Patent GB-980687-A (GB)
Abstract: 980,687. Automatic train control systems. LONDON TRANSPORT BOARD, and R. DELL. May 30, 1962 [March 2, 1961], No. 7698/61. Heading B7N. An automatic train control system for driverless trains comprises a known coded current signalling system in which coded currents of a plurality of different frequencies are applied to sections of the track, the frequency of the current in any section being determined by the traffic conditions ahead of the train and a command current system in which currents at frequencies other than those used in the coded current system are superimposed thereon at points on the track whereby the train is controlled by the command signals for normal operation, i.e. slowing down and stopping at signals and braking to a halt at stations, and is controlled by the coded current system in the event of failure of the command system and to restart the train after it has come to a halt. The known coded current system comprises means for selectively applying a signal at either 420 c/m. (full speed), 270 c/m. (22 m.p.h. and restart), 180 c/m. (less than 22 m.p.h.) or 120 c/m. or no signal (emergency stop) to insulated sections of the track in accordance with the ahead traffic. Command signals are superimposed on the coded signals at predetermined short sections of the track, these signals are generated in units each comprising an oscillator A, Fig. 1, a counter D which controls the gating of an amplifier B via which the oscillator signal is applied via driver and output stages C and F to the rails. The counter counts 128 cycles of the output of the oscillator then prevents the passage of signals from the amplifier to the driver stage during a period corresponding to the next 128 cycles from the oscillator, the command signal thus comprises a series of signal bursts each comprising 128 cycles. The frequency of the oscillator may be related to train speed, i.e. a signal of 2500 c/s. commanding a speed of 25 m.p.h., or may be spot frequencies of 15 kc./s. or 20 kc./s. which command the cutting-off of motor current and a service brake application, respectively. On the train two counters are provided, one of which counts the track pulses and provides an output signal when 128 pulses have been counted and the other counts pulses generated on the train at a frequency which is related to the actual train speed in the same manner as the frequency of the track pulses are related to required speed. The output signal from the track pulse counter stops the train pulse counter and from the count in the train pulse counter a diode matrix L (not shown) and a circuit M determine whether the train is " too slow," " slow," " correct " or " fast " and these conditions are each signalled by the energization of one of lines 60-63 to the braking and train control unit N, which acts to control the train to the required speed. The Specification describes how by the use of a number of command positions each generating signals at a progressively lower frequency a train is brought to a halt at a station and how a train is controlled at signals and in approach to a station with clear tracks or when the station is occupied by a preceding train.