Patent GB-468158-A (GB)
Title: Improvements in track-actuated train control signal systems
IPC: B61L3/12
Filed: 1936-08-08
Abstract: 468,158. Train-control and cab-signalling systems. GENERAL RAILWAY SIGNAL CO. Aug. 8, 1936, No. 21888. Convention date, March 23. [Class 105] A train-control or cab-signalling system with inductor circuits at locations along the track is such that with the track inductor in one condition a normally energized relay means on the train is de-energized to give a restrictive signal while with' the inductor in another condition a normally de-energized electro-responsive means on the train is energized to give a clear signal, but without deenergization of the said relay means, by energy derived from the traincarried source through a reflection from the track inductor. The apparatus is protected against stray magnetic fields giving a false clear signal. The train and track apparatus each comprise two longitudinal cores and a transverse core, the two series windings of the latter core being wound so that a flux through the full length, such as a stray flux, creates opposing E.M.F.'s. The two windings A1, A2 of each longitudinal core A on the train are included in a resonant circuit fed by a turbogenerator TG and a rectifier 10 is tapped across an impedance 9 to energize a two-coil relay RA having its armature pivoted at the centre of mass and having the two coils offset to act oppositely on the two ends of the armature to give additive torques. If the windings TA1, TA2 of the co-operating track longitudinal core TA are open-circuited or in circuit with a suitably chosen condenser 21, the effect will be to detune and reduce the current in the train circuit so that the relay RA will drop. The relays RA, RB are such that they remain dropped until a current above normal is applied. Caution or danger signals are given according as only one or both relays RA, RB are dropped. If a clear signal is to be given the windings of the two longitudinal track cores are connected in series with an additional condenser 26 and a transformer 25, the step-down secondary of which feeds a full-wave rectifier 24 energizing the windings TC1, TC2 of the transverse track core TC. The two fluxes are in opposite directions and therefore give additive voltages in the oppositely wound windings C1, C2 of the locomotive transverse core C. The effect is to give an alternating current of double frequency in the corresponding windings C1, C2 of the transverse core C on the train and such current by means of a tuned transformer 19 ignites a gaseous conduction device VT which thereafter energizes a " clear " signal G until a key K is depressed to open that circuit. The presence of the additional condenser 26 in the circuit of the track inductors prevents the current in the train circuits from being reduced sufficiently to drop the relays RA, RB. The different connections for the track inductor windings are effected by the switch arm 27. For a caution signal the switch arm 27 joins the wire 42 and thus the coils TB1, TB2 are shortcircuited and so do not cause the relay RB to drop, but the coils TA1, TA2 are now connected only with the condenser 21 and so cause the train relay RA to drop. Fig. 6 shows arrangements whereby the clear signal is extinguished after an interval, the driver can cancel a caution braking by an acknowledging key AS, or can re-set the apparatus after a stop braking has brought the train to a standstill to permit access to a reset key RS. At a caution signal the track core TA causes the train relay RA or RB to drop according as the vehicle head is facing one way or the other. In either case the caution-braking valve 50 has its magnet CV de-energized to give such braking and also to sound a whistle 51. The de-energization is effected by the opening of contacts 64, 68 of repeater relays RAP, RBP for the relays RA, RB. Operation of the acknowledging key AS closes contacts 81, 82 to pick up the relays RA, RB by cutting out the resistances 11, 15 in the circuits of such relays. At a danger signal the windings of both the longitudinal track cores are in circuit only with their condensers 21 so that both of the train relays RA, RB are dropped and therefore the two feed lines to the stick '' stop " relay SR are opened at contacts 71, 72. The dropping of contact 78 of relay SR de-energizes the magnet SV for the emergency-braking valve 55. For resetting, the keys AS, RS must both be operated as the contacts 71, 72 must be closed before the reset key RS can be effective. The automatic cancellation of a clear signal is normally effected by a dashpot retarded contact arm 86 which is opened by a spring 88 under pressure applied by a solenoid 85. A caution or stop signal cancels the clear signal at once by the opening of a contact 91 or 92 of the relays RAP, RBP. The receiver cores have sufficient height clearance normally to be unaffected by stray iron, i.e. any iron on the track not forming part of the track inductor devices, but if necessary, copper shields can be provided for such stray iron. The track inductor 'casings have ramped ends to deflect any dragging equipment and may have wear inserts for engagement by the collector shoes of electric trains. The transverse core on the locomotive is shaped to avoid any water troughs. A false clear signal will not be given by stray field flux since such flux passes through the full length of the transverse core C and induces opposing voltages in the coils C1, C2. The use of double frequency current to give the clear signal prevents a false clear signal being given by any leakage flux from the longitudinal cores A, B passing into the transverse core C.