Patent GB-385302-A (GB)
Title: Improvements in electric signalling systems for controlling road traffic
IPC: G08G1/085
Filed: 1931-06-16
Abstract: 385,302. Road-traffic control signals. SIEMENS & GENERAL ELECTRIC RAILWAY SIGNAL CO., Ltd. and STARR, T. R., Caxton House. Westminster. June 16, 1931, No. 17514. [Class 118.(ii).] The signals, red, red and yellow, green, yellow for one road and the corresponding signals for the other road of an intersection are given by the sequential operation of four short-circuiting switches. These switches 1 . . 4, Fig. 1, are connected in series.; the (E-W) red, 5, and (N-S) red signal, 6, are paralleled across switches 1, 2 and 3, 4 respectively ; the (N-S) green, 8, is across switch 1, the (E-W) green, 9, is across switch 3, and the yellow signals 7 are connected across 2, 4. These switches are operated in turn, one being opened as the previously opened one is closed, at successive steps of a cam shaft 12, Fig. 2, which carries a contact 19 connecting with fixed contacts 15 . . 18 in the open positions of switches 1 .. 4 respectively, and is rotated by the energization of stepping coils 14. The control unit comprises an impulser 33, Fig. 2, adapted to step a ratio controller 25 which in turn controls a contactor 10, and may operate as a " master " or " slave " controller. In the former case the impulser which is described in Specification 361,891, [Group XXXVII], is connected across the mains, D.C. or A.C. by means of switch 20 and pulses by self-interruption at contacts 37, 42 under the time control of a dashpot 41. The pulsing frequency may be varied by rotating a knob 45 a cam 44 secured thereto altering the position of arm 43, and a pulsating supply for operating " slave " controllers may be obtained by interrupting a D.C. supply at contacts operated by the armature 35 the arm 32 of which steps the ratchet wheel 31 of the ratio controller 25. When operating as a " slave " controller, a switch 46 is opened and the impulser pulses in step with the pulsating supply connected' across terminals 47 and negative. Ratio controller. The ratchet wheel 31 is secured to a hollow shaft 63, Fig. 8, which carries a fixedly mounted snail cam 29 and a similar cam 30 rotatable thereon but held in position by means of balls 68 engaging recesses in cam 30 and in a member 67 secured to shaft 63, a spring 69 forcing the cam into engagement with the balls. The angle of lead of cam 29 may be' varied by manually displacing cam 30 against spring 69 and rotating it so that different recesses therein engage the balls 68. Pivoted at 73 to the frame 66 are rocking members 70, 72, spring biased so that rollers 74 thereon bear against cams 29, 30 respectively. Member 70 is U-shaped and on its arms carries insulated contacts 21, 22 respectively ; member 72 carries a spring arm 71, a contact 27 thereon normally engaging contact 22. Stepping of shaft 63 rocks members 70, 72 in turn, contact 27 rocking to contact 21 and then back again to 22, the time of contact of 27 and 21 being proportional to the angular displacement of cams 29, 30. A further two-way switch 23, 24, 26 similar to 21, 22, 27 is mounted on rocking members 75, 76 operated similarly by cams 29, 30. These rocking members are however pivoted at 77 to an arm 78 secured to a shaft 65 which is rotatable by means of a knob 67, a pointer fixed thereto indicating on a suitably calibrated dial the relative angular positions of the two two-way switches. Contactor. The shaft 12, Fig: 3, carries cams 11, 54 for operating switches 1 .. 4 to contact member 19 (four contacts) with 15 .. 18 respectively, and an eight-toothed ratchet 52 adapted to be stepped at each energization of the coils 14, Fig. 2. A reversed ratchet with a suitable stop pawl prevents overdriving. Operation. From Fig. 2 it is seen that one cycle of signal operations corresponds to. one revolution of the ratio controller; the angular displacement between cams 29, 30 gives the proportional time of the yellow signal and the angular displacement between the two two-way switches gives the relative times of,the red and green signals. Manual operation. Contact 48, Fig. 2, is moved to bridge contacts 49 and a pushbutton is connected across contacts 50, each operation of the pushbutton stepping the contactor 10 to effect a signal change. Modifications. Contacts 21, 23, Fig. 10, are connected to 15, 17 through contacts 82 operated by armature 35, Fig. 2, and arranged to be open when contact 26 or 27 engages 23 or 21 respectively so that operation of the yellow signal is delayed until contacts 82 close. A manually-operated short-circuiting switch 83 is provided. An emergency switch may be provided for illuminating all the red signals and disconnecting all others, a number of such switches for a number of controllers being remotely controlled together by means of relays. A pedestrian pushbutton may be provided, operation thereof causing the impulser, normally at rest, to complete a cycle of signal operations, the signals normally showing green to traffic and red to pedestrians. Alternatively, this pushbutton may be operated by the vehicles. 'The pulsating supply to " slave " controllers may operate through relays.