Patent GB-517737-A (GB)
Title: An improved automatic control for vehicle lights
IPC: B60Q1/14
Filed: 1938-07-30
Abstract: 517,737. Photo-electric control of lighting systems; mercury switches ; actuation of switches. BAKER, W. M. July 30, 1938, No. 22756. [Class 40 (iii)] [Also in Groups XXXV and XXXVII] In a vehicle lighting system provided with a light sensitive device operated automatically to control a switch in a lamp circuit according to the ambient illumination, a member or device which has a specific setting on the vehicle when the vehicle is left unattended is combined with a master switch which normally maintains the automatic control ineffective and which is operated by the adjustment of the said member or device to its specific setting to render the lamp circuit completely under control of the automatically controlled switch. As shown in Fig. 1, the system comprises in the usual way an ignition control switch 13 which in the " ON " position connects the ignition leads 16 to a battery 10, a generator 18 with an electro-magnetic switch 19, 20 for automatically charging the battery, an indicator lamp 21 to indicate whether or not the battery is being operated, and a lamp controlling switch 22 for connecting up the side and tail lights 25, 26 alone or these lights and the headlights 27. In addition, the system now comprises an extra position for the ignition switch marked " PARK " where a contact 28 is connected to a switch 29 controlled by a light sensitive apparatus 30. When the car is parked, the switch 13 is turned to " PARK " position instead of " OFF position. Then, when ambient light fails, the switch 29 closes and the side and tail lights are automatically turned on. To inform the driver that he has correctly set the switch 13 to "PARK position, an indicator lamp 32 is provided in series with a contact 31, which is closed when switch 13 is in the " PARK " position, and also with a switch 33, which is closed when the door of the car is opened thereby giving a temporary signal and avoiding waste of current when the door is closed. If the indicator lamp 32 is a weak one, the door controlled switch 33 may be omitted. The member 13 instead of being an ignition switch member may be controlled by a hand-brake. The light sensitive device may be placed in a sheltered position, for example, in a recess in the dash-board or within a hood and may be provided with a light-filter or a neutral tinted screen or an opaque screen having a selected size of aperture in it. The light sensitive device may be a photoelectric cell or a selenium cell, but preferably is an electrolytic cell, Fig. 2, comprising a chamber 34 containing electrodes 35, 36 immersed in a solution of hydrochloric acid or an acidulated solution of an alkaline or alkaline earth salt. A wall of the chamber 34 is a flexible diaphragm transmitting pressure to mercury in U-tubes 39, 40. When the chamber 34 is exposed to light, the hydrogen and chlorine generated by the electrodes 35, 36 recombine and no pressure develops in the chamber. This is the condition shown in Fig. 2, in which the electrodes 35, 36 are connected to a battery 46 through a low resistance 48. When the ambient light fails, the hydrogen and chlorine do not recombine and pressure develops in the chamber 34. Mercury in the U-tube 39 rises and makes contact with a terminal 41 thereby closing circuit of lamp 43 if a switch 45 is closed, the switch 45 corresponding to switch 13, 28 of Fig. 1. The mercury in the other U-tube 40 also rises and breaks the connection between terminals 49, 50 thereby throwing a high resistance 47 in the circuit of the electrode 35, 36 to prevent development of excessive pressure in the chamber 34.