With the wide application of electronic technology in automobiles, automobile circuit diagram has become the necessary technical data for automobile maintenance personnel. At present, most cars are equipped with many electronic control devices, which are high in technology and complicated in circuit, so it is difficult to master them. It also needs some skills to read the automobile circuit diagram correctly. Circuit diagram is an important information to understand the work of various electrical systems of automobiles. It is very important to understand the types and characteristics of automobile circuits, the circuit characteristics and expressions of automobile systems, and the reading methods, rules and skills of circuit diagrams of various systems, so as to guide readers how to read and use circuit diagrams correctly.
The automobile circuit is a single-wire parallel circuit. Generally speaking, there are series, parallel and series-parallel circuits in local circuits. In fact, the whole vehicle circuit is composed of various circuits, and each circuit can be separated independently, simplifying the complexity. According to its basic purposes, the vehicle circuit can be divided into lighting, signal, instrument, starting, ignition, charging, auxiliary and other circuits. Each circuit has its own load conductor connected to the control switch or fuse box.
Keywords: circuit, one-way wire system, wires and various car lights
Table of Contents: (1) Connection Principles of Vehicle Lines
(2) Basic requirements for reading the circuit diagram
(3) Take Dongfeng EQ 1090 freight car line as an example to identify and read the whole car line.
A. Power system circuit B. Starting system circuit C. Ignition system circuit
D. Instrument system circuit E. Lighting and signal system circuit
(4) Conductor of vehicle circuit
(5) Matters needing attention in reading drawings
Talking about the reading method of automobile circuit
In a car, a wire harness is often wrapped around dozens or even dozens of wires, so dense that it is difficult to distinguish their directions. In addition, electricity is invisible and intangible, so the car circuit is a very complicated thing for many people. But everything has its regularity, and car circuits are no exception.
General household electricity is a two-wire parallel circuit of alternating current, and electrical appliances have at least two external power lines. From the automobile circuit, the negative wire (return wire) of the load (electrical appliance) should be directly connected to the negative terminal of the battery. If this wiring method is adopted, hundreds of wires will be connected to the negative terminal of the battery. In order to avoid this situation, the designer uses the metal frame of the car body as the negative pole of the circuit, such as the girder. Therefore, the automobile circuit is obviously different from the general household electricity: the automobile circuit is all DC, and the single-wire parallel circuit is implemented, as long as the electrical appliance has an external power line.
The negative pole of the battery and the negative pole of the load are connected to the metal frame, which is also called "grounding". In this way, the negative lead from the load can be connected nearby, and the current flows back to the negative lead of the battery through the metal frame. With the increasing application of nonmetallic materials such as plastic parts in automobiles, many automobiles now adopt public grounding grid wiring harness to ensure the reliability of grounding, that is, the negative wire of the load is connected to the grounding grid wiring harness, and the grounding grid wiring harness is connected to the negative electrode of the battery.
The automobile circuit is a single-wire parallel circuit. Generally speaking, there are series, parallel and series-parallel circuits in local circuits. In fact, the whole vehicle circuit is composed of various circuits, and each circuit can be separated independently, simplifying the complexity. According to its basic purposes, the vehicle circuit can be divided into lighting, signal, instrument, starting, ignition, charging, auxiliary and other circuits. Each circuit has its own load conductor connected to the control switch or fuse box.
Lighting circuit refers to the circuit system that controls the combination switch, headlights and small lights; Signal circuit refers to the circuit system that controls the combination switch, turn signal and alarm light; Instrument circuit refers to the ignition switch, instrument panel and sensor circuit system; Starting circuit refers to the ignition switch, relay and starter circuit system; Charging circuit refers to the circuit system of regulator, generator and battery. The above circuit system is essential and constitutes the basic part of the vehicle circuit. Auxiliary circuit refers to the circuit system that controls wipers, stereos, etc. With the increase of automobile electrical equipment, such as electric seats, electric doors and windows, electric skylights, etc. There will be more and more auxiliary circuits.
The circuit of an old car is relatively simple. Generally, their positive wires (commonly known as live wires) are respectively connected with the fuse box, and their negative wires (commonly known as ground wires) are used for * * *. There are three important nodes, namely fuse box, relay and combination switch. Most circuit systems have fuses or switches at one end and relays or electrical equipment at the other. However, with more and more electrical equipment in modern cars, there will be more and more wire harnesses and wiring will become more and more complicated. With the development of automobile electronic technology, modern automobile circuits have been combined with electronic technology, and multi-channel control devices have been adopted, instead of being transmitted through separate wires like old cars.
With the multi-channel control device, the input signals sent by various electrical loads are converted into digital signals by the electronic control unit (ECU), and the digital signals are transmitted from the sending device to the receiving device, where they are converted into required signals to control related components. Therefore, it is necessary to add a multi-channel control device in the circuit between fuse, switch and electrical equipment (see the schematic diagram of Guangzhou Accord rear fog lamp circuit). A system use multiple control lines can.
the second part
The second part briefly introduces the principle, requirements and methods of vehicle line reading and the specifications of circuit lines. This paper mainly expounds its application in Dongfeng EQ 1090 automobile circuit and electrical system. It includes power supply system, starting system, ignition system, lighting and signal system, instrument system and auxiliary electrical system. Through the systematic study of Dongfeng EQ 1090, it lays a solid foundation for future contact with various types of vehicles.
First, the connection principle of vehicle lines
The wiring of the whole vehicle varies according to the vehicle structure, the number of electrical equipment, the installation location and the wiring mode, but the wiring is generally based on the following principles:
(1) The connection of various electrical equipment in automobiles is mostly single-wire system;
(2) The two power sources (generator and battery) equipped on the vehicle must be connected in parallel;
(3) All kinds of electrical equipment are connected in parallel and controlled by their own switches;
(4) The ammeter must be able to detect the charging and discharging current of the battery. Therefore, whenever the battery supplies power, the current must pass through the loop formed by the ammeter and the battery. But the starting current with large power consumption and short working time is an exception, that is, the starting current does not pass through the ammeter;
(5) All types of cars are equipped with safety devices to prevent short circuit from burning out electrical equipment.
Understanding the above principles is very helpful for analyzing and studying various types of electrical circuits and correctly judging electrical faults.
Second, the basic requirements
Generally speaking, there are three forms of vehicle circuit, namely: circuit diagram, schematic diagram and wiring diagram.
(A), read the basic requirements of the circuit diagram
To understand the circuit of the whole vehicle, we must first look at the circuit diagram of the car, because the electrical appliances on the circuit diagram are represented by graphic symbols and shapes, which are easy to identify. In addition, the position of electrical equipment on the circuit diagram corresponds to the position of the actual car, so it is easy to identify the actual position of the main equipment on the car, and at the same time, we can have a perceptual understanding of the function of the equipment.
When reading the circuit diagram, the relative distribution position of the main electrical equipment should be determined according to the functions of the electrical equipment; Identify the connection relationship of electrical equipment and preliminarily understand the composition of unit circuit; Know the type of wire and the direction of current.
(2), read the basic requirements of the schematic diagram
Schematic diagram is a graphical symbol way, which connects the electrical equipment, controller and power supply of the whole vehicle in a certain order. Its characteristic is to arrange each unit circuit in turn, which is convenient for analyzing and understanding the automobile circuit in principle.
When reading the schematic diagram, we should understand the composition of the whole vehicle circuit, find out the current path of each unit circuit and analyze the working process of the circuit.
(3), read the basic requirements of the harness diagram
The wiring harness diagram is a guide diagram to explain the installation of electric wires on the vehicle. The color and label of each wire on the drawing are the color of the wire on the real vehicle and the number printed on the terminal. Connect the wires to the terminals of the specified related electrical equipment several times, and the connection task is completed. Even if you don't understand the principle, you can connect by time.
Generally speaking, mastering the whole vehicle line (bus line) should be carried out according to the following steps:
(1) Have a certain understanding of the structure and principle of the electrical equipment used in this vehicle, and know its specifications.
(2) Read the circuit diagram carefully to understand the name, quantity and actual arrangement position of the electrical equipment used in the whole vehicle; Number and name of terminals used in the equipment.
(3) Reading the schematic diagram, you should understand that each terminal of the main electrical equipment is connected with the terminals of those electrical equipment; Equipment branch line; Functions of switches, fuses and relays on distribution lines; Control mode and process.
(4) When looking at the wiring diagram, you should know how many wire harnesses there are in the car, the name of each wire harness and the installation position on the car; Each branch of the wire harness is in the same direction as the electrical equipment, and each branch has several wires and their colors and labels, and these wires are connected to those terminals; What connectors do cars have and their connections?
(5) Master the typical circuit and draw inferences. Many parts of automobile circuits are similar, and they are all basic circuits with the same nature. The difference is only a few cases.
Third, the recognition of the whole vehicle line.
Taking Dongfeng EQ 1090 truck line as an example, the characteristics of each electronic system circuit are analyzed and explained. The whole line of Dongfeng EQ 1090 freight car is mainly composed of power supply system, starting system, ignition system, lighting and signal system, instrument system and auxiliary electrical system.
(1) Wiring of power supply system
The power supply system includes battery, alternator and regulator. Dongfeng EQ 1090 car is equipped with electronic voltage regulator, and the power supply circuit is shown in the figure. Its characteristics are as follows:
(1) The generator is connected in parallel with the battery, and the charging and discharging current of the battery is indicated by an ammeter. When wiring, it should be noted that the-terminal of the ammeter is connected to the positive electrode of the battery, and the+terminal of the ammeter is connected to the A terminal or the B terminal of the armature of the alternator, and the current of the electrical equipment is also led out from the+terminal of the ammeter, so that the ammeter can correctly indicate the charging and discharging current value of the battery.
(2) The negative pole of the battery is controlled by the main power switch. When the rotation speed of the generator is very low and the output voltage does not reach the specified voltage, the battery provides magnetic field current to the generator.
(2) Starting system circuit
The starting system consists of battery, starter and starting relay (some Dongfeng EQ 1090 cars are equipped with compound relays), and the system circuit is shown in the figure.
When starting the engine, put the ignition switch in the "start" position, start the relay (or compound relay) to work, and connect the electromagnetic switch circuit of the starter, thus connecting the circuit between the starter and the battery. The battery provides the starter with a large current of 400~600A, and the starter generates driving torque to start the engine.
After the engine is started, if the driver fails to release the ignition switch in time, when the alternator voltage rises and its neutral point voltage reaches 5V, the electromagnetic switch of the starter will be automatically released under the action of the compound relay, thus cutting off the circuit between the battery and the starting motor, and the starter will automatically stop working.
According to the national standard GB9420-88, the voltage drop (voltage difference per 100 amp) of starting motor circuit for automobile shall not exceed 0.2V for electrical system and 0.4V for 24V electrical system. Therefore, the cable connecting the starting motor and the battery must use a special cable with sufficient cross-sectional area and be firmly connected to prevent poor contact.
(3) Wiring of ignition system
The ignition system includes an ignition coil, a distributor, an ignition switch and a power supply. System circuit as shown in the figure, its characteristics:
(1) The ignition switch is connected in series in the low-voltage circuit to switch on and off the primary winding current;
(2) The ignition coil has two low-voltage terminals, of which the'-'or' 1' terminal should be connected to the low-voltage terminal of the distributor, while the'+'or' 15' terminal is connected with two wires, and the blue wire (note: the wire color may be different due to different factory years) led from the electromagnetic switch of the starter should be connected to the additional resistance of the electromagnetic switch. The white wire comes from the ignition switch and is an additional resistance (resistance value is about 1.7 ohm), so it cannot be replaced by ordinary wire. When the engine is started, the primary current does not pass through the white wire, but directly flows from the storage battery into the ignition coil through starting the electromagnetic switch and the blue wire, so that the additional resistance wire is short-circuited, thereby reducing the resistance of the low-voltage circuit, increasing the low-voltage current and ensuring the smooth start of the engine.
(3) In the high-voltage circuit, the wires from the distributor to the spark plug are called high-voltage lines and must be connected in turn according to the ignition sequence of the cylinders.
(4) Wiring of instrument system
The instrument system includes ammeter, oil pressure gauge, water temperature gauge and sensors matched with fuel gauge. The system circuit is shown in the figure. Its characteristics are as follows:
(1) The ammeter is connected in series in the power supply circuit to indicate the charging and discharging current of the battery. Several other instruments are connected in parallel and controlled by the ignition switch.
(2) The power regulator is used for the water thermometer and fuel meter, so as to stabilize the instrument power supply when the power supply voltage fluctuates and ensure the accurate reading of the water thermometer and fuel meter. The output voltage of the power regulator is 8.64V+/-0.15V.
The alarm device includes a low oil pressure alarm lamp and a low air pressure buzzer, which are controlled by their respective alarm switches. When the oil pressure is lower than 50~90kpa, the low oil pressure alarm switch will get an electric shock, and the low oil pressure indicator circuit will light up, indicating that the oil pressure in the main oil circuit of the engine is too low, so it should be stopped for maintenance in time. Dongfeng EQ 1090 car adopts pneumatic braking system. When the air pressure of the braking system drops to 340 ~ 370 kPa, the buzzer will sound when the air pressure is too low to show a warning.
(5) Lighting and signal system lines
The lighting and signal system includes all the lighting, lighting signals and audio signals of the whole vehicle, and the system circuit is shown in the figure. Its characteristics are as follows:
(1) Headlight consists of two lamps, with double filament bulbs;
(2) The outer side of the headlamp is the front side lamp, which adopts a single filament, and its optical axis forms an included angle of 20 degrees with the floodlight axis, that is, it inclines 20 degrees to the left and right respectively. Therefore, when driving at night, if the headlights and the front side lights are turned on at the same time, the front and left and right sides of the car will have good lighting, and even when the car turns sharply, it can illuminate the road ahead, thus greatly improving the lighting conditions when the car is driving on the road with many bends and sharp turns;
(3) Headlights, front lower lights, front side lights and tail lights are all controlled by handle light switches;
(4) equipped with lightning protection circuit;
(5) The brake signal lamp is not controlled by the main switch of the lamp, but is directly connected to the power supply through a fuse. As long as you step on the brake pedal, the brake light switch will open the brake light circuit and make the brake light shine;
(6) The turn signal is controlled by the turn signal switch;
(7) The electric horn is controlled by horn button and horn relay.