Patent GB-1277600-A (GB)
Title: Control signal transmission system
IPC: B61L27/00
Filed: 1969-10-02
Abstract: 1277600 Automatic train control WESTINGHOUSE AIR BRAKE CO 2 Oct 1968 [2 Oct 1968] 48467/69 Heading B7H In an automatic train control system in which speed signals, determined in accordance with the traffic in advance, are applied to a train via train carried coils coupled to the track rails and in which the speed signals are transmitted to track side locations from a control office and occupation signals are transmitted from the track side locations to the control office by a time division multiplex system, the speed signal for the track section directly to the rear of an occupied section is transmitted from the control office via a direct line. In addition a track section relay at the control office, which is released when its corresponding track section is occupied, is not picked up when the section is vacated until proof is obtained, by release of the associated track relay, that the train has entered the next section. The track is continuous and is divided into sections AT, BT, &c. by cross bonds CB1, CB2 &c. Each trackside location at the cross bond between sections is coupled to the control office by a time division multiplex system including a synchronizing pulse line, a transmitter command line and a receiver information line and in addition each location is coupled by a cable pair, AB, CD, EF &c. to its corresponding control circuit including a vital safety protection unit VSP at the control office. When the first synchronizing pulse is generated the VSP unit B controls a speed command generator SCGA to provide a speed command which is transmitted via the opened gate to the transmit line and via terminals AB, now short circuited by front contact C of the track relay BTR at the control station, and the second opened gate at the trackside location to the speed command memory. This supplies a signal to frequency shift modulate a carrier f1 and the modulated signal at frequencies f1 and f1<SP>1</SP> is applied to the track at the cross bond CB 1. The signal in section AT acts as a speed control signal for a train in that section and the signal in section BT acts with receiver F1, F1<SP>1</SP> to detect the presence of a train in that section. During the second synchronizing pulse the output from the receiver is applied via a gate, a line driver, the receive line and the gate associated with unit B to a speed comparison unit and its presence and the result of its comparison with the speed signal sent by generator SCGA provide input signals to the unit VSPB to maintain relay BTR energized. When train enters section BT relay BTR de-energizes and opens its hold circuit at front contact a. On release of the relay at restricted speed command signal is transmitted via back contact c of the relay and the line B to the speed command memory to cut down the speed of or stop any train now entering section A. When the train leaves section BT and enters section CT relay CTR releases and at back contact b provides a circuit whereby a relay BTR can now be re-energized. Signals at three different frequencies are used in sequence in the track circuit.