Railway switches and signals – Block-signal systems – Automatic
Reexamination Certificate
2002-05-31
2003-12-23
Le, Mark T. (Department: 3617)
Railway switches and signals
Block-signal systems
Automatic
C246S00100C, C246S003000, C246S014000, C246S18200B
Reexamination Certificate
active
06666411
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to an improved system and method of vehicle control. More specifically, the present invention is directed to a Communications based Train Control (CBTC) system that utilizes low-cost, readily available hardware to control and direct various trains in a safe and efficient manner.
BACKGROUND OF THE INVENTION
For over a hundred years the movement of trains, or other track guided vehicles, has been controlled such that increasing numbers of vehicles can operate within a network of tracks in a safe and efficient manner. Both people and freight are transferred on trains between locations separated by distances ranging from hundreds of feet to thousands of miles. With a single train running on a single track or network of tracks, with no obstacles, control of the train is simple. Since there is little concern for the train coming into contact with any other objects, the train can run at maximum speed, limited only by the speed performance of the train, the train's stopping ability once it reaches its destination, and the train's ability to stay on the track, i.e., while travelling around turns, etc.
However, as additional trains are placed on the track, or track network, to take advantage of the unused capacity of the tracks and provide viable transportation alternatives, controlling the trains to keep them operating in a safe and efficient manner becomes more complex. For example, as two trains approach one another from opposite directions, in order to avoid a collision, one of the trains must be switched to another track. Similarly, as two trains approach one another from the same direction, i.e., on the same track with the one behind the other travelling at a faster speed than the train in front, either the train in front must be sped up, or the one behind must be slowed down. Accordingly, Railways are provided with signaling primarily to ensure that there is always enough space between trains to allow one to stop before it hits the one in front.
In typical systems, signaling is achieved by dividing each track into sections or “blocks”, which is a length of track of defined limits. The length of a block is usually determined to be the distance it takes a train, running at full speed, to come to a complete stop under the worst possible conditions. Each block is protected by a signal placed at its entrance. If the block is occupied by a train, the signal will display a red “aspect”, to instruct the conductor to stop the train. If the section is clear, the signal can show a green or “proceed” aspect.
A track circuit is typically the mechanism by which the presence of a train in a block is usually detected. Many rail-lines with moderate or heavy traffic are equipped with color light signals operated automatically or semi-automatically by track circuits. When the track circuits detect a train, the signal shows a red aspect. If no train is detected and the circuit is complete and the signal shows a green aspect (or yellow, in a multi-aspect signaled area).
A low voltage from a battery is applied to one of the running rails in the block and returned via the other rail. A relay at the entrance to the section detects the voltage and is energized to connect a separate supply to the green lamp of the signal.
When a train enters the block, the leading wheelset short circuits the current, which causes the relay to de-energize and drop the contact so that the signal lamp supply circuit activates a red signal lamp. The system is “fail-safe”, or “vital” as it is sometimes called, when any break in the circuit will cause a danger signal to be displayed.
The above is a simplified description of a track circuit. Actually, a “fixed-block” section is conventionally electrically separated from its adjacent sections by insulated joints in the rails. However, more recent installations use electronics to allow jointless track circuits. Also, some areas have additional circuits which allow the signals to be manually held at “red” from a signal box or control center, even if the section is clear. These are known as semi-automatic signals.
The development of signaling and train control technology can generally be separated into two periods, with 1920 as the dividing point. Before 1920, the major areas of technological advance were interlocking control and block signaling (manual and automatic).
After 1920, the demand for moving heavier traffic at higher speeds and with increased safety led to major developments such as centralized traffic control, continuous cab signaling, coded track circuits, and automatic train control (ATC). Generally, innovative signaling and train control technology for rail rapid transit was derived from railroads and lagged behind railroad application by about 10 years. There were some notable exceptions; the development of automatic junction operation and automatic train dispatching was pioneered in rail rapid transit. Very recently, since roughly 1960, there has been some experimentation with techniques and equipment solely for rail rapid transit and small people-mover systems.
Over the years, technological advances in several areas of communication has lead to vast improvements in train control. For example, centralized control has typically replaced the need for block signaling such as described above.
The original and most important purpose for control devices and/or systems is to prevent collisions between vehicles moving in the track network. For this purpose, as mentioned above, it has been known to divide the line into blocks and to prevent, by central control, any train from entering into a block unless the block is free of other vehicles. This “real-block” type of system may be suitable for less dense traffic, however, it is not suitable for use within track networks where the traffic has to be dense and where the length of the blocks would, thus, have to be extremely short, leading to major investment and control cost.
One known conventional system provides a calculation of the movement within a block by means of a message sent to a central unit from the train about its speed. The central unit then performs a distance calculation by multiplying the train's speed by the desired time increment. Accordingly, the speed may be centrally controlled if a collision risk occurs. By being able to determine, at least approximately, the position within a block of each train, several trains can be permitted into the same block as long as the central surveillance unit, as well as the communication with the train, functions properly. By using this method of calculating train positions, however, the position determinations obtained are so uncertain, that either the blocks must be made very small, so that the calculation must be updated frequently, or the number of allowed trains within the same block must be strictly limited. Also, as the demand to increase traffic density rises, prohibitively small blocks would be required, making it practically impossible to build such a system at a reasonable cost and with a reasonable control capacity.
Another known conventional train control system also includes dividing the tracks into blocks where, within each block, movement of the train is determined by means of a rotation meter on the wheels of each train. The position determination within the block is then made centrally by emitting clock pulses that are returned by the train with a delay corresponding to the distance of travel within the block, measured by the rotation meter.
In both of the conventional systems mentioned above, the passage of each train past a block borderline is reported to the central unit, whereupon information about speed and distance traveled is repeatedly determined. The central unit calculates the location of each train within the block and controls the velocity of at least one of the trains to avoid a collision, if two or more, trains are approaching each other.
The conventional systems, thus described, require a physical division of the track network into blocks, with installations that, w
Hart Harvey R.
McCabe Jeff
Alcatel
Le Mark T.
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