Patent GB-360992-A (GB)
IPC: B61L23/16
Filed: 1930-08-19
Abstract: 360,992. Railway signalling systems. WESTINGHOUSE BRAKE & SAXBY SIGNAL CO., Ltd., 82, York Road, King's Cross, London.-(Assignees of Mc- Cann, R.A.; of Union Switch & Signal Co., Swissvale, Pennsylvania, U.S.A.) Aug. 19, 1930, No. 24807. Convention date,. Oct. 2, 1929. [Class 105.] In a railway signalling system for the operation of cab signals or train control apparatus on the train bv code currents in the rails, the code currents are produced by periodic interruption of an alternating current derived from an alternator device operated by direct current. The code current is superposed on the track-circuit direct current, and is only supplied to a section of track when that section is occupied ; the frequency of interruption of the code current is determined by the condition of the track ahead of the section concerned. Fig. 1 shows the system arranged to give two indications only. The track is divided by insulated joints into sections de, ef, which are fed by batteries 3, through the secondary windings of transformers t, and have track relays R<3>, R<4> respectively. Two coders D<1>, D<2>, energized through a contact of relay P, have series armatures 23 fixed to pendulums 25 which normally hold the contacts 23 closed and which determine the frequency with which the contacts vibrate ; the armatures 23 are coupled to armatures 20 which control the application of current to the primary winding of transformer t; the two coders are arranged to operate at different frequencies. When the track section de is occupied, track relay R3 drops and energizes an approach relay P, which closes the circuit of an alternator A of the vibrating reed type. The alternator supplies current alternately in opposite directions to the two halves of the primary winding of a transformer T, the secondary of which supplies alternating current through the contact 20 of coder D<1> or D<2> to the primary winding of the transformer t. If the section ef is clear when relay P is energized, the front contacts of track relay R<4> are closed to bring coder D<2> into action, so that the alternating current supplied to transformer t from transformer T is interrupted with the frequency of coder D2, and a corresponding code current is supplied to the rails of section de from the secondary winding of t. If the section ef is occupied coder D<1> is brought into operation instead, and the code current has a different frequency. A slow-acting relay K is energized through a contact of relay P to conserve the battery by breaking the circuit of the alternator A and the coders if the track section is occupied for longer than usual. In a modification, Fig. 2 (not shown), the relay K is dispensed with, and the current to the armature of the alternator A is taken direct from the battery ; the return circuit from the winding of the alternator is taken through a contact of relay P. In a further modification, Fig. 3 (not shown), a third coder controlled by a second section is used, the system giving three indications according to whether the first section is occupied, the first section is clear but the second is occupied, or both sections are clear. In Fig. 4 the alternator and transformers at j are controlled as in Fig. 3, and the coders D<1>, D2 as in Fig. 1, except that the coder operating circuits include an arm contact 47 which is open when the signal S4 is at "danger." A train entering the section hi will de-energize track relay R<6> to pick up approach relay P<1> and bring into operation the alternator and coder D<4> or D<5>, according to the position of polarized relay W, which is controlled by a polechanger 7 operated by signal S<4>; if track relay R<7> is de-energized, owing to the occupation of the section ij, W is de-energized and neither coder operates, but in this case no other train can occupy section hi. When the train enters section ij, approach relay P is energized from battery Q<2> through the back contact of relay R<7>, and coder D<1> or D<2> operates, according to the position of track relay R<8>; neither coder operates if the section jk is clear but signal S<4> remains at "danger." In a modification, Fig. 5 (not shown), the track relay R<7> is replaced by a polarized relay and the polarized relay W is dispensed with, the.polechanger 7 being connected between the battery 3 and the track. The system may equally well be used without fixed signals.