Patent GB-558142-A (GB)
Title: Improvements in electric signalling plants for vehicle traffic
IPC: B61L1/12
Filed: 1941-12-11
Abstract: 558,142. Vehicle traffic signalling system. SOC. SUISSE D'ELECTRICITE ET DE TRACTION. Dec. 11, 1941, No. 15983. Convention date, Dec. 11, 1940. [Class 105] [Also in Groups XXXVI and XXXVIII] In a signalling system, described as applied to trolley-bus traffic, for indicating at a stopping place the distance of (or, assuming a mean working speed, the time before the arrival of) the next vehicle to arrive, alternating signal current is supplied from a source 1a, Fig. 1, to the power lines 1 at the end of a section towards which the vehicles are moving, and each vehicle carries a device 1c for shortcircuiting the lines. If a constant signal current tension U is applied across the lines at 1a, the tension decreases lineally along the lines, as shown by line a, to zero at the position short-circuited by the vehicle. At an intermediate stopping place S at a fixed distance D from the signal current source Us gives the tension between the lines with a vehicle at distance X. Similarly Us1 gives the tension for a vehicle at a greater distance. The tension as measured at a stopping place thus decreases as the nearest short-circuiting vehicle approaches and the invention uses a voltmeter, suitably graduated in time or distance and arranged to indicate the minimum tension due to short-circuiting by the nearest vehicle, as an indicator at the stopping place. The Specification describes a layout in which several routes have a section of line with stopping-places in common. In this case different signal frequencies are allotted to the various routes and each stopping place has separate indicators for the different routes each responding only to the appropriate frequency. Fig. 3 shows the signal-current supply arrangement comprising an alternator 4 driven by motor 3 which also controls a switch 10. A regulator 5 keeps the supply tension constant. Filters 2, 7, 8, 9 pass or stop predetermined frequencies, and impedance 12 limits the signal current as a vehicle approaches the feeder. Fig. 4 shows the vehiclecarried short-circuiting device comprising contact 6 opened and closed at pre-determined intervals by a cam driven through reducing gear 13 from motor 32, the short-circuit including filters 14, 15. Fig. 5 shows a stopping- place indicator comprising a voltmeter 17 the pointer 17a of which carries a pawl co-operating with a normally locked ratchet-wheel 21 limiting the pointer to "down-scale" movement so that only the lowest tension appropriate to the nearest vehicle is registered. When the voltage drops to zero on arrival of the vehicle contacts 17b are closed to energize relay 21a and release wheel 21 so that the pointer is free to move up scale to register tension appropriate to the next following vehicle. The pointer also carries a pawl 22 co-operating with a normally free ratchet wheel which becomes locked on energizing a no-voltage relay 22a, the arrangement preventing pointer 17a from moving to zero under no-voltage conditions produced by a vehicle which has passed the stopping-place. The voltmeter circuit includes filters 18, 19 and rectifier 20. A modified system is described in which the signal-current is supplied to line intermittingly and the vehicles carry time-lag relays which break the short-circuit when energized by signal current, so that the current is transmitted to following vehicles in succession.