The lighting control of modern automobile headlights includes relay control and electronic control.
Relay-controlled headlamp system is composed of light switch, dimmer switch and headlamp in combination switch, and there are two control types: unloading control and protection control.
Unload the relay element used to control the headlamp. When the light switch is turned on, the relay coil is energized with a small current, thereby reducing the opening load of the light switch and protecting the light switch. The coil is energized to attract the normally open contact of the relay and turn on the headlight power supply.
Some light and medium trucks such as EQ 1092, CA 1092, Yuejin and Toyota all adopt this type of control mode, and their circuit schematic diagrams are slightly different. The former connects the light switch in series between the power supply and the relay, and the relay controls the dimmer switch. In the latter, a relay is connected in series between the power supply and the light switch, and the relay coil circuit is connected with the light switch, and then the relay controls the power supply of the headlight, and the dimming switch controls the dimming of the headlight.
Double relay unloading control headlight circuit is used in many imported models. In this control mode, the battery is used to directly supply power to the headlamp, and the light switch is connected in series between the power supply and the combination relay. Relay 1 is responsible for turning on the headlight high beam and relay 2 is responsible for turning on the headlight low beam.
The protective control headlamp also has a relay, but when the power supply circuit, fuse, small lamp or main headlamp works normally, the protective relay does not work. When the power supply circuit is short-circuited, the fuse is blown, and the power supply of the small lamp or the main headlight is short-circuited, the relay starts to work and automatically turns on the high beam of the auxiliary headlight or the headlight to ensure driving safety.
The single relay protection control headlamp circuit, in which the light switch is connected in series between the power supply and the dimmer switch, is still aimed at protecting the switch so as to reduce the disconnection load of the light switch. The auxiliary headlamp is only controlled by the light switch in normal operation, and controlled by the relay in abnormal conditions.
Fig. 5 is a circuit for protecting and controlling a headlamp of a double relay type, in which a combined relay is connected in series between a power supply and a dimmer switch. When the headlamp works normally, the turn-on of the relay II coil circuit is controlled by the light switch. When the power supply is short-circuited and the fuse is blown, the relay I will automatically turn on the headlight high beam circuit to ensure driving safety.
The electric control headlight system has the functions of automatic dimming when passing, automatic dimming when natural light intensity and automatic delay when the headlight is turned off, so as to automatically control the light intensity, high beam and low beam of the headlight. In order to realize the above functions, the electronically controlled headlamp system is equipped with an automatic dimmer for passing the headlamp, an automatic attenuator for the natural light intensity headlamp, an automatic delay device for turning off the headlamp and other components.
The automatic dimmer for passing headlights, which is widely used in modern cars, is an electronic control device that automatically changes the high beam of headlights into the low beam and then changes the low beam back to the high beam when driving at night. There are three kinds of automatic dimmers for passing headlights, which use photoresistors, photodiodes and phototransistors as photosensitive elements. Photosensitive elements are electronic elements that generate photocurrent when the resistance decreases or diodes and triodes are turned on under the action of illumination.
There is an automatic headlamp dimming circuit with photodiode as photosensitive element, which is installed in Cadillac and other cars of American General Motors Company, but still retains the dimming control of pedal mechanism. The distance between the high beam and the low beam is about 150 ~ 200 m when the car meets at night. After the car meets, the high beam will automatically recover without the driver repeatedly stepping on the dimmer switch. The system has stable and reliable performance, small volume and high sensitivity. The automatic dimming circuit has two independent control devices, manual and automatic.
From: China Power Grid/Technical Library/Automobile Headlamp Electronic Control System.