U.S. patent application number 10/925696 was filed with the patent office on 2005-04-14 for method and apparatus for detecting guideway breaks and occupation.
Invention is credited to Turner, Steven.
Application Number | 20050076716 10/925696 |
Document ID | / |
Family ID | 34316442 |
Filed Date | 2005-04-14 |
United States Patent
Application |
20050076716 |
Kind Code |
A1 |
Turner, Steven |
April 14, 2005 |
Method and apparatus for detecting guideway breaks and
occupation
Abstract
The present invention provides a method and system for detecting
guideway anomalies. In particular, the present invention generates
and couples a wave pulse into a guideway. The wave pulse travels
down the guideway until it reaches an anomaly. The anomaly causes a
return wave pulse. The time difference between the generated wave
and the return wave allows calculation of the deference to the
anomaly.
Inventors: |
Turner, Steven; (Guernsey,
WY) |
Correspondence
Address: |
HOLLAND & HART, LLP
555 17TH STREET, SUITE 3200
DENVER
CO
80201
US
|
Family ID: |
34316442 |
Appl. No.: |
10/925696 |
Filed: |
August 24, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60500385 |
Sep 5, 2003 |
|
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|
Current U.S.
Class: |
73/579 |
Current CPC
Class: |
B61L 23/041 20130101;
B61L 23/044 20130101; B61L 23/047 20130101 |
Class at
Publication: |
073/579 |
International
Class: |
B61L 021/00 |
Claims
I claim:
1. A method of determining a distance to an anomaly in a guideway,
the method preformed on a processor comprising the steps of:
generating a wave pulse; coupling the wave pulse into the guideway;
waiting a predetermined wait time to receive a return pulse from
the guideway; if the return pulse is received within the
predetermined wait time, determining whether an anomaly exists on
the guideway; and after the predetermined wait time, repeating the
generating, coupling, and waiting step.
2. The method of claim 1, wherein the wave pulse comprises at least
one of an electrical wave pulse, an acoustic wave pulse, a magnetic
wave pulse, an electromagnetic wave pulse, or a radio frequency
wave pulse.
3. The method of claim 1, wherein the guideway comprises at least a
pair of conductive members.
4. The method of claim 3, wherein the pair of conductive members
are at least partially isolated.
5. The method of claim 1, wherein the determining whether an
anomaly exists step comprising detecting impedance variations.
6. The method of claim 3, where the step of detecting impedance
variations comprises detecting impedance variations in both
conductive members of the pair of conductive members.
7. The method of claim 5, wherein an increase in impedance provides
an indication of an anomaly consistent with a break in the guideway
and a decrease in impedance provides an indication of an
obstruction in the guideway.
8. The method of claim 1, wherein the step of generating a wave
pulse generates the pulse over a predetermined pulse timeframe.
9. The method of claim 8, wherein the step of generating a wave
pulse generates a plurality of relatively short wave pulses over
the predetermined pulse timeframe.
10. The method of claim 9, wherein the plurality of short wave
pulses comprise at least a first short wave pulse at a first
frequency and a second short wave pulse at a second frequency,
different from the first frequency.
11. The method of claim 2, wherein the wave pulse is modulated.
12. The method of claim 8, wherein the predetermined pulse
timeframe and the predetermined wait timeframe are based on a
minimum distance and maximum distance for which the anomaly is to
be detected over the guideway.
13. The method of claim 12, wherein the wave pulse is a short
duration high frequency tone burst.
14. The method of claim 1, wherein the predetermined wait time
comprises a plurality of predetermined wait timeframes.
15. The method of claim 14, wherein each particular wait timeframe
is selected from the plurality of predetermined wait timeframes
according to a preselected code basis.
16. The method of claim 14, wherein each particular wait timeframe
is selected from the plurality of predetermined wait timeframes on
at least one of a random or a pseudo-random basis.
17. The method of claim 1, wherein the step of generating a wave
pulse comprises generating a plurality of wave pulses having at
least one different characteristic.
18. The method of claim 17, wherein the at least one different
characteristic comprises at least one characteristic selected from
the group of characteristics consisting of: frequency, modulation
code, phase, and amplitude.
19. A system for detecting anomalies in a guideway, the system
comprising: at least one signal generator; at least one coupler
connected to the at least one signal generator, the at least one
coupler to transmit the signal generated by the at least one signal
generator into the guideway; at least one signal receiver, the at
least one signal receiver connected to the at least one coupler
such that a return signal is transmitted from the guideway to the
at least one signal receiver; and a processor, the processor
coupled to the signal generator and the at least one signal
receiver, such that the processor can determine whether the return
signal is indicative of an anomaly based on the signal generated by
the at least one signal generator.
20. The system of claim 19, wherein the at least one signal
generator and at least one signal receiver form a transceiver.
21. The system of claim 19, wherein the processor causes the at
least one signal generator to periodically generate a signal to be
transmitted to the guideway.
22. The system of claim 19, wherein the at least one signal
processor generates a plurality of signals, at least one of the
plurality of signals has at least one different characteristic.
23. The system of claim 19, wherein the at least one signal
generator has a uniquely identifiable operating characteristic.
24. The system of claim 19 further comprising at least one waveform
transformer, the waveform transformer coupled between the at least
one signal generator and the at least one coupler to convert the at
least one signal generated by the at least one signal generated
into a form transmittable to the guideway by the at least one
coupler.
25. The system of claim 19, wherein the at least one signal
receiver receives a plurality of return signals and the processor
correlates the plurality of return signals to compensate for
relative movement of the system between transmission and
return.
26. The system of claim 19 further comprising at least one data
link and at least one memory, the at least one data link and the at
least one memory coupled to the processor such that the processor
can store information regarding detected anomalies.
27. The system of claim 26, wherein the stored information
comprises at least one type of information selected from the group
of information consisting of: location of the anomaly, impedance
variation, rate of movement of anomaly, expected impedance, signal
propagation information, guideway imperfections, environmental
conditions, or guideway conditions.
28. The system of claim 27, wherein the stored information is
provided to the processor to assist in detecting anomalies.
29. The system of claim 19, wherein the at least one signal
generator and the at least one signal receiver are located remote
from each other such that. anomalies are detected by variations in
expected signals received at the at least one signal receiver.
30. The system of claim 19 wherein the processor detects anomalies
using time domain reflectometry based on the return signal being a
reflection of the wave pulse.
31. The system of claim 19 wherein the system is mounted on an
object traveling along the guideway.
32. The system of claim 31, wherein the object is a rail
vehicle.
33. The system of claim 32, wherein the rail vehicle is at least
one of a locomotive engine and a railcar.
34. The system of claim 31 further comprising: a remote signal
generator; and a remote coupler to transmit the signal from the
remote signal generator to the guideway such that the processor can
detect anomalies using through-transmission between the remote
signal generator and the at least one signal receiver and time
domain reflectometry between the at least one signal generator and
the at least one signal receiver.
35. The system of claim 19 further comprising a data link and a
communication link to a broadcast or distributed timing reference
such as a global positioning system such that a plurality of
systems can be coordinated.
36. The system of claim 19, further comprising at least one
indicator, the at least one indicator providing at least one
indication selected from a group of indications consisting of: a
warning indication, a stop indication, a go indication, distance to
anomaly indication, and a rate of approach of anomaly
indication.
37. The system of claim 36, wherein the at least one indicator
comprises at least one of a light, a display, a whistle, a bell,
and a barrier.
38. A system for detecting breaks, potential breaks, or obstruction
in railroad tracks, the system comprising: at least one rail
vehicle; and a pair of conductive rail tracks at least partially
isolated from each other; the at least one rail vehicle comprising:
a processor; at least one signal generator, the at least one signal
generator coupled to the processor such that the processor causes
the at least one signal generator to generate electrical waveform
information at a selected time; at least one waveform generator
connected to the at least one signal generator to covert the
waveform information into a transmittable waveform capable of
traveling along at least one track of the pair of conductive rail
tracks; at least one track coupler to transfer the transmittable
waveform from the at least one waveform generator to the at least
one track and to transfer a return waveform from the at least one
track; at least one signal receiver coupled to the at least one
track coupler to receiver the return waveform from the at least on
track and convert the return waveform into a return signal useable
by the processor; the at least one signal receiver coupled to the
processor to transfer the return signal to the processor, wherein
the processor can detect anomalies.
Description
[0001] The patent application claims priority to U.S. Provisional
Patent Application Ser. No. 60/500,385, filed Sep. 5, 2003, titled
METHOD AND APPARATUS FOR DETECTING RAIL BREAKS AND OCCUPATION,
incorporated herein as if set out in full.
FIELD OF THE INVENTION
[0002] The present invention relates to track detection systems
and, more particularly, to a detection system that detects local
and distant rail breaks and track occupation.
BACKGROUND OF THE INVENTION
[0003] Trains and other rail or guideway moving vehicles and/or
objects travel along common tracks at various speeds. The stopping
distance of some trains can be many miles, but driver visibility is
often less than this distance because of fixed conditions such as
curves, embankments, trees, tunnels through hilly or mountainous
terrain, and the like, or variable conditions such as poor weather.
To maintain the desired operating speeds, train drivers need to
know that the track ahead is free of breaks and not occupied by
other vehicles. Thus, an automated warning system is frequently
employed with the primary goal of detecting other trains on the
track ahead and signaling the driver to slow or stop as necessary
to avoid a collision.
[0004] Currently, track occupation detection involves a signaling
system that is substantially external to the trains. The present
signaling system regulates traffic flow and ensures train
separation by dividing the entire length of track into a multitude
of relatively short fixed blocks of various lengths, typically each
no longer than some one to two miles. At the approach to each
block, a visual indicator instructs the train crew to proceed
according to the status of the track ahead, typically by providing
a general speed range (go, may-have-to-stop, stop-immediately) that
is based on whether or not other trains exist in the next few
blocks of track. In particular, the indicator device provides a
"go" or "proceed at normal speed" indication (meaning no train
exists in the next few blocks), a "may have to stop" or "proceed
with caution" indication (meaning a train is not in the next block
of track but ahead in a subsequent block), or a "stop immediately"
indication (meaning a train exists in the next block).
[0005] In order to detect the presence of a train in a signaling
block, an electrical circuit method is usually employed. An
electrical signal generator applies a continuous signal (generally
a DC, audio frequency AC, or pulse coded voltage) between the two
rails at one end of the block, and a relay or similar detection
device measures the signal voltage between the two rails at the
other end of the block. The rails of each block are electrically
isolated from the rails of the adjoining blocks using special rail
joints known as Insulated Joints (IJs). If no trains exist in the
block, the rails act as an electric circuit with the signal
generator at one end of the block energizing the relay at the other
end of the block through the two conducting rails. A train at some
location in a block is determined in a manner similar to a short
circuit detection. Any locomotive or railcar axles, or any other
conductive member, within the block act as a circuit shunt between
the two rails to greatly diminish the signal voltage so that the
relay becomes de-energized, thus closing a set of contacts
connected to the signal indicators. The signal indicators will then
warn any approaching vehicle to stop before entering the block
because the track is already occupied.
[0006] The present system also has the added benefit that a fault
or break in either rail within the track block can be determined in
a manner similar to open circuit detection. A mechanical failure of
a rail often leads to a small separation gap at the break because
the rail is typically in tension at low to average temperatures.
This interrupts the signal current path and also de-energizes the
signaling relay. Based on the detection of an open circuit in a
block, an approaching vehicle will be apprized to stop before
entering the block because the track has a fault indication in
it.
[0007] Generally, the electronic equipment and visual indicators
exist as wayside equipment. The actual indicator may be, for
example, a set of lights (a.k.a. "signals") on the side of the
track. The "go" indication is typically a green light that means no
known breaks and no other trains in the next two or more blocks of
track. The "may-have-to-stop" indication is typically a yellow
light that means no known break or other train in the next block of
track, but a break or train may exist in a subsequent track block.
The "stop-immediately" indication is typically a red light that
means the next block of track has a break or is occupied. Thus the
train operator should proceed at normal speed upon seeing a green
light, stop upon seeing a red light, or slow on seeing a yellow
light in anticipation of a possible red light at the next set of
signals.
[0008] As can be imagined, the existing external detection system
requires significant wayside infrastructure for every relatively
short block of track. The signal generation circuitry, detection
circuitry and the indicator lights require electrical power and are
often located in remote and sometimes difficult to reach locations.
The cost per mile of new track installation is burdened by the
capital outlay for signaling equipment and interconnecting cabling,
additional construction and installation expense, and costs
associated with providing electrical power at regular intervals
along the track. In operation, the wayside infrastructure has high
maintenance and upkeep costs per mile of track. Signaling equipment
is subjected to extreme temperatures and poor weather conditions,
and is susceptible to equipment failures that sometimes lead to
expensive traffic delays.
[0009] Many railroad companies are investigating Communication
Based Train Control ("CBTC") as an alternative means of regulating
the speed and separation of track vehicles. It is proposed that GPS
location and speed information from each vehicle would be sent via
data communication, such as radio frequency broadcast, to a central
coordinating facility, somewhat akin to an air traffic control
center. The optimum desired speed would then be sent back to each
vehicle via the same communication system. CBTC would allow for
more flexible train spacing and more graduated speed control to
optimize traffic flow, improve safety, and maximize rail
utilization efficiency. CBTC would also provide improved fuel
efficiency by avoiding cycles of breaking and acceleration that the
present system sometimes produces.
[0010] The implementation of CBTC is intended to replace the
primary signaling system function of traffic regulation and could
potentially provide additional significant cost savings by allowing
the removal of the present signaling system and associated wayside
infrastructure, except that this system serves an important
secondary function. The signaling system current passing through
the rails provides for the detection of any rail break that
interrupts the current flow. This feature has averted many
potential train derailments, and therefore an alternative method to
detect rail breaks is required. A viable alternative must be more
cost effective than maintaining the present signaling system for
the sole remaining purpose of detecting broken rails; should
provide at least equivalent protection in terms of range (monitored
distance ahead of the train) and sensitivity to various break
types; and should be as compatible as possible with present track
designs, structures, and track maintenance practices.
[0011] It should be noted that CBTC would only protect against
collisions with other vehicles that are being accurately tracked in
the database of the central coordinating facility, i.e., only those
vehicles equipped with CBTC, GPS, and data communication systems,
and where all systems were operating correctly. For example, CBTC
would not protect against collisions involving non-CBTC track
occupation such as an unexpected detached railcar.
[0012] Thus, it would be desirous to develop an alternative
apparatus and method for the detection of rail breaks and
unexpected track occupation.
SUMMARY OF THE INVENTION
[0013] The foregoing and other features, utilities and advantages
of the invention will be apparent from the following more
particular description of a preferred embodiment of the invention
as illustrated in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWING
[0014] The accompanying drawings, which are incorporated in and
constitute a part of this specification, illustrate embodiments of
the present invention, and together with the description, serve to
explain the principles thereof. Like items in the drawings are
referred to using the same numerical reference.
[0015] FIG. 1 is a functional block diagram illustrative of one
example of an embodiment of the present invention;
[0016] FIG. 2 is illustrative of a flowchart showing one method of
implementing an embodiment of the present invention;
[0017] FIG. 3 is a side elevation view of a locomotive containing
an embodiment of the present invention; and
[0018] FIG. 4 is a bottom elevation view of a potential track
coupler shown in FIG. 1.
DETAILED DESCRIPTION
[0019] The present invention will now be described with particular
reference to the figure(s). While the present invention is
described with particular reference to railroads, locomotives, and
the associated tracks, one of ordinary skill in the art will now
recognize that the present invention could be used with any system
that has a "guideway" where a signal can be transmitted along the
guideway. Such guideways include, for example, rail tracks,
conveyer belt systems, assembly lines, and other systems where the
longitudinal members of the guideways are conductive and at least
partially isolated from each other. Alternatively, non-conductive
guideways can be made conductive by adding conductors, such as
wires or conductive rods.
[0020] The present invention describes an improved rail break
detection system operating independently from the existing wayside
signaling system. The invention may be used in conjunction with
present signaling systems to provide specific advantages such as
determining the exact break location, but the invention is
particularly suitable to be used in conjunction with CBTC as a
replacement for the present signaling system. The combination of
CBTC and the present invention will supersede all of the functions
of the present signaling system by providing advanced traffic
management as well as improved broken rail detection. As an adjunct
to the CBTC system, the present invention can also indicate track
occupation as a failsafe to avoid vehicle collisions.
Method Selection
[0021] Several methods of broken rail detection and track
occupation are possible. However, it has been determined that any
viable replacement system should avoid replacing the existing
wayside electrical equipment with an alternative wayside system.
Replacing one wayside infrastructure system with another would
likely not significantly reduce maintenance expenses, which are a
major component of ongoing railroad costs, or solve the reliability
problems associated with a widely distributed infrastructure
operating in harsh field conditions. Thus it was established that
the ideal system would be one that mounted on the lead locomotive
of each train. On average, the number of locomotives employed by a
railroad is far less than the number of existing signaling blocks,
so far fewer systems would be required. It would then become
feasible to increase reliability by providing redundant systems on
each locomotive. Key components would be housed in the
better-controlled environment of the locomotive cab, further
improving reliability. Maintenance of a locomotive-based system
could be centralized to existing locomotive workshops and coincide
with regular locomotive maintenance, rather than requiring a large
number of distributed support and maintenance personnel in the
field.
[0022] It was also established that the replacement system should
perform real time rail break detection ahead of the train with a
sufficient range and warning time to allow stopping or at least
significantly slowing the train. The ability for fast, real time
rail break detection is made more important because the CBTC
potentially decreases separation between sequential trains, and
rail breaks can be precipitated by the preceding train.
[0023] With these constraints in mind, it was determined an ideal
method to detect rail breaks would be for the lead locomotive of
the train to transmit a wave signal that would propagate along the
rail. If the propagating wave signal encountered a break, a
reflection would be sent back towards the lead locomotive that
would be received by a receiving unit in the lead locomotive.
Instead of a separate transmitter and receiver, the present
invention could use a transceiver.
[0024] Types of wave signals that could be sent from a transmitter
mounted on a train, propagated along the rails, reflected by a rail
break, and detected by a receiver mounted on the train include, for
example, acoustic waves and electromagnetic waves. Acoustic waves
might have the capability to detect some rail integrity failures
(and partial or immanent failures) that electromagnetic waves would
not. For example, acoustic waves might detect large internal
defects or internal fractures in the rail indicative of a pending
break, allowing repair prior to an actual break occurring.
Furthermore, it is also possible for a rail to be broken (i.e.,
mechanically separate) and yet maintain electrical continuity. One
example is an "S" shaped rail break originating as a horizontal web
defect in which the non-vertical faces of the two rail parts rest
against each other. Other possibilities include a break resting on
a conductive metal tie plate, or a break occurring with the rail at
an elevated temperature and therefore under compression due to
thermal expansion. Acoustic waves might detect these failures
because the acoustic wave travel may be impeded by the defect or
break. Whereas an electromagnetic wave would not see the failure
because a complete electrical connection still exists, allowing
transmission of the electromagnetic signal.
[0025] One major disadvantage with acoustic waves, however, is that
they would be attenuated over relatively long distances by the
regular firm mechanical anchoring of the rail to the track
structure using wooden, concrete, or steel cross ties. Acoustic
waves would also be greatly attenuated by common track components,
such as bolted rail joints and track turnouts. Thus, acoustic waves
would have a limited range and would be "blinded" beyond existing
joints, turnouts and other common track structures unless major
changes were made to existing track components, construction
methods, and maintenance procedures. Also, many other common track
features such as normal bolt holes would probably cause
false-positive indications because the acoustic wave would be
partially reflected, even though the bolt holes are deliberate and
do not represent structural defects. Although a well designed
system might map and track these numerous reflectors in a database,
new acoustic reflectors such as added bolt holes and rail ends
(e.g. plated defects and temporary plug rail repairs) would have to
be continuously updated in the database to avoid unnecessary
traffic delays.
[0026] For these reasons, electromagnetic waves may provide better
detecting than acoustic waves. While potentially not as efficient
at detecting partial rail breaks or breaks with maintained
electrical continuity, electromagnetic waves are very compatible
with existing detection sensitivity and rail maintenance
procedures, because the basic detection principle is the same; that
is, the detection of a local dramatic variation in rail
conductivity due to a rail break. Therefore, all breaks that are
detectable by the existing signaling system are likely to be
detectable by the present invention. The major difference is that
detection will be based on the reflection of an electrical pulse
that is both generated and received at the moving locomotive,
rather than the interruption of a continuous electrical current
between two separate fixed locations using wayside equipment.
[0027] Another system may combine both acoustic and electrical
signals for detection. The acoustic wave, it is believed, may
provide superior short distance detection, while the
electromagnetic wave, it is believe, may provide superior long
distance detection. Thus, combining both wave forms into a single
detector system may provide a system that overcomes the drawbacks
of either wave form used alone.
[0028] FIG. 1 shows a simple functional block diagram of a sample
rail break detection system 100. The rail break detection system
includes a waveform generator 102, a wave transmitter 104, a track
coupler 106, a wave receiver 108, and a processor 110. Processor
110 is connected to a data link 112. Data link 112 may connect the
present invention to the CBTC system. Data link 112 could be a
cable connection, a wireless connection, antenna, a bus connection,
a network connection (LAN, WAN, Ethernet, or Internet), or the
like. The device is mounted in a locomotive (not specifically
shown) in this example, but could be installed on other rail
vehicles, at fixed locations, or on any device traveling over a
guideway as described above. An appropriate processor controls the
entire system with software modules configured to instruct the
various components and process the results. Waveform generator 102
may be caused to operate with particular unique operating
characteristics to allow for easy of identification of generators.
For example, one or more generators could be identified according
to the entire code or a subset of the code used to modulate the
initial transmitted pulses. Data link 112 could be connected to a
memory or storage unit 114 or a global positioning system 116.
Finally, while the components of system 100 are shown discretely,
the various components may be combined into less components or
separated into still other components.
[0029] Referring to FIG. 2, a flowchart 200 showing the operation
of system 100 is provided. First, processor 110 causes wave
generator 102 to generate a wave pulse over a predetermined length
of time, step 202. The generated wave pulse is coupled or
transmitted into the guideway by track coupler 106, step 204. Next
processor 110 causes system 100 to wait for a return signal, step
206. The wait period is provided to allow system 100 to receive a
return or echo pulse from the guideway anomaly, if any exist.
System 100 receives the return or echo pulse at track coupler 106,
step 208, which is sent to receiver 108 for processing, step 208.
The processing may include filtering, amplification, verification
that the received signal is the return or echo and not noise, or
the like. Receiver 108 converts the signal into a format usable by
processor 110, step 210, and transmits the signal to processor 110,
step 212. Processor 110 processes the signal, step 214. Processor
110 may calculate or process the information to determine features
such as whether an anomaly exists, type of anomaly indicated (break
or obstruction), distance to anomaly, alternative routes to avoid
the anomaly, rate of approach, or the like. Processor 110 may
transmit information using data link 112 to a central coordination
system to update information. Anomalies may include, for example,
actual breaks, guideway occupation, pending breaks, or the
like.
[0030] Waveform generator 102 is shown as a single generator, but
waveform generator 102 may actually comprise one or more
generators. Also, a single generator may produce a plurality of
waveforms. A plurality of waveforms may be generated substantially
simultaneously, simultaneously, or discretely to provide different
information. For example, a high frequency signal may be provided
with a lower frequency signal to provide wave pulses capable of
measuring both short distance anomalies and long distance anomalies
without significant interference, as the high and lower frequency
signals are distinguishable. Instead of frequency changes, waveform
generator may comprise alternative differentiation characteristics,
such as, for example, different phases, different modulations,
different type of waveforms, different wait periods, or the
like.
[0031] In operation, processor 110 would trigger wave generator 102
to generate an electronic signal that the wave transmitter 104
converts into an electromagnetic, acoustic, electric, magnetic,
radio frequency pulse or the like that can travel along the rails.
Track coupler 106, which could be, for example, the locomotive
wheels or an inductive wire loop 402 (shown in FIG. 4) disposed
adjacent to the two rails, couples the electromagnetic wave into
the rail. Other potential devices to couple a signal into the rails
are disclosed by U.S. Pat. No. 1,517,549, issued Nov. 19, 1919,
titled Rail Signaling System, incorporated herein by reference.
While the '549 Patent discloses direct, inductive, and capacitive
coupling techniques to direct a wave in a rail, it should be
understood that the '549 Patent discloses coupling a continuous
wave into the track with signal generation and analysis occurring
concurrently. Track conditions ahead are determined by measuring
modifications of rail input impedance caused by the standing waves
that result from the interaction of outgoing and reflected waves.
However, the '549 Patent does not work at any useful detection
range, and is not presently implemented. The changes in rail
characteristic impedance caused by distant rail breaks or track
occupation are not statistically significant due to the large
signal attenuation between the original and reflected wave
components of the standing wave. Conversely, instead of using a
continuous wave, the present invention uses a pulse-echo method so
that the transmit time period is not concurrent with the receive
time period. The large difference in signal level between the
original transmitted pulse and the reflected, potentially highly
attenuated pulse is irrelevant since the received signal can be
amplified to a suitable level by receiver 108 at a time when
transmitter 104 is inactive. Further, the pulse-echo timing
indicates the exact distance to the reflector rather than relying
on the interpretation of small variations in signal levels, which
are also subject to many extraneous variables, to detect small
track impedance changes caused by reflected waves (as required by
the '549 Patent).
[0032] Time Domain Reflectometry (TDR) is often employed to
identify and locate electrical faults in transmission line cables.
Every transmission line has an associated characteristic impedance
determined by the physical cross section and the electrical
properties of the conducting and insulating materials used in
construction. An electrical fault in the cable will cause a local
deviation from the characteristic impedance, with a complete short
circuit or a complete open circuit representing the most extreme
cases. A TDR-based cable tester operates by injecting an electrical
pulse at a test location to propagate outward along the cable. If a
change in impedance is encountered, some amount of the pulse is
reflected back to the test location where it is measured and
analyzed. The amount of reflection is determined by the degree of
impedance mismatch (100% reflection in the case of an open or short
circuit), the phase of the reflected signal indicates whether the
fault is a higher or lower impedance than the characteristic value,
and the time delay between transmitting and receiving the pulse is
used to calculate the distance to the fault for a given propagation
velocity. The use of TDR pulse-echo testing to locate and identify
transmission line faults is well known in the art and will not be
further explained herein.
[0033] In the present invention the electromagnetic signal is
coupled into the track with the two rails acting as a two-wire
differential transmission line, as disclosed in the '549 Patent.
Methods of coupling radio pulses into and from a two-wire
differential transmission line are well known in the art and will
not be further explained herein. For broken rail detection, a
change in transmission line impedance will be caused by the rail
break, i.e., an open circuit. For occupied rail detection, the
axles and wheels of the preceding train acts as a shunt or short
circuit between the two rails that will also cause a reflection.
When either of these conditions is encountered, a reflection is
returned towards the locomotive. Track coupler 106 transfers the
reflected pulse from the track to wave receiver 108. Wave receiver
108 supplies the received information to processor 110. Processor
110 uses the information to determine whether a break or occupation
of the track exists. Processor 110 can measure the time between the
outgoing wave pulse being generated and the reception of the
reflection pulse to calculate the distance to the break. Also, if
additional information, such as train speed, is input to processor
110, additional processing can be performed and additional useful
data can be calculated. Such additional data could include time to
break, rate of approach, or the like. An automated emergency
breaking function could also be provided according to a predefined
set of rules and safety requirements.
[0034] Apart from replacing the broken rail detection function of
the present signaling system and eliminating the need for wayside
equipment, the proposed method has many additional advantages. For
example, the exact location of the break or occupying train can be
indicated rather than just the signal block, so a driver response
can be more appropriate and rail breaks can be more quickly found
and repaired. A further advantage is that the maximum detection
range will be determined by a broader set of parameters, rather
than just the accumulated shunt loss of signal between the rails
due to track bed conductance (a.k.a. "ballast leakage current")
that sets the usual upper range limit (maximum block length) for
present signaling systems. Although the range of the present
invention is also affected negatively by the shunt conductance
acting to attenuate the differential pulse signal, methods are
available for increasing the transmitted energy (longer pulse,
higher power) and recovering weak received signals from noise
(coherent signal averaging and signal processing) to compensate for
higher attenuation of the signal at greater distances. This
provides an opportunity to overcome the usual range (block length)
limitation of present systems, typically given as 1, 2 or so
miles.
[0035] The lead locomotive would have a signal coupling mechanism
106 that would allow a radio frequency (RF) pulse to be
differentially coupled into the rail pair to travel forward, ahead
of the train. The two rails act as a differential pair transmission
line to propagate the electrical pulse to the rail break. At the
break, the interruption of current flow would cause a partial
reflection of the RF pulse back toward the train. The same or
similar coupling mechanism (used in reverse) would then convert the
arriving pulse into an electrical signal to be amplified and then
processed by correlating the received signal to the original
transmitted signal. The exact time delay between the transmitted
and any received signal would be calculated by processor 110, and,
based on the known or measured electromagnetic propagation speed,
the distance to the reflector would be determined and
displayed.
[0036] It is contemplated that the RF pulse would be a high power
pulse to provide greater distance of travel. Each train could use a
specific modulation code and/or pulse repetition timing sequence so
multiple trains in a specific area could each identify their own
signals. This coding could optionally be used in conjunction with
"matched filtering" of the received signals to provide "pulse
compression" and "processing gain". These signal correlation
techniques improve timing accuracy and allow very small signals to
be recovered, even from below the level of ambient electrical noise
and interference. Correlation of signals received in different
pulse-echo test cycles would require appropriate compensation for
the change in locomotive location between transmitted pulses.
Methods of small signal recovery, signal correlation, movement
compensation, reflector classification and reflector range
determination are well known in the art, particularly in the fields
of electromagnetic pulse-echo RADAR, acoustic pulse-echo ultrasonic
testing and acoustic pulse-echo SONAR, and will not be further
explained herein.
[0037] A further benefit of this method of detecting broken rails
is that it would provide an auxiliary safety mechanism to avoid
train collisions and maintain appropriate traffic separation.
Transmission line theory indicates that any impedance change will
cause a reflection (relative to the degree of impedance mismatch),
and the voltage phase of the reflected signal will be inverted for
a lower impedance (e.g., short circuit) or non-inverted for a
higher impedance (e.g., open circuit). Any rail shunt, such as the
last axle of the preceding train, would cause a signal reflection,
and the phase of the return signal would distinguish the rail shunt
from a broken rail. Thus while CBTC is expected to provide the
primary means of ensuring safe separation of traffic, each train
will also be able to independently measure the distance to the
train ahead (within the achievable detection range) to help
maintain a safe stopping distance in case of an emergency
situation. It should be noted that a rail failure can be triggered
by the passage of the preceding train. If such a broken rail occurs
under the preceding train, and the distance to that train is being
continuously monitored by the following train using the present
invention, the signal phase of the reflected signal will invert as
soon as the last axle of the preceding train has passed beyond the
break. In this way, the presence and location of the broken rail
can be indicated to the driver of the following train at the
earliest possible moment so that appropriate action can be taken.
The ability to detect and locate any rail shunt in the track ahead
is also highly desirable since CBTC will not provide protection
against any track shunting equipment or individual railcars that
are not registered in the CBTC system.
[0038] Present signaling systems detect a break or track occupation
based on the electrical properties of the track. Each rail is
normally highly conductive while conduction between the rails of
unoccupied track is normally reasonably low. A break will usually
lead to poor rail conductance while track occupation results in
high rail to rail conductance. Although the detection method is
very different, the present invention relies on the same
fundamental electrical properties of tracks, breaks and occupation,
so converting to the new method will be straightforward, i.e., no
major changes in track construction or maintenance procedures will
be required. For example, a temporary bolted track repair that was
compatible with the existing signaling system (i.e., with suitable
intrinsic or added electrical conduction to allow normal signal
operation) would also be suitable for the proposed system and would
not introduce a new "false" signal reflector. No changes in the
installation, replacement or repair of Continuous Welded Rail (CWR)
track would be required; although new installations or major
re-railing projects would benefit from not needing to add signaling
IJs at regular intervals. The usual practice would continue of
using bond wires to electrically bypass any poorly or
intermittently conducting ordinary joints in jointed track, or
where occasional joints were necessary in CWR.
[0039] Many existing signaling systems use IJs to electrically
isolate the signal blocks. These IJs would simply be electrically
bypassed and the signaling system turned off. Over time, these IJs
could be replaced with welded plug rails and signaling equipment
could be removed. If desired, it would be possible to operate the
new and old systems in parallel during a gradual changeover period.
By using suitably tuned filter circuits to bypass the signal IJs at
the RF pulse frequency, the new system could provide protection
beyond IJs while the operation of the signaling system at DC or low
frequency AC would not be affected.
[0040] It would be beneficial to continue protection beyond track
turnouts and crossing diamonds. This could be achieved by providing
electrical circuit switching to operate in parallel with the
mechanical track switching. The electrical continuity of the rail
pairs would correspond to the track selection through the turnout,
so that breaks or occupation in the track that the train was about
to enter (after the turnout) would be properly detected while the
status of the other track (e.g., a siding occupied by a waiting
train) would be properly ignored. IJs would be required in the
immediate vicinity of the turnout to electrically isolate the
separate tracks so that only the selected pair of rails was
electrically connected around the turnout. An additional benefit of
this approach is that if a train was approaching a turnout that was
set against it (i.e., traveling toward the turnout along the
unselected track) the track would indicate appropriately as an
unconnected or "broken" rail. Crossing diamonds (used at the
intersection of two tracks) would also require IJs, with permanent
crossing cables providing the proper electrical continuity of each
pair of rails. In this case, a fixed wayside system may be
justified to interlink the two tracks via relays so that a train
approaching or across the intersection on either track would
register as an occupation of both tracks.
[0041] In order to determine reflector location and to properly
compensate for train movement when correlating signal reflections
measured in different test cycles, processor 110 requires input
from some form of sensor indicating the speed and/or location of
the train. This information could be provided, for example, by an
independent GPS receiver on the locomotive. Preferably, processor
110 could have a data link to the CBTC system. This link could
provide access to the locomotive GPS data utilized by the CBTC
system, and also provide new and useful information back to the
CBTC system, such as, rail failure location or rail pending failure
location, unidentified track occupation, or the like. Further, the
location of other track vehicles known to the CBTC system could be
compared to track occupations determined by the present invention
to verify the correct operation of both systems, and to indicate
any unexpected track occupation not identified within the CBTC
system (e.g., an uncoupled freight railcar). Also, a centralized
database of known partial reflectors could be maintained within the
CBTC system so that the location of any detected reflector might
first be checked against the known reflector locations before
raising an alarm. Such partial reflectors would include, for
example, road crossings where the application of salt for winter
ice control may lead to a slight, local track impedance variation
due to higher conductance between the rails. It may also be useful
to combine information from the present invention with information
from the CBTC system onto a common display for the locomotive crew,
depicting all useful information on the status and conditions of
the track ahead.
[0042] While the present system is described as forward-looking
with respect to the locomotive, a similar system could be installed
at the rear end of the train to send a backwards-traveling pulse as
well. This backwards-traveling pulse could tell a locomotive of an
approaching locomotive, which would be especially useful if the
front train was slow moving (or reversing) and the approaching
train was not equipped with detection equipment. Also, the
backwards-traveling pulse could indicate rail failures caused by
the passage of the train. This would be useful in conjunction with
the data CBTC uplink because the failure location could be relayed
to the following train, and a repair crew immediately dispatched.
Further, the CBTC system could reroute following trains based on
track failure information.
[0043] The present invention has been largely described as
operating from a moving vehicle, such as a locomotive, to detect
rail breaks or occupation. FIGS. 3 and 4 show possible placement
of, for example, system 100 in a locomotive 302. Referring
specifically to FIG. 3, an elevation/cut-away view of locomotive
302 is shown. As with conventional locomotives, locomotive 302 has
a driver or conductor control stand 304. An interface unit 306
located about the stand contains conventional controls as well as
an interface 308, such as a display, monitor, light, bell, whistle,
buzzer, or other indicator connected to processor 110. Information
determined by processor 110 can be provided to interface 308 such
that the driver can act. Processor 110, and other components of
system 100, may be mounted in various locations, but typically
processor 110 would be mounted in electronics cabinet 310. Track
coupler 106 could be located in the locomotive axle 400 or
somewhere on the locomotive. FIG. 4 shows a particular track
coupler 402. Coupler 402 comprises a wire trace or coil that
provides inductive signal coupling to tracks 404.
[0044] However, instead of mounting system 100 on a locomotive,
such as shown in FIGS. 3 and 4, the present invention would also be
useful at a fixed location to detect breaks or determine the exact
speed and distance for an approaching track vehicle. One example
would be to automatically adjust the timing of road crossing
warning signals and gates so that road drivers would have adequate
warning to stop even for the fastest trains, but not become
impatient (and perhaps attempt to circumvent the barrier) waiting
for the slowest trains. A further example would be to indicate
train proximity for pedestrians or passengers waiting at a station.
Rail workers operating on or near a track could also use a portable
system to warn of approaching trains.
[0045] The present invention has been largely described to detect
unexpected rail breaks or occupation. However, it would also be
possible to locate reflectors placed deliberately in the railroad
system at predetermined locations to provide calibration signals,
location markers, track status signals or the like. Typically, the
deliberate reflectors would be partial reflectors to allow the
present invention to distinguish between actual breaks and/or
occupation and a calibration signal, or the like. Further, partial
reflectors allow some of the pulse energy to travel beyond the
partial reflector to provide continuing detection of any subsequent
unexpected reflectors. Also, rail workers could place deliberate
reflectors (such as a track shunt) to signal their location to
approaching locomotives.
[0046] Instead of using passive reflectors, the track status
indicators, calibration devices and/or worker locators could be
active transponders. Rather than passively reflecting an arriving
signal, a transponder would actively transmit a response that could
include additional identification or status information. These
signals would typically be received by the receiver on the
locomotive as a specially modified signal that would be readily
distinguishable from a normal rail break or occupation signal.
Alternatively, one leg of the normal pulse-echo path through the
track could be substituted with another path such as a direct
atmospheric radio link, similar in principle to the operation of
aircraft RADAR transponders.
[0047] The placement of predefined markers for calibration is
helpful because changes in environmental conditions can also change
the transmission line properties of the rails (whether using
acoustic or electromagnetic waves). Thus, having preset calibration
points would allow for real time calibration of processor 110 for
range, transmit signal level, break location accuracy and the
like.
[0048] Each locomotive could also provide several different pulses
at various frequencies. For example, high frequency pulses
generally allow shorter pulse lengths which would be useful for
avoiding overlapping timing of the transmit pulse and reflected
signal from nearby reflectors. Also, higher frequencies have
shorter wavelengths and would generally provide better resolution
of the reflector location. However, because of the nature of the
rail transmission line parameters, signal attenuation increases
rapidly at higher frequencies indicating that lower frequencies are
probably more appropriate for detecting reflectors at greater
distances. Thus, a locomotive may send two or more pulses at
various frequencies to cover the required detection range for the
encountered track conditions. These various frequencies could be
generated simultaneously, substantially simultaneously, or
sequentially as a matter of design choice.
[0049] Railroad authorities and companies are extremely concerned
with the safety of employees. In order to help insure the safety of
the locomotive crew, the present invention could include a signal
monitoring means to ensure sufficiently low levels of radiated RF
energy in and around the locomotive to meet RF exposure safety
guidelines. Further, such monitoring means would be useful to
indicate the general proper operation of the system and would
detect, for example, excessive signal radiation caused by a failure
or incorrect adjustment of the track coupler 106.
[0050] Using the present invention in conjunction with the CBTC
GPS-based system or with an independent GPS receiver would provide
access to the standardized, highly precise reference clock
incorporated into each GPS satellite. Using the GPS timing
reference would allow for a high degree of coordination between
multiple units utilizing the present invention on various
locomotives and fixed locations. This timing reference could be
used to avoid overlapping pulse-echo test cycles between multiple
units, or to calculate the distance to various other units by
observing the arrival time of the transmitted pulses from those
other units.
[0051] While the above invention has been described to provide a RF
pulse into a track, system 100 would operate very similarly if an
acoustic pulse was utilized. For example, wave transmitter 104
could produce an ultrasonic pulse that would be coupled into the
track and directed forward of the locomotive. Additionally,
combinations of pulses could be provided. For example, a RF pulse
could be used in combination with an acoustic pulse. The RF pulse
would provide detection for actual breaks and occupation that can
be characterized by an electrical impedance change, but the
acoustic pulse would provide detection of some breaks and pending
failures that may only be evident as an acoustic impedance
change.
* * * * *