Patent GB-190607831-A (GB)
Title: Improvements in and relating to Signalling Systems for Railways and the like.
Filed: 1906-03-31
Granted: 1907-03-28
Abstract: 7831. British Thomson-Houston Co., [General Electric Co.]. March 31. Automatic systems; electric railways and tramways, signalling on; semaphore signals; locking signals.-Semaphore signals used on electric railways and tramways in an automatic system are operated by current taken from the power circuit and locked by current from the signalling-circuit, which differs in character from the power circuit. An operating-mechanism for a three-position signal and a locking-magnet are shown in Figs. 1 and 3. The signal-rod A is drawn upwards by two magnets B, C, and carries a switch which closes various circuits to operating and locking magnets in its three positions. The magnet B moves the rod to set the arm at 'caution' from 'danger ' by means of the pivoted lever b and a pin-and-slot connexion to the sleeve a, which is loose on the rod A and engages the shoulder a<1> thereon. This movement lifts the lever c to bring the armature of the magnet C into an effective position for operation by that magnet to set the signal from 'caution' to 'clear.' Two separate dash-pots are used, one in connexion with each pivoted lever b, c, that for the latter D<2> only acting as a brake when the magnet C is energized ; a port is provided in the side so that air freely escapes during the first part of the stroke. This arrangement gives a brake action more accurately in proportion to the pull of the solenoid than would be given by one dash-pot only. The signalrod A is locked in its two upper positions by the latch e' entering notches in the rod. The latch is moved forward by the toggle-levers e<1> when the armature e is attracted by the magnet E which is energized by the alternating signalling current. In order to avoid chattering due to alternations of magnetic flux, the poles of this magnet are provided on the face with short-circuited conductors e<3> which produce a secondary flux displaced in phase from the primary one which serves to maintain the armature without chattering, and enables a reduced current to hold the armature. The invention is not limited to the system shown in Fig. 2, in which the signal-rods are shown as being moved downwards to put the signal to 'safety.' The track is divided into insulated sections R', R<2>, R<3>, and adjacent ends of sections are bonded in the known manner through transformer windings T<1>, t<1> &c., which serve as returns for the direct power current and one of which T' impresses an electromotive force between the rails and the other t<1> acts as primary of a transformer having a relay coil in series with the secondary. The relays r<1>, r<2>, r<3> are of the two-phase motor type, one coil being energized from the fine-wires L. The power current is derived from the main R. A train on the section R<3> de-energizes the coil t<3> and the relay r<3> drops its armature, breaking the operating and locking circuits and allowing the signal to go to danger. The train having cleared the section R<2>, the -relay r<2> draws its armature, and the operating circuit from the main R to the switch F<2>, operating-magnet B', and the rails causes the arm S<2> to go to 'caution,' and the switch F<2> is moved to the position shown and opens the circuit to magnet B' and closes that of the locking-magnet E<2>. When the train clears the section R<2>, the relay o' is energized by the contact-arm of the relay r<2>, closing its circuit from lower line L, coil o', arm of relay r<2>, and the upper line L, and the relay o<1> therefore draws its armatures, breaks the lock-magnet circuit, and .closes that to the coil C<1>, which sets the signal S' clear and causes the switch F' to complete the locking-circuit and open the operating-circuit.