Patent GB-636882-A (GB)
Title: Improvements in or relating to railway signalling systems
IPC: B61L3/18
Filed: 1946-08-26
Abstract: 636,882. Railway signalling systems. SOC. AUXILIARE d'ETUDES ELECTRO-TECHNIQUES. Aug. 26, 1946, No. 25504. Convention date, July 5, 1945. [Class 105] In a railway signalling system in which a generator (constant-frequency alternator) on the locomotive, giving a voltage proportional to its speed, feeds a line wire arranged in section lengths corresponding to the track-circuit sections but adapted to be connected up, by a relay device at the entrance to each section, to an over-all length dependent on the voltage, the system is so arranged that the track relay of an ahead occupied section causes the linewire circuit, which hitherto was earthed to the rails at the entrance end of the occupied section, to be equivalently extended by means of a transformer coupling up to the rearmost axle of the occupied section. Fig. 1 shows the arrangement at a track section and Fig. 2 the locomotive apparatus. A tachometric generator 50 on the locomotive applies a current to the line wire 5 of its section at a voltage dependant on the speed and this current so long as it exceeds a certain value causes at successive track sections a relay 6 to be energized to connect up the line wires 5 of successive sections until such an overall length is reached that the line impedance reduces the current below the value necessary to cause operation of the next relay 6. The relay 6 is picked up by the line wire current passing over a back contact 38 of this relay 6 to the primary winding of a transformer 9 the secondary of which energizes over front contacts 17 of the track relay 25 a winding 15 of a device A which thereupon closes its front contact 30 whereby the track-circuit source 46 energizes over a front contact 27 of the track relay a holding winding 36 for the device A, and also energizes the winding of the relay 6 which thereupon moves its contact 38 to its front points thereby linking up the section line wire 5 to the line wire 51 of the next section. Similar actions occur at successive track sections until such an overall length is reached that the line-wire current is below the value necessary to cause operation of the winding 15 of the next device A. At an occupied section however the track relay 25 is de-energized and its open front contact 27 prevents the holding winding 36 of the device A and the relay 6 being energized ; thus the line-wire 5 is connected by back contact 38 of relay 6 and primary of transformer 9 to the track rail 1 of the occupied section. The secondary of the transformer feeds a circuit comprising wire 12, rejector 13 (for track-circuit frequency), windings 15, 20 of device A, wire 21, back contact 22 of track relay 25, wire 23, rail 21, axle B, rail 1 and wire 24 ; thus the line-wire circuit is extended (through the transformer coupling) by an amount equivalent to the length of rail in the occupied section up to the rear axle of the ahead vehicle. The locomotive apparatus comprises a wattmeter type relay in the circuit to the line-wire, and inductor coils 67, 76 arranged over the rails one of which coils 67 normally is energized by the track-circuit current in the rails to energize a relay 70 through an amplifier 69 tuned to the frequency of the track-circuit current. The other coil 76 is normally inactive but receives current from the locomotive generator on entry into an occupied section thereby setting up current of line-wire-current frequency in the rails to actuate the first coil 67 which through an amplifier 80 tuned to the frequency of the line-wire current energizes a transformer 81 feeding a second set of current coils 84, 85 in the wattmeter relay. On entry into an occupied section the coil 67 no longer receives energy from track-circuit current in the rails since this is absent so that the relay 70 becomes deenergized so removing generator current from the circuit comprising the line-wire and return rail by reason of its open front contact 63 while at its back contact 72 the locomotive generator is applied to the coil 76 to induce current in the rail circuit provided by the rails, the rear axle of the ahead train already in the section, and the front axle of the entering train. The wattmeter relay controls circuits to cab signals showing " clear " and " danger " (" proceed at sight "). The generator circuit and the circuits of the coils above the rails include relays front contacts of which are included in the circuits to the cab signals thereby to give warning of any failure by the disappearance of all signals (" clear or " danger ").