Railcar cushion device tester and method

A railcar cushion device is tested by applying a force necessary to move the cushion device in a controlled motion at a predetermined velocity or velocities according to a motion profile. The cushion device's performance is analyzed by measuring the force applied at various positions during the motion profile and comparing the force to a standard for cushion devices in good condition at the positions. Alternatively, a damping coefficient or other performance parameter for the cushion device is calculated from the force applied and position of the cushion device and compared to a standard to analyze cushion device performance. A tester for performing cushion device testing comprises a hydraulic ram and an electronic motion controller for applying the force to the cushion device. The motion controller uses motion feedback from a position transducer to provide the controlled motion to the cushion device.

FIELD OF THE INVENTION 
The present invention relates to methods and apparatus for testing railcar 
cushion devices. More particularly, this invention relates to a method and 
apparatus for applying controlled kinetic energy to a railcar coupling 
cushion device and analyzing the cushion device's performance in response 
to the applied energy. 
BACKGROUND OF THE INVENTION 
In general everyday use, railcars collide together frequently. For example, 
the railcars of a train in motion generally bump into each other when the 
train slows or stops. Also, railcar collisions occur when assembling 
railcars into a train. The difference in velocity between the railcars in 
such collisions is typically low. However, due to the large mass of the 
railcars, the railcars collide with sufficient impact energy, unless 
otherwise absorbed, to cause damage to the railcars and any cargo carried 
by the railcars even in these collisions at low velocity differences. To 
absorb the impact of normal railcar collisions, a railcar generally 
includes cushion devices mounted at each end of the railcar between the 
railcar and its couplers. (In some railcars, a centrally mounted cushion 
device and sliding sill are used.) 
Currently in common use on railcars are hydraulic cushion units which 
generally comprise a piston within a cylinder barrel filled with a 
hydraulic fluid, typically oil. In general, the devices can be described 
as non-linear hydraulic shock absorbers. In a railcar collision, the 
piston is displaced through the barrel. As the piston travels through the 
barrel, the hydraulic fluid in the barrel is compressed by the piston, 
forcing the fluid through orifices in the cylindrical wall of the barrel. 
The action of forcing the fluid through orifices acts to absorb impact 
energy by heating the fluid. Generally, the amount of force that can be 
translated into heat energy is proportional to the square of the piston 
velocity. 
Typically, hydraulic cushion units are configured to absorb a constant 
force throughout the piston stroke by varying the number of orifices 
through which the fluid vents as the piston is displaced. More 
specifically, the orifices are distributed along the length of the barrel. 
Therefore, during the course of the piston's travel through the barrel, 
the piston bypasses orifices one (or more) by one, leaving fewer and fewer 
orifices through which the fluid can vent. When the force absorbed by a 
cushion device is maintained substantially constant, the rate of change of 
acceleration is minimal. Thus, this configuration serves to minimize 
sudden changes in velocity or "jerking" motions of railcars connected in a 
train. After absorbing an impact, the piston is returned to its initial 
position in the barrel of the cushion device by mechanical springs or a 
gas charged device. 
In the typical operating environment, railcar cushion devices are subject 
to failure, particularly in the hydraulic seals, from the wearing of 
moving parts and from rust and corrosion. Failure can also result from the 
stress of impacts greater than the rated capacity of the devices. To 
assure proper functionality of the devices, the performance of the devices 
is periodically tested. 
Various test methods are known. Some test methods involve visual inspection 
for noticeable signs of impairment, e.g. rust, breaks, and leaked 
hydraulic fluid. However, failures frequently occur without producing 
noticeable signs of impairment. Therefore, with visual inspection alone, 
many failures remain undetected. Also, the cushion devices may be 
difficult to inspect visually while installed on a railcar. 
Another type of test, referred to herein as range of motion testing, 
involves moving the cushion devices through a normal range of motion to 
detect failures that result in binding or obstruction of free movement. 
This type of test can detect impairments that are not visually apparent, 
but fails to detect abnormal cushion device operation short of binding. It 
is possible to perform this type of test on an installed cushion device. 
Most other test methods are of a type, referred to herein as impact 
testing, that involves exposing a cushion device to kinetic energy and 
then analyzing the forces produced by the cushion device to detect 
nonconforming operation. A variety of means for exposing the cushion 
device to kinetic energy are known. 
One such means is a drop hammer. In general, a drop hammer comprises a 
hammer member and an anvil member. The cushion device is removed from the 
railcar and mounted on top of the anvil member. The hammer member is 
raised on a vertical frame or track above the cushion device and anvil 
member by pulleys or the like. The hammer member is then allowed to drop 
on the cushion device from a predetermined height above the cushion device 
thereby applying a known amount of kinetic energy to the cushion device. 
The forces produced by the cushion device are measured using a load cell 
comprising a pressure transducer, a piston, and a fluid filled cylinder in 
the anvil member. 
One disadvantage of the drop hammer is that it requires removal of the 
cushion device from the railcar. Removing and reinstalling the cushion 
device is time-consuming and expensive. The railcar must be placed out of 
service while the cushion device is removed, possibly resulting in lost 
revenue to the railroad company for the cargo that could have been carried 
by the railcar during this time. Further, to allow regular testing of 
cushion devices involving removal of cushion devices from railcars, a 
railroad company may be required to maintain more rolling stock or a 
larger stock of replacement cushion devices. 
The standard means in the railroad industry of applying kinetic energy to a 
cushion device involves simply running a rolling railcar into a stationary 
railcar on which the cushion device is installed. Typically, the rolling 
railcar is released from a predetermined elevation on an incline so that 
the amount of kinetic energy is applied to the cushion device can be 
estimated. The forces produced by the cushion device are typically 
calculated indirectly from a measurement of the post-collision velocity of 
the stationary railcar. 
The disadvantages of this method are that the method is inexact, 
time-consuming to carry out, not easily repeatable or reproducible, and 
can result in damage to one or both railcars. More specifically, the 
amount of kinetic energy applied to the cushion device is generally 
assumed from the elevation on the incline at which the rolling railcar was 
released. The actual final velocity of the rolling railcar at the time of 
the collision, however, is affected by friction and other forces. 
Typically, there is significant variance in the final velocity between 
repetitions of the test and for different rolling railcars used in the 
test. Since kinetic energy is a function of the square of velocity, this 
variance in final velocity can significantly affect the actual kinetic 
energy applied by the rolling railcar to the cushion device at the time of 
the collision. The applied kinetic energy is also a function of the mass 
of the rolling railcar which typically varies for different rolling 
railcars used to test cushion devices and may not be accurately known. 
Results of this test methodology are therefore inexact and not 
sufficiently repeatable. 
In general, prior impact testing methods and apparatus apply a 
predetermined amount of kinetic energy in an initial impact to a railcar 
cushion device and analyze the forces produced by the cushion device. 
However, after the initial impact, the motion of the cushion device is 
uncontrolled and generally unknown, being dependent on the function or 
performance of the cushion device itself and other factors. An analysis of 
the forces produced by cushion devices according to such tests are 
therefore often not comparable to those of other cushion devices because 
the applied motion after the initial impact is not identical and not 
known. 
A test method and apparatus is therefore needed to provide repeatable and 
reproducible testing of railcar cushion devices in a short amount of time 
with or without removal of the cushion device from the railcar. Further, a 
test method and apparatus is needed for accurately diagnosing conformance 
of railcar cushion device performance with rated parameters. 
SUMMARY OF THE INVENTION 
The present invention provides railcar cushion device testing that is 
repeatable, reproducible, and accurate. In accordance with the present 
invention, a force is applied to a cushion device to move the cushion 
device in a predetermined motion (the motion profile). Identical motion 
profiles are produced when testing various cushion devices regardless of 
the particular cushion device being tested through use of a feedback 
control system. By controlling the cushion device's motion according to 
the motion profile, the test produces repeatable and reproducible results 
regardless of cushion device performance. The force applied to the tested 
cushion device to attain the motion profile is analyzed to produce a force 
or damping coefficient profile that permits accurate comparison to 
specified performance standards. 
In one embodiment of the invention, the force is applied to the cushion 
device under test by a hydraulic ram. A transducer, electronic motion 
controller, and servo valve provide positional feedback control to drive 
the hydraulic ram according to the motion profile. Accumulators are used 
to store the amount of energy needed to simulate the forces and speeds 
experienced in normal railcar collisions. The forces produced by the 
cushion device when subjected to the motion profile are measured by 
pressure sensors in the hydraulic ram and analyzed by a computer or data 
processing device to form a force or damping coefficient profile 
indicative of cushion device performance. 
In accordance with another aspect of the invention, a portable cushion 
device tester of the nature described above is provided to permit field 
testing of cushion device performance without requiring removal of the 
cushion device under test from its railcar. For portability, the hydraulic 
ram with feedback control is mounted on a portable truck having wheels for 
supporting the truck on a standard railroad track. To test a cushion 
device on a railcar, the portable tester is placed on the track and 
securely attached to one end of the railcar where the cushion device is 
installed. In one embodiment of the invention, the portable tester 
includes fork lift tubes to facilitate placement of the tester on the 
rails and further includes arms with hydraulic clamps mounted on a 
vertically and horizontally adjustable carriage for versatile and secure 
attachment to the railcar. 
Additional features and advantages of the invention will be made apparent 
from the following detailed description of a preferred embodiment which 
proceeds with reference to the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
With reference to FIG. 1, a conventional hydraulic, end-of-car coupling 
cushion device 20 is generally installed in a sill 22 at each end of a 
railcar 24 (FIG. 2) to absorb the kinetic energy of collisions, such as 
may occur between the railcar 24 and other railcars. The sill 22 is an 
elongated, horizontal supporting structure which is longitudinally and 
centrally located under the railcar 24. The cushion device 20 comprises a 
housing 28 which defines a cavity 30 filled with a hydraulic fluid, 
preferably a premium anti-wear hydraulic oil such as the ISO series 
produced by Mobil Corporation. Encased within the cavity of the housing is 
a cylindrical barrel 32. One end 36 of a rod 38 is fixedly mounted to the 
sill 22 in a back stop casting 39. A piston 40 at a distal end 42 of the 
rod 38 is slidingly received within the barrel 32. The rod extends through 
suitable seals 46, 48 to prevent oil leakage from the barrel 32 and 
housing 28 and is encased in an accordion sheath 49 between the housing 28 
and casting 39. 
The cushion device 20 absorbs the kinetic energy of an impact or collision 
by transforming the kinetic energy to heat energy. The energy transfer is 
accomplished by the action of the piston 40 forcing the hydraulic fluid 
through orifices 50 in the barrel 32. The railcar 24 has mounted at each 
end thereof a conventional coupler 51 (FIG. 2) for attaching the railcar 
to other railcars in a train. Each of the couplers, such as the coupler 
51, is attached to a cushion device 20 with a pin 52 which engages in a 
cooperative opening in a butt end 57 of the cushion device. In a railcar 
collision, the housing 28 of the cushion device 20, which is normally held 
against a sill lug stop 54 by mechanical springs or a gas charged device 
under the sill (not shown) is moved inwardly toward the railcar (to the 
right in FIG. 1) by a force applied through the coupler 51 and pin 52 to 
the butt end 57. The rod 38 and piston 40 remain stationary relative to 
the railcar because of the fixed mounting of the rod end 36 to the sill 22 
in the back stop casting 39. The piston 40 thus presses against the 
hydraulic fluid within the barrel 32 forcing the fluid to vent through the 
orifices 50. The piston 40 is sealed with an O-ring 58 to prevent the 
fluid from escaping past the piston. In a railcar cushion device of this 
type, the amount of impact energy absorbed is generally proportional to 
the squared velocity of the piston 40 within the cushion device 20. 
As the piston 40 travels through the barrel 32, the piston bypasses the 
orifices 50 one or more at a time, leaving progressively fewer orifices 
through which the compressed hydraulic fluid can vent. The progressively 
smaller stepping of the number of orifices creates a relatively constant 
resistive force through out the stroke of the piston 40. 
Inward motion of the cushion device is halted when a back stop 62 of the 
housing 28 engages the back stop casting 39. The cushion device 20 is in 
full buff position when the back stop 62 engages the back stop casting 39. 
When the inward force on the cushion device ceases, the mechanical springs 
or gas charged device returns the cushion device 20 to its normal or draft 
position where a stop 64 on the cushion device housing 28 engages the sill 
lug stop 54. 
In accordance with the embodiment of the invention illustrated in FIGS. 2 
and 3, a railcar cushion device tester 70 provides a portable apparatus 
for testing the performance of railcar cushion devices such as the 
hydraulic cushion device 20 on the railcar 24. Although illustrated as 
testing hydraulic end-of-car railcar cushion devices, it is to be 
understood that the invention is applicable to the testing of other types 
of railcar cushion devices including draft gear types. 
For portability, the tester 70 preferably comprises a truck 74 which 
supports testing equipment. The truck 74 includes a frame 76 mounted on 
fixed front and rear axles 78, 79. Flanged wheels 80, 81 are rotatably 
mounted at opposite ends of each of the axles 78, 79 for engaging parallel 
rails 84, 85 of a railroad track 86. Parallel fork lift tubes 88, 89 are 
mounted laterally on the frame 76. The tubes 88, 89 are hollow and 
generally rectangular in cross section. A fork lift (not shown) is thereby 
able to engage the tester 70 for transportation by inserting its elevating 
fork arms into the tubes 88, 89. The tester 70 is therefore portable in 
the sense that it is an integrated testing apparatus that can be 
transported to a field testing site such as a rail yard on a flatbed 
pickup truck, railcar, or the like where it is lifted by a fork lift onto 
a railroad track 86 and moved on rails 84, 85 to a position adjacent to 
the railcar 24 whose cushion device 20 is to be tested. 
The tester 70 attaches to the railcar 24 using hydraulic clamps 92-95 on 
support arms 98, 99 preparatory to testing the cushion device 20. Each of 
the hydraulic clamps comprise a pair of vertically opposed, hydraulically 
actuated jaws 96 for gripping onto a part of the railcar 24. In FIG. 2, 
the tester is shown with the hydraulic clamps 92-95 attached to a flange 
97 on the sill 22 of the railcar 24. However, attachment can also be made 
to a bolster plate or other structure of the railcar 24 as shown in FIG. 
14 and described below. The support arms 98, 99 are mounted on lift 
carriages 100, 101, which in turn are mounted on an arm carriage 102 to 
permit horizontal and vertical adjustment of the hydraulic clamps relative 
to the railcar 24. The arm carriage 102 comprises a pair of U-shaped 
channels 104, 105 mounted laterally to the frame 76 forward of the front 
axle 78 in parallel, horizontal orientation, one above the other, with 
their open sides or grooves facing each other. The grooves of the U-shaped 
channels 104, 105 operate as dual tracks for receiving rectangular 
block-shaped extensions 108 of the lift carriages 100, 101. 
The lift carriages 100, 101 also comprise pairs of U-shaped channels 
112-115 mounted in parallel, vertically oriented relation to base plates 
116, 117 with their grooves facing each other. The base plates 116, 117 
are, in turn, mounted to the lift carriage extensions 108 which engage the 
arm carriage 102 as described above. Elongated, outwardly extending 
flanges at a base or proximal end 118, 119 of each of the support arms 98, 
99 are slidingly engaged in the U-shaped channels 112 of the lift 
carriages 100, 101 to permit vertical movement of the support arms 98-99. 
The hydraulic clamps 92-95 are attached to the support arms 98-99 near 
distal ends 120, 121 thereof. Using the lift and arm carriages 100-102, 
the distance separating opposing pairs of the hydraulic clamps 92-95 from 
each other and their height above the track 86 can be adjusted to 
facilitate attachment of the hydraulic clamps to railcars of various 
configurations. 
To further facilitate attachment of the hydraulic clamps to railcars of 
differing configurations, the position of the hydraulic clamps 92-95 on 
the support arms 98, 99 is adjustable. Portions 122, 123 of the support 
arms 98, 99 adjacent their distal ends 118, 119 are formed with the shape 
of hollow, rectangular cross section beams of uniform width and height. 
The hydraulic clamps 92-95 are mounted on rectangular cross section 
sleeves 126-129 of larger width and height than the support arm portions 
122, 123 to fit around the support arm portions. With the support arm 
portions 122, 123 inserted into the sleeves 126-129, the sleeves are 
slidingly engaged on the support arms allowing the distance of the 
hydraulic clamps 92-95 from the truck 74 along the support arms 98, 99 to 
be adjusted. Preferably, the carriages 100-102 and sleeves 126-129 are 
individually hydraulically actuated and electronically controlled for ease 
of adjustment. A hydraulic cylinder and electronically controlled valve 
(not shown) for each carriage and sleeve can be provided for this purpose. 
The hydraulic clamps 92-95 on support arms 98, 99 have the further 
advantage of permitting the tester 70 to apply force in two directions to 
the cushion device 20 to both compress and extend the cushion device 20 
while maintaining secure attachment to the railcar 24. 
Referring to FIGS. 2-4, the tester 70 employs a hydraulic system 134 
comprising a hydraulic ram 136 to apply a controlled motion to the cushion 
device 20 and analyze cushion device performance. The hydraulic ram 136 
comprises a piston 138 on one end 140 of a rod 142 within a cylinder 144. 
An opposite end 148 of the rod 142 projects outwardly from the cylinder 
144 through a cooperative circular opening in a front end 151 of the 
cylinder. The hydraulic ram 136 is mounted longitudinally to the top of 
the frame 76 of the truck 74 on brackets 152, 153, with the end 148 of the 
rod 142 projecting forwardly (towards the railcar 24). A conventional 
coupler 154 of the type used to couple railcars together is mounted to the 
rod 142 at the forwardly projecting end 148. 
The hydraulic ram 136 is operated by introducing hydraulic oil into or 
discharging the oil from the cylinder 144 on either side of the piston 
138. The introduction of hydraulic oil to and discharge from the cylinder 
144 is controlled by a servo valve 158 (FIG. 4). The servo valve 158 is 
connected to the cylinder 144 with rear and front fluid conveying lines 
160-161, one to each end of the cylinder. Hydraulic oil under pressure is 
supplied to the servo valve 158 for introduction into the cylinder 144 by 
an accumulator bank 164 comprising one or more accumulators 166, 167. The 
tester 70 is illustrated in FIGS. 2-4 with two accumulators 166, 167, but 
can comprise any number of accumulator of various configurations so long 
as the accumulator bank 164 has sufficient capacity to store the energy 
needed to test the cushion device 20 of the railcar 24. 
Prior to testing the cushion device 20, hydraulic oil is pumped into the 
accumulators 166, 167 by a pump 170 driven by a motor 172 to build up the 
pressure in the accumulators. A hydraulic oil reservoir 174 contains a 
supply of hydraulic oil for use by the hydraulic system 134. The hydraulic 
oil is provided from the reservoir 174 to the pump 170 through a supply 
line 176 and manually operated shut-off valve 178. The pump 170 forces the 
hydraulic oil from an outlet line 180 through a main pressure filter 182 
and check valve 184 to a feed manifold 186 connected to the servo valve 
158 and connected through manually operated shut-off valves 187 to the 
accumulators 166, 167. The check valve 184 prevents the hydraulic oil in 
the feed manifold from backing up to the outlet line 180 and pump 170. An 
accumulator pressure switch 185 regulates the pressure in the feed 
manifold 186 and accumulators 166, 167, by activating the pump 170 when 
the pressure drops below a desired minimum level and deactivating the pump 
170 when the pressure is sufficient. 
The servo valve 158 and accumulators 166, 167 are also connected to a 
discharge manifold 188 for discharging the hydraulic oil back into the 
reservoir 174 through a main return filter 190 and heat exchanger 192. The 
accumulators 166, 167 connect to the discharge manifold 188 with a 
manually operated shut-off valve 194 which is normally closed. The 
pressure in the accumulators 166, 167 can also be relieved by discharging 
hydraulic oil from the feed manifold 186 to the discharge manifold 188 
through an electrically actuated accumulator dump valve 196. The pressure 
in the outlet line 180 of the pump 170 can also be relieved by discharging 
hydraulic oil from the outlet line to the discharge manifold 188 through 
an electrically actuated unloading valve 197. The pressure in the rear and 
front lines can be relieved through electrically actuated unloading valves 
198, 199. The pressure throughout the system is normally relieved for 
emergencies or for system shut-downs when the tester 70 is taken out of 
service for extended periods. 
The servo valve 158 operates to drive the piston 138 and rod 142 of the 
hydraulic ram 136 forwardly and rearwardly. To drive the piston 138 
forwardly towards the railcar 24, the servo valve 158 connects the feed 
manifold 186 to the rear line 160 and the discharge manifold 188 to the 
front line 161. This introduces additional hydraulic oil into the cylinder 
144 to the rear of the piston 138 and discharges hydraulic oil from the 
cylinder forward of the piston. The increased pressure of the hydraulic 
oil on a rear face or blind end 200 of the piston 138 and decreased 
pressure on a forward face or rod end 201 creates a force to drive the 
piston 138 forwardly. To drive the piston 138 rearwardly, the servo valve 
158 connects the feed manifold 186 to the front line 161 and the discharge 
manifold 188 to the rear line 160. This creates a force on the piston 138 
which drives the piston rearwardly. 
With reference to FIG. 5, the operation of the servo valve 158 is 
controlled by an electronic motion controller 204 in an electrical system 
206. The electronic motion controller 204 controls the motion applied by 
the hydraulic ram 136 to the cushion device 20 according to a 
predetermined motion profile described below. The motion controller 204 is 
preferably implemented with a microprocessor which operates according to a 
custom designed software program. A change in operation of the motion 
controller 204 can thereby be made without changing its hardware circuits 
by simply altering its software code. A suitable motion controller of this 
type is the Programmable Digital Servo Controller model XDC 700 available 
from MTS Systems Corporation, Machine Controls Division of Eden Prairie, 
Minn. 
The motion controller 204 is housed in an enclosure 208 mounted on the 
frame 76 of the cushion device tester 70. The enclosure 208 can further 
house necessary peripheral equipment including power supplies, and relays. 
The enclosure 208 is preferably located on top of the tester 70 and within 
reach of an operator standing alongside the tester. In the illustrated 
embodiment, the enclosure 208 is a Nema 4 type enclosure. 
The motion controller 204 receives electrical signals from a position 
transducer 210 and pressure transducers 212, 214 as inputs. The position 
transducer 210 can be suitably implemented with a magnetostrictive 
absolute linear position transducer such as the TEMPOSONICS (TM) linear 
displacement transducers available from MTS Systems Corporation, Sensors 
Division of Research Triangle Park, N.C. A position transducer of this 
type comprises a hollow, cylindrical transducer rod 216 within the 
cylinder 144. One end 218 of the transducer rod 216 is fixedly attached at 
a rear end of the cylinder 144 to a transducer head enclosure 217. An 
opposite end 219 of the transducer rod 216 is slidingly engaged within a 
cylindrical cavity through the center of the piston 138 and rod 142. An 
annular magnet 220 (see FIG. 4) located in the piston 138 and encircling 
the transducer rod 216 produces a magnetic field around the transducer rod 
216 in the vicinity of the piston 138. Responsive to the magnetic field, 
conventional electronic circuits (not shown) in the head enclosure 217 
produce an electrical signal related to the position of the piston 138 
within the cylinder 144. 
The pressure transducers 212, 214 are connected to the rear and forward 
lines 160, 161, respectively, of the hydraulic system 134. Responsive to 
the pressure in the lines 160, 161, the pressure transducers 212, 214 
produce electrical signals related to the pressure of the hydraulic oil in 
the cylinder 144 on the blind and rod ends 200, 201, respectively, of the 
piston 136. The pressures on the blind and rod ends 200, 201 are related 
to the force exerted on the piston 136 in the forward and rearward 
directions, respectively. 
Since the motion controller 204 is implemented with digital electronics, 
the analog electrical signals produced by the transducers 210, 212, and 
214 must be converted to digital numerical data prior to processing. The 
motion controller comprises analog-to-digital converters 222 to convert 
the pressure transducer signals to digital. A servo control module 224 
contains similar converter circuitry for converting the position 
transducer signal to digital. 
The motion controller 204 also receives operator inputs from controls 
232-240 on an operator's console 242 and from a data entry keypad 244. The 
console 242 is connected to an interface port 246 on the motion controller 
204. The data entry keypad 244 and a display 250 are located on a front 
panel 252 of the motion controller 204. Using the controls 232-240 which 
include buttons, switches and indicator lights, an operator can perform a 
test procedure or series of test procedures on the cushion device 20 as 
described below in connection with FIGS. 6-11. Parameters for the cushion 
device tests are entered into the motion controller using the keypad 244. 
The test parameters are displayed on the display 250 for monitoring 
purposes. 
With reference to FIGS. 12 and 13, the cushion device tests generally 
involve moving the cushion device 20 in a predetermined motion so that 
various aspects of the performance of the cushion device can be accurately 
measured and analyzed. The predetermined motion is referred to herein as a 
motion profile. The motion profile can be described by graphs 254, 255 of 
the position of the piston 138 as a function of time and graphs 256, 257 
of the velocity of the piston 138 as a function of time. The particular 
motion profile produced by the tester 70 is determined by the test 
parameters entered into the motion controller 204 with the keypad 244. 
Different motion profiles applied to the cushion device 20 can be used to 
analyze different aspects of cushion device performance. 
Referring again to FIG. 5, the motion controller 204 operates to move the 
piston 138 and, consequently, the cushion device 20 in a predetermined 
motion profile regardless of the performance of the cushion device. The 
electrical signal produced by the position transducer 210 is used to 
provide motion feedback to the motion controller 204. Responsive to the 
position transducer signal, the motion controller 204 drives the servo 
valve 158 with a control signal generated by the servo control module 224 
to regulate the introduction and discharge of hydraulic oil from the 
cylinder 144 through the lines 160, 161. For example, when driving the 
piston 138 forwardly according to the predetermined motion profile, the 
motion controller 204 uses the position transducer signal to sense the 
current position of the piston in the cylinder and determine whether the 
piston position lags or leads the motion profile. If the actual position 
of the piston lags the motion profile, the motion controller drives the 
servo valve 158 with a control signal to increase the introduction of 
hydraulic oil into the cylinder 144 through the rear line 160 and/or 
increase the discharge of hydraulic oil from the cylinder through the 
front line 161. This serves to increase the net forward force on the 
piston, speeding the forward movement of the piston. If, however, the 
actual piston position leads the motion profile, the controller retards 
the piston's forward motion by decreasing the introduction of oil to the 
rear line 160 and discharge from the front line 161. This decreases the 
forward force on the piston. The position transducer 210, motion 
controller 204, and servo valve 158 thus act as a feedback control system 
operative to servo piston motion to the desired motion profile. The motion 
controller 204 can also operate in reverse to apply a controlled reverse 
motion to the cushion device 20. 
To analyze the performance of the cushion device 20, the motion controller 
204 processes electrical signals generated by the pressure transducers 
212, 214 to determine a parameter related to the performance of the 
cushion device 20 such as the force that must be applied to the cushion 
device 20 to attain the motion profile or the damping coefficient of the 
cushion device 20. The signals generated by the pressure transducers 212, 
214 are related to the pressure of the hydraulic oil in the cylinder 144 
on the blind end 200 and the rod end 201 of the piston 138. The force 
applied by the hydraulic ram 136 to the cushion device 20 to obtain the 
predetermined motion profile is a function of these pressures, as follows: 
EQU F=A.sub.1 .multidot.P.sub.1 -A.sub.2 .multidot.P.sub.2 (1) 
where F is the force applied to the cushion device 20, A.sub.1 and A.sub.2 
are the surface areas of the blind end 200 and rod end 201 of the piston 
138, respectively, and P.sub.1 and P.sub.2 are the hydraulic oil pressures 
on the blind end 200 and rod end 201, respectively. 
Referring again to FIGS. 12 and 13, the force that must be applied to the 
cushion device 20 to obtain the predetermined motion profile is indicative 
of its performance. A force profile or graph 260, 261 of the force as a 
function of time can be determined by the motion controller 204 from the 
pressure transducer signals by recording the force determined according to 
equation (1) during the applied motion profile. In the illustrated 
embodiment, for example, the force is determined at measurement intervals 
occurring every 2-5 milliseconds during the applied motion profile to form 
a force profile. A cushion device in good condition has a force profile 
260 similar to that shown in FIG. 12. A force profile 261 (FIG. 13) of a 
defective cushion device having a large leak around its piston seals 
differs substantially from the force profile 260. 
Referring again to FIG. 5, in the illustrated embodiment of the invention, 
the motion controller 204 is programmed to determine whether the force 
profile of the tested cushion device 20 meets empirically determined 
standards for a cushion device in good condition. Standards defining an 
acceptable magnitude for the force applied to a cushion device in good 
condition at each force measurement interval during a test is stored in a 
table within the motion controller 204. The motion controller 204 compares 
the force applied to the cushion device 20 being tested at each 
measurement interval to the standard defined in the table. When a force 
outside of a predetermined tolerance limit from the empirically determined 
standards must be applied to the cushion device 20 to attain the motion 
profile, the cushion device fails the test. Failure of the cushion device 
20 to meet the standards is indicated by illuminating a test failure 
indicator light 236 on the operator console 242. 
In the illustrated embodiment, information generated by the motion 
controller 204 during a test (including the force profile of a tested 
cushion device 20) is recorded by a data acquisition computer 264 (or like 
data processing device) such as a lap top-style personal computer. The 
motion controller 204 transmits the information to the data acquisition 
computer 264 from an interface port 266. The data acquisition computer 264 
preferably includes a video monitor, mass storage device such as hard or 
floppy disk storage, and a built-in printer. The data acquisition computer 
264 is thereby capable of displaying the information on the video monitor, 
storing the information on the mass storage device, or printing the 
information on its printer. Alternatively, in other embodiments of the 
invention, the motion controller 204 is programmed to process or record 
test result information and directly print, store or display the 
information on attached recording and/or displaying devices such as a 
strip chart recorder. 
The motion controller 204 can alternatively analyze cushion device 
performance by processing the position transducer signal and pressure 
transducer signals to determine the cushion device's damping coefficient. 
The damping coefficient of the cushion device 20 is a function of the 
pressures on the piston 138 and the velocity of the piston as follows: 
##EQU1## 
and where K is the damping coefficient; V is the velocity of the piston 
138; P.sub.1 and P.sub.2 are the hydraulic oil pressures on the blind end 
200 and the rod end 201 of the piston, respectively: A.sub.1 and A.sub.2 
are the areas of the blind and rod ends, respectively; and A.sub.CD is the 
working area of the cushion device. Similar to force profile analysis, the 
motion controller 204 compares the damping coefficient of the cushion 
device 20 at a number of measurement intervals during a test to 
empirically determined damping coefficient standards for cushion devices 
in good condition. The plural damping coefficient measurements form a 
damping coefficient profile of the cushion device. Failure of the cushion 
device 20 to fall within a predetermined tolerance of the standards is 
indicated by illuminating the test failure indicator light 236. Damping 
coefficient information can also be transferred to the data acquisition 
computer 264 or other recording and displaying devices. 
The advantage of using a cushion device's damping coefficient to analyze 
its performance is that the damping coefficient is independent of the test 
velocity. The force produced by the cushion device is not. Therefore, with 
damping coefficient performance analysis, any variations of the actual 
test velocity from the desired motion profile can be ignored. Also, the 
same damping coefficient standards can be used for tests at different 
velocities. 
With reference to FIGS. 5-7, the operators console 242 houses various 
controls 232-240 for operating the tester 70, including an emergency stop 
button 232, control power button 233, clamp button 235, start test button 
238, jog forward button 239, jog reverse button 240, manual/test selector 
switch 237, test ready indicator light 234, and test failure indicator 
light 236. In other embodiments of the invention, other types of controls 
can be used. For example, a joy-stick type control can be used in place of 
the jog forward and reverse buttons 239-240. In some embodiments of the 
invention, controls in addition to those described are provided such as a 
separate joy-stick type control for adjusting the position of the 
hydraulic clamps 92-95. The controls 232-240 are used by an operator 
according to an interactive test procedure 280 set forth in FIGS. 6-11 to 
test the performance of the cushion device 20. 
In the test procedure 280, initialization steps 282-284 are performed first 
to prepare the tester 70 for operation. As indicated at a decision step 
286, the initialization steps 282-284 are omitted if they have already 
been performed in a previous execution of the test procedure 280. At 
initialization step 282, the tester 70 is positioned on the railway track 
86 adjacent to and facing the railcar 24, with the tester coupler 154 and 
hydraulic clamps 92-95 extended towards the railcar. Next, power to the 
electrical control system 206 is turned on (step 283). Then, in 
initialization step 284, the operator checks the parameters of the test 
using the keyboard 244 and display 250 on the motion controller 204. 
At step 290, the tester 70 is switched to a manual mode of operation using 
the two-position, manual/test selector switch 237. The tester 70 has two 
modes of operation, manual and test. In the manual mode of operation, the 
jog forward and jog reverse buttons 239, 240 are active, permitting manual 
operation of the hydraulic ram 136. The start test button 238 is not 
active. In the test mode of operation, the start test button 238 is active 
and the jog forward and reverse buttons 239, 240 are inactive. 
Steps 292-294 prepare the hydraulic system 134 for operation. In step 292, 
power for the hydraulic system 134 is turned on. The motor 172 can then 
drive the pump 170 to fill the accumulators 166, 167 with hydraulic oil. 
In steps 293-294, the operator waits for the hydraulic system 134 to come 
up to full pressure by pumping hydraulic oil into the accumulators 166, 
167. When the hydraulic system 134 is up to pressure, the test ready 
indicator light 234 comes on. 
Next in attachment steps 296-298, the tester 70 is attached to the railcar 
24. First, in step 296, the piston 138 is moved to its fully retracted 
position within the cylinder 144. In the illustrated embodiment, the jog 
forward and jog reverse buttons 239-240 are used to manually position the 
piston 138. The motion controller 204 retracts the piston 138 when the jog 
reverse button 240 is activated and nudges the piston 138 forward when the 
jog forward button 239 is activated. 
In step 297, the tester 70 is clamped to the railcar 24. The hydraulic 
clamps 92-95 are positioned to clamp onto the sill 22 of the railcar 24 by 
adjusting the arm and lift carriages 100-102 and the sleeves 126-129. A 
separate set of controls (not shown) such as one or more joy-stick type 
controls are provided for making these adjustments. When the hydraulic 
clamps 92-95 are properly positioned, the operator activates the hydraulic 
clamps 92-95 by pulling out the clamp engaged button 235 which is an 
illuminated push/pull type button. Pulling the clamp engaged button 235 
causes the motion controller 204 to drive electrically controlled valves 
(not shown) connected to the hydraulic and electrical systems 134, 206 
which actuate the hydraulic clamps 92-95. 
In step 298, the tester and railcar couplers 51, 154 are coupled together. 
Using the jog forward button 239, the operator nudges the piston 138 
forwardly until the couplers 51, 154 engage. Then, in steps 300-301, the 
operator again waits for the hydraulic system 134 to come up to full 
pressure. 
Steps 302-303 (see FIG. 7) prepare the data acquisition computer 264. If, 
at decision step 302, the data acquisition computer 264 has already been 
set-up, then set-up step 303 is omitted. In the set-up step 303, the data 
acquisition computer 264 is prepared by turning the computer 264 on, 
starting a data acquisition program, and entering test data such as 
identification information for the railcar 24 and the cushion device 20. 
After the preparatory steps 286-303 have been completed, the tester 70 is 
ready to begin cushion device testing. The test ready indicator light 234 
should be illuminated at this time. The tester 70 in the illustrated 
embodiment performs a series of four tests, a pin-stop test, a buff test, 
a return test, and a draft test. To initiate the tests in step 304, the 
operator switches the tester 70 to test mode using the manual/test 
selector switch 237 and activates the start test button 238. 
With reference to FIG. 8, after the start test button 238 is activated, the 
tester 70 first performs a pin-stop test 308 at step 310 (FIG. 7). The 
purpose of the pin-stop test 308 is to determine the amount of "slop" in 
the pin 52 connecting the railcar coupler 51 to the cushion device 20. The 
pin-stop test should begin with the piston 138 initially at a "zero" 
position. The zero position is the position at which the piston 138 is 
retracted farthest in the cylinder 144 away from the railcar 24 with the 
couplers 51, 154 engaged. In this position, the piston is prevented from 
retracting farther into the cylinder away from the railcar 24 by the 
cushion device stop 64 engaging the sill lug stop 54 (FIG. 1). If the 
piston 138 is not in the zero position at the beginning of the pin-stop 
test 308 (step 314), the piston is moved to the zero position in steps 
315-317. To move the piston to the zero position, the tester 70 is 
switched to manual mode using the manual/test selector switch 237 (step 
315). Then, in step 316, the piston is retracted to the zero position by 
activating the jog reverse button 240 until the stops 64, 54 engage. 
Finally, in step 317, the test is restarted by switching back to the test 
mode using the manual/test selector switch 237 and by activating the test 
start button 238. 
Next, in step 320 (FIG. 8), the motion controller 204 moves the piston 138 
forwardly from the zero position at a predetermined controlled velocity. 
As described above, the position transducer 210 provides feedback to 
monitor the position of the piston 138 and ensure that the predetermined 
velocity is maintained. As the piston 138 is moved forwardly, the motion 
controller 204 also monitors the force applied to the cushion device 20 in 
steps 321-325. In step 321, the motion controller 204 samples the pressure 
on the blind and rod ends 200, 201 of the piston 138 from the signals 
generated by the pressure transducers 212, 214. In step 322, the motion 
controller 204 determines the force applied to the cushion device 
according to equation (1) above. The position and force information 
generated by the motion controller 204 in steps 320 and 323 is then 
transmitted to the data acquisition computer 264 (step 324). In decision 
step 325, the motion controller 204 compares the force calculated in step 
323 to a predetermined threshold magnitude. While there is still slop in 
the coupler pin 52, the force will be less than the threshold magnitude. 
However, when the slop is taken up and the forward motion of the piston 
begins to compress the cushion device, the force will increase to a 
magnitude greater than the threshold magnitude. Steps 321-325 are repeated 
until the force applied to the cushion device 20 is greater than the 
threshold magnitude, indicating that the slop in the coupler pin 52 has 
been taken up. 
In step 326, the current position of the piston 138 (where the motion of 
the piston begins to compress the cushion device 20) is recorded by the 
motion controller 204. The forward motion of the piston 138 is then 
stopped and the piston returned to the zero position (step 327). In step 
328, the motion controller 204 compares the distance travelled by the 
piston between the zero and ending positions (i.e., the amount of coupler 
pin slop) to a predetermined standard distance. If the distance travelled 
is less than the standard distance, then the coupler pin 52 has an 
acceptable amount of slop and has passed the pin-stop test (step 330). In 
step 331, the motion controller 204 transmits a signal to the data 
acquisition computer 264 indicating that the test was a success. If, 
however, the distance travelled is greater than the standard distance, 
then the amount of slop is unacceptable and the test is failed (step 334). 
When the pin-stop test 308 is failed, the motion controller 204 
illuminates the test failure indicator light 236 on the operator console 
242 and transmits a signal to the data acquisition computer 264 to 
indicate the test was failed (step 335). Failure of the pin-stop test 308 
also ends the test procedure 280 (step 337 and step 338 of FIG. 7). 
With reference to FIG. 9, after a successful completion of the pin-stop 
test 308, the test procedure 280 continues to the buff test 344 (step 336 
of FIG. 8 and steps 338, 340 of FIG. 7). In step 348 the buff test 344, 
the cushion device 20 is compressed in a controlled motion by the motion 
controller 204 according to a predetermined motion profile 354-357 as 
described above. While the cushion device 20 is being compressed, steps 
350-354 are continuously repeated. At step 351, the motion controller 204 
determines a parameter related to the performance of the cushion device 20 
such as the force applied to the cushion device 20 or the damping 
coefficient of the cushion device 20 (the performance parameter) from the 
pressure and position transducer signals as described above. At step 352, 
the performance parameter determined from the transducer signals and the 
position of the piston 138 determined from the position transducer signal 
are transmitted to the data acquisition computer 264. The buff test 344 is 
failed at step 353 if the performance parameter determined in step 351 is 
not within a predetermined tolerance of an empirically determined standard 
described above for cushion devices in good condition at the current 
position in the motion profile. The buff test 344 is also failed at step 
350 if the motion controller 204 generates a fault. The motion controller 
204 generates a fault if diagnostic sensors indicate a problem in the 
tester 70. For example, float level switches (not shown) in the hydraulic 
system 134 (FIG. 4) signal the motion controller when a loss in hydraulic 
oil occurs due to a break or leak in the hydraulic system. Other sensors 
can be used to detect excessively high temperatures or a drop in pressure 
below an acceptable minimum level. When the buff test 344 is failed, the 
motion controller 204 illuminates the test failure indicator light 236, 
signals the data acquisition computer 264 that the test was failed, and 
ends the test procedure 280 by returning to the initial step 286 (steps 
356-357 and step 358 of FIG. 7). 
The steps 350-354 of the buff test 344 continue repeating until either the 
test is failed or the movement of the cushion device 20 is halted such as 
by the back stop 62 (FIG. 1) engaging the back stop casting 39. When 
cushion device movement is halted, the motion controller 204 records the 
distance moved in the buff test 344 and transmits the distance information 
to the data acquisition computer 264 (step 362). The test procedure 280 
then continues to the cushion return test 366 (steps 358-368 of FIG. 7). 
Referring to FIG. 10, the cushion return test 366 is performed at step 368 
(FIG. 7) to determine whether the mechanical springs or gas charged device 
used to return the cushion device 20 to the draft position is functioning 
properly. The cushion return test 366 is performed by, first, relieving 
the pressure in the cylinder 144 (step 370). The motion controller 204 
relieves the pressure in the cylinder 144 by activating the unloading 
valves 198, 199. With the pressure relieved, the mechanical springs or gas 
charged device can freely operate to return the cushion device 20 to the 
draft position. At step 371, after relieving the pressure, the motion 
controller 204 starts an internal timer. Then, in step 372, the motion 
controller 204 determines the position of the piston 138 from the position 
transducer signal and transmits the position information to the data 
acquisition computer 264. Step 372 is repeated until the timer reaches a 
predetermined time (step 373). 
When the predetermined time has elapsed, the motion controller 204 
calculates a return position error equal to the difference between the 
zero position and the current position of the piston 138 (step 376). In 
step 378, the motion controller 204 compares the return position error to 
a predetermined standard return position error for a cushion device in 
good condition. If the return position error is greater than the standard, 
then the return test 366 is failed. When the return test 366 in failed, 
the motion controller 204 illuminates the test failure indicator light 
236, signals the data acquisition computer 264 that the return test 366 
was failed, and ends the test procedure 280 by returning to the initial 
step 286 of FIG. 6 (steps 380-381 and step 384 of FIG. 7). If, however, 
the return position error is not greater than the standard, the return 
test 366 passes and the test procedure 280 continues to the draft test 388 
(steps 384, 390 of FIG. 7). 
Referring to FIG. 11, in the draft test 388, the performance of the cushion 
device 20 is analyzed while being forcibly extended or decompressed from 
the buff position to the draft position according to a predetermined 
motion profile. First, in step 392, the cushion device 20 is compressed to 
the buff position where the back stop 62 engages the back stop casting 39. 
From the buff position, the motion controller 204 begins retracting the 
piston 138 to expand the cushion device 20 in a controlled motion 
according to a predetermined motion profile (step 394). While the piston 
138 is being retracted, the motion controller 204 continuously repeats 
steps 396-400. 
In steps 397-398, the motion controller 204 determines a performance 
parameter of the cushion device 20 such as the force applied to the 
cushion device 20 or its damping coefficient then transmits the 
performance parameter and distance information to the data acquisition 
computer 264. At step 399, the motion controller 204 determines whether 
the performance parameter is within a predetermined tolerance of an 
empirically determined standard for cushion devices in good condition at 
the current position in the motion profile. If the performance parameter 
is not within the tolerance, then the test is failed. The test is also 
failed if the motion controller 204 generates a fault at step 396. Steps 
396-400 are repeated until the test is failed or the retracting motion of 
the piston is stopped by the cushion device stop 64 engaging the stop 54 
in the cushion device's draft position (step 400). 
If the draft test 388 is failed at steps 396, 399, the motion controller 
204 turns on the test failure indicator light 236 and signals to the data 
acquisition computer 264 that the test was failed (steps 402-403 and steps 
404-405 of FIG. 7). If the draft test 388 is successful, the motion 
controller 204 determines the distance travelled by the piston 138 in the 
test and transmits the distance travelled to the data acquisition computer 
264 for recording (step 408). After the draft test 388 is completed, the 
test procedure 280 returns to its initial step 286 (FIG. 6). The test data 
acquired by the data acquisition computer 264 can then be displayed, 
printed, or stored. 
Referring to FIG. 14, a portable railcar cushion device tester 420 
according to a second embodiment of the invention has hydraulic clamps 
424-427 configured to attach to a bolster plate 430 of a railcar 432. The 
hydraulic clamps 424-427 each have a pair of sleeves or bushings 434-437 
that are slidingly engaged on pairs of parallel support arms 440-441 that 
are circular in cross section and extend forwardly from the tester 420, 
one pair to each side of the railcar 432. The support arms 440-441 are 
mounted on arm and lift carriages 446-449 at a forward end 450 of the 
tester 420 to permit vertical and lateral horizontal adjustment. In 
contrast to the lift and arm carriages 100-102 (FIGS. 2, 3) of the first 
embodiment which travel in the grooves of spaced parallel channels 
112-115, each of the carriages 446-449 travels on spaced, parallel 
circular cross section bars 452-455. 
Each of the hydraulic clamps 424-427 have a pair of laterally extending, 
vertically opposed, hydraulically actuated jaws 460-463 for gripping the 
bolster plate 430. The jaws 461, 463 of the forward most hydraulic clamps 
425, 427 are on a back side of the clamps 425, 427 while the jaws 460, 462 
of the rearward most hydraulic clamps 424, 426 are on a front side. The 
booster plate 430 can therefore be gripped between the hydraulic clamps 
424-425 and 426-427 on each pair of support arms 440-441, respectively. 
The tester 420 further includes a rod carriage 468 which is slidably 
engaged on guide bars 470-471 to permit longitudinal horizontal travel. 
The rod carriage 468 is propelled forwardly and rearwardly along the guide 
bars 470-471 by an electronically controlled hydraulic ram 474. A coupler 
478 mounted on a forward side of the rod carriage 468 is vertically 
adjustable along a vertical guide bar 480. With the rod carriage 468, the 
height of the coupler 478 can be adjusted to match the height of a coupler 
482 on the railcar 432. An hydraulic drive system and an electronic 
control system such as described above is provided to drive the ram 474 
and analyze the condition of the cushion device of the railcar 432. 
Referring to FIG. 15, a stationary railcar cushion device tester 500 
according to a third embodiment of the invention comprises a hydraulic ram 
502 mounted on a supporting frame 504. The frame 504 is attached with 
hydraulically actuated rail clamps 508-509 to parallel rails 512 of a 
railroad track 514. With the rail clamps 508-509, the tester 500 can be 
installed on the track 514 as a permanent or semi-permanent stationary 
test fixture. 
The tester 500 also comprises a hydraulic drive system and an electronic 
control system such as described above to drive the ram 502 and analyze 
the condition of a cushion device 518 of a railcar 520. While the cushion 
device 518 is being tested, the railcar 520 is clamped to the rails 512 
using hydraulically actuated rail and wheel clamps 522-525 to prevent the 
railcar from moving. 
Referring to FIGS. 16-17, a stationary railcar cushion device tester 540 
according to a fourth embodiment of the invention comprises a hydraulic 
ram 542 mounted in a supporting frame 544 and driven by a hydraulic drive 
system 546 and an electronic control system 547 such as described above. A 
cushion device 548 which is to be tested is attached at its butt end 550 
to a cylinder back stop 552 on the frame 544 with a pin 554 received in 
cooperative openings in the cushion device and back stop. The hydraulic 
ram 542 operatively engages a ram carriage 558 to which an extending end 
560 of the cushion device's rod 562 is coupled. As described above, the 
hydraulic ram 542 applies force to the cushion device 548 to effect a 
predetermined, controlled motion of the cushion device so that the cushion 
device's performance can be analyzed by the electronic control system. 
Having described and illustrated the principles of our invention with 
reference to a preferred embodiment, it will be recognized that the 
invention can be modified in arrangement and detail without departing from 
such principles. In view of the many possible embodiments to which the 
principles of our invention may be put, it should be recognized that the 
detailed embodiments are illustrative only and should not be taken as 
limiting the scope of our invention. Rather, we claim as our invention all 
such embodiments as may come within the scope and spirit of the following 
claims and equivalents thereto.