JOINTLESS TRACK CIRCUIT
Publication Date: 2011-Nov-28
The IP.com Prior Art Database
A new jointless track circuit system for railway tracks is disclosed. The new system would allow signaling installation on a track without use of insulated joints to define the block boundaries. This design uses a number of transmitters and multiple frequencies for communication and train detection. The transmitters are sequentially numbered with the odd and even transmitters transmitting at low and high frequencies. Relay points are located within a short distance of the block boundaries which receive a message from the low frequency transmitters, and then modulate the high frequency signals with the same message. The system effectively transmits messages from one end of a block to the other. This design allows insulated joints to be eliminated from the signaling systems and the system works under all weather conditions.
This publication relates to the jointless track circuit for signaling in railways. Track circuit is a simple electrical device used to detect the absence of a train on rail tracks, used to inform signalers and control relevant signals. Many methods have already been proposed for signaling in railways. These methods use AC (audio frequency) signals to detect trains, rail breaks, and provide communication. The audio frequency signaling systems can only be used with relatively short blocks. US freight service covers long distances and hence needs longer signaling blocks than those currently used in rapid transit and short-haul rail applications. Current jointed track circuits require excessive maintenance on a large number of joints, which causes both cost and availability issues, since tracks cannot be used when they are being inspected. There are train signaling systems today that do not use insulated joints to define block boundaries. The normal track circuit is shown in Figure 1 showing different signaling points.
Figure 1: Normal track circuit
In train detection technique, dead zone and ambiguity zone can be detected. Dead zone is an area around a track receiver or transmitter where the presence of a train shunt is undetectable. The dead zone must be less than a car length. Ambiguity zone is an area around a track receiver or transmitter where a train is detected, but the block where the train shunt is located cannot be determined. The ambiguity zone must be less than approximately 13’ in order not to put a false red signal in the face of a train.
The general communication protocol when the train is nearing the block boundary is shown in Figure 2 and it is explained by two steps. The first step is to transmit message from second signaling point (SP2) to first passive signaling device (PSD1) on a low frequency (LF) carrier (<50Hz). At these frequencies, there is enough track impedance between the transmitter and the train to allow reception at the PSD. The second step is to transmit message from the PSD1 to first signaling point (SP1) using medium frequency (MF) (1-2 kHz) applied by SP1.
Figure 2: Communication protocol when train is near the block boundary
The North American freight service covers long distances, but the signaling devices currently available cover only an area of 2.5 miles of track ahead of the train. So in general there is a need for new approach of detection for longer distances.
BRIEF DESCRIPTION OF DRAWINGS
Jointless track circuit is described further with reference to the following figures:
i) Figure 1 shows the technical approach of the existing detection system
ii) Figure 2 shows the communication protocol when the train is near a block boundary
iii) Figure 3 shows the NGTC timeline
iv) Figure 4 shows the JTC 2007 technology demo
The new system disclosed in t...