares into an essentially rectangular
block portion 70 which is integral with guide foot 19. A
pair of substantially planar, parallel upper and lower sur-
faces 72, 74 are provided from which extend a pair 76, 78
of suitably apertured mounting flanges for attachment of
brake shoe 28. As indicated, brake shoe 28 comprises a
composition brake shoe 28A and a mounting bracket 28B. Ex-
tending from mounting bracket 28B are a pair of mounting
flanges 80, 82 which include substantially planar stop sur-
104~945
faces 84, 86 which are situated to make contact with sur-
faces 72, 74 should brake shoe 28 move substantially rel-
ative to brake head 18 during braking. Suitable fasteners
88, 90, such as rivets or nuts and bolts, attach brake heads
28 to mounting flanges 76, 78.
FIG. 5 shows a section view of the weld joining
tubular portion 16 to cylindrical portion 62 of brake head
18. As indicated, brake head 18 includes an axially ex-
tending, cylindrical male portion 92 having an outer dia-
meter slightly smaller than the inner diameter of tubularportion 16. A radially oriented stop surface 94 extends
outwardly from male portion 92 to limit the depth of pene-
tration of portion 92 into tubular portion 16. Axially ex-
tending weld root portion 95 joins chamfered portion 98
which extends to the exterior of cylindrical portion 62 of
brake head 18. The ability to use this type of weld geom-
etry is an important feature of the invention. Because of
low bending and axial stresses, the central portion of both
the master and secondary beams may be a tubular section
and the brake heads may be attached by a simple circumfer-
ential weld. The brake heads 18 and 22 are held against
the tubular section on centers which correspond to the
center line of the tubular section. The entire assembly
is rotated or spun around this center while a simple weld-
ing head is used to deposit the necessary weld material
to complete the joint. This provides a low cost assembly
procedure and at the same time yields the strength of the
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1(;~4894S
steel tubular section of the beam without sacrificing any
of the versatility of the cast brake head.
FIG. 6A shows an exploded view of spherical joint
58 which connects push rods 56 to the brake force applying
arms of bell cranks 30. Brake force transfer arm 34 includes
at its outer end one-half of spherical pivot joint 58. A
pair of spaced upper and lower, essentially parallel surfaces
102, 104 are bounded along the edge 106 facing toward the
wheel and axle assembly 2 by an essentially perpendicular
cylindrical surface 108 which extends approximately to the
center of end 110 of arm 34. From end 110, a short planar
segment 112 extends essentially on a tangent from surface
108 to merge with a spherical bearing surface 114 which ex-
tends between surfaces 102, 104 along the edge 116, facing
toward secondary beam 8. An upwardly extending vertical
boss 118 and downwardly extending vertical boss 120 (in
phantom) are integrally formed on surfaces 102 and 104 on
an axis containing the center of curvature of spherical
surface 114. Bosses 118 and 120 are elongated across sur-
faces 102 and 104 and have their long axis oriented to face
approximately along the axis of force transmission from arm
34 to push rod 56.
Push rod 56 includes at its primary beam end a
yoke 122 which forms the other half of spherical joint 58.
Yoke 122 comprises a cylindrical stem 124 having a threaded
bore at one end for receiving push rod 56. See Figure 4.
A lock nut 126 secures push rod 56 within a threaded bore
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1048945
in stem 124. A pair of essentially parallel arms 128, 130
extend from stem 124 and are spaced from each other a dis-
tance slightly greater than the spacing between surfaces
102, 104 of arm 34. one sixteenth inch clearance is con-
sidered sufficient. Arms 128, 130 include a pair of opposed,
interior counterbores 132, 134 which are sized to rotatably
receive bosses 118, 120. A pair of radially extending slots
136, 138, sized to slidably receive bosses 118, 120, extend
outwardly from interior counterbores 132, 134 to permit yoke
122 to receive bosses 118, 120 within counterbores 132, 134.
Slots 136, 138 are oriented approximately transversely to
the axis of push rods 56. The flat rims 140, 142 of coun-
terbores 132, 134 are essentially parallel and spaced to
provide adequate clearance with surfaces 104 and 106 of arm
34, as previously mentioned. The surface 144 on stem 124
between arms 128 and 130 is spherically shaped to accommodate
surface 114 when joint 58 is assembled.
Referring to Figures 6B and 6C, the manner of
assembly of spherical ~oint 58 may be understood. Figure
6B indicates schematically the orientation of bell crank 60
and push rod 56 just before spherical joint 58 is assembled.
Bosses 118 and 120 are aligned with radial slots 136 and
138 as indicated and yoke 122 is moved over the end of arm
34 so that bosses 118 and 120 enter counterbores 132 and
134 through slots 136, 138. At this time as shown in Figure
6C, push rod 56 is rotated about the end of arm 34 so that
spherical surface 144 mates with spherical surface 114 to
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1~348945
complete spherical joint 58. Thus, slots 136, 138 are
oriented at an angle to bosses 118, 120 so that joint 58
cannot come uncoupled without rotating yoke 122 back to the
position shown in Figure 6s. Due to the clearance between
flat surfaces 140 and 142, push rod 56 is enabled to move
about the center of curvature of surfaces 144 and 114 to
provide the necessary flexibility for joint 58.
FIG. 7 shows a perspective view of secondary beam
brake head 22 and push rod joint 60. Brake head 22 com-
prises a unitary steel casting having a circular cylin-
drical inboard end portion 150 which includes a male weld
preparation 152 of the type shown in Figure 5. Weld pre-
paration 152 mates with central tubular section 20, in the
manner previously discussed. A cylindrical boss 154 pro-
trudes from cylindrical portion 150 toward primary beam 6
in position to receive the other end of push rod 56 and
form spherical joint 60, as will be discussed with respect
to Figure 8.
Cylindrical portion 150 fares into an essentially
rectangular block portion 156 integral with cylindrical
portion 150. Block portion 156 includes a pair of sub-
stantially planar upper and lower surfaces 158, 160 from
which extend a suitably apertured upper mounting flange
162 and a similar lower mounting flange (not shown), such
as shown in Figure 4. Brake shoe 28 is identical to that
shown in Figure 4 and includes an upper 164 and lower (not
shown) mounting flange similar in function to flanges 82
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1048945
and 84 shown in Figure 4. Upper 166 and lower (not shown)fasteners secure brake shoe 28 to brake head 22 in the
familiar fashion.
FIG. 8 shows a perspective view of spherical joint
60 which connects push rod 56 to brake head 22. Push rod
56 includes at its secondary beam end a spherical portion
170 of approximately 60 included angle. Boss 154 extends
from cylindrical portion 150 of brake head 22 and surrounds
a bore 172 slightly larger in diameter than spherical por-
tion 170. Bore 172 terminates in a spherical surface 174
and includes an essentially concentric bore 176 for attach-
ment of a lubrication fitting (not shown). A U-shaped keeper
178 passes through axially aligned holes 180 located on chords
of the circumference of boss 154 (only one pair shown) to
lock spherical portion 170 within bore 172 and thereby form
spherical joint 60. Keeper 178 is narrower across its legs
than the maximum width of portion 170.
To assemble the apparatus shown in Figures 1-7 in
a conventional rail car, master and secondary beams6 and 8
are first installed in the side frame members 12 and 14.
Before brake cylinder 38 and slack adjustor 40 are attached
to bell cranks 30, the bell cranks are rotated toward the
center of the bolster 10 to expose the end of crank arm 34.
At this time, yoke 122 of push rod 56 is assembled to crank
arm 34 to establish spherical joint 58 and the bell cranks
30 are rotated in the opposite direction. Push rods 56 are
then screwed into yokes 122 and spherical portions 170 are
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104~94~
inserted within bores 172. Keepers 178 are then inserted
and locked in place to complete the assembly of the beams
and push rods. At this time, the brake cylinder and slack
adjustor assembly is attached to the arms 32 of bell cranks
30 as indicated in Figures 1 and 2 and the handbrake cable
46 is attached.
Figure 9 shows an elevation view, partially in
section, of the brake cylinder 38 and slack adjustor 40 used
in the brake apparatus according to the invention. A cy-
linder housing 190 includes an end wall 192 formed inte-
grally with cylindrical sidewalls. End wall 192 includes
a pressurized air inlet port 194 leading to the interior of
housing 190 and a pair of axially extending flanges 196
which form part of pivot joint 42, when the apparatus is
assembled. Housing 190 is closed by end cap 198 which is
secured to a radial flange 200 formed integrally with hous-
ing 190 by a plurality of bolts or fasteners 202. End cap
198 includes a hollow, elongated housing extension 204,
the interior of which communicates with the interior of
housing 190, as indicated. Slidably mounted within housing
190 is a piston 206 having a rubber packing cup 207 affixed
to the side thereof adjacent end wall 192. A pressure
chamber 208 is defined between end wall 192 and piston 206.
A central bore 210 through piston 206 includes a
radially inwardly extending mounting flange 212. Located
in bore 210 on the end thereof adjacent packing cup 207 is
a circular thrust plate 214 which rests on one side of
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~14894~
flange 212. A counter bore 216 in thrust plate 214 includes
on its bottom surface a centrally located boss 218 on which
a thrust bearing 220 is mounted. Thrust plate 214 also in-
cludes a plurality of circumferentially located through-
bores for a plurality of fasteners 222 which secure an elon-
gated stop tube retraction cylinder 224 to the other side of
flange 212 and to thrust plate 214.
Retraction cylinder 224 includes a radially in-
wardly extending flange 226 having a central bore there-
through which slidably receives a cylindrical bronze bushing
228, which is coaxial with bearing 220. Bushing 228 in-
cludes a central bore having a radially inwardly extending
flange 230. Mounted between flange 230 and thrust bearing
220 are a plurality of belleville springs 232 which are
biased at assembly to urge bushing 128 away from thrust
plate 214. Bushing 228 also includes a radially outwardly
extending flange 234 which bears upon a hardened thrust
washer 236 surrounding bushing 228 and resting on flange
226 of retraction cylinder 224. Piston 206 is normally
biased to the left as indicated in Figure 9 by a return
spring 238 which bears on the side of piston 206 opposite
packing cup 207 and on a groove 240 located in end cap 198.
Belleville springs 232 are much stiffer than spring 238 to
prevent disengagement of flange 234 and hardened thrust
washer 236 under all but the highest loadings, as will be
discussed.
The right end of bronze bushing 228 as seen in
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1~8945
Figure 9 and the bore of flange 226 are chamfered inwardly
at 242 and 244, respectively. When flange 234 is in con-
tact with hardened washer 236 and the latter is in contact
with flange 226, chamfered end 242 of bronze bushing 228
extends a short distance beyond the chamfered bore 244 of
flange 226. A bearing 246 is mounted on the side of flange
230 opposite belleville springs 232 and is secured within
bronze bushing 228 by a snap ring 248.
Mounted for rotation within and axial movement
through bearing 244 is a non-self locking lead screw 250,
also mounted for rotation into, out of, or axial translation
with a hollow push rod 252. A high lead nut 254 is mounted
within push rod 252 and threadingly supports lead screw 248
within push rod 252. At its left end, lead screw 250 in-
cludes a short, cylindrical stub or boss portion 256 adapted
for rotating and/or sliding movement in bearing 246. Stub
portion 256 includes a snap ring 247 at its end to limit the
sliding axial movement of lead screw 250 through bearing 244.
A chamfered flange or conical head 258 extends radially from
lead screw 250 adjacent boss 256 in position to sequentially
contact chamfered end 242 and chamfered bore 244 during
operation of the device, as will be discussed subsequently.
An end cap 260, threadingly mounted in the right
end of housing extension 204, includes a central bore 262 for
slidingly receiving push rod 252. Packing 264 prevents en-
try of dirt and other contaminates into the housing. The out-
board end of push rod 252 includes a pair of axially extending
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1048945
flanges 266 which comprise a portion of pivot point 44.
Surrounding push rod 252 is a stop tube 268 which
includes a snap ring 270 mounted in a groove at the left
end thereof, as viewed in Figure 9. Retraction cylinder
224 includes in its right end an inwardly directed flange
272 having a circumferential groove 274 on the inner dia-
meter thereof. Located in groove 274 and captured between
retraction cylinder 224 and stop tube 268 is a bronze fric-
tion ring 276, which has a slight interference fit with stop
tube 268. The left end of flange 272 is prevented from
moving past the end of stop tube 268 by snap ring 270.
Stop tube 268 is guided in its movement by a pair
of inwardly directed, circumferential flanges 278, 280 in-
tegral with housing extension 204. At the right end of
stop tube 268, a ring 282 is pivoted on a hinge 284 affixed
to stop tube 268. Ring 282 is biased into the illustrated
canted position by a spring 286 mounted diametrically op-
posite hinge 284. Contact between ring 284 and flange
280 also serves to cant ring 282 to the illustrated posi-
tion. The inner diameter of ring 282 is chosen so thatwhen the ring is canted as shown, contact between ring 282
and push rod 252 prevents push rod 252 from moving further
to the left into the housing, yet allows push rod 252 to
continue moving to the right if necessary.
The inner end 288 of end cap 260 is spaced from
the outer end 281 of flange 280 by a distance A which is
chosen to be equal to the desired clearance between brake
-20-
1~48945
shoes 28 and the rail car wheels. In practice, the desired
clearance may vary, however, about three-quarters of an inch
is adequate in most cases. During brake application, stop
tube 268 will be pushed to the right due to friction between
ring 276 and retraction cylinder 224 until ring 282 contacts
inner end 288 as illustrated in phantom. If necessary to
establish contact between brake shoes 28 and the rail car
wheels, push rod 252 may continue to move outward through
end cap 260, since ring 282 is ineffective to prevent such
movement. when the brakes are released, push rod 252 will
be forced back into housing extension 204 as brake shoes 28
withdraw from the rail car wheels due to the effects of
gravity, thereby forcing bell cranks 30 to rotate in the
opposite direction. As piston 206 withdraws under the in-
fluence of spring 238, stop tube 268 will move to the left
until ring 282 contacts flange 280, thereby stopping move-
ment of stop tube 268 and locking push rod 252 from further
retraction into housing extension 204.
To facilitate slack adjustment due to wear of the
brake shoes or rail car wheels or to replacement of the
brake shoes or rail car wheels, means are provided for pre-
venting rotation of lead screw 250 into push rod 252 once
piston 206 has moved a pre-selected distance during brake
application. To this end, flange 226 includes a depending
pivot flange 288 on which is pivotably mounted an elongated
clutch release finger 290 which moves about pivot 291 with-
in a slot 292 located in the wall of retraction cylinder
-21-
10~945
224. At a distance from pivot 291, finger 290 includes a
cam~ing surface 294. When piston 206 is in the fully with-
drawn position as illustrated, the leading edge 295 of cam-
ming surface 294 is spaced a distance A' from the lead-in
edge 296 of bore 298 of housing extension 204. Distance A'
is approximately equal to distance A, previously mentioned,
and to the desired brake shoe to wheel clearance. Retrac-
tion cylinder 224 rides within bore 298. Radially extend-
ing from pivot 291 is a finger 300 which contacts one end
of a plunger 302 slidably mounted in a bore in flange 226.
The opposite end of plunger 302 abuts the under surface of
hardened washer 236. The function of clutch release finger
290 will be discussed subsequently.
With reference to Figures 1 and 9, the structure
of the emergency or handbrake application system of the
invention may be understood. Crank arms 48, pivoted at
points 50, include bores 304 which slidably receive a pair
of diametrically spaced brake application rods 306, 308
having load transferring head flanges 310, 312 on the outer
ends thereof. Rods 306, 308 are slidably received in bores
314 located in end cap 198. Bores 314 include a bushing
316 for guiding the movement of rods 306, 308 and a seal
318. Finally, screws 320 rigidly attach rods 306, 308 to
the right hand surface of piston 306, as indicated.
In operation, the brake actuator according to the
invention converts pneumatic pressure to mechanical pressure
at the brake shoes, while simultaneously adjusting the posi-
tion of its elements to provide the correct brake shoe to
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rail car wheel clearance after brake release. Considering
first the application of the brakes in a system where shoe
clearances are correct prior to brake application, air under
pressure is introduced through port 294 into chamber 208,
which forces piston 206 to the right as illustrated in Fig-
ure 9. Piston 206 compresses return spring 238 and, due to
the frictional engagement between friction ring 276 and re-
traction stop tube 268, carries retraction stop tube 268 to
the right until canted ring 282, affixed to retraction stop
tube 268 as previously discussed, abuts inner end 288 of
end cap 260, as indicated in phantom. Simultaneously with
the movement of piston 206, brake actuating force is trans-
mitted through boss 218 of thrust plate 214, thrust bearing
220, belleville washers 232, bronze bushing 228, conical
head 258 of lead screw 250 and lead nut 254 to cause push
rod 252 to move to the right and apply the brakes. As brake
application is achieved in the case where initial shoe
clearance was correct, clutch release finger 290 has just
entered bore 298 in housing extension 204. Further motion
of piston 206 to the right is accompanied only by forcing
the brake shoes 228 harder against the wheels. When ~he
pressure in chamber 208 is vented to achieve a brake re-
lease, return spring 238 forces piston 206 to the left to
its illustrated position, while the brake shoes withdraw
under the force of gravity. As piston 206 moves leftward,
the frictional engagement between stop tube 268 and friction
ring 276 pulls stop tube 268 back to its illustrated posi-
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tion, where the canted ring 282 locks push rod 252 and stop
tube 268 from further leftward movement, thereby preserving
the correct brake shoe clearance.
Suppose, now, that the rail car wheels have been
replaced with new wheels having larger diameters. The ef-
fect of such a change is to reduce the brake shoe clearance
at all wheels. If the brakes are now applied, push rod 252
will stop its rightward movement at an earlier time due to
the reduced clearance. When this happens, the pressure in
chamber 208 will cause piston 206 to compress belleville
springs 232, when chamfered end 242 of bronze bushing 228
is pressed against conical head 258 of lead screw 250. This
tends to reduce the axial force causing flange 234 of bronze
bushing 228 to be held against hardened washer 236, thereby
reducing the frictional force which prevents rotation of
bronze bushing 228, belleville springs 232, bearing 220 and
lead screw 250. When the frictional force has been suffi-
ciently reduced, lead screw 250 will rotate into lead nut
254 allowing piston 206 and stop tube 268 to continue to
move to the right. Although belleville springs 232 are
compressed, the full braking force is still transferred from
piston 206 to lead screw 250.
As finger 290 enters bore 298 in housing extension
204, it rotates on pivot 291 due to the camming action of
bore 298 and cam surface 294 of finger 290. This presses
plunger 302 to the left. Movement of plunger 302 lifts
hardened washer 236 completely away from flange 226, thereby
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1048945
pulling chamfered clutch surface 242 of bronze bushing 228
out of contact with conical head 258 of lead screw 250.
The lead screw 250 thus comes into frictional contact with
chamfered bore or clutch surface 242 of flange 226 and is
prevented from further rotation. At this point, the slack
of the actuator has been reduced as necessary and further
pressure increases in chamber 208 will only result in forc-
ing the brake shoes harder against the wheels. When chamber
208 is vented to release the brakes, the parts return to
their illustrated position, just as in the case where the
initial clearance was correct.
Finally, consider the instance where the initial
shoe clearance is larger than desired. As chamber 208 is
pressurized, piston 206 will move to the right carrying
stop tube 268, until finger 290 enters bore 298 in housing
extension 204. Actuation of finger 290 permits conical
head 258 of lead screw 250 to move into frictional engage-
ment with clutch surface 244 of flange 226, thereby pre-
venting rotation of lead screw 250. So, piston 206 and
push rod 252 continue to move to the right until the excess
clearance has been travelled and brake shoe contact has
been established at the wheels. Further increases in the
pressure in chamber 208 will result in forcing the brake
shoes harder against the wheels.
When chamber 208 is vented, return spring 238
forces piston 206 to the left, drawing along stop tube 268
in the manner previously described, until canted ring 282
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locks push rod 252 and stop tube 268 from further leftwardmovement. As previously discussed, push rod 252 retracts
due to the forces of gravity. At this point, piston 206
will not yet have completed its movement in the brake re-
leasing direction. Since stop tube 268 and push rod 252 can
no longer move, release spring 238 will force piston 206 to
the left. As piston 206 continues its leftward movement,
the frictional force between friction ring 276 and stop tube
268 is overcome. Simultaneously, conical head 258 of lead
screw 250 loses contact with one of clutch surfaces 242 or
244, which ever is then engaging it, and lead screw 250 is
pulled leftward while rotating in lead nut 254 by flange
226, hardened washer 236, bronze bushing 228, snap ring 248,
thrust bearing 246 and snap ring 247, until piston 206
reaches its illustrated position. Thus, the appropriate
amount of extra length is provided in the actuator to adjust
it for increases in brake shoe clearance so that the brakes
will have the correct clearance for the following brake
application.
Having described our invention in sufficient de-
tail to enable those skilled in the art to make and use it,
We claim:
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