Patent GB-352601-A (GB)
Title: Improvements in or relating to traffic control signal systems
IPC: G08G1/08
Filed: 1930-05-01
Abstract: 352,601. Road-traffic signals; electromagnetic switches and relays. GILL, H. A., 51, Chancery Lane, London.-(Automatic Signal Corporation ; 205, Church Street, New Haven, U.S.A.) May 1, 1930, No. 13462. [Class 118 (ii).] . The timing system of signals S, Fig. 1, at cross roads is determined automatically by means dependent on the density of traffic along one of the roads, one of two signal time controls A, B being selected by a device C according to the frequency or duration of contacts made by vehicles on a road'ramp V or like means. In one selecting device, Fig. 2, at each passage of a vehicle over the ramp a contact 90 is closed and a condenser 26 receives a charge from a battery 29, either for a predetermined uniform time from a device 30 or for the duration of the contact of the vehicle with the ramp. The condenser is in series with a variable resistance 28, and a gas discharge tube 16 and a relay winding 19 is in shunt with the condenser, the arrangement being such that the condenser will reach the critical voltage of tube 16 after the passage of say, 60 vehicles. A similar circuit comprising battery 3, resistance 2, condenser 1, gas discharge tube 14 and relay winding 6 serves to charge the condenser 1 continuously and so that it reaches the critical voltage of the tube 14 in say one minute. The relays control both condenser circuits and also the circuits of another relay 37 effecting the selection of the signal timers. With the device in the position shown the lights S will be controlled by timer A, and so long as the density of traffic is below 60 vehicles per minute, at each minute the relay 6 will operate to attract the armatures 10, 12 and discharge both condensers and momentarily an armature 8 leaves a contact 9. As, however, contact at 45, 46 is open the relay 37 is unaffected and the signal timer A remains in action. When the traffic exceeds 60 vehicles per minute the relay 19 will operate and close contacts 22 23 and 24, 25 to discharge both condensers, and also close contact 20, 21 to energize relay 37, which now attracts armature 46, to lock the relay, and the armature 41 to change from the timer A to, the timer B. At the same time an armature 40 closes contact 39 to shunt out a part of the resistance 28, whereby the condenser 26 receives a bigger charge by each vehicle, so that the change from timer B back to timer A is not effected until the traffic falls considerably below the 60 cars per minute. In the second selecting system described, the passage of a vehicle closes a contact 117, Fig. 3, and through an electromagnet 141 gives a stepped feed to a ratchet wheel 139 on the shaft of a worm 135 gearing with a wheel 134 carrying a radial contact arm 132, movable over adjustable strips 149, 150, the wheel 134 and strips being mounted on a plate 142 pivoted at 143. The plate is held raised by a spring 145, but is pulled down when a relay 144 is energized, to disengage the wheel 134 from the worm 135 and allow a spiral spring to restore the arm 132 to the zero or starting position against a stop 153. A constant-speed motor 155 drives a rotary contact arm 159, which when it meets a contact 164 closes the circuit of the relay 144. When the arm reaches a second contact 165 current flows to arm 132, and if this arm has not moved off the strip 149 since the preceding zeroizing action, no change of signal timing takes place. If it has reached the other strip 150, a magnet 121 is energized and an arm 122 is rocked to change the timing from system 111 to 112. No change takes place if the arm 132 is between the strips 149, 150, and the distance between them may be adjusted so that the traffic may exceed the critical density by a desired amount before the signal timing is affected. Another magnet 120 for the rocking arm 122 is energized at the reverse change of timing.