There are many switches used to control electrical equipment in automobiles, including mechanical switches and electromagnetic switches.
There are two kinds of mechanical switches, hand-operated and foot-operated, which are installed in different positions of the cab according to their use.
1. power master switch
In order to prevent the battery from leaking through the external circuit when the car is stopped, the main switch of the power supply is installed on some trucks, which is seldom used in modern cars.
The main switch of power supply has two types: switch type and electromagnetic type. The former depends on manually switching on or off the negative poles of the power supply circuit (e.g. Dongfeng series cars), while the latter depends on the magnetic field attraction of electricity.
TKL-20 power supply main switch (also known as battery relay) is an electromagnetic switch. Its structure is shown in the figure.
2. ignition switch
Ignition switch, also known as ignition lock or door lock, is mainly used to control ignition circuit. In addition, it also controls generator magnetic field circuit, instrument circuit, starting relay circuit and some auxiliary electrical appliances.
Generally, the steering wheel can be automatically locked when pulled out. The commonly used ignition switch has three and four gears.
Three-gear ignition switch has 0, I, II (or LOCK, ON, START) gear. The key can be inserted or pulled out freely in "0" gear. Rotate clockwise from 40 degrees to I gear. Continue to rotate 40 degrees to I gear. When the external force is eliminated, the key can be automatically reset to I gear. Fig. 6-47 shows the working principle of Jetta ignition switch.
Four-gear ignition switch is widely used in modern automobiles. It has 0, I, II, II I (or LOCK, ACC, ON, START) gears. On the basis of three gears, an AC electrical accessory component working gear is added, while the others remain unchanged. Fig. 6-48 shows the working principle of Fukang four-gear ignition switch.
3. lighting switch
The illumination switch is installed on the instrument panel to control the headlamp, fog lamp, small lamp and back lamp, emergency alarm lamp switch, etc. As shown in Figure 6-49, the push-pull lighting switch is commonly used. It has five connecting posts and is equipped with bimetallic circuit breaker.
4. variable light switch
There are two kinds of headlamp light-changing switches, mechanical and photoelectric, which are widely used.
The mechanical dimmer switch is installed beside the clutch pedal and operated by the driver's left foot to change the far and near light of the headlamp, as shown in the figure.
The photoelectric headlamp dimmer switch is used to automatically change the far light of the headlamp into the near light when the vehicle meets the vehicle. After the vehicle passes by, it can automatically change the headlamp from the near light to the far light without manual control.
The photoelectric headlamp light-changing switch is mainly composed of a photosensitive element (CDS) and a small relay, as shown in the figure.
5. Brake light switch
Hydraulic and pneumatic brake light switches are used in modern automobiles.