Patent GB-409877-A (GB)
Title: Improvements in and relating to road traffic control systems
IPC: G08G1/085
Filed: 1933-03-16
Abstract: 409,877. Road signals for controlling traffic. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London, and CANSDALE, J. H., 40, Murray Road, Rugby. March 16, 1933, No. 7990. [Class 118 (ii).] The traffic signals at a road intersection are controlled by two electromagnetic contactors, energized cyclically under the control of an adjustable cam, driven by an electric motor, to give the various circuit combinations by opencircuiting those lamps which are not required. Provision is made for varying the time of a signal cycle, the relative times of the signals of a cycle, and also for manual operation. For automatic working the two-way switches 6, 7 are thrown to the down position and switch 16 remains in the upper position shown. The motor 1 is energized over contact 5 and drives the cam 2 continuously to operate rollers 2a, 2b which lift contacts 3, 4 to close the circuits of windings A1, B1 of contactors A, B respectively. In the position of cam 2 shown, A1 and B1 are de-energized and right-of-way is with the main street, the main street green lamps GM being lit over the circuit L1, 18, 8, 14, 10 to L2 and the cross street red lamp RC over the circuit L1, 18, 8, 14 to L2. Where cam 2 closes contact 3 to energize coil A the main road green lamp GM is extinguished and over contact 9 of contactor A both amber lamps AM, AC are lit. These conditions remain until the contact 4 is closed by cam 2, when, both contactors being energized, the main street red and the cross street green lamps, RM, GC are lit over contacts 8, 13, 17, and 8, 13, 12, respectively. When contact 3 is released by cam 2, the cross street green lamp is extinguished and both amber lamps lit over contacts 8, 13, 11, and when contact 4 is also released, right-of-way is given to the main street thus completing a signal cycle. The relative right-of-way times for the main and cross streets are determined by the angles subtended by the lower and higher portions of cam 2, while the time of the warning signal depends on the angular distance between the rollers 2a, 2b. To vary the relative times of the green signals, the cam 2, Fig. 2, comprises two sectors 24, 25 (Fig. 2). Sector 24 is rigid with the motor driven shaft 39 but sector 25 is freely mounted, and adapted to be fixed in various angular positions relative to sector 24 by a pin 50 projecting from the latter adapted to engage any one of a series of holes in sector 25 marked with the corresponding percentage ratio of the unraised to the raised portion of the cam, and by a thumbnut 40. The contacts 3, 4, Fig. 1, comprise fixed springs 90 and springs 28, resiliently mounted on moulded arms 60 pivoted at 26, 27, and carrying roller arms 70. The arms 60 normally abut against stops 31, and the angular distance between the rollers 8 may be varied to alter the time of the amber signal by sliding the arms 70 longitudinally with respect to arms 60 to which they are fixed by thumb screws 29. The time of a complete signal cycle may be varied by altering the motor speed or the gear ratio between the motor and shaft 30. For manual control, switch 6, Fig. 1, is thrown to the up position and coils A1, B1 energized to effect the signal changes as before, through a hand operated four-way switch 22. The amber lights may be left illuminated by moving switches 6, 7 to the up position and switch 16 to the down position, the circuit for the lamps being L1, 18, 20, 21, 11 AC and AM in parallel to L2. Reference has been directed by the Comptroller to Specification 379,326.