Patent GB-830144-A (GB)
Title: Improvements relating to intermittent inductive automatic train control systems
IPC: B61L3/12
Filed: 1956-04-04
Abstract: 830,144. Magnetic amplifiers. WESTINGHOUSE BRAKE & SIGNAL CO. Ltd., KING, K. G., and TUCKER, A. W. March 26, 1957 [April 4, 1956], No. 10293/56. Class 40 (9). [Also in Group XXX] Train-carried apparatus for interaction with successively-traversed track permanent and electromagnets for giving the driver a warning of an approaching distant signal and an indication of the aspect of the signal and, if this latter is at " caution," the electromagnet then being de-energized, also for initiating an automatic application of the brakes unless prevented by the driver's intervention within a predetermined period of time, comprises a transductor TD1, Fig. 5, having an A.C. winding X1 in series with a load R1, a feed-back winding X2 and a control winding X3, a feed-back circuit including the winding X2 energized in accordance with the load current and arranged as by including a saturable magnetic choke L1 having a low impedance at maximum and a high impedance at minimum feed-back current so that when the load is maximum the feed-back maintains it substantially so, but at minimum load, the feedback is insufficient to raise the load substantially above minimum and further including magnetically saturable means such as a transformer T1 comprised in the receiver mounted to be responsive to the fluxes of the track magnets to reduce the feed-back current from its maximum to its minimum to trigger the transductor from the stable condition of maximum output to the other stable condition of minimum output, resetting means for supplying a current pulse to the control winding X3 to restore the feed-back current to maximum output and means for energizing the brake magnet valve BM in accordance with the feed-back current to bring about a brake application when said feedback current falls below a predetermined value as when the signal is at caution and the track electromagnet is de-energized. The resetting means conveniently comprises a coil RS so mounted in the receiver that it passes through the flux of each track magnet, following the saturable transformer T1. The control winding X3 may be incorporated in the feed-back winding. As shown, the feed-back winding X2 is energized by direct current derived from a rectifier M1 energized by the output of the saturable transformer T1 the primary winding of which is coupled across the resistor R1 and a resistor R2 reduces the harmonic currents in the feed-back circuit. The saturable magnetic choke L1 in series with the primary winding of a transformer T2 matching the supply transformer T3 is connected across the resistor R1 and the secondary winding of transformer T2 energizes the primary winding of the saturable transformer T1 with the feed-back current and the brake valve magnet BM is energized with direct current viz. the output from a rectifier M2 contained in the feed-back circuit, which output after amplification in the control winding X2 of a second transductor TD2 is fed to the brake valve magnet BM. To reset the circuit should the train stop with the receiver T1 over the track permanent magnet (otherwise the automatic train control system would have to be switched out), the brake magnet BM is prevented from being de-energized until the receiver T1 has moved away from the track magnet by including in the receiver T1 an auxiliary saturable choke L2 if low impedance (as also are the transductors TD1 and TD2) connected in series with a low voltage supply transformer T8 and a step-up matching transformer T9, the rectified output of which from a rectifier M11, is connected in series with the amplified direct current output of the rectifier M2 from transductor TD2 so as to assist in holding the brake magnet energized. An indicator transductor TD3, Fig. 6, and a bell transductor TD4 control respectively a visual indicator having windings B, Y, and a warning bell BL, the transductors TD3 and TD4 having first control windings X4, X3, respectively energized with direct current in conductors 1T1, 1T2 derived from the feed-back current of transductor TD1, the current through winding X4 having such polarity as to maintain the output of transductor TD3 at a minimum value so that when the feed-back current is reduced to a minimum the output of transductor TD3 is increased to energize the winding B of the indicator as whenever the train passes over the track magnets. The winding B is de-energized by operation of the reset button P by the driver which at the same time energizes winding Y by completing the A.C. input circuit of a rectifier M10, feeding D.C. to winding Y to display a distinctive indication to the driver that the last distant signal passed was at " caution " and this indication will remain until passing over the next permanent magnet causes the energization of winding B. The bell is required to ring only when the apparatus is reset automatically, when the train passes over a permanent magnet and an energized electromagnet in succession on approaching a "clear" signal. The control winding X3 of transductor TD4 is fed in series with a rectifier switch M6 with current derived across a resistor R3 in series with the control winding X4 of the indicator transductor TD3. This latter transductor has a second control winding X3 fed with direct current from a rectifier M9, supplying D.C. energizing current for the bell BL. The A.C. winding X1 of the indicator transductor TD3 is fed in series with rectifiers M4, M5, the former of which energizes the feed-back winding X2 of transductor TD3 opposing the windings X3, X4 and is such as to provide sufficient self-excitation to produce a triggering action. The bell transductor TD4 has a feedback winding X2 fed with D.C. from a rectifier M8, in series with the rectifier M9 in an A.C. supply circuit and the feed-back winding is assisted by the control winding X3. The winding X4 of transductor TD4 is a biasing winding opposing the windings X2, X3. The rectifier switch M6 is rendered conductive across its A.C. terminals when D.C. current is supplied through a high resistance R4 in the forward direction of the rectifier bridge and derived from a transformer T6 and rectified by rectifier M7, the D.C. terminals of which are connected in series with a current limiting resistor R5 and a normally open contact IC across the primary of an impulse transformer T7, the secondary winding of which is connected to the manual reset winding X4 on transductor TD1, Fig. 5. The output from the rectifier M7 also charges a condenser C2. Under normal running conditions, the transductor TD3 is held in the region of its bi-stable condition by the output current of the tripping circuit, Fig. 5, flowing in its control winding X4 and is in the " off " state. The bell transductor TD4 is biased to the " off " state, by the current supplied to its control winding X3. Thus there is only a small residual output current from both transductors. When the train approaches a signal having a " clear " aspect, there is a short interruption of the current supplied to the control winding of transductor TD2 and thus in the control winding X4 of transductor TD3 which triggers to the " on " state and energizes winding B of the indicator. The output from transductor TD3 also charges the capacity C2 and renders rectifier switch M6 conductive across its A.C. terminals by virtue of the current through the resistor R4, to establish a conducting path between the shunt resistor R3 and control winding X3 of the transductor TD4, but since there is substantially no current in winding X4 of transductor TD3 no appreciable voltage is developed across resistor R3 and the bell transductor remains " off." When the current in the tripping circuit is restored, the receiver T1 having passed both track magnets; control winding X3 of transductor TD4 is energized in a direction to switch " on " and the bell is caused to ring. Transductor TD3 is not switched off directly by the restoration of said current but remains " on " until switched "off" after a fraction of a second by current in its control winding X3 from the output of transductor TD4 obtained from rectifier M9. During this delay condenser C2 is charged to its maximum voltage even at the highest train speed. The values of capacity C2 and resistor R4 are chosen to give a long time constant (several seconds) and after transductor TD3 is switched " off " rectifier switch M6 remains conductive so long as the discharge current through resistor R4 is high enough, after which transductor TD4 becomes switched " off " and the bell stops ringing and conditions are fully restored to normal. When the train approaches a signal having a " caution " aspect, as in the " clear " aspect case, initially the current in winding X4 of transductor TD3 is reduced substantially to zero and this transductor is triggered " on," energizing the indicator winding B and rendering rectifier switch M6 conductive. In this case, the track electromagnet is not energized and the current in the winding X4 of transductor TD3 is not restored automatically but by operating the reset push-button P, Fig. 6, to open contact P1 and close contact P2. Energization of the indicator winding Y closes contact IC to discharge capacity C2 through the primary winding of transformer T7 which feeds the impulse through the reset winding X4 of transductor TD1 to render this latter conductive and the apparatus is restored to normal, with the exception of the indicator which continues to indicate that the last signal passed displayed a " caution " aspect until indicator winding B is again energized on passing over the next permanent magnet. At this time the indicator contact IC is closed and prevents the energization of rectifier switch M6 by providing a discharge path for capacity C2 of lower impedance so that the transductor TD4 is not rendered conductive and the bell does not ring. As an alternative to the capacity C2 with a long time constant there may be used a transduc