METHOD FOR DETECTION OF RAIL BREAKS ON OCCUPIED BLOCKS TO SUPPORT REDUCED TRAIN SPACING
A method for detecting broken rail and track occupancies measures both the electrical current and voltage on each end of the block of track. This allows a broken rail to be detected even with a shunting axle (occupancy) in the same detection block. The method also provides broken rail detection capability to support modes of operation in which a following train maintains safe spacing from a leading train without the use of track circuit information for train location, allowing for reduced train spacing. The current and voltage measurements are used to make binary decisions, in order to minimize the sensitivity to variations in track impedance characteristics. When combined with train location information, this method also allows for identifying the location of a rail break.
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The present application is based on and claims priority to the Applicant's U.S. Provisional Patent Application 62/534,307, entitled “Method for Detection of Rail Breaks on Occupied Blocks to Support Reduced Train Spacing,” filed on Jul. 19, 2017.
GOVERNMENT LICENSE RIGHTSThis invention was made with government support under work sponsored by the Federal Railroad Administration of the U.S. Department of Transportation. The government has certain rights in the invention.
BACKGROUND OF THE INVENTION Field of the InventionThe present invention relates generally to the field of methods for detecting rail breaks on railroad tracks. More specifically, the present invention discloses a method for detecting rail breaks in occupied blocks of track.
Statement of the ProblemThe following definitions apply to the following terms in this disclosure:
“Detection block” means a section of track with defined limits in which broken rails or occupancies can be detected, but that is not limited to a signal block.
“Signal block” means a section of track with defined limits that utilizes conventional wayside or cab signals and may refer to an intermediate, controlled, or absolute permission block.
“Intermediate (automatic) block” means a section of track associated with a single track circuit for automatic block signaling within a controlled block.
“Controlled (absolute) block” means a section of track spanning between control points, the movement into which is controlled by a dispatcher or control operator and may include multiple intermediate blocks.
“Moving block” means a type of train control in which train separation is determined dynamically according to the braking distance of the following train. A moving block is related to a virtual block.
Track circuits are one of the basic components of conventional fixed block railroad signaling systems. Conventional signal systems typically use track circuits to perform two functions: (1) Detect occupancy and broken rails in each block; and (2) Communicate the status of each block to adjacent blocks. Track circuits utilize the steel rails as a path for electrical current flow. The track is separated into electrically isolated sections, or blocks, using insulated joints in the rails to isolate each block. A voltage is placed across the rails at one end of the block and the presence or absence of electrical current is detected at the opposite end of the block. Electrical continuity throughout the length of the block provides information on whether the block is clear of shunting vehicles and broken rails or not. When a train is occupying a block, the wheels and axles of the train shunt the rails together so there is no longer sufficient electrical current at the end of the block to indicate the block is unoccupied. Similarly, a broken rail will result in an open circuit, preventing any current flow through the track circuit. Consequently, track circuits are utilized to detect train occupancy and broken rails.
In conventional signaling systems, signal aspects are determined by the status of the block over which the signal governs movement, as indicated by the track circuit in that block, as well as the status of adjacent blocks. Information about the status of each block is typically transmitted to adjacent blocks through the use of coded track circuits, although there are other methods used in some cases. With coded track circuits, the electrical signal that is transmitted through the rails is coded using different pulse rates to indicate the signal aspect that block is currently displaying. This information is interpreted by the equipment at the adjacent block and used in determining the proper aspect to display for the signal governing movement over that block.
The minimum required length of the track circuit is based on braking distances at track speed and the number of signal aspects that can be displayed. For example, with 4-aspect signaling, the blocks are spaced such that two blocks represent no less than the distance of normal service braking for the worst-case braking train. This creates safe separation between trains as seen in
Modern track circuits for freight applications typically use DC coded track circuits. The DC signals sent through the track are pulsed to form codes, providing aspect information that is communicated between the blocks. To allow for bi-directional traffic, DC circuits work in both directions with coordinated pulse timing to avoid interfering with one another. Additional features often include a handshaking protocol to send and receive data within a block, and alternating polarity current to prevent code detection from an adjacent block.
The railroad industry is interested in identifying new technologies that use the rails as the broken rail and track occupancy sensing medium and have potential to support new methods of train control (e.g., communications-based). New train control is intended to improve the capacity of the line with moving block operation and variants thereof. The potential capacity improvement with a moving block (or similar) train control system is limited if conventional fixed blocks are still required to maintain broken rail detection.
Conventional track circuits cannot detect a broken rail that occurs in the same block that a train is occupying since the axles will be shunting the block. The broken rail can then be detected after the train has left that particular block. Also, conventional track circuits do not detect or indicate where within a block a broken rail or occupancy is located. Hence train control systems must protect the entire block when a break or occupancy has been detected. This is the primary limitation in their ability to support moving block operation.
Solution to the ProblemIn contrast to the prior art, the present system detects both the current and voltage at the ends of the track circuit. The combination of current and voltage can be used to detect a broken rail even if the block is occupied by a train.
SUMMARY OF THE INVENTIONThis invention provides a method for detecting rail breaks in occupied blocks of track by measuring both the current and voltage at the ends of the track circuit. The combination of current and voltage allows detection of a rail break even if the block is occupied.
These and other advantages, features, and objects of the present invention will be more readily understood in view of the following detailed description and the drawings.
The present invention can be more readily understood in conjunction with the accompanying drawings, in which:
Interfaces and Detection Methods.
Track circuits typically provide binary information for a fixed block. The track circuit can either be clear (i.e., no occupancy and no broken rail) or not clear (i.e., occupancy and/or broken rail).
With today's PTC (Positive Train Control) and other newer proposed train control systems (especially those that are communications-based), the track circuit information may be transmitted to a server (that may be located in the office) or directly to the locomotive's onboard computer as seen in
Monitoring of the transmission current can be performed on each side of the track circuit.
In the present methodology, additional information is obtained by also monitoring of voltage by the next generation track circuit. If the voltage detected at A and/or B drops to approximately zero, but the current in the block is substantial, then an occupancy can be determined to be present in the block. This produces additional binary information from each end of the block. Table 1 presents the various combinations of information provided by voltage and current for each end of the block. The next generation track circuit can also be used to detect an open or shunt caused by a device (e.g., turnout or track obstruction detector) interfaced with the track circuit.
Moving Blocks.
In this disclosure, modern train control is understood to be a moving block or similar (e.g., virtual block) operation. The advantage of moving blocks compared to fixed block operation is seen in
Detection Blocks.
The concept for next generation track circuits is to perform as detection blocks that provide broken rail identification and roll-out protection against unexpected or unmonitored occupancies. The next generation control system can use the binary track circuit status information for these functions but does not require it for train location determination and separation, all of which are available functions with conventional track circuits.
Next generation track circuit technology will improve the spatial and temporal resolution of rail breaks compared with conventional track circuit technology. The proposed next generation track circuit method utilizes both electrical voltage and current on both ends of the detection block as described above. This improves the spatial resolution as a broken rail can be detected between a shunting axle and one end of the block. The spatial resolution of rail break location can be improved even more significantly if the train control system uses rear-of-train location reported by a leading train in conjunction with the next generation track circuit information described here. Furthermore, temporal resolution is improved in the sense that a broken rail can be detected while there is a shunting axle in the block. Conventional technology can only detect a broken rail once the signal block is unoccupied.
In conventional fixed block signaling systems, the minimum length of the signal block is determined by the braking distance of the trains operating over the territory at the maximum allowable speed. This provides safe separation of trains. In a modern train control system with next generation track circuits, safe separation of trains is provided by a moving block train control method. Furthermore, the track circuits communicate status to trains in the area through a wireless communications system or to a server via any of various communications media, as opposed to only communicating status via signal aspect to trains approaching the block. In this concept, longer detection blocks may be practical but can reduce the potential capacity gained through the moving block train control system. Therefore, it is the maximum detection block length that needs to be specified, in order to optimize the capacity of the operation with a modern train control system.
In other words, while in conventional fixed block signal systems, the minimum length of the signal block is determined to provide safe train separation for a specified number of available signal aspects, in this system, the maximum length of the detection block is determined to provide the desired balance between track circuit cost and line capacity. For the next generation track circuit, the length of the track circuit is still driven by the braking distance of the train, including the desired warning distance: (1) If the braking distance plus warning distance is less than the detection block length, train separation is dictated by the detection blocks; or (2) If the braking distance plus warning distance is greater than the detection block length, train separation is dictated by the moving block train control system. Therefore, with this system, an analysis of the utilization of each specific line where it is to be implemented and the typical braking distance plus warning distance of the trains operating on the line should be conducted to optimize the length of the detection blocks on the line.
Broken Rails Between Trains.
The next generation track circuit detects broken rails between trains, albeit before they simultaneously occupy the same block. The proposed concept is for broken rails to be detected by the received voltage signal as well as monitoring the current in the loop, as described above. Monitoring the current in the loop allows a broken rail to be detected, even if an axle is shunting in the same detection block, as long as the train is not spanning across the broken rail.
Once the broken rail is detected, the information will be transmitted to the office (or other off-board system) and/or locomotive. Enforcement braking will occur in time to stop the train before reaching the rail break. If a train is following another train as closely as the moving block control system will allow (i.e., by the warning distance), and the broken rail occurs directly beneath the leading train, the break will be detected as soon as the leading train is no longer over the break, leaving sufficient time for the following train to receive the broken rail notification and stop short of the broken rail as long as the following train has not yet entered the block.
Movement Authorities.
The context for the next generation track circuit is that train separation is controlled by modern methods of train control (e.g., moving block). The train control system will separate the following train from the rear of the leading train by the following train's braking distance plus warning distance and margin. Modern train control systems use movement authorities and/or stop targets to ensure train separation. In order to apply the proposed next generation track circuit the following rules should be considered.
A movement authority rule could be designed into the system to account for the case when a following train enters an occupied detection block, thereby masking the broken rail protection between trains. See
The stop target would be replaced with a new stop target behind the latest reported leading train location once the leading train clears the block and the track circuit determines there is no rail break in the block in advance of the following train. Clearing an occupied block can be determined by a database with detection block boundary locations and the known rear of train location
The proposed movement authority rule would be designed into the system to protect the following train in the case of broken rails between trains. See
Deployment.
Next generation track circuits may also need to support current methods of operation in different types of signaled territory, as seen in
The above disclosure sets forth a number of embodiments of the present invention described in detail with respect to the accompanying drawings. Those skilled in this art will appreciate that various changes, modifications, other structural arrangements, and other embodiments could be practiced under the teachings of the present invention without departing from the scope of this invention as set forth in the following claims.
Claims
1. A method for detecting rail breaks in a block of track having first and second ends, said method comprising
- applying a voltage across the tracks at the first end and detecting the resulting voltage and current at the second end;
- applying a voltage across the tracks at the second end and detecting the resulting voltage and current at the first end; and
- determining the existence of broken rail from the combination of voltages and currents detected at the first and second ends.
2. The method of claim 1 wherein the block of track is determined to be unoccupied by a vehicle and to have no broken rail if the magnitudes of all of the detected voltages and currents exceed predetermined threshold values.
3. The method of claim 1 wherein the block of track is determined to have a broken rail if the block of track is unoccupied by a vehicle and the magnitudes of all of the detected voltages and currents do not exceed predetermined threshold values.
4. The method of claim 1 wherein, if the block of track is occupied by a vehicle, the block of track is determined to have a broken rail between the first end and the vehicle, and a broken rail between the second end and the vehicle, if the magnitudes of all of the detected voltages and currents do not exceed predetermined threshold values.
5. The method of claim 1 wherein the block of track is determined to be occupied by a vehicle and to have no broken rail if the magnitudes of the detected voltages at both ends are do not exceed predetermined threshold values, and the magnitudes of the detected currents at both ends exceed predetermined threshold values.
6. The method of claim 1 wherein the block of track is determined to be occupied by a vehicle and to have a broken rail between the first end and the vehicle if the magnitude of the current detected at the second end exceeds a predetermined threshold value and the magnitudes of the other detected voltages and currents do not exceed predetermined threshold values.
7. The method of claim 1 wherein the block of track is determined to be occupied by a vehicle and to have a broken rail between the second end and the vehicle if the magnitude of the current detected at the first end exceeds a predetermined threshold value and the magnitudes of the other detected voltages and currents do not exceed predetermined threshold values.
8. The method of claim 1 wherein the block of track is determined to have a broken rail if the magnitude of the current detected at either the first end or the second end does not exceed a predetermined threshold value.
9. The method of claim 1 wherein the block of track is determined to be occupied by a vehicle if the magnitude of the detected voltage at either the first end or the second end does not exceed a predetermined threshold value.
10. The method of claim 1 further comprising limiting the movement authority of a following vehicle behind a leading vehicle on the block of track by determining the location of the leading train on the block of track when the magnitude of the current detected behind the leading vehicle falls below a predetermined threshold value.
11. The method of claim 1 further comprising limiting the movement authority of a following vehicle behind a leading vehicle on the block of track by determining the location of the leading train on the block of track when the following train enters the block.
12. The method of claim 1 wherein the block of track has a length determined by the braking distance plus a warning distance for trains operating on the track.
13. The method of claim 1 further comprising determining the location of the rail break in a block of track having a vehicle moving along the block of track by determining the location of the vehicle when the magnitude of the current detected behind the vehicle falls below a predetermined threshold value.
Type: Application
Filed: Jul 10, 2018
Publication Date: Nov 15, 2018
Applicant: Transportation Technology Center, Inc. (Pueblo, CO)
Inventors: Joel Donald Kindt (Colorado Springs, CO), Alan Lee Polivka (Pueblo West, CO), Joseph David Brosseau (Pueblo, CO)
Application Number: 16/031,863