Patent GB-122472-A (GB)
Title: Improvements in and relating to Railway Signalling.
IPC: B61L3/22
Filed: 1918-01-23
Abstract: 122,472. McKenzie, Holland, & Westinghouse Power Signal Co., (Union Switch & Signal Co.). Jan. 23, 1918. Electrical systems, automatic; track apparatus actuating signals on trains and for stopping trains.- The permissible speed of a train is automatically varied in accordance with its distance from the next train ahead or with the nature of the track ahead. Alternating electromotive forces of different frequency are impressed upon the track rails, and the speed of the train is limited at any point according to the number of currents of different frequency received from the track rails, the apparatus carried by the train being arranged to respond selectively to currents of different frequency. Fig. 3 shows a length of track to which currents of four frequencies g<1>, g<2>, g<3>, g<4> are supplied through transformers referenced by the frequency concerned from generators G<1>, G<2>, G<3>, G<4> connected to a pair of line wires. The train carries apparatus as shown in Fig. 4, which comprises a coil 10, in which currents are induced from the track rails, this coil being connected to an amplifier P and four transformers supplying current to four relays S<1>, S<2>, S<3>, S<4>, the circuits are made resonant so that each relay is energized when the coil 10 is supplied with current of the frequency to which the relay circuit is tuned. The contacts of these relays are arranged so that, according to the number of relays energized, a lamp signal F<1> indicating the allowable speed is illuminated and the circuit of the brake-valve magnet 42 is closed through the contacts of the governor-controlled drum. This drum is moved by the governor 44 to open, in succession, the circuits from the left of the drawing as the speed of the governor increases. At very low speeds, all the contacts are closed and the circuit to the magnet 42 is closed even if all the relays are de-energized. If any one relay is energized, the magnet 42 receives current through the second contact of the drum and the circuit is maintained at a rather higher speed, the lamp 10 also being illuminated in place of the lamp 5. If two, three, or four relays are energized, the appropriate lamp 25, 45, 60 is illuminated and the circuit of the brake magnet is closed through a contact nearer to the right of the drawing. A train V<1>, Fig. 3, would receive current to energize all four relays S<1>, S<2>, S<3>, S<4> while in the position shown and until it passes the point c, and is thus uncontrolled as to speed. After passing c since a train V shunts current g<3>, currents g<1>, g<2>, g<4> only are received and hence the speed must not exceed that indicated by lamp 45; as it approaches the train V, currents g<4>, g<1>, g<2> are successively cut off and the speed must be reduced to that indicated by lamps 25, 10, 5. If the train V proceeds ahead, current g<3> will be supplied to the train V<1> and greater speed will be permitted. At down grades, curves or similar positions requiring reduced speed, one or more of the several frequencies are not supplied to the length of track concerned, and currents of these frequencies from the track ahead are shunted by tuned cross bands between the rails so that a train on the section concerned can only receive such number of currents as will allow the predetermined maximum speed.