I. Composition of Automotive Circuits
The basic circuit in automobiles is composed of power supply, insurance, switch, electrical appliances and wires. Use wires to connect them together to form a complete circuit. When the switch is closed, the circuit is connected, and the current passes through the electrical appliance. The electrical appliance starts to work, as shown in Figure 1-1-1.
Every circuit in a car evolves from this basic circuit. It's just that multiple circuits are connected in parallel or in series, which makes the circuit look more complicated. As long as the current is always flowing from the positive to the negative of the battery or power supply, the circuit diagram can be read clearly.
1. power supply
The automobile uses double power supply of storage battery and generator. When the engine stops, the automotive appliances are powered by batteries. After the engine starts, the generator charges the batteries (if necessary) and supplies power to the whole automotive appliances.
2. insurance
The function of the safety device is to protect the circuit. When the current in the circuit exceeds the prescribed current, cut off the circuit to prevent burning out the circuit connecting wire and electrical equipment. The safety devices in automobiles include fuses, circuit breakers and fusible wires.
3. switch
Manual and electronic switches for controlling electrical equipment. The manual switch is operated directly by the occupant, and the electronic switch is automatically controlled according to the need.
4. electrical appliances
That is, electrical equipment. Including light bulbs, all kinds of motors (such as electric seats, electric windows, skylights, etc.), meters, sensors, actuators, audio and other automotive electrical equipment.
5. conductor
The wire connects the above mentioned power supply, insurance, switch and electrical equipment together to form a closed circuit. The diameter and color of automobile conductors vary according to the system of electrical equipment.
II. Basic Characteristics of Automotive Circuits
The basic characteristics of automobile circuit are summarized as follows:
Low Voltage (12V or 24V) of Battery and Generator Dual Power Supply; Single Wire Parallel Connection of Full Vehicle Circuit; Battery Negative Body Riding Iron; Fuse Protection Circuit; Relay Protection Switch; Central Distribution Panel Unified Control Circuit Connection.
1. Low Voltage (12V or 24V) DC Power Supply for Batteries and Generators
Battery is an auxiliary power supply. When the engine is not started, it supplies power to part of the electrical equipment. Generator is the main power supply. When the engine starts, the generator supplies power to the whole vehicle electrical equipment, and charges the battery at the same time.
2. Single-wire Parallel Connection of Full Vehicle Circuit
The single-wire system refers to the use of a single conductor to connect the power supply to the electrical equipment, and the body frame as the negative pole of the battery. Single-wire system saves wires and clear connections, and is convenient for installation and maintenance. Therefore, single-wire system is adopted in modern automobiles. The power supply on the car and all electrical equipment are connected in parallel.
3. Battery Negative Placement
When using single-wire system, one of the electrodes of the battery needs to be connected to the frame or body, commonly known as "iron-lapping".
4. Fuse protection circuit, relay protection switch
In order to prevent the wiring harness from burning out due to short circuit and direct tapping, protective devices such as fuses and fusible wires are usually installed in the circuit.
Some switches often have large currents passing through, such as ignition switches. Generally, relays are installed in the circuits passing through with large current. The characteristics of small current of relays are used to control large current to protect switches, so as to avoid the damage of switches caused by large current flowing through the switches.
5. Unified Control Circuit Connection of Central Distribution Panel
In Volkswagen, the unified control circuit of distribution panel is used to connect. The origin of the circuit is in the distribution panel. Orderly circuit connection brings great convenience to fault maintenance. Other car systems have different names. BMW has front and rear power supply module, relay box assembly and wiring box assembly of Toyota car system, fuse box of general car system, etc.
