Patent GB-1334399-A (GB)
Title: Vehicle lighting systems
IPC: B60Q1/14
Filed: 1971-04-22
Abstract: 1334399 Transistor switching Circuits SOC ANON POUR L'EQUIPEMENT ELECTRIQUE DES VEHICULES SEV MARCHAL 22 April 1971 [22 April 5 April 1971] 10893/71 Heading H3T [Also in Divisions G1 and F4] A vehicle lighting system comprises main beam headlights 21, dipped beam headlights 20, a photosensitive receiver 105 and control circuitry responsive to the receiver for changing over to dipped beam illumination when the signal from the receiver exceeds a predetermined dazzle threshold or to an attenuated main beam illumination when the signal exceeds an intermediate threshold and for changing back to full main beam illumination when the signal drops below a predetermined darkness threshold. The receiver 105, which comprises a gallium arsenide photocell, detects the lights of an oncomingvehicle and provides an output signal which is amplified by a D.C. amplifier including transistors 108, 112. Zener diodes 122, 123 and 124 establish the darkness, intermediate and dazzle thresholds respectively. If the signal at the output 121 of the amplifier is lower than the darkness threshold, the diode 122 and a transistor 125 are non- conductive so that a transistor 127 conducts. Current therefore flows from the positive supply line 106, through a coil 129 of a relay 130, the transistor 127 and a diode 128 to the negative supply line 107. Contacts 167, 168 are closed to illuminate the main beam headlights 21. If the signal at the output 121 exceeds the darkness threshold the transistor 125 is conductive and the transistor 127 is non-conductive so that a capacitor 131 is charged. A thyristor 134 is switched on and turns on a transistor 160 which enables illumination of the headlights 21 but but with a slight reduction in intensity. As the approaching vehicle gets nearer the signal at the output 121 exceeds the intermediate threshold so that a transistor 135 becomes conductive and a transistor 137 becomes non-conductive. A capacitor 146 is therefore charged via a resistor 138 and a thyristor 153 is switched on to charge a capacitor 163a and extinguish the thyristor 134. A resistor 157 has a value such that the transistor 160 allows a reduced illumination of the headlights 21. Assuming that the oncoming vehicle is also equipped with a similar system, the reduction in intensity of its main headlights causes the Zener diode 123 to become non- conductive. However, as the vehicles get closer, the diode 123 again becomes conductive and causes a thyristor 154 to be switched on, the resistor 158 having a value such that the current though the transistor 160 is again reduced. A further reduction in the intensity of the main headlights occurs when the last thyristor 155 is switched on by the approaching vehicle. When the dazzle threshold is exceeded, the diode 124 conducts to cause a transistor 140 to conduct and contacts of a relay 145 are changed over to switch on the dipped beam headlights 20. When the vehicles pass, the system enables energization of the coil 129 so that the main beam headlights are again illuminated. Reference has been directed by the Comptroller to Specification 1,048,946.